JP3044705B2 - Coated paper for gravure printing - Google Patents

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 gravure printing which is excellent in operability during coating and gravure printing suitability.

[0002]

2. Description of the Related Art Gravure printing is intaglio printing in which the ink in the concave portions of the plate is transferred to paper under pressure, and has excellent tone reproducibility. Gravure printing suitability required for coated paper, which is a printing medium, is mainly required to have few misdots (missing halftone dots), high print surface glossiness, and the like. Gravure printing is a metal roll whose plate is harder than offset printing, and misprints are likely to occur because the printing plate surface is hard to adhere to the paper at the time of printing. Generally, in gravure printing, in order to obtain good dot reproducibility, smoothness and cushioning properties are required as coated paper physical properties. For this reason, a synthetic polymer latex (hereinafter referred to as a latex) having a low glass transition temperature and soft particles has been used as the adhesive.

Latex is mainly composed of styrene, butadiene,
It is a polymer compound obtained by synthesizing a monomer such as methyl methacrylate. Latex used for gravure printing coated paper (hereinafter referred to as gravure latex) and latex used for offset printing coated paper (hereinafter referred to as offset latex) have different monomer compositions due to differences in their printing methods. Usually, gravure latex is softened by adding a large amount of butadiene having a low glass transition temperature represented by Tg in order to enhance the cushioning property of the coating layer. The glass transition temperature of butadiene alone is -82 ° C, and that of styrene alone is 100 ° C. The glass transition temperature of a gravure latex containing a large amount of butadiene is generally about -40 ° C, and none exceeds -20 ° C. For example, Japanese Patent Application Laid-Open No. 60-224895 states that "in the low region where the glass transition temperature is -25 ° C or lower, the polymer is imparted with flexibility, the cushioning property of the coated paper is improved, and excellent gravure printing suitability is exhibited." Are listed. This is because if the glass transition temperature increases, the coating layer becomes hard and the number of misdots increases. However, latex having a low glass transition temperature has good suitability for gravure printing, but has the following problems.

[0004] Coated paper for gravure printing is usually 6 gm after coating.
The super calender treatment is performed under pressure by a roll heated to 0 to 80 ° C. At this time, a gravure latex having a low glass transition temperature is melted, and a trouble such as calendar contamination adhering to the heating roll is likely to occur. Further, when coated paper is used as a rolled product, the problem of blocking, in which the paper surface adheres to the front and back surfaces, is likely to occur.

[0005] Many gravure latexes have a high butadiene content and a particle size of 1500 Å or more. For example, Japanese Patent Application Laid-Open No. 2-139500 discloses that the particle size of latex is specified to be 2000 to 4000 angstroms, and if it is less than 2000 angstroms, the effect of reducing dot dropout cannot be sufficiently exhibited. However, as the particle size of the latex increases, the viscosity of the coating liquid, particularly in the high shear rate region, increases.
Since the shear stress of the coating liquid increases, it is necessary to control the coating amount corresponding to the stress. As a result, in a commonly used blade coater, it is necessary to increase the pressure of the blade, and in other coating methods, it is necessary to increase the pressure of a bar, a roll, air, etc. in the same manner as the blade pressure. is there. The surface coated with high blade pressure tends to be rough, so that the smoothness is deteriorated and the gloss is reduced. In addition, due to high blade pressure, line-shaped coating defects such as paper breakage, streaks, and scratches are likely to occur, and the blades are severely worn, thereby reducing the operability of the coater.

[0006] In recent years, the blade pressure tends to be higher and higher due to a higher coating speed of 1000 m / min or more or a coating solution concentration of 60% or more. A coating material having a high viscosity in a high shear speed region is desirable. Absent. About it,
JP-T-6-504328 and JP-A-Kagaku Gijutsu, Vol. 48, No. 1, P203 (1994) describe that the viscosity in the high shear rate region decreases as the particle size of the latex decreases. The above-mentioned patent relates to a coated paper for gravure printing using a latex having an average particle size of less than 2000 Å, and does not include any viscous, film-forming hydrophilic polymer material. The coating liquid used has low viscosity and low water retention, so that the coating liquid penetrates the base paper significantly during coating, streak, scratches and other streaky coating defects easily occur, There was a problem that it was difficult to obtain a coating amount, and the obtained paper had poor gravure printing suitability.

