Here are some solutions to the common problems of offset printing:
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Pulling is one of the common faults in printing. During the printing process, the ink on the printing plate or blanket is partially transferred to the surface of the paper and then separated at the very short moment of imprinting. If the peeling force of the ink is greater than the surface strength of the paper during the separation, the ink layer will be peeled off. Particles such as fine fibers and rubber on the paper surface cause blistering and blistering on the paper surface, which may cause peeling of the paper in severe cases.
First, the impact of the phenomenon of printing on printing
The phenomenon of pulling hair will cause pollution in the graphic part and affect the quality of the printed matter. On the one hand, the position of the peeled particles on the paper surface is white spots due to the transfer of the ink; on the other hand, the peeled particles are adhered to the printing plate by the transfer of the blanket, and the printing plate is first contacted with the dampening solution. Being wetted. In the subsequent contact with the ink, the ink is repelled, so that the printing image portion is not inked, resulting in a large number of white spots on the surface of the printed product. Or the peeled small particles are not found at first, and will accumulate on the surface of the blanket and the printing plate as the printing progresses, causing the printing plate to wear and increase the number of times the blanket is cleaned. Some small particles can even be transferred to the ink tank and the water tank, making printing impossible.
Second, the analysis of the causes of the phenomenon of pulling
In the short moment of imprinting, there is a very complicated force between ink, paper and blanket. The viscosity of the ink itself creates an adhesion to the surface of the paper when it is separated. The blanket is also viscous and will also produce adhesion. The interaction between the ink, paper, and blanket also produces a peeling tension.
If the above formula is not satisfied, the pulling occurs, which affects the printing quality and increases the frequency of cleaning the blanket.
Third, the factors affecting the speed of pulling
The complex effect of ink, paper and blanket on the imprinting makes the surface strength of the paper sometimes not low, but it still produces hair, which indicates that the pulling speed of the paper is not only affected by the printing speed, but also with the ink. Viscosity, thickness of ink layer, printing pressure, temperature, etc.
1. Relationship with printing speed
The pulling speed is based on the theory that the separation force of the fluid between the planes is proportional to the speed at the time of separation, that is, the greater the printing speed, the greater the separation force. For the ink fluid, as the printing speed is increased to a certain extent, the separation force generated by the ink is greater than the bonding force of the paper surface, the tearing and fluffing visible to the naked eye is generated, and the minimum speed is called the pulling speed.