JP2008065285A - Two-component developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-component developer which achieves good charge buildup performance and good development efficiency even in an image forming apparatus using a noncontact development method, whereby image variation and reduction of image density are suppressed; and to provide an image forming method using the two-component developer. <P>SOLUTION: The two-component developer comprises a toner and a carrier, wherein the toner contains toner base particles and an external additive; the toner base particles contains a binder resin, a charge control agent, and a colorant; and the toner base particles and/or the external additive contains metal oxide fine particles having a volume resistivity of 100-1,000 Ω cm and a bulk density of 600-1,000 g/l. The image forming method uses the two-component developer in an image forming apparatus using a noncontact development method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a two-component developer used for developing a latent image formed in electrophotography, electrostatic recording method, electrostatic printing method, and the like, and an image forming method using the two-component developer.

In Patent Document 1, by externally adding conductive titanium oxide to the toner as conductive metal fine particles, charge can be transferred between the toner particles via the conductive titanium oxide, and variation in charge amount is small. There is disclosed a toner that enables clear and high-quality printing without causing rash or blur.
JP 2002-108002 A

  However, the toner described in Patent Document 1 in which inorganic fine particles having a large particle diameter are used has a drawback that streaks are likely to occur and image unevenness is likely to occur.

  Occurrence of image unevenness and a decrease in image density are related to charge rise characteristics and development efficiency. In particular, in a non-contact development type image forming apparatus, when the development efficiency is lowered, the development efficiency is extremely deteriorated. .

  SUMMARY OF THE INVENTION An object of the present invention is to provide a two-component developer capable of obtaining good charge rising property and developing efficiency even in a non-contact development type image forming apparatus and reducing image unevenness and image density reduction, and the two-component developer. An object of the present invention is to provide an image forming method using the above.

The present invention
[1] A toner having toner base particles containing a binder resin, a charge control agent and a colorant and an external additive, wherein the toner base particles and / or the external additive have a volume resistivity of 100 to 100. A two-component developer comprising a toner and a carrier containing metal oxide fine particles having a bulk density of 600 to 1000 g / l at 1000 Ω · cm, and [2] the two-component developer according to [1] above The present invention relates to an image forming method used in an image forming apparatus of a non-contact development type.

  The two-component developer according to the present invention has excellent effects such that good charge rising property and development efficiency can be obtained even in a non-contact development type image forming apparatus, and unevenness in image and reduction in image density are reduced. It is.

  The two-component developer of the present invention has a great feature in that metal oxide fine particles having specific volume resistivity and bulk density are contained in the toner.

  The volume resistivity of the metal oxide fine particles is 100 Ω · cm or more from the viewpoint of preventing the toner charge from leaking and obtaining stable chargeability, and 1000 Ω · cm or less from the viewpoint of reducing electrostatic adhesion. It is. From these viewpoints, the volume resistivity of the metal oxide fine particles is 100 to 1000 Ω · cm, preferably 200 to 800 Ω · cm, more preferably 200 to 500 Ω · cm. The semiconductive metal oxide fine particles adjusted to have a volume resistivity within the above range reduce the electrostatic attractive force between the toner and the developing roller and improve the developing efficiency. In particular, in a non-contact development type image forming apparatus in which the developing roller and the photosensitive member are in a non-contact state, if the developing efficiency is lowered, the developing efficiency is extremely deteriorated, so that the adhesion force between the toner and the developing roller is reduced. It is a very important issue. The volume resistivity of the metal oxide fine particles is measured by the method described in Examples described later.

  The bulk density of the metal oxide fine particles is 600 g / l or more from the viewpoint of increasing the stirring efficiency of the toner and the carrier and improving the charge rising property, and 1000 g / l or less from the viewpoint of preventing embedding. From these viewpoints, the bulk density of the metal oxide fine particles is 600 to 1000 g / l, preferably 600 to 800 g / l, more preferably 700 to 800 g / l. The metal oxide fine particles within the bulk density range improve the stirring efficiency of the toner and carrier in the two-component development system and improve the charging start-up property. Even in continuous printing, stable development efficiency can be maintained. As a result, the occurrence of image density reduction and image unevenness is reduced. The bulk density of the metal oxide fine particles is measured by the method described in Examples described later.

