Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/083—Magnetic toner particles
  • G03G9/0839—Treatment of the magnetic components; Combination of the magnetic components with non-magnetic materials
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/083—Magnetic toner particles
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/083—Magnetic toner particles
  • G03G9/0831—Chemical composition of the magnetic components
  • G03G9/0833—Oxides
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/083—Magnetic toner particles
  • G03G9/0836—Other physical parameters of the magnetic components
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/087—Binders for toner particles
  • G03G9/08742—Binders for toner particles comprising macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08773—Polymers having silicon in the main chain, with or without sulfur, oxygen, nitrogen or carbon only
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/09—Colouring agents for toner particles
  • G03G9/0902—Inorganic compounds
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/09—Colouring agents for toner particles
  • G03G9/0902—Inorganic compounds
  • G03G9/0904—Carbon black

Definitions

• the present invention relates to a black magnetic toner and black magnetic composite particles for the black magnetic toner, and more particularly, to black magnetic composite particles for high-resistant black magnetic toner, which are not only more excellent in fluidity and blackness but also show an excellent dispersibility in a binder resin due to a less amount of carbon black desorbed or fallen-off from the surface of each particle; a process for producing the black magnetic composite particles; and a high-resistant black magnetic toner using the black magnetic composite particles which is more excellent in fluidity and blackness.
• a magnetic toner comprising composite particles prepared by mixing and dispersing magnetic particles such as magnetite particles in a resin, without using a carrier.
• the conventional development methods of using one-component magnetic toner have been classified into CPC development methods of using a low-resistance magnetic toner, and PPC development methods of using a high-resistant magnetic toner.
• the low-resistance magnetic toner used therefor has an electric conductivity, and is charged by the electrostatic induction due to electric charge of the latent images.
• the charge induced on the magnetic toner is lost while the magnetic toner is transported from a developing zone to a transfer zone, the low-resistance magnetic toner is unsuitable for the PPC development method of using an electrostatic transfer method.
• the insulated or high-resistant magnetic toners having a volume resistivity as high as not less than 1 ⁇ 10 13 ⁇ •cm.
• the developing characteristics thereof are affected by magnetic particles exposed to the surface of the magnetic toner, or the like.
• the magnetic toners tend to be electrostatically agglomerated, resulting in deterioration of fluidity thereof
• black magnetic toners widely used at the present time have been required to show a high degree of blackness and a high image density for line images and solid area images on copies.
• the fluidity of the magnetic toner is largely varied depending upon surface condition of the magnetic particles exposed to the surface of the magnetic toner. Therefore, the magnetic particles themselves have been strongly required to show an excellent fluidity.
• the degree of blackness and density of the magnetic toner are also largely varied depending upon the degree of blackness and density of the magnetic particles as a black pigment contained in the magnetic toner.
• magnetite particles have been widely used from the standpoints of magnetic properties such as saturation magnetization or coercive force, low price, color tone or the like.
• carbon black fine particles may be added.
• the volume resistivity thereof is lowered to less than 1.0 ⁇ 10 13 ⁇ •cm, so that it is not possible to use the obtained toner as an insulated or high-resistant magnetic toner. Further, the dispersibility of the magnetite particles in the binder resin is deteriorated.
• Black magnetic composite particles for black magnetic toner which have not only a more excellent fluidity and blackness, but also an excellent dispersibility in a binder resin, are presently strongly demanded. However, black magnetic composite particles capable of satisfying all of these requirements have not been obtained yet.
• the above-mentioned spherical magnetite particles show a higher fluidity than those of cubic magnetite particles, octahedral magnetite particles or the like.
• the fluidity of the spherical magnetite particles is still insufficient, and further the blackness is disadvantageously low.
• black magnetic composite particles having an average particle size of 0.06 to 1.0 ⁇ m, comprising: magnetic iron oxide particles as core particles; a coating layer comprising an organosilicon compound which is formed on the surface of each magnetic iron oxide particle; and a carbon black coat formed onto at least a part of the surface of the coating layer in an amount of 26 to 55 parts by weight based on 100 parts by weight of the magnetic iron oxide particles, the obtained black magnetic toner not only exhibits a more excellent fluidity and a more excellent blackness, but also has a high volume resistivity value and, therefore, can realize a high image quality and a high copying speed.
• the present invention has been attained on the basis of the finding.
• a black magnetic toner comprising: a binder resin, and black magnetic composite particles having an average particle diameter of 0.06 to 1.0 ⁇ m, comprising: magnetic iron oxide particles; a coating layer formed on the surface of the magnetic iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
• black magnetic toner comprising: a binder resin, and black magnetic composite particles having an average particle diameter of 0.06 to 1.0 ⁇ m, comprising:
• black magnetic composite particles for a black magnetic toner comprising: magnetic iron oxide particles having an average particle diameter of 0.055 to 0.95 ⁇ m; a coating layer formed on the surface of the magnetic iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
• black magnetic composite particles for a black magnetic toner comprising:
• a process for producing black magnetic composite particles defined in the third aspect comprises: mixing as core particles magnetic iron oxide particles having an average particle size of 0.055 to 0.95 ⁇ m together with at least one compound selected from the group consisting of:
• the black magnetic composite particles according to the present invention comprise magnetic iron oxide particles as core particles; a coating layer comprising organosilicon compound, formed on the surface of each magnetic iron oxide particle; and a carbon black coat formed in a large amount, and have an average major axial diameter of 0.06 to 1.0 ⁇ m.
• the magnetic iron oxide particles used as core particles in the present invention there may be exemplified magnetite particles ( FeO x •Fe 2 O 3 ; 0 ⁇ X ⁇ 1), maghemite particles ( ⁇ -Fe 2 O 3 ) or a mixture of these particles.
• the magnetite particles are preferred.
• the magnetic iron oxide particles as core particles from the viewpoint of a particle shape thereof, there may be exemplified isotropic particles having a sphericity (ratio of an average particle length to an average particle breadth; hereinafter referred to merely as "sphericity") of usually not less than 1.0 and less than 2.0, such as spherical particles, granular particles or polyhedral particles, e.g., hexahedral particles or octahedral particles, or anisotropic particles having an aspect ratio (ratio of an average major axial diameter to an average minor axial diameter; hereinafter referred to merely as “aspect ratio”) of not less than 2:1, such as acicular particles, spindle-shaped particles or rice ball-shaped particles.
• the magnetic iron oxide particles having an isotropic shape are preferred. Among them, the spherical particles are more preferred.
• the average particle size (diameter) thereof is 0.055 to 0.95 ⁇ m, preferably 0.065 to 0.75 ⁇ m, more preferably 0.065 to 0.45 ⁇ m.
• the sphericity thereof is usually not less than 1.0:1 and less than 2.0:1, preferably 1.0:1 to 1.8:1, and in case where the shape of the magnetic iron oxide particles is spherical, the sphericity thereof is preferably 1.0:1 to 1.4:1, more preferably 1.0:1 to 1.3:1.
• the average major axial diameter thereof is 0.055 to 0.95 ⁇ m, preferably 0.065 to 0.75 ⁇ m, more preferably 0.065 to 0.45 ⁇ m, and the aspect ratio thereof is 2:1 to 20:1, preferably 2:1 to 18:1, more preferably 2:1 to 15:1.
• the obtained black magnetic composite particles are coarse particles and are deteriorated in tinting strength.
