JP4776341B2 - Method for producing copolymer latex, copolymer latex and paper coating composition - Google Patents

Description

  The present invention relates to a conjugated diene copolymer latex used for pigment binders, carpet backing agents, adhesives, pressure-sensitive adhesives, fiber binders and paints in paper coating. More particularly, the present invention relates to a copolymer latex that provides a coated paper excellent in operability in the paper coating process, in particular, in the coating operability related to the suitability of dirt on the backing roll, and in pick strength and wet pick strength, and inking property. .

Coated paper is used for the purpose of improving paper printability and optical properties such as gloss, and pigments such as kaolin clay, calcium carbonate, satin white, talc, titanium oxide, and binders on the surface of the base paper. A paper coating composition comprising a copolymer latex as a main component and a water-soluble polymer such as starch, polyvinyl alcohol or carboxymethyl cellulose as a viscosity modifier or an auxiliary binder is coated.
Here, as a copolymer latex as a binder, a styrene-butadiene copolymer latex obtained by emulsion polymerization using styrene and butadiene as main monomer components, a so-called SB latex has been conventionally used.

In recent years, with the increasing demand for color-printed magazines, pamphlets, and advertisements, the printing speed has been increased, and the required level of coated paper and pigment binders has become increasingly sophisticated. Among them, ink pick resistance, so-called pick strength, and wet pick strength that is ink pick resistance when water is applied, which is important when printing in the presence of dampening water, and ink when wet There is a need to improve the inking property, which is the transferability of the material.
In addition, the production of coated paper itself is also accelerated, and there is a strong demand for improving resistance to dirt on the backing roll among coating operability. It is known that the resistance to backing roll soiling correlates strongly with the wet stickiness of the latex film.
As described above, improvements in various properties are required for copolymer latex. For example, in “Patent Document 1” (Japanese Patent Application Laid-Open No. Hei 6-2111911), a copolymer having a specific anionic surfactant is used for emulsion polymerization using a monomer having a specific monomer composition. A method for obtaining a good pick strength by setting the number average particle diameter of the latex to 110 nm or less is described. However, when the particle size is further reduced, the polymerization stability is reduced, and aggregates are easily generated, resulting in a decrease in yield.

Further, in “Patent Document 2” (Japanese Patent Laid-Open No. 10-7706), an alkylbenzene sulfonate and an alkyl diphenyl ether disulfonic acid are used in combination as emulsifiers to obtain a copolymer latex having a number average particle diameter of 100 nm or less. A method for obtaining strength has been proposed. However, since the amount of alkylbenzene sulfonate used is large, the water resistance is lowered and a good wet pick strength cannot be obtained.
Furthermore, in “Patent Document 3” (Japanese Patent Application Laid-Open No. 7-316212), in emulsion polymerization of a monomer having a specific monomer composition in the presence of α-methylstyrene dimer, the first and second stages are used. There has been proposed a method for improving pick strength and wet pick strength by setting the number average particle diameter in the range of 60 to 160 nm by setting the amount of water to be used in a certain range. It cannot meet the current requirements for sex.

Further, studies have been made in terms of solubility parameters of the copolymer latex. In "Patent Document 4" (Japanese Patent Laid-Open No. 2001-49038), when emulsion polymerization is performed by multistage polymerization, the solubility parameter of the copolymer obtained from the composition of the monomer mixture added in the first step and the second There has been proposed a method for improving pick strength and coating operability by setting the difference in solubility parameter of the copolymer obtained from the composition of the monomer mixture added in the process within a certain range. However, in this technical field in recent years, it is required to achieve a higher balance of physical properties, and it can be said that this method has insufficient physical properties.
Further, in “Patent Document 5” (Japanese Patent Application Laid-Open No. 10-17602), in emulsion polymerization by multi-stage polymerization, a specific amount of unsaturated carboxylic acid is charged into each stage, whereby pick strength, wet pick strength, and inking. A method for improving the balance in a balanced manner has been proposed. However, this method cannot satisfy the requirements for coating operability, so it is not sufficient as a method for improving resistance to backing roll dirt and pick strength, wet pick strength, and inking balance in coated paper. .
As described above, the conventional technology cannot cope with further increase in the speed of printing and coated paper production, and the copolymer latex as a binder that increases the productivity and enables the production of high-quality coated paper. It is the present situation that the appearance of is strongly demanded.

