Analysis of the phenomenon of inverted hair in offset printing
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First, what is the downturn
When printing solid lines, lines or text, burrs are produced at the edges of the graphic. This is what is often said to be down. The burr is called the hair in the direction of the bite, and the burr is called the hair in the direction of the tip. It has a consistent orientation on the plates, blankets and prints, otherwise it may be a phenomenon of squeezing or a phenomenon of ghosting.
Second, the influencing factors
When the following three factors are present at the same time, the inverted hair will be produced:
1. The plate cylinder and the rubber roller are not properly lined, so that the radius of the plate cylinder is not equal to the radius of the blanket cylinder, and the difference is large.
2. There are more paper, powder, sand, etc. on the surface of the paper falling off on the blanket.
3. The metal substrate of the plate material is not strong enough.
The above three factors are all related to the impression cylinder.
Third, failure analysis and solution
1. Inverted hair: the generation of inverted hair. In the case of the above three factors, when the linear velocity of the surface of the R-printed R rubber plate is greater than the linear velocity of the surface of the blanket, the sliding friction is generated in both of the combined pressures. The two of the combined pressures generate friction so that the ink on the printing plate and the blanket are squeezed in opposite directions from each other. Since the R printing is fast, the ink on the surface is elongated in the direction of the trailing tip; while the surface speed of the blanket is slow, the ink on the surface is elongated in the direction of the biting.
The elongated ink on the printing plate is removed by the action of the water roller and the water syrup in addition to the sensory action and the ink collecting action of the ink roller. Although the elongated ink is constantly produced, it is continuously removed. Therefore, the ink on the printing plate is elongated, so it does not become the source of the reverse. The elongated ink on the blanket cannot be transferred to the paper. Due to the adhesive force of the ink blot, more paper is deposited at the print than elsewhere. These sheddings become oily deposits when mixed with the ink blot. When the printing plate and the blanket are embossed to produce sliding friction, it slides and accumulates on the blanket in the direction in which the printing plate generates a force. As the oily deposit on the blanket grows and becomes thicker in the direction in which the imprint is elongated, the plate sand that contacts the place is worn and damaged. It is also attacked by oil, gradually feeling fat and oily, and finally produces burrs, and the burrs will become longer and longer. This is why the burr on the plate shines when the hair is thrown.
Solution: Reduce the plate pad, the number of pads removed is increased in the blanket, and the center distance between the blanket cylinder and the impression cylinder is appropriately increased. If the number of blankets of the blanket meets the standard data, the center distance between the plate cylinder and the blanket cylinder should be reduced after the liner is removed.
2, smooth hair: When R printing > R oak, under the three factors that produce inverted hair, it produces smooth hair. Its imprinting direction is opposite to that of inverted hair, and the principle of generation is the same as that of inverted hair.
Treatment: Reduce the liner in the blanket. If the plate liner is lower than the standard data, increase the liner in the plate and reduce the center distance between the impression cylinder and the blanket cylinder. If the plate liner thickness meets the standard data, the center distance between the three rollers needs to be reduced at the same time.