TRANSFERS AND METHODS OF DECORATING USING SAME

Abstract: A transfer element adapted to be applied to an article in face-up orientation by mechanical means comprises a base or carrier (1) on which is supported a release layer (2) of thermoplastic material, an intermediate support layer (3), a pattern or design (4) superimposed on the support layer, a second support layer (5) applied over the pattern or design, and a cover coat (6) of an adhesive material. The transfer is applied by raising its temperature to a temperature causing the release layer to melt and the cover coat to become tacky whereby the cover coat, design, support layers and a portion of the release layer may be separated from the base or carrier and applied to the surface of an article, the temperatures of the release layer and cover coat being controlled so that they attain a state whereby the degree of adherence of the release layer to the surface of the article exceeds the degree of adherence of the cover coat to the transfer member, so that the latter may be withdrawn leaving the transfer adhered to the surface of the article.

Description: This invention relates to transfers and to methods of decoration using transfers. Decoration of ceramic ware by means of transfers has a number of advantages. In particular because at the printing stage the design is printed on to a flat support sheet or substrate rather than directly on to the contoured surfaces of the article to be decorated, a wide range of conventional printing techniques may be employed and patterns incorporating fine detail can be more readily produced. Hitherto however such transfers have been difficult to apply mechanically since they require to be removed from the substrate or carrier, transferred to the article and adhered thereto without destroying the integrity of the design or pattern or introducing folds or creases. Most mechanical decoration of ceramic ware by means of transfers has therefore been effected by applying the transfer face down on to the surface of the article to be decorated while still carried by its supporting substrate which is then peeled away. Thereafter the transfer is subjected to a firing operation to fuse it to the surface of the article to form a permanent decoration. Application of transfers face down in this way is disadvantageous in that the pattern or decoration requires to be printed in reverse or mirror image on the substrate. Additionally the presence of the supporting substrate during application interferes with the flexibility of the transfer and renders this method inappropriate for the decoration of contoured surfaces. In European patent No. 55395 there is disclosed a technique for the mechanical application of transfers to articles of ware in a face-up manner utilizing transfers comprising a carrier, a release layer of thermoplastic material and a design or pattern superimposed on the release layer. The release layer is temperature sensitive and serves the dual function of releasing the design elements from the carrier and adhering them to the surface of the article of ware to be decorated. An additional strengthening layer of a non-adhesive nature may be applied above or beneath the individual elements of the design if desired. Transfers constructed in accordance with European patent No. 55395 have little if any practical utility. The elements of the design layer will not pick up using conventional silicone or similar transfer pads and in the case of patterns consisting of discrete separate design elements relative movement and distortion occur. It is an object of the present invention to obviate or mitigate this disadvantage. The invention provides a transfer element adapted to be applied to an article in face-up orientation by mechanical means, the element comprising a base or carrier on which is supported a release layer of thermoplastic material, an intermediate support layer, a pattern or design superimposed on said support layer, a second support layer applied over said pattern or design, and a cover coat of an adhesive material. The support layers preferably comprise thermoplastic film-forming resins, the preferred materials being poly n-butyl methacrylate or a co-polymer of butyl methacrylate and methyl methacrylate. The release layer preferably has a melt temperature in the region of 60 to 80 °C and an "open time" of around 0.5 to 5 seconds. The open time is the time for which the release layer remains tacky after removal of the heat source. Preferably also the pattern or design is formed from vitrifiable materials, the remaining layers being formed from materials which volatilize at or below the vitrification temperature of the pattern or design. The invention also provides a method of decorating an article by application of a transfer as aforesaid, the method comprising raising the temperature of the transfer to a temperature causing said release layer to melt and said cover coat to become tacky whereby said cover coat, design, support layers and at least a portion of said release layer may be separated from said base or carrier, applying the separated elements of the transfer to the surface of an article of ware to be decorated, and