阅读说明：本技术 胶乳浸渍液、橡胶组合物以及它们的制备方法 (Latex dipping liquid, rubber composition and preparation method thereof ) 是由 高木芽衣 伊藤康太郎 加藤隼人 于 2020-04-20 设计创作，主要内容包括：本发明的课题在于提供：橡胶组合物,其与未混合纤维素纳米纤维而制作的橡胶组合物相比,断裂强度和拉伸伸长率优异；以及胶乳浸渍液,其是上述橡胶组合物的原料,在胶乳浸渍工序中使用。即,本发明提供：胶乳浸渍液,其含有(1)橡胶胶乳、(2)平均纤维长度为200nm～400nm的改性纤维素纳米纤维、以及(3)消泡剂；以及橡胶组合物,其是使用所得的胶乳浸渍液经过胶乳浸渍工序而制作的。(The subject of the invention is to provide: a rubber composition which is superior in breaking strength and tensile elongation to a rubber composition produced without mixing cellulose nanofibers; and a latex dipping solution which is a raw material of the rubber composition and is used in a latex dipping step. Namely, the present invention provides: a latex dipping solution containing (1) a rubber latex, (2) a modified cellulose nanofiber having an average fiber length of 200 to 400nm, and (3) an antifoaming agent; and a rubber composition produced by using the obtained latex dipping solution through a latex dipping step.)

1. A latex dipping solution comprising the following (1) to (3):

(1) a rubber latex;

(2) modified cellulose nanofibers having an average fiber length of 200nm to 400 nm; and

(3) and (4) defoaming agent.

2. The latex-dipping solution according to claim 1, wherein the component (2) comprises oxidized cellulose nanofibers.

3. The latex dipping solution according to claim 2, wherein the oxidized cellulose nanofibers are TEMPO oxidized cellulose nanofibers.

4. The latex dipping solution according to claim 3, wherein the amount of the carboxyl group in the TEMPO oxidized cellulose nanofibers is 0.2 to 2.0 mmol/g.

5. The latex dipping solution according to any one of claims 1 to 4, wherein the component (3) contains at least 1 selected from the group consisting of polyether, silica and mineral oil.

6. The dipping solution for latex according to any one of claims 1 to 5, which has a B-type viscosity of 10 to 500 mPas after 24 hours from the production.

7. A method for preparing a latex dip, the method comprising: mixing (1) and (2) to obtain a mixed solution; curing the mixed solution; and spraying the component (3) to the aged liquid mixture.

8. A rubber composition comprising the latex-dipped liquid as claimed in any one of claims 1 to 6 as a raw material.

9. A method for producing a rubber composition, which comprises using the latex dipping solution according to any one of claims 1 to 6 as a raw material.

Technical Field

The present invention relates to a latex dipping solution, a rubber composition and a method for producing the same, and more particularly to a latex dipping solution, a rubber composition produced through a latex dipping step using the latex dipping solution, and a method for producing the same.

Background

Rubber products such as rubber gloves made of a thin rubber film are produced through a latex dipping process. For example, patent document 1 describes a method for producing a rubber glove, which comprises the steps of: after dipping a mold corresponding to the three-dimensional shape of the glove in a latex composition containing rubber or resin and blended with biomass nanofibers, the mold is pulled up, and the latex composition attached to the mold is dried and cured.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-094038.

Disclosure of Invention

Problems to be solved by the invention

However, the latex composition used in the method of patent document 1 is high in viscosity. In the case of dipping a sheet as a mold in a latex composition having a high viscosity, the dipping liquid cannot be uniformly adsorbed on the dipped sheet, and the rubber product produced has open pores. This makes it impossible to obtain a uniform rubber film, resulting in a rubber product having low strength. In addition, the viscosity of the impregnation liquid mixed with the cellulose nanofibers similarly increases, and the resulting rubber product cannot have sufficient strength.

The invention aims to: rubber products can be produced through a latex dipping step by controlling the viscosity of a dipping solution obtained by mixing and stirring a dispersion of a rubber component such as latex and cellulose nanofibers. Further, a rubber composition having physical properties higher than those of a rubber composition prepared without mixing cellulose nanofibers in breaking strength and tensile elongation is provided.

Means for solving the problems

The present invention provides the following <1> to <9 >.

<1 >: a latex dipping solution containing the following (1) to (3):

(1) a rubber latex;

(2) modified cellulose nanofibers having an average fiber length of 200nm to 400 nm; and

(3) and (4) defoaming agent.

<2 >: <1> the latex dipping solution according to the above, wherein the above (2) is oxidized cellulose nanofibers.

<3 >: <2> the latex dipping solution, wherein the oxidized cellulose nanofibers are TEMPO oxidized cellulose nanofibers.

<4 >: <3> the latex dipping solution, wherein the amount of carboxyl groups in the TEMPO-oxidized cellulose nanofibers is from 0.2mmol/g to 2.0 mmol/g.

<5 >: the liquid for dipping latex according to any one of <1> to <4>, wherein the above (3) contains at least 1 kind selected from the group consisting of polyether, silica and mineral oil.

<6 >: the dipping solution for latex according to any one of <1> to <5>, wherein the B-type viscosity of the dipping solution for latex is 10 to 500 mPas after 24 hours from the preparation.

<7 >: a method for preparing a latex dip, the method comprising: mixing (1) and (2) to obtain a mixed solution; curing the mixed solution; and spraying the component (3) to the aged liquid mixture.

<8 >: a rubber composition comprising the latex-dipped liquid according to any one of <1> to <6> as a raw material.

<9 >: a method for producing a rubber composition, which comprises using the latex-dipped liquid according to any one of <1> to <6> as a raw material.

Since the aqueous cellulose nanofiber dispersion has a high viscosity, a dipping solution obtained by blending the aqueous cellulose nanofiber dispersion in a latex generally has a high viscosity. Therefore, in the latex dipping step, the dipping solution cannot be uniformly adsorbed on the sheet, and a rubber film having a uniform thickness cannot be obtained. By using short-fiber cellulose nanofibers having a low viscosity, the viscosity of the latex and the cellulose nanofibers can be controlled while stirring, and the impregnation solution can be uniformly adsorbed on the plate.

Effects of the invention

According to the present invention, a latex dipping solution having a low viscosity can be obtained. Since a uniform film can be formed on the surface of the mold dipped in the latex dipping solution of the present invention, the obtained rubber composition can exhibit a higher strength than a rubber composition produced by using only natural rubber. Therefore, the present invention is also useful for preparing various rubber compositions, for example, rubber compositions of complicated shapes.

Detailed Description

The present invention will be explained below. In the present specification, a numerical range including "to" includes end values. That is, "X to Y" includes the values X and Y at both ends thereof.

[1. latex dipping solution ]

The latex dipping solution of the present invention contains at least components (1) to (3). The latex dipping solution of the invention can be used in a latex dipping process in the preparation of a rubber composition.

