Patent Application
20050028895
The invention relates to a precious metal preparation capable of radiation curing, in particular a burnished gold preparation which contains, in addition to a precious metal, in particular elementary gold, and a flux, a printing medium capable of radiation curing, in particular UV-curable. The invention also relates to transfers containing the precious metal preparation and to a method for the decoration of substrates capable of decoration firing by direct and indirect printing.
DE patent specification 22 08 915 teaches burnished or powdered gold preparations for the production of on-glaze gold decorations. The preparation contains gold powder, a flux, and a printing medium, the latter involving resins and/or inorganic solvents. To adjust the colour, the preparation may include besides gold, other precious metals such as platinum, palladium, rhodium, iridium and silver. To enhance firing stability, the preparation may also contain additional compounds such as purple of Cassius, tin oxide or aluminium oxide. It is expedient, before application of the gold preparation, to apply to the siliceous base layer a high-melting intermediate layer comprised of zirconium oxide, zirconium silicate, tin oxide, silicon oxide or aluminium oxide, or a mixture of at least two of these compounds. This intermediate layer may also contain colouring substances, such as inorganic pigments so that, in the creation of the decoration, its colour stands out better from the siliceous base layer. To produce the on-glaze decoration, the gold preparation is applied by means of a screen printing process to a transfer carrier which may be provided with the intermediate layer beforehand. After drying of the image coating, the latter is provided, in a known manner, with an enamel coating. The transfer thus obtained is transferred to the siliceous base layer and then fired on at 1100 to 1400° C. The disadvantages of these precious metal preparations are the long drying times of the image coating, and the associated ecological problems due to evaporation of organic solvents.
Also the screen printing paste for gold decorations according to DE-OS 21 11 729 contains a commercially available screen printing oil, such as solutions of polymethyl methacrylate or ethyl cellulose in high-boiling solvents such as ethyl glycol acetate, butyl acetate or test benzine.
The gold preparation according to DE patent 24 35 859 contains, besides gold, one or more non-precious metals such as titanium, iron and nickel, and if required also an adhesive oxide or a glass flux. By means of screen printing, this preparation may be printed without a special base layer directly on to the substrate to be decorated or on to a transfer carrier. Two typical gold preparations contain additionally 2.5% by weight of a red pigment, but its function is nowhere disclosed. It is assumed that the red pigment serves to make the print image more clearly recognisable. This gold preparation too contains a conventional screen printing medium with the drawbacks described above.
In efforts to minimise the aforementioned drawbacks, attempts have been made to replace the purely organic printing medium by one containing or capable of dilution with water—see DE 35 44 339 C1 and DE-OS 38 07 290. The disadvantages of such preparations are their unsatisfactory drying properties and to some extent inadequate decoration quality.
To avoid the problems attached to conventional organic printing media, i.e. the long drying times and ecological problems due to evaporation of solvents, radiation-curing media, in particular UV-curing media have been developed, which can be used in bright precious metal preparations or in burnished gold preparations. DE patent specification 30 48 823 teaches accordingly a resinous substance which may be cured by UV radiation, comprised of a special saturated copolymer, a polymerisable component with one, together with such a component with two or more polymerisable groups, a photosensitiser and where applicable other synthetic resins, pigments, slip additives, flow-control agents and thixotropic agents for the purpose of adjusting the printing properties, and inhibitors of the thermal polymerisation.
Depending on the intended purpose of the UV-curable resinous substance according to DE 30 48 823 C2, it may contain known inorganic pigments such as are generally used for the decoration of siliceous substrates. Alternatively the UV-curable resinous substance may also contain organic pigments, but such systems are decorating preparations for the decoration of substrates which will not be subjected to decoration firing. No indication may be gained from this document to suggest that a UV-curable burnished gold preparation could also contain an organic pigment and/or a polymer which is insoluble/non-swelling in the binder system.
The bright precious metal preparation for the decoration of glass, ceramics and porcelain according to DE-PS 38 19 414 contains a soluble organic precious metal compound and a UV-curable organic carrier based on isobornyl acrylate and dicyclopentadienyl acrylate and a photo-initiator dissolved therein. The preparation may also contain one or more oligomers with acrylate and/or methyl acrylate groups. Organic solvents, natural and synthetic resins, means for adjusting and modifying viscosity, and pigments may also be included. It is also disclosed that, by adding gold powder and/or a slightly soluble gold compound to the bright gold preparation, curable burnished gold may be obtained through photo-polymerisation. Not disclosed in this document is the type of pigments involved, and in what quantity and for what purpose these are used—here too evidently the colouring matter is used to make the print image more clearly recognisable.
