JP2003255591A - Two-component developer for electrophotography - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To form a high quality image with excellent durability and environmental characteristics. SOLUTION: The two-component developer is a toner including a carrier including a carrier core material as magnetic particles and a coating material covering the outer periphery of the carrier core material, and a conductive fine powder as conductive fine particles. And Since the carrier core material is coated with the coating material such that the weight of the coating material with respect to the weight of the carrier core material exceeds 5.0% by weight, a reduction in the life of the carrier due to frictional wear in the developing tank is suppressed. In addition, the peeling resistance of the coating material from the carrier core material can be improved. In addition, the conductive fine powder included in the toner can improve and stabilize the chargeability, and can reduce the amount of low-charge toner and reverse-charge toner. This makes it possible to provide a two-component developer for electrophotography having excellent durability and environmental characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-component electrophotographic developer for developing an electrostatic latent image to form a toner image in an electrophotographic image forming method.

[0002]

2. Description of the Related Art As an image forming method using a toner, an electrophotographic method based on an application of the Carlson process is widely used. An image forming apparatus adopting an electrophotographic method is, for example, an organic photoconductor (abbreviation: Organic Photoconductor).
An OPC type material is provided on the surface of the photosensitive drum, a charging unit, an exposing unit, a developing unit, a transferring unit, a fixing unit, a cleaning unit, and a charge eliminating unit.

An image forming operation in the image forming apparatus will be described below. First, in a dark place, the surface of the photosensitive drum is uniformly charged by the charging section. The light based on the image information is applied to the uniformly charged surface of the photoconductor drum in the exposure section, and the electric charge in the part where the light is applied is attenuated to form an electrostatic latent image on the surface of the photoconductor drum. . Next, the developing unit supplies toner to the surface of the photosensitive drum, and the toner adheres to the portion where the electrostatic latent image is formed, forming a visible image. After the transfer unit applies a charge having a polarity opposite to that of the toner to transfer the toner to the recording medium, the fixing unit applies heat and pressure to fix the toner on the recording medium to form a stable image.

The toner remaining on the surface of the photoconductor drum is removed by the cleaning unit, and the surface of the photoconductor drum is decharged by the decharging unit to erase the electrostatic latent image. By repeating the above operation, continuous image formation is performed.

A two-component developer is known as one of the developers used for developing an image by such an image forming apparatus. FIG. 1 is a schematic sectional view showing a simplified configuration of the two-component developer 1. As shown in FIG. 1A, the two-component developer 1 is composed of a toner 2 and a carrier 3. Toner 2
Is the toner particles 4 and 1 or 2 as shown in FIG.
It consists of one or more kinds of externally added fine powder 5. The toner particles 4 melt a binder resin that is a component that determines the main characteristics of the toner, a colorant that colors and visualizes an image, a charge control agent that controls the triboelectric charging property of the developer, and a wax that prevents offset. It is manufactured by a method typified by a melt-kneading pulverization method of kneading, cooling and solidifying, and then pulverizing and classifying. It may also be produced by a suspension polymerization method or an emulsion polymerization method. Further, the fine powder 5 made of fine particles such as silica (SiO ₂ ) for improving the powder fluidity and triboelectric chargeability of the toner is externally added to the toner particles 4 manufactured as described above, and the toner is added. The toner 2 is formed by adhering to the surface of the particles 4.

The carrier 3 comprises a carrier core material 6 which is magnetic particles, and a coating material 7 which coats the carrier core material 6. The carrier 3 is, for example, ferrite (MO.Fe ₂
The surface of a carrier core material 6 made of magnetic particles such as O ₃ : M is a divalent metal atom) is coated with a coating material 7 made of a resin such as a fluoropolymer. Coating 7
The chemical structure and coating state of the developer determine the chargeability of the developer and environmental characteristics such as stability of physical properties against changes in the use environment.

