JP2007131964A - Copolymer latex composition, coating composition for coating printing paper, and coated paper for printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a latex composition having high pick strength and the like, wet stickiness resistance, an effect of suppressing backing roll dirt, and high productivity.
SOLUTION: A latex composition for coated paper comprising a solid phase part mainly containing latex and an aqueous phase part mainly containing a dispersant, the latex comprising a conjugated diene monomer and a dibasic ethylene A monomer composition containing a specific amount of an ethylenically unsaturated carboxylic acid monomer containing an unsaturated carboxylic acid monomer, a vinyl cyanide monomer, and another copolymerizable monomer, respectively. The emulsion is polymerized through at least a two-stage polymerization step, and the dispersant is at least one of polyacrylic acid and its metal salt, pyrophosphoric acid and its metal salt, hexametaphosphoric acid and its metal salt, and a solid surface carboxylic acid The amount and the amount of carboxylic acid in water in the aqueous phase are in a specific range.
[Selection figure] No selection figure

Description

  The present invention relates to a copolymer latex composition used as a pigment binder in paper coating, a composition for printing coated paper using the copolymer latex composition, and a coating treatment for the composition for printing coated paper. It relates to a coated paper for printing. More specifically, a copolymer latex composition having high adhesive strength (pick strength and wet pick strength), printability on actual machines, coating operability, and excellent productivity, and composition for printing coated paper And a coated paper for printing on which the composition for printed coated paper is coated.

  Copolymer latexes and compositions thereof have been used in a wide range of applications such as pigment binders in paper coating, carpet backing agents, various adhesives and tackifiers, fiber binders and paints. The copolymer latex and the composition thereof used for these applications are required to have excellent adhesion to a substrate and a pigment to be blended.

  Coated paper is used to improve the smoothness of the surface of the paper and improve the gloss and printability. The base paper is composed of inorganic pigments such as kaolin clay, calcium carbonate, satin white, talc, titanium oxide, and plastic pigments. These organic pigments are applied, and diene copolymer latex is generally used as a binder for these pigments. It is known that the properties of the copolymer latex used as a pigment binder have a great influence on the surface strength of coated paper using this.

  In recent years, with the increasing demand for color-printed magazines, pamphlets, advertisements, etc., the printing speed has been increased, especially resistance to the destruction of the paper surface due to ink tack (so-called pick strength and wetness). Improvements in pick strength have become more demanding than ever before. In addition, due to the increase in printing speed, foreign matter such as paper dust accumulates on the rolls of the printing press, and the occurrence of adverse effects (so-called piling trouble) that deteriorates the quality of printed matter is also a problem to be solved. In addition, reducing the cost of products is one of the main challenges for paper manufacturers that produce coated paper, and it is required to reduce the proportion of copolymer latex used. Improvement of adhesive strength (pick strength and wet pick strength) is desired.

  On the other hand, in the production of coated paper, the coating speed has been increased to improve the production capacity and productivity, and again, the quality requirements for copolymer latex, which affects the coating operability, are increasing. Yes. In the production of coated paper, the coating liquid containing the copolymer latex as the main binder described above is applied to the base paper by the flooded nip roll or jet fountain method, and the excess coating liquid is scraped off by a blade or the like. It is common practice to take, apply a predetermined amount of coating liquid and dry. Coated paper is often printed on both the front and back sides. For this reason, in coated paper production, after coating and drying on one side (front side) of the base paper, the other side (back side) is processed in the same way. Is done.

  When weighing with this blade, the coated paper receives a high shear and pressure between the blade and the backing roll, and the surface layer of the coating layer on the front surface is transferred to the backing roll, especially during backside coating. Roll stains may occur, and if the occurrence of stains becomes significant, it becomes necessary to perform roll cleaning by cutting out of the base paper or frequent polishing, and productivity is lowered. In order to improve the coating operability, it is useful to reduce the tackiness of the copolymer latex in order to reduce the transfer to the roll. That is, it is effective to reduce the wet stickiness resistance of the copolymer latex.

  For manufacturers that produce copolymer latex commercially, improving product productivity is a major issue. Generally, during the production of copolymer latex, due to the fact that dispersion stability is impaired by mechanical shearing force, etc., a part of the copolymer aggregates to generate a coagulum, which needs to be removed. Yes, this is done by filtering the copolymer latex. It is effective to improve productivity by shortening the time required for the filtration.

  Various improvements have been made to the copolymer latex for the purpose of improving the quality of the coated paper as described above, solving operational problems in the production of the coated paper, and improving the productivity of the copolymer latex. For example, for the purpose of improving the pick strength, there is a method of increasing the composition ratio of the conjugated diene monomer to lower the glass transition temperature of the copolymer. However, this method still has a problem that the glossiness of the white paper is lowered and the wet stickiness resistance is lowered.

  In addition, for example, many improvements of copolymer latexes in which polymerization is performed in a two-stage or multi-stage with a specific monomer composition have been proposed (Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document). 5, Patent Document 6, Patent Document 7). However, these inventions are insufficient as means for achieving both improvement in pick strength and wet pick strength of coated paper and improvement in backing roll dirt characteristics. In these inventions, it is impossible to raise the suitability of the coated paper to a sufficient level, and it does not have an effect of improving the productivity of the copolymer latex.

Further, as a technique for preventing a piling trouble, a method of using a styrene butadiene copolymer latex having a high methyl methacrylate content for cast coated paper is disclosed (Patent Document 8). Also, a copolymer latex having a glass transition temperature in a specific range obtained in the presence of a specific compound is disclosed for an undercoat for a heat-sensitive recording material (Patent Document 9). However, neither invention can solve the above-mentioned problems.
Further, in order to improve the productivity of the copolymer latex, a method for reducing the amount of coagulum generated in the polymerization process is disclosed from the viewpoint of shortening the time required for filtration of the copolymer latex (Patent Document). 10, Patent Document 11). However, in practice, it is impossible to significantly improve (shorten) the time required for filtration simply by reducing the amount of coagulum, and copolymer latex can be applied to paper-coated paper without filtration. Even if the amount of coagulum is very small, there is a concern that streaks and scratches may be generated on the coated paper in the coated paper manufacturing process, so that it is practically impossible. Therefore, an improvement in shortening the time required for filtration from a viewpoint different from the prior art is desired.
Japanese Examined Patent Publication No. 62-58371 Japanese Patent Publication No.62-31116 Japanese Patent Publication No. 64-2716 Japanese Patent Publication No. 60-19927 JP-A-4-41502 JP-A-5-272094 JP-A-7-247327 JP-A-5-239799 JP 2005-103941 A JP-A-5-9336 JP 2000-262877 A

  From the above situation, the present invention improves the pick strength and wet pick strength of the coated paper, improves the pileability at the time of printing, and further has an excellent resistance to wet stickiness and has an effect of suppressing backing roll stains. Another object of the present invention is to provide a copolymer latex composition having high product productivity. Preferably, it aims at providing the coating composition for printing paper coating which uses this copolymer latex composition, and the coating paper for printing.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has limited the monomer composition as a starting material to a specific range and performs a multistage polymerization method on a copolymer latex, and performs a specific dispersion. As a result of diligent investigation, focusing on the distribution of the copolymer latex particles to the surface layer of the copolymer latex particles and the aqueous phase of the copolymer latex composition with respect to the ethylenically unsaturated carboxylic acid, The present invention has been reached.

That is, the present invention is as follows.
[1] A copolymer latex composition for coated paper comprising a solid phase portion mainly containing a copolymer latex (α) and an aqueous phase portion containing a dispersant (β), wherein the copolymer latex ( α) is (a) 25 to 60% by mass of a conjugated diene monomer, and (b) an ethylenically unsaturated carboxylic acid monomer 1.5 to 7 containing a dibasic ethylenically unsaturated carboxylic acid monomer. % By weight, (c) 10-30% by weight of vinyl cyanide monomer, and (d) 3-63.5% by weight of other copolymerizable monomers (provided that (a) + (b) + (c) + (D) = 100 mass%) is obtained by emulsion polymerization through at least a two-stage polymerization step, and the dispersant (β) is polyacrylic acid and a metal salt thereof. , Pyrophosphoric acid and its metal salt, hexametaphosphoric acid and its metal salt And the amount of surface carboxylic acid (X) in the solid phase portion and the amount of carboxylic acid in water (Y) in the aqueous phase portion satisfy the following formula (1): A copolymer latex composition.

