JPH04352898A - Production of cast-coated paper - Google Patents

Abstract

PURPOSE:To provide a method for producing cast-coated paper having a high gloss and effectively solved in the troubles of irregular glosses and pinholes in high productivity. CONSTITUTION:The above-mentioned purpose is achieved by employing a pigment containing soft calcium carbonate comprising hexagonal calcite primary particle aggregates having a secondary particle average size D10 of 0.5-2.5mum, a D30/D10 of <=0.5 and a BET specific surface area of 15-30m<2>/g in an amount of 10-80 pts. per 100 pts. of the total amount of the pigment as the pigment of the cast-coated paper. The D10 is an average diameter of the secondary particles subjected to an ultrasonic dispersion treatment for 10 min and measured with a sedigraph, and the D30 is an average diameter of the secondary particles subjected to the treatment for 30 min.

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 cast coated paper, and more particularly to a method for producing cast coated paper with high efficiency and high quality.

0002

[Prior Art] Methods for producing highly glossy coated paper for printing, called cast coated paper, include the wet casting method, in which a wet coating layer is pressed against a heated mirror drum for a glossy finish; After drying the coating layer of the state,
Rewet casting method, in which the wet coating layer is plasticized and moistened using a rewetting liquid, and then pressed against a heated specular drum for a glossy finish; and gel casting, in which the wet coating layer is made into a gel state, and then pressed against a heated specular drum, for a glossy finish. Casting methods such as the following are generally known.

[0003] All of these casting methods have in common that the surface of the coating layer, which is in a wet plastic state, is pressure-adhered to a heated specular drum, dried, and released to form a specular surface. In this method of manufacturing cast coated paper, the coating layer dries in contact with the heated mirror drum surface, so
All moisture in the coating layer or in the rewetting liquid passes from the coating layer into the paper layer and out to the other side where it evaporates and dries. For this reason, cast coated paper is currently operated at extremely low speeds compared to general art paper and coated paper, which are dried from both sides. In the production of cast coated paper, it is important to obtain a high-quality paper surface while simultaneously increasing operating speed and productivity.

Kaolin in the form of plate-shaped crystals is mainly used as the pigment constituting the coating layer of cast coated paper. However, kaolin tends not only to be oriented side by side on the surface of the coating layer, but also to be oriented in the same way within the coating layer. As a result, while it is easy to obtain high gloss, it is difficult to increase production speed due to poor moisture permeability.
There is also the problem that pinholes are likely to occur, causing uneven gloss and white spots in printing.

[0005] As a method to improve the production speed and quality problems of cast coated paper, aluminum hydroxide, titanium dioxide, barium sulfate, calcium sulfite, zinc oxide, etc., which have better moisture permeability than kaolin, have been proposed. It has been known to use light calcium carbonate, heavy calcium carbonate, etc., which have grain-like, spindle-like, spherical, or amorphous particle shapes, in combination with kaolin or alone.

More recently, cubic calcium carbonate with an average particle size of 0.1 to 1.0 μm is disclosed in Japanese Patent Publication No. 1-28155, and kaolin with an average particle size of 0.5 μm or less is disclosed in Japanese Patent Application Laid-Open No. 1-118691. The combined use of columnar or acicular calcium carbonate with a major axis of 1 to 3 μm is disclosed in JP-A-1-2.
In 92197, the average particle size is 0.2 to 2.0 μm.
, it is proposed to use plate-shaped basic calcium carbonate with an aspect ratio of 4 to 20, and urea formaldehyde resin with an average aggregate particle size of 1 to 5 μm as a pigment in the cast coating layer in JP-A-63-19003. However, none of them have a sufficient effect of improving gloss unevenness and pinholes, and there is a problem that the gloss decreases.

[0007] Furthermore, in JP-A-1-260096, amorphous silica with an average aggregate particle size of 0.5 to 10 μm is
It has been proposed for use as a pigment in cast coatings. However, this method also has the problem that although pinholes are effectively eliminated, a reduction in gloss is unavoidable.

[0008] As described above, in the method for manufacturing cast coated paper in which the cast coating layer is press-contacted to a specular drum while it is in a wet state for a cast finish, the gloss that is characteristic of cast coated paper is extremely excellent, It is extremely difficult to effectively eliminate gloss unevenness and pinholes while also achieving high productivity, and the current situation is that cast paper is manufactured at the expense of either quality or productivity to some extent. be.

