JPH05148796A - Coated paper for printing - Google Patents

Abstract

PURPOSE:To obtain coated paper for printing, having a high coated layer strength and offset printability capable of withstanding high-speed offset printing and high blister fitness in offset rotary printing and useful for double coating. CONSTITUTION:Coated paper for printing is obtained by coating with a coating composition for topcoating layer provided in at least two layers for each one side at a high solid concentration. The coating composition is composed of at least two kinds of pigments having a specific particle size and a synthetic polymer latex. Thereby, operating efficiency is improved without causing streaks or scratches, etc., and coated paper is excellent in coated layer strength, blister fitness, printing gloss and inking properties without any unevenness of inking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel coated paper, which has good coatability in a blade coater, excellent offset printability, and particularly excellent offset rotary printability. It is related to the coated paper.

[0002]

2. Description of the Related Art In recent years, the speed of offset printing has increased,
There is a demand for a coated paper for printing that does not impair the printability such as coating layer strength that can withstand it, printing gloss and ink receptivity, that is, aesthetics. Particularly, in rotary offset printing, since printing is performed at a very high speed, a coating layer having high strength that can withstand high-speed printing and a property that does not cause blistering caused by drying after printing are also required. ing.

In order to obtain high coating layer strength in response to these requirements, the amount of binder such as starch or synthetic polymer latex is generally increased. However, increasing the amount of the binder reduces voids in the coating layer, leading to deterioration in ink receptivity and occurrence of blisters. In particular, when the amount of starch is increased, the viscosity of the coating liquid at the time of coating increases, causing streaks, scratches, and the like, which also lowers the suitability for coating.

In order to improve the printing gloss, a pigment having a high aspect ratio (delaminated clay, talc, etc.) is mixed in the coating composition, and the gel amount showing the degree of the crosslinked structure of the synthetic polymer latex. However, in the case of the former, the viscosity of the coating solution increases, handling during preparation is difficult, and streak, scratches, etc. occur, and the coating suitability also decreases. It is necessary to lower the coating liquid concentration. As a result, the migration of the coating composition to the surface of the coating layer and the permeation into the base paper layer become non-uniform, causing unevenness of ink inking called mottling. On the other hand, increasing the gel amount reduces the voids in the coating layer, resulting in the formation of blisters.

In order to improve ink receptivity, a hydrophilic monomer typified by carboxylic acid is introduced at the time of polymerizing a synthetic polymer latex, or the coating composition is finely aggregated to make it porous. An amide monomer is introduced in order to form a proper coating layer, but the viscosity of the coating solution increases, so streaks, scratches, etc. occur and the coating suitability deteriorates. Further, if the solid content concentration of the coating liquid is lowered in order to improve the coating suitability, ink unevenness due to it will occur and the appearance of the printed matter will be impaired.

In order to avoid the occurrence of blister, the internal bond strength of the base paper and the porosity of the coating layer are related (for example, Tappi, 50 (1): 14 (196).
7)), In the base paper formulation, there is a means for designing by increasing the internal bond strength of the base paper so as to withstand the water vapor pressure generated when the ink is dried.
Increasing the internal bond strength of the base paper by impregnating it with polyvinyl alcohol or the like deteriorates the suitability for offset breakage printing, which is one of the suitability for offset rotary printing, and cannot be increased so much. In addition, in the formulation of the coating liquid, there is a method of increasing the porosity of the coating layer to disperse the water vapor pressure and further increase the air permeability.
However, in order to increase the porosity of the coating layer, if the amount of the binder or the amount of gel is decreased, or if a commercially available paper-making chemical such as a printability improver such as a melamine-formaldehyde resin or a polyamideurea-formaldehyde resin is added, the former In this case, it is necessary to considerably reduce the amount of binder or gel, and it is not possible to obtain a coating layer strength that can cope with recent printing speeds. In the latter case, the viscosity of the coating liquid increases, so streaks, scratches, etc. occur and the coating suitability deteriorates. To improve the coating suitability, lower the solid content concentration of the coating liquid. The need arises, and ink unevenness associated with it is generated, impairing the aesthetic appearance of the printed matter.