0.3 <(X) / ((X) + (Y)) <0.7 (1)
[2] The copolymer latex (α) is obtained by polymerizing at least 60% by mass or more of the dibasic ethylenically unsaturated carboxylic acid in the second and subsequent stages of the polymerization step. The copolymer latex composition for coated paper as described in [1] above, which is obtained by starting addition at a time when the rate is in the range of 65 to 95% by mass.
[3] The copolymer latex (α) is a monomer mixture used in each polymerization stage of the at least two-stage polymerization process (however, the dibasic ethylenically unsaturated group used in the second polymerization stage and thereafter). The solubility parameter (SP value) of the copolymer obtained from (excluding the carboxylic acid monomer) has an increment in the immediately subsequent polymerization stage with respect to the value in the previous polymerization stage of 0.01 to 0.8. Copolymer latex composition for coated paper as described in [1] or [2] above.
[4] A coating composition for coating a printing paper containing the copolymer latex composition according to any one of [1] to [3].
[5] A printing paper having a surface coated with the printing paper coating composition according to [4].

  According to the copolymer latex composition of the present invention, it is possible to achieve both improvement in pick strength and wet pick strength of coated paper and improvement in wet stickiness resistance. As a result, the operability in the coating process using a coating composition for coating a printing paper containing a copolymer latex, particularly a backing roll stain trouble can be suppressed, and the pick strength and excellent printing coating paper Wet pick strength can be imparted and piling troubles during printing can be prevented. Furthermore, extremely high product productivity can be realized in the production of the copolymer latex composition.

  Hereinafter, the present invention will be specifically described with a focus on preferred embodiments. The copolymer latex composition for coated paper of the present invention comprises a solid phase portion mainly containing a copolymer latex (α) and an aqueous phase portion containing a dispersant (β). Here, the solid phase portion refers to a portion that is water-dispersible and settles by a centrifugation method described later. Here, mainly containing the copolymer latex means that 50% by mass or more of components other than water in the solid phase portion (hereinafter sometimes referred to as solid phase components) is the above-mentioned monomers (a) to (d). ) As a starting material.

  The aqueous phase portion refers to a portion of an aqueous solution that does not settle by the centrifugal separation method described later. The aqueous phase part contains a dispersing agent (β) and other low molecular weight components such as an unreacted monomer, a water-soluble oligomer, and an emulsifier that does not bind to or adsorb to the copolymer particles.

  First, the copolymer latex (α), which is the main component constituting the copolymer latex composition, will be described. The copolymer latex (α) comprises (a) 25 to 60% by mass of a conjugated diene monomer, and (b) an ethylenically unsaturated carboxylic acid monomer containing a dibasic ethylenically unsaturated carboxylic acid monomer. 1.5-7% by mass, (c) 10-30% by mass of vinyl cyanide monomer, and (d) 3-63.5% by mass of other copolymerizable monomers (provided that (a) + (b ) + (C) + (d) = 100% by mass) is obtained by emulsion polymerization through at least two stages of polymerization. Hereinafter, these will be sequentially described.

  (A) Conjugated diene monomer, which is one of the raw materials for copolymer latex (α), is an essential component for imparting flexibility to the copolymer and providing pick strength and impact absorption. When the total monomer constituting the copolymer is 100% by mass, it is used in a proportion of 25 to 60% by mass, preferably 30 to 55% by mass, and most preferably 32 to 50% by mass. By setting the amount of the monomer used within the above range, the copolymer can be imparted with appropriate flexibility and elasticity to improve the pick strength and further improve the wet stickiness resistance. 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. .

  One of the raw materials, (b) an ethylenically unsaturated carboxylic acid monomer whose essential component is a dibasic ethylenically unsaturated carboxylic acid monomer, has the dispersion stability required for the copolymer latex. It is an essential component for increasing the pick strength. When the total monomer constituting the copolymer is 100% by mass, it is 1.5 to 7% by mass, preferably 2 to It is used in a proportion of 6% by mass, more preferably 2.5-5% by mass. By setting the amount of this monomer to be within the above range, it becomes possible to keep the wet-sticking resistance of the copolymer latex and its composition good (not sticky), and various problems in the coating process. Occurrence can be avoided. It is also possible to adjust the viscosity of the copolymer latex composition to an appropriate range that does not hinder handling.

  Preferred examples of the ethylenically unsaturated carboxylic acid monomer include monobasic ethylene unsaturated carboxylic acid monomers such as acrylic acid and methacrylic acid, dibasic ethylene series such as itaconic acid, maleic acid, and fumaric acid. An unsaturated carboxylic acid monomer etc. are mention | raise | lifted and these are used 1 type or in combination of 2 or more types.

  What is important here is that a dibasic ethylenically unsaturated carboxylic acid monomer is used as an essential component, and it may be used in combination with a monobasic ethylenically unsaturated carboxylic acid monomer. Although not more than 40% by mass, preferably 50% by mass or more, and most preferably 55% by mass or more of the dibasic ethylenically unsaturated carboxylic acid, based on the total mass of the ethylenically unsaturated carboxylic acid monomer used. It is a monomer. By setting the use ratio of the dibasic ethylenically unsaturated carboxylic acid monomer within this range, it becomes possible to adjust the wet stickiness resistance to a good level.

  In addition, (c) vinyl cyanide monomer, which is one of the raw materials, is an essential component for improving wet stickiness resistance, and when the total monomer constituting the copolymer is 100% by mass , 10 to 30% by mass, preferably 13 to 25% by mass, and more preferably 15 to 22% by mass with respect to the total monomers. By setting the amount of the monomer used within the above range, the effect of improving the wet stickiness resistance is obtained, and the polymerization stability of the copolymer latex is not lowered. Preferable examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile and the like, and these are used alone or in combination of two or more.

  Further, as other raw materials, (d) other monomers copolymerizable with the above monomers are included. Various properties can be imparted to the copolymer latex and the composition thereof by appropriately selecting other copolymerizable monomers. Preferred examples of other copolymerizable monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, and p-methylstyrene, methyl acrylate, ethyl acrylate, butyl acrylate, Acrylic acid alkyl esters such as 2-ethylhexyl acrylate, alkyl methacrylates such as methyl methacrylate and butyl methacrylate, hydroxyalkyl esters such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate, acrylic acid Aminoalkyl esters such as aminoethyl, dimethylaminoethyl acrylate and diethylaminoethyl acrylate; pyridines such as 2-vinylpyridine and 4-vinylpyridine; glycidyl esters such as glycidyl acrylate and glycidyl methacrylate Amides such as acrylamide, acrylamide, methacrylamide, N-methylol acrylamide, N-methyl acrylamide, N-methyl methacrylamide, glycidyl methacrylamide, N, N-butoxymethyl acrylamide, vinyl acetates such as vinyl acetate, Examples thereof include vinyl halides such as vinyl chloride, p-styrenesulfonic acid and its sodium salt, and these may be used alone or in combination.

  This (d) copolymerizable monomer is preferably 3 to 63.5% by mass, preferably 100% by mass based on the total amount of monomers constituting the copolymer latex (α). Is used in a proportion of 23 to 50.5% by mass. By using this monomer in the above range, suitable adhesive strength is exhibited.

  The method for producing the copolymer latex (α) is carried out using an emulsion polymerization method apparatus that has been used commercially in the past. However, a multi-stage polymerization method including at least a two-stage polymerization step should be employed. Is necessary, thereby achieving the intended task. The multi-stage polymerization method is, for example, a monomer mixture prepared by preparing a plurality of monomer mixtures having different compositions and adding them to the system as the polymerization reaction proceeds, as disclosed in JP-A-2002-226524. Is a polymerization method in which the composition is changed during the polymerization reaction.

  In order to obtain the copolymer latex (α), the composition of the monomer mixture in each polymerization stage is important in carrying out the multistage polymerization. When arranged from the viewpoint of time series in the polymerization reaction, the first process is the first polymerization stage, the subsequent process is the second polymerization stage, and the subsequent third polymerization stage may be present. As for the glass transition temperature of the copolymer obtained from the monomer mixture in each polymerization stage, it is desirable that the composition of the monomer mixture is such that a higher Tg is obtained in the subsequent polymerization stage. The mass ratio of the amount of the monomer mixture used in the first polymerization stage and the total amount of the monomer mixture used in each polymerization stage after the second polymerization stage falls within the range of 40:60 to 80:20. It is preferable that it falls within the range of 45:55 to 65:35. By entering this range, it is possible to improve the pick strength / wet pick strength and wet stickiness resistance of the copolymer latex (α) and its composition. The most preferred range is in the range of 55:45 to 62:38.

