SE468754B - SETTING AT FLEXO AND DEEP PRESSURE MACHINES PREVENT THE RISE OF GAS BUBBLES IN PRINT - Google Patents

Description

-I> - Ch co -J m .za 2 solvents. Even small air or gas bubbles increase the internal friction (viscosity) of the dye liquid, and the paradox happens that a certain amount of small gas bubbles, which reduces the amount of pigment per unit volume, increases the viscosity, which leads to a supply of solvent, which in turn leads to a further reduction of the pigment concentration. In other words: the error becomes larger instead of smaller through regulatory intervention. Because part of the available space in each engraved cell is occupied by gas instead of paint, the amount of color transferred per cell is further reduced, and the error is further amplified.

Water-diluted paints have a significantly higher foaming tendency than paints diluted with other solvents, which is why constant printing results with water-based paints are much more difficult to achieve. At the same time, air in the paint contributes to initiating the polymerization of the carrier, which leads to filling tendencies of the engraved cells in the raster or gravure roller. This in turn leads to a reduced volume of paint being transferred for each emptying of the cell and, unless raster or gravure printing rollers are thoroughly cleaned. carefully immediately after completion of printing, to permanently reduced function and sometimes to total destruction of the roller. Similar problems also exist for paints based on other solvents, but the problems are smaller, mainly due to the solvent there evaporating and leaving the pigment part, while water-based paints are based on a polymerization of the carrier. Once polymerized, it is very difficult to remove, while the addition of new solvents to a solvent-based dried paint dissolves it again, whereupon it can be easily removed. A high production rate presupposes rapid polymerization for water-based paints, which increases the above-mentioned problems.

The prevention of foaming in the printing ink is thus very important in order to be able to achieve high production, repeatable printing results and to prevent scrapping and reduced function for gravure and raster rolls. Traditionally, attempts have been made to solve the 46-8 754 3 foam problem by adding chemical-based defoamers. As a large proportion of the printed products are used for food packaging, a defoamer must of course be approved for food packaging and not cause a deterioration of the color, which significantly limits possible chemicals. Furthermore, they must be judged to be harmless to both the external and internal environment.

The present invention aims to solve the problem without the use of chemicals, and to use a method which prevents clogging and t.o.m. cleans already filled cells in raster and gravure rollers.

It has been found that the use of ultrasound in ink leads to a total degassing thereof. The ultrasound can be applied either from the outside through an external mounting in direct metal contact with the chamber squeegee or paint vessel, or internally in the chamber squeegee chamber or in the paint vessel for flexo and gravure printing procedures. In this way, one also helps to effectively prevent clogging of cells in resp. rollers. Should the rollers already be partially clogged, they can also be cleaned by circulating a liquid with mild detergent instead of ink in the ink circulation for ink and at the same time adding ultrasound via chamber squeegee or paint vessel.

In addition, the addition of ultrasound to the ink will effectively disperse the color pigments, leading to better opacity for the same amount of color per unit area. One can thus expect a certain color saving by ultrasonic application, and one also enables a higher pigment concentration in the ink because the dispersion gives a more homogeneous color.

This in turn enables higher production speeds where drying is a production limiting factor. By introducing the above-mentioned measures, conditions have also been created for meaningful viscosity regulation.

To achieve these results, ultrasound is also added externally or internally to the paint container from which the paint -Iß- 0 \ CO 4 In this way, all gas in the paint is removed before it is pumped up until the paint vessel is circulated via the paint vessel and / or chamber squeegee. or chamber squeegee, and the emergence of new gas bubbles is prevented by the ultrasound applied to the squeegee or squeegee while keeping all cells in the raster roll or gravure roll completely open, or alternatively opening in cases where they are partially or completely clogged.

As can be seen from the foregoing, the presence of gas bubbles in the ink is the primary cause of printing problems. The present invention addresses this problem easily and efficiently while preventing and eliminating secondary effects in the form of clogging of cells in raster or For a person skilled in the art it is clear, modifications can be made for introductions of ultrasound into gravure rollers. many inks, for example, via raster or gravure rollers, but these are intended to be within the scope of the invention.

Claims (5)

PATENT REQUIREMENTS 1. In the case of flexo and gravure printing machines during continuous printing, achieve a constant, even transfer of ink to the printed object, characterized in that the appearance of gas bubbles in the ink and in the engraved cells in screen rolls or printing cylinders is eliminated and prevented by supplying ultrasonic energy to the ink, and that the ink is simultaneously dispersed. 2. A method according to claim characterized in that the ultrasonic energy is supplied with the ink so that the engraved cells in raster rollers or printing cylinders are kept open during printing by the ultrasonic cleaning effect, and for opening already clogged cells. 3. A method according to claim 1 or 2, characterized in that the ultrasonic energy is supplied from the outside, via machine elements in the printing station. 4. Methods of cleaning raster rollers or printing cylinders in a printing machine, characterized in that the ink is replaced with a cleaning liquid, and that this is supplied with ultrasonic energy. 5. A method according to any one of the preceding claims, characterized in that the ultrasonic energy is supplied discontinuously.