Heat Release Layer for Decalcomanias

The present invention is directed to heat release decalcomanias. Still more particularly, the present invention relates to papers for use in the production of heat release decalcomanias. Still more particularly, the present invention relates to decalcomanias which include a heat release layer disposed on a paper backing sheet, including a barrier coat, a design layer, and a heat-activatable adhesive layer disposed on the design layer, so that upon heating, the heat release layer permits release of the design layer from the backing sheet while simultaneously the adhesive layer is activated and permits retention of the design layer upon the ware. Still more particularly, the present invention relates to methods for forming such decalcomanias, including applying a heat release layer to a backing sheet, applying a design layer to the heat release layer, and applying a heat activatable adhesive layer to the design layer. In addition, the present invention is also directed to the decoration of various substrates by applying such decalcomanias thereto in the presence of heat and pressure.

For many years various types of decalcomanias (decals) have been utilized for the decoration of articles or wares of various types, including glassware, china ware, pottery, aluminum, porcelain enamel, etc. These decalcomanias originally included the water or "slide-off" type in which a paper backing had a design layer disposed thereon and the paper carried a thin layer of a water soluble gum with a vitreous design imprinted thereon. Subsequently, however, as this art developed, decalcomanias of the "heat-release" type were developed, including a backing sheet, a design or pigment layer generally formed from inorganic pigments or oxides, and an optional protective layer applied on the design layer. These types of decalcomanias preferably included a release layer disposed between the backing sheet and the design layer to facilitate release of the design from the backing sheet during heating. Examples of typical heat-releasable decalcomanias are disclosed in a number of U.S. patents, including U.S. Pat. Nos. 2,970,076 to Porth; 3,007,829 to Akkeron; 2,991,221 to Bower; 3,411,458 to Milliken; 3,445,309 to Milliken; and 3,642,551 to Laconich et al.

In order to utilize such heat release types of decalcomanias, the article or ware to be decorated is generally preheated and the decalcomania can then be applied to the article with the backing sheet up so that the layer of heat-activatable adhesive directly contacts that article. Thus the heat applied to the article effects both a preliminary bonding of the design layer, via the heat-activatable adhesive, to the article or ware, while the heat also effects the release of the backing sheet, preferably including a barrier layer, and a portion of the release layer, from the design layer. The article can then be fired at high temperatures in the usual manner so that the design layer is melted and permanently fused to the article, and the combustible organic ingredients including the remaining portion of the release layer, and the resinous carrier for the design layer are preferably consumed during such firing.

The heat-release layers generally employed in such decalcomanias include those disclosed in the above-noted Porth and Akkeron patents. In particular, these include normally solid mixtures of polyethylene glycol compounds, and preferably as disclosed in the Akkeron patent including at least one polyethylene glycol compound which has an average molecular weight of from about 15,000 to about 20,000, but preferably in combination with lower molecular weight polyethylene glycol compounds, such as those having a molecular weight of from about 3,000 to 3,700 (such as CARBOWAX 4000--CARBOWAX being a trademark of the Union Carbide Corporation). These compounds have generally been employed as alternatives to vegetable or mineral waxes having melting points within the range of from about 130.degree. F. to about 220.degree. F. These types of decalcomanias, as noted above, have been employed for decorating various wares or articles. In connection with same, such decalcomanias of both the "underglaze" and "overglaze" type have been utilized. In the former case, the decalcomania is applied to the ware after its formation, but prior to its being glazed, which is accomplished after application of the decal to the ware. The glazes employed generally comprise vitreous coatings which generally require very high temperatures to form the glass from their raw materials. This procedure thus results in a protective coating over the pigments in the decal, but the high temperatures required tend to destroy certain colors, leaving only a limited color palette. Thus "overglaze" decalcomanias have also been developed in which application to the ware is carried out after it has been glazed. These decalcomanias generally include silk screen and lithographic decals. The present invention is intended for application in connection with all of these various types of decal applications of the heat release type.

In addition, in U.S. Pat. No. 4,068,033 of Hazel Meade, which was based on an application filed on Nov. 11, 1976, a novel heat activatable adhesive composition for use in such decalcomanias is disclosed. This adhesive composition is intended for use in connection with such ware decoration in a manner such that heating of the ware itself can be eliminated. These compositions thus include a "delayed tack" feature whereby the adhesive composition after it has been heated to above its softening point retains its tackiness or adhesive character for a sufficient amount of time for it to be applied to the ware, without the ware itself having to be heated. That portion of this patent is incorporated herein by reference hereto, and will be discussed in more detail below in connection with the novel heat release layer of this invention. It is also noted that this patent is based on a parent application Ser. No. 555,076, filed on Mar. 3, 1975, which includes a disclosure of the optional use of certain fatty acid amides, such as ARMID HT, a product of Armak Chemical Co., in the adhesive composition of decalcomanias.

