JPH04161967A - Image forming device in contact electrostatic charge system and electrostatic charge roller therefor - Google Patents

Abstract

PURPOSE:To electrostatically charge the surface of a latent image bearer to a required potential stably by furnishing a layer with a medium resistance substantially in the electroconductive base body of a charging member, and forming that surface layer side of this layer, which contacts the surface of the bearer, with a resistance higher than the conductive base body side. CONSTITUTION:A medium resistance layer 12 is covered in roller form with fluoric resin 12b, wherein electroconductive carbon 12a is dispersed around a core 11 consisting of an electroconductive material, and thus an electrostatically charging roller 5 is constructed. This medium resistance layer 12 has a greater dispersion amount of conductive carbon 12a in the part nearer the core 11, that decreases gradually as approaching the surface which is contacting a photo-sensitive belt 1, and the resistance heightens toward the surface, and the volume resistance of the whole charging roller 5 will become 3X10<8>OMEGAcm approximately. A charging bias voltage is impressed on the peripheral surface of this charging roller 5 from a power supply 10 through the core 11. Thereby the latent image bearer can be charged stably to a required potential even with a comparatively low impressed voltage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to electrophotographic image forming apparatuses such as laser printers, copying machines, and facsimile machines, and in particular, to electrophotographic image forming apparatuses such as laser printers, copying machines, and facsimile machines. The present invention relates to a contact charging type image forming apparatus that charges its surface by contacting it, and a charging roller thereof.

[Conventional technology]

In an electrophotographic image forming apparatus such as a copying machine, the surface of a latent image carrier such as a photoreceptor drum or a photoreceptor belt is uniformly charged by a charging unit, and then exposed to light by an exposure device to remove static electricity. A latent image is formed, and the developing roller in the developing device applies toner to make the latent image visible.The latent image is transferred to paper from the paper feed unit by the transfer unit, and the residual toner on the surface of the latent image carrier is removed. Removed by cleaning equipment.

Incidentally, the surface of the latent image carrier is generally charged by a corona discharge method.

However, the corona discharge method requires a power source with high voltage and large current capacity, which hinders space saving and cost reduction. Furthermore, since ozone is generated, there are concerns about deterioration of the latent image carrier and the effects on the human body.

Therefore, in order to solve these problems, in recent years, image formation using a contact charging method has been developed, in which a charging member to which a voltage is applied, such as a charging roller, is brought into contact with the surface of the latent image carrier, thereby charging the surface of the latent image carrier. A device is being developed.

However, in this method, if the charging member is made to have a low resistance, if there is a defect in the coating film on the latent image carrier, a voltage drop will occur due to leakage when the charging member comes into contact with it, and the defect will be charged at the same time. Charging failure occurs in the area of the latent image carrier that comes into contact with the member, which appears in the image as a horizontal white band in the case of the regular development method and a horizontal black band in the case of the reversal development method. was there.

Conversely, if the charging member has a high resistance, there is a possibility that the latent image carrier cannot be charged to the required potential even if the applied voltage is increased.

Therefore, in order to solve such problems, as can be seen in JP-A-64-66675, JP-A-64-73364, JP-A-1-93760, etc., a conductive substrate has been developed. It has been proposed to use a charging member in which two or more resistor layers are provided and the outermost layer (contact layer with the latent image carrier) has a higher resistance than the inner layer.

On the other hand, there is a roller charging method as one of the contact charging methods. This method uses a charging roller as a charging member, and charging rollers made of conductive rubber are widely known.

This conductive rubber may be deteriorated by ozone or deformed by heat. Furthermore, if the charging roller is made of a material such as conductive rubber that has a hardness of tJs, and a cleaning member for cleaning the roller is provided, there is a risk that the charging roller will be worn out due to contact with the cleaning member.

Therefore, in order to solve this problem, for example,
As seen in Japanese Patent No. 0-843, there is also one in which the charging roller is made of ceramics.

[Problem to be solved by the invention]

However, when the charging member has a multilayer structure, the structure of the charging member becomes complicated, and the material of each layer must be carefully selected to prevent the inner layer from deforming or deteriorating when covering the inner layer with the outer layer during the manufacturing process. Need to decide.

In addition, when the charging roller is made of ceramics, ceramics generally have many bubbles, and when many bubbles are lined up in the thickness direction of the roller, voids are formed in the roller, which become high resistance areas and charge the latent image carrier. This may cause defects.

