JPS6143607A - Alkali-soluble copolymer latex - Google Patents

Abstract

PURPOSE:The titled latex, obtained by incorporating specific components such as an ethylenically unsaturated monocarboxylic acid vinyl acetate, etc. in a specific proportion, having a specific HLB value, and capable of imparting improved fluidity and water retentivity to aqueous liquid compositions for coating paper. CONSTITUTION:An alkali-soluble copolymer latex obtained by emulsion polymerizing 30-50wt% ethylenically unsaturated monocarboxylic acid, preferably methacrylic acid, with 30-65wt% alkyl acrylate having 1-8C alkyl group, e.g. methyl acrylate, and 5-20wt% vinyl acetate, preferably in the presence of sodium persulfate, etc. as a polymerization initiator at 3.0-5.0pH, and having 12.4-17.9HLB. EFFECT:Also with effect as a binder.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an aqueous liquid composition for paper coating with excellent fluidity and excellent water retention effect, and has an effect as a binder. The present invention relates to an alkali-soluble copolymer latex.

[Conventional technology]

Aqueous dispersions have been studied for paper coating liquids such as gravure printing inks in order to avoid flammable and toxic organic solvents. It consists of additives such as a binder and a water retention agent. Conventionally, as a binder, a synthetic rubber aqueous dispersion centered on a styrene-butadiene polymer Latinx and a water-soluble natural polymer substance such as casein or starch have been used in combination. Also, kaolinite clay, calcium carbonate, heavy calcium carbonate, etc. are used as pigments. Furthermore, carboxymethyl cellulose, methyl cellulose, sodium alginate, and the like are conventionally known as water retention agents.

From the viewpoint of energy saving, which has become particularly important since the oil crisis, it is required to increase the concentration of the coating liquid composition. This is because the greatest energy consumption during coating is due to dehydration, ie, drying, after coating. Furthermore, in order to improve productivity in coating (speed up coating), it is required that the liquid composition has good fluidity, that is, the viscosity is not too high. Particularly at high concentrations, fluidity inevitably decreases, so good fluidity becomes even more important. On the other hand, from the viewpoint of the quality of the coated product, the water retention property of the liquid composition is important. This is because if a coating liquid with insufficient water retention is applied, quality problems such as streaks may occur due to concentration changes due to rapid penetration of water in the coating liquid into the base paper. Also, good water retention is important for speeding up coating while maintaining the quality of the coated product. However, improvement in fluidity and improvement in water retention are often contradictory requirements, as described below, and this can be said to be a difficult problem.

From the viewpoint of these required properties, water-soluble natural polymer substances such as casein and starch, which also have the effect of binding agents themselves, make the composition highly viscous and have problems in terms of fluidity. . However, it also has the advantage of providing high water retention.

In order to improve fluidity, attempts have been made to use synthetic polymers instead of water-soluble natural polymers, and carboxymethylcellulose, methylcellulose, sodium alginate, etc., as mentioned above, have been used as water retention agents. In all cases, the viscosity of the coating liquid increases under low and high shear rates, and this tendency is especially noticeable with high concentration coating liquids.
There is a drawback that handling of the coating liquid and good coating are difficult. From the perspective of pigments, heavy calcium carbonate has been proposed to improve fluidity, but it is inferior to kaolinite clay in terms of water retention.

[Problem that the invention seeks to solve]

As mentioned above, the fluidity and water retention properties of paper coating liquid compositions, which are important in terms of energy saving and productivity improvement, are mutually contradictory properties. It is understood that it is extremely difficult to improve.

An object of the present invention is to provide a copolymer latex that simultaneously imparts excellent fluidity and excellent water retention to a paper coating liquid composition and has an effect as a binder.

The present inventors conducted extensive research to simultaneously improve water retention and fluidity of a paper coating liquid composition. As a result, the composition of the alkali-soluble copolymer latex and the HL B (hydrophile 1yophile) of the latex were determined.
It has been found that by defining the balance), the technical problem of simultaneously improving fluidity and water retention, which has been considered difficult, can be solved at once. Furthermore, it was surprisingly discovered that when the HLB of the alkali-soluble copolymer latex is defined, it exhibits the effect as a binder in addition to the effect as a water retention agent, leading to the completion of the present invention. Ta.

