JPH05239113A - Production of copolymer latex - Google Patents

Abstract

PURPOSE:To produce a latex having excelled operability and physical properties of coated paper such as pick strength and greasiness resistance by polymerizing a conjugated diene-based monomer with an aromatic vinyl-based monomer, a carboxylic acid monomer, methacrylonitrile, etc., at two stages. CONSTITUTION:In subjecting 100 pts.wt. monomers consisting of (A) 20-70 pts.wt. conjugated diene-based monomer, (B) 0-78 pts.wt. aromatic vinyl-based monomer, (C) 0.5-10 pts.wt. ethylenic unsaturated carboxylic acid monomer, (D) 1-20 pts.wt. methacrylonitrile, (E) 0-50 pts.wt. methacrylamide and (F) 0-50 pts.wt. copolymerizable vinyl monomer to emulsion polymerization, 70-99 pts.wt. monomers comprising at least the components A and C are subjected to emulsion polymerization as the first stage. In polymerizing 1-30 pts.wt. monomers comprising at least components D and E in the presence of the prepared polymer latex as the second stage, the total amount of the components D and E is adjusted to exceed 50wt.% total amount of the monomers polymerized at the second stage.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a copolymer latex. More specifically, it relates to a method for producing a high performance copolymer latex suitable as a binder for paper coating.

[0002]

2. Description of the Related Art Conventionally, synthetic copolymer latex has been widely used as, for example, a binder for paper coating, a binder for carpet backsizing, a binder for fiber bonding such as non-woven fabric or artificial leather, or an adhesive for various materials. Has been. When the copolymer latex is used for such an application, the copolymer latex is required to have high adhesive strength, water resistance, and blister resistance by drying and heating.

For example, coated paper has kaolin clay, calcium carbonate, satin white, talc, titanium oxide, etc. on the surface of the raw paper produced for the purpose of improving printability of the paper and optical properties such as gloss. Pigments, copolymer latex as their binder and starch, casein as a water retention agent or auxiliary binder,
A coating liquid containing a water-soluble polymer such as polyvinyl alcohol or carboxymethyl cellulose as a main constituent is applied. As the copolymer latex, a styrene-butadiene copolymer latex obtained by emulsion polymerization of styrene and butadiene as main monomer components, so-called SB latex, is generally used.

By the way, in recent years, the production of coated paper has remarkably increased along with the increasing demand for color printed magazines, pamphlets, and advertisements. In particular, with the trend toward high-speed printing in offset printing, the required standard for the quality of coated paper and pigment binders is also becoming more and more sophisticated.Therefore, among the quality of coated paper, ink pick resistance, so-called pick strength There is a strong demand for improvement.
Moreover, since this pick strength performance has a negative correlation with other printed physical properties, such as wet pick strength, blister resistance, and dot reproducibility, improvement to balance these physical properties to a high level is further required. Is required. These properties of coated papers make SB used as a pigment binder.
Since it strongly depends on the performance of the latex, various studies have been made on the performance of the SB latex. For example, it has been confirmed that the ratio of the insoluble portion of the copolymer latex film to solvents such as benzene, toluene, and tetrahydrofuran is a controlling factor for pick strength and blister resistance. Specifically, it has been proposed to exert excellent performance by adjusting the composition and gel fraction of the copolymer in the latex within a specific range (Japanese Patent Publication No. 59-3598). Gazette, Japanese Patent Publication No. 60-17
879, JP-A-58-4894). This gel fraction is generally adjusted by the polymerization temperature and the chain transfer agent.

However, when the gel fraction is adjusted by a chain transfer agent, the pick strength of coated paper is generally S.
The gel fraction of B latex is 75 to 95% by weight.
It is recognized that the blister resistance is better as the gel fraction is lower, while in order to improve both pick strength and blister resistance to a high level at the same time, None of the above techniques are fully satisfactory.

Further, with the increase in the production amount of coated paper, high-speed coating has been advanced in order to improve the production capacity. High solidification of coating liquid is being promoted in order to cope with the decrease in drying capacity due to high-speed coating and to improve production efficiency. In order to highly solidify the coating liquid, improve the fluidity from the pigment side by increasing the blending ratio of heavy calcium carbonate and reduce the water-soluble binder with large viscosity increase such as starch and increase the amount of latex binder From the aspect, the improvement of fluidity is taken. However, in the improvement from the binder side, there is a problem of backing roll and calender roll contamination, and it is the present situation that it has not been solved yet. In particular,
Copolymer latex with a low gel fraction set for the purpose of improving the blister resistance of web offset printing paper is inferior in stickiness resistance and mechanical stability of the coating liquid, and the backing roll stain tends to become a problem. It is in. Further, in the production of gravure printing paper, a low Tg copolymer latex is used in order to enhance the dot reproducibility, so the stickiness resistance is poor and super calendar stains are likely to occur.

