Screen printing, that is, screen printing, refers to the use of a screen as a plate base, and through the method of the photosensitive plate, using the screen printing plate graphic part of the mesh can be through the ink, the non-graphic part of the mesh can not be through the ink printing principle, made with the graphic screen printing plate.
Principle of screen printing
The basic principle of screen printing is: the use of screen printing plate graphic part of the mesh through ink, the basic principle of the non-graphic part of the mesh is not through ink printing.
When printing, ink is poured into one end of the screen printing plate, and a certain pressure is applied to the ink part of the screen printing plate with the scraper while moving towards the other end of the screen printing plate. The ink is squeezed by the scraper from the mesh of the graphic part to the substrate as it moves.
Due to the viscosity of the ink and imprinting fixed within a certain range, the printing process scraper and screen plate and substrate line contact, contact line with the scraper moving, because of the screen plate and substrate to maintain a certain gap between the printing screen plate through its tension and produce a reaction force on the scraper, the reaction force is called resilience.
Due to the action of resilience, the screen printing plate and substrate are only mobile line contact, and the other parts of the screen printing plate and the substrate is out of state.
The ink and screen fracture motion ensures printing precision and avoids dirty substrate. When the scraper is lifted after scraping the entire page, the screen plate is also lifted, and the ink is gently scraped back to the initial position, so that is a printing stroke.
Screen printing consists of five elements, screen printing plate, scraper, ink, printing table, and substrate.
The graphic accuracy of silk screen printing is lower than that of the photochemical method, but the process is simple, high production efficiency, low cost, and suitable for mass production of screen printed products with low requirements.
The advantages of silk screen printing
(1) Not limited by the size and shape of the substrate
General printing can only be carried out on a flat surface, but screen printing can not only be carried out on a flat surface but also on a special shape of the molding, such as a spherical surface. Anything with shape can be carried out by screen printing.
(2) The layout is soft and the printing pressure is small
The silkscreen is soft and elastic.
(3) The ink layer coverage is strong
It can be logo printed in white on all-black paper for a strong three-dimensional impression.
(4) Suitable for all types of ink
(5) Strong optical rotation resistance
Can make the screen print luster unchanged. (Temperature and daylight made no difference). This enables the printing of some self-adhesive, without additional coating and other processes.
(6) Flexible printing methods
(7) Plate making is convenient, cheap, and easy to master
(8) Strong adhesion
(9) Can be pure manual screen printing, also can be machine printing
(10) Suitable for long-term display, outdoor advertising is expressive
Process anomaly and analysis
1. The drawing is not clear
Reason: the choice of ink or ink itself has quality problems; The ink is too fast so that the printing pattern or line is not clear, the pattern is incomplete or the line is broken; The viscosity of the ink is too high, and the pattern is incomplete or the line is broken when printing.
The printing plate blocking phenomenon affects the normal ink; Insufficient or uneven pressure of scraper during printing results in uneven ink; The printing surface of the substrate is uneven.
Solution: replace the appropriate ink; Use slower drying solvent to prepare ink; Dilute ink or add the thixotropic agent to reduce viscosity; Correct choice of slow dry solvent dilution ink, and pay attention to the printing screen ink performance;
Increase the force of the scraper when printing, and pay attention to the uniformity of the scraping force; Processing substrate surface (such as printing coarse grain substrate can first use up oil or other materials before printing).
2. There are obvious mesh lines
Reason: Ink is too fast dry; the viscosity of the ink is too high, the fluidity is not enough; the mesh used is too thick.
Solution: Use a slower dry solvent to deploy ink; Dilute ink or add the thixotropic agent to reduce viscosity, and improve ink flow performance; Use higher mesh.
3. Poor ink drying
Reason: The selection of improper solvent, corrosion substrate (especially when printing soft PVC or coated nylon cloth is easy to produce); Too slow drying solvent, or insufficient drying time.
Solution: Choose the solvent suitable for the substrate; Choose a faster drying solvent or extend the drying time.
4. Ink adhesion is poor
Reason: The selection of ink and substrate do not adapt; the substrate surface is not clean, there is an oil or surface treatment agent (such as preservative/de film agent, etc.);
Some special materials, due to the surface tension being too low will affect the adhesion of ink; insufficient drying time, ink is not fully cured; adding too many additives or adding additives is improper; excessive addition of additives or improper ink.
Solution: Correct selection of ink suitable for the substrate; treat the surface of the substrate or replace the substrate;
Extend the drying time, so that the ink can be completely cured, especially for some chronic crosslinking ink (such as PET, PP, PE, etc., must be cured for a long time to have good adhesion; proper addition of relevant auxiliaries, too much defoaming agent will affect the adhesion.