JP2000112292A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device excellent in durability and handleability and capable of being surely driven, which is constituted so that an image carrier can be surely and stably brought into contact with a developing roller and the other abutting members. SOLUTION: The thin cylindrical image carrier 140 having flexibility is supported by a pair of disk-like members rotatably fitted to a shaft 110 which does not rotate by itself. Besides, the shaft 110 is rotatably provided with a backup drum 150 via a decentering bearing 154. The drum 150 is fitted to the shaft 110 inside the carrier 140 so as to support the carrier 140 from the inside at a position where a cleaning blade 210 abuts on the carrier 140 from the outside. Then, the Vickers hardness of the metal-made base material of the carrier 140 is defined as Hv (BASE) and that of the drum 150 is defined as Hv (BASE), and a conditional expression being Hv (BASE)>Hv (BACK)+50 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a facsimile, and a copying machine for forming an image by using an electrophotographic technique.

[0002]

2. Description of the Related Art Generally, an image forming apparatus using an electrophotographic technique includes a photosensitive member having a photosensitive layer on an outer peripheral surface, a charging device for uniformly charging the outer peripheral surface of the photosensitive member, and one charging device. Exposure means for selectively exposing the charged outer peripheral surface to form an electrostatic latent image, and applying a toner as a developer to the electrostatic latent image formed by the exposure means to form a visible image Developing means for forming a (toner image), transfer means for transferring the toner image developed by the developing means to a transfer medium such as paper, and a cleaning blade for removing the developer remaining on the outer peripheral surface of the photoreceptor after the transfer. have.

As the photoreceptor, a hard photoreceptor drum having a photosensitive layer formed on the outer peripheral surface and a flexible photoreceptor belt having a photosensitive layer formed on the surface are generally known.

Further, as the developing means, a roller-shaped one which is brought into contact with the surface of the photoreceptor is known, and as the roller, a hard roller and a roller made of soft rubber are known.

[0005] A hard photoconductor drum is used as the photoconductor,
If a hard roller is used as the developing roller to be brought into contact with the roller, there is naturally a limit in manufacturing the photosensitive drum and the hard roller with high accuracy, and an error always occurs. It is difficult. If the two do not contact uniformly, there is a problem that a gap is locally formed to cause uneven development, or the photosensitive drum and the developing roller are damaged by being pressed more than necessary.

Therefore, it is not usually practiced that both the photosensitive member and the developing roller to be brought into contact with the photosensitive member are made of a hard material. Is made of soft rubber, and when a hard developing roller is used, a photosensitive belt having flexibility is used as a photosensitive member.

However, when the developing roller to be brought into contact with the photoreceptor is made of soft rubber, there are the following problems.

When the developing roller to be brought into contact with the photoreceptor is constituted by a rubber roller, conductive particles such as carbon are dispersed in order to impart conductivity thereto. There is a problem that the rubber hardness changes due to variations and variations in the hardness on the roller surface, so that a good adhesion state to the photoreceptor cannot be obtained.

Conversely, when the dispersion amount of carbon is reduced in order to obtain a good adhesion state to the photoreceptor, there has been a problem that the conductivity is varied to cause uneven development.

Further, if a plasticizer to which a plasticizer is added is used in order to enhance flexibility, the plasticizer may seep out to the surface depending on long-term use or use environment. However, there is a problem that the photoconductive material in the photoconductor is denatured by adhering to the photoconductor, or the surface of the photoconductor is peeled off by sticking of the photoconductor to the roller.

Such a problem can be solved by using a hard developing roller and using a photosensitive belt having flexibility as a photosensitive member.

However, when a photoreceptor belt is used as the photoreceptor, at least two
The necessity of the book supporting rollers not only complicates the structure, but also increases the size of the apparatus.

Therefore, it is desired to solve such a problem at the same time.

As a device that has responded to such a demand, a photoconductor driving device described in Japanese Patent Application Laid-Open No. 4-188164 has been known.

FIG. 6 is a view showing the photoconductor driving device.
(A) is a side view, (b) is a perspective view.