  The solubility parameter (SP value) of the copolymer obtained from the monomer mixture used in each polymerization stage (excluding the dibasic ethylenically unsaturated carboxylic acid monomer used in the second polymerization stage and thereafter) ) With respect to the SP value of the copolymer obtained from the monomer mixture composition used in a certain polymerization stage, the copolymer obtained from the monomer mixture composition used in the polymerization stage immediately after that polymerization stage. It is preferable that the monomer mixture composition of each polymerization polymerization stage is adjusted so that the SP value increment (hereinafter referred to as ΔSP value) falls within the range of 0.01 to 0.8. That is, it is preferable that the SP values of the adjacent polymerization stages have this difference. When this ΔSP value falls within the range of 0.01 or more and 0.8 or less, the copolymer latex (α) and the composition excellent in all of wet stickiness resistance, pick strength, wet pick strength and piling aptitude are obtained. can get. A more preferable range of the ΔSP value is 0.1 or more and 0.6 or less, and a more preferable range is 0.2 or more and 0.5 or less. The SP value of each polymerization stage can be adjusted by the type and amount of monomers constituting the monomer mixture. In particular, (a) a conjugated diene monomer having a low SP value, and an SP value. (C) The amount of vinyl cyanide monomer used is a significant factor.

  Furthermore, it is preferable to limit the method of using the carboxylic acid under certain specific conditions. As mentioned above, it is an essential condition to use a dibasic ethylenically unsaturated carboxylic acid monomer as a starting material. Thus, the ratio between the amount present in the system and the amount post-added into the system after the start of polymerization and the timing of post-addition into the system are important.

  That is, at least 60% by mass or more of the amount of the dibasic ethylenically unsaturated carboxylic acid monomer is such that the polymerization conversion rate of the monomer added to the system after the second polymerization stage and before that point is 65%. It is preferable to start the post-addition into the system from any point in the range of ~ 95% by mass, and when this condition is satisfied, the obtained copolymer latex (α) and its composition are good. A coating composition for coating a printing paper, which has wet stickiness resistance and uses this copolymer latex composition, has good coating operability. In addition, it is possible to simultaneously increase the reaction conversion rate of the dibasic ethylenically unsaturated carboxylic acid monomer to an appropriate range. A more preferable range of the amount ratio of the dibasic ethylenically unsaturated carboxylic acid monomer added later in the system is 80% by mass or more, and most preferably 90% by mass or more. The amount of the dibasic ethylenically unsaturated carboxylic acid monomer used in this step may be in the range of 1.5 to 3.5 parts by mass when the total monomer used is 100 parts by mass. preferable. Since the ratio and amount of the dibasic ethylenically unsaturated carboxylic acid monomer added later in the system are within this range, the copolymer latex (α) and the composition thereof have high wet-sticking resistance. Have.

  The post-addition start timing of the post-added dibasic ethylenically unsaturated carboxylic acid monomer into the system is such that the polymerization conversion rate of other monomers added to the system up to that point is 70 to 90 It is more preferable to start post-addition into the system from the point of mass%.

  Examples of the dibasic ethylenically unsaturated carboxylic acid monomer to be added later in the system include itaconic acid and fumaric acid. The copolymer latex (α) and its composition picked are obtained. Itaconic acid is most preferable from the viewpoints of strength and wet pick strength and ease of handling. The addition method of the dibasic ethylenically unsaturated carboxylic acid monomer to be added later is a method of mixing in a monomer mixture after the second polymerization stage (emulsified in advance if necessary), single amount In addition to the body mixture, there is a method of adding it alone into the system, etc., but in order to make the resulting copolymer latex (α) and the composition its wet stickiness resistance good, or other In order to start addition from the point of time when the polymerization conversion rate of the monomer becomes appropriate, the dibasic ethylenically unsaturated carboxylic acid monomer is made into an aqueous solution alone and separately from other monomer mixtures. It is preferable to add to the system. The aqueous solution concentration of the dibasic ethylenically unsaturated carboxylic acid monomer to be added later is preferably in the range of 5 to 30% by mass, and preferably in the range of 10 to 20% by mass, considering the efficiency in mass production facilities. In order to suppress the alteration and polymerization of the dibasic ethylenically unsaturated carboxylic acid monomer before being added to the system, and to stabilize the temperature in the system after being added to the system, The temperature of the aqueous solution is preferably 30 to 80 ° C, preferably 40 to 65 ° C.

  The time required for the addition of the dibasic ethylenically unsaturated carboxylic acid monomer to be added later to the system is preferably 45 to 120 minutes from the start of the post-addition, and the entire amount is preferably added to the system. By adding it to the system over time, the resulting copolymer latex (α) and the composition thereof are excellent in wet stickiness resistance.

  In producing the copolymer latex (α), there is no particular limitation except for the specific method described above, and a method such as polymerization using a radical initiator in the presence of a surfactant in an aqueous medium is used. Can do.

  There is no restriction | limiting in particular also about the emulsifier to use, A conventionally well-known anion, a cation, an amphoteric, and a nonionic surfactant can be used. Examples of preferred surfactants include anionic surfactants such as aliphatic soaps, rosin acid soaps, alkyl sulfonates, alkyl sulfosuccinates, polyoxyethylene alkyl sulfates, polyoxyethylene alkyl ethers, polyoxyethylenes Nonionic surfactants such as alkyl allyl ether and polyoxyethylene oxypropylene block copolymer are listed, and these are used alone or in combination of two or more. The amount of the surfactant used is preferably 0.3 to 2.0 parts by mass per 100 parts by mass of the monomer.

  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, and the like. Specifically, potassium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2 -Azobisbutyronitrile, cumene hydroperoxide, etc. are mention | raise | lifted and these can be used individually or in combination of 2 or more types. Further, a so-called redox polymerization method in which a reducing agent such as acidic sodium sulfite, 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.

  When the copolymer latex (α) is produced, 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-lauryl mercaptan, which is one of dimers of nucleus-substituted α-methylstyrene. Examples include mercaptans, disulfides such as tetramethylthiudium disulfide and tetraethylthuradium disulfide, halogenated derivatives such as carbon tetrachloride and carbon tetrabromide, and 2-ethylhexyl thioglycolate. These may be used alone or in combination. Can be used in combination. The addition method of the chain transfer agent is not particularly limited, and known addition methods such as batch addition, batch addition, and continuous addition are used.

  The polymerization temperature for producing the copolymer latex (α) is not particularly limited, and it is generally performed in the range of 40 to 100 ° C., but the production efficiency and the obtained copolymer latex (α ) And the quality of the composition, such as pick strength, the temperature is preferably in the range of 55 to 85 ° C., more preferably 60 to 80 ° C. in the period from the start of polymerization to the end of addition of the monomer mixture. Range. It is also possible to provide a method of raising the polymerization temperature (so-called cooking process) in order to increase the polymerization conversion rate of each monomer after the addition of all the monomers in the polymerization system. Is preferably in the range of 80 to 100 ° C.

  In the case of producing the copolymer latex (α), the polymerization solid content concentration is 35 to 60% by mass, more preferably 40 to 50% by mass, from the viewpoint of production efficiency and particle size control during emulsion polymerization. The solid content concentration mentioned here refers to the ratio of the solid content mass obtained by drying to the original copolymer latex mass.

  Regarding the method for producing the copolymer latex (α), there is no particular limitation on the means for adding the monomer mixture of each polymerization stage in the emulsion polymerization system. A method in which a part of the monomer mixture is charged into the emulsion polymerization system in advance and polymerized, and then the remaining monomer mixture is charged continuously or intermittently, or the monomer mixture is added from the beginning of each polymerization stage. A method of charging continuously or intermittently may be adopted, and polymerization may be performed by combining these polymerization methods. However, in terms of removal of heat of polymerization generated on a commercial production basis, product productivity is considered. In such a case, a method of continuously adding it to the system particularly after the second polymerization stage is preferable.

  In the production of the copolymer latex (α), it is possible to use a known seed polymerization method for adjusting the particle diameter, and after preparing the seed, the internal seed is polymerized in the same reaction system. A method such as an external seed method using a seed or a separately prepared seed can be appropriately selected and used.

