JPH10204218A - Copolymer latex and composition for coating paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a copolymer latex capable of improving flowability of a high concentration coating under a high shear rate, improving mechanical stability, highly preventing tackiness, improving coating operability and improving coated paper performances such as adhesive strength, print gloss and rigidity, when especially used for a paper-coating composition, and to obtain the paper-coating composition using the copolymer latex. SOLUTION: This copolymer latex comprises (a) 20-80wt.% of an aliphatic conjugated dienic monomer, (b) 0.5-8wt.% of a water-soluble ethylenic monomer and (c) 20-79.5wt.% of one or more of other vinylic monomers, and has an average particle diameter of 50-150nm, a potassium ion/sodium ion molar ratio of 0-2 and a zeta potential of -80 to -10mV on the surfaces of the particles. The paper-coating composition contains the copolymer latex.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copolymer latex having excellent fluidity and mechanical stability during high-concentration, high-speed coating, and excellent coating paper performance and coating operability. The present invention relates to a used paper coating composition.

[0002]

2. Description of the Related Art With the practical use of neutral papermaking in recent years,
As a composition for paper coating, the coating is highly concentrated due to the use of inexpensive calcium carbonate in large amounts, and in addition to improving the quality of coated paper, speeding up the coater for the purpose of improving productivity,
Attempts are being made to reduce paint costs and drying energy during coating. Reflecting this trend of high-concentration, high-speed coating, the performance requirements for paints are becoming more and more stringent.Today, with the high fluidity of paints, even higher coatings are required for high-speed coating. There is also a need for stability with respect to mechanical operations such as operation with an industrial blade. by the way,
When the concentration of the coating material is increased, the fluidity is generally deteriorated, and under high-speed coating in which a high step speed acts, the fluidity of the coating material is further adversely affected, and problems such as bleeding are likely to occur. Moreover, in the case of paints with poor mechanical stability,
Not only does the backing roll become easily soiled and residue on the blade of the coating blade adheres, the workability during coating is greatly affected, but the quality of the coated paper deteriorates. As a method of improving the fluidity of such a high-concentration paint under a high shear rate (hereinafter, referred to as “high-speed fluidity”), conventionally, with respect to the constituents of the paint, for example, the pigment having a small particle diameter has a small particle size. In addition to reducing the amount of natural water-soluble binders such as casein and starch, which have a large thickening effect, in the case of carboxy-modified latex, which is a synthetic binder, Is a method for improving the polymerization method of the ethylenically unsaturated carboxylic acid, such as making the latex into small particles (for example, JP-A-6-173198, JP-A-7-166495, and JP-A-7-70).
No. 988) has been proposed. However, among these methods, the method of increasing the usage ratio of heavy calcium carbonate or decreasing the usage ratio of natural water-soluble binder leads to a decrease in the rigidity of the coated paper, and the water retention ability and adhesive strength of the paint are also reduced. Be impaired. Further, when the particle size of the carboxy-modified latex is reduced, the high-speed fluidity of the coating material is improved, but the mechanical stability of the latex particles is reduced, causing a problem in suitability for high-speed coating. Further, in order to increase the mechanical stability of the latex, a method of increasing the use ratio of ethylenically unsaturated carboxylic acid or the like in the latex can be considered, but in this case, the viscosity of the coating material increases and the fluidity decreases. Is generated. As described above, it is extremely difficult to satisfy both the high-speed fluidity and the mechanical stability at the same time, and the improvement thereof has been desired. further,
With the application of high-speed coating in the production of coated paper, the improvement of coating operability, especially the improvement of roll fouling, which is a major obstacle, that is, the reduction of the copolymer latex tackiness (improvement of non-stickiness) is also strong. In order to meet such a demand, the present applicant has already reported that the copolymer is -100 to +50.
Water resistance, stiffness, ink drying property, printing gloss, etc., by having at least two glass transition points in the range of ° C and making the difference between the highest and lowest glass transition points 5 ° C or more. In addition to the above-mentioned coated paper performance, a carboxy-modified copolymer latex having improved anti-stickiness and excellent coating operability is proposed (JP-A-7-324112). However, even with respect to such a copolymer latex, further improvement has been desired in terms of high-speed fluidity without impairing the coated paper performance.

[0003]

The object of the present invention is to improve the high-speed fluidity of a high-concentration paint, to provide excellent mechanical stability, and to prevent stickiness, especially when used in a paper coating composition. It is to provide a copolymer latex which is excellent in coating operability due to high coating performance, and also excellent in coated paper performance such as adhesive strength, print gloss, rigidity, etc., and a paper coating composition using the same. .

