IMPROVEMENTS IN PRINTING

Abstract: A toner for electrostatic printing, e.g. using a two-part developer in a colour photocopier, comprises 71 to 90 wt.% of an inorganic ceramic colour, and 29 to 10 wt.% of an organic material. Such toners can be formulated in colour sets and yield effective decals when printed onto waterslide paper.

Description: IMPROVEMENTS IN PRINTING The present invention concerns improvements in printing, more especially it concerns improvements in transfer or direct printing of ceramic colours onto substrates. It is well established to screen print inks or suspensions of ceramic colours onto water-slide paper in order to form decals. Such decals are used for the decoration of ware such as table china and porcelain, for domestic or hotel/restaurant use. tiles, giftware and promotional ware, earthenware objects, glass and glass ceramics and vitreous enamelled metals by well established procedures including wetting the decal to release the printed pattern, positioning the decal on the ware and then firing the combination to produce a durable decoration on the surface of the ware. This technology can be used for highly decorative colour prints yielding high value decorated objects. However, the screen printing process requires the preparation of a separate screen for each colour, extended drying times for the inks used and may create environmental problems arising from the solvents released from the inks during drying, and possible dimensional changes to the paper substrate. It has been proposed, almost from the introduction of electrostatic photocopiers, to use photocopying onto conventional water-slide paper in order to produce decals in a rapid manner and without the use of solvent-based inks. We mention the following published patent specifications as examples of these prior proposals: GB 2151 189. GB 2238985, DE 4041358, DK 3917156 and EP 647885. Other proposals have been identified recently, namely JP08- 1 19668 ( onica), JP08-1 1496 (Brother) and EP 751.434 (Ricoh). These proposals are from photocopier manufacturers and. in our view, fail to teach decals that can be fired onto ware with reliable colour, gloss and density. It has been proposed to incorporate coloured pigments in toner particles for two-part developers (see Xerox Corporation EP 22638). but no guidance is given regarding pigment content except for carbon black, for which 10% is quoted. We believe that state-of-the-art colour photocopier toners exclusively use organic pigments or dyes in concentrations below 10% by weight, eg 3 to 5wt%. Where inorganic pigments have been used, eg black magnetic toner particles, we believe that quantities of from 20wt% up to 60wt% may be used. The prior proposals to print decals have not. however, been adopted commercially, despite the apparent desirable characteristics of a photocopying-based process. We believe that certain of the problems found in such prior proposals have been either difficulty in depositing adequate colour density or. where a thick deposit of toner has been deposited, difficulty in applying the decal because of brittleness. reticulation of the covercoat. and in firing the decal without bubbling and distortion caused by the organic material in the toner. Our own tests have shown that the use of a photocopying process is far from straightforward, and that there remains a need for a commercially acceptable ceramic printing process based on electrostatic or electrophotographic printing. It must be understood that conventional photocopying or laser printing processes and equipment are intended to produce a permanent print on paper, for which fixing the toner onto the paper by heat fusion and. usually, pressure, forms an essential part. For decal manufacture, the pigment or toner deposit may be regarded as temporary, and a covercoat provides integrity. The terms "electrostatic printing " as used hereinafter, is intended to cover the broadest possible scope, including charged area development, discharged area development or development by charging an insulating surface, including electrography or ionography. The present invention now provides electrophotographic printing toner particles comprising 71 to 90wt% of inorganic ceramic colour and 29 to 10wt% of an organic polymeric material The invention further provides a two-part developer for electrostatic printing comprising 2 to 22%. suitably 2 to 20wt% preferably 2 to 18wt%. more preferably 3 to 17wt%. especially 4 to 12wt% of the toner particles of the invention, in combination with a carrier The upper limit arv according to the particular ceramic colour and therefore differ in a four-colour set It is to be understood that the toner particles ot the invention if properlv formulated, may be used in mono- component developers espeualh of the non-magnetic The ceramic colour is desirably a combination of a ceramic pigment and a glass frit, in a weιght% of 40 to 95wt%. preterabK 60 to 90wt% of the colour Such ceramic pigment/glass f rit combinations are generalK known in the art as "enamels", in which the usual amount ot frit is 60 to 90% Suitable inorganic ceramic pigments are well known to those skilled in the art. and we refer, for example to "Classification and Chemical Description of the Complex Inorganic Pigments" 3rd Edition. 1991. published by the Dry Colour Manufacturers ' Association. Alexandria. VA. USA Inorganic colours are generally metal oxides or mixed metal oxides To be considered as ceramic pigments for use in this invention are also metal powders or flakes, especially of the precious metals, and iridescent fluorescent or micaceous-type pigments. In some instances, it is desirable to sinter a pigment/glass frit mixture, then to crush the sintered product to the desired particle size. This may assist size classification and colour development. Although any colour or set of colours may be used in the present invention, preferably a four-colour set of colours are used, namely cyan, black, yellow and magenta, especially for on-glaze decoration. Conveniently, the cyan and black are spinel-type colours, for example cobalt zinc aluminate blue spinel, zinc chrome cobalt aluminium spinel, iron cobalt chromite black spinel or possibly iron cobalt black spinel. Preferably, the yellow used is a pyrochlore or rutile structure, eg lead antiminaie yellow pyrochlore or nickel antimony titanium yellow rutile. and the magenta is a colloidal gold colour, or a