JP3240572B2 - Composition for paper coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper coating composition, and more particularly, to a paper coating composition satisfying inconsistent properties between dry strength and blister resistance or wet strength.

[0002]

2. Description of the Related Art In recent years, with the rapid development of printing technology, performance required for coated paper has become severe.
There is a need for a paper coating composition that satisfies the contradictory properties of dry strength and blister resistance or wet strength and has a good balance. As a paper coating composition, for example, a paper coating composition containing a latex of a styrene-butadiene-acrylonitrile-methyl methacrylate copolymer is known (JP-A-61-342297 or JP-A-Showa 57). -51703). In these inventions,
In the latex, when the amount of acrylonitrile used is large, the adhesive strength is reduced. Therefore, the latex of the polymer to be contained in the paper coating composition is used in an amount of 30% by weight or less or 1 to 20% by weight of the nitrile. Are copolymerized. However, these styrene-butadiene-
In the latex of acrylonitrile-methyl methacrylate copolymer, it is not possible to improve both the inconsistent properties of dry strength and blister resistance or wet strength and obtain satisfactory properties. Further, a polymer latex obtained by copolymerizing acrylonitrile and methacrylonitrile in an amount of 10 to 30% by weight is known (Japanese Patent Laid-Open No. Sho 62-62).
222889). However, this latex has insufficient blister resistance and wet strength.

[0003]

SUMMARY OF THE INVENTION The present invention provides an improved paper coating composition which satisfies the contradictory properties of dry strength and blister resistance or wet strength and can form a well-balanced paper coating composition. To provide a copolymer latex.

[0004]

Means for Solving the Problems The present inventors have found that 20 to 70% by weight of a conjugated diene monomer unit, 0.5 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer unit and the above-mentioned formula (I)
By preparing a latex of a copolymer having as a main component more than 30% by weight and not more than 70% by weight of a vinyl cyanide monomer unit represented by the following formula, and using this as a paper coating composition, Was solved. The copolymer latex used in the present invention can be produced by emulsion polymerization of a monomer mixture in a known manner, that is, using an emulsifier, a polymerization initiator, a polymerization chain transfer agent and the like in an aqueous medium.

[0005] Among the monomers constituting the copolymer of the synthetic copolymer latex of the present invention, the monomers represented by the above formula (I) are those represented by R ₁ , R ₂ and R ₃ is represented by hydrogen or an alkyl group. As the alkyl group,
Examples include a methyl group, an ethyl group, and an isobutyl group. Also,
It may be a substituted alkyl group in which a hydroxyl group, a halogen group or the like is substituted. R ₁ , R ₂ and R ₃ may be the same or different, but at least one of them is an alkyl group. The total number of carbon atoms of the vinyl cyanide monomer represented by the formula (I) is not particularly limited, but is preferably less than 7. If it exceeds 7, the copolymer becomes hard and the ink acceptability may decrease. Specific examples of the vinyl cyanide monomer represented by the formula (I) include, for example, 2-methylpropenenitrile, 2-ethylpropenenitrile,
-Propylpropenenitrile, 2-butenenitrile, 2
-Pentenenitriles and the like. The monomer is preferably used in a range where the monomer unit is more than 30% by weight and 70% by weight or less, preferably more than 30% by weight and 60% by weight or less. When acrylonitrile is used as the vinyl cyanide monomer, as is clear from the results of Comparative Examples 3, 4, and 5 in Table 2, the gel content increases, and the dry strength, blister resistance, and wet strength decrease. Even when the vinyl cyanide monomer represented by the formula (I) is used, as is apparent from the results of Comparative Examples 1 and 2 in Table 2, the amount used is 30% by weight.
If it is less than 70% by weight or more than 70% by weight, sufficient dry strength and wet strength cannot be obtained. Examples of the aliphatic conjugated diolefin monomer include 1,3-butadiene,
2-methyl-1,3-butadiene, 2-chloro-1,3
-Butadiene and the like. Usually, these monomers are used in a range where the monomer unit is 20 to 70% by weight, preferably 30 to 60% by weight. If the amount is less than 20% by weight, the copolymer becomes too hard, and the bonding force with the pigment decreases. If the amount exceeds 70% by weight, the water resistance decreases. Examples of the ethylenically unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. These monomers are used in the range of 0.5 to 10% by weight, preferably 1 to 7% by weight of the monomer unit. However, if it exceeds 10% by weight, the viscosity of the latex increases. In addition to the above monomers, monomers such as ethylenically unsaturated amide, acrylonitrile, ethylenically unsaturated carboxylic acid ester, and vinyl aromatic which can be copolymerized with these monomers can also be copolymerized. Examples of the ethylenically unsaturated amide include (meth) acrylic monomers exemplified by acrylamide, N-methylolacrylamide, methacrylamide, and the like. These monomers are used in an amount of usually from 0 to 6% by weight, preferably from 0 to 3% by weight, in order to improve the mechanical stability of the latex. Examples of the ethylenically unsaturated carboxylic acid ester include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl Examples include itaconate, monomethyl fumarate and monoethyl fumarate. These monomers usually have a monomer unit of 0 to improve the ink deposition property.
It is used within a range of 40% by weight, preferably 0 to 30% by weight. Examples of the vinyl aromatic monomer include styrene, α-methylstyrene, vinyltoluene, and dimethylstyrene. These monomers are used in an amount of usually from 0 to 60% by weight, preferably from 0 to 50% by weight, in order to give the copolymer an appropriate hardness. Acrylonitrile is used in an amount of usually from 0 to 25% by weight, preferably from 0 to 20% by weight, in order to improve oil resistance and increase printing gloss.

