JPH0819638B2 - Method for producing cast coated paper - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing cast coated paper, and in particular, the back coated layer has low white paper gloss, but high ink gloss.
The present invention relates to a method for efficiently producing a cast coated paper having a so-called matte-gloss type matte back coating layer.

"Prior Art" Cast coated paper has excellent gloss and smoothness among coated papers for printing, and is widely used as a cover for various magazines, catalogs, pamphlets, annual reports and the like.

Conventionally, as a method for producing cast coated paper, a wet cast method (USP 1719166) and a rewet cast method (USP
2759847), gelation casting method (USP 2919205), etc., which are all heated while the coating layer composed mainly of a mineral pigment and an adhesive contains water and is in a plastic state. In principle, the method is common in that it is pressed and dried on the finished surface to be finished. Most of the cast coated papers produced according to these production methods are so-called single-sided cast coated papers having a strong glossy surface with one surface being cast finished, and the back surface having a fine paper-like surface.

On the other hand, matte coated paper gives an elegant and calm image compared to coated paper having high gloss, and therefore, it has recently become an important printing paper for monochromatic prints such as text papers to various multicolored prints. It is widely used as one of the grades.

Here, for example, when the cast coated paper is used as the cover of magazines, catalogs, annual reports, etc., when the cover is opened, the back side of the cast coated paper and the text paper using the matte coated paper do not feel uncomfortable. It is necessary to show the same blank paper quality and print quality, and for that purpose, it is strongly demanded that the back surface of the cast coated paper be a matte coated paper corresponding to the text paper.

As a method for obtaining the cast coated paper as described above, the basic method itself of the cast finish is not changed as described above, but the back surface is coated with a pigment having good ink acceptability, retentivity and plate reproducibility. Use a base paper that is provided with a layer and, if necessary, calenders it and smoothes it.Pressing the heat-finished surface while the pigment coating layer provided on the surface of this base paper contains water and is in a plastic state Then, a method of drying and finishing is proposed. However, although this method improves the printing quality on the back surface, it is considerably inferior in terms of smoothness and ink gloss as compared with general coated paper for printing because super calendering is not applied. It has also been proposed to perform a super calender treatment after the cast finish, but the surface of the cast coated paper will be bumpy, and the appearance of the cast surface will be greatly impaired. There is a problem that is too high.

As another method for the back coating layer to exhibit high smoothness and high ink gloss, for example, a method of laminating a single-sided cast coated paper and a matte coated paper using a thermoplastic polymer binder is used. Although it has been proposed, it has not been actually carried out due to problems such as smashing on the cast surface and difficulty in curl control after bonding depending on the kind of the bonding agent.

"Problems to be Solved by the Invention" In view of the present situation, the inventors of the present invention have conducted diligent research on a method for improving the above-mentioned drawbacks that accompany heating calendering after casting, and as a result, heating We have found that the surface roughness and hardness of the elastic rolls that make up the render are extremely important factors for the roughness of the cast coated paper surface and the smoothness of the back coating layer.

That is, in order to smooth the back surface of the cast coated paper, the heating calendering process is performed so that the front surface of the cast coated paper contacts the heating metal roll and the back surface contacts the elastic roll. In this case, the cast surface has a very smooth and glossy surface that is the mirror surface of the heating drum, but if the surface of the elastic roll of the heating calender is deformed or roughened due to temperature and pressure, the effect will be affected. It was revealed that the cast coating layer surface was extended and, as a result, the high gloss and smoothness of the cast surface were impaired.

Therefore, by defining the surface roughness of the elastic roll according to the hardness of the roll and the surface temperature of the metal roll, high smoothness is imparted to the back surface of the obtained cast coated paper, and moreover, the cast coated paper is provided. It was found that the cast coated paper can be produced with high efficiency without the occurrence of fluffiness and poor gloss on the surface, and finally the present invention has been completed.