The photoconductor driving device has a photoconductor belt 20 formed as a cylindrical thin film sheet, and an outer diameter circumference shorter than the inner diameter circumference of the photoconductor belt 20. A friction coefficient between the drive roller 21 and the photoreceptor belt 20 which is inside and rotates the photoreceptor belt 20 is set smaller than a friction coefficient between the drive roller 21 and the photoreceptor belt 20. A pressing member 22 that slidably presses the photosensitive belt 20 while keeping the photosensitive belt 20 in close contact with the drive roller 21 within a predetermined range in the circumferential direction is provided. In FIG. 6, reference numeral 24 denotes a charger, 25 denotes an exposure device, 26 denotes a developing roller, 27 denotes a transfer charger, and 28 denotes a cleaning roller.

According to such a photoconductor driving device, the photoconductor belt 20 is driven by the pressing member 22 in a state of being partially adhered to the surface of the driving roller 21, and the pressing member 2 is driven.
In a portion where there is no 2, a bend 23 is formed due to a difference in circumferential length from the drive roller 21.

For this reason, the photoreceptor belt 20 can be used as a hard material because the hardness of the photoreceptor belt 20 is simulated by the hardness of the driving roller 21 at the contact portion with the pressing member 22, and there is no pressing member 22. Since the flexure 23 is formed in the portion, it can be used as an elastic body.

Therefore, according to this device, the cleaning roller 28 made of an elastic material can be brought into contact with the contact portion of the photosensitive belt 20 with the pressing portion 22, and the bending portion 23 is made of a hard material. The developing roller 26 can be brought into contact.

The contact of the developing roller 26 is stably performed with a sufficient nip width and a low pressure contact force even when the developing roller 26 is made of a hard material because the bending 23 acts as an elastic body. .

That is, according to this apparatus, even if a hard developing roller is used, the photosensitive member and the developing roller are not damaged, and the size of the apparatus can be prevented.

An apparatus similar to this apparatus is disclosed in
No. 27859, JP-A-6-258989, and the like.

[0023]

SUMMARY OF THE INVENTION The above-mentioned JP-A-4-14-1
In the photoconductor driving device described in JP-A-88164, the photoconductor belt 20 is guided by the pressing member 22 provided partially on the peripheral portion of the photoconductor belt 20. When approaching 22,
At the entrance portion 22a, bending stress is likely to be generated at the peripheral portion (edge portion) of the photoreceptor belt 22, whereby the end portion of the photoreceptor belt 20 is likely to be broken, cracked, or peeled of the photosensitive layer. (Poor in durability). As a result, there is a problem that the photoreceptor belt 20 may be broken from the edge or may not be broken, but may cause a serious image defect.

The photoreceptor belt 20 must be handled as a single unit until the photoreceptor belt 20 is assembled in the apparatus as shown in FIG. However, since the photoreceptor belt 20 is formed as a cylindrical thin film sheet as described above and does not have sufficient rigidity, there is a problem that it is difficult to handle the photoreceptor belt 20.

Further, in the above apparatus, the photosensitive belt 20
Since the flexure 23 is formed at a portion where the pressing member 22 that presses both ends of the photoconductor belt 20 is not formed, the photosensitive belt 20 and the driving roller 21 are formed at both ends of the portion where the flexure 23 is formed. Opening 2 between
9 is formed.

For this reason, the toner floating in the apparatus,
Foreign substances such as toner external additives and paper powder easily enter between the photoreceptor belt 20 and the drive roller 21 through the openings 29 and 29, and the friction between the photoreceptor belt 20 and the drive roller 21 due to the entry of these foreign substances. There is a problem that the force is reduced and the photosensitive belt 20 may not be driven.

An object of the present invention is to solve the above-mentioned various problems, and an object of the present invention is to obtain a reliable and stable contact state between an image carrier and a developing roller and other contact members. It is an object of the present invention to provide an image forming apparatus which is excellent in durability and handleability of the image carrier and can drive the image carrier reliably.

[0028]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a shaft which does not rotate by itself; and a pair of disk-shaped members rotatably mounted on the shaft. A member, a flexible thin-walled cylindrical metal base material formed on the surface of the base material, and having both ends supported and fixed by the pair of disk-shaped members and driven to rotate together with the disk-shaped members. A flexible thin cylindrical image carrier having an image carrier layer, and an eccentric bearing having an outer diameter slightly smaller than the inner diameter of the image carrier and inside the image carrier with respect to the shaft. And a backup drum supporting the image carrier from the inside at an abutting position where the abutting member abuts against the image carrier from the outside. Unit and the image carrier of this image carrier unit And, a developing roller abutting at a position that is not supported by the backup drum, the Vickers hardness of the metallic substrate Hv (BAS
E), the Vickers hardness of the backup drum is Hv (B
ACK), the image carrier and the backup drum are configured such that the condition of Hv (BASE)> Hv (BACK) +50 is satisfied.