The search has continued for a new heat release composition which can be easily applied to the backing sheet, which has a melt viscosity such that release of the design layer is easily facilitated, which does not result in the application of a tacky surface to the outer surface of the design layer after it has been applied to the ware, and which can be completely burned off during firing without any adverse effects to the decoration itself. In addition, the search has also continued for a combination of heat release and heat activatable adhesive layers in such decalcomanias which includes all of these properties with regard to the heat release layer as well as the above-noted properties regarding the heat activatable adhesive layer, including the ability to remain tacky or adhesive after heating for a suitable period of time so that application to a cold ware can be effected, i.e. without heating of the ware itself and all of its concomitant problems.

Such a decalcomania has been recently discovered and is disclosed in the applicant's U.S. Pat. No. 4,117,182, which issued on Sept. 26, 1978, and which is assigned to the assignee of the present application. This patent discloses a decalcomania paper and decalcomania which has been highly successful commercially, and which possesses all of the desired properties discussed above. It includes a heat release layer comprising a normally solid, straight chain, primary aliphatic oxyalkylated alcohol, such as those marketed by BASF Wyandotte under the trademark PLURAFAC.

In accordance with the present invention, still further improvements in heat release layers for use in connection with heat release decalcomanias have now been discovered. In particular, in connection with heat release decalcomanias including a backing sheet, a design layer, and a heat activatable adhesive layer disposed on the design layer, a heat release layer disposed between the backing sheet and the design layer is provided which includes a combination of a normally solid straight chain, primary aliphatic oxyalkylated alcohol with an additive comprising either a normally solid polyethylene glycol having an average molecular weight of greater than about 1000, or an amide of a fatty acid, preferably an amide of a C.sub.8 to C.sub.18 fatty acid. By utilizing such a combination of ingredients in the heat release layer, during the manufacture of these decalcomanias it is possible to produce a more desirable decalcomania in a shorter period of time. Normally, paper or some other substrate coated with the heat release layer is initially prepared, and then subsequently employed to manufacture the decalcomania, e.g. by application of the design layer, etc. thereto. It is therefore necessary to apply heat to the coated paper in order to liquify the release layer, and it is desirable both that the initially liquified release layer applied to the paper during its manufacture and the re-liquified release layer re-crystallize as rapidly as possible in order to facilitate the high speed production of the coated paper and the finished decalcomania product. This can be accomplished in a highly desirable manner with the heat release layer of this invention. Furthermore, it is also highly desirable for there to be a smooth and clean release of the backing sheet from the remainder of the decalcomania during application thereof. This can also be accomplished without the heat release layer "picking" or "pulling" at the design layer during transfer, by utilizing the novel heat release layer hereof. Finally, it is also noted that any residue from the heat release layer hereof which remains on the design layer during transfer, or application of the decalcomania to a ware, does not interfere with the subsequent firing thereof. By employing the above-noted additives in the heat release layer of this invention it is also possible to reduce the solubility of the release layer in organic solvents, such as those employed in the barrier layer and design layer of various decalcomanias, and also to render the best release layer harder and stronger than has previously been possible.

In a preferred embodiment of the present invention, the heat release layer includes from about 1 to about 50 weight percent of the normally solid polyethylene glycol component, but the precise amount employed relates somewhat to the molecular weight thereof. For example, where the polyethylene glycol component has a molecular weight of about 4000, it will be most preferred to employ from about 10 to about 40 weight percent, and most preferably about 25 weight percent thereof.

In another preferred embodiment of the present invention, the heat release layer includes from about 1 to about 25 weight percent of the amide of a fatty acid, and preferably will include from about 2 to about 10 weight percent thereof, such as a hydrogenated tallow amide sold commercially under the trademark ARMID HT.

In another embodiment of the present invention, the normally solid, straight chain, primary oxyalkylated alcohol employed will have a molecular weight above about 1350, and also preferably have a melting point above about 110.degree. F.

In accordance with another aspect of the present invention, a release paper for use in the preparation of heat release decalcomanias is provided, including a paper backing sheet coated with a heat release layer as described above, that is including a combination of the described oxyalkylated alcohol and an additive, i.e., the polyethylene glycol material and/or amide of a fatty acid.

In another embodiment of the present invention, this novel heat release layer is employed in combination with a heat activatable adhesive layer comprising either (A) an acrylic resin as the adhesive base material, or (B) a suitable cellulosic derivative, preferable in connection with a straight chain, primary aliphatic oxyalkylated alcohol as the adhesive base component, a plasticizer, or as referred to herein, a tackifier, for that adhesive base component, and a major amount of an organic solvent. The tackifier is selected so as to be capable of providing an adhesive which softens when subjected to heat and remains tacky at a temperature substantially below its melting point. In particular, the tackifiers preferably employed in this combination, which can be cleanly burned upon final firing without deposition of a harmful residue, include (A) when an acrylic resin is employed as the adhesive base component; a polyethylene glycol, and/or a solid polyoxyalkylene derivative of propylene glycol or ethylene diamine, and in a highly preferred embodiment, a combination of tackifiers is utilized, including these tackifiers in combination with a second tackifier including one or more aromatic acid esters of monomeric or polymeric alkyl polyols. On the other hand, (B) when a suitable cellulosic derivative is employed as the adhesive, the tackifiers include various plasticizers including solid plasticizers such as dicyclohexyl phthalates and/or liquid plasticizers such as dioctyl phthalate, as well as the normally solid straight chain, primary aliphatic oxyalkylated alcohol.

