Sheet metal waterless offset printing is a lithographic offset printing method that uses special silicone rubber-coated printing plates and inks, and does not require isopropyl alcohol or other chemical dampening solutions that are necessary in conventional lithographic offset printing. The waterless offset printing process is simple in operation and does not require adjustment of the ink-water balance relationship to transfer the ink to the printing plate within a certain temperature range. Due to the non-absorbing properties of the metal plate, the elimination of the wetting water is more advantageous for the printing of the metal plate. Therefore, waterless offset printing has been promoted and applied in foreign metal plate printing.
1 Waterless Offset Printing Technology Development
In the early 60s, the United States 3M Company first patented and industrialized the waterless offset printing technology. However, due to some technical problems that were not well resolved, 3M stopped the production of waterless offset printing in the early 1970s. Since then, the technical staff of the world's printing industry have continuously explored and studied according to this idea, and the waterless printing technology has continued to mature, and has made great progress. For example, Toray Corporation of Japan began to officially sell the company's R&D in the mid-1970s. Waterless offset printing plate. From the 1980s to the 1990s, Japan Paper Cheungtang Co., Ltd. substantially changed the ordinary lithographic offset printing to waterless offset printing. The output of waterless offset printing reached approximately 85%, and computerized management of production scheduling control was achieved. And economic efficiency has greatly improved.
2 waterless printing principle
Ordinary lithographic offset printing is based on the principle of ink and ink repulsion. On the same printing plate, there are both water and ink. Part of the graphic and text on the plate is printed with ink and the blank (non-graphic) part is filled with water. The quality of the printed matter depends mainly on the balance between water and ink. If the layout of water is too large, there will be ink emulsification phenomenon, so that the ink color dilute, tinting strength is reduced, the ink cohesion is poor, resulting in dirty and ink roller deinking phenomenon; if the layout of water is too small, will cause the blank part of the printing plate dirt, Graphic part of the paste, ink becomes too deep.
Waterless offset printing plate is coated with a layer of silica gel adhesive layer on the photosensitive layer. Before exposure, the photosensitive layer and the silicon adhesive layer are firmly adhered together. After the exposure, the photosensitive site (non-graphic part) produces optical polymerization. The cross reaction causes the upper silicone adhesive layer to adhere and fix, and has silicone oil repellency characteristics.
Waterless offset printing plate is a kind of plano gravure (the graphic part of the layout is lower than the surface of the printing plate), and the printing plate adopts positive type horizontal printing plate or negative type horizontal printing plate, which not only improves the glossiness of printed goods. At the same time, it is beneficial to the drying of the ink layer. It has the advantages of easy operation, good image reproducibility, high printing density, brilliant colors, and good print quality.
The key to the development of a waterless offset printing plate is to cut off the silica gel layer corresponding to the graphic part. The shear force is stronger than the adhesion between the silicone layer and the photosensitive layer in the graphic part. Applying it to the interface between the two layers can remove the graphic part of the silicone layer. Use appropriate P. P. G (polypropylene glycol) and P. E. G (polyethylene glycol) will swell the photosensitive layer of the image part (unexposed part), and the silicone rubber layer floats. After the adhesive force between the two layers is greatly weakened, the nylon brush is uniformly removed. The silicone layer of the interface can be completed without the watermark version.
3 Advantages of waterless offset printing
1) Improve the quality of printed products. Since the dampening solution is eliminated, it is no longer necessary to consider the ink balance problem that is difficult to grasp, and at the same time, the ink emulsification problem is solved, and the ink drying speed is accelerated. Therefore, waterless offset printing has the ability to print more stable dots, a higher number of mesh lines, and the ability to obtain color stability, and can print clearer, brighter images.
2) Wide range of printing materials. Waterless offset printing can not only print paper, metal plates, but also print materials such as plastics. For non-absorbent substrates, such as metal plates, synthetic paper, etc., because it does not absorb the fountain solution, the fountain solution can only return to the ink fountain along the ink path, causing severe emulsification of the ink, causing great changes to the printing color, The use of waterless offset printing can effectively guarantee the quality of printed products.
3) Reduced consumption and increased production efficiency. The change of ink and ink balance in traditional offset printing can cause ink emulsification. Operators need to have rich experience. They should not only be familiar with the offset printing process, but also need to understand the structure of the printing press, water hardness, PH value, conductivity, alcohol content, and substrates. The water absorption, etc., in order to properly control the ink balance. Waterless offset printing does not have ink-ink balance problems, simplifying the printing process and eliminating many of the factors that cause changes in the process. It can make the dots of printed products full of ink and bright colors in graphic and text. Eliminates the quality problems such as ink unevenness, ink emulsification, water spot, reverse stain, and water roller print caused by fountain solution. Therefore, the preparation time before starting the machine is shortened, the downtime caused by the fountain solution is greatly reduced, the consumption of the substrate is saved, and the printing cost is reduced.
4) Simple operation and low labor intensity. Since waterless offset printing is significantly simpler than ordinary offset printing, it is easy for operators to master the technology, which helps to ensure and stabilize the quality of printed products, while reducing the labor intensity of workers and the number of operators.
5) Conducive to environmental protection. Waterless offset printing no longer uses volatile organic compounds in the fountain solution, reducing the amount of volatile organic emissions and reducing environmental pollution.
Sheet metal waterless offset printing press mainly consists of plate cylinder, blanket cylinder, impression cylinder and inking device. Plate material, ink and temperature control are the key to waterless offset printing technology and directly affect the development speed of waterless offset printing. The plate is the core of waterless offset printing. Although it is different from the PS plate, the plate making process is the same as the PS plate. Therefore, the resistance of a waterless offset printing plate depends on operating conditions and environment. The special formula waterless offset printing ink has the characteristics of low viscosity, high viscosity, high thixotropy, and stable performance. At present, the plates and inks used for waterless offset printing mainly rely on imports, and the prices are relatively high. However, as the technology continues to advance, the cost of plates and inks will decline. With the advancement of printing technology and the use of laser on-machine platemaking systems, the prepress process will be greatly simplified, the imposition and printing process will be eliminated, the quality of printed products will be improved, and the cost will be reduced. With the advancement of technology and the increase in labor productivity costs, waterless offset printing technology will be further developed and promoted.
Source: Qilu Graphic Arts Network
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