JPH09316797A - Coated paper for gravure printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coated paper for gravure printing, high in rigidity, slightly causing missing dots, excellent in gravure printability. SOLUTION: This coated paper for gravure printing is obtained by coating a base paper with an aqueous composition consisting essentially of a pigment and an adhesive and finishing by calendering. Especially a copolymer latex having 15-45 deg.C glass transition temperature and 5-55% gel content is used as the adhesive. The amount of the copolymer latex blended is 3-15wt.% based on the pigment. The base paper is passed through a calender in which metal rolls are heated to 100-230 deg.C and finished under pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated paper, and more particularly to a coated paper for gravure printing, which has high rigidity, has few missing dots, and is excellent in gravure printing suitability.

[0002]

2. Description of the Related Art Gravure printing is widely used because it is excellent in reproducibility from a highlight portion to a halftone and beautiful photographic printing is possible. In general, gravure printing is a printing method in which ink is transferred directly from the intaglio plate of a metal roll to the paper surface, and printing effects are impaired if halftone dots (hereinafter referred to as missing dots) occur. Especially requires high smoothness and high cushioning property.

For example, in order to impart cushioning properties to paper, it is often the case that in the case of base paper, a high proportion of mechanical pulp is mixed, or the size press is water-coated during the papermaking process, and the size press is not performed. . In the aqueous composition, a copolymer latex having a low glass transition temperature (hereinafter referred to as Tg) (usually Tg = -60 to 0) is used as an adhesive.
C.) is preferably used, and starches that are rigid and tend to harden the paper surface are rarely used. As the pigment, flattened pigments such as delaminated kaolin and talc, calcined kaolin, low bulk density inorganic pigments such as light calcium carbonate, or organic pigments of various shapes such as hollow pigments are blended to obtain high smoothness. In addition, a coating layer having a high cushioning property is obtained.

On the other hand, in order to obtain high smoothness, in addition to blending the above-mentioned inorganic and organic pigments, the calendered paper passing conditions after coating and drying are strengthened to crush the coated paper. I often finish it. Therefore, there is a problem that the coated paper for gravure printing has lower rigidity than the coated paper for offset printing.

As a technique for improving the rigidity of paper, a method of blending a rigid softwood kraft pulp (NKP) into the base paper at a high ratio, a surface treatment of the base paper by a size press or a high ratio of starch in the coating layer is used. Alternatively, it is known to blend a copolymer latex having a high glass transition temperature as an adhesive. However, although the above-mentioned method has an effect of improving the rigidity, it tends to decrease the smoothness or the cushioning property, and in reality, the rigidity and the gravure printing suitability cannot be compatible with each other.

Although the purpose of increasing the rigidity is not a direct purpose, it is a method of finishing coated paper with a thermal calender having a heating metal roll and using a copolymer latex under specific conditions as an adhesive. , For example, Tg of 5
Method using polymer latex at 25 ° C. (JP-A-56-
68188) and a method using a copolymer latex having a Tg of 38 ° C. or higher (Japanese Patent Publication No. 53-7964, Japanese Patent Publication No. 56-107098, etc.) are known. According to these methods, the gloss of coated paper becomes high,
Moreover, a coated paper having improved rigidity can be obtained. On the other hand, when the coated paper obtained in this manner is subjected to gravure printing, it is difficult to obtain good smoothness, so that the occurrence of missing dots is severe, and a product having excellent gravure printing suitability cannot be obtained.

Further, in JP-A-6-287503, a copolymer latex having a gel content of 20 to 50% measured as a tetrahydrofuran insoluble matter at Tg of 20 to 50 ° C. is exemplified as a coating layer latex. ing. However, the technical gist of the same certificate is to improve gloss and blister resistance of coated paper, and there is no disclosure that such a copolymer latex is applied to an adhesive for coated paper for gravure printing. Further, in a coated paper for gravure printing, an example in which the gel content of a copolymer latex is specified to be 10 to 60% as an adhesive for a coating layer (JP-A-4-209895).
However, the Tg of the copolymer latex is -10 to + 10 ° C.

