JP2001343829A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device in which an image defect caused by the pinhole of the non-image part of a latent image carrier can be restrained and which has a developing roller which can be easily and inexpensively formed. SOLUTION: After performing sand blast treatment to the toner carrying area 4c of a developing roller 4 made of metal, anodizing treatment is performed to the toner carrying area 4c and the toner non-carrying area 4d of the developing roller 4. A comparatively thin oxide film is formed on the surface of the roller 4 by such anodizing treatment. The outer peripheral surface part of the roller 4 whose electric resistance is extremely small has specified electric resistance and has specified hardness owing to the oxide film. Therefore, even when the toner developer non-carrying area 4d of the roller 4 directly comes into contact with the pinhole 10 existing at the non-image part of the photoreceptive layer 2a of a photoreceptor 2, a situation that a high current flows to the roller 4 from the photoreceptor 2 is restrained and the image defect caused by the pinhole 10 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a developing device used for an image forming apparatus such as an electrostatic copying machine or a printer, and more particularly, to a developing roller which carries a developer and transports it to a latent image carrier. Belongs to the technical field of a contact developing type developing device that comes into contact with a latent image carrier.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrostatic copying machine or a printer, an electrostatic latent image carried on a latent image carrier such as a photoreceptor is developed by a developer of a developing device and then developed. Transfer the image on the latent image carrier to a recording medium such as paper,
Further, by fixing the transferred image transferred to the recording medium,
You get an image.

In a conventional developing device of such an image forming apparatus, a developing roller b for carrying a developer and transporting it to a latent image carrier a as shown in FIG. There is a developing type developing device. In this contact developing type developing device, a one-component developer is supplied to a developing roller b from a supply roller c, and the one-component developer is supplied by the developing roller b toward a latent image carrier a with which the developing roller b contacts. The electrostatic latent image on the latent image carrier a is developed with the one-component developer. In this case, an aluminum or iron-based metal roller is used as the developing roller b.
In particular, aluminum metal rollers are often used because they are easy to process and inexpensive.

As shown in FIG. 10, in this developing device, a predetermined potential (ground, ie, 0 V in the illustrated example) is set to the latent image carrier a and a predetermined voltage (see FIG. 10) is applied to the developing roller b. In the example shown, good development is performed by applying a development bias of a negative voltage), and by applying a supply bias of a predetermined voltage lower than the voltage of the development bias to the supply roller c, Good developer supply is performed.

Further, a photosensitive layer d is formed on the surface of the latent image carrier a. As shown in FIG. 11, an image area e where the electrostatic latent image is formed is located at the center of the photosensitive layer d. And a non-image portion f which is located at both ends of the photosensitive layer d and on which an electrostatic latent image is not formed. The developing roller b has a developer carrying region (that is, a developer carrying region) and a developer non-bearing region (that is, a developer non-transporting region) corresponding to the image portion e and the non-image portion f of the latent image carrier a, respectively. Area) is set.

On the other hand, by contacting a felt material made of a flocking material of a polyfluoroethylene fiber with the peripheral surface of the developer non-supporting region at both ends of the developing roller, the developer is axially moved from both ends of the developing roller. Japanese Patent Application Laid-Open No. 4-134374 proposes a developing device for preventing leakage and scattering. In the developing device disclosed in this publication, scattering of the developer outside the casing is effectively prevented by effectively using the developer non-carrying regions at both ends of the developing roller.

[0007]

By the way, as shown in FIG. 10, the photosensitive layer d of the latent image carrier a may have a pinhole g in which a very small portion of the photosensitive layer d is missing. . As shown in FIG. 11, when the pinhole g is formed in the non-image portion f of the photosensitive layer d, in the above-described contact developing type developing device, the developer non-supporting region of the developing roller b carries the developer. Therefore, it comes into direct contact with the pinhole g. Then, a current larger than the allowable current value flows from the latent image carrier a to the developing roller b as shown by a solid arrow in FIG. 10, and the voltage of the developing roller b rises to or near the potential of the latent image carrier a. As a result, the potential difference from the latent image carrier a becomes smaller. For this reason, since the voltage of the developing roller b is not maintained at the predetermined voltage, the development is not properly performed in the portion of the pinhole g, and as shown in FIG. Streak-like white spots occur, leading to image defects.

Further, as described above, the increase in the voltage of the developing roller b causes not only a current larger than the allowable current value to flow from the developing roller b to the supply roller c as shown by a dotted arrow in FIG. The supply of the developer from the supply roller c to the developing roller b becomes excessive. For this reason, as shown in FIG. 11, a streak-like black portion is generated following the white spot generated in the image portion of the latent image carrier a, which similarly causes an image defect.

Further, in the developing device described in the above-mentioned publication, the developer can be prevented from being scattered in the axial direction outside the casing by the felt material contacting both ends of the developing roller. It is not possible to prevent image defects due to pinholes in the part.

The present invention has been made in view of such circumstances, and an object thereof is to suppress image defects due to pinholes formed in a non-image portion of a latent image carrier, and An object of the present invention is to provide a developing device having a developing roller that can be formed easily and at low cost.

[0011]

In order to solve this problem, according to the first aspect of the present invention, a developing bias is applied to a developing roller that carries a developer on a surface and transports the developer to a latent image carrier. In a contact developing type developing device in which the developing roller is provided in contact with a latent image carrier, the developing roller is formed of a metal roller, and a predetermined electric charge is applied to a developer non-supporting area of the metal roller. It is characterized by having resistance.