magenta colour based on silver in a zirconia lattice (see EP 651030). A non-magnetic black pigment, such as the copper chromite black may be used. The present invention includes as an aspect, such novel yellow and magenta toners which are useful for electrostatic printing. For under-glaze or in-glaze decoration, yellow and blue zircon colours may be used and a chrome tin pink may be used. The particular glass frit may be chosen according to the substrate ware onto which the decal is eventually fired in order to bind the colour onto the ware or into the glaze as appropriate. Thus, for example, for bone china ware the frit may be a leaded or unleaded frit. Softening point of the frit, thermal expansion and composition, may be chosen by the skilled man. In general, it may be said that the softening point of the frit should be such as to allow maturation within the temperature range of from 750 to 900°C. which are typical on-glaze enamelling temperatures for decoration on bone china, earthenware or hotelware pieces. In certain circumstances, for example for under-glaze decoration, it may be desirable that the ceramic colour consists essentially of the ceramic pigment and the frit content may be 5wt% or less. It is contemplated that the ceramic colour may be entirely the ceramic pigment. In order to ensure adequate durability of the decal after firing, a cover glaze layer should be then printed on top of the ceramic pattern, by any suitable method including electrostatic deposition or deposition of a slurry of ground glaze particles in an organic solvent and binder, in manner analogous to the established screen printing process Such a cover glaze should be matched to the particular substrate ware and anv glaze thereon, and this is within the competence of the skilled man. The inorganic colour desirably has a particle si/e. before incorporation into the toner particles, of 0.1 to 20um. preferably of 0.2 to 15μm, more preferably 0.5 to 1 O m or especiallv 2 to 6 m. It may be desirable to classify the colour, after milling, to give a narrow size distribution. In general, the particle size distribution is chosen according to the application: for glass or on-glaze application the particle sizes will be smallest, with increasing particle sizes for in-glaze then under-glaze applications. Traditional toner production methods include particularly blending the components, extruding a molten mixture of the components to produce large particles, and milling to produce toner particles of the desired size. This process requires the polymer component to have acceptable melt flow characteristics and to have a glass transition temperature (T ) well above 30°C. eg 50 to 72°C. to permit milling. Other methods incorporate spray drying, encapsulation, melt blending, extrusion and chipping, particle formation and crushing or solution polymerisation. Most desirably, a method is used which yields a more or less continuous skin or film of organic polymer around particles of ceramic colour, and for this, solution or suspension polymerisation or flocculation are preferred. Such methods are generally known in the art, but an especially preferred method is flocculation of polymer using acid addition, which is a method in use in the organic pigment industry, but it is not believed to be in commercial use for toner manufacture. Flocculation may also be possible using a base, a salt, a surfactant (anionic. cationic or nonionic) or another organic flocculant. The use of this method removes the restrictions of melt flow behaviour and T g on the organic polymer, required by traditional production methods. Further, we beiieve it to offer particular advantages in the production of highly-loaded ceramic decal toners. The organic polymeric component of the toner particles may be any polymer which exhibits acceptable burn-out characteristics on firing and having the ability to form toners, that is having acceptable electrostatic properties and having physical properties permitting the production of toners having the required loading of ceramic colour by a suitable method. The actual polymer chosen for the organic component of the toner particles is desirably an acrylate- based oligomer or polymer including polymers of methyl methacrylate or methyl methacrylate-butyl methacrylate copolymers and including other co-polymers such as styrene- or vinyl-acrylates such as polystyrene-n-butylmethacrylate or polystyrene-n-butylacrylate, preferably 65% styrene 35% n-butyl methacrylate copolymer. Other polymers, however, may be used as alternative to. or blended w ith, the preferred acrylate-based materials. The organic- component or components thereof may be selected from olefin polymers such as polyethylene or polypropv lene. dienepolymers such as polybutadiene. polyisobutylene or polychloroprene. v inv l or v inylidene polymers such as polystyrene, styrene butyl- methacrylate copolymers. st rene-acrylonitπle copolymers. acrylonitrile-butadiene styrene terpolymers. polyvinyl butyral. polyvinylethers or polyvinyl ketones. fluorocarbon polymers such as poiytetrafluoroeth lcnc and ιnylidene fluoride, heterochain thermoplastics such as polyamides. polv esters, polyethancs. polypeptides. casein, polyglycols. polv sulphides and polycarbonates, and cellulosic copolymers such as regenerated cellulose, cellulose acetate and cellulose nitrate. In all cases, the organic component must meet the requirements set out at the beginning of this paragraph. The toner particles contain 71 to 90wt% of total ceramic colour, that is. including glass frit Preferred colour quantities arc 71 to 82wt% Many of the early proposals known to us did not contain any guidance on colour content of toner particles, the earliest proposals appear to use standard commercial toners incorporating iron components. As mentioned above, we believe that standard photocopying toners incorporate about 5 to 10wt% of colouring matter. EP 647885 teaches a quantity of 10 to 70wt%, but there are no working examples for further guidance. We have found that most toners containing below 60wt% do not yield adequate colour density unless the thickness of the deposited layer is far beyond that acceptable for burn-out properties. The particle size of the toners is desirably 2 to 40μm. preferably 5 to 30 m, most preferably 7 to 2 um. Classification of the toner after manufacture may be desirable in order to remove fines and over-size particles: this may be