Overview of Pad Printing Process (I)

To print on the surface of a small workpiece such as a button, or to print on a profiled surface such as a toothbrush handle, the screen printing process has a great limitation, and the pad printing process can be completed very satisfactorily. In fact, the printing process does not exist independently. It is always produced in special printing companies like silk-screen printing twin sisters, occupying an important position in the decorative printing of plastics, electronics, toys, watches and other industries.
First, the principle of the printing process The printing process is a bit like a rubber stamp, but the rubber stamp itself is made into a convex text. After drawing the ink and moving it to the desired place, it will be printed with a simple text. The pad printing process transfers the ink by means of a deformable pad printing head. The surface of the pad printing head does not contain graphics; the required graphics are first dried and etched into pad printing intaglio, and then printed on the intaglio printing surface. The ink is applied, and the ink on the surface of the printing plate is scraped off with a hard scraper, the ink at the pit of the printing plate is picked up with a plastic head, lifted, and moved to the surface of the substrate for printing. Since the pad printing process adopts an indirect printing method, there is no strict requirement on the relative position of the plate and the substrate. The pad printing head can be made relatively small, so it is very suitable for the printing of small workpieces; and the pad printing head is easily deformed and formed. The shape of the surface of the printing material conforms to the shape of the printing surface, and there are irreplaceable advantages of other printing processes for the printing of irregularities, matte surfaces, spherical surfaces, and arc surfaces.
Second, the printing plate traditional printing process is not to use the printing plate as a graphic carrier to distinguish the graphic and non-graphic area. The pad printing process is no exception. The pad printing process uses a plane intaglio plate that is concave on the plane of the printing plate as a graphic and text carrier. Similar to the gravure cylinder used for gravure printing, the manufacturing principle and method are similar, but it is not cylindrical. Another difference is that the pad printing process is commonly used in labor-intensive special printing companies. The cost cannot be too high. The plate used is not based on chrome plated copper plates. The Rockwell hardness HRC is mainly between 45-60. alloy steel.
1, the thickness of 10 ~ 15MM pad printing plate The earliest pad printing machine to take the ink supply mode, the main use of a thickness of 10 ~ 15MM pad printing steel, the substrate after grinding, polishing, grinding, to achieve surface roughness RA A mirror effect of 0.025 μM can be used for plate making. The surface of the steel plate is first coated with a layer of polyvinyl alcohol emulsion, dried and then attached to the printing plate. The film is exposed under a vacuum printing machine. The water (Fuji photoresist is used in special gasoline) is developed, and the intaglio is etched with an etching agent. Printing on the machine. Nowadays, domestic production of pad printing machines generally uses thick steel plates.
2, the thickness of 0.25 ~ 0.5MM of printing thin steel plate swept the 1980s, the green wave is also constantly flowing into the printing industry, located in the wave position of offset, flexo, gravure, etc. have washed away dust, put on green . The special printing industry in Bogu is affected by a bit more or less. Although it is only a small change, it also makes people feel that the health requirements of people engaged in the special printing industry are also very important.
The printing process is based on solvent-based screen printing inks. The volatilization of solvents is harmful to the human body. However, the use of water-based inks is not practical. The first is that the steel plates tend to rust, and the second is that the ink viscosity does not meet the requirements. The pad printing head has almost no affinity for aqueous ink. Therefore, foreign countries first proposed the design concept of ink cartridges for ink. The solvent-based ink is sealed in an oil crucible. The oil crucible absorbs the thin steel plate by its own magnetic force, and it achieves the two purposes of ink coating and ink scraping by oscillating the oil crucible. It not only prevents the ink solvent from evaporating, but also saves the scraper device. . The reason why the ink cartridge ink supply method adopts thin steel plate instead of thick wood plate is mainly to install and remove ink cartridges. The thin steel plate is easily removed and flipped, and the ink cartridge is removed. If the ink cartridge is directly removed, the ink will be left behind. Above the steel plate, the thick steel plate is too thick and heavy, and it is not flexible enough to fit it.
The vast majority of the printed sheet steel is pre-coated with a polyvinyl alcohol emulsion and protected by a black PE film. The protective film can be removed directly during use. The printing process and corrosion process are the same as for the thick steel plate.
3. The nylon gravure pad printing plate with a thickness of 0.5 to 1 MM also has a tendency of non-metallization. Among thermoplastics, nylon has excellent abrasion resistance, and has good corrosion resistance to solvents in inks, and modified ternary nylon is still an ideal photographic material, so nylon gravure has a tendency to replace the printing plate. Nylon gravure also lays a material foundation for digital plate making in the future.
Nylon gravure is usually pre-coated on the zinc plate or aluminum plate, because during the printing process ink and nylon surface directly contact with the substrate zinc plate or aluminum plate across the nylon layer, so do not have to mention their strength.
Nylon gravure is supplied with a fixed size, protected with a PET film, and the protective film is removed when it is used. The printing film is applied and exposed, developed with ethanol, and rinsed with warm water.
4, chrome plated high-definition copper plated sometimes used chrome plated copper, copper organization structure is detailed, easy to show dot structure, very conducive to the performance of details, in the use of printing process for small dishes, bottle caps when printing Copper plates can also be used.
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 rubber head The difference between the printing process and the offset printing process is that the blanket is in line contact with the plate cylinder and the blanket cylinder; the contact between the printing pad and the printing plate and the substrate is in surface contact, and the surface contact is maximum. 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. . (To be continued)