GB2095855A - Toner compositions - Google Patents

Abstract

In two-component toner compositions for use in developing latent electrostatic images and of the type comprising toner particles formed of a solid thermoplastic material and a colouring agent together with carrier particles having an average particle size equal to or greater than that of the toner particles, at least a part of the colouring agent in the toner particles is a sublimable dyestuff, subliming at a temperature of from 100 to 220 DEG C at atmospheric pressure. The compositions are used to form images containing the sublimable dyestuff by an electrographic process, on a suitable substrate, such as paper, to form a transfer sheet for use in a heat transfer printing process which comprises bringing the transfer sheet into contact with an appropriate substrate, such as a textile, and heating that substrate, in contact with the transfer sheet, to a temperature and for a time sufficient to cause sublimable dyestuff on the transfer sheet to transfer to the substrate and print it.

Description

SPECIFICATION Toner compositions This invention is concerned with improvements in and relating to toner compositions for use in electrographic reproduction systems and, more particularly, is concerned with two-component toner compositions for use in the preparation of transfer sheets for use in a heat transfer printing process.

Electrographic reproduction systems are well known and the process involved basically comprises forming a latent electrostatic image on the surface of a substrate and then "developing" the image by contacting the substrate with finely divided coloured particles (typically comprising a colouring agent and a solid polymeric carrier and generally referred to as "toner" particles) so that the finely divided coloured particles are selectively adhered to the latent electrostatic image to render it visible.

The substrate to which the toner particles are applied may be the substrate of the final imaged product (in which case the substrate will generally be a treated or coated substrate such as a zinc oxide coated paper) or may be an intermediate substrate (typically a drum in many forms of electrographic copying apparatus) from which the image is subsequently transferred to the desired final substrate. For simplicity, the first such process will be referred to as a "direct" process and the second such process as an indirect" process.

The toner composition applied to the substrate may comprise a dispersion of the finely divided particles (toner) in a liquid medium such as a high boiling liquid hydrocarbon, or may be a dry powder, in which latter case the toner composition may simply comprise the finely divided coloured particles (a "one-component" toner composition) or a mixture of the finely divided coloured particles with relatively coarse carrier particles (a "two-component" toner composition).

When using a two-component composition the apparatus employed to carry out the electrographic reproduction process is so arranged that the coarse, carrier particles carry the finely divided coloured particles to the charged imaged areas on the substrate (by means of triboelectric charges developed between the toner particles and the carrier particles), leave the coloured particles on these imaged areas and then fall away, to be re-used after topping up with additional toner particles from time to time.

There are two basic ways in which to two componenttoners may be applied. In the "magnetic brush" process, the coarse carrier particles are of a magnetic material and, carrying their finely divided coloured partner with them, form a brush of magnetized whiskers which make contact with the sensitized image area. The colourant sticks to the image electrostatically and the carrier particles are recycled. In the "cascade" process the coarse particles, carrying the finely divided particles with them, are caused to cascade over the charged image with the same result but in this latter case it does not matter whether or not the coarse particles of the carrier are made of magnetic material.Thus, for use in the "magnetic brush" process the carriers may be made of ferromagnetic materials (for example, iron, steel, iron oxide or ferrite) whilst for the "cascade" process the carriers may be made of such ferromagnetic materials or silica or glass. Typically irregular ferromagnetic carriers are used in conjunction with a magnetic brush developer unit whereas cascade developer units employ rounded or spherical metallic or non-magnetic carriers which are allowed to cascade and tumble over the surface of the substrate bearing the latent electrostatic image.

It has now been found, in accordance with the present invention, that by using as toner particles in a two-component toner composition, particles comprising a solid thermoplastic polymeric carrier and a sublimable dyestuff, it is possible to produce a transfer sheet for use in a heat transfer printing process; i.e. a process in which a substrate to be printed is brought into contact with a substrate bearing an image formed of a heat sublimable dyestuff (a transfer sheet) and then heated (either in the dry or in the presence of moisture) whereby the heat sublimable dyestuff sublimes from the transfer sheet to the substrate to be printed to form a corresponding image thereon.