desirable in particular to match the requirements of the print engine selected. In addition, account should be taken of the different densities of different inorganic ceramic colours and components thereof. The second part of a two-part developer is a carrier, which may be conducting (eg steel or ferrite) or non-conducting and is generally a ferromagnetic particle, such as a copper zinc ferrite. a magnetite, a strontium-based ferrite or a composite, of particle size suitably 30 to 200 m. preferably 40 to lOO m. most preferably about 40 to 90μm. The carrier itself, unless it is a composite, has a thin surface coating of an organic material which acts to modify the surface or the carrier particles are surface treated. The carrier must exhibit the appropriate electrostatic characteristics for the particular machine used. The machine may work in conductive magnetic brush mode or insulative magnetic brush mode. At this time, the vast majority of digital printers or laser colour photocopiers require the toner particles to acquire a negative charge and hence the carrier particles must generate a positive charge. A surface coating of an acrylic resin, styrene acrylate or modification thereof, may be used in such cases. Many single colour photocopiers require the toner particles to acquire a positive charge and hence the carrier particles must generate a negative charge. A surface coating of a fluorocarbon or epoxy resin may be used in such cases. For a selected print engine, the actual carrier particles and their surface coating, and the organic component of the toner, and the additives selected, need to be chosen in order to achieve the desired charge magnitude and distribution to yield optimum development of the latent image, without carrier pull-out (ie transfer) onto the printed image, and this may be done by the skilled man. using background knowledge. He may refer to the triboelectric table as an empirical guide. In general, it may be said that a balance needs to be struck in the choice of these components, and that experiment will be necessary. The toner used in the present invention will generally include relatively small quantities eg from about 0.1 wt% up to 7wt%. preferably below 5wt%. of other components as required, including particularly charge control or charge reversal agents and flow modifiers. Conventional charge control agents as used in the printer/ photocopier industry include the nigrosine dyes, metal complexes of monoaza dyes, graphite and desirably colourless charge control agents. A standard flow enhancer is a fine fumed silica for example of 10 to 100 nanometre diameter, although other fine particles such as alumina, titanium dioxide or talc may be used if desired. The toner particles desirably incorporate the charge control agent, or they may be bound to the surface of the toner particles, but the other additives may simply be blended with the toner particles. The present invention may utilise a variety of single colour or four- colour printing engines, which are generally commercially available at this time from companies such as Canon. Ricoh Xerox. Rank Xerox and Xeikon. and Agfa and IBM machines. In selecting a printing engine, it should exhibit, with the toners of the invention, acceptable life of machine components such as photoreceptor drum or plate and belt, sufficient resolution, good registration, grey scale or colour gradation capabilities, ability to deposit adequate amounts of the toner and not exhibit background staining. Printing according to the present invention may be carried out onto a suitable paper-type substrate, including preferably a commercial water-slide paper of the type commonly used for screen-printing decals and a waxed carrier for heat release transfers, and it is envisaged that printing may be carried out directly onto ware, tiles being the simplest substrate. In such a case, it is envisaged that it could be useful to coat the tile with a very thin layer of an organic material such as an acrylate in order to permit the surface to acquire adequate charge to accept the print of ceramic colour. Although the majority of colour print engines utilise a four-colour set of toners, namely cyan, black, yellow and magenta, there exist certain machines that can print more than four colours and for example a printing of white may be useful to bring out highlights in an image. The use of two print engines in tandem may be used to produce eight-colour, high value, prints. It should be understood that the present invention also encompasses single colour, eg black or white, printing, and that the printing may not be decorative but may consist of wording or other information in any form including bar codes. The invention also offers the possibility of printing unique or other security decals. For example, it is possible to formulate a fluorescent toner that is white, or other desired colour, under normal daylight or normal lighting conditions, but which fluoresces strongly when exposed to UV light. This offers the possibility of producing a unique identifier on all types of high value products, ranging from china and porcelain to other consumer products such as watches, television screens, video cassette recorders, etc. This may permit identification in the case of theft, or identification of counterfeit products. For convenience, however, broad terms referring to coloured decorative printing are used herein. Suitabl . the deposit of toner on the substrate is in the region of 5 to 20 m thickness per colour. If this cannot readily be achieved from the print engine used, it is envisaged that a second or multiple pass through the machine may be used. It is noteworthy that EP 647885 teaches deposits of 0.1 to 3mm. preferably 0.3 to 0.6mm. which is 300 to 60()um. Conventional print engines utilise a heated roller to fix the image onto the paper. We have found that certain machines use a thin film of a silicone oil on such a roller, and that small quantities of such oil are transferred onto the printed pattern and interfere with the adherence of a conventional acrylatc-based covercoat. It is preferred to use a covercoat to giv e integrity to the printed pattern, especially for water-slide transfers, and such a cov ercoat is well known in the production of screen-printed transfers. A covercoat may be applied to an electrostatic transfer according to the invention, preferably using the conventional method of screen