JPH05273840A - Electrifying member - Google Patents

Abstract

PURPOSE:To improve electrifying efficiency by specifying the resistivity of the surface layer and conductive layer of the electrifying member to an adequate relation. CONSTITUTION:This electrifying roller 102 is constituted of an arbor 102a made of 10phi stainless steel, an elastic layer 102b laminated with epichlorhidrin gum, having 3X10<3>OMEGA.cm resistivity at 3mm thickness and a surface layer 102c coated with a mixture composed of epichlorhidrin gum having 8X10<10>OMEGA.cm resistivity and fluororesin at 30mum thickness. The difference in the resistivity between the surface layer 102c and the elastic layer 102b is specified to order of the >=5th power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member having a surface layer in contact with a photoconductor and an inner layer formed inside the surface layer, and more specifically, to the resistivity of the surface layer and the conductive layer. The present invention relates to a charging member in which the charging efficiency is improved by making the appropriate relationship.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a corona charger that charges a photosensitive member by corona discharge is widely used. However, a corona discharger generally requires a voltage of 5 KV or more applied to the discharge wire,
There is a problem in terms of safety and economy, and ozone generated during discharge is a problem.

On the other hand, recently, for example, a roller charger (contact charging device) using a charging roller has been put into practical use. The roller charger charges the photoconductor by discharging through a gap existing between the charging roller and the surface of the photoconductor, and requires a lower voltage than the corona charger,
Although it has the advantage that the amount of ozone generated is small, it has the drawback of low reliability regarding the uniformity of charging. Factors that reduce the uniformity of charging include defects such as scratches and pinholes on the photoconductor. This is because the defective part of the photoconductor has a lower resistance than other parts, so that leakage occurs and the charging potential is lowered, and further, the electric charge is locally concentrated to cause dielectric breakdown. This is because

To improve the above-mentioned drawbacks, for example, there is a "contact charging device" disclosed in Japanese Patent Laid-Open No. 64-73364. The charging member disclosed in the above publication comprises a conductive substrate covered with at least two resistance layers, and the resistivity of the outermost resistance layer (surface layer) is set as a lower layer (conductive layer) of the surface layer. By making the resistivity higher than that of the resistance layer, the leak caused by the defect of the photoconductor (charged body) is reduced as much as possible.

FIG. 5 is a sectional view showing the structure of a charging roller to which the publication is applied. Charging roller 501 shown in FIG.
Is a core metal 501a made of stainless steel having a diameter of 10φ, an elastic layer 501b in which a carbon-dispersed silicon rubber having a resistivity of 2 × 10 ⁸ Ω · cm is laminated to a thickness of 3 mm, and a resistivity of 8 ×.
The surface layer 501c is formed by applying a hydrin rubber / fluorine resin mixture of 10 ¹⁰ Ω · cm to a thickness of 50 μm.

[0006]

However, according to the charging member disclosed in the "contact charging device" of Japanese Patent Laid-Open No. 64-73364, the resistivity of the surface layer is made larger than that of the conductive layer. However, when a pulsating voltage (a DC voltage and an AC voltage are superimposed) is applied to the charging member, uniform charging is achieved depending on the resistivity of the surface layer and the conductive layer. In order to do so, a large peak-to-peak voltage is required, and the charging efficiency is poor.

The present invention has been made in view of the above, and it is an object of the present invention to improve the charging efficiency by making the resistivity of the surface layer and the conductive layer have an appropriate relationship.

[0008]

In order to achieve the above-mentioned object, the present invention provides a charging member comprising a surface layer in contact with a photoreceptor and an inner layer formed inside the surface layer. When the resistivity is Rt and the resistivity of the inner layer is Rd, a charging member satisfying the relationship of Rd ≦ Rt × 10 ⁻⁵ is provided.

In the above structure, the thickness dt of the surface layer is preferably dt ≧ 30 μm.

