1. Ink indicators

In production process of membrane switches, the raw materials refer to film, ink and solvent. There are several basic indicators of ink that are listed within the scope of membrane switch testing: viscosity, fineness, hue, and adhesion fastness.

When testing viscosity, we need to dilute the matching mixed solvent to a specific viscosity (such as 18s/25°C), and calculate the amount of solvent added, so as to eliminate the "false viscosity" that may be caused by some inks (the ink looks thick, but the solvent can't mix in).

The quality of the solvent directly affects silkscreen printing. The main indicators to distinguish the quality of solvents are purity and moisture content. The quantitative and qualitative tests of solvents are through chromatography, but the instruments required are xpensive, and the technical requirements are high. If we only talk about printing (without dry lamination process), here are some simple and practical methods.

The solvent should look clear and transparent. It's bad when there is turbidity or floating matter.

After being exposed to commonly used solvents for a long time, we will have a general impression of the smell of a specific solvent. If the smell goes wrong, it can be sure that the solvent is not pure. There must be some impurities.

We can use the principle of uneven dissolution effects to roughly determine the moisture content in the solvent. Use a 100ml glass measuring cylinder to take half a cup of transparent toluene solvent. Take a small amount of the ester or ketone solvent to be measured, and pour it evenly into toluene. When the solvent is first poured into toluene, observe whether there is turbidity (milky white). If so, the water content in the solvent seriously exceeds the standard.

Experience shows that when the water content exceeds 0.5%, turbidity is obvious. The moisture test of benzene solvents can be determined by extracting the solvent through a long glass tube. Observe whether there is stratification.

2. Surface treatment

In fact, the surface of PET membrane switch has low affinity for most inks. Although manufacturers of conductive ink has chosen appropriate solvents to solve this problem, and strives to print on the untreated PET surface. However, due to the precipitation of certain additives and lipid substances in the film, as well as the existence of oil stains, those reduce the adhesion of conductive ink.

So, an activation treatment should be carried out. There are some ways, such as flame oxidation, solvent treatment, corona treatment, etc. For PET, corona treatment is the best. Corona treatment uses high-voltage discharge to generate sparks to treat the surface of the film to remove oil stains.

The surface treatment of the PET membrane switch not only removes oil stains, but also eliminates the static electricity of the material to prevent the material from absorbing dust in the air and ruining the silkscreen printing. Static elimination is an important process for membrane switches.

3. Static elimination

There are some simple ways to remove static electricity, such as wiping with an antistatic cloth, blowing with negative ions, etc. But these are less effective. The most popular specialized equipment now is the 600HK anti-static machine, which is specially designed for silkscreen printing.

The thickness of the workpieces it processes ranges from 0.10 to 5 mm. The width of the workpieces is 80 mm. The length of a single piece can reach 1 meter. The processing capacity per minute can reach 11m.