[0004]

The gist of the present invention is as follows. First, (a) 20 to 80% by weight of an aliphatic conjugated diene monomer and (b) 0.5 to 80% by weight of a water-soluble ethylene monomer. 8% by weight,
And (c) 20 to 79.5% by weight of another vinyl monomer copolymerizable with the components (a) and (b) (provided that (a) + (b) + (c) = 100% by weight) %), The latex has an average particle size of 50 to 150 nm, and the molar ratio of potassium ion to sodium ion (potassium ion / sodium ion) contained in the latex is 0 to 0%. 2 and the zeta potential of the particle surface is −80 to −10 mV.

The gist of the present invention is, secondly, a paper coating composition characterized by containing the copolymer latex,
Consists of

Hereinafter, the present invention will be described in detail. Copolymer Latex The copolymer latex according to the present invention has a monomer composition of (a) 20 to 80% by weight of an aliphatic conjugated diene monomer, and (b) a water-soluble ethylene A monomer comprising 0.5 to 8% by weight of a monomer and 20 to 79.5% by weight of another vinyl monomer copolymerizable with the component (a) and the component (b). It is obtained from a mixture. Examples of the (a) aliphatic conjugated diene monomer used in the copolymer latex of the present invention include:
1,3-butadiene, isoprene, chloroprene, 2,
Examples thereof include 3-dimethyl-1,3-butadiene, and preferably 1,3-butadiene. These (a) aliphatic conjugated diene monomers can be used alone or in combination of two or more. The (a) aliphatic conjugated diene-based monomer is an essential component for imparting appropriate flexibility and elongation to the obtained copolymer and imparting impact resistance. It is 20 to 80% by weight, preferably 30 to 70% by weight, based on the monomer. (A) When the use ratio of the aliphatic conjugated diene monomer is less than 20% by weight, the copolymer becomes too hard and the adhesive strength is not improved,
On the other hand, if it exceeds 80% by weight, the stickiness prevention property deteriorates.

The (b) water-soluble ethylene monomers include, for example, unsaturated carboxylic acid monomers such as (meth) acrylic acid, maleic acid, fumaric acid and itaconic acid; (meth) acrylamide, N Amide group-containing vinyl monomers such as N, N-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide and N-methylol (meth) acrylamide; 2-hydroxyethyl (meth) acrylate, Hydroxy group-containing vinyl monomers such as hydroxypropyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate; and epoxy group-containing monomers such as glycidyl (meth) acrylate and allyl glycidyl ether. These (b) water-soluble ethylene monomers can be used alone or in combination of two or more. The proportion of the water-soluble ethylene monomer (b) used is 0.5 to 8% by weight, preferably 0.8 to 6% by weight, more preferably 1.5 to 4% by weight, based on all monomers. %. (B) When the use ratio of the water-soluble ethylene monomer is less than 0.5% by weight, the stability of the latex during polymerization is poor, and a large amount of coagulated material is generated. The viscosity of the latex increases greatly, and the high-speed fluidity deteriorates.

In the present invention, as the water-soluble ethylene monomer (b), an unsaturated carboxylic acid monomer is preferably used in an amount of 0.5 to 4% by weight based on all monomers.
More preferably, 1 to 4% by weight, particularly preferably 1.5% by weight.
~ 3.5% by weight. In this case, if the proportion of the unsaturated carboxylic acid monomer used is less than 0.5% by weight, the stability of the latex during polymerization may be reduced, or the mechanical stability of the obtained latex may be poor, On the other hand, if it exceeds 4% by weight, bleeding or the like may occur during high-speed coating.

On the other hand, in the present invention, considering the high-speed fluidity of the copolymer latex, it is preferable that the amount of the unsaturated carboxylic acid monomer used is as small as possible.
If extremely low, in addition to the problems described above,
The latex becomes sensitive to alkali, and when the alkali is added when neutralizing the latex after polymerization, aggregation may occur. In order to prevent this, it is effective to use the amide group-containing vinyl monomer in combination with the unsaturated carboxylic acid monomer. In this case, the use ratio of the amide group-containing vinyl monomer is preferably 0.1 to
It is 4% by weight, more preferably 0.1 to 2% by weight.
When the proportion of the amide group-containing vinyl monomer is within the above range, the latex has excellent stability. Further, the total use ratio of the unsaturated carboxylic acid monomer and the amide group-containing vinyl monomer is, with respect to all the monomers,
Preferably 1.5 to 4% by weight, more preferably 2 to
3.5% by weight.