[0007] In offset printing, the unevenness of ink inking that causes the appearance of the printed matter to be impaired is caused by the fountain solution transferred to the paper or the uneven penetration of the ink. This is due to the non-uniformity of the coated paper surface, and in general, in order to suppress this, partial migration to the surface of the coating composition and the drying conditions of the coated coating liquid and It controls the penetration into the base paper. However, when the solid content concentration of the coating liquid is low, the coating liquid partially penetrates into the base paper before drying the coating liquid, and drying control can suppress the occurrence of ink inking unevenness. Can not. For this reason, increasing the sizing degree of the base paper and accelerating the immobilization of the coating liquid are desirable as countermeasures.

However, due to the presence of the sizing agent, the strength of the base paper is lowered, and on the contrary, foreign matter which is a seed for the generation of streaks and scratches is likely to occur. In addition, there is a coating solution with a high solid content concentration as a method of accelerating immobilization, but coating with a solid content concentration that does not cause ink unevenness is a coating solution under a high shear rate. Since the shearing stress of No. 2 increases, it is necessary to control the coating amount corresponding to the stress. As a result, in the blade coater commonly used today,
Although it is necessary to increase the pressure applied to the blade, the surface coated with a high blade pressure is likely to be roughened, resulting in poor smoothness and reduced gloss. Further, due to the high blade pressure, paper breakage, streaks, scratches and the like are likely to occur and the operability of the coater is reduced. For these reasons, it is the current situation that the solid content concentration cannot be made too high.

Regarding the coating solution having a high solid content, as shown in Japanese Patent Publication No. 2-480, the particle size of the pigment in the coating composition is regulated so that the fluidity at a high shear rate is obtained. To improve problems in coater operation.
It is not always possible to obtain sufficient effects. This is because streaks, scratches, etc. occur not only in the fluidity of the coating liquid, but also in the support on which the coating liquid is coated, that is, the base paper absorbs the water in the coating liquid to reduce the concentration of the coating liquid. This is because it is also generated when the fiber is raised or the filler is not fixed on the surface of the base paper. Generally, in a blade coater, an application mechanism such as a roll or a nozzle is used to supply the coating liquid to the base paper, and then the blade is scraped to a prescribed coating amount. At this time, after being applied, by the time it reaches the blade, the water in the coating solution penetrates into the base paper, but the coating solution with a high degree of this penetration, that is, if the water retention is poor, At this time, the fluidity of the coating liquid is considerably deteriorated due to the influence of the increase in the solid content concentration, which causes problems in coater operation.

From this, in order to supplement the water retention of the coating solution having a high solid content, for example, as shown in Japanese Patent Publication No. 1-22399, the time from the applicator to the blade is short, that is, There is a coater application in which the penetration time of water in the coating liquid into the base paper is shortened.However, the coating paper produced with such a coater has water penetration from the coating liquid after passing through the blade. Therefore, there is a drawback that the fibers are swollen and inferior in smoothness. Further, even if the sizing of the base paper is increased, static water permeation can be suppressed, but water permeation at the time of application under high fluid pressure such as a roll of a high speed blade coater or a nozzle cannot be suppressed. Furthermore, the occurrence of streaks, scratches, etc. is not only caused by the fluidity of the coating liquid, but when fibers or fillers that have not been fixed on the surface of the base paper are present, they become detached as nuclei under the blade. There are also many.

It is also possible to prevent the migration of water from the top coating liquid to the base paper by forming a coating layer by performing multi-layer coating, that is, by providing an undercoat layer.
By providing the undercoat layer, the smoothness of the surface of the undercoat layer is improved, there is no escape place for foreign matters and the like during the application of the overcoat coating liquid, and streaks and scratches are likely to occur. In addition, the presence of the sizing agent lowers the strength and may cause streaks to increase streaks and scratches. Since the binder in the undercoat layer penetrates into the base paper layer, it is necessary to add a large amount of binder in the undercoat layer when the coating amount of the undercoat layer is small. As a result, the undercoat layer is formed with a binder film that is less likely to allow water vapor to permeate, and thus blisters are likely to occur.

[0012]

In view of the present situation, an object of the present invention is to provide a coating for printing which has excellent operability in a blade coater, and has high offset printing suitability, particularly high offset rotary printing suitability. To obtain paper with excellent runnability.