  The glass transition temperature (Tg) of the copolymer latex (α) obtained as described above is not particularly limited, but the pick strength / wet pick strength in coated paper applications and the wet stickiness of the latex are not limited. From the viewpoint of achieving compatibility, it is preferably −20 ° C. to + 40 ° C., more preferably −15 ° C. to + 35 ° C., and still more preferably −10 to + 30 ° C. Tg is not limited to only one point in one type of copolymer latex, and may have a plurality of Tg.

  Moreover, it is preferable that the particle diameter of copolymer latex ((alpha)) is 50-150 nm. More preferably, it is in the range of 60 to 110 nm. By setting the particle diameter within this range, the viscosity of the latex can be adjusted to a suitable range, and workability is not lowered. Furthermore, it is possible to suppress a decrease in pick strength / wet pick strength and an increase in paint viscosity.

  Moreover, it is preferable that the gel fraction (toluene insoluble content) of copolymer latex ((alpha)) exists in 70-98 mass%, More preferably, it is 80-97 mass%, Most preferably, it is the range of 88-96 mass%. It is to be. By adjusting the gel fraction within this range, it is possible to simultaneously improve the wet stickiness resistance of the copolymer latex and its composition and the pick strength of the coated paper.

  Next, the dispersant (β), which is the second component constituting the copolymer latex composition, will be specifically described. As the dispersant (β), it is necessary to use at least one selected from the group consisting of polyacrylic acid and its metal salt, pyrophosphoric acid and its metal salt, hexametaphosphoric acid and its metal salt. By using such a specific dispersant (β), it becomes possible to improve the wet stickiness resistance of the copolymer latex composition and to shorten the time required for filtration of the copolymer latex composition. . Among these, polyacrylic acid and its metal salt are preferable, and the most preferable is sodium polyacrylate. When sodium polyacrylate is used, it is desirable to use one having an average molecular weight of about 1000 to 10,000. Moreover, as addition amount of a dispersing agent ((beta)), it is 0.2-3 mass parts per 100 mass parts of solid content of copolymer latex ((alpha)), wet stickiness resistance, wet pick strength improvement, From the viewpoint of shortening the time required for filtration. The most preferable range is 0.4 to 1.5 parts by mass.

The copolymer latex composition needs to satisfy specific conditions with respect to the site where the ethylenically unsaturated carboxylic acid monomer is present. Is the ethylenically unsaturated carboxylic acid used herein included in various additives such as those used directly as raw materials for producing the copolymer latex, those produced as a by-product of the reaction, and dispersants? Or what is produced | generated by reaction from this is included. Regarding these ethylenically unsaturated carboxylic acid monomers, the amount present in the copolymer latex composition bonded to the particle surface of the copolymer latex, that is, the amount of surface carboxylic acid (X), and the copolymer latex It is necessary that the ratio of the amount present in the aqueous phase of the composition, ie the amount of carboxylic acid in water (Y), falls within a certain range. That is, it is necessary to satisfy the following formula (1) with respect to (X) and (Y).
0.3 <(X) / ((X) + (Y)) <0.7 (1)

  In addition, the value of (X) and (Y) has shown the acid amount (meq / g) per 1g of solid content of a copolymer latex composition. Here, solid content means the remaining component which removed water and other volatile components from copolymer latex.

  By satisfying the above formula, the copolymer latex composition has good performance in terms of pick strength, wet pick strength, suitability for piling, and wet stickiness resistance, and is used for printing paper coating using the copolymer latex. The coating composition can have good coating operability. Furthermore, the time required for filtration of the copolymer latex composition can be dramatically shortened, and the product productivity is greatly improved. The reason for this is not clear, but the factors are that the viscosity of the copolymer latex composition can be reduced and that the clogging of the pores of various meshes installed in the filtration device is less likely to occur due to the suppression of adhesiveness. .

  The value of (X) / ((X) + (Y)) is preferably in the range of 0.4 to 0.6. The value of (X) / ((X) + (Y)) is the type and amount of the ethylenically unsaturated carboxylic acid monomer used as the raw material of the copolymer latex, the amount of polymerization initiator and the amount of chain transfer agent. It is possible to adjust the polymerization reaction rate appropriately to the desired range by controlling the polymerization reaction rate by adjusting the amount, the method of adding the ethylenically unsaturated carboxylic acid monomer, the type and amount of the dispersant added, and the addition conditions. is there.

  In the copolymer latex composition, various known polymerization regulators can be used 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 the solid content concentration as a final product of a copolymer latex composition, Usually, solid content concentration is diluted or concentrated in the range of 30-60 mass%, and is prepared.

  As long as the effect is not impaired, the copolymer latex composition can be added with various additives as necessary, or can be used by mixing with other latex, for example, besides the dispersant, An antifoaming agent, an anti-aging agent, a water resistant agent, a bactericidal agent, a printing suitability agent, a lubricant, and the like can be added, and an alkali-sensitive latex, an organic pigment, and the like can be mixed and used. Here, when a lubricant composed of a copolymer of fatty acid ester is added, the effect of wet sticking resistance is further enhanced.

  Next, a coating composition for printing paper coating is obtained by using the above-mentioned copolymer latex composition as a binder for coating paper coating. This can be produced in the usual manner. 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 composition together with various additives such as water-soluble polymers such as carboxymethylcellulose, thickeners, dyes, antifoaming agents, preservatives, water-resistant agents, lubricants, printability improvers, and water retention agents And mixing to obtain a uniform dispersion (coating composition for coating printing paper).

  Here, the copolymer latex composition exhibits a particularly remarkable pick strength improvement effect when the pigment constituting the coating composition for paper coating is mainly used with a pigment having a small average particle diameter. . That is, for kaolin clay, the effect is more prominent when a pigment having a particle size of 2 μm or less is 90% by mass or more for calcium carbonate and a pigment having a particle size of 2 μm or less is 90% by mass or more. .

  The use ratio of the pigment and the copolymer latex composition can be appropriately determined depending on the purpose of use of the composition, but 3 to 30 parts by mass of the copolymer latex composition may be used with respect to 100 parts by mass of the pigment. preferable. The printing paper coating composition can be applied to the base paper by an ordinary method using various blade coaters, roll coaters, air knife coaters, bar coaters, etc., but it is preferable to use a blade coater. . 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 composition can be used for both the undercoat pigment composition and the overcoat pigment composition.

  Next, a coating paper for printing can be obtained by coating the surface using the coating composition for coating a printing paper described above. The printing coated paper is preferably used for various printing papers such as offset sheet-fed printing paper, offset rotary printing paper, gravure printing paper, letterpress printing paper, and paperboard, cardboard paper, wrapping paper, and the like. In particular, it is preferably used for offset sheet-fed printing paper and offset rotary printing paper.

  Furthermore, the above-mentioned copolymer latex composition can also be used for paper coating agents, carpet backing agents, other adhesives, and various paints.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to the specific aspect of these Examples.

[Evaluation method of each physical property]
(1) Pick strength:

Using an RI printing tester (Meiji Seisakusho), printing ink (SD Super Deluxe 50 Red B; Tack 18 manufactured by T & K TOKA; Tack 18) (product name) 0.4 cc was printed once, and the picking state appeared on the rubber roll. It 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 surface of the coated paper with a sleeve roll using an RI printing tester (manufactured by Meisei Seisakusho). Immediately after that, printing ink (SD Super Deluxe 50 Red B; Tack 15 manufactured by T & K TOKA) was printed 0.4 cc once. The picking state that appeared on the rubber roll 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.
(3) Piling suitability of coated paper:

Using an RI printing tester (Meiji Seisakusho), 0.4 cc of printing ink (TK High Echo Indigo M) manufactured by Toyo Ink Manufacturing Co., Ltd. was overprinted 20 times, and the picking state that appeared on the rubber roll was lined up on another mount. The state was observed. The evaluation was based on a 10-point evaluation method, and the smaller the picking phenomenon, the higher the score.
(4) Polymerization conversion rate of monomer mixture added in the system:

A sample taken out from the polymerization tank at an arbitrary time of reaction is dried at 130 ° C. for 1 hour in a hot air dryer, and the solid content concentration (%) is determined from the mass before drying and the mass after drying. Next, the polymerization conversion rate is obtained by the following formula (2).
Polymerization conversion rate (%) = 100 × (solid content concentration−nonvolatile content concentration) / volatile content concentration (2)

