JP7000632B2 - Coated paper and its manufacturing method - Google Patents

Description

The present invention relates to coated paper and a method for producing coated paper. In particular, the present invention relates to coated paper containing dextrin as an adhesive (binder) for a pigment coating layer.

Generally, in the case of producing coated paper, a coating layer mainly composed of a pigment and an adhesive for binding the pigment is formed in order to improve printability. As an adhesive, it is mainly petroleum-based from the viewpoints of good paint fluidity, good coating suitability in coating equipment, and easy to impart print surface strength as coated paper quality. Adhesives derived from synthetic materials are used.

However, in recent years, due to cost reductions and heightened environmental awareness, inexpensive and highly biodegradable materials have been attracting attention instead of petroleum-based synthetic materials. Among them, adhesives made from starch-based materials are attracting attention (Patent Document 1). However, when a high amount of starch-based material is added to the paint (pigment coating liquid), the viscosity of the paint increases remarkably, and the operability and the aptitude for coating deteriorate. Even if the viscosity is adjusted by diluting the paint, the amount of water increases, which increases the load on the drying process after coating, which has an adverse effect on productivity such as a decrease in coating speed. Even if the product is manufactured at a reduced coating speed, the paint concentration is low and the water retention of the paint is low, so that the paint penetrates into the base paper significantly, resulting in a decrease in the glossiness of the blank paper and a decrease in the surface strength. Quality deterioration is inevitable.

Therefore, Patent Document 2 proposes a technique of using a starch-based polymer having a low viscosity after a lapse of a certain period of time from the start of steaming as an adhesive when an aqueous slurry containing a starch-based polymer is steamed. Further, Patent Document 3 proposes to improve the water retention property of the coating liquid by using a plurality of dextrins having different average molecular weights of 50 kDa or more in combination.

Japanese Unexamined Patent Publication No. 2010-84311 International release WO2012 / 133487 Special Table 2016-526111 Gazette

However, in the technique described in Patent Document 2, blanket pyring tends to occur at the time of offset printing, and especially when the coating liquid concentration is low, the blanket piring is remarkably deteriorated. Blanket piring is the accumulation of paper dust and ink on the periphery of the image area on the blanket and raising it. Further, in the technique described in Patent Document 3, the glossiness of the coated paper tends to be lowered.

Increasing the concentration of the coating liquid contributes to the improvement of productivity by reducing the drying load because the water content is reduced, and the reduction of the penetration of the coating liquid into the base paper to improve the surface strength. However, if the concentration of the coating liquid is high, the viscosity increases and the operability and coating suitability deteriorate. Therefore, it is recommended to dilute the coating liquid to the extent that it does not adversely affect the drying load and surface strength. It is the actual situation.

In view of such a situation, the subject of the present invention is to improve the blank sheet glossiness and print glossiness of the coated paper without increasing the paint viscosity so much even if it is highly blended in the paint, and to make a blanket at the time of offset printing. The purpose is to search for a starch-based adhesive that can suppress the piring of the paper, and to develop a technology for producing high-quality coated paper with high operability.

As a result of diligent studies to solve the above problems, it was found that a coated paper having excellent surface gloss can be produced by using specific dextrins having different molecular weights in combination, and the present invention has been completed.

The present invention includes, but is not limited to, the following inventions.
(1) A coated paper having a pigment coating layer containing a pigment and an adhesive on a base paper, wherein the adhesive comprises a first dextrin and a second dextrin, and the first dextrin. The coated paper having a weight average molecular weight (M1) and a weight average molecular weight (M2) of the second dextrin of less than 500 kDa and M1-M2 of 60 kDa or less.
(2) The coated paper according to (1), wherein the combined use ratio (weight ratio) of the first dextrin and the second dextrin is 2: 8 to 8: 2.
(3) The coated paper according to (1) or (2), wherein the first dextrin and the second dextrin are both white dextrins.
(4) The coated paper according to any one of (1) to (3), wherein both M1 and M2 are 150 to 400 kDa.
(5) A method for producing coated paper, which comprises a step of adjusting a coating liquid containing a pigment and an adhesive and a step of applying the coating liquid to a base paper, wherein the adhesive is the first. It contains 1 dextrin and 2nd dextrin, and the weight average molecular weight (M1) of the 1st dextrin and the weight average molecular weight (M2) of the 2nd dextrin are both less than 500 kDa, and M1-M2 is 60 kDa or less. The above method.

