JPH0314960B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a composition for coated paper that can extremely efficiently produce coated paper having excellent printability, and particularly to a composition for coated paper that significantly improves the smoothness of the surface of coated paper. The present invention relates to a paper coating composition. [Prior Art] In recent years, as printed matter has become more visible and sophisticated, there has been a demand for coated paper that has excellent printability even under high-speed printing conditions. Because of the required characteristics, the smoothness of the surface of the coated paper is attracting attention as an extremely important factor. On the other hand, in order to improve the productivity and save energy of coated paper for printing, there is an increasing demand for higher concentrations of coating liquids, and the pigments that make up the coating liquids are used in various types of adhesives, etc. are being considered. Among them, fine grained heavy calcium carbonate can be used to prepare a highly concentrated slurry and can lower the viscosity of the resulting coating liquid under high shear stress.
It is attracting attention as a pigment for coated paper. However, although highly concentrated paints containing fine particles of heavy calcium carbonate exhibit excellent effects in terms of energy saving, productivity improvement, and whiteness improvement, they have problems with the smoothness of the coated paper surface and the smoothness of the printed surface. As a result, the current situation is that it is not possible to sufficiently satisfy the demands associated with the trend toward higher quality printed materials as described above. The tendency for the smoothness of the coated paper surface to decrease becomes more pronounced as the proportion of fine-grained heavy calcium carbonate increases, but the reason for this is that the properties of fine-grained heavy calcium carbonate essentially These include a low aspect ratio, low surface energy, and low water retention. Although these properties are favorable for preparing highly concentrated pigment slurries and coating liquids, the resulting coating layer is dense and low in bulk, and the coverage of the base paper fiber surface is also poor. Therefore, it is thought that the smoothing effect of super calender or gloss calender in the finishing process is reduced, and the smoothness of the coated layer and printed surface of the final product is reduced. Conventionally, in order to improve the smoothness of the coated paper surface, there have been methods such as increasing the coating amount, adding pigments such as delaminated kaolin with a large aspect ratio to improve coating properties, and increasing the coating liquid. A method has been proposed to improve coating properties by reducing the shrinkage of the coating layer due to water evaporation during the drying process by destabilizing the coating liquid by increasing the concentration or adding salt or coagulants. has been done. However, these methods do not necessarily give satisfactory results because new defects are created as the smoothness of the surface of the coated paper is improved. For example, when a pigment with a large aspect ratio is used, ink receptivity decreases, and when the coating liquid is made highly concentrated, streaks and scratch troubles are likely to occur during coating. In addition, adding salt or flocculants to the coating solution impairs the fluidity and water retention of the coating solution, which tends to cause streaks, scratches, and uneven coating during high-speed coating, and increases the surface strength of the coating layer. As a result, paper smearing occurs in the coated layer during printing. A method has also been proposed in which a copolymer latex having cationic and anionic amphoteric properties is used as an adhesive to form a bulky coating layer to enhance the calendering effect. However, since conventional amphoteric latexes use an anion of an ethylenically unsaturated carboxylic acid and a cation of an ethylenically unsaturated amine, the interaction between kaolin and clay is strong, but heavy calcium carbonate, which has a low surface energy, On the other hand, the interaction was weak, and as a result, it was difficult to obtain a satisfactory bulk with a coating liquid containing heavy calcium carbonate. [Problems to be Solved by the Invention] In view of the current situation, the present inventors have attempted to form a coating layer with sufficiently satisfactory bulk even with a coating liquid containing heavy calcium carbonate. As a result of intensive research to develop a composition for coated paper, it was found that by selecting heavy calcium carbonate with a specific particle size distribution as the pigment and using a specific amphoteric copolymer latex as the adhesive, both The present inventors have discovered that, due to the interaction, a sufficiently bulky coating layer can be formed even in a coating composition containing a high proportion of heavy calcium carbonate, leading to the completion of the present invention. The coating layer thus formed exhibits a satisfactory calendering effect and can significantly improve the serious defect of the prior art, which is the poor smoothness of the coated and printed surfaces of the resulting coated paper. [Means for solving the problems] The present invention provides (a) a pigment having a particle content of 55 to 95 μm or less;
(b) Contains 20 to 100 parts by weight of heavy calcium carbonate having 30% by weight or less of fine particles of 0.2μ or less; (b) 1 to 10 parts by weight of at least one amphoteric surfactant as an adhesive; ●Aliphatic conjugated diene compound 30-70 parts by weight●Ethylenically unsaturated carboxylic acid 0.5-5 parts by weight●Ethylenically unsaturated amine 0.2-5 parts by weight●Copolymerizable unsaturated compound containing an amide bond
1 to 5 parts by weight ●Unsaturated carboxylic acid ester containing a hydroxyl group
A copolymer latex obtained by emulsion polymerizing 100 parts by weight of a monomer mixture consisting of 1 to 5 parts by weight and 10 to 67.3 parts by weight of a monomer copolymerizable with these at a pH of 6 or higher.
