GB2196301A - Glass-etching - Google Patents

Abstract

An image is etched in glass by transfer to the glass surface of a pattern delineating the image, from a carrier of tissue paper or plastics film onto which that pattern has been copied electrophotographically using toner composed for example, by weight, of at least approximately 10 parts carbon black to 90 parts styrene butyl methacrylate, and fused to the carrier by radiant heat. For the transfer, the carrier is bonded to the glass surface with the toner-pattern down onto that surface, and the carrier when plastics film, but not tissue, is then stripped away from the toner-free areas prior to the etch by acid or sand-blast. Copying may be onto a carrier-coating of cellulose-based varnish which disperses from the toner-free areas during the fusing of the toner, and the carrier may be bonded by heat-rolling to the glass surface using an adhesive that adheres to the toner alone. <IMAGE>

Description

SPECIFICATION Glass-etching This invention relates to glass-etching, and to products of processes which include such etching.

The etching of decorative or other images in glass by the use of hydrofluoric acid applied to areas of the surface of the glass delineated by a resist, has been known for many years.

Although small images can be readily produced in this way by silk-screen printing of the appropriate resist-pattern on the glass, problems arise where the image required is of a significant size, as regards providing both the resist pattern itself, and a silk-screen printing table capable of accommodating the pattern-size. Difficulties in both respects generally arise, for example, where the image is required to be of the order of 0.5 metre or more in either dimension, and especially where one or more photographic enlargements are required from the master image to achieve an appropriately-sized pattern to lay down in re sist on the glass.

It is an object of the present invention to provide a glass-etching method by which the above difficulties can be reduced to a significant extent.

According to one aspect of the present invention, there is provided a method of etching an image in glass, in which a resist-pattern to delineate that image, or a pattern on which the resist pattern is to be built up, is formed on a carrier, and the pattern carried by the carrier is transferred to the surface of the glass for the establishment of the resist pattern on that surface' prior to etching, wherein the pattern is formed on the carrier electrophotographically.

The invention avoids the need for silkscreen printing onto the glass-surface, and allows advantage to be taken of the facility for enlargement provided in many electrophotographic installations. In this respect, electrographic machines are available that are capable of direct copying, or enlargement up to widths of 1 metre and unlimited length. More especially it has been found that the toner used by such machines, as subjected to radiant heat for fusion in the provision of copies by the machine, is suitable alone, or at least as the base for, the provision of an adequate resist both as regards etching by hydrofluoric acid or sand-blasting.

The carrier may be tissue paper, in particular pottery-transfer tissue, or may be a plastics film, for example, of polyethylene telephtalate, and may be bonded to the glass surface with the toner-pattern onto that surface. When the carrier is a plastics film it is preferably stripped away from the toner-free areas prior to the etch by acid or sand-blast; when tissue-paper is used, stripping is not normally Two methods of glass-etching according to the present invention will now be described, by way of example.

In the first method, artwork in accordance with the image to be reproduced in the glasssurface is copied electrophotographically, directly or through enlargement, onto potterytransfer tissue. The copier machine used is capable of accommodating tissue of up to 1 metre in width fed from a roll, and the desired image is reproduced in fused toner on an upper surface of this in reverse-hand. The toner used in the machine is composed, by weight, of at least approximately 10 parts carbon black to 90 parts styrene butyl methacrylate, and in the process performed by the machine is fused to the paper by radiant heat. Depending upon whether the image is to be revealed in the un-etched areas of the glass-surface, or in the etched areas, so the copy reproduces the image in reverse hand, as, respectively, toner-covered or toner-free areas of the tissue upper-surface.

The glass surface to be etched. is cleaned and coated with a cassein adhesive. The adhesive is rolled out to ensure an even filmcoating, and the tissue carrier is then applied to this with its upper surface down towards the glass. The application of the tissue to the glass is carried out by winding it onto a largediameter drum and then rolling it out from the drum down onto the glass surface. Particular care is taken to ensure that the tissue is smoothly distributed over the glass surface, and is evenly bonded to it; if unevenness remains in the toner-free areas of the tissue, a striation effect corresponding to the unevenness may be produced in the etched areas-in some circumstances this may be welcomed and contrived, towards giving an added decorative effect.

