JPH09197799A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device which is capable of forming good images free from image quality defects, such as a development ghost and has the excellent environmental stability of image densities under any environments. SOLUTION: The developing device 3 has a developer carrying member 4 which carries a developer 6 on a coating layer 4b for coating the outer peripheral surface of a cylindrical substrate 40a and transports the developer 6 to a developing region A where the electrostatic latent image 2 formed on an image holder 1 is developed. The coating layer 4b consists of a conductive resin layer contg. potassium titanate conductive whiskers which are conductive particles and carbon black. A potassium titanate-based conductive whisker is expressed by the formula K2 O.nTiO2-x and preferably incorporated into the coating layer at 5 to 50wt.% of the binder resin which is the constituting component of the coating layer 4b. In the formula, (n) is an integer from 1 to 4 and (x) denotes the numerical value existing within the range of 0 to 1. When x is a numerical value exclusive of 0, it is meant that carbon atoms, etc., are doped or added in the whiskers.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to a developing device in an image forming apparatus such as a printer, a facsimile, and a composite OA device of these. More specifically, the present invention relates to a developing device in which the surface of a developer bearing member for visualizing an electrostatic latent image formed on an image holding member such as an electrophotographic photosensitive member or an electrostatic recording dielectric member comprises a conductive resin layer.

[0002]

2. Description of the Related Art In an image forming apparatus adopting an electrophotographic system, various methods have been conventionally known as a method for developing an electrostatic latent image formed on an image carrier according to the kind of developer used. Has been. Among them, there is a method of developing the developer carried on the developer carrying body by bringing the developer into contact with the photoconductor or non-contactingly flying to the photoconductor, and the surface of the developer carrying body carrying the developer. Also, various resin layers have been proposed. For example, in Japanese Patent Laid-Open No. 63-311367, in order to improve gradation and reproducibility of fine gradation of fine lines and halftone dots, specific volume resistivity (1 × 10 ⁶ to 1 × 10 ¹³
There is disclosed a developer carrying member provided with an outer layer having a predetermined relationship between Ω · cm) and thickness. In addition, JP-A-4-1668
No. 64 discloses that a thin layer of a composite material containing positively chargeable resin particles is formed on the surface in order to prevent a decrease in initial image density due to a broad charge amount distribution of a developer when the developing device is started up. , A developer carrier using a negatively charged magnetic toner as a developer is disclosed. Japanese Patent Laid-Open No. 4-246676 discloses a resin and a graphat in order to prevent the fading phenomenon that the density of a part of the paper becomes thin along the feeding direction of the paper when the same image pattern is repeatedly printed. There is disclosed a developer carrier in which a coating layer containing a is subjected to polishing processing to limit the average spacing Sm of the irregularities and the centerline average roughness Ra to a specific range.

However, all the conventional developer carrying members have the following problems. That is,
In the developer carrier described in Japanese Patent No. 311367, the resistance of the outer layer is generally high. Therefore, during development, electric charge remains in the outer layer portion where the developer has transferred to the photoreceptor, and the amount of electric charge in this portion is larger than in other portions, and the newly carried developer is strongly adsorbed to the outer layer. It becomes difficult to transfer to the photoconductor.
As a result, the density of the portion of the newly developed toner image corresponding to the previously developed toner image becomes low, so-called development ghost occurs, and the image quality deteriorates. JP-A-4-1
In the developer carrier described in Japanese Patent No. 66864, the resistance of the thin layer becomes non-uniform due to the dispersion of the positively chargeable resin particles, and bias leak and development ghost are likely to occur. In the developer carrying member described in JP-A-4-246676, since the surface coating layer is subjected to polishing, the coating layer surface is smooth. As a result, the amount of developer conveyed decreases and the developer is insufficiently charged, resulting in a decrease in image density.