Further, (c) another vinyl-based monomer copolymerizable with the above-mentioned components (a) and (b) (hereinafter,
It is referred to as "(c) other vinyl-based monomer". ) Includes, for example, an aromatic vinyl compound, a substituted or unsubstituted alkyl (meth) acrylate, a vinyl cyanide compound,
Examples thereof include vinyl acetate. Among them, examples of the aromatic vinyl compound include, for example, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene.
Methyl styrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene and the like can be mentioned, with styrene being particularly preferred. Examples of the alkyl (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i. -Butyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-
Octyl (meth) acrylate, cyclohexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, benzyl (meth) acrylate, isobornyl (meth) acrylate, 2-cyanoethyl (meth) acrylate, etc., and particularly methyl Methacrylates are preferred. Examples of the vinyl cyanide compound include (meth) acrylonitrile, α-chloroacrylonitrile, and vinylidene cyanide, and acrylonitrile is particularly preferable. These other vinyl monomers (c) can be used alone or in admixture of two or more. (C) The other vinyl-based monomer is used mainly to give the copolymer a proper glass transition point according to the purpose, and the ratio thereof is based on all monomers. It is 20 to 79.5% by weight, preferably 25 to 69% by weight. If the proportion of the other vinyl-based monomer (c) used is less than 20% by weight, the stickiness-preventing property is lowered, while if it exceeds 79.5% by weight, the copolymer becomes too hard and the adhesive strength is poor.

The average particle size of the copolymer latex of the present invention is 50 to 150 nm, preferably 50 to 120 nm.
More preferably, it is 50 to 110 nm. If the average particle size of the copolymer latex is smaller than 50 nm, the composition for paper coating will have poor fluidity, gloss development, ink transferability, etc., while if it is larger than 150 nm, it will be used for paper coating. The high-speed fluidity of the composition decreases. The average particle size of the copolymer latex can be controlled by adjusting the amounts of water, emulsifier, polymerization initiator and the like used during the polymerization.

The copolymer latex of the present invention has a molar ratio of potassium ion to sodium ion (potassium ion / sodium ion) (hereinafter referred to as "K / Na ion ratio") of 0 in the latex. 2, preferably 0 to 1.5, particularly preferably 0 to 1. When the K / Na ion ratio exceeds 2, the high-speed fluidity of the composition for paper coating decreases, which is not preferable. Further, when the K / Na ion ratio is in the range of 0 to 2, when the K / Na ion ratio is 0 or almost 0, the high-speed fluidity is particularly excellent, and the K / Na ion ratio is significantly larger than 0. For example, in the case of 0.01 to 2, the water resistance is particularly excellent. K / Na in the copolymer latex of the present invention
The ion ratio is determined, for example, by the amounts of potassium ions and sodium ions derived from reagents such as a polymerization initiator and / or an emulsifier used during polymerization, a pH adjuster added during and / or after polymerization, and various additives. It can be adjusted appropriately.

Further, the copolymer latex of the present invention has a zeta potential on the particle surface of -80 to -10 mV, preferably -70 to -10 mV, particularly preferably -65 to -20 mV.
V. When this zeta potential is lower than -80 mV,
Since the high-speed fluidity of the composition for paper coating decreases, it is not preferable when performing high-speed coating.
If it is higher than this, the stability of the latex at the time of polymerization decreases, which is not preferable.

Further, the copolymer latex of the present invention has at least two glass transition points in the range of -100 to + 50 ° C, and the difference between the highest glass transition point and the lowest glass transition point is 5 ° C. Or higher, preferably 10 ° C. or higher,
More preferably, the temperature is 15 ° C. or higher. If the low glass transition point of the copolymer latex is lower than -100 ° C, the tackiness tends to decrease, while if the high glass transition point is higher than + 50 ° C, the adhesive strength tends to decrease. The preferred copolymer latex in the present invention has at least two glass transition points in the range of −100 to + 50 ° C., and may have three or more glass transition points. It is particularly preferred that one is present. When the difference between the highest glass transition point and the lowest glass transition point of the copolymer latex satisfies the above condition, a paper coating composition having an excellent performance balance can be obtained.

