阅读说明：本技术 预处理液、油墨组及图像记录方法 (Pretreatment liquid, ink set, and image recording method ) 是由 佐藤悠贵 于 2019-09-04 设计创作，主要内容包括：本发明提供一种部件腐蚀性得到抑制且能够良好地抑制图像不均匀的预处理液、油墨组及图像记录方法。该预处理液、油墨组及图像记录方法中,含有重均分子量为5000以上的水溶性聚合物和酸,且含有一部分上述酸的盐,上述酸为羧酸,上述酸的盐为上述羧酸的盐。(The invention provides a pretreatment liquid, an ink set and an image recording method, wherein the corrosion of components is inhibited, and the image unevenness can be well inhibited. The pretreatment liquid, the ink set and the image recording method contain a water-soluble polymer having a weight average molecular weight of 5000 or more and an acid, and contain a part of a salt of the acid, the acid is a carboxylic acid, and the salt of the acid is a salt of the carboxylic acid.)

1. A pretreatment liquid containing a water-soluble polymer having a weight-average molecular weight of 5000 or more, an acid and a salt of the acid,

at least one of the acids is a carboxylic acid and at least one of the salts of the acid is a salt of the carboxylic acid.

2. The pretreatment liquid according to claim 1,

the pH of the pretreatment liquid is less than the maximum pKa of the acid groups contained in the acid and the salt of the acid.

3. The pretreatment liquid according to claim 1 or 2,

the water-soluble polymer contains at least one selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, and polyacrylic acid.

4. The pretreatment liquid according to any one of claims 1 to 3,

the water-soluble polymer is a nonionic water-soluble polymer.

5. The pretreatment liquid according to any one of claims 1 to 4,

the content of the water-soluble polymer is 0.1 to 9% by mass based on the total mass of the pretreatment solution.

6. The pretreatment liquid according to any one of claims 1 to 5,

the total content of acid groups in the acid and the acid salt is 0.25mol or more based on 100g of the pretreatment solution.

7. The pretreatment liquid according to any one of claims 1 to 6, further comprising at least one of phosphoric acid and a salt of phosphoric acid.

8. The pretreatment liquid according to any one of claims 1 to 7,

the salts of the carboxylic acids are salts of alkali metals.

9. An ink set comprising:

the pretreatment liquid of any one of claims 1 to 8; and

an ink composition containing water and a colorant.

10. An image recording method, comprising:

a pretreatment liquid applying step of applying the pretreatment liquid in the ink set according to claim 9 to a recording medium; and

an ink applying step of applying the ink composition in the ink set according to claim 9 to the recording medium to which the pretreatment liquid is applied in the pretreatment liquid applying step.

11. The image recording method according to claim 10, further comprising:

and a heat fixing step of heat-fixing the image recorded in the ink applying step.

Technical Field

The invention relates to a pretreatment liquid, an ink set and an image recording method.

Background

In the field of image recording, a technique using a pretreatment liquid containing a coagulant for coagulating components in an ink is known. The pretreatment liquid is sometimes used for the following purposes: blurring of an image recorded by the ink is prevented by applying the pretreatment liquid onto the recording medium before applying the ink onto the recording medium.

As the above-described technique, for example, patent document 1 describes a combination of an ink containing a pigment and a water-soluble resin, and a reaction liquid having a buffering capacity in an acidic region, wherein the pigment is a self-dispersible pigment having a surface charge amount of 0.20mmol/g or more as determined by colloid titration, and the water-soluble resin is a copolymer having a unit derived from (meth) acrylic acid.

Patent document 2 describes an ink set containing: an ink composition containing a pigment and water; and a treatment liquid containing an organic acidic compound, a polymer compound containing a structural unit represented by the following general formula (A) and a structural unit represented by the following general formula (B), and water.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 2012-223975

Patent document 2: japanese patent No. 5554290

Disclosure of Invention

Technical problem to be solved by the invention

As the above-mentioned coagulant, for example, an acid may be used, and when an acid is used as the coagulant, it is considered that the blurring of an image can be suppressed and the image quality can be improved.

However, in the case where an acid is used as the coagulant, the pH of the pretreatment liquid is lowered, and therefore, there are some risks of work safety (for example, adhesion of the pretreatment liquid to the skin, eyes, etc. of workers during handling; etc.), corrosion of parts of the system, and the like.

Therefore, from the viewpoint of improving the work safety and the corrosion of parts by acids by increasing the pH of the pretreatment liquid, it is conceivable to add a salt of an acid (for example, obtained by neutralizing the acid) in addition to the acid as a coagulant.

Here, in order to maintain the coagulation function of the pretreatment liquid, it is necessary to increase the contents of the acid and the salt of the acid in the pretreatment liquid, but if the contents of the acid and the salt of the acid are increased, the problem that image unevenness is likely to occur depending on the type of the recording medium applied to the pretreatment liquid becomes conspicuous.

The cause of the image unevenness is not clear, but the following is presumed to be one of the causes of the image unevenness.

When the pretreatment liquid is applied to and dried on the surface of the recording medium, a region where the pretreatment liquid is sufficiently dried and a region where the pretreatment liquid is insufficiently dried are generated due to unevenness in shape, composition, and the like of the surface of the recording medium, and unevenness in drying of the pretreatment liquid is generated. It is also estimated that a difference in the concentration of the ink composition in each region occurs between a region where the pretreatment liquid is sufficiently dried and a region where the drying of the pretreatment liquid is not sufficient, and as a result, the difference becomes one of the causes of the occurrence of image unevenness.

On the other hand, the pretreatment liquid of the present invention contains a water-soluble polymer having a weight average molecular weight of 5000 or more, and thus the water-soluble polymer can be made to exist on the surface of the recording medium without excessively penetrating into the inside of the recording medium. This makes it possible to uniformly cover the surface of the recording medium with a film made of a water-soluble polymer, thereby reducing the drying unevenness and suppressing image unevenness.

In the invention described in patent document 1, it is considered that the polymer has a small molecular weight and easily permeates into the recording medium, and therefore, the suppression of image unevenness cannot be expected.

In the invention described in patent document 2, since it is estimated that the pH of the treatment liquid is low, corrosion of parts may become remarkable.

An object of embodiments of the present invention is to provide a pretreatment liquid and an ink set that can suppress corrosion of members and can favorably suppress image unevenness.

Another object of the present invention is to provide an image recording method capable of suppressing the corrosion of a member and satisfactorily suppressing the unevenness of an image.

Means for solving the technical problem

The solution to the above problem includes the following means.

<1> a pretreatment liquid containing a water-soluble polymer having a weight-average molecular weight of 5000 or more, an acid and a salt of the acid, wherein at least one of the acids is a carboxylic acid and at least one of the salts of the acid is a salt of the carboxylic acid.

<2> the pretreatment liquid according to <1>, wherein the pH is less than the maximum pKa of the acid group contained in the acid or the salt thereof.

<3> the pretreatment solution according to <1> or <2>, wherein the water-soluble polymer contains at least one selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, and polyacrylic acid.

<4> the pretreatment liquid according to any one of <1> to <3>, wherein the water-soluble polymer is a nonionic water-soluble polymer.

<5> the pretreatment liquid according to any one of <1> to <4>, wherein a content of the water-soluble polymer is 0.1% by mass to 9% by mass with respect to a total mass of the pretreatment liquid.

<6> the pretreatment liquid according to any one of <1> to <5>, wherein a total content of the acid group in the acid and the salt of the acid is 0.25mol or more based on 100g of the pretreatment liquid.

<7> the pretreatment liquid according to any one of <1> to <6>, further comprising at least one of phosphoric acid and a salt of phosphoric acid.

<8> the pretreatment liquid according to any one of <1> to <7>, wherein the salt of the carboxylic acid is a salt of an alkali metal.

<9> an ink set comprising: the pretreatment liquid described in any one of <1> to <8 >; and an ink composition containing water and a colorant.

<10> an image recording method, comprising: a pretreatment liquid application step of applying the pretreatment liquid in the ink set according to <9> to a recording medium; and an ink applying step of applying the ink composition of the ink set according to <9> to the recording medium to which the pretreatment liquid is applied in the pretreatment liquid applying step.

<11> the image recording method according to <10>, further comprising: and a heat fixing step of heat-fixing the image recorded in the ink applying step.

Effects of the invention

According to the embodiment of the present invention, it is possible to provide a pretreatment liquid and an ink set which can suppress the corrosion of members and can favorably suppress the unevenness of images.

According to another embodiment of the present invention, an image recording method capable of suppressing the corrosiveness of a member and favorably suppressing the unevenness of an image can be provided.

Drawings

Fig. 1 is a diagram conceptually showing characters in a character image used in evaluation of blurring of an image in the embodiment.

Fig. 2 is a diagram for explaining details of evaluation criteria for blurring of an image in the embodiment.

Detailed Description

In the present invention, the numerical range represented by "to" represents a range including numerical values described before and after "to" as a lower limit value and an upper limit value.

In the numerical ranges recited in the present invention in stages, the upper limit value or the lower limit value recited in a certain numerical range may be replaced with the upper limit value or the lower limit value recited in other numerical ranges recited in stages, and may be replaced with the values shown in the examples.

In the present invention, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition indicates the total amount of the plurality of substances present in the composition unless otherwise specified.

In the present invention, the term "step" includes not only an independent step but also a step that can achieve a desired purpose even when it is not clearly distinguished from other steps.

In the present invention, "image recording" or "recording of an image" means that an image is drawn on a substrate using the 1 st ink composition and the 2 nd ink composition.

In the present invention, "image quality" refers to the fineness of an image.

In the present invention, a combination of the preferred embodiments is a more preferred embodiment.

In the present invention, "acid group" includes acid groups contained in acids and acid salts. For example, in the case where the acid and the salt of the acid are a carboxylic acid and a salt of a carboxylic acid, -COOH and-COO^-Is an acid group.

< pretreatment solution >

The pretreatment liquid of the present invention contains a water-soluble polymer having a weight average molecular weight of 5000 or more, an acid and a salt of the acid, wherein at least one of the acids is a carboxylic acid, and at least one of the salts of the acid is a salt of the carboxylic acid.

The pretreatment solution of the present invention contains an acid and a part of the salt of the acid, whereby the pH of the pretreatment solution can be increased. This improves the working safety and reduces the corrosiveness of the pretreatment liquid.

However, in order to maintain the aggregating function of the pretreatment liquid, it is necessary to increase the contents of the acid and the salt of the acid in the pretreatment liquid, but when the contents of both are increased, image unevenness (density unevenness) is liable to occur in an image recorded by applying a colored ink after applying the pretreatment liquid, depending on the kind of recording medium to which the pretreatment liquid is applied. This image unevenness tends to occur particularly remarkably, for example, in the case of a coated paper used for paper container packaging and the like.

On the other hand, the pretreatment liquid of the present invention contains an acid and a salt of the acid as a coagulating component and contains a water-soluble polymer having a weight-average molecular weight of 5000 or more, and thereby the water-soluble polymer can be made to exist on the surface of the recording medium without excessively penetrating into the inside of the recording medium while maintaining the coagulating function of the pretreatment liquid. This makes it possible to uniformly cover the surface of the recording medium with a film made of a water-soluble polymer, thereby reducing the drying unevenness and suppressing image unevenness.

The pretreatment liquid of the present invention will be described in detail below.

(Water-soluble Polymer)

The pretreatment liquid of the present invention contains a water-soluble polymer having a weight average molecular weight of 5000 or more.

The weight average molecular weight of the water-soluble polymer is 5000 or more, whereby the water-soluble polymer can be prevented from excessively permeating into the inside of the recording medium. In addition, when an ink composition described later is applied after the pretreatment liquid is applied, the coagulation rate of the ink composition can be suppressed to some extent, and the surface of the recording medium is covered with a water-soluble polymer having high hydrophilicity, whereby the spreading of ink droplets of the ink composition can be improved. This can favorably suppress image unevenness.

In the present invention, water solubility means that the amount of water dissolved in 100g of water at 25 ℃ is 1g or more (preferably 3g or more).

The weight average molecular weight of the water-soluble polymer is preferably 7500 or more, more preferably 10000 or more, from the viewpoint of suppressing permeation into a recording medium and suppressing image unevenness.

