JP2005179784A - Paper coating liquid and coated paper using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve water-holding properties of a coating liquid so as to be effective for use in a size press (a rod metering size press) of a paper machine. <P>SOLUTION: The coating liquid consists essentially of a pigment and an adhesive. In the coating liquid, starch carbamate is contained in an amount of 0.5-10 wt.% based on 100 pts.wt. of the pigment. In this case, 30-70 wt.% of the pigment is calcium carbonate, heavy and the balance is clay. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a paper coating solution having good water retention and a coated paper having a coating layer provided on the surface thereof.

  Coated paper (coated paper) is produced by applying a coating liquid (coating liquid) to a base paper (paper substrate) and drying. This coating liquid (paper coating liquid) is usually a slurry in which a white pigment such as clay or heavy calcium carbonate and an adhesive such as latex or starch are dispersed in water.

  By the way, in coating of the coating liquid, during the process from the coating process to the drying process, moisture in the coating liquid is absorbed by the base paper, and clay, calcium carbonate (heavy calcium carbonate, light calcium carbonate), latex, Components such as starch penetrate into the base paper, resulting in problems such as poor smoothness and layer thickness mismatch. As a result, printability deteriorates. It is known to be caused by indefiniteness of

  In order to adjust the coating properties such as viscosity, fluidity, water retention, etc., a small amount of polymer material such as CMC or sodium alginate is usually added to the coating liquid, but it prevents the decrease in water retention. Therefore, if the amount of these high molecular substances is increased, the viscosity of the coating solution is remarkably increased and the fluidity is deteriorated. As a result, high-speed coating becomes impossible and productivity is lowered. It is inevitable that surface properties such as picking resistance, printability, and smoothness will deteriorate.

  In addition, when applying a conventional coating liquid with a paper machine size press (rod metering size press), the high shear viscosity of the coating liquid is low, so the coating amount cannot be increased by increasing the papermaking speed. The speed of the paper machine is limited. Therefore, in the rod metering size press, in order to increase the coating amount in the process of maintaining or increasing the paper making speed, it is necessary to increase the high shear viscosity of the coating liquid (if the high shear viscosity is low, the coating amount is increased). Absent).

  However, in order to increase the high shear viscosity, it is known to increase the blending of clay among pigments (clay, calcium carbonate, etc.), but there is a problem that the whiteness decreases.

In order to solve such problems, it has been proposed to use urea-phosphate esterified starch as an adhesive (see Patent Document 1). According to this, the water retention effect of the coating liquid is maintained, but since it contains a phosphate group, the pH of the starch slurry is in the acidic region near 5.5 to 6, and with the pigment slurry and other adhesives Due to poor compatibility, it was found that agglomeration (shock) was caused when blended with the pigment slurry. Further, in order to adjust the pH of the coating solution immediately before coating to about 9 to 9.5, it is necessary to increase the amount of alkali chemicals such as caustic soda and ammonia. However, when the amount of the alkali chemical added is increased, the odor of the coating solution is strong, and the problem of deteriorating the working environment occurs.
JP-A-11-71403

  The purpose of the present invention is to improve the water retention of the coating liquid and increase the high shear viscosity, thereby stabilizing the high-speed coating property particularly in a paper machine size press (rod metalling size press) and improving the coating surface. It is providing the paper coating liquid for improving a surface feeling, and the coated paper manufactured using this. Another object of the present invention is to provide a paper coating solution that improves the working environment by reducing the amount of alkaline chemicals (ammonia, caustic soda, etc.) used when adjusting the coating solution, and a coated paper using the same. It is in.

  As a result of many studies and studies to achieve the above-mentioned problems, the present inventors have used carbamic acid starch in a coating liquid for producing coated paper, in particular, coated paper for printing. The water retention is further improved, the high shear viscosity is increased, and the stability of the high-speed coating property is maintained especially in the paper machine size press (rod metalling size press). I found it to be improved.

The present invention has been made based on this. That is, according to the present invention, the following (1) to (3) are provided.
(1) A paper coating liquid characterized by containing a carbamate starch in a ratio of 0.5 to 10 parts by weight per 100 parts by weight of pigment in a coating liquid mainly composed of a pigment and an adhesive.
(2) The paper coating solution according to claim 1, wherein 30 to 70% by weight of the pigment is heavy calcium carbonate and the remaining amount is clay.
(3) The coating layer of the coating liquid according to claim 1 or 2 is provided on at least one surface of the base paper so as to have a solid content adhesion amount of 5 to 20 g / m ² by a rod metalling size press. Characterized coated paper.

  Since the coating liquid of the present invention contains carbamic acid starch, the water retention of the coating liquid is improved, there is little variation in viscosity due to the buffering action of urea, and the carbamic acid starch has no ions. Therefore, a coating solution having a high concentration can be prepared, the supply efficiency of the coating solution to the base paper is improved, and there are effects such as improvement of the coating surface feeling and improvement of the glossiness of appearance.

