WO2018163795A1

WO2018163795A1 - Coated paper

Info

Publication number: WO2018163795A1
Application number: PCT/JP2018/005848
Authority: WO
Inventors: 遼外岡; 詩織柿木; 吉松　丈博; 俊宏遠藤
Original assignee: 日本製紙株式会社
Priority date: 2017-03-06
Filing date: 2018-02-20
Publication date: 2018-09-13
Also published as: TW201842262A; JPWO2018163795A1

Abstract

The present invention addresses the problem of providing a high-bulk coated paper with excellent printability. By incorporating starch grains in a pigment-coating layer on the basis of the invention, it is possible to produce a high-bulk coated printing paper with excellent printability.

Description

Coated paper

The present invention relates to coated paper. In particular, the present invention relates to a coated paper containing starch granules in a pigment coating layer.

The coated paper for printing is widely used in the commercial field for the purpose of advertising and promotion such as flyers, catalogs, pamphlets and direct mail. Particularly in recent years, both printing and processing have become more and more complex, and the demand for printing paper has become more severe in an environment such as on-demand printing and machine speedup.

Coated paper is used for various purposes such as books, posters, and wrapping paper. In any application, weight reduction is remarkable. Paper weight reduction is also demanded from the viewpoint of cost reduction such as material cost, warehouse storage cost, transportation cost, etc., and also from the aspect of ensuring the ease of transportation of consumers against recent lightweight media such as e-books and smartphones. Quality. In the world of coated paper for printing, in order to satisfy both the need for weight reduction and the high-class feeling of paper, there is an expectation for a bulky technology that reduces the weight while maintaining the paper thickness.

In addition to attempts to increase the bulk of the base paper, attempts to increase the bulk of the pigment coating layer have been studied as techniques for increasing the bulk of the coated paper for printing (a technique for reducing the density). As a technique for making a base paper bulky, for example, Patent Document 1 describes that a paper is made bulky by adding a nonionic surfactant. Patent Document 2 discloses a coating liquid containing 10 to 50 parts by weight of starch per 100 parts by weight of pigment on a bulky base paper (density: 0.70 g / cm ³ or less) containing mechanical pulp. It has been proposed to produce a bulky printing paper by coating by a transfer method. Furthermore, Patent Document 3 discloses a bulky printing coating by applying a coating layer containing a pigment having a large particle diameter to a low-density base paper (density: 0.50 to 0.75 g / cm ³ or less). It has been proposed to produce paper.

Japanese Patent Laid-Open No. 11-200263 JP 2011-026752 A JP 2005-248379 A

The technique of blending a surfactant described in Patent Document 1 to reduce the density of a base paper has a problem that the strength of the base paper, especially the interlayer strength of the base paper, is reduced. Further, in the technology for reducing the density of the base paper by blending the mechanical pulp according to Patent Document 2, the stiffness of the base paper is increased, and the cushioning property of the paper at the time of printing is lowered, and the printability may be lowered. Furthermore, as in Patent Document 3, when a pigment having a large particle size is used in the pigment coating layer, the pigment having a large particle size is easily removed from the coating layer, and the pigment particles have no cushioning property. There were problems such as insufficient strength and deterioration of the printing surface.

Japanese Patent Application Laid-Open No. 2007-303048 proposes further applying special starch particles processed with silicone on the pigment coating layer in order to reduce ink rubbing of the matte coated paper for printing. Has been. However, when a surface layer containing coarse starch particles is further coated on the pigment coating layer, the starch particles are exposed on the coated paper surface, and defects (holes) are formed on the coated paper surface due to the dropping of the starch particles. ) May be possible. In this method, it is necessary to separately apply a surface layer containing starch particles, and since special starch particles processed with silicone need to be used, there are problems in operation and cost.

In view of such a situation, an object of the present invention is to provide a bulky coated paper excellent in printability.

