JP2011195974A - Composition for coating paper, and coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition of excellent viscosity stability and fluidity for coating paper, and coated paper of a high strength exhibited in a printing process and of high white paper gloss.SOLUTION: The composition for coating paper comprising calcium carbonate in an amount of more than 40 wt.% in 100 wt.% of the total pigments, is characterized by comprising a copolymer latex insensitive to an alkali prepared by the emulsion polymerization of an aliphatic conjugated diene monomer in an amount of 20 to 70 wt.%, a vinyl cyanide monomer in an amount of 1 to 50 wt.%, an ethylenically unsaturated carboxylic acid monomer in an amount of 0.1 to 20 wt.%, and another monomer copolymerizable with the monomers, in an amount of 0 to 78.9 wt.% (the total of the monomers being 100 wt.%), with its pH being 9.6 or higher.

Description

  The present invention relates to a paper coating composition and coated paper. Specifically, it is a paper coating composition excellent in fluidity, water retention and viscosity stability, and the coated paper obtained by coating the paper coating composition has a dry pick strength and white paper gloss. The present invention relates to an excellent paper coating composition and its coated paper.

In recent years, coated paper has been used in a large number of printed materials because of its high printing effect. Even in periodicals such as quarterly and monthly papers, the use of coated paper on all pages has increased considerably. In particular, most direct mails and product catalogs in the mail order business use coated paper for all pages.
In general, a paper coating composition is a water dispersion composed of a pigment dispersion in which a white pigment such as clay or calcium carbonate is dispersed in water, a binder for adhering and fixing the pigments to each other and a base paper, and other additives. It is a paint. As the binder, a synthetic emulsion binder represented by styrene-butadiene copolymer latex and a natural binder represented by starch and casein are used. Among them, styrene-butadiene copolymer latex has a large degree of freedom in quality design, and is widely used as the most suitable binder for paper coating compositions today, and the performance of styrene-butadiene copolymer latex. However, it is known that it affects the performance of the composition for paper coating, the operability at the time of preparing the coated paper, or the quality of the final coated paper product, such as the surface strength and printing gloss.

On the other hand, in recent years, as the cost rationalization has been promoted more and more, the blending ratio from expensive kaolin as a pigment to inexpensive calcium carbonate tends to increase, and there is a need for a paper coating composition suitable for such a formulation. It has been. There are many cases where measures to reduce the glossiness of white paper due to the increase in the proportion of calcium carbonate in the paper coating composition are made by reducing the particle size of the calcium carbonate pigment. The effect of latex on coated paper, such as covering by improvement, is becoming increasingly important.
Moreover, when the calcium carbonate blending ratio in the paper coating composition is increased, the stability of the composition is impaired and aggregates are generated, and there is a concern about operational stains due to poor water retention of the composition. Therefore, improvement in the mechanical stability of the composition, improvement in the redispersibility of the composition that can be easily washed away even if dirt is attached, improvement in water retention of the composition, etc. are important in coating operability. It has become a challenge.

In order to solve the above-mentioned problems, for example, Japanese Patent Application Laid-Open No. 58-13798 (Patent Document 1) discloses a composition for paper / paperboard coating, 10-70% by weight of precipitated calcium carbonate in all pigments, The product of the Hercules viscosity and the composition concentration in the composition containing a sensitive copolymer latex and adjusted to pH 8-13 is in a specific range, improving printability, white paper gloss, coatability, etc. There is a technical disclosure.
JP-A-2009-68129 (Patent Document 2) uses a copolymer latex in which the composition and particle diameter are defined in a paper coating composition containing 90% by weight or more of calcium carbonate. In spite of the high calcium carbonate formulation, there is a technical disclosure that the water retention is excellent and the gloss of white paper is improved.
Furthermore, in Japanese Patent Application Laid-Open No. 2009-68130 (Patent Document 3), in a composition for paper coating containing 90% by weight or more of calcium carbonate, by using a copolymer latex that defines a surface acid density, There is a technical disclosure that a coated paper having excellent printability including dry pick strength can be obtained.
However, these various improved technologies have not yet reached a level that sufficiently satisfies the performance required for a paper coating composition in which the blending ratio of calcium carbonate is increased. It was sought after.

JP 58-13798 A

JP 2009-68129 A

JP 2009-68130 A

  The present invention is a paper coating composition excellent in fluidity, water retention, and viscosity stability, and the dry pick strength, blank gloss of coated paper obtained by coating the paper coating composition An object of the present invention is to provide a paper coating composition and a coated paper which are excellent in the above.

