JPH0246717B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing cast-coated paper, and in particular to an improved rewet casting method that enables production at high speed without producing spots or uneven gloss due to uneven adhesion on the surface of the coating layer. There are two methods of producing highly glossy coated paper for printing, called cast coated paper: the wet cast method, in which the wet coating layer is pressed against the surface of a heated drum for a glossy finish, and the wet coating method, in which the wet coating layer is made into a gel state. Known methods include a gel cast method in which a wet coating layer is brought into contact with the heated drum surface to achieve a glossy finish, and a rewet cast method in which a wet coating layer is once dried and then plasticized by rewetting and then brought into pressure contact with the heated drum surface. All of these cast finishing methods dry the coating layer in a plastic state by pressing it against the surface of a heated drum.
Although they are common in that they release from the mold, they each have the following problems in operability and quality of the resulting cast coated paper due to differences in the plasticity state of the coated layer. First, in the wet casting method, if the temperature of the heating drum surface is raised to 100°C or higher, the coating liquid will boil and the coating layer will be destroyed, so it is impossible to raise the temperature above 100°C. Currently, they are forced to operate at high speeds. In the gel cast method, since the coating layer is in a gel state, it is possible to raise the temperature of the heating drum surface to over 100℃, but it is possible to raise the temperature of the heating drum surface to over 100℃. Finishing is not done at very high speeds in practice because it needs to be transferred to the base paper layer in the nip formed by the pressure roll, and it is also difficult to control the degree of gelation of the coated layer. do not have. In the rewet cast method, the coating layer is once dried, so it is possible to raise the temperature of the heated drum surface to 90 to 180℃, but in order to rewet the coating layer once dried, plasticization is required. The degree of Therefore, although a coated paper with a relatively uniform high gloss can be obtained when operating at low speeds, the uniformity of the gloss rapidly decreases as the operating speed increases. This phenomenon is caused by pinhole-like spots and uneven gloss, and is thought to occur because the coating layer is not evenly adhered to the heating drum surface due to low plasticization. In order to improve these problems in the rewet cast method, for example, there are methods in which the coated layer is subjected to excessive supercalendering to smooth it before rewetting, and a method in which the coated layer is pressed against the finished surface is smoothed. There are proposals for methods of increasing the press roll pressure. However, these methods have the disadvantage that the advantages of cast-coated paper, which are low tension, bulk, and high hardness, are significantly impaired. Therefore, as a method for improving the uneven adhesion without impairing the bulk, a method has been proposed in which coated paper is treated with a brush before being rewetted. However, while this method can smooth the coated surface, it tends to make the coated layer surface denser, so when producing cast coated paper at high speeds, It is difficult for the water in the rewetting liquid to evaporate through the base paper layer, so in reality, the casting speed cannot be increased unless sufficient water evaporation is ensured. The printing ink also dries slowly,
It also has the disadvantage of causing problems with ink set-off. For this reason, in any of the above-mentioned cast finishing methods, it is difficult to produce high-quality cast-coated paper at high speed without causing spots due to uneven adhesion or uneven gloss on the surface of the coated layer. The current situation is that it is technologically behind. As a result of many years of research into producing high-quality cast-coated paper at high speeds, the inventors of the present invention found that among the three cast finishing methods described above, it is the one that is most capable of high-speed production due to its properties. By paying attention to the rewetting cast method, which has hidden properties, and conducting technical studies on its rewetting liquid in particular, they finally established a technology that satisfies the above objectives. Therefore, the structure of the present invention is a method for manufacturing cast coated paper in which a dried coating layer mainly composed of pigments and adhesives is re-wetted and pressed against a heated mirror surface to give a high gloss finish. , the rewetting liquid contains an amide compound as a plasticization accelerator. By the way, the conventional rewetting liquid used in the rewetting cast method is generally water or water containing a surfactant, and phosphates, which have a dispersion function for pigments, are generally used. It is also known to use aqueous solutions of. However, in order to obtain enough plasticity to prevent uneven adhesion of the coated layer to the heating drum surface due to phosphate, a fairly long immersion time of 2 to 3 seconds is required; The disadvantage is that excessive water permeates into the layer, which ultimately takes time to dry, making it difficult to cast at high speed. It is also known to use ammonia and hexamethylenetetramine as external rewetting liquids to promote plasticization of hydrophilic adhesives such as casein. Although these rewetting solutions promote plasticization in a short time and produce a homogeneous, highly glossy cast-coated paper, they do not remove the mold release agent (oleic acid, stearic acid, etc.) attached to the heating drum surface. It has the disadvantage that it has the effect of dissolving thin films of fatty acids (such as fatty acids), and cannot be operated for a long time. On the other hand, the amide compound used in the present invention is so fast-acting that the plasticization time of the coating layer is comparable to that of ammonia, hexamethylenetetramine, etc., and it does not adhere to the heating drum surface. It has been confirmed that this method does not have the effect of dissolving the release agent film, and is extremely effective in producing homogeneous, high-gloss cast-coated paper without uneven gloss at high speed. Although the mechanism by which amide compounds act effectively in this way is not yet clear, it is said that an aqueous solution of an amide compound has a larger volume than water alone, which increases the solvation effect. It is thought that it promotes plasticization of the coated layer and, as a result, exhibits a rewetting effect equivalent to that of ammonia or hexamethylenetetramine. The amide compounds used in the present invention include:
It is referred to as amide or imide as described in the Physical and Chemistry Dictionary (Iwanami Shoten), and specifically,
These include urea, formic acid amide, acetic acid amide, benzoic acid amide, oleic acid amide, stearic acid amide, succinimide, glutarimide, phthalimide and derivatives thereof, and in the present invention, cyanamide and dicyandiamide derived from cyanamide, thiourea, It also targets guanidine. These amide compounds are used alone or in combination of two or more, and among them, urea,
Thiourea and dicyandiamide are very effective. Further, when these amide compounds are used as a rewetting solution, the solution concentration is preferably 0.05% to 10%, preferably 0.2% to 5.0%. Incidentally, if it is less than 0.05%, the plasticity effect is small;
This is because, at best, the plasticizing effect has a negative effect on printability, such as a decrease in the surface strength of finished cast-coated paper and poor ink transferability, which is undesirable. In the present invention, the surface of the coating layer is re-wetted with such a wetting liquid and dried under pressure on the surface of the heating drum, but at this time, the re-wetting liquid contains a material that makes it easy for the coated paper after casting to peel off from the heating drum. It is preferable to include a mold release agent in order to ensure stable operation. In the method of the present invention, the coating composition used to form the coating layer is a composition containing pigments and adhesives as main components, similar to conventional cast coated paper compositions. Examples of pigments include clay, kaolin, aluminum hydroxide, calcium carbonate, titanium oxide,
One or more types of general pigments for coated paper such as barium sulfate, zinc oxide, satin white, and plastic pigments are used. In addition, adhesives include casein, soybean protein, methanol, acetic acid, proteins such as proteins extracted from unicellular bacterial cells, styrene, etc.
Conjugated diene polymer latex such as butadiene copolymer, methyl methacrylate/butadiene copolymer, acrylic polymer latex such as polymer or copolymer of acrylic acid ester and/or methacrylic acid ester, ethylene/vinyl acetate copolymer, etc. Vinyl polymer latices such as polymers, alkali-soluble or alkali-insoluble polymer latexes obtained by functionally modifying these various polymers with monomers containing functional groups such as carboxyl groups, polyvinyl alcohol, olefins, etc. General coated paper adhesives such as synthetic resin adhesives such as maleic anhydride resin and melamine resin, starches such as positive starch and oxidized starch, and cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose can be used alone or in combination. It will be done. These adhesives are pigmented 100%
It is used in an amount of 5 to 50 parts by weight, generally 10 to 30 parts by weight. Various auxiliary agents such as antifoaming agents, coloring agents, mold release agents, and flow modifiers may also be used as appropriate. In the present invention, the coating composition can be applied to a blade coater, an air knife coater, a roll coater, a brush coater, a curtain coater, a chain coater, a bar coater, a gravure coater, a size press coater, which are commonly used in the production of coated paper. The base paper is coated in one layer or in multiple layers by an on-machine or off-machine coater equipped with a coating device such as the above. The solid separation degree of the coating composition at that time is generally 40 to 70% by weight, but in consideration of operability, it is preferably in the range of 45 to 65% by weight. As the base paper, a paper-based or board-based base paper with a weightage of 30 to 400 g/m ² used for general printing coated paper or cast coated paper is used. These are base papers made by acidic or alkaline papermaking, and of course medium base papers containing about 10% by weight or more of high-yield pulp can also be used. Further, coated paper such as preliminary stamp or cast coated paper with a general pigment coating provided on the back side can also be used as the base paper. The coating amount of the coating composition on such base paper is about 10 to 50 g/ ^m2 in terms of dry weight, but in terms of improving the blank quality of the resulting cast coated paper and the speed of the cast coated paper, Most preferably, it is adjusted within the range of 15 to 35 g/m ² . Drying of the coating composition coated on the base paper is carried out using a conventional drying device for coated paper, such as a hot air dryer, an air foil dryer, an air cap dryer, a cylinder dryer, an infrared dryer, or an electron beam dryer. The degree of drying of coated paper varies depending on the type of base paper, the type of coating composition, etc., but generally the paper moisture is in the range of about 1 to 11%, and it is possible to dry the coated paper to a range of about 3 to 8%. is desirable. The coated paper after drying can be subjected to a calendering process such as a machine calendering process if necessary, but naturally it is necessary to avoid a calendering process that significantly impairs the bulk and hardness characteristic of cast coated paper. Examples of the present invention will be described below, but it goes without saying that the present invention is not limited only to these Examples. In the examples, parts represent parts by weight. Examples 1 to 3 (Comparative Examples 1 to 3) (1) Common matters of each Example and Comparative Example 95 parts of coating clay, 5 parts of Sachin White (concentration 28%, PH 12.0) (solid content), A pigment slurry having a concentration of 60% was prepared by dispersing 0.3 parts of sodium hydroxide into 66 parts of water using a Coles disperser. To this, 0.5 parts of tributyl phosphate as an antifoaming agent, 0.5 parts of calcium stearate as a mold release agent, 10 parts of a 15% aqueous casein solution (solid content) dissolved using ammonia as an adhesive, and styrene-butadiene latex. (Manufactured by Sumitomo Nogatatsu Co., Ltd., product name "SN-307")
15 parts (solid content), add water to increase the solid content concentration.