[0013]

Means for Solving the Problems As a result of various studies to achieve the above object, the inventors of the present invention have found that a coating layer containing a pigment and a binder as main components is two layers per one side of a support. In the provided coated paper for printing, the coating composition for the overcoat layer contains (a), (b) and (c) below as essential components, and the kaolin and the ground calcium carbonate are 20-80% by weight and 80-20% by weight in the total pigment,
The synthetic polymer latex is contained in an amount of 5 to 15% by weight based on all pigments, and the solid content concentration of the coating composition at the time of coating is
The coated paper for printing is characterized by being 65 to 73% by weight. (A) Kaolin having a particle size of 0.5 μm or less of 40% by volume or more. (B) Heavy calcium carbonate having a particle size of 2.0 μm or less and 90% by volume or more. (C) A synthetic polymer latex having an average particle size of 0.05 to 0.10 μm.

In the coated paper for printing of the present invention, it is desirable that the amount of the binder blended in the coating composition for the undercoat layer is 5 to 50% by weight based on all pigments.

Further, if the coating amount of the coating composition for the undercoat layer is 10 g / m ² or less, the effect of the present invention is certain.

The coated paper for printing applied to the present invention has a two-layer structure in which an undercoat layer is provided on a support, that is, a base paper, and an overcoat layer is provided thereon, and this structure is provided on one side or You may provide on both sides. By providing the undercoat layer, desorption of unfixed fibers and fillers present on the surface of the base paper, further operability of the coater due to an increase in the concentration of the overcoat coating liquid due to the movement of water to the undercoat layer, especially streak,
The occurrence of scratches can be prevented and productivity can be improved. Further, since the binder permeation speed of the overcoat coating liquid is slowed, the binder remains uniformly in the overcoat coating liquid, and ink unevenness is not generated, and a printing coated paper with high printing gloss can be obtained. ..

By providing the undercoat layer, it is possible to prevent the occurrence of streaks, scratches, etc. as described above, but the smoothness of the surface of the undercoat layer becomes too high, and the high coating liquid of the topcoat coating has a high cutoff. If the fluidity at a low speed is poor, there is no escape for fine foreign matter or soft agglomerates in the coating liquid, and streaks and scratches are likely to occur. Therefore, it is necessary to improve the fluidity of the top coating liquid.

The pigment of the coating composition for the overcoat layer applied to the present invention includes kaolin having a particle diameter of 0.5 μm or less of 40 vol% or more and heavy pigment having a particle diameter of 2.0 μm or less of 90 vol% or more. It is necessary to use calcium carbonate. When kaolin having a particle size of 0.5 μm or less is less than 40% by volume, streaks, scratches, etc. occur during coating, good coater operability cannot be obtained, and the coating amount increases, so There is also a problem of coating amount control such that it becomes difficult to obtain the coating amount. In addition, high gloss cannot be obtained unless the ground calcium carbonate has a particle size of 2.0 μm or less and 90% by volume or more. Further, the kaolin is present in the total pigment in an amount of from 20 to 80% by weight, and the heavy calcium carbonate is in an amount of from 80 to 20% by weight, that is, the kaolin and the heavy calcium carbonate are allowed to coexist in a specific range. Good coater operability, control of coating amount, and high gloss can be obtained. However, when the kaolin content is less than 20% by weight or when the ground calcium carbonate content is less than 20% by weight, good coater operability cannot be obtained, and when the kaolin content exceeds 80% by weight. It becomes difficult to control the coating amount, and the coating layer strength also decreases. Further, when the heavy calcium carbonate exceeds 80% by weight, the water retention is lowered, streaks and scratches are likely to occur, and gloss is also lowered.