Accordingly, one embodiment of the present invention provides a two-component toner com position for use in an electrographic reproduction system and comprising ta) finely divided particles comprising a solid polymeric material and a colouring agent and (b) carrier particles therefor, in which the said finely divided particles comprise a solid thermoplastic polymeric material and a heat-sublimable dyestuff which sublimes at a temperature of from 100 to 220"C at atmospheric pressure.

The invention also provides a method of producing a transfer sheet for use in a heat transfer printing process which comprises forming on a substrate in image comprising a heat sublimable dyestuff by a direct or indirect electrographic process, using as toner a two-component toner composition as defined above.

Further, the invention also provides a method of heat transfer printing a substrate which comprises contacting the substrate with a transfer sheet produced as described above and heating the substrate in contact with the sheet to a temperature and for a time sufficient to cause sublimable dyestuff on the transfer sheet to transfer to the substrate and print it.

The carrier particles of the toner composition of the invention will generally have an average particle size equal to or greater than that of the toner particles. The actual ratio of the average particle sizes of carrier and toner particles will be largely dependent upon the design of the copying apparatus in which the toner composition is to be employed. In general, toner compositions for use in apparatus operating on the cascade principle may contain coarser carrier particles (relative to the toner particles) than will compositions to be used in apparatus operating on the magnetic brush principle.

The first component ofthetonercompositions of the invention comprises finely divided toner particles comprising a heat sublimable dyestuff and a solid thermoplastic polymeric material. The sublim able dyestuffs employed are such as sublime at temperatures of from 100 to 220"C, preferably from 160 to 200 C, at atmospheric pressure and examples of such dyes include nitro acrylamine dyes, azo dyes, anthrquinone dyes, quino-phthalone dyes, acridine dyes and diazine dyes. Specific examples of such dyes include Cl Disperse Blue 60, Cl Disperse Blue 95 and various dyestuffs sold under the trade mark "Sublaprint".

The sublimable dyestuff suitably forms from 0.5 to 20% by weight of the toner particles and preferably from 2.5 to 10% by weight of the toner particles.

The solid polymeric component of the toner particles may be a natural or synthetic polymer and suitably forms from 50 to 98% by weight of the toner particles. Examples of suitable thermoplastic polymeric materials include polystyrene, polyalphamethylstyrene, poly-2,4-dimethylstyrene, polyvinyl acetates, polyvinylpropionates, polymers of alpha, beta unsaturated mono carboxylic acid esters (such as methyl acrylate, n-butyl acrylate, isobutyl methactylate, lauryl methacrylate, 2-ethylhexyl methacrylate and dimethyl aminoethyl acrylate), polyvinyl butyral, polyolefins (such as polyethylene, polypropylene and polyisobutylene) polydienes such as polybutadiene and polychloroprene), polyvinyl ketones, fluorocarbon polymers, polyamides, polyesters, polyurethanes, polypeptides, casein, polysulphides, polycarbonates, regenerated cellulose, cellulose esters (such as cellulose acetates and nitrates), epoxy resins, gum copal resin, cumarone indene resins, gilsonite, rosin esters, maleic resin and phenolic resins. Such polymeric materials may be used alone or in admixture.

The thermoplastic polymeric material preferably has a softening point (ring and ball) of from 60 to 140"C and particularly preferred classes of thermoplastic materials are (i) polymers (i.e. homopolymers or copolymers) derived from one or more of styrene, vinyl toluene, methyl styrene, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate and vinyl chloride; (ii) epoxy resins which are condensation products of a polyphenol with a halohydrin; and (iii) polyester resins which are the reaction products of a polyhydroxy alcohol with a polybasic carboxylic acid.

In addition, the toner particles may contain conventional, non-sublimable colouring agents which serve as indicators showing where the desired image has been formed. Such other, non-sublimable colouring agents are suitably present in the toner particles in amounts of from 0.5 to 20% by weight and examples of such include carbon black, nigrosine, iron oxide black, metal complex dyes, chrome yellow, Hansa yellow, diarylide yellow, quinacridone pigment, rhodamine pigment, Prussian blue, para-red,toluidine red, lithol red, lithol rubine, BON maroon, phthalocyanine blue, phthalocyanine green (polychlorinated) and perylene red.

The toner particle may further contain other toner modifying materials such as waxes, plasticisers, surfactants and melt flow and powder flow modifying agents.