controlling the temperatures of said release layer and said cover coat in such manner that they attain a state whereby the degree of adherence of the release layer to the surface of the article of ware exceeds the degree of adherence of the cover coat to the transfer member, whereby the latter may be withdrawn leaving the elements of the transfer adhered to the surface of the article. The temperature of the transfer may be raised by application of heat thereto through the base or carrier member from a heated support, by raising the temperature of said transfer member, or both. Preferably the article of ware to be decorated is unheated whereby on contact with its surface the temperature of said release layer is reduced relative to that of said cover coat whereby to produce said temperature control enabling the transfer member to be withdrawn from the article leaving the transfer elements affixed to the article. Preferably the transfer is initially heated to a temperature in the region of 80 to 100 °C. Preferably also said transfer member is withdrawn from the surface of the article of ware when the temperature of said release layer is in the region of 30 to 40 °C and the temperature of said cover coat is in the region of 40 to 50 °C. Typically the transfer member is maintained in contact with the surface of the article of ware for between 0.5 and 2 seconds. The invention also provides a method of decorating an article by application of a transfer as aforesaid, comprising raising the temperature of the transfer to a temperature above the melt temperature of said release layer to melt same and to render said cover coat tacky, bringing a transfer member into contact with said cover coat before or after raising the temperature thereof, whereby to cause adherence of the transfer to the transfer member, moving the transfer member away from the base or carrier while retaining the latter against movement, whereby to separate the base or carrier from the other elements of the transfer, maintaining the surface of the article to be decorated at a temperature below the melt temperature of said release layer, applying the released elements of the transfer to the surface of the article by pressing the transfer member and the released elements carried thereby into contact with the surface of the article whereby the release layer adheres to the surface of the article due to cooling below its melt temperature, and withdrawing the transfer member while the degree of adherence of the cover coat to the transfer member is less than the degree of adherence of the release layer to the article, whereby the transfer remains on the surface of the article. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing which is a diagrammatic cross-section through one form of transfer according to the invention. Referring to the drawing, the transfer comprises a series of superimposed layers or elements mounted on a base or carrier sheet 1, generally of paper, the upper surface of which is provided with an overall coating of thermoplastic material serving as a release layer 2 by means of which the remaining elements of the transfer may be separated from the support paper 1 during application of the transfer to an article of ware to be decorated. Superimposed on the release layer 2 is a support layer 3 comprising a thermoplastic film-forming resin acting as a support for a design layer 4 applied to the upper surface of the support layer 3 by a suitable printing technique such as silk screen printing. The design layer will generally be multi-coloured and built up in a series of printing operations in each of which a different colour is applied. In most instances the elements of the design layer will not cover the whole surface of the support layer 3 so that portions of the surface of the latter will be visible between elements of the design layer. A further support layer 5, generally identical to the support layer 3, is applied over the design layer 4 and finally an upper surface layer or cover coat 6 of adhesive is applied over the printed design. The carrier paper 1 and release layer 2 together form a heat release transfer paper generally supplied commercially by coated paper manufacturers and on which the remaining layers of the transfer are applied by a transfer printer. The thermoplastic release layer may consist of a mixture of hydrocarbon waxes, mineral oils and hydrocarbon resins. An alternative suitable material is ethylene glycol distearate. Other compositions which may be employed include polyethylene glycols, polyoxyethylated alcohols, styrene-butadiene or nitrile-butadiene latices, hydrocarbon resin emulsions, ethylenevinylacetate co-polymer emulsions, alkyd emulsions, vinyl chloride emulsions and polyamides. The essential properties of the material are that it shall melt at a predetermined temperature and remain tacky for a sufficient period of time (the open time) after removal of the heat source to permit separation of the superimposed transfer layers from the base paper and their application to the surface of an article to be decorated. The release layer must function when heated to permit such separation and also have the requisite