JP4486861B2 - Coating composition for coated paper and coated paper using the same - Google Patents

Description

  The present invention relates to a coating composition for coated paper mainly composed of a pigment and an adhesive, and a coated paper using the same.

  Recently, papers mainly composed of mechanical pulp and waste paper pulp have been used as coated paper, and in particular, from the viewpoint of environmental problems such as an increase in dust and resource saving, a multi-use waste paper is required. Compared with the coated paper which compounded many chemical pulp like the past, there exists a tendency for the intensity | strength of paper itself to also fall.

Furthermore, in recent years, printing, offsetting, colorization, and speeding-up are rapidly progressing, and better color printing suitability and printing workability are required for printing coated paper as a printing medium. In particular, in offset printing, dampening water and ink are simultaneously applied to a plate cylinder in which the image area is made oleophilic and the non-image area is hydrophilic, and ink is applied only to the image area using the repulsion of water and oil. It is a plate to be attached. The ink is transferred to a rubber plate called a blanket next to the plate cylinder, and then transferred to paper for printing. At this time, water in the non-image area is also transferred to the paper. In order to reduce the mixing of water and ink, compared to the conventionally used letterpress printing method, it uses a relatively strong tack printing ink, and the paper absorbs water during printing. The paper is required to have a high surface strength. If the surface strength is weak, the fiber released from the base paper or the pigment contained in the coating layer accumulates on the blanket, the so-called blanket piling problem, the so-called scumming etc. This causes troubles such as deterioration in printing quality and printing workability. In addition, white paperboard used for aesthetic boxes and the like needs to be printable, but strongly adheres the pigment in the coating layer so that the pigment on the surface does not peel off due to rubbing, scratching, etc. It is necessary to form a layer.
Thus, the demand for improving the surface strength against printing and rubbing is increasing with time.

  As a measure for improving the surface strength of the coated paper, the latex type that is part of the adhesive for the coating layer is generally changed. This is because latex has the strongest adhesive strength and is a major factor affecting the surface strength. Adhesives other than latex have many roles as an auxiliary agent for latex, and starch also has the effect of enhancing the water retention of the paint in addition to the adhesiveness, but if anything, the latter performance tends to be emphasized.

  In addition to changing the latex type, other adhesives can be added to improve surface strength, such as a method of adding an acrylamide water-soluble polymer (Patent Document 1) or a polyaminoamide-based curing agent, particularly wet printing strength. There is a method for improving the above (Patent Document 2). However, the use of an expensive synthetic reagent, the former improving the strength using a relatively high adhesive, and the latter improving the wet strength by making the adhesive water resistant. Neither the dry strength is improved so much, and none of them has a sufficient effect for improving the surface strength due to the synergistic effect of the adhesive performance.

Japanese Patent Laid-Open No. 10-46490 JP-A-7-229092

  An object of the present invention is to provide a coated paper having improved surface strength of a conventional coated paper obtained by using a coating composition mainly composed of starch and a pigment, and improved suitability for printing. .

The present inventors have reviewed the use of starch as an adhesive in a coating composition for coated paper, and as a result of intensive studies, have found that a C _8-24 -alkyl methacrylate group is present in the coating composition for coated paper. It has been found that the surface strength of the coated paper obtained by applying a composition containing a styrene acrylic polymer having a surface of the base paper to the surface of the base paper and drying is greatly improved, and has led to the present invention.

That is, the present invention includes the following inventions.
(1) A coating composition for coated paper containing starch, a styrene acrylic polymer having a C _8-24 -alkyl methacrylate group, and a pigment.
(2) The above-mentioned containing 1 to 30 parts by mass of starch and 0.001 to 3 parts by mass of a styrene acrylic polymer having a C _8-24 -alkyl methacrylate group in terms of solid content with respect to 100 parts by mass of pigment ( The coating composition for coated paper as described in 1).

