阅读说明：本技术 油墨组和印刷物的制造方法 (Ink set and method for producing printed matter ) 是由 饭冈直明 仁尾刚启 庄子友理 保坂正喜 于 2018-11-29 设计创作，主要内容包括：本发明要解决的课题在于提供一种油墨组,其能够形成减少了渗色、混色的印刷物。本发明为一种油墨组,其为包含静态表面张力(a1)为20mN/m～40mN/m范围的黑色颜料油墨(a)、以及选自由品红色颜料油墨和黄色颜料油墨组成的组中的至少一种颜料油墨(b)的油墨组,其特征在于,所述颜料油墨(b)的静态表面张力比所述静态表面张力(a1)小0.1mN/m～0.7mN/m。(The present invention addresses the problem of providing an ink set that can form a printed matter with reduced bleeding and color mixing. The present invention is an ink set comprising a black pigment ink (a) having a static surface tension (a1) in the range of 20 to 40mN/m, and at least one pigment ink (b) selected from the group consisting of magenta pigment inks and yellow pigment inks, characterized in that the static surface tension of the pigment ink (b) is 0.1 to 0.7mN/m lower than the static surface tension (a 1).)

1. An ink set comprising a black pigment ink (a) having a static surface tension (a1) in the range of 20 to 40mN/m, and at least one pigment ink (b) selected from the group consisting of magenta pigment inks and yellow pigment inks, characterized in that the static surface tension of the pigment ink (b) is 0.1 to 0.7mN/m lower than the static surface tension (a 1).

2. The ink set of claim 1, further comprising a cyan pigment ink having any static surface tension.

3. The ink set according to claim 1 or 2, wherein the pigment ink (b) is discharged onto a recording medium by an inkjet recording method after the black pigment ink (a) is discharged by an inkjet recording method and landed on the recording medium.

4. The ink set according to claim 1, which is an ink set comprising the black pigment ink (a), a magenta pigment ink and a yellow pigment ink as the pigment ink (b), and the cyan pigment ink,

discharging the black pigment ink (a), the cyan pigment ink, the magenta pigment ink and the yellow pigment ink in this order onto a recording medium by an ink jet recording method,

the static surface tension of the magenta pigment ink is smaller than the static surface tension (a1) by 0.1 to 0.7mN/m, and

the static surface tension of the yellow pigment ink is smaller than the surface tension of the magenta pigment ink by 0.1mN/m to 0.7mN/m,

the static surface tension of the cyan pigment ink is arbitrary.

5. The ink set according to any one of claims 1 to 4, used in an ink jet recording system in which a distance from a surface (x) of an ink jet head having an ink discharge port to a position (y) where a perpendicular line to the surface (x) intersects a recording medium is 2mm or more.

6. The ink set according to any one of claims 1 to 5, wherein the recording medium has a water absorption capacity of 10g/m when the recording surface of the recording medium is in contact with water for 100 msec²The following.

7. The ink set according to claim 6, wherein the recording medium is corrugated paper, or has a water absorption capacity of 10g/m²Corrugated paper of the following layers.

8. A method for producing a printed matter by discharging an ink set containing a black pigment ink (a), a magenta pigment ink and a yellow pigment ink as the pigment ink (b), and the cyan pigment ink onto a recording medium by an ink jet recording system,

the following ink sets were used:

discharging the black pigment ink (a), the cyan pigment ink, the magenta pigment ink and the yellow pigment ink in this order onto a recording medium by an ink jet recording apparatus,

the static surface tension of the magenta pigment ink is smaller than the static surface tension (a1) by 0.1 to 0.7mN/m, and

the static surface tension of the yellow pigment ink is smaller than the surface tension of the magenta pigment ink by 0.1mN/m to 0.7mN/m,

the static surface tension of the cyan pigment ink is arbitrary.

9. A method for manufacturing a printed matter, comprising a printing step: discharging the ink set according to any one of claims 1 to 7 onto a recording medium by an ink jet recording method to obtain a printed matter,

in the printing step, the shortest distance between the ink discharge port of the ink jet head and the recording medium is 2mm or more.

Technical Field

The present invention relates to an ink set that can be used when a printed matter is produced by an inkjet recording method.

Background

Since pigment inks for inkjet recording can form printed matters excellent in light resistance and the like, they have been studied for use in printing on various media such as plain paper, coated paper, plastic films, metals, and fabrics.

Particularly, with the rapid growth of the Print On Demand (Print On Demand) market in recent years, there has been a Demand for a water-based pigment ink for inkjet recording that can be printed On a recording medium at high speed and can produce a high-quality printed matter comparable to a printed matter obtained by a lithographic printing method.

In order to print high-quality printed matter at high speed, it is necessary to suppress bleeding at color boundaries between inks of different hues. As a method for preventing the bleeding between the inks, for example, an ink set which can be ejected onto a medium and has a pixel density of 650dpi or more and a recording speed of 0.5m is known²An ink set for an image forming apparatus for forming an image at a speed of at least min, the ink set including an ink composition containing at least an ink composition A and an ink composition B, and satisfying a predetermined condition (for example, see patent document 1).

However, when the ink is used for high-speed printing on a non-absorptive recording medium or a low-absorptive recording medium such as coated paper, or a plastic film, for example, bleeding at the color boundary between inks of different hues cannot be sufficiently suppressed in practical use, and as a result, a printed matter of high image quality may not be obtained.

Disclosure of Invention

Problems to be solved by the invention

The present invention addresses the problem of providing an ink set that can form a printed matter with reduced bleeding and color mixing.

Means for solving the problems

The present inventors have found that the above problems can be solved by using an ink set comprising a black pigment ink (a) having a static surface tension (a1) in the range of 20 to 40mN/m and at least one pigment ink (b) selected from the group consisting of magenta pigment inks and yellow pigment inks, wherein the static surface tension of the pigment ink (b) is 0.1 to 0.7mN/m lower than the static surface tension (a 1).

Effects of the invention

According to the ink set of the present invention, a printed matter with reduced bleeding and color mixing can be produced.

Drawings

FIG. 1 is a schematic representation of a microreactor for use in the present invention.

Detailed Description

The ink set of the present invention is an ink set comprising a black pigment ink (a) having a static surface tension (a1) in the range of 20 to 40mN/m, and at least one pigment ink (b) selected from the group consisting of magenta pigment inks and yellow pigment inks, wherein the static surface tension of the pigment ink (b) is 0.1 to 0.7mN/m lower than the static surface tension (a 1).

The black pigment ink (a) used in the present invention is an ink having a static surface tension (a1) at 25 ℃ of 20mN/m or more as the lower limit, and is more preferably 23mN/m or more, and still more preferably 25mN/m or more. On the other hand, as the black pigment ink (a), an ink having an upper limit of static surface tension (a1) at 25 ℃ of 40mN/m or less, preferably 35mN/m or less, and more preferably less than 30mN/m is used. By using the black pigment ink (a) having a static surface tension (a1) in the above range, white streaks can be suppressed from occurring on a printed matter, and by using the black pigment ink (a) in combination with the pigment ink (b) and the like described later, bleeding and color mixing of the printed matter can be reduced. The black pigment ink (a) having a static surface tension in the above range is rapidly spread to a level capable of achieving both satisfactory drying performance and suppression of bleeding and color mixing after being landed on the surface of a recording medium.

Even if the shortest distance between the ink discharge port of the ink jet head and the recording medium (i.e., the distance from the surface (x) of the ink jet head having the ink discharge port to the position (y) where the perpendicular to the surface (x) intersects the recording medium) is 2mm or more, the black pigment ink (a) and the ink set containing the same can reduce the landing position deviation on the recording medium due to the flying curvature of the discharged droplets in appearance, and can effectively prevent the occurrence of streaks on the printed matter.

In the ink set of the present invention, the pigment ink (b) is used in combination with the black pigment ink (a).

As the pigment ink (b), an ink having a static surface tension at 25 ℃ which is 0.1mN/m to 0.7mN/m lower than the static surface tension (a1) is used, and an ink having a static surface tension which is 0.1mN/m to 0.3mN/m lower is preferably used.

When the static surface tension of the pigment ink (b) is the same as the static surface tension (a1), is less than the static surface tension (a1) by less than 0.1mN/m, or is greater than the static surface tension (a1), the black pigment ink (a) tends to move to the pigment ink (b) on the surface of the recording medium, and color mixing or bleeding tends to occur. The bleeding and color mixing which are problems to be solved by the present invention are particularly noticeable when the black pigment ink (a) is transferred to the pigment ink (b) on the surface of the recording medium.

On the other hand, when the static surface tension of the pigment ink (b) is smaller than the static surface tension (a1) by more than 0.7mN/m, excessive movement of ink components tends to occur between the black pigment ink (a) and the pigment ink (b) on the surface of the recording medium, and color mixing and bleeding tend to occur.

In order to suppress the migration, it is estimated that the migration of the black pigment ink (a) to the pigment ink (b) and further the migration of the pigment ink (b) to the black pigment ink (a) can be further suppressed by using, as the pigment ink (b), an ink set in which an ink having a static surface tension which is 0.1mN/m to 0.7mN/m lower than the static surface tension (a1) is selected and which is combined with the black pigment ink (a).

As described above, by using the black pigment ink (a) having the static surface tension (a1) in the above range in combination with the pigment ink (b), it is possible to more effectively suppress the occurrence of bleeding and color mixing between the colors (color boundary) of the black pigment ink (a) and the pigment ink (b), and to suppress the occurrence of ink discharge failure and flight bending due to the leakage of the black pigment ink (a) and the pigment ink (b) from the vicinity of the ink discharge nozzle when the black pigment ink (a) and the pigment ink (b) are discharged.

Further, according to the ink set in which the black pigment ink (a) having the static surface tension (a1) in the above range and the pigment ink (b) are combined, even when the black pigment ink (a) and the pigment ink (b) land on a recording medium and ink droplets thereof come into contact with each other, migration of components from one ink to the other ink can be suppressed, and therefore, even when the ink set is printed on a recording medium such as a non-absorptive recording medium or a low-absorptive recording medium, a printed matter in which occurrence of bleeding or color mixing is further reduced can be obtained.