The toner particles will generally be prepared by blending the ingredients thereof, grinding the blended ingredients and then, if necessary, subjecting the ground material to size classification.

In the blending step, the raw materials are suitably mixed by processes such as melting, blending, bali-milling or extrusion and in this connection it may be noted that the sublimable dyestuff may be introduced into the blending mixture as a solution in a solvent therefor, as a particulate dispersion in a suitable liquid dispersion medium or in solid form. The blending of the raw materials is suitably carried out at temperatures low enough to reduce any losses of the sublimable dye by vaporisation and it will be additionally useful to control the temperature of the blending since many of the polymers used soften at temperatures below 1500C.

After the blending step, the resultanttonermater- ial is ground and then, if necessary, classified, e.g. by sieving or by air-classification, to the desired weight average particle size which is generally between about 2 and 50 microns in diameter, a usually preferred weight average particle size being from 5 to 30 microns and a more preferred weight average particle size being from 10 to 20 microns. As is conventional in two-component toner technology, the particle size distribution of the ground toner may be adjusted to give the optimum compromise between good resolution and printability and unwanted background density coupled with a satisfactory working life.

The two-component toner composition of the invention is prepared by blending the toner particles with the carrier particles and, suitably, the toner particles form from 0.5 to 15%, preferably from 1 to 8%, typically about 4% by weight of the total weight of toner and carrier higher levels of toner being used with finercarrier particles and vice versa. Generally, the carrier will be formed of a different material from the toner so that rubbing and friction between the two materials generates a static electric charge between them. The carriers used may be porous or non-porous and may range in size from 5 microns to 1,000 microns, as determined by sieving. Carriers for use in a "cascade" process include non-magnetic materials such as glass beads, hard resin particles and metallic beads or composites. Further, ferromagnetic particles, beads spheres or shot may be used as carrier for a two-component toner composition for use in a cascade process.

The carriers for toners to be used in the magnetic brush process are magnetic and commonly comprise particles of iron, steel, nickel, cobalt, chromium, iron oxide, ferrites, or alloys of manganese-copper-aluminium or chromium dioxide which do not contain any ferromagnetic material but which develop ferromagnetism on appropriate heat treatment. Other carriers may be synthesised from finely divided magnetic particles by binding them together into composites and thus for example a finely divided iron powder or magnetic iron oxide may be bound together with a resinous or polymeric binder to form particles having a particle size of from 5 to 1,000 microns.

Many carriers, both for use in the cascade and magnetic brush processes, may be blended or coated with other materials such as polymers, carbon black or polyetetrafi uoroethylene. The potential performance of the toner composition may be estimated by measuring its specific charge by means of a Faraday cage as described by Dessaeur and Clark (Xerography and Related Processes, Focal Press 1965). Suitably the specific charge of the toner composition will be from 5 to 20 micro C/gram.

As will be appreciated, in use, the toner composition in accordance with the invention becomes depleted in toner particles and apparatus for using two-component toner compositions generally comprises a toner replenishing means to maintain the concentration of toner in the composition at a reasonably constant level.

The toner composition of the invention is used to form an image upon a suitable substrate using a direct or indirect electrographic process, in the manner described above. In such a process, the latent electrostatic image upon the substrate to be developed may be formed by any well known means, such as an electrophotograph process or a direct process or a direct electrification process.

In order to form a transfer sheet for use in a heat transfer printing process, the final substrate coated in the electrophotographic process is suitably a paper substrate.

As is common in electrophotographic reproduction processes, the final image-bearing substrate may be subjected to a fixing step such as a heating fixing step or a pressure fixing, solvent fixing or vapour fixing step. As will be appreciated the fixing stage of the process should be carried out under conditions such that excessive sublimation orvap- ourisation of the sublimable dye from the toner does not arise.

The transfer sheet produced in accordance with the invention may then be used in a heat transfer process, that is the transfer sheet is placed in contact with the substrate to be printed under controlled conditions of heat, pressure and time under which the dye sublimes from the transfer sheet to the subs trade to be printed. Underthese conditions, the polymer component (and the non-sublimable colouring component, if any) of the toner on the transfer sheet will remain fixed to the substrate of the transfer sheet and only dye will penetrate to the item to be coloured or printed. This means, therefore, that the colour of the toner in bulk is not important. Thus, for example, a toner may be manufactured which contains a polymer, a carbon black pigment and the sublimable dye (which may be of any colour).In the mass, the toner would appear black but on heating to the appopriate temperature, only the subliming dye would be vapourised and transfered to the item to be dyed.