As a binder, 0.05 to 0.10 μ
5 to 15% by weight of a synthetic polymer latex having a particle diameter of m is mixed with all pigments to obtain fluidity under a high shear rate, strength without blistering under high speed offset printing conditions, and blister. It is possible to obtain a coated paper for printing that does not generate
When the particle size of the synthetic polymer latex exceeds 0.10 μm or when the compounding amount of the synthetic polymer latex is less than 5% by weight, sufficient coating layer strength cannot be obtained,
If the blending amount of the synthetic polymer latex exceeds 15% by weight, blisters occur. Furthermore, the solid content concentration of the coating composition for the overcoat layer during coating is 65 to 73% by weight.
In the above, it is possible to obtain satisfactory offset printing suitability in terms of operability with a coater, gloss, coating layer strength, ink receptivity, uneven ink replenishment, occurrence of blisters, and the like. When the solid content concentration is less than 65% by weight, the distance between the pigments in the coating liquid of the overcoat layer becomes large, so that the history remains even after drying, that is, the distance between the pigments is It is large and the binder required for adhering the pigments to each other is insufficient, so that the coating layer strength is reduced, and blistering occurs when a large amount of binder is blended in order to cope with it. In addition, the permeation of the coating composition results in an uneven distribution, which causes unevenness of ink inking. With a coating liquid having a solid content concentration of more than 73% by weight, it becomes difficult to control the coating amount.

The amount of the binder blended in the coating composition for the undercoat layer applied to the present invention is 5 to 50 with respect to all pigments.
When the content is 5% by weight, it is possible to obtain a high-coating strength and a coated paper for printing which does not cause blister generation.
If it exceeds, blisters will occur.

Usually, when an undercoat layer is provided, blisters are likely to occur, and blisters are likely to occur even if the particle size of the synthetic polymer latex is reduced. However, since the coating layer strength can be improved, the amount of the binder in the topcoat layer can be reduced, and the higher coating concentration can be obtained by increasing the concentration of the topcoat liquid. Since the amount can be further reduced, the occurrence of blisters can be avoided.

The coating amount of the coating composition for the undercoat layer applied to the present invention is preferably 10 g / m ² or less.
When it is at least g / m ² , the smoothness of the undercoat layer becomes too high, and it becomes impossible to suppress the occurrence of story and scratches.

As the pigment in the coating composition for the overcoat layer used in the present invention, a pigment other than those described above can be mixed and used. For example, kaolin or heavy calcium carbonate other than those specified above, light calcium carbonate, satin white, talc, titanium oxide, aluminum hydroxide, silica, zinc oxide, activated clay, silicon earth, barium sulfate, calcium sulfate, plastic pigment. Etc. can be blended.

The synthetic polymer latex in the coating composition for the overcoat layer used in the present invention includes acrylic, styrene-acrylic, styrene-butadiene, vinyl acetate-
Various copolymers such as acrylic, butadiene-methylmethacrylic, vinyl acetate-butyl acrylate, etc. can be used. Further, other binders may be used, such as synthetic binders such as polyvinyl alcohol, oxidized starch, etherified starch, esterified starch, enzyme-modified starch and cold water-soluble starch obtained by flash-drying them, casein, soybean protein, etc. Natural binders of In addition, if necessary, a dispersant, a thickener, a water retention agent,
Various commonly used auxiliaries such as a defoaming agent, a water resistant agent, and a coloring agent can be appropriately used.

Examples of the pigment in the coating composition for the undercoat layer used in the present invention include kaolin, heavy calcium carbonate, light calcium carbonate, satin white, talc, titanium oxide,
Aluminum hydroxide, silica, zinc oxide, activated clay, silicon earth, barium sulfate, calcium sulfate, plastic pigment and the like can be added.

The synthetic polymer latex in the coating composition for the undercoat layer used in the present invention includes acrylic, styrene-acrylic, styrene-butadiene, vinyl acetate-
Various copolymers such as acrylic, butadiene-methylmethacrylic, vinyl acetate-butyl acrylate, etc. can be used. Further, other binders may be used, such as synthetic binders such as polyvinyl alcohol, oxidized starch, etherified starch, esterified starch, enzyme-modified starch and cold water-soluble starch obtained by flash-drying them, casein, soybean protein, etc. Natural binders of In addition, if necessary, a dispersant, a thickener, a water retention agent,
Various commonly used auxiliaries such as a defoaming agent, a water resistant agent, and a coloring agent can be appropriately used.