(3) The method according to (1) or (2) above, wherein a paste obtained by gelatinizing a mixture containing starch and a styrene acrylic polymer having a C _8-24 -alkyl methacrylate group is mixed with a pigment. Coating composition for coated paper.
(4) The method according to (1) or (2) above, wherein the starch is gelatinized and then a paste obtained by mixing a styrene acrylic polymer having a C _8-24 -alkyl methacrylate group and a pigment are mixed. Coating composition for coated paper.

(5) The said (1) or (2) characterized by mixing the paste liquid obtained by gelatinizing the mixture containing starch and the styrene acrylic polymer which has _C8-24 -alkyl methacrylate group, and a pigment. The manufacturing method of the coating composition for coated paper of description.
(6) The above-mentioned (1) or (2), wherein the paste is mixed with a paste obtained by mixing a styrene acrylic polymer having a C _8-24 -alkyl methacrylate group after gelatinizing the starch. The manufacturing method of the coating composition for coated papers as described in).

(7) A coated paper obtained by applying the coated composition for coated paper according to any one of (1) to (4) above to a base paper and drying it.
(8) A method for producing a coated paper, wherein the coated composition for coated paper according to any one of (1) to (4) is applied to a base paper and dried.

  According to the present invention, it is possible to provide a coated paper that has a very excellent surface strength and can withstand a large printing load. In particular, not only wet surface strength but also dry surface strength is improved.

  As starch for starch used in the present invention, for example, raw starch such as corn starch (corn starch), waxy corn starch, potato starch, tapioca starch, wheat starch, sweet potato starch, rice starch, etc., known to these raw starch Chemically modified starch or the like into which substituents such as cationization, phosphate esterification, acetylation, hydroxyethylation, hydroxypropylation and the like have been introduced can be used. Moreover, these starches can also be used in combination of two or more.

  In the present invention, a starch that has been subjected to a low-viscosity treatment so that the raw material starch can be easily used as an adhesive for a coating composition for coated paper by a known method is preferably used. That is, oxidized starch obtained by oxidation by a method using hypochlorous acid, urea phosphoric acid starch obtained by heating and baking using phosphoric acid, urea, hydrochloric acid, hydrochloric acid or phosphoric acid. It is preferable to use acid-modified starch obtained by heat roasting or starch slurry reaction. Moreover, you may use the paste liquid which carried out enzyme modification | denaturation and APS (ammonium persulfate) modification | denaturation, and made low molecular weight. In addition, although there is no restriction | limiting range in particular in the degree of conversion of various starches, 50 degreeC and 20% B-type viscosity of starch paste liquid so that coating composition (paint) viscosity may increase remarkably and coating may not be troubled. Is preferably subjected to chemical treatment so as to be in the range of 5 to 500 mPa · s.

The styrene acrylic polymer used in the present invention comprises a methacrylic acid ester monomer (A) having a C _8-24 -alkyl group, an α, β-monoethylenically unsaturated carboxylic acid monomer (B), and styrene. It is a copolymer obtained from a type monomer (alkenyl aromatic monomer) (C).

Examples of the methacrylic acid ester monomer (A) include octyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, Examples include heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, and eicosyl methacrylate. Particularly preferred are those having a C _12-20 -alkyl group, and more preferred are those having a C _12-18 -alkyl group.

  Examples of the α, β-monoethylenically unsaturated carboxylic acid monomer (B) include (meth) acrylic acid, ethyl acrylic acid, crotonic acid, itaconic acid, (anhydrous) maleic acid, fumaric acid, preferably acrylic. Examples include acid, methacrylic acid, and ethyl acrylic acid.

  The styrene monomer (C) refers to a compound having a styrene skeleton and no unsaturated bond other than the styrene portion, such as styrene, vinyl ketone, α-methylstyrene, chlorostyrene, preferably styrene. Can be mentioned.