A composition for coated paper, characterized in that it contains parts by weight. [Function] As mentioned above, the heavy calcium carbonate blended into the coated paper composition of the present invention has a particle content of 55 to 95% by weight of 1μ or less, and 30% by weight of fine particles of 0.2μ or less.
Hereinafter, those having a specific particle size distribution, more preferably 25% by weight or less, are selectively used. With heavy calcium carbonate containing 30% by weight or more of fine particles with a size of 0.2μ or less, the fine particles form a dense and low-volume coating layer due to the filling effect of filling the gaps between large particles. Even if a latex is used in combination, a sufficient synergistic effect cannot be obtained, making it difficult to obtain the desired effect of improving the smoothness of coated paper. Heavy calcium carbonate having such a specific particle size distribution is produced by mechanically pulverizing and classifying limestone, marble, chiyok, etc., for example, by the method described in Japanese Patent Publication No. 15834/1983. can be adopted. In the coated paper composition of the present invention, it is possible to contain the above-mentioned specific heavy calcium carbonate as a pigment in an amount of 20% by weight or more and up to 100% by weight, and a large amount of heavy calcium carbonate may be blended. The above-mentioned various excellent effects obtained by this method are realized. Pigments other than the above-mentioned specific heavy calcium carbonate are not particularly limited, and for example, kaolin, talc, aluminum hydroxide, titanium dioxide, satin white, light calcium carbonate, barium sulfate, etc. are used in combination as appropriate. In the coated paper composition of the present invention, the specific copolymer latex used as the adhesive component of the pigment contains at least one amphoteric surfactant.
~10 parts by weight is used as an emulsifier, ●Aliphatic conjugated diene compound 30-70 parts by weight●Ethylenically unsaturated carboxylic acid 0.5-5 parts by weight●Ethylenically unsaturated amine 0.2-5 parts by weight●Co-containing an amide bond Polymerizable unsaturated compound
1 to 5 parts by weight ●Unsaturated carboxylic acid ester containing a hydroxyl group
It is produced by emulsion polymerizing 100 parts by weight of a monomer mixture consisting of 1 to 5 parts by weight and 10 to 67.3 parts by weight of a monomer copolymerizable with these at a pH of 6 or higher. The amphoteric surfactant used in the present invention is
It is a surfactant that has both an anionic and a cationic hydrophilic group in the same molecule, and the anionic part is a carboxylate, sulfuric acid ester salt, sulfonate, and phosphoric acid ester salt, and the cationic part is an amine salt. , quaternary ammonium salts. Specifically, the alkyl betaine salts include lauryl betaine, stearyl betaine, cocoamidopropyl betaine, and 2-undecyl-hydroxyethylimidazolium betaine, and the amino acid type includes lauryl-β-.
