JP2016065355A - Printing paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printing paper having high whiteness and high opacity.SOLUTION: There is provided a printing paper containing a violet pigment and/or a blue pigment and having opacity of 85% or more, basis weight of the printing paper of more than 70 g/mand aof 0 or more and less than 7 and bvalue of -15 or more and less than -3 in a measurement including ultraviolet of a color tone of the paper measured by a method of JIS P 8150.SELECTED DRAWING: None

Description

  The present invention relates to a printing paper having both high whiteness and high opacity.

  In recent years, printing paper, particularly coated paper for printing, is used for catalog printed matter for mail order sales and the like, and thus there is a significant tendency to demand white that gives a visually strong impression. There are various types of coated paper, such as high-quality coated paper (A1 coat, A2 coat, A3 coat, fine-coated paper), medium-sized coated paper, and ultra-light coated paper. Brands with different whiteness, gloss, smoothness, color tone, etc. have been commercialized by various companies.

  Printing paper using high-quality raw materials is mainly bleached and pulp made from kraft pulp is used. Therefore, although there is little colored foreign matter and whiteness is high, opacity is low. On the other hand, printing paper using medium-quality raw materials contains a lot of recycled pulp and mechanical pulp in addition to bleached kraft pulp. There is a problem that it is lower than high-quality printing paper.

  Thus, there is a demand for printing paper to increase both whiteness and opacity. In this regard, high basis weight printing paper may have both relatively high whiteness and opacity, but it is required to be white enough to give a stronger visual impression. There is a demand for higher opacity.

  When both whiteness and opacity are required, titanium oxide with a high refractive index is added internally or externally, hollow plastic pigment is added to the coating layer, etc. Methods such as combination are disclosed (Patent Document 1, Patent Document 2). However, both are expensive raw materials, and there is a problem that costs increase.

JP 2000-336593 A Japanese Patent Publication No. 52-118116

  As a result of considering the background as described above, an object of the present invention is to provide a printing paper having high whiteness and high opacity.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have high whiteness by including one or more pigments having purple and blue colors in the components constituting the printing paper. The present inventors have found that printing paper with high opacity can be obtained, and have completed the present invention.

That is, the present invention includes the following inventions.
(1) A printing paper containing a violet pigment and / or a blue pigment and having an opacity of 85% or more,
When the basis weight of the printing paper is higher than 70 g / m ^{2 and} the hue of the paper measured by the method of JIS P 8150 includes ultraviolet rays, the a ^* value is 0 or more and less than 7, and the b ^* value is −15 or more − Printing paper that is less than 3.
(2) The printing paper as described in (1) whose content of a purple pigment and / or a blue pigment is 0.7-3.5 mg / m < ² >.
(3) The printing paper according to (1) or (2), wherein the content of chemical pulp in the raw material pulp is 60% by weight or more.
(4) The printing paper according to any one of (1) to (3), wherein the pigment is present in one or more layers constituting the printing paper.
(5) The printing paper according to any one of (1) to (4), wherein the printing paper is coated paper and the pigment is present in a pigment coating layer.
(6) The printing paper is coated paper,
The pigment coating layer is selected from the group consisting of one or more first pigments selected from the group consisting of kaolin, clay, engineered kaolin and delaminated clay, and the group consisting of heavy calcium carbonate and light calcium carbonate The printing paper as described in (1)-(5) containing 2nd or more types of 2nd pigments.
(7) The printing according to (6), wherein the printing paper is a coated paper having a multilayer pigment coating layer, and the outermost pigment coating layer contains the first pigment and the second pigment. Paper.
(8) The printing paper according to (6) or (7), wherein the ratio of the total of the first pigment and the total of the second pigment is 40/60 to 70/30 (weight ratio).

  According to the present invention, it is possible to obtain a printing paper having both high whiteness and high opacity properties. In particular, the printing paper of the present invention has a strong white appearance, and the whiteness is more conspicuous than the whiteness measured by the instrument. The printing paper of the present invention exhibits excellent high opacity. In addition, the printing surface feeling and printing gloss are excellent, the smoothness is high, the ink is well-positioned, and the printability is excellent. In addition, according to the present invention, even when a large amount of chemical pulp having low opacity is used as the raw material, the opacity of the printing paper can be kept high.

