GB1586193A - Low specific gravity magnetic carrier material - Google Patents

Description

(54) LOW SPECIFIC GRAVITY MAGNETIC CARRIER MATERIAL (71) We, XEROX CORPORATION of Rochester, New York State, United States of America, a Body Corporate organized under the laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates in general to electrophotography, and more particularly, to a carrier material useful in the magnetic-brush type development of electrostatic latent images, and to a process for preparing such a carrier material.

The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrostatographic process, as taught by C.F Carlson in U.S. Patent 2,297,691, involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting electrostatic latent image by depositing on the image a finely-divided electroscopic material referred to in the art as "toner". The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This powder image may then be transferred to a support surface such as paper.

The transferred image may subsequently be permanently affixed to the support surface as by heat. Instead of latent image formation by uniformly charging the photoconductive layer and then exposing the layer to a light and shadow image, one may form the latent image by directly charging the layer in image configuration. The powder image may be fixed to the photoconductive layer if elimination of the powder image transfer step is desired. Other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing step.

Many methods are known for applying the electroscopic particles to the electrostatic latent image to be developed. One development method, as disclosed by E.N. Wise in U.S. Patent 2,618,522 is known as "cascade" development. In this method, a developer material comprising relatively large carrier particles having finely-divided toner particles electrostatically clinging to the surface of the carrier particles is conveyed to and rolled or cascaded across the electrostatic latent image-bearing surface. The composition of the toner particles is so chosen as to have a triboelectric polarity opposite that of carrier particles. As the mixture cascades or rolls across the image-bearing surface, the toner particles are electrostatically deposited and secured to the charged portion of the latent image and are not deposited on the uncharged or background portions of the image.Most of the toner particles accidentally deposited in the background are removed by the rolling carrier, due apparently, to the greater electrostatic attraction between the toner and the carrier than between the toner and the discharged background. The carrier particles and unused toner particles are then recycled. This technique is extremely good for the development of line copy images. The cascade development process is the most widely used commercial electrostatographic development technique. A general purpose office copying machine incorporating this technique is described in U.S.

patent 3,099,943.

Another technique for developing electrostatic latent images is the "magnetic brush" process as disclosed, for example, in U.S. Patent 2,874,063. In this method, a developer material containing toner and magnetic carrier particles is carried by a magnet. The magnetic field of the magnet causes alignment of the magnetic carriers in a brush-like configuration.

This "magnetic brush" is engaged with an electrostatic-image bearing surface and the toner particles are drawn from the brush to the electrostatic image by electrostatic attraction.

In magnetic-brush development of electrostatic latent images the developer is commonly a triboelectric mixture of finely-divided toner powder comprised of dyed or pigmented thermoplastic resin mixed with coarser carrier particles of a soft magnetic material such as "ground chemical iron" (iron filings), reduced iron oxide particles or the like. The conductivity of the ferromagnetic carrier particles which form the "bristles" of a magnetic brush provides the effect of a development electrode having a very close spacing to the surface of the electrophotographic element being developed. By virtue of this development electrode effect, it is possible to develop part of the tones in pictures and solid blacks as well as line copy.

Magnetic brush development sometimes makes this mode of developing advantageous where it is desired to copy materials other than simply line copy.

While ordinarily capable of producing good quality images, conventional developing materials suffer serious deficiencies in certain areas. Some developer materials, though possessing desirable properties such as the required triboelectric characteristics, are unsuitable because they tend to cake, bridge and agglomerate during handling and storage.

Furthermore, with some polymer coated carrier materials flaking of the carrier surface will cause the carrier to have nonuniform triboelectric properties when the carrier core is composed of a material different from the surface coating thereon. In addition, the coatings of most carrier particles deteriorate rapidly when employed in continuous processes which require the recycling of carrier particles by bucket conveyors partially submerged in the developer supply such as disclosed in U.S. Patent 3,099,943. Deterioration occurs when portions of or the entire coating separates from the carrier core. The separation may be in the form of chips, flakes or entire layers and is primarily caused by fragile, poorly adhering coating material which fails upon impact and abrasive contact with machines parts and other carrier particles.Carriers having coatings which tend to chip and otherwise separate from the carrier core or substrate must be frequently replaced thereby increasing expense and loss of productive time. Print deletion and poor print quality occur when carriers having damaged coatings are not replaced. Fines and grit formed from carrier disintegration tend to drift to and from undesirable and damaging deposits on critical machine parts.

