UV offset printing has shown its vitality in the world. UV offset printing has advantages over traditional offset printing in terms of surface texture, protection, wear resistance and production efficiency.
Its main performance is:
(1) The printed matter has been solidified at the part where the paper is received, and there is no need to spray powder.
(2) The ink cures quickly, making it easy to print on non-absorbent or special materials, such as plastic film and metal foil paper.
(3) The bright colors of UV printing, the special glazing effect, and the eye-catching high gloss of the printing surface.
(4) Post-press processing can be performed immediately after UV printing is completed, which improves production efficiency.
UV offset printing is not popular in China, and there are many failures in practice, mainly manifested in:
One ink emulsification
The water-ink balance tolerance of UV ink is very narrow, and it is easy to cause serious ink emulsification, dirty version and affect the printing quality during printing.
[Case 8-3]
A factory introduced the Heidelberg 6+ 1 LX multi-color offset printing machine, using aluminum foil cardboard to print the cigarette pack outer box, using the UV offset printing process. When it was ready to start printing after the current work was completed, it was found that there was a little hair around the dots, and the pictures were not clear.
The above-mentioned case is caused by the imbalance of water and ink. The emulsified ink accumulates on the inking roller and remains on the plate and blanket.
[Approach]
Reduce the printing speed. In addition, reconstitute the wetting liquid, usually isopropyl alcohol 11% to 13%, special water bucket liquid 3%, water 83%. The measured conductivity us = 1860, PH value is 5.6-6 , The temperature is 5 ~ 10 ℃.
[Expert Tips]
Severe emulsification of ink occurs, mainly because at the beginning of printing, the supply of ink in the ink fountain is not very good compared to UV inks, so the supply will gradually increase during operation, causing serious emulsification of ink. So pay special attention to the supply of ink and wetting fluid. Also, the concentration of the wetting fluid must be well controlled to avoid wavy longitudinal and light-colored streaks. In addition, the humidity of the workshop is 50% to 60%, and the summer temperature is 20 to 25 ° C.
Dichroic order
The color sequence of UV offset printing is much more complicated than that of traditional offset printing. The printing samples must be carefully analyzed before printing to discharge a reasonable color sequence.
[Case 8-4]
A factory used Heidelberg 6 + 1 LX to print a batch of medical packaging boxes. The background ink layer is thicker, and the color sequence is black, cyan, magenta, yellow, and light blue. The color is not full.
Treatment method: Change the tone sequence, print the color with a smaller ink amount first, and finally print the black with a larger ink amount, so that the ink amount can be maximized and the color can be fuller.
[Expert Tips]:
In all kinds of UV inks, ultraviolet light is generally easy to pass through magenta ink and yellow ink, but it is difficult to pass through cyan ink and black ink. Especially for black ink, if the color density is excessively increased in order to improve the printing effect, it will cause poor curing, poor adhesion, and even cause backside smearing. In UV printing, pay special attention to the print density of black ink. In addition, the color sequence The arrangement must be determined depending on the job.
Poor three curing
The substrates of UV offset printing products are mostly non-absorbent materials such as plastic film base or cardboard with mirror effect. Under normal circumstances, the printing pressure is large and the ink layer is thick, which often prevents the ink from curing well.
Treatment method: Firstly reduce the printing speed properly, so that the UV lamp irradiation time of each color group is properly extended to allow the ink to completely cure, and secondly adjust the distance between the UV lamp tube and the substrate to increase the UV light irradiation intensity. In addition, pay attention to the ambient light to the UV The effect of ink.
Four printing overprint is not allowed
In the UV offset printing process, the UV ink needs to be irradiated by the UV lamp to cause the substrate to expand due to heat, which leads to inaccurate overprinting. Obviously, this contradicts the UV ink curing, because the ink curing requires a longer time for the UV lamp to irradiate the The guidelines require a shorter UV lamp exposure time.
Treatment method: UV curing after the last color is printed. Under special circumstances, the intermediate color group can also be irradiated with UV lamps, but the time must be controlled.
Five drops of ink and drawing ink
UV ink has high viscosity and poor fluidity. When the room temperature is too high or the temperature is too low, the printing machine will run at a high speed for a long time, which will make the ink viscosity smaller, the fluidity will increase, and ink droplets will be generated.
[Case 8-5]
A factory prints a batch of fine work pieces, using UV offset printing. After the work pieces are printed, many prints are found with ink drops, and the inspectors treat them as waste.
Treatment method: reduce the room temperature, increase the air humidity, and maintain a constant low-speed printing.
Ramo
UV offset printing is prone to pull ink when printing a solid plate. The main reason is that the printing surface is not properly selected, and the machine is turned on in a cold machine.
Approach:
(1) Correctly select the printing surface of the substrate (2) The machine is idling and preheating, and some thinner is properly poured on the ink roller.
(3) Choose inks with low viscosity and strong fluidity for printing.
Six positive and negative sticky
The main cause of stickiness is insufficient ink curing, especially black ink.
Approach:
(1) Control the PH value of the wetting fluid and the balance of water and ink.
(2) Check whether the power of the UV lamp is in the effective range.
(3) The printing speed is controlled at 6000 ～ 8000 prints / hour.
(4) The wavelength of UV ink and UV lamp match.
Uneven color of seven inks
The unevenness of the ink color of the mouth and trailing edge sometimes occurs during printing.
Approach:
(1) Effectively control the water-ink balance.
(2) Check the water and ink roller pressure.
(3) Adjust the initial static point position of the center ink roller.
Cool Tech Fat Freezing Machine,360 Criolipolisis Double Chin Removal,Fat Freezing Slimming Machine
Xi'an Double H Health Technology Co., Ltd , https://www.xadoubleh.com