JP2599779B2 - Paper coating agent - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of the Invention The present invention relates to a coating agent for paper, and in particular, to a high level of surface strength and a property of low absorption or permeability of air, oil or organic solvent, that is, a high level of barrier property. The present invention relates to a paper coating agent having a property of imparting to paper.

B. Conventional technology Conventionally, polyvinyl alcohol (hereinafter abbreviated as PVA) has been used as a clear coating agent to improve surface properties such as surface strength, smoothness, gloss or barrier properties of paper, and as a binder in pigment coating. Widely used. It is widely known that PVA has excellent performance unrivaled by other sizing agents in film forming property and strength.

However, in recent years, there has been a demand for a PVA that further enhances the surface properties of paper, such as surface strength, under the tendency of a decrease in surface strength due to an increase in the ratio of the southern material contained in the pulp raw material or an increase in printing speed. Further, PVA capable of imparting a higher buyer property has been required for barrier paper which has seen great development in recent years, but conventional PVA, that is, using vinyl acetate and methanol, and having an azeotropic point of 60 ° C
However, the conventional PVA containing more than 1.5 mol% of 1,2 glycol bonds obtained by the conventional industrial method of polymerizing vinyl acetate by the above method has a drawback that these requirements cannot be sufficiently satisfied.

In addition, it is generally known that the use of high polymerization degree PVA can improve the surface properties of paper.However, if the degree of polymerization increases, the solution viscosity increases, so the concentration must be reduced. At low coating weights
In the case of A, there is a disadvantage that the above-mentioned required performance cannot be satisfied.

C. Problems to be Solved by the Invention The present inventors have conducted intensive studies to improve such disadvantages, and as a result, surprisingly, the amount of 1,2 glycol bond is 1.5 mol% or less, more preferably 1.2 mol% or less. When using a paper coating agent containing PVA with a low 1,2-glycol content, surface properties such as paper surface strength, printability, and buyer properties can be obtained even when a low concentration, low viscosity aqueous solution and a low coating amount are used. Have been found to be able to significantly improve the present invention, and the present invention has been completed.

D. Means for Solving the Problems PVA used in the paper coating agent of the present invention is 1,2.
It is essential that the amount of glycol bond be 1.5 mol% or less. It is more preferably at most 1.2 mol%.

As a method for producing such a low 1,2-glycol-bonded PVA, a method of saponifying a polyvinyl ester obtained by subjecting a vinyl ester to low-temperature polymerization at 50 ° C. or lower by bulk polymerization, solution polymerization, emulsion polymerization, or suspension polymerization by a conventional method. (For example, JP
No. 148209, Japanese Patent Application No. 61-182097).

Although there is no particular limitation on the degree of polymerization, 100 or more, especially 500
The above is preferably used.

The degree of saponification is not particularly limited as long as it is a water-soluble physician, but usually 80 mol% or more is used, preferably 95 mol% or more, and more preferably 98 mol% or more.

When the 1,2 glycol engagement amount is more than 1.5 mol%,
When used as a low-concentration, low-viscosity aqueous solution, the remarkable effects described above cannot be obtained.

Further, the low 1,2-glycol bond amount PVA used in the present invention includes a carboxyl group, an anionic group such as a sulfonic acid group, a cationic group such as an ammonium group, and a carbon number of 4 to 18 carbon atoms.
May contain a small amount of 10 mol% or less of a hydrophilic group such as a hydrophobic group, an amide group and the like, and a reactive group such as an acetoacetyl group and a silanol group.

The coating agent of the present invention may contain known additives such as a normal water-proofing agent, a plasticizer, an antifoaming agent, and a release agent, if necessary. Further, other known coating agents, modified PVA, starch, CMC, various synthetic resin emulsions and the like can be mixed. The coating agent is generally suitably used for clear coating of paper, but may be used for pigment coating by appropriately adding a pigment such as clay, calcium carbonate or titanium dioxide.

As the paper for coating the paper coating agent of the present invention,
Although not particularly limited, it is suitably used for paperboard such as manila balls, white balls, and liners, printing paper such as general high-quality paper, medium-quality paper, gravure paper, release paper, and information processing paper.

When the coating agent is applied to such a paper, the aqueous solution concentration may be such that the low PVA binding amount PVA is 20%.
It is appropriate to select from a range of not more than 5% by weight, preferably not more than 5% by weight.

In applying this, any known method such as a size breath, a roll coater, an air knife coater, and a blade coater is employed.