< ingredient (2): modified cellulose nanofibers >

In the present specification, the Cellulose Nanofibers (CNF) are fine fibers having an average fiber diameter of about 2 to 500nm, which are obtained by refining a cellulose raw material such as pulp to a nanometer level. The average fiber diameter and the average fiber length of the modified cellulose nanofibers can be obtained by observing each fiber using an Atomic Force Microscope (AFM) or a Transmission Electron Microscope (TEM), and averaging the fiber diameter and the fiber length obtained from the observation results, respectively.

In the present specification, the modified cellulose nanofibers mean cellulose nanofibers obtained by modifying (usually chemically modifying) and refining a cellulose raw material. In the present specification, chemical modification refers to chemical modification, and examples thereof include: anion modification and cation modification. Examples of the method for producing the modified cellulose nanofibers include: a method of refining (for example, defibrating (nano-defibrating)) modified cellulose obtained by modification (for example, chemical modification such as anionic modification (for example, oxidation (carboxylation), etherification, phosphorylation), and cationic modification) of a cellulose raw material. The average fiber length and the average fiber diameter of the fine fibers can be adjusted by chemical modification treatment (for example, oxidation treatment), refining treatment (for example, defibration treatment), and if necessary, alkaline hydrolysis treatment.

The average fiber diameter of the modified cellulose nanofibers is usually 2 to 500nm, preferably 2 to 100nm, more preferably 2 to 50nm, still more preferably 2 to 15nm, and still more preferably 2 to 10 nm. The average fiber length is 200 to 400nm, preferably 200 to 350nm, and more preferably 200 to 330 nm. By using the modified cellulose nanofibers satisfying at least either one of the average fiber diameter and the average fiber length, preferably at least the average fiber length, and more preferably both, an increase in viscosity of the impregnation liquid can be suppressed. Thus, a rubber composition having no pores can be prepared from a rubber composition produced through a latex dipping step, and a rubber composition having a tensile strength and a tensile elongation higher than those of a rubber composition produced using only natural rubber can be provided.

In the present specification, a modified cellulose nanofiber having an average fiber length of 200nm to 400nm may be referred to as a short-fiber cellulose nanofiber.

The average aspect ratio of the modified cellulose nanofibers is typically 50 or more. The upper limit is not particularly limited, but is usually 1000 or less. The average aspect ratio can be calculated by the following formula:

aspect ratio = average fiber length/average fiber diameter.

(cellulose Material)

The cellulose material is not particularly limited, and examples thereof include: paper pulp; powdered cellulose obtained by pulverizing pulp with a high-pressure homogenizer, a mill or the like; microcrystalline cellulose powder obtained by refining the pulp by chemical treatment such as acid hydrolysis. As other examples, there may be also enumerated: cellulose raw materials derived from plants such as kenaf, hemp, rice, bagasse, bamboo, jute, etc.; cellulose raw materials derived from microorganisms such as algae and acetobacter (Acetobacter); farmland wastes; and (3) cloth. Examples of the pulp derived from wood include: pulp obtained by kraft cooking after hydrolysis (DKP: for example, needle-leaved dissolving kraft pulp), needle-leaved unbleached kraft pulp (NUKP), needle-leaved bleached kraft pulp (NBKP), broad-Leaved Unbleached Kraft Pulp (LUKP), broad-Leaved Bleached Kraft Pulp (LBKP), needle-leaved unbleached sulfite pulp (NUSP), needle-leaved bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), needle-leaved dissolving pulp, broad-leaved dissolving pulp, regenerated pulp, and waste paper pulp. DKP, powdered cellulose, microcrystalline cellulose powder are preferred. By using these, cellulose nanofibers which can give a dispersion (usually an aqueous dispersion) having a lower viscosity even at a high concentration can be produced. Cellulose nanofibers that give a low viscosity dispersion can also be produced from a cellulose raw material derived from a broad-leaved tree with low electricity consumption, and therefore, such a cellulose nanofiber is preferable. By using the modified cellulose nanofibers having the above average fiber length obtained from these cellulose raw materials as the component (2), an increase in viscosity of the latex dipping solution can be suppressed.

(chemical modification)

The modified cellulose nanofiber may be either of an anion-modified cellulose nanofiber and a cation-modified cellulose nanofiber. When an optional component such as a filler or a dispersant is mixed with the modified cellulose nanofibers in the mixed solution obtained in the impregnation, it is preferable to select the modified cellulose nanofibers in which the optional component is well dispersed. When an anionic polymer compound is used as the dispersant, the anionic modified cellulose nanofibers are preferable in order to easily obtain a synergistic effect for suppressing aggregation of the filler.

The anion-modified cellulose nanofibers are cellulose nanofibers into which functional groups have been introduced by anion modification. Examples of the functional group introduced by anion modification include: carboxyl, carboxyalkyl, sulfo, phosphate, nitro. Among them, a carboxyl group, a carboxyalkyl group and a phosphate group are preferable, and a carboxyl group is more preferable.

(salt type and acid type)

The functional group introduced by chemically modifying the cellulose raw material may be an acid-type functional group or a salt-type functional group. For example, when a cellulose raw material is oxidized, a hydroxyl group is modified into a carboxyl group, and the oxidized cellulose fiber usually contains both a group represented by-COOH (acid-type carboxyl group) and a group represented by-COO (salt-type carboxyl group).

Examples of the counter cation of the salt-type functional group include: alkali metal ions such as sodium and potassium; the ammonium ion can be selected according to the type of the functional group, and is preferably selected so as to improve the defibrination and dispersibility of the modified cellulose.

(Oxidation (carboxylation))

Oxidized cellulose can be obtained by oxidizing (carboxylating) a cellulose raw material by a known method. The amount of carboxyl groups in the oxidized cellulose is preferably 0.2mmol/g or more, more preferably 0.5mmol/g or more, based on the absolute dry mass (absolute dry mass) of the oxidized cellulose nanofibers. Thus, a highly transparent and uniform nanofiber dispersion can be obtained without requiring a large amount of energy in the process of defibering. Further, when the modified cellulose nanofibers are blended into latex, the residue of coarse materials (which may become starting points of breakage) such as undeveloped fibers can be suppressed. The upper limit is usually 2.0mmol/g or less. Therefore, the amount of carboxyl groups in the oxidized cellulose nanofibers is preferably 0.2 to 2.0mmol/g, more preferably 0.5 to 2.0mmol/g, and is generally the same as the amount of carboxyl groups in the oxidized cellulose before the pulverization. The amount of carboxyl groups can be calculated from the change in conductivity.

As an example of the oxidation (carboxylation) method, there can be cited: in the presence of N-oxyl (N-oxyl)A method for oxidizing a cellulose raw material in water using an oxidizing agent in the presence of a compound and a reagent selected from bromide, iodide or a combination of 2 or more thereof. By this oxidation reaction, the primary hydroxyl group at C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized to give a cellulose having an aldehyde group and a carboxyl group (-COOH) or a carboxylate group (-COO) on the surface^-Carboxylate radical). The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

The N-oxyl compound is a compound which can generate a nitroxyl radical (nitroxy radial). Any compound may be used as the N-oxyl compound as long as it promotes the desired oxidation reaction. Examples thereof include: 2,2,6, 6-tetramethylpiperidin-1-oxyl radical (TEMPO) and its derivatives (e.g., 4-hydroxy TEMPO). In the present specification, oxidized cellulose nanofibers subjected to oxidation using 1 or more species selected from TEMPO and derivatives thereof are sometimes referred to as TEMPO oxidized cellulose nanofibers.

