The specific operation of plate making can be divided into such steps as washing net→drying→coating (foil)→drying→exposure→development→middle edition→drying→sealing→paste. The specific approach is described below.
1. Wash net
Washing the net is a stain and grease on the screen plate. Dust and other clean, so that the photosensitive layer on the screen has a better adhesion, thereby increasing the screen printing resistance. Note that when you wash the new screen, it is best to grind the surface of the screen with a grind. For repetitive screens, you should carefully remove ghosts on the screen. A simple way to determine if the screen is clean or not is to see if the surface of the mesh can be evenly covered with a film of water.
2. Coated sensitized film (or capillary film)
Whether it is coated with photosensitive adhesive or photosensitive film, the purpose is to form a thick layer of uniform photosensitive coating on the screen.
(1) Several problems that should be paid attention when coating photosensitive adhesive
1 The screen must be completely dry before coating.
2 The edge of the sizing machine used for coating should be smooth to avoid scratching the mesh.
3 The adhesive should be coated evenly, and the thickness should be adjusted according to the characteristics of the printed graphic.
4 Photosensitive adhesive should not be placed in the sizing device for too long. The coated screen should be placed in a dark place to avoid light exposure.
5 The photosensitive layer should be completely dry, otherwise it will lead to loose adhesion, but the drying temperature can not be too high, should be controlled at about 40 °C.
6 The coating sequence is the first step after the printing surface is coated with ink,
(2) Transfer method of capillary photosensitive film
1 Wet the washed screen to form a uniform film of water on the surface.
2 Carefully attach the emulsion surface of the capillary photosensitive film to the water film.
3 Use a spatula to remove excess water.
When attaching a film, care should be taken to avoid air bubbles and dust, and the applied force should be even when scraping off excess water. At the same time, excessive moisture should be avoided to form flow marks in the diaphragm area.
3. Sunnet
Sunnet refers to the process of using photopolymer to cure with UV light and no longer dissolve in water, and transfer the film and graphics to the screen.
(1)Film. The first is to select the angle at which the film is placed on the screen according to the characteristics of the film. The purpose is to avoid moire, because of the mesh characteristics of the mesh weaving and the mesh properties of the mesh adjustment film, it is easy to hit the mesh when the grid meshes of the two are superimposed, forming some irregular lines, namely moire, However, the purpose of reducing or eliminating the moiré can be achieved by adjusting the intersection angle of the cable. The actual angle selection method is to superimpose the dot film on the stretched screen to observe the light, and rotate the cable to the film and the wire of the mesh does not produce obvious marks. Line up.
(2) Exposure. Exposure screen is best placed directly above the exposure light source. The exposure time should be based on the depth of the film and the power of the exposure light source. The distance between the exposure light source and the screen is adjusted appropriately. Be sure to wait for the vacuum to stabilize before starting the exposure light source.
In this process, special attention should be paid to screen printing due to the limitations of its plate making methods and screen materials, and there are also some requirements for printing plates. The film side of the film should face upwards and should be positive. The number of lines of the film should match the specifications of the mesh used. The higher the number of lines, the higher the requirement of the mesh, and the higher the flowability of the used ink, the better the effect of the printed image.
4. development
(1) The development must be sufficient. The uncured photosensitive film must not have any residue, and the cured photosensitive film cannot be washed away.
(2) The development time cannot be too long, otherwise the photosensitive layer will swell and the adhesive force will decrease, which will affect the resistance to printing.
(3) The pressure of the water gun during development should not be too large, and the spray should be uniform.
(4) When developing, if it is a film with a gradual effect, it should try to avoid direct flushing with a high pressure water gun.
5. Closure
(1) The screen should be carefully observed before the application of the net, and the bad phenomena such as the presence of sand holes and film layers on the screen should be promptly repaired.
(2) Seal all the areas other than the graphic that should not be transmitted through the ink with the sealer paste. The plugging should be done as much as possible to flatten the plugging paste and not to form rugged crucibles so as not to scratch the adhesive during printing.
6, paste network
Sticking web is a very important process and should be given enough attention. Many defects in the printing process are caused by the lack of attention when attaching the web. Sticking to the net should be based on the idea that "the sharpening of the knife does not mistakenly cut the firewood." For some areas where the photosensitive layer is often damaged during printing, it should be protected before the machine, such as the inner ring of the photosensitive diaphragm and the outer edge of the outer ring.
When affixing the web, it should also take into account that different machines have different requirements for stencil sealing and need to be properly adjusted. The viscosity of the ink also has a certain influence on the distance of the position attached to the web.
This part of the plate making process is of utmost importance. The quality of the printing process throughout the printing process is directly related to the printing effect.