JP2018162551A - Coated paper and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of effectively producing a coated paper having excellent blank paper glossiness, smoothness, and surface strength and suppressed blanket piling by using a starch-based polymer.SOLUTION: A coated paper having excellent glossiness and surface strength is producible by using, as adhesive for a pigment coated layer, a starch-based polymer having extremely low viscosity when a certain period of time elapses after digestion, and having a high weight average molecular weight.SELECTED DRAWING: None

Description

  The present invention relates to a coated paper and a method for producing the coated paper. In particular, the present invention relates to a coated paper containing a low-viscosity polymer compound as an adhesive and a method for producing the coated paper.

  In general, when a coated paper is produced, a coating layer mainly composed of a pigment and an adhesive for binding the pigment is formed in order to improve printability. Mainly petroleum-based from the viewpoints of good paint fluidity as an adhesive, good coating suitability in a coating device, and easy imparting of printing surface strength as coated paper quality Adhesives derived from these synthetic materials are used.

However, in recent years, not only petroleum-based synthetic materials but also materials that are inexpensive and excellent in biodegradability are attracting attention due to cost reduction and increased environmental awareness. Among them, an adhesive using a starch-based material as a raw material has attracted attention (Patent Document 1). However, when a starch-based material is highly blended in the paint (pigment coating liquid), the viscosity of the paint is remarkably increased, and the operability and coating suitability are deteriorated. Even if the viscosity is adjusted by dilution of the paint, the water content increases, so the load of the drying process after coating increases, and there is an adverse effect on productivity such as a decrease in coating speed. In addition, even if the coating speed is reduced, the coating concentration is low and the water retention of the coating is reduced. Therefore, the penetration of the coating into the base paper is large, and the glossiness of the white paper and the surface strength are reduced. Quality deterioration is inevitable.
Therefore, Patent Document 2 proposes a technique in which, when an aqueous slurry containing a starch polymer is cooked, a starch polymer having a low viscosity after a certain time has elapsed from the start of cooking as an adhesive.

JP 2010-84311 A International Publication WO2012 / 133487

However, in the technique described in Patent Document 2, blanket piling tends to easily occur during offset printing, and blanket piling is significantly deteriorated particularly when the coating liquid concentration is low. Blanket piling is the accumulation of paper dust and ink on the periphery of the image area on the blanket.
The higher concentration of the coating liquid contributes to the improvement of the surface strength by improving the productivity by reducing the drying load and reducing the penetration of the coating liquid into the base paper because the water content decreases. However, if the concentration of the coating solution is high, the viscosity increases and the operability and coating suitability are deteriorated. Therefore, the coating solution is diluted to the extent that it does not adversely affect the drying load and surface strength. It is a fact.
In view of such a situation, the problem of the present invention is that the viscosity of the coated paper is not increased so much even if it is highly blended in the paint, and the glossiness and surface strength of the coated paper are improved, and the blanket for offset printing is also improved. The aim is to search for starch-based adhesives that can suppress piling and to develop a technology for producing high-quality coated paper with high operability.

As a result of intensive studies to solve the above problems, it was found that when a starch-based polymer showing a characteristic viscosity behavior at the time of steaming was used as an adhesive (binder) for the pigment coating layer even though the molecular weight was relatively large, it was excellent. It was found that coated paper can be produced with high operability. Concerning viscosity behavior, when an aqueous slurry containing starch-based polymers is cooked, it is not the maximum viscosity at the time of cooking or the minimum viscosity when the viscosity subsequently decreases, but the viscosity after a certain time has elapsed since the start of cooking. In addition, when a starch polymer having a molecular weight of a certain level or more is used as an adhesive for the coating layer of the coated paper, it is found that a coated paper excellent in surface gloss and surface strength can be produced, and the present invention is completed. It came to.

