JP2000290894A - Coating agent for paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating agent which is used for paper, can improve the surface strength of the paper and can especially express a brilliant and uniform color when printed by the same method as printed all over the surface of the paper. SOLUTION: This coating agent for paper comprises (A) 100 pts.wt. of a polyvinyl alcohol-based resin having a saponification degree of >=60 mol.% and a 4% aqueous solution viscosity of >=1.5 mPa.s at 20 deg.C and (B) 0.1 to 10 pts.wt. of a surfactant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a paper coating agent.

[0002]

2. Description of the Related Art Conventionally, polyvinyl alcohol (hereinafter referred to as P
VA) is used as a clear coat agent for improving surface properties such as surface strength, smoothness, and gloss of paper, as a binder in pigment coating, and as an undercoat agent for base paper for release paper for improving barrier properties. It has been widely used in the paper field.

[0003] Compared with other coating agents such as oxidized starch, PVA has a good film-forming property and a high film strength.
It forms a film with excellent smoothness on the paper surface, and can obtain a surface strength 2 to 4 times higher than that of oxidized starch, and is extremely useful as a coating agent for papers such as liners, paperboards, and bags. It is well known that this is effective.

However, when a paper coating solution containing PVA is applied to the paper surface, the surface strength, smoothness, and gas barrier properties are generally improved because the PVA is generally concentrated and distributed near the paper surface. However, during printing, especially during high-quality color printing, the ink is repelled by the PVA layer on the paper surface, or the ink penetration changes during solid printing due to the slight difference in the thickness of the PVA layer. There is a disadvantage that clear and uniform printing cannot be performed due to shading of the image. In particular, recently, color printing has been frequently performed on corrugated cardboard, and the vividness and uniformity of printing have been particularly viewed as a problem.

Recently, from the viewpoints of environmental conservation and effective use of resources, utilization of waste paper has been called for.
There is a tendency for the so-called recycled paper usage rate of recycled paper to increase. However, when used paper is used, various hydrophobic substances cannot be prevented from being mixed, and when a water-soluble coating agent is used for such recycled paper, pinholes are easily generated around the hydrophobic substance, so that printing is difficult. It is easy to cause unevenness.

When a polyacrylamide (hereinafter abbreviated as PAM) coating agent is used as the above-mentioned coating agent,
Although the above disadvantages during printing are slightly improved, the surface strength is P
Compared to VA, PAM is not as good as PVA.
It is an expensive coating agent and disadvantageous in terms of economy.

[0007]

DISCLOSURE OF THE INVENTION The present invention relates to a paper surface coating which has a high effect of improving the surface properties such as the surface strength of coated paper, and which exhibits excellent color development during printing, especially during high quality color printing. It is intended to provide an agent.

[0008]

The method of the present invention achieves the above object. (A) The saponification degree is 60 mol% or more, and the viscosity of a 4% aqueous solution at 20 ° C. is 1.5 mP.
With respect to 100 parts by weight of PVA-based resin that is
(B) 0.1 to 5 parts by weight of a surfactant is blended.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. The PVA-based resin used in the present invention has a saponification degree of 60 mol% or more and a 4% aqueous solution viscosity at 20 ° C. of 1.5 mPa · s or more.

The degree of saponification is at least 60 mol%, preferably 7
If it is 0 mol% or more, more preferably 88 mol% or more, and if the degree of saponification is less than 60 mol%, the aqueous solution may cause phase separation and coating may be difficult. 4% at 20 ° C
Aqueous solution viscosity is 1.5 mPa · s or more, preferably 5 mP
a · s or more. When the viscosity of the 4% aqueous solution at 20 ° C. is less than 1.5 mPa · s, the improvement in the surface strength of the coated paper is small.

The PVA resin used in the present invention is obtained by polymerizing an aliphatic vinyl ester by a known method such as bulk, solution, suspension or emulsion polymerization, for example, alcohols such as methanol, methyl acetate and ethyl acetate. In a mixed solvent of esters and alcohols such as sodium hydroxide such as sodium hydroxide or an alcoholate such as sodium methylate by a known method using a saponification catalyst. Can be Drying and pulverizing methods of the saponified product are performed by various known methods.

The above-mentioned aliphatic vinyl esters include:
Examples thereof include vinyl formate, vinyl acetate, vinyl propionate, and vinyl pivalate, and industrially, vinyl acetate is preferred.