In the present invention, a more preferred copolymer latex has at least one low glass transition point in the range of -100 to 0 ° C. and a high glass transition point of-
There is at least one in the range of 5 to + 50 ° C., and particularly preferred copolymer latex has at least one low glass transition point in the range of −90 to −5 ° C.
And at least one high glass transition point exists in the range of 0 to + 40 ° C. When a copolymer latex having such a glass transition point is used as a paper coating composition, more excellent printability and coating operability can be exhibited. Thus, the copolymer latex of the present invention,
By having a heterophasic structure in which polymer portions having different glass transition points within a specific temperature range coexist in the same particle, a paper coating composition containing the latex, high-speed coating suitability, coating properties, It is excellent in the balance of coated paper performance, coating operability, etc., and can be used very suitably for various printing papers, especially offset printing papers.

In the present invention, the preferred copolymer latex having at least two glass transition points within the above-mentioned specific temperature range is particularly preferably composed of a polymer part A and a polymer part B described below. That is, polymer part A
Are (a) 25 to 100% by weight, preferably 35 to 90% by weight of an aliphatic conjugated diene-based monomer, and (b) 0 to 10% by weight, preferably 0 to 5% by weight of a water-soluble ethylene-based monomer. ,
More preferably, 0 to 3% by weight, and (c) 0 to 75% by weight of another vinyl monomer, preferably 7 to 52% by weight.
(However, (a) + (b) + (c) = 100% by weight), and has a glass transition point of −100 to 0 ° C., preferably −90 to −3 ° C., and more preferably −70 to −5. (Co) polymer portion in the range of ° C. When the use ratio of the (a) aliphatic conjugated diene-based monomer in the polymer portion A is less than 25% by weight based on all monomers, the copolymer tends to be too hard, and the adhesive strength tends to decrease, (B) The water-soluble ethylene monomer is used in an amount of 10% by weight based on all monomers.
When it exceeds, the viscosity of the latex increases and the coating operability tends to decrease. (C) When the use ratio of other vinyl monomers exceeds 75% by weight based on all monomers, The copolymer becomes too hard, and the adhesive strength tends to decrease. When the glass transition point of the polymer portion A is higher than 0 ° C., the adhesive strength tends to decrease. Further, the polymer portion B comprises (a) 10 to 60% by weight, preferably 20 to 50% by weight of an aliphatic conjugated diene-based monomer, and (b) 0.5 to 30% by weight of a water-soluble ethylene-based monomer. , Preferably 0.8 to 2
0% by weight, more preferably 1 to 10% by weight, and (c) 10 to 89.5% by weight, preferably 40 to 79% by weight of other vinyl monomers (provided that (a) + (b) +
(C) = 100% by weight) and has a glass transition point in the range of -5 to + 50 ° C, preferably 0 to + 45 ° C, and more preferably +5 to + 40 ° C. If the proportion of the aliphatic conjugated diene-based monomer (a) used in the polymer portion B is less than 10% by weight based on the total weight of the monomers, the copolymer becomes too hard and the adhesive strength tends to decrease. On the other hand, if it exceeds 60% by weight, the stickiness prevention property tends to decrease. If the proportion of the water-soluble ethylene monomer (b) is less than 0.5% by weight based on all monomers, the stability during polymerization may be reduced, or the mechanical stability of the obtained latex may be reduced. On the other hand, if it exceeds 30% by weight, the viscosity of the latex tends to increase and the coating operability tends to decrease. On the other hand, if the proportion of the other vinyl monomer (c) is less than 10% by weight relative to the total amount of the monomers, the stickiness-preventing property tends to decrease.
If it exceeds 5% by weight, the copolymer tends to be too hard and the adhesive strength tends to be lowered. When the glass transition point of the polymer portion B is higher than + 50 ° C., the adhesive strength tends to decrease. In addition, the polymer part A and the polymer part B
The term “(co) polymer” in the above means that the polymer is composed of at least one of a homopolymer and a copolymer.
Further, the ratio of the polymer part A to the polymer part B (A / B)
Is preferably 10 parts by weight based on 100 parts by weight of the total copolymer.
/ 90 to 80/20, more preferably 15/85 to 7
5/25, particularly preferably 20/80 to 70/30. If this ratio is less than 10/90, the adhesive strength may be insufficient, while if it exceeds 80/20, the tackiness tends to decrease.

The copolymer latex of the present invention is characterized in that the K / Na ion ratio is in a specific range and has a specific range of zeta potential. By using such a copolymer latex, An excellent paper coating composition can be obtained. That is, since the copolymer latex has a small charge density on the particle surface, the interaction with the pigment under a high shear rate becomes smaller, and the copolymer latex is excellent in high-speed fluidity. Furthermore, the copolymer latex of the present invention exhibits more excellent coated paper performance and coating operability by coexistence of a polymer portion having a low glass transition point and a polymer portion having a high glass transition point in the latex particles. be able to. That is, the polymer portion having a low glass transition point exhibits high resistance to shock deformation, which has a very high deformation rate in high-speed printing, and thereby can exhibit high adhesive strength. In addition, the polymer portion having a high glass transition point can maintain coated paper performance such as strength and stiffness at a high level, and since the tackiness is improved, more excellent coating operability can be achieved. It can be expressed.