Further, the invention of claim 2 is characterized in that the non-developer carrying area of the developing roller is set at both ends of the developing roller. Furthermore, the invention of claim 3 is characterized in that a developer seal member is provided on the outer peripheral surfaces of both ends of the developing roller to prevent the developer from leaking in the axial direction of the developing roller. Further, in the invention according to claim 4, the alumite treatment is performed on the outer peripheral surface of the developer non-supporting region of the developing roller, or on the outer peripheral surface of the developer non-supporting region of the developing roller and the axial end surface continuous from the outer peripheral surface. The application is characterized in that the developer non-supporting area of the developing roller has the predetermined electric resistance.

Further, in the invention according to claim 5, the latent image carrier is a soft latent image carrier softer than the developing roller, and the axial length of the latent image carrier is the axial length of the developing roller. It is characterized by being set longer than the length. Furthermore, the invention of claim 6 is characterized in that the soft latent image carrier is formed of a thin metal cylinder. Further, the invention of claim 7 is characterized in that the developing bias is formed by superimposing an alternating current on a direct current.

[0014]

The metal roller forming the developing roller has a predetermined electric resistance in the developer non-carrying region. The predetermined electric resistance causes the latent image carrier to move from the latent image carrier to the developing roller even if the developer non-carrying region of the developing roller directly contacts a pinhole present in the non-image portion of the photosensitive layer of the latent image carrier. The flow of a large current is suppressed.
As a result, the voltage of the developing bias in the developing roller does not approach the potential of the latent image carrier due to the pinhole, and the development is favorably performed even in the image portion of the latent image carrier at the pinhole position. . Therefore, streak-like white spots due to pinholes, which occur in the image portion of the latent image carrier, are prevented, and a high-quality image without defects can be obtained.

In a developing device in which the supply roller is provided in contact with the developing roller, when a developer non-supporting area of the developing roller directly contacts the pinhole, the voltage of the developing bias to the developing roller is reduced. Since the potential of the latent image carrier does not approach, a large current does not flow from the developing roller to the supply roller. Therefore, excessive supply of the developer from the supply roller to the developing roller is prevented, and a streak-like black portion is not generated on the image portion of the latent image carrier, so that a high-quality image without defects is obtained. Can be

In particular, according to the third aspect of the present invention, the developer sealing member prevents the developer from leaking out of the casing of the developing device along the axial direction of the developing roller on the outer peripheral surfaces of both ends of the developing roller. Will be done. Therefore, at both ends of the developing roller where image defects due to pinholes are likely to occur, while this image defect is effectively prevented,
In addition, leakage of the developer at both ends of the developing roller is effectively prevented.

In the invention according to claim 4, the alumite is formed on the outer peripheral surface of the developer non-supporting region of the metal roller, or on the outer peripheral surface of the developer non-supporting region of the metal roller and the axial end surface continuous from the outer peripheral surface. Treatment (anodizing treatment) is performed, and an oxide film is formed on each of these surfaces. This oxide film has a cell structure composed of a thick porous layer having a large number of micropores and a dense and very thin active layer. In this case, since the active layer has electric resistance, the non-developer carrying area of the metal roller having a relatively low electric resistance has a predetermined electric resistance by alumite treatment. At this time, since the above-described respective surfaces of the metal roller are uniformly alumite-treated, the electric resistance can be more uniformly obtained over the entire alumite-treated portion of the metal roller. Thus, regardless of the position of the pinhole in the non-image portion of the latent image carrier, the influence of the pinhole described above is reliably prevented, and a high-quality image free of image defects can be obtained.

Moreover, since it is not necessary to use a special material having a predetermined electric resistance in advance as a material of the developer non-carrying region of the developing roller, the developer non-carrying region has a uniform electric resistance of a predetermined size. The developing roller can be formed inexpensively and easily from an inexpensive metal roller having extremely low electric resistance. Furthermore, since the electrolysis reaction due to the alumite treatment almost penetrates from the surface of the metal roller to the inside, the thickness of the oxide film formed on the surface of the metal roller is small. For this reason, even if the oxide film is formed on the outer peripheral surface of the developer non-supporting region of the metal roller, almost no step is formed between the metal roller and the outer peripheral surface of the developer carrying region. Therefore, in the developing device in which the developer sealing members are in contact with the outer peripheral surfaces of both ends of the developing roller, there is no step between the outer peripheral surface of the developer carrying region and the outer peripheral surface of the developer non-bearing region of the developing roller. Therefore, it is possible to more effectively prevent the developer from leaking in the axial direction of the developing roller.

Further, in the present invention, the latent image carrier is constituted by a soft latent image carrier which is softer than the developing roller, and the length of the latent image carrier in the axial direction is equal to the axis of the developing roller. It is set longer than the length in the direction. As a result, good development can be obtained in the contact-developing type developing device. However, if a pinhole is located at the corner of the developing roller at this time, electric discharge occurs due to the large curvature of the corner of the developing roller. Since a large current flows from the latent image carrier to the developing roller, the effect of the pinhole on the image increases. However, since an extremely thin oxide film is formed at the corners of the developing roller by alumite processing, even if the latent image carrier is composed of such a soft latent image carrier, the influence of the pinhole is more effective. And a good image can be obtained. In this case, in the invention according to claim 6, since the soft latent image carrier is formed of a cylindrical thin metal base material such as nickel, the developing roller can be formed easily at low cost. .