The toner 2 is charged by friction with the coating material 7 of the carrier 3. Therefore, in order to stably charge the toner 2, the types of the carrier core material 6 and the coating material 7 and the weight of the coating material 7 are used. It is necessary to study carrier design such as optimization of the percentage with respect to the weight of the carrier core material 6. Further, as the speed of image forming processing in image forming apparatuses such as copiers and printers increases and the applications diversify, it is necessary to improve the durability and environmental characteristics of the developer. A technique for providing a two-component color developer excellent in durability and environmental characteristics in response to such a need is disclosed in JP-A-4-177369.

The technique disclosed in Japanese Unexamined Patent Publication No. 4-177369 is a method of externally adding titanium oxide (TiO ₂ ) or alumina (Al ₂ O ₃ ) to toner particles so as to improve fluidity without deteriorating the charging stability. And the weight of the coating material containing a nitrogen-containing compound that stabilizes the electrostatic charge of the developer is 0.1% by weight as a percentage of the weight of the carrier core material.
The content of 5.0% by weight improves the durability and environmental characteristics of the two-component developer.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The technique disclosed in Japanese Patent No. 77369 has the following problems. The developer used in the image forming apparatus, which has been further speeded up and downsized, is more frequently collected and repeatedly used by the cleaning unit described above, and the stirring speed of stirring in the developing unit is increased. Depending on things, the load given increases, so
Further improvements in durability and environmental properties are needed.
In a high-speed and downsized image forming apparatus, when the image is developed using the two-component developer provided by the technique disclosed in Japanese Patent Laid-Open No. 4-177369, the usage time becomes longer. As a result, the coating material is peeled off from the carrier core material to expose the surface of the carrier core material, and the characteristics of the carrier greatly differ from the characteristics at the start of use, which may cause a decrease in image density. That is, even when the two-component developer disclosed in the above-mentioned prior art is used, the durability cannot be said to be sufficient when it is used in a high-speed and small-sized image forming apparatus.

Although the problem of durability can be improved by increasing the percentage of the coating material with respect to the weight of the carrier core material, by increasing the percentage, the environmental characteristics are deteriorated, especially under high temperature and high humidity conditions. In the lower part, toner scatters due to deterioration of chargeability during friction with toner, and low-charged toner and reverse-charged toner developed in the non-latent image area on the photoconductor are transferred onto the recording medium (paper surface). The so-called white background fogging, which is a non-image part (white background part) contamination phenomenon caused by the above, is caused.

An object of the present invention is to provide a two-component developer for electrophotography which is excellent in durability and environmental characteristics and can form high quality images.

[0012]

The present invention is directed to a carrier including a carrier core material which is a magnetic particle and a coating material which coats the outer periphery of the carrier core material, and a conductive fine powder which is a fine particle having conductivity. And a toner containing the toner, and the weight of the coating material with respect to the weight of the carrier core material exceeds 5.0% by weight as a percentage.

According to the present invention, by coating the carrier core material with the coating material so that the weight of the coating material with respect to the weight of the carrier core material exceeds 5.0% by weight, frictional wear in the developing tank is achieved. As a result, it is possible to prevent the life of the carrier from being shortened and to improve the peeling resistance of the coating material from the carrier core material. Therefore, it is possible to improve the durability of the carrier, that is, the two-component developer. In addition, by including conductive fine powder in the toner, it is possible to improve and stabilize the charging property under conditions of high temperature and high humidity, and it is possible to reduce low-charged toner and reverse-charged toner, so toner scattering and white background fog are prevented. It is possible to form an image with stable image density that does not occur. Therefore, it becomes possible to provide a two-component developer for electrophotography which is excellent in durability and environmental characteristics.

According to the present invention, the conductive fine powder is 0.30% by weight or more and 2.0% by weight with respect to the weight of the toner.
It is characterized in that it is externally added so as to be less than or equal to wt%.

According to the present invention, the conductive fine powder is externally added so that the percentage of the weight of the toner is 0.30% by weight or more and 2.0% by weight or less. By externally adding the conductive fine powder to the toner in an appropriate range, the environmental characteristics of the two-component developer are improved, and excessive conductive fine powder does not scratch the surface of the photosensitive drum during development. The wear of the photosensitive layer on the surface of the photosensitive drum can be suppressed.

