JPH0792776A - Charging member, charger and process cartridge attachable/detachable to/from image forming device - Google Patents

Abstract

PURPOSE:To reduce charging noise and eliminate any poor image due to toner deposition, in a contact charging member. CONSTITUTION:A charging roller 2 has a core metal 2a encircled with an elastic body 2B which is formed with a foaming member 2b and a tube 2c. The tube 2c is thrusted against and brought into contact with a photosensitive drum 1 by a pressurizing spring 3 and a charging bias is applied to the core metal 2a with a power supply 4 so as to uniformly charge the surface of the photosensitive drum 1 via the elastic body 2B. An Asker C hardness on the contact surface of the elastic body 2B with the photosensitive drum 1 is 55 deg. or less and an international rubber hardness standard IRHD is 80 deg. or less so as to reduce charging noise and toner deposition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member for charging an object to be charged such as an image carrier, a charging device, and a process cartridge attachable to and detachable from an image forming apparatus.

[0002]

[Background Art] In contact charging, a charging member to which a voltage is applied is brought into contact with an image carrier (hereinafter, referred to as a photosensitive drum), and charges are directly transferred to the photosensitive drum to make the surface of the photosensitive drum a desired potential. In comparison with a corona discharge device that has been widely used as a charging device, the applied voltage required to obtain a desired potential on the photosensitive drum surface can be lowered, and the charging process The amount of ozone generated in 1 is very small and the need for an ozone removal filter is eliminated, and therefore the configuration of the exhaust system of the device is simplified,
It has advantages such as being maintenance-free and having a simple configuration.

Therefore, for example, in an image forming apparatus such as an electrophotographic apparatus (copier, laser beam printer), electrostatic recording apparatus, etc., as a means for charging a photosensitive member, an image carrier such as a dielectric member, and other photosensitive drums. It is drawing attention as an alternative to a corona discharge device.

In order to perform uniform charging processing in this contact charging method or apparatus, an oscillating voltage in which a DC voltage is superimposed on an AC voltage is applied to the contact charging member, and the contact charging member is brought into contact with the photosensitive drum to perform charging. There is a method.

FIG. 22 shows one embodiment thereof. Reference numeral 1 denotes a photosensitive drum, which is, for example, a drum type electrophotographic photosensitive member or an electrostatic recording dielectric member that is rotationally driven at a predetermined peripheral speed (process speed) in the clockwise direction of arrow R1.

Reference numeral 2 is a conductive roller (charging roller) as a contact charging member. The charging roller 2 is made of solid type rubber such as conductive urethane rubber and EPDM 2r, and has a hardness of 60 to 70 degrees (ASKER-
C). The charging roller 2 is acted on both ends of the cored bar 2a by the pressing force of the pressing spring 3, and the photosensitive drum 1
It is pressed against the surface with a predetermined pressing force, and is driven to rotate in the direction of arrow R2 as the photosensitive drum 1 rotates.

Reference numeral 4 denotes a voltage application power source for the charging roller 2, which is twice the charging start voltage of the photosensitive drum 1 via a contact leaf spring (not shown) brought into contact with the cored bar 2a of the charging roller 2 by the power source 4. A voltage (V which is obtained by superposing the oscillating voltage Vac having the peak-to-peak voltage Vpp and the DC voltage Vdc
(ac + Vdc) is applied to the charging roller 2 to uniformly charge the outer peripheral surface of the photosensitive drum 1 which is rotationally driven.

[0008]

However, the above charging roller has the following problems. That is, since the solid type charging roller has a high hardness, a part of the charging roller may be separated from the photosensitive drum, resulting in charging failure. This charging failure is likely to occur in the central portion of the charging roller in the longitudinal direction.

Further, since the solid type charging roller has a high hardness, when an oscillating voltage is applied, a vibrating sound called "charging sound" is generated due to hitting between the charging roller and the photosensitive drum, which causes an unpleasant sensation. I understood.

As a method of reducing this charging noise, there is a means for inserting a filling material such as metal into the photosensitive drum.
However, there are problems in terms of weight and cost of the filling.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a charging member, a charging device and a process cartridge in which the hardness of the charging member is reduced.

Another object of the present invention is to provide a charging member, a charging device, and a process cartridge which stabilize the contact of the charging member with the member to be charged and perform good charging.

Another object of the present invention is to provide a charging member, a charging device and a process cartridge which reduce charging noise.

Another object of the present invention is to provide a charging member, a charging device, and a process cartridge in which an elastic body of the charging member includes a foam member.

[0015]

To achieve the above object, the present invention provides:
A charging member for charging an object to be charged has a base body and an elastic body supported by the base body and provided on the surface of the charging member. The elastic body covers a foam member and the foam member. A coating layer, and the surface of the charging member has an ASKER-C hardness of 55 ° or less and the surface of the charging member has an international rubber hardness (IRHD) of 80 ° or less. . Alternatively, the present invention applies the above charging member to a charging device and a process cartridge.

[0016]

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

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.
It is a schematic diagram which shows the cross section in the direction along the core metal 2a.

