JPH0451056A - Charging member - Google Patents

Abstract

PURPOSE:To prevent poor charging by forming a conductive elastic layer made of >= 2 kinds of elastomers different form each other in the solubility parameter by >= 0.5 and not compatible with each other, and localizing one of them in the thickness direction of the layer. CONSTITUTION:The charging member 5 is provided on the conductive support 5a with the conductive elastic layer 5b made of >= 2 kinds of elastomers different in solubility parameter from each other by >= 0.5 and not compatible with each other, and one of them is localized in the layer thickness direction, thus permitting the resistance of the conductive elastic layer to be constant in the generating line direction, therefore, uniform charging to be executed, and poor charging to be prevented in the case of occurrence of defects on the photosensitive body.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a charging member used in an electrophotographic image forming apparatus, and more particularly, the present invention relates to a charging member used in an electrophotographic image forming apparatus, and in particular, a charging surface of the charging member is pressed against an electrostatic latent image carrier. The present invention relates to a contact charging type charging member that is charged by a contact charging method.

[Conventional technology]

In recent years, a contact charging device has been proposed that charges the photoreceptor by directly contacting it, as described in JP-A-63-167380, which requires a lower applied voltage than the conventional corona charging method. can be used.

It also has the advantage of generating less ozone.

In this contact charging method, for example, as shown in FIG. 1, a charging roller 5, which is a charging member, is contacted and rotated by an electrophotographic photosensitive drum 1, and a voltage (Vac +Vnc ) 3 to charging roller 5
By applying the voltage to the photosensitive drum 1, the photosensitive drum 1 can be uniformly charged.

As can be understood from the above, the charging roller 5 needs to maintain conductivity, and conventionally, around the core metal 5a, EPDM,
A conductive elastic layer 5b formed by dispersing carbon in elastic rubber such as NBR is used.

Furthermore, in order to prevent charging defects in photoreceptor surface defects such as pinholes, for example,
A contact charging device has been proposed that has a two-layer structure in which an elastic layer made of rubber or the like imparted with conductivity is further coated with a material having a volume resistivity of 4.0×10”Ω・1 or more, as shown in FIG. There is.

[Problem to be solved by the invention]

However, when a contact charging device with a two-layer structure is used for a long time or when a load is applied to the contact charging device, such as when installed in a high-speed electrophotographic device, the resistance layer that is the surface layer may be damaged, or the photoreceptor may be damaged. Charging failure occurs due to the loss of . This phenomenon is particularly noticeable at the ends of the photoreceptor where the contact pressure is relatively high and variations in molding dimensions tend to be large.

On the other hand, it is possible to eliminate the charging failure by increasing only the resistance at the end portions, but this may cause problems such as lower production stability and a narrower tolerance range of resistance.

Therefore, an object of the present invention is to provide a charging member that solves the above-mentioned drawbacks.

A further object of the present invention is to provide a charging member that does not cause charging defects even when a photoreceptor or charging member is damaged.

Furthermore, another object of the present invention is to provide a charging member in which the resistance of the elastic layer is constant in the direction of the rotation axis of the charging member.

[Means to solve the problem]

That is, the present invention provides a charging member having a conductive elastic layer on a conductive support, in which the conductive elastic layer has a solubility parameter difference of 0.5 or more and is incompatible with each other.
The charging member is characterized in that it is formed of more than one type of elastomer, and one type of the elastomer is unevenly distributed in the layer thickness direction.

The present invention will be explained in detail below.

First, as a result of studies conducted by the present inventors, when a mixture of two or more mutually incompatible elastomers with a difference in solubility parameter (hereinafter abbreviated as SP) value of 0.5 or more is formed into a roller shape, photosensitive In the molding method in which the raw material mixture is pushed in the direction of the rotating axis of the charging member into a mold whose contact surface with the body is uniformly finished, contact with metal such as the mold contact surface and the core metal contact surface is avoided. It was observed that materials with high SP values were formed on the surface. This is considered to be because the adhesiveness between the mold surface and the material is correlated with the SP value.

