Complex UV offset printing process

UV offset printing products have advantages over traditional offset printing products in terms of surface texture, protection, abrasion resistance and production efficiency, especially for non-absorbent materials such as plastic sheets and gold and silver cardboard. These advantages make printing companies that use UV offset technology stand out from the competition. However, the UV offset printing process is more complicated. How do package printing companies deal with the problems in the process of UV offset printing? How should packaging and printing companies intending to use UV offset printing be prepared? For these issues, this article passes Mr. Li Zhuobin, Dongguan Hu Cai Printing Co., Ltd. Managers of the production department of Beijing Colorful Printing Co., Ltd. Yang Hao, Mr. Liu Jiyang of Chengdu Jiuxing Printing and Packaging Co., Ltd., and Mr. Wang Wei, who has worked in UV offset printing for many years, gained insights.

UV offset printing problem solving

For UV offset printing to work better, the main issues that need to be addressed are the following.

1. Designing plate

The design draft for producing UV printing must determine the output format according to the work order, such as the film surface swept forward or reverse sweep, the number of output network lines, the angle of the network cable and so on. Some special printing requirements are higher, such as 3D printing, the resolution must be very high, the network line angle must match with the printing materials to avoid hitting the net; transparent plastic sheet and aluminized paper often need to add white ink, should pay attention to the printing material stretching Impact, pre-correction of film to achieve the best quality.

2. Adhesion
Since the permeability of substrates such as plastic sheets or gold-silver cardboard is poor, the adsorption of ink is weak, so even if UV ink printing is used, the ink adhesion is poor and the printing quality is not high. It can be solved by surface treatment of the material.

3. Ink emulsification
UV ink ink balance tolerance is very narrow, easy to cause ink emulsification, dirty version, affect the printing quality.

Solution: Reduce the printing speed and control the printing speed at 5000 to 8000 prints/hour.

4. Curing degree
In order to improve the color saturation of printed products, when printing on the surface of a plastic sheet or the like, the printing pressure is large, the ink layer is thick, and the dots are increased so that the ink is not easily cured. In order to ensure print quality, printing pressure cannot be greatly adjusted. The solution is to first moderately reduce the printing speed, so that the UV lamp irradiation time is properly extended, so that the ink is completely cured; followed by adjusting the distance between the UV lamp and the substrate, increase the UV light irradiation intensity, so that the ink curing. UV curing effective wavelength range is 200 ~ 400nm, some of the light source in the printing room is also within this range, it will lead to a slight cure of the ink surface, so should pay attention to the effect of ambient light on UV inks.

5. Color order arrangement
UV offset color arrangement problem is more complicated. Due to the limitation of inking principle, the ink layer on the substrate is relatively thin. When a relatively thick ink layer is needed, it is difficult for the printing product to achieve the desired reproduction effect. For example, in the case of four-color overprinting, the commonly used printing sequence is black, cyan, magenta, and yellow. Because black fills almost all the space, the ink strength of cyan, magenta, and yellow is lower, and the total amount of ink is insufficient. The color is not full.

Solution: Change the color sequence, first print the ink with a smaller amount of color, and then print the black with a larger amount of ink, so that you can get the highest amount of ink and the fuller color.

6. Print registration
UV offset printing uses UV light irradiation for ink curing. The main problem caused by curing is the thermal expansion of the substrate, resulting in inaccurate overprinting. This is inconsistent with the UV ink curing because the UV curing requires a longer irradiation time for the ink, and the printing sleeve criteria requires a shorter UV lamp irradiation time.

Solution: After the last color is printed, perform UV curing. Even if the substrate expands, lowering the temperature for a period of time can minimize the deformation of the substrate. Under special circumstances, the middle color group can also be exposed to UV light, but the shorter the irradiation time, the better. Or you can use cold UV technology.

Source: "Printing Technology"