printing a solution of covercoat. It is envisaged that an electrophotographic printing of solid covercoat may be developed. The invention thus also contemplates modifying the print engine to dispense with the heated roller, and using a non-contact fixing or fusing means such as an infra-red heater or a flash heater to bring the organic polymer component of the toner after deposition of the pattern to fusing or consolidation temperature. As an alternative. and bearing in mind that the presently preferred method of production widens the polymer type usable and also that the final print is not intended to be fixed permanently to the paper substrate, it is envisaged that the present invention may dispense completely with fixing the printed pattern in a conventional way, and use a covercoat to coat the image or pattern and give it sufficient integrity for subsequent handling. Thus, a covercoat solution may be applied to an unfixed print, as it emerges from the print engine providing that no damage to the printed image is done. Although the invention has operated successfully in trials on the basis of photocopying a master pattern, it is believed to offer particular advantages when the printing engine is controlled digitally. Many colour photocopiers have an optional extra of a computer interface, which enables a computer to control the movement of the laser used to form the latent image in the photocopier. Thus it is possible for an original piece of artwork to be scanned and converted into a digital record, so that the print engine uses a digital memory record rather than a master pattern. Once the image is digitised, there are huge possibilities for modification of the image, ranging from simple size change, through colour changes, merging with other images, to serial changes in successive printings. Transmission of a digitised image is also facilitated. The production of very small runs of printed patterns becomes economic. The invention is believed to offer particular advantages at this time when used with equipment based on laser printers or photocopiers, but is not to be considered as limited thereto, and may for example be used with analogous electrostatic or electrophotographic printing systems. The printed ceramic pattern produced by the invention may be used in broadly conventional manner. If the pattern is printed onto a waxed heat release paper, a heated deformable hemisphere of silicone rubber may be applied to the pattern so that the wax softens to the extent that the pattern has greater adherence to the silicone rubber than to the paper, and hence the pattern may be lifted off the paper, the silicone rubber hemisphere moved over a substrate such as a ceramic plate, and applied so that the pattern is adhered to the substrate. As has been mentioned above, the invention may be used for direct printing especially of tiles, but the presently preferred application of the invention is to produce transfers on water-slide paper. In all cases, when the pattern is applied to substrate ware, the ware needs to be fired in a kiln to cause the coloured pattern to fix into the ware surface or into a glaze, as the case may be. These steps are conventional and well known to the man skilled in the art. The present invention may find use in the production of decals for on-glaze decoration, under-glaze or in-glaze decoration, for sanitary ware, glass (both decorative and toughened, eg automotive glass or architectural glass) or enamelled steel. In another embodiment, the present invention provides a two-part developer composition comprising a carrier and a ceramic toner, characterised in that the toner is present in an amount of from 2 to 22wt%. suitably 2 to 20wt%, preferably 3 to 17wt%, of the composition and said toner comprises 50 to 80wt% of inorganic- colour and 40 to 20wt% of polymeric material. Preferably, the toner contains 65 to 75wt% of inorganic colour. The present invention will now be more particularly described by way of example only, in which all particle size measurements refer to a D 90 unless stated otherwise and were measured on a Malvern Mastersizer X using version 1 .1 software. Colour measurements were carried out on a Datacolour International Spectraflash 500 using Chroma QC version 3 software. Measurements were taken in the reflectance mode with D65 illumination and a 10° standard observer angle employed with a small circular aperture of radius 12mm. Thermogravimetric analysis was carried out using a Stanton Redcroft ST780 instrument, with Trace software version 4.0. EXAMPLE 1 Cyan Toner Containing 75wt% Ceramic This is an unoptimised toner with regard to composition, triboelectric charge, particle size and flow . No additional charge control or flow agents are added. 45g of a Cookson Matthey Ceramics and Materials Ltd (CMC) cyan enamel (97N4000) was dispersed in 300ml distilled water using a conventional laboratory magnetic stirrer. 33g of an aqueous acrylate polymer dispersion (Rohm and Haas E2976 - 45% solids) was added to this with stirring. 6ml of 2M hydrochloric acid was added over 2 minutes with rapid stirring. Stirring was continued and the flocculated slurry was heated to 90°C for approximately 2 minutes. The heat was turned off and the suspension allowed to cool to room temperature with continuous stirring. The solid material was filtered through a conventional Whatman 541 filter paper, washed thoroughlv with distilled water and dried overnight at room temperature in air. Alternatively, the solid material may be dried in an oven, in a vacuum oven. using infra red heating or other technique. The dried material was passed through a 38 micron sieve. The particle size distribution and triboelectric charge of the powder is given in Table 1. Printing Trials The powder was mixed with a commercial carrier (Ricoh FT developer. type 410) to produce approximately t% toner in the developer. Print trials were carried out on a Ricoh FT44 I machine using the " medium " setting. Images were obtained on standard paper and vvaterslide paper. Samples of the decals were covercoated and transferred to porcelain ware. This was fired using a conventional cycle ( 150°C/hour to 810 C C. soak for 1 hour and cool). Good adherence and colour strength (see Table 1 ) were obtained. The colour obtained is very similar to that of the screen printed standard. EXAMPLE 2 Cyan Toner Containing 85wt% Ceramic This is an unoptimised toner with regard to composition, triboelectric charge and particle size. No addition charge control or flow agents are added. 