JPH03241095A - Paper coating composition and production of coated paper using same composition - Google Patents

Abstract

PURPOSE:To provide the subject composition mainly composed of a specified pigment and a specified amount of binder resin, having a high-grade gloss and whiteness and capable of providing a coated paper suitable for various printings. CONSTITUTION:An objective composition containing 25-80wt.% binder resin (solid matter) based on 100wt.% pigment (preferably containing >=70wt.% calcium carbonate and >=10wt.% titanium dioxide) containing >=70 wt.% pigment having 0.1-1.0mum average particle size. In addition, the above-mentioned binder resin preferably contains an aqueous resin having 20-100 deg.C glass transition temperature in an amount of >=80wt.%.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a paper coating composition for obtaining coated paper having high gloss, excellent printability, etc., and coating using the same. Concerning a paper manufacturing method.

[Conventional technology]

Cast coating has been known as a method for producing coated paper with a high degree of gloss.

The cast coating method involves applying a coating agent whose main components are pigments and adhesives, and while the coating agent is still wet, the coating layer is pressed under heat on a chrome-plated drum with a mirror surface, and then dried. The wet casting method involves drying the wet coating layer and then re-wetting it to plasticize it, pressing the coating layer onto the mirror-surfaced cast drum surface, drying it, and then peeling it off. wet cast method,
Furthermore, a gel casting method is known in which a wet coating layer is turned into a gel state and pressed against a drum surface having a mirror surface.

In both of these methods, a coating layer that has been made plastic (wet) with water, etc. is pressed against the surface of a cast drum with a mirror surface using a Luss roll, dried on the cast drum, and then peeled off to create a mirror finish. They have one thing in common.

Coating agents used in these cast coating methods include JP-A-57-117694 and JP-A-59-21.
As disclosed in No. 6996, it is composed of pigments such as kaolin and clay and adhesives such as casein and styrene-butadiene copolymer latex, and the pigment ratio in the solid content is about 80%. It had been.

On the other hand, as a method for high-speed gloss finishing of coated paper, the coating layer in a dry state or a slightly hydrated state (hereinafter simply referred to as dry state) is coated with a super calender device having heated rolls or drums. A method of finishing with a calender device is known. In this method, the coated paper is pressed in a dry state through the roll nip of a calender, and the coated paper is given a glossy finish by contact with the roll surface. .

The coating agent used in this method is also disclosed in JP-A-56-1489.
As disclosed in No. 93, a coating agent having a composition similar to that of the coating agent used in the cast coating method and having a high pigment content (solid content) (approximately 80%) was used.

[Problem to be solved by the invention]

As mentioned above, the cast coating method has the advantage of providing excellent specular gloss, but since both methods use water etc. as a plasticizer, the cast drum surface may peel off until the coating layer dries. There is a problem in that productivity is kept extremely low.

In order to speed up this drying speed, methods include increasing the temperature of the heating drum surface, minimizing the amount of plasticizer such as water, or controlling the location and method of wetting with plasticizer such as water. Various efforts have been made. However, if the temperature of the cast drum surface is made higher than necessary, explosive water evaporation occurs when the wet coating layer and the drum surface come into contact, which disturbs the coating layer and makes it impossible to obtain sufficient specular gloss. become unable.

Also, if the amount of plasticizer such as water is reduced more than necessary, air will be trapped when the cast drum surface and wet coating layer are pressed together, and this part will not come into contact with the cast drum surface, resulting in uneven gloss. The current situation is that sufficient effects have not yet been obtained. Furthermore, in the coating agent used in the above-mentioned cast coating method, since a large amount of plate-like crystal kaolin or clay is used as a pigment that tends to produce gloss, moisture permeability during processing is significantly reduced. There was a problem in that the working speed (particularly the drying speed) was further reduced.On the other hand, when the amount of kaolin used was reduced, the gloss was also reduced.

On the other hand, in super calenders and gloss calenders, the coated paper usually leaves the nip between the pressurized rolls,
Because it is a type that can be wound up as is, due to the uneven thickness of the base paper, thicker parts are pressed harder and thinner parts are pressed weaker, so it has the disadvantage that unevenness and uneven gloss are likely to occur. Ta.

When these unevenness and uneven gloss become noticeable,
Not only is it impossible to obtain specular gloss, but the product value is significantly reduced.