The amount of the N-oxyl compound to be used is not particularly limited as long as it is an amount of a catalyst capable of oxidizing the cellulose as the raw material. For example, the amount of the cellulose is preferably 0.01 to 10mmol, more preferably 0.01 to 1mmol, and still more preferably 0.05 to 0.5mmol, per 1g of the cellulose in absolute dry (absolute dry). Further, the amount of the catalyst is preferably about 0.1 to 4mmol/L relative to the reaction system.

The bromide means a bromine-containing compound, and examples thereof include alkali metal bromides which dissociate in water to be ionized. In addition, the iodide means an iodine-containing compound, and examples thereof include alkali metal iodides. The amount of bromide or iodide used may be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100mmol, more preferably 0.1 to 10mmol, and still more preferably 0.5 to 5mmol, per 1g of absolutely dry cellulose.

As the oxidizing agent, known oxidizing agents can be used, and for example, halogen, hypohalous acid, perhalogenic acid, or salts thereof, oxyhalides, peroxides can be used. Among them, sodium hypochlorite is preferred which is inexpensive and has little environmental load. The amount of the oxidizing agent used is, for example, preferably 0.5 to 500mmol, more preferably 0.5 to 50mmol, still more preferably 1 to 25mmol, and most preferably 3 to 10mmol, per 1g of the cellulose in absolute dry state. Further, it is preferable that the amount of the N-oxyl compound is, for example, 1 to 40mol based on 1mol of the N-oxyl compound.

The oxidation of cellulose can be carried out efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40 ℃ or about 15 to 30 ℃. Since carboxyl groups were generated in the cellulose as the reaction proceeded, it was confirmed that the pH of the reaction solution was lowered. In order to efficiently perform the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution so as to maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. The reaction medium is preferably water in order to have advantages such as good operability and little side reaction.

The reaction time in the oxidation reaction may be appropriately set according to the degree of progress of oxidation, and is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours.

In addition, the oxidation reaction can be carried out in 2 steps. For example, by filtering and separating the oxidized cellulose obtained after the reaction in the 1 st step is completed and oxidizing the oxidized cellulose again under the same or different reaction conditions, the oxidation can be efficiently performed without being hindered by the reaction of common salt by-produced in the reaction in the 1 st step.

As another example of the oxidation (carboxylation) method, there can be cited: a method for oxidation by bringing an ozone-containing gas into contact with a cellulose raw material. By this oxidation reaction, at least the hydroxyl groups at the 2-and 6-positions of the glucopyranose ring are oxidized, while decomposition of the cellulose chain occurs. The concentration of ozone in the ozone-containing gas is preferably 50 to 250g/m³More preferably 50 to 220g/m³. The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the solid content of the cellulose raw material. The ozone treatment temperature is preferably 0 to 50 ℃, and more preferably 20 to 50 ℃. The ozone treatment time is not particularly limited, and is usually about 1 to 360 minutes, preferably about 30 to 360 minutes. If the conditions of the ozone treatment are within these ranges, cellulose can be preventedIs excessively oxidized and decomposed, and the yield of oxidized cellulose can be good. After the ozone treatment, an additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include: chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving the oxidizing agent in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and then immersing the cellulose raw material in the solution.

The amount of the carboxyl group in the oxidized cellulose can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent added and the reaction time.

(etherification)

Etherified cellulose can be obtained by etherifying a cellulose raw material by a known method. Examples of the etherification include: etherification based on a reaction selected from the group consisting of methylation, ethylation, cyanoethylation, hydroxyethylation, hydroxypropylation, ethylhydroxyethylation and hydroxypropylmethylation, preferably carboxyalkylation, more preferably carboxymethylation. The modified cellulose obtained by carboxyalkylation (carboxyalkylated cellulose) preferably has a structure in which at least 1 hydroxyl group of the cellulose is carboxyalkylated. The carboxyalkyl substitution Degree (DS) per anhydroglucose unit of the carboxyalkylated cellulose is preferably 0.01 to 0.50. The DS is the ratio of groups substituted with carboxyalkyl groups (the number of carboxyalkyl groups per 1 glucose residue) among the hydroxyl groups originally contained in each anhydroglucose (glucose residue) constituting the cellulose, and can be calculated from the amount of carboxyalkyl groups.

Examples of the method for carboxyalkylation include: a method of mercerizing a cellulose-based raw material as a starting material and then etherifying the mercerized raw material. As an example of the carboxymethylation method, the following method can be cited. Cellulose is used as a starting material, and water, a lower alcohol (for example, water, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, or tert-butanol) in an amount of 3 to 20 times by mass, or a mixed medium of water and a lower alcohol is used as a solvent. When lower alcohols are mixed, the mixing ratio of the lower alcohols is usually 60 to 95% by mass. Examples of mercerizing agents include: alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of the mercerizing agent is preferably 0.5 to 20 times by mole per anhydrous glucose residue of the starting material. The starting materials, solvent and mercerizing agent are mixed to perform mercerization. The reaction temperature of the mercerization is usually 0 to 70 ℃, preferably 10 to 60 ℃. The reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Then, a carboxymethylating agent is added to the system to carry out etherification. The carboxymethylating agent is usually added in an amount of 0.05 to 10.0 times by mole per glucose residue. The reaction temperature is usually 30 to 90 ℃ and preferably 40 to 80 ℃. The reaction time is usually 30 minutes to 10 hours, preferably 1 hour to 4 hours.

In the present specification, "carboxymethylated cellulose" which is one of modified celluloses means a cellulose which maintains at least a part of a fibrous shape even when dispersed in water. Therefore, the present invention is distinguished from carboxymethyl cellulose (carboxymethyl cellulose) as a water-soluble polymer exemplified as a dispersant in the present specification. When an aqueous dispersion of "carboxymethylated cellulose" was observed under an electron microscope, fibrous substances were observed. On the other hand, even when an aqueous dispersion of carboxymethyl cellulose, which is one of water-soluble polymers, was observed, fibrous substances were not observed. In addition, the "carboxymethylated cellulose" shows a peak of cellulose type I crystals when measured by X-ray diffraction, but cellulose type I crystals are not observed in the water-soluble polymer carboxymethylcellulose.

(phosphoric acid esterification)

The phosphorylated cellulose can be obtained by a method of mixing a powder or an aqueous solution of the phosphoric acid-based compound a with a cellulose raw material or a method of adding an aqueous solution of the phosphoric acid-based compound a to a slurry of a cellulose raw material.