"Means for Solving the Problems" The present invention forms a pigment coating layer containing a pigment and an adhesive as the main components on the back surface of a base paper, and then uses the pigment and the adhesive as the main components on the surface of the base paper. A pigment coating layer is formed, and while the coating layer on the surface is in a plastic state, it is pressed against a heating drum surface having a mirror surface and dried to obtain a cast coating layer, and then the cast finished surface is further heated on a metal roll surface. In addition, in the method for producing a cast coated paper in which the back side pigment coating layer surface is heated and calendered so as to be in contact with the elastic roll surface to give a strong gloss finish, the surface roughness Rmax of the elastic roll (specified by JIS B0651 Satisfies the following formula, and JIS P8 of the back coating layer surface
According to the 142 method, the smoothness is measured so that the measured value of white paper gloss is 40% or less and the smoothness by a smoother smoothness meter is 15 cmHg or less, and the backside is a matte coating layer. It is a method of manufacturing paper.

(Note) Rmax≤-0.1D-0.01T + 35 [Remarks] Rmax: Surface roughness of elastic roll (μm) D; Sure hardness of elastic roll D hardness (°) T; Surface temperature of metal roll during operation (° C) Action] Thus, the pigment coating composition for forming the back surface in the method of the present invention contains a pigment and an adhesive as main components, as in the conventional coating composition for printing.

As the pigment, for example, one or two kinds of pigments for ordinary coated paper such as clay, kaolin, aluminum hydroxide, calcium carbonate, titanium dioxide, barium sulfate, zinc oxide, satin white, calcium sulfate, talc, and plastic pigment. The above is appropriately selected and used.

In particular, in the present invention, the back surface has high smoothness and high ink gloss, but has low white paper gloss, and is intended to obtain a so-called back surface matte coated paper cast coated paper. Is 40% or less by measurement according to JIS P8142, and the smoothness by a smoother smoothness meter is intended to obtain a matte coating layer having 15 cmHg or less, and therefore as a pigment used for the back surface coating layer, It is preferable to add 50% by weight or more of calcium carbonate to all pigments, and it is more preferable to use calcium carbonate having an average particle size of 0.3 to 2 μm, which is more likely to obtain a smoothing effect by a heat calendering treatment after casting.

Examples of the adhesive include casein, soybean protein, styrene-butadiene copolymer, conjugated diene polymer latex such as methyl methacrylate-butadiene copolymer, polymer or copolymer of acrylic acid ester and / or methacrylic acid ester. Acrylic polymer latex such as, vinyl polymer latex such as ethylene-vinyl acetate copolymer, or alkali-soluble or alkali obtained by modifying these various polymers with a functional group-containing monomer such as a carboxyl group Non-soluble polymer latex, polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, silicon-containing modified polyvinyl alcohol, olefin-maleic anhydride resin, melamine resin, and other synthetic resin systems Chakuzai, positive starch, starches such as oxidized starch, carboxymethyl cellulose, cellulose derivatives such as hydroxyethyl cellulose, general coated paper for adhesive is used alone or in combination. These adhesives are used in an amount of 5 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the pigment. Further, as the auxiliary agent, for example, an antifoaming agent, a colorant, a release agent, a flow modifier, etc. may be appropriately used, and as the auxiliary agent for promoting the solidification of the coating layer, for example, amine, amide Further, polyacrylic amine or the like or polyvalent metal salt such as zinc, aluminum, magnesium, calcium, barium or the like may be added in an amount of about 0.1 to 10 parts by weight with respect to 100 parts by weight of the pigment.

The coating composition thus prepared is used in general coated paper production, for example, blade coater, air knife coater, roll coater, reverse roll coater, brush coater, curtain coater, champlex coater, bar coater, gravure coater. The base paper is coated in one layer or in multiple layers by an on-machine or off-machine coater provided with a coating device such as a coater or a size press coater. The solid content concentration of the coating composition at that time is generally 40 to 75% by weight, but considering the operability,
A range of 45-70% by weight is preferred. In addition, as the base paper,
US square meter used for general printing coated paper and cast coated paper
A base paper of a paper base or a board base of 30 to 400 g / m ² is used, but the papermaking method of the base paper is not particularly limited, and either acidic papermaking or alkaline papermaking may be used,
Of course, a medium-quality base paper containing high-yield pulp can also be used. Further, a base paper pre-coated with a size press, bill blade or the like can also be used.

