JP3475970B2 - Charging device and image forming apparatus having the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a video printer, a facsimile, a copying machine and a display, and more particularly to a charging device used for this apparatus. More specifically, the present invention relates to a charging device that performs a charging process or a charge removing process on a surface of an object to be charged by contacting an object to be charged with a charging member to which a voltage is applied from the outside.

[0002]

2. Description of the Related Art A charging device used in an image forming apparatus for forming an image by an electrophotographic method using a photoconductor as a member to be charged will be described below as an example.

In a charging device for charging the surface of a member to be charged by contacting the member to be charged with a voltage applied from the outside with the member to be charged, the member for charging is brought into contact with the surface of the photosensitive member as the member to be charged. A gap (that is, a discharge gap) is formed in the vicinity of the contact portion between the charging member and the photoconductor, and the photoconductor is charged by the discharge phenomenon generated in the gap. This charging device has attracted attention and has been put to practical use because it has advantages such as a lower power supply voltage and an extremely small amount of ozone generated as compared with a corona charging device.

Here, as a charging member, Japanese Patent Laid-Open No. 55-55
-29837, a conductive fiber brush as disclosed in JP-A-56-132356, a conductive elastic roller as disclosed in JP-A-56-132356, and a conductive blade as disclosed in JP-B-2-14701. was there.

Further, in recent years, a charging device using a flexible film as a charging member has been proposed.

Japanese Unexamined Patent Publication (Kokai) No. 4-86681 discloses a structure in which both ends of a flexible film (described as a sheet in the specification) are supported and the center of the slack portion is brought into contact with the photoconductor. A charging device has been disclosed. Also, USP51
No. 92974 discloses a charging device having a structure in which one end of a flexible film is supported and a free end is brought into contact with a photoconductor. In addition, in USP 5243387,
A charging device has been disclosed in which a tube having an inner diameter larger than the roller diameter is covered around a rotatable roller, the side of the tube farther from the photoconductor is pressed against the roller, and the slack portion is brought into contact with the photoconductor.

Further, in order to ensure uniform charging property, a patent has been filed which defines the surface roughness of the charging member. For example, Japanese Unexamined Patent Publication No. 56-132356 discloses the relationship between the surface roughness of a conductive elastic roller and uneven charging. In U.S. Pat. No. 5,008,706, the relationship of surface roughness between the charging member and the photoconductor is specified. JP-A-2-
In 198468, the maximum roughness range of the charging member is specified.

[0008]

However, Japanese Unexamined Patent Application Publication No.
The charging device disclosed in Japanese Patent No. 86681 is uncertain because the contact state between the charging member and the photoconductor is determined by how the film is loosened. Since the contact state is uncertain, the discharge gap formed near the contact location is also uncertain and unstable. Therefore, there is a problem that the uniformity of charging cannot be obtained. Further, since the contact state of the film is uncertain, there is a problem that the film hits the photoconductor to generate a charging sound.

Further, the charging device disclosed in US Pat. No. 5,243,387 is also uncertain because the contact state between the charging member and the photosensitive member is determined by how the tube is loosened.
Therefore, there is a problem that the uniformity of charging cannot be obtained. Further, there is a problem that the configuration is complicated.

Further, in the charging device disclosed in US Pat. No. 5,192,974, the ridgeline at the free end of the film is slightly deformed, and if the ridgeline is not accurate, the contact between the film and the photoconductor becomes uneven. Become. As a result, the discharge gap formed in the vicinity of the contact portion also becomes non-uniform and poor in stability. Therefore, there is a problem that the uniformity of charging cannot be obtained.

Incidentally, Japanese Patent Laid-Open No. 4-86681 discloses that
It is described that an electric field is generated between the charging member and the conductor layer on the back side of the member to be charged to generate an electric force. However, in this publication, only the electric force is grasped as the cause of the vibration or noise when the AC voltage is superposed, and there is no idea that the electric force is positively used as the pressure contact force.

Therefore, the present invention solves these problems, and an object thereof is to reliably and uniformly maintain the discharge gap formed in the vicinity of the contact portion between the charging member and the photosensitive member. An object of the present invention is to provide a possible charging device.

Another object of the present invention is to provide a charging device which is resistant to frictional deterioration of the photosensitive member or the charging member and which can perform stable and highly reliable charging processing. Another object of the present invention is to provide a charging device in which foreign matter such as toner, toner external additive, and paper dust that has slipped through the cleaning blade is less likely to stay near the contact portion between the charging member and the photoconductor.

Another object of the present invention is to provide an image forming apparatus equipped with a charging device having excellent stability and reliability and capable of obtaining a high quality image.

[0015]

In order to solve the above-mentioned problems, the charging device according to the invention of claim 1 performs a charging process by bringing a charging member to which a voltage is applied from the outside into contact with a member to be charged. In the charging device, the charging member is a structure in which both ends of a flexible film are fixedly supported by support members, and the voltage is applied to the charging region from the contact region between the film and the charged body. The radius of curvature of the film on the downstream side in the moving direction of the charged body is smaller than the radius of curvature on the upstream side in the moving direction of the charged body from the contact area, and the fixed end of the film is formed. When the distance between them is L1 and the length on the curve of the film that gives the maximum distance of the film is L4, L1 <L4, and L1 is 0 ≦ L1 ≦ 1 (mm). To do. Further, the charging device of the invention of claim 2 is characterized in that the film shape is similar to a teardrop.

Further, in the charging device of the third aspect of the invention, the bending moment M of the film is M ≧ 0.002 (kg · mm), where M is M = w · t ³ · E / ( 12 · ρ) w: Effective charging width (mm) t: Film thickness (mm) E: Young's modulus of the film (kg / mm ² ) ρ: Radius of curvature of the film downstream of the contact area between the film and the charged body It is characterized by being.

Furthermore, in the charging device according to the invention of claim 4, the film is selected from at least nylon resin, polyethylene resin, olefin resin, polyester resin, polyurethane resin, epichlorohydrin-ethylene oxide copolymer rubber. It is characterized in that it contains a substance as a constituent.

Further, in the charging device of the invention of claim 5, the resistance value R of the film is 3 × 10 ⁵ (Ω) ≦ R ≦ 1 × 10.
It is characterized in that it is ⁸ (Ω). Further, in the charging device according to the invention of claim 6, the resistance value R of the film is 1 × 10.
It is characterized in that ⁶ (Ω) ≦ R ≦ 3 × 10 ⁷ (Ω). Further, the image forming apparatus of the invention of claim 7 is the image forming apparatus of claim 1.
It is characterized by comprising the charging device according to any one of to.

[0019]

The operation of the charging device of the present invention is as follows.

First, in the invention according to claims 1 to 6, the curvature on the downstream side of the contact portion with the member to be charged is made smaller than that on the upstream side so that the charging member can be charged even when the member to be rotated or voltage is applied. Since the shape of the member is not easily deformed, as a result, it becomes possible to reliably and uniformly maintain the discharge gap formed in the vicinity of the contact portion between the charging member and the body to be charged. Therefore, it is possible to provide a charging device that is unlikely to cause frictional deterioration of the body to be charged or the charging member and that can perform stable and highly reliable charging processing.

[0021]

According to the second aspect of the invention, the shape of the charging member is specifically defined to further improve the stability.

According to the third aspect of the present invention, by setting the properties (bending moment, bending stiffness, thickness, Young's modulus) of the charging member within a predetermined range, it is possible to prevent deformation of the charging member and to make it more stable. Contact can be made.

According to the present invention, the resistance value of the charging member is set within a predetermined range.
An image of excellent quality can be formed by performing stable charging processing. This shows conditions for preventing overcharge and insufficient charge due to charge injection.
In particular, by setting the resistance value range within the range of 1 × 10 ⁶ Ω to 3 × 10 ⁷ Ω, charging is performed mainly by Paschen's discharge, so that extremely stable charging processing can be performed.

[0025]

[0026]

[0027]

In the invention according to claim 7, stability
By providing a highly reliable charging device, there is no overcharge, insufficient charge, or uneven charge, so that a high-quality image can be obtained.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic sectional view showing an embodiment of a charging device according to the present invention.

