JP2968833B2 - Coated paper for printing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to offset printing coated paper, in an offset printing coated paper for coating a base paper with a coating liquid containing at least calcium carbonate, excellent workability with a blade coater, further obtained coated paper Smoothness, hiding power,
The present invention relates to improvements in gloss, coating fluidity, and the like.

[Prior art]

Conventionally, in the production of coated paper, pigments and adhesives are the main components, and as the pigment, kaolin, clay, titanium oxide, heavy calcium carbonate, light calcium carbonate, satin white, titanium dioxide, pyrophyllite clay are generally used. , Calcium sulfite, calcium sulfate, aluminum hydroxide, zinc oxide, zeolite, barium sulfate,
Inorganic minerals such as amorphous silica, talc, plastic pigment and organic pigments are used. Of these pigments, calcium carbonate has excellent characteristics such as whiteness, ink receptivity, air permeability, hiding power, and the like, and thus has been increasingly used in paper coating in recent years. In general, calcium carbonate can be roughly classified into light calcium carbonate obtained by a chemical reaction and heavy calcium carbonate obtained by pulverizing naturally occurring limestone. Further, heavy calcium carbonate is roughly classified into a dry grinding method (dry heavy calcium) and a wet grinding method (wet heavy calcium) depending on the grinding method. As an advantage of dry heavy calcium carbonate, it is inexpensive because of its easy manufacturing method, and it also has high whiteness and enables high concentration dispersion.However, as a disadvantage, limestone is mechanically dry-pulverized, Since only the classification is performed, the average particle diameter is large and the width of the particle size distribution is wide as compared with the light calcium carbonate. Further, since the water retention is reduced, the suitability for coating with a blade coater such as streaks, scratches, and bleeds is also poor. On the other hand, wet heavy calcium carbonate is used, which has been pulverized with a sand glider or the like to an average particle size of 1 μm or less, has excellent fluidity under high shearing force, and has a strong coating layer strength. There are advantages such as increase, but gloss and smoothness are slightly lower than kaolin. On the other hand, light calcium carbonate shows high gloss and smoothness, but has poor coating layer strength and slurry fluidity, and is extremely poor in coating suitability in a blade coater or the like. In particular, since the spindle-shaped light calcium carbonate has a spindle shape, the aspect ratio is large, a bulky coating layer is obtained, and the surface coverage is excellent, so that the gloss, smoothness, and hiding power are higher than those of heavy calcium carbonate. Excellent. However, since its aspect ratio and surface area are larger than heavy calcium carbonate, the strength after coating and drying and the fluidity of the coating liquid are inferior. On the other hand, as described in JP-A-57-106797, 0.1.
The fluidity of the slurry is improved by adsorbing polyacrylic acid on 1-1.0 µm cubic light calcium carbonate, but this method is sufficient to obtain a slurry with a solid concentration of about 60%. , Is not sufficient to prepare a slurry having a very high solid content of 70% or more, and it is difficult to obtain good coating suitability with a high-speed blade coater using this technique alone. Until now, Japanese Patent Application Laid-Open No. 59-192796 has disclosed a method of using cubic light calcium carbonate wet-pulverized by a sand mill as a method for producing a coating composition for gravure printing. The purpose of the present invention is to improve the printability in offset printing, especially the decrease in the coating layer strength, and is therefore limited to gravure paper. Further, there is no description on the improvement of the coating suitability and offset printing suitability of the spindle-shaped light calcium carbonate.

[Problems to be solved by the invention]

The present invention relates to a printing coating in which a coating composition having improved fluidity of a coating liquid and improved strength after coating and drying is incorporated into a pigment without impairing the smoothness, gloss and hiding power of a spindle-shaped light calcium carbonate. To get the paper.

[Means for Solving the Problems]

The present invention is a coated paper for printing characterized in that a pigment produced by mixing and wet-grinding spindle-shaped light calcium carbonate and heavy calcium carbonate is blended in a coating layer on a paper substrate. The average particle size of spindle-shaped light calcium carbonate (Dpμm) before grinding and the average particle size of heavy calcium carbonate (Dgμm)
And the weight ratio (P) of the spindle-shaped light calcium carbonate in the mixed and crushed product satisfies the following two conditions: 0.1 ≦ P ≦ 0.8 0.25P ≦ R ≦ 2.0P It is desirable that the average particle size is 0.5 to 1.5 μm. Furthermore, a mixed and ground product of spindle-shaped light calcium carbonate and heavy calcium carbonate is contained in 100 parts by weight of the pigment of the coating composition.
By including 10 to 100 parts by weight, the effect can be made clearer. The average particle size described in this document is a value of a volume-weighted average particle size measured by a laser diffraction type particle size analyzer (Microtrac particle size analyzer SPA type manufactured by Nikkiso Co., Ltd.). When heavy calcium carbonate and spindle-shaped light calcium carbonate are mixed and pulverized by a wet pulverizer such as a sand mill, the degree of pulverization of light calcium carbonate is larger than that of heavy calcium carbonate. That is, the spindle-shaped light calcium carbonate is more easily pulverized than the heavy calcium carbonate. For this reason, after the spindle-shaped light calcium carbonate and heavy calcium carbonate are crushed to the same average particle size by wet singly, the fluidity of the pigment slurry under high shear is improved as compared with a mixture of the crushed light calcium carbonate and heavy calcium carbonate. This is considered to be the result of increasing the filling rate of the pigment by mixing and grinding light calcium carbonate and heavy calcium carbonate. Furthermore, the mixed and ground product of spindle-shaped light calcium carbonate and heavy calcium carbonate used in the coating composition of the present invention has a higher gloss than the above-mentioned pigment slurry mixture,
Improvements in opacity, air permeability, blister suitability, etc. can also be obtained. Light calcium carbonate has a variety of crystal forms, such as cubic, spindle-shaped, and needle-shaped.However, in the case of the spindle-shaped, the mixing and crushing effect with heavy calcium carbonate is similar to that of spindle-shaped light calcium carbonate and heavy calcium carbonate. This is because the average particle size of the spindle-shaped light calcium carbonate before and after pulverization is large even if the pulverization is performed under the conditions described in the above. Although this mechanism is not always clear, it can be inferred from the results of observation with an electron microscope and the like that the fact that the spindle-shaped light calcium carbonate crystal is easily broken at the center of the long axis is a major factor. If the average particle size of the calcium carbonate mixed and crushed product is smaller than 0.5 μm, it indicates that not only light calcium carbonate but also heavy calcium carbonate has been excessively pulverized. The fluidity under low shear deteriorates and the concentration of the pigment slurry decreases. Also, the strength of the coating layer is reduced. On the other hand, if it is larger than 1.5 μm, it means that the pulverization of the light calcium carbonate has not progressed so much, so that the gloss, the smoothness and the like cannot be improved much. When the ratio of light calcium carbonate is too small, the paper properties are reduced. When the ratio is too large, the fluidity of the coating liquid is reduced. Therefore, when the ratio (P) of light calcium carbonate in the mixed and pulverized product is 0.1 or less, the gloss is high. Paper properties such as smoothness and the like are hardly improved with respect to simple wet-pulverized heavy calcium carbonate. Further, when the ratio P of the spindle-shaped light calcium carbonate in the mixed and crushed material becomes large, the spindle-shaped light calcium carbonate is more easily crushed than the heavy calcium carbonate. In order to store the powder, the degree of pulverization (the amount of power required for pulverization per unit weight pulverized material) becomes lower than when heavy calcium carbonate is large, that is, when P is a low value. For this reason, heavy calcium carbonate which is difficult to grind remains as coarse particles, increases the viscosity under high shear, and deteriorates the coating suitability. Therefore, when P increases, it is necessary to reduce the average particle size of the heavy calcium carbonate before pulverization to make it easier to pulverize and to approach that of the spindle type light calcium carbonate. That is, the average particle diameter of the spindle-shaped light calcium carbonate (Dp
