Problems needing attention in UV printing of the h

Problems that should be paid attention to in UV printing of packaging offset printing

packaging offset printing is more and more adopted by our customers because of its fast speed, high efficiency, good point reduction, strong texture of patterns, and a wide range of printing. For some non absorbent substrate materials such as aluminum paperboard and plastic sheet, packaging offset printing generally adopts UV printing process. Because UV offset printing has the following advantages over traditional offset printing:

1 Fast curing speed

ordinary offset printing takes several hours or even more to completely dry the ink and enter the next processing process. UV offset printing can be completely cured in one to several seconds, so it is especially suitable for printing some non absorbent substrates

2. Strong wear resistance

after UV ink solidifies into a film, its friction resistance is good, which reduces the loss caused by friction during the use and transportation of packaged products

3. The effect of green computer comes down to the collection, transmission, reaction, analysis, display and printing of test data

UV ink does not contain solvents, does not volatilize solvents, and will not pollute the atmosphere. It belongs to green printing

4. Powder free

because it can be cured and dried in time after UV irradiation, it does not need powder spraying, which greatly improves the working environment. At the same time, it is also conducive to post press processing, such as film coating, glazing and other 3-yuan copolymer polypropylene films, transparent impact polypropylene, rapid prototyping transparent polypropylene and other high-end polyolefin products to replace 205000 tons of imported products

5. High efficiency, good quality

UV offset printing has short production cycle, high production capacity, clear printing points and good quality. However, due to the complexity of the packaging UV offset printing process and the short application time, it is still necessary to constantly summarize the application of the printing process. We should see the shortcomings of UV offset printing and continue to improve it. I would like to talk about my views on the problems that should be paid attention to in packaging UV offset printing:

the curing device

because the curing of UV ink depends on the polymerization and cross-linking reaction of monomers and prepolymers after UV radiation is absorbed by photoinitiators. Therefore, UV lamps must be installed for offset printing UV. Generally, offset printing machines need to install 3 ~ 6 UV light tubes and exhaust pipes. The UV lamp must adopt a suitable wavelength, generally in the range of 200 ~ 450 nm, and the distance from the irradiation surface must be well controlled. In addition, Qingdao Institute of energy has developed new polyurethane materials? It is expected that foreign countries will also be equipped with spotlights. Under the same lamp tube, the efficiency will vary a lot if the light concentration of the lampshade is good or bad. Under the irradiation of UV lamp, ozone is produced in the air, so ventilation equipment such as exhaust pipe is required. UV lamp will age and weaken its energy after a certain period of use. Its service life is generally about 1000 hours. Therefore, in normal printing, pay attention to the focusing of UV tubes, and wipe away any dust. The use time of UV lamp should also be remembered. Pay attention to the curing fastness of UV ink often after the use time, so as to replace the UV lamp in time. UV light is harmful to human body, so shading measures must be taken

use of ink

some components in UV ink will produce certain irritation and even cause skin allergic reaction when contacting human skin. Therefore, avoid skin and ink contact when using, such as wearing gloves or washing hands frequently. If UV ink and ordinary ink are exchanged for printing on a machine, we must clean the ink roller and ink bucket. If ordinary ink is not washed clean, it will affect the curing and drying of UV ink. Ink auxiliary materials cannot be used casually. Special auxiliary materials matching UV ink must be used

3. Adhesion

substrates such as plastic sheet and aluminum foil have poor permeability and weak adsorption on ink. In order to improve the adhesion fastness of UV ink to these non absorbent materials, UV offset printing requires the surface energy of the substrate to be 40dyn or above. We must check the surface energy of the substrate before printing. One of the surface energy treatment methods is corona treatment. It has timeliness. Generally, it will degrade automatically after corona treatment for a week. If it is reused, corona treatment must be carried out again, otherwise it will affect the curing and drying and the fastness of the ink layer

4. Ink emulsification and water ink balance

offset printing places great emphasis on water ink balance and the control of emulsification value. If UV ink emulsification leads to the opacity of UV ink film, it will affect the passing rate of UV radiation energy, thus slowing down the film-forming drying time. Even though the ink is cured, there is still water in the ink film. Once it is rubbed or pasted with adhesive tape, it will be found that the ink layer is pulled off

5. Control the temperature and humidity

if the temperature is low and the humidity is high, the UV curing reaction of the ink is slow, and the binding ability between the ink and the substrate is reduced. Therefore, the ambient temperature and humidity of the workshop must be well controlled during UV printing. The general temperature is about 18 ℃ ~ 25 ℃, and the relative humidity is about 50% - 65%

6. Control the printing speed

the speed of printing will affect the curing and drying of UV ink. The speed is fast, the UV irradiation time is relatively short, and the curing and drying condition is poor, so we must control the printing speed. The printing speed is generally controlled at about 6000 ~ 7000 sheets/hour

7. The arrangement of printing color sequence is very important, which should be carefully considered according to the characteristics of printing products. The thickness of the ink on the substrate will affect the quality of the point, but also affect the curing speed of the ink. This is mainly a problem of ink overprint rate. Therefore, when printing, we should first print colors with small printing area and less ink. On the one hand, it can achieve the highest ink volume and full color, on the other hand, it will not affect the curing and drying

8. Printing registration

the accuracy of overprint is very important. UV lamp irradiation will bring a certain degree of substrate deformation, so it is generally taken to irradiate the UV lamp after the last color is printed. In case of special circumstances, UV lamp irradiation must be carried out in the middle, and it is recommended that the irradiation time be as short as possible

in short, environmental friendly offset UV printing is the development trend of printing in the future. It can achieve 100% curing, no solvent volatilization, no powder spraying, instantaneous drying, stable ink color, accurate overprint, convenient processing after printing, and the ink layer has high wear resistance and high-strength gloss, which is especially suitable for printing of non absorbent substrate materials

with our continuous exploration of the process operation of UV offset printing and the continuous development of new processes and materials in the future, the level of UV offset printing will be further improved