Discussion on the Causes and Countermeasures for the Insufficient Adhesion of Plastic Intaglio Printing Inks

With the rapid development of China's packaging and printing industry, the continuous improvement of plastic film printing technology, print quality has a direct impact on the status of the product market competition, because the plastic gravure ink printing is a very professional technology, so the plastic When the film is gravure printing, it often produces a series of failure problems. One of the common problems is that the ink is not firmly attached. How to minimize the probability of failure is also a topic of common concern to ink manufacturers and ink printers.

As we all know, the method of judging the adhesion of printing ink is generally measured by using transparent tape sticking. The printing attachment fastness varies with the ink type, which requires the ink printing user to carefully read the product specification to find out the specific use. The main causes of the solutions and failure solutions are:

(1) Misuse of ink or dissimilar inks. We all know that there are many kinds of films, and there are special types of inks. If misuse of inks or miscellaneous inks is mixed, it will cause the failure of adhesion. For example, polypropylene (PP) film can use chlorinated polypropylene resin type ink, polyester (PET) film can use polyurethane type ink, low pressure polyethylene (HDPE) film can use low pressure polyethylene special ink, etc., in actual printing use In order to adjust the viscosity of the ink, (typical printing viscosity is 18-25 seconds / 25 coated No. 4 cup) and volatilization speed (10-30 seconds for primary drying, 60-100 seconds for thorough drying), usually a certain amount of mixing is added The composition of the solvent and the mixed solvent should also use a solvent with a lower surface tension to reduce the surface tension of the entire ink system. The lower the surface tension of the ink, the more favorable the wettability and the attachment fastness to the film.
(B) poor surface treatment of printed substrates. For polyethylene, polypropylene and other films, if the corona treatment is not performed, or the treatment effect is not good, or the treatment effect is deteriorated due to long-term storage after treatment, the ink will not be firmly adhered. Because the plastic film is different from paper, the paper surface has a certain degree of roughness, has a capillary effect, strong ink absorption and easy to dry the conjunctiva, so the printing fastness is good, and the plastic film surface is smooth, not easy to accept ink infiltration, this type of non-polar The printability of the printing film of the high molecular polymer is poor, so that the surface tension of the printing material is equal to or greater than the surface tension of the ink in order to fully infiltrate the ink and the plastic film, so it must be processed to change its surface quality and chemistry. The structure increases the surface roughness and the polarity between the molecules so that the ink and the film can adhere firmly. We all know that corona (ie, spark) treatment is the main method for pretreatment of plastic film before printing (ie, high-frequency high-pressure or medium-frequency high-pressure surface treatment of plastic film). Generally, after the surface treatment of the film, the surface tension is greater than 38. Dyne/cm can only meet and achieve the desired print fastness.

(c) The surface moisture absorption of the film has a great influence on the printing performance of films such as polyamide and cellophane. Once moisture is absorbed, the fastness of the ink is reduced. Therefore, the storage conditions and printing conditions of these films should be kept as dry as possible. The dampness eventually increases the adhesion of the ink to the film.

(d) Drying temperature. In general, the higher the drying temperature, the better the fastness of the ink to the film. If the drying temperature is low, not only the residual solvent is high, the adhesion is low, but also the whitening of the ink is caused, and the “whitening” is the case in which the ink is exposed to cold air. The water vapor becomes a water droplet and mixes in the ink, causing the gelatinization to become turbid and precipitated. The “whitening” causes the gloss, transparency, and adhesion fastness of the product to be significantly reduced. The solution is to increase the printing speed and increase the amount of quick-drying solvent.

(5) The ink formulation is too thin, diluting the resin content. We all know that adding too much solvent to the ink at the time of printing will relatively reduce the effective component that the ink adheres to the film, and it will also cause the adhesion fastness to decrease. The solution is to add a resin glue or other suitable compatible adhesive resin glue corresponding to the ink in the diluent or ink to improve the attachment fastness.

In summary, there are many factors that affect the fastness of ink adhesion, as long as we carefully sum up, prevent and step by step, to minimize the failure. Of course, no matter what kind of printing failure occurs, as long as they can calmly and patiently look for the cause of the malfunction, they should also communicate closely with the ink factory, seriously consult the product related use matters, and jointly discuss the solutions to the failures in production and use, and only rely on printing manufacturers. In collaboration with ink manufacturers, they can work together to create a new chapter for the common development of ink printing and ink manufacturing.

Source: 21st Century Fine Chemicals Network