JP2000136496A - Production of coated paper for printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a coated paper for printing, having high glossiness of a blank paper, excellent in opacity, printing-through properties, a printed surface strength and high-speed operability. SOLUTION: This producing method of a coated paper for printing, for coating a coating liquid containing a pigment and a binder on a base paper comprises wet-milling an acicular or columnar precipitated calcium carbonate produced by slaking a quick lime with water or a weak liquid (a liquid slightly containing the white liquor) in the step of the causticization in a pulping process by a sulfate process or a soda process, and carrying out a causticization reaction with a green liquor, so as to have 2.0-5.0 μm longer diameter and 0.2-1.0 μm shorter diameter, as a pigment component, preparing the coating liquid containing 20-90 wt.% acicular or columnar precipitated calcium carbonate after the wet-milling based on 100 wt.% pigment components, and coating the prepared coating liquid by a blade type coating apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a coated paper for printing in which a base paper is coated with a coating liquid comprising a pigment and an adhesive.

[0002]

2. Description of the Related Art In recent years, demand for printing paper in the field of commercial printing for advertising and promotion such as flyers, catalogs, brochures, and direct mail has been growing. Although these commercial prints have low commercial value themselves, it is important that the purpose be achieved as an advertising medium, and therefore, low-cost, high-quality prints have been demanded. Particularly in the field of mail-order catalogs, postal charges have been revised, and paper used for cost reduction has been further reduced in weight. However, since opacity and print strikethrough become more problematic as the weight is reduced, paper having higher opacity and less print strikethrough even at a low basis weight is required. In addition, in the case of flyers and catalogs, if the color of the printed matter is different from the actual color, a problem (complaint, returned goods, etc.) occurs, and therefore, a paper with high color reproducibility and high whiteness is required. In general, as means for improving opacity, use of fillers having a large specific surface area (white carbon, finely divided silica, etc.), fillers having a high refractive index, use of pigments (titanium dioxide, etc.), pigments for forming bulky coating layers ( Plastic pigments, delaminated clay, etc.) and increased use of mechanical pulp. However, in general, these fillers and pigments are expensive and tend to have a high viscosity of the coating liquid. When mechanical pulp is used, the whiteness is poor. Therefore, in particular, in light weight coated paper, light calcium carbonate having a specific shape (cubic shape, spindle shape, columnar shape, needle shape, etc.) is used in the base paper filler or coating in consideration of overall quality balance and operability. In recent years, the method used for pigments for liquids has tended to be widely adopted, and among these light calcium carbonates, aragonite crystalline acicular, columnar light calcium carbonate has a high refractive index and a large light scattering property. Express excellent opacity.
However, if the needle liquid or the columnar light calcium carbonate is blended in a high amount in the coating liquid, the viscosity of the coating liquid becomes too high. For example, the coating liquid is coated on the base paper by a blade type coating apparatus. If the coating speed is too high, lactide and bleeding (phenomenon of agglomeration of the coating liquid adhering to the blade edge) will occur on the blade edge, causing defects such as streaks on the paper surface.
At present, the coating speed has a limit, which causes a decrease in high-speed operability and productivity. In addition, because the dynamic water retention of the coating liquid is greatly reduced, the coating liquid is soaked into the base paper, resulting in poor base paper covering properties. At the same time, a problem that the printing surface strength is reduced due to the shortage of the binder is caused. As an existing technique using acicular or columnar calcium carbonate as a coating liquid pigment, for example, the major axis is 3 μm or more and 100 μm or less, and the minor axis is 0.3 μm or more and 4 μm or more.
m or less of acicular calcium carbonate as a pigment in the coating liquid.
0-wt% or more (JP-A-7-70986), and a method of applying a coating liquid containing 5-70 wt% or more of aragonite-type light calcium carbonate as a pigment by a curtain coating device (JP-A-7-70986). 166493), a method in which a coating liquid containing 10 to 40% by weight of needle pigment calcium carbonate having a major axis / minor axis of 5 to 10 with respect to all pigments is applied by a vent blade coating method (Japanese Patent Laid-Open No. Hei 7 (1999)).
However, even if these techniques are used, not only the high-speed operability is inferior, but also the glossiness of the white paper and the decrease in the printing surface strength cannot be improved to a sufficient level. Also, Japanese Patent Application Laid-Open No. Hei 10-226974
In the bulletin, in the causticizing step of the pulp manufacturing process by the sulfate method or the soda method, the quicklime was slaked with white liquor, followed by a causticizing reaction with green liquor to produce needle-like light calcium carbonate. The use of needle-like light calcium carbonate as a filler or pigment provides a method for improving printability such as opacity and gloss after printing on coated paper. On the other hand, no sufficient effect was obtained.

