JPH0770985A - Cast-coated paper - Google Patents

Abstract

PURPOSE:To obtain excellent cast-coated paper especially excellent in production efficiency, having high smoothness and free from unevenness of gloss or pinhole. CONSTITUTION:This cast-coated paper is obtained by providing a coated layer consisting essentially of pigments and an adhesive on base paper using a lip coater type coating apparatus, subjecting the coated layer to gelation or once drying the coated layer and then re-humidifying the coated layer and pressing the surface of the coated paper to heated metal drum face having mirror surface to finish the surface so as to have high gloss.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to cast coated paper,
The present invention relates to an excellent cast coated paper that has high production efficiency, high smoothness, and eliminates uneven gloss and pinholes.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a strong glossy paper for printing called cast coated paper, after a base paper is coated with a coating liquid for casting containing a pigment and an adhesive as a main component, a coated layer is formed. Wet casting method of pressing (pressing) to the surface of the heating drum having a mirror surface while in a wet state, drying and gloss finishing, and coating layer in a wet state once dried, then plasticized by rewetting liquid, Generally known are a rewet casting method in which the surface of the heating drum is pressed, and a gelling casting method in which the coating layer in a wet state is put into a gel state and pressed into contact with the surface of the heating drum to give a gloss finish.

All of these cast finishing methods are common in that the surface of the coating layer in a plastic state is pressed against the surface of the heating drum, dried, and released from the surface of the drum to take a mirror surface.

In such a method for producing cast coated paper, since the coated layer is pressed against the heating drum surface to dry, most of the water in the coated layer passes through the paper layer and the non-cast surface side. Will be evaporated from. When the evaporation rate exceeds a certain limit, a part of the evaporated water is evaporated toward the mirror surface drum, resulting in pinholes and uneven gloss on the surface of the coating layer of the resulting cast coated paper. However, compared to the case of general coated paper manufacturing that can dry both sides of cast coated paper, it is necessary to suppress rapid drying, so it is forced to operate at extremely low speed. It is the actual situation.

Of these casting finishing methods, the gelling casting method and the rewet casting method are both gelled or dried before the cast coating layer is pressed against the mirror-finished drum surface. It can be cast-finished by press contact with a relatively high temperature mirror-finished drum having a temperature of 90 ° C. or higher. Therefore, these casting methods can increase the drying speed as compared with the wet casting method,
Excellent in productivity.

By the way, the cast coating layer in the gelling casting method and the rewet casting method is generally 25 to 30 g / in order to cover the unevenness of the base paper and obtain a cast coated paper without a feeling of roughness and gloss unevenness. A dry coating amount of about m ² is required, and at the same time smoothness and bulkiness are required. Therefore, it is conceivable to use a blade coater as a coating device for obtaining a coating layer for casting having excellent smoothness. However, the blade coater has a very large shearing force, and the effect of pushing the coating liquid into the base paper by the blade blade tends to densify the coating layer and deteriorate air permeability. As a result, it is difficult for the evaporated water in the coating layer to escape to the back side of the base paper during cast finishing,
Pinholes will be generated on the surface of the cast coating layer. In addition, in order to make the coating layer bulky and porous, it is generally widely used to use a salt having a thickening and coagulating action in the coating layer, but a coating solution containing a salt is applied. In that case, there is a drawback that streaks, scratches and the like are likely to occur.

[0007] When a roll coater is used as a coating device, there are also drawbacks that a rough coating layer is easily formed along the irregularities of the base paper as a support, the smoothness is poor, and a roll mark is easily generated. is there. In addition, since a roll coater cannot generally perform thick coating, it is not suitable when a desired high coating amount is to be coated once. Further, when a rod coater is used as a coating device, the smoothness is relatively good, but rod marks are easily generated, and further, the low shear viscosity of the coating liquid is limited, and the coating speed is It has the drawback of being slow.