The above-mentioned PVA resin may be a copolymer of an unsaturated monomer copolymerizable with the aliphatic vinyl ester and an aliphatic vinyl ester. As the unsaturated monomer copolymerizable with the aliphatic vinyl ester, for example, ethylene, α-olefins such as propylene, crotonic acid, unsaturated base acids such as acrylic acid or salts thereof,
Unsaturated dibasic acids such as maleic acid, itaconic acid and fumaric acid or salts thereof, or monoalkyl esters of unsaturated dibasic acids such as monomethyl maleate and monomethyl itaconate, (meth) acrylates, acrylamide, diamide Acetone acrylamide, dimethyl acrylamide, N-methylol acrylamide, N-vinyl-2-
Amide group-containing monomers such as pyrrolidone, alkyl vinyl ethers such as lauryl vinyl ether and stearyl vinyl ether, silyl group-containing monomers such as trimethoxy vinyl silane, and hydroxyl group-containing monomers such as allyl alcohol, dimethylallyl alcohol and isopropenyl allyl alcohol , Allyl acetate, dimethyl allyl acetate,
Acetyl group-containing monomers such as isopropenyl allyl acetate, sodium vinyl sulfonate, acrylamide-2-
Examples thereof include vinyl sulfonic acid group-containing monomers such as sodium methylpropanesulfonate, halogen-containing monomers such as vinyl chloride and vinylidene chloride, and aromatic monomers such as styrene, but are not limited thereto.

The PVA resins used in the present invention include different types of PVA resins such as those having different degrees of saponification, those having different aqueous solution viscosities, those not copolymerized and modified, and those modified by copolymerization. May be used as a blend of two or more. The blending may be performed in a powder state, an aqueous solution state, or a polyvinyl ester state before saponification.

The surfactant (B) used in the present invention is a surfactant having various known structures, for example, known anions such as carboxylate, sulfate, sulfonate and phosphate salt. Surfactants, primary amine salts,
Cationic surfactants such as secondary amine salt, tertiary amine salt and quaternary amine salt; amphoteric surfactants such as amino acid type and betainic acid type; ethylene glycol type, acetylene glycol type and polyhydric alcohol type And other nonionic surfactants, fluorine-based surfactants and the like.
Among them, nonionic surfactants are preferred. Moreover,
Polyethylene glycol nonionic surfactants such as higher fatty alcohol ethylene glycol adducts, fatty acid ethylene glycol adducts, and polypropylene glycol ethylene glycol adducts are more preferred.

The surfactant used in the present invention is 20 ° C.
The surface tension of the 0.1% aqueous solution at 46 dyne / c
m or less is preferable. Furthermore, 35 dyne / c
m or less are more preferable.

The amount of the surfactant used in the present invention is 0.1 to 10 parts by weight, preferably 1 to 8 parts by weight, per 100 parts by weight of PVA. When the amount of the surfactant is less than 0.1 part by weight, the effect of improving the color developability during color printing is not observed. Because it does not go up
This is disadvantageous in terms of cost and bleeds out of the surfactant, resulting in adverse effects such as reduction in paper strength and quality.

The paper coating agent of the present invention is generally used by dissolving in water in the same manner as ordinary PV #. On this occasion,
A mixture of (A) a PVA-based resin and (B) a surfactant may be added to water to dissolve the mixture, and (B) may be added to the aqueous solution of (A).
May be added.

Known additives such as a plasticizer, an antifoaming agent, a fungicide, and an antistatic agent can be added to the paper coating agent of the present invention, if necessary. Further, other coating agents within the range not impairing the effects of the present invention, for example, starches, carrageenan and agarose-agaropectin, sodium alginate, chitin, polysaccharides such as chitosan, or acrylic emulsion, various synthetic resin emulsions such as SBR, Inorganic pigments, organic pigments and the like can be mixed.

The paper to be coated with the paper coating agent of the present invention is not particularly limited. For example, information processing paper, general high quality paper, medium quality paper, gravure paper, printing paper such as newsprint, liner paper, manila ball And white paperboard.

When the coating agent is applied to such paper, the concentration of the aqueous solution is suitably 30% by weight or less, preferably 1 to 20% by weight as a solid content.

In applying this, a known arbitrary method such as a gate roll coater, a size press, an air knife coater, a blade coater or the like is employed.

The coating amount of the paper coating agent of the present invention is not particularly limited, but is usually 0.01 to 30 g / g depending on the purpose of use.
m is about ² coating.

[0024]

The present invention will be described more specifically with reference to the following examples.

Example 1 As a component (A), 100 parts by weight of PVA having a saponification degree of 98 mol%, a 4% aqueous solution viscosity at 28 ° C. of 28 mPa · s and (B) a polyethylene glycol type surfactant (Sammorin 11, Sanyo) And 2 parts by weight of Kasei Co., Ltd.) to obtain a coating agent. After dispersing this coating agent in water,
What was heated and melted at 80 ° C. to prepare an aqueous solution having a concentration of 4% was used as a coating liquid. A coated paper was prepared using the coating liquid by the following method, and an evaluation test was performed on the coated paper.