JP-A-6-2111911 Japanese Patent Laid-Open No. 10-7706 JP 7-316212 A JP 2001-49038 A Japanese Patent Laid-Open No. 10-17602

  As described above, conventional paper coating binders cannot simultaneously satisfy coated paper physical properties such as coating operability, coated paper pick strength, wet pick strength, and inking properties. Accordingly, an object of the present invention is to provide a high-performance copolymer latex excellent in coating operability and excellent in coated paper physical properties such as pick strength, wet pick strength, and inking properties in coated paper. .

The inventors of the present invention have intensively studied to solve the above-mentioned problems and have come to make the present invention.
That is, the first of the present invention is (a) 20 to 80% by mass of a conjugated diene monomer, and (b) 0.5 to 10% by mass of an ethylenically unsaturated carboxylic acid monomer, and (c) (a ), 10 to 79.5% by mass of another monomer copolymerizable with (b) (provided that 100 parts by mass of a monomer comprising (a) + (b) + (c) = 100% by mass)) When emulsion polymerization is carried out using 0.2 to 2 parts by mass of (i) alkyl diphenyl ether disulfonate and (b) 0.01 to 0.29 parts by mass of alkylbenzene sulfonate which are emulsifiers,
First step: 3) to 30 parts by mass of at least one monomer selected from (a) a conjugated diene monomer and (c) another copolymerizable monomer is (b) an alkylbenzene sulfonate Step 2 for performing polymerization using 50% by mass or more: Step 3 for polymerizing 10 to 67 parts by mass of at least one monomer selected from (a) and (c) Third and subsequent steps: Remaining single amount The emulsion polymerization is performed by dividing into at least three steps of the step of polymerizing the body, and the mass ratio of (1) monomer / (2) water added to the polymerization system by the end of the second step is 0.2. It is -0.75, Comprising: It is a manufacturing method of copolymer latex characterized by obtaining copolymer latex with a number average particle diameter of 100 nm or less.
In the second aspect of the present invention, the ratio of the (a) conjugated diene monomer in the monomer used in the third step and thereafter is the (a) conjugated diene system in the monomer used up to the second step. 2. The method for producing a copolymer latex according to claim 1, wherein the copolymer latex is smaller than a monomer ratio.
The third of the present invention is a copolymer latex obtained by the production method of claim 1 or 2.
A fourth aspect of the present invention is a paper coating composition containing the copolymer latex according to claim 2.

  The present invention has an effect of providing a high-performance copolymer latex that is excellent in coating operability and excellent in coated paper properties such as pick strength, wet pick strength, and inking properties in coated paper.

The present invention will be specifically described below.
(A) The conjugated diene monomer is an essential component for imparting flexibility to the copolymer latex and providing adhesive strength and shock absorption, and is included in all the monomers constituting the copolymer latex. It is used in a proportion of 20 to 80% by mass, preferably 25 to 70% by mass, more preferably 28 to 60% by mass. The copolymer latex obtained from the fact that high impact resistance can be expressed by using it in the range of 20% by mass or more has high adhesive strength, and the copolymer latex obtained by using it in the range of 80% by mass or less. The combined latex does not become too soft, and high coating operability can be maintained. Preferable examples of the conjugated diene monomer used include 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene and the like, and these are used alone or in combination of two or more. .

