JPH0561397B2 - - Google Patents

Description

[Detailed description of the invention]

B. Object of the invention [Industrial field of application] The present invention relates to a paper coating composition. More specifically, by using a synthetic copolymer latex obtained by using a specific emulsifier, coated paper with good printability such as wet pick strength, dry pick strength, ink receptivity, and blister resistance can be produced. The present invention relates to an improved paper coating composition. [Prior Art] Anionic surfactants such as alkyl sulfates and alkylbenzenesulfonates have been used as emulsifiers for synthetic copolymer latexes used in paper coating compositions. [Problems to be solved by the present invention] Recent developments in paper coating technology and printing technology include:
There is something remarkable. In addition, in order to cope with the increase in the number of printed materials, as well as to rationalize and save labor, efforts are being made to speed up coating and printing processes. In order to speed up printing, rotary offset printing (hereinafter referred to as "off-wheel") printing has been adopted in recent years, and its popularity is remarkable today. With the spread of off-wheel printing, coated papers are required to have various properties such as wet pick strength, dry pick strength, ink receptivity, and blister resistance to withstand high speed off-wheel printing. It is known that these performances are influenced by the properties of the synthetic copolymer latex contained as the main binder component in the paper coating composition. However, it is also known that the properties of the coated papers described above are in a contradictory relationship. That is, improving dry pick strength and wet pick strength performance may result in a decrease in blister resistance, and improving ink receptivity may result in a decrease in dry pick strength and wet pick strength. At present, there is a problem in that a paper coating composition that satisfies all printability has not been obtained, and improvements are desired. As a result of intensive studies aimed at solving these problems, the present inventors have discovered a paper mainly containing a synthetic copolymer latex obtained by emulsion polymerization using a specific anionic surfactant and a mineral pigment. It has been discovered that by coating paper with a coating composition, the properties of the resulting coated paper, such as wet pick strength, dry pick strength, ink receptivity, and blister resistance, are significantly improved. , we have completed the present invention. B. Structure of the Invention [Means for Solving the Problems] That is, the present invention comprises 19.5 to 39% by weight of aliphatic conjugated diene monomers, 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid monomers, and An anionic surfactant represented by the following general formula (a) and/or (b) for 100 parts by weight of a monomer mixture consisting of 51 to 80% by weight of a monoolefin monomer copolymerizable with
The present invention provides a paper coating composition mainly containing a copolymer latex obtained by emulsion polymerization of the monomer mixture in the presence of 0.1 to 5 parts by weight, and a mineral pigment. be. General formula: (a) Here, R is an alkyl group having 4 to 20 carbon atoms or a hydrocarbon group containing an aromatic ring, n is an integer of 2 to 70, and M is Na, K or _NH4 . (b) R′-O(-CH ₂ CH ₂ O)- _o ′SO ₃ M′ where R′ is an alkyl group having 4 to 20 carbon atoms,
n' is an integer from 2 to 70 and M' is Na, K or
It is _NH4 . The present invention will be explained in more detail below. The aliphatic conjugated diene monomers used in the present invention include 1,3-butadiene, 2-methyl-
Examples include 1,3-butadiene and 2-chloro-1,3-methylbutadiene, with 1,3-butadiene being particularly preferred. Aliphatic conjugated diene monomer: 19.5 to 39% by weight
However, if it is less than 19.5% by weight, dry
Pick strength decreases, and if it exceeds 39% by weight, wet pick strength decreases, which is not preferable. Examples of the ethylenically unsaturated carboxylic acid monomer used in the present invention include acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, etc., and these may be used alone or in combination of two or more. be able to. Ethylenically unsaturated carboxylic acid monomer is used at 0.5 to 10% by weight, but 0.5
If it is less than 10% by weight, the dry pick strength and mechanical stability of the latex will decrease, and if it exceeds 10% by weight, the viscosity of the latex will become too high, which is not preferred. The copolymerizable monoolefin monomers used in the present invention include alkenyl aromatic monomers, unsaturated carboxylic acid alkyl ester monomers,
unsaturated monomers containing hydroxyalkyl groups,
Examples include vinyl cyanide monomers and ethylenically unsaturated carboxylic acid amide monomers. Examples of alkenyl aromatic monomers include styrene,
Examples include alphamethylstyrene, methylalphamethylstyrene, and vinyltoluene, with styrene being particularly preferred. Unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, dimethyl fumarate, dimethyl maleate, diethyl maleate, Examples include dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and methyl methacrylate is particularly preferred. Examples of the unsaturated monomer containing a hydroxyalkyl group include β-hydroxyethyl acrylate,
