Screen printing common problems and solutions (below)

After the printing, ink bubbles sometimes appear on the ink film. The reasons for bubbles appear in the following aspects.

1 The substrate is poorly processed before printing, dust and oil traces are attached to the surface of the substrate.

2 There are air bubbles in the ink. In order to adjust the viscosity of the ink, solvents and additives are often added to the ink. When stirring, some air bubbles will be generated, and the ink with low viscosity will be naturally defoamed, and the ink with high viscosity cannot be defoamed naturally. In the printing, some of these bubbles are naturally eliminated due to the transfer of ink, while others become larger and larger. In order to remove these bubbles, defoamers are often used, and the amount of defoamer added is generally about 0.1% to 1%. If the amount exceeds the prescribed amount, it will cause foaming.

3 If the printing speed is too fast or the printing speed is uneven, bubbles may also be generated. At this time, the printing speed should be appropriately reduced to maintain the uniformity of the printing speed.

7, net marks

Due to the poor fluidity of the ink, traces of the screen sometimes appear on the ink film surface of the print. During the screen printing process, when the printing plate is lifted, the ink transferred to the printing material fills the screen traces with its own flow, so that the ink film surface is smooth and flat. If the ink has poor fluidity and the screen 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 printed materials, consider using the following methods: use liquid inks for printing; use inks with slower drying speeds; increase the ink flow time to gradually flatten and cure the ink; When possible, use finer, monofilament mesh.

8, poor overprint

Overlapping ink film is called overprinting. In the case of multi-color printing, this problem arises when printed ink cannot be clearly printed on the printed ink film. For example, for oxidative polymerization type inks, in order to promote excessive addition of desiccant, when the ink film is oxidized and hardened excessively, the two-color inks will repel each other; if the volatilization type ink is added in excess, the anti-foaming agent is in the ink film. A film forms on the surface and prevents overprinting. The solution is to use inks with good overprint properties, reduce the viscosity of the ink, add additives to the ink, and reduce the drying speed of the ink.

9, drawing

Caused by the phenomenon of wire drawing: the ink is not evenly grinded; the squeegee is slow from the plate during printing; the plate surface around the printed image

Accumulation; there is static electricity, resulting in ink drawing; or the squeegee angle is too small.

10, enlarge the size of printed products

The viscosity of the ink is relatively low and the fluidity is too large, and the print size enlargement sometimes occurs after the net brush. The enlargement of the screen size at the time of manufacture is also a cause of the increase in the print size. In order to avoid the large ink flow caused by the size of the ink film in printing, consider adding a certain amount of thickener to the ink with excessive fluidity to reduce the flowability of the ink; you can also use fast-drying ink. Accelerate the drying speed of ink after printing and reduce the flow of ink. When making screen printing plates, we must ensure the quality of screen printing plates.

11, ink film cracking

The cracking of the ink film is caused by the effect of the solvent and the large temperature change, and the substrate material itself also causes the ink film.

Cracking occurs. To prevent cracking, consider the nature of the ink and solvent resistance of the substrate when selecting the solvent.

Sex. Use solvent-resistant and oil-resistant materials as printing materials, and pay attention to keeping the temperature in the shop constant and in multi-color printing

It is necessary to fully dry after each color printing, and strictly control the drying temperature, which can effectively prevent the occurrence of ink film cracking phenomenon.

12, AIDS

Ink-wetting refers to the dot-like blotting of the graphics and dark-sounding parts of the substrate, which impairs the printing effect. The reasons are as follows: ink drying is too slow; ink layer too thin; ink thixotropy too much; electrostatic effects; The solution is: to improve the ink's fluidity, use fast-drying solvents, print with high-viscosity inks as much as possible, use inks with small amount of oil absorption as possible, and minimize static electricity.

13, the back of the dirty

Dirty back refers to the phenomenon that the ink on the print below sticks to the back of a print when the prints are stacked. The main reason for the back stickiness is poor ink drying. Solve the back of the dirty way is to adjust the ink viscosity, use fast-drying ink, add driers in the ink, spray powder on the surface of semi-finished products, or add backing paper.

14, adhesion

In the process of accumulation, adhesion occurs between the prints. The phenomenon of adhesion causes prints to have quality problems and even to be scrapped. The causes of adhesion are as follows.

1 After the printing, when the ink is not dry, the printed matter is piled up and piled up, causing smearing and adhesion.

2 When the softening point of the film-forming material of the synthetic resin in the net brush ink is relatively low or the thermoplastic resin is used for the ink, the resin is poor in durability. If the solvent remains on the ink film after printing, the ink film will soften, causing the print to stick. Especially in summer, due to the relatively high temperature, it is easy to cause the phenomenon of adhesion between prints.

3 Printing inks have a certain degree of dissolution on the substrate and can also cause adhesion between the prints. Some solvents in the ink have great solubility to the substrate. After printing, the ink will produce a certain amount of dissolution on the surface of the substrate. At this time, although the surface of the ink is already dry, the contact portion between the ink and the substrate has not yet dried out, and the gravity is Adhesion may occur under the effect. If the substrate material is a soft polyethylene material, part of the plasticizer in the polyethylene material after printing will be transferred to the ink film, resulting in softening of the ink film and the phenomenon of blocking. In order to prevent the adhesion phenomenon, we must first select the ink and solvent suitable for printing materials; secondly, we should use the ink with faster drying speed, and pay attention to fully dry; strictly follow the process requirements.

15, lose ink, leak ink

A part of the printing image loses ink, which is called lost ink. The reasons are: a part of the squeegee blade is wounded; the pressure of the squeegee is too large; the gap between the screen plate and the substrate is too large; the plate frame is deformed and the printing pressure is insufficient; the viscosity of the ink is too high; the ink is not Uniform; wire mesh too thin; printing speed too fast. If the printing material and the ink are mixed with dust and then processed without printing, the plate film is damaged due to the pressure of the squeegee, and the pinhole is generated when the plate is underexposure, and the printing film may leak ink. From the back of the plate, attach it to the emergency department. In the manual printing feeding process, when the metal plate and the hard plastic plate are placed on the printing table, the sharp corner puncture film is liable to occur, and it should also be avoided with care; in order to prevent ink leakage, it is necessary to The plate is checked or repaired, the pinholes of the plate must be filled, the plates must be fully reinforced, and printing must begin.

16, image distortion

The main reason is that the pressure of the squeegee running on the screen is too large or uneven, which causes the screen to stretch and cause image distortion. The printing pressure of the squeegee on the printing plate can make the line contact between the printing plate and the printed object, and the printing pressure can not be too large. Screen printing is a kind of printing with the lowest printing pressure in various printing methods. Forget that this is not a good print.

Source: Nanning Tianbo Screen Printing Co., Ltd.