Method and apparatus for image development using a two component developer with contact and non-contact development steps alternated by vibration of magnetic particles subject to electric and magnetic fields

Claim 1

A method of developing an electrostatic latent image using a developer including a mixture of electrically chargeable toner particles and high resistance magnetic carrier particles chargeable to a polarity opposite to that of the toner particles, comprising: providing a developing zone where a developer carrying member for carrying the developer is opposed to an electrostatic latent image bearing member bearing the electrostatic latent image to be developed with a development clearance D; providing a layer of the developer on the developer carrying member, the developer layer having a thickness less than the clearance D in the developing zone; maintaining the magnetic particles in the developer layer out of contact with the electrostatic latent image bearing member in the developing zone by magnetic field generating means disposed behind the developer carrying member; and applying an external electric field in the developing zone wherein the electric field vibrates the magnetic particles under influence of a magnetic field provided by the magnetic field generating means for intermittently contacting the magnetic particles with the latent image bearing member, and for reciprocating the toner particles in the developer layer between the latent image bearing member and the magnetic carrier particles in the developing zone to develop the electrostatic latent image.

Claim 2

A method of developing an electrostatic latent image using a developer including a mixture of electrically chargeable toner particles and high resistance magnetic carrier particles chargeable to a polarity opposite to that of the toner particles, comprising: providing a developing zone where a developer carrying member for carrying the developer is opposed to an electrostatic latent image bearing member bearing the electrostatic latent image to be developed with a development clearance D; providing a layer of the developer on the developer carrying member, the developer layer having a thickness less than the clearance D in the developing zone; maintaining the magnetic particles in the developer layer out of contact with the electrostatic latent image bearing member in the developing zone by magnetic field generating means disposed behind the developer carrying member; and applying an external electric field in the developing zone wherein the electric field vibrates the magnetic particles under influence of a magnetic field provided by the magnetic field generating means for intermittently contacting the magnetic particles with the latent image bearing member, and for reciprocating the toner particles in the developer layer between the latent image bearing member and the magnetic carrier particles in the developing zone to develop the electrostatic latent image.

Claim 14

An apparatus for developing an electrostatic latent image on a latent image bearing member using a developer including a mixture of electrically chargeable toner particles and high resistance magnetic carrier particles chargeable to a polarity opposite to that of the toner particles, comprising: a developer carrying member for opposing the latent image bearing member with a developing clearance D to form a developing zone therebetween, and for conveying the developer thereon into the developing zone; a stationary magnetic field generating means disposed behind said developer carrying member, said magnetic field generating means having magnetic poles of opposite magnetic polarities between which it is opposed to the developing zone to form magnetic lines of force substantially along a surface of said developer carrying member to maintain the developer thereon out of contact with the latent image bearing member; and electric field applying means for applying an electric field for vibrating the magnetic carrier particles under influence of the magnetic field provided by said magnetic field generating means so as to contact the magnetic carrier particles with the latent image bearing member, and for reciprocating the toner particles between the magnetic carrier particles and the latent image bearing member.

Claim 15

An apparatus for developing an electrostatic latent image on a latent image bearing member using a developer including a mixture of electrically chargeable toner particles and high resistance magnetic carrier particles chargeable to a polarity opposite to that of the toner particles, comprising: a developer carrying member for opposing the latent image bearing member with a developing clearance D to form a developing zone therebetween, and for conveying the developer thereon into the developing zone; a stationary magnetic field generating means disposed behind said developer carrying member, said magnetic field generating means having magnetic poles of opposite magnetic polarities between which it is opposed to the developing zone to form magnetic lines of force substantially along a surface of said developer carrying member to maintain the developer thereon out of contact with the latent image bearing member; and electric field applying means for applying an electric field for vibrating the magnetic carrier particles under influence of the magnetic field provided by said magnetic field generating means so as to contact the magnetic carrier particles with the latent image bearing member, and for reciprocating the toner particles between the magnetic carrier particles and the latent image bearing member.

