JPH0743983A - Electrostatic charging member, process cartridge and image forming device - Google Patents

Abstract

PURPOSE:To eliminate a defective image caused by the attachment of toner as for a contact type electrostatic charge member. CONSTITUTION:An electrostatic charge roller 2 is constituted by surrounding a core bar 2a by an elastic body 2B obtained by laminating a foaming member 2b, a tube 2c, an electrical conductive layer 2d, a middle resistance layer 2e and a protection layer 2f in turn from the inside. By pressing the core bar 2a by a pressure spring 3, the roller 2 is made to abut on an image carrier 1. Then, the surface of the carrier 1 is uniformly electrostatically charged through the elastic body 2B by impressing an electrostatic charge bias on the core bar 2a by a power source 4. Besides, the maximum diameter of a void 2g formed on a boundary in between the tube 2c on the outside circumferential surface of the foaming member 2b is set to be <=5mm. Thus, the residual toner slipping through a cleaning device is prevented from being attached on the surface of the roller 2 corresponding to the void 2g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging which applies an oscillating voltage (a voltage whose voltage value changes periodically with time) and charges the image carrier by coming into contact with or in proximity to the image carrier. The present invention relates to a member, a process cartridge including the charging member, and an image forming apparatus.

[0002]

2. Description of the Related Art A contact type charging device is known as a charging device such as an image forming apparatus. In this contact type charging device, a conductive charging member to which a voltage is applied is brought into contact with an image carrier as a member to be charged, and the charge is directly transferred from the charging member to the photosensitive drum to thereby transfer the surface of the image carrier. Is charged to a predetermined potential. Such a contact charging device can reduce the applied voltage, simplify the power supply, and reduce the amount of ozone generated during the charging process as compared with the non-contact type corona discharge device which has been widely used. It has the advantages that it is a minute amount, therefore the structure of the exhaust system can be simplified by eliminating the ozone removal filter, and that it is maintenance-free. For this reason, the contact charging type charging device is used in an image forming apparatus such as an electrophotographic apparatus (copier, laser beam printer), electrostatic recording device, etc., including an image carrier such as a photoconductor and a dielectric, and other photosensitive drums. As a means for charging (hereinafter, simply referred to as "photosensitive drum"), it has attracted attention as a substitute for a corona discharge device and has been put into practical use.

In the above-mentioned contact charging device, in order to uniformly and uniformly charge the surface of the photosensitive drum, an oscillating voltage in which a DC voltage is superimposed on an AC voltage is applied to a conductive contact charging member, and this charging member is charged. A charging method is known in which charging is performed by bringing the photosensitive drum into contact with the photosensitive drum.
149669).

However, in the above-mentioned charging system, a vibration noise called a charging noise is generated due to the vibration voltage, which is a serious problem.

As a measure for reducing the charging noise, the elastic body of the charging member, which has been hard so far, is made of a very flexible foam member to suppress the vibration between the charging member and the photosensitive drum. It is possible to reduce the charging noise to a level that does not bother you.

However, in a charging member having a foamed member as a main constituent member, the hardness of the foamed member itself is low, and the hardness thereof greatly changes depending on the external environment such as temperature and humidity. When receiving the force, permanent deformation may occur due to the force, and charging failure or the like may appear on the image.

As a measure to prevent this, a method of covering the outer peripheral surface of the foam member with a tube member (hereinafter simply referred to as "tube") which is a resistance layer having a hardness higher than that of the foam member has been considered. As a result, the force applied to the foam member is reduced, and the charging noise does not increase. Furthermore, since the foamed member has poor surface properties, covering it with a tube having excellent surface properties eliminates the problem of image unevenness.

FIG. 12 shows an embodiment thereof. In the figure,
Reference numeral 1 denotes a photosensitive drum (image bearing member), for example, an arrow R1.
And a drum type electrophotographic photosensitive member, an electrostatic recording dielectric member, and the like, which are rotationally driven in a predetermined peripheral speed (process speed).