L ^* a ^* b ^* Hue change after colorant addition in hue system

  The printing paper of the present invention may be a coated paper having a coating layer mainly composed of a pigment and an adhesive, or a printing paper without the coating layer. It is easy to exert the effects of the invention. The coated paper for printing has a base paper (hereinafter sometimes referred to as “base paper” in this specification) and at least one coating layer on one side or both sides of the base paper. Is mainly composed of a pigment and an adhesive. In the present specification, a printing paper having a pigment coating layer containing a white pigment is referred to as a printing coated paper, and a printing paper having no pigment coating layer is referred to as a non-printing paper for printing.

Purple pigment and / or blue pigment In the present invention, the printing paper contains a purple pigment and / or a blue pigment. In the present invention, the color material means a colored pigment or dye other than white. The pigment is a white or colored powder that is insoluble, hardly soluble or dispersed in water, oil, an organic solvent or the like, and includes inorganic and organic powders. In the present invention, either inorganic or organic materials may be used. A dye is an organic dye that absorbs or reflects visible light and has a unique color, and is dyed onto fibers or pigments by an appropriate dyeing method. It can be used as a solvent (water, organic solvents, etc.). It is melted. In the present invention, a dye may be used in combination, but a purple pigment and / or a blue pigment are used from the viewpoint of excellent light resistance and preventing discoloration / coloring of paper over time.

As the pigment of the present invention, a blue or purple pigment can be used. Examples of the blue pigment include EMT-Blue DS-18 manufactured by Toyo Ink Co., Ltd. SA Violet C12896 made by Gokoku Dye Co., Ltd. The pigment may be blue alone, purple alone, or a combination of both, but a purple pigment is preferably used to improve opacity. In the present invention, color materials other than blue and purple, such as black, red, and yellow, may be added as necessary.

  As the blue pigment / purple pigment, both inorganic pigments and organic pigments can be used. Specific examples of blue pigments include, for example, ultramarine, azurite, prussian blue, ultramarine, smalto, cobalt blue (cobalt aluminate), cerulean blue (cobalt stannate), cobalt chrome blue, cobalt, aluminum, and silicon. Examples thereof include oxide, cobalt / zinc / silicon oxide, manganese blue, and phthalocyanine. Specific examples of purple pigments include, for example, cobalt violet (cobalt arsenate, cobalt phosphate, cobalt lithium phosphate, hydrous ammonium phosphate, cobalt borate, etc.), purple ultramarine blue, iron oxide purple, manganese violet, mineral Examples thereof include inorganic pigments such as violet, indigoid, quinacridone, oxazine, anthraquinone, carbonium, and xanthene organic pigments.

  In a preferred embodiment of the present invention, by containing a certain amount of blue / purple pigment, the hue of the printing paper is in the range described later, thereby making the surface color of the printing paper pale, enhancing the whiteness of appearance, and increasing the opacity. It is possible to improve and prevent show-through during printing.

The blue and purple pigments in the present invention are color materials that change the color of the printing paper when it is contained in the printing paper. When each color material is added, the hue of the paper can be changed in the direction shown in FIG. FIG. 1 shows changes in the hue of paper that does not contain the color material of the present invention and paper that has been incorporated, based on the L ^* a ^* b ^* color system. When the hue is expressed as 0 ° in the (+) direction of the a ^* value, 180 ° in the (−) direction, b ^* (90) in the (+) direction, and 270 ° in the (−) direction, Assuming that the position of the origin is zero, when a blue color material is added, the hue of the paper after the addition changes to the portion of 210 ° or more and less than 280 ° shown in FIG. When it is added, it indicates that the hue of the paper after the addition changes to a portion of 280 ° to less than 335 ° shown in FIG. 1 as “purple”.

