JP2002304041A - Electrifying member, process cartridge and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrifying member constituted so that the slippage of a tube may be prevented by an easy and simple means not using adhesive, besides, soil on the electrifying member by toner may be avoided when using an image forming apparatus, and to provide a process cartridge and the image forming apparatus. SOLUTION: As for the electrifying member 1 constituted by laminating an elastic layer (b) arranged on a conductive substrate (a) with two or more tubes, the surface roughness of the outermost layer tube (d) positioned as the outermost layer among two or more layered tubes is different from the surface roughness of the inner layer tube (c) coming into contact with the elastic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member mainly used in an electrophotographic apparatus, a process cartridge having the charging member, and an image forming apparatus.

[0002]

2. Description of the Related Art In recent years, as a charging device used for an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a charging apparatus of a contact charging system has been adopted. A contact charging type charging device has a charging member that contacts a member to be charged and a high-voltage power supply that applies a voltage to the charging member. The charging device is charged by applying a voltage to a charging member that is arranged in contact with the member to be charged. The body is charged to a predetermined polarity and potential, and the voltage of the power supply can be reduced. In addition, there is an advantage that the generation of corona products such as ozone can be reduced, the structure is simple and the cost can be reduced.

There is a system (DC application system) in which only a DC voltage is applied to a voltage applied to a charging member. However, since charging is performed by discharging from the contact charging member to the member to be charged, charging is started by applying a voltage equal to or higher than a certain threshold voltage (Vth). That is, in the contact charging method, in order to obtain the surface potential Vd of the electrophotographic photoreceptor to be mainly charged in the image forming apparatus, the charging member needs to have Vd + V
That is, a DC voltage higher than required is required. Further, since the resistance value of the contact charging member changes due to environmental fluctuations, it has been difficult to set the potential of the photosensitive member to a desired value.

Therefore, an oscillating electric field having a peak-to-peak voltage of twice (2 × Vth) or more the charging start voltage of the member to be charged when a DC voltage is applied to the contact charging member (the voltage value periodically changes with time) (An electric field to be applied) is formed between the contact charging member and the member to be charged, and the surface of the member to be charged is charged (AC application method). This is for the purpose of accommodating the potential with AC, and the potential of the charged body is A
It converges to Vd, which is the center of the peak of the C voltage, and is not affected by disturbances such as the environment. Therefore, the AC application method can perform more uniform charging, and is used favorably.

Further, the contact charging device is a roller type charging device using a charging member as a roller-shaped member (charging roller) (Japanese Patent Application Laid-Open No. Sho.
No. 91253), blade-shaped member (charged blade)
Such as a blade-type charging device (JP-A-64-24264 and JP-A-56-194349) and a brush-type charging device as a brush-like member (charging brush) (JP-A-64-24264). Are roughly divided into Among them, the charging roller has advantages such that the contact width with the member to be charged can be reduced, friction can be suppressed, and the durability of the member to be charged can be improved.

[0006] Such a charging roller is rotatably held by a bearing and pressed against a member to be charged at a predetermined pressure, and is rotated by the movement of the member to be charged.

As shown in FIG. 1, the charging roller is usually provided with a metal core a provided at the center as a conductive base, a conductive elastic layer b provided in a layer around the metal core a, and It has a multilayer structure having a plurality of protective layers such as a resistance control layer c and a surface layer d provided on the outer periphery, each having a specific function of surface property and electric resistance.

[0008] Of the above layers, the core metal a is a rigid body for maintaining the shape of the roller, and also has a role as a power supply electrode layer. In addition, the elastic layer b is usually 10 ⁴ to 10 ⁹ Ω.
Since it is required to have a volume specific resistance of 1 cm and a function of ensuring uniform contact with the member to be charged by elastic deformation, rubber hardness (JI
SA) A vulcanized rubber having flexibility of 70 degrees or less is used. Conventional charging rollers include a foam type using a rubber foam (or sponge-like rubber) as the elastic layer b and a solid type using no rubber foam.

The protective layers such as the resistive layer c and the surface layer d improve the uniformity of charging of the member to be charged by the additives added when they are formed, and are caused by pinholes on the surface of the member to be charged. A function to prevent the occurrence of leaks, and to prevent toner particles and paper dust from sticking, and also to prevent bleeding of a softener such as an oil or a plasticizer used for lowering the hardness of the elastic layer b. It also has functions. The volume resistance of the protective layers c and d is usually 10 ⁵ to 10 ¹³ Ω ·
cm. As a method for producing the protective layers c and d, a method using a coating liquid such as a dip coating method and a roll coating method is generally used.

However, since the method of coating the coating liquid requires drying, there is a problem that the cost is high due to a capital investment of a drying furnace and an increase in the number of steps by adding a drying step.

As the demand for the charging member increases, the number of coating layers, such as electrode layers and resistance control layers, which are protective layers laminated on the elastic layer tends to increase. When the number of coats is increased, the number of drying steps is required as many as the number of protective layers.

Therefore, recently, a method of manufacturing a charging roller which does not need to be dried and which can be obtained by simply coating a seamless tube 2 as a protective layer as shown in FIG.

