In the market of self-adhesive label materials, the biggest difference between film self-adhesive materials and paper is that its surface is not absorbent. At present, most printing companies use UV ink on film self-adhesive labels. Come to print, because UV ink printing can adopt the method of ultraviolet ray instant drying and its good adhesion. Although UV ink has the advantages of fast drying speed, good printing effect, scratch resistance and solvent resistance, after all, UV ink is a new technology that has only been developed in recent years, and customers often encounter it during the printing process. Some problems, the most common problem is the adhesion of UV ink on the surface of the film material.
1. What is the poor adhesion of UV ink?
The so-called poor adhesion of ink is that the ink is detached from the film surface through a certain test method. According to the different requirements of end users, there may be differences in test methods for each customer. In the self-adhesive label printing industry, most customers will use 3M 810 or 3M 610 tape for adhesion testing.
2. Analysis of the cause of poor ink adhesion
1. Poor drying of UV inks In the actual printing production, customers often encounter UV inks irradiated by ultraviolet lamps, the surface of the ink has been dried but the inside is not completely dry. In this case, there is no completely dried ink, and the bonding force on the surface of the film material is relatively weak. It is easy to tear the ink off the surface of the material when tested with tape.
2. The surface tension of the PE / PP film material is not enough. Before printing, use a dyne pen or dyne liquid to check the surface tension of the PE film material. If you want to ensure good UV ink adhesion, the surface tension must be at least 42 dyne / cm. If the surface tension does not meet the requirements before printing, it will result in poor ink adhesion.
3. The use of ink does not match. For some film materials (such as PET, BOPP), in order to enable the material to be printed, the material supplier will process a coating layer on the surface. Because different inks use different resins, printing on the same coating layer will often show different results. Purchase materials with coatings should consult the material supplier's ink brand for the material.
For the three situations encountered above, we propose the following solutions:
1. When judging whether the ink has been completely dried, we can use the thumb pressing method, that is, use the thumb to press hard on the surface of the ink and then press back and forth several times. . There are many reasons why the ink is not completely dried. There may be a problem with the ink itself, or it may be a problem with the UV drying system. Here we mainly pay attention to the following aspects:
(1) If the UV ink is not used up, be sure to cover the lid, and avoid dark when storing. The ambient temperature for storage should be around 20 ° C, and should not be too high.
(2) The use time of UV lamp is generally about 1000 hours. Once the UV lamp has exceeded the service life, its spectral curve has changed, and the emitted ultraviolet light no longer meets the requirements of dry ink. Therefore, we should correctly record the use time of the UV lamp and replace it in time.
2. For film materials, we can be divided into two categories in terms of suitable for printing. One is: materials that require corona treatment to print; the other is that the material itself has been processed with a printable coating. For customers, according to the capabilities of their printing equipment, such as whether there is a corona device that is processed in-line to determine what kind of materials to buy. If you have a corona treatment unit on your printer, you can purchase corona treatment materials. Before printing, we must measure the surface tension of the material. If it is lower than 42 dynes / cm, we must perform in-line corona treatment before we can print. In this way, good ink adhesion can be guaranteed. If there is already a printable coating on the surface of the material, the customer should consult the material manufacturer should use the brand of ink, because different coating formulas are suitable for different brands of ink. Only in the case of coating and ink matching can the problem of ink adhesion be solved.
In summary, if we encounter the problem of film material ink adhesion in production, we should analyze the reason correctly so that we can find the correct solution to the problem.
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