[Means and effects for solving the problems] The present invention has a monoethylenically unsaturated carboxylic acid of 30 to 30% as a monomer composition.
An alkali-soluble copolymer latex consisting of 50% by weight, 30% to 65% by weight of an acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms, and 5% to 20% by weight of vinyl acetate, and the HLB of the latex is 12. .4-17
．． The present invention relates to an alkali-soluble copolymer latex characterized by having No. 9.

The present invention will be explained in detail below.

Examples of the monoethylenically unsaturated carboxylic acid used in the present invention include methacrylic acid, acrylic acid, crotonic acid, halfester of dicarboxylic acid, and the like, with methacrylic acid and/or acrylic acid being particularly preferred.

If monoethylenically unsaturated carboxylic acid is used in an amount exceeding 50% by weight, a large amount of residue will be generated during emulsion polymerization and a stable latex cannot be obtained, and if it is used in an amount less than 30% by weight, it will not be sufficient for paper coating liquid compositions. Does not provide water retention properties.

Examples of the acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms include methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, etc., and the HLB of the alkali-soluble copolymer latex is , 12.4 to 17.9.

The reason why the HLB of the alkali-soluble copolymer latex is a problem even though it is not used alone is that it is closely related to the effects when used in combination with other synthetic latexes. . When the HLB of the alkali-soluble copolymer latex is less than 12.4, sufficient water retention is not imparted to the coating liquid composition. Furthermore, if the HLB of the alkaline earth metal polymer latex exceeds 17.9, the adhesive strength will decrease and the effect as a binder will be lost.

The term "adhesive strength" used in the present invention refers to the surface strength (pinking resistance) of coated paper. In addition, the proportion of acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms is as follows:
The HLB of the alkali-soluble copolymer latex is 12.
It is determined to fall within the range of 4 to 17.9, and is necessarily determined from the amounts of monoethylenically unsaturated carboxylic acid and vinyl acetate used.

If vinyl acetate is used in an amount exceeding 20% by weight, a large amount of residue will be generated during emulsion polymerization, making it impossible to obtain a stable latex, and if it is used in an amount less than 5% by weight, it will not provide sufficient water retention to the coating composition. do not.

To adjust the molecular weight of the alkali-soluble copolymer latex, commonly used chain transfer agents such as t-dodecyl mercaptan, carbon tetrachloride, bromoform, and thioglycolic acid can be used. By adjusting the molecular weight of the alkali-soluble copolymer latex, the fluidity of the paper coating composition can be freely adjusted, and the paper coating liquid composition has fluidity suitable for each coating machine. I can give things.

Next, a method for producing an alkali-soluble copolymer latex will be described. The latex can be obtained by polymerizing the above-mentioned monomer components using a known emulsion polymerization technique. That is, the polymerization initiator includes ordinary persulfates, peroxides, azo compounds,
A redox catalyst or the like is used in an amount of 0.01 to about 5% by weight based on the monomer. In particular, water-soluble persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate are preferred, and are used alone or in a redox system.

As the emulsifier used, ordinary anionic emulsifiers and/or nonionic emulsifiers (for example, sodium n-dodecylbenzenesulfonate, nonylphenyl ethers of polyethylene glycol, etc.) are used in an amount of 0.1 to about 5% of the monomer weight.
It is used in a range of % by weight.

Emulsion polymerization can be carried out, for example, by adding the monomer mixture continuously or intermittently, or by charging the monomer mixture all at once.

The alkali-soluble copolymer latex thus obtained has a solid content of 10 to 32% by weight, preferably 25 to 30M.
% to the paper coating liquid composition.

The "alkali-soluble copolymer latex" referred to in the present invention refers to the latex having a concentration of 3% by weight, to which a 3% by weight aqueous sodium hydroxide solution is added dropwise, and the pH of the mixture is 6.
The viscosity at 5 or more is 10 centipoise (cps) or more, and the light transmittance of the mixture at 470 nm is 4
It means 0% or more.

That is, the alkali-soluble copolymer latex in the present invention is preferably one that is insoluble in an acidic aqueous medium with a pH of less than 6.5, and is preferably solubilized at a pH of 6.5 or higher.

In order to obtain the alkali-soluble copolymer latex, p
Low pH below H6.5, preferably between pH 3.0 and 5.0
It is necessary to carry out emulsion polymerization in the area.

Regarding HLB, it is necessary to use as raw material a monomer mixture precalculated to fall within the scope of the present invention.

