Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-09-05
2001-12-04
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111350, C430S111300
Reexamination Certificate
active
06326118
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to specially alloyed metallic carriers for use in an electrostatographic developer material.
2. Description of Related Art
The electrostatographic process, and particularly the xerographic process, is well known. This process involves the formation of an electostatic latent image on a photoreceptor, followed by development of the image with a developer and subsequent transfer of the image to a suitable substrate. Numerous different types of xerographic imaging processes are known wherein, for example, insulative developer particles or conductive developer particles are selected depending on the development systems used.
The use of coated carrier particles in two-component developers is well known in the art.
Carrier particles for use in the development of electrostatic latent images are described in many patents including, for example, U.S. Pat. No. 3,590,000. These carrier particles may consist of various cores, including steel, with a coating thereover of fluoropolymers, and terpolymers of styrene, methacrylate, and silane compounds.
Typical carriers, coated carriers, their method of manufacture and developer compositions containing such carriers are disclosed in U.S. Pat. Nos. 4,233,387; 4,937,166; 4,935,326 and 5,567,562, the complete disclosure of which patents is incorporated herein by reference.
The main purpose of applying polymeric coatings on an iron or steel carrier core is to achieve high triboelectric and conductivity properties. However, aging or removal of these coatings by attrition results in poor triboelectric stability and triboelectric decay which is particularly a problem in color imaging using cyan, magenta and yellow toners.
Thus, it is desirable to provide developer carrier material which not only provides improved triboelectric and conductivity properties, but also maintains these properties over a longer period of time.
SUMMARY OF THE INVENTION
The present invention provides a developer material for use in an electrostatographic imaging process comprising a mixture of colored toner material and metallic carrier particles, the surface of said carrier particles comprising a layer of one or more alloy metals diffusion bonded thereto.
The invention also provides a coated carrier for use in an electrostatographic imaging process comprising metallic carrier particles, the surface of said carrier particles comprising a layer of one or more alloy metals diffusion bonded thereto, said particles being further overcoated with a coating comprising one or a mixture of polymers.
The carrier material with the surface alloy treatment provides many advantages over conventional metallic carriers. The surface alloy treatment is a chemical process which alters the surface chemistry of the metal as a result of diffusion of one or more metals without changing the magnetics of the bulk carrier core. Therefore, the magnetics of the bulk core are insensitive to the surface treatment and are essentially the same as that of the untreated iron core. Since the surface alloy treatment is a physical part of the carrier core rather than a simple coating, it will not be easily worn away or eroded during use thereby improving the triboelectric stability of the developer.
DETAILED DESCRIPTION OF THE INVENTION
The metallic particles used in the present invention may be characterized as particles of relatively pure iron (containing less than 0.2 wt % of carbon) or steel (containing about 0.2 to 1.5 wt % carbon) which have a layer of one or more other alloying metals diffused into the outer surfaces of the otherwise non-alloyed particle. The core of the particles is essentially iron or steel over which the alloy coating is formed by diffusion of one or more alloy metals into the outer surface of the particles. Generally, the alloy is formed only at the surface of the particle and at a thickness of less than about 2% of the particle diameter or less than about 1 micron. The shape of the metallic particles used in the present invention may vary from spherical to highly irregular, with the particles of highly irregular shape produced by standard water atomization or sponge steel production methods.
These particles may be manufactured by first forming the metallic particles by conventional processes and applying a coating or slurry of the desired alloy metal or mixed metals in the form of a reducable metal compound, or by forming a metal coating on the ferrite by ion vapor deposition, evaporation or electrodeposition methods. The coated cores may then be heated in an inert or reducing atmosphere at high temperature (up to 1000° C.) for a period of time sufficient such that the alloy metal diffuses into the surface of the metallic particle to form an iron/metal alloy.
Suitable metals which may be surface alloyed with iron include manganese, chromium, silicon, copper, nickel, molybdenum, aluminum, cobalt, silver, tin and zinc, as well as mixture of two or more such metals. The amount of metal surface alloyed is generally less than about 10% by weight, preferably less than about 6% by weight, based on the weight of the metal particle.
Suitable surface alloyed particles for use in the developer compositions of this invention are commercially available as metallurgical molding powders from the Hoganas AB (Sweden) under the trade names DISTALOY AB, AE, SA and SE, as well as ASTOLOY-Mo, ASTALOY-Cr, ASTALOY-CrM/77 and ASTALOY Mo/77. These materials are more generally described in U.S. Pat. Nos. 5,926,686 and 6,039,784, the disclosures of which patents are incorporated herein by reference.
The metallic carrier particles used in this invention may vary from spherical to highly irregular in shape and have a volume medium diameter in the range of from about 20 to 200 microns, more preferably from about 40 to 150 microns and most preferably about 50-125 microns, as measured by standard laser diffraction techniques, and a density as determined by ASTM Test B-212-89 in the range of about 2 to 4 g/cm
3
, more preferably about 2.5 to 3.5 g/cm
3
. The preferred embodiment for the shape of the metallic particles is irregular, with a surface morphology characteristic of that produced by water atomization of steel.
The carrier particles may be employed as a component in a developer composition with or without an additional polymer coating overlying the surface alloy layer. In a preferred embodiment, the carrier particles are further coated with one or a mixture of polymers to further modify the conductivity and triboelectric properties of the developer. Suitable polymers include those thermoplastics known in the prior art such as acrylic and methacrylic polymers, polyolefens, polystyrenes, polyvinylidene fluorides and like materials.
In a most preferred embodiment the metallic particles are coated with one or a mixture of at least two dry polymer components, which dry polymer components are preferably set not in close proximity thereto in the triboelectric series, and most preferably of opposite charging polarities with respect to the toner selected.
The electronegative polymer, i.e., the polymer that will generally impart a positive charge on the toner which it is contacted with, is preferably comprised of a polyvinylidenefluoride polymer or copolymer. Such polyvinylidenefluoride polymers are commercially available, for example under the tradename Kynar from Pennwalt. Kynar 301F is polyvinylidenefluoride and Kynar 7201 is copolyvinylidenefluoride/tetrafluorothylene.
The electropositive polymer, i.e., the polymer that will generally impart a negative charge on the toner which it is contacted with is preferably comprised of a polymer or copolymer of polymethyl methacrylate (PMMA), optionally having carbon black or another conductive material dispersed in the polymer. The PMMA may be copolymerized with any desired comonomer, so long as the resulting copolymer retains a suitable particle size. Suitable comonomers can include monoalkyl, or dialkyl amines, such as dimethylaminoethyl methacrylate, diethylamisoethyl methacrylate, diisopropylam
DeYoung Morris
Galloway Merrilee
Silence Scott
Perman & Green LLP
Rodee Christopher
Xerox Corporation
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