β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxybutyl methacrylate, di-(ethylene glycol) maleate, di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis-
Examples include (2-hydroxyethyl) maleate and 2-hydroxyethyl fumarate, with β-hydroxyethyl acrylate being particularly preferred. Examples of vinyl cyanide monomers include acrylonitrile, alpha chloracrylonitrile, methacrylonitrile, and alpha ethyl acrylonitrile, with acrylonitrile being particularly preferred. These monoolefin monomers can be used alone or in combination of two or more. Furthermore, the monoolefin monomer is used in an amount of 51 to 80% by weight, but if it is less than 51% by weight, the wet pick strength will decrease, and if it exceeds 80% by weight, the dry pick strength will decrease.
This is not preferable because the pick strength decreases. The anionic surfactant used in the present invention is a compound represented by the following general formula (a) and/or (b) in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the monomer mixture. However, if it is less than 0.1 part by weight, the stability of the latex will decrease, and if it exceeds 5 parts by weight, the wet pick strength will decrease, which is not preferable. General formula: (a) Here, R is an alkyl group having 4 to 20 carbon atoms or a hydrocarbon group containing an aromatic ring, n is an integer of 2 to 70, and M is Na, K or _NH4 . (b) R′-O(-CH ₂ CH ₂ O)- _o ′SO ₃ M′ where R′ is an alkyl group having 4 to 20 carbon atoms,
n' is an integer from 2 to 70 and M' is Na, K or
It is _NH4 . Further, the number of moles of ethylene oxide added in the anionic surfactants (a) and (b) is an integer of 2 to 70, but if it deviates from this range, the wet pick strength will decrease, which is not preferred. The method of adding various components in the emulsion polymerization of the present invention is not particularly limited, and may be any of a batch addition method, a divided addition method, and a continuous addition method. Alternatively, a so-called two-stage polymerization method or a power fed polymerization method in which the monomer composition is changed during the polymerization process may be used. Furthermore, in emulsion polymerization, commonly used polymerization initiators, electrolytes, polymerization promoters, chain transfer agents, chelating agents, etc. may be used. The gel content of the copolymer latex obtained in the present invention is 10 to 60% when used for off-wheel printing.
Preferably, it is in the range of % by weight. Examples of mineral pigments used in the present invention include titanium dioxide, satin white, kaolin, aluminum hydroxide, calcium carbonate, etc., and these may be used alone or in combination of two or more. Furthermore, the paper coating composition of the present invention contains commonly used binders such as starch, casein, and polyvinyl alcohol, as well as thickeners, crosslinking agents,
Various additives such as water retention agents, alkali stabilizers, antifoaming agents, and surfactants may be used as necessary. [Examples] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited by the Examples in any way. Incidentally, all percentages and parts used in the examples mean percentages by weight and parts by weight unless otherwise specified. Γ Example 1 Into 10 pressure containers, monomers, anionic surfactants, and chain transfer agents in the numbers shown in Table 1,
0.8 parts of potassium persulfate, 0.4 parts of sodium hydrogen carbonate, and 100 parts of pure water were charged, and emulsion polymerization was carried out at 65°C with stirring. The polymerization conversion rates of the obtained copolymer latexes were all 97% or more. Next, after adjusting the pH of the copolymer latex to 7 with an aqueous sodium hydroxide solution, unreacted monomers were removed by steam distillation to obtain copolymer latexes A to D. Using the copolymer latexes A to D, paper coating compositions were prepared based on the following formulations, and coated papers were obtained. per coated paper obtained
Tests were conducted for RI wet pick strength, RI dry pick strength, ink receptivity and blister resistance. The results are shown in Table-2. (Formulation) Kaolin clay 80 parts Calcium carbonate 20 parts Modified starch 8 parts Copolymer latex 12 parts (solid content) (Measurement method) - RI wet pick strength When printed using dampening water on an RI printing machine The degree of picking was visually determined and evaluated on a five-point scale from grade 1 (best) to grade 5 (worst). The average value of 6 times is shown.・RI Dry Pick Strength The RI wet pick strength described above except that dampening water is not used.
It was evaluated using the same method as the pick strength measurement method. - Ink receptivity Using an RI printing machine, water was supplied using a rubber roll and a Molton roll, and the acceptability of the ink during printing was judged visually. - Blister resistance After adjusting the humidity of double-sided coated paper to approximately 6%, it was placed in a heated oil bath, and the lowest temperature at which blistering occurred was determined. Γ Comparative Example 1 Tests were conducted in the same manner as in Example 1, except that sodium dodecylbenzenesulfonate or lauryl sulfate in the numbers shown in Table 1 were used as emulsifiers, and copolymer latexes a and b were tested in the same manner as in Example 1. Obtained. Next, a coated paper was prepared and tested in the same manner as in Example-1. The results are shown in Table-2.