[0003]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a method for producing a coated paper for offset printing in which a base paper is coated with a coating liquid comprising a pigment and an adhesive. It is an object of the present invention to provide a method for producing a coated paper for printing, which has a high degree of opacity, print strikethrough, printing surface strength, and high-speed operability.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies on the above-mentioned problems, and as a result, have found that a method for producing a coated paper for printing, in which a base paper is coated with a coating liquid containing a pigment and an adhesive. In the causticizing step of the pulp manufacturing process by the sulfate method or the soda method as a pigment component, slaked quicklime with water or a weak solution, and then a needle-like or columnar light product produced by a causticizing reaction with a green solution Calcium carbonate with a major axis of 2.0 ~
Coating that is wet-pulverized so as to have a thickness of 5.0 μm and a minor axis of 0.2 to 1.0 μm, and contains 20 to 90% by weight of needle-like or columnar light calcium carbonate after the grinding with respect to 100% by weight of the pigment component. The present invention was accomplished by preparing a liquid and applying the coating liquid with a blade type coating apparatus.

In the present invention, the opacity, print strikethrough, printing surface strength, white paper glossiness, high-speed operability of a printing coated paper are obtained by using wet-pulverized needle-like or columnar light calcium carbonate. Can be improved. The opacity and print strike-through are greatly improved because the needle-like or columnar light calcium carbonate is not only originally light-scattering than heavy calcium carbonate or other light calcium carbonate, but also has a moderate wet It is considered that the pulverization increased the surface area of the pigment and further improved the expression of opacity. In addition, the printing surface strength and the glossiness of the white paper are improved because the surface area of the pigment is increased by appropriately wet-grinding the needle-like or columnar light calcium carbonate, and the dynamic water retention of the coating liquid is improved. It is considered that by greatly improving the base paper, it is possible to prevent the coating liquid from soaking into the base paper too much to prevent the undercoating coating layer from becoming insufficient with the adhesive, and at the same time, to exhibit excellent base paper covering properties.

[0006] The high-speed operability is improved because the viscosity of the pigment slurry itself of light calcium carbonate is reduced by appropriately wet-grinding the needle-like or columnar light calcium carbonate, and as a result, the coating liquid It is considered that the high-speed fluidity of the coating liquid was improved by greatly lowering the viscosity under high shear. The reason why the viscosity of the light calcium carbonate pigment slurry is reduced by the pulverization is not clear at this time, but the detailed mechanism is not clear. It is thought that this is because the cohesion inherent in the light or columnar light calcium carbonate is reduced, the particles hardly re-aggregate, and the dispersant added to the slurry works more effectively.

The amount of the needle-like or column-like light calcium carbonate used in the present invention is based on 100% by weight of the total pigment.
20 to 90% by weight. If the amount is less than 20% by weight, the effect of improving opacity and print strikethrough is poor. If the amount exceeds 90% by weight, high-speed operability is poor.

