Offset printing belongs to the indirect printing method. It utilizes the hydrophobic property of the rubber roller of the elastomer to transfer the printing ink on the printing plate to the printing paper. In order to make the printed ink uniform, clear dots, rich tone levels, offset blanket must have the characteristics of moderate hardness, small compression deformation, good ink transfer performance and small expansion rate. The quality of the blanket depends mainly on the materials used and their structure.

Offset blankets are air-cushioned blankets and ordinary blankets. Because the ordinary rubber does not shrink in volume during the imprinting process, it can only be pressed in the direction of force, so that the rubber layer on the surface of the blanket appears a raised convex bulge in front of the imprinting line. In the case of an offset printing press operating at a high speed, such a convex hull cannot instantaneously flatten down to restore the original surface of the blanket, thus often resulting in quality problems such as distortion of printed dots, blurred images, and poor reproducibility of double-printing or high-profile portions.

1 Quality requirements for offset printing blankets

In the offset printing process, the function of the blanket is to transfer the graphic on the plate completely and clearly to the substrate. In order to make the transfer of images and texts as ideal as possible, the blanket must have the following characteristics:

1) Thickness should be uniform. The uniform thickness of the blanket ensures that the printing pressure is evenly distributed, and the density of the ink is also relatively uniform, and the graphic size is not easily changed during the graphic transfer process.

2) It has good elasticity. The better the elasticity of the blanket, the better the effect of the transfer of printing and graphics and the ink-absorbing performance, and the better the quality of the printed product.

3) With less elongation. The structure of the blanket is dense, and the mechanical strength is good, which is conducive to the increase of tensile strength, and thereby reducing the amount of deformation of the graphic transfer.

4) The ink-absorbing performance and transfer performance are good, ensuring that the ink is well-balanced and clear in writing.

5) Acid resistance, alkali resistance, oil resistance, wear resistance, heat resistance, and anti-aging properties are excellent, which can extend the life of the product.

2 difference between ordinary blanket and air blanket

1) Different fabrics and rubber layers. The main difference between an air-cushioned blanket and an ordinary blanket is that not only different fabric layers and rubber layers but also a gas-filled layer are sandwiched between them, thereby constituting an elastic layer. The gas-filled layer is mainly divided into a micro-bubble shape and an air-slot shape, and a solid carrier layer is provided between the surface layer and the micro-porous layer to reinforce the adhesion between the upper and lower layers.

The air-cushion blanket is based on the principle of air compression. When the rubber blanket is pressed during offset printing, no convex bulge is generated, and it has compressibility and the surface is not easily damaged.

2) The air-cushioned rubber blanket has impact resistance, especially the Offset 08 machine uses a neutral lining, and the use of an air-cushioned blanket can be better. However, do not use air cushions for offset press proofers because the better the elasticity of the air-cushion blanket, the better the effects of graphic and text transfer and the ink-absorbing performance.

3) The air-cushioned blanket has the property of quickly peeling the paper, and the relatively thin printing paper (65-80g) has better effect and no peeling phenomenon occurs.

4) The air-cushion blanket has a small stretch rate and high flatness. Due to the low expansion and contraction rate of the air-cushioned blanket, the structure is dense and the mechanical strength is good, which is beneficial to the increase of the tensile strength and thereby reducing the amount of deformation of the graphic and text transfer.

5) Solid general rubber blankets can only be used for 3 to 4 months if books, magazines and magazines work for 8 hours a day. In addition, air-filled blankets produced in Tianjin can be used for more than half a year. As long as there are no tattered papers or multiple sheets of pressed rubber, the traces of air-cushioned blanket printing are less. Air-cushioned rubber blankets are oil-resistant, wear-resistant, heat-resistant, and have good anti-aging properties and long service life.

6) The air-cushion blanket has good ink-absorbing performance to ensure that the ink is well-proportioned, clear in writing, clean in printing dots, and has a small dot enlargement rate during the printing process.