GB2051678A

GB2051678A - Printing compositions

Info

Publication number: GB2051678A
Application number: GB8017011A
Authority: GB
Original assignee: Ramsden & Co Ltd C
Current assignee: Ramsden & Co Ltd C
Priority date: 1979-05-23
Filing date: 1980-05-22
Publication date: 1981-01-21

Abstract

A printing composition especially for use in decoration of ceramic materials, glass or metals comprises a carried medium (e.g. resins and/or waxes) and a non- vitreous filler (e.g. alumina) which is refractory in nature when subjected to a firing process. The composition may also contain a water-repellant material such as a silicone. The printing composition does not bond firmly to the substrate to which it is applied even after firing so that if an area of a substrate is printed with the composition and the substrate is then coated with a glaze or enamel and fired, the glaze or enamel coating and the residual elements of the printing composition can subsequently be removed from the printed area by brushing or rubbing thereby exposing the surface of the substrate.

Description

SPECIFICATION Printing compositions The invention relates generally to decorating mediums and methods of decorating and is especially applicable to the decoration of ceramic materials, glass or metals.

One known method of producing decorative effects on ceramic articles is known as "resist" decorating, which involves the application of a decoration to the surface of the article using a printing ink or resist medium which will repel a subsequently applied coating of glaze, so that when the article is subsequently fired the area from which the glaze has been repelled appears as a distinct separate area surrounded by normal glazed areas. Generally the glazed areas are in a colour or tone contrasting with that of the area from which glaze has been repelled. This technique is used in the decoration of a wide range of ceramic pieces such as tiles, tableware and ornamental articles.

One of the drawbacks of resist decorating is that currently available resist mediums do not always produce satisfactory rejection of the glaze especially when it is applied by spraying. The glaze coating can adhere to some areas from which it is intended to be rejected and this results in unacceptable ware which requires to be discarded. It is an object of the present invention to obviate or mitigate this disadvantage.

The present invention provides a printing composition comprising a carrier medium and a non-vitreous filler which is refractory in nature or becomes refractory in nature when subject to a firing process.

Preferably the filler comprises an inorganic oxide, sulphate, silicate or carbonate which may contain water of hydration or hydroxyl groups which may be partially or completely lost during subsequent firing. Alternatively the filler may comprise one or more materials selected from bauxite materials, silicates, silicas, sulphates, carbonates, or oxides. The filler is preferably present in a range of 20 - 90% by weight of the composition. In a preferred composition the filler comprises activated alumina and may include an amount of silicone, generally in the region of 0.05-5% and preferably around 1% by weight of the filler. Alternatively the silicone may comprise or be incorporated in the carrier medium.The filler preferably has a melting point above 500"C and a primary particle size range of between 0.012-53.0 micrometres.

The carrier medium may comprise any medium conventionally used in the production of decorating inks and may be a thermoplastic medium for use in hot screen printing or liquid medium suitable for cold screen printing, offset printing, stamping, banding or other means of printing, the medium being selected in accordance with known criteria dependant on the printing technique to be utilised and the nature of the surface to be printed.

Printing compositions according to the invention do not bond firmly to the substrate to which they are applied even after firing. Consequently if an area of a substrate is printed with a printing composition according to the invention and the substrate is then coated with a glaze or enamel and fired, the glaze or enamel coating and the residual elements of the printing composition can subsequently be removed from the printed area by brushing or rubbing.

Generally the printing composition will serve to at least partially repel the glaze or enamel coating in which case only the residual elements of the printing composition require to be removed after firing. Where the glaze or enamel has been only partly repelled, the unwanted glaze or enamel is only loosely bonded to the substrate due to the intervening printing composition and may be removed together with the residual elements of the printing composition to expose the surface of the substrate.

The following are examples of printing compositions according to the invention: Example 1 A thermoplastic ink for use as a resist decorating composition on pottery or glass comprises: Alumina 66.60% Stearyl alcohol flake 29.58% Carnauba wax 3.82% Example 2 An alternative printing ink suitable for application at room temperature consists of: Alumina 75.00% Pine oil 22.50% Ethyl cellulose 2.50% The alumina may be in the form of, for example, alumina hydrate, calcined alumina or activated alumina or may be replaced by alternative materials such as finely ground kyanite or whiting.Particularly advantageous results have been achieved using activated alumina or y-AI203. Activated aluminas from either of two principal precursors have been found equally effective, the first being aluminium hydrate Al(OH)3 and the second being aluminium isopropoxide Al(OCH2.CH2.CH3).

The organic medium acting as a carrier for the filler may consist of various waxy materials alone or in combination with suitable resinous compounds. The waxy materials may, for example, include fatty acids or fatty alcohols in the range C,2-C22, candellila wax or paraffin wax. Suitable resinous compounds include esters of hydrogenated rosins, compounds of cellulose and various polymethacrylate resins.

Particularly satisfactory results can be attained by incorporating with the filler a water repellant material, particularly a silicone, prior to preparation of the printing composition. In most cases it is necessary that the filler should be finely ground and preferably have a primary particle size range of between 0.012-53.0 micrometres. The filler should also have a melting point above about 500"C.

