JPH09241999A - Paper coating agent - Google Patents

Abstract

(57) [Summary] [Structure] Composition of component (B) based on 100 parts by weight of component (A), which is composed of modified polyvinyl alcohol (A) having an ethylene unit content of 3 to 15 mol% and alkali metal ions (B). Paper coating agent with a proportion of 0.003 to 1 part by weight [Effect] Since the paper coating agent of the present invention has excellent solubility in hot water, there are no undissolved substances in the coating agent aqueous solution. When the paper coating agent of the present invention is used as a paper surface treating agent, a coated paper having no coloring and excellent in surface strength, air permeability and printability can be obtained.
Further, when the paper coating agent of the present invention is used as a paper pigment coating agent, a coated paper which is not colored and is excellent in water resistance strength and printability can be obtained.

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to a coating agent for paper. More specifically, it relates to a coating agent for paper, which can provide a coated paper having excellent surface properties such as water resistance.

[0002]

2. Description of the Related Art Conventionally, polyvinyl alcohol has been used as a clear coating agent or a pigment coating agent in order to improve surface properties of paper such as surface strength, smoothness, gloss, gas barrier property, water resistance, printability and solvent resistance. (Hereafter, P
(Abbreviated as VA) is widely used. In recent years, the surface strength of paper has tended to decrease with an increase in the ratio of southern materials and waste paper contained in pulp raw materials. Further, with the increase in printing speed, there is a demand for improvement in the surface strength of paper.
In the case of barrier paper, higher barrier properties are required. In the case of paper used for offset printing or the like using water, high water resistance is required. In order to solve such a problem, a paper coating agent made of modified PVA containing 1 to 10 mol% of an α-olefin unit having 4 or less carbon atoms has been proposed (Japanese Patent Laid-Open No. 63-112).
794, JP-A-63-85198). However, the modified PVA has a problem in solubility in water at 90 ° C. or higher (hereinafter, abbreviated as hot water), and there is a problem in that an undissolved substance exists in the coating agent aqueous solution.

[0003]

The object of the present invention is to obtain a coated paper which is excellent in surface strength, barrier property (a property that absorption and permeation of air, oil, organic solvent, etc. are small), water resistance and printability. The present invention provides a coating agent for paper.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a modified polyvinyl alcohol (A) having an ethylene unit content of 3 to 15 mol%.
And an alkali metal ion (B), the component (A)
The compounding ratio of the component (B) to 100 parts by weight is 0.00
The present invention has been completed by finding a coating agent for paper which is 3 to 1 part by weight.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The modified PVA used in the present invention has an ethylene unit content of 3 to 15 mol%, and 3 to 13%.
Mol% is preferable, 3.5-12 mol% is more preferable, 4-11 mol% is especially preferable. Modified PV of the present invention
When A further contains a hydrophilic group such as an ionic group, the content of ethylene units is preferably 5 to 15 mol%, more preferably 6 to 14.5 mol%. When the content of the ethylene unit is less than 3 mol%, the water resistance of the coated paper decreases. When the content of the ethylene unit is more than 15 mol%, the solubility of the modified PVA in hot water may decrease,
The water resistance of coated paper decreases.

The viscosity-average degree of polymerization (hereinafter abbreviated as degree of polymerization) of the modified PVA is preferably from 50 to 8,000, and more preferably from 100 to 8,000.
6000 is more preferable, and 200 to 4000 is particularly preferable. The polymerization degree (P) of the modified PVA is JIS-K672.
Measured according to 6. That is, after the modified PVA is re-saponified and purified, it is determined by the following formula from the intrinsic viscosity [η] measured in water at 30 ° C. P = ([η] × 10 ³ /8.29) ^{(1 / 0.62) When the} degree of polymerization is less than 50, the surface strength of the coated paper decreases. When the degree of polymerization is greater than 8000, the viscosity of the coating agent aqueous solution becomes too high, and the coatability deteriorates.

