JPH07243195A - Copolymer latex for paper coating - Google Patents

Abstract

PURPOSE:To obtain a copolymer latex for paper coating having excellent balance between blister resistance and dry pick strength and other physical properties of coated paper such as printing luster. CONSTITUTION:This copolymer latex for paper coating comprises a copolymer obtained by subjecting monomers composed of (a) 20-50wt.% of an aliphatic diene-based monomer, (b) 0.5-10.wt.% of an ethylenic unsaturated carboxylic acid monomer and (c) 40-79.5-wt.% of another monomer polymerizable with these monomers ((a)+(b)-(c)=100wt.%) to emulsion polymerization. The prepared copolymer has <20wt.% toluene insoluble content and >=80,000 weight-average molecular weight of tetrahydrofuran soluble content.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copolymer latex for paper coating, and more specifically, it has excellent blister resistance-dry pick strength balance, and other coated paper physical properties such as printing gloss. It relates to a copolymer latex for coating.

[0002]

2. Description of the Related Art Conventionally, a paper coating composition mainly composed of a pigment and an aqueous binder has been applied to paper to produce coated paper having excellent printability. Due to its excellent adhesive strength, it is used as the main binder of paper coating compositions. In recent years, as printing has become more sophisticated and faster, the performance required for coated paper has become more severe, and improvements in adhesive strength, water resistance, rigidity, ink transfer, printing gloss and blister resistance are required. Came to be. In particular, high-speed printing in offset rotary printing requires high-temperature and high-speed drying, so that so-called "blister" is likely to occur. When this blister occurs, the commercial value of the printed matter is significantly impaired, and there is a strong demand for improvement in the blister resistance in the quality of the coated paper. Further, in recent years, there has been an increasing demand for reducing the amount of binder for the purpose of reducing the cost of manufacturing coated paper, and therefore, a binder showing sufficient surface strength even with a smaller addition amount is required. Therefore, there has been a demand for further improvement in the balance between strength and blister resistance. However, in the prior art, the dry strength and the blister resistance are antithetical properties, and it is difficult to improve both properties at the same time. For example, as a method for improving the blister resistance, a method of lowering the toluene insoluble content of the copolymer latex has been conventionally performed.
However, in this case, the dry strength is extremely reduced,
In addition, the print gloss decreases. On the contrary, if the toluene insoluble content is increased to increase the dry strength, the blister resistance is extremely reduced.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned technical problems, and it greatly improves the balance between dry strength and blister resistance, which are conventionally in a contradictory relationship, and prints. An object of the present invention is to provide a copolymer latex for paper coating which is excellent in other physical properties of coated paper such as gloss and wet strength.

[0004]

The present invention comprises (a) 20 to 50% by weight of an aliphatic conjugated diene monomer, (b) 0.5 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer, (c) Emulsion polymerization of a monomer composition consisting of 40 to 79.5% by weight of another monomer copolymerizable therewith (however, (a) + (b) + (c) = 100% by weight) And a toluene-insoluble content of the obtained copolymer is less than 20% by weight, and a tetrahydrofuran-soluble content has a weight average molecular weight of 80,000 or more. The present invention provides a copolymer latex for paper coating.

Examples of the (a) aliphatic conjugated diene-based monomer used in the copolymer of the present invention include 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene and chloroprene. Is particularly preferably 1,3-butadiene. These (a) aliphatic conjugated diene-based 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 latex, and the proportion thereof is 20 to 50% by weight, preferably 25 to It is 45% by weight. If it is less than 20% by weight, the flexibility and elongation of the film as described above are inferior.
If it exceeds 5% by weight, the water resistance becomes poor.

Examples of the ethylenically unsaturated carboxylic acid monomer (b) include itaconic acid, acrylic acid, methacrylic acid, fumaric acid and maleic acid. (b)
The ethylenically unsaturated carboxylic acid monomers may be used alone or in combination of two or more. The amount of the (b) ethylenically unsaturated carboxylic acid monomer used is 0.5 to 1
It is 0% by weight, preferably 1 to 7% by weight. If it is less than 0.5% by weight, the stability of the latex during polymerization is poor, coagulation is likely to occur, and the mechanical and chemical stability of the obtained latex is low. Inferior to. On the other hand, if it exceeds 10% by weight, the viscosity of the obtained latex becomes too high, the handling thereof becomes difficult, the workability deteriorates, and the practicality is lacking.