The pigment in the coating composition for the overcoat layer specified in the present invention significantly improves the fluidity of the coating liquid prepared by the coating composition, but it is not sufficient, and higher flowability is obtained. In order to obtain the property, it is necessary to mix the synthetic polymer latex having the particle size specified in the present invention as a binder. However, the occurrence of streaks, scratches, etc., which are problems in coater operation, is not only due to the fluidity of the coating liquid, but the degree of penetration of water in the coating liquid into the base paper and the fixing that exists on the base paper surface. Unused fibers and fillers are also a significant cause. Therefore, by providing an undercoat layer to cover the surface of the base paper and slowing the permeation speed of the coating liquid into the base paper, and preventing the detachment of fibers and fillers, it is only for printing that complete streaks and scratches do not occur. It is possible to manufacture coated paper. Moreover, this undercoat layer is
It is also possible to delay the permeation that occurs from the coating of the coating composition of the overcoat layer to the drying, so that the coating composition of the overcoat layer is coated at a solid content concentration of 65% by weight or more as in the present invention. When used in combination with offset printing suitability, that is, coating layer strength, ink receptivity, ink receptivity unevenness, printing gloss, etc., it is possible to significantly improve the blister in offset rotary printing suitability. Incidentally, when the undercoat layer is not provided, coater operability at the time of coating the topcoat layer with a high solid content concentration is lowered, and when the topcoat layer is not coated with a high solid content concentration, the undercoat layer is Even if it is provided, in recent years, it is not possible to obtain a satisfactory printability corresponding to an offset printing machine which is becoming faster.

The base paper used in the present invention is LBKP, N
Chemical pulp such as BKP, GP, PGW, RMP, TM
Mechanical pulp such as P, CTMP, CMP, CGP, DI
Including pulp such as waste paper pulp such as P, light calcium carbonate, heavy calcium carbonate, talc, clay, various fillers such as kaolin, sizing agents, fixing agents, retention agents, cationizing agents, paper strengthening agents, etc. It contains various additives and is made acidic, neutral or alkaline. As the base paper of the present invention, a non-size press base paper, a size press or anchor-coated base paper with starch, polyvinyl alcohol or the like is used.

The method of applying the coating composition for the undercoat layer according to the present invention to the base paper is not particularly limited, and various blade coaters, roll coaters, air knife coaters, bar coaters, rod blade coaters, short dwell coaters, Various coating devices such as the above can be used on-machine or off-machine. The method for applying the coating composition for the overcoat layer according to the present invention is not particularly limited, but blade coating is preferably performed on-machine or off-machine. As the blade coater, bevel type or bent type blade coater, bill blade,
A rod blade, a short dwell coater, a twin blade, etc. are used.

The coated paper obtained by coating the coating composition of the present invention is commercialized as a printing coated paper using a finishing device such as a super calendar, a gloss calendar, a soft calendar, etc. It is possible to obtain a matte printing coated paper having a low gloss with or without finishing treatment. Further, the printing coated paper of the present invention can be offset printed by either sheet-fed or wound. Further, gravure printing or flexographic printing can be applied.

[0031]

EXAMPLES The effects of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Further, "parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively. The various measured values in the examples are obtained by the following methods.

1) Particle size distribution of pigment: 0.1 part of commercially available sodium polyacrylate (100 parts of pigment) was added to the pigment and the dispersed slurry was sampled to obtain a Microtrack particle size analyzer (model 7995-30; Nikkiso) to measure the particle size distribution. 2) B-type viscosity: using a B-type viscometer, a temperature of 25 ° C., 60
Measured in rpm. 3) White paper glossiness: Measured at an angle of 75 degrees according to JIS P8142. 4) Double-color printing glossiness: A sample was printed on a Roland offset printing machine, left at room temperature for one day, and then black,
Cyan, magenta, and yellow four-color overprinting solid print portions were measured at an angle of 60 degrees. 5) Coating strength: I using a RI printing machine (manufactured by Akira Seisakusho)
Printing was performed with the PI ink (No. 8), and the degree of peeling of the printed surface was visually evaluated in three grades (3: good, 2: acceptable, 1: not possible).
The actual level of offset printing is 2 or higher. 6) Ink ink receptivity: A sample was printed on a Roland offset printing machine, and the degree of ink receptivity at a dot rate of 50% was visually checked.
A graded evaluation (3: good, 2: acceptable, 1: not possible) was performed. When the evaluation value is 1, the ink receptivity is poor. 7) Ink inking unevenness: A sample is printed by a Roland offset printing machine, and three-color overprinting of cyan, magenta, and yellow is performed, and unevenness of inking in a solid printed portion is visually evaluated in three stages (3: good, 2: acceptable, 1: No) When the evaluation value is 1, unevenness of ink inking is conspicuous and spoils the appearance of the printed matter. 8) Blister suitability: A commercially available offset rotary printing ink was printed on both sides of the sample by an RI printing machine (manufactured by Akira Seisakusho), and dried and conditioned (20 ° C., 65 RH%). Then, the sample was wrapped in an aluminum foil and placed in silicone oil at 250 ° C. for 3 seconds, and the occurrence of blisters was visually evaluated in 3 grades (3: good, 2: acceptable, 1: not possible). A level of 2 or more is not a problem in an actual offset rotary printing press. 9) Coater operability: Occurrence of streaks, scratches, etc. when coated with a blade coater was visually evaluated in three grades (3: good, 2: acceptable, 1: not possible). It is 1 that shows a decrease in productivity, such as running out of paper or becoming a product. 10) Control of coating amount: When the coating liquid was scraped off with a blade coater and the coating amount was controlled, the stress applied to the blade was evaluated in three grades (3: good, 2: acceptable, 1: not possible). If the evaluation value is 1, the stress is too high and paper breakage occurs, resulting in lower productivity and smoothness of the coated paper surface, leading to lower quality. Becomes

