JPS6410638B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a manufacturing method capable of providing highly glossy coated paper having excellent printability stably and with high productivity. Conventionally, methods for producing highly glossy paper include (1) the wet cast method (for example, the
38-25160) (2) After drying the wet coating layer,
Rewet casting method (for example, US Patent No. 2759847), in which the coating layer is plasticized by rewetting and then dried by pressing it against a smooth heated surface (for example, US Pat. No. 2,759,847). Gel cast method in which pressure is applied to dry
Methods such as No. 1, US Pat. No. 3,377,192) are known. All of these methods have a common principle in that the coating layer, which is mainly composed of mineral pigments and adhesives, is dried by pressing it against a heated finished surface while it is in a plastic state due to water content. I am using it. For this reason, the moisture contained in the coating layer must be dried and solidified to a considerable extent while being pressed against the finished surface, so the manufacturing speed is only a few tenths of that of ordinary pigment-coated paper. The current situation is that it is several steps behind. Furthermore, as a conventional method for obtaining high-gloss pigment-coated paper at high speed, dry or slightly water-containing coated paper is processed using a gloss calendering device having heated rolls or drums, a supercalendering device, etc. A method is known in which paper is passed through a roll nip under strong pressure. The use of supercalender equipment is at a relatively high nip pressure of around 200Kg/cm and the temperature of the steel finishing roll is around 70℃. This process has the disadvantage of compressing and densifying the coated paper. On the other hand, a method of finishing paper by thermal calendering, known as gloss calendering, involves pressing the coated paper against an abrasive finishing drum under temperature conditions that induce a temporary plastic state in the paper. A coated paper for printing with superior opacity and a bulkier paper quality compared to supercalenders can be obtained. The pressure conditions for gloss calenders are generally lower than those for super calenders, around 90 kg/cm, and the temperature conditions are generally high, around 150°C. In the case of using a heating calender as described above, the gloss and smoothness of the coating layer surface are obtained by softening deformation (plastic deformation) of the coating layer under heating and pressure, so the coating layer itself is heated. It is desirable for the adhesive in the coating layer to be easily plastically deformed under pressure. Therefore, if the adhesive in the coating layer is thermoplastic, it will immediately plastically deform under heat and pressure, allowing it to copy the finished surface of a metal roll, etc. Advantageous in providing good gloss and smoothness. On the other hand, the tendency of the coating layer surface to stick to the finishing roll surface gradually increases, and the accumulation of minute foreign matter eventually makes continuous operation impossible. In order to eliminate this tendency to stick, waxes,
Add release agents such as fats, fatty acids, soaps, surfactants, and silicone resins to the paint, or
Alternatively, coating is often carried out continuously on a finishing roll, but the release agent gradually accumulates on the surface of the finishing roll, forming an excessive release agent film, which significantly reduces the gloss of the coated paper. In addition, it is very difficult to appropriately control the amount of release agent added, and adding a large amount of release agent may cause a decrease in printability, which is not necessarily a preferable solution. On the other hand, in order to obtain better gloss and smoothness, U.S. Pat. According to the above method, it is difficult to apply an optimum amount of water, and furthermore, the above-mentioned tendency for heating calender staining increases, which is undesirable. An object of the present invention is to provide a method for producing coated printing paper having better gloss and smoothness with good workability. Thus, the present invention provides an aqueous coating liquid whose main components are a coating pigment and a hydrophilic adhesive, in which the adhesive mainly contains a polymer latex having a glass transition temperature (hereinafter referred to as Tg) of 38°C or higher. The aqueous coating fluid has a bump size of 0.4 to 10 after 5 seconds of contact with water.
