JP4979072B2 - Carrier for two-component developer - Google Patents

Description

  The present invention relates to a carrier for a two-component developer used for developing a latent image formed in an electrophotographic method, an electrostatic recording method, an electrostatic printing method, and the like, and a method for producing the same.

  In a developing system using a developer composed of two components of a carrier and a toner, frictional charging is generated by stirring and mixing the carrier and the toner, thereby imparting chargeability to the toner. Therefore, since the chargeability of the toner is influenced by the charging characteristics of the carrier, a technique for improving the charging characteristics of the carrier has been conventionally required.

In Patent Document 1, physical durability and / or chemical treatment are applied to control the shape of the dimples on the core surface, thereby enhancing the durability of the carrier. In Patent Document 2, by reducing the content of the small particle size carrier and increasing the content of the large particle size carrier, the amount of the small particle size carrier deposited on the photoreceptor (hereinafter referred to as carrier adhesion) amount. And the reduction of the charge amount due to the carrier adhesion is prevented. Patent Document 3 uses a carrier having a small average particle size and a very narrow particle size distribution, and regulates the apparent density of the carrier by regulating the amount of treatment of the carrier with an insulating resin. An image with excellent image quality is obtained.
Japanese Patent No. 2905338 Japanese Patent Publication No.7-113785 Japanese Patent No. 2759528

  However, in the method of Patent Document 1, the core material originally has an uneven surface created at a low firing temperature, but since the formed dimple shape is not constant, it is difficult to form a good resin coating. Moreover, although the carrier adhesion of the patent document 2 is reduced, durability and high resistance are not sufficient. The carrier of Patent Document 3 is inferior in durability because an acrylic resin is used for the insulating resin, and even if the amount of treatment with the resin is specified, the durability depends on the type of coating resin and the carrier content. Is greatly affected.

  An object of the present invention is to maintain an image having a high image density and a good image quality by maintaining a high toner density even in printing resistance by a copying machine (hereinafter referred to as printing durability). Another object of the present invention is to provide a carrier for a two-component developer capable of suppressing in-machine contamination and a method for producing the same.

The present inventors have found that the durability of the carrier (that is, the printing durability as a developer) is improved by using a carrier core material obtained through a specific mechanical processing step. Furthermore, the fine particles contained in the carrier core and the carrier are known in contrast to the contradictory characteristics that the image density is lowered when the carrier resistance is increased and the image quality is deteriorated (lowered) when the carrier resistance is lowered. A carrier capable of achieving both image density and image quality, which has been difficult until now, by controlling the content of each fine particle contained in the coating and coating the surface of the carrier core material with a specific resin. It was found that can be obtained. The present invention has been completed by devising such a prescription relating to durability and a prescription relating to image / image quality.

That is, the present invention
[1] A core material having an edge portion is polished by mechanical treatment, whereby the edge portion is polished, and once the core material particles are separated from the core material by the polishing, What is supposed to be present together with coarse core material mother particles is further subjected to mechanical treatment, whereby the core material child particles are converted to the surface of the core material mother particles or grains (sintered primary particles). A carrier for a two-component developer comprising a core material formed by reattaching to a groove between the core material and a resin covering the surface of the core material, and having a volume-median particle size (Dc ₅₀ ) of 40 to 80 μm The content (A) of carrier particles having a particle size of 25 μm or less in the carrier is 0.5 to 7.0% by volume, and the content (B) of core material particles having a particle size of 25 μm or less in the core material Is 1.2 to 5 times that of (A), and the resin is a silicone resin Two-component developer carrier,
[2] The method for producing a carrier for a two-component developer according to [1] above, comprising a step of polishing a core material having an edge portion by mechanical treatment, and [3] an apparatus having a rotating stirring blade. A step of performing mechanical treatment on the core material under the condition of rotating the stirring blade at a linear velocity of 400 m / min or more and 2000 m / min or less at the outer peripheral portion of the stirring blade, and the core material obtained in the above step The present invention relates to the method for producing a carrier for a two-component developer according to the above [1], which comprises a step of coating the surface with a silicone resin.

  The carrier for two-component development of the present invention can provide an image having a good image quality by maintaining a high image density and maintaining a stable toner density even in printing durability. There is an excellent effect that contamination can be suppressed.

The present invention relates to a carrier for a two-component developer comprising a core material and a resin covering the surface of the core material, and having a volume median particle size (Dc ₅₀ ) of 40 to 80 μm, wherein the core material is a core material mother Particles and core particles, the content of carrier particles having a particle size of 25 μm or less in the carrier, and the content of core material particles having a particle size of 25 μm or less in the core material are specific amounts, respectively. There is a big feature in a certain thing.

  The surface of a conventional core material has a sharp edge portion formed in the original manufacturing process, and such a sharp edge portion is difficult to be covered with a coating resin, and charges are generated in a high electric field environment such as a developing portion. Leakage is likely to cause serious damage to the photoreceptor, for example. When such a core material is mechanically processed by a device having a rotating stirring blade, the edge portion is polished, and once the core material particles are separated from the core material by the polishing, a relatively coarse particle is obtained. The core material particles are present on the surface of the core material mother particles or in the grooves between the grains (sintered primary particles) by further performing mechanical treatment. A carrier that can be reattached and has excellent durability can be obtained. In the present invention, the mechanical treatment refers to a treatment that gives a mechanical share to the surface of the core material by a rotary device having a rotating stirring blade, which will be described later, and controls the strength and time of the mechanical treatment. Thus, it is possible to manufacture a core material whose surface state is controlled as described above.

  Since the core material particles contained in the core material easily adhere to the surface of other particles, when the core material particle adheres to a relatively smooth surface, fine convex portions are formed on the carrier surface. Thereby, the adhesiveness of the coating film and core material by coat resin is improved, and the effect which suppresses peeling of a coating agent is acquired. Further, when the gap between the grains on the core surface is large, the core material particles enter the grooves between the grains on the core surface, and there is an effect of making the coating with the coating resin uniform.

  In the present invention, the content of core particles having a particle size of 25 μm or less in the core material and the content of carrier particles having a particle size of 25 μm or less in the entire carrier are defined. This has the effect of smoothing the edge of the surface of the core material, making the coating with the coating resin uniform, improving the stability of the charge amount as a developer, and suppressing carrier adhesion. As a result, both image density and image quality can be made compatible.

  The core material in the present invention is composed of core material mother particles and core material child particles. Core material mother particles mean particles excluding fine particles generated by mechanical treatment, and core material subparticles mean fine particles generated by mechanical treatment. The average particle size ratio (core material mother particle / core material particle) of the core material mother particle and the core material child particle is preferably 1000/1 to 10/1, more preferably 800/1 to 50/1. Have a satisfying relationship. For example, when the average particle diameter of the core material mother particles is 10 to 100 μm, the average particle diameter of the core material child particles is preferably 0.1 to 1 μm. Further, in this specification, the average particle diameter of the core material mother particles and the core material child particles is obtained by photographing the core material with a scanning electron microscope and taking data from the extracted samples of the 100 core material particles. This means the measured number average particle diameter, and can be determined by comparing the state before and after the mechanical treatment, that is, by determining whether or not the fine particles are generated by the mechanical treatment. In this specification, the core material particles mainly mean particles having an average particle diameter of 2 μm or less.

  The metal constituting the core material is not particularly limited, and examples thereof include iron, magnesium, zinc, manganese, copper, lithium, strontium, etc. Among these, iron, magnesium, zinc, manganese and copper are preferable. These may constitute a core material as a metal oxide, and these may be contained in the core material as a metal oxide.

  The manufacturing method of the core material includes a cutter mill, a hammer mill, an atomizer, an attritor, a vertical granulator, a Henschel mixer, a super mixer, and a spira from the viewpoint of containing core particles generated by polishing the edge portion in the core material. There is no particular limitation as long as the method includes a step of mechanically processing the core material using an apparatus having rotating stirring blades such as flow and granulex. 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. Specifically, using the above-mentioned cutter mill, hammer mill, atomizer, attritor, vertical granulator, Henschel mixer, super mixer, Spiraflow, granurex, etc., the linear velocity at the outer periphery of these stirring blades Is 400 to 2000 m / min, preferably 600 to 1800 m / min, more preferably 800 to 1400 m / min. When the linear velocity at the outer peripheral portion of the stirring blade is 400 m / min or more, the edge of the core material is sufficiently polished, and the coating with the coating resin is good, and when it is 2000 m / min or less, the core material is broken. Is unlikely to occur. The processing time can be determined according to the linear velocity. However, if the processing time is too short, the edge of the core material is not sufficiently polished, and the processing becomes uneven. If the processing time is too long, the core material is cracked. It is easy for problems such as For example, when the linear velocity is 800 to 1400 m / min, a treatment time of 1 to 70 minutes is preferable, and 5 to 60 minutes is more preferable. In addition, the content of the core material particles in the core material is the strength of mechanical processing, specifically, cutter mill, hammer mill, atomizer, attritor, vertical granulator, Henschel mixer, super mixer, spira flow, It can be adjusted by changing the linear velocity, processing time, etc. of a stirring blade such as Granurex. For example, when the apparatus is used, the content increases when the linear velocity of the stirring blade is increased, and the content increases when the treatment time is lengthened, but the content decreases when the treatment is continued as it is.

  The content (B) of the core material particles having a particle size of 25 μm or less in the core material is preferably 0.6 to 10.0% by volume, more preferably 1.5 to 4.0% by volume. In the present invention, the content (B) of the core material particles having a particle size of 25 μm or less is (A) when the content of the carrier particles having a particle size of 25 μm or less in the entire carrier is (A). ) 1.2-5 times, preferably 1.5-3.5 times, more preferably 2.0-3.0 times. When the content (B) of the core particles having a particle size of 25 μm or less is 5 times or less of the content (A) of the carrier particles having a particle size of 25 μm or less, the core material surface is coated with a silicone resin. After that, since the carrier fine particle becomes an appropriate amount, the carrier adhesion is reduced and the carrier is suitable for printing durability. Further, when the content (B) of the core particles having a particle size of 25 μm or less is 1.2 times or more the content (A) of the carrier particles having a particle size of 25 μm or less, the core material is sufficiently polished. In addition, since the effect of the core material particles generated by the polishing of the core material can be expected, the carrier is suitable for printing durability. In addition, in this specification, content (B) of the core material particle which has a particle size of 25 micrometers or less is measured by the method described later.

  The carrier of the present invention also has one feature in that the resin covering the surface of the core material is a silicone resin. Therefore, when the carrier of the present invention is manufactured, the mechanical material is added to the core material. A step of performing a treatment, that is, using a device having a rotating stirring blade, mechanically applied to the core under the condition that the stirring blade is rotated at a linear velocity of 400 m / min or more and 2000 m / min or less on the outer periphery of the stirring blade It is desirable to have a process of processing and a process of coating the surface of the core material obtained in the process with a silicone resin. Examples of such silicone resins include straight silicone resins such as methyl silicone resins (for example, dimethyl silicone resins, methyl silicone resins, and methyl-dimethyl silicone resins) that are composed of organosiloxane bonds, 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, the core material is preferably coated with a straight silicone resin, more preferably with a methylsilicone resin.

  The core material coating method includes, 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 core material, or a method of simply mixing with a powder, and the like. Not. It is efficient to adjust the coating amount of the core material by changing the surface shape of the core material by, for example, processing using a ball mill or the like and changing the specific surface area.

  The coating amount of the silicone resin is preferably 0.5 to 3.0 parts by weight, more preferably 0.8 to 1.5 parts by weight with respect to 100 parts by weight of the core material from the viewpoint of fluidity, durability and chargeability. . 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 core material. Since the amount and the amount used are substantially the same, they are expressed as “coating amount”.

The volume median particle size (Dc ₅₀ ) of the carrier is 40 to 80 μm, preferably 55 to 75 μm, more preferably 65 to 70 μm. Further, the content (A) of carrier particles having a particle size of 25 μm or less in the carrier is 0.5 to 7.0% by volume, preferably 0.8 to 6.0% by volume, and more preferably 1.0 to 4.0% by volume. When the volume median particle size (Dc ₅₀ ) of the carrier is 40 μm or more, the adhesion of the carrier is reduced, the fluidity is stabilized, and the change in the charge amount and the toner concentration is small, which is suitable for printing durability. When the volume median particle size (Dc ₅₀ ) of the carrier is 80 μm or less, the change in the charge amount and the toner concentration is reduced, the generation of toner dust is reduced, and it is also suitable for printing durability. Furthermore, when the content (A) of the carrier particles having a particle size of 25 μm or less is 0.5% by volume or more, the generation of toner dust is reduced, which is suitable for printing durability, and the carrier particles having a particle size of 25 μm or less. The content (A) of 7.0% by volume or less is preferable because carrier adhesion is reduced and it is suitable for printing durability. In the present specification, the volume-median particle size (Dc ₅₀ ) of the carrier and the content (A) of particles having a particle size of 25 μm or less are measured by the methods described in the examples below.

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 of the image quality, and 40 Am ² / kg or more from the viewpoint of preventing carrier adhesion and toner scattering. preferable.

  The toner that can be used in combination with the carrier of the present invention is not particularly limited, and can be mixed with a known toner and used as a two-component developer. For example, a binder resin, a colorant, and other additives A toner containing a toner raw material such as can be used.

  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 singly or in combination of two or more. The toner mixed with the carrier of the present invention is Any of black toner, color toner, and 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 volume median particle size (Dt ₅₀ ) of the toner to be mixed is preferably 8.0 to 9.0 μm, more preferably 8.2 to 8.8 μm, and more preferably 8.4 to 8.6 μm. The coefficient of variation with respect to the volume particle size distribution is preferably 23 to 28%, more 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 content is preferably 0.5 to 10 parts by weight and more preferably 2 to 8 parts by weight with respect to 100 parts by weight of the carrier.

[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 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]
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.

[Volume-median particle size of carrier (Dc ₅₀ ), content of particles having a particle size of 25 μm or less of carrier (A), and content of particles having a particle size of 25 μm or less of core material (B)]
In the present specification, the volume-median particle diameter (Dc ₅₀ ) of the carrier means the particle diameter of the carrier at which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle diameter.
Measuring machine: Laser diffraction particle size distribution measuring instrument “HELOS & RODOS” (Sympatec GmbH)
Measurement conditions: 5 to 10 g of carrier and core material dispersed at a dispersion pressure of 0.2 MPa were measured, the carrier volume median particle size (Dc ₅₀ ), the content of carrier particles having a particle size of 25 μm or less, and the core The content of core material particles having a particle size of 25 μm or less is determined.

[Average particle diameter of core material mother particles and core material child particles]
The average particle size of the core material mother particles and the core material child particles is the number average particle size, and is determined by the following method.
The core material was photographed with a scanning electron microscope, and after extracting 100 core material mother particles and core material child particles at random, the diameter in the major axis direction and the diameter in the minor axis direction were measured and averaged. The value can be determined as the diameter of each particle. The average particle diameter of the core material mother particles or the core material child particles can be calculated from the diameters of the obtained particles. The major axis diameter means the longest axial length of each particle, and the minor axis diameter means the shortest axial length of each particle.

Example 1 (Carrier 1)
Fe ₂ O ₃ : MgO: ZnO: MnO ₂ : CuO = 56: 1: 18: 3: 22 (molar ratio) core material particles were mixed with a Henschel mixer, and the kiln was 900 ° C for 3 hours. 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 core material of carrier 1 was obtained by performing mechanical treatment for 40 minutes at a linear velocity of 900 m / min. Table 1 shows the average particle size of the core material mother particles and the core material child particles, and the content of the core material particles having a particle size of 25 μm or less in the core material.

A methyl-dimethyl silicone resin (SR-2410, manufactured by Toray Dow Corning) was dispersed in 1.0 part by weight of toluene with respect to 100 parts by weight of the obtained core material to prepare a resin solution. The resin solution is spray coated on the 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 1 was obtained, whereby Carrier 1 was obtained. Table 1 shows the volume-median particle size (Dc ₅₀ ) of the carrier and the content of carrier particles having a particle size of 25 μm or less in the carrier.

Example 2 (Carrier 2)
A carrier 2 was produced in the same manner as in Example 1 except that the time for mechanical treatment by the cutter mill was changed to 70 minutes.

Example 3 (Carrier 3)
A carrier 3 was produced in the same manner as in Example 1 except that the time of mechanical treatment by the cutter mill was changed to 20 minutes.

Comparative Example 1 (Carrier 4)
A carrier 4 was produced in the same manner as in Example 1 except that the mechanical processing step by the cutter mill was omitted.

Comparative Example 2 (Carrier 5)
A carrier 5 was produced in the same manner as in Example 1 except that the linear velocity in the mechanical treatment step by the cutter mill was changed to 2500 m / min.

Resin production example 1 (for toner A)
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 under nitrogen atmosphere and normal pressure The mixture was reacted at 210 ° C. for 5 hours at 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 (for toner A)
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 example 1
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 size (Dt ₅₀ ) of 8.5 μm and a CV value of 20%. The obtained toner base particles had a softening point of 103 ° C. and a glass transition point of 55 ° C.

  0.9 parts by weight of “R972” (hydrophobic silica, manufactured by Nippon Aerosil Co., Ltd.) and 1.0 part by weight of “NAX50” (hydrophobic silica, manufactured by Nippon Aerosil Co., Ltd.) are added to 100 parts by weight of the obtained toner base particles for 90 seconds After stirring, the toner A was obtained by sieving with a metal mesh having an opening of 100 μm.

Test example 1
The amount of toner shown in Table 2 and the carrier were mixed and stirred so that the toner concentration would be the value shown in Table 2 to obtain two-component developers 1-5. The obtained two-component developer was mounted on “Variostream 9000” manufactured by Oce Printing Systems GmbH, and printed with a linear speed of 1000 mm / sec, printing up to 100,000 sheets at a printing rate of 9%. The image density (solid image), toner density, charge amount, and in-machine contamination due to toner dust were evaluated by the following methods after 1000 sheets and 100000 sheets at a printing rate of 9%. The results are shown in Table 2.

[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: 1.5 or more, 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 ○: Some dust, but no problem in use △: Many dusts in the machine and paper stains occur, but acceptable level in actual use ×: There is a problem in using many dusts XX: Printing continues very much dust impossible

  From the above results, the two-component developers 1 to 3 using the carriers 1 to 3 of the examples are more durable than the two-component developers 4 and 5 using the carriers 4 and 5 of the comparative example. It can be seen that the image density is high, the toner density and the amount of charge are small, and toner dust is little generated, which is excellent. From this, it is important that the ratio of the content of carrier particles having a particle size of 25 μm or less in the carrier and the content of core particles having a particle size of 25 μm or less in the core material is within a specific range. It is thought that it is.

  As mentioned above, although the Example of this invention has been described concretely, this invention is not limited to these.

  The carrier 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 (6)

By polishing the core material having the edge portion by mechanical treatment, the edge portion is polished, and once the core material particles are separated from the core material by the polishing, a relatively coarse core is obtained. What is supposed to be present together with the base material mother particles is further subjected to mechanical treatment, so that the core material child particles are grooved between the surface of the core material base particles or grains (sintered primary particles). A carrier for a two-component developer comprising a core material formed by reattachment to the resin and a resin covering the surface of the core material, and having a volume median particle size (Dc ₅₀ ) of 40 to 80 μm, The content (A) of carrier particles having a particle size of 25 μm or less in the carrier is 0.5 to 7.0% by volume, and the content (B) of core particles having a particle size of 25 μm or less in the core is (A) 1.2-5 times), and the resin is a silicone resin Component developer carrier.   2. The carrier for a two-component developer according to claim 1, wherein an average particle size ratio (core material mother particle / core material child particle) of the core material mother particle and the core material child particle is 1000/1 to 10/1.   The carrier for a two-component developer according to claim 1 or 2, wherein the coating amount of the silicone resin relative to 100 parts by weight of the core material is 0.5 to 3.0 parts by weight. The method for producing a carrier for a two-component developer according to any one of claims 1 to 3, comprising a step of polishing the core material having the edge portion by mechanical treatment.   The method for producing a carrier for a two-component developer according to claim 4, wherein the mechanical treatment is performed using an apparatus having a rotating stirring blade.   Using a device having a rotating stirring blade, performing a mechanical treatment on the core under the condition of rotating the stirring blade with the linear velocity at the outer peripheral portion of the stirring blade being 400 m / min or more and 2000 m / min or less; and The manufacturing method of the carrier for two-component developers of any one of Claims 1-3 including the process of coat | covering the surface of the core material obtained at the process with silicone type resin.