In another embodiment of the present invention, heat release decalcomanias are formed by a method including the application of a heat release layer to a backing sheet, the application of a design layer to the heat release layer, and the application of a heat activatable adhesive layer to the design layer in which the heat release layer includes the combination of normally solid, straight chain, primary aliphatic oxyalkylated alcohols and the polyethylene glycol and/or fatty acid amide additives described above. In another highly preferred embodiment of the present invention, the heat activatable adhesive layer applied to the design layer which is used in connection with this heat release layer comprises the particular heat activatable adhesive layer described above, including preferably a combination of tackifiers as described therein.

FIG. 1 is a diagrammatic cross-sectional representation of a heat releasable decalcomania in accordance with the present invention; and

FIG. 2 is a diagrammatic cross-sectional representation of another embodiment of the heat releasable type decalcomanias in accordance with the invention.

FIG. 1 illustrates a heat release decalcomania in accordance with the present invention which includes a decalcomania backing 10 consisting of a paper sheet 12, with barrier layer 14, and covered by release layer 16. A sealant layer 18 of a cellulosic derivative is preferably disposed over the release layer 16, and design layer 20 is disposed over cellulosic derivative or sealant layer 18, which serves as an imprint receiving support for the design layer. Over the design layer 20 is disposed the layer 22 of heat activatable adhesive material which serves as a temporary binder for securing the design layer 20 to the article or ware to be decorated.

The heat release layer 16 in accordance with the present invention includes as one component of the combination hereof a normally solid straight chain, primary aliphatic oxyalkylated alcohol. Preferably, this component will include an oxyethylated alcohol of this type, and will have a melting point above about 110.degree. F. Also, it will preferably have a molecular weight above about 1350, most preferably between about 1350 and 1750.

The preferred compounds so employed thus include such normally solid, straight chain, primary aliphatic oxyethylated alcohols marketed by BASF Wyandotte under the Trademark PLURAFAC. These compounds are generally manufactured by the addition of about 75 to 95% of Ethylene oxide to a straight chain, primary fatty alcohol. Most of these products are, however, either liquids or pastes at room temperature, and are not usable in accordance with the present invention. Some are, however, normally solid, and these include PLURAFAC A-38 and most particularly PLURAFAC A-39, and are particularly preferred herein.

The other component employed in combination with these oxyalkylated alcohols in the heat release layer 16 comprise at least one of the additives disclosed above. These compounds are soluble in the oxyalkylated alcohols, but will re-crystallize at a faster rate than these alcohols will, so that they will reduce the period of time that these materials will remain in the liquid phase. The normally solid polyethylene glycol will have an average molecular weight of greater than about 1000, and preferably would either have a molecular weight of from about 1000 to about 6000, most preferably from about 3000 to 3700, or have a molecular weight of greater than about 6000, i.e., such as between about 6000 and 20,000. Polyethylene glycols are polymers formed by the addition of ethylene oxide to ethylene glycol, and their general structure is as follows:

These compounds are normally solid when their molecular weight is above about 1000. Such materials are available commercially from a number of sources, including the materials sold by Union Carbide Corporation under the trademark CARBOWAX.

In determining which particular polyethylene glycol composition to employ in the heat release layer of this invention, it is first noted that all of the various normally solid polyethylene glycol compositions having molecular weights above about 1000 are soluble in the normally solid straight chain, primary aliphatic oxyalkylated alcohols hereof, and furthermore will, to varying degrees, impart desired properties to that component when utilized in these heat release layers. In particular, their combination will exhibit a shortened supercooled period subsequent to melting, i.e., when the temperature is then lowered. They will thus be usable in the supercooled state for effecting transfer from a paper substrate, but will not remain in that state so long as to present a problem during the coating of the decalcomania paper. Furthermore, as noted above, the heat release layer will be rendered less soluble in various organic solvents, such as those used in the barrier and/or design layers of these decalcomanias, and they will exhibit superior strength and hardness characteristics.

Generally, however, the amount of the polyethylene glycol component can be lowered where the higher molecular weight polyethylene glycols are employed. One of the commercially available CARBOWAX compounds, for example, has an average molecular weight of from about 15,000 to about 20,000 and is designated CARBOWAX Compound 20M. When such a polyethylene glycol material having an average molecular weight of from about 15,000 to 20,000 is thus utilized, it will generally be employed in amounts from about 1 to 10 percent of the heat release layer, preferably from about 1 to 5 percent of the heat release layer. Other commercially available CARBOWAX compounds include CARBOWAX Compound 4000, having an average molecular weight of from 3000 to about 3700, and CARBOWAX Compound 6000, having an average molecular weight of from about 6000 to about 7500. When the polyethylene glycol composition utilized has an average molecular weight of from about 1000 to about 6000, from about 3 to about 50 percent of the heat release layer should comprise such compositions, preferably from about 3 to about 25 percent. On the other hand, when the composition has an average molecular weight of greater than about 6,000, i.e., from about 6000 to about 20,000, from about 1 to about 25 percent of the heat release layer should comprise such compositions.