The degree of saponification of the modified PVA is 80 to 99.99.
Mol% is preferable, 85-99.9 mol% is more preferable, 88-99.8 mol% is more preferable, 97-9
9.8 mol% is particularly preferred. When the degree of saponification is less than 80 mol%, the solubility of the modified PVA in hot water decreases, and the water resistance of the coated paper decreases. The degree of saponification is 99.99
When it is more than mol%, the coatability is lowered and the viscosity stability of the coating agent aqueous solution is lowered.

The modified PVA of the present invention is obtained by saponifying a copolymer of vinyl ester and ethylene. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate and vinyl versatate, among these. Vinyl acetate is preferred. The modified PVA of the present invention may further contain an anion group or a cation group. The monomer having an anion group or a cation group, a monomer having a carboxyl group derived from fumaric acid, maleic acid, itaconic acid, maleic anhydride, phthalic anhydride, trimellitic anhydride or itaconic anhydride Ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2
A monomer having a sulfonic acid group derived from acrylamido-2-methylpropanesulfonic acid; vinyloxyethyltrimethylammonium chloride, vinyloxybutyltrimethylammonium chloride, vinyloxyethyldimethylamine, vinyloxymethyldiethylamine,
N-acrylamidomethyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylamidodimethylamine,
Examples include monomers having a cationic group derived from allyltrimethylammonium chloride, methallyltrimethylammonium chloride, dimethylallylamine, allylethylamine, and the like. Among these monomers, maleic anhydride, maleic anhydride half ester, itaconic acid, allylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, from the viewpoint of easy availability and copolymerizability, Monomers derived from N-acrylamidomethyltrimethylammonium chloride and N-acrylamidoethyltrimethylammonium chloride are preferred. The content of these monomer units is usually 10 mol% or less, and more preferably 0.1 to 8 mol%.

The modified PVA of the present invention may contain a monomer unit other than a vinyl alcohol unit and a vinyl ester unit as long as the effects of the present invention are not impaired. Examples of such a monomer include acrylic acid and salts thereof; acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate and i-propyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, Methacrylic acid esters such as ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate; acrylamide; N-methyl acrylamide, N-
Acrylamide derivatives such as ethyl acrylamide; methacrylamide; methacrylamide derivatives such as N-methyl methacrylamide, N-ethyl methacrylamide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether; acrylonitrile, methacryloyl Nitriles such as nitriles; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl compounds such as allyl acetate, allyl chloride; maleic acid, its salts or its esters; itaconic acid, its salts or its Esters; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like. The content of these monomer units is preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 3 mol% or less.

The blending ratio of the alkali metal ion (B) in the paper coating agent of the present invention is such that the modified PVA (A).
0.003 to 1 part by weight with respect to 100 parts by weight,
0.005-0.8 parts by weight is more preferable, and 0.007
To 0.6 parts by weight are more preferable, and 0.02 to 0.5 parts by weight is particularly preferable. Examples of the alkali metal ion include potassium ion and sodium ion. When the blending ratio of the alkali metal ion is less than 0.003 parts by weight, the solubility of the modified PVA in hot water decreases. When the content of alkali metal ions is more than 1 part by weight, the coated paper is colored during drying after applying the coating agent.