[0029]

According to the image forming apparatus of the first aspect, the following effects can be obtained.

(A) Both ends of a thin cylindrical image carrier are
Since it is supported and fixed by the pair of disk members rotatably attached to the shaft, when the disk members are driven to rotate, the image carrier is reliably driven to rotate.

Further, since both ends of the image carrier are supported and fixed by a pair of disk-shaped members, the durability is excellent.

(B) The image carrier is a flexible thin cylinder having a flexible thin cylindrical metal substrate and an image bearing layer formed on the surface of the substrate. Since the two ends are supported by the disc-shaped members, the center of the image carrier that is not supported by the disc-shaped members can be deformed inward.

Therefore, the portion of the central portion of the image carrier which is not supported from the inside by the backup drum can be used as a pseudo soft material, so that the developing roller to be brought into contact with the portion is not used. Even with a hard roller, a reliable and stable contact state can be obtained, and an image can be reliably formed on an image carrier or an image can be carried thereon.

On the other hand, a contact member such as a cleaning blade is brought into contact with the outer peripheral surface of the image carrier, and at the contact position, the image carrier is supported from the inside by a backup drum. Therefore, the contact member such as the cleaning blade can be reliably contacted.

Furthermore, if the contact member such as a cleaning blade is brought into contact with the image carrier without the backup drum, the thin cylindrical image carrier may be creep-deformed. According to the image forming apparatus described in item 1, such a fear is eliminated.

(C) Both ends of the image carrier are supported and fixed by a pair of disc-shaped members rotatably mounted on the shaft, and a backup drum is mounted on the shaft inside the image carrier. Since it is configured as a unit by being attached, handling becomes easy.

As described above, according to the image forming apparatus of the present invention, a reliable and stable contact state between the image carrier and the developing roller and other contact members can be obtained. The effect of being excellent in the durability and handleability of the body and of reliably driving the image carrier can be obtained.

Further, the backup drum has an outer diameter slightly smaller than the inner diameter of the image carrier, and is rotatably supported on the shaft via an eccentric bearing. Such an operation and effect can be obtained.

(D) Since the backup drum is rotatably supported on the shaft via an eccentric bearing,
The structure is simple, so that it can be manufactured with high precision and can be easily assembled.

(E) The backup drum has an outer diameter slightly smaller than the inner diameter of the image carrier, and is rotatably supported on the shaft via an eccentric bearing. The image carrier can be supported over a wide range from the inside at the contact position where the contact member such as the cleaning blade contacts from the outside.

(F) Since the backup drum is rotatably supported on the shaft via an eccentric bearing,
When the outer peripheral surface of the image carrier comes into contact with the inner peripheral surface of the image bearing member, the image carrier is rotated. Therefore, the load on the image carrier can be reduced, and the driving torque of the image carrier can be reduced.

Further, according to the image forming apparatus of the first aspect, the Vickers hardness of the metal substrate of the image carrier is H.
v (BASE), where Vickers hardness of the backup drum is Hv (BACK), the image carrier and the backup drum are configured such that the condition of Hv (BASE)> Hv (BACK) +50 is satisfied. Therefore, the following operation and effect can be obtained.

(G) the image carrier is a flexible thin cylindrical cylinder having a flexible thin cylindrical metal substrate and an image bearing layer formed on the surface of the substrate; In a configuration provided with a backup drum that supports the image carrier from the inside at the contact position where a contact member such as a cleaning blade contacts the image carrier from the outside, if any measures are taken, If this is not done, the following problems arise.

That is, in the manufacturing process of the thin cylindrical metal base material of the image carrier, local abnormal protrusions may be generated on the back surface. For example, when a thin cylindrical metal substrate is formed by an electroforming method, a protrusion corresponding to a defect on the surface of the matrix is formed on the back surface of the metal substrate. In this case, in order to prevent protrusions,
It suffices to eliminate the defects of the matrix, but it is extremely difficult and impossible to say that it is not feasible.

