JPH0790799A - Coated paper for printing use - Google Patents

Abstract

PURPOSE:To provide the coated paper excellent in printing workability and printability, having high rigidity with highgrade sense. CONSTITUTION:The objective coated paper for printing use can be obtained by providing a sheet of base paper with a coating layer consisting mainly of a pigment and an adhesive. The coating layer contains, based on 100 pts.wt.of the pigment, (A) 5-25 pts.wt., on a solid basis, of the adhesive, a copolymer latex-25-35 deg.C in the lowest film-forming temperature and 0.09-0.13mum in particle diameter and (B) 0.5-5 pts.wt. of carboxyl-modified soybean protein <=150000 dalton in molecular weight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated paper for printing, and more particularly to a coated paper for printing which is excellent in printing workability and has a high-grade feeling and high rigidity.

[0002]

2. Description of the Related Art In recent years, the visualization, colorization, high quality, weight reduction and thinning of printed matter have progressed, and not only the glossiness, whiteness and smoothness of printed paper but also the improvement of rigidity with a sense of high quality. Demand is growing. Further, with the progress of printing technology, high-speed printing has come to be performed, and there is a demand for a coated paper for printing which is excellent in printing workability and has a strong rigidity.

As a conventional technique for improving the rigidity of coated paper for printing, there is a method in which NKP of pulp fibers is mixed in a high proportion in the base paper, and in the coating composition, use of a plate-like pigment having a high aspect ratio, There is a method of blending starch at a high rate.
Also, a high proportion of latex with a high glass transition temperature is blended,
A method of imparting luster and strength by a high temperature calender and consequently increasing rigidity (JP-A-56-148994 and JP-A-54-125712), and further reducing calender conditions in the finishing process. , A method of improving the rigidity by keeping the paper thickness high (JP-A-54-156).
No. 806) and the like.

However, in these methods, the expression of rigidity is not sufficient, or the surface strength of the coated surface is lowered, the smoothness and gloss are lowered, the operability in a high temperature calender is lowered, and the high glass transition point latex is used. The current situation is that high quality and high rigidity coated papers have not been obtained due to the occurrence of mottling during printing due to use.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to a coated paper for printing which is excellent in rigidity and printability and has a high-grade feeling.

[0006]

SUMMARY OF THE INVENTION The present invention is a coated paper for printing in which a coating layer containing a pigment and an adhesive as a main component is provided on a base paper, and the coating layer serves as an adhesive and has a minimum film forming temperature of 25. ~ 35
C., 5 to 25 parts by weight (solid content) of a copolymer latex having a particle diameter of 0.09 to 0.13 .mu.m, and 100 parts by weight of carboxy-modified soybean protein having a molecular weight of 150,000 daltons or less. And 0.5 to 5 parts by weight with respect to the coated paper for printing.

The inventors of the present invention use a copolymer latex having a high minimum film forming temperature to obtain a coated paper having high rigidity, sufficient surface strength and smoothness, and high quality without printing mottling. As a result of diligent research for identifying the particle size of the copolymerized latex having a specific minimum film-forming temperature, and using this latex and a specific soybean protein, a coated paper for printing having excellent quality characteristics was obtained. Therefore, the present invention has been completed.

First, the copolymer latex which is the first requirement will be described. The copolymer latex for providing a coated paper with high rigidity is closely related to the minimum film forming temperature and the particle size. For example, when there are two kinds of latexes having different particle diameters which are copolymer latexes using the same monomer, in order to have the same minimum film forming temperature, the latex having a large particle diameter has a poor film forming property. It is necessary to increase the blending ratio of the soft monomer, and as a result, the rigidity tends to be lower than that of a latex having a small particle size.

The copolymer latex used in the present invention must have a minimum film-forming temperature in the range of 25 to 35 ° C. If the minimum film-forming temperature is lower than 25 ° C, coated paper with high rigidity cannot be obtained, while if it exceeds 35 ° C and higher, the film-forming property of the latex becomes insufficient and the surface strength during printing cannot be obtained. It cannot be expected to improve rigidity.

The particle size of the above latex is 0.0
It is necessary to set in the range of 9 to 0.13 μm. 0.0
If it is less than 9 μm, the film-forming property becomes strong and the rigidity of the coated paper is improved, but the ink absorbability during printing is extremely deteriorated, and the set-off and the ink receptivity are deteriorated, which is not preferable. On the other hand, when the thickness exceeds 0.13 μm, even if the minimum film-forming temperature is in the above range, the effect of developing the rigidity is small as described above, which is not preferable.