According to the present invention, the fluidity of the coating liquid is good, and the coating liquid is easy to handle, so that the coating suitability is excellent, and the operation efficiency in the production of the coated paper is improved. In addition, since the water retention of the coating liquid is improved, the penetration of the coating liquid into the base paper is suppressed, so that the glossiness of the obtained coated paper is improved and various coatings such as suppression of piring are performed. Paper quality is improved.

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 is used for offset printing, gravure printing, letterpress printing and the like. Of course, the coated paper may be a white paperboard having a pigment coating layer on the base paper.

In the coated paper of the present invention, one or more pigment coating layers containing pigments are provided on the base paper. The base paper may or may not be coated with a coating liquid (size press liquid) containing no pigment.

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 ash content to increase the opacity.

Dextrin In the present invention, a pigment coating liquid containing mainly a pigment, an adhesive (binder), and water is used to provide a pigment coating layer, but a specific molecular weight (weight average molecular weight) is used as the adhesive (binder). Add the starch-based polymer to have. In the present invention, dextrin is used as a starch-based polymer, but since the viscosity after a certain period of time after steaming is particularly low, the viscosity does not increase significantly even when blended in a pigment coating solution, and the pigment is used. The concentration of the coating liquid can be increased, thereby improving the print quality of the coated paper. That is, since the penetration of the paint into the base paper is suppressed and the effective coating layer is increased, the quality of various coated papers such as the improvement of glossiness and the improvement of surface strength are improved.

In the present invention, a plurality of dextrins having different molecular weights are used as the adhesive. Dextrin can be obtained by hydrolyzing starch, and dextrins having different molecular weights can be produced by adjusting the degree of hydrolysis. As described above, in the present invention, the adhesive used for the pigment coating layer comprises the first dextrin and the second dextrin, and the weight average molecular weight (M1) of the first dextrin and the second dextrin. The weight average molecular weight (M2) of each is less than 500 kDa, and M1-M2 is 60 kDa or less.

The molecular weight of the two dextrin mixtures used in the present invention is less than 500 kDa by weight average. It is preferably 450 kDa or less, more preferably 400 kDa or less, still more preferably 350 kDa or less, and may be 300 kDa or less. If the molecular weight is too large, the viscosity of the paste liquid becomes high, the viscosity at the time of blending the paint increases, and the workability may be inferior. The molecular weight of the mixture of the two dextrins used in the present invention is preferably 100 kDa or more, more preferably 150 kDa or more, and even more preferably 200 kDa or more.

The weight average molecular weight of the dextrin used in the present invention is preferably 100 kDa or more, more preferably 150 kDa or more, and even more preferably 200 kDa or more. If the molecular weight is too small, blanket pyring is likely to occur when printing on an offset rotary press. The reason for this is that the water retention of the coating liquid decreases and the binder sinks, and the binder does not stay on the surface of the coating layer, so the strength of the coating layer is insufficient, and the coating layer peels off during printing and is on the blanket. It is thought to be deposited in. To prevent this, the coating liquid concentration may be increased, but if the coating liquid concentration is increased, there is a problem that the operability is deteriorated.

Further, in the present invention, it is preferable that the weight average molecular weight of each of the two types of dextrins used in combination is 100 kDa or more and less than 500 kDa. When the low molecular weight dextrin is less than 100 kDa, the viscosity of the coating liquid is low, so that the surface strength may be low. Further, when the molecular weight of the high molecular weight dextrin is 500 kDa or more, the viscosity of the paste solution of the dextrin may increase too much and the workability may be inferior, and the viscosity at the time of blending the paint may become too high. In the present invention, since two kinds of dextrins within the above-mentioned molecular weight range are used, the advantages of using a dextrin having a high molecular weight and a dextrin having a low molecular weight can be enjoyed. That is, the surface strength of the paper can be improved without impairing workability.