[0004]

As described above, in the conventional developer carrier having the surface coated with the resin layer, the charge amount of the developer imparted by frictional charging is insufficient and the resistance of the resin layer is not uniform. Therefore, there is a problem that a development ghost occurs. Further, the conventional developer carrying member having a conductive resin layer on its surface has a problem that the image density is lowered under high temperature and high humidity and low temperature and low humidity. Therefore, the present invention is intended to solve the above problems,
It is an object of the present invention to provide a developing device capable of avoiding the occurrence of a development ghost and forming a good image because the resin layer has an appropriate electric resistance. Further, in the present invention, it has environmental stability that can form a good image even in an environment of high temperature and high humidity and low temperature and low humidity, and causes filming such as sticking of a developer even after repeated use. It is to provide a developing device having excellent durability.

[0005]

SUMMARY OF THE INVENTION The inventors of the present invention have developed a developing device equipped with a developer carrier having a surface made of a conductive resin layer to improve image quality and improve durability of the developer carrier by conductive fine particles. As a result of repeated studies and studies aimed at improving the performance, it was found that as conductive fine particles dispersed in the conductive resin layer, the use of potassium titanate-based conductive whiskers, which was conventionally used as an electromagnetic wave sealing material, in combination with carbon black. The present invention has been accomplished by finding that the above object is achieved by the above. That is, in the developing device of the present invention, the developer is carried in the coat layer that covers the outer peripheral surface of the cylindrical support, and the developer is provided in the developing area where the electrostatic latent image formed on the image carrier is developed. Is provided, the coat layer is made of a conductive resin layer containing conductive fine particles, and potassium titanate-based conductive whiskers and carbon black are used as the conductive fine particles.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
It should be noted that, in order to facilitate understanding of the present invention, the elements of the present invention are denoted by the reference numerals in parentheses corresponding to the elements of the embodiments described below, but the present invention is not limited to the embodiments. .
The developer carrier (4) in the developing device (3) of the present invention has a coating layer (4b) carrying the developer (6) on the outer peripheral surface of the cylindrical support (4a). The coat layer (4b) is composed of a conductive resin layer in which conductive fine particles are dispersed in a binder resin. As the support (4a), a non-magnetic and electrically conductive cylindrical member such as aluminum or stainless steel is used.
The binder resin forming the coat layer (4b) includes phenol resin, melamine resin, urea resin, alkyd resin,
Epoxy resin, polyamide, polyimide, polyester, polyurethane, polycarbonate, polyphenylene oxide, polyether sulfone, styrene resin,
Fluorine resin, acrylic resin, silicone resin, etc. are used. In particular, a resin with excellent mechanical strength such as phenol resin, polyamide, polyester, polyurethane, polycarbonate, polyphenylene oxide, polyether sulfone, and styrene resin, or excellent releasability such as fluorine resin and silicone resin. The resin used is preferably used.

As the conductive fine particles dispersed in the coat layer, potassium titanate type conductive whiskers and carbon black are used. In addition, various conductive metals or alloys such as graphite, aluminum and stainless steel, and various conductive metal oxides such as tin oxide, indium oxide, titanium oxide and tin oxide-indium oxide solid solution can be used. The potassium titanate-based conductive whisker in the present invention is represented by the following chemical formula, and either one of them can be used alone or both can be mixed and used. _{K 2 O · nTiO 2 -x /} C K 2 O · nTiO 2 -x / SnO 2 · Sb 2 O 5 ( wherein, n is an integer from 1 to 4, x is values in the range of 0 to 1 Here, when x is 0, K ₂ O.nTiO ₂ represented by the above chemical formula is coated with carbon black or a double salt of tin oxide and antimony oxide, and when x is other than 0, , K ₂ O · nTiO ₂ -x is doped or added with a carbon atom or tin oxide and antimony oxide or a double salt thereof.) Physical properties of the potassium titanate-based conductive whiskers are generally described below. , Black or white gray acicular crystals, having an average fiber length of 10 to 20 μm, an average fiber diameter of 0.3 to 0.6 μm, a true specific gravity of 3.3 to 3.6, and a Mohs hardness of 4.