degree of adherence to the surface of the article when applied thereto by a mechanical transfer member such that the transfer member may be withdrawn leaving the elements of the transfer attached to the surface of the article. One of the problems encountered in producing satisfactory transfers is the need to maintain the integrity of the design layer during separation from the base paper, application to the ware and withdrawal of the transfer member. For this purpose the illustrated transfer incorporates the upper and lower support layers 3 and 5 both of which comprise a thermoplastic film forming resin serving firstly to give strength and flexibility to the transfer while resisting relative movement of the design elements superimposed upon it, and secondly to protect the release layer 2 from attack by solvents employed in the materials from which the design layer is formed. The support layers are generally in the region of 15 to 20 microns in thickness and are applied in liquid form in a suitable solvent by coating if continuous or by printing if discontinuous. Generally the support layers consist of plasticized poly n-butyl methacrylate or a co-polymer of butyl methacrylate and methylmethacrylate in an aromatic hydrocarbon solvent. Suitable plasticizers are phthalate esters. Other suitable materials for the support layer include cellulosic derivatives particularly esters and ethers; examples include methyl and ethyl-cellulose, cellulose acetate, cellulose acetate butyrate and propionate and nitro cellulose. Other suitable materials include acrylic resin systems modified using cellulosic materials, melamine resins, phenolics, polyacrylamides, polybutadiene resins, polyesters, polyurethanes, polyvinyl acetate and its co-polymers and polyvinyl butyral. All such materials form strong flexible films or sheets isolating the design layer from the release layer and the cover coat and providing strength and flexibility during application of the transfer while maintaining the integrity of the design layer. The design layer is applied as a series of sequential printings of the individual colours making up the design or pattern. Each printing comprises a layer, generally 5 to 10 microns in thickness of a ceramic colour consisting of an inorganic pigment and flux dispersed in a printing medium. The printing medium must necessarily have film forming properties to permit application by conventional printing techniques such as silk screen printing and is incorporated with the ceramic colour in a suitable solvent. Suitable printing media comprise acrylic and methacrylic polymers and co-polymers such as a polyalkyl methacrylate co-polymer disolved in n-butyl lactate as solvent, the medium generally including a plasticizer such as a mixture of phthalate esters. Cellulosic derivatives similar to those which may be employed in the support layer referred to above may be used as may printing media based on drying oils, a typical formulation incorporating linseed oil mixed with an alkyd resin and including a drier, generally a cobalt or manganese salt, which catalyses the polymerisation process. Other resinous materials which may be used include alkyds, phenolics, urea-formaldehyde, melamine-formaldehyde, melamine alkyds, vinyl derivatives and polyesters. The upper support layer may be constructed in the same manner as and serves a similar function as the lower support layer 2 in that it imparts additional strength and stability to the transfer during the stage between removal from the support paper and application to the article to be decorated. As in the case of the lower support layer the upper support layer may be continuous or discontinuous provided in the latter case that it at least covers the areas of the transfer to which the design layer has been applied. Following application of the design layer 4 and the upper support layer 5, the adhesive cover coat 6 is applied. This layer serves to cause adherence of the transfer to the surface of the pad or other transfer member employed to separate the upper elements of the transfer from the support paper and apply them to the surface of the article to be decorated. The layer 6 is applied as a melt adhesive and extends at least over the area of the transfer occupied by the design layer. As in the case of the upper and lower support layers 3 and 5, and as shown in the drawing, the layer 6 need not extend to the full area of the coated base paper. The preferred material for the cover coat is an ethylcellulose/rosin ester mixture activated with a chlorinated diphenyl plasticizer. The coating is applied as a solution in an aromatic hydrocarbon solvent and develops tack at around 80 °C. An alternative melt adhesive system which may be employed comprises an acrylic or methacrylic resin co-polymer tackified with polyethylene glycol and/or polyoxyalkylene derivatives of propylene glycol and/or ethylenediamine. A second tackifier, for example an ester of an alkyl polyol and an aromatic acid, or a solid phthalate ester may also be incorporated. Cellulosic derivatives, alkyd resins and polystyrene plasticizers may be used to modify the properties of the adhesive. In a further alternative system