JPH03119199A - Production of cast coated paper - Google Patents

Abstract

PURPOSE:To obtain in high efficiency a high-gloss cast coated paper improved in straightness by putting a coated paper to pressure contact on the surface of a hot drum followed by drying the paper to immobilize the coating layer thereon and then imparting the back surface of the paper with water. CONSTITUTION:A base paper <=70g/m<2> in area weight is provided with a coating layer comprising pigment and adhesive, and the resulting paper is put to pressure contact on the surface of a hot drum and dried to immobilize the coating layer. Thence, at a position after such immobilization, the back surface of the coated paper is imparted with water. The coated layer in a moistened state is then put to pressure contact on the specular surface of a hot drum and dried to make a high-gloss finishing, thus obtaining the objective cast coated paper.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a method for producing cast coated paper, and in particular to a method for producing strong gloss that improves gloss unevenness and characteristic curls and paper curls found in thin cast coated paper. The present invention relates to a method for efficiently manufacturing cast iron products.

``Prior art'' Methods for producing cast coated paper include the wet casting method, in which a wet coating layer mainly composed of pigment and adhesive is pressed onto the surface of a heated drum having a mirror surface, and then dried to give a glossy finish;
After the wet coating layer is once dried, it is plasticized by re-wetting and pressed onto the surface of a heating drum that has a mirror surface, and is then dried to give a glossy finish.A heating drum that has a mirror surface by turning the wet coating layer into a gel state. A gel casting method is known, in which the surface is pressed and dried to give a glossy finish.

All of these casting methods have in common that the coating layer in a plastic state is pressed against the surface of a heated drum and dried to give it a strong gloss finish.

However, although cast coated papers obtained by these casting methods have a strong gloss after being released from the heated drum surface, they commonly have a strong gloss finish on the outside and a back side (uncoated side). A so-called reverse vertical curl occurs with the coated paper (finished surface) facing inside and the center direction of the paper as the axis. This reverse vertical curl often causes paper feeding troubles on multicolor printing machines, which have recently become faster, and greatly disturbs printing work efficiency.

In order to improve this reverse vertical curl, curl breaker
However, since it is necessary to apply ironing with a roll to the highly glossy side, the gloss and smoothness, which are the characteristics of cast coated paper, are significantly impaired due to flattening. turn into. Also, a method has been proposed in which steam is applied to the surface of the cast coating layer after the mold is released from the drum (for example, Japanese Patent Publication No. 1-40157), but this method involves recovering excess steam that does not adhere to the paper, and preventing condensed water from flowing into peripheral equipment. There are some problems with the treatment. The method disclosed in Japanese Patent Publication No. 62-12359, in which water is applied to the back side of the paper using a press nip that presses the coating layer against the drum surface, is extremely effective in eliminating the reverse vertical curl peculiar to cast coated paper. However, in the case of wet casting, especially thin cast coated paper, the reverse vertical curl can be improved, but the negative point is that the cast coating layer has a width of 1 to 2 ts and a length of 5 to 3 ts.
There is a drawback that uneven luster of a cedar bark-like pattern occurs on the order of 0 dragons. This uneven glossiness (hereinafter referred to as "stable") not only impairs the appearance of the white paper, but also causes uneven glossiness and unevenness in ink density when printed, which significantly impairs the image of the product.

This stipple phenomenon often occurs when water is applied to the back side of the paper at the press nip where the coating layer is pressed against the heating drum surface, before the press nip, or immediately after the press nip in the method of manufacturing cast coated paper. Stipple occurs strongly, and stipple does not occur when water is not applied. In addition, the stipple strength and amount are determined using thick cast coated paper (base paper 70g/m
(above), it hardly occurs, but it tends to occur more and more strongly as the weight of thin cast coated paper (base paper basis weight 70 g/m2 or less) becomes lighter, and in the casting method, it is noticeable in the wet casting method. In the case of the waend cast method, the stipple remains extremely light even with thin cast coated paper. In the case of the gel casting method, the occurrence of stipple is milder than that in the wet casting method, but it is undeniable that the product value is lowered by the stipple.