The amides of fatty acids which can also be employed as an additive in connection with the heat release layers hereof are solids at room temperature, and generally have melting points of between about 120.degree. and 250.degree. F. An example of such a fatty acid amide particularly suitable for use herein as ARMID HT, a hydrogenated tallow amide sold by Armak Chemical Co., and having a melting point of about 215.degree. F. ARMID HT is an amide of a combination of C.sub.14 to C.sub.18 fatty acids. Generally, however, amides of C.sub.8 to C.sub.18 fatty acids should be employed, most preferably amides of C.sub.12 to C.sub.18 fatty acids, and preferably in amounts ranging from about 1 to 10 weight percent of the heat release layer, more preferably from about 1 to about 5 weight percent thereof.

One of the heat activatable adhesive layers 22 which may be used in combination with the heat release layer of the present invention is, as discussed above, fully disclosed in U.S. Pat. No. 4,068,033. The disclosure of that patent is incorporated herein by reference thereto. In particular, the description of the heat activatable adhesive layer in that patent is also incorporated herein by reference thereto, and comprises an (a) acrylic resin which serves as the adhesive base component, (b) one or more tackifiers including a polyethylene glycol and/or solid polyoxyalkylene derivatives of propylene glycol and/or ethylene diamine, and (c) a major amount of an organic solvent. Preferably, however, component (b) will also include a second tackifier including one or more aromatic acid esters of monomeric and polymeric alkyl polyols (reference is made to column 5, lines 18 et seq of U.S. Pat. No. 4,068,033, which is incorporated herein by reference thereto).

Furthermore, these adhesive layers may also include a cellulosic derivative which moderates the tackiness of the mixture of the acrylic resin and tackifiers and enhances the cohesiveness of such mixtures. The adhesive layer 22 also preferably includes an alkyd resin and a polystyrene plasticizer, as described in the above-noted Hazel Meade application. Furthermore, other solid plasticizers may also be added thereto as additional tackifiers, and the adhesive may also optionally include other components which will have a softening effect on the cellulosic derivative and/or the acrylic resin or will improve the firing characteristics of the decal.

As indicated, these adhesive base components of this particular adhesive composition which may be used in the decalcomanias of the invention preferably comprises one or more acrylic resins including acrylic and methacrylic polymers and copolymers such as polybutylacrylate, methyl methacrylate/butyl methacrylate copolymer, polyethyl acrylate, etc. Particularly suitable are acrylic resins of the Carboset series (trademark of B. F. Goodrich) such as Carboset 514A which is a 70% solution of low molecular weight acrylic copolymer in isopropyl alcohol, and Acryloid resins, such as ethyl methacrylate copolymer B-72 and methyl methacrylate copolymer B48N, produced by Rohm and Haas Co., Inc.

The polyethylene glycols employed as one of the tackifiers in the adhesive composition of the invention include the polyethylene glycols discussed above, and are intended to provide the desired and required tackifying effect so that these adhesives will be suitable for use herein. These components are crystalline solids which when melted have a relatively long open liquid phase, become tacky and remain tacky for a relatively long period after they cool down to below their melting point and eventually solidify. It has been found that conventional liquid plasticizers by themselves, such as diethylhexyl pthalate, dibutyl pthalate and the like do not provide the necessary prolonged tackiness to the adhesive composition so that when such adhesive is heated, it will adhere to the unheated article being decorated. Examples of such polyethylene glycols suitable for use as a tackifier component herein are solids of molecular weights ranging from 700 to 25,000 and preferably from about 3,000 to about 8,000 such as the Carbowax polyethylene glycols discussed generally above, and including mixtures of one or more such glycols. Such glycols add tack to the adhesive composition while giving a waxy quality thereto so as to inhibit blocking when the decalcomanias including the same are stacked for storage purposes.

The solid polyoxyalkylene derivatives of propylene glycol and/or ethylenediamine suitable for use as a tackifier component herein are solids generally having an average molecular weight of greater than about 5,000, preferably greater than about 8,000. These materials are preferably block polymers. Particular examples of such polyoxyalkylene derivatives of propylene glycol include the non-ionic series of related difunctional block polymers terminating in primary hydroxyl groups sold by BASF Wyandotte under the trademark Pluronic. Again, the solid members of this series of block polymers are useful in the present invention. An example of the polyoxyalkylene derivatives of ethylenediamine are the non-ionic tetrafunctional series of polyether block polymers sold by BASF Wyandotte under the trademark Tetronic. Once again, the solid members of this series of block polymers are useful in accordance with the present invention. Specific examples of the Pluronic polyols preferred in accordance with the present invention include Pluronic F108, in a flake form having an average molecular weight of about 14,000, Pluronic F98, Pluronic F127, and Pluronic 25R8. Examples of the Tetronic compositions which are most highly preferred in accordance with the present invention include Tetronic 1508, which is in the solid form having an average molecular weight of about 27,000, Tetronic 1307, etc.

The aromatic acid esters of monomeric and polymeric alkyl polyols can also be employed as one of the second tackifier components when a combination of such tackifiers is used in this adhesive composition of the invention, again to provide the desired and required tackifying effect so that these adhesives will be suitable for use herein. Examples of such aromatic ester tackifiers suitable for use herein include, but are not limited to, benzoic acid esters of alkylene or polyalkylene glycols such as neopentyl glycol dibenzoate (Benzoflex S-312), triethylene glycol dibenzoate (Benzoflex S-358), glyceryl tribenzoate (Benzoflex S-404), trimethylolethane tribenzoate (Benzoflex S-432), and pentaerythritol tetrabenzoate (Benzoflex S-552), (Benzoflex being a registered trademark of Velsicol Chemical Corp., Chicago, Ill.), as well as other polyol benzoates having melting points ranging from 47.degree. to 99.degree. C., and which have an unusual tendency to supercool and to recrystallize slowly.

The solid plasticizers which may be used as a tackifier in these adhesive compositions will thus include the aryl phthalates, such as diphenyl phthalate and dicyclohexyl phthalate.

The cellulosic derivatives can be used to moderate the acrylic resin, and to make it less tacky or less sticky. In addition, it will improve the firing or "burn-off" quality of the adhesive composition when it is fired. Examples of suitable cellulosic derivatives include cellulose acetate butyrate, ethyl cellulose, hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, and the like. Preferred are cellulose acetate butyrates having a melting point ranging from about 265.degree. to about 465.degree. F.

The alkyd resins can be employed as modifiers for the adhesive composition, causing it to be easily softened upon application of heat thereto. Furthermore, they inhibit formation of pinholes in the decalcomania during firing and lift-off of the decal from the ware. The alkyd resins suitable for use herein preferably comprise long oil alkyds such as a long oil soya type alkyd, for example BURNOK 4040-LOMS-60 or BURNOK 4040-OMS-60, products of Washburn-Lanson Company of Chicago, Ill. In addition, the adhesive composition may also preferably include a polystyrene plasticizer in admixture with the tackifier. Examples of such polystyrene plasticizers suitable for use herein are polymerized alphamethyl, styrenes, such as DOW resins 276-V2 and 276-V9.

Finally, these components of the adhesive compositions are employed in conjunction with one or more organic solvents which will substantially dissolve all solids to provide a flowable, but viscous, lacquer-like consistency to the composition. Thus, these adhesive components are not employed in aqueous solutions or dispersions, as are the prior delayed tack adhesives discussed above. Such solvents may thus include any of the known organic solvents for these components. Examples of such solvents include aromatic solvents such as any of the Solvesso (trademark of Exxon Corp.) line of solvents such as Solvesso 150 and 100, alcohols such as butyl alcohol, and diacetone alcohol, chlorinated hydrocarbons such as trichlorobenzene, ketones such as cyclohexanone, esters such as ethyl lactate, butyl lactate and isobutylacetate, methyl, butyl and ethyl Cellosolve (trademark of Union Carbide Corporation), monomethyl ether acetate of ethylene glycol, monomethyl ether of ethylene glycol and mixtures thereof, and the like.

As an alternative adhesive composition, however, may be utilized (a) a cellulosic derivative, (b) a straight chain, primary aliphatic oxyalkylated alcohol, in combination with (c) a tackifier and (d) a major amount of an organic solvent.

The cellulosic derivative used in this adhesive composition is fully described above, including such suitable cellulosic derivatives as cellulose acetate butyrate, ethyl cellulose (e.g. ranging from Ethyl Cellulose N-7 up to Ethyl Cellulose N-300), hydroxy propyl cellulose, ethyl hydroxyethyl cellulose, and the like.

The normally solid straight chain, primary aliphatic oxyalkylated alcohol preferred for use in connection with these adhesive compositions may include the same normally solid straight chain primary aliphatic oxyalkylated alcohols discussed above in connection with the paper coating or release layer thereof.

The tackifiers useful in these adhesive compositions, include both normally solid plasticizers as well as combinations of liquid and solid plasticizers. The solid plasticizers preferred are those listed above, including the aryl phthalates, such as diphenyl phthalate and dicyclohexyl phthalate, and the liquid plasticizers include various conventional liquid plasticizers such as diethylhexyl phthalate, dibutyl phthalate, etc.

Also, the organic solvents utilized in connection with these adhesive compositions are the same organic solvents mentioned above with regard to the other adhesive compositions which may be employed in connection with this invention.

Furthermore, it is also possible to utilize the other compounds discussed above in combination with the adhesive coat mentioned herein, i.e. including the alkyd resins and the polystyrene plasticizers. Also, it is preferred to employ an aromatic acid ester of a monomeric or polymeric alkyl polyol in combination with the tackifiers used in connection with the adhesive compositions employing such suitable cellulosic derivatives. These include the benzoic acid esters of alkylene or polyalkylene glycols discussed above, particularly the benzoflex compositions mentioned herein.

