JPH09319183A - Electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrifying device having a stable electrifying performance for a long period and capable of being served also as a cleaning blade. SOLUTION: An insulated part 11 and a semiconductor part 13 supported by a conductive supporting member 15 are provided on the surface of an image carrier by the contact angle A with the surface. This angle A satisfies the following inequality, tanA<=0.15(W1+Dmin). Wherein, A is the angle formed by an electrifying member in the vicinity of the image carrier contact part and the image carrier, and is calculated on the position away by 1mm from the contact part of the electrifying member with the image carrier, W1 is the width (mm) in the processing direction of the insulated part and Dmin is the minimum discharge width (Dmin=PS/600) decided by the processing speed PS (mm/sec). Moreover, the contact angle A is defined as >=2 degrees similarly to the cleaning blade and the pressure applied to the image carrier on the contact part of the electrifying member is defined as >=0.7g/mm being similarly to the cleaning blade, then the electrifying operation is executed while being in contact with the image carrier surface to clean simultaneously the surface of the image carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device applicable to a copying machine or a printer to which an electrophotographic process is applied, and more particularly to a contact type blade charging device.

[0002]

2. Description of the Related Art In a contact charging device, a semiconductive roll or the like is brought into contact with a charge acceptor, and a direct current or a superimposed voltage of direct current and alternating current is applied to discharge in a minute gap near the contact portion to perform charging. Roller type and blade type charging devices are known. The roll-type contact charging device requires an appropriate rubber resistance for the blade material in order to carry out charging while maintaining the hardness of the rubber to obtain uniform contact with the charge acceptor by appropriate contact pressure. A conductive agent or a cross-linking agent is added to the roll in order to obtain an appropriate rubber resistance, but the conductive agent or the cross-linking agent may be transferred to the charge acceptor upon contact, which may adversely affect the image quality. Further, the outer shape accuracy of the roll is required for uniform charging, and the manufacturing of the roll with high accuracy leads to a decrease in yield and the like, leading to an increase in cost. On the other hand, the blade-type charging device is a device in which an elastic blade or the like is brought into contact with the image carrier and discharge is performed by using a wedge-shaped minute void portion formed by the blade and the image carrier. Has the characteristics that relatively stable microvoids can be formed and can be provided at low cost. The blade type charging device is disclosed in, for example, Japanese Patent Laid-Open Nos. 1-93760 and 4-2600.
No. 68 is disclosed.

[0003]

Unlike the roll type charging device, the blade type charging device has a problem that the contact portion is worn due to friction with the image carrier. In the contact charging device, a resistance layer or a protective layer is provided at a contact portion with the image carrier to prevent pinhole leak and transfer of a conductive agent or a cross-linking agent to the image carrier. However, when the blade type charging device is used for a long period of time, the protective layer may be worn and pinhole leak or transfer of a conductive agent or a cross-linking agent to the image carrier may cause a serious image defect. Furthermore, if the electrode portion is in direct contact with the image bearing member, toner and external additives will gradually adhere to the vicinity of the contact portion between the electrode portion and the image bearing member when used for a long period of time, especially under high humidity. It was confirmed that in such a case, the adhering substance absorbs moisture and the resistance is lowered, and the electric charge may be injected from the electrode portion through the adhering substance into the image carrier to make the charging potential non-uniform.

In order to solve these problems, the applicant of the present invention, in a blade-shaped charging device that elastically contacts the image bearing member to charge the image bearing member, receives a bias voltage and discharges the image bearing member. The semi-conductive part
It has an insulating part that contacts the image carrier so that the semi-conductive part does not come into contact with the surface of the image carrier and that the distance between the semi-conductive part and the surface of the image carrier gradually increases. We developed a charging device. In the case of this blade type charging device, it is qualitatively clear that the wider the discharge region is, the more stable the charging potential is. However, in a device that forms a gap in which the distance from the surface of the image carrier gradually increases, when discharging is performed in a wide air gap with a wide discharge region width, spark discharge may occur and uniform charging may not be possible. found. Further, if the process speed becomes faster, uniform charging may not be obtained under the conditions when used at a slow process speed.

In view of these circumstances, in the present invention, a semiconductive portion which receives a bias voltage and discharges the image carrier, and a semiconductive portion which is not in contact with the surface of the image carrier and the surface of the image carrier. (EN) A charging device having an insulating portion that contacts and positions an image carrier so as to maintain a gap in which the distance gradually increases is provided with stable charging performance for a long period of time.