In addition, conductive particles that are added to make the charging member have a medium resistance range can be added to only one type of elastomer to create a master bunch, and then mixed with other incompatible elastomers. Only the layer of elastomer can be made conductive. When a charging roller was molded using the above-mentioned molding method using this mixture, it was possible to unevenly distribute one type of elastomer in the layer thickness direction, that is, to form a separation layer with a specific conductivity on the surface side. Ta.

Therefore, when conductive particles are added to the side with a low SP value, the surface side (that is, the side with a high SP value) becomes a relatively high resistance layer, and the resistance in the radial direction is the resistance value of this layer. Since the layers are shaped relatively uniformly, variations in resistance in the generatrix direction are reduced. Conversely, if conductive particles are added to the side with a high SP value, the surface side will have low resistance, and even if a voltage is applied in the layer thickness direction, the current will mainly flow in the direction of the rotation axis, and the resistance in the direction of the rotation axis will decrease. Variations will be eliminated.

As a result of various studies conducted by the present inventors, it has been confirmed that in a system in which conductive particles are added to the side with a higher SP value, the conductive particles are more stable and exist within a single layer.

Next, examples of two or more elastomers that have a difference in solubility parameter of 0.5 or more and are incompatible with each other include silicone rubber (S P = 7.3), EPD, etc.
M (8,0), SBR (8,4~8.7), BR
(8,4~8.6), NR (7,9~8.4), N
Commonly used elastomers such as BR (8,7 to 10.5) may be combined as appropriate; for example, SBR (SP=
8.6), silicone rubber (7,3), NR (8,1)
), CR(9,4), NBR(9,5)
, EPDM (8,0); Combinations of CR and silicone rubber, NR, BR (8,5), EPDM, etc. may be mentioned.

Note that the SP value in the present invention may be actually measured, or a literature value or a theoretical value may be used.

In the present invention, conductive carbon blanks, conductive metal oxides, metal powders, etc. are used as conductive materials.

The uneven distribution of the elastomer in the present invention is confirmed as follows.

A portion of 50 μm on the surface side and a portion below it are cut out and used as measurement samples, and quantified using the analyzer described below. Analyzers include SEM, IR, and UV.

DSC, TG-DTA, etc. are used. In SEM, a layered structure can be confirmed because contrast occurs due to the difference in conductivity in the non-deposited state. Furthermore, for IR and UV, sampling methods using reflection and total reflection are simple, and quantitative determination is performed by absorbance using the characteristic peak of each elastomer. In addition, the layered structure can be confirmed by quantitative analysis using endothermic peaks and thermal loss curves obtained by thermal analysis such as DSC and TO-DTA. Regarding measurement points, measure at least 5 points in the axial direction, and 5 points from the end.
Compare the average value of the measured values of the area within 50 mm with the average value of the measured values within 51 points on the left and right sides of the center.

The preferred resistance value range in the present invention is lX1
0' to 6 x 10" ohm. If it is less than 1 x 10" ohm, if the insulation of the photoreceptor is broken, such as when a defect occurs on the photoreceptor due to long-term use, the bias will not be applied during charging. This is not preferable because it causes a decrease in charging capacity and a charging failure occurs. 6X
If it exceeds 10"Ω, the voltage drop at the charging member will increase and charging failure will occur, which is undesirable. A more preferable range is lXl0' to lXl0"Ω. The resistance value in the present invention is measured as follows.

As shown in FIG.
Apply 0V and measure the current value 1 minute later with ammeter 8, 250 (V)/current value [A] = measurement part resistance [Ω]
Measure the resistance from the relationship.

In addition, further layer separation can be achieved by combining elastomers with different viscosities at the compounding stage, and by combining carbon-based resins with materials such as silicone rubber that have different intermolecular distances. Further layer separation can also be achieved by: Also,
The most significant layer separation occurs with combinations of elastomers that differ in both SP value and intermolecular distance, such as the combination of silicone rubber and EPM.

