JP2746310B2 - Contact charging device and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging device, and more particularly, to a contact charging device used in an image recording apparatus such as an electrophotographic apparatus using an electrophotographic photosensitive member, an electrostatic recording apparatus, and the like. The present invention relates to a contact charging device to be used and a method for manufacturing the contact charging device.

[Prior Art] Recently, a contact charging device for directly contacting and charging a photoreceptor has been proposed, for example, as described in Japanese Patent Application No. 61-29819 (Japanese Patent Application Laid-Open No. 63-167380). Have been. Heretofore, it has been known that the contact charging method not only can use a lower applied voltage than the corona charging method, but also has advantages such as less generation of ozone. This contact charging method will be described with reference to the drawings. For example, as shown in FIG. 1, a charging roller 5 serving as a charging member is driven to rotate in contact with an electrophotographic photosensitive drum 1, and a voltage (Vac + Vdc) 3 in which an AC voltage Vac and a DC voltage Vdc are superimposed thereon is applied thereto. By applying the voltage to the charging roller 5, the photosensitive drum 1 can be uniformly charged.

As understood from the above description, the charging roller 5 needs to maintain conductivity. For that purpose, a conventional EP around core 5a
A member formed by forming a conductive elastic member 5b in which carbon is dispersed in an elastic rubber such as DM or NBR is used.

Furthermore, in order to prevent defective charging at a defective portion (for example, a pinhole) on the surface of the photoreceptor, for example, JP-A-1-191161
As shown in the publication, a contact charging device having a two-layer structure in which an elastic layer made of a conductive rubber or the like is further covered with a member having a volume resistivity of 4.0 × 10 ⁹ Ω · cm or more has been proposed. .

However, even if this method is used, when the device is used for a long time, when it is mounted on a high-speed electrophotographic device, or when a load is applied to a contact charging device, the surface of the electric resistance layer or the photoconductor is lost. Charging failure often occurs. It was confirmed that this phenomenon was particularly prominent at the end of the photoconductor. The phenomenon is that, under the condition that a relatively high pressing force is applied at the end portion, the variation in the shape and size of the molded product tends to be large, and the contact with the photoconductor tends to be uneven in the circumferential direction. Appears to appear under conditions.

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

A second object of the present invention is to provide a contact charging device which has high durability and can be mounted on a high-speed machine.

A third object of the present invention is to provide a contact charging device that hardly causes poor charging even when a defect occurs in a photoconductor or a contact charging device.

[Means for Solving the Problems] The above objects can be achieved by a combination of the following improvements: (i) In a contact charging device in which a charging member is in contact with an electrophotographic photosensitive member, the charging member is connected to the photosensitive member. An upper layer which is an electric resistance layer in contact with a body (however, the upper layer does not contain a grafted polyamide resin and conductive particles), and has both conductivity and elasticity as a lower layer of the upper layer A lower layer at the axial end of the charging member is 10 to 1000 times the electric resistance of the lower layer at the axial center of the charging member. Contact charging device.

(Ii) an upper layer in which a charging member is in contact with the electrophotographic photoreceptor, and the charging member is in contact with the photoreceptor; an upper layer (provided that the upper layer is grafted with a polyamide resin and conductive particles); And a lower layer having both conductivity and elasticity as a lower layer of the upper layer, wherein the lower layer is formed in the axial direction of the charging member. In a method for manufacturing a contact charging device formed by pressing a raw material into a mold and then vulcanizing and curing by heating, a pressure difference is generated in the axial direction of the charging member during the vulcanization and curing. A method of making the electrical resistance of the lower layer different in the axial direction of the charging member.

Hereinafter, the configuration of the present invention will be specifically described with reference to the drawings again.

In FIG. 2 (1), reference numeral 51 denotes a lower layer forming the charger 5, which is formed by dispersing carbon black or the like in an elastic base material such as rubber to impart conductivity, and 52 denotes an upper layer. This is a layer in which carbon black or the like is dispersed in a synthetic resin or a thermoplastic elastomer base material to impart conductivity. Reference numeral 9 denotes a core material serving as a rotation axis of the charger 5;
Usually, a rod having a circular cross section made of metal such as steel penetrates the center of the cylindrical body forming the lower layer.

The electric resistance value in the present invention is measured as follows: As shown in FIG. 2 (2), a metal foil 6 having a width of 1 cm is wound around a charger 5, and a metal core portion 9 and a metal foil portion 6 are wound. And apply a voltage of 250 V between them, measure the current value one minute later, and calculate the electrical resistance using the following equation.