It is important to use the copolymer latex in an amount of 5 to 25 parts by weight, preferably 7 to 20 parts by weight, based on 100 parts by weight of the pigment, as the solid content of the latex. If it is less than 5 parts by weight, the effect on the rigidity is not remarkable, and if it exceeds 25 parts by weight, the porosity of the coating layer is extremely lowered, the ink absorbency is deteriorated and the ink receptivity during offset printing is deteriorated. However, it is not preferable.

The copolymer latex which can be used in the present invention means a synthetic adhesive which is an ordinary term in ordinary coated paper for printing, and includes not only rubber latex but also synthetic resin emulsion, for example, styrene. -Conjugated diene-based polymer latex such as butadiene copolymer, acrylic acid-based polymer latex and / or methacrylic acid ester polymer or copolymer latex, or vinyl-based polymer latex such as ethylene / vinyl acetate copolymer Alternatively, an alkali-soluble or non-soluble polymer latex obtained by modifying these various polymer latexes with a functional group-containing monomer such as a carboxyl group can be used.

When the copolymer latex satisfying the above-mentioned conditions is used, coated paper having excellent surface strength and high rigidity can be obtained without carrying out high temperature calendering treatment. However, since latex having a high minimum film-forming temperature has an insufficient film-forming property as compared with ordinary latex, ink absorption unevenness called mottling due to uneven ink absorption during printing is likely to occur.

On the other hand, as the latex has a smaller particle size, migration of the latex is more likely to be promoted during the step of drying the coating layer, so that the particle size is small and the minimum film-forming temperature is relatively high as in the present invention. The use of copolymer latex tends to facilitate mottling. As a result of further intensive research on the method of improving this mottling, the present inventors have found that the addition of carboxy-modified soybean protein is very effective for suppressing uneven migration.

It has been found that the carboxy-modified soybean protein, when used together with the latex used in the present invention, has excellent high-speed coating operability and has an extremely excellent effect on improving mottling. This effect is not always clear,
Soy protein, which is essentially an amphoteric substance, is stabilized in the coating liquid by carboxy modification, but the anion of soy protein is reduced by decreasing the PH of the coating liquid during the drying process of the coating layer. It is considered that immobilization of the coating layer is promoted.

The molecular weight of the carboxy-modified soybean protein used in the present invention is preferably 150,000 daltons or less. When it exceeds 150,000 daltons, the tendency of thickening is so great that streaks and scratches are generated and the concentration of the coating liquid is unavoidably lowered.

The soybean protein of the present invention is mixed in 10 parts by weight.
It is important to be 0.5 to 5 parts by weight with respect to 0 parts by weight. If it is less than 0.5 part by weight, the effect of improving the mottling is small, whereas if it exceeds 5 parts by weight, the tendency of thickening of the coating liquid is so great that the coating operability is deteriorated, which is not preferable.

As the pigment, those which are generally used in the production of coated paper for printing can be used, for example, clay,
Kaolin, aluminum hydroxide, barium sulfate, calcium carbonate, satin white, titanium dioxide, zinc oxide,
One or more pigments for ordinary coated paper such as calcium sulfate, talc, and organic pigments are appropriately selected and used.

As the adhesive, in addition to the copolymer latex of the present invention, for example, a conjugated diene polymer latex such as styrene / butadiene copolymer, a polymer or copolymer of acrylic acid ester and / or methacrylic acid ester. Acrylic polymer latices such as polyvinyl alcohol, synthetic resin adhesives such as polyvinyl alcohol, olefin / maleic anhydride resin, melamine resin; casein, proteins other than the present invention such as soybean proteins and synthetic proteins; positive starch, oxidized starch Adhesives for coated papers such as starches such as; and cellulose derivatives such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose and the like can be appropriately selected and used in combination.

Generally, the total adhesive is adjusted in the range of 5 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the pigment.

Further, various auxiliary agents such as an antifoaming agent, a coloring agent and a release agent are appropriately blended in the coating composition, if necessary.
As an auxiliary agent for accelerating the solidification of coated paper, for example, amine, amide, polyacrylamine, etc. or polyvalent metal salt such as zinc, aluminum, magnesium, potassium, barium, etc. is added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the pigment. You may add about a part.

The coating composition obtained under the above conditions is a coater used in the production of general coated paper for printing, for example, a blade coater, an air knife coater, a roll coater, a reverse roll coater, a bar coater, a curtain coater, Die slot coater, gravure coater,
An on-machine or off-machine coater provided with a coating device such as a Champlex coater size press coater is used to coat the base paper in one layer or in two or more layers.