The static surface tension of the black pigment ink (a) and the pigment ink (b) is a value measured under the following conditions using an automatic surface tensiometer using the Wilhelmy method. The Wilhelmy method described above can measure the static surface tension and the dynamic surface tension.

A measuring device: automatic surface tension meter (K100 MK3 manufactured by KRUSS Co., Ltd.)

Measuring temperature: 25 deg.C

Measuring head: platinum plate

The static surface tension (a1) of the black pigment ink (a) and the static surface tension of the pigment ink (b) can be adjusted to a target range by adjusting the kind and amount of a surfactant, a solvent, or the like, for example, and can be adjusted particularly by adjusting the kind and amount of a surfactant.

As the pigment ink (b), at least one selected from the group consisting of magenta pigment inks and yellow pigment inks can be used, and magenta pigment inks and yellow pigment inks are more preferably used.

In the case of using an ink set in which a magenta pigment ink and a yellow pigment ink, which are the pigment ink (b), are used in combination and the black pigment ink (a) is used, it is preferable to set the ink set so as to be discharged onto a recording medium by an ink jet recording method in the order of the black pigment ink (a), the magenta pigment ink, and the yellow pigment ink, in order to achieve the effect of suppressing bleeding and color mixing. In this case, from the viewpoint of achieving the effect of suppressing bleeding and color mixing, it is preferable to use a combination of inks in which the static surface tension of the magenta pigment ink is smaller than the static surface tension (a1) of the black pigment ink (a) by 0.1 to 0.7mN/m, preferably by 0.1 to 0.5mN/m, and preferably by 0.1 to 0.3mN/m, and the static surface tension of the yellow pigment ink is smaller than the static surface tension of the magenta pigment ink by 0.1 to 0.7mN/m, preferably by 0.1 to 0.5mN/m, and preferably by 0.1 to 0.3 mN/m.

In the case of using an ink set in which a magenta pigment ink and a yellow pigment ink are used as the pigment ink (b) and these are combined with the black pigment ink (a) and a cyan pigment ink which is any ink other than the above, it is preferable to set the cyan pigment ink, the black pigment ink (a), the magenta pigment ink, and the yellow pigment ink in this order to be discharged onto a recording medium by an ink jet recording method in order to achieve the effect of suppressing bleeding and color mixing. In this case, from the viewpoint of achieving the effect of suppressing bleeding and color mixing, it is preferable to use a combination of inks which have a static surface tension of 0.1 to 0.7mN/m, preferably 0.1 to 0.5mN/m, and preferably 0.1 to 0.3mN/m lower than the static surface tension (a1), a static surface tension of the yellow pigment ink which is 0.1 to 0.7mN/m, preferably 0.1 to 0.5mN/m, and preferably 0.1 to 0.3mN/m lower than the surface tension of the magenta pigment ink, and a static surface tension of the cyan pigment ink.

In the case of using an ink set in which a magenta pigment ink and a yellow pigment ink are used as the pigment ink (b) and these are combined with the black pigment ink (a) and a cyan pigment ink which is any ink other than the above, it is preferable to set the ink set so that the black pigment ink (a), the cyan pigment ink, the magenta pigment ink, and the yellow pigment ink are discharged onto a recording medium by an ink jet recording method in this order from the viewpoint of achieving the effect of suppressing bleeding and color mixing. In this case, from the viewpoint of achieving the effect of suppressing bleeding and color mixing, it is preferable to use a combination of inks in which the static surface tension of the magenta pigment ink is 0.1 to 0.7mN/m, preferably in the range of 0.1 to 0.5mN/m, and preferably 0.1 to 0.3mN/m lower than the static surface tension (a1), and the static surface tension of the yellow pigment ink is 0.1 to 0.7mN/m, preferably in the range of 0.1 to 0.5mN/m, and preferably 0.1 to 0.3mN/m lower than the surface tension of the magenta pigment ink, and the static surface tension of the cyan pigment ink is arbitrary.

As the cyan pigment ink, as in the pigment ink (b), an ink having a static surface tension which is smaller than the static surface tension (a1) of the black pigment ink (a) by 0.1 to 0.7mN/m, preferably in the range of 0.1 to 0.5mN/m, and preferably 0.1 to 0.3mN/m can be used, but bleeding and the like are not noticeable even when the black pigment ink (a) moves to the cyan pigment ink, and therefore, a cyan pigment ink having an arbitrary static surface tension can be used as an arbitrary ink other than the pigment ink (b).

In this case, the cyan pigment ink preferably has a lower limit of static surface tension at 25 ℃ of 20mN/m or more, more preferably 23mN/m or more, and particularly preferably 25mN/m or more. On the other hand, as the cyan pigment ink, an ink having an upper limit of static surface tension (a1) at 25 ℃ of 40mN/m or less is preferably used, more preferably 35mN/m or less is used, and particularly preferably less than 30mN/m is used.

The static surface tension (a1) of the black pigment ink (a) and the static surface tension of the pigment ink (b) can be set within the above ranges by adjusting the type and content of the surfactant, solvent, and the like contained therein, for example, and the influence of the surfactant in adjusting the static surface tension is considered to be large.

When the same surfactant or a surfactant having the same degree of surface tension reducing energy is used in the black pigment ink (a) and the pigment ink (b), a method of adjusting the static surface tension to the above range by adjusting the content of the surfactant is exemplified. When the same surfactant or a surfactant having the same degree of surface tension lowering energy is used, the static surface tension tends to be lower in an ink containing a large amount of the surfactant than in an ink containing a small amount of the surfactant. Therefore, in order to make the static surface tension of the black pigment ink (a) and the pigment ink (b) within the predetermined range, it is a simple method to adjust the content of the surfactant.

On the other hand, the static surface tension is not necessarily the same for the black pigment ink (a) and the pigment ink using the same surfactant in the same amount. This is because the affinity with the surfactant differs depending on the type of pigment contained in the ink.

In the present invention, if the same substance is used as the surfactant, it is preferable to adjust the content (mass ratio) of the surfactant contained in the entire cyan pigment ink that can be used in the pigment ink (b) to be in the range of 0.5 to 1.5 when the content (mass ratio) of the surfactant contained in the entire black pigment ink (a) is 1. Particularly preferably in the range of 0.8 to 1.2. The content (mass ratio) of the surfactant contained in the entire magenta pigment ink that can be used in the pigment ink (b) is preferably adjusted to be in the range of 0.5 to 1.5. Particularly preferably in the range of 0.8 to 1.2. The content (mass ratio) of the surfactant contained in the entire yellow pigment ink that can be used in the pigment ink (b) is preferably adjusted to be in the range of 0.5 to 1.5. Particularly preferably in the range of 0.8 to 1.2.

After the black pigment ink (a) is discharged by an ink jet recording method and landed on a recording medium, the pigment ink (b) is discharged by an ink jet recording method onto the recording medium. If the black pigment ink (a) is discharged onto a recording medium by an inkjet recording method after the pigment ink (b) is discharged by an inkjet recording method and landed on the recording medium, the black pigment ink (a) may easily move into the pigment ink (b). According to the ink set of the present invention in which the black pigment ink (a) and the pigment ink (b) having different static surface tensions are combined and the discharge order in the inkjet recording system is determined, the effect of suppressing bleeding and color mixing can be achieved.

(Black pigment ink (a))

The black pigment ink (a) will be specifically described.

As the black pigment ink (a), for example, an ink containing a surfactant, a pigment, water, and an organic solvent can be used.

The surfactant may be used in order to adjust the static surface tension (a1) of the black pigment ink (a) to the above range.

Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and the like, and nonionic surfactants are more preferably used.

Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate ester salt of higher fatty acid ester, sulfonate salt of higher fatty acid ester, sulfate ester salt and sulfonate salt of higher alcohol ether, higher alkyl sulfosuccinate, polyoxyethylene alkyl ether carboxylate, polyoxyethylene alkyl ether sulfate, alkyl phosphate, and polyoxyethylene alkyl ether phosphate, and specific examples thereof include dodecylbenzene sulfonate, isopropylnaphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylphenyl sulfonate, and dibutylphenylphenol disulfonate.

Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid hydroxyamides, alkylolamides, acetylene glycols, ethylene oxide adducts of acetylene glycols, polyethylene glycol polypropylene glycol block copolymers, and the like, with polyoxyethylene nonylphenyl ethers, polyoxyethylene octylphenyl ethers, polyoxyethylene dodecylphenyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid, The use of an acetylene surfactant such as a fatty acid hydroxyamide, acetylene glycol, an oxyethylene adduct of acetylene glycol, or a polyethylene glycol polypropylene glycol block copolymer, and more preferably acetylene glycol or an oxyethylene adduct of acetylene glycol, has an effect of greatly reducing the static surface tension (a1) of the black pigment ink (a) in a small amount, and is easily adjusted to the above range, and when used in combination with the pigment ink (b), the occurrence of bleeding or color mixing of a printed matter can be reduced.

As the surfactant, in addition to the above surfactants, silicone surfactants such as silicone alkoxy ethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers; biosurfactants such as penicillic acid, rhamnolipids, lysolecithins, and the like, and more preferably silicone surfactants as silicone alkoxyethylene adducts, have an effect of greatly reducing the static surface tension (a1) of the black pigment ink (a) in a small amount, are easily adjusted within the above range, and can reduce the occurrence of bleeding and color mixing of printed matter when used in combination with the pigment ink (b).

The surfactant is preferably used in a range of 0.001 to 4% by mass, more preferably 0.01 to 2% by mass, based on the total amount of the black pigment ink (a), and further preferably 0.1 to 1.5% by mass, from the viewpoint of obtaining an ink set capable of further reducing the occurrence of bleeding and color mixing even when printed on a recording medium such as a non-absorptive recording medium or a low-absorptive recording medium.

As the pigment that can be used in the black pigment ink (a), carbon black can be used. As the carbon black, for example, carbon black produced by a known method such as a contact method, a furnace method, a thermal method, or the like can be used.