[0008] The long and short diameters of the needle-like or columnar light calcium carbonate used in the present invention after wet pulverization are as follows.
0 to 5.0 μm, and the minor axis is 0.2 to 1.0 μm. When the minor axis is smaller than 0.2 μm, the particle diameter becomes too small and the viscosity of the coating liquid becomes too high. When the coating liquid is coated with a blade, stalactit or bleeding (of the blade) At the same time, problems such as the phenomenon that the coating liquid aggregates adhere to the cutting edge) occur, and the printing surface strength is inferior. On the other hand, if the minor axis is larger than 1.0 μm, the particle diameter becomes too large, and the glossiness of white paper decreases. On the other hand, when the major axis is larger than 5.0 μm, the pigment is liable to be caught on the blade edge of the blade, so that streak is generated and, at the same time, the particle diameter becomes too large, and the glossiness of white paper is reduced. On the other hand, when the major axis is smaller than 2.0 μm, the printing surface strength is inferior, and stalactite and bleeding occur. More preferably, the major axis of the needle-shaped or columnar light calcium carbonate is 2.5 to 4.5 μm, and the minor axis is 0.1 μm.
2 to 0.8 μm.

In the present invention, high-speed operability when using a blade type coating apparatus can be improved.
There are two types of blades, a bevel type and a vent type. The bevel type is more susceptible to the influence of the degree of penetration of the coating liquid into the base paper, and tends to be difficult to improve high-speed operability. However, according to the present invention, since the high-speed fluidity of the coating liquid is improved, even if the coating is performed at a high speed of 1100 m / min or more, the occurrence of structrite or bleeding occurs with a bevel-type blade type coating apparatus. Can be operated without

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The needle-like or columnar light calcium carbonate used in the present invention is one produced in a causticizing step of a pulp producing step by a sulfate method or a soda method. In the pulp production process by the sulfate method or the soda method, wood chips are digested under a high temperature and a high pressure using a chemical solution in which sodium hydroxide and sodium sulfide are mixed in order to isolate fibrin in the wood. The fibrous material is separated and purified into a pulp as a solid phase, and elution components other than fibrous material from the chemical solution and wood are recovered as black liquor, and concentrated to a concentration that can be burned by the recovery boiler. Further, sodium sulfate is added to supplement sodium and sulfur lost in a series of processes, and then burnt in a recovery boiler. At that time, the organic substance in the black liquor is recovered as a heat source, and the inorganic substance is mainly recovered as sodium carbonate and sodium sulfide. These inorganic substances are called smelt and are taken out of the recovery boiler in a molten state. The smelt removed from the recovery boiler is dissolved in water or a weak liquid (a liquid containing a small amount of a white liquor component obtained after washing calcium carbonate with water) to become a green liquor. The causticizing process is a process for converting sodium carbonate in green liquor into sodium hydroxide as a cooking chemical, a slaking reaction (1) for converting quicklime into slaked lime, and mixing slaked lime and green liquor to form a hydroxide. It consists of a caustic reaction (2) that produces sodium and light calcium carbonate. The liquor obtained by the causticization reaction is called white liquor, separated from light calcium carbonate, clarified and sent to the digestion step. In the present invention, calcium carbonate that has been separated and recovered and washed sufficiently with water is used. CaO + H2O → Ca (OH) 2 (1): slaking reaction Ca (OH) 2 + Na2CO3 → CaCO3 + 2NaO
H (2): Causticizing reaction Since this calcium carbonate is a by-product when producing white liquor, which is a main product, it is much higher than light calcium carbonate obtained by a conventional method of reacting milk of lime and carbon dioxide. The product can be manufactured at low cost.

Further, the needle-shaped or columnar light calcium carbonate specified in the present invention is produced for the first time according to the following production method. That is, (1) quicklime generated in the causticizing step and / or introduced from outside the causticizing step,
(2) A liquid (water or weak liquid) having a pH of 5.5 to 14 is added to the quicklime containing 0.1 to 10% by weight of calcium carbonate such that the quicklime concentration becomes 20 to 60% by weight. The first step of producing milk of lime and / or lime mud by slaking with stirring or mixing, and then the lime milk and / or lime mud is generated in the causticizing step to produce white liquor. The lime milk and / or lime mud is subjected to a caustic reaction at a reaction temperature of 20 to 105 ° C. to produce a required amount of green liquor. The obtained needle-like or columnar light calcium carbonate is appropriately wet-pulverized by a pulverizer such as a bead mill and used.