As the base paper, a base paper having a basis weight of about 30 to 400 g / m ² used for a general printing coated paper is used. The papermaking method is not particularly limited and may be either acidic papermaking or alkaline papermaking, and of course, medium-quality base paper containing high-yield pulp can also be used. Further, a base paper precoated with a size press, a gate roll coater, a film size press, a bill blade coater, a short dwell coater, or other blade coater can be used.

The coating amount on the base paper is generally about 3 to 50 g / m ^{2 in} terms of dry weight, but considering the white paper quality of the obtained coated paper, the printability, and the drying ability by high speed coating, 6 It is desirable to adjust in the range of about 25 g / m ² . As a method for drying the wet coating layer, various methods such as steam drying, hot air drying, gas heater heating, electric heater heating, and infrared heater heating are adopted.

As the finishing method, for example, various calenders including a metal roll such as a super calender, a gross calender, a soft compact calender, or a drum and an elastic roll are appropriately used. As the elastic roll, a roll of resin such as urethane or epoxy, a roll formed of cotton, asbestos, nylon, aramid fiber or the like is appropriately used.

[0026]

EXAMPLES The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited thereto. Also,
Unless otherwise specified, "part" and "%" in the examples mean "part by weight" and "% by weight", respectively.

[Evaluation Method] The evaluation method of each evaluation item is as follows. Rigidity The critical length (unit: mm) in a test width of 30 mm was measured with a Clark stiffness tester (manufactured by Kumagai Riki Kogyo Co., Ltd.), and the measured values were the average values of the grain length and the grain width of the coated paper. Printing mottling Using an RI printing machine (manufactured by Akira Seisakusho Co., Ltd.), two-color offset printing inks were used for overprinting, and unevenness of inking at that time was visually determined. The evaluation criteria are as follows. ○ There is no unevenness of inking. △ Slight unevenness in thickness occurs. × Remarkably occurs. Ink absorbency After printing with offset printing ink using an RI printer (manufactured by Akira Seisakusho Co., Ltd.), the ink is transferred to high-quality paper, and the ink absorbency is determined by three types of standard paper (absorbance 1. 0, 3.0, 5.0) was used as an index for visual determination. The evaluation criteria are as follows. 1.0 (fast absorption) ← → 5.0 (slow absorption). The offset of the standard paper having an absorbency of 5.0 was the lower limit in the offset printing.

Example 1 Kaolin (trade name: HT, manufactured by Engelhard) 65
Parts, fine grained heavy calcium carbonate (trade name: Carbital 9
0, manufactured by ECC Co., Ltd.) with 35 parts of sodium polyacrylate as a dispersant, and dispersed with a Choles disperser,
A pigment slurry with a solid content of 74% was prepared. 2 parts of oxidized starch (solid content), a minimum film-forming temperature of 26 ° C., 15 parts of styrene-butadiene copolymer latex (solid content) having a particle diameter of 0.12 μm, and carboxy-modified soybean protein having a molecular weight of 130,000 daltons ( Product name: SP2500, Protein Technology International Co., Ltd.) 1
Then, water was added to prepare a coating liquid having a solid content of 60%.

The dried coated amount of this coating to be liquid 90 g / m ² base paper to obtain a double-sided coated paper and coated dried blade coater so that the one surface per 20 g / m ^2. The obtained coated paper was subjected to pressure treatment in a 12-stage super calender to obtain a coated paper for printing. Table 1 shows the adhesive conditions and quality measurement results of the coated paper obtained.

Example 2 In Example 1, the minimum film forming temperature was 30 ° C. and the particle size was 0.1.
Example 1 was repeated except that 12 parts of 1 μm styrene / butadiene copolymer latex (solid content) was used.

Example 3 Coating was carried out in the same manner as in Example 2 except that 2 parts of carboxy-modified soybean protein having a molecular weight of 110,000 daltons (trade name: PC5000, manufactured by Protein Technology International) was used. A liquid was obtained.
Using this coating liquid, a coated paper having a water content of 6% was obtained by the same coating and drying method as in Example 1, and then pressure treatment was performed with a 2 stack soft calender installed in an on-coater. A coated paper for printing was obtained. The results are shown in Table 1.

Example 4 In Example 2, the minimum film forming temperature was 34 ° C. and the particle size was 0.1.
Same as Example 2 except that 22 parts of 3 μm styrene / butadiene copolymer latex (solid content) was used.

