JP5166164B2 - Two-component developer - Google Patents

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 or the like.

  In recent years, with high image quality of printers, high performance is required for toner.

  Regarding image quality improvement using an external additive, for example, Patent Document 1 discloses a technique in which strontium titanate having a specific particle size and alumina are used as an external additive to improve fog and image streaks. .

In Patent Document 2, inorganic particles such as hydrophobic silica and hydrophobic titania having a specific particle diameter, inorganic particles having a number average particle diameter of 80 to 1200 nm, and a fatty acid metal salt are used as external additives, and are used for fixation and photosensitivity. A technique for improving body wear and the like is disclosed.
JP 2007-3631 A JP 2001-100452 A

  However, in the two-component development method using a two-component developer in which a toner and a carrier are mixed, due to spent on the carrier, the image density of the resulting image is lowered, the transfer is lost during printing, and the charge amount is lowered. Fog is likely to occur due to. In Patent Documents 1 and 2, studies are mainly made on a one-component developer, but not on a two-component developer using a carrier.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a two-component developer having a high inhibitory effect on the occurrence of fogging due to a decrease in image density, a transfer defect during printing durability, and a decrease in charge amount.

The present invention
A two-component developer comprising a toner in which an external additive is added to toner base particles containing a binder resin and a colorant, and a carrier,
The external additive is based on 100 parts by weight of toner base particles.
0.05 to 2.0 parts by weight of hydrophobic silica A having a number average particle diameter of 5 to 20 nm,
0.05 to 2.0 parts by weight of hydrophobic titania having a number average particle size of 5 to 40 nm,
1.0 to 5.0 parts by weight of hydrophobic silica B having a number average particle diameter of more than 20 nm and 70 nm or less,
The present invention relates to a two-component developer comprising 0.1 to 1.0 part by weight of strontium titanate having a weight average particle diameter of 30 to 75 nm and 0.01 to 0.1 part by weight of zinc stearate having a volume median particle diameter of 1.5 to 12 μm.

  The two-component developer of the present invention exhibits a high suppression effect on the occurrence of fogging due to a decrease in image density, a transfer defect during printing durability, and a decrease in charge amount.

  The present invention relates to a two-component developer containing a toner in which an external additive is added to a toner base particle containing a binder resin and a colorant, and a carrier. The hydrophobic silica, hydrophobic titania, strontium titanate, and zinc stearate are included, and the average particle size and content of these external additives are adjusted to a specific range. Has characteristics. In particular, the combined use of strontium titanate, zinc stearate, and titania has a remarkable effect on long-term suppression of fog and maintenance of good image density. The toner in the present invention exhibits the effects of the invention with respect to the two-component development system. For the one-component development system, it is difficult to apply the toner because the toner easily slips on the developing roller.

As an external additive, as described above, at least five types of inorganic particles, that is, 100 parts by weight of toner base particles,
(1) 0.05 to 2.0 parts by weight of hydrophobic silica A having a number average particle diameter of 5 to 20 nm,
(2) 0.05 to 2.0 parts by weight of hydrophobic titania having a number average particle size of 5 to 40 nm,
(3) 1.0 to 5.0 parts by weight of hydrophobic silica B having a number average particle diameter of more than 20 nm and 70 nm or less,
(4) 0.1 to 1.0 parts by weight of strontium titanate having a weight average particle diameter of 30 to 75 nm, and
(5) 0.01 to 0.1 part by weight of zinc stearate having a volume median particle size of 1.5 to 12 μm.

  Hydrophobic silica A is mainly effective in reducing the fog of the obtained image.

  The number average particle diameter of the hydrophobic silica A is 5 to 20 nm, preferably 7 to 18 nm, more preferably 7 to 15 nm. The number average particle diameter of the hydrophobic silica A is determined from the BET specific surface area.

  The content of the hydrophobic silica A is 0.05 to 2.0 parts by weight, preferably 0.05 to 1.5 parts by weight, and more preferably 0.1 to 1.0 parts by weight with respect to 100 parts by weight of the toner base particles.

  Hydrophobic titania is mainly effective for improving image density reduction of the obtained image.

  The number average particle diameter of the hydrophobic titania is 5 to 40 nm, preferably 7 to 35 nm, more preferably 10 to 30 nm. The number average particle diameter of hydrophobic titania is determined from the BET specific surface area.

  The content of the hydrophobic titania is 0.05 to 2.0 parts by weight, preferably 0.05 to 1.5 parts by weight, and more preferably 0.1 to 1.5 parts by weight with respect to 100 parts by weight of the toner base particles.

  Hydrophobic silica B is mainly effective in improving the image density of the obtained image and preventing toner transfer omission. The number average particle diameter of the hydrophobic silica B is determined from the BET specific surface area.

  The number average particle diameter of the hydrophobic silica B is more than 20 nm and 70 nm or less, preferably more than 20 nm and 60 nm or less, more preferably 25 to 55 nm.

  The content of the hydrophobic silica B is 1.0 to 5.0 parts by weight, preferably 1.0 to 4.5 parts by weight, and more preferably 1.5 to 4.5 parts by weight with respect to 100 parts by weight of the toner base particles.

Examples of hydrophobizing agents for hydrophobic silicas A and B and hydrophobic titania include hexamethyldisilazane (HMDS), dimethyldichlorosilane, silicone oil, and methyltriethoxysilane. The treatment amount of the hydrophobizing agent is preferably 1 to 7 mg / m ² per surface area of the inorganic fine particles.

  Strontium titanate is mainly effective in reducing fog at the time of printing.

  The weight average particle diameter of strontium titanate is 30 to 75 nm, preferably 35 to 75 nm, and more preferably 40 to 75 nm. As for the weight average particle diameter of strontium titanate, a 50% particle diameter based on weight is obtained from an equivalent electron diameter from a transmission electron micrograph.

  From the viewpoint of chargeability of the toner, the weight average particle diameter of strontium titanate is preferably larger than the number average particle diameter of hydrophobic silica B, and the difference between the average particle diameters of both is preferably 50 nm or less, 15 to 45 nm is more preferable.

  The content of strontium titanate is 0.1 to 1.0 part by weight, preferably 0.1 to 0.8 part by weight, and more preferably 0.2 to 0.7 part by weight with respect to 100 parts by weight of the toner base particles.

  From the viewpoint of chargeability of the toner, the weight ratio of hydrophobic titania to strontium titanate (hydrophobic titania / strontium titanate) is preferably 1/1 to 7/1, more preferably 1/1 to 6/1. More preferably, 1/1 to 4/1.

  Zinc stearate is mainly effective in reducing fog at the time of printing.

  The volume median particle size of zinc stearate is 1.5 to 12 μm, preferably 2.0 to 11 μm, more preferably 3.0 to 10 μm. The volume median particle size of zinc stearate is dispersed in ethanol and obtained with a laser diffraction particle size distribution analyzer.

  The content of zinc stearate is 0.01 to 0.1 parts by weight, preferably 0.01 to 0.08 parts by weight, and more preferably 0.01 to 0.06 parts by weight with respect to 100 parts by weight of toner base particles.

  From the viewpoint of chargeability of the toner, the weight ratio of strontium titanate to zinc stearate (strontium titanate / zinc stearate) is preferably 4/1 to 35/1, more preferably 5/1 to 30/1. 5/1 to 15/1 is more preferable.

  From the viewpoint of chargeability of the toner, the weight ratio of hydrophobic titania to zinc stearate (hydrophobic titania / zinc stearate) is preferably 10/1 to 30/1, and more preferably 15/1 to 30/1.

  The presence or absence of hydrophobizing treatment in strontium titanate and zinc stearate is not particularly limited. preferable. Examples of the hydrophobic treatment include those obtained by treating the particle surface with a hydrophobic treatment agent such as polydimethylsiloxane, silicone oil, hexamethyldisilazane and the like.

  The external additive may contain other external additives as long as the effects of the present invention are not impaired, but the total amount of the five types of external additives is 80% by weight or more in the external additive. Is preferable, 90% by weight or more is more preferable, and substantially 100% by weight is further preferable.

  Examples of the binder resin contained in the toner base particles include polycondensation resins such as polyester, vinyl resins such as styrene-acrylic resins, epoxy resins, polycarbonates, and polyurethanes. Among these, toners From the viewpoint of fixing property and durability, polyester is preferable. The polyester content in the binder resin is preferably 90% by weight or more, and more preferably 95% by weight or more.

  The polyester is not particularly limited, and can be obtained by polycondensing a raw material monomer containing an alcohol component composed of a divalent or higher alcohol and a carboxylic acid component composed of a divalent or higher carboxylic acid compound.

  As the dihydric or higher alcohol, from the viewpoint of the storage stability of the toner, the formula (I):

(In the formula, RO and OR are oxyalkylene groups, R is an ethylene and / or propylene group, x and y indicate the number of added moles of alkylene oxide, each being a positive number, and the sum of x and y. 1 to 16 is preferable, 1 to 8 is more preferable, and 1.5 to 4 is more preferable)
An alkylene oxide adduct of bisphenol A represented by The content of the alkylene oxide adduct of bisphenol A is preferably 50 mol% or more, more preferably 60 mol% or more, and further preferably 80 mol% or more in the alcohol component.

  Examples of the alkylene oxide adduct of bisphenol A represented by the formula (I) include polyoxyethylene-2,2-bis (4-hydroxyphenyl) propane and other ethylene oxide adducts having 2 carbon atoms, such as polyoxypropylene. Examples thereof include propylene oxide adducts having 3 carbon atoms such as -2,2-bis (4-hydroxyphenyl) propane.

  As alcohol components other than the alkylene oxide adduct of bisphenol A, ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol, polyethylene glycol, polypropylene glycol, bisphenol A, hydrogenated bisphenol A, sorbitol , Pentaerythritol, glycerol, trimethylolpropane and the like.

  Examples of the divalent or higher carboxylic acid compound include adipic acid, fumaric acid, maleic acid, succinic acid (e.g., n-dodecenyl succinic acid, isododecenyl succinic acid, n-dodecyl succinic acid, isooctenyl succinic acid, Aliphatic carboxylic acids such as succinic acid substituted with alkyl groups having 1 to 20 carbon atoms or alkenyl groups having 2 to 20 carbon atoms such as isooctyl succinic acid, phthalic acid, isophthalic acid, terephthalic acid, 1,2, 4-Benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, aromatic carboxylic acids such as pyromellitic acid, anhydrides of these acids and lower alkyl (C1-3) esters, etc. Is mentioned. In addition, the acids as described above, anhydrides of these acids, and alkyl esters of the acids are collectively referred to as carboxylic acid compounds in this specification.

  The alcohol component may contain a monovalent alcohol, and the carboxylic acid component may contain a monovalent carboxylic acid compound as appropriate from the viewpoint of adjusting the molecular weight and improving the offset resistance of the toner.

  The condensation polymerization of the alcohol component and the carboxylic acid component can be performed, for example, in an inert gas atmosphere at a temperature of 180 to 250 ° C., but may be performed in the presence of an esterification catalyst, a polymerization inhibitor, or the like. preferable. Examples of the esterification catalyst include tin (II) compounds having no Sn-C bond such as dibutyltin oxide, titanium compound, tin octylate, etc., and these are used alone or in combination. .

  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.

  The softening point of the polyester is preferably 90 to 150 ° C, more preferably 100 to 140 ° C, from the viewpoint of toner durability.

  The glass transition point of the polyester is preferably from 50 to 85 ° C, more preferably from 55 to 80 ° C, from the viewpoint of toner storage stability. The acid value is preferably 0.5 to 40 mg KOH / g from the viewpoint of environmental stability of the toner.

  As the colorant, all of dyes and pigments used as toner colorants can be used. Carbon black, black pigment, 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, Isoindoline, Disazo yellow and the like can be used alone or in combination of two or more of the present invention. The toner may be either black toner or color toner. 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.

  Toner raw materials other than the binder resin and colorant include additives such as charge control agents, mold release agents, conductivity modifiers, extender pigments, reinforcing fillers such as fibrous substances, antioxidants, and antioxidants. Can be mentioned.

  As the charge control agent, any one of negative chargeability and positive chargeability can be used. Examples of the negatively chargeable charge control agent include metal-containing azo dyes, copper phthalocyanine dyes, metal complexes of alkyl derivatives of salicylic acid, polymers of phenols and aldehydes such as nitroimidazole derivatives and calixarene, and the like. Examples of the positively chargeable charge control agent include nigrosine dyes, triphenylmethane dyes, quaternary ammonium salt compounds, polyamine resins, and imidazole derivatives. Also, a polymer type such as a resin can be used. The content of the charge control agent is preferably 0.1 to 8 parts by weight and more preferably 0.2 to 5 parts by weight with respect to 100 parts by weight of the binder resin.

  As the release agent, low molecular weight polypropylene, low molecular weight polyethylene, low molecular weight polypropylene polyethylene copolymer, aliphatic hydrocarbon waxes such as microcrystalline wax, paraffin wax, and Fischer-Tropsch wax and their oxides, carnauba wax, Examples include ester waxes such as montan wax, sasol wax and their deoxidized wax, fatty acid amides, fatty acids, higher alcohols, fatty acid metal salts and the like. The content of the release agent is preferably 1 to 20 parts by weight and more preferably 2 to 10 parts by weight with respect to 100 parts by weight of the binder resin. The melting point of the release agent is preferably 60 to 120 ° C., more preferably 70 to 100 ° C., and further preferably 70 to 90 ° C. from the viewpoint of toner fixing properties. Two or more release agents can be used in combination.

  The method for producing the toner base particles may be any known method such as a kneading and pulverizing method, an emulsification phase inversion method, and a polymerization method, but the kneading and pulverizing method is preferred because it is easy to produce. For example, in the case of pulverized toner by a kneading pulverization method, a binder resin, a charge control agent, a colorant, wax, and the like are uniformly mixed with a mixer such as a Henschel mixer, and then a sealed kneader or a single or twin screw extruder It can be produced by melt-kneading with an open roll kneader or the like, cooling, pulverizing and classifying. A toner is obtained by adding at least the five kinds of external additives to the obtained toner base particles.

  As the mixer used for mixing the toner base particles and the external additive, a high-speed stirrer such as a Henschel mixer or a super mixer, or a stirrer used for dry mixing such as a V-type blender is preferable. 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.

  In order to mix the external additives according to the present invention with the toner base particles, hydrophobic silica B, strontium titanate are used from the viewpoint of improving the adhesion of these external additives to the toner base particles and suppressing the occurrence of fogging. It is preferable to mix the hydrophobic silica A and the hydrophobic titania after mixing the zinc stearate with the toner base particles.

The volume median particle diameter (D ₅₀ ) of the toner is preferably 3 to 15 μm, more preferably 4 to 10 μm. 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.

As the carrier, a carrier with low saturation magnetization that weakens the area around the magnetic brush is preferable 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.

  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 preventing spent. 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, when the toner is negatively charged, the chargeability and surface From the viewpoint of energy, a silicone resin is preferable. The method for 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 obtained by mixing the toner and the carrier, the toner to carrier weight ratio (toner / carrier) is preferably 1/99 to 15/85, and more preferably 2/98 to 10/90.

[Softening point of resin]
Using a flow tester (Shimadzu Corporation, CFT-500D), a 1 g sample is heated at a heating rate of 6 ° C / min. While applying a load of 1.96 MPa with 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 of the sample flows out.

[Glass transition point of resin]
Using a differential scanning calorimeter (Seiko Denshi Kogyo Co., Ltd., DSC210), the sample was heated to 200 ° C at a rate of 10 ° C / min and cooled to 0 ° C at a rate of 10 ° C / min. Start measurement at / min. The glass transition point is defined as the temperature at the intersection of the base line extension below the glass transition point and the tangent that indicates the maximum slope from the peak rising portion to the peak apex.

[Acid value of the resin]
Measured by 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)).

[Melting point of release agent]
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 maximum peak temperature of heat of fusion is taken as the melting point.

[Volume-median particle size of toner (D ₅₀ )]
In this specification, the volume-median particle size (D ₅₀ ) of the toner means the particle size of the toner in which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle size.
Measuring instrument: Coulter Multisizer II (Beckman Coulter, Inc.)
Aperture diameter: 100μm
Analysis software: Coulter Multisizer AccuComp version 1.19 (Beckman Coulter)
Electrolyte: Isoton II (Beckman Coulter)
Dispersion: Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether, HLB: 13.6) 5% by weight Electrolyte dispersion condition: 10 mg of measurement sample was added to 5 mL of dispersion, and dispersed for 1 minute with an ultrasonic disperser. Thereafter, 25 mL of an electrolytic solution is added, and further dispersed with an ultrasonic disperser for 1 minute.
Measurement conditions: The dispersion is added to 100 mL of the electrolytic solution so that the particle size of 30,000 toner particles can be measured in 20 seconds, and 30,000 particles are measured. Determine the median particle size (D ₅₀ ).

[Number average particle diameter of hydrophobic silica, hydrophobic titania and alumina]
Number average particle diameter (nm) = 6 / (ρ × specific surface area (m ² / g)) × 1000
In the formula, ρ is the specific gravity of silica (2.2), the specific gravity of titania (4.2) or the specific gravity of alumina (4.0), and the specific surface area is the BET specific surface area determined by the nitrogen adsorption method of the raw material before hydrophobization treatment. It is.
Note that the above equation assumes a sphere with a particle size R,
BET 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

[Weight average particle diameter of strontium titanate]
The weight average particle diameter of strontium titanate is determined by a weight-based 50% particle diameter measured by an equivalent circular diameter using a transmission electron micrograph.

[Volume-median particle diameter of zinc stearate (D ₅₀ )]
Add a sample of spatula (5-10 mg) to 20 ml of methanol, stir with ultrasonic for 300 seconds, and then measure with a laser diffraction particle size analyzer (LA-920, manufactured by Horiba, Ltd.) The particle size distribution is measured by inputting “112a000I” as the parameter of the refractive index of the apparatus, and the volume median particle size (D ₅₀ ) is obtained. This refractive index parameter is based on the relative refractive index of 1.12 obtained from the refractive index of 1.49 of zinc stearate and the refractive index of methanol of 1.33.

[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
Polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane 1750 g, polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane 1625 g, terephthalic acid 1145 g, dodecenyl succinic acid 172 g, And 25 g of tin octylate is placed in a 5 liter four-necked flask equipped with a nitrogen inlet tube, dehydration tube, stirrer and thermocouple, and reacted under a nitrogen atmosphere at 230 ° C until the reaction rate reaches 90%. Then, the reaction was performed at 8 kPa for 1 hour. Thereafter, the mixture was cooled to 210 ° C., 480 g of trimellitic anhydride was added, reacted at normal pressure for 1 hour, and then reacted at 40 kPa until the desired softening point was reached to obtain a polyester. The obtained polyester is referred to as Resin A. Resin A had a softening point of 121.2 ° C., a glass transition point of 64.3 ° C., and an acid value of 21.9 mgKOH / g. The reaction rate means a value of the amount of produced reaction water / theoretical product water amount × 100.

Examples 1-4 and Comparative Examples 1-13
Resin A 88.0 parts by weight, charge control agent “T-77” (Hodogaya Chemical Co., Ltd.) 1.0 part by weight, release agent “Carnauba Wax C1” (manufactured by Kato Yoko Co., Ltd., melting point: 83 ° C.) 4.0 parts by weight, release Molding agent “HNP-9” (Nippon Seiki Co., Ltd., paraffin wax, melting point: 79 ° C.) 2.0 parts by weight and carbon black “Mougul-L” (Cabot Co., Ltd.) 5.0 parts by weight were mixed in advance using a Henschel mixer. Thereafter, the obtained mixture was kneaded with a continuous two-open roll type kneader “NIDEX” (manufactured by Mitsui Mining Co., Ltd.) to obtain a kneaded product.

The continuous two-open roll type kneader used has a roll outer diameter of 0.14 m and an effective roll length of 0.8 m, and the operating condition is that the rotation speed of the high rotation side roll (front roll) is 75 r. / min, the rotation speed of the low rotation side roll (rear roll) was 50 r / min, and the roll gap was 0.1 mm. The heating and cooling medium temperature in the roll is 150 ° C. on the raw material input side of the high rotation side roll, 100 ° C. on the kneaded product discharge side, 35 ° C. on the raw material input side of the low rotation side roll, and the kneaded product The temperature on the discharge side was set to 35 ° C. The feed rate of the raw material mixture was 10 kg / hr. Next, the obtained kneaded product was cooled in air, and then coarsely pulverized with a Rotoplex (manufactured by Hosokawa Micron) to obtain a coarsely pulverized product having a maximum diameter of 2 mm. The coarsely pulverized product was pulverized and classified using a collision plate pulverizer and a dispersion separator to obtain an untreated toner having a volume median particle size (D ₅₀ ) of 8.5 μm. The content of particles of 5 μm or less in the untreated toner was 2.9% by volume.

  Silica B, strontium titanate and zinc stearate (or alumina) shown in Table 1 are added to 100 parts by weight of this untreated toner, mixed with a Henschel mixer, then further added with silica A and titania, and mixed with a Henschel mixer. As a result, a black toner was obtained.

Example 5
As raw materials, 88.0 parts by weight of resin A, 1.0 part by weight of charge control agent “LR-147” (manufactured by Nippon Carlit Co., Ltd.), 4.0 parts by weight of release agent “carnauba wax C1” (manufactured by Hiroyuki Kato, melting point: 83 ° C.) Example 1 except that 2.0 parts by weight of paraffin wax “HNP-9” (manufactured by Nippon Seiki Co., Ltd., melting point: 79 ° C.) and 5.0 parts by weight of cyan pigment “ECB-301” (manufactured by Dainichi Seika) were used. In the same manner as above, an untreated toner having a volume median particle size (D ₅₀ ) of 8.5 μm was obtained. The content of particles of 5 μm or less in the untreated toner was 2.7% by volume.