As mentioned above, if water is applied to the back side of the paper at the press nip area or before and after the press nip to eliminate the reverse vertical curl peculiar to cast coated paper, the reverse vertical curl will be improved, but Stibbling occurs, which is a serious defect in the quality of coated paper, especially thin cast coated paper produced by wet casting.

As a measure to eliminate the stipple, (81) reducing the amount of water applied to the back side of the paper suppresses the occurrence of stipple, but does not eliminate the reverse vertical curl.

fb) If the coating amount of the cast coating layer is reduced, the stability becomes milder, but the gloss level decreases. (C) Use base paper with a strong size to reduce expansion and contraction of the base paper,
Even if base paper is reinforced with a wet paper strength agent to make the base paper water resistant, stapling cannot be sufficiently suppressed, and ultra-thin paper (base paper
g/%, ○○g/M) is extremely difficult to manufacture.

``Problems to be Solved by the Invention'' The purpose of the present invention is to suppress the serious defects that occur during the production of thin cast coated paper, namely reverse vertical curls and stibling on highly glossy surfaces, and to coat thin cast coated paper with uniform gloss. The present invention provides a method for stably producing a paper cover.

``Means for Solving the Problems'' The present invention provides a strong gloss finish by press-contacting a coating layer mainly composed of pigment and adhesive onto the surface of a heated drum having a mirror surface on a base paper with a basis weight of 10 g/m or less. A method for producing cast coated paper, characterized in that the coated paper is brought into pressure contact with the drum surface and water is applied to the back side of the paper at a position after the coated paper is dried and the coated layer becomes immobilized. This is the manufacturing method.

"Function" As mentioned above, the present invention has been proposed to eliminate the reverse vertical curl that occurs during the production of thin cast coated paper. It exhibits an excellent effect in improving the stibling phenomenon that occurs, provides a uniform glossy surface, and provides cast-coated paper with excellent printability.

Normally, cast coated paper is produced by pressing a coating layer formed on one side of the base paper against a heated drum with a mirror surface while it is wet and fluid, drying it, and then copying the smooth surface of the drum and separating it. The base paper, which is mainly made of wood valves, expands and contracts due to its moisture. In general, water in base paper is classified into crystal water in the cellulose molecules, capillary water in the tiny gaps of the valve, and water attached to the surface of the valve fibers. Capillary water causes the fibers themselves to expand and contract, and adhering water causes the base paper, which is a collection of fibers, to expand and contract.

A portion of the water in the paint coated on the base paper percolates into the base paper layer and enters the capillary tubes, or adheres to the fiber surface. Also, water applied from the back side of the paper in the press roll nip penetrates into the base paper layer, similar to the water in the paint, and expands the base paper. On the other hand, due to the manufacturing method of base paper, the fibers of base paper are mostly oriented along the flow direction of the base paper, and the degree of expansion and contraction of base paper due to the influence of water is several times greater in the horizontal direction at a 90 degree displacement than in the flow direction. It's bigger than that. The water that has entered the base paper is vaporized and dried by the heat of the heating drum. When water leaves the base paper, the base paper shrinks to its original dimensions.

The shrinkage force at this time is extremely strong, and it can be imagined that it is a positional force that attracts even the half-immobilized paint layer that is in the process of drying.

In view of this phenomenon, the present inventors have conducted extensive research into improving this stapling phenomenon based on their many years of experience in producing cast coated paper.

As a result, during the process in which the wet coating layer is pressed onto the drum surface and subsequently dried, the moisture content of the coated paper is higher the thinner the coated paper is, and since the wet casting method has a higher moisture content than other casting methods, Until immobilization is completed by drying of the coating layer, the base paper stretches due to the large amount of water, and then under semi-immobilized conditions the base paper shrinks due to water evaporation. At this time, it was determined that since the coated layer was in a semi-immobilized state, it did not shrink uniformly and became finely wrinkled, resulting in uneven coating amount, uneven gloss, and the occurrence of a stibling phenomenon.

