How to Eliminate the Electrostatic Discharge in CD Screen Printing

Printing, especially in screen printing, often occurs when the stencil is ejected from the substrate. The ink in the stencil portion will also follow the stencil to form a fluffy “spider” that is pulled up from the substrate and floats. And when the screen continues to rise, this “spider” spills onto the substrate before and after the wind drifts, making the surface of the substrate dirty and the edges of the pattern not sharp. This phenomenon is annoying because any printer does not want to see it. This is an electrostatic phenomenon.

What is the problem of those static electricity? From an atomic point of view: All neutral materials, such as plastics, paper and other insulators, that is, the positively charged nuclei in each atom are neutralized with negatively charged electron clouds, when the material passes After the frictional contact is separated, the electrons in the insulating material will be free to the surface of the material. For example, in the middle school physics, the glass rods were rubbed with silk, and static electricity generated on the glass rods sucked up the scraps. The electron-reduced material surface is positively charged, while the electron-added material with excess electrons is negatively charged. If the electron-reduced material is supplemented with negative electricity and the electron-increased material is supplemented with positive electricity, the two materials are in balance between positive and negative electricity. The two materials are neutral.

In optical disc printing, so-called screen printing is a process in which ink is transferred to a substrate under a certain squeegee pressure by relative displacement of a screen plate and a squeegee. The screen (screen) and the squeegee (polyurethane squeegee) are insulators. In the screen printing, they are rubbed against each other in the relative position, especially when the humidity is low, static electricity will affect the surface charge of the substrate. Distribution status. In particular, insulating materials, such as PC substrates for optical discs, PET sheets for touch-opening, and PVC used in name and signage, PP, PE in plastic bottles, etc., are basically insulators, and are not noticed in screen printing operations. Static electricity will be produced. For example, when screen printing membrane switch decorative inks are used, the surface of the PET film is protected by a layer of PVC and other self-adhesive films after the film is produced, so that it will not be scratched during cutting and packaging. However, after screen printing, the protective film must be peeled off before screen printing. Often, some operators remove the film at a very high speed. Do you not know that the protective film and the PET sheet are rapidly separated at the instant of quick release of the film? In the process, static electricity is generated on the surface of the PET sheet, especially under low humidity. As a result, the ink on the edge of the handwriting on the screen printing has flying hair, and the fluffy pattern-like ink on the transparent PET sheet sinks to the quality problem. This is a typical example, which has caused great confusion for the silk screen printing unit.

First, because of the existence of static electricity, the production difficulties caused by static electricity, etc. in printing are the bodies. The performances in screen printing are:

1. After silk screen printing, the ink on the blotting is pulled up with the screen plate, and the “flying” filaments are only disconnected after the workpiece is removed.

2. When overprinting, the front and back color ink edges and pattern edges are mutually exclusive and do not fit well, so that ink cannot be printed between inks of two colors.

3. In screen printing, the workpiece is stuck on the screen, especially when the wiper moves to the end of the screen.

4 printing materials stick together can not be separated

5. In the process of squeegeeing, the ink spreads hard on the screen, and the cake sticks together

6. The substrate sucks dust, and ink marks, pits, rough surfaces, etc. after screen printing

The above problems are mainly caused by the presence of static electricity. However, sometimes the presence of static electricity is also related to the fact that the printing process does not meet the requirements. For example, when the humidity is low and the amount of solvent in the ink is insufficient, the humidity in the air is low and the static electricity cannot Through the transmission of moisture, at the same time, the ink solvent is small, and the viscosity is large. With such a large viscosity, the ink itself naturally generates a drawing; if the printing speed is faster during the screen printing process, the squeegee and the screen strongly rub against each other to generate static electricity. Especially in the case of high-tension screens, when the squeegee pressure on the screen is high, the squeezing speed of the squeegee on the screen can be the most likely to cause the occurrence of static electricity. It is often said that frictional electrification is the reason.

Screen printing because of the existence of static electricity can cause many quality problems, and even printing can not continue, then how to avoid and eliminate static electricity in screen printing?

First of all, from the process conditions of the wire mesh itself, under the high tension of the screen, reduce the mesh distance as much as possible. When the net pitch is reduced, the pressure of the scraper is reduced, and the scraper reduces the possibility of static electricity generation due to the friction of the screen plate. In the screen printing of the optical disc, in order to ensure the accuracy of the printing pattern and reduce the occurrence of moiré and overprint characters on the pattern while avoiding the production of static electricity, the tension of the disc is as high as 26N/cm, and the mesh distance is as small as 1.0mm. If the screen is printed under the above conditions, static electricity may still appear. At this time, adjustment of the squeegee speed may be avoided.

Screen printing environment conditions matching, screen printing better printing environment temperature at 23 °C ± 2 °C relative humidity of 60% ~ 70%, which solvent solvent evaporation speed control, good control of the viscosity of UV light solid ink favorable , Stabilize the viscosity of the ink, you can meet the printability of the ink, the printability of the ink is good, because the ink itself can not appear drawing phenomenon.

Second, if the control of the above process conditions is obtained, then the method of controlling the power is:

1. The workpiece itself is charged. In this case, the electrostatic brush or the static electricity removing cloth may be used to perform electric treatment on the surface before screen printing. The method is very simple: wipe the workpiece with static electricity or wipe the surface of the workpiece in one direction with an antistatic cloth and print it after processing.

2. Screen printing plastic workpieces with static electricity. Antistatic agents can be added to plastic formulations in advance, which requires the production of plastic raw material suppliers.

3. It is also possible to eliminate the static electricity by adding an anti-static coating to the surface of the workpiece with static electricity.

4. Reasonable use of ink solvents. Even if the ink solvent mixing performance is good, and the conductivity of the solvent is good to adjust the ink viscosity.

5. Increase the grounding of the workpiece from the screen printing equipment so that the charge is released and static electricity is eliminated.

6. In the screen-printing workshop without moisture control measures, the water splashing to the ground was increased in the low-humidity season, and the humidity of the screen printing environment in the process of moisture evaporation on the local surface was adjusted. This method is not used in the humidity control equipment, and the simple production units are used in many ways. Apart from the humidity control, it also has the effect of preventing the dust in the control.

In short, for the generation and elimination of static electricity, specific conditions and conditions should be analyzed and corresponding measures should be taken so that the printing work can be carried out smoothly and smoothly under the guarantee of product quality.