A 45% coating liquid was obtained. Using this coating liquid, rewet casting was performed using the apparatus shown in FIG. That is, 100 yen tsubo
The above coating liquid was applied to base paper 1 of g/m ² to a dry weight of 28 g/m ² using an air knife coater 2, and dried in a dryer 3 to a paper moisture content of 6%. The paper is then passed through a press nip 6 formed by a urethane rubber-coated press roll 4 with a diameter of 750 mm and a chrome-plated cast drum 5 with a diameter of 1220 mm, where the surface of the coating layer is re-wetted with a re-wetting liquid supplied from a nozzle 7. Moisten, then press nip pressure 200Kg/cm, drum surface temperature
Cast drum 5 with rotation speed of 65m/min at 120℃
After drying, the paper was peeled off from the cast drum with a take-off roll 8 to produce cast-coated paper 9. (2) Differences between Examples and Comparative Examples In producing the above cast coated paper, a rewetting liquid was used as a rewetting liquid. In Example 1, a rewetting liquid having the following composition was used: Urea 1.0 parts Potassium oleate 0.5 parts Water 98.5 parts In Example 2, a rewetting solution having the following composition was used: Dicyandiamide 1.0 parts Potassium oleate 0.5 parts Water 98.5 parts In Example 3, a rewetting solution having the following composition was used: Formic acid amide 1.0 parts Potassium oleate 0.5 parts Water 98.5 parts In Comparative Example 1, a rewetting solution with the following composition was used Potassium oleate 0.5 parts Water 99.5 parts In Comparative Example 2, a rewetting solution with the following composition was used Ammonia 1.0 part Olein Potassium acid 0.5 parts Water 98.5 parts In Comparative Example 3, a rewetting solution with the following composition was used: Sodium pyrophosphate 1.0 parts Potassium oleate 0.5 parts Water 98.5 parts (3) The effects of each of the above examples and comparative examples are shown in the table below. It was like that.

【table】

[Table] Example 4 80 parts of coating clay, heavy calcium carbonate (Fuji Kaolin) containing 95% particles with a particle size of 2μ or less
Co., Ltd., trade name "Carbital 95") and 0.5 parts of sodium polyacrylate were dispersed in 50 parts of water using a Coles disperser to prepare a pigment slurry with a concentration of 66%. Tributyl phosphate is added to this as an antifoaming agent.
0.5 parts ammonium oleate as mold release agent
0.25 parts, 6 parts (solid content) of an 18% aqueous solution of soybean protein dissolved using ammonia as an adhesive, and 17 parts of styrene-butadiene latex (manufactured by Sumitomo Naugatatsu Co., Ltd., trade name "SN-311") (solid content), and further water was added to obtain a coating liquid with a solid content concentration of 55%. Using this coating liquid, rewet casting was carried out using the apparatus shown in FIG. That is, the pulp composition is
30 parts of NBKP, 70 parts of LBKP, and base paper 1 with a weight of 90 g/m ² using an alkyl ketene dimer as a sizing agent were coated with the above coating liquid using a blade coater 2 so that the dry weight was 25 g/m ² . The paper was dried in dryer 3 so that the paper moisture content was 5.5%. The paper is then passed through a press nip 6 formed by a press roll 4 with a diameter of 800 mm and a chrome-plated cast drum 5 with a diameter of 3000 mm, where 1.5 parts of thiourea and 0.3 parts of polyethylene emulsion are supplied from a nozzle 7.
The surface of the coating layer was re-wetted with a re-wetting solution consisting of 98.2 parts of water and 98.2 parts of water, followed by a press nip pressure of 150 kg/cm.
A cast-coated paper 9 was produced by pressing the paper against a cast drum 5 with a drum surface temperature of 105° C. and a rotation speed of 70 m/min, drying, and then peeling it off from the cast drum with a take-off roll 8. Almost no adhesion unevenness was observed on the coated surface of the obtained cast-coated paper, and the gloss level was 90%. In addition,
Using the method of this example, the operability and quality of the cast-coated paper did not deteriorate even after continuous operation for more than 8 hours.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing an example of a cast coater used in producing cast coated paper according to the present invention. 1...Base paper, 2...Air knife coater,
2'...Blade coater, 3...Dryer, 4...
...Press roll, 5...Cast drum, 6...
Press nip, 7... nozzle, 8... take-off roll, 9... cast coated paper.

Claims (1)

[Claims] 1. In the method for manufacturing cast coated paper, in which a dried coating layer mainly composed of pigments and adhesives is re-wetted and pressed against a heated mirror surface to give a high gloss finish, the re-wetting liquid is a plasticization accelerator. A method for producing cast coated paper, characterized in that it contains an amide compound.