How to deal with problems in UV offset printing
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To make UV offset work better, the main problems that need to be solved are as follows:
1. Design plate making
The design draft for UV printing must be based on the work order to determine the output format, such as film surface sweep or back sweep, output cable count, cable angle, etc. Some special printing requirements are high, such as 3D printing, the resolution is very high, the cable angle must match the printing material to avoid hitting the net; transparent plastic sheets and aluminized paper often need to be printed with white ink, should pay attention to the influence of printing material expansion and contraction , by correcting the film in advance to achieve the best quality.
2, adhesion
Since the permeation performance of the substrate such as plastic sheet or gold-silver cardboard is poor, the adsorption force to the ink is weak, and even if the ink is printed using UV ink, the adhesion of the ink is poor, and the printing quality is not high. It can be solved by surface treatment of the material.
3, ink emulsification
The ink ink has a narrow tolerance of ink balance, which is easy to cause ink emulsification and dirty printing, which affects the printing quality.
Solution: Reduce the printing speed and control the printing speed to 5000-8000 impressions/hour.
4, the degree of curing
In order to improve the color saturation of the printed matter, when the UV printing is performed on the surface of the substrate such as a plastic sheet, the printing pressure is large, the ink layer is thick, and the dot is enlarged, which makes the ink difficult to cure. In order to ensure the printing quality, the printing pressure cannot be greatly adjusted. Solution: Firstly reduce the printing speed moderately, properly lengthen the UV lamp irradiation time, and let the ink cure completely. Secondly, adjust the distance between the UV lamp tube and the substrate, increase the UV light irradiation intensity, and make the ink solidify. The effective wavelength range of UV curing is 200-400nm. The wavelength of some light sources in the printing workshop is also within this range, which will cause the surface of the ink to be slightly cured. Therefore, attention should be paid to the influence of ambient light on UV ink.
5, color sequence arrangement
The problem of UV offset color sequence arrangement is more complicated. Due to the limitation of the principle of inking, the ink layer on the substrate is relatively thin, and when a relatively thick ink layer is required, it is difficult for the printed product to achieve the desired copying effect. For example, when four-color overprinting, the commonly used printing color order is black, cyan, magenta, and yellow, because black almost fills all the space, cyan, magenta, and yellow have lower inking power, and the total amount of ink is insufficient, which will result in The color is not saturated.
The solution is to change the color sequence, first print the color with a smaller amount of ink, and finally the black with a larger amount of ink, so that the ink can reach the highest and the color is fuller.
6, printing registration
UV offset printing uses UV lamp illumination for ink curing. The main problem with curing is that the substrate is thermally expanded, resulting in inaccurate overprinting. This contradicts the UV ink curing, because the ink curing requires a longer UV lamp illumination time, and the printing sleeve criterion requires a shorter UV lamp illumination time.
Solution: UV curing is performed after the last color is printed. At this time, even if the substrate is inflated, the substrate can be deformed to a minimum by lowering the temperature for a while. In special cases, the intermediate color group can also be illuminated by UV light, but the shorter the irradiation time, the better.