CA1103079A - Semi-conductive steel carrier particles - Google Patents
Semi-conductive steel carrier particlesInfo
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- CA1103079A CA1103079A CA272,453A CA272453A CA1103079A CA 1103079 A CA1103079 A CA 1103079A CA 272453 A CA272453 A CA 272453A CA 1103079 A CA1103079 A CA 1103079A
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Abstract
SEMI-CONDUCTIVE STEEL CARRIER PARTICLES
ABSTRACT OF THE DISCLOSURE
Magnetically-responsive electrostatographic carrier particles having semi-conductive properties are prepared by firing steel shot particles in an oxygen deficient atmosphere as to provide the carrier particles with an oxide coating.
More particularly, commercially available steel shot is placed in a furnace wherein the atmosphere has an oxygen content of less than about 18 percent oxygen and the steel shot is fired at a temperature of between about 900°F and about 1600°F
for a period of time of between about 10 minutes and up to about 2 hours. When employed with finely-divided toner particles to develop electrostatic latent images in a magnetic-brush development apparatus, the carriers have been found to provide developed images having lower background densities and higher resolution than prior known carrier materials.
ABSTRACT OF THE DISCLOSURE
Magnetically-responsive electrostatographic carrier particles having semi-conductive properties are prepared by firing steel shot particles in an oxygen deficient atmosphere as to provide the carrier particles with an oxide coating.
More particularly, commercially available steel shot is placed in a furnace wherein the atmosphere has an oxygen content of less than about 18 percent oxygen and the steel shot is fired at a temperature of between about 900°F and about 1600°F
for a period of time of between about 10 minutes and up to about 2 hours. When employed with finely-divided toner particles to develop electrostatic latent images in a magnetic-brush development apparatus, the carriers have been found to provide developed images having lower background densities and higher resolution than prior known carrier materials.
Description
~1~3Q~9 ~-BACKGRO~ND OF T~ INVENTION
. . _ This invention relates in general to electrophotography and more particularly, to a process for preparing carrier materials useful in the magnetic~brush type development of electrostatic latent images.
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 subse~uently 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 clectrostatic latent image to be developed. One 3~7~
development method, as disclosed by E. N. Wise in U. S. Patent
. . _ This invention relates in general to electrophotography and more particularly, to a process for preparing carrier materials useful in the magnetic~brush type development of electrostatic latent images.
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 subse~uently 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 clectrostatic latent image to be developed. One 3~7~
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
yeneral 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 7~
and the toner particles are drawn from the brush ~o the electro-static image by electrostatic attraction.
In magnetic-brush development of electrostatic images, the developer is commonly a triboelectric mixture of finely-divided toner powder comprised of dyed or pigmented thermoplastic resin 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 to some extent possible to develop part of the tones in pictures and solid blacks as well as line copy. This brush developing sometimes makes this mode of developing advantageous where it is desired to copy materials other than simple line copy. One difficulty with such counter-electrode development is that the exposure latitude obtainable is limited. Consequently, for certain applications, it is desirable to suppress the counter-electrode effect in order to obtain improved exposure latitude.
One method of suppressing the counter-electrode effect is to use a carrier material which has a high electrical resistance.
It is well-known to provide a carrier material which has a high electric resistance. A conventional method of obtaining a carrier material which has a high electrical resistance is to apply a coating of insulating material to a carrier substrate.
However, coated carrier beads are subject to deterioration when the coating separates from the carrier core as the carrier particles are repeatedly impacted and abraded against machine parts and 11~3V~i'9 other carrier particles. The separated coatings form chips and flakes which cause print deletion and poor print quality; and fines and grit which tend to drift and form unwanted deposits on critical machine parts. In addition, the triboelectric properties of the carrier material vary with deterioration of the coating, resulting in inefficient carrier performance.
Further, most currently available insulated ferro-magnetic carrier particles having an electrical resistance which is too high to produce good quality solid area development. When not insulated, they are too conductive to entirely suppress the counter-electrode effect. One reason for the lack of uniformity in the electrical properties of uncoated carrier particles is that the particles carry surface dirt, such as grease, oil, and other contaminants. It has been suggested in the prior art that typical conductive carrier particles can be treated with methanol, iso-propanol, and other alcohols to rid the carrier of grease, oil, etc.
However, the prior art has not recognized the hetero-geneous nature of the surface of the uncoated carriers used in this art. In addition, no recognition has been given to the resulting complications in magnetic-brush processing which arise from using some of the presently available materials. The extraneous surface dirt found on the available carrier particles is only part of the problem. In addition to the dirt, the carrier particles invariably carry a non-uniform distribution of oxide. When materials of this type are used in conventional magnetic brushes, the carrier is in continuous motion and the constant friction of the particles against one another and against the various mechanical parts gradually remove bits of this non-uniform surface material.
The attrition will, of course, vary from point to point on a
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
yeneral 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 7~
and the toner particles are drawn from the brush ~o the electro-static image by electrostatic attraction.
In magnetic-brush development of electrostatic images, the developer is commonly a triboelectric mixture of finely-divided toner powder comprised of dyed or pigmented thermoplastic resin 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 to some extent possible to develop part of the tones in pictures and solid blacks as well as line copy. This brush developing sometimes makes this mode of developing advantageous where it is desired to copy materials other than simple line copy. One difficulty with such counter-electrode development is that the exposure latitude obtainable is limited. Consequently, for certain applications, it is desirable to suppress the counter-electrode effect in order to obtain improved exposure latitude.