The potassium titanate conductive whiskers are
It has the effect of reinforcing the coating layer, and the coating layer containing the conductive whiskers has excellent abrasion resistance, so that the strength of the coating layer may decrease even after repeated use of the developer carrier. Absent. Further, by dispersing the conductive whiskers in the coating layer in a predetermined content, the surface roughness of the coating layer falls within an appropriate range, so that the developer can be provided with an appropriate triboelectric charge amount. In addition, even when it is repeatedly used for a long period of time, the developer or the like does not adhere to the coat layer and filming does not occur. Therefore, the developer carried on the coat layer can be stably attached, conveyed and charged. Carbon black is dispersed in the coating layer in order to prevent the developer from being overcharged, and has a function of flowing out excess charges. In order to further enhance the surface lubricity of the coat layer, it is preferable to mix graphite with the above-mentioned conductive fine particles. That is, the lubricity of graphite can further prevent the developer or the like from sticking to the surface of the coating layer.

The coating layer preferably contains 5 to 50% by weight of potassium titanate type conductive whiskers and 10 to 40% by weight of carbon black with respect to the binder resin. When the content of the potassium titanate-based conductive whiskers is less than 5% by weight, the effect of adding the conductive whiskers is small, the developer cannot be maintained at an appropriate charge, and a development ghost is formed on the formed image. It tends to occur. On the other hand, if the content exceeds 50% by weight, the coat layer formed on the surface of the developer carrying member becomes brittle and its mechanical strength decreases. When the content of carbon black is less than 10% by weight, the volume resistivity of the coat layer becomes higher than the proper value. Therefore, it becomes impossible to release the excessively charged charge of the developer, and a development ghost occurs in the formed image. On the other hand, the content is 40% by weight
If it exceeds the range, not only the film-forming property at the time of forming the coat layer is impaired, but also the charge amount of the developer is insufficient and the image density is lowered. The preferable content is 15 to 30% by weight. When graphite is used as the conductive fine particles, it is preferably 20% by weight or less with respect to the binder resin.

The thickness of the coat layer is preferably in the range of 10 to 40 μm, and particularly preferably in the range of 15 to 30 μm. When the film thickness is less than 10 μm, the conductive fine particles are more likely to be exposed from the surface of the coating layer, and the surface of the developer carrying member becomes unnecessarily rough. On the other hand, 40 μm
When the thickness is thicker, the coating liquid drips from the cylindrical support during curing, which makes it difficult to form a uniform film thickness. Also,
The volume resistivity of the coat layer is 2.0 × 10 ^{-2 to} 1.0Ω.
It is preferably in the range of cm, particularly from 3.0 × 10 ^-2
The range of 0.80 Ωcm is more preferable. If the volume resistivity is less than 2.0 × 10 ⁻² Ωcm, the amount of charge of the developer is small and the image density is lowered. On the other hand, the volume resistivity is 1.
When it exceeds 0 Ωcm, the charge amount of the developer is increased to a level where development ghost is likely to occur. The surface roughness Ra (arithmetic mean roughness: JIS B 0601) of the coat layer is in the range of 0.8 to 2.5 μm, and further 1.0 to 2.2.
It is preferably in the range of μm. When the surface roughness Ra is less than 0.8 μm, the surface of the coating layer is too smooth, the amount of developer conveyed is small, and the image density is lowered. on the other hand,
If Ra exceeds 2.5 μm, the amount of developer conveyed becomes too large and the charge amount of the developer becomes low, resulting in a decrease in image density.

The coat layer can be formed as follows. First, a binder resin, conductive fine particles, a diluent (solvent) and the like are mixed, and a solid content is uniformly dispersed by a sand mill or the like to prepare a coating liquid. At this time, the viscosity and film-forming property of the coating solution are adjusted by adjusting the mixing ratio of the diluent. Then, while rotating the cylindrical support, the surface of the support is coated with an application liquid by air spray or the like.
The binder resin is cured at 250 ° C. Diluents include hydrocarbons such as hexane, benzene, toluene, xylene, ketones such as acetone, methyl ethyl ketone, cyclohexanone, alcohols such as methanol, ethanol, isopropanol, butanol, dibutyl ether, tetrahydrofuran, propylene glycol monomethyl ether, etc. And ethers such as ethyl acetate, butyl acetate, and ethyl butyrate. These diluents and the binder resin may be used alone or in a mixture of 2
You may mix and use more than one kind. In the coating layer thus formed, at least potassium titanate-based conductive whiskers and carbon black fine particles are dispersed, and the coating layer surface has fine irregularities in which some of the conductive fine particles are exposed. It has a shape. The developer used in the developing device of the present invention may be a carrier-free magnetic one-component or non-magnetic one-component developer,
Alternatively, it may be a two-component developer using a carrier.