The present invention is also characterized in that the conductive fine powder preferably has a particle size of 0.30 μm or more.

According to the present invention, the conductive fine powder preferably has a particle size of 0.30 μm or more. Even if the particle size of the conductive fine powder is less than 0.30 μm, it is possible to improve the environmental characteristics of the two-component developer, but by setting the particle size of the conductive fine powder to 0.30 μm or more, charging Since the function of improving the property is further strengthened, the particle diameter is 0.
The environmental characteristics of the two-component developer can be improved with a small addition amount as compared with the case of less than 30 μm, and cost efficiency can be improved. As a result, the environmental characteristics can be improved with a smaller addition amount than in the case of using the conductive fine powder having a particle diameter of less than 0.30 μm.

Further, the present invention is characterized in that the conductive fine powder is magnetite (FeO.Fe ₂ O ₃ ).

According to the present invention, the electroconductive fine powder is magnetite, and the magnetite has electroconductivity suitable for stabilizing the charge amount of the two-component developer and is easily available at low cost. It is possible to realize a two-component developer for electrophotography having excellent durability and environmental characteristics at a low manufacturing cost.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A two-component developer for electrophotography (hereinafter abbreviated as a developer), which is an embodiment of the present invention, includes a carrier core material which is magnetic particles and an outer periphery of the carrier core material. It includes a carrier containing a coating material for coating and a toner containing conductive fine powder which is fine particles having conductivity.

The carrier comprises a carrier core material and a coating material for coating the carrier core material. The carrier core material is, for example, magnetic particles such as ferrite, and has a shape of a magnetic brush formed by an interaction with a magnetic member in a developing roll provided in the developing unit of the image forming apparatus, and a developer in the developing unit. Determine stirrability.

The coating material is, for example, a fluorine-based polymer, which imparts electric charge to the toner and determines the charge amount, environmental characteristics and durability of the developer depending on the chemical structure and coating state of the coating material. The weight of the coating material with respect to the weight of the carrier core material is configured to exceed 5.0% by weight in percentage.

The weight percentage of the coating material with respect to the carrier core material is limited to more than 5.0% by weight for the following reason. At 5.0% by weight or less, when the carrier is used as a developer in an image forming apparatus such as a high-speed and downsized copying machine, abrasion and peeling are likely to occur mainly due to friction in the developing tank, and the durability is improved. The life is shortened.
Therefore, the weight percentage of the coating material with respect to the carrier core material is set to more than 5.0% by weight.

The toner is composed of toner particles and conductive fine powder externally added to the toner particles. Toner particles
At least, it contains a binder resin that is a component that determines the main characteristics of the toner, a colorant that colors and visualizes an image, a wax that prevents offset and a charge control agent that controls the triboelectric chargeability of the developer, and if necessary, If necessary, it contains other additives.

Examples of the binder resin include polystyrene, styrene-acryl copolymer, styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, styrene-acryl-maleic anhydride copolymer, polyvinyl chloride, There are polyolefin resin, epoxy resin, silicone resin, polyamide resin, polyurethane resin, urethane-modified polyester resin, acrylic resin and the like, and one kind selected from these groups is used alone or in combination of two or more kinds. Further, a block polymer or graft polymer of the above-mentioned resin is used. Further, the resin is not limited to the above-mentioned one, and a resin having the same molecular weight distribution as the above-mentioned resin can be used.

The binder resin has a glass transition point Tg of 40.
Those having a temperature of not less than 0 ° C and not more than 70 ° C are preferable. The binder resin having a glass transition point of less than 40 ° C. may melt at the glass transition point or higher inside the image forming apparatus when the temperature inside the image forming apparatus rises, and toner particles may aggregate. Because it is expensive. Further, a binder resin having a glass transition point of higher than 70 ° C. has a low fixing performance on a recording medium and does not satisfy the function required as the binder resin.

Examples of the colorant include oil-soluble dyes and pigments such as carbon black, iron black and alloy azo dyes. The colorant is 1 per 100 parts by weight of the binder resin.
It is preferable to add 10 to 10 parts by weight. This is because the dispersibility with the binder resin during kneading can be improved.