[0007]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to find a coating composition having good fluidity and coating properties, and to reduce operability such as poor coating and calendar stains. While improving, there is no blocking during winding,
An object of the present invention is to provide a coated paper for gravure printing having excellent dot reproducibility.

[0008]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventors have found that a pigment and an adhesive having an average particle diameter of 700 to 1300 angstroms and a glass transition temperature of -20 to 20 ° C. are formed on a support. The present invention has been achieved by providing a coating layer containing a synthetic polymer latex and a viscosity modifier. The present invention is characterized in that a latex having a fine particle size and a high glass transition point is used together with a viscosity modifier as compared with a conventional gravure latex, whereby paper breakage, poor coating, blade wear, and backing roll contamination are caused. Thus, problems such as calendar dirt and product blocking can be solved, and more excellent gravure printing suitability can be provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The synthetic polymer latex as an adhesive used in the present invention preferably has an average particle size of 700 to 1300 angstroms, particularly preferably 800 to 1100 angstroms. The average particle size of the latex is 70
If the thickness is smaller than 0 Å, misdots increase and the gravure printing suitability is poor. If the average particle size of the latex is larger than 1300 angstroms, the viscosity in the high shear rate region increases, and the shear stress of the coating liquid increases, so that streak, scratch-like coating defects such as scratches are likely to occur, Blade wear is also severe, and the operability of the coater is reduced. The glass transition temperature of the synthetic polymer latex is preferably from -20 to 20C, more preferably from -10 to 10C. When the glass transition temperature is lower than −20 ° C., calendar stains and blocking of winding of the product occur. Glass transition temperature is 20 ℃
If it is higher, the cushioning property is poor, misdots increase, and the suitability for gravure printing is poor. Known latexes can be used as the type of latex to be used. For example, styrene-butadiene-based latex, conjugated diene-based copolymer latex such as methyl methacrylate-butadiene copolymer, acrylate and / or methacrylate ester An acrylic latex such as a polymer or a copolymer, a vinyl latex such as an ethylene-vinyl acetate copolymer, or an alkali-soluble or alkali obtained by modifying these various latexes with a monomer containing a functional group such as a carboxyl group. One or more types of insoluble latex are appropriately selected and used. In general, the synthetic polymer latex is adjusted to 3 to 15 parts by weight, preferably 4 to 10 parts by weight, based on 100 parts by weight of the pigment. If the amount is less than 3 parts, the surface strength becomes weak, which causes a problem. If it exceeds 15 parts, the coat layer becomes hard, so that misdots increase and the suitability for gravure printing decreases.

[0010] A viscosity modifier is required in the coating solution. Examples of the viscosity modifier used include carboxymethylcellulose (CMC) and hydroxymethylcellulose (HM
C) Cellulose derivatives such as hydroxyethylcellulose (HEC), polyether-modified polyurethane, sodium alginate, acrylic synthetic products and the like, and one or more kinds of viscosity modifiers for coating are appropriately selected and used. In these, H
EC and acrylic synthetic products are preferred, and the acrylic synthetic product viscosity modifier is preferably of the associative type. Since the viscosity modifier may also have some effects as an adhesive, an adhesive such as starch can be used as the viscosity modifier. Many viscosity modifiers have the effect of increasing the water retention of the paint. The amount of the viscosity modifier used is preferably 0.05 to 3.0 parts, particularly 0.1 to 3.0 parts.
2.0 parts is preferred.

