JPH0259181B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the use of calcium carbonate as a coating pigment in gravure printing papers. The coated paper is coated with a composition containing essentially a binder and a pigment in the form of a mineral filler. A description of the composition of coating materials for paper and their use can be found, for example, in Pulp and Paper Chemistry and Technology, by James P. Casey.
Technology), Chapter 19, Volume (1961). In the field of printing technology, three different printing methods are known. namely letterpress printing, offset printing and gravure printing. Letterpress printing is known as the relief method. As in the case of a rubber stamp, the part of the image is raised from the rest of the letterpress plane. Coated paper containing kaolin or calcium carbonate is used for printing. Offset printing is known as lithography. That is, the image and the non-image area are in the same plane. The difference between the two is that the image area accepts and releases oil (i.e. printing ink) and is water repellent, while the non-image area is water retentive and oil repellent (i.e. ink). It is. The rotating printing cylinder first passes the wet cylinder and then the ink cylinder. However, this method does not print directly onto paper, but onto a rubber "blanket" stretched over a cylinder. An image is formed on the paper only when it is pressed by a cylinder against a rubber blanket. Kaolin and calcium carbonate are also used in this method as coating pigments for paper. In gravure printing, the printed portion of the cylinder is below the polished surface. The cylinder first passes through a bath filled with liquid ink and then passes through a doctor blade, which is a steel blade that removes excess ink. The printing ink is then retained in the cells until the printing cylinder picks the paper onto it, and the ink is then absorbed by the paper. For gravure printing, it is usually kaolin that is actually used as the coating pigment. Calcium carbonate has been described in documents related to coated papers for gravure printing (DE-OS3132841 and DE-OS2943653), but in reality it has rarely been used in gravure printing. This is because it has been the view of those skilled in the art that calcium carbonate does not have substantially good properties in gravure coated papers. Moreover, the literature has even discouraged those skilled in the art from using calcium carbonate as a coating pigment in gravure coated papers because it results in poor print quality. For illustrative purposes only, two citations from the literature on this point are mentioned here. 1 “ECC International”, an in-house
periodical, 1981, “How developments
incoating pigments affect paper
“printability”, Dr.Ken Beazley, Research
and Development, pages 1 and 2: In this publication, one of the "current conditions" is that ground calcium carbonate is inferior to kaolin.
It is described that it is a coating pigment for coated paper for gravure printing. On the second page,
It has again been pointed out that calcium carbonate results in poor printability. 2 Tappi Coatings Proceedings 1979:
“Possibilities and Limitations of High
"Solids Colors", page 39: point 4, summary, No. 3, print quality is inferior when using ground calcium carbonate than when using kaolin at the same or higher solids concentration. However, the use of kaolin as a coating pigment in gravure printing paper inevitably has the following disadvantages: in particular - poor rheological behavior; therefore, high solids concentration; - It is not possible to apply the coating in a vacuum and as a result it requires a large amount of energy to dry the coating. - It requires a large amount of binder. - It is uneconomical due to the high cost factor. - It is difficult to elongate the coating. Therefore, the object of the present invention is to avoid such disadvantages and to provide a material, especially for gravure printing papers, which can be coated at high solids concentrations, requires a small amount of binder and is energy efficient. Calcium carbonate for gravure printing paper is a coated pigment that can save a lot of energy and gives gravure printing paper higher gloss and opacity and better bleed-through and transmission properties than prior art coated pigments. The purpose of the present invention is to provide a method for using calcium carbonate as a pigment.After many years of research and experimentation, surprisingly, contrary to the conventional opinion of those skilled in the art, the present inventors have found that calcium carbonate can be used as a pigment in the present patent application. It has been discovered that the above objects can be achieved if the characteristics as defined in the scope are provided.The present invention is therefore characterized by a combination of three very specific features relating to calcium carbonate. That is, 50 to 70% of the particles have a particle size smaller than 1 micron, and less than 10% (particularly 1 micron) have a particle size smaller than 0.2 micron.
10%) and has a specific surface area of 10 m ² /g or less as measured by the BET method. Preferably, the particle size of the products of this invention is between 3 and 10 microns. It has been found that within the scope of the invention all alkaline earth metal carbonates and mixtures thereof, such as dolomite, can be used effectively. Precipitated calcium carbonate can also solve the above problems very well. Natural calcium carbonate, limestone, limestone and marble or mixtures thereof have proven to be of excellent quality. Preferred embodiments of the invention are set out in particular in the claims 2 to 5. All percentages listed are percentages by weight.
The particle size stated in microns corresponds to the diameter as a sphere. Other features and advantages of the invention will be better seen in the examples below. Example 1 Manufacture of experimental product Natural calcium carbonate was dry pre-milled by a known method. Fine pulverization is carried out using a wet method in a sand mill, and the pulverization conditions are such that particles smaller than 1 micron and
The percentage of particles smaller than 0.2 microns as well as the specific surface area were chosen so that they could be varied widely. The viscosity distribution was measured by sedimentation analysis and the specific surface area was
Measured by BET method. By the method described above, three products were produced with different proportions of particles smaller than 1 micron in order to demonstrate the effect of these percentages on paper coating formulations. These three products were tested in gravure coating formulations. Coating formulation binder (acrylic acid-containing copolymer)
4.5 parts by weight (absolutely dry) Dispersant (sodium salt of polycarboxylic acid)
0.6 parts by weight (absolutely dry) Calcium stearate 0.8 parts by weight Cationic polyethyleneimine 0.12 parts by weight Anionic acrylate thickener 0.3 parts by weight Coating pigment 100.0 parts by weight The solid concentration of the coating colorant was adjusted to 65%. Coating conditions Coating base paper Wood 36 to 37 g/m ² Coating weight Felt side 7 g/m ² (coating layer) Wire side 8 g/m ² Coating machine Combi blade coater (Combi
Blade Coater) Operating speed 1000m/min Drying Airfoil 250℃ Calendar Super calendar, operating speed
200m/min, linear pressure 250Kp/cm, roll temperature 70
°C Test conditions Glossiness Opacity according to Tappi T 480os−78 Laboratory gravure printing press according to DIN 53146 Pru¨fbau press for gravure test printing cylinder Engraving printing speed 5 m/s Ink Rotary gravure ink (black) ) Print quality was evaluated visually. The evaluation grade was determined. Glossiness of Printed Surface Glossiness was determined by the Tappi method at 75° C., and the incident angle and reflection angle were measured on the entire surface of a gravure print produced in the laboratory. Reverse-through and Transparency Using laboratory gravure prints. The regular reflectance (=R) of unprinted coated paper and the regular reflectance (=Rfr) of black printed on the entire surface were measured. The calculation is performed using the following formula. R-Rfr/R×100 Test printing press in actual printing method Wifag Rotomaster Printing cylinder Engraving cylinder rotation speed/hour 15000 Color sequence Yellow, magenta, blue, black All papers have static electricity Printed without using printing aids. The actual printing test was visually evaluated. The evaluation grade was determined.

[Table] Lower particles
Specific surface area 8.0m ² 〓g 9.1m ² 〓g 10.2m ² 〓g

[Table] Particle content of 1 micron or less is 62%
The VP60 product gave the best results in terms of gloss, surface gloss, opacity and bleed through + transparency, as well as in actual tests. This is followed by products VP70 and VP50, with a particle content of 70% and 53% below 1 micron, respectively. According to the present invention, the optimum content of particles smaller than 1 micron is between 50 and 50.
70%, preferably 60%. Example 2 Using the same method as described in Example 1, the content (%) of particles larger than 1 micron and the content (%) of particles smaller than 1 micron were the same, but
Two types of products were produced, one with high and one with a low percentage of particles smaller than 0.2 microns, and one with a high and a low specific surface area. This makes it possible to point out the differences between the calcium carbonate according to the invention and the calcium carbonate which does not solve the problem that the invention seeks to solve. These two products were tested as gravure coating formulations. Coating formulation binder (acrylic ester-containing copolymer)
3.5 parts by weight (absolutely dry) Dispersant (sodium salt of polycarboxylic acid)
0.6 parts by weight (absolutely dry) Calcium stearate 0.8 parts by weight Cationic polyethyleneimine 0.12 parts by weight Anionic acrylate thickener 0.3 parts by weight Coating pigment 100.0 parts by weight The solids content of the coating colorant was adjusted to 65%. Coating conditions Coating base paper Wood 37g/ ^m2 Coating weight Felt side 8g/ ^m2 (coating layer) Wire side g/ ^m2 Coating machine Combi blade coater Operating speed: 1000m/min Drying Airf oil 250℃ Calendaring Super calendar, operation speed
200m/min, linear pressure 250Kp/cm, roll temperature 70
C. The test was conducted under the test conditions described in Example 1, and the following characteristics were obtained.

【table】

[Table] The product VP5 of the present invention solves the problem that is the object of the present invention, but VP14 gave only unsatisfactory results. This result is surprising since VP5 is a coarser calcium carbonate particle than VP14. Example 3 By the method described in Example 1, a product was produced which is a preferred embodiment for particle counts below 1 micron, particle counts below 0.2 microns, and specific surface area values. This product was tested in comparison to kaolin, a product commonly used in gravure coating formulations, i.e., currently used in the industry.

[Table] Minute content
Coating conditions Base paper Wood 36g/m ² Coating weight Felt side 8g/m ² (coating layer) Wire side 9g/m ² Coating machine Combi blade coater Operating speed 1000m/min Drying Airf oil 250℃ Calendaring Super calendar, operation speed
200m/min, linear pressure 250Kp/cm, roll temperature 70
C. Under the test conditions described in Example 1, the following properties were obtained.

【table】

[Table] The VP60/6 calcium carbonate used in this example contains 60% of particles of 1 micron or less, 6% of particles of 0.2 micron or less, and has a specific surface area of
7.8 m ² /g but gives the same gloss and printed surface gloss as kaolin. In opacity and bleed-through, transparency, and laboratory gravure printing tests.
The VP60/6 product gave better results than kaolin. In actual printing tests, both were of the same grade. These results indicate that when gravure printing paper is manufactured using calcium carbonate equivalent to the product VP60/6, coated paper that is equivalent to or superior to gravure printing paper manufactured using kaolin can be obtained. I understand. Also, as can be seen from the coating formulation of Example 3, when calcium carbonate is used, about 20% less binder can be used to obtain a coated paper with similar or better properties. This ability to reduce the amount of binder used is an important factor that can reduce the cost of papermaking. Because calcium carbonate has good rheological properties, it is possible to produce high solids coating formulations (high solids coatings), which is not possible with kaolin. As a result, when drying the coated paper, energy is saved, ie, costs are reduced, and paper manufacturing costs are substantially reduced.

Claims (1)

[Claims] 1. Produced by crushing and/or classification, a) 50 to 70 particles smaller than 1 micron;
%, b) Contains 10% or less of particles smaller than 0.2 microns c) A method of using calcium carbonate, which has a specific surface area of 10 m ² /g or less by the BET method, as a coating pigment on coated paper for LWC-gravure printing. . 2. Calcium carbonate a) contains 55 to 65 particles smaller than 1 micron.
%, b) contains 10% or less of particles smaller than 0.2 microns, and c) has a specific surface area of 10 m ² /g or less by BET method. 3. Calcium carbonate is characterized by having a) 60% particles smaller than 1 micron, b) 10% or less particles smaller than 0.2 micron, and c) a specific surface area measured by BET method of 10 m ² /g or less. A method according to claim 1. 4 Calcium carbonate contains a) 60% particles smaller than 1 micron, b) 4 to 6% particles smaller than 0.2 micron.
c) The method according to claim 1, characterized in that the specific surface area measured by the BET method is 10 m ² /g or less. 5 Calcium carbonate contains a) 60% particles smaller than 1 micron, b) 4 to 6 particles smaller than 0.2 micron.
% c) The method according to claim 1, characterized in that the specific surface area measured by BET method is 8 m ² /g or less. 6. The method according to any one of claims 1 to 5 for use in coated paper for LWC gravure printing as a calcium carbonate suspension having a solids content of 65 to 85% by weight. .