With the development of economy, people's demands for corrugated paper boxes have been increasing. It is required that corrugated boxes not only play a role in protecting commodities and facilitating transportation, but also play a role in displaying goods, beautifying goods, and promoting sales. In large-scale supermarkets, beautifully printed color cartons are more attractive to customers, raising the interest of Gu Jiashi and stimulating customers' desire to purchase. This requires that the corrugated box not only has sufficient strength but also has excellent surface printing quality.
At present, there are many printing methods for corrugated cartons in China, including offset printing, flexo printing, flexo printing, and gravure printing.
Offset printing can be used to obtain exquisite cartons. However, the process is complicated and the rejection rate is high, which also affects the strength of the corrugated board after the roll. From the perspective of the development trend of the foreign packaging industry, the method of offset printing and offsetting will fade out of the corrugated box industry.
Flexo-type direct printing corrugated cartons are of good quality and high speed, and occupy a large proportion in corrugated box printing in developed countries. In China, due to the restrictions of technology and equipment, most of the flexographic printing can only print medium and low-grade cartons. The printing quality needs to be further improved.
In Europe, America, Japan, and other developed regions, preprinting by carton printing is common, and flexographic preprinting accounts for a larger proportion than gravure preprinting. This is because the flexographic preprinting technology in developed regions is relatively mature. In China, due to the large number of paper gravure printing machines introduced in the past few years, together with the fact that China's gravure printing technology is more mature than flexographic printing technology and has a solid mass base, our country currently prints gravure in advance. Preprinted mainly. Whether it is gravure preprinting or flexo preprinting, it is currently an ideal printing method for high-volume, high-quality color carton printing.
The method of flexo-printing pre-printed color corrugated cartons is to use a flexo printing machine to print on webs, and still print them into webs after printing, and then use the printed webs as corrugated cardboard on cardboard boxes. The production line is made of corrugated cardboard boxes and then die-cut by a die-cutting machine.
1, the advantages of flexo preprinting
(1) Non-toxic, non-polluting and conducive to environmental protection. It is a green printing method and has great advantages in the printing of green cartons such as food boxes and medicine boxes.
(2) Low cost. The low cost of flexo printing has formed a broad consensus in foreign countries and there are different opinions in the country. Mainly due to the current domestic use of flexographic printing machines, flexographic printing plates rely on imports of most of the imported, resulting in higher costs. Offset printing and gravure printing are relatively inexpensive in this regard. With the local production of flexographic equipment and its plate in China, its cost will gradually decrease.
(3) Large-format, multi-color, high-quality color cartons can be printed. The maximum width of foreign roll-up flexo printing machines can reach 2.4m, and the satellite flexographic printing unit can reach 8 colors.
(4) Printing with different screens, fine prints and strong consistency. Can use 100 lines / inch, 133 lines / inch, 175 lines / inch performance patterns, delicate dots, colorful eye-catching.
(5) In the corrugated board production line, the retort paper and corrugated paper are re-bonded one at a time to improve and improve the compressive strength and impact strength of the corrugated box.
(6) Fast printing speed and high output. The speed of a satellite flexographic printing press is generally 200—
400m/min, can meet the needs of a number of automatic corrugated cardboard production lines.
(7) A wide range of printing materials, printing 80-400g/m2 paper and cardboard.
2. The lack of flexo preprinting
(1) In the process of plate making, for the continuous manuscript revision, the Gao Le section of the pattern is markedly polarized, and the small dot (less than 8% of dot) is either lost during the printing and becomes a net or severe Expanded, close to midtones outlets. In the dark tone, about 85% of the dots at the tone will be merged into the field. It can be seen from the introduction that the gradation range that can be copied when the flexographic printing uses the amplitude modulation dot network for continuous tone copying is narrow, about 8% to 85%. In other words, when printing more than 85% of the area, due to the increase in the number of outlets, there will be a parallel level phenomenon, so that the dark tone area will be dead and non-hierarchy; when the area is printed below 8%, the dots are too small to be printed on the plate. On the "stop." Therefore, it is difficult for some rich manuscripts to present their rich layers and colors with flexo.
(2) From the perspective of the number of printed screens, the highest number of lines for offset and gravure is higher than for flexo. The ideal number of screens for flexo printing is generally less than 150 lines/inch, and more than 175 lines/inch will increase the difficulty of flexo plate making and shorten the service life of plates.
(3) It is not appropriate to use thin lines and small texts. Because the flexographic printing plate will be deformed during the printing process, lines that are too thin may be easily deformed due to too small text. If the small anti-white or anti-white lines, due to the shallow relief, it is very easy to cause paste death. Therefore, use thicker lines as much as possible. The contrast between the lines used to decorate and the main lines should be greater.