As a result of intensive studies on the above problems, it was found that a bulky printing paper can be obtained by adding starch particles in the pigment coating layer of the printing paper, and the present invention has been completed. . Although not limited to this, this invention includes the following aspect.
(1) A coated paper for printing having a pigment coating layer containing starch granules and a white pigment and a base paper.
(2) The coated paper according to (1), wherein the starch granules have an average particle size of 8 to 25 μm.
(3) The coated paper according to (1) or (2), wherein the weight ratio of starch granules to the total of starch granules and white pigment constituting the pigment coating layer is 0.5 to 10%.
(4) The coated paper according to any one of (1) to (3), wherein the coated paper has a plurality of pigment coated layers, and the starch granules are present at least in the outermost coated layer. .
(5) The coated paper according to (4), wherein the weight ratio of the starch granules to the total of the starch granules and the white pigment constituting the outermost coating layer is 0.5 to 10%.
(6) Based on the JAPAN TAPPI paper pulp test method No. 47, when a white paper sample of coated paper is vapor-dyed using an iodine solution (quantitative method), the stained starch particles having a diameter of 2 to 50 μm The coated paper according to any one of (1) to (5), wherein the number is 1 to 300 pieces / 1 mm ² .

According to the present invention, bulky coated coated paper can be produced by adding uncooked starch granules to the pigment coated layer.

FIG. 1 is a graph showing the particle size distribution of starch particles used in the examples. FIG. 2 is a photograph when the number of starch particles on the surface of the coated paper according to Sample 1-5 was measured. FIG. 3 is a graph showing the particle size distribution of starch particles on the surface of the coated paper according to Sample 1-5. FIG. 4 is a photograph of a cross section containing starch particles observed with an electron microscope for the coated paper according to Sample 1-5.

In the present invention, starch granules are used for the pigment coating layer. In general, starch is applied to a base paper or a coating layer using starch, which has been subjected to a steaming process in which heat is applied in the presence of water to gelatinize the starch granules, as a binder. In the present invention, granular starch is used for pigment coating. Used for construction layers. Examples of granular starch include starch that has not been cooked and starch that has been shaped into granules after cooking. ADVANTAGE OF THE INVENTION According to this invention, while being able to reduce the density of the coating layer of the coating paper for printing, the printability of coated paper can be improved.

The coated paper of the present invention is not particularly limited as long as the pigment coated layer containing a white pigment is provided on the base paper, and printing used for offset printing, gravure printing, letterpress printing, inkjet printing, and the like. Of course, white paperboard having a pigment coating layer on the paperboard base paper may be used. The coated paper of the present invention has one or more pigment coating layers on the base paper, but may have two or more pigment coating layers. The number of pigment coating layers is not particularly limited, but it is preferably 3 layers or less in consideration of weight reduction of paper. Further, the coated paper of the present invention may have a pigment coating layer only on one side of the base paper, or may have a pigment coating layer on both sides of the base paper. In addition, it is not necessary to apply the coating liquid (size press liquid) which does not contain a pigment on the base paper.

The coating amount of the coated paper in the present invention can be appropriately selected depending on the application, but in general, the solid content per side is 2 to 20 g / m ² , and may be 4 to 19 g / m ² . It may be 6 to 18 g / m ² or 8 to 17 g / m ² .

The pigment (white pigment) used in the coating layer of the present invention is not particularly limited, and those conventionally used for coated paper can be used, for example, kaolin, clay, engineered kaolin, delaminator. Ted clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, satin white and other inorganic pigments and solid, hollow or core shell Organic pigments such as molds can be used alone or in admixture of two or more as required. In addition, as a kind of pigment, it is preferable to contain kaolin or clay from the viewpoint of reducing paper smoothness and ink rubbing, the amount of binder required is small, surface strength can be improved with a small amount of adhesive, and high whiteness. From the viewpoint of the degree of drying and the drying property of the ink at the time of printing, heavy calcium carbonate and light calcium carbonate are preferable, and from the viewpoint of improving opacity, light calcium carbonate having a uniform particle diameter and shape is particularly preferable. This is because the bulky coating layer structure scatters light efficiently.