Reference numeral 1 denotes a rotary photosensitive drum having a negative or positive charging electrode as a member to be charged. 2 is a charging roller as a contact charging member.
Metal core 2a made of stainless steel or the like as a supporting member
A foamed member (foamed layer) 2b formed concentrically and in a roller shape on the outer periphery of the cored bar 2a, and a conductive tube 2c having a medium resistance coated on the outer peripheral surface of the foamed member 2b. .

With such a construction, the foaming member 2b is first produced and then the core metal 2a and the tube 2c are inserted (FIG. 3), or the core metal 2a is erected inside the tube 2c and foamed. There is a method (FIG. 4) in which the raw material of the member 2b is inserted into the core metal 2a and foamed in a fixed state. Since the former method causes waviness, deviation, etc. due to insertion, and it is difficult to obtain a stable image, the charging roller of the present invention is manufactured by the latter method.

The tube 2c covering the conductive foam member 2b is substantially separated from the conductive foam member 2b. The same applies to the core metal 2a and the conductive foam member 2b. Furthermore, in order to prevent axial displacement, the tube 2c
The conductive foam member 2b and the core metal 2a and a part of the conductive foam member 2b may be fixed. As a result, even if an oscillating voltage is applied to the cored bar 2a, the heavy cored bar 2a does not vibrate, but only the light conductive foam member 2b and the tube 2c vibrate to strike the photosensitive drum 1, and the energy thereof is It becomes smaller and the charging noise also becomes smaller. Further, since the conductive foam member 2b is likely to have irregularities due to the cells on the surface, covering the tube 2c having a good surface property can prevent charging failure on the image.

Further, since the tube 2c is harder than the conductive foam member, there is an advantage that the charging roller 2 is prevented from being deformed by a force from the outside.

However, due to the hardness of the tube 2c, the charging roller 2 is subjected to a particularly high temperature and high humidity environment (32.5).
At 90 ° C., 90%), toner adheres to the surface of the charging roller 2 and charging failure occurs due to local increase in resistance, which is a new problem.

In this embodiment, the relationship between the Asker C hardness of the charging roller (charging member), the value of the international rubber hardness standard IRHD of the tube member, the charging sound, and the toner fixation will be described.

First, regarding the charging sound, there is a correlation between the sound pressure of the charging sound and the Asker C hardness of the charging roller, and the sound pressure of the charging sound can be lowered by lowering the Asker C hardness. As the Asker C hardness decreases,
This is because the vibration energy of the charging member becomes low. FIG. 5 shows the relationship between Asker C hardness and charged sound pressure when the frequency of the oscillating voltage applied to the charging member (hereinafter referred to as “charging frequency”) is 1500 Hz. FIG. 6 shows the relationship between the charging frequency and the sound pressure when the Asker C hardness of the charging member is 65 ° and 55 °. It is understood from FIGS. 5 and 6 that if the Asker C hardness is 55 ° or less, the charging sound pressure can be 50 dB or less up to the charging frequency of 1500 Hz. According to the study by the present inventors, if the charging sound pressure is 50 dB or less, the charging sound will not be annoying in a normal printing operation.

Next, regarding toner adhesion, it is recognized that toner adhesion to the charging member due to durability has a correlation with the minute hardness of the surface of the charging member (here, the hardness of the tube member), and the minute hardness is low. It was found that the toner adhesion amount was small. It is considered that the reason for this is that the cause of toner adhesion is as follows. That is, in the cleaning device, when residual toner on the photosensitive drum that could not be completely removed or scattered toner in the main body of the device adheres to the surface of the charging roller, if the surface of the charging roller has a high micro hardness, The toner is rubbed at the contact portion and fixed.

FIG. 7 shows a high temperature and high humidity environment (32.5 ° C., 90 ° C.).
%) Of the international rubber hardness standard IRHD (measured by a micro rubber hardness meter manufactured by Wallace, hereinafter referred to as “Wallace hardness”) in relation to toner adhesion. As shown in FIG. 7, the problem of toner sticking can be eliminated by setting the Wallace hardness to 80 ° or less.

A detailed description will be given below with reference to the drawings.

1 and 2, the foam member 2b is, for example, a foam member made of polystyrene / polyolefin / polyester / polyurethane / polyamide or EPDM.
This is a member in which conductive powder such as carbon / tin oxide is dispersed in a flexible member obtained by foaming (terpolymer of ethylene propylene diene) or urethane to adjust the volume resistivity. In this embodiment, carbon is dispersed in foamed polyurethane. Reference numeral 2b 'is a bubble portion (enclosed bubble of air, nitrogen, argon gas, etc.) of this foam member.

As the conductive tube, for example, urethane resin, polyester resin, polyethylene resin,
Fluorocarbon resins such as PFA (perfluoroalkoxy), FET (fluorinated ethylene propylene) and PTFE (polytetrafluoroethylene), synthetic rubbers such as EPDM and styrene butadiene rubber, conductive carbon, tin oxide,
It is formed by extrusion molding or the like after kneading and dispersing conductive powder such as titanium oxide or indium oxide. In this embodiment, a polyester urethane resin in which carbon is dispersed is used.

The specifications of the charging roller 2 in this embodiment are summarized below.

Core 2a: Stainless steel round bar having a diameter of 6 mm and a length of 260 mm Foaming member 2b; Carbon-dispersed polyurethane foam Volume resistance value 10 ² Ωcm to 10 ⁶ Ωcm Layer thickness 2.5 mm, length 230 mm Tube 2c; Polyurethane heat Plastic elastomer Volume resistance value 10 ³ Ωcm to 10 ⁹ Ωcm Layer thickness 250 μm Weight 68 g of the charging roller 2. When the hardness of this charging roller was measured, the Asker C hardness was 42 ° and the Wallace hardness was 70 °. The volume resistivity of the tube 2c is preferably larger than that of the foaming member 2b in order to prevent streak-shaped charging failure due to leak current from the charging roller 2 to the photosensitive drum.

Like the conventional charging roller 2 shown in FIG. 22, the charging roller 2 also holds both ends of the cored bar 2a by bearing members (not shown), and presses the pressing spring 3 toward one direction of the photosensitive drum. The photosensitive drum 1 is urged and pressed against one surface of the photosensitive drum at a predetermined pressing force, in this embodiment, a total pressure of 1000 g, and is rotated by rotation of the photosensitive drum 1. The charging roller 2 is supplied from a power source 4 through a sliding electrode (not shown) in contact with the charging roller core metal 2a. AC voltage; in this embodiment, 2.0 KVpp, 1500 Hz DC voltage; A superposed oscillating voltage (Vac + Vdc) with the DC voltage is applied. As a result, the peripheral surface of the rotary thermosensitive drum 1 is uniformly contact-charged to the target charging potential by the AC application method.

The sound was measured by the charging roller of this embodiment and the conventional solid rubber integral charging roller.

Conventional solid rubber integral charging roller 2
For example, a core metal 2a; a stainless steel rod having a diameter of 6 mm and a length of 260 mm; a rubber roller 2r; a carbon-dispersed solid EPDM conductive rubber; a volume resistance value of 10 ⁵ Ωcm; a layer thickness of 2.8 mm; a length of 230 mm; and a charging roller 2 weight of 120 g. The Asker C hardness of this charging roller was 62 °.

The contact charging device of this embodiment was set in an anechoic chamber, and the generated noise (charging sound) was measured under the above-mentioned oscillating voltage application conditions. The measurement was performed according to ISO 7779, item 6. As a result, the generated charging noise was 68 dB when the conventional solid integral charging roller was used, whereas it was as low as 41 dB in the charging roller of this embodiment. In order to reduce the charging noise as described above, the foaming state of the foaming member may be single foam or continuous foam.

Next, the charging roller of this embodiment was set in a laser beam printer, and a high temperature and high humidity environment (32.5
The image was printed on up to 6000 sheets of A4 paper at 90 ° C. and 90%) and the image was durable.

As a result, toner adhesion on the surface of the charging roller did not occur, and image defects due to poor charging did not occur.

As described above, by setting the Asker C hardness to 55 degrees or less and the international rubber hardness standard IRHD to 80 degrees or less, the charging noise can be sufficiently reduced and the toner on the surface of the charging roller can be reduced. Since it is possible to prevent sticking, it is possible to provide a laser beam printer which can obtain a high-quality image that is quiet and has no harshness.

(Embodiment 2) In the charging roller 2 of this embodiment, the conductive foam member 2b is covered with a tube 2c having a medium resistance, and the tube 2c is provided with a conductive layer 2d and a medium resistance layer 2e.
And a protective layer 2c is further provided on the outer peripheral surface thereof. FIG. 8 is a schematic view showing a vertical cross section of the charging roller of this embodiment.

Protective layer 2f provided on the outer peripheral surface of the medium resistance layer 2e
By using a material having a good compatibility with the surface layer of the photosensitive drum 1, it is possible to prevent the surface layer of the photosensitive drum 1 and the charging roller 2 from being contaminated. As an example of such a protective layer, for example, N-methoxymethylated nylon, polyvinyl butyral resin, polyvinyl chloride resin, polyvinyl alcohol resin, ethylene vinyl acetate resin, polyurethane resin, acrylic resin, or other resin is coated with conductive powder. Dispersed ones are used. In this example, N-methoxymethylated nylon having carbon dispersed therein was used.

In addition, the charging roller 2 of this embodiment has the structure shown in FIG.
As shown in FIG. 3, the taper 2c 'is provided at both ends in the longitudinal direction of the tube 2c.

When the raw material of the foaming member was foamed in the tube without the taper 2c '(FIG. 4), the foaming pressure of the foaming member was significantly lower at both end portions than in the central portion in the longitudinal direction of the tube 2c. . This is because the foaming at the central portion in the longitudinal direction of the tube 2c is the foaming in the closed space, whereas the force acting to foam outward from the opening of the tube 2c acts at both ends. Therefore, the foaming pressure in the tube 2c is reduced accordingly. A foamed member that has been foamed under a low foaming pressure tends to have a larger size of bubbles formed therein, and as a result, the hardness of the foamed member is reduced and the volume resistivity is increased.