Further, a method of finishing a coated paper for gravure printing with a calender having a so-called heating metal roll, which is called a thermal calender, a gross calender or a soft calender, is also disclosed in Japanese Patent Laid-Open No. 3-234895.
Japanese Patent Laid-Open No. 4-370293. According to the former method, the final product is not obtained by only the soft calendering, but the super calendering is performed after the soft calendering, and the heating roll temperature of the super calender is 80 ° C. or less. On the other hand, the latter is to apply heating steam to the paper surface immediately before soft calender finishing, but suppressing the generation of missing dots and increasing the amount of heating steam to obtain higher smoothness, It suffers from the fact that rolls in the soft calendar tend to get dirty.

[0009]

The present invention relates to a coated paper for printing, and particularly to a coated paper for gravure printing which has high rigidity, has few occurrence of missing dots, and has excellent gravure printing suitability. It is a thing.

[0010]

According to the present invention, an aqueous composition containing a pigment and an adhesive as a main component is coated on a base paper and dried,
In a coated paper for gravure printing that is calendered, a copolymer latex having a glass transition temperature and a gel content of 15 to 45 ° C. and 5 to 55%, respectively, is used as the adhesive, and The polymer latex was blended in an amount of 3 to 15% by weight based on the solid content of the pigment, and the metal roll temperature was 100 to 100%.
It is a coated paper for gravure printing, which is characterized by being passed through a calender heated to 230 ° C. for pressure finishing.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted extensive studies on a coated paper for gravure printing, which has high rigidity, few occurrence of missing dots, and excellent gravure printing suitability. As a result, when the smoothness of the coated paper is sufficiently high and the surface of the coated paper and the gravure plate are surely brought into contact with each other under the printing pressure nip during the gravure printing, the cushioning property that has been conventionally required is almost unrelated. Heading out, the present invention has been completed.

Conventionally, thermal calendering of coated paper is a widely used technique in the production of coated paper for printing, but in the production of coated paper for gravure printing, good smoothness is obtained. Is difficult to obtain and has not been widely used. Therefore, as means for obtaining good smoothness such that no missing dots are generated, for example, a method of performing thermal calender finishing followed by super calender finishing as disclosed in JP-A-3-234895 or JP-A-4 Japanese Patent Laid-Open No. 370293 proposes a method of applying thermal steam to the surface of the coating layer immediately before calendering to carry out thermal calender treatment.

By the way, the present inventors have focused their attention on polymer latex, which is an adhesive used for a coated layer, to improve the smoothness of the coated paper (layer) obtained by the thermal calender treatment, and its influence. We conducted a thorough study. As a result, the Tg of the copolymer latex affects the stiffness, adhesive strength and calender operability of the coated paper, and the higher the Tg, the better the stiffness and calender operability of the coated paper. It was found that although the adhesive strength was slightly lowered, it did not significantly affect the smoothness of the coated paper.
On the other hand, it was found that the gel content has a great influence on the smoothness of the coating layer, and the lower the gel content, the higher the smoothness obtained by the thermal calender treatment.

That is, in the present invention, the copolymer latex used in the aqueous composition (hereinafter referred to as paint) constituting the coating layer has a Tg of 15 to 45 ° C. and a gel content of 5%. Coated paper for gravure printing obtained by using a copolymer latex of 55% to 55% and further coating a coating layer containing such a copolymer latex under pressure with a heat calender at 100 to 230 ° C. Is.

The coated paper obtained by such a finishing method is subjected to a final calendering treatment by a super calender after the thermal calender treatment as described above, or as a coating layer immediately before the thermal calender treatment. It is possible to impart high rigidity and high smoothness to the coated paper without taking special measures such as applying heated steam. As a result, it is possible to obtain a coated paper which has extremely few missing dots and has excellent gravure printing suitability.

Incidentally, when Tg is less than 15 ° C., the effect of developing rigidity is small, while when it exceeds 45 ° C., the decrease in adhesive strength becomes large, which is not preferable. Considering the balance between the adhesive strength and the rigidity, the T of the copolymer latex is
The range of 15 to 35 ° C. is more preferable as g. On the other hand, if the gel content is less than 5%, roll stains are likely to occur at the time of thermal calender finishing, while if it exceeds 55%, the smoothness of the coated paper obtained by thermal calender finishing is poor and the present invention However, the desired good gravure printing suitability cannot be obtained. In consideration of the balance between roll fouling and improvement of smoothness, the gel content of the copolymer latex is more preferably in the range of 10 to 45%.