When calcium carbonate is used for the coating layer, the content of light calcium carbonate, heavy calcium carbonate, or both is preferably 50 parts by mass or more per 100 parts by mass of pigment, more preferably 70 parts by mass or more, and 80 More preferred is part by mass or more. Further, from the viewpoint of forming a uniform coating layer on the base paper and the drying property at the time of printing, the average particle diameter of the coating pigment is 0.2 to 5 μm as measured by a laser diffraction particle size distribution measuring machine. Preferably, 0.2 to 3 μm is more preferable.

In the present invention, any commonly used coater may be used. An on-machine coater or an off-machine coater may be used, and if it is an on-machine coater, a roll coater such as a size press coater, a gate roll coater, a rod metering size press coater, a bill blade coater, a blade metering size press coater, a short dwell blade A coater such as a coater or a jet fountain blade coater can be used. The coating speed is not particularly limited, but is preferably, for example, 150 to 2000 m / min, and more preferably 400 to 1500 m / min. With current technology, 150 to 1800 m / min for blade coaters and 150 to 2000 m / min for size press coaters are preferred.

In the present invention, the method for drying the wet coating layer is not limited, and various methods such as a steam superheated cylinder, a heated hot air air dryer, a gas heater dryer, an electric heater dryer, and an infrared heater dryer may be used alone or in combination. it can.

In the present invention, granular starch is used for the pigment coating layer. In general, when starch is cooked, the grains collapse, but in the present invention, uncooked granular starch (starch granules) or starch granules formed into granules after cooking is used. Starch refers to a mixture composed of amylose and amylopectin, and generally the mixing ratio varies depending on the plant that is the raw material of starch. As the starch, various processed starches and dextrins can be suitably used.

In the present invention, the average particle diameter of the starch granules is preferably 8 to 25 μm, more preferably 10 to 20 μm, in terms of median diameter (d50) measured by a laser diffraction particle size distribution analyzer such as Mastersizer S manufactured by Malvern. More preferably, it is 12 to 17 μm. Here, the median diameter is a diameter in which the large side and the small side are equal when the powder is divided into two from a certain particle diameter. In the present invention, the median diameter based on volume is used. Can do. The particle diameter distribution range can be measured by, for example, laser diffraction, and preferably 90% of the starch particles are distributed to 50 μm or less, more preferably 2 to 50 μm, and even more preferably. Is distributed in the range of 5 to 30 μm, and most preferably in the range of 5 to 25 μm.

The starch of the present invention is not particularly limited as long as it is a granular starch granule, and the modification method, raw material varieties, and the like are also free. Examples of modified starch, modified starch, and the like include oxidized starch, hydroxyesterified starch (HES), phosphate starch, esterified starch, and dextrin. Moreover, as a preferable raw material of the starch used by this invention, corn, a potato, tapioca etc. can be mentioned.

In a preferred embodiment, the compounding amount of the starch granules in the present invention is 0.5 to 10% with respect to the total of the white pigment and the starch granules constituting one layer of the pigment coating layer, and more preferably 8% or less. It may be 5% or less. When two or more pigment coating layers are provided, the starch granules of the present invention may be contained in any layer, but in order to exert the effects of the present invention greatly, the outermost pigment coating farthest from the base paper is used. It is preferable to make it contain in a construction layer. When starch particles are contained in the outermost coating layer, it is possible to greatly reduce the problem of ink rubbing that occurs when the coated papers immediately after printing are overlaid. Even when contained in a layer other than the outermost pigment coating layer, a bulky coated paper can be obtained.