Based on this knowledge and as a result of further intensive research, the present inventors have determined that the stipple phenomenon, which has long been desired to be improved, is a serious defect in the thin cast coated paper manufacturing method.
By applying water from the back side of the paper after the time when the cast wet coating layer is stuck to the surface of the heating drum and is drying, the coating layer paint becomes immobilized and is not affected by the expansion and contraction of the base paper. We have found that this can be effectively improved and have achieved the present invention.

Next, the apparatus and method for implementing the present invention will be specifically described. The pattern in which a wet coating layer is pressed against a heating drum and dried by heating is an initial drying zone where the wet coating layer is still fluid immediately after being pressed against the drum via a press roll. It can be divided into a mid-drying zone where the wet coating layer has progressed to dry and the fluidity of the coating layer has disappeared, and a final drying zone where the wet coating layer dries and reaches the mold release point where it is released from the drum. Water is applied from the back side of the paper to the intermediate drying zone and/or final drying zone, where the coated layer has lost its fluidity and has become immobile, avoiding the initial drying zone.

Incidentally, if the water applied from the back side of the paper is placed in the initial drying zone immediately after the press roll, the applied water will cause the base paper to expand and contract while the coated layer still has fluidity, resulting in a severe stipple phenomenon, which will reduce the desired effect. I can't get anything. On the other hand, if water is applied from the back side in the final drying zone, the paper will not be stable and will have no uneven gloss, but drying will be delayed and it will be necessary to reduce the production rate. The optimum position for hydrolysis is the mid-drying zone, where the wet coating layer no longer has fluidity due to drying and becomes immobile. For example, in the case of a cast drum with a diameter of 36,001 mm, the distance from the press roll nip to the release point where the coated paper separates from the drum is usually about 7 m, and the mid-drying zone depends on the casting method, cast drum temperature, base paper size, etc. The range is 1.5 to 4.5 m from the press roll nip position, although it varies somewhat depending on the tsubo, paint concentration, coating amount on the cast side, presence or absence of backside coating, and the coating amount. Therefore, it is sufficient to apply water within this range of 1.5 to 4.5 m, but the water addition treatment is preferably carried out within the range of 2 to 4 m, more preferably 2 to 3 m. In addition, the amount of water applied from the back side of the paper is adjusted depending on the basis paper weight, paint concentration, coating amount, cast drum temperature, etc., and is determined by testing as necessary. Generally, it is desirable that the amount is in the range of 2 to 25 g, preferably 5 to 15 g per square meter. If the amount of water applied is less than the optimum amount, the cast-coated paper will have some reverse vertical curl. If the amount of water applied is too large, the cast coated paper will curl in sideways under high humidity conditions such as R880%.

In the method of the present invention, the water treatment device that applies water from the back side of the paper in the medium drying zone may be any method as long as it can uniformly apply and adjust the water i from 12 to 25 g/m.
Although an air knife coater, a spray coater, a reverse roll coater, a blade coater, etc. can be used, the method of measuring with an air knife after a sprayer is preferable because it is a simple device and the amount of water can be easily adjusted.

In addition, in order to improve pinhole-like spots, which are another defect of cast coated paper, and to increase drying power, near-infrared irradiation and hot air blowing are carried out before or after the processing equipment of the present invention, and conventionally coated paper It is of course possible to use a suitable combination of various techniques known in the manufacturing field.

In the present invention, the coating composition used to form the coating layer contains pigments and adhesives as main components, similar to conventional cast coated paper compositions.

As the pigment, one or more types of ordinary pigments for coated paper, such as clay, kaolin, aluminum hydroxide, calcium carbonate, titanium dioxide, barium sulfate, zinc oxide, satin white, and plastic pigments, can be selected as appropriate. used.

