Magnetic developer, image forming method and image forming apparatus

Claim 2

A magnetic developer for developing an electrostatic latent image, comprising hydrophobic silica fine powder and an insulating magnetic toner comprising at least a binder resin and a magnetic material; wherein 0.16 to 1.6 wt. parts of the hydrophobic silica fine powder is mixed with 100 wt. parts of the insulating magnetic toner; said magnetic developer having a BET specific surface area of 1.8 to 3.5 m²/g, a triboelectric chargeability of -20 to -35 µC/g, an aerated bulk density of 0.40 to 0.52 g/cm³, and a true density of 1.45 to 1.8 g/cm³; said magnetic material having an average particle size of 0.1 to 0.35 micron and comprising 50 % by number or more of spherical magnetic particles of which surfaces substantially comprise curved surfaces; said insulating magnetic toner containing 70 - 120 wt. parts of spherical magnetic particles with respect to 100 wt. parts of the binder resin; said developer containing 17 - 60 % by number of magnetic toner particles having a particle size of 5 microns or smaller, containing 5 - 50 % by number of magnetic toner particles having a particle size of 6.35 - 10.08 microns, and containing 2.0 % by volume or less of magnetic toner particles having a particle size of 12.7 microns or larger; wherein the magnetic toner has a volume-average particle size of 6 - 8 microns, and the magnetic toner particles having a particle size of microns or smaller has a particle size distribution satisfying the following formula: N/V = -0.05N + k, wherein N denotes the percentage by number of magnetic toner particles having a particle size of 5 micron or smaller, V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, k denotes a positive number of 4.6 to 6.7, and N denotes a positive number of 17 to 60.

Claim 3

A developer according to Claim 1, wherein the hydrophobic silica fine powder has been treated with a silicone oil or a silicone varnish.

Claim 4

A developer according to Claim 1, wherein the hydrophobic silica fine powder has been treated with a silane coupling agent.

Claim 5

A developer according to Claim 1, wherein the hydrophobic silica fine powder has been treated with a silane coupling agent and a silicone oil.

Claim 6

A developer according to Claim 1, wherein the hydrophobic silica fine powder has been treated with a silicone oil having a viscosity of 50 - 1000 centistoke at 25 °C.

Claim 7

A developer according to Claim 1, wherein the insulating magnetic toner has an electric resistance of 10¹⁴ ohm.cm or higher, a residual magnetization σ r of 1 - 5 emu/g, a saturation magnetization σ s of 15 - 50 emu/g, and a coercive force of 20 - 100 Öe.

Claim 8

A developer according to Claim 1, wherein the insulating magnetic toner contains a crosslinked styrene-type copolymer as a binder resin.

Claim 9

A developer according to Claim 1, wherein the insulating magnetic toner contains a crosslinked polyester as a binder resin.

Claim 10

A developer according to Claim 1, wherein the hydrophobic silica fine powder is used in an amount of 0.7 - 1.4 wt. parts with respect to 100 wt. parts of the insulating magnetic toner.

Claim 11

A developer according to Claim 1, wherein the hydrophobic silica fine powder has a BET specific surface area of 70 - 300 m²/g, a triboelectric chargeability of -100 to -300 µC/g, and a hydrophobicity of 90 % or higher with respect to ion-­exchanged water.

Claim 12

A developer according to Claim 1, which has a BET specific surface area of 1.9 - 3.0 m²/g.

Claim 13

A developer according to Claim 1, which has a residual magnetization σ r of 2 - 4.5 emu/g, a saturation magnetization σ s of 20 - 40 emu/g, and a coercive force of 40 - 100 Öe.

Claim 14

An image forming method, comprising: disposing an electrostatic image-bearing member carrying thereon an electrostatic image, and a toner-carrying member carrying a magnetic toner on the surface thereof with a predetermined clearance therebetween, wherein the toner-carrying member has a surface covered with a film of a phenolic resin containing electroconductive carbon and graphite; and the magnetic toner comprises an insulating one-­component magnetic toner comprising at least a binder resin and a magnetic material; and the magnetic toner has a triboelectric chargeability of -20 to -35 µC/g and a volume-average particle size of 6 - 8 microns; said magnetic material comprising 50 % by number or more of spherical magnetic particles of which surfaces substantially comprise curved surfaces; said toner containing 17 - 60 % by number of magnetic toner particles having a particle size of 5 microns or smaller, containing 5 - 50 % by number of magnetic toner particles having a particle size of 6.35 - 10.08 microns, and containing 2.0 % by volume or less of magnetic toner particles having a particle size of 12.7 microns or larger; wherein the magnetic toner particles having a particle size of 5 microns or smaller has a particle size distribution satisfying the following formula: N/V = -0.05N + k, wherein N denotes the percentage by number of magnetic toner particles having a particle size of 5 micron or smaller, V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, k denotes a positive number of 4.6 - 6.7, and N denotes a positive number of 17 - 60; conveying the magnetic toner to a developing position while regulating the toner so as to provide a thickness smaller than said clearance; and developing the electrostatic image formed on the image-bearing member in the developing position in the presence of an alternating electric field, thereby to form a toner image on the latent image-bearing member.