FIG. 1A is a schematic sectional view of the charging member. The charging member 101 is a flexible film 10
Both ends of No. 2 are supported and fixed by the support members 103 to 105, and the unsupported side of the film 102 is directed vertically downward. The film 102 has a fixed end S
A flexible portion is formed downward from S1 and S2. As shown in the figure, this bending portion has a distance between the fixed ends (fixed ends S1 and S2).
When the straight line distance of 2) is shortened, the shape resembling a tear drop is drawn by the repulsive force against bending.

The charging member 101 shown in FIG. 1 (a) is formed so that the side not supported by the film to be charged 110 is directed to the downstream side in the rotating direction of the film to be charged 110 (arrow in the figure). The contacted state is shown in FIG. As shown, the film 102 exhibits a teardrop-like shape. Then, the film 102 contacts the charged body 110 in the contact region N, and the film 102 in the region P2 on the downstream side of the radius of curvature of the film 102 in the region P1 on the upstream side in the rotation direction of the charged body 110 in the region N. The radius of curvature of the film 102 is smaller. Such a configuration in which the film 102 is brought into contact with the member 110 to be charged is a typical example of the present invention.

Next, an example in which such a charging member is brought into contact with a photosensitive member which is a member to be charged and a charging process is performed will be described.

In FIG. 1B, the charged body 110 is
The undercoat layer 112 and the photosensitive layer 113 are formed in this order on the conductive substrate 111. It is configured to be rotatable in the direction of the arrow by a driving unit (not shown). On the other hand, in the charging device 100, the support member 104 of the charging member 101 is connected to the power source 106. Then, when the charged body 110 is moved in the direction of the arrow and at the same time a voltage is supplied from the power supply 106 to the charging member 101, the charged body 110 is charged.

Here, the charged member 110 is moved at a linear velocity of 30 (m).
While rotating at m / s), a DC voltage Va was supplied to the charging member 101 by the power supply 106, and the surface potential Vs of the charged body 110 immediately after the charging process was measured. However, the surface potential Vs is initialized between the surface potential measurement and the charging process by a discharging means (not shown). The photosensitive layer 113 of the member to be charged 110 used was a function-separated organic photosensitive layer for negative charging, and had a relative dielectric constant of 3.3 and a thickness of 20 (μm).

The shape of the film 102 maintained the shape shown in FIG. 1 (b) even after the charging treatment. That is,
The shape of the film 102 did not change even when the charged body 110 was rotated and a voltage was applied.

The supplied voltage Va and the obtained surface potential Vs
The relationship with is shown in FIG. In the figure, the horizontal axis represents the voltage Va applied to the charging member 101, and the vertical axis represents the surface potential Vs. In the figure, a circle indicates a measurement point, and a solid line is a line connecting the measurement points. From the results, 0 (V)>Va> -565
In the range of (V), the charged body 110 is not charged. That is, the charging start voltage Vth is −565 (V). In the region where the absolute value of Va is 565 (V) or more, the graph is a straight line with a slope of 1. That is, the surface potential Vs (V) of the charged body 110 is Vs = 0 0>Va> −565 Vs = Va + 565 −565 ≧ Va. This can be explained as follows using FIG.

FIG. 3 is a diagram showing a Paschen curve and a relationship curve of the air gap voltage Vg with respect to the air gap distance g. In the figure, the horizontal axis represents the gap distance g between the member to be charged and the charging member, and the vertical axis represents the void voltage Vg or breakdown voltage Vb.
Indicates. A curve 131 (shown by a solid line) is a Paschen's curve showing the breakdown voltage Vb determined by the air gap distance g. A curve 132 (shown by an alternate long and short dash line) is a relationship curve between the air gap distance g and the air gap voltage Vg when the potential difference between the member to be charged and the charging member is relatively large.
(Indicated by a broken line) is a relationship curve between the air gap distance g and the air gap voltage Vg when the limit potential difference in which the discharge occurs exists in the air gap.

The air gap voltage Vg divided into the air gap (discharge gap) existing between the charging member and the surface of the member to be charged is
When the breakdown voltage Vb determined by the gap distance g is exceeded, a discharge phenomenon occurs from the charging member to the body to be charged. More specifically, when the charging member and the surface of the body to be charged gradually come close to each other, the gap distance g decreases. And the voltage Vg
Goes from the point A1 to the point A2, and the air gap voltage Vg decreases as the capacitance of the air gap increases. Then, when the air gap voltage Vg reaches the breakdown voltage Vb (point A2), charges are discharged from the charging member to the body to be charged (discharge phenomenon). As a result, the surface potential of the body to be charged becomes Vc. Then, the discharge phenomenon continues along the Paschen's curve 131 as the air gap distance g decreases, and reaches the point A3. Point A3 is a point where the void voltage Vg does not exceed the breakdown voltage Vb even if the void distance g is further reduced, and the discharge phenomenon ends here. As a result, the charging process is completed, and the body to be charged is charged to the surface potential Vs.

Here, the breakdown voltage Vb (that is, the curve 13
1) is a formula in a region where the gap distance g is larger than 8 (μm), Vb = −312−6.2g ...
It is represented by (1). In addition, the film thickness of the photosensitive layer of the charged body is dpc,
When the relative permittivity of the photosensitive layer is εpc, the void voltage Vg (that is, the curve 132) is expressed by Vg = (Va-Vc) · g / {(dpc / εpc) + g} ... (2) It Note that Va is the voltage applied to the charging member,
Vc is the surface potential of the body to be charged before or during the charging process.

Here, the thickness of the photosensitive layer used in the experiment dpc =
20 (μm), the relative permittivity of the photosensitive layer ε pc = 3.3 is calculated by the formula (2)
To obtain (Va-Vs) and g at the point A3 at which the discharge phenomenon ends (since the surface potential of the charged body at the end of the discharge phenomenon is Vs, Vc is set to Vs in the equation (2). Rewritten). Vb = Vg, Va
If −Vs = Vth and the condition that the curve 131 is in contact with the curve 132 (that is, the condition that the quadratic equation regarding g has a multiple solution) is obtained, Vth = −565 (V) g = 17.4 (μm) . The value of this Vth matches the threshold value shown in FIG.

From the above results, it was confirmed that the charging process of the charging device of the present invention was caused by the discharge phenomenon in the gap (discharge gap) between the charging member and the member to be charged.

Next, the extent of the discharge gap area will be estimated.

For example, the surface potential Vs of the member to be charged is -700.
As an example of charging to (V), when Va = Vs + Vth = −1265 (V), the air gap distance at which the discharge of the point A2 starts is calculated from the equations (1) and (2), and it becomes g = 146 (μm) .

From the above results, in the charging process of the charging device of the present invention, the gap distance between the charging member and the body to be charged is about 1.
It can be seen that the discharge phenomenon is utilized in the region between 50 (μm) and approximately 17 (μm). Therefore, it is necessary to gradually form a region where the distance between the charging member and the surface of the photoconductor is close to each other and the gap distance is approximately 150 (μm) or less over the entire charging region. The charging device of the present invention has a configuration capable of stably forming the discharge gap between the charging member and the photoconductor.

The reason will be described below with reference to FIG.

As described above, in the charging device of the present invention, the film 102 is brought into contact with the member 110 to be charged in the contact area N,
The radius of curvature of the film 102 in the region P2 on the downstream side is smaller than the radius of curvature of the film 102 in the region P1 on the upstream side in the rotation direction of the charged body 110 in the region N.

The reason for forming the contact region N is to form a stable discharge gap between the film 102 and the member 110 to be charged before and after the region N. This region N needs to be stably formed along the axial direction of the body to be charged (that is, in the effective charging width region).

In the case of the charging device of the present invention, the film 102
Has a relatively weak mechanical contact force and contacts the charged body 110 to form a region N. Then, when a voltage is supplied from the power source 106, the film 102 in the region N and the charged body 11
An electrostatic attraction force acts between the conductive substrate 111 and the conductive substrate 111. Due to this electrostatic attraction, the film 102 in the area N is
Abut on the body 110 to be charged.

Here, if the force for forming the region N is only a mechanical force, it is difficult to disperse the force in the axial direction of the charged body so that the film closely follows the charged body. . For example, when unevenness exists on the body to be charged, the mechanical force concentrates on the convex portion. Therefore, although the film contacts the vicinity of the convex portion of the member to be charged, in other regions, a region which does not contact the member to be charged occurs. As a result, the film cannot be made to follow the axial direction of the charged body.