Content of Pigment The content of the purple pigment and / or blue pigment in the present invention is not particularly limited, but the total amount of these pigments is preferably 0.7 mg or more and 3.5 mg or less per 1 m ^{2 of} printing paper. 0.9 mg or more and 3.0 mg or less is more preferable, and 2.0 mg or more and 3.0 mg or less is particularly preferable. In general, when the amount is less than 0.7 mg, light absorption by the pigment is small, so that the concealability contributing to opacity is insufficient, which is not preferable. In general, if the amount is more than 3.5 mg, the amount of light absorbed by the pigment is large, which greatly contributes to the improvement of opacity, but the hue deviates greatly from 0 and is not preferable because it does not feel white. The pigment content can be appropriately adjusted within the above range depending on the whiteness of the raw material or raw paper.

  The total amount of the blue pigment and the purple pigment is obtained by adding the amounts of the blue pigment and the purple pigment contained in each layer. For example, when the printing paper is composed of a base paper layer, a size press layer, and a pigment coating layer, it is obtained by the following formula.

Layer containing pigment The blue / purple pigment used in the present invention may be contained in any layer of the printing paper. In a preferred embodiment, the printing paper can be produced relatively easily by allowing the pigment of the present invention to be present in one of the layers constituting the printing paper or in two or more layers. In particular, the coating layer may contain a blue / purple pigment.

The pigment used in the present invention may be contained in the base paper, may be contained in the size press liquid, or may be contained in the coating layer if it is a printing paper provided with a coating layer. Also good. Moreover, when there are two or more base paper layers and / or coating layers, they may be contained in any layer or in all layers. From the viewpoint of easy production, it is preferable that it is contained in the coating layer. When the same layer (for example, a coating layer provided on both sides) is present on both sides of the base paper, the presence of blue / purple pigment in one layer means that the coating layer on both sides contains the blue / purple pigment. In this case, or one of the coating layers on both sides, it means that one coating layer contains a blue / violet pigment.

  In general, printing paper is classified into coated paper with a pigment coating layer and non-coated paper without a pigment coating layer, and water-soluble starch, polyacrylamide, polyvinyl alcohol, etc., if necessary. An aqueous solution (size press solution) of a polymer binder is coated on the base paper to provide a clear (transparent) coating layer. Therefore, the printing paper of the present invention may be provided with either or both of the clear coating layer and the pigment coating layer on one side or both sides of the base paper.

  Therefore, in one embodiment, the printing paper of the present invention is a coated paper having a base paper layer and a pigment coating layer, and a purple pigment and / or a blue pigment is present in both or one of the base paper layer and the pigment coating layer. Exists. In another aspect, the printing paper of the present invention is a coated paper having a base paper layer, a clear coating layer, and a pigment coating layer, and the purple pigment and / or the blue pigment is a base paper layer, a clear coating layer, It exists in one layer or a plurality of layers selected from the pigment coating layer. In yet another aspect, the printing paper of the present invention is a non-coated paper having a base paper layer and a clear coating layer, and a purple pigment and / or a blue pigment is present in both or one of the base paper layer and the clear coating layer. Exists. When the blue / violet pigment of the present invention is present in a plurality of layers, the ratio of the purple pigment and / or blue pigment present in each layer is not particularly limited, but the ratio of the pigment present in the outermost coating layer is increased. Thus, the effect of the invention can be enjoyed efficiently with a small amount of pigment.For example, the amount of purple / blue pigment present in the outer layer is more than the amount of purple / blue pigment present in the inner layer. More is preferable.

Production of printing paper The printing paper of the present invention can be produced by a known method. For example, the coated paper for printing of the present invention can be produced by making the papermaking raw material described below in the wire part, and then using the press part and the predryer part to produce the base paper, and then in the coater part After the coating liquid described later is coated on the base paper, it can be used for after-dryer part, calendar part, reel part, winder part and the like. In the case of non-coated paper for printing, the paper-making raw material is made in the wire part, then used in the press part and pre-dryer part to produce the base paper, and the water-soluble polymer (binder) is coated on the base paper in a clear coating. Can be manufactured.

Base Paper The printing paper of the present invention has at least a base paper layer. The base paper used in the present invention may be single-layer paper or multilayer paper. When the base paper of the present invention has a multilayer structure, a violet pigment and / or a blue pigment may be contained in any one or more of a plurality of layers constituting the base paper. In order for the purple pigment and / or blue pigment to be present in the base paper layer, the base paper may be made from a papermaking raw material containing the purple pigment and / or blue pigment. The method for producing the base paper used in the present invention is not particularly limited and can be a known method using a known raw material.

