Silk Screen Printing Technology and Details (Part 2)

Fourth, indirect diaphragm law network printing plate


The indirect diaphragm market is available for sale. The thickness of the diaphragm can be selected according to the characteristics of the print. The indirect diaphragm production screen is mainly used to achieve fine lines and dot-level printing, and generally does not require too thick ink layer. The thicker the film thickness, the thicker the printing ink layer, and the thicker printing ink layer will roughen the layering.


Indirect membrane method of film formation process for the printing film and indirect film adhesion → exposure → development → rinse → transfer photosensitive film → drying → sealing network.


1. exposure


The emulsion film with the cut indirect film facing downward is placed on the pad of the printing machine, the emulsion film of the printing film is placed on the indirect film, and the vacuum is evacuated inside the cushion so that the printing film The position of the photographic film must be correct. The order of light transmission is the film base of the printing film → the film emulsion layer → the plastic film base of the indirect film → the emulsion layer of the indirect film.


2. Developing and rinsing


Development and rinsing are two completely different processes. Development is the dissolution of unsensitized sensitized film with a developer to make the graphic appear. Flushing removes the dissolved material from the plate with water.


Indirect film method of photosensitive adhesive is iron salt photosensitive adhesive, adhesive material is acrylic resin, high resolution, coated on PET film film flatness is quite high. The photosensitive film requires strict development conditions. Developing hydrogen peroxide solution. Manufacturers in the production of indirect film are prepared with a special development A powder and B powder, when used to produce a concentration of 1.5% of hydrogen peroxide solution. Rinse with water after development. The flushing pressure should not be too high.


The indirect diaphragm is developed by exposing the indirect diaphragm emulsion layer upwards and placing it in a developing bowl larger than the indirect diaphragm. The prepared developer is quickly poured onto the diaphragm and the liquid surface is submerged. After developing for 90s, the developing process should continuously shake the developing basin uniformly. The development process is a chemical reaction process, and the temperature will affect the formation of the image. The temperature of the image should be strictly controlled between 18 and 23°C. If the developing temperature is too high, the emulsion layer is easily detached; if the developing temperature is too low, the concentration of the H2O2 component in the developing solution, the concentration exceeding 1.5%, will damage the image layer, and if the rich bottom is less than 1.5%, the development will be difficult.


Rinse after development is very important, with the water residue will be washed off the film on the surface of the film, so that graphics and non-graphics more clearly separated. The smear on the indirect diaphragm surface is in a free state and is easily washed away by water. The method of flushing the ears is to remove the indirect film from the developing disc and put the emulsion layer up on a flat surface and rinse it with warm water of 37-40°C for a few minutes until the unexposed film is completely washed away. Then use a little lower temperature than room temperature to rinse the film for about 30 seconds to stabilize the latex layer so as not to damage the image edge during transfer.


3. Diaphragm repost


The bottom layer of the indirect membrane is coated with a water-soluble adhesive, which makes it very easy to transfer the photosensitive membrane to the surface of the screen. Flatten the emulsion layer of the indirect membrane with the developed rinse ear facing upwards. Wet the two sides of the screen with the adhesive solution. Place the screen printing side down and hold both sides of the screen with your hands. At the same time, slowly put on the indirect diaphragm, so that the diaphragm is in the exact position, and pay attention to prevent the text from being scratched. Scrape the screen with a squeegee so that the water passes through the mesh so that the screen surface is in close contact with the emulsion layer of the indirect diaphragm, and then the newsprint and a clean fleece are used to draw water from the squeegee.


4. dry


Screen drying is a critical process. Drying is not complete, the residual moisture in the adhesive layer will cause the screen plate to be brittle, the resistance to printing force will drop, the graphic image will be rough, and the pinholes and adhesive layers will be sticky and soft. The indirect diaphragm method often needs to be dried before the film is peeled off. Due to the blocking of the film base, it is difficult to evaporate water. The screen plate can be erected and blown with an electric fan to the squeegee surface of the screen plate for wind drying. If it can be combined with the drying box, the drying effect will be better, that is, vertical drying for a period of time, peeling the film base and putting it into the drying box to further dry it.


5. Closure


Sealing net refers to sticking the non-inked screen through holes on the dried screen printing plates with glue, so that when the printing plate is inked and printed, the ink does not overflow and leak and cause product sticking.


