DECAL TRANSFER FOR DECORATING CERAMIC ARTICLES OR GLASSWARE

Abstract: Aqueous composition useful for manufacturing the decal transfer used to decorate ceramic articles or glassware enabling the elimination of the emission of volatile organic compounds during the manufacture of the decal transfer itself.

Description: DECAL TRANSFER FOR DECORATING CERAMIC ARTICLES OR GLASSWARE. The object of the present invention is an aqueous composition useful for manufacturing the decal transfer used to decorate ceramic articles or glassware and to give them specific features of aesthetic and/or functional order. More specifically the composition of the present invention enables the elimination of the emission of volatile organic compounds during the manufacture of decal transfer. Normally the term decal transfer is referred to the film or sheet, possibly made of ceramic glaze, comprising an image or pattern which is to be transferred to a support. Fundamentally two types of decal transfer are manufactured and used to decorate ceramic articles and glassware which are respectively known as "traditional or cold" and "heat release" decal transfer. The manufacture of decal transfer essentially consists of two main steps: - a first step in which the image is formed on a support, generally a sheet of paper, by means of any printing method. - a second step in which a continuous, thin and flexible polymeric film dissolved in a suited solvent is laid on said image, by means of screen- printing or other techniques. This polymeric film is generally referred to as covercoat. For specific applications the order of the above described steps may be inverted. Conventional screen-printing is the printing method mainly used in the first step and consists of a series of superimposed impressions, one for each colour forming the final image. In this step continuous layers of special materials may also be applied, including fluxing agents to help the image fixation during the firing, or ceramic frits. The main difference between traditional and heat release decal transfer manufacturing is to be found in the type of the sheet, usually paper, used as support. In traditional decal transfer the surface of the paper sheet is treated with polysaccharide derivatives or with other water-soluble compounds. By dipping in water the decal transfer, the water passes through the paper dissolving the water-soluble layer, thus allowing the easy detachment of the covercoat bearing the decoration and the possible other layers. In heat release decal transfer, which are more suitable to automated systems, the support sheet is coated with low melting polymers or with polymers exhibiting poor adhesion with the covercoat bearing the decoration: the covercoat is removed from the supporting paper by putting it in contact with a pre-heated pad of siliconic rubber of suited shape and dimension; then the pad itself transfers the decal transfer on to the object which is to be decorated, in the proper position. According to the prior art there are several techniques for the manufacture of decal transfer, some of which are reported in EP 1.052.175. Known techniques comprehend, by way of example, a decal transfer printed on a sheet of paper coated with polyethylene or with a siliconic polymer, or also on plastic films of the same low adhering polymers, this enabling its detachment by means of a simple machinery; a decal transfer wherein the image is printed directly on the covercoat film which is its sole support; a transfer sheet made up with a layer of particles of ceramic powders incorporated in a polymeric matrix or anyhow sufficiently bounded together to allow their detachment and handling without the covercoat layer. The thickness of the layers comprising the image, the possible flux and/or the frit is generally comprised between 5 and 40 micron for common graphic image; between 40 and 100 micron for thick tri-dimensional patterns and between 30 and 300 micron when the layers will constitute a ceramic glaze coating. Normally the covercoat is from 15 to 70 micron thick. The printing ink for the image and the possible layers of other materials are normally made of a solid ceramic portion dispersed in a liquid portion; the liquid portion carries the solids during printing and then it helps its consolidation . The impression of the image on a ceramic surface or on glass requires that the solid portion is made by solid vitrifiable materials, or in other terms by