The (b) ethylenically unsaturated carboxylic acid monomer in the present invention is an essential component for imparting the necessary dispersion stability to the copolymer latex and enhancing the adhesive force, and all the components constituting the copolymer latex are used. The monomer is used in a proportion of 0.5 to 10% by mass, preferably 0.8 to 8% by mass, more preferably 1 to 5% by mass. By using 0.5% by mass or more of an ethylenically unsaturated carboxylic acid, it is possible to maintain the dispersion stability required when mixing the pigment and in the coating process. Moreover, the viscosity of copolymer latex can be suppressed and water resistance can be maintained by making the range of this monomer 10 mass% or less. Preferable examples of the ethylenically unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and the like, and these are used alone or in combination of two or more.
In the present invention, (c) another monomer copolymerizable with (a) and (b) is required. Various properties can be imparted to the copolymer latex by appropriately selecting other monomers capable of copolymerization.

  Preferred examples of other copolymerizable monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, and p-methylstyrene, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and the like. Vinyl cyanide monomers, alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, alkyl methacrylates such as methyl methacrylate, butyl methacrylate, acrylic acid 2 -Hydroxyethyl, hydroxyalkyl esters such as 2-hydroxyethyl methacrylate, aminoalkyl esters such as aminoethyl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, 2-vinylpyridine, 4-vinyl Pyridines such as pyridine, glycidyl esters such as glycidyl acrylate and glycidyl methacrylate, acrylamide, methacrylamide, N-methylolacrylamide, N-methylacrylamide, N-methylmethacrylamide, glycidylmethacrylamide, N, N-butoxymethyl Examples thereof include amides such as acrylamide, carboxylic acid vinyl esters such as vinyl acetate, and vinyl halides such as vinyl chloride. These may be used alone or in combination.

The other monomers copolymerizable with (c), (a) and (b) are 10 with respect to the total monomers when the total monomer constituting the copolymer latex is 100 parts by mass. Used in a ratio of ˜79.5% by mass.
It is essential that the mass ratio of monomer / water added to the system by the end of the second step in the present invention is 0.2 to 0.75. By suppressing the dispersion within the range of 0.75 or less, the dispersion stability during the polymerization can be kept good, so that the particle diameter can be suppressed to 100 nm or less. Moreover, productivity at the time of copolymer latex manufacture can be improved by setting it as 0.2 or more. Preferably it is the range of 0.30-0.65, More preferably, it is the range of 0.35-0.6.

The glass transition temperature (Tg) of the copolymer latex of the present invention is generally in the range of −60 ° C. to + 50 ° C. from the viewpoint of achieving both adhesive strength in coated paper applications and latex wet-resistance stickiness. Is. Tg which is preferably in the range of −40 ° C. to + 45 ° C., more preferably −30 to + 40 ° C. may have not only one point but also a plurality of Tg in one type of copolymer latex.
In the production method of the present invention, it is essential that the number average particle diameter of the copolymer latex is 100 nm or less. By setting the number average particle diameter to 100 nm or less, necessary pick strength and wet pick strength can be obtained. Moreover, in order to suppress the viscosity of latex rising more than necessary, it is preferably 50 nm or more, and more preferably in the range of 60 to 90 nm.

  In the present invention, 0.1 to 2 parts by mass of (i) alkyl diphenyl ether disulfonate and 0.01 to 0.29 parts by mass of (b) alkylbenzene sulfonate are essential as emulsifiers with respect to 100 parts by mass of the monomer. (Ii) The preferred amount of alkyl diphenyl ether disulfonate is 0.2 to 1.5 parts by weight, and the number of latexes that maintain dispersion stability in emulsion polymerization by making the amount used be 0.1 parts by weight or more. An average particle diameter can be made into 100 nm or less, and a water resistance fall can be prevented and wet pick strength can be raised by making it into 2.0 mass parts or less. (B) The preferred amount of alkylbenzene sulfonate used is 0.05 to 0.25 parts by mass, and the number average molecular weight of the generated particles in emulsion polymerization is 100 nm or less by making the amount used 0.01 parts by mass or more. When the amount is 0.25 parts by mass or less, the water resistance is prevented from being lowered and the wet pick strength can be increased.

