How to replace UV flexo with low cost technology?
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Flexo printing has gradually become the mainstream in the domestic high-end label industry. The traditional configuration of this process is to use UV ink. Because the price of flexo UV ink is very expensive, it squeezes the cost space of the label, and because the UV ink itself has technical and environmental hazards, it starts with the reform process, and replaces the traditional UV with ink printing + UV coating. Flexo printing reduces costs and improves environmental protection. Is this scheme feasible? Here, the author analyzes this issue with everyone.
Response to the question of ink and wash
At present, the label industry still has doubts about the quality of ink, mainly including the following problems: 1 ink is not easy to adhere on the film material; 2 the ink dot is enlarged on the coated paper and film material, and it is difficult to control; 3 ink Drying too fast, the ink is easy to stick to the printing plate, causing blockage failure; 4Ink printing process needs to constantly monitor the fluctuation of pH value, and timely add pH stabilizer, the operation is inconvenient; 5 pH stabilizer contains ammonia water, It can lead to odors in the production environment and label products.
1. Adhesion on the film
In response to this problem, in fact, the division of labor between ink companies and printing companies should be very clear. Ink companies should know the matching characteristics of their products with the film, and should strictly control the solubility between the water-based resin and the film, that is, the polarity is similar, the solubility parameters are similar, and new hydrogen bonds should be generated. Printing companies should be able to use laboratory methods to analyze, select and screen out appropriate ink, pay attention not to easily veto, dump all the inks that are still defective, but do not blindly test the machine, increase the test cost.
2. Drying on the film
The main way of drying the ink on the film is volatilization, and drying is the main means. Therefore, the long-term solution to the drying problem is to increase the temperature, increase the air volume, slow down the speed or reduce the depth of the plate pocket. There is also a saying that ink drying is divided into three stages: the dry section is based on volatilization, allowing water to run away; then the relatively close of the binder molecules, extruding water; and finally the resin is solidified by intermolecular forces (including catalyst Cross-linking reaction under action).
One of the different arguments is the same, that is, the dry segments are volatilized, there is no other way. All other methods can only be followed by a drying tunnel to produce a chemical reaction under the influence of temperature, including desiccant technology. Therefore, it is still effective to determine the dryness of the ink surface by using the scraper fineness meter to determine the dry length of the ink. This method can know the speed of the ink drying speed before the machine is on, and can judge the failure probability of the printing on the machine. How high.
3. The dot expansion in printing
What is the difference in the print on the above picture? In fact, the viscosity of the ink, the viscosity of the ink and the UV ink are not on one level, and the difference between the two is 1 to 2 times. In other words, the expansion of the ink dot is related to its low viscosity. Then, can high-viscosity inks be used to solve the problem of network expansion? The answer is yes. The picture below shows a 150 line/inch 1% dot and a 175 line/inch 1% dot printed with high viscosity ink. From the arrangement spacing of adjacent dots, the diameter of the dot can be clearly distinguished. The viscosity of the ink is 15dPa s, which is twice the viscosity of the UV ink (7dPa s).
Why can I print with such high viscosity ink? Since a flexographic unit with an ink roller structure is used (as shown in the figure below), if a flexographic unit with a closed doctor blade structure is used, high-viscosity ink cannot be used. The root cause of determining the viscosity of the ink is the structure of the inking unit of the flexo press. On the same printing unit, the UV ink can be used for high viscosity. Why do you have to use low ink when using ink?
4. Easy to dry on the plate
The success of UV flexo printing is because UV ink has a very important feature, that is, the surface tension is very stable, generally in the range of 31 ~ 32mN / m, whether it is Hanghua's UV ink, or Shengweike or Flint The UV inks, the measured surface tension data are all within this range. That is to say, the surface tension of the UV ink is substantially fixed, and the surface tension of the two can be matched by selecting a suitable surface tension of the printing plate. Similarly, when using ink printing, as long as you control the matching of the surface tension between the printing plate and the ink, you can also achieve self-cleaning of the printing plate to avoid the occurrence of blockage failure.
5. Ink pH and its stability
The ink should be measured and adjusted in time, which makes the frontline operators feel inconvenient. So, is there any ink that does not monitor and adjust the pH during the printing process? The answer is yes, but you must learn to screen a lot of ink. In the printing process, the main reason for the fluctuation of the pH value of the ink is the evaporation of ammonia as a stabilizer, and the evaporation of ammonia is the cause of fluctuations in the pH of the ink. Then, if there is ink without ammonia, the answer is yes. In fact, the ammonia water process is only one of the three major processes of aqueous resin amination. The other two processes, the organic amine process and the inorganic alkali process, are two processes with better stability in the ink system.
The use of organic ammonia or inorganic alkali processes without ammonia is already a mature process for ink production. Moreover, the ink without ammonia is as convenient as the UV ink in use, and also eliminates the unpleasant odor of the ink. Some of the inks currently on the market still use ammonia as a stabilizer, mainly due to cost and price considerations. Therefore, for the printing enterprise, in order to keep the pH value of the ink ink stable during the printing process, and it is not necessary to monitor and adjust it from time to time, the key lies in the screening of ink, especially under laboratory conditions.
Why do we still need UV glazing?
The main resin of ink is water-dispersed modified acrylic. When the ink film is dry, it is irreversible to water, but it is not necessarily irreversible to many chemicals. Compared with the ink film resistance of UV inks, there are still gaps in the physical properties of ink films of inks, so ink prints also require UV varnish to enhance their surface properties. Moreover, the surface of the self-adhesive label is originally required to be glazed to meet the high gloss, matte, low coefficient of friction or high overprinting requirements of the label itself, so that the original UV glazing process is maintained and used. It is not difficult to get up.
Because UV varnish does not contain pigments, it can avoid the energy loss of UV ink in the drying process due to the absorption characteristics of light waves by different pigments, and its drying efficiency is relatively high. Moreover, the photoinitiator in the varnish is more in the UVC frequency band, and the characteristics of the UV ink and the UVA distribution are significantly different. The matching with the current metal halide lamp is better, and it is not difficult to select the UV lamp. The scheme of flexo ink + UV varnish is very feasible in the process, and does not need to deliberately make great changes to the equipment and the main raw materials. The most critical point is that the price of UV varnish is not high, and the price of tens of yuan per kilogram is affordable for label companies. With obvious cost reduction, constant print quality, improved affinity with the environment, and exploring new technologies for self-adhesive flexo labels, is there any need to try?