Examples of the carbon Black usable for the Black pigment include No.2300, No.2200B, No.900, No.960, No.980, No.33, No.40, No. 45L, No.52, HCF88, MA7, MA8, MA100 manufactured by Mitsubishi chemical corporation, Raven 5750, Raven 5250, Raven 5000, Raven3500, Raven1255, Raven 700 manufactured by Columbia corporation, Regal 400R, Regal 46330R, Regal R, Mogul L, Mogul 700, Monarch800, Monarch880, Monarch900, Monarch1000, Monarch1100, Monarch1300, Monarch1400 manufactured by Kabet corporation, Black FW1, Color cia 2, Color 2, Black 364, Black 18, Black 300, Printx FW 160, Printx Color FW 170, Color NIFW 170, Printx Color FW 1400, Color FW 170, Printx Color FW 1400, Color FW 170, and other colors.

In the production of the black pigment ink (a), a pigment dispersion obtained by dispersing the black pigment in a solvent such as water in advance is preferably used.

In the case of using the pigment dispersion, it is preferable to use a black pigment which can be stably dispersed in the solvent as the black pigment.

As the pigment dispersion, for example, a pigment dispersion obtained by dispersing the pigment in a solvent such as water using a pigment dispersant such as a polymer dispersant, a surfactant, or a pigment derivative can be used.

As the pigment that can be dispersed in the solvent, a pigment having a group (hydrophilic group or a salt group thereof) that imparts dispersibility on the surface thereof can be used.

In addition, as the above pigment, a self-dispersible pigment which can be dispersed in an aqueous solvent without using the above pigment dispersant may also be used.

As the self-dispersible pigment, for example, a pigment produced by introducing (grafting) a group imparting dispersibility to the surface of a pigment by subjecting the pigment to physical treatment or chemical treatment can be used.

Examples of the method for physically or chemically treating the pigment include: a wet oxidation method in which the surface of a pigment is oxidized with an oxidizing agent in water, such as a vacuum plasma treatment, an oxidation treatment with a hypohalous acid and/or hypohalite, or an oxidation treatment with ozone, or a method in which a carboxyl group is bonded to the surface of a pigment through a phenyl group by bonding p-aminobenzoic acid to the surface of a pigment.

In order to obtain the necessity of sufficient image density and to ensure dispersion stability of the pigment in the ink, the pigment is preferably 1 to 20% by mass, more preferably 1 to 10% by mass.

As water that can be used in the black pigment ink (a), pure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, and distilled water, or ultrapure water can be used.

As the black pigment ink (a), an ink containing an organic solvent can be used. For example, the organic solvent may be suitably used in order to improve the drying property of the ink or to suppress excessive spreading of the black pigment ink (a) after landing on a recording medium to such an extent that color mixing or bleeding occurs.

As the organic solvent, for example, a water-soluble organic solvent having a boiling point of 100 ℃ to 200 ℃ and a vapor pressure of 0.5hPa or more at 20 ℃ can be used.

The black pigment ink (a) containing the water-soluble organic solvent is excellent in drying property after being landed on a recording medium such as a non-absorptive recording medium or a low-absorptive recording medium, and therefore, a printed matter in which bleeding or color mixing is reduced is easily formed.

As the water-soluble organic solvent, for example, two or more of the following may be used alone or in combination: 3-methoxy-1-butanol, 3-methyl-3-methoxy-1-butanol, 3-methoxy-3-methyl-1-butyl acetate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol tert-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, 4-methoxy-4-methyl-2-pentanone, ethyl lactate, and the like.

Among these, the water-soluble organic solvent is preferably a hydrogen bonding term of HSP (hansen solubility parameter) from the viewpoint of storage stability of the black pigment ink (a) and suitability for members of an ink jet device_HIs a water-soluble organic solvent in the range of 6 to 20. The compatibility with the member of the ink jet apparatus means that the member swells or dissolves due to the contact of the head portion, the flow path in the apparatus, and the ink over a long period of time, thereby deteriorating the ink jet apparatus.

As the water-soluble organic solvent having HSP within the above range, for example, 3-methoxy-1-butanol, 3-methyl-3-methoxy-1-butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol tert-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and particularly, 3-methoxy-1-butanol, 3-methyl-3-methoxy-1-butanol are preferably used.

In the present invention, it is preferable to use propylene glycol and at least one organic solvent selected from the group consisting of glycerin, diglycerin, glycerin derivatives, and diglycerin derivatives in combination with the water-soluble organic solvent, in order to prevent the black pigment ink (a) from being dried or solidified in the vicinity of the ink discharge nozzle to form a coating film without impairing the excellent drying property after the black pigment ink (a) lands on the recording medium, and to ensure the excellent discharge property by being redispersed in the newly supplied black pigment ink (a) even when the coating film is formed.

Examples of the glycerin derivative and the diglycerin derivative include polyglycerin, diglycerin fatty acid ester, polyoxypropylene (n) polyglycerin ether represented by the general formula (1), and polyoxyethylene (n) polyglycerin ether represented by the general formula (2), and two or more of these may be used together. In the present invention, it is particularly preferable to select glycerin or polyoxypropylene (n) polyglyceryl ether having n of 8 to 15.

[ solution 1]

[ solution 2]

In the general formula (1) and the general formula (2), m, n, o and p each independently represent an integer of 1 to 10.

The water-soluble organic solvent is preferably used in a range of 1 to 20% by mass, more preferably 1 to 15% by mass, based on the mass of the black pigment ink (a), and particularly preferably in a range of 1 to 10% by mass, from the viewpoint of forming a printed matter in which bleeding and color mixing are further reduced even when the printed matter is printed on a recording medium such as a non-absorptive recording medium or a low-absorptive recording medium.

The propylene glycol is preferably used in a range of 1 to 30% by mass, more preferably 1 to 25% by mass, based on the mass of the black pigment ink (a), and particularly preferably 1 to 20% by mass, from the viewpoint of obtaining an ink for ink jet recording which does not affect the quick drying property of the ink and has good discharge properties.

Further, the at least one organic solvent selected from the group consisting of glycerin, diglycerin, glycerin derivatives, and diglycerin derivatives is preferably used in a range of 1 to 20 mass%, more preferably in a range of 2 to 18 mass%, with respect to the mass of the black pigment ink (a), and particularly preferably in a range of 4 to 15 mass% in terms of suppressing drying of the black pigment ink (a) near the ink discharge nozzle.

As the organic solvent, a water-soluble solvent other than the water-soluble organic solvent can be used, and for example, two or more of the following can be used alone or in combination: ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; alcohols such as methanol, ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol and 2-methoxyethanol; tetrahydrofuran, 1, 4-bisEthers such as alkane and 1, 2-dimethoxyethane; glycols such as dimethylformamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and polypropylene glycol; diols such as butanediol, pentanediol, hexanediol, 3-methyl-1, 5-pentanediol, and diols belonging to the same group as these diols; glycol esters such as propylene glycol laurate; glycol ethers such as diethylene glycol monoethyl ester, diethylene glycol monobutyl ester, respective ethers of diethylene glycol monohexyl ester, propylene glycol ether, dipropylene glycol ether, and cellosolve including triethylene glycol ether; alcohols such as methanol, ethanol, isopropanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, pentanol, and alcohols belonging to the same group as these alcohols; or sulfolane; lactones such as γ -butyrolactone; lactams such as N- (2-hydroxyethyl) pyrrolidone and the like.

As the black pigment ink (a), an ink containing a pigment-dispersed resin can be used.

The pigment dispersion resin is not particularly limited, and a known polymer dispersant, surfactant, and pigment derivative can be used.

As the pigment dispersion resin, can use the aqueous resin, as its preferred example, can be cited polyvinyl alcohol, polyvinyl pyrrolidone, acrylic acid-acrylate copolymer and other acrylic resin, styrene-acrylic acid copolymer, styrene-methacrylic acid-acrylate copolymer, styrene- α -methyl styrene-acrylic acid copolymer, styrene- α -methyl styrene-acrylic acid-acrylate copolymer and other styrene-acrylic resin, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinyl naphthalene-acrylic acid copolymer, and the salt of the aqueous resin.

The pigment dispersion resin is preferably a polymer (a) described below, from the viewpoint of obtaining a black pigment ink (a) in which the presence of coarse particles is significantly reduced.

The polymer (A) used in the present invention has a solubility in water of 0.1g/100ml or less, a number average molecular weight of 1000 to 6000, and an anionic group. It is further preferable that the anionic group is neutralized with a basic compound at a neutralization rate of 100% to form fine particles in water.

The solubility of the above polymer (A) in water is defined as follows. 0.5g of a polymer having a particle size adjusted to a range of 250 to 90 μm using a sieve having a mesh size of 250 μm and 90 μm was sealed in a bag made of a 400 mesh metal net, immersed in 50ml of water, slowly stirred at 25 ℃ and left to stand for 24 hours. After 24 hours of immersion, the 400 mesh metal net with the polymer enclosed therein was dried in a dryer set at 110 ℃ for 2 hours. The weight change of the 400 mesh metal net with the polymer enclosed therein before and after water immersion was measured, and the solubility was calculated by the following formula.

[ number 1]

Solubility (g/100ml) — (400 mesh metal net (g) with polymer enclosed before impregnation) -400 mesh metal net (g) with polymer enclosed after impregnation) × 2

In the present invention, whether or not fine particles are formed in water when the neutralization rate of the anionic group by the basic compound is 100% is determined as follows.

(1) The acid value of the polymer was determined in advance by an acid value measurement method based on JIS test method K0070-1992. Specifically, 0.5g of the polymer was dissolved in tetrahydrofuran (hereinafter, may be referred to as THF) solvent, and the solution was titrated with 0.1M potassium hydroxide alcoholic solution using phenolphthalein as an indicator to determine the acid value.

(2) After adding 1g of the polymer to 50ml of water, 0.1 mol/L mol of an aqueous potassium hydroxide solution just required to neutralize the acid value obtained to 100% was added to conduct 100% neutralization.

(3) The 100% neutralized liquid was irradiated with ultrasonic waves at a temperature of 25 ℃ for 2 hours in an ultrasonic washer (SND ultrasonic washer US-102, 38kHz self-oscillation), and then allowed to stand at room temperature for 24 hours.

After leaving for 24 hours, a sample liquid obtained by sampling a liquid located at a depth of 2 cm from the liquid surface was subjected to determination as to whether or not light scattering information on the formation of fine particles was obtained using a dynamic light scattering type particle size distribution measuring apparatus ("Microtrac particle size distribution analyzer UPA-ST 150", manufactured by japan ltd.

