Optical Screen Printing Process and Its Key Points

Silk screen printing is an abbreviation for screen printing. For silk screen printing, it is mainly composed of screen printing screen printing and printer operation. Each of these two parts is different in its focus, but mutual support and mutual restraint are complementary. Any mistake in the whole process of screen printing work will affect the final screen printing effect on screen printing work quality. Therefore, the system introduced to improve the quality of screen printing and the work to be done should all be considered from the overall process. Only in this way can it be more effective.

In order to facilitate the description of the problem, in fact, the specific work content in the whole process of screen printing work can be roughly divided into the following detailed steps:

In the production of screen printing screens: stretch net -> wash net -> coating photosensitive paste (paste film) -> drying net -> developing net -> drying, sealing trap -> Paste these several processes.

In the printing operation are: the control of the printing machine -> screen alignment adjustment -> based on the initial selection of ink brands and scraper hardness -> special effects when the need to adjust the oil -> disc on the machine printing Pre-cleaning process (machine table, disc)-->Sampling and control of printing quality in the process of printing boot-->Selection of printing surface and information surface-->Disc, packaging, packing--> Counting, registering and filling in forms --> handling warehousing, roughly the above.

Each specific job has some matters and requirements that one should pay attention to. After the operators clarify these requirements and precautions, they will be more clearly aware of the cause and effect of the printing defects, and will greatly improve the quality of work in all processes so as to improve the quality of screen printing.

Stretch net

First, some things that should be noted during the stretching process:

1, iron frame surface treatment. Go to gray sand, degreasing, deburring. Dust and dirt can cause the glue and the iron frame to be loosely bonded. Burrs and sand may puncture the mesh when it is fixed, causing the entire panel to break.
2, pre-coated adhesive mesh. The thickness of the pre-coated adhesive on the frame should be moderate and uniform. The adhesiveness of the glue is too thin and the adhesion force of the iron frame is not easy to be pulled out by the tension; if the glue coating between the mesh cloth and the iron frame is too thick, it is easy to increase the ductility of the coating to easily shrink and deform during the drying process; The unevenness of the layer causes troubles in bonding and even breaking of the net when fixing the net.

3, the placement of the frame angle. When the number of film lines is too high, several screens with different angles should be drawn. However, under normal circumstances, it can be an angle. In theory, when the angle is 22.5 degrees, the picture and text of the film is the least affected by the screen interference, and its reproducibility is the best.

4, clip net. The net clips on all sides of the stretcher should be in the middle of this side. When gripping the mesh, the warp and weft threads of the mesh should be held parallel to the mesh and kept as straight as possible. Sometimes the screens that come out of the sun only have a moiré pattern in some areas because the meshes are not straight and have a curved surface.

5, early pull. Because of the weaving properties of the screen, it is required to slowly apply force during stretching to facilitate the adjustment of the shape of the mesh and the acceleration of tension relaxation. At the same time, it is also possible to prevent the danger of net breakage when the tension is pulled down to a high tension, and it is only stretched to about 60% of the rated tension when it is pulled.

6, re-pull. The loss of tension is compensated once every 15 to 20 minutes, and tension is repeated until the tension is stable at the rated value. Generally, it is necessary to repeatedly tighten three times or so, and when the retensioning measurement tension is stopped, the tension values ​​of the net yarns in the five positions of the stretch netting machine and the center in the warp and weft directions should be approximately the same. The tension is not as great as possible. Excessive elasticity beyond the material limits the screen to become brittle and easy to tear. The lack of tension in the screen also lacks resilience, and it is prone to elongation during printing. The tension ratings of different specifications are different: The common specifications are as follows:

Tension at the beginning of pulling tension after retraction
140-31 Y TW 15N/CM about 18-20N/CM
165-31 Y PW 15N/CM left and right 18-21N/CM
165-34 Y TW 17N/CM left and right 19-22N/CM
180-27 Y PW 15N/CM Left and right 18-20N/CM

The specific conditions will be appropriately adjusted according to the objective conditions in the process of pulling the net at that time, but the Henderson press design requires that the screen tension should not be less than 18 N/CM.

7, fixed network. It is the use of glue to bond the mesh cloth to the iron frame firmly. If a thick and uniform color appears on the surface of the adhesive network when the net is fixed, it indicates that the adhesive is sufficient. If there is a light-colored area, it indicates that there is insufficient adhesion of the adhesive in the area. When fixing the network, you should try not to let the glue drop into the printing area of ​​the screen. Because when the net is cleaned, a slight carelessness in removing the glue during the wiping process may cause scratches on the net cloth.

8, the whole edge, mark. Stretched screens are best labelled with mesh specifications at the convenience of the frame. If there are different pull angles, it is best to specify the angle so that it is convenient for repeated use.

(to be continued)