In addition, in order to eliminate unevenness and uneven gloss, increasing the number of passes between pressurized rolls or increasing the pressing force will lead to a decrease in the bulk of the base paper, as well as a decrease in bending resistance. The problem was that the strength of the paper deteriorated.

Furthermore, coated paper that has been subjected to cast coat mojiku super calendering and gloss calendering using the above-mentioned coating agent uses a coating agent with an extremely high pigment ratio (approximately 80% solid content), and a large amount of pigment is used. Because the pigment is coated on the surface, the coating agent layer has poor bendability, which not only greatly limits the usage of coated paper, but also reduces the acceptability of ink in printing and the gloss of ink. But there was.

Therefore, an object of the present invention is to solve the problems of the above-mentioned conventional methods. The purpose of the present invention is to provide a composition for coating paper, and a method for producing coated paper using the same.

[Means to solve the problem]

That is, the present invention uses a pigment with an extremely fine particle size in a coating composition for paper coating, while significantly increasing the solid content ratio of the resin in the composition, thereby improving workability and
The first invention aims to improve gloss, suitability for various prints, bending resistance, etc., and the first invention is a paper coating composition containing a pigment and a binder resin as main components. Containing 70% by weight or more of a pigment in the range of .1 to 1.0 μm, and based on 100% by weight of the total pigment,
The purpose is to provide a paper coating composition in which the binder resin (solid content) is in the range of 25 to 80% by weight.
Claim 1>.

The present invention also provides a paper coating composition (claim 2) containing 70% by weight or more of calcium carbonate in the total pigment, and a paper coating composition (claim 2) containing 10% by weight or more of titanium oxide in the total pigment. A coating composition for paper coating comprising the composition (Claim 3) and 80% by weight or more of an aqueous resin having a glass transition temperature in the range of 20 to 100°C in the binder resin (solid content). 4).

Furthermore, the present invention provides a method for coating a base paper with the paper coating composition according to claims 1 to 4 and drying it, and then applying the coated surface of the coated paper to a heated mirror roll surface in a dry state. The purpose of the present invention is to provide a method for producing coated paper, which is characterized in that the coated paper is pressure-bonded with a press roll and then peeled off.

Hereinafter, the paper coating composition according to the present invention will be specifically explained.

First, the characteristic structure of the coating agent according to the present invention is that it contains 70% by weight or more of pigments having an average particle size in the range of 0.1 to 1.0 μm out of all the pigments used.

If there are many pigments with an average particle diameter of less than 0.1 μm, the hiding power and whiteness will be insufficient, and the average particle diameter will be less than 1.0 μm.
When the amount of pigment exceeds m, problems arise in terms of gloss, ink receptivity, ink drying properties, coating agent stability, etc.

Examples of pigments include calcium carbonate, titanium oxide, aluminum hydroxide, kaolin, clay, barium sulfate, and zinc oxide, which have been conventionally used in coating agents, and can be used alone or in combination.

However, among these, calcium carbonate accounts for 70% of all pigments.
Containing at least % by weight is effective in improving the affinity with ink, that is, the suitability for various types of printing. When the amount of calcium carbonate used decreases, it becomes difficult to obtain the above suitability.

In addition, calcium carbonate has a variety of particle shapes such as cubic, rice grain, spindle, and spherical shapes, but it does not reduce the gloss of coated paper and improves the above-mentioned printability, especially ink receptivity, and ink drying. Cubic calcium carbonate is particularly preferred in order to significantly improve properties.

Examples of cubic calcium carbonate sold in Tokyo include Hakuenka DD, CC, and TDD manufactured by Shiroishi Kogyo Co., Ltd.

In addition, the above effects can be expected by using calcium carbonate, but since there is a limit to how much whiteness can be improved with calcium carbonate alone, when a high degree of whiteness is required, it is desirable to use titanium oxide in combination, and all pigments It is preferable to use it in a range of 10 to 30% by weight. It is also preferable to use titanium oxide and aluminum hydroxide together in order to improve whiteness.

Although kaolin and clay are inferior to whiteness, they have smoothness and
It can be used in combination with calcium carbonate to improve gloss and hiding properties.

In addition, the following characteristic structure of the coating agent according to the present invention is as follows:
The mixing ratio of pigment and binder resin is solid content, the former is 1
00 parts by weight, the latter is 25 to 80 parts by weight, more preferably 50 to 70 parts by weight,
This configuration makes it possible to significantly improve workability, improve paper surface strength, that is, increase strength, and improve bending resistance.