The transfer printing process of the invention may be applied to a wide variety of substrates including textiles formed of polymers such as polyesters, acrylics, nylons acetates, triacetates and blends, polyethylene glycols, polyurethanes and epoxys. In addition to fibres, PVC sheets, PVC coated fabrics, polyester coated metals, films and acrylic leathers and the like may also be printed using the transfer sheet produced in accordance with the invention.

In order that the invention may be well understood the following examples are given by way of illustration only. In the examples all parts and percentages are by weight unless otherwise stated.

EXAMPLE 1 42 Parts of a hydrocarbon resin (Hercules A120) and 49 parts of a copolymer of polyvinyl chloride and polyvinyl isobutyl ether (Laroflex MP45) were melt blended together with 2 parts of a metal containing azo-type dye (Neozapon Black RE - a nonsubliming dye) and 7 parts of yellow sublimable dyestuff (Sublaprint 70000).

After cooling, the solid mass was roughly ground in a hammer mill and finely pulverised by a pulveriser of an air-jet type. The resulting finely divided powder was then sieved and classified to select particles of approximately 5-25 microns which were used as toner particles.

2.5 Parts of the toner powder were dry blended with 97.5 parts of an atomised iron powder (Hoganas ASC 100-29) which had a particle spread between 20-200 microns to make a two-component toner composition having a specific charge of 23 micro C/gram.

A zinc oxide coated sheet of paper, the photoconductor, was uniformly charged in darkness with a negative electrostatic charge and was then imagewise exposed to light via a photographic negative image. On developing the remaining electrostatic charge with a magnetic brush unit containing the toner composition, a clear black positive toner image was produced on the zinc oxide sheet, The image was fixed in an oven type tunnel fuser.

The image-bearing zinc oxide sheet was contacted with a polyester type fabric at 200"C for a period of 15 seconds and a clear yellow dyed image was transferred to the fabric, the black toner remaining fixed to the zinc oxide carrier sheet.

EXAMPLE2 95 Parts of a styrene: n-butyl methacrylate copolymer (60 :40) was melt blended with 5 parts of a sublimable blue dye (Sublaprint Blue 70013).

After cooling, the solid mass was coarsely ground in a hammer mill followed by fine grinding on an airjettype pulveriser. After sieving and classifying to select particles between 5-25 microns to give a toner a developer mix was made. 4 Parts of the toner were blended with Höganäs W40.37 Cox carburised and oxidised iron powder to produce a developer mix having a specific charge of 10 micro C/gram.

A selenium photoconductorwas uniformly charged with a positive electrostatic charge and imagewise exposed to an original. On developing the remaining electrostatic charge with a magnetic brush containing the developer mix of Example II, a blue toner image was produced. The image was readily electrostatically transferred to a sheet of bond paper on which it was then heat fixed. On contacting this sheet with a film of polyethylene terephthalate (Mylat) at 200"C for a period of 20 seconds, a clear dyeed image was transferred to the film.

After this process, a further dyed image could be transferred from the paper sheet to a fresh polyethylene terephthalate film using the dye that remained in the toner image from the first transfer process.

Example 3 45 Parts of a non-reactive polyamide resin (Versamid 933 - Cray Valley Products Ltd) were melt blended with a maleic condensate resin (Pentalyn G - Hercules Powder Co.) and 5 parts of a nonsublimable nigrosine base dye (Williams of Hounslow, Middlesex) and 5 parts of a sublimable dye (Sublaprint Blue 70032).

After manufacturing a toner and developer mix from the blend, in the same manner as described in Example 1, a negatively charged zinc oxide coated sheet of paper was exposed to a positive original.

On developing the latent electrostatic image with a magnetic brush containing the developer, a clear, positive toner image was made and could be transferred electrostatically to plain paper. The toner image was fixed on the paper by heat.