Although this invention is not limited to this, The following invention is included.
(1) A coated paper having a pigment coating layer containing a pigment and an adhesive on a base paper, wherein the adhesive contains a starch polymer having a weight average molecular weight of 200,000 or more, Using a Rapid Visco Analyzer (RVA), a slurry having a solid content concentration of 35% by weight was heated to 98 ° C. in 5 to 5 minutes and 98 minutes for 4 to 5 minutes. Maintained at ℃, temperature decreased to 50 ℃ in 3 minutes for 3-12 minutes, and when cooked under steaming conditions of maintaining at 50 ℃ for 4 to 12/16 minutes, the viscosity after 16 minutes from the start of cooking was 1000 mPa · s The coated paper as described below.
(2) The coated paper according to (1), wherein the starch-based polymer has a weight average molecular weight of 25 to 400,000.
(3) The coating according to (1) or (2), wherein a copolymer latex is not used as the adhesive, or a copolymer latex of 4 parts by weight or less is used with respect to 100 parts by weight of the pigment. Craft paper.
(4) The coated paper according to any one of (1) to (3), comprising 50 parts by weight or more of calcium carbonate per 100 parts by weight of the pigment.
(5) The coated paper according to any one of (1) to (4), wherein the pigment coating layer contains 5 to 50 parts by weight of a starch polymer per 100 parts by weight of the pigment.
(6) The coated paper according to any one of (1) to (5), wherein the starch polymer compound is white dextrin.
(7) A method for producing a coated paper comprising a step of coating a pigment coating layer containing a pigment and an adhesive on a base paper, wherein the adhesive is a starch system having a weight average molecular weight of 200,000 or more. A slurry containing a polymer and having a solid content concentration of 35% by weight of the starch polymer is heated to 98 ° C. in 5 minutes from 0 to 5 minutes using a Rapid Visco Analyzer (RVA). Keeping at 98 ° C. for 4 minutes to 9 minutes, dropping to 50 ° C. in 3 minutes for 9 to 12 minutes, and 16 minutes from the start of cooking when cooking under the steaming conditions of holding at 50 ° C. for 4 minutes to 12 to 16 minutes The said method whose viscosity after a minute is 1000 mPa * s or less.

  In the present invention, a specific starch-based polymer compound is used as an adhesive, and the fluidity of the coating liquid is good. When the fluidity is improved, handling of the coating liquid is facilitated and the coating suitability is also improved, so that the operation efficiency in the production of coated paper is improved. In addition, since the water retention of the coating liquid is improved, it suppresses the penetration of the coating liquid into the base paper, so that the glossiness of the obtained coated paper is improved, the surface strength is improved, the suppression of piling, etc. Various coated paper quality is improved.

FIG. 1 is a graph showing the results of analyzing various starch polymers with a rapid visco analyzer.

  The coated paper of the present invention is not particularly limited as long as it is a coated paper in which a pigment coating layer containing a white pigment and an adhesive is provided on the base paper, and printing used for offset printing, gravure printing, letterpress printing, etc. Of course, white paperboard having a pigment coating layer on the paperboard base paper may be used.

In the coated paper of the present invention, one or more pigment coated layers containing a pigment are provided on a base paper. On the base paper, a coating solution (size press solution) containing no pigment may be applied or not.
The ash content in the coated paper of the present invention is preferably 10% by weight or more, and more preferably 30% by weight or more. In the case of coated paper for printing, it is preferable to increase the opacity by increasing the ash content.

In the present invention, a pigment coating layer containing a pigment, an adhesive (binder), and water is mainly used to provide a pigment coating layer. As an adhesive (binder), starch having a specific viscosity is used. Add the derived polymer compound. The starch-derived polymer compound of the present invention has a particularly low viscosity after elapse of a certain time after cooking, so that the viscosity of the pigment coating liquid is not greatly increased even when blended in the pigment coating liquid. The density can be increased, thereby improving the print quality of the coated paper. That is, since the coating of the base paper is suppressed and the effective coating layer is increased, the quality of various coated papers such as improvement of glossiness and surface strength is improved.