51 g of a CMC cyan enamel (97N4000) was dispersed in 300ml of distilled water using a conventional laboratory magnetic stirrer. 20g of an aqueous polymer dispersion (Rohm and Haas. Primal E2976) was added to this with stirring. 6ml of 2M hydrochloric acid was added over 2 minutes with rapid stirring. Stirring was continued and the flocculated slurry was heated to 90 °C for approximately 2 minutes. The heat was turned off and the suspension allowed to cool to room temperature with continuous stirring. The solid material was filtered through a conventional Whatman 541 filter paper, washed thoroughly with distilled water and dried overnight at room temperature in air. The dried material was passed through a 38 micron sieve. The particle size distribution and triboelectric charge of the powder is eiven in Table 1. Print Trials The powder was mixed with a commercial carrier (Ricoh FT developer, type 410) to produce 3vvt% toner in the developer. Print trials were carried out on a Ricoh FT4418 machine using the "medium " setting. Images were obtained on standard paper and waterslide paper. Samples of the decals were covercoated and transferred to porcelain ware. This was fired using a conventional cycle ( 150°C/hour. to 810 C C. soak for 1 hour and cool). Good adherence and colour strength (see Table 1 ) were obtained. The colour obtained was weaker than the screen printed standard. EXAMPLE 3 Cyan Toner Containing 75.2wt% Ceramic This is an unoptimised toner with regard to composition, triboelectric charge and particle size and flow. 75g of a CMC cyan enamel (97N4000) was dispersed in approximately 300ml distilled water. 55g of Primal E2976 was added to this with stirring and the volume was made up to 400ml with water. The slurry was passed through a Buchi 190 mini spray dryer using the following conditions. The toner sample produced was collected from both the cyclone chamber and the drying column and passed through a 38 micron sieve. Print Trials The powder was mixed with the carrier (Ricoh Developer FT. type 410) to produce approximately 3wt% toner concentration This was printed onto the waterslide paper on the Ricoh FT4418 using the medium setting. The toner was not permanently fused to the paper and could be rubbed off the paper by use of a finger nail. However, sufficient adherence was obtained to allow covercoating of the images. The decals were applied to the ware (as in Example 1 ). Good colour strength (see Table 2) and gloss was obtained. EXAMPLE 4 Cyan Toner C ontaining 80.0 lwt% Ceramic This is an unoptimised toner with regard to composition, triboelectric charge, particle size and flo . 80g of a CMC cyan enamel (97N4000) was dispersed in approximately 200ml of distilled water. 44.4g of Primal E2976 was added to this with stirring and the volume was made up to 250ml w ith water. The slurr was passed through a Buchi 190 minispray dryer using the conditions given in F ' xample 3. The material was collected from the cyclone chamber and drying column and passed through a 38 micron sieve. Print Trials The toner was mixed with the carrier (Ricoh Developer FT. type 41 ) to produce approximatelv 3wt% toner concentration. This was printed onto waterslide paper on the Ricoh FT441 8 using the medium setting. The toner was not permanently fused to the paper and could be rubbed off the paper by use of a finger nail. It appeared that the fusion was lower than that in Example 3. However, sufficient adherence was obtained to allow covercoating of the images. The decais were applied to the are and fired (as in Example 1 ) Good colour strength (see I able 2) and gloss was obtained. EXAMPLE 5 Yellow Toner Containing 73.1wt% Ceramic This is an unoptimiscd toner with regard to composition, triboelectric charge, particle size distribution and flow This formulation contains both charge control additive and flow additive. 225g of a CMC yellow enamel (97H4000) which is a pyrochlore yellow was dispersed in 800ml distilled water using a Silverson stirrer at room temperature. 9g of charge control agent ( Bontron E84) and 167ml of Primal E2976 were added to 500ml water and dispersed using a Silverson stirrer for 3 minutes. The charge control/polymer suspension was added to the ceramic suspension with stirring. 50ml water was used to rinse the charge control agent/polymer dispersion into the vessel. The mixture was sheared for 2 minutes. This mixture was transferred to a 3 litre reaction vessel fitted with an electric heating mantle using 1 litre of distilled water to ensure total transfer. The ceramic/charge control agent/polymer suspension was then stirred at 300 to 350rpm using an overhead stirrer fitted with a PTFE paddle. This stirring was continued right through to the filtralion stage. 50ml of 2M HC1 was placed in a dropping funnel. 100ml water was used to rinse the measuring cylinder into the funnel. The vessel was heated to 27 "C. The acid was added at a steady rate over approximately 5 minutes. After addition of the acid, the funnel was rinsed through with a further 20ml water. The electric heating mantle was turned on to maximum until the thermometer indicated 56°C. The heat was turned off. Final temperature of the suspension was 60°C. 100ml water was used to rinse any solids on the wall of the flask into the vessel. The suspension was allowed to cool. Stirring was stopped below 30°C. The suspension was filtered through a Whatman 541 filter paper and washed with 4 x 200ml aliquot of water. The product was allowed to dry in air for 16 hours on the filter paper. The dry toner was sieved through a 38 micron sieve. l wt% silica (Degussa AG R972) was added to the toner by dry dispersion. The total ceramic loading is calculated at 73.1 wt.%. Thermogravimetric analysis to 600 °C of the toner confirmed 73.04wt% residue, that is. inorganic ceramic material. Print Trials The toner was mixed with a commercial carrier material (Xerox) to produce a 10wt% toner concentration. The mixture was loaded into a Ricoh NC5006 colour photocopier and printed using standard machine conditions. The fused toner decal was then covercoated and the motif was applied to porcelain ware. Good colour strength and gloss was achieved. The colour co-ordinates for a fast fired decal are given in Table 3. EXAMPLE 6 Magenta Toner Containing 73wt% Ceramic This is an unoptimised toner with regard to composition, triboelectric charge, particle size distribution and flow. This formulation contains flow additive. 