Screen printing 1000 questions (52-57)

â–¼52. What are the main technical requirements for screen printing on plate making?

The main technical requirements of screen printing for plate making are as follows.
1 The photosensitive material should have good photosensitivity and high speed.
2 The photosensitive material should have good preservation.
3 Screen printing plates should have good workability and should be easy to operate.
4 The screen printing plate should have high anti-printing force and good abrasion resistance.
5 screen printing plates must maintain a certain degree of accuracy.
6 Screen printing plates should have high water resistance and solvent resistance.
7 Photosensitive materials should have strong film-forming power, high resolution, and do not require special temperature and shadow development.

â–¼53. What are the main technical requirements for scrapers?

In screen printing, ink is formed by moving a squeegee through a screen plate under a certain pressure and transferring it onto a substrate to form a graphic. Therefore, various indicators of the scraper affect the printing effect. Due to the wide variety of substrates and their different shapes, they can be broadly divided into two types: flat surfaces and curved surfaces (including spherical surfaces). Therefore, the following factors should be taken into account when selecting the squeegee according to the shape of the substrate and the surface of the substrate. .
1Scraper Hardness The amount of ink transferred and the reproducibility of graphics and text are related to the hardness of the scraper. Generally, when printing on a hard substrate, a soft scraper can be used so that the pressure applied during the scraping can be used to make the scraper hardness. The layout is in full contact with the substrate to improve the printing effect. On the other hand, when printing soft substrates, rigid squeegees are used to make the stencil and the substrate in good contact. The reason is the same. Due to the wide variety of substrates, the substrates are also different. Generally, a harder scraper is used for the smoother substrates. On the contrary, the softer squeegee is more ideal for printing. Scraper due to its application of a certain pressure in the scraping, the scraper will occur a certain degree of bending, therefore, when using the scraper, we must consider the scraper bending fatigue and mechanical strength, requiring scraper with a certain degree of flexibility. Scraper will generate heat due to friction at the same time as the scraping and printing. When the temperature rises, the hardness will change. When selecting the scraper material, it is necessary to select the material that is not easily deformed by heat. Generally, the hardness of the scraper material should be selected at the Shore hardness. 60 to 90 degrees is good.
2 The abrasion resistance of the squeegee is due to the direct contact between the squeegee and the screen printing plate, and friction occurs each time the squeegee is printed (up to tens of thousands when printing in the screen printing). Therefore, it is required that the scraper has good wear resistance, lubrication and certain mechanical strength, so that friction can be reduced as much as possible during scraping so as to ensure the service life of the scraper.
3 The solvent-resistant gender plate of the scraper should be used in contact with various inks and solvents, such as ethanol and gasoline. All kinds of rubber materials have different affinities for solvents. Scraper will change to varying degrees after contacting with ink or solvent. Commonly, the hardness of the scraper changes, and the volume expansion after contact with the solvent is deformed. If the squeegee expands, the edge accuracy of the squeegee will be reduced. When printing, ink leakage will be uneven and affect the printing quality. It is generally believed that a rubber with a high hardness has a large cross-link density, and molecules of the ink and the solvent are hardly immersed in the molecules of the rubber, so the coefficient of expansion is small. In the selection of the wiper can be considered in the premise of meeting the printing requirements as much as possible, in order to minimize the deformation, choose a high hardness rubber scraper.

â–¼54. What are the main materials used for scraper?

Since the squeegee is exposed to various inks and solvents in the printing and requires high abrasion resistance, it has a certain hardness. In order to meet the screen printing requirements, the materials used for making the wiper are generally natural rubber and synthetic rubber. The scraper used in the printing and dyeing industry is mostly made of natural rubber. The scraper on the screen printing machine is mostly made of silicone rubber, and the scraper made of natural rubber, synthetic rubber and polyurethane rubber is used in manual printing.

â–¼55. What are the common specifications for scrapers?

Screen printing squeegee specifications generally refer to market specifications. In use, the length of the squeegee is determined according to the use requirements. There are two kinds of squeegees that are sold on the market. One is a squeegee on which a handle or a jig has been mounted. The squeegee can be directly used for printing by selecting an appropriate length according to use. The other is a scraper rubber strip that can only be used after the rubber strip has been installed.

â–¼56. What is the function of the ink wiper?

Screen printers, such as the NOVAMEC S-type screen printer, have two squeegees. One squeegee is a squeegee and the other squeegee. The squeegee squeegee and the ink squeegee are alternately moved back and forth during the operation of the printing press. When printing, the squeegee squeegee presses the ink for printing, and the squeegee squeegee is lifted off the screen printing plate after the return stroke. The ink delivery squeegee starts to work, the squeegee contacts with the screen printing plate, and the ink is sent back. The working procedure of the squeegee squeegee and the ink supply squeegee is: Squeegee squeegee prints ink from the screen plate. One end (starting end) is squeegeeed to the other end (end). In order to make the squeegee squeegee re-squeegee with enough ink, the ink delivery squeegee must scrape the ink back to the original position of the ink. Therefore, in addition to the squeegee squeegee, the screen printer must be equipped with a squeegee blade for returning the ink, and then scrape the ink scraped to the end of the screen plate. In addition to ink delivery, the ink delivery squeegee also serves the purpose of blocking the mesh portion of the graphics and text with ink, so as to prevent the ink in the mesh from drying and affect the printing of the next time (sheet). Ink scrapers are mostly aluminum or metal products.
For manual squeegee printing, only one squeegee squeegee is used, and the squeegee is used for printing and ink return.

â–¼57. What preparations must I make before printing?

Preparing for printing is an indispensable task for ensuring the smooth progress of printing. Before printing production, the following basic preparations must be made.
1 Clear up the printing site to ensure that there is a certain operating space around the printing table or printing machine to prevent other objects from obstructing work. Keep the site clean and avoid the effects of dust, etc. on the print quality.
2 Pay attention to adjust the humidity and temperature of the printing shop to meet the printing requirements.
3 Prepare a suitable squeegee and inspect the squeegee for any bruises. Grind the squeegee if there is a scratch to prevent it from affecting the print quality.
4 Check whether the screen printing plate is in good condition, and find that the problem is corrected in time to ensure that the screen printing plate is surrounded by the screen and text to avoid the phenomenon of ink leakage in the non-graphic part. Wipe the plate with a damp cloth to remove any dust on the plate.
5 According to the characteristics of the substrate, adjust the appropriate gap between the screen printing plate and the substrate.
6 Check that the color and viscosity of the ink used meet the requirements.
7 According to the size of the substrate, determine its position on the printing table. Fix the rules for printing auxiliary equipment.
8 Make preparations for using drying racks and other drying equipment. If using a dryer, adjust the drying temperature in advance. Prepare for the above inspections and start printing.
In addition, according to actual needs, we must pay attention to other related preparations.

--Qi Lu Graphic Arts