Further, the difference in molecular weight between the two types of dextrin is preferably less than 60 kDa. When the difference in molecular weight between the two types of dextrin exceeds 60 kDa, the high molecular weight dextrin causes shrinkage of the paper surface, which may reduce the glossiness. The difference in molecular weight between the two dextrins may be small, but may be, for example, 10 kDa or more.

In the present invention, the weight average molecular weight can be measured by, for example, size exclusion chromatography multi-angle light scattering method (SEC-MALS method).

In a preferred embodiment, the dextrin of the present invention has a slurry viscosity of 1000 mPa · s or less after being steamed under certain conditions. When dextrin is contained in the coating liquid, heating is required to dissolve the dextrin. Therefore, where the viscosity of the slurry after steaming under certain conditions is important, the dextrin of the present invention has a low viscosity of the slurry after steaming, so that the concentration of the slurry can be increased. When a starch compound is usually suspended in water and heated, the starch granules absorb water and gradually expand. When heating is continued, the starch granules eventually disintegrate and change into a gel. This phenomenon is called gelatinization. At this time, the starch suspension gradually becomes transparent from a cloudy state and rapidly increases in viscosity. The viscosity becomes maximum when the particles absorb the maximum amount of water, and the viscosity decreases due to the decay of the particles. In the present invention, after the viscosity is maximized by steaming, the viscosity when the temperature is lowered and the mixture is allowed to stand is used in a certain range.

For example, cold water-soluble starch represented by pregelatinized starch also has a low slurry viscosity, but these cold water-soluble starches are treated so as to be soluble in cold water, and dextrin and the like have higher surface strength. Is high and 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-based polymer can be measured using a measuring device called a Rapid Visco Analyzer (RVA, model RVA-4, manufactured by New Port Scientific). In a preferred embodiment of the present invention, when a starch-based polymer slurry having a concentration of 35% by weight is steamed under the following steaming conditions, dextrin having a viscosity of 1000 mPa · s or less at 50 ° C. 16 minutes after the start of steaming is used. .. In one aspect of the present invention, dextrin is used as an adhesive for the pigment coating layer, and the adhesive strength as a binder is developed by steaming (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
・ After that: 160 rpm
(Steaming conditions)
・ 0 to 5 minutes: temperature rise to 98 ° C in 5 minutes ・ 5 to 9 minutes: hold at 98 ° C ・ 9 to 12 minutes: temperature down to 50 ° C in 3 minutes ・ 12 to 16 minutes: hold at 50 ° C The viscosity of the dextrin measured as described above at the stage of holding at 50 ° C. 16 minutes after steaming is preferably 1000 mPa · s or less, and more preferably 850 mPa · s or less.

Further, the maximum viscosity of the dextrin of the present invention due to gelatinization of starch is preferably 2000 mPa · s or less, and more preferably 1600 mPa · s or less when the viscosity is measured using RVA under the above conditions. 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 the coating liquid.

The dextrin of the present invention preferably has the above-mentioned viscosity, but the modification method and the like are not particularly limited, and the varieties of raw materials are also free. In addition, preferred raw materials for dextrin used in the present invention include corn, potato, tapioca and the like, and waxy corn (waxy corn) and tapioca are particularly preferable.

In the present invention, roasted dextrin such as white dextrin is preferable as the adhesive because the viscosity is low and the viscosity is high. 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. Normal starch has a large molecular weight, but dextrin is an intermediate product produced in the process of hydrolyzing starch, and conventionally, the molecular weight is generally about an oligomer (a combination of several to several tens of glucose). there were. Roasted dextrin is a dextrin produced by adding an acid and baking it 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. Further hydrolysis of white dextrin results in so-called yellow dextrin, but yellow dextrin has low stability and may color the pigment coating layer. Therefore, the use of white dextrin is preferable in the present invention.

The white dextrin of the present invention preferably has many branches in the dextrin. When there are many branches, the strength is likely to be developed. The degree of branching is related to the radius of inertia, and if the molecular weight is the same, it is considered to be linear with many branches when the radius of inertia is small and few branches when the radius of inertia is large. Therefore, the white dextrin of the present invention preferably has a small inertial radius.

The dextrin of the present invention has good fluidity when blended in a coating liquid. When the 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. The quality of coated paper is improved.

