JP3013059B2 - Production method of double-sided 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 double-sided cast coated paper used for wrapping paper, wrapping cartons, notebook and book covers, files, catalogs, printing paper, and the like. The present invention relates to a method for producing a double-sided cast-coated paper having high gloss and excellent smoothness without blocking even under high pressure by a rewetting method.

[0002]

2. Description of the Related Art Methods for producing cast coated paper include a wet cast method, a gel cast method and a rewet cast method. In the wet coating method, the paint coated on the paper is dried in advance, then a rewetting liquid containing water as a main component is applied to the dried paint surface to swell and plasticize the paint, and then polished to a mirror surface. This is a method for obtaining a smooth, high-gloss cast-coated paper by pressing it against the cast drum and drying it, and has a feature that the productivity is higher than the wet method and the gelling method.

As a method for producing a double-sided cast coated paper, a method of simultaneously forming both front and back cast layers in one step has been proposed, but generally, the first step of forming a cast layer on one side of the base paper is completed. And a second step of forming a cast coat layer on the opposite surface after winding the coated paper. When a double-sided cast paper is manufactured by a rewetting method using a conventional coating composition of a conventionally known cast-coated paper, there is no problem at low temperature, low humidity and low pressure, but high temperature of 30 ° C. or more and high temperature of 90% or more. Humidity, 3
Under a high pressure of t / m ² or more, the coating surfaces are blocked and adhere to each other alone or under composite conditions,
In addition to the necessity of the deblocking operation at the time of post-processing such as a printing process, there is a problem that, in extreme cases, the paper surface is broken when the deblocking is released.

As a binder for cast-coated paper, styrene-butadiene (SB) is used as a synthetic resin-based latex.
R), methyl methacrylate-butadiene,
There are acrylic ester type, vinyl acetate type latex and the like, but SBR is generally used. Although SBR is often recently copolymerized with methyl methacrylate, it should be strictly referred to as an SMB latex. However, these are also referred to as SBR . To explain the relationship between blocking and binder, SBR
Since is a thermoplastic resin, the larger the mixing ratio, the greater the blocking at high temperatures. Water-soluble binders include starch, polyvinyl alcohol, casein, and the like. However, casein is generally used for cast-coated paper because of its high water resistance and excellent cast drum releasability. Excessive use of casein causes swelling due to moisture at high humidity and accelerates blocking.

[0005] Paints for coated paper are composed of a pigment, a binder that bonds the pigments to each other, and a binder for adhering the paint to the paper surface, and auxiliary agents such as a dispersant, an antifoaming agent, and a release agent. The pigment, which is the main constituent material of the paint, is a white pigment, which not only greatly affects the quality characteristics of cast coated paper such as white paper gloss, smoothness, printability, but also air permeability, which is an indicator of water vapor permeability. It greatly affects productivity and also controls productivity.
Pigments are roughly divided into inorganic pigments and organic pigments. As inorganic pigments, purified natural mineral pigment kaolin clay, talc, ground calcium carbonate, composite synthetic pigment satin white, semi-synthetic pigment titanium oxide,
Precipitating calcium carbonate, aluminum hydroxide and the like. Even though the inorganic pigments are classified as the same component, there are many particle shapes and particle sizes depending on the place of production and the production method, and the selection thereof not only controls the quality of the cast-coated paper, but also greatly affects the productivity.

As the organic pigment, there are a plastic pigment composed of various resins, alone or in combination, a binder pigment combining a pigment and a part of an adhesive, and a large number of organic pigments such as a hollow structure and a double core-sheath structure. Pigments are on the market. Plastic pigments include those composed of only a single resin such as styrene and urea resin, and those having a double structure in which styrene is used as a nucleus and acrylic ester, methyl methacrylate, acrylonitrile, butadiene, etc. are arranged on the outer periphery. The covering resin having an adhesive function may be classified as a binder pigment as described above. The average particle size of the primary particles is approximately 0.2 to
0.5 micron, there are solid type and hollow type.

[0007]

As one of the measures for preventing blocking in double-sided cast coated paper, there is a countermeasure from a binder used for a paint. That is, as a countermeasure to reduce the high-temperature blocking properties of SBR used as a binder, a low blend of soft and sticky butadiene and a high blend of hard and non-stick styrene were copolymerized. High SBR
Although the use of is remarkable, the paint becomes harder, causing not only troubles such as breakage and breakage at the time of folding processing such as bookbinding and crease marking after printing but also lowering of adhesive strength and picking. If the ratio of binder is increased to prevent the occurrence of defects, the gap between the pigment particles is filled, and the air permeability becomes poor, causing blister trouble. (The blister here means that after the cast coat surface is formed on the base paper surface and the drum surface temperature is heated to a high temperature when passing through the cast drum in the second step of processing the opposite surface, the paint and rewet When the moisture in the liquid becomes water vapor and passes through the base paper and the coating layer of the first step and evaporates, the water vapor cannot pass through the paint layer and swells in the paper layer, that is, in the paper layer or delamination. The phenomenon that causes.)

In order to prevent blistering, the temperature of the cast drum must be lowered to suppress rapid generation of water vapor. However, when the temperature is lowered, the strength of the paint surface is reduced due to insufficient curing of the binder, This causes troubles such as poor picking during printing. In order to prevent such troubles, the speed must be greatly reduced, and there is a problem that productivity is reduced. The present invention has been made in order to solve the above-described problems of the related art, and it is an object of the present invention to provide a method for improving blocking resistance while maintaining blank glossiness and smoothness of a double-sided cast coated paper. With the goal.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies as a means for securing the blocking resistance of a double-sided cast coated paper, and have found that an aqueous solution containing at least one metal salt containing zinc, magnesium, aluminum and titanium can be obtained. When used as a rewetting liquid, the fact that blocking does not occur even under high temperature, high humidity and high pressure, or even if it is very slight, it is reduced to such a degree that it is easily released in the base paper setting work in the printing process It was found and solved.

A typical aqueous solution of zinc sulfate among the above metal salts is widely used to improve the water resistance of the coated surface during the calendering treatment of a pigment-coated paper containing casein. In the production of cast paper by the rewetting method, it was impossible to use it as a rewetting liquid by the conventional method. In other words, when an aqueous solution of zinc sulfate is used as a rewetting liquid for cast paper, even if the concentration is as low as about 0.5%, penetration and plasticization of the once-dried paint layer are poor, and cast paper is most noticeable. Poor white paper gloss, which is a special feature, does not eliminate pinholes and craters. This is not limited to zinc sulfate, but other metal salts of the present invention, namely, zinc,
When an aqueous solution of a metal salt such as sulfuric acid, nitric acid, acetic acid, formic acid , oxalic acid , and chloride containing magnesium, aluminum, and titanium is used as a rewetting liquid in the production of a double-sided cast paper, the blocking resistance is excellent as described above. Glossiness of cast cast paper is JIS P 8
The value measured by the 75-degree specular gloss according to 142 is 70% or less, which is a low gloss that cannot be used as cast coated paper. This is presumably because these metal salt aqueous solutions are inferior in the function of swelling and plasticizing the dried paint surface.

[0011] SB used for paper coating paint
R has a carboxyl group, an amide group, an epoxy group, a hydroxyl group, etc., so that a crosslinking reaction is generated by the heat of the dryer or secondary additives in order to obtain the essential strength of paint such as water resistance, abrasion resistance, picking as well as adhesive strength. Is generally copolymerized, and the present invention also uses an SBR having a functional group. Note that SBR having a functional group is referred to as modified SBR. The use of a metal salt as described above as a rewetting liquid in a double-sided cast paint using a modified SBR and casein as a binder does not necessarily result in a significant improvement in blocking, but the metal constituting the salt and the binder in the paint are not clear. It reacts with a functional group of a certain SBR to form a cross-linked structure and suppresses the adhesiveness of the SBR to prevent blocking at a high temperature, and reacts with a hydroxyl group of casein to form a metal complex to increase the water resistance to increase the water resistance. It is believed to provide blocking resistance in moisture .

In order to examine the drying conditions of the paint and the application conditions of the rewet liquid in the manufacturing process, the moisture in the coating layer at the outlet of the dryer for drying the paint after coating the paint is adjusted to 10 to 25.
%, More preferably from 12 to 20%. Immediately after the outlet of the dryer, when the rewetting liquid composed of the aqueous metal salt solution is damped and pressed against the cast drum before the paper surface temperature decreases, moisture is applied to the coating layer. and that it is quite residual coating position of the rewetting solution coating layer since it is immediately after dryer outlet is easily swelled plasticized for holding the heat in the dryer, the pressure roll and cast drum It is easily formed by nip pressurization and at the same time, the reaction between the metal in the salt used in the rewet liquid and the functional group of the binder is promoted to form a crosslinked structure, and the coated surface has sufficient white paper gloss and smoothness It has been found that a double-sided cast-coated paper having both properties and blocking resistance can be obtained, and this has been solved.

In general, if the paint is not sufficiently dried by heating in a dryer, the strength of the paint surface will not be exhibited, causing a problem of poor picking in the printing process. However, when a metal salt aqueous solution having excellent reactivity with a binder as in the present invention is used in an amount of 0.3% or more, more preferably 0.5% or more, a cross-linking reaction is immediately formed and the metal salt solution passes through a heated cast drum. To develop sufficient picking strength. Further, since the cast paper thus obtained has an action of partially gelling the binder on the surface, a microporous is generated on the surface of the coating layer, and a cast paper excellent in printability is obtained.

To obtain blocking resistance, usually,
The purpose can be achieved by using a metal salt aqueous solution on only one side, but in order to exhibit a higher degree of blocking resistance, it is necessary to use a metal salt aqueous solution in the same manner as above for the rewetting liquid in the second step. is there. However, in the second step, the residual moisture in the paint and the first, the re-wetting liquid is likely to cause blisters when passing through the second coated surface and volatilized, so excessive heating in the cast drum is not preferable, As the drum temperature decreases, the picking strength decreases. In order to avoid this, the passage time of the casting drum in the second step is extended and the drying is performed slowly, so that it is inevitable that the speed is reduced as compared with the first step.

In order to carry out the present invention while preventing a decrease in productivity as much as possible, it is necessary to maintain high air permeability, that is, water vapor permeability, and to combine strong glossiness with good printability and picking strength. It is necessary, and for this, facing from the paint composition side is required. Pigment used in the present invention, at the stage of finishing the one-sided cast coated paper by coating the coating material on one side of the paper, below 000 seconds Gurley, JIS
Blank paper gloss 8 at 75 degree incident angle according to P 8142
It is desirable to simultaneously satisfy 0% or more. However, the relationship between the air permeability and the glossiness of white paper is a trade-off relationship that the larger the pigment particle size, the better the air permeability, but conversely the glossiness decreases. In addition, the air permeability and the glossiness of the white paper greatly differ depending on the shape of the pigment. For this reason, it is important to select a pigment having a particle size and shape that simultaneously satisfies both physical properties.

As a result of a test of a large number of inorganic and organic pigments, it was found that kaolin from Engel Hard Corporation was used as an inorganic pigment which simultaneously satisfies appropriate air permeability and high gloss so as not to reduce the productivity as cast coated paper. UW-90 and Heidilite H-43, an aluminum hydroxide manufactured by Showa Denko KK, were selected. Kaolin, which is the mainstream among inorganic pigments, is the most common pigment for paper paints, and the smaller the particle size, the better the whiteness and glossiness of the coated paper, but air permeability, which is an indicator of water vapor permeability. Inferior. Aluminum hydroxide has a thin hexagonal plate-like crystal type and is effective not only for improving whiteness, glossiness and smoothness but also for improving air permeability.

As the organic pigment, Upearl C-122, a urea-based resin pigment of Mitsui Toatsu Co., Ltd., having excellent air permeability, was selected. Eupearl C-122 has an average primary particle diameter of about 0.2 μm, but when used as a paint pigment, it forms a secondary aggregate to form an average particle diameter of 5 to 10 μm or more. However, there is a problem in expressing a high degree of white paper gloss due to the aggregates. For this reason, the addition ratio used is limited. If the addition ratio is as high as 30% or more, it is difficult to maintain the white gloss of the cast-coated paper at 80% or more.