As a method of improving stickiness resistance, a method of introducing an amide group-containing ethylenically unsaturated monomer into a copolymer latex has been proposed. (JP-A-63-012
However, these methods do not sufficiently improve the stickiness resistance of the copolymer latex, and particularly the stickiness resistance of the low-gel latex and the low-Tg copolymer latex is low. It has inferior drawbacks. As described above, the conventional technology cannot cope with the further increase in the speed of coated paper production and printing, and the appearance of the copolymer latex as a binder that enables the production of high-quality coated paper is strong. The current situation is what is being sought.

[0008]

As described above, in the conventional copolymer latex for paper coating, the coated paper obtained by using the latex has pick strength, wet pick strength, inking property, blister resistance, There is a problem that the requirements for coated paper physical properties such as print gloss and gravure printability and operability could not be fully satisfied at the same time, and a copolymer that satisfies all of these coating physical properties and operability. Latex is desired.

[0009]

Under the circumstances described above, the present invention is directed to pick strength, wet pick strength, blister resistance, halftone dot reproducibility, stickiness resistance and coating liquid resistance of coated paper. As a result of various studies aimed at providing a high-performance copolymer latex for further improving the balance of mechanical stability, (a) a conjugated diene-based monomer, (b) ) Aromatic vinyl monomers, (c) ethylenically unsaturated carboxylic acid monomers, (d) methacrylonitrile, (e) methacrylamide and (f) other copolymerizable vinyl monomers. Monomer 70 containing at least (a) and (c) is used as the first step when 100 parts by weight of these monomers are emulsion-polymerized in an aqueous medium using at least 5 kinds of monomers. Emulsion polymerization of about 99 parts by weight to obtain the second stage. In polymerizing 1 to 30 parts by weight of these monomers containing at least (d) and (e) in the presence of the polymer latex, the total of (d) and (e) is It has been found that this object can be achieved by polymerizing more than 50% by weight of the total amount of these monomers to be polymerized, and the present invention has been completed based on this finding.

That is, according to claim 1 of the present invention, in an aqueous medium, 20 to 70 parts by weight of (a) a conjugated diene monomer, (b) 0 to 78 parts by weight of an aromatic vinyl monomer,
(C) Ethylenically unsaturated carboxylic acid monomer 0.5 to 10
Parts by weight, (d) 1 to 20 parts by weight of methacrylonitrile,
(E) 0.5-10 parts by weight of methacrylamide and (f) 0-50 parts by weight of another copolymerizable vinyl monomer, which is obtained by emulsion polymerization of at least 5 kinds of monomers. In producing a polymer latex, as a first step, 70 to 99 parts by weight of a monomer containing at least (a) a conjugated diene monomer and (c) an ethylenically unsaturated carboxylic acid are polymerized, In two stages, in the presence of the obtained polymer latex, 1 to 4 of these monomers containing at least (d) methacrylonitrile and (e) methacrylamide.
A method for producing a copolymer latex, characterized in that, upon polymerizing 30 parts by weight, the total of (d) and (e) exceeds 50% by weight of the total amount of these monomers polymerized in the second stage. A second aspect of the invention is a paper coating composition containing a pigment and the copolymer latex of the first aspect as main components.

The present invention will be described in detail below. Examples of the (a) conjugated diene-based monomer used in the present invention include
For example, butadiene, isoprene, 2-chloro-1,3-
Butadiene etc. are mentioned. These conjugated diene-based monomers may be used alone or in combination of two or more,
The amount used is 20 to 7 based on the weight of all monomers.
0 parts by weight, preferably 25 to 60 parts by weight in terms of cohesive strength. If the amount used is less than 20 parts by weight, the resulting polymer will be too brittle, and if it exceeds 70 parts by weight, it will be too soft and a high cohesive force cannot be obtained in any case, and the object of the present invention cannot be sufficiently achieved.