The thickness of the elastic layer is preferably 0.5 m or more; if it is less than 0.5 m, deformation due to pressure will not be sufficient and it will be difficult to make uniform contact with the photoreceptor, which is not preferred.

In the present invention, it is more preferable to further provide a resistance layer for adjusting the resistance on the elastic layer.By providing the resistance layer, it is possible to suppress variations in resistance in the elastic layer. It's for a reason.

The resistance layer used in the present invention has a resistance value of 1 x 104 to 8 x 10'Ω when provided on the elastic layer, and (resistance value after coating)/(resistance value before coating) -10 to 1000. and the film thickness is 3 to 50.
It is applied so that it becomes μ-. Any material that satisfies this resistance value range can be preferably used. For example, carbon blank, zinc oxide,
By adding all conductive substances such as titanium oxide and metal powder, the resistance value can be adjusted.

It is also possible for the resistance layer to have the property of blocking substances generated from the elastic layer, and for this reason, for example, if a polar substance is used in the elastic layer, a non-polar substance may be used. .

If the resistance value when a resistance layer is provided is less than lXl0'Ω,
If the photoreceptor is damaged, current will concentrate in that area, causing defects in the image, which is undesirable.

Moreover, if it exceeds 8×10''Ω, the current will be insufficient and charging failure will occur, which is not preferable.

If the resistance ratio before/after coating is less than 10, the resistance cannot be adjusted in the resistance layer, and it will be directly affected by the resistance variation in the elastic layer, which is undesirable because charging defects will occur at the ends. . Moreover, if it is more than 1000, bias will be concentrated on the resistance layer, which will promote deterioration, which is not preferable.

If the coating thickness is less than 3 .mu.m, there is no pressure resistance against bias, which is not preferable. On the other hand, if it exceeds 50 .mu.m, the surface hardness of the resistive layer will increase and damage to the photoreceptor will be accelerated, which is undesirable.

The charging member of the present invention uses an organic photoconductor (
This is particularly effective for electrophotographic devices that use PCs. This is because OPC photoreceptors have poorer wear resistance than other inorganic photoreceptors and are more likely to cause damage to their surfaces.

The charging member of the present invention is particularly effective in a reversal development system using toner of the same polarity as the charging polarity of the photoreceptor. This is because when a charging failure occurs in the reversal development method,
This is because development is performed on areas where the surface potential of the photoreceptor is low, and charging failures directly result in image defects.

The present invention is particularly effective for devices in which the bias of the charging member is driven by a constant current. This is because, under constant current driving, if an overcurrent occurs due to, for example, a defect in the photoreceptor, the applied voltage decreases and the charging of other normal parts is also dissipated.

〔Example〕

The present invention will be explained below with reference to Examples.

Example 1 The above materials were cooled to 20°C and rolled for 30 minutes on two rolls.
A raw rubber was prepared by kneading and mixing for a minute.

100 parts of the above mixture was added and further mixed on a roll for 2 hours to obtain a raw rubber. Measure this into a mold equipped with a 6φ core metal, push it into the mold using a transfer method, and heat it to 160°C.
It was heated for 20 minutes at a temperature of -2 to perform post-vulcanization. Furthermore, after demolding, secondary vulcanization was performed at 160° C. for 3 hours to obtain an elastic layer of a charging member.

The surface side part and bulk part of this elastic layer were cut out, and IR
By the OATR method (total reflection), 1020 value -1 (peak due to silicone rubber) and 2870cx-' (E P D
When the relative amount of the ratio to the peak due to M was measured, it was confirmed that EPDM was unevenly distributed on the surface side. The average resistance value of this elastic layer was 2×10'Ω, and it was confirmed that it was the same at both the ends and the center. Furthermore, in order to provide a resistance layer on the elastic layer, a coating solution was prepared by dissolving 100 parts of methylolated nylon and 3 parts of carbon black in methanol, and a resistance layer of 20μ mist was formed on the elastic layer by dipping. was formed and dried at 150° C. for 20 minutes to obtain a contact charging member.