Examples of the phosphate compound a include: phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. The phosphoric acid-based compound a is preferably a phosphoric acid-group-containing compound for reasons of low cost, easy handling, and improvement in defibration efficiency by introducing a phosphoric acid group into a cellulose raw material such as pulp. Examples of the compound having a phosphate group include: phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate. These may be used in 1 kind or 2 or more kinds in combination. Among these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are preferable from the viewpoints of high phosphoric acid group introduction efficiency, easy defibration, and easy industrial applicability. Sodium dihydrogen phosphate and disodium hydrogen phosphate are more preferable. In addition, the phosphoric acid compound a is preferably used in the form of an aqueous solution from the viewpoint of improving the uniformity of the reaction and improving the efficiency of phosphate group introduction. The pH of the aqueous solution of the phosphoric acid compound a is preferably 7 or less from the viewpoint of improving the efficiency of introducing phosphoric acid groups, but is preferably 3 to 7 from the viewpoint of suppressing hydrolysis of a cellulose raw material such as pulp.

As an example of the phosphorylation method, the following method can be cited. The phosphoric acid-based compound A is added to a dispersion of a cellulose raw material (for example, at a solid content concentration of 0.1 to 10% (v/w)) while stirring the phosphoric acid-based compound A, so as to introduce a phosphoric acid group into the cellulose. The amount of the phosphoric acid compound a added is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more in terms of the amount of phosphorus element, relative to 100 parts by mass of the cellulose raw material. This can further improve the yield of the microfibrous cellulose. The upper limit is usually 500 parts by mass or less, preferably 400 parts by mass or less. This is preferable from the viewpoint of cost, because the effect of improving the yield can be prevented from reaching the limit. Therefore, it is preferably 0.2 to 500 parts by mass, more preferably 1 to 400 parts by mass.

When introducing a phosphoric acid group into cellulose, a powder or an aqueous solution of the compound B may be mixed in addition to the cellulose raw material and the phosphoric acid compound a. The compound B is not particularly limited as long as it is a compound other than the cellulose raw material and the phosphoric acid-based compound a, and is preferably a nitrogen-containing compound exhibiting basicity. "basic" is defined herein as: the aqueous solution appears pink to red in the presence of phenolphthalein indicator, or the pH of the aqueous solution is greater than 7. The nitrogen-containing compound having basicity is not particularly limited, but a compound having an amino group is preferable. Examples thereof include: urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine and hexamethylenediamine. Among them, urea which is low in cost and easy to handle is preferable. The amount of the compound B to be added is preferably 2 to 1000 parts by mass, more preferably 100 to 700 parts by mass, per 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95 ℃ and more preferably 30 to 90 ℃. The reaction time is not particularly limited, but is usually about 1 to 600 minutes, preferably 30 to 480 minutes. When the conditions of the esterification reaction are within these ranges, the cellulose can be prevented from being excessively esterified and easily dissolved, and the yield of the phosphorylated cellulose can be improved. After the obtained suspension of phosphorylated cellulose is dehydrated, it is preferable to perform a heat treatment (for example, 100 to 170 ℃) in order to suppress hydrolysis of cellulose. In addition, it is preferable that the heat treatment is performed by preheating (usually 130 ℃ or lower, preferably 110 ℃ or lower) while containing water to remove water, and then performing the heat treatment (for example, 100 to 170 ℃).

The phosphate group substitution degree of each glucose unit of the phosphorylated cellulose is preferably 0.001 to 0.40. By introducing phosphate group substituents into the cellulose, the cellulose is electrically repulsive to each other. Therefore, the cellulose having the phosphate group introduced therein can be easily defibered. If the substitution degree of the phosphate group per glucose unit is 0.001 or more, the fiber can be sufficiently defibrated. On the other hand, if the substitution degree of the phosphate group per glucose unit is 0.40 or less, swelling or dissolution can be suppressed, and it may not be obtained as nanofibers. In order to effectively perform defibration, the above-obtained phosphorylated cellulose raw material is preferably boiled and then washed with cold water.

(cationization)

The cationized cellulose can be obtained by cationizing the oxidized cellulose. Examples of the method for cationizing the oxidized cellulose include: a method in which glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium halide, a cationizing agent such as a halohydrin thereof, and a catalyst such as alkali metal hydroxide (e.g., sodium hydroxide or potassium hydroxide) are reacted with oxidized cellulose in the presence of water or an alcohol (e.g., an alcohol having 1 to 4 carbon atoms).

The cationic substitution degree of each glucose unit is preferably 0.02 to 0.50. By introducing cationic substituents into the cellulose, the cellulose is electrically repelled from each other. Therefore, cellulose having a cationic substituent introduced therein can be easily defibrated. By setting the degree of substitution of cations per glucose unit to 0.02 or more, sufficient defibration can be achieved. On the other hand, if the cationic substitution degree per glucose unit is 0.50 or less, swelling or dissolution occurs, and thus the cellulose cannot be obtained in the form of nanofibers in some cases. In order to effectively perform defibration, it is preferable to wash the cation-modified cellulose raw material obtained as described above. The degree of substitution of the cation can be adjusted by the amount of the cationizing agent added in the reaction and the composition ratio of water or alcohol having 1 to 4 carbon atoms.

(hydrolysis treatment)

The modified cellulose is usually obtained in the form of a dispersion (for example, an aqueous dispersion), and the dispersion preferably has excellent fluidity. The dispersion liquid having excellent fluidity is suitable for suppressing the increase in viscosity of the latex dipping liquid. Examples of the method for improving fluidity include: a method for hydrolyzing modified cellulose in an alkaline solution having a pH of 8-14. In the present method, water is preferably used as a reaction medium in order to suppress side reactions. In addition, an oxidizing agent or a reducing agent is preferably used as an auxiliary agent. As the oxidizing agent or the reducing agent, a substance having activity in an alkaline region of pH 8-14 can be used. As examples of the oxidizing agent, there may be mentioned: oxygen, ozone, hydrogen peroxide, hypochlorite, or a combination of 2 or more thereof. Among these, oxidizing agents which do not easily generate radicals (e.g., oxygen, hydrogen peroxide, hypochlorite) are preferable, and hydrogen peroxide is more preferable from the viewpoint of preventing coloration. From the viewpoint of suppressing coloring, an oxidizing agent such as ozone which is less likely to generate radicals is preferably used in a small amount, and more preferably is not substantially used. The oxidizing agent is further preferably hydrogen peroxide alone. Examples of the reducing agent include: sodium borohydride, dithionite, sulfite, or a combination of 2 or more thereof. From the viewpoint of reaction efficiency, the addition amount of the auxiliary is preferably 0.1 to 10% (w/v), more preferably 0.3 to 5% (w/v), and still more preferably 0.5 to 2% (w/v) with respect to the absolutely dry cellulose raw material.