In a preferred embodiment, the blending amount of the dextrin of the present invention is used in the range of 0.1 to 30 parts by weight, more preferably 0.5 to 15 parts by weight per 100 parts by weight of the pigment.

In the present invention, only the above-mentioned dextrin can be used as the adhesive, but in addition to the above-mentioned dextrin, an adhesive conventionally used for coated paper can also be used in combination. Examples of the above-mentioned adhesives other than starch include various copolymers (latex) such as styrene / butadiene type, styrene / acrylic type, ethylene / vinyl acetate type, butadiene / methyl methacrylate type, vinyl acetate / butyl acrylate type, etc. Synthetic adhesives such as polyvinyl alcohol, maleic anhydride copolymers, and acrylic acid / methylmethacrylate copolymers; proteins such as casein, soybean protein, and synthetic proteins; oxidation other than the above starch-derived polymer compounds. Starches such as starch, positive starch, urea phosphate esterified starch, etherified starch such as hydroxyethyl etherified starch; and ordinary coating paper adhesives such as cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose and hydroxymethyl cellulose are included. Is done. One or more kinds of adhesives can be appropriately selected and used. In the present invention, it is preferable to use a latex having different characteristics from the starch-based polymer compound as an adhesive, and in that case, it is preferable to use more dextrin than the amount of latex used. Although both the advantages of dextrin and latex can be obtained by the combined use, it is preferable to use a large amount of dextrin in order to exert the effect of the present invention to a large extent.

Further, in a preferred embodiment of the present invention, latex is not used as an adhesive, or the amount of latex used is 4 parts by weight or less with respect to 100 parts by weight of the pigment. Further, it is preferable that the amount of latex used is 2.5 parts by weight or less. By not using or reducing the amount of latex used, there are advantages such as prevention of backing roll stains, improvement of blister resistance, and cost reduction by reducing the use of expensive latex.

In the present invention, the total amount of the adhesive to be blended 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 preferably 5 to 12 parts by weight per 100 parts by weight of the pigment. Is preferable. When dextrin and other adhesives are used in combination as the adhesive, the total amount thereof is preferably in 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 a blade type coater is used, the solid content concentration of the coating liquid is preferably 40 to 70% by weight, more preferably 50 to 65% by weight. The viscosity of the coating liquid is preferably 50 to 3500 mPa · s, more preferably 100 to 2500 mPa · s, and may be 150 to 1500 mPa · s or 200 to 500 mPa · s with a JIS K 7117-1 B-type viscometer. ..

In the present invention, various auxiliary agents blended in ordinary coated paper pigments such as dispersants, thickeners, water retention agents, defoamers, water resistant agents, and colorants can be appropriately used, if necessary. ..

Coating Pigment The pigment (white pigment) used for 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 inorganic pigments and solid, hollow type , Or organic pigments such as core-shell type can be used alone or in combination of two or more, if necessary. As the type of pigment, heavy calcium carbonate and light calcium carbonate are preferable from the viewpoint of low binder requirement and a small amount of adhesive can improve surface strength and high whiteness, and also improve opacity. From the viewpoint, light calcium carbonate having a uniform particle size and shape is particularly preferable. This is because the bulky coating layer structure scatters light efficiently.

When calcium carbonate is added to the coating liquid, the total content of light calcium carbonate, heavy calcium carbonate, or both is preferably 50 parts by weight or more, more preferably 70 parts by weight or more per 100 parts by weight of the pigment. 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, which is a value measured by a laser diffraction type particle size distribution measuring machine such as Mastersizer S manufactured by Malvern. .3 to 3 μm is more preferable.

Coating In the present invention, any commonly used coater may be used. It can be an on-machine coater or an off-machine coater, and if it is an on-machine coater, it can be 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, or a short duel blade. Coaters such as coaters and jet fountain blade coaters can be used. The coating speed is not particularly limited, but in the current technology, it is preferably 500 to 1800 m / min for a blade coater and 500 to 2000 m / min for a size press coater.

In the present invention, there is no limitation on the method of drying the wet coating layer, and various methods such as a steam superheat cylinder, a heated hot air air dryer, a gas heater dryer, an electric heater dryer, and an infrared heater dryer can be used alone or in combination. can.