Examples of the (b) aromatic vinyl-based monomer used in the present invention include styrene, α-methylstyrene, vinyltoluene, P-methylstyrene and the like. The amount of the aromatic vinyl-based monomer used is 0 to 78 parts by weight, preferably 10 to 70, based on the weight of all the monomers.
It is selected within the range of parts by weight. If the amount used exceeds 78 parts by weight, the pick strength of the coated paper becomes poor, which is not preferable.

Examples of the (c) ethylenically unsaturated carboxylic acid monomer used in the present invention include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and crotonic acid. These carboxylic acids may be used alone or in combination of two or more, and the amount thereof used is 0.5 to 10 parts by weight based on the weight of the entire polymer,
It is preferably selected in the range of 1 to 7 parts by weight. When this amount is less than 0.5 parts by weight, the dispersion stability of the latex is not sufficient, various problems occur during coating solution preparation and coating, and the pick strength is low. Also, the viscosity of the coating solution becomes too high and the water resistance tends to decrease, which is not preferable.

The amount of (d) methacrylonitrile used in the present invention is 1 to 2 based on the weight of all monomers.
It is selected in the range of 0 part. If this amount is less than 1 part by weight, the effect of improving the stickiness resistance of the copolymer latex, the mechanical stability of the coating solution, and the effect of improving the wet pick strength of the coated paper are not sufficiently exhibited, and the amount is 20 parts by weight. If it exceeds, the polymerization stability of the latex is deteriorated, which is not preferable.

The amount of (e) methacrylamide used in the present invention is 0.5 based on the weight of all monomers.
It is selected in the range of 10 to 10 parts by weight. If this amount is less than 0.5 parts by weight, the effect of improving the stickiness resistance of the copolymer latex and the effect of improving the water resistance of the coated paper are not sufficiently exhibited, and 10
If the amount is more than parts by weight, the viscosity of the copolymer latex is increased and the fluidity of the paper coating solution is lowered, which is not preferable.

Other copolymerizable monomers (f) used in the present invention include methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate, glycidyl methacrylate and the like. Acrylic acid or methacrylic acid alkyl esters, vinyl acetate and other carboxylic acid vinyl esters, vinyl chloride and other vinyl halides, aminoethyl acrylate, dimethylaminoethyl acrylate and other ethylenic amines, sodium styrenesulfonate, Further, vinyl cyanide monomers other than methacrylonitrile and amide group-containing ethylenically unsaturated monomers other than methacrylamide can be mentioned. These copolymerizable monomers may be used alone or in combination of two or more, and the amount thereof used is selected in the range of 0 to 50 parts by weight based on the weight of all the monomers. Be done. If the amount used exceeds 50 parts by weight, it is not preferable in order to bring out the effect of the present invention.

The copolymer latex of the present invention is produced by a two-step emulsion polymerization. That is, 70 to 99 parts by weight, preferably 85 to 97 parts by weight of a monomer containing at least (a) and (c) is emulsion-polymerized as the first stage, and the weight obtained in the first stage is used as the second stage. In the presence of the combined latex, the remaining monomers 1-containing at least (d) and (e)
Emulsion polymerization of 30 parts by weight, preferably 3 to 15 parts by weight. Less than 1 part by weight of monomer polymerized in the second stage and 30
If the amount is more than parts by weight, the balance of pick strength, water pick strength, stickiness resistance, and mechanical stability of the coating solution deteriorates, and the effect of the present invention does not appear, which is not preferable. The monomer polymerized in the second stage must contain (d) and (e), and the (d) monomer is 1 to 20 parts by weight, preferably 2
10 to 10 parts by weight, and (e) the monomer is 0.5 to 10 parts by weight, preferably 2 to 7 parts by weight. Of the monomers polymerized in the second stage, the total weight of (d) and (e) is the second
Greater than 50% of the total weight of monomers polymerized in stages,
It is preferable in order to bring out the effect of the present invention. The polymerization yield of the first-stage monomer at the time of starting the second-stage polymerization is 80
It is preferable that the content is at least wt% in order to bring out the effect of the present invention.

