Coating glazing process analysis

The on-line coating coating units provided by the offset press now use the following two coating systems:

1. Double roller coating system

The feature of the double roll glazing system is that there is nothing in the lacquer coating process that can press the glazing oil, so that the coating amount of the glazing oil can be increased to 8g/m2. The roller coating system controls the coating amount of the varnish, which is adjusted by the rotation speed of the liquid bucket roller and the pressure between the liquid bucket roller and the metering roller (also referred to as a coating roller). When using a larger viscosity varnish, you can replace the polishing plate roller with a chrome plated anilox roller. This chrome-plated anilox roller has a relatively large amount of varnish, and the coating weight of varnish can reach more than 10g/m2. The chrome-plated anilox roller is used to measure the coating quantity of the varnish. Under normal operating conditions, once the coating quantity of varnish is determined, even if the speed of the printing press is changed, the coating quantity of the varnish is basically the same. Do not need to adjust again.

2. Box scraper coating system (liquid knife type)

The box type blade coating system is currently an ideal glazing system. It is suitable for coating gold or silver low-viscosity inks with different weight elements and coating oils. Box type scraper coating system consists of two scrapers and laser engraved ceramic anilox roller and other closed box-like structure, the box of paint is in a state of non-stop circulation. The supply of coating oil is controlled by a laser-engraved ceramic anilox roller, which guarantees continuous and constant coating of uniform coating oil. Even if a very thin coating coating is required, the coating coating system can still fulfil requirements. It is suitable for coating a variety of different coating oils. The coating amount of coating oil can be controlled by replacing the anilox roll with different transmission properties.

3. The choice of polishing system

Different coating systems should be used depending on the product. The oiler can use either a roller type coating system or a color box type coating system. When the varnish has a viscosity of 25 to 40 seconds (40mm DIN cup), a two-roller coating system can be used. A slightly higher viscosity varnish can also be used with a roller glazing system, but before use it should be checked for the drying properties of the varnish on the substrate to be used. When passing the oil through the oil machine, it is recommended to control the viscosity of the varnish to about 35s. When the viscosity of the coating oil is 20 to 80 seconds, the box type chaos knife coating system can be used. Higher viscosity (less than 120s) can be applied to the box type blade coating system, but before use, the drying properties of the coating oil on the substrate to be used must also be checked. It is recommended that the viscosity of the coating oil be controlled at 60 to 80 s. The oil machine will not affect the size of the paper to be printed. If the width of the oil exceeds 1020 mm, a special anilox roller is needed. When not equipped with a drying device, you can not use the oil machine, otherwise it will make the printed material sticky.

4. Offset printing machine with on-line coating function

Now the offset printing machine with on-line coating function used by the printing factory adopts the following structures.

(1) Box-type scraper coating unit for printing unit plus UV, water and oil;

(2) Printing unit plus UV box scraper coating unit;

(3) Printing unit plus metering roller type glazing unit.

For the first two structures, that is, the coating method using the box type blade coating unit, there are two options, of which the standard coating amount of varnish is 9cm3/m2; the other coating amount of varnish is 13cm3/m2. , It is generally used to make local oil prints more.

Note: In the above mode, less than 50% of the varnish transferred by the anilox roller can be transferred to the desired coated paper. For the third type, which is the metering roller in-line coating method, the coating thickness can be calculated by referring to the following data. The "basic position" corresponds to 99% of the maximum oil layer and has a thickness of 0.3 mm. This 0.3mm adjustment range is divided into 0 to 99% scale, that is, each 1% corresponds to a coating thickness of 0.003mm.

Fourth, coating coating precautions

Attention must be given to the flash point of the varnish, cleaning agents and solvents. The use of varnishes, cleaning agents, and solvents that meet fire and explosion regulations must be used.

According to these regulations, only varnishes, cleaners, and solvents that have a fire point of at least 15°C above the temperature achievable in use are permitted. For glazing, cleaning agents and solvents must be fired at temperatures above 55°C.