[0006]

SUMMARY OF THE INVENTION A charging device according to the present invention comprises a semi-conductive portion which receives at least a bias voltage and discharges the image carrier, and a semi-conductive portion which contacts the surface of the image carrier. A charging member having an insulating portion arranged in parallel with a semi-conductive portion for positioning is disposed so that the contact angle A with the surface of the image bearing member is supported by the supporting member at an angle satisfying the following expression (1). The discharge gap is formed such that the distance between the charging member and the surface of the image carrier gradually increases. tanA ≦ 0.15 / (W1 + Dmin) ... Equation 1 A: Calculated at an angle of 1 mm from the contact portion between the charging member and the image carrier at the angle formed by the charging member and the image carrier near the contact portion of the image carrier. W1: Width in the process direction of the insulating portion (mm). Dmin: Minimum required discharge width determined by process speed PS (mm / sec) Dmin = PS / 600 [mm] Further, the contact angle A of the charging member with the surface of the image carrier is 2 degrees or more, and the contact portion of the charging member is It is provided with a structure in which the pressure on the image carrier is 0.7 g / mm or more.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 An example of an electrophotographic process to which the charging device according to the present invention is applied is shown in FIG. The image bearing member (photoreceptor) 50 is charged to a predetermined potential by the charging device 10 for charging the image bearing member 50, and then the image information is exposed (laser beam exposure or the like) by the exposure means 51 to form an electrostatic latent image. Is formed.
The developer is attached to the electrostatic latent image by the developing device 53 to form a visible image. The sheet P sent from the sheet cassette 30 is superposed on the charge receptor (photoreceptor), and the transfer charging device 55
The developer on the image carrier 50 is transferred to the paper P by applying the ions. The developer is fixed on the sheet by the fixing device 57 to form a copied image. On the other hand, the toner remaining on the photoconductor is cleaned by the cleaning blade 59.

2 and 3 illustrate the structure of the charging device 10. The blade type charging device 10 includes an image carrier 50.
An insulating portion 11 is provided at the contact portion with. As the material of the insulating portion 11, a material having a volume resistivity of 10 ¹⁰ Ω · cm or more can be used. In this embodiment, urethane rubber having a high insulating property of 10 ¹² Ω · cm or more is used in consideration of abrasion resistance. Width W of the insulating portion 11 in the process direction (rotational direction of the image carrier)
1 is about 0.05 mm to 2 mm. Here, the width is set to about 0.1 mm to 0.5 mm, which is a desirable width dimension in order to maintain a proper gap for the electric discharge between the semiconductive portions 13 and the image carrier 50 that are arranged in parallel. The thickness dimension is t1.
A semiconductive portion 13 is arranged in parallel on the downstream side of the insulating portion 11 in the process direction.

The semiconductive portion 13 has a volume resistivity of 10 ³ Ω · c.
Materials of m to 10 ¹⁰ Ω · cm can be used, but in consideration of charging uniformity, 10 ⁴ Ω · cm to 10 ⁷ Ω · cm
A material having a volume resistivity of the order of magnitude is used. Semi-conductive layer 1
As the material of 3, the resistance is adjusted by dispersing an electronic conductive agent such as carbon in urethane rubber, the dispersion of carbon in EPDM (terpolymer of ethylene, propylene and diene) rubber, the urethane A material in which an ion conductive agent such as LiClO4 is added, or a material in which an electronic conductive agent such as carbon and an ion conductive agent such as LiClO4 are hybrid-dispersed in urethane rubber or the like are used.
The insulating portion 11 and the semiconductive portion 13 are attached to the conductive support member 15.

The conductive support member 15 is formed of a conductive elastic member having excellent straightness and flatness. For the conductive support member 15, SUS, phosphor bronze plate or the like is used. A desired elasticity can be obtained by the thickness t2 of the conductive support member 15.

As described above, in the charging device including the insulating portion 11, the semiconductive portion 13, and the conductive support member 15, the insulating portion 11 is arranged in contact with the surface of the image carrier 50.
The contact width of the insulating portion 11 with the image carrier 50 is W3 in the process direction. The contact width W3 between the charging device and the image carrier is narrower than the width W1 of the insulating portion 11, and W1> W3. As a result, in the charging device 10, the semiconductive portion 13 is supported without contact with the image carrier 50. The conductive support member 15 has a length L as a free end and is fixed to the holder 17. The bias power source 20 may be connected to the conductive support member 15 or may be via the holder 17. As the bias voltage, a direct current or a direct current superposed with an alternating current is used.