materials which a following firing step at 600°- 1300° C will transform into ceramic. These materials are oxides, pigments, frits, glasses and other ceramic powders, all in form of solid particles having size in the range between 0.5 to100 micron. The liquid medium essentially comprises: - a binding portion - a solvent portion The binding portion is normally constituted by polymers and copolymers (both terms briefly indicated as "polymers" in the present description) of acrylic and methacrylic acid esters, i.e. ethyl, n-butyl, i-butyl acrylate and methacrylate, or by cellulose acetate, cellulose butyrate or other cellulose derivatives. The binding portion acts as a consolidating agent for the solid particles, avoiding their removal during the consecutive impressions; it must be easily removable during the firing, without interfering with the vitrification of the ceramic solid portion of the ink. An important property of the binding portion is its flexibility, or in other terms its low glass transition temperature which can be further decreased by suitable plasticizing agents. The solvent portion is normally constituted by aromatic solvents (i.e. white spirits and by compounds selected among glycol ethers, glycol ethers acetates, aliphatic hydro-carbons, aliphatic esters, turpentine and other terpene derivatives . The solvent must possess a high volatility in order to be easily removed by evaporation after the application of the ink. The removal of the solvent takes place at a temperature typically comprised between the ambient temperature and 60°C, and in any case at a temperature which does not damage the characteristics of the supporting sheet and of the binding polymers. In the second step of the manufacture of decal transfer, the covercoat is applied on the printed image. Among the polymers which can be used to form the covercoat, the polymers and the copolymers of acrylic and methacrylic acid esters, (i.e. ethyl acrylate and methacrylate, n-butyl acrylate and methacrylate, iso-butyl acrylate and methacrylate), cellulose acetate, cellulose butyrate, nitro-cellulose and polyurethane are particularly suitable. The covercoat must exhibit suitable mechanical characteristics; more specifically it must be as much flexible and plastic as to let the decal transfer adhere also on curved surface and resisting enough not to break when the decal transfer is detached from the supporting paper and laid on the ceramic ware. Its breaking load at elongation must exceed 10 Kg/cm 2 . Normally a covercoat film which can be folded and unfolded twice or three times without breaking is considered suitable for use. Furthermore the covercoat must not be sticky, or the decal transfer piled for storage could stick to each other, and during firing, it must volatilize easily even at the lowest temperature, in order not to interfere with the layers lying below. Among the solvents which can be used in the application of the covercoat aromatic hydrocarbons, aliphatic hydrocarbons, glycol ethers, glycol ethers acetate, acetone, 2-butanone, diacetone alcohol, methyl alcohol, ethyl alcohol, isopropyl alcohol , n-butyl alcohol, terpene derivatives such as dipentene, are the most suitable. By soluting the polymers, the solvent enables the application of the covercoat by means of a screen-printing manifold or roller machines. The solvent must exhibit a high volatility in order to be easily removed by evaporation at a temperature typically comprised between the room temperature and 60°C. Normally, during the production of decal transfer, the amount of solvent to be removed by evaporation ranges between 50 and 150 g/m 2 of decal transfer, if only the solvents in the ink and in the covercoat are considered. A further consumption of solvent is to be added to this amount, due to the necessity of cleaning the printing machinery and particularly all the parts and the tools (screens, rollers and squeegees which become in touch with the printing media and the covercoat. The chemical composition of the above mentioned solvents ( aromatics, iso- paraffins, glycol ethers, glycol ethers acetate, acetone, 2-butanone, diacetone alcohol, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, terpene derivatives such as dipentene), imply an eco-toxicolologic profile which exposes the workers, the environment and the social community to notable risks. Besides the question related to the toxicology and the occupational health, the problem of labour accidents