JPH04241196A - Production of cast-coated paper - Google Patents

Abstract

PURPOSE:To provide the subject method capable of a high-speed production while keeping smoothness and excellent gloss of the surface in production of a two-side cast-coated paper by the rewet method. CONSTITUTION:In production of a two-side cast-coated paper by the rewet method, aluminum hydroxide and an urea resin-based organic pigment or a precipitated calcium carbonate are used respectively as the first component and the second component of a coating pigment for the surface to be coated in the first step so as to control the air-permeability to <=1000sec by the Gurley method. The method for production of the two-side cast-coated paper enables a high-speed production of the two-side cast-coated paper free from generation of blister by facilitating permeation of steam evaporated by heating a rewetting liquid during passing through a cast drum in the second step for application of a coating material to the opposite side.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing cast coated paper used for packaging paper, packaging cartons, notebook and book covers, files, catalogs, printing paper, etc. Cast coated paper is manufactured with high productivity by the rewetting method.

0002

BACKGROUND OF THE INVENTION Methods for producing cast coated paper include wet casting, gel casting, and rewet casting. Among these methods, the rewet casting method involves pre-drying the paint coated on paper, and then applying a rewetting liquid containing water as the main component to the dry paint surface to make the paint swell and soften. This is a method to obtain smooth, highly glossy cast-coated paper by applying pressure to a polished cast drum and drying, and is characterized by a faster production rate than the wet method or gelling method.

[0003] The production of double-sided cast coated paper consists of a first step of forming a cast layer on one side, a second step of winding up the coated paper, and subsequently forming a cast coat layer on the opposite side. . With the general paint formulation for conventionally known cast coated paper, the cast surface in the first step is easily formed, but when passing through the cast drum in the second step to form the cast coated surface on the opposite side, the drum surface temperature rises. When the water in the rewetting liquid turns into water vapor and evaporates through the first and second coating layers because it is heated to 95°C or higher, the water vapor evaporates if the air permeability is poor. cannot pass through the paint layer, and a blistering within the paper layer called a blister occurs, that is, a phenomenon of separation within or between the paper layers occurs. In order to prevent blistering, it is necessary to lower the temperature of the cast drum to suppress the sudden generation of water vapor, but lowering the temperature reduces the strength of the paint surface due to insufficient curing of the binder, which can lead to picking problems during printing. This may cause problems such as defects. In order to prevent such troubles, the speed must be significantly reduced, resulting in a reduction in productivity.

0004

Problems to be Solved by the Invention In order to produce double-sided cast-coated paper that does not cause blister while maintaining productivity, it is necessary to maintain the air permeability of the paint layer as good as possible. Air permeability varies greatly depending on the paper weight, type, presence, degree, and type of paper used;
When using high-quality paper grade base paper of 0 to 150 g/m2, it is necessary to use the Gurley method for 1000 seconds or less. In order to maintain the above air permeability, inorganic pigments such as kaolin and clay used in coatings must have an average particle size of 2 to 3.
There is a method of selecting and using pigments larger than microns, but
If the pigment particle size is large, the vaporized water vapor from the rewetting liquid can easily pass through the gaps between the pigment particles and suppress the occurrence of blisters, but if the pigment particle size is large, it may be difficult for cast coated paper This results in disadvantages in that the most necessary high gloss is impaired and, in severe cases, surface smoothness is also impaired.

[0005]

[Means for Solving the Problems] The present invention has achieved a Gurley air permeability of 1000, which is an essential condition for manufacturing without reducing productivity while maintaining the high gloss and smoothness characteristic of cast coated paper. It's about how to keep it under seconds. Coating paints generally consist of pigments, adhesives that bind them together, and auxiliary agents such as dispersants, antifoaming agents, and mold release agents. The pigment that is the main constituent material of the paint is a white pigment,
It not only has a large impact on the quality characteristics of cast coated paper, such as white paper gloss, smoothness, and printability, but also controls productivity through air permeability, etc. Pigments can be broadly divided into inorganic pigments and organic pigments. As an inorganic pigment,
These include refined natural mineral pigments such as clay, talc, and ground calcium carbonate, composite synthetic pigments such as Sachin White, and semi-synthetic pigments such as titanium oxide, precipitated calcium carbonate, and aluminum hydroxide. Examples of organic pigments include plastic pigments made of various resins alone or in combination;
There are plastic binders that combine parts of pigments and adhesives, and there are also many organic pigments on the market, including those with hollow structures and dual core/sheath structures. Even if inorganic pigments are classified as the same component, there are many particle shapes and sizes depending on the production area and manufacturing method, and the selection of these particles not only controls the quality of cast coated paper but also has a large impact on productivity. It is something.

Kaolin, which is the mainstream among inorganic pigments, is the most common pigment for paper coatings, and the smaller the particle size, the better the whiteness and gloss of coated paper, but it is not an indicator of water vapor permeability. It is inferior to a certain degree of air permeability. Precipitated light calcium carbonate has particle shapes such as cubic, spindle-shaped, acicular, and columnar, and the effects on the physical properties of coated paper vary depending on these shapes and particle sizes, but when mixed with kaolin, it creates a porous coating. Forming a layer improves ink receptivity and also improves water vapor permeability, but this generally has a negative effect on gloss, which is an essential condition for cast coated paper. Aluminum hydroxide has a thin hexagonal plate-like crystal structure, and is effective not only in improving whiteness, gloss, and smoothness, but also in improving air permeability.

Plastic pigments include those consisting only of single resins such as styrene and urea resin, and those with styrene as the core.
Some have a double structure with acrylic ester, methyl methacrylate, acrylonitrile, butadiene, etc. arranged on the outer periphery, and those where the resin covering the outer periphery has an adhesive function are sometimes classified as plastic binders. The average particle size of the primary particles is approximately 0.2 to 0.5 microns, and there are solid types and hollow types. The inorganic pigment used in the present invention has a Gurley air permeability of 1000 seconds or less at the stage where one side of the paper is coated with a paint to create one-sided cast-coated paper.
White paper gloss level 8 using a Hunter reflectometer at an incident angle of 75°
0% or more must be satisfied at the same time. However, the relationship between air permeability and white paper gloss is a trade-off: the larger the pigment particle size, the better the air permeability, but conversely the lower the gloss. Air permeability and white paper gloss also vary greatly depending on the shape of the pigment. Therefore, it is important to select a particle size and shape that simultaneously satisfy both physical properties.

[0008] Furthermore, the air permeability is greatly influenced by the coating amount. In order to maintain good air permeability, it is desirable to keep the air permeability to 20 g/m2 or less, but as the amount of coating decreases, the white paper gloss decreases and it becomes difficult to maintain 80%. If the coating amount is 25 g/m2 or more, the paper gloss will be good, but the air permeability will be poor. The present invention was researched to develop a white paper gloss of 80% or more with a coating amount of about 20 g/m2.

[0009] Air permeability varies greatly depending on the base paper used. It varies greatly depending on not only the basis weight, but also the N/L ratio of the pulp blend, whether or not waste paper is used, the ratio, the presence or absence of filler, type, extent, distribution state, density, etc.

[0010] As a result of preliminary tests of many inorganic pigments, particle size, particle shape, etc., aluminum hydroxide was found to have a good balance between air permeability and white paper gloss. Showa Denko Co., Ltd., which satisfies both moderate air permeability and strong gloss to prevent it from dropping.
Hygilite, H-4 with an average particle size of 1.0 μm
3 and 0.6 micron m H-42 were selected. Precipitated calcium carbonate is similarly columnar with an average major axis of 1.5 and a minor axis of 0.
．． Tama Pearl TP123 and TP-HGA015 manufactured by Okutama Kogyo Co., Ltd., which have a diameter of 3 microns or less, were selected.

[0011] When the various plastic pigments and plastic binders mentioned above were compared and tested as organic pigments, it was found that the urea resin organic pigment, Upar C-122 manufactured by Mitsui Toatsu Co., Ltd., had the best air permeability. did. Although other organic pigments are superior in terms of gloss and ink receptivity, their air permeability facilitates water vapor permeation of the rewetting liquid when the double-sided cast-coated paper passes through the raster drum in the second step, and None were good enough to maintain productivity.

0012

[Operation] U-Pearl C-122 has a primary particle size of approximately 0.
2 micrometers, but when used as a paint pigment, it aggregates to form an average secondary particle size of 5 to 10 micrometers or more, so it has excellent air permeability but exhibits a high degree of white gloss. I can't do that. For this reason, there is a limit to the amount of addition used, and if the addition is as high as 30% or more, it is difficult to maintain the white paper gloss of cast coated paper at 80% or more. In addition, there are restrictions on the type and particle size of the inorganic pigments that can be used in combination, and calcium carbonate and U-Pearl, which do not produce luster compared to other inorganic pigments and organic pigments, should be used together at a high blending ratio from the viewpoint of white paper gloss. I can't. For this reason, the present invention uses aluminum hydroxide, which has excellent air permeability and white paper gloss, as the main ingredient, and contains U-Pearl or calcium carbonate to form a pigment composition in which E-Pearl and calcium carbonate do not coexist. By using such a formulation, it is possible to produce double-sided cast-coated paper that simultaneously satisfies a high degree of white gloss while maintaining good air permeability, which is an essential condition for maintaining high productivity. .

[0013]

[Examples] The present invention will be explained below with reference to Examples. Parts and percentages shown in Examples are parts by weight and percentages by weight. Tables 1 and 2
Examples and comparative examples are shown below.

[Table 1]

[Table 2]

In the paints shown in Tables 1 and 2, the amount of pigment is 100, and the amounts of auxiliary agents and binders are in parts by weight relative to the pigment. The solid content of the paints was adjusted to 40% for Examples 1, 3, 5, 7, 9, 11 and Comparative Examples 1 and 3, in which U-Pearl was added, due to their high viscosity, and to 45% for the others, using a conventional method. Created. The above paint was coated on the surface of high-quality paper with a basis weight of 100 g/m2 to a solid content of 20 g/m2 using an air knife coater, with a linear pressure of 150 kg/cm and a diameter of 500 g/m2.
Using a device consisting of a 1500 mm diameter pressure roll and a 1500 mm diameter cast drum heated to a predetermined temperature,
It is cast coated by a rewet casting method using zinc sulfate or calcium formate aqueous solution as a rewetting solution and then wound up. The processing speed at this time was 70 m/min, the gloss was 83 to 88%, and the air permeability of this single-sided cast-coated paper was 530 to 980 seconds for Gurley. As a second step, on the reverse side of the rolled cast coated paper, Table 1,
Coat with the paint from step 2 in the same manner and perform rewet casting. Considering the occurrence of blisters, the drum temperature was adjusted to <2 levels as shown in Tables 1 and 2. The processing speed was adjusted within the range of 45 m/min to 35 m/min in order to prevent the picking strength of the coated layer surface from decreasing due to a decrease in drum temperature. When passing through the cast drum in the first step, no blister phenomenon occurred, and a double-sided cast-coated paper with a white paper gloss of 83 to 88%, no pinholes, and good picking strength was obtained.

[0015]

[Comparative Examples] Comparative Examples 1, 2, 3, and 4 are shown in Table 2. When the total value of urea-based pigments and aluminum hydroxide or calcium carbonate, which have good air permeability, is 40% or less, the air permeability of single-sided cast-coated paper at the end of the first step will exceed 1000 seconds and water vapor will not evaporate. It becomes defective and causes blisters. In order to prevent this, even if the temperature of the drum was set at 100 to 95° C., not only was it not possible to prevent blistering, but also the picking strength of the paint surface in the second step was poor.

[0016]

[Effect of the invention] In recent years, due to the market demand for high-quality products, double-sided cast paper, which is the most luxurious type of coated paper, has been widely used for automobile catalogs, mail-order pamphlets, company information, etc. However, on the other hand, cast coated paper manufacturers are expanding their facilities and engaging in fierce sales competition. In order to maintain competitiveness, it is necessary to maintain not only high quality but also high productivity, and the present invention provides a manufacturing method that can meet these demands.

Claims (3)

[Claims] [Claim 1] Paint is coated on both sides of paper, and after drying, the coated surface is swollen and made brittle by a rewetting liquid, and then pressed against a mirror-polished heated drum to produce highly glossy cast paper. In the production of rewet double-sided cast coated paper, aluminum hydroxide is the first essential component of the paint applied to the coated surface in the first step, and urea resin organic pigment or precipitated calcium carbonate is the second essential component. A method for producing cast coated paper. Claim 2: The average particle diameter of aluminum hydroxide, which is a paint pigment, is 1 micron m or less, the primary average particle diameter of the urea-based organic pigment is 0.3 micron m or less, and the secondary average particle diameter is 13 micron m or less. , the calcium carbonate has a columnar cubic shape and an average particle diameter of 1.5 microns or less,
2. The method for producing cast coated paper according to claim 1, wherein the short axis is 0.4 microns or less. 3. The method for producing cast coated paper according to claim 1, wherein the total of the pigments of the first essential component and the second essential component among the pigment components of the paint is 40 parts or more.