FI98235C - Printing paper, method of making it and its use - Google Patents

Description

• 9823b

Printing paper, method of making it and its use

The invention relates to a printing paper according to the preamble of claim 1, which is intended to be used in particular for offset or gravure printing. The invention further relates to a method for producing printing paper and its use.

DE-AS 12 21 893 describes the production of coated printing paper in which the starch is made partially cold soluble by mechanical grinding treatment so that it still dissolves in the coating paste under the action of evaporating water in the drying after coating and acts in a dissolved, pasted or pasted manner. such as chalk. The paper produced is reported to have a high gloss. Problems with the abrasion resistance of inks are not addressed.

20

DE-C2 26 05 575 discloses a banknote paper in which the surface is provided with a coating containing a special plastic binder, 0.5-25 10 parts by weight of very fine rice starch and possibly also inorganic pigments in order to prevent the fibers from coming off and to improve the resistance to soiling. Abrasion resistance problems do not occur with such papers.

30 In recent years, the excellent suitability of non-gloss matt printing papers for high-quality printing, such as pictorial works, representative brochures and annual reports, has been increasingly seen. A major advantage of matte printing papers is that they do not exhibit disturbing reflections when viewed on the finished printed product, and on the other hand provide excellent print gloss in printing, in particular with 2 98235 inks suitable for multicolor printing, which increases the quality of the printed product.

In the manufacture of such matt printing papers 5, calcium carbonate has become increasingly popular in recent years.

The German magazine "Wochenblatt fur Papierfa-briquette, 112 no. 17, pp. 609-613, (1984)" discusses in detail the properties of matt papers - including those in which calcium carbonate is used as a coating component. despite the widespread use of them since the mid-1970s, 15 highlighted their poor abrasion resistance and the formation of glossy streaks.

By abrasion resistance is meant the resistance of the ink layer to mechanical stresses 20 due to the compressive and frictional loading of the printing sheets during their further processing and during the use of the finished printed products.

However, abrasion can cause adverse gloss effects already in paper mill further processing machines, such as sheet metal cutters, in which case the usability of the matte-coated paper can be reduced to non-existent ones.

30 In order to improve abrasion resistance, various measures are proposed in the previous literature, all of which are relatively complex or costly for the final product if, for example, the finished printing sheets are coated with an extra layer of matt lacquer 35, and the proposed measures have not yet yielded satisfactory results.

It is therefore an object of the present invention to provide a matte-coated printing paper having improved abrasion resistance and a reduced tendency to gloss.

According to the invention, this object is solved by a printing paper according to the preamble of claim 1, which has the features defined in its characterizing part.

Preferred embodiments of printing paper are defined in claims 2-9. Claims 10 and 11 disclose a method for producing matt coated printing paper and claim 12 discloses the use of printing paper.

15

It has now surprisingly been found that by using non-pasted starch granules according to the invention, which are in practice as coating pigments in an amount of 10-65% by weight of the coating, based on the dry content of the paste 20, , whose abrasion resistance and resistance to gloss streaking-75 have been substantially improved.

Although such offset papers have not hitherto needed to be post-processed by calendering to achieve better smoothness, since the offset method does not place particularly high demands on the smoothness of matte paper, the use of such papers for gravure printing has only been possible in inferior prints. The gravure printing method places very high demands on the surface of the coated paper-35 in terms of the smoothness and evenness of the coating. If good smoothness has been desired with the previously known calcium carbonate-containing coating pastes 4,982,35, the coated paper must have undergone a calendering post-treatment. In the paper industry, of course, conventional supercalenders have been able to improve smoothness, in which case this improvement has necessarily been accompanied by an increase in gloss, and in which case the desired matt effect has not been achieved.

The coated paper according to the invention can now also provide a smooth, yet non-glossy paper for gravure printing, which can be used especially in high-printing printed products.

The printing paper according to the invention preferably contains 15 starch particles, the gluing temperature of which has been raised by a chemical modification known per se. Such a modification is particularly preferably achieved with the starch granules defined in the characterizing part of claims 3 and 4, whereby the pasting temperature 20 can be influenced by the choice of the degree of etherification and esterification.

The size of the starch granules is suitably selected on the basis of the average size of the calcium carbonate pigment. Preferred are starch granules having an average grain diameter of 7 to 50, but particularly preferred are starch granules having an average grain diameter of 15 to 25. The sorting can then be carried out by known separation techniques, such as, for example, hydrocyclone separation 30 in accordance with DE-OS 2341570.

Non-pasted starch granules are, in particular, maize, potato, wheat, rye, rice or tapioca starches. However, maize or potato starches are particularly preferred because they are readily available and sufficiently inexpensive.