The weight average molecular weight of the water-soluble polymer is preferably 40000 or less, more preferably 30000 or less, from the viewpoints of coatability when applied to a recording medium by a coating method, ejection property when applied to a pretreatment liquid by an ink jet method, and solubility in the pretreatment liquid.

In addition, the weight average molecular weight can be measured by Gel Permeation Chromatography (GPC). For example, HLC-8020GPC (manufactured by Tosoh Corporation) can be used as GPC, and as a column, for example, 3 TSKgel, Super Multipore HZ-H (manufactured by Tosoh Corporation, 4.6 mmID. times.15 cm) can be used, and as an eluent, THF (tetrahydrofuran) can be used. The conditions were 0.45 mass% for the sample concentration, 0.35ml/min for the flow rate, 10. mu.l for the sample injection amount, 40 ℃ for the measurement temperature, and an IR detector. Further, the calibration curve can be obtained, for example, according to "standard sample TSK standard, polystyrene" manufactured by Tosoh Corporation: 8 samples of "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000" and "n-propylbenzene" were prepared.

The content of the water-soluble polymer in the pretreatment solution in the present invention is not particularly limited, but is preferably 0.1 to 9% by mass based on the total mass of the pretreatment solution.

When the content is 0.1% by mass or more, the spreading of ink droplets can be further promoted, and when the content is 9% by mass or less, the thickening of the pretreatment liquid can be further suppressed.

When the content is 9% by mass or less, precipitation, phase separation and the like of the water-soluble polymer due to coagulation or salting out of the water-soluble polymer and an acid salt described later can be avoided, and the liquid stability of the pretreatment solution can be improved.

From the same viewpoint as described above, the content of the water-soluble polymer is more preferably 0.5 to 9% by mass based on the total mass of the pretreatment solution.

Examples of the water-soluble polymer include cellulose derivatives, polyethylene derivatives, polyacrylic acid, and polyol polymers.

Among them, the water-soluble polymer is preferably a polyethylene derivative, polyacrylic acid, or a polyol polymer, from the viewpoint of suppressing image unevenness.

The water-soluble polymer preferably contains at least one selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, polyacrylamide, polymethyl vinyl ether, and polyisopropylacrylamide, and more preferably contains at least one selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, and polyacrylic acid, from the viewpoint of more favorably suppressing image unevenness.

The water-soluble polymer may be a copolymer, and may be a copolymer of a monomer such as vinylpyrrolidone, acrylic acid, or ethylene glycol with another monomer.

The water-soluble polymer is preferably a nonionic water-soluble polymer. This makes it possible to maintain the liquid stability of the pretreatment liquid more favorably.

Examples of the nonionic water-soluble polymer include polyvinylpyrrolidone, polyacrylamide, polymethyl vinyl ether, and polyisopropylacrylamide.

(acid, acid salt)

The pretreatment liquid in the present invention contains an acid and a salt of the acid, at least one of the acids is a carboxylic acid, and at least one of the salts of the acid is a salt of the carboxylic acid.

That is, the pretreatment liquid of the present invention includes a case where a carboxylic acid and a salt of a carboxylic acid and other acids and/or salts thereof are contained, in addition to a case where only a carboxylic acid and a salt of a carboxylic acid are contained.

-acid-

The pretreatment liquid of the present invention contains at least one carboxylic acid, whereby the carboxylic acid can aggregate an ink composition described later. Further, by containing a carboxylic acid, which is a weak acid, as compared with a strong acid, even if the pretreatment liquid contains an acid group in an amount sufficient to coagulate the ink, the decrease in pH can be suppressed. Since the decrease in the pH of the pretreatment liquid can be suppressed, the corrosion of the parts by the pretreatment liquid can be suppressed well.

The acid is preferably a compound having two or more carboxyl groups in one molecule.

The compound having two or more carboxyl groups in one molecule is preferably tartaric acid, phthalic acid, 4-methylphthalic acid, DL-malic acid, succinic acid, citric acid, pimelic acid, malonic acid, glutaric acid, adipic acid, dimethylmalonic acid, or maleic acid, and more preferably DL-malic acid, malonic acid, succinic acid, citric acid, glutaric acid, dimethylmalonic acid, or maleic acid. These may be used alone or in combination of two or more.

Further, as the acid, a compound represented by the following general formula (I) is also preferable. This further improves the cohesion and can further suppress the movement of ink droplets applied to the recording medium.

C_nH_2n+2-m(COOH)_m… … general formula (I)

[ in the general formula (I), n represents an integer of 2 or more, and m represents an integer of 3 or more. Angle (c)

In the general formula (I), n is preferably an integer of 3 to 5.

In the general formula (I), m is preferably an integer of 3 to 5.

Specific examples of the compound represented by the above general formula (I) include 1,2, 3-propanetricarboxylic acid, 1, 3, 5-pentanetricarboxylic acid, 1,2, 3, 4-butanetetracarboxylic acid and the like.

The content of the acid contained in the pretreatment solution in the present invention can be appropriately selected within a range in which the total content of the acid group in the acid and the salt of the acid described later is 0.25mol or more based on 100g of the pretreatment solution.

Salts of acids

The pretreatment liquid of the present invention contains salts of acids, and at least one of the salts of acids is a salt of a carboxylic acid.

The pretreatment liquid contains at least one salt of a carboxylic acid, whereby the pH can be raised to a certain extent without impairing the coagulation function possessed by the carboxylic acid. This improves the image quality of the recorded image and suppresses corrosion of the member.

The salt of the carboxylic acid can be obtained by, for example, neutralizing a part of the acid (carboxylic acid) with a basic compound.

The basic compound is not particularly limited, and examples thereof include hydroxides of alkali metals and hydroxides of alkaline earth metals. Among them, from the viewpoint of solubility in the pretreatment solution, hydroxides of alkali metals are preferable.

That is, for example, a salt of a carboxylic acid obtained by neutralizing a part of the carboxylic acid with a hydroxide of an alkali metal is also preferably a salt of an alkali metal.

Examples of the alkali metal hydroxide and the alkaline earth metal hydroxide include potassium hydroxide, sodium hydroxide, magnesium hydroxide, and calcium hydroxide. Among them, sodium hydroxide and potassium hydroxide are preferable from the viewpoint of solubility in the pretreatment solution. From the viewpoint of solubility in the pretreatment solution, sodium hydroxide and potassium hydroxide are compared, and potassium hydroxide is more preferable, but sodium hydroxide and potassium hydroxide are preferable in practical use.

As described above, in the case of neutralizing an acid to obtain a salt of the acid, after the neutralization is performed, the pH of the pretreatment liquid is preferably less than the maximum pKa of the acid and the acid group contained in the salt of the acid. That is, in the case where a plurality of acid groups are mixed together, the pH of the pretreatment liquid is preferably lower than the pKa of the acid having the largest pKa. This makes it possible to increase the pH of the pretreatment liquid while maintaining the acid coagulation function satisfactorily, thereby more satisfactorily suppressing corrosion of the member.

In the present invention, the pKa is the value described in item 625 of the handbook of analytical chemistry (revision 6) edited by the japan society of analytical chemistry.

The maximum pKa of the acid group contained in the acid and the acid salt means a pKa showing the maximum among the pKa of all the acid groups contained in the acid and the acid salt.

The total content of acid groups in the acid and the acid salt is preferably 0.25mol or more based on 100g of the pretreatment solution.

This can more favorably coagulate the ink composition, and can improve the image quality of the obtained image. Further, blurring (bleeding) of the image can be suppressed.

From the above-mentioned viewpoint, the total content of the acid groups in the acid and the acid salt is more preferably 0.3mol or more, and still more preferably 0.4mol or more, based on 100g of the pretreatment liquid.

The total content of acid groups in the acid and the acid salt may be 1.0mol or less based on 100g of the pretreatment solution. In addition, the total content of acid groups can be calculated by multiplying the valence number of the acid used. For example, if 0.05mol of malonic acid (2 valent) and 0.05mol of tripotassium citrate are dissolved in 100g of the pretreatment liquid, the content of the acid group can be calculated by 0.05 × 2+0.05 × 3 ═ 0.25 mol.

The content of the acid salt relative to the total mass of the acids may be appropriately selected within a range in which the total content of the acids and the acid groups in the acid salt, which will be described later, is 0.25mol or more relative to 100g of the pretreatment solution.

The pretreatment liquid in the present invention preferably further contains at least one of phosphoric acid and a salt of phosphoric acid as an acid and a salt of an acid.

For example, in the case where calcium carbonate is contained in the recording medium, by making the pretreatment liquid contain phosphoric acid, calcium carbonate reacts with phosphoric acid in the pretreatment liquid to insolubilize calcium in calcium carbonate, thereby making it possible to suppress precipitation of calcium on the image surface. This can further suppress the occurrence of white spots (white spots, i.e., white precipitates in the image) in the recorded image due to the precipitation of calcium.

As the phosphoric acid, for example, orthophosphoric acid (hereinafter, also simply referred to as "phosphoric acid"), phosphorous acid, hypophosphorous acid, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, or salts thereof can be used.

In the pretreatment liquid of the present invention, the content of the carboxylic acid and the salt of the carboxylic acid is not particularly limited with respect to the total of the acid and the salt of the acid, but from the viewpoint of exhibiting favorable aggregation, it is preferable that 60% or more of the carboxylic acid or the salt of the carboxylic acid is contained in all acid groups in terms of the number ratio of the acid groups.

(Water)

The pretreatment liquid in the present invention preferably contains water. The content of water is not particularly limited, but is preferably within a range of 10 to 99 mass%, more preferably 50 to 90 mass%, and still more preferably 60 to 80 mass%.

(organic solvent)

The pretreatment liquid in the present invention preferably contains at least one selected from organic solvents.

The organic solvent is preferably an organic solvent (hereinafter, also referred to as "water-soluble organic solvent") capable of dissolving 5g or more in 100g of water at 20 ℃.

As the water-soluble organic solvent, the same solvent as the water-soluble organic solvent contained in the ink described later can be used. Among them, from the viewpoint of suppressing curling and reducing the surface tension of the pretreatment liquid to improve coatability, polyalkylene glycol or a derivative thereof is preferable, and at least one selected from the group consisting of diethylene glycol monoalkyl ether, triethylene glycol monoalkyl ether, dipropylene glycol, tripropylene glycol monoalkyl ether, polyoxypropylene glycerol ether, and polyoxyethylene polyoxypropylene glycol is more preferable.

The content of the organic solvent in the pretreatment liquid is not particularly limited, but is preferably 0.5 to 30% by mass, more preferably 0.5 to 10% by mass, based on the whole pretreatment liquid, from the viewpoints of suppressing curling and reducing the surface tension of the pretreatment liquid to improve coatability.

(Nitrogen-containing heterocyclic compound and organic mercapto compound)

The pretreatment solution in the present invention may contain at least one selected from the group consisting of a nitrogen-containing heterocyclic compound and an organic mercapto compound.

Nitrogen-containing heterocyclic compounds

The structure of the nitrogen-containing heterocyclic compound is preferably a nitrogen-containing 5-membered ring structure or a nitrogen-containing 6-membered ring structure, and among these, a nitrogen-containing 5-membered ring structure is more preferred.

In the nitrogen-containing 5-membered ring structure or the nitrogen-containing 6-membered ring structure, a 5-or 6-membered heterocyclic structure containing at least one atom selected from a carbon atom, a nitrogen atom, an oxygen atom, a sulfur atom and a selenium atom is preferable.

The heterocyclic ring may be formed by fusing a carbon aromatic ring or a heteroaromatic ring.

Examples of the heterocyclic ring include a tetrazole ring, a triazole ring, an imidazole ring, a thiadiazole ring, an oxadiazole ring, a selenobizole ring, an oxazole ring, a thiazole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, a pyrimidine ring, a triazaindene ring, a tetraazaindene ring, and a pentaazaindene ring.