• the average particle size is less than 0.055 ⁇ m, the intermolecular force between the particles is increased due to the reduction in particle size (fine particle), so that agglomeration of the particles tends to be caused. As a result, it becomes difficult to uniformly coat the surfaces of the magnetic iron oxide particles with the organosilicon compounds, and uniformly form the carbon black coat on the surface of the coating layer comprising the organosilicon compounds.
• the particles tend to be entangled with each other, and it also becomes difficult to uniformly coat the surfaces of the magnetic iron oxide particles with the organosilicon compounds, and uniformly form the carbon black coat on the surface of the coating layer composed of the organosilicon compounds.
• the geometrical standard deviation value thereof is preferably not more than 2.0, more preferably not more than 1.8, still more preferably not more than 1.6.
• the geometrical standard deviation value thereof is more than 2.0, coarse particles are contained therein, so that the particles are inhibited from being uniformly dispersed. As a result, it also becomes difficult to uniformly coat the surfaces of the magnetic iron oxide particles with the organosilicon compounds, and uniformly form the carbon black coat on the surface of the coating layer composed of the organosilicon compounds.
• the lower limit of the geometrical standard deviation value is 1.01. It is industrially difficult to obtain particles having a geometrical standard deviation value of less than 1.01.
• the BET specific surface area of the magnetic iron oxide particles thereof is not less than 0.5 m 2 /g.
• the BET specific surface area is less than 0.5 m 2 /g, the magnetic iron oxide particles may become coarse particles, or the sintering between the particles may be caused, so that the obtained black magnetic composite particles also may become coarse particles and tend to be deteriorated in tinting strength.
• the BET specific surface area of the magnetic iron oxide particles is preferably not less than 1.0 m 2 /g, more preferably 1.5 m 2 /g.
• the upper limit of the BET specific surface area of the magnetic iron oxide particles is usually 95 m 2 /g, preferably 90 m 2 /g, more preferably 85 m 2 /g.
• the fluidity index thereof is about 25 to about 43.
• the spherical particles are excellent in fluidity, for example, the fluidity index thereof is about 30 to about 43.
• the lower limit thereof is usually 18.0 when represented by L* value, and the upper limit thereof is usually 26.0, preferably 25.0 when represented by L* value.
• the lower limit thereof is usually more than 18.0 when represented by L* value, and the upper limit thereof is usually 34.0, preferably 32.0 when represented by L* value.
• the L* value exceeds the above-mentioned upper limit, the lightness of the particles is increased, so that it is difficult to obtain black magnetic composite particles having a sufficient blackness.
• the coercive force value thereof is usually 0.8 to 31.8 kA/m (10 to 400 Oe), preferably 1.6 to 30.2 kA/m (20 to 380 Oe);
• the saturation magnetization value in a magnetic field of kA/m (10 kOe) is usually 50 to 91 Am 2 /kg (50 to 91 emu/g), preferably 60 to 90 Am 2 /kg (60 to 90 emu/g);
• the residual magnetization value in a magnetic field of 795.8 kA/m (10 kOe) is usually 1 to 35 Am 2 /kg (1 to 35 emu/g), preferably 3 to 30 Am 2 /kg (3 to 30 emu/g).
• the core particles there may be used magnetic iron oxide particles wherein at least a part of magnetic iron oxide particles is preliminarily coated with at least one compound selected from the group consisting of hydroxide of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon (hereinafter referred to as "hydroxides and/or oxides of aluminum and/or silicon")
• the dispersibility of the obtained composite particles in a vehicle may become improved as compared to those having no undercoat composed of hydroxides and/or oxides of aluminum and/or silicon, because the percentage of desorption of carbon black from the nonmagnetic acicular black iron-based composite particles is lessened.
• the amount of the hydroxides and/or oxides of aluminum and/or silicon coat is 0.01 to 50 % by weight calculated as Al, SiO 2 or a sum of Al and SiO 2 , based on the weight of the magnetic iron oxide particles as the core particles.
• the amount of the hydroxides and/or oxides of aluminum and/or silicon coat is less than 0.01 % by weight, the improvement of the dispersibility of the obtained black magnetic composite particles in a vehicle cannot be achieved because of failing to achieve the improvement of lessening the percentage of desorption of carbon black therefrom.
• the amount of the hydroxides and/or oxides of aluminum and/or silicon coat is more than 50 % by weight, the obtained black magnetic composite particles can exhibit a good dispersibility in a vehicle by the improvement of lessening the percentage of desorption of carbon black therefrom, but the coating effect is saturated and, therefore, it is meaningless to add such an excess amount of the hydroxides and/or oxides of aluminum and/or silicon coat.
• the black magnetic composite particles using as core particles the magnetic iron oxide particles having the coat composed of the hydroxides and/or oxides of aluminum and/or silicon may be substantially identical in a particle size, a geometrical standard deviation, a BET specific surface area, a blackness (L* value), a fluidity and a magnetic property, to those having no hydroxides and/or oxides of aluminum and/or silicon coat.
• the particle shape and particle size of the black magnetic composite particles according to the present invention are considerably varied depending upon those of the magnetic iron oxide particles as core particles.
• the black magnetic composite particles have a similar particle shape to that of the magnetic iron oxide particle as core particle, and a slightly larger particle size than that of the magnetic iron oxide particles as core particles.
• the obtained black magnetic composite particles according to the present invention have an average particle size of usually 0.06 to 1.0 ⁇ m, preferably 0.07 to 0.8 pm, more preferably 0.07 to 0.5 ⁇ m and a sphericity of usually not less than 1.0:1 and less than 2.0:1, preferably 1.0:1 to 1.8:1, and in case where the shape of the magnetic iron oxide particles is spherical, the sphericity thereof is preferably 1.0:1 to 1.4:1, more preferably 1.0:1 to 1.3:1.
• the obtained black magnetic composite particles according to the present invention have an average particle size of usually 0.06 to 1.0 ⁇ m, preferably 0.07 to 0.8 ⁇ m, more preferably 0.07 to 0.5 ⁇ m and an aspect ratio of usually 2:1 to 20:1, preferably 2.5:1 to 18:1, more preferably 2:1 to 15:1.
• the obtained black magnetic composite particles may be coarse particles, and deteriorated in tinting strength.
• the average particle size thereof is less than 0.06 ⁇ m, the black magnetic composite particles may tend to be agglomerated by the increase of intermolecular force due to the reduction in particle size, thereby deteriorating the dispersibility in a binder resin upon production of the magnetic toner.
• the black magnetic composite particles may be entangled with each other in the binder resin, so that the dispersibility in binder resin may tend to be deteriorated.
• the geometrical standard deviation value of the black magnetic composite particles according to the present invention is preferably not more than 2.0, more preferably not more than 1.8, still more preferably not more than 1.6.
• the lower limit of the geometrical standard deviation value thereof is preferably 1.01.
• the geometrical standard deviation value thereof is more than 2.0, the tinting strength of the black magnetic composite particles may be likely to be deteriorated due to the existence of coarse particles therein. It is industrially difficult to obtain such particles having a geometrical standard deviation of less than 1.01.
• the BET specific surface area of the black magnetic composite particles according to the present invention is usually 1.0 to 100 m 2 /g, preferably 1.5 to 95 m 2 /g, more preferably 2.0 to 90 m 2 /g.
• the BET specific surface area thereof is less than 1.0 m 2 /g, the obtained black magnetic composite particles may be coarse, and the sintering between the black magnetic composite particles may be caused, thereby deteriorating the tinting strength.
