NL8302549A - CALCIUM CARBONATE, PARTICULARLY FOR CLADING PAPER FOR DEEP PRESSURE. - Google Patents

Description

* »»; VO 4935

Calcium carbonate, especially for coating intaglio paper.

The invention relates to calcium carbonates, in particular natural calcium carbonates, to processes for their preparation and to their preferred use as coating pigments for gravure paper.

Coated papers are coated with a mass containing as essential ingredients a binder and a pigment in the form of a mineral filler. A description of the components of paper coating materials and their use can be found, for example, in James P. Casey's book "Pulp and Paper 10 Chemistry and Technology," Chapter XIX, Part III (1961).

In the printing technique, essentially three different methods are known, namely letterpress printing, offset printing and gravure printing.

Letterpress is a so-called letterpress printing method. As with a stamp, the surface to be printed forms an elevation on the printing form. The raised image plane is inked in by rolling. Coated paper containing kaolin or calcium carbonate is also used in this printing process.

Offset printing is a so-called flat printing method, which means that both the printing and the non-printing parts are in one plane. They differ from each other in that the printing parts receive and release fat, namely printing ink, but repel water, while the non-printing parts retain water, but repel fat (ink).

The rotary printing cylinder first passes the water-supplying roller and then the ink-supplying roller. However, he does not print directly on the paper, but on a rubber blanket stretched on a cylinder. The paper then takes over the printing image of the rubber blanket when it is pressed against the rubber cylinder by a cylinder. In this method, both kaolin and calcium carbonate are used as coating pigments.

In gravure printing, the pressing parts of the cylinder are located under the polished surface. The cylinder first passes through the liquid ink-filled container and then the doctor blade, a steel ruler, which removes the excess ink, while the ink intended for printing is held in pans until the paper is brought against the 35 pans and the ink thereby 8302549 is removed from the cups

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For gravure, the coating pigment used in practice is very predominantly exclusively kaolin. However, the literature (German Offenlegungsschrift 3,132,841 and 2,943,653) has also described calcium 5 carbonate in combination with gravure papers. Calcium carbonate, however, was by no means actually used in gravure printing, especially since it has hitherto been believed in the prior art that kaolin would have considerably better properties in coated gravure papers. .

In addition, the use of calcium carbonate as a coating pigment in gravure papers is even strongly discouraged in the literature to those skilled in the art, for the reason that it achieves poor printing results. Only by way of example can reference be made to the following two references: 1. "ECC International", Haus-Zeifschrift, 1981, "How developments in coating pigments affect paper printability" by Dr. Ken Beazley, Research and Development, pages 1 and 2:

This publication literally states that one of the established facts is that ground calcium carbonate is a worse coating pigment for gravure papers than kaolin.

On page 2 it is again pointed out that calcium carbonate has poor printability.

2. Tappi Coatings Proceedings 1979: "Possibilities and Limitations of High Solids Colors", p. 39: 25 Under point 4 "Summary" Nr. 3, it is stated that the printing quality is worse when using ground calcium carbonate than when using kaolin at an equal and higher solids concentration.

However, the use of kaolin as a coating pigment for gravure papers has a number of drawbacks, in particular - poor rheological behavior; therefore, it is not possible to coat with a high solids content, which leads to high energy costs in drying the coated layer; - the fact that a large amount of binder must be used; 35 - an uneconomic process, because costs are unfavorable.

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An object of the present invention is therefore to avoid these drawbacks and in particular to provide a coating pigment for intaglio papers which can be coated at a high concentration of solid with a low binder content, which can save energy, which leads to to obtain high gloss gravure paper with high opacity and which yields better throughput and translucency values than the prior art coating pigments.

Surprisingly, it has now been found after years of extensive research 10 that, contrary to the current belief in the art, calcium carbonates can still be used to achieve the previously described purpose, when using calcium carbonate, which is obtained by grinding and / or classification according to particle size is made suitable, and it contains a) 50-70% of particles smaller than 11 µm, b) less than 10% of particles smaller than 0.2 µm, and c) a BET surface area which has is less than 10 m ^ / g.

The invention is thus characterized by a very specific combination of three characteristics, in which 50 - 70% of the particles are smaller than 1 less than 10% (in particular between 1 and 10%) of the particles are smaller than 0.2 ^ tm, and the specific surface area according to BET is less than 10 m ^ / g. Preferably the largest diameter of the present products is 3-10 µm.

It has been found that in the present invention, all alkaline earth metal carbonates and mixtures thereof, such as dolomite, can be used successfully. Precipitated calcium carbonates are very well suited for the intended purpose. The natural calcium carbonates of limestone, chalk and marble and mixtures thereof have proved to be excellent.

Preferred embodiments of the invention are set forth in the subclaims 2-5 associated with this description. All percentage values are indicated in% by weight. The particle size, indicated in µm, always refers to a corresponding diameter in diameter.

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Further features and benefits. of the present invention may be seen from the following description of embodiments.