If there is a local abnormal protrusion on the back surface of the metal base in the image carrier, as shown in FIG. 5A, when the protrusion 2a reaches the support portion by the backup drum 4, the image is The portion 1a on the front surface corresponding to the protrusion 2a on the back surface of the support 1 rises in a convex shape. When the projection 1a reaches a contact position with the contact member 5 such as a cleaning blade as shown in FIG. 4B, the protrusion 1a comes into contact with the contact member 5 more strongly than the other portions 1b. . Therefore, when the apparatus is used for a long period of time, the image bearing layer 3 in the convex portion 1a is gradually scraped off as compared with the other portions 1b. At the position where the image carrier 1 is not supported by the backup drum 4, the portion (1 a) scraped off in this way becomes a concave portion 3 a as shown in FIG. The contact state between the developing roller 6 and the concave portion 3a that is in contact with the body 1 becomes incomplete, resulting in a problem that a dot-like image defect occurs.

On the other hand, according to the image forming apparatus of the present invention, the Vickers hardness of the metal substrate (2) is Hv (BASE), and the Vickers hardness of the backup drum (4) is Hv. (BACK), Hv (BASE)> Hv (B
ACK) +50, since the image carrier and the backup drum are configured to satisfy the condition of 50, there is a local abnormal protrusion 2a on the back surface of the metal base material (2), and the protrusion 2a is backed up. Even if it reaches the support part by the drum (4), the projection part 2a will be buried in the backup drum (4). That is, since the backup drum is sufficiently soft (to the extent that abnormal projections enter) with respect to the metal base material, the projections are buried in the backup drum.

Therefore, the projection 2 on the back surface of the image carrier 1
A portion 1a on the surface corresponding to a does not bulge in a convex shape, and as a result, the above-described concave portion 3a does not occur, so that a point-like image defect does not occur.

[0048]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross sectional view (FIG. 3) showing an image carrier unit in an embodiment of the image forming apparatus according to the present invention.
2 is a schematic partial side view of an image forming apparatus incorporating the image carrier unit, and FIG. 3 is a partially enlarged view of FIG.

As shown in FIGS. 1 and 3, the image carrier unit 100 has a shaft 110 which does not rotate by itself,
A pair of disk-shaped members 120, 120 rotatably attached to the shaft 110, and both ends supported and fixed by the pair of disk-shaped members 120, 120, rotate together with the disk-shaped members 120, 120. A thin cylindrical image carrier 140 having flexibility, and a cleaning blade 210 attached to the shaft 110 inside the image carrier 140 and serving as an abutting member against the image carrier 140 from the outside. At the contact position where the image carrier 1 contacts
And a backup drum 150 that supports the inside 40 from the inside.

Each of the pair of disk-shaped members 120, 120 is rotatably provided on a shaft 110 via a bearing 114, and the outer peripheral surfaces 121, 121 of the disk-shaped members 120, 120 enable the image carrier. 140 at both ends 14
1 is supported. Both ends 141 of the image carrier 140 are formed on the outer peripheral surfaces 121 and 12 by appropriate means, for example, by bonding.
Fixed to 1. A driving gear (not shown) is fixed to at least one of the disc-shaped members 120 on an outer surface thereof.

In this embodiment, the image carrier 140 is configured as a photoreceptor, and as shown in an enlarged sectional view of FIG. 4, as shown in FIG.
0b is formed by forming a photosensitive layer 140c on the surface (outer peripheral surface). As the metal substrate 140b,
For example, a nickel seamless tube manufactured by an electroforming method can be used. The photosensitive layer 140c is a so-called OP
C (organic photoreceptor) can be formed by dipping. Since the flexibility, that is, the flexibility of the photoconductor 140 can be determined by adjusting the thickness and the diameter of the base material, the flexibility can be appropriately set according to the image forming apparatus to be used. It is possible. For example, substrate thickness 20
The thickness is appropriately set in a range of from about 200 μm to a diameter of the base material of from 10 to 300 mm. Since OPC is mainly made of resin,
Although excellent in terms of flexibility, the base material 140b and OP are used to secure adhesion to the base material and take measures against laser light interference.
It is desirable to form an undercoating layer between C and C. As the undercoat layer, a layer in which particles capable of absorbing laser light such as zinc oxide and titanium oxide are dispersed in a resin such as a nylon resin is preferable.

