Label printing covers several main printing methods, in the plate making stage. According to the nature of different products, different printing methods are selected, and the plate-making process is also different for different printing methods. This paper takes the flexographic plate making process as an example for a brief introduction.
The process flow of flexographic plate making is as follows: original manuscript-film (negative film)-exposure-rinsing-drying-post-processing.
1. original. The original design suitable for flexographic printing should have the following characteristics: a large number of colors. But the overprinting is less; it is not required to reproduce particularly small details; the network cable is not too high, but the color printing effect can be achieved; it can be packaged online.
2. Film (vaginal film). It meets the needs of plate making, with clear pictures and texts, and accurate size and size specifications; using frosted film, the four corners of the film are required to have the same density; using the drug film orthography; using a transmission densitometer, the white level density is below 0.06; the black level density is above 3.5.
3. Exposure includes back exposure and main exposure.
① Back exposure. The photosensitive resin plate with the support film up and the protective film down is laid flat in the exposure drawer for exposure. Ultraviolet light penetrates the support film to cure the photosensitive adhesive layer. In order to establish a stable base, it can also control the depth of plate washing and strengthen the bonding force between the support film and the photosensitive resin layer. The back exposure time is determined according to the desired substrate thickness.
②Main exposure. Also known as front exposure, the photosensitive resin plate support film faces down and the protective film faces up. Tiled in the exposure drawer. Tear off the protective film once in a row, and then stick the film surface on the photosensitive resin plate. The inspection method of the vacuum film is covered on the film (non-drug film is evacuated, so that the film and the photosensitive resin layer are closely attached. The ultraviolet rays pass through the vacuum film and the light-transmitting part of the film to make the plate photosensitive Partial polymerization and curing. The length of the main exposure time is determined by the type of plate material and the strength of the light source. If the exposure time is too short, the gradient of the graphics and text will be too straight, the lines will be curved, and the small characters and small dots will be washed out. Otherwise, the exposure time will be too long. , the handwriting is blurred. If there are big, small, thick and thin lines on the same printing plate, it can be covered with black film and exposed separately according to the situation. The small part will not be lost due to washing, so as to ensure the quality of the printing plate.
4. rinse. The non-photosensitive part is washed and dissolved, and the photopolymerized relief is preserved. The length of the plate washing time is determined according to the thickness of the printing plate and the depth of the printing pattern. If the washing time is too short, the unphotosensitive resin will be left on the plate and affect the depth of the plate making. fall off.
5. drying. Remove the plate washing solvent to restore the plate to its original size and thickness. The baking temperature is between 50-60 degree . The baking time is determined according to the thickness of the plate and the length of the washing time, generally two hours for the thick plate and one hour for the thin plate. If the baking time is too long and the baking temperature is too high, the printing plate will become brittle and affect the printing life. If the baking temperature is too low, the drying time will be prolonged, and if the baking time is too short, there will be a rotten version during printing.
6. post-processing. That is, de-sticking and post-exposure. Make the photosensitive resin completely harden (polymerize) to achieve the proper hardness index, and eliminate the viscosity of the printing plate, so as to facilitate the transfer of ink. The post-processing time is obtained from the test, and the purpose is to not crack or stick.