Further, (c) other copolymerizable monomers include aromatic vinyl compounds, alkyl (meth) acrylates, vinyl cyanide compounds, vinyl acetate, and (alkylmeth) acrylamide compounds. . Among these, as the aromatic vinyl compound, for example, styrene,
Examples thereof include α-methylstyrene, p-methylstyrene, vinyltoluene and chlorostyrene, and styrene is particularly preferable. As the alkyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, benzyl ( (Meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, glycidyl (meth) acrylate, hydroxyethyl (meth) acrylate,
Examples thereof include hydroxypropyl (meth) acrylate, isobornyl (meth) acrylate, 2-cyanoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and among them, methylmethacrylate is particularly preferable. Furthermore, examples of the vinyl cyan compound include acrylonitrile and methacrylonitrile, and among these, acrylonitrile is particularly preferable. Further, examples of the (alkylmeth) acrylamide compound include acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, N, N-dimethylaminopropyl (meth) acrylamide and the like. These (c) other monomers may be used alone or in combination of two or more. These other monomers (c) are for imparting appropriate hardness and adhesiveness to the copolymer, and the amount thereof is 40 to 79.5% by weight, preferably 45 to 75%. % By weight. If the amount of the other monomer (c) used is less than 40% by weight, the copolymer will be too soft, while if it exceeds 79.5% by weight, it will be too hard and the adhesive strength will be poor.

The toluene insoluble content of the copolymer latex of the present invention is required to be less than 20% by weight, and when the toluene insoluble content is 20% by weight or more, sufficient blister resistance cannot be obtained. The toluene insoluble content of the copolymer latex here is measured as follows. The copolymer latex is adjusted to pH 8.0, coagulated with isopropanol, the coagulated product is washed and dried, and then a predetermined amount (about 0.03 g) of the sample is immersed in a predetermined amount (100 ml) of toluene for 20 hours. . Then, the mixture is filtered through a 120-mesh wire net, and the weight% of the total solid content of the resulting residual solid content is determined.

In the present invention, the molecular weight of tetrahydrofuran (hereinafter referred to as "THF") soluble component of the copolymer latex is 80,000 or more, preferably 80,000 to.
1,000,000, particularly preferably 100,000-
500,000, more preferably 150,000 to 4
It is necessary to be 00,000, and if it is less than 80,000, the adhesive strength decreases. The molecular weight of the THF-soluble component of the copolymer latex here is measured as follows. A cation exchange resin was added to about 0.3 g of the copolymer latex prepared to have a solid content of 48% by weight to remove cations, 50 ml of THF was added, and the mixture was allowed to stand for 2 hours. Next, a PTFE membrane filter (AD
The product was filtered through VANTEC, and the filtrate was obtained as a polystyrene-equivalent molecular weight with a GPC (gel permeation chromatography) measuring device. The particle size of the copolymer latex of the present invention is preferably 50 to 350 nm, more preferably 60 to 250 nm.

The emulsion polymerization of the monomer used in the present invention can be carried out by a known method using an emulsifier, a polymerization initiator, a molecular weight modifier and the like in an aqueous medium. Here, as the emulsifier, an anionic surfactant,
Nonionic surfactant, amphoteric surfactant alone,
Alternatively, two or more kinds can be used in combination. Examples of the anionic surfactant include sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and sulfates of polyethylene glycol alkyl ethers. As the nonionic surfactant, an ordinary polyethylene glycol alkyl ester type, alkyl ether type, alkyl phenyl ether type or the like is used. Examples of the amphoteric surfactant include those having a carboxylate salt, a sulfuric acid ester salt, a sulfonate salt, and a phosphoric acid ester salt as the anion portion, and those having an amine salt or a quaternary ammonium salt as the cation portion. Betaines such as lauryl betaine and stearyl betaine, lauryl-β-alanine, stearyl-β
-Amino acids such as alanine, lauryldi (aminoethyl) glycine, octyldi (aminoethyl) glycine, etc. are used.

As the polymerization initiator, sodium persulfate,
Water-soluble polymerization initiators such as potassium persulfate and ammonium persulfate, benzoyl peroxide, lauryl peroxide,
An oil-soluble polymerization initiator such as 2,2′-azobisisobutylnitrile and a redox polymerization initiator in combination with a reducing agent can be used alone or in combination. Known molecular weight regulators, chelating agents, inorganic electrolytes and the like can be used. Examples of the molecular weight modifier include halogenated hydrocarbons such as carbon tetrachloride, chloroform and carbon tetrabromide, n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-
It is possible to use all mercaptans such as dodecyl mercaptan and thioglycolic acid, xanthogens such as dimethylxanthogen disulfide, diisopropylxanthogendisulfide, and α-methylstyrene dimer that can be used in ordinary emulsion polymerization.