[0010]

In the charging member according to the present invention, the charging efficiency is improved by forming the surface layer and the conductive layer using members having an order difference of 5 or more.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of an image forming system of an image forming apparatus (experimental apparatus) to which this embodiment is applied.
A 40φ drum-shaped photoconductor 101 using C, and a charging roller 102 that abuts the surface of the photoconductor 101 to negatively charge
A power source 103 for applying a pulsating current voltage obtained by superimposing an AC voltage on a DC voltage to the charging roller 102; an image writing unit 104 for performing an exposure process with a laser beam on the photoconductor 101 subjected to the charging process; The developing unit 105 that attaches toner to visualize the electrostatic latent image formed by the above, the registration roller 106 that conveys the recording paper P toward the photoconductor 101 at a predetermined timing, and the conveyed recording. Transfer roller 107 that transfers the toner image on photoconductor 101 onto paper P
The cleaning unit 108 that removes the toner remaining on the photoconductor 101 after the transfer process is completed, the destaticizing lamp 109 that erases the residual charge on the photoconductor 101 that has completed the cleaning process, and the recording paper P are carried. The fixing unit 110 fixes a toner image.

The charging roller 102 according to this embodiment is also used.
As shown in FIG. 2, is a core 10 made of stainless steel of 10φ.
2a and an elastic layer 102b in which epichlorohydrin rubber having a resistivity of 3 × 10 ³ Ω · cm is laminated to a thickness of 3 mm.
And a surface layer 102c coated with a mixture of epichlorohydrin rubber having a resistivity of 8 × 10 ¹⁰ Ω · cm and a fluororesin to a thickness of 30 μm.

The operation of the above configuration will be described. The photoconductor 101 rotates clockwise toward FIG. 1 by a drive system (not shown). The charging roller 102 is a power supply unit 103.
A pulsating voltage is applied to charge the photoreceptor 101 negatively,
Subsequently, the photosensitive member 101 that has completed the charging process is the image writing unit 1.
04 exposure processing is performed, and the photoconductor 1
The charge on 01 is erased (charged) to form an electrostatic latent image. The electrostatic latent image is reversely developed by the developing unit 105 to be visualized, and the toner image is transferred onto the recording paper P transported by the registration roller 106 by the action of the transfer roller 107. The toner remaining on the photoconductor 101 after the transfer process is removed by the cleaning unit 108, and the residual charge of the photoconductor 101 after the cleaning process is erased by irradiating the static elimination lamp 109 with light. The recording paper P on which the toner image has been transferred is subjected to a fixing process by the fixing unit 110 and is ejected outside the machine.

Next, an experiment for investigating the relationship between the peak-to-peak voltage of the pulsating current voltage and the uniformity of charging will be described. This experiment was performed using the image forming apparatus of FIG. 1, and specifically, the pulsating voltage was applied to the charging roller to expose the photoconductor 10
1 is charged, and the charged photosensitive member 101 is subjected to the developing process by adjusting the developing bias without performing the exposure process.
The charging unevenness is evaluated from the toner adhesion amount (density) on No. 1. Therefore, it is possible to evaluate the charging unevenness on the photoconductor 101 (variation of toner density in the background portion) as a whole.

FIG. 3 is a graph showing the results of this experiment, where the horizontal axis shows the peak-to-peak voltage of the AC voltage, and the vertical axis shows the variation when the average toner concentration is used as a reference. Here, in FIG. 3, a circle indicates the charging roller 10 of this embodiment.
2, triangle marks show the results of the conventional charging roller 501, and the order difference of the resistivity between the surface layer and the elastic layer is 7th power in this embodiment,
Conventionally, it is squared.