The coating amount of the coating composition on the base paper is generally about 10 to 50 g / m ² on a dry weight basis, but it is 15 to 30 g in consideration of the blank quality of the resulting cast coated paper, printability, etc. / m ²
It is desirable to adjust within a range. Further, as a method for drying the wet coating layer, conventionally publicly known steam heating, hot air heating, gas heater heating, electric heater heating,
Various methods such as infrared heater heating, high frequency heating, laser heating, and electron beam heating can be appropriately adopted.

The opposite side (front side) of the base paper coated on the back side as described above
The coating composition is mainly composed of various inorganic pigments such as clay, kaolin, calcium carbonate, aluminum hydroxide and titanium oxide, and plastic pigments, and natural and synthetic adhesives such as casein, starch and synthetic resin latex. While the coating layer contains water and is in a plastic state, the coating layer is pressed and dried on the heat-finished surface, and after the water content in the coating layer is substantially evaporated, it is released from the finish surface and cast-coated. A coated paper is obtained. Such a cast finishing method itself is not particularly limited, and may be a conventional wet casting method, gelling casting method, rewet casting method, or the like. -A so-called cast finishing method of drying is applicable to the present invention.

In the production method of the present invention, the cast coated paper thus obtained is passed through a heated calender for surface finishing. Examples of calenders include a super calender and a gloss calender (special Kaisho 40-13
No. 2305, published patent publication 63-500188), soft compact calender (Paper and Pulp Technology Times, August 1987 issue,
31-36; PPI, November 1987, 45-47; WFP, 1985,
22, pp. 873-877) etc. are used in the form of on-machine or off-machine. The surface of the metal roll may be mirror-finished by hard chrome plating or the like.

In the method of the present invention, an elastic roll having a surface roughness satisfying the following formula is selectively used as the elastic roll of the above-mentioned various calenders.

Rmax ≦ −0.1 D−0.01T + 35 [Remarks] Rmax; Surface roughness of elastic roll (μm) D; Sure hardness of elastic roll D hardness (°) T; Surface temperature of metal roll during operation (℃) From the above relational expression As is apparent, the elastic roll used in the method of the present invention needs to have a smaller surface roughness Rmax as the Shore D hardness of the elastic roll becomes harder.

Conventionally, no particular attention has been paid to the surface roughness of the elastic roll that constitutes the calender, and the surface roughness of the elastic roll is related to the Shore D hardness of the elastic roll and the surface temperature of the metal roll as in the present invention. By defining the
No technical idea is known to improve the fluffiness of the resulting cast coated paper.

According to the experiments by the present inventors, the surface roughness Rm by polishing
Even with an elastic roll having an ax of 5 μm or less, the surface temperature of the metal roll is raised to 60 ° C. or more at a high speed of 200 m / min or more, and the linear pressure is increased.
It was clarified that when the cast coated paper was treated under the condition of 100 kg / cm or more, the surface roughness rapidly decreased due to unevenness of the texture and unevenness of the coated paper. Especially in thick paper, the unevenness of the texture and the smoothness are inferior, so the surface roughness is remarkably reduced, and if an elastic roll with low hardness or an elastic roll made of a material with small restorability is used, the tendency is further reduced. It was also revealed that

Therefore, in the method of the present invention, it is necessary to specify the surface roughness of the elastic roll that is actually used, and if the surface roughness of the elastic roll deviates from the specifications of the present invention during operation, It is necessary to stop the render and replace it with a roll that satisfies the conditions.

As the material of the elastic roll, it is possible to use, for example, cotton, fill mat cotton, white cotton, woolen paper, asbestos, etc. which have been conventionally used in a calendar for coated paper, but these natural fibers are the main materials. Since the elastic rolls are inferior in high-temperature durability and have a rapid tendency to decrease in surface roughness, urethane, polyamide, epoxy, isocyanate, silicon, vinylidene fluoride, phenol or the like resin can be used as a single layer or a multilayer roll. (JP-A-62-282093), an elastic roll formed by containing 50% or more of synthetic fibers such as nylon, tetron, and aramid (hereinafter collectively referred to as a resin roll) is preferable. In particular, a resin roll of aramid, epoxy, polyamide or the like having a high heat resistance is more preferably used.