caused by the flammability of the above mentioned solvents, their mixtures and their vapours must be carefully considered. In fact, in the view of the regulations regarding the storage, the transportation, the handling of chemical products, the main part of the solvents used in the production of decal transfer are flammable liquids. From an economic point of view, the regulated disposal of the exhausted solvents, their recycling by means of a recovery plant and the disposal of their packages and waste, are notable items in the balance sheet of a factory producing decal transfer. It is a main object of the present invention an aqueous composition for the production of decal transfer, which replaces the normally used solvent-based compositions, comprising from 10 to 60% of one or more polymers selected in the group consisting of acrylic polymers, vinylic polymers, polyurethanes, alkydic polymers, polyesters, styrene-butadiene polymers. Examples of polymers suitable for the realisation of the present invention are polymers of acrylic acid esters and of methacrylic acid esters, polyvinyl alcohol, copolymers of vinyl acetate, omopolymers and copolymers of vinylpirrolidinone, polyurethanes, styrene-butadiene resins, which can be used in the form of aqueous dispersions or solutions. When they are not water soluble, their aqueous composition must be stabilised. According to a main aspect of the present invention, the aqueous compositions useful for the production of decal transfer are stabilised by adding one or more stabilising agents, preferably selected among surfactants and water-soluble polymers. The preferred water-soluble polymers are polyvinyl alcohol, cellulose ethers and polyvinylpirrolidinone. In the preferred form of realisation of the present invention the particles dispersed in water have a size comprised between 0,01 micron and 40 micron, preferably between 0,1 and 6 micron. When aqueous emulsions of polymers are used, the covercoat film formation takes place while water evaporates and the polymer particles combine together. To help the polymer particle coalescence, the aqueous compositions of the present invention may advantageously contain liquid water soluble substances able to solute the polymers. Said substances are to be removed by evaporation after coalescence and must exhibit a sufficient volatility; they are typically carbitol glycol ethers, cellosolve glycol ethers, dipropyleneglycol monomethylether, ethyl lactate; their amount in the aqueous compositions ranges between 2 and 30 % by weight. Beside the above mentioned substances, the aqueous compositions of the present invention may contain one or more other substances acting as de- foamers, biocides, dispersants or plasticiser agents. Advantageusly, the decal transfer produced by means of the aqueous compositions of the invention are supported by paper coated with polyesters or siliconic polymers. The traditional paper coated on the surface with water-soluble polymers, cannot be used, because the coating layer would be damaged during the manufacture of the decal transfer by the water of the liquid media and by the aqueous composition of the covercoat. According to another aspect of the invention, the aqueous compositions useful for the production of decal transfer, advantageously contain a wetting and levelling agent, which increases the adhesion of the ink and of the covercoat with the coated paper. According to a particularly advantageous feature of the present invention the machinery normally used for producing decal transfer are suitable without the need of any modification. EXAMPLES. Example 1 (comparative). A decal transfer is produced using the traditional solvent based compositions. A liquid medium with the following composition is prepared for the ink (parts are by weight) (Medium 1 ): Aromatic fluid Solvesso 150 ® 60 Poly-methylmethacrylate 15 Poly-n-butylmethacrylate 25 An ink is prepared by mixing and refining on three rollers mill: 40 parts by weight of Medium 1 60 parts by weight of a mixture of grey-blue ceramic pigments, manufactured by Cerdec (Fiorano Milanese) under the trademarks Pigmento Ceramico 650/101 and Pigmento Ceramico 300/437 (Ink 1- grey/blue). Using the same procedure, an other ink is prepared blending: 40 parts by weight of Medium 1 60 parts by weight of a mixture of purple ceramic pigments manufactured by Cerdec (Fiorano Milanese) under the trademarks Pigmento ceramico 690/106, Pigmento Ceramico 