Examples include salts of alanine, stearyl-β-alanine, lauryldi(aminoethyl)glycine, octyldi(aminoethyl)glycine, and dioctyldi(aminoethyl)glycine. Ampholytic surfactants have less deterioration in water resistance than anionic or nonionic surfactants, and can provide white paper with excellent gloss and printability. The effects of the present invention can be achieved by using these amphoteric surfactants alone or in combination as an emulsifier during polymerization. Other anionic, cationic, nonionic surfactants, etc. may be used in combination, but copolymer latex emulsion polymerized using other surfactants,
Simply adding an amphoteric surfactant afterwards does not provide the effects of the present invention. The amount of the amphoteric surfactant to be used is 1 to 10 parts by weight, preferably 2 to 6 parts by weight, per 100 parts by weight of the monomer mixture. If it exceeds this, it becomes difficult to maintain the water resistance required for coated paper for printing. Using an emulsifier containing at least one of the above amphoteric surfactants, ethylenically unsaturated carboxylic acid, ethylenically unsaturated amine, together with an aliphatic conjugated diene compound as a monomer that provides appropriate elasticity to the coating film of the coating composition. By polymerizing a copolymerizable unsaturated compound containing an amide bond and an unsaturated carboxylic acid ester containing a hydroxyl group, the effects of the present invention can be further enhanced, and a coating layer having particularly good adhesive strength can be formed. It is something. As the aliphatic conjugated diene compound, butadiene, isoprene, 2-chloro-1,3-butadiene, 1-chloro-1,3-butadiene, etc. are used, but butadiene is particularly preferred. usage is 30
If it is less than % by weight, sufficient elasticity and adhesive strength cannot be obtained.
If it exceeds 70% by weight, the stickiness becomes too large.
Therefore, it is preferably adjusted within the range of 35 to 65% by weight. As the ethylenically unsaturated carboxylic acid, mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid are used, but acid anhydrides and monoalkyl esters of dicarboxylic acids can also be used. The ethylenically unsaturated carboxylic acid is used in an amount of 0.5 to 5% by weight, preferably 1 to 3% by weight. If it is less than 0.5% by weight, the adhesive strength and mechanical stability will decrease.
If it exceeds % by weight, water resistance decreases. Examples of ethylenically unsaturated amines include aminoalkyl esters of ethylenically unsaturated carboxylic acids such as methylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and methylaminoethyl (meth)acrylamide. , dimethylaminoethyl (meth)acrylamide, dimethylaminopropyl (meth)acrylamide and other aminoalkylamides of ethylenically unsaturated carboxylic acids; and alkenylpyridines such as 2-vinylpyridine, 4-vinylpyridine and 2-methyl-5vinylpyridine. Examples include the following. The ethylenically unsaturated amine is used in an amount of 0.2 to 5% by weight, preferably 0.5 to 3% by weight. If it is less than 0.2% by weight, printability will decrease, and if it exceeds 5% by weight, adhesive strength will decrease. Copolymerizable unsaturated compounds containing an amide bond include acrylamide, methacrylamide,
Examples include N-methylolacrylamide, N-butoxyacrylamide, diacetone acrylamide, etc., 1 to 5% by weight, preferably 1.5 to 3% by weight.
Used in proportions by weight. If it is less than 1% by weight, the printability will decrease, and if it exceeds 5% by weight, the viscosity of the latex will become extremely high and handling will become difficult. Examples of unsaturated carboxylic acid esters containing a hydroxyl group include 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, di-(ethylene glycol) itaconate, and di-(ethylene glycol) maleate. , 2-hydroxyethyl maleate, and 2-hydroxyethylmethyl fumarate, which are used in an amount of 1 to 5% by weight, more preferably 1.5 to 3% by weight.
If it is less than 1% by weight, dispersion stability and adhesive strength will decrease,
If it exceeds 5% by weight, water resistance will decrease. Other monomers that can be copolymerized with these include styrene, α-methylstyrene, vinyltoluene,
Aromatic vinyl compounds such as paramethylstyrene, alkyl esters of acrylic acid or methacrylic acid such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyne acrylate, methyl methacrylate, glycidyl (meth)acrylate, etc. unsaturated fatty acid glycidyl ester,
Examples include vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl methyl ethyl ketone, vinyl methyl ether, vinyl acetate, vinyl formate, allyl acetate, methalyl acetate, acrolein, and allyl alcohol. Its usage is
10 to 67.3% by weight, preferably 23 to 61.5% by weight. Polymerization of the copolymer latex of the present invention can be carried out in an aqueous medium using an emulsifier, a polymerization initiator, and a chain transfer agent according to a known method, but the pH in the polymerization system is preferably 6 or higher. Must be maintained at 7.5 or higher. If polymerization is carried out at a pH of less than 6, the stability of the polymerization system will be significantly deteriorated. As an emulsifier, as mentioned above, anionic, cationic, nonionic surfactants, etc. are used in combination with the essential component amphoteric surfactant, as required. is preferred. Examples of anionic surfactants include sulfuric esters of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, etc. Nonionic surfactants include ordinary alkyl esters of polyethylene glycol, alkyne ethers, etc. type, alkyl phenyl ether type, etc. As an initiator, water-soluble initiators such as sodium persulfate, potassium persulfate, ammonium persulfate, etc.
