JP2011026757A - Printing paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing paper having a combination of high whiteness and high opacity. <P>SOLUTION: The printing paper contains a purple pigment and/or blue pigment. In the printing paper, as to the hue as determined by the JIS P 8150 Standard specified for printing paper, b* value is -10 or greater but less than -0.5 as determined using rays including ultraviolet ones. <P>COPYRIGHT: (C)2011,JPO&INPIT

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. 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), medium-sized coated paper, fine-coated paper, and ultra-light-weight coated paper. Brands with different amounts, whiteness, glossiness, 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. In addition, printing paper using medium-quality raw materials is often blended with recycled pulp and mechanical pulp in addition to bleached kraft pulp, so although it is relatively opaque compared to high-quality printing paper, the whiteness is There is a problem that it is lower than high-quality printing paper.

Furthermore, in recent years, printing paper containing more recycled pulp has been increasing from the viewpoint of effectively utilizing resources. There is a problem that such printing paper has a lower whiteness.
Up to now, when seeking both whiteness and opacity, adding titanium oxide with a high refractive index internally or externally, providing a hollow plastic pigment in the coating layer, etc., providing an appropriate size void in the coating layer, Moreover, methods, such as combining these, 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 found that the whiteness can be increased 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 having high and 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 the hue of the paper measured by the method of JIS P 8150 of the printing paper is b ^* value of −10 or more and −0 in the measurement including ultraviolet rays Printing paper that is less than .5.
(2) The printing paper according to (1), wherein the content of deinked pulp (DIP) in the base paper is 60% by weight or more based on the absolute dry weight of the whole pulp.
(3) The printing paper according to (1) or (2), wherein the pigment content is 0.4 to 3.5 mg / m ² .
(4) The printing paper according to any one of (1) to (3), wherein the opacity of the printing paper is 90% or more.
(5) The printing paper according to any one of (1) to (4), wherein the basis weight of the printing paper is 70 g / m ² or less.
(6) The printing paper according to any one of (1) to (5), wherein the base paper layer contains a blue, purple, or red dye.
(7) The printing paper according to any one of (1) to (6), wherein the printing paper is a coated paper having at least a base paper layer and a pigment coating layer.
(8) The printing paper according to (7), wherein the pigment coating layer contains 75 parts by weight or more of heavy calcium carbonate with respect to 100 parts by weight of a pigment excluding a violet pigment and a blue pigment.

  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. 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. Even if deinked pulp is used as the raw material pulp, a printing paper having both high whiteness and high opacity properties can be obtained.

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 is a printing paper having a base paper (hereinafter sometimes referred to as “base paper” in this specification) and at least one coating layer on one or both sides of the base paper. The coating layer 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 has a unique color by selectively absorbing or reflecting visible light, and is dyed on 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 is 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 (bitumen), 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, hydrated ammonium cobalt 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 ^* value in the 90 ° direction 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 the blue pigment in the present invention is not particularly limited, but the total of these pigments is preferably 0.4 to 3.5 mg per 1 m ^{2 of} printing paper. More preferably, it is from 9 mg to 3.0 mg. In general, when the amount is less than 0.4 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 in opacity, but 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 the base paper. In the present invention, the numerical range includes its end points.

  Further, as described later, in the present invention, the hue can be adjusted by adding a dye to the base paper. In this case, the total amount of the purple and blue pigments contained in the printing paper layer other than the base paper layer is 0. .4 mg to 2.5 mg is preferable, and 0.5 to 2.0 mg is more preferable.

  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 purple / blue pigment of 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 any one of the layers constituting the printing paper.

  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 is present on both sides of the base paper (for example, a coating layer provided on both sides), the presence of purple / blue pigment in one layer means that the coating layer on both sides contains purple / blue pigment. This means that one of the coating layers on both sides contains a purple / blue 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 substances such as starch, polyacrylamide, and polyvinyl alcohol as needed. 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 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.

  Opacity and whiteness are affected by light reflection within the paper surface or within the paper layer and absorption within the paper layer. The opacity defined in JIS P 8149 is the value expressed by the ratio of the single sheet luminous reflectance R0 to the intrinsic luminous reflectance R∞ in the same sample, and is the Z-axis direction (thickness direction) of the coated paper Even if violet and blue pigments are present in this area, they are hardly affected. On the other hand, the whiteness defined in JIS P 8148 is the reflectance (inherent reflectance) of a sample in which a sufficient number of samples are stacked so that there is no change in the measured reflectance, and is affected by the pigment contained in the outermost layer. Receive. Therefore, when the purple / blue pigment is present in a plurality of layers, the effect of the present invention can be obtained efficiently by increasing the ratio of the pigment present in the outermost coating layer. However, if the coating layer, which is the outermost layer, contains a large amount of violet / blue pigment, the bluish white becomes stronger and the apparent white may be lowered.

  In addition, when the proportion of deinked pulp contained in the base paper is high, it contains a lot of mechanical pulp, etc. derived from deinked pulp. End up. Therefore, in the present invention, it is preferable that the ratio of the purple / blue pigment present in the base paper layer is higher than that of the other layers, or the purple / blue pigment is present only in the base paper layer. By doing so, excessive blueness can be suppressed, yellowing color caused by containing a lot of mechanical pulp can be efficiently suppressed, and high opacity and high whiteness can be achieved. preferable. As will be described later, the same effect can be obtained by incorporating a dye such as purple or blue into the base paper layer.

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.

  The base paper may contain a blue dye, a purple dye, or a red dye. In order for these dyes to be present in the base paper layer, the base paper may be made from a papermaking raw material containing these dyes. As described above, since the dye is dyed on fibers, pigments, and the like, the base paper is easily dyed. Moreover, although a dye may cause discoloration with time, such discoloration can be suppressed by including the dye in the innermost base paper layer. Furthermore, when many deinked pulps are used in the present invention, even if discoloration occurs due to a dye, the apparent whiteness does not decrease so much. The base paper layer may contain either the dye or the violet / blue pigment, or may contain both the dye and the violet / blue pigment.

  Therefore, in one embodiment, the printing paper of the present invention is a printing paper in which the base paper layer contains the dye and the other layer contains a violet / blue pigment. In another aspect, the printing paper of the present invention is a printing paper in which the base paper layer contains the dye and the violet / blue pigment and the other layer contains the violet / blue pigment.

The content of the dye or the amount of the color material in the printing paper is obtained in the same manner as for the purple / blue pigment.
In the present invention, the hue of the base paper is measured with the dye and / or the violet / blue pigment, and the b ^* value is −10 or more and less than −0.5, more preferably −3 in the measurement including ultraviolet rays according to the method of JIS P 8150. When adjusted to 0.0 or more and less than -0.5, the effect of the present invention is more easily achieved. Therefore, printing paper including a base paper whose hue is adjusted to the above range and a coating layer provided on the base paper has excellent whiteness even when the amount of purple / blue pigment used in the printing paper is reduced. , Has opacity.

  On the other hand, when a base paper having a hue outside the above range is used, it is necessary to increase the amount of purple / blue pigment contained in the coating layer or the like in order to obtain a desired whiteness. For this reason, the pigment in the coating liquid tends to remain in the pipe when changing the brand, and the operation loss tends to increase. However, this can be avoided by using a base paper having a hue within the above range. Furthermore, when using a base paper whose hue is out of the above range and adjusting the hue to a desired whiteness mainly by a layer other than the base paper layer, when the blueness of the printing paper becomes too strong, the apparent whiteness decreases. There is a possibility that the whiteness may be lowered and the adjustment is relatively difficult. However, using a base paper having a hue in the above range makes it easy to avoid such a situation.

Even if the base paper has a hue within the above range, a base paper having a relatively low b ^* value can be used to obtain a desired hue even if the amount of purple / blue pigment contained in the coating layer is small. Therefore, the above operation loss is less likely to occur.

The a ^* value of the base paper layer is not particularly limited because it does not greatly contribute to the whiteness and opacity of the printing paper, but is usually preferably −1 or more and less than 7, more preferably −1 or more and less than 5, and −1. More preferably less than 3. If it is out of the range, the color of the printing paper may not appear white, which is not preferable.

There are direct dyes, acid dyes, basic dyes, vat dyes, disperse dyes, reactive dyes, and other types of dye dyes contained in the base paper. Basic dyes and direct dyes are commonly used for cellulosic fibers. And vat dyes. The basic dye binds to the object to be dyed by Coulomb force between ions, hydrogen bond, van der Waals force, etc., and the direct dye binds to the object to be dyed by hydrogen bond, van der Waals force, etc. . Of these, basic dyes having a high dyeing power and a vivid color tone are preferred. Examples of basic dyes include azo dyes, diphenyl and triphenylmethane dyes, azine dyes, oxazine dyes, and thiazine dyes. Examples of direct dyes include azo dyes from ditolidine and dianisidine. The vat dyes include those classified into indigo / thioindigo, anthraquinone, and phthalocyanine.

  In the present invention, blue, purple or red dyes can be used. Examples of the blue dye include Eisen Basic Paper Blue RH Liquid manufactured by Hodogaya Chemical Co., Ltd., and examples of the red dye include those manufactured by Astraphloxin G Liquid Chemilla (all of which are bases). Dyes).

Blue / purple dyes have the same effect as blue / purple pigments, setting the hue of the printing paper to a specific range, making the surface color of the printing paper pale, enhancing the whiteness of appearance, and improving opacity, Prevents show-through during printing. On the other hand, the red dye has an effect of lowering the b ^* value, although slightly. In addition, since the a ^* value shifts in the minus direction only with the blue dye, that is, the hue may shift to green, the red dye can easily suppress this and make the a ^* value in the range of −1 or more and 7 or less. To do.

  In the present invention, blue, purple, or red dyes may be used alone or in combination. However, from the viewpoint of increasing opacity, it is preferable to use a blue dye. The base paper layer may contain a color material other than blue and red, such as black and yellow, as necessary.

  The addition amount of the dye in the base paper is not particularly limited. For example, the basic dye is 0.001 to 0.01% by weight and the direct dye is 0.015 to 0.15 based on the absolute dry weight of the whole pulp. % By weight.

Raw material pulp The raw material pulp of the present invention is not particularly limited. For example, chemical pulp, groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemiground pulp (CGP), semi-chemical pulp (SCP) and the like can be mentioned. . Chemical pulps include those produced by the kraft pulp method and those produced 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 the present invention, the use of deinked pulp (DIP) is more effective. For the deinking pulp (DIP), it is possible to use deinking 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. Further, in the present invention, when high whiteness pulp selected mainly from high-quality paper is used as deinked pulp, printing paper with higher whiteness can be obtained. However, since purple and blue pigments are used in the present invention, printing paper having high whiteness can be obtained even if pulp not derived from fine paper is used as deinked pulp.

  The deinked pulp is preferably used in combination with the generally used pulp described above. In this case, the content of the deinked pulp (DIP) in the raw pulp is 50% by weight based on the absolute dry weight of all the pulps (the sum of the absolute dry weight of the deinked pulp and the absolute dry weight of other pulps). Preferably, 60% by weight or more is more preferable, 65% by weight or more is further preferable, and 70% by weight or more is particularly preferable. If the blending amount of DIP is less than 60% by weight, it may be disadvantageous in terms of opacity. The weight of the deinked pulp is the total amount of the weight of the deinked pulp and the weight of non-separable filler or the like attached to the deinked pulp. In general, paper containing deinked pulp has a tendency to decrease in whiteness, but as described above, in the present invention, by adding a purple / blue pigment to obtain a specific hue, the whiteness of appearance and the breakthrough are observed. Can be improved.

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, Non-manufactured 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 with mineral acid Inorganic fillers such as crystalline 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.

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.

Basis weight of base paper Although the base weight of the base paper of the present invention is not particularly limited, it is preferably low from the viewpoint of cost reduction in production or transportation, specifically 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. Therefore, the effect of the present invention becomes more remarkable as the base paper has a lower basis weight. 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.

Ash content of base paper The ash content in the base paper of the printing paper of the present invention is preferably 10% by weight or more, more preferably 15% by weight or more. When the ash content in the base paper of the printing paper is less than 10% by weight, the opacity is not sufficiently improved.

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, 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 multiple layers, but a single layer is preferred from the viewpoint of obtaining a low basis weight printing paper. 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 20 to 100 kN / m, more preferably 50 to 100 kN / m. Moreover, the moisture content of the base paper at the time of pre-calendar treatment 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. Moreover, as a kind of pigment, heavy calcium carbonate and light calcium carbonate are preferable from a viewpoint of high whiteness. When the printing paper of the present invention contains deinked pulp, the opacity is relatively high due to the filler derived from the deinked pulp. Therefore, in such a case, it is particularly preferable to use heavy calcium carbonate that can give higher whiteness as the white pigment. When blending heavy calcium carbonate in the coating liquid, the content is preferably 50 parts by weight or more, more preferably 75 parts by weight or more, and still more preferably 80 parts by weight or more per 100 parts by weight of the white pigment. 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 copolymers; proteins such as casein, soy protein, synthetic proteins; 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 5 to 25 parts by weight and more preferably 8 to 13 parts by weight with respect to 100 parts by weight of the white pigment from the viewpoint of printability and coating suitability. preferable. When the amount of the adhesive exceeds 25 parts by weight, the viscosity of the coating liquid increases, and for example, coating defects such as streaks and scratches are likely to occur in a blade coater. On the other hand, when the amount of the adhesive is less than 5 parts by weight, it is difficult to obtain sufficient surface strength. In addition to pigments and adhesives, the coating liquid used in the present invention is optionally blended with dispersants, thickeners, water retention agents, antifoaming agents, water resistance agents, and ordinary coated paper pigments. 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 liquid is preferably in the range of 500 to 2000 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 it is preferably 500 to 1800 m / min for a blade coater and 500 to 3000 m / min for a size press coater in the current technology.

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, the effect of improving the opacity can be exhibited even if the coating amount is small.

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. Further, if the surface temperature of the metal roll is a high temperature soft nip calendering treatment at 40 ° C. to 250 ° C., the linear pressure is 60 to 400 kN / m, preferably 150 to 300 kN / m, more preferably 100 to 350 kN / m. is there. Increasing the temperature improves the gloss and smoothness of the coated paper surface.

Printing paper [basis weight]
Although the basic weight of the printing paper of this invention is not specifically limited, From a viewpoint of cost reduction, such as manufacture or transportation, 70 g / m < ² > or less is preferable. 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. Therefore, in this invention, it is easy to exhibit an effect in the area | region where basic weight is low. The effect is more likely to occur when the basis weight is 60 g / m ² or less.

[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. If the ash content of the printing paper is less than 10% by weight, the opacity may not be sufficiently improved.

[Hue]
The hue of the printing paper of the present invention has a b ^* value of −15 or more and less than −0.5, but a b ^* value of −6 or more and less than −1 in the measurement including ultraviolet rays specified in JIS P 8150. Is more preferable. Thus, by relatively reducing the b ^* value, the apparent whiteness of the printing paper can be enhanced, the opacity can be improved, and the show-through during printing can be prevented. Further, the a ^* value in the same measurement is not particularly limited because it does not greatly contribute to the whiteness and opacity of the printing paper, but is usually preferably −1 or more and less than 7, more preferably −1 or more and less than 5. -1 or more and less than 3 is more preferable. If it is out of the range, the color of the printing paper may not appear white, which is not preferable.

[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 the fluorescent whitening intensity is 1.0 or more from the viewpoint of improving the whiteness. Is preferred.

[Opacity]
The opacity of the printing paper of the present invention is preferably 85% or more, and more preferably 90% 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. 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 measurement method (a ^* , b ^* ): According to JIS P8150, color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd., using a light source including ultraviolet light on the felt surface of the base paper or printing paper. It was measured.
(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) Appearance whiteness: The whiteness of the printing paper surface was visually evaluated under indoor fluorescent lighting. 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.
(6) Back-through at the time of printing: A printing paper on which one side was printed with a black solid on an offset rotary press was observed from the back side of the print, and the back-through was visually evaluated. 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.

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. Pigment ・ Fine heavy calcium carbonate (FMT97, manufactured by Phimatech, average particle size 0.7 to 1.0 μm)
-Fine kaolin (manufactured by Hydra Gloss CaMin)
2. 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.)
・ Blue dye (Blue RH Liquid, Eisen Basic Paper)
・ Red dye (made by Astra Phloxin G Liquid Chemilla)
3. Adhesive ・ Styrene-butadiene synthetic polymer latex Water-soluble polymer ・ Urea phosphate esterified starch (Starcoat 16 manufactured by Nippon Shokuhin Kako Co., Ltd.)
5. Deinked pulp (DIP)
・ Mainly used newspaper and magazine paper, disaggregated in water, dust removed in the screening process, deinked using a floatator, then bleached and washed, whiteness of about 55%, white Deinked pulp slurries having a degree of 60% to 70% and a whiteness of 70% or more were combined and used as a deinked pulp having a whiteness of 66% to 73%.

[Preparation of paper materials]
Softwood kraft pulp (NBKP), deinked pulp (DIP), and hardwood kraft pulp (LBKP) were prepared, and a pulp slurry was prepared at a blending ratio shown in Table 1. To this pulp slurry, light calcium carbonate (trade name: Albuquer 5970, manufacturer; manufactured by Specialty Minerals Inc.) is added to the pulp slurry so as to be 15% in the paper, and cationic paper strength is enhanced as an internal paper strength agent. A paper stock was prepared by adding 0.5% of an agent (polyacrylamide) to pulp.

[Adjustment of pigment coating solution]
As pigment, 75 parts of fine heavy calcium carbonate and 25 parts of fine kaolin hydra gloss (CaMin) are blended, and the monomer composition is mainly styrene and butadiene with respect to the total of these white pigments. 7 parts of synthetic polymer latex and 4.5 parts of urea phosphated starch as a water-soluble polymer are blended, and the colorant is mixed and stirred at room temperature with the composition shown in Table 1, so that the solid content concentration is 67 A coating solution of wt% was obtained. 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 was made with a paper machine having a twin wire at a paper making speed of 1100 m / min to obtain a base paper having a basis weight of 35 g / m ² .

Subsequently, the above coating solution was applied to both sides of the base paper with a blade coater at a coating speed 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 with a high temperature soft nip calender with 2 nips, a maximum processing temperature of 200 ° C., and a maximum processing linear pressure of 250 kN / m.

As is apparent from the table, the printing paper of the present invention containing one or more blue and violet pigments has both high whiteness and high opacity, and has no noticeable show-through during printing, particularly during offset printing. Excellent coated paper for printing with a wide reproduction range. In particular, blue and red dye coated printing papers of Examples 1 and 2 by increasing the content was adjusted to b ^* values in the base paper to a relatively low value of the base paper is, the b ^* value of the base paper is relatively Although it is high, the whiteness tends to be slightly higher than Example 3 in which the hue is adjusted by increasing the amount of blue and purple pigment in the coating layer, and the total content of purple and blue pigments is small, but excellent Have high opacity. On the other hand, the comparative example was inferior to the product of the present invention in terms of whiteness of appearance, breakthrough during printing, and the like.

Claims (8)

Printing paper containing a purple pigment and / or a blue pigment,
A printing paper in which the hue of the paper measured by the method of JIS P 8150 of the printing paper has a b ^* value of −10 or more and less than −0.5 in the measurement including ultraviolet rays.   The printing paper according to claim 1, wherein the content of the deinked pulp (DIP) in the base paper is 60% by weight or more based on the absolute dry weight of the whole pulp. The printing paper of Claim 1 or 2 whose content of the said purple pigment and / or a blue pigment is 0.4-3.5 mg / m < ² >.   The printing paper according to any one of claims 1 to 3, wherein the opacity of the printing paper is 90% or more. The printing paper of any one of Claims 1-4 whose basic weight of the said printing paper is 70 g / m < ² > or less.   The printing paper according to any one of claims 1 to 5, wherein the base paper layer contains a blue dye, a purple dye, or a red dye.   The printing paper according to any one of claims 1 to 6, wherein the printing paper is a coated paper having at least a base paper layer and a pigment coating layer.   The printing paper according to claim 7, wherein the pigment coating layer contains 75 parts by weight or more of heavy calcium carbonate with respect to 100 parts by weight of a pigment excluding a violet pigment and a blue pigment.

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