Example I

5 Preparation of the test products:

Natural calcium carbonate was dry-ground in a manner known per se. The grinding was carried out wet in a sand mill. The grinding conditions were chosen in such a way that the content of particles less than 1 µm and less than 0.2 µm as well as the specific surface could be varied widely. The grain size distribution was determined by sedimentation analysis and the determination of the specific surface area according to the BET method.

In the manner described above, three products were prepared with different levels of particles less than 100% in order to investigate the influence of these contents on the paper coating.

These products were tested in a gravure paper coating.

Coating recipe; binder (acrylic acid ester-containing copolymer) 4.5 parts (abs. dry) dispersant (Na salt of a polycarboxylic acid) 0.6 parts (abs. dry) calcium stearate 0.8 parts cationic polyethyleneimine 0, 12 parts anionic acrylate thickener 0.3 parts 25 coating pigment 100.0 parts

The solids content of the coating composition was adjusted to 65%.

Coating conditions: 2 rough paper to be coated: 36-37 g / m wood containing 1 8302549 2 30 amount of coating: top side = 7 g / m; sieve side = 8 g / m coating device: Combi-Blade-Coater; coating speed 1000 m / min

drying: Air Foils 250 ° C

satinize: super calender; throughput speed 200 m / min;

Line pressure 250 kg / cm; rolling temperature 70 ° C

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Research conditions:

Shine; according to Tappi at an incidence and reflection angle of 75 °

Opacity; according to DIN 53.146 5 Gravure printing in laboratory; printing device; experimental proofing device for gravure printing cylinder; engraved printing speed; 5 m / sec 10 ink; rotary gravure ink (black)

The print quality was visually assessed. A ranking was made.

Pressure gloss:

The gloss measurement was performed according to Tappi at an incidence and reflectance angle of 75 ° on the entire plane of the laboratory gravure printed paper.

Push through and shine through;

Papers printed by gravure in the laboratory were used.

The degree of remission of the coated unprinted paper (= R) and the degree of remission of the underside of the printed whole surface (= Rfr) were measured.

R - Rfx

The calculation was made according to the formula -. 100

R

Printing proofs in practice; 25 printing machine: Wifag Rotomaster printing cylinder; engraved cylinder revolutions / h; 15,000 ink order; yellow, magenta, cyan, black

All papers were printed without static printing aid.

The practical proofs were visually assessed.

A ranking was made.

Characteristics; VP 50 VP 60 VP 70 quantity less than 1 µm. 53% 62% 70% quantity less than 0.2 Jan 7% 9% 12% 35 specific surface area 8.0 m1 / g 9.1 m1 / g 10.2 m1 / g 8302549 -6-

Research results; VP 50 VP 60 yp 70 gloss 46% 50% 48% print gloss 72% 74% 72% opacity 90.8% 92.2% 91.4% 5 press through and see through 13.1 10.6 11.9 intaglio tests in the 2 practice (ranking) ^

The product VP 60 with an amount of 62% less than 11 µm gave the best results with respect to gloss, pressure gloss, opacity, printing and translucency and in the practical tests. Thereafter, the products VP 70 and VP 50 followed in an amount of 70 and 53%, respectively, less than 1 µm. The optimum amount of particles smaller than 11 µm according to the invention is between 50 and 70%, preferably at 60%.

Example II

In the manner described in Example 1, two products were prepared with an equal amount of particles smaller than 1 µm, but with a large and small amount of particles smaller than 0.2 µm, respectively, with a large and small specific surface area. in order to demonstrate the difference between the invention and a calcium carbonate unsuitable for achieving the object of the present invention.

These products were tested in a gravure paper coating.

25 Coating recipe; binder (acrylic acid-containing copolymer) 3.5 parts (abs. dry) dispersant (Na salt of a polycarboxylic acid) 0.6 parts (abs. dry) calcium stearate 0.8 parts 30 cationic polyethyleneimine 0, 12 parts by weight of anionic acrylate thickener 0.3 parts by weight of coating pigment 100.0 parts by weight

The solids content of the coating composition was adjusted to 65%.

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Coating conditions; rough panel to be coated: 37 g / m2 wood-containing 2 2 amount of covering: top = 8 g / m; sieve side = 9 g / m coating device: Combi-Blade-Coater; coating speed 5 1000 m / min

drying: Air Foils 250 ° C

satinize: super calender; throughput speed 200 m / min; line pressure 250 kg / cm; rolling temperature 70 ° C.

Under the test conditions described in Example I, the following results were obtained:

Features: VP 5 VP 14 quantity less than 1 yr. 59% 60% quantity less than 0.2 ^ tm 5% 14% specific surface area 8.9 m2 / g 12.1 m2 / g 15 Research results: 'gloss 55% 47% pressure gloss 82% 72% opacity 91.4% 90 , 8% press-through and see-through 11.8 12.6 20 intaglio tests in laboratory ^ 2 (ranking)

While the present product VP 5 achieved the stated goal, unsatisfactory results were obtained with VP 14, which is incidentally also surprising due to the fact that VP 5 is a coarser calcium carbonate than VP 14.