Oil-soluble initiators such as benzoyl peroxide and redox-based initiators are used. Known chain transfer agents, chelating agents, inorganic salts, etc. for emulsion polymerization can also be used. The specific copolymer latex used in the present invention is produced by a conventional emulsion polymerization method at a polymerization temperature of 5 to 100° C. in a batch, semi-batch, or continuous polymerization method. The specific copolymer latex thus obtained has a solid content of 3 to 20 parts by weight based on 100 parts by weight of the pigment containing the specific fine particulate heavy calcium carbonate.
It is blended in the proportion of parts by weight. If the amount is less than 3 parts by weight, the desired effect of the present invention cannot be obtained, and if it exceeds 20 parts by weight, the smoothness of the coated paper may deteriorate in the finishing process. In addition, adhesives for various well-known coated paper compositions such as protein-based adhesives such as casein, soybean protein, and petroleum protein, starch-based adhesives such as oxidized starch, etherified starch, and esterified starch, and other latex-based adhesives are also available. Of course, it is also possible to use agents in combination. Furthermore, various auxiliary agents such as thickeners, water retention agents, flow modifiers, dispersants, antifoaming agents, dyes, lubricants, and waterproofing agents can be appropriately incorporated into the coating composition of the present invention. The coated paper composition of the present invention thus prepared is generally prepared to have a solid content concentration of 55% by weight or more, and in particular, fine-grained heavy calcium carbonate having a specific particle size distribution is selected as the pigment. 60% by weight due to the fact that a specific copolymer latex is used as an adhesive component.
Even when prepared as a highly concentrated paint, it has excellent fluidity and water retention, and the coating layer quickly becomes immobile during the drying process after coating, forming an extremely bulky coating layer. It is. [Example] The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these. Note that parts and % in the examples mean parts by weight and % by weight, respectively. Example 1 Raw material heavy calcium carbonate with a particle content of 325 mesh or less of 98% and an average particle size of 19 μm was made into a slurry with a solid content concentration of 73% using a dispersant, and the solid content concentration was reduced by sand milling. A fine grained heavy calcium carbonate slurry was obtained, with a particle content of 72%, a particle content of 1μ or less being 63%, and a fine particle content of 0.2μ or less being 15%. On the other hand, the following monomers were polymerized at pH 7.9 in the presence of a polymerization initiator, a polymerization regulator, and water, and further concentrated to form a copolymer with a solid content concentration of 45% and an average particle size of 0.20μ. Obtained a combined latex. ●Butadiene 39 parts●Styrene 31 parts●Methyl methacrylate 23 parts●Itaconic acid 2 parts●Butylaminoethyl methacrylate 1 part●Acrylamide 2 parts●Hydroxyethyl methacrylate 2 parts Lauryl is an amphoteric surfactant used as an emulsifier. 2.5 parts of betaine sodium salt was used. Using the thus obtained heavy calcium carbonate slurry and copolymer latex, a composition for coated paper was prepared at the following blending ratio by adding dilution water so that the solid content concentration was 60%. . ●Kaolin (commercial No. 1 grade) 20 parts ●Heavy calcium carbonate slurry (solid content) 80 parts ●Dispersant (sodium polyacrylate) 0.3 parts ●Oxidized starch paste liquid (solid content) 3 parts ●Co-weight Combined latex (solid content) 9 parts The resulting composition was coated on 64 g/m ² of high-quality paper to a dry weight of 20 g/m ² and dried, supercalendered and coated on one side of the paper. Obtained. The obtained coated paper had excellent coated and printed surface smoothness, and had good white paper gloss and paper surface strength. Example 2 A coated paper composition was prepared in the same manner as in Example 1, except that a copolymer latex obtained by emulsion polymerization of the monomer mixture shown in Table 1 was used. Single-sided coated paper was obtained and the quality evaluation results are listed in Table 1. Examples 3 to 5 Raw material heavy calcium carbonate having a particle size of 5 to 10 mm was dry-pulverized and coarse particles were removed by air classification to obtain heavy calcium carbonate having an average particle size of 5 μm. After using a dispersant to make a slurry with a solid content concentration of 75%, it was processed with a sand mill to make a solid content concentration of 74%.