Claim 15

An image forming method, comprising: disposing an electrostatic image-bearing member carrying thereon an electrostatic image, and a toner-carrying member carrying a magnetic toner on the surface thereof with a predetermined clearance therebetween, wherein the toner-carrying member has a surface covered with a film of a phenolic resin containing electroconductive carbon and graphite; and the magnetic toner comprises an insulating one-­component magnetic toner comprising at least a binder resin and a magnetic material; and the magnetic toner has a triboelectric chargeability of -20 to -35 µC/g and a volume-average particle size of 6 - 8 microns; said magnetic material comprising 50 % by number or more of spherical magnetic particles of which surfaces substantially comprise curved surfaces; said toner containing 17 - 60 % by number of magnetic toner particles having a particle size of 5 microns or smaller, containing 5 - 50 % by number of magnetic toner particles having a particle size of 6.35 - 10.08 microns, and containing 2.0 % by volume or less of magnetic toner particles having a particle size of 12.7 microns or larger; wherein the magnetic toner particles having a particle size of 5 microns or smaller has a particle size distribution satisfying the following formula: N/V = -0.05N + k, wherein N denotes the percentage by number of magnetic toner particles having a particle size of 5 micron or smaller, V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, k denotes a positive number of 4.6 - 6.7, and N denotes a positive number of 17 - 60; conveying the magnetic toner to a developing position while regulating the toner so as to provide a thickness smaller than said clearance; and developing the electrostatic image formed on the image-bearing member in the developing position in the presence of an alternating electric field, thereby to form a toner image on the latent image-bearing member.

Claim 16

A method according to Claim 13, wherein the electroconductive carbon has an electric resistance of 0.5 ohm/cm or below.

Claim 17

A method according to Claim 13, wherein the electroconductive carbon and graphite are contained so as to provide a mixing wt. ratio of 1/10 to 100/1.

Claim 18

A method according to Claim 13, wherein the electroconductive carbon and graphite are contained so as to provide a mixing wt. ratio of 1/1 to 100/1.

Claim 19

A method according to Claim 13, wherein the mixture of the electroconductive carbon and graphite is contained in the phenolic resin so as to provide a mixing wt. ratio of 1/3 to 2/1 therebetween.

Claim 20

A method according to Claim 13, wherein the magnetic toner has been mixed with hydrophobic silica fine powder.

Claim 21

A method according to Claim 13, wherein the magnetic toner is triboelectrically charged by the contact with the surface of the toner-carrying member, and the magnetic toner having the triboelectric charge develops the electrostatic image while being applied with an alternating bias having an AC component having a frequency of 200 - 40,000 Hz and a Vpp of 500 - 3,000 V.

Claim 22

A method according to Claim 18, wherein the hydrophobic silica fine powder has been treated with a silicone oil or a silicone varnish.

Claim 23

A method according to Claim 18, wherein the hydrophobic silica fine powder has been treated with a silane coupling agent.

Claim 24

A method according to Claim 18, wherein the hydrophobic silica fine powder has been treated with a silane coupling agent and a silicone oil.

Claim 25

A method according to Claim 18, wherein the hydrophobic silica fine powder has been treated with a silicone oil having a viscosity of 50 - 1000 centistoke at 25 °C.

Claim 26

A method according to Claim 13, wherein the insulating magnetic toner has an electric resistance of 10¹⁴ ohm.cm or larger, a residual magnetization σ r of 1 - 5 emu/g, a saturation magnetization σ s of 15 - 50 emu/g, and a coercive force of 20 - 100 Öe.

Claim 27

A method according to Claim 13, wherein the insulating magnetic toner contains a crosslinked styrene-type copolymer as a binder resin.

Claim 28

A method according to Claim 13, wherein the insulating magnetic toner contains a crosslinked polyester ass a binder resin.

Claim 29

A method according to Claim 18, wherein the hydrophobic silica fine powder is used in an amount of 0.6 - 1.7 wt. parts with respect to 100 wt. parts of the insulating magnetic toner.

Claim 30

A method according to Claim 18, wherein the hydrophobic silica fine powder has a BET specific surface area of 70 - 300 m²/g, a triboelectric chargeability of -100 to -300 µC/g, and a hydrophobicity of 90 % or higher with respect to ion-­exchanged water.

Claim 31

A method according to Claim 13, wherein said magnetic developer has a BET specific surface area of 1.9 - 3.0 m²/g.

