JPH08272147A - Carrier for development of electrostatic charge image - Google Patents

Abstract

PURPOSE: To provide a carrier which is used in a toner recycle system, spend less toner even through a long time of service, and presents good durability. CONSTITUTION: A toner image is formed by developing a latent image on a carrier, and the produced toner image is transferred from the carrier onto a transferring material, and the toner on the carrier is collected by cleaning the carrier after transfer, and the collected toner is supplied to the developing process and re-used. This image forming method includes a carrier for development of electrostatic charge image, which has at least one maximum between 25 and 500V/cm when the relation of the volume specific resistance (V-axis) of the carrier to the impressed voltage (X-axis) is plotted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention develops a latent image on a latent image carrier to form a toner image, transfers the formed toner image from the latent image carrier to a transfer material, and transfers the latent image after transfer. The present invention relates to an electrostatic charge image developing carrier used in an image forming method in which a carrier is cleaned to collect toner on a latent image carrier and the collected toner is supplied to a developing device to be used in a developing process.

[0002]

BACKGROUND OF THE INVENTION Conventionally, as a method for developing an electrostatic latent image using toner, a cascade developing method (US Pat.
No. 552) and a magnetic brush developing method (see US Pat. No. 2,877,403). In any of these methods, a two-component dry developer is used.

In this two-component dry developer, fine toner particles are held on the surface of relatively large carrier particles by the electrostatic force generated by the friction between the two particles, and when the electrostatic latent image is approached, the toner particles become static. The attractive force of the electric field formed by the electrostatic latent image on the toner particles in the direction of the latent image overcomes the binding force between the toner particles and the carrier particles, and the toner particles are attracted and attached on the electrostatic latent image. Is to be visualized. Then, the developer is repeatedly used while replenishing the toner consumed by the development.

In this case, the toner particles must always have the correct chargeability and charge to be preferentially attracted to the desired image area on the photoconductor. In addition, the carrier must always be triboelectrified to have a desired polarity and a sufficient amount of charge for the toner particles during long-term use. If the carrier is to be used in a magnetic brush development process, it must also have suitable magnetism.

Therefore, iron powder carriers, ferrite carriers, binder type carriers (resin particles in which magnetic fine particles are dispersed), etc. have been developed and put into practical use as carriers used in the magnetic brush development method. Iron powder carriers include flake-shaped, sponge-shaped, and spherical shapes, but have a true specific gravity of 7 to 8 and a bulk density of 3 to 4 g / cm.
^Since it is as large as ³ , a large driving force is required to stir in the developing device, mechanical abrasion is often caused, so-called spent toner is formed, chargeability of the carrier itself is deteriorated, and the photoreceptor is easily damaged.

Further, the ferrite carrier has a spherical shape,
Since the true specific gravity is 4.5 to 5.5 and the bulk density is 2 to ³ g / cm ³ , the weight which is a defect of the iron powder carrier can be solved to some extent, but the rotation speed of the developing sleeve or the magnet in the sleeve is reduced. However, it is not enough to support high-speed copiers and high-speed laser beam printers for general-purpose computers. In order to solve such a problem of spent forming, a binder type carrier whose true specific gravity and bulk density are smaller than those of an iron powder carrier or a ferrite carrier is being developed. Regarding the binder type carrier, JP-A-59-31967 and JP-A-5-31967
There have been proposed carriers by various manufacturing methods such as those described in JP-A-9-24416 and JP-A-58-136052. Since the binder type carrier has smaller true specific gravity and bulk density than the ferrite carrier, mechanical stress applied to the developer is reduced, and toner spent is less likely to occur.

However, the binder type carrier has a problem that carrier adhesion due to the exposure of the magnetic substance becomes a problem and that a large amount of the magnetic substance cannot be introduced. For this reason, the following binder type carriers have been proposed. [JP-A-2-220068] Composite particles of ferromagnetic fine particles and a phenol resin. Due to its low specific gravity, it is highly durable and can introduce a larger amount of magnetic material than conventional binder type carriers, so it is a technology that can greatly improve the problem of carrier adhesion, but phenol resin is a resin that contains a lot of oxygen. Therefore, the surface energy is relatively high, and the toner easily fuses. Further, the problem of carrier adhesion due to injection of latent image charges into the exposed portion of the magnetic body still remains.

Therefore, a type coated with the following resin has been proposed. [JP-A-4-86749] JP-A-2-22006
The surface of the composite particles of JP-A-8 is coated with a styrene resin or the like, which is characterized by the ease of controlling the charging property.
The coating method is that "1 kg of the composite particles and 30 g of styrene resin were put in a Henschel mixer under a nitrogen stream, heated to 120 ° C. with stirring, and stirred at the same temperature for 1 hour." In the case of, the mixing amount of silicone resin (KR-255, manufactured by Shin-Etsu Chemical Co., Ltd.) is 2
The same method is used except that the amount is changed to 0 g. According to the examples, the resin coating amount is disclosed to be 1.2 to 4.5% by weight.