In the gelling cast method or the rewet cast method, an air knife coater is generally used as a coating device in many cases. With the air knife coater, a bulky and porous coating layer can be obtained without causing problems such as scratches even if the coating contains salts. But,
The low shear viscosity of the paint to be applied is limited to about 1500 cps (upper limit), and a part of the excess paint scraped off with an air knife becomes a fine mist that stains the blade edge of the air doctor, causing the dirt to cause a coating surface. There was a problem such as streaking. Alternatively, since the coating amount is scraped off by air, large coating unevenness occurs on the coated surface, and the smoothness is inferior to the case where a blade coater is used. In addition, in the coating method using these blade coater, roll coater, rod coater and air knife coater, in order to collect the paint and reuse it in circulation, it is necessary to have a circulation system for the paint, which requires maintenance measures and power consumption. This consumes energy for use, causes a large economic loss, and has a drawback in that in the case of changing the type of product brand, it takes time to clean the circulation system and the operation rate decreases.

[0009]

From the actual situation as described above,
The inventors of the present invention have conducted extensive studies in order to obtain an excellent cast coated paper which is highly smooth and has no gloss unevenness or pinholes without lowering the operability in the gelling cast method or the rewet cast method. As a result, by using a lip coater type coating device on the base paper, by providing a coating layer for casting, it has extremely excellent smoothness desired by the present inventors, and uneven gloss and pinholes. It has been found that a cast-coated paper without the above can be obtained.

[0010]

According to the present invention, a coating layer containing pigments and adhesives as main components is provided on a base paper by using a lip coater type coating apparatus, and the coating layer is gelled or The cast coated paper is characterized in that it is dried and then rewet and pressed against a metal drum surface having a heated mirror surface to give a strong gloss finish.

[0011]

As described above, the inventors of the present invention have been keen to obtain a cast coated paper which has excellent smoothness in the gelling cast or rewet cast method and which is free from uneven gloss and pinholes. I examined it repeatedly. As a result, it was found that by providing the coating layer for casting by using a specific coating device, all the problems that were difficult in the conventional casting method can be solved, and the present invention has been completed.

That is, the present invention relates to a cast coated paper obtained by a gelling system or a rewet system, and when a cast coating layer containing a pigment and an adhesive as a main component is provided on a base paper, a specific coating is applied. A cast coated paper, which is obtained by forming a coated layer using a processing device.

The coating device in this case is as proposed in Japanese Patent Laid-Open No. 2-152574 (FIG. 1), and specifically, a nozzle having a doctor edge below the backing roll. This is a lip coater type coating apparatus in which a head is arranged and a coating liquid is supplied from the nozzle head by applying pressure to the coating liquid to discharge the coating liquid onto a web (web).

That is, a first liquid storage chamber is provided in the width direction inside the nozzle head, an outflow passage leading from the first liquid storage chamber to the front of the doctor edge is provided inside the nozzle head, and the front portion of the nozzle head is connected to the backing roll. To the lower surface Paper web (web)
A liquid reservoir wall is erected with a running gap left, and the part formed by the lower peripheral surface of the backing roll, the liquid reservoir wall and the entire doctor edge is expanded as a second liquid reservoir chamber forward from the outlet of the outflow passage. Furthermore, it is formed to have a volume larger than that of the outflow passage, pressure detection means is provided in the second liquid storage chamber, and control means for controlling the supply device according to the pressure detected by the pressure detection means is provided.

In the lip coater type coating apparatus having the above-mentioned structure, the web (web) is filled with the second coating liquid.
It travels to the doctor edge through the liquid storage chamber, and the coating liquid is applied by the linear pressure of the blade edge of the doctor edge. In this case, the second liquid storage chamber expands forward from the outlet of the outflow passage and is formed larger than the volume of the outflow passage.
It is easy to keep the inside of the second liquid storage chamber at a pressure higher than atmospheric pressure and at a constant pressure, and therefore, when the web (web) is carried into the second liquid storage chamber through the gap between the liquid storage wall and the backing roll. Moreover, air does not enter the inside of the second liquid storage chamber. Further, the pressure of the coating liquid in the second liquid storage chamber is detected by the pressure detection means and transmitted to the control means, and the control means controls the supply means by the transmitted pressure to coat the second liquid storage chamber interior. Keep the working fluid pressure constant.