The backup drum 150 is composed of a pair of side plates 151, 151 and a cylindrical member 152 whose both ends are fixed by the outer peripheral surfaces of these side plates 151, 151. The outer diameter D1 of the cylindrical member 152 is formed slightly smaller than the inner diameter D2 of the image carrier 140. Side plate 15
1 is provided with a bearing hole 153, and an eccentric bearing 154 is interposed between the bearing hole 153 and the shaft 110. Therefore, the backup drum 150 is rotatably supported on the shaft 110 via the eccentric bearing 154. As shown in FIG. 3, the eccentric bearing 154 has an eccentric amount on the contact position side (the right side in FIG. 3) where the cleaning blade 210 and the charging roller 220 (the charging roller 220 is also a contact member) contact. A part of the outer peripheral surface of the backup drum 150 (the outer peripheral surface of the cylindrical member 152) supports the image carrier 140 from the inside over a relatively wide range at the contact position. It has become.

Since the backup drum 150 is rotatably supported on the shaft 110 via the eccentric bearing 154, as shown in FIG. 3, at least at the contact position of the cleaning blade 210 and the charging roller 220, When the outer peripheral surface 152 a of the cylindrical member 152 contacts the inner peripheral surface 140 a of the photoconductor 140, the cylindrical member 152 rotates following the photoconductor 140.

The image carrier unit 100 as described above is
As shown in FIG. 2, a driving gear (not shown) of the main body of the image forming apparatus is engaged with a driving gear (not shown) provided on the disc-shaped member 120, which is incorporated in the image forming apparatus. The body (photoconductor) 140 is driven to rotate in the direction of the arrow.

In FIG. 2, L is a laser beam for selectively exposing the surface of the photosensitive member 140, and 300 (Y, M, C, K)
Denotes a developing device, 210 denotes the cleaning blade described above, 2
Reference numeral 20 denotes the charging roller described above.

The charging roller 220 contacts the outer peripheral surface of the photoreceptor 140 and uniformly charges the outer peripheral surface. The charging roller 220 is incorporated in the sub case 240, and is driven by a compression spring 221 (see FIG. 3).
The photosensitive member 140 is rotated by being pressed against the photosensitive member 140.

The laser beam L is emitted from an exposing unit (not shown), and selectively exposes the surface of the photoconductor 140 to form an electrostatic latent image on the surface of the photoconductor 140.

Each of the developing devices 300 (Y, M, C, K) has a built-in yellow, magenta, cyan, and black toner. Each of the developing devices 300 is configured to be able to come into contact with and separate from the photoconductor 140, and only one of the developing devices can come into contact with the photoconductor 140 during image formation. Reference numeral 310 (Y, M, C, K) denotes a developing roller that comes into contact with the photoconductor 140, and is constituted by a metal roller having a roughened surface or a hard resin roller.

The intermediate transfer belt 400 is brought into contact with the photosensitive member 140, and this contact position forms a primary transfer portion T1. The intermediate transfer belt 400 includes a drive roller 410, a tension roller 420, a backup roller 430 for the secondary transfer roller 460, and a cleaning blade 470.
Are wound around a backup roller 440 and a positioning roller 450 for forming the primary transfer portion T1, and are circulated by a drive roller 410 in the direction of the arrow shown in the figure. In a process in which the intermediate transfer belt 400 is driven to circulate, in the primary transfer portion T1, the photosensitive member 1
40 is transferred onto the intermediate transfer belt 400, and the toner image transferred onto the intermediate transfer belt 400 is
The image is transferred onto a recording medium (not shown) such as a sheet supplied between the secondary transfer roller 460 and the intermediate transfer belt 400.

The upper portion of the cleaning blade 210 is fixed to a blade holder 211 as shown in FIG. The blade holder 211 has arms 212 (only one is shown) provided at both ends of the blade holder 211 slidably attached to a side 241 of the sub case 240 by a shaft 213. Subcase 240 and blade holder 21
1, a blade biasing spring (compression coil spring) 2
The tip (edge) of the cleaning blade 210 is moved by the urging force of the blade urging spring 242 and the elastic force of the blade 210 itself.
0 is pressed against the surface.

In the sub case 240, a receiving portion 243 for receiving the toner scraped off by the blade 210 is formed.