[JP-A-5-150557] JP-A-2-220068 discloses a composite particle in which the surface is covered with a silicone resin and cured. [JP-A-6-118725] JP-A-2-2200
Japanese Patent Publication No. 68-A technique in which the surface of composite particles similar to silicone resin is covered with a silicone resin to secure the toner spent resistance of the silicone resin, and further the strength of the carrier itself is increased, so that desorption of the magnetic material and destruction of the carrier do not occur. Is proposed. The coating method uses a fluidized bed type coating apparatus, and the resin coating amount is 6% by weight.

However, although any of the above techniques can prevent the toner spent and the latent image charge injection type carrier from adhering, the latent image on the latent image carrier is developed to form a toner image, and the formed toner image is latently formed. An image forming method in which the image is transferred from the image carrier to a transfer material, the latent image carrier after the transfer is cleaned to recover the toner on the latent image carrier, and the recovered toner is supplied to a developing device to be used in a developing process. That is, in the toner recycling system, deteriorated toner returns to the developing device. (1) Charge-up due to use (especially when coated with silicone resin) and image quality change due to it (2) Counter accompanying toner development Accumulation of charge and carrier adhesion to non-image area due to the charge accumulation (3) Decrease in toner charge amount under high temperature and high humidity due to low water content on the carrier surface (toner under high temperature and high humidity) Although the water content is increased, the carrier moisture content almost does not change caused an estimate) such problems would be amplified.

[0011]

DISCLOSURE OF THE INVENTION The object of the present invention is to provide a carrier having a toner recycling system that (1) has a small toner spent and a good durability even during long-term use. (2) Reproducibility of fine lines and solid part Provides carriers compatible with high levels of high concentration (3) Provides carriers without carrier adhesion to the image area (latent image charge injection type) or carrier adhesion to the non-image area (countercharge accumulation type) (4) Providing a carrier that does not charge up due to use and does not decrease in density or thin horizontal lines (5) Provide a carrier that does not reduce the charge amount even under high temperature and high humidity, without fog, toner scattering, and thickening of vertical lines. Is.

The object of the present invention is to develop a latent image on a latent image carrier to form a toner image, transfer the formed toner image from the latent image carrier to a transfer material, and carry the latent image after transfer. A carrier for electrostatic charge image development used in an image forming method, in which a toner is collected on a latent image bearing member by cleaning the body, and the collected toner is supplied to a developing process to be used. Achieved by a carrier for developing an electrostatic charge image, which has at least one local maximum value between 25 V / cm and 500 V / cm when the relationship between (Y axis) and applied voltage (X axis) is plotted. It

Further, the latent image on the latent image carrier is developed to form a toner image, the formed toner image is transferred from the latent image carrier to a transfer material, and the latent image carrier after the transfer is cleaned. A carrier for electrostatic charge image development used in an image forming method, wherein toner collected on a latent image carrier is collected, and the collected toner is supplied to a developing step for use, and at least ferromagnetic fine particles,
And the surface of core particles containing a thermosetting resin is coated with a resin, and the coating resin has a resin coating portion having a sufficient thickness and an extremely thin resin coating portion. This is accomplished with an image developing carrier.

Particularly, the latent image on the latent image carrier is developed to form a toner image, the formed toner image is transferred from the latent image carrier to a transfer material, and the latent image carrier after the transfer is cleaned. Collect the toner on the latent image carrier and supply the collected toner to the development process (for example, supply it to the developing device or toner hopper).
A carrier for developing an electrostatic charge image used in an image forming method used as, wherein at least the surface of ferromagnetic particles and core particles containing a thermosetting resin are coated with a resin. Has a resin-coated portion having a sufficient thickness and an extremely thin resin-coated portion, and is 25 V / cm when the relationship between the volume resistivity of the carrier (Y axis) and the applied voltage (X axis) is plotted. To 500 V / cm with at least one local maximum, which is achieved by an electrostatic charge image developing carrier.

In the above electrostatic charge image developing carrier, the thermosetting resin is preferably a phenol resin, and the coating resin is preferably a silicone resin. Hereinafter, the present invention will be described in detail.
In the case of uniform resin coating as in the past, thick coating tends to cause changes in image quality due to charge-up and carrier adhesion to non-image areas due to accumulation of counter charge, further increasing the electrical resistance of the carrier. A low concentration near the center of the solid part cannot be avoided. On the other hand, when a thin coating is applied, carriers are likely to adhere to the image area due to the injection of latent image charges, and the electric resistance of the carriers is further lowered, so that the reproducibility of fine lines due to the reduction of the edge effect cannot be avoided.

Therefore, as a result of earnestly researching such problems, as shown in FIGS. 1 (a) and 1 (b), a resin-coated portion having a sufficient thickness on the carrier surface and an extremely thin resin-coated portion are formed. It has been found that, by forming both of the above and the above, it is possible to have a well-balanced portion for retaining charges and a portion for releasing charges, and it is possible to obtain a carrier that solves the above-mentioned drawbacks.

