Analysis of UV offset faults

UV offset printing has shown its vitality worldwide. UV offset printing products have advantages over traditional offset printing products in surface texture, protection, abrasion resistance and production efficiency.

Its main performance is:

(1) The printed matter has been cured on arrival at the delivery section without the need for dusting.
(2) The ink cures quickly and is easy to print on substrates such as non-absorbent or special materials, such as plastic films and metal foils.
(3) Bright color of UV printing, special glazing effect, and eye-catching high gloss of printing surface.
(4) After the UV printing is completed, the post-press processing can be performed immediately, which improves the production efficiency.

UV offset printing in China is not universal, there are many failures in practice, mainly in:

Ink emulsification

UV ink ink balance tolerance is very narrow, printing is likely to cause more serious ink emulsification, dirty version, affect the printing quality.

[Case 8-3]

A factory introduced the 6+ 1 LX multicolor offset printing press from Hyderabad and used aluminum foil paperboard to print the cigarette pack outside the box. The UV offset printing process was used. When the current work was finished and preparations were made for printing, it was found that the outlets were a bit hairy around the border. clear.

The above-mentioned cases are caused by the imbalance of the ink and ink, and the emulsified ink accumulates on the ink roller and remains on the plate and the blanket.

[Approach]

Reduce the printing speed, in addition, the reconstitution of the wetting fluid, usually 11% to 13% of isopropyl alcohol, 3% of the special water bucket liquid, water 83% which measured the conductivity us=1860, the PH value of 5. 6 ~ 6 The temperature is 5 to 10°C.

[Expert Tips]

The emulsification of the ink is more serious, mainly at the beginning of printing. Compared with the oil ink, the ink supply in the ink fountain is not very good, so the operation will increase the supply gradually, resulting in more serious emulsification of the ink. So pay special attention to the supply of ink and dampening fluid. Also the concentration of the wetting fluid must be well controlled so as to avoid wavy longitudinal and light-colored stripes. In addition, the workshop humidity is 50% to 60%, and the summer temperature is 20 to 25°C.

Two color sequence

The color sequence of UV offset printing is much more complex than that of traditional offset printing. Before printing, the printed sample must be carefully analyzed and a reasonable color sequence must be discharged.

[Case 8-4]

A factory used Heidelberg 6+1 LX to print a number of pharmaceutical packaging boxes with a thick base ink layer. The color sequence was black, blue, magenta, yellow and light blue. As a result, the total amount of ink in the printed product was insufficient. The color is not full.

Processing method: Change the hue sequence, first print the color with less ink, and finally print the black with the larger ink volume, so that you can get the highest amount of ink, and the color is fuller.

[Expert Tips]:

In various colors of UV inks, ultraviolet light is generally easily transmitted through the magenta ink and the yellow ink, but it is difficult to pass through the cyan ink and the black ink. In particular, black ink, if it is to increase the printing effect and excessively increase the color density, will cause poor curing, poor adhesion, and even cause the back of the dirty, in the UV printing should pay special attention to the black ink printing density, In addition, the color sequence of The arrangement must be determined by the job.

Three poor curing

The substrates of UV offset printing products are mostly non-absorbent materials such as plastic film bases or paperboards with mirror effects. Under normal circumstances, the printing pressure is relatively large and the ink layers are relatively thick, which often causes the inks to not cure well.

Processing methods: First, reduce the printing speed, make the UV lamp irradiation time of each color group lengthen properly, let the ink completely solidified, then adjust the distance between the UV lamp and the substrate, increase the intensity of UV light irradiation, in addition, pay attention to ambient light on UV The effect of ink.

Four printing overprint is not allowed

In the UV offset process, UV inks need to be exposed to UV light to cause the substrate to expand by heat, resulting in overprinting. Obviously, this is inconsistent with the UV ink curing, because the ink curing requires a longer UV light irradiation time, and the printing sleeve The guidelines require shorter UV light exposure times.

Treatment method: UV curing after the last color is printed. Under special circumstances, the middle color group can also be exposed to UV light, but to control the time.

Five drops of ink and ink

UV inks have large viscosity and poor fluidity. In the case of high room temperature or low temperature, the high speed operation of the printing press will make the viscosity of the ink smaller and the fluidity enhanced, resulting in ink droplets.

[Case 8-5]

A certain factory printed a batch of fine work pieces and used UV offset printing. After the job was printed, it was discovered that many printed products had ink droplets on it, and the inspectors treated them as waste products.

Treatment methods: Reduce the room temperature, increase the air humidity, and maintain a constant low-speed printing.

Lamo

UV offset printing is easy to produce ink-pulling phenomenon when printing in the field version. The main reason is that the printing surface is not properly selected, and the cold machine is opened.

Approach:

(1) Correctly select the printing surface of the substrate (2) Preheat the machine idly, and pour some thinner on the roller.
(3) Choose inks with low viscosity and high fluidity to print.

Six positive and negative sticky

The main cause of stickiness is insufficient ink curing, especially black ink.

Approach:

(1) Control the pH of the wetting fluid and the ink balance.
(2) Check if the UV lamp power is within the valid range.
(3) The printing speed is controlled at 6000 to 8000 prints/hour.
(4) UV inks match the wavelength of the UV lamp.

Seven shades of ink are uneven

The unevenness of the color of the ink and the tip of the mouth can sometimes occur during printing.

Approach:

(1) Effectively control ink and water balance.
(2) Check the water and ink roller pressure.
(3) Adjust the initial static point position of the center chain roller.