The minimum film forming temperature of the copolymer latex of the present invention is preferably from 0 to 60 ° C, more preferably from 5 to 50 ° C, particularly preferably from 10 to 40 ° C. If the minimum film-forming temperature is lower than 0 ° C, the stickiness preventing property tends to decrease, while if it is higher than 60 ° C, the adhesive strength tends to decrease.

The copolymer latex of the present invention can be produced by a known emulsion polymerization method of a predetermined monomer mixture in an aqueous medium in the presence of an emulsifier, a polymerization initiator, a molecular weight regulator and the like. As the emulsifier, for example, an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, or the like can be used alone or in combination of two or more. Examples of the anionic surfactant include sulfuric acid ester salts of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and polyethylene glycol alkyl ether sulfate ester salts. Examples of the nonionic surfactant include, for example, an alkyl ester type, an alkyl ether type, and an alkyl phenyl ether type of ordinary polyethylene glycol. As the amphoteric surfactant, for example, a carboxylate salt, a sulfate ester salt, a sulfonate salt as an anion moiety,
Examples thereof include those having a phosphate ester salt and the like, and having an amine salt, a quaternary ammonium salt, etc. as a cation moiety, and specifically, betaines such as lauryl betaine and stearyl betaine; lauryl-β-alanine, stearyl- Amino acid types such as β-alanine, lauryldi (aminoethyl) glycine, octyldi (aminoethyl) glycine, and the like. Examples of the polymerization initiator include water-soluble polymerization initiators such as sodium persulfate, potassium persulfate and ammonium persulfate; oil-soluble polymerization initiators such as benzoyl peroxide, lauroyl peroxide, and 2,2′-azobisisobutyronitrile. Polymerization initiator; a redox polymerization initiator obtained by combining an oxidizing agent and a reducing agent, etc. may be used alone or in combination of two or more kinds. Examples of the molecular weight regulator include halogenated hydrocarbons such as chloroform and carbon tetrabromide; mercaptans such as n-hexylmercaptan, n-octylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan, and thioglycolic acid. ; Xanthogens such as dimethylxanthogen disulfide, diisopropylxanthogendisulfide, and terpinolene, α-methylstyrene dimer, etc. all of which can be used in ordinary emulsion polymerization, alone or in combination of two or more be able to. Furthermore, at the time of emulsion polymerization, a known pH is used.
Adjusters, chelating agents, inorganic electrolytes and the like can also be added.

As for the polymerization method, in the same manner as in the case of seed polymerization, a polymer portion A is prepared in advance by emulsion polymerization in a separate polymerization vessel, and then a predetermined amount of the polymer portion A is added. A method of producing the united portion B by emulsion polymerization, a method of producing the polymer portion A and the polymer portion B by multistage emulsion polymerization of at least two stages in the same polymerization vessel, and the like. In the polymerization method, as a method of charging the monomer mixture, for example, a method of charging the monomer mixture at once, after polymerizing a part of the monomer mixture,
Examples thereof include a method of continuously or intermittently adding the rest, a method of continuously or intermittently adding a monomer mixture from the beginning of polymerization, and these charging methods can be combined. The polymerization temperature is usually preferably 5 to 80 ° C, more preferably 5 to 50 ° C when producing the polymer part A, and preferably 20 to 80 ° C when producing the copolymer part B. ℃, more preferably 20
~ 60 ° C. The polymerization time is usually 10 to 30 hours.