Furthermore, when used as a water retention agent, it is necessary to adjust the pH to 6.5 or higher. In the pn range (pH less than 6.5) where the alkali-soluble copolymer latex is insoluble, the paper coating liquid composition does not have a sufficient water retention effect. In order to use it as a paper coating liquid composition, it is necessary to adjust the pH of the paper coating liquid composition to 6.5 or more, preferably pHB, 5 to 13.0 with an alkaline substance. Examples of alkaline substances include sodium hydroxide, potassium hydroxide, and ammonia.

When the alkali-soluble copolymer latex of the present invention is used to prepare a paper coating liquid composition, the pigment, the binder, and the alkali-soluble copolymer latex are added in this order, and after thorough stirring, an alkaline substance is added. It is preferable to adjust the pH to 01. If the alkali-soluble copolymer latex is adjusted to pH 6.5 or higher in advance, the viscosity increases significantly and handling becomes difficult, which is not preferable. When the alkali-soluble copolymer latex is actually added to create a paper coating liquid composition, the pll is less than 6.5, preferably 3.0.
~5.0, with a viscosity of 500 cps or less, preferably 1
00 cps or less is easier to handle.

Next, an example will be described in which the alkali-soluble copolymer latex of the present invention is actually used as a water retention agent (and binder).

Binders for paper coating liquid compositions include commonly used synthetic rubber latexes such as styrene-butadiene copolymer latexes, acrylic latexes, styrene-acrylic latexes, and vinyl acetate latexes. etc. can be used arbitrarily.

Furthermore, the p of the synthetic latex used as a binder
By adjusting H to less than 6.5, preferably 6.0 or less, the alkali-soluble copolymer latex of the present invention can be mixed in advance into the synthetic latex in any proportion.

If the pH of the synthetic latex is 6.5 or more, the viscosity of the mixture increases when the alkali-soluble copolymer latex is mixed, making it difficult to handle. That is, when the alkali-soluble copolymer latex of the present invention is mixed with a synthetic latex used as a binder, it is preferable to mix in a pH range where the alkali-soluble copolymer latex is insoluble. Then, in the step of creating a paper coating liquid composition, pHt
It is preferable to perform verse 11.

By pre-mixing the alkali-soluble copolymer latex of the present invention with the binder described above, it is also possible to dramatically shorten the process for preparing a paper coating liquid composition.

The alkali-soluble copolymer latex of the present invention is used as a water retention agent (
If necessary, water-soluble natural polymeric substances such as casein and starch may be added as a binder to the paper coating liquid composition used as a binder prior to use. Naturally, it is also possible to use it in combination with a fl agent such as sodium alginate. Furthermore, various auxiliary agents such as a dispersant, an antifoaming agent, a lubricant, and a dye can be appropriately blended.

〔Effect of the invention〕

According to the present invention, from the formulation of the conventional paper coating liquid composition,
An alkali that gives the paper coating liquid composition enough water retention to omit part or all of the water-soluble natural polymer substance with good water retention, and at the same time gives excellent fluidity, and also has the effect of acting as a binder. A soluble copolymer latex can be provided.

〔Example〕

Next, examples will be shown. The following percentages and parts are by weight unless otherwise specified.

In addition, the measurement method of each physical property in an Example is as follows.

Calculation of HLB: Using the calculation formula (6) described on page 705 of Chemical Handbook Basic Edition (revised 2nd edition, Chemical Society of Japan, page 1) and the data in Table 6゜66, calculate the monomer of the alkali-soluble copolymer latex. Calculated from the composition.

Judgment of viscosity of alkali-soluble copolymer latex: 20L
Measured at 25°C by type viscometer (60 rpm+ No., 2 spindles).

Transmittance: Measured at a wavelength of 470 n+++ using a photoelectric spectrometer (manufactured by Te Rika Kenkyusho Co., Ltd., 10DEL 6B).

Coating liquid viscosity: Measured at 25°C with a BL type viscosity needle (60 rpm No., 4 spindles).

Water retention test: Use a particle size gauge (manufactured by Yoshimitsu Kagaku Co., Ltd.).

Apply the coating liquid to the particle size gauge and immediately cover the coating base paper on top. Measure the time it takes for the coating solution to dry to a depth of 70 microns on the gauge. The longer the time, the better the water retention.

Surface strength of coated paper: Mei Seisakushosha! Using an IRI printing tester, perform overprinting several times with ink of tack 10, and visually judge the picking state of the printed surface.