Preparation of Coated Paper A bar coater was applied to one side of uncoated fine paper (basis weight 65 g / m ² ) so that the coating amount of the coating agent was 0.5 g / m ^2. Was used for coating. Immediately after coating, use a drum dryer for 95 minutes.
C., dried for 2 minutes, and then humidified in an atmosphere of 20.degree. C. and 65% RH for 2 days to prepare a coated paper.

Evaluation test of coated paper (1). Surface Strength (Test for Surface Strength of Paper Using Wax) A test was conducted in accordance with JIS P8129.

(2). Printability. Color Unevenness Test Water-based poster color (Red) manufactured by Turner Co., Ltd. was applied to the coated surface with a brush and the color unevenness was visually observed and evaluated according to the following criteria. Evaluation criteria ○: No color unevenness Δ: Slight color unevenness ×: Color unevenness is clearly present. Colorimeter test Shin asahi flower stamp ink (red)
The density of the red color on the printing surface when a round solid mark having a diameter of 3 cm is pressed with a spectroscopic colorimeter SE-20 manufactured by Nippon Denshoku Industries Co., Ltd.
It was measured at 00. Δa: The larger the value, the larger the vector in the red direction of the color.

(3). Comprehensive evaluation Comprehensive evaluation was performed based on the following criteria based on the above evaluation. ：: Both surface strength and printability are excellent. X: One or both of surface strength and printability are poor. As shown in Table 1, the results of the above evaluation test showed that the surface strength was good, there was no color unevenness, and deep red could be expressed.
Excellent overall evaluation was obtained.

Example 2 A modified PVA obtained by saponifying a copolymer of vinyl acetate and monomethyl maleate in place of the PVA of Example 1.
(Saponification degree 97 mol%, viscosity of 4% aqueous solution at 20 ° C. 3
A coating liquid was prepared and tested in the same manner as in Example 1 except that 0 mPa · s and a degree of modification of monomethyl maleate of 1.9 mol%) were used, and the amount of the surfactant was changed to 0.5 part by weight. As shown in Table 1, the results were excellent.

Example 3 In place of the PVA of Example 1, the degree of saponification was 80 mol%, 20
PVA whose 4% aqueous solution viscosity at 5.1 ° C. is 5.1 mPa · s
And polyethylene glycol type surfactant (Newpol PE-61, manufactured by Sanyo Chemical Co., Ltd.) 8
A coating solution was prepared and tested in the same manner as in Example 1 except that the amount was changed to parts by weight. The results are shown in Table 1,
It was excellent.

Example 4 Example 1 was repeated except that 0.5 parts by weight of an acetylene glycol type surfactant (Surfinol 104E, manufactured by Nissin Chemical Co., Ltd.) was used in place of the surfactant of Example 1. A coating solution was prepared and tested in the same manner. As shown in Table 1, the results were excellent.

Example 5 A test was conducted in the same manner as in Example 1 except that paper containing 30% of used paper (basis weight: 65 g / m ² ) was used. As shown in Table 1, the results were excellent.

Comparative Example 1 As a component (A), 100 parts by weight of PVA having a saponification degree of 98 mol% and a 4% aqueous solution viscosity at 28 ° C. of 28 mPa · s was dispersed in water, and then heated and dissolved at 80 ° C. And concentration 4
% Was prepared as a coating solution. The coating and evaluation methods were tested as in Example 1. As shown in Table 1, the results were particularly poor in color unevenness.

Comparative Example 2 A coating liquid was prepared and tested in the same manner as in Example 1 except that the amount of the surfactant (B) in Example 1 was changed to 0.05 part by weight. As shown in Table 1, the results were particularly poor in color unevenness.

Comparative Example 3 Paper containing about 30% of used paper (basis weight 65 g / m ² ) was used.
A coating solution was prepared and tested in the same manner as in Example except that the component (B) was not used. As shown in Table 1, the results were particularly poor in color unevenness.

Comparative Example 4 A test was carried out in the same manner as in Example 1 except that gelatinized starch was used instead of the coating agent of the present invention. As shown in Table 1, the results were particularly poor in strength.

[0038]

[Table 1]

[0039]

According to the paper coating agent of the present invention, PVA
Is present with an appropriate concentration distribution from the coated surface of the paper to the center, improving the surface strength, making it difficult for delamination to occur, and at the same time printing, especially when applying a solid ink. Also, clear and uniform printing with less color unevenness can be achieved.

Claims (1)

[Claims] (A) When the saponification degree is 60 mol% or more,
It is characterized by comprising 0.1 to 10 parts by weight of a surfactant (B) per 100 parts by weight of a polyvinyl alcohol resin having a 4% aqueous solution viscosity of 1.5 mPa · s or more at 0 ° C. Coating agent for paper.