The coating pigments that can be used in the present invention include inorganic pigments such as clay, kaolin, heavy calcium carbonate, and natural mineral inorganic pigments such as talc, light calcium carbonate, satin white, titanium oxide, and aluminum hydroxide. Ordinary pigments such as synthetic inorganic pigments such as silica, zinc oxide, barium sulfate and calcium sulfate, and plastic pigments as organic pigments can be used. The clay includes calcined clay, delaminated clay, engineered clay and the like. These pigments can be used alone or as a mixture of two or more as needed. Generally, considering the suitability for gravure printing, 100% clay is preferred. In addition, since the acrylic synthetic product and HEC have a structure in which the viscosity is adjusted also by the interaction with the charge on the clay surface, a higher effect is obtained with a higher clay content. However, as the high-speed and high-concentration coating proceeds, calcium carbonate may be used in combination to improve the fluidity of the coating solution. The ratio depends on the required quality, but is 40 parts or less for gloss products and 70 parts or less for mat products.

As the adhesive other than the synthetic latex used in the present invention, esterified starch such as oxidized starch and phosphated starch, and hydroxyethyl etherified starch (H
ES), etc., starches such as etherified starch, positive starch, enzyme-modified starch, dextrin and derivatives thereof; proteins such as casein, soybean protein, synthetic protein, etc .; synthesis of polyvinyl alcohol, olefin / maleic anhydride resin, melamine resin, etc. A resin adhesive or the like is used.

In the coating solution, various auxiliaries such as a dispersant, an antifoaming agent, a waterproofing agent, a coloring agent, a release agent and a pH adjuster can be used.

[0014] The coating solution thus prepared is a blade, bar, roll, air knife coater, gate roll (G
(RC), using a device such as a pre-metering size press, the material is divided into single or multiple layers, and is usually coated on the base paper one by one on both sides or simultaneously on both sides. The solid content concentration of the coating liquid at that time is about 30 to 70% by weight, but considering the operability, its low shear rate viscosity is 500 to 5000 m.
Pa. It is preferable to adjust so as to be s.

The support includes a general coated base paper, a plastic film, a synthetic paper and the like. As the base paper for coating, base paper such as high quality or medium quality paper or paperboard having a basis weight of 30 to 400 g / m ² is appropriately used, and the paper making method is not particularly limited. In addition, base paper which has been subjected to size processing of starch, PVA or the like in advance by a size press, a gate roll, a bill blade, or the like, or base paper pre-coated with pigment can be used. As a drying method, a known method such as steam heating, hot air heating, gas heater heating, or infrared heating can be appropriately used.

The coated paper dried and coated as described above is
A finishing process such as a super calender and a soft calender may be performed.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but it is needless to say that the present invention is not limited to these examples. Unless otherwise specified, parts and% in the examples indicate% by weight, respectively. The evaluation method is as follows.

<Evaluation method> (1) Coating liquid viscosity B type viscosity: BL type viscometer (rotational speed 60 rpm, NO.
The viscosity at a coating liquid temperature of 30 ° C. was measured with a 4 spindle) (low shear rate viscosity).

Hercules Viscosity: High shear viscometer (Caltech Scientific model DV-1)
Using FF Bob 0), the coating solution temperature 3 at a rotational speed of 6600rpm (share rate 1.4 × 10 ^-5 / sec)
A 0 ° C. viscosity measurement was made (high shear rate viscosity).

(2) Uniformity of coating amount and streak,
Scratch condition: This is a visual evaluation by observing the surface feeling of the coated paper after passing through the blade during the coating experiment.

(3) Status of occurrence of calender stain and blocking: For the calender stain, the roll was observed when the sample after coating was subjected to a super calender treatment after humidity control. In addition, since it was known from the factory operation that the degree of calendar stains and the state of occurrence of blocking of product winding were almost the same, evaluation was made from calendar stains.

(4) Gravure printing: Monochromatic printing was carried out using a gravure printing tester of the Ministry of Finance Ministry of Finance, and the number of misdots in the halftone portion of 40% was counted.

(5) Visual evaluation: The dot shape of the gravure-printed sample was visually evaluated. ◎ (Excellent) ~ ××
(Poor) [Example 1] First-class kaolin (Engelhard UW-9)
0) 10 parts, 70 parts of secondary kaolin (Hydraspers, Huber Co.) and 20 parts of fine heavy calcium carbonate (FMT-90, Fimatic) as a dispersant as a dispersing agent with sodium polyacrylate (Toa Gosei Chemical) (Aron-T40) was dispersed in a Serie mixer to prepare a pigment slurry having a solid content of 70%.
5 parts of latex (average particle size of 1050 Å, glass transition temperature of -5 ° C., alkali insolubility) was added to the pigment slurry thus obtained, and an associative acrylic synthetic product (Alco Gum, Alco Chemical Co., Ltd.) was used as a viscosity modifier. L
-89) was added in an amount of 0.2 part. 0.7 parts of a release agent (San Nopco's Nopcoat C-104H) was added, and the solid content was 6%.
The coating liquid was adjusted to 3% and pH 9.5.

The coating liquid was applied to a base paper having a basis weight of 56 g / m ² at a coating speed of 1000 m using a blade coating device (blade edge angle 35 °, thickness 0.5 mm, applicator roll).
/ Min, coated on both sides one by one so that the dry coating amount per one side is 10 to 11 g / m ^2, and dried with hot air to obtain a coated paper sample. This was conditioned in a room at a temperature of 20 ° C. and a humidity of 60%, and then subjected to a super calender treatment at a roll temperature of 65 ° C. to obtain a coated paper for gravure printing.

[Example 2] In Example 1, the latex was prepared by averaging 810 angstroms and having a glass transition temperature of 1.
A coated paper for gravure printing was obtained in the same manner as in Example 1, except that the addition was changed to 5 parts at 5 ° C. and insoluble in alkali.

Example 3 Gravure coating was carried out in the same manner as in Example 1 except that the latex was changed to an average particle diameter of 1250 Å, a glass transition temperature of -17 ° C., and 5 parts of an alkali-soluble latex. Obtained paper.

Example 4 A coated paper for gravure printing was obtained in the same manner as in Example 1 except that the viscosity modifier was changed to 0.2 parts of hydroxyethyl cellulose (Admiral 3089FS, Aqualon Co.).

Example 5 Gravure printing was performed in the same manner as in Example 1 except that the viscosity modifier was changed to 0.3 parts of a non-associative acrylic synthetic product (Alcogum L-37, manufactured by Alcochemical Co.). A coated paper was obtained.

Example 6 A coated paper for gravure printing was obtained in the same manner as in Example 1 except that the viscosity modifier was changed to 0.3 parts of carboxymethylcellulose (LC coated by Somar Co.).

Comparative Example 1 A coated paper for gravure printing was obtained in the same manner as in Example 1 except that no viscosity modifier was added.

[Comparative Example 2] In Example 1, the latex is conventionally used as a gravure latex. The average particle size is 1700 angstroms and the glass transition temperature is -40.
A coated paper for gravure printing was obtained in the same manner as in Example 1 except that the temperature was changed to 8 ° C and alkali solubility (L-1457, Asahi Kasei Corporation) was changed to 8 parts, and no viscosity modifier was added.

[Comparative Example 3] In Example 1, the latex was conventionally used as a gravure latex, and the average particle size was 1700 angstroms and the glass transition temperature was -40.
Example 1 except that the addition of 8 parts of an alkali-soluble (A-1K Asahi Kasei Co., Ltd. L-1457) and 0.2 parts of carboxymethyl cellulose (Somal LC Coat) was added as a viscosity modifier. In the same manner as described above, a coated paper for gravure printing was obtained.

[Comparative Example 4] In Example 1, the latex is conventionally used as a gravure latex, and the average particle size is 1700 angstroms and the glass transition temperature is -40.
Example 1 except that the temperature was changed to 8 parts of alkali-soluble (A-1) and 8 parts of alkali-soluble (Asahi Kasei Co., Ltd. L-1457), and 0.2 parts of an associative acrylic synthetic product (Alco-Gum L-89) was added as a viscosity modifier. In the same manner as described above, a coated paper for gravure printing was obtained.