Example III

In the manner described in Example 1, a product was prepared which is a preferred embodiment with respect to the amounts less than 1 µm, less than 0.2 µm and the surface area.

The examination of this product was made in comparison with a commonly used kaolin in a paper coating for intaglio printing, ie with a prior art product.

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Coating recipe; VP 60/6 Kaolin binder (acrylic acid ester - 3.5 parts by weight 4.5 parts by weight of copolymer (abs. Dry) (abs. Dry) dispersant 0.6 parts by weight 0.3 parts by weight 5 (abs. dry) (abs. dry) calcium stearate 0.8 parts by weight 0.8 parts by weight of cationic polyethyleneimine 0.12 parts by weight 0.12 parts by weight of anionic acrylate 0.3 parts by weight of 0.3 parts by weight of thickener1 Coating pigment 100.0 parts by weight 100.0 parts by weight of the solids content of the coating composition 65% 56% was adjusted to

Coating conditions: 15 rough paper to be coated: 36 g / m2 wood containing amount of coating: top side = 8 g / m2; sieve side = 9 g / m2 t coating device: Combi-Blade-Coater; coating speed 1000 m / min

drying: Air Foils 250 ° C

Satinize: super calender; throughput speed 200 m / min; line pressure 250 kg / cm; rolling temperature 70 ° C.

Under the test conditions described in Example 1, the following results were obtained: coating with

Characteristics: kaolin / gravure 25 quantity less than 1 ^ un 60% 49% quantity less than 0.2 ^ im 6% 17% specific surface area 7.8 f / g 13.0 m2 / g

Research results: gloss 63% 64% 30 pressure gloss 85% 85% opacity 92.6% 90.0% push-through and see-through 10.7 13.5 intaglio tests in laboratory ^ 2 (ranking) 35 intaglio tests in practice 1 ^ (ranking) 8302549 -9-

The calcium carbonate according to the invention used in this example VP 60/6 with 60% particles smaller than 1 and 6% particles smaller than 0.2 µm and with a specific surface area of 7.8 m2 / g gave the same values for gloss and the printing gloss as the kaolin used as a comparison material. The VP 60/6 gave better results in terms of opacity as well as through-printing and translucency and in the laboratory proofs than the kaolin used as reference material. Both products were judged equally in the printing tests.

These results prove that a calcium carbonate such as the product VP 60/6 can readily produce a gravure paper coating, thereby obtaining a coated paper equivalent and in part better than the conventional gravure papers obtained by use to make from kaolin.

From the coating recipes according to example III it appears that when using calcium carbonate about 20% less binder can be used to obtain the same and partly better properties. The reduction of the binder content represents significant cost savings for the manufacturer.

The good rheological behavior of the present calcium carbonate makes it possible to prepare coating compositions with a higher solid content, which is not possible with kaolin. As a result, less energy is required to dry the applied coating, which also means considerable cost savings for the paper manufacturer.

8 3 0 2 5 4 ö

Claims (9)

Calcium carbonate, in particular natural calcium carbonate, characterized in that the calcium carbonate is made suitable by fine grinding and / or classification according to particle size, and a) contains 50 - 70% of particles smaller than 1 µm, 5 b ) contains less than 10% of particles smaller than 0.2 11011, and c) has a BET specific surface area of less than 10 m2 / g. Calcium carbonate according to claim 1, characterized in that the calcium carbonate contains a) 55-65% of particles smaller than 1 µm, b) less than 10% of particles smaller than 0.2 µm, and c ) has a specific surface area of less than 10 m2 / g. 3. Calcium carbonate according to claim 1 or 2, characterized in that the calcium carbonate contains 15 a) 60% of particles smaller than 11 µm, b) less than 10% of particles smaller than 0.2 µm, and c) has a specific surface area of less than 10 m2 / g. Calcium carbonate according to claims 1-3, characterized in that the calcium carbonate contains 20 a) 60% of particles smaller than 1 µm, b) 4-6% by weight of particles smaller than 0.2 µm and c) has a specific surface area of less than 10 m2 / g. Calcium carbonate according to claims 1-4, characterized in that the calcium carbonate contains 25 a) 60% of particles smaller than 1 µm, b) 4-6% of particles smaller than 0.2 µm, and c) has a specific surface area of less than 8 m2 / g. 6. Process for preparing calcium carbonate according to claims 1-5, characterized in that the calcium carbonate is first dry milled in a known manner and then rendered suitable by wind sieving by particle size classification. 8302549 ST .. t -11- Process for preparing calcium carbonate according to claims 1-5, characterized in that the calcium carbonate is prepared in a known manner by wet grinding. Use of calcium carbonate according to claims 1-7, 5 as a coating pigment for LWC gravure papers. Use of calcium carbonate according to claims 1-8, in suspensions with a solids content of 65 - 85% by weight for LWC gravure papers (coatings with a high solids content). % - 8302549