As shown in FIG. 3, the density variation of the charging roller 102 according to the present embodiment is about 1400 V peak-to-peak voltage even if the trailing edge is gentle, but there is no problem in practical use. Then, although the fall is steep, a peak-to-peak voltage of 1700 V or higher is required. From this result, it can be seen that when the resistance values of the surface layer and the elastic layer are more than a certain value, uniform charging can be performed even if the peak-to-peak voltage is small (that is, the power consumption is small), and the charging efficiency is good. Recognize. Further, this has an effect of preventing the occurrence of dielectric breakdown because the peak-to-peak voltage may be small.
The difference in the resistivity between the surface layer and the elastic layer is slightly different depending on the material to be formed and the resistivity of the material as a result of conducting an experiment using another charging roller, but the order difference is 5th power or more. It was found that good charging can be performed in the case of. This phenomenon occurs because of the difference in electron mobility between the surface layer and the elastic layer.

Next, an experiment for investigating the relationship between the thickness of the surface layer of the charging roller and the flowing current will be described. In this experiment, electrodes were wound around the surface of the charging roller and the current flowing through the charging roller when a DC voltage was applied was measured.
The charging roller used has the same core metal and elastic layer, and only the thickness of the surface layer has been changed.
No sign is used to avoid confusion. Figure 4
Are characteristic charts showing the results of this experiment. The circles show the results when the thickness of the surface layer is 20 μm, the triangles show the results when the thickness is 30 μm, and the squares show the results when the thickness is 50 μm.

When this experiment was conducted, the thickness of the surface layer was 2
In the case of 0 μm, dielectric breakdown occurred when a voltage of −500 V or higher was applied (for this reason, measurement at −500 or higher was not performed). In the other two cases, -1000V
Dielectric breakdown did not occur even when the voltage of
The result shows that a sharp increase in current is observed at 000V.

From these results, it can be seen that there is a large difference in the likelihood of dielectric breakdown when the surface layer thickness is 20 μm and 30 μm. In addition, since this experiment was performed by winding the electrodes around the surface of the charging roller, dielectric breakdown is more likely to occur than in the case of performing normal image formation. Considering these points, in order to reliably prevent the occurrence of dielectric breakdown, it is desired that the surface layer has a thickness of 30 μm or more.

According to the present invention, the resistivity of the surface layer and the elastic layer has an order difference of 5 or more, and the thickness of the surface layer is 30 μm or more. However, when the resistivity of the elastic layer is large, When the thickness is thick, the resistance value of the charging member also increases, which lowers the charging efficiency. Therefore, it is necessary that the resistivity of the surface layer and the elastic layer, the thickness of the surface layer, and the like be appropriate according to the application.

In the present embodiment, the present invention is applied to the charging roller, but in addition to this, the charging member may be a belt-shaped or blade-shaped member, and the present invention may be applied to a charge eliminating member. It may be applied.

[0022]

As described above, according to the present invention, in a charging member having a surface layer in contact with a photosensitive member and an inner layer formed inside the surface layer, the surface layer has a resistivity of Rt and an inner layer of If the resistivity is Rd, the relationship of Rd ≦ Rt × 10 ⁻⁵ is satisfied. Therefore, by making the resistivity of the surface layer and the conductive layer proper, it is possible to improve the charging efficiency.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an image forming system of an image forming apparatus to which this embodiment is applied.

FIG. 2 is an explanatory diagram showing a configuration of a charging roller according to the present exemplary embodiment.

FIG. 3 is a graph showing the relationship between the peak-to-peak voltage of the pulsating voltage applied to the charging roller and the variation in background density.

FIG. 4 is a graph showing the relationship between the thickness of the surface layer of the charging roller and the current value.

FIG. 5 is an explanatory diagram showing a configuration of a conventional charging roller.

[Explanation of symbols]

 102 charging roller 102a core metal 102b elastic layer 102c surface layer

Claims (2)

[Claims] 1. A charging member comprising a surface layer in contact with a photoconductor and an inner layer formed inside the surface layer,
A charging member characterized by satisfying a relationship of Rd ≦ Rt × 10 ⁻⁵ , where Rt is a resistivity of the surface layer and Rd is a resistivity of the inner layer. 2. The charging member according to claim 1, wherein the thickness dt of the surface layer is dt ≧ 30 μm.