Regarding the hardness of the elastic roll, a roll having a Shore D hardness of 75 ° or more is desirable in consideration of durability under high temperature and high pressure and resistance to surface roughening under paper passing. Further, the higher the surface temperature of the elastic roll, the faster the roughening of the surface of the roll progresses. Therefore, it is preferable to cool the elastic roll from the inside or outside of the roll with a cooling liquid or a cooling air.

In the method of the present invention, the surface roughness of the elastic roll
Rmax is measured based on the method defined in JIS B0651, but the calender roll width of ordinary cast coated paper is 15
Since it is about 00 to 3800 mm, the measured values vary considerably in the width direction of the roll. Therefore, for example, a Surftest 201 manufactured by Mitoyo Seisakusho is used as a measuring instrument, and the maximum measurement length (L) is set to 8 mm, and the entire width of the elastic roll is at least 10 mm.
Measure the number of times (if the roll width is wide, measure more times) and use the average of the measured values to obtain the surface roughness Rmax.
Need to be specified. Various treatment conditions for surface treatment of coated paper with a heating calender are appropriate depending on the type of target coated paper, base paper conditions, coating layer properties, coating amount, paper moisture, finishing speed, etc. Adjusted.

The pressurizing condition of the calendar roll is a linear pressure of 100 to 500 kg / c.
A range of about m is preferable, and the number of pressure nips per one calender is usually 2 to 6 nip per one drum or roll in the case of a soft compact calender. By the way, in the case of a super calender, about 3 to 13 nips is common.

Therefore, the cast coated paper has a surface finish of 2-12.
It will be in pressure contact with an elastic roll of this size. The degree of decrease in the surface roughness of the elastic roll is the texture of the cast coated paper to be passed, uneven coating, the weight of the rice, the paper moisture, the material of the elastic roll,
Since it depends on many conditions such as hardness, roll temperature, pressure, speed, etc., it is troublesome to constantly measure and manage,
In the method of the present invention, at least one of the elastic rolls in the latter half, which has a great influence on fluttering, needs to be operated by using a roll having a surface roughness Rmax satisfying the relation of the general formula. Of course, it is most preferable that all elastic rolls satisfy the general formula.

The water content of the cast coated paper before entering the nip of the calender is preferably about 3 to 10%, and the finishing speed of the calender is 100 to 400 m / min, although it varies greatly depending on the weight of the paper, the type of paper, etc. Is preferred. Also, a water coating device using a roll, an electrostatic humidifying device, a steam humidifying device, or the like is installed in order to control and humidify the cast coated paper after the surface treatment, and it has been conventionally known in the coated paper manufacturing field. Of course, it is possible to use various techniques in an appropriate combination.

"Examples" The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. Further, unless otherwise specified, parts and% in the examples represent parts by weight and% by weight, respectively.

Examples 1 to 5 Sachin White (trade name; Satin White, manufactured by Shiroishi Industry Co., Ltd.) 5 parts, Kaolin (trade name: UW-90, manufactured by EMC) 30
Parts, 65 parts of heavy calcium carbonate having an average particle diameter of 1.73 μm (trade name: Softon 1800, manufactured by Bihoku Kouka Co., Ltd.) are dispersed in a chores disperser using 0.2 parts of sodium polyacrylate as a dispersant. Then, a pigment slurry having a solid content concentration of 65% was prepared. Add 3 parts of phosphoric acid modified starch (solid content) to this pigment slurry.
And 12 parts of styrene / butadiene copolymer latex (trade name; JSR0696, manufactured by Japan Synthetic Rubber Co., Ltd.) (solid content) were added, and water was further added to prepare a coating solution having a solid content concentration of 60%.
This coating solution was coated on the back side of a base paper of 75 g / m ^{2 by} a blade coater so that the dry coating amount was 20 g / m ^2, and dried by a dryer at 120 ° C. to obtain a one-side coated paper with a water content of 6%. .