5,982,355

The coating for receiving the ink may contain 25 to 70% by weight of calcium carbonate and 10 to 65% by weight of unglued starch granules, in addition to these, white pigments known in the art of paper coating technology. Thus, ordinary coating kaolin, titanium dioxide to increase brightness and opacity, glossy white to improve brightness, gypsum from a flue gas desulphurisation plant as a cheap pigment, talc, but also known and synthetic silicate, alumina or plastic pigments may be present. These pigments suitably do not exceed 15% by weight of the solids content of the coating, the sum of all proportions, including binders and auxiliaries, being 100% by weight.

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The method according to the invention for producing the printing paper according to the invention comprises coating an ordinary coated base paper with an absolute dry basis weight of 30-170 g / m 2 on one or both sides with a coating paste in coating weights of 8-24 g / m 2 (calculated in absolute dry parts by weight = abs. dry) using conventional coating techniques such as roll coating, air scraper coating, rod or rod scraper or scraper coating, in which the coating paste additionally contains 10-65% by weight of uncoated starch in addition to calcium carbonate. In addition, the coating paste contains 5-14% by weight, preferably less than 10% by weight of common binders, such as plastic latex, pasted, dispersed starch or other binders known in the paper coating technique, a dispersant, optionally other white pigments and a viscosity adjuster. The solids content of the coating paste is adjusted to 40-72% by weight, preferably 55-63% by weight. The viscosity of the coating paste is adjusted to 500-4000 m Pas, measured with a Brookfield viscometer, spindle no. 4.50 rpm. In this case, a higher viscosity is recommended for roll application and a lower viscosity for scraper, air scraper or blade coating, in which case the viscosity adjustment can be carried out by adding ordinary, known water-soluble polymers such as polyvinyl alcohol, carboxymethylcellulose or polyaculose. The pH of the coating paste is 8-10, preferably 8.8-9.2, and is adjusted during the preparation of the coating paste, possibly by adding alkali. In the preparation of the coating paste, it has proved particularly advantageous to add unglued starch as one of the last components of the preparation-10 in order to avoid excessive abrasion of the starch granules. If large amounts of starch granules are added to the batch, it is suitable to increase the proportion of inorganic or organic dispersants to 0.5 to 1 part by weight, as it has been shown that non-adherent natural starch gives the coating paste a flowability of dilettant.

After application and smoothing of the coating paste, the coated paper is dried by known drying methods 1-20, such as an IR dryer, a hot air fluid dryer or a cylinder dryer to a final dry moisture content of 92-96%, and then cut to the desired roll or sheet width.

2.5. If the coated paper thus produced is used for gravure printing, it is subjected to a calendering treatment known per se, in which the paper is given the required smoothness with 2-8 roll nip penetrations at a line pressure of 50-400 da N / cm without a significant increase in gloss.

If a higher basis weight in the range of 80-250 g / m 2 is desired for the finished matt-coated paper, it is first possible to coat the base paper with a so-called precoat-35 coating, and only to coat the actual matte coating intended for receiving the ink on this precoat.

7 98235

The usual precoat composition contains, for example, as a calcium carbonate pigment, 100 parts by weight of ground chalk with a grain size of 70% <2 μm, 10 parts by weight of oxidized, 5 parts of pasted starch and 9 parts by weight of abs. Dry styrene-butadiene plastic binder To adjust pH and viscosity. The solids content of such a pre-coating paste is always 55-72 10% by weight abs. Dry, depending on the coating method of the pre-coating device, the amount of coating per paper side being chosen to be 6-15 g / m 2 abs. Dry.

The method according to the invention can be used for the production of coated matt paper on one side and on both sides.

The invention is illustrated in more detail by the following examples: 20 A Pre-coating composition 100 parts by weight of powdered calcium carbonate 10 parts by weight of oxidized starch 9 parts by weight of butadiene-styrene latex (abs. Dry) 25 0.5 parts by weight of urea formaldehyde resin .0 solids content 60.4% viscosity Brookfield, spindle no. 4: 5100 m Pas, 50 rpm 30 B Coating composition for receiving an ink layer

Example 1: 35 80 parts by weight of ground calcium carbonate 20 parts by weight of chemically modified natural maize 98235 8 starches 0.7 parts by weight of dispersant 3 parts by weight of oxidized decomposed starch 6 parts by weight of butadiene-styrene latex (abs. 5 1 part by weight calcium stearate solids content 60.5% by weight pH value 9.0

Example 2: 10 60 parts by weight of ground calcium carbonate 40 parts by weight of chemically modified natural maize starch other proportions as in Example 1 15 solids content 57.0% by weight pH 9.1

