JPH07109698A - Paper coating agent - Google Patents

Abstract

PURPOSE:To obtain a paper coating agent composed of polyvinyl alcohol fine particles each having a particle diameter within a specified range and excellent in application properties. CONSTITUTION:This paper coating agent is produced by preparing an aqueous slurry containing polyvinyl alcohol fine particles having an average particle size of 0.01 to 1mum, especially 0.2 to 0.9mum as the dispersed material. This paper coating agent is excellent in application properties, especially suitability for blade coater application or roll coater application without reducing the characteristics of PVA, e.g. film forming properties or strength. A coated paper excellent in surface strength and barrier properties can be obtained by applying this coating agent and drying it at 90 to 300 deg.C, especially 100 to 180 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating agent for paper, and more particularly to a coating agent for paper excellent in suitability for blade coater or roll coater.

[0002]

2. Description of the Related Art Conventionally, polyvinyl alcohol (hereinafter referred to as P
(Abbreviated as VA) is widely used as a clear coating agent for improving surface properties such as surface strength, smoothness, gloss or barrier property of paper, and as a binder in pigment coating. PVA is
It is widely known that it has an excellent performance in film-forming property and strength that cannot be followed by other sizing agents. However, in recent years, with the increase of the coating speed or the change of the coating method such as coating with a roll coater, in the conventional coating with an aqueous solution, for example, the viscosity increase under a high shear rate condition in a blade coater (dilatancy),
Alternatively, there are many problems such as the formation of streak-like coating film and the occurrence of mist-like scattering in high-speed roll coating, which leads to the situation that stable and uniform coating cannot be performed.

[0003]

DISCLOSURE OF THE INVENTION The present invention maintains the characteristics such as film-forming property and strength of PVA as described above,
It is intended to provide a coating agent for paper which is excellent in coating suitability.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that the average particle size is 0.
By using the fine particle PVA of 0 to 1 μm, particularly by using the fine particle PVA which is substantially insoluble in cold water and maintains a slurry state and dissolves in a drying process after coating to form a film. Have found that the above-mentioned problems can be achieved. The present invention has been completed based on these findings. That is, the present invention has an average particle size of 0.0
It is intended to provide a coating agent for paper which is composed of fine particle PVA having a particle size of 1 to 1 μm (preferably 0.1 to 1 μm, more preferably 0.2 to 0.9 μm). The viscosity average degree of polymerization of the particulate PVA used in the present invention (hereinafter, abbreviated as degree of polymerization) is not particularly limited, but 550 or more is preferable, and 700 or more is more preferable from the viewpoint of strength physical properties of coated paper. 1000 or more is particularly preferable. The upper limit of the degree of polymerization is not particularly limited, but is preferably 30,000 or less, more preferably 20,000 or less. The saponification degree of the particulate PVA is not particularly limited, but is preferably 70 to 100 mol%, more preferably 80 to 100 mol%,
90 to 100 mol% is more preferable, and a higher saponification degree is more preferable. When the particle size of the particulate PVA is larger than 1 μm, the particulate PVA is not sufficiently dissolved in the drying process after coating, so that the effect of the present invention cannot be sufficiently obtained. If the particle size of the fine particles PVA is smaller than 0.01 μm, the viscosity of the water slurry tends to be high, which is not suitable for the purpose of the present invention.

As a method for obtaining the fine particle PVA used in the present invention, for example, a dispersion polymerization or emulsion polymerization of a vinyl ester, particularly vinyl acetate, is carried out to 0.0.
A method in which polyvinyl ester fine particles having a size of 1 to 1 μm are prepared and saponified in an alcohol or a solvent such as paraffin, or a polyvinyl ester obtained by an ordinary solution polymerization method is spray dried or the like to have a particle diameter of 0.01.
Examples of the method include, but are not limited to, a method of saponifying it in alcohol or a solvent such as paraffin, and the like.

