Fine mesh screen printing technology six questions and answers

Q: How to locate multicolor overlays?

Answer: In order to meet the accuracy of multi-color overlay printing, the key to printing is to master the positioning method. There are four types of positioning commonly used in multi-color printing.

Edge positioning method is suitable for straight-edge workpiece printing; hole positioning method is suitable for high-precision imprint printing of the same graphics; coincidence positioning method is suitable for transparent color material overprint; border positioning method is suitable for special-shaped workpieces in the printing. In four-color screen printing, whether manual or mechanical printing, the positioning accuracy error is equal to zero. In printing, suitable positioning methods can be selected according to business requirements.

Q: How to determine the screen tension and grid spacing?

A: The screen tension has a great influence on the ink transmittance. For example, the tension below 25 N/cm cannot be printed on the small dots in the high light area. After the tension is increased to 5~10 N/cm, fine dots can be printed.

It is not advisable to increase the tension of the screen by increasing the distance between the screens. Increasing the net pitch has the effect of increasing the screen tension, but the net pitch is increased, and the pressure of the scraper is then increased, and the printing dots will increase. Therefore, it is not possible to increase the screen tension by using a method that increases the distance between the screens. The correct surface tension should be set when the screen is stretched.

Q: How to master the scraper in the mesh version?

Answer: 1. The role of the scraper: the size of the printed matter ink depends not only on the pressure of the scraper but also on the scraping angle of the scraper and the layout, the scraper hardness, the scraping speed, the shape of the scraper edge, etc. .

Japanese friends said that mastering scraper technology requires three years of effort to illustrate the importance of mastering the scraping technology.

2. Scraper edge shape: scraper edge shape as many as 7 kinds, commonly used square mouth and round mouth. Fabric printing multi-use round mouth scraper.

3. Scratching angle: theoretically the best angle 45 °, scraper edge and layout of the smallest contact area. However, in actual operations, the squeegee angles are all greater than 45 degrees, and some even reach 65 to 80 degrees. The common angle is 75 degrees.

4. Scraper pressure and ink master: increase the squeegee pressure, the thickness of the missing ink layer is also increased, mechanical squeegee, scraper pressure has a special mechanical control and adjustment. Hand-scraping mainly depends on the printing experience. The pressure is too thick and the darkness of the mesh is darker. The 50% outlets have serious angles, and 80% of the outlets are on the ground. The pressure is too small, the ink layer is thin, the dark tone level can be reproduced, and the high-profile and fine dots are lost. Only with moderate pressure, all press lines are straight and the pressure is consistent to print high-quality prints with rich color balance and rich layers.

Q: How to master ink thickness?

A: The screen printing ink thickness is 1/3~1/4 of the screen printing plate thickness. The thickness of the ink layer consists of five major elements in the screen printing (screen, squeegee, ink, substrate material, screen printing machine performance) and five major variables (squeegee angle, mesh distance, printing pressure, and squeegee speed) The correct operation of the ink viscosity and the selection of high quality materials are determined. In actual printing, to increase the thickness of the ink layer 3 to 4 times, it is necessary to increase the film thickness of the printing plate to achieve. If the thickness of the printed ink layer is 25 μm, the thickness of the screen should be set to 75 to 100 μm.

Q: How to adjust the loading and printing press?

A: When loading the plates, press the plates in the printing order, confirm the printing position, and perform debugging.

1. Mechanical adjustment: adjust the printing press, upper edition. Find a good rule, determine the distance. The network distance is generally determined to be accurate. In order to achieve a good overprint accuracy, the network distance must be set lower, about 3 to 4 mm, and the small frame should be set to 2 to 3 mm, and the large format can be set to a high level, 5 to 6 mm. The parameters of the pitch are determined according to the size of the screen and the degree of tightness of the stretch.

2. Preparation of Scraper: At present, polyurethane or oil-resistant silicone rubber scraper with soft and hard moderate degree is used. Scraper hardness is calculated in Shore hardness. Generally four, 40~45 degrees for the low hardness scraper, 50~55 degrees for the hardness scraper, 60~65 degrees for the medium hardness scraper, 70~75 degrees for the hard scraper. The printing platform should use a hard scraper with a scraper thickness of 10~12 mm. The length of the scraper depends on the size of the frame, generally 20~30 mm wider than the sides of the figure.

Q: How to clean the plate?

A: The plate material should be processed after screen printing is stopped. Otherwise, the printing quality will be affected. When the printing is completed, the plate should be cleaned immediately with the corresponding solvent, and no ink should be left to prevent the residual ink from blocking the screen and re-printing the tone.

When the printing stoppage is more than 15 hours, it should be stopped after the plate is washed. When cleaning, use paper or plastic cloth to cover the stamp pad and level the plate.

1. Wash the plate gently in the tank and gently scrub it. Do not wash it in order to avoid affecting screen tension and loose mesh.

2. Color tone printing should be continuous production, in multi-color printing, the interval between the previous color and the next color should not exceed 1 d (days), in order to avoid the substrate stretching or printing ink glass, affect the screen printing quality.