Signage screen printing failure analysis (6-11)

Six, net marks

Screen marks sometimes appear on the surface of the ink film. The main cause of the screen marks is the poor fluidity of the ink. During the screen printing process, when the printing plate is lifted, the ink transferred to the printing material fills the stencil by its own flow, so that the ink film surface is smooth and flat. If the ink has poor fluidity, when the screen printing plate is lifted, the ink flow is relatively small, and the screen marks cannot be filled, and a smooth and smooth ink film cannot be obtained. To prevent the appearance of screen marks on prints, the following method can be used.

Use high-flowing ink for printing.

Consider using a slow drying ink to print, increase the ink flow time to gradually flatten and cure the ink.

Use silky, fine monofilament mesh when making plates.

Seven, the printing position is not accurate

Even if there are no problems with the size of the screen, the printing press, etc., the inconsistent shape of the printing material, the excessive shrinkage of the material, and the inconsistency of the printing material will cause the printing position to be inaccurate. If the paper is printed in color, one color is printed and then dried. The change in temperature causes a change in its size. As a result, when the second and third printing are performed, overprinting failures occur. When the printed material is a plastic product, changes in the temperature and humidity of the printing place can cause changes in its size, affect the printing accuracy, and the shapes, molding conditions (such as temperature, time) of plastic products are not exactly the same, when printing All must be considered, take appropriate measures, and make corrections as much as possible in advance.

Bad overprint

Overlapping ink film is called overprinting. In the case of multi-color printing, ink printed on the previous ink cannot be clearly printed on the ink film of the previous printing. This phenomenon is easily caused by some kinds of ink, and some are not easily produced. For example, an oxidative polymerization type ink has a large amount of desiccant added to promote drying, and when the ink film is oxidized and hardened excessively, two colors of ink repel each other. In addition, if an antifoaming agent is added in excess to the volatile ink, the antifoaming agent forms a film on the surface of the ink film, preventing the overprinting. The remedy is to use inks with good overprint properties to reduce the viscosity of the ink, add additives to the ink, and reduce the drying speed of the ink.

Nine, the size of the finished ink film

After screen printing, the print size sometimes increases. The main reason for the increase in printing size is the low viscosity of the ink and excessive flow;

The increase in size at the time of manufacture is also the cause of the increase in print size.

In order to avoid ink flowability causing the printing ink to flow around, resulting in a larger print size, consider adding a certain amount of thickener to the ink with excessive fluidity to reduce the flowability of the ink. Fast-drying inks accelerate the drying speed of the ink after printing, reducing the flow of ink. When making screen printing plates, the quality of the screen printing plates must be strictly guaranteed.

Ten, ink film cracking

The cracking of the ink film is caused by the effect of the solvent and the large temperature change. Substrate material itself can also cause ink film cracking.

In order to prevent the occurrence of ink film cracking, the nature of the ink, the substrate, and the solvent resistance should be taken into consideration when selecting the solvent. Use solvent-resistant and oil-resistant materials as printing materials, and pay attention to maintaining a balanced shop temperature. In multi-color overprinting, it is necessary to fully dry each color after printing, and strictly control the drying temperature to effectively prevent ink film turtles. Cracking occurs.

Eleven, ink

Ink is the phenomenon of ink overflowing outside the printed lines. As shown in Figure 4-36, when printing a line, ink spills on the side of the direction of the squeegee and affects the neat lines. This phenomenon is called bleed. The ink can be solved by adjusting the relationship between the printing plate and the ink, the operation of the squeegee, and the relationship of the screen stretching angle. The shape of the through hole portion of the screen printing plate varies depending on the plate making method (indirect method, direct method, straight line method). The ideal through hole should be able to seal with the surface of the substrate during the squeegeeing. With the ideal through hole shape of the printing plate, the printed ink film is sharp, neat, and accurate in size, without ink. In order to prevent the occurrence of smoke and ink phenomenon, the film should have appropriate thickness, elasticity, and smoothness. For this purpose, a soft nylon mesh and a high-precision polyester mesh plate can be used. In order to prevent blemishes, it is best to use diagonal stretching in the plate making process.

Source: Wujiang Golden Eagle Copper Sign Factory