Heat release offset transfer material

Abstract

 A transfer material for use in decorating ceramic or glass surfaces by a heat release transfer method using a transfer pad is disclosed. The transfer material comprises a substrate (l) having a layer (2) thereon formed of a fatty acid ester, a design layer (3) and a protective coat (4) on or under the design layer (3). The fatty acid ester layer (2) serves to attach the design layer (3) to an article to be decorated.

Description

[0001] This invention relates to a transfer material for the application of decals or transfers to articles, especially but not exclusively for the decoration of ceramic or glass surfaces by a heat release transfer method, and to a method of applying decals to articles such as ceramics or glassware.

[0002] Heat release decals of the direct application type have been a useful complement to the more traditional water slide decals for many years. An important advantage of heat release decals is that they are more suitable for application with automated equipment. A disadvantage is that they do not satisfactorily conform to severely curved surfaces. This is because the decal includes a backing sheet or substrate which is present when the decal is applied to the article to be decorated but which is then removed. The presence of the backing sheet during application to the article makes it difficult to ensure that the decal properly conforms to the surface. Examples of typical direct application heat-releasable decals and method of application are disclosed in U.S. Patent Nos 2,970,076 to Porth; 3,007,829 to Akkeron; 3533822 to Bailey; 4,068,033 to Meade; 4,322,467 to Heimbach and Johnson and 4,477,5l0 to Johnson and Wu.

[0003] An indirect, or offset, transfer application method using a deformable transfer pad to effect the transfer of a design layer sandwiched between two adhesive layers from a wax-coated substrate to an article to be decorated, is disclosed in U.S. Patent No. 3,967,02l. The two adhesive layers are heat sensitive but are tacky over different temperature ranges. This enables the printed design to be adhered to the transfer pad and released from the substrate and thereafter adhered to the article to be decorated and released from the transfer pad. The transfer pad used in the indirect method gives conformation to different shapes of articles with greater flexibility than the direct method. However, a disadvantage of the above method is that, due to the use of two adhesive layers which have different tacky temperature ranges, the process is time consuming and not ideal for mass production.

[0004] EP-A-0055395 discloses a substrate, a layer of thermoplastic heat-sensitive adhesive material formed directly on said substrate and a design layer formed on said adhesive layer. In use, the substrate is placed on a heated platen and a heated silicone transfer pad is pressed onto the design layer with the adhesive layer in a tacky state so that the adhesive layer becomes attached to the transfer pad and is released from the substrate. The transfer pad is then pressed against the object to be transfer-printed, and the adhesive layer, and thereby the design layer, becomes adhered to the article to be decorated. Subsequently the article is fired. The adhesive layer disclosed in EP-A-0055395 is a complex mixture of waxes, oils and thermoplastic adhesive resins. Such a mixture has a relatively high melt temperature and high melt viscosity. We have found that effective transfer on a mass production basis using such a technique is difficult to achieve. Slight heat loss due to contact of the transfer pad with the cold article is a major problem with continuous running, as is a build-up of wax (from the adhesive layer) on the transfer pad.

[0005] Transfer of wax to biscuit ware can give glaze reticulation in a once-fire system and pinholing during firing can occur with fast-fire-, glass- and heavy colour-deposits onto glazed articles.

[0006] Accordingly it is an object of the present invention to provide a relatively simple transfer material and method which is more cost effective and overcomes many of the difficulties experienced with the more complex prior art wax/adhesive formulations.

[0007] According to the present invention, there is provided a transfer material comprising a substrate, a design layer, a fatty acid ester layer between the design layer and the substrate, and a protective coat associated with the design layer.

[0008] The present invention also resides in the use of a transfer material comprising a substrate, a design layer, a fatty acid ester layer between the design layer and the substrate, and a protective coat associated with the design layer, in a method of decorating an article by means of a heated transfer pad which (l) removes (a) the design layer and (b) at least part of the fatty acid ester layer from the substrate so that said layers become temporarily attached to the transfer pad with the design layer being disposed between the transfer pad and the fatty acid ester layer; and (2) presses the fatty acid ester layer against the article to be decorated so that the previously molten fatty acid ester layer solidifies and so attaches the design layer to the article.

[0009] The present invention further resides in the use of a coated substrate comprising a substrate and a fatty acid ester layer thereon, in a method of decorating an article by means of a heated transfer pad which (l) removes (a) a design layer which has previously been provided on the coated substrate and (b) at least part of the fatty acid ester layer from the substrate so that said layers become temporarily attached to the transfer pad with the design layer being disposed between the transfer pad and the fatty acid ester layer; and (2) presses the fatty acid ester layer against the article to be decorated so that the previously molten fatty acid ester layer solidifies and so attaches the design layer to the article.