  Methacrylic acid ester monomer (A), α, β-monoethylenically unsaturated carboxylic acid monomer (B) and styrene type monomer (alkenyl aromatic monomer) (C) in the styrene acrylic polymer Are preferably 5 to 60% by mass of monomer (A), 5 to 50% by mass of monomer (B), and 90 to 20% by mass of monomer (C), more preferably monomer. (A) 10-50 mass%, monomer (B) 5-40 mass%, and monomer (C) 85-10 mass%.

  The number average molecular weight of the styrene acrylic polymer is usually 2,000 to 50,000, preferably 3,000 to 30,000, and more preferably 5,000 to 15,000.

  The styrene acrylic polymer may be used in the form of a salt such as an alkali metal salt, an alkali metal earth salt, an ammonium salt, or a salt with an organic amine. Examples of the alkali metal that forms the salt include sodium, potassium, and lithium; examples of the alkaline earth metal include calcium, magnesium, and aluminum; examples of the organic amine include alkanolamines (ethanolamine, triethanolamine, dimethylmethanolamine, and the like). ), Alkylamines (methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, etc.) and the like.

  The ratio of the starch and the styrene acrylic polymer in the coating composition of the present invention is usually 100: 0.1 to 10.0, preferably 100: 0.5 to 5.0 in terms of mass ratio.

  In the production of the coating composition of the present invention, the starch may be gelatinized (glued) and then mixed with a styrene acrylic polymer, but the mixture containing the starch and the styrene acrylic polymer is gelatinized (glue). It is more preferable to cook.

Hereinafter, the preferable aspect of manufacture of the paste liquid in this invention is demonstrated.
First, the aqueous solution of the styrene-acrylic polymer is mixed with starch (preferably, starch whose viscosity has been reduced so that it can be easily used as an adhesive for a coating composition for coated paper), and dried with a hot air dryer. A powder having a moisture content of 18% or less is obtained. Although the apparatus which mixes starch and a styrene acrylic polymer is not specifically limited, The method of spraying the aqueous solution of a styrene acrylic polymer to starch by spraying is preferable so that it may mix uniformly.

  It is preferable to adjust the pH of the aqueous solution of the styrene acrylic polymer in advance so that the pH of the 10% by mass slurry of the starch and styrene acrylic polymer mixture is 6.0 to 8.0. When the starch slurry is gelatinized by heating, if the pH is less than 6.0, a large amount of starch aging is likely to occur in the paste, and if the pH is greater than 8.0, depolymerization of starch molecules occurs during the heating gelatinization. , Starch molecules are easily cleaved and insoluble substances are easily generated.

  After mixing the starch and the aqueous solution of the styrene acrylic polymer, the moisture is dried within 18%, but it is preferable to use a hot air dryer such as a flash dryer. In addition, there is no restriction | limiting in particular in the temperature at the time of drying, if this mixture does not gelatinize by heating at the time of drying.

  In the present invention, either the normal pressure or the pressurization method may be used for cooking the paste, but it is preferable not to make the heating time longer than necessary. If the pH at 25 ° C. of the paste containing 10% by mass of the starch and styrene acrylic polymer mixture after cooking the paste is 6.0 to 8.0, the intended paste is obtained.

  The coating composition of the present invention can be obtained by mixing the paste liquid and the pigment obtained as described above.

  Examples of the pigment include ordinary clays such as calcined clay, structured kaolin and delaminated clay, inorganic pigments such as heavy calcium carbonate, light calcium carbonate, titanium dioxide, aluminum hydroxide, silica, satin white and talc, In recent years, organic pigments have been used to improve glossiness, smoothness, and weight reduction of coated paper, but acrylic polymers, styrene polymers, solid particles of styrene-acrylic copolymers, One or more kinds of pigments used in the general coated paper manufacturing field such as organic pigments of hollow particles can be used.