One method of suppressing the counter-electrode effect is to use a carrier material which has a high electrical resistance.
It is well-known to provide a carrier material which has a high electric resistance. A conventional method of obtaining a carrier material which has a high electrical resistance is to apply a coating of insulating material to a carrier substrate.
However, coated carrier beads are subject to deterioration when the coating separates from the carrier core as the carrier particles are repeatedly impacted and abraded against machine parts and 11~3V~i'9 other carrier particles. The separated coatings form chips and flakes which cause print deletion and poor print quality; and fines and grit which tend to drift and form unwanted deposits on critical machine parts. In addition, the triboelectric properties of the carrier material vary with deterioration of the coating, resulting in inefficient carrier performance.
Further, most currently available insulated ferro-magnetic carrier particles having an electrical resistance which is too high to produce good quality solid area development. When not insulated, they are too conductive to entirely suppress the counter-electrode effect. One reason for the lack of uniformity in the electrical properties of uncoated carrier particles is that the particles carry surface dirt, such as grease, oil, and other contaminants. It has been suggested in the prior art that typical conductive carrier particles can be treated with methanol, iso-propanol, and other alcohols to rid the carrier of grease, oil, etc.
However, the prior art has not recognized the hetero-geneous nature of the surface of the uncoated carriers used in this art. In addition, no recognition has been given to the resulting complications in magnetic-brush processing which arise from using some of the presently available materials. The extraneous surface dirt found on the available carrier particles is only part of the problem. In addition to the dirt, the carrier particles invariably carry a non-uniform distribution of oxide. When materials of this type are used in conventional magnetic brushes, the carrier is in continuous motion and the constant friction of the particles against one another and against the various mechanical parts gradually remove bits of this non-uniform surface material.
The attrition will, of course, vary from point to point on a
3~
carrier particle depending on the nature of the deposit, its thickness, friability, adhesion to the underlying structure, and the like. Thus, with the available carrier materials, a progressive change occurs in the character of the carrièr surface during use.
Correspondingly, the nature of the admixed toner also changes as it becomes contaminated with the fine particles which have separated from the surface of the carrier.
Accordingly, there is a need for electrostatographic carriers which will present a more nearly homogeneous surface and which will have stable triboelectric and other properties even during continued use. Furthermore, there is a need for carrier particles which will enhance the counter-electrode effect and thus improve the solid-area type development obtainable in magnetic brush processing. Also, there is a need for carrier particles which can repress the counter-electrode effect so that fringing development will be induced with its accompanying improvement in exposure latitude.
It is, therefore, an object of an aspect of this invention to provide a method for preparing electrostatographic carrier materials which overcomes the above noted deficiencies.
It is an object of an aspect of this invention to provide a simple economic process for preparing magnetically responsive carrier particles having a homogeneous surface.
It is an object of an aspect of this invention to provide a process for preparing magnetically responsive carrier particles which have semi-conductive properties.
An object of an aspect of this invention is to provide new developer compositions for use in magnetic brush development.
It is an object of an aspect of this invention to provide developer materials having physical and electrical ~, ~;. :. ....................................................... .
~3~'7~
properties superior to those of known developer material.
In accordance with one aspect of this invention there is provided a magnetically-responsive, semi-conductive electrostatographic carrier particle having an average particle diameter of from between about 30 microns and about 1,000 microns, said carrier particle having been prepared by firing metallic, magnetic particles in an atmosphere having an oxygen content of between about 1 percent and about 18 percent by weight at a temperature of between about 900F and about 1600F for between about 10 minutes and up to about 2 hours whereby said particles are provided with an oxide coating having a thickness of between about 0.25 micron and.about 5 microns.
In accordance with another aspect of this inven-15 tion there is provided an electrostatographic developer mixture comprising finely-divided toner particles electro-statically, clinging to the surface of a carrier, said carrier comprising magnetically-responsive, semi-conductive electrostatographic carrier particles ha~ing an average partiale diameter of from between ahout 30 microns and about 1,000 microns, said carrier particles having been prepared by firing metallic, magnetic parti.cles in an atmosphere having an oxygen content of . .
between about 1 percent and about 18 percent by weight 25 at a temperature of between about 900F and about 1600F for between about 10 minutes and up to about 2 . -hours whereby said carrier particles are.provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns.
In accordance with another aspect of this inven-tion there is provided an electrostatographic imaging . .~ i ~3~
process comprising the steps of providing an electro- . .
statographic imaging member having a recording surface, forming an electrostatic latent image on said recording surface, and contacting said electrostatic latent image with a developer mixture comprising finely-divided toner particles electrostatically clinging to the surface of a carrier, said carrier comprising magnetic-ally-responsive, semi-conductive electrostatographic carrier particles having an average particle diameter of from~between about 30 microns and about 1,000 microns, said carrier particles having been prepared by firing metallic, magnetic particles in an atmosphere having an oxygen content of between about 1 percent and about 18 percent by weight at a temperature of between about 900F and about 1600F for between about 10 minutes and up to about 2 hours whereby said carrier particles are provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns, whereby at least a portion of said finely-divided toner particles are attracted to and deposited on said record-ing surface in conformance with said electrostatic latent image.