In the present invention, other conventionally known anions, cations, amphoteric and nonionic surfactants and reactive emulsifiers can be used in combination. Examples of preferred surfactants include anionic surfactants such as aliphatic soap, rosin acid soap, alkylsulfosuccinate, polyoxyethylene alkyl sulfate, polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene alkyl allyl ether, Nonionic surfactants such as oxyethyleneoxypropylene block copolymers are listed, and one or more of them can be used as necessary.
The radical initiator initiates addition polymerization of the monomer by radical decomposition in the presence of heat or a reducing agent, and either an inorganic initiator or an organic initiator can be used. Preferred examples include peroxodisulfates, peroxides, azobis compounds, etc., specifically potassium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2, Examples thereof include 2-azobisbutyronitrile and cumene hydroperoxide, and these can be used alone or in combination of two or more. In addition, a so-called redox initiator in which a reducing agent such as sodium bisulfite, ascorbic acid or a salt thereof, erythorbic acid or a salt thereof or Rongalite is used in combination with a polymerization initiator can also be used.

  In the production method of the present invention, a known chain transfer agent usually used in radical polymerization can be used. Preferred examples of the chain transfer agent include α-methylstyrene dimer, n-butyl mercaptan, t-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t which is one of dimers of nucleus-substituted α-methylstyrene. -Mercaptans such as dodecyl mercaptan and n-lauryl mercaptan; disulfides such as tetramethylthuradium disulfide and tetraethylthuradium disulfide; halogenated derivatives such as carbon tetrachloride and carbon tetrabromide; These may be used alone or in combination of two or more. As the addition method of the chain transfer agent, known addition methods such as batch addition, batch addition, and continuous addition are used.

The polymerization temperature during production of the copolymer latex of the present invention is generally performed in the range of 0 to 100 ° C., but from the viewpoint of quality such as production efficiency and adhesive strength of the obtained copolymer latex. Is preferably in the range of 40-95 ° C.
When the copolymer latex of the present invention is produced, the means for adding the monomer mixture into the emulsion polymerization system is as follows: (a) conjugated diene monomer, (c) other copolymerizable monomer At least one selected from (a) and (c), wherein (b) 3 to 30 parts by mass of at least one monomer selected from the body is polymerized using (b) 50% by mass or more of the alkylbenzene sulfonate A multi-stage polymerization method in which emulsion polymerization is carried out by dividing into at least 3 steps after the second step of polymerizing 10 to 67 parts by mass of one or more monomers and the third step of polymerizing the remaining monomers is used. By performing such a multistage polymerization method, the stickiness when the latex film is wet can be improved while maintaining the required pick strength.

In addition, the ratio of (A) the ratio of the conjugated diene monomer used in the third step and thereafter / (B) the ratio of the conjugated diene monomer used until the second step should be less than 1.00. Is preferred. More preferably, it is 0.2 to 0.95, and most preferably is in the range of 0.3 to 0.9. By setting it within this range, the stickiness when the latex film is wet can be improved.
Various known polymerization regulators can be used in the copolymer latex of the present invention as necessary. These are, for example, pH adjusters, chelating agents, etc. Preferred examples of pH adjusting agents include sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium hydrogen carbonate, disodium hydrogen phosphate, and the like. Preferable examples include sodium ethylenediaminetetraacetate.

There is no restriction | limiting in particular also about solid content as a final product of the copolymer latex obtained by this invention, Usually, solid content is prepared by diluting or concentrating in the range of 30-60 mass%.
Various additives can be added to the copolymer latex obtained in the present invention as needed, or other latexes can be mixed and used. For example, a dispersant, an antifoaming agent, anti-aging, etc. An agent, a water-resistant agent, a bactericidal agent, a printability improving agent, etc. can be added, and an alkali-sensitive latex, a plastic pigment, and the like can be mixed and used.
When using the copolymer latex obtained by this invention as a binder of the coating material for paper coating, it can carry out by the embodiment currently performed normally. That is, inorganic water such as kaolin clay, calcium carbonate, titanium dioxide, aluminum hydroxide, satin white, and talc, organic pigments known as plastic pigment and binder pigment, starch, casein, and polyvinyl alcohol in water in which the dispersant is dissolved Add copolymer latex together with various additives such as water-soluble polymers such as carboxymethyl cellulose, thickeners, dyes, antifoaming agents, preservatives, water resistance agents, lubricants, printability improvers, water retention agents, etc. It is an aspect which mixes and makes it a uniform dispersion liquid. Here, the copolymer latex obtained in the present invention is a particularly remarkable pick strength, wetness when the pigment constituting the paint for paper coating is mainly used with a pigment having a small average number average particle diameter. Expresses pick strength. That is, for kaolin clay, particles having a particle size of 2 μm or less are 84 parts by mass or more, and for calcium carbonate, a pigment having 2 μm or less particles of 90 parts by mass or more is preferable.