In the coating agents used in the conventional cast coating method, super calender, and gloss calender method,
As mentioned above, some coating agents contain approximately 80% by weight of pigment, and the proportion of resin is extremely low.
This had the problems mentioned above.

In addition, in the coating agent according to the present invention, if the mixing ratio (solid content) of the binder resin to 1 part by weight of pigment is less than 25 parts by weight, gloss and smoothness may decrease, bending resistance, and coating film strength may decrease. The pick resistance is insufficient, and on the other hand, the
If it exceeds 0 parts by weight, removability will decrease due to adhesion during processing,
This causes problems in ink acceptability, etc. A more preferable amount of the binder resin used is in the range of 50 to 70 parts by weight, and higher gloss, workability, and various printability can be obtained.

Further, as the binder resin used in the paper coating composition of the present invention, various water-based resins exemplified below can be used alone or in combination, and the glass transition temperature (Tg
) is preferably in the range of 20 to 100°C.

If the Tg is low, there will be problems with the peelability from the roller and gloss, and if it is high, the strength of the coating film of the coating agent will be insufficient. If it is necessary to use a water-based resin with a Tg lower than the above range in order to further improve the bulk strength,
It can be used in combination in an amount of 20% by weight or less based on the total aqueous resin (solid content).

Specific examples of the aqueous resin that can be used in the paper coating composition of the present invention include casein, soybean protein, starches such as phosphate esterified starch and oxidized starch, cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose,
Conjugated diene polymer latex such as styrene-butadiene copolymer, styrene-butadiene-acrylic I copolymer, acrylic-butadiene copolymer, acrylic ester polymer, styrene-acrylic copolymer, styrene-acrylic-maleic copolymer, etc. Various acrylic polymer latexes such as polymers, vinyl polymer latexes such as ethylene vinyl acetate copolymer, and polyvinyl alcohol, acrylic, styrene-acrylic, styrene-maleic, maleic, etc. Examples include water-soluble or alkaline water-soluble resins.

Among these exemplified aqueous resins, those used in combination with acrylic latex, conjugated diene polymer latex such as styrene-butadiene copolymer, acrylic alkaline water-soluble resin, and starch such as casein are preferred.

In addition, in the coating agent of the present invention, in addition to the pigment and binder resin, various additives such as an antifoaming agent, a coloring agent,
A release agent, water or a solvent for adjusting fluidity, drying properties, etc. can be appropriately blended as necessary.

Various types of paper are coated using the coating agent according to the present invention as described above, but the base paper to which the coating agent is applied is rice paper, which is used for general printing coated paper and cast coated paper. 30~45 tsubo
General paper and paperboard with a degree of 0g/rn2N can be used. In addition, as a coating machine for coating the coating agent on the above base paper,
Rod coater used for manufacturing general coated paper,
Any of blade coater, air knife coater, curtain coater, bar coater, gravure coater, etc. can be used. In addition, the coating method can be applied to one or both sides of the base paper, and the coating amount is usually in the range of 10 to 40 g/m2 (dry weight) in one coat or multiple coats. will be constructed.

Furthermore, since the coating agent according to the present invention is effective when forming the outermost coating layer of paper, the coating agent according to the present invention is effective when forming the outermost coating layer of paper. It can also be used as an agent.

In addition, the method for producing coated paper using the coating agent according to the present invention includes applying the coating agent to a base paper, and then applying the coating to the coated paper in a dry state or a slightly hydrated state. The machined surface is pressed onto the surface of a heated mirror-finished roll using a press roll, and then peeled off.

After coating the base paper, it is necessary to dry it, and various heaters such as hot air heating and infrared heaters can be used as a means for drying.

The conditions for press-bonding the mirror roll surface with a press roll and imparting gloss are as follows: the surface temperature of the heated mirror roll is 100-200°C, and the pressure of the raster press is 8C1-200) cg/cs. , speed 3
It can be carried out at a speed of 0 to 350 m/min.

In addition, in the present invention, since the mirror roll surface and the press roll are pressed against the dry coating layer,
It is suitable for processing at extremely high speeds, usually 150 to 350 m and 7 minutes.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

In addition, parts and percentages shown in the examples are each expressed by weight.

