DE3316949A1 - CALCIUM CARBONATE, ESPECIALLY NATURAL CALCIUM CARBONATE - Google Patents

Description

description

The invention relates to calcium carbonates, in particular natural calcium carbonates, to processes for their production and preferably to them Use as coating pigments in gravure papers.

Coated papers are coated with a composition that is essentially a binder and a pigment in the form of a contains mineral filler. A description of the constituents of paper coating materials and their uses is z. B. in the book by James P. Casey "Pulp and Paper Chemistry and Technology", Chapter XIX, Vol. III (1961) given.

There are essentially three different processes in printing technology known, namely letterpress, offset printing and gravure printing.

Letterpress is a so-called letterpress process. As with Stamp the area to be printed is raised in the printing form. The raised image surface is colored by means of a roller. With this one The printing process also uses coated paper that contains kaolin or calcium carbonate.

Offset printing is a so-called flat printing process, i. H. the printing and non-printing parts lie in one plane. They differ in that the printing parts are fat

Accept and release (i.e. printing ink), but repel water, while the non-printing parts hold water but grease Reject (color). The rotating printing cylinder first passes the water-bearing and then the ink-bearing roller. However, it does not print directly on the paper, but on a cylinder using a cylinder stretched rubber blanket. Only from this does the paper take the print image, pressed against the rubber cylinder by means of a cylinder away. In this process, both kaolin and calcium carbonate are used as coating pigments.

In gravure printing, the printing parts of the cylinder lie under the polished surface. The cylinder passes the with first a tub filled with liquid ink, then the squeegee, a steel ruler that removes excess ink while it is intended for printing Color is held in pots until this is rolled over by the impression roller leading the paper and the color is sucked out in the process.

In practice, the only coating pigment used for gravure printing is predominantly kaolin. True, is in the literature (DE-OS 31 32 841 and DE-OS 29 43 653) already described calcium carbonate in connection with gravure papers. However, it was Calcium carbonate is actually mostly not used in gravure printing, especially because the experts have so far been of the opinion believed that kaolin had much better properties in painted Would show rotogravure papers.

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In addition, it becomes even insistent in the literature to the person skilled in the art Advised against using calcium carborate as a coating pigment in gravure papers on the grounds that poor print results would be achieved. For example only, reference is made to two relevant literature references below:

1. "ECC International", House Journal, 1981, "How developments in coating pigments affect paper printability "by Dr. Ken Beazley, Research and Development, pages 1 and 2:

In this publication it is stated verbatim that one of the "facts of life" is that something is ground Calcium carbonate is a worse coating pigment for gravure papers than kaolin. On page 2 it is pointed out again that calcium carbonate gives poor printability.

2. Tappi Coatings Proceedings 19 79: "Possibilities and Limitations of High Solids Colors ", page 39:

Under point 4 "Summary" No. 3 it is stated that the pressure quality when using ground Calcium carbonate is worse than when using kaolin with the same and higher solids concentration .

The use of kaolin as a coating pigment in gravure papers, however, is associated with a number of disadvantages, in particular

- Bad theological behavior; because of that it is not possible to paint with high solids content, which is high Conditional energy costs for the drying process.

- High binder requirement.

- Inefficient as it is inexpensive.

It is therefore an object of the present invention to provide this To avoid disadvantages and, in particular, to provide a coating pigment for gravure papers that works at high solids concentrations can be coated with a low proportion of binder, with which energy can be saved, compared to a rotogravure paper with high gloss and high opacity leads and better values for strike through and show through than the coating pigments according to the state of the art.

Surprisingly, after many years and extensive Series tests found that, contrary to the opinion of experts, calcium carbonates were used to solve the above problem if they have the features specified in claim 1.

The invention is thus characterized by a very specific combination of three features, with 50-70% of the particles being smaller than 1 μm, less than 10% (in particular between 1 and 10%) of particles smaller than 0.2 μm being present and the BET specific surface area is less than 10 m ² / g. The upper section of the products according to the invention is preferably 3 to 10 μm.

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It has been found that within the scope of the invention, all alkaline earth metal carbonates and their mixtures such as dolomite can be used successfully. Precipitated calcium carbonates solve the problem very good. The natural calcium carbonates limestone, chalk and marble or their mixtures have proven to be excellent .

Preferred embodiments of the invention are in the claims 2 to 5 marked. All percentages are% by weight. The particle size information in μπι relates in each case to a corresponding spherical diameter.

Further features and advantages of the invention emerge from the following description of exemplary embodiments:

Example 1: Manufacture of the test products:

Natural calcium carbonate was made in a manner known per se
pre-ground dry. The fine grinding was carried out wet in a
Sand mill. The grinding conditions were chosen so that
the proportions of particles smaller than 1 μm and smaller than 0.2 μm and the specific surface could be varied greatly.

The particle size distribution was measured by means of sedimentation analysis, the measurement of the specific surface after the

• a a ·

BET method.

In the manner described above, 3 products with different Proportions of particles smaller than 1 μπι made to to show the influence of these proportions in the paper coating color.