Examples 1 to 6 <Raw paper blending> The following pulp and internal additive chemicals were prepared, and the raw paper made into a paper having a basis weight of 50 g / m ² (absolutely dry) was used. (Pulp) -LBKP (water level 350mlcsf) 70 parts-NBKP (water level 420mlcsf) 30 parts (internal additive) -Calcium carbonate 10 parts-Commercial alkyl ketene dimer internal additive sizing agent (AKD) 0.03 part・ Commercially available cationic polyacrylamide retention aid 0.03 parts

<Composition of Undercoat Layer> 0.1 part of a commercially available polyacrylic acid-based dispersant was added to the following pigment to disperse it, and then the binder amount shown in Table 1 was added to prepare a coating solution for the undercoat layer. The pH was adjusted to 9.5 with ammonium hydroxide, and the concentration of this coating solution was adjusted to 48%. This coating solution was applied to both sides by a gate roll coater (abbreviated as GRC) so that the coating amount per one side was 5 g / m ² . (Pigment) -Calcium carbonate (Escalon # 1500: Sankyo Seiko Co., Ltd.) 100 parts (Binder) -Phosphate esterified starch (MS4600: Nippon Shokuhin Kako Co., Ltd.) 12 parts-Styrene butadiene latex (0617: Nippon Gosei Gomu Co., Ltd.) ) 13 copies

<Composition of Topcoat Layer> The coating compositions for the topcoat layer shown in Table 1 were compounded using the following pigments, binders and water retention agents. The coating liquids for these coating compositions were prepared by using a Choles disperser, 0.3 parts of commercially available calcium stearate was added at the final stage, and the pH was adjusted to 9.5 with sodium hydroxide. It was adjusted to the coating solution concentration shown in. These coating solutions were applied to both surfaces of the undercoat layer shown in Table 1 at a coating amount of 15 g / m ² per side using a blade coater at a speed of 1000 m / min. The obtained coated paper is a super calendar finishing device (number of stages: 10 stages, rigid roll: chilled roll with outer diameter of 400 mm, elastic roll: cotton roll with outer diameter of 420 mm, linear pressure: 220 kg / c
m) was used for calendering. (Pigment) -Kaolin A: The Caulim da Amasonia
Particle size 0.5 μm or less 42% by volume Kaolin B: Hydrasperse (manufactured by Huber);
Particle size 0.5 μm or less 11% by volume Calcium carbonate A: Escalon # 1500 (manufactured by Sankyo Seiki Co., Ltd.) was added with 1 part of a commercially available polyacrylic acid-based dispersant to obtain a slurry. Mitsui Miike Co., Ltd.) and pulverized twice. This calcium carbonate has a particle size of 2 μm
The following was 89% by volume. (Binder) -Phosphate esterified starch (MS4600: Nippon Shokuhin Kako Co., Ltd.)-Latex A: Calvoxy-modified styrene-butadiene latex; average particle diameter 0.052 μm-Latex B: Caloxy-modified styrene-butadiene latex; average particle diameter 0.097 μm latex The average particle size of the above was obtained by treating the latex with osmic acid and enlarging it with an electron microscope 30,000 times to obtain the number of 1000 particles in the micrograph obtained by number average. (Water retention agent) ・ Carboxymethyl cellulose (abbreviated as CMC)