〔Example〕

For 100 parts by weight of each pigment shown below,
Add 40 parts by weight of aqueous resin A (6 parts by weight of solid content) and disperse with a Coles disperser to produce a pigment dispersion of each pigment alone.

Incidentally, pigment dispersions having various average particle sizes are prepared depending on the degree of dispersion.

In the examples, the materials shown below are used.

(Pigment) The following A to C are used.

A: Calcium carbonate, Shiraika TDD (manufactured by Shiraishi Kogyo Co., Ltd.)
(Cubic shape) B: Titanium oxide, W-10 (manufactured by Ishiwa Sangyo Co., Ltd.) C; Clay, UW-90 (manufactured by EMC Co., Ltd.) (water-based resin) A-C below
use.

A: Alkaline aqueous solution of casein (solid content 15%) B: Alkaline aqueous solution of styrene-acrylic copolymer (Tg,
98°C, solid content 25%, molecular weight 17.000) C: Styrene-acrylic-malein copolymer latex, (Tg, 71°C, solid content 50%) Examples 1-8 Comparative Examples 1-5 Using the pigment dispersion obtained in the production example, mix according to Table 1, and add aqueous resins B and C to prepare each coating agent.Note that the solid content of the coating agent is 45%.
% with water, and finish by adding a small amount of fine particle polyethylene wax and tributyl phosphate antifoaming agent.

Shiba 4" UL Using the coating agents prepared in Examples 1 to 8 and Comparative Examples 1 to 5, the dry coating amount was 15 g/I on a paperboard base paper with a basis weight of 280 g/l112! Coat with a rod coater to give I2 and dry with a hot air dryer.

Next, a rubber-coated press roll and chrome plating,
Using a device consisting of a mirror-finished heated roller, the surface temperature of the heated mirror-finished roll was 138°C, and the press pressure was 150°C.
Pressing is performed under the following conditions: kg/cn, processing speed 150 m, 7 minutes.

Each obtained coated paper is evaluated on the following items.

The evaluation of each item is as follows.

Paper surface gloss: 60" gloss is measured using a gloss meter GM-26D manufactured by Murakami Color Research Institute.

Whiteness: Certified based on JIS8123.

Using surface strength Nido ink, dry and wet printing is evaluated.

Note that the evaluation is based on a 5-level scale indicating the degree of picking. (
The surface strength decreases as the value increases from 5 to 1.> Folding resistance: The coated paper after processing is folded in half, and evaluated based on the state of cracks in the coating layer at the folded portion.

Ink density (ink receptivity): Print offset black ink on coated paper after processing using an RI tester, and measure the density of the solid area using a densitometer.

Printing gloss (ink gloss): Print offset black ink on the coated paper after processing using an RI tester, and measure the 60" gloss using the gloss meter.

Ink drying properties: Print a high tack offset ink on coated paper after processing using an offset RI tester, and evaluate based on the time it takes for the ink to set (ink does not stick to hands). (Temperature: 25° C., Humidity: 60%) Peelability: Determined from the adhesion of the coating agent to the surface of the heated mirror roll.

The results of each of the above evaluations are added to Table 1.

〔effect〕

As shown in the Examples and the like above, it can be seen that the coating agent according to the present invention has high gloss and whiteness, and has excellent suitability for various types of printing.

Furthermore, according to the method for producing coated paper of the present invention, the above-mentioned problems in the conventional method for producing glossy paper are solved, and coated paper with a high degree of gloss can be produced extremely efficiently. It is something.

Claims (1)

[Scope of Claims] 1) A paper coating composition containing a pigment and a binder resin as main components, wherein the pigment has an average particle diameter of 0.1 to 1.0 μm.
Binder resin (solid content) containing 70% by weight or more of a pigment in the range of
is in the range of 25 to 80% by weight. 2) The paper coating composition according to claim 1, which contains 70% by weight or more of calcium carbonate in the total pigment. 3) The paper coating composition according to claim 1, which contains 10% by weight or more of titanium oxide in the total pigment. 4) The paper coating composition according to claim 1, wherein the binder resin (solid content) contains 80% by weight or more of an aqueous resin having a glass transition temperature in the range of 20 to 100°C. 5) After coating the base paper with the composition paste for paper coating according to claims 1 to 4 and drying, the coated surface of the coated paper is pressed onto the heated mirror roll surface with a press roll. , and then peeling off the coated paper.