the acrylic or methacrylic resin co-polymer is replaced with a cellulosic derivative, usually methyl-ethyl- or hydroxypropyl cellulose ether. The extent of the support layers 3 and 5 and the cover coat 6 may be varied dependent on the nature of the design layer and the stage of manufacture of the article at which the transfer is applied. Transfer decoration of ceramic articles is generally applied either "underglaze" or "on-glaze". In the case of underglaze decoration the transfer is applied when the article is in the "biscuit" state, following which a glaze medium is applied over the surface of the article and the transfer and the article is then subjected to a final firing step which fuses the glaze and the transfer to the surface. During the firing operation volatile materials are burned off leaving the glaze and the ceramic colour only fused to the surface of the article. In on-glaze decoration the article is provided with an overall glaze coating which is fired prior to application of the transfer. The latter is then applied to the glazed article and subjected to a further firing to fuse the design to the surface and burn off volatile materials. It will be appreciated that in the first case the glaze medium is applied over the transfer while in the second case it is applied under the transfer and this requires certain modifications in the construction of the transfer itself, particularly as regards the nature of the support layers 3 and 5 and the adhesive cover coat 6 as referred to hereafter. In order for the transfer to function satisfactorily it is only necessary for the upper and lower support layers 3 and 5 and the adhesive cover coat 6 to coincide with the actual extent of the design layer 4. In some patterns, for example where lines are applied around the edge region of a plate, the design "layer" extends only over a very small area of the article as a whole. For the purpose of saving in material costs therefore it is appropriate in such cases to confine the support layers 3 and 5 and the adhesive cover coat 6 to the area actually occupied by the design elements. In the most common instance the effect is that these layers are of essentially annular form and do not extend over the central region of the transfer and hence the thermoplastic release layer 2 on the surface of the base paper 1 is exposed in this central region. However by virtue of the fact that the support layers and the adhesive cover coat extend over the design areas, which will all generally be linked to one another either in annular or other form, the coherence of the design layer is maintained during transfer despite the absence of such layers in the central or other regions of the transfer to which no design layer is applied. This arrangement is satisfactory for on-glaze decoration where the glaze medium has been applied to the surface of the article and fired prior to application of the transfer. However in underglaze decoration the heat release materials forming the release layer 2 generally reject glaze mediums applied as aqueous suspensions and in the case of underglaze decoration therefore it is necessary that at least one of the support layers 3 and 5 or the adhesive cover coat 6 are applied as continuous unbroken films across the entire area of the transfer which is contacted by the transfer member. In this way when the transfer has been attached to the surface of the ware none of the thermoplastic material of the release layer 2 is exposed to the glaze medium which is applied subsequently over the whole surface of the article including the transfer itself. In such cases the support layers 3 and 5 and optionally the cover coat layer 6 are modified by the addition of a flux designed to match the glaze and by the incorporation of involatile liquid or solid plasticizers. The transfer is applied to the article to be decorated by means of a transfer member generally in the form of a flexible pad of silicone rubber or other suitable material. Generally the operation will be carried out with the transfer and the article to be decorated in generally horizontal positions, the transfer pad first being brought down into contact with the surface of the transfer and heat being applied either through the pad or through the support on which the transfer is carried, or both, sufficient to raise the temperature of the release layer 2 to around 80 °C. The heat also serves to cause adherence of the adhesive cover coat 6 to the pad, the arrangement being such that due to melting of the release layer 2 the degree of adherence of the pad to the layer 6 exceeds the degree of adherence of the support layer 3 to the base paper 1. The pad may therefore be lifted clear of the base paper, which is retained against upward movement, and carries with it the cover coat 6, upper support layer 5, design layer 4, lower support layer 3 and at least some of the release layer 2, the remainder of which remains attached to the base paper 1. The pad is then brought to a position over the ware to be decorated and is moved downwards into contact with the ware which is preferably maintained at room temperature. Since the temperature of the ware is considerably lower than the