As the above-mentioned polyvinyl ester, other unsaturated monomers copolymerizable with vinyl ester,
For example, olefins such as styrene, alkyl vinyl ether, vinyl versatate, (meth) acrylamide, ethylene, propylene, α-hexene and α-octene,
Unsaturated acids such as (meth) acrylic acid, crotonic acid, maleic acid (anhydrous), fumaric acid, itaconic acid, and their alkyl esters, alkali metal salts, 2-acrylamido-
Sulfonic acid-containing monomers such as 2-methylpropanesulfonic acid and alkali metal salts thereof, trimethyl-3- (1-acrylamido-1,1-dimethylpropyl) ammonium chloride, trimethyl-3- (1-acrylamidopropyl) ammonium Polyvinyl ester obtained by copolymerizing a cationic monomer such as chloride, 1-vinyl-2-methylimidazole and a quaternary compound thereof, a silyl group-containing monomer such as trimethoxyvinylsilane, etc. in a small proportion can also be used. .

The fine particle PVA used in the present invention is 10
It can be rendered substantially insoluble in cold water by ordinary drying at 0 ° C. or higher, heat treatment at 100 ° C. or higher in air, or heat treatment at 100 ° C. or higher in methanol using an autoclave. Here, substantially insoluble in cold water,
It means that the solubility in water at 20 ° C. is 50% or less. So far, fine particles P having an average particle diameter of about 30 μm obtained by pulverizing PVA having a degree of polymerization of 500 or less.
Although VA is known, the particle diameters of PVA obtained by the pulverization method are all over 1 μm, and PVA having such a particle diameter is insoluble in cold water and has a solubility in the dryness after coating. Both properties cannot be satisfied at the same time, and if the degree of polymerization is 500 or less, the strength physical properties are not sufficient, which is not suitable for the purpose of the present invention.

The coating agent of the present invention contains, if necessary, water-proofing agents such as glyoxal and urea resins, plasticizers such as glycols and glycerin, pH adjusting agents such as ammonia, caustic soda, sodium carbonate and phosphoric acid. Known additives such as a foaming agent, a release agent, and a surfactant can be added. Still other coating agents such as PVA,
Modified PVA (eg, carboxyl group-modified PVA, sulfonic acid group-modified PVA, acrylamide-modified PVA, cationic group-modified PVA, long-chain alkyl group-modified PVA), starch, modified starch, casein, carboxymethylcellulose (CMC) or synthetic resin emulsion ( Styrene
A butadiene latex, a polyacrylic acid ester emulsion, a vinyl acetate-acrylic acid ester copolymer emulsion, a vinyl acetate-ethylene copolymer emulsion) or the like can be mixed.

The coating agent of the present invention can be used as a clear coating agent or a pigment coating agent, and is particularly effective in coating with a high speed roll coater or a blade coater, but is not limited thereto. When the coating agent of the present invention is used as an aqueous slurry, the fine particle PVA in the aqueous slurry is used.
The concentration of 0.5 to 50% by weight is preferable, 1 to 40% by weight is more preferable, and 2 to 30% by weight is particularly preferable.
When used as a pigment coating agent, the concentration of the pigment in the aqueous slurry is preferably 2 to 70% by weight.
-60% by weight is more preferable, and 10-50% by weight is particularly preferable. Fine particle PV in the coating agent of the present invention
The amount of solid content applied to the paper surface of A is 1 to 30 g / m ²
Is preferred. The coating speed when the coating agent of the present invention is applied to paper as an aqueous slurry is not particularly limited, but is preferably 100 to 2000 m / min, and 300 to
1500 m / min is more preferable. There is no particular limitation on the drying temperature (air temperature) after coating the paper with the coating agent of the present invention as an aqueous slurry, but 90 to 30
0 degreeC is preferable, 100-200 degreeC is more preferable, 1
Even more preferably from 00 to 180 ° C. The reason why the coating agent of the present invention is remarkably excellent as described above is estimated as follows. That is, since it behaves as particles at the time of application, it has a low viscosity, remarkably good applicability as compared with the case of solution-like PVA, and easily dissolves at the time of drying after application. It is presumed that the strength and the like are expressed.

EXAMPLES Hereinafter, the paper coating agent of the present invention will be described in more detail by way of examples. Hereinafter, “part” or “%” is based on weight unless otherwise specified.

Cold water solubility: 4 parts of fine particle PVA was added to 100 parts of water at 20 ° C., and after stirring for 30 minutes, the particles were separated by centrifugation and calculated from the PVA concentration in the supernatant. Cold water solubility (%) = (amount of dissolved PVA) / (amount of fine particle PVA) × 100 High shear viscosity: measured at 20 ° C. using an extrusion viscometer composed of a capillary having a diameter of 0.5 mm and a length of 5.0 mm. . Surface strength: measured with ink M and speed P using an IGT printability tester. Air Permeability: Measured with a Woken air permeability meter. Average particle size of fine particles PVA: Fine particles PVA are dispersed in acetone and measured by an electrophoretic light scattering photometer (ELS-800) manufactured by Otsuka Electronics Co., Ltd. using the cumulant method.

