Complex UV offset printing process
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UV offset printing has the advantages of traditional offset printing 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 those printing companies that use UV offset technology stand out from the competition. However, the UV offset printing process is more complicated. How do packaging and printing companies deal with the problems in the UV offset printing process? How should packaging printing companies planning to adopt UV offset printing prepare?
UV offset printing
To make UV offset work better, the main problems that need to be solved are as follows.
1. Design plate
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, and so on. Some special printing requirements are higher, 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 printing material expansion and contraction The effect is to correct the film in advance to achieve the best quality.
2. Adhesion
Since the penetration property of the substrate such as plastic sheet or gold-silver cardboard is poor, the adsorption force on the ink is weak, so 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 between 5000 and 8000 impressions/hour.
4. Degree of cure
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. The solution is to first moderately reduce the printing speed, so that the UV lamp irradiation time is appropriately lengthened, so that the ink is completely cured; secondly, the distance between the UV lamp tube and the substrate is adjusted, and the UV light irradiation intensity is increased to make the ink solidify. The effective wavelength range of UV curing is 200-400 nm. 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 order 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. When a 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 full.
Solution: 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 amount of ink can be maximized 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. Or cold UV technology can be used.