The method for blending the alkali metal ion (B) is not particularly limited, but when saponifying a copolymer of vinyl ester and ethylene in a solvent, an alkaline substance containing an alkali metal ion is used as a saponification catalyst. A method is preferred in which an alkali metal ion is added to the modified PVA by use, and the modified PVA obtained by saponification is washed with a washing liquid to remove excess alkali metal ion in the modified PVA. Examples of the alkaline substance used as the saponification catalyst include potassium hydroxide or sodium hydroxide. The molar ratio of the alkaline substance used in the saponification catalyst is preferably 0.004 to 0.5 with respect to the vinyl acetate unit,
5 to 0.3 is particularly preferable. The saponification catalyst may be added all at once at the beginning of the saponification reaction, or may be additionally added during the saponification reaction. Examples of the solvent for the saponification reaction include methanol, methyl acetate, dimethyl sulfoxide, dimethylformamide and the like. Among these solvents, methanol is preferable, methanol having a water content controlled to 0.001 to 1% by weight is more preferable, and water content is 0.00
Particularly preferred is methanol controlled to 5 to 0.8% by weight. Examples of the cleaning liquid include methanol, acetone, hexane, water and the like, and among these, methanol is more preferable. The amount of the cleaning liquid is set so as to satisfy the blending ratio of the alkali metal ion (B), but is usually 300 to 100 with respect to 100 parts by weight of the modified PVA.
00 parts by weight is preferable, and 500 to 5000 parts by weight is more preferable. The washing temperature is preferably 5 to 80 ° C,
20-70 degreeC is more preferable. The washing time is preferably 20 minutes to 10 hours, more preferably 1 hour to 6 hours.

The modified PVA of the present invention preferably has a swelling degree of 1.2 to 4 times, more preferably 1.2 to 3 times, and more preferably 1.2 to 2 when immersed in water at 20 ° C. 3 times is particularly preferable. Modified PVA having these swelling degrees,
Due to its excellent solubility in hot water, there is no undissolved substance in the aqueous coating agent solution, and a coated paper excellent in surface properties such as water resistance can be obtained. The swelling degree of the modified PVA is 16
Mesh pass ~ 32 mesh on modified PVA with particle size
Was immersed in a large excess of water at 20 ° C for 2 hours, then 3000 rp
It is the degree of swelling after centrifugal dehydration at m for 3 minutes and is calculated by the following formula. Swelling degree = (weight of wet modified PVA after immersion) / (weight of absolutely dry modified PVA before immersion) Drying temperature after saponification and washing is 60 to 120 ° C.
Is preferable, and 70-110 degreeC is more preferable. The drying time is preferably 30 minutes to 10 hours, more preferably 1 hour to 5 hours. When dried under these drying conditions, a modified PVA having a small volatile content (organic solvent) due to the cleaning liquid and having the above-mentioned swelling degree can be obtained.

The paper coating agent of the present invention is a modified P containing an alkali metal ion obtained by the above method.
It can be prepared by dissolving VA in hot water. The concentration of the modified PVA in the paper coating agent of the present invention is determined from the viewpoint of coatability of the aqueous coating agent solution.
The range of about 0.1 to 30% by weight is preferable.

In the paper coating agent of the present invention, if necessary, water resistance agents such as glyoxal, urea resins, melamine resins, polyvalent metal salts and water-soluble polyamide resins; glycols, plasticizers such as glycerin, and ammonia. A pH adjusting agent such as caustic soda, sodium carbonate, and phosphoric acid; various additives such as a defoaming agent, a release agent, and a surfactant can also be added. Further, the paper coating agent of the present invention includes non-modified PVA; carboxyl-modified PVA, sulfonic acid group-modified P
VA, acrylamide-modified PVA, cationic group-modified PV
A, various modified PVs such as long-chain alkyl group-modified PVA
A: Water-soluble polymers such as starch, modified starch, casein and carboxymethyl cellulose; synthetic resins such as styrene-butadiene latex, polyacrylic ester emulsion, vinyl acetate-ethylene copolymer emulsion, vinyl acetate-acrylic ester copolymer emulsion The emulsion may be used together within a range that does not impair the effects of the present invention.

The coating amount of the paper coating agent of the present invention is not particularly limited, but usually 0.1 to 30 g / m in terms of solid content.
^{About 2} . The paper for the paper coating agent of the present invention is not particularly limited, and examples thereof include paperboard such as manila balls, white balls, and liners; and printing paper such as general high-quality paper, medium-quality paper, and gravure paper. Examples of the coater used when applying the paper coating agent of the present invention include a size press coater, an air knife coater, a blade coater, and a roll coater. The paper coating agent of the present invention is applied to the surface of paper using these coaters, dried in a drying step, and then finished through a super calendar.

