JPH11209436A - Preparation of seed latex and copolymer latex and paper coating composition containing copolymer latex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a copolymer latex from which a paper coating composition excellent in flowability under high shear can be prepared by emulsion polymerizing an aliphatic conjugated diene monomer, an aromatic vinyl monomer, an ethylenically unsaturated carboxylic acid monomer and a monomer copolymerizable with these having a specific composition. SOLUTION: 4-20 wt.% of an ethylenically unsaturated carboxylic acid monomer, 10-96 wt.% of an aromatic vinyl monomer and 0-86 wt.% of another monomer copolymerizable with these are emulsion polymerized to obtain a seed latex having a number average particle diameter of 20-60 nm, a surface acid density of the carboxylic acid of 1.15×10<-21> -3.5×10<-20> meq/nm<2> and a pH of 5 or higher. It is also preferable to emulsion polymerize 10-80 wt.% of an aliphatic conjugated diene monomer, 10-90 wt.% of an aromatic vinyl monomer, 0.5-10 wt.% of an ethylenically unsaturated carboxylic acid monomer and 0-79.5 wt.% of another monomer copolymerizable with these in the presence of this seed latex.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seed latex, a process for producing a copolymer latex obtained by seed emulsion polymerization using the seed latex, and a coating composition for paper containing the copolymer latex. Things.

[0002]

2. Description of the Related Art It is well known that a so-called butadiene-based copolymer latex containing butadiene as a main component is widely used as a binder in the field of paper processing or carpet backsizing. I'm going. In recent years, in the paper processing field, speeding up of paper coating and printing has been promoted from the viewpoint of labor saving and rationalization, and paper coating compositions that can withstand high-speed coating, can withstand high-speed printing There is a demand for coated paper of excellent quality. That is, as a performance at the time of coating, the paper coating composition is required to have good mechanical stability and excellent fluidity under high shear. Water resistance and the like are required.

[0003] One of the causes of impairing the mechanical stability of a paper coating composition is fine coagulated products generated during the production of a copolymer latex. If the proportion of the fine solidified matter is large, streaks and roll stains occur during coating, and in coated paper, the adhesive strength is reduced. In addition, fine coagulated products generated in the polymerization system easily adhere to the inner wall of the reactor, hindering control of the polymerization temperature, and lowering productivity.

In general, a method of increasing the amount of an emulsifier at the time of polymerization or after polymerization is used to suppress the generation of fine coagulated products during the production of a copolymer latex, but the copolymer latex tends to foam. This often causes operational problems or lowers the water resistance of the coated paper, and has not been sufficiently solved. In addition, there is a method of removing the fine coagulated product by filtering the copolymer latex after the production, but this is not preferable in terms of productivity and operation.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, in the production of copolymer latex, the use of seed latex having good dispersion stability has led to a problem. Has greatly improved the polymerization stability of the seed polymerization method. Further, the inventors have found that a coating composition for paper containing such a copolymer latex has excellent fluidity under high shear, and reached the present invention.

That is, the present invention relates to a method for preparing 4 to 20% by weight of an ethylenically unsaturated carboxylic acid monomer, 10 to 96% by weight of an aromatic vinyl monomer and 0 to 10% of another monomer copolymerizable therewith. The number average particle diameter obtained by emulsion polymerization of a monomer consisting of 86% by weight is 20 to 60 nm, and the surface acid density of the carboxylic acid defined by Formula 1 is 1.15 × 1
A seed latex having a range of 0 ^{-21 to} 3.5 × 10 ^-20 (meq / nm ² ) and a pH of 5 or more. Further, in the presence of the seed latex, 10 to 80% by weight of an aliphatic conjugated diene monomer, 10 to 90% by weight of an aromatic vinyl monomer, and 0.5 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer. A method for producing a copolymer latex, which comprises emulsion-polymerizing a monomer consisting of 0 to 79.5% by weight and another monomer copolymerizable therewith, and containing the copolymer latex. To provide a paper coating composition.