Examples of the wax include polyolefin waxes such as polyethylene, polypropylene and ethylene-propylene polymer. At least one of these waxes is used as a binder resin 100.
It is preferable to add 1 to 10 parts by weight with respect to parts by weight. This is because the dispersibility with the binder resin during kneading can be improved.

Charge control agents include positive charge toner control agents and negative charge toner control agents. Positive charge toner control agents include, for example, quaternary ammonium compounds and nigrosine dyes. Examples of the negatively chargeable toner control agent include azo metal complexes and carboxylic acid metal complexes. The charge control agent is preferably added in an amount of 0.1 to 5 parts by weight with respect to 100 parts by weight of the binder resin. This is because the dispersibility with the binder resin at the time of kneading is good, and this amount can be controlled to an amount of electric charge that does not easily cause deterioration of environmental characteristics such as white background fog.

In addition to the binder resin, the colorant, the wax and the charge control agent, magnetic fine powder that imparts magnetism to the toner and prevents a decrease in the triboelectric charge amount of the toner may be added. As the magnetic fine powder, there is a fine powder made of metal oxide fine particles having magnetism and containing elements such as iron, cobalt, nickel, copper, magnesium, manganese, aluminum and silicon.

As the conductive fine powder externally added to the toner particles, there are metal fine powders such as titanium oxide, magnetite and ferrite, which are selected from these groups.
One kind or two or more kinds are used. Further, among the above-mentioned conductive fine powders, magnetite is preferably used.

Further, the surface of these fine powders may be treated with a silane coupling agent such as dimethyldichlorosilane and amylosilane or a treating agent such as silicone oil, or a fluorine-containing component or the like may be added before use.

The above-mentioned conductive fine powder is externally added so that the percentage of the weight of the toner is 0.30% by weight or more and 2.0% by weight or less. The range of the externally added weight of the conductive fine powder is 0.30 as a percentage of the weight of the toner.
The reason why it is set to be not less than 2.0% by weight is as follows. By externally adding to the range of 0.30% by weight or more and 2.0% by weight or less, the environmental characteristics of the developer are improved, and excess magnetite does not rub the surface of the photosensitive drum during development. This is because it is possible to suppress wear of the photosensitive layer on the surface of the photosensitive drum.

The reason why the particle size of the conductive fine powder is preferably 0.30 μm or more is as follows. When the particle size is 0.30 μm or more, the function of improving the charging property becomes stronger, so that the particle size is 0.30 μm.
The environmental characteristics of the developer can be improved with a smaller addition amount than in the case of less than m, and the cost efficiency can be improved.

The reason why magnetite is preferably used as the conductive fine powder is as follows. Magnetite has conductivity suitable for stabilizing the charge amount of the developer and is easily and easily available, so that a developer excellent in durability and environmental characteristics can be realized at a low manufacturing cost. Because there is.

(Examples) Examples of the present invention will be described below. The toner manufacturing example is an example, and the present invention is not limited to this.

Example I In Example I, the proper range of the weight of the coating material with respect to the weight of the carrier core material was verified. In Example I, a toner was manufactured as shown below. Polyethylene as wax (trade name PE1 manufactured by Clariant Japan Co., Ltd.) with respect to 100 parts by weight of the binder resin.
30) 1 part by weight, polypropylene (Mitsui Chemicals, Inc .: trade name NP-505) 1.5 parts by weight, charge control agent (Hodogaya Chemical Co., Ltd .: trade name S-34) 1 part by weight, magnetic fine powder 1.5 parts by weight of magnetite (Kanto Denka Co., Ltd .: trade name KBC-100) as a body, 5 parts by weight of carbon black (Cabot Co .: trade name 330R) as a coloring agent, and a super mixer (Kawata Co .: product) First name V-
20) was thoroughly mixed, and the resulting mixture was melt-kneaded by a biaxial kneader (made by Ikegai Tekko KK: trade name PCM-30). The resulting kneaded product was crushed by a jet crusher (manufactured by Nippon Pneumatic Mfg. Co., Ltd .: trade name IDS-2), and then classified to obtain toner particles having a volume average particle diameter of about 7.5 μm. Toner was obtained by externally adding 0.3 parts by weight of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: trade name R972) to 100 parts by weight of the toner particles.