• the BET specific surface area is more than 100 m 2 /g, the black magnetic composite particles may tend to be agglomerated together by the increase in intermolecular force due to the reduction in particle size, thereby deteriorating the dispersibility in a binder resin upon production of the magnetic toner.
• the fluidity index thereof is preferably 48 to 90, more preferably 49 to 90, still more preferably 50 to 90.
• the fluidity index thereof is less than 48, the fluidity of the black magnetic composite particles may become insufficient, thereby failing to improve the fluidity of the finally obtained magnetic toner. Further, in the production process of the magnetic toner, there may tend to be caused defects such as clogging of hopper, etc., thereby deteriorating the handling property or workability.
• the upper limit of the blackness of the black magnetic composite particles is usually 19.5, preferably 18.8, more preferably 17.8 when represented by L* value.
• the upper limit of the blackness of the black magnetic composite particles is usually 19.5, preferably 19.0, more preferably 18.8 when represented by L* value.
• the L* value thereof is more than 19.5, the lightness of the obtained black magnetic composite particles may become high, so that the black magnetic composite particles having a sufficient blackness may not be obtained.
• the lower limit of the blackness thereof is 15 when represented by L* value.
• the dispersibility in binder resin of the black magnetic composite particles according to the present invention is preferably 4th or 5th rank, more preferably 5th rank when evaluated by the method described hereinafter.
• the percentage of desorption of carbon black from the black magnetic composite particles according to the present invention is preferably not more than 20 %, more preferably not more than 10 %.
• the desorbed carbon black may tend to inhibit the black magnetic composite particles from being uniformly dispersed in the binder resin upon production of the magnetic toner.
• the magnetic properties of the black magnetic composite particles according to the present invention can be controlled by appropriately selecting kind and particle shape of the magnetic iron oxide particles as core particles.
• the coercive force of the black magnetic composite particles according to the present invention is usually 0.8 to 31.8 kA/m (10 to 400 Oe), preferably 1.6 to 30.2 kA/m (20 to 380 Oe);
• the saturation magnetization in a magnetic field of 795.8 kA/m (10 kOe) is usually 50 to 91 Am 2 /kg (50 to 91 emu/g), preferably 60 to 90 Am 2 /kg (60 to 90 emu/g);
• the residual magnetization in a magnetic field of 795.8 kA/m (10 kOe) is usually 1 to 35 Am 2 /kg (1 to 35 emu/g), preferably 3 to 30 Am 2 /kg (3 to 30 emu/g).
• the coating layer formed on the surfaces of the core particles comprises at least one organosilicon compound selected from the group consisting of (1) organosilane compounds obtainable from alkoxysilane compounds; and (2) polysiloxanes, or (2') modified polysiloxanes selected from the group consisting of (A) polysiloxanes modified with at least one compound selected from the group consisting of polyethers, polyesters and epoxy compounds (hereinafter referred to merely as "modified polysiloxanes”), and (B) polysiloxanes whose molecular terminal is modified with at least one group selected from the group consisting of carboxylic acid groups, alcohol groups and a hydroxyl group (hereinafter referred to merely as " terminal-modified polysiloxanes").
• organosilicon compound selected from the group consisting of (1) organosilane compounds obtainable from alkoxysilane compounds
• polysiloxanes or (2') modified polysiloxanes selected from the group consisting of (A) polys
• the organosilane compounds (1) may be produced by drying or heat-treating alkoxysilane compounds represented by the formula (I): R 1 a SiX 4-a wherein R 1 is C 6 H 5 -, (CH 3 ) 2 CHCH 2 - or n-C b H 2b+1 - (wherein b is an integer of 1 to 18); X is CH 3 O- or C 2 H 5 O-; and a is an integer of 0 to 3.
• R 1 a SiX 4-a wherein R 1 is C 6 H 5 -, (CH 3 ) 2 CHCH 2 - or n-C b H 2b+1 - (wherein b is an integer of 1 to 18); X is CH 3 O- or C 2 H 5 O-; and a is an integer of 0 to 3.
• the drying or heat-treatment of the alkoxysilane compounds may be conducted, for example, at a temperature of usually 40 to 200°C, preferably 60 to 150°C for usually 10 minutes to 12 hours, preferably 30 minutes to 3 hours.
• alkoxysilane compounds may include methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethyoxysilane, diphenyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane or the like.
• methyltriethoxysilane, phenyltriethyoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane and isobutyltrimethoxysilane are preferred, and methyltriethoxysilane and methyltrimethoxysilane are more preferred.
• polysiloxanes (2) there may be used those compounds represented by the formula (II): wherein R 2 is H- or CH 3 -, and d is an integer of 15 to 450.
• polysiloxanes having methyl hydrogen siloxane units are preferred.
• modified polysiloxanes (2'-A) there may be used:
• the polysiloxanes modified with the polyethers represented by the formula (III) are preferred.
• terminal-modified polysiloxanes (2'-B) there may be used those represented by the formula (VI): wherein R 13 and R 14 are -OH, R 16 OH or R 17 COOH and may be the same or different; R 15 is -CH 3 or -C 6 H 5 ; R 16 and R 17 are -(-CH 2 -) y -; y is an integer of 1 to 15; w is an integer of 1 to 200; and x is an integer of 0 to 100.
• the polysiloxanes whose terminals are modified with carboxylic acid groups are preferred.
• the amount of the coating layer composed of the organosilicon compounds is usually 0.02 to 5.0 % by weight, preferably 0.03 to 4.0 % by weight, more preferably 0.05 to 3.0 % by weight (calculated as Si) based on the weight of the magnetic iron oxide particles coated with the organosilicon compounds.
• a carbon black coat is formed on at least a part of the surface of coating layer composed of the organosilicon compounds, and is composed of at least two carbon black layers integrally adhered with each other through an adhesive. If required, 3 or more carbon black layers are integrally adhered with each other through an adhesive to form the carbon black coat.
• the amount of the carbon black coat is 26 to 55 parts by weight based on 100 parts by weight of the magnetic iron oxide particles as core particles.
• the amount of the carbon black coat formed is less than 26 part by weight, it becomes difficult to obtain black magnetic composite particles having a sufficient fluidity and blackness.
• the amount of the carbon black coat formed is more than 55 parts by weight, the carbon black tend to be desorbed from the coating layer composed of the organosilicon compound. As a result, the obtained black magnetic composite particles tend to be deteriorated in dispersibility in a binder resin upon the production of magnetic toner.
• the thickness of carbon black coat formed is preferably not more than 0.06 ⁇ m, more preferably not more than 0.05 ⁇ m, still more preferably not more than 0.04 ⁇ m.
• the lower limit thereof is more preferably 0.0001 ⁇ m.
• the black magnetic composite particles according to the present invention at least a part of the surface of the magnetic iron oxide particles as core particle may be preliminarily coated with hydroxides and/or oxides of aluminum and/or silicon.
• the obtained black magnetic composite particles can show a higher dispersibility in a binder resin as compared to in the case where the magnetic iron oxide particles are uncoated with hydroxides and/or oxides of aluminum and/or silicon, because of achieving the improvement of lessening the percentage of desorption of carbon black therefrom.
• the percentage of desorption of carbon black from the obtained black magnetic composite particles of the present invention is preferably not more than 10 %, more preferably not more than 5 %.
