Plate Printing Technology Discussion (Part I)

Foreword
The printing process is a special printing technology that has just been introduced to China in the 1980s. Due to its obvious advantages in printing on small-area, irregular-surfaced products, it has made up for the deficiencies in screen printing processes and, as a result, has developed very rapidly in recent years. . In the early 1990s, with the further opening up of the Chinese market, a large number of foreign-funded enterprises with electronic products, plastics, gifts, toys, and other traditional industries as the main products entered the Chinese market one after another. Pad printing technology and screen printing technology as the main decoration methods were obtained. Extraordinary development, according to incomplete statistics, the use of pad printing technology and screen printing technology in the above industries reached 27%, 64%, 51%, 66% respectively.

While all printing processes are exploring their respective strengths to converge, today's printing technology still maintains its independent identity. The link between paper and pad printing technology is still blank, but pad printing technology does not stop its rapid growth. Because the areas that printing technology is good at can't be accomplished by any other printing process. The prosperity of the Pearl River Delta industry supports the high growth rate of the printing industry at an annual rate of 18%. Every year, the employment opportunities created by the printing of technology-related industries have also been of concern to government agencies.

In general, the technical level of the pad printing process is not high, and it is very difficult to continue to develop in the case of high production costs in developed countries. Therefore, the pad printing industry has shifted to low-cost developing countries such as China. It is an inevitable trend. At present, in addition to the few foreign companies that also manufacture highly automated printing lines, most companies have moved their production bases to China. This is a historic opportunity for China. What is the current level of development of the printing process in China? Where is the latest development? The superficial ideas of this topic hope to bring some help to the readers.

Plate Printing Process
Detailed printing plate making process

Platemaking is the prelude to printing. The traditional printing is not realized by first transferring the graphic on the manuscript to the surface of the printing plate. In terms of printing plate making, it should be a combination of intaglio plate making technology and corrosion signboard technology. . The gravure plate making technology has now developed into electronic engraving and laser engraving, and the corrosion of the signboard has also gradually eliminated the acid etching technology. However, the printing plate making still remains in the very old process, which is related to the conditions of the pad printing technology itself. The first is that the cost of the printing process is relatively low, and the use of electronic engraving and laser engraving is too expensive, and the average enterprise cannot afford it. Many companies have proposed electrocorrosion technology, but no one company's technology can guarantee that the corroded plates can be printed. The process of acid corrosion is easy to grasp and low in cost. Despite severe environmental pollution, it is still used by most enterprises.

The use of pad printing steel plate printing plates in the printing process is dominant, 100% oil pad printing machines and 16% oil pad printing machines use thick steel plates with a thickness of about 15mm; another 77 The squeegee type pad printing machine of % uses a thin steel plate with a thickness of 0.25 mm and 0.5 mm, and the plate making process is the same regardless of whether it is a thin steel plate or a thick steel plate. The substrate used is also about the same. The steel plate must have a finely organized structure with a sufficiently high surface finish. The former guarantees the regularity of the edge of the image after etching, and thus ensures the integrity of the dot structure, so that the trimming sharpness and color reproduction of printed graphics and texts are achieved to the utmost extent; the latter ensures the cleanness of the scraping ink and the durability of the ink. The thick steel plate used on the ink pad printing machine requires higher surface tolerances. Excessive surface tolerances on the one hand accelerate the wear of the oil squeegee, and on the other hand, it also relates to the sealing property of the ink. It is used on an oil pan type pad printing machine. The steel plate to be used in the oil pan machine to ensure a higher surface finish and lower flatness tolerances.

The thin steel plate has better flexibility, so the degree of cleanness of the scraping ink is easy to guarantee, but this is related to the manufacturing precision of the substrate supporting the thin steel plate. The tolerance of the surface roughness of the substrate is unsatisfactory, and the ink slides on the oil file and the steel plate. Leak in the middle. Another factor is the manufacturing accuracy of the oil guide sliding guide shaft, such as surface roughness and fit tolerance, which is reflected in the index of the assembly level of the whole machine. It is very important to control the tolerance of the parallelism between the guide shaft and the steel plate. From this point of view, the thick steel version of the ink pad printing machine is more difficult to manufacture.