Tapers 2 are provided on both ends of the tube 2c in the longitudinal direction.
When c'is attached, the opening of the tube 2c becomes smaller, so that the raw material of the foaming member is prevented from escaping to the outside, and the inner wall of the taper 2c 'portion tends to push back the foaming toward the central portion in the longitudinal direction. Power is born. In this way, the raw material of the foamed member is tapered 2c 'at both ends in the longitudinal direction.
When foaming is performed in the tube 2c provided with a bubble, a foaming pressure similar to that of the central portion in the longitudinal direction can be obtained even at both ends in the longitudinal direction, and the size of the bubbles formed inside the foaming member is in the longitudinal direction. It becomes uniform over the entire area. The foamed member in which the size of the bubbles formed inside is uniform has uniform hardness and volume resistivity. By charging the photosensitive drum with the charging member configured by such a foaming member, the surface potential on the photosensitive drum becomes uniform, and as a result, a good image without uneven charging can be obtained.

FIG. 10 shows the experimental result for determining the proper area of the taper portion. Here, the size of the tapered portion 2c 'is the ratio of the area of the end opening to the cross-sectional area of the tube 2c at the central portion in the longitudinal direction, and the angle α of the tapered portion 2c' with respect to the surface of the photosensitive drum 1 (see FIG. 9). ), The effect was confirmed by confirming the hardness and volume resistivity of the foam member 2b foamed at the longitudinal end of the tube 2c, and further by drawing out. As can be seen from FIG. 10, if the area of the openings at both ends in the longitudinal direction of the tube 2c is 90% or less of the cross-sectional area at the central portion, a uniform image can be obtained, preferably 80% or less. By this, the hardness and volume resistivity of the foam member 2b become uniform in the longitudinal direction and the circumferential direction, and more stable charging is possible. Also, the taper portion 2
If the angle α of c ′ is 5 ° or more, an even image can be obtained. Preferably, the angle α is 20 ° or more so that the hardness and volume resistivity of the foam member 2b in the longitudinal direction and the circumferential direction can be improved. It becomes uniform and more stable charging becomes possible.

The specific specifications of this embodiment will be summarized below.

Foaming member 2b: Carbon-dispersed foamed epichlorohydrin rubber Volume resistance value 10 ² Ωcm to 10 ⁶ Ωcm Layer thickness 2.5 mm, length 230 mm Tube 2c; Polyester urethane thermoplastic elastomer Volume resistance value 10 ³ Ωcm to 10 ⁹ Ωcm Layer thickness 250 μm Conductive layer 2d; N-methoxymethylated nylon dispersed with conductive powder such as carbon and tin oxide Volume resistance value 10 ¹ Ωcm to 10 ⁶ Ωcm Layer thickness 10 μm Medium resistance layer 2e; Epichlorohydrin rubber Volume resistance value 10 ⁷ Ωcm to ^{10 10} Ωcm Layer thickness 200 μm Protective layer 2 f; N-methoxymethylated nylon Volume resistance value 10 ⁷ Ωcm to 10 ¹² Ωcm Layer thickness 5 μm Weight of charging roller 2 70 g Hardness of this charging roller 2 is measured Then, the Asker C hardness was 48 ° and the Wallace hardness was 75 °.

With respect to the charging roller 2, the charging noise was measured and the image forming test was performed in a high temperature and high humidity environment as in the first embodiment. The measurement result of the charging noise was 44 dB, which was small. Further, in the image output test, as in Example 1, toner adhesion did not occur on the surface of the charging roller 2 and a good image was obtained.

(Embodiment 3) In this embodiment, the same charging roller 2 as in Embodiment 2 was used and the tensile stress of the tube 2c was changed to observe the plastic deformation (sag).

Since the charging roller 2 is pressed against the photosensitive drum 1, the more flexible the foaming member 2b of the charging roller 2 is, the more easily it is deformed. If the deformation does not recover, the rotation of the charging roller 2 is shaken at the deformed portion. Occurs, which causes a poorly charged image and image blurring.

Experiments have revealed that the charging roller 2 of the present invention is advantageous for plastic deformation because the tube 2c covers the foam member 2b and greatly depends on the tensile stress of the tube 2c.

FIG. 11 shows the image evaluation of the charging roller 2 of Example 2 in which the sagging amount of the charging roller when the tensile stress of the tube 2c was changed was obtained.

The measuring method of the tensile stress is as follows:
For a sample of the same material as the tube having a width of 10 mm and a width of 10 mm, the tensile portion was set to 50 mm, and measurement was performed using a tensile tester. The pulling speed at this time is 50 mm / mi
The constant speed was n. The load at the time when the elongation of the sample reached 100% was read and defined as F ₁₀₀ . The value obtained by dividing this value by the cross-sectional area is the tensile stress M ₁₀₀ . ((1)
Formula) M ₁₀₀ [kg weight / cm ² ] = F ₁₀₀ [kg weight] / sample cross-sectional area [cm ² ] (1) The measuring method of the amount of sag is as follows. ) Was measured, and after leaving the charging roller 2 against the photosensitive drum 1 at a total pressure of 1000 g for 1 month in an environment of temperature 40 ° C. and humidity 95%, D2 was calculated as shown in FIG. (D1-D
2) was set as a sag amount.