(Equation 2)

Hereinafter, the present invention will be described in detail. First, the seed latex will be described. As the ethylenically unsaturated carboxylic acid monomer used for the polymerization of the seed latex in the present invention, mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid can be used. Can be mentioned. In particular, it is preferable to use acrylic acid.

The ethylenically unsaturated carboxylic acid monomer has the effect of improving the dispersion stability of the obtained latex. The surface acid density of the carboxylic acid given by Equation 1 is 1.
When it is smaller than 15 × 10 ⁻²¹ (meq / nm ² ), the amount of the ethylenically unsaturated carboxylic acid monomer is too small, so that the dispersion stability decreases and the storage stability of the seed latex decreases. On the other hand, when the surface acid density of the carboxylic acid exceeds 3.5 × 10 ⁻²⁰ (meq / nm ² ),
Although the amount of the ethylenically unsaturated carboxylic acid monomer is large and the dispersion stability of the seed latex is improved, the polymerization stability in the seed polymerization in the next step is inferior, and is not suitable for use as a seed latex. Therefore, in the present invention, it is important to keep the surface acid density of the carboxylic acid within an appropriate range.

Here, the particle surface acid amount and the particle surface area shown in Equation 1 are defined as follows. The particle surface acid content is defined as the amount of carboxyl groups from an electric conductivity curve obtained when an excessive amount of 0.1N hydrochloric acid is added to a 1% by weight aqueous solution of seed latex and back titrated with a 0.1N aqueous sodium hydroxide solution. (Meq / g). Also,
The particle surface area is the total surface area (nm ² ) based on the number-based particle size distribution of the seed latex obtained by the dynamic light scattering method.
It is a value obtained by (total volume (nm ³ ) × density (g / nm ³ )). Here, density = 1 g / cm ³ = 10 ⁻¹² g
/ Nm ³ .

The surface acid density of the carboxylic acid of the seed latex is preferably 3 × 10 ^-21 to 8 × 10 ^-21 meq / nm ² . This surface acid density is 3 × 10 ^-21 me
If it is less than q / nm ² or more than 8 × 10 ⁻²¹ meq / nm ² , the tendency to increase the amount of fine coagulates when producing the copolymer latex in the next step is seen.

The amount of the ethylenically unsaturated carboxylic acid monomer used is 4 to 20% by weight, preferably 4 to 20% by weight based on the total 100% by weight of the monomers used for the polymerization of the seed latex.
It is in the range of 12% by weight. When the amount of the ethylenically unsaturated carboxylic acid monomer used is less than 4% by weight, the storage stability of the seed latex is reduced. Coagulated material is easily generated.

Next, in the present invention, examples of the aromatic vinyl monomer used for the polymerization of the seed latex include styrene, α-methylstyrene, methyl α-methylstyrene, vinyltoluene and divinylbenzene. One or more kinds can be used. Styrene is particularly preferred, and the amount used is 10 to 96% of the total 100% by weight of the monomers used for the polymerization of the seed latex.
% By weight. At this time, when the amount of the aromatic vinyl monomer used is less than 10% by weight, the polymerization stability during the production of the seed latex decreases, and when it exceeds 96% by weight, the storage stability of the seed latex decreases. descend.

Other monomers copolymerizable with the above-mentioned ethylenically unsaturated carboxylic acid monomer and aromatic vinyl monomer include unsaturated carboxylic acid alkyl ester monomers and hydroxyalkyl groups. Examples include an unsaturated monomer, a vinyl cyanide monomer, and an unsaturated carboxylic acid amide monomer. In the present invention, the amount of the other copolymerizable monomer used is adjusted to 100% by weight in combination with the amounts of the ethylenically unsaturated carboxylic acid monomer and the aromatic vinyl monomer. I can decide.