The inventors of the present application have found that the transfer quality and decoration quality of burnished gold preparations containing as medium a conventional UV-curable medium are unsatisfactory. Evidently on account of the poor flow properties of such preparations, printing results in an uneven and in particular grained surface. To improve the flow of the printing paste, conventional flow-control agents have also been added to such systems. Such flow-control agents are generally silicone-based products with a low interfacial tension. While the use of such products does indeed improve flow properties, at the same time there is a further problem, namely a lack of capacity for overprinting, as a result of poor wettability. The use of such a flow-control agent in a gold preparation means that it is no longer possible to produce accurately matching multi-colour print images.
The problem of the present invention therefore is to find a way of overcoming the problems described above. The precious metal preparations, in particular burnished gold preparations to be prepared according to the invention, should therefore flow perfectly without the use of flow-control agents so that, when used in direct or indirect printing, i.e. using the transfer method, aesthetically pleasing decorations with high surface quality are obtained.
It has been found that the aforementioned problems and other problems revealed in the description which follows may be solved by a significant increase in the pigment volume concentration (PVK) of the preparation through the addition of organic substances which are insoluble in the paste. It is assumed that one of the causes of the poor flow of burnished gold preparations capable of radiation curing is the low pigment volume concentration of the paste to be printed. Even when, by adopting the measure according to the invention, namely increasing the pigment volume concentration, the flow is significantly improved, it is not possible to rule out that the improved quality of the preparations according to the invention and of the decorations produced from them may also be due to other causes.
The subject of the invention is therefore a precious metal preparation capable of radiation curing, in particular a burnished gold preparation, containing one or more precious metals from among gold, silver, platinum and palladium in elementary and/or alloyed form and/or in the form of a compound, one or more fluxes from among compounds of Mg, Al, B, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Rh, Ru, Sn, Sb, Pb and Bi, and a printing medium capable of radiation curing, characterised in that it contains at least one organic compound in particle form which is insoluble and incapable of swelling in the printing medium and burns substantially completely in decoration firing, as a means of increasing the pigment volume concentration (PVC). The subsidiary claims are directed towards preferred embodiments of the precious metal preparation capable of radiation curing.
The preparations according to the invention contain as precious metal one or more metals from among gold, silver, platinum and palladium, in elementary and/or alloyed form; usually the amount of gold used exceeds that of the other precious metals, which are used mainly to modify the colour shade. The preparations according to the invention may also contain precious metals in the form of compounds which are soluble or insoluble in the medium. The use of organic compounds of one or more precious metals in combination with elementary precious metal is suitable for adjusting the desired colour. The soluble precious metal compounds are in particular so-called precious metal resinates and sulpho-resinates, also mercaptides from organic compounds containing one or more mercapto groups. Insoluble precious metal compounds are for example gold sulphide, gold cyanide, gold oxide, and cyano- and sulphito gold complexes.
The amount of precious metals used in preparations according to the invention is usually in the range of 5 to 50% by weight containing preferably more than 8% by weight of burnished gold preparation, preferably with 16 to 40% by weight of gold. In addition to gold, one or more precious metals from among platinum, palladium, silver, rhodium, copper, ruthenium and osmium may be present.
As is generally known among experts, the precious metal preparations according to the invention also contain one or more fluxes. These fluxes involve organic or inorganic compounds of non-precious metals, also rhodium and ruthenium, which are preferably dissolved in the medium. Preferred fluxes contain as metal magnesium, sodium, potassium, calcium, boron, aluminium, silicon, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, tin, indium, antimony, lead and bismuth, together with rhodium and ruthenium. With the aim of obtaining optimal flow and good adhesion of the preparation to the substrate to be decorated, generally several fluxes are used, for example combinations of compounds of: bismuth and boron; bismuth and vanadium and/or silicon; bismuth, vanadium and rhodium, and also if required additionally chromium, silicon, copper and/or zirconium; chromium and cobalt and if required one or more compounds of in particular Ti, In, B, Si, Zr and Rh, or Ru (see DE 194 10 20 A1). The non-precious metal compounds used as fluxes involve inorganic and/or organic compounds such as resinates, sulfo-resinates, alkanoates, naphthenates, salts of carboxylic acids, such as acetate. The flux elements may also be used in the form of their oxides, salts, borates and glasses, as for example alkali borosilicate.