216g of a CMC magenta enamel (97A4000) was dispersed in 800ml of distilled water at room temperature in a reaction vessel fitted with an electric heating mantle. 199g of Zeneca Resins Ltd Neocryl A-633 a commercial styrene-acrylate polymer emulsion was added to 3 litres of water and dispersed using a Silverson stirrer for 3 minutes. The ceramic suspension was then added to the polymer with stirring. 500ml of water was used to rinse the ceramic suspension into the vessel. The ceramic/polymer suspension was stirred at 300 to 350φm using an overhead stirrer fitted with a PTFE paddle This stirring was continued right through to the filtration stage described below 50ml of 2M I IC1 was placed in a dropping funnel. The acid was added to the suspension at a steady rate over approximatelv 5 minutes. 120ml of water was used to rinse the measuring cy linder and funnel into the reaction vessel. The electric heating mantle was turned on to maximum until the thermometer indicated 78 °C. The heat was turned off. Final temperature of the suspension was 80°C. 100ml of water was used to rinse any solids on the wall of the flask into the vessel. The suspension was allowed to cool. Stimng was stopped below 30°C. The suspension was filtered through a Whatman 541 filter paper and the collected solids were washed with 4 x 500ml aliquot of water. The product was allowed to dry in air for 16 hours on the filter paper. The resulting dry toner was sieved through a 38 micron sieve. lwt% of silica (R972) was added to the toner by dry dispersion. Print Trials Print trials were carried out with a Xerox carrier at two concentrations: 5 and 10wt% toner. The mixture was loaded into a Ricoh NC5006 photocopier and printed using standard machine conditions. The toner is negatively charged. The fused toner decals were covercoated and the motifs applied to porcelain ware and conventionally fired (see Example 1 ). Good colour strength and gloss was achieved. The colour co-ordinates for the 5 and I0wt% prints are given in Table 4. Examples 7 to 1 1 are unoptimised toners with regard to composition, triboelectric charge, particle size distribution and flow. The product toners were used as positively charged toners in a single- colour machine. EXAMPLE 7 Magenta Toner Containing 64 t% Ceramic Printed at 3.7wt% 40g of a CMC magenta enamel (97A4000) was dispersed in 300ml of distilled water with stirring. To this was added 50g of a Primal E2976 suspension with vigorous stirring. 6ml of 2M HCl was added dropwise over 2 minutes. The resultant slurry was then heated to 80°C with stirring. The suspension was maintained at temperature for 5 minutes and then allowed to cool to room temperature with stirring. The solids were removed by filtration through a Whatman 541 filter paper and thoroughly washed with distilled water. The precipitate was then allowed to dry in air overnight at ambient temperature. The solids were then sieved through a 38 micron mesh. Print Trials The powder was mixed with a commercial (Ricoh FT developer, type 410) to produce wt% toner in the developer. Print trials were carried out on a Ricoh FT441 photocopier machine using the "medium "" setting. Images were obtained on standard paper and waterslide paper. Samples of the decals were covercoated and transferred to porcelain ware. This was fired using a conventional cycle (see Example 1 ). Good adherence, gloss and colour strength (see Table 5) were obtained. The colour obtained is very similar to that of the screen printed standard. EXAMPLE 8 Yellow Toner Containing 64wt% Ceramic Printed at 3.7wt% Toner Example 7 was repeated using a yellow CMC enamel (97H4000) instead of a magenta enamel. Print Trials Print trials identical to those described in Example 6 were carried out. Good colour strength, adherence and gloss were obtained when the decals were fired using conventional and fast firing cycles (see Table 5). EXAMPLE 9 Black Toner Containing 64wt% Ceramic Printed at 3.7wt% Toner Example 7 was repeated using 40g of CMC black enamel (97E4000) instead of a magenta enamel. Print Trials Print trials identical to those described in Example 6 were carried out. Good colour strength, adherence and gloss were obtained on firing. Colour co-ordinates for the conventional fired ware are eiven in Table 5. EXAMPLE 10 Cyan Toner Containing 65wt% Ceramic Printed at 3.7wt% Toner Example 7 was repeated using 39g of CMC cyan enamel (97N4000) instead of a magenta enamel and 47g of Primal E2976. Print Trials Print trials identical to those described in Example 6 were carried out. Ciood colour strength, adherence and gloss were obtained on firing onto ware. The colour co-ordinates for the conventional firing is given in Table 5. EXAMPLE 1 1 Cyan Toner Containing 55wt% Ceramic Printed at 3.7wt% Toner Example 1 was repeated using 33g of CMC cyan enamel (97N4000) and 60g of Primal E2976. Print Trials Print trials were conducted as described in Example 1 . Good colour strength and adherence were obtained (see Table 5). EXAMPLE 12 Cyan Toner Containing 66wt% Ceramic This is an unoptimised toner with respect to triboelectric charge, particle size distribution, flow and T„. The following reaction was carried out under a nitrogen atmosphere. The monomers were washed before use ith NaOH using conventional practice. 600ml of distilled water was placed in a multi-necked baffled reaction flask. O.OOlg of PVA in aqueous solution was added to this and the flask purged with nitrogen for 15 minutes. 0.303g of Ser-FAl 96 (Huls) was weighed into a 100ml conical flask. To this was added 10ml of styrene (Aldrich. catalogue number 24,086-9) and 15ml of butylmathacrylate (Aldrich. catalogue number 23.586-5) monomers. 0.75g of benzoyl peroxide was dissolved in the monomer mixture as an initiator. 