JP4889798B2 - Printing paper - Google Patents

Description

  The present invention relates to a low basis weight 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. On the other hand, there is a demand for both an increase in the number of pages in a booklet and a reduction in paper costs and transportation and mail costs, and demand for low basis weight products is increasing.

  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, so it has little colored foreign matter and high whiteness, but it has low opacity, especially when printed with thin materials. It is a problem. 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.

  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 Shoko 52-118116

  As a result of considering the background as described above, an object of the present invention is to provide a low basis weight 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 purple pigment and / or a blue pigment and having an opacity of 85% or more, wherein the printing paper has a basis weight of 70 g / m ² or less, and measured by the method of JIS P 8150 The printing paper has a hue of a * value of 0 or more and less than 7 and b * value of −15 or more and less than −3 in the measurement including ultraviolet rays.
(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 as described in (1) or (2) whose content of the chemical pulp in raw material pulp is 60 weight% or more.
(4) The printing paper according to any one of (1) to (3), wherein the pigment is present in any one layer of 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 according to any one of (1) to (4), wherein the printing paper is uncoated paper and the pigment is present in a base paper layer.

  According to the present invention, it is possible to obtain a low basis weight 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. In addition, it exhibits excellent high opacity, particularly in low basis weight products. 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 in order to improve opacity, it is preferable to use a purple pigment. 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 violet pigment and / or the blue pigment in the present invention is not particularly limited, but is preferably 0.7 mg or more and 3.5 mg or less per 1 m ^{2 of} printing paper in total of the pigment. More preferably, it is 0.9 mg or more and 3.0 mg or less. In general, when the amount is less than 0.7 mg, light absorption by the pigment is small, and the concealability contributing to opacity is insufficient, which is not preferable. In general, when the amount is more than 3.5 mg, although the amount of light absorbed by the pigment is large and greatly contributes to improvement in opacity, the hue is greatly deviated from 0 and it is not preferable to 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 a value obtained by adding the contents of the base paper layer, the size press layer, and the pigment coating layer, and is obtained by the following formula.
Total amount (mg / m ² )
= {Base paper basis weight (g / m ² ) × pulp content in base paper × contents of blue pigment and purple pigment in base paper (mg / pulp 1 g)}
+ [Coating amount of size press liquid (both sides) (g / m ² ) × {total weight part of blue pigment and purple pigment in size press liquid / weight part of total solid in size press liquid}
+ Coating amount of pigment coating solution (both sides) (g / m ² ) × {total weight part of blue pigment and purple pigment in pigment coating solution / weight part of total solid content in pigment coating solution}] × 1000
Layer containing pigment The blue / purple pigment of the present invention may be contained in any layer of the printing paper. In a preferred embodiment, when the pigment of the present invention is present in any one of the layers constituting the printing paper, the printing paper can be produced relatively easily. In particular, a blue / purple pigment is added to the coating layer. It is good to contain.

  The pigment of the present invention may be contained in a base paper, may be contained in a size press solution, or may be contained in a coating layer as long as it is a printing paper provided with a coating layer. 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 the blue / purple pigment in one layer means that the two coating layers contain the blue / purple pigment. In this case, or one of the two coating layers, 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 is provided with either or both of a clear coating layer and a 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 of the present invention is not particularly limited, and can be performed by a known method using known raw materials.

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. 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 of 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 component derived from wood, 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. In the low-basis weight printing paper used, it was a big problem to improve the opacity, but according to the present invention, the opacity can be improved.

  In a preferred embodiment of the present invention, the content of the chemical pulp in the raw pulp is 60% by weight or more in the total pulp, more preferably 80% by weight or more, more 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, 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.

Paper Making Method / Paper Making Machine The paper making method of 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 paper machine. It can be performed using a paperboard machine combined with a net paper machine or a Yankee dryer machine. 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 base paper having a basis weight of the present invention of the base paper is preferably 60 g / ^{m 2} or less, more preferably 20 to 60 g / ^{m 2,} more preferably from 20 to 40 g / ^{m 2.} In general, paper with high basis weight has high paper thickness and high opacity, whereas paper with low basis weight has low opacity due to thin paper thickness. However, the opacity can be increased.

When the coated paper is produced according to the present invention, 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 a single layer is preferred. When the pigment coating layer of the present invention has a multilayer structure, a purple pigment and / or a blue pigment may be contained in any one or more of a plurality of layers constituting the pigment coating layer. 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 The pigment (white pigment) used in the coating layer of the present invention may be those conventionally used for coated paper, such as kaolin, clay, engineer. Ard 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. An organic pigment such as a hollow type or a core-shell type can be used alone or in admixture of two or more as required. Further, as the kind of pigment, heavy calcium carbonate and light calcium carbonate are preferable from the viewpoint of high whiteness, 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.

  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.

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, and 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.

Coating amount The coating amount of the coating liquid in the present invention is preferably ² to 15 g / m ² , more preferably 5 to 12 g / m ² , and even more preferably 5 to 10 g / m ² in terms of solid content on one side. In the present invention, when the coating amount is small, the advantage is high, and the effect of improving the opacity can be exhibited.

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 70 g / m ² or less. In general, paper with high basis weight has high paper thickness and high opacity, but paper with low basis weight has low opacity because of its thin paper thickness. The opacity can be increased. In the present invention, it is easy to exert an effect in a region with a low basis weight, and the effect is more likely to appear when the basis weight is 60 g / m ² or less.

[Hue]
Color of the printing paper of the present invention, less than 7 and ^{b *} value ^{a *} value is 0 or more in the measurement containing the ultraviolet defined in JIS P 8150 is adjusted to be less than -15 or -3, ^{a *} value more preferably but less than 0 or less than 5 and ^{b *} value is -10 or more -5, further preferably ^{a *} value is 0 or more 5 than and ^{b *} value is less than -5 to -9. 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 printing paper of the present invention can obtain sufficient whiteness even if the fluorescent whitening intensity is 5.5 or less, but from the viewpoint of improving whiteness, the fluorescent whitening intensity is 4.0 or more. Is preferred.

[Opacity]
According to the present invention, the opacity of the printing paper can be 85% or more.

  The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the examples. In addition, the part and% in an example show a weight part and 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 blended in the size press solution and coating solution is as follows.
1. Oxidized starch (SK-20 manufactured by Nippon Corn Starch Co., Ltd.)
2. Pigment-Fine light calcium carbonate-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.)
・ Black pigment (SA Black A035, Gokoku Color Co., Ltd.)
4). Fluorescent dye (BLANKOPOR NCC LIQUID Chemilla Japan Co., Ltd.)
5. Adhesive ・ Styrene-butadiene synthetic polymer latex Water-soluble polymer ・ Urea phosphate esterified starch (Starcoat 16 manufactured by Nippon Shokuhin Kako Co., Ltd.)
[Preparation of paper materials]
A pulp slurry containing 65% hardwood kraft pulp (LBKP) and 35% softwood kraft pulp (NBKP) was prepared, and light calcium carbonate was added as a filler at the blending ratio shown in Table 1, and an internal paper strength agent A paper stock was prepared by adding 0.5% of a cationic paper strength enhancer to the pulp. In Example 13, a pigment was added to the paper stock.

[Preparation of size press liquid (surface treatment liquid)]
The materials shown in Table 1 were mixed and stirred at room temperature to obtain a size press solution having a solid content concentration of 8% by weight. In addition, the compounding quantity of a coloring material is a value with respect to 100 weight part of oxidized starch. The coating amount of this size press solution was 0.5 g / m ² in all Examples and Comparative Examples.

[Adjustment of pigment coating solution]
As a pigment, 85 parts of fine light heavy calcium carbonate and 15 parts of hydra gloss (CaMin), which is fine kaolin, are blended. Synthetic polymer latex whose monomer composition is mainly styrene and butadiene for all pigments. 7 parts, 4 parts of phosphoric acid esterified starch as a water-soluble polymer, 4 parts of fluorescent dye, further mixing and stirring the colorant at room temperature with the composition shown in Table 1, solid content concentration A coating solution of 67% by weight was obtained. In addition, the compounding amount of the coloring material, the adhesive, and the water-soluble polymer is a value with respect to 100 parts by weight of the pigment.

[Manufacture of printing paper]
Using the above-mentioned stock, paper is made with a paper machine having a twin wire at a paper-making speed of 1100 m / min, and the above-mentioned size press liquid (surface treatment liquid) is applied to one side of the coating amount with a gate roll coater. A base paper having a basis weight of 41.8 g / m ² was obtained by size pressing on both sides so as to be 0.5 g / m ² and drying.

Subsequently, the above coating solution was applied to both sides of the base paper with a blade coater at a coating rate of 1100 / min so as to have the values shown in Table 1 per side with a blade coater and dried.
Since papermaking and coating were continuously performed online, the coating speed and calendar speed were also 1100 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.

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, Comparative Examples 1 and 2 in which the opacity and paper hue (a ^* , b ^* ) are out of the scope of the present invention are those of the present invention in terms of appearance whiteness, back-through during printing, color unevenness and the like. It was inferior to implementation product.

Claims (4)

A coated paper for offset printing having a pigment coating layer having an opacity of 85% or more,
The basis weight of the printing paper is 70 g / m ² or less,
The printing coated paper contains a purple pigment and / or a blue pigment,
The hue of the coated paper for printing measured by the method of JIS P 8150 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.
The content of chemical pulp in the raw material pulp is 60% by weight or more,
In 100 parts by weight of the white pigment in the pigment coating layer , containing 80 parts by weight or more of calcium carbonate,
The coated paper for printing. The coated paper for printing of Claim 1 whose content of a purple pigment and / or a blue pigment is 0.7-3.5 mg / m < ² >. The coated paper for printing according to claim 1 or 2 , wherein the purple pigment and / or blue pigment is present in any one layer of the coated paper for printing. The coated paper for printing according to any one of claims 1 to 3 , wherein the purple pigment and / or blue pigment is present in the pigment coating layer.

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