【table】

[Table] The method for measuring gel content in copolymer latex is as follows. a. A copolymer latex film is prepared by drying at room temperature, and the film is placed in benzene of about 200 to 800 times its strength, and after being allowed to stand for 48 hours, it is filtered using No. 2 paper. b Dry the liquid under reduced pressure at 70°C, weigh it, and determine the benzene soluble content (%) of the copolymer latex film. c The value obtained by subtracting the benzene soluble content (%) from 100%, that is, the benzene insoluble content (%), is calculated as the gel content.

[Table] Γ Example 2 A test was conducted in the same manner as in Example 1 using the monomers, anionic surfactant, and chain transfer agent in the parts shown in Table 3, and copolymer latex E~
I got J. Next, coated paper ~ was prepared in the same manner as in Example 1 and tested. The results are shown in Table 4. Γ Comparative Example 2 A test was conducted in the same manner as in Example 1 using the monomers, anionic surfactant, and chain transfer agent in the parts shown in Table 3, and copolymer latexes c to f were obtained.
I got it. However, copolymer latex e lacked stability during emulsion polymerization and agglomerated, making it impossible to obtain a latex sample. Next, coated paper and paper were prepared and tested in the same manner as in Example-1. The results are shown in Table 4.

[Table] (Note) *1 to *5: The contents are shown in Table-1.
*6: Agglomeration during polymerization.

[Effects of the present invention]

As described above, by using the paper coating composition of the present invention, wet pick strength and dry
Coated paper with excellent printability such as pick strength, ink receptivity, and blister resistance can be obtained.

Claims (1)

[Claims] 1. 19.5 to 39% by weight of aliphatic conjugated diene monomer,
The following general formula (a) is added to 100 parts by weight of a monomer mixture consisting of 0.5 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer and 51 to 80% by weight of a monoolefin monomer copolymerizable with these monomers. and/or a copolymer latex obtained by emulsion polymerization of the monomer mixture in the presence of 0.1 to 5 parts by weight of an anionic surfactant represented by (b), and a mineral pigment. A paper coating composition characterized by: General formula: (a) Here, R is an alkyl group having 4 to 20 carbon atoms or a hydrocarbon group containing an aromatic ring, n is an integer of 2 to 70, and M is Na, K or _NH4 . (b) R′-O(-CH ₂ CH ₂ O)- _o ′SO ₃ M′ where R′ is an alkyl group having 4 to 20 carbon atoms,
n' is an integer from 2 to 70 and M' is Na, K or
It is _NH4 . 2. The paper coating composition according to claim 1, wherein the aliphatic conjugated diene monomer is 1,3-butadiene. 3. Claim 1 in which the monoolefin monomer is an alkenyl aromatic monomer alone or a mixture with an unsaturated carboxylic acid alkyl ester monomer
The paper coating composition according to item 1 or 2. 4 the alkenyl aromatic monomer is styrene,
The paper coating composition according to claim 3, wherein the unsaturated carboxylic acid alkyl ester is methyl methacrylate. 5 The monoolefin monomer is an alkenyl aromatic monomer, an unsaturated carboxylic acid alkyl ester monomer, a vinyl cyanide monomer, and an unsaturated monomer containing a hydroxyalkyl group. The paper coating composition according to item 1 or 2.