The role of the blanket
The function of the blanket is to faithfully transfer the graphic information on the printing plate and transfer it to the printing material without any mistakes.
Structurally, it is classified into an air-cushion type having a fine porous compression layer and a solid type having no compression layer (see FIG. 1). The expansion coefficient of the surface rubber of the deformed part of the air-cushion nip line is small, and thus the change rate of the circumferential increase is small (see FIG. 2 ). Therefore, it is possible to suppress ghosting, blurring, dot gain, misregistration, and misprinting. Other issues have become the mainstream of current blanket use.
The blanket is a combination of synthetic rubber and a woven fabric. The woven fabric layer is usually formed by attaching 3 to 4 layers of fabric to a synthetic rubber. Synthetic rubber generally uses nitrile rubber, except in special circumstances. Its thickness is divided into 1.68mm, 1.95mm, 2.05mm and other specifications, depending on the use of the application.
The ideal characteristics of the blanket
Flexible blankets that can be flexibly handled according to different printing requirements should have ideal characteristics. Here, the two major characteristics of the blanket, namely the compressibility and the surface rubber properties, are described.
Compressibility
Compressibility is the hardness of the blanket, which directly affects the transfer of ink and the passage of paper. The harder the blanket is, the better the ink transferability is, but the paper-passability will be worse. The relationship between field density, persistence of ink transfer, registration, and compressibility is summarized in Table 1.
Surface rubber properties
The ink is directly received and transferred by the surface rubber and is presented on the substrate. For this reason, like the compressibility (hardness), the surface rubber properties affect the ink transferability and the paper flowability. The physical and chemical properties of the surface rubber itself, that is, the properties of the rubber, the thickness of the surface rubber, and the chemical affinity of the ink are all important factors.
Among the physical properties of the surface rubber, the hardness of the rubber is particularly important. The harder the surface rubber, the improvement in dot gain, ghosting, and registration, etc., but the deterioration of solid density and ink transfer persistence.
The thickness of rubber on the surface of the blanket increases with the density of the spot on the ground, and the relationship between the shape of the dot and the feedability is shown in Table 2.
Future issues
First, with the increase in the speed of printing machinery and the need to cope with long-run job printing, paper feeding and durability will become important issues for blankets. It is required to change the shape of the blanket itself, and the demand for cylinders, metal pads and the like will increase. However, its quality and price factors have yet to be further addressed.
On the other hand, in the field of short-lived printing, the emergence of on-demand printers requires that the blanket's function should perform well in dealing with all kinds of special jobs. (Text/Ding Yi)
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