  The blending ratio of the pigment, starch and the styrene acrylic polymer in the coating composition of the present invention is a solid content conversion amount with respect to 100 parts by mass of the pigment, and the starch is preferably 1-30 parts by mass, more preferably. Is 3 to 25 parts by mass, and the styrene acrylic polymer is preferably 0.001 to 3 parts by mass, and more preferably 0.05 to 1.5 parts by mass. By the way, if the blending ratio of starch is less than 1 part by mass, sufficient coating surface smoothness and air permeability will not be exhibited, so it will not be possible to obtain good printability, while if it exceeds 30 parts by mass, The viscosity of the coating liquid increases and high-speed operability decreases.

  In the coating composition of the present invention, components other than starch, the styrene acrylic polymer and the pigment may be appropriately blended within a range not impairing the effects of the present invention.

  For example, as an adhesive component, in addition to starch, conjugated diene polymer latex such as styrene / butadiene copolymer, methyl methacrylate / butadiene copolymer, polymer or copolymer of acrylate ester and / or methacrylate ester. An acrylic acid polymer latex such as a polymer, a vinyl polymer latex such as an ethylene / vinyl acetate copolymer, or an alkali obtained by modifying these various polymer latexes with a monomer containing a functional group such as a carboxyl group One or more soluble or non-alkali soluble polymer latexes are appropriately selected and used. Furthermore, an adhesive used in the field of production of general coated paper can be appropriately used as long as the effects of the present invention are not impaired. Specific examples include, for example, proteins such as casein, soybean protein, and synthetic proteins, synthetic resin adhesives such as polyvinyl alcohol, olefin / maleic anhydride resin, and melamine resin, and cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose. And two or more of these may be used in combination.

  In addition, pH adjusters such as dispersants, caustic soda, aqueous ammonia, antifoaming agents, preservatives, fluorescent dyes, mold release agents, dyes, water resistance agents, flow modifiers, etc. may be added as necessary. it can.

Next, the coated paper of the present invention and the manufacturing method thereof will be described.
The coated paper of the present invention is obtained by applying the above-described coating composition of the present invention to one side or both sides of a base paper and drying it. The coating composition of the present invention can be applied to any of the undercoat layer and the topcoat layer in single coating or double coating. The coating amount of the paint comprising the coating composition of the present invention is not particularly limited.

  The coating apparatus for applying the coating is not particularly limited. For example, an air knife coater, a blade coater, a rod coater, a bar coater and a gate roll coater, a roll coater such as a size press, a bill blade coater, and a short coater. A well-known coater is used.

  In addition, the smoothing process of the paper which provided the base paper and the undercoat layer previously can also be performed using a machine calendar, a soft calendar, a Yankee dryer, etc. before coating. In addition, if necessary, after applying and drying the overcoat layer paint, a smoothing treatment can be performed using a machine calendar, a soft calendar, a super calendar, or the like.

  It does not specifically limit as a pulp which comprises a base paper, For example, 1 type, or 2 or more types, such as a chemical pulp, a mechanical pulp, a used paper pulp, are mixed suitably and used. In addition, auxiliaries such as a sizing agent, a paper strength enhancer, a filtering agent, a filler, a colorant, and a fluorescent brightening agent can be appropriately added to the base paper as necessary.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Unless otherwise specified, “parts” and “%” represent “parts by mass” and “% by mass”, respectively.

[Preparation of adhesive]
(Preparation of adhesive A)
Ace A (oxidized starch manufactured by Oji Cornstarch Co., Ltd .; 50 parts of starch paste, 20% B-type viscosity 200 mPa · s) 100 parts styrene acrylic polymer 30% aqueous solution (tetradecyl methacrylate / styrene / acrylic acid = 20 / 45/35%; number average molecular weight 7000) 1.0 part (each solid content conversion) was sprayed and mixed, and then dried to a moisture of 12% with a flash dryer to obtain an adhesive A. The 10% slurry pH of the adhesive A was 7.5, and the 10% paste pH was 6.8.

