EP0078175A1

EP0078175A1 - Toner compositions

Info

Publication number: EP0078175A1
Application number: EP82305664A
Authority: EP
Inventors: John Patrick Nelson Haxell; Stephen Charles Clements; Derek Edward Wilson
Original assignee: Coates Brothers and Co Ltd
Current assignee: Coates Brothers and Co Ltd
Priority date: 1981-10-23
Filing date: 1982-10-25
Publication date: 1983-05-04
Also published as: WO1983001518A1

Abstract

A developer for use in an electrographic reproduction system comprises magnetic particles comprising (a) a film-forming carrier, (b) magnetic material and (c) a heat-sublimable dyestuff in which the film-forming carrier consists of a wax.

The developer may be used to produce a heat-transfer sheet for use in a heat transfer printing process by forming on a substrate an image comprising a heat-sublimable dyestuff by a direct or indirect electrographic process using the developer as defined above. The resultant transfer sheet may be used in a method of heat transfer printing a substrate by contacting the substrate with the transfer sheet 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.

Description

This invention is concerned with improvements in and relating to toner compositions for use in electrographic reproduction systems and, more particularly, is concerned with one-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).
The present invention is concerned with one-component toners for use in a so-called "magnetic brush" method, i.e. the toner particles contain particles of a magnetic (generally a ferromagnetic) material.
It has now been found, in accordance with the present invention, that certain waxes may be used to form the film-forming carrier component of toner particles containing a heat-sublimable dyestuff and that the toners containing such waxes as film-forming carrier material are particularly suitable for use in the production of heat transfer sheets 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 developer for use in an electrographic reproduction system and comprising magnetic particles comprising (a) a film-forming carrier, (b) magnetic material and (c) a heat-sublimable dyestuff, in which the film-forming carrier consists of a wax as hereinafter defined.
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 an image comprising a heat sublimable dyestuff by a direct or indirect electrographic process, using as toner a 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 toner compositions of the invention comprise finely divided toner particles comprising a heat sublimable dyestuff, a solid wax and magnetic material. The sublimable dyestuffs employed are suitably 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 azo dyes, anthraquinone dyes, quinophthalone dyes, acridine dyes and diazine dyes. Specific examples of such dyes include CI Disperse Yellow 54, CI Disperse Yellow 65, CI Vat Red 31, CI disperse Blue 60, CI 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 to 10% by weight of the toner particles.
The magnetic material component of the toner particles may be any of a wide variety of magnetic materials such as particles of iron, steel, nickel, cobalt, chromium, iron oxide, ferrites, or alloys of manganese-copper-aluminium or chromium dioxide which have been heat treated to develop ferromagnetism. Suitably the magnetic material is present in an amount of from 5 to 57.5%, preferably from 40 to 85% by weight, based on the total weight of the toner particles.
The film-forming carrier composition of the toner particles of the invention consists of one more waxes. The waxes for use in accordance with the invention are solid waxes having the following properties:

(i) a melting point of from about 80 to about 180°C, preferably from 85 to 150 °C, and
(ii) a melt viscosity of not more than 10 poises when measured at a temperature of about 40°C centigrade above the melting point.

Further the waxes are not "thread-pulling". That is, if the wax is melted and a needle or thin rod is dipped into the molten material and then withdrawn, no continuous thread of material is attached to the needle or rod.
Examples of suitable waxes, which may be employed alone or in admixture, include polyethylene waxes, polypropylene waxes, oxidised polyethylene waxes, ethylene copolymer waxes (such as ethylene/vinyl acetate copolymer waxes), fatty amide waxes (such as ethylene or methylene bis-fatty amide waxes) and chlorinated hydrocarbon waxes and natural waxes having the above required characteristics.
The wax or waxes are suitably present in the toner particles in an amount of from 10 to 40% by weight.
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 plasticisers, surfactants and melt flow and powder flow modifying agents.
The toner particles will generally be prepared by blending the ingredients thereof, grinding and 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, ball-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. In some cases, the sublimable dyestuff will be capable of forming a true solution in the wax (as may readily be determined by simple experiment). If the dyestuff does not form such a solution it is suitably introduced, in solid or disperse form, in the form of fine particles, e.g. having a particle size of 2 microns or less. 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 the wax used may soften at temperatures below 150°C.
After the blending step, the resultant toner material is ground and then, if necessary, classified, e.g. by sieving or by air classification, to the desired average particle size which is generally between about 2 and 50 microns in diameter, a usually preferred average particle size being from l5to 30microns expressed as weight average particle size.
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 electrification process.
In order to form a transfer sheet for use in a heat transfer printing process, the final substrate in the electrographic- process is suitably a coated paper substrate.
As is common in electrographic 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 or vapourisation 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 substrate to be printed. Under these conditions, the wax 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 sublimable 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 appropriate temperature, only the subliming dye would be vapourised and transferred 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