temperature at which the material of the release layer 2 carried by the transferred elements solidifies, the release layer adheres to the surface of the article. By appropriate selection of the materials such that on cooling the degree of adherence of the release material to the surface of the ware exceeds the degree of adherence of the adhesive cover coat 5 to the transfer pad, the pad may be withdrawn leaving the transfer adhered to the surface of the article. By virtue of the flexible nature of the pad it flattens on picking up the transfer from the base sheet 1 and conforms to the contours of the article when applying the transferred elements thereto thereby preventing the formation of folds or creases. The provision of the support layers 3 and 5 assists in maintaining the integrity of the design layer during the transfer operation. This is particularly the case where the design area occupies a relatively small part of the total surface area of the article and the design layer is therefore essentially of a fragile nature readily susceptible to distortion and damage. The transfer construction and method of decoration described are particularly advantageous for detailed geometric designs where even slight distortion during application would render the decorated product commercially unacceptable. It will be appreciated that since the transfer is maintained in a "face-up" disposition throughout the process of application to the ware, the design layer may be printed face-up, that is as it appears on the final article. This is a substantial advantage compared with previously proposed transfers which are applied "face-down" to the article and which therefore require that the design is printed in mirror image. By virtue of the arrangement described there is provided a transfer which may be satisfactorily applied to an article of ware by mechanical means but does not require to be printed in mirror image. The transfer is so constructed as to maintain its integrity during the transfer process even in the case of designs or patterns occupying only a small area of the surface of the article to be decorated and which are therefore of an essentially fragile and readily deformable nature. It is also unnecessary to heat the surface of the ware to be decorated, the necessary temperature changes being effected by heating and cooling of the transfer itself.

Claims: 1. A transfer element, adapted to be applied to an article in face-up orientation by mechanical means, the element comprising a base or carrier (1) on which is supported a release layer (2) of thermoplastic material, an intermediate support layer (3), a pattern or design (4) superimposed on said support layer, a second support layer (5) applied over said pattern or design, and a cover coat (6) of an adhesive material. 2. A transfer element according to claim 1 characterised in that said support layers (3,5) comprise thermoplastic film-forming resins. 3. A transfer element according to claim 2 characterised in that said thermoplastic film-forming resins are selected from poly n-butyl methacrylate and butyl methacrylate/methyl methacrylate copolymers. 4. A transfer element according to claim 2 characterised in that said film-forming resins are selected from methyl cellulose, ethyl-cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, nitro cellulose, acrylic resin systems modified using cellulosic materials, melamine resins, phenolic resins, polyacrylamides, polybutadiene resins, polyesters, polyurethanes, polyvinyl acetate and its co-polymers and polyvinyl butyral. 5. A transfer element according to any of claims 1 to 4 characterised in that said release layer (2) has a melt temperature of 60-80°C and an open time of 0.5 - 5 seconds. 6. A transfer element according to any of claims 1 to 5 characterised in that said release layer (2) is selected from hydrocarbon waxes, mineral oils, hydrocarbon resins, ethylene glycol distearate, polyethylene glycols , polyoxyethylated alcohols, styrene-butadiene or nitrile-butadiene latices, hydrocarbon resin emulsions, ethylenevinylacetate co-polymer emulsions, alkyd emulsions, vinyl chloride emulsions and polyamides. 7. A transfer element according to any preceding claim characterised in that said pattern or design (4) is formed from vitrifiable materials, said release layer (2) and support layers (3,5) being formed from materials which volatize at or below the vitrification temperature of the pattern or design. 8. A transfer element according to claim 7 characterised in that said pattern or design (4) comprises an inorganic pigment and a flux dispersed in a printing medium having film-forming properties, the printing medium being selected from acrylic and methacrylic polymers and co-polymers, alkyd resins, phenolic resins, urea-formaldehyde, melamine-formaldehyde, melamine alkyds, vinyl derivatives and polyesters, dissolved in a suitable solvent and optionally including a plasticizer. 9. A transfer element according to claim 8 characterised in that said printing medium comprises polyalkyl methacrylate co-polymer dissolved in n-butyl lactate as solvent. 