The coating amount is wide depending on the purpose and is not particularly limited, but is usually 0.01 to 30 g / m ² , preferably about 0.05 to 1 g / m ² .

E. Effects and Effects of the Invention The paper coating agent of the present invention is applied to paper using a low-concentration, low-viscosity aqueous solution, and when a low coating amount is applied to paper, the surface strength, printability, It has excellent performance that can significantly improve paper surface properties such as barrier properties.

Hereinafter, the coating agent for paper of the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the example, "%"
And "parts" are on a weight basis.

Examples 1 to 5 and Comparative Examples 1 to 2 Using a PVA aqueous solution as shown in Table 1- (a), using a size press at 60 ° C., nip pressure, 10 kg / cm, 100 kg
basis weight 73 g / m ² in m / min, fine paper and air permeability 220 of air permeability 15 seconds
After coating on glassine paper for 2 seconds and drying on a roll at 100 ° C. for 1 minute, a calender roll at 60 ° C.-100 kg / cm-10 m / min was passed three times.

Table 1 shows the barrier properties (air permeability) of the obtained coated paper.
(B). [Here the air permeability (second) is JIS P-8130
Was measured by However, the degree of polymerization was measured by a method according to JIS K-6726 using an aqueous PVA solution having a specific viscosity (ηsp) of 0.4 to 0.8. The 1,2-glycol bond amount (mol%) was measured by NMR.

From the results shown in Table 1- (b), the paper coating agent of the present invention containing a 1,2 glycol-bonded amount of 1.5 mol% or less and containing a low 1,2-glycol-bonded amount PVA imparts a remarkably high barrier property. It is clear that it has the properties to gain.

Example 6, Comparative Examples 3 and 4 Aqueous solution (Example 6) used in Example 1 and Comparative Example
Using the 2% aqueous solution used in 1 and 2 (Comparative Examples 3 and 4),
The cardboard liner paper of 220 g / m ² was applied by a bar coater, 100 ° C., after drying 1 minute was line summer and humidified, Kiyarenda finish under the conditions of 60 ℃ -100kg / cm-10m / min Was done. The coated paper is kept at a temperature of 20 ° C and a relative humidity of 65.
% In a constant temperature room for 48 hours, and then the physical properties of the paper were measured. Table 2 shows the results.

The PVA having a low 1,2-glycol content of the present invention has a better yield on the paper surface and a higher film-forming strength than those having a higher 1,2-glycol content, and thus clearly shows excellent physical properties.

(Note 1) Surface strength: Performed by an IGT printability tester using an IGT pickle oil H ink, a printing pressure of 35 kg / cm, and a spring drive A. The higher the value, the higher the surface strength.

(Note 2) Wear strength; according to TAPPI standard method T476. The smaller the value, the higher the wear strength.

(Note 3) Water absorption: The contact time between water and paper was 2 minutes according to JIS P-8140. Water resistance is so high that a numerical value is small.

(Note 4) Printability: Using a RI printability tester, apply Snap Dry Ink (manufactured by Dainippon Ink and Chemicals Co., Ltd.) to a thickness of 5 μm and comprehensively evaluate the ink receptivity, print gloss, picking, etc. And evaluated on three levels: excellent, good, and acceptable.

Example 7, Comparative Examples 5 to 6 The ratio of the PVA used in Example 1 (Example 7) and the PVA used in Comparative Examples 1 and 2 (Comparative Examples 5 and 6) and the powder of denoxide was 1: The mixture was mixed at a ratio of 9 to 3: 7, water was added, and the mixture was heated and dissolved to prepare a 5% solution, which was used as a coating solution. This coating solution is sized with a nip pressure of 10 kg / cm, 100
at a rate of m / min, it was applied to wood containing paper with a basis weight of 64g / m ^2, 100 ℃
After drying on a roll for 1 minute, temperature 20 ° C, relative humidity 65%
The room was conditioned for 24 hours. Physical properties of the obtained coated paper surface were measured and compared. Table 3 shows the results.

From the results in Table 3, it can be seen that the 1,2-glycol binding amount of the present invention is 1.5
The coating agent for paper containing less than 1 mol% of PVA having a low 1,2-glycol content has excellent strength and barrier properties and excellent physical properties because the coating film is very strong.

Claims (2)

(57) [Claims] 1. A paper coating agent comprising polyvinyl alcohol having a 1,2-glycol bond content of 1.5 mol% or less. 2. The paper coating agent according to claim 1, wherein the 1,2-glycol bond amount of the polyvinyl alcohol is 1.2 mol% or less and the saponification degree is 95 mol% or more.