  The metal oxide fine particles in the present invention are not only fine particles selected from metal oxides whose volume resistivity and bulk density are within the above ranges, but also the volume resistance of the metal oxide fine particles by pulverization treatment or changing the coating agent. The rate and / or bulk density may be adjusted. The volume resistivity can be adjusted by the material of the coating agent, the coating amount, etc. For example, by using conductive tin oxide as the coating agent, a conductive film is formed on the surface of the metal oxide, and the metal oxide itself Can have a low volume resistivity. The bulk density can be adjusted by a crushing process or the like. For example, the bulk density of the metal oxide itself can be lowered by applying a crushing process for a predetermined time with a jet mill or the like.

  In addition, the metal oxide fine particles in the present invention have a thin hue as compared with, for example, a general conductivity imparting agent such as carbon black, and the above effects can be exhibited without impairing the hue even in a color toner.

  Examples of the metal oxide fine particles in the present invention include fine particles comprising titanium dioxide, zinc oxide, alumina and the like. These metal oxide fine particles may be added to the toner as they are, but from the viewpoint of imparting electrical conductivity, it is preferable that a film is formed on the surface with a metal oxide such as tin oxide.

  A conventionally well-known method can be used for formation of the film by metal oxides, such as a tin oxide. For example, an aqueous suspension of titanium dioxide fine particles is prepared and adjusted to a predetermined temperature, and then tin tetrachloride oxide is dropped and neutralized to form a tin oxide film on the surface of the titanium oxide fine particles. .

  As described above, when tin oxide coating is applied to metal oxide fine particles, oxidation in the metal oxide fine particles after tin oxide coating is performed from the viewpoint of maintaining semiconductivity and preventing charge leakage into the toner. The content of tin is preferably 10 to 90% by weight, and more preferably 20 to 80% by weight.

  In addition, metal oxide fine particles or metal oxide fine particles formed with a metal oxide coating are made of an organic compound such as silicone oil, modified silicone oil, fatty acid, fatty acid compound, etc. from the viewpoint of fluidity and environmental stability. Organic surface treatment is preferred.

  The organic surface treatment is a method in which the organic compound is directly put into the stirring metal oxide fine particles, and then heated and dried. The organic compound is dissolved in an organic solvent, and the solution is stirred into the metal oxide fine particles. It can carry out by the method of drying, etc. after dripping.

  When the metal oxide fine particles are subjected to an organic surface treatment as described above, the content of the organic compound is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the metal oxide fine particles from the viewpoint of charge amount and environmental stability. 0.5 to 5 parts by weight is more preferable.

  The average particle diameter of the metal oxide fine particles is preferably from 1 to 1000 nm, more preferably from 50 to 500 nm, from the viewpoints of prevention of embedding and desorption. The average particle diameter of the metal oxide fine particles is measured by the method described in Examples described later.

  The metal oxide fine particles may be contained in either the toner base particles or the external additive in the toner having the toner base particles and the external additive, but the viewpoint of imparting the function more effectively with a small content. Therefore, it is preferably contained in the external additive.

  When the metal oxide fine particles are contained in the external additive, the content is preferably 0.01 to 20 parts by weight with respect to 100 parts by weight of the toner base particles from the viewpoint of imparting an appropriate charge level, More preferred is ˜10 parts by weight. In addition, the content when the metal oxide fine particles are contained in the toner base particles, or the total content when the metal oxide fine particles are contained in both the toner base particles and the external additive is determined from the same viewpoint as described above. The amount is preferably 0.01 to 20 parts by weight and more preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the toner base particles excluding the oxide fine particles.

  In the present invention, the toner base particles contain at least a binder resin, a charge control agent, and a colorant.

  Examples of the binder resin in the present invention include vinyl resins such as polyester and styrene-acrylic resins, epoxy resins, polycarbonates, polyurethanes, hybrid resins having two or more resin components, and the like. When the toner has a carboxyl group as a charge control agent, polyester is preferable. The synergistic action of the carboxyl group of the polyester and the carboxyl group of the charge control agent further makes the charge on the toner surface more uniform, so that the effect of the present invention can be exhibited more remarkably. The polyester content is preferably 50 to 100% by weight in the binder resin, more preferably 70 to 100% by weight, and still more preferably 100% by weight.

