Signage screen printing failure analysis (12-18)

Twelve, the back of the dirty

Dirty on the back refers to the phenomenon that the ink on the lower print sticks to the back of the upper print when the prints are stacked. If this phenomenon is not controlled, it will cause the page to stick and affect the printing of the other side of the double-sided print. The main reason for the back stickiness is poor ink drying.

The solution to the problem of sticking on the back side is to adjust the viscosity of the ink, use a quick-drying ink, add a driers to the ink, or spray powder on the surface of the semifinished product, or a liner.

Thirteen, sticky page

In the accumulation process of screen printing products, adhesion failures may occur between the printing sheets, which is also called adhesion failure. Adhesion can cause print quality problems and even scrap. The main reasons for the occurrence of adhesions are the following:

After printing, the printing ink is not dry enough. When the ink is not dried, the prints are piled up and piled up, causing smearing and blocking.

The improper selection of the constituent materials of the screen printing ink is also the cause of the adhesion between printed materials. When the softening point of the synthetic resin film forming material in the ink is low or the volatility of the ink is not good, blocking occurs. In general, a thermoplastic resin is used for the evaporative drying ink, and the resin has poor heat resistance. If the solvent remains on the ink film after printing, the ink film will soften, causing the print to stick. Especially in the summer, due to the relatively high temperature, the adhesion between prints is likely to occur.

The ink used for printing has a certain dissolution effect on the substrate, and it also causes adhesion between the printed materials. Some of the solvents used in printing are very soluble to the substrate. When printing, the ink produced a certain amount of dissolution on the surface of the substrate. At this time, although the surface of the ink has dried, the contact portion between the ink and the substrate has not yet dried out, and adhesion phenomenon will occur under the action of the gravity. When the substrate is a soft vinyl material, part of the plasticizer in the vinyl material after printing is transferred to the ink film, resulting in softening of the ink film and also causing blocking.

In order to prevent adhesion, first select the ink and solvent that are suitable for the substrate. Secondly, ink with faster drying speed is selected, and sufficient drying is taken care of. Strictly follow the process requirements. General glossy inks are prone to blocking, so pay full attention.

Scraper rubber strip wear, the blade was rounded, resulting in thickening of the ink film scraping, or printing pressure is too large, ink film thickening, can also cause adhesion failure.

XIV. Printing ink leak

Part of the printing ink leakage, known as the ink leakage failure, the reasons are: a part of the scraper is injured; the pressure of the scraping ink is large; the gap between the printing plate and the printing material 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; the screen is too fine; the printing speed is too fast.

If the printing material and the ink are mixed with dust and printing is performed without processing, the plate film may be damaged due to the pressure of the squeegee; when the plate is under-exposed, the pinhole occurs, and the printing film may leak ink. At this time, adhesive tapes, etc. can be used for emergency handling from the back of the plate. If this operation is very rapid, the ink on the plate will be dried, and the entire plate must be wiped with solvent. Wipe plates are also the cause of delamination of the plate, so it is best avoided. The ink leakage of the printing plate often occurs in the ink staying part, so it is better to strengthen this part in the plate making.

In the manual printing feeding process, when the metal plate and the hard plastic plate are inserted into the printing table, a sharp corner puncture film is liable to occur, so care must be taken. It is generally best to check and reinforce before printing.

In order to prevent ink leakage, the printing plate should be inspected or repaired before printing begins: the pinholes of the printing plate should be filled, the printing plate must be fully reinforced, and printing should begin.

Fifteen, image deformation

The printing pressure applied to the printing plate by the squeegee during printing can bring the line contact between the printing plate and the printed material. It should not exceed. If the printing pressure is too high, the printing plate is in surface contact with the substrate, which will cause the screen to expand and contract, resulting in deformation of the printed image. Screen printing is the smallest type of printing in various printing methods. If we forget this, we cannot print good prints.

If you cannot print without increasing the pressure, reduce the gap between the plate and the surface of the substrate so that the pressure on the blade can be reduced.

XVI.

Ink-wetting refers to the dot-like blotting of the graphics and dark-sounding parts of the substrate, which impairs the printing effect. In particular, the use of transparent ink is more likely to produce this phenomenon. The reasons are as follows: printing speed and ink drying are too slow; ink layer is too thin; ink thixotropic; electrostatic effects; Dot blots.

The improved methods are: improving the fluidity of the ink; using a fast-drying flux; printing with a high-viscosity ink as much as possible; using as much ink as possible with a small amount of oil; minimizing the influence of static electricity.

Seventeen, flying ink

Flying ink is the phenomenon of ink drawing, which is caused by: uneven grinding of the ink; slower off-printing of the squeegee during printing; less white space around the printed image; electrostatic generation, resulting in ink drawing; the angle of the squeegee is too small.

Eighteen, electrostatic fault

Electrostatic current is generally very small, the potential difference is very large, and there may be the phenomenon of attraction, repulsion, conduction, and discharge. These phenomena will lead to deterioration of the product, degraded performance, fire, fire and human body and other adverse consequences.

Bad screen printing. In the screen during printing, the rubber portion and the screen are charged by the pressure scraping of the blade rubber. If the screen itself is charged, it will affect the normal inking and produce blockage failures; it will be absorbed by the screen at the moment when the substrate is output.

a. Synthetic resin inks are easily charged.

b. Substrate is water-absorbent even though it is papery, but static electricity can also be generated when the air is dry. Plastic substrates have good insulation properties, are not affected by temperature, and are prone to static electricity.

c. The printing area is large and the charging is also large, which is easy to produce bad effects.

d. Since spark discharge can cause flames, be very careful when using flammable solvents.

e. Electrocution due to static electricity is caused by contact with a charged object, or the accumulation of static electricity during grounding caused by spark discharge. Although the electric current generated by electric shock is small, no danger will occur, but electric shocks often occur, which will have an adverse effect on the operator's psychology.

How to prevent static electricity. The methods for preventing the generation of static electricity include: adjusting the ambient temperature and increasing the air humidity. The appropriate temperature is generally about 20° C. and the relative humidity is about 60%. A small amount of antistatic agent is put into the alcohol used for scrubbing printing materials; the friction pressure and the speed are reduced; Minimize the friction, pressure and impact of substrates; install general grounding devices; use ionization of flame, infrared, and ultraviolet rays; and use ionization of corona discharge with high-voltage currents.

Source: Wujiang Golden Eagle Copper Sign Factory