(Operation of the Invention) The developing device (3) of the present invention is
The coating layer (4b) on the surface of the developer carrier (4) contains conductive particles such as potassium titanate type conductive whiskers and carbon black. Among these conductive particles, potassium titanate-based conductive whiskers are used to impart abrasion resistance to the coating layer (4b) and to coat the coating layer (4b).
(4b) has a function to secure the surface roughness in an appropriate range,
On the other hand, carbon black has a function of preventing excessive charging of the developer (6) on the carrier (4). Therefore, according to the developing device (3) of the present invention, when the developer (6) is transported to the vicinity of the developing area (A) on the image carrier (1) on which the electrostatic latent image (2) is formed, An appropriate amount of the developer (6) is attached and carried on the coat layer (4b) of the developer carrier (4). In addition, the coat layer (4
When the developer (6) carried on (b) is triboelectrically charged, the charge amount applied to the developer (6) is adjusted to an appropriate value, so that the image density can be increased. Moreover,
The developer (6) can be stably conveyed and charged for a long period of time without generating a development ghost or filming. Further, since the developing device (3) of the present invention is excellent in environmental stability of image density, the image density can be kept high even under high temperature and high humidity and low temperature and low humidity.

[0013]

The present invention will be specifically described below with reference to examples. In FIG. 1, an image carrier (photoreceptor) 1 is a photoconductive drum having an organic photosensitive layer of a negative charging type, and is uniformly charged by a charging means (not shown), The electrostatic latent image 2 is formed by the potential difference caused by the irradiation. The surface potential when the electrostatic latent image 2 is formed is, for example, −600 V in the image portion and −120 V in the background portion that becomes a white display portion during image formation. The developing device 3 includes a developer carrying member 4 arranged so as to face the image holding member 1. The container 5 of the developing device 3 stores the magnetic one-component developer 6 carried on the carrier 4. The container 5 accommodates the carrier 4 and is carried at a portion facing the image carrier 1 and opening. The surface of the body 4 is partially exposed, and the carrier 4 and the image carrier 1 are arranged so as to be close to each other.

The rotation of the developer carrying member 4 causes the developer 6 adhering to the surface of the developer carrying member 4 to come into contact with the image holding member 1 in the developing area A.
Transport to Carrier 4 and image carrier 1 in development area A
The minimum gap between and is set to be about 200 μm. Inside the carrier 4, a plurality of magnets are arranged along the peripheral surface, and a magnet roll 7 fixed so as not to rotate is provided. The plurality of magnets form a magnetic pattern in which S poles and N poles are arranged along the peripheral surface. According to this magnetic pattern, the developer 6 can be attracted to the surface of the carrier 4. I have. The developer carrier 4 is composed of a cylindrical aluminum support 4a having an outer diameter of 20 mm and a wall thickness of 0.7 mm, and a coat layer 4b formed on the peripheral surface thereof. In this coat layer 4b, potassium titanate-based conductive whiskers and conductive carbon black fine particles are dispersed. Coat layer 4b
Is a coating film having a thickness of 20 μm formed by coating the support 4a with the coating solution described below in which the potassium titanate-based conductive whiskers and the carbon black fine particles are dispersed in a binder resin and a diluent. .