From the results of this experiment, it can be seen that the higher the tensile stress M ₁₀₀ of the tube 2c, the smaller the amount of sag of the charging roller 2. This is a tube 2 with strong tensile stress
Because of the presence of c, the force when the charging roller 2 is pressed against the photosensitive drum 2 is dispersed over a wide area within the tube 2c, and the rapid deformation of the charging roller 2 at the contact portion is alleviated. is there. If the amount of settling is reduced, it is possible to suppress charging failure and image blurring accordingly.

In this embodiment, the sag amount that does not cause image defects is 0.2 mm or less, and the tensile stress M ₁₀₀ of the tube 2c satisfying this condition is 100 kgf / cm ² or more.

As described above, the tube 2c having a tensile stress M ₁₀₀ of 100 kgf / cm ² or more is used to form the charging roller 2 with less sag and excellent surface property. Therefore, it is possible to sufficiently reduce the charging noise, prevent the occurrence of charging failure, and obtain a good image.

(Embodiment 4) In the present embodiment, the same charging roller 2 as in Embodiment 2 is used to evaluate the image such as poor charging of air bubbles formed on the outer surface of the foam member in contact with the back side of the tube 2c. went.

The charging roller 2 of this embodiment foams the raw material of the foaming member as described above with reference to FIG. In that case, since there is no escape route for the air at the interface with the tube, the air accumulates as it is and remains as innumerable bubbles (hereinafter, these bubbles are referred to as voids). This state seems to have good surface appearance at first glance, but when this charging member makes contact with the photosensitive drum and the photosensitive drum rotates, the waste toner that has slipped through the cleaning blade is not transferred between the charging member and the photosensitive drum. It has been found that the waste toner easily enters the portion where the inside interface of the tube of the charging member is a bubble, and the waste toner easily accumulates on the image, resulting in poor charging and black spots.

Although the voids can be eliminated by polishing the surface of the foamed elastic layer, the accuracy of straightness and runout in the longitudinal direction cannot be maintained because the foamed member is polished. And it leads to cost increase.
In this embodiment, the foamed member has an integral skin layer on its surface, and the cells of the foamed member are not exposed. Thus, voids are distinct from cells.

In the present embodiment, in order to solve the above problems, voids 2g having various shapes were formed on the charging roller 2 having the structure of Embodiment 2 and image evaluation such as charging failure due to durability was performed. The number of durable sheets is 10,000.

FIG. 13 shows a case where the void 2g has a substantially circular shape. The results are summarized in FIG. It can be seen from FIG. 14 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. Furthermore, the outer diameter is 5
It can be seen that if the thickness is less than or equal to mm, a poorly charged image does not occur.

Next, a case was observed in which the void 2g had an elliptical shape and was long in the circumferential direction. Foam member 2 in this case
The state of the void 2g on the surface b is shown in FIG.

The inner surface of the tube 2c is randomly roughened in the circumferential direction and the longitudinal direction by sand pepper, and the core metal 2a,
A conductive rubber, which is a raw material of the foaming member 2b, was inserted and integrally foamed to form a void 2g having an elliptical shape and long in the circumferential direction. In the case of roughening only in the circumferential direction, voids 2g are formed all around because the air escape path is only in the circumferential direction.

The correspondence between the maximum diameter of the void 2g and the image evaluation is summarized in FIG. Oval void 2g long in the circumferential direction
It can be seen that in the case of the maximum diameter of 5 mm or less, an image with poor charging does not occur.

Further, the case where the void 2g has an elliptical shape and is long in the longitudinal direction was also observed. The state of the void 2g on the surface of the foam member 2b in this case is shown in FIG.

The height of the inner surface of the tube 2c is 0.
Insert about 150 3mm grooves, and insert metal core 2a into it.
By inserting the conductive rubber, which is the raw material of the foaming member 2b, and integrally foaming, a void 2g having an elliptical shape and long in the longitudinal direction is formed.
made.

The correspondence between the maximum diameter of the void 2g and the image evaluation is summarized in FIG. Different from the above embodiment, void 2g
It can be seen that a charge-defective image does not appear when is up to about 7 mm in the longitudinal direction.

As described above, it is understood that the charging failure is likely to occur when the void 2g is long in the circumferential direction.

Image evaluation was performed on the shapes of the three voids 2g, but in order to always obtain a good image, the maximum diameter of the voids 2g should be 5 mm or less.

Next, the relationship between the void and the image was examined when the thickness and hardness of the tube 2c of the charging roller 2 were changed.

FIG. 19 and FIG. 20 show the correspondence between the void 2g maximum diameter and the charging failure image when the thickness and hardness of the tube 2c are varied. In each figure, a circle indicates that a good image was obtained, and a cross indicates that a poorly charged image was generated.