In the present invention, a starch-derived polymer compound is used as the adhesive. As the starch-derived polymer compound, starches including various processed starches and dextrins obtained by hydrolyzing starch can be preferably 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.
The molecular weight of the starch polymer of the present invention is 200,000 MW or more in terms of weight average molecular weight. More preferably, it is 250,000 MW or more. When the molecular weight is less than 200,000 MW, blanket piling tends to occur when printing is performed on an offset rotary press. The reason for this is that the water retention of the coating liquid decreases and the sinking of the binder occurs, the binder does not stay on the surface of the coating layer, the strength of the coating layer is insufficient, and the coating layer peels off during printing. It is thought that it will be deposited on. To prevent this, the concentration of the coating solution may be increased, but there is a problem that the operability is deteriorated when the concentration of the coating solution is increased. The upper limit of the molecular weight is not particularly limited. However, the larger the viscosity, the higher the viscosity of the paste solution, and the higher the viscosity at the time of blending the paint, resulting in poor workability. More preferably, it is 400,000 MW or less.

In this invention, a weight average molecular weight shows the value measured by the size exclusion chromatography multi-angle light scattering (SEC-MALS) method with the following apparatuses and conditions.
-Separation column: 2 Shodex GPC KB-806M, 1 Shodex GPC KB-802-Column temperature: 40 ° C
Mobile phase solvent: 0.1 mol / L NaNa ₃ aqueous solution Mobile phase flow rate: 0.5 mL / min
・ Injection volume: 300 μL
Detector 1: Multi-angle light scattering detector (manufactured by Wyatt, “DAWN HELEOSII”)
Detector 2: Refractive index (RI) detector (manufactured by Waters, “2414 type”)
Sample: [steamed] stirred at 100 ° C. for 20 minutes [concentration] 0.4 w / v%
[Filtration] Chromatodisc pore size 0.45μm (Kurabo)
・ Data processing: ASTRA (manufactured by Wyatt)

The starch-derived polymer compound of the present invention is a starch-derived polymer compound having a slurry viscosity of 1000 mPa · s or less after steaming under certain conditions.
When starch compounds are suspended in water and heated, the starch granules absorb water and gradually expand. When the heating is continued, the starch granules eventually disintegrate and change into a gel. This phenomenon is called gelatinization. At this time, the starch suspension becomes gradually transparent from the cloudy state and rapidly increases in viscosity. The viscosity becomes maximum when the particles absorb water to the maximum extent, and the viscosity decreases due to the collapse of the particles. In the present invention, after the viscosity is maximized by cooking, the one having a certain range of viscosity when it is allowed to stand at a reduced temperature is used.
When the starch-based polymer compound is contained in the coating liquid, heating for dissolving the polymer compound is required. Therefore, the viscosity of the slurry after cooking under certain conditions is important.
Since the starch-derived polymer compound of the present invention has a low viscosity of the slurry after cooking, the concentration of the slurry can be increased.
Also, for example, cold water-soluble starch represented by pregelatinized starch has a low slurry viscosity, but these cold water-soluble starches are treated so that they are soluble in cold water, and dextrin and the like are more surface strength. Highly advantageous. Therefore, the starch-based polymer compound of the present invention preferably has a solubility in water at 20 ° C. of less than 20%.
The behavior of such a starch polymer can be measured using a measuring instrument called Rapid Visco Analyzer (RVA, model RVA-4, manufactured by New Port Scientific). In the present invention, when a starch-based polymer slurry having a concentration of 35% by weight is steamed under the following steaming conditions, a starch-based polymer having a viscosity at 50 ° C. 16 minutes after the start of steaming is 1000 mPa · s or less. . In one embodiment of the present invention, a starch-based polymer is used as an adhesive for the pigment coating layer, and the adhesive strength as a binder is manifested by cooking (cooking) the slurry.