Example 3: 20 parts by weight of ground calcium carbonate 50 parts by weight of chemically modified natural maize starch Other proportions as in Example 1 solids content 56.1% by weight 25 pH value 9.0 C Comparative example: 100 parts by weight of ground calcium carbonate 30 0 .4 parts by weight of carboxymethylcellulose 0.9 parts by weight of polyvinyl alcohol 10 parts by weight of plastic latex binder 0.5 part by weight of urea formaldehyde resin solids content 62.6% by weight 35 pH value 9.0

The wood-free base paper with a basis weight of 67 9 8 2 ό 5 9 g / m 2 was first coated on both sides with a precoating of 11 g / m 2 (abs. Dry) in each case and then dried. Then, in the second step, the blade pastes of Examples 1-3 and Comparative Example 5 were coated on both sides in coating weights of 13 g / m 2 (abs. Dry) and dried. Some of the papers thus coated were further post-treated with a laboratory calender to obtain a smooth surface. The table below shows the examination of the samples and the results obtained.

The basis weight of the coated papers was 115 g / m2 in each case, measured in accordance with DIN 53102 and ISO 536. The bulk was measured according to DIN 53105 and the smoothness according to DIN 53107 and 15 gloss with a gloss measuring device according to Lehmann at a reflection angle of 75 degrees.

Fluff tests were performed according to the IGT instrument instruction sheet, with the evaluation being performed on a rating scale of 20 1-6.

To evaluate the abrasion resistance, the so-called weighted prints of the non-calendered samples of Examples 1-3 and the Comparative Example were first prepared with a so-called weighted 25 prints on a Priifbau test printing apparatus. After the ink was completely dry, after at least 24 hours, the abrasion resistance tests were performed with an Oser abrasion resistance measuring device under the specified conditions. The printed surface was compared to the same or left-30 surface of the paper, in each case at unprinted points, for 3 minutes with a load of 625 grams. The evaluation can be performed visually or with an Elrepho device by contrast measurement from unprinted points. The visual evaluation then gave the following evaluation of the examples on a scale of 1-6 35: 10 98235

Example 1 review 2 2 1 3 1 5 Comparative Example 5

It can be seen from the above table that the examples according to the invention have a substantially lower gloss in both the non-calendered and the calendered state than in the comparative example, and that as the proportion of natural unglued starch in the coating paste increases, so-called matte effect without increasing the tendency of the uncalendered dry coating to gloss streak. However, if the coated paper is calendered, the gloss on the one hand does not increase substantially higher than in the uncalendered comparative example, and on the other hand a sufficient increase in smoothness can be achieved, making the printing paper according to the invention suitable for gravure printing.

20 t

Claims (12)

1. A matte surface, specially designed for offset and gravure printing, but not banknote and security document paper, which exhibits calcium carbonate as a coating pigment and a binder containing a coating for receiving printing ink, characterized in that the coating contains starch grains, however, not rice starch grains, in an amount of 10-65 10% by weight, and 5-14% by weight binder, calculated ρέ its total substance. Printing paper according to claim 1, characterized in that the starch grains are chemically modified. 15 Printing paper according to claim 1 or 2, characterized in that the starch grains are etherated. Printing paper according to claim 1 or 2, characterized in that the starch grains are esterified. Pressure applicator according to any of claims 1-4, characterized in that the starch grains have an average diameter of 7-50 μιη. 25 6. Printing paper according to any of claims 1-5, characterized in that the starch grains consist of potato, maize, wheat, shrimp or tapioca starch or mixtures of these starches. 30 7. Printing paper according to any one of claims 1-6, characterized in that the coating contains calcium carbonate in an amount of 25-70% by weight calculated on the solids content. 35 8. Printing paper according to any of claims 1-7, characterized in that the coating contains ground or C ρ 9 X tr. 14 ° C / o .. precipitated calcium carbonate. Printing paper according to any of claims 1-8, characterized in that the coating contains, in addition to calcium carbonate, such as another pigment, kaolin and / or titanium oxide and / or satin white and / or plaster and / or taik and / or other common natural or synthetic white pigments. 10. A process for producing a matte surface printing paper according to any one of claims 1-9, in which, on the coating's base paper, which is optionally provided with a coating, calcium carbonate and binder containing coating paste, and dried, are characterized. hence, that the coating paste contains unstressed starch grains, but not rice starch grains, in an amount of 10-65% by weight based on its solids, the addition of the starch grains being carried out only after the addition of other coating components. 20 11. A process according to claim 10 for the production of printing paper, biscuit-marked thereof, that upon printing the coating, the printing paper is smoothed with a calendering known per se. 25 Use of a matte-coated paper according to claim 1, excluding banknote and security document paper, which is provided with a coating for receiving printing ink and containing non-sticky starch grains, in addition to rice starch grains, in an amount of 10-65% by weight based on of its solids content, and calcium carbonate, for the production of durable and / or gloss-free printed matter. i. IM i Iti, li, | 11 «: