FI78141C - FOERFARANDE FOER FRAMSTAELLNING AV BELAEGGNINGSMEDEL FOER PAPPER OCH ANDRA CELLULOSAHALTIGA AEMNEN. - Google Patents

Description

A

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A process for preparing a coating agent on paper and other cellulosic materials. - Förfarande för framställning av beläggningsmedel för papper ochra andra cellulosahaltiga ämnen.

The invention relates to a process for preparing a coating agent for paper and other cellulosic materials, which coating agent is formed from pigments, dispersants and binders.

By coating or brushing the paper with a liquid product, it is desired to obtain a surface in the paper which is resistant to wet abrasion. This feature is especially important in the offset system, which is currently widely used to produce high quality printed products. For the offset method, it is essential that the surface of the papers and cartons to be printed have good abrasion resistance. If the surface layer of the paper adheres to the surface of the tool, the printing result is negative because a layer of brush pigment adheres to the printing rollers and thus an incorrect print image is formed. Abrasion resistance is achieved by currently known methods by using resin and chemical reaction products, e.g., reaction products between calcium sulfoaluminate and protein or starch.

However, these systems are becoming increasingly undesirable because the materials used for them are expensive and paper handling becomes considerably expensive.

The paper is mainly coated with three components: 1. pigments with a certain appearance, 2. dispersants, 3. natural or synthetic binders.

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The pigments then give the paper smoothness, opacity and gloss, the dispersants allow a high pigment content with low viscosity and the binders bind the pigments to the surface of the paper.

The object of the present invention is to improve the coating material of the type mentioned at the beginning so that the wear resistance of the coated paper surface increases and a good printing image is obtained at low operating costs. In addition, the stability (processing time) of the coating material must be extended and the compatibility with different types of inks during printing must be optimized.

According to the invention, this object is solved by means of the features set out in the claim, whereby for the first time the processing of calcium ion-containing pigments became possible. The pigment preferably consists of calcium sulphate having two molecules of water, which when wet is ground in a colloid mill to a corresponding grain size. The use of anhydrous calcium sulphate is also possible, in which case a dry grinding process can be used.

With conventional dispersants, the pigment cannot be dispersed because of the high solubility of calcium ion. The pigment is now reacted with a colloid which acts both as a dispersant and also as a binder and suspension stabilizer. It not only binds the calcium ions of the suspension but also fixes the pigment to the carrier material, i.e. to the surface layer of the paper to be treated.

The above-mentioned properties of the colloid are obtained by the reaction of a polysaccharide with a combination of phosphoric acid and an ammoniacal base, preferably urea. The reaction is carried out in an autoclave at a temperature of 180 to 200 ° C to obtain a high dispersion colloidal polyphosphate capable of reacting with calcium ion i 3 781 41 by exchanging ammonium groups. The chemical reaction between the colloid and the pigment gives a uniform substance which has substantially better smoothness and opacity properties than a simple mixture of pigment and binder. The addition of the pigment is preferably carried out at a temperature below 45 ° C in order to prevent the formation of dextrin from the polyphosphates.

In order to optimally adjust the ink compatibility, it is necessary to provide an additional substance as a micropigment when performing the process.

Surprisingly, it has been found that aluminum hydroxide with a grain size of 1 to 6 pn is particularly well compatible with calcium sulphate.

Aluminum hydroxide makes it possible to keep the viscosity of the calcium sulphate suspension at a low level during the dispersion process or in connection with the wet grinding of calcium sulphate with the colloid according to the invention.

Of course, it is also possible to try to prepare a paste or slurry which is also suitable for mixing with other pigments, e.g. kaolin. This is possible in principle; however, it should be noted that the proportion of protective colloid must then be higher. In this case, the dispersants used must be tested in advance to determine whether they are compatible with the protective colloid, since its increased polyphosphate content could have an effect on the properties of the paint.

If the paste or slurry is mixed with calcium carbonate or similar pigments, the above caution is not necessary to such an extent because the processing of calcium sulfates is easier than the processing of kaolins and because the protective colloid can be used as a dispersant.

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No other precautions are required in this case, as the dispersion force with conventional dispersants is similar.

The product obtained by the method described herein is compatible with all types of latex, which allow the high flexibility necessary for brush paints, for use on papers and paperboards.

The surface thus treated is resistant to wet wear because the protective colloid has undergone a reaction which produces a certain degree of insolubility, which allows any kind of offset printing. If the described product is used in connection with pigments which do not contain calcium ions, its advantages in its property as a binder, which has the advantage of its cold water solubility, are reduced, which makes pre-dissolution at elevated temperature unnecessary.

Other advantages of a colloidal product are described by its amphoteric nature and by its ability to use it over a wide pH range. In order to simplify the description, three figures are attached, in which, by way of example but not as fully as in the claims, the possibility of manufacturing a product for brushing paper according to the described principles is shown.

Figure 1 shows a schematic diagram for the preparation of a basic pigment with calcium ions dry. The pigment is later reinforced with micropigments with aluminum ions.