Another factor affecting the stability of the triboelectric properties of carrier particles is the susceptibility of carrier coatings to "toner impaction". When carrier particles are employed in automatic machines and recycled through many cycles, the many collisions which occur between the carrier particles and other surfaces in the machine cause the toner particles carried on the surface to the carrier particles to be welded or otherwise forced onto the carrier surfaces. The gradual accumulation of impacted toner material on the surface of the carrier causes a change in the triboelectric value of the carrier and directly contributes to the degradation of copy quality by eventual destruction of the toner carrying capacity of the carrier.This problem is especially aggravated when the carrier particles, and particularly the carrier cores, are prepared from materials such as iron or steel having a high specific gravity or density since during mixing and the development process the toner particles are exposed to extremely high impact forces from contact with the carrier particles. It is apparent from the descriptions presented above as well as in other development techniques, that the toner is subjected to severe physical forces which tend to break down the particles into undesirable dust fines which become impacted onto carrier particles.Various attempts have been made to decrease the density of the carrier particles and reduce the concentration of the magnetic component by admixture of a lighter material, such as a resin, either in the form of a coating or as a uniform dispersion throughout the body of the carrier granule. This approach is useful in some instances but the amount of such lighter material sufficient to produce a substantial decrease in density has been indicated as seriously diminishing the magnetic response of the carrier particles as to cause a deterioration in the properties of a magnetic brush formed therefrom. One such attempt is disclosed in Belgian Patent Specification No. 726,806, wherein the carrier particles comprise a low density, non-magnetic core such as a resin or glass, for example having coated thereon a thin, continuous layer of a ferromagnetic material.

It can be seen from that speficiation that a coating of finely powdered iron or other subdivided ferromagnetic material does not show the high response to a magnetic field which can be displayed by carrier materials in accordance with the present invention. Another earlier attempt at low density carrier materials is disclosed in U.S. 2,880,696 wherein the carrier material is composed of particles having a magnetic portion. The core therein may consist entirely of a magnetic material, or it may be formed of solid insulating beads such as glass or plastic having a magnetic coating thereon, or the core may consist of a hollow magnetic ball.

However, for unknown reasons, the recited materials have apparently never been commercially successful. Thus, there is a continuing need for a better developer material for developing electrostatic latent images.

According to the present invention, there is provided a magnetically-responsive, low density electrostatographic composite particulate carrier material having an average particle diameter of from 10 microns to 850 microns, said carrier particle comprising a porous silicaceous material having an average bulk density of between 0.2 and 3.0 grams/cm3, said silicaceous material being micro-reticulated and having pores with an average pore size of from 10 to 500 Angstroms, said porour silicaceous material being impregnated with a magnetic or magnetically-attractable transition metal and/or metal oxide thereof.

The present invention also comprehends a process for preparing a magnetically-responsive low density electrostatographic composite carrier material, said process comprising thermally decomposing a transition metal carbonyl, substantially in the absence of air and moisture, and in the presence of particles of a porous silicaceous material having a bulk density of between 0.2 and 3.0 grams/cm3 and an average particle diameter of from 10 microns to 850 microns, said silicaceous material being microreticulated and having pores with an average pore size of from 10 to 500 Angstroms, whereby said silicaceous material is impregnated with the magnetic elemental metal and/or metal oxide.In accordance with one embodiment, the thermal decomposition of said metal carbonyl is carried out by forming a mixture of said particles of porous silicaceous material, said carbonyl and a suspendirig medium in a vessel, and heating the mixture with agitation to reflux temperature, substantially in the absence of air and moisture, for up to 24 hours at the temperature of said suspending medium. In accordance with another embodiment, the thermal decomposition of said metal carbonyl is carried out by forming, in a fluidising bed apparatus, a mixture of said particles of porous silicaceous material and said carbonyl, said mixture being heated with agitation to reflux temperature, substantially in the absence of air and moisture.

The present invention further comprehends an electrostatographic developer mixture comprising finely-divided toner particles electrostatically clinging to the surfaces of a particulate carrier material in accordance with the invention.

The present invention still further comprehends a method of developing an electrostatic latent image on an electrostatic latent image-bearing surface, the method comprising: contacting said surface with an electrostatographic developer mixture in accordance with the invention whereby at least a portion of the toner particles of the developer mixture are attracted to and deposited on said surface in conformance with said electrostatic latent image.

Magnetically, carrier material in accordance with the invention can respond like a collection of solid, fine iron particles but, when employed in electrostatographic magnetic brush development systems, can form more uniform and "softer" magnetic brushes due to their very low bulk densities which in some cases are more than an order to magnitude less than the density of iron. Magnetic measurements have indicated that the carrier materials are magnetic equivalents to their magnetic constituent, taking into account the significant difference in density between the composite and that of its magnetic constituent.

In an example of the embodiment of the invention which involves applying the metal deposit to the porour silicaceous beads by the thermal decomposition of a transition metal carbonyl toi the elemental metal in the presence of the beads with a suitable suspending medium, porous glass beads may be impregnated with magnetic iron by placing them in a suitable vessel with iron pentacarbonyl and a suspending medium such as n-octane. Air and moisture are excluded by displacement with a dry inert gas such as nitrogen, and the contents are heated and stirred so that the iron pentacarbonyl boils, and the mixture is refluxed until the temperature rises to that of the suspending medium whereupon deposition of iron on the beads is complete. The mixture is then cooled, the beads are washed with fresh suspending medium, air dried, and the beads recovered.The magnetic low density spheres obtained typically are highly lustrous.

Thus, the thermal decomposition of typical transition metal carbonyls may be exemplified by the following equations for (1) iron pentacarbonyl, and (2) dicobalt octacarbonyl; Fe(COs) A Fe + 5CO (1) CO2(CO)8 t; 2CO + 8CO (2) The decompositon of the transition metals is performed in the presence of porous silicaceous substrates and utilized to prepare composite materials having both chemical and mechanical stability and which display highly magnetic behavior. The configuration of the silicaceous beads is essentially retained throughout the coating process. The bulk magnetic response of the composite materials may be controlled by varying the mass of the magnetic metal in proportion to the coated particle mass.

Any suitable magnetic or magnetically-attractable transition metal or metal oxide thereof may be employed to impregnate the silicaceous substrates of the carrier particles of this invention. Typical such transition metals may be provided from iron pentacarbonyl, di-iron nonacarbonyl, tri-iron dodecacarbonyl, iron carbonyl cluster compounds; dicobalt octacarbonyl, nickel tetracarbonyl, any other thermally extrudable compound of such transition metals, and mixtures thereof. Oxides may be provided by subsequent oxidation of these transition metals, for example by the procedure described and claimed in the specification of our co-pending Patent Application No. 31713/77.

Any suitable porous silicaceous material may be employed as the substrate for the carrier particles of this invention. Typical suitable porous silicaceous materials include glass particles in various micro-reticulated forms.

In addition, suitable porous vitreous materials may also be used. Thus, a wide variety of particulate, micro-reticulated low density materials the pores of which can be impregnated with a magnetic or magnetically-attractable transition metal or metal oxide thereof may be employed in accordance with this invention. As indicated, particles of the carrier material of this invention may vary in size and shape. However, it is preferred that the carrier particles have a spherical shape as to avoid rough edges or protrusions which have a tendency to abrade more easily. Particularly useful results are generally obtained when the carrier material has an average particle size from 50 microns to 300 microns, although satisfactory results may be obtained when the composite material has an average particle size of between 10 microns and 850 microns.The size of the carrier particles employed will, of course, depend upon several factors, such as the type of images ultimately developed, and the machine configuration, for example.

The low density silicaceous material employed as the substrate for the composite magentic carrier particles of this invention has an average bulk density of between 0.2 and 3.0 grams/cm3. However, it is preferred that the silicaceous material have an average bulk density of less than 2.5 grams/cm3 because stress levels are substantially reduced thereby reducing toner impaction and developer degradation.

The low density porous, micro-reticulated silicaceous material employed as the substrate or matrix for the carrier particles of this invention have an average pore size of between 1 oA and 500 A. The low density silicaceous material may have a surface area of up to about 250 m2/gram.

The magnetic metal may be deposited within the pores of the carrier beads in the form of continuous threads or networks which provides a practical advantage in that the magnetic metal is well protected against abrasion.

A range of volume ratios of silicaceous material to magnetic elemental metal that will generally provide satisfactory magnetically-responsive composite carrier particles is from between 5:1 to 20:1.

To achieve further variation in the properties of the carrier particles of this invention, well known insulating polymeric resin coating materials may be applied thereto. That is, it may be desirable for some applications to alter and control the conductivity or triboelectric properties of the magnetic composite carrier particles of this invention. Thus, this may be accomplished by applying thereto typical insulating carrier coating materials as described by L.E.

Walkup in U.S. Patent 2,618,551; B.B. Jacknow et al in U.S. Patent 3,526,533; and R.J.

Hagenbach et al in U.S. Patents 3,533,835 and 3,658,500. Typical electrostatographic carrier particle coating materials include vinyl chloride-vinyl acetate copolymers, poly-pxylylene polymers, styrene-acrylate-organosilicon terpolymers, natural resins such as caoutchouc, colophony, copal, dammar, Dragon's Blood, jalap, storax; thermoplastic resins including the polyolefins such as polyethylene, polypropylene, chlorinated polyethylene, and chlorosulfonated polyethylene; polyvinyls and polyvinylidenes such as polystyrene, polymethylstyrene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ethers, and polyvinyl ketones; fluorocarbons such as polytetrafluorethylene, polyvinyl fluoride, polyvinylidene fluoride; and polychlorotrifluoroethylene; polyamides such as polycaprolactam and polyhexamethylene adipamide; polyesters such as polyethylene terephthalate; polyurethanes; polysulfides, polycarbonates; thermosetting resins including phenolic resins such as phenol-formaldehyde, phenol-furfural and resorcinol formaldehyde; amino resins such as urea-formaldehyde and melamineformaldehyde; polyester resins and epoxy resins.

When the magnetic composite carrier particles of this invention are overcoated with an insulating resinous material any suitable electrostatographic carrier coating thickness may be employed. However. a polymeric coating having a thickness at least sufficient to form a thin continuous film on the carrier particle is preferred because the carrier coating will then possess sufficient thickness to resist abrasion and prevent pinholes which adversely affect the triboelectric properties of the coating carrier particles. Generally, for cascade and magnetic brush development, the carrier coating may comprise from 0.1 percent to 30.0 percent by weight based on the weight of the coated composite carrier particles.Preferably, the carrier coating should comprise from 0.2 percent to 2.0 percent by weight based on the weight of the coated carrier particles because maximum durability, toner impaction resistance, and copy quality are generally achieved.

Any suitable solvent or suspending medium may be employed in the above-outlined thermal decomposition process of preparing the carrier particles of this invention. Typical solvents and suspending mediums may be hydrocarbon solvents with boiling points preferably above that of the transition metal compound employed. Satisfactory results have been obtained with n-octane.

In addition to preparing the carrier particles of this invention by solution phase thermal decompositon of transition metal carbonyls, it is also possible to prepare them via chemical vapour deposition usingfluidized bed techniques. Thus, magnetic nickel deposits, for example, may be placed in the pores of a low density silicaceous substrate by thermal decomposition of nickel tetracarbonyl in a fluidizing bed apparatus. Typically, such a reactor has a cone-shaped bottom with proportionately-zied capillary tube gas inlets at the apex. To avoid plugging of the apparatus by premature decomposition of the carbonyl, the capillary zone and about one-half of the cone height is usually cooled by heat transfer means. In addition, the top half of the cone and a portion of the reactor is heated to provide the desired temperature to the substrate.In operation, nickel carbonyl vapor is supplied by bubbling a fluidizing gas such as hydrogen through the liquid at room temperature to provide the desired volume percent vapor in the reactant stream. Where desired, carbon monoxide may be added to the reactant stream to suppress gas phase decomposition of the carbonyl. The gas stream from the reactor is then passed through an oil bubbler and burned in a hood to oxidize poisonous carbon monoxide and any unreacted carbonyl vapors as well as to avoid accumulation of explosive mixtures of hydrogen. Preferably, the apparatus is located in a well-ventilated area or in a fume hood to preclude accidental exposure to noxious fumes. Vibrators are preferably attached to the reactor to promote uniformity of coating deposition and aid in returning to the fluidized bed those particles which may adhere to reactor walls above the active bed.

Any suitable well known toner material may be employed with the carriers of this invention. Typical toner materials include gum copal, gum sandarac, rosin, cumaroneindene resin asphaltum, gilsonite, phenolformaldehyde resins, rosin modified phenolformaldehyde resins, methacrylic resins, polystyrene resins, polypropylene resins, epoxy resins polyethylene resins, polyester resins, and mixtures thereof. The particular toner material to be employed obviously depends upon the separation of the toner particles from the magnetic carrier in the triboelectric series and the separation should be sufficient to cause the toner particles to electrostatically cling to the carrier surface. Among the patents describing electrocscopic toner compositions are U.S. Patent 2,659,670 to Copley; U.S. Patent 2,753,308 to Landrigan; U.S. Patent 3,079,342 to Insalaco; U.S.Patent Reissue 25,136 to Carlson and U.S. Patent 2,788,288 to Rheinfrank et al. These toners generally have an average particle diameter between 1 and 30 microns.

Any suitable colorant such as a pigment or dye, may be employed to color the toner particles. Toner colorants are well known and include, for example, carbon black, nigrosine dye, aniline blue, Calco Oil Blue, chrome yellow, ultramarine blue, Quinoline Yellow, methylene blue chloride, Monastral Blue, Malachite Green Ozalate, lampblack, Rose Bengal, Monastral Red, Sudan Black BM, and mixtures thereof. The pigment or dye should be present in a quantity sufficient to render it highly coloured so that it will form a clearly visible image on a recording member. Preferably, the pigment is employed in an amount from 3 percent to 20 percent by weight based on the total weight of the coloured toner because high quality images can be obtained. If the toner colourant employed is a dye, substantially smaller quantities of colourant may be used.