(Preparation of adhesive B)
Ace Y (Oxidized starch produced by Oji Cornstarch Co., Ltd .; 50 parts of starch paste, 20% B-type viscosity 90 mPa · s) 100 parts styrene acrylic polymer 30% aqueous solution (tetradecyl methacrylate / styrene / acrylic acid = 20 / 45/35%; number average molecular weight 7000) 1.5 parts (converted to each solid content) was sprayed and mixed, and then dried to a moisture of 12% with a flash dryer to obtain an adhesive B. The 10% slurry pH of the adhesive B was 7.5, and the 10% paste pH was 6.8.

(Preparation of adhesive C)
Ace P-140 (urea cornstarch urea phosphate starch; starch paste at 50 ° C., 20% B-type viscosity 60 mPa · s) 100 parts styrene acrylic polymer 30% aqueous solution (tetradecyl methacrylate / styrene / acrylic) Acid = 20/45/35%; number average molecular weight 7000) 1.5 parts (in terms of each solid content) was sprayed and mixed, then dried to 12% with a flash dryer to obtain adhesive C . The 10% slurry pH of the adhesive C was 7.2, and the 10% paste pH was 7.0.

(Preparation of adhesive D)
ETHYLEX-2020 (hydroxyethylated starch produced by STALEY; 50 ° C. of starch paste, 20% B-type viscosity 100 mPa · s) 100 parts of styrene acrylic polymer 30% aqueous solution (tetradecyl methacrylate / styrene / acrylic acid = 20/45/35%; number average molecular weight 7000) 1.5 parts (converted to each solid content) was sprayed and mixed, and then dried to a moisture of 12% with a flash dryer to obtain an adhesive D. The 10% slurry pH of the adhesive D was 7.3, and the 10% paste pH was 6.8.

[Preparation of starch paste]
300 parts of water was added to 100 parts of each adhesive, and gelatinized by heating at 95 ° C. for 30 minutes while stirring the slurry. The obtained paste was adjusted to 25% (solid content) by adding water, and stored at 80 ° C. for 30 minutes.

Example 1
[Preparation of paint]
As a pigment, 80 parts of Kaolin clay (trade name: UW-90 / Engelhard) and 20 parts of heavy calcium carbonate (trade name: Hydrocurve 90 / Bihoku Powdered Company) are used, and a dispersant (trade name) : Aron A-9 / Toagosei Co., Ltd.) 0.1 part, 0.1 part of sodium hydroxide and water were added and dispersed well to prepare a pigment slurry. To this slurry, 10 parts of latex (trade name: T-2621 / Nippon Synthetic Rubber Co., Ltd.) and 5 parts of adhesive liquid A (in terms of each solid content) were added, and water was further added to give a solid content concentration of 62%. A paint was prepared.

[Create coated paper]
A fine paper base (64 g / m ² ) is coated with the paint obtained above using a bar coater so that the dry weight per side is 7 g / m ² , dried with a drum dryer, and then soft calender. The coated paper was obtained by 2 nip treatment. Table 1 shows the RI printing strength results of the coated paper obtained.

  The RI printing wet strength was measured immediately after the dampening water was applied to the test piece with a Morton roll using an RI printer. V. = 13 (printing test ink, manufactured by Toyo Ink) was used for printing, and the state of paper peeling after printing was visually observed. One point was inferior (pigment and paper was totally removed), and three points were comparative examples. Relative evaluation with 5 points being excellent (pigment, no paper peeling) was performed, equivalent to 1, and the water resistance of the starch applied to the paper was confirmed.

  Further, the RI printing dry strength was evaluated in the same manner except that the Molton roll for measuring the wet strength was not used.

(Example 2)
A coated paper was obtained in the same manner as in Example 1 except that the coating liquid of Example 1 was changed to the adhesive solution B (trade name: GRS-T120 / manufactured by Oji Cornstarch). Table 1 shows the RI printing strength results of the coated paper obtained.