The pH of the reaction solution in the hydrolysis reaction is preferably 8 to 14, more preferably 9 to 13, and still more preferably 10 to 12. By adjusting the pH to 8 or more, the occurrence of insufficient hydrolysis can be avoided, and a modified cellulose nanofiber dispersion having excellent fluidity can be obtained. Further, by adjusting the pH to 14 or less, hydrolysis proceeds, and coloring of the oxidized cellulose after hydrolysis can be suppressed. The base used for adjusting the pH may be water-soluble, but sodium hydroxide is most suitable from the viewpoint of production cost. In addition, from the viewpoint of reaction efficiency, the temperature is preferably 40 to 120 ℃, more preferably 50 to 100 ℃, and still more preferably 60 to 90 ℃. When the temperature is 40 ℃ or higher, sufficient hydrolysis is not likely to occur, and a modified cellulose nanofiber dispersion having excellent fluidity can be obtained. On the other hand, hydrolysis can be progressed by 120 ℃ or lower, and coloring of oxidized cellulose after hydrolysis can be suppressed. The reaction time for hydrolysis is preferably 0.5 to 24 hours, more preferably 1 to 10 hours, and further preferably 2 to 6 hours. From the viewpoint of reaction efficiency, the concentration of the oxidized cellulose raw material in the reaction liquid (usually, dispersion liquid) is preferably 1 to 20 mass%, more preferably 3 to 15 mass%, and still more preferably 5 to 10 mass%.

The energy required for defibering in the subsequent step can be reduced by hydrolyzing the modified cellulose in an alkaline solution having a pH of 8-14. For example, when the modified cellulose is oxidized cellulose, the following reason is presumed. Carboxyl groups are dispersed in an amorphous region of oxidized cellulose obtained by oxidation using an N-oxyl compound. The hydrogen at the C6 position, which is present in the carboxyl group, is in a state of charge shortage due to the attraction of electrons to the carboxyl group. Therefore, under alkaline conditions of pH 8-14, the hydrogen is easily extracted by hydroxide ions. In this way, a cleavage reaction by beta-detached glycosidic bonds proceeds, and the oxidized cellulose material forms short fibers. By shortening the fiber length of the oxidized cellulose in this manner, the viscosity of the dispersion containing the raw material can be reduced. As a result, the energy required for defibration is reduced. However, if hydrolysis is carried out only under alkaline conditions, the cellulose raw material may be colored yellow. The reason is considered to be that: double bonds are formed upon beta elimination. Therefore, in the hydrolysis under the alkaline condition of pH 8-14, if an oxidizing agent or a reducing agent is used, the double bond can be oxidized or reduced and removed, so that the coloring can be inhibited. When hydrogen peroxide is used as an oxidizing agent so that radicals are not easily generated, coloring is not easily generated.

Other methods for improving the fluidity of the dispersion include, for example: a method of irradiating modified cellulose with ultraviolet rays, a method of oxidative decomposition with hydrogen peroxide and ozone, a method of hydrolysis with an acid, and a combination of 2 or more of these. These other methods may be combined with the above-described method of performing hydrolysis in an alkaline solution.

(micronization treatment)

In the refining treatment of the modified cellulose, defibration is generally performed. The device for defibrating is not particularly limited, and examples thereof include: high-speed rotary type apparatus, colloid mill type apparatus, high-pressure type apparatus, roll mill type apparatus, ultrasonic type apparatus. In the defibration, it is preferable to apply a shearing force to the modified cellulose dispersion, and it is more preferable to apply a shearing force having a strong effect to the modified cellulose (usually, the dispersion) while applying a pressure of 50MPa or more. The application of pressure and/or shear force is preferably performed by means of a device, more preferably a wet high-or ultra-high pressure homogenizer. The pressure applied to the modified cellulose (usually, the dispersion liquid) is more preferably 100MPa or more, and still more preferably 140MPa or more. Before the defibration and dispersion treatment in the high-pressure homogenizer, the modified cellulose dispersion may be subjected to a pretreatment using a known mixing, stirring, emulsifying, and dispersing apparatus such as a high-speed shear mixer, if necessary. The number of passes in the defibrator may be 1 or 2 or more, preferably 2 or more.

The dispersion treatment of the modified cellulose or nanofibers may be performed before, after, or simultaneously with the defibration treatment. In the dispersion treatment, the modified cellulose is usually dispersed in a solvent, or the solid content concentration of a dispersion of the modified cellulose or nanofibers is adjusted by using a solvent. The solvent is not particularly limited as long as it can disperse the modified cellulose, and examples thereof include: water, an organic solvent (e.g., a hydrophilic organic solvent such as methanol), or a mixed solvent thereof. Since the cellulose material is hydrophilic, the solvent is preferably water.

The solid content concentration of the modified cellulose or nanofibers in the dispersion is usually 0.1% (v/w) or more, preferably 0.2% (v/w) or more, and more preferably 0.3% (v/w) or more. Thus, it is effective to obtain an appropriate amount of liquid with respect to the amount of the cellulose fiber material. The upper limit is usually 10% (v/w) or less, preferably 6% (v/w) or less. Whereby fluidity can be maintained.

Before the defibration treatment or the dispersion treatment, pretreatment may be performed as needed. The pretreatment can be carried out by using a mixing, stirring, emulsifying or dispersing apparatus such as a high-speed shear mixer.

(desalination treatment)

The modified cellulose nanofibers may contain more acid-type functional groups than salt-type functional groups, or may contain more salt-type functional groups than acid-type functional groups. The modified cellulose nanofibers may be subjected to desalting treatment in addition to the modification treatment and the micronization treatment, whereby the salt-type functional groups of the modified cellulose nanofibers can be converted into acid-type functional groups. In the present specification, the case where "acid type" is given to cellulose nanofibers or cellulose means that desalting has been performed, and the case where "salt type" is given means that desalting has not been performed. Examples of the desalting treatment include: acid treatment using an inorganic acid, and a method using a cation exchange resin. The desalting treatment may be performed after the modification, or before or after the micronization.

(optional treatment of others)

The modified cellulose nanofibers may be subjected to any treatment other than the above-described treatment.

For example, the modified cellulose nanofibers can be used after being rendered hydrophobic by a method using a cationic additive.

A modifier may be added to the modified cellulose nanofibers. Examples of the modifying agent include an anionic modified cellulose nanofiber modifying agent including: nitrogen-containing compounds, phosphorus-containing compounds, onium ions. When the modifier is bonded to the anionic group on the surface of the cellulose nanofiber, the properties such as polarity can be changed, and thus the affinity for a solvent and the dispersibility of the filler can be adjusted.

When an acid-type functional group is present in the anion-modified cellulose nanofibers, a basic compound such as sodium hydroxide or ammonium may be added as appropriate to form a salt form. This can suppress the deterioration of dispersibility due to the presence of the acid-type functional group.

The content of the component (2) (the amount of the solid component of the modified cellulose nanofibers) in the latex dipping solution is usually 0.01 to 20 parts by mass, preferably 0.05 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass, relative to 100 parts by mass of the component (1) (the dry rubber component).