From the viewpoint of further improving the dispersion stability in water, the fine particles composed of the polymer (A) used in the present invention are preferably those having a volume average particle diameter in the range of 5nm to 1000nm, more preferably 7nm to 700nm, and particularly preferably 10nm to 500 nm.

The smaller the particle size distribution of the fine particles, the more excellent the dispersibility tends to be, but the wider the particle size distribution is, the implementation is not hindered. The volume average particle diameter and the particle size distribution were measured by using a dynamic light scattering particle size distribution measuring apparatus (dynamic light scattering particle size measuring apparatus "Microtrac particle size distribution analyzer UPA-ST 150", manufactured by Nikkiso K.K.) in the same manner as the method for measuring fine particles.

(neutralization Rate of Polymer (A))

The neutralization degree of the polymer (a) used in the present invention is determined by the following formula.

[ number 2]

The neutralization rate (%) ((mass (g) × 56 × 1000)/(acid value (mgKOH/g) × of the polymer (a): equivalent × of the basic compound) (mass (g) of the polymer (a))) × 100

The acid value of the polymer (A) is measured in accordance with JIS test method K0070-. Specifically, the amount of the compound was determined by dissolving 0.5g of a sample in a THF solvent, and titrating the solution with 0.1M alcoholic potassium hydroxide solution using phenolphthalein as an indicator.

The acid value of the polymer (A) is preferably 40 to 400mgKOH/g, more preferably 40 to 300mgKOH/g, and most preferably 40 to 190 mgKOH/g.

The number average molecular weight of the polymer (A) is preferably 1000 to 6000, more preferably 1300 to 5000, and most preferably 1500 to 4500, from the viewpoint of imparting good pigment dispersibility.

In the present invention, the number average molecular weight is a value in terms of polystyrene measured by GPC (gel permeation chromatography), specifically, a value measured under the following conditions.

(method of measuring number average molecular weight (Mn))

The measurement was performed by a Gel Permeation Chromatography (GPC) method under the following conditions.

Measurement device-high efficiency GPC device (H L C-8220GPC, Tosoh Co., Ltd.)

A chromatographic column: the following columns manufactured by Tosoh corporation were connected in series and used.

"TSKgel G5000" (7.8mmI.D. × 30cm) × 1 roots

"TSKgel G4000" (7.8mm I.D. × 30cm) × 1 roots

"TSKgel G3000" (7.8mm I.D. × 30cm) × 1 roots

"TSKgel G2000" (7.8mmI.D. × 30cm) × 1 roots

A detector: RI (differential refractometer)

Temperature of the column: 40 deg.C

Eluent: tetrahydrofuran (THF)

Flow rate 1.0m L/min

Injection amount 100. mu. L (sample concentration 0.4% by mass in THF)

Standard sample: the standard curve was made using the following standard polystyrene.

(Standard polystyrene)

TSKgel Standard polystyrene A-500 manufactured by Tosoh corporation "

TSKgel Standard polystyrene A-1000 manufactured by Tosoh corporation "

TSKgel Standard polystyrene A-2500 manufactured by Tosoh corporation "

TSKgel Standard polystyrene A-5000 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-1 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-2 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-4 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-10 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-20 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-40 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-80 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-128 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-288 manufactured by Tosoh corporation "

TSKgel Standard polystyrene F-550 manufactured by Tosoh corporation "

The polymer (a) is preferably a polymer which is insoluble or poorly soluble in a state where all of the anionic groups are not neutralized and which forms fine particles in a state where all of the anionic groups are neutralized.

As the polymer (a), a polymer having a hydrophobic group in addition to the anionic group of the hydrophilic group can be used. Examples of the polymer include a block polymer having a polymer block having a hydrophobic group and a polymer block having an anionic group.

The number of the hydrophobic groups and the anionic groups is more likely to cause no formation of fine particles when the solubility in water exceeds 0.1g/100ml or the neutralization rate of the anionic groups by the basic compound is 100%. From this viewpoint, it is preferable that the number of the anionic groups is not too high. In the polymer, the number of anionic groups and the solubility in water are not necessarily determined by the acid value or the number of anionic groups in designing the polymer, and for example, even in the case of a polymer having the same acid value, a polymer having a low molecular weight tends to have a high solubility in water, and a polymer having a high molecular weight tends to have a low solubility in water. Thus, in the present invention, the polymer (A) is determined by its solubility in water.

The polymer (a) may be a homopolymer, but is preferably a copolymer, and may be a random polymer, a block polymer, or an alternating polymer, and among them, a block polymer is preferred. The polymer may be a branched polymer, but is preferably a linear polymer.

The polymer (a) is preferably a vinyl polymer in view of the degree of freedom in design, and is preferably produced by "living polymerization" such as living radical polymerization, living cationic polymerization, and living anionic polymerization as a method for producing a vinyl polymer having a desired molecular weight and solubility characteristics in the present invention.

Among them, the polymer (a) is preferably a vinyl polymer produced using a (meth) acrylate monomer as one of raw materials, and as a method for producing such a vinyl polymer, living radical polymerization and living anion polymerization are preferable, and further living anion polymerization is preferable from the viewpoint of enabling more precise design of the molecular weight and each segment of the block polymer.

As the polymer (a) produced by living anionic polymerization, specifically, a polymer represented by the general formula (3) can be used.

[ solution 3]

In the formula (3), A¹Denotes an organolithium initiator residue, A²Represents a polymer block of a monomer having an aromatic ring or a heterocyclic ring, A³Represents a polymer block containing an anionic group, n represents an integer of 1 to 5, and B represents an aromatic group or an alkyl group.

In the general formula (3), A¹Examples of the organolithium initiator include alkyllithium such as methyllithium, ethyllithium, propyllithium, butyllithium (n-butyllithium, sec-butyllithium, isobutyllithium, tert-butyllithium, etc.), pentyllithium, hexyllithium, methoxymethyllithium, ethoxymethyllithium, etc., phenylalkyllithium such as benzyllithium, α -methylphenyllithium, 1-diphenyl-3-methylpentyllithium, 1-diphenylhexyllithium, phenylethyllithium, etc., alkenyllithium such as vinyllithium, allyllithium, propenyllithium, butenyllithium, etc., alkynylithium such as ethynyllithium, butynylithium, pentynylium, hexynylium, etc., aryllithium such as phenyllithium, naphthyllithium, etc., heterocyclic lithium such as 2-thienyllithium, 4-pyridyllithium, 2-quinolylium, etc., lithium magnesium alkyllithium complexes such as tri (n-butyl) magnesium lithium, trimethylmagnesium lithium, etc.

The organolithium initiator initiates polymerization by breaking the bond between the organic group and lithium to form an active end on the organic group side. An organic group derived from organolithium is bonded to the terminal of the resulting polymer. In the present invention, the organic group derived from organolithium bonded to the terminal of the polymer is referred to as an organolithium initiator residue. For example, if a polymer is produced using methyllithium as an initiator, the organolithium initiator acid group is a methyl group, and if a polymer is produced using butyllithium as an initiator, the organolithium initiator acid group is a butyl group.

In the above general formula (3), A²Represents a polymer block having a hydrophobic group. A. the²In addition to the purpose of obtaining a proper solubility balance as described above, a group having high adsorption to a pigment when it comes into contact with the pigment is preferable, and from this viewpoint, a²Preferred are polymer blocks of monomers having aromatic or heterocyclic rings.

The polymer block of a monomer having an aromatic ring or a heterocyclic ring is specifically a polymer block of a homopolymer or a copolymer obtained by homopolymerizing or copolymerizing a monomer having an aromatic ring such as a styrene monomer or a monomer having a heterocyclic ring such as a vinylpyridine monomer.

Examples of the monomer having an aromatic ring include styrene monomers such as styrene, p-tert-butyldimethylsiloxystyrene, o-methylstyrene, p-tert-butylstyrene, m-tert-butylstyrene, p-tert-ethoxymethyl (1-ethoxymethyl) styrene, m-chlorostyrene, p-fluorostyrene, α -methylstyrene and p-methyl- α -methylstyrene, and vinylnaphthalene and vinylanthracene.

Examples of the monomer having a heterocyclic ring include vinylpyridine monomers such as 2-vinylpyridine and 4-vinylpyridine.

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

In the above general formula (3), A³Represents a polymer block containing an anionic group. A. the³In addition to the purpose of imparting appropriate solubility as described above, there is also the purpose of imparting dispersion stability in water when forming a pigment dispersion.

The above-mentioned polymer block A³Examples of the anionic group in (b) include a carboxyl group, a sulfonic acid group, and a phosphoric acid group. Among them, carboxyl groups are preferred in view of their preparation, abundance in monomer species, and availability. Further, the acid anhydride group may be one obtained by subjecting two carboxyl groups to intramolecular or intermolecular dehydration condensation.

A above³The method for introducing the anionic group (2) is not particularly limited, and for example, in the case where the anionic group is a carboxyl group, the anionic group may be introduced byThe polymer block (PB1) of a homopolymer or copolymer obtained by homopolymerization or copolymerization of (meth) acrylic acid with another monomer may be a polymer block (PB2) of a homopolymer or copolymer obtained by homopolymerization or copolymerization of (meth) acrylate having a protecting group that can be regenerated into an anionic group by deprotection, in which a part or all of the protecting group that can be regenerated into an anionic group is regenerated into an anionic group.

The polymer block A is³The term (meth) acrylic acid as used herein refers to acrylic acid and methacrylic acid, and the term (meth) acrylate refers to acrylate and methacrylate.

As the (meth) acrylic acid ester, specifically, two or more of the following may be used alone or in combination: methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, allyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-pentyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-lauryl (meth) acrylate, n-tridecyl (meth) acrylate, n-stearyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, 4-tert-butylcyclohexyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecyl (meth) acrylate, allyl (meth), Dicyclopentadienyl (meth) acrylate, adamantyl (meth) acrylate, glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate, pentafluoropropyl (meth) acrylate, octafluoropentyl (meth) acrylate, pentadecafluorooctyl (meth) acrylate, heptadecafluorodecyl (meth) acrylate, N-dimethyl (meth) acrylamide, (meth) acryloylmorpholine, (meth) acrylonitrile, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, polyethylene glycol-polypropylene glycol (meth) acrylate, propylene glycol-ethylene glycol (meth) acrylate, propylene glycol-propylene glycol (meth) acrylate, propylene glycol (, And (meth) acrylates containing a polyalkylene oxide group such as polyethylene glycol-polybutylene glycol (meth) acrylate, polypropylene glycol-polybutylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, ethoxypolyethylene glycol (meth) acrylate, butoxypolyethylene glycol (meth) acrylate, octoxypolyethylene glycol (meth) acrylate, lauryloxypolyethylene glycol (meth) acrylate, stearyloxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate, and octoxypolyethylene glycol-polypropylene glycol (meth) acrylate.

In the living anion polymerization method, when the monomer used is a monomer having a group having an active proton such as an anionic group, the living end of the living anion polymer is immediately reacted with the group having an active proton to be inactivated, and thus a polymer cannot be obtained. In living anion polymerization, it is difficult to directly polymerize a monomer having a group having an active proton, and therefore it is preferable to polymerize the monomer in a state where the group having an active proton is protected, and then to regenerate the group having an active proton by deprotecting the protecting group.

For this reason, the polymer block A is³Among them, a monomer containing a (meth) acrylate having a protecting group which can be regenerated into an anionic group by deprotection is preferably used. By using such a monomer, the inhibition of the polymerization can be prevented at the time of polymerization. In addition, the anionic group protected by a protecting group can be regenerated into an anionic group by deprotection after the block polymer is obtained.

For example, when the anionic group is a carboxyl group, the carboxyl group can be regenerated by esterifying the carboxyl group and deprotecting the carboxyl group by hydrolysis or the like as a subsequent step. As the protective group which can be converted into a carboxyl group in this case, a group having an ester bond is preferable, and examples thereof include primary alkoxycarbonyl groups such as methoxycarbonyl, ethoxycarbonyl, n-propoxycarbonyl and n-butoxycarbonyl; a secondary alkoxycarbonyl group such as an isopropoxycarbonyl group or a secondary butoxycarbonyl group; a tert-alkoxycarbonyl group such as a tert-butoxycarbonyl group; a phenylalkoxycarbonyl group such as a benzyloxycarbonyl group; and alkoxyalkyl carbonyl groups such as ethoxyethylcarbonyl.

When the anionic group is a carboxyl group, examples of monomers that can be used include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, sec-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate (lauryl (meth) acrylate), tridecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate (stearyl (meth) acrylate), nonadecyl (meth) acrylate, and mixtures thereof, Alkyl (meth) acrylates such as eicosyl (meth) acrylate; phenyl alkylene (meth) acrylates such as benzyl (meth) acrylate; alkoxyalkyl (meth) acrylates such as ethoxyethyl (meth) acrylate, and the like. These (meth) acrylic acid esters (c1) may be used singly or in combination of two or more. Among these (meth) acrylates (c1), tert-butyl (meth) acrylate and benzyl (meth) acrylate are preferably used because a conversion reaction to a carboxyl group is likely to occur. In addition, tert-butyl (meth) acrylate is more preferable in view of the easiness of industrial availability.

In the general formula (3), B represents an aromatic group or an alkyl group having 1 to 10 carbon atoms. And n represents an integer of 1 to 5.

In the living anion polymerization method, when it is desired to directly polymerize a (meth) acrylate monomer with the living end of a styrene-based polymer having a strong nucleophilicity, the polymerization may be disabled due to nucleophilic attack to a carbonyl carbon. Thus, in the above A¹-A²When the polymerization of the (meth) acrylate monomer is carried out as described above, the following is carried out: after adjusting the nucleophilicity using a reaction adjuster, the (meth) acrylate monomer is polymerized. In the general formula (3)The reaction modifier includes, for example, diphenylethylene, α -methylstyrene, p-methyl- α -methylstyrene and the like.

(living anion polymerization Using microreactor)

The living anion polymerization method may be carried out by a batch method such as that used in conventional radical polymerization by adjusting the reaction conditions, or may be a continuous polymerization method using a microreactor. In the microreactor, since the mixing property of the polymerization initiator and the monomer is good, the reaction starts simultaneously, the temperature can be made uniform, and the polymerization rate can be made uniform, so that the molecular weight distribution of the produced polymer can be narrowed. Further, since the growth ends are stable, a block copolymer in which two components of the block are not mixed together can be easily produced. In addition, since the controllability of the reaction temperature is good, the side reaction is easily suppressed.

A general method of living anion polymerization using a microreactor will be described with reference to fig. 1 which is a schematic diagram of the microreactor.

The first monomer and a polymerization initiator for initiating polymerization are introduced from the tubular reactors P1 and P2 (7 and 8 in fig. 1) respectively into a T-type micromixer M1 (1 in fig. 1) having a flow path capable of mixing a plurality of liquids, and the first monomer is living-anionically polymerized in the T-type micromixer M1 to form a first polymer (step 1).

Next, the obtained first polymer was transferred to a T-type micromixer M2 (2 in fig. 1), and the growth end of the obtained polymer was captured by a reaction control agent introduced from a tubular reactor P3 (9 in fig. 1) in the mixer M2 to perform reaction control (step 2).

In this case, the number of n in the general formula (3) can be controlled depending on the kind and the amount of the reaction modifier used.

Subsequently, the reaction-regulated first polymer in the T-type micromixer M2 was transferred to a T-type micromixer M3 (3 in fig. 1), and the second monomer introduced from the tubular reactor P4 and the reaction-regulated first polymer were continuously subjected to living anion polymerization in the mixer M3 (step 3).

Then, the reaction is quenched with a compound having an active proton such as methanol, thereby producing a block copolymer.

In the case where the polymer (a) represented by the above general formula (3) is produced by using the microreactor, the polymer (a) is obtained by using a monomer having an aromatic ring or a heterocyclic ring as the first monomer and reacting the monomer with the organolithium initiator as the initiator²The polymer block of a monomer having an aromatic ring or a heterocyclic ring (in the polymer block A)²Has as the above A bonded to one end thereof¹The organic group of the organolithium initiator residue of (a).

Next, after the reactivity of the growth end is adjusted using a reaction adjuster, a monomer containing a (meth) acrylate having a protecting group capable of being regenerated into the anionic group is reacted as the second monomer to obtain a polymer block.

Then, the compound is deprotected by hydrolysis or the like to regenerate an anionic group, thereby obtaining the compound A³I.e. a polymer block comprising anionic groups.

A method of regenerating an ester bond of a protecting group which can be regenerated into an anionic group by a deprotection reaction such as hydrolysis will be described in detail.

The hydrolysis reaction of the ester bond may be carried out under acidic conditions or basic conditions, and the conditions are slightly different depending on the group having the ester bond. For example, when the group having an ester bond is a primary alkoxycarbonyl group such as a methoxycarbonyl group or a secondary alkoxycarbonyl group such as an isopropoxycarbonyl group, a carboxyl group can be obtained by hydrolysis under basic conditions. In this case, examples of the basic compound under basic conditions include metal hydroxides such as sodium hydroxide and potassium hydroxide.

In addition, when the group having an ester bond is a tert-alkoxycarbonyl group such as a tert-butoxycarbonyl group, a carboxyl group can be obtained by hydrolysis under acidic conditions. In this case, examples of the acidic compound under acidic conditions include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; bronsted acids (ブレステッド acids) such as trifluoroacetic acid; lewis acids such as trimethylsilyl trifluoromethanesulfonate. As to the reaction conditions under which the t-butoxycarbonyl group is hydrolyzed under acidic conditions, for example, the one disclosed in "Synthesis IV of organic Compound of Experimental chemistry lecture 16, 5 th edition, Japan chemical society".

Further, as a method for converting a tert-butoxycarbonyl group into a carboxyl group, a method using a cation exchange resin instead of the above-mentioned acid can be cited. Examples of the cation exchange resin include resins having a carboxyl group (-COOH) and a sulfo group (-SO) in side chains of polymer chains₃H) The cation exchange resin used in the present invention is commercially available, and examples thereof include a strongly acidic cation exchange resin "AMBER L ITE" manufactured by Organo corporation, and the amount of the cation exchange resin used is preferably in the range of 5 to 200 parts by mass, more preferably 10 to 100 parts by mass, per 100 parts by mass of the polymer represented by the above general formula (3) because of efficient hydrolysis.

In addition, when the group having an ester bond is a phenylalkoxycarbonyl group such as benzyloxycarbonyl, the group can be converted to a carboxyl group by hydrogenation reduction. In this case, the reaction is carried out at room temperature in the presence of a palladium catalyst such as palladium acetate using hydrogen as a reducing agent as a reaction condition, whereby the phenylalkoxycarbonyl group can be quantitatively regenerated into a carboxyl group.

As described above, the reaction conditions for converting into a carboxyl group vary depending on the kind of the group having an ester bond, and for example, t-butyl (meth) acrylate and n-butyl (meth) acrylate are used as A³The polymer obtained by copolymerizing the raw materials (a) has a tert-butoxycarbonyl group and a n-butoxycarbonyl group. Here, since n-butoxycarbonyl group is not hydrolyzed under acidic conditions under which t-butoxycarbonyl group is hydrolyzed, only t-butoxycarbonyl group can be selectively hydrolyzed and deprotected to a carboxyl group. Therefore, by appropriately selecting as A³The hydrophilic block (A) can be adjusted by using a monomer containing a (meth) acrylate having a protecting group capable of being regenerated into an anionic group as a raw material monomer of (1)³) Acid value of (3).

In the polymer (A) represented by the above general formula (3), the polymer block (A) is²) With a polymer block (A)³) The separation is clearly carried out, which is advantageous in terms of the stability of the resulting aqueous pigment dispersion. Polymer Block (A)²) With a polymer block (A)³) In a molar ratio of²：A³Preferably 100: 10-100: 500, or less. In A³Is relative to A²When 100 is less than 10, the dispersion stability of the pigment and the discharge stability at the time of ink jet discharge tend to be poor. On the other hand, if A³Is relative to A²When 100 is more than 500, the hydrophilicity of the polymer becomes too high, and the polymer easily penetrates into a recording medium such as paper, thereby lowering the color developability. The ratio is particularly preferably A²：A³＝100：10～100：450。

Further, in the polymer (A) represented by the above general formula (3), the polymer block (A) is constituted²) The number of the aromatic ring-or heterocyclic ring-containing monomers (2) is preferably in the range of 5 to 40, more preferably 6 to 30, and most preferably 7 to 25. Further constituting the polymer block (A)³) The number of anionic groups (2) is preferably in the range of 3 to 20, more preferably in the range of 4 to 17, and most preferably in the range of 5 to 15.