Example 1 (Polymerization Example) Polymerization of alkali-soluble copolymer latex (al) In a pressure-resistant polymerization vessel equipped with a dropping device and a stirrer, 190 parts of water, 2.0 parts of sodium dodecylbenzenesulfonate, and 0.02 parts of sodium ethylenediaminetetraacetate were added. 85℃
heated to. After replacing the inside of the container with nitrogen, add 1 vinyl acetate.
A monomer mixture consisting of 0 parts, 35 parts of methacrylic acid, 55 parts of ethyl acrylate, and 0.1 part of t-dodecylmercaptan, 35 parts of water, 0.8 parts of sodium dodecylbenzenesulfonate, and 0.2 parts of sodium hydroxide. , and an aqueous solution consisting of 0.8 parts of sodium persulfate were added dropwise at the same time, and the addition was completed in 3 hours while maintaining the temperature at 85° C., and the polymerization was continued for an additional 1 hour. In this way, the polymerization rate was 98.6%.
, pF14.4, solids content 30.1%, viscosity 6.5 cp
An alkali-soluble copolymer latex (a) of s was obtained.

Next, the alkali-soluble copolymer latex (al) was diluted with water to 3%, a 3% aqueous sodium hydroxide solution was added dropwise, and the viscosity and transmittance at p[I6.5 were measured. It was confirmed that it was a soluble copolymer latex.The results are shown in Table 1.

Examples 2 to 5 (Polymerization Examples) Polymerization of alkali-soluble copolymer latex) to (e) Example 1 except that the monomer mixture shown in Table 1 was polymerized.
Alkali-soluble copolymer latexes) to (e) were obtained by the same polymerization method as in Example 1, and confirmed to be alkali-soluble copolymer latexes in the same manner as in Example 1. The results are shown in Table 1.

Example 6 (Usage Example) Carboxy-modified styrene-butadiene copolymer latex (L-1956 manufactured by Asahi Kasei Corporation, latex containing 50% by weight of butadiene as a monomer) was used as a binder, and the alkali-soluble copolymer of the present invention was used as a water retention agent. Polymer latex (
A composition having the following formulation was prepared using a), and then the pH of this was adjusted to 9.5 with an aqueous sodium hydroxide solution to obtain a coating liquid.

^) Clay (FIT” manufactured by HMC)
85 Calcium carbonate 15
(Super 1700 manufactured by Kyuubi Calcium Co., Ltd.) Dispersant (Aron T-40 manufactured by Toagosei Co., Ltd.) 0.3L-195
610 The viscosity and water retention of this coating liquid composition were measured, and then it was coated on commercially available high-quality paper, and the surface strength was measured. The results are shown in Table 2.

Examples 7 to 10 (Usage Examples) Paper coating liquid compositions shown in Table 2 were prepared, viscosity and water retention were measured, and then coated on commercially available high-quality paper to measure surface strength. . The results are shown in Table 2.

Examples 11 to 13 (Usage Examples) Paper coating liquid compositions shown in Table 3 were prepared, and the viscosity and water retention were measured to see the relationship with the solid content of the paper coating liquid composition. The results are shown in Table 3.

Comparative Examples 1 to 6 (Examples of use) (Examples with caution) When the monomer composition of the alkali-soluble copolymer latex and the part B are out of the range of the present invention, Example 1 was carried out with the monomer composition shown in Table 4. Polymerization was carried out in the same manner. The result (f)
Stable latex was obtained for (g) and (1), but a large amount of residue was generated for (g) and (hl), making them unusable.
When the transmittance of f) and (1) was measured, it was confirmed that they were not alkali-soluble copolymer latexes as referred to in the present invention. The results are shown in Table 4.

Coating liquids for (f) and (1) were prepared using the same formulations as in Examples, and the viscosity and water retention were measured. The results are shown in Table 5.

Comparative Examples 7 to 9 (Usage Examples) Paper coating liquid compositions shown in Table 6 were used to examine the effects of commonly used water retention agents on the solid content and water retention properties of coating liquid compositions. was prepared and its viscosity and water retention were measured. The results are shown in Table 6.