g/m ² on base paper or undercoated paper, and after drying, the coated surface is pressed against a gloss calendar at a temperature higher than the Tg of the polymer to produce coated paper for printing with higher gloss and smoothness. That is. The reasons for limiting the knob size of the base paper or undercoated paper according to the present invention are considered to be as follows. The moisture content of the coated layer is a major factor in achieving better plastic deformation when it is instantaneously pressed against a heated surface to obtain strong gloss. Of course, the higher the moisture content, the better against deformation. However, if the amount of moisture is excessive, stains will occur on the heating surface. Efficiently retaining an appropriate amount of this moisture in the coating layer during pressure welding is important in order to obtain a highly glossy surface with good workability. For this purpose, the lump size of the base paper or undercoated paper after 5 seconds of contact with water is adjusted to 0.4 to 10 g/m2, preferably ² to 10 g/m2.
Limiting it to 7g/m ² is very effective. Cob size degree of base paper and undercoat paper after 5 seconds is 10
If it exceeds g/m ² , the moisture in the intercoating layer, which undergoes plastic deformation between the heating nips, will not be completely retained, and as a result, better gloss will not be obtained. on the other hand
If the cob size is less than 0.4 g/m ² , the adhesive in the coating liquid will not penetrate sufficiently into the base paper, causing problems in the adhesive strength of the coated paper. Incidentally, the degree of bump size mentioned here is a value measured according to the method shown in JIS.P.8140. In particular, the reason why the measurement time is specified as 5 seconds is as follows. If the degree of bump size is measured over a too long measurement time, it will be difficult to differentiate between the measured values and it will be difficult to correlate with the effect referred to in the present invention. Therefore, the shorter the measurement time, the better; however, if the measurement time is too short, the measurement error will be large and it is not suitable for practical use. Five seconds is defined as a measurement time that allows stable measurement and has a correlation with the effects referred to in the present invention. In other words, the measurement is the same method as JIS.P.8140,
The contact time with water is set to 5 seconds. In the present invention, the thermoplastic synthetic polymer emulsion (polymer latex) with a Tg of 38°C or higher means:
Examples include, but are not limited to, polyvinyl acetate emulsion, styrene-butadiene copolymer latex, styrene-isoprene copolymer emulsion, polystyrene emulsion, acrylic polymer emulsion, and the like. The reason for limiting Tg to 38℃ or higher is JP-A-49-
As is clear from No. 110906, it does not form a film at room temperature, and its purpose is to form a discontinuous layer of emulsion particles, which is then softened and glossed on a cast drum, and is generally used on coated paper. This is because when using a synthetic emulsion with a low Tg, which is used for coating, it has a film-forming property after coating, so even if it is softened and pressed on a cast drum, the desired strong gloss cannot be obtained. The aqueous coating liquid of the present invention mainly uses a polymer latex with a Tg of 38°C or higher as the adhesive as described above,
In addition, thermoplastic resins and thermosetting resins having a Tg of 38° C. or less can be appropriately mixed and used as long as there is no problem. Furthermore, antifoaming agents, foam inhibitors, mold release agents, thickeners, flow modifiers, coloring agents, etc. may be used as appropriate depending on the purpose. On the other hand, the heating calender device used for mirror finishing in the present invention may be a general glossing or smoothing device such as a gloss calender or a super calender, but the pressure is relatively low, so it is advantageous for preventing calendar stains. In particular, it is desirable to use a gloss calender device because the quality of the resulting coated paper is high and bulky. Coating paper with the coating liquid of the present invention is generally used in the production of coated paper. A coater equipped with a coating device such as an air knife coater, roll coater, doctor coater, blade coater, brush coater, curtain coater, bar coater, gravure coater, triplex coater, size press coater, etc.
It is possible to apply the coating in multiple layers. The coating amount is usually 10 to 40 g/m ² , preferably 10 to 30 g/m ² . Drying after coating is done using a normal drying method, such as a gas heater, electric heater, steam heater,
Various methods such as hot air heating are used. The present invention will be described below with reference to examples, but it is not limited to these examples. In addition, parts and percentages shown in Examples mean parts by weight and percentages by weight. Methods for measuring various physical property values in Examples are shown below. (1) White paper glossiness 75° and 20° gloss was measured using a gloss measuring device (manufactured by Nippon Rigaku KK). % (2) Printing glossiness After printing with an RI printing aptitude tester (manufactured by Mei Seisakusho) and drying, the glossiness measurement device (Nihon Rigaku KK) was used.