These rings may have a substituent(s) such as nitro group, a halogen atom (e.g., chlorine atom, bromine atom), mercapto group, cyano group, an alkyl group (e.g., methyl group, ethyl group, propyl group, t-butyl group, cyanoethyl group, etc.), an aryl group (e.g., phenyl group, 4-methanesulfonamidophenyl group, 4-methylphenyl group, 3, 4-dichlorophenyl group, naphthyl group, etc.), an alkenyl group (e.g., allyl group), an aralkyl group (e.g., benzyl group, 4-methylbenzyl group, phenethyl group, etc.), a sulfonyl group (e.g., methylsulfonyl group, ethylsulfonyl group, p-toluenesulfonyl group, etc.), a carbamoyl group (e.g., unsubstituted carbamoyl group, methylcarbamoyl group, phenylcarbamoyl group, etc.), a sulfamoyl group (e.g., unsubstituted sulfamoyl group, methylsulfamoyl group, phenylsulfamoyl group, etc, Substituted with a carbonamide group (e.g., each group such as acetamide or benzamide), a sulfonamide group (e.g., each group such as methanesulfonamide, benzenesulfonamide or p-toluenesulfonamide), an acyloxy group (e.g., each group such as acetoxy or benzoyloxy), a sulfonyloxy group (e.g., methanesulfonyloxy), a ureido group (e.g., each group such as unsubstituted ureido, methylureido, ethylureido or phenylureido), an acyl group (e.g., each group such as acetyl or benzoyl), an oxycarbonyl group (e.g., each group such as methoxycarbonyl or phenoxycarbonyl), an oxycarbonylamino group (e.g., each group such as methoxycarbonylamino, phenoxycarbonylamino or 2-ethylhexyloxycarbonylamino), a hydroxyl group. The substituents may be multiply substituted in one ring.

Specific examples of preferred nitrogen-containing heterocyclic compounds include the following compounds.

That is, imidazole, benzimidazole, indazole, benzotriazole, tetrazole, benzoxazole, benzothiazole, pyridine, quinoline, pyrimidine, piperidine, piperazine, quinoxaline, morpholine and the like are mentioned, and these may have a substituent such as an alkyl group, a carboxyl group, a sulfo group and the like described above.

Preferred nitrogen-containing 6-membered ring compounds are compounds having a triazine ring, a pyrimidine ring, a pyridine ring, a pyrroline ring, a piperidine ring, a pyridazine ring or a pyrazine ring, and among them, compounds having a triazine ring and a pyrimidine ring are preferred. These nitrogen-containing 6-membered ring compounds may have a substituent, and examples of the substituent in this case include an alkyl group having 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, a hydroxyl group, a carboxyl group, a mercapto group, an alkoxyalkyl group having 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, and a hydroxyalkyl group having 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms.

Specific examples of preferred nitrogen-containing 6-membered ring compounds include triazine, methyltriazine, dimethyltriazine, hydroxyethyltriazine ring, pyrimidine, 4-methylpyrimidine, pyridine and pyrroline.

Organic mercapto compounds-

Examples of the organic mercapto compound include alkyl mercapto compounds, aryl mercapto compounds, and heterocyclic mercapto compounds.

Examples of the alkylmercapto compound include cysteine, thiomalic acid and the like, examples of the arylmercapto compound include thiosalicylic acid and the like, examples of the heterocyclic mercapto compound include 2-phenyl-1-mercaptotetrazole, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptopyrimidine, 2, 4-dimercaptopyrimidine, 2-mercaptopyridine and the like, and these may have a substituent such as an alkyl group, a carboxyl group, a sulfo group and the like.

Among the above-mentioned nitrogen-containing heterocyclic compounds and the above-mentioned organic mercapto compounds, benzotriazole, 5-methylbenzotriazole, 5-aminobenzotriazole, 5-chlorobenzotriazole, tetrazole, 5-aminotetrazole, 5-methyltetrazole, and 5-phenyltetrazole are particularly preferable, and benzotriazole is most preferable.

The nitrogen-containing heterocyclic compound and the organic mercapto compound may be used singly or in combination of two or more.

The content (total content) of the nitrogen-containing heterocyclic compound and the organic mercapto compound in the pretreatment solution is not particularly limited, but is preferably 0.1 to 5.0% by mass, and more preferably 0.1 to 3.0% by mass, based on the total amount of the pretreatment solution.

(surfactant)

The pretreatment liquid in the present invention may contain at least one of surfactants. Surfactants may be used as surface tension modifiers. Examples of the surface tension adjusting agent include nonionic surfactants.

Specific examples of the surfactant include nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylallyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene alkylamines, glycerin fatty acid esters, and oxyethylene oxypropylene block copolymers.

(antifoaming agent)

The pretreatment liquid of the present invention may contain an antifoaming agent.

The defoaming agent in the present invention is not particularly limited, and a polysiloxane-based defoaming agent can be used. For example, BYK-038 is an example of a silicone defoaming agent.

(other agglomerating components)

The pretreatment liquid of the present invention may contain other aggregating components in addition to the above acids as long as the effects of the present invention are not impaired. Examples of the other flocculant include polyvalent metal salts and polyallylamine.

Examples of the polyvalent metal salt include salts of alkaline earth metals of group 2 of the periodic table (for example, magnesium and calcium), transition metals of group 3 of the periodic table (for example, lanthanum), cations derived from group 13 of the periodic table (for example, aluminum), lanthanoids (for example, neodymium), polyallylamine, and polyallylamine derivatives. As the salt of the metal, nitrate, chloride and thiocyanate are preferable.

The content of the polyvalent metal salt in the pretreatment solution may be, for example, 1 to 10% by mass.

Other additives

The pretreatment liquid of the present invention may be constituted to contain other additives in addition to the above components. The other additives in the pretreatment liquid are the same as those in the ink composition described later.

Physical property of pretreatment liquid is as long as

The surface tension of the pretreatment solution is not particularly limited, and is, for example, preferably 25mN/m or more, more preferably 25mN/m to 60mN/m, and still more preferably 25mN/m to 45 mN/m.

The surface tension of the pretreatment solution can be adjusted by adding a surfactant, for example.

The Surface tension of the pretreatment solution was measured by a plate method at 25 ℃ using an Automatic Surface Tensiometer (Automatic Surface Tensiometer) CBVP-Z (Kyowa Interface Science Co., Ltd.).

From the viewpoint of the coagulation rate of the ink composition, the pH (25 ℃ ± 1 ℃) of the pretreatment liquid in the present invention is preferably 6.0 or less, more preferably 5.5 or less, and still more preferably 5.0 or less.

From the viewpoint of corrosion of parts, the pH (25 ℃ ± 1 ℃) of the pretreatment liquid in the present invention is preferably 2.5 or more, more preferably 3.0 or more, further preferably 3.5 or more, and particularly preferably 4.0 or more. The pH (25 ℃. + -. 1 ℃) of the pretreatment liquid in the present invention is preferably 4.0 to 5.0 from the viewpoints of corrosiveness of parts and coagulation rate of the ink composition.

In the present invention, the pH can be measured at 25 ℃ using, for example, a pH meter (model: HM-31, manufactured by DKK-TOA CORP ORATION).

From the viewpoint of the aggregation speed of the ink composition, the viscosity of the pretreatment liquid is preferably in the range of 1 to 30 mPas, more preferably in the range of 1 to 20 mPas, further preferably in the range of 2 to 15 mPas, and particularly preferably in the range of 2 to 10 mPas. The viscosity was measured at 25 ℃ using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD.).

< ink set >)

The ink set of the present invention comprises the pretreatment liquid described in the present invention and an ink composition containing water and a colorant. The pretreatment solution is preferably the same as described above.

< ink composition >

The ink composition of the present invention contains water and a colorant.

The ink composition contains resin particles, a pigment dispersant (polymer dispersant), an organic solvent, a neutralizer, water, and other components as necessary.

(coloring agent)

The ink composition of the present invention contains a colorant.

As the colorant in the present invention, known dyes, pigments, and the like can be used without particular limitation. Among them, from the viewpoint of coloring property of the ink, a colorant which is hardly soluble in water or water is preferable. Specific examples thereof include various pigments, disperse dyes, oil-soluble dyes, pigments forming J-associations, and the like, and among them, pigments are more preferable.

(pigment)

The ink composition of the present invention preferably contains at least one pigment.

The pigment is not particularly limited in kind, and conventionally known organic pigments and inorganic pigments can be used. Examples thereof include: polycyclic pigments such as azo lake pigments, azo pigments, phthalocyanine pigments, perylene, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; basic lake dyes, acid lake dyes, and the like; organic pigments such as nitro pigments, nitroso pigments, aniline black and fluorescent pigments; inorganic pigments such as titanium oxide, iron oxide and carbon black. Any pigment not described in color index may be used as long as it can be dispersed in an aqueous phase. Further, a pigment obtained by surface-treating the above pigment with a surfactant, a polymer dispersant, or the like, a grafted carbon, or the like can be used.

Among these pigments, azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, and carbon black pigments are particularly preferable.

Dispersant as long as

In the ink composition of the present invention, the pigment is preferably dispersed in a dispersant.

Among these forms, a form in which the pigment is dispersed by the polymer dispersant, that is, a form in which at least a part of the pigment is coated with the polymer dispersant is particularly preferable. Hereinafter, a pigment at least a part of which is coated with a polymer dispersant is also referred to as a "resin-coated pigment".

The dispersant may be a polymer dispersant or a low-molecular surfactant dispersant. The polymer dispersant may be a water-soluble polymer dispersant or a water-insoluble polymer dispersant.

As the low-molecular-weight surfactant-type dispersant, the surfactant-type dispersants described in paragraphs 0016 to 0020 of Japanese patent application laid-open No. 2010-188661 can be used.

Among the above-mentioned polymer dispersants, a hydrophilic polymer compound can be used as a water-soluble polymer dispersant.

As the water-soluble polymer dispersant, for example, a natural hydrophilic polymer compound described in paragraphs 0021 to 0022 of Japanese patent application laid-open No. 2010-188661 can be used.

Further, as the water-soluble polymer dispersant, a synthetic hydrophilic polymer compound may be used.

Examples of the synthetic hydrophilic polymer compound include vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether, polyacrylamides, polyacrylic acid or salts of an alkali metal thereof, acrylic resins such as water-soluble styrene acrylic resins, water-soluble styrene maleic acid resins, water-soluble vinyl naphthalene acrylic resins, water-soluble vinyl naphthalene maleic acid resins, alkali metal salts of polyvinyl pyrrolidone, polyvinyl alcohol, and β -naphthalenesulfonic acid formalin condensates, and polymer compounds having a salt having a cationic functional group such as a quaternary ammonium group or an amino group in a side chain.

Among them, from the viewpoint of dispersion stability and coagulability of the pigment, a carboxyl group-containing polymer compound is preferable, and for example, a carboxyl group-containing polymer compound such as an acrylic resin such as a water-soluble styrene acrylic resin, a water-soluble styrene maleic acid resin, a water-soluble vinyl naphthalene acrylic resin, or a water-soluble vinyl naphthalene maleic acid resin is particularly preferable.

Among the above-mentioned polymer dispersants, a polymer having both a hydrophobic portion and a hydrophilic portion can be used as the water-insoluble dispersant. Examples thereof include a styrene- (meth) acrylic acid copolymer, a styrene- (meth) acrylic acid- (meth) acrylate copolymer, (meth) acrylate- (meth) acrylic acid copolymer, a polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymer, a benzyl (meth) acrylate- (meth) acrylic acid methyl ester copolymer, a styrene-maleic acid copolymer, and the like.

The styrene- (meth) acrylic acid copolymer, the (meth) acrylate- (meth) acrylic acid copolymer, the polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymer, and the styrene-maleic acid copolymer may be a binary copolymer or a ternary or higher copolymer.

Among these, the polymer dispersant is preferably a (meth) acrylate- (meth) acrylic acid copolymer and a benzyl (meth) acrylate- (meth) acrylic acid methyl ester copolymer, and more preferably a benzyl (meth) acrylate- (meth) acrylic acid methyl ester terpolymer.

Here, (meth) acrylic acid means acrylic acid or methacrylic acid, and (meth) acrylate means acrylate or methacrylate.

The weight average molecular weight of the polymer dispersant is preferably 3,000 to 200,000, more preferably 5,000 to 100,000, still more preferably 5,000 to 80,000, and particularly preferably 10,000 to 60,000.

The acid value of the polymer dispersant is not particularly limited, but from the viewpoint of cohesiveness, it is preferable that the acid value of the polymer dispersant is larger than the acid value of the resin particles (preferably self-dispersible resin particles) described later, which may be used as needed.