690/128, Pigmento Ceramico 690/175 (Ink 1- purple). For the covercoat of the decal transfer, a solvent-based composition is prepared (Covercoat Composition 1 ), having the following recipe: Aromatic fluid Solvesso 150 ® 57.9 Dibutylphthalate 4 Poly-n-butylmethacrylate 38 Siliconic additive* 0.1 *A 0,5% of Baysilon OL ® (manufactured by Bayer) in xylene solution. The decal transfer (Decal transfer 1 ) is made following the traditional procedure, using as support a sheet of paper of 180g/m 2 , coated with a polysaccaride layer having a weight of 3,5 g/m 2 . The image is printed by screen-printing, with two consecutive impressions (the first one with Ink 1- grey-blue, the second one with Ink 1 -purple); each impression is followed by desiccation for two hours at 25°C (Relative Humidity of air: 55%; The Covercoat Composition 1 is then applyed by slik-screening covering all the surface of the decal transfer and so that the film weight is equal to 70 g/m 2 after being drying for 15 hours at 25°C (Relative Humidity of air: 55%; The decal transfer (Decal transfer 1) may be detached by a quick immersion in water, it is on the average 40 micron thick and exhibit a breaking load at elongation of 25 Kg/cm 2 , measured by universal testing machine and applying load at the rate of 0,1 kg per second. It can be folded at least twice without breaking. The Decal transfer 1 is then applyed onto an extruded, glazed and fired ceramic listel; after third firing at 900° C (maximum temperature), the image is perfectly transferred. Example 2. A decal transfer is produced by means of the aqueous compositions of the invention. A water based liquid medium with the following composition is prepared for the ink (parts are by weight) (Medium 2): Demineralized water 37 Polyvinylpirrolidinone K 30 (1) 10 Mono propylene glycol 25 Butyl glycol 28 (1) Low molecular weight polyvinylpirrolidinone manufactured by ISP International Specialty Products - Wayne, NJ, USA. An ink is prepared by mixing and refining on three rollers mill: 45 parts by weight of Medium 2 55 parts by weight of a mixture of grey/blue ceramic pigments, manufactured by Cerdec (Fiorano Milanese) under the trademarks Pigmento Ceramico 650/101 and Pigmento Ceramico 300/437 (Ink 2- grey/blue). Using the same procedure, an other ink is prepared with: 45 parts by weight of Medium 2 55 parts by weight of a mixture of purple ceramic pigments manufactured by Cerdec (Fiorano Milanese) under the trademarks Pigmento ceramico 690/106, Pigmento Ceramico 690/128, Pigmento Ceramico 690/175 (Ink 2- purple). For the covercoat of the decal transfer, a water based composition is prepared (Covercoat Composition 2), having the following recipe (parts by weight): Water 7 Soluble copolymer vinylpirrolidinone-vinyl acetate (2) 3 Copolymer of methacrylic acid and butyl acrylate (3) 98,89 Defoamex 42 (4) 0.1 (2) PVP/VA 630 ® manufactured by ISP International Specialty Products - Wayne, NJ, USA (3) Resicel E/50 manufactured by Lamberti SpA (a 45% polymeric dispersion in water) (4) Anti-foam and wetting agent manufactured by Lamberti SpA. The decal transfer (Decal transfer 2) is made following the traditional procedure, using as support a sheet of paper coated with polyester of 295 g/m 2 . The image is printed by screen-printing, with two consecutive impressions (the first one with Ink 2- gre-/blue, the second one with Ink 2-purple); each impression is followed by drying for two hours at 25°C (Relative Humidity of air: 55%). The Covercoat Composition 2 is then applyed by slik-screening covering all the surface of the decal transfer and so that the film weight is equal to 120 g/m 2 after being desiccated for 12 hours at 25°C (Relative Humidity of air: 55%). The decal transfer (Decal transfer 2) may be detached by simple traction, it is on the average 100 micron thick and exhibit a breaking load at elongation of 30 Kg/cm 2 , measured by universal testing machine and applying load at the rate of 0.1 kg per second. It can be folded at least twice without breaking. The Decal transfer 2 is then applyed on to an extruded, glazed and fired ceramic listel; after third firing at 900° C (maximum temperature), the image is perfectly transferred. Example 3. A thick decal transfer is produced by means of the aqueous compositions of the invention. A water based liquid medium with the following composition is prepared (parts are by weight) (Medium 3): Copolymer of methacrylic acid and butyl acrylate (5) 74,43 Copolymer