Reference numeral 2 denotes a conductive charging roller as a contact charging member, which comprises a cored bar (supporting member) 2a and a foam member 2b as an elastic body formed on the outer periphery thereof. The charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force by pressure springs 3 for urging both ends of the core metal 2a toward the photosensitive drum 1, respectively. Along with the rotation in the R1 direction, the driven rotation is performed in the arrow R2 direction.

Reference numeral 4 denotes a power source for applying a voltage to the charging roller 2, and the charging roller 2 is driven by the power source 4 to make the core metal 2
A predetermined charging voltage is applied via a contact leaf spring (not shown) brought into contact with a to uniformly charge the surface of the photosensitive drum 1 that is being rotationally driven. The predetermined charging voltage at this time is
It is a superposed voltage (Vac + Vdc) obtained by superposing the oscillating voltage Vac having the peak-to-peak voltage Vpp that is at least twice the charging start voltage of the photosensitive drum 1 and the DC voltage Vdc.

FIG. 13 is a vertical sectional view showing the structure of the charging roller 2. The charging roller 2 is composed of a core metal 2a and an elastic body 2B surrounding the core metal 2a. The elastic body 2B includes a foaming member 2b made of polyurethane or the like in which conductive powder such as carbon is dispersed, a tube 2c as a resistance layer, and a conductive layer 2 on the outer periphery of the elastic body 2B.
d, the medium resistance layer 2e, and the protective layer 2f. In this charging roller 2, as a method of covering the foam member 2b with the tube 2c, as shown in FIG.
First, for example, a method of preparing a foamed member 2b in which conductive rubber is foamed as a raw material and inserting the cored bar 2a into the foamed member 2b, or as shown in FIG. There is a method in which the raw material of 2b is inserted into the cored bar 2a, and the cored bar 2a is foamed in a fixed state. But,
Considering the surface property, accuracy, and cost, the latter is superior.

The operation of the image forming apparatus having the charging roller 2 will be briefly described with reference to FIG.

The photosensitive drum 1 is rotationally driven in the direction of arrow R1, and the charging roller 2 is driven to rotate in the direction of arrow R2. The power source 4 uniformly charges the surface of the photosensitive drum 1 via the core metal 2a and the elastic body 2B. The surface of the photosensitive drum 1 whose surface is uniformly charged is then exposed to the exposure means 5 to form an electrostatic latent image on the surface. Toner (developer) is attached to the electrostatic latent image by the developing device 6 to form a toner image,
This toner image is transferred by the transfer device 8 to the transfer material 7 which is transferred by a transfer device (not shown). The transfer material 7 on which the toner image is transferred is then fixed to a fixing device (not shown).
Then, the toner image is fixed and discharged as a final copy to the outside of the apparatus main body.

On the other hand, the photosensitive drum 1 after the toner image transfer is
The residual toner remaining on the surface is removed by the cleaning device 9 and is subjected to the next image forming process.

[0015]

However, according to the above-mentioned conventional technique, the following problems occur when the conductive rubber which is the raw material of the foaming member 2b is foamed.

When the raw material of the foaming member 2b is foamed as shown in FIG. 15, there is no escape path for air at the interface with the tube 2c, so the air remains as it is and remains as innumerable air bubbles (hereinafter, this air bubble). Is called "void".) In this state, the surface property seems to be good at first glance, but in reality, when the charging roller 2 comes into contact with the photosensitive drum 1 and the photosensitive drum 1 rotates, the residual toner that has slipped through the cleaning device 9 and the charging roller 2 are exposed. This residual toner easily enters the portion of the surface of the charging roller 2 that corresponds to the inner void through the tube 2c, causing charging failure, and the image has a black spot pattern on the image. It will appear as a defect.

Therefore, according to the present invention, the maximum diameter of bubbles formed on the outer surface of the foam member is set to 5 mm or less,
An object of the present invention is to provide a charging member, a process cartridge, and an image forming apparatus that prevent charging failure.