Any suitable conventional toner concentration may be employed with the low density magnetic carriers of this invention. Typical toner concentrations for development systems include 1 part toner with 10 to 200 parts by weight of carrier. When employing the carriers of this invention for development of electrostatic latent images, the amount of toner material present generally should be from 10 percent to 100 percent of the surface area of the carrier particles.

The carrier materials of the present invention may be mixed with finely-divided toner particles and employed to develop electrostatic latent images on any suitable electrostatic latent image-bearing surface including conventional photoconductive surfaces. Typical inorganic photoconductor materials include: sulfur, selenium, zinc sulfide, zinc oxide, zinc cadmium sulfide, zinc magnesium oxide, cadmium selenide. zinc silicate, calcium strontium sulfide, cadmium sulfide, mercuric iodide, mercuric oxide, mercuric sulfide, indium trisulfide, gallium selenide arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfoselenide, and mixtures thereof.Typical organic photoconductors include: quinacridone pigments, phthalocyanine pigments, triphenylamine, 2,4-bis(4,4' diethylaminophenol)-1,3,4-oxadiazol, N-isopropylcarbazole, triphenylpyrrole, 4,5diphenylimidazolidinone, 4,5-diphenylimidazolidinethione, 4,5-bis-(4' amino-phenyl)- imidazolidinone, 1 ,4-dicyanonaphthalene, 1 ,4-dicyanonaphthalene, aminophthalocinitrile, nitrophthalodinitrile, 12,3,5,6-tetra- azacyclooctatetraene-(2,4,6,8), 2-mercaptobenzothiazole-2- phenyl-4-diphenylidene-oxazolone, 6hydroxy-2,3-di(p-methoxyphenyl)- benzofurane, 4-dimethylamino-benzlyidene- The carrier materials produced by the process of this invention provide numerous advantages when employed to develop electrostatic latent images.For example, it has been found that carrier of reduced density reduces levels of mechanical stress in xerographic developer compositions, the reduction resulting in lower toner impaction levels.

In the following Examples, iron pentacarbonyl (99.5 percent purity) was obtained from Ventron Corporation, Danvers, Mass. and filtered before use to remove iron oxides.

N-octane (practical) was obtained from Eastman-Kodak Company, Rochester, N.Y. and refluxed over sodium for at least 24 hours and distilled before use. Dicobalt octacarbonyl was obtained from Strem Chemical Company, Andover, Mass.

Porous glass beads were obtained from PPG Industries, Pittsburg, Pa. and were used as received. Similar porous glass particles were obtained from Corning Glass Works, Corning, N.Y. as 7930 glass in the form of chips and were used as received. Material transfers from the pretreatment stages to suspension in a solvent was effected in an inert atmosphere of dry nitrogen.

Thermal decompositions of the carbonyls were carried out in solution in round-bottom flasks with reflux condenser and heating mantle under dry nitrogen at approximately one atmosphere pressure. All decompositions were carried out in vented hoods and in some cases CO effluent was passed through solutions of phosphomolybdic acid in the present of palladium chloride to produce molybdenum blue and carbon dioxide.

The following Examples further define, describe, and compare preferred methods of preparing and utilizing the carriers which were, in each case, in accordance with the present invention in electrostatographic applications. Parts and percentages are by weight unless otherwise indicated.

EXAMPLE I A mixture of about 10 grams of porous glass beads (XO- 1, PPG) having an average particle diameter of between 80 and 150 microns, about 10 ml of Fe(CO)5, and about 50 ml of n-octane was refluxed for about 24 hours in a 300 ml flask. No stirring was provided. Coated bead clumping within the flask was noted and about 5 grams of material was isolated by collecting the suspended solid, after cooling by filtration, washing it with octane, acetone and ethyl either, and then drying it. The beads thus obtained had a brilliant luster.

EXAMPLE II A mixture of about 20 grams of porous glass beads (XO- 1, PPG) having an average particle diameter of between 8 and 150 microns, about 40 ml of Fe(CO)5, and about 200 ml of n-octane was refluxed in a 500 ml flask for about 24 hours with gentle stirring. Approximately 30 grams of shiny black beads were isolated as in Example I. The beads appeared to be impregnated with iron or an iron oxide.

EXAMPLE III A mixture of about 1 gram of glass chips (Corning 7930) having an average particle diameter of between 90 and 140 microns, about 2 ml of Fe(CO)5, and about 10 ml of n-octane was refluxed in a 50 ml flask for about 2 hours. The contents were filtered after cooling and about 1.2 grams of material was recovered which had a bulk density of about 1 g/cm3.

Microscopic examination of the chips at 70X showed a reflective iron coat on the chips. The bulk material appeared black, probably due to high absorption by the multi-reflective chips.

