GB2242397A - A method of forming indicia on a substrate - Google Patents

Abstract

A method of forming indicia on a substrate 1 e.g. packaging material, comprising the steps of:- (a) applying a layer 4 of a first ink to the substrate 1, the first ink having a relatively high adhesion to the substrate 1; (b) applying a layer 5 of a second ink over at least a part of the layer 4 of the first ink, the first and second inks being such that they interact to increase the heat resistance of the second ink and have relatively high adhesion for each other; (c) applying a layer 6 of a third ink over at least a part of the layer 5 of the second ink, the third ink adhering to the second ink with relatively low adhesion; and (d) selectively removing portions of the layer 6 of the third ink by the use of heat or abrasion whereby the second ink is exposed and left adhered to the substrate and the indicia are formed thereby. <IMAGE>

Description

INDICIA FORMATION This invention concerns the formation of indicia on surfaces for example on packaging materials.

Packaging materials are provided with various types of indicia, for example general get-up, the name of the packaged goods and product, the manufacturer's name etc.

Much of the information provided by these indicia remains the same over long periods of time. Indeed, consumers identify products by their packaging because it doesn't change.

However, manufacturers of packaged products often require to identify where and/or when a product was packaged, and, particularly in the case of perishable products, they provide the vendor of the product and/or the consumer with information as to when the packaged product should be removed from sale or consumed. This information has hitherto been applied to individual packages either by printing the desired indicia using an ink or using a coding tape from which the indicia are applied using a heated tool.

Printing with an ink is often unsatisfactory since many inks do not adhere well to certain types of surface, and coding tapes suffer from the disadvantages of being relatively expensive and more particularly from causing shut-downs of the packaging machinery when the tape breaks or it runs out.

Thus there is a need for a technique which avoids the application of indicia to packaging materials involving the application of an ink or print from a coding tape.

Heat sensitive date stamp inks have also been proposed for forming indicia, the inks being printed over a heat resistant ink of a different, usually lighter, colour. The disadvantage of this method of forming indicia is that removal of the heat sensitive date stamp ink often causes discolouration of the underlying ink due to the heat resistant ink softening during removal of the heat sensitive ink. The result has been poor indicia definition and an unaesthetic appearance.

According to the present invention there is provided a method of forming indicia on a substrate, the method comprising the steps of: (a) applying a layer of a first ink to the substrate, the first ink having a relatively high adhesion to the substrate; (b) applying a layer of a second ink over at least a part of the layer of the first ink, the first and second inks being such that they interact to increase the heat resistance of the second ink, and have relatively high adhesion for each other; (c) applying a layer of a third ink over at least a part of the layer of the second ink; and (d) selectively removing portions of the layer of the third ink using physical means whereby the second ink is exposed and left adhered to the substrate and the indicia are formed thereby.

The present invention enables indicia to be formed having particularly good legibility. The increased heat resistance usually, in addition, confers improved grease resistance, which is advantageous when packaging certain products. The improvement in the heat resistance of the second ink resulting from its reaction with the first ink can furthermore enable a wider range of inks to be used for the third layer than has hitherto been possible with heat sensitive date stamp inks. The ability to avoid the use of heat sensitive date stamp inks has enabled inks to be used for the third ink layer which are conventionally used for printing other parts of a pack design. The result is that indicia in the colour of the second ink layer can be formed in a layer of the third ink forming a part of the pack design, and not just in a special panel of a different colour as has been the case hitherto.

Various physical means can be used to remove portions of the third layer of ink from the second ink layer, for example heat or abrasion. Abrasion has the advantage of providing a rub-removable effect to reveal for example promotional messages, e.g. prizes etc.

The first and second ink layers should be such that they react to increase the heat resistance of the second ink layer. Furthermore, the first ink layer should provide adequate adhesion to the substrate after the reaction has taken place, so that only the third ink layer is removed during indicia formation.

The ink used for the first ink layer is preferably an epoxyamine ink having free epoxy groups. Such inks generally exhibit a good adhesion to a variety of substrates. Although the first ink layer will usually contain a pigment, and conveniently it can be used to print one of a number of different colours on a substrate, it should be appreciated that it may be a composition without a pigment. Compositions containing an epoxyamine with free expoxy groups with or without a pigment, are, however, generally preferred.

The second ink layer is advantageously of a polyamide ink, particularly when the first ink layer is of an epoxyamine ink having free epoxy groups. The polyamide in the second ink layer reacts with the free epoxy groups in the second layer to increase the heat resistance of the polyamide ink.

Removal of the third ink layer can be facilitated by the inclusion of a wax in the second ink layer.