In accordance with another aspect of this invention there is provided a process for preparing magnetically-responsive, semi-conductive electrostato-graphic carrier particles having an average particle diameter of from between about 30 microns and about 1,000 microns, said process comprising firing metallic, magnetic particles in an atmosphere having an oxygen content of betwee~ about 1 percent and about 18 percent by weight at a temperature of between about 900F
-7a-and about 16000F for between about 10 minutes and up to about 2 hours whereby said carrier particles are provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns.
By way of added explanation, in accordance with an aspect of this invention steel shot carrier particles are fired in an oxygen deficient atmosphere as to provide the carrier particles with an oxide coating. That is, steel carrier particles are fired in a controlled atmos-phere under preselected conditions of time and temperature ~as to generate a suitable oxide coating on the particles.
More particularly, commercially available steel shot is placed in a furnace wherein the atmosphere has an oxygen content of less than about 18 percent oxygen and the steel shot is fired at a temperature of between about 900F
and about 1600F for a period of time of between about 10 ~inutes and up to about 2 hours. Steel shot carrier par-ticles fired in accordance with this invention are found to possess a surface oxide layer which is highly desirable with respect to their use in magnetic brush development electrostatographic copying and duplicating devices.
More specifically, steel shot carrier particles prepared in accordance with this invention when employed with finely-divided toner particles to develop electrostatic latent images in a magnetic-brush development apparatus have been found to provide developed images having lower background densities and higher resolution than prior known carrier materials. Although not wishing to be bound by any theory, it is believed that the improved results obtained are due to the semi-conductive properties of the carrier materials prepared by the process of this invention.
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.
The carrier materials which are suitable for treatment in accordance with this invention include ferromagnetic materials .~ .
~ -7c-3~:79 such as steel and iron powder in various forms. Thus, a wide variety of particulate, magnetically responsive materials the surface of which can be oxidized including materials in such forms as steel and iron particles produced by atomization of molten metal and subsequent cooling of the droplets; particles produced by grinding, milling, filing, turning, etc.; as well as particles of steel and iron alloys having oxidizable iron on the surface thereof such as stainless steel and iron alloys containing nickel and/or cobalt may be treated in accordance with this invention. The treated ferromagnetic carrier particles may vary in size and shape with useful results being obtained with average particle sizes of from about 30 microns to about 1,000 microns.
Particularly useful results are obtained with average particle sizes from about 50 microns to about 500 microns. The size of the carrier particles employed will, of course, depend upon several factors, such as the type of images ultimately developed, the machine configuration, and so forth.
In accordance with this invention, semi-conductive magnetically-responsive carrier particles having satisfactory electrostatoyraphic properties may be obtained by firing ferro-magnetic particles in an atmosphere containing between about 1 percent and about 18 percent by weight of oxygen at a temperature of between about 900F and about 1600F for between about 10 minutes and about 2 hours. However, it is preferred that the carrier particles of this invention be obtained by firing ferro-magnetic particles in an atmosphere containing between about 1 percent and about 12 percent by weight of oxygen at a temperature of between about 900F and about 1500F for between about 30 minutes and about 60 minutes to control oxide species and quality.
3~7~
optimum results are obtained when the carrier particles of this invention are fired in an atmosphere containing between about 4 percent and about 10 percent by weight of oxygen at a temperature of between about 965F and about 1470F for between about 30 minutes and about 60 minutes.
Any suitable type of furnace may be employed to fire the carrier particles of this invention. Typical furnaces include a static furnace, a rotary kiln, a tunnel kiln, or an agitated bed furnace. The static furnace type will generally provide for long residence times, while the rotary kiln and agitated bed type of furnace generally provide more uniform product reaction, con-sistent residence time, and high capacity throughout. During the treatment of the carrier particles as described, it is highly desirable to agitate the particles at least occasionally, so as to completely expose the surfaces of the particles for more uniform treatment thereof. In any event, a furnace providing a controlled firing temperature and controlled atmosphere profile provides a more controlled method of preparing the carrier particles.
The oxide coating produced upon the carrier particles of this invention may be any suitable thickness or weight percent.
However, an oxide sufficiently distributed at or near the surface to produce semi-conductive electrical characteristics is preferred because the carrier will then possess desirable triboelectric features and allow their application in electrode development sys-tems where RC (Resistance-Capacitance) time constant considerations are of importance in preventing high electrical discharges between the development electrode and the photoreceptor. Preferably the oxide should be so distributed through the preparation so that the carrier, where measured in the bead aggregate, should possess a volume resistivity between about 105 ohm-cm and 1012 ohm-cm. An oxide coating having a thickness of between about 0.25 micron and about 5 microns has been found to provide satisfactory results.
Any suitable well known toner material may be employed with the oxide coated 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 oxide coated carrier in the tribo-electric series and should be sufficient to cause the toner particles to electrostatically cling to the carrier surface. Among the patents describing electroscopic 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 about 1 and 30 microns.
Any suitable colorant such as a plgment 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 ~il Blue, chrome yellow, ultramarine blue, Quinoline Yellow, methylene blue chloride, Monastral Blue, Malachite Green Gzalate, 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 colored so that it will form a clearly visible image on a recording member.
.
.
'~7S
Preferably, the pigment is employed in an amount from about 3 percent to about 20 percent by weight based on the total weight of the colored toner because high quality images are obtained.
If the toner colorant employed is a dye, substantially smaller quantities of colorant may be used.
Any suitable conventional toner concentration may be employed with the oxide coated carriers of this invention.