After the tissue carrier has become firmly bonded to the glass, the surface is flooded with hydrofluoric acid to etch away the areas of the glass surface not covered by the resist formed by the fused toner; the acid passes through the tissue paper where toner-free. The etchant used may be hydrofluoric acid diluted to a 40% strength, and the surface may be flooded with it to a depth of some 3 millimetres; this will give a depth of etch of some 2 millimetres in about 1 hour. Other strengths of etchant may be used to achieve variation in the resultant etch.

Once the required degree of etch has been achieved, the hydrofluoric acid is withdrawn, and the surface is washed with clean water (or a solution of sodium phosphate) and then dried. The washing releases ther tissue and resist from the glass-surface, thereby revealing the required etched-image.

In the second method, the resist-bearing carrier is produced in the same way as in the first method, except that tissue is not used as the carrier. Instead, the carrier is provided by clear film of polyethylene telephtalate that has first been coated, by roller application, with an adhesive composed of a cellulose-based plas ticised varnish. The film may, for example, have a thickness of five-thousandths of an inch (0.127 millimetres) and may be such as that sold under the trade mark "POLYMEX".

The adhesive may be that sold as E T Marler Varnish MS 2500.

The dried coating of the adhesive varnish is almost not visible on the film, and it is onto this coating that the required- image is copied by the copier machine. The radiant heat ap plied within the machine fuses the toner to the coating, but disperses the varnish coating from the toner-free areas (or otherwise affects it such that discontinuity of state results be tween the areas of coating which are toner covered and those which are toner-free, in or der that those different areas may shear cleanly from one another).

A coating of a second adhesive is now ap plied to the carrier, also by roller application, to cover the toner-pattern. This second adhe sive, which may be a hitac shearable adhesive such as that sold as E T Marler Hitac Adhe sive SP 1901, adheres to the toner only.

Once the adhesive has set, the carrier is placed toner-pattern down, on the glass. The toner-pattern is now transferred to the glass surface by rolling down, using a roller heated to 70-80"C, and simply stripping away the film backing. The carrier has been found to shear precisely and cleanly at the edge of the toner however delicate the pattern.

Etching may now proceed, using either hy drofluoric acid as in the first-described method, or sand-blasting.

Although a more-rubbery composition of the second adhesive might be appropriate where sand-blasting is employed, the E T Marler Hi tac Adhesive SP 1901 identified above, has been found suitable for use whether etching is by acid or sand-blasting.

It has been found that the constructions of photocopier marketed as the Shacoh 920 Type RC Copier by the Shacoh Co., and the Harper 5225 Copier by Harper & Tunstall Ltd., are especially well-adapted for use in both etching methods described above.

The methods described above may be used to produce etched-glass moulds for the pro duction of plaster or fibre-glass plaques or panels, as well as for producing decoratively or otherwise etched glass panels and other items.

Claims (13)

1. A method of etching an image in glass, in which a resist-pattern to delineate that im age, or a pattern on which the resist pattern is to be built up, is formed on a carrier, and the pattern carried by the carrier is transferred to the surface of the glass for the establishment of the resist pattern on that surface prior to etching, wherein the pattern is formed on the carrier electrophotographically.

2. A method according to Claim 1 wherein the carrier is of paper.

3. A method according to Claim 2 wherein the paper is tissue paper.

4. A method according to any one of Claims 1 to 3 wherein the carrier is bonded to the glass surface with the electrophotographically-produced pattern onto that surface.

5. A method according to Claim 1 wherein the carrier is a plastics film.

6. A method according to Claim 5 wherein the plastics film is of polyethylene telephtalate.

7. A method according to Claim 5 or Claim 6 wherein the film has a coating onto which the image is electrophotographically copied as a fused-toner pattern, and the coating is such as to be dispersed by the electrophotograhic process from the toner-free areas of the carrier.

8. A method according to Claim 7 wherein the coating is a cellulose-based varnish.

9. A method according to any one of Claims 5 to 8 wherein the electrophotographically-produced toner pattern is transferred to the glass surface by bonding the carrier with the toner pattern onto that surface, and the film is then stripped away from the toner-free areas.

10. A method according to Claim 9 wherein the carrier is bonded to the glass surface by rolling with a heated roller after coating with a second adhesive that adheres only to the toner.

11. A method according to any one of the preceding claims wherein the toner used in the electrophotographic process is composed, by weight, of at least approximately 10 parts carbon black to 90 parts styrene butyl methacrylate.

12. A method of etching an image in glass substantially as hereinbefore described by way of first or second example.

13. A glass product etched according to the method of any one of the preceding claims.