<RVA viscosity measurement conditions>
The paddle is rotated under the following conditions, the torque applied to the stirring paddle is measured, and the viscosity is calculated.
(Stirring conditions)
・ 10 seconds after the start of measurement: 960 rpm
-Then: 160rpm
(Steaming conditions)
・ 0 to 5 minutes: raised to 98 ° C. in 5 minutes ・ 5 to 9 minutes: held at 98 ° C. ・ 9 to 12 minutes: lowered to 50 ° C. in 3 minutes ・ 12 to 16 minutes: held at 50 ° C. The viscosity of the starch-based polymer compound measured as described above at a stage of holding at 50 ° C. after 16 minutes after cooking is 1000 mPa · s or less, more preferably 850 mPa · s or less.

The starch polymer of the present invention preferably has a maximum viscosity due to gelatinization of starch of 2000 mPa · s or less, preferably 1600 mPa · s or less, when the viscosity is measured under the above conditions using RVA. More preferred. When the maximum viscosity at the time of gelatinization is in such a range, handling is easy, and an excessive increase in viscosity does not occur when blended in a coating solution.
The starch-derived polymer compound of the present invention is not particularly limited as long as it has the above viscosity, and the modification method, the raw material type, 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. Of these, dextrin is preferred because the fluidity is further improved (low viscosity) when blended in a paint. Moreover, as a preferable raw material of the starch polymer used in the present invention, corn, potato, tapioca and the like can be mentioned, and waxy corn (waxy corn) and tapioca are particularly preferable.
Examples of the starch polymer satisfying the viscosity of the present invention include low-viscosity hydroxyethyl starch (HES), oxidized acetylated tapioca starch, and dextrin. These starch polymers are low in viscosity, stable in viscosity, and excellent in strength.
In the present invention, since the viscosity is low and the viscosity stability is high, dextrin, particularly roasted dextrin is preferable as the adhesive. Dextrin is a general term for starch-based polymers obtained by hydrolyzing starch, and α-glucose is polymerized by glycosidic bonds, and is also called glue. Ordinary starch has a large molecular weight, but dextrin is an intermediate product produced in the starch hydrolysis process. Conventionally, it has a molecular weight of about an oligomer (a mixture of several to tens of glucose). there were. The roasted dextrin is a dextrin produced by adding an acid and baking with dry heat, and there are types such as white dextrin, yellow dextrin, and British gum. In the present invention, it is particularly preferable to use white dextrin. When the white dextrin is further hydrolyzed, it becomes a so-called yellow dextrin. However, since the yellow dextrin has low stability and the pigment coating layer may be colored, the use of white dextrin is preferred in the present invention.
The white dextrin of the present invention preferably has more branches in the dextrin. When there are many branches, strength is easily developed. The degree of branching is related to the radius of inertia. If the molecular weight is the same, it is considered that if the inertia radius is small, there are many branches. Therefore, the white dextrin of the present invention preferably has a smaller inertial radius.

  The starch-derived polymer compound of the present invention has good fluidity when blended in a coating solution. When fluidity is improved, it becomes possible to increase the concentration of the coating liquid, suppress the penetration of the coating liquid, and increase the effective coating layer, thereby improving the gloss development, whiteness, surface strength, etc. Improved coated paper quality.

  In a preferred embodiment, the amount of the starch-derived polymer compound of the present invention is 5 to 50 parts by weight, more preferably 5 to 30 parts by weight per 100 parts by weight of the pigment.