As the polymerization method, for example, a method in which the whole amount of the monomer mixture is charged and polymerized, a method in which a part of the monomer mixture is polymerized and the rest is continuously or intermittently added, or a single method is used. A method of continuously adding the monomer mixture from the beginning of the polymerization, a method of using seed particles, or the like can be adopted. The polymerization temperature is usually 20 to 70.
℃, preferably 20 to 50 ℃, the polymerization time is usually 10
30 hours.

The paper coating composition in which the copolymer latex in the present invention is used is prepared by adding the above-mentioned copolymer latex to the inorganic or organic pigment, and optionally other binder and various auxiliary agents. used. The blending amount of the above-mentioned copolymer latex is 1 to 30 parts by weight (as a solid content) of the copolymer latex, preferably 3 to 25 parts by weight, relative to 100 parts by weight of the pigment. 1 copolymer latex
If it is less than 1 part by weight, the adhesive strength is significantly reduced, while 3
If the amount exceeds 0 part by weight, the ink drying property is deteriorated. Kaolin clay, talc, barium sulfate, titanium oxide, calcium carbonate, aluminum hydroxide, zinc oxide, satin white and the like are used as the inorganic pigment, and polystyrene latex and the like are used as the organic pigment. These may be used alone or in combination of two or more depending on the purpose.

Further, as the other binder, water-soluble substances such as casein, casein modified product, starch, starch modified product, polyvinyl alcohol, carboxymethyl cellulose, or polyvinyl acetate latex, acrylic latex, etc. may be combined as required. Can be used. Further, in the paper coating composition, various compounding agents generally used, for example, water resistance improver, pigment dispersant,
Viscosity modifier, color pigment, viscosity modifier, fluorescent dye and p
An H regulator may be optionally mixed.

The copolymer latex of the present invention is preferably used for an offset rotary printing machine, but also for various printings such as an offset sheet-fed printing machine, letterpress printing and gravure printing, and a paper coating agent. It can also be used as an adhesive for carpet backing agents, various other adhesives, and as a paint.

[0016]

EXAMPLES Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the examples, parts and% indicating proportions mean parts by weight and% by weight, respectively. (Production of Copolymer Latex) Example 1 150 parts of water, 0.5 part of sodium lauryl sulfate, 5 parts of butadiene, 12 parts of styrene, 5 parts of methyl methacrylate, and acryl in an autoclave equipped with a stirrer and capable of controlling temperature. Acid 2 parts, itaconic acid 1 part, α-methylstyrene dimer 0.5 part, t-dodecyl mercaptan 0.2 part,
A component consisting of 1.5 parts of potassium persulfate and 0.5 part of sodium bisulfite was charged and reacted at 55 ° C. for 3 hours. Then, as the second stage component, 24 parts of butadiene, 26 parts of styrene, methacrylic acid were added. Methyl 25 parts, α-methylstyrene dimer 1.5 parts, t-dodecyl mercaptan 0.
Polymerization was continued by continuously adding 5 parts at 65 ° C. for 7 hours, and after completion of the continuous addition, 65 parts was added for 65 hours.
The reaction was carried out at ° C. The final polymerization addition rate was 98%.

Examples 2 to 5 The copolymer latexes shown in Tables 1 and 2 were polymerized in the same manner as in Example 1 except that the monomers and other components shown in Tables 1 and 2 were used. did. The average particle size of the obtained copolymer latex was determined by a conventional method using a submicron analyzer (model N4) manufactured by Coulter. The toluene insoluble content of the copolymer latex was measured as follows. The copolymer latex is adjusted to pH 8.0, coagulated with isopropanol, the coagulated product is washed and dried, and then a predetermined amount (about 0.03 g) of the sample is immersed in a predetermined amount (100 ml) of toluene for 20 hours. . Then, the mixture is filtered through a 120-mesh wire net, and the weight% of the total solid content of the resulting residual solid content is determined. The molecular weight of the THF-soluble component of the strong polymer latex here was measured as follows. A cation exchange resin was added to about 0.3 g of the copolymer latex prepared to have a solid content of 48% to remove cations, 50 ml of THF was added, and the mixture was allowed to stand for 2 hours. Then, filter with a membrane filter and filter the filtrate to G
The molecular weight was calculated as polystyrene by using a PC (gel permeation chromatography) measuring device.