The composition of the specific copolymer latex is not particularly limited, and those similar to the copolymer latex usually used in the field of producing coated paper can be used. For example, a conjugated diene copolymer latex such as a styrene-butadiene copolymer, an acrylic (co) polymer latex such as a polymer or copolymer of acrylic acid ester and / or methacrylic acid ester, an ethylene-vinyl acetate copolymer Appropriately use vinyl copolymer latex such as polymer, or alkali-sensitive or alkali-insensitive copolymer latex obtained by modifying these various copolymer latex with a monomer containing a functional group such as carboxyl group. can do. Of course, two or more kinds of the above-mentioned polymer latex may be appropriately mixed and used. The amount used at that time is based on the pigment in the paint.
It is usually adjusted in the range of 3 to 15% by weight based on the solid content.
By the way, if it is less than 3% by weight, the desired effect of the present invention cannot be obtained. On the other hand, if it exceeds 15% by weight, sticking of the coating layer to the thermal calender roll and deterioration of smoothness of the coating layer are caused. Not desirable because of concern.

The method for producing these copolymer latexes includes, for example, continuous emulsion polymerization method, batch emulsion polymerization method,
Well-known emulsion polymerization methods such as a two-step emulsion polymerization method and a divided emulsion polymerization method can be adopted, and there is no particular limitation. Further, in emulsion polymerization, known emulsifiers, chain transfer agents, polymerization initiators,
Additives and auxiliaries commonly used in emulsion polymerization such as chelating agents can be used. The method for obtaining the required Tg can be adjusted by selecting the monomer (monomer) to be subjected to the polymerization, or by operating the copolymerization ratio of the monomer, while the gel content is adjusted by the emulsion polymerization. It can be carried out depending on the type and amount of chain transfer agent added. In any case, the type and amount of monomers used in the copolymerization reaction,
Furthermore, a desired copolymer latex can be obtained by appropriately combining the respective reaction requirements such as the type and amount of chain transfer agent.

In the present invention, in addition to the above-mentioned specific copolymer latex, a starch-based adhesive processed as an adhesive by oxidation, etherification, acetylation, cationization, etc., synthetic resin such as polyvinyl alcohol, melamine resin, etc. A system adhesive, a protein adhesive such as casein, soybean protein, and a synthetic protein, a cellulose derivative such as carboxymethyl cellulose, hydroxyethyl cellulose, and the like can also be used in combination as long as the effects of the present invention are not impaired.

As the pigment used in the paint,
The kaolin, delaminated kaolin, calcined kaolin, structured kaolin, talc, heavy calcium carbonate, light calcium carbonate, satin white, calcium sulfite, gypsum, which are widely used as conventional pigments for coated papers, are not particularly limited. , Barium sulfate, titanium dioxide, aluminum hydroxide, inorganic pigments such as sericite and polystyrene,
Organic pigments such as styrene-acrylic copolymer resin or urea formaldehyde resin can be used in appropriate combination.

In the paint, in addition to the above-mentioned pigments and adhesives, a dispersant, a thickener, a water retention agent, a defoaming agent, a water resistance agent, and
For the purpose of promoting solidification as a lubricant, a dye, a pH adjusting agent, etc., and as a passivating agent for the applied coating, for example, amine, amide, polyacrylamine, etc., and zinc, aluminum, magnesium, potassium, barium, etc. Various auxiliaries such as valent metal salts are appropriately added.

When the coating material obtained as described above is applied to a base paper, a known coating device such as a blade coater, an air knife coater, a roll coater, a curtain coater, a die slot coater, a gravure coater is provided. An on-machine or off-machine coater can be used to form the coating layer in one or more layers.

The coating amount on the base paper is generally about 3 to 50 g / m ^{2 in} terms of dry weight, but the quality of the obtained product is white paper, print quality and printability, or the drying ability in high speed coating. 5 to 30 g / m
It is adjusted in the range of about ² . As a method for drying the wet coating layer, various methods such as steam drying, gas heater drying, electric heater drying, and infrared heater drying are appropriately adopted.

Next, in the present invention, as the thermal calender used, various calenders composed of heatable metal rolls (heat rolls) and elastic rolls such as a super calender, a gross calender, a soft calender, etc. It can be used with on-machine or off-machine specifications. The surface of the heat roll may be mirror-finished by chrome plating or the like. The surface temperature of the heat roll is adjusted in the range of 100 to 230 ° C. By the way, 10
If it is lower than 0 ° C, plasticization and film formation of the copolymer latex specified in the present invention will be insufficient, and good smoothness and sufficient surface strength cannot be obtained. The layer becomes easier to stick to the heat roll surface,
Stable calendar operation is difficult.