A rake sheet 244 is provided below the tip of the cleaning blade 210. The base of the rake sheet 244 is fixed to the sub case 240, and the leading edge of the rake sheet 244 is pressed against the surface of the photoconductor 140 by the elastic force of the sheet 244 itself, and
And prevents the toner scraped off by the cleaning blade 210 from leaking downward.

A toner conveying screw 245 is provided in the sub case 240, and the toner is conveyed by the toner conveying screw 245 toward a waste toner tank (not shown).

The sub-case 240 in which the cleaning blade 210 and the like are incorporated is provided in the image carrier unit 10.
0 can be combined with a single unit.

The image forming apparatus as described above is an apparatus capable of forming a full-color image using four color toners of yellow (Y), magenta (M), cyan (C) and black (K). The operation is as follows.

(I) When a print command signal (image forming signal) is input from a host computer (not shown) such as a personal computer, the photosensitive member 140 and the intermediate transfer belt 400 are driven to rotate.

(Ii) The outer peripheral surface of the photosensitive member 140 is uniformly charged by the charging roller 220.

(Iii) The outer peripheral surface of the uniformly charged photoreceptor 140 is selectively exposed L in accordance with image information of the first color (for example, yellow) by an exposing means (not shown), and a yellow electrostatic charge is applied. A latent image is formed.

(Iv) The developing roller 310 of the developing device 300Y for the first color (for example, yellow) is mounted on the photosensitive member 140.
Only the Y contacts, the electrostatic latent image is developed, and the toner image of the first color (for example, yellow) is
Formed on 40.

(V) The toner image formed on the photoconductor 140 is transferred onto the intermediate transfer belt 400 in the primary transfer section T1, ie, between the photoconductor 140 and the primary transfer roller 230. At this time, the secondary transfer roller 460 is separated from the intermediate transfer belt 400.

(Vi) After the toner remaining on the photosensitive member 140 is removed by the cleaning blade 210, the photosensitive member 140 is neutralized by a neutralizing means (not shown).

(Vii) The above operations (ii) to (vi) are repeated as necessary. That is, the second color, the third color, the fourth color,
Are repeated on the intermediate transfer belt 400 to form a toner image corresponding to the content of the print command signal.

(Viii) At a predetermined timing, the secondary transfer portion T2 (the intermediate transfer belt 400 and the secondary transfer roller 460)
The recording medium such as paper is supplied to the contact portion with the recording medium, and the toner image (basically a full-color image) on the intermediate transfer belt 400 is transferred onto the recording medium.

By the way, as in the image forming apparatus described above, the image carrier 140 is a thin cylindrical metal substrate 140b having flexibility and the image carrier layer formed on the surface of the substrate 140b. 140c, which is a flexible thin cylindrical shape, and the image carrier 140 is placed inside the image carrier 140 at a contact position where a contact member such as the cleaning blade 210 contacts the image carrier 140 from outside. If no measures are taken in the configuration having the backup drum 150 supported from the side, the problem described above with reference to FIG. 5 occurs.

That is, in the manufacturing process of the thin cylindrical metal base material 140b of the image carrier 140, local abnormal protrusions may occur on the back surface.

In this embodiment, since the thin cylindrical metal substrate 140b is formed by electroforming, the projection 140b1 (see FIG. 4) corresponding to the defect on the surface of the matrix is formed by the metal substrate. It will be formed on the back surface of 140b.

Then, such a local abnormal protrusion 14
When the protrusion 140b1 reaches the support portion of the backup drum 150 when the protrusion 140b1 is provided, the portion of the surface corresponding to the protrusion 140b1 on the back surface of the image carrier 140 rises in a convex shape, and the image bearing layer 140c in the protrusion is formed. Are gradually scraped off as compared with the other portions, and the cut-off portion becomes a concave portion at a position where the image carrier 140 is not supported by the backup drum 150. The contact state between the developing roller 310 and the concave portion, which is in contact with the concave portion, becomes incomplete, and as a result, a point-like image defect occurs. Such a problem occurs even when the height of the abnormal protrusion is about several μm to several tens μm.

Therefore, in this embodiment, the Vickers hardness (JISZ2244) of the metal base 140b is set to Hv (BASE), the backup drum 150, more precisely, at least to the metal base 140b ( The Vickers hardness of the cylindrical member 152 which is directly supported) is Hv (BAC
When K is satisfied, the image carrier 140 and the backup drum 150 are configured so that the condition of Hv (BASE)> Hv (BACK) +50 is satisfied. That is, the backup drum 150 is made of a material that is sufficiently soft (to the extent that the abnormal protrusion 140b1 enters) with respect to the metal base material 140b.