21g of a CMC black enamel (97E4000) was added to this with stirring. The monomer/ceramic/initiator mixture was then de-gassed using a nitrogen purge. This was then added to the reaction vessel with stirring. Care was taken to minimise atmosphere ingress. The nitrogen purge was reduced and the reaction flask was immersed into a water bath pre-heated to 70 °C. The reaction was continued for 4 hours with the temperature being maintained between 70 and 85 °C. The mixture was then allowed to cool and filtered through a Whatman 541 filter, washed with distilled water and allowed to dry in air at room temperature. The dry powder was then sieved through a 38 micron mesh. Thermogravimetric analysis showed 66% residue at 600 °C. A glass transition temperature of 52 °C was obtained using differential scanning calorimetry. Print Trials The powder was mixed with a commercial carrier (Ricoh FT developer, type 410) to produce approximately 3wt% toner in the developer. Print trials were carried out on a Ricoh FT4418 photocopier machine using the "medium "" setting. Images were obtained on standard paper and waterslide paper. A small amount of hot offset was observed during printing. However, samples of the decals were covercoated and transferred to porcelain ware. This was fired using a conventional cycle ( 150°C/hour to 810°C. soak for 1 hour and furnace cool). A strong dark print was obtained, but this was patchy due to toner pull-off on the hot roller. TABLE 1 Single-Colour Acry late Toner Prepared by Kloccuhition (Positive l oner) CO (L = lightness, C = chroma, H = hue) 15 10 co co 15 TABLE 3 Four-Colour Acrylate Toner Prepared b Flocculation (Negative Toner-Containing CCA and Flow Additive) 3 TABLE 4 Four-Colour Styrene Acrylate Toner Prepared bv Flocculation Negative Toner Containing Flow Additive TABLE 5 Single-Colour Acrylate Toner Prepared by Flocculation Positive Toner Containing No Charge Control Agent or Flow Additive EXAMPLES Tor all the follo ing examples when the colour co-ordinates for the xerographic samples and screen pπnted standards versus are quoted they are for the same type of ware That is when the colour co-ordinates are quoted for xerography on porcelain, the figures quoted for screen printing have also been measured on the same type of porcelain EXAMPLE 13 Fluorescent Toner C ontaining 64 wt % Ceramic Printed at 3.7\vt% Toner A fluorescent enamel was prepared bv wet gπnding in a ball mill lOg of a commercial phosphor (manganese-doped zinc silicate obtained from Phosphor Technology Middle Street Nazeing. Essex. EN9 2LP. United kingdom) with 90g ot an unleaded onglaze tπi Example 7 was repeated using 40g of the above enamel instead of a magenta enamel Print Trials Pπnt trials identical to those descπbed in Example 6 were carried out Images were made ot a backstamp. a bar code and a secuntv marking Good gloss was obtained on firing the images onto bone china. However, under visible light the image could not be distinguished from the remainder of the ware. However, on exposure to short wavelength ultra violet radiation the images fluoresced strongly (green light). This is an example of using toner technology for security marking. By using a digital copier, every item could be marked with a unique code which would not ruin the aesthetic quality of the ware. EXAMPLE 14 Magenta Toner Containing 64 wt% Ceramic Printed at 3.7 wt% Toner A magenta enamel was prepared by wet grinding in a ball mill 12.5g of CMC Cerise base with 87.5g of a glass frit (ex Corning Glass. USA). Example 7 was repeated using 40g of the above enamel instead of a magenta enamel. Print Trials Print trials identical to those described in Example 6 were carried out. The images were fired onto a range of Corning glass-ceramic ware using the appropriate calcination cycles. Good colour strength was obtained. EXAMPLE 15 1 kilogram Preparation of Black Toner Containing 75 wt % Ceramic This is an unoptimised toner with regard to particle size distribution. This formulation contains flo additive. 595g of an aqueous styrene acrylate polymer dispersion (Zeneca Neocryl A-633. 42wl % solids) was added to 12 litres of distilled water in a 20-litre spherical reaction vessel. 750g of a CMC black enamel (97E4000) was dispersed in approximately 3 litres of distilled water. The enamel suspension was added to the polymer solution with stirring (overhead stirrer). A further 1 litre of distilled water was used to wash any residue into the reaction flask. 450mi of 0.66M hydrochloric acid was added to this ceramic/polymer suspension over 2 minutes with continuous stirring. The flocculated slurry was then heated to 100°C using an electric heating mantle. The temperature was maintained for 1 minute. After this, the mantle was turned off. The suspension was allowed to cool gradually with continuous stirring. The solid material was filtered through a Whatman 541 filter paper and washed with 10 litres of tap water. The press cake was then transferred to stainless steel drying trays and allowed to dry overnight at room temperature. The dried powder was passed through a 38 micron sieve. 1 wt% silica (Degussa AG. Aerosil 200) was then added by dry blending. Print Trials The toner was mixed with a commercial carrier material (Xerox, steel) to produce a toner loading of 13.04wt %. This mixture was loaded into a Ricoh NC5006 colour photocopier and printed using standard machine conditions. The fused toner was then covercoated, applied to porcelain ware and fired using a conventional slow fire cycle (see Example 1 ). Good strength and gloss were achiev ed (see Table 6). A second print trial was then carried out. The toner was mixed with a commercial ferrite carrier (Xerox) to produce a toner loading of 13wt%. The mixture was printed using the Ricoh NC5006. Good strength and gloss were achieved. EXAMPLE 16 2 kilogram Preparation of Yellow Toner Containing 75 wt % Ceramic This formulation contains no charge control agent. 1.5kg ot a CMC yellow enamel (97H4000) was dispersed in 2 litres of distilled water using a Silverson shearer in a 5 litres beaker. To this was added 1.19kg of Neocryl A-633. 500ml of distilled water was used to ensure complete transfer of the polymer suspension Shearing was continued throughout the addition. The suspension was then transferred to a 20-litre reaction flask, using a further 10 litres of water to ensure complete transfer. An overhead stirrer was used to provide agitation. 750ml of 0.66 M HC1 was added over approximately 3 minutes with stirring. The flocculated slurry was then heated to 90°C over a 50-mιnute period. The heater was then turned off and the suspension allowed to cool gradually with stirring. The material was then filtered through a Whatman 541 paper and thoroughly washed with distilled water. The cake was then transferred to drying trays and allowed to dry for 3 days at room temperature (trials showed that fluid bed drying, spray drying and drum drying could all be used to accelerate drying without loss of performance. Most desirably, drying may be carried out at or above the minimum film-forming temperature, preferably with agitation. The dried material was then air classified (Alpine 50 ATP) to break up agglomerates and remove fines (see Table 6). 