Next, ferrite was used as a carrier core material and tetrafluoroethylene was used as a coating material to coat the carrier core material. At this time, the weight of the coating material with respect to the weight of the carrier core material is 2.2% by weight, 4.1% by weight,
Coating was performed so as to be 5.1% by weight and 8.0% by weight. The obtained toner and each carrier were mixed and frictionally charged to obtain a developer. Here, the weight percentage of the coating material with respect to the carrier core material is 2.2% by weight, 4.1% by weight, and 5.
The developers containing the carriers coated to be 1% by weight and 8.0% by weight are referred to as sample numbers a to d.

The performance of the developer was evaluated as follows. Commercially available monochrome copying machine (Sharp: product name AR
-450), the image density of the image initially printed with the obtained four kinds of developers and five originals having a printing rate of 5% are intermittently printed on 100,000 sheets (hereinafter, 100 k sheets). The image density of the image formed after image formation (shown) was compared. The image density was measured by a Macbeth reflection densitometer (manufactured by Macbeth Co., Ltd .: trade name RD-914), and a case where the image density after passing 100 k sheets was less than 1.30 was poor (denoted as x), 1.30. Above, the case of 1.32 or less is good (○
It was evaluated as excellent (expressed as ⊚) when it exceeds 1.32. Table 1 shows the measurement results and evaluation results.

[0040]

[Table 1]

When image formation was performed using the developers of sample numbers a and b in which the weight ratio of the coating material to the weight of the carrier core material was 2.2% by weight and 4.1% by weight, 100 k sheets were printed. The image density after that was greatly reduced compared with the initial image density. When image formation was carried out using the sample Nos. C and d developers in which the weight of the coating material with respect to the weight of the carrier core material was 5.1% by weight and 8.0% by weight, the initial image density and 100 k were obtained. The image density after passing a single sheet was almost the same value, and a stable image could be formed. As described above, it has been clarified that the life of the developer is lengthened by the composition of more than 5.0% by weight.

Example II In Example II, Example I
The environmental characteristics of the developer containing the carrier having excellent durability, which was clarified in Section 3, were evaluated.

(Example 1) 1 part by weight of polyethylene (made by Clariant Japan: trade name PE130) and polypropylene (made by Mitsui Chemicals: trade name NP-505) as wax to 100 parts by weight of a binder resin. 1.5
Parts by weight, charge control agent (Hodogaya Chemical Co., Ltd .: S-3
4) 1 part by weight, 1.5 parts by weight of magnetite (Kanto Denka Co., Ltd .: trade name KBC-100) as magnetic fine powder, and 5 parts by weight of carbon black (Cabot Co .: trade name 330R) as a coloring agent. , Using a super mixer (manufactured by Kawada Co., Ltd .: trade name V-20), and the resulting mixture was melt-kneaded by a biaxial kneader (manufactured by Ikegai Tekko KK: trade name PCM-30). The obtained kneaded product is a jet type crusher (product name: IDS-2, manufactured by Nippon Pneumatic Mfg. Co., Ltd.)
Were pulverized, and then classified to obtain toner particles having a volume average particle diameter of about 7.5 μm. To 100 parts by weight of toner particles, 0.3 parts by weight of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: trade name R972) and 0.3 parts by weight of magnetite (manufactured by Titanium Industry Co., Ltd.) having a particle diameter of 0.13 μm (toner weight) Externally added (0.30% by weight in percentage) to obtain a toner.

Next, using ferrite as a carrier core material and tetrafluoroethylene as a coating material, the carrier core material was coated such that the weight of the coating material was 8.0% by weight relative to the weight of the carrier core material. The obtained toner and carrier were mixed and frictionally charged to obtain a developer.