The polymerization system of the polymer latex of the present invention is
Both a batch polymerization system and a continuous polymerization system are possible.
The method of adding the various components in the emulsion polymerization is not particularly limited, and may be any of a batch addition method, a divided addition method, and a continuous addition method. In the polymerization, known emulsifiers, polymerization initiators, chain transfer agents and the like are used. Emulsifiers include anionic surfactants such as higher alcohol sulfates, alkylbenzene sulfonates and aliphatic sulfonates, and nonionic surfactants such as polyethylene glycol alkyl ester, alkyl phenyl ether and alkyl ether types. Are used alone or in combination of two or more. In consideration of the water resistance of the obtained copolymer latex, it is preferable to use the copolymer latex in an amount of 2 parts by weight or less based on the total amount of monomers. As the initiator, a water-soluble initiator such as potassium persulfate, ammonium persulfate, or sodium persulfate, a redox-based initiator, or an oil-soluble initiator such as benzoyl peroxide can be used. As the chain transfer agent, mercaptans, halogenated hydrocarbons and the like can be used.

[0007] The paper coating composition of the present invention includes mineral pigments generally used for paper coating such as clay, barium sulfate, titanium oxide, calcium carbonate, and satin white.
The copolymer latex of the present invention and, if necessary, a natural or synthetic binder such as casein, starch and polyvinyl alcohol can be blended. The preferred use ratio of the copolymer latex of the present invention and the pigment is 5 to 40 parts by weight of the copolymer latex based on 100 parts by weight of the pigment. Furthermore, various compounding agents generally used in the field of coating, such as water resistance improvers, water resistance reaction accelerators, pigment dispersants, viscosity modifiers, coloring pigments, organic or inorganic developers, pH regulators, A foaming agent and other additives can be optionally added. Next, examples will be shown to make the present invention easier to understand, but the present invention is not limited thereto.

[0008]

【Example】

Example 1 As examples of the present invention, each of the monomers shown in Table 1 and α-
Methylstyrene dimer and t-dodecyl mercaptan were charged to a 10-liter autoclave at the indicated weight ratio and polymerized at 70 ° C. to produce a synthetic latex. All polymerization conversions were 95% or more. Similarly, as a comparative example, a polymer latex was produced by polymerizing each monomer, α-methylstyrene dimer and t-dodecylmercaptan shown in Table 2. All polymerization conversions were 95% or more. The obtained copolymer latex was adjusted to pH 8.0, coagulated with isopropanol, washed and dried, immersed in a predetermined amount (about 0.3 g) of the sample in a predetermined amount (100 ml) of tetrahydrofuran for 40 hours, and then immersed in tetrahydrofuran. The insoluble content was measured and expressed in terms of% by weight based on the sample, and was defined as the gel content. The results are shown in Tables 1 and 2. Example 2 Each component shown in Table 3 was blended in the weight ratio shown there to produce a coating liquid. Using this coating solution, a base paper for coated paper is coated using a coater and dried.
g / m ² ). RI dry pick, RI of the obtained coated paper
Wet topics and blister resistance were measured.
The results are shown in Tables 1 and 2. As is clear from the results in Table 1, the coating liquid containing the polymer latex of the present invention as a main component has excellent RI dry pick, RI wet topic and blister resistance. And the balance is good. In addition, about each said performance, it tested by the test method shown below. RI dry pick The degree of picking when printed with an RI printing machine was visually determined and evaluated by a five-point method. The higher the score, the better. Displayed as the average of six measurements. RI Wet Topic The degree of picking when a dampening solution was applied using a Molton roll with an RI printing machine was visually judged, and evaluated by a five-point method. The higher the score, the better. Displayed as the average of six measurements. Blister resistance Indicates the lowest temperature at which blistering occurs when the paper coated on both sides is humidified (about 6%) and thrown into a heated oil bath.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

[0012]

According to the present invention, there is provided a paper coating composition which is excellent in dry strength, wet strength and blister resistance and has a good balance among them.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-34297 (JP, A) JP-A-57-51703 (JP, A) JP-A-5-295695 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) D21H 11/00-27/42

Claims (1)

(57) [Claims] 1. A conjugated diene monomer unit of 20 to 70% by weight, an ethylenically unsaturated carboxylic acid monomer unit of 0.5 to 1
A paper latex containing 0% by weight and a copolymer latex containing more than 30% by weight and not more than 70% by weight of a vinyl cyanide monomer unit represented by the formula (I). Composition. Embedded image (However, R ₁ , R ₂ and R ₃ are hydrogen or an alkyl group, and at least one of R ₁ , R ₂ and R ₃ is an alkyl group.)