Therefore, by using such a coating apparatus, there is a problem in the prior art as described above, that is, streaks due to dirt on the air doctor blade in the air knife coater, uneven coating, and rod in the rod coater. Mark, productivity reduction due to low speed, roll mark in roll coater, coating smoothness, streak and scratch troubles in blade coater, and decrease in air permeability can all be eliminated.

In particular, the greatest advantage of using the above-mentioned lip coater type coating apparatus for forming the coating layer for casting is that the coated surface has high smoothness equivalent to that of the case of using a blade coater. Moreover, even if the coating solution contains salts, the streak has a structure in which the coating solution can be applied leaving a gap between the doctor edge and the web (web). That is, it is possible to form a coating layer that is bulky and porous without causing scratches and scratches.
As a result, it has been found that a cast coated paper having high smoothness and excellent in quality in which uneven gloss and pinholes are eliminated can be obtained.

Furthermore, since there is no need for a paint circulating system for collecting and circulating and reusing the paint (for the cast coating layer), it is possible to replace the paint in a short time and to leave the residual paint. Since the loss at the time of exchanging etc. can be minimized, highly efficient production became possible.

The cast coated paper according to the present invention is one in which a cast coating layer is formed on a base paper by using the above-mentioned coating apparatus. In this case, the coating layer is a conventional cast coated paper. It is mainly composed of pigments and adhesives used in the field and is not particularly limited. Examples of the pigment include kaolin, aluminum hydroxide, satin white, barium sulfate, heavy calcium carbonate, light calcium carbonate, talc, calcined clay, titanium dioxide, plastic pigment, and the like, and at least one of them is appropriately used. Used by choice.

Examples of the adhesive include proteins such as casein and soybean protein, styrene-butadiene copolymer, methylmethacrylate-butadiene copolymer conjugated diene polymer latex, acrylic polymer latex, ethylene-vinyl acetate. Vinyl-based polymer latex such as copolymer, or these various polymers with functional group-containing monomer such as carboxyl group, functional group-modified alkali-soluble or alkali-insoluble polymer latex, polyvinyl alcohol, Olefin-maleic anhydride resin,
Synthetic resin adhesive such as melamine resin, positive starch,
Adhesives generally known for coated papers, such as starches such as oxidized starch and esterified starch, and cellulose derivatives such as carboxymethyl cellulose and hydroxymethyl cellulose, can be used alone or in combination.

The amount of the adhesive used is adjusted in the range of 5 to 50 parts by weight, usually 10 to 30 parts by weight, based on 100 parts by weight of the pigment.

Further, in the coating layer for casting used in the present invention, more preferable results can be obtained by using a salt having a thickening and coagulating action in addition to the pigment and the adhesive. That is, the salts in this case are zinc, aluminum,
Magnesium or calcium sulfate, nitrate,
It is composed of acetate or formate, and when at least one of these salts is contained in the coating layer, it causes thickening and coagulation in the process of drying the coating layer, and the coating layer is extremely porous. Further, by combining with the coating device specified in the present invention, the porous property thereof is further increased, and the surface of the coating layer is smoothed to obtain a uniform coating layer. As a result, the gel cast method,
Or, in the process of being pressed against the heated mirror surface drum by the rewet casting method and dried, vapor transmission becomes easy, and because the adhesion between the coating layer and the mirror surface drum is excellent, there is no gloss unevenness, pinholes, and high quality It was found that a cast coated paper can be efficiently obtained.