[0009]

[Problems to be Solved by the Invention] In light of the above-mentioned circumstances, the present inventors have developed a structure for a cast coating layer that can effectively eliminate gloss unevenness and pinholes, provide high gloss, and exhibit high productivity. As a result of extensive research into pigments, it has been discovered that the desired effect can be obtained by using light calcium carbonate having specific properties.

0010

[Means for Solving the Problems] The present invention provides a coating layer mainly composed of a pigment and an adhesive on a base paper, and presses the coating layer against a heated mirror drum while the coating layer is in a wet state. In the method for producing cast-coated paper that has a glossy finish, the average particle diameter D10 of secondary particles consisting of aggregates of hexagonal calcite primary particles is 0.5 to 2.5 μm, and D30/D
10 is 0.5 or more, and the BET specific surface area is 15 to
30m2/g of light calcium carbonate, total pigment 1
This is a method for producing cast coated paper, characterized in that it is contained in an amount of 10 to 80 parts by weight in 0.00 parts by weight. D10 is the average particle diameter of secondary particles measured by Sedigraph, and D30 is the measured value when ultrasonic dispersion was carried out for 10 minutes, and D30 was similarly measured for 30 minutes.

[0011]

[Function] In the production of cast coated paper, the factors that increase the gloss of the paper are not only the orientation of the pigments, but also the adhesive film formation, and the amount of adhesive in the cast coated layer, especially the coating The higher the amount of adhesive on the coating surface, the higher the gloss. Therefore, when a pigment with an extremely large specific surface area such as amorphous silica is used, uneven gloss and pinholes can be effectively eliminated, but on the other hand, the amount of adhesive consumed is large, resulting in a decrease in gloss. There is a tendency to

[0012] In general cubic calcium carbonate, columnar calcium carbonate, plate calcium carbonate, etc., if the specific surface area is small, it is not possible to increase the gloss of the paper, and even if the specific surface area is large, the shape remains constant. Therefore, it is easy to orient, and the problem of uneven gloss and pinholes cannot be sufficiently solved.

Furthermore, since the urea formaldehyde resin has a low specific gravity and has a strong tendency to exist selectively on the surface of the cast coating layer, it is not only impossible to improve the moisture permeability of the entire coating layer. On the other hand, since the adhesive on the surface of the cast coating layer is consumed, the gloss tends to decrease significantly.

However, when the average particle diameter of the secondary particles was measured using Sedigraph Model 500 manufactured by Shimadzu Corporation, approximately 0.8 g of the sample dry weight was added to 25 ml of 0.1% sodium polyphosphate solution, and the sample was heated at 45 KHz. , the average particle diameter D10 of the secondary particles is 0.5 to 2.0, D10 is the value measured after dispersing for 10 minutes with ultrasonic waves with an output of 30 W, and D30 is the value measured after dispersing for 30 minutes in the same manner as above. 5μ
When light calcium carbonate having a D30/D10 ratio of 0.5 or more and a BET specific surface area of 15 to 30 m2/g is used as a pigment for a cast coating layer, it becomes normal cubic calcium carbonate, Compared to conventional pigments such as columnar calcium carbonate, platelet calcium carbonate, urea formaldehyde resin, amorphous agglomerated silica, etc., the cast coating surface has higher gloss, and uneven gloss and pinholes can be effectively eliminated. The production speed of top cast coated paper can be increased.

Although the detailed reason is not clear, since it is light calcium carbonate, it can be uniformly dispersed in the cast coating layer even when used in combination with other pigments such as kaolin. Light calcium carbonate consists of fused aggregates of hexagonal calcite primary particles, and has an optimal specific surface area to maintain the balance between gloss and pinholes. While secondary particles, which are ordinary aggregates, tend to be easily dispersed into primary particles, the secondary particles of the present invention were dispersed by ultrasonic waves for 10 minutes, as shown in the measurement method above. The average particle size of the secondary particles when dispersed for 30 minutes is more than half the particle size, and the complex shape is maintained even in the coating layer, making it difficult for moisture to pass through. Being able to improve your sexuality. Furthermore, it is presumed that the generation of uneven gloss can be prevented by optimizing the particle diameter of the secondary particles.