Further, in the invention of claim 7, the developing bias is formed by superimposing alternating current on direct current. The influence of the pinhole is more effectively suppressed by the superposition of the alternating current. Further, the superimposition of the alternating current suppresses the adhesion of the developer to the non-image portion of the latent image carrier, thereby preventing the fogging of the developer, and imparting an appropriate edge effect to the image. Is reproduced, and the gradation is improved. Since the porous layer has a large number of micropores, foreign matter is likely to be attached thereto and corroded easily. However, by performing a sealing treatment for sealing the large number of micropores, the porous layer is inactivated to achieve environmental stability. Will be improved.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing an example of an embodiment of the developing device of the present invention. As shown in FIG. 1, a developing device 1 of this example includes a photosensitive member 2 as a latent image carrier on which an electrostatic latent image is formed, and a toner 3 as a developer.
, A supply roller 5 for supplying toner 3 to the developing roller 4, and regulating the toner 3 supplied from the supply roller 5 and conveyed by the developing roller 4. A regulating member 6. The developing device 1 is a contact developing type developing device in which a developing roller 4 is in contact with the photoconductor 2.
The peripheral speed of the developing roller 4 is set to be higher than the peripheral speed of the photoconductor 2 (peripheral speed ratio = the peripheral speed of the developing roller 4 / the peripheral speed of the photoconductor 2> 1). The supply roller 5 is in contact with the developing roller 4, and the regulating member 6 is constantly in pressure contact with the developing roller 4.

The developing roller 4 is formed of a metal roller made of aluminum. As shown in FIG. 2, a toner carrying area for carrying and conveying the toner 3 at the center of the outer peripheral surface thereof (that is,
A toner carrying area 4c is set, and a toner non-carrying area (that is, a toner non-carrying area) 4d that does not carry the toner 3 is set at both ends of the outer peripheral surface. Then, a sand blasting process is performed on the toner carrying region 4c on the surface of the metal roller (in FIG. 2, a large number of ".") Is used. By this sand blasting process, an uneven surface is formed on the surface of the metal roller.
As shown in FIG. 3, in this uneven surface, a convex portion, that is, an edge (ridge line) 4b at a boundary between concave portions 4a adjacent to each other is clearly formed.

Further, as shown in FIG. 2, the entire outer peripheral surface of the metal roller, that is, the toner carrying region 4c and the toner non-bearing region 4d are subjected to alumite treatment (shown by oblique lattices in FIG. 2). . When the alumite treatment is performed on the surface of the metal roller as described above, a reaction of electrolysis permeates into the metal roller, so that a relatively thin oxide film is formed on the surface of the metal roller. Since this oxide film has a predetermined electric resistance and a predetermined hardness, an outer peripheral surface portion of an aluminum metal roller having an extremely low electric resistance has a predetermined electric resistance and a predetermined hardness. . At this time, the surface of the developing roller 4 can be further hardened by setting the temperature of the aqueous solution for electrolysis in the alumite processing to a relatively low temperature and performing the processing slowly.

As described above, even if the surface of the metal roller is subjected to an alumite treatment to form an oxide film, the oxide film is extremely thin. It is not hindered by the oxide film and hardly changes. Therefore, FIG.
As shown in (1), the unevenness of the surface of the metal roller after the alumite treatment is substantially the same as that of the sandblast treatment. Since the oxide film has a porous layer composed of a large number of fine pores, a sealing treatment for sealing the large number of the fine pores is performed to inactivate the porous layer, so that foreign substances are hardly adhered and hardly corroded. And environmental stability has been improved.

Further, as shown in FIG.
One developing roller 4 has a developing bag in the same manner as a conventional developing device.
The bias is applied. In that case, the developing device of this example
In 1, the DC of the DC power supply 7 and the AC of the AC power supply 8 are superimposed.
The applied developing bias is applied to the developing roller 4.
As shown in FIG. 5, the image area of the photoconductor 2 (the developing roller 4
Potential (corresponding to the toner carrying area 4c)_on(Example of illustration
In this case, grounding, that is, 0 V)
(Corresponding to the toner non-carrying area 4d of the developing roller 4)
Potential V_o(Negative voltage in the example shown)
Developing bias potential V of developing roller 4_dIs its maximum value
V_dmaxIs the potential V of the image portion_onIs set equal to
In the meantime, its minimum value V_dminIs the potential V of the non-image portion_oBigger
Is set well. That is, the developing bias potential V
_dIs the potential V of the non-image portion_oThe potential V of the image portion_onPredetermined
Is set to a value, and the potential V of the non-image portion is_oBeyond the image section
Potential V_{o n}Is not set on the other side. This allows development
3 toner particles on roller 4 adhere to non-image area of photoreceptor 2
More effectively. Also supply roller
5, a supply bias is applied similarly to the conventional developing device.
Have been. This supply bias is supplied by the DC of the DC power supply 9.
The voltage is applied to the roller 5.

