Blanket selection needs to consider 5 elements
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The blanket is an intermediate for the transfer of offset ink, and its quality directly affects the quality of the printed matter. Moreover, the price of the blanket is high, and excessive replacement of the blanket during the printing process is undoubtedly a disguised increase in the cost of the product.
When selecting a blanket, the elasticity of the blanket, the ink transfer performance, the corrosion resistance, the penetration resistance and the flatness are the five most important factors to be considered.
1. Elasticity
The moment the blanket exits the embossing zone, the deformation due to printing pressure is restored. This is the most basic and important technical requirement for the blanket, which determines whether the printing ink can be transferred normally.
The blanket cylinder is between the impression cylinder and the plate cylinder. When printing, each unit on the blanket is in contact with the two rollers once during one rotation, that is, two deformations are generated by the printing pressure, and at the same time The process by which ink is transferred from the plate to the blanket and then transferred from the blanket to the substrate. Assuming that the sheetfed offset press is normally printed at a speed of 10,000 sheets per hour, each unit on the blanket is deformed once every 0.18 seconds and is required to recover deformation before the next deformation (within 0.18 seconds). The time required for the deformation recovery of the high-speed rotary press blanket is shorter. If the deformation cannot be restored, then after each unit on the blanket transfers the ink onto the blanket from the printing plate, the ink can no longer be transferred to the substrate, or after the ink is transferred to the substrate. The ink transferred from the plate cannot be accepted, and the printing process cannot be completed.
2. Ink transferability
Ink transferability is another important technical requirement for blankets. It is often measured by the ratio of the amount of ink transferred from the blanket to the substrate and the amount of ink transferred from the plate to the blanket. The ratio is higher. High is more conducive to the transfer of ink. The poor ink transfer performance of the blanket causes the ink to accumulate on the blanket, increasing the number of times the blanket is cleaned, and at the same time causing the operator to think that the amount of ink is too small to increase the amount of ink, thereby wasting a large amount of ink. For prints, the darkness of the image is not deep enough, the density in the field is not enough, and the high-level level is lost, which seriously affects the quality of the product.
3. Corrosion resistance
The fountain solution used in the printing process is generally weakly acidic and may be alkaline due to formulation reasons. Both acidic and alkaline have a certain ability to corrode, and dampening fluid is often transferred to the blanket through the printing plate, which requires the blanket to have a certain degree of corrosion resistance.
4. Impermeability
All kinds of inks contain certain auxiliary materials. After infiltrating into the blanket, they will expand and fall off layer by layer, which will affect the service life of the blanket, which requires it to have certain anti-seepage properties.
5. Flatness
The so-called flatness refers to the uniformity of the thickness of the blanket, and the error is often required to be within a few tens of micrometers. If the error is too large, the transfer of the ink will be unstable, the ink color of the printed matter will be uneven, and the dot will be deformed. Therefore, the flatness is particularly important for offset blankets.