Printing plate etching manual operation method

Due to its small area and shallow nicks, the steel plate is mostly hand-processed and can be brushed, dip-coated, or shower-coated. Some people also taped steel plates around to form a "box." Then inject the etchant into the “box” and shake it. After the etching is completed, pour out the etchant, clean it, and remove the tape. Then, the protective layer of the photo ink should be removed by immersing it in a 5% aqueous solution of caustic soda at a temperature of 80-90° C. until the film is completely removed. When the temperature is high, the film can be stripped quickly. Generally, it can be 1 to 2 minutes.

Three printing methods for printing steel plates

1. The resin glue was mixed 1:1 with the corundum (volume ratio), a curing agent was added, and cast on an iron plate having a thickness of 5 mm and an area of ​​150 mm×300 mm. After solidification, a diamond milling cutter is used to regularly slot the groove in a certain geometric shape so that it can see the iron bottom so as to achieve the purpose of circulation of the electrolyte and conduction. Then level with a surface grinder.

2. The rectangular strips or ladder strips of the whetstone were adhered to an iron plate with a thickness of 5 mm on a regular, spaced-apart basis at a distance of 300 mm x 150 mm, and were pressed with a thick flat glass and set aside for use.

3. Graphite plates are used as electrolytic grinding blocks because of their dual role of electrolytic grinding and EDM grinding, so their speed is extremely fast. However, it is also easy to wear, so it is often necessary to trim.

The need for the performance of the steel plate for printing

1. Has good wear resistance. The steel plate will be damaged in each contact friction with the blade. The blade is made of high carbon steel. The surface of the steel plate should be scraped off. The surface of the blade should be smooth and smooth, and it should have a high hardness. If the surface of the steel plate is scratched, the degree of scratching will be affected. The usual test method is to mount the steel plate on the pad printing machine for 3,000 times and observe the surface with a microscope. The qualified steel plate should have no trace exceeding 5 μm in depth.

2. Has better processing performance. The substrate steel plate provided by the manufacturer can not generally be used for direct plate making, and it must first be subjected to grinding, grinding and polishing processes so that the surface thereof can achieve the surface roughness of the mirror effect. Therefore it is very important to have good mechanical processing properties.

3. With a fine and uniform structure. The finer the structure of the steel plate, the smoother the surface can be polished. More importantly, after the steel plate is corroded, the quality of the picture and text edge obtained is better, and the reproducibility of the dot is also more excellent, and it is easy to improve the printing quality. The reaction process between steel plate and concentrated HNO3 is also easier to control.

4. Has good corrosion resistance. The corrosion resistance of the steel plate shows that pitting and rust spots do not occur easily in contact with the ink and the solvent. The steel plate is corroded, the pits are filled with ink, the scraping blade does not clean the ink, and the printing quality is affected. Corrosion at the graphic and graphic will destroy the integrity of the graphic and make the steel plate obsolete. The corrosion of the steel plate is mainly related to the chemical composition of the steel.

All types of alloy tool steels include impact-resistant steels. To improve its hardness and wear resistance, heat treatment can be performed. Heat treatment can also uniformly and refine the microstructure.

Resin version Resin version applied to the printing process is not long, but it has been paid attention to. The resin plate is mainly made of nylon sensitized plastic and cast on the surface of the zinc plate, similar to the resin plate used on the sticker trademark. Nylon has very good abrasion resistance, and it can withstand the repeated rubbing of oil rakes or squeegees after curing. The advantage of using a resin plate is that, first of all, it is easy to obtain extremely fine dots. When printing delicate small items, the use of a resin plate is preferred. If it is said that the manufacture of ink pad printing machine reflects the manufacturing level of a company, it will be more difficult to manufacture a pad printing machine using a resin plate. After all, a nylon photosensitive adhesive belongs to a polymer material, and when the manufacturing accuracy of the substrate supporting it is poor, printing is performed. It is not easy to complete general printing. The surface state of polymer materials is very fine, and slight defects will seriously affect the printing quality.