(Example 2) Manufactured in the same manner as in Example 1 except that the amount of magnetite added externally to 100 parts by weight of toner particles was 0.50 parts by weight (0.50% by weight based on the weight of toner). Developer.

Example 3 Except that the amount of magnetite added to 100 parts by weight of toner particles was 1.0 part by weight (0.99% by weight as a percentage of toner weight).
A developer manufactured with the same formulation as in Example 1.

Example 4 Manufactured in the same manner as in Example 1, except that the amount of magnetite added to 100 parts by weight of toner particles was 2.0 parts by weight (2.0% by weight as a percentage of toner weight). Developer.

Example 5 A developer produced by the same formulation as in Example 1 except that magnetite having a particle size of 0.30 μm (manufactured by Kanto Denka Kogyo Co., Ltd.) is used.

Example 6 Manufactured in the same manner as in Example 5, except that the external addition amount of magnetite to 100 parts by weight of toner particles was 0.50 parts by weight (0.50% by weight as a percentage of toner weight). Developer.

Example 7 Except that the amount of magnetite added externally to 100 parts by weight of toner particles was 2.0 parts by weight (2.0% by weight as a percentage of the weight of toner).
A developer manufactured according to the same formulation as in Example 5.

(Comparative Example 1) Sample number d in Example I
Developer.

(Comparative Example 2) Except that the amount of magnetite externally added was 0.1 part by weight (0.10% by weight based on the weight of the toner) relative to 100 parts by weight of the toner particles.
Developer manufactured with the same formulation as in Experiment 1.

(Comparative Example 3) Except that the amount of magnetite added externally to 100 parts by weight of toner particles is 0.2 parts by weight (0.20% by weight as a percentage of toner weight).
A developer manufactured with the same formulation as in Example 1.

(Comparative Example 4) The same formulation as in Example 1 except that the amount of magnetite added externally was 2.1 parts by weight (2.1% by weight based on the weight of the toner) relative to 100 parts by weight of the toner particles. Developer manufactured in.

(Comparative Example 5) Except that the amount of magnetite externally added was 0.2 parts by weight (0.20% by weight based on the weight of toner) with respect to 100 parts by weight of toner particles.
A developer manufactured according to the same formulation as in Example 5.

The evaluation of environmental characteristics was performed as follows.
Commercially available monochrome copying machine (Sharp: AR-450)
After supplying the developer to a developing unit provided in the image forming apparatus under high temperature and high humidity environment (temperature: 35 ° C., humidity 80%) using
It was left for 17 hours. After standing for 17 hours, an image was formed and the fog density showing the fog on the white background of the formed image was measured, and the environmental characteristics were evaluated based on the fog density. Since the increase in toner concentration in the developer along with the fog concentration causes toner scattering, the toner replenishment time, which is an index thereof, was measured.

The fog density of the image formed after the developer was allowed to stand for 17 hours was measured by a whiteness meter (manufactured by Nippon Denshoku Industries Co., Ltd .: Hunter whiteness meter). A fog density value of less than 0.5 is excellent (expressed as ◎), 0.5 or more and less than 1.0 is good (expressed as ◯), and 1.0 or more and less than 1.5 is acceptable (as Δ). (Notated), and 1.5 or more were regarded as defective (denoted as x).

The comprehensive evaluation is an evaluation result of environmental characteristics and an evaluation result of an amount (hereinafter referred to as a film slip amount) in which the thickness of the organic conductor layer on the surface of the photosensitive drum is reduced by friction between the toner and the surface of the photosensitive drum. Went by. The amount of film slippage was measured by a Fischer Scope MMS (manufactured by Fischer KK), and the evaluation standard was a monochrome copying machine AR-450.
Since the photoconductor drum life in 50 is 50k sheets, it is excellent when 80k sheets or more that can sufficiently exceed the life is possible (marked as ◎), when 50k sheets or more and less than 80k sheets are possible Is good (denoted by ○),
When it is possible to make a copy of 40 k sheets or more and less than 50 k sheets, it is considered as acceptable (denoted by Δ), and when it is possible to make a copy of less than 40 k sheets, it is designated as defective (denoted as x). Table 2 shows the measurement results and evaluation results.