As the elastic roll used in the thermal calender, a resin roll made of urethane resin, epoxy resin, polyamide resin, phenol resin, polyacrylate resin or the like, or a roll formed by molding cotton, nylon, aramid fiber or the like is used. As an elastic roll, the Shore D hardness is 85 to 9 in order to obtain high smoothness.
The use of elastic rolls having a hardness of 5 ° is preferred.

The base paper used in the present invention is not particularly limited, but for example, as the base paper of the rice paper, it is appropriately used in the range of about 30 to 300 g / m ² according to the purpose. The pulp used to make the base paper is
Chemical pulp obtained by KP method or SP method using plant fibers such as wood or hemp, or GP, TMP, CT
Mechanical pulp (high-yield pulp) such as MP, CGP, or SCP, bleached pulp, used paper pulp, synthetic pulp, inorganic fiber, etc. are appropriately selected and used. The papermaking method is also not particularly limited,
A conventional papermaking method, for example, acidic papermaking at a papermaking pH of around 4.5, or a so-called neutral papermaking pH of about 6 to about 9 which contains an alkaline pigment as a filler Paper is made by the papermaking method. As the paper machine, a Fourdrinier paper machine, a paper machine equipped with a twin wire, a cylinder paper machine, a Yankee paper machine, or the like can be used as appropriate.

As the paper-making filler to be blended with the pulp in the paper-making raw material, a filler generally used in the paper-making industry is used. For example, heavy calcium carbonate, light calcium carbonate, calcium sulfite, gypsum, talc, kaolin, clay, calcined kaolin, amorphous silica, delaminated kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, hydroxide. Examples thereof include inorganic pigments such as calcium, magnesium hydroxide and zinc hydroxide, organic resin particles such as polystyrene resin fine particles, urea formalin resin fine particles and fine hollow particles, and pigments contained in used paper, brokes and the like can be recycled. Further, if necessary, one kind or two or more kinds of fillers may be appropriately combined and used.

In addition to pulp fibers and fillers, the base paper contains a variety of conventionally used anionic, nonionic, cationic, or amphoteric yields within a range that does not impair the intended effects of the present invention. An internal additive for papermaking such as an agent, a drainage improving agent, a paper strength improving agent, and an internally added sizing agent is selected and used as necessary. In addition, dyes, optical brighteners, p
An internal additive for papermaking such as an H-adjusting agent, a defoaming agent, a pitch control agent, and a slime control agent can be appropriately added depending on the application.

The base paper thus produced can be size-pressed within a range that does not impair the intended effects of the present invention. Size press liquids include water, starch, various modified starches, various water-soluble celluloses, various polyvinyl alcohols, various polyacrylamides, latexes, alkyl ketene dimers, styrene-acrylics, olefins-maleic anhydrides,
Various surface sizing agents of higher fatty acid type, waterproofing agents such as epoxy compounds, optical brighteners, defoaming agents, wetting agents, antistatic agents,
Various inorganic pigments, various organic pigments, dyes, starch particles and various additives can be added according to the purpose. For the coating method of the size press liquid, for example, two-roll size press, metering blade type size press, bill blade size press, gate roll size press,
A commonly used size press device such as a calender size press, a coater, or the like is used as appropriate, and is applied on both sides or one side of paper and dried to be finished as a base paper.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples. Of course, the invention is not limited to these examples. In addition, part and% in an example show a weight part and weight%, respectively.

[Evaluation Method] Glass Transition Temperature (Tg): A copolymer latex film was prepared in a room temperature atmosphere, and a differential scanning calorimeter (DS) was used.
It was measured using C).