Further, the toner 3 used in the developing apparatus 1 of this embodiment is formed as a non-magnetic one-component toner in which an external additive made of relatively hard silica is attached to toner base particles made of a relatively soft polyester resin. ing. In this case, the hardness (hardness) of the surface of the developing roller 4 is set lower than the hardness (hardness) of the external additive of the toner 3. More specifically, the hardness of the surface of the developing roller 4 is set to such a degree that the irregularities on the surface of the developing roller 4 are reduced to some extent but not excessively reduced with respect to the hardness of the external additive of the toner 3. .

In addition, the toner 3 has a particle sphericity of 0.9 to 1, which is the practical sphericity of Wardel, and
It is suitable for faithfully visualizing a high-definition latent image on the photoconductor 2. The practical spherical degree of Wardell of the toner 3 is represented by the ratio of the diameter of a circle having an area equal to the projected area of the particle in the projected image of the toner particle to the diameter of the smallest circle circumscribing the projected image of the particle. It is a numerical value.

The reason that the degree of sphericity of the toner 3 is suitable for faithful visualization of a high-definition latent image is proposed by the inventor of the present invention and has been filed by the present applicant. 9-
Since it is disclosed in Japanese Patent Publication No. 31544, it can be easily understood by referring to this publication. To put it simply, the reason is that the toner 3 on the developing roller 4 is developed by the photoreceptor in the developing operation by making the shape of the toner 3 approximate to a true sphere with a practical sphericality of 0.9 to 0.9-1. When the toner 3 adheres to the photosensitive member 2 according to its potential, the particles of the toner 3 easily form a densely packed adhesion layer on the photoreceptor 2, and faithfully and clearly reproduce the image contour portion of the latent image details. That is because The practical degree of sphericality of Wardell can be measured using an image processing apparatus equipped with an optical microscope (manufactured by Apionix Co.), and the measuring procedure is described in the above-mentioned JP-A-9-31544. The description is omitted because it can be easily understood by referring to this publication.

In the developing device 1 of this embodiment, the toner 3 supplied from the supply roller 5 onto the developing roller 4 is regulated by the developing roller 4 rotating counterclockwise in FIG. 6 is conveyed. The amount of toner 3 that has reached the regulating member 6 is regulated by the regulating member 6 to be conveyed toward the photoconductor 2, and excess toner is returned to the supply roller 5. Further, the toner 3 that has passed through the regulating member 6 forms a thin toner layer 3 a having a predetermined thickness on the developing roller 4. The thinned toner 3 is conveyed toward the photoreceptor 2 by the developing roller 4, and the toner 3
As a result, the electrostatic latent image on the photoconductor 2 is developed, and a toner image is formed on the photoconductor 2.

According to the developing device 1 of this embodiment, since the toner non-carrying area 4d of the metal roller forming the developing roller 4 has a predetermined electric resistance, the non-image area of the photosensitive layer 2a of the photosensitive member 2 is formed. Even if the toner non-carrying region 4d of the developing roller 4 directly contacts the pinhole 10 existing in the above, the flow of a large current from the photoconductor 2 to the developing roller 4 can be suppressed by the predetermined electric resistance. As a result, the voltage of the developing bias in the developing roller 4 can be prevented from approaching the potential of the photoconductor 2 by the pinhole 10, and the pinhole 10
Developing can also be performed well in the image portion of the photoconductor 2 at the position. Therefore, it is possible to prevent streak-like white spots due to the pinholes 10 occurring in the image portion of the photoconductor 2, and to obtain a high-quality image without defects. Moreover, when the toner non-carrying area 4b of the developing roller 4 comes into direct contact with the pinhole 10, the pinhole 10
As a result, the voltage of the developing bias applied to the developing roller 4 does not approach the potential of the photoconductor 2, so that a large current can be prevented from flowing from the developing roller 4 to the supply roller 5. Therefore, the excessive supply of the toner 3 from the supply roller 5 to the developing roller 4 can be prevented, and the stripe-shaped black portion generated in the image portion of the photoreceptor 2 can be prevented, so that a high-quality image without defects can be obtained. be able to.

Further, since a predetermined electric resistance is given to the toner non-carrying area 4d of the developing roller 4 by the alumite treatment, the electric resistance is made more uniform over the entire axial direction of the toner non-carrying area 4d of the metal roller. Obtainable. Accordingly, no matter where the pinhole 10 is located in the non-image portion of the photoconductor 2, image defects due to the pinhole 10 can be more reliably prevented. Further, since it is not necessary to use a special material having a predetermined electric resistance in advance as a material of the developing roller 4, the developing roller 4 can be formed inexpensively and easily from a metal having a predetermined size and a uniform electric resistance. Become like

Further, since the developing bias is formed by superimposing an alternating current on a direct current, the influence of the pinhole 10 can be more effectively suppressed by the superimposition of the alternating current. In addition, by appropriately controlling the developing bias on which the AC is superimposed, the discharging of the developing bias from the developing roller 4 can be prevented. In particular, since the maximum potential of the developing bias 4 is set lower than the potential set for the non-image portion of the photoconductor 2, discharge of the developing bias can be more effectively prevented, and Adhesion of the toner 3 can be suppressed, and fogging of the toner 3 can be prevented.
Moreover, by superimposing an alternating current on a direct current, an appropriate edge effect can be given to the image, a uniform intermediate color of the image can be reproduced, and the gradation can be improved.