  The polyester is obtained by polycondensing a known alcohol component and a known carboxylic acid component such as a carboxylic acid, a carboxylic acid anhydride, or a carboxylic acid ester as raw material monomers.

  Examples of the alcohol component include alkylenes of bisphenol A such as polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane and polyoxyethylene (2.0) -2,2-bis (4-hydroxyphenyl) propane. (Carbon number 2 to 3) Oxide (average added mole number 1 to 16) adduct, ethylene glycol, propylene glycol, glycerin, pentaerythritol, trimethylolpropane, hydrogenated bisphenol A, sorbitol, or alkylene thereof (carbon number 2 -4) Oxide (average added mole number 1-16) adduct and the like.

  The carboxylic acid component includes dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, fumaric acid, maleic acid, adipic acid and succinic acid, alkyl groups having 1 to 20 carbon atoms such as dodecenyl succinic acid and octenyl succinic acid, or carbon. Trivalent or higher polyvalent carboxylic acids such as succinic acid, trimellitic acid, and pyromellitic acid substituted with an alkenyl group having 2 to 20 carbon atoms, anhydrides of these acids, and alkyls of those acids (1 to 3 carbon atoms) ) Esters and the like. The acids as described above, and anhydrides and alkyl esters of these acids are collectively referred to herein as carboxylic acid compounds.

  The carboxylic acid component preferably contains fumaric acid and / or maleic acid. When the content of fumaric acid or maleic acid or both are contained, the total content thereof is preferably 40 to 100 mol%, more preferably 50 to 90 mol%, further preferably 60 to 80 mol%. Resins using fumaric acid and / or maleic acid as a raw material monomer have a low resistance of the resin itself because there is no electronically rich benzene ring compared to benzene derivatives such as isophthalic acid and terephthalic acid. The toner containing a resin also has a low toner resistance, a reduced electrostatic adhesion, and a high development efficiency. Further, stable developability can be obtained even in a high-speed developing machine that requires quick charge rise and quick charge.

  The alcohol component may contain a monovalent alcohol, and the carboxylic acid component may contain a monovalent carboxylic acid compound as appropriate from the viewpoints of molecular weight adjustment and offset resistance improvement.

  The polyester is obtained, for example, by subjecting an alcohol component and a carboxylic acid component to condensation polymerization at a temperature of 180 to 250 ° C. in an inert gas atmosphere, if necessary, in the presence of an esterification catalyst.

  In the present invention, the polyester may be a polyester modified to such an extent that the characteristics are not substantially impaired. Examples of the modified polyester include grafting and blocking with phenol, urethane, epoxy and the like by the methods described in JP-A-11-133668, JP-A-10-239903, JP-A-8-20636, and the like. Polyester.

  From the viewpoint of durability and fixability, the softening point of the polyester is preferably 80 to 165 ° C, the glass transition point is preferably 50 to 85 ° C, and the acid value is preferably 0.5 to 60 mgKOH / g.

  As the colorant, it is possible to use dyes, pigments, and the like that are used as colorants for black toners or color toners. Carbon black, phthalocyanine blue, permanent brown FG, brilliant first scarlet, pigment green B, Rhodamine-B base, solvent red 49, solvent red 146, solvent blue 35, quinacridone, carmine 6B, disazo yellow and the like can be used, and these can be used alone or in combination of two or more. The toner is black toner However, the metal oxide fine particles in the present invention have a thin hue, and even in the case of a color toner, the effect of the present invention is exhibited without impairing the hue. The content of the colorant is preferably 1 to 40 parts by weight and more preferably 3 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  The charge control agent may be either a positively chargeable charge control agent or a negatively chargeable charge control agent, and these may be used in combination.

  Examples of the positively chargeable charge control agent include nigrosine dyes, quaternary ammonium salts, and the like, but quaternary ammonium salts are preferable from the viewpoint of little influence on the color tone of the toner.

  As quaternary ammonium salts of carboxylic acids, the formula (I):

(Wherein R ^{1 to} R ⁴ may be the same or different and each may be substituted with a halogen atom, a lower alkyl group having 1 to 8 carbon atoms, an alkyl group or alkenyl group having 8 to 22 carbon atoms, or aryl group or aralkyl group having 6 to 20 carbon atoms, Y ^- represents a carboxylate ion)
The compound represented by these is preferable.

