Pad Printing Process Overview (2)

Third, printing rubber head printing rubber head can be said to be a sign of the printing process, it plays a role in adsorption and transfer of ink. From the perspective of whether the printing plate is in contact with the substrate, the printing can be divided into two categories: direct printing and indirect printing. Offset transfer of ink by blankets is representative of indirect printing; embossing, flexo printing, gravure printing, screen printing It is obvious direct printing. It is obvious that the pad printing process also belongs to standard indirect printing. Both the print head and the blanket have a great influence on the print quality.
1. The shape of the printing pad The pad printing process differs from the offset printing process in that the blanket is in line contact with the plate cylinder and the blanket cylinder; the contact between the pad printing plate and the printing plate and the substrate is surface contact, and the maximum surface contact is The disadvantage is that it easily traps air and forms bubbles. For this purpose, the pad printing heads are all designed to have the shape shown in the drawings. In the middle of the printing, the printing plate or the substrate is firstly contacted. As the pressure increases, it gradually extends to all the graphic areas. The air is also extruded step by step. . The shape of the pad printing head includes parabolic body, sphere and approximate cone. In the case of a sphere with the same amount of compression, the printed surface should be larger than the parabola and the approximate cone, but when printing a small area of ​​small text, use a parabola and an approximate cone. The pad printing head can be made into various special shapes and combined to print various complicated printing surfaces.
2, the hardness of the printing plastic head RTV silicone rubber in the vulcanization process by adjusting the amount of softener to control the hardness of the printing head. Hardness is usually expressed in terms of Shore hardness, which reflects the ability of the print head to resist deformation. When printing flat workpieces and gradation patterns, the hardness of the plastic head should be selected to obtain smaller deformation and lower dot gain; and when printing curved workpieces, softer rubber heads should be used to achieve greater deformation. . However, when the graphic on the flatbed printing plate is transferred to the surface of the surface of the substrate, it will be deformed. If the hardness of the plastic head is softer, the deformation will be greater. The choice of controlling the deformation of the printing head only depends on the hardness of the printing head. It is necessary to compensate for deformation when making a printing plate according to the deformation trend.
3. Deformation of the printing head The deformation of the printing head is the basis for ink transfer. However, this deformation is also the main reason for the deformation of the imprint. The complete transfer of the imprinting does not result in significant deformation, and it is best to control. The deformation is less than 10mm, that is to say the effective value of the cross-sectional area of ​​the printing head is 110% of the area of ​​the graphic when the central part is compressed by 10mm. Sometimes the shape of the surface of the substrate is rather special, and it can be designed as a plastic head with a similar cross-sectional area after the deformation and the surface of the substrate in order to control the compression amount below 10 mm. Of course, the amount of deformation of the print head is related to the hardness. Selecting a harder head under the premise of controlling the amount of deformation below 10 mm can obtain an ideal print.
Fourth, pad printing equipment Pad printing machinery is a relatively simple structure in the printing machinery, mostly consists of the following components:
1. The workbench bench is used to place fixtures and substrates. The workbench of a monochrome pad printer is usually a three-part mechanism capable of three-dimensional position adjustment; the two-color pad printer workbench is mainly based on a shuttle workbench and can The two printing positions move back and forth to realize two-tone color printing; the multi-color printing machine includes a rotary table and a rotary table, which can perform continuous color printing, and the productivity is relatively high.
The automatic up and down of the printing plate reflects the direction of the development of modern printing machines. It greatly reduces the labor intensity of workers, can reduce production costs and increase labor productivity. In particular, pad printers for professional products, such as optical disc printers, do not need to manually disassemble worktables for printing materials.
2. Printing device The printing device is the core of the pad printing machine. It consists of a plastic head translation mechanism and a plastic head drop mechanism. The drop mechanism mainly completes the basic operations of ink sticking and lifting and printing and lifting; the plastic head translation mechanism uses To complete the reciprocating transformation of the rubber head at the plate position and the substrate position. Modern pad printing machines mainly have the basic movement of pneumatically controlled printing devices.
The adjustment of the drop motion of the glue head in the printing device is performed by adjusting the position of the magnetic induction switch of the machine side wall. The drop stroke of the rubber head directly affects the stamping force of the rubber head.
3. Ink supply device and squeegee device The ink supply device of the pad printer is also very simple. There are two ways to supply ink, ink cartridges for ink and ink roller for ink. Ink supply ink is ink and diluent is adjusted and packaged in the ink cartridge, inverted on the printing plate, using its own magnetic suction to the thin steel plate, the ink rod connected to the piston shaft can be reciprocally moved , To achieve overwrite ink and scrape ink. Most of the current printers in the domestic market are ink rollers for ink supply, the printing plate is placed at the front of the ink tank, and the scraper device with the ink and diluent at the rear end and the translation device of the plastic head are fixed together carries the ink coating roller itself. In the ink coating stage, the squeegee blade is in the raised position, and the ink coating roller is immersed in the ink tank. When the plastic head seat moves forward, the ink coating roller is driven to the surface of the printing plate to start coating, and then the squeegee falls down and scrapes the ink. Ink roller back to the starting position.
4. Control system The control system is used to arrange the above mechanical actions in an orderly manner to make the printing process automatic. Now the pad printer basically realizes microcomputer control, and the performance is relatively stable and reliable.
During the commissioning phase, the machine must be able to perform single-body motion tests, such as a plastic head dropping motion, a cyclic motion, and an idle stroke uniform ink motion. These actions have a single function button for individual control operations; in the normal production phase, the magnetic induction switch is equivalent. The position sensor sends a signal to the central microprocessor after detecting the position signal of the plastic head piston shaft. The central microprocessor then sends a voltage command to each control solenoid valve to push the cylinder to move. The printing machine continuously prints according to the printing process requirements.
Fifth, the status quo and development trend of the printing process Progress of printing technology is mainly reflected in the mainstream of printing, printing process is basically no much improvement, whether it is desktop publishing or direct plate-making, digital printing has no effect on the printing process, The ubiquitous printing industry that still exists in the special printing industry is still taking the photo film, corroding the printing plate, and printing a simple text block pattern with a pad printing device. With the progress of society, the use of printing methods to print beautifully-printed prints will become a kind of fashion. The printing process of printing will slowly move forward in the direction of environmental protection, security, digitalization, and high quality.