Further, the air permeability is greatly affected by the amount of coating. In order to maintain good air permeability, the amount is preferably 20 g / m ² or less. However, when the coating amount is small, gloss of white paper is reduced and it is difficult to maintain 80%. When the coating amount is 25 g / m ² or more, the glossiness of the white paper becomes good, but the air permeability becomes poor. The present invention has been studied so that a white paper gloss of 80% or more is exhibited at a coating amount of about 20 g / m ² . The air permeability varies greatly depending on the base paper used. Not only the rice basis weight, but also the N / L ratio of the pulp composition, the presence / absence of waste paper, the ratio, the presence / absence of filler, the type, degree, distribution state, density, etc., vary greatly.

[0019]

The pigment content is excellent in air permeability, and the paint moisture at the outlet of the dryer is 10 to 25%, more preferably 12 to 20 %.
%, Sulfuric acid, nitric acid containing zinc, magnesium, aluminum, titanium, etc.
An aqueous solution of a metal salt such as acetic acid, formic acid, oxalic acid, and chloride is applied and reacted with the functional group of the latex to form a crosslinked structure, thereby improving picking strength and reducing the tackiness of the latex. sealed together to improve the water resistance, it has been high temperature, high humidity, together with allowed to express anti-blocking property under high pressure, by applying the microporous properties of the binder allowed gelation,
Air permeability and picking strength are maintained at a high level.

[0020]

EXAMPLES The present invention will be described below with reference to examples. Parts and% shown in Examples are parts by weight and% by weight. Table 1 shows the paint formulation, Table 2 shows the examples, Table 3 shows the comparative examples, and FIG. 1 shows a side view of the manufacturing apparatus.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

FIG.

Example 1 One side of a high quality paper of 100 g / m ² of rice tsubo was coated with the coating material shown in Table 1 by an air knife coater so that the coating amount became about 20 g / m ^2, and the water content of the coating surface was reduced to 12 by a dryer.
After drying to about 20%, a 3% aqueous solution of zinc sulfate is applied at the position 5 in FIG. 1 immediately after the outlet of the dryer.
The roll is pressed into contact with a device comprising a pressure roll having a linear pressure of 150 kg / cm and a diameter of 600 mm and a cast drum having a diameter of 1,500 mm heated to 120 ° C., and is cast and wound. The processing speed at this time is 70m /
And the glossiness was 84%. In the second step, the opposite side of the rolled cast coated paper is coated in the same manner as in the first step, dried, coated with a liquid, and subjected to a double-sided wet cast process. In the second step, the drum temperature is adjusted to 100 ° C. to prevent the occurrence of prestar, and the processing speed is reduced to 40 m / min in order to prevent the picking strength on the coating layer surface from being lowered due to the drop in the drum temperature. I
Was. The blank gloss and the pinholes are good as shown in Table 2. The obtained double-sided cast paper was cut into 5 cm x 5 cm, and the front and back surfaces were alternately set and set between stainless steel plates of the same size. A load of 10 kg (4 t / m ² ) was applied to adjust the temperature to 30 ° C and 95% RH. It was placed in the constant temperature / humidity chamber and the blocking state was checked after 48 hours.

Example 2 The first step was the same as Example 1 except that the concentration of zinc sulfate was 5%.
Processing was performed in the same manner as described above . The second step was carried out at 6 shown in FIG. 1 near the drum at the coating position near the drum by sufficiently drying with a drier by a usual rewetting method, using water as a rewetting liquid.
The processing speed in the second step was 50 m / min. The blocking of the cast paper was good enough to be easily released by slight ironing.

Example 3 In Example 3, 0.5% zinc sulfate was used in the first step and the second step, and processed in the same manner as in Example 1. The processing speed in the first and second steps is the same as that in Example 1, but the blocking is slightly inferior, but is good enough to be easily released by light ironing . Example 4 In the first step, zinc nitrate was used, and in the second step, a 3% solution of zinc formate was used at each of the application positions, 5/5 in FIG. The blocking required a small force to release, but was acceptable. Examples 5, 6, and 7 In each of the first step and the second step, tests were performed by changing the type of the metal salt aqueous solution as shown in Table 2. Processing speed is Example 1
Is the same as

[0028]

Comparative Example Table 3 shows a comparative example. Comparative Example 1 As shown in Table 3, water was used as the rewet liquid, and the drying of the coating layer and the application position of the rewet liquid were the same as those in the ordinary rewetting method.
6. Although the glossiness of blank paper was high, the blocking was large, and the substrate of the sample was broken when peeled off. Comparative Example 2 A polyethylene emulsion-based release agent was intentionally used in a large amount of 1% in the rewetting liquid, but the adhesion to the drum was poor, so many pinholes were generated, and the blocking property was lower than the large amount of the release agent. Was bad. Comparative Example 3 Although calcium formate was used, the white paper glossiness was the highest, but the blocking was poor, and it was found that some kinds of metal salts were not effective in blocking resistance.

Comparative Example 4 Zinc sulfate which was most excellent in blocking had a white paper glossiness of 6 to 7 by the ordinary rewetting method even at a low concentration of 0.2%.
Low point and poor blocking. Comparative Examples 5, 6, 7 Comparative Example 5 shows that at a high concentration of zinc sulfate of 15%, the moldability of the surface is not sufficient regardless of the water content of the paint surface. In Comparative Example 6, a 3% solution of zinc sulfate was used by the ordinary rewetting method, but it did not plasticize and had poor gloss and poor pinholes . Comparative Example 7 is the same as Example 1 except that the application position of the rewet liquid is near the drum. The blocking resistance is good, but the glossiness and pinholes are insufficient for cast coated paper.

[0030]

As described above, double-sided cast-coated paper is positioned as the highest grade among various paint-coated papers, and has been used in automobile catalogs, mail-order brochures, company guides, etc. in accordance with the recent trend toward higher-grade products. However, there is a problem that blocking occurs at high temperature and high humidity in summer. If this preventive measure is required for latex, new problems such as cracking due to curing of the paint and printability arise. However, in the present invention, the water content of the coated surface is set to 10 to 25%, more preferably 12 to 20%. A re-wetting solution consisting of an aqueous solution of a metal salt was used immediately after the outlet of the dryer to establish a method for preventing blocking while maintaining a high degree of white paper gloss, smoothness and crack resistance.

[0031]

[Brief description of the drawings]

FIG. 1 is an explanatory view of an apparatus used for a method for producing a cast-coated paper sheet by a rewetting method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Unreel 2 Applicator roll 3 Air knife 4 Dryer 5 Rewetting liquid application position immediately after dryer exit 6 Rewetting liquid application position near drum 7 Pressure roll 8 Cast drum 9 Popril

Claims (3)

(57) [Claims] 1. A paper coated with a synthetic latex having a functional group and a water-soluble polymer as an adhesive on both sides of a paper, and after drying, the coated surface is swelled and plasticized with a rewetting liquid and polished into a mirror surface. In the production of double-sided cast-coated paper by wet contact with a heated drum to produce a high-gloss paper, one or both of the coated surfaces having a moisture content of 10% or more and 25% or less before the application of the rewetting liquid are applied. Zinc, as rewetting liquid,
A method for producing a double-sided cast-coated paper, characterized by using an aqueous solution containing at least one metal salt containing magnesium, aluminum, and titanium. 2. Zinc, magnesium, aluminum,
2. The double-sided cast-coated paper according to claim 1, wherein the salt containing titanium is a metal salt such as sulfuric acid, nitric acid, acetic acid, formic acid, oxalic acid and chloride, and has a concentration of 0.3% or more and 10% or less. Production method. 3. The method for producing double-sided cast-coated paper according to claim 1, wherein the coating position of the rewetting liquid after coating and drying to a predetermined moisture is immediately after the dryer outlet.