The amount of the coating liquid to be applied in the present invention can be appropriately selected depending on the intended use, but generally, the solid content per side is 2 to 13 g / m ² , and 4 to 11 g / m ² or 6 to 9 g. It may be / m ² .

The concentration of the coating liquid of the present invention is not particularly limited, but in consideration of print quality, it is preferably 40% by weight or more, preferably 55% by weight or more and 75% by weight or less. Since a specific dextrin is used as an adhesive in the present invention, the concentration of the coating liquid can be increased. However, if the concentration of the coating liquid is too high, the coating liquid becomes thick and the operability deteriorates. In the present invention, it is possible to maintain good operability by more preferably 65% by weight or less. The Brookfield viscosity (B-type viscosity, 60 rpm) of the coating liquid of the present invention is preferably 50 mPa · s or more and 3500 mPa · s or less, and 100 mPa · s or more and 3000 mPa · s or less from the viewpoint of operability and the like. Is preferable, 150 mPa · s or more and 2000 mPa · s or less is more preferable, and 200 mPa · s or more and 1000 mPa · s or less may be used.

Base Paper The coated paper of the present invention has at least a base paper layer. The base paper can be produced by a known method. For example, a papermaking material (paper material) can be made in a wire part and then used in a press part and a pre-dryer part to produce the base paper. The base paper used in the present invention may be single-layer paperboard or multi-layer paperboard, but when producing white paperboard, it is preferable to use multi-layer paperboard. The method for producing the base paper of the present invention is not particularly limited, and a known method can be used using a known raw material. The base paper used in the present invention is not particularly limited, with the exception of commonly used high-quality paper, medium-quality paper, stencil paper, machine-coated paper, art paper, cast-coated paper, synthetic paper, resin-coated paper, plastic film, and the like. Can be used without.

The basis weight of the base paper of the present invention is not particularly limited and can be appropriately selected depending on the intended use. For example, it can be 30 to 150 g / m ² , 33 to 100 g / m ² or 35 to 75 g / m ² . May be good.

Chemical pulp can be used as the pulp raw material used for the base paper of the present invention. In addition to chemical pulp, various types of pulp can be used depending on the application, such as deinked pulp (DIP), crushed wood pulp (GP), refiner crushed wood pulp (RGP), thermomechanical pulp (TMP), and chemi-thermo. Examples thereof include mechanical pulp (CTMP), chemigrand pulp (CGP), and semi-chemical pulp (SCP). As the deinking pulp, it is possible to use sorted waste paper such as high-quality paper, medium-quality paper, low-grade paper, newspaper, leaflets, magazines, and deinked pulp made from unsorted used paper in which these are mixed.

In the present invention, a known filler can be arbitrarily used as a filler for the base paper, and for example, heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica complex, kaolin, calcined kaolin, deramikaolin, white. Amorphous produced by mineralization 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, and phenol resin can be used alone or in combination. Among these, heavy calcium carbonate and light calcium carbonate, which are typical fillers in neutral paper and alkaline paper, are preferably used for improving opacity. The filling ratio in the paper is not particularly limited, but 1 to 40% by weight of solid content is preferable, and 10 to 35% by weight of solid content is more preferable.

In the present invention, known papermaking additives can be used. For example, aluminum sulfate band, various anionic, cationic, nonionic or amphoteric yield improvers, drainage improvers, various paper strength enhancers, internal sizing agents and other papermaking aids as needed. Can be used. Examples of the dry paper strength improving agent include polyacrylamide and cationized starch, and examples of the wet paper strength improving agent include polyamide amine epichlorohydrin. These chemicals are added within a range that does not affect the formation or operability. Examples of the neutral sizing agent include alkyl ketene dimer, alkenyl succinic anhydride, and a neutral rosin sizing agent. Further, a dye, a fluorescent whitening agent, a pH adjusting agent, a defoaming agent, a pitch control agent, a slime control agent and the like can be added as needed.

The method of making the base paper in the present invention is not particularly limited, and a long net paper machine including a top wire, an on-top former, a gap former, a round net paper machine, a long net paper machine and a round net paper machine are used in combination. This can be done using a paperboard machine, a yankee dryer machine, or the like. The pH at the time of papermaking may be acidic, neutral or alkaline, but neutral or alkaline is preferable. The papermaking speed is not particularly limited.