That is, the protective layers such as the resistance control layer c and the surface layer d to be laminated on the elastic layer b are formed in advance as a heat-shrinkable tube or a non-heat-shrinkable tube by extrusion molding or the like. As shown in FIG. 2, the inner diameter of the tube 2 is increased by using a tube that contracts by heating or by air or the like. Then, the elastic layer b which is the lower layer thereof
After inserting the unfinished roller 1 ′ provided with the protective layer c on the cored bar a into the widened tube 2, the tube 2 contracts by heat shrinkage or cutting off the air, and the tube 2 is brought into close contact with the lower layer. A large number of layers can be formed on the elastic layer b on the outer periphery of the cored bar a in a short time and with a small number of steps at low cost irrespective of the liquid coating.

[0014]

However, the charging roller manufactured by the method of covering the elastic body b of the roller 1 with the seamless tube 2 forming the protective layers c and d has the following problems.

When the charging roller is incorporated into the image forming apparatus with the tube covered on the elastic body, the charging roller is pressed at the end thereof, so that different forces are applied to the center and the end of the charging roller. Will be. When image evaluation is performed in this state, at the stage when several thousand sheets have passed, a part of the tube is displaced from the elastic layer, causing wrinkles, and the surface of the charging roller is not uniform.

As a result, uneven resistance occurs along the wrinkles on the surface of the charging roller, which appears as a defect on an image. This phenomenon is hereinafter referred to as “tube deviation”. As a method for preventing tube displacement, a method of roughening the surface roughness of the tube, a method of imparting tackiness to the tube, and a method of coating the tube after applying an adhesive to the elastic layer are considered. Can be

However, if the surface roughness of the tube is made rough or the tube is made tacky, dirt such as toner easily accumulates on the charging member with the use of the image forming apparatus, and toner contamination occurs. . When toner contamination occurs, resistance unevenness occurs on the surface of the charging roller, and thus appears as an image defect.

Further, when the adhesive is applied, the steps of applying and drying the adhesive are required, so that the merit of the tube coating that the labor of applying the liquid can be reduced is reduced. Further, since the elastic layer and the tube are deteriorated by the solvent in the adhesive, it is not desirable from the viewpoint of obtaining a uniform charging member in the longitudinal direction and the circumferential direction. Further, when unevenness in application of the adhesive or the like occurs, there is a concern that the portion may become uneven in resistance, which may cause image defects.

Accordingly, an object of the present invention is to provide a charging member, a process cartridge, and an image forming apparatus which prevent tube displacement by a simple means which does not use an adhesive and which avoids toner contamination on the charging member during use. It is to provide.

[0020]

The above object is achieved by a charging member, a process cartridge, and an image forming apparatus according to the present invention. In summary, the first aspect of the present invention relates to a charging member in which at least two or more tubes are coated on an elastic layer provided on a conductive substrate, the charging member being located at the outermost layer among the two or more tubes. A charging member, wherein the surface roughness of the outermost layer tube is different from the surface roughness of the inner layer tube circumscribing the elastic layer.

According to a second aspect of the present invention, there is provided a process cartridge detachable from an image forming apparatus main body, comprising: an electrophotographic photosensitive member; and a process means having at least a charging member acting on the electrophotographic photosensitive member. A process cartridge, wherein an elastic layer provided on a conductive substrate is covered with at least two layers of tubes,
A process cartridge wherein the surface roughness of the outermost layer tube located at the outermost layer of the two or more layers of tubes is different from the surface roughness of the inner layer tube circumscribing the elastic layer.

Here, the process cartridge may further include a developing unit and / or a cleaning unit as the process unit.

According to a third aspect of the present invention, there is provided an image forming apparatus having an electrophotographic photosensitive member and a charging member, wherein the charging member comprises:
An elastic layer provided on a conductive substrate is formed by covering at least two or more layers of tubes. Of the two or more layers of tubes, a surface roughness of an outermost layer tube located at an outermost layer, An image forming apparatus characterized in that a surface roughness of an inner tube that is circumscribed is different from that of an inner tube.

According to one of the first to third embodiments of the present invention, the surface roughness of the inner tube is greater than the surface roughness of the outermost tube, or the surface roughness of the tube provided on the elastic layer Of these, the inner tube has the smallest surface roughness, and the outer tube has the smallest surface roughness.

According to another embodiment of the first to third aspects of the present invention, a difference between the surface roughness of the outermost tube and the surface roughness of the inner tube in terms of surface roughness Rz. Is 1 μm or more and 20 μm or less.

According to another embodiment of the first to third aspects of the present invention, the elastic layer has a crown shape.

According to another embodiment of the first to third aspects of the present invention, the elastic layer is a foam.

According to another embodiment of the first to third aspects of the present invention, the outermost tube has a surface roughness Rz of 0.1 μm to 5 μm, and the inner layer tube has a surface roughness of not more than 5 μm. The surface roughness is a numerical value in the range of 2 μm or more and 25 μm or less in surface roughness Rz.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a charging member, a process cartridge, and an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 5 shows a schematic configuration of an electrophotographic image forming apparatus which is an example of the image forming apparatus of the present invention.

In the image forming apparatus, recording paper P as a recording medium is supplied from a paper supply cassette (not shown), and an image is formed on the electrophotographic photosensitive member 10 in synchronization with the recording paper.