This invention has been made in view of the above points, and it solves the above-mentioned problems and stably charges the surface of a latent image carrier to a necessary potential over a long period of time using a charging member with a simple configuration. The purpose is to make it possible.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a contact charging type image forming apparatus including a charging member that comes into contact with the surface of a latent image carrier to charge the surface of the latent image carrier. A layer having substantially medium resistance is provided on the substrate, and the surface side of this layer that contacts the surface of the latent image carrier has a higher resistance than the side of the conductive substrate.

In addition, the charging roller has a medium resistance ceramic layer impregnated with a medium resistance agent on the outer periphery of a conductive roller-shaped core material, and a medium-resistance layer with a Shore hardness of 8o or more on the outer periphery of the conductive roller-shaped core material. A formed charging roller is also provided.

[For production]

In the contact charging type image forming apparatus according to the present invention, the surface layer side (photoreceptor side) of the medium resistance layer of the charging member is made to have a higher resistance than the conductive substrate side. Even if there is a defect, there will be no voltage drop due to leakage, and charging defects will not occur, so good images can be obtained, and the latent image carrier can be stably charged to the required potential even with a relatively low applied voltage. becomes possible.

In addition, since the conductive substrate side of the medium resistance layer has a lower resistance than the surface layer side, the charge movement in the medium resistance layer in the thickness direction (vertical direction between the conductive substrate and the contact portion of the latent image carrier) is This facilitates the movement of charges in other directions (circumferential and longitudinal directions for rollers), so even if there is a part of the non-contact area between the conductive substrate and the medium resistance layer, the latent image of the charging member The voltage at the contact portion with the carrier becomes uniform, and the latent image carrier can be stably charged.

Furthermore, a charging roller in which a medium-resistance ceramic layer impregnated with a medium-resistance agent is formed on the outer periphery of a conductive roller-shaped core material can prevent charging defects and maintain high image quality.

Furthermore, a charging roller in which a medium resistance layer with a Shore hardness of 80 or more is formed on the outer periphery of a conductive roller-shaped core material can prevent the charging roller from being worn out by the roller cleaning member.
The lifespan of the charging roller can be extended.

〔Example〕

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

FIG. 2 is a schematic diagram showing the belt and surroundings of a contact charging type image forming apparatus according to a first embodiment of the present invention.

In the figure, a photoreceptor belt (belt-shaped latent image carrier) 1
is stretched by a belt driving roller 2 and a driven roller 3.about.a charging roller 5 to which a negative charging bias voltage (for example, 500 V) is applied to a core metal 11 by a DC power supply lO, Developing device6. Transfer device 7
．． Cleaning devices 8 are sequentially arranged.

The charging roller 5 is in contact with the surface of the photoreceptor belt 1,
The surface of the photoreceptor belt 1 is charged by rotating at a constant speed along with the photoreceptor belt 1 rotating in the direction of the arrow.

The surface of the charged photoreceptor belt 1 is exposed to light from an exposure device (not shown) to form an electrostatic latent image, and toner is applied to the latent image by a developing roller 6a in a developing device 6 to make it visible. After that, the transfer device 7 transfers the image onto the paper fed from the paper feed section through the transfer entrance paper guide 9. Thereafter, the toner remaining on the photoreceptor belt 1 is removed by the cleaning blade 8a of the cleaning device 8.

Note that 6b in the developing device 6 is a toner thinning blade;
c is a toner supply roller, and 6d is an agitator.

FIG. 1 is a schematic diagram of a contact charging device in this image forming apparatus.

The charging roller 5, which is the charging member in this embodiment, has conductive carbon 12a around a core bar 11 made of a conductive material.
The medium resistance layer 12 is made of the fluororesin 12b in which
is formed into a roller-shaped coating.

In this medium resistance layer 12, the dispersion amount of conductive carbon 12a is larger closer to the core metal 11, and gradually decreases as it gets closer to the surface in contact with the photoreceptor belt 1, and the resistance becomes higher as it gets closer to the surface. At the same time, the volume resistance of the charging roller 5 as a whole is approximately 3×10'Ωc11.

Further, this charging roller 5 is connected to the power source 10 via the core metal 11.
A charging bias voltage is applied to the outer peripheral surface of.

Here, the volume resistance of the charging roller 5 is 3×10”Ωc
The reason why it is set to about m will be explained with reference to FIGS. 3 and 4.

