Flexographic varnishing plates

Details Flexographic varnishing plates Flexographic varnishing plates

1997-05-23

2001-04-17

Ahmad, Nasser (Department: 1772)

Stock material or miscellaneous articles

Layer or component removable to expose adhesive

Dissimilar adhesives

C428S040100, C428S041300, C428S041500, C428S041700, C428S042100, C428S042200, C428S913000, C430S253000, C430S256000, C430S258000, C430S260000

Reexamination Certificate

active

06217965

ABSTRACT:

FIELD OF INVENTION
The invention relates to printing and more specifically to printing with elastomeric plates, a field known as flexography.
BACKGROUND OF THE INVENTION
In printing it is often required to add an overcoat of varnish on top of the printed area in order to change gloss, scratch resistance, water resistance or other properties. The varnish is normally clear but special coatings such as adhesives, metallic coatings, special colors etc. can also be used. The selective application of varnish is administered using flexographic plates which are generated by exposing a photo-polymer and washing away the unexposed areas. Photo-polymer flexographic plates are expensive and require a long preparation process. For simple jobs a cut rubber sheet mounted with pressure-sensitive adhesive can be used, however any adhesive sufficiently weak to allow peeling off the undesired rubber is also too weak for extended printing runs, in particular when the varnish used can dissolve the adhesive. The use of plates based on pressure sensitive adhesive is discussed in U.S. Pat. No. 5,484,684, in which a narrow range of peel strength was selected as a best compromise between durability and ease of peeling. It is an object of the invention to provide a low cost flexographic plate particularly suitable for spot varnishing which is easy to prepare by peeling the unneeded elastomer but which is durable when used with a wide range of varnishes and other coatings. Another object is to provide a durable plate not requiring any chemicals during the platemaking process. A third object is to provide a flexographic varnishing plate with better varnish carrying capability than photo-polymer plates, in particular for water based varnishes. Current plates perform poorly with water based varnishes as most elastomeric photo-polymers are hydrophobic and are not wetted properly by a water based coating.
SUMMARY OF THE INVENTION
The invention discloses a method of preparing a flexographic printing plate. The printing plate may have at least three layers including a dimensionally stable substrate layer, an elastomer layer, and a curable adhesive layer therebetween. The method of preparation of the flexographic plate may comprise the steps of imagewise cutting the elastomer layer (outlining a border between the “printing areas” and the “non-printing areas” of the plate), peeling the elastomer layer from the substrate layer in the non-printing areas, and curing the adhesive layer between the remaining elastomer layer and the substrate in the printing areas.
The curing step may increase the adhesion strength between the elastomer layer and the substrate, making it possible to use the flexographic plate in extended printing runs. Curing may be achieved in a number of ways including U.V. irradiation of a photo-sensitive adhesive and heating a thermo-sensitive adhesive. A transparent substrate, such as polyester, is particularly well suited for the U.V. curing process.
The cutting step may be executed with a sharp blade cutting tool or alternatively with a laser cutting tool, both of which may be computer controlled. Finally, a top coat may be applied to the elastomer layer in order to increase its surface energy or to give it some other selected property to improve the functionality of the flexographic printing plate.
The U.V. exposure cross-links the adhesive and renders it insoluble in most liquids used in varnishing and coatings. Since the elastomer is mechanically cut and need not be photo-sensitive, the choice of elastomers is significantly wider than in photo-sensitive plates. For example, a hydrophilic top layer can be added to the elastomer for improved wetting by water based coatings.


REFERENCES:
patent: 4181752 (1980-01-01), Martens et al.
patent: 4820746 (1989-04-01), Rice et al.
patent: 4917990 (1990-04-01), Herrmann
patent: 5166226 (1992-11-01), Rice et al.
patent: 5484684 (1996-01-01), Telser et al.

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