In the present invention, as the adhesive, only the starch-derived polymer compound can be used, but in addition to the starch-derived polymer compound, an adhesive conventionally used for coated paper is used. It can also be used together. Examples of adhesives other than the above-mentioned starch-derived polymer compounds include styrene / butadiene, styrene / acryl, ethylene / vinyl acetate, butadiene / methyl methacrylate, vinyl acetate / butyl acrylate, Synthetic adhesives such as coalescence (latex), polyvinyl alcohol, maleic anhydride copolymer, and acrylic acid / methyl methacrylate copolymer; proteins such as casein, soy protein, synthetic protein; Oxidized starch other than molecular compounds, positive starch, urea phosphated starch, etherified starch such as hydroxyethyl etherified starch, starch such as dextrin; normal coating such as cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, etc. Includes paper adhesive. One or more types of adhesives can be appropriately selected and used. In the present invention, it is preferable to use a latex having a different characteristic from that of the starch polymer compound as an adhesive, and in that case, it is preferable to use more starch polymer compound than the latex. Although both advantages of the starch compound and latex can be obtained by the combined use, it is preferable to increase the amount of the starch polymer compound used in order to exert the effect of the present invention. When a starch polymer compound and latex are used in combination as an adhesive, the latex content of the entire adhesive is preferably less than 50% by weight.
Moreover, in the preferable aspect of this invention, latex is not used as an adhesive agent, or the usage-amount of latex shall be 4 weight part or less with respect to 100 weight part of pigments. The amount of latex used is preferably 2.5 parts by weight or less. By not using or reducing the amount of latex used, there are advantages such as prevention of dirt on the backing roll, improvement in blister resistance, and cost reduction by reducing the use of expensive latex.

  In the present invention, the total amount of the adhesive in the coating liquid is not particularly limited, but is preferably 5 to 50 parts by weight, more preferably about 5 to 30 parts by weight, and further 5 to 12 parts by weight per 100 parts by weight of the pigment. Is preferred. When the starch-derived polymer compound and other adhesives are used in combination as the adhesive, the total amount is preferably within the above range.

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. When using a blade type coater, the solid content concentration of the coating solution is 40 to 70% by weight.
Is more preferable, and 60 to 70% by weight is more preferable. The viscosity of the coating liquid is preferably 500 to 3500 mPa · s, more preferably 1000 to 3000 mPa · s, according to JIS K7117-1 B-type viscometer.

In the present invention, various auxiliary agents blended in ordinary pigments for coated paper, such as dispersants, thickeners, water retention agents, antifoaming agents, water resistance agents, and colorants, can be used as necessary. .
Coating pigment 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. , Delaminated 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 solid pigments, solid type, hollow type Or, an organic pigment such as a core-shell type can be used alone or in admixture of two or more. In addition, as a kind of pigment, heavy calcium carbonate and light calcium carbonate are preferable from the viewpoint of a low binder requirement and improving surface strength with a small amount of adhesive, and high whiteness, and also improve opacity. From the viewpoint, 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 blending calcium carbonate in the coating liquid, the light calcium carbonate or heavy calcium carbonate, or the combined content thereof is preferably 50 parts by weight or more per 100 parts by weight of pigment, more preferably 70 parts by weight or more, 80 weight or more is more preferable. Further, from the viewpoint of forming a uniform coating layer on the base paper, the average particle size is preferably 0.2 to 5 μm as measured by a laser diffraction type particle size distribution analyzer such as Mastersizer S manufactured by Malvern. 2 to 3 μm is more preferable.

In the present invention, any coater that is usually used 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 with the current technology, a blade coater is preferably 500 to 1800 m / min, and a size press coater is preferably 500 to 2000 m / min.
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.

Although the coating amount of the coating liquid in this invention can be suitably selected according to a use, generally it is 2-13 g / m < ² > in solid content per single side | surface.
Although the density | concentration of the coating liquid of this invention is not specifically limited, When printing quality is considered, about 55 weight% or more and about 75 weight% or less are preferable. In this invention, since the high molecular compound derived from a specific starch is used as an adhesive agent, a coating liquid can be highly concentrated. However, if the concentration of the coating liquid is too high, the coating liquid thickens and the operability deteriorates. In the present invention, it is possible to keep good operability by setting the weight to 65% by weight or less. The Brookfield viscosity (B type viscosity, 60 rpm) of the coating liquid of the present invention is preferably about 100 mPa · s or more and 3000 mPa · s or less from the viewpoint of operability. More preferably, it is 500 mPa · s or less.