(Leaving space below) Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Procedural amendment (voluntary) November 5, 1985 1988 Patent glI No. 164891 2, Title of invention Alkali-soluble copolymer latex 3 , Relationship with the case of the person making the amendment Patent applicant: 1-2-6-4 Dojimahama, Kita-ku, Osaka-shi, Osaka Prefecture; Agent address: 3-7 Yotsuya, Shinjuku-ku, Tokyo; Katsushin Building 5
B6. Number of inventions increased by amendment None 7. Description subject to amendment 1. Name of invention Alkali-soluble copolymer latex 2. Scope of claims (1) Monomer composition: 30-50% by weight of blood, 30-65% by weight of acrylic acid alkyl ester having an alkyl group having 1-8 carbon atoms
, an alkali-soluble copolymer latex consisting of 5 to 20% by weight of vinyl acetate, and the HLB of the latex is 1.
An alkali-soluble copolymer latex having a molecular weight of 2.4 to 17.9.

3. Detailed description of the invention [Industrial application field] The present invention provides an aqueous liquid composition for paper coating with excellent fluidity and excellent water retention effect, and has an effect as a binder. The present invention relates to an alkali-soluble copolymer latex.

[Prior Art] Aqueous dispersions have been studied for paper coating liquids such as gravure printing inks in order to avoid flammable and toxic organic solvents. consists of additives such as dyes and pigments, binders, and water retention agents. Conventionally, as a binder, a synthetic rubber aqueous dispersion centered on a styrene-butadiene copolymer latex and a water-soluble natural polymer substance such as casein or starch have been used in combination.

Also, kaolinite clay, calcium carbonate, etc. are used as pigments. Furthermore, carboxymethyl cellulose, methyl cellulose, sodium alginate, and the like are conventionally known as water retention agents.

From the viewpoint of energy conservation, which has become particularly important since the oil crisis, higher concentration of liquid compositions is required. This is because the greatest energy consumption during coating is due to dehydration, ie, drying, after coating. Also, improve productivity in coating (coating speed amplifier)
For this purpose, it is required that the liquid composition has good fluidity, that is, the viscosity does not have a direct flow f. Particularly at high concentrations, fluidity inevitably decreases, so good fluidity becomes even more important. Also, the water retention property of the liquid composition is important.

This is because if a coating liquid with insufficient water retention is applied, problems with operation and quality such as streaks may occur due to concentration changes due to rapid penetration of water in the coating liquid into the base paper. In addition, good water retention is very important for maintaining the quality of the coated product and speeding up the coating process. However, improvement in fluidity and improvement in water retention are often contradictory requirements, as described below, and this can be said to be a difficult problem.

Water-retaining agents such as water-soluble natural polymer binders, carboxymethylcellulose, methylcellulose, and sodium alginate are
Although it has the advantage of imparting high water retention to liquid compositions, it has problems in terms of fluidity of liquid compositions. In other words, the viscosity of the coating liquid increases under low and high shear rates, and this tendency becomes particularly noticeable with high-concentration coating liquids, making handling of the coating liquid and good coating difficult. doing.

Also, from the perspective of pigments, heavy calcium carbonate has been proposed to improve fluidity, but it is inferior to kaolinite clay in terms of water retention.

[Problem that the invention seeks to solve]

As mentioned above, the fluidity and water retention properties of paper coating liquid compositions, which are important in terms of energy saving and productivity improvement, are mutually contradictory properties. It is understood that it is extremely difficult to improve.

An object of the present invention is to provide a copolymer latex that simultaneously imparts excellent fluidity and excellent water retention to a paper coating liquid composition and has an effect as a binder.

The present inventors conducted extensive research to simultaneously improve water retention and fluidity of a paper coating liquid composition. As a result, the composition of the alkali-soluble copolymer latex and the HL B (hydrophile 1yophile) of the latex were determined.
It was discovered that by defining the balance), the technical problem of simultaneously improving fluidity and water retention, which had been considered difficult, could be solved at once. Furthermore, it was surprisingly discovered that when the HLB of the alkali-soluble copolymer latex is defined, it exhibits the effect as a binder in addition to the effect as a water retention agent, leading to the completion of the present invention. Ta.

[Means and effects for solving the problems] The present invention provides an ethylenically unsaturated monocarboxylic acid of 30 to
An alkali-soluble copolymer latex consisting of 50% by weight, 30 to 65% by weight of acrylic acid furkyl ester having an alkyl group having 1 to 8 carbon atoms, and 5 to 20% by weight of vinyl acetate, and the HLB of the latex is 12. .4-17
．． The present invention relates to an alkali-soluble copolymer latex characterized by having No. 9.

The present invention will be explained in detail below.