The photosensitive drum 10 is uniformly charged by the charging roller 1 of the charging device 20 of the present invention. Thereafter, a latent image is formed on the electrophotographic photoreceptor 10 by image exposure L from a laser optical system 29 as an exposure device, and toner is supplied to the latent image from a developer container 28 as a developer supply unit. The toner is selectively adhered by the replenished developing device 24 to form a visible image as a toner image. The recording paper P is nipped and conveyed between the electrophotographic photoreceptor 10 and a transfer roller 25 as a transfer device, and the toner image on the electrophotographic photoreceptor 10 is transferred from the transfer roller 25 via the recording paper P to the reverse of the toner. By applying a polarity voltage, the image is transferred onto the recording paper P.

The toner image transferred onto the recording paper P is nipped and conveyed by the fixing device 26 and is fixed on the recording paper P by applying heat and pressure. Next, the recording paper P is conveyed in the discharge direction P ′ and discharged out of the image forming apparatus.

On the other hand, the toner and paper dust remaining on the electrophotographic photosensitive member 10 are removed by a cleaner 27 as a cleaning means.

In the present embodiment, the charging member according to the present invention is:
It is applied as the charging roller 1 constituting the charging device 20 of the electrophotographic photosensitive member 10 in FIG.

The charging roller 1 of the present invention will be described with reference to FIG. 1. An elastic body b is formed on the outer peripheral surface of a conductive substrate a such as a stainless steel core, and semiconductive tubes c and d as protective layers. It is made by coating.

As the elastic body b, a conductive elastic body in which conductive carbon is dispersed in silicone rubber can be used. The conductive elastic body includes rubbers and thermoplastic elastomers such as isoprene rubber, styrene rubber, butadiene rubber, nitrile rubber, chloroprene rubber, butyl rubber, acrylic rubber, urethane rubber, fluorine rubber, ethylene propylene rubber and epichlorohydrin rubber, and graphite. Alternatively, a conductive material such as a metal fine powder and a metal oxide may be added in an appropriate amount.

The elastic body is formed into a tube shape by extrusion molding, and the core metal a is inserted into the elastic body b to form the elastic layer b. The elastic layer b usually has a volume resistivity of 10 ⁴ to 10 ⁹ Ω · cm, and is required to have a function of ensuring uniform contact with the member to be charged, here, the electrophotographic photosensitive member 10 by elastically deforming. Therefore, the rubber hardness (JI
SA) A vulcanized rubber having flexibility of 70 degrees or less is used. In order to make uniform contact with the member to be charged, here the photoreceptor 10, a foam type foam using a rubber foam (or sponge-like rubber) as the elastic layer b is preferable for the charging roller 1. It is.

In this embodiment, on the elastic layer b made of the elastic body b, as a protective layer, a resistance layer c as an inner tube which is a semiconductive seamless tube and a surface layer d which is an outermost tube. Are provided.

According to the present embodiment, each protective layer of the inner layer tube c and the outermost layer tube d provided on the elastic layer b is formed by adding a conductive agent, a surface roughness adjusting agent, etc. to the base resin described below. With the addition of the agent, the inner layer tube is formed as the resistance control layer c and the outermost layer tube is formed as the surface layer d according to the respective purposes. These have the function of improving the charging uniformity of the member to be charged, preventing the occurrence of leaks due to pinholes on the surface of the member to be charged, preventing the toner particles and paper dust from being fixed, and the function of the elastic layer. It also has a function of preventing bleeding such as a softener such as an oil or a plasticizer used for lowering the hardness of b. The volume resistance of the protective layers such as the resistance control layer c and the surface layer d is usually 10 ⁵ to
10 ¹³ Ω · cm.

The seamless tube forming the protective layer is
The heat-shrinkable tube and the non-heat-shrinkable tube are roughly classified according to the coating method, and the present invention can be applied to any of them.

When a heat-shrinkable tube is used, the heat-shrinkable tube is formed to have an inner diameter larger than the maximum outer shape of the tube to be covered, and the object to be covered is inserted inside the tube and heat is applied to shrink the tube to cover the tube. Integrated with the object.

When a non-heat-shrinkable tube is used, thermoplastic elastomer tubes such as thermoplastic styrene elastomers, thermoplastic urethane elastomers, thermoplastic olefin elastomers, thermoplastic amide elastomers, thermoplastic polyester elastomers, and polymer alloys thereof are used. Is used as a base resin, and additives such as a conductive agent are blended according to the purpose of use.

The composition thus obtained is extruded into a tube 2 which is covered by it and has an inner diameter smaller than the minimum outer shape, to obtain a non-heat-shrinkable tube. Referring to FIG. 2, the inner layer tube 2 serving as the resistance layer c is replaced with a core metal a
When coating the base material 1 ′, which is an unfinished roller provided with an elastic layer, air A is blown into the inside of the tube 2 until the inner diameter becomes larger than the maximum outer shape of the elastic layer b of the base material 1 ′. When the base material 1 'is inserted while the tube 2 is inflated and the widening means such as air pressure is shut off, the elasticity of the tube 2 attempts to return to the initial inner diameter, and the tube 2 and the lower elastic layer b adhere to each other. Then, when integrated, the tube 2 becomes the resistance layer c.