The amount of flux elements required may lie within wide ranges. Usually fluxes can be present in a total amount of up to around 20% by weight, calculated in the form of compounds and based on the preparation. Preferably the preparation contains 0.1 to 15% by weight of flux, in particular 0.1 to 8% by weight. The person skilled in the art will easily determine the optimal amount required and the flux constituents to be chosen through orientation tests.
The feature of the precious metal preparation which is important for the invention is the presence of an organic medium described below as a “means of increasing the PVC”, which is in particle form, will not dissolve or swell in the printing medium under the usual application temperatures, i.e. in particular below around 60° C., and burns substantially completely in decoration firing. The “means of increasing the PVC” according to the invention is used in the form of a single compound or of several different compounds, and specifically in an overall amount of up to 20% by weight, preferably up to 15% by weight and in particular 1 to 10% by weight, based on the preparation. By the use of the “means of increasing the PVC” according to the invention the pigment volume concentration of the precious metal preparation, which is very low owing to the high density of the precious metal, is significantly increased. An increase in the pigment volume concentration of 30 to 300% leads to significantly improved flow of the preparation and thus to high-quality decorations. The means of increasing the PVC thus acts as an organic filler.
The means of increasing the volume concentration (PVC) according to the invention involve at least one but in many cases several organic compounds in particle form, which substantially burn away completely in decoration firing. The expression “substantially completely” indicates that the organic constituents of such compounds burn away completely, but metal atoms—for example of metal complexes—which are present become part of the flux.
It has been found that organic pigments are very suitable for increasing the PVC of the precious metal preparations according to the invention, thereby improving flow properties and decoration quality in an effective manner. An advantage of the organic pigments is that they generally already have a particle distribution such as is used in the production of non-ceramic printing pastes. Precious metal preparations according to the invention generally contain up to 10% by weight of one or more means of increasing the PVC. Especially preferred means contain 0.5 to 5% by weight of an organic pigment.
In principle, organic pigments of the most widely varying chemical constitution may be used. Preference is given to those pigments with the lowest possible UV absorption and which do not tend to graphitisation under the conditions of ceramic decoration firing. Organic pigments which may be used are assigned for example to the following classes of substance: yellow and red mono- and disazo pigments, naphthol-AS pigments, benzimidazolone pigments, yellow disazo condensation pigments, metal complex pigments based on azo compounds, azomethines and isoindolinones, phthalocyanine pigments, thioindigo pigments. Although quinacridone pigments, perinone and perylene pigments, also anthraquinone pigments and pyranthrone pigments are suitable for increasing the PVC, they tend towards graphitisation. A certain disadvantage of many organic pigments lies in the fact that they absorb UV light to a greater or lesser extent, after which curing time is extended.
A further class of suitable means of increasing the pigment volume concentration of precious metal preparations according to the invention is that of polymers, also including copolymers, which under the normal conditions of use are insoluble and incapable of swelling in the printing medium. The polymers and copolymers may be assigned to different classes of substance, the only important factor being that they are insoluble and incapable of swelling in the precious metal preparation, and will burn away completely under the conditions of decoration firing. The polymers may for example include polyolefins, vinyl, acryl or methacryl polymers, polyesters, polyamides or phenol formaldehyde resins, polymethylene ureas or polyethers, with the proviso that the degree of polymerisation is sufficiently high or the polymer is crosslinked, so as to rule out any solubility or swelling capacity in the printing medium. The amount required of this class of means for increasing PVC is usually in the range of up to 10% by weight, in particular in the range from 0.5 to 7% by weight.
An advantage of the last-mentioned class of means for increasing pigment volume concentration lies in the fact that their UV absorption is significantly less than that of organic pigments. This minimises any negative effect on the curing behaviour of the printing medium which is capable of radiation curing.
A problem of the polymer means of increasing PVC lies in the fact that they are in some cases not available in the optimal particle distribution. While means with an average particle size of around or over 10 μm do give good flow of the precious metal preparation, decoration faults may occur during decoration firing on account of the coarse particles. Decoration faults may be avoided using a polymer medium of lower average grain size, for example around or below 5 μm, but a high level of use may lead to a sharp rise in viscosity, a reduction in flow and also to flatting. It has been found that compositions based on polymers insoluble in the UV-curable medium, such as polymethyl urea with finely dispersed silicic acid, as obtainable commercially, also provide the desired effect very satisfactorily, on the strength of findings to date.