In the present invention, R ^{1 to} R ⁴ are each a lower alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom, carbon number, since the charging characteristics are more stable and the fixability can be improved. 12-18 alkyl groups, phenyl groups and benzyl groups are preferred, and Y ⁻ is preferably an aromatic carboxylate ion or an aliphatic carboxylate ion, more preferably an aromatic carboxylate ion. Examples of the aromatic carboxylate ion include a carboxylate ion having a benzoic acid structure.

  Examples of the carboxylic acid having a benzoic acid structure include benzoic acid and dithiodibenzoic acid.

  Furthermore, as a more preferred quaternary ammonium salt of dithiodibenzoic acid, in the present invention, a compound of formula (Ia):

The compound represented by these is mentioned.

  As a commercial product containing the compound represented by the formula (Ia), “COPY CHARGE PSY” (manufactured by Clariant) and the like can be mentioned.

  Examples of the negatively chargeable charge control agent include metal-containing azo dyes, copper phthalocyanine dyes, metal complexes of salicylic acid compounds, nitroimidazole derivatives, and the like. Metal complexes are preferred.

  As a metal complex of a salicylic acid compound, the formula (II):

Wherein R ⁵ , R ⁶ and R ⁷ are each independently a hydrogen atom, a linear or branched alkyl group or alkenyl group having 1 to 10 carbon atoms, M is zinc, zirconium, chromium, aluminum, Copper, nickel or cobalt, m is an integer of 2 or more, and n is an integer of 1 or more)
The metal complex of the salicylic acid compound represented by these is preferable.

In the formula (II), R ⁶ is preferably a hydrogen atom, and R ⁵ and R ⁷ are preferably a branched alkyl group, more preferably a tert-butyl group.

  As M, zinc and chromium having high electronegativity and good charging effect are preferable, and chromium is more preferable.

Commercially available chromium complexes of salicylic acid compounds in which R ⁶ is a hydrogen atom and R ⁵ and R ⁷ are tert-butyl groups preferably used in the present invention include “Bontron E-81” (Orient Chemical Industries, Ltd.) As a commercial product of a zinc complex of a salicylic acid compound in which R ⁶ is a hydrogen atom and R ⁵ and R ⁷ are tert-butyl groups, “Bontron E-84” (manufactured by Orient Chemical Co., Ltd.), etc. Is mentioned.

  The content of the charge control agent varies depending on the type and the like, but is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin. For example, in the case of a quaternary ammonium salt, 0.1 to 5 parts by weight is preferable with respect to 100 parts by weight of the binder resin, and 0.3 to 3 parts by weight is more preferable. In the case of a metal complex of a salicylic acid compound, the content thereof is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 7 parts by weight with respect to 100 parts by weight of the binder resin. When a quaternary ammonium salt and a metal complex of a salicylic acid compound are used in combination, from the viewpoint of imparting proper chargeability to the toner base particles, when imparting positive chargeability to the toner base particles, a quaternary ammonium salt and The weight ratio of the metal complex of the salicylic acid compound (metal complex of the salicylic acid compound / quaternary ammonium salt) is preferably 1/10 to 1/3, and more preferably 1/8 to 1/5. From the same viewpoint, when the toner base particles are provided with negative chargeability, the weight ratio of the metal complex of the quaternary ammonium salt to the salicylic acid compound (quaternary ammonium salt / metal complex of the salicylic acid compound) is 1 / 8 to 1/2 is preferable, and 1/5 to 1/3 is more preferable.

  Furthermore, additives such as release agents, conductivity modifiers, extender pigments, reinforcing fillers such as fibrous substances, antioxidants, anti-aging agents, and magnetic materials are added as appropriate to the toner of the present invention. May be.

  Examples of the external additive include inorganic fine particles such as silica, alumina, titania, zirconia, tin oxide, and zinc oxide. Among these, silica having a small specific gravity is preferable from the viewpoint of preventing embedding.

