Experts talk: screen mesh problems (on)

In the screen printing, the screen is the support of the screen, and the good combination of the screen and the photosensitive or photosensitive film is the basis for the smooth progress of screen making and printing. How to improve the firmness of the screen and the stencil in the process of making the screen and improve the stencil resistance of the screen has always been a concern and research issue of screen printing operators and technicians. It is not difficult to see from the feedback results of interviews and questionnaires issued by some companies in the screen printing industry from CoinMedia recently that 100% of the respondents are deoiling and recycling the screens related to screen quality in screen printing production. How to remove the screen and how to improve the printing resistance of screens raises their own questions.

In fact, it is clear to those who are engaged in screen printing that one of the necessary ways to improve the fastness of screens and stencils is to clean and roughen the screens to increase the wettability of the screen surface. There are two aspects, one is the cleaning, degreasing and roughening of the new mesh, and the second is the removal of the old screen. In addition, there are a wide variety of grinding pastes and film removers used for roughening screens and removing films, and the effects of their use are different. Why are there still many problems in screen printing production? This is a positive word in the screen printing industry spread a word: screen printing will see it, do it silly. Therefore, it is necessary to continuously summarize the experience and guidance of experts in order to combine the materials and processes correctly and flexibly and apply it to the actual production of various screen printing.

To this end, Ke Yin Media consulted senior screen printing experts, Mr. Zheng Dehai, Vice Chairman of the China Screen Printing and Imaging Association, Mr. Jiang Shengjing, Deputy Director of the Beijing Screen Printing Technology Research Institute, and Technical Center of Hunan Changde Jinpeng Printing Co., Ltd. Ms. Li Haifang, an online printing expert of the General Department, and Ms. Yin Fuxia, Sales Manager of Shanghai Yarn Mesh Co., Ltd., asked them to provide targeted answers to some very specific production issues and summarized their views as follows.

Degreasing and roughening of new mesh

At present, the screen materials used for screen printing are mainly polyester screens and nylon screens. According to our investigation, polyester screens are characterized by good dimensional stability, high tensile strength, and good resistance. In the screen printing of products, the usage rate has accounted for 95%. However, since the polyester web is hydrophobic, the water-based screen sensitive adhesive is not easy to produce good wetting, and the combined fastness with the photosensitive adhesive film is poor, and the adhesive film is easily detached during printing. Therefore, the degreasing of mesh fabrics, especially polyester fabrics, is an important part of screen printing plates, which can greatly improve the fastness of the adhesive film and the screen, and improve the resistance of the screen. The experts proposed several effective degreasing methods based on the usual technology accumulation and the experience gained in guiding the production of screen printing plants.

1) Apply household laundry detergent, 20% aqueous caustic soda solution, or a commercially available screen cleaner to wipe on the mesh and rinse with a spray gun. The degreasing effect of this method is good, and the wetting performance of the photosensitive adhesive and the mesh cloth can be obviously improved. The feature is economical and convenient, but it has little effect on the coarsening of the screen.

2) Experts advocate that the degreasing and coarsening of the mesh should be carried out at the same time, that is, degreasing and roughening of the mesh using a degreasing product with a grinded mesh, such as the commonly used “Yarn Degreasing Agent” and “Ke Tu "Thai Mill Paste" is an ideal product for degreasing and coarsening of mesh cloth, which has been approved by many screen printers. Professor Li Haifang reminded the reader that if a single type of grinding paste is used, it must be de-oiled again, and a concentrated degreasing agent can be used for the treatment, so that the degreasing effect is good and the speed is high. It should be noted that both sides of the screen should be polished with a degreasing agent, and the other side should be ground immediately after polishing, and water cannot be used in the middle. Otherwise, grease will remain on one side of the screen. Unlike grinding with a greasing cream, the brush used for grinding should be a large brush with softer hair and higher density. After all the mesh cloth is polished with degreasing agent, it should be washed as soon as possible. Never use a high-pressure water gun to flush. Only use normal water pressure to clean the screen. After washing, do not allow the screen to touch anything, especially not touching it. Place it directly in a clean oven and dry it.

3) Mr. Jiang Shengjing also taught a simple and economical method of grinding, that is, smearing with squid bone powder on the new mesh, directly grinding, and its degreasing and roughening effect is also very good. However, in order to avoid the powdered mesh of the cuttlefish bone, use a high pressure water gun. Interested readers may wish to try.

Screen recovery film

For some small-screen screens, most manufacturers will need to recycle and remove the membranes before applying them again. Some small factories even have to recycle dozens of times. There are two kinds of problems often encountered in the recovery and removal of the film. First, after the film is treated, there is a residual film on the mesh cloth. Second, due to the printing materials used in the printing, such as ink, paste, etc. in the printing process, and the mesh cloth And remain on the net cloth, resulting in "ghosting", and the darker the color of the printed material or paste, the more obvious "ghosting". The experts analyzed the problem of incomplete membrane removal and "ghosting" that were widely concerned by everyone and proposed corresponding solutions.

1) Causes and measures for the formation of residual film

1 caused by improper membrane removal. If the amount of the release agent is not enough, the operation time is short, the release film and the film do not fully react, the brushing intensity is not enough, the release agent stays on the surface of the film, and does not immerse into the film. The solution is to identify the improper operation, increase the amount of release agent, or extend the stripping time, or increase the intensity of brushing to remove the residual film. Also, it is best to remove the film in place when the screen is recycled.

2 caused by photosensitive adhesive coating and printing operation. When printing, the exposure time is too long or re-exposure, so that the cross-linking hardening reaction of the photoresist is too thorough, so that the film removal difficulties. Therefore, in addition to mass production or special requirements for printed products, the screen exposure time can be appropriately reduced, that is, the tan is “soft”, and it is important to remember that it cannot be baked. In addition, relatively speaking, the dot layer version is relatively easy to remove due to relatively small exposure.

If the photosensitive adhesive coating is not uniform, it will cause the film to have a thick and thin film. When printing, the exposure time is too long at the place where the film is thin, and a cross-linking reaction may occur, making the film hardened and difficult to remove. Therefore, for screens that are ready for recycling, make sure that the coating is even when applied.

The experts also reminded the operator that when removing the film, it is best to use a film-removing agent that is compatible with the photosensitive adhesive. This is more targeted and the film is better!

(to be continued)