Adhesive In the present invention, an adhesive conventionally used for coated paper can be used. Examples of the adhesive used for the pigment coating layer include various copolymers such as styrene / butadiene, styrene / acryl, ethylene / vinyl acetate, butadiene / methyl methacrylate, vinyl acetate / butyl acrylate, and polyvinyl alcohol. , Synthetic adhesives such as maleic anhydride copolymer and acrylic acid / methyl methacrylate copolymer; proteins such as casein, soy protein, synthetic protein; oxidized starch, positive starch, urea phosphated starch, hydroxy Examples include etherified starch such as ethyl etherified starch and starches such as dextrin; cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose. One or more types of adhesives can be appropriately selected and used. In the present invention, it is preferable to use a starch polymer compound and latex as an adhesive. Combined use provides both the advantages of starch compounds and latex.

In the present invention, the content of the adhesive in the pigment coating layer is preferably 5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the pigment. When using latex, the content thereof is preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the pigment. Even when blended in an amount of more than 15 parts by mass, the printing surface strength is excellent, but the cost is high and further effects cannot be expected. Moreover, when using a starch type polymer as an adhesive agent, 1 to 15 weight part is preferable, More preferably, it is 1 to 10 weight part. When two or more pigment coating layers are provided, the innermost pigment coating layer close to the base paper preferably has a higher latex content than the starch polymer, and the outermost pigment coating layer farthest from the base paper. The layer preferably has more starch-based polymer than latex.

In the present invention, the method for preparing the coating liquid is not particularly limited and can be appropriately adjusted depending on the type of coater. Although not limited thereto, the solid content concentration of the coating liquid is preferably 40 to 75% by weight, more preferably 50 to 72% by weight, and may be 60 to 69% by weight. The viscosity of the coating solution is preferably 300 to 2000 mPa · s, more preferably 500 to 1500 mPa · s, when measured with a JIS K 71117-1 B-type viscometer.

In the present invention, various assistants to be blended in ordinary coated paper pigments such as dispersants, thickeners, water retention agents, antifoaming agents, water resistance agents, colorants, fluorescent whitening agents, etc. Agents can be used as appropriate.

Base Paper The coated paper of the present invention has a base paper layer. A base paper can be manufactured by a well-known method, for example, a paper-making raw material (paper material) can be made in a wire part, and then it can be used for a press part and a pre-dryer part to manufacture a base paper. The base paper used in the present invention may be single-layer paper or multi-layer paper, but when producing white paperboard, it is preferable to use multi-layer paper. The method for producing the base paper of the present invention is not particularly limited, and can be performed by a known method using known raw materials. The base paper used in the present invention is not particularly limited, and generally used high-quality paper, medium-quality paper, paperboard, reprinted paper, machine-coated paper, art paper, cast-coated paper, synthetic paper, resin-coated paper, plastic film, etc. Can be used without exception.

As the pulp raw material used for the base paper of the present invention, chemical pulp can be used. As the chemical pulp, hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP) can be suitably used. In addition to chemical pulp, various pulps can be used depending on the application, for example, deinked pulp (DIP), groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermo. Examples include mechanical pulp (CTMP), chemi-ground pulp (CGP), and semi-chemical pulp (SCP). As the deinked pulp, it is possible to use deinked pulp made from selected waste paper such as high quality paper, medium quality paper, lower grade paper, newspaper, flyers, magazines, etc., or unselected waste paper mixed with these.

In the present invention, known fillers can be arbitrarily used as fillers for base paper, such as heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, deramikaolin, white Amorphous produced by neutralization of carbon, talc, magnesium carbonate, barium carbonate, barium sulfate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, sodium silicate Inorganic fillers such as silica and organic fillers such as urea-formalin resin, melamine resin, polystyrene resin, phenol resin can be used alone or in combination. Among these, heavy calcium carbonate and light calcium carbonate, which are typical fillers for neutral papermaking and alkaline papermaking, are preferably used to improve opacity. The filler content in the paper is not particularly limited, but is preferably 1 to 40 solids by mass, more preferably 5 to 35 solids by mass, and even more preferably 10 to 30 solids by mass.

