JPH04110872A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To perform a uniform electrostatic charging process for the surface of an electrostatically charged body stably for a long period by constituting a conductive member which has plural edge members contacting the surface of the electrostatically charged body. CONSTITUTION:The conductive member 4 is provided with the edge parts which are positioned in order in a relative moving direction and contact the surface of the electrostatically charged body, and at least one of the edges of the member is made abut on the electrostatically charged body surface in the counter direction. Consequently, the most upstream side edge part is stained with a dirt material wiped off the electrostatically charged body surface and the electrostatic charging process of the electrostatically charged body surface by this most upstream side edge part itself becomes irregular, but the irregularly charged surface of the electrostatically charged body is charged electrostatically by the next and successive edge parts, thereby eliminating the irregularity in the electrostatic charging.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a conductive member to which a voltage is applied or which is grounded (
The present invention relates to a contact charging type (direct charging type) charging device in which a charging member (charging member) is brought into contact with the surface of an object to be charged and the two are moved relative to each other to charge the surface of the object to be charged (including a charge removal process).

(Prior Art) For example, in image forming apparatuses such as electrophotographic apparatuses and electrostatic recording apparatuses, non-conventional devices have conventionally been used as means for charging the surface of an image bearing member as a charged body such as a photoreceptor or dielectric member. Contact-type corona discharge devices (corona chargers) are widely used.

A corona discharge device is effective as a means for uniformly charging the surface of an object to be charged, such as an image carrier, to a predetermined potential. However, there are problems such as requiring a high-voltage power supply, poor power efficiency, large and complicated structure and high cost, relatively large amounts of undesirable ozone generated by corona discharge, and the possibility of contamination or breakage of the discharge wire. have.

In contrast to this type of corona discharge device, there is a contact charging type charging device as described above, which uses a low voltage power source, has a simple structure, does not require wires to be cut, and generates only a very small amount of ozone. Because of these advantages, it has attracted attention as a means to replace corona discharge devices, for example, in image forming apparatuses, for charging the surfaces of image carriers such as photoreceptors and dielectrics, and other objects to be charged. Research on its practical application is underway (Japanese Patent Application Laid-open No. 57-178267 and 56-10435)
・58-40566.58-139]5[i・58-1
50975, etc.).

The conductive member can be in the form of a roller type, brush type, plate type, or the like.

(Problems to be Solved by the Invention) A problem with the contact charging type charging device is that it is easy to see non-uniform charging (charging unevenness) due to dirt on the conductive member serving as the charging member.

That is, since the contact charging type charging device performs charging by bringing a conductive member as a charging member into contact with the surface of the charged object, the contact portion of the conductive member with the surface of the charged object is the surface of the charged object. It is easy to get dirty by picking up dirt substances adhering to the surface, and uneven charging occurs between the surface of the charged object corresponding to the dirt and other parts.

For example, when the object to be charged is an image bearing member such as a photoreceptor of a transfer type image forming apparatus, developer (toner) etc. that have passed through the cleaning means for cleaning the surface of the image bearing member may be removed from the image bearing member. It is carried to the contact area between the conductive member and the conductive member, and it adheres to the surface of the conductive member and becomes dirt. This dirty portion causes non-uniform charging on the surface of the image carrier and causes defects in the output image.

The present invention has been proposed in view of the above, and an object of the present invention is to provide a contact charging type charging device that is devised so as to be able to perform uniform charging treatment on the surface of a charged object stably over a long period of time. shall be.

(Means for Solving the Problems) The present invention provides a charging device that charges the surface of the charged object by bringing a conductive member into contact with the surface of the charged object and moving the two relatively. a member having a plurality of edge portions that are sequentially located in the direction and respectively contact the surface of the charged object;
or a plurality of members having edge portions that come into contact with the surface of the object to be charged, at least one edge portion of the members having the edge portions, or at least one of the plurality of members having edge portions.
The charging device is characterized in that two members are brought into contact with the surface of the object to be charged in a counter direction.

(Function) That is, by having the above-mentioned configuration, (1) the charging process of the surface of the charged object is performed by using a plurality of electrically conductive members that are located in order in the direction of relative movement between the conductive member and the surface of the charged object and contact the surface of the charged object, respectively. or on individual edges of a plurality of conductive members having rough edges.

■And each edge part has the function of wiping (collecting) the adhering dirt substances existing on the surface of the charged object by rubbing against the surface of the charged object, and the adhering dirt substances existing on the surface of the charged object are Among the plurality of edge portions that are sequentially located in the direction of relative movement between the conductive member and the surface of the charged object and are in contact with the surface of the charged object, the edge portion on the most upstream side in the relative movement direction is used for wiping. be swept away.

(2) Therefore, the most upstream edge is likely to be contaminated with dirt that has been wiped from the surface of the charged object, and the charging process on the surface of the charged object by this most upstream edge itself tends to be uneven. The non-uniformly charged surface of the body is also subjected to charging treatment at the next or subsequent edge portions, so that the non-uniform charging is evened out. On the surface of the object to be charged, the adhering contaminants present on the surface are substantially removed at the most upstream edge, so the surface that passes through this edge is cleaned and can be used at the next or subsequent edge. It does not stain, or the progress of staining is extremely slow.

(2) Therefore, even if the most upstream edge itself is contaminated with the dirt that has been wiped from the surface of the charged object, and the surface of the charged object is unevenly charged, the next or