[Comparative Example 5] In Example 1, the latex was conventionally used as a gravure latex, and the average particle size was 1600 Å, the glass transition temperature was 3 ° C,
Same as Example 1 except that 5 parts of alkali-insoluble (ZEON LX407F) was added and 0.2 parts of an associative acrylic synthetic product (Alcogum L-89) was added as a viscosity modifier. A coated paper for gravure printing was obtained.

[Comparative Example 6] In Example 1, the latex is conventionally used as a gravure latex. The average particle diameter is 670 Å, the glass transition temperature is 12 ° C,
Example 1 was repeated except that alkali-insoluble (Asahi Kasei Co., L-1457) 8 parts was added and the viscosity modifier was 0.2 parts of an associative acrylic synthetic product (Alco Chemical L-89). Similarly, a coated paper for gravure printing was obtained.

The obtained results are shown in Tables 1 and 2.

[0037]

[Table 1]

[Table 2] As is clear from these examples and comparative examples, when the coating liquid for gravure printing coated paper according to the present invention is used, the coating workability is excellent, and the operation stability is also excellent. . Because the latex has a small average particle size, high shear rate viscosity (high shear viscosity) at the time of coating is reduced, resulting in good coating workability. As a result, smoothness and cushioning property of the coating layer are obtained. Is thought to increase. However, low shear viscosity is required to some extent in order to obtain good coating suitability. When the low shear viscosity is low, the coating liquid penetrates the base paper significantly, causing streaks and scratches. By adding the viscosity modifier, the low shear viscosity can be adjusted to an appropriate range. In particular, the associative acrylic synthetic viscosity modifier has a high effect of increasing the low shear viscosity, significantly lowers the high shear viscosity, and can be adjusted to a coating liquid viscosity suitable for coating.

At the same time, the relatively high glass transition temperature reduces stickiness of the coating layer and reduces calendar contamination during operation and blocking of product winding.

Similarly, as in the embodiment, the coated paper prepared by using the coating material for gravure printing coated paper according to the present invention has less occurrence of misdots.

The acrylic synthetic viscosity modifier improves gravure printing suitability as compared with CMC which is a natural polymer.
Although the reason is not clear, it is considered that the acrylic synthetic viscosity modifier does not expand and contract during the drying process of the coating layer, and the coating layer maintains more cushioning properties. Since oxidized starch causes expansion and contraction more than CMC, it is considered that the water retention effect is high, but the dot reproducibility is rather deteriorated.

The latex used in Comparative Examples 2, 3, and 4 is the most predominant type of conventional latex for gravure, and has a low Tg and a large particle size due to a large amount of butadiene and a softening of latex particles. Is big. Such a conventional latex is inferior in both coating suitability and operability.

[0042]

According to the constitution of the present invention, the coating suitability is improved together with the backing roll dirt, the calendar dirt and the streaks and scratches on the coated surface during operation, and the number of mis-dots during blocking of product winding and printing is reduced. It is possible to obtain a coated paper for gravure printing in which the dot reproducibility when printed is remarkably improved.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Isao Tobita 2-2-1 Nanmitsucho, Ishinomaki-shi, Miyagi Nihon Paper Industries Ishinomaki Mill (72) Inventor Hidetomo Takahashi 2-chome Nankocho, Ishinomaki-shi, Miyagi No. 2 1 Nihon Paper Industries Co., Ltd. Ishinomaki Mill (56) References JP-A-63-66397 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D21H 19/00-27 / 42

Claims (4)

(57) [Claims] 1. A pigment on a support having an average particle size of 700 to 13.
Glass transition temperature -20 to 20 ° C at 00 Å
Coated paper for gravure printing, having a coated layer containing the synthetic polymer latex of claim 1 and a viscosity modifier. 2. The coated paper for gravure printing according to claim 1, wherein the viscosity modifier is an acrylic synthetic product. 3. The coated paper for gravure printing according to claim 1, wherein the viscosity modifier is an associative acrylic synthetic product. 4. The coated paper for gravure printing according to claim 1, wherein the viscosity modifier is hydroxyethyl cellulose.