On contacting this transfer sheet with a polyester/cotton blend fabric at 210"C for 30 seconds, a clear blue dyed image was transferred to the fabric and the toner image remained on the paper (by virtue of the presence of the non-subliming nigrosine).

Claims (28)

1. Atwo-component toner composition for developing latent electrostatic images comprising (a) finely divided toner particles comprising a solid polymeric material and a colouring agent and (b) carrier particles therefor, in which the said finely divided toner particles comprise a solid thermoplastic polymeric material and a heat-sublimable dyestuff which sublimes at a temperature of from 100 to 220"C at atmospheric pressure.

2. Atoner composition as claimed in claim 1 in which the heat sublimable dyestuff is one which sublimes at a temperature of from 160 to 2000C at atmospheric pressure.

3. Atoner composition as claimed in claim 1 or claim 2 in which the sublimable dyestuff forms from 0.5 to 20% by weight of the toner particles.

4. A toner composition as claimed in claim 3 in which the sublimable dyestuffs from 2.5 to 10% by weight of the toner particles.

5. A toner composition as claimed in any one of the preceding claims in which the solid polymeric material forms from 50 to 98% by weight of the toner particles.

6. Atoner composition as claimed in any one of the preceding claims in which the toner particles also contain a non-sublimable colouring agent.

7. Atoner composition as claimed in claim 6 in which the non-sublimable colouring agent forms from 0.5 to 20% by weight of the toner particles.

8. Atoner composition as claimed in any one of the preceding claims in which the toner particles have a weight average particle size of from 2 to 50 microns.

9. Atoner composition as claimed in claim 8 in which the toner particles have a weight average particle size of from 5 to 35 microns.

10. Atoner composition as claimed in claim 9 in which the toner particles have a weight average particle size of from 10 to 20 microns.

11. A toner composition as claimed in any one of the preceding claims containing from 0.5 to 15% by weight of the toner particles.

12. Atonercomposition as claimed in claim 11 containing from 1 to 8% by weight of the toner particles.

13. Atonercomposition as claimed in any one of the preceding claims in which the carrier particles have an average particle size of from 20 to 1,000 microns.

14. Atoner composition as claimed in any one of the preceding claims in which the thermoplastic polymeric material has a ball and ring softening point of from 60 to 140"C.

15. Atoner composition as claimed in any one of the preceding claims in which the thermoplastic polymeric material is a polymer derived from one or more of styrene, vinyl toluene, methyl styrene, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate or vinyl chloride.

16. Atonercomposition as claimed in any one of claims 1-14 in which the thermoplastic polymeric material is an epoxy resin which is a condensation product of a polyphenol with a halohydrin.

17. Atoner composition as claimed in any one of claims 1-14 in which the thermoplastic polymeric material is a polyester resin which is the reaction product of a polyhydroxy alcohol with a polybasic acid.

18. Atoner composition as claimed in any one of the preceding claims in which the sublimable dyestuff is a nitro arylamine, azo or anthraquinone dyestuff.

19. Atoner composition as claimed in any one of the preceding claims for use as a developer in a cascade or magnetic brush developing process in which the carrier particles are formed of ferromagnetic material.

20. Atoner composition as claimed in any one of claims 1-18 for use as a developer in a cascade developing process in which the carrier particles are formed of a non-magnetic material.

21. Atoner composition as claimed in claim 1 substantially as herein before described with referpence to the Examples.

22. A method of producing a transfer sheet for use in a heat transfer printing process which comprises forming an image comprising a heat sublimable dyestuff on a substrate by a direct or indirect electrographic process employing as developer a toner composition as claimed in any one of the preceding claims.

23. A method as claimed in claim 22 in which the substrate is a paper substrate.

24. A method as claimed in claim 22 substantially as hereinbefore described with reference to the Examples.

25. Atransfer sheet when produced by a process as claimed in any one of claims 22-24.

26. A method of heat transfer printing a substrate which comprises contacting the substrate with a transfer sheet as claimed in claim 25 and heating the substrate in contact with the sheet to a temperature and for a time sufficient to cause sublimable dyestuff on the sheet to transfer to the substrate and print it.

27. A method as claimed in claim 26 in which the substrate is a textile.

28. A method as claimed in claim 26 substantially as hereinbefore described with reference to the Examples.