The copolymer latex of the present invention comprises the conjugated diene monomer, aromatic vinyl monomer, ethylenically unsaturated carboxylic acid monomer, methacrylonitrile, methacrylamide, and It is obtained by carrying out a two-step emulsion polymerization of another copolymerizable monomer. The emulsion polymerization method is not particularly limited, and a conventionally known method, for example, water and the above-mentioned monomer, a chain transfer agent, a surfactant, a radical polymerization initiator, and other additive components used as necessary may be used. In a dispersion system as a basic constituent, an aqueous dispersion of copolymer particles by polymerizing the monomer,
That is, a method for producing a copolymer latex is used. The concentration of the copolymer in the copolymer latex is selected in the range of 40 to 60% by polymerization, and the particle size thereof is 0.05 to 1 μm, preferably 0.07 to 0.3 μm.
Is advantageously in the range. The average particle size can be adjusted by the use ratio of the surfactant or seed latex, etc. Generally, the higher the use ratio, the smaller the average particle size of the produced copolymer latex. Examples of the chain transfer agent include mercaptans such as n-butyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, n-dodecyl mercaptan and t-dodecyl mercaptan, disulfides such as tetramethyl thiuram disulfide and tetraethyl thiuram disulfide, and four Halogenated derivatives such as carbon chloride and carbon tetrabromide, 2-ethylhexyl thioglycolate, α
-Methylstyrene dimer and sodium phosphinate as a water-soluble chain transfer agent are mentioned, and one or more of these are used. In addition, if necessary, in combination with the chain transfer agent, diphenylethylene, 2,6-di-t
It is preferable to use an oil-soluble polymerization rate inhibitor such as -butylhydroxytoluene. Further, a method in which a part of the chain transfer agent is continuously added after the addition of the monomer is more preferable.

Examples of the surfactant include aliphatic soap, rosin acid soap, alkyl sulfonate, dialkylaryl sulfonate, alkylsulfosuccinic acid, polyoxyethylene alkyl sulfate, polyoxyethylene alkylaryl sulfate, and the like. Examples thereof include anionic surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, polyoxyethylene sorbitan fatty acid esters, and nonionic surfactants such as oxyethyleneoxypropylene block copolymers. This surfactant is usually used alone or in an anionic / nonionic mixed system, and the amount thereof is usually in the range of 0.05 to 2% by weight based on the weight of all monomers. To be elected.

The radical polymerization initiator has a function of radically decomposing by heat or a reducing substance to cause addition polymerization of a monomer, and as such a substance, for example, water-soluble or oil-soluble. Peroxodisulfate, peroxide, azobis compound, etc., specifically, potassium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2- Examples thereof include azobisisobutyronitrile and cumene hydroperoxide. Among these, peroxodisulfate is particularly preferable. The amount of the polymerization initiator used is usually selected in the range of 0.2 to 1.5% by weight based on the weight of all the monomers.

The polymerization temperature in this emulsion polymerization is usually 6
It is selected in the range of 0 to 100 ° C., but if acceleration of the polymerization or polymerization at a lower temperature is desired, a reducing agent such as acidic sodium sulfite, ascorbic acid or its salt, erythorbic acid or its salt, or Rongalit is initiated. The so-called redox polymerization method can be adopted by using it in combination with the agent.

In the present invention, if desired, various polymerization regulators, for example, pH regulators such as sodium hydroxide, potassium hydroxide, sodium hydrogen carbonate, sodium carbonate and disodium hydrogen phosphate, and various chelates such as ethylenediamine tetrasodium. Agents and the like can be added. Further, if necessary, an alkali-sensitive latex may be added to the copolymer latex of the present invention.

The pigment according to claim 2 of the present application is one in which the sum of the volume fractions of clay and / or calcium carbonate accounts for 60% or more of the total volume of the inorganic pigment. If it is 60% or less, the effect of the present invention cannot be exhibited sufficiently. Further, as other inorganic pigments, aluminum hydroxide, titanium oxide, satin white, talc, activated clay and the like can be used as required up to 40% of the total volume of the inorganic pigment. It is also a preferred embodiment of the present invention to use together with the inorganic pigment, a plastic pigment such as polystyrene particles.

When the copolymer latex of the present invention is used as a binder for a coating material for paper coating, it is usually used in a conventional manner, for example, in water in which a dispersant is dissolved, inorganic / organic pigments and water-soluble pigments are highly soluble. A method in which the copolymer latex is added together with molecules and various additives and mixed and used as a uniform dispersion liquid can be adopted. Then, this paper coating solution can be applied to the base paper by an ordinary method using various blade coaters, roll coaters and the like.