However, when the film is brought into contact with the member to be charged by electrostatic attraction, even if the member to be charged has irregularities, the force acting on the film is substantially equal in both the concave portion and the convex portion. It is possible to closely follow the axial direction of the body to be charged. As a result, a stable discharge gap can be formed. Note that the film is required to have flexibility in order to follow the film well in the axial direction of the body to be charged by electrostatic attraction.

Next, in the region P2 on the downstream side of the region N,
The reason for forming a region having a smaller radius of curvature than the region P1 will be described.

First, since the region P1 on the upstream side of the region N of the film 102 has a large radius of curvature, the discharge gap formed between the film 102 and the member to be charged gradually narrows as it approaches the region N. . In such a discharge gap, the discharge is stably started and continued, and as a result, the surface potential of the member 110 to be charged can always be a stable value.

Further, as described above, the film 1 in the region N is
A force toward the downstream side acts on 02 by the rotation of the charged body 110 or the application of a voltage. By this power,
The film tends to deform downstream. However, when a region having a small radius of curvature is formed in the region P2 on the downstream side of the region N, the force that prevents the deformation of the film 102 is applied to the region P.
Work in the vicinity of 2. Further, the force toward the downstream side increases in proportion to the area of the region N, but by forming a region having a small radius of curvature in the region P2 on the downstream side of the region N, the region N has a minimum required area. Therefore, the force itself toward the downstream side can be reduced. As a result, the film shape does not change.

In addition to the film shape shown in FIG. 1, an example of a shape in which both ends of the film are supported and a force for preventing deformation of the film is generated is shown in FIGS.

FIG. 4 is a schematic sectional view showing another embodiment of the charging device according to the present invention.

In FIG. 4, the film forming the charging member is replaced with a tubular film. The supporting member 203 is put inside the tubular film 202, and the film 202 is put together with the supporting member 203 with other supporting members 20.
4 and the charging member 201 is formed. At this time, the film has fixed ends S3 and S4. Then, the unsupported side of the film 202 is brought into contact with the charged body 110 so as to face the downstream side in the rotation direction of the charged body 110 (arrow in the figure). As shown, the film 202 is
Shows a shape resembling a teardrop. Then, the film 202 contacts the charged body 110 in the contact area N, and the area P2 on the downstream side of the radius of curvature of the film 202 on the area P1 on the upstream side in the rotation direction of the charged body 110 in the area N. The radius of curvature of the film 202 is smaller.

If a tubular film is used, the method of supporting the film on the supporting member can be simplified.

FIG. 5 is a schematic sectional view showing another embodiment of the charging device according to the present invention.

In FIG. 5, the film forming the charging member is replaced with a film having a multi-layer structure. Further, the distance between the fixed ends of the film was set to 0 (mm).

FIG. 11A is a diagram showing a state when the apparatus is not in operation. Both ends of the film 252 in which the resistance layer 254 is formed on the conductive layer 253 are overlapped and adhered to the supporting member 255 to form the charging member 251. The film 252 is installed such that the unsupported side of the film 252 faces the downstream side of the rotation direction of the body 110 to be charged (the broken line arrow in the drawing).
A charging device is configured. A resistance layer 254 is formed on the surface of the film 252 that is in contact with the member 110 to be charged.

In the non-operating state, the film 2
Reference numeral 52 represents a state in which the member to be charged 110 is not in contact, or is in contact with the member to be charged 110 but is not in firm contact therewith. Here, the state where the film is not in strong contact refers to the state where the mechanical contact force of the film is 10 (g / cm) or less.

FIG. 11B is a diagram showing a state during operation. This is a state in which the body to be charged is rotated in the direction of the arrow and a voltage is supplied from a power source (not shown).

By applying a voltage, the power source → supporting member 255 → conductive layer 253 (moving in the plane) → resistive layer 2
The charge (current) moves along a path 54 (movement in the thickness direction). Then, an electrostatic attraction force is generated between the film 252 and the charged body 110, and the film 252 contacts the charged body 110 in the contact area N. By this force, the film 2
52 is slightly displaced toward the charged body 110 side while maintaining its shape. Then, the film 252 follows the axial direction of the member 110 to be charged and is pressed against it. At that time, the film 252 exhibits a shape similar to a tear drop. Then, the radius of curvature of the film 252 in the downstream region P2 is smaller than the radius of curvature of the film 252 in the upstream region P1 in the rotation direction of the charged body 110 in the region N.

In this case, at the start or end of the operation (when the voltage is on or off), the film 252 is slightly displaced, but it is not displaced during the operation.
Region N is extremely stable. This is because the film shape is such that the radius of curvature of the film 252 in the region P2 is smaller than the radius of curvature of the film 252 in the region P1.

FIG. 6 is a schematic sectional view showing another embodiment of the charging device according to the present invention.

FIG. 6 shows a modified method of supporting the film. The charging member 301 of FIG.
Both ends of 02 are fixed ends S5 to the support members 303 and 304,
It is the structure supported so as to become S6. When a voltage is supplied from a power source (not shown), the film 302
An electrostatic attraction force is generated between the charged body 110 and the charged body 110, and this force causes the film 302 to cover the charged body 110 in an area N.
Contact with. The film 302 from the upstream fixed end S5 to the region N in the rotation direction (arrow in the figure) of the member to be charged 110 has a substantially linear region P1 and extends from the region N to the downstream fixed end S6. The film 302 has a region P2 having a small radius of curvature. Also in this case, the radius of curvature of the region P2 is smaller than that of the region P1.

FIG. 11B shows the supporting member 30 of FIG.
4 in the direction of arrow 310, and the charged body 1
The radius of curvature of the region P2 on the downstream side of the rotational direction 10 (arrow in the figure) is smaller than that in FIG.

Compared with FIG. 6A, the charging device shown in FIG. 6B has a smaller radius of curvature in the region P2. Therefore, the force for preventing the deformation of the film is increased, which is more desirable.

As another constitution of the film constituting the charging member of the charging device according to the present invention, a single layer film (that is, a film constituted only by a resistance layer), two layers of a resistance layer and a surface layer There are various variations such as a film and a multilayer film in which a conductive layer and a resistance layer are formed in this order on an insulating base material.

The resistance layer is a layer formed of a conductive material dispersion layer, a conductive resin, or a semiconductive resin. As the conductive material dispersion layer, the following substance groups a) and b) are in a resin selected from the following substance groups c) to f), or a substance having rubber elasticity selected from the following substance groups g) to j): Dispersed or compatible with
It is formed in layers. Examples of the conductive resin include substances selected from the following substance group b). Examples of the semiconductive resin include substances selected from the following substance group c).

The conductive layer plays a role of supplying electric charge (current) from the support member of the charging member to the resistance layer at the portion in contact with the body to be charged. Therefore, the resistance may be lower than that of the resistance layer. Examples of the conductive layer include a metal vapor deposition layer, a conductive particle dispersion layer, and a layer formed of a conductive resin. Examples of the metal vapor deposition layer include layers of metal such as aluminum, indium, nickel, tin, and copper, and alloys vapor-deposited. Examples of the conductive substance dispersion layer include layers formed by dispersing or compatibilizing the following substance groups a) and b) in a resin selected from the following substance groups c) to f). Examples of the conductive resin include substances selected from the following substance group b).

The surface layer is a layer formed on the surface of the film that contacts the member to be charged. Protect the film from abrasion,
It is composed of a substance selected from the following substance groups c) to f), which plays a role of preventing the low molecular weight component from seeping out from the layer below the protective layer and enhancing the releasability of the toner and the like. Further, there may be mentioned those obtained by dispersing or compatibilizing the following substance groups a) and b) in a resin selected from the following substance groups c) to f).

As the insulating base material, the following substance groups d) to f)
The resin selected from

Regarding the resistance values of the resistance layer and the surface layer, it has been found that even if the volume resistivity is specified, it does not correspond one-to-one with the resistance value in actual use, as will be described later. This is because the resistance of the resistance layer and the protection layer generally has a current dependency. For the resistance value of the film,
It is measured by the method described below.

