JP3257284B2 - Manufacturing method of cast coated paper - Google Patents

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 cast-coated paper, and more particularly to a method for producing a cast-coated paper having excellent white paper gloss, excellent print gloss and surface strength, and excellent operability. .

[0002]

2. Description of the Related Art Cast coated paper has very high surface gloss, excellent smoothness, and excellent printability.
As high-grade printing paper, it is widely used not only for covers of general books and the like, but also for high-quality labels, fashion bags, and the like. There are three typical methods for producing such cast coated paper having high gloss and high smoothness. That is, the wet coating method is pressed against the surface of the heating drum that has been subjected to mirror finishing with the coating layer in the wet state, dried, released, and gloss-finished by wet casting. Wet again, after plasticizing, press-contact the heated cast drum surface, re-wet casting method to finish by releasing, further gelling the wet coating layer, press-contact the heated cast drum surface, It is a gel casting method that finishes by releasing. These casting methods are common in that the coating layer in the wet or plasticized state is pressed against the surface of the heating drum, dried, released from the heating drum, and the mirror surface is copied.

In such a method for producing a cast coated paper, since the coating layer is dried in contact with the surface of the heating drum, the moisture in the coating layer or the re-wetting of the coating layer is required. All the water of the used rewetting liquid passes through the paper layer, escapes to the back surface (non-cast surface side), and evaporates.
For this reason, in the production of cast coated paper, it is currently necessary to operate at an extremely low speed in comparison with the production of general art paper and coated paper dried from both sides of the coated paper. .

[0004] Among the above-mentioned methods for producing cast coated paper, the rewet casting method can perform a casting finish at a casting drum temperature of 100 ° C. or higher, so that the speed is relatively much higher than the wet casting method. It has the advantage that production is possible. However, on the other hand, the degree of wet plasticization is significantly lower than in the other methods because the coating layer once dried is rewet. As a result, it is difficult for the coating layer to be evenly adhered to the heated casting drum surface, and as the operation is performed at a higher speed, pinholes and uneven gloss occur, the uniformity of the coated surface is lost, and the gloss decreases. It has the difficulty of being easy. In the rewet casting method, in order to improve the above-mentioned problems, a method of adding a metal salt to the coating composition in the coating composition (Japanese Patent Application Laid-Open No.
No. 146097), but in order to sufficiently improve pinholes and uneven gloss, the amount of metal salts must be increased, and when the amount is increased, the viscosity of the coating composition increases. In fact, it is difficult to operate under stable conditions.

[0005]

SUMMARY OF THE INVENTION According to the present invention, in a rewet casting system, cast coated paper having particularly excellent surface strength and extremely high paper gloss can be produced with high efficiency by eliminating uneven gloss and pinholes. It is intended to provide a manufacturing method.

[0006]

According to the present invention, a coating composition comprising a pigment and an adhesive as a main component is coated on a base paper and dried to form a coating layer. After applying the rewet liquid and moistening and plasticizing, it is pressed against the heated mirror drum,
In the method for producing cast coated paper having a high gloss finish,
The coating composition has an average particle size of 0.23 to
0.35μm and a polymer latex to the pigment solid content of 10 wt% or more, further cross-linking reaction prompting the coating object composition
Calcium sulfate, zinc sulfate, calcium acetate as promoter
, Magnesium acetate, calcium formate, magnesium sulfate
Um, at least one <br/> cast coated paper manufacturing method of the metal salt is characterized by being the additional inclusion 0.2-3 wt% relative to pigment solids selected from aluminum sulfate (provided that The coating composition is an acrylic emulsion and
Not containing modified aqueous urethane resin) .

[0007]

Based on the above facts, the present inventors have conducted intensive studies on the production of cast coated paper, especially in the rewet casting method, in order to obtain cast coated paper excellent not only in operability but also in quality. Was. As a result, by using a specific polymer latex as an adhesive in the coating layer and using a specific metal salt in combination, it has high gloss, no uneven gloss and no pinholes, and excellent printing surface strength The present inventors have found that cast cast coated paper can be obtained efficiently (at high speed), and have completed the present invention.

