The wide application of label and the continuous development of label varieties naturally promote the development of label printing technology. Label printing covers flat, convex, concave, mesh and other printing methods, the application of different countries are not the same. However, it can be seen from the development trend of global labels in recent years that flexographic printing, narrow-range rotary printing and digital printing have become the new bright spots of label printing in European and American countries, and also the development trend of label printing.

Prepress processing

In the aspect of pre-press processing, many orders designed by customers are mainly offset printing or gravure printing. If flexo printing is adopted for this kind of manuscript, many quality problems will occur in the sample, such as the color is not in place, the layers are not obvious, and hard edges appear. Therefore, to solve such problems, timely communication with customers is very necessary.

Nowadays, label printing is done by hand, and many monochrome labels are done by machine .Which can improve the production efficiency. Although the printing accuracy of many newly developed label printing machines is not high, they have improved the printing efficiency and the printing quality needs to be improved.

Plate making process

Label printing covers several main printing methods in the platemaking stage. According to different product nature, choose different printing methods, according to different printing methods, plate – making process is also different. This paper takes the flexible plate making process as an example to make a brief introduction.

The process flow of flexible plate-making is as follows: original manuscript (artwork), film (negative film), exposure, rinse, drying and treatment.

1. The manuscript(artwork). The original design suitable for flexible printing should have the following characteristics: large number of colors. But less overprint; There is no requirement to reproduce particularly small details; The cable is not too high, but can achieve color printing effect; Packaging processing can be done online.

2. Film (negative film). Meet the needs of plate making, clear pictures and texts, accurate size specifications; With matte film, the density of the four corners of the film should be consistent. The use of drug film orthography; The white potential density was below 0.06 measured by the transmission density meter. The black bit density is above 3.5.

3. Exposure includes back exposure and main exposure.

Back exposure. Photosensitive resin version of the supporting film up, protective film down tile in the exposure drawer to receive exposure. Uv light penetrates the supporting film to solidify the photosensitive adhesive layer. To establish a solid base, can also control the depth of wash, strengthen the bond between the supporting film and photosensitive resin layer. The back exposure time is determined according to the required base thickness.

Main exposure. Also known as the front exposure, photosensitive resin plate material support film down, protective film up. It’s tiled in the exposure drawer. Tear off the protective film one time in a row, then paste the film surface on the photosensitive resin plate. The test method is applied to the film (non-drug film is vacuumed to make the film adhere closely to the photosensitive resin layer. The ultraviolet ray penetrates the vacuum film and the film transparent part, causes the plate photosensitive part polymerization to solidify. The length of main exposure time is determined by the type of plate and the intensity of light source. Exposure time is too short will make the graph and text slope is too straight, curved lines, small words, small points are washed out, on the contrary, exposure time is too long will apply version, the handwriting is blurred. If there are large, small, thick, thin lines on the same plate. Cover with black film as appropriate and expose separately. Small parts will not be lost due to washing, to ensure the quality of the plate.

4. Rinse. Wash the photosensitive part of the solution, retain the light polymerization of the relief. The length of the wash time according to the thickness of the plate and the depth of the print, the wash time is too short, the plate will leave no photosensitive resin and affect the depth of the plate, the wash time is too long will make the plate expansion, resulting in the fine part deformation or fall off.

5. Drying. Remove washing solvent, so that the plate to restore the original size of the thickness. The baking temperature is between 50-60 ℃. Baking time according to the thickness of the plate and wash the length of time to determine, the general thick version of two hours, a thin version of an hour. Baking time is too long, baking plate temperature is too high will make the plate brittle and affect the printing life. Baking temperature is too low will prolong the drying time, baking time is too short, printing will appear rotten version phenomenon.

6. Post-processing. That is, after the removal of adhesion and exposure. Make the photosensitive resin completely hardened (polymerized) to achieve the due hardness index, and eliminate the plate viscosity, in order to facilitate the transfer of ink. The post-treatment time was obtained by testing for the purpose of not cracking or sticking.