As for the method of forming a film, first, a base material is formed. Here, the base material includes an insulating base material, a conductive layer, and a resistance layer. The base material can be created by heat-melting → dispersing, compatibilizing → extrusion molding the materials that make up the base material into a film shape, or dissolving in a solvent → dispersing, compatibilizing → (polymerization) → extrusion molding. However, there is a method such as forming into a film shape. As a method of forming a conductive layer, a resistance layer, and a protective layer on a substrate, there is a method of dissolving each substance in a solvent → dispersion or compatibility → (polymerization) → dip coating or spray coating.

(Substance group) a) Carbon black (eg furnace black, acetylene black, carbon filler), metal oxide powder (eg ITO powder, SnO ₂ powder), metal, alloy powder (eg Ag powder, Al powder) ), Salt (for example, quaternary ammonium salt, perchlorate) b) Conductive resin such as polyvinylaniline, polyvinylpyrrole, polydiacetylene, polyethyleneimine c) Ethylcellulose, nitrocellulose, methoxymethylated nylon, ethoxymethyl Nylon chloride, copolymer nylon, polyvinylpyrrolidone, resin such as casein, or a mixture of these resins d) polyacrylate, acrylic resin such as polymethacrylate, polystyrene, styrene resin such as poly-1-methylstyrene, butyral resin, Polyvinyl chloride,
Polyvinylidene chloride, polyvinyl fluoride,
Thermoplastic resins such as polyvinylidene fluoride, polyester resins, polycarbonate resins, cellulose resins, polyarylate resins, polyethylene resins, nylon resins and polypropylene resins, or copolymers or mixtures thereof.

E) Polyvinyl alcohol, polyallyl alcohol, polyvinylpyrrolidone, polyvinylamine, polyallylamine, polyvinylacrylic acid, polyvinylmethacrylic acid, polyvinylsulfuric acid, polylactic acid, casein, hydroxypropylcellulose, starch, gum arabic, polyglutamic acid, polyasparagine Water-soluble resins such as acids and nylon resins, or copolymers and mixtures thereof.

F) Thermosetting resins such as epoxy resin, silicone resin, urethane resin, melamine resin, alkyd resin, polyimide resin, polyamide resin and fluororesin.

G) Natural rubber.

H) Silicone rubber, fluororubber, fluorosilicone rubber, urethane rubber, acrylic rubber, hydrin rubber, epichlorohydrin rubber, butadiene rubber, styrene butadiene rubber, nitrile butadiene rubber, isoprene rubber, chloroprene rubber, isobutylene isoprene rubber, ethylene propylene rubber , Synthetic rubbers such as chlorosulfonated polyethylene, thiochol, etc., or blends thereof.

I) Elastomer materials containing styrene resin, vinyl chloride resin, polyurethane resin, polyethylene resin, methacrylic resin and the like.

J) Soft foam materials such as polyurethane foam, polystyrene foam, polyethylene foam, elastomer foam and rubber foam.

Further, the voltage supplied to the charging member of the charging device according to the present invention is not limited to the DC voltage, but may be a voltage obtained by superposing the AC voltage on the DC voltage. Further, instead of supplying voltage, current may be supplied.

The supporting member has a function of supporting the film and a function of supplying a voltage (current) to the film. However, it is not necessary to form all the supporting members with conductive members. For example, in the case of FIG. 1, only the support member 104 may be made of a conductive member, and the support members 103 and 105 may be made of an insulating member.

The characteristics of the charging member required to obtain the above-described structure of the present invention will be described in detail below with reference to specific examples.

(Specific Example 1) As a specific example 1, the result of investigation of the relationship between the cross-sectional shape of the film and the charging performance will be described. Regarding the charging performance, the charging device is mounted on the image forming apparatus and the resolution is 600 (DPI = Dot Per Inc.).
In step h), a 2 × 2 pattern was formed on A4 size recording paper, and the state of uneven charging was examined from the state of the image on the recording paper. Furthermore, the state of the charging device was observed when the image forming apparatus was operating and when it was not operating.

First, the image forming apparatus used in the experiment will be described.

FIG. 7 is a schematic sectional view of the image forming apparatus used in the experiment, and shows an example in which the charging device shown in FIG. 1 is mounted as the charging device.

On a grounded, cylindrical conductive substrate (aluminum tube), an undercoat layer (alumite layer), a photosensitive layer (negative-charging function-separated organic photosensitive layer, photosensitive layer thickness 20 (μ)
m) and a photosensitive layer relative permittivity 3.3) are formed in this order.
Upon receiving the image formation start signal, the charged body 110 having an outer diameter of 30 (mmφ) starts to rotate at 30 (mm / s) in the arrow direction by the conveying means (not shown) (start of operation). A voltage Va = -1.17 (kV) is supplied (energized) from the power supply 106 to the support member 104 of the charging member 102. Then, in the discharge gap on the upstream side of the region N, charges move from the film 102 to the charged body 110 (discharge phenomenon), and the surface of the charged body 110 has a potential Vs≈−600.
It is charged to (V). The effective charging width is 220
(Mm).

Then, a latent image of 600 (DPI) is formed on the charged body 110 by the light 141 emitted from a latent image forming device (not shown). Here, the latent image to be formed has a 2 × 2 pattern. The 2 × 2 pattern means a pattern in which 2 dots × 2 dots square is exposed out of 4 dots × 4 dots square of 600 (DPI). The latent image is reversely developed by the developing device 142. The developing device 142 mainly includes a developing roller, a supply roller that is in sliding contact with the outer periphery of the developing roller, a thin-plate spring-like elastic blade made of metal or resin, and toner. The toner supplied to the developing roller by the supply roller is formed into a thin layer by the elastic blade,
0 is conveyed to the developing area where the developing roller is in pressure contact. In the process, the toner is negatively charged. Then, the toner is selectively developed on the exposed portion of the charged body 110 by the potential contrast (latent image) of the charged body 110 and the developing electric field formed by the developing power source (not shown). The toner developed on the member 110 to be charged is transferred by the transfer device 144 onto the recording paper 143 of A4 size that moves in the arrow direction. The transfer device 144 is mainly composed of a transfer roller that is in pressure contact with the member 110 to be charged and is rotationally driven at substantially the same speed as the member 110 to be charged. By supplying a voltage having a polarity opposite to the charging polarity of the toner to the transfer roller, the toner on the charged body 110 is electrostatically transferred onto the recording paper 143.
Then, the recording paper 143 is fixed by a fixing unit (not shown).
The toner is fixed on the top.

The toner remaining on the member 110 to be charged after the transfer is removed by the cleaning device 145. The cleaning device is mainly composed of a cleaning blade that comes into contact with the member 110 to be charged, and removes the toner remaining on the member 110 to be charged by a mechanical contact force of the cleaning blade. Then, the charged body 110 is charged again by the charging device.

In this way, an image is formed on the recording paper 143.

Now, the charging device used in the experiment will be described with reference to FIG. Note that FIG. 8 is a diagram for explaining attachment parameters of the charging member, and is basically a diagram equivalent to FIG.

The charging devices 1 to 3 shown in Table 1 were prepared. The film was obtained by melt-kneading Nylon resin 90 (wt%) and Furnace Black 10 (wt%).
It was formed by extrusion so as to have a thickness of (μm). When the Young's modulus of the formed film was measured according to JIS K7127, it was 50 (kg / mm ² ).

Here, the distance between the fixed ends S1 and S2 is L1 (mm) (not shown), and the fixed end S1 to the fixed end S
The length of the film 102 reaching 2 is L2 (mm) (not shown), the midpoint of the fixed ends S1 and S2 is a point Q1, the center of the charged body is a point O, and the apex of the charged body 110 is a point. Q2, the distance of the line segment OQ1 is L3 (mm) (not shown), the line segment OQ2
With reference to, the rotation direction of the body to be charged is the positive direction, and ∠
Q1OQ2 is α (°), and ∠S2Q1O is β
(°) Further, on the curve of the film 102, the point Q
The point that is farthest from 1 is the point Q3, and the length that gives the maximum distance of the film 102 in the direction perpendicular to the line segment Q1Q3 is L4 (m
m).

Table 1 shows detailed setting conditions in the charging devices 1 to 3.

[0098]

[Table 1]

First, the states of the charging devices 1 to 3 when operating and not operating were observed.

The states of the charging devices 1 to 3 during operation are shown in FIG.
It shows in (a)-(c). In the same figure (a)-(c),
The charging members are numbered 401, 411, and 421, respectively.
The films correspond to 402, 412, 422.