That is, adhesives generally used for cast coating compositions include natural adhesives such as casein and starch,
Synthetic latex such as styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer are mainly used. These adhesives not only bond the pigment to the pigment or the pigment to the base paper, but also form a film at the time of casting and serve as a medium for copying the mirror surface of the cast drum, and have an effect of expressing high gloss.

On the other hand, these adhesives have a problem that the porosity of the coating layer is reduced and the air permeability is deteriorated. In the present invention, in particular, as a result of repeated studies and researches to solve these difficulties, the average particle diameter is reduced to 0 in place of the synthetic latex having a conventional average particle diameter of 0.16 to 0.22 μm. It has been found that good air permeability can be obtained when a large particle size latex of 0.23 to 0.35 μm is used. However, although the use of latex having such a large particle size improves air permeability and is excellent in adhesion to the drum surface, on the other hand, there is a disadvantage that the surface strength is reduced, and it is not sufficiently satisfactory. Was. Therefore, as a result of further study, by using a coating composition containing the specific large particle diameter latex and a specific metal salt in combination, while maintaining the effect of improving air permeability and adhesion, gloss unevenness and the like. It was found that pinholes were largely eliminated and cast coated paper excellent in printing surface strength was efficiently obtained. By the way, when the average particle diameter is less than 0.23 μm, uneven gloss and pinholes tend to be deteriorated, and when it exceeds 0.35 μm, the gloss decreases and the surface strength is further decreased, Not preferred.

On the other hand, as described above, when a synthetic latex having a large particle diameter is used, air permeability and adhesion to the drum surface are improved, but there are disadvantages such as a decrease in surface strength.
It is difficult to commercialize as it is. Therefore, as a result of repeated studies, the surface strength is greatly improved by using such a large particle diameter latex and a specific metal salt in combination, and it is not necessary to increase the addition amount of the metal salt so much. Efficiently produce cast coated paper having high gloss and excellent surface strength, which eliminates so-called pinholes and uneven gloss, which is desired by the present invention, without significantly affecting the physical properties of the coating composition. We found that we could produce well.

The average particle diameter of the latex is generally determined by a seed polymerization method in which a polymer latex (referred to as a seed) of small particles that have been polymerized in advance is placed in a reaction vessel and an emulsifier, a monomer, and a catalyst are added and polymerization is performed. The required average particle size can be obtained by controlling the amount of, the particle size of the seed, and the amount of the monomer used.

By the way, in ordinary coated papers and the like, the metal salt tends to lower the surface strength and the like, and is not necessarily a preferable material from the viewpoint of the surface strength when it is put into a coating layer. There are no additives. On the other hand, the reason why the surface strength is improved by adding a metal salt to the cast coating layer is not clear, but is presumed as follows.

[0013] It is considered that the re-wet casting method is largely different from the ordinary coated paper in the coating finish method. That is, in the case of a general coated paper, the metal salt in the coating composition has an action of gelling the paint, and as a result, the dry paint can be finished in a bulky manner. High smoothness and high gloss can be obtained by leaving the crushing allowance in the apparatus. For this reason, the density of the coating layer is low due to the metal salt in the dry coating layer, and as a result, the bonding strength of the adhesive contained therein (pigment and pigment,
Alternatively, it is assumed that the force for joining the pigment and the base paper) is also reduced accordingly.

On the other hand, in the case of the re-wet cast method,
Since the dry coating layer is re-wetted and is brought into contact with the metal surface heated with strong pressure, it does not become a bulky coating layer, but rather the strong pressure and high temperature cause the metal salt to react with other adhesives and the like. It is presumed that the cross-linking reaction is promoted, and as a result, the water resistance is imparted and the surface strength is enhanced.

