With the application of non-absorbable printing materials such as gold and silver cardboard and laser transfer paper in cigarette packages, UV offset printing technology is also increasingly widely used in cigarette package printing. However, the control of UV offset printing process is also relatively difficult, and many quality problems are easy to occur in the production process.
Ink roller glaze
In the process of UV offset printing, the glossy glaze phenomenon will occur when the ink roller runs at high speed for a long time, resulting in poor inking, and the balance of ink and water is difficult to be guaranteed.
It is found in the actual production that a batch of new ink rollers will not produce glossy glaze in the first month of use, so immersing the ink rollers in the ink roller reducing paste for 4 to 5 hours every month can fully recover the performance of the ink rollers, thus reducing the generation of glossy glaze of the ink rollers.
Ink roller expansion
As we all know, UV ink is highly corrosive, so the ink roller surrounded by UV offset ink will also expand.
When the ink roller expands, appropriate treatment measures must be taken in time to avoid adverse consequences. The most important thing is to prevent the expansion from causing excessive pressure on the ink roller, otherwise it will cause bubbles, gel breakage and other phenomena, and even cause fatal damage to the UV offset printing equipment in serious cases.
The printing inaccuracy in UV offset printing of cigarette packets can be divided into the following two types.
(1) UV curing color deck printing is not solid.
In this case, the color sequence should be reasonably arranged, and the UV lamp between color decks should be avoided as far as possible. Usually, the white ink layer of the first printing is thickened and UV curing is carried out; When printing white ink for the second time, the ink layer will be thinned without UV curing. After overprinting with other color decks, the flat effect can also be achieved.
(2) Large area of field printing is not true.
There are many factors affecting the large area of field printing. To avoid large area of field printing, first check whether the ink roller pressure is correct to ensure that the ink roller has no glaze; Confirm that the process parameters of the fountain solution are correct; The surface of the blanket shall be free of dirt, pinholes, etc.. In addition, the test has proved that the air compression of a group after large area field printing will have immediate effect on improving the flatness of large area field printing.
Ink back pull
In UV offset printing, ink back-pulling is a common failure, mainly because UV offset printing ink is not fully cured after UV irradiation, and it is not firmly attached to the substrate. Under the effect of the printing pressure of the subsequent color decks, the ink is pulled up and stuck to the blanket of other color decks.
When ink back-pulling occurs, it can usually be solved by reducing the water content of the UV curing color group, increasing the water content of the ink drawing color group, and reducing the printing pressure of the ink drawing color group; If the problem still cannot be solved, cure it by UV
This problem can be improved by adding an appropriate amount of tensile agent to the ink of the color deck. In addition, the aging of rubber blanket is also an important reason for the ink back pull phenomenon.
Bad barcode printing
For UV offset printing of cigarette packages, the quality of barcode printing is a key indicator. Moreover, due to the strong reflection of gold and silver cardboard to light, it is easy to cause the bar code detection to be unstable or even substandard. Generally, there are two main situations when the UV offset barcode of cigarette package fails to meet the standard: defect degree and decoding degree. When the defect degree is not up to standard, check whether the white ink printing is flat and whether the paper is covered completely; When the decodeability is not up to the standard, check the ink emulsification of the barcode printing color deck and whether the barcode has ghosting.
UV offset printing inks with different color phases have different transmittance to UV. Generally, UV is easier to penetrate yellow and magenta UV offset printing inks, but it is difficult to penetrate cyan and black UV offset printing inks, especially black UV offset printing inks. Therefore, in UV offset printing, if the thickness of black UV offset ink is increased to improve the printing effect of barcode, it will result in poor drying of the ink, poor adhesion of the ink layer, easy to fall off, and even bad adhesion.
Therefore, special attention should be paid to the thickness of the black ink layer in UV offset printing to prevent the barcode from sticking.
Storage of UV offset printing ink
UV offset printing ink must be stored in a dark place below 25 ℃. If stored at a high temperature, UV offset printing ink will solidify and harden. In particular, UV offset gold and silver ink is more prone to solidification and poor gloss than general UV offset ink, so it is better not to store it for a long time.
In short, the UV offset printing process is difficult to master. The technicians of cigarette package printing enterprises must carefully observe and summarize in the printing production. On the basis of mastering some necessary theoretical knowledge, combining theory and experience is more conducive to solving the problems encountered in UV offset printing.
Post time: Mar-23-2023