The contact area (nip) N between the film and the member to be charged during operation is 0.4 (mm) for both charging devices 1 to 3.
Met. Then, a uniform region N is formed in the axial direction of the member to be charged. Further, the radius of curvature of the region P2 of the film during operation is about 0.5 (mm) in all the charging devices 1 to 3, and the radius of curvature of the region P1 is approximately 4 (m).
m), 3 (mm) and 3 (mm). The film shape of the charging devices 1 to 3 when not in operation was the same as the shape of the film when operating, and the shape similar to teardrops was maintained. The regions N were also equal (thus, the non-operating state is not shown in the figure). Further, the film shape during operation and the region N were always stable. The reason for this is that, as described above, a region having a small radius of curvature (a radius of curvature of about 0.5 (mm)) is formed in the region P2, and the region N is 0.4.
(Mm), which is small.

The film shape similar to teardrops is L1 <
It can be obtained by supporting the film on a supporting member so as to have L4.

Next, a 2 × 2 image was formed.

The charging devices 1 to 3 were able to form good and uniform images. The reason for this is as follows. Since the region P1 of the film has a large radius of curvature, the discharge gap formed between the film and the member to be charged gradually narrows as it approaches the region N. As described above, this discharge gap is stable because the shape of the film does not change. Therefore, stable discharge starts and continues,
As a result, uniform charging was possible. Therefore,
A 2 × 2 image also becomes a uniform image.

Next, the force acting between the film of the charging devices 1 to 3 and the member to be charged was measured.

For the measurement, a thread having a spring balance attached to the other end was wound around the circumference of the body to be charged, and the thread was 30 (mm / mm).
The force generated only in the spring when pulled in (s) was measured. The value obtained by dividing the measured value by the coefficient of kinetic friction was taken as the force acting between the film and the body to be charged. The measurement was carried out when no voltage was applied to the charging member (when not operating, mechanical contact force of the film with the member to be charged) and when voltage was applied. The dynamic friction coefficient was measured according to JIS K7125. As a result, the dynamic friction coefficient was 0.3.

The results are shown in Table 2.

[0108]

[Table 2]

As shown in Table 2, both charging devices 1 to 3
The mechanical contact force is weak, and the contact force during operation is also relatively weak. However, during operation, as described above, the electrostatic attraction force works. This electrostatic attraction force causes the film to follow the axial direction of the body to be charged.

When the film is brought into contact with the member to be charged by electrostatic attraction as in the present invention, even if the member to be charged has irregularities, the force acting on the film is substantially equal in both the concave and convex portions. . Moreover, its power does not concentrate on the parts.
Therefore, the film can be made to follow the axial direction of the body to be charged with a relatively weak force. As a result, a stable discharge gap can be formed.

Further, in the charging device of the present invention, the contact force of the charging member with the member to be charged is weak. Therefore, the member to be charged or the charging member is not deteriorated by friction. further,
Foreign substances such as toner, toner external additive, and paper dust that have slipped through the cleaning blade can be made to flow to the downstream side of the region N. Further, the foreign matter is not excessively retained on the upstream side of the region N. Therefore, it is possible to perform stable and uniform charging treatment for a long period of time.

Further, the contact force of the charging member with respect to the member to be charged is weaker when not in operation. Therefore, if a voltage is applied after the rotation of the charged body starts, or if the rotation of the charged body is stopped after the supply of the voltage is stopped, the foreign matter staying in the vicinity of the area N is more effectively downstream of the area N. It is desirable because it can be drained. Alternatively, the same effect can be obtained by temporarily cutting off the voltage supplied to the charging member outside the image area.

(Specific Example 2) As Specific Example 2, the conditions under which a force for preventing the deformation of the film can be generated were examined by focusing on the bending moment of the film. As described above, when the region P2 having a small radius of curvature was formed on the downstream side of the region N, it was examined whether or not there is a relationship between the bending moment of the region P2 and the film blocking force.

Based on the charging device 2 shown in the specific example 1,
Table 3 shows the film material without changing the mounting method of the charging member.
Experiments were carried out by changing the material shown in. Evaluation is specific example 1
I went in the same way. In addition, in Table 3, the value of the charging device 2 is also shown.

Here, the bending moment of the film will be described.

The Young's modulus of the film is E (kg / m
m ² ), thickness t (mm), effective charging width w (mm),
If the radius of curvature is ρ (mm), the second moment of inertia I (mm ⁴ ) and the bending moment M (kg
mm) is a ^{I = w · t 3/12} M = E · I / ρ = w · t 3 · E / (12 · ρ). In the calculation shown in Table 3, ρ = 0.5 (mm) and w = 220 (mm) based on the results of Specific Example 1.

[0117]

[Table 3]

The states of the charging devices 4 to 11 when operating and not operating were observed.

The charging devices 4 to 10 had the same film shape when not in operation and when operating. further,
The film shape during operation and the region N were always stable.

The charging device 11 was slightly deformed so that the film was pulled to the downstream side in the rotation direction of the member to be charged when the operation was started. Then, during the operation, the region N vibrated very slightly. However, the film shape during operation was stable.

Next, a 2 × 2 image was formed.

The charging devices 4 to 10 are good and uniform 2 × 2.
An image could be formed. In the charging device 11, an intermittent low-density portion that extends vertically and thinly was extremely rarely generated, but this was not a problem in practical use.

From the results, it was found that the desirable bending moment range of the film is 0.002 (kg · mm) or more. As a result, a force that prevents the deformation of the film can be generated, and thus the region P1 on the upstream side of the region N can be stably maintained.

(Specific Example 3) As Specific Example 3, the conditions under which the region N can be properly formed in the axial direction of the member to be charged were examined by focusing on the bending stiffness of the film. That is, the flexibility required for the film was investigated.

The experiment was carried out based on the charging device shown in FIG. The following charging devices 12 to 21 were prepared by changing the film material without changing the mounting method of the charging member. Table 4 shows how to attach the charging member according to the first specific example. The evaluation was performed in the same manner as in Example 1.

[0126]

[Table 4]

<Charging Device 12> A resistance layer made of polyurethane having a thickness of 0.04 (mm) in which lithium perchlorate is compatible is formed, and carbon black is dispersed on the back surface thereof to a thickness of 0.005 (mm). The film having a conductive layer made of the polyethylene resin of 1) was used. The resistance of the conductive layer was sufficiently lower than that of the resistance layer. The resistance value of the charging member was R = 4 × 10 ⁶ (Ω).

<Charging Device 13> A resistance layer made of polyurethane having a thickness of 0.07 (mm) in which carbon black is dispersed is formed, and a polyethylene resin having a thickness of 0.005 (mm) in which carbon black is dispersed is formed on the back surface thereof. And a surface layer having a thickness of 0.01 (mm) made of N-methylmethoxylated nylon mixed with citric acid as a cross-linking agent is formed on the surface of the resistance layer (on the side without the conductive layer). The used film was used. For the resistance layer,
The conductive layer has a sufficiently low resistance. The resistance value of the charging member is
It was R = 1 × 10 ⁷ (Ω).

<Charging Device 14> A resistance layer made of a conductive polyurethane resin having a thickness of 0.04 (mm) in which carbon black is dispersed is formed, and a carbon black is dispersed on its back surface to a thickness of 0.005 (mm). A film having a conductive layer made of polyethylene resin was used. In addition,
The resistance of the conductive layer was sufficiently lower than that of the resistance layer. The resistance value of the charging member was R = 8 × 10 ⁶ (Ω).

<Charging Device 15> A film having a resistance layer formed of a conductive polyurethane resin having a thickness of 0.040 (mm) in which carbon black was dispersed was used. The resistance value of the charging member was R = 1 × 10 ⁷ (Ω).

<Charging Device 16> A resistance layer having a thickness of 0.010 (mm) and made of an N-methylmethoxylated nylon layer mixed with melamine as a cross-linking agent was added to 0.025 (mm).
A film formed on a thick polyester substrate was used. The resistance value of the charging member was R = 2 × 10 ⁷ (Ω).