Example 7 A base paper and an undercoat layer obtained under the same conditions as in Examples 1 to 6 were
Example 1 was prepared by adding 6 parts of dextrin (MF30: Nitto Kagaku Co., Ltd.) to the pigment and latex of the topcoat formulation shown in Table 2.
Liquid preparation, coating, and calendering treatment were performed under the same conditions as those for ~ 6.

[0037]

[Table 1]

Comparative Example 1 A raw paper prepared under the same conditions as in Examples 1 to 6 was subjected to starch (MS3800: MS3800:
The same as in Examples 1 to 6 except that Nippon Food Kako Co., Ltd.) was size-pressed with an adhesion amount of 1.0 g / m ² and the coating liquid concentration of the coating liquid shown in Example 5 was 65%. Liquid preparation, coating, and calendering were performed under the conditions.

Comparative Examples 2 to 12 Base papers and undercoat layers obtained under the same conditions as in Examples 1 to 6 were coated with the coating compositions for the overcoat layer having the formulations shown in Table 2 under the same conditions as in Examples 1 to 6. And coating and calendering. The calcium carbonate B, latex C, and kaolin C blended in Comparative Examples 3 and 8 and 12 were as follows.・ Calcium carbonate B: Escalon # 1500 (manufactured by Sankyo Seiko Co., Ltd.) was added with 1 part of a commercially available polyacrylic acid-based dispersant, and the resulting slurry was passed once through a pulverizer (universal mill: manufactured by Mitsui Miike). Crushed. This calcium carbonate has a particle size of 2 μm
The following was 85% by volume. Latex C: carboxy-modified styrene butadiene latex; average particle size 0.140 μm The particle size was determined by the same method as for latex A and latex B. Kaolin C: Hydra Gloss 90 (manufactured by Huber); particle size 0.5 μm or less, 30% by volume

[0040]

[Table 2]

As is clear from Examples 1 to 7 and Comparative Example 1, by providing the undercoat layer on the base paper, the coating liquid applied thereon has an excellent coating liquid concentration even if the coating liquid is high. It can be seen that the coating suitability in. Moreover, the quality and printability are excellent. However, when kaolin and ground calcium carbonate having a specific particle size are not used as the pigments to be blended in the overcoat layer from Comparative Examples 2 and 3, the coating suitability and the glossiness of the white paper are reduced. Further, it can be seen from Comparative Examples 4 to 7 that the compounding amounts of the specified kaolin and ground calcium carbonate also have a specific range. Further, when the particle size of the latex compounded in the overcoat layer from Comparative Example 8 is large, problems arise in coating amount control and coating layer strength, and from Comparative Example 9 when the latex amount compounded in the overcoat layer is large and Example 10
Therefore, if the coating liquid concentration of the coating liquid of the topcoat layer is low, there is a problem in quality, and if the coating liquid concentration is too high, it becomes difficult to control the coating amount and the glossiness of the white paper decreases. It turns out that there is a tendency. Further, although the coater operability is improved by making the particle size of kaolin blended from Comparative Example 12 finer, it is understood that the coating amount control is difficult unless the specified kaolin is blended.

Examples 8 to 13 Base papers were made under the same conditions as in Examples 1 to 6. For the undercoat layer, 0.1 part of a commercially available polyacrylic acid-based dispersant was added to the same pigment as in Examples 1 to 6 and dispersed, and then the binder amount shown in Table 3 was added to adjust the pH of the coating solution for the undercoat layer. Was adjusted to 9.5 with ammonium hydroxide, and the concentration of this coating solution was adjusted to 48%. This coating solution was applied to both sides by a gate roll coater (abbreviated as GRC) with the coating amount shown in Table 3 per side. The topcoat layer was formed by applying the coating liquid shown in Example 5 at a coating speed of 1000 m / min and the coating amount shown in Table 3 and calendering it under the same conditions as in Examples 1-6.