In the present invention, a known paper additive can be used. For example, sulfuric acid bands and various anionic, cationic, nonionic or amphoteric yield improvers, drainage improvers, various paper strength enhancers and internal additive sizing agents, etc. Can be used. Examples of the dry paper strength improver include polyacrylamide and cationized starch, and examples of the wet paper strength improver include polyamidoamine epichlorohydrin. In order to obtain a higher bulking effect, a bulking agent may be added to the base paper. These chemicals are added within a range that does not affect the formation and operability. Examples of neutral sizing agents include alkyl ketene dimers, alkenyl succinic anhydrides, and neutral rosin sizing agents. Furthermore, dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like can be added as necessary.

The paper making method of the base paper in the present invention is not particularly limited, and a long paper machine including a top wire, an on-top former, a gap former, a round paper machine, a long paper machine and a round paper machine are used in combination. Paper board machine, Yankee dryer machine, etc., and may be single-layer or multi-layer. The pH during papermaking may be acidic, neutral or alkaline, but neutral or alkaline is preferred. The paper making speed is not particularly limited.

The basis weight of the base paper of the present invention is not particularly limited and can be appropriately selected depending on the application. For example, the basis weight of the base paper may be 25 to 160 g / m ² , 35 to 150 g / m ² , or 45 to 140 g / m ² for general printing coated paper. If so, it may be 200 g / m ² or more.

The base paper used for the coated paper of the present invention may have a clear (transparent) coating layer on one side or both sides. By applying clear coating on the base paper, the surface strength and smoothness of the base paper can be improved, and the coating property when applying pigment can be improved. In the present invention, the aforementioned adhesive can be used as a binder in the clear coating layer. The amount of the clear coating is preferably 0.1 ~ 4.0g / ^{m 2} by solid per side content, more preferably 0.5 ~ 2.5g / ^{m 2.}

In the present invention, clear coating means, for example, various starches such as starch and oxidized starch using a coater (coating machine) such as a size press, a gate roll coater, a pre-metering size press, a curtain coater, and a spray coater. It means that a coating liquid (surface treatment liquid) mainly composed of a water-soluble polymer such as polyacrylamide or polyvinyl alcohol is applied (size press) on a base paper.

In the present invention, it is preferable to perform pre-calendar processing on the base paper before coating by an online soft calendar, online chilled calendar, etc., and smooth the base paper in advance in order to make the coating layer after coating uniform. . In this case, the treatment linear pressure is preferably 30 to 100 kN / m, more preferably 50 to 100 kN / m. Further, the moisture content of the base paper during the precalender treatment is also important, and the moisture content is preferably 3 to 5%.

Coated paper surface In the present invention, the coated paper produced as described above may be surface-treated as necessary, but it is difficult to obtain the bulky effect of the present invention, and therefore it is preferable not to perform calendar treatment. . When performing the smoothing process, a smoothing processing apparatus such as a normal super calendar, gloss calendar, soft calendar, thermal calendar, shoe calendar, or the like can be used. The smoothing apparatus is appropriately used on-machine or off-machine, and the form of the pressure apparatus, the number of pressure nips, heating, and the like are appropriately adjusted, but calendering at low pressure is preferable.

The coated paper of the present invention can correspond to various printing methods, such as coated paper for offset printing, coated paper for letterpress printing, coated paper for gravure printing, inkjet paper, dry electrophotographic paper, wet electronic paper. Can be used for photographic paper.

As described above, the coated paper according to the present invention uses starch particles in the pigment coating layer. However, if the coarse starch particles are exposed too much on the coated paper surface, the starch particles may fall off. It becomes easy. Based on the JAPAN TAPPI paper pulp test method No. 47, when a blank sample of coated paper is vapor-dyed using an iodine solution (quantitative method), the number of stained starch particles having a diameter of 2 to 50 μm is 1 to 300 pieces / 1 mm ² is preferable, 2 to 200 pieces / 1 mm ² is more preferable, 3 to 150 pieces / 1 mm ² is further preferable, 4 to 100 pieces / 1 mm ² is further more preferable, and 5 to 50 pieces / 1 mm ² are more preferable. ^It may be ² .