• the black magnetic toner according to the present invention comprises the black magnetic composite particles, and a binder resin.
• the black magnetic toner may further contain a mold release agent, a colorant, a charge-controlling agent and other additives, if necessary.
• the black magnetic toner according to the present invention has an average particle size of usually 3 to 15 ⁇ m, preferably 5 to 12 ⁇ m.
• the amount of the binder resin used in the black magnetic toner is usually 50 to 900 parts by weight, preferably 50 to 400 parts by weight based on 100 parts by weight of the black magnetic composite particles.
• binder resins there may be used vinyl-based polymers, i.e., homopolymers or copolymers of vinyl-based monomers such as styrene, alkyl acrylates and alkyl methacrylates.
• vinyl-based polymers i.e., homopolymers or copolymers of vinyl-based monomers such as styrene, alkyl acrylates and alkyl methacrylates.
• styrene monomers there may be exemplified styrene and substituted styrenes.
• alkyl acrylate monomers there may be exemplified acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate or the like.
• the above copolymers contain styrene-based components in an amount of usually 50 to 95 % by weight.
• the above-mentioned vinyl-based polymers may be used in combination with polyester-based resins, epoxy-based resins, polyurethane-based resins or the like, if necessary.
• the fluidity index is usually 78 to 100, preferably 79 to 100, more preferably 80 to 100.
• the fluidity index is less than 78, the black magnetic toner may not show a sufficient fluidity.
• the blackness of the black magnetic toner according to the present invention is usually not more than 19.0, preferably not more than 18.8, more preferably not more than 18.5 when represented by L* value. When the blackness thereof is more than 19.0, the lightness of the black magnetic toner may be increased, resulting in insufficient blackness.
• the lower limit of the blackness of the black magnetic toner is usually about 15 when represented by L* value.
• the volume resistivity of the black magnetic toner according to the present invention is usually not less than 1.0 ⁇ 10 13 ⁇ •cm, preferably not less than 3.0 ⁇ 10 13 ⁇ •cm, more preferably not less than 5.0 ⁇ 10 13 ⁇ •cm.
• the upper limit of the volume resistivity is 1.0 ⁇ 10 17 ⁇ •cm.
• the coercive force thereof is usually 0.8 to 31.8 kA/m (10 to 400 Oe), preferably 1.6 to 30.2 kA/m (20 to 380 Oe);
• the saturation magnetization value in a magnetic field of 795.8 kA/m (10 kOe) is usually 10 to 85 Am 2 /kg (10 to 85 emu/g), preferably 20 to 80 Am 2 /kg (20 to 80 emu/g);
• the residual magnetization in a magnetic field of 795.8 kA/m (10 kOe) is usually 1 to 20 Am 2 /kg (1 to 20 emu/g), preferably Am 2 /kg (2 to 15 emu/g;
• the saturation magnetization in a magnetic field of 79.6 kA/m (1 kOe) is usually 7.5 to 65 Am 2 /kg (7.5 to 65 emu/g), preferably 10 to 60 Am 2 /kg (10 to 60 emu/g
• (1) octahedral magnetite particles can be produced by passing an oxygen-containing gas through a suspension containing ferrous hydroxide colloid having a pH value of not less than 10, which is obtained by reacting an aqueous ferrous salt solution with an aqueous alkali solution having a concentration of not less than one equivalent based on Fe 2+ in the aqueous ferrous salt solution, thereby precipitating magnetite particles, and then subjecting the obtained magnetite particles to filtering, washing with water and drying (Japanese Patent Publication (KOKOKU) No.
• hexahedral magnetite particles can be produced by passing an oxygen-containing gas through a suspension containing ferrous hydroxide colloid having a pH value of 6.0 to 7.5, which is obtained by reacting an aqueous ferrous salt solution with an aqueous alkali solution having a concentration of not more than one equivalent based on Fe 2+ in the aqueous ferrous salt solution to produce magnetite core particles, further passing an oxygen-containing gas through the obtained aqueous ferrous salt reaction solution containing the magnetite core particles and the ferrous hydroxide colloid, at a pH value of 8.0 to 9.5, to precipitate magnetite particles, and then subjecting the precipitated magnetite particles to filtering, washing with water and drying (Japanese Patent Application Laid-Open (KOKAI) No.
• spherical magnetite particles can be produced by passing an oxygen-containing gas through a suspension containing ferrous hydroxide colloid having a pH value of 6.0 to 7.5, which is obtained by reacting an aqueous ferrous salt solution with an aqueous alkali solution having a concentration of not more than one equivalent based on Fe 2+ in the aqueous ferrous salt solution to produce magnetite core particles, adding alkali hydroxide in an amount of not less than equivalent based on the remaining Fe 2+ to adjust the pH value of the suspension to not less than 10, heat-oxidizing the resultant suspension to precipitate magnetite particles, and then subjecting the precipitated magnetite particles to filtering, washing with water and drying (Japanese Patent Publication (KOKOKU) No. 62-51208(1987).
• the isotropic maghemite particles can be obtained by heating the above-mentioned isotropic magnetite particles in air at 300 to 600°C.
• the anisotropic magnetite particles can be produced by passing an oxygen-containing gas through a suspension containing either ferrous hydroxide colloid, iron carbonate, or an iron-containing precipitate obtained by reacting an aqueous ferrous salt solution with alkali hydroxide and/or alkali carbonate, while appropriately controlling the pH value and temperature of the suspension, to produce acicular, spindle-shaped or rice ball-shaped goethite particles, subjecting the obtained goethite particles to filtering, washing with water and drying, and then reducing the goethite particles in a heat-reducing gas at 300 to 800°C.
• the anisotropic maghemite particles can be produced by heat-oxidizing the above-mentioned anisotropic magnetite particles in an oxygen-containing gas at 300 to 600°C.
• the coating of the magnetic iron oxide particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes may be conducted (i) by mechanically mixing and stirring the magnetic iron oxide particles together with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes; or (ii) by mechanically mixing and stirring both the components together while spraying the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes onto the magnetic iron oxide particles.
• substantially whole amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes added can be applied onto the surfaces of the magnetic iron oxide particles.
• the magnetic iron oxide particles are preliminarily diaggregated by using a pulverizer.
• wheel-type kneaders may include an edge runner (equal to a mix muller, a Simpson mill or a sand mill), a multi-mull, a Stotz mill, a wet pan mill, a Conner mill, a ring muller, or the like.
• an edge runner, a multi-mull, a Stotz mill, a wet pan mill and a ring muller are preferred, and an edge runner is more preferred.
• ball-type kneaders may include a vibrating mill or the like.
• blade-type kneaders may include a Henschel mixer, a planetary mixer, a Nawter mixer or the like.
• roll-type kneaders may include an extruder or the like.
• the conditions of the above mixing or stirring treatment may be appropriately controlled such that the linear load is usually 19.6 to 1960 N/cm (2 to 200 Kg/cm), preferably 98 to 1470 N/cm (10 to 150 kg/cm), more preferably 147 to 980 N/cm (15 to 100 kg/cm); and the treating time is usually 5 to 120 minutes, preferably 10 to 90 minutes. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
• the amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes added is preferably 0.15 to 45 parts by weight based on 100 parts by weight of the magnetic iron oxide particles.
• the amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes added is less than 0.15 part by weight, it may become difficult to form the carbon black coat on the coating layer.