65 Parts of a Bayer black di-iron trioxide magnetic pigment of average particle size 0.2 microns were hot-melt blended with 32 parts of an N-N'-ethylene-bis-stearamide wax of mp 142°C and 3 parts of a heat-subliming magonta dye (Resiren Red TB).
After cooling, the solid mass was ground, sieved and classified to yield a fine black powder with a particle size distribution between 0 and 53 microns with a d₅₀ peak at 22 microns. A dry addition of a conductive, medium colour furnace carbon black was made to adjust the resistivity of the powder to be 4 x 10⁴ ohm. cm when measured at a field strength of 100 volts/cm.
This toner powder was then used in a magnetic applicator to develop a latent electrostatic image which had been formed on a negatively charged sheet of zinc oxide sealed paper.
A clear image was formed and then fixed to the paper by means of a set of polished steel rollers set at a pressure of approximately 50 Kg/linear cm.
On contacting the image bearing zinc oxide sheet with a polyester type fabric at 200°C for a period of 30 seconds under moderate pressure; a clear magenta image was transferred to the fabric whilst a black toner image remained on the zinc oxide carrier sheet.

EXAMPLE 2

65 Parts of a black magnetic oxide of iron, Fe₃O₄, of cubic structure (particle size approximately 0.8 microns) from BASF were melt blended with 30 parts of an N-N' ethylene bis-stearamide wax of mp 140-143°C. 5 parts of a subliming dye (Sublaprint yellow 70,000) were dispersed into the pigment suspension and a toner powder produced in a manner similar to Example 1.
On pressure fixing the toner to a zinc oxide carrier sheet, a clear, smudge free toner image was formed. This image was contacted against a film of polyethylene terephthalate (Mylar) at 200°C for 20 seconds when a clear, dyed image was produced on the film.

EXAMPLE 3

80 Parts of a diiron trioxide were hot melt blended with 10 parts of a polyethylene/polyvinyl acetate wax (MW = 2000) of melting point 96°C and 5 parts of N-H'-ethylene bis-stearamide wax, melting point 140 - 143°C. 5 Parts of a dye (Sublaprint Blue 70014) were added to the pigment suspension.
Again, following the procedure of Example 1, a magnetic, single component toner powder was made and a toner image produced onto a zinc oxide sheet. On contacting the pressure fixed image with a fabric comprising a 50% cotton/polyester blend at 210°C for 20 seconds, a clear blue dyed image was produced on this textile.

Claims

1. A developer for use in an electrographic reproduction system and comprising magnetic particles comprising (a) a film-forming carrier, (b) magnetic material and (c) a heat-sublimable dyestuff, in which the film-forming carrier consists of a wax.

2. A developer as claimed in claim 1 in which the sublimable dyestuff is one which sublimes at a temperature of from 160 to 220°C at atmospheric pressure.

3. A developer as claimed in claim 1 or claim 2 in which the sublimable dyestuff forms from 0.5 to 20% by weight of the magnetic particles.

4. A developer as claimed in claim 3 in which the sublimable dyestuff forms from 2-10% by weight of the magnetic particles.

5. A developer as claimed in any one of the preceding claims in which the magnetic material forms from 40 to 85% by weight of the magnetic particles.

6. A developer as claimed in any one of the preceding claims in which the wax forms from 5 to 57.5% by weight of the magnetic particles.

7. A developer as claimed in claim 6 in which the wax forms from 10 to 40% by weight of the magnetic particles.

8. A developer as claimed in any one of the preceding claims also containing from 0.5 to 20% by weight, based on the weight of the magnetic particles, of a non-sublimable colouring material.

9. A developer as claimed in any one of the preceding claims in which the magnetic particles have a weight average particle size of from 2 to 50 microns.

10. A developer as claimed in claim 9 in which the magnetic particles have a weight average particle size of from 15 to 30 microns.

11. A method of producing a transfer sheet for use in a heat transfer printing process which comprises forming on a substrate an image comprising a heat sublimable dyestuff by a direct or indirect electrophotographic process, using as developer a developer as claimed in any one of claims 1-10.

₁₂. A method of heat transfer printing a substrate which comprises contacting the substrate with a transfer sheet produced as claimed in claim 11 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.