  That is, the present invention relates to a paper coating composition containing calcium carbonate in an amount of more than 40% by weight in 100% by weight of the total pigment, comprising 20 to 70% by weight of an aliphatic conjugated diene monomer and a vinyl cyanide monomer. 1 to 50% by weight of monomer, 0.1 to 20% by weight of ethylenically unsaturated carboxylic acid monomer, and 0 to 78.9% by weight of other monomers copolymerizable therewith (100% in total of monomers) %)) And a non-alkali-sensitive copolymer latex obtained by emulsion polymerization, and the composition has a pH of 9.6 or more. It is.

  According to the present invention, a paper coating composition having excellent fluidity, water retention, and viscosity stability is obtained. By applying the paper coating composition to paper, dry pick strength and white paper gloss can be obtained. It provides excellent coated paper.

The copolymer latex used in the paper coating composition of the present invention is a non-alkali sensitive copolymer latex. Non-alkali-sensitive copolymer latex is a copolymer latex that is not sensitive to changes in viscosity when the pH is in the alkaline region, and has a remarkable viscosity in the alkaline region that is generally used as a sole binder. This means that it is not an alkali-sensitive copolymer latex that shows an increase. This non-alkali-sensitive copolymer latex emulsifies aliphatic conjugated diene monomers, vinyl cyanide monomers, ethylenically unsaturated carboxylic acid monomers and other monomers copolymerizable therewith. Obtained by polymerization.
Aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted Examples thereof include linear conjugated pentadienes, substituted and side chain conjugated hexadienes and the like, and these can be used alone or in combination. In particular, the use of 1,3-butadiene is preferred.

  Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and the like, and one or more of these can be used. In particular, the use of acrylonitrile or methacrylonitrile is preferred.

  Examples of the ethylenically unsaturated carboxylic acid monomer include monobasic acids or dibasic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Or 2 or more types can be used.

  Examples of other monomers copolymerizable with the above aliphatic conjugated diene monomers, vinyl cyanide monomers and ethylenically unsaturated carboxylic acid monomers include alkenyl aromatic monomers and unsaturated carboxylic acids. Examples thereof include alkyl ester monomers, unsaturated monomers containing a hydroxyalkyl group, and unsaturated carboxylic acid amide monomers.

  Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyltoluene and divinylbenzene, and these can be used alone or in combination. In particular, use of styrene is preferable.

  Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, Examples thereof include monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate, and the like can be used alone or in combination. In particular, the use of methyl methacrylate is preferred.

  Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl. Methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, and the like. Or 2 or more types can be used. In particular, the use of β-hydroxyethyl acrylate is preferred.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide, and the like, and one or more of these may be used. it can. Particularly preferred is the use of acrylamide or methacrylamide.

  Further, in addition to the above monomers, any of the monomers used in ordinary emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride can be used.

  The monomer composition is 20 to 70% by weight of aliphatic conjugated diene monomer, 1 to 50% by weight of vinyl cyanide monomer, and 0.1 to 20% by weight of ethylenically unsaturated carboxylic acid monomer. And it is necessary to be in the range of 0 to 78.9% by weight of other monomers copolymerizable with these (total monomer of 100% by weight).

  If the aliphatic conjugated diene monomer is less than 20% by weight, the strength at the time of printing of the coated paper is inferior, and if it exceeds 70% by weight, the stickiness (adhesiveness) of the latex film is inferior. Adverse effects such as coating operability, especially easy adhesion to backing rolls. Preferably it is 30 to 60% by weight.

  If the vinyl cyanide monomer is less than 1% by weight, the dry pick strength and ink setting properties of the coated paper are particularly poor, and if it exceeds 50% by weight, the wet pick strength of the coated paper is particularly strong. And the glossiness of the white paper decreases. Preferably, it is 10 to 45% by weight.

  If the ethylenically unsaturated carboxylic acid monomer is less than 0.1% by weight, the mechanical stability of the copolymer latex itself and the paper coating composition is inferior. The gloss is lowered and the viscosity of the latex itself is too high, and the handling property is deteriorated, for example, the transportability of the latex by the liquid feeding pump is inferior. Preferably, it is 1 to 15% by weight.

  When the copolymerizable monomer exceeds 78.9% by weight, the dry pick strength of the coated paper is lowered. Preferably it is 10 to 60% by weight.