On the resistance layer c thus formed, a surface layer d
The same applies when the outermost tube is coated.

At this time, the surface roughness of the resistance layer c as the inner layer tube is different from the surface roughness of the surface layer d as the outermost layer tube provided on the resistance layer c.
There is a difference of 1 μm or more and 20 μm or less in z. In the case of the present embodiment, the surface of the resistance layer c is roughened, and the surface roughness Rz is 2
μm to 25 μm, and using the surface layer d as a release layer so that the surface roughness Rz is 0.1 μm to 5 μm, the surface roughness Rz of the resistance layer c is reduced to the surface roughness of the surface layer d. R
It is made to be larger than z. At this time, the surface roughness R
z is a 10-point average surface roughness Rz defined by JIS.

When the resistance layer c and the surface layer d have the same surface roughness, the conventional tendency that tube slippage occurs when the surface roughness is small is strong. Even if displacement can be prevented, toner contamination will accumulate due to accumulation of dirt such as toner on the charging roller.

In the present invention, 1 is set between the two surface roughnesses Rz.
By providing a difference of 20 μm to 20 μm and roughening either surface, it is difficult to generate tube wrinkles that are likely to occur due to the small surface roughness of either surface. To prevent toner contamination on the
The smooth surface of the two layers adds releasability,
This prevents toner contamination on the roller 1. That is, the defect of the rough surface, the defect of the smooth surface, and the defect of both are alleviated.

Particularly, in the case of this embodiment, since the resistance layer c, which is the inner tube in contact with the elastic layer b, has a large surface roughness,
Tube displacement with the elastic layer b and the surface layer d hardly occurs,
In addition, since the surface roughness of the surface layer d which is closest to the photoreceptor 10 and is easily contaminated with toner is small, it is difficult for the entire roller to be contaminated with toner. Further, since the surface of the surface layer d is smooth, there is little rubbing with the photoreceptor 10 and there is also durability.

The feature of the present invention is that the tube surface in direct contact with the member to be charged such as the photoreceptor and the tube surface in contact with the elastic layer have different surface roughnesses, thereby preventing tube misalignment. By roughening the tube surface of the inner layer tube and reducing the surface roughness of the outermost layer tube, it also prevents image defects due to toner contamination,
The point is that a charging roller having excellent durability stability was obtained.

Experimental Example 1 In this experimental example, a charging roller having the same configuration as the charging roller 1 described with reference to FIGS. 1 and 2 was prepared under the following conditions.

(Preparation of Elastic Body b) A vulcanizing agent and a foaming agent were mixed with EPDM rubber in which conductive carbon was dispersed by two rolls, and formed into a tube by extrusion. When this tube-like molded product was foamed in a vulcanizing tube, the length 2
A sponge tube having a diameter of 40 mm, an inner diameter of 5 mm, and an outer diameter of 15 mm was obtained.

(Insertion of core a into elastic body b) A core a having a length of 240 mm and an outer diameter of 6 mm was inserted into the sponge tube to form an elastic layer b.

(Adjustment of Length of Elastic Layer b)
The sponge elastic layer b was adjusted to a length of 220 mm so that both ends of the core bar a remained 10 mm at a time.

(Polishing of Elastic Layer b) This elastic layer b with a cored bar
Was ground to form a finished elastic layer b having an outer diameter of 11.35 mm.

(Formation of Resistance Control Layer c) Conductive carbon,
A thermoplastic urethane elastomer in which magnesium oxide as an anti-tack agent and urethane particles (radius 5 to 6 μm) as a surface roughness regulator are dispersed is formed into a seamless tube having an inner diameter of 10.2 mm and a thickness of 400 μm by extrusion. A seamless tube to be the resistance control layer c was obtained. At this time, when the 10-point average roughness Rz of the seamless tube was measured, it was 15 μm.

(Formation of Surface Layer d) Conductive carbon and
A thermoplastic styrene elastomer in which magnesium oxide was dispersed as an anti-tack agent was extruded to form a seamless tube having an inner diameter of 10.5 mm and a thickness of 250 μm to obtain a seamless tube as a surface layer. The finished tube has a surface roughness of 10 points average roughness Rz.
It was 5 μm.

(Coating of Resistance Control Layer c and Surface Layer d) FIG.
The method of coating the resistance control layer c and the surface layer d of the charging roller of this experimental example will be described with reference to FIG.

The seamless tube 2 serving as the resistance control layer c blows air in the direction shown by the arrow A, and the inner diameter of the resistance control layer tube 2 is larger than the outer diameter of the base 1 ′ in which the core metal a is inserted into the elastic layer b. Inflate until it becomes larger. When the inner diameter of the tube 2 becomes sufficiently large, the base material 1 ′ is inserted in the direction of arrow B, and when the widening by the air pressure is interrupted, the elasticity of the tube 2 attempts to return to the initial inner diameter. 1 'adheres and integrates.

Thereafter, the surface layer d was coated in the same manner.

In this way, the resistance control layer c and the surface layer d can be provided by a simple method without depending on the method of coating the coating liquid, and the elastic layer can be formed without using an adhesive or the like. b and the resistance control layer c can be adhered to each other.