Examples of adhesives include proteins such as casein, soybean protein, and synthetic proteins, conjugated diene polymer latex such as styrene-butadiene copolymer, acrylic esters, and/or
Alternatively, acrylic copolymer latex such as a polymer or copolymer of methacrylic acid ester, vinyl copolymer latex such as ethylene/vinyl acetate copolymer, or various polymer latexes thereof with functional groups such as carboxyl groups. Alkali-soluble or alkali-insoluble polymer latex modified with containing monomers, synthetic resin adhesives such as polyvinyl alcohol, olefin/maleic anhydride resin, and melamine resin, starches such as positive starch, oxidized starch, etc. , cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and ordinary adhesives for coated paper, which are appropriately selected and used.

The amount of adhesive used is generally 5 to 50 parts by weight, more preferably 10 to 30 parts by weight, based on 100 parts by weight of the pigment.

Furthermore, various auxiliary agents such as antifoaming agents, colorants, mold release agents, flow modifiers, etc. are appropriately blended into the coating composition as necessary. For example, polyvalent metal salts such as zinc, aluminum, magnesium, calcium, and barium can be used as auxiliary agents to promote gelation of pigments.
It is also possible to add 0.5 to 10 parts by weight per part by weight.

In addition, the coating composition for the back side of the back-coated cast coated paper is the same as the coating composition for printing coated paper commonly used in the past, as well as the cast coating composition. I can do it.

Coating equipment used in general coated paper manufacturing, such as blade coaters, air knife coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, die slot coaters, gravure coaters, and chamber mixers, can be used. It is coated on the base paper in one layer or in multiple layers using a coater, size press coater, etc.

The solid content concentration of the coating composition is generally adjusted to a range of about 40 to 70%, but in consideration of operability, it is adjusted to about 45 to 6%.
A range of 5% by weight is preferred.

As the base paper, base paper with a weight of 60 g/m2 or less, which is used for general printing coated paper and cast coated paper, is used, but there are no particular restrictions on the paper making method, and it may be acid paper or alkaline paper. Of course, medium-quality base paper containing high-yield valves can also be used.

The coating amount of the cast coating composition is generally about 5 to 35 g/lri in terms of dry weight, but it has the effect of improving the quality of the resulting cast coated paper, such as smoothness and gloss, and the cast coating speed. In this respect, it is desirable to adjust the amount within a range of about 8 to 30 g/a. In addition, the coating amount of the back coating layer is 5 to 30 g/rr in terms of dry weight in order to obtain good smoothness and printability.
r, more preferably in the range of 10 to 25 g/%. Incidentally, if it is less than 5 g/rtr, good smoothness and printability cannot be obtained, while if it exceeds 30 g/nr, the production rate will drop significantly, which is not preferable.

Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these Examples. In addition, in the examples, "part" means part by weight, and "%" means weight %.

Example 1 30 parts of kaolin (manufactured by EMC, trade name: rUW-90J), 20 parts of micronized heavy calcium carbonate (manufactured by Fuji Kaolin, trade name: "Carbital 90J"), 0.2 part of sodium polyacrylate, oxidized starch A coating liquid with a solid content concentration of 55% was prepared, consisting of 3 parts of styrene-butadiene copolymer latex (solid content) and 13 parts of styrene-butadiene copolymer latex (solid content).
g/m2 base paper was coated on one side with a rod blade coater to a dry weight of 12 g/m'' and dried using an air floating dryer and a cylinder dryer.Then, it was treated with a 5-stage metal roll calender to form a cast coated paper. I got Kawara paper.

Separately, a coating liquid for cast coated paper having a concentration of 53% was prepared, consisting of 80 parts of kaolin, 20 parts of calcium carbonate, 10 parts of casein (solid content), and 8 parts of styrene-butadiene copolymer latex (solid content).

This coating liquid was applied to the coated surface of the single-sided coated base paper using a wet-on-wet type casting device equipped with a water application mechanism on a heated drum having a mirror surface, as shown in Fig. 1, to give a cast finish. .