Further, the irregularities formed on the surface of the toner carrying area of the developing roller 4 after the alumite processing can be maintained to be substantially the same as the irregularities formed by the sandblasting. Therefore, the toner 3 can be transported more reliably due to the unevenness of the surface of the developing roller 4, and the transportability of the toner 3 can be improved. Further, since the uneven shape is maintained by the sandblasting process, the contact area of the developing roller 4 with the particles of the toner 3 can be increased. Thereby, the friction between the developing roller 4 and the particles of the toner 3 is sufficiently performed, and the particles of the toner 3 can be effectively frictionally charged. Therefore, the chargeability of the toner 3 can be improved. Further, since the surface of the developing roller 4 is hardened by the oxide film formed by the alumite treatment, both the wear resistance and the mechanical strength of the developing roller 4 can be improved.

Further, the hardness of the surface of the developing roller 4 is set lower than the hardness of the external additive of the toner 3 so that the surface of the developing roller 4 is slightly scraped or slightly scraped by friction with the external additive of the toner 3. In the developing roller 4
The filming of the developing roller 4 can be prevented by suppressing the adhesion of the toner 3 to the developing roller 4. In particular, in a developing device in which the regulating member 6 contacts the developing roller 4, the toner 3 tends to adhere near the position where the regulating member 6 contacts the developing roller 4. Is more effectively removed by being scraped off by the friction of the external additive.
Filming can be prevented. In addition, a slight edge (ridge line) in the uneven shape on the surface of the developing roller 4 allows a new edge (ridge line) to be formed on the uneven shape on the surface of the developing roller 4.

Furthermore, since the alumite treatment is applied to the toner carrying area of the developing roller 4, the oxide carrying film can also provide the toner carrying area of the developing roller 4 with a uniform electric resistance of a predetermined size. Therefore, it is possible to prevent the injection of excessive charges into the toner 3 due to the developing bias via the toner carrying area of the developing roller 4. In particular, in the contact developing type developing device 1 in which the developing roller 4 comes into contact with the photoconductor 2 as in this example, the pressure of the particles of the toner 3 sandwiched between the photoconductor 2 and the developing roller 4 increases. However, if the pressure is large, the injection of excess charge into the toner 3 is increased, and thus such uniform electric resistance can prevent the injection of excess charge into the toner 3 more effectively. Thus, according to the developing device 1 of this example,
A high-quality image free from image defects such as streak-like white spots, streak-like black portions, or uneven density due to the pinholes 10 can be obtained for a long period of time.

Further, since the peripheral speed of the developing roller 4 is set to be higher than the peripheral speed of the photosensitive member 2, the particles of the toner 3 roll due to the speed difference in the developing section where the developing roller 4 contacts the photosensitive member 2. By rubbing, the toner 3 can be effectively recharged. As a result, the charge amount of the toner having a small charge amount can be increased, so that the toner adhered to the non-image portion of the photoconductor 2 can be reliably collected toward the developing roller 4 and the toner 3 can be collected in the image portion of the photoconductor 2. The toner 3 can be surely adhered to the position where it should originally adhere, and so-called image dust, which is a shift in the position where the toner 3 is adhered, can be prevented.

In addition, the degree of sphericity of the toner 3 is set to 0.9 to 1 as a practical spherical degree of Wardel, and is closer to a true sphere, so that the particles of the toner 3 roll more reliably. As a result, the toner 3 can be recharged even more effectively. As a result, the developer in the non-image area of the photoconductor 2 can be reliably collected toward the developing roller 4 in the same manner as described above, and image dust in the image area of the photoconductor 2 can be prevented. High-precision latent image can be faithfully visualized.

FIG. 6 is a view showing a developing roller in a developing device according to another embodiment of the present invention. In the following description of each example, the same components as those in the example preceding the example are denoted by the same reference numerals, and detailed description thereof will be omitted. In the developing roller 4 of the example shown in FIG. 2 described above, the outer peripheral surface of the toner carrying region 4c is subjected to sandblasting, and the entire outer peripheral surface of the toner carrying region 4c and the non-toner carrying region 4d of the developing roller 4 is subjected to alumite treatment. But
In the developing roller 4 of this example, as shown in FIG. 6, only the outer peripheral surface of the toner non-carrying region 4d at both ends of the developing roller 4 is subjected to alumite processing. Further, the outer peripheral surface of the toner carrying area 4c of the developing roller 4 in this example is not subjected to the sandblasting processing in the above-described example. The other configuration of the developing device 1 of this example is the same as the example shown in FIG.

In the developing device 1 of this embodiment, the alumite treatment is applied only to the outer peripheral surface of the toner non-carrying region 4d at both ends of the developing roller 4, and this toner non-carrying region 4d
Is increased to a predetermined resistance. As described above, by performing the alumite treatment only on the outer peripheral surface of the toner non-carrying region 4d of the developing roller 4, a predetermined electric resistance can be more easily and inexpensively provided in the toner non-carrying region 4d of the developing roller 4. Can be made. Other functions and effects of the developing device 1 of this example are the same as those of the example shown in FIG. 2 except for the functions and effects of the sand blast processing and the functions and effects of the alumite processing performed on the outer peripheral surface of the toner carrying area 4c of the developing roller 4. It is. Note that, in the metal roller 4 of this example, the outer peripheral surface of the toner carrying region 4c of the developing roller 4 is subjected to sand blasting, and then the outer peripheral surface of the toner carrying region 4c is replaced with a metal other than alumite treatment, such as nickel plating. A plating process can also be performed.

