UV printing has advantages unmatched by traditional offset printing products in terms of surface texture, protection, wear resistance and production efficiency, especially for printing non-absorbent materials such as plastic sheets and gold and silver cardboard. PVC bags, PVC bags , PVC bags, PVC boxes. These advantages make those printing companies that use UV offset technology stand out from the competition. However, the UV offset printing process is relatively complicated, and packaging and printing companies often encounter the following problems in the UV offset printing process.

UV offset common problem solving

(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, 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) 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. 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 causes 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 more full.

(3) Adhesion

Since the penetration property of the substrate such as plastic sheet or gold-silver cardboard is poor, the adsorption force to 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.

(4) Ink emulsification

UV ink has a narrow tolerance of ink balance, which is easy to cause ink emulsification and dirty printing, which affects printing quality.

Solution: Reduce the printing speed and control the printing speed from 5000 to 8000 impressions/hour.

(5) 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 is in contradiction with the curing of UV inks, which require a longer UV lamp illumination time, and the printing sleeve guidelines require 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 expanded, 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.

(6) degree of curing

In order to improve the color saturation of the printed product, 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 firstly reduce the printing speed moderately, so that the UV lamp irradiation time is appropriately lengthened, and 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 layer of the ink to be slightly cured. Therefore, attention should be paid to the influence of ambient light on UV ink.

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