â–¼46. What is the principle of screen printing plate imaging?
From the foregoing, it can be seen that the screen is formed by weaving a certain material, and the latitude and longitude lines intersect to form a mesh. During the process of plate-making, a certain thickness of photosensitive resist is coated on the screen and dried, and a photosensitive film is formed on the screen, and then the positive-texture plate-making negative film and the coated screen are attached and exposed by a human exposure machine. In this way, the graphic portion of the screen is not cured due to light reception, and the non-graphic portion is cured by light. After developing and rinsing, part of the uncured photosensitive material is washed away, and the screen hole is a through hole. The non-graphic part of the photosensitive material solidifies the mesh. When printing, the silkscreen hole in the graphic part leaks ink, and the non-graphic part does not leak ink, thus obtaining the printing ink. This is the imaging principle of screen printing plates.
â–¼47. How is the screen printing plate developed and fixed?
Screen printing plate production process is relatively simple, with the continuous emergence of new photosensitive materials this feature is more prominent. Use modern photographic materials to make screen printing plates, use photographic plates and stencils coated with photosensitive materials to fit the printing plates, and put the frame in water, warm water or pharmaceutical water for about 10 minutes after printing, and the graphic shows Come out (different photosensitive material development time is also different). Then, the screen printing plate was gently scrubbed with water in a sponge, so that the mesh part of the picture and text basically became a through hole. Then the pressurized water is sprayed to remove the unexposed material left in the graphic part, so that all the screen holes in the graphic part are changed. Finally, the water mark is wiped and dried to make a screen printing plate.
â–¼48. How to determine the thickness of screen printing plate?
The thickness of the screen printing plate refers to the thickness after coating the photosensitive resin on the screen. That is, the thickness of the screen printing plate is equal to the sum of the thickness of the screen and the thickness of the photosensitive film.
The thickness of the screen printing plate is determined according to the printing requirements. Usually the height of the ink layer after printing is closely related to the thickness of the screen printing plate. Under normal circumstances, when the screen printing plate used is thicker, the ink layer after printing is used. On the other hand, if the screen plate used is thinner, the ink layer will be lower after printing. In special cases, it is required to use screen printing plates of thick-film photosensitive materials with a thickness of up to 1 mm. For example: Making Braille The thickness of the screen printing plate is generally between 0.1-0.250 mm.
With the direct platemaking method, the thickness of the screen printing plate is obtained by coating the photosensitive resist several times. The coating is applied once and dried once. The required thickness of the screen printing plate can be obtained by performing the cycle operations in sequence.
In the case of indirect plate-making or direct-to-plate printing, the thickness of the screen printing plate is obtained by selecting different thicknesses of the photosensitive film according to the printing requirements.
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.
--Qi Lu Graphic Arts