In the polymerization of the above polymer block (A)²) With a polymer block (A)³) In a molar ratio of²：A³With a block of a structuring polymer (A)²) The number of moles and the composition of the compound having an aromatic ring or a heterocyclic ring (A)³) When the molar ratio of the number of moles of the anionic group(s) is expressed, it is preferably 100: 7.5-100: 400.

the acid value of the polymer (A) represented by the general formula (3) is preferably 40 to 400mgKOH/g, more preferably 40 to 300mgKOH/g, and most preferably 40 to 190 mgKOH/g. When the acid value is less than 40mgKOH/g, the dispersion stability of the pigment and the discharge stability at the time of ink jet discharge may be insufficient. On the other hand, when the acid value exceeds 400mgKOH/g, the hydrophilicity of the polymer becomes high, and the polymer easily penetrates into the recording medium, so that the color developability is lowered. When the acid value exceeds 190mgKOH/g, the water resistance of the resulting ink may be affected.

The acid value of the polymer in the present invention is an acid value obtained by the same acid value measurement method as the above-described measurement method of the fine particles of the polymer (a).

The anionic group of the polymer (a) is preferably neutralized.

As the basic compound for neutralizing the anionic group of the polymer (a), any of conventionally known and used basic compounds can be used, and for example, inorganic basic substances such as alkali metal hydroxides including sodium hydroxide and potassium hydroxide; organic basic compounds such as ammonia, triethylamine and alkanolamine.

In the present invention, the amount of neutralization of the above-mentioned polymer (A) present in the aqueous pigment dispersion does not need to be 100% neutralization of the acid value of the polymer. Specifically, the neutralization is preferably performed so that the neutralization rate of the polymer (a) is 20% to 200%, more preferably 80% to 150%.

As the black pigment ink (a), additives such as a binder resin, a urea-based wetting agent (drying inhibitor), a penetrant, an antiseptic, a viscosity modifier, a pH modifier, a chelating agent, a plasticizer, an antioxidant, and an ultraviolet absorber may be used as necessary.

As the binder resin, for example, one or two or more of the following may be used in combination: polyvinyl alcohol, gelatin, polyethylene oxide, polyvinyl pyrrolidone, acrylic resins, polyurethane resins, dextran, dextrin, carrageenan (kappa, iota, lambda, etc.), agar, pullulan, water-soluble polyvinyl butyral, hydroxyethyl cellulose, carboxymethyl cellulose, and the like.

Among them, as the binder resin, an acrylic resin is preferably used, an acrylic resin having an amide group is preferably used, and an acrylic resin having an amide group, an alkoxysilyl group, or the like is particularly preferably used because of excellent redispersibility in an aqueous ink. The "acrylic resin" refers to a polymer containing a monomer having a (meth) acryloyl group as one of raw materials.

(acrylic resin having amide group)

The acrylic resin having an amide group has an effect of improving the redispersibility of the black pigment ink (a) of the present invention.

The acrylic resin having an amide group can be obtained, for example, by polymerizing a monomer component containing an acrylic monomer having an amide group. From the viewpoint of obtaining a printed matter having further excellent redispersibility and excellent scratch resistance, the acrylic monomer having an amide group is preferably used in a range of 5% by mass or less, preferably 0.5% by mass to 5% by mass, more preferably 0.5% by mass to 4% by mass, and particularly preferably 1.5% by mass to 3% by mass, relative to the total amount of the monomer components.

Examples of the acrylic monomer having an amide group include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, N-methylol (meth) acrylamide, N-isopropyl (meth) acrylamide, N-butyl (meth) acrylamide, N-dimethyl (meth) acrylamide, N-diethyl (meth) acrylamide, N-dipropyl (meth) acrylamide, N-dimethylaminopropyl (meth) acrylamide, diacetone (meth) acrylamide, and hydroxyethyl (meth) acrylamide.

Examples of the other monomer that can be used in combination with the acrylic monomer having an amide group include (meth) acrylic acid, alkali metal salts thereof, (meth) acrylic acid ester monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like, (meth) acrylic monomers such as (meth) acrylonitrile, 2-dimethylaminoethyl (meth) acrylate, and glycidyl (meth) acrylate.

Examples of the other monomers include aromatic vinyl compounds such as styrene, α -methylstyrene, p-tert-butylstyrene, vinylnaphthalene and vinylanthracene, vinylsulfonic acid compounds such as vinylsulfonic acid and styrenesulfonic acid, vinylpyridine compounds such as 2-vinylpyridine, 4-vinylpyridine and naphthylvinylpyridine, vinyltriethoxysilane, vinyltrimethoxysilane, p-vinyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane and 3-acryloxypropyltrimethoxysilane.

As the other monomer, a monomer having an aromatic group such as styrene or benzyl (meth) acrylate is preferably used in order to further improve the affinity with the pigment.

As the acrylic resin having an amide group, among the above resins, acrylic resins having an amide group, an alkoxysilyl group, and the like are preferably used from the viewpoint that a coating film can be formed by suppressing the drying or solidification of the black pigment ink (a) in the vicinity of the ink discharge nozzle, and even when the coating film is formed, the acrylic resin can be redispersed in a newly supplied black pigment ink (a) to ensure excellent discharge properties.

The acrylic resin having an amide group, an alkoxysilyl group, and the like can be produced, for example, by polymerizing the amide group-containing monomer with a monomer having an alkoxysilyl group and the like, which is generally called a silane coupling agent.

Examples of the silane coupling agent having an ethylenically unsaturated group include ethylenically unsaturated groups such as vinyltriethoxysilane, vinyltrimethoxysilane, p-vinyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane.

The silane coupling agent having an ethylenically unsaturated group can provide a crosslinked structure to the acrylic resin having an amide group, an alkoxysilyl group, and the like. The silane coupling agent is preferably used in a range of 0.05 to 2% by mass, more preferably 0.05 to 1.5% by mass, based on the total amount of the monomers used for producing the acrylic resin having an amide group, an alkoxysilyl group, and the like, and particularly preferably 0.1 to 1.0% by mass, from the viewpoint of increasing the strength of a coating film after printing and drying and exhibiting a function of improving the scratch resistance of a printed matter.

In addition, in order to improve the adhesion of the black pigment ink (a) used in the present invention to a recording medium such as the non-absorbent recording medium or the low-absorbent recording medium, the acrylic resin may contain a component which is insoluble in Tetrahydrofuran (THF) which is a developing solvent used in the measurement of the molecular weight by gel permeation chromatography and thus the measurement of the molecular weight is difficult.

The component insoluble in THF as a developing solvent when the molecular weight is measured by gel permeation chromatography of the acrylic resin is considered to have a number average molecular weight of at least 100,000 and a mass average molecular weight of at least 500,000.

When an ink containing the binder resin is used as the black pigment ink (a), an aqueous dispersion of the acrylic resin may be used as a raw material for producing the ink.

Examples of the aqueous dispersion of the acrylic resin include: an aqueous dispersion obtained by dispersing the acrylic resin in water or a water-soluble solvent using an emulsifier; an aqueous dispersion obtained by dispersing an acrylic resin having a hydrophilic group in a solvent such as water.

Examples of the emulsifier include nonionic emulsifiers such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether and polyoxyethylene polyoxypropylene copolymer, anionic emulsifiers such as alkyl sulfate ester salts, alkylbenzene sulfonate, polyoxyethylene alkyl ether sulfate ester salts and polyoxyethylene alkyl phenyl ether sulfate ester salts, and cationic emulsifiers such as quaternary ammonium salts. The emulsifier is preferably used in a range of 20 parts by mass or less with respect to 100 parts by mass of the acrylic resin, and more preferably in a range of 5 parts by mass to 15 parts by mass from the viewpoint of obtaining a printed matter excellent in water resistance.

The aqueous dispersion of the acrylic resin can be produced, for example, by an emulsion polymerization method.

The emulsion polymerization method may be a radical emulsion polymerization method using a radical polymerization initiator.

Examples of the radical polymerization initiator include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate, azo compounds such as 2,2 '-azobisisobutyronitrile and dimethyl-2, 2' -azobisisobutyrate, organic peroxides such as benzoyl peroxide and tert-butyl peroxy-2-ethylhexanoate, and redox initiators comprising an organic peroxide such as cumene hydroperoxide and a reducing agent such as iron oxide in combination. The amount of the radical polymerization initiator used is usually preferably in the range of 0.01 to 5 parts by mass, more preferably in the range of 0.05 to 2 parts by mass, based on 100 parts by mass of the total mass of the monomers used for producing the acrylic resin.

In the emulsion polymerization method, a chain transfer agent, a pH adjuster, and the like may be used as necessary.

The emulsion polymerization method may be carried out in 100 to 500 parts by mass of water per 100 parts by mass of the total monomers used for producing the acrylic resin.

The emulsion polymerization may be carried out at a temperature of preferably 5 to 100 ℃ and more preferably 50 to 90 ℃ for 0.1 to 10 hours.

In addition, as the acrylic resin dispersion in which the acrylic resin having a hydrophilic group is dispersed in a solvent such as water, for example, an acrylic resin having a hydrophilic group such as an anionic group, a cationic group, or a nonionic group can be used.

Examples of the anionic group include a carboxyl group, a phosphoric acid group, an acidic phosphate group, a phosphorous acid group, a sulfonic acid group, and a sulfinic acid group, and a group obtained by neutralizing these groups with an alkaline compound is preferably used.

Examples of the basic compound used for neutralizing the anionic group include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, 2-aminoethanol, 2-dimethylaminoethanol, ammonia, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, tetra-n-butylammonium hydroxide, and trimethylbenzylammonium hydroxide.

Examples of the cationic group include a primary amino group, a secondary amino group, a tertiary amino group, and an ammonium hydroxide group, and a group obtained by neutralizing these groups with an acidic compound is preferable.

Examples of the acidic compound used for neutralizing the cationic group include formic acid, acetic acid, propionic acid, lactic acid, monomethyl phosphate, methanesulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, hydrochloric acid, sulfuric acid, and nitric acid.