Examples of the ethylenically unsaturated monocarboxylic acid used in the present invention include methacrylic acid, acrylic acid, crotonic acid, halfester of dicarboxylic acid, and the like, with methacrylic acid and/or acrylic acid being particularly preferred.

If the amount of ethylenically unsaturated monocarboxylic acid exceeds 50% by weight, a large amount of residue will be produced during emulsion polymerization, making it impossible to obtain a stable latex; if it is used in an amount less than 30% by weight,
Does not impart sufficient water retention to the paper coating liquid composition.

Examples of the acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms include methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, etc., and the HLB of the alkali-soluble copolymer latex is , 12.4 to 17.9.

The reason why the HLB of the alkali-soluble copolymer latex is a problem even though it is not used alone is that it is closely related to the effects when used in combination with other synthetic latexes. . When the HLB of the alkali-soluble copolymer latex is less than 12.4, sufficient water retention is not imparted to the coating liquid composition. Furthermore, if the HLB of the alkali-soluble copolymer latex exceeds 17.9, the adhesive strength will decrease and the effect as a binder will be lost.

The term "adhesive force" used in the present invention refers to the surface strength (pinking resistance) of coated paper. In addition, the proportion of acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms is as follows:
The HLB of the alkali-soluble copolymer latex is 12.
It is determined to fall within the range of 4 to 17.9, and is necessarily determined from the amounts of ethylenically unsaturated monocarboxylic acid and vinyl acetate used.

If vinyl acetate is used in an amount exceeding 20% by weight, a large amount of residue will be produced during emulsion polymerization, making it impossible to obtain a stable latex. Furthermore, if it is used in an amount less than 5% by weight, sufficient water retention will not be imparted to the coating composition.

To adjust the molecular weight of the alkali-soluble copolymer latex, commonly used chain transfer agents such as L-dodecyl mercaptan, carbon tetrachloride, bromoform, and thioglycolic acid can be used. By adjusting the molecular weight of the alkali-soluble copolymer latex, the fluidity of the paper coating composition can be freely adjusted, and the paper coating liquid composition has fluidity suitable for each coating machine. I can give things.

Next, a method for producing an alkali-soluble copolymer latex will be described. The latex can be obtained by polymerizing the above-mentioned monomer components using a known emulsion polymerization technique. That is, the polymerization initiator includes ordinary persulfates, peroxides, azo compounds,
A redox catalyst or the like is used in an amount of 0.01 to about 5% by weight based on the monomer. In particular, water-soluble persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate are preferred, and are used alone or in a redox system.

As the emulsifier used, ordinary anionic emulsifiers and/or nonionic emulsifiers (for example, sodium n-dodecylbenzenesulfonate, nonylphenyl ethers of polyethylene glycol, etc.) are used in an amount of 0.1 to about 5% of the monomer weight.
It is used in a range of % by weight.

Emulsion polymerization can be carried out, for example, by adding the R-mer mixture continuously or intermittently, or by charging the monomer mixture all at once.

The alkali-soluble copolymer latex thus obtained is provided to a paper coating liquid composition with a solid content of 10 to 32% by weight, preferably 25 to 30% by weight.

In the present invention, the "alkali-soluble copolymer latex" refers to a latex with a concentration of 3% by weight, in which a 3% by weight aqueous sodium hydroxide solution is added dropwise, and the pH of the mixture is 7.
The viscosity at 5 or more is lθ centivoise (cps) or more, and the light transmittance at 470 nm of the mixture is 4
It means 0% or more.

That is, the alkali-soluble copolymer latex in the present invention is preferably insoluble in an aqueous medium with a pH of less than 7.5, and preferably solubilized with a pH of 7.5 or higher.

In order to obtain the alkali-soluble copolymer latex, p
Low pi of H less than 7.5, preferably pH 3.0 to 5.0
It is necessary to carry out emulsion polymerization in the area.

Regarding HLB, it is necessary to use as raw material a monomer mixture precalculated to fall within the scope of the present invention.

Furthermore, when used as a water retention agent, it is necessary to adjust the pH to 7.5 or higher. In a pH range in which the alkali-soluble copolymer latex does not dissolve (pH less than 7.5), a sufficient water retention effect is not imparted to the paper coating liquid composition. That is, in order to use the alkali-soluble copolymer latex as a water retention agent (and binder), the pH of the paper coating liquid composition should be 7.5 or higher, preferably 8.5 to 13.0. It is necessary to adjust with an alkaline substance. Examples of alkaline substances include sodium hydroxide, potassium hydroxide, and ammonia.