The modified cellulose nanofibers of component (2) are usually a dispersion, but the dispersion may further contain any component. As the optional components, there may be mentioned: dispersing agent and filling material. Examples of the dispersant include: a water-soluble polymer. Examples of the water-soluble polymer include: cellulose derivatives (e.g., carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginates, Pullulan (Pullulan), starch, arrowhead flour, arrowroot flour, positive starch, phosphorylated starch, corn starch, gum arabic, gellan gum (gellan gum), polydextrose (polydextrose), pectin, chitin, water-soluble chitosan, casein, albumin, soy protein solubles, peptone (peptone), polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acid, polylactic acid, polymalic acid, polyglycerol, latex, sizing agents of rosin series, petroleum resin-based sizing agents, urea resin (urea resin), and starch gum, Melamine (melamine) resins, epoxy resins, polyamide/polyamine resins, polyethyleneimines, polyamines, vegetable gums, polyethylene oxide, hydrophilic cross-linked polymers, polyacrylates, starch polyacrylic acid copolymers, tamarind gum, guar gum (guar gum), and colloidal silica, and combinations thereof. Among them, carboxymethyl cellulose or a salt thereof is preferably used from the viewpoint of solubility. Examples of the filler include: carbon black, silica, talc, clay, calcium carbonate, fillers other than these that are commonly used in the rubber industry.

The component (2) may be 1 type of modified cellulose nanofibers, or may be a combination of 2 or more types.

< ingredient (1): rubber latex >

In the present specification, the rubber latex is a material which is a raw material of rubber and becomes rubber by crosslinking. There are a rubber component for natural rubber and a rubber component for synthetic rubber, and both can be used in the present invention, or both can be combined. In the present specification, the rubber component for rubber is sometimes referred to as a rubber polymer for convenience. The rubber components for natural rubber and synthetic rubber are sometimes referred to as "natural rubber polymer" and "synthetic rubber polymer", respectively.

Examples of the Natural Rubber (NR) polymer include: a natural rubber polymer in a narrow sense (e.g., HA latex, LA latex) without chemical modification; chemically modified natural rubber polymers such as chlorinated natural rubber polymers, chlorosulfonated natural rubber polymers, epoxidized natural rubber polymers, and the like; hydrogenated natural rubber polymers; deproteinized natural rubber polymers. Examples of the synthetic rubber polymer include: diene rubber polymers such as Butadiene Rubber (BR) polymers, styrene-butadiene copolymer rubber (SBR) polymers, Isoprene Rubber (IR) polymers, acrylonitrile-butadiene rubber (NBR) polymers, Chloroprene Rubber (CR) polymers, styrene-isoprene copolymer rubber polymers, styrene-isoprene-butadiene copolymer rubber polymers, and isoprene-butadiene copolymer rubber polymers; non-diene rubber polymers such as butyl rubber (IIR) polymers, ethylene-propylene rubber (EPM, EPDM) polymers, acrylate rubber (ACM) polymers, epichlorohydrin rubber (CO, ECO) polymers, fluoro rubber (FKM) polymers, silicone rubber (Q) polymers, urethane rubber (U) polymers, chlorosulfonated polyethylene (CSM) polymers, and the like. The rubber polymer may be used alone or in combination of two or more. Among these, diene rubber polymers containing a Natural Rubber (NR) polymer are preferable from the viewpoint of reinforcement. Examples of preferable diene rubber polymers include: natural Rubber (NR) polymers, Isoprene Rubber (IR) polymers, Butadiene Rubber (BR) polymers, styrene-butadiene copolymer rubber (SBR) polymers, butyl rubber (IIR) polymers, acrylonitrile-butadiene rubber (NBR) polymers, modified natural rubber polymers as described above.

The rubber component may be prepared as a solution dissolved in an organic solvent for mixing, in addition to a dispersion (latex) dispersed in a dispersion medium such as water. The amount of the liquid medium is preferably 10 to 5000 parts by mass with respect to 100 parts by mass of the rubber component.

The component (1) may be 1 kind of rubber latex or a combination of 2 or more kinds.

< ingredient (3): defoaming agent >

The defoaming agent contained in the dipping solution of the present invention is used for producing a rubber composition free from a pore defect or the like due to bubbles with respect to the rubber composition produced through the latex dipping step. The kind of the defoaming agent to be used is not particularly limited. Examples thereof include: polyethers, sorbitan fatty acid esters, fatty acid glycerides, polyoxyalkylene alkyl ethers, polyoxyalkylene alkyl ether derivatives, fatty acid esters of polyoxyethylene glycols, glycerin alkylene oxide adducts, mono-and diesters of polyoxyalkylene glycols with fatty acids, alkylaryl sulfonates, alkyldiphenyl ether disulfonates, dodecylbenzene sulfonates, dodecyldiphenyl ether disulfonates, calcium dodecylbenzene sulfonates, calcium dodecyldiphenyl ether disulfonates, and calcium dodecyldiphenyl ether disulfonates, with polyethers being preferred, but not limited thereto. The number of carbon atoms of the defoaming agent is not particularly limited, and a functional group may be added. In addition, the defoamer may contain mineral oil or silica, preferably at least 1 of polyether, silica and mineral oil, preferably polyether, silica and mineral oil. Examples of the mineral oil include: the paraffinic mineral oil and the naphthenic mineral oil may be natural mineral oil, or may be refined mineral oil subjected to refining treatment (for example, vacuum distillation, oil deasphalting, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, clay refining, hydrorefining, or a combination of 2 or more kinds selected from these). The mineral oil may be 1 kind or a combination of 2 or more kinds. Examples of the silica include: the fine silica (for example, aerosol silica, precipitated silica, fumed silica) may be either surface-untreated or hydrophobized silica. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

The content of the component (3) in the latex dipping solution is usually 0.05 part by mass or more, preferably 0.1 part by mass or more, relative to 100 parts by mass of the component (1) (dry rubber component). The upper limit is usually 1.0 part by mass or less, preferably 0.5 part by mass or less. Therefore, the amount is usually 0.05 to 1.0 part by mass, preferably 0.1 to 0.5 part by mass.

The component (3) may be 1 kind of defoaming agent or a combination of 2 or more kinds.

< optional Components >

The latex dipping solution of the present invention may contain any components other than the components (1) to (3) as required. Examples of the optional components include: zinc oxide, stearic acid, a blending agent for crosslinking (for example, a crosslinking agent (for example, sulfur, a sulfur halide, an organic peroxide, a quinone dioxime, an organic polyamine compound, an alkylphenol resin having a methylol group), a vulcanization accelerator (for example, N-oxydiethylene-2-benzothiazylsulfenamide, N-t-butyl-2-benzothiazylsulfenamide), a vulcanization accelerator aid, a scorch retarder), a pH adjuster, an antioxidant, a reinforcing agent (or a filler, for example, carbon black, silica, calcium carbonate, etc.), a silane coupling agent, an oil, a cured resin, a wax, an antiaging agent, a colorant, a softener/plasticizer, a curing agent (for example, a phenol resin, a high styrene resin, etc.), a foaming agent, an adhesive (for example, a macaron resin, a phenol resin, a terpene-based resin, a crosslinking agent (for example, sulfur, a quinone dioxides, an organic polyamine compound, an alkyl phenol resin having a methylol group), a curing agent, a pH adjuster, a curing agent, and a curing agent, Petroleum hydrocarbon resins, rosin derivatives, etc.), dispersants (e.g., fatty acids), adhesion promoters (e.g., organic cobalt salts), lubricants (e.g., paraffin wax, hydrocarbon resins, fatty acids, fatty acid derivatives), and blending agents other than those described above that can be used in the rubber industry. Among them, zinc oxide, sulfur, a vulcanization accelerator, a pH adjuster (e.g., potassium hydroxide), and an antioxidant are preferable. The content of the crosslinking agent is preferably 0.5 parts by mass or more, and more preferably 1.0 part by mass or more, relative to 100 parts by mass of the rubber component. The upper limit is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and further preferably 5 parts by mass or less. The content of the vulcanization accelerator is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and further preferably 0.4 part by mass or more, relative to 100 parts by mass of the rubber component. The upper limit is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and further preferably 2 parts by mass or less.