Claim 32

A method according to Claim 13, wherein the magnetic developer has a residual magnetization σ r of 2 - 4.5 emu/g, a saturation magnetization σ s of 20 - 40 emu/g, and a coercive force of 40 - 100 Öe.

Claim 33

An image forming apparatus comprising: an electrostatic image-bearing member for carrying an electrostatic image; a toner-carrying member for carrying a magnetic toner on the surface thereof; means for disposing the electrostatic image-­bearing member and the toner-carrying member so that they are disposed opposite to each other with a predetermined clearance therebetween; and a member for regulating the magnetic toner so as to provide a thickness thereof which is smaller than said clearance; wherein the toner-carrying member has a surface covered with a film of a phenolic resin containing electroconductive carbon and graphite; and the magnetic toner comprises an insulating one-­component magnetic toner comprising at least a binder resin and a magnetic material; and has a triboelectric chargeability of -20 to -35 µC/g and a volume-average particle size of 6 - 8 microns; said magnetic material comprises 50 % by number or more of spherical magnetic particles of which surfaces substantially comprise curved surfaces; said toner contains 17 - 60 % by number of magnetic toner particles having a particle size of 5 microns or smaller, contains 5 - 50 % by number of magnetic toner particles having a particle size of 6.35 - 10.08 microns, and contains 2.0 % by volume or less of magnetic toner particles having a particle size of 12.7 microns or larger; wherein the magnetic toner particles having a particle size of 5 microns or smaller has a particle size distribution satisfying the following formula: N/V = -0.05N + k, wherein N denotes the percentage by number of magnetic toner particles having a particle size of 5 micron or smaller, V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, k denotes a positive number of 4.6 - 6.7, and N denotes a positive number of 17 - 60.

Claim 34

An image forming apparatus comprising: an electrostatic image-bearing member for carrying an electrostatic image; a toner-carrying member for carrying a magnetic toner on the surface thereof; means for disposing the electrostatic image-­bearing member and the toner-carrying member so that they are disposed opposite to each other with a predetermined clearance therebetween; and a member for regulating the magnetic toner so as to provide a thickness thereof which is smaller than said clearance; wherein the toner-carrying member has a surface covered with a film of a phenolic resin containing electroconductive carbon and graphite; and the magnetic toner comprises an insulating one-­component magnetic toner comprising at least a binder resin and a magnetic material; and has a triboelectric chargeability of -20 to -35 µC/g and a volume-average particle size of 6 - 8 microns; said magnetic material comprises 50 % by number or more of spherical magnetic particles of which surfaces substantially comprise curved surfaces; said toner contains 17 - 60 % by number of magnetic toner particles having a particle size of 5 microns or smaller, contains 5 - 50 % by number of magnetic toner particles having a particle size of 6.35 - 10.08 microns, and contains 2.0 % by volume or less of magnetic toner particles having a particle size of 12.7 microns or larger; wherein the magnetic toner particles having a particle size of 5 microns or smaller has a particle size distribution satisfying the following formula: N/V = -0.05N + k, wherein N denotes the percentage by number of magnetic toner particles having a particle size of 5 micron or smaller, V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, k denotes a positive number of 4.6 - 6.7, and N denotes a positive number of 17 - 60.

Claim 35

An apparatus according to Claim 31, wherein the electroconductive carbon has an electric resistance of 0.5 ohm/cm or below.

Claim 36

An apparatus according to Claim 31, wherein the electroconductive carbon and graphite are contained so as to provide a mixing wt. ratio of 1/10 to 100/1.

Claim 37

An apparatus according to Claim 31, wherein the electroconductive carbon and graphite are contained so as to provide a mixing wt. ratio of 1/1 to 100/1.

Claim 38

An apparatus according to Claim 31, wherein the mixture of the electroconductive carbon and graphite is contained in the phenolic resin so as to provide a mixing wt. ratio of 1/3 to 2/1 therebetween.

Claim 39

An apparatus according to Claim 31, wherein the magnetic toner has been mixed with hydrophobic silica fine powder.

Claim 40

An apparatus according to Claim 31, wherein the toner-carrying member has a characteristic such that it imparts a negative triboelectric charge to the magnetic toner.

Claim 41

An apparatus according to Claim 31, wherein the electrostatic image-bearing member has cleaning means and charging means.

Claim 42

An apparatus according to Claim 31, wherein the electroconductive image-bearing member or toner-­carrying member has means for applying an alternating bias in a developing position.

Claim 43

An apparatus according to Claim 36, wherein the hydrophobic silica fine powder has been treated with a silicone oil or a silicone varnish.

Claim 44

An apparatus according to Claim 36, wherein the hydrophobic silica fine powder has been treated with a silane coupling agent.

Claim 45

An apparatus according to Claim 36, wherein the hydrophobic silica fine powder has been treated with a silane coupling agent and a silicone oil.