When the paper coating agent of the present invention is used as a paper pigment coating agent, pigments such as clay, kaolin, calcium carbonate, titanium white, and satin white are used. As a dispersant for these pigments, sodium pyrophosphate, sodium hexametaphosphate, sodium polyacrylate and the like are used. When used as a pigment coating agent for paper, the modified PVA of the present invention is used in an amount of preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight, based on 100 parts by weight of the pigment. The solid content concentration of the coating liquid is appropriately selected from the range of 30 to 65% by weight.

[0017]

The present invention will be described in more detail with reference to the following examples. In the following examples, “parts” and “%” mean on a weight basis unless otherwise specified.

<< Evaluation Method of Coating Agent Aqueous Solution >> The physical properties of the coating agent aqueous solution were evaluated by the following methods. <Presence or absence of undissolved matter> After the modified PVA powder of 16 mesh pass to 32 mesh on was stirred in water at 90 ° C for 1 hour, the presence or absence of undissolved matter was visually observed. <Aqueous solution viscosity> 6 using a Brookfield viscometer
It was measured at 0 rpm and 30 ° C.

<< Physical Properties of Coated Paper >> The physical properties of the coated paper were evaluated by the following methods. <Wetlab Method> About 0.1 ml of ion-exchanged water at 20 ° C. was dropped on the surface of the coated paper, and the surface was rubbed with a fingertip, and the elution state of the coating agent was observed. 5: Excellent water resistance and no slimy feeling. 4: There is a slimy feeling, but there is no change in the coating layer. 3: Part of the coating agent is emulsified. 2: The whole coating agent is re-emulsified. 1: The coating agent dissolves. <Wet Pick Method> After the coated surface was moistened with water at 20 ° C., the occurrence of picking was observed using an RI tester (manufactured by Mei Seisakusho) and evaluated in the following 5 grades. 5: No picking occurred. 4: Picking occurs very slightly. 3: Picking considerably occurs. 2: Picking occurs almost entirely. 1: Picking occurs on the entire surface. <Printability> Using a RI printability tester, apply snap dry ink (manufactured by Dainippon Ink) to a film thickness of 5 μm,
The ink acceptability and print gloss were observed and evaluated comprehensively in the following three stages. Excellent: The printing density is high, there is no uneven printing density, and the boundary between the printing portion and the non-printing portion is clear. Good: The print density was somewhat light, the print density unevenness was a little, the print portion was slightly blurred, and the boundary between the print portion and the non-print portion was somewhat unclear. Acceptable: The print density is low, the print density unevenness is considerable, the print portion is considerably blurred, and the boundary between the print portion and the non-print portion is unclear. <Surface Strength> Using an IGT printing aptitude tester, ink of IGT pick oil M (manufactured by Dainippon Ink and Chemicals, Inc.), printing pressure 35 kg / cm, and spring drive B were used. The larger the value, the higher the surface strength. <Air permeability> The air permeability was measured by an Oken type air permeability measuring machine. The larger the value, the higher the barrier property.

Example 1 A methanol solution (water content: 0.05%) having a solid content of 30% of a copolymer having an ethylene unit content of 5 mol% and a vinyl acetate unit content of 95 mol% was added to caustic soda (acetic acid). A molar ratio of 0.05 to vinyl units) was added to give 40
Saponification was carried out at 0 ° C for 1 hour, and then saponification reaction was carried out at 60 ° C for 1 hour. To 100 parts of the obtained polymer, 2000 parts of methanol was used and washed at 60 ° C. for 1 hour, and then the liquid was removed. After repeating this methanol washing again,
By drying for 3 hours, the content of ethylene units is 5
Mol%, saponification degree of vinyl acetate unit 99.0 mol%, degree of polymerization 1200, modified PVA1 measured by atomic absorption method
A water-soluble modified PVA having a sodium ion content of 0.2 part per 100 parts was obtained. Then, while vigorously stirring 82.5 parts of an aqueous solution containing 0.3 part of sodium polyacrylate, 100 parts of kaolin clay was added,
An aqueous dispersion of kaolin clay was prepared. Modified P above
To 25 parts of a 20% aqueous solution of VA, 182.5 parts of an aqueous dispersion of kaolin clay was added and mixed to prepare an aqueous coating agent solution having a solid content concentration of 45% and a viscosity of 600 mPa · s at 30 ° C. This coating agent aqueous solution was applied to a high-quality paper base paper (basis weight 60 g / m ² ) using a test flexible blade coater so that the solid coating amount was 15 g.
/ M ² and dried at 105 ° C for 2 minutes, and then calendered under the conditions of a surface temperature of 85 ° C and a linear pressure of 100 kg / cm. The coated paper obtained was heated at 20 ° C for 6
After controlling the humidity at 5% RH for 72 hours, the physical properties of the coated paper were measured.
Table 2 shows the results.