<Charging device 17> A thickness of 0.01 (mm) is formed on a resistance layer (resistive layer having elasticity) made of epichlorohydrin-ethylene oxide copolymer rubber having a thickness of 0.1 (mm) in which carbon black is dispersed. The film which formed the surface layer which consists of N-methyl methoxylated nylon which mix | blended the polypyrrole of was used. In addition, for the surface layer,
The resistance layer has a low resistance. The resistance value of the charging member is R = 2
It was × 10 ⁷ (Ω).

<Charging device 18> A thickness of 0.01 (mm) is formed on a resistance layer (resistive layer having elasticity) made of epichlorohydrin-ethylene oxide copolymer rubber having a thickness of 0.44 (mm) in which carbon black is dispersed. The film which formed the surface layer which consists of N-methyl methoxylated nylon which mix | blended the polypyrrole of was used. The resistance layer had a lower resistance than the surface layer. The resistance value of the charging member is R
= 2 × 10 ⁷ (Ω).

<Charging Device 19> A film was used in which furnace black was dispersed and a polyester resin having a thickness of 0.09 (mm) was formed as a resistance layer. The resistance value of the charging member was R = 1 × 10 ⁷ (Ω).

<Charging Device 20 (Comparative Example)> Thickness 0.07
A conductive layer made of a 0.005 (mm) thick polyethylene resin in which carbon black was dispersed was formed on a 5 (mm) polyester substrate, and N-methylmethoxy containing citric acid as a crosslinking agent was further formed. A film having a resistance layer of 0.02 (mm) in thickness made of synthetic nylon was used. The resistance of the conductive layer was sufficiently lower than that of the resistance layer. The resistance value of the charging member was R = 1 × 10 ⁷ (Ω).

<Charging Device 21 (Comparative Example)> On the resistance layer (resistive layer having elasticity) made of epichlorohydrin-ethylene oxide copolymer rubber having a thickness of 0.6 (mm) in which carbon black is dispersed, a thickness of 0. A film having a surface layer made of N-methylmethoxylated nylon containing 1 (mm) of polypyrrole was used. The resistance layer had a lower resistance than the surface layer. The resistance value of the charging member was R = 2 × 10 ⁷ (Ω).

The bending stiffness of the film will be described below.

The Young's modulus of the film is E (kg / m
m ² ), the thickness is t (mm), and the effective charging width is w (mm), the second moment of inertia I (mm ⁴ ) and the bending stiffness B (kg · mm ² ) of the film are I = w · t a ^{3/12 B = E · I} = w · t 3 · E / 12. In the calculation shown in Table 5, w = 225 (mm)
And The Young's modulus E shown in Table 5 is JIS K7.
It measured according to 127.

[0139]

[Table 5]

The states of the charging devices 12 to 21 in operation and in non-operation were observed. In both cases, the film shape when not in operation was the same as the film shape when in operation. Further, the film shape during operation and the region N were always stable.

Next, a 2 × 2 image was formed. Charging device 1
Nos. 2 to 19 could form a good and uniform 2 × 2 image. However, in the charging devices 20 and 21, a thin low density portion extending vertically and a high density portion extending vertically are generated, and a uniform image (that is, charging) cannot be obtained. This is a problem in practical use.

This is because in the case of the charging devices 12 to 19, the film in the area N is moved so as to follow the charged body by the electrostatic attraction force acting between the film and the conductive substrate of the charged body during operation. Contact. However, in the case of the charging devices 20 and 21,
Because the film is stiff (because it has a large bending stiffness), the film cannot be brought into contact with the charged body by electrostatic attraction, and the film cannot follow the axial direction of the charged body well. it is conceivable that. As a result, it is considered that a stable discharge gap could not be formed and uneven charging occurred.

From the above results, it was found that the bending stiffness of the film needs to be 3.8 (kg · mm ² ) or less.

Further, M: bending moment of film B: bending stiffness of film w: effective charging width (mm) t: film thickness (mm) E: Young's modulus of film (kg / mm ² ) ρ: film and charged Assuming the radius of curvature of the film on the downstream side of the body contact area, the results of Examples 2 and 3 are:

[0145]

[Equation 1]

It is From the inequalities (3) and (4), the relational expression 0.024 · ρ ≦ w · t ³ · E ≦ 45.6 (5) is derived. Here, if w = 220 (mm) and ρ = 0.5 (mm), then the inequality (5) becomes 0.00005 ≦ t ³ · E ≦ 0.21 ... (6) it can. Therefore, the film of the charging member of the charging device of the present invention is preferably a film that satisfies the inequality (6). The material of the film is preferably nylon resin, polyethylene resin, olefin resin, polyester resin, polyurethane resin, epichlorohydrin-ethylene oxide copolymer rubber, or the like. In particular, nylon resin, polyethylene resin, and polyester resin are preferable.

(Specific Example 4) In Specific Example 4, an example is shown in which the mechanical contact force of the film to the member to be charged is 0 (g / cm).

FIG. 10 is a schematic sectional view showing another embodiment of the charging device according to the present invention.

FIG. 14A is a diagram showing a state when the apparatus is not operating. Both ends of the film 502 in which the resistance layer 504 is formed on the conductive layer 503 are overlapped and adhered to the support member 505 to form the charging member 501. In the charging member 501, α is approximately 70 (°) and β is approximately 160 (°).
Will be installed. When installed in this way, an extremely small gap is formed between the film 502 and the member 110 to be charged in the non-operating state.

FIG. 10B is a diagram showing a state during operation. This is a state in which the body to be charged is rotated in the direction of the arrow and a voltage is supplied from a power source (not shown).

In FIG. 15A, by applying a voltage from a power source (not shown), the power source → supporting member 50
Charge (current) moves along a path of 5 → conductive layer 503 (movement in the plane) → resistance layer 504 (movement in the thickness direction). Then, an electrostatic attraction force is generated between the film 502 and the charged body 110, and the film 502 contacts the charged body 110 in the contact area N. This force causes the film 502 to
In the state where the shape is maintained, it is slightly displaced to the charged body 110 side. Then, the charged body 110 is pressed along the axial direction. The film 502 has a shape in which the radius of curvature of the film 252 in the downstream area P2 is smaller than the radius of curvature of the film 502 in the upstream area P1 with respect to the rotation direction of the charged body 110 in the area N.

In the charging device having such a mounting method,
The film 252 makes contact with and separates from the member 110 to be charged during operation and non-operation. When the contact force of the film 252 with respect to the charged body was measured, it was 0 (g / cm) when not operating and 2.4 (g / cm) when operating (note that the film 252 and the charged body 110 were The dynamic friction coefficient was 0.73).

In this case, at the start or end of the operation (when the voltage is on or off), the film 252 is slightly displaced, but it is not displaced during the operation, and the film 252 is not moved during the operation. The area N is extremely stable.

When the film is brought into contact with the member to be charged only by the electrostatic attraction force as in this example, even if the member to be charged has unevenness, the force acting on the film is Almost equal. Moreover, its power does not concentrate on the parts. Therefore, the film can be made to follow the axial direction of the body to be charged with a relatively weak force. As a result, a stable discharge gap can be formed.

Further, the contact force of the charging member with the body to be charged is weak. Therefore, the member to be charged or the charging member is not deteriorated by friction.

Further, the contact force of the charging member to the member to be charged works only when the voltage is applied. Therefore, by applying a voltage after starting the rotation of the charged body, or by stopping the rotation of the charged body after stopping the supply of the voltage,
The foreign matter staying in the vicinity of the region N can be made to flow to the downstream side of the region N. As a result, foreign matter is not retained on the upstream side of the region N. Therefore, it is possible to perform stable and uniform charging treatment for a long period of time.

(Specific Example 5) In Specific Example 5, the resistance value R of the charging member was examined.

Based on the charging device 1 shown in the specific example 1, the film composition ratio, the film thickness, and the effective charging width were changed without changing the mounting method of the charging member. Here, the resistance value R of the charging member was changed by changing the film composition ratio (the composition ratio of the nylon resin and the conductive agent). The film thickness was 45 (μm) and the effective charging width was 225 (mm).

Then, the member to be charged was charged by charging members having different resistance values R, and the charging characteristics were examined. However,
In the present invention, the resistance value R means a resistance when a current required for charging is applied to the charging member. Further, actually, an image forming apparatus shown in Example 1 was used to form 2 × 2, solid white, and solid black images, and the image quality was also examined.