Separately, an aqueous coating solution for casting having a solid content concentration of 53%, which was composed of 80 parts of kaolin, 20 parts of light calcium carbonate, 10 parts of casein (solid content), and 8 parts of styrene-butadiene latex (solid content), was obtained. This coating solution was applied to the front surface of the back coated base paper and cast-finished according to the wet-on-wet method as shown in JP-B-38-25160. That is, the surface of the coated base paper was coated with a first coating device with a coating liquid for casting to a dry weight of 11 g / m ² , and then immediately while the coating layer was in a wet state. The same coating liquid as in the case of the first coating device was applied to the second coating device so that the dry weight was 9 g / m ² , and immediately pressed onto a chrome-plated cast drum having a surface temperature of 90 ° C. Then
After drying, the mold was released to obtain a cast coated paper.

This cast coated paper is a polyurethane roll having a metal roll having a surface temperature of 60 ° C. and a surface roughness Rmax of 5 μm (Example 1), 16 μm (Example 2), 20 μm (Example 3) and a Shore D hardness of 86 °. Using a 4-nip super calender consisting of a resin elastic roll (trade name; Ellagrass, manufactured by Kinyosha Co., Ltd.) so that the surface of the cast coated paper comes into contact with the metal roll, speed 200 m / min, linear pressure 150 kg / Surface pressure finishing was performed under the condition of cm to obtain a cast coated paper.

The cast coated papers obtained were evaluated according to the evaluation items, and the results are shown in Table 1.

Comparative Examples 1 to 4 Comparative Example 1 was cast-finished in Example 1 and was not calendered, and Comparative Examples 2 to 4 each had a resin elastic roll Rmax used in Example 1 of 37 μm (Comparative Example 2), A cast coated paper was produced in the same manner as in Example 1 except that the thickness was 42 μm (Comparative Example 3) and 50 μm (Comparative Example 4).
The evaluation results are shown in Table-1.

Example 4 A cast coated paper was manufactured in the same manner as in Example 1 except that the Shore D hardness of the resin elastic roll used in Example 1 was 78 °, and the evaluation results are shown in Table 1.

Example 5 Example 5 except that 65 parts of light calcium carbonate (trade name; Tamapearl 121, manufactured by Okutama Industry Co., Ltd.) having an average particle size of 1.10 μm was used as the calcium carbonate of the back side coating layer pigment used in Example 1. A cast coated paper was manufactured in the same manner as in No. 1, and the evaluation results are shown in Table 1.

Comparative Example 5 70 parts of heavy calcium carbonate (trade name; BF-100, manufactured by Bihoku Kogyo Co., Ltd.) having an average particle size of 8.60 μm instead of the light calcium carbonate having an average particle size of 1.10 μm used in Example 5 Cast coated papers were produced in the same manner as in Examples 1 and 5 except that was used, and the evaluation results are shown in Table 1.

Examples 6 to 7 20 parts of kaolin, heavy calcium carbonate having an average particle diameter of 1.73 μm (trade name: Softon 1800, manufactured by Bihoku Powder Co., Ltd.)
50 parts, light calcium carbonate with an average particle size of 1.10 μm (trade name; Tamapearl 121, Okutama Industry Co., Ltd.) 30 parts, oxidized starch (solid content) 3 parts, styrene-butadiene latex (trade name; JSR 0696 Nihon Gosei) A coating liquid having a solid content concentration of 45% was prepared from 13 parts by Rubber Co., Ltd. This coating liquid 80
Using an air knife coater on the back surface of g / m ² of fine atoms, apply and dry to a dry weight of 20 g / m ² ,
A back coated atom for casting was created.

Separately, 60 parts of kaolin, 40 parts of light calcium carbonate and 0.5 part of sodium polyacrylate were dispersed in water using a Choles disperser to prepare a pigment slurry having a solid content concentration of 60%.
0.5 parts of tributyl phosphate as an antifoaming agent,
1.0 part ammonium stearate as a release agent, 10 parts 15% casein solution (solid content) dissolved with ammonia as an adhesive and acrylic acid / butadiene / methyl methacrylate (ratio; 2/33/65) copolymer latex (Solid content) 16 parts was added, and ZnSO ₄ 3 parts and water were further added to prepare a coating liquid having a solid content concentration of 45%. The obtained coating liquid was cast-finished according to the rewet casting method disclosed in JP-A-59-216996.