• the amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes added is more than 45 parts by weight, a sufficient amount of the carbon black coat can be formed on the surface of the coating, and therefore, it is meaningless to add such an excess amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes.
• a part of the alkoxysilanes coated on the surfaces of the core particles may be converted into the organosilane compounds via the coating step thereof. Even in such a case, the subsequent adhesion step with carbon black is not adversely affected.
• the carbon black fine particles are added to the magnetic iron oxide particles coated with the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes, and the resultant mixture is mixed and stirred to form a first carbon black coat on the surfaces of the coating composed of the the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes added.
• the conditions of the above mixing or stirring treatment can be appropriately controlled such that the linear load is usually 2 to 200 Kg/cm, preferably 10 to 150 Kg/cm more preferably 15 to 100 Kg/cm; and the treating time is usually 5 to 120 minutes, preferably 10 to 90 minutes. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
• the amount of the carbon black fine particles added for forming the first carbon black coat is usually 1 to 25 parts by weight, preferably 5 to 25 parts by weight based on 100 parts by weight of the magnetic iron oxide particles.
• the amount of carbon black fine particles added for forming the first carbon black coat is less than 1 part by weight, the amount of the adhesive capable of adhering onto the first carbon black coat also may become insufficient.
• carbon black fine particles for forming a second carbon black coat are subsequently added such that the total amount of carbon black adhered is not less than 26 parts by weight based on 100 parts by weight of the magnetic iron oxide particles as core particles, the desorption percentage of carbon black is disadvantageously increased, resulting in deteriorated dispersibility in a binder resin upon production of the magnetic toner.
• the carbon black adhered when the amount of carbon black adhered is as large as more than 25 parts by weight, the carbon black tends to be desorbed or fallen-off from the surface of each composite particle. Therefore, the carbon black also tends to be desorbed or fallen-off from the surfaces of the obtained black magnetic composite particles, resulting in deteriorated dispersibility in a binder resin upon production of the magnetic toner.
• carbon black fine particles used in the present invention there may be exemplified commercially available carbon blacks such as furnace black, channel black or the like.
• commercially available carbon blacks usable in the present invention may include #3050, #3150, #3250, #3750, #3950, MA100, MA7, #1000, #2400B, #30, MA77, MA8, #650, MA11, #50, #52, #45, #2200B, MA600, etc. (tradename, produced by MITSUBISHI CHEMICAL CORP.), SEAST 9H, SEAST 7H, SEAST 6, SEAST 3H, SEAST 300, SEAST FM, etc.
• the use of carbon black fine particles having a DBP oil absorption of not more than 150 ml/100g is preferred.
• Specific examples of the commercially available carbon blacks usable in the present invention may include MA100, MA7, #1000, #2400B, #30, MA77, MA8, #650, MA11, #50, #52, #45, #2200B, MA600, etc.
• the average particle size of the carbon black fine particles used is usually 0.002 to 0.05 ⁇ m, preferably 0.002 to 0.035 ⁇ m. When the average particle size of the carbon black fine particles used is less than 0.002 ⁇ m, the carbon black fine particles used are too fine to be well handled.
• the average particle size thereof is more than 0.05 ⁇ m, since the particle size of the carbon black fine particles used is much larger, it is necessary to apply a larger mechanical shear force for forming the uniform carbon black coat on the coating layer composed of the organosilicon compounds, thereby rendering the coating process industrially disadvantageous.
• carbon black fine particles are added little by little and slowly, especially about 5 to 60 minutes.
• the conditions of the above mixing or stirring treatment can be appropriately controlled such that the linear load is usually 19.6 to 1960 N/cm (2 to 200 Kg/cm), preferably 98 to 1470 N/cm (10 to 150 Kg/cm), more preferably 147 to 980 N/cm (15 to 100 Kg/cm); and the treating time is usually 5 to 120 minutes, preferably 10 to 90 minutes. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
• a second carbon black coat is formed onto the first carbon black coat through an adhesive such as dimethylpolysiloxanes.
• the first and second carbon black coats can be bonded to each other by adhering the carbon black themselves through the adhesive, thereby obtaining a carbon black coat wherein the first and second carbon black coats are integrated.
• dimethylpolysiloxanes represented by the following formula is preferably used as the adhesive. wherein v' is a is an integer of 15 to 450.
• the amount of the adhesive added is usually 0.1 to 5.0 parts by weight, preferably 0.2 to 4.0 parts by weight, more preferably 0.3 to 3.0 parts by weight based on 100 parts by weight of the core particles.
• the amount of the adhesive adhered is less than 0.1 part by weight, it may be difficult to sufficiently bond the second carbon black coat onto the first carbon black coat, thereby failing to obtain black magnetic composite particles exhibiting a more excellent fluidity and a more excellent blackness.
• the carbon black can be adhered thereon in such an amount enough to achieve the more excellent fluidity and blackness of the obtained black magnetic composite particles.
• the effect is already saturated, it is unnecessary to use such a large amount of the adhesive.
• the amount of the adhesive is usually 0.04 to 1.89 % by weight, preferably 0.08 to 1.51 % by weight, more preferably 0.11 to 1.13 % by weight (calculated as Si) based on the weight of the magnetic iron oxide particles.
• the carbon black fine particles are added to, and then mixed and stirred with the resultant mixture to form the second carbon black coat onto the first carbon black coat through the adhesive, thereby integrating the carbon black coats.
• the thus obtained composite particles may be dried and heat-treated, if required.
• the mixing and stirring conditions for adhering the adhesive onto the composite particles on which the first carbon black coat is formed may be appropriately selected such that the adhesive can be uniformly coated onto the first carbon black coat of each composite particle.
• the linear load used for the mixing and stirring is usually 19.6 to 1,960 N/cm (2 to 200 kg/cm), preferably 98 to 1,470 N/cm (10 to 150 kg/cm), more preferably 147 to 980 N/cm (15 to 100 kg/cm); the treating time is 5 to 120 minutes, preferably 10 to 90 minutes; and the stirring speed is usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
• the amount of the carbon black fine particles added for forming the second carbon black coat is 1 to 30 parts by weight based on 100 parts by weight of the magnetic iron oxide particles.
• the amount of the carbon black fine particles added is less than 1 part by weight, the total amount of carbon black adhered becomes insufficient, so that it may be difficult to obtain aimed black magnetic composite particles which are more excellent in fluidity and blackness.
• the amount of the carbon black fine particles added is more than 30 part by weight, the carbon black tends to be desorbed or fallen-off from the surfaces of the obtained black magnetic composite particles, resulting in deteriorated dispersibility in a binder resin upon production of the magnetic toner.
• the mixing and stirring conditions for forming the second carbon black coat onto the first carbon black coat through the adhesive may be appropriately selected such that the second carbon black coat can be uniformly coated onto the first carbon black coat through the adhesive.
• the linear load used for the mixing and stirring is usually 19.6 to 1,960 N/cm (2 to 200 kg/cm), preferably 98 to 1,470 N/cm (10 to 150 kg/cm), more preferably 147 to 980 N/cm (15 to 100 kg/cm); the treating time is 5 to 120 minutes, preferably 10 to 90 minutes; and the stirring speed is usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
• the resultant black magnetic composite particles may be dried or heat-treated, for example, at a temperature of usually 40 to 200°C, preferably 60 to 150°C for usually 10 minutes to 12 hours, preferably 30 minutes to 3 hours.
• At least a part of the surface of the magnetic iron oxide particles as core particles may be coated with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon, in advance of mixing and stirring with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes.