In the present invention, a metal salt, which is another important element, has already been disclosed in JP-A-60-14.
No. 6097 has been proposed. As described above, it is not possible to obtain a sufficient effect only by adding these metal salts, especially when performing a high-speed casting finish of 100 m / min or more. For this reason, an attempt has been made to increase the amount of addition, but in that case, the viscosity of the coating material increases and gelation occurs, and a stable coating composition cannot be obtained.

In the present invention, by using these metal salts in combination with the latex having a large particle diameter, unevenness of gloss and pinholes on the surface of the cast-coated paper can be remarkably eliminated with a relatively small amount of metal salts added. In addition, since the stable coating fluidity is maintained, a cast coated paper having excellent quality can be obtained very efficiently.

The method for producing a cast coated paper according to the present invention will be described below in detail. The coating composition for forming the cast coating layer contains a pigment and an adhesive as main components. First, as described above, the latex used as the adhesive has an average particle diameter of 0.23 to 0.35 μm.
It is essential to use the polymer latex at m.
And, it does not particularly specify the material of the polymerization monomer, for example, styrene, α-methylstyrene, methylstyrene, as a monomer to be polymerized or copolymerized,
Olefinic aromatic monomers such as chlorostyrene,
Methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, glycidyl acrylate, glycidyl methacrylate And olefinic aliphatic monomers such as vinyl acetate, butadiene and the like. Then, it is possible to use a styrene-butadiene copolymer latex or a methyl methacrylate-butadiene copolymer latex obtained by copolymerizing a butadiene monomer and a styrene monomer, or a butadiene monomer and a methyl methacrylate monomer as main components. It is particularly preferable in terms of white paper gloss, printing surface strength, and releasability of the paper.

Further, if necessary, acrylamide,
Methacrylamide, N-methylolacrylamide,
One or more of ethylenically unsaturated carboxylic acid amides such as diacetone acrylamide and unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile may be appropriately combined.

In the present invention, the average particle size is from 0.23 to 0.1.
In addition to the polymer latex having a particle size of 35 μm, it is also possible to use a latex having a usual average particle diameter used in general cast coated paper. In addition, the compounding ratio of the large particle diameter latex in the present invention is 10% by weight or more, more preferably 15 to 30% by weight, based on the solid content, based on all pigments. If the amount is less than 10% by weight, it is difficult to obtain a desired and sufficient effect on gloss unevenness and pinholes, whereas if it exceeds 30% by weight, the releasability tends to decrease.

In addition to the latex, for example, proteins such as casein, soybean protein and synthetic protein, various starches such as etherified starch and oxidized starch, polyvinyl alcohol, cellulose derivatives such as carboxymethylcellulose and methylcellulose, and olefin-anhydrous One or more general adhesives for coated paper, such as a maleic acid resin, can be used in combination as appropriate.

Next, pigments other than heavy calcium carbonate, such as kaolin, clay, calcined clay, amorphous silica, zinc oxide, aluminum oxide, aluminum hydroxide, light calcium carbonate, satin white, aluminum silicate,
Various pigments known and used in the coated paper manufacturing field, such as magnesium silicate, magnesium carbonate, diatomaceous earth, styrene plastic pigment, urea resin plastic pigment, and benzoguanamine plastic pigment, can be used.

In the present invention, metal salts which are important components include, for example, zinc, aluminum, calcium, or magnesium such as calcium sulfate, zinc sulfate, calcium acetate, magnesium acetate, calcium formate, magnesium sulfate, and aluminum sulfate. A metal salt selected from at least one of the following. The amount of addition is adjusted in the range of 0.2 to 3% by weight, more preferably 0.5 to 2% by weight, based on the solid content of the pigment. By the way, 0.2
If the amount is less than 3% by weight, the effect of improving uneven gloss and pinholes is not sufficient. In addition, an antifoaming agent, a coloring agent, a release agent, a flow modifying agent, a waterproofing agent, a preservative, and the like may be used as necessary.

The base paper for casting is not particularly limited, and acidic paper or neutral paper used for general coated paper is applied. On one or both sides of the base paper, if necessary, a coated paper pre-coated with a general pigment coating composition in advance, and if necessary, the pre-coated coated paper in advance, a super calender, Smoothed products such as brushing and cast finishing are also used as base paper for casting.