μm) and the average particle size (Dg μm) of heavy calcium carbonate R = Dp / Dg is preferably in the range of 0.25 P or more and 2.0 P or less. However, it is not preferable that P exceeds 0.8 in view of a decrease in coating layer strength. The number of mixed and ground calcium carbonate in 100 parts by weight of all pigments is 1
If the amount is less than 0 parts by weight, the advantages of the paper properties and the fluidity of the coating liquid, which are features of the present invention, are not sufficiently utilized. More preferably, 20 parts by weight or more is appropriate. As a pigment component of another coating composition of the mixed and crushed spindle-shaped light calcium carbonate and heavy calcium carbonate, for example, kaolin, clay, titanium oxide, heavy calcium carbonate, light calcium carbonate, satin white, titanium dioxide, pyrophyllite Clay, calcium sulfite, calcium sulfate, aluminum hydroxide, zinc oxide, zeolite, barium sulfate, amorphous silica, talc, plastic pigment, etc. are used.
Alkali-sensitive or non-alkali such as various copolymers such as butadiene, styrene / acrylic / vinyl acetate / acrylic, ethylene / vinyl acetate, butadiene / methyl methacrylic, vinyl acetate / butyl acrylate and polyvinyl acetate Sensitive adhesives, synthetic adhesives such as polyvinyl alcohol, maleic anhydride / styrene copolymer, isobutene / maleic anhydride copolymer, acrylic acid / methyl methacrylate copolymer, oxidized starch, etherified starch Various commonly known adhesives such as esterified starch, enzyme-modified starch and natural adhesives such as cold-water-soluble starch obtained by flash-drying them, casein, soy protein, etc. are pigment 100.
It is used in an amount of about 1 to 30 parts by weight with respect to parts by weight, and various auxiliary agents such as a dispersant, a thickener, a water retention agent, a defoaming agent, a waterproofing agent, a lubricant, a dye, and an alkali agent are appropriately compounded as necessary. Is done. In addition, the wet pulverization treatment is performed by a device such as a sand mill with an average particle size of 5 mm or less, more preferably 4 mm or less natural or synthetic fine particles, such as mineral fine sand, glass fine particles, hard plastic fine particles, metal fine particles. Filling the container with 30% to 90% by volume of particles (the following particles are called beads)
The slurry is mixed with light calcium carbonate and heavy calcium carbonate once or a plurality of times while mechanically stirring the fine particles through a stirring blade of an arbitrary shape. Base paper used in the present invention includes chemical pulp such as LBKP, NBKP, etc., mechanical pulp including GP, PGW, RMP, TMP, CTMP, CMP, CGP, etc., and waste paper pulp such as DIP, light calcium carbonate and heavy calcium carbonate. It contains various fillers such as talc, clay, kaolin, etc., sizing agents, fixing agents, retention agents, cationizing agents, paper strength agents and the like, and is made into an acidic, neutral or alkaline paper. Paper machines for making this base paper include various formers such as cylinders, long nets, twin wires, and the like, and paper machines that combine these various formers and make paper. The coating composition of the present invention is monolayer or multilayer coated on both sides or one side of the base paper. In this case, there is no particular limitation on the coating method that can appropriately change the composition of the coating composition constituting each layer when forming the coating composition on both surfaces and each layer when performing multi-layer coating. Various coating equipment such as coater, roll coater, paddle and inverter type blade coater with bevel and vent type blades, as well as various blade coaters such as building blade, twin blade, chanplex and short dwell coater Is used. Smeared paper obtained using the coating composition of the present invention is a super calendar, a gloss calendar, a brush calendar,
Finished through various finishing devices such as temperature gradient calendar and soft calendar. The coated paper for printing of the present invention can be applied to various types of printing such as sheet offset printing, transfer offset printing, gravure printing, flexographic printing, letterpress printing, photographic printing, and stencil printing. Hereinafter, the present invention will be described in more detail with reference to examples, but is not limited thereto.