Hereinafter, the present invention will be described in more detail with specific experimental examples, but the present invention is not limited to the following experimental examples. In addition, unless otherwise specified, in this specification, a numerical range is described as including its end points, and “part” and “%” indicate “part by weight” and “% by weight”, respectively.

Evaluation method (1) Paper quality / basis weight: Measured according to JIS P 8124.
-Paper thickness / density: Measured according to JIS P 8118.
Ash content: Measured according to ISO 1762-1974.

(2) Blank paper gloss (%)
Measurement was performed based on JIS-P8142.

(3) Print glossiness (%)
Using offset sheet-fed ink (4 colors) manufactured by Roland, using offset sheet-fed ink (NEX-M manufactured by Toyo Ink Co., Ltd.), the ink density of the solid part is 1.60 indigo at a printing speed of 8000 sheets / hr. Printing was performed in the order of Crimson (CMY) so that the color was 1.50 and yellow 1.10. The glossiness of the indigo red (CMY) solid printed part of the obtained printed matter was measured based on JIS P-8142.

(4) Gloss level difference (points)
The value obtained by subtracting the white paper glossiness from the print glossiness is defined as the glossiness difference. If the glossiness difference is 20 points or more, the difference in gloss between the printed part and the white paper part is sufficiently obtained, and the printed matter is easy to visually recognize. .
・ Glossiness difference = Printing glossiness (%)-Blank paper glossiness (%)

(5) Feeling of printing Using offset sheet-fed printing machine (4 colors) manufactured by Roland, using offset sheet-fed ink (NEX-M manufactured by Toyo Ink), the ink density of the solid part at a printing speed of 8000 sheets / hr. After printing so that the ink was 1.80, the printing surface feeling of the black solid printing part was evaluated in three stages. Evaluation criteria are as follows and evaluated visually.
-3 (◯): No unevenness is observed in the printed part.
2 (Δ): Slight unevenness is observed in the printed part, but there is no practical problem.
1 (x): Many unevennesses are observed in the printing part.

(6) Ink rubbing Using an offset sheet-fed ink (NEX-M manufactured by Toyo Ink Co., Ltd.) with an offset sheet-fed printing machine (4 colors) manufactured by Roland Co., Ltd. The ink was printed so that the ink was 1.80. Next, the ink was conditioned for 24 hours in accordance with JIS P8111 and rubbed once with a load of 500 gf so that the black solid print portion would fit the blank paper portion using the Gakushin type friction fastness tester, and transferred to the blank paper portion. Was visually evaluated in 5 stages as ink rubbing.
* 5: No ink transfer.
-4: Almost no ink transfer.
-3: There is a slight ink transfer, but there is no practical problem.
-2: There is much transfer of ink.
* 1: There are very many ink transfers.

(7) Number of starch particles on the coated paper surface After preparing an iodine solution (quantitative method) based on JAPAN TAPPI paper pulp test method No. 47 and vapor-dyeing a blank paper sample, a digital microscope (VHX manufactured by Keyence Corporation) is used. Using 900, the number of stained starch granules having a diameter of 2 to 50 μm within the range of 1.5 mm × 2.1 mm was measured, measuring four places at a magnification of 200 times, The average number was calculated.

(8) Average particle size and particle size distribution of starch particles The average particle size (d50) and particle size distribution of starch particles were measured by laser diffraction. Specifically, starch particles were analyzed using Mastersizer S manufactured by Malvern.

