What do I need to pay attention to when converting offset screen printing to gravure printing?
A company has developed 8 new cigarette packs, of which 5 products have been successfully converted from offset printing and screen printing process to gravure printing process. As a major driver and participant in the process conversion of these products, the company would like to talk about some of its shallow experience.
The offset printing process is converted into the gravure printing process
1. On-site printing
Under normal circumstances, when the offset printing process is used to print a large area of cigarette packets, it needs to be printed twice to make the ink layer thicker. The first printing ink layer is thin, which plays a role in priming; The second pass prints the ink layer thick, and the hue can be adjusted. After converting to gravure printing process, the effect of two times printing of offset printing process can be achieved by using one printing.
2. Small graphic printing
When the offset printing process is converted into gravure printing process, the lines of the small graphics should be appropriately thickened, and the distance between the lines should be widened, so as to avoid the printing quality problems such as the printing of small lines and the pasting of the entire graphic and text, it is recommended that the gravure should be processed by laser engraving process, and at the same time, an appropriate amount of slow drying agent should be added to the gravure ink to improve the transfer effect of the ink.
3. Printing registration
The registration accuracy of the offset printing process is better than that of the gravure printing process, and individual small graphics and texts can be printed twice, but when the offset printing process is converted into the gravure printing process, it is necessary to consider the registration problem, try to put the color sequence with high registration requirements in the front and rear adjacent color groups, and expand the hollow part that needs to be overprinted.
4. Color text printing
After offset printing is converted into gravure printing process, if the background color is printed on the ground, and then the dots are printed on the background color, the color effect can be achieved, but because the registration accuracy of gravure printing is not as good as offset printing, quality problems such as poor overprinting and thickening of fonts often occur, which affects the pass rate of the product, so gravure color text is printed in spot color as much as possible to make up for the lack of registration accuracy of gravure equipment.
5. Dot printing
Dot printing is the short board of gravure printing, especially gradient screen printing is extremely difficult, so when designing gradient mesh, the gradual effect of dots should be appropriately elongated to achieve a smooth gradient. Electrostatic ink absorption device is installed during printing; Use slow drying agent in moderation; Try to use high-viscosity inks, otherwise it is easy to cause pasting.
6. Barcode reading
The edge of the barcode printed by the offset printing process is relatively smooth and easy to read, while the edge of the barcode printed by the gravure process has zigzags, especially the gravure made by the electronic engraving process, the jagged edge of the printed barcode is more obvious, and the gravure made by the laser engraving process, although the jagged edge of the printed barcode is not too obvious, it is easy to dry the plate.
7. Die-cutting shrinkage
When the offset printing process is converted to gravure printing process, the influence of die-cutting shrinkage should be tested, and the size of the die-cut plate should be adjusted appropriately.
8. The ink is bursting
Because the ink type and drying method of offset printing and gravure printing are different, it is necessary to pay attention to the problem of ink bursting, in order to prevent ink bursting, you can use more flexible ink to print, and carry out the burst test before batch printing.
9. Large version imposition
When offset printing is converted to gravure printing process, the problem of imposition should be considered, and all the plates should be imposed as far as possible, so as to avoid the impact of the gravure scraper blade on the ink transfer.
10. Ironability
The offset varnish is relatively thin, and the gravure varnish is thicker, so for the cigarette packs that need to be hot stamped after glazing, the hotness test should be done before hot stamping.
The screen printing process is converted into gravure printing process
When the screen printing process is used to print cigarette packs, special inks are usually used, and when the screen printing process is converted to gravure printing process, the characteristics and drying methods of these special inks must be considered.
1. Ink drying
The printing speed of the screen printing machine is slow, the production line is long, and the printed product is fully dried; The gravure press is compact and the printing speed is fast, so it is necessary to increase the power and number of drying lamps of the gravure press.
2. Plate-making parameters
After the screen printing process is converted to the gravure printing process, the gravure plate-making parameters should be adjusted as much as possible to make the gravure effect close to the screen printing effect. For example, the plate-making parameters of the embossed ink gravure process are 60 lines/cm and 35μm cavity depth.
3. Small graphic printing
Under normal circumstances, small graphics and texts are usually appropriately bolded during screen printing pre-processing. However, when the screen printing process is converted to the gravure printing process, the small graphics and texts should be adjusted to the original effect.
4. Printing registration
Because the registration accuracy of screen printing is not as good as gravure printing, it is possible to hot stamping the printed product first, and then screen printing, and the relative position of the register can be appropriately expanded. However, when the screen printing process is converted to the gravure printing process, the relative position of the register can be adjusted to the original state.
5. Die-cutting shrinkage
When the screen printing process is converted to the gravure printing process, the influence of die-cutting shrinkage should be tested, and the size of the die-cut plate should be adjusted appropriately.