WO1993010979A1

WO1993010979A1 - A presensitized plate for printing equipment

Info

Publication number: WO1993010979A1
Application number: PCT/IT1992/000035
Authority: WO
Inventors: Sergio Aloisi
Original assignee: Fin. Stella S.R.L.
Priority date: 1991-11-29
Filing date: 1992-03-20
Publication date: 1993-06-10
Also published as: IT1254066B; ITBO910446A0; AU1644992A; ITBO910446A1

Abstract

A presensitized litho plate (1) for offset printing comprises a backing film (2) fashioned in plastic material, a sheet of aluminium foil (4) bonded to the backing film by means of adhesive (3), and a coating (7) of photosensitive varnish applied to the metal foil (4); the thickness of the backing is one to four times greater than the thickness of the aluminium foil.

Description

Dj ;cription

A presensitized plate for printing equipment

Technical Field

The present invention relates to a presensitized plate for printing equipment.

Throughout the printing trade, and among operators of offset printing presses in particular, it is the practice to utilize aluminium plates coated on one side with a thin film of light-sensitive varnish. Graphic images to be printed (figures and/or text) are projected onto the light-sensitive surface by a photographic process, whereupon the areas of film exposed to light will be respectively soluble or insoluble, according to the type of light-sensitive material utilized, in a special developing bath. Thus, in practical terms, once the plates have been exposed to the light and immersed in the developer, certain parts of the plates retain their coating of light-sensitive varnish whilst other parts have the coating removed. Continuing the process, a plate that has undergone the aforementioned steps passes through a system of wetting and inking rollers, receiving a thin film of ink that adheres only to the areas where varnish remains; thereafter, the plate is pressed against a blanket (normally rubber) , onto which the ink is transferred. The blanket is then pressed against a ■aper support, thereby transferring the ink further and leaving a printed image. The image produced on the paper will be a right image, as on the plate, whereas that carried by the blanket is a reverse image, clearly enough; it is the inclusion of the blanket element that gives the "offset" printing process its name.

As to the aluminium backing today conventionally used for photolitho plates, the positive features of the material are compromised to a degree by the high cost of the raw material, also the fact that the plate is heavy, hence unwieldy, and delicate, with a tendency to bend and deface in storage and transport. • Accordingly, the object of the present invention is to provide a presensitized plate for use in offset printing, which remains unaffected by the drawbacks associated with the prior art as outlined above, in particular as regards cost, whilst affording all the requisite technical characteristics, and the advantage that it can be used in any conventional machine without prior adaptation.

Disclosure of the invention

The stated object is realized in a presensitized plate for offset printing presses as characterized by the appended claims, which comprises a backing film of plastic material, a sheet of metal foil bonded to the backing film by means of a layer of adhesive material, and a coating of photosensitive varnish applied to the metal foil. The invention will now be described in detail, by way of example, with the aid of the accompanying drawing, which illustrates a preferred embodiment of the plate viewed in section. Referring to the accompanying drawing, 1 denotes a presensitized plate, in its entirety, for use in an offset printing press (not illustrated) . The plate l comprises a backing film 2 of plastic material, preferably polyester resin (of thickness between 100 and 350 μm) and, applied to one surface of the film 2 by means of a layer 3 of adhesive material (12...100 μm thick), a sheet 4 of metallic foil (50...100 μm) such as aluminium or an alloy of aluminium. 5 denotes an ultra-thin outer layer of the foil 4 which, once the foil has been bonded to the backing film 2, is subjected to a chemical or mechanical "micrograining" treatment. Micrograining is a surface treatment whereby microscopic craters are formed in a material to the end of increasing the exposed surface area; the grained surface thus enables the foil 4 to retain a greater quantity of water, if wetted, when the plate 1 is used during the printing process. Once micrograined, the outer layer 5 of the foil 4 is subjected to an anodic treatment to the end of providing increased protection and resistance to abrasion; in the example illustrated, 6 denotes the anodized surface of the foil 4. Finally, 7 denotes a thin coating of photosensitive varnish some 2 μm thick applied to the anodized surface 6, which serves to modify the structure of those areas exposed to light. Two basic types of photosensitive varnish are used for the application in question, namely positive or negative. Positive photosensitive varnishes become soluble in solvents (generally alkaline water) when exposed to light, whereas negative varnishes become insoluble in such solvents when exposed to light. The method of assembling the

is conventional, and consists in spreading the ac. sive material 3 (a dual-compound polyurethane product suitable for bonding aluminium) over the backing film 2, drying in an oven, and then uniting the film and the foil by dry rolling in a press; the laminate produced in this way is left to cure until the adhesive has fully reticulated (a period of some 24 to 72 hours, depending on the storage temperature) , after which it can- be used for printing in the normal way. It will be clear that a plate 1 embodied in this manner, i.e. with the top layer of aluminium foil 4 gauged to an extremely fine thickness in comparison to the plastic backing film, is exceptionally light and easily manipulated. Moreover, the small amount of extra work involved in manufacturing the plate 1 disclosed is compensated by the saving achieved as the result of using a small quantity of aluminium, a material of somewhat high cost replaced in this instance, almost entirely, by a lower cost plastic material (perhaps even recycled plastics) ; indeed the cost advantage over traditional photosensitive plates is not inconsiderable.

Similarly, it will be clear that such a lightweight plate 1 affords notable advantages as regards ease and convenience in the operations of transport and storage, and equally clear, given the flexibility of the plastic material utilized in fashioning the backing film 2, the plate 1 disclosed is rendered distinctly tougher than conventional plates and less liable to damage through impact.

The foregoing specification implies no limitation; in an alternative embodiment, for example, the polyester resin might be replaced by polypropylene, cellulose acetate, polycarbonate, etc..

Claims

1) A presensitized plate for offset printing equipment, comprising: a backing film fashioned from plastic material, a sheet of metal foil bonded to the backing film by means of a layer of adhesive material, and a coating of photosensitive varnish applied to the metal foil.

2) A presensitized plate as in claim 1, wherein the backing film is of thickness between 1 and 4 times the thickness of the metal foil.

3) A presensitized plate as in claim 1, wherein the sheet of metal foil is fashioned from aluminium.

4) A presensitized plate as in claim 1, wherein the sheet of metal foil is fashioned from an alloy of aluminium.

5) A presensitized plate as in claim 1, wherein the backing film is polyester resin based.

6) A presensitized plate as in claim 1, wherein the backing film is polypropylene based.

7) A presensitized plate as in claim 1, wherein the backing film is cellulose acetate based.

8) A presensitized plate as in claim 1, wherein the backing film is polycarbonate based.