The copolymer latex used in the paper coating composition of the present invention has at least three polymerization steps consisting of different monomer compositions within the above-mentioned range. Further preferred. Specifically, the monomer composition is 1.5 to 24% by weight of aliphatic conjugated diene monomer, 5.1 to 25% by weight of vinyl cyanide monomer, and ethylenically unsaturated carboxylic acid monomer. A total of 13 to 34% by weight of monomers composed of 4.1 to 20% by weight of monomer and 0 to 23.3% by weight of other monomers copolymerizable therewith, 10 to 60% by weight of aliphatic conjugated diene monomer, 5 to 30% by weight of vinyl cyanide monomer, 0 to 13% by weight of ethylenically unsaturated carboxylic acid monomer and other monomers copolymerizable therewith A total of 66 to 87% by weight of monomers composed of 0 to 72% by weight of monomer is polymerized. Use of such a copolymer latex by multistage polymerization is preferable because the balance between the dry pick strength of the coated paper and the gloss of the white paper is further improved.
In addition, 60% by weight or more of the total amount of the ethylenically unsaturated carboxylic acid monomer is added in the first stage polymerization process, and it is not added in the final stage. It is preferable because of its tendency to be good.

  If the first-stage aliphatic conjugated diene monomer is less than 1.5% by weight, the dry pick strength of the coated paper is unfavorable, and if it exceeds 24% by weight, the wet pick strength of the coated paper is inferior.

  When the first stage vinyl cyanide monomer is less than 5.1% by weight, the fluidity of the paper coating composition, the dry pick strength of the coated paper, and the ink setting property tend to be inferior, and 25% by weight. Exceeding this is not preferable because wet adhesion such as wet pick strength required during printing tends to be inferior.

  If the first stage ethylenically unsaturated carboxylic acid monomer is less than 4.1% by weight, the redispersibility of the paper coating composition, the dry pick strength of the coated paper, and the ink setting properties tend to be inferior. If it exceeds 20% by weight, the glossiness of the white paper of the coated paper is lowered and the viscosity of the latex itself becomes too high, and the transportability of the latex by the liquid feed pump is inferior.

  If the amount of the other copolymerizable monomer in the first stage exceeds 23.3% by weight, the dry pick strength of the coated paper tends to decrease, such being undesirable.

  When the total amount of monomers at the first stage is less than 13% by weight, the viscosity stability and fluidity of the paper coating composition are poor, and when it exceeds 34% by weight, the strength at the time of printing of the coated paper is lowered.

  If the aliphatic conjugated diene monomer in the second and subsequent stages is less than 10% by weight, the dry pick strength of the coated paper is too high. If it exceeds 60% by weight, the fluidity of the paper coating composition is poor, and the coated paper is poor. The wet pick strength tends to be inferior.

  If the amount of vinyl cyanide monomer in the second and subsequent stages is less than 5% by weight, the strength during printing of the coated paper tends to decrease, and if it exceeds 30% by weight, the strength during printing of the coated paper and the gloss of white paper Is not preferable because of a tendency to decrease.

  If the ethylenically unsaturated carboxylic acid monomer in the second and subsequent stages exceeds 13% by weight, the viscosity of the latex itself becomes too high, and the transportability of the latex by the liquid feed pump is inferior, and the handleability deteriorates. .

  If the second and subsequent copolymerizable monomers exceed 72% by weight, the dry pick strength tends to decrease, such being undesirable.

  A known emulsifier (surfactant) can be used for the polymerization of the copolymer latex used in the paper coating composition of the present invention. For example, sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, formalin condensates of naphthalene sulfonic acid, nonionic surface activity Nonionic surfactants such as anionic surfactants such as sulfuric acid ester salts, polyethylene glycol alkyl ester type, alkylphenyl ether type, alkyl ether type, etc., and one or more of these should be used Can do.

  In the polymerization of the copolymer latex, a known chain transfer agent (molecular weight adjusting agent) can be used without limitation. For example, xanthogen compounds such as alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, dimethylxanthogen disulfide, diisopropylxanthogen disulfide, etc. Thiuram compounds such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetramethyl thiuram monosulfide, phenol compounds such as 2,6-di-t-butyl-4-methylphenol, styrenated phenol, and allyl compounds such as allyl alcohol , Halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide, α-benzyloxystyrene, α-benzyloxyacrylonitrile And vinyl ethers such as ril, α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, terpinolene, α-methylstyrene dimer, etc. One or more of these can be used. More preferred are alkyl mercaptans such as t-dodecyl mercaptan and α-methylstyrene dimer. Although there is no restriction | limiting about the usage-amount of the said chain transfer agent, For example, 0.05-10 weight part is used with respect to 100 weight part of monomers, More preferably, 0.1-5 weight part is used.