The developer regulating member 8 comprises an elastic member 8a that abuts the surface of the developer carrying member 4 and a leaf spring 8b to which the elastic member 8a is adhered. The other end of the leaf spring 8b is the developing device 3
It is fixedly supported by the body. The contact portion of the elastic member 8a with respect to the carrier 4 is located on the upstream side in the rotation direction of the carrier 4 with respect to the developing area A. The elastic member 8a has a width of 15 mm,
The plate spring 8b is made of stainless steel having a thickness of 1.00 mm and a rubber hardness of 50 °, and the leaf spring 8b is made of stainless steel having a thickness of 0.1 mm. A DC superimposed AC voltage, which is a bias voltage, is applied to the support 4a of the developer carrying member 4 by a high-voltage AC power supply 9 and a DC power supply 10 connected in series, so that the image carrier 1
An alternating electric field is generated in the developing area A between the conductive support (not shown) and the support 4a.

The operation of the developing device of this embodiment is as follows. When the developing device 3 is operated, the developer 6 in the container 5 adheres to the surface of the rotating developer carrier 4, and the elastic member 8a of the developer regulating member 8 and the coat layer 4b having fine irregularities on the surface. Is rubbed by. In particular, since part of the potassium titanate-based conductive whiskers is exposed on the surface of the coat layer 4b, the carrier 4 is adjusted to have an appropriate surface roughness. As a result, a sufficient layer thickness of the developer 6 for developing the electrostatic latent image 2 can be formed on the carrier 4. At the same time, since the carbon black is dispersed in the coat layer 4b, it is possible to impart a uniform and sufficient triboelectric charge to the developer 6. The thinned developer 6 is
The charged developer 6 particles fly and reciprocate in an alternating electric field that is conveyed to the developing area A as the carrier 4 rotates and is generated in the gap between the carrier 4 and the image carrier 1. In addition, the particles of the developer 6 collide with each other due to the reciprocating motion, and the entire developer 6 becomes cloud-like. The cloud of the developer 6 is attracted to the electrostatic latent image 2 of the image carrier 1 by the DC component of the bias voltage, and the development is completed.

Example 1 A method for forming the coat layer (4b) is shown below. Binder resin Phenolic resin 100 parts by weight Conductive particles Carbon black coated potassium titanate conductive whiskers 10 parts by weight Carbon black 15 parts by weight Diluent propylene glycol monomethyl ether 100 parts by weight Isopropanol 150 parts by weight In the above composition The conductive fine particles are dispersed by a sand mill, and the obtained coating solution is sprayed and coated on an aluminum support (4a), followed by heat curing at 160 ° C for 30 minutes in a heat drying oven to form a coating layer (4b). Formed. The volume resistivity of this coat layer (4b) was 0.18 Ωcm, and the surface roughness Ra was 1.0 μm. The developer carrying member (4) thus prepared by fixing the magnet roll (7) inside the support (4a) is shown in FIG.
The developing device (3) of the present embodiment was mounted on (3).

Hereinafter, developing devices (3) of Examples 2 and 3 and Comparative Example were produced in the same manner as in Example 1 except that the amount of potassium titanate type conductive whiskers used was changed. In each of the examples and comparative examples, the amount of the conductive whiskers used, the specific volume resistivity and the surface roughness R of the coating layer (4b) were measured.
a. Example 2 The amount of potassium titanate-based conductive whiskers used was 30 parts by weight. The formed coat layer had a volume resistivity of 0.11 Ωcm and a surface roughness Ra of 1.5 μm. Example 3 The amount of potassium titanate-based conductive whiskers used was 45 parts by weight. The formed coating layer has a volume resistivity of 8.2 × 10 ⁻² Ωcm and a surface roughness Ra of 1.8 μm.
Met. Comparative Example Potassium titanate-based conductive whiskers were not added to the composition (the amount of conductive whiskers used was 0 part by weight). The volume resistivity of the formed coat layer is 2.1Ω
cm, and the surface roughness Ra was 0.5 μm.

