Gravure printing adopts the direct printing mode of circular pressing and rotary. Its characteristics are: simple structure of printing machine, high printing resistance, fast printing speed, thick ink color, rich layers, low cost in mass printing. There are many types of gravure printing, which can be divided into three categories according to their uses: gravure press for books and periodicals, gravure press for soft package and gravure press for hard package. The book gravure printing machine is used to print magazines, books, pictorials, etc., with folding device at the back; the flexible packaging gravure press is used to print packaging materials such as cellophane, plastic film, aluminum foil and paper, and the back can be equipped with composite, glazing, die cutting and other devices. According to the way of plastic can be divided into two types: sheet fed gravure press and web gravure press, most of which use web gravure. According to the color number classification, it can be divided into monochrome gravure press and multi-color gravure press. According to the arrangement position of printing color group, it can be divided into satellite gravure press and combined gravure press. Satellite gravure printing machine several color sets share an imprint roller, and each color set of combined gravure press is arranged horizontally into an assembly line.
For gravure printing, according to the requirements of the work order and sample sheet, collect the ink and substrate; then install the printing cylinder; adjust the lining on the embossing cylinder to make the pressure of each part of the plate consistent; and adjust the angle and distance of the squeegee to the plate, and start the trial printing. After the trial printing sample sheet is qualified, it can be officially printed after being signed by the workshop supervisor and the customer. The following is a brief introduction to the printing process by taking the combined gravure press as an example
1. Unwinding device and adjustment
1) The web stand is used to install the web or plastic film roll on the printing machine with a conical tip. When the paper roll is nearly used up, the automatic paper receiving device will automatically bond the new paper roll or plastic film roll to the running paper tape, and cut off the old paper tail to complete the roll change without stopping the machine.
2) Tension automatic control system paper or film in pre press unwinding process, multi-color printing process or after printing paper receiving process, it is necessary to maintain a certain tension, too large tension is easy to produce longitudinal wrinkles, too small tension is easy to produce horizontal wrinkles, in short, the fluctuation of tension will affect the accuracy of overprint.
3) In order to ensure that the horizontal regulation of the printing material roll into the printing part or rewinding, it is necessary to adjust the horizontal deviation. The lateral deviation can be adjusted by pneumatic (hydraulic) cylinder or by horizontal regulation roller.
2. Adjustment of scraper and embossing cylinder
1) The scraper adjusts the pressure required to scrape off the printing plate surface ink and the pressure required to resist the impact of ink. The pressure is directly proportional to the printing speed. Generally, the speed is fast, and the pressure should be large. In addition, the selection of the angle between the scraper and the plate is generally 30 ° - 70 °. In this way, the knife edge will not damage the layout, and the quality of the printed products can be better.
2) Adjust the imprint cylinder, the plate cylinder can be adjusted after the cylinder. For different substrates, the printing pressure of the imprint cylinder is different. For example: cellophane, plastic film, printing pressure is 1-5pa. The printing pressure is 8-15pa. The printing pressure of white board paper is 20-30pa.
3. Adjustment of ink drying temperature
At present, gravure inks are mostly solvent based inks. When printing, the operator should adjust the drying temperature of each unit according to the type of substrate, printing speed, graphic area and ink layer thickness. Drying temperature is not easy to be too high, generally should be controlled below 80 ℃, and the maximum should not exceed 100 ℃. Otherwise, it will cause the substrate shrinkage, affect registration, too low ink drying.
4. Overprint
After the adjustment of the machine, the overprint can be carried out. First, register the layout with the manual adjustment button, and then the computer adjustment can be carried out. The vertical error of overprint depends on the tension adjustment, and the transverse error depends on the paper belt horizontal position control system and the push-pull plate cylinder adjustment.
5. Check the printing sample in formal printing
During the formal printing, the operator should check the printing sample with the standard sample, check whether there is any error, and make necessary adjustment.
(manufacturer of antistatic aluminum foil bag, fruit bag, daily chemical packaging bag, packaging roll film manufacturer of Beite (China) packaging Co., Ltd.)