  For polymerization of the copolymer latex, known polymerization initiators include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate, cumene hydroperoxide, benzoyl peroxide, t- Oil-soluble polymerization initiators such as butyl hydroperoxide, acetyl peroxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide can be appropriately used. In particular, it is preferable to use potassium persulfate, sodium persulfate, cumene hydroperoxide, or t-butyl hydroperoxide. The amount of the polymerization initiator is not particularly limited, but is appropriately adjusted in consideration of a combination of the monomer composition, the pH of the polymerization reaction system, and other additives.

  Specific examples of the reducing agent preferably used in the polymerization of the copolymer latex include sulfite, bisulfite, pyrosulfite, nitrite, nithionate, thiosulfate, formaldehyde sulfonate, and benzaldehyde sulfone. Acid salts, carboxylic acids such as L-ascorbic acid, erythorbic acid, tartaric acid and citric acid and salts thereof, and reducing sugars such as dextrose and saccharose, and amines such as dimethylaniline and triethanolamine . In particular, L-ascorbic acid and erythorbic acid are preferable.

  For polymerization of the copolymer latex, saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, cycloheptane, pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, 1-methylcyclohexene, etc. Hydrocarbon compounds such as unsaturated hydrocarbons, aromatic hydrocarbons such as benzene, toluene and xylene can be used. In particular, cyclohexene and toluene, which have a moderately low boiling point and can be easily recovered and reused by steam distillation after the completion of polymerization, are suitable from the viewpoint of environmental problems, although they are different from the object of the present invention.

  For copolymerization of the copolymer latex used in the paper coating composition of the present invention, known additives such as oxygen scavengers, chelating agents, and dispersing agents may be used as necessary. Neither the type nor the amount used is particularly limited, and an appropriate amount can be used as appropriate. Furthermore, known additives such as antifoaming agents, anti-aging agents, antiseptics, antibacterial agents, flame retardants, and UV absorbers may be used. I can do it. The copolymer latex can be appropriately blended with other latexes depending on the purpose of use.

  In the production of the copolymer latex, the method for adding the monomer and other components is not particularly limited, and any of batch addition method, divided addition method, continuous addition method, and power feed method may be adopted. Can do. In the present invention, any one-stage polymerization, two-stage polymerization or multi-stage polymerization, seed polymerization, etc. can be employed, but two-stage or more multi-stage polymerization is preferred.

  The particle diameter of the copolymer latex used in the paper coating composition of the present invention is not particularly limited, but is preferably 50 to 150 nm. If the number average particle diameter is less than 50 nm, the glossiness of white paper is inferior, and if it exceeds 150 nm, the strength of the coated paper during printing is not easily exhibited. Preferably it is 70-130 nm.

  The gel content of the copolymer latex used in the paper coating composition of the present invention is not limited, but the gel content is preferably 50 to 100% by weight. If the gel content is less than 50% by weight, the dry pick strength of the coated paper tends to decrease. Particularly preferred is 70 to 99% by weight.

The paper coating composition of the present invention contains calcium carbonate in an amount of more than 40% by weight in 100% by weight of the total pigment, but other pigments include, for example, kaolin clay, talc, barium sulfate, oxidation Inorganic pigments such as titanium, aluminum hydroxide, zinc oxide, and satin white, or organic pigments such as polystyrene latex can be used alone or in combination.
When the content of calcium carbonate is 40% by weight or less, the viscosity stability, fluidity, and dry pick strength of the coated paper are lowered.
The content of the copolymer latex in the paper coating composition is preferably 1 to 30 parts by weight (solid content) with respect to 100 parts by weight (solid content) of the pigment. More preferably, it is 1-20 weight part (solid content). When the content of the copolymer latex is 1 part by weight or less, the pigment cannot be sufficiently adhered, which is not preferable.

  If necessary, modified starches such as starch, oxidized starch and esterified starch, natural binders such as soybean protein and casein, or water-soluble synthetic binders such as polyvinyl alcohol and carboxymethyl cellulose may be used. Furthermore, synthetic latex such as polyvinyl acetate latex and acrylic latex may be used in combination with the copolymer latex used in the present invention.