Magnetic measurements were made with a Princeton Applied Research Vibrating Sample Magnetometer, which measures magnetization M, at fields from 0 to 7,000 gauss. The instrument has a sensitivity of better than I x 104 emu/gauss and the accuracy and resettability of the applied field is within 1 gauss. The system was calibrated with a Ni standard (55.0 emu/gm) in a saturation field of 7 kilogauss. The magnetization, M, is read out digitally, directly in emu's. Mass magnetization, a, was obtained by dividing M by the sample mass in grams. The samples were contained in cylindrical Kel-F holders approximately 1/4 inch in diameter and height. The amount of material used, 25 to 35 mg. was varied so that the volume of the sample would remain approximately the same. In the values reported, no attempt was made to account for the bulk shape demagnetization effects of the samples. The magnetization values obtained below the saturation region are the effective values for the above sample configuration. Packing density of the material was assumed to be the same in the hand tamped holder and in an uncompressed but tamped container. The materials of the Examples can be efficiently collected into magnetic brushes and manipulated magnetically with a bar magnet or in laboratory magnetic brush fixtures. The magnetic properties of the materials of the Examples were characterized as follows.

The magnetic parameters of the carrier materials produced in Examples I to III are listed in Table I and the actual magnetization curves obtained with the vibrating sample magnetome ter are shown in Figures 1 and 2. The field limit of the magnet used was 7 kilogauss and this was taken as the saturation field, although as can be seen in Figure 1, saturation for some of the samples has still not been attained.Table I is as follows: TABLEI Magnetic Parameters of Transition Metal Coated Low Density Substrates Example Description Saturation MagnestizationRemanenceCoercive Force Permeability r at field of cratfieldof 7000G 200G R Hc (emu/g) (emu/g) (emu/g) (Gauss) 1èff I Fe/porousglass 37.3 17.4 1.3 14 II jFe/porousglass 26.4 5.8 3.5 90 III Fe/porous glass 5.9 1.90 1.0 90 1.1 The material of Example I consists of elemental iron on a pure (99.5 percent) SiO2 substrate. This material has basically the following magnetic characteristics; that is, high saturation magnetization and initial susceptibility, small remanence and coercive force.

Furthermore, the magnetic behavior displayed by this material is consistent with that of magnetically soft iron.

Referring to Example III, the effective permeability, CLeff, may be obtained from the field H, the initial susceptibility data a and the measured bulk density (calculated within 5 percent) eof the materials by the following relation: gaeff = 1 +4ir(M/H) = 1 4 7r ((r < /H) where magnetization, M, is in emu/cm3. Since these magnetically coated carrier particles are spherical, the initial permeability of the individual bead is dependent upon shape demagnet ization effects and in this case is limited to a value of 3. However, in the compacted "powder" form in which the beads are measured, particle-particle interactions and the shape demagnet ization of the bulk sample can also introduce changes in the effective demagnetization effects.

The value given in Table I falls within the expected range.

The materials of Examples II and III show a distinct departure in the magnetic parameters (Figure 2) Xi (initial susceptibility), a sat (magnetic moment at saturation), aR (remanence) and He from those of Example I. The initial susceptibility is now quite small and the magnetization shows a very flat approach to saturation at high fields (Figure 1). In all cases the coercive force He has increased significantly. These changes in Xi and He for the present Examples reflect the morphological changes in the coating where we are no longer dealing with pure elemental iron. Optical examination of the material of Example III (glass chips) showed a wide variation in the coating of this material.The material of Example II differed entirely from the preceding iron coated porous bead material, i.e., Example I in that no surface coat of elemental iron appeared; rather, the beads appeared impregriated, possibly with black iron oxides. The reason for this change in final material as compared with that of Example i is not clear. Reaction mixture contamination or reaction time may be responsible.

The magnetic changes observed in the materials of Examples II and III are believed to be due to the different surface compositions, resulting from the formation of discontinuous coating regions of isolated iron or iron oxide particles on the surface of the materials.

From these observations, it may be concluded that the thermal decomposition of transition metal carbonyls such as iron pentacarbonyl onto low density silicaceous substrates produces mechanically and chemically stable composites which have the original substrate configura tion, and which, additionally, display highly magnetic behaviour. The magnetic behaviour observed for these low density magnetic composites ranges from that typical of magnetically soft iron to that typical of magnetically hard cobalt. The composites are, therefore, magnetic equivalents to their magnetic constituent yet afford a drastic -reduction in density. The composites show good initial magnetic response (indicated by a relatively high ,a in the case of Example [II) indicating the use of these materials as low density magnetic carrier particles.