The arrangement of the charging section (blade) of the blade type charging device will be described below. FIG. 4 is a schematic diagram for explaining the setting angle SA and the bite amount N of the blade. The insulating portion 11 and the semi-conductive portion 13, which are adhesively supported by the elastic conductive support member 15, form an angle between the tip of the insulating portion 11 and the surface of the image carrier 50 at a predetermined angle SA.
(See FIG. 4a). The image carrier 50
If there is not, the insulating portion 11 is pressed into contact with the image carrier 50, with the amount of biting that the insulating portion 11 would bite as N. At this time, the charging device 10 bends and the tip of the insulating portion 11 contacts the image carrier 50 in the range of W3 <W1. The charging device 10 configured as described above is connected to the DC power from the bias power source 20.
A bias with AC superimposed on is applied. Charging device 10
A surface electrometer 40 is arranged on the downstream side of to measure the charging potential of the image carrier. Electric discharge occurs between the semiconductive portion 13 and the image carrier 50. The width D of the discharge is determined by the charging device 10 and the image carrier 5.
It is determined by the shape of the gap near the contact portion with 0 and the peak voltage of the AC bias.

Here, the charging state depending on the discharge width will be examined. Adjusting the setting angle SA and the biting amount N to make the gap shape different, the discharge width D from 0.05 mm to 1.
The charging test was performed by changing the scale from 0 mm in 10 steps. The charged state is affected by the process speed PS of the image carrier 50. In this experiment, the process speed is 30mm
/ Sec, 150 mm / sec, and 300 mm / sec.

The results are shown in FIG. Here, an embodiment of each member of the charging device will be shown. Insulation material: Urethane rubber Hardness: 70 ° Width W1: 0.3mm Thickness t1: 2mm Semi-conductive material: LiClO4 added urethane Volume resistance: 10 ⁵ Ω · cm Width W2: 8mm Thickness t1: 2mm Support member Material: Phosphor bronze plate Thickness t2: 0.1 mm The bias conditions to be applied are as follows. DC component Vdc: -650V AC voltage peak value: 2KV AC wave number: 2KHz

The process speed of the image carrier 50 is 30 m.
When it was as slow as m / sec, uniform charging (marked with ◯) was obtained in all discharge widths. However, when the process speed is 150 mm / sec, the discharge width D is 0.3.
Uniform charging was obtained in a region of mm or more. Further, at the process speed of 300 mm / sec, uniform charging was obtained in the region where the discharge width D was 0.5 mm or more. In this way, the discharge width D required to carry out uniform charging differs depending on the process speed. In consideration of this point, in the charging device, it is necessary to determine the blade setting angle SA and the bite amount N.

Next, setting angle SA = 17
In a charging device in which the degree of biting was N = 1.3 mm, the charging voltage was evaluated by changing the peak voltage of the applied voltage. The evaluation result is shown in FIG. The discharge width widens as the peak voltage increases. However, the peak voltage is 2.5V
If it exceeds, uniform charging could not be obtained. Here, the relationship between the discharge width D and the discharge gap H will be examined with the charging member set constant (see FIG. 8). The higher the peak voltage applied to the blade 10B, the larger the discharge width D of the image carrier. As the discharge width D increases and D1 <D2 <D3, the discharge gap H increases and H1 <H2 <H3. In this case, the discharge width D1 is larger than the discharge gap H1.
2. When both discharge gaps H2 were large, charging was better. However, by further increasing the peak voltage,
When the discharge width D = D3 and the discharge gap H = H3, the charging was defective. This is because the discharge width D widens due to the high peak voltage, and spark discharge occurs in a range where the discharge gap H exceeds a predetermined height. Then, looking at the occurrence of spark discharge due to discharge with a high peak voltage, when the discharge gap H exceeds 0.15 mm, spark discharge due to discharge occurred.

As described above, when the charging device is applied to the actual electrophotographic process, in order to carry out uniform charging, the charging device secures the minimum required discharge width D depending on the process speed and the discharge gap. H is 0.15 m
It is necessary to discharge in an air gap area of m or less. Therefore, the charging device of the present invention is configured so that the mounting angle A of the charging device with respect to the image bearing member satisfies the following relationship. tanA ≦ 0.15 / (W1 + Dmin) (1) A (degree): An angle formed by the blade and the image carrier near the contact portion of the image bearing member, and calculated at a position of 1 mm from the contact portion of the blade and the photosensitive member. W1 (mm): width of the insulating portion in the process direction. Dmin (mm): Process speed PS (mm / se
Minimum required discharge width according to c) Dmin = PS / 600 [mm]

Here, the relational expression of Dmin is an empirical equation obtained from the relation between the peak voltage and the process speed (see FIG. 7). The contact angle A of the charging blade is substantially determined by the setting angle SA °, the biting amount N and the free length L of the blade. Here, a method of determining the contact angle A at the setting angle SA ° and the biting amount N will be described with reference to FIG. The blade 10B including the insulating portion 11 and the semiconductive portion 13 is an elastic body and is curved and contacts the image carrier 50. Therefore, this charging device 10 is
The angle A is set at a position 1 mm from the contact portion 11S between B and the image carrier 50. The angle A can be measured by using a camera or the like to photograph the blade from the side, or by pouring silicone rubber or the like into the contact portion between the blade and the image carrier. In this embodiment, the structural analysis is performed using the die-casting method using silicon rubber and the finite element method.