• the coat of the hydroxides and/or oxides of aluminum and/or silicon may be conducted by adding an aluminum compound, a silicon compound or both the compounds to a water suspension in which the magnetic iron oxide particles are dispersed, followed by mixing and stirring, and further adjusting the pH value of the suspension, if required, thereby coating the surfaces of the magnetic iron oxide particles with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon.
• the thus obtained particles coated with the hydroxides and/or oxides of aluminum and/or silicon are then filtered out, washed with water, dried and pulverized. Further, the particles coated with the hydroxides and/or oxides of aluminum and/or silicon may be subjected to posttreatments such as deaeration treatment and compaction treatment.
• aluminum compounds there may be exemplified aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride or aluminum nitrate, alkali aluminates such as sodium aluminate or the like.
• the amount of the aluminum compound added is 0.01 to 50 % by weight (calculated as Al) based on the weight of the magnetic iron oxide particles.
• the amount of the aluminum compound added is less than 0.01 % by weight, it may be difficult to sufficiently coat the surfaces of the magnetic iron oxide particles with hydroxides and/or oxides of aluminum, which can achieve the improvement of lessening the percentage of desorption of carbon black therefrom, thereby failing to achieve the improvement of the dispersibility in the binder resin upon the production of the magnetic toner.
• the amount of the aluminum compound added is more than 50 % by weight, the coating effect is saturated and, therefore, it is meaningless to add such an excess amount of the aluminum compound.
• silicon compounds there may be exemplified water glass #3, sodium orthosilicate, sodium metasilicate, colloidal silica or the like.
• the amount of the silicon compound added is 0.01 to 50 % by weight (calculated as SiO 2 ) based on the weight of the magnetic iron oxide particles.
• the amount of the silicon compound added is less than 0.01 % by weight, it may be difficult to sufficiently coat the surfaces of the magnetic iron oxide particles with hydroxides and/or oxides of silicon, which can achieve the improvement of lessening the percentage of desorption of carbon black therefrom, thereby failing to achieve the improvement of the dispersibility in the binder resin upon the production of the magnetic toner.
• the amount of the silicon compound added is more than 50 % by weight, the coating effect is saturated and, therefore, it is meaningless to add such an excess amount of the silicon compound.
• the total amount of the aluminum and silicon compounds added is preferably 0.01 to 50 % by weight (calculated as a sum of Al and SiO 2 ) based on the weight of the magnetic iron oxide particles.
• the black magnetic toner according to the present invention may be produced by a known method of mixing and kneading a predetermined amount of a binder resin and a predetermined amount of the black magnetic composite particles together, and then pulverizing the mixed and kneaded material into particles. More specifically, the black magnetic composite particles and the binder resin are intimately mixed together with, if necessary, a mold release agent, a colorant, a charge-controlling agent or other additives by using a mixer. The obtained mixture is then melted and kneaded by a heating kneader so as to render the respective components compatible with each other, thereby dispersing the black magnetic composite particles therein. Successively, the molten mixture is cooled and solidified to obtain a resin-kneaded product. The resin-kneaded product is then pulverized and classified, thereby producing a magnetic toner having an aimed particle size.
• the mixers there may be used a Henschel mixer, a ball mill or the like.
• the heating kneaders there may be used a roll mill, a kneader, a twin-screw extruder or the like.
• the pulverization of the resin mixture may be conducted by using pulverizers such as a cutter mill, a jet mill or the like.
• the classification of the pulverized particles may be conducted by known methods such as air classification, etc., as described in Japanese Patent No. 2683142 or the like.
• the other method of producing the black magnetic toner there may be exemplified a suspension polymerization method or an emulsion polymerization method.
• the suspension polymerization method polymerizable monomers and the black magnetic composite particles are intimately mixed together with, if necessary, a colorant, a polymerization initiator, a cross-linking agent, a charge-controlling agent or the other additives and then the obtained mixture is dissolved and dispersed together so as to obtain a monomer composition.
• the obtained monomer composition is added to a water phase containing a suspension stabilizer while stirring, thereby granulating and polymerizing the composition to form magnetic toner particles having an aimed particle size.
• the monomers and the black magnetic composite particles are dispersed in water together with, if necessary, a colorant, a polymerization initiator or the like and then the obtained dispersion is polymerized while adding an emulsifier thereto, thereby producing magnetic toner particles having an aimed particle size.
• a point of the present invention lies in such a fact that the black magnetic composite particles according to the present invention which are obtained by firmly adhering carbon black onto the surfaces of magnetic iron oxide particles in an amount of 26 to 55 parts by weight based on 100 parts by weight of the magnetic iron oxide particles, are not only more excellent in fluidity and blackness, but also have a less amount of carbon black desorbed or fallen-off from the surface of each particle.
• the black magnetic composite particles of the present invention can exhibit a more excellent fluidity, is considered as follows.
• the carbon black tends to act as aggregates because of its fineness.
• the carbon black since the carbon black is uniformly and densely adhered and bonded onto the surface of each magnetic iron oxide particle, it is considered that many fine irregularities are formed on the surface of each magnetic iron oxide particle.
• the reason why the black magnetic composite particles of the present invention can exhibit a more excellent blackness is considered as follows. That is, since a uniform carbon black coat having an appropriate thickness is formed by densely adhering and bonding carbon black onto the surface of each magnetic iron oxide particle, the color of the magnetic iron oxide particles is hidden behind the carbon black coat, so that an inherent black color of the carbon black can be effectively exhibited.
• the functional groups in the polysiloxanes or modified polysiloxanes onto which the carbon black coat is formed are strongly bonded to the surface of the magnetic iron oxide particle.
• each black magnetic composite particle due to the less amount of carbon black desorbed or fallen-off from the surface of each black magnetic composite particle, materials present in the system can be well dispersed together without any disturbance by the desorbed carbon black. Further, since irregularities are formed on the surface of each magnetic iron oxide particle by the carbon black adhered and bonded thereonto, the particles are prevented from contacting with each other, resulting in excellent dispersibility in a binder resin upon production of the magnetic toner.
• the black magnetic toner according to the present invention obtained by using the above black magnetic composite particles adhered with a large amount of carbon black, can exhibit more excellent fluidity and blackness while maintaining as high a resistivity as not less than 1 ⁇ 10 13 ⁇ •cm.
• the reason why the black magnetic toner of the present invention exhibits a more excellent fluidity is considered as follows. That is, the black magnetic composite particles obtained by uniformly adhering a large amount of carbon black onto the surface of each magnetic iron oxide particle, are exposed to the surface of the black magnetic toner, thereby forming many fine irregularities thereon.
• the reason why the black magnetic toner of the present invention exhibits a more excellent blackness, is considered by the present inventors as follows. That is, the black magnetic composite particles having a more excellent blackness are blended in the black magnetic toner.
• carbon black is present in the form of aggregated particles constituted from parallel-stacked crystallites each having a pseudo-graphite structure. Further, the carbon black fine particles are chemically and physically bonded with each other to form a cluster-like (grape-like cluster) structure. It is known that the larger the cluster-like structure, the higher the electrical conductivity of carbon black becomes. In the case where the carbon black fine particles having such a cluster-like structure are added to and mixed with a binder resin, those exposed to the surface of the magnetic toner also have the cluster-like structure, thereby increasing a conductivity of the magnetic toner. As a result, it is difficult to obtain a magnetic toner having a high volume resistivity value.