Raw Material Pulp Chemical pulp can be used as a pulp raw material used for the base paper used in 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. Moreover, when using deinked pulp in this invention, it is preferable to mix | blend the high whiteness pulp selected centering on quality paper.

  In a preferred embodiment of the present invention, the base paper used in the present invention is made from a pulp raw material containing chemical pulp. There are chemical pulps manufactured by the kraft pulp method and those manufactured by the sulfite pulp method, and both of them can be used in the present invention. In the specification, it may be simply referred to as kraft pulp) from the viewpoint of production cost. In general, chemical pulp removes lignin, which is a wood-derived component, in the production process, so the whiteness of the pulp is high, but on the other hand, the opacity of the produced paper tends to be low. However, according to the present invention, opacity can be improved even when chemical pulp is used.

  In a preferred embodiment of the present invention, the content of chemical pulp in the raw material pulp is 60% by weight or more in the total pulp, more preferably 80% by weight or more, further preferably 90% by weight or more, and most preferably 100% by weight. . When the content of the chemical pulp is 100% by weight, lignin is not contained and the component for coloring the printing paper is the smallest. In addition, since it does not contain lignin, the absorption of ultraviolet rays can be suppressed so that the efficacy of the fluorescent dye is not inhibited, and the whiteness of the printing paper can be increased. The lower the chemical pulp content, the more disadvantageous in terms of whiteness.

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.
40% solids by weight is preferred and 10-35% solids by weight is more preferred.

  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.

Papermaking method / papermaking machine The papermaking 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. Can be carried out 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.

The basis weight of the base paper in a basis weight present invention of the base paper is not particularly ^{limited, 30g / m 2 ~200g / m} 2 is preferred. More ^preferably, a ^{40g / m 2 ~130g / m 2} . In the case of producing coated paper, the base paper may be smoothed in advance by an online soft calendar, online chilled calendar or the like before the coating process.

Clear coating The printing paper of the present invention may have a clear (transparent) coating layer on one 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 the present invention, a violet pigment and / or a blue pigment can be contained in the clear coating layer. In that case, a violet pigment and / or a blue pigment is blended in the clear coating liquid, and this is used as a base paper. Just coat it on top. The amount of clear coating is preferably 0.1 to 1.0 g / m ² , more preferably 0.2 to 0.8 g / m ² in terms of solid content per 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.

Pigment Coating The printing paper of the present invention can be made into a coated paper by providing a pigment coating layer by pigment coating. The pigment coating layer in the printing paper of the present invention may be a single layer or a multilayer, but from the viewpoint of obtaining a high basis weight printing paper, the pigment coating layer is preferably a multilayer. When the pigment coating layer has a multilayer structure, a violet pigment and / or a blue pigment may be contained in any one or more of a plurality of layers constituting the pigment coating layer. However, as described above, it is preferable that the outermost layer contains a violet pigment and / or a blue pigment. In order for the purple pigment and / or blue pigment to be present in the pigment coating layer, the pigment coating may be performed using a paint containing a purple pigment and / or a blue pigment. In the present invention, the coating method is not particularly limited, and can be performed by a known method using known raw materials.

Pre-calendar treatment In the present invention, pre-calendar processing is performed on the base paper before coating by online soft calendar, online chilled calendar, etc., and the base paper is smoothed in advance, so that the coating layer after coating is made uniform This is preferable. 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%.

Coating process The coated paper for printing according to the present invention may be formed by applying and drying a coating liquid mainly composed of a pigment and an adhesive on the base paper obtained as described above. it can. The coating may be on one side or both sides of the base paper, but double-sided coating is preferred because it does not curl and the physical properties of the front and back sides do not differ.

Pigments contained in the coating layer As pigments other than the purple and blue pigments used in the coating layer of the present invention, 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, etc. Inorganic pigments and organic pigments such as solid type, hollow type, or core-shell type can be used alone or in admixture of two or more as required. In the present invention, these pigments are sometimes referred to as “white pigments” in order to distinguish them from purple and blue pigments.