Raw material of coated paper (base paper)
・ Chemical pulp: Nippon Paper Industries LBKP (hardwood bleached kraft pulp)
・ Light calcium carbonate: Nippon Paper's internal filler

(Pigment)
・ Heavy calcium carbonate: FMT97 manufactured by Pfematec Co., Ltd. (average particle diameter d50 = 0.64 μm measured by laser diffraction method, ratio of particles having a particle diameter of 2 μm or less by laser diffraction method: 97%)
・ Light calcium carbonate: Nippon Paper Co., Ltd. pigment for coating (average particle diameter measured by laser diffraction method d50 = 0.92 μm, ratio of particles having a particle diameter of 2 μm or less by laser diffraction method: 89%)
-Kaolin: KCS manufactured by Imeris (average particle diameter measured by laser diffraction method d50 = 4.05 μm)
Starch particles: Y-3P manufactured by Nippon Corn Starch (unmodified corn starch, average particle diameter d50 measured by laser diffraction method: about 15 μm)
FIG. 1 shows the particle size distribution of starch particles measured using Mastersizer S (laser diffraction particle size distribution measuring machine) manufactured by Malvern.

(binder)
Styrene / butadiene copolymer latex: A & L PB1537 (average particle size 110 nm, glass transition temperature 10 ° C.)
Styrene / butadiene copolymer latex: PB9501 manufactured by A & L (average particle size 80 nm, glass transition temperature -12 ° C.)
・ Oxidized starch: Nippon Cornstarch SK200 (corn starch)

Experiment 1: Production of coated paper (two-layer coating)
On base paper having a basis weight of 75 g / ^{m 2,} the pigment coating layer dry coating amount per side is 6.5 g / ^{m 2} (under layer), dry coating amount per one side 10.5 g / A coated paper for printing provided with a pigment coating layer (top layer: outermost coating layer) of m ² was produced (samples 1-1 to 1-7, basis weight: about 109 g / m ² ).

(Base paper)
A high quality paper having a basis weight of 98 g / m ² and a density of 0.73 g / cm ³ was used as a base paper. The pulp blend was 100% chemical pulp (LBKP 100% by weight) and contained 13% by weight light calcium carbonate as a filler.

(Under coating)
Heavy calcium carbonate is used as the pigment, and 7 parts by weight of styrene / butadiene copolymer latex (A & L PB1537) and steamed oxidized starch (manufactured by Nippon Corn Starch Co., Ltd.) with respect to 100 parts by weight (solid content) of the pigment. SK200) 3 parts by weight was added, and water was further added to obtain an under coating liquid having a solid concentration of 66% by weight.

On the base paper, an under pigment coating solution is coated on both sides with a blade coater at a coating speed of 650 m / min so that the dry coating amount per side is 6.5 g / m ^2, and then dried and undercoated. A construction layer was provided on the base paper.

(Top coating)
As coating pigment, heavy calcium carbonate slurry and starch particles (Y-3P manufactured by Nippon Corn Starch Co., Ltd., uncooked) were used in the amounts shown in the table below, and styrene was used as an adhesive for 100 parts by weight (solid content) of pigment. -Blending 4 parts by weight of butadiene copolymer latex (PB9501 manufactured by A & L) and 6 parts by weight of steamed oxidized starch (SK200 manufactured by Nippon Corn Starch Co., Ltd.) and adding water to top coating with a solid content concentration of 66% by weight A pigment coating solution was obtained.

On top of the undercoated base paper, the top coating pigment coating solution is coated on both sides with a blade coater so that the dry coating amount per side is 10.5 g / m ^2, and then dried for printing. Wrought paper was obtained (Samples 1-1 to 1-6).

Also, Sample 1-7 was produced as a coated paper in which starch particles were blended in the under layer. Specifically, the coating used for the under coating was the same as Sample 1-6, except that 90 parts by weight of heavy calcium carbonate and 10 parts by weight of starch particles (Y-3P manufactured by Nippon Cornstarch, uncooked) were used. Thus, a coated paper for printing was produced.

Furthermore, the sample was used except that the heavy calcium carbonate used for the under layer and the top layer was replaced with light calcium carbonate, and starch particles (Y-3P, uncooked by Nippon Corn Starch Co., Ltd.) were used for the under layer with the composition shown in the table below. In the same manner as in 1-1, coated paper for printing was produced (Samples 1-8 to 1-9).