The seed latex of the present invention has a number average particle size of 20 to 60 nm. When the particle diameter is less than 20 nm, the storage stability of the seed latex decreases. On the other hand,
If the number average particle size exceeds 60 nm, during the production of the copolymer latex in the next step, aggregation of particles is likely to occur,
This leads to a decrease in polymerization stability.

In the present invention, in the emulsion polymerization for obtaining the seed latex, a sulfate of a higher alcohol, an alkyl benzene sulfonate, an alkyl phenyl ether sulfonate, an aliphatic sulfonate, a nonionic interface are used as emulsifiers. One or two or more anionic surfactants such as a sulfuric acid ester salt of a surfactant or nonionic surfactants such as an alkyl ester type, an alkyl phenyl ether type and an alkyl ether type of polyethylene glycol can be used. Particularly, dodecylbenzenesulfonate is preferred. Such a surfactant is used to obtain monodisperse particles having a number average particle diameter of 20 to 60 nm.
In order to suppress the generation of fine coagulates during the polymerization of the seed latex, it is preferable to use 5 to 30 parts by weight based on the total 100 parts by weight of the monomers used for the polymerization of the seed latex.

As the initiator, a water-soluble initiator such as potassium persulfate, ammonium persulfate and sodium persulfate, or a redox initiator or an oil-soluble initiator such as benzoyl peroxide can be used. Such a polymerization initiator is preferably used in the range of 0.1 to 10 parts by weight based on 100 parts by weight of the total of monomers used for the polymerization of the seed latex.

In the emulsion polymerization of the present invention, one or more chain transfer agents represented by mercaptans can be used. The use amount of these chain transfer agents is not particularly limited and can be appropriately adjusted depending on the purpose, but it is 0.05 to 1 with respect to 100 parts by weight of the monomer mixture.
Preferably, it is used in the range of 0 parts by weight.

In the polymerization of the seed latex of the present invention, the polymerization temperature is not particularly limited, but in order to obtain a suitable seed latex for producing a copolymer latex, the polymerization is carried out at a temperature in the range of 60 to 90 ° C. Is preferred. The above-mentioned monomers and polymerization aids may be added to the reaction vessel by any of batch, divided and continuous methods.

The seed latex thus obtained needs to be adjusted to pH 5 or more by alkali after the polymerization is completed, and is preferably adjusted to pH 5 to 12. This has the effect of increasing the storage stability and dispersion stability of the carboxy-modified seed latex and increasing the polymerization stability in the next step. When the pH is lower than 5, the storage stability is poor, and the seed latex aggregates during storage, making it impossible to use it in the next step. On the other hand, if the pH is higher than 12, the amount of fine coagulated product in the next step tends to increase, which is not preferable.

Next, a copolymer latex using the obtained seed latex will be described. The second invention of the present invention relates to a method for producing an aromatic conjugated monomer comprising 10 to 80% by weight of an aliphatic conjugated diene monomer,
Emulsion polymerization of a monomer comprising 0 to 90% by weight, 0.5 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer and 0 to 79.5% by weight of another monomer copolymerizable therewith. This is a method for producing a copolymer latex. The use of the seed latex in an amount of 0.1 to 10% by weight (in terms of solid content) with respect to 100% by weight of the monomer used in the production of the copolymer latex can result in polymerization stability during the production of the copolymer latex. Is significantly improved, and further, a copolymer latex which is excellent in fluidity under high shear when a coating material is formed is preferred.

Examples of the aliphatic conjugated diene monomer for obtaining the copolymer latex include 1,3-butadiene, 2-methyl-1,3-butadiene and 2,3-dimethyl-1,3.
-Butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like, and one or more kinds can be used. In particular, 1,3-butadiene is preferred. At this time, the amount of the aliphatic conjugated diene monomer used was 10% by weight.
When the amount is less, the dry pick strength of the coated paper using the paper coating composition containing the obtained copolymer latex is low, and when the amount used exceeds 80% by weight, the obtained copolymer latex is used. The wet topical strength of the coated paper using the paper coating composition containing the compound becomes poor.