FIG. 3 is a diagram showing the relationship between the size of stains on an image, which corresponds to the size of scratches on the photoreceptor, and the volume resistance of the charging roller when reverse development is performed.

As you can see from this figure, the volume resistance of the charging roller is 5
It has an inflection point at
No voltage drop occurs on the charging roller,
It was found that no smudges such as horizontal black bands appeared on the image, and a good image could be obtained.

On the other hand, FIG. 4 is a diagram showing the relationship between the charging potential of the photoreceptor and the voltage applied to the charging roller.

As you can see from this figure, the volume resistance of the charging roller is 2
If it is as high as X 10”ΩC, the volume resistance lX109
Compared to a charging roller of Ωcps, a larger applied voltage is required to charge the photoreceptor, and even if the applied voltage is increased, it may not be possible to charge the photoreceptor to the required potential.

Therefore, the volume resistance of the charging roller 5 is 5 x 10'Ωc
11 or more, 2X10” 90m or less, as small as possible 3
It is preferable to set it to approximately 10'Ωcm.

Next, a process for forming the charging roller 5 will be explained.

A core metal 11 is placed at a predetermined position in a mold, and a fluororesin 12b containing conductive carbon 12a is melted and poured into the mold. At this time, the core metal 11 is cooled and the mold is heated to create a temperature gradient between them.

By providing a temperature gradient, the fluororesin 12b is cured from the surface side where the temperature increases depending on the mold to the core metal 11 side where the temperature does not easily rise due to the influence of the core metal 11. As the fluororesin 12b hardens, the conductive carbon 12a tends to move toward the uncured portion, so if the temperature gradient is made sufficiently large, the fluororesin 12b
The amount of dispersion of conductive carbon 12a inside is small on the surface side,
It increases on the core metal 11 side.

In this embodiment, since a belt-shaped latent image carrier is used, the charging roller 5 can be made of a material that does not have elasticity.

FIG. 5 is a schematic diagram of a contact charging device showing a second embodiment of the present invention.

The charging member in this embodiment is a charging blade 21, which includes a metallic fixed substrate 22 for applying a charging bias voltage from a power source 10, one end of which is fixed to the fixed substrate 22, and a surface on the rear end side of the photoreceptor belt. 1 and a medium resistance blade 23 in contact with the blade 1.

This medium resistance blade 23 is also a medium resistance layer made of polyurethane resin 23b in which conductive carbon 23a is dispersed.
The resistance is increased as it approaches the surface that contacts the photoreceptor belt l from the side.

Note that iron, aluminum, stainless steel, or the like can be used for the core metal 11 and fixed substrate 22 shown in FIGS. 1 and 5 in each of the above-described embodiments.

In addition, fluororesin 12b and polyurethane resin 23b
In addition to resins such as polyester and polypropylene, it is also possible to use rubber materials such as silicone rubber and evichlorohydrin rubber as substitutes.

FIG. 6 is a longitudinal sectional view of a charging roller according to a third embodiment of the present invention, and FIG. 7 is an enlarged view of its ceramic layer.

The charging roller 31, which is the charging member in this embodiment, is made of stainless steel and has a roller-shaped support (core metal) as shown in FIG.
As shown in FIG. 7, on the outer periphery of 32, a ceramic M34 is formed in which air bubbles are impregnated with a medium resistance agent 33 such as liquid NBR.

Here, the forming process of this charging roller 31 will be explained.
Resistance 1014ΩcI! of Al2O, and SnO, (1
A clay is made by mixing a low-resistance metal oxide such as 0"0 cm) with a binder in an appropriate ratio, and this clay is fired to produce plate-shaped ceramics with medium resistance.

This ceramic is crushed into particles with a diameter of several microns, heated, and irradiated onto the heated support 32 eight times to form a ceramic layer 34 with a thickness of several tens of microns.

Then, the medium resistance agent 3 is added to the air bubbles in the ceramic layer 34.
Impregnate with 3.

FIG. 8 is a schematic diagram of a charging roller and a cleaning blade according to a fourth embodiment of the present invention, and parts corresponding to those in FIG. 1 are given the same reference numerals.

The charging roller 41, which is the charging member in this embodiment, has a core metal 4
An elastic layer 43 made of conductive rubber such as carbon-dispersed silicone rubber is coated on the outer periphery of the support 44, and a ceramic layer 46 impregnated with a medium resistance agent 45 is formed on the surface of the elastic layer 43. There is.