Typical toner concentrations for development systems include about 1 part toner with about 10 to about 200 parts by weight of carrier.
The carrier materials of the instant 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 sur-faces. 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 tri-sulfide, gallium selenide arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfoselenide, and mixtures thereof.
Typical organic photoconductors include: quinacridone pigments, phthalocyanine pigments, txiphenylamine, 2,4-bis(4,4'-diethylamino-phenol)-1,3,4-oxadiazol, N-isopropylcarbazole, triphenylpyrrole,
carrier particle depending on the nature of the deposit, its thickness, friability, adhesion to the underlying structure, and the like. Thus, with the available carrier materials, a progressive change occurs in the character of the carrièr surface during use.
Correspondingly, the nature of the admixed toner also changes as it becomes contaminated with the fine particles which have separated from the surface of the carrier.
Accordingly, there is a need for electrostatographic carriers which will present a more nearly homogeneous surface and which will have stable triboelectric and other properties even during continued use. Furthermore, there is a need for carrier particles which will enhance the counter-electrode effect and thus improve the solid-area type development obtainable in magnetic brush processing. Also, there is a need for carrier particles which can repress the counter-electrode effect so that fringing development will be induced with its accompanying improvement in exposure latitude.
It is, therefore, an object of an aspect of this invention to provide a method for preparing electrostatographic carrier materials which overcomes the above noted deficiencies.
It is an object of an aspect of this invention to provide a simple economic process for preparing magnetically responsive carrier particles having a homogeneous surface.
It is an object of an aspect of this invention to provide a process for preparing magnetically responsive carrier particles which have semi-conductive properties.
An object of an aspect of this invention is to provide new developer compositions for use in magnetic brush development.
It is an object of an aspect of this invention to provide developer materials having physical and electrical ~, ~;. :. ....................................................... .
~3~'7~
properties superior to those of known developer material.
In accordance with one aspect of this invention there is provided a magnetically-responsive, semi-conductive electrostatographic carrier particle having an average particle diameter of from between about 30 microns and about 1,000 microns, said carrier particle having been prepared by firing metallic, magnetic particles in an atmosphere having an oxygen content of between about 1 percent and about 18 percent by weight at a temperature of between about 900F and about 1600F for between about 10 minutes and up to about 2 hours whereby said particles are provided with an oxide coating having a thickness of between about 0.25 micron and.about 5 microns.
In accordance with another aspect of this inven-15 tion there is provided an electrostatographic developer mixture comprising finely-divided toner particles electro-statically, clinging to the surface of a carrier, said carrier comprising magnetically-responsive, semi-conductive electrostatographic carrier particles ha~ing an average partiale diameter of from between ahout 30 microns and about 1,000 microns, said carrier particles having been prepared by firing metallic, magnetic parti.cles in an atmosphere having an oxygen content of . .
between about 1 percent and about 18 percent by weight 25 at a temperature of between about 900F and about 1600F for between about 10 minutes and up to about 2 . -hours whereby said carrier particles are.provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns.
In accordance with another aspect of this inven-tion there is provided an electrostatographic imaging . .~ i ~3~
process comprising the steps of providing an electro- . .
statographic imaging member having a recording surface, forming an electrostatic latent image on said recording surface, and contacting said electrostatic latent image with a developer mixture comprising finely-divided toner particles electrostatically clinging to the surface of a carrier, said carrier comprising magnetic-ally-responsive, semi-conductive electrostatographic carrier particles having an average particle diameter of from~between about 30 microns and about 1,000 microns, said carrier particles having been prepared by firing metallic, magnetic particles in an atmosphere having an oxygen content of between about 1 percent and about 18 percent by weight at a temperature of between about 900F and about 1600F for between about 10 minutes and up to about 2 hours whereby said carrier particles are provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns, whereby at least a portion of said finely-divided toner particles are attracted to and deposited on said record-ing surface in conformance with said electrostatic latent image.
In accordance with another aspect of this invention there is provided a process for preparing magnetically-responsive, semi-conductive electrostato-graphic carrier particles having an average particle diameter of from between about 30 microns and about 1,000 microns, said process comprising firing metallic, magnetic particles in an atmosphere having an oxygen content of betwee~ about 1 percent and about 18 percent by weight at a temperature of between about 900F
-7a-and about 16000F for between about 10 minutes and up to about 2 hours whereby said carrier particles are provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns.
By way of added explanation, in accordance with an aspect of this invention steel shot carrier particles are fired in an oxygen deficient atmosphere as to provide the carrier particles with an oxide coating. That is, steel carrier particles are fired in a controlled atmos-phere under preselected conditions of time and temperature ~as to generate a suitable oxide coating on the particles.
More particularly, commercially available steel shot is placed in a furnace wherein the atmosphere has an oxygen content of less than about 18 percent oxygen and the steel shot is fired at a temperature of between about 900F
and about 1600F for a period of time of between about 10 ~inutes and up to about 2 hours. Steel shot carrier par-ticles fired in accordance with this invention are found to possess a surface oxide layer which is highly desirable with respect to their use in magnetic brush development electrostatographic copying and duplicating devices.
More specifically, steel shot carrier particles prepared in accordance with this invention when employed with finely-divided toner particles to develop electrostatic latent images in a magnetic-brush development apparatus have been found to provide developed images having lower background densities and higher resolution than prior known carrier materials. Although not wishing to be bound by any theory, it is believed that the improved results obtained are due to the semi-conductive properties of the carrier materials prepared by the process of this invention.