In accordance with a preferred embodiment, both organic pigments and also additionally one or more organic fillers are used as means of increasing the pigment volume concentration. The combination of the two classes of substance leads to optimal matching of both flow properties and also rheological properties. Expediently a precious metal preparation according to the invention therefore contains 0.5 to 5% by weight of an organic pigment and 0.5 to 7% by weight of a polymer organic filler, preferably involving a crosslinked organic polymer. Especially preferred precious metal preparations contain as means of increasing the pigment volume concentration around 1 to 3% by weight of one or more organic pigments and around 2 to 6% by weight of one or more polymer organic fillers. Such a combination has an outstanding property profile both in respect of flow, leading to a perfect decoration surface, and also with regard to trouble-free and rapid full curing of a decoration coating applied to a substrate to be decorated or to a transfer carrier.
The printing medium which is capable of radiation curing generally involves a multi-component system containing at least one monomer and/or oligomer compound capable of polymerization by radiation, together with a photo-initiator and if necessary a resin dissolved in the monomer or oligomer. With regard to the monomer and oligomer polymerisable substances to be chosen, reference is made to the teaching of DE patent specifications 30 48 823 and 38 19 414. According to DE-PS 30 48 823, the printing medium contains a saturated copolyester dissolved in a polymerisable component. The polymerisable component involves a combination of a polymerisable component and a polymerisable double bond, and in addition a compound with two or more polymerisable double bonds in the molecule. Examples of suitable photo-polymerisable compounds with a polymerisable double bond in the molecule are: (i) styrene, α-methyl styrene; (ii) alkyl acrylates and methacrylates, wherein alkyl stands in particular for methyl, ethyl, isopropyl, n-propyl, n-, sec.- and t-butyl, 2-ethylhexyl, lauryl, stearyl, cyclohexyl, methoxyethyl, ethoxyethyl, butoxyethyl, hydroxyethyl, poly(ethyleneoxy)ethyl, (iii) monoacrylates and -methacrylates from adducts of bisphenol A and alkylene oxides, such as ethyl oxide or propylene oxide, (iv) urethane-modified monoacrylates and methacrylates containing an acryloyloxy- or methacryloyloxy group in the molecule, (v) epoxy-group-modified acrylates and methacrylates, oligoestermono-acrylates and -methacrylates. The amount of photo-initiator required in the printing medium usually lies in the range from 0.1 to 20% by weight but mostly in the range from 1 to 10% by weight.
Suitable photomerisable compounds with two or more double bonds are for example: alkylene glycol diacrylate or dimethyl acrylate, wherein alkylene stands for ethylene, propylene, 1,4-butylene, neopentyl- and hexamethylene; diethylene glycol- and triethylene glycol diacrylate or -methacrylate; trimethylol propane trimethacrylate.
In accordance with an especially preferred embodiment, the printing medium capable of radiation curing contains a so-called solid resin dissolved in a monomer acrylate or if applicable methacrylate, which may be in particular a polymethyl-methacrylate copolymer, for example a copolymer based on polymethyl-methacrylate/polybutyl-methacrylate. Preferably such a printing medium is comprised of around 20 to 40% by weight of one or more dissolved solid resins, 45 to 70% by weight of one or more acrylic and/or methacrylic monomers, and 1 to 10% by weight, in particular 2 to 6% by weight of one or more photo-initiators and where necessary other auxiliaries such as thixotropic agents, inhibitors of thermal polymerisation, such as hydroquinone, hydroquinone methyl ether and tertiary-butylated phenols, and amine synergists, in an amount of altogether up to 10% by weight, in each case related to the printing medium.
Suitable as photo-initiators are: benzoins, e.g. benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin, α-methyl benzoin; anthraquinones, such as 2-chloro-anthraquinone; benzophenones, such as benzophenone, p-chloro-benzophenone, p-dimethylamino benzophenone; sulphur compounds such as diphenyl disulphide, tetramethyl thiuram disulphide; xanthones and thioxanthones such as 2- or 3-methyl xanthone, 2- or 3-ethyl xanthone, 3-ethyloxy xanthone, 2,7-dichloroxanthone, 2-nitroxanthone and analogous derivatives of thioxanthone; aryl-alky-phosphine oxide.
To enhance the effect of the photo-initiators, they may be used together with synergists from the range of amines, such as triethanolamine, N,N-diethyl aminoethylacrylate.
The radiation curing is effected by means of radiation-induced polymerisation, involving short-wave radiation, in particular radiation in the range close to visible light (α around 420 nm) and in the entire UV range, in particular α 300-400 nm.