  In general, when the blending amount of clays such as kaolin, clay, engineered kaolin, and delaminated clay is increased, white paper glossiness is improved while whiteness is lowered. However, in the present invention, by containing a violet / blue pigment, high quality can be maintained without lowering the whiteness even if the clay is highly blended.

  Further, as the pigment for improving whiteness, heavy calcium carbonate and light calcium carbonate are preferable, and light calcium carbonate having a uniform particle diameter and shape is particularly preferable from the viewpoint of improving opacity. This is because the bulky coating layer structure scatters light efficiently. 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. The average particle diameter described below is a value measured by the above method.

  Therefore, in the present invention, as the white pigment in the pigment coating layer, one or more pigments selected from the group consisting of kaolin, clay, engineered kaolin, and delaminated clay (also referred to as “first pigment”), It is preferable to use in combination with one or more pigments selected from the group consisting of heavy calcium carbonate and light calcium carbonate (also referred to as “second pigment”). Among these, it is preferable to use kaolin as the first pigment and light calcium carbonate as the second pigment. The blending ratio (weight ratio) of the total of the first pigment and the second pigment is preferably 40/60 to 70/30, more preferably 46/54 to 60/40, and further preferably 50/50 to 60/40. preferable. When the blending ratio of the first pigment is less than 40, the glossiness tends to decrease. On the other hand, when the blending ratio of the first pigment is more than 70, the whiteness of the printing paper tends to decrease. As described above, the violet / blue pigment is preferably present in the pigment coating layer. In this case, the violet / blue pigment is 0.001 to 0.05 wt. It is preferable that it exists about a part.

  In the present invention, as described above, the pigment coating layer is preferably a multilayer. In this case, as the white pigment in the outermost layer, the first pigment and the second pigment may be used in the above ratio, and any white pigment may be used as the white pigment in the inner layer (the base paper side layer) that is not the outermost layer. However, considering the balance between whiteness and gloss, the white pigment in the inner layer preferably contains light calcium carbonate or heavy calcium carbonate. The total content of light calcium carbonate or heavy calcium carbonate in the inner layer is preferably 50 parts by weight or more, more preferably 70 parts by weight or more, and still more preferably 80 parts by weight or more per 100 parts by weight of the total white pigment in the inner layer. When the pigment coating layer is a multilayer, the purple / blue pigment can be present in one or both of the inner layer and the outermost layer, but it is preferable that the amount present in the outermost layer is large as described above. In this case, the purple / blue pigment is present in the outermost layer in an amount of 0.001 to 0.05 parts by weight with respect to a total of 100 parts by weight of the white pigment, and 0 to It is preferably present in an amount of 0.001 to 0.01 parts by weight.

Adhesive There is no restriction | limiting in particular about the adhesive agent (binder) used by this invention, The adhesive agent conventionally used for coated paper can be used. For example, as preferred adhesives, various copolymers such as styrene / butadiene, styrene / acrylic, ethylene / vinyl acetate, butadiene / methyl methacrylate, vinyl acetate / butyl acrylate, and polyvinyl alcohol and maleic anhydride copolymers. Synthetic adhesives such as acrylic acid / methyl methacrylate copolymer; Proteins such as casein, soybean protein, synthetic protein; Etherification of oxidized starch, positive starch, urea phosphated starch, hydroxyethyl etherified starch, etc. One or more ordinary adhesives for coated paper such as starches and starches such as dextrin; cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, and hydroxymethylcellulose can be appropriately selected and used.

  The amount of the adhesive used in the present invention is preferably 20 to 40 parts by weight and more preferably 25 to 35 parts by weight with respect to 100 parts by weight of the pigment from the viewpoint of printability and coating suitability. . This range is preferable when the total amount of the adhesive exceeds 40 parts by weight, the viscosity of the paint becomes high, and operation troubles such as boiling are likely to occur when coating by the film transfer method. This is because it is difficult to obtain sufficient surface strength when coated on a base paper by a film transfer method.

In the coating liquid of the present invention, in addition to the pigment and the adhesive, if necessary, it is blended with a dispersant, a thickener, a water retention agent, an antifoaming agent, a water resistant agent, and a normal pigment for coated paper. Various auxiliary agents can be used as appropriate.
Adjustment of Coating Liquid 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 60 to 70% by weight. The viscosity of the coating solution is preferably in the range of 500 to 1000 mPa · s as measured by the B-type viscosity measured at 60 rpm.

