Overprinting Problems in Golden Printing

In multi-color printing, the adhesion of the ink of the latter color on the ink layer of the previous color is called ink overprinting and is also called transfer of the ink. The more ink that is overprinted or carried onto the previous ink layer, the better the color reproduction. When overprinting is bad, the printed ink is easy to pan "white", which looks dull, or the former color appears a little bit of "splitting" due to being pulled off by the latter color, which seriously affects the quality of the printed product. Propose some ways to solve the problem of overprinting.

First, adjust the adhesiveness of ink

The printing process is a process in which the ink film is split and transferred to the corresponding printing surface. When the cohesion of the ink (ie the force between the ink molecules) is less than the adhesion between the ink and the printing surface, the first is the split and then transfer, the ability of the ink film in the dynamic process to prevent the ink film from breaking is called the adhesion of the ink. Sex. If the adhesiveness of the former color is greater than the adhesiveness of the latter ink, the ink of the latter color can adhere well to the first ink layer, and the overprinting effect is good. Conversely, the latter color ink cannot adhere well to the previous color ink layer, creating a mutual repulsion phenomenon, and will pull off the previous color ink, resulting in poor overprinting or overprinting that cannot be achieved at all. It can be seen that the adhesiveness of ink is of great significance to the overprinting of ink.

The adhesiveness of the ink changes with the degree of drying of the ink. At the beginning, the adhesiveness increases as the degree of drying increases, reaches a certain maximum value, and then slowly decreases with increasing degree of drying, and the adhesiveness is lost when the ink is completely dried. Therefore, by controlling the ink before drying can control the adhesion of the ink, so as to achieve the purpose of solving the problem of overprinting. How to control the drying of ink?

1. The former color of the drying air volume is appropriately smaller than the latter, and the temperature should be appropriately lower.

2. The pre-colored layout should be kept as moist as possible. First, xylene and isopropyl alcohol with slower volatilization speed should be used. Second, the distance between the point where the squeegee is in contact with the plate and the point where the roller contacts the plate should be maintained. May be smaller; third is to appropriately increase the speed of printing.

3. In the front color, additives for inhibiting ink drying are added. You can touch the ink layer with your finger and analyze it with the stickiness of the hand and the amount of ink on your finger. When you feel that the ink in the front color is dry and dry, the quality of the overprint will be better. In addition, it should be noted that the same type of ink used in the same ink factory should be used for the two colors. Otherwise, the type or composition of the two inks will be different. When the affinity is poor, overprinting will also occur, and it is difficult to adjust and solve by other methods. .

Sometimes operators add silicon lubricants to inks in hot weather, which can also produce overprint defects that should absolutely be avoided. Slow-drying solvents should be used instead.

Second, increase the amount of ink for the latter-color printing plate

In multicolor continuous printing, the post-color ink is generally split at the centerline of the ink layer where the two inks overlap. A small portion is transferred to the uncolored ink layer of the previous color ink, most of which remains on the surface of the printing plate. Therefore, the larger the amount of ink for the back color ink supplied to the printing plate is, the thicker the ink layer attached to the first color ink is, and the phenomenon that the rear color pulls off the front color is less likely to occur. Therefore, the ink supply of the post-color printing plate should be greater than the previous color.

Third, the correct arrangement of color printing sequence

The printing sequence in multi-color printing is usually black, blue, red, yellow, white or black, red, blue, yellow, or white. The arrangement order is because the yellow color dries quickly (relatively black, blue, and red), so Print in later colors to facilitate ink overprinting. The situation that affects the overprinting effect of the ink on the plate-making should be provided to the plate-making personnel before the plate-making, so as to avoid causing problems in the printing process.

Fourth, the use of a more flexible rubber roller, and can increase the pressure of the roller

Also found that such a phenomenon: that there is a certain amount of printing plate, the ink printing effect is generally better than the new version. This may be due to the fact that the amount of ink after the printing plate is used increases during the use of the printing plate (because the texture is smoothed by the ink, the mesh is enlarged), or there are other reasons. The mechanism is to be analyzed.

Reprinted from: Printed in China