An especially preferred burnished gold preparation according to the invention contains 10 to 45% by weight of gold in elementary form, 0.1 to 20% by weight, in particular 0.1 to 5% by weight of flux, 30 to 80% by weight, in particular 45 to 65% by weight of radiation curing medium, and 1 to 10% by weight, in particular 3 to 8% by weight of means of increasing the pigment volume concentration according to the invention. Expediently the preparation for increasing the pigment volume concentration contains both an organic pigment and also a polymer organic filler. The radiation curing medium comprises preferably a polymer dissolved in a photo-polymerisable monomer, in particular an acryl- or methacryl monomer, and a photo-initiator, wherein the amount of photo-initiator required lies in the range of 1 to 20% by weight, in particular 0.1 to 10% by weight, relative to the printing medium.
The precious metal preparation according to the invention is made in a similar fashion to that used in the production of known precious metal preparations: the precious metals in powder form, the flux and the means of increasing the pigment volume concentration according to the invention are pasted into a printing medium capable of radiation curing using common pasting equipment, for example a multiroll mill. The photo-initiator may either be already present in the medium or else added to the paste at the end. To the extent necessary, other aids such as thixotropic agents and further polymerisable solvents for the purpose of adjusting print viscosity are incorporated in the paste.
A further subject of the invention is directed to a transfer for the production of precious metal decorations, in particular burnished gold decorations. The production of transfers is in principle known to the experts in this field: a transfer carrier with a water-soluble or thermally activable interlayer is printed by means of a printing process, in particular a screen printing process using a radiation-curing precious metal preparation according to the invention, to produce an image coating. The image coating is irradiated from a suitable radiation source, in particular a radiation source for UV light, by which the image coating is cured. After curing the image coating is filmed over with a conventional lacquer film, generally an acrylic or methacrylic resin film.
Through the use of precious metal preparations according to the invention, containing one or more means according to the invention for increasing the pigment volume concentration, it is possible to obtain high-quality transfer carriers which have a perfect surface and also give a decoration of high quality after decoration firing. In accordance with an especially preferred embodiment of the transfers according to the invention, the image coating contains a precious metal preparation, the printing medium of which contains a monoacrylate or monomethacrylate, but not a multi-functional acrylate or methacrylate. By dispensing with multi-functional acrylates or methacrylates in the printing medium, transfers with greater flexibility and therefore a lower tendency to cracking of the image coating are made accessible.
The precious metal preparations according to the invention may be used to produce a precious metal decoration, in particular a burnished gold decoration, on a substrate capable of decoration firing, wherein the precious metal preparation may be applied by direct or indirect printing (transfer method) on the substrate to be printed. Decoration firing is effected in an intrinsically known manner at a temperature geared to the substrate which for porcelain and ceramics lies in the range from 700 to 1400° C., in particular 800 to 1250° C. To produce burnished gold decorations, the fired-on decoration is polished in a known manner.
If desired, the precious metal preparation according to the invention may contain additional substances for enhancing firing stability, such as are known from the prior art.
In similar fashion, a base layer known from the prior art may also be provided beneath an image coating, according to the invention, of a transfer carrier, to improve adhesion and/or resistance to scratching.
A further subject of the invention is directed towards the production of a precious metal decoration, in particular a burnished gold decoration, on a substrate capable of decoration firing, such as glass, ceramics and porcelain. This involves printing the preparation according to the invention on to the substrate in a known manner, undertaking radiation curing to the extent still necessary, and finally firing under conditions of decoration firing.
It was not foreseeable that, through the use of means according to the invention of increasing the pigment volume concentration, the flow and thereby the decoration quality of the precious metal preparation could be significantly improved. Equally it was not foreseeable that, through the combination of an organic pigment with a polymer organic filler, the flow properties of the preparation and thereby the decoration qualities of the resultant decoration could be improved while maintaining good, i.e. rapid, radiation curing.
The contents are thoroughly homogenised in a ball mill and then pasted to form the medium.
The printing of the screen printing paste is effected with a 300 mesh/inch steel screen on Trucal brand transfer paper on a PLC printing machine. Curing takes place in a downstream UV drier, followed by overfilming with a commercially available film solution (product no. 83450 of the company dmc2 AG) and a 27 filament/cm polyester screen. The transfers are transferred to porcelain and fired in 90 min (cold to cold) at 1230° C. The decorations are then polished. The polished decorations, made with the paste of the example, have a beautiful yellow burnt-out shade of colour with silk matt gloss.
In contrast to the example according to the invention, the transfer carriers produced using the paste of the comparative example showed craters even in the unfired state. This fault is also visible subsequently in the fired-on transfer carrier.
| Number | Date | Country | Kind |
|---|---|---|---|
| 01121227.1 | Sep 2001 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP02/09360 | 8/21/2002 | WO |