Examples of the nonionic group include groups having a polyether chain such as polyoxyethylene and polyoxypropylene.

The acrylic resin having a hydrophilic group can be produced, for example, by polymerizing a monomer having a hydrophilic group together with the amide group-containing monomer and the silane coupling agent.

Examples of the monomer having a hydrophilic group include acrylic monomers having a carboxyl group such as (meth) acrylic acid and 2-carboxyethyl (meth) acrylate, alkali metal salts thereof, (meth) acrylamide having a tertiary amino group such as N, N-dimethyl (meth) acrylamide, (meth) acrylic acid esters having a tertiary amino group such as dimethylaminoethyl (meth) acrylate, and quaternary ammonium compounds thereof, and among them, it is preferable to use (meth) acrylic acid or dimethylaminoethyl (meth) acrylate.

The dispersion of the acrylic resin having a hydrophilic group can be produced, for example, by polymerizing the monomer in an organic solvent to produce an acrylic resin having a hydrophilic group, and then dispersing the acrylic resin in a solvent such as water.

As the organic solvent, for example, two or more of the following may be used alone or in combination: aliphatic or alicyclic hydrocarbons such as n-hexane, n-heptane, n-octane, cyclohexane, cyclopentane, etc.; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; esters such as ethyl acetate, n-butyl acetate, n-pentyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, and ethylene glycol monobutyl ether acetate; alcohols such as methanol, ethanol, isopropanol, n-butanol, isobutanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, propylene glycol mono-n-propyl ether, and diethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, and cyclohexanone; dimethoxyethane, tetrahydrofuran, bisEthers such as alkane, ethylene glycol dimethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, and diethylene glycol dibutyl ether; n-methylpyrrolidone, dimethylformamide, dimethylacetamide, ethylene carbonate, and the like.

As the radical polymerization initiator that can be used for the polymerization in the organic solvent, various azo compounds such as 2,2 '-azobis (isobutyronitrile) and 2, 2' -azobis (2, 4-dimethylvaleronitrile); and various peroxides such as t-butyl peroxypivalate, t-butyl peroxybenzoate, and t-butyl peroxy-2-ethylhexanoate.

The method of dispersing the obtained acrylic resin having a hydrophilic group in an aqueous medium is preferably a method of dispersing by a phase inversion emulsification method.

The phase inversion emulsification method comprises the following steps: a method of mixing an organic solvent solution of an acrylic resin obtained by neutralizing a hydrophilic group with a basic compound or an acidic compound as necessary with a solvent such as water, and dispersing (phase inversion emulsification) the acrylic resin in the solvent. After the phase inversion emulsification, the organic solvent may be removed as necessary. In addition, in the phase inversion emulsification, an emulsifier may be used as needed within a range to achieve the object of the present invention.

As the solvent of the acrylic resin dispersion, water, a water-soluble solvent, or a mixture thereof can be used.

The particle size of the acrylic resin is not particularly limited, but is preferably small from the viewpoint of the ejection property of the inkjet head. For example, the particles preferably have a volume average particle diameter in the range of 10 to 200nm as measured by "Microtrac particle size Analyzer" UPA-EX150 "available from Nikkiso K.K.

The binder resin represented by the acrylic resin is preferably used in an amount of 3 to 15 mass% (solid content) based on the mass of the black pigment ink (a), more preferably 5 to 12 mass%, and particularly preferably 7 to 10 mass%, from the viewpoint of obtaining a printed matter having good gloss and suppressing clogging of an ink discharge nozzle.

The urea includes urea or a urea derivative. Urea and urea derivatives have high moisturizing functions and function as solid wetting agents. Therefore, the urea can prevent the aqueous ink from drying or solidifying in the vicinity of the discharge nozzle, and ensure good ink discharge performance.

Further, since the black pigment ink (a) containing the urea is quickly dried by heating or the like after being landed on a recording medium, occurrence of bleeding or color mixing can be more effectively reduced even when printing is performed on a recording medium such as a non-absorptive recording medium or a low-absorptive recording medium.

Examples of the urea derivative include ethylene urea, propylene urea, diethyl urea, thiourea, N-dimethyl urea, hydroxyethyl urea, hydroxybutyl urea, ethylene thiourea, and diethyl thiourea, and two or more of these may be used together.

As the urea, ethylene urea, or 2-hydroxyethyl urea is particularly preferably used because it is easily dissolved in water and easily available.

From the viewpoint of improving the ink discharge property and the drying property of the printed matter, the content of the urea is preferably in the range of 1.0 to 20.0% by mass, more preferably in the range of 2.0 to 15.0% by mass, and still more preferably in the range of 3.0 to 10.0% by mass, based on the mass of the black pigment ink (a).

When the urea is used, the urea is preferably used in combination with the water-soluble organic solvent having a boiling point of 100 ℃ to 200 ℃ and a vapor pressure of 0.5hPa or more at 20 ℃. The water-soluble organic solvent and the urea are preferably used in an amount of 1 to 25% by mass, more preferably 3 to 20% by mass, and particularly preferably 5 to 18% by mass, based on the mass of the black pigment ink (a), because the ink is not easily transferred even when another recording medium is laminated on the printing surface immediately after the printed matter is produced.

In addition, in the case of using the propylene glycol and at least one organic solvent selected from the group consisting of glycerin, diglycerin, glycerin derivatives, and diglycerin derivatives, the total mass of the water-soluble organic solvent having a boiling point of 100 ℃ or higher and 200 ℃ or lower and a vapor pressure at 20 ℃ of 0.5hPa or higher, the urea, the propylene glycol, and at least one organic solvent selected from the group consisting of glycerin, diglycerin, glycerin derivatives, and diglycerin derivatives is preferably used in a range of 20 to 50 mass%, more preferably in a range of 20 to 40 mass%, and particularly preferably in a range of 22 to 35 mass%, with respect to the mass of the black pigment ink (a), because the ink is not easily transferred even when another recording medium is laminated on the printing surface immediately after the printed matter is produced.

The wetting agent may be used for the purpose of preventing the black pigment ink (a) from drying. The wetting agent is preferably 3 to 50% by mass based on the total amount of the black pigment ink (a).

The humectant is preferably 1, 3-butanediol, because it has high safety and is excellent in drying property and discharge property of the black pigment ink (a), and it has a mixing property with water to obtain an effect of preventing clogging of a head of an ink jet printer, and it includes ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol having a molecular weight of 2000 or less, dipropylene glycol, tripropylene glycol, 1, 3-propanediol, isopropylene glycol, isobutylene glycol, 1, 4-butanediol, 1, 3-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, erythritol, pentaerythritol, and the like.

The penetrant may be used for the purpose of improving the permeability into the recording medium and adjusting the dot diameter on the recording medium.

Examples of the penetrant include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether, and the penetrant is preferably used in a range of 0.01 to 10% by mass based on the total amount of the black pigment ink (a).

The black pigment ink (a) can be produced, for example, by stirring and mixing the pigment and water as essential components, and if necessary, a surfactant, a pigment dispersion resin, a binder resin, and the like, and then dispersing and kneading the mixture using various dispersing machines, kneading machines such as a bead mill, an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a roll mill, a sand mixer, a sand mill, a dino mill (DYNO-MI LL), a DISPERMAT, SC mill, a NonoMizer, and the like.

The black pigment ink (a) may be produced by the above-mentioned method and then subjected to centrifugal separation or filtration treatment.

(pigment ink (b))

In the ink set of the present invention, a pigment ink having a static surface tension which is 0.1mN/m to 0.5mN/m lower than the static surface tension (a1) of the black pigment ink (a) is used as the pigment ink (b) used in combination with the black pigment ink (a).

As the pigment ink (b), an ink containing the same substances as exemplified as the substances usable in the black pigment ink (a) such as a surfactant, water, an organic solvent, a binder resin represented by a pigment dispersion resin such as a polymer (a) as an optional component, ureas, a neutralizer and the like can be used.

The pigment ink (b) may be produced by the same method as exemplified as the method for producing the black pigment ink (a).

As the pigment that can be used in the production of the pigment ink (b), an organic pigment or an inorganic pigment can be used.

As the organic pigment, for example, azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, perylene pigments, perinone pigments, etc.), and the like can be usedOxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, and the like), lake pigments (for example, basic dye type chelates, acidic dye type chelates, and the like), nitro pigments, nitroso pigments, aniline black, and the like.

Examples of pigments that can be used in the yellow pigment ink include c.i. pigment yellow 1,2, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 174, 180, and 185.

Examples of pigments that can be used in the magenta pigment ink include c.i. pigment red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), and 57: 1. 112, 122, 123, 146, 168, 176, 184, 185, 202, 209, 269, 282, etc., c.i. pigment violet 19, etc.

Examples of pigments that can be used in the cyan pigment ink include c.i. pigment blue 1,2, 3, 15: 3. 15: 4. 16, 22, 60, 63, 66, etc.

Further, as the pigment, an unacidified pigment or an acidic pigment can be used.

As a method for adjusting the static surface tension of the pigment ink (b), the same method as that for adjusting the static surface tension of the black pigment ink (a) can be used, and for example, a method for adjusting the kind and content of the surfactant is preferred because of simplicity.

As the surfactant, the same surfactant as that used in the black pigment ink (a) or a surfactant having the same degree of surface tension lowering energy is preferably used.

When the same surfactant as that used in the black pigment ink (a) or a surfactant having the same degree of surface tension lowering energy is used, it is preferable that the amount of the surfactant used in the pigment ink (b) is larger than that used in the black pigment ink (a) so that the static surface tension of the pigment ink (b) is smaller than the static surface tension (a1) of the black pigment ink (a) by 0.1mN/m to 0.5 mN/m.

However, as described above, in the case where the same surfactant or a surfactant having the same degree of surface tension lowering energy is used for the black pigment ink (a) and the pigment ink (b), even when the amount of the surfactant used for the pigment ink (b) is made larger than the amount of the surfactant used for the black pigment ink (a), the static surface tension of the pigment ink (b) may not be within the above range. This is because the affinity with the surfactant differs depending on the type of pigment contained in the ink.

In this case, as described above, the surfactant is preferably used within a range according to the kind of the pigment.

