JPH03246566A - Contact electrifier and production thereof - Google Patents

Abstract

PURPOSE:To prevent the electrification defect by the chipping of the surface of a photosensitive body by constituting an electrifying member of an upper layer which is an electric resistance layer in contact with the photosensitive body and a lower layer having an electrical conductivity and elasticity in combination and specifying the electric resistance at the end of the lower layer to specific times the electric resistance in the central part. CONSTITUTION:The lower layer 51 forming the electrifier 5 is constituted by dispersing carbon black, etc., into a base material consisting of an elastic material, such as rubber, to impart the electrical conductivity thereto and the upper layer 52 is formed by dispersing the carbon black, etc., into the base material of a synthetic resin or thermoplastic elastomer to impart the electrical conductivity thereto. A core material 9 which is the revolving shaft of the electrifier 5 is a rod material of a circular section consisting of a metal, such as steel, and penetrates the center of the cylindrical body forming the lower layer 51. The resistance at the end of the elastic layer is 10 to 1000 times the resistance of the central part. The electrification defect by the chipping of the photosensitive body is prevented in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a contact charging device, and in detail,
The present invention relates to a contact charging device used in an image recording device such as an electrophotographic device or an electrostatic recording device using an electrophotographic photoreceptor, and a method for manufacturing the contact charging device.

[Prior Art] Recently, a contact charging device has been proposed that charges a photoreceptor by bringing it into direct contact with the photoreceptor.
No. 63-167380). Conventionally, the contact charging method is known to have advantages such as being able to use a lower applied voltage (and generating less ozone) than the corona charging method. The system will be explained based on the drawings.For example, as shown in FIG.
By applying a voltage (Vac+Vdc) 3, which is a superimposition of the AC voltage Vac and the DC voltage Vdc, to the charging roller 5, the photoreceptor drum 1 can be charged uniformly.

As understood from the above, the charging roller 5 needs to maintain electrical conductivity. For this purpose, conventionally, E
A conductive elastic member 5b in which carbon is dispersed in elastic rubber such as PDM or NBR is used.

Furthermore, in order to prevent charging defects at defects (for example, pinholes) on the surface of the photoreceptor, for example, Japanese Patent Laid-Open No. 1-1911
As shown in Publication No. 61, a two-layer contact charging device has been proposed in which an elastic layer made of conductive rubber or the like is further covered with a member having a volume resistivity of 4.0 x 10" Ω・Cm or more. There is.

However, even if you follow this method, if you continue to use it for a long time,
When installed in a high-speed electrophotographic device or when a load is applied to a contact charging device, charging failures often occur due to defects in the surface electrical resistance layer or defects in the photoreceptor. It has been confirmed that this phenomenon is particularly noticeable at the edges of the photoreceptor. This phenomenon occurs under conditions where a relatively high pressure contact force is applied at the end, and variations in the shape and dimensions of the molded product tend to become large, and the contact with the photoreceptor tends to be uneven in the circumferential direction. It appears to appear under certain conditions.

[Problems to be Solved by the Invention] An object of the present invention is to provide a contact charging device that substantially solves the above-mentioned drawbacks.

A second object of the present invention is to provide a contact charging device that is highly durable and can be installed on high-speed machines.

A third object of the present invention is to provide a contact charging device that hardly causes charging defects even if a defect occurs in the photoreceptor or the contact charging device.

[Means for Solving the Problems] The above objects can be achieved by combining the following improvements: (i) In an image forming apparatus in which a charging member is in contact with an electrophotographic photoreceptor, the charging member is in contact with the photoreceptor. An upper layer (hereinafter referred to as "resistance layer") is an electrically resistive layer in contact with the upper layer, and a lower layer (hereinafter referred to as "resistance layer") that is both electrically conductive and elastic as a lower layer of the upper layer.
1. A contact charging device comprising an elastic layer ("an elastic layer"), wherein the resistance at the end of the elastic layer is 10 to 1000 times greater than the resistance at the center.

(if) A manufacturing method in which the elastic layer in the contact charging device is formed by pushing the raw material into a mold in the axial direction of the charging member, shaping it by heating, and then vulcanizing and curing it. 2. The method of manufacturing a contact charging device according to claim 1, wherein a pressure difference is generated in the axial direction during molding, and the electric resistance value in the elastic layer is accordingly changed in the axial direction.

(iii) The pressure during primary vulcanization is 1 compared to the indentation pressure.
3. The method for manufacturing a contact charging device according to claim 2, wherein the contact charging device is less than /2.

The configuration of the present invention will be specifically explained below based on the drawings again.

In FIG. 2 (1), 51 is a lower layer forming the charger 5, and carbon black or the like is dispersed in an elastic base material such as rubber to impart conductivity, and 52 is an upper layer. It is a layer in which carbon black or the like is dispersed in a synthetic resin or thermoplastic elastomer base material to impart electrical conductivity. Reference numeral 9 denotes a core material serving as a rotating shaft of the charger 5, and is usually a bar material with a circular cross section made of metal such as steel, and passes through the center of the cylindrical body forming the lower layer.