From the viewpoint of environmental stability, the silica is preferably hydrophobic silica that has been subjected to a hydrophobic treatment. The hydrophobizing method is not particularly limited, and examples of the hydrophobizing agent include hexamethyldisilazane (HMDS), dimethyldichlorosilane, silicone oil, methyltriethoxysilane, and the like. Among these, hexamethyldisilazane is included. Is preferred. The treatment amount of the hydrophobizing agent is preferably 1 to 7 mg / m ² per surface area of the inorganic fine particles.

  The average particle diameter of the external additive is preferably from 3 to 300 nm, more preferably from 5 to 100 nm, from the viewpoint of chargeability and prevention of scratches on the photoreceptor.

  The content of the external additive (when the metal oxide fine particles are contained in the toner as an external additive, the content of the external additive excluding the metal oxide fine particles) is 100 parts by weight of the toner base particles. 0.01 to 10 parts by weight is preferable, and 0.1 to 5 parts by weight is more preferable.

  The toner of the present invention is obtained through a step of surface-treating toner base particles containing a binder resin, a charge control agent and a colorant and, if necessary, various additives with an external additive. The toner base particles are preferably pulverized toner. For example, a binder resin, a colorant, and the like are mixed with a mixer such as a Henschel mixer or a ball mill, and then melt-kneaded with a hermetic kneader or a uniaxial or biaxial extruder. After cooling, coarsely pulverized using a hammer mill or the like, further pulverized by a fine pulverizer or mechanical pulverizer using a jet stream, and predetermined by a classifier using a swirling airflow or a classifier using the Coanda effect It is obtained by classifying to a particle size of

  The surface treatment step of the toner base particles with the external additive is preferably a dry mixing method in which the external additive and the toner base particles are mixed using a high-speed stirrer such as a Henschel mixer or a super mixer, a V-type blender or the like. The external additives may be mixed in advance and added to a high-speed stirrer or a V-type blender, or may be added separately.

The volume median particle size (D ₅₀ ) of the toner of the present invention is preferably 3 to 15 μm, more preferably 4 to 9 μm, as the particle size before adding the external additive. In the present specification, the volume-median particle size (D ₅₀ ) means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% when calculated from the smaller particle size.

In the two-component developer of the present invention, as the carrier, it is preferable to use a carrier having a low saturation magnetization that weakens the area around the magnetic brush from the viewpoint of image characteristics. Saturation magnetization of the carrier is preferably ^{40~100Am 2 / kg, 50~90Am 2 /} kg is more preferable. The saturation magnetization is preferably 100 Am ² / kg or less from the viewpoint of adjusting the hardness of the magnetic brush and maintaining gradation reproducibility, and preferably 40 Am ² / kg or more from the viewpoint of preventing carrier adhesion and toner scattering. The saturation magnetization of the carrier is measured by the method described in Examples described later.

  As the core material of the carrier, those made of known materials can be used without particular limitation, for example, ferromagnetic metals such as iron, cobalt, nickel, magnetite, hematite, ferrite, copper-zinc-magnesium ferrite, Examples include alloys and compounds such as manganese ferrite and magnesium ferrite, and glass beads. Among these, iron powder, magnetite, ferrite, copper-zinc-magnesium ferrite, manganese ferrite, and magnesium ferrite are preferable from the viewpoint of chargeability. From the viewpoint of image quality, ferrite, copper-zinc-magnesium ferrite, manganese ferrite and magnesium ferrite are more preferable.

  The surface of the carrier is preferably coated with a resin from the viewpoint of reducing carrier contamination. The resin that coats the carrier surface varies depending on the toner material. For example, fluororesin such as polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin such as polydimethylsiloxane, polyester, styrenic resin, Acrylic resins, polyamides, polyvinyl butyral, amino acrylate resins, and the like can be used, and these can be used alone or in combination of two or more. However, if the toner is negatively charged, the chargeability and surface From the viewpoint of energy, a silicone resin is preferred. The method of coating the core material with the resin is not particularly limited, for example, a method in which a coating material such as a resin is dissolved or suspended in a solvent and applied to the core material, or a method of simply mixing with a powder.

  In the two-component developer of the present invention obtained by mixing the toner and the carrier, the toner to carrier weight ratio (toner / carrier) is preferably 1/99 to 10/90, and 5/95 to 7/93. More preferred.