(Print Test) The developing device (3) manufactured in Examples 1 to 3 and Comparative Example was used as a laser printer (FX).
4109 modified machine: made by Fuji Xerox Co., Ltd., and charged in the developing device (3) with a negatively chargeable magnetic one-component developer (6) having an average particle size of 7 to 9 μm, and at room temperature and normal humidity (25 ° C., RH5
0%), low temperature and low humidity (10 ° C., RH 10%) and high temperature and high humidity (30 ° C., RH 85%). In the print sample, the image density was measured with a densitometer (Model 404A: manufactured by X-Rite), and the development ghost was visually evaluated. The evaluation criteria of image density and development ghost are as follows.
Table 1 shows the results. Evaluation criteria for image density and development ghost ◎ Density 1.50 or more, almost no image quality defects are observed ○ Density 1.40 or more and less than 1.50 Image quality defects are slightly seen △ Density 1.30 or more but less than 1.40 Some image quality Defects are seen, but there is no problem in practical use. × Density less than 1.30 Clear image defects are seen.

[0020]

[Table 1]

In the developing devices of the respective examples, as the content of the potassium titanate type conductive whiskers in the coat layer increases, the change in the charge amount in each environment becomes smaller.
Therefore, in each environment, the image density and the development ghost were obtained with practically no problem. On the other hand, in the developing device of the comparative example in which the potassium titanate-based conductive whiskers were not added to the coat layer, the change in the charge amount in each environment was large. Under normal temperature and normal humidity and high temperature and high humidity, a development ghost was slightly generated although there was no problem in practical use, and under low temperature and low humidity, an image quality defect due to the development ghost was clearly observed. As described above, as the content of the conductive whiskers in the coating layer increases, a better image can be obtained, and the image quality defect due to the development ghost does not occur particularly in a low temperature and low humidity environment.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, but various modifications can be made within the scope of the claims.
For example, a ferromagnetic blade having a minute gap with the surface of the developer carrier can be arranged in place of the developer regulating member for thinning the developer on the developer carrier. Further, in the above-mentioned embodiment, the magnetic one-component developer is used as the developer, but when the non-magnetic one-component developer is used, the developer regulating member (8) is attracted by the magnet roll (7), for example. The developing method of can be adopted.

[0023]

EFFECT OF THE INVENTION The developing device of the present invention contains the conductive particles of the potassium titanate type conductive whiskers together with the carbon black particles in the coating layer on the surface of the developer carrier.
Since the coat layer has an appropriate surface roughness, an appropriate amount of charge can be uniformly applied to the developer. as a result,
It has excellent image density environmental stability that can effectively prevent the occurrence of image quality defects due to development ghosts and can keep the image density high under each environment. Therefore, it is possible to form a good image that is excellent in environmental stability of image density and does not cause image quality defects such as a development ghost. Further, the potassium titanate-based conductive whiskers can impart excellent wear resistance to the coating layer. Therefore, even if the developer carrier is repeatedly used, filming such as sticking of the developer does not occur, and the developer carrier has excellent durability,
The developer can be stably conveyed and charged for a long period of time. Further, according to the developing device in which the coating layer containing the potassium titanate-based conductive whiskers in an amount of 5 to 50% by weight with respect to the binder resin is formed on the surface of the developer carrier, the environmental stability of the image density is particularly excellent, In addition, a development ghost does not occur, and a uniform and high-quality image without density unevenness can be formed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a developing device shown as an embodiment of the present invention.

[Explanation of symbols]

A ... developing area, 1 ... image carrier, 3 ... developing device, 4 ... developer carrier, 4a ... support, 4b ... coat layer, 6 ... developer.

Claims (2)

[Claims] 1. A developing method in which a developer is carried on a coat layer that covers the outer peripheral surface of a cylindrical support, and the developer is conveyed to a developing area where the electrostatic latent image formed on the image carrier is developed. A developing device comprising an agent carrier, wherein the coating layer comprises a conductive resin layer containing conductive fine particles, and potassium titanate-based conductive whiskers and carbon black are used as the conductive fine particles. 2. The potassium titanate-based conductive whiskers are contained in an amount of 5 to 5 relative to a binder resin which is a constituent of the coating layer.
The developing device according to claim 1, wherein the developing device contains 0% by weight.