In addition, 47 is a cleaning blade as a cleaning member for cleaning the roller.

Here, the forming process of this charging roller 41 will be explained.
A1□03, Cr, O, and a binder are mixed in an appropriate ratio, and a pipe-shaped medium resistance ceramic with a thickness of 3 mm is made from this.

This ceramic was impregnated with a mixture of polyester polyol and isocyanate at a ratio of 1:0.8 using thinner as a medium resistance agent 45, and heated to 100°C.
Heat and dry for 60 minutes.

This will be referred to as the ceramic layer 46. When this ceramic layer 46 is formed into a sheet, its surface resistance is 1Xl.
It becomes 0”Ω.

Then, a support 44 in which the core metal 42 is coated with the above-mentioned elastic layer 43 is inserted inside this ceramic pipe. Electrical connection between the core metal 42 and the ceramic layer 46 can be obtained by this elastic layer 43 made of conductive rubber.

Note that when using a belt-shaped latent image carrier like the photoreceptor belt 1, the charging roller should be made of ceramics or thermosetting resins that have a Shore hardness of 80 or more and have little elasticity, such as phenol-formaldehyde resins. It also becomes possible to use

Therefore, in the image forming apparatus shown in FIG. 2, the charging roller is constructed by laminating, for example, a contact layer made of phenol-formaldehyde resin in which conductive carbon is dispersed on the support 44 in FIG. You can.

The embodiments in which the present invention is applied to charging members have been described above, but the present invention can also be applied to contact members such as transfer rollers, cleaning rollers, and developing rollers.

〔Effect of the invention〕

As explained above, the contact charging type image forming apparatus according to the present invention does not cause a voltage drop in the charging member due to leakage even if the latent image carrier has scratches such as coating defects, and is relatively Since it is possible to stably charge the latent image carrier to the required potential even with a low applied voltage, good images can always be obtained.

Furthermore, even if there is a part of the non-contact area between the conductive substrate and the medium resistance layer, the voltage of the charging member in contact with the latent image carrier becomes uniform, and the latent image carrier is stably charged. can do.

By using the charging roller according to the second aspect of the invention, charging failures can be prevented and high image quality can be maintained.

If the charging roller according to the third aspect of the present invention is used, it is possible to prevent the charging roller from being worn out by the roller cleaning member, and to extend the life of the charging roller.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the contact charging device shown in FIG. 2, FIG. 2 is a diagram showing the belt and surroundings of a contact charging type image forming apparatus according to the first embodiment of the present invention, and FIG. 3 is a reversal development diagram. A diagram showing the relationship between the size of scratches on the photoconductor, the size of dirt on the image, and the volume resistance of the charging roller when performing 5 is a schematic diagram of a contact charging device according to a second embodiment of the present invention; FIG. 6 is a vertical sectional view of a charging roller according to a third embodiment of the present invention; The figure is an enlarged view of the ceramic layer. FIG. 8 is a schematic diagram of a charging roller and a cleaning blade according to a fourth embodiment of the present invention. 1... Photoreceptor belt 5, 31, 41... Charging roller 10... DC power supply 11.42... Core metal 12... Medium resistance layer 12a, 23a... Conductive carbon 12b... Fluorine System resin 21...Charging blade 2
2. Fixed board 23. Medium resistance blade 23b
... Polyurethane resin 32.44 ... Support 33.45 ... Medium resistance agent 34.46 ... Ceramic layer 43 ... Elastic layer 4
7...Cleaning blade:, -;=; Fig. 1 Fig. 5 Fig. 3 Volume resistance of charging roller [Ω(1)] Fig. 4 Applied voltage [-V]

Claims (1)

[Scope of Claims] 1. In a contact charging type image forming apparatus equipped with a charging member that charges the surface of a latent image carrier by contacting the surface of the latent image carrier, the charging member is substantially attached to a conductive substrate. Image formation using a contact charging method, characterized in that a layer of medium resistance is provided, and the surface side of this layer that contacts the surface of the latent image carrier has a higher resistance than the side of the conductive substrate. Device. 2. A charging roller characterized in that a medium resistance ceramic layer impregnated with a medium resistance agent is formed on the outer periphery of a conductive roller-shaped core material. 3 Shore hardness is 80 on the outer periphery of the conductive roller-shaped core material.
A charging roller characterized by forming the above medium resistance layer.