The charging roller 1 was brought into contact with the electrophotographic photosensitive member 10 to obtain a contact type charging device in which a pressing force of 500 g was applied to both ends of the core a.

This contact-type charging device is connected to the electrophotographic photosensitive member 1
When the image evaluation was performed by incorporating the image forming apparatus shown in FIG. 5 as the charging device 20 of 0, the image was good over the entire length of the charging area. Further, when the image evaluation was continued, A4
Even after printing 10,000 sheets, the image was very good without any deterioration.

Comparative Example 1 The charging roller 11 in this comparative example did not disperse urethane particles as a surface roughness adjusting agent in the resistance control layer c as shown in FIG. The configuration is exactly the same as that of the charging roller 1 of Experimental Example 1 except that the configuration is such that the 10-point average roughness Rz is 2.5 μm.

Therefore, in this comparative example, the surface roughness of the resistance layer c and the surface layer d are the same when Rz = 2.5 μm.

The charging roller 11 is brought into contact with the photoreceptor 10, and a contact-type charging device in which a pressing force of 500 g is applied to both ends of the core bar a is assembled at the position of the charging device 20 of the image forming apparatus of FIG. When the image evaluation was performed, the initial image was good. However, when the image evaluation was continued and 5000 sheets of A4 size were printed, an abnormal image such as a streak occurred at the longitudinal end of the halftone image. .

When the surface of the charging roller 11 at that time was observed, it was confirmed that wrinkles approached the end of the charging roller 11. The shape of the wrinkle corresponded to the shape of the abnormal image on the halftone image.

This is because the surface roughness of the tube is small due to pressing and rotating the charging roller 11 against the photoreceptor 10, so that a deviation occurs between the tube and the elastic layer a, and the tube is wrinkled. And wrinkles appear on the image as uneven resistance.

Comparative Example 2 The charging roller 12 in this comparative example was prepared by dispersing urethane particles as a surface roughness adjuster in a material for a surface layer d as shown in FIG. Rz is 15
The configuration is the same as that of the charging roller 1 of Experimental Example 1 except that the charging roller 1 is manufactured so as to have a thickness of μm.

That is, in Comparative Example 2, in order to prevent image defects such as wrinkles due to tube deviation in the charging roller 11 of Comparative Example 1, the surface roughness of both the resistance layer c and the surface layer d was increased to reduce the surface roughness. The charging roller 12 made at Rz = 15 μm is used.

The charging roller 12 is connected to the electrophotographic photosensitive member 10.
, And a contact charging device in which a pressing force of 500 g is applied to both ends of the core metal, the charging device 20 of the electrophotographic photosensitive member 10
As a result, when the image was evaluated at the position of the fixing device 20 of the image forming apparatus shown in FIG. 5 and the tube surfaces were both rough, no tube displacement occurred and the initial image was good, but the image evaluation was continued. When 5000 sheets of A4 size were printed, an abnormal image in which the center of the halftone image looked like a haze occurred.

When the surface of the charging roller 12 at that time was observed, dirt such as toner was deposited on the center of the surface of the charging roller 12 and was contaminated. Since both the resistance layer c and the surface layer d have rough surfaces, unevenness in resistance occurs on the surface of the charging roller 12 in response to contamination of the central portion of the charging roller 12, resulting in image defects.

Table 1 summarizes the results of Comparative Examples 1 and 2.

[0074]

[Table 1]

Normally, when the tubes on the elastic layer b have the same surface roughness, if the surface roughness is smaller than Rz = 5 μm, unevenness due to tube misalignment occurs.
When Rz is larger than 5 μm, the toner adheres to the charged body, causing image defects due to toner contamination, and results as shown in Comparative Example 1 and Comparative Example 2 shown in Table 1.

Comparative Example 3 The charging roller 11 of Comparative Example 1 and the charging roller 12 of Comparative Example 2
As described above, when the resistance layer c and the surface layer d have the same surface roughness, a specific defect occurs depending on the degree of the surface roughness. According to Table 1, in the present invention, in the experimental example 1, the surface roughness Rz of the resistance layer c and the surface layer d was different, and further, the surface roughness Rz of both was different by 12.5 μm. At the same time, the roller 1 is used to roughen the surface roughness of the resistance layer c to prevent tube displacement, and simultaneously smooth the surface layer d to add releasability and prevent toner contamination. went.

Here, similarly to the charging roller 1, a difference of 12.5 μm in surface roughness Rz was provided between the resistance layer c and the surface layer d. An example using a charging roller 13 in which the surface of a certain resistance layer c is made smooth and the surface roughness of the surface layer d of the outermost layer tube is roughened will be described in this comparative example.

The charging roller 13 used in this comparative example is shown in FIG.
Except for using a resistance control layer c containing no urethane particles as a surface roughness adjuster dispersed in the resistance control layer c of the charging roller 12 of Comparative Example 2 as shown in FIG. It is a structure of.

The surface roughness of the resistance control layer c in this comparative example was 2.5 μm as a 10-point average roughness Rz.

That is, the surface roughness Rz of the resistance layer c as the inner layer tube was 2.5 μm and the surface roughness Rz of the surface layer d as the outermost tube was 15 μm. And tubes c and d with the surface roughness reversed.

