Thirteen, the back of the dirty
Dirty on the back refers to the phenomenon in which the ink on the lower print sticks to the back of the upper print when the printed product is 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 overcome the stickiness on the backside is to adjust the ink viscosity, use faster than the ink, add driers in the ink, or spray powder on the surface of the semi-finished products, or add backing paper.
XIV. Sticky pages
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:
1 After printing, the printing ink is not dry enough. When the ink is not dried, the printed matter is piled up and piled up, resulting in dirt and adhesion.
(2) The improper selection of the constituent materials of screen printing ink is also the cause of adhesion between printed materials. When the softening point of the film-forming material of the synthetic resin in the ink is relatively low or the ink is not good in volatility, 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.
3 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 the softening of the ink film and the phenomenon of blocking.
4 In order to prevent adhesion phenomenon, we must first select the ink and solvent suitable for printing materials. 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.
5 scraper plastic strip wear, knife-shaped round, resulting in thickened ink film scraping, or printing pressure is too large, ink film thickening, it will lead to adhesion failure.
Fifteen, 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 printed without processing, the printing plate will be damaged due to the pressure of the squeegee; when the plate is exposed, pinholes are generated in the wooden foot, and the printing film will leak ink. . At this time, adhesive tapes, etc. can be used for emergency handling from the back of the plate. If this operation is not very fast, the ink on the layout will be dried, and the whole of the plate will have to 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 process of manually printing the binder, when inserting a metal plate and a rigid plastic plate into the printing table, it is easy to puncture the plate with a sharp corner, so be very careful. 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.
Sixteen, image distortion
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 contacts with the printing material and the screen may expand and contract, causing the printing image to be deformed. 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.
Seventeen, AIDS
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.
Eighteen, flying ink
Ink flying is the phenomenon of ink drawing. The causes are: the ink is unevenly grinded; the squeegee is slow from the print during printing; the white space around the printed image is less; static electricity is generated, resulting in the angle of the ink pulling squeegee being too small.
19. 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.
1 adverse effects on screen printing. In the screen during printing, the rubber portion and the screen are charged by the pressurization 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. The human body's electric shock due to static electricity is caused by contact with a charged object, or by electrostatic discharges that generate spark discharges when grounded. 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.
2 method 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.