Examples of the pulverizer used in the present invention include an attritor, a vibration mill, a ball mill, a vertical sand mill, a horizontal sand mill, a jet mill, etc., which are generally used for wet pulverization of pigments for papermaking. Examples of the pulverizing media include spherical balls made of hard raw materials such as glass, ceramic, alumina, zirconia, and agate, and the particle diameter is preferably 0.1 to 10 mm. Considering the crushing efficiency, it is preferable that the filling rate of the medium is as high as possible.However, if the filling rate is too high, the movement of the medium in the crushing chamber is restricted, and conversely, the crushing efficiency may be reduced. Adjust appropriately according to the machine.

The pigments used in the present invention are not particularly limited except for the above-mentioned light calcium carbonate, and heavy calcium carbonate, kaolin, clay, talc, satin white, silica, titanium dioxide generally used for papermaking are used. And inorganic pigments such as barium sulfate, potassium sulfate, and zinc oxide; and organic pigments such as plastic pigment. The adhesive used for the coating liquid in the present invention is a styrene / butadiene copolymer, a styrene / butadiene / acrylic copolymer or a modified product thereof, such as a polymer synthetic latex, an oxidized starch, a phosphorylated starch, and an ether. Water-soluble natural polymers such as modified starch, enzyme-modified starch, cold water-soluble starch, and carboxymethyl cellulose are used. The amount of the adhesive is preferably 5 to 20 parts by weight based on 100 parts of the pigment.

In the coating liquid of the present invention, various auxiliaries, such as a dispersant, a thickener, a water retention agent, a defoaming agent, and a water-proofing agent, which are blended with ordinary pigments for coated paper may be used. good.

The base paper used in the present invention may be a base paper having a basis weight of 30 to 100 g / m used for general printing coated paper.
The base paper is high quality paper and medium paper depending on the purpose. The coating composition thus prepared is simply applied onto base paper by an on-machine or off-machine coater provided with a coating device such as a blade coater, an air knife coater, a roll coater, a bar coater, etc., which are used in the production of general coated paper. Layered or multilayer coated. Concentration of coating liquid is 60 ~
68% is preferred, and the coating amount is usually 5 solids per side.
-20 g / m2 is preferred. The coated paper which has been coated with the top coating liquid and dried is subjected to a surface treatment as it is or a super calender, a soft calender, a mat calender or the like to give a gloss.

[0016]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited by these examples. In the examples, parts and% indicate parts by weight and% by weight, respectively. <Quality evaluation method> (1) Observation of light calcium carbonate morphology: Light calcium carbonate after pulverization was washed with water, filtered, dried, and the shape, short diameter and long diameter average were measured with a scanning electron microscope (JEOL JSM-5300). . (2) Blank paper glossiness: Angle 7 according to JIS P-8142
The specular gloss was measured at 5 degrees. (3) Opacity: JIS P using a Hunter whiteness meter
-8138, measured according to Method A. (4) Printing strike-through: Using a RI-II type printing machine (manufactured by Akira Seisakusho), printing with a constant ink amount of 0.45 cc using TV Mark V New 617 (manufactured by Toyo Ink) as a printing ink, and Hunter white JIS P-8123 using a degree meter
And was calculated by the following equation.

Print strike-through (%) = whiteness of blank paper−whiteness of backside of printed matter (5) Dry strength: Using a RI-II type printing machine (manufactured by Meiji Seisakusho), TV-24 (manufactured by Toyo Ink) as a printing ink ) Was used to print with a constant ink amount of 0.35 cc, and the degree of picking on the printing surface was visually evaluated.

◎: not generated at all, ほ と ん ど: hardly generated, Δ: generated, ×: remarkable generation (6) Evaluation of stalactites: The state of generation at the blade edge during coating was visually evaluated.

◎: almost no occurrence, ：: slight occurrence, Δ: occurrence, X: remarkable occurrence, (7) Streak evaluation: The condition occurring at the time of coating was visually evaluated.