While the specific materials referred to above have been found to produce particularly satisfactory results, the essential characteristic of suitable fillers is that they are non-vitreous at the temperatures applied during subsequent firing, the most suitable fillers being refractory materials although these may not be formed until firing takes place. For example a hydrate may be used which is calcined during the firing process to form the corresponding oxide. Typical examples of suitable materials are alumina hydrate, calcined alumina, whiting, kyanite, zirconium, oxide, zirconium silicate, magnesite, calcined magnesite, talc, gypsum, mica, silica and feldspar. These comprise essentially inorganic sulphates, oxides, silicates and carbonates which may contain water of hydration or hydroxyl groups which may be partially or completely lost during the firing process.The carbonates may decompose completely or partially during firing. Satisfactory results have also been achieved using naturally occurring raw materials including bauxite minerals, silicates, sulphates silicas, carbonates and oxides. Some of these minerals may be altered chemically and physically during the firing process to form more stable refractory compounds.

A particular advantage of printing compositions according to the invention is that they may be applied to the articles to be printed in a variety of ways and indeed most techniques commonly used for this purpose can be employed including screen printing, offset printing, stamping, banding, spraying, transfer printing and brushing. The carrier medium in which the filler is contained can be any conventional medium which will be selected in accordance with the printing or decorating technique to be employed and the nature of the substrate to which the printing is to be applied.

In the decoration of ceramic articles, the printing composition may be applied to the surface of the article in the unfired clay state or in the so-called "biscuit" state. For this purpose the printing or decoration is applied by a suitable conventional technique to the surface of the article and the article is then coated with a glaze medium by dipping, spraying or other suitable means. Dependant on the composition of the printing ink selected and the method of applying the glaze, the glaze medium will either be repelled from the printed areas or will remain but will only bond loosely to the substrate in these areas.

Thereafter the glaze coated article is fired in conventional manner at a temperature of around 700-1400"C resulting in fusion of the glaze coating to the substrate except in the printed areas where only poor adhesion takes place. After firing, the surface of the article may be brushed or wiped to remove any of the fired layer of glaze which remains attached to the printed areas together with residual elements of the printing composition thereby exposing the surface of the article and producing a contrast with the surrounding glazed areas.

In some cases, and particularly where a wax carrier medium and activated alumina filler are utilised, the glaze medium may be repelled entirely from the printed area so that after subsequent firing only the residual elements of the printing composition, principally alumina, require to be rubbed away or otherwise removed from the printed area. In other cases the glaze medium may not be completely repelled or may form a loosely adhered coating over the entire printed area, in which case the glaze which remains on the printed area after firing is brushed or rubbed off together with the residual alumina.

In use of the technique in relation to the decoration of glass articles, a desired pattern or other decoration is printed on the surface of the article by any suitable technique and a coating of an enamel, which will generally be pigmented, is applied over part or all of the surface of the article including the printed area. The article is then subjected to firing at a temperature in the region or 500-800"C causing the enamel to fuse with the surface of the article except in the printed areas where the printing composition prevents satisfactory adherence. After firing, the fired enamel coating and the residual elements of the printing composition may be removed from the printed areas by rubbing or wiping, thereby exposing the surface of the glass article itself and producing a contrasting effect. This technique is particularly suitable for the decoration of glassware by means of motifs, logos, lettering or the like set into an overall coloured panel.

While various ink compositions and decorating techniques have been referred to above, it should be appreciated that various modifications may be made without departing from the scope of the invention. For example, it is possible to incorporate organic or inorganic pigments in the printing composition but care is necessary to avoid the use of pigments which include vitrifiable elements and hence reduce the effectiveness of the printing composition as a resist medium. In such cases it may prove impossible to achieve complete rejection of the overall glaze or enamel coating even in the case where activated alumina filler is used, but the poorly adhered fired coating together with the residual elements of the printing composition may still be removed from the surface of the article by rubbing or the like after firing. Moreover while reference has been made primarily to the decoration of ceramic or glass articles the invention may also be used to decorate other articles, for example, for enamelling metal articles.

Claims

1. A printing composition comprising a carrier medium and a non-vitreous filler which is refractory in nature or becomes refractory in nature when subjected to a firing process.

2. A printing composition according to claim 1 wherein the filler comprises an inorganic oxide, sulphate, silicate or carbonate.

3. A printing composition according to claim 1 wherein the filler comprises one or more materials selected from bauxite materials, silicates, silicas, sulphates, carbonates or oxides.

4. A printing composition according to claim 1 wherein the filler comprises activated alumina.

5. A printing composition according to any preceding claim wherein the filler is present in an amount of 20-90% by weight of the composition.

6. A printing composition according to any preceding claim wherein the filler incorporates in an amount of 0.05-5.0% by weight of the filler.

7. A printing composition according to any preceding claim wherein the filler has a melting point in excess of 500"C.

8. A printing composition according to any preceding claim wherein the filler has a primary particle size range between 0.012 and 53.0 micrometres.

9. A printing composition according to any preceding claim wherein the carrier medium comprises a thermoplastic medium.

10. A printing composition according to any of claims 1 to 8 wherein the carrier medium is a liquid medium.

11. A printing composition according to any preceding claim wherein the carrier medium incorporates silicone.

1 2. A printing composition substantially in accordance with Example 1.

1 3. A printing composition substantially in accordance with Example 2.

1 4. Any novel subject matter or combination including novel subject herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.