• the carbon black coat is formed onto the surface of each magnetic iron oxide particle without forming the cluster-like structure. Therefore, since the magnetic toner using such black magnetic composite particles are also free from carbon black having the cluster-like structure, thereby maintaining a high volume resistivity value.
• the black magnetic composite particles according to the present invention are not only more excellent in fluidity and blackness, but also show an excellent dispersibility in a binder resin due to a less amount of carbon black desorbed or fallen-off from the surface of each particle. Therefore, the black magnetic composite particles of the present invention are suitable as black magnetic particles capable of achieving a high image quality and a high copying speed.
• the black magnetic composite particles of the present invention have an excellent dispersibility, i.e., an excellent handling property and are, therefore, industrially advantageous.
• the black magnetic toner obtained by using such black magnetic composite particles having more excellent fluidity and blackness can also exhibit more excellent fluidity and blackness and is, therefore, suitable as black magnetic toner for achieving a high image quality and a high copying speed.
• the black magnetic toner of the present invention can maintain a high volume resistivity value nevertheless the use of black magnetic composite particles adhered with a large amount of carbon black. Therefore, the black magnetic toner of the present invention is suitable as high-resistant or insulating magnetic toner.
• the average particle size, the average major axial diameter and average minor axial diameter of magnetic iron oxide particles, composite particles, black magnetic composite particles and carbon black fine particles were respectively expressed by the average of values (measured in a predetermined direction) of about 350 particles which were sampled from a micrograph obtained by magnifying an original electron micrograph ( ⁇ 20,000) by four times in each of the longitudinal and transverse directions.
• the aspect ratio of the particles was expressed by the ratio of an average major axial diameter to an average minor axial diameter thereof.
• the sphericity of the particles was expressed by the ratio of an average particle length to an average particle breadth thereof.
• the geometrical standard deviation of particle sizes was expressed by values obtained by the following method. That is, the particle sizes (major axial diameters) were measured from the above magnified electron micrograph. The actual particle sizes (major axial diameters) and the number of the particles were calculated from the measured values. On a logarithmic normal probability paper, the particle sizes (major axial diameters) were plotted at regular intervals on the abscissa-axis and the accumulative number (under integration sieve) of particles belonging to each interval of the particle sizes (major axial diameters) were plotted by percentage on the ordinate-axis by a statistical technique.
• Geometrical standard deviation ⁇ particle size (major axial diameters) corresponding to 84.13 % under integration sieve ⁇ / ⁇ particle size (major axial diameters) (geometrical average diameter) corresponding to 50 % under integration sieve ⁇
• the specific surface area was expressed by the value measured by a BET method.
• the thickness of carbon black coat formed on the surfaces of the magnetic iron oxide particles is expressed by the value which was obtained by first measuring an average thickness of carbon black coat formed onto the surfaces of the particles on a photograph ( ⁇ 5,000,000) obtained by magnifying (ten times) a micrograph ( ⁇ 500,000) produced at an accelerating voltage of 200 kV using a transmission-type electron microscope (JEM-2010, manufactured by Japan Electron Co., Ltd.), and then calculating an actual thickness of carbon black coat formed from the measured average thickness.
• JEM-2010 transmission-type electron microscope
• the fluidity of magnetic iron oxide particles, composite particles, black magnetic composite particles and magnetic toner was expressed by a fluidity index which was a sum of indices obtained by converting on the basis of the same reference measured values of an angle of repose, a degree of compaction (%), an angle of spatula and a degree of agglomeration as particle characteristics which were measured by a powder tester (tradename, produced by Hosokawa Micron Co., Ltd.). The closer to 100 the fluidity index, the more excellent the fluidity of the particles.
• the blackness of magnetic iron oxide particles, composite particles, black magnetic composite particles and magnetic toner was measured by the following method. That is, 0.5 g of sample particles and 1.5 ml of castor oil were intimately kneaded together by a Hoover's muller to form a paste. 4.5 g of clear lacquer was added to the obtained paste and was intimately kneaded to form a paint. The obtained paint was applied on a cast-coated paper by using a 6-mil (150 pm) applicator to produce a coating film piece (having a film thickness of about 30 ⁇ m).
• the thus obtained coating film piece was measured according to JIS Z 8729 by a multi-light source spectrographic colorimeter MSC-IS-2D (manufactured by Suga Testing Machines Manufacturing Co., Ltd.) to determine an L* value of colorimetric indices thereof.
• the blackness was expressed by the L* value measured.
• the L* value represents a lightness
• the smaller the L* value the more excellent the blackness
• the thus obtained particles were dried at 100°C for one hour, and then the carbon content thereof was measured by the "Horiba Metal, Carbon and Sulfur Analyzer EMIA-2200 Model" (manufactured by Horiba Seisakusho Co., Ltd.).
• the dispersibility in a binder resin of the black magnetic composite particles was evaluated by counting the number of undispersed agglomerated particles on a micrograph ( ⁇ 200) obtained by photographing a sectional area of the obtained black magnetic toner particle using an optical microscope (BH-2, manufactured by Olympus Kogaku Kogyo Co., Ltd.), and classifying the results into the following five ranks.
• the 5th rank represents the most excellent dispersing condition.
• the average particle size of the black magnetic toner was measured by a laser diffraction-type particle size distribution-measuring apparatus (Model HELOSLA/KA, manufactured by Sympatec Corp.).
• the thus obtained cylindrical test piece was exposed to an atmosphere maintained at a temperature of 25°C and a relative humidity of 60 % for 12 hours. Thereafter, the cylindrical test piece was set between stainless steel electrodes, and a voltage of 15V was applied between the electrodes using a Wheatstone bridge (TYPE2768, manufactured by Yokogawa-Hokushin Denki Co., Ltd.) to measure a resistance value ( ⁇ ).
• a Wheatstone bridge TYPE2768, manufactured by Yokogawa-Hokushin Denki Co., Ltd.
• the cylindrical test piece was measured with respect to an upper surface area A (cm 2 ) and a thickness t 0 (cm) thereof.
• the measured values were inserted into the following formula, thereby obtaining a volume resistivity X ( ⁇ •cm).
• Resistance value ( ⁇ •cm) R ⁇ (A/t 0 )
• the magnetic properties of the magnetic iron oxide particles, the composite particles and the black magnetic composite particles were measured using a vibration sample magnetometer "VSM-3S-15" (manufactured by Toei Kogyo Co., Ltd.) by applying an external magnetic field of 795.8 kA/m (10 kOe) thereto.
• the magnetic properties of the black magnetic toner were measured by applying external magnetic fields of 79.6 kA/m (1 kOe) and 795.8 kA/m (10 kOe) thereto.
• the obtained slurry containing the spherical magnetite particles was passed through a transverse-type sand grinder (tradename "MIGHTY MILL MHG-1.5L", manufactured by Inoue Seisakusho Co., Ltd.) five times at an axis-rotating speed of 2,000 rpm, thereby obtaining a slurry in which the spherical magnetite particles were dispersed.
• a transverse-type sand grinder tradename "MIGHTY MILL MHG-1.5L", manufactured by Inoue Seisakusho Co., Ltd.
• the particles in the obtained slurry which remained on a sieve of 325 meshes (mesh size: 44 ⁇ m) was 0 %.
• the slurry was filtered and washed with water, thereby obtaining a filter cake containing the spherical magnetite particles.