The coated paper of the present invention may have a clear (transparent) coated layer on one side or both sides of the above-mentioned base paper. By applying a clear coating on the base paper, the surface strength and smoothness of the base paper can be improved, and the coatability at the time of pigment coating can be improved. In the present invention, the clear coating layer may contain the starch-derived polymer compound of the present invention as a binder. The amount of clear coating is preferably 0.1 to 4.0 g / m ² and more preferably 0.5 to 2.5 g / m ² in terms of solid content per surface.

In the present invention, clear coating refers to various starches such as starch and oxidized starch by using a coater (coating machine) such as a size press, a gate roll coater, a premetering size press, a curtain coater, and a spray coater. , Polyacrylamide, polyvinyl alcohol, etc., which is a coating liquid (surface treatment liquid) containing a water-soluble polymer as a main component, is applied (size pressed) on the 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, an online chilled calendar, etc. to smooth the base paper in advance in order to make the coating layer after coating uniform. .. In this case, the processing linear pressure is preferably 30 to 100 kN / m, more preferably 50 to 100 kN / m. In addition, the moisture content of the base paper during the pre-calendar treatment 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 surface-treated as necessary. For the smoothing process, a smoothing processing device such as a normal super calendar, a gloss calendar, a soft calendar, a thermal calendar, or a shoe calendar can be used. The smoothing processing device is appropriately used on-machine or off-machine, and the form of the pressurizing device, the number of pressurizing nips, heating, and the like are appropriately adjusted. In a preferred embodiment, the coated paper of the present invention can be surface-treated with a calendar such as a super calendar or a high-temperature soft nip calendar. The surface treatment can improve the smoothness and glossiness of the coated paper. In the present invention, soft nip calendar processing is preferable. By performing soft nip calendar processing, both whiteness and opacity are improved. In the soft nip calender processing, the linear pressure at which the surface temperature of the metal roll is 20 ° C. to 60 ° C. is 30 to 60 kN / m, more preferably 40 to 60 kN / m. Further, in the case of high temperature soft nip calendar processing in which the surface temperature of the metal roll is 40 ° C. to 250 ° C., the linear pressure is 60 to 400 kN / m, preferably 150 to 300 kN / m, and more preferably 100 to 350 kN / m. be. Increasing the temperature improves the gloss and smoothness of the surface of the coated paper.

The present invention will be described in detail with reference to specific examples below, but the present invention is not limited to the following examples. In the present specification,%, parts, etc. are based on weight, and the numerical range is described as including the end points thereof.

Method for Producing Roasted Dextrin Hydrochloric acid was added to raw corn starch and heated at 130 ° C. for 90 minutes using a Proshear Mixer (Pacific Machinery & Engineering Co., Ltd.) to produce roasted dextrin. Specifically, white roasted dextrins having different molecular weights were obtained by changing the amount of hydrochloric acid added as follows.

The weight average molecular weight of roasted dextrin can be measured using GPC under the following measurement conditions.
-Separation column: 2 Shodex GPC KB-806M, 1 Shodex GPC KB-802-Column temperature: 40 ° C.
-Mobile phase solvent: Sodium nitrate aqueous solution (0.1 mol / L)
-Mobile phase flow rate: 0.5 mL / min
・ Injection amount: 300 μL
-Detector 1: Multi-angle light scattering detector (Wyatt, "DAWN HELEOS II")
-Detector 2: Refractive index (RI) detector (Waters, "2414 type")
-Sample: [Steamed] Stir at 100 ° C. for 20 minutes, [Concentration] 0.4 w / v%, [Filtration] Chromatographic disk Pore diameter 0.45 μm (manufactured by Kurabo Industries)
-Data processing: ASTRA (manufactured by Wyatt)