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.
The carrier materials which are suitable for treatment in accordance with this invention include ferromagnetic materials .~ .
~ -7c-3~:79 such as steel and iron powder in various forms. Thus, a wide variety of particulate, magnetically responsive materials the surface of which can be oxidized including materials in such forms as steel and iron particles produced by atomization of molten metal and subsequent cooling of the droplets; particles produced by grinding, milling, filing, turning, etc.; as well as particles of steel and iron alloys having oxidizable iron on the surface thereof such as stainless steel and iron alloys containing nickel and/or cobalt may be treated in accordance with this invention. The treated ferromagnetic carrier particles may vary in size and shape with useful results being obtained with average particle sizes of from about 30 microns to about 1,000 microns.
Particularly useful results are obtained with average particle sizes from about 50 microns to about 500 microns. The size of the carrier particles employed will, of course, depend upon several factors, such as the type of images ultimately developed, the machine configuration, and so forth.
In accordance with this invention, semi-conductive magnetically-responsive carrier particles having satisfactory electrostatoyraphic properties may be obtained by firing ferro-magnetic particles in an atmosphere containing between about 1 percent and about 18 percent by weight of oxygen at a temperature of between about 900F and about 1600F for between about 10 minutes and about 2 hours. However, it is preferred that the carrier particles of this invention be obtained by firing ferro-magnetic particles in an atmosphere containing between about 1 percent and about 12 percent by weight of oxygen at a temperature of between about 900F and about 1500F for between about 30 minutes and about 60 minutes to control oxide species and quality.
3~7~
optimum results are obtained when the carrier particles of this invention are fired in an atmosphere containing between about 4 percent and about 10 percent by weight of oxygen at a temperature of between about 965F and about 1470F for between about 30 minutes and about 60 minutes.
Any suitable type of furnace may be employed to fire the carrier particles of this invention. Typical furnaces include a static furnace, a rotary kiln, a tunnel kiln, or an agitated bed furnace. The static furnace type will generally provide for long residence times, while the rotary kiln and agitated bed type of furnace generally provide more uniform product reaction, con-sistent residence time, and high capacity throughout. During the treatment of the carrier particles as described, it is highly desirable to agitate the particles at least occasionally, so as to completely expose the surfaces of the particles for more uniform treatment thereof. In any event, a furnace providing a controlled firing temperature and controlled atmosphere profile provides a more controlled method of preparing the carrier particles.
The oxide coating produced upon the carrier particles of this invention may be any suitable thickness or weight percent.
However, an oxide sufficiently distributed at or near the surface to produce semi-conductive electrical characteristics is preferred because the carrier will then possess desirable triboelectric features and allow their application in electrode development sys-tems where RC (Resistance-Capacitance) time constant considerations are of importance in preventing high electrical discharges between the development electrode and the photoreceptor. Preferably the oxide should be so distributed through the preparation so that the carrier, where measured in the bead aggregate, should possess a volume resistivity between about 105 ohm-cm and 1012 ohm-cm. An oxide coating having a thickness of between about 0.25 micron and about 5 microns has been found to provide satisfactory results.
Any suitable well known toner material may be employed with the oxide coated 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 oxide coated carrier in the tribo-electric series and should be sufficient to cause the toner particles to electrostatically cling to the carrier surface. Among the patents describing electroscopic 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 about 1 and 30 microns.
Any suitable colorant such as a plgment 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 ~il Blue, chrome yellow, ultramarine blue, Quinoline Yellow, methylene blue chloride, Monastral Blue, Malachite Green Gzalate, 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 colored so that it will form a clearly visible image on a recording member.
.
.
'~7S
Preferably, the pigment is employed in an amount from about 3 percent to about 20 percent by weight based on the total weight of the colored toner because high quality images are obtained.
If the toner colorant employed is a dye, substantially smaller quantities of colorant may be used.
Any suitable conventional toner concentration may be employed with the oxide coated carriers of this invention.
Typical toner concentrations for development systems include about 1 part toner with about 10 to about 200 parts by weight of carrier.
The carrier materials of the instant 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 sur-faces. 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 tri-sulfide, gallium selenide arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfoselenide, and mixtures thereof.
Typical organic photoconductors include: quinacridone pigments, phthalocyanine pigments, txiphenylamine, 2,4-bis(4,4'-diethylamino-phenol)-1,3,4-oxadiazol, N-isopropylcarbazole, triphenylpyrrole,
4,5-diphenylimidazolidinone, 4,5-diphenylimidazolidinethione, 4,5-bis-(4'amino-phenyl)-imidazolidinone, 1,5-dicyanonaphthalene, 1,4-dicyanonaphthalene, aminophthalocinitrile, nitrophthalo-dinitrile, 1,2,5,6-tetra-azacyclooctatetraene-(2,4,6,8), 2-mercaptobenzothiazole-2-phenyl-4-diphenylidene-oxazolone, 6-hydroxy-2,3-di(p-methoxyphenyl)-benzofurane, 4-dimethylamino-3~79 benzylidene-benzhydrazide, 3-benzylidene-aminocarbazole, polyvinyl carbazole, (2-nitrobenzylidene)-p-bromoaniline, 2,4-diphenyl-quinazoline, 1,2,4-triazine, 1,5-diphenyl-3-methyl-pyrazoline, 2-(4'-dimethylamino phenyl)-benzoxazole, 3-amine-carbazole, and mixtures thereof. Representative patents in which photoconductive materials are disclosed include U. S.