FIG. 11 shows the relationship between the resistance value R of the charging member and the charging characteristics. In FIG. 11, the horizontal axis represents the logarithmic value log (R) (Ω) of the resistance value R of the charging member, and the vertical axis represents the absolute value of the surface potential Vs of the body to be charged. The symbols in the figure represent the measurement environment, □ indicates NN environment (20 ° C, 50% RH), ○ indicates HH environment (35 ° C, 65% RH), Δ indicates LL environment (10 ° C, 15% RH). ).

As shown in FIG. 11, the charging performance differs depending on the environment, but the surface potential V
It can be seen that there is a region where s is constant regardless of the resistance value R. This area is an area where charging is performed by the above-mentioned Paschen's discharge. In this region, the resistance value R of the charging member is within the range of 10 ^{6 to} 3 × 10 ⁷ (Ω).

When the resistance value R is 10 ⁶ (Ω) or less, Pas
Charging by the discharge of chen and charging by so-called charge injection are performed. This is due to the Paschen in the discharge gap formed between the charging member and the body to be charged.
Is charged by the discharge of the
Inside, charging is performed by charge injection. Therefore, the surface potential Vs of the member to be charged is the resistance value R of the charging member.
Has a larger absolute value than the surface potential Vs in the case of 10 ^{6 to} 3 × 10 ⁷ (Ω). Then, as the resistance value of the charging member decreases, the contribution of charging due to charge injection increases, and therefore the absolute value of the surface potential Vs increases. For example, when the resistance value R of the charging member decreases by one digit, the absolute value of the surface potential Vs increases by about 200 (V).

Even if the resistance value R is 10 ⁸ (Ω) or more, Pas
Charging is performed by discharging the chen. However, a phenomenon called "time constant delay" occurs, in which the current required for charging is not supplied in time, and the charging efficiency decreases. Therefore, the surface potential Vs of the member to be charged has a smaller absolute value than the surface potential Vs when the resistance value R of the charging member is 10 ^{6 to} 3 × 10 ⁷ (Ω). Then, as the resistance value R of the charging member increases, the charging efficiency significantly decreases, so that the absolute value of the surface potential Vs becomes smaller. For example, when the resistance value of the charging member increases by one digit, the absolute value of the surface potential Vs decreases by 400 (V) or more.

Next, FIG. 12 shows the relationship between the surface potential Vs and the image quality. In FIG. 12, the vertical axis represents the absolute value of the surface potential Vs, and the horizontal axis represents the item of image quality. The image quality was evaluated by the image density of a solid black image, the image unevenness of a 2 × 2 image, and the degree of white background stain of a solid white image. ○, △, × marks plotted in the figure are good or uneven, respectively.
Staining is not recognized (◯), there is no problem in practical use (Δ), insufficient density or unevenness, and stain is noticeable, which is a practical problem (×). The environment was used as a parameter for each item.

From FIG. 12, when the absolute value of the surface potential Vs increases, the image density decreases, the image unevenness and the degree of white background stain deteriorate, and the absolute value of the surface potential is 740 (V ) It turns out that: Also,
It can be seen that when the absolute value of the surface potential Vs becomes smaller, the degree of image unevenness and white background stain becomes worse, and the absolute value of the surface potential at which the degree is practically no problem is 450 (V) or more. That is, the surface potential Vs required to secure the image quality is −
It can be seen that the range is 740 to -450 (V). The more desirable surface potential depends on the environment, and is -600 (V) in the NN environment, -620 (V) in the HH environment, and L.
It can be seen that it is −580 (V) in the L environment.

When the preferable range of the resistance value of the charging member is determined with reference to FIG. 11, it is 3 × 10 ⁵ to 1 × 10 ⁸ (Ω). More preferably, it is 1 × 10 ^{6 to} 3 × 10 ⁷ (Ω) in a region where charging is performed by Paschen's discharge. When the resistance value R of the charging member is within the above range, it is possible to secure a surface potential that can guarantee image quality.

Here, a method of measuring the resistance value R of the charging member will be described.

In the charging device shown in FIG. 1B, the surface moving speed of the cylindrical electrode, the pressing force of the charging member against the cylindrical electrode, etc., except that the body to be charged is replaced by a conductive cylindrical electrode having the same shape. Are the same as the actual charging conditions. Then, the same current as that required to charge the body to be charged to the predetermined surface potential Vs is passed through the charging member. The resistance value R of the charging member is obtained by measuring the voltage between the charging member and the cylindrical electrode at that time. The most important point of this measuring method is to flow a current necessary for charging through the charging member to obtain the resistance value of the charging member.

The current required for charging can be obtained by measuring the current value during the actual charging process or by the following equation.

I = εpcεowvpVs / dpc where I (μA) is the current necessary to charge to a predetermined surface potential Vs (V), and w (mm) is the effectiveness of the charging member. Charge width, dpc (mm) is the thickness of the photosensitive layer of the charged body, εp
c is the relative dielectric constant of the photosensitive layer of the member to be charged, vp (mm / se
c) is the surface moving speed of the body to be charged, and εo (F / mm) is the dielectric constant of vacuum. Incidentally, in this embodiment, the current required to charge the photosensitive drum to the surface potential Vs = −600 (V) is I = −5.9 (μA).

As is apparent from the above, the resistance of the charging member according to the present invention reflects the state at the time of actual charging, and is different from the simple volume resistivity of the charging member.

More specifically, the resistance value of the charging member depends on the current (or voltage). Generally, as the current changes, so does the resistance. Furthermore, since the charging member is in contact with the body to be charged, the resistance of the charging member during actual charging includes electrical contact resistance, and the contact state between the charging member and the body to be charged. Depends on. For example, if the moving speed of the charged body is changed, the resistance also changes. Therefore,
A resistance measured by applying a current necessary for charging to the charging member and setting the contact state between the charging member and the electrode to be the same as that of the member to be charged reflects the actual state at the time of charging.

Regarding the contents described in Example 5,
The content is not limited to the present invention, but is the content generally applied to a charging device in which a charging member is fixed and an object to be charged is charged. For example, it is applicable to a charging device in which the charging member is a deck brush, a charging device in which the charging member is a blade, and the like.

(Example 2) When a charging member was formed by changing the type of film and an image was formed, stripe-like high density portions (white stripes) were formed in the image in parallel with the traveling direction of the paper. There was a case to do. This is because an overcharged portion was generated for some reason. .

Then, when the film corresponding to the overcharged portion was observed, a protrusion was present on the film surface in the vicinity of the region N. The region including the protrusion was observed with a scanning laser microscope (1LM21 manufactured by Lasertec).

FIG. 13 shows the cross-sectional profile of the film. The solid line in the figure is the cross-sectional profile, and the broken line is the center line. From the figure, measure the height of the protrusion and the size of the protrusion (indicated as height and size in the figure), the height of the protrusion is 6.2 (μ
m), and the size of the protrusion was 83 (μmφ).
The height of the protrusion is the height from the center line.

As described above, when the sudden protrusion is present in the vicinity of the region N, an abnormal spark discharge is generated from the tip of the protrusion toward the charged body. Alternatively, if it exists in the region N, an excessive pressure is applied to that portion, and as a result, electric charges are directly injected into the charged body. It is considered that due to this, an overcharged portion is generated on the member to be charged.

Here, the surface roughness of the film is measured according to JIS B
When measured according to 0601, Rz = 1.2 (μ
m) and Rmax = 1.8 (μm). Where J
The surface roughness defined by ISB0601 is a value obtained by a random sampling test for estimating a population mean. Therefore, it is necessary to extract the reference length (measurement area) from an area without extraordinarily high peaks and deep valleys that are considered to be scratches. Therefore, the reference length is selected by excluding the region of the protrusion that is suddenly present. Therefore, JIS
The surface roughness defined by B0601 does not reflect any sudden protrusions.

In other words, it has been found that uniform charging cannot be performed unless a sudden protrusion that is not reflected in the surface roughness defined by JIS is taken into consideration. Hereinafter, in order to distinguish a sudden protrusion from a surface roughness defined by JIS, the surface roughness defined by JIS is referred to as a base roughness.