Claim 19

An apparatus for developing an electrostatic latent image on a latent image bearing member using a developer including a mixture of electrically chargeable toner particles and high resistance magnetic carrier particles chargeable to a polarity opposite to that of the toner particles, comprising: a developer carrying member for opposing the latent image bearing member with a developing clearance D to form a developing zone therebetween, and for conveying the developer thereon into the developing zone; a stationary magnetic field generating means disposed behind said developer carrying member, said magnetic field generating means forming a magnetic brush opposed to the latent image bearing member and maintaining it out of contact with the latent image bearing member; and electric field applying means for applying an electric field for vibrating the magnetic carrier particles under influence of the magnetic field provided by said magnetic field generating means so as to contact the magnetic carrier particles with the latent image bearing member, and for reciprocating the toner particles between the magnetic carrier particles and the latent image bearing member.

Claim 20

An apparatus for developing an electrostatic latent image on a latent image bearing member using a developer including a mixture of electrically chargeable toner particles and high resistance magnetic carrier particles chargeable to a polarity opposite to that of the toner particles, comprising: a developer carrying member for opposing the latent image bearing member with a developing clearance D to form a developing zone therebetween, and for conveying the developer thereon into the developing zone; a stationary magnetic field generating means disposed behind said developer carrying member, said magnetic field generating means forming a magnetic brush opposed to the latent image bearing member and maintaining it out of contact with the latent image bearing member; and electric field applying means for applying an electric field for vibrating the magnetic carrier particles under influence of the magnetic field provided by said magnetic field generating means so as to contact the magnetic carrier particles with the latent image bearing member, and for reciprocating the toner particles between the magnetic carrier particles and the latent image bearing member.

Claim 23

A method of developing an electrostatic latent image using a developer including a mixture of electrically chargeable toner particles and high resistance magnetic carrier particles chargeable to a polarity opposite to that of the toner particles comprising: providing a developing zone where a developer carrying member for carrying the developer is opposed to an electrostatic latent image bearing member bearing the electrostatic latent image to be developed with a development clearance D; providing a layer of the developer on the developer carrying member, the developer layer having a thickness less than the clearance D in the developing zone; maintaining the magnetic particles in the developer layer out of contact with the electrostatic latent image bearing member in the developing zone by magnetic field generating means disposed behind the developer carrying member; and applying an external electric field in the developing zone wherein the electric field vibrates the magnetic particles under influence of a magnetic field provided by the magnetic field generating means for intermittently contacting the magnetic particles with the latent image bearing member, and for reciprocating the toner particles in the developer layer between the latent image bearing member and the magnetic carrier particles in the developing zone to develop the electrostatic latent image; wherein a clearance between the latent image bearing member and a surface of the developer layer under influence of the magnetic field generating means is not more than 100 microns; wherein a resistance of the magnetic carrier particles is not less than 10 6 ohm-cm and not more than 10 14 ohm-cm, when it is measured between electrodes without pressure in an electric field of 10,000 V/cm; and wherein a magnetic property of the magnetic carrier particles is not less than 30 emu/g and not more than 100 emu/g in a magnetic field of 10,000 Gausses.

Claim 24

A method of developing an electrostatic latent image using a developer including a mixture of electrically chargeable toner particles and high resistance magnetic carrier particles chargeable to a polarity opposite to that of the toner particles comprising: providing a developing zone where a developer carrying member for carrying the developer is opposed to an electrostatic latent image bearing member bearing the electrostatic latent image to be developed with a development clearance D; providing a layer of the developer on the developer carrying member, the developer layer having a thickness less than the clearance D in the developing zone; maintaining the magnetic particles in the developer layer out of contact with the electrostatic latent image bearing member in the developing zone by magnetic field generating means disposed behind the developer carrying member; and applying an external electric field in the developing zone wherein the electric field vibrates the magnetic particles under influence of a magnetic field provided by the magnetic field generating means for intermittently contacting the magnetic particles with the latent image bearing member, and for reciprocating the toner particles in the developer layer between the latent image bearing member and the magnetic carrier particles in the developing zone to develop the electrostatic latent image; wherein a clearance between the latent image bearing member and a surface of the developer layer under influence of the magnetic field generating means is not more than 100 microns; wherein a resistance of the magnetic carrier particles is not less than 10 6 ohm-cm and not more than 10 14 ohm-cm, when it is measured between electrodes without pressure in an electric field of 10,000 V/cm; and wherein a magnetic property of the magnetic carrier particles is not less than 30 emu/g and not more than 100 emu/g in a magnetic field of 10,000 Gausses.