The ratio of the pigment and the copolymer latex obtained in the present invention can be appropriately determined depending on the purpose of use of the composition, but is preferably 3 to 30 parts by mass of latex with respect to 100 parts by mass of pigment. The paper coating solution can be applied to the base paper by a usual method using various blade coaters, roll coaters, air knife coaters, bar coaters and the like. The coating form can be applied to one side of the base paper, or both sides of the front and back sides, and the number of times of coating per side is one so that the coating process is performed twice, in addition to single coating. It can also be used for double coating. In this case, the copolymer latex of the present invention can be used for both the undercoat pigment composition and the overcoat pigment composition.
The composition for paper coating using the copolymer latex obtained in the present invention includes various printing papers such as offset sheet-fed printing paper, offset rotary printing paper, gravure printing paper, letterpress printing paper, and paperboard. It is preferably used for corrugated cardboard paper, wrapping paper, etc., but is particularly preferably used for offset sheet-fed printing paper and offset rotary printing paper.
Furthermore, the copolymer latex obtained in the present invention can be used for paper coating agents, carpet backing agents, other adhesives, and various paints.

The present invention will be described based on examples.
Each physical property was evaluated by the following methods.
(1) Pick strength: Using an RI printing tester (manufactured by Mei Seisakusho), 0.4 cc of printing ink (SD Super Deluxe 50 Crimson B; Tack 18) manufactured by T & K Toka Co., Ltd. was overprinted and appeared on a rubber roll. The picking state was backed on another mount and the state was observed. The evaluation was based on a 10-point evaluation method, and the smaller the picking phenomenon, the higher the score.
(2) Wet pick strength: Water was applied to the coated paper surface with a sleeve roll using an RI printing tester (Meiji Seisakusho), and immediately after that, printing ink (SD Super Deluxe 50 Red B, manufactured by T & K Toka Co., Ltd .; tack) 15) Printed once for 0.4 cc, picked up the appearance of the rubber roll with another backing paper, and observed the state. The evaluation was based on a 10-point evaluation method, and the smaller the picking phenomenon, the higher the score.
(3) Inking property: Using a RI printing tester (manufactured by Meisei Seisakusho), apply water thinly on the coated paper surface with a roll, and immediately after that, printing ink (Toyo Ink Mfg. Co., Ltd. HiEcho Indigo M) 0.4 cc1 Reprinted and observed the amount of ink transferred to the coated paper.

(4) Number average particle diameter of copolymer latex: measured using a particle size analyzer (model 9230UPA) manufactured by MICROTRAC.
(5) Latex film stickiness when wet: The copolymer latex obtained on the PET film is No. It was coated with 18 wire bars and dried at 130 ° C. for 30 seconds. This film is overlaid with black lasha paper soaked in water at 30 ° C. for 5 seconds, passed through a super calendar at a temperature of 80 ° C. and a linear pressure of 19600 N / m, and then the black lasha paper is peeled off. The state of transition of the black lasha paper fiber latex film due to stickiness was visually evaluated. The evaluation was performed by a 10-point evaluation method, and the smaller the transition, the higher the score.
(6) Gel fraction of copolymer latex: The obtained copolymer latex is dried at 130 ° C. for 30 minutes to obtain a latex film. About 0.5 g of this latex film is taken and weighed. This is mixed with 30 ml of toluene and shaken for 3 hours, and then the dry mass of the residue is weighed when filtered through a metal mesh having an opening of 32 μm. The ratio of the dry mass of the residue to the original latex film mass is defined as the gel fraction (% by mass).