With regard to these adhesive compositions, i.e. employing the cellulosic derivatives as the adhesive base component, the cellulosic derivative will generally be present in an amount constituting from about 6 to 30 weight percent of the total adhesive composition, depending upon the viscosity of the particular cellulosic derivative employed, the normally solid, straight chain primary aliphatic oxyalkylated alcohol in an amount generally from about 3 to 15 weight percent of the total adhesive composition, the plasticizers, generally in an amount from about 6 to 30 weight percent of the total adhesive composition, preferably including from about 3 to 15 weight percent of the solid plasticizer and from about 3 to 15 weight percent of the liquid plasticizer, the aromatic acid ester of a monomeric or polymeric alkyl polyol in an amount generally from about 3 to 15 weight percent of the total adhesive composition, and the remainder of the adhesive will comprise the organic solvent, preferably from about 25 to 75 weight percent of the total adhesive composition, or more.

Those adhesive compositions of the invention which are based upon acrylic resins will generally contain the acrylic resin in an amount within the range of from about 10 to about 40% by weight, preferably from about 10 to about 35% by weight, and more preferably from about 12 to 26% by weight, and most preferably from about 6 to 26% by weight. The polyethylene glycols and/or polyoxyalkylene derivative tackifier component will generally be used in an amount within the range of from about 1 to about 25% by weight, and preferably from about 4 to about 25% by weight, and most preferably from about 6 to about 25% by weight. The aromatic ester tackifier component, when used, will generally be used in an amount within the range of from about 2 to about 25% by weight, preferably from about 3 to about 20% by weight, more preferably from about 3 to about 15% by weight, and most preferably from about 5 to about 7% by weight. The remainder of the adhesive will thus comprise the organic solvent, with or without the optional components as set out above.

With respect to the optional components which may be present in the adhesive composition of the invention, the solid plasticizers can be present in an amount within the range of up to about 20%, preferably from about 3 to 15% by weight, and most preferably from about 5 to 12% by weight. The cellulosic derivative may be present in an amount within the range of up to about 15% by weight, preferably up to about 8% by weight, more preferably from about 2 to about 8% by weight, and most preferably from about 3 to 5% by weight; the alkyd resin may be present in an amount within the range of up to about 10% by weight, preferably up to 7% by weight, most preferably from about 1 to 5% by weight; the polystyrene plasticizers may be present in an amount within the range of up to about 25% by weight, preferably to about 10% by weight, most preferably from about 2 to 6% by weight.

The following are preferred formulations of adhesive compositions in accordance with the invention:

The adhesive composition may be applied over the design layer 20 by silk screening techniques, by the use of a doctor blade, and by other conventional techniques as will be apparent to one skilled in the art.

In attempting to provide a heat releasable vitreous decalcomania by utilizing a wax coated paper as the temporary backing, difficulty may be encountered with proper release of the design layer from the backing upon application of heat. It has been found that such difficulty is accounted for at least in part by the fact that the molten wax under certain conditions tends to be absorbed into the porous paper sheet before the sheet and the vitreous design can be separated. Consequently, the ceramic colors have an opportunity to make direct contact with the paper sheet and tend to stick or adhere tenaciously to the same if there is not intervening film of wax or similar release material.

The temporary backing sheet 12 may comprise a suitable sheet material which is relatively non-porous and substantially impervious to the release layer of wax or equivalent material when the latter is in softened or molten condition. For example, the temporary backing may comprise a plastic film such as cellulose acetate or a thin metal foil or a fabric. However, in most cases it will be found most economical to employ a paper backing sheet 12 with a barrier coating 14 of a character which will resist penetration by molten wax or the like.

Generally, the barrier layer 14 may be in the nature of a surface sizing or seal coating such as starch, casein, glue alkali metal silicate, etc., either with or without a clay type filler. A highly satisfactory barrier layer comprises starch, as well as water glass or other alkali metal silicate having dispersed therein talc, clay or like filler. As will be well understood, presence of the barrier coating 14 on the paper 12 prevent excessive penetration and absorption of the release layer 16 when the latter becomes soft or molten under heat release conditions.

The design layer 20 may be applied to the backing as one or more layers of an ink comprising an oxide colorant and a printing medium or vehicle with or without a glass flux or binder. The ink should contain from about 30 to 70% or more by weight oxide colorant. The printing medium or vehicle may be formed, for example, from one or more of such materials as drying oils, varnishes or resins. Examples of suitable resins are various alkyds and acrylics. Various additives may be incorporated into the vehicles, for example, dryers, promoters and/or accelerators.

The coloring agents of the design layer comprise ceramic pigments, having an average particle size within the range of from about 0.5 to about 2 microns which are incorporated into the binder or vehicle. Preferably, the pigments are metallic oxides of fine particle size, such as of an average particle size of less than about 1 micron. The pigments which may be used and the manner of their use are known to those skilled in the art. The oxides of the following elements are mentioned merely by way of example of some suitable ceramic pigments and the colors obtainable therefrom.