When the alkali-soluble copolymer latex of the present invention is used to prepare a paper coating liquid composition, the pigment, the binder, and the alkali-soluble copolymer latex are added in this order, and after thorough stirring, an alkaline substance is added. A method of adjusting pHg is preferred. The alkali-soluble copolymer latex is
When i is 7.5 or more, the viscosity increases significantly and handling becomes difficult, which is not preferable. When the alkali-soluble copolymer latex is actually added to prepare a paper coating liquid composition, the pH is less than 7.5, preferably 3.0 to 3.0.
5.5 and the viscosity is below 500 cps, preferably 10
It is easier to handle if it is 0 cps or less.

Next, an example will be described in which the alkali-soluble copolymer latex of the present invention is actually used as a water retention agent (and binder).

Binders for paper coating liquid compositions include synthetic rubber latexes such as styrene-butadiene copolymer latex, acrylics, styrene-acrylics, and ethylene-
Any binder commonly used as a binder, such as vinyl acetate, vinyl acetate-acrylic, or vinyl acetate, can be used.

Furthermore, the p of the synthetic latex used as a binder
By adjusting H to less than 7.5, preferably 6.0 or less, the alkali-soluble copolymer latex of the present invention can be mixed in advance into the synthetic latex in any proportion.

If the pH of the synthetic latex is 7.5 or higher, the viscosity of the mixture increases when the alkali-soluble copolymer latex is mixed, making handling difficult. That is, when the alkali-soluble copolymer latex of the present invention is mixed with a synthetic latex used as a binder, it is preferable to mix in a pH range where the alkali-soluble copolymer latex is insoluble. In the stage of preparing the paper coating liquid composition, it is preferable to adjust the pH using the method for preparing the paper coating liquid composition described above.

By pre-mixing the alkali-soluble copolymer latex of the present invention with the binder described above, it is also possible to dramatically shorten the process for preparing a paper coating liquid composition.

The alkali-soluble copolymer latex of the present invention is used as a water retention agent (
If necessary, water-soluble natural polymeric substances such as casein and starch may be added as a binder to the paper coating liquid composition used as a binder prior to use. Naturally, it is also possible to use it in combination with a water retention agent such as sodium alginate. Furthermore, various auxiliary agents such as a dispersant, an antifoaming agent, a lubricant, and a dye can be appropriately blended.

〔Effect of the invention〕

According to the present invention, from the formulation of the conventional paper coating liquid composition,
An alkali that gives the paper coating liquid composition enough water retention to omit part or all of the water-soluble natural polymer substance with good water retention, and at the same time gives excellent fluidity, and also has the effect of acting as a binder. A soluble copolymer latex can be provided.

(Example) Next, an example will be shown.The following percentages and parts are by weight unless otherwise specified.

In addition, the measurement method of each physical property in an Example is as follows.

Calculation of HLB: Using the calculation formula (6) described on page 705 of the Basics of the Chemical Handbook (revised 2nd edition, published by the Chemical Society of Japan) and the data in Table 6゜66, calculate the monomer of the alkali-soluble copolymer latex. Calculated from the composition.

Determined biviscosity of alkali-soluble copolymer latex: BL
Measured by type viscometer (60 rpm NO, 2 spindles) at 25°C.

Transmittance: Measured at a wavelength of 470 nm using a photoelectric spectrometer (Model 6B, manufactured by Te Rika Kenkyusho Co., Ltd.).

Coating liquid viscosity Measured at 25°C with a BL type viscosity needle (60 rpm, 4 spindles).

Water retention test using two particle size gauges (manufactured by Yoshimitsu Kagaku Co., Ltd.).

Apply the coating liquid to the particle size gauge and immediately cover the coating base paper on top. Measure the time it takes for the coating solution to dry to a depth of 70 microns on the gauge. The longer the time, the better the water retention.

Surface strength of coated paper: Using an iRI printing tester manufactured by Mei Seisakusho Co., Ltd., overprinting is performed several times with ink from tank 10, and the picking state of the printed surface is judged with the naked eye.