◎: hardly generated, ：: slightly generated, Δ: generated, x: remarkable generation [Example 1] Produced in the causticizing step of the kraft pulp manufacturing process, having a major axis of 7.0 μm. , The minor axis is 0.4μ
To 100 parts of the needle-like light calcium carbonate m, 0.5 part of a sodium polyacrylate dispersant was added, and a pigment dispersion having a concentration of 70% was prepared using a Cowles disperser (manufactured by Imex). .

Next, hard glass beads (manufactured by Toshiba Barotini) having an average particle diameter of 1.5 mm were charged into a vertical sand mill (manufactured by Imex Co., Ltd.), and the needle-like light calcium carbonate was wet-ground. The major axis of the pulverized needle-like light calcium carbonate was 4.1 μm, and the minor axis was 0.38 μm. Next, 50 parts of the pulverized needle-like light calcium carbonate,
To a pigment containing 25 parts of heavy calcium carbonate and 25 parts of kaolin, 0.3 part of a sodium polyacrylate-based dispersant is added, and the mixture is dispersed in water using a Cowles disperser. 5 parts and 10 parts of a styrene-butadiene copolymer latex were blended to prepare a coating solution having a concentration of 66%.

Using a bevel-type fountain blade coater, the coating weight of the bleached bleached kraft pulp solely having a basis weight of 41 g / m2 was applied to a base paper having a solid content per surface of 1%.
After being coated on both sides at a coating speed of 1200 m / min so as to be 3 g / m2 and dried, using a 2-roll / 4-stack soft calender under the conditions of a processing linear pressure of 250 kgf / cm and a processing temperature of 160 ° C. Then, surface treatment was performed online to produce a coated paper. Example 2 Needle-like light calcium carbonate was pulverized with 30
Coated paper was produced according to Example 1, except that 40 parts by weight, 40 parts of heavy calcium carbonate and 30 parts of kaolin were blended. Example 3 Needle-like light calcium carbonate after pulverization was 75
Coated paper was manufactured according to Example 1, except that 25 parts by weight and 25 parts by weight of kaolin were blended. [Example 4] The major axis was 6.5 µm and the minor axis was 0.26 produced in the causticizing step of the kraft pulp producing step.
μm columnar light calcium carbonate with a long diameter of 3.8μ
m, a coated paper was manufactured according to Example 1 except that wet grinding was performed so that the minor axis was 0.25 μm. [Comparative Example 1] 10 parts of pulverized acicular calcium carbonate, 65 parts of heavy calcium carbonate, and 25 parts of kaolin in a coating solution after pulverization.
A coated paper was manufactured in accordance with Example 1 except that parts were blended. Comparative Example 2 A coated paper was manufactured according to Example 1, except that 95 parts of pulverized acicular calcium carbonate and 5 parts of kaolin were mixed in the coating liquid. [Comparative Example 3] A long diameter of 7.0 μm and a short diameter of 0.4 μm produced in the causticizing step of the kraft pulp production step.
A coated paper was manufactured according to Example 1 except that the needle-like light calcium carbonate having a molecular weight of m was used without pulverization. [Comparative Example 4] A long diameter of 7.0 μm and a short diameter of 0.5 μm produced in the causticizing step of the kraft pulp production step.
Needle-like calcium carbonate having a long diameter of 1.5 μm
m, coated paper was manufactured according to Example 1 except that the powder was wet-pulverized so that the minor axis became 0.46 μm. [Comparative Example 5] The major axis was 9.0 µm and the minor axis was 0.5 µm produced in the causticizing step of the kraft pulp producing step.
m of needle-like light calcium carbonate having a major axis of 6.2 μm
m, coated paper was manufactured in accordance with Example 1 except that the minor diameter was 0.47 μm. [Comparative Example 6] A long diameter of 7.0 μm and a short diameter of 0.1 μm produced in the causticizing step of the kraft pulp production step.
m of the needle-like light calcium carbonate having a long diameter of 4.0 μm.
m, a coated paper was manufactured according to Example 1 except that wet grinding was performed so that the minor axis became 0.08 μm. [Comparative Example 7] The major axis was 8.0 µm and the minor axis was 1.5 µm produced in the causticizing step of the kraft pulp producing step.
m of the needle-like light calcium carbonate having a long diameter of 4.0 μm.
m, a coated paper was manufactured according to Example 1 except that the powder was wet-pulverized so as to have a minor axis of 1.3 μm. Comparative Example 8 The major axis was 4.1 μm and the minor axis was 0.38, which was produced in the causticizing step of the kraft pulp production step.
A coated paper was manufactured according to Example 1 except that the needle-like light calcium carbonate having a size of μm was used without being pulverized. [Comparative Example 9] A long diameter of 7.0 µ manufactured by a carbon dioxide method.
m, a coated paper was manufactured according to Example 1 except that the needle-like light calcium carbonate having a minor axis of 0.4 μm was wet-pulverized so that the major axis was 4.1 μm and the minor axis was 0.38 μm.