  In preparing the paper coating composition of the present invention, further auxiliary agents such as dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.), antifoaming agents (polyglycol, fatty acid ester) , Phosphate esters, silicone oils, etc.), leveling agents (funnel oil, dicyandiamide, urea, etc.), preservatives, mold release agents (calcium stearate, paraffin emulsion, etc.), fluorescent dyes, color water retention agents (sodium alginate, etc.) May be added as necessary.

The pH of the paper coating composition of the present invention needs to be adjusted to 9.6 or higher. When the pH is less than 9.6, the dry pick strength and white paper gloss effect of the coated paper are small. Preferably it is pH 9.8-13, More preferably, it is 9.9-12.
The alkaline aqueous solution for adjusting the pH is not particularly limited, and examples thereof include an aqueous solution of sodium hydroxide, potassium hydroxide, and ammonia.

  Further, any known technique such as an air knife coater, blade coater, roll coater or bar coater may be used as a method for applying the paper coating composition to the coated paper. Also, after coating, the surface is dried and finished by calendaring or the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded. In the examples, parts and percentages indicating percentages are based on weight unless otherwise specified. In addition, various physical properties in the examples were evaluated by the following methods.

A latex film is prepared in an atmosphere at a measurement temperature of 40 ° C. and a humidity of 85% for the gel content of the copolymer latex . Thereafter, about 1 g of the latex film is weighed to obtain Xg. This is put into 400 ml of toluene and swelled and dissolved for 48 hours. Thereafter, this is filtered through a weighed 300 mesh wire net, and then toluene is evaporated to dryness. The mesh weight is subtracted from the weight after drying, and the weight after drying of the sample is weighed to obtain Yg.
Gel content (%) = Y / X * 100

Evaluation of Viscosity Stability of Paper Coating Composition The viscosity immediately after preparation of the paper coating composition obtained above and the viscosity after 1 day at room temperature were measured and evaluated as follows.
R = | viscosity immediately after preparation-viscosity after 1 day at room temperature | / viscosity immediately after preparation ◎: 0 ≦ R ≦ 2: very good temporal stability ○: 2 ≦ R ≦ 4: good temporal stability Δ: 4 <R ≦ 8: Stability over time is poor ×: 8 <R: Stability over time is very poor

Evaluation of fluidity of the composition for paper coating A double-cylinder Hercules high shear viscometer (manufactured by Kumagai Riki Kogyo Co., Ltd.) was used. Using the inner cylinder Bob F, the apparent viscosity (mPa · s) of each paper coating composition at 6000 rpm giving a high shear rate was measured. The lower the value, the lower the apparent viscosity and the better the fluidity. In the measured values of the apparent viscosity of the paper coating compositions of the examples and comparative examples in each experiment, the lowest one is considered as good fluidity ◎, the highest one as poor fluidity as x, as follows: Evaluation was made in 4 stages. However, the width of one rank, such as ◎ and ○, was at least 2 mPa · s.
(Excellent) ◎>○>△> × (poor)

Evaluation of dry pick strength of coated paper Judges the degree of picking when the coated paper sample in each experiment is simultaneously printed with an RI printer, and relatively compares from grade 5 (excellent) to grade 1 (inferior) Visual evaluation was made.

Synthesis of copolymer latex (A, I) In a polymerization pressure-resistant polymerization reactor, 150 parts of polymerization water and 1 part of potassium persulfate were charged and stirred sufficiently, and then the monomers shown in Tables 1 and 2 were used. And other compounds were added and the temperature was raised to 70 ° C. to initiate the polymerization, and the polymerization was terminated when the final polymerization conversion rate exceeded 97%.
Next, the copolymer latex obtained was adjusted to pH 7 using sodium hydroxide and potassium hydroxide, and unreacted monomers and other low-boiling compounds were removed by steam distillation to obtain a copolymer latex. A and I were obtained.

Synthesis of copolymer latex (B, C, J, K) In a polymerization reactor made of pressure resistant, 150 parts of polymerization water and 1 part of potassium persulfate were charged and stirred sufficiently. The monomers and other compounds shown in the above were added and the temperature was raised to 70 ° C. to initiate the polymerization. For the second stage polymerization, the second stage polymerization was performed when the first stage polymerization conversion exceeded 50%. The respective monomers and other compounds of the eye were added for polymerization, and the polymerization was terminated when the final polymerization conversion rate exceeded 95%.
Next, the copolymer latex obtained was adjusted to pH 7 using sodium hydroxide and potassium hydroxide, and unreacted monomers and other low-boiling compounds were removed by steam distillation to obtain a copolymer latex. B, C, J and K were obtained.