Here, the non-volatile content concentration is a total value of mass ratios (%) of non-volatile components such as an initiator, an emulsifier, and a carboxylic acid in the monomer mixture added to the reaction system by the time of sampling. The volatile content concentration is a total value of mass ratios (%) of volatile components such as butadiene and styrene in the monomer mixture added to the reaction system by the time of sampling.
(5) Particle diameter of copolymer latex:

Measurement was performed by a dynamic light scattering method using a light scattering photometer (Model 6000, manufactured by CNN Wood) at an initial angle of 45 degrees and a measurement angle of 135 degrees.
(6) The amount of surface carboxylic acid in the solid phase portion of the copolymer latex composition and the amount of carboxylic acid in water in the aqueous phase portion:
-Total amount of total acid amount of solid phase surface of copolymer latex composition and amount of carboxylic acid in water of aqueous phase portion

5 g of a copolymer latex composition having a known solid content concentration is weighed, and distilled water is added to dilute the total amount to 50 g. This diluted copolymer latex composition is set in an automatic titrator (manufactured by Hiranuma Sangyo Co., Ltd .: COM-980), and stirring is started. Then, 1N sulfuric acid is added until the pH of the copolymer latex composition is 2 or less (this operation eliminates the influence of strong acid such as persulfate and reduces the amount of ethylenically unsaturated carboxylic acid only). Can be detected). Then, potentiometric titration was performed using a 0.5N aqueous potassium hydroxide solution, and the potential value was plotted against the titration value. From the titration between the two inflection points, the solid content of the copolymer latex composition per gram of the solid content The acid amount (meq / g) is calculated. Let this value be (Z).
○ Surface carboxylic acid content of solid phase

  First, an operation for removing components (water phase components) other than water contained in the aqueous phase of the copolymer latex composition is performed. An appropriate amount of a copolymer latex composition having a known solid content concentration is weighed, and a 1% aqueous solution of a nonionic surfactant (Nippon Emulsifier Co., Ltd .: New Coal 506) (trade name) is added to the copolymer latex composition. Dilute until the solids concentration of the product is 5%. Centrifugation is performed at 26,000 rpm for 2 hours using a centrifuge (manufactured by Hitachi Koki Co., Ltd .: CR26H) to separate the copolymer latex composition into a particle layer and an aqueous phase. The component which settled by this operation is extract | collected, said nonionic surfactant aqueous solution is added, and it is re-dispersed with a shaker. These centrifugation and redispersion processes are repeated, and the third redispersion is carried out using distilled water instead of a nonionic surfactant aqueous solution. 5 g of ion exchange resin (Mitsubishi Kasei: DIAION SK1B) (trade name) is added to the copolymer latex from which the aqueous phase component has been removed and redispersed, and after stirring for 5 minutes, the ion exchange resin is removed by filtration. To do. This operation (ion exchange resin addition / removal) is repeated until the pH of the copolymer latex does not change, and the above-mentioned centrifugation / redispersion treatment and ion exchange treatment result in the original copolymer latex composition. The aqueous phase component therein is completely removed, and a redispersed copolymer latex is obtained. The solid content concentration of the obtained copolymer latex is measured in advance.

  Subsequently, 15 g of the copolymer latex obtained by the above treatment is weighed and diluted with distilled water so that the total amount becomes 50 g. This is set in an automatic titrator (manufactured by Hiranuma Sangyo Co., Ltd .: COM-980), stirring is started, and conductivity titration is performed using a 0.1 N aqueous potassium hydroxide solution. There is a point where the electric potential starts to increase as the titration amount increases. From the amount of potassium hydroxide aqueous solution added up to this point, the total acid amount is not limited to the carboxylic acid on the surface of the solid phase part of the copolymer latex. This is defined as the amount of acid per 1 g of solid content of the copolymer latex (meq / g), Xa.

  Next, separately from the above measurement, 15 g of copolymer latex having a known solid content concentration obtained by removing the aqueous phase component is weighed, and diluted with distilled water to a total amount of 50 g. This is set in an automatic titrator (manufactured by Hiranuma Sangyo Co., Ltd .: COM-980), stirring is started, and potentiometric titration is performed using a 0.01 N aqueous sodium hydroxide solution. The potential changes according to the amount of sodium hydroxide added, and this inflection point is taken as the end point. From the amount of sodium hydroxide required up to the end point, the amount of strong acid on the surface of the solid phase of the copolymer latex is obtained (meq / g), which is defined as (Xb). This value is an ethylenically unsaturated carboxylic acid. It is not derived from the acid monomer but is based on the persulfate used in the copolymerization.

Accordingly, the surface carboxylic acid amount (X) of the solid phase portion of the copolymer latex is a value obtained by subtracting (Xb) from the above (Xa), and the amount of carboxylic acid in water of the aqueous phase component of the copolymer latex composition. (Y) indicates a value obtained by subtracting (X) from (Z).
(7) Wet stickiness resistance of copolymer latex composition:

A copolymer latex composition was prepared as It applied to the mylar film with 12 wire bars and dried at 130 ° C. for 30 seconds. This film is immersed in water at 30 ° C. for 5 seconds, then superimposed on black lasha paper, passed through a super calender having a temperature of 60 ° 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.
(8) Amount of coagulum in copolymer latex composition:

1000 ml of a copolymer latex composition adjusted to a solid content concentration of 50% is collected and passed through a 200-mesh stainless steel wire mesh whose mass has been measured in advance to separate the coagulum. Next, the wire mesh to which the solidified material is attached is dried at 130 ° C. for 60 minutes to remove volatile components, and the mass is measured again. By subtracting the mass of the wire mesh before the above-mentioned operation from this value, the amount of coagulum (g / L) in the copolymer latex composition can be obtained.
(9) SP value of the copolymer obtained from the monomer mixture in each polymerization stage:

Robert F. Each monomer compound structure and monomer composition were calculated by the method prescribed by Fedors. (Refer to POLYMER ENGINNEERING AND SCIENCE, 1974, Vol. 14, No. 2, 147-154 pages)
(10) Viscosity of copolymer latex composition:

The solid content concentration of the copolymer latex composition was adjusted to 50%, and measured using a B-type viscometer in an environment of 25 ° C.
(11) Final reaction conversion rate of dibasic acid:

The amount of each dibasic acid remaining in the copolymer latex was measured using liquid chromatography and calculated by comparison with the amount used as a raw material.
(12) Time required for filtration of the copolymer latex composition:

First, 30 m ^{3 of a} copolymer latex composition having a solid content concentration adjusted to 50% by mass was prepared. In order to eliminate the influence of the latex temperature, the temperature of the copolymer latex composition used in the test was all adjusted to 28 ° C. As a filtration device, a cylindrical centrifugal separation method filtration device described in JP-A-9-194529 was used in all tests. As in Example 1 of this publication, the filter material used was a material: nylon 66, yarn thickness 50 μm, knitting method: single knitting, and mesh 200 mesh. Also, the rotation shaft angle is fixed at 22 degrees and the rotation speed is fixed at 600 rpm, and the flow rate is adjusted to the maximum amount for each copolymer latex composition so that it does not leak outside without passing through the filter medium. The time required for all of the prepared 30 m ³ copolymer latex composition to pass through the filtration apparatus was measured. The shorter this required time, the higher the product productivity.
[Example 1]

○ Manufacture of copolymer latex A In a pressure-resistant reactor for mass production, equipped with a stirrer, a hot water jacket for adjusting the internal temperature, and a quantitative addition facility for various raw materials, A polymerization initial raw material containing 0.4 parts by mass of sodium dodecylbenzenesulfonate, 0.4 parts by mass of α-methylstyrene dimer, and 0.5 parts by mass of polystyrene latex having an average particle diameter of 20 nm as a seed latex is charged all at once. Stir well at 0 ° C. Next, 13.5 parts by mass of styrene prepared for the first polymerization stage, 29 parts by mass of butadiene, 1.4 parts by mass of methyl methacrylate, 12 parts by mass of acrylonitrile, 0.8 parts by mass of hydroxyethyl acrylate, acrylic acid Of the monomer and chain transfer agent mixture consisting of 0.8 parts by weight, 0.05 parts by weight of t-dodecyl mercaptan, and 0.8 parts by weight of α-methylstyrene dimer, 12% by weight is collectively contained in this pressure resistant reactor. Then, after stirring and mixing, 0.6 parts by mass of a sodium peroxodisulfate aqueous solution having a concentration of 30% by mass (in terms of solid content) was added to the pressure vessel over 5 minutes to initiate the polymerization reaction.

