Relief Printing Letterpress printing is characterized by the fact that the picture and text on the printing plate are convex and lie in the same plane, and the concave blank part is not coated with printing ink. The letterpress prints are vivid in ink and clear in writing. They can use relatively cheap ordinary paper and have a low paper loss rate.
The disadvantages are the long time for plate and pad printing, and the small format for printing plates; the picture quality is inferior to offset printing and gravure plates, and lead alloy pollution is harmful to the environment. Therefore, after the 1950s, it was gradually replaced by other printing methods. Only the flexography made of photosensitive resin can maintain its development trend in package printing and newspaper printing.
Lithographic lithography originated from lithographs, and its feature is that there is no clear difference between graphic and text parts on the layout.
The chemical properties of the two are different: the graphic part is oleophilic and the blank part is hydrophilic. Wet the platen before printing and apply the ink to the graphic section. Due to the heavy and expensive price of the stone plate, it was soon replaced by a surface-polished metal plate and printed on a circular press.
In 1905, the American IWRubel invented the indirect lithographic printing through the blanket cylinder transfer, which is commonly known as offset stencil printing in China.
The feature of stencil printing is that there are many fine holes in the graphic part of the printing plate, and the blank part is closed. Printing ink passes through the graphic part and adheres to the surface of the substrate. Common hole editions are available in both scratch and screen versions.
The printing version is simple and convenient, suitable for printing a small number of documents, handouts, and has now been replaced by a copying machine.
The screen printing equipment is simple and the plate making is convenient. It can print ink layers with thickness of 30 to 100 μm on different substrates. The color is bright and thick, and the prints can be printed and weathered. The drying speed can be accelerated with infrared or hot air, or UV can be used. The ink cures under ultraviolet light.
Therefore, it is particularly suitable for the printing of various kinds of printed matter, metal signs, plastic products, ceramic decals, glassware, and printed circuit boards in medium and small batches, with a wide range of applications, rapid growth, and broad prospects for development. However, screen printing is not suitable for printing trumpet characters. Color screen printing is prone to moire, and printing speed is diffuse. In the field of large-scale books, newspapers and newspapers, it is difficult to compete with other printing methods.

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