UV glazing method on common ink (1)

1. Closed scraper provides uniform ink film thickness

Manroland has worked with its customers and supply partners to develop a closed scraper method in 1993. This method ensures a very uniform coating thickness. Anilox rollers with different carrying capacities ensure an accurate amount of glazing and can be carried out repeatedly. The amount of paint carried by the rollers varies from job to job. The normal rule is between 6 and 30 cm3 per square meter. In fact, only 25% to 35% of the wet paint of the above nominal load is transferred to the surface of the substrate. Different screen conditions on the surface of the anilox roller allow the machine to transfer different required amounts of coating. A good circulatory system is an important factor. The quality of the coating's stability is related to the paint's feed, storage, and pumping principles, plus temperature stability. These factors must be matched to the glazing unit used.

2. Measuring luster with reflected light

One reflection angle can be used to measure the gloss. The "mirror surface" reflects 100% of light. Since the coating surface reflects only a portion of the light, the degree of gloss must be chosen to provide a reliable measure of the gloss change. The angle of measurement is very important, because the pigment penetrates deep and has a phenomenon of dispersion. The human eye responds more strongly to gloss on a black background.

3 scratch resistance and adhesion test

The scratch resistance and adhesion of the coating are important factors in the post-printing process and an important factor in the durability of the printed product. Users sometimes use unscientific methods to determine these properties, such as scratching with nails or sticking with tape. These are subjective methods of judgment, relying primarily on the judgment of each client, and have no measurable data, but they can be used as a reference. Without objective test conditions, the adhesion of the coating, if not stabilized after a few days after production, can only be maintained for several hours. During this time, the ink is oxidized and dried, resulting in the generation of gas that builds up between the ink layer and the paint layer, thereby breaking the bond. Therefore, it is reasonable to check the degree of adhesion only a few days after printing. Acetone is very suitable for testing the degree of curing of UV coatings. The method is to use a cloth impregnated with acetone to wipe over the coating. If the curing is poor, the coating will be dissolved. The German Printing Association (FOGRA) recommends several test devices for checking the resistance to peeling and blocking. The resistance of printed matter can be tested according to the methods provided by "German Industrial Standard" DIN 16524 and DIN 16525.

4. Substrates are basic elements

The important factors affecting the glazing effect are the basic materials, the method of machine coating, and the quality and uniformity of these factors. In our test, eight different quality substrates were used. Including recycled materials (GT and GD) and new fiber materials (GC). Not only do these materials have different grades, but the quality of machine coating is also different. Usually two or three machine coats are used. The tools used include a doctor roll, air brush, air knife, and mucous membrane machine. (Note: In order to avoid confusion, we must distinguish between different coatings. Coatings (powder) on paper or paperboard in paper mills, and coatings that enhance the effects of prints are glazing coatings, in order to perform a series of useful under the same conditions. In the test, the thickness of each material used was the same, and on different grades of paper, the coating times of the powder had a significant effect on the quality.

The effect of adding two coaters on recycled materials was much less than on three coats. The cardboard made of new fiber was coated only twice and then gluing. The surface was smooth and had a gloss like three times of coating. The on-machine coated surface hardness also has an effect on gloss - harder coating tools produce a smoother surface and increase gloss.

It is not useful to predict the gloss that can be achieved based on water absorption and oil absorption. In the lab, the gloss properties of different grades of paperboard are more practical than on-line ultraviolet (UV) glossing after the coating process is applied.

Depending on the amount of ink and coating used, the properties of the substrate itself have a considerable influence on the gloss level. The smoothness and absorbency of the powder coating surface determine the effect of the coating. In high-grade paperboard, the surface has a consistent smoothness, although minor changes are unavoidable, especially cardboard made from natural materials, but it also affects gloss.

The grade of the board has an effect on the result of up to 30%. It should be noted that even if increasing the amount of paint can reduce the difference in glossiness, this test has nothing to do with the grade of the paint (due to the use of different manufacturers' paints).

On the other hand, a better smooth surface can be obtained with the same amount of paint applied at a time on a three-time coated cardboard. The difference between the coating materials on the third machine can be attributed to the formulation of the coating powder on the machine, the coating tools, and the processing sequence.