These products were tested in a paper coating color for gravure printing.

Coating color formulation: (atro = absolutely dry)

Binder (acrylic acid ester-containing copolymer 4.5 GT (dry)

Dispersing agent (Na salt of a polycarboxylic acid) 0.6 GT (atro) Calcium stearate 0.8 parts by weight

Cationic.Polyethyleneimine 0.12GT

Anionic acrylate thickener 0.3 parts by weight

Coating pigment 100.0 pbw

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

Cancellation conditions:

Coated base paper: 36-37 g / m ² wood-containing

Coating application: OS = 7 g / m ² SS = 8 g / m ²

Coating unit: Combi-Blade-Coater; 1000 m / min.

Working speed
Drying: Air Foils 250 ⁰ C

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Calendering: supercalender; 200 m / min. Working speed, 250 Kp / cm line pressure and 70 ⁰ C roller temperature

OS = top

SS = sieve side

Test conditions :

Shine: according to Tappi in a 75 angle of incidence and radiation

Opacity: according to DIN 53 146

Laboratory proof-gravure ι Printing device: Impression cylinder: Printing speed, color: Prüfbau Gravure-proof printing device engraved

5 m / s

Rotogravure ink (black)

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

Print gloss:

The gloss measurement is carried out according to Tappi at a 75 ° angle of incidence and radiation on the full surface of the laboratory proof gravure.

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Strike through and show through;

The laboratory proofs-rotogravure prints are used.

The degree of remission of the coated, unprinted paper is measured (= R) and the reflectance of the back of the printed full area (= Rfr).

The calculation is based on the formula

100

Practice printing tests: printing machine printing cylinder cylinder revolutions / h color sequence

Wifag Rotomaster

engraved

15 ¹ OOO

Yellow, magenta, cyan, black

All papers were printed without a static printing aid.

The practical printing tests were evaluated visually. A ranking was established.

Characteristics; Proportion less than 1 μπι Proportion less than 0.2 μΐη specific surface

VP 50
53%

7%

8.0 m ² / g

VP 60

VP 70

62% 70% 9% 12% 9.1 m ² / g 10.2 m

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- · ·
_% · · · * ·
.. '· - *' Test results: • VVV
. · * ■ *
T2 ** - 50 % VP 60 % 3316949 shine VP % 50 % VP 70 Print gloss 46 8th % 74 2% 48% opacity 72 92, 72% Penetration + penetration 90, 1 6th 91.4% seem 10, Practice pressure tests deep 13, 11.9 pressure (order of precedence) 1 2 3

The product VP 60 with a proportion of 62% smaller than 1 µm gives the best results for gloss, print gloss, opacity, strike through + show through and in practical tests. This is followed by the products VP 70 and VP 50 with a proportion of 70 respectively. 53% smaller than 1 μπι. The optimal proportion of particles less than 1 μπι is according to the invention between 50 and 70%, preferably at 60%.

Example 2:

According to a manner described in Example 1, 2 products with the same proportion of particles were smaller than 1 μπι, but high and a low proportion of particles smaller than 0.2 μm, respectively. high and low specific surface area made to make the difference to show between the invention and a calcium carbonate that is unable to achieve the object of the invention.

These products were tested in a paper coating color for gravure printing.

Coating color formulation;

Binder (copolymer containing acrylic acid ester) 3.5. GT (atro) Dispersing agent (Na salt of a polycarboxylic acid) 0.6 GT (atro) Calcium stearate 0.8 part by weight of cationic polyethyleneimine 0.12 part by weight of anionic acrylate thickener o ', 3 part by weight Coating pigment 100.0 pbw

The solids content of the coating slip was

set to 65%.

Cancellation conditions:

Base paper: 37 g / m ² wood-containing

Coating application: OS = 8 g / m ² SS = 9 g / m ²

Coating unit: Combi-Blade-Coater; 1000 m / min.

Working speed

Drying: Air Foils 250 ⁰ C

Calendering: supercalender; 200 m / min. Working

speed, 250 Kp / cm line pressure and 70 C roller temperature

According to the test conditions described in Example 1, the following are obtained

Features: VP 5 VP 14

Share less than 1 μm 59% 60%

Share less than 0.2 μm 5% 14%

Specific surface area 8.9 m ² / g 12.1 m ² / g

Test results:

55 ^% 47 8th 82 % 72 6th 91 , 4% 90, 11th ,8th 12, 1 2

Print gloss

opacity

Strike through + shine through

Laboratory proof of gravure (ranking) 1

While the product according to the invention VP 5 the task set solves, unsatisfactory results are obtained with VP 14, which, by the way, is also surprising because VP 5 is a coarser one Calcium carbonate is available as VP 14.

Example 3:

According to the manner described in Example 1, a product produced, which.eine preferred embodiment with respect to the values for the proportions smaller than 1 μm, smaller than 0.2 μm and has the specific surface area.

This product was tested in comparison with a kaolin usually used in practice in a paper coating slip for rotogravure printing, i.e. a state-of-the-art product

of the technique.