Coating Method / Coating Machine 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 coater such as a roll coater such as a size press coater or a gate roll coater, a bill blade coater, or a blade metering size press 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 3000 m / min.

The coating amount of the coating amount coating solution is appropriately adjusted so that the basis weight of the obtained printing paper exceeds 70 g / m ² , but preferably 15 to 40 g / m ² in terms of solid content per side, 18 to more preferably 37 g / ^{m 2,} more preferably 21~34g / ^{m 2.} In the present invention, printing paper with high opacity can be obtained even with a relatively small amount of coating.

Drying process 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 are used alone or in combination. be able to.

Surface Treatment In the present invention, the paper produced as described above is subjected to a surface treatment as necessary. In a preferred embodiment, the printing 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 printing 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. Moreover, if the surface temperature of the metal roll is a high temperature soft nip calender treatment of 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.

Printing paper [basis weight]
The basis weight of the printing paper of the present invention is higher than 70 g / m ² . In general, paper having a high basis weight has high paper thickness and high opacity, but the printing paper of the present invention has higher opacity and whiteness.

[Hue]
The hue of the printing paper of the present invention has an a ^* value of 0 or more and less than 7 and a b ^* value of −15 or more and less than −3 in the measurement including ultraviolet rays specified in JIS P 8150. a ^* is more preferable that the value is less than -5 0 or less than 5 and ^{b *} value is -10 or more, ^{a *} value is 0 or more 5 than and ^{b *} values more to be below -5 or -9 preferable. By making b ^* relatively low in this way, the apparent whiteness of the printing paper can be enhanced, the opacity can be improved, and the show-through during printing can be prevented.

[ash]
The ash content in the printing paper of the present invention is preferably 10% by weight or more for non-coated paper, and preferably 30% by weight or more for coated paper. When the ash content of the printing paper is less than 10% by weight, the opacity is not sufficiently improved.

[Fluorescent whitening intensity]
The fluorescent whitening intensity of the printing paper of the present invention is preferably 4.0 or more from the viewpoint of improving whiteness. In the present invention, sufficient whiteness can be obtained even if the fluorescent whitening intensity is 5.5 or less.

[Opacity]
The opacity of the printing paper of the present invention is 85% or more.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the examples. Parts and% in the examples indicate parts by weight and% by weight, respectively.

[Quality evaluation method]
The quality of the printing paper of the present invention was evaluated by the quality evaluation method described below.
(1) Hue measuring method (a ^* , b ^* ): Based on JIS P8150, the color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd. was used to measure with a light source including ultraviolet light.
(2) ISO whiteness measurement method: Based on JIS P8148, it was measured with a color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd. using a light source including ultraviolet light.
(3) Opacity measuring method: Based on JIS P8149, it was measured with Murakami Color Co., Ltd. color difference meter CMS-35SPX.
(4) Ash content measurement method: Measured according to JIS P8251.
(5) Fluorescent whitening intensity: White color measured with a light source not containing ultraviolet light from a value of ISO whiteness measured with a light source containing ultraviolet light using a color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd. The difference obtained by subtracting the degree value was defined as the fluorescent whitening intensity.
(6) Tint: The tint on the surface of the printing paper was visually evaluated under indoor fluorescent lighting.
(7) Appearance whiteness: The whiteness of the printing paper surface was visually evaluated under indoor fluorescent lamp illumination. This is because the whiteness of the color does not necessarily correlate with the whiteness when viewed with the human eye. Visual evaluation was made into 4 steps. A: Very white, B: White, B: Slightly dull, or slightly yellowish, B: Dullish, or yellowish.
(8) Back-through at the time of printing: A printing paper on one side of which was printed with black solid on an offset rotary press was observed from the back side of the print, and the back-through was evaluated visually. Visual evaluation was made into 4 steps. A: The printed part on the back is hardly recognized, B: The printed part on the back is inconspicuous, Δ: The printed part is slightly noticeable, X: The printed part is noticeable, and the image quality or appearance on the back is deteriorated.
(9) Color unevenness: Color unevenness of the printing paper was visually evaluated in four stages according to the following criteria. A: Color unevenness cannot be recognized, B: Conspicuous color unevenness, Δ: Color unevenness, x: Color unevenness is conspicuous.

In addition, quality items other than those described above were also measured for the printing paper of the present invention.
[material]
Each material mix | blended with the coating liquid is as follows.
1. Oxidized starch (SK-20 manufactured by Nippon Corn Starch Co., Ltd.)
2. Pigment ・ Fine light calcium carbonate (average particle size: 0.8μm)
-Fine kaolin (manufactured by Hydra Gloss CaMin)
3. Coloring material ・ Blue pigment (EMT-Blue DS-18, manufactured by Toyo Ink Co., Ltd.)
・ Purple pigment (SA Violet C12896 Gokoku Color Co., Ltd.)
4). 4. Fluorescent dye (BLANKOPOR NCC LIQUID Chemilla Japan Co., Ltd.) Adhesive ・ Styrene-butadiene synthetic polymer latex Water-soluble polymer ・ Urea phosphate esterified starch (Starcoat 16 manufactured by Nippon Shokuhin Kako Co., Ltd.)
Example 1
[Paper adjustment]
A pulp slurry containing 90% hardwood kraft pulp (LBKP) and 10% softwood kraft pulp (NBKP) was prepared, 15% light calcium carbonate was added as a filler, and cationic paper was used as an internal paper strength agent. A paper stock was prepared by adding 0.5% of a strength enhancer to the pulp.

[Preparation of pigment coating (under coating) solution]
100 parts of fine light calcium carbonate, 21 parts of oxidized starch, 3.5 parts of styrene-butadiene synthetic polymer latex, and 0.004 part of purple pigment are mixed and stirred at room temperature, and undercoating with a solid content concentration of 60% by weight. A liquid was obtained.

[Preparation of pigment coating (top coating) solution]
As a pigment, 54 parts of fine light calcium carbonate and 46 parts of fine kaolin hydra gloss (manufactured by CaMin) are blended, and a synthetic polymer whose monomer composition is mainly styrene and butadiene with respect to the total of these pigments. 10 parts of latex, 2.3 parts of phosphate esterified starch as a water-soluble polymer, 4 parts of fluorescent dye, 0.01 part of purple pigment, 0.003 part of blue pigment, All materials were mixed and stirred at room temperature to obtain a coating solution having a solid content concentration of 67% by weight. In addition, the compounding quantity of a coloring material, an adhesive agent, and a water-soluble polymer is a value with respect to 100 weight part of white pigments.

[Manufacture of printing paper]
Using the above paper stock, paper making speed is 1000 m / min, and paper making is performed with a paper machine having twin wires, and the above under coating liquid (surface treatment liquid) is applied per one side with a gate roll coater. Undercoat was applied to both sides so as to be 4.0 g / m ² and dried to obtain a base paper having a basis weight of 52.1 g / m ² .

Subsequently, the above coating solution was applied to both sides of a base paper with a blade coater at a coating amount of 9.5 g / m ² and a coating speed of 1000 m / min and dried.
Since papermaking and coating were continuously performed online, the coating speed and calendar speed were also 1000 m / min. Further, the coated paper for printing was obtained by surface treatment under conditions of 4 nips with a high temperature soft nip calender, a maximum processing temperature of 200 ° C., and a maximum processing linear pressure of 250 kN / m.

Example 2
Using the above paper stock, paper making speed is 1000 m / min, and paper making is performed with a paper machine having twin wires, and the above under coating liquid (surface treatment liquid) is applied per one side with a gate roll coater. Undercoat was applied to both sides so as to be 4.5 g / m ² and dried to obtain a base paper having a basis weight of 54.6 g / m ² .

Subsequently, the above coating solution was applied to both sides of the base paper with a blade coater at a coating amount of 10.0 g / m ^{2 at} a coating rate of 1000 m / min and dried.
The surface treatment with the high temperature soft nip calender was performed in the same manner as in Example 1 to obtain a coated paper for printing.

Example 3
The raw material pulp is made into a pulp slurry containing 85% of hardwood kraft pulp (LBKP) and 15% of softwood kraft pulp (NBKP), and the papermaking speed is 1000 m / min. Undercoat liquid (surface treatment liquid) was coated on both sides with a gate roll coater so that the coating amount was 4.0 g / m ² on one side and dried, and the basis weight was 56.6 g / m ^2. I got the base paper.

The pigment coating liquid contains 47 parts of fine light heavy calcium carbonate and 53 parts of hydra gloss (CaMin), which is fine kaolin, and the monomer composition is mainly styrene with respect to the total of these pigments. And 10.5 parts of synthetic polymer latex which is butadiene, 2.3 parts of phosphate esterified starch as water-soluble polymer, 4 parts of fluorescent dye, 0.009 parts of purple pigment, blue 0.002 part of pigment is blended, and all materials are mixed and stirred at room temperature to obtain a coating solution having a solid content concentration of 67% by weight. The coating amount is 10.5 g / m ² per side with a blade coater on the base paper, The coating was applied on both sides at a coating speed of 1000 m / min and dried.
The surface treatment with the high temperature soft nip calender was performed in the same manner as in Example 1 to obtain a coated paper for printing.

Example 4
Instead of blending 54 parts of fine light calcium carbonate and 46 parts of hydra gloss (CaMin), which is fine kaolin, into the pigment coating (top coating) liquid, 30 parts of fine light calcium carbonate and hydra A coated paper for printing was obtained in the same manner as in Example 1 except that 70 parts of gloss (CaMin) was blended.

Comparative Example 1
A coated paper for printing was obtained in the same manner as in Example 1 except that the purple and blue pigments were not blended in the pigment coating (under coating) solution and the pigment coating (top coating) solution.

Comparative Example 2
A coated paper for printing was obtained in the same manner as in Example 3 except that the purple and blue pigments were not blended in the pigment coating (under coating) solution and the pigment coating (top coating) solution.

As is apparent from Table 2, the printing paper of the present invention containing one or more blue and violet pigments has both high whiteness and high opacity, and the show-through during printing, particularly offset printing, is not noticeable. Excellent coated paper for printing with a wide color reproduction range. On the other hand, the comparative example containing no blue or violet pigment was inferior to the product of the present invention in terms of apparent whiteness, show-through during printing, color unevenness, and the like.

The coating amount of the coating weight coating solution is the basis weight of the printing paper obtained is appropriately prepared to exceed 70 g / ^{m 2,} preferably 15 to 40 g / ^{m 2} in terms of solid per sided content, 18 more preferably 37 g / ^{m 2,} more preferably 21~34g / ^{m 2.} In the present invention, printing paper with high opacity can be obtained even with a relatively small amount of coating.

Claims (8)

A printing paper containing a violet pigment and / or a blue pigment and having an opacity of 85% or more,
When the basis weight of the printing paper is higher than 70 g / m ^{2 and} the hue of the paper measured by the method of JIS P 8150 includes ultraviolet rays, the a ^* value is 0 or more and less than 7, and the b ^* value is −15 or more − Printing paper that is less than 3. The printing paper of Claim 1 whose content of a purple pigment and / or a blue pigment is 0.7-3.5 mg / m < ² >.   The printing paper of Claim 1 or 2 whose content of the chemical pulp in raw material pulp is 60 weight% or more.   The printing paper according to claim 1, wherein the pigment is present in one or more layers constituting the printing paper.   The printing paper according to any one of claims 1 to 4, wherein the printing paper is coated paper and the pigment is present in a pigment coating layer. The printing paper is coated paper,
The pigment coating layer is selected from the group consisting of one or more first pigments selected from the group consisting of kaolin, clay, engineered kaolin and delaminated clay, and the group consisting of heavy calcium carbonate and light calcium carbonate The printing paper of any one of Claims 1-5 containing 2nd or more types of 2nd pigments. The printing paper is a coated paper having a multilayer pigment coating layer,
The printing paper according to claim 6, wherein the outermost pigment coating layer contains the first pigment and the second pigment.   The printing paper according to claim 6 or 7, wherein a ratio of the total of the first pigment and the total of the second pigment is 40/60 to 70/30 (weight ratio).

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