For example, when an acetylene-based surfactant such as acetylene glycol or an oxyethylene adduct of acetylene glycol is used as the black pigment ink (a) and the pigment ink (b), it is preferable to adjust the content (mass ratio) of the surfactant contained in the entire cyan pigment ink usable in the pigment ink (b) to be in the range of 0.5 to 1.5 when the content of the acetylene-based surfactant is 1 based on the entire black pigment ink (a). Particularly preferably in the range of 0.8 to 1.2. The content (mass ratio) of the surfactant contained in the entire magenta pigment ink that can be used in the pigment ink (b) is preferably adjusted to be in the range of 0.5 to 1.5. Particularly preferably in the range of 0.8 to 1.2. The content (mass ratio) of the surfactant contained in the entire yellow pigment ink that can be used in the pigment ink (b) is preferably adjusted to be in the range of 0.5 to 1.5. Particularly preferably in the range of 0.8 to 1.2.

The ink set of the present invention may be an ink set comprising the black pigment ink (a) and the pigment ink (b) as essential components and, if necessary, any ink other than the black pigment ink (a) and the pigment ink (b). As the pigment ink (b), either or both of the magenta pigment ink and the yellow pigment ink can be used as described above. Therefore, the ink set of the present invention may be composed of two or more kinds of inks, and the upper limit thereof is not limited.

In the ink set of the present invention, the difference in static surface tension between the ink having the highest static surface tension and the ink having the lowest static surface tension is preferably 0.1mN/m to 2.0mN/m, and more preferably 0.3mN/m to 1.0mN/m in terms of achieving the effect of suppressing bleeding and color mixing.

In the ink set of the present invention, the ink having the highest static surface tension may be the black pigment ink (a) described above, or may be any cyan pigment ink. The ink with the lowest static surface tension is preferably a yellow pigment ink.

The ink set of the present invention can be printed on a recording medium having excellent ink absorbency such as a copy paper (PPC paper) generally used in a copier, a recording medium having an ink absorbing layer, a non-absorbing recording medium having no ink absorbency at all, or a low-absorbing recording medium having low ink absorbency. In particular, the ink set of the present invention can provide a printed matter in which bleeding and color mixing are suppressed even when printing is performed on a recording medium having non-ink-absorbing properties or low ink-absorbing properties.

As the low-absorbency recording medium, it is preferable that the recording medium has a water absorption capacity of 10g/m when the contact time of the recording medium with water is 100 msec, from the viewpoint of obtaining a printed matter in which bleeding and color mixing are suppressed²The following recording media are used in combination with the ink set of the present invention.

The water absorption capacity was determined as a100 msec water absorption capacity by measuring a transfer capacity of pure water at a contact time of 100ms under a condition of 23 ℃ and a relative humidity of 50% using an autoscan absorptometer (KM 500win, manufactured by kusho processor corporation). The measurement conditions are shown below.

[ helical method ]

Contact time: 0.010 to 1.0 (second)

Pitch: 7(mm)

Length of each sample: 86.29 (degree)

Starting radius: 20(mm)

End radius: 60(mm)

Minimum contact time: 10(ms)

Maximum contact time: 1000(ms)

Sample preparation: 50

Number of sampling points: 19

[ Square head ]

Slit span: 1(mm)

Width: 5(mm)

Examples of the recording medium having ink absorbency include plain paper, cloth, corrugated paper, and wood. The recording medium having the absorbing layer includes, for example, a Paper exclusive for inkjet, specifically, a picticopro Photo Paper of pictoco.

As the low-absorption recording medium having low ink water absorption, coated paper such as corrugated paper and printing paper, coated paper, light-weight coated paper, micro-coated paper, or the like, which has a colored layer on the surface thereof, which is difficult to absorb a solvent in the ink, can be used.

Examples of the low-absorbency recording medium include paper having a coating layer formed by applying a coating material to the surface of high-grade paper, neutral paper, etc., mainly made of cellulose and generally having no surface treatment, and the low-absorbency recording medium may be light-weight coating paper (A3) such as "overhead Coat" manufactured by Wangzi paper (Ltd.), and "Aurora S" manufactured by Japan paper (Ltd.), and light-weight coating paper (OKCoat L manufactured by Wangzi paper (Ltd.) or "Aurora L" manufactured by Japan paper (Ltd.), and "OK TopCoat + (weight 104.7g/m per square meter) manufactured by Wangzi paper (Ltd.)²The water absorption capacity at 100 msec contact time (hereinafter, the same water absorption capacity) was 4.9g/m²) "Aurora Coat" manufactured by Nippon paper company, and Finesse Gloss (manufactured by UPM Co., Ltd., 115 g/m)²Water absorption capacity of 3.1g/m²) And Finess Matt (115 g/m)²Water absorption 4.4g/m²) Plastic films such as coated papers (A2 and B2), coated papers (A1) such as "OK jin Teng +" made by prince paper (Kabushiki Kaisha) and "Techaba Art" made by Mitsubishi paper (Katsubishi paper). Examples of the plastic film include polyester films made of polyethylene terephthalate, polyethylene naphthalate, and the like, polyolefin films made of polyethylene, polypropylene, and the like, polyamide films made of nylon and the like, polystyrene films, polyvinyl alcohol films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, polylactic acid films, and the like. As the plastic film, a polyester film, a polyolefin film, and a polyamide film are preferably used, and a polyethylene terephthalate film, a polypropylene film, and a nylon film are preferably used.

As the plastic film, a film coated with a coating layer of polyvinylidene chloride or the like for imparting barrier properties, a film having a metal layer of aluminum or the like and a vapor-deposited layer of a metal oxide of silica, alumina or the like may be used.

The plastic film may be an unstretched film or a uniaxially or biaxially stretched film. The surface of the film may be untreated, but is preferably subjected to various treatments for improving adhesiveness, such as corona discharge treatment, ozone treatment, low-temperature plasma treatment, flame treatment, and glow discharge treatment.

The film thickness of the plastic film may be appropriately changed depending on the application, and for example, in the case of flexible packaging, the film having flexibility, durability and curl resistance is preferably 10 to 100 μm, more preferably 10 to 30 μm.

The ink set of the present invention can be suitably used for printing on corrugated paper or the like in which the recording medium is mainly composed of a cardboard which easily absorbs a solvent contained in the ink, and a colored layer which is provided on a surface of the cardboard and hardly absorbs the solvent contained in the ink.

As the corrugated paper, for example, corrugated paper obtained by laminating a liner on one or both surfaces of a corrugated core molded in a wave shape can be used, and single-faced corrugated paper, double-faced corrugated paper, triple-faced corrugated paper, and the like can be used.

As the corrugated paper, specifically, it can be suitably used for printing on corrugated paper made of cardboard which easily absorbs a solvent contained in ink, corrugated paper provided with a colored layer or a waterproof layer on the surface of the cardboard which hardly absorbs a solvent contained in ink, and the like. The ink of the present invention is capable of effectively suppressing the occurrence of streaks in printed matter, because the ink that lands on the surface of a non-absorbent or poorly absorbent recording medium such as corrugated paper having a colored layer or a water-repellent layer on the surface of the paperboard, which layer is difficult to absorb solvents in the ink, is likely to spread on the surface of the recording medium.

When the ink set of the present invention is used for ink jet printing of the corrugated paper, even if the distance from the surface (x) having the ink discharge port to the position (y) where the perpendicular line to the surface (x) intersects with the recording medium is 2mm or more, the ink set spreads sufficiently after being landed on the recording medium, and thus the occurrence of streaks in the printed matter can be effectively prevented.

Among the corrugated papers, those having a coloring layer, a waterproof layer, and the like provided on the surface thereof can be used, for example, those having a coating film formed by applying a coloring agent or a waterproof agent to the surface of the corrugated paper made of the above-mentioned cardboard by a curtain coating method, a roll coating method, and the like.

Examples of the colored layer include a colored layer having a whiteness of 70% or more.

In order to achieve a water-repellent effect of a printed matter, it is preferable that the layer such as the colored layer or the water-repellent layer of the corrugated paper has a water absorption capacity of 10g/m when the contact time between the recording surface of the recording medium such as the corrugated paper and water is 100 msec²The following.

Examples of the method for producing a printed matter using the ink set of the present invention include a method including the steps of: when an ink set including a combination of a black pigment ink (a), a magenta pigment ink and a yellow pigment ink as the pigment ink (b), and a cyan pigment ink as an ink other than the above is discharged onto a recording medium by an ink jet recording method to produce a printed matter, the black pigment ink (a), the cyan pigment ink, the magenta pigment ink, and the yellow pigment ink are discharged onto the recording medium by an ink jet recording apparatus in this order. From the viewpoint of achieving the effect of suppressing bleeding and color mixing, it is preferable to use an ink set composed of a combination of the following inks: the static surface tension of the magenta pigment ink is smaller than the static surface tension (a1) by 0.1 to 0.7mN/m, preferably by 0.1 to 0.5mN/m, preferably by 0.1 to 0.3mN/m, and the static surface tension of the yellow pigment ink is smaller than the surface tension of the magenta pigment ink by 0.1 to 0.5mN/m, and the static surface tension of the cyan pigment ink is arbitrary.

Further, as a method for producing a printed matter using the ink set of the present invention, for example, a method having the following steps: when an ink set including a combination of a black pigment ink (a), a magenta pigment ink and a yellow pigment ink as the pigment ink (b), and a cyan pigment ink as an ink other than the above is discharged onto a recording medium by an ink jet recording method to produce a printed matter, the cyan pigment ink, the black pigment ink (a), the magenta pigment ink, and the yellow pigment ink are discharged onto the recording medium by an ink jet recording apparatus in this order. From the viewpoint of achieving the effect of suppressing bleeding and color mixing, it is preferable to use an ink set composed of a combination of the following inks: the static surface tension of the magenta pigment ink is 0.1 to 0.7mN/m, preferably 0.1 to 0.5mN/m, preferably 0.1 to 0.3mN/m, smaller than the static surface tension (a1), and the static surface tension of the yellow pigment ink is 0.1 to 0.7mN/m, preferably 0.1 to 0.5mN/m, preferably 0.1 to 0.3mN/m, smaller than the surface tension of the magenta pigment ink, and the static surface tension of the cyan pigment ink is arbitrary.