Specifically, when the metal base material 140b is formed of a nickel electroformed tube, at least the cylindrical member 152 of the backup drum 150 is formed of an aluminum tube. Vickers hardness (Hv (BASE)) of nickel is 15
0, Vickers hardness (Hv (BACK)) of aluminum is 6
7, and the condition of Hv (BASE)> Hv (BACK) +50 is satisfied.

According to the above-described image forming apparatus, the following operation and effect can be obtained.

(A) Since both ends 141 of the thin cylindrical image carrier 140 are supported and fixed by a pair of disk members 120, 120 rotatably mounted on the shaft 110, the disk is When the member 120 is driven to rotate,
The image carrier 140 is reliably driven to rotate.

Further, both ends 141 of the image carrier 140 are
Since it is configured to be supported and fixed by the pair of disk-shaped members 120, 120, it has excellent durability.

(B) The image carrier 140 is a thin cylindrical member having flexibility, and both ends 141 of the image carrier 140 are disc-shaped members 12.
Because it is a configuration supported by 0,120,
In the image carrier 140, a central portion 142 (see FIG. 1) that is not supported by the disk-shaped members 120, 120 can be deformed inward.

Therefore, the central portion 14 of this image carrier is
2, a portion that is not supported from the inside by the backup drum 150 can be used as a so-called pseudo soft material, and a member to be brought into contact with the portion is a hard roller such as the developing roller 310 or the like. However, a reliable and stable contact state can be obtained, and an image can be reliably formed on the image carrier 140 or the image can be carried.

On the other hand, the outer peripheral surface of the image carrier 140 is provided with a cleaning blade 21 as a contact member.
0, the charging roller 220 is brought into contact with the image bearing member 140 at the contact position.
Therefore, the cleaning blade 210 and the charging roller 220 can be reliably brought into contact with each other.

That is, the cleaning blade 210 is reliably brought into contact with the image carrier 140, so that the toner remaining on the outer peripheral surface of the image carrier 140 can be reliably removed and charged reliably.

In addition, if the cleaning blade 210 and the like are not in the state where the backup drum 150 is not provided,
When the image carrier 140 is brought into contact with the image carrier 40, the thin cylindrical image carrier 140 may be creep-deformed. According to the present embodiment, such a possibility is eliminated.

(C) The image carrier 140 has a pair of disk-shaped members 120 rotatably mounted on the shaft 110.
Since both ends 141 of the image carrier 140 are supported and fixed by 120, and the backup drum 150 is attached to the shaft 110 inside the image carrier 140 to form a unit, so that handling is easy. Become.

As described above, according to the image forming apparatus of this embodiment, it is possible to obtain a reliable and stable contact state between the image carrier 140 and the developing roller 310 and other contact members 210. In addition, the effect that the image carrier 140 is excellent in durability and handleability and the image carrier 140 can be reliably driven can be obtained.

Further, the backup drum 150 has an outer diameter D1 slightly smaller than the inner diameter D2 of the image carrier 140, and is rotatably supported on the shaft 110 via an eccentric bearing 154. Therefore, the following operation and effect can be obtained.

(D) The backup drum 150 is
Since it is configured to be rotatably supported by the eccentric bearing 154 via the eccentric bearing 154, the structure is simple, so that it can be manufactured with high accuracy and can be easily assembled.

(E) The backup drum 150 has an outer diameter D1 slightly smaller than the inner diameter D2 of the image carrier 140 and is rotatably supported on the shaft 110 via an eccentric bearing 154. At a position where the cleaning blade 210 and the like abut against the image carrier 140 from the outside, the image carrier 140 can be supported over a wide range from the inside (FIGS. 2 and 3). reference).

(F) The backup drum 150 is
10 is rotatably supported by an eccentric bearing 154 via an eccentric bearing 154, so that the outer peripheral surface 152 a of the image carrier 140 is driven to rotate by contact with the inner peripheral surface 140 a of the image carrier 140.
Therefore, the load on the image carrier 140 can be reduced, and the driving torque of the image carrier 140 can be reduced.