The coating composition for casting composed of the above-mentioned materials is generally adjusted to a solid content of about 20 to 70% by weight, and dried on a base paper for casting having a rice area of about 20 to 400 g / m ^2. Various known materials such as a blade coater, an air knife coater, a roll coater, a brush coater, a champlex coater, a bar coater, and a gravure coater may be used so as to have a weight of about 10 to 50 g / m ² , more preferably about 20 to 30 g / m ² . After being coated by the coating device, it is dried.

After the coating composition for casting is coated on the base paper by the above-mentioned method and dried, the re-wet casting method, that is, the coating layer is re-wetted, is pressed against a heated mirror-surface drum, and is glossy. Finished. At this time, the air permeability of the coated paper before rewet is 700 seconds / 100 cc or less, more preferably 100 seconds or less, in accordance with JIS P-8117.
500 seconds / 100 cc. By the way, 700 seconds / 10
If it exceeds 0 cc, the vapor permeability of the coating layer tends to deteriorate, and as a result, uneven gloss and pinholes tend to deteriorate. If it is less than 100 seconds / 100 cc, the surface strength tends to decrease. On the other hand, to adjust the air permeability,
It can be appropriately carried out by selecting and combining materials such as pigments and adhesives, adjusting the coating amount, and the like.

The rewet liquid is not particularly limited, but generally, as a release agent, for example, polyethylene emulsion, salts or derivatives of fatty acids, microcrystalline wax, funnel oil, etc. are dissolved or dispersed in water. The used liquid is used. Further, of course, phosphates such as sodium hexametaphosphate and organic acids, salts of organic acids, etc. may be used in combination for the purpose of promoting plasticization of the dry coating layer.
It is possible. It is also effective to perform a smoothing process such as super calendering or brushing before rewetting the coating layer.

[0027]

Next, the present invention will be described in detail with reference to examples, but it is needless to say that the present invention is not limited to these examples.
Unless otherwise specified, parts and% in the examples indicate parts by weight and% by weight, respectively.

Example 1 50 parts of kaolin, 50 parts of light calcium carbonate, and 0.3 parts of sodium polyacrylate were dispersed in water using a Cores disperser to prepare a pigment slurry having a solid content of 65%. 0.3 parts of tributyl phosphate as an antifoaming agent, 1.0 part of ammonium stearate as a releasing agent, 20 parts of a styrene-butadiene copolymer latex having an average particle diameter of 0.25 μm as an adhesive, and ammonia are used in this slurry. 5 parts of a 15% aqueous solution of casein dissolved therein was added, and 1.5 parts of calcium formate and water were further added to prepare a coating solution for casting having a finished concentration of 45%.

This coating solution for casting was prepared by adding 105 g of rice tsubo /
After coating on a base paper of m ^{2 with} an air knife coater so as to have a dry weight of 25 g / m ² , it was dried with an air floating drier. The air permeability of the coated paper is 500 seconds / 100 by a method based on JISP-8117.
cc. Next, the coated paper is passed through a press nip formed by a press roll and a cast drum, where the coated paper is coated with a rewetting liquid comprising 1% of an aqueous solution of polyethylene emulsion and 1% of sodium citrate supplied from a nozzle. After the layer surface was rewet, it was pressed against a cast drum having a surface temperature of 110 ° C. at a linear pressure of 220 kg / cm, dried and peeled to obtain a cast coated paper.

Example 2 A cast coated paper was obtained in the same manner as in Example 1 except that 1.5 parts of magnesium sulfate was added instead of calcium formate. The air permeability of the cast coated paper before rewet (before cast coating) is JIS P-8117.
Was 600 seconds / 100 cc according to the method in accordance with.

Example 3 A cast coated paper was obtained in the same manner as in Example 1, except that 2.5 parts of zinc sulfate was added instead of calcium formate. The air permeability of the cast coated paper before rewet (before cast coating) was 300 seconds / 100 cc by a method based on JIS P-8117.