The electrical resistance value in the present invention is measured as follows: As shown in FIG. 2 (2), a metal foil 6 with a width of 1 cm is wrapped around the charger 5, and the metal Apply a voltage of 250v between the two and measure the current value one minute later.
Calculate the electrical resistance using the following formula.

In addition, measurements were taken at five or more measurement points in the axial direction of the charger 5, and the average value of the measured values at a portion within 5 cm from the end of the charger 5 and each point within 5 cm on the left and right across the center of the charger 5 were calculated. Compare the measured values with the average value.

The electrical resistance value of the elastic layer in the present invention is 20°C/
Under 60% RH, it is preferable that the center part: 102 to 107 [Ω], and the end part: 104 to 108 [Ω]. And the ratio of the resistance value at the end of the enclosure to the resistance value at the center of the charger 5: end resistance value [Ω
C/Central resistance value [Ω1=preferably in the range of 10 to 1000. If the resistance value at the center is 95 [Ω] or less, the voltage drop in the lower layer is too small, so the total applied voltage (hereinafter referred to as "bias") to the upper resistive layer is reduced.
As a result, the resistance layer deteriorates due to dielectric breakdown and the like. Also, the resistance value is 1.5×108 [01
In the above case, the bias voltage will be lowered by the elastic layer. As a result, charging failure occurs, which is undesirable.

The resistance value at the end of the charger 5 is 9.5X10" [Ω]
In the following, when damage occurs to the photoreceptor or the like, the voltage drop at the photoreceptor portion is reduced. As a result, most of the bias voltage is applied to the charger 5, causing deterioration of the resistance layer, which is not preferable.

In addition, if the resistance value is 1.5X10" [01 or more,
This is not preferable since the bias voltage is insufficiently applied, resulting in insufficient charging.

The ratio (resistance ratio) between the edge resistance value and the center resistance value is for properly distributing the applied bias voltage, and is particularly important to prevent damage to the resistance layer at the edges or damage caused by repeated use. This is a necessary characteristic to prevent defects on the image as much as possible even if damage to the photoreceptor occurs.

FIG. 3 is a graph illustrating the tendency in the axial direction of the electrical resistance value of the lower layer forming the charger 5 used in the device of the present invention.

In the present invention, it is preferable that the resistance values at each end tend to increase toward the end. In particular, a lower layer in which the ratio of the maximum value to the minimum value of each resistance value at the end portion is twice or more is preferably used.

If the resistance ratio is 10 or less, the same bias as that in the center will be applied to the ends. This is particularly undesirable because the resistance layer deteriorates at the edges where the photoreceptor is likely to be damaged. Moreover, if the ratio is 1500 or more, the bias at the end portions will be insufficient and charging failure will occur, which is undesirable. That is, when the resistance layer of the charger used in the present invention is provided on the elastic layer, its resistance value is usually 104 to 10e [Ω] and (resistance value after coating)/(resistance value before coating). )=10~10
00, and the film thickness is usually 5 to 50[
μm]. Any substance that satisfies this range can be suitably used.

For example, conductive substances such as carbon black, zinc oxide, titanium oxide, or metal powder are dispersed in materials that are flexible at room temperature, such as polyamide, polyimide fluororesin, silicone rubber, PVA, and polyester, to increase the resistance value. However, it is not limited to these. The resistance layer can also be given the property of blocking various substances generated from the elastic layer. For example, for polar substances, non-polar substances can also be used.

If the resistance value on the surface of the resistive layer is less than 9.5×10” [Ω], it is not preferable because if damage occurs to the photoreceptor, current will concentrate in that area and cause image defects.1.
If it is more than 5×10”[01, the current will be insufficient and charging failure will occur, which is not preferable.

If the resistance value before application/resistance value after application (resistance ratio) is 9 or less, it becomes difficult to adjust the resistance value in the resistance layer. Therefore, it is directly affected by the slope of the resistance value on the elastic layer, resulting in charging failure at the ends. Also, the ratio 150
If it is 0 or more, bias will concentrate on the resistance layer and promote deterioration, which is not preferable.

If the coating film thickness is 3 μm or less, it is not preferable because the withstand voltage against bias is insufficient. If the value is 50 μm or more, the surface hardness of the resistance layer increases excessively, which promotes damage to the photoreceptor, which is not preferable.

The charging device of the present invention and the method for manufacturing the elastic layer used therein include pushing the raw material in the axial direction of the charging device, releasing the pressure on the end by separating the inner mold from the outer mold, etc., and then heating and vulcanizing the material. Examples of manufacturing methods include:

The present invention will be specifically illustrated by examples below, but is not limited thereto.

Example 100 parts by weight of silicon raw material rubber [Product name K
E-9310 (manufactured by Shin-Etsu Chemical) 1 vulcanizing agent (dicumyl peroxide) 1 part by weight carbon black
10 parts by weight [trade name (Ketchen Black) 1] Each of the above materials was cooled to 20°C on two rolls,
Raw material rubber was prepared by mixing and mixing for several minutes. Measure out the raw rubber into a mold to which a core metal with a diameter of 6 mm has been attached in advance,
100 kgf/ in the inner mold by one type of transfer
It was pushed in with a pressure of 1.5 cm.