In addition, the measurement points are provided at five or more points in the axial direction of the charger 5 and measured. The average value of the measured values within 5 cm from the end of 5 and each of the points within 5 cm on the left and right across the center are measured. The measured value is compared with the average value.

The electric resistance value of the elastic layer in the present invention is 20 ° C./6
At 0% RH, the central part is preferably 10 ² to 10 ⁷ [Ω], and the end part is preferably 10 ⁴ to 10 ⁸ [Ω]. In addition, it is preferable that the ratio of the resistance value at the end of the charger 5 to the resistance value at the center of the charger 5: end resistance [Ω] / center resistance [Ω] = 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 that the entire applied voltage (hereinafter, “bias”) is applied to the upper resistance layer. Then, the resistance layer is degraded due to dielectric breakdown or the like. Also, if the resistance value is 1.5
Above × 10 ⁸ [Ω], on the contrary, the bias voltage drops due to the elastic layer. As a result, charging failure occurs, which is not desirable.

When the resistance value at the end of the charger 5 is 9.5 × 10 ³ [Ω] or less, the voltage drop in the photoconductor portion is reduced when the photoconductor or the like is damaged. As a result, most of the bias voltage is applied to the charger 5 to cause deterioration of the resistance layer, which is not preferable. If the resistance value is 1.5 × 10 ⁹ [Ω] or more, the application of the bias voltage becomes insufficient.
Unsatisfactory electrification occurs, which is not desirable.

The ratio (resistance ratio) between the end resistance value and the center resistance value is for appropriately distributing the applied bias voltage. In particular, the resistance layer at the end portion may be damaged or damaged after a number of durable uses. This characteristic is necessary in order to minimize the occurrence of defects on the image even when the photosensitive member is damaged.

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

In the present invention, it is preferable that each resistance value at the end shows a tendency to become higher toward the end. In particular, a lower layer in which the ratio between the maximum value and the minimum value of each resistance value at the end is twice or more is preferably used.

If the resistance ratio is less than 10, a bias equivalent to that at the center is applied to the end. In particular, the resistance layer is deteriorated at the end where the photoconductor is easily damaged, which is even more undesirable. On the other hand, if the ratio is 1500 or more, the bias at the end portions is insufficient, and poor charging occurs, which is not preferable. 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 10%.
⁴ to 10 ⁹ [Ω] and (resistance after coating) / (resistance before coating) = 10 to 1000, and the film thickness is usually 5 to 50 [μm]. It is produced by coating. Any substance that satisfies this range can be suitably used.

For example, a conductive material such as carbon black, zinc oxide, titanium oxide or metal powder is dispersed in a material having flexibility at ordinary temperature, such as polyamide, polyimide, fluorine resin, silicon rubber, PVA, and polyester, to obtain a resistance value. It can be adjusted, but is not limited to these. The resistance layer can further have a property of stopping various substances generated from the elastic layer. For example, a non-polar substance can be used for a polar substance.

When the resistance value on the surface of the resistance layer is 9.5 × 10 ³ [Ω] or less, when the photosensitive member is damaged, current is concentrated on the portion to cause image defects, which is not preferable. Also, 1.5 × 10 ⁹
Above [Ω], the current is insufficient and charging failure occurs, which is not preferable.

If the resistance value before application / the resistance value after application (resistance ratio) is 9 or less, it is difficult to adjust the resistance value in the resistance layer. Therefore, as a result of being directly affected by the inclination of the resistance value on the elastic layer, poor charging at the end occurs. Also, the ratio 1500
Above is not preferable because the bias is concentrated on the resistance layer to promote the deterioration.

When the coating film thickness is 3 μm or less, the withstand voltage with respect to the bias does not reach, so that it is not preferable. If the value is 50 μm or more, the surface hardness of the resistance layer is excessively increased, and the damage of the photoconductor is promoted.

As a method of manufacturing the charging device of the present invention and the elastic layer used in the charging device, the raw material is pushed in the axial direction of the charging device, and then the inner die is released from the outer die, and the pressure on the end is released, and then heating and vulcanization is performed. A manufacturing method comprising:

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

Example 1-Silicon raw rubber 100 parts by weight [Product name KE-931U (manufactured by Shin-Etsu Chemical Co., Ltd.)]-Vulcanizing agent (dicumyl peroxide) 1 part by weight-Carbon black 10 parts by weight [Product name (Ketjen black)] The above materials were kneaded and mixed for 30 minutes on two rolls cooled to 20 ° C. to prepare a raw rubber. The raw rubber was measured in a mold in which a core having a diameter of 6 mm was previously attached, and was pressed into the inner mold at a pressure of 100 kgf / cm ² by a transfer method. Next, the inner mold was removed from the outer mold, and heated at a temperature of 160 ° C. for 20 minutes to perform primary vulcanization. Next, the primary vulcanizate was removed from the inner mold and kept at 100 ° C for 3 hours.
Further, secondary vulcanization was performed to obtain a charger with an elastic layer having an outer diameter of 12 mm and a length of 225 mm. Processing of the measurement of the electric resistance of the elastic layer, 10 ⁴ at the center [Omega], were at the end 10 ² [Omega].