1 wt% of silica (R972) was added to the toner by dry blending. Print Trials 60g of the toner sample was mixed with 305g of a commercial steel carrier (Xerox) to produce 16.4wt % toner in developer. Print trials were carried out on a Ricoh NC5006 colour copier using standard machine conditions. The fused toner images were then covercoated. applied to a tile and fast fired (45-minute cold-to-cold. 890°C peak). Good strength and gloss were achieved (see Table 6). A second trial was carried out using a commercial ferrite carrier (Xero ) at a 16vvt % toner loading. Good colour strength and gloss were achieved on fired motifs prepared from decals produced using the Ricoh NC5006. A third trial was carried out using a "small" ferrite carrier (Hoganas AB) at a 16wt% toner loading. Good strength and gloss were achieved from fired motifs prepared from decals produced on the Ricoh NC5006. EXAMPLE 17 1 kilogram Preparation of Yellow Toner Containing 85 wt % Ceramic 850g of a CMC enamel (97H4000) was dispersed in 1 litre of distilled water using a Silverson shearer. To this was added 357g of Neocryl A-633. A further 339ml of distilled water was used to ensure complete transfer of the polymer dispsersion. After mixing for 5 minutes, the suspension was transferred to a 10-litre reaction flask. 5 litres of distilled water was used to ensure complete transfer. An overhead stirrer was used to agitate the reaction. 450ml of 0.66M HCl was added over approximately 2 minutes. The flocculated slurry was heated to 90°C over 50 minutes. The temperature was maintained for 1 hour and the allowed to cool gradually. Stirring was maintained throughout the reaction. The cool suspension was filtered through a Whatman 541 paper, washed thoroughly with distilled water and dried at room temperature for 3 days in stainless steel drying trays. lwt% silica (R972) was added by dry blending. Print Trials 80g of the the toner sample was mixed with 300g of a commercial carrier (Hoganas AB) to produce 21wt% toner in developer. Print trials were carried out on a Ricoh NC5006 colour copier. The fused decals were covercoated. applied to ware and fired. Good strength and gloss were achieved compared to screen (see Table 6). TABLE 6 Four-Colour Styrene Acrylate Toner Prepared By Flocculation Negative Toner-Containing Flow Additive 10 15 20

Claims: CLAIMS 1. Electrostatic printing toner particles comprising 71 to 90wt% of eramic colour and 29 to 10wt% of an organic poly meric material. Toner particles according to claim 1. wherein the organic material comprises an acrylic polymer. 3. Toner particles according to claim 2. wherein the aery lie polymer is a polymer or copolymer of methyl methacrylate and butyl methacrylate. 4. Toner particles according to any one of the preceding claims, wherein the ceramic colour is a pyrochlore or rutile structure yellow. 15 5. Toner particles according to any one of claims 1 to 3. wherein the ceramic colour is a colloidal gold magenta or a silver in zirconia lattice magenta. 8. Toner particles according to claim 7. wherein the colour has a particle size of 0.5 to 10 m. 9. Toner particles according to claim 8. wherein the colour has a particle size of 2 to 6u . 10. Toner particles according to any one of the preceding claims, having a majority of particles in the size range from 2 to 40 m. 1 1. Toner particles according to claim 10. having a majority of particles in the size range from 5 to 30μm. 12. Toner particles according to claim 1 1. having a majority of particles in the size range from 7 to 20μm. 13. Toner particles according to any one of the preceding claims, formulated to act as a mono-component developer. 14. A two-part developer for electrostatic printing of ceramic decoration. comprising 2 to 22wt% of the developer, of toner particles according to any one of claims 1 to 12. 15. A developer comprising 2 to 20wt% of the developer, of toner particles according to claim 14. 16. A developer according to claim 14. wherein the amount of the toner particles is 3 to 17wt% of the developer. 17. A two-part developer comprising a carrier and a ceramic toner, characterised in that said ceramic toner is present in an amount of 2 to 24wt% of the developer and said toner comprises 50 to 5wt% of inorganic ceramic colour and 50 to 15wt% of polymeric material. 18. A developer according to claim 17. herein the toner comprises 65 to 75wt% of inorganic ceramic colour. 19. The use of a toner according to any one of claims 1 to 13, in an electrostatic printing method for the production of ceramic decals. 20. The use of a two-part developer according to any of claims 14 to 18. in an electrostatic printing method for the production of ceramic decals. 21. A method for the production of inorganic ceramic toner particles, comprising the flocculation of an organic polymeric material from an aqueous suspension of said material and particles of an inorganic ceramic colour to yield ceramic toner particles having a desired content of ceramic colour in the range 60 to 90wt%. 22. A method according to claim 21. wherein flocculation is effected by acid addition. 23. A method according to claim 21 or 22. wherein the inorganic colour particles are of particle size of 0.1 to 20μm. 24. A method according to any of claims 21 to 23. wherein the toner particles produced have a desired content of ceramic colour in the range 65 to 75wt%.

Inventors: DUNFORD DOMINIC MANTON, EADON DESMOND GERARD, EVANS IONA GWAWR, HOGAN GERALDINE BRIDGET MARTIN, HOLLOWAY JOANNE MARGARET, RICHARDS DAVID GREGORY, SUTTON ANDREW EDWARD, DUNFORD, DOMINIC, MANTON, EADON, DESMOND, GERARD, EVANS, IONA, GWAWR, HOGAN, GERALDINE, BRIDGET, MARTINA, HOLLOWAY, JOANNE, MARGARET, RICHARDS, DAVID, GREGORY, SUTTON, ANDREW, EDWARD
Applicants: COOKSON MATTHEY CERAMICS PLC, DUNFORD DOMINIC MANTON, EADON DESMOND GERARD, EVANS IONA GWAWR, HOGAN GERALDINE BRIDGET MARTIN, HOLLOWAY JOANNE MARGARET, RICHARDS DAVID GREGORY, SUTTON ANDREW EDWARD, DUNFORD, DOMINIC, MANTON, EADON, DESMOND, GERARD, EVANS, IONA, GWAWR, HOGAN, GERALDINE, BRIDGET, MARTINA, HOLLOWAY, JOANNE, MARGARET, RICHARDS, DAVID, GREGORY, SUTTON, ANDREW, EDWARD
Application year: 1997
Main classification: G03G9
IPC codes: G03G7, G03G9