Gel content: The pH of the copolymer latex was adjusted to 8 with a sodium hydroxide solution, the latex was put on a glass plate with a Teflon sheet so as to have a thickness of 1 mm, dried overnight, and further decompressed overnight. Dried.
About 1 g of the copolymer latex film thus obtained was precisely weighed, then dissolved in 400 ml of toluene by standing for 48 hours, filtered through a wire mesh of known 300 mesh, and the toluene-insoluble matter on the wire mesh was dried and weighed. The gel content was calculated by the following formula. Gel content (%) = [weight of insoluble matter on wire mesh / weight of latex film before dissolution in toluene] (g) × 100

Stiffness of Coated Paper: Clark stiffness was measured according to JIS P8142. However, the average value mm of the critical lengths in the MD and CD directions (paper flow direction, lateral direction) of the paper in the test width of 30 mm was expressed.

Surface Strength: The degree of picking was visually judged with an RI printer and judged as follows. In normal handling in gravure printing and subsequent handling ◎: The coating layer does not peel off, and powder does not fall off on the cutting surface during binding etc. ○: Some powder falls on the cutting surface, but there is no practical problem X: A lot of powder was dropped on the cutting surface, which was a problem in practical use.

Gravure printability (missing dot rate)
: Using a printing station type gravure printing suitability tester (manufactured by Kumagai Riki Kogyo Co., Ltd.), printing pressure 20 kg / cm ² , printing speed 50 m /
After printing with a gravure printing ink whose ink viscosity measured with Zahn cup No. 3 is 20 seconds under the conditions of minutes, the number of missing dots at the dot area of 10% is measured and the percentage is calculated. did.

Examples and Comparative Examples (Base Paper) To 100 parts of a pulp slurry consisting of 90 parts of beaten LBKP and 10 parts of NBKP was added 10 parts of light calcium carbonate (Tamapearl TP-121 / Okutama Kogyo Co., Ltd.), and then aluminum sulfate of 0. 5 parts, cationic starch (Amilofax 2200 / Matsuya Chemical Co., Ltd.) 0.4
Part, alkyl ketene dimer (size pine K-287
/ Arakawa Chemical Industry Co., Ltd.) 0.1 part, anionic polyacrylamide (Arafix-504 / Arakawa Chemical Industry Co., Ltd.)
0.02 parts was added and the stock was prepared. The stock thus obtained was paper-made by an on-top twin-wire type paper machine to obtain 70 g / m ² of base paper.

(Preparation and coating of coating material) 60 parts of delaminated kaolin (α plate / manufactured by ECC) having an average particle diameter of 0.35 μm and acicular light calcium carbonate (TP)
123CS / Okutama Kogyo) 40 parts, dispersant 0.2 parts,
Preservative 0.05 part, antifoam 0.1 part, thickener (Alcogum L-28 / Kanebo NSC) 0.4 part and styrene-butadiene copolymer latex shown in Table 1 8 parts (each solid Minute base) was blended to prepare a coating composition having a solid content of 60%. Next, papermaking under the above conditions 70 g / m
^2. The base paper of No. ² was coated on both sides with a blade coater so that the dry weight was 18 g / m ² per side, dried, and the water content was 5.
5% coated paper was obtained.

(Thermal Calender Finish) Using a soft calender consisting of a chrome-plated heat roll and a cover material having a Shore D hardness of 90 ° (Mirrormax YCR5400 / Yamauchi Corp.), each elastic roll. The heat-roll temperature and linear pressure conditions shown in Table 1 were further passed through the heat calender at a speed of 600 m / min so that each surface of the coated paper obtained as described above was contacted with the heat roll twice. Paper was used for finishing.

The evaluation results of the missing dot ratio, rigidity and surface strength of the thus obtained coated paper for gravure printing are summarized in Table 1.

[0040]

[Table 1]

[0041]

As is clear from Table 1, the coated paper according to the present invention has an excellent coating for gravure printing, which has a high rigidity and a small number of missing dots, and has a good balance between the rigidity and the gravure printing suitability. It was paper. Incidentally, Comparative Example 8,
No. 9 was a thermal calender finish, and the coated layer was stuck to a heat roll and could not be finished as a coated paper having good smoothness.

Claims (1)

[Claims] 1. A gravure coated paper which is calendered after coating an aqueous composition containing a pigment and an adhesive as a main component on a base paper, drying the base paper, and using a glass transition temperature and a gel as the adhesive. Content is 15-45 ℃,
A copolymer latex of 5 to 55% is used, and the amount of the copolymer latex is 3 to 15% by weight based on the solid content of the pigment. A coated paper for gravure printing, characterized by being passed through a calender heated to ~ 230 ° C and subjected to pressure finishing.