[0018]

The present invention has been made in view of the above circumstances, and an elastic body held by a supporting member is brought into contact with an image carrier to apply a charging voltage to the supporting member. In the charging member for charging the image carrier via the elastic body, the elastic body surrounds the foamed member supported by the support member and directly or on another layer on the image carrier. And a tube member as a resistance layer that is in contact with the foamed member, and the maximum diameter of bubbles formed on the outer surface of the foam member is 5 mm or less.

Further, the process cartridge includes at least the image carrier, the above-mentioned electric member, and a cartridge container for accommodating the image carrier and the charging member integrally, with respect to the main body of the image forming apparatus. The feature is that it is detachably attached.

Further, the image forming apparatus includes the image carrier, the above-mentioned charging member, exposing means for exposing the image carrier to form an electrostatic latent image, and toner attached to the electrostatic latent image. It is characterized in that it is provided with a developing device for forming a toner image by means of this and a transfer device for transferring the toner image onto a transfer material.

The image forming apparatus is also characterized by having mounting means for mounting the above-mentioned process cartridge detachably.

[0022]

According to the above structure, since the maximum diameter of the bubbles on the surface is 5 mm or less on the outside of the foam member contacting the back side of the tube, the residual toner that has slipped through the cleaning device enters between the charging member and the image carrier. Prevents accumulation in voids and prevents poor charging.

The above-mentioned action is particularly effective when the tube thickness is 0.15 mm or more and 0.3 mm or less and the international rubber hardness of the charging member is 35 ° or more and 50 ° or less. This range is where the above-mentioned charging member can be put into practical use, and is most suitable for obtaining stable production of the tube and for the problem of charging noise that occurs when an AC voltage is applied.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a schematic view showing a vertical section of a charging roller 2 as a charging member according to the present invention, and FIG. 2 is a schematic view showing a section of one end side in a direction along a cored bar 2a. is there.

In these figures, 1 is a member to be charged (image carrier)
Is a rotary type photosensitive drum having a negative or positive charging polarity. Reference numeral 2 denotes a charging roller as a contact charging member. The charging roller 2 is composed of a core metal 2a made of metal such as stainless steel as a supporting member and an elastic body 2B surrounding the core metal 2a. The elastic body 2B includes a foam member (foam layer) 2b which is concentrically and integrally formed on the outer periphery of the core metal 2a in the shape of a roller, and a tube 2c which covers the outer peripheral surface of the foam member 2b so as to surround it. It is composed of a conductive layer 2d that covers the tube 2c, a medium resistance layer 2e that covers the conductive layer 2d, and a protective layer 2f that further covers the middle resistance layer 2e. The diameter of the charging roller 2 as a whole is 12 mm.

The foam member 2b is made of polystyrene, for example.
It is a member in which conductive powder such as carbon or tin oxide is dispersed in a foamed member made of polyolefin, polyester, polyurethane, polyamide or the like, or a flexible member made by foaming EPDM or urethane to have a low volume resistivity.

The tube 2c is made of a thermoplastic elastomer such as urethane, stainless rubber or high baron, and the resistance value of the tube 2c may be determined so that the overall resistance of the charging roller 2 becomes an appropriate value.

In the foaming member 2b described above, carbon is dispersed in foamed polyurethane in this embodiment. Two
Reference numeral b'denotes a bubble portion (filled bubble of air, nitrogen, argon gas, etc.) of the foam member 2b. And this bubble part 2
The void b is formed at the interface between the foam member 2b and the tube 2 sheet, and in this embodiment, the maximum diameter of the void 2g is 3 mm.

The specific specifications of the charging roller 2 in this embodiment are as follows.