The charging roller 13 was installed at the position of the charging device 20 as a contact charging device in contact with the electrophotographic photosensitive member 10 of the image forming apparatus of FIG.
When image evaluation was performed by applying a pressing force in units of g, as in Experimental Example 1, the surface of the surface layer d was rough, so that wrinkles due to tube displacement were prevented, and at the same time, the surface of the resistance layer c was smooth. Compared with Comparative Example 2, toner contamination was also prevented, the initial image was good, and no abnormalities such as image failure occurred up to 7,500 sheets of A4 size.

However, the image evaluation is continued and the A4 size 7
When 500 sheets were printed, an abnormal image was observed in which the center of the halftone image had a hazy appearance.

When the surface of the charging roller 13 at that time was observed, dirt such as toner was deposited at the center of the charging roller 13 and was contaminated. For this reason, resistance unevenness occurred on the surface of the charging roller 13 in response to the contamination of the central portion of the charging roller 13, which appeared as an image defect.

This is because the surface roughness of the surface layer d is large, so that the surface of the charging roller 13 is susceptible to toner contamination, and resistance unevenness is likely to occur.

The reason why the number of durable sheets is larger than that of the charging roller 12 of Comparative Example 2 is that, in the charging roller 12 of Comparative Example 2, both the resistance layer c and the surface layer d have large surface roughness. When the surface layer d is covered, the irregularities appear as undulations on the surface of the charging roller. Here, since the surface roughness of the resistance layer c is small, undulation on the surface of the charging roller hardly occurs. is there.

The results of Experimental Example 1 and Comparative Examples 1 to 3 are summarized in Table 2.

[0087]

[Table 2]

Therefore, the resistance layer c as in Comparative Examples 1 and 2
When the surface roughness is the same as that of the surface layer d, a defect peculiar to the surface roughness occurs depending on the degree of the surface roughness.
These problems can be solved by manufacturing the charging roller so that the resistance layer c and the surface layer d have different surface roughness. However, when the surface of the surface layer d is made rough and the resistance layer c is made smooth like the charging roller 13 of Comparative Example 3,
Their effects cannot be maintained for long.

That is, in the charging roller 1, the resistance layer c of the inner tube, which is a seamless tube on the elastic layer b, and the surface layer d of the outermost tube have different surface roughness. Since the surface roughness of the inner layer tube c in contact with the elastic layer b is larger than the surface roughness, a good image can be formed when the tube is attached to the image forming apparatus.

As described above, the charging member of the present invention can be used as a protective layer on at least the elastic layer provided on the conductive substrate.
It has a charging roller that covers more than one layer of tubes, and the difference in surface roughness between the surface of the outermost layer tube located in the outermost layer and the surface of the inner layer tube in contact with the elastic layer results in a tube slippage. In addition, it is possible to prevent image defects due to toner contamination, and further, by making the surface roughness of the inner layer tube rougher than the surface of the outermost layer tube, roughening the surface of the resistance layer which is the inner layer tube and applying frictional force. It has been clarified that these effects can be maintained for a long time by preventing tube misalignment and smoothing the surface layer, which is the outermost layer tube, so that toner contamination does not accumulate.

The surface roughness of the inner tube provided on the elastic layer of the charging roller is usually 2 μm to 25 μm, and the surface roughness of the outermost tube is 0.1 μm to 5 μm.

In the description of the above embodiments and the like, the description has been made on the assumption that the coating with the seamless tube has two layers.
The charging member is not limited to only the layers, and may be a charging member coated with three or more layers of seamless tubes. In this case, in each tube, dielectric layer, resistance adjustment layer, protective layer, etc.
It is often configured to have separate functions.

When the number of seamless tubes is three or more, at least the outermost tube and the inner tube in contact with the elastic layer have different surface roughness. At this time, each layer of all the seamless tubes has a different surface roughness, the innermost tube in contact with the elastic layer is the roughest, the outermost tube becomes smoother, and the outermost tube has the lowest surface roughness. desirable. Also at this time, the difference between the surface roughness Rz of the outermost layer tube and the inner layer tube in contact with the elastic layer is 1 μm to 20 μm.
m or less.

Although the embodiment has been described using a contact-type charging roller, the form of the charging member is not limited to this, and a box-like or semi-cylindrical having the layer structure surface in contact with the photoreceptor is used. Any form is applicable.

Although the charging member of the charging device of the AC application type has been described above, the application method of the bias is not limited to this, and an application method in which an AC voltage is superimposed on a DC voltage, or a DC power supply is used. It goes without saying that a DC application method may be used.

Embodiment 2 In this embodiment, FIG. 3 is a longitudinal sectional view of a charging roller.
As described above, the shape of the elastic layer b, which is the base layer of the charging roller 1, is a crown shape.

Generally, a contact charging device is used to apply a DC voltage to A
When the surface of the photoconductor is charged by applying a bias in which the C electric field is superimposed, a charging noise generated when the charging roller 1 vibrates the photoconductor 10 due to the AC vibration voltage becomes a problem.

In particular, if the contact state between the charging roller 1 and the photosensitive member 10 is not uniform in the longitudinal direction, the beat of the charging sound is apt to occur in the rotation cycle of the charging roller 1, and an unpleasant sound is generated. .