In addition, since the amount of -OCONH ₂ group (carbamic acid group) increases due to the presence of carbamic acid starch in the coating liquid, the amount of alkaline chemicals used for pH adjustment can be reduced and the physical properties of the coating liquid can be reduced. There is also a stabilizing effect.

  Furthermore, since the coating liquid containing the starch carbamate has a high shear viscosity, there is an effect that a stable operation at the time of high speed coating of the rod metalling size press is performed.

  Furthermore, since the carbamic acid starch itself has a low high shear viscosity, there is an effect that the coating amount can be easily adjusted with a rod metering size press.

  The coating liquid of the present invention is mainly characterized in that it contains a pigment and an adhesive as main components and contains carbamic acid starch.

  The carbamic acid starch can be obtained by mixing urea and an inorganic acid (sulfuric acid) into the starch, removing moisture, and then heating and reacting at a high temperature (temperature of 120 ° or higher).

  As the starch substrate that can be used in the present invention, all known starches are used, for example, corn starch, potato starch, sweet potato starch, tapioca starch, wheat starch, sago starch, starch such as rice starch, amylose, amylopectin, etc. Containing polysaccharides such as plant mucilage such as arabic gum and locust bean gum. Depending on the purpose, starch derivatives such as acid-treated starch, oxygen-treated starch, oxidized starch, etherified starch, and esterified starch can also be used.

  The carbamic acid starch is white powder in appearance, moisture is 11.0 ± 2.0%, pH is 7.0-8.0, ionicity is nonionic, paste viscosity (95 ° C, heat gelatinized for 20 minutes) Thereafter, it is preferably cooled to 50 ° C. and measured with a B-type viscometer (60 rpm)) having a physical property value of 70 ± 20 mPa · s (18%).

  Such a carbamic acid starch is (i) easily dispersed in water with a white viscosity, (ii) heat gelatinization is easier than other types of starch, and produces a slightly yellow transparent to translucent paste liquid. In addition to batch-type gelatinization, gelatinization with continuous gelatinizers is also possible. (Iii) Good viscosity stability of the prepared paste liquid. (Iv) Nonionic properties add to ionic pigments. However, it is difficult to cause agglomeration (color shock) of the coating liquid, and (v) because there is little color shock when added to the coating liquid, high water retention is obtained while keeping the apparent viscosity (B-type viscosity) low. (Vi) it has a low apparent viscosity and thus a high solid content is easy, and (vii) itself has a low high shear viscosity and thus contributes to stable operation during high-speed coating.

  As the coating liquid pigment, kaolin, talc, clay, calcium carbonate (including heavy calcium carbonate and light calcium carbonate), inorganic pigments such as titanium white, titanium dioxide, and silica, and organic pigments such as plastic pigments are used. However, it is preferable that 30 to 70% by weight of heavy calcium carbonate, and the other is composed of clay.

  When carbamic acid starch is added to a coating solution in which heavy calcium carbonate is used as a pigment, the coating solution is particularly excellent in fluidity. Further, when heavy calcium carbonate is used as a pigment, when clay is used in combination with this, an effect that the gloss of white paper is maintained is brought about. In particular, in the coating liquid of the present invention, when the pigment component is composed of 30 to 70 parts by weight of heavy calcium carbonate and the remaining clay, the above effect is more remarkable.

  Although it does not specifically limit as an adhesive agent used by this invention, It is desirable that it is water-soluble.

  As water-soluble adhesives, oxidized starch, positive starch, esterified starch, starches such as dextrin, synthetic resin adhesives such as polyvinyl alcohol, proteins such as casein, soy protein, and synthetic protein are used. In addition, for example, conjugated diene copolymer latex such as styrene-butadiene copolymer, acrylic copolymer latex such as acrylate polymer or copolymer, vinyl such as ethylene-vinyl acetate polymer, etc. So-called ordinary polymer latex, or an alkali-soluble, alkali-swellable or alkali-insoluble polymer latex in which these various polymer latexes are modified with a functional group-containing monomer such as a carboxyl group. Various adhesives used in the paper industry can be appropriately selected and used.

  The blending ratio of the pigment and the adhesive is suitably 5 to 20 parts by weight, preferably 8 to 15 parts by weight with respect to 100 parts by weight of the pigment. Moreover, the compounding quantity of carbamic acid starch is 0.5-10 weight part with respect to 100 weight part of pigments, Preferably it is 3-8 weight%. If the blending amount of the carbamic acid starch is less than 0.5 parts by weight, the water retention of the coating solution is insufficient, and the viscosity of the coating solution exceeding 10% by weight becomes too high, causing gelation.

  In addition to the pigments, adhesives, and carbamic acid starch, the coating liquid may include dispersants, thickeners, water retention agents, antifoaming agents, water resistance agents, lubricant dyes, pH adjusters, etc. These auxiliary agents are appropriately blended and adjusted to a solid content concentration of about 50 to 70%.

  The coating solution thus prepared has high water retention and forms a good coating surface.