[0025]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, each characteristic was calculated | required as follows. (1) Properties of copolymer latex (gel fraction of copolymer): Copolymer latex is uniformly coated on a polypropylene film with a No26 wire bar and dried in a dryer at 50 ° C for 1 hour to form a film. Was formed. Next, peel off this latex film, accurately weigh about 0.5 g with an analytical balance, immerse in a container containing 300 cc of toluene, and stir for 6 hours at room temperature with a shaker. Was filtered through a 325 mesh wire mesh that was precisely weighed in advance,
The residue remaining on the wire mesh was weighed. After that, it was dried in a dryer at 50 ° C. for 2 hours, and the gel fraction was determined by the following formula.

[0026]

[Equation 1]

(2) Evaluation of paper coating performance (a) Blister resistance A printing ink (made by Dainippon Ink and Webb Zett) on both sides of the coated paper using an RI printing tester (made by Mei Seisakusho)
(Yellow) 0.3 cc was solid printed. The printed coated paper was cut into an appropriate size, and the test piece was immersed in a silicon oil thermostatic bath adjusted to a predetermined temperature to observe whether or not blisters were generated. This test is conducted by changing the temperature of the constant temperature bath, and the higher the temperature at which the blister is generated, the better the blister resistance. ◎ (excellent) ~ × (poor).

(B) Pick strength Using an RI printing tester (manufactured by Akira Seisakusho Co., Ltd.), 0.4 cc of printing ink (SD Super Deluxe 50 Red B; Tuck 18) manufactured by Toka Dye Co. was overprinted and appeared on a rubber roll. The picking condition was lined on another mount and the condition was observed. The evaluation was carried out by a 10-point evaluation method, and the smaller the picking phenomenon, the higher the score.

(C) Wet pick strength Using a RI printing tester (Myo Seisakusho), water is applied to the surface of the coated paper with a molton roll, and immediately after that, printing ink (SD Super Deluxe 50 Hong B manufactured by Toka Dye Co., Ltd.) is used. Tack 15) 0.4 cc was printed once, and the picked state appearing on the rubber roll was lined on another mount and the state was observed. The evaluation was carried out by a 10-point evaluation method, and the smaller the picking phenomenon, the higher the score.

(D) Stickiness resistance Latex is applied to a mylar film with a No. 13 wire bar, and then dried at 130 ° C. for 60 seconds. Superimpose it on black Racha paper and pass it through a supercalender with a temperature of 70 ° C and a linear pressure of 100 kg / cm. The black Rasha paper is peeled off from the Mylar film, and the transfer of the Rasha paper fibers onto the latex film is visually observed. ◎ (excellent) ~ × (poor).

(E) Appropriateness for gravure printing A gravure printing machine of the Ministry of Finance Printing Laboratory is used. Printing is performed using a halftone dot gravure plate, the number of miss dots in the halftone portion is counted, and classified into ⊚ (excellent) to × (poor). (F) Mechanical stability The mechanical stability of the paper coating liquid is measured using the Maron stability test.

Evaluation Criteria ⊚: Residual Occurrence Rate 0.02% or Less ∘: Residual Incidence Rate 0.02 to 0.05% or Less Δ: Residual Incidence Rate 0.05 to 0.2% ×: Residual Occurrence Proportion of 0.2% or more Production of copolymer latex: 2 parts by weight of an aqueous dispersion of seed particles having a diameter of 0.04 µm (seed solid content concentration 25%), a pressure resistant reaction vessel equipped with a stirrer and a temperature control jacket. 70 parts by weight of water, 0.1 part by weight of sodium lauryl sulfate, 1 part by weight of fumaric acid, and 1.5 parts by weight of itaconic acid were charged, the internal temperature was raised to 80 ° C., and then the unit temperature shown in Table 1 was used. Initiator consisting of monomers other than itaconic acid and fumaric acid in monomer A, 15 parts by weight of water, 1 part by weight of sodium peroxodisulfate, 0.1 part by weight of sodium lauryl sulfate and 0.2 part by weight of sodium hydroxide. System aqueous solution for 5 hours and It was added at a constant flow rate over 6 hours. Further, the monomer mixture B shown in Table 1 was added 30 minutes after the addition of the monomer mixture A was completed. Then, the temperature of 80 ° C. is kept as it is for 2 hours, followed by cooling, then the pH of the produced copolymer latex is adjusted to 7 with sodium hydroxide, and then unreacted monomers are removed by a steam stripping method. It was filtered through a wire mesh of 200 mesh. The copolymer latex was adjusted so that the final concentration of solid content would be 50% by weight. The latex thus obtained is referred to as a copolymer latex A.