Example 1 Polymerization degree 1750, saponification degree 985 mol%, particle diameter 02 μ
10 parts of fine particle PVA having a water solubility of 1% at 20 ° C. in m was put into a slurry obtained by decomposing 100 parts of kaolin clay into 110 parts of water to prepare a coating composition having a solid content of 50%. The high shear viscosity (shear rate = 5 × 10 ⁵ sec ⁻¹ ) of this coating composition was 50 centipoise (cp) (20 ° C.). This coating composition was applied at 20 ° C. to a fine paper base paper using a blade coater so that the solid content was 20 g / m ² .
Dry for 2 minutes at 105 ℃, surface temperature 80 ℃, linear pressure 100
Calendar finishing was performed under the condition of kg / cm. The obtained coated paper was conditioned for 72 hours at a constant temperature of 20 ° C. and a relative humidity of 65%, and its performance was evaluated. The results are shown in Table 1.
Shown in.

Comparative Examples 1 to 4 Instead of the fine particle PVA used in Example 1, P shown in Table 1 was used.
The same operation as in Example 1 was performed except that VA was used. The results are also shown in Table 1.

[0013]

[Table 1]

* 1 ··· 20 ° C, shear rate = 5 × 10 ⁵ sec ^-1 * 2 · · There are undissolved PVA particles in the coating layer * 3 · · High dilatancy prevents uniform coating at high speed

Examples 2 to 4 An aqueous slurry of fine particle PVA as shown in Table 2 was applied at 20 ° C. to a paper having an air permeability of 10 seconds at a speed of 300 m / min using a gate roll coater (3 roll coater). The solid content was applied at a coating amount of 4 g / m ² , dried at 105 ° C. for 2 minutes, and then the air permeability was measured. The results are shown in Table 2.

Comparative Examples 5 to 7 The same operations as in Example 2 were carried out except that the PVA as shown in Table 2 was used instead of the fine particle PVA used in Example 2. The results are also shown in Table 2.

[0017]

[Table 2]

* 1 ··· PVA is not sufficiently dissolved and the coating layer is often cracked. * 2 ... There are many streaks in the coating layer, resulting in a non-uniform coating.

Example 5 The fine particle PVA used in Example 1 was dispersed in water at 20 ° C.,
A 4% water slurry was prepared. This water slurry was continuously charged between the first roll and the second roll of a three-roll coater, rotated at a speed of 500 m / min, and the water slurry from between the second roll and the third roll was changed. The state of scattering was observed. There was almost no scattering, and the liquid was transferred uniformly onto the roll.

Comparative Example 8 The same operation as in Example 5 was carried out except that the fine particle PVA slurry used in Example 5 was replaced with a 4% aqueous solution of PVA having a polymerization degree of 1750 and a saponification degree of 985 mol%. .
In this case, the PVA aqueous solution was scattered in a mist.

Examples 6 to 9 The same operations as in Example 1 were performed except that the fine particle PVA shown in Table 3 was used instead of the fine particle PVA used in Example 1. The results are shown in Table 3.

[0022]

[Table 3]

* 1 ... 20 ° C., shear rate = 5 × 10 ⁵ sec ⁻¹

[0024]

The paper coating agent of the present invention is PVA.
The coating suitability, especially the blade coater or roll coater suitability is remarkably excellent while maintaining the characteristics such as film forming property and strength. That is, the paper coating agent of the present invention provides a coated paper which is excellent in high-speed coating properties and is also excellent in surface strength and barrier properties.

Claims (3)

[Claims] 1. A coating agent for paper, which comprises fine particles of polyvinyl alcohol having an average particle diameter of 0.01 to 1 μm. 2. A paper coating agent comprising an aqueous slurry containing a fine particle polyvinyl alcohol having an average particle diameter of 0.01 to 1 μm as a dispersoid. 3. A method for producing coated paper, which comprises applying the coating agent for paper according to claim 1 on the surface of paper and then drying at 90 to 300 ° C.