Coating color formulation:

VP 60/6

kaolin

Binder (copolymer containing acrylic acid ester), dispersant Calcium stearate Cationic polyethyleneimine Anionic acrylate thickener Coating pigment The solids content of the coating color was adjusted to

3.5 GT (atro) 4.5 GT (atro)

0.6 GT (dry weight) 0.3 GT (dry weight)

0.8 wt. 0.8 wt

0.12 wt. 0.12 wt

0.3 GT 0.3 GT

100.0 wt. 100.0 wt

65

56

String conditions: coating base: Coating application: coating unit:

Drying:
Satinage:

3 6 g / m ² wood containing
OS = 8 g / m ² SS = 9 g / m ² combi-blade coater; 1000 m / min. Working speed air foils. 250 ° C

Supercalender; 200 m / min. Working speed, 250 Kp / cm line pressure and 70 C roller temperature

The following test conditions are obtained according to the test conditions described in Example 1

Features: VP 60/6 coating kaolin / gravure printing

Share less than 1 ^ _1n 60% 49%

Share less than 0.2 μm 6% 17%

specific surface 7.8 m ² / g 13.0 m ² / g

Test results:

Shine . 63% 64% Print gloss 85% 85% Opacity 92.6% 90.0% Strike through #. Show through 10.7 13.5 laboratory proof gravure

(Order of precedence) 1 2

Practice printing tests
Gravure (ranking) 1 1

The inventive calcium carbonate VP 60/6 used in this example with 60% of particles smaller than 1 μm and 6% of particles smaller than 0.2 μm and a specific surface area of 7.8 m ² / g provides the same gloss and print gloss values as the comparative kaolin. The VP 60/6 delivers better results than the comparative kaolin in terms of opacity, strikethrough and shine through, and laboratory pressure. In the practical printing tests, both products are assessed equally.

These results show that with a calcium carbonate accordingly the product VP 60/6 easily a paper coating color, for the

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Gravure printing can be produced and thereby a coated paper is obtained, which is usually using Gravure printing papers produced by kaolins are on a par and in some cases superior.

The coating slip formulations according to Example 3 show that around 20% less binding agent is used with calcium carbonate could be in order to arrive at the same and in some cases better properties. The reduction in the proportion of binder represents a significant cost saving for the paper manufacturer.

The good rheological behavior of calcium carbonate enables coating colors with a higher solids content (high solids coating) to produce what is not possible with kaolin. This results in lower energy costs with the line drying, what for Paper maker also represents a significant cost saving.

Claims (1)

REINHARD, KREÜTZ & SKUHRA PATENT LAWYERS Reinhard. Kreutz & Skuhra ■ LeopoldstraSe 51 - D-BOOO Munich 40 Applicant: Plüss-Staufer AG DR. ERNST STURM <1951-198O) DR. HORST REINHARD DIPL-ING. KARL JÜRGEN KREUTZ DIPL-ING. UDO SKUHRA LEOPOLDSTRASSE 51 D-8000 MUNICH 40 TELEPHONE: 0 89/33 40 TELEX: 5 21 28 39isard TELEGRAM: ISAR PATENT Our sign / our ref. P1646 Dr.R./Sch Your sign / your ref. Date May 5th 1983 Calcium carbonates, especially natural calcium carbonate Claims 1/. Calcium carbonate, especially natural calcium carbonate, characterized, that it is made by grinding and / or classification according to particle size is processed, and a) 50-70% of particles smaller than 1 μm, b) less than 10% of particles smaller than 0.2 μητ. and c) has a BET specific surface area of less than 10 m ² / g. 2. Calcium carbonate according to claim '1, characterized in that it a) 55-65% of particles smaller than 1 pm, b) less than 10% of particles smaller than 0.2 µm and c) has a specific surface area of less than 10 in ² / g. 3. calcium carbonate according to claim 1 or 2, characterized in that that it a) 60% 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 m ² / g. 4. calcium carbonate according to any one of claims 1 to 3, characterized in that that it a) 60% of particles smaller than 1 pm, b) 4-6% by weight of particles smaller than 0.2 μm and c) has a specific surface area of less than 10 m ² / g. 5. calcium carbonate according to any one of claims 1 to 4, characterized in that that it a) 60% of particles smaller than 1 μΐη, b) 4-6% of particles smaller than 0.2 μm and c) has a specific surface area of less than 8 m ² / g. 6. A method for producing the calcium carbonates according to any one of claims 1 to 5, characterized, that they first dry-dry in a manner known per se and then processed by classification according to particle size by means of air sifting. 7. A method for producing the calcium carbonates according to any one of claims 1 to 5, characterized, that they are produced by wet grinding in a manner known per se will. 8. Use of the calcium carbonates according to one of the claims 1 to 7 as coating pigments for LWC gravure papers. 9. Use of the calcium carbonates according to one of the claims 1 to 8 in suspensions with a solids content of 65 - 85 % By weight for LWC (High Solid Coatings) gravure papers.