As known to those skilled in the art, the composition of the vehicle or binder of the design layer is varied depending upon the oxide or oxides used as a coloring agent and whether or not glass is present in the design layer. Again, the ink formulation must be varied depending upon the oxides employed, and it will be known to those skilled in the art. Again, the remaining discussion of these ink formulations contained in the Hazel Meade U.S. Pat. No. 4,068,033 is also incorporated herein by reference thereto.

The sealant layer 18 which provides a base or support for a design layer generally comprises a cellulosic derivative or resinous film-forming agent which is capable of being completely consumed on firing of the design layer to the ware to be decorated at the usual firing temperatures. Furthermore, such cellulosic derivative or resinous film forming agent must be a liquid or capable of being dissolved in a suitable solvent or vehicle which has no substantial effect on the release layer, so that it can be applied as a fluid formulation on the release layer. Upon drying of the fluid formulation, the resulting solid layer must adhere or bond to the release layer. Where the design layer is to be imprinted on the sealant layer by, for example, lithographic techniques, the sealant layer must remain tighly bonded to the release layer so that the design layer can be printed thereon without pulling the sealant layer off.

The cellulosic derivative film-forming agent suitable for use herein is usually employed in conjunction with one or more solvents, bonding agents and/or plasticizers and should be capable of adhering to the release layer even while imprinted thereon by lithographic techniques. Examples of suitable cellulosic derivatives include cellulose acetate butyrate, nitrocellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate admixed with from about 10 to about 85% by weight acrylic resin, such as Carboset resin (B. F. Goodrich Co.), ethyl cellulose, and the like.

The sealant layer preferably comprises cellulose acetate butyrate having a melting point ranging from about 265.degree. to about 465.degree. F.

The above cellulosic derivatives are usually employed in conjunction with one or more solvents such as those discussed above with respect to the adhesive compositions, so that the cellulosic derivative may be deposited as a liquid on the wax layer.

Where necessary a bonding agent may also be employed in conjunction with the cellulosic derivative to ensure that the cellulosic derivative will adhere to the release layer. Such bonding agent may comprise one or more of the above solvents such as the Solvesso solvents, for example Solvesso 100, butyl lactate, ethyle lactate and the like.

The sealant layer may be formed of cellulosic derivative in an amount ranging from about 5 to about 30% preferably from about 10 to about 25%, with from about 50 to about 85% and preferably from about 60 to about 80% solvent and/or bonding agent and/or from about 5 to about 25%, preferably from about 8 to about 15% plasticizer and/or bonding agent, all such percentages being based on the total weight of the sealant layer.

It will be understood that where the sealant layer is to be imprinted by silk screening, the sealant layer need not be strongly bonded to the release layer as when it is to be imprinted by lithographic techniques. Thus, where silk screening is employed, the sealant layer may not require a bonding agent, and/or plasticizer.

FIG. 2 shows another embodiment of the heat-release decalcomania of the invention which includes a protective layer of glass flux over the design layer, in situ, in the decalcomania. Such heat-release decalcomania includes a decalcomania backing as shown in FIG. 1 including a backing sheet, such as a paper sheet 12, a barrier layer 14, and heat release layer 16. Over heat release layer 16 is a sealant layer 18. Disposed on sealant layer 18 is a protective layer 24 which preferably comprises a prefused glass flux layer. A second sealant layer 26 is disposed on the glass flux layer 24 and a design layer 28 is imprinted on the second sealant layer 26. Disposed over the design layer 28 is a heat-activated adhesive layer 22 as employed in the decalcomania shown in FIG. 1.

The glass flux protective layer 24 is preferably a powdered prefused glass layer or coating which is colorless so that it does not interfere with or mask the colors of the design layer.

An amount of the glass flux should be deposited on the sealant layer 18 so that the protective glass coating thereafter formed will have a thickness within the range of from about 6 to about 28 microns and preferably from about 9 to about 20 microns. Thus, the ratio of thickness of the glass protective layer to the design layer should be within the range of from about 0.25:1 to about 5:1 and preferably from about 0.5:1 to about 3:1.

The coating or layer of powdered glass may be a low melting point glass or a high melting point glass having an average particle size within the range of from about 0.5 to 12 microns depending upon the manner in which the glass layer is laid down. The essential requirement is that the glass should fuse at the firing temperature employed to bond the design to the ware. A low melting point glass may be composed essentially of powdered prefused lead boro-silicate glass which may also contain increments of one or more of the oxides of lithium, sodium, potassium, magnesium, calcium, aluminum, cadmium, zirconium, tin or titanium.

A prefused flux may, for example, be formed according to the following formulation.

The protective glass layer may be applied over the sealant layer 18 by various methods, such as silk screening, offset printing, or by printing a clear film over the sealant layer 18 then dusting a prefused frit over the film. For example, by one method, a layer of varnish may be applied by a lithographic process to the areas it is desired to protect and the powdered glass then dusted on. This procedure could be repeated until desired thickness has been built up. If desired, the dusting operation may be eliminated by incorporating powdered glass into a film such as printing varnish, oil or resin.

Another method which may be used to suspend the powdered glass is one of the various commonly known screening media or pastes. The contents of this past may vary between 60 to 80 percent by weight of powdered glass and 40 to 20 percent by weight of the liquid vehicle. This paste may then be applied over the desired area by means of a silk or metal screening fabric acting as a stencil. By this method of the area of application is easily controlled. When using this method of application, sealant layer 18 may not be required.

After the protective glass flux layer is applied over the sealant layer 18, the second sealant layer 26 is applied over the protective layer 24. The second sealant layer 26 and the first sealant layer 18 may be of the same or different compositions. Inasmuch as it is more difficult to bond the sealant layer 18 to the release layer 16 than it is to bond the sealant layer 26 to the protective glass layer 24, the sealant layer 26 may or may not include a bonding agent or other means for bonding the cellulosic derivative film-forming agent to the protective glass layer 24 where the glass layer is deposited by silk screen.

The second sealant layer 26 thus will generally comprise a cellulosic derivative film forming agent such as any of the cellulosic derivatives set out hereinbefore and preferably is cellulose acetate butyrate. In addition, if desired, such cellulosic derivative may include solvents, bonding agents, and/or plasticizers as described above in conjunction with the first sealant layer 18. A preferred second sealant layer 26 comprises the sealant layer composition set out hereinbefore with respect to FIG. 1.

The design layer 28 will generally comprise coloring agents, and a printing medium or vehicle and optionally glass particles as described hereinbefore with respect to the design layer 20 in FIG. 1. Design layer 28 can be imprinted on the second sealant layer 26 employing any conventional printing techniques such as described above in conjunction with FIG. 2.

It has been found that the design layer 28 cannot be imprinted directly on the protective layer 24 by lithographic techniques inasmuch as the color pigments of the design layer have been found to stain the protective layer and thus render the resulting decalcomania unacceptable. In accordance with the present invention, it has been found that in order to employ a protective glass layer over the design layer (deposited by lithographic techniques) in a heat-release decalcomania, it is necessary to separate the protective layer and the design layer from each other by employing a sealant layer 26 as described above.

In using the heat-release decalcomania shown in FIG. 2, adhesive layer 22 of the decalcomania is heated to its melting point and is applied to a ware to be decorated which causes heat-activated adhesive layer 22 to bond the design layer 28 as well as the second sealant layer 26, the protective glass layer 24 and the first sealant layer 18, and perhaps a portion of the heat release layer 16, to the ware or article. At this time, the backing sheet 10 including the barrier layer 14, and a portion of the heat release layer 16 is released from the remainder of the decalcomania. Upon firing of the assemblage, the protective glass layer fuses and tightly binds the design layer to the ware and forms a contiguous, durable protective coating over the design on the surface of the ware. The organic combustibles of the heat-activated adhesive layer, the two sealant layers and the remainder of the heat release layer are burned off during the firing.

The article is usually fired at a relatively low temperature and the powdered glass fuses so as to form an integral part of the article and provides a glass layer which protects the pigment of the design layer from chemical or mechanical action. A relatively low temperature can be used where the layer of glass powder is made up of prefused glass which will melt at much lower temperature then is required to fuse the raw materials from which the glaze on the ceramic ware itself is formed, in the case of an overglase decalcomania. The usual firing temperature required for this operation is between 1000.degree. F. and 1600.degree. F. It should be particularly noted at this point that this low temperature unlike the high temperature used in applying the glaze to the entire article, does not operate to destroy or impair the color values of the pigments used. When using this decalcomania, as with all overglaze decals, the glaze is applied and fired on the ware before the decalcomania is transferred to the article, and thus the decalcomania is not subject to high temperatures. But in this case to protect the decalcomania and provide a permanent design preferable a low melting point glass is used over the pigments. The pigment is protected in much the same manner as the underglased decals and yet the color values are not impaired by the application of very high temperatures such as are required in firing the glaze. Pigments of the type which are affected by contact with molten glass are affected in this case at the surface only and not sufficiently to impair color value of decalcomania.

Each of the embodiments of the decalcomania of the invention may be provided with a release layer disposed over the outer surface of the backing sheet 12 (that is the surface disposed away from the barrier layer 14). Such a release layer may be employed in lieu of a slip sheet and will facilitate stacking of a group of the decalcomanias and inhibit blocking or sticking of the decalcomanias to each other. The release layer may comprise any conventional types of release layers employed for this purpose.

The decalcomanias of the invention may be employed as decorations for ceramic ware, glassware, pottery, aluminum, porcelain enamel, or any other ware or surface which is normally decorated at 1600.degree. F., or below, as well as for bisque or green ware, at higher tempertures.

It will be appreciated that the present description has been by way of example only and is not intended as a limitation to the scope of the invention.