The charging roller 2 specified in FIG. 19 is the second embodiment.
The hardness of the tube 2c is the same as the above, but the hardness is about 40 degrees in international rubber hardness (IRHD) and the thickness of the tube 2c is 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 the problem of stability in manufacturing the tube 2c. Also, due to the problem of charging noise, 0.3
Since the tube 2c of mm or more is unsuitable, 0.15
The maximum diameter of the void 2g was associated with the image in the range of mm to 0.3 mm. As can be seen from the figure, even if the thickness of the tube 2c changes, the maximum diameter of the void 2g is 5 mm.
It can be seen that a good image is obtained when:

The charging roller 2 shown in FIG. 20 is similar to that of the second embodiment, and the tube 2c has a thickness of about 0.25 mm. Hardness refers to International Rubber Hardness (IRHD). Regarding the hardness, the lower limit of the tube 2c was about 30 degrees, and when the hardness was shaken within a region of about 50 degrees, the border line of the maximum diameter of the void 2g for obtaining a good image was 5 mm. When the tube 2c has an international rubber hardness of less than 30 °, if the charging roller and the photoconductor are left stationary, it is difficult to recover the settling of the charging roller and discharge failure easily occurs. It is good to

As described above, in the charging roller 2, in order to obtain a good image with respect to the void 2g, the maximum diameter of the void 2g should be 5 mm or less, but especially the tube 2c.
When the thickness is 0.15 mm or more and 0.3 mm or less, or the international rubber hardness of the charging roller 2 is 30 degrees or more, the effect is great. This range is where the charging roller 2 can be put to practical use, and the above range is most suitable for obtaining stable production of the tube 2c and the problem of charging noise that occurs when an AC voltage is applied.

The first to fourth embodiments described above may be combined appropriately. In particular, ASKER- on the surface of the charging member
The C hardness is 55 ° or less, the international rubber hardness (IRHD) is 80 ° or less, the tensile stress when the tube member is stretched 100% is 100 kgf / cm ² or more, and the maximum diameter of bubbles on the outer surface of the foam member is It is desirable to set it to 5 mm or less.

Next, the charging members shown in Examples 1 to 4 were
An example in which the image carrier is charged by a charging member incorporated in a process cartridge that can be attached to and detached from the image forming apparatus will be described.

The present embodiment is a process cartridge of an image forming apparatus using a charging member or a charging device as a charging means of an image carrier. FIG. 21 shows the structure of the process cartridge.

The process cartridge of this embodiment includes four process devices including a rotary drum type electrophotographic photosensitive member 1 as an image bearing member, a charging roller 2 as a contact charging member, a developing device 6 and a cleaning device 9. It will be. However, the process cartridge only needs to include at least the photoconductor 1 and the charging member 2.

The charging roller 2 has the same structure as in the first embodiment, the second embodiment, the second embodiment, the third embodiment, or the fourth embodiment.

In the developing device 6, 60 is a developing sleeve,
Reference numeral 61 is a developer (toner), and 62 is a developing blade for coating the developing sleeve 6 with the toner 61 in a uniform thickness.

In the cleaning device 9, 90 is a cleaning blade.

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 broken line. When the process cartridge is taken out from the image forming apparatus main body (not shown), it is in the closed state shown by the solid line, and the externally exposed part surface of the photosensitive drum 1 is hidden to protect the photosensitive drum surface.

When adhering the process cartridge to the main body of the image forming apparatus, the shutter 11 is opened as shown by the broken line, or the shutter 11 automatically opens during the mounting process of the process cartridge, and the process cartridge is properly operated. When it is mounted on, the externally exposed portion surface of the photosensitive drum 1 is in a state of being pressed against the transfer roller 8 on the image forming apparatus main body side.

Further, the process cartridge and the image forming apparatus main body are mechanically and electrically coupled to each other, so that the drive mechanism on the image forming apparatus main body side can drive the photosensitive drum 1 and the developing sleeve 60 on the process cartridge side. Further, it becomes possible to apply a charging bias to the charging roller 2 and a developing bias to the developing sleeve 60 via the electrode contacts on the process cartridge side by the power source (electrical circuit) on the image forming apparatus main body side, and the image forming operation is performed. Is ready to execute.

Reference numeral 5 denotes an output laser beam from a laser scanner (not shown) on the image forming apparatus main body side, which enters the process cartridge and scans and exposes the surface of the rotary photosensitive drum 1.

As described above, by making the charging process detachable as the process cartridge without fixing it to the laser printer main body, the vibration caused by the impact of the charging roller and the photosensitive drum, which is the cause of the charging noise, is generated in the process cartridge. It tends to be transmitted to the whole and the charging sound tends to be amplified. Therefore, there is a drawback that the beat of the charging sound, which has a problem to be solved by the present invention, is amplified and sounds more harsh.

However, by using the charging roller 2 having the above-described structure, even if an oscillating voltage in which a DC voltage is superposed on an AC voltage is applied, a charging noise is hardly generated, so that the charging noise is substantially inaudible. In addition, it is possible to configure a compact process cartridge that can obtain a high-quality image without charging failure or the like.