As described above, the charging device shown in this embodiment is
The minimum required discharge width can be secured depending on the process speed, and the problem of poor charging uniformity due to spark discharge does not occur, and stable charging can be maintained for a long time.

Example 2 In this example, the charging device also serves as a cleaning blade in the electrophotographic process (see FIG. 10).
The charging device 100 charges the image carrier 50 and cleans the toner T on the image carrier 50 that has not been transferred to the transfer material P. The mounting angle A of the blade 100B of the charging device 100 forms a good discharge gap with the image carrier 50 so as to satisfy the relational expression (1) described in the first embodiment. Further, in order for the blade 100B to form the discharge gap with the image carrier 50 and to simultaneously clean the toner T, the blade 100B needs to have a cleaning blade arrangement angle. As is well known, the disposition angle A of the cleaning blade needs to satisfy A ≧ 2 °. Further, unless the blade 100B comes into contact with the image carrier 50 with a predetermined pressure, the toner slips from the blade edge and the cleaning action cannot be executed. This type of cleaning blade usually needs to contact the surface of the image carrier 50 with a pressing force of 0.7 g / mm or more. Therefore, the charging blade 100B that also serves as this cleaning blade
, The contact pressure (line pressure) to the image carrier 50 is 0.7.
It is set to be g / mm or more.

A printing test was conducted by using the charging device thus constructed in an electrophotographic process. The test conditions in this case are shown below. Image carrier Organic photoconductor Moving speed (process speed): 300 mm / sec Charging device Setting angle SA: 17 ° Biting amount N: 1.5 mm Angle A: 4.5 ° Bias: dc component −650 V, AC peak-to-peak voltage 2 kV , Frequency 2.5 KHz toner average particle size: 7 μm charging polarity: negative As a result, it was confirmed that good image quality could be obtained in printing 100,000 sheets of the image bearing member, and good charging and cleaning were performed. It was confirmed. As described above, the charging device according to the present embodiment can secure the minimum required discharge width depending on the process speed, and can maintain stable charging for a long time without occurrence of poor charging uniformity due to spark discharge. It was Further, since this charging device can perform charging and cleaning at the same time, it is possible to provide a low cost and space saving charging and cleaning process.

[0022]

In the charging device according to the present invention, the problem of poor charging uniformity due to spark discharge can be solved and the minimum required discharge width can be secured depending on the process speed, so that stable charging can be maintained for a long time. Is. Furthermore, since this charging device can perform charging and cleaning at the same time, a low cost and space saving charging and cleaning process can be provided.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of an electrophotographic process to which the present invention is applied.

FIG. 2 is an explanatory diagram of a charging device.

FIG. 3 is an explanatory view of an arrangement of a charging device.

FIG. 4 is an explanatory diagram of a blade setting method.

FIG. 5 is a configuration diagram in which a measuring device for charging characteristics is provided.

FIG. 6 is a chart of charge evaluation according to discharge width and process speed.

FIG. 7 is a diagram of evaluation of chargeability according to peak voltage and process speed.

FIG. 8 is an explanatory diagram of a relationship between a discharge width and a discharge gap.

FIG. 9 is an explanatory diagram of a blade setting method.

FIG. 10 is a structural explanatory view of an electrophotographic process according to a second embodiment.

[Explanation of symbols]

10 charging device, 11 insulating part, 13 semi-conductive part,
15 conductive support member, 17 holder, 20
Power source, 40 surface electrometer, 50 image carrier.

Claims (3)

[Claims] 1. A semi-conductive portion that receives at least a bias voltage to discharge the image carrier and a semi-conductive portion that contacts the surface of the image carrier and positions the semi-conductive portion are arranged in parallel. A charging member having an insulating portion and a supporting member for supporting the charging member are provided, and the insulating portion is brought into contact with the surface of the image carrier to form a discharge gap in which the distance between the charging member and the surface of the image carrier gradually increases. In the charging device configured as described above, the charging member is arranged on the support member so that the contact angle A with the surface of the image bearing member satisfies the following expression (1). tanA ≦ 0.15 / (W1 + Dmin) ... Equation 1 A: Calculated at an angle of 1 mm from the contact portion between the charging member and the image carrier at the angle formed by the charging member and the image carrier near the contact portion of the image carrier. W1: Width in the process direction of the insulating portion (mm). Dmin: Minimum required discharge width Dmin = PS / 600 [mm] determined by process speed PS (mm / sec) 2. A contact angle A between the charging member and the surface of the image carrier.
The charging device according to claim 1, wherein is 2 degrees or more. 3. The charging device according to claim 1, wherein the pressure on the image carrier at the contact portion of the charging member is 0.7 g / mm or more.