As described above, the coating liquid for coating layer may include, in addition to pigments, adhesives and salts, auxiliary agents such as defoaming agents and
A colorant, a release agent, a flow modifier, a water-proofing agent, a preservative and the like can be appropriately used as necessary. The coating liquid composed of the above materials generally has a solid content concentration of 35 to 65.
The lip coater type coating device is applied to the base paper so that the dry weight is adjusted to about 5 to 30 g / m < ² >. The coating liquid pressure in the coating liquid storage chamber in the coater head is set to 2000 mmA in order to suppress the permeation of the coating liquid into the base paper and effectively obtain a bulky coating layer.
q It is preferable to control the coating amount to the following and coat it.

The base paper for cast coated paper is not particularly limited, and acid paper or neutral paper generally used in the field of coated paper is applied. If necessary, a general pigment coating composition may be pre-coated on one side or both sides of the base paper in advance. In this case, the coating amount is 5 to 30 g / dry weight per side. About m ² is desirable. If necessary, the precoated base paper may be subjected to smoothing treatment such as super calendering, brushing, or cast finishing in advance.

After the coating layer is provided on the base paper by the above-mentioned coating device, the coating layer is gelled or once dried and then re-wetted by a usual gelation casting method or rewet casting method. Then, the cast coated paper is obtained by pressing and drying the surface of the metal drum having a heated mirror surface.

[0026]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively.

Example 1 70 parts of kaolin, 30 parts of calcium carbonate, and 0.5 parts of sodium polyacrylate were dispersed in water using a Choles disperser to prepare a pigment slurry having a solid content concentration of 65%.
0.5 parts of tributyl phosphate as an antifoaming agent and ammonium stearate as a releasing agent were added to this slurry.
0 parts, 15% dissolved with ammonia as adhesive
A casein aqueous solution (8 parts, solid content) and a styrene-butadiene copolymer latex (18 parts, solid content) were added to prepare a coating solution for rewet casting having a solid content concentration of 45%. Wet cast finish.

That is, the rewet cast was applied to the base paper 7 having a weight of 64 g / m ^{2 by using} a lip coater type coating device 8 (lip coater manufactured by Hirano Techseed Co., Ltd.) so that the dry weight was 20 g / m ^2. After applying the coating liquid for use with the coating liquid, it was dried by an air floating dryer 9. Then
A rewetting liquid 13 made of polyethylene emulsion supplied from a nozzle is passed through a press nip 12 formed by a press roll 10 and a heating mirror surface drum 11.
After rewetting the surface of the coating layer with (1.0% concentration), press pressure 20 on a cast drum with a surface temperature of 105 ° C.
After being pressed and dried at 0 kg / cm, the cast coated paper 15 is peeled off from the drum by the take-off roll 14.
Got

Example 2 A cast coated paper was obtained in the same manner as in Example 1 except that 3 parts of zinc sulfate was added to the casting coating solution.

Example 3 A cast coated paper was obtained in the same manner as in Example 1 except that 2 parts of calcium acetate was added to the casting coating solution.

Example 4 80 parts of kaolin, 10 parts of calcium carbonate, 10 parts of aluminum hydroxide and 0.5 part of sodium polyacrylate were dispersed in water using a Choles disperser to obtain a solid content concentration of 65%.
A pigment slurry of was prepared. 0.5 parts of tributyl phosphate as an antifoaming agent, 1.5 parts of funnel oil as a releasing agent, 14 parts of a 15% casein aqueous solution (solid content) dissolved using ammonia as an adhesive and styrene-butadiene 10 parts of polymer latex (solid content) and 0.1 part of aluminum sulfate were further added to prepare a coating solution for gelling cast having a solid content concentration of 38%, and gelling cast finish was performed by the apparatus shown in FIG. .

That is, the above gelling was applied to a base paper 16 having a weight of 64 g / m ^{2 by using} a lip coater type coating device 17 (lip coater manufactured by Hirano Techseed Co., Ltd.) so that the dry weight was 20 g / m ² . After applying the coating liquid for casting, the water content after coating with the air floating dryer 18 is 1
Pre-dried to 0%. Then, after the coating layer is gelled with a 1% formic acid aqueous solution 19, the cast drum 21 having a surface temperature of 105 ° C. is pressed against the cast drum 21 at a pressing pressure of 150 kg / cm and dried, and then the take-off roll 22 is removed from the drum. The cast coated paper 23 was obtained by peeling with.