The aromatic vinyl monomers include styrene, α-methylstyrene, methyl α-methylstyrene,
Vinyl toluene and divinyl benzene, and the like,
One or more kinds can be used. Particularly, styrene is preferred. At this time, if the amount of the aromatic vinyl monomer used is less than 10% by weight, the adhesive strength and water resistance of the coated paper using the obtained paper coating composition containing the copolymer latex are low. If it exceeds 90% by weight, the adhesive strength and water resistance of the coated paper using the obtained paper coating composition containing the copolymer latex are reduced.

Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. When the amount of the ethylenically unsaturated carboxylic acid monomer is less than 0.5% by weight, the obtained copolymer latex has poor mechanical stability and storage stability, and when it exceeds 10% by weight, it is obtained. The viscosity of the copolymer latex is too high.

Other monomers copolymerizable with the aliphatic conjugated diene-based monomer, aromatic vinyl-based monomer and ethylenically unsaturated carboxylic acid monomer include unsaturated carboxylic acid alkyl esters. And unsaturated monomers containing a hydroxyalkyl group, vinyl cyanide monomers, unsaturated carboxylic acid amide monomers, and the like.

The 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 methacrylate Examples include itaconate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate, and the like, and one or more kinds can be used. Particularly, methyl methacrylate is preferred.

Examples of the unsaturated monomer containing a hydroxyalkyl group include 2-hydroxyethyl acrylate,
-Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate,
Hydroxybutyl acrylate, hydroxybutyl methacrylate, 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 can be mentioned, and one kind or two or more kinds can be used. Particularly, 2-hydroxyethyl acrylate is preferable.

Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile and α-ethylacrylonitrile.
One or more kinds can be used. Acrylonitrile is particularly preferred.

The unsaturated carboxylic acid amide monomers include:
Acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N,
N-dimethylacrylamide and the like can be mentioned, and one kind or two or more kinds can be used. Acrylamide is particularly preferred.

Further, in addition to the above monomers, fatty acid vinyl esters such as vinyl acetate and vinyl propionate;
Basic monomers such as aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, 2-vinylpyridine, and 4-vinylpyridine, vinyl chloride, and vinylidene chloride can be used. it can.

In the emulsion polymerization of the copolymer latex in the present invention, known emulsifiers, chain transfer agents, polymerization initiators and the like can be used.

In the polymerization of a copolymer latex using the seed latex, sulfates of higher alcohols, alkylbenzene sulfonates, alkylphenyl ether sulfonates, as emulsifiers for stabilizing growing latex particles, Anionic surfactants such as aliphatic sulfonic acid salts, aliphatic carboxylate salts, sulfate salts of nonionic surfactants, and nonionic interfaces such as polyethylene glycol alkyl ester type, alkyl phenyl ether type and alkyl ether type. One or more activators can be used.

Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, dimethyl xanthogen sulfide, and the like.
Xanthogen compounds such as diisopropylxanthogen disulfide; thiuram-based compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide;
-Di-t-butyl-4-methylphenol, phenolic compounds such as styrenated phenol, allyl compounds such as allyl alcohol, dichloromethane, dibromomethane,
Halogenated hydrocarbon compounds such as carbon tetrachloride and carbon tetrabromide, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, α-methylstyrene dimer, terpinolene, triphenylethane, pentane Phenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate and the like can be mentioned, and one or more kinds can be used.

The use amount of these chain transfer agents is not limited at all, and can be appropriately adjusted according to the performance required for the copolymer latex, but is preferably 0.1 to 100 parts by weight of the monomer mixture. The range is from 0.5 to 5 parts by weight.

As the initiator, a water-soluble initiator such as potassium persulfate, ammonium persulfate and sodium persulfate, or a redox initiator or an oil-soluble initiator such as benzoyl peroxide can be used.

In the above emulsion polymerization, cyclopentene, cyclohexene, cycloheptene, 4-
Cyclic unsaturated hydrocarbon having one unsaturated bond in a ring such as methylcyclohexene, 1-methylcyclohexene,
Benzene, toluene, cyclohexane and the like may be added. Such a compound is preferably used in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the monomer.

The method of adding the various components in the present invention is not particularly limited, and any of a batch addition method, a division addition method, and a continuous addition method can be employed. Also, there is no particular limitation on the emulsion polymerization method, and any one of single-stage polymerization, two-stage polymerization, and multi-stage polymerization can be employed. Further, in the emulsion polymerization, conventional electrolytes, polymerization accelerators, chelating agents and the like can be used.

A paper coating composition can be obtained from the pigment and the copolymer latex obtained by the above-mentioned production method.
The obtained paper coating composition is characterized by having excellent fluidity under high shear. In the paper coating composition of the present invention, the copolymer latex is used in an amount of 2 to 100 parts by weight, preferably 5 to 30 parts by weight in terms of solid content, based on 100 parts by weight of the pigment. Further, if necessary, other binders 0
An aqueous dispersion is prepared together with 30 parts by weight.

Here, as the pigment, kaolin clay,
Talc, barium sulfate, titanium oxide, calcium carbonate,
Examples thereof include inorganic pigments such as aluminum hydroxide, zinc oxide and satin white, and organic pigments such as polystyrene latex, and these are used alone or in combination.

If necessary, modified starches such as starch, oxidized starch and esterified starch, natural binders such as soybean protein and casein, and synthetic latexes such as polyvinyl alcohol, polyvinyl acetate latex and acrylic latex are used. May be.

To prepare the paper coating composition of the present invention,
Furthermore, other auxiliaries, such as dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.), defoamers (polyglycols, fatty acid esters, phosphate esters, silicone oils, etc.), leveling agents (funnel oil, Dicyandiamide, urea, etc.),
Preservatives, waterproofing agents, release agents (calcium stearate,
Paraffin emulsion), a fluorescent dye, and a color water retention enhancer (such as carboxymethyl cellulose and sodium alginate) are added as necessary.

Further, the method of applying the paper coating composition to the coated paper may be a known technique, for example, an air knife coater,
It is performed by a coating machine such as a blade coater, a roll coater, and a bar coater. After coating, the surface is dried and finished with a calender ring or the like.

[0042]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist. In the examples, parts and percentages indicating percentages are based on weight.

Example 1 (1) Production of Seed Latex A reaction vessel having a capacity of 5 liters was charged with 8 parts of acrylic acid, 92 parts of styrene, 0.5 part of t-dodecyl mercaptan, 12 parts of sodium dodecylbenzenesulfonate, and hydrogen carbonate. 0.6 part of sodium and 1 part of potassium persulfate were charged and emulsion-polymerized at a reaction temperature of 85 ° C. under a nitrogen atmosphere. As a result, the conversion of the emulsion polymerization was 99% or more, the number average particle diameter was 24 nm, and the surface acid density of the carboxylic acid was 4.22.
A seed latex of × 10 ^-21 meq / nm ² was obtained.
Further, the pH of the seed latex was adjusted to 7 using sodium hydroxide. This is seed latex (A)
And

Examples 2 to 4 and Comparative Examples 1 to 3 The seed latex (B) according to the present invention was prepared in the same manner as the seed latex (A) except that the monomers shown in Table 1 were emulsion-polymerized. , (C) were prepared and adjusted to the pH described in Table 1. Also, a seed latex (D) having a different pH from the seed latex (A) was produced, and the results are shown in Table 1. Table 1
Comparative Example Seed Latexes (E) and (F) were produced in the same manner as the seed latex (A), except that the monomers shown in (1) were emulsion-polymerized. Further, a seed latex (G) having a different pH from the seed latex (B) was produced, and the results are shown in Table 1.

[0045]

[Table 1]

(Example 5) (Production of copolymer latex) In a 20-liter autoclave, 0.4 parts of seed latex (A) and 9 parts of water were added.
0 parts, sodium dodecylbenzenesulfonate 0.4
Parts, 0.25 parts of sodium hydrogencarbonate, 1.0 part of sodium persulfate, and monomers and a chain transfer agent shown in Table 2 were charged and emulsion polymerization was carried out at a reaction temperature of 81 ° C. Conversion rate of 99
% Or more. Thereafter, the obtained copolymer latex was adjusted to pH 6.5 using sodium hydroxide, and unreacted monomers were removed by heating under reduced pressure. After the recovery of the unreacted monomer was completed, the amount of fine coagulated product of 50 μm or less contained in the copolymer latex was observed, and the polymerization stability was evaluated. (Preparation of Paper Coating Composition) Next, using the obtained copolymer latex, a paper coating composition was prepared according to the following formulation. (Solid content) Pigment; UW-90 (kaolin) 60 parts C-90 (calcium carbonate) 40 parts Additives: NaOH 0.18 parts Binder; Copolymer latex 10 parts MS-4600 (starch oxide) 4 parts Water; Amount that total solid content becomes 64% (Preparation and evaluation of coated paper) Commercially available hot-air coating dryer MLC-
Using 100S type, coated base paper (basis weight 55g / m2)
Was coated with the obtained paper coating composition to prepare a coated paper. Coating conditions: Coating was performed with a hot air coating dryer MLC-100S using a wire bar so that the coating amount of the above composition was 13 g / m2 on one side. Coating speed is 46m / mi
n. Set to. Drying conditions: About 0.5 seconds after the coating, drying was performed for 3 seconds with hot air at a temperature of 210 ° C and a wind speed of 33 m / second in a drying furnace at 150 ° C. The obtained coated paper was conditioned for 24 hours at a relative humidity of 65% and a temperature of 20 ° C., and then subjected to a linear pressure of 60 kg / cm and a temperature of 5 ° C.
The paper was subjected to super calendering under the conditions of 0 ° C., a paper passing speed of 7 m / min, and a total of four passes, two times for each of the front and back sides. The coated paper thus obtained was subjected to each test and evaluated.

(Examples 6 to 9) Copolymers were prepared by emulsion polymerization in the same manner as in Example 5, except that the seed latex shown in Table 1 was used to carry out seed polymerization with the monomers shown in Table 2. After preparing latex and further adjusting the coating composition for paper, a coated paper was obtained. The physical properties are shown in Table 2.

(Comparative Examples 4 to 7) Except that seed polymerization was carried out using the seed latexes (E) and (F), or without using the seed latex, at the charged composition and reaction temperature shown in Table 3. A copolymer latex was produced in the same manner as in Example 5 to obtain a paper coating composition and a coated paper using the same. Table 3 shows the physical properties. Since the pH of the seed latex (G) was not adjusted to 5 or more after the polymerization, it solidified and could not be used for seed polymerization.

[0049]

[Table 2]

[0050]

[Table 3]

The physical properties in Tables 1 to 3 were measured and evaluated by the following methods. (Number average particle size) The number-based particle size distribution of the seed latex and the number average particle size of the seed latex and the copolymer latex were determined by a dynamic light scattering method using LPA-3000 / 3100 (manufactured by Otsuka Electronics).

(Surface Acid Density of Carboxylic Acid) The particle surface acid content of the seed latex is determined from an electric conductivity curve obtained when a 1% by weight aqueous solution of the seed latex is back titrated with a 0.1N aqueous sodium hydroxide solution. , The amount of carboxyl group (meq / g) was determined, and this was defined as the amount of acid on the particle surface.
Next, the particle surface area (nm ² / g) of the seed latex is calculated by calculation from the number-based particle size distribution obtained by the method described above, and these are substituted into the above-mentioned formula 1 to obtain the surface acid density of the carboxylic acid and the surface acid density. did.

(Storage stability) Seed latex was placed in a test tube, allowed to stand at room temperature, and one month later, it was visually checked whether or not a coagulated product had formed at the bottom of the test tube. A sample without the generation of a solidified product was evaluated as ○, a sample with the generation of a solidified product was evaluated as ×, and a sample completely solidified was evaluated as XX.

(Polymerization stability) The amount of coagulated material having a size of 50 μm or less in the copolymer latex was observed with a microscope.
The evaluation is performed in the following three stages. The smaller the fine coagulated material, the better the polymerization stability. ：: very little △: little ×: many

(Fluidity of coating composition for paper) The high shear viscosity of the coating composition for paper was measured using a Hercules viscometer.
Ob F, a value of 6000 rpm measured under the conditions of 400,000 and 8800 rpm was used. The lower the value, the better the fluidity.

(Dry Pick Strength of Coated Paper) Each coated paper sample was overprinted several times with an RI printing machine, the degree of picking on the printed surface was judged with the naked eye, and a relative five-point evaluation was performed. The higher the number, the better.

(Wet Pick Strength of Coated Paper) Using a RI printing machine, dampening water was applied to each coated paper sample with a Molton roll, and immediately after printing, the degree of picking of the printed surface was visually checked. , And relatively evaluated in five steps. The higher the number, the better.

From the above results, the acid density of the surface carboxylic acid defined by Formula 1 in the seed latex was 1.1.
When a seed latex out of the range of 5 × 10 ^{−21 to} 3.5 × 10 ⁻²⁰ (meq / nm ² ) is used, the polymerization stability of the copolymer latex obtained by seed polymerization decreases. When the pH is lower than 5, the storage stability of the seed latex is poor, and when the pH is 12 or higher,
There is a tendency for polymerization stability to decrease during seed polymerization in the next step. On the other hand, in a paper coating composition using a copolymer latex obtained by a polymerization method other than seed polymerization, fluidity under high shear is poor.

[0059]

According to the present invention, a composition for paper coating having excellent flowability under high shear can be prepared by performing seed polymerization in the presence of a seed latex obtained by a predetermined method. Copolymer latex can be produced. Furthermore, the use of the seed latex according to the present invention improves the polymerization stability during the production of the copolymer latex.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI D21H 19/44 D21H 1/28 Z (72) Inventor Kazushi Miyamoto 3-1-198 Kasuganaka, Konohana-ku, Osaka-shi, Osaka Kay AVS Latex Stock Company In-house

Claims (6)

[Claims] 1. An ethylenically unsaturated carboxylic acid monomer 4-2.
The number average particle diameter obtained by emulsion polymerization of a monomer composed of 0% by weight, 10 to 96% by weight of an aromatic vinyl monomer and 0 to 86% by weight of another monomer copolymerizable therewith is as follows. 20 ~
60 nm, and the surface acid density of the carboxylic acid defined by Formula 1 is 1.15 × 10 ^{−21 to} 3.5 × 10 ^−20.
(Meq / nm ² ) and a pH of 5 or more. (Equation 1) 2. A carboxylic acid having a surface acid density of 3 × 10 ^-21 to
^{2. The method according to} claim 1, wherein the amount is in the range of 8 × 10 ⁻²¹ (meq / nm ² ).
A seed latex according to item 1. 3. The seed latex according to claim 1, wherein the ethylenically unsaturated carboxylic acid monomer is acrylic acid. 4. An aliphatic conjugated diene monomer in an amount of 10 to 80% by weight in the presence of the seed latex according to claim 1.
It comprises 10 to 90% by weight of an aromatic vinyl monomer, 0.5 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer and 0 to 79.5% by weight of another monomer copolymerizable therewith. A method for producing a copolymer latex, comprising subjecting a monomer to emulsion polymerization. 5. The method for producing a copolymer latex according to claim 4, wherein 100 parts by weight of the monomer is emulsion-polymerized in the presence of 0.1 to 10 parts by weight of the seed latex according to claim 1. 6. A paper coating composition containing the copolymer latex according to claim 4.