Reasons and Solutions for Screen Printing Network Expansion (2)

Mesh developed after drying

The specific manifestation of this failure is that the graphic part of the ink on the dried surface appears to be transparent, but the surface has a thin layer of “water film” that affects the overprinting of the screen when printing. The picture is incomplete. This problem can be analyzed from two aspects. First, the operation, drying time is not enough, the drying temperature is too high (normally 40 ~ 45 °C), the recovery screen plate is not net and so on. If this is not the reason, the problem lies in the photosensitive material. Experts analyzed that the main reason for this phenomenon is that the photosensitive adhesive contains too much resin (such as epoxy resin), and partial cross-linking reaction occurs before exposure. , and attached to the entire mesh, forming a transparent layer of "water film"; if the exposure time is insufficient, the resin in the photosensitive resin can not be fully crosslinked, in the drying oven, the resin crosslinks, will also form a water A "water film" with a resin. When this phenomenon occurs, the operator touches the photosensitive layer by hand, and feels that the adhesive layer is slightly sticky and has a clear watermark when it is erected and dried.

The way to avoid "water film" is:

1 Adding a photosensitizer in the photo-resist so that the resin in the photo-resist is fully exposed to a photo-sensitive cross-linking reaction;

2 extended exposure time;

3 The drying temperature should not exceed 45 °C to prevent the cross-linking reaction of the incompletely cross-linked resin from occurring at high temperatures and sticking to the mesh.

Sensitive adhesive and mesh are not firmly bonded

In the printing process, when the film-breaking failure caused by the weak adhesion between the photosensitive adhesive and the mesh cloth occurs, the first reason is to analyze whether it is the degreasing of the new wire cloth and the removal of the screen plate due to the analysis of specific reasons. In addition to incomplete results, the printing time and the quality of the emulsion are also important factors. If it is entirely detached, it means that the drying time is not enough or the exposure time is short in the coating process of the photographic emulsion; if both of these data are normal, it may be caused by the expired sensitizing glue; in addition, if the photographic emulsion is mixed with oiliness Substances also produce release phenomena. The solution is very simple: clean the screen thoroughly; check the production and shelf life of the sensitized adhesive. If it is determined to be a problem with the sensitized adhesive, replace the sensitive material in time; if the exposure time is inappropriate, perform the exposure test to determine the correct exposure. In addition, it is necessary to ensure that the screen is completely dry both in the coating process and after development.

How to improve the screen printing resistance

To improve the screen printing resistance, first of all to enhance the adhesion of the photosensitive adhesive and mesh, which is the basis of screen printing.

You can control the screen quality from the following points in the platemaking process:

1 Degreasing thoroughly;

2 Photoresist can not have grease pollution;

3 The oven should be clean, and the screen plate coated with sensitized adhesive can not be put together with the screen plate cleaned with solvent;

4 The photosensitive layer must meet the corresponding requirements and must not be too thick or too thin;

5 When printing, the exposure should be sufficient. After the development and drying, proper sun drying can enhance the screen printing resistance.

Second, in the printing process to reduce friction on the screen, such as:

1 The photosensitive adhesive and ink cannot have any fine impurities;

2 The workshop is kept clean at all times, it is recommended to use a vacuum cleaner;

3 printing ink is best not to use large particles of ink, such as the use of sand, silver sand, you can choose to use fine sand and fine silver sand;

4 When printing, the use of slow-drying solvents is more appropriate, because fast-drying solvents can easily cause screen blockage, directly affecting the speed of squeegee printing and resistance to printing forces.

5 The yellow light should be used for the printing lamps so as to avoid the photo-curing and brittleness of the non-graphical photosensitive resin in the printing process, which affects the screen printing resistance.

In particular, Professor Zheng Dehai emphasized that to improve the screen printing resistance, we must also regulate the existing production process, especially some small factories. We must strictly follow the plate materials provided by the manufacturer in the plate making process, such as the degreasing grinding agent and sensitization. The use of glue is required to be done while also matching the variables of the mesh used. 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 choice of the angle and tension of the stretched 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 abrasion resistance, as well as the sensitizer residence time and blending time, coating of the photosensitive adhesive Methods, drying methods, drying temperature and humidity, and drying time; type of light source used in printing, exposure distance of the substrate, exposure time, developing method, developing temperature, developing time, etc. are all related to the improvement of the printing resistance of the screen.

(to be continued)