In the ink composition of the present invention, the mass ratio of the pigment to the dispersant (pigment: dispersant) is preferably in the range of 1: 0.06 to 1: 3, more preferably in the range of 1: 0.125 to 1: 2, and still more preferably in the range of 1: 0.125 to 1: 1.5.

The average particle diameter of the pigment (the average particle diameter of the resin-coated pigment in the case of the resin-coated pigment, the same applies hereinafter) is preferably 10nm to 200nm, more preferably 10nm to 150nm, and still more preferably 10nm to 110 nm. When the average particle diameter is 200nm or less, the color reproducibility is good, the ejection characteristics when the ejection is performed by the ink jet method are good, and when the average particle diameter is 10nm or more, the light resistance is good. The particle size distribution of the pigment is not particularly limited, and may be either a broad particle size distribution or a monodisperse particle size distribution. Two or more kinds of coloring materials having a monodisperse particle size distribution may be mixed and used.

The average particle diameter and the particle diameter distribution of the pigment were determined by measuring the volume average particle diameter by a dynamic light scattering method using a nanosrac particle size distribution measuring apparatus UPA-EX150 (manufactured by Nikkiso co., ltd.).

In the present invention, the content of the pigment in the ink composition is preferably 1 to 25% by mass, more preferably 2 to 20% by mass, and particularly preferably 2 to 10% by mass, relative to the total amount of the ink composition, from the viewpoint of image density.

The pigment may be used singly or in combination of two or more.

(Water)

The ink composition of the present invention preferably contains water. The content of water is not particularly limited, but is preferably within a range of 10 to 99 mass%, more preferably 30 to 80 mass%, and still more preferably 50 to 70 mass%.

(resin particles)

The ink composition of the present invention preferably contains at least one type of resin particles.

The resin particles are particles that are present separately from the pigment, unlike the polymer dispersant (polymer dispersant that covers at least a part of the pigment).

The resin particles are coagulated by the organic acidic compound in the pretreatment liquid. This further improves the fixing property and the aggregation speed of the image.

By using the ink composition containing the resin particles and the pretreatment liquid containing the specific polymer compound, the coagulation rate can be suppressed to some extent to promote the spread of the ink droplets, and thus the decrease in the uniformity of the image due to the insufficient spread of the ink droplets can be further improved.

The resin particles are preferably water-insoluble or water-insoluble resin particles.

The term "water-insoluble or water-insoluble" as used herein means that the amount of resin dissolved in 100g of water at 25 ℃ is 15g or less when the resin is dried at 105 ℃ for 2 hours. From the viewpoint of improving the continuous ejection property and ejection stability of the ink, the above-mentioned dissolved amount is preferably 10g or less, more preferably 5g or less, and further preferably 1g or less. The above-mentioned amount of dissolution is an amount of dissolution when 100% neutralization is performed with sodium hydroxide or acetic acid depending on the kind of salt-forming group of the water-insoluble polymer.

Examples of the resin particles include particles of resins having anionic groups, such as thermoplastic, thermosetting or modified acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenolic, silicone or fluorine resins, vinyl chloride, vinyl acetate, polyvinyl alcohol, polyvinyl butyral and other polyethylene resins, alkyd resins, phthalic resins and other polyester resins, melamine formaldehyde resins, amino alkyd co-condensation resins, urea resins and other amino materials, or copolymers or mixtures thereof. Among these, the anionic acrylic resin is obtained by polymerizing, for example, an acrylic monomer having an anionic group (anionic group-containing acrylic monomer) and another monomer copolymerizable with the anionic group-containing acrylic monomer in a solvent, if necessary. Examples of the anionic group-containing acrylic monomer include acrylic monomers having at least one selected from the group consisting of a carboxyl group, a sulfonic acid group and a phosphonic acid group, and among them, acrylic monomers having a carboxyl group (for example, acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid and the like) are preferable, and acrylic acid or methacrylic acid is particularly preferable.

The resin particles that can be used in the present invention are preferably particles of a self-dispersible resin (self-dispersible resin particles) from the viewpoint of ejection stability and solution stability (particularly, dispersion stability) of a system containing a pigment. Here, the self-dispersible resin refers to a water-insoluble polymer that can be dispersed in an aqueous medium by a functional group (particularly, an acid group or a salt thereof) of the polymer itself when the polymer is dispersed by a phase inversion emulsification method in the absence of a surfactant.

Here, the dispersed state includes both an emulsified state (emulsion) in which the water-insoluble polymer is dispersed in an aqueous medium in a liquid state and a dispersed state (suspension) in which the water-insoluble polymer is dispersed in an aqueous medium in a solid state.

The aqueous medium is a medium containing water. The aqueous medium may contain a hydrophilic organic solvent as required. The aqueous medium is preferably composed of water and a hydrophilic organic solvent in an amount of 0.2% by mass or less relative to water, and more preferably composed of water.

The self-dispersible resin is preferably a self-dispersible resin particle in a dispersed state in which a water-insoluble polymer is dispersed in a solid state, from the viewpoint of the aggregation speed and the fixing property when contained in an ink composition.

As a method for obtaining the emulsified state or dispersed state of the self-dispersible resin, that is, a method for producing an aqueous dispersion of self-dispersible resin particles, a phase inversion emulsification method is exemplified.

Examples of the phase inversion emulsification method include the following methods: the self-dispersible resin is dissolved or dispersed in a solvent (for example, a water-soluble organic solvent or the like), and then directly put into water without adding a surfactant, and stirred and mixed in a state in which a salt-forming group (for example, an acidic group) of the self-dispersible resin is neutralized, and after removing the solvent, an aqueous dispersion in an emulsified state or a dispersed state is obtained.

The stable emulsified state or dispersed state in the self-dispersible resin means: after mixing and stirring (apparatus: stirring apparatus with stirring blade, rotation speed 200rpm, 30 minutes, 25 ℃) a solution obtained by dissolving 30g of water-insoluble polymer in 70g of organic solvent (for example, methyl ethyl ketone), a neutralizing agent (sodium hydroxide if the salt-forming group is anionic, acetic acid if the salt-forming group is cationic) capable of 100% neutralizing the salt-forming group of the water-insoluble polymer, and 200g of water, and removing the organic solvent from the mixed solution, the emulsified state or the dispersed state remained stable at 25 ℃ for at least 1 week (that is, the state of precipitation could not be confirmed by visual observation).

Further, the stability of the emulsified state or the dispersed state in the self-dispersible resin can also be confirmed by an accelerated test of precipitation by centrifugal separation. The stability confirmed by an accelerated test of a precipitate by centrifugal separation can be evaluated, for example, according to the following method: the aqueous dispersion of resin particles obtained by the above method was adjusted to a solid content concentration of 25% by mass, and then centrifuged at 12000rpm for 1 hour, and the solid content concentration of the supernatant after centrifugation was measured.

If the ratio of the solid content concentration after the centrifugal separation to the solid content concentration before the centrifugal separation is large (if it is a numerical value close to 1), it means that the resin particles are not precipitated by the centrifugal separation, that is, the aqueous dispersion of the resin particles is more stable. In the present invention, the ratio of the solid content concentration before and after the centrifugal separation is preferably 0.8 or more, more preferably 0.9 or more, and particularly preferably 0.95 or more.

The content of the water-soluble component that exhibits water solubility when the self-dispersible resin is in a dispersed state is preferably 10% by mass or less, more preferably 8% by mass or less, and still more preferably 6% by mass or less. By setting the water-soluble component to 10 mass% or less, swelling of the resin particles and fusion between the resin particles can be effectively suppressed, and a more stable dispersed state can be maintained.

Further, an increase in viscosity of the aqueous ink composition can be suppressed, and for example, when the aqueous ink composition is applied to an inkjet method, ejection stability becomes better.

Here, the water-soluble component is a compound contained in the self-dispersible resin and dissolved in water when the self-dispersible resin is dispersed. The water-soluble component is a water-soluble compound which is by-produced or mixed in the production of the self-dispersible resin.

The main chain skeleton of the water-insoluble polymer is not particularly limited, and examples thereof include vinyl polymers and condensation polymers (epoxy resins, polyesters, polyurethanes, polyamides, celluloses, polyethers, polyureas, polyimides, polycarbonates, and the like). Among them, vinyl polymers are particularly preferable.

Preferred examples of the vinyl polymer and the monomer constituting the vinyl polymer include those described in Japanese patent laid-open Nos. 2001-181549 and 2002-088294. Further, a vinyl polymer obtained by introducing a dissociable group at the end of a polymer chain by radical polymerization of a vinyl monomer using a chain transfer agent or polymerization initiator having a dissociable group (or a substituent group from which a dissociable group can be derived), and an initiation-transfer-termination agent, or by ionic polymerization using a compound having a dissociable group (or a substituent group from which a dissociable group can be derived) in either of the initiator and the termination agent, may be used.

Further, preferred examples of the condensation polymer and the monomer constituting the condensation polymer include polymers described in Japanese patent application laid-open No. 2001-247787.

From the viewpoint of self-dispersibility, the self-dispersible resin particles that can be used in the present invention preferably contain a water-insoluble polymer containing a hydrophilic structural unit and a structural unit derived from an aromatic group-containing monomer or a cyclic aliphatic group-containing monomer.

The "hydrophilic structural unit" is not particularly limited as long as it is a structural unit derived from a hydrophilic group-containing monomer, and may be a structural unit derived from one hydrophilic group-containing monomer or a structural unit derived from two or more hydrophilic group-containing monomers. The hydrophilic group is not particularly limited, and may be a dissociative group or a nonionic hydrophilic group.

The hydrophilic group is preferably a dissociative group, and more preferably an anionic dissociative group, from the viewpoint of promoting self-dispersion and the viewpoint of stability of an emulsified state or a dispersed state to be formed. Examples of the dissociable group include a carboxyl group, a phosphoric group, and a sulfonic group, and among them, a carboxyl group is preferable from the viewpoint of fixability when the ink composition is formed.

From the viewpoint of self-dispersibility and cohesiveness, the hydrophilic group-containing monomer is preferably a dissociative group-containing monomer, and more preferably a dissociative group-containing monomer having a dissociative group and an ethylenically unsaturated bond.

Examples of the dissociative group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

Specific examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid.

Specific examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate.

Specific examples of the unsaturated phosphoric acid monomer include vinylphosphonic acid, vinylphosphate, bis (methacryloyloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, and the like.

Among the above monomers containing a dissociative group, an unsaturated carboxylic acid monomer is preferable, and acrylic acid and methacrylic acid are more preferable, from the viewpoint of dispersion stability and ejection stability.

The self-dispersible resin particles preferably contain a polymer having a carboxyl group, and more preferably contain a polymer having a carboxyl group and an acid value of 25mgKOH/g to 100mgKOH/g, from the viewpoints of self-dispersibility and an aggregation rate when contacting with a pretreatment solution.

The acid value is more preferably from 25mgKOH/g to 80mgKOH/g, and particularly preferably from 30mgKOH/g to 65mgKOH/g, from the viewpoints of self-dispersibility and aggregation speed when the pretreatment solution is contacted therewith.

In particular, when the acid value is 25 or more, the stability of self-dispersibility becomes good, and when it is 100 or less, the cohesiveness is improved.

The aromatic group-containing monomer is not particularly limited as long as it is a compound containing an aromatic group and a polymerizable group. The aromatic group may be a group derived from an aromatic hydrocarbon or a group derived from an aromatic heterocycle. In the present invention, aromatic groups derived from aromatic hydrocarbons are preferable from the viewpoint of the shape stability of particles in an aqueous medium.

The polymerizable group may be a condensation polymerizable group or an addition polymerizable group. In the present invention, from the viewpoint of the shape stability of particles in an aqueous medium, an addition polymerizable group is preferable, and an ethylenically unsaturated bond-containing group is more preferable.

The aromatic group-containing monomer is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond. The aromatic group-containing monomer may be used alone or in combination of two or more.

Examples of the aromatic group-containing monomer include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and styrene-based monomers. Among them, from the viewpoint of the balance between hydrophilicity and hydrophobicity of the polymer chain and ink fixability, the aromatic group-containing (meth) acrylate monomer is preferable, at least one selected from phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth) acrylate is more preferable, and phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are further preferable.

In addition, "(meth) acrylate" means acrylate or methacrylate.

The cyclic aliphatic group-containing monomer is preferably a monomer having a cyclic aliphatic group derived from a cyclic aliphatic hydrocarbon and an ethylenically unsaturated bond, and more preferably a cyclic aliphatic group-containing (meth) acrylate monomer (hereinafter, may be referred to as an alicyclic (meth) acrylate).

The alicyclic (meth) acrylate refers to a compound including a structural site derived from (meth) acrylic acid and a structural site derived from an alcohol and having a structure containing at least one unsubstituted or substituted alicyclic hydrocarbon group (cyclic aliphatic group) at the structural site derived from an alcohol. The alicyclic hydrocarbon group may be a structural site derived from an alcohol itself, or may be bonded to the structural site derived from an alcohol via a linking group.

The alicyclic hydrocarbon group is not particularly limited as long as it is a hydrocarbon group containing a cyclic non-aromatic hydrocarbon group, and includes a monocyclic hydrocarbon group, a bicyclic hydrocarbon group, and a polycyclic hydrocarbon group having at least three rings. Examples of the alicyclic hydrocarbon group include a cycloalkyl group such as a cyclopentyl group or a cyclohexyl group, a cycloalkenyl group, a bicyclohexyl group, and an norbomene groupFilm base, isobornyl, dicyclopentyl, dicyclopentenyl, adamantyl, decahydronaphthyl, perhydrofluorenyl, tricyclo [5.2.1.0^2，6]Decyl and bicyclo [4.3.0]Nonyl radical.

The alicyclic hydrocarbon group may have a substituent. Examples of the substituent include an alkyl group, an alkenyl group, an aryl group, an aralkyl group, an alkoxy group, a hydroxyl group, a primary amino group, a secondary amino group, a tertiary amino group, an alkylcarbonyl group, an arylcarbonyl group, and a cyano group. The alicyclic hydrocarbon group may form a condensed ring. The alicyclic hydrocarbon group in the present invention preferably has 5 to 20 carbon atoms in the alicyclic hydrocarbon group moiety from the viewpoint of viscosity and solubility.

Specific examples of the alicyclic (meth) acrylate are shown below, but the invention is not limited to these.

Examples of the monocyclic (meth) acrylate include cycloalkyl (meth) acrylates having a cycloalkyl group of 3 to 10 carbon atoms such as cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclononyl (meth) acrylate, and cyclodecyl (meth) acrylate.

Examples of the bicyclic (meth) acrylate include isobornyl (meth) acrylate and norbornyl (meth) acrylate.

Examples of the tricyclic (meth) acrylate include adamantyl (meth) acrylate, dicyclopentyl (meth) acrylate, and dicyclopentenyloxyethyl (meth) acrylate.

These may be used alone or in combination of two or more.

Among these, from the viewpoint of dispersion stability, fixing property and blocking resistance of the self-dispersible resin particles, at least one of a bicyclic (meth) acrylate and a polycyclic (meth) acrylate having at least three rings is preferable, and at least one selected from isobornyl (meth) acrylate, adamantyl (meth) acrylate and dicyclopentanyl (meth) acrylate is more preferable.

The self-dispersible resin is preferably an acrylic resin containing a structural unit derived from a (meth) acrylate monomer, more preferably an acrylic resin containing a structural unit derived from an aromatic group-containing (meth) acrylate monomer or an alicyclic (meth) acrylate, and still more preferably a structural unit derived from an aromatic group-containing (meth) acrylate monomer or an alicyclic (meth) acrylate, and the content thereof is 10 to 95% by mass. The content of the structural unit derived from the aromatic group-containing (meth) acrylate monomer or the alicyclic (meth) acrylate is 10 to 95 mass% based on the total mass of the resin, whereby the stability of the self-emulsified or dispersed state is improved, and the increase in the viscosity of the ink can be further suppressed.

The content of the structural unit derived from the aromatic group-containing (meth) acrylate monomer or the alicyclic (meth) acrylate is more preferably 15 to 90 mass%, more preferably 15 to 80 mass%, and particularly preferably 25 to 70 mass% with respect to the total mass of the resin, from the viewpoints of stability of a self-dispersed state, stabilization of the particle shape in an aqueous medium by hydrophobic interaction between aromatic rings or alicyclic rings, and reduction of the amount of water-soluble components by appropriate hydrophobization of the particles.

The self-dispersible resin may be configured using, for example, a structural unit derived from an aromatic group-containing monomer or a cyclic aliphatic group-containing monomer and a structural unit derived from a dissociable group-containing monomer. Further, other structural units may be contained as necessary.

The monomer forming the other structural unit is not particularly limited as long as it is a monomer capable of copolymerizing the aromatic group-containing monomer and the dissociable group-containing monomer. Among them, from the viewpoint of flexibility of the polymer backbone and ease of control of the glass transition temperature (Tg), an alkyl group-containing monomer is preferable.

Examples of the alkyl group-containing monomer include: alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, and ethylhexyl (meth) acrylate; ethylenically unsaturated monomers having a hydroxyl group such as hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, and hydroxyhexyl (meth) acrylate; dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate; n-hydroxyalkyl (meth) acrylamides such as N-methylol (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, and N-hydroxybutyl (meth) acrylamide; and (meth) acrylamides such as N-alkoxyalkyl (meth) acrylamide and the like, such as N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (N, i) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide, and N- (N, i) butoxyethyl (meth) acrylamide and the like.

The molecular weight range of the water-insoluble polymer constituting the self-dispersible resin particles is preferably 3000 to 20 ten thousand, more preferably 5000 to 15 ten thousand, and further preferably 10000 to 10 ten thousand in terms of weight average molecular weight. By setting the weight average molecular weight to 3000 or more, the amount of the water-soluble component can be effectively suppressed. Further, the self-dispersion stability can be improved by setting the weight average molecular weight to 20 ten thousand or less.

The weight average molecular weight was measured by Gel Permeation Chromatography (GPC). HLC-8020GPC (manufactured by Tosoh Corporation) was used for GPC, and as a column, 3 TSKgel, Super Multipore HZ-H (manufactured by Tosoh Corporation, 4.6 mmID. times.15 cm) and as an eluent, THF (tetrahydrofuran) was used. The conditions were 0.45 mass% for the sample concentration, 0.35ml/min for the flow rate, 10. mu.l for the sample injection amount, 40 ℃ for the measurement temperature, and an IR detector. And, the calibration curve was measured according to "standard sample TSK standard, polystyrene" manufactured by Tosoh Corporation: 8 samples of "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000" and "n-propylbenzene" were prepared.

From the viewpoint of controlling the hydrophilicity/hydrophobicity of the polymer, the water-insoluble polymer constituting the self-dispersible resin particles preferably contains a structural unit derived from an aromatic group-containing (meth) acrylate monomer (preferably a structural unit derived from phenoxyethyl (meth) acrylate and/or a structural unit derived from benzyl (meth) acrylate) or a cyclic aliphatic group-containing monomer (preferably an alicyclic (meth) acrylate) at a copolymerization ratio of 15 to 80 mass% of the total mass of the self-dispersible resin particles.

From the viewpoint of controlling the hydrophilicity/hydrophobicity of the polymer, the water-insoluble polymer preferably contains 15 to 80 mass% of a structural unit derived from an aromatic group-containing (meth) acrylate monomer or an alicyclic (meth) acrylate monomer, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid) at a copolymerization ratio, more preferably, the resin composition contains 15 to 80% by mass of a structural unit derived from phenoxyethyl (meth) acrylate and/or a structural unit derived from benzyl (meth) acrylate, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester having 1 to 4 carbon atoms of (meth) acrylic acid) in a copolymerization ratio.

The water-insoluble polymer preferably has an acid value of 25 to 100 and a weight average molecular weight of 3000 to 20 ten thousand, and more preferably has an acid value of 25 to 95 and a weight average molecular weight of 5000 to 15 ten thousand.

Specific examples of the water-insoluble polymer constituting the self-dispersible resin particles include compounds B-01 to B-23, but the present invention is not limited to these. In addition, the mass ratio of the copolymerization components is shown in parentheses.

B-01: phenoxyethyl acrylate/methyl methacrylate/acrylic acid copolymer (50/45/5)

B-02: phenoxyethyl acrylate/benzyl methacrylate/isobutyl methacrylate/methacrylic acid copolymer (30/35/29/6)

B-03: phenoxyethyl methacrylate/isobutyl methacrylate/methacrylic acid copolymer (50/44/6)

B-04: phenoxyethyl acrylate/methyl methacrylate/ethyl acrylate/acrylic acid copolymer (30/55/10/5)

B-05: benzyl methacrylate/isobutyl methacrylate/methacrylic acid copolymer (35/59/6)

B-06: styrene/phenoxyethyl acrylate/methyl methacrylate/acrylic acid copolymer (10/50/35/5)

B-07: benzyl acrylate/methyl methacrylate/acrylic acid copolymer (55/40/5)

B-08: phenoxyethyl methacrylate/benzyl acrylate/methacrylic acid copolymer (45/47/8)

B-09: styrene/phenoxyethyl acrylate/butyl methacrylate/acrylic acid copolymer (5/48/40/7)

B-10: benzyl methacrylate/isobutyl methacrylate/cyclohexyl methacrylate/methacrylic acid copolymer (35/30/30/5)

B-11: phenoxyethyl acrylate/methyl methacrylate/butyl acrylate/methacrylic acid copolymer (12/50/30/8)

B-12: benzyl acrylate/isobutyl methacrylate/acrylic acid copolymer (93/2/5)

B-13: styrene/phenoxyethyl methacrylate/butyl acrylate/acrylic acid copolymer (50/5/20/25)

B-14: styrene/butyl acrylate/acrylic acid copolymer (62/35/3)

B-15: methyl methacrylate/phenoxyethyl acrylate/acrylic acid copolymer (45/51/4)

B-16: methyl methacrylate/phenoxyethyl acrylate/acrylic acid copolymer (45/49/6)

B-17: methyl methacrylate/phenoxyethyl acrylate/acrylic acid copolymer (45/48/7)

B-18: methyl methacrylate/phenoxyethyl acrylate/acrylic acid copolymer (45/47/8)

B-19: methyl methacrylate/phenoxyethyl acrylate/acrylic acid copolymer (45/45/10)

B-20: methyl methacrylate/isobornyl methacrylate/methacrylic acid copolymer (20/72/8)

B-21: methyl methacrylate/isobornyl methacrylate/methacrylic acid copolymer (40/52/8)

B-22: methyl methacrylate/isobornyl methacrylate/dicyclopentyl methacrylate/methacrylic acid copolymer (20/62/10/8)

B-23: methyl methacrylate/dicyclopentyl methacrylate/methacrylic acid copolymer (20/72/8)

The method for producing the water-insoluble polymer constituting the self-dispersible resin particles is not particularly limited, and examples thereof include: a method of carrying out emulsion polymerization in the presence of a polymerizable surfactant and covalently bonding the surfactant and a water-insoluble polymer; a method of copolymerizing a monomer mixture containing the hydrophilic group-containing monomer and the aromatic group-containing monomer or the alicyclic group-containing monomer by a known polymerization method such as a solution polymerization method or a bulk polymerization method. Among the above polymerization methods, the solution polymerization method is preferable from the viewpoint of the coagulation rate and the ejection stability when used as an ink composition, and the solution polymerization method using an organic solvent is more preferable.

From the viewpoint of the aggregation rate, the self-dispersible resin particles preferably contain a polymer synthesized in an organic solvent, and the polymer is prepared as a polymer dispersion having water as a continuous phase by neutralizing a part or all of anionic groups (carboxyl groups) of the polymer having anionic groups (carboxyl groups) (preferably having an acid value of 20 to 100).

That is, the production of the self-dispersible resin particles is preferably performed by providing the following steps: a step for synthesizing a polymer in an organic solvent; and a dispersing step for preparing an aqueous dispersion in which at least a part of the anionic groups (carboxyl groups) of the polymer is neutralized.

The dispersing step preferably includes the following steps (1) and (2).

Step (1): stirring a mixture containing a polymer (water-insoluble polymer), an organic solvent, a neutralizing agent and an aqueous medium

Step (2): removing the organic solvent from the mixture

The step (1) is preferably performed as follows: first, a polymer (water-insoluble polymer) is dissolved in an organic solvent, and then a neutralizing agent and an aqueous medium are gradually added thereto, mixed, and stirred to obtain a dispersion.