60° gloss was measured using % (3) Smoothness Smoother smoothness measuring device (Toei Electronics Industry Co., Ltd.)
(manufactured by KK). mmHg (4) Coated paper surface strength The surface strength of the coated paper was determined using an RI printability tester (Mei Seisakusho). Dry: A sample was printed with ink having a certain tack, and the surface of the sample was evaluated visually. Wet: A very small amount of water was applied to the surface of the sample, immediately printed with ink having a certain tack, and the surface of the sample was evaluated visually. As the ratio increases from 5 to 1, the surface strength becomes worse. Example 1 Kaolin clay 90 parts, precipitated calcium carbonate 10 parts
A clay slurry with a solids content of 70% was prepared by dispersing the pigment consisting of 1.0 parts in water with 0.2 parts of sodium pyrophosphate. This stuff contains 3 phosphate esterified starches.
15 parts of styrene-butadiene latex having a glass transition temperature of 60 DEG C. were added thereto and sufficiently stirred to obtain a coating liquid having a total solids content of 62%. This coating liquid was prepared by changing the amount of internal sizing agent.
The bump size after seconds is (A) 0.2g/m ² (B) 1.5g/m ²
(C) 6g/m ² (D) 9.8g/m ² (E) 15g/m ²
Each base paper with a basis weight of 80 g/ ^m2 has a dry solids content of 16
g/m ² with a blade coater, and dried with an air cap dryer heated to 120-130°C, with a nip pressure of 80 kg/cm and a surface temperature of
Gloss calendering was performed at 130° C. and a speed of 120 m/min to obtain five types of coated papers. The properties of the coated paper obtained are listed in Table 1.

[Table] As shown in Table 1, the material values of S-No. 2, 3, and 4, especially S-No. 3, are excellent, and the effect of the present invention is remarkable. Example 2 Kaolin clay 90 parts, precipitated calcium carbonate 10 parts
A clay slurry with a solids content of 70% was prepared by dispersing the pigment consisting of 1.0 parts in water with 0.2 parts of sodium pyrophosphate. To this, add 3 parts of phosphoric acid esterified starch and 15 parts of styrene-butadiene latex with a glass transition temperature (F) of 40°C (G) of 0°C, and stir thoroughly until the total solids content reaches 62%. A coating liquid was obtained. This coating liquid was applied as an undercoating liquid with a composition of 50 parts of kaolin, 50 parts of heavy calcium carbonate, 10 parts of oxidized starch, and 15 parts of styrene-butadiene latex to 75 g/m ² of base paper, 6 g/m ² on one side. The dry solid content of the base coated paper coated with a gate roll coater is 16
g/m ² with a blade coater, and dried with an air cap dryer heated to 120-130℃, with a nip pressure of 80 kg/cm and a surface temperature of
Gloss calendering was performed at 130°C and a speed of 120 m/min to obtain coated paper. The nob size of the undercoated paper used after 5 seconds was 7 g/m ² . The properties of the coated paper obtained are listed in Table 2.

【table】 From Table 2, the effects of the present invention are clear.

Claims (1)

[Claims] 1. In an aqueous coating liquid whose main components are a coating pigment and a hydrophilic adhesive, the adhesive mainly contains a polymer latex with a glass transition temperature of 38°C or higher. It is characterized in that it is applied to a base paper or undercoated paper with a bump size of 0.4 to 10 g/m ² after a contact time of 5 seconds, and after drying, the coated surface is pressed against a gloss calender at a temperature higher than the glass transition temperature of the polymer latex. A method for producing highly glossy printing paper.