Evaluation method (1) Basis weight: Measured according to JIS P 8124.
(2) Paper thickness: Measured according to JIS P 8118.
(3) Density: Obtained from the basis weight and paper thickness according to JIS P 8118.
(4) Blank paper glossiness Measured at an angle of 75 degrees according to JIS P-8142.
(5) Printing gloss After printing in 4 colors (ink, indigo, red, yellow) using an offset rotary press (Toshiba offset BT600) and offset printing ink (manufactured by Toyo Ink Mfg. Co., Ltd .: Leox M), The surface of the solid indigo portion of the printed matter was measured based on JIS P 8142.
(6) Ash content: Measured according to JIS P8251.
(7) B-type viscosity of paint The prepared coating liquid was measured with a B-type viscometer (model: LVDV-I, manufactured by Eiko Seiki Co., Ltd.) at a liquid temperature of 30 ° C. and a rotation speed of 60 rpm.
(8) High Shear Viscosity of Paint The prepared coating liquid was measured with a Hercule High Shear Viscometer (model: DV-10, manufactured by Kaltec Scientific) at a liquid temperature of 30 ° C., a rotation speed of 8800 rpm, and a bob of F2.5.

Manufacture and evaluation of pigmented paper To a pulp slurry consisting of 65 parts of recycled paper pulp, 20 parts of NBKP, and 15 parts of LBKP, light calcium carbonate is added as a filler so that the ash content in the paper is 16%, and it is used as an internal paper force agent. 0.7 parts of cationized starch and 0.3 parts of polyacrylamide (PAM) were added to adjust the paper content.

Using this paper material, paper was made with a roll-and-blade former type gap former paper machine at a paper making speed of 1500 m / min, and two tandem shoe presses (press linear pressure 1000 kN / m) were used for the second press part. The wet paper was squeezed and dried using a transfer belt contacting the wire surface side of the paper) to obtain a medium-weight coated base paper of 35.7 g / m ² .

Next, for 100 parts of heavy calcium carbonate (FMT97: average particle size 0.90 μm) as a pigment, 1.5 parts of carboxy-modified styrene-butadiene copolymer latex (NP100C) and roasted dextrin 10 as an adhesive. A coating solution was prepared by blending 0.0 parts. In Production Example 1 (Comparative Example), dextrin having an average molecular weight separated by 300 kDa or more was used in combination, but in Production Example 2 (Example), dextrin having an average molecular weight difference of about 50 kDa was used in combination.

Using this coating liquid, the above coating liquid was continuously applied to both sides with a jet fountain type blade coater so that the coating amount was 7.0 g / m ² per one side of the base paper, and dried.

Subsequently, in the finishing process, a 2-roll / 6-stack soft calendar having an elastic roll with a shore hardness of D94 ° was used, the surface temperature of each metal roll was 130 ° C, and the line pressure of each nip was 250 kN / m. Processing was performed.

Since papermaking, coating, and calendar processing were performed continuously, the coating speed and calendar speed were also 1500 m / min.

As is clear from the table, when dextrins having different molecular weights are used in combination, coated paper having excellent blank paper glossiness and print glossiness was obtained in Production Example 2 in which the difference in weight average molecular weight of dextrins was 50 kDa.

Claims (5)

A coated paper having a pigment coating layer containing a pigment and an adhesive on a base paper.
The adhesive comprises a first dextrin and a second dextrin, and the weight average molecular weight (M1) of the first dextrin and the weight average molecular weight (M2) of the second dextrin are both less than 500 kDa. The coated paper having a weight average molecular weight of a mixture of the first dextrin and the second dextrin of 300 kDa or less and M1-M2 of 10 kDa or more and 60 kDa or less. The coated paper according to claim 1, wherein the combined ratio of the first dextrin and the second dextrin is 2: 8 to 8: 2. The coated paper according to claim 1 or 2, wherein the first dextrin and the second dextrin are both white dextrins. The coated paper according to any one of claims 1 to 3, wherein both M1 and M2 are 150 to 400 kDa. The process of adjusting the coating liquid containing the pigment and the adhesive,
The process of applying the coating liquid to the base paper and
A method of manufacturing coated paper, including
The adhesive comprises a first dextrin and a second dextrin, and the weight average molecular weight (M1) of the first dextrin and the weight average molecular weight (M2) of the second dextrin are both less than 500 kDa. The above method, wherein the weight average molecular weight of the mixture of the first dextrin and the second dextrin is 300 kDa or less, and M1-M2 is 10 kDa or more and 60 kDa or less.