(Example 3)
A coated paper was obtained in the same manner as in Example 1 except that the adhesive liquid was changed to the adhesive C in the preparation of the paint of Example 1. Table 1 shows the RI printing strength results of the coated paper obtained.

Example 4
A coated paper was obtained in the same manner as in Example 1 except that the adhesive liquid was changed to the adhesive D in the preparation of the paint of Example 1. Table 1 shows the RI printing strength results of the coated paper obtained.

(Example 5)
In preparation of the coating material of Example 1, ace A (manufactured by Oji Cornstarch) was paste-cooked and then a styrene acrylic polymer (tetradecyl methacrylate / styrene / acrylic acid = 20/45/35%; number average molecular weight 7000) 1.0. Coated paper was obtained in the same manner as in Example 1, except that the paste was changed to the paste obtained by adding the part (10% paste pH 6.8). Table 1 shows the RI printing strength results of the coated paper obtained.

(Comparative Example 1)
Coated paper was obtained in the same manner as in Example 1, except that the coating liquid of Example 1 was changed to the paste solution of Ace A (manufactured by Oji Cornstarch). Table 1 shows the RI printing strength results of the coated paper obtained.

(Comparative Example 2)
A coated paper was obtained in the same manner as in Example 1 except that the coating liquid of Example 1 was changed to the paste liquid of Ace Y (manufactured by Oji Cornstarch). Table 1 shows the RI printing strength results of the coated paper obtained.

(Comparative Example 3)
A coated paper was obtained in the same manner as in Example 1 except that the coating liquid of Example 1 was changed to the paste solution of Ace P-140 (manufactured by Oji Cornstarch). Table 1 shows the RI printing strength results of the coated paper obtained.

(Comparative Example 4)
A coated paper was obtained in the same manner as in Example 1 except that the coating liquid of Example 1 was changed to a paste solution of ETHYLEX-2020 (manufactured by STALEY). Table 1 shows the RI printing strength results of the coated paper obtained.

Claims (8)

(i) starch , and (ii) a methacrylic acid ester monomer (A) having a C _8-24 -alkyl group, an α, β-monoethylenically unsaturated carboxylic acid monomer (B), and a styrene type method for producing a coated paper for coated composition you characterized by mixing size liquid and pigments obtained a mixture containing styrene-acrylic polymer obtained from the monomer (C) by gelatinized. After gelatinizing starch, a methacrylic acid ester monomer (A) having a C _8-24 -alkyl group, an α, β-monoethylenically unsaturated carboxylic acid monomer (B), a styrene type monomer method for producing a dimer by mixing styrene-acrylic polymer obtained from (C), and then the resulting paste solution and that coated paper for coated composition you wherein mixing the pigment. The methacrylic acid ester monomer (A) used in the styrene acrylic polymer is C _12-24 The production method according to claim 1 or 2, which is a methacrylic acid ester monomer having an alkyl group. The method according to claim 1 or 2, wherein the methacrylic acid ester monomer (A) used in the styrene acrylic polymer is tetradecyl methacrylate. The manufacturing method according to any one of claims 1 to 4, wherein 1 to 30 parts by mass of starch and 0.001 to 3 parts by mass of the styrene acrylic polymer are used in terms of solid content with respect to 100 parts by mass of the pigment. . The manufacturing method of any one of Claims 1-5 in which the coating composition for coated paper contains latex. Latex is a conjugated diene polymer latex, an acrylic acid polymer latex, a vinyl polymer latex, or an alkali-soluble or non-alkali-soluble polymer obtained by modifying the polymer latex with a monomer containing a functional group The production method according to claim 6, which is one or more selected from latex. After manufacturing the coating composition for coated paper by the manufacturing method of any one of Claims 1-7 , apply | coating the obtained coating composition for coated paper to a base paper, and drying. A method for producing coated paper as a feature.