Experiment 2: Production of coated paper (single-layer coating)
On base paper having a basis weight of 75 g / m ^2, the pigment coating layer dry coating weight per one side is 15 g / m ² to both surfaces coated to produce a coated printing paper (sample 2-1 2-2, basis weight: about 105 g / m ² ).

As the pigment, 53.5 parts by weight of heavy calcium carbonate slurry (solid content), 45 parts by weight of kaolin (solid content), 1.5 parts by weight of uncooked starch particles, and 100 parts by weight of the pigment, the adhesive As a blend, 4 parts by weight of styrene / butadiene copolymer latex (PB9501 manufactured by A & L) and 6 parts by weight of steamed oxidized starch (SK200 manufactured by Nippon Corn Starch Co., Ltd.) were added, and water was added to give a pigment with a solid content concentration of 66% by weight. A working solution was obtained.

On the base paper of Experiment 1, this pigment coating solution was coated on both sides with a blade coater so that the dry coating amount per side was 15.0 g / m ^2, and then dried to obtain a coated paper for printing. (Sample 2-1).

Also, a coated paper for printing was obtained in the same manner as in Sample 2-1, except that uncooked starch particles were not blended and the amount of heavy calcium carbonate was changed to 55 parts by weight (Sample 2-2: Comparative Example). .

Further, a coated paper for printing was produced in the same manner as Sample 2-1 and Sample 2-2 except that heavy calcium carbonate was replaced with light calcium carbonate (Samples 2-3 to 2-4).

As is clear from the table, low-density coated coated paper could be obtained by adding uncooked starch granules to the pigment coated layer. Since the specific gravity of starch particles is smaller than that of inorganic pigments, the density of the pigment coating layer is reduced by blending the starch particles, and when the starch particles are blended in the outermost coating layer, the paper thickness is increased by the starch particles. Therefore, it is thought that the density of the coated paper is reduced as a whole.

The coated paper for printing of the present invention had little ink rubbing after printing and was excellent in coating suitability. The unevenness of the coated paper surface increases due to the starch particles present near the surface of the coated paper, the contact area between the superimposed coated papers decreases, and the ink rub is reduced due to the cushioning properties of the starch particles. Conceivable.

2 to 4 show the results of analyzing the coated paper according to Sample 1-5. FIG. 2 shows a surface photograph when the surface of the coated paper according to Sample 1-5 is analyzed, and 11 starch granules having a diameter of 2 to 50 μm per 1.5 mm × 2.1 mm (per 1 mm ² It was about 3.5). Further, as apparent from the cross-sectional photograph shown in FIG. 4, the coated paper according to the present invention does not expose the starch particles excessively by printing the starch particles in the pigment coating layer. In addition, it was a pigment coating layer in which starch particles hardly fall off.

Claims

A coated paper for printing having a pigment coated layer containing starch granules and a white pigment and a base paper.
The coated paper according to claim 1, wherein the starch granules have an average particle size of 8 to 25 µm.
The coated paper according to claim 1 or 2, wherein the weight ratio of the starch granules to the total of the starch granules and the white pigment constituting the pigment coating layer is 0.5 to 10%.
The coated paper according to any one of claims 1 to 3, wherein the coated paper has a plurality of pigment coated layers, and the starch granules are present at least in the outermost coated layer.
The coated paper according to claim 4, wherein the weight ratio of the starch granules to the total of the starch granules and the white pigment constituting the outermost coating layer is 0.5 to 10%.
Based on the JAPAN TAPPI paper pulp test method No. 47, when a blank sample of coated paper is vapor-dyed using an iodine solution (quantitative method), the number of stained starch particles having a diameter of 2 to 50 μm is 1 is a 300/1 mm 2, coated paper according to any one of claims 1 to 5.