Further, under high temperature and high humidity, the resin-coated portion having a sufficient thickness is difficult to adsorb moisture, but the extremely thin coated portion is likely to adsorb moisture due to the influence of the magnetic substance contained in the core particles. As a result, it was considered that the difference from the amount of adsorbed water of the toner was small and the decrease in the amount of charge under high temperature and high humidity was reduced.
In the present invention, "a resin-coated portion having a sufficient thickness"
The “extremely thin resin-coated portion” can be defined by a photograph taken using a scanning electron microscope. Although there are various scanning electron microscopes, a field emission scanning electron microscope was used in the present invention. Specifically, a field emission scanning electron microscope JSM-6400F (manufactured by JEOL Ltd.) was used to observe the carrier surface not subjected to pretreatment such as gold or gold-palladium sputtering under the following measurement conditions.

Acceleration voltage: 2 kV Emission current: 8 μAmpsable squeeze: 4 Working Distance: 15 mm Probe Current: 3 × 10 ^-11 A Then, Polaroid Model 5 attached to the electron microscope was used.
45 (manufactured by Polaroid) using Polapan 4X
5 Instant Sheet Film "Prof
Take a picture with "essential 52".

In this photograph, the black portion is defined as "resin coated portion having sufficient thickness" and the white portion is defined as "extremely thin resin coated portion". This is because the resin-coated part with a sufficient thickness has a low electron density because it is a resin, so it looks black, and conversely, the extremely thin resin-coated part has electron beams up to the core particle where there is a ferromagnetic material with a high electron density. It looks white to enter. Since the penetration depth of electrons changes depending on the accelerating voltage of the electron beam, the thickness can be discussed by determining the accelerating voltage. The portion not covered with the resin is included in the "extremely thin resin-coated portion".

The area ratio between the resin-coated portion having a sufficient thickness and the extremely thin resin-coated portion is preferably 20:80 to 80:20 from the viewpoint of performance balance. Here, the area is a picture taken by a scanning electron microscope, and an image analysis device SPIC
It was obtained by binarization processing by CA (manufactured by Nippon Avionics Co., Ltd.). In the carrier of the present invention, the ratio of the resin-coated portion is more preferably 80% or more of the carrier surface. That is, it is because the portion not covered with the resin surely causes carrier adhesion due to injection of latent image charges or tends to cause toner spent. Here, the "resin-coated portion" is measured by the following X-ray photoelectron spectroscopy.

Device: ESCA-1000 (manufactured by Shimadzu Corporation) Measurement conditions X-ray source: Mg anode, 10 kV-30 mA Pass Energy: 78.75 eV Sample Time: 200 ms Repeat Time: 10 times (example) Si ... Binding Energy is 94.
Using the Si2p peak obtained in the range of ~ 110 eV.
Performs Savitzky smoothing and backs
Ground is Lo. Of Non Linear. + Av
e was applied.

The atomic peak area intensity was used for the quantitative calculation of the atomic concentration, and the sensitivity coefficient was in accordance with the sensitivity correction coefficient table for Shimadzu ESCA-1000. When the amount of a specific element (= element not included in the coating resin) on the surface of the core particles is A atom% and the amount of the element after resin coating is B atom%, the ratio of the resin-coated portion Is {(A−B) / A} × 100 (%)
Is defined.

The carrier having the non-uniform thickness of the coated surface thus exhibits unique resistance characteristics. FIG. 2 shows the applied voltage dependence of the typical volume resistivity of the carrier of the present application. The conventional carrier is Japanese Examined Sho 63-11662
The carrier of the present invention shows at least one maximum value in the range of 25 to 500 V / cm, while it shows a flat or downward sloping tendency with respect to the applied voltage as seen in the examples and comparative examples of the publication. Is characteristic. It is considered that this unique resistance characteristic realizes fine line reproducibility and high concentration near the center of the solid part.

The absolute value of the volume resistivity of the carrier is 5
When the applied voltage is 00V, 1 × 10 ⁶ to 1 × 10 ¹² Ω · c
Particularly preferably m. The method for measuring the volume resistivity of the carrier is as follows. 1.0 g of the carrier was filled in an insulating cylindrical container having a cross-sectional area of 1.0 cm ² , tapping was performed 100 times, the sample height was obtained under a load of 500 g, and then a voltage of DC 25 V was applied to obtain a current value. To measure. The volume resistivity was calculated from the obtained sample height and current value by the following formula.

Volume resistivity value (Ω · cm) = 25 (V) · cross-sectional area (c
m ² ) / current value (A) / sample height (cm) The same measurement was performed at DC 50V, 100V, 250V, 500
Perform with V. Any method may be used to make the thickness of the coating layer non-uniform, but in the case of spray coating using a fluidized bed coating device or coating by the dipping method, the viscosity of the coating solution (solid content It is advisable to control the concentration) and the total coating amount.