The above results are shown in Tables 1 and 2.

[0024]

[Table 1]

[0025]

[Table 2] As is clear from Tables 1 and 2, Examples 1 to 4 have high white paper glossiness, excellent opacity, printing strikethrough, and dry strength, and no generation of stalactite or streak. In contrast, Comparative Example 1 is inferior in opacity and print strikethrough. In Comparative Example 2, generation of stalactite and streak was observed. In Comparative Example 3, generation of streaks and stalactite was remarkable, the glossiness of white paper was low, and the dry strength was poor. In Comparative Example 4, the dry strength was inferior, and the occurrence of stalactite and streaks was remarkable. In Comparative Example 5, white paper glossiness was low and streaking was observed. Comparative Example 6 had poor dry strength,
Starctite and streaks were observed. Comparative Example 7 has a low blank gloss level. In Comparative Example 8, streaks and stalactite were remarkably generated, and the white paper gloss was low and the dry strength was poor. Comparative Example 9 has low blank gloss and poor dry strength.

Therefore, the coated paper for printing produced according to the present invention provides unprecedented excellent coated paper quality, and the effect thereof is extremely large.

[0027]

As described above, it is possible to provide a coated paper for printing which has a high glossiness of white paper and is excellent in opacity, print strikethrough, printing surface strength and high-speed operability.

Continued on the front page (72) Inventor Mayumi Oishi 2-81-1, Iida-cho, Iwakuni-shi, Yamaguchi Japan Japan Paper Manufacturing Co., Ltd. (72) Inventor, Katsunori 2-2-1, Iida-cho, Iwakuni-shi, Yamaguchi No. Nippon Paper Industries Co., Ltd. Iwakuni Technical Research Institute (72) Inventor Yasunori Minamisato 2-8-1, Iida-cho, Iwakuni-shi, Yamaguchi Japan Japan Paper Manufacturing Co., Ltd. Iwakuni Technical Research Institute F-term (reference) AG48 AG63 AG76 AG89 AG94 AG97 AG98 AH02 AH37 AJ04 BC06 BC07 CH12 EA16 EA32 FA12 FA13 FA22 GA19

Claims (2)

[Claims] 1. A method for producing a coated paper for printing in which a base paper is coated with a coating liquid containing a pigment and an adhesive, in a causticizing step of a pulp production step by a sulfate method or a soda method as a pigment component, Needle-like or columnar light calcium carbonate produced by slaking quicklime with water or a weak liquid and then subjecting it to a caustic reaction with green liquor has a major axis of 2.0-5.0 μm and a minor axis of 0.2-1. 0.0 μm, and then pulverized needle-like or columnar light calcium carbonate was added to the pigment component 100.
Preparing a coating liquid containing 20 to 90% by weight based on the weight%,
A method for producing a coated paper for printing, wherein the coating liquid is coated with a blade type coating apparatus. 2. The method according to claim 1, wherein the blade type coating device is a bevel type.