(7) Preparation of coating color: First, a master color was prepared with the following constituent materials excluding the copolymer latex.
Fine kaolin clay 50 parts by weight Coarse grain kaolin clay 20 parts by weight Heavy calcium carbonate (fine particles) 20 parts by weight Heavy calcium carbonate (coarse grains) 10 parts by weight Sodium polyacrylate 0.2 parts by weight Sodium hydroxide 0.1 parts by weight Part Phosphoric esterified starch 2.5 parts by weight Water (added so that the total solid content of the coating solution is 68% by weight)
The fine kaolin clay is Hydra Gloss 90 (US, manufactured by JM HUBER; the ratio of particle diameter is 2 μm or less = 96 mass% or more), and the coarse kaolin clay is Hydra Sparse (US, JM). Manufactured by HUBER; ratio of particle size of 2 μm or less = 80 to 82% by mass), as fine heavy calcium carbonate, Carbital 97 (manufactured by Imeris Minerals Japan; ratio of particle size of 2 μm or less = 97% by mass or more), The coarse heavy calcium carbonate is Carbital 75 (Imeris Minerals Japan Co., Ltd .; the ratio of particle size 2 μm or less = 75 mass%), and the sodium polyacrylate is Aron T-40 (Toagosei Co., Ltd.) and phosphoric acid. MS-4600 (manufactured by Nippon Food Processing Co., Ltd.) was used as the esterified starch. The master color is filtered through a metal net having an opening of 50 μm, and is divided into small portions. Each master color is coated with a copolymer latex at a ratio of 12 parts by mass per 100 parts by mass of pigment, and a final solid content of 64. Water was added and mixed so that it might become mass%.
(8) Preparation of coated paper: After coating each coated color on a coated base paper having a basis weight of 74 g / m ^{2 with} a blade coater so that the coated amount is 13 g / m ² on one side, and drying Then, a super calender treatment was performed at a roll temperature of 50 ° C. and a linear pressure of 147000 N / m to obtain a coated paper. The obtained coated paper was used for a printing test.

"Example 1"
The initial polymerization raw material shown in Table 1 and the monomer and chain transfer agent in the first step were placed in a pressure-resistant reaction vessel equipped with a stirrer and a temperature control jacket, and the internal temperature was adjusted to 75 ° C. Polymerization was started by adding 0.8 part by mass of sodium disulfate. After 15 minutes, as a second step, the monomers and chain transfer agent shown in Table 1 were added to the reactor over 3 hours. From 30 minutes after the start of the second step, the aqueous solutions described in “Table 1” were added at a constant rate until the end of the second step. The monomers and chain transfer agents listed in Table 1 were added at a constant rate for 2 hours from the start of the third step. A 15% by mass aqueous solution using the ethylenically unsaturated carboxylic acid shown in Table 1 was continuously added over 1 hour and 30 minutes after 10 minutes from the start of the third step. The temperature was raised to 95 ° C. over 1 hour after the addition of the monomer was completed, and then maintained at 95 ° C. for 40 minutes to obtain a copolymer latex. The obtained latex was filtered through a 200 mesh wire mesh, and the pH was adjusted to 7.5 by adding an aqueous sodium hydroxide solution to the copolymer latex. Unreacted monomers were removed by a steam stripping method, and after further concentration, an aqueous sodium hydroxide solution was added, and the copolymer latex was finally adjusted to a solid content concentration of 50% and pH 8. The obtained copolymer latex was designated as Latex A.

"Examples 2, 3, 5, 6"
Polymerization was carried out in the same manner as in Example 1 except for the matters described in “Table 1” to obtain latexes B, C, E and F.