  Ten minutes after the completion of the addition of the sodium peroxodisulfate solution, the remaining monomer and chain transfer agent mixture (corresponding to 88% by mass for the first polymerization stage) for the first polymerization stage are placed in the pressure vessel. The addition was started and added continuously for 3 hours and 20 minutes. Meanwhile, simultaneously with the addition of the remaining monomer and chain transfer agent mixture for the first polymerization stage, 17 parts by mass of water, 0.1 parts by mass of sodium hydroxide, 0.7 parts by mass of sodium dodecyl diphenyl ether disulfonate, and The addition of an aqueous mixture consisting of 0.6 parts by weight of sodium peroxodisulfate was started and continuously added over 3 hours and 10 minutes to accelerate the polymerization reaction.

  When the addition of the monomer and chain transfer agent mixture for the first polymerization stage was completed, the addition of the monomer and chain transfer agent mixture for the second polymerization stage was started immediately. The monomer and chain transfer agent mixture for the second polymerization stage were 11.8 parts by mass of styrene, 15 parts by mass of butadiene, 1.4 parts by mass of methyl methacrylate, 10.3 parts by mass of acrylonitrile, 0. 7 parts by weight, 0.8 parts by weight of acrylic acid, 0.05 parts by weight of t-dodecyl mercaptan, 0.7 parts by weight of α-methylstyrene dimer, and continuously added to this pressure vessel in 2 hours Then, the polymerization reaction was continued.

  After 30 minutes from the start of addition of the monomer and chain transfer agent mixture in the second polymerization stage, a 50 ° C. itaconic acid aqueous solution containing 2.5 parts by mass of itaconic acid and having a solid concentration of 15% by mass to this pressure vessel The whole amount was added over 60 minutes. The polymerization conversion rate of the monomer mixture in the container at the start of the addition of the itaconic acid aqueous solution was 73% by mass.

  After the addition of the monomer mixture in the second polymerization stage, the reaction is continued for 30 minutes while maintaining the temperature in the pressure vessel at 65 ° C., and then the temperature is raised to 95 ° C. over 60 minutes. The polymerization reaction was continued for 30 minutes to increase the polymerization conversion rate of each monomer. The final reaction conversion rate of itaconic acid added later was 97% by mass.

To this copolymer latex, potassium hydroxide and sodium hydroxide are added to adjust the pH to 6.0 or higher, and unreacted monomers are removed by a steam stripping method. Then, sodium hydroxide is used. The pH was adjusted to 8.0, and the solid content concentration was adjusted to 54 mass% using a concentration facility. These production conditions are summarized in Table 1.
-Preparation of copolymer latex composition

To 100 parts by mass of the solid content of this copolymer latex, 1 part by mass of sodium polyacrylate (manufactured by Toa Gosei Co., Ltd., trade name: Aron T-50, having an average molecular weight of 6000) in terms of solid content is added sufficiently. Stir and mix. The temperature of the copolymer latex composition at this time was 30 ° C. Finally, the copolymer latex composition was filtered through the filter with the above-described filtration apparatus and conditions, and the filtration time was measured and used for each physical property evaluation. This copolymer latex composition is designated as Composition A. Table 3 shows the evaluation results of each physical property of the copolymer latex composition A. The filtration time was short, and excellent wet stickiness resistance was obtained.
-Preparation of printing paper coating composition

Next, this copolymer latex composition A and the following constituent materials were used and mixed uniformly to prepare a printing paper coating composition. In addition, the following mixing | blendings (mass part) are the values converted into solid content altogether except water.
Kaolin clay 60 parts by weight Heavy calcium carbonate 40 parts by weight Sodium polyacrylate 0.2 parts by weight Sodium hydroxide 0.1 parts by weight Oxidized starch 2.0 parts by weight Copolymer latex composition A 10 parts by weight Water (Coating Add so that the total solid concentration of the liquid is 66% by mass)

  As kaolin clay, Khao Fine (US, manufactured by THIEL KAOLIN; ratio of particle size of 2 μm or less = 95% by mass or more) (trade name), as heavy calcium carbonate, Carbital 97 (manufactured by ECC; particle size of 2 μm). The following ratio = 97% by mass or more) (trade name), Aron T-50 (made by Toagosei Co., Ltd.) (trade name) as sodium polyacrylate and Mermaid 210 (made by Shikishima Starch) as oxidized starch (product) Name).

Next, the coating composition for printing paper coating thus obtained was applied to a coated base paper having a basis weight of 74 g / m ² with a blade coater so that the coating amount was 13 g / m ² on one side. After drying, a super calender treatment was performed at a roll temperature of 50 ° C. and a linear pressure of 150 kg / cm to obtain a coated paper. The obtained coated paper was used for a printing test. The pick strength of this coated paper was evaluated. The results are shown in Table 3. Excellent pick strength, wet pick strength, and suitability for piling were obtained, and it was possible to achieve both excellent wet stickiness resistance.
[Example 2]
○ Manufacture of copolymer latex

  In the same pressure resistant reactor as in Example 1, 100 parts by weight of water, 0.2 part by weight of sodium dodecylbenzenesulfonate, 0.2 part by weight of sodium dodecyldiphenyl ether disulfonate, and α-methylstyrene dimer 0 as raw materials at the initial stage of polymerization were used. Polymerization initial raw materials containing 4 parts by mass were charged all at once and sufficiently stirred at 70 ° C. Next, 25 parts by mass of styrene prepared for the first polymerization stage, 22.7 parts by mass of butadiene, 1.2 parts by mass of methyl methacrylate, 8 parts by mass of acrylonitrile, 0.6 parts by mass of hydroxyethyl acrylate, t- 15 mass% of the monomer and chain transfer agent mixture consisting of 0.1 part by weight of dodecyl mercaptan and 0.6 part by weight of α-methylstyrene dimer was charged into this pressure-resistant reaction vessel in a lump, and after stirring and mixing, A polymerization reaction was initiated by adding 0.4 parts by mass (in terms of solid content) of an aqueous sodium peroxodisulfate solution having a concentration of 30% by mass to the pressure vessel over 5 minutes. Ten minutes after the end of the addition of the sodium peroxodisulfate aqueous solution, the remaining monomer for the first polymerization stage and the chain transfer agent mixture were added into the pressure vessel and continuously added in 2 hours and 50 minutes. went. On the other hand, from 10 minutes after the start of addition of the remaining monomer and chain transfer agent mixture for the first polymerization stage, 17 parts by mass of water, 0.1 part by mass of sodium hydroxide, sodium dodecyl diphenyl ether disulfonate, 0. The addition of an aqueous mixture composed of 7 parts by mass and 1 part by mass of sodium peroxodisulfate was started and continuously added over 3 hours and 40 minutes to accelerate the polymerization reaction.

  The addition of the monomer and chain transfer agent mixture for the second polymerization stage was started 1 hour after the addition of the monomer and chain transfer agent mixture for the first polymerization stage was completed. In this system, an interval time during which no monomer or chain transfer agent was added was provided in the system between the first polymerization stage and the second polymerization stage to increase the polymerization conversion rate of the first polymerization stage. The monomer and chain transfer agent mixture for the second polymerization stage were 16.8 parts by mass of styrene, 12.8 parts by mass of butadiene, 2 parts by mass of methyl methacrylate, 7 parts by mass of acrylonitrile, 1 part by mass of hydroxyethyl acrylate, It consists of 0.2 parts by mass of t-dodecyl mercaptan, 0.8 parts by mass of α-methylstyrene dimer, and 0.4 parts by mass of acrylic acid. Was continued.

  On the other hand, simultaneously with the start of addition of the monomer and chain transfer agent mixture in the second polymerization stage, an itaconic acid aqueous solution having a solid content concentration of 15% by mass and containing 2.5 parts by mass of itaconic acid is supplied to this pressure vessel. The whole amount was added over 60 minutes. The polymerization conversion rate of the monomer mixture in the container at the start of addition was 78.3 mass%.

  After the addition of the monomer mixture in the second polymerization stage, the temperature in the pressure vessel is raised to 95 ° C. over 60 minutes, and the polymerization reaction is continued for 30 minutes to obtain a polymerization conversion rate of each monomer. Increased. The final reaction conversion of itaconic acid after addition was 98.0%.