Region N of the above-mentioned film and above that,
The surface in the region of 0.5 (mm) downstream was inspected thoroughly with a scanning laser microscope. As a result, in addition to the above-mentioned sudden protrusion, one sudden protrusion having a height of 3.4 (μm) and a size of 42 (μmφ) was confirmed. However, white streaks due to overcharge could not be confirmed in the image of the portion corresponding to this protrusion.

Therefore, the relationship between the sudden protrusion and the charging uniformity was examined. By intentionally forming several sudden projections in the vicinity of the region N, the relationship between the sudden projections and the image was examined.

Table 6 shows a list of the results. In addition, in Table 6,
The height of the intentionally produced protrusion and whether white stripes occurred in the image of the portion corresponding to the protrusion are described. In the image column, ◯: white streaks were not observed, and x: white streaks were observed.

[0183]

[Table 6]

Next, the roughness of the base is Rz = 2.5 (μ
m) and Rmax = 3.6 (μm) were prepared. On this film, several sudden protrusions were intentionally formed near the nip. And this film was evaluated similarly.

Table 7 shows a list of the results.

[0186]

[Table 7]

Here, the height of the protrusion is the height from the center line, but the line obtained by adding the value of Rz / 2 to the center line is used as the reference line and the height from the reference line. The newly defined protrusion height is called the effective protrusion height.

FIG. 14 is a diagram for explaining the defined effective projection height. This figure is a diagram showing the defined effective protrusion height in the cross-sectional profile shown in FIG. In the figure, the solid line is the sectional profile, the broken line is the center line, and the alternate long and short dash line is the reference line. Further, the height from the reference line is the effective protrusion height.

Refocusing Tables 6 and 7, paying attention to the effective protrusion height. The results are shown in Table 8.

[0190]

[Table 8]

From the results shown in Table 8, there is a relation between the effective protrusion height and the image. When the effective protrusion height is 4.4 (μm) or more, the protrusion causes the charged body to be excessively charged. ,
Therefore, it can be seen that white stripe-shaped image defects occur. That is, it can be seen that the height is (Rz / 2 + 4.4) (μm) or more, and no sudden protrusion should exist near the region N.

From this result, when the height of the abrupt protrusion existing in the vicinity of the area N of the charging member is less than (Rz / 2 + 4.4) (μm), abnormal charging can be prevented and uniform charging is possible. Becomes

This discussion can be applied to all contact type charging devices. For example, a roller charging device and a blade charging device.

[0194]

The charging device of the present invention has the following effects.

According to the invention described in claims 1 to 6, it is possible to reliably and uniformly maintain the discharge gap formed in the vicinity of the contact portion between the charging member and the member to be charged.

Further, it is possible to provide a charging device which is unlikely to cause frictional deterioration of the body to be charged or the charging member and which can perform stable and highly reliable charging processing.
Further, it becomes possible to provide a charging device in which foreign matter such as toner, toner external additive, and paper dust that has slipped through the cleaning blade is less likely to stay near the contact portion between the charging member and the photoconductor.

According to the second aspect of the invention, the shape stability of the charging member can be further improved by specifically defining the shape of the charging member.

According to the third aspect of the present invention, it is possible to prevent deformation of the charging member and achieve more stable contact.

According to the fifth and sixth aspects of the present invention, an image of excellent quality can be formed by performing stable charging processing. In particular, by setting the resistance value range within the range of 1 × 10 ⁶ Ω to 3 × 10 ⁷ Ω, the charging is mainly Paschen.
Since it is carried out by the discharge of, it is possible to perform extremely stable charging treatment.

[0200]

[0201]

[0202]

According to the seventh aspect of the present invention, since the charging device having excellent stability and reliability is provided, there is no overcharge, insufficient charge, or uneven charge, so that a high quality image can be obtained. . In addition, foreign matter such as toner, toner external additive, and paper dust that has slipped through the cleaning blade does not stay in the charging device.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a charging device according to the present invention. FIG. 7A is a schematic cross-sectional view of the charging member, and FIG. 6B is a schematic cross-sectional view of a charging device equipped with the charging member of FIG.

FIG. 2 is a diagram illustrating a charging device according to the present invention, in which a voltage Va supplied to a charging member and a surface potential V of a charging target obtained are obtained.
It is a figure which shows the relationship with s.

FIG. 3 is a diagram showing a Paschen curve and a relationship curve of the air gap voltage Vg with respect to the air gap distance g.

FIG. 4 is a schematic cross-sectional view showing another embodiment of the charging device according to the present invention.

FIG. 5 is a schematic sectional view showing another embodiment of the charging device according to the present invention. The figure (a) shows the non-operation state,
FIG. 3B shows a state during operation.

6A and 6B are schematic cross-sectional views showing another embodiment of the charging device according to the present invention.

FIG. 7 is a schematic sectional view of an image forming apparatus equipped with a charging device according to the present invention.

FIG. 8 is a diagram for explaining attachment parameters of a charging member of the charging device according to the present invention.

9 (a) to 9 (c) are schematic cross-sectional views showing a state during operation of the charging device according to the present invention.

FIG. 10 is a schematic sectional view showing another embodiment of the charging device according to the present invention. The figure (a) shows the state of non-operation, and the figure (b) shows the state at the time of operation.

FIG. 11 is a diagram showing a relationship between a resistance value of a charging member and a charging characteristic of the charging device according to the present invention.

FIG. 12 is a diagram showing the relationship between the surface potential of the body to be charged and the image quality in the image forming apparatus equipped with the charging device according to the present invention.

FIG. 13 is a diagram showing a cross-sectional profile of the film surface that has caused a charging failure.

FIG. 14 is a diagram for explaining a defined effective protrusion height.

Front page continued (72) Inventor Akihiko Ikegami 3-5 Yamato, Suwa City, Nagano Seiko Epson Co., Ltd. (72) Inventor ▲ Hama ▼ Takashi 3-5 Yamato, Suwa City, Nagano Prefecture Seiko In Epson Corporation (72) Inventor Kenjiro Yoshioka 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation (56) Reference JP-A-7-104552 (JP, A) JP-A-7-295329 (JP, A) JP 4-86681 (JP, A) JP 7-28296 (JP, A) JP 6-51614 (JP, A) JP 6-51554 (JP, A) Kaihei 5-241423 (JP, A) JP 4-143775 (JP, A) JP 6-35263 (JP, A) JP 5-307315 (JP, A) JP 3-17669 ( JP, A) JP 7-295365 (JP, A) Actual development 7-5149 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/02 G03G 15/16 103

Claims (7)

(57) [Claims] 1. A charging member to which a voltage is applied from the outside
In a charging device that performs a charging process by contacting an object to be charged
The charging member supports both ends of the flexible film.
It is a structure that is fixed and supported by a holding member, and voltage is supplied.
In the state before the contact area between the film and the body to be charged.
The curvature half of the film on the downstream side in the moving direction of the charged body
The diameter is upstream of the contact area in the moving direction of the charged body.
The film shape is smaller than the radius of curvature on the side.
If the distance between the fixed ends of the film is L1 and the length that gives the maximum distance of the film on the curve of the film is L4, then L1 <L4, and L1 is 0 ≦ L1 ≦ 1 (mm ) shall be the feature that it is a
Band collector. 2. A film shape, a charging device according to claim 1, characterized in that the shape similar to a teardrop. 3. The bending moment M of the film is M ≧
The charging device according to claim 1 , wherein the charging device is 0.002 (kg · mm). However, M ^{is, M = w · t 3 ·} E
/ (12 · ρ) w: Effective charge width (mm) t: Film thickness (mm) E: Young's modulus of the film (kg / mm ² ) ρ: Curvature of the film downstream of the contact area between the film and the body to be charged Is the radius. 4. The film contains at least a substance selected from nylon-based resins, polyethylene-based resins, olefin-based resins, polyester-based resins, polyurethane-based resins, epichlorohydrin-ethylene oxide copolymer-based rubbers as a constituent element. The charging device according to claim 3 . 5. The resistance value R of the film is 3 × 10.
^{5 (Ω) ≦ R ≦ 1} × 10 8 (Ω) charging device according to claim 1, characterized in that the. 6. The resistance value R of the film is 1 × 10.
^6. The charging device according to claim 5, wherein ⁶ (Ω) ≦ R ≦ 3 × 10 ⁷ (Ω). 7. An image forming apparatus comprising the charging device according to any one of claims 1 to 6 .