%, a fine grained heavy calcium carbonate slurry was obtained in which the content of particles of 1μ or less was 85% and the content of fine particles of 0.2μ or less was 25%. A coated paper composition was prepared in the same manner as in Example 1, except that a copolymer latex obtained by emulsion polymerization of the monomer mixture shown in Table 1 was used, and one side was coated in the same manner. The paper was obtained and the quality evaluation results are listed in Table 1. Comparative Example 1 Raw material heavy calcium carbonate with a particle content of 325 mesh or less of 60% and an average particle size of 25μ is made into a slurry with a solid content concentration of 73% using a dispersant, and then sand milled to reduce the solid content concentration. A fine particle heavy calcium carbonate slurry was obtained, with a particle content of 72%, a particle content of 1μ or less being 75%, and a fine particle content of 0.2μ or less being 35%. Except for using this fine grained heavy calcium carbonate and using the same copolymer latex as in Example 3,
A coated paper composition was prepared in the same manner as in Example 1,
Similarly, single-sided coated paper was obtained and the quality evaluation results are shown in Table 1. The obtained coated paper had poor printing surface smoothness and poor printing reproducibility, and could not be used as high-quality printed matter. Comparative Example 2 The same procedure as Example 1 was used, except that the heavy calcium carbonate used in Comparative Example 1 was used and a copolymer latex obtained by emulsion polymerization of the monomer mixture shown in Table 1 was used. A coated paper composition was prepared in the same manner, and single-sided coated paper was obtained in the same manner, and the quality evaluation results are shown in Table 1. The obtained coated paper had poor printing smoothness, poor printing reproducibility, and poor printing effects, and could not be used as high-quality printed matter. Comparative Examples 3 to 7 Examples except that the heavy calcium carbonate used in Example 1 was used and a copolymer latex obtained by emulsion polymerization of the monomer mixture shown in Table 1 was used. A coated paper composition was prepared in the same manner as in Example 1, and single-sided coated paper was obtained in the same manner, and the quality evaluation results are shown in Table 1. The various measurement and evaluation methods in Table 1 are as follows. The particle size and particle size distribution of heavy calcium carbonate are:
Measurement was performed using Sedaygraph 5000 (manufactured by Shimadzu Corporation). White paper gloss was measured by JIS method. Printing surface smoothness was measured using RI printing machine (manufactured by Mei Seisakusho)
The condition of the printed surface was visually judged. As for the evaluation criteria, a printed surface with sufficient ink transfer to the paper surface and no ink unevenness was rated 5, and a printed surface with uneven ink transfer but poor transfer was rated 1. The paper surface strength is rated 5 when printed with an RI printing machine and has almost no paper unevenness on the surface of the standard paper, and 1 when there is a lot of paper unevenness.
It was evaluated as [Operation and Effect] As is clear from the results in Table 1, the coated paper produced using the coated paper composition of the present invention has a large amount of fine grained heavy calcium carbonate. All of them had excellent printability, especially the smoothness of the coated paper surface and the printing surface.

【table】

[Table] *Post-addition after polymerization

Claims (1)

[Claims] 1 (a) As a pigment, the content of particles of 1 μ or less is 55
~95% by weight, containing 20 to 100 parts by weight of heavy calcium carbonate with not more than 30% by weight of fine particles of 0.2μ or less; (b) 1 to 10 parts by weight of at least one amphoteric surfactant as an adhesive; ●Aliphatic conjugated diene compound 30 to 70 parts by weight●Ethylenically unsaturated carboxylic acid 0.5 to 5 parts by weight●Ethylenically unsaturated amine 0.2 to 5 parts by weight●Copolymerizable unsaturated compound containing amide bond Compound
1 to 5 parts by weight ●Unsaturated carboxylic acid ester containing a hydroxyl group
A copolymer latex obtained by emulsion polymerization of 100 parts by weight of a monomer mixture consisting of 1 to 5 parts by weight and 10 to 67.3 parts by weight of a monomer copolymerizable with these at a pH of 6 or higher.
A composition for coated paper, characterized in that it contains parts by weight.