By adding a neutralizing agent and an aqueous medium to a water-insoluble polymer solution dissolved in an organic solvent, self-dispersible resin particles having a particle diameter with higher storage stability can be obtained without strong shearing force.

The method of stirring the mixture is not particularly limited, and a commonly used mixing and stirring device or a disperser such as an ultrasonic disperser or a high-pressure homogenizer, which is used as needed, may be used.

In the step (2), the organic solvent is distilled off from the dispersion obtained in the step (1) by a conventional method such as vacuum distillation to convert the phase into aqueous, whereby an aqueous dispersion of self-dispersible resin particles can be obtained. The organic solvent in the aqueous dispersion obtained is substantially removed, and the amount of the organic solvent is preferably 0.2% by mass or less, and more preferably 0.1% by mass or less.

Preferable examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents. As the organic solvent, the organic solvent exemplified in paragraph 0059 of Japanese patent application laid-open No. 2010-188661 can be used.

As the above-mentioned neutralizing agent, the neutralizing agent exemplified in paragraphs 0060 to 0061 of Japanese patent application laid-open No. 2010-188661 can be used.

The average particle diameter of the resin particles (particularly, self-dispersible resin particles) that can be used in the present invention is preferably in the range of 10nm to 400nm, more preferably in the range of 10nm to 200nm, further preferably in the range of 10nm to 100nm, and particularly preferably in the range of 10nm to 50nm, in terms of volume average particle diameter. When the volume average particle diameter is 10nm or more, the production applicability is improved. When the volume average particle diameter is 400nm or less, the storage stability is improved. The particle size distribution of the resin particles is not particularly limited, and may be any of resin particles having a broad particle size distribution or resin particles having a monodisperse particle size distribution. Two or more of the above resin particles may be mixed and used.

The average particle diameter and the particle diameter distribution of the resin particles were determined by measuring the volume average particle diameter by a dynamic light scattering method using a nanosrac particle diameter distribution measuring apparatus UPA-EX150 (manufactured by Nikkiso co., ltd.).

When the ink composition of the present invention contains resin particles (preferably self-dispersible resin particles), one kind of resin particles (preferably self-dispersible resin particles) may be contained alone, or two or more kinds may be contained.

When the ink composition of the present invention contains the resin particles (preferably, self-dispersible resin particles), the content (total content) of the resin particles (preferably, self-dispersible resin particles) in the ink composition is preferably 1 to 30% by mass, and more preferably 3 to 15% by mass, relative to the total amount of the ink composition, from the viewpoint of the glossiness of an image and the like.

(organic solvent)

The ink composition of the present invention further preferably contains at least one organic solvent (preferably a water-soluble organic solvent). By containing an organic solvent, particularly by containing a water-soluble organic solvent, drying can be prevented and penetration can be promoted.

When a water-soluble organic solvent is used as the anti-drying agent, clogging of the nozzles, which may occur due to drying of the ink at the ink ejection ports, can be effectively prevented when the ink composition is ejected by the ink jet method to record an image.

To prevent drying, a water-soluble organic solvent having a lower vapor pressure than water is preferred. Specific examples of the water-soluble organic solvent suitable for preventing drying include: polyhydric alcohols typified by ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol, 2-methyl-1, 3-propanediol, 1,2, 6-hexanetriol, acetylene glycol derivatives, glycerin, trimethylolpropane, and the like; lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monoethyl (or butyl) ether, and tripropylene glycol monomethyl (or ethyl) ether; heterocycles such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1, 3-dimethyl-2-imidazolidinone, and N-ethylmorpholine; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 3-sulfolene; polyfunctional compounds such as diacetone alcohol and diethanolamine; urea derivatives, and the like.

Among them, polyhydric alcohols such as glycerin and diethylene glycol are preferable. These may be used alone or in combination of two or more. These water-soluble organic solvents are preferably contained in an amount of 10 to 50% by mass in the ink composition.

In addition, in order to promote penetration, a water-soluble organic solvent is preferably used from the viewpoint of allowing the ink composition to better penetrate into the recording medium. Specific examples of the water-soluble organic solvent suitable for promoting permeation include alcohols such as ethanol, isopropanol, butanol, di (tri) ethylene glycol monobutyl ether, tripropylene glycol monomethyl (or ethyl) ether, and 1, 2-hexanediol, sodium lauryl sulfate, sodium oleate, and nonionic surfactants. These ink compositions can provide excellent effects when they contain 5 to 30% by mass of the ink composition. These water-soluble organic solvents are preferably used in an amount within a range that does not cause print blur or print through (print through).

In addition, the water-soluble organic solvent can be used for adjusting the viscosity. Specific examples of the water-soluble organic solvent which can be used for adjusting the viscosity include alcohols (e.g., methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol), polyhydric alcohols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexylene glycol, pentanediol, glycerol, hexanetriol, thiodiglycol), glycol derivatives (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, triethylene glycol monomethyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, and, Ethylene glycol monophenyl ether), amines (e.g., ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, tetramethylpropylenediamine), and other polar solvents (e.g., formamide, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide, sulfolane, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-oxazolidinone, 1, 3-dimethyl-2-imidazolidinone, acetonitrile, acetone).

The water-soluble organic solvent may be used alone or in combination of two or more.

(surfactant)

The ink composition of the present invention preferably contains at least one surfactant.

Examples of the surfactant include nonionic surfactants, cationic surfactants, anionic surfactants, and betaine surfactants. From the viewpoint of the aggregation rate, an anionic surfactant or a nonionic surfactant is preferable.

In order to favorably perform ejection by the ink jet method, the surfactant is preferably contained in an amount that can adjust the surface tension of the ink composition to 25mN/m or more and 40mN/m or less. The content of the surfactant is preferably an amount capable of adjusting the surface tension to 27mN/m to 37 mN/m.

Also, these surfactants can be used as defoaming agents. As the surfactant, a fluorine-based compound, a silicone-based compound, a chelating agent typified by EDTA, or the like can be used.

(polymerizable Compound, polymerization initiator)

The ink composition of the present invention may contain a polymerizable compound in addition to the above components. The polymerizable compound is a compound having a polymerizable group, and the polymerizable group may be a condensation polymerizable group or an addition polymerizable group. The polymerizable group is preferably an addition polymerizable group, and more preferably a group containing an ethylenically unsaturated bond, from the viewpoint of particle shape stability in an aqueous medium.

The ink composition of the present invention may further contain a polymerization initiator in addition to the polymerizable compound. Examples of the polymerization initiator include thermal polymerization initiators and photopolymerization initiators.

(other additives)

The ink composition of the present invention may contain other additives in addition to the above components. Examples of the other additives include known additives such as a discoloration inhibitor, an emulsion stabilizer, a penetration enhancer, an ultraviolet absorber, a preservative, a fungicide, a pH adjuster, an antifoaming agent, a viscosity adjuster, a dispersion stabilizer, a rust inhibitor, and a chelating agent. These various additives may be added directly after the preparation of the ink composition, or may be added at the time of the preparation of the ink composition.

As the pH adjuster, a neutralizer (organic base or inorganic base) can be used.

The pH adjuster is preferably added to the ink composition so that the pH of the ink composition is 6 to 10, more preferably 7 to 10, from the viewpoint of improving the storage stability of the ink composition.

From the viewpoints of ejection stability when ejected by an ink jet method and aggregation speed when a pretreatment liquid described later is used, the viscosity of the ink composition of the present invention is preferably in the range of 1 to 30mPa · s, more preferably in the range of 1 to 20mPa · s, further preferably in the range of 2 to 15mPa · s, and particularly preferably in the range of 2 to 10mPa · s.

Viscosity was measured by using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD.) at 25 ℃ in the ink composition.

The ink composition of the present invention preferably contains a pigment coated with a polymer dispersant having a carboxyl group and resin particles, and has a solid content of 7 to 10% by mass, and a content ratio of solid components other than the pigment of 0.8 to 1.6 by mass relative to the pigment, more preferably contains a pigment coated with an acrylic polymer and self-dispersible resin particles, and has a solid content of 7 to 9% by mass and a content ratio of solid components other than the pigment of 1.0 to 1.4 by mass relative to the pigment.

The ink set of the present invention has been described above, but the specific structure of the ink set of the present invention is not particularly limited as long as it contains the ink composition and the pretreatment liquid.

Preferred examples of the ink set of the present invention include: a structure (3-color structure) including a combination of a cyan ink as the ink composition, a magenta ink as the ink composition, a yellow ink as the ink composition, and the pretreatment liquid; or a combination of a black ink as the ink composition, a cyan ink as the ink composition, a magenta ink as the ink composition, a yellow ink as the ink composition, and the pretreatment liquid (4-color structure).

However, the ink set of the present invention may be a 1-color structure or a 2-color structure ink set including one or two types of ink compositions and a pretreatment liquid, as required.

The ink set of the present invention may further contain, in addition to the above-mentioned ink compositions, another ink composition such as at least one selected from light cyan ink, light magenta ink and light yellow ink, if necessary. As the other ink composition, a known ink composition can be used without particular limitation.

The ink set of the present invention may contain two or more pretreatment liquids as necessary.

The ink set of the present invention is suitable for the image recording method of the present invention described below.

< image recording method >

The image recording method of the present invention uses the above-described ink set of the present invention, and includes: a pretreatment liquid applying step of applying the pretreatment liquid to a recording medium; and an ink applying step of applying the ink composition to the recording medium to which the pretreatment liquid is applied in the pretreatment liquid applying step.

With the image recording method of this configuration, a decrease in the uniformity of the image can be suppressed.

(pretreatment liquid application step)

The pretreatment liquid applying step is a step of applying the pretreatment liquid to a recording medium.

The pretreatment liquid can be applied by a known method such as a coating method, an ink-jet method, or a dipping method. The coating method can be performed by a known coating method using a bar coater, an extrusion die coater, an air knife coater, a blade coater, a bar coater, a knife coater, an extrusion coater, a reverse roll coater, a bar coater, or the like. Details of the ink-jet method will be described later.

The pretreatment liquid applying step is provided before the ink applying step using the ink composition.

That is, before the ink composition is applied (ejected) onto the recording medium, a pretreatment liquid for aggregating components in the ink composition is applied in advance, and the ink composition is ejected so as to be in contact with the pretreatment liquid applied onto the recording medium to form an image.

This makes it possible to increase the speed of ink jet recording and obtain an image with high density and high resolution even when high-speed recording is performed.

Further, in the present invention, it is preferable that after the pretreatment liquid is applied to the recording medium, the pretreatment liquid on the recording medium is heat-dried until the ink composition is applied. This makes it possible to record a visible image having good color density and hue by preventing ink coloring such as bleeding from being good.

The heat drying is performed by a known heating mechanism such as a heater, an air blowing mechanism using air blowing such as a dryer, or a combination of these mechanisms.

Examples of the heating method include: a method of heating from the side opposite to the side to which the pretreatment liquid of the recording medium is applied by a heater or the like; a method of applying warm air or hot air to the surface of the pretreatment liquid for a recording medium; and a heating method using an infrared heater, and the like, and a plurality of these methods may be combined to perform heating.

(ink applying step)

The ink applying step applies (ejects) the ink composition onto (onto) the recording medium to which the pretreatment liquid is applied, by an ink jet method.

In this step, the ink composition can be applied to a recording medium, and a desired visible image can be recorded. Further, the details of the ink composition are as described above.

The ink JET method is not particularly limited, and may be any of a known method, for example, a charge control method in which ink is ejected by electrostatic attraction, a drop-on-demand (pressure pulse) method in which oscillation pressure of a piezoelectric element is used, an acoustic ink JET method in which an electric signal is changed into an acoustic beam and ink is ejected by radiation pressure, and a thermal ink JET (BUBBLE JET (registered trademark)) method in which ink is heated to form BUBBLEs and the pressure generated is used. As the ink jet method, among the methods described in japanese patent application laid-open No. 54-059936, an ink jet method is particularly effective in which ink is ejected from a nozzle by a biasing force generated by a change in state of the ink due to a rapid volume change of the ink caused by thermal energy.