< method for producing latex dipping solution >

The method for preparing the latex dipping solution is not particularly limited, and the following examples are given.

First, components (1) and (2) were mixed to obtain a mixed solution. When mixing, the component (2) is preferably a modified cellulose nanofiber dispersion (preferably an aqueous dispersion). The mixing may be carried out while stirring as required, and a homogenizer, propeller stirrer or the like may be used. The mixing is preferably carried out at room temperature (for example, 20 to 30 ℃), and the conditions (rotation speed, time) other than temperature can be appropriately adjusted.

Subsequently, the mixture was aged to obtain an immersion liquid. The aging is usually carried out for about 1 day (for example, 20 to 30 hours). When an arbitrary component is used, the arbitrary component is added to the mixed solution before aging. In the present specification, when an optional component contains a crosslinking admixture, the dipping solution is sometimes referred to as a pre-vulcanized latex. The addition of the crosslinking admixture for precuring can be expected to provide effects such as prevention of cracking of the rubber product and improvement of gloss. The optional components (for example, the crosslinking admixture) are preferably mixed in advance before being added to the mixed solution to prepare a reagent slurry.

Then, the component (3) was added to the dipping solution (precured latex) to obtain a latex dipping solution. The method of adding the component (3) is not particularly limited, but a method of spraying the component into the immersion liquid is preferable, and it is preferable to perform blowing until bubbles in the immersion liquid are removed.

< viscosity of latex dipping solution >

The latex dip is preferably of low viscosity. For example, the B-type viscosity (25 ℃ C., 60rpm) of the latex dipping solution after 24 hours from the preparation is usually 500 mPas or less, preferably 450 mPas or less, more preferably 400 mPas or less, further preferably 350 mPas or less, and further preferably 300 mPas or less. The lower limit value is preferably 10mPa · s or more, more preferably 20mPa · s or more, and further preferably 50mPa · s or more, 70mPa · s or more, or 100mPa · s or more. For example, the latex dip may be left at 25 ℃ and the B-form viscosity may be measured at 60rpm after 24 hours.

[2. rubber composition ]

In the present invention, the rubber composition uses the latex dipping solution as a raw material. Examples of the method for producing the rubber composition include the following methods: dipping the mold in a coagulant to obtain a surface-treated mold; dipping the surface-treated mold in the latex dipping solution; and forming a film and peeling the film from the mold. Thereby, a rubber composition integrally formed of a film of rubber as a whole can be prepared. Examples are as follows.

First, a mold having a desired shape is prepared. Examples of the material of the mold include: ceramic (pottery), but not particularly limited. Then, the surface of the mold is treated with a coagulant (e.g., an aqueous calcium chloride solution) to obtain a surface-treated mold. In general, the treatment may be carried out by immersing the mold in a coagulant (usually, 5 to 60 seconds) and then drying it (for example, 80 to 150 ℃). The drying time is usually 10 to 20 seconds, but is not particularly limited. Then, the surface-treated mold is dipped in a latex dipping solution. The immersion may be carried out for 5 to 60 seconds, and is not particularly limited. After dipping, the mold was pulled up to attach the latex dipping solution to the surface of the mold, and the latex dipping solution was peeled off from the mold to form a film. The film formation is usually carried out by drying (for example, 80 to 150 ℃ C.). The drying time is usually 10 to 20 seconds, but is not particularly limited. The rubber glove can be produced by simply preparing a mold for the rubber glove as a mold of a desired shape. Examples of the integrally molded article other than the rubber glove include: medical devices (e.g., catheters), contraceptive devices.

Examples

The present invention will be described in further detail below with reference to production examples and examples, but the present invention is not limited to these examples.

< preparation of cellulose nanofiber Dispersion >

[ preparation example 1]

5g of absolute dry softwood dissolving kraft pulp (Buckeye) was added to 500ml of an aqueous solution in which 7.8mg (0.05mmol) of TEMPO (Sigma Aldrich) and 755mg (7mmol relative to 1g of absolute dry cellulose) of sodium bromide were dissolved, and stirred until the pulp was uniformly dispersed. After 11.3ml of an aqueous sodium hypochlorite solution (concentration: 2.1mol/L) was added to the reaction solution, the pH was adjusted to 10.3 with 0.5N aqueous hydrochloric acid solution, and the oxidation reaction was started. During the reaction, the pH of the reaction mixture was lowered, but 0.5N aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. After the reaction for 170 minutes, the reaction mixture was filtered through a glass filter and sufficiently washed with water to obtain oxidized cellulose.

The amount of carboxyl groups in the obtained oxidized cellulose was measured in the following manner, and the result was 1.6 mmol/g.

(method of measuring carboxyl group amount)

60ml of a 0.5 mass% slurry (aqueous dispersion) of oxidized cellulose was prepared, a 0.1M aqueous hydrochloric acid solution was added to make pH2.5, and then a 0.05N aqueous sodium hydroxide solution was added dropwise until pH 11 was reached to measure the electric conductivity, and the amount of sodium hydroxide consumed in the neutralization stage of a weak acid whose change in electric conductivity was gradual was calculated from the following formula: amount of carboxyl group [ mmol/g oxidized cellulose ] = a [ ml ] × 0.05/mass of oxidized cellulose [ g ].

A5% (w/v) aqueous dispersion of oxidized cellulose was prepared, and 1% (w/v) hydrogen peroxide was added to the aqueous dispersion (absolute dry) of oxidized cellulose, and the pH was adjusted to 12 with 1M sodium hydroxide. The aqueous dispersion was heated at 80 ℃ for 2 hours to hydrolyze the oxidized cellulose, and then filtered with a glass filter and sufficiently washed with water.

The oxidized cellulose obtained in the above-mentioned step was adjusted to 1.0% (w/v) with water, and treated 3 times with an ultrahigh-pressure homogenizer (20 ℃ C., 150MPa) to obtain a dispersion of oxidized cellulose nanofibers (TEMPO-oxidized cellulose nanofibers).

When the average fiber diameter and the average fiber length of the obtained oxidized cellulose nanofibers were measured as follows, the average fiber diameter was 5.7nm and the average fiber length was 311 nm.

(method of measuring average fiber Length)

Regarding the average fiber diameter and average fiber length of the oxidized cellulose nanofibers, an atomic force electron microscope (AFM) was used, the average fiber diameter was analyzed for 50 fibers selected at random, and the average fiber length was analyzed for 200 fibers selected at random.