  The two-component developer of the present invention can be used for both a contact development method and a non-contact development method, but may be used in an image forming apparatus of a non-contact development method that requires higher development efficiency. Thus, good charge rising property and development efficiency are obtained, and image unevenness and image density reduction are reduced. Therefore, the present invention further provides an image forming method using the two-component developer of the present invention for a non-contact developing type image forming apparatus.

  In the image forming method of the present invention, in the image forming apparatus, an image is formed through a known process except that the developing process for developing the electrostatic latent image is performed by a non-contact developing method. As a process in the image forming method, in addition to the development process, for example, a process of forming an electrostatic latent image on the surface of the photoreceptor (charging / exposure process), and a process of transferring the developed toner image to a transfer material such as paper ( A transfer process), a process of fixing the transferred toner image (fixing process), a process of removing toner remaining on a developing member such as a photosensitive drum (cleaning process), and the like.

[Softening point of resin]
Using a flow tester (Shimadzu Corporation, CFT-500D), a 1 g sample was heated at a heating rate of 6 ° C / min, and a load of 1.96 MPa was applied by a plunger and extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. . Plot the plunger drop amount of the flow tester against the temperature, and let the softening point be the temperature at which half the sample flowed out.

[Glass transition point of resin]
Using a differential scanning calorimeter (Seiko Denshi Kogyo Co., Ltd., DSC210), the temperature was raised to 200 ° C, and the sample was cooled to 0 ° C at a temperature drop rate of 10 ° C / min. The temperature at the intersection of the extended line of the baseline below the maximum peak temperature of endotherm and the tangent line indicating the maximum slope from the peak rising portion to the peak apex.

[Acid value of the resin]
Measured according to the method of JIS K0070. However, only the measurement solvent was changed from the mixed solvent of ethanol and ether specified in JIS K0070 to the mixed solvent of acetone and toluene (acetone: toluene = 1: 1 (volume ratio)).

[Volume-median particle diameter of toner (D ₅₀ )]
Measuring machine: Coulter Multisizer II (Beckman Coulter, Inc.)
Aperture diameter: 100μm
Analysis software: Coulter Multisizer AccuComp version 1.19 (Beckman Coulter)
Electrolyte: Isoton II (Beckman Coulter, Inc.)
Dispersion: Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether, HLB: 13.6) is dissolved in the electrolytic solution to a concentration of 5% by weight to obtain a dispersion.
Dispersion conditions: 10 mg of a measurement sample is added to 5 ml of the dispersion, and dispersed for 1 minute with an ultrasonic disperser, then 25 ml of an electrolyte is added, and further dispersed for 1 minute with an ultrasonic disperser. Prepare a dispersion.
Measurement conditions: After adjusting the particle size of 30,000 particles to a concentration that can be measured in 20 seconds by adding the sample dispersion to 100 ml of the electrolyte solution, 30,000 particles are measured, Determine the volume median particle size (D ₅₀ ).

[Volume resistivity of metal oxide fine particles]
Place the sample in a 40 mmφ aluminum ring, press mold at 500 kgf / cm ² , and use a 4-terminal probe with a 4-terminal 4-probe constant current application resistivity meter Loresta AP (manufactured by Dia Instruments Co., Ltd.). Measure the volume resistance. The room temperature is 20-25 ° C. and the humidity is 40-60%.

[Measurement of bulk density of metal oxide fine particles]
Slowly put a predetermined amount of sample into a graduated cylinder (capacity 100 ml), measure the weight, and after loading, leave the graduated cylinder for 1 minute, read the volume, weight / volume x 1000 = bulk density (g / l). The room temperature is 20-25 ° C. and the humidity is 40-60%.