• 11.0 kg of the dried particles were then charged into an edge runner "MPUV-2 Model" (tradename, manufactured by Matsumoto Chuzo Tekkosho Co., Ltd.), and mixed and stirred at 294 N/cm (30 Kg/cm) and a stirring speed of 22 rpm for 30 minutes, thereby lightly deagglomerating the particles.
• methyltriethoxysilane (tradename: "TSL8123", produced by GE Toshiba Silicone Co., Ltd.) was mixed and diluted with 200 ml of ethanol to obtain a methyltriethoxysilane solution.
• the methyltriethoxysilane solution was added to the deagglomerated spherical magnetite particles under the operation of the edge runner.
• the spherical magnetite particles were continuously mixed and stirred at a linear load of 392 N/CM (40 Kg/cm) and a stirring speed of 22 rpm for 60 minutes to form a coating layer composed of methyltriethoxysilane on the spherical magnetite particles.
• carbon black fine particles A particle shape: granular shape; average particle size: 0.022 ⁇ m; geometrical standard deviation value: 1.68; BET specific surface area value: 134 m 2 /g; DBP oil absorption: 89 ml/100 g; and blackness (L* value): 16.6 were added to the spherical magnetite particles coated with methyltriethoxysilane for 10 minutes while operating the edge runner. Further, the mixed particles were continuously stirred at a linear load of 392 N/cm (40 Kg/cm) and a stirring speed of 22 rpm for 60 minutes to form the carbon black coat on the coating layer composed of methyltriethoxysilane, thereby obtaining composite particles.
• dimethylpolysiloxane (tradename: "TSF451", produced by GE Toshiba Silicone Co., Ltd.) was added to the above composite particles while operating an edge runner, and the obtained mixture was then mixed and stirred together at a linear load of 588 N/cm (60 Kg/cm) and a stirring speed of 22 rpm for 30 minutes, thereby obtaining composite particles on which dimethylpolysiloxane was uniformly adhered.
• 1,650 g of the above carbon black fine particles A were added to the above obtained particles for 10 minutes while operating the edge runner, and then mixed and stirred together at a linear load of 588 N/cm (60 Kg/cm) and a stirring speed of 22 rpm for 30 minutes, thereby bonding the second carbon black coat onto the first carbon black coat through the dimethylpolysiloxane as an adhesive. Thereafter, the obtained particles were heat-treated at 105°C for 60 minutes using a drier, thereby obtaining black magnetic composite particles.
• the obtained black magnetic composite particles had an average particle diameter of 0.24 ⁇ m, and a sphericity of 1.2:1 as shown in the electron photograph.
• the black magnetic composite particles showed a geometrical standard deviation of 1.42, a BET specific surface area value of 12.3 m 2 /g, fluidity index of 58, a blackness (L* value) of 17.6, and a desorption percentage of carbon black: 7.8 %.
• the amount of the carbon black coat formed on the coating layer composed of the organosilane compound produced from methyl triethoxysilane is 26.01 % by weight (calculated as C) based on the weight of the black magnetic composite particles (corresponding to 30 parts by weight based on 100 parts by weight of the spherical magnetite particles).
• the thickness of the carbon black coat formed was 0.0027 pm.
• the amount of dimethylpolysiloxanes adhered was 0.70 % by weight (calculated as Si).
• the obtained black magnetic composite particles had an a coercive force value of 4.9 kA/m (61 Oe), a saturation magnetization value (in a magnetic field of 795.8 kA/m (10 kOe)) of 76.9 Am 2 /kg (76.9 emu/g), a residual magnetization value (in a magnetic field of 795.8 kA/m (10 kOe)) of 7.0 Am 2 /kg (7.0 emu/g),
• the obtained mixed particles were melt-kneaded at 140°C using a continuous-type twin-screw kneader (T-1), and the obtained kneaded material was cooled, coarsely pulverized and finely pulverized in air. The obtained particles were subjected to classification, thereby producing a black magnetic toner.
• T-1 continuous-type twin-screw kneader
• the obtained black magnetic toner had an average particle size of 9.9 ⁇ m, a dispersibility of 5th rank, a fluidity index of 84, a blackness (L* value) of 17.8, a volume resistivity of 8.4 ⁇ 10 13 ⁇ •cm, a coercive force value of 4.7 kA/m (59 Oe), a saturation magnetization value (in a magnetic field of 795.8 kA/m (10 kOe)) of 32.2 Am 2 /kg (32.2 emu/g), a residual magnetization value (in a magnetic field of 795.8 kA/m (10 kOe)) of 4.1 Am 2 /kg (4.1 emu/g), a saturation magnetization value (in a magnetic field of 79.6 kA/m (1 kOe)) of 25.3 Am 2 /kg (25.3 emu/g), and a residual magnetization value (in a magnetic field of 79.6 kA/m (1 kOe
• Magnetic iron oxide particles 1 to 4 are Magnetic iron oxide particles 1 to 4:
• Example 2 Various magnetic iron oxide particles were prepared by known methods. The same procedure as defined in Example 1 was conducted by using the thus prepared particles, thereby obtaining deagglomerated magnetic iron oxide particles as core particles.
• Example 2 The same procedure as defined in Example 1 was conducted by using 20 kg of the deagglomerated octahedral magnetite particles (core particles 1) and 150 liters of water, thereby obtaining a slurry containing the octahedral magnetite particles.
• the pH value of the obtained re-dispersed slurry containing the octahedral magnetite particles was adjusted to 4.0 by adding acetic acid, and then the concentration of the slurry was adjusted to 98 g/liter by adding water thereto.
• the pH value of the slurry was adjusted to 7.5 by adding acetic acid. After further allowing the slurry to stand for 30 minutes, the slurry was subjected to filtration, washing with water, drying and pulverization, thereby obtaining the octahedral magnetite particles coated with hydroxides of aluminum and oxides of silicon.
• Magnetic iron oxide particles 6 to 8 are Magnetic iron oxide particles 6 to 8:
• Example 2 The same procedure as defined in Example 1 was conducted except that kind of magnetic iron oxide particles to be treated, addition or non-addition of an alkoxysilane compound or polysiloxane in the coating treatment with alkoxysilane compound or polysiloxane, kind and amount of the alkoxysilane compound or polysiloxane added, treating conditions of edge runner in the coating treatment, kind and amount of carbon black fine particles added in the first carbon black coat forming step, and treating conditions of edge runner used in the process for forming the first carbon black coat, were varied, thereby obtaining composite particles.
• the composite particles obtained in Examples 3 to 14 were observed by an electron microscope. As a result, almost no independent carbon black was recognized. Therefore, it was confirmed that a substantially whole amount of the carbon black contributed to the formation of the first carbon black coat on the coating layer composed of organosilane compound produced from the alkoxysilane compound or polysiloxane.
• Example 2 The same procedure as defined in Example 1 was conducted except that kind of composite particles, kind and amount of adhesive added, edge runner treatment conditions used in the adhesive-treating step, kind and amount of carbon black fine particles added in the second carbon black coat-adhering step, and edge runner treatment conditions used in the second carbon black coat-adhering step, were changed variously, thereby obtaining black magnetic composite particles.
• Example 2 The same procedure as defined in Example 2 was conducted by using the black magnetic composite particles obtained in Examples 15 to 26, composite particles obtained in Example 5, Core particles 1 to 4, and Comparative Examples 3 and 5 to 11, thereby obtaining black magnetic toners.

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