Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2000-01-10
2003-03-11
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C523S335000
Reexamination Certificate
active
06531256
ABSTRACT:
This application is the national phase of international application PCT/GB98/00964 filed Apr. 1, 1998 which designated the U.S.
The present invention relates to a process for making particulate compositions. Such compositions have particular utility in the field of electroreprography. Preferred aspects of the invention relate to processes for making toner compositions for use in electroreprography.
Electroreprography is any process in which an image is reproduced by means of electricity and incident radiation, usually electromagnetic radiation, more usually visible light. Electroreprography comprises the technology of electrophotography which encompasses photocopying and laser printing technologies. In both these technologies a latent, electrostatic image is produced, in charge, by exposure of a photoconductive drum to light. The exposure can either be from light reflected from an illuminated image (photocopying) or from a laser which scans the drum, usually under instruction from a computer (laser printing). Once a latent image has been produced in charge it must be developed to form a visible image on the drum which can then be transferred onto a suitable substrate so a hard copy of the image is obtained (e.g. by printing onto paper).
Suitable developers, which may be liquid or dry compositions, comprise particles of a toner which are electrostatically attracted to the latent image. Liquid developers comprise a toner dispersed in a suitable insulating liquid. Dry developers may comprise single component systems comprising a toner, or two component systems which comprise a mixture of a toner and a carrier. A toner may comprise particles of a polymeric component, a colouring agent and optionally other internal and/or external additives such as charge control agents and/or surface additives to improve the flowability of the toner particles. The polymeric component of the toner is electrically insulating to enable the toner to be electrostatically charged during the electroreprographic process. The polymer also acts to fix the toner to the printed substrate, usually by fusion of the polymer onto the substrate by heating. The colouring agent, which is usually a pigment, imparts the required colour to the toner.
During use in an electroreprographic device, friction between particles of toner with their carrier and/or with parts of the device, cause the toner particles to become charged with an electrostatic charge (tribocharge). The exact mechanism which produces the toner image will then vary according to the specific device used. For example in a conventional photocopier the toner composition may be formulated so that tribocharged toner particles will be opposite in sign to the latent image on the drum. Thus toner will be attracted to the latent image on the drum to develop, on the drum, an image in toner which corresponds to the original document. The developed image is then transferred to a substrate such as paper (e.g. by a pressure roller and/or voltage). The transferred image is then fixed to the substrate (e.g. by heat, pressure and/or suitable solvents) to produce a hard copy of the image. The image drum is then cleaned and the device is ready to produce the next copy. Thus developer compositions are used both to develop the latent image on the drum and to produce the final hard copy.
There are a number of methods for making toners. The most common method is to mix the polymer and optional other ingredients (e.g. colorant) together by kneading in a ball mill above the melting temperature of the resin. The optional ingredients may be added simultaneously or sequentially to the resin before or after melting the resin, but are generally added to the resin when molten. Generally, this involves mixing the molten composition for several hours at temperatures from 120° C. to 200° C., in order to uniformly distribute any optional ingredients (if present) throughout the toner resin. The resultant melt may then be cooled, extruded and then formed into particles with a mean diameter of typically below 20 &mgr;m. The particle formation is achieved by physical processes such as crushing, grinding, milling, and/or pulverising the extrudate. The fine powder of toner or toner-resin so obtained is either used directly, is diluted with an inert solid as carrier, and/or is coated with surface additives such as silica by mixing for example in a suitable blending machine.
As well as being extremely energy intensive, such physical processes result in a wide distribution of particle sizes within the toner. This leads to significant disadvantages. A wide particle size range generates more uneven tribocharge within the toner which leads to an uneven print density in the final image. The fine dust within such toner compositions leads to fogging of the image produced and more readily contaminates the interior of the device in which the toner is used. The presence of larger toner particles reduces the resolution of images that may be developed with the toner. Methods for classifying this wide particle size (such as air classification or sieving) are wasteful of the rejected material. If material outside the required size range is recycled this also adds to the cost.
Modern electroreprographic devices require toners (and processes for making them) which avoid some or all of the preceding disadvantages and exhibit some or all of the properties listed below which are desired in toners (and processes for making them). Ideally a toner image can be fixed onto the printed substrate at low temperature and toner fusion occurs over a wide temperature range. Conveniently toners produce little contamination of the device in which they are used. Desired toners generate tribocharge at a controlled level, which is stable with time and which is reasonably independent of either temperature or humidity. Toners with a small particle size (preferably <7 &mgr;m) and narrow size distribution provide good image resolution. Toners should be cheap to produce in large volumes. It is also desirable that colorant(s) and other additives [e.g. charge control agents (CCAs) and waxes] can be dispersed uniformly in a toner. Ideal toners can produce images which are matt or gloss as required; have a high optical density; a wide colour gamut; and/or are resistant to smudging and smearing. These properties are strongly influenced by the choice of toner resins. It is not feasible or cost effective to produce a toner having these parameters using the conventional extrusion and milling processes described above.
Therefore to overcome these disadvantages, methods for chemically producing toners have been developed in which the toner particles are prepared by chemical processes such as aggregation or suspension rather than being abraded from much larger sized materials by physical processes. Chemically produced toners made by prior art suspension methods are unsatisfactory as it is difficult to control particle shape or obtain a narrow distribution of particle size using these suspension routes. Aggregation provides a greater degree of control of the properties of resultant toner particles such as size distribution, particle shape and/or particle composition.
Certain prior art applications (for example JP 2-259770, JP 2-259771, JP 2-11968, JP 2-061650 and JP 2-093659 [Kokai] and U.S. Pat. No. 4,983,488, U.S. Pat. No. 5,066,560 and EP 0162577 all to Hitachi) disclose methods for chemical production of toners using an irreversible coagulation method for particle growth. JP 2-061650 is typical of these and describes mixing aqueous dispersions of latex and a pigment followed by a coagulation step. These Hitachi patents all describe use of coagulating agents, such as suitable salts, which reduce the stability of the colloid to irreversibly form a semi-solid gelatinous mass. These processes do not readily control particle growth, indeed the coagulated solids have to be further sized and/or classified (e.g. by milling and sieving) to produce particles of the desired size which negates one of the advantages of chemically pr
Abhinava Kumar
Bedells Alison Dawn
Edwards Martin Russell
Morris Daniel Patrick
Wood William Malcolm Logan
Avecia Limited
Pillsbury & Winthrop LLP
Rodee Christopher
LandOfFree
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