[Average particle diameter of metal oxide fine particles and external additives]
Obtained from the following formula.
Average particle diameter (μm) = 6 / (ρ × specific surface area (m ² / g))
In the formula, ρ is the specific gravity of the external additive, for example, the specific gravity of titanium dioxide is 4.0, and the specific gravity of silica is 2.2. The specific surface area is a BET specific surface area determined by a nitrogen adsorption (BET) method. In the case of a hydrophobized external additive, the specific surface area of the raw material before the hydrophobizing treatment is used.
The above formula is assumed to be a sphere having a particle diameter R,
Specific surface area = S x (1 / m)
m (weight of particle) = 4/3 x π x (R / 2) ³ x specific gravity
S (surface area) = 4π (R / 2) ²
Is an expression obtained from

[Carrier saturation magnetization]
(1) Fill a plastic case with a lid of 7 mm outer diameter (6 mm inner diameter) and 5 mm height while tapping the carrier, and calculate the mass of the carrier from the difference between the weight of the plastic case and the weight of the plastic case filled with the carrier. .
(2) Set a plastic case filled with a carrier in the sample holder of the magnetic property measuring device “BHV-50H” (VSMAGNETOMETER) of RIKEN ELECTRONICS CO., LTD., While vibrating the plastic case using the vibration function, Saturation magnetization is measured by applying a magnetic field of 79.6 kA / m. The obtained value is converted into saturation magnetization per unit mass in consideration of the mass of the filled carrier.

Resin production example 1
1,040 g of polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, 10 g of polyoxyethylene (2.0) -2,2-bis (4-hydroxyphenyl) propane, 199 g of terephthalic acid and esterification catalyst 4 g of dibutyltin oxide was placed in a 5-liter four-necked flask equipped with a nitrogen inlet tube, a dehydrating tube, a stirrer and a thermocouple, reacted at 230 ° C. under normal pressure for 5 hours, and then brought to 8.3 kPa. For 2 hours. The reaction solution was cooled to 210 ° C., 209 g of fumaric acid and 1 g of hydroquinone as a polymerization inhibitor were added, reacted for 5 hours, and further reacted at 8.3 kPa until a predetermined softening point was reached. Polyester). The obtained resin A had a softening point of 109.5 ° C., a glass transition point of 64.4 ° C., and an acid value of 21.3 mgKOH / g.

Production Example 1 of Metal Oxide Fine Particles
200 g of titanium dioxide was dispersed in 3 liters of water to form a suspension. The suspension was heated to 70 ° C. and 100 g of tin tetrachloride (SnCl ₄ / 5H ₂ O) was added. Then, 20% by volume dilute sulfuric acid aqueous solution and 10% by weight sodium hydroxide aqueous solution are added over 1 hour so that the pH is maintained at 2 to 3, and a tin oxide film is formed on the surface of the titanium dioxide particles. did. Thereafter, the suspension is filtered and washed, then fired at a temperature of 600 ° C. for about 1 hour, crushed by a jet mill, and a tin oxide-coated titanium dioxide having a BET specific surface area of 15 m ² / g and an average particle diameter of 100 nm. A (tin oxide content: 15% by weight) was obtained.

  To 100 g of the resulting tin oxide-coated titanium dioxide A, 30 ml of a 15% by weight methanol solution of silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., KF96L) was added dropwise and stirred with a mixer. Then, it heat-dried at 100 degreeC and obtained the metal oxide fine particle A which performed the organic surface treatment.

Production example 2 of metal oxide fine particles
A BET specific surface area of 12.5 m ² / g and an average particle size of 120 nm are the same as in Production Example 1 of metal oxide fine particles except that the amount of tin tetrachloride (SnCl ₄ / 5H ₂ O) is changed to 150 g. Of tin oxide coated titanium dioxide B (tin oxide content: 19% by weight) was obtained.

  To 100 g of the obtained tin oxide-coated titanium dioxide B, 30 ml of a 15% by weight methanol solution of silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., KF96L) was added dropwise and stirred with a mixer. Then, the metal oxide fine particle B which heat-dried at 100 degreeC and gave the organic surface treatment was obtained.

Production Example 3 of metal oxide fine particles
Metal oxide fine particles C were obtained in the same manner as in Production Example 1 except that a tin oxide-coated titanium dioxide having an average particle size of 40 nm was obtained.

Production Example 4 of Metal Oxide Fine Particles
1 g of stearic acid (manufactured by Kao, Lunac) was added to 100 g of tin oxide-coated titanium dioxide A, and after stirring with a mixer, heat treatment was performed at 100 ° C., and the organic surface treatment was performed, as in Production Example 1. Thus, metal oxide fine particles D were obtained.