  External additives shown in Table 1 were added to 100 parts by weight of the untreated toner and mixed with a Henschel mixer to obtain a cyan toner.

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

Test Example 1 [Fog]
A two-component developer is mounted on a copier “AR-S330” (made by Sharp) with a printing speed modified to 38 ppm, and a character image with a printing rate of 5% is printed on an A4 size (210 mm x 297 mm) paper sheet at 30,000. Sheets were printed continuously. After printing 30,000 sheets (after printing), print 3 sheets of blank paper (printing rate: 0%), once stop the machine, and transparent mending tape (Scotch (registered trademark) mending tape on the surface of the photoreceptor) 810, manufactured by 3M, width: 18 mm). The peeled tape was affixed to unused white paper, and white cardboard was overlaid on the tape-pasted paper. The density of the tape part is measured with an absolute white standard using a colorimeter (Gretag-Macbeth, Spectroeye) and the light emission condition is a standard light source D50, an observation field of view 2 °, and a density standard DIN NB. The difference from the mending tape was calculated. The results are shown in Table 2.

[Evaluation criteria for fogging]
SA: Concentration difference is less than 0.02 A: Concentration difference is 0.02 or more and less than 0.03 B: Concentration difference is 0.03 or more and less than 0.05 C: Concentration difference is 0.05 or more

Test Example 2 [Image density]
A two-component developer is mounted on a copier “AR-S330” (made by Sharp Corporation) with a printing speed modified to 38ppm, and a character image with a printing rate of 5% is printed on a sheet of A4 size (210mm x 297mm). After continuous printing, 2000 sheets were continuously printed on a white paper having a printing rate of 0% and a paper of A4 size (210 mm × 297 mm). On the way, a solid image is printed at the time of printing (initial stage) within 20 sheets, and the image density is measured with a colorimeter (Gretag-Macbeth, Spectroeye), the light emission conditions are standard light source D50, observation field of view 2 °, It was measured with an absolute white standard in the density standard DIN NB. Similarly, after printing 3000 sheets, a solid image was printed, the image density was measured, and evaluated according to the following evaluation criteria. The results are shown in Table 2.

[Image density evaluation criteria]
(A) Black toner A: 1.40 or more B: 1.20 or more, less than 1.40 C: less than 1.20

(B) Cyan toner A: 1.30 or more B: 1.10 or more, less than 1.30 C: less than 1.10

Test Example 3 [Transfer missing]
After the printing endurance in Test Example 1, characters were printed, and transfer omission was confirmed with a microscope (magnification: 50 times).
A: Almost no missing transfer B: No missing transfer

  From the above results, in comparison with Comparative Examples 1 to 13, Examples 1 to 5 can maintain a good image density even after printing, and both transfer omission and fogging are suppressed. I understand.

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

Claims (5)

A two-component developer comprising a toner in which an external additive is added to toner base particles containing a binder resin and a colorant, and a carrier,
The external additive is based on 100 parts by weight of toner base particles.
0.05 to 2.0 parts by weight of hydrophobic silica A having a number average particle diameter of 5 to 20 nm,
0.05 to 2.0 parts by weight of hydrophobic titania having a number average particle size of 5 to 40 nm,
1.0 to 5.0 parts by weight of hydrophobic silica B having a number average particle diameter of more than 20 nm and 70 nm or less,
A two-component developer comprising 0.1 to 1.0 part by weight of strontium titanate having a weight average particle diameter of 30 to 75 nm and 0.01 to 0.1 part by weight of zinc stearate having a volume median particle diameter of 1.5 to 12 μm. The weight ratio of strontium titanate and zinc stearate (strontium titanate / zinc stearate) is a 4 / 1-35 / 1, the two-component developer according to claim 1 Symbol placement. The two-component developer according to claim 1 or 2 , wherein the weight ratio of hydrophobic titania to strontium titanate (hydrophobic titania / strontium titanate) is 1/1 to 7/1. The two-component developer according to any one of claims 1 to 3 , wherein the weight ratio of hydrophobic titania to zinc stearate (hydrophobic titania / zinc stearate) is 10/1 to 30/1. The two-component developer according to any one of claims 1 to 4 , wherein the weight average particle diameter of strontium titanate is larger than the number average particle diameter of hydrophobic silica B.