FIG. 7 is a view showing a developing roller in a developing device according to still another example of the embodiment of the present invention. In the developing device 1 of the example shown in FIG. 6 described above, the developing roller 4 in which the alumite treatment is applied only to the outer peripheral surface of the toner non-carrying region 4d
The developing device 1 of this example is used as shown in FIG.
However, similarly to the developing roller 4 of the example shown in FIG. 6, only the outer peripheral surface of the toner non-carrying area 4d of the developing roller 4 is subjected to an alumite treatment. Further, in the developing device 1 of this example,
The toner seal member 11 is in contact with the outer peripheral surface of the toner non-carrying region 4d of the developing roller 4 on which the alumite processing has been performed. In this case, the toner seal member 11 is provided non-rotatably so as to surround an outer peripheral surface of the outer peripheral surface of the toner non-carrying region 4d of the developing roller 4 except for a predetermined region including a portion in contact with the photosensitive member 2. I have.

The toner seal member 11 prevents the toner 3 carried in the toner carrying region 4c of the developing roller 4 from leaking along the axial direction around the toner non-bearing region 4d as shown by an arrow. I have. This toner seal member 1
For example, the seal material disclosed in the above-mentioned publication can be used as the material 1, but the material is not limited thereto, and any material can be used as long as it can prevent the toner 3 from leaking as described above. May be something. The other configuration of the developing device 1 of this example is the same as the example shown in FIG.

According to the developing device 1 of this embodiment, the toner seal member 11 can prevent the toner 3 from leaking along the axial direction on the outer peripheral surfaces of both ends of the developing roller 3. In this case, since the thickness of the oxide film formed on the outer peripheral surface of the toner non-carrying region 4d of the metal roller by the alumite treatment is thin as described above, this oxide film is formed on the outer peripheral surface of the toner non-carrying region 4d of the metal roller. Even if this is done, there is almost no step between the outer peripheral surface of the toner carrying region 4c of the metal roller and the outer peripheral surface of the non-toner carrying region 4d, and flatness therebetween is ensured. Therefore, since the flatness can be ensured without such a step, the toner seal member 11 contacting the outer peripheral surfaces of both ends of the developing roller 4 can further effectively prevent the toner 3 from leaking from both ends of the developing roller 4 in the axial direction. Can be prevented. Moreover, since the alumite treatment can ensure flatness between the outer peripheral surface of the toner carrying region 4c of the metal roller and the outer peripheral surface of the non-toner carrying region 4d, there is no need to perform a process for flattening the surface of the metal roller. Further, it is possible to set a predetermined electric resistance in the toner non-carrying region 4d of the metal roller more easily and at a lower cost.

As described above, according to the developing device 1 of this embodiment, the image defect can be effectively prevented at both ends of the developing roller 4 where the image defect due to the pinhole 10 is most likely to occur. Thus, scattering of toner at both ends of the developing roller 4 can be effectively prevented. Other functions and effects of the developing device 1 of this embodiment are the same as those of the embodiment shown in FIG.
The toner seal member 11 can be provided in the developing device 1 shown in FIG.

FIG. 8 is a view showing a developing device according to still another example of the embodiment of the present invention, and FIG. 9 is a view for explaining an alumite process performed on a developing roller in the developing device of the example shown in FIG. is there. As shown in FIG. 8, in the developing device 1 of this example, the photosensitive member 2 is formed of a soft photosensitive member that is softer than the developing roller 4. In this soft photoreceptor, for example, a photosensitive layer 2a having a predetermined thickness is provided on an outer peripheral surface of a relatively soft cylindrical metal thin base material 2b made of nickel or the like. End member 2 having
Both ends in the axial direction are closed by d. As a result, the photoconductor 2 is formed relatively soft,
When the developing roller 4 comes into contact with the developing roller 4, the developing roller 4 elastically bends by a predetermined amount. The axial length of the photoconductor 2 is set to be longer than the axial length of the developing roller 4.

On the other hand, in the developing device 1 of the example shown in FIG. 6, the alumite processing is performed only on the outer peripheral surface of the toner non-carrying area 4d of the developing roller 4, but as shown in FIG. In the developing roller 4, an alumite treatment is performed on the outer peripheral surface of the toner non-carrying region 4d of the developing roller 4 as in the developing roller 4 of the example shown in FIG. The alumite treatment is performed from the vicinity of the rotating shaft 4g of the axial end face 4f of the developing roller 4 which continues through the corner 4e. Therefore,
The toner non-carrying region 4d on the outer peripheral surface of the developing roller 4, the corner 4e of the developing roller 4, and the axial end surface 4e of the developing roller 4 all have a predetermined electric resistance.

As described above, in order to perform the alumite treatment from the outer peripheral surface of the toner non-carrying region 4d including the corner portion 4e to the vicinity of the rotation shaft 4g of the axial end surface 4e, as shown in FIG. 4 g of rotating shafts at both ends with cap 1
In the state covered with 2, the corner portion 4e, the toner non-carrying region 4d, and the axial end surface 4e are immersed in an electrolytic solution such as sulfuric acid or nitric acid to carry out alumite treatment. Thereby, the toner non-carrying area 4d on the outer peripheral surface of the developing roller 4
Further, the alumite treatment is surely performed not only on the axial end surface 4e of the developing roller 4 but also surely on the pinpoint of the corner 4e of the developing roller 4 (in FIG. 9, the alumite treatment is performed). The bold lines are shown for clarity of the implementation location). Developing device 1 of this example
The other configuration is the same as the example shown in FIG.