of methacrylic acid and ethyl acrylate (6) 0,2 Copolymer ethylene-vinyl acetate (7) 18 Dipropyleneglycol monomethylether 4,95 Defoamex 42 (8) 1 ,2 (5) Resicel E/50 manufactured by Lamberti SpA, a 45% polymeric dispersion in water. (6) Sipacril 27390F manufactured by VEPI (Urgnano - BG, Italy), a 30% polymeric dispersion in water. (7) Vinavil EVA 2615/ , manufactured by Vinavil (Villadossola - DO, Italy). (8) Anti-foam and wetting agent manufactured by Lamberti SpA. An solid dispersion (Dispersion 3) is prepared by mixing; 45 parts by weight of Medium 3 55 parts by weight of a mixture of ceramic powders, transparent and matt frits, having particle size between 1 and 45 micron. For the covercoat of the decal transfer, a water based composition is prepared (Covercoat Composition 3), having the following recipe (parts by weight): Copolymer of methacrylic acid and butyl acrylate (9) 76,58 Copolymer of methacrylic acid and ethyl acrylate (10) 20 Defoamex 42 (11) 0,1 (9) Resicel E/50 manufactured by Lamberti SpA (a 45% polymeric dispersion in water) (10)Sipacril 27390F manufactured by VEPI (Urgnano - BG, Italy), a 30% polymeric dispersion in water. (11)Anti-foam and wetting agent manufactured by Lamberti SpA. The decal transfer (Decal transfer 3) is made following the traditional procedure, using as support a sheet of paper coated with polyester of 295 g/m 2 . Dispersion 3 is applied by screen-printing so that the film weight is equal to 300g/m 2 after being dried for 18 hours at 25°C (Relative Humidity of air: 55%) The Covercoat Composition 3 is applyed by screen-printing too, covering all the surface of the decal transfer and so that the film weight is equal to 100 g/m 2 after being dried for 1 hours at 40°C in forced air drying unit. The decal transfer (Decal transfer 3) may be detached by simple traction, it is on the average 300 micron thick, its weight is about 400 g/m 2 and exhibit a breaking load at elongation of 30 Kg/cm 2 , measured by universal testing machine and applying load at the rate of 0.1 kg per second. It can be folded at least once without breaking. The Decal transfer 3 is then applyed onto an extruded, glazed and fired ceramic listel; after third firing at 1180° C (maximum temperature) and firing cycle of 10 hours, the listel is coated by a continuous and uniform layer of ceramic glaze, perfectly vitrified.

Claims: CLAIMS 1. Aqueous composition for the production of decal transfer comprising from 10 to 60% of one or more polymers selected in the group consisting of acrylic polymers, vinylic polymers, polyurethanes, alkydic polymers, polyesters, styrene-butadiene polymers. 2. Aqueous composition for the production of decal transfer according to Claim 1 , containing one or more stabilising agents selected in the group consisting of surfactants and water-soluble polymers. 3. Aqueous composition for the production of decal transfer according to Claim 2, wherein the water-soluble polymers are polymers or copolymers of polyvinyl alcohol and/or of polyvinylpirrolidinone, and cellulose ethers. 4. Aqueous composition for the production of decal transfer according to Claim 1 , wherein said aqueous composition are in the form of an aqueous emulsion. 5. Aqueous composition for the production of decal transfer according to Claim 4, wherein the particles dispersed in water have a size comprised between 0,01 micron and 40 micron. 6. Aqueous composition for the production of decal transfer according to Claim 4 containing from 2 to 30% by weight of carbitol glycol ethers, cellosolve glycol ethers, dipropyleneglycol monomethylether, ethyl lactate. 7. Aqueous composition for the production of decal transfer according to Claim 1 containing one or more substances selected in the group consisting of de- foamers, biocides, dispersants, plasticiser agents. 8. Process for the production of decal transfer using aqueous composition comprising from 10 to 60% of one or more polymers selected in the group consisting of acrylic polymers, vinylic polymers, polyurethanes, alkydic polymers, polyesters, styrene-butadiene polymers.

Inventors: CHIAVACCI DARIO, CRESPI STEFANO, LI BASSI GIUSEPPE, NAPPA ALAN, CHIAVACCI, DARIO, CRESPI, STEFANO, LI BASSI, GIUSEPPE, NAPPA, ALAN
Applicants: CHIAVACCI DARIO, CRESPI STEFANO, LAMBERTI SPA, LI BASSI GIUSEPPE, NAPPA ALAN, CHIAVACCI, DARIO, CRESPI, STEFANO, LI BASSI, GIUSEPPE, NAPPA, ALAN
Application year: 2001
Main classification: B44C1
IPC codes: B41M3, B41M7, B44C1, C08L33, C09J131