Patents 2,803,542 to Ullrich, U. S. Patent 3,121,0Q7 to Middleton, and U. S. Patent 3,151,982 to Corrsin.
The oxide coated carrier materials produced by the process of this invention provide numerous advantages when employed to develop electrostatic latent images. For example, when mixed with an appropriate toner material, the resultant developer composition is found to greatly reduce the development electrode effect of a magnetic brush. In addition, such a developer composition induces fringing development with an accompanying increase in exposure latitude. Further, such developer compositions are found to provide lower background densities, higher image resolutions, and greatly improved overall print qualities.
In the following examples, the relative triboelectric values generated by contact of carrier beads with toner particles is measured by means of a Faraday Cage. The device comprises a brass cylinder having a diameter of about one inch and a length of about one inch. ~ 100-mesh screen is positioned at each end of the cylinder. The cylinder is weighed, charged with about 0.5 gram mixture of carrier and toner particles and connected to ground through a capacitor and an electrometer connected in parallel. Dry compressed air is then blown through the brass cylinder to drive all the toner from the carrier. The charge on the capacitor is then read on the electrometex. Next, the ~3i[3 ~
chamber is reweighed to determine the weight loss. The resulting data is used to calculate the toner concentration and the charge in micro-coulombs per gram of toner. Since the triboelectric measurements are relative, the measurements should, for comparative purposes, be conducted under substantially identical conditions.
Thus, a toner comprising a styrene-n-butyl methacrylate copolymer and carbon black as disclosed by M. A. Insalaco in U. S. Patent 3,079,342 is used as a contact triboelectrification standard.
Obviously, other suitable toners such as those listed above may be substituted for the toner used in the examples.
The following examples, other than the control examples, further define, describe, and compare preferred methods of pre-paring and utilizing the oxide coated carriers of the present invention in electrostatographic applications. Parts and percen-tages are by weight unless otherwise indicated.
EXAMPLE I
A control developer mixture was prepared by mixing about 6 grams of toner particles comprising a styrene-n-butyl methacrylate copolymer and carbon black with about 300 grams of carrier particles. The carrier particles comprised steel shot having an average particle size of about 100 microns which is commercially available from Nuclear Metals, West Concord, Mass.
(Division of Whittaker Corporation). The developer mixture was employed to develop electrostatic latent images in a copying machine equipped with a magnetic brush development device. Said magnetic brush development fixture comprised 5 magnetic rolls, in series, which transported developer to the electrostatic image area which had been previously formed on the flat plate photo-conductive imaging surface of the fixture. During the test, 1~3~
extreme powder cloud effect was found. Background densities were approximately half of the solid area densities as measured with a Welch densitometer. Image resolution was very poor. It was concluded that this developer mixture was unsatisfactory.
EXAMPLE II
A developer mixture was prepared by mixing about 6 grams of toner particles as in Example I with about 300 grams of carrier particles. The carrier particles were as in Example I
except that they were treated as follows: the carrier particles were placed in a muffle furnace and heated to about 800C for about one hour in an atmosphere containing about 5 percent of oxygen.
After this treatment, the carrier particles were allowed to cool to ambient temperature and examined. The treated carrier particles were found to be gray-black in color and to have an oxide coating of between about 0.25 micron and about 5 microns in thickness.
The carrier particles were mixed with toner particles and employed to develop electrostatic latent images as in Example I. The oxidized carrier developer composition was found to exhibit much better qualities than that of Example I. That is, this developer composition provided images having good resolution with very good print quality. Background densities were very low, that is, on the order of about 0.002 at very high (1.3 - 1.4) solid area densities. A slight powder cloud effect was found at a solid area density of 1.35. The electrical characteristics of the carrier material were found to be within the desired semiconductive range and determined to be acceptably stable over a wide range of environmental humidity conditions as shown in Figure 1. Thus, reasonable assurance is provided for triboelectric charging capability and favorable RC development electrode field relaxation characteristics over a practical environmental humidity range.
It was concluded that this developer mixture was satisfactory.
~03~ ~
EXAMPLE III
A developer mixture was prepared by mixing about 6 grams of toner particles as in Example I with about 300 grams of carrier particles. The carrier particles were as in Example I
except that they were treated as follows: the carrier particles were placed in a high temperature rotary furnace and heated to about 500C for about 30 minutes in an atmosphere containing about 10 percent of oxygen. After this treatment, the carrier particles were allowed to cool to ambient temperature and examined.
The treated carrier particles were found to be gray-black in color and to have an oxide coating of between about 0.25 micron and about 1 micron in thickness. The carrier particles were mixed with toner particles and employed to develop electrostatic latent images as in Example I. The oxidized carrier developer composition was found to exhibit much better qualities than that of Example I. That is, this developer composition provided images having good resolution with very good print quality. Background densities were very low at very high (1.3 - 1.4) solid area densities. The electrical characteristics of the carrier material were found to be within the desired semi-conductive range and determined to be acceptably stable over a wide range of environmental humidity conditions as shown in Figure 2. It was concluded that this developer mixture was satisfactory.
Other modifications of the present invention will occur to those skilled in the art upon a reading of the present dis-closure. These are intended to be included within the scope of this invention.
Patents 2,803,542 to Ullrich, U. S. Patent 3,121,0Q7 to Middleton, and U. S. Patent 3,151,982 to Corrsin.
The oxide coated carrier materials produced by the process of this invention provide numerous advantages when employed to develop electrostatic latent images. For example, when mixed with an appropriate toner material, the resultant developer composition is found to greatly reduce the development electrode effect of a magnetic brush. In addition, such a developer composition induces fringing development with an accompanying increase in exposure latitude. Further, such developer compositions are found to provide lower background densities, higher image resolutions, and greatly improved overall print qualities.
In the following examples, the relative triboelectric values generated by contact of carrier beads with toner particles is measured by means of a Faraday Cage. The device comprises a brass cylinder having a diameter of about one inch and a length of about one inch. ~ 100-mesh screen is positioned at each end of the cylinder. The cylinder is weighed, charged with about 0.5 gram mixture of carrier and toner particles and connected to ground through a capacitor and an electrometer connected in parallel. Dry compressed air is then blown through the brass cylinder to drive all the toner from the carrier. The charge on the capacitor is then read on the electrometex. Next, the ~3i[3 ~
chamber is reweighed to determine the weight loss. The resulting data is used to calculate the toner concentration and the charge in micro-coulombs per gram of toner. Since the triboelectric measurements are relative, the measurements should, for comparative purposes, be conducted under substantially identical conditions.
Thus, a toner comprising a styrene-n-butyl methacrylate copolymer and carbon black as disclosed by M. A. Insalaco in U. S. Patent 3,079,342 is used as a contact triboelectrification standard.
Obviously, other suitable toners such as those listed above may be substituted for the toner used in the examples.
The following examples, other than the control examples, further define, describe, and compare preferred methods of pre-paring and utilizing the oxide coated carriers of the present invention in electrostatographic applications. Parts and percen-tages are by weight unless otherwise indicated.
EXAMPLE I
A control developer mixture was prepared by mixing about 6 grams of toner particles comprising a styrene-n-butyl methacrylate copolymer and carbon black with about 300 grams of carrier particles. The carrier particles comprised steel shot having an average particle size of about 100 microns which is commercially available from Nuclear Metals, West Concord, Mass.
(Division of Whittaker Corporation). The developer mixture was employed to develop electrostatic latent images in a copying machine equipped with a magnetic brush development device. Said magnetic brush development fixture comprised 5 magnetic rolls, in series, which transported developer to the electrostatic image area which had been previously formed on the flat plate photo-conductive imaging surface of the fixture. During the test, 1~3~
extreme powder cloud effect was found. Background densities were approximately half of the solid area densities as measured with a Welch densitometer. Image resolution was very poor. It was concluded that this developer mixture was unsatisfactory.
EXAMPLE II
A developer mixture was prepared by mixing about 6 grams of toner particles as in Example I with about 300 grams of carrier particles. The carrier particles were as in Example I
except that they were treated as follows: the carrier particles were placed in a muffle furnace and heated to about 800C for about one hour in an atmosphere containing about 5 percent of oxygen.
After this treatment, the carrier particles were allowed to cool to ambient temperature and examined. The treated carrier particles were found to be gray-black in color and to have an oxide coating of between about 0.25 micron and about 5 microns in thickness.
The carrier particles were mixed with toner particles and employed to develop electrostatic latent images as in Example I. The oxidized carrier developer composition was found to exhibit much better qualities than that of Example I. That is, this developer composition provided images having good resolution with very good print quality. Background densities were very low, that is, on the order of about 0.002 at very high (1.3 - 1.4) solid area densities. A slight powder cloud effect was found at a solid area density of 1.35. The electrical characteristics of the carrier material were found to be within the desired semiconductive range and determined to be acceptably stable over a wide range of environmental humidity conditions as shown in Figure 1. Thus, reasonable assurance is provided for triboelectric charging capability and favorable RC development electrode field relaxation characteristics over a practical environmental humidity range.
It was concluded that this developer mixture was satisfactory.
~03~ ~
EXAMPLE III
A developer mixture was prepared by mixing about 6 grams of toner particles as in Example I with about 300 grams of carrier particles. The carrier particles were as in Example I
except that they were treated as follows: the carrier particles were placed in a high temperature rotary furnace and heated to about 500C for about 30 minutes in an atmosphere containing about 10 percent of oxygen. After this treatment, the carrier particles were allowed to cool to ambient temperature and examined.
The treated carrier particles were found to be gray-black in color and to have an oxide coating of between about 0.25 micron and about 1 micron in thickness. The carrier particles were mixed with toner particles and employed to develop electrostatic latent images as in Example I. The oxidized carrier developer composition was found to exhibit much better qualities than that of Example I. That is, this developer composition provided images having good resolution with very good print quality. Background densities were very low at very high (1.3 - 1.4) solid area densities. The electrical characteristics of the carrier material were found to be within the desired semi-conductive range and determined to be acceptably stable over a wide range of environmental humidity conditions as shown in Figure 2. It was concluded that this developer mixture was satisfactory.
Other modifications of the present invention will occur to those skilled in the art upon a reading of the present dis-closure. These are intended to be included within the scope of this invention.
Claims (12)
1. A magnetically-responsive, semi-conductive electrostatographic carrier particle having an average particle diameter of from between about 30 microns and about 1,000 microns, said carrier particle having been prepared by firing metallic, magnetic particles in an atmosphere having an oxygen content of between about 1 percent and about 18 percent by weight at a temperature of between about 900°F and about 1600°F for between about 10 minutes and up to about 2 hours whereby said particles are provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns.
2. A magnetically-responsive, semi-conductive electrostatographic carrier particle in accordance with claim 1 wherein said atmosphere has an oxygen content of between about 1 percent and about 12 percent by weight and said particles are fired at a temperature of between about 900°F and about 1500°F for between about 30 minutes and about 60 minutes.
3. A magnetically-responsive, semi-conductive electrostatographic carrier particle in accordance with claim 1 wherein said atmosphere has an oxygen content of between about 4 percent and about 10 percent by weight and said particles are fired at a tempera-ture of between about 965°F and about 1470°F for between about 30 minutes and about 60 minutes.
4. A magnetically-responsive, semi-conductive electrostatographic carrier particle in accordance with claim 1 wherein said oxide coating comprises from between about 0.25 micron to about 1 micron in thickness.
5. A magnetically-responsive, semi-conductive electrostatographic carrier particle in accordance with claim 1 wherein said metallic particles are selected from the group consisting of ferromagnetic and iron alloys.
6. A magnetically-responsive, semi-conductive electrostatographic carrier particle in accordance with claim 1 wherein said carrier particle has a volume resistivity of between about 105 ohm-cm and 1012 ohm-cm.
7. An electrostatographic developer mixture comprising finely-divided toner particles electro-statically clinging to the surface of a carrier, said carrier comprising magnetically-responsive, semi-conductive electrostatographic carrier particles having an average particle diameter of from between about 30 microns and about 1,000 microns, said carrier particles having been prepared by firing metallic, magnetic particles in an atmosphere having an oxygen content of between about 1 percent and about 18 percent by weight at a temperature of between about 900°F and about 1600°F for between about 10 minutes and up to about 2 hours whereby said carrier particles are provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns.
8. An electrostatographic imaging process comprising the steps of providing an electrostato-graphic imaging member having a recording surface, forming an electrostatic latent image on said recording surface, and contacting said electrostatic latent image with a developer mixture comprising finely-divided toner particles electrostatically clinging to the surface of a carrier, said carrier comprising magne-tically-responsive, semi-conductive electrostatographic carrier particles having an average particle diameter of from between about 30 microns and about 1,000 microns, said carrier particles having been prepared by firing metallic, magnetic particles in an atmosphere having an oxygen content of between about 1 percent and about 18 percent by weight at a temperature of between about 900°F and about 1600°F for between about 10 minutes and up to about 2 hours whereby said carrier particles are provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns, whereby at least a portion of said finely-divided toner particles are attracted to and deposited on said recording surface in conformance with said electrostatic latent image.
9. A process for preparing magnetically-respon-sive, semi-conductive electrostatographic carrier particles having an average particle diameter of from between about 30 microns and about 1,000 microns, said process comprising firing metallic, magnetic particles in an atmosphere having an oxygen content of between about 1 percent and about 18 percent by weight at a temperature of between about 900°F and about 1600°F for between about 10 minutes and up to about 2 hours whereby said carrier particles are provided with an oxide coating having a thickness of between about 0.25 micron and about 5 microns.
10. A process for preparing magnetically-responsive, semi-conductive electrostatographic carrier particles in accordance with claim 9 wherein said atmosphere has an oxygen content of between about 1 percent and about 12 percent by weight and said particles are fired at a temperature of between about 900°F and about 1500°F for between about 30 minutes and about 60 minutes.
11. A process for preparing magnetically-responsive, semi-conductive electrostatographic carrier particles in accordance with claim 9 wherein said atmosphere has an oxygen content of between about 4 percent and about 10 percent by weight and said particles are fired at a temperature of between about 965°F and about 1470°F for between about 30 minutes and about 60 minutes.
12. A process for preparing magnetically-responsive, semi-conductive electrostatographic carrier particles in accordance with claim 9 wherein said metallic particles are selected from the group consisting of ferromagnetic materials such as steel and iron alloys in various forms.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US67331976A | 1976-04-05 | 1976-04-05 | |
| US673,319 | 1976-04-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1103079A true CA1103079A (en) | 1981-06-16 |
Family
ID=24702161
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA272,453A Expired CA1103079A (en) | 1976-04-05 | 1977-02-23 | Semi-conductive steel carrier particles |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1103079A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0359041A2 (en) * | 1988-09-13 | 1990-03-21 | BASF Aktiengesellschaft | Oxide-coated carrier, its manufacturing process and its use |
| US4925762A (en) * | 1987-08-17 | 1990-05-15 | Basf Aktiengesellschaft | Carrier for reprography and production of this carrier |
-
1977
- 1977-02-23 CA CA272,453A patent/CA1103079A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4925762A (en) * | 1987-08-17 | 1990-05-15 | Basf Aktiengesellschaft | Carrier for reprography and production of this carrier |
| EP0359041A2 (en) * | 1988-09-13 | 1990-03-21 | BASF Aktiengesellschaft | Oxide-coated carrier, its manufacturing process and its use |
| EP0359041A3 (en) * | 1988-09-13 | 1990-07-04 | Basf Aktiengesellschaft | Oxide-coated carrier, its manufacturing process and its use |
| US5039587A (en) * | 1988-09-13 | 1991-08-13 | Basf Aktiengesellschaft | Oxide-coated carriers and preparation and use thereof |
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