Base Paper The coated paper of the present invention has at least 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, except for commonly used high-quality paper, medium-quality paper, renewal paper, machine-coated paper, art paper, cast-coated paper, synthetic paper, resin-coated paper, plastic film, etc. It can be used without.
Although the basic weight of the base paper of this invention is not specifically limited, Although it can select suitably according to a use, it can be set as 35-150 g / m < ² >, for example, and it is good also as 40-100 g / m < ² >.

Raw material pulp Chemical pulp can be used as a pulp raw material used for the base paper of the present invention. 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.

Filler In the present invention, a known filler can be arbitrarily used as a base paper filler, such as heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, deramikaolin, Amorphous produced by neutralization of white 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 porous silica and organic fillers such as urea-formalin resin, melamine resin, polystyrene resin and 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% by weight, and more preferably 10 to 35% by weight.

  In the present invention, known papermaking additives 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. 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. It can be performed using a paperboard machine, a Yankee dryer machine or the like. The pH during papermaking may be acidic, neutral or alkaline, but neutral or alkaline is preferred. The paper making speed is not particularly limited.
Clear coating The coated paper of the present invention may have a clear (transparent) coating layer on one side or both sides of the base paper described above. 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 this invention, you may contain the high molecular compound derived from the starch of this invention as a binder in a clear coating layer. The amount of clear coating is preferably 0.1 to 4.0 g / m ² , more preferably 0.5 to 2.5 g / m ² in terms of solid content on one side.

  In the present invention, the 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.

Pre-calendar treatment In the present invention, pre-calendar processing is performed on the base paper before coating by an online soft calendar, online chilled calendar, etc., and smoothing the base paper in advance makes the coating layer after coating uniform. Preferred above. In this case, the treatment linear pressure is preferably 30 to 100 kN / m, more preferably 50 to 100 kN / m. Moreover, the moisture content of the base paper at the time of pre-calendering is also important, and the moisture content is preferably 3 to 5%.

Surface Treatment In the present invention, the paper produced as described above is subjected to a surface treatment as necessary. For smoothing processing, a smoothing processing device 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 device, the number of pressure nips, heating, and the like are also adjusted as appropriate. In a preferred embodiment, the coated paper of the present invention can be surface-treated with a calendar such as a super calender or a high temperature soft nip calender. By the surface treatment, the smoothness and glossiness of the coated paper can be improved. In the present invention, soft nip calendering is preferred. Both softness and opacity are improved by soft nip calendering. In the soft nip calendering process, the linear pressure at the surface temperature of the metal roll of 20 ° C. to 60 ° C. is 30 to 60 kN / m, more preferably 40 to 60 kN / m. Further, if the surface temperature of the metal roll is a high temperature soft nip calendering treatment at 40 ° C. to 250 ° C., the linear pressure is 60 to 400 kN / m, preferably 150 to 300 kN / m, more preferably 100 to 350 kN / m. is there. Increasing the temperature improves the gloss and smoothness of the coated paper surface.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. In the present specification, “%”, “part”, and the like are based on weight, and the numerical range is described as including the end points.