Therefore, the average particle diameter of the secondary particles of light calcium carbonate of the present invention is less than 0.5 μm, or BE
When the T specific surface area exceeds 30 m2 /g, there will be problems such as decreased gloss and weak adhesive strength, and the average particle diameter of the secondary particles will exceed 2.5 μm, or BE
When the T specific surface area is less than 15 m2/g, it is undesirable because it causes uneven gloss, worsens pinholes, and reduces production speed.

[0017] If the ratio D30/D10 of Sedigraph average particle diameter when dispersed with ultrasonic waves for 30 minutes and 10 minutes is less than 0.5, light calcium carbonate may be Because the secondary particle size of paint fluctuates widely, it is difficult to produce a paint of constant quality. Furthermore, if paint preparation is carried out using a dispersing machine with a strong dispersion effect such as a Coles dispersing machine, the agglomerated secondary particles break down and a large proportion of them exist as primary particles, making it impossible to obtain the desired effect. .

Furthermore, if the amount incorporated in the cast coating layer is less than 10 parts by weight based on 100 parts of the total pigment, the effect of improving gloss unevenness and pinholes will be insufficient, and if it exceeds 80 parts by weight, the gloss will decrease. Therefore, it is undesirable.

[0019] The method of the present invention can produce excellent effects in any of the following casting methods: wet casting, rewetting casting, and gelling casting.

Pigments for the cast coating layer to be used in combination with light calcium carbonate having specific properties of the present invention include, for example, kaolin, aluminum hydroxide, satin white, barium sulfate, ground calcium carbonate, anisotropic light calcium carbonate, Examples include inorganic pigments such as talc, calcined clay, structured clay, and titanium dioxide, and organic pigments such as plastic pigments and binder pigments.
One or more types can be appropriately selected and used from these.

Examples of adhesives used with inorganic pigments and organic pigments include casein, soy protein, conjugated diene polymer latex such as styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, acrylic ester and/or methacryl. Acrylic polymer latex such as acid ester polymer or copolymer, vinyl polymer latex such as ethylene/vinyl acetate copolymer,
Alternatively, alkali-soluble or alkali-insoluble polymer latex, polyvinyl alcohol, olefin/maleic anhydride resin, melamine resin, etc. are obtained by functionally modifying these various polymers with a monomer containing a functional group such as a carboxyl group. synthetic resin adhesives, starches such as positive starch, oxidized starch, and esterified starch, carboxymethyl cellulose,
Cellulose derivatives such as hydroxyethyl cellulose, etc.
Adhesives known for general coated paper can be used alone or in combination.

The amount of adhesive used is 5 to 50 parts by weight, generally 10 to 30 parts by weight, per 100 parts by weight of the pigment.

[0023] As auxiliary agents, for example, antifoaming agents, coloring agents, mold release agents, flow modifiers, waterproofing agents, preservatives, etc. may be used as appropriate.

[0024] The cast coating layer composed of the above-mentioned materials is generally prepared to have a solid component concentration of about 45 to 65% by weight, and is coated on a base paper or porous film having a basis weight of about 35 to 400 g/m2. 5-50g/m2 dry weight
After applying it to a certain degree, finish it by casting.

The base paper for cast coating paper is not particularly limited, and acidic paper or neutral paper generally used in the field of cast coating can be used. If necessary, a general pigment coating composition may be pre-coated on one or both sides of the base paper, in which case the coating amount is preferably about 5 to 30 g/m2 in terms of dry weight per side. .

As a coating device, a known device such as a blade coater, an air knife coater, a roll coater, a brush coater, a champlex coater, a bar coater, or a gravure coater is used, and after coating, a wet casting method or a rewet casting method is used. , or to a glossy finish either by the gel cast method.

[0027]

EXAMPLES The present invention will be specifically explained below, but is not limited thereto. Unless otherwise specified, parts and percentages in the examples refer to parts by weight and percentages by weight, respectively.