[0032]

Example4  In Example 1, styrene having an average particle size of 0.25 μm was used.
Average particles instead of butadiene copolymer latex
Styrene-butadiene copolymer latex having a diameter of 0.30 μm
Except for using the paint, the same method as in Example 1 was used for cast coating.
A paper was obtained. Before re-wetting of this cast coated paper (cast
Air permeability (before coating) conforms to JIS P-8117
It was 400 seconds / 100 cc by the method.

Embodiment5  70 parts kaolin, 30 parts light calcium carbonate, Polyac
0.4 parts of sodium acrylate was dissolved in water using a Kohles disperser.
In a pigment slurry having a solid content of 65%.
Was. Tributyl phosphate is added to this slurry as an antifoaming agent.
0.3 parts of zinc stearate 1.0 as a release agent
Part, methylmeta having an average particle size of 0.24 μm as an adhesive
Acrylate-butadiene copolymer latex 17 parts,
15% aqueous solution of casein dissolved with ammonia
4 parts, and then 1.0 part of calcium acetate and water.
Preparation of a coating solution for casting with a finished concentration of 45%
Was. The coating liquid for casting was prepared by adding 105 g / m²Nohara
25g dry weight on paper using air knife coater
/ M²After coating so that it becomes air floating
Dried with a dryer. The air permeability of this coated paper is JIS
600 seconds / 100cc by the method based on P-8117
there were.

Next, the coated paper is passed through a press nip formed by a press roll and a cast drum, and coated with a rewetting liquid (1% concentration) of ammonium stearate supplied from a nozzle. After rewetting the layer surface, press linear pressure 2
By pressing, drying and peeling at 50 kg / cm,
A cast coated paper was obtained.

Comparative Example 1 In Example 1, the average particle diameter of the adhesive was 0.25 μm.
A cast coated paper was obtained in the same manner as in Example 1 except that a styrene-butadiene copolymer latex having an average particle diameter of 0.18 μm was used instead of the styrene-butadiene copolymer latex of m. The air permeability of the cast coated paper before rewet (before cast coating) was 1000 seconds / 100 cc according to a method based on JISP-8117.

Comparative Example 2 A cast coated paper was obtained in the same manner as in Comparative Example 1, except that the amount of calcium formate was changed to 5 parts by weight. The air permeability of the cast coated paper before rewet (before cast coating) was 450 seconds / 100 cc according to a method based on JIS P-8117.

Comparative Example 3 30 parts of kaolin, 70 parts of light calcium carbonate, and 0.5 part of sodium polyacrylate were dispersed in water using a Cores disperser to prepare a pigment slurry having a solid content of 60%. 0.2 parts of tributyl phosphate as an antifoaming agent, 1.0 part of calcium stearate as a release agent, 5 parts of a styrene-butadiene copolymer latex having an average particle diameter of 0.25 μm as an adhesive, and 5 parts of an average particle diameter of 0 15 parts of a methyl methacrylate-butadiene copolymer latex of 0.21 μm, 6 parts of a 15% aqueous solution of casein dissolved using ammonia, 1.5 parts of zinc acetate and water were added, and the pH was adjusted to 8 with ammonia. hand,
A coating solution for casting having a finished concentration of 45% was prepared. Using this coating liquid, a cast coated paper was obtained on the same base paper as in Example 1 by the same method as in Example 1. The air permeability of this cast coated paper before re-wetting (before cast coating) is JIS
900sec / 100cc by the method based on P-8117
Met.

Comparative Example 4 A cast coated paper was obtained in the same manner as in Example 1 except that calcium formate was not added. The air permeability of the cast coated paper before rewet (before cast coating) is 1200 seconds / 1 by a method in accordance with JIS P-8117.
It was 00 cc.

Comparative Example 5 A cast coated paper was obtained in the same manner as in Example 1, except that 1.5 parts of sodium acetate was used instead of calcium formate. The air permeability of the cast coated paper before rewet (before cast coating) is JIS P-8117.
Was 1050 sec / 100 cc according to the method based on JIS.