Figure 2 shows the preparation of a protective colloid intended to be a dispersant and a binder for the above-mentioned macropigments and micropigments.

Figure 3 shows the combination of pigments with a protective colloid.

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The elements marked with the numbers in the drawing correspond to the numbering used in the following.

The calcium sulphate is treated dry by means of a rotary kiln, the feed opening 1 of which receives the material, feeds it to the rotary kiln 2 and then leads via an endless conveyor 3 to a receiving device 4 with a stirrer. 5, storage tank 7).

The control device 8 at the outlet of the hopper prevents the product from sticking.

The rotary kiln 2 operates continuously at a temperature of about 800 ° C. The receiving device 4 contains a material with the desired degree of DIN fineness. The vibrating screen 10 eliminates unwanted material that could interfere with the calcium sulfate micronization process. The operating pressure of the jet mill 5 is between 10-14 kg / cm 2. · The wind turbine 6 can separate particles up to an average maximum diameter size of 5 μm.

The manufacturing step according to Figure 2 involves, in a limited capacity process, the use of an autoclave 11 for a colloid, which autoclave is equipped with a vane agitator driven by a speed-adjustable motor 12. The entire device is provided with a thermal insulation jacket 13. The autoclave outlet 14 delivers predetermined quantities of product.

The continuous process uses a mixing tank 15 driven by a motor 16, the outlet of which simultaneously forms an inlet for a continuous vessel 18 of the rotary drum type - the operation of which corresponds to the apparatus indicated by reference numeral 2 - and the outlet of the vessel 6 78141 at the vibrating screen 19. to stock 20.

Starch polyphosphate is used as a binder and dispersant for calcium sulfate, as described above. When using corn starch, the working temperature must be between 180 and 190 ° and when using potato starch, the temperature must be between 160 and 170 ° C.

The last step of the process is carried out with the devices shown in Figure 3, the cooking vessel 21 being provided with special mixing plates 22 like a plow mixer and operated at an adjustable speed by means of a motor 23. In the second part, it is shown that the disperser tank 24 is provided with a cooling device and a disperser mixer 25, whereby the speed of the mixer can be adjusted by means of a motor 26. The vibrating screen 27 sorts the material and leads it to intermediate storage.

In boiler 21, the starch polyphosphate is prepared at a temperature between 70 and 80 ° C and a solids content of about 20%. The reaction is maintained for 90 min, cooling to 60 ° C. The pigment of micronized calcium sulfate provided with a protective colloid is then added to the dispersion tank 24 with constant stirring. The temperature then drops to 40 ° C, but in the future rises to 60 ° C due to increased shear forces. Further temperature rises must be prevented by cooling.

If the calcium sulfate is dispersed, aluminum hydroxide is added as the second pigment, and this process of dispersion is continued, resulting in a stable paste with the highest possible solids content. A microbiocide is then added to prevent fermentation of the starch polyphosphate.

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The resulting paste must not contain particles with an average diameter of more than 6 pm.

Application

In the smear test, first-class (100% cellulose, short and long fibers) carrier paper (140 g / m 2) was used. · The paper received a starch layer of 2 g / m 2 on both sides.

The carrier was pre-coated with about 10 g / m 2 of the coating agent according to the invention by means of a squeegee and then with a layer of 20 g / m 2 with the coating agent according to the invention by means of a blowpipe. The papers obtained were suitable for all printing methods. The paper was printed at a printing speed of 20 m / s. Even at high printing speeds such as 50 m / s, no displacement or other impurities could be detected in the print.

After four hours of operation, neither the main body nor the rollers needed to be cleaned; no deterioration of the print could also be observed after a longer period of use.

Claims (8)

A process for the preparation of a coating agent for paper and other cellulosic substances, which coating agent consists of pigments, dispersants and adhesives, capable of preparing the adhesive by adding a mixture of a phosphoric acid and an ammonium base. a starch such as colloid, the three components reacting in an autoclave at a temperature of 160 - 220 ° C for a period of 180 - 240 minutes and then rapidly cooling to a temperature below 45 ° C and by di-splicing, hydration and drying is converted into a colloid at a temperature above 80 ° C. 2. A process according to claim 1 for the preparation of a coating agent for paper and other cellulosic substances, characterized in that, to an aqueous solution of the colloid, a calcium ion-containing pigment is added, maintaining a temperature below 45 ° C. dispersion is performed for longer than 30 minutes. Process according to any of the preceding claims for the preparation of a coating agent for paper and other cellulosic substances, characterized in that the mixture contains micropigments whose grain size is between 1-6 n. * - 4 · A method according to any preceding claim for the preparation of paper and other cellulosic substances, which may be used as an ammonium base urea and as a starch potato starch. A process according to any of the preceding claims for the preparation of paper and other cellulosic substances, characterized in that the components of the colloid consist of 1 - 20% phosphoric acid, 1 - 50% ammonium base, the remainder consisting of starch. . 6. A process according to any preceding claim for the preparation of papers and other cellulosic substances, known in the art.