That is, the first coating device (3) is applied to the coating surface of the coating base paper (2).
) at a dry weight of 5 g/m”
Then, while this coated layer is in a wet state, immediately coat it with the same cast coated paper paint using the second coating device (4) to give a dry weight of 6 g/m2. Immediately, it was pressed against a chrome-plated heating drum (7) with a surface temperature of 90°C with a diameter of 3.6 m using a press roll (6), and a rubber coating with a diameter of 30 cm was applied at a position 2 m behind the press roll nip. Press the water draining roll (8) from the back side of the coated paper with a linear pressure of 20 kg/cI1). Immediately after that, apply enough water with the shower (5), and then use the air knife (9) set at 1 ml from the water draining roll. The amount of water applied was adjusted by changing the air blowing speed, and after drying, it was released from the mold with a take-off roll 00) and wound up with a winder αυ. The amount of water applied at this time was 1Occ/m2.
The surface speed of the heating drum was 80 m/min.

Stibble and curl of the cast coated paper obtained were as shown in the attached table.

Example 2 In Example 1, the amount of water applied to the back side of the paper was changed to 15c.
A cast coated paper was obtained in the same manner as in Example 1, except that the paper was changed to "c/m".

The stipple and curl of the cast coated paper obtained were as shown in the attached table.

Example 3 A cast coated paper was obtained in the same manner as in Example 1 except that 50.4 g/m2 base paper was used.

The stipple and curl of the cast coated paper obtained were as shown in the attached table.

Comparative Example 1 A cast coated paper was obtained in the same manner as in Example 1, except that water was not applied to the back side of the coated paper during the manufacturing stage of the cast coated paper.

The stipple and curl of the cast coated paper obtained in this comparative example were as shown in the attached table.

Comparative Example 2 In the manufacturing process of cast coated paper, 10 cc/m'' of water was applied from the back side of the paper at the press roll nip, and after the coating layer became immobilized, water was applied to the back side of the paper. A cast coated paper was obtained in the same manner as in Example 1, except that this was not carried out.

The stipple and curl of the cast coated paper obtained in this comparative example were as shown in the attached table.

Table-1 Quality evaluation method [Stable]: Evaluated visually.

○: No occurrence of curling ×: Significant occurrence of curling [curl]: Cast coated paper cut into 10cm x 10cm squares was left in a constant temperature room at 20°C and RH 60χ for 24 hours. The curl direction (a curl with the cast surface inward is called a normal curl, and a curl with the inside direction of the paper as an axis is called a vertical curl) and its degree are shown in terms of the radius of curvature (cm) of the curl surface.

The higher the number, the less curl there will be.

〔effect〕

As is clear from Table 1, according to the method for producing cast coated paper of the present invention, the reverse vertical curl peculiar to thin cast coated paper is eliminated, and it has a uniform strong gloss without the occurrence of stibble. A thin cast coated paper is obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a manufacturing apparatus for manufacturing uninvented cast coated paper, in which the coated paper is brought into pressure contact with the surface of a heating drum, dried, and the coated layer is immobilized. It is an explanatory view constituted so that water may be applied to the back side. FIG. 2 is an explanatory diagram of a conventionally used cast coating device. ■... Unwinder 2... Cast base paper 3... First coating device 4... Second coating device

Claims (2)

[Claims] (1) After providing a coating layer containing pigment and adhesive as main components on base paper with a weight of 70 g/m^2 or less, the wet coating layer is pressed against the surface of a heated drum with a mirror surface and dried. A method for producing cast coated paper with a high gloss finish, characterized by applying water to the back side of the paper at a position after the coated paper is brought into pressure contact with the surface of a heating drum and dried to immobilize the coated layer. A method for manufacturing cast coated paper. (2) The amount of water applied to the back side of the paper is 2 to 25 g/
The method for producing cast coated paper according to claim (1), wherein m^2.