Core metal 2a; diameter 6 mm, length 256 m
m stainless round bar Foaming member 2b; Carbon-dispersed foamed epichlorohydrin rubber Volume resistance value 10 ² Ω · cm to 10 ⁵ Ω · cm Layer thickness 2.6 mm, length 230 mm Tube 2c; Polyurethane thermoplastic elastomer Volume resistance value 10 ⁴ Ω · cm to 10 ⁸ Ω · cm Layer thickness 250 μm Conductive layer 2d; Large amount of carbon in EPDM and urethane,
Conductive powder such as tin oxide dispersed Volume resistance value 10 ² Ω · cm to 10 ⁵ Ω · cm Layer thickness 10 μm Medium resistance layer 2e; epichlorohydrin rubber Volume resistance value 10 ⁷ Ω · cm to ^{10 10} Ω · cm Layer thickness 180 μm Protective layer 2f; N-methoxymethylated nylon Volume resistance value 10 ⁷ Ω · cm to 10 ¹¹ Ω · cm Layer thickness 5 μm Charging roller 2 weight 70 g, hardness 40 ° to 50 ° (Asker C) Pressing force on the photosensitive drum 1 Total pressure 1000 g In the above charging roller 2, from the core metal 2 a to the tube 2 c
In order to prevent the charge from being uniformly supplied to the tube 2c and the charge amount on the surface of the tube 2c from becoming uneven,
A conductive layer 2d having a low volume resistance value is provided on the outer peripheral surface of the.
The protective layer 2f provided on the outer peripheral surface of the medium resistance layer 2e can prevent the surface layer of the photosensitive drum 1 and the charging roller 2 from being contaminated by using a material having a good compatibility with the surface layer of the photosensitive drum 1. .

The charging roller 2 having the structure as in this embodiment was produced, and the image evaluation such as charging failure due to the durability was performed. After that, the void 2 at the interface between the foam member 2b and the tube 2c.
The state of g was observed. The number of durable sheets is 10,000. The shape of the void 2g in this case is substantially circular as shown in FIG. The results are summarized in Fig. 4. It can be seen from FIG. 4 that the appearance of the charging failure image depends not on the depth of the void 2g but on the size of the outer diameter. Further, it can be seen that charging failure does not occur if the outer diameter is 5 mm or less.

As described above, by adopting a structure in which the outer diameter of the void 2g is 5 mm or less, it is possible to obtain a stable image without a charging failure. <Embodiment 2> In this embodiment, the shape of the void 2g is an elliptical shape elongated in the circumferential direction. The structure of the charging roller 2 is the same as that of the first embodiment. FIG. 5 shows the state of voids 2g on the surface of the foam member 2b of this embodiment.

In this embodiment, the inner surface of the tube 2c is randomly roughened with sandpaper in the circumferential direction and the longitudinal direction, and the core metal 2a and the conductive rubber as the raw material of the foaming member 2b are inserted into the inner surface of the tube 2c to form an integral body. By foaming, an elliptical void 2g elongated in the circumferential direction was formed. If roughened only in the circumferential direction, the air escape path is only in the circumferential direction, so void 2
g is formed over one round.

Similar to Example 1, the correspondence between the maximum diameter of the void 2g and the image evaluation is summarized in FIG. It can be seen that even in the case of an elliptical void 2g that is long in the circumferential direction, an image with poor charging does not occur if the maximum diameter is 5 mm or less. <Embodiment 3> In this embodiment, the shape of the void 2g is an ellipse elongated in the longitudinal direction. The structure of the charging roller 2 is the same as that of the first embodiment. The shape of the void 2g on the surface of the foam member 2b of this embodiment is shown in FIG.

In this embodiment, about 150 grooves having a depth of 0.3 mm are formed in the longitudinal direction of the inner surface of the tube 2c, and the conductive rubber which is the raw material of the core metal 2a and the foaming member 2b is inserted therein. By integrally foaming, the void 2g having an elliptical shape elongated in the longitudinal direction was formed.

Similar to Example 1, the correspondence between the maximum diameter of the void 2g and the image evaluation is summarized in FIG. Example 1 above
It can be seen that, unlike in Example 2, if the void 2g is up to about 7 mm in the longitudinal direction, a defective charging image does not appear.

From the second and third embodiments, it is also found that the charging failure is likely to occur when the void 2g is long in the circumferential direction. <Embodiment 4> In this embodiment, the tube 2c of the charging roller 2 is used.
This is the case where the thickness and hardness of the are changed.

