JP4864807B2 - 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.

  The fluidity of the two-component developer is affected by the chargeability of the toner, the interparticle adhesion due to the surface state of the toner particles, and the particle size distribution. For example, in continuous printing with low coverage and low toner usage, many toner particles are agitated with the carrier for a long time, and the silica on the toner surface is embedded and fluidity is deteriorated, or silica is embedded. It is easy to change the charge amount. On the other hand, in continuous printing with a high printing rate and a large amount of toner used, new toner is frequently introduced into the developing tank, so it is not sufficiently stirred with the carrier, resulting in an increase in highly charged or low charged particles. It's easy to do. In either case, the change in the charge amount or the change in the surface state of the toner particles results in a change in the fluidity of the developer. For example, when developing with the toner concentration controlled by a magnetic permeability sensor or the like. May cause malfunction, and an appropriate toner concentration cannot be obtained. Furthermore, when the carrier is loaded in the developing tank in advance and mixed later with the toner and the developing tank, the change in the fluidity at the initial stage of printing becomes remarkable.

On the other hand, as a technique paying attention to the particle size distribution of the carrier, a two-component developer containing a carrier having a single particle size distribution and a sharp carrier and a toner (see Patent Document 1), the particle size distribution is sharp, and Contains a two-component developer containing a carrier having a specific resistance of core particles increased and a toner (see Patent Document 2), a carrier having a sharp particle size distribution, and a toner containing a specific amount of particles having a particle size of 5 μm or less. And a two-component developer (see Patent Document 4) containing a carrier and a toner whose resistance is increased by controlling the particle size distribution and the apparent density. Further, as a carrier suitable for a toner having a small particle size or a narrow distribution, a carrier in which the average particle size or particle size distribution of core particles is in a specific small range is disclosed (see Patent Document 5).
Japanese Patent Publication No.7-113785 JP-A-8-160671 Japanese Patent No. 2759528 JP 2003-156877 A JP 2005-195960 A

  However, if a carrier with a sharp particle size distribution is used, it is possible to reduce the carrier jump into the apparatus and provide a high-quality image, but the fluidity is reduced due to subtle changes in surface properties due to printing durability. When the change becomes large and the particle size of the carrier is reduced, the chargeability is excellent, but it is difficult to ensure fluidity in continuous use. On the other hand, a carrier having a high specific resistance of core particles is excellent in durability and charge imparting property to toner, but when used continuously in high-speed printing, spent is generated and the resistance is further increased, and image deterioration is likely to occur.

  The object of the present invention is to maintain stable chargeability and fluidity even at different printing rates in long-term printing by the two-component development method, and also in a system that controls toner density with a permeability sensor. An object of the present invention is to provide a two-component developer capable of preventing toner density fluctuation caused by fluid instability, preventing in-machine contamination due to carrier skipping, image density reduction, and the like, and maintaining excellent image quality. .

The present invention is a two-component developer containing a carrier and a toner, wherein the carrier is a ferrite core material coated with a silicone-based resin, and has a cumulative frequency of 50% in the volume particle size distribution of the carrier. The volume particle diameter (Dc ₅₀ ) of the carrier is 65 to ₈₀ μm, the volume particle diameter (Dc ₉₀ ) of the carrier having a cumulative frequency of 90% is 100 to 120 μm, and the saturation magnetization of the carrier is 64 to 69 Am ² / kg, The toner has a volume median particle size of 8.0 to 9.0 μm, a coefficient of variation with respect to the volume particle size distribution of the toner of 23 to 28%, and a toner concentration of 5.0 to 10% by weight.

  The two-component developer of the present invention has excellent chargeability and fluidity even during long-term printing at different printing rates, can prevent in-machine contamination and image density reduction due to carrier skipping, and can maintain excellent image quality. There is an excellent effect.

The two-component developer of the present invention has one characteristic in that it contains a carrier having a specific particle size and particle size distribution and a toner having a specific particle size and particle size distribution. The carrier has a volume particle size distribution in which the volume particle size (Dc ₅₀ ) of the carrier having a cumulative frequency of 50% is 65 to 80 μm, and the volume particle size (Dc ₉₀ ) of the carrier having a cumulative frequency of 90% is 100 to 120 μm, The toner has a volume median particle size of 8.0 to 9.0 μm and a coefficient of variation with respect to the volume particle size distribution of 23 to 28%. A combination of a carrier containing a certain amount of large particles and a broad toner stabilizes the fluidity of the developer in the developer tank even if the toner surface condition or charge amount changes during continuous printing. Can do.

The carrier in the present invention has a volume particle size (Dc ₅₀ ) of the carrier having a cumulative frequency of 50% in the volume particle size distribution of 65 to 80 μm, preferably 68 to 78 μm, from the viewpoint of image quality, fluidity, chargeability and carrier jump. More preferably, it is 70-75 micrometers. Further, from the viewpoint of the flowability of the developer, the volume particle size (Dc ₉₀ ) of the carrier having a cumulative frequency of 90% is 100 to 120 μm, preferably 100 to 110 μm. In the present specification, the volume particle diameter (Dc ₅₀ and Dc ₉₀ ) of the carrier is measured by the method described in the examples described later.

  A ferrite core material is used for the carrier. The ferrite core material preferably contains at least 40 to 60% by weight of iron (Fe), and more preferably contains 45 to 55% by weight. Examples of the metal other than iron constituting the ferrite core material include copper, zinc, magnesium, manganese, lithium, and strontium. Among these, zinc and copper are preferable. In the present specification, the content of iron (Fe) in the ferrite core material is measured by the method described in Examples described later.

  The manufacturing method of the core material is a cutter mill, a hammer mill, an atomizer, an attritor, a vertical granulator, a Henschel from the viewpoint of containing fine particles (core particle particles) generated by mechanically processing the core material in the core material. If it is a method including the process of performing the mechanical process by the apparatus which has a stirring blade which rotates, such as a mixer, a super mixer, Spiraflow, and granurex, there will be no limitation in particular. For example, the raw material of the core material is prepared so as to have a desired composition, mixed with a mixer such as a Henschel mixer, ball mill, V blender, etc. The powder particles obtained through the steps of crushing and classification are subjected to mechanical treatment. In this specification, the mechanical treatment refers to a treatment that gives a mechanical share to the core material surface by a rotary device having a rotating stirring blade as described above, and changes the strength of the mechanical treatment. By doing so, the surface state of the core material can be controlled, and the area where the core material is covered with the resin can be adjusted regardless of the amount of coat resin used and the particle size distribution of the core material. Specifically, when using a rotary device such as a cutter mill, a hammer mill, an atomizer, an attritor, a vertical granulator, a Henschel mixer, a super mixer, a spira flow, or a granurex, the linear velocity of the stirring blade is increased, The Fe / Si ratio described later can be increased by increasing the processing time.

  The two-component developer of the present invention also has one feature in that the carrier is a ferrite core material coated with a silicone resin, and as the silicone resin, methyl silicone composed of an organosiloxane bond is used. And straight silicone resins such as dimethyl silicone resins (for example, dimethyl silicone resins, methyl silicone resins, methyl-dimethyl silicone resins), modified silicone resins, and the like. Commercially available straight silicone resins include “KR-271” and “KR-255” manufactured by Shin-Etsu Chemical, “SR-2410”, “SR-2406”, “SR-2411” manufactured by Toray Dow Corning, Toshiba There are “TSR-127B” and “TSR-144” manufactured by Silicone. As modified silicone resins, modified silicone resins such as alkyd resins, polyester resins, epoxy resins, polyurethane resins, acrylic resins, etc. can be used, and commercially available products include “KR-206” (alkyd resin modified) manufactured by Shin-Etsu Chemical Co., Ltd. ), “KR-9706” (modified with acrylic resin), “ES-1001N” (modified with epoxy resin), “SR-2101” (modified with alkyd resin) manufactured by Toray Dow Corning. A catalyst or the like may be added to these silicone resins as necessary. Among these, from the viewpoint of fluidity and durability, it is desirable that the ferrite core material be coated with a straight silicone resin, more preferably with a methyl silicone resin.

  The method for coating the ferrite core material is not particularly limited, for example, a method in which a coating material such as a silicone resin is dissolved or suspended in a solvent and applied to the ferrite core material, or a method of simply mixing with a powder. . In addition, the coating amount of the ferrite core material can be adjusted by changing the specific surface area by changing the surface shape of the core material before coating by using, for example, a ball mill.

  In the present invention, a part where the coating with the silicone resin is thin is partially present in the ferrite core material, and by reducing the resistance at the time of printing, sufficient image density can be obtained, and further stable fluidity can be obtained. I can do it. Therefore, in the present invention, from such a viewpoint, X-ray photoelectron spectroscopy (electron spectroscopy for chemical analysis, ESCA) suitable for analyzing the metal of the material surface layer as an index indicating the coverage of the silicone-based resin of the carrier The measured value according to is preferably in a specific range. That is, in the measurement by ESCA of the carrier, the weight ratio (Fe / Si) of iron (Fe) to silicon (Si) on the carrier surface is preferably 4.5 / 1 to 7.0 / 1, 5.0 / 1 to 6.5 / 1 It is more preferable that The method for adjusting the weight ratio (Fe / Si) of iron (Fe) and silicon (Si) on the carrier surface is not particularly limited, and can be performed, for example, by adjusting the processing time of the mechanical processing described above. In the present specification, the “carrier surface” means a layer several tens of nm thick from the carrier surface, and the weight ratio of iron (Fe) and silicon (Si) is a method described in Examples described later. Measured by

  The coating amount of the silicone-based resin is preferably 0.5 to 3.0 parts by weight and more preferably 0.8 to 1.2 parts by weight with respect to 100 parts by weight of the ferrite core material from the viewpoint of fluidity, durability and chargeability. preferable. In the present invention, the “coating amount” refers to the amount of silicone resin used (the amount of resin charged in the resin solution used for coating the core material) with respect to 100 parts by weight of the ferrite core material. In the present invention, Since the coating amount and the usage amount are substantially the same, it is expressed as “coating amount”.

The saturation magnetization of the carrier, upon application of a magnetic field of 1.1 (MA / m), a 64~69Am ² / kg, preferably 65~68Am ² / kg. When the saturation magnetization of the carrier is within the above range, an appropriate magnetic brush can be formed while preventing the carrier from rising, so that high-quality image quality can be obtained. In this specification, the saturation magnetization of the carrier is measured by the method described in the examples described later.

The toner of the present invention has a volume median particle size (Dt ₅₀ ) of 8.0 to 9.0 μm, preferably 8.2 to 8.8 μm, more preferably 8.4 to 8.6 μm. Further, the coefficient of variation with respect to the volume particle size distribution is 23 to 28%, preferably 24 to 27%. In this specification, the coefficient of variation (CV value) is expressed by the following formula:
CV value (%) = [standard deviation in volume particle size distribution] / [volume median particle size] × 100
The volume-median particle size (Dt ₅₀ ) and coefficient of variation of the toner are measured by the method described in Examples below.

  The toner is not particularly limited, and may contain toner raw materials such as a binder resin, a colorant, and other additives.

  Examples of the binder resin include polycondensation resins such as polyester, polyester / polyamide, and polyamide, vinyl resins such as styrene-acrylic resin, epoxy resins, polycarbonate, and polyurethane.

  Polyester is obtained by using an alcohol component and a carboxylic acid component as raw material monomers and subjecting them to condensation polymerization.

  As alcohol components, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,4-butenediol, 1,2-propanediol, 1,3-butanediol, neopentyl glycol, 2-butyl-2-ethyl-1,3 -Aliphatic diols such as propanediol; polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, etc. Aromatic diols such as alkylene oxide adducts of bisphenol A; trihydric or higher polyhydric alcohols such as glycerin and pentaerythritol.

  Examples of carboxylic acid components include oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, etc. An aliphatic dicarboxylic acid such as cyclohexanedicarboxylic acid; an aromatic dicarboxylic acid such as phthalic acid, isophthalic acid or terephthalic acid; a trivalent or higher polyvalent carboxylic acid such as trimellitic acid or pyrrolemetic acid; and These acid anhydrides, alkyl (C1-3) esters and the like can be mentioned. Such acids, anhydrides of these acids, and alkyl esters of these acids are collectively referred to herein as carboxylic acid compounds.

  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. in the presence of an esterification catalyst if necessary.

  As the colorant, all of dyes and pigments used as toner colorants can be used, such as 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 in the present invention is black toner, color Either toner or full color toner may be used. 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.

  Other additives include charge control agents, mold release agents, conductivity modifiers, extender pigments, reinforcing fillers such as fibrous substances, antioxidants, anti-aging agents, magnetic materials, etc. It may be.

  The toner can be produced by a known method using the above toner raw materials. For example, after binder resin, colorant, and various additives are mixed with a mixer such as a Henschel mixer or a ball mill, they are melt-kneaded with a hermetic kneader or a single or twin screw extruder, and after cooling, a cutter Coarsely pulverize using a mill, etc., further pulverize with a fine pulverizer or mechanical pulverizer using a jet stream, and classify to a predetermined particle size with a classifier using a swirling airflow or a classifier using the Coanda effect. Obtained. Furthermore, a fluidity improver such as hydrophobic silica may be added to the coarsely pulverized product in the production process or the surface of the obtained toner, if necessary.

  The softening point of the toner is preferably from 95 to 120 ° C., more preferably from 100 to 110 ° C., from the viewpoints of fixability and durability. The glass transition point is preferably 50 to 60 ° C, more preferably 53 to 57 ° C, and the acid value is preferably 5 to 30 mgKOH / g, more preferably 10 to 25 mgKOH / g, from the viewpoint of storage stability. In addition, in this specification, a softening point, a glass transition point, and an acid value are measured by the method as described in the below-mentioned Example.

The two-component developer of the present invention has another feature that the toner concentration is 5.0 to 10% by weight, preferably 5.0 to 8.0% by weight, more preferably 5.5 to 7.0% by weight. . When the toner concentration is in the above range, the charging change that occurs when the toner concentration is low is not increased, the fluidity is stable, the low charged particles that are generated when the toner concentration is high, and the fogging is not increased. And dust generation are suppressed. In the present invention, the toner concentration is expressed by the following formula:
Toner concentration (% by weight) = toner weight / two-component developer weight × 100
The value calculated by

  The two-component developer of the present invention is a two-component development method in which the toner is continuously stirred, and can maintain the toner fluidity and chargeability properly over a long period of time and maintain excellent image quality. It can be suitably used for an image forming method using a developing device having a magnetic permeability sensor for controlling the density.

  As an aspect of using the two-component developer of the present invention for image formation, the above-mentioned developing device is mounted with the two-component developer of the present invention as it is, and the carrier and toner of the two-component developer of the present invention are mounted separately. The mode to do is mentioned. In the latter embodiment, it is preferable that the two-component developer is prepared and used by mixing the carrier and toner in the developing tank and then mixing the carrier and toner in the developing tank. For example, in the formation of a two-component color image composed of several colors, a developer for each color is usually required. However, in the above-described image forming method, the carrier and the toner are converted into a developer in the developing tank. Are commonly used, and it is not necessary to prepare a two-component developer for each toner.

  The process itself of the image forming method is not particularly limited, and a developing device having a magnetic permeability sensor may be used in a developing process for developing an electrostatic image. As other processes, an electrostatic latent image is formed on the surface of the photoreceptor. Developing process (charging / exposure process), developing process for developing the electrostatic latent image, transferring the developed toner image to a transfer material such as paper (transfer process), fixing the transferred toner image (fixing process) And a step (cleaning step) of removing toner remaining on the developing member such as a photosensitive drum.

[Softening point of resin and toner]
Using a flow tester (Shimadzu Corporation, “CFT-500D”), a 1 g sample was heated at a heating rate of 6 ° C./min, and a 1.96 MPa load was applied by a plunger, from a nozzle with a diameter of 1 mm and a length of 1 mm. Extrude. The amount of plunger drop of the flow tester is plotted against the temperature, and the temperature at which half of the sample flows out is taken as the softening point.

[Glass transition point of resin and toner]
Using a differential scanning calorimeter (“DSC210” manufactured by Seiko Denshi Kogyo Co., Ltd.), the sample was heated to 200 ° C. and cooled to 0 ° C. at a temperature decrease rate of 10 ° C./min. Measure and set the temperature at the intersection of the base line extension below the maximum peak temperature of the endotherm and the tangent that indicates the maximum slope from the peak rise 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 (Dt ₅₀ ) and coefficient of variation of toner]
In the present specification, the volume-median particle size (Dt 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: 50μm
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) is dissolved in the electrolyte so as to have 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 above dispersion, and dispersed for 1 minute with an ultrasonic disperser, then 25 mL of electrolyte is added, and further dispersed for 1 minute with an ultrasonic disperser. Prepare a dispersion.
Measurement conditions: By adding the sample dispersion to 100 mL of the electrolytic solution, the particle size of 30,000 particles is adjusted to a concentration that can be measured in 20 seconds, and then 30,000 particles are measured, Determine the volume median particle size (Dt ₅₀ ) and coefficient of variation.

[Carrier volume particle size]
In the present specification, the volume particle size (Dc ₅₀ ) of the carrier having a cumulative frequency of 50% and the volume particle size (Dc ₉₀ ) of the carrier having a cumulative frequency of 90% in the volume particle size distribution of the carrier are the cumulative calculated by the volume fraction. It means the particle size of the carrier whose volume frequency is 50% and 90%, respectively, calculated from the smaller particle size.
Measuring instrument: Laser diffraction particle size measuring instrument “LA-920” (manufactured by HORIBA)
Dispersion: Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether, HLB: 13.6) is dissolved in ion-exchanged water to a concentration of 5% by weight to obtain a dispersion.
Dispersion condition: 10 mg of a measurement sample is added to 5 mL of the above dispersion, and dispersed for 1 minute with an ultrasonic disperser to prepare a sample dispersion.
Measurement conditions: After adding ion-exchanged water to the measurement cell, the sample dispersion is added, and the particles are measured at a concentration at which the absorbance is in an appropriate range, and each volume particle size (Dc ₅₀ and Dc ₉₀ ) is determined from the particle size distribution. Ask for.

[Weight ratio of iron (Fe) and silicon (Si) on the carrier surface]
The weight of iron (Fe) and silicon (Si) is measured by X-ray photoelectron spectroscopy (ESCA), and the ratio (Fe / Si) is calculated. In addition, what was fixed with the conductive carbon tape as a measurement sample is measured.
Equipment: “PHI-5400” (manufactured by ULVAC-PHI)
Measurement conditions: X-ray source MgKα 15keV-20mA (300W)
Measurement area 1mmφ
Detection angle 45 °

[Content of iron (Fe) in ferrite core material]
The ferrite core material is measured by fluorescent X-ray analysis, and the content (% by weight) of iron (Fe) is calculated.
Device: “ZSX-100e” (Rigaku)
Measurement conditions: X-ray source Rh (4kW)
Measurement area 30mmφ

[Carrier saturation magnetization]
Using a vibration type magnetometer “VSMP-1S” manufactured by Toei Kogyo Co., Ltd., a sample is filled in a measurement capsule (0.0565 mL) and measured with a magnetic field of 1.1 (MA / m).

Resin production example 1
Polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane 1,050 g, fumaric acid 355 g, hydroquinone (polymerization inhibitor) 1 g and dibutyltin oxide (esterification catalyst) 1.4 g in a nitrogen atmosphere The reaction was carried out at 210 ° C. for 5 hours under reduced pressure (101.3 kPa), and then reacted at 210 ° C. under reduced pressure (8.3 kPa) to obtain Resin A. Resin A had a softening point of 102.0 ° C., an acid value of 19.8 mgKOH / g, and a glass transition point of 58.0 ° C.

Resin production example 2
830 g of polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, 320 g of polyoxyethylene (2.0) -2,2-bis (4-hydroxyphenyl) propane, 233 g of terephthalic acid, dodecenyl succinic anhydride 245 g, trimellitic anhydride 140 g and dibutyltin oxide (esterification catalyst) 4 g were reacted in a nitrogen atmosphere under normal pressure (101.3 kPa) at 230 ° C. for 8 hours, and further reacted under reduced pressure (8.3 kPa). Resin B was obtained. Resin B had a softening point of 138.5 ° C., an acid value of 25.8 mg KOH / g, and a glass transition point of 65.8 ° C.

Toner production examples 1 to 3
80 parts by weight of resin A as binder resin, 20 parts by weight of resin B, 6 parts by weight of carbon black “Mogal L” (manufactured by Cabot) as a colorant, “Bontron S-34” (manufactured by Orient Chemical Industries) as a charge control agent 1 Part by weight and 2 parts by weight of polypropylene wax “NP105” (Mitsui Chemicals Co., Ltd.) are mixed with a Henschel mixer, then melt-kneaded using a twin-screw kneader “PCM-45” (Ikegai Co., Ltd.), and drum flaker After cooling, the mixture was coarsely pulverized with a cutter mill. Thereafter, the mixture was finely pulverized with a jet mill and classified with an airflow classifier to obtain toner base particles having a volume-median particle diameter (Dt ₅₀ ) and coefficient of variation shown in Table 1. The obtained toner base particles had a softening point of 103 ° C. and a glass transition point of 55 ° C.

  `` R972 '' (hydrophobic silica, manufactured by Nippon Aerosil Co., Ltd.) 0.9 part by weight and 1.0 part by weight of `` NAX50 '' (hydrophobic silica, manufactured by Nippon Aerosil Co., Ltd.) are charged for 90 seconds with respect to 100 parts by weight of the obtained toner base particles. After stirring, toners 1 to 3 were obtained by sieving with a wire mesh having an opening of 100 μm.

Carrier production examples 1-8
Ferrite core material adjusted to Fe ₂ O ₃ : MgO: ZnO: MnO ₂ : CuO = 56: 1: 18: 3: 22 (molar ratio) is mixed with a Henschel mixer, and then at 900 ° C. for 3 hours in a kiln. Pre-baking was performed. The obtained powder was mixed with water and pulverized with a ball mill for 8 hours. Polyvinyl alcohol and a dispersant were added to the pulverized product to form a slurry solution, which was then granulated and dried with a spray dryer. The obtained dried product was baked in an electric furnace at 1220 ° C. for 4 hours, pulverized by a crusher, classified by a gyro shifter, and 10 kg of the obtained powder was used at the outer periphery of the stirring blade using a cutter mill. The following time treatment was carried out at a linear velocity of 1300 m / min, and ferrite core materials of carriers 1 to 8 were obtained. The iron (Fe) content in the cores of the carriers 1 to 8 was 50.4% by weight.
Carrier 1 10 minutes Carrier 2 30 minutes Carrier 3, 4, 5, 6, 85 minutes Carrier 7 20 minutes

  To 100 parts by weight of the obtained ferrite core material, methyl-dimethyl silicone resin (SR-2410, manufactured by Toray Dow Corning) was added and dispersed in toluene in the amount shown in Table 2 to prepare a resin solution. . This resin solution is spray coated on the ferrite core material using a fluidized bed coating apparatus. Thereafter, heat treatment was performed in a fluidized bed at 290 ° C. for 30 minutes, and classification was performed again with a gyro shifter so that the particle size distribution shown in Table 2 was obtained, whereby Carriers 1 to 8 were obtained.

Test example 1
A two-component developer was obtained by mixing 5000 g of the carrier shown in Table 3 and the amount of toner shown in Table 3 and stirring the toner concentration to the value shown in Table 3. The obtained two-component developer is mounted on “Variostream 9000” manufactured by Oce Printing Systems GmbH, and the linear speed is 1000 mm / sec. The print rate is 9% and up to 100,000 sheets, and then the print rate is set to 1%. Furthermore, 10,000 sheets were printed. In-machine due to image density (solid image), toner density, charge amount, and toner dust after 1000 sheets at a printing rate of 9%, after 40000 sheets, after 100,000 sheets, and after 10,000 sheets printed with a printing rate of 1% Contamination was evaluated by the following method. The results are shown in Tables 3 and 4.

[Image density]
The optical reflection density (OD) was measured as an image density with a reflection densitometer “RD-915” (manufactured by Macbeth), and the image density was evaluated according to the following evaluation criteria.

[Image density evaluation criteria]
A: Image density of 1.8 or more O: Image density of 1.7 or more and less than 1.8 Δ: Image density of 1.5 or more and less than 1.7 ×: Image density of less than 1.5 Note that 1.5 or more is the actual use level.

[Toner concentration and charge amount]
Using a blow type charge amount measuring device “q / m-meter” (Epping), a 500 mesh was attached to the cell, and the charge amount was measured. In parallel with the measurement of the charge amount, [weight of attracted toner (g)] / [weight of developer before suction (g)] × 100 was calculated as the toner concentration (% by weight). The difference in the absolute value of the charge amount after printing for each number of sheets was 5 μC / g or less, and the difference in toner concentration after printing for each number of sheets was determined to be 0.5% or less.

[In-machine contamination by toner dust]
The state of in-machine contamination by toner dust was visually observed, and the contamination state was evaluated according to the following evaluation criteria.

[Toner dust evaluation criteria]
◎: Almost no dust ○: There is some dust, but there is no problem in use △: A lot of dust is contaminated in the machine and paper stains, but it is acceptable level in actual use ×: There is a problem in using much dust

From the above results, comparing Comparative Example 1 and Example 1, and Comparative Example 2 and Example 2, the two-component developer of Example has little change in toner density and charge amount, and toner dust generation is also small. This shows that it is better that the toner particles are not too sharp and not too broad and have an appropriate particle distribution. On the other hand, from the comparison between Comparative Examples 3 to 6 and Example 1, Comparative Example 3 has a carrier having a volume particle size (Dc ₅₀ ) of 65 μm or less and a volume particle size (Dc ₉₀ ) of 100 μm or less. Since the amount is small and the carrier of small particle size is used as a whole, the charge amount and toner scattering are good, but the change in the toner concentration is large and is not suitable for printing durability. In Comparative Example 6, the volume particle size ( Dc ₉₀ ) is moderately sized, but a carrier having a volume particle size (Dc ₅₀ ) of 65 μm or less, that is, a coarse particle content is moderate but overall a small particle size carrier is used. Therefore, although toner scattering is small and the toner density is relatively stable, the change in charging is large and it is not suitable for printing durability. In Comparative Examples 4 and 5, the volume particle size (Dc ₅₀ ) is moderate, but since the volume particle size (Dc ₉₀ ) is 125 and 98 μm, respectively, the toner contains a large amount of coarse particles in the carrier. It can be seen that when the amount of dust is large and the number of coarse particles is small, the change in the toner density and the charge amount is large, resulting in a large amount of toner dust, both of which are inferior to the examples. From Comparative Examples 7 and 8, even if the toner and the carrier have preferable particle sizes, the charge amount is not stable when the set toner concentration is low, and toner dust is generated when the set toner concentration is high. It turns out that neither is preferable.

  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 (4)

A two-component developer comprising a carrier and a toner, wherein the carrier is a ferrite core material coated with a silicone resin, and the volume particle of the carrier having a cumulative frequency of 50% in the volume particle size distribution of the carrier. The diameter (Dc ₅₀ ) is 65 to 80 μm, the volume particle size (Dc ₉₀ ) of a carrier having a cumulative frequency of 90% is 100 to 120 μm, the saturation magnetization of the carrier is 64 to 69 Am ² / kg, and the toner has a volume A two-component developer having a median particle size of 8.0 to 9.0 μm, a coefficient of variation with respect to the volume particle size distribution of the toner of 23 to 28%, and a toner concentration of 5.0 to 10% by weight.   The two-component developer according to claim 1, wherein the ferrite core material contains at least 40 to 60% by weight of iron (Fe).   The two-component development according to claim 1 or 2, wherein the weight ratio (Fe / Si) of iron (Fe) to silicon (Si) on the carrier surface measured by X-ray photoelectron spectroscopy is 4.5 / 1 to 7.0 / 1. Agent.   The two-component developer according to any one of claims 1 to 3, wherein a coating amount of the silicone resin with respect to 100 parts by weight of the ferrite core material is 0.5 to 3.0 parts by weight.