According to the present invention, the charging noise is set by setting the Asker C hardness of the contact surface of the elastic body of the charging member with the image carrier to 55 degrees or less and the IRHD of the international rubber hardness standard to 80 degrees or less. It is possible to sufficiently reduce the amount of toner, and it is possible to prevent toner from sticking to the surface of the charging member.

[0088] Further, by setting the tensile stress at 100% elongation of the tube member to 100kg weight / cm ² or more, less sag, and excellent in surface properties, it is possible to prevent the occurrence of charging failure.

Further, by setting the maximum diameter of bubbles formed on the outer surface of the foaming member to 5 mm or less, it is possible to suppress the toner accumulation and prevent the generation of the poorly charged image as described above.

As described above, it is possible to provide an image forming apparatus equipped with a charging device, which is capable of obtaining a high-quality image that is quiet and has no harshness.

The oscillating voltage applied to the charging member described above may be a voltage that periodically changes with time,
As the waveform of the oscillating voltage, a sine wave, a triangular wave, a rectangular wave, or the like can be used. Further, the oscillating voltage may be in the form of a superimposed voltage of the AC voltage and the DC voltage, which is formed by repeatedly turning the DC power supply on and off. The peak-to-peak voltage of the oscillating voltage is preferably at least twice as high as the charging start voltage of the charged body in order to prevent uneven charging of the charged body. The charging start voltage is a DC voltage value applied when the charging of the charging target starts, if a DC voltage is applied between the charging member and the charging target.

[0092]

According to the present invention, the Asker C hardness of the contact surface of the elastic member of the charging member with the member to be charged is 55.
By setting the IRHD of the international rubber hardness standard to 80 degrees or less, it is possible to sufficiently reduce the charging noise and prevent toner adhesion on the surface of the charging member.

[0093] Further, by setting the tensile stress at 100% elongation of the tube member to 100kg weight / cm ² or more, less sag, and excellent in surface properties, it is possible to prevent the occurrence of charging failure.

Further, by setting the maximum diameter of the bubbles formed on the outer surface of the foaming member to 5 mm or less, the toner accumulation can be suppressed, and similarly to the above, the generation of the poorly charged image can be prevented.

As described above, it is possible to provide an image forming apparatus such as a laser beam printer which can obtain a high-quality image that is quiet and has no harshness.

[Brief description of drawings]

FIG. 1 is a schematic view showing a vertical cross-sectional view of a charging member of Example 1.

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 diagram showing a method of manufacturing a charging roller.

FIG. 4 is a diagram showing a method of manufacturing a charging roller.

FIG. 5 is a diagram showing a relationship between Asker C hardness and charging sound pressure.

FIG. 6 is a diagram showing a relationship between charging frequency and sound pressure.

FIG. 7 is a diagram showing the relationship between Wallace hardness and toner adhesion.

FIG. 8 is a schematic view showing a vertical cross section of a charging member of Example 2.

FIG. 9 is a schematic diagram showing a cross section in the core bar direction in the vicinity of the end of the charging member.

FIG. 10 is a diagram showing the relationship between the size and angle of the taper portion and the hardness and volume resistivity.

FIG. 11 is a graph showing the relationship between the tensile stress of the tube of Example 3 and the amount of sag of the charging roller.

FIG. 12 is an explanatory diagram of the amount of squat

FIG. 13 is a perspective view showing the shape of voids on the surface of the foam member of Example 4.

FIG. 14 is a diagram showing the relationship between the maximum diameter and depth of voids and image evaluation.

FIG. 15 is a perspective view showing the shape of voids on the surface of the foam member.

FIG. 16 is a diagram showing the relationship between the maximum diameter and depth of voids and image evaluation.

FIG. 17 is a perspective view showing the shape of voids on the surface of the foam member.

FIG. 18 is a diagram showing the relationship between the maximum diameter and depth of voids and image evaluation.

FIG. 19 is a diagram showing a relationship between the tube thickness and the maximum void diameter.

FIG. 20 is a diagram showing a relationship between the hardness of the tube and the maximum diameter of the void.

FIG. 21 is a vertical sectional view showing the structure of a process cartridge.

FIG. 22 is a diagram showing a configuration of a conventional charging roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image bearing member (charged member, photosensitive drum) 2 Charging member (charging roller) 3 Pressure spring 4 Power supply 5 Exposure means 6 Developing device 7 Transfer material 8 Transfer device 9 Cleaning device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masashi Ojima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Koichi Suwa 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 Stock In the company

Claims (41)