[0010] The use of a fatty acid ester layer between the substrate and the design layer enables fast separation of the design layer from the substrate and fast application of the design layer to an article to be decorated using a transfer pad because such a fatty acid ester layer is highly temperature sensitive so that release and adhesion can be effected with short dwell times in respect of pad-to-substrate contact and pad-to-article contact. Additionally, the transfer process can be effected economically because, for many applications, it is only necessary to heat the transfer pad. However, it is within the scope of the present invention to heat the transfer material eg using a heated platen upon which the material rests, before contact with the heated transfer pad.

[0011] Also according to the present invention, there is provided a method of decorating an article comprising the steps of providing a transfer material comprising a substrate, a design layer, a fatty acid ester layer between the substrate and the design layer, and a protective coat associated with the design layer; contacting a heated transfer pad with a surface of the transfer material opposite to that on which the substrate is provided; before or during said contacting step, melting the fatty acid ester layer; separating the transfer pad from the substrate so that the protective coat, the design layer and at least part of the fatty acid ester layer become attached to the pad and separated from the substrate; pressing the transfer pad with the attached layers against an article to be decorated so that the fatty acid ester layer solidifies and attaches the design layer to the article; and separating the transfer pad from the article.

[0012] In a preferred embodiment, the transfer pad is heated to a temperature which is above the melting point of the fatty acid ester layer so that melting occurs during said contacting step. In such an embodiment, it is preferred to use a heat-insulating surface for supporting the transfer material so that heat loss from the transfer pad is minimised during said contacting step. However, it is within the scope of the present invention to utilise a support surface which is heated to reduce heat loss from the transfer pad or to augment the heating effect of the transfer pad.

[0013] Typically, the substrate is formed of clay-coated paper, although other barrier coated papers, e.g. starch-, PVA-, casein- or alkali metal silicate-coated paper may be employed. Typically, the substrate has an average weight per unit area in a range of from l00 to 200 g/m²

[0014] Preferably, the ester layer is formed of a fatty acid ester of a monomeric glycol, eg ethylene glycol. The fatty acid is preferably stearic acid, although palmitic acid may be employed. Most preferably, the fatty acid ester is ethylene glycol monostearate or distearate, or a mixture thereof e.g. the reaction product of ethylene glycol and stearic acid. Such a material has a relatively low melting point (about 60°C) and it needs less energy to release it from the substrate. Such a material is relatively economic to use. It has a low melt viscosity which enables smooth, easy release from the substrate. It has no adhesive properties when molten but has a very fast setting time when cooled which allows it to attach to a substrate to be decorated with minimum contact time. The ester layer preferably has an average weight per unit area in a range of from 5 to 20 g/m².

[0015] The protective coat can be a standard cover coat over the design layer which is used to protect the design layer against distortion and maintain it in its printed form during the transfer process. It is found that the inherent tackiness of such a standard cover coat when heated is sufficient to enable temporary attachment thereof to the transfer pad which is normally formed of a soft silicone rubber. Such a transfer pad is slightly tacky to the touch, particularly when heated. Typically, a standard cover coat is thermoplastic e.g. it is formed of a resilient thermoplastic resin (e.g. an acrylic or methacrylic resin) which can be completely volatilised upon firing. Alternatively or additionally, a similar protective coat can be provided between the design layer and the ester layer.

[0016] The protective coat is preferably a complete coat which prevents any effective contact between the fatty acid ester and the transfer pad in use.

[0017] In the accompanying drawings:-

Fig. l is a cross-section through a transfer according to the present invention, and

Fig. 2 is a schematic illustration showing the use of the transfer of Fig. l in the decoration of a ceramic article.

[0018] Referring now to Fig. l, the transfer comprises a backing sheet or substrate l, a fatty acid ester layer 2 formed directly on the substrate l, a design layer 3 deposited directly on the layer 2, and a cover coat or protective layer 4 covering the design layer 3.

[0019] In a particular example, the substrate l is formed of a clay-coated paper, the layer 2 is formed of ethylene glycol distearate which is the reaction product of ethylene glycol and stearic acid/and which therefore contains a minor proportion of the monostearate. A typical example is ethylene glycol distearate as supplied by Leek Chemical Ltd of Leek, Staffordshire. The layer 2 is applied to the paper by any known coating technique at an average weight per unit area of 8 to l2 g/m². The design layer 3 is applied directly to the fatty acid ester layer 2 by any suitable printing technique, and a protective resilient methacrylic resin layer 4 is provided over the design layer. The layer 4 may be contour coated or may form a complete (or overall) coating so no part of the ester layer contacts the transfer pad upon transfer.