The ink jet method includes a method of ejecting a large amount of low density ink called Photo ink (Photo ink) in a small volume, a method of improving image quality by using a plurality of inks having substantially the same hue and different densities, and a method of using colorless and transparent ink.

The inkjet head used in the inkjet method may be a drop-on-demand inkjet head or a continuous inkjet head. Specific examples of the ejection method include an electro-mechanical conversion method (for example, a single-chamber type, a double-chamber type, a bender (bender) type, a piston type, a common mode type, a shared wall type, and the like), an electro-thermal conversion method (for example, a thermal ink JET type, a BUBBLE JET (registered trademark) type, and the like), an electrostatic attraction method (for example, an electric field control type, a slit JET type, and the like), and an electric discharge method (for example, a spark JET type, and the like), and any of the ejection methods can be used.

The ink jet nozzle and the like used for recording by the above ink jet method are not particularly limited and may be appropriately selected according to the purpose.

As the ink jet head, there are the following modes: a shuttle system in which recording is performed while scanning an ink jet head in the width direction of a recording medium using a short Serial head (Serial head); and a Line type using a Line head (Line head) in which recording elements are arranged in the entire region corresponding to one side of the recording medium. In the line system, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, and a conveyance system such as a carriage (carriage) that scans with a short head is not required. Further, since only the recording medium is moved without performing complicated scanning control of the carriage and the recording medium, the recording speed can be increased as compared with the reciprocating method.

The image recording method of the present invention can be applied to any of these methods, and when the method is applied to a line system in which the pseudo ejection is not usually performed, the effect of improving the ejection accuracy and the abrasion resistance of the image is large.

The ink applying step is preferably started within 10 seconds, more preferably within 0.1 to 10 seconds, after the pretreatment liquid applying step. This enables high-speed image recording.

Further, in the image recording method of the present invention, by using the above-described ink set, impact interference between inks is suppressed even in the case of recording an image at high speed, and a high definition image can be recorded.

Here, "start within 10 seconds after the pretreatment liquid application step" means that the time from the end of application/drying of the pretreatment liquid to the first ink droplet landing on the recording medium is within 10 seconds.

In the ink application step, the amount of droplets of ink to be applied (ejected) is preferably 1.5pL to 3.0pL, and more preferably 1.5pL to 2.5pL, from the viewpoint of high-definition printing.

The amount of the ink droplets can be adjusted by appropriately selecting the ejection conditions in the ink jet method according to the ink composition to be ejected.

(Heat fixation Process)

In the present invention, it is preferable that a heat fixing step of heat-fixing the image (ink) recorded in the ink applying step be provided after the ink applying step.

The image on the recording medium is fixed by the heat fixing, and the abrasion resistance of the image is further improved.

The heating is preferably performed at a temperature equal to or higher than the minimum film-forming temperature (MFT) of the resin particles in the image. The image is strengthened by heating to a temperature not lower than MFT to coat the particles.

When the pressurization is performed in addition to the heating, the pressure at the time of pressurization is preferably in the range of 0.1 to 3.0MPa, more preferably in the range of 0.1 to 1.0MPa, and further preferably in the range of 0.1 to 0.5MPa, from the viewpoint of surface smoothness.

The heating method is not particularly limited, and a non-contact drying method is preferably used, and examples thereof include a method of heating with a heating element such as a nichrome wire heater, a method of supplying warm air or hot air, and a method of heating with a halogen lamp, an infrared lamp, and the like.

The method of heating and pressing is not particularly limited, and examples thereof include a method of pressing a hot plate against the image recording surface of the recording medium, a method of using a pair of heating and pressing rollers, a pair of heating and pressing belts, or a heating and pressing device including a heating and pressing belt disposed on the image recording surface side of the recording medium and a holding roller disposed on the opposite side thereof, and passing the recording medium through the pair of rollers.

When the heating and pressing are performed, the nip (nip) time is preferably 1 millisecond to 10 seconds, more preferably 2 milliseconds to 1 second, and further preferably 4 milliseconds to 100 milliseconds. The holding width is preferably 0.1mm to 100mm, more preferably 0.5mm to 50mm, and still more preferably 1mm to 10 mm.

The heating and pressing roller may be a metal roller, or a roller in which a coating layer made of an elastic body and a surface layer (also referred to as a release layer) provided as necessary are provided around a metal core. The latter metal core may be formed of, for example, a cylindrical body made of iron, aluminum, SUS, or the like, and preferably, at least a part of the surface of the metal core is covered with a clad layer.

The coating layer is particularly preferably formed of a silicone resin or a fluororesin having releasability. Further, it is preferable that a heating element is incorporated in one metal core of the heating and pressing roller, and the heating treatment and the pressing treatment can be performed simultaneously by passing the recording medium between the rollers, or the heating can be performed by sandwiching the recording medium between two heating rollers as necessary. As the heating element, for example, a halogen lamp heater, a ceramic heater, a nichrome wire, or the like is preferable.

As a belt base material constituting the heating and pressing belt used in the heating and pressing device, seamless electroformed nickel is preferable, and the thickness of the base material is preferably 10 μm to 100 μm. As the material of the tape base, aluminum, iron, polyethylene, or the like may be used in addition to nickel. When a silicone resin or a fluororesin is provided, the thickness of the layer formed using these resins is preferably 1 μm to 50 μm, and more preferably 10 μm to 30 μm.

In order to realize the above-described pressure (nip pressure), for example, an elastic member such as a spring having a tensile force may be selected and disposed at both ends of a roller such as a heat-pressing roller so that a desired nip pressure is obtained in consideration of a nip gap.

The conveying speed of the recording medium when the heat pressure roller or the heat pressure belt is used is preferably 200 mm/sec to 700 mm/sec, more preferably 300 mm/sec to 650 mm/sec, and further preferably 400 mm/sec to 600 mm/sec.

(recording Medium)

In the image recording method of the present invention, as described above, an image is recorded on a recording medium.

The recording medium is not particularly limited, and a general printing paper mainly composed of cellulose used in general offset printing or the like can be used.

Furthermore, as the recording medium, so-called coated paper is preferable.

Coated paper is paper in which a coating layer (also referred to as a coating layer) containing an inorganic pigment or the like is provided on the surface of high-quality paper, which is mainly composed of cellulose as a support and is not usually subjected to surface treatment, or neutral paper or the like. The coated paper tends to easily cause image unevenness of the image portion, but in the case where the above-mentioned pretreatment liquid contains phosphoric acid or a phosphoric acid compound, the occurrence of image unevenness of the image portion can be effectively suppressed. Specifically, art paper, coated paper, lightweight coated paper, or micro-coated paper is preferable.

The inorganic pigment contained in the coating layer is not particularly limited, but is preferably at least one selected from the group consisting of silica, kaolin, clay, calcined clay, zinc oxide, tin oxide, magnesium sulfate, alumina, aluminum hydroxide, pseudoboehmite, calcium carbonate, satin white, aluminum silicate, montmorillonite, zeolite, magnesium silicate, magnesium carbonate, magnesium oxide, and diatomaceous earth, and more preferably calcium carbonate, silica, and kaolin.

As the recording medium, there can be used a recording medium generally commercially available, for example, fine PAPERs (A) such as "OK PRINCE HIGH GRADE" made by Oji Paper Co., Ltd, "OK EVER LIGHT COATS CO" made by NIPPON PAPER INDUSTRIES CO., LTD "SHIRAOI" and NIPPON PAPER INDUSTRIES CO., LTD "NEW NPI HIGH GRA DE" made by LTD, micro-coated PAPERs (A3) such as "AURORA S" made by Oji Paper Co., Ltd, "COAAT L" made by Ltd and NIPPON PAPER INDUSTRIES CO., LTD "AURORA L" made by LTD, light-weight coated PAPERs (A3) such as "NAFLEX L", Oji PAPER CO., LTD "AURORA L" made by Oji Paper Co., LTD, "TOP COA COAS" made by LtdUS "and NIPPON PAPER INDUSTRIES CO., NAFLY" made by NIPPON PAPER INDUSTRIES CO., LTD ", NAFLY L", NAFLY "3" made by Oji PAPER CO., LTD ", KAJI PAPER CO., LTD" made by "and KAJI PAPER 2" POPT CO., LTD ", KAJO, and ART papers (A1) such as "UFCOAT" manufactured by Ltd and "TOKUBASISHI ART" manufactured by Mitsubishi Paper Mills Limited. Also, various photographic papers for inkjet recording can be used.

Among the above, from the viewpoint of obtaining a high-quality image having a large effect of suppressing the migration of the coloring material and having a color density and a hue better than those of the conventional ones, the water absorption coefficient Ka is preferably 0.05mL/m²·ms^1/2～0.5mL/m²·ms^1/2More preferably 0.1mL/m²·ms^1/2～0.4mL/m²·ms^1/2More preferably 0.2mL/m²·ms^1/2～0.3mL/m²·ms^1/2The recording medium of (1).

The water absorption coefficient Ka is similar to that of JAPAN TAPPI Pulp and Paper Testing Method No 51: 2000 (published: JAPAN TAPPI), and specifically, the water absorption coefficient Ka was calculated from the difference between the water transfer amounts at a contact time of 100ms and a contact time of 900ms using an automatic scanning liquid absorptometer KM500Win (manufactured by KUMAGAI RIKI KOGYO Co., Ltd.).

In the present invention, the amount of the pretreatment liquid and the amount of the aqueous ink are preferably adjusted as necessary. For example, the amount of the pretreatment liquid to be added may be changed in order to adjust the physical properties such as viscoelasticity of an aggregate obtained by mixing the pretreatment liquid and the aqueous ink, depending on the recording medium.

Examples

The present invention will be described in more detail below with reference to examples. The scope of the present invention is not limited to the specific examples shown below. Unless otherwise specified, "part" and "%" are based on mass.

In this example, the weight average molecular weight, pH and pKa were measured by the methods described above.

< examples 1 to 17 and comparative examples 1 to 4 >)

< Synthesis of Polymer dispersant P-1 >

The polymer dispersant P-1 was synthesized according to the following scheme by the method shown below.

[ chemical formula 1]

A1000 ml three-necked flask equipped with a stirrer and a condenser was charged with 88g of methyl ethyl ketone, heated to 72 ℃ under a nitrogen atmosphere, and a solution prepared by dissolving 0.85g of dimethyl 2, 2' -azobisisobutyrate, 60g of benzyl methacrylate, 10g of methacrylic acid, and 30g of methyl methacrylate in 50g of methyl ethyl ketone was added dropwise thereto over 3 hours. After completion of the dropwise addition, the reaction mixture was further reacted for 1 hour, and then a solution prepared by dissolving 0.42g of dimethyl 2, 2' -azobisisobutyrate in 2g of methyl ethyl ketone was added thereto, and the mixture was heated to 78 ℃ for 4 hours.

The resulting reaction solution was reprecipitated twice in a large excess amount of hexane, and the precipitated resin was dried to obtain 96g of a polymer dispersant P-1. In addition, the numbers of the respective structural units of the polymer dispersant P-1 shown above represent mass ratios.

The composition of the obtained resin is as follows¹It was confirmed by H-NMR that the weight-average molecular weight (Mw) determined by GPC was 44,600. The acid value was determined to be 65.2mgKOH/g by the method described in JIS (JIS K0070: 1992).

< preparation of pigment Dispersion >

(preparation of cyan Dispersion)

Pigment blue 15 as a cyan pigment was mixed: 5 parts of 3 (phthalocyanine blue-A220, Dainiciseika Color & Chemicals Mfg. Co., Ltd.), 5 parts of the above-mentioned polymer dispersant P-12 parts, 42 parts of methyl ethyl ketone, 5.5 parts of a 1-specified NaOH aqueous solution and 87.2 parts of ion-exchanged water were dispersed for 2 to 6 hours by a bead mill using 0.1 mm. phi. zirconia beads.

After methyl ethyl ketone was removed from the resulting dispersion under reduced pressure at 55 ℃ and a part of water was further removed, centrifugation was further performed for 30 minutes using a high-speed centrifugal chiller 7550 (manufactured by KUBOTA Corporation co., ltd.) and 8000rpm (revolutions per minute) using a 50mL centrifuge tube, and a supernatant other than the precipitate was recovered. Then, the pigment concentration was determined from the absorption spectrum, and a dispersion of resin-coated pigment particles (pigment coated with a polymer dispersant) having a pigment concentration of 10.2 mass% (cyan dispersion C) was obtained. The cyan dispersion C obtained had an average particle size of 105 nm.