This cast coated paper is composed of a metal roll having a surface temperature of 105 ° C. and an elastic roll made of an epoxy resin having a surface roughness Rmax of 7 μm (Example 6), 19 μm (Example 7) and a Shore D hardness of 90 °. Using a 4 nip soft compact calender, speed 300 m / min, linear pressure 200 kg /
The cast coated paper was passed under the condition of cm so that the surface of the cast coated paper was in contact with the metal roll, and surface pressure finishing was performed to obtain a cast coated paper. The evaluation results for each coated paper are shown in Table-1.

Comparative Example 6 A cast coated paper was produced in the same manner as in Example 5 except that the elastic roll used in Example 6 had an Rmax of 42 μm (Comparative Example 6), and the evaluation results are shown in Table 1. .

"Effects" As is clear from the results in Table 1, the cast coated papers obtained in the examples of the present invention are significantly improved in the fluffiness of the surface, and the smoothness of the back surface and the ink gloss are extremely high. It was an excellent cast coated paper. When these were used as cover sheets, there was almost no difference in quality from the text sheets.
In particular, the simultaneous use of the double-sided matte coated paper finished with the same coating layer as the back surface pigment coated layer shown in the examples of the present invention as the text sheet at the same time causes no discomfort between the back surface of the cast cover sheet and the text sheet. Instead, it was finished as an extremely luxurious magazine.

(Remarks) Each evaluation method in Table-1 is as follows [Surface fluttering] (visual judgment of cast surface) ◎: Very good ○; Good △; Inferior ×; Very poor [Gloss] (The larger the value, the better the gloss. ) The Murakami Color Research Laboratory (GM-3D) showed a gloss value (measured value) of 75 degrees.

[Backside smoothness] (The smaller the value, the better the smoothness) The smoothness was measured with a smoother measuring device (manufactured by Toei Denshi Co., Ltd.) DSM-01.

[Backside ink gloss]

Four-color printing was performed at a printing speed of 8,000 sheets / hour using a Mitsubishi Heavy Industries diamond offset printing machine, and the ink gloss of the four-color overlapping portion was visually evaluated.

⊚: Very good ◯: Good Δ: Inferior ×: Very inferior (Note) Surface roughness Rmax Measured with a Surftest 201 manufactured by Mitoyo Seisakusho with a measurement length (L) of 8 mm.

Claims (3)

[Claims] 1. A pigment coating layer containing a pigment and an adhesive as a main component is formed on the back surface of a base paper, and then a pigment coating layer containing a pigment and an adhesive as a main component is formed on the surface of the base paper. While the coated layer on the surface is in a plastic state, it is pressed against a heating drum surface having a mirror surface and dried to obtain a cast coated paper, and the cast finished surface is further applied to the heated metal roll surface, and the back pigment coated layer surface. In a method for producing a cast coated paper by applying a heating calender so as to be in contact with the elastic roll surface to give a strong gloss finish, the surface roughness Rmax (defined by JIS B0651) of the elastic roll satisfies the following formula. And JIS P8 of the back coating layer surface
According to the 142 method, the smoothness is measured so that the measured value of white paper gloss is 40% or less and the smoothness by a smoother smoothness meter is 15 cmHg or less, and the backside is a matte coating layer. Paper manufacturing method. (Note) Rmax≤-0.1D-0.01T + 35 [Remarks] Rmax; Surface roughness of elastic roll (μm) D; Sure hardness of elastic roll D hardness (°) T; Surface temperature of metal roll during operation (° C) 2. Calcium carbonate is used as a pigment for the back coating layer.
The method for producing cast coated paper according to claim 1, wherein the content of the cast coated paper is 50% by weight or more. 3. The average particle size of calcium carbonate is 0.3 to 2.0 μm.
The method for producing a cast coated paper according to claim 2, wherein m is m.