Screen Printing 150 Questions (49-56)

â–¼49. Platemaking accuracy and what factors?

When making screen printing plates, platemaking accuracy is mainly related to the following factors.

(1) Screens include the types of screens used, the height of the screen mesh, the thickness of the wire diameter, the size of the screen opening area, the size of the screen expansion and contraction, the method of weaving the screen, and the color of the screen.

(2) Frames, including the material of the frame, the size of the frame, and the strength of the frame.

(3) The size of the tension.

(4) The choice of stretch angle.

(5) The method of bonding the frame and the screen.

(6) Pre-treatment of the screen.

(7) Photosensitive materials, including sensitivity level, resolution level, adhesiveness of photosensitive materials, expansion and contraction rate of photosensitive film, photosensitive film thickness and photosensitive film hardness, water resistance, solvent resistance, abrasion resistance, and resistance to printing The rate of high and low.

(8) The sensitizing agent blending time, the time after blending.

(9) Coating method of a sensitizer.

(10) Drying methods and conditions, including drying temperature, humidity, and drying time.

(11) Printing, including the type of light source used, the length of the exposure time, and the distance between the substrate and the light source during exposure.

(12) The density of the photographic plate master.

(13) Development, including developing methods: water development, warm water development, drug development; development conditions: temperature, soaking time, type and use of the water sprayer, and the like.

(14) Drying temperature and time after development.

(15) The choice of secondary exposure time.

(16) Revised edition.

â–¼50. How to deal with screen printing plate production?

Screen printing plate production is completed, to conduct a comprehensive inspection and post-processing. The processing method mainly proceeds from the following aspects.

1 Check the quality of the screen printing plate, including whether the picture and text are all developed, the picture and text points, lines are burrs, incomplete, broken pens, and the phenomenon of blocking the mesh, etc. If the above conditions are found, various methods should be promptly taken to remedy the situation. If it cannot be remedied, consider remaking the plate to ensure future print quality.

(2) Check whether there are bubbles, trachoma and near the end of the net frame in the omentum. The air bubbles and trachoma should be promptly remedied. The four-sided screen is screened to avoid ink leakage during printing.

3 Check whether the printing plate orientation mark meets the requirements of the printing sheet.

4 Glue the screen to the adhesive part of the frame with tape to improve the firmness of the screen and the frame.

5 paste the label, in the unified frame position on the paste version, indicate the following: the name of the print, color, color number, screen mesh number, plate number, photosensitive material model, plate making date, plate maker.

6 Transfer the complete set of plates to the printing process.

â–¼51 . How to keep screen printing plates?

The screen frame with a good mesh, the screen plate with good printing, and the screen plate that needs to be preserved after printing should be properly kept. If you do not save it well, you will not be able to continue to use it if it breaks the screen, causing it to be scrapped.

Screen frames or screen printing plates are usually stored on a stencil and stored in horizontal and vertical formats. The horizontal type is to place the same specification of the screen printing plate in a layer of the plate frame, which can be placed in an overlapping manner. Upright type is to erect the screen plate in the groove of the plate frame, and the larger screen plate is preferably used for vertical storage to prevent the screen plate from sagging. The last thing that should be mentioned is that, regardless of the form in which the plates are stored, the dust of the screens cannot be ignored.

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.