Production Example 5 of metal oxide fine particles
Metal oxide fine particles E were obtained in the same manner as in Production Example 1 except that a tin oxide-coated titanium dioxide having an average particle diameter of 60 nm was obtained.

Examples 1-4 and Comparative Examples 1-8
Resin A 100 parts by weight, quinacridone pigment “Fastogen Super Magenta R” (Dainippon Ink Chemical Co., Ltd.) 5 parts by weight, salicylic acid compound chromium complex “Bontron E-81” (Orient Chemical Co., Ltd.) 3.5 parts by weight, carvone 1 part by weight of quaternary ammonium salt of acid “COPY CHARGE PSY” (manufactured by Clariant) and 1 part by weight of polypropylene wax “NP-105” (manufactured by Mitsui Chemicals) are mixed with a Henschel mixer and then melted with a twin screw extruder. After kneading and cooling, it was roughly pulverized to about 1 mm using a hammer mill. The obtained coarsely pulverized product was finely pulverized by an air jet type pulverizer and classified to obtain negatively chargeable toner base particles having a volume-median particle size (D ₅₀ ) of 8.5 μm.

  100 parts by weight of the obtained toner base particles, metal oxide fine particles or hydrophobic silica shown in Table 1 as an external additive, and hydrophobic silica “R972” (manufactured by Nippon Aerosil Co., Ltd., hydrophobizing agent: dimethyldichlorosilane) 0.9 parts by weight of an average particle size of 16 nm) was mixed with a Henschel mixer for 3 minutes to obtain a toner subjected to external addition treatment.

6 parts by weight of the obtained toner and 94 parts by weight of ferrite carrier (volume average particle diameter: 60 μm, saturation magnetization: 68 Am ² / kg) were mixed to obtain a two-component developer.

Test example 1
A two-component developer is mounted on a non-magnetic two-component development type image forming apparatus "Vario stream 9000" (Oce Printing Systems), and after adjusting the toner concentration to 6%, the printing rate is 9% and the linear speed is 1000mm. 30,000 copies were printed at / sec. Solid images were printed at the time of printing 1000 sheets (initial printing) and 30,000 sheets (after printing), and the image density and image unevenness were evaluated by the following methods. The results are shown in Table 1.

[Image density]
The image density was measured at five points on the image printing portion with a color meter “GretagMacbeth Spectroeye” (manufactured by Gretag), the average value was calculated as the image density (ID), and the image density was evaluated according to the following evaluation criteria.

◎: Image density is 1.2 or more ○: Image density is 1.1 or more, less than 1.2 △: Image density is 1.0 or more, less than 1.1 ×: Image density is less than 1.0

[Image unevenness]
The presence or absence of unevenness in the solid image was visually observed and evaluated according to the following evaluation criteria.

A: There is no unevenness.
○: There is almost no unevenness.
Δ: There is a little unevenness.
X: There is unevenness.

  From the above results, it can be seen that, in contrast to Comparative Examples 1 to 8, Examples 1 to 4 can maintain the image density even after printing, and a good image without image unevenness is obtained. . It can be seen that fog is suppressed and no streaks on the developing roller that cause image streaks are generated, and the developability and solid followability are good. This is due to the fact that in the embodiments, the efficiency of the toner and the carrier is high and the toner has a good charge rising property, so that high development efficiency is maintained even in continuous printing.

  The two-component developer of the present invention is used for developing a latent image formed in electrophotography, electrostatic recording method, electrostatic printing method and the like.

Claims (5)

  A toner having toner base particles containing a binder resin, a charge control agent and a colorant and an external additive, wherein the toner base particles and / or the external additive have a volume resistivity of 100 to 1000 Ω · cm. A two-component developer comprising a toner and a carrier containing metal oxide fine particles having a bulk density of 600 to 1000 g / l.   The two-component developer according to claim 1, wherein the toner is a color toner.   The two-component developer according to claim 1 or 2, wherein the binder resin contains polyester.   The two-component developer according to claim 3, wherein the polyester is a polyester obtained by condensation polymerization of an alcohol component and a carboxylic acid component containing 40 to 100 mol% of fumaric acid and / or maleic acid.   An image forming method using the two-component developer according to claim 1 for an image forming apparatus of a non-contact developing system.