According to the developing device 1 of this embodiment, the toner non-carrying region 4d, the corner portion 4e, and the axial end surface 4e of the developing roller 4 can reliably have a predetermined electric resistance. On the other hand, the soft photoreceptor elastically bends by a predetermined amount when the developing roller 4 comes into contact, so that the outer peripheral surface thereof comes into contact with the toner non-carrying region 4d and the corner portion 4e of the developing roller 4, and furthermore, on the axial end surface 4e. Partially comes into contact. At this time, even if the pinhole 10 of the soft photoreceptor contacts either the toner non-carrying region 4d or the axial end surface 4e, the predetermined electric resistance of the toner non-carrying region 4d and the axial end surface 4e causes the pinhole 10 to be in the above-described manner. Since a large current does not flow from the photosensitive member 2 to the developing roller 4, a predetermined potential difference can be maintained between the potential of the photosensitive member 2 and the potential of the developing roller 4 in the same manner as described above. Can be prevented.

When the pinhole 10 of the soft photoreceptor comes into contact with the corner 4e, the curvature of the corner 4e is high, so that the discharge increases and a large current easily flows from the photoreceptor 2 to the developing roller 4. Since the electrical resistance at the corner 4e is set to a predetermined resistance, a predetermined potential difference between the potential of the photoconductor 2 and the potential of the corner of the developing roller 4 can be more reliably maintained. Image defects can be more effectively prevented. Other functions and effects of the developing device 1 of this embodiment are the same as those of the embodiment shown in FIG.

In each of the above-described examples, the alumite treatment is used to provide the toner non-carrying region 4d, the corner portion 4e and the axial end surface 4e of the developing roller 4 with a predetermined electric resistance. The present invention is not limited to this, and it is possible to provide these portions of the developing roller 4 with a predetermined electric resistance except for the alumite processing. For example, a predetermined electric resistance can be obtained by coating an electric resistance material so as to be embedded on the surface of these portions of the developing roller 4. However, in this case, the developing roller 4
By incorporating an electric resistance material on the outer peripheral surface of the toner non-carrying region 4d, a step is easily generated between the outer peripheral surface of the toner carrying region 4c and the outer peripheral surface of the toner non-carrying region 4d. It is difficult to secure the flatness of For this reason, processing for flattening the surface of the metal roller is required, and the setting of the electrical resistance in the toner non-carrying region 4d of the metal roller becomes troublesome. Moreover, the corner portion 4 of the developing roller 4
Since it is extremely difficult to form a coating film of this electric resistance material on e in a pinpoint manner, it is difficult to give a predetermined electric resistance to the corner portion 4e by coating by incorporating the electric resistance material. Therefore, it is advantageous to obtain a predetermined electric resistance by alumite treatment.

As another method for providing a predetermined electric resistance to the above-mentioned portion of the developing roller 4, a ring-shaped electric resistance member is joined to both ends of the toner carrying region 4c of the metal roller, so that the metal roller has the above-described configuration. A predetermined electrical resistance can also be obtained at the location. However, also in this case, a step easily occurs between the outer peripheral surface of the toner carrying region 4c and the outer peripheral surface of the toner non-carrying region 4d, and it is difficult to secure the flat outer peripheral surface therebetween. For this reason, processing for flattening the surface of the metal roller is required as in the case of the above-mentioned coating, and the setting of the electric resistance in the toner non-carrying area 4d of the metal roller becomes complicated. Therefore, it is advantageous to obtain a predetermined electric resistance by alumite treatment.

[0051]

As is apparent from the above description, according to the developing device of the first to seventh aspects of the present invention, the developing roller has a predetermined electric resistance in the non-developer carrying area of the developing roller. Due to the predetermined electric resistance, a large current flows from the latent image bearing member to the developing roller even if the developer non-bearing region of the developing roller directly contacts a pinhole present in the non-image portion of the photosensitive layer of the latent image bearing member. Flow can be suppressed. This allows
Since good development can be performed also in the image portion of the latent image carrier at the pinhole position, it is possible to prevent the occurrence of streak-like white spots due to the pinhole in the image portion of the latent image carrier, High quality images without defects can be obtained.

In the case of a developing device in which the supply roller is provided in contact with the developing roller, a large current can be prevented from flowing from the developing roller to the supply roller by a pinhole. Oversupply of the developer can be prevented. Therefore, it is possible to prevent the occurrence of a streak-like black portion in the image portion of the latent image carrier, and it is possible to obtain a high-quality image without defects.

In particular, according to the third aspect of the present invention, the developer seal member can prevent the developer from leaking along the axial direction on the outer peripheral surfaces of both ends of the developing roller, so that an image defect due to a pinhole can be prevented. The image defect can be more effectively prevented at both ends of the developing roller where the toner is easily generated, and the leakage of the developer at both ends of the developing roller can be effectively prevented.

