In the printing process, if we encounter the problem of poor adhesion between the film material and the UV ink used, we should analyze the reason correctly to find the correct solution to the problem in the first place.
Compared with paper adhesive materials, film adhesive materials have the characteristics of good waterproof, good transparency, high strength, good durability and other publications, so it is used more and more in daily chemical products and electronic products. Commonly used for making film stickers
Films include: polyethylene (PE), polypropylene (PP), polyester (PET), polyvinyl chloride (PVC), polystyrene (PS), polyolefin (PE and PP blend), etc. But unlike the paper, the film is not absorbent, so the printing of film stickers is mainly used
UV relief printing and UV flexo printing. In the printing process, the problem often encountered by label printing companies is the poor adhesion of UV ink on the surface of the film. This article will analyze the reasons and explain the troubleshooting methods for this problem.
Cause Analysis
The reasons for the poor adhesion of UV ink on the film surface can be summarized as the following.
1. Poor curing of UV ink
In the actual printing process, customers often encounter the situation that after the UV ink is irradiated by the ultraviolet lamp, the surface of the ink has been cured but the interior has not been completely cured. The adhesion of UV ink that has not been fully cured to the film surface is relatively weak, when tested with tape
It is easy to tear the ink layer off the film surface.
2. The surface tension of the film is not enough.
The surface tension of the film must be at least 42mN / m. We know that Adobe adopts the method of corona treatment to increase the surface tension of film materials (such as PE / PP), but the time-effectiveness of corona treatment will be affected by factors such as the material storage environment and transportation environment. Before printing, the operator must use a dyne pen or dyne liquid to check the surface tension of the film material. If the surface tension does not reach the required packaging machinery, it will result in poor UV ink adhesion.
3. The UV ink used does not match
For some film materials, such as PET and BOPP, in order to improve their printability, material suppliers will add a coating layer on their surface. Because different UV inks use different kinds of resins, printing on the same coating layer often shows different results. If the UV ink used does not match the coating layer of Epson, the problem of poor adhesion of the UV ink on the film surface will occur. [next]
Troubleshooting
In response to the three situations encountered above, we propose the following solutions.
(1) Determine whether the UV ink has been completely cured. We can use the thumb press method, that is, press the thumb firmly on the surface of the ink layer, and then press it back and forth several times. If there is ink on the thumb, it can be determined that the UV ink is not completely cured. There are many reasons why UV inks are not fully cured. It may be a problem with the ink itself, or it may be a problem with the UV curing system. Attention should be paid to the following two aspects.
①If the UV ink is not used up, be sure to cover the cap of the ink tank and avoid light when storing. We know that there is also ultraviolet light in ordinary sunlight, and UV inks will also undergo chemical investigations after prolonged exposure to sunlight, causing the ink to deteriorate. In addition, the ambient temperature of UV ink storage should be around 20 ℃, should not be too high.
â‘¡The service life of the UV lamp is generally around 1000 hours. Some label printing companies often encounter the situation that the UV lamp has been used for more than 1000 hours and can be lit, but it can no longer completely cure the UV ink. This is because once the UV lamp reaches the end of its service life, its spectral curve will change, and the emitted ultraviolet rays no longer meet the curing requirements of UV inks. Therefore, we should correctly record the use time of the UV lamp, and replace the UV lamp that has reached the service life in time.
(2) Film materials can be divided into two categories according to the different printing suitability: one category requires corona treatment before printing; the other category itself has been processed with a layer of printable coating. For label printing companies, they should decide what kind of film material to buy according to the capabilities of the printing equipment (such as whether there is a corona treatment device, etc.). If there is a corona treatment device on the printing press, you can purchase the first type of film material. Before printing, measure the surface tension of the film material, if it is lower than 42mN / m,
This material must be corona-treated before printing, so as to ensure good adhesion between the UV ink and the film surface. If there is already a coating layer that can be printed on the surface of the purchased film material, label printing companies should consult the material supplier about which brand of ink should be used, because different coating formulations are suitable for different brands of ink. Only when the coating layer matches the UV ink can the problem of poor ink adhesion be solved.
In summary, in the printing process, if we encounter the problem of poor adhesion between the film material and the UV ink used, we should analyze the reason correctly to find the correct solution to the problem in the first place.
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