Polymerization was carried out in the same manner as the copolymer latex A except that the polymerization components B to M shown in Tables 1 and 2 were used to obtain copolymer latexes B to M. Copolymer latices A to G are copolymer latices of Examples, and copolymer latices H to M are copolymer latices of Comparative Examples. The gel contents of these copolymer latexes are also shown.

[0034]

[Table 1]

[0035]

[Table 2]

Formulation of paper coating liquids (preparation of paper coating liquids A to M): Copolymer latices A to M were used to obtain paper coating liquids A to M at the following mixing ratios. (Compounding prescription: weight ratio) Clay 70 Calcium carbonate 30 Polysodium acrylate 0.2 Sodium hydroxide 0.1 Phosphate esterified starch 2.5 Copolymer latex (AM) 12 Water (total solid content is 65 %)

[0037]

Examples 1 to 3 Each of the obtained paper coating liquids A, B and C was applied to a base paper having a basis weight of 75 g / m ² and a coating amount of 12 g / m ^{2 on} one side.
Blade coating to obtain each sheet offset paper. The results of evaluation according to the evaluation method described above are shown in Table 3.

[0038]

[Comparative Examples 1 and 2] Each of the obtained paper coating liquids H and I was added to a basis weight of 7
Blade coating was applied to a coated base paper of 5 g / m ^{2 so} that the coating amount was 12 g / m ² on one side, to obtain each sheet offset paper. The evaluation results are shown in Table 3 according to the evaluation method described above.
Shown in.

[0039]

Examples 4 to 5 Each of the obtained paper coating liquids D and E had a basis weight of 7
Each web offset paper was obtained by blade coating on a coated base paper of 5 g / m ^{2 so} that the coating amount was 12 g / m ² on one side. The evaluation results are shown in Table 4 according to the evaluation method described above.
Shown in.

[0040]

[Comparative Examples 3 to 4] Each of the obtained paper coating liquids J and K had a basis weight of 7
Each web offset paper was obtained by blade coating on a coated base paper of 5 g / m ^{2 so} that the coating amount was 12 g / m ² on one side. The evaluation results are shown in Table 4 according to the evaluation method described above.
Shown in.

[0041]

[Examples 6 to 7] Each of the obtained paper coating solutions F and G had a basis weight of 7
Blade coating was performed on a coated base paper of 5 g / m ^{2 so} that the coating amount was 12 g / m ² on each side, to obtain each gravure paper. The results of evaluation according to the evaluation method described above are shown in Table 5.

[0042]

[Comparative Examples 5 to 6] Each of the obtained paper coating liquids L and M had a basis weight of 7
Blade coating was performed on a coated base paper of 5 g / m ^{2 so} that the coating amount was 12 g / m ² on each side, to obtain each gravure paper. The results of evaluation according to the evaluation method described above are shown in Table 5. As is clear from the examples, various printing papers using the prepared paper coating liquids A to G within the applicable range showed excellent performance.

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

[Table 5]

[0046]

As is clear from the examples, in the present invention, the balance between the pick strength and other properties of the coated paper for printing, the stickiness resistance relating to the coating operability, and the mechanical stability of the coating liquid. It is possible to easily obtain a high-performance copolymer latex capable of improving the properties.

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location D21H 19/36 19/56 19/44 7199-3B D21H 1/28 Z

Claims (2)

[Claims] 1. (a) Conjugated diene-based monomer 20 to 70 parts by weight (b) Aromatic vinyl-based monomer 0 to 78 parts by weight (c) Ethylenically unsaturated carboxylic acid monomer 0.5 to 10 parts by weight (d) Methacrylonitrile 1 to 20 parts by weight (e) Methacrylamide 0.5 to 10 parts by weight (f) Other copolymerizable vinyl-based monomer 0 to 50 parts by weight Upon emulsion polymerization of 100 parts by weight,
As a first stage, 70 to 99 parts by weight of a monomer containing at least (a) and (c) is emulsion polymerized, and as a second stage, at least (d), (in the presence of the obtained polymer latex, In polymerizing 1 to 30 parts by weight of these monomers containing e), the sum of (d) and (e) is characterized by exceeding 50% by weight of the total amount of these monomers polymerized in the second stage. Method for producing copolymer latex. 2. A paper coating composition comprising a pigment and the copolymer latex according to claim 1 as main components.