JP3019879B2 - Coated paper excellent in gloss and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated paper excellent in gloss and gloss after printing and a method for producing the same.

[0002]

2. Description of the Related Art Generally, in order to increase the gloss of paper, the surface of the paper must be optically flat, that is, fine irregularities present on the surface of the paper that reflects light are 1/16 or less of the wavelength of incident light. Needs to be In general, methods for improving the gloss of paper include a method of smoothing the paper surface by calendering or supercalendering, and a method of coating a pigment such as kaolin or calcium carbonate on a paper surface together with a polymer material such as latex or starch. Then, there is a method of coating the coated paper with calendering or supercalendering after coating the fine voids formed by the pulp fiber with a pigment.

However, when calendering or supercalendering is performed without coating with a pigment, there is a limit to the improvement in gloss. In the case of applying a pigment, a coating amount of at least about 5 g / m ² is required to cover the voids existing on the paper surface and improve the gloss.

[0004] In addition to the above, as a method for improving paper gloss and print gloss, US Pat. No. 4,861,427 proposes a method of treating the paper surface with bacterial cellulose. This method includes a method of filtering a bacterial cellulose dispersion through a support and a method of applying bacterial cellulose by a size press, a short dwell coater, or a blade metering method.

[0005]

In the case of the above-mentioned method using bacterial cellulose, although the filtration method enables uniform coating of the paper surface with bacterial cellulose, it requires a large-scale facility, so that it requires an experiment. Although sample preparation at the laboratory stage is possible, application to actual production is questionable. Also, when applying by size press, short dwell coater, blade metering method,
Due to insufficient coverage of the paper surface with bacterial cellulose, the gloss of the paper has been slightly improved.

[0006] An object of the present invention is to provide a coated paper excellent in gloss even when using a low coating amount and a method for producing the same, on the premise that bacterial cellulose is used.

[0007]

SUMMARY OF THE INVENTION The present invention has been made based on the finding that when bacterial cellulose is applied in a curtain system, a uniform coating layer is obtained which is significantly different from other coating systems. The invention according to the coated paper according to the first aspect is characterized in that a coating solution containing bacterial cellulose is curtain-coated on a paper support, and the second aspect according to the second aspect. The invention according to the method for producing coated paper, the coating liquid containing bacterial cellulose is vertically dropped in a curtain shape on the upper surface of a running paper support,
The invention according to the method for producing coated paper according to claim 3, characterized in that the concentration of bacterial cellulose in the coating solution is 1% or less. According to a fourth aspect of the present invention, there is provided the method for producing a coated paper, wherein the coating liquid disperses bacterial cellulose using a dispersant.
The invention according to the method for producing a coated paper described in above, is characterized in that the dispersant is carboxymethyl cellulose.

[0008] The term "bacterial cellulose" as used in the present invention refers to cellulose fibers produced by microorganisms, and is typically sold under the trademark "Cellulon" by the US company Weuerhauser.
The bacterial cellulose is an ultra-fine cellulose fiber having a width of 0.1 μm, which is discharged by a microorganism, in particular, a kind of acetic acid bacterium. Further, since "Cellulon" is produced by rotary culture, its fibers are severely branched and entangled in a net shape (Japanese Patent Application Laid-Open No. 62-175190).

In the present invention, the bacterial cellulose is curtain-coated. When dispersing the bacterial cellulose in water, it is desirable to use a dispersant, particularly carboxymethyl cellulose (CMC), and the blending ratio of the bacterial cellulose is determined by weight. : CMC = approximately 4: 1. The concentration of bacterial cellulose in the coating solution of the present invention is determined depending on whether curtains can be formed or the product quality required for coated paper, and is usually 0.1 to 1.5%, particularly 0.1 to 1.5%. 1-1.0% is preferred. If the concentration exceeds 1.5%, the dispersibility of the bacterial cellulose is extremely reduced, so that the operability is deteriorated. At a concentration of 0.1% or less, the amount of coating is small.
It becomes difficult to sufficiently coat the paper surface with bacterial cellulose.

The paper support used in the present invention may be ordinary paper, synthetic paper, or coated paper. In the case of coated paper, this coated layer functions as an undercoat.

[0011]

[Function] Bacterial cellulose has a very fine fiber diameter of about 0.1 μm, a very large specific surface area, and those made by spinning culture have a high fiber content because they are entangled in a mesh. It is difficult to make a concentrated bacterial cellulose dispersion. Therefore, in many cases, the bacterial cellulose dispersion must have a low concentration. However, this dispersion can be applied to a paper support by various blades, various types of metalling, and a size press method which are general paper coating methods. When applied, the following problems occur. First, it is not possible to increase the amount of bacterial cellulose to be applied, which causes limitations. Second, in such a general coating method, when transferring the coating liquid to the paper surface, a physically large pressure is applied by a pressing or scraping operation. Will penetrate inside.

On the other hand, in the present invention, since the coating liquid containing bacterial cellulose is applied by the curtain coating method, the pressure at which the coating liquid is transferred to the paper surface is small, and the coating liquid is entangled in a mesh. The bacterial cellulose fibers cover the paper surface in a film form as it is, and the bacterial cellulose is not buried in voids existing on the paper surface.

[0013]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. In addition,
Parts and% represent parts by weight and% by weight, respectively.

Example 1 4 parts of bacterial cellulose (trade name "Cellulon", manufactured by Weahauser, USA) were mixed in 1 part of a CMC aqueous solution (dry solid), and dispersed well to reduce the bacterial cellulose concentration to 0.1%. It was adjusted to 96%. The viscosity of this bacterial cellulose solution was 2900 cps at 20 ° C., and the surface tension was 32 dyne / cm.

Next, the bacterial cellulose solution was supplied to the liquid supply head at a supply rate of 5.0 l / min using an extrusion coating apparatus having a slit having a width of 500 mm and a gap width of 0.3 mm, and a height of 20 cm. Was formed on a paper support having a width of 400 mm and a basis weight of 126 g / m ² continuously running at 400 m / min and dried to obtain a coated paper. The coated amount of the obtained coated paper was 0.30 g / m ² , and the coated amount of bacterial cellulose was 0.24 g / m ² .

Example 2 Using a bacterial cellulose solution having the same composition as in Example 1, a bacterial cellulose concentration of 0.64% was prepared. This solution had a viscosity of 700 cps at 20 ° C. and a surface tension of 34 dyne / cm. A coated paper was obtained under the same conditions as in Example 1 except that the coating speed was set to 600 m / min using this solution. The coated amount of the obtained coated paper was 0.13 g / m ² , and the coated amount of bacterial cellulose was 0.104 g / m ² .

[Comparative Example 1] 100 m / roll
The same bacterial cellulose solution as in Example 1 was applied on a paper support running continuously for 1 minute, and then a pressure of 2000 mmAq was applied from an air nozzle having a slit width of 0.35 mm.
The excess coating solution was scraped off so that the coating amount became 0.30 g / m ² by applying air, and dried to obtain a coated paper.

Comparative Example 2 The same bacterial cellulose solution as in Example 1 was transferred to an applicator roll by a roll transfer method, and the coated amount was 0.30 g / m ^{2 on a} paper support running continuously at 200 m / min. However, the transfer to a roll was poor and the coating was hardly applied to the paper support, and the coated amount of the obtained coated paper was 0.05 g / m ² as a result.

[Comparative Example 3] 200 m / roll
The same bacterial cellulose solution as in Example 1 was applied to a paper support running continuously for 1 minute, and then an excess coating solution was applied using a bar blade to an application amount of 0.30 g / m ^2. It was scraped off and dried to obtain a coated paper. The bar blade used was a plain one with no winding.

Comparative Example 4 Coating was performed in the same manner as in Comparative Example 3 except that a bar wire wound with a piano wire of 0.2 mm was used to obtain a coated paper. However, since the amount of application became considerably large, it was diluted to 0.30 g / m ² and re-coated to obtain a coated paper.

[Comparative Example 5] 200 m / roll
The same bacterial cellulose solution as in Example 1 was applied to paper running continuously for 1 minute, and then SK having a thickness of 0.5 mm was applied.
The excess coating solution was scraped off using a 4-made blade so that the coating amount was 0.30 g / m ² , and dried to obtain a coated paper.

With respect to the coated papers obtained in the above Examples and Comparative Examples, those subjected to a super calender treatment at a pressure of 150 kg / cm and those not yet treated were prepared and used as test samples. Table 1 shows the results of examining the following items for this sample. Gross: According to JIS P8142. Beck smoothness: according to JIS P8119. K & N ink acceptability; JTAPPI No. According to 46. Gurley air permeability: According to JIS P8117. Suitability for printing with a Prüfbau printing tester; Dainippon Ink CAPS GS black ink as printing ink, metal plate as printing plate, printing temperature 22 ° C, printing humidity adjusted to 56%, printing area: 4 × 20cm , Ink supply amount: 250 μl, printing pressure: 25 N / min, printing speed: 1.5
Printed at m / s.

[0023]

[Table 1]

According to Table 1, the coated papers of Examples 1 and 2, which were coated by the curtain coating method, exhibited high gloss and smoothness despite the small amount of coating by being subjected to a super calender treatment. The density and gloss after printing were also found to be very good. In addition, even before the super calendar processing, the print density and the print gloss show high values.

[0025]

The coated paper according to the present invention is produced by coating bacterial cellulose with a curtain method, so that excellent gloss and smoothness can be obtained, and gloss after printing is also excellent. In particular, even with a coating solution having a low concentration of 0.1 to 1.5% of bacterial cellulose, a coated paper with excellent gloss can be obtained, and when CMC is used as a dispersant, the aqueous solution of bacterial cellulose can be used. Is more favorable, so that a uniform coated surface can be obtained.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) D21H 19/00-27/42

Claims (5)

(57) [Claims] 1. A coated paper excellent in gloss obtained by curtain-coating a coating solution containing bacterial cellulose on a paper support. 2. An excellent gloss, characterized in that a coating solution containing bacterial cellulose is vertically dropped in a curtain shape onto the upper surface of a running paper support and coated on the surface of the paper support. Manufacturing method of coated paper. 3. The method for producing coated paper according to claim 2, wherein the concentration of bacterial cellulose in the coating liquid is 1% or less. 4. The method for producing coated paper according to claim 2, wherein the coating liquid contains bacterial cellulose dispersed using a dispersant. 5. The method for producing coated paper according to claim 4, wherein the dispersant is carboxymethyl cellulose.