Next, the inner mold was removed from the outer mold and heated at a temperature of 160° C. for 20 minutes to perform secondary vulcanization. Next, this primary vulcanizate was removed from the inner mold and further subjected to secondary vulcanization at a temperature of 100° C. for 3 hours to obtain a charger with an elastic layer having an outer diameter of 12 mm and a length of 225 mm. The electrical resistance values of this elastic layer were measured and were 104 [Ω] at the center and 102 [Ω] at the ends.

The following materials were used as coating materials for the resistance layer to be laminated on the elastic layer: - Methylolated nylon 100 parts by weight (manufactured by Teikoku Kagaku Co., Ltd.) - Carbon black 3 parts by weight [trade name (Ketchen Black) 1 The contact charger 5 was prepared by preparing a coating liquid by dissolving the above-mentioned elastic layer in methanol, immersing the charger on which the elastic layer was formed in the same liquid, and forming an electrically resistive layer with a thickness of 20 μm using a dipping method. I got it. The electrical resistance of this charger was 106 [Ω] at the center and 107 [Ω] at the ends.

This charger is used as a laser beam printer [Product name: LB
P-8-II (manufactured by Canon Inc.)] was attached to the primary charger position of a developing cartridge used, and charged under the following conditions while applying a pressure of 500 g to the rotating bearings at both ends. : Apply bias to all cores with DC voltage (Voc) = -700V, AC current (IAc) = 120μA, and frequency f = 1000Hz.

A 10,000-sheet paper test was conducted while checking the state of charge using a non-contact surface electrometer, and the charge remained stable from the beginning. Even when the end of the photoreceptor had many scratches due to scraping after passing 10,000 sheets, no similar problem was observed in the charging characteristics. The results are shown in Table 1.

The evaluation was made based on the following observations observed at the initial stage and after 10,000 sheets of durable use.

■Charging characteristics: Charger period read from surface electrometer recording paper (38mm
The potential unevenness of pitch) is ranked according to the following.

0: less than 5V ○: 5 to 20V △: 20 to 50V
The potential unevenness (mm pitch) is ranked according to the following.

0: less than 5V ○: 5-20V △: 20-50V The evaluation was carried out as follows. The results are shown in Table 1.

Example 3 Evaluation was carried out in the same manner as in Example 1 except that the thickness of the resistance layer was 5 μm. The results are shown in Table 1.

Example 4 Evaluation was carried out in the same manner as in Example 1, except that the primary vulcanization was performed at a pressure of 30 kgf/cm2.

The results are shown in Table 1.

Example 5 Evaluation was carried out in the same manner as in Example 4, except that the amount of carbon black added to the raw rubber was 15 parts.

The results are shown in Table 1.

Example 6 Evaluation was carried out in the same manner as in Example 4, except that the amount of carbon black added to the raw rubber was 7 parts. The results are shown in Table 1.

Comparative Example 1 Image formation was carried out in the same manner as in Example 1, except that the primary vulcanization was performed at a pressure of 100 kgf/cm2. The results are shown in Table 1.

[Effects of the Invention] (a) The present invention uses a shaped photoconductor (OP
This is particularly effective for electrophotographic devices using C).

(b) The present invention is particularly effective for a reversal development system using toner having the same polarity as the charged polarity of the photoreceptor.

(c) The present invention is particularly effective for devices in which the bias of the charging device is driven by a constant current.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a contact charging device, FIG. 2 (1) is a sketch of the charger of the present invention, FIG. 2 (2) is a sketch of the resistance measuring device of the charger, and FIG. 3 is a sketch of the charger of the present invention. FIG. 3 is a resistance distribution diagram in the axial direction of the charger. 5 Contact charger main body 51 Contact charger lower layer 52 Whole upper layer 6 10 mm width metal foil 7 250V DC power supply 8 Ammeter

Claims (3)

[Claims] (1) In an image forming apparatus in which a charging member is in contact with an electrophotographic photoreceptor, the charging member has both conductivity and elasticity as an upper layer that is an electrically resistive layer that contacts the photoreceptor and a lower layer of the upper layer. 1. A contact charging device comprising a lower layer having an electrical resistance of 10 to 1000 times greater at the ends of the lower layer than at the center. (2) A manufacturing method in which the lower layer of the contact charging device is formed by forcing raw material into a mold in the axial direction of the charging member, shaping it by heating, and then vulcanizing and curing it. A method for manufacturing a contact charging device, characterized in that a pressure difference is generated in the axial direction during molding, and the electric resistance value in the lower layer is accordingly changed in the axial direction. (3) The method for manufacturing a contact charging device according to claim 2, wherein the pressure during primary vulcanization is 1/2 or less of the indentation pressure of the raw material.