[0059]

[Table 2]

Examples 1-7 and Comparative Examples 1-3 and 5
As can be seen from the above, when magnetite was added in an amount of 0.3% by weight or more, the environmental characteristics were improved. On the other hand, in the case of 2.1% by weight of Comparative Example 4, the amount of film slippage of the photosensitive drum was remarkably increased. Further, in Comparative Example 4, so-called filming, which is a state in which the toner component is widely attached to the surface of the photosensitive drum, occurs.

As is clear from comparison between Example 1 and Example 5, when the amount of magnetite added is the same, Example 5 having a larger magnetite particle size has a smaller fog concentration and environmental characteristics. Excellent in. Further, as is clear from comparison between Example 6 and Examples 3 and 4, Example 6 having a large magnetite particle size and a small addition amount was compared with Examples 3 and 4 having a small magnetite particle size and a large addition amount. However, the fog density is small and the environmental characteristics are excellent.

As described above, the weight percentage of the coating material with respect to the carrier core material is added so as to exceed 5.0% by weight,
The amount of magnetite added externally is 0.3 with respect to the toner weight.
By setting it to 0% by weight or more and 2.0% by weight or less,
A two-component developer excellent in durability, environmental characteristics, and film slip resistance was obtained. The particle size of magnetite is 0.3
By setting the thickness to 0 μm or more, good environmental characteristics were obtained with a small amount of external addition.

[0063]

As described above, according to the present invention, it is possible to prevent the carrier life from being shortened due to frictional wear in the developing tank.
Since the peeling resistance of the coating material from the carrier core material can be improved, the durability of the two-component developer can be improved. In addition, by including conductive fine powder in the toner, the chargeability can be improved and stabilized under high temperature and high humidity conditions, and low-charged toner and reverse-charged toner can be reduced, so toner scattering and white background fog can be prevented. It is possible to form an image with stable image density that does not occur. Therefore, it becomes possible to provide a two-component developer for electrophotography which is excellent in durability and environmental characteristics.

According to the present invention, the conductive fine powder is externally added to the toner in an appropriate range to improve the environmental characteristics of the two-component developer and suppress the abrasion of the photosensitive layer on the surface of the photosensitive drum. can do.

Further, according to the present invention, by setting the particle size of the conductive fine powder to 0.30 μm or more, the environmental characteristics of the two-component developer can be reduced by adding a small amount as compared with the case where the particle size is less than 0.30 μm. Can be realized,
It is possible to improve cost efficiency.

Further, according to the present invention, magnetite has a conductivity suitable for stabilizing the charge amount of the two-component developer and can be easily obtained at low cost, so that it has excellent durability and environmental characteristics. It is possible to realize a two-component developer for electrophotography at a low production cost.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a simplified configuration of a two-component developer 1.

[Explanation of symbols]

1 two-component developer 2 toner 3 career 4 toner particles 5 Fine powder 6 Carrier core material 7 coating material

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshitaka Urata             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Kanshiro Okamoto             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Eiji Tenjiku             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Kazuru Matsumoto             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 2H005 AA08 BA02 BA06 CB03 DA09                       EA05 EA07 FA01

Claims (4)

[Claims] 1. A carrier including a carrier core material which is a particle having magnetism, and a coating material which coats an outer periphery of the carrier core material, and a toner including a conductive fine powder which is a fine particle having conductivity, The weight of the coating material with respect to the weight of the carrier core material,
A two-component developer for electrophotography, characterized in that the percentage exceeds 5.0% by weight. 2. The conductive fine powder is 0.30% by weight or more in percentage with respect to the weight of the toner,
The two-component developer for electrophotography according to claim 1, which is externally added so as to be 2.0% by weight or less. 3. The two-component developer for electrophotography according to claim 1, wherein the conductive fine powder has a particle diameter of preferably 0.30 μm or more. 4. The two-component developer for electrophotography according to claim 1, wherein the conductive fine powder is magnetite (FeO.Fe ₂ O ₃ ).