For this reason, it is necessary that the charging roller 1 is uniformly contacted in the longitudinal direction. However, when the elastic layer b has a straight shape, both ends of the charging roller 1 are pressed to contact the photosensitive member 10. If they are brought into contact, the central part of the resistance layer c and the outermost layer d of the charging roller 1 slightly rises. Then, when the elastic layer b is straight, the contact between the resistance layer c as the inner layer tube and the elastic layer b (part α in FIG. 3) becomes incomplete. For this reason, the beating of the charging noise becomes noticeable.

By making the shape of the elastic layer b inside the surface tube into a crown shape, even if the outermost layer d and the resistance layer c rise, the elastic layer b rises outward only by the crown portion α. There is an elastic layer surface α immediately below the resistance layer c, which is
Can be made uniform in the longitudinal direction, and the beat of the charging noise can be made inconspicuous.

Experimental Example 2 In this experimental example, the charging roller 1 used in Experimental Example 1 was used.
Was formed under the following conditions so that the elastic layer b had a crown shape as shown in FIG.

(Preparation of Elastic Body b) Same as in Experimental Example 1.

(Insertion of Core Metal Layer a into Elastic Body b) Experimental Example 1
Same as

(Adjustment of Length of Elastic Layer b) Same as in Experimental Example 1.

(Preparation of Crown α of Elastic Layer b) The elastic layer with a cored bar was finished to an outer diameter of 11.25 mm at the end and an outer diameter of 11.35 mm at the center by polishing to prepare an elastic layer b with a crown. The crown amount of the elastic layer b is 100 μm.

(Formation of Resistance Control Layer c) Same as in Experimental Example 1.

(Formation of Surface Layer d) Same as in Experimental Example 1.

(Coating of Resistance Control Layer c and Surface Layer d) Same as in Experimental Example 1.

The charging roller 1 having a three-layer structure as described above
Was prepared, and its outer diameter was measured.
2 mm and 11.95 mm at the center, and the crown amount was 30 μm.

The charging roller 1 was brought into contact with the photoreceptor 10 to obtain a contact type charging member in which a pressing force of 500 g was applied to both ends of the metal core a.

The contact-type charging member was installed at the position of the charging device 20 of the image forming apparatus shown in FIG. 5, and the image was evaluated. As a result, the image was good over the entire charging area. Further, when the image evaluation was continued, even if 10,000 sheets of A4 size were printed, the image did not show any deterioration and was very good.

Further, no beating of the charging noise occurred.

Embodiment 3 In this embodiment, as shown in FIG. 4, a photosensitive drum 10, which is an electrophotographic photosensitive member, a charging member 1 for uniformly charging the photosensitive drum 10, and a toner image on an electrostatic latent image A developing device 24 for forming, a process of incorporating a cleaning device 27 into the integral housing 3 for scraping off residual toner remaining on the photosensitive drum 10 after transferring the toner image to the transfer material, and for performing the next image formation. The cartridge 30 is configured to be detachable from the image forming apparatus. Here, as the charging member 1, the charging roller 1 described in Embodiment 1 or the charging roller 1 in which the elastic layer b of the charging roller 1 was formed in a crown shape as in Embodiment 2 was attached.

By adopting the above configuration, in addition to obtaining the effects described in the first and second embodiments, it becomes possible to easily replace these components. Therefore, the maintainability of the image forming apparatus is significantly improved. In addition, by replacing the cartridge 30, important components of the electrophotograph are replaced with new ones, so that a high-quality image can be always maintained.

The charging roller 1 of the second embodiment was incorporated into the charging member 1 of the process cartridge 30 and attached to an image forming apparatus. The image was evaluated in the same manner as in the second embodiment. It was good. Furthermore,
When the image evaluation was continued, even if 10,000 sheets of A4 size were printed, no deterioration was observed in the image and it was very good.

Further, the configuration of the process cartridge 30 is not limited to the above configuration, and one of the developing device 24 and the cleaner 27 and the photosensitive drum 10
And the charging member 1, or a configuration in which the charging member 1 and the photosensitive drum 10 are integrated.

The charging member of the present invention is used as a charging member of the charging device 20 of the electrophotographic photosensitive member 10 in the above-described image forming apparatus, but is not limited thereto. It can be embodied as a charging member.

[0118]

As described above, the charging member of the present invention, the process cartridge and the image forming apparatus provided with the charging member, and the process cartridge include the elastic layer in which the charging member is provided on the conductive substrate. The surface roughness of the outermost layer tube which is formed by covering at least two or more layers of tubes on the outermost layer of the two or more layers of tubes,
Since the surface roughness of the inner layer tube in contact with the elastic layer is different from that of the inner layer tube, (1) it is possible to obtain a charging member free from tube displacement while ensuring uniformity of the charging member surface with a simple configuration. (2) Further, the surface roughness of the inner tube is made rougher than the surface of the outer tube for the surface of the outermost tube and the surface of the inner tube in contact with the elastic layer, thereby preventing toner contamination of the charging member. The effect can be maintained for a long time under heavy use. (3) In addition, since the elastic layer has a crown shape, A
The charging noise accompanying the application of the C voltage can be reduced. (4) Further, by integrating at least a charging member and a cartridge having a photoreceptor as a member to be charged, maintenance properties such as replacement of parts are improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of a charging member according to the present invention.