[0028]

[Table 1]

Example 1 As a coating liquid for casting, 20 parts of light calcium carbonate shown in Table 1, trade name: Albuquer PO (calcite in which primary particles close to spherical form secondary particles) manufactured by Pfizer MSP were used. and 80 parts of kaolin for 100 parts of pigment, 0.5 part of antifoaming agent, 1.0 part of stearic acid as a mold release agent, and 10 parts (solid content) of a 15% casein aqueous solution dissolved in ammonia as an adhesive. A cast coating liquid with a concentration of 48% consisting of 12 parts (solid content) of styrene/butadiene/methyl methacrylate (ratio: 40/30/30) copolymer latex was prepared, and cast finishing was performed by a wet casting method.

That is, 64 g of the above cast coating liquid
/m2 of casting base paper to a dry weight of 10 g/m2 using the first coating device, and then using the second coating device to coat the same casting coating solution as above to a dry weight of 10 g/m2.
m2, the coated layer was immediately pressed against a specular cast drum with a surface temperature of 80°C using a press roll, and after drying, it was peeled off from the cast drum to obtain a cast coated paper. Table 2 shows the quality and workability of the cast coated paper obtained.

Comparative Example 1 Cast coating was carried out in the same manner as in Example 1, except that the light calcium carbonate in Example 1 was replaced with Albafil (hexagonal columnar calcite), manufactured by Pfizer MSP, with the trade name shown in Table 1. I got the covering paper. Table 2 shows the quality and workability of the cast coated paper obtained.

Comparative Example 2 In Example 1, the pigment formulation of the cast coating liquid was changed to a urea formaldehyde resin whose secondary particles had an average particle diameter of 2.1 μm (according to the Coulter Counter method) and a BET specific surface area of 20 m2/g. A cast coated paper was obtained in the same manner as in Example 1, except that 20 parts and 80 parts of kaolin were used. Table 2 shows the quality and workability of the cast coated paper obtained.

Comparative Example 3 The same procedure as in Example 1 was carried out except that the light calcium carbonate shown in Table 1, Albuquer PO, manufactured by Pfizer MSP Co., Ltd. was changed to 5 parts and kaolin was changed to 95 parts. A cast coated paper was obtained. Table 2 shows the quality and workability of the cast coated paper obtained.

[0034]

[Table 2]

Example 2 Pigment 1 containing 50 parts of light calcium carbonate, Albuquer PO and 50 parts of kaolin as shown in Table 1 was used as a coating liquid for casting.
00 parts, 7 parts (solid content) of a 15% casein aqueous solution dissolved using 0.5 parts of an antifoaming agent, 1.0 parts of ammonium stearate as a mold release agent, and ammonia as an adhesive.
and 18 parts (solid content) of styrene-butadiene copolymer latex and 2 parts of ZnSO4 were added to prepare a coating liquid for casting with a solid content concentration of 45%, and a cast finish was performed using a rewet casting method. .

That is, the above cast coating liquid was applied at 64 g/m
The base paper for casting No. 2 was coated with an air knife coater to a dry weight of 20 g/m 2 and dried with an air floating dryer. Next, this coated paper is passed through a press nip formed by a press roll and a cast drum, where the surface of the coated layer is coated with a rewet liquid (0.5% concentration) made of polyethylene emulsion supplied from a nozzle. After rewetting, it was pressed against a mirror cast drum with a surface temperature of 105°C at a press pressure of 200 kg/cm.
After drying, it was peeled off from the cast drum using a take-off roll to obtain cast coated paper. Table 3 shows the quality and workability of the cast coated paper obtained.

Comparative Example 4 In Example 2, light calcium carbonate was replaced with Hakuenka PX (calcite in which primary particles close to a cubic shape form secondary particles), manufactured by Shiraishi Kogyo Co., Ltd., with the trade name shown in Table 1. Otherwise, cast coated paper was obtained in the same manner as in Example 2. Table 3 shows the quality and workability of the cast coated paper obtained.

Comparative Example 5 The same procedure as in Example 2 was carried out except that the light calcium carbonate in Example 2 was replaced with Brilliant S-15 (calcite with a nearly cubic shape) manufactured by Shiraishi Kogyo Co., Ltd. shown in Table 1. A cast coated paper was obtained. Table 3 shows the quality and workability of the cast coated paper obtained.

