Blanket is the intermediate for the
transfer of offset printing ink. The quality of the blanket directly affects
the quality of the printed matter. And blankets are expensive, and replacing
the blankets too much during the book printing process is
undoubtedly a disguised increase in the cost of the product.
When selecting a blanket, the elasticity of
the blanket, ink transfer performance, corrosion resistance, penetration
resistance, and flatness are the five most important factors to be considered.
The moment the blanket leaves the embossed
area, the deformation due to the 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 located between the
impression cylinder and the plate cylinder. When book printing, each
unit on the blanket should be contact with the two cylinders once during the
rotation process, that is, twice deformation due to the printing pressure, and
at the same time the process of transferring the ink from the plate to the
blanket and then transferring it from the blanket to the substrate. Assume that
a sheet-fed offset press prints normally at a rate of 10,000 sheets per hour.
Each unit on the blanket is then compressed and deformed once every 0.18
seconds, and it is required to be able to recover its deformation before the next
(0.18 second) deformation. High-speed rotary press blanket deformation recovery
time requirements shorter. If deformation cannot be restored, each unit on the
blanket can no longer transfer ink to the substrate after transferring ink from
the plate to the blanket, or after transferring the ink 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 rubber 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. Gaoyue is 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, the operator mistakes that the amount of ink is
too small to increase the amount of ink, thereby wasting a large amount of ink.
For printed matter, the dark tone of the image is not deep enough, the density
in the field is not enough, and the high-profile 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 the formulation.
Both acidity and alkalinity have a certain amount of corrosion, and the
fountain solution is often transferred to the blanket through the plate, which
requires the blanket to have a certain degree of corrosion resistance.
All kinds of inks contain a certain amount
of auxiliary materials. After infiltrating the blanket, it will expand and fall
off layer by layer, which will affect the service life of the blanket. This
requires it to have a certain anti-penetration performance.
The so-called flatness refers to the uniformity of the blanket thickness, error
often requires within tens of microns. Excessive errors often result in
unstable ink transfer, uneven ink prints, and dot distortion. Therefore, the
flatness is particularly important for offset blankets.