FIG. 2 is a diagram illustrating a method of covering a seamless tube in a charging member of the present invention.

FIG. 3 is a schematic longitudinal sectional view of another embodiment of the charging member of the present invention.

FIG. 4 is a schematic configuration diagram of a process cartridge of the present invention.

FIG. 5 is a schematic configuration diagram of an image forming apparatus of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 charging roller (charging member) 2 seamless tube 10 electrophotographic photosensitive member (charging member) 11, 12, 13, charging roller (charging member of comparative example) 20, charging device 30 process cartridge a core metal b elastic layer c resistance Layer (inner tube) d Surface layer (outermost tube)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H200 FA07 FA08 GA23 GA34 GA44 GB12 GB22 GB25 HA02 HB12 HB43 HB45 HB46 HB47 JA02 MA01 MA03 MA08 MA14 MA20 MB01 MB04 MC01 MC06

Claims (22)

[Claims] 1. A charging member in which at least two or more layers of tubes are coated on an elastic layer provided on a conductive substrate, wherein the surface roughness of the outermost layer tube located at the outermost layer among the two or more layers of tubes. And a surface roughness of an inner tube circumscribing the elastic layer. 2. The charging member according to claim 1, wherein the surface roughness of the inner tube is greater than the surface roughness of the outermost tube. 3. The charging member according to claim 1, wherein, of the tubes provided on the elastic layer, the inner tube has the smallest surface roughness and the outermost tube has the smallest surface roughness. . 4. The difference between the surface roughness of the surface of the outermost layer tube and the surface roughness of the surface of the inner layer tube in the surface roughness Rz is 1 μm or more and 20 μm or less. 1, 2 or 3 charging members. 5. The charging member according to claim 1, wherein the elastic layer has a crown shape. 6. The charging member according to claim 1, wherein the elastic layer is a foam. 7. The surface roughness of the outermost layer tube is 0.1 μm or more and 5 μm or less in surface roughness Rz, and the surface roughness of the inner layer tube is 2 μm or more and 25 μm in surface roughness Rz.
2. A numerical value within a range of not more than m.
7. The charging member according to any one of Items 6 to 6. 8. A process cartridge detachably mountable to an image forming apparatus main body, comprising: an electrophotographic photosensitive member; and process means having at least a charging member acting on the electrophotographic photosensitive member. The charging member is formed by coating at least two or more tubes on an elastic layer provided on a conductive substrate, and among the two or more tubes, the surface roughness of an outermost layer tube located at the outermost layer is reduced. A process cartridge, wherein the inner layer tube circumscribing the elastic layer has a different surface roughness. 9. The process cartridge according to claim 8, wherein a surface roughness of said inner tube is larger than a surface roughness of said outermost tube. 10. The process cartridge according to claim 8, wherein, of the tubes provided on the elastic layer, the inner tube has the smallest surface roughness, and the outermost tube has the smallest surface roughness. . 11. The difference in numerical value of the surface roughness Rz between the surface roughness of the outermost tube and the surface roughness of the inner tube is 1 μm or more and 20 μm or less. 8, 9 or 10 process cartridges. 12. The process cartridge according to claim 8, wherein the elastic layer has a crown shape. 13. The process cartridge according to claim 8, wherein the elastic layer is a foam. 14. The outermost tube has a surface roughness of 0.1 μm or more and 5 μm or less in surface roughness Rz, and the inner layer tube has a surface roughness of 2 μm or more and 25 μm or less in surface roughness Rz. The process cartridge according to any one of claims 8 to 13, wherein the value is a numerical value within the range. 15. The process cartridge further comprises:
The process cartridge according to claim 8, further comprising a developing unit and / or a cleaning unit as the process unit. 16. An image forming apparatus having an electrophotographic photoreceptor and a charging member, wherein the conductive member is formed by coating an elastic layer provided on a conductive substrate with at least two or more tubes. An image forming apparatus, wherein the surface roughness of the outermost layer tube located at the outermost layer of the two or more layers tube is different from the surface roughness of the inner layer tube circumscribing the elastic layer. 17. The image forming apparatus according to claim 16, wherein a surface roughness of said inner tube is larger than a surface roughness of said outermost tube. 18. The image forming apparatus according to claim 16, wherein, among the tubes provided on the elastic layer, the inner tube has the smallest surface roughness, and the outermost tube has the smallest surface roughness. apparatus. 19. The difference between the surface roughness of the surface of the outermost layer tube and the surface roughness of the surface of the inner layer tube in the surface roughness Rz is 1 μm or more and 20 μm or less. 16. The image forming apparatus according to 16, 17 or 18. 20. The image forming apparatus according to claim 16, wherein said elastic layer has a crown shape. 21. The image forming apparatus according to claim 16, wherein the elastic layer is a foam. 22. A surface roughness of the outermost layer tube is 0.1 μm or more and 5 μm or less in surface roughness Rz, and a surface roughness of the inner layer tube is 2 μm or more in surface roughness Rz.
22. The image forming apparatus according to claim 16, wherein the numerical value is within a range of 5 [mu] m or less.