Among them, in the case of spraying using a fluidized bed type coating apparatus or applying by dipping method, there is a method of thinly coating the resin in a state where the viscosity of the coating solution is low and positively forming surface irregularities. Particularly preferred. The viscosity of the coating liquid can be roughly controlled by the concentration of the solid content (coating resin), and the preferable range is 3 to 25% by weight. Here, the solid content concentration is a percentage of the coating resin weight ratio with respect to the total weight of the coating resin and the solvent. The total coating amount for thinning is preferably 0.05 to 1.5% by weight. 0.05% by weight
If it is less than the
If it is more than 1.5% by weight, it is difficult to form appropriate coating unevenness. Here, the total coating amount is the ratio of the coating resin amount to the total of the core particles and the coating resin expressed in%.

As the ferromagnetic fine particles, magnetite,
Spinel ferrites such as γ-iron oxide, metals other than iron (M
n, Ni, Zn, Mg, Cu, etc.) may be used, and magnetoplumbite ferrite such as spinel ferrite, barium ferrite or the like containing fine particles of iron or alloy having an oxide layer on the surface can be used. The shape may be granular, spherical, or acicular. In particular,
When high magnetism is required, ferromagnetic fine particle powder such as iron can be used, but in consideration of chemical stability, magnetite, magnetoplumbite type such as spinel ferrite containing barium ferrite and γ-iron oxide. It is preferable to use a ferromagnetic fine particle powder of ferrite. By properly selecting the type and content of the ferromagnetic fine particle powder, composite particles having a desired saturation magnetization can be obtained.

Examples of the thermosetting resin for the core particles include phenol resin, urea resin, melamine resin, epoxy resin, unsaturated polyester resin, silicone resin and the like. Among them, a large amount of magnetic material can be contained and the cost is low. Further, the phenol resin is particularly preferable because the resin coating can be easily controlled. The composite core particles of the ferromagnetic fine particles and the thermosetting resin mentioned here are obtained by melt-kneading the thermosetting resin and the ferromagnetic fine powder, and then adding a curing agent to heat-harden the mixture.
A method of pulverizing and classifying the resulting cured product, a method of dissolving a thermosetting resin in a solvent such as toluene, further dispersing magnetic fine powder, spray-granulating and drying, and further curing by heating, a method of classifying Examples include a method of granulating and polymerizing a monomer constituting a thermosetting resin in the presence of magnetic fine particles to cure the monomer. Among the above-mentioned methods, a method that can easily be made spherical and can obtain carrier particles having high hardness is preferable. If the surface is spherical, precise control of the resin coating becomes easy. Japanese Patent Laid-Open No. 2-220
Although the method described in Japanese Patent No. 068 and the like can be mentioned, the method is not limited to this.

On the other hand, as the coating resin, epoxy resin,
One or a mixture of polyester resin, styrene resin, acrylic resin, silicone resin, fluororesin, polyamide resin, polyacrylonitrile resin, polyolefin resin and the like can be used. Among them, the silicone resin is preferable in view of the toner spent resistance and the control of the thickness of the resin coating layer.

The silicone resin used in the present invention may be any silicone resin. For example,
A straight silicone resin having only an organosiloxane bond represented by the following formula and a silicone resin modified with alkyd, polyester, urethane or the like can be mentioned. Specifically, KR271, K manufactured by Shin-Etsu Chemical Co., Ltd.
R255 and SR2411, SR2 made by Toray Silicone Co., Ltd.
There are 406 etc.

[0031]

Embedded image

[R is a hydrogen atom, a halogen atom, a hydroxy group, a methoxy group, a lower alkyl group having 1 to 4 carbon atoms, a phenyl group] In the case of a silicone resin coating, after coating, 20
It is preferable to include a step of curing at a temperature of 0 to 250 ° C. because the charging property is improved and the film strength is improved. Phenolic resin is used as the thermosetting resin for the core particles, and
When a silicone resin is combined with the coating resin, it is easy to form appropriate coating unevenness, and as a result, the effects of the present invention can be maximized. The reason for this is not clear,
It is estimated that the surface energies of the phenolic resin and the silicone resin are significantly different.

The carrier particles preferably have an average particle size of 30 to 200 μm in order to obtain good image quality. The average particle diameter of the carrier particles means an average particle diameter on a volume basis, and is measured by a laser diffraction type particle size distribution measuring device “HELOS (manufactured by SYMPATEC)” equipped with a wet dispersion machine. In order to improve the resistance of the carrier, conductive fine particles may be added to the silicone resin coating layer. Examples of the conductive fine particles include carbon black, titanium oxide, zinc oxide and tin oxide.

Further, a silane coupling agent may be added to the carrier in order to improve the adhesion between the core particles and the silicone resin coating layer and the charging property. Examples of the silane coupling agent include those described in JP-A-6-118725. The raw material for the toner used in the present invention may be any material. Examples of the binder resin include polyester resin, styrene-alkyl acrylate resin, styrene-alkyl methacrylate resin, styrene-butadiene resin, styrene-acrylonitrile resin, styrene-acryl-polyester resin, styrene-acryl-crystal. Examples thereof include a hydrophilic polyester-based graft resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl chloride, polyamide, polyvinyl butyral, rosin, modified rosin, phenol resin, and xylene resin.

Examples of coloring agents include carbon black, chrome yellow, DuPont oil red, quinoline yellow, phthalocyanine blue, and magnetic materials. Ferrite, magnetite and other iron, cobalt, nickel and other ferromagnetic metals or alloys, or compounds containing these elements, or magnetic materials that do not contain ferromagnetic elements, but can be strengthened by appropriate heat treatment Examples thereof include magnetic alloys such as manganese-copper-aluminum and manganese-copper-tin, which are called Heusler alloys containing manganese and copper.

Examples of the releasing agent include low molecular weight polyethylene having a number average molecular weight (the number average molecular weight is a polystyrene molecular weight conversion value in high temperature GPC) of 1500 to 5000, low molecular weight polypropylene, low molecular weight polyethylene.
Polyolefin wax such as polypropylene copolymer, high-melting paraffin wax such as microwax and Fischer-Tropsch wax, ester wax such as fatty acid lower alcohol ester, fatty acid higher alcohol ester and fatty acid polyhydric alcohol ester, amide wax, etc. Can be used.

Then, the above-mentioned raw materials are appropriately blended,
Colored particles are obtained through the steps of mixing, melting, cooling, pulverizing and classifying. Alternatively, the colored particles can be obtained by a method in which the raw materials are dissolved and dispersed in a solvent and then polymerized. Next, inorganic fine particles and other substances as necessary are mixed as external additives, and as the inorganic fine particles, for example, silica, alumina, titania, barium titanate, magnesium titanate, calcium titanate, strontium titanate, Examples thereof include zinc oxide, cerium oxide, antimony trioxide, zirconium oxide, silicon carbide and silicon nitride. These may be hydrophobized before use, and particularly hydrophobized silica is preferable. In recent years, negatively chargeable organic photoconductors have become the mainstream of the photoconductors, and toners having positive chargeability have been demanded. Therefore, the chargeability of the hydrophobic silica fine particles is also required to be positively chargeable, for example, an amino-modified silane coupling agent,
A hydrophobic silica surface-treated with an amino-modified silicone oil, a quaternary ammonium salt compound of polysiloxane, an organopolysiloxane and an amine-modified silicone compound such as 3-aminopropyltriethoxysilane can be preferably used. Other external additives include zinc stearate, lubricants such as polyvinylidene fluoride, and fixing aids such as low molecular weight polypropylene. The amount of the inorganic fine particles used is 0.
The range of 01 to 5 parts by weight (particularly 0.05 to 2 parts by weight) is preferable.

The charge control agent added to the toner is preferably an organic one containing no metal. Not only is it suitable for environmental protection, but it is also excellent in that it suppresses excessive charge leakage at the extremely thin resin coating portion of the carrier surface. As such an organic charge control agent, a quaternary ammonium salt compound and a triphenylmethane compound can be preferably used for the positively charged toner, and calixarene can be suitably used for the negatively charged toner.

The present invention will be described below with reference to specific examples.

[0040]

【Example】

[Example 1] According to the method described in JP-A-4-86749, in the presence of magnetite fine particles having a particle diameter of 0.23 µm, phenol and formalin are condensed in an aqueous medium to give a magnetite content of 89. %, And a phenol resin core particle 1 having an average particle diameter of 90 μm was obtained. Next, under a nitrogen stream, 5000 parts by weight of the core particles 1 and 1000 parts by weight of a toluene solution of a monomethyl silicone resin having a solid content of 5% by weight were put in a Henschel mixer, and the temperature was raised to 120 ° C. with stirring. The mixture was stirred at the same temperature for 1 hour (total coating amount: 1.0% by weight). Then 200
Cured at ℃ for 2 hours. This is carrier 1.

According to an electron microscope observation, this carrier 1 has a resin coating portion X having a sufficient thickness and an extremely thin resin coating portion Y, and the area ratio X: Y is 68:32. It was The ratio of the resin-coated portion was 82%. The ratio of the portion coated with the iron resin on the surface of the resin-coated carrier was calculated from the following ESCA data (atomic% based on peak area). In particular,
It was calculated by {(atomic% of surface Fe of core particle)-(atomic% of surface Fe of resin-coated carrier)} × 100 / (atomic% of surface Fe of nuclear particle).

Atomic% (based on peak area) Si CO Fe core particles 1 0.81 78.93 19.42 0.84 Resin-coated carrier 37.42 26.11 36.32 0.15 Further, when the volume resistivity was measured, the following result was obtained, which was between 25V and 500V. Had one local maximum.

DC applied voltage Volume resistivity (Ω · cm) 25V 5 × 10 ¹⁰ 50V 1 × 10 ¹¹ 100V 2 × 10 ¹¹ 250V 3 × 10 ¹¹ 500V 3 × 10 ⁹ Meanwhile, styrene / n-butyl acrylate / methyl methacrylate = 88/10/2 (weight ratio) Copolymer 100 parts by weight Carbon black 10 parts by weight Polypropylene (number average molecular weight 4000) 3 parts by weight Quaternary ammonium salt-based positive charge control agent 1 part by weight The mixture was kneaded, pulverized and classified to obtain colored particles having a volume average particle diameter of 7.6 μm.

Further, with respect to 100 parts by weight of the colored particles, silica having an average particle size of 8 nm which was first subjected to a hydrophobic treatment with dimethyldichlorosilane and then with an ammonium functional polysiloxane was subjected to a hydrophobic treatment with 1.0 part by weight. Average particle size 30 nm
0.8 parts by weight of titanium oxide was added. This is designated as Toner 1. 6 parts by weight of this toner 1 and 94 parts by weight of the carrier 1 were mixed to obtain a developer 1.

This developer 1 was heated at a temperature of 20 ° C. and a humidity of 50%.
Under the environment, the electrophotographic copying machine "Koni" is equipped with a recycling mechanism that collects the residual toner after transfer and returns it to the developing device.
ca4145 "(manufactured by Konica Corporation) was used to evaluate the copied image, and the image density was 1.35 and the fog was 0.00.
A high quality image of 1 was obtained. After that, a durability test was performed on 200,000 sheets in the same environment, and good images were obtained as in the initial stage. On the way, the test was conducted in a low temperature and low humidity environment room for 50,000 to 100,000 copies, but there was no density decrease due to charge-up and no thin horizontal line. Further, the test was conducted in a high temperature and high humidity environment room for 100,000 to 150,000 copies, but the charge amount did not particularly decrease, and there was no fog, toner scattering, and vertical line thickening.
There was no damage on the photoreceptor due to carrier adhesion, which was good.

Next, the recycling unit was removed, the developing bias was raised to 300 V, and the potential of the white background was 50.
Set to V, copy 1000 sheets on a white background chart,
After collecting the carriers accumulated in the cleaning unit,
Since it was only 3 mg, it was felt that there was little carrier adhesion to the non-image area. The image densities were measured by using the Macbeth densitometer to measure the densities of the copied images having original densities 1 to 4. For background fog, the relative density of the white background portion of the copied image to new paper was measured. When the density corresponding to the background fog is 0.010 or less, there is no practical problem.

Example 2 According to the method described in JP-A-4-86749, the magnetite was condensed with phenol and formalin in an aqueous medium in the presence of magnetite fine particles having a particle diameter of 0.23 μm. Phenol resin core particles 2 having a content rate of 89% and an average particle size of 80 μm were obtained. Next, under a nitrogen stream, 5000 parts by weight of the core particles 2 and 10 parts by weight of a toluene solution of a monomethyl silicone resin having a solid content concentration of 20% by weight are placed in a Henschel mixer.
0 parts by weight was added, the temperature was raised to 120 ° C. with stirring, and the mixture was stirred at the same temperature for 1 hour (total coating amount: 0.4% by weight). Then, it hardened at 240 degreeC for 2 hours. This is Carrier 2.

According to an electron microscope observation, this carrier 2 has a resin coating portion X having a sufficient thickness and an extremely thin resin coating portion Y, and the area ratio X: Y is 25:75. It was The ratio of the resin-coated portion was 80%. The ratio of the portion coated with the iron resin on the surface of the resin-coated carrier was calculated from the following ESCA data (atomic% based on peak area).

Atomic% (based on peak area) Si CO Fe core particles 2 2.88 57.80 36.31 3.01 Resin-coated carrier 31.72 27.05 40.62 0.60 Further, when the volume resistivity was measured, the following result was obtained, which was between 25V and 500V. Had one local maximum.

DC applied voltage Volume resistivity (Ω · cm) 25V 4 × 10 ¹⁰ 50V 6 × 10 ¹¹ 100V 7 × 10 ⁹ 250V 8 × 10 ⁸ 500V 2 × 10 ⁸ On the other hand, cross-linked polyester 100 parts by weight carbon black 10 parts by weight Purified carnauba wax 3 parts by weight 0.5 parts by weight of calixarene negative charge control agent were mixed, melted, kneaded, crushed and classified to have a volume average particle size of 6.
Colored particles of 8 μm were obtained.

Further, to 100 parts by weight of the colored particles, 1.0 part by weight of hydrophobized silica having an average particle size of 12 nm and 0.8 part by weight of hydrophobized titanium oxide having an average particle size of 30 nm were added. . This is designated as toner 2. 6 parts by weight of this toner 2 and 94 parts by weight of the carrier 2 are mixed,
Developer 2 is obtained.

This developer 2 was heated at a temperature of 20 ° C. and a humidity of 50%.
Under the environment, a recycle mechanism that collects the residual toner after transfer and returns it to the developing device is installed, and further, laser exposure / reverse development (developing condition: VH = 750V, VL = 100V, bias potential 600V) is used as an electrophotographic copying machine "Konic."
When a copy image was evaluated using a modified machine of "a4145" (manufactured by Konica), the image density was 1.37 and the fog was 0.001.
A high-quality image of was obtained. After that, a durability test was performed on 200,000 sheets in the same environment, and good images were obtained as in the initial stage. On the way, the test was conducted in a low temperature and low humidity environment room for 50,000 to 100,000 copies, but there was no density decrease due to charge-up and no thin horizontal line. The test was conducted in a high-temperature and high-humidity environment room for 100,000 to 150,000 copies, but the charge amount did not particularly decrease, there was no fog, toner scattering, and vertical line thickening, and the photoconductor due to carrier adhesion It was good without any scratches.

Next, the recycling unit is removed and V
When H was raised to 800V, the bias potential was set to 500V, 1000 sheets were copied on the white background chart, and the carriers accumulated in the cleaning unit were collected.
There was only g and it was good. [Example 3] According to the method described in JP-A-4-86749, by condensing phenol and formalin in an aqueous medium in the presence of magnetite fine particles having a particle diameter of 0.23 µm, the magnetite content of 91 %, And phenol resin core particles 3 having an average particle diameter of 50 μm were obtained. Next, under a nitrogen stream, 4000 parts by weight of the core particles 3 and 500 parts by weight of a toluene solution of a monomethyl silicone resin having a solid content of 5% by weight were put in a Henschel mixer.
The temperature was raised to 120 ° C with stirring, and the mixture was stirred at the same temperature for 1 hour (total coating amount: 0.6% by weight). Then, it hardened at 240 degreeC for 3 hours. This is carrier 3.

According to electron microscope observation, this carrier 3 has a resin-coated portion X having a sufficient thickness and an extremely thin resin-coated portion Y, and the area ratio X: Y is 43:57. It was The ratio of the resin-coated portion was 94%. The ratio of the portion coated with the iron resin on the surface of the resin-coated carrier was calculated from the following ESCA data (atomic% based on peak area).

Atomic% (based on peak area) SiC O Fe nuclear particles 3 0.42 65.63 30.33 3.63 Resin coated carrier 37.80 26.30 35.69 0.21 Further, when the volume resistivity was measured, the following result was obtained, which was between 25V and 500V. Had one local maximum.

DC applied voltage Volume specific resistance (Ω · cm) 25V 7 × 10 ¹⁰ 50V 1 × 10 ¹¹ 100V 3 × 10 ¹¹ 250V 7 × 10 ¹¹ 500V 5 × 10 ⁸ Next, 9 parts by weight of the toner 1 was used. The carrier 3 was mixed with 91 parts by weight to obtain a developer 3.

This developer 3 was heated at a temperature of 20 ° C. and a humidity of 50%.
Under the environment, a recycle mechanism for collecting the residual toner after transfer and returning it to the developing device is installed, and further, amorphous silicon photoconductor / laser exposure / reverse development (developing condition: VH = 4
The copy image was evaluated using a modified electrophotographic copying machine "Konica 4145" (manufactured by Konica Corp.) at 00V, VL = 100V, and bias potential of 300V), and the image density was 1.35, and the fog was high at 0.001. A quality image was obtained. After that, a durability test was performed on 200,000 sheets in the same environment, and good images were obtained as in the initial stage. 50,000 ~
The test was conducted in a low temperature and low humidity environment room for 100,000 copies, but there was no density decrease due to charge-up and no thin horizontal line. In addition, the test was conducted in a high temperature and high humidity environment room for 100,000 to 150,000 copies, but the charge amount did not particularly decrease, and fog,
There was no toner scattering and vertical line thickening, and there were no photoreceptor scratches due to carrier adhesion.

Comparative Example 1 Under a nitrogen stream, 5000 parts by weight of the core particles 1 and 1000 parts by weight of a toluene solution of a monomethyl silicone resin having a solid content of 30% by weight were placed in a Henschel mixer, and the mixture was stirred for 120 hours. The temperature was raised to ° C and the mixture was stirred at the same temperature for 1 hour (total coating amount: 6.0% by weight). This is designated as Comparative Carrier 1.

According to electron microscope observation, this comparative carrier 1 was composed of only a resin-coated portion having a sufficient thickness. Also, the ratio of the resin-coated part is 98%
Met. The ratio of the portion coated with the iron resin on the surface of the resin-coated carrier was calculated from the following ESCA data (atomic% based on peak area).

Atomic% (based on peak area) Si CO Fe core particles 1 0.81 78.93 19.42 0.84 Resin-coated carrier 36.70 27.13 36.10 0.02 Further, when the volume resistivity was measured, the following result was obtained, which was between 25V and 500V. There was no maximum.

DC applied voltage Volume resistivity (Ω · cm) 25V 7 × 10 ¹⁰ 50V 1 × 10 ¹¹ 100V 3 × 10 ¹¹ 250V 7 × 10 ¹¹ 500V 1 × 10 ¹² Toner 1 (6 parts by weight) and this comparison carrier Comparative Developer 1 was obtained by mixing 1 and 94 parts by weight.

The comparative developer 1 was evaluated in the same manner as in Example 1. Initially, the image density was 1.25 and the fog was 0.00.
Two images were obtained. However, after that, when a durability test of 200,000 sheets was performed in the same environment, various image errors occurred. First, during the 2500 copies from the initial stage, a decrease in density and thinning of horizontal lines, which are considered to be due to charge-up, occurred. In addition, when 100,000 to 150,000 copies were tested in a high temperature and high humidity environment room, the charge amount was 32 μC at low temperature and low humidity.
/ G rapidly dropped to 18 μC / g, and problems such as fog, toner scattering, and vertical line thickening occurred.

Next, the recycling unit was removed, the developing bias was raised to 300 V, and the potential of the white background was 50.
Set to V, copy 1000 sheets with blank chart,
After collecting the carriers accumulated in the cleaning unit,
It was as high as 16 mg. Further, the surface of the organic photoconductor after 200,000 copies had tens of scratches, and a portion corresponding to the scratches appeared in the image.

[Comparative Example 2] Core particles 2 not coated with silicone resin were used as they were. The following results were obtained when the volume resistivity of the nuclear particles 2 was measured.
There was no maximum between V and 500V. DC applied voltage Volume resistivity (Ω · cm) 25V 7 × 10 ⁸ 50V 3 × 10 ⁸ 100V 1 × 10 ⁸ 250V 5 × 10 ⁷ 500V Breakdown Then, 9 parts by weight of the toner 3 and this comparison carrier 2 were used. 91 parts by weight were mixed to obtain Comparative Developer 2.

When this comparative developer 2 was evaluated in the same manner as in Example 3, the initial image density was 1.40 and the fog was 0.
002 images were obtained. However, after that, 2
Various image errors occurred when a durability test was performed on 0,000 sheets. One is that carrier adhesion to line image edges, which is considered to be caused by injection of latent image charges, is abnormally large.
Also, when the test was performed in a high temperature and high humidity environment room for 100,000 to 150,000 copies, image blurring that seems to be caused by the adsorption of water on the magnetic material or phenol resin (especially remarkable in halftone) There has occurred.

When the surface of the carrier which had been subjected to 200,000 copies was observed with an electron microscope, a large number of toner fused substances of about 1 to 2 μm were found.

[0067]

[Effect] Excellent reproducibility of fine lines and high density of solid parts are both achieved, high chargeability and small charge-up can be realized, durability is good, and further, the environment dependence of chargeability can be reduced, so that it can be used in various environments. It is possible to obtain stable high image quality. In particular, it has great features in the toner recycling system.

[Brief description of drawings]

1A and 1B are schematic surface views and schematic cross-sectional views of a carrier.

FIG. 2 is a graph showing the applied voltage dependence of the volume resistivity of the carrier of the present application.

Claims (4)

[Claims] 1. A latent image on a latent image carrier is developed to form a toner image, the formed toner image is transferred from the latent image carrier to a transfer material, and the latent image carrier after transfer is cleaned. A carrier for electrostatic charge image development used in an image forming method, comprising collecting the toner on a latent image carrier and supplying the collected toner to a developing step for use. The carrier has a volume resistivity (Y axis) and Applied voltage (X axis)
When plotting the relationship with
A carrier for developing an electrostatic charge image, which has at least one maximum value in V / cm. 2. A latent image on the latent image carrier is developed to form a toner image, the formed toner image is transferred from the latent image carrier to a transfer material, and the latent image carrier after the transfer is cleaned. A carrier for developing an electrostatic charge image, which is used in an image forming method in which toner on a latent image carrier is collected, and the collected toner is supplied to a developing step for use, and at least ferromagnetic fine particles and a thermosetting resin. A carrier for developing an electrostatic charge image, characterized in that the surface of core particles containing is coated with a resin, and the coating resin has a resin coating portion having a sufficient thickness and an extremely thin resin coating portion. 3. When the relationship between the volume resistivity of the carrier (Y axis) and the applied voltage (X axis) is plotted, it is 25 V / c.
The carrier for developing an electrostatic charge image according to claim 2, which has at least one local maximum between m and 500 V / cm. 4. The thermosetting resin is a phenol resin and the coating resin is a silicone resin.
Electrostatic charge image developing carrier.