Claim 46

An apparatus according to Claim 36, wherein the hydrophobic silica fine powder has been treated with a silicone oil having a viscosity of 50 - 1000 centistoke at 25 °C.

Claim 47

An apparatus according to Claim 31, wherein the insulating magnetic toner has an electric resistance of 10¹⁴ ohm.cm or larger, a residual magnetization σ r of 1 - 5 emu/g, a saturation magnetization σ s of 15 - 50 emu/g, and a coercive force of 20 - 100 Öe.

Claim 48

An apparatus according to Claim 31, wherein the insulating magnetic toner contains a crosslinked styrene-type copolymer as a binder resin.

Claim 49

An apparatus according to Claim 31, wherein the insulating magnetic toner contains a crosslinked polyester as a binder resin.

Claim 50

An apparatus according to Claim 36, wherein the hydrophobic silica fine powder is used in an amount of 0.7 - 1.4 wt. parts with respect to 100 wt. parts of the insulating magnetic toner.

Claim 51

An apparatus according to Claim 36, wherein the hydrophobic silica fine powder has a BET specific surface area of 70 - 300 m²/g, a triboelectric chargeability of -100 to -300 µC/g, and a hydrophobicity of 90 % or higher with respect to ion-­exchanged water.

Claim 52

An apparatus according to Claim 31, wherein the magnetic developer has a BET specific surface area of 1.9 - 3.0 m²/g.

Claim 53

An apparatus according to Claim 31, wherein the magnetic developer has a residual magnetization σ r of 2 - 4.5 emu/g, a saturation magnetization σ s of 20 - emu/g, and a coercive force of 40 - 100 Öe.

Claim 54

A facsimile comprising an image forming apparatus and receiving means for receiving image information from a remote terminal; said image forming apparatus comprising; an electrostatic image-bearing member for carrying an electrostatic image; a toner-carrying member for carrying a magnetic toner on the surface thereof; means for disposing the electrostatic image-­bearing member and the toner-carrying member so that they are disposed opposite to each other with a predetermined clearance therebetween; and a member for regulating the magnetic toner so as to provide a thickness thereof which is smaller than said clearance; wherein the toner-carrying member has a surface covered with a film of a phenolic resin containing electroconductive carbon and graphite; and the magnetic toner comprises an insulating one-­component magnetic toner comprises at least a binder resin and a magnetic material; and has a triboelectric chargeability of -20 to -35 µC/g and a volume-average particle size of 6 - 8 microns; said magnetic material comprises 50 % by number or more of spherical magnetic particles of which surfaces substantially comprise curved surfaces; said toner contains 17 - 60 % by number of magnetic toner particles having a particle size of 5 microns or smaller, contains 5 - 50 % by number of magnetic toner particles having a particle size of 6.35 - 10.08 microns, and contains 2.0 % by volume or less of magnetic toner particles having a particle size of 12.7 microns or larger; wherein the magnetic toner particles having a particle size of 5 microns or smaller has a particle size distribution satisfying the following formula: N/V = -0.05N + k, wherein N denotes the percentage by number of magnetic toner particles having a particle size of 5 micron or smaller, V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, k denotes a positive number of 4.6 - 6.7, and N denotes a positive number of 17 - 60.

Claim 55

A facsimile comprising an image forming apparatus and receiving means for receiving image information from a remote terminal; said image forming apparatus comprising; an electrostatic image-bearing member for carrying an electrostatic image; a toner-carrying member for carrying a magnetic toner on the surface thereof; means for disposing the electrostatic image-­bearing member and the toner-carrying member so that they are disposed opposite to each other with a predetermined clearance therebetween; and a member for regulating the magnetic toner so as to provide a thickness thereof which is smaller than said clearance; wherein the toner-carrying member has a surface covered with a film of a phenolic resin containing electroconductive carbon and graphite; and the magnetic toner comprises an insulating one-­component magnetic toner comprises at least a binder resin and a magnetic material; and has a triboelectric chargeability of -20 to -35 µC/g and a volume-average particle size of 6 - 8 microns; said magnetic material comprises 50 % by number or more of spherical magnetic particles of which surfaces substantially comprise curved surfaces; said toner contains 17 - 60 % by number of magnetic toner particles having a particle size of 5 microns or smaller, contains 5 - 50 % by number of magnetic toner particles having a particle size of 6.35 - 10.08 microns, and contains 2.0 % by volume or less of magnetic toner particles having a particle size of 12.7 microns or larger; wherein the magnetic toner particles having a particle size of 5 microns or smaller has a particle size distribution satisfying the following formula: N/V = -0.05N + k, wherein N denotes the percentage by number of magnetic toner particles having a particle size of 5 micron or smaller, V denotes the percentage by volume of magnetic toner particles having a particle size of 5 microns or smaller, k denotes a positive number of 4.6 - 6.7, and N denotes a positive number of 17 - 60.