[0041] In Comparative Example 6 Example 5, except that the calcium acetate and no addition is to obtain a cast coated paper in the same manner as in Example 5. The air permeability of the cast coated paper before rewet (before cast coating) is 1150 seconds / 1 according to a method in accordance with JIS P-8117.
It was 00 cc.

Comparative Example 7 A cast coated paper was obtained in the same manner as in Example 1, except that the amount of calcium formate added was changed to 0.1 part. Before re-wetting of this cast coated paper (before cast coating)
Has an air permeability of 10 in accordance with JIS P-8117.
30 seconds / 100 cc.

Comparative Example 8 In Example 1, 0.36 μm of a styrene-butadiene copolymer latex having an average particle diameter of 0.25 μm was used instead of 0.36 μm.
A cast coated paper was obtained in the same manner as in Example 1 except that a styrene-butadiene copolymer latex of μm was used. Before re-wetting of this cast coated paper (before cast coating)
Has a gas permeability of 43 in accordance with JIS P-8117.
It was 0 seconds / 100 cc.

In the cast coated paper thus obtained, the average particle diameter and the amount of the copolymer latex used in the production thereof, and the type of the metal salt used in combination with the copolymer latex and the amount thereof In Table 1,
In addition, blank gloss, gloss unevenness of the obtained cast coated paper,
The printing surface strength and the releasability from the drum during operation were evaluated as described below, and the obtained results were shown in Table 2.
It was shown to.

"White paper gloss" was measured according to JIS P-8142.

"Gloss unevenness" Gloss unevenness on the surface of the cast coated paper was visually evaluated according to the following criteria. ：: No gloss unevenness was observed. ：: The gloss unevenness is slightly observed, but there is no practical problem. Δ: Gloss unevenness is observed. ×: Many gloss unevenness is observed.

[Printing surface strength] An ink for sheet offset (Gr. Manufactured by Dainippon Ink and Chemicals, Inc.) was measured using an RI printing tester.
af-G black) The surface of the cast coated paper was printed five times using 0.4 cc, and the state of the surface after printing was observed and judged according to the following criteria. ：: Excellent surface strength, no peeling of the coating layer on the surface of the cast coated paper. Δ: Peeling of the coating layer on the surface of the cast coated paper was slightly observed, but there was no practical problem. X: The coating layer on the surface of the cast coated paper was remarkably peeled.

"Paint stability" ：: The paint viscosity is stable and continuous operation is possible. ×: The coating gelled, and uniform coating was not possible.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

As is clear from Table 2, the cast coated paper obtained in the examples according to the present invention has no gloss unevenness.
The glossiness of the white paper and the printing surface strength were extremely excellent, the operability was excellent, and the production was efficient.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-223170 (JP, A) JP-A-6-2299 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D21H 19/00-27/42

Claims (2)

(57) [Claims] 1. A base paper is coated with a coating composition containing a pigment and an adhesive as main components, dried to form a coating layer, and then a rewetting liquid is applied to the coating layer to wet the coating layer. In a method for producing a cast coated paper, which is plasticized and then pressed against a heated mirror drum to give a high gloss finish, the coating composition has an average particle diameter of 0.23 to 0.35 μm as an adhesive. A certain polymer latex is 10% by weight or more based on the solid content of the pigment, and calcium sulfate is used as a crosslinking reaction accelerator in the coating composition.
, Zinc sulfate, calcium acetate, magnesium acetate, ants
Calcium sulfate, magnesium sulfate, aluminum sulfate
At least one cast coated paper manufacturing method of the metal salt is characterized by being the additional inclusion 0.2-3 wt% relative to pigment solids selected et (However, coating the composition Accession
Ril emulsion and modified aqueous urethane resin
No) 2. The cast coating according to claim 1, wherein the coated paper provided with the dry coating layer before applying the rewetting liquid has an air permeability according to JIS P-8117 of 700 seconds / 100 cc or less. Paper manufacturing method.