The third ink layer should be such that it has a lower adhesion to the second ink layer than the first ink layer has to the substrate, the first and second layers being strongly adhered as a result of reaction therebetween. The third ink layer should, of course be such that it can be removed by heat, for example using a heated date stamp, without the removal of significant amounts of the second ink. Good ink removal has been achieved using an acrylic ink as the third ink, particularly when the second ink is a polyamide ink. Removal of the third ink layer can also be facilitated by the presence of a wax in the second ink layer.

All three ink layers can be applied to the substrate by known methods, for example by flexographic or gravure printing. In general, the various ink layers can be applied using conventional printing machinery in which inks are applied to a substrate sequentially.

The present invention can be used to form indicia on a variety of substrates. The substrates can be flexible or rigid, and can be of paper or board, although the present invention has particular application to flexible films, for example of synthetic polymers, for example polyolefins, e.g.

polyethylene or polypropylene, polyesters or polyamides, or of regenerated cellulose. The present invention can therefore be used to form indicia on oriented polypropylene films, which may be voided or unvoided, e.g. by the orientation of polypropylene containing a particulate filler. The filler can be organic, e.g. a polyamide or inorganic, e.g. chalk. The present invention can also be used to form indicia on metallised substrates, for example metallised polymeric films referred to hereinbefore.

As will be appreciated by those skilled in the art, it will sometimes be necessary to provide the substrate with a treatment which promotes adhesion of the first ink layer to the substrate. Examples of such treatments include flame and corona discharge treatment, for example for polyolefin and other films.

The present invention will now be described, by way of example, with reference to the accompanying drawing which illustrates a section through a substrate having indicia formed in accordance with the present invention.

Referring to the drawing, the substrate 1 is a biaxially oriented film consisting of a layer 2 of a propylene homopolymer having two outer heat seal layers 3 of a propylene ethylene copolymer, one of which has been corona discharge treated.

Applied to the corona discharge treated heat seal layer 3 by flexographic printing is a layer 4 of white ink which is an epoxyamine 2-component ink, and on the layer 4 is a layer 5 of a yellow polyamide ink, also applied by flexographic printing. On the layer 5 is an outer ink layer 6 of a red acrylic-based ink, again produced by flexographic printing.

Although not wishing to be bound by theory, it is believed that free epoxy groups in the 2-component epoxyamine of the layer 4 react with the polyamide of the layer 5 to increase the heat resistance of the layer 5 and to promote adhesion of the layer 5 to the layer 4, which in turn has good adhesion to the substrate 1, and in particular the corona discharge treated heat-seal layer 3.

The accompanying drawing also shows a heated date stamp 7 with lands 8 having formed indicia 9 by contact with and removal of portions of the outer ink layer 6. The removed portions of the outer layer 6 of red ink reveal the exposed upper surface of the layer of yellow ink 4.

Although the accompanying drawing shows the three ink layers 4, 5 and 6 as being superimposed, it will be appreciated that each of these respective layers can be printed as desired to form a multi-coloured pattern or image formed from one or more of the respective inks, for example to provide information about a product packaged in the printed film using these three colours. Other inks can also be present on the substrates, for example to provide regions of different colour from those specifically referred to above.

Claims (13)

1. A method of forming indicia on a substrate, the method comprising the steps of: (a) applying a layer of a first ink to the substrate, the first ink having a relatively high adhesion to the substrate; (b) applying a layer of a second ink over at least a part of the layer of the first ink, the first and second inks being such that they interact to increase the heat resistance of the second ink and have relatively high adhesion for each other; (c) applying a layer of a third ink over at least a part of the layer of the second ink, the third ink adhering to the second ink with relatively low adhesion; and (d) selectively removing portions of the layer of the third ink using physical means whereby the second ink is exposed and left adhered to the substrate and the indicia are formed thereby.

2. A method according to claim 1, wherein the third ink is removed by heat.

3. A method according to claim 1, wherein the third ink is removed by abrasion.

4. A method according to any of the preceding claims, wherein the first ink layer is of an epoxyamine ink having free epoxy groups.

5. A method according to any of the preceding claims, wherein the said second ink comprises a polyamide ink.

6. A method according to any of the preceding claims, wherein the second ink layer includes a wax.

7. A method according to any of the preceding claims, wherein the third ink layer comprises an acrylic ink.

8. A method according to any of the preceding claims, wherein the first in layer does not contain a pigment.

9. A method according to any of the preceding claims, wherein the indicia produced are in the form of a date.

10. A method according to any of the preceding claims, wherein the substrate is a polyolefin film.

11. A method according to any of the preceding claims, substantially as herein described.

12. A printed substrate having indicia formed by a method according to any of the preceding claims.

13. A printed substrate having indicia formed thereon and being substantially as herein described.