Correspondence between the maximum void diameter and the image of defective charging when the thickness and hardness of the tube 2c are changed is shown in FIGS. 9 and 10, respectively. In each figure, ◯ indicates that a good image was obtained, and x indicates that a poorly charged image was generated.

The charging roller 2 used in FIG.
The hardness is similar to that of the International Rubber Hardness (IRHD) of about 40 °, and the thickness of the tube 2c is appropriately changed. Regarding the thickness of the tube 2c, it is difficult to manufacture a thin tube 2c having a thickness of less than 0.15 mm due to a problem of stability in manufacturing the tube 2c. Further, due to the problem of charging noise, the tube 2c of 0.3 mm or more is unsuitable, so that the void 2 in the range of 0.15 mm to 0.3 mm
The correspondence between the maximum diameter of g and the image was taken. As is apparent from FIG. 9, it is understood that a good image can be obtained when the maximum diameter of the void 2g is 5 mm or less, even if the thickness of the tube 2c changes.

The charging roller 2 shown in FIG. 10 is the same as that in the first embodiment, and the tube 2c has a thickness of 0.25 mm. Hardness refers to International Rubber Hardness (IRHD). Also in hardness, the lower limit is about 3 depending on the material and thickness of the tube 2c.
It is 0 °, and the upper limit is around 50 ° due to the problem of charging noise. I tried to change the hardness in this area, but the borderline of the maximum diameter of void 2g is 5m to obtain a good image.
It was m.

As described above, among the charging rollers 2 having the constitution of the present invention, the effect of the present invention is great in the range of the thickness and hardness of the tube 2c within the above range. <Fifth Embodiment> A fifth embodiment will be described with reference to FIG.

The present embodiment is a process cartridge of an image forming apparatus using the contact type charging member or the charging device described in any one of the first to fourth embodiments as a charging means of an image carrier.

The process cartridge of this embodiment is a drum-shaped electrophotographic photosensitive member (photosensitive drum) as an image bearing member.
1, a charging roller 2 as a contact charging member, a developing device 6,
The four process devices of the cleaning device 9 are integrally incorporated in the cartridge container C. Also,
The apparatus main body of the image forming apparatus to which the process cartridge is mounted is provided with mounting means for mounting the process cartridge in a detachable manner (not shown).

As the charging roller 2, those described in Embodiments 1 to 4 can be used.

In the developing device 6, 60 is a developing sleeve, 61 is a container for storing toner (developer) T, and 62 is a toner stirring rod in the storing container 61. The toner T is stirred and directed toward the developing sleeve 60. Send out. Reference numeral 63 is a developing blade for coating the developing sleeve 60 with the toner T to a uniform thickness.

In the cleaning device 9, 90 is a cleaning blade and 91 is a cleaning blade 90.
It is a toner reservoir for accumulating the toner T collected in.

Reference numeral 11 denotes a drum shutter of the process cartridge, which can be opened and closed freely from a closed state shown by a solid line to an opened state as shown by a dotted line. Drum shutter 11
Is in the closed state shown by the solid line when the process cartridge is taken out from the apparatus main body (not shown) of the image forming apparatus, and the surface of the photosensitive drum 1 that is exposed to the outside is concealed to protect the surface of the photosensitive drum 1. .

When the process cartridge is adhered to the main body of the apparatus, the drum shutter 11 is opened as shown by the dotted line, or the drum shutter 11 is automatically opened during the mounting process of the process cartridge, and the process cartridge is properly opened. When mounted, the exposed surface of the photosensitive drum 1 is in pressure contact with the transfer roller (transfer device, see FIG. 12) 8 on the image forming apparatus main body side.

Further, the process cartridge and the apparatus main body are mechanically and electrically coupled to each other, and the drive mechanism on the apparatus main body side can drive the photosensitive drum 1, the developing sleeve 60, the stirring rod 62 and the like on the process cartridge side. The application of a charging bias to the charging roller 2 on the process cartridge side by the electric circuit on the apparatus main body side, the developing sleeve 60
A developing bias can be applied to the image forming apparatus, and the image forming operation can be executed.