Example 1 (Polymerization Example) Polymerization of alkali-soluble copolymer latex (a) In a pressure-resistant polymerization vessel equipped with a dropping device and a stirrer, 190 parts of water, 2.0 parts of sodium dodecylbenzenesulfonate, and 0° of sodium ethylenediaminetetraacetate were added. Prepare 02 parts, 85℃
heated to. After replacing the inside of the container with nitrogen, add 1 vinyl acetate.
A monomer mixture consisting of 0 parts, 35 parts of methacrylic acid, 55 parts of ethyl acrylate, and 0.1 part of t-dodecylmercaptan, 35 parts of water, 0.8 parts of sodium dodecylbenzenesulfonate, and 0.2 parts of sodium hydroxide. , sodium persulfate 0. The dropwise addition was completed in 3 hours while maintaining the temperature at 85°C, and the polymerization was continued for an additional hour. In this way, the polymerization rate was 98.6%.
, pH 4.4, solids content 30.1%, viscosity 6.5 cps
An alkali-soluble copolymer latex (al) was obtained. Next, the alkali-soluble copolymer latex (a) was diluted with water for 30 minutes.
%, dropwise add 3% aqueous sodium hydroxide solution,
The viscosity and transmittance at pH 6.5 were measured, and it was confirmed that the latex was an alkali-soluble copolymer latex as referred to in the present invention. The results are shown in Table 1.

Examples 2 to 5 (Polymerization Examples) Polymerization of alkali-soluble copolymer latex (bl to (e)) Alkali-soluble copolymer latex (bl to (e)) was prepared by the same polymerization method as in Example 1 except that the monomer mixture shown in Table 1 was polymerized. (in copolymer latex) to (e) were obtained, and in the same manner as in Example 1,
It was confirmed that it was an alkali-soluble copolymer latex. The results are shown in Table 1.

Example 6 (Usage example) Carboxy-modified styrene-butadiene copolymer latex (L-1956 manufactured by Asahi Kasei Kogyo Co., Ltd., latex containing 50% by weight of butadiene as an IT product) as a binder, and the alkali-soluble copolymer of the present invention as a water retention agent. Combined latex (
β) was used to prepare a composition having the following formulation, and then mixed with an aqueous sodium hydroxide solution to a pl+ of 9.5 to obtain a coating solution.

^ ) Clay (EMC HT) 8
5 Calcium carbonate 15 (Super 1700 manufactured by Maruo Calcium Co., Ltd.) Dispersant (Aron T-40 manufactured by Toagosei Co., Ltd.) 0.3L-19561
0 The viscosity and water retention of this coating liquid composition were measured, and then it was coated on commercially available high-quality paper, and the surface strength was measured. The results are shown in Table 2.

Examples 7 to 10 (Usage Examples) Paper coating liquid compositions shown in Table 2 were prepared, viscosity and water retention were measured, and then coated on commercially available high-quality paper to measure surface strength. . The results are shown in Table 2.

Examples 11 to 13 (Usage Examples) Paper coating liquid compositions shown in Table 3 were prepared, and their viscosity and water retention were measured to see the relationship with the solid content of the paper coating liquid composition. The results are shown in Table 3.

Comparative Examples 1 to 6 (Polymerization Examples) (Usage Examples) When the monomer composition and IILII of the alkali-soluble copolymer latex are out of the range of the present invention Example 1 with the monomer composition shown in Table 4
Polymerization was carried out in the same manner. Results (f) and (1)
Stable latex was obtained in (g) and (hl), but a large amount of residue was generated in (f) and (hl), making it unusable.
When the transmittance of 1) was measured, it was confirmed that it was not an alkali-soluble copolymer latex as defined in the present invention. The results are shown in Table 4.

Coating liquids for (f) and (1) were prepared using the same formulations as in Examples, and the viscosity and water retention were measured. The results are shown in Table 5.

Comparative Examples 7 to 9 (Usage Examples) Paper coating liquid compositions shown in Table 6 were used to examine the effects of commonly used water retention agents on the solid content and water retention properties of coating liquid compositions. was prepared and its viscosity and water retention were measured. The results are shown in Table 6.

Table 1 Table 2 Table 3 Table 4

Claims (1)

[Claims] (1) Monomer composition: 30 to 50% by weight of monoethylenically unsaturated carboxylic acid, 30 to 65% by weight of acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms,
An alkali-soluble copolymer latex consisting of 5 to 20% by weight of vinyl acetate, and the HLB of the latex is 12.
．． An alkali-soluble copolymer latex having a molecular weight of 4 to 17.9.