The toluene insoluble content and average molecular weight of the obtained copolymer latex are shown in Table 3.

[0019]

[Table 1]

[0020]

[Table 2]

Preparation of Paper Coating Composition Using the copolymer latex prepared by the above method, a paper coating composition was prepared according to the following formulation. Compounded kaolin clay 70.0 parts Calcium carbonate 30.0 parts Dispersant 0.2 parts Sodium hydroxide 0.1 parts Starch 4.0 parts Latex (as solid content) 10.0 parts Water Total solid content becomes 60% Add an appropriate amount so that the composition for coated paper is coated on the base paper to be coated on one side 1
It was coated with an electric blade coater (manufactured by Kumagai Riki Co., Ltd.) so as to be 5.0 ± 0.5 g / m ^2, and dried for 15 seconds by an electric hot air dryer at 150 ° C. The obtained coated paper was left in a thermo-hygrostat at a temperature of 23 ° C. and a humidity of 50% for a whole day and night, and then subjected to supercalendering treatment 4 times under the conditions of a linear pressure of 100 kg / cm and a roll temperature of 50 ° C. The performance of the obtained coated paper was evaluated by the following method.

1) Dry Pick Strength The degree of picking when printed by an RI printing machine was visually judged and evaluated by a 5-step method. The less the picking phenomenon, the higher the score. The numerical value was shown as the average value of 6 times of measurement. 2) Wet Pick Strength The surface of the coated paper was wetted with a water-absorbing roll using an RI printing machine, and the degree of picking when printed with the RI printing machine was visually judged and evaluated by a 5-step method. The less the picking phenomenon, the higher the score. The numerical value was shown as the average value of 6 times of measurement. 3) Printing gloss Using an RI printing machine, apply a solid coating of the offset ink,
It was measured at an angle of 60 degrees using a Murakami gloss meter. 4) Blister resistance The double-sided coated paper was subjected to humidity control (about 6%) and then placed in a heated oil bath to indicate the minimum temperature at which blister occurs. The results of evaluation by the above evaluation method are shown in Table 3.

[0023]

[Table 3]

Examples 1 to 5 are coating compositions for offset printing papers using the copolymer latex within the scope of the present invention, which is the object of the present invention, that is, excellent in blister resistance, adhesive strength and printing. A product with excellent gloss was obtained. Comparative Examples 1 and 2 In the same manner as in Example 1, polymerization was carried out by adding the components of the first stage and the components of the second stage shown in Tables 1 and 2. The final polymerization conversion rate was 98 to 99%. Table 3 shows the toluene-insoluble matter, average molecular weight, and coated paper physical properties of the obtained copolymer latex. The molecular weights of Comparative Examples 1 and 2 are smaller than those of Examples. A copolymer having a high toluene insoluble content and a high molecular weight at the same time could not be synthesized. Comparative Example 1 has a low toluene-insoluble content and thus has good blister resistance, but has extremely poor strength and printing gloss. Comparative Example 2 is an example of an intermediate toluene-insoluble content and a molecular weight of the both, but it shows intermediate properties in terms of the physical properties of the coated paper and is inferior in balance as compared with the Examples.

[0025]

The offset printing paper coating composition using the copolymer latex of the present invention has extremely excellent blister resistance, adhesive strength, which cannot be achieved by the conventional offset printing paper coating composition. It has a printing gloss and has extremely high industrial value. That is, when the blister resistance is the same as in the prior art, even if the amount of the copolymer latex used is reduced by 1 to 2 parts, the strength and the printed light can be kept the same. When the values are the same, the blister resistance can be improved by 20 to 30 ° C.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Niigae 2-11-24 Tsukiji, Chuo-ku, Tokyo Japan Synthetic Rubber Co., Ltd.

Claims (1)

[Claims] 1. (a) Aliphatic conjugated diene monomer 20 to 5
0% by weight, (b) ethylenically unsaturated carboxylic acid monomer
5 to 10% by weight, (c) 40 to 79.5% by weight of another monomer copolymerizable with these (provided that (a) + (b) + (c) = 10
(0% by weight), which is a copolymer obtained by emulsion polymerization of a monomer having a toluene insoluble content of 2%.
A copolymer latex for paper coating, which is less than 0% by weight and has a weight-average molecular weight of the tetrahydrofuran-soluble component of 80,000 or more.