V. Direct Diaphragm Screen Printing


Direct diaphragm market, direct diaphragm and indirect diaphragm structure is basically the same, but the coated sensitizer is diazo sensitizer, direct diaphragm is supported by PET film, diaphragm base will not be deformed, flatness is very it is good.


The process of film formation of the direct film is a cutting film → transfer film → film lamination → drying → exposure → development → washing → drying → sealing.


1. Diaphragm repost


Diaphragm transfer is to put the cut direct film emulsion layer up on a flat surface, wet the screen with veneer on both sides, lift up the wetted screen plate, and turn the screen printing surface down. Slowly place it on the direct diaphragm and place the diaphragm in the middle of the screen. Scrape the mesh with the scraper, so that the water passes through the mesh so that the screen surface is in close contact with the emulsion layer of the direct diaphragm. Use a newsprint or a clean flannel to draw moisture from the squeegee side.


2. Laminated thickening


The screen printing product has a thick ink layer and a strong three-dimensional effect, which is far more than offset printing, flexo printing, and gravure printing. This is mainly due to the ease of control of the screen thickness and the film thickness. The advantage of the direct diaphragm is not the level of printing, but rather the three-dimensional strong fine graphic printing, so only by the increase in the thickness of the ink layer can not be achieved, the need to use lamination to increase the thickness of the version of the film.


After the film is dried, the screen plate is dried and the film is placed in a sink. The screen is placed in the sink with the printing surface facing upward. The water is immersed in the screen for about 25 cm. Another direct film is immersed in water with the emulsion layer facing down. Press on the screen plate, then put the screen plate out of the sink, scrape the printing surface with a scraper, so that the moisture and air between the two layers of the film overflow, and then use sponge or paper towel to absorb water, so as to increase The thickness of the plate. Laminating is the advantage of the direct diaphragm method. It has the characteristics of thick and uniform film thickness. It can not only obtain the thick film version of the screen plate for direct legal use, but also can obtain the same screen plate as the indirect film method. Ink uniformity.


3. exposure


The direct diaphragm method is the same as the indirect method. The exposure is performed after the plate is formed on the surface of the screen. When the direct diaphragm method is used to print, there is a slight gap between the screen and the film, which affects the accuracy of the exposure. Sexuality has an impact on the quality of screen images.


The exposure operation, the position of the printing film and the printing film must be correct, and the light transmission order is the printing film base → the printing film emulsion layer → the printing film system. The emulsion layer of the printing film is close to the printing surface of the screen, so as to reduce the scattering phenomenon of the photosensitive film exposed by the light source to reduce the latent corrosion of the photoresist.


4. Development and washing


The direct diaphragm method uses a diazonium salt emulsion, and the direct diaphragm is exposed. Its non-photosensitive cross-linking component can be dissolved in water, so the development can be directly used with water.


The direct diaphragm is blocked by the wire mesh. If the flushing ear listens to too low pressure, the smear particles will clog the mesh, and it is difficult for the purple to flush the surface to meet the requirements of the printing plate. Direct diaphragm development requires a high pressure water jet to rinse with strong water.


5. dry


The direct membrane method and the indirect membrane method dry the same, but some aspects should be noted. Laminated direct film, if not completely dry, will cause the interlayer adhesion to weaken, leading to exposure in the photographic method if the screen is not fully dry, the sensitivity of the photosensitive adhesive will decline.


6. Closure


The sealing net is to block the non-inking screen mesh on the screen plate with the glue liquid. When the printing plate is inked and printed, the ink will not leak out and cause the printing product to be contaminated.


Screen printing is a complicated task, and many factors affect the quality of the printing plate. In the plate making, we must strictly follow the manufacturer's plate-making materials, such as the use of the degreasing grinding agent and the application requirements of the sensitization chest. At the same time, it must be matched with all the mesh fabric variables. Such as the height of the screen mesh, the thickness of the wire diameter, the size of the screen opening area; the material of the frame, the size of the frame and the strength of the frame; the selection of the angle and tension of the stretch net, the frame and the screen Adhesive method; Sensitivity and resolution of the photosensitive adhesive, Adhesion of the photosensitive adhesive, Stretch rate, Hardness, Thickness; Solvent resistance and rub resistance, and sensitizer loading time and blending time, photosensitive coating Cloth method, drying method, drying temperature and humidity and drying time; printing plate type light source and type, exposure distance of light source, exposure time, developing method, developing temperature, developing time and the like are all related to the printing plate resistance.



Source: PACK, CN

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