According to the fourth aspect of the present invention, the outer peripheral surface of the non-developer carrying region of the metal roller or the outer peripheral surface of the non-developer carrying region of the metal roller and the axial end surface continuous from the outer peripheral surface are provided. Since the alumite treatment is performed, a predetermined electric resistance can be given to the developer non-carrying region of the metal roller having a relatively small electric resistance. Moreover, since these surfaces of the metal roller are uniformly alumite-treated,
The electric resistance can be obtained more uniformly over the entire alumite-treated portion of the metal roller. Thereby, regardless of the position of the pinhole in the non-image portion of the latent image carrier,
The effect of the pinhole described above can be reliably prevented,
A high-quality image without image defects can be obtained.

Furthermore, since it is not necessary to use a special material having a predetermined electric resistance in advance as a material of the developer non-carrying region of the developing roller, the developer non-carrying region has a uniform electric resistance of a predetermined size. The developing roller can be formed inexpensively and easily from an inexpensive metal roller having an extremely small electric resistance. Furthermore, since the thickness of the oxide film formed on the surface of the metal roller by the alumite treatment is small, there is almost no step between the outer peripheral surface of the developer-carrying region of the metal roller and the outer peripheral surface of the developer-carrying region of the metal roller. Without this, flatness between them can be ensured. Therefore,
In the developing device in which the developer seal members are in contact with the outer peripheral surfaces of both ends of the developing roller, it is possible to more effectively prevent the developer from leaking in the axial direction of the developing roller.

Further, according to the fifth and sixth aspects of the present invention,
Since the latent image carrier is composed of a soft latent image carrier that is softer than the developing roller, good development can be obtained in a contact developing type developing device, and a pinhole is located at a corner of the developing roller. However, the effect of the pinhole can be more effectively suppressed, and a good image can be obtained. In this case, according to the invention of claim 6, since the soft latent image carrier is formed of a cylindrical thin metal base material such as nickel, the developing roller can be formed easily at low cost. .

Further, according to the invention of claim 7, since the developing bias is formed by superimposing an alternating current on a direct current, the influence of a pinhole can be more effectively suppressed by the superimposition of the alternating current. . Further, by superimposing the alternating current, the adhesion of the developer to the non-image portion of the latent image carrier can be suppressed, so that the fogging of the developer can be prevented, an appropriate edge effect can be given to the image, and the gradation can be further improved. Performance can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating an example of an embodiment of a developing device of the present invention.

FIG. 2 is a view showing a developing roller of the developing device of the example shown in FIG.

FIG. 3 is an enlarged view of a concavo-convex surface on the developing roller shown in FIG. 2 formed by a sandblasting process with a microscope.

FIG. 4 is an enlarged view of a concavo-convex surface on the developing roller shown in FIG. 2 after alumite processing by a microscope.

FIG. 5 is a diagram showing a developing bias applied to the developing roller of the example shown in FIG. 1 on which alternating current is superimposed.

FIG. 6 is a diagram showing a developing roller in a developing device according to another example of the embodiment of the present invention.

FIG. 7 is a diagram illustrating a developing roller in a developing device according to still another example of the embodiment of the present invention.

FIG. 8 is a diagram illustrating a developing device according to still another example of the embodiment of the present invention.

FIG. 9 is a view for explaining an alumite process performed on a developing roller in the developing device of the example shown in FIG. 8;

FIG. 10 is a diagram showing an example of a conventional contact developing type developing device.

FIG. 11 is a diagram for explaining a development failure due to a pinhole of a photoconductor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Developing apparatus, 2 ... Photoconductor (latent image carrier), 2a ... Photosensitive layer, 2a ... Metal thin base material, 3 ... Toner (developer), 4 ...
Developing roller, 4c: toner carrying area (toner conveying area), 4d: toner non-carrying area (toner non-conveying area),
4e: corner portion, 4f: axial end face, 5: supply roller, 6: regulating member, 7, 10: DC power supply, 8: AC power supply, 9: pinhole, 11: toner seal member

Claims (7)

[Claims] 1. A contact developing device wherein a developing bias is applied to a developing roller for carrying a developer on a surface and transporting the developing agent to a latent image carrier, and the developing roller is provided in contact with the latent image carrier. The developing device according to claim 1, wherein the developing roller is formed of a metal roller, and has a predetermined electric resistance in a non-developer carrying area of the metal roller. 2. A non-developer carrying area of the developing roller,
The developing device according to claim 1, wherein the developing device is set at both ends of the developing roller. 3. On the outer peripheral surfaces of both ends of the developing roller,
3. The developing device according to claim 2, further comprising a developer seal member for preventing the developer from leaking in the axial direction of the developing roller. 4. An alumite treatment is performed on an outer peripheral surface of a developer non-supporting region of the developing roller, or on an outer peripheral surface of a developer non-supporting region of the developing roller and an axial end surface continuous from the outer peripheral surface, The developing device according to claim 2, wherein the developer non-carrying region of the developing roller has the predetermined electric resistance. 5. The latent image carrier is a soft latent image carrier that is softer than the developing roller, and an axial length of the latent image carrier is set longer than an axial length of the developing roller. The developing device according to claim 4, wherein: 6. The developing device according to claim 5, wherein said soft latent image carrier is formed of a cylindrical thin metal base material. 7. The developing bias according to claim 1, wherein an alternating current is superimposed on a direct current.
The developing device according to any one of the above items.