10. A transfer element according to claim 8 characterised in that said printing medium comprises linseed oil mixed with an alkyd resin and a colbalt or manganese salt as drier/catalyst. 11. A transfer element according to any preceding claim characterised in that said cover coat (6) comprises an ethylcellulose/rosin ester mixture activated with a chlorinated diphenyl plasticizer. 12. A transfer element according to any of claims 1 to 11 characterised in that said cover coat (6) is selected from an acrylic or methacrylic resin co-polymer, methyl-, ethyl- or hydroxypropyl cellulose ether, and a tackifier. 13. A transfer element according to claim 12 characterised in that said tackifier is selected from one or more polyethylene glycol and/or polyoxyalkylene derivatives of propylene glycol and/or ethylene diamine, an ester of an alkyl polyol and an aromatic acid, and a solid phthalate ester. 14. A transfer element according to any preceding claim characterised in that said cover coat (6) becomes tacky in the region of 80°C. 15. A transfer element according to any preceding claim characterised in that one or more of said support layers (3,5) and said cover coat (6) are confined to those areas of the transfer member occupied by said pattern or design (4). 16. A method of decorating an article by application of a transfer element according to any of claims 1 to 15 characterised by raising the temperature of the transfer to a temperature causing said release layer (2) to melt and said cover coat (6) to become tacky whereby said cover coat (6), design (4), support layers (3,5) and at least a portion of said release layer (2) may be separated from said base or carrier (1), applying the separated elements of the transfer to the surface of an article of ware to be decorated, and controlling the temperatures of said release layer (2) and said cover coat (6) in such manner that they attain a state whereby the degree of adherence of the release layer to the surface of the article of ware exceeds the degree of adherence of the cover coat to the transfer member, whereby the latter may be withdrawn leaving the elements of the transfer adhered to the surface of the article. 17. A method according to claim 16 characterised in that the temperature of the transfer element is raised by application of heat thereto through said base or carrier member. 18. A method according to claim 16 or 17 characterised in that the temperature of the transfer element is raised by application of heat thereto from a heated support. 19. A method according to any of claims 16 to 18 characterised in that the article of ware to be decorated is unheated whereby on contact with its surface the temperature of said release layer (2) is reduced relative to that of said cover coat (6) whereby to produce said temperature control enabling the transfer member to be withdrawn from the article leaving the transfer elements affixed to the article. 20. A method according to any of claims 16 to 19 characterised in that the transfer element is initially heated to a temperature in the region of 80-100°C. 21. A method according to any of claims 16 to 20 characterised in that said transfer member is withdrawn from the surface of the article of ware when the temperature of said release layer is in the region of 30 to 40°C and the temperature of said cover coat is in the region of 40 to 50°C. 22. A method according to any of claims 16 to 21 characterised in that the transfer member is maintained in contact with the surface of the article of ware for between 0.5 and 2 seconds. 23. A method of decorating an article by application of a transfer element according to any of claims 1 to 15, characterised by raising the temperature of the transfer element to a temperature above the melt temperature of said release layer (2) to melt same and to render said cover coat (6) tacky, bringing a transfer member into contact with said cover coat before or after raising the temperature thereof, whereby to cause adherence of the transfer element to the transfer member, moving the transfer member away from the base or carrier (1) while retaining the latter against movement, whereby to separate the base or carrier from the other elements of the transfer, maintaining the surface of the article to be decorated at a temperature below the melt temperature of said release layer (2), applying the released elements of the transfer to the surface of the article by pressing the transfer member and the released elements carried thereby into contact with the surface of the article whereby the release layer (2) adheres to the surface of the article due to cooling below its melt temperature, and withdrawing the transfer member while the degree of adherence of the cover coat (6) to the transfer member is less than the degree of adherence of the release layer (2) to the article, whereby the transfer remains on the surface of the article. 24. A method according to any of claims 16 to 23 characterised in that said transfer member comprises a pad of flexible material. 25. A method according to claim 24 characterised in that said pad is formed from silicone rubber.

Inventors: COX, BRUCE
Applicants: JOSIAH WEDGWOOD & SONS LIMITED
Application year: 1988
Main classification: B44C1
IPC codes: B44C1