Examples 2 to 7 Coated papers were produced in the same manner as in Example 1 except that the modified PVA shown in Table 1 was used instead of the modified PVA used in Example 1 to prepare coated papers. Was measured. Table 2 shows the results.

Comparative Examples 1 to 3 In place of the modified PVA used in Example 1, non-modified PVA or modified PVA shown in Table 1 was used, except that
A coated paper was manufactured in the same manner as in Example 1, and the physical properties of the coated paper were measured. Table 2 shows the results.

Comparative Examples 4 to 5 Coated paper in the same manner as in Example 1 except that the modified PVA shown in Table 1 obtained by the following method was used in place of the modified PVA used in Example 1. Was manufactured and the physical properties of the coated paper were measured. Table 2 shows the results. Comparative Example 4: Modified PVA in which the same methanol washing as in Example 1 was carried out 4 times when the modified PVA used in Example 3 was produced. Comparative Example 5: Modified PV that was not washed with methanol when producing the modified PVA used in Example 3
A.

[0024]

[Table 1]

[0025]

[Table 2]

Example 8 4.5 parts of the modified PVA used in Example 1 was mixed with 95% of water.
A coating agent aqueous solution having a concentration of 4.5% was prepared by adding to 5 parts and heating. Using a test size press machine (manufactured by Kumagai Riki Kogyo Co., Ltd.), a high-quality paper having a basis weight of 64 g / m ^{2 was} subjected to size press coating with an aqueous coating agent solution at 50 ° C. Nip pressure of 18kg / c for size press coating
m, 60 m / min. The coating amount of the coating agent in terms of solid content was 1.0 g / m ² . The obtained coated paper was conditioned at 20 ° C. and 65% RH for 72 hours, and then the physical properties of the coated paper were measured. The results are shown in Table 4.

Examples 9 to 13 Coated papers were produced in the same manner as in Example 8 except that the modified PVA shown in Table 3 was used instead of the modified PVA used in Example 8 to prepare coated papers. Was measured. The results are shown in Table 4.

Comparative Examples 6 to 10 In place of the modified PVA used in Example 8, unmodified PVA or modified PVA shown in Table 3 was used, except that
A coated paper was produced in the same manner as in Example 8, and the physical properties of the coated paper were measured. The results are shown in Table 4.

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

As is apparent from the above examples, the paper coating agent of the present invention has excellent solubility in hot water, and therefore there is no undissolved substance in the aqueous coating agent solution.
When the paper coating agent of the present invention is used as a paper surface treating agent, a coated paper having no coloring and excellent in surface strength, air permeability and printability can be obtained. Further, when the paper coating agent of the present invention is used as a paper pigment coating agent, a coated paper which is not colored and is excellent in water resistance strength and printability can be obtained.

Claims (1)

[Claims] 1. A modified polyvinyl alcohol (A) having an ethylene unit content of 3 to 15 mol%, and an alkali metal ion (B), wherein the mixing ratio of the component (B) to 100 parts by weight of the component (A) is 0.1. A coating agent for paper which is 003 to 1 part by weight.