[ preparation example 2]

5g of absolute dry softwood dissolving kraft pulp (Buckeye) was added to 500ml of an aqueous solution in which 7.8mg (0.05mmol) of TEMPO (Sigma Aldrich) and 755mg (7mmol) of sodium bromide were dissolved, and stirred until the pulp was uniformly dispersed. After 6.4ml of an aqueous sodium hypochlorite solution (concentration: 2.1mol/L) was added to the reaction mixture, the pH was adjusted to 10.3 with 0.5N aqueous hydrochloric acid solution, and the oxidation reaction was started. During the reaction, the pH of the reaction mixture was lowered, but 0.5N aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. After 80 minutes of the reaction, the reaction mixture was filtered through a glass filter and sufficiently washed with water to obtain oxidized cellulose.

When the carboxyl group content of the obtained oxidized cellulose was measured, it was 1.0 mmol/g.

A5% (w/v) aqueous dispersion of oxidized cellulose was prepared, and 1% (w/v) hydrogen peroxide was added to the aqueous dispersion to adjust the pH to 12 with 1M sodium hydroxide. The aqueous dispersion was heated at 80 ℃ for 2 hours to hydrolyze the oxidized cellulose, and then filtered with a glass filter and sufficiently washed with water.

The oxidized cellulose obtained in the above-mentioned step was adjusted to 1.0% (w/v) with water, and treated 3 times with an ultrahigh-pressure homogenizer (20 ℃ C., 150MPa) to obtain a dispersion of oxidized cellulose nanofibers (TEMPO-oxidized cellulose nanofibers). The obtained oxidized cellulose nanofibers had an average fiber diameter of 5.4nm and an average fiber length of 307 nm.

[ preparation example 3]

5.00g of absolutely dry bleached unbleached kraft pulp from conifers (85% whiteness) was added to 500ml of an aqueous solution in which 39mg (0.25mmol) of TEMPO (Sigma Aldrich) and 514mg (5.0mmol) of sodium bromide were dissolved and stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system to 6.0mmol/g, and the oxidation reaction was started. During the reaction, the pH in the system was lowered, but 0.5M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. After the reaction for 90 minutes, the reaction mixture was filtered through a glass filter and sufficiently washed with water to obtain an oxidized cellulose raw material.

When the carboxyl group content of the obtained oxidized cellulose was measured, it was 1.6 mmol/g.

The oxidized pulp obtained in the above-mentioned step was adjusted to 1.0% (w/v) with water, and treated 3 times with an ultrahigh-pressure homogenizer (20 ℃ C., 150MPa) to obtain a dispersion of oxidized cellulose nanofibers (TEMPO-oxidized cellulose nanofibers). The obtained oxidized cellulose nanofibers had an average fiber diameter of 2.7nm and an average fiber length of 600 nm.

< preparation of rubber composition and evaluation of physical Properties >

[ example 1]

As the cellulose nanofibers, the TEMPO-oxidized cellulose nanofibers obtained in preparation example 1 (amount of carboxyl group: 1.6mmol/g, average fiber length: 311nm) were used. A mixed solution of latex and cellulose nanofibers was obtained by mixing an aqueous dispersion of cellulose nanofibers in an amount of 2 parts by mass in terms of solids with 100 parts by mass of a dry rubber component of natural rubber latex (trade name: HA latex, manufactured by Reditex corporation, solid content concentration: 28%) and stirring the mixture for 15 minutes at 3000rpm using a high throughput homogenizer (manufactured by SMT). To the mixed solution, a chemical slurry prepared by mixing 1 part of sulfur, 1 part of zinc oxide, 0.5 part of a vulcanization accelerator (noxeler MSA-G, manufactured by daikon chemical industries), 0.5 part of an antioxidant (K-840, manufactured by kyoto grease corporation), and 0.5 part of potassium hydroxide with respect to 100 parts by mass of the dry rubber component was added, and then the mixture was stirred by a high-throughput homogenizer and aged for 1 day to obtain a precured latex. To eliminate the bubbles generated during the stirring, an antifoaming agent (Deformer 777, manufactured by SAN NOPCO) was added in a form of spray to the obtained pre-vulcanized latex in an amount of 0.1 to 0.5 wt% based on 100 mass% of the dry rubber component of the latex, and the latex was stirred at a rotation speed of 120rpm using a Three-One Motor, and then, the absence of bubbles was visually confirmed to obtain a latex dipping solution. Next, the ceramic plate was immersed in a 30% calcium chloride aqueous solution for 10 seconds, and then dried at 120 ℃ for 15 minutes to obtain a ceramic plate having a surface treated with a coagulant. The ceramic plate thus obtained was immersed in the latex dipping solution for 10 seconds, then pulled up from the dipping solution, and dried at 120 ℃ for 30 minutes to form a film. The film-formed sample was peeled off from the ceramic plate to obtain a rubber composition.

< measurement of viscosity >

The B-type viscosity (mPas) of the prevulcanized latex was measured. The viscosity of the precured latex after 24 hours from the preparation was measured at 25 ℃ using a viscometer of type B (DV-I Prime, manufactured by BROOKFIELD) using a spindle S63 at 60 rpm. The results are shown in Table 1.

< evaluation of physical Properties >

The obtained rubber composition was punched out into a dumbbell shape, and a dumbbell-shaped test piece No. 3 described in JIS K6251 "tensile test method for vulcanized rubber" was prepared. Then, using these test pieces, tensile stress M100 (MPa) at 100% elongation, tensile stress M300 (MPa) at 300% elongation, breaking strength (MPa), and elongation (%) at break were measured according to the method described in JIS K6251. The results are shown in Table 2.

[ example 2]

The procedure of example 1 was repeated, except that the TEMPO-oxidized cellulose nanofibers obtained in preparation example 1 were changed to the TEMPO-oxidized cellulose nanofibers of preparation example 2 (amount of carboxyl groups: 1.0mmol/g, average fiber length: 307 nm).

Comparative example 1

The procedure of example 1 was repeated, except that the TEMPO-oxidized cellulose nanofibers obtained in preparation example 1 were not used.

Comparative example 2

The procedure of example 1 was repeated, except that the TEMPO-oxidized cellulose nanofibers obtained in preparation example 1 were changed to the TEMPO-oxidized cellulose nanofibers of preparation example 3 (amount of carboxyl groups: 1.6mmol/g, average fiber length: 600 nm).

[ Table 1]

[ Table 2]

< results >

From the results of table 1, it can be seen that: the latex impregnants of the systems using the short-fiber cellulose nanofibers described in examples 1 and 2 had lower viscosities than the systems using the ordinary cellulose nanofibers described in comparative example 2. From the results of table 2, it can be seen that: the rubber compositions using the short-fiber cellulose nanofibers described in example 1 or example 2 exhibited high values of breaking strength and breaking elongation as compared to the rubber compositions using only the NR latex described in comparative example 1. The rubber composition using the ordinary cellulose nanofibers described in comparative example 2 was too viscous to form a film of the rubber composition.