Paper Coating Composition The paper coating composition of the present invention generally comprises the above-mentioned copolymer latex as an inorganic or organic pigment, and if necessary, other binder, various auxiliaries and the like. It is prepared by blending with. The amount of the copolymer latex in the paper coating composition is usually 1 to 30 parts by weight (as a solid content), preferably 3 to 25 parts by weight, based on 100 parts by weight of the pigment. is there. If the content of the copolymer latex is less than 1 part by weight, the adhesive strength tends to decrease, while if it exceeds 30 parts by weight, the ink drying property tends to decrease. As the inorganic pigment used in the paper coating composition, for example, clay, barium sulfate, titanium oxide, calcium carbonate, satin white, talc, aluminum hydroxide, zinc oxide, and the like, and as the organic pigment, For example, polystyrene particles, urea formalin resin and the like can be mentioned. These pigments may be used alone or in admixture of two or more, depending on the purpose.
Examples of the auxiliaries used in the paper coating composition include commonly used water resistance improvers, pigment dispersants, viscosity modifiers, coloring pigments, fluorescent dyes, pH regulators, and the like. Further, the paper coating composition of the present invention, particularly when used for offset printing, as a pigment binder, in addition to the copolymer latex, casein, casein modified, starch, starch modified, polyvinyl alcohol, A water-soluble substance such as carboxymethyl cellulose can be used in combination as needed. The paper coating composition of the present invention is particularly preferably used for offset sheet-fed printing paper and offset rotary printing paper, but is also useful for various other printing papers such as letterpress printing and gravure printing. , And paper coating agents, carpet backing agents, adhesives,
It can also be used as a paint or the like.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. “Parts” and “%” in Examples and Comparative Examples are both based on weight.

【Example】

(Production and Evaluation of Copolymer Latex) Examples 1 to 5 and 8 In an autoclave equipped with a stirrer and a temperature controller, 1
As the step component, 200 parts of water, 0.5 part of sodium dodecylbenzene sulfonate and sodium bisulfite of 0.
5 parts, the monomer shown in Table 1, the molecular weight modifier and the polymerization initiator were charged all at once, and then reacted at 45 ° C. for 6 hours to produce a polymer part A. The polymerization conversion rate at this time was 70% or more. Then, as the second-stage component, the monomer and the molecular weight modifier shown in Table 1 were continuously added at 60 ° C. for 7 hours to continue the polymerization, and the reaction was continued at 70 ° C. for 6 hours after the completion of the continuous addition. Then, a polymer part B was produced. Final polymerization conversion is 98-99
%Met. Thereafter, the pH was adjusted to 7.8 with an aqueous sodium hydroxide solution, and then the mixture was concentrated to a predetermined concentration under reduced pressure.

With respect to each of the obtained copolymer latexes,
The average particle size, toluene-insoluble matter, glass transition point, K / Na ion ratio and zeta potential were determined by the following methods. Table 2 shows the results. Average particle size Submicron analyzer (Model N
It was determined by the usual method using 4). After adjusting the copolymer latex of toluene-insoluble matter to pH 8.0, it was coagulated with isopropanol, and the coagulated product was washed and dried.
Next, a predetermined amount (about 0.03 g) of the dried sample is immersed in a predetermined amount (100 ml) of toluene for 20 hours.
The mixture was filtered through a 120-mesh wire net, and the ratio of the remaining solids to the total solids charged was determined. After coating each glass latex copolymer latex on a substrate, 100
The film was vacuum-dried at 20 degreeC for 20 hours, and the film was produced. This dried film was measured according to the ASTM method using a differential scanning calorimeter (DSC: manufactured by DuPont). K / Na ion ratio After diluting each copolymer latex to a predetermined concentration, centrifugation was performed, and potassium ion and sodium ion were quantified by liquid chromatography with respect to the obtained supernatant, and the K / Na ion ratio was determined from the value. Was calculated. Zeta potential The zeta potential of the obtained copolymer latex was determined by a conventional method using a zeta potential analyzer manufactured by Brookhaven Instruments.

(Production and Evaluation of Copolymer Latex) Examples 6-7 200 parts of water and 0.5 parts of sodium dodecylbenzenesulfonate were used as the first-stage components in the same autoclave as in Examples 1-5 and 8. , 0.5 parts of sodium bisulfite,
0.2 parts of t-dodecyl mercaptan and 0.5 parts of α-methylstyrene dimer, a polymerization initiator, a monomer and other components shown in Table 1 were charged all at once, followed by reaction at 45 ° C. for 6 hours. Thus, a polymer part A was produced. At this time, the polymerization conversion rate was 70% or more. Next, as a second stage component, the monomers and molecular weight regulators shown in Table 1 were added all at once, and the temperature was raised to 60 ° C.
The reaction was carried out at 60 ° C. for a time to produce a polymer part B. The final polymerization conversion was 98%. afterwards,
After adjusting the pH to 7.8 with an aqueous sodium hydroxide solution, the mixture was concentrated to a predetermined concentration under reduced pressure. About each obtained copolymer latex, average particle diameter, toluene-insoluble matter,
The glass transition point, the K / Na ion ratio and the zeta potential were determined in the same manner as in Examples 1 to 5 and 8. Table 2 shows the results.