Example 14 The base paper was made under the same conditions as in Examples 1-6. For the undercoat layer, 0.1 part of a commercially available polyacrylic acid-based dispersant was added to the same pigment as in Examples 1 to 6 and dispersed, and then the binder amount shown in Table 3 was added to adjust the pH of the coating solution for the undercoat layer. Was adjusted to be 9.5 with ammonium hydroxide, and the concentration of this coating solution was adjusted to 53%. Use this coating liquid with a blade coater (BL
Is abbreviated), and both sides are coated with a coating amount of 10 g / m ² per side. For the top coat layer, the coating liquid shown in Example 5 was applied at a coating speed of 1
It was applied at 000 m / min and calendered under the same conditions as in Examples 1-6.

Example 15 The base paper was made under the same conditions as in Examples 1-6. For the undercoat layer, 0.1 part of a commercially available polyacrylic acid-based dispersant was added to the same pigment as in Examples 1 to 6 and dispersed, and then the binder amount shown in Table 3 was added to adjust the pH of the coating solution for the undercoat layer. Was adjusted to 9.5 with ammonium hydroxide, and the concentration of this coating solution was adjusted to 48%. This coating solution was applied to both sides by a gate roll coater (abbreviated as GRC) with the coating amount shown in Table 3 per side. The topcoat layer was formed by applying the coating liquid shown in Example 5 at a coating speed of 1000 m / min and the coating amount shown in Table 3 and calendering it under the same conditions as in Examples 1-6.

Example 16 The composition of the base paper and the undercoat layer and the coating apparatus were the same as in Example 14, and the coating amount of the undercoat layer was 13 g / m ² . The topcoat layer was formed by applying the coating liquid shown in Example 5 at a coating speed of 1000 m / min and the coating amount shown in Table 3 and calendering it under the same conditions as in Examples 1-6.

Comparative Example 13 The base paper was made under the same conditions as in Examples 1-6. An undercoat layer was not provided, and coating was performed on the base paper at a coating speed of 1000 m / min with the coating liquid concentration of the coating liquid shown in Example 5 set to 65%. Rendered.

[0047]

[Table 3]

As is apparent from Table 3, it is understood that better quality can be obtained when the binder amount in the undercoat layer is in the range of 5 to 50 parts. Further, by using a blade coater as the coating device for the undercoat layer, the coater operability of the overcoat layer is slightly lowered, but higher gloss can be obtained. However, if the amount of the binder in the undercoat layer exceeds 50 parts or if the amount of the undercoat layer applied exceeds 10 g / m ² , the blister suitability is slightly lowered. In particular, when the coating amount of the undercoat layer exceeds 10 g / m ² , streaks and scratches are slightly generated and coater operability is slightly lowered, but it is within an allowable range. Further, in the case where the undercoat layer was not provided, the coating suitability and the coating layer strength of the topcoat layer were deteriorated, and unevenness of ink deposition was caused, as in Comparative Example 1 in which the size press was applied. Also,
Comparative Example 13 generated many smaller blisters than Comparative Example 1.

[0049]

As is apparent from the examples, according to the present invention, it is possible to obtain a coated printing paper having high offset printing suitability, particularly high offset rotary printing suitability, with excellent workability.

Claims (3)

[Claims] 1. In a coated paper for printing, wherein two coating layers each containing a pigment and a binder as main components are provided on one side of a support, and the coating composition of the overcoat layer has the following (a):
(B) and (c) are essential components, the kaolin and the ground calcium carbonate are 20 to 80% by weight and 80 to 20% by weight in all pigments, and the synthetic polymer latex is in all pigments. On the other hand, the coated paper for printing is characterized in that the content of the coating composition is 5 to 15% by weight, and the solid content concentration of the coating composition at the time of coating is 65 to 73% by weight. (A) Kaolin having a particle size of 0.5 μm or less of 40% by volume or more. (B) Heavy calcium carbonate having a particle size of 2.0 μm or less and 90% by volume or more. (C) A synthetic polymer latex having an average particle size of 0.05 to 0.10 μm. 2. The coated paper for printing according to claim 1, wherein the amount of the binder contained in the coating composition for the undercoat layer is 5 to 50% by weight based on the total pigment. 3. The coating amount of the coating composition for the undercoat layer is 10
The coated paper for printing according to claim 1 or 2, which is g / m ² or less.