【Example】

Examples 1 to 12 Heavy calcium carbonate and spindle-shaped light calcium carbonate 100
Parts by weight as shown in Table 1 and 0.8 parts by weight of sodium polyacrylate were used.
% Of the slurry, pulverized by a sand mill, and the obtained mixed and pulverized product, individually crushed spindle-shaped light calcium carbonate, heavy calcium carbonate, and commercially available first-grade kaolin (UW90 manufactured by Engelhard Co.) and commercially available second-grade Kaolin (Engelhart HT) is blended in the ratio shown in Table 1,
10% by weight of sodium polyacrylate as a dispersant was used at 0.07 part per 10 parts by weight of kaolin to obtain a solid content concentration of 72%. After mixing 5 parts by weight of the phosphorylated ester and 0.4 parts by weight of calcium stearate as a lubricant, the pH was adjusted to 9.5 with NaOH,
A coating product of 63% solids concentration was obtained. 80 parts of LBKP (filtration 300mlcsf) and NBKP (filtration
350mlcsf) as internal additives, 5 parts of commercially available calcium carbonate, 0.03 parts of commercially available neutral internal sizing agent, and 0.03 parts of commercially available retention aid, prepared as a long net at a speed of 800 m / min. Using a blade coater on base paper manufactured by a paper machine
Coating was performed at a speed of 1000 m / min so that the coating amount was 12 g / m ² on one side, and after drying, supercalendering was performed to obtain offset printing paper. The quality of the obtained offset printing paper was evaluated, and the results are shown in Table 1. Comparative Examples 1 to 5 Various types of calcium carbonate (average particle size: 1.1 μm) shown in Table 1 were used in place of the mixed and ground products of spindle-shaped light calcium carbonate and heavy calcium carbonate under the same conditions as in Examples 1 to 12. Offset printing paper was obtained. The results are shown in Table 1. Comparative Example 6 The primary kaolin and 2 shown in Table 1 were used in place of the crushed product of the spindle type light calcium carbonate and heavy calcium carbonate.
Offset printing paper was obtained using grade kaolin under the same conditions as in Examples 1 to 12. The results are shown in Table 1. The specifications and conditions of the super calender are as follows: ・ Number of steps: 10 steps ・ Rigid roll: chilled roll, outer diameter 400mmφ ・ Elastic roll: cotton roll, outer diameter 420mmφ ・ Processing speed: 600m / min ・ Line pressure: 200kg / cm is there. In addition, each measurement condition is as follows. 1) Smoothness: Smoother smoothness tester (Toei Denshi KK
Manufactured). 2) Gloss on white paper: Measured at an angle of 75 ° according to JISP8142. 3) Coating layer strength: The surface strength of the coated paper was visually evaluated using a RI printing suitability tester (Meiji Seisakusho) by a five-step evaluation. Good 5>4>3>2> 1 Poor 4) Average particle size: The average particle size was measured by a Microtrac particle size distribution analyzer. 5) Whiteness and opacity: Numerical values measured by a digital hunter whiteness meter. 6) B-type viscosity: measured with a Brookfield type viscometer No. 1 spiddle at 60 rpm. 7) High shear viscosity: Measured with a No. 2 plate at 1000 rpm using a high shear rheometer (Ishida Seisakusho). 8) Coater workability: Specified by the occurrence of streaks during coating work. Good 5>4>3>2> 1 bad

【The invention's effect】

As is apparent from Table 1, the coated paper for printing produced using the coated paper composition shown in the present invention has good liquid properties, excellent coater workability, good gloss, It was found that smoothness and suitability for offset printing were obtained.

Claims (3)

(57) [Claims] 1. A coated paper for printing, characterized in that a pigment produced by mixing and wet-grinding spindle-shaped light calcium carbonate and heavy calcium carbonate is blended into a coating layer on a paper substrate. 2. The ratio (R = Dp / Dg) of the average particle diameter (Dp μm) of the spindle-shaped light calcium carbonate and the average particle diameter (Dg μm) of heavy calcium carbonate before wet milling, and the light calcium carbonate in the mixed milled product The weight ratio (P) satisfies the following two conditions, and 0.1 ≦ P ≦ 0.8 0.25P ≦ R ≦ 2.0P The average particle size of the mixed and pulverized product is 0.5 to 1.5 μm. Coated paper for printing. 3. The coated paper for printing according to claim 1, wherein the mixed and ground product of light calcium carbonate and heavy calcium carbonate is contained in an amount of 10 to 100 parts by weight based on 100 parts by weight of the pigment.