(Preparation and Evaluation of Compositions for Paper Coating) Examples 9 to 16 Using the copolymer latexes obtained in Examples 1 to 8, the composition for paper coating for offset printing was prepared according to the following formulation. The thing was prepared. Prescription copolymer latex (solid content) 10.0 parts Kaolin clay 70.0 parts Calcium carbonate 30.0 parts Dispersant 0.2 parts Sodium hydroxide 0.1 parts Starch 4.0 parts Water 60% total solids Each of the obtained paper coating compositions was subjected to the following high-speed coating suitability test, coating property test, coated paper performance test, and coating operability test. <High-speed coating suitability test> Each paper coating composition was weighed 64 g /
on a high-quality coating base paper of m ^2, CLC (CYLINDRICAL LABORATO
RY COATE: manufactured by Warehauser), 1500 m /
After coating at a coating speed of 1 minute, the coated paper was dried, and the degree of occurrence of spitz and the like on the surface of the obtained coated paper was visually observed and evaluated according to the following criteria. ⊚: Not generated, ○: Very slightly generated, △: Slightly generated,
X: remarkably generated (not practical). <Coating property test> Mechanical stability under heat Each paper coating composition was diluted with water to a concentration of 50% and # 300
After filtration through a mesh wire mesh, the mixture was heated to 50 ° C. Next, sample 150g in a container
Keep warm water circulating. ), A load of 15 kg × 25 minutes was applied by a Maron tester (manufactured by Rigaku Kogyo Co., Ltd.), and the mixture was filtered through a # 300 mesh wire gauze, dried, and the amount of filtration residue was measured. The ratio to the solid content was calculated. High-speed fluidity The viscosity at a sample temperature of 25 ° C. and 6600 rpm was measured using a Hercules viscometer (manufactured by Kumagai Riki Kogyo Co., Ltd.).

<Coated Paper Performance Test> Each of the paper coating compositions was coated on a base paper so that the coating amount was 18.0 ± 0.5 g / m ^{2 on} one side. The coating was performed using Kiki Kogyo Co., Ltd.), and dried for 15 seconds with an electric hot air dryer at 150 ° C. Next, the coated paper thus obtained was left in a thermo-hygrostat at a temperature of 23 ° C. and a humidity of 50% for one day and a night, and then a linear pressure of 100 kg / cm and a roll temperature of 50 were obtained.
Perform super calender treatment 4 times under the condition of ℃,
The performance of the coated paper was evaluated by the following method. Dry pick strength The degree of picking when printed with an RI printing machine was visually observed, and the smaller the picking phenomenon, the higher the score, and the evaluation was made on a five-point scale. The numerical value was shown as the average value of 6 times of measurement. Wet pick strength Using a RI printing machine, after moistening the coated paper surface with a water-absorbing roll, visually observing the degree of picking when printing with the RI printing machine, the less score the picking phenomenon, the higher the score. The evaluation was made in five stages. Number is the number of measurements 6
It is shown by the average value of times. Printing Gloss Using an RI printing machine, the offset ink was solid coated and measured at an angle of 60 degrees using a Murakami gloss meter. Stiffness According to JIS P8143, the hardness was measured using an automatic Clark stiffness tester (manufactured by Kumagai Riki Kogyo Co., Ltd.). <Coating operability test> Non-stickiness Each copolymer latex was coated on a polyethylene terephthalate film with No. 1 After applying with 18 rods, 1
The film was dried at 20 ° C. for 30 seconds to form a film. Next, this film and Kurosa paper were put together and pressed by a bench super calender under the conditions of a linear pressure of 200 kg / m and a temperature of 70 ° C.
The degree of transfer of Kuroshisa paper to latex was visually observed, and the less transfer the higher the score, the higher the score was evaluated. The numerical values are shown as an average value of six measurements. Table 3 shows the evaluation results of the respective paper coating compositions. As a result, the paper coating compositions of Examples 8 to 14 use the copolymer latex of the present invention obtained in Examples 1 to 7, and have an adhesive strength (dry pick strength, wet pick strength). Excellent,
In addition, print gloss, rigidity, and tackiness were all excellent.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

(Production and Evaluation of Copolymer Latex) Comparative Example 1 Water 1 was added to the same autoclave as in Examples 1-5 and 8.
00 parts, sodium dodecylbenzenesulfonate 0.3
Parts and 0.5 part of sodium bisulfite, and a monomer, a molecular weight regulator and a polymerization initiator shown in Table 4 were charged at once, reacted at 45 ° C. for 7 hours, and then heated to 60 ° C.
The reaction was allowed to proceed for an additional 7 hours. The final polymerization conversion was 98%. Then, the pH was adjusted to 7.8 with an aqueous sodium hydroxide solution, and then concentrated under reduced pressure to a predetermined concentration. About the obtained copolymer latex, the average particle diameter, toluene-insoluble matter, glass transition point, K / Na ion ratio, and zeta potential were determined in the same manner as in Examples 1 to 5 and 8. Table 5 shows the results.