Comparative Example 1 A cast coated paper was obtained in the same manner as in Example 1 except that the coating material used in Example 1 was applied with an air knife coater.

Comparative Example 2 A cast coated paper was obtained in the same manner as in Example 1 except that the coating material used in Example 1 was applied by a blade coater.

Comparative Example 3 A cast coated paper was obtained in the same manner as in Example 2 except that the coating material used in Example 2 was applied with an air knife coater.

Comparative Example 4 A cast coated paper was obtained in the same manner as in Example 2 except that the coating material used in Example 2 was applied with a blade coater.

Comparative Example 5 A cast coated paper was obtained in the same manner as in Example 2 except that the coating material used in Example 2 was applied by a rod coater.

Comparative Example 6 A cast coated paper was obtained in the same manner as in Example 4, except that the coating material used in Example 4 was applied with a blade coater.

Table 1 shows the white gloss, pinholes, uneven gloss, and operability of the cast coated paper thus obtained. The above evaluation method was performed as follows.

[Glossiness of white paper] It was measured according to JIS P8142.

[Pinhole] Pinholes on the surface of the cast coated paper were observed with a stereoscopic microscope and judged according to the following criteria. ◎: ² pin hole is less than 10 hair in 1cm ○: pin-hole is less than 10 to 20 hair in 1cm ² △: 1cm ² pin hole is less than 20 to 50 hairs in ×: pin hole 50 in 1cm ² More than

[Gloss unevenness] The gloss unevenness of the surface of the cast coated paper was visually evaluated according to the following criteria. ⊚: No gloss unevenness ○: Slight gloss unevenness is observed, but there is no problem in practical use. Δ: Uneven gloss is observed. X: Many uneven glosses are seen.

[Operability] O: Stable operation is possible. ×: Continuous operation is impossible due to streaks and rod marks.

[0044]

[Table 1]

[0045]

As is apparent from Table 1, the cast coated paper obtained by the method of the present invention was free from pinholes and gloss unevenness, and was extremely excellent in white paper gloss and printability. Further, it was found that the maximum production speed did not decrease and the workability was excellent.

[Brief description of drawings]

FIG. 1 is an example of a coating head portion of a lip coater type coating apparatus used in the present invention.

FIG. 2 is a schematic view of a rewet casting device used in Examples 1 to 3 of the present invention.

FIG. 3 is a schematic view of a gelling cast device used in Example 4 of the present invention.

[Explanation of symbols]

 1 Backing Roll 2 Doctor Edge 3 First Liquid Reservoir 4 Second Liquid Reservoir 5 Outflow Path of Coating Liquid 6 Liquid Retaining Wall 7,16 Base Paper 8,17 Lip Coater Coating Device 9,18 Dryer 10,20 Press roll 11,21 Cast drum 12 Press nip 13 Rewetting liquid 14,22 Take off roll 15,23 Cast coated paper 19 1% aqueous solution of formic acid

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuo Hojo 4-3-1, Jokoji Temple, Amakosaki City, Hyogo Prefecture Kanzaki Paper Co., Ltd. Kanzaki Mill

Claims (3)

[Claims] 1. A base paper is provided with a coating layer containing a pigment and an adhesive as main components by using a lip coater type coating device, and the coating layer is gelled or once dried, and then rewet. A cast coated paper characterized by being pressed into contact with a metal drum surface having a mirror surface that has been heated by heating to give a high gloss finish. 2. The cast coated paper according to claim 1, wherein the coating layer contains at least one salt of zinc, aluminum, magnesium or calcium. 3. The cast coated paper according to claim 2, wherein each salt of zinc, aluminum, magnesium or calcium is one of sulfate, nitrate, acetate or formate.