[0020] In use, and as shown in Fig. 2, a conventional resiliently deformable silicone rubber transfer pad 5 heated to at least 90°C (i.e. substantially above the melting point of the ester) is applied to the transfer so as to engage against the layer 4 (Fig. 2b). The heat of the transfer pad 5 serves to melt the fatty acid ester so that when the pad is lifted, the layer 4, the design layer 3 and some of the fatty acid ester layer 2 become detached from the substrate l (Fig. 2c). The substrate l is held down at this stage e.g by suction applied to the underside of the substrate l, on a perforated platen 7 formed of a heat-insulating material to minimise heat loss from the transfer pad 5. The design layer 3 is temporarily attached to the transfer pad 5 by the tackiness of the heated layer 4.

[0021] The transfer pad 5 is then pressed against an unheated article 6 to be decorated with the design, for example a piece of ceramic ware, glassware or, particularly advantageously, a piece of underglaze biscuit ware (Fig. 2d). The article 6 is relatively cold (well below the melting point of the ester) and cools the fatty acid ester sufficiently for it to solidify and become attached to the article 6 so that the design layer becomes detached from the transfer head and attached to the article 6 (Fig. 2e). The transfer pad 5 is then re-heated to at least 90°C by any suitable means eg radiant heat, before being used to pick up another design. The heating at this stage is effected so that the temperature of the transfer pad 5 during a transfer operation is always above, preferably substantially above, the melting point of the fatty acid ester. During subsequent firing of the article 6, the fatty acid ester and the cover coat are volatilised away leaving the design layer adhered to the article 6.

[0022] In further embodiments, a sealant layer similar to the cover coat layer is employed between the fatty acid ester layer and the design layer instead of or, more preferably in addition to, the cover coat layer. A thermoplastic or heat activatable adhesive layer consisting of any suitable thermoplastic resinous adhesive, such as those used in direct heat release transfers, may be provided over the cover coat layer.

Claims

1. A transfer material comprising a substrate (l), a design layer (3), a fatty acid ester layer (2) between the design layer (3) and the substrate (l), and a protective coat (4) associated with the design layer (3)

2. A transfer material as claimed in claim l, wherein the ester layer (2) is formed of a fatty acid ester of a glycol.

3. A transfer material as claimed in claim 2, wherein the glycol is ethylene glycol.

4. A transfer material as claimed in claim l, 2 or 3, wherein the fatty acid is stearic acid.

5. A transfer material as claimed in claim l, wherein the fatty acid ester is ethylene glycol monostearate or distearate, or a mixture thereof.

6. A transfer material as claimed in any preceding claim wherein the protective coat (4) is provided on the design layer (3).

7. A transfer material as claimed in any preceding claim, wherein the protective coat (4) is a complete cover coat.

8. The use of a coated substrate comprising a substrate (l) and a fatty acid ester layer (2) thereon, in a method of decorating an article by means of a heated transfer pad (5) which (l) removes (a) a design layer (3) which has previously been provided on the coated substrate (l) and (b) at least part of the fatty acid ester layer (2) from the substrate (l) so that said layers (2 and 3) become temporarily attached to the transfer pad (5) with the design layer (3) being disposed between the transfer pad (5) and the fatty acid ester layer (2); and (2) presses the fatty acid ester layer (2) against the article (6) to be decorated so that the previously molten fatty acid ester layer (2) solidifies and so attaches the design layer (3) to the article (6).

9. A method of decorating an article comprising the steps of providing a transfer material comprising a substrate (l), a design layer (3), a fatty acid ester layer (2) between the substrate (l) and the design layer (3), and a protective coat (4) associated with the design layer (3); contacting a heated transfer pad (5) with a surface of the transfer material opposite to that on which the substrate (l) is provided; before or during the contacting step, melting the fatty acid ester layer (2); separating the transfer pad (5) from the substrate (l) so that the protective coat (4), the design layer (3) and at least part of the fatty acid ester layer (2) become attached to the pad (5) and separated from the substrate; pressing the transfer pad (5) with the attached layers (2, 3 and 4) against an article (6) to be decorated so that the fatty acid ester layer (2) solidifies and attaches the design layer (3) to the article (6); and separating the transfer pad (5) from the article (6).

l0. A method as claimed in claim 9, wherein the transfer pad (5) is heated to a temperature above the melting point of the fatty acid ester layer (2) so that melting of the latter occurs during said contacting step.

11. A method as claimed in claim 9 or l0, wherein the protective coat is provided on the design layer.

12. A method as claimed in claim 9, l0 or ll wherein the protective coat (4) is provided over an area such as to prevent any contact between the transfer pad (5) and the ester layer (2).

Drawing