To this copolymer latex, potassium hydroxide and sodium hydroxide are added to adjust the pH to 6.0 or higher, and unreacted monomers are removed by a steam stripping method. Then, sodium hydroxide is used. The pH was adjusted to 8.0, and finally the solid content concentration was adjusted to 53% by mass using the concentrator as in Example 1. These production conditions are summarized in Table 1.
-Preparation of copolymer latex composition

  To 100 parts by mass of this copolymer latex, 0.5 parts by mass of sodium polyacrylate (manufactured by Toa Gosei Co., Ltd., trade name: Aron A-210, average molecular weight 2000) is added in terms of solids. The mixture was thoroughly stirred. The liquid temperature of the copolymer latex composition at this time was 40 ° C. Finally, the copolymer latex composition was filtered through the filter with the above-described filtration apparatus and conditions, and the filtration time was measured and used for each physical property evaluation. This copolymer latex composition is designated B. The evaluation results of the physical properties of copolymer latex composition B are shown in Table 3. The filtration time was short, and excellent wet stickiness resistance was obtained.

Next, a printing paper coating composition and coated paper were prepared in the same manner as in Example 1 except that the copolymer latex composition B obtained above was used instead of the copolymer latex composition A. Obtained. The evaluation results are shown in Table 3. Excellent pick strength and wet pick strength were obtained, and it was possible to achieve both excellent wet stickiness resistance.
[Example 3]
○ Manufacture of copolymer latex

  In the same pressure-resistant reaction vessel as in Example 1, 130 parts by weight of water, 0.2 parts by weight of sodium dodecylbenzenesulfonate, 0.4 parts by weight of sodium dodecyldiphenyl ether disulfonate, α-methylstyrene dimer 0. 4 parts by mass, 0.1 part by mass of fumaric acid, and initial polymerization raw material containing 0.5 part by mass of a seed latex of a polystyrene copolymer having an average particle size of 20 nm were charged all at once and sufficiently stirred at 60 ° C. . Next, 24.8 parts by mass of styrene prepared for the first polymerization stage, 19.2 parts by mass of butadiene, 2 parts by mass of methyl methacrylate, 8 parts by mass of acrylonitrile, 2 parts by mass of hydroxyethyl acrylate, t-dodecyl mercaptan 10 mass% of the monomer and chain transfer agent mixture consisting of 0.06 mass part, α-methylstyrene dimer 0.6 mass part and methacrylic acid 1 mass part is charged all at once into the pressure-resistant reaction vessel. After stirring and mixing, 0.6 parts by mass of an aqueous solution of sodium peroxodisulfate adjusted to a concentration of 30% by mass (in terms of solid content) was added to the pressure vessel in 5 minutes to initiate the polymerization reaction. 25 minutes after the completion of the addition of sodium peroxodisulfate, the remaining monomer and chain transfer agent mixture for the first polymerization stage were started to be added to the pressure vessel, and continuously added in 3 hours and 30 minutes. It was. On the other hand, 10 minutes after the start of addition of the remaining monomer for the first polymerization stage and the chain transfer agent mixture, 10 parts by weight of water, 0.7 parts by weight of sodium dodecyl diphenyl ether disulfonate, and sodium peroxodisulfate The addition of an aqueous mixture consisting of 0.4 parts by mass was started and continuously added over 3 hours and 10 minutes to accelerate the polymerization reaction.

  When the addition of the monomer and chain transfer agent mixture for the first polymerization stage is completed, the temperature in the pressure vessel is raised to 65 ° C., and the monomer and chain transfer agent mixture for the second polymerization stage is increased. The addition started. The monomer and chain transfer agent mixture for this second polymerization stage were 20 parts by mass of styrene, 10 parts by mass of butadiene, 1 part by mass of methyl methacrylate, 7 parts by mass of acrylonitrile, 1 part by mass of hydroxyethyl acrylate, 1 methacrylic acid 1 It consists of mass parts, 0.05 parts by mass of t-dodecyl mercaptan, and 0.5 parts by mass of α-methylstyrene dimer. It was continuously added to the pressure vessel in 2 hours and the polymerization reaction was continued.

  On the other hand, about 30 minutes after the start of addition of the monomer and chain transfer agent mixture in the second polymerization stage, an itaconic acid aqueous solution at 55 ° C. having a solid content concentration of 15% by mass containing 2.5 parts by mass of itaconic acid. The addition to the pressure vessel was started and the whole amount was added over 90 minutes. The polymerization conversion rate of the monomer mixture in the container at the start of addition of the itaconic acid aqueous solution was 70.3% by mass.

  After completion of addition of the monomer and chain transfer agent mixture in the second polymerization stage, the polymerization reaction was advanced while maintaining the temperature at 65 ° C., and then the temperature in the pressure vessel was raised to 95 ° C. over 60 minutes. The polymerization reaction was continued for 30 minutes at 95 ° C. to increase the polymerization conversion rate of each monomer. The final reaction conversion of itaconic acid after addition was 97.6%.

To this copolymer latex, potassium hydroxide and sodium hydroxide are added to adjust the pH to 6.0 or higher, and unreacted monomers are removed by a steam stripping method. Then, sodium hydroxide is used. Then, the pH was adjusted to 8.0, and using the same concentration device as in Example 1, the solid content was concentrated to 54%. These production conditions are summarized in Table 1.
-Preparation of copolymer latex composition

  To 100 parts by mass of the solid content of the copolymer latex, 1.5 parts by mass of sodium polyacrylate (manufactured by Toa Gosei Co., Ltd., trade name: Aron T-50, having an average molecular weight of 6000) is added in terms of solid content. The mixture was thoroughly stirred. The liquid temperature of the copolymer latex composition at this time was 50 ° C. Finally, the copolymer latex composition was filtered through the filter with the above-described filtration apparatus and conditions, and the filtration time was measured and used for each physical property evaluation. Let this copolymer latex composition be C. The evaluation results of the physical properties of the copolymer latex composition C are shown in Table 2. The filtration time was short, and particularly excellent wet stickiness resistance was obtained. Table 3 shows the evaluation results of each physical property of the copolymer latex C.

Next, a printing paper coating composition and coated paper were prepared in the same manner as in Example 1 except that the copolymer latex composition C obtained above was used instead of the copolymer latex composition A. Obtained. The evaluation results are shown in Table 3. Excellent pick strength was obtained, and it was possible to achieve both excellent wet stickiness resistance.
[Example 4]
○ Manufacture of copolymer latex

  In the same pressure resistant reactor as in Example 1, initial polymerization raw materials containing 90 parts by mass of water, 0.1 parts by mass of sodium dodecyl diphenyl ether disulfonate, and 0.3 parts by mass of α-methylstyrene dimer as raw materials for the initial stage of polymerization were batched. Then, the mixture was sufficiently stirred at 75 ° C. Subsequently, 16 parts by mass of styrene prepared for the first polymerization stage, 27 parts by mass of butadiene, 6 parts by mass of methyl methacrylate, 8 parts by mass of acrylonitrile, 0.3 part by mass of t-dodecyl mercaptan, α-methylstyrene dimer Of the monomer and chain transfer agent mixture consisting of 0.6 parts by mass, 17% by mass was charged all at once into this pressure-resistant reaction vessel, and after stirring and mixing, an aqueous solution of sodium peroxodisulfate having a concentration of 30% by mass was added. Mass part (solid content conversion) was added in the pressure vessel over 5 minutes to initiate the polymerization reaction. After 10 minutes from the end of the addition of the aqueous sodium peroxodisulfate solution, the remaining monomer for the first polymerization stage and the chain transfer agent mixture were started to be added into the pressure vessel, and continuously added in 3 hours and 20 minutes. went. On the other hand, from 10 minutes after the start of addition of the remaining monomer for the first polymerization stage and the chain transfer agent mixture, 20 parts by mass of water, 0.1 part by mass of sodium hydroxide, sodium dodecyl diphenyl ether disulfonate 0. The addition of an aqueous mixture consisting of 4 parts by mass and 1.1 parts by mass of sodium peroxodisulfate was started and continuously added over 4 hours and 10 minutes to accelerate the polymerization reaction.