Evaluation method (1) Basis weight: Measured according to JIS P 8124.
(2) Paper thickness: Measured according to JIS P 8118.
(3) Density: Determined from basis weight and paper thickness according to JIS P 8118.
(4) Glossiness of white paper Measured at an angle of 75 degrees according to JIS P-8142.
(5) Oken type smoothness JAPAN TAPPI paper pulp test method no. It was measured according to 5-2: 2000 (paper and paperboard—smoothness and air permeability test method—part 2: Oken method).
(6) Surface strength After printing four colors (black, indigo, red, yellow) using an offset rotary press (Toshiba Offset BT600) and offset printing ink (Toyo Ink Mfg. Co., Ltd .: Leo X M), printed matter The vessel picks in the indigo solid portion and the two-color (red, yellow) solid portion were visually judged (evaluation criteria: ＝= not generated at all, ○ = not generated at most, Δ = generated, × = remarkably generated).
(7) Blister resistance After printing four colors (black, indigo, red, yellow) using an offset rotary press (Toshiba Offset BT600) and offset printing ink (Toyo Ink Manufacturing Co., Ltd .: Leo X M), It was dried with a drier, and the occurrence of blisters in the printed matter was visually judged (evaluation criteria: ◎ = not generated at all, ○ = not generated at most, Δ = generated, × = remarkably generated).
(8) Blanket piling After printing four colors (black, indigo, red, yellow) using an offset rotary press (Toshiba Offset BT600) and offset printing ink (Toyo Ink Manufacturing Co., Ltd .: Leo X M), 2 The degree of deposition on the blanket after printing all parts was visually judged (evaluation criteria: ＝= not generated at all, ○ = not generated at all, Δ = generated, × = remarkably generated).
(9) Backing roll soiling After 72 hours of continuous operation, the soiling state of the roll was visually evaluated (Evaluation criteria: ◎ = No backing roll soiling occurred, ○ = Backing roll soiling occurred slightly, △ = Backing roll soiling occurred. Considerably occurs, x = backing roll dirt is significantly generated).
(10) Blade load Evaluated from the amount of blade pushing during blade coating (evaluation criteria: ◎ = blade pushing amount reduced, ○ = blade pushing amount at the same level, △ = blade pushing amount increased, × = High load and cannot be applied)
Example 1
Add light calcium carbonate as a filler to a pulp slurry consisting of 60 parts of waste paper pulp, 30 parts of NBKP, and 10 parts of LBKP so that the ash content in the paper is 16%, and add 3 parts of cationized starch as an internal paper strength agent. The paper stock was adjusted.
Using this stock, paper was made on a gap-former type paper machine of roll and blade former type at a paper making speed of 1500 m / min, and two tandem shoe presses (press linear pressure 1000 kN / m, second one) The wet paper was squeezed using a transfer belt in contact with the wire surface side of the paper and dried to obtain a 35.7 g / m ² medium-coated base paper.
Next, 100 parts of heavy calcium carbonate as a pigment, 1.8 parts of carboxy-modified styrene / butadiene copolymer latex and white dextrin (Stabilys A025, Roquette, Inc .: after cooking, that is, after 16 minutes of cooking, as an adhesive The RVA viscosity at 160 rpm is 780
(mPa · s, weight average molecular weight 270,000) 6.0 parts is blended to prepare a coating liquid having a B-type viscosity of 130 mPa · s, a dehydration amount of 59.5 g / m ² , and a solid content concentration of 60.6% by weight. did.
Using this coating solution, the coating solution was continuously applied on both sides with a jet fountain blade coater so that the coating amount was 7.0 g / m ² per side of the base paper, and dried.
Subsequently, a 2-roll / 6-stack soft calender having an elastic roll with a shore hardness of D94 ° was used in the finishing process, each metal roll surface temperature was 130 ° C., and each nip line pressure was 250 kN / m. Processed.
Since papermaking, coating, and calendaring were performed continuously, the coating speed and calendar speed were also 1500 m / min.

Examples 2-4
As the starch polymer, white dextrin (Stabilys A023, Roquette, Inc .: RVA viscosity at 160 rpm after steaming, that is, 16 minutes after steaming, 828 mPa · s, weight average molecular weight 300,000) is used. A coated paper for printing was produced in the same manner as in Example 1 except that a coating liquid having physical properties was prepared.
Example 5
As a starch polymer, white dextrin (after steaming, that is, RVA viscosity at 160 rpm after 16 minutes of steam, 789 mPa · s, weight average molecular weight 380,000) is used. A coated paper for printing was produced in the same manner as in Example 1 except that it was prepared.
Comparative Example 1
As a starch polymer, white dextrin (Stabilys A040, Roquette, Inc .: after steaming, that is, RVA viscosity at 160 rpm after steaming for 16 minutes, 97 mPa · s, weight average molecular weight 90,000), A coated paper for printing was produced in the same manner as in Example 1 except that a coating liquid having physical properties was prepared.
Comparative Example 2
As the starch polymer, white dextrin (Stabilys A030, Roquette, Inc .: RVA viscosity at 160 rpm after cooking, that is, 16 minutes after cooking, 374 mPa · s, weight average molecular weight 180,000), A coated paper for printing was produced in the same manner as in Example 1 except that a coating liquid having physical properties was prepared.
Comparative Example 3
As a starch polymer, an oxidation-modified starch (M210, Shikishima Starch Co., Ltd .: after steaming, that is, RVA viscosity at 160 rpm after 16 minutes of steaming of 1592 mPa · s, weight average molecular weight of 800,000) is shown in Table 1. A coated paper for printing was produced in the same manner as in Example 1 except that a coating liquid having the above properties was prepared.