Example 4
Until the start of the third step, the polymerization was carried out in the same manner as in Example 1 except for the items described in “Table 1”, and the monomers described in “Table 1” at a constant rate for 1 hour after the start of the third step. And chain transfer agent was added. A 15% by mass aqueous solution using the ethylenically unsaturated carboxylic acid shown in Table 1 was continuously added over 1 hour from 30 minutes after the start of the third step. Then, the monomer and chain transfer agent of Table 1 were added over 30 minutes as a 4th process. The temperature was raised to 95 ° C. over 1 hour to 1 hour after completion of the monomer addition in the fourth step, and maintained at 95 ° C. for 40 minutes to obtain a copolymer latex. The obtained copolymer latex was treated in the same manner as in Example 1 to obtain latex D.
As is clear from the descriptions in “Table 1” and “Table 3”, the copolymer latex corresponding to the constituent requirements of the present invention has a particle size of less than 100 nm, and the obtained copolymer latex It has excellent stickiness when wet. Furthermore, when the copolymer latex of the present invention was used, the pick strength, wet pick strength, and inking of the coated paper were all at a high level.

"Comparative Examples 1-5"
Polymerization was carried out in the same manner as in Example 1 except for the matters described in “Table 2” to obtain G, H, I, J, K, and L. “Table 2” describes the results of those outside the scope of the copolymer latex of the present invention. As is clear from the description of “Table 3”, Comparative Example 1 is the second. The monomer / water ratio at the start of the process is outside the range of the present invention, the particle size is increased, and the pick strength / wet pick strength of the coated paper is low. In Comparative Example 2, the emulsifier amount was outside the range of the present invention, and the emulsifier amount was too large, resulting in a decrease in the inking property. Further, since the amount of the emulsifier is excessive, the particles are enlarged and coarse particles are generated, so that the number average molecular weight is increased and pick strength / wet pick strength is lowered. In Comparative Examples 5 and 6, the amount of the emulsifier was outside the range of the present invention, and the particle size was enlarged and the pick strength / wet pick strength of the coated paper was lowered. In Comparative Example 3, the amount of conjugated diene monomer was out of the range, and the pick strength and wet pick strength of the coated paper were low. In Comparative Example 4, the amount of the ethylenically unsaturated carboxylic acid was outside the range of the present invention, and the operability of the copolymer latex and the pick strength of the coated paper were low.

  The copolymer latex obtained by the present invention is used in pigment binders, carpet backing agents, adhesives, fiber binders and paints in paper coating. More specifically, the copolymer latex obtained in the present invention is excellent in operability related to suitability for backing roll stains among the operability in the paper coating process, and has high pick strength, wet pick strength, and wearability. In order to give the coated paper which has, it is used suitably in the field of the coated paper for printing.

Claims (4)

Copolymerized with (a) 20-80% by mass of conjugated diene monomer, (b) 0.5-10% by mass of ethylenically unsaturated carboxylic acid monomer, and (c) (a), (b) 100 parts by weight of a monomer composed of 10 to 79.5% by weight of another possible monomer (where (a) + (b) + (c) = 100% by weight) is used as the emulsifier (i) alkyl. When performing emulsion polymerization using 0.1 to 2 parts by mass of diphenyl ether disulfonate and 0.01 to 0.29 parts by mass of (ro) alkylbenzenesulfonate,
First step: 3) to 30 parts by mass of at least one monomer selected from (a) a conjugated diene monomer and (c) another copolymerizable monomer is (b) an alkylbenzene sulfonate Step 2 for performing polymerization using 50% by mass or more: Step 3 for polymerizing 10 to 67 parts by mass of at least one monomer selected from (a) and (c) Third and subsequent steps: Remaining single amount The emulsion polymerization is performed by dividing into at least three steps of the step of polymerizing the body, and the mass ratio of (1) monomer / (2) water added to the polymerization system by the end of the second step is 0.2. A method for producing a copolymer latex, characterized in that a copolymer latex having a number average particle diameter of 100 nm or less is obtained.   The proportion of (a) conjugated diene monomer in the monomer used in the third step and after is greater than the proportion of (a) conjugated diene monomer in the monomer used up to the second step. 2. The method for producing a copolymer latex according to claim 1, wherein the copolymer latex is small.   A copolymer latex obtained by the production method according to claim 1 or 2.   A paper coating composition comprising the copolymer latex according to claim 3.