[Claims] 1. A charging member for charging a body to be charged, comprising: a base; and an elastic body supported by the base and provided on the surface of the charging member, wherein the elastic body is a foam member.
And a coating layer for coating the foamed member, wherein the surface of the charging member has an ASKER-C hardness of 55 ° or less and the surface of the charging member has an international rubber hardness (IRHD) of 80 °.
The following is a charging member. 2. The charging member according to claim 1, wherein the coating layer includes a tube member. 3. The international rubber hardness (I
The charging member according to claim 1 or 2, wherein RHD) is 30 ° or more. 4. The charging member according to claim 1, wherein a voltage can be applied to the charging member. 5. The charging member according to claim 4, wherein the voltage is an oscillating voltage. 6. The charging member according to claim 4, wherein the voltage has a shape of a superimposed voltage of an AC voltage and a DC voltage. 7. The volume resistivity of the coating layer is higher than the volume resistivity of the foamed member.
To 6 charging members. 8. The charging member according to claim 2, wherein the coating layer includes a conductive layer and a resistance layer in that order outside the tube member. 9. The charging member according to claim ² , wherein the tensile stress when the tube member is stretched 100% is 100 kgf / cm ² or more. 10. The charging member according to claim 2, wherein a maximum bubble diameter formed on the surface of the foamed member on the side closer to the tube member is 5 mm or less. 11. The tube member has a thickness of 0.15 m.
3. The thickness is not less than m and not more than 0.3 mm.
Charging member. 12. The charging member according to claim 2, wherein in the vicinity of the longitudinal end portion of the charging member, the tube member has a taper portion that bends inward toward the longitudinal end portion. 13. The charging member according to claim 1, wherein the charging member has a roller shape. 14. The charging member according to claim 1, wherein the charging member is capable of contacting the charged body to charge the charged body. 15. A charging device for charging a body to be charged, comprising a base member and a charging member supported by the base body, the charging member being capable of contacting the body to be charged for charging the body to be charged. An elastic body provided on the surface of the elastic body, the elastic body including a foaming member and a coating layer covering the foaming member; and a voltage between the charging member and the charged body. And a means for allowing the application of the ASKER-C hardness of 5 on the surface of the charging member.
International rubber hardness of less than 5 ° and on the surface of the charging member (I
RHD) is 80 ° or less, a charging device. 16. The charging device according to claim 15, wherein the coating layer includes a tube member. 17. The charging device according to claim 15, wherein the surface of the charging member has an international rubber hardness (IRHD) of 30 ° or more. 18. The charging device according to claim 15, wherein the voltage is an oscillating voltage. 19. The charging device according to claim 15, wherein the voltage is in the form of a superimposed voltage of an AC voltage and a DC voltage. 20. The charging device according to claim 15, wherein a volume resistivity of the coating layer is larger than a volume resistivity of the foam member. 21. The charging device according to claim 16, wherein the coating layer includes a conductive layer and a resistance layer in that order outside the tube member. 22. The charging device according to claim 16, wherein the tensile stress when the tube member is stretched 100% is 100 kgf / cm ² or more. 23. The charging device according to claim 16, wherein the maximum bubble diameter formed on the surface of the foam member on the side close to the tube member is 5 mm or less. 24. The tube member has a thickness of 0.15 m.
2. The thickness is not less than m and not more than 0.3 mm.
6. Charging device. 25. The charging device according to claim 16, wherein in the vicinity of the longitudinal end portion of the charging member, the tube member includes a taper portion that bends inward toward the longitudinal end portion. 26. The charging device according to claim 15, wherein the charging member has a roller shape. 27. The charging device according to claim 15, wherein the charging device is used for charging an image carrier that carries an image in an image forming apparatus. 28. A process cartridge detachable from an image forming apparatus, comprising: a charged body capable of carrying an image; and a charging member capable of contacting the charged body to charge the charged body, A voltage can be applied between the charging member and the member to be charged by the power source of the main body of the device, and the substrate is supported by the substrate.
An elastic body provided on the surface of the charging member, the elastic body having a foaming member and a charging member having a coating layer for covering the foaming member; ASKER-C hardness is
International rubber hardness of less than 55 ° and the surface of the charging member (I
RHD) is a process cartridge characterized by being 80 ° or less. 29. The process cartridge according to claim 28, wherein the coating layer comprises a tube member. 30. The process cartridge according to claim 28, wherein the surface of the charging member has an international rubber hardness (IRHD) of 30 ° or more. 31. The process cartridge according to claim 28, wherein the voltage is an oscillating voltage. 32. The process cartridge according to claim 28, wherein the voltage is in the form of a superimposed voltage of an AC voltage and a DC voltage. 33. The process cartridge according to claim 28, wherein the coating layer has a volume resistivity higher than that of the foam member. 34. The process cartridge according to claim 29, wherein the coating layer is provided with a conductive layer and a resistance layer in that order outside the tube member. 35. The process cartridge according to claim 29, wherein the tensile stress when the tube member is stretched 100% is 100 kgf / cm ² or more. 36. The process cartridge according to claim 29, wherein the maximum bubble diameter formed on the surface of the foam member on the side closer to the tube member is 5 mm or less. 37. The tube member has a thickness of 0.15 m.
3. The thickness is not less than m and not more than 0.3 mm.
9 process cartridges. 38. The process cartridge according to claim 29, wherein in the vicinity of the longitudinal end portion of the charging member, the tube member has a taper portion that bends inward toward the longitudinal end portion. 39. The process cartridge according to claim 28, wherein the charging member has a roller shape. 40. The process cartridge according to claim 28, wherein the member to be charged is an electrophotographic photosensitive member. 41. The process cartridge according to claim 28, wherein the process cartridge has a developing device for developing the electrophotographic photosensitive member.