(preparation of magenta Dispersion)

In the preparation of the cyan dispersion, instead of pigment blue 15: a dispersion of resin-coated pigment particles (pigment coated with a polymer dispersant) (magenta dispersion M) was prepared in the same manner as in the preparation of the cyan dispersion, except that pigment red 122 was used as the magenta pigment (phthalocyanine blue-a 220, dainicheika Color & Chemicals mfg.co., ltd.). The mean particle diameter of the magenta dispersion M obtained was 85 nm.

< preparation of self-dispersible resin particles >

A2L three-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet was charged with 360.0g of methyl ethyl ketone, and then the temperature was raised to 75 ℃. While the temperature in the reaction vessel was kept at 75 ℃, a mixed solution containing phenoxyethyl acrylate 180.0g, methyl methacrylate 162.0g, acrylic acid 18.0g, methyl ethyl ketone 72g, and "V-601" (manufactured by FUJIFILM Wako Pure Chemical Corporation) 1.44g was added dropwise at a constant rate to complete the dropwise addition within 2 hours. After completion of the dropwise addition, a solution containing 0.72g of "V-601" and 36.0g of methyl ethyl ketone was added, and after stirring at 75 ℃ for 2 hours, a solution containing 0.72g of "V-601" and 36.0g of isopropyl alcohol was further added, and after stirring at 75 ℃ for 2 hours, the temperature was raised to 85 ℃ and further stirring was continued for 2 hours. The weight average molecular weight (Mw) of the obtained copolymer was 64000 (TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (manufactured by TOSOH CORPORATION)) as a column used in terms of polystyrene in accordance with Gel Permeation Chromatography (GPC), and the acid value was 38.9 (mgKOH/g).

Then, 668.3g of the polymerization solution was weighed, 388.3g of isopropyl alcohol and 145.7ml of a 1mol/L aqueous NaOH solution were added, and the temperature in the reaction vessel was raised to 80 ℃. Subsequently, 720.1g of distilled water was added dropwise at a rate of 20ml/min to conduct water dispersion. Then, the temperature in the reaction vessel was held at 80 ℃ for 2 hours, at 85 ℃ for 2 hours, and at 90 ℃ for 2 hours under atmospheric pressure, and then the pressure in the reaction vessel was reduced to distill off 913.7g in total of isopropyl alcohol, methyl ethyl ketone, and distilled water, thereby obtaining a water dispersion (emulsion) of the self-dispersible resin particles (B-01) having a solid content concentration of 28.0%. In addition, the numbers of the respective structural units of the compound example (B-01) shown below represent mass ratios. Hereinafter, the same applies to each structural formula.

[ chemical formula 2]

< preparation of ink >

Using the pigment dispersions (cyan dispersion C and magenta dispersion M) and the self-dispersible resin particles B-01 obtained above, the respective components were mixed to have the compositions of inks shown in table 1 below, and ink compositions (magenta ink composition M and cyan ink composition C) were prepared, respectively.

Each of the prepared ink compositions was filtered through a PVDF5 μ M filter (Millex SV, 25mm diameter, manufactured by Millipore Corporation) in a plastic disposable syringe to prepare inks (magenta ink M and cyan ink C).

[ Table 1]

	Cyan ink C	Magenta ink M
			Cyan pigment (pigment blue 15: 3)	5% by mass	-
Magenta pigment (pigment Red 122)	-	5% by mass
			Polymer dispersant P-1	2% by mass	2% by mass
Glycerol	2% by mass	2% by mass
			Propylene glycol	12% by mass	12% by mass
Self-dispersible resin particle (B-01)	8% by mass	8% by mass
			OLFINE E1010	1% by mass	1% by mass
Water (W)	70% by mass	70% by mass

< description of Table 1>

OLFINE E1010 … … Nissin Chemical Industry co., ltd

< preparation of pretreatment solution >

The following compositions were mixed to prepare pretreatment liquids 1 to 21.

Composition of the pretreatment liquid

Malonic acid … … in the amounts shown in Table 2

Citric acid … … in the amounts shown in Table 2

Phosphoric acid (orthophosphoric acid) … … in the amounts shown in Table 2

Water-soluble Polymer … … shown in Table 2 in the amounts shown in Table 2

Diethylene glycol monoethyl ether … … 1 mass%

Potassium hydroxide … … in the amounts shown in Table 2

BYK-038 (antifoaming agent) … … 0.01.01% by mass

Ion-exchanged water … … in balance

< ink set >

Ink sets 1 to 21 were prepared by combining the above-described inks (magenta ink M and cyan ink C) and the pretreatment liquids (pretreatment liquid 1 to pretreatment liquid 21).

< ink jet image recording >

UF COAT (manufactured by Oji Paper co., ltd.) was prepared as a recording medium having a coating layer containing calcium carbonate, and images were recorded under the following image recording conditions using the above-described ink sets 1 to 21.

In the image recording described below, the ink ejection was started within 10 seconds or less after the pretreatment liquid application step.

(pretreatment liquid application step)

Immediately before applying ink to the recording medium, the pretreatment liquid was applied using a coating bar (coating amount was 1.7 g/m)²) Onto the surface of the recording medium.

Next, the pretreatment liquid applied to the recording medium was dried under the following conditions.

Drying condition (air supply drying) for about pretreatment liquid

Wind speed: 15m/s

Temperature and heating method: the recording medium was heated from the back surface (the surface to which the pretreatment liquid was not applied) thereof by a contact flat heater so that the surface temperature of the recording medium (the temperature to which the pretreatment liquid was applied) became 60 ℃.

An air supply area: 450mm (drying time 0.7 second)

(ink applying step)

Under the following conditions, 2-color single-pass (single-pass) image recording was performed on the recording medium to which the pretreatment liquid was applied.

Specifically, under the following conditions, the inks of the respective colors were applied (ejected) to the pretreatment liquid of the recording medium to which the pretreatment liquid was applied to record an image.

A spray head: a head configured with four colors of 1,200dpi/20inch wide piezoelectric full line heads was used.

The amount of sprayed liquid drops: set to 2.4 pL.

Driving frequency: set to 30kHz (recording medium transport speed of 635 mm/sec).

Next, the ink applied to the recording medium was dried under the following conditions.

Drying condition (air supply drying) for printing ink

Wind speed: 15m/s

Temperature: the recording medium was heated from the back surface (the surface to which ink was not applied) thereof by a contact flat heater so that the surface temperature of the recording medium (the temperature to which ink was applied) became 60 ℃.

An air supply area: 640mm (drying time 1 second)

(Heat fixation Process)

The image recorded by applying the ink was heat-fixed using a silicone rubber roller (hardness 50 ° and nip width 5mm) under the following conditions.

Thus, a sample having an image recorded on the recording medium was obtained.

Condition of heating and fixing

Roll temperature: 90 deg.C

Pressure: 0.8MPa

< evaluation >

(image unevenness)

In the ink application step, a blue dense image (halftone dot ratio of 30%) was recorded using the cyan ink C and the magenta ink M.

The obtained dense image was subjected to the above-described heat fixing treatment.

The dense image after the heat fixing was observed with the naked eye, and the uniformity of the image was evaluated according to the following criteria as an index of the image unevenness. The evaluation results are shown in table 2 below.

Evaluation criteria-

6: color unevenness was not observed as a whole, and it was uniform.

5: if carefully observed, some color non-uniformity, but roughly uniform overall, can be observed.

4: color unevenness was observed, but the difference in shade was extremely small.

3: a small amount of color unevenness was observed, and partial shading was observed.

2: there was scattered color unevenness and partial shading was observed, but within a practically allowable range.

1: a large striped depth is produced, exceeding the practically allowable range.

(evaluation of white spots)

In the ink application step, a blue dense image (halftone dot ratio 100%) was recorded using the cyan ink C and the magenta ink M.

The obtained dense image was subjected to the above-described heat fixing treatment.

After the heat fixing, the finger moistened with water was gently wiped with a cloth to be in contact with the surface of the image, and was removed after standing for 1 second. The region of the image touched by the finger was observed with the naked eye, and the degree of white spots was evaluated based on the following criteria. The evaluation results are shown in table 2 below.

White spots refer to white portions on the recorded image caused by the deposition of calcium.

Evaluation criteria-

A: no white spots were produced.

B: white spots are produced but can be erased.

C: white spots were generated and failed to erase.

(corrosiveness of parts)

A stainless steel plate (SUS303) having a size of 15 mm. times.10 mm. times.5 mm was prepared, and the stainless steel plate was immersed in the pretreatment liquid for 3 days while being heated at 60 ℃ to visually evaluate the degree of corrosion. The evaluation was performed according to the following evaluation criteria.

Evaluation criteria-

3: no corrosion was observed at all.

2: some corrosion was observed, but within practically allowable limits.

1: the corrosion was significant and was outside the practically allowable range.

(liquid stability)

After the preparation of the pretreatment liquid, the pretreatment liquid was left to stand at 25 ℃ for 1 hour, and generation of precipitates and/or phase separation was visually observed, and the liquid stability of the pretreatment liquid was evaluated according to the following evaluation criteria.

Evaluation criteria-

A: after the preparation of the pretreatment liquid, no precipitate and/or phase separation occurred.

B: after the pretreatment liquid was prepared, precipitates and/or phase separation were generated.

(evaluation of blur (bleeding) of image)

In the ink application step, a character image was recorded using the cyan ink C.

The obtained character images were subjected to the above-described heat-fixing treatment, and the character images shown in FIG. 1 were recorded (unicode: U +9DF 9; 2pt, 3pt, 4pt and 5 pt).

The recorded character image was observed, and the blur of the image was evaluated based on the following evaluation criteria.

The results are shown in Table 2.

In the evaluation criterion described below, the level at which the blur of the image is maximally suppressed is "5".

Evaluation criteria for blurring of images-

5: the 2pt character can be reproduced.

4: characters of 3pt can be reproduced, but characters of 2pt cannot be reproduced.

3: characters of 4pt can be reproduced, but characters of 3pt or less cannot be reproduced.

2: characters of 5pt can be reproduced, but characters of 4pt or less cannot be reproduced.

1: the 5pt character cannot be reproduced.

In addition, the above-mentioned "reproducible" indicates that, when confirmation is performed from a position 0.5m away, in the character image shown in fig. 2, the horizontal line indicated by 111 shown in fig. 2 is separated from the horizontal line indicated by 112 shown in fig. 2.

The details of each component described in table 2 are as follows.

PEG 1: polyethylene glycol (polyethylene glycol 2000, manufactured by FUJIFILM Wako Pure Chemical Corporation, weight average molecular weight 2000)

PEG 2: polyethylene glycol (polyethylene glycol 4000, manufactured by FUJIFILM Wako Pure Chemical Corporation, weight average molecular weight 4000)

PEG 3: polyethylene glycol (polyethylene glycol 6000, manufactured by FUJIFILM Wako Pure Chemical Corporation, weight average molecular weight 6000)

PVP 1: polyvinylpyrrolidone (polyvinylpyrrolidone K-15, manufactured by FUJIFILM Wako pure chemical Corporation, weight-average molecular weight 10000)

PVP 2: polyvinylpyrrolidone (polyvinylpyrrolidone K-30, weight-average molecular weight 2450, FUJIFILM Wako Pure chemical Corporation)

PVP 3: polyvinylpyrrolidone (polyvinylpyrrolidone K-90, manufactured by FUJIFILM Wako Pure chemical Corporation, weight average molecular weight 40000)

Polyacrylic acid: polyacrylic acid (25,000, manufactured by FUJIFILM Wako Pure Chemical Corporation, weight average molecular weight 25000)

As shown in table 2, examples 1 to 17 were excellent in image unevenness and corrosion of parts.

Among them, example 1 using polyethylene glycol as a nonionic water-soluble polymer is superior in image unevenness to example 2 using polyacrylic acid as an ionic water-soluble polymer.

In examples 1 to 14 in which the total content of the acid group in the acid and the salt of the acid was 0.25mol or more based on 100g of the pretreatment liquid, the blurring of the image was further suppressed as compared with examples 15 and 16.

Description of the symbols

Drawing 111-11, drawing 112-12.