Example 5 Kaolin (trade name: HT, manufactured by Engelhard) 80
Parts, fine grained heavy calcium carbonate (trade name: Carbital 9
0, manufactured by ECC) and 20 parts of sodium polyacrylate as a dispersant, and 0.2 parts of sodium polyacrylate was used to disperse the mixture in a Choles disperser
A pigment slurry with a solid content of 74% was prepared. To this slurry, 4 parts of carboxy-modified soybean protein having a molecular weight of 110,000 daltons (trade name: PC5000, manufactured by Protein Technology International Co., Ltd.) and a minimum film forming temperature of 30
At 8 ° C, 8 parts of a styrene-butadiene copolymer latex (solid content) having a particle diameter of 0.09 µm was added, and water was further added to prepare a coating liquid having a solid content concentration of 60%. 40 times this coating liquid
Drying laydown base paper of g / m ² was obtained a double-sided coated paper was coated with a blade coater so that the one surface per 10 g / m ^2. The coated paper obtained was subjected to a pressure treatment with a 12-stage super calender to obtain a coated paper for printing. The obtained results are shown in Table 1.

Example 6 The procedure of Example 3 was repeated except that the carboxy-modified soybean protein was 1.0 part and 2 parts of oxidized starch (trade name: Ace A, manufactured by Oji Konstarch) was added. .

Comparative Example 1 In Example 1, the minimum film forming temperature was 22 ° C. and the particle size was 0.1.
Same as Example 1 except that 12 parts of 1 μm styrene / butadiene copolymer latex (solid content) was added.

Comparative Example 2 In Example 1, the minimum film forming temperature was 40 ° C. and the particle size was 0.1.
Example 1 was repeated except that 15 parts of 1 μm styrene / butadiene copolymer latex (solid content) was added.

Comparative Example 3 In Example 1, the minimum film forming temperature was 30 ° C. and the particle size was 0.0.
Same as Example 1 except that 12 parts of 8 μm styrene-butadiene copolymer latex (solid content) was added.

Comparative Example 4 In Example 1, the minimum film forming temperature was 30 ° C. and the particle size was 0.1.
Example 1 was repeated except that 15 parts of 5 μm styrene / butadiene copolymer latex (solid content) was added.

Comparative Example 5 In Example 5, the compounding number of latex was changed to 4 parts,
The soybean protein content is 4 parts, and the minimum film forming temperature is −
The same procedure as in Example 5 was carried out except that 3 parts of a styrene / butadiene copolymer latex (solid content) having a particle diameter of 0.15 μm at 10 ° C. was added.

Comparative Example 6 In Example 5, a coating solution was prepared with 6 parts of latex and 7 parts of soybean protein. However, the coating solution was remarkably thickened and streaks were frequently generated. The procedure of Example 5 was repeated, except that the coating density was reduced by 5%.

Comparative Example 7 Coating was carried out in the same manner as in Example 2 except that 2 parts of carboxy-modified soybean protein having a molecular weight of 180,000 daltons (trade name: SP4000, manufactured by Protein Technology International) was added. I got the liquid,
The procedure of Example 2 was repeated, except that the coating liquid was thickened remarkably and streaks were frequently generated, so that the coating concentration was reduced by 3% to perform coating.

Comparative Example 8 The procedure of Example 3 was repeated, except that 2 parts of oxidized starch (trade name: Ace A, manufactured by Oji Corn Starch Co., Ltd.) was added instead of soybean protein.

Comparative Example 9 The procedure of Example 2 was repeated, except that the mixing ratio of latex was 26 parts.

Comparative Example 10 The procedure of Example 2 was repeated except that the soybean protein content was 0.3 parts, but the water retention of the coating liquid deteriorated and streaks frequently occurred.

[0045]

[Table 1]

[0046]

As is clear from the results shown in Table 1, the coated papers for printing obtained in the respective examples of the present invention had a strong stiffness of the paper and excellent printability.

Claims (1)

[Claims] 1. A coated paper for printing, comprising a base paper and a coating layer containing a pigment and an adhesive as main components, wherein the coating layer serves as an adhesive and has a minimum film forming temperature of 25 to 35 ° C. and a particle diameter of 0. 09-0.1
5 to 25 parts by weight (solid content) of 3 μm copolymer latex per 100 parts by weight of pigment and 0.5 to 5 parts by weight of carboxy-modified soybean protein having a molecular weight of 150,000 daltons or less per 100 parts by weight of pigment. A coated paper for printing, comprising: