JP7181267B2 - Coated paper for printing - Google Patents

Description

TECHNICAL FIELD The present invention relates to a coated printing paper that can be used as a coated paper for offset printing or the like.

Coated paper for printing is required to have high whiteness, high opacity, etc. from the viewpoint of printability. Therefore, Patent Document 1 proposes that a coated paper for offset printing has a high content of deinked pulp of 50% or more, and that the coating layer contains a purple pigment, a blue pigment, and heavy calcium carbonate. . According to the document, this "makes it possible to obtain a printing paper having both physical properties of high whiteness and high opacity".

However, when the deinked pulp is mixed in a high amount of 50% by mass or more, there arises a problem that the brightness, which is one of printability, is lowered.

The document also proposes that the base paper contains a blue dye, a purple dye, or a red dye as a more preferable printing paper. However, dyes are chemically unstable. Therefore, according to this proposal, there arises a problem of color fading due to deterioration over time, that is, a problem of variation in brightness and the like.

Japanese Patent No. 5686984

The main problem to be solved by the present invention is to provide a coated printing paper which has high whiteness and high opacity, but does not have the possibility of lowering the brightness.

The inventors of the present invention have made intensive studies to solve the above problems. As a result, even if the base paper has a natural color, by adding both purple and blue pigments and a fluorescent brightening agent to the coating layer for bluing (coloring), high whiteness and high opacity can be achieved. However, we have found that it is possible to obtain a coated printing paper which does not have the risk of lowering the brightness and preferably does not have the problem of color fading. Aspects that serve as references for solving the above problems based on this knowledge are as follows.

(Reference mode of claim 1)
A coated paper having a base paper and a coating layer,
The JIS P 8150 hue of the base paper has an a ^* value of 0.1 or more and less than 0.7 and a b ^* value of -0.2 or more and less than 0.6 in a measurement including ultraviolet light,
The coating layer contains both a purple pigment and a blue pigment, and an optical brightener,
The opacity of JIS P 8149 of the coated paper is 85% or more, the brightness of JIS P 8150 is 85% or more in the measurement including ultraviolet rays,
The JIS P 8150 hue of the coated paper has an a ^* value of 0.5 or more and less than 2.5 and a b ^* value of -5 or more and less than -2 in a measurement including ultraviolet light.
A coated printing paper characterized by:

(Reference mode of claim 2)
The coating layer contains a white pigment,
The total content of the purple pigment and the blue pigment in the coating layer with respect to 100 parts by mass of the white pigment is 0.001 to 0.005 parts by mass in terms of solid content,
70% by mass or more of the white pigment is calcium carbonate,
The coated printing paper according to claim 1.
(Reference mode of claim 3)
The calcium carbonate is light calcium carbonate,
The coated printing paper according to claim 2.

(Reference mode of claim 4)
The content of the fluorescent whitening agent is 10 to 80 mg/m ² ,
The fluorescent brightener in the coating layer is 0.05 to 0.8 parts by mass with respect to 100 parts by mass of the white pigment.
The coated printing paper according to claim 2 or 3.

(Reference mode of claim 5)
Deinked pulp is used as raw material pulp for the base paper at 30 to 45 mass% of the total raw material pulp on an absolute dry basis, and the ash content of the base paper measured according to JIS P 8251 (525 ° C.) is 3.0. The opacity of the coated paper is set to 85% or more by setting it to 9.5%,
The coated printing paper according to any one of claims 1 to 4.

(Reference mode of claim 6)
The JIS P 8150 brightness of the base paper is 75% or more in a measurement including ultraviolet rays, and the brightness of the coated paper is 85% or more.
The coated printing paper according to any one of claims 1 to 5.

(Reference mode of claim 7)
An inorganic pigment having a particle size of 0.2 to 0.4 μm is used as the purple pigment and the blue pigment, and the total content of the purple pigment and the blue pigment is 0.1 to 1.4 mg/m ² ,
The coated printing paper according to any one of claims 1 to 6.

(Reference mode of claim 8)
The hue of JIS P 8150 is a ^* value of 0.1 or more and less than 0.7 and b ^* value of -0.2 or more and less than 0.6 in measurements including ultraviolet rays. A method for producing coated paper by forming a layer,
The coating layer contains both a purple pigment and a blue pigment, and a fluorescent brightening agent,
The opacity of JIS P 8149 of the coated paper is 85% or more, the brightness of JIS P 8150 is 85% or more in the measurement including ultraviolet rays,
The hue of JIS P 8150 of the coated paper is a ^* value of 0.5 or more and less than 2.5 and b ^* value of -5 or more and less than -2 in measurement including ultraviolet light,
A method for producing a coated printing paper, characterized by:

According to the present invention, it is possible to obtain a coated printing paper that has high whiteness and high opacity, but does not have the possibility of lowering the brightness.

1 is a cross-sectional view of a coated printing paper of this embodiment; FIG. FIG. 4 is a diagram showing changes in hue when a purple pigment and a blue pigment are contained.

Next, the form for implementing this invention is demonstrated. In addition, the present invention is not limited at all by the following embodiments. Various modifications can be made without departing from the gist of the invention.
As shown in FIG. 1, the coated printing paper 1 of this embodiment includes a base paper 2 and a coating formed on one side ((1) in FIG. 1) or both sides ((2) in FIG. 1) of the base paper 2. It has a coating layer 4 . However, this is only an example, and other layers such as a primer coating layer may be present under the coating layer 4, that is, between the coating layer 4 and the base paper 2, for example. For reference, (3) in FIG. 1 shows a configuration in which the undercoat layer 3 is formed on one side of the base paper 2, and (4) in FIG. It shows the morphology.

The coating layer 4 contains a purple pigment, a blue pigment, and a fluorescent whitening agent. A detailed description will be given below.

(base paper)
The base paper 2 is mainly composed of raw pulp and filler.

The base paper 2 may be a single layer or multiple layers.

(raw material pulp)
Raw material pulp includes, for example, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), chemical pulp such as sulfite pulp, groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermo Mechanical pulp (CTMP), chemigrand pulp (CGP), semi-chemical pulp (SCP), etc. can be used.

Chemical pulp has a high degree of whiteness due to the removal of lignin. On the other hand, there is a problem that the opacity of the produced paper becomes low. This problem is particularly pronounced in the case of low basis weight coated papers.

Therefore, in this embodiment, it is essential to use deinked pulp (DIP) as the raw pulp for the base paper 2 . The amount of deinked pulp is preferably 30% by mass or more and 45% by mass or less, more preferably 32% by mass or more and 43% by mass or less, particularly preferably 35% by mass or more and 40% by mass or less, of the total raw material pulp on an absolute dry basis. It is below. If the amount of deinked pulp is less than the above range, the opacity may not be sufficiently high. On the other hand, if the amount of the deinked pulp exceeds the above range, there is a risk that the whiteness and brightness will not be sufficiently high even with adjustment using a coloring material or the like.

In addition, a coloring material means a colored pigment or dye other than white. In addition, the mass of the deinked pulp includes the mass of the deinked pulp itself, as well as the mass of unseparable fillers and the like adhering to the deinked pulp.

Examples of raw materials for deinked pulp include sorted waste paper such as high-quality paper, medium-grade paper, low-grade paper, newspaper, leaflets, and magazines, and unsorted waste paper in which these waste papers are mixed.

(filler)
Examples of fillers include heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, delaminated kaolin, white carbon, talc, magnesium carbonate, barium carbonate, barium sulfate, water. Inorganic fillers such as aluminum oxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, and amorphous silica, organic fillers such as urea-formalin resin, melamine resin, polystyrene resin, phenol resin, etc. can be used.

However, from the viewpoint of improving opacity, it is preferable to use heavy calcium carbonate or light calcium carbonate. From the viewpoint of improving whiteness, brightness and opacity, it is preferable to use light calcium carbonate. Furthermore, as the light calcium carbonate, it is preferable to use light calcium carbonate coated with an inorganic substance such as silica or aluminum, or an aggregate obtained by aggregating light calcium carbonate. Of course, these light calcium carbonates can be used in combination as appropriate.

(colorant)
The base paper 2 may be internally added with a violet pigment or a blue pigment as a filler.

The base paper 2 may contain a purple dye, a blue dye, a yellow dye, a green dye, a red dye, or the like. Since the dye is dyed to the fiber, the coloring efficiency is good. Although the dye may discolor, if it is contained in the base paper 2, since at least the coating layer 4 is present on the base paper 2, there is little effect on the appearance.

The internal addition of the purple pigment or the blue pigment is preferably carried out so that the base paper 2 has a natural color. Specifically, in the measurement in which the hue of the base paper 2 according to JIS P 8150 includes ultraviolet rays, the a ^* value is preferably 0.1 or more and less than 0.7, and the b ^* value is -0.2 or more and less than 0.6, more preferably a ^* value of 0.2 or more and less than 0.6, b ^* value of −0.1 or more and less than 0.5, particularly preferably a ^* value of 0.25 or more and less than 0.55, b ^* value of −0.05 or more and 0 less than .45. By adjusting in this way, the whiteness and brightness of the base paper 2 itself can be improved, and the whiteness and brightness after forming the coating layer 4 can be improved.

The brightness of the base paper 2 according to JIS P 8150 is preferably 75% or more, more preferably 78% or more, and particularly preferably 80% or more when measured including ultraviolet rays.

(Additive)
Additives can be added to the base paper 2, if necessary.

Examples of additives include coagulants, antifoaming agents, fluorescent whitening agents, aluminum sulfate, retention improvers, drainage improvers, paper strength enhancers, sizing agents, dyes, and the like.

(Undercoat coating layer)
As described above, one or both sides of the base paper 2 can be provided with the undercoat coating layer (clear coating layer) 3 .

As the raw material for the undercoat layer 3, for example, a natural polymer system, a synthetic polymer system, or the like can be used.

Examples of natural polymer systems include enzyme-degraded starch, oxidized starch, hydroxyethylated starch, cationized starch, urea phosphorylated starch, modified One or two or more selected from oxidized starch, carboxymethylated cellulose (CMC), carboxyethylated cellulose (CEC) and the like can be used.

As the synthetic polymer system, for example, one or more of polyacrylamide (PAM), polyethylene glycol (PEG), and the like can be selected and used.

Additives such as antifoaming agents, fluorescent whitening agents, waterproofing agents, and sizing agents can be incorporated into the undercoat layer 3 .

The coating amount of the undercoat layer 3 is preferably 0.1 to 1.0 g/m ² , more preferably 0.2 to 0.8 g/m ² , particularly preferably 0.3 to 0.8 g/m 2 per side. 6 g/m ² .

The coating amount of the undercoat layer 3 can be determined using a coater such as a size press coater, a gate roll coater, a rod metering coater, a Billboud coater, and a blade coater.

The undercoat layer 3 may be colored by blending pigments or dyes. However, if the undercoat layer 3 is colored, the whiteness and lightness of the base paper 2 are lowered, so it is preferable that the undercoat layer 3 is not colored.

(Coating layer)
The coating layer 4 is mainly composed of a violet pigment and a blue pigment as color materials, a fluorescent whitening agent, and an adhesive.

The coating layer 4 may be a single layer or multiple layers.

When the coating layer 4 has a plurality of layers, the purple pigment, the blue pigment, and the fluorescent whitening agent should be contained in at least one layer. However, from the viewpoint of increasing whiteness, brightness, opacity, and printability (bleed-through, definition, etc.), it is preferable to include a purple pigment, a blue pigment, and a fluorescent brightening agent in at least the outermost layer. .

(Purple pigment and blue pigment)
The reasons for using the violet pigment, the blue pigment, and the fluorescent brightening agent are described below.
In order to make the coated paper look white, there is a technique called bluing (coloring) in which a violet pigment and a blue pigment are added to balance the reflected light of the coated paper as a whole. Purple pigments and blue pigments absorb light in the long wavelength portion (approximately 500 to 700 nm) of visible light, that is, light in the yellow portion, so that the additional color of blue is conspicuous. However, since the amount of reflected light is reduced by the amount of light that is absorbed, the lightness of the coated paper is lowered and becomes gray or nearly black.

Therefore, in this embodiment, a violet pigment, a blue pigment, and a fluorescent brightening agent are used. According to this form, it is believed that the fluorescent whitening agent converts ultraviolet light (wavelength: about 300 to 400 nm) into visible light, blue light (wavelength: about 450 nm). Therefore, even when a purple pigment and a blue pigment are used, high visual brightness can be obtained.

In addition, the opacity of the coated paper 1 is improved by including a purple pigment and a blue pigment, which are coloring materials, and the strike-through of the ink is prevented.

Both inorganic pigments and organic pigments can be used as the purple pigment and the blue pigment. However, it is preferable to use inorganic pigments as the purple pigment and the blue pigment because the resulting coated paper 1 has excellent hiding properties and excellent physicochemical stability such as light resistance. preferable.

Further, it is more preferable to use inorganic pigments having a particle size of 0.2 to 0.4 μm. Basically, it is thought that the smaller the particle size, the higher the hiding power.

In addition, the said particle diameter means the volume average particle diameter measured by the laser analysis method. In the laser analysis method, 10 mg of a sample is added to 8 ml of a methanol solution and dispersed for 3 minutes with an ultrasonic disperser (output: 80 W). , manufactured by Nikkiso Co., Ltd.).

Examples of purple pigments include cobalt arsenate, cobalt phosphate, cobalt-lithium-phosphate, hydrous ammonium cobalt phosphate, cobalt violet such as cobalt borate, inorganic pigments such as purple ultramarine, iron oxide purple, manganese violet, mineral violet, etc. Indigoid, quinacridone, oxazine, anthraquinone, carbonium, and xanthene organic pigments can be used. As a commercially available purple pigment, for example, SA Violet C12896 (Mikuni Color Co., Ltd.) can be used.

Examples of blue pigments include ultramarine, azurite, prussian blue (prussian blue), ultramarine blue, smalt, cobalt blue (cobalt aluminate), cerulean blue (cobalt stannate), cobalt chrome blue, cobalt/aluminum/silicon oxide, Cobalt-zinc-silicon oxide, manganese blue, phthalocyanine, etc. can be used. As a commercially available blue pigment, for example, EMT-Blue DS-18 (Toyo Ink Mfg. Co., Ltd.) can be used.

The total content of the purple pigment and the blue pigment in the coating layer 4 is preferably 0.1-1.4 mg/m ² , more preferably 0.2-0.6 mg/m ² , and particularly preferably 0.3-0.6 mg/m 2 . 0.45 mg/m ² . If the total content is less than the above range, the pigment may not sufficiently absorb light, and high opacity may not be obtained. On the other hand, if the total content exceeds the above range, the hue deviates greatly from the origin (see FIG. 2), and the apparent whiteness may be lost.

The total content of the purple pigment and the blue pigment in the coating layer 3 is preferably 0.001 to 0.005 parts by weight, more preferably 0.0015 parts by weight, based on 100 parts by weight of the white pigment described later, in terms of solid content. to 0.0035 parts by mass, particularly preferably 0.002 to 0.003 parts by mass. If the total content is less than the above range, the opacity of the coated paper 1 may be insufficient, and the desired hue may not be achieved. On the other hand, if the total content exceeds the above range, the brightness of the coated paper 1 may be insufficient.

In addition, the said total content is the value calculated by the following formulas.
Total content of purple pigment and blue pigment (mg/m ² ) = (total coating amount (g/m ² ) x total mass of purple pigment and blue pigment (parts by mass)/total solid content in coating solution Parts by mass (parts by mass)) x 1000
In addition, the said mass part is a value at the time of solid content conversion.

(other pigments)
Pigments other than violet pigments and blue pigments, such as red pigments, yellow pigments, green pigments, and the like, can also be contained as the coloring material, if necessary. In addition, it is not preferable to contain a black pigment as a coloring material. If a black pigment is contained, the brightness of the coating layer 4 may be lowered, and the coated paper 1 may not have the desired brightness or clearness after printing.

(Fluorescent brightener)
By including the fluorescent brightening agent in the coating layer 4, the coating layer 4 can be colored and the brightness can be improved.

Examples of fluorescent brighteners that can be used include stilbenzene-based, benzimidazole-based, imidazole-based, imidazolone-based, virazolin-based, coumarin-based, and naphthalimide-based fluorescent brighteners. As a commercially available fluorescent brightening agent, for example, Kayahole SIM (L) (manufactured by Nippon Kayaku Co., Ltd.) can be used.

However, as the fluorescent brightening agent, a stilbenzene-based stilbenzylsulfonic acid derivative is preferably used, and more preferably a tetra-type one in which four sulfo groups are derived. When the coated paper 1 is made, waste paper or the like at the time of paper making is usually blended as a circulating raw material. Therefore, by using a tetra-type fluorescent brightening agent, it is possible to suppress excessive coloring of the base paper 2 and fading of brightness.

The total content of the fluorescent brightening agent in the coating layer 4 is preferably 10-80 mg/m ² , more preferably 15-70 mg/m ² , and particularly preferably 20-45 mg/m ² . If the total content is less than the above range, the desired brightness and hue of the coated paper may not be obtained. On the other hand, if the total content exceeds the above range, the color of the fluorescent brightening agent itself may appear, resulting in a decrease in brightness and a strong effect of fading.

The total content of the fluorescent brightening agent in the coating layer 4 is preferably 0.05 to 0.8 parts by mass, more preferably 0.15 to 0.6 parts by mass, with respect to 100 parts by mass of the white pigment described later. , and particularly preferably 0.2 to 0.4 parts by mass.

In addition, the said total content is the value calculated by the following formulas.
Total content of fluorescent brightening agent (mg/m ² ) = (total coating amount (g/m ² ) × total mass of fluorescent brightening agent (parts by mass)/total solid mass in coating solution (parts by mass)) × 1000
In addition, the said mass part is a value at the time of solid content conversion.

(white pigment)
The coating layer 4 is made to contain a white pigment, if necessary.

The white pigment may be an inorganic pigment or an organic pigment.

Examples of white pigments include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica. , satin white, etc. can be used.

However, from the viewpoint of improving the whiteness, it is preferable to use heavy calcium carbonate or light calcium carbonate, and it is particularly preferable to use light calcium carbonate.

The content of precipitated calcium carbonate is preferably 70% by mass or more, more preferably 72% by mass or more, and particularly preferably 75% by mass or more, based on the total amount of the white pigment.

(glue)
Examples of adhesives (binders) include styrene-butadiene-based adhesives, styrene-acrylic-based adhesives, ethylene-vinyl acetate-based adhesives, butadiene-methyl methacrylate-based adhesives, vinyl acetate-butyl acrylate-based adhesives, polyvinyl Alcohol, casein, soybean protein, synthetic protein, oxidized starch, positive starch, urea phosphate esterified starch, carbamate esterified starch, hydroxyethyl etherified starch, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, etc. can be used. .

The amount of the adhesive compounded is preferably 2 to 15 parts by mass, more preferably 3 to 12 parts by mass, and particularly preferably 5 to 11 parts by mass, based on 100 parts by mass of the white pigment described above, in terms of solid content. .

(others)
The coating layer 4 may contain various auxiliary agents such as a dispersant, a thickener, a water retention agent, an antifoaming agent, and a water resistance agent, if necessary.

The coating layer 4 can be formed using a coater such as a size press coater, a gate roll coater, a rod metering coater, a Billboud coater, and a blade coater. However, when the coating layer 4 is a single layer, especially when the coated paper 1 is lightly coated paper with a basis weight of 60 g/m ² or less, film transfer using a gate roll coater, rod metering coater, etc. It is preferable to form the coating layer 4 by the method. In the case of lightly coated paper, when formed by a film transfer method, even if the coating amount is as low as 5.0 to 8.0 g / m ² per side, it can be coated efficiently. (improved operability). In addition, when light calcium carbonate is used as a white pigment in the coating layer 4, the particle size distribution of the particle size is sharper than that of heavy calcium carbonate. tends to get worse. However, in the film transfer coating method, the coating can be applied even at a coating amount of 5.0 to 8.0 g/m ² .

The coating amount of the coating layer 4 is preferably 5.0 to 8.0 g/m ² , more preferably 5.2 to 7.5 g/m ² , particularly preferably 5.5 to 7.0 g/m 2 per side. / ^m2 . If the coating amount is less than the above range, the ratio of the coating layer 4 to the entire coated paper 1 is small, and there is a risk that the desired brightness and hue cannot be obtained. On the other hand, if the coating amount exceeds the above range, the ratio of the base paper 2 to the entire coated paper 1 is small, and the desired opacity may not be obtained.

(Coated paper for printing)
(basis weight)
The basis weight of the coated paper 1 is preferably 40-60 g/m ² , more preferably 42-59 g/m ² , particularly preferably 45-58 g/m ² . In the case of lightly coated paper, particularly when the basis weight is 60 g/m ² or less, the effects of the present invention are fully exhibited. However, if the basis weight is less than 40 g/m ² , the opacity may be insufficient.

(Opacity)
The opacity of Coated Paper 1 is a value measured according to JIS P8149.

The opacity is preferably 85% or higher, more preferably 86% or higher, particularly preferably 87% or higher. To adjust the opacity to the above range, for example, the amount of deinked pulp (DIP) or ash in the base paper 2 may be adjusted, or the coloring of the coating layer 4 may be adjusted.

The ash content of the base paper 2 is preferably a value measured according to JIS P 8251 (525° C.), taking into account not only opacity but also lightness and stiffness of coated paper. 3.0 to 9.5%, more preferably 4.0 to 9.3%, particularly preferably 5.0 to 9.0%.

(brightness)
The brightness of the coated paper 1 is a value measured according to JIS P 8150, including ultraviolet rays.

The brightness of the coated paper 1 is preferably 85% or higher, more preferably 86% or higher, particularly preferably 87% or higher. To adjust the lightness to the above range, for example, the amount of deinked pulp (DIP) or ash in the base paper 2 may be adjusted, or the coloring of the coating layer 4 may be adjusted.

(hue)
The hue of the coated paper 1 is a value measured according to JIS P 8150, including ultraviolet rays.

In this hue, the a ^* value is preferably 0.5 or more and less than 2.5, more preferably 0.6 or more and less than 2.0, and particularly preferably 0.7 or more and less than 1.8. The b ^* value is preferably −5 or more and less than −2, more preferably −4.8 or more and less than −2.5, and particularly preferably −4.6 or more and less than −2.8. When the hue (a ^* value and b ^* value) is within the above range, the surface of the coated printing paper 1 becomes bluish and white in appearance stands out.

Hue (a ^* and b ^* values) can be controlled by adding violet and blue pigments.
FIG. 2 shows L ^* a ^* b ^* system chromaticity coordinates. L ^* in the figure represents the degree of black and white in lightness. When a ^* is + (plus), it increases the degree of redness, and when it is - (minus), it increases the degree of greenness. When b ^* is + (plus), the degree of yellowness increases, and when it is - (minus), the degree of bluishness increases. If the case where no purple pigment or blue pigment is added is positioned at the origin, when the blue pigment is added, b* changes to - (minus) and a* also changes to - (minus). Also, when a purple pigment is added, the hue changes toward - (minus) for b* and + (plus) for a*.

Next, examples of the present invention will be described. In addition, the present invention is not limited at all by the following examples. Various modifications can be made without departing from the gist of the invention.
(Test example 1)
Hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), and deinked pulp (DIP) were used as raw material pulp to obtain a pulp slurry. The mixing ratio of each raw material pulp was as shown in the table below. Light calcium carbonate (Tamapearl TP121-6S (manufactured by Okutama Kogyo Co., Ltd.), TAMAPEARL is a registered trademark), a coagulant, a retention agent, and a paper strength agent were internally added to the pulp slurry.

The obtained pulp slurry was made into paper by a gap former to obtain a base paper.

An oxidized starch was undercoated on the resulting base paper. The coating amount was 0.8 g/m ² on both sides.

On the other hand, an adhesive, a coloring material, a white pigment, and a fluorescent whitening agent were mixed to obtain a coating liquid.

SB latex (PB2901 (manufactured by Nippon A&L Co., Ltd.)) and starch (RC#20 (manufactured by Nihon Shokuhin Kako Co., Ltd.)) were used as the adhesive. As color materials, a purple pigment (SA Violet BOX (manufactured by Mikuni Color Co., Ltd.)) and a blue pigment (SA Blue 12422 (manufactured by Mikuni Color Co., Ltd.)) were used. As white pigments, heavy calcium carbonate (Carbital 90 (manufactured by Imerys Minerals Japan), CARBITAL is a registered trademark) and clay (KAOFINE (manufactured by Shiraishi Calcium)) were used. (ZDMV (L) (manufactured by Blancophore)) was used as the fluorescent brightener. The mixing ratios of these various materials were as shown in the table below.

Using the obtained coating solution, coating layers were formed on both sides of the base paper (undercoat coating layer). This formation was performed by a film transfer method. The coating amount of the coating layer was as shown in the table below.

The basis weight, opacity, brightness, and hue of the coated paper thus obtained were examined. The results are shown in the table below.

Subsequently, solid printing of indigo, red, and yellow was performed on the obtained coated paper by an offset rotary printing machine, and the three-color overlapping portion was measured by a Macbeth reflection densitometer RD-918 (manufactured by Colmorgen Corporation, USA). , the three-color multiplication portion was measured. Printing was performed so that the ink density was 2.0. The coated paper (printed matter) after printing was sensory evaluated for strike-through and definition. The results were as shown in the table below. In addition, the evaluation criteria of sensory evaluation were as follows.

(back through)
The printed material was visually observed from the back side of the printed surface under an indoor fluorescent light, and evaluated according to the following four grades.
◎: There is no set-off (bleed-through) 〇: Set-off is slightly observed, but it is hardly noticeable and there is no practical problem △: Some set-off is observed, and it is somewhat difficult to put it to practical use Case ×: Set-off is severe and not practical at all

(Sharpness)
An arbitrary number of 30 people visually inspected the boundary between the printed part and the blank part of the printed matter under indoor fluorescent light, and evaluated 5 points (5: the boundary between the printed part and the blank part of the printed matter was clearly visible, and the blank part is clear and bright white>1: The border between the printed portion and the blank portion of the printed matter appears blurred, and the blank portion appears dull and dark white). The obtained evaluation values were averaged and classified into the following four grades.
A: When the average value is 4.0 or more. It can be said that it is suitable as printing paper.
O: When the average value is 3.5 or more. It can be said that there is no problem in use as printing paper.
Δ: When the average value is 3.0 or more. It can be said that it is somewhat difficult to put it to practical use as printing paper.
×: When the average value is less than 3.0. It can be said that it is not suitable as printing paper.

(Other test examples)
The same test as in Test Example 1 was performed by changing the raw materials and blending ratios of the coated paper as shown in the table below. The results are shown in the table below.

As the black pigment, SA Black 5207 (manufactured by Mikuni-Color Co., Ltd.) was used. As light calcium carbonate, Tamapearl TP-121-7C (manufactured by Okutama Kogyo Co., Ltd., Tamapearl \TAMAPEARL is a registered trademark) was used.

(Discussion)
From the test examples, it was found that lack of even one blue pigment, violet pigment, and optical brightener results in insufficient opacity, brightness, or sensory evaluation.

INDUSTRIAL APPLICABILITY The present invention is applicable as a coated printing paper that can be used as a coated paper for offset printing or the like.

DESCRIPTION OF SYMBOLS 1... Coated paper, 2... Base paper, 3... Undercoat coating layer, 4... Coating layer.

Claims (5)

A coated paper having a base paper and a coating layer,
The coating layer contains both a purple pigment and a blue pigment, and an optical brightener,
The opacity of JIS P 8149 of the coated paper is 85% or more, the brightness of JIS P 8150 is 85% or more in the measurement including ultraviolet rays,
The base paper contains deinked pulp as raw material pulp, and the content of the fluorescent brightener in the coating layer is 10 to 80 mg/m ² ,
The ash content of the base paper measured according to JIS P 8251 (525 ° C.) is 3.0 to 9.5%.
A coated printing paper characterized by: The fluorescent brightening agent is a tetra-type stilbenzene-based stilbenzylsulfonic acid derivative in which four sulfo groups are induced.
The coated printing paper according to claim 1. 3. The coated printing paper according to claim 1, wherein deinked pulp as raw material pulp for said base paper accounts for 30 to 45% by mass of all raw material pulp on an absolute dry basis. The JIS P 8150 hue of the coated paper is less than b* value -2 in measurements including ultraviolet light.
The coated printing paper according to any one of claims 1 to 3. The JIS P 8150 hue of the coated paper has an a* value of 0.5 or more and less than 2.5 and a b* value of -5 or more and less than -2 in a measurement including ultraviolet light.
The coated printing paper according to any one of claims 1 to 4.

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