Reference numeral 12 denotes an exposure window provided between the cleaning device 9 of the process cartridge and the developing device 6,
Output laser light (exposure means) 5 from a laser scanner (not shown) on the apparatus main body side passes through the exposure window 12 and enters the process cartridge, and the surface of the photosensitive drum 1 is scanned and exposed.

As described above, the charging roller 2 has the void 2
By setting the maximum diameter of g to 5 mm or less, it is possible to configure a process cartridge that can obtain high-quality image quality without defective charging.

[0052]

As described above, according to the present invention,
By setting the maximum diameter of the voids formed at the interface between the foaming member and the tube forming the charging member to be 5 mm or less, the residual toner that has slipped through the cleaning device during rotation of the image carrier (photosensitive drum) is It is possible to prevent accumulation in the void portion and always obtain a stable and uniform image without charging failure.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating a vertical cross section of a charging member according to a first exemplary embodiment.

FIG. 2 is a schematic view showing a cross section in the core bar direction in the vicinity of the end of the charging member.

FIG. 3 is a perspective view showing the shape of voids on the surface of the foam member.

FIG. 4 is a diagram showing the relationship between the maximum diameter and depth of voids and image evaluation.

FIG. 5 is a perspective view showing the shape of voids on the surface of the foam member of Example 2.

FIG. 6 is a diagram showing the relationship between the maximum diameter and depth of voids and image evaluation.

FIG. 7 is a perspective view showing the shape of voids on the surface of a foam member of Example 3.

FIG. 8 is a view showing the relationship between the maximum diameter and depth of voids and image evaluation.

FIG. 9 is a diagram showing the relationship between the tube thickness and the maximum void diameter in Example 4.

FIG. 10 is a diagram showing a relationship between the hardness of the tube and the maximum diameter of the void.

FIG. 11 is a vertical cross-sectional view showing the configuration of the process cartridge according to the fifth embodiment.

FIG. 12 is a schematic diagram showing the vicinity of a photosensitive drum of a conventional image forming apparatus.

FIG. 13 is a vertical cross-sectional view showing the configuration of a conventional charging roller.

FIG. 14 is a diagram showing a method of manufacturing a charging roller.

FIG. 15 is a diagram showing another method of manufacturing the charging roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image bearing member (charged member, photosensitive drum) 2 Charging member (charging roller) 2B Elastic body 2a Support member (core metal) 2b Foaming member (elastic body) 2b 'Bubble part 2c Tube member (tube) 2d Conductive layer 2e Medium resistance layer 2f Protective layer 2g Void 3 Pressure spring 4 Power supply 5 Exposure means (output laser light) 6 Developing device 7 Transfer material 8 Transfer device 9 Cleaning device C Cartridge container

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koichi Suwa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masashi Ojima 3-30-2 Shimomaruko, Ota-ku, Tokyo No. Canon Inc. (72) Inventor Hiroshi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tetsuya Sano 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. In the company

Claims (4)

[Claims] 1. A charging member for bringing an elastic body held by a supporting member into contact with an image carrier and applying a charging voltage to the supporting member to charge the image carrier through the elastic body, wherein the elastic body is used. Includes a foam member supported by the support member, and a tube member as a resistance layer surrounding the foam member and contacting the image carrier directly or through another layer, the outer member of the foam member Maximum diameter of bubbles on the surface is 5m
The charging member is characterized by having a thickness of m or less. 2. At least the image carrier, the charging member according to claim 1, and a cartridge container for accommodating the image carrier and the charging member integrally, and to the apparatus main body of the image forming apparatus. A process cartridge characterized by being detachably mounted. 3. The image bearing member, the charging member according to claim 1, an exposing unit that exposes the image bearing member to form an electrostatic latent image, and a toner is attached to the electrostatic latent image. An image forming apparatus comprising: a developing device that forms a toner image; and a transfer device that transfers the toner image onto a transfer material. 4. An image forming apparatus, comprising: mounting means for removably mounting the process cartridge according to claim 2.