Synthesis of copolymer latex (D to H, L to R) In a polymerization reactor made of pressure resistant, 150 parts of polymerization water and 1 part of potassium persulfate were charged and stirred sufficiently. Each monomer and other compounds shown were added and the temperature was raised to 70 ° C. to initiate polymerization. For the second stage polymerization, when the first stage polymerization conversion rate exceeds 50%, the second stage monomers and other compounds are added and polymerized. When the polymerization conversion up to the stage exceeded 80%, the monomers and other compounds of the third stage were added and polymerized, and when the final polymerization conversion exceeded 95%, the polymerization was terminated.
Next, the copolymer latex obtained was adjusted to pH 7 using sodium hydroxide and potassium hydroxide, and unreacted monomers and other low-boiling compounds were removed by steam distillation to obtain a copolymer latex. DH and LR were obtained.

Preparation and evaluation of composition for paper coating
Experiment 1
According to the formulation shown in Table 4, compositions A to 1-4 were prepared using A as the copolymer latex. Sodium hydroxide was used to adjust the pH. Table 5 shows the physical properties of the resulting paper coating composition.
Experiment 2
In the compounding prescription 1 of Table 4, copolymer latex used B, adjusted pH with sodium hydroxide, and created the paper coating compositions 5-12. The physical properties of the obtained paper coating composition are shown in Table 6.
Experiment 3
In the compounding prescription 2 of Table 3, copolymer latex A-R was used, it adjusted so that pH might be set to 10-10.5 with sodium hydroxide, and the composition 13-30 for paper coating was created. The physical properties of the obtained paper coating composition are shown in Tables 7 and 8.

Preparation and Evaluation of Coated Paper Wire to the coated base paper (basis weight 55 g / m2) so that the coating amount per side of the above paper coating compositions 1 to 30 is 12 ± 0.5 g / m2. After coating using a bar and drying, calendering was performed under conditions of a linear pressure of 60 kg / cm and a temperature of 50 ° C. to obtain coated paper. The obtained coated paper was subjected to each test and evaluated, and the results are shown in Tables 5-8.

  As shown in Tables 5 to 8, the paper coating compositions according to the present invention are all excellent in viscosity stability and fluidity, and the resulting coated paper has good dry pick strength and white paper gloss.

  As described above, the paper coating composition of the present invention is excellent in fluidity, water retention, and viscosity stability, and can provide a coated paper excellent in dry pick strength and white paper gloss. is there.

Claims (4)

  A paper coating composition containing calcium carbonate in an amount of more than 40% by weight in 100% by weight of the total pigment, the aliphatic conjugated diene monomer being 20 to 70% by weight, the vinyl cyanide monomer being 1 to 50% by weight, 0.1 to 20% by weight of ethylenically unsaturated carboxylic acid monomer and 0 to 78.9% by weight of other monomers copolymerizable therewith (100% by weight in total) A paper coating composition comprising a non-alkali-sensitive copolymer latex obtained by polymerization and having a pH of 9.6 or higher.   The copolymer latex has at least three stages of polymerization steps having different monomer compositions, and the first stage is 1.5 to 24% by weight of aliphatic conjugated diene monomer, and vinyl cyanide monomer 5 0.1 to 25% by weight, 4.1 to 20% by weight of an ethylenically unsaturated carboxylic acid monomer, and 0 to 23.3% by weight of other monomers copolymerizable with these monomers in total 13 to 13% 34 wt% is polymerized, and after the second stage, the aliphatic conjugated diene monomer is 10 to 60 wt%, the vinyl cyanide monomer is 5 to 30 wt%, and the ethylenically unsaturated carboxylic acid monomer is 0 to 13 2. The paper coating composition according to claim 1, wherein a total of 66 to 87% by weight of a monomer consisting of 0% to 72% by weight and other monomers copolymerizable with these is polymerized. .   The co-polymer according to claim 1 or 2, wherein 60% by weight or more of the total amount of the ethylenically unsaturated carboxylic acid monomer is added in the first stage polymerization step and not added in the last stage polymerization step. Polymer latex.   Coated paper obtained by coating the paper coating composition according to any one of claims 1 to 3.