(Production and Evaluation of Copolymer Latex) Comparative Examples 2 to 4 Into the same autoclave as in Examples 1 to 5 and 8, 200 parts of water and 0.8 parts of sodium dodecylbenzenesulfonate were used as the first stage components. And sodium bisulfite 0.5
And a monomer, a molecular weight regulator and a polymerization initiator shown in Table 4 were charged all at once and reacted at 45 ° C. for 6 hours. At this time, the polymerization conversion rate was 70% or more. Then 2
As the stage components, the monomers and the molecular weight regulators shown in Table 4 were continuously added at 60 ° C. for 7 hours to continue the polymerization, and after the continuous addition, the polymerization was continued for 6 hours.
The reaction was carried out at ℃. The final polymerization conversion was 98-99%. Thereafter, the pH was adjusted to 7.8 with an aqueous sodium hydroxide solution, and then the solution was concentrated to a predetermined concentration under reduced pressure. About the obtained copolymer latex, the average particle diameter, toluene-insoluble matter, glass transition point, K / Na ion ratio, and zeta potential were determined in the same manner as in Examples 1 to 5 and 8. Table 5 shows the results.

(Production and Evaluation of Copolymer Latex) Comparative Example 5 A copolymer latex was prepared in the same manner as in Example 5 except that potassium hydroxide was used instead of sodium hydroxide when adjusting the pH after polymerization. Manufactured. For the obtained copolymer latex, the average particle diameter, toluene insoluble content, glass transition point, K / Na ion ratio and zeta potential were measured in Examples 1 to 1.
Determined in the same manner as in 5 and 8. Table 5 shows the results.

(Preparation and Evaluation of Paper Coating Compositions) Comparative Examples 6 to 10 Using the copolymer latexes obtained in Comparative Examples 1 to 5 and carrying out offset printing in the same manner as in Examples 8 to 16. Prepare a composition for paper coating, high-speed coating aptitude test, paint property test,
A coated paper performance test and a coating operability test were performed. Table 6 shows the evaluation results of the respective paper coating compositions. As a result, K / Na
It is clear that when the ion ratio exceeds 2 (Comparative Example 10) or the zeta potential becomes lower than −80 mV (Comparative Example 9), the apparent viscosity at a high shear rate is significantly increased. Further, the average particle diameter of the copolymer latex is out of the range of 50 to 150 nm (Comparative Examples 1 and 3), or the use ratio of the water-soluble ethylene monomer exceeds 8% by weight (Comparative Example 2). ), The suitability for high-speed coating and the coating properties are deteriorated.

[0034]

[Table 4]

[0035]

[Table 5]

[0036]

[Table 6]

[0037]

EFFECT OF THE INVENTION The copolymer latex of the present invention has a specific monomer composition, an average particle size, a molar ratio of potassium ion and sodium ion, and a zeta potential, so that, for example, during high-concentration and high-speed coating. In addition, it can maintain a high degree of fluidity, has excellent mechanical stability, has high stickiness prevention properties, has excellent coating operability, and has excellent coated paper properties such as adhesive strength, print gloss, and rigidity. A paper coating composition can be provided. Further, the paper coating composition of the present invention has the above-described excellent properties and is suitable for high-speed coating, and can be used particularly suitably for offset printing paper, as well as letterpress printing and gravure printing. It is also useful for various other printing papers such as printing and has extremely high industrial value.

Claims (2)

[Claims] 1. (a) Aliphatic conjugated diene monomer 20 to
80% by weight, (b) water-soluble ethylene-based monomer 0.5 to 8
% By weight, and (c) 20 to 79.5% by weight of another vinyl-based monomer copolymerizable with the components (a) and (b) (provided that (a) + (b) + (c)). = 100% by weight), the latex has an average particle diameter of 50 to 150 nm, and the molar ratio of potassium ion to sodium ion (potassium ion / sodium ion) contained in the latex. Is 0 to 2 and the zeta potential on the particle surface is -80 to -10 mV. 2. A composition for paper coating, comprising the copolymer latex according to claim 1.