In the coated paper of the present invention, the above coating solution is provided on at least one surface of the base paper so that the solid content is 5 to 20 g / m ² . As the base paper, a paper base or paperboard base paper having a basis weight of about 40 to 130 g / m ² used for general coated paper is used as appropriate. There is no particular limitation on the paper making method of the base paper, and the paper making is carried out using an acid paper making machine, a neutral paper making method, or an alkaline paper making method using a long web machine, a round net machine, a paperboard machine using both of them, a Yankee dryer machine, etc. Of course, it may be any of the base papers, and of course, a medium base paper containing mechanical pulp and a base paper containing recovered waste paper pulp can also be used.

  The coating apparatus is not particularly limited. For example, a two roll size press, a blade metalling size press, a rod metalling size press, a gate roll coater, a blade rod coater bar coater, a rod blade coater, an air knife coater, etc. Although it can be used as appropriate, a rod metering size press is preferably used.

  In the coated paper of the present invention, the above-mentioned coating solution is applied onto a base paper and dried as before, and then the surface is smoothed as necessary to finish the product. In this case, a calendar is usually used for smoothing, but a soft calendar having a large smoothing effect without increasing the pressure condition is preferably used. The coating layer can be formed not only on one side of the base paper but also on both sides, but by forming the coating layer on both sides, a coated paper with no difference between the front and the back can be obtained even if the base paper has a difference between the front and the back. Can be obtained.

  The present invention will be described more specifically with reference to the following examples. However, the examples do not limit the scope of the present invention. The part here is% by weight. In addition, the physical property of the coating liquid in each case and the coated paper was calculated | required according to the following method.

(1) Water retention of coating liquid Using AA-GWR water retention meter (manufactured by SMT), the coating liquid whose temperature was adjusted to 23 ° C. was measured at a pressure of 2.0 kg / cm ² and a contact time of 30 seconds. . A smaller value indicates better water retention.
(2) B-type viscosity of coating liquid The B-type viscosity of 60 rpm was measured at a temperature of the coating liquid of 30 ° C.
(3) High shear viscosity (HSV) of coating liquid
Using a Hercules high shear viscometer (manufactured by Kumagai Riki Kogyo Co., Ltd.), the coating solution adjusted to 25 ° C. was measured under the conditions of F Bob and 4400 rpm.
(4) Amount of ammonia used in coating solution The amount of ammonia used to adjust the pH to 9.5 was measured.
(5) Solid content concentration of coating liquid According to 105 ° C. absolutely dry method.
(6) PH of coating solution
It measured with the glass electrode type PH meter.
(7) Glossiness of coated paper Measured according to JIS P8142.
(8) Whiteness of coated paper Measured according to JIS P8123.
(9) Smoothness of coated paper Measured according to JIS P8119.
(10) Picking resistance of coated paper

  Printing was performed on the surface of the coated paper using an RI printing machine (manufactured by Meisei Seisakusho), and the occurrence of picking was observed.

(Example 1)
Using 50 parts by weight of heavy calcium carbonate, 50 parts by weight of clay, 10 parts of styrene-butadiene latex and 6 parts of starch of carbamate (manufactured by Nippon Food Chemical Co., Ltd., Star Coat # 27), these are mixed, diluted and solid A coating solution having a partial concentration of 65% was prepared. The physical properties of this product are shown in Table 1. Next, this coating solution is applied and dried by a rod metering size press of a paper machine so that the solid content is 8 g / m ² on one surface of a high-quality paper (basis weight 48 g / m ² ). Made paper. The physical properties of this coated paper are shown in Table 1.

(Example 2)
In Example 1, a coating solution was prepared in the same manner as in Example 1 except that the pigment was changed to 30 parts of heavy calcium carbonate and 70 parts of clay, and further coated paper was produced. Table 1 shows the physical properties of the coating liquid and coated paper.

(Comparative Example 1)
In Example 1, a coating solution was prepared in the same manner as in Example 1 except that urea phosphate starch was used instead of carbamic acid starch, and coated paper was further produced. Table 1 shows the physical properties of the coating liquid and coated paper.

(Comparative Example 2)
In Example 1, a coating solution was prepared in the same manner as in Example 1 except that hydroxyethylated starch was used instead of carbamic acid starch, and coated paper was further produced. Table 1 shows the physical properties of the coating liquid and coated paper.

As is apparent from Table 1, it can be seen that the paper coating solution of the present invention is superior in water retention compared to the comparative example. Moreover, it turns out that the coated paper manufactured using the paper coating liquid of this invention balances glossiness, whiteness, smoothness, and printability at a high level compared with the thing of a comparative example.

Claims (3)

  A paper coating solution comprising a coating solution containing a pigment and an adhesive as main components, wherein the carbamate starch is contained at a ratio of 0.5 to 10 parts by weight per 100 parts by weight of the pigment.   The paper coating solution according to claim 1, wherein 30 to 70% by weight of the pigment is heavy calcium carbonate and the remaining amount is clay. The coating layer of the coating liquid according to claim 1 or 2 is provided on at least one surface of the base paper so as to have a solid content adhesion amount of 5 to 20 g / m ² by a rod metalling size press. Coated paper.