(G) Metal substrate 140 of image carrier 140
When the Vickers hardness of b is Hv (BASE) and the Vickers hardness of the backup drum 150 is Hv (BACK), Hv
Since the image carrier 140 and the backup drum 150 are configured so that the condition of (BASE)> Hv (BACK) +50 is satisfied, there is a local abnormal protrusion 140b1 on the back surface of the metal base material 140b. Projection 140b1
Reaches the support portion of the backup drum 150, the protrusion 140b1
(More specifically, the surface of the cylindrical member 152). That is, since the backup drum 150 is sufficiently soft (to the extent that the abnormal protrusion 140b1 enters) with respect to the metal base material 140b, the protrusion 140b1 is buried in the backup drum.

Therefore, the portion of the front surface corresponding to the projection 140b1 on the back surface of the image carrier 140 does not rise in a convex shape, and as a result, the above-described concave portion (see 3a in FIG. 5C) does not occur. Therefore, point-like image defects do not occur.

[0097]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The shaft 110 is constituted by a metal shaft.

The side plate 151 of the backup drum 150,
The cylindrical member 152 is made of aluminum.

The positional accuracy of the backup drum 150 in the radial direction is desirably about ± 100 μm. Further, it is desirable that the positional accuracy in the circumferential direction (the rotation direction of the image carrier 140) be within ± 1 °.

The charge roller 22 with respect to the image carrier 140
0, the contact amount of the developing roller 310 (the concave amount of the image carrier 140) is desirably 0.5 mm or less.

The embodiments and examples of the present invention have been described above. However, the present invention is not limited to the above-described embodiments or examples, and can be appropriately modified within the scope of the present invention. It is.

For example, in the above-described embodiment, the image carrier unit has been described as a photoconductor unit. However, the image carrier unit of the present invention is not limited to this, and may be configured as an intermediate transfer medium unit. In this case, the image carrier is a thin cylindrical intermediate transfer medium.

For a metal substrate, Hv (BASE)> Hv
Examples of the material of the backup member that satisfies the condition of (BACK) +50 include plastic (such as ABS) and FRP (fiber reinforced plastic).

[0104]

According to the image forming apparatus of the first aspect,
A reliable and stable contact state between the image carrier and the developing roller and other abutting members can be obtained, and the durability and handleability of the image carrier are excellent, and the image carrier can be reliably driven. The effect is obtained.

Further, it can be manufactured with high precision, can be easily assembled, and can be easily assembled at an abutting position where a cleaning blade or the like as an abutting member abuts against the image carrier from outside. The image carrier can be supported over a wide range from the inside, the load on the image carrier can be reduced, and the driving torque of the image carrier can be reduced.

In addition, the effect that no dot-like image defects occur is obtained.

[0107]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view (a partly omitted II cross-sectional view in FIG. 3) showing an image carrier unit in an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic partial side view of an image forming apparatus incorporating the image carrier unit.

FIG. 3 is a partially enlarged view of FIG. 2;

FIG. 4 is a partially enlarged cross-sectional view of the image carrier.

FIGS. 5A to 5C are conceptual diagrams for explaining a problem.

FIGS. 6A and 6B are explanatory diagrams of a conventional technique.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 image carrier unit 110 shaft 120 disk member 140 image carrier 140 b metal base 140 c photosensitive layer (image carrier layer) 150 backup drum 154 eccentric bearing 210 cleaning blade (contact member) 310 developing roller

Claims (1)

[Claims] 1. A shaft that does not rotate by itself, a pair of disk-shaped members rotatably mounted on the shaft,
A flexible thin-walled cylindrical metal base material and an image-carrying layer formed on the surface of the base material, both ends of which are supported and fixed by the pair of disk-shaped members and driven to rotate together with the disk-shaped members. A flexible thin cylindrical image carrier having an outer diameter slightly smaller than the inner diameter of the image carrier, and an eccentric bearing with respect to the shaft inside the image carrier. An image carrier unit having a backup drum that is rotatably supported and supports the image carrier from the inside at the contact position where the contact member abuts against the image carrier from the outside; A developing roller that abuts on the image carrier of the image carrier unit at a position not supported by the backup drum, wherein the Vickers hardness of the metal base material is Hv (BASE), and the Vickers of the backup drum is Of the time that the Hv (BACK), Hv (BASE)> Hv (BACK) to +50 following condition is satisfied, the image forming apparatus, wherein the image bearing member and the backup drum is configured.