The resistance value of this charging member was lXl0''Ω, and was equal at the ends and the center.

This charging member was brought into contact with the primary charger position of the cartridge used in LBP-8-II (manufactured by Canon) with a total pressure of 1
At 000 g, install a charger and attach Voc to the core metal part.
= 700V, Iac = 120μA, f = 1000
A 10,000-sheet paper feeding test was conducted by applying a Hz bias to charge the paper, and checking the state of the charge using a non-contact surface electrometer. Even in a state where there were many scratches due to scraping on the end of the photoreceptor after passing 10,000 sheets, no problem was observed in the charging characteristics.

The results are shown in Table 1.

The image evaluation was performed on the following items at the initial stage and after a durability test of 10,000 sheets.

(2) Charging characteristics The potential unevenness of the charger cycle (38 pitches) read from the surface electrometer recording paper is evaluated based on the following criteria.

Less than 0857 0: 5 parts or more and less than 10V △: 10V or more and less than 30V x: 3QV or more (unpractical level; image defect).

(Fog) ■Pinhole resistance Similarly to the above, the photoreceptor period (93
m pitch) potential unevenness is evaluated using the following criteria.

Less than 0257 ○: 5V or more and less than 20V △: 20■ or more and less than 50V X: 50V or more (unpractical level; image defect).

Example 2 Tests and evaluations were carried out in the same manner as in Example 1, except that Compound-1 was NBR (10,3) and Compound-2 was EPDM (8,0). Furthermore, the characteristic absorption is N
B R2250c+++-', EPDM 720c
It was set as m-'. The results are shown in Table 1.

Example 3 Tests and evaluations were conducted in the same manner as in Example 1, except that Compound-1 was NBR (10,3) and Compound-2 was BR (8,5). In addition, the characteristic absorption is B R1
310 cm-' and NBR2250 cm+-'.

The results are shown in Table 1.

Comparative Example 1 Compound-1 to 5BR(8,5), Compound-1
Tests and evaluations were conducted in the same manner as in Example 1, except that BR(8,5) was used instead of BR(8,5). In addition, the characteristic absorption is S B R1
750 cm-', B R1310 cm-'.

The results are shown in Table 1.

Example 4 Tests and evaluations were carried out in the same manner as in Example 1 except that the amount of carbon blank was 5 parts and no resistance layer was formed on the elastic layer. The results are shown in Table 1.

〔Effect of the invention〕

According to the charging member of the present invention, since the resistance of the conductive elastic layer is constant in the direction of the generatrix, uniform charging is possible, and even if a defect occurs on the photoreceptor, charging defects will not occur. do not have.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the charging member of the present invention. FIG. 2 is a schematic diagram of a resistance measuring device used in the present invention. 1: Electrophotographic photosensitive drum la: Conductive support 1b: Photosensitive layer 3: Power source 5 that superimposes DC voltage and AC voltage: Charging roller 5a: Conductive support (core metal) 5b: Conductive elastic layer 6: Metal foil 7: DC power supply (250V) 8: Current meter 9: Core metal part

Claims (4)

[Claims] (1) In a charging member having a conductive elastic layer on a conductive support, the conductive elastic layer is formed of two or more elastomers that have a difference in solubility parameter of 0.5 or more and are incompatible with each other. 1. A charging member characterized in that the elastomer is unevenly distributed in the layer thickness direction. (2) Claim (1) characterized in that the conductive elastic layer is formed of two types of elastomers, and the elastomer with a higher solubility parameter is unevenly distributed on the surface side of the elastic layer. The charging member described. (3) Claim (2) characterized in that the elastomer with a higher solubility parameter contains conductive particles.
) Charging member as described. (4) The charging member according to any one of claims (1) to (3), further comprising a resistance layer provided on the conductive elastic layer.