Further, the various magnetic parameters, ms (saturation magnetisation), Hc, ,u eff of the low density magnetic materials can be controlled by varying the preparation and starting components of the materials. This type of control offers a wide latitude in design parameters not easily achieved with solid or high density magnetic carriers. In addition, there is a direct relationship between the magnetic characteristics of the low density composites and their surface composition and morphology as reflected in the relative values of Xi, Ms and He for the materials of the various Examples.

EXAMPLES IV- IX One lot of spherical particles coated with chemical vapour deposited nickel 2.0 microns thick on porous glass beads; and five lots of spherical particles coated with chemical vapor deposited iron from 0.9 to 1.5 microns thick on porous glass beads were prepared. Coatings and impregnations were prepared by thermal decompositon of the respective carbonyls using fluidized bed techniques. The materials were characterized with respect to coating thickness.

Table II summarizes these results.

TABLEII Coating Density, g/cm 3 Example No. Substrate(a) Material Thickness, Bulk(b) Absolute(", Weight, g IV Porous Glass Ni 2.0 --- 0.8 10 V Porous Glass Fe --(d) -- --- 27 VI Porous Glass Fe 1.5 --- --- 42 VII Porous Glass Fe 1.2 0.797 1.246 420 VIII Porous Glass Fe 0.9 0.736 1.191 540 IX Porous Glass Fe 1.0 0.772 1.256 480 (a) Porous glass, XO-5: 100-,u average beads, furnished by Pittsburg Plate Glass Inc., Pittsburg, Pa.

(b) Based on weight of vibratorily compacted known volume of particles.

(c) Determined by xylene pycnometer method.

(d) Deposit penetrated substrate; no coating.

WHAT WE CLAIM IS:- 1. A process for preparing a magnetically-responsive low density electrostatographic composite carrier material, said process comprising thermally decomposing a transition metal carbonyl, substantially in the absence of air and moisture, and in the presence of particles of a porous silicaceous material having a bulk density of between 0.2 and 3.0 grams/cm3 and an average particle diameter of from 10 microns to 850 microns, said silicaceous material being micro-reticulated and having pores with an average pore size of from 10 to 500 Angstroms, whereby said silicaceous material is impregnated with the magnetic elemental metal and/ or metal oxide.

2. A process according to claim 1, wherein the thermal decomposition of said metal carbonyl is carried out by forming a mixture of said particles of porous silicaceous material, said carbonyl and a suspending medium in a vessel, and heating the mixture with agitation to reflux temperature, substantially in the absence of air and moisture, for up to 24 hours at the temperature of said suspending medium.

3. A process according to claim 2, wherein said suspending medium is a hydrocarbon solvent.

4. A process according to claim 3,wherein said hydrocarbon solvent is n-octane.

5. A process according to claim 1, wherein the thermal decompositon of said metal carbonyl is carried out by forming, in a fluidising bed apparatus, a mixture of said particles of porous silicaceous material and said carbonyl, said mixture being heated with agitation to reflux temperature. substantially in the absence of air and moisture.

6. A process according to anyone of claims 1 to 5, wherein said metal or metal oxide is deposited within said pores of said silicaceous material in the form of continuous threads or networks.

7. A process according to any one of claims 1 to 6. wherein said silicaceous material and said elemental metal are present in a volume ratio of from between 5:1 to 20: 1.

8. A process according to any one of claims I to 7, wherein said silicaceous material has a surface area of up to 250 m2/gram.

9. A process according to any one of claims 1 to 8, including overcoating said composite carrier particles with an insulating polymeric resin in an amount sufficient to form a thin

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (22)

**WARNING** start of CLMS field may overlap end of DESC **. Further, the various magnetic parameters, ms (saturation magnetisation), Hc, ,u eff of the low density magnetic materials can be controlled by varying the preparation and starting components of the materials. This type of control offers a wide latitude in design parameters not easily achieved with solid or high density magnetic carriers. In addition, there is a direct relationship between the magnetic characteristics of the low density composites and their surface composition and morphology as reflected in the relative values of Xi, Ms and He for the materials of the various Examples. EXAMPLES IV- IX One lot of spherical particles coated with chemical vapour deposited nickel 2.0 microns thick on porous glass beads; and five lots of spherical particles coated with chemical vapor deposited iron from 0.9 to 1.5 microns thick on porous glass beads were prepared. Coatings and impregnations were prepared by thermal decompositon of the respective carbonyls using fluidized bed techniques. The materials were characterized with respect to coating thickness. Table II summarizes these results. TABLEII Coating Density, g/cm 3 Example No. Substrate(a) Material Thickness, Bulk(b) Absolute(", Weight, g IV Porous Glass Ni 2.0 --- 0.8 10 V Porous Glass Fe --(d) -- --- 27 VI Porous Glass Fe 1.5 --- --- 42 VII Porous Glass Fe 1.2 0.797 1.246 420 VIII Porous Glass Fe 0.9 0.736 1.191 540 IX Porous Glass Fe 1.0 0.772 1.256 480 (a) Porous glass, XO-5: 100-,u average beads, furnished by Pittsburg Plate Glass Inc., Pittsburg, Pa. (b) Based on weight of vibratorily compacted known volume of particles. (c) Determined by xylene pycnometer method. (d) Deposit penetrated substrate; no coating. WHAT WE CLAIM IS:-