Table 1 shows the results. As is clear from Table 1, in Examples 1 to 5 where a starch polymer having a viscosity after cooking for 16 minutes of 1000 mPa · s or less and a weight average molecular weight of 200,000 or more was used as an adhesive, A coated paper having good gloss, smoothness and surface strength could be produced with high operational efficiency. In addition, the coated paper obtained in Examples 1 to 5 also suppressed the occurrence of blanket piling during offset printing.
The above examples and comparative examples are examples in which the solid content concentration of the coating liquid was adjusted to about 60% by weight, and the drying load was reduced, but the examples and the weight average molecular weight were 200,000 or less. When compared with Comparative Examples 1 and 2 using a certain starch polymer, in Comparative Examples 1 and 2, blanket piling occurred and the backing roll was poorly soiled. In addition, when comparing the example and Comparative Example 3 using a starch polymer having a viscosity after 16 minutes of cooking exceeding 1000 mPa · s, the blade load is increased and the operability is deteriorated. Resistance increased and blister resistance slightly deteriorated.

Claims (7)

A coated paper having a pigment coating layer containing a pigment and an adhesive on a base paper,
The adhesive contains a starch polymer having a weight average molecular weight of 200,000 or more, and a slurry having a solid content concentration of 35% by weight of the starch polymer is obtained using a Rapid Visco Analyzer (RVA). , Raised to 98 ° C in 5 to 5 minutes, held at 98 ° C for 4 to 5 minutes, lowered to 50 ° C in 3 minutes to 9 to 12 minutes, 50 for 4 to 12 to 16 minutes The above coated paper, which has a viscosity of 1000 mPa · s or less after 16 minutes of steaming when steamed under the steaming condition of maintaining at ° C.   The coated paper according to claim 1, wherein the starch polymer has a weight average molecular weight of 25 to 400,000.   The coated paper according to claim 1 or 2, wherein no copolymer latex is used as the adhesive, or 4 parts by weight or less of the copolymer latex is used with respect to 100 parts by weight of the pigment.   The coated paper according to any one of claims 1 to 3, comprising 50 parts by weight or more of calcium carbonate per 100 parts by weight of the pigment.   The coated paper according to any one of claims 1 to 4, wherein the pigment coating layer contains 5 to 50 parts by weight of a starch polymer per 100 parts by weight of the pigment.   The coated paper according to any one of claims 1 to 5, wherein the starch polymer compound is white dextrin. A method for producing a coated paper comprising a step of coating a pigment coating layer containing a pigment and an adhesive on a base paper,
The adhesive contains a starch polymer having a weight average molecular weight of 200,000 or more, and a slurry having a solid content concentration of 35% by weight of the starch polymer is obtained using a Rapid Visco Analyzer (RVA). , Raised to 98 ° C in 5 to 5 minutes, held at 98 ° C for 4 to 5 minutes, lowered to 50 ° C in 3 minutes to 9 to 12 minutes, 50 for 4 to 12 to 16 minutes The above method, wherein the viscosity after 16 minutes of cooking is 1000 mPa · s or less when steamed under the steaming condition of maintaining at ° C.