Comparative Example 6 In Example 2, the pigment formulation of the cast coating liquid was changed to a urea formaldehyde resin whose secondary particles had an average particle diameter of 2.1 μm (according to the Coulter Counter method) and a BET specific surface area of 20 m2/g. A cast coated paper was obtained in the same manner as in Example 2, except that the amount of kaolin was changed to 20 parts and 80 parts. Table 3 shows the quality and workability of the cast coated paper obtained.

Comparative Example 7 Cast coated paper was obtained in the same manner as in Example 2, except that the light calcium carbonate and Albuquer PO shown in Table 1 were changed to 85 parts and kaolin was changed to 15 parts. . Table 3 shows the quality and workability of the cast coated paper obtained.

[0041]

[Table 3]

Example 3 As a coating liquid for casting, pigment 1 containing 45 parts of light calcium carbonate and Albuquer PO and 55 parts of kaolin as shown in Table 1 was used.
00 parts, 12 parts (solid content) of a 15% casein aqueous solution dissolved using 0.5 parts of an antifoaming agent, 3.0 parts of calcium stearate as a mold release agent, and ammonia as an adhesive.
and 16 parts (solid content) of styrene-butadiene copolymer latex were added to prepare a coating liquid for casting with a solid content concentration of 49%, and cast finishing was performed using a gel casting method.

That is, the above-mentioned coating liquid was applied to a casting base paper of 64 g/m2 by a roll coater so that the dry weight was 20 g/m2, and then a calcium formate aqueous solution with a concentration of 0.5% was applied. The coating layer was gelled upon contact. This coated layer was pressed against a specular cast drum with a surface temperature of 98° C. at a press pressure of 100 kg/cm using a press roll, and after drying, it was peeled off from the cast drum using a take-off roll to obtain a cast coated paper. Table 4 shows the quality and workability of the cast coated paper obtained.

Comparative Example 8 A cast coated paper was obtained in the same manner as in Example 3, except that Albafil shown in Table 1 was used instead of light calcium carbonate. Table 4 shows the quality and workability of the cast coated paper obtained.

Comparative Example 9 In Example 3, the light calcium carbonate was replaced with the product name shown in Table 1: Hakuenka PZ (calcite in which primary particles close to a cubic shape form secondary particles) manufactured by Shiraishi Kogyo Co., Ltd. Cast coated paper was obtained in the same manner as in Example 3 in other respects. Table 4 shows the quality and workability of the cast coated paper obtained.

[0046]

[Table 4]

[Evaluation Method] The operability was evaluated based on the maximum operable speed of the obtained cast coated paper, and the quality was evaluated using the following method for glossiness, gloss unevenness, and pinholes. Glossiness is determined by JIS and P-8142. Gloss unevenness is visually judged according to the following criteria: ○: No gloss unevenness △: Slight gloss unevenness is seen, but there is no practical problem ×:
Pinholes that are unsuitable for practical use due to uneven gloss are determined visually based on the following criteria: ○: Almost no pinholes △: There are a few pinholes, but there is no practical problem ×: There are many pinholes, and it is not suitable for practical use

[0048]

Effects of the invention: As is clear from the results in Tables 2 to 4, the cast coated paper obtained in the examples of the present invention has high gloss and high quality, and is effective in reducing uneven gloss and pinholes. It was possible to efficiently obtain cast-coated paper with excellent cast-coated paper, which was free from problems, at high operating speeds.

Claims (1)

[Claims] Claim 1: Cast-coated paper in which a coating layer mainly composed of pigment and adhesive is provided on a base paper, and the coating layer is pressed against a heated mirror drum while it is in a wet state to give a glossy finish. In the manufacturing method, the average particle diameter D10 of secondary particles consisting of aggregates of hexagonal calcite primary particles is 0.5 to 2.
．． 5 μm, D30/D10 is 0.5 or more, and BET specific surface area is 15 to 30 m2/g, and is characterized by containing 10 to 80 parts by weight in 100 parts by weight of the total pigment. Method for manufacturing cast coated paper. D10 is the average particle diameter of secondary particles measured by Sedigraph, and D30 is the measured value when ultrasonic dispersion was carried out for 10 minutes, and D30 was similarly measured for 30 minutes.