In practice, there will be a difference between the eng […]
In practice, there will be a difference between the engraved profile of the two glazing types, full and partial. Even the glazing printing plate used for full glazing has an engraved profile because the recessed part at the edge must be deeper to keep the applied glazing oil there. The purpose of partial glazing is to enhance the contrast between gloss or matt gloss and the substrate or other page elements, or to emphasize them with the effect of paint. The vacant part of the full-page glazing printing plate is mainly limited to the area to be glued (folding carton), printed or stamped later.
When choosing a glazing printing plate, a key criterion is the maximum engraving depth required to avoid the accumulation of glazing oil on the raised image elements. However, the deeper the recess, the more unstable the profile, especially on delicate, small elements. When using photosensitive resin printing plates, fine individual lines and dots are not a problem for glazing: because these elements are not as delicate as those in screen-tone flexo printing. The situation is different in the glazing printing plates made by cutting and peeling methods: the vertical cutting can make the more delicate elements unstable, they cannot withstand any shearing force, and are easy to deform or break. So it’s best to make sure that the side is slightly angled, at least when hand-engraving the rubber.
Cutting and peeling (lifting, detaching) are two processes. In these two processes, the outline of the coating varnish is cut out, and the area without varnish on the blanket or printing plate is manually removed or directly using a computer The plate making system and a cutting plotter are removed. In essence, any blanket can be cut and peeled to achieve some acceptable quality.
Peeling, other key criteria are the ability of the fabric to accept and transfer varnish, and its swelling resistance relative to oil-based inks, different varnishes and detergents. The compressible layer in the rubber blanket plays a decisive role in peeling: If the tight layer must be cut, the peeling of the cut part will be very difficult. However, the open cell structure makes peeling easy. If it can be cut to a polyester or aluminum liner (which is usually the case on thinner blankets), the peeling will be easier. Some manufacturers recommend combining an incompressible glazing blanket that can be cut deeply with a compressible lining. Other manufacturers use the compressible layer in the glazing blanket as a separating layer, from which the cut can be easily peeled off.
Tools for manual cutting and a heating plate to assist in peeling are provided, but the glazing image must first be copied to an opaque rubber fabric to generate a template. The easiest way to accomplish this is by means of a photosensitive diazonium film placed on the rubber, so that the rubber can be exposed and developed as an analog printing plate made by transparent positive photo film. Those transparent films to be glued to the aluminum base plate should be mounted on the aluminum plate that has been imaged according to the coating pattern.
The cutting plotter is controlled by CAD data generated by packaging design software or contour data, for example. But even so, the cut part must be removed manually. Some special blankets and printing plates that can be cut by a cutting plotter are protected by a non-scratched or non-sticky film, which must be removed after cutting and plotting. As shown in Figure 6-36, STIGroup in Lauterbach (Germany) produces rubber coating plates for KBA Rapida 142: Generate CAD data for folding cartons, check the empty parts on the blank binding samples, and cut them on the cutting plotter For the printing plate, peel off the mounting holes, peel off the rubber layer to expose the peeled glazing printing plate, install the printing plate and remove it after printing is completed.