During the review process, for relief works, our focus is on whether the works can overcome their inherent characteristic defects in various printing techniques. For relief works, we observe the fine features of the relief dot to judge the control of the printing pressure of the printing company.
Good relief works have uniform ink color and small deformation of the dot, presenting a clean circular mesh, which proves that both pressure setting and equipment status are well-controlled during printing. It also indirectly proves that the quality of the relief works produced by rational use of relief printing technology is not inferior to that of flexographic works.
Relief works that have been screened out often have characteristic defects, namely, the center point is deep, surrounded by a circle of fine lines, and there is lighter ink between the point and the circle.
To avoid the appearance of characteristic defects and to make relief works look genuine, the equipment must be adjusted first. As seen in the figure below, this label achieves the effect of overlapping green dots by adding a blue plate on a yellow background, but these green dots have obvious relief feature defects.
People often think that this is due to excessive pressure setting or the operator's mistake. Actually, we should consider equipment adjustment. The appearance of this type of dots often indicates that the hardness of the rubber impression roller in the equipment is significantly higher than that of the relief plate, and their hardness no longer matches.
In the relief transfer mechanism, there is hardness matching between the impression roller and the plate roller, which means that there must be a buffer layer due to the inevitable motion error of the mechanical drum during operation. Theoretically, the impression roller is made by wrapping a layer of rubber on a metal roller, and the role of the rubber layer is to act as a buffer to ensure no deformation of the synthetic resin plate when the gap between the plate roller and the impression roller is too small or the pressure is too high due to mechanical errors.
Therefore, the reasonable approach is not to let the rubber hardness exceed that of the relief plate, and to make the rubber layer the buffer, rather than letting the relief plate become the buffer. The characteristic defects of relief printing we see today are actually caused by the relief plate becoming the buffer. This type of malfunction is relatively rare in new equipment, but as the equipment is running for a long time, the rubber layer will age and become more severe, especially in satellite-type relief presses where UV devices surround the rubber rollers.
The essence of flexo press machine is also relief printing, as it uses foam double-sided adhesive tape to attach the plate, which serves as the buffer layer, so even if the printing pressure is too high, there will be no deformation of the plate dots as in the characteristic defects of relief printing.
Why use relief to chase flexographic printing? From the perspective of printing companies, cost is always an important factor to consider when completing an order. Different techniques present different effects, and cost will vary accordingly. Choosing suitable techniques and equipment determines the success of the work. The cost of flexographic printing is higher than that of relief printing, but by using less expensive equipment and materials to achieve a far superior effect in terms of technique level, the quality of work is improved while cost is controlled, hitting two birds with one stone. This is where the vitality of relief printing lies in its vigorous development.
The above are some opinions on typical label cases during our review process. When the machine flexo is overwhelmed while relief presses remain idle in the daily production process, the latter can be used to deceive people. But "deception" is never "the gem," just solving an urgent problem, which is not the best solution to the predicament. Choosing appropriate techniques for different works, returning to the techniques themselves, and overcoming their inherent characteristic defects are the sources of continuous growth for printing companies.