  One hour after the addition of the monomer and chain transfer agent mixture for the first polymerization stage was completed, the internal temperature of the pressure-resistant reactor was raised to 80 ° C., and the monomer and chain for the second polymerization stage were increased. The transfer agent mixture addition was started. Also in this system, as in Example 2, an interval time during which no monomer or chain transfer agent was added was provided between the first polymerization stage and the second polymerization stage, and the polymerization conversion rate of the first polymerization stage Increased. The monomer and chain transfer agent mixture for this second polymerization stage were 16 parts by mass of styrene, 14 parts by mass of butadiene, 2 parts by mass of methyl methacrylate, 7 parts by mass of acrylonitrile, 1 part by mass of hydroxyethyl acrylate, t-dodecyl mercaptan. It was composed of 0.2 part by mass and 0.8 part by mass of α-methylstyrene dimer, and was continuously added to the pressure vessel in 2 hours to continue the polymerization reaction.

  On the other hand, simultaneously with the start of addition of the monomer and chain transfer agent mixture in the second polymerization stage, an itaconic acid aqueous solution having a solid content concentration of 15% and containing 3 parts by mass of itaconic acid is added to this pressure vessel. The whole amount was added over 60 minutes. The polymerization conversion rate of the monomer mixture in the container at the start of addition was 85.8% by mass.

  After the addition of the monomer and chain transfer agent mixture in the second polymerization stage, the temperature in the pressure vessel was raised to 95 ° C. over 40 minutes, and the polymerization reaction was continued for 40 minutes to allow each monomer to continue. The polymerization conversion of was increased. The final reaction conversion of itaconic acid after addition was 96.5%.

To this copolymer latex, potassium hydroxide and sodium hydroxide are added to adjust the pH to 6.0 or higher, and unreacted monomers are removed by a steam stripping method. Then, sodium hydroxide is used. Then, the pH was adjusted to 8.0, and finally the solid content concentration was adjusted to 53% by mass using the concentrator as in Example 1.
Preparation of copolymer latex composition To 100 parts by mass of the solid content of this copolymer latex, sodium polyacrylate (made by Toa Gosei Co., Ltd., trade name: Aron T-50, average molecular weight 6000) was converted to solid content. The copolymer latex composition at this time was 40 ° C. Finally, the copolymer latex composition was added to the above-described filtration device and The filter was passed through a filter under the conditions, and the filtration time was measured and used for each physical property evaluation, and this copolymer latex composition was defined as D. The evaluation results of each physical property of the copolymer latex composition D were as follows. The results are shown in Table 3. The filtration time was short, and excellent wet stickiness resistance was obtained.

Next, a printing paper coating composition and coated paper were prepared in the same manner as in Example 1 except that the copolymer latex composition D obtained above was used instead of the copolymer latex composition A. Obtained. The evaluation results are shown in Table 3. Excellent pick strength and wet pick strength were obtained, and it was possible to achieve both excellent wet stickiness resistance.
[Examples 5 to 7]

Raw material composition of each step for producing copolymer latex, polymerization temperature, amount and type of dibasic unsaturated carboxylic acid to be added later, other single amount at the start of dibasic unsaturated carboxylic acid to be added later Copolymer latex composition in the same manner as in Example 4 except that the polymerization conversion rate of the polymer, the type and amount of the dispersant added to the copolymer latex, and the temperature at the time of addition were changed as shown in Table 1. Product E was obtained. Table 3 shows the evaluation results of the physical properties of the copolymer latex composition E and the coated paper using the copolymer latex composition E. Excellent pick strength and wet stickiness resistance were obtained, and filtration time was short. (Example 5). Next, a copolymer latex was produced under exactly the same conditions as in Example 4. As shown in Table 2, sodium hexametaphosphate (HMA) was used as a dispersant at 60 ° C. with respect to 100 parts by mass of the copolymer latex. 2.0 parts by mass (in terms of solid content) was added (manufactured by Taiyo Chemical Co., Ltd.) to obtain a copolymer latex composition F. The evaluation results are shown in Table 4. Excellent pick strength and wet pick strength were obtained. (Example 6). Further, the copolymer latex composition was made in the same manner as in Example 4 except that the use of the dibasic unsaturated carboxylic acid in producing the copolymer latex was changed as shown in Table 2. Product G was obtained. The evaluation results are shown in Table 4. Excellent pick strength, wet pick strength and wet stickiness resistance were exhibited, and the filtration time was short. (Example 7).
[Comparative Example 1]

  As shown in Table 2, with respect to the addition start time of the itaconic acid aqueous solution to be added later in the pressure vessel (polymerization reaction system), the result was changed 60 minutes after the addition start time of the monomer mixture in the second polymerization stage, Except for changing to (X) / ((X) + (Y)) = 0.28, all operations were performed in the same manner as in Example 2 to obtain a copolymer latex composition H. The evaluation results of the physical properties of the copolymer latex composition K are shown in Table 4. The wet stickiness resistance was poor, and it took a long time for filtration.

Next, a printing paper coating composition and coated paper were prepared in the same manner as in Example 1 except that the copolymer latex composition H obtained above was used instead of the copolymer latex composition A. Obtained. The evaluation results are shown in Table 4. The results were inferior in pick strength, wet pick strength and piling aptitude.
[Comparative Example 2]

  As described in Table 2, all the examples except for the change to (X) / ((X) + (Y)) = 0.74 as a result of changing the method of using dibasic ethylenically unsaturated carboxylic acid The same operation as in No. 1 was performed to obtain a copolymer latex composition I. The evaluation results of the physical properties of the copolymer latex composition I are shown in Table 4. The wet stickiness resistance was poor, and it took a long time for filtration.

Next, a printing paper coating composition and coated paper were prepared in the same manner as in Example 1 except that the copolymer latex composition I obtained above was used instead of the copolymer latex composition A. Obtained. The evaluation results are shown in Table 4. The pick strength and wet pick strength were also inferior.
[Comparative Example 3]

  The copolymer latex produced in Example 1 was used as it was without adding a dispersant. At this time, (X) / ((X) + (Y)) = 0.76, resulting in inferior wet-sticking resistance, resulting in an extremely long time for filtration. This is designated as copolymer latex composition J.

  Next, a printing paper coating composition and coated paper were prepared in the same manner as in Example 1 except that the copolymer latex composition J obtained above was used instead of the copolymer latex composition A. Obtained. The evaluation results are shown in Table 4. The pick strength, wet pick strength, and piling aptitude were also inferior.

Claims (5)

A copolymer latex composition for coated paper comprising a solid phase part mainly comprising a copolymer latex (α) and an aqueous phase part containing a dispersant (β),
The copolymer latex (α) comprises (a) 25 to 60% by mass of a conjugated diene monomer, and (b) an ethylenically unsaturated carboxylic acid monomer containing a dibasic ethylenically unsaturated carboxylic acid monomer. 1.5-7% by mass, (c) 10-30% by mass of vinyl cyanide monomer, and (d) 3-63.5% by mass of other copolymerizable monomers (provided that (a) + (b ) + (C) + (d) = 100 mass%) is obtained by emulsion polymerization through at least two polymerization steps,
The dispersant (β) is at least one selected from the group consisting of polyacrylic acid and its metal salt, pyrophosphoric acid and its metal salt, hexametaphosphoric acid and its metal salt,
Furthermore, the amount of surface carboxylic acid (X) in the solid phase portion and the amount of carboxylic acid in water (Y) in the aqueous phase portion satisfy the following formula (1).
0.3 <(X) / ((X) + (Y)) <0.7 (1)   The copolymer latex (α) contains at least 60% by mass or more of the dibasic ethylenically unsaturated carboxylic acid in the second and subsequent stages of the polymerization step, and the polymerization conversion rate of the monomer in the system is 65. The copolymer latex composition for coated paper according to claim 1, wherein the latex composition is obtained by starting addition from the point of time when it is in the range of ˜95 mass%.   The copolymer latex (α) is a monomer mixture used in each polymerization stage of the at least two-stage polymerization process (however, a dibasic ethylenically unsaturated carboxylic acid monomer used in the second polymerization stage and thereafter). The solubility parameter (SP value) of the copolymer obtained from the above (excluding the monomer) has an increase in the immediately subsequent polymerization stage with respect to the value in the previous polymerization stage is 0.01 to 0.8. The copolymer latex composition for coated paper according to claim 1 or 2.   The coating composition for printing paper coating containing the copolymer latex composition in any one of Claims 1-3. A coated paper for printing, wherein the composition for coating a printed paper according to claim 4 is coated on the surface.