As a coating material for a resistance layer laminated on this elastic layer,
The following were used:-100 parts by weight of methylolated nylon (manufactured by Teikoku Chemicals Co., Ltd.)-3 parts by weight of carbon black [Product name (Ketjen black)] was dissolved in methanol to prepare a coating solution, and the above elasticity was obtained. By immersing the charger with the layer formed in the same liquid and forming an electric resistance layer having a thickness of 20 μm by a dipping method,
A contact charger 5 was obtained. The electrical resistance of this charger is at the center
10 ⁶ [Ω] and 10 ⁷ [Ω] at the end.

This charger is used as a laser beam printer [trade name: LBP-
8-II (manufactured by Canon Inc.)], and charged under the following conditions while applying 500 g to each of the rotating bearing portions at both ends by applying to the primary charger position of the developing cartridge: core A bias voltage of DC voltage (V _DC ) = -700 V, AC current (I _AC ) = 120 µA, and frequency f = 1000 Hz were applied to all.

A paper-passing test of 10,000 sheets was performed while checking the state of the charging with a non-contact type surface electrometer. As a result, the charging was stably maintained from the beginning. Even after the passage of 10,000 sheets, the same problem was not recognized in the charging characteristics even in the state where the scratches due to the scraping occurred frequently at the end of the photoreceptor. Table 1 shows the results.

In addition, evaluation was performed based on the observations of the following items at the initial stage and after the 10,000 sheets were used.

Charging-like: The potential unevenness of the charger cycle (38 mm pitch) read from the surface electrometer recording paper is ranked according to the following.

◎: less than 5V ○: 5 to 20V △: 20 to 50V ×: 50V or more (impractical level: image defect; fog) Pinhole resistance: In the same manner as described above, the photoconductor period which can be read from recording paper (93
(mm pitch) is ranked according to the following.

◎: less than 5 V ○: 5 to 20 V △: 20 to 50 V ×: 50 V or more (impractical level: image defect; black stripe) Example 2 Same as Example 1 except that the thickness of the resistance layer was 40 μm. Was evaluated. Table 1 shows the results.

Example 3 Evaluation was performed in the same manner as in Example 1 except that the thickness of the resistance layer was changed to 5 μm. Table 1 shows the results.

Example 4 Except that the primary vulcanization was performed under the condition of a pressure of 30 kgf / cm ² ,
Evaluation was performed in the same manner as in Example 1. Table 1 shows the results.

Example 5 Evaluation was performed in the same manner as in Example 4 except that the amount of carbon black added to the raw rubber was changed to 15 parts.
Table 1 shows the results.

Example 6 Evaluation was performed in the same manner as in Example 4 except that the amount of carbon black added to the raw rubber was changed to 7 parts.
Table 1 shows the results.

Comparative Example 1 Except that the primary vulcanization was performed under the condition of a pressure of 100 kgf / cm ² ,
Image formation was performed in the same manner as in Example 1. Table 1 shows the results.

[Effects of the Invention] According to the present invention, it is possible to provide a contact charging device that is less likely to cause poor charging at the end of the photoreceptor even when used durably.

[Brief description of the drawings]

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

Claims (2)

(57) [Claims] In a contact charging device in which a charging member is in contact with an electrophotographic photoreceptor, the charging member is an upper layer which is an electric resistance layer in contact with the photoreceptor, provided that the upper layer is grafted. And a lower layer having both conductivity and elasticity as a lower layer of the upper layer, and an electric resistance of the lower layer at an axial end of the charging member. Is 10 to 1000 times the electric resistance of the lower layer portion at the central portion in the axial direction of the charging member. 2. An upper layer which is an electric resistance layer in which a charging member is in contact with the electrophotographic photoreceptor, and the charging member is in contact with the photoreceptor. And a lower layer having both conductivity and elasticity as a lower layer of the upper layer, wherein the lower layer comprises a shaft of the charging member. In a method of manufacturing a contact charging device formed by pressing a raw material into a mold in a direction and then vulcanizing and curing by heating, a pressure difference occurs in the axial direction of the charging member during the vulcanization and curing. The method of manufacturing a contact charging device, wherein the electric resistance value of the lower layer is varied in the axial direction of the charging member.