1. A process for preparing a magnetically-responsive low density electrostatographic composite carrier material, said process comprising thermally decomposing a transition metal carbonyl, substantially in the absence of air and moisture, and in the presence of particles of a porous silicaceous material having a bulk density of between 0.2 and 3.0 grams/cm3 and an average particle diameter of from 10 microns to 850 microns, said silicaceous material being micro-reticulated and having pores with an average pore size of from 10 to 500 Angstroms, whereby said silicaceous material is impregnated with the magnetic elemental metal and/ or metal oxide.

2. A process according to claim 1, wherein the thermal decomposition of said metal carbonyl is carried out by forming a mixture of said particles of porous silicaceous material, said carbonyl and a suspending medium in a vessel, and heating the mixture with agitation to reflux temperature, substantially in the absence of air and moisture, for up to 24 hours at the temperature of said suspending medium.

3. A process according to claim 2, wherein said suspending medium is a hydrocarbon solvent.

4. A process according to claim 3,wherein said hydrocarbon solvent is n-octane.

5. A process according to claim 1, wherein the thermal decompositon of said metal carbonyl is carried out by forming, in a fluidising bed apparatus, a mixture of said particles of porous silicaceous material and said carbonyl, said mixture being heated with agitation to reflux temperature. substantially in the absence of air and moisture.

6. A process according to anyone of claims 1 to 5, wherein said metal or metal oxide is deposited within said pores of said silicaceous material in the form of continuous threads or networks.

7. A process according to any one of claims 1 to 6. wherein said silicaceous material and said elemental metal are present in a volume ratio of from between 5:1 to 20: 1.

8. A process according to any one of claims I to 7, wherein said silicaceous material has a surface area of up to 250 m2/gram.

9. A process according to any one of claims 1 to 8, including overcoating said composite carrier particles with an insulating polymeric resin in an amount sufficient to form a thin

continuous film thereon.

10. A process according to any one of claims 1 to 9, wherein said transition metal carbonyl is selected from: iron pentacarbonyl, dicobalt octacarbonyl, and nickel tetracarbonyl.

11. A process according to any one of claims 1 to 9, wherein said magnetic metal is selected from: iron, nickel, and cobalt.

12. A process for preparing a magnetically responsive, low density electrostatographic composite carrier material, said process being substantially as described in any one of the foregoing Examples I to IX.

13. A particulate carrier material whenever prepared by a process in accordance with any one of claims 1 to 12.

14. A magnetically-responsive, low density electrostatographic composite particulate carrier material having an average particle diameter of from 10 microns to 850 microns, said carrier particle comprising a porous silicaceous material having an average bulk density of between 0.2 and 3.0 grams/cm3, said silicaceous material being micro-reticulated and having pores with an average pore size of from 10 to 500 Angstroms, said porous silicaceous material being impregnated with a magnetic or magnetically-attractable transition metal and/or metal oxide thereof.

15. A carrier material according to claim 14, wherein said metal or metal oxide is deposited within said pores of said silicaceous material in the form of continuous threads or networks.

16 A carrier material according to claim 12 or claim 13, wherein said silicaceous material has a surface area of up to 250 m2/gram.

17. A carrier material according to any one of claims 14 to 16, wherein said silicaceous material and said metal or metal oxide are present in a volume ratio of from between 5:1 to 20:1.

18. A carrier material according to any one of claims 14 to 17, wherein said composite carrier particle has an overcoating of an insulating polymeric resin in an amount sufficient to form a thin continuous film thereon.

19. A carrier material according to any one of claims 14 to 18, wherein said metal or metal oxide is selected from: iron, nickel, and cobalt.

20. An electrostatographic developer mixture comprising finely-divided toner particles electrostatically clinging to the surfaces of a particulate carrier material in accordance with any one of claims 13 to 20.

21. A developer mixture according to claim 20, wherein said toner particles are present in an amount of from 10 percent to 100 percent of the surface area of the carrier particles.

22. A method of developing an electrostatic latent image on an electrostatic latent image-bearing surface, the method comprising: contacting said surface with an electrostatographic developer mixture in accordance with claim 20 or claim 21, whereby at least a portion of the toner particles of the developer mixture are attracted to and deposited on said surface in conformance with said electrostatic latent image.