Claims
- 1. A one-component magnetic developer powder for developing an electrostatic latent image formed according to an electrophotographic process by the magnetic brush method, the particles of the developer powder being substantially spherical and having an electrically conductive multi-layer structure, said structure having a core portion and a surface layer, said core portion consisting essentially of 40-55% by weight of a plastic binder, 0.5-8% by weight of electric conductive particles dispersed throughout said binder and the balance of magnetite, said core portion having an electric resistivity ranging between 10.sup.2 and 10.sup.12 ohm-cm in a 100 volts/cm D.C. electrical field, said surface layer comprising additional electrically conductive particles embedded in the surface of the spherical particle forming a greater concentration of electrically conductive particles in the surface layer; the total conductive particles being 1.5-10% by weight; the resistivity of the surface layer of said spherical particle being less than that of the core portion; and the average electric resistivity of said developer powder being in the range of 10.sup.2 and 10.sup.8 ohm-cm in a 100 volts/cm D.C. electrical field.
- 2. A one-component magnetic developer powder according to claim 1, wherein the content of the additional electrically conductive particles is 1.0-2.0% by weight.
- 3. A one-component magnetic developer powder according to claim 1, wherein the particles of the developer powder have a particle size in the range of 1 to 100.mu..
- 4. A one-component magnetic developer powder according to claim 1, wherein the particles of the developer powder have a particle size in the range of 5 to 40.mu..
- 5. A one-component magnetic developer powder according to claim 1, wherein the plastic binder is selected from the group consisting of thermoplastic resins, thermosetting resins and mixture thereof, the electrically conductive particles having a particle size in the range of 10 to 40 m.mu. and are selected from the group consisting of carbon-black, metal powders, alloy powders, inorganic oxides and electric conductive polymers, and the magnetite has a particle size in the range of 0.1 to 1.mu..
- 6. A one-component magnetic developer powder according to claim 1, wherein the developer particles powder has an average electric resistivity in the range of 10.sup.2 to 10.sup.6 .OMEGA.cm in a 100 volts/cm D.C. electrical field.
- 7. A one-component magnetic developer powder according to claim 1, wherein the developer powder particles comprises up to 1.0 weight % of a dry lubricating powder selected from the group consisting of stearate compounds, silica and alumina, the dry lubricating powder having a particle size in the particle size range of 3 to 40 m.mu..
- 8. A one-component magnetic developer powder according to claim 7, wherein the dry lubricating powder is 0.2 to 0.5 weight % of silica.
- 9. A one component magnetic developer powder according to claim 1, wherein the plastic binder is selected from the group consisting of microcrystalline wax, ethylene-vinyl acetate copolymer, styrene resin and epoxy resin.
- 10. A one-component magnetic developer powder according to claim 1, wherein the amount of electric conductive particles contained in the developer powder particles is in the range of 2 to 9 weight %.
- 11. A one-component magnetic developer powder for developing an electrostatic latent image formed according to an electrophotographic process by the magnetic brush method, the particles of the developer powder being substantially spherical and having an electrically conductive multi-layer structure, said structure having a core portion and a surface layer, said spherical particles having a particle size in the range of 5 to 40.mu., said core portion having a electric resistivity in the range of 10.sup.2 to 10.sup.12 .OMEGA.cm in a 100 volts/cm D.C. electric field, said spherical particles consisting essentially of 40 to 55 weight % of a plastic binder selected from the group consisting of thermoplastic resins, thermosetting resins, and mixtures thereof, 0.5 to 8 weight % of electric conductive carbon-black dispersed throughout said core portion and having a particle size in the range of 10 to 4 m.mu., 1.0 to 2.0 weight % of electrical conductive carbon-black embedded in the surface layer and having a particle size in the range of 10 to 40 m.mu. and magnetite having a particle size in the range of 0.1 to 1.mu., the total content of carbon-black being 1.5-10 weight %, wherein the developer powder particles have an average electric resistivity in the range of 10.sup.2 and 10.sup.8 .OMEGA.cm in a 100 volts/cm D.C. electrical field.
- 12. A one-component magnetic developer powder according to claim 11, wherein the developer powder particles comprises up to 0.5 weight % of silicon dioxide dry lubricating powder blended therewith.
- 13. A method of preparing a one component magnetic developer powder of essentially spherical particles of improved flowability, each particle having an electrically conductive multi-layer structure, said structure having a core portion and a surface layer, for developing an electrostatic latent image formed according to an electrophotographic process by the magnetic brush developing method comprising the steps of:
- mixing 40 to 55 weight % of a plastic binder selected from the group consisting of thermoplastic resins, thermosetting resins, and mixtures thereof, 0.5 to 8 weight % of electric conductive carbon-black having a particle size in the range of 10 to 40 m.mu. and the balance magnetite having a particle size in the range of 0.1 to 1.mu., at a temperature ranging between 130.degree. and 170.degree.0 C.
- pulverizing the mixture into particles less than 40.mu. after cooling,
- dispersing the pulverized particles into a hot air stream ranging between 500.degree. and 540.degree. C. thereby spheroidizing the particles into core portion particles.
- mixing the resulting spheroidized core portion particles with 1.0 to 2.0 weight % of electric conductive carbon-black having a particle size in the range of 10 to 40 m.mu., thereby the total content of carbon-black in the spherical particles being 1.5 to 10 weight %.
- dispersing the mixture of spheroidized core portion particles and electric conductive carbon-black into a hot air stream ranging between 390.degree. and 420.degree. C. thereby embedding the carbon-black on a spherical surface of the core portion articles, and
- classifying the particles, each particle having an electrically conductive multi-layer structure, said structure having a carbon-black containing core portion and a carbon-black containing surface layer having an electric resistivity relatively less than that of the core portion, into an appropriate particle size whereby the resulting developer powder has an average electric resistivity in the range of 10.sup.2 to 10.sup.8 .OMEGA.cm in a 100 volts/cm D.C. electrical field.
Priority Claims (1)
Number |
Date |
Country |
Kind |
50/20989 |
Feb 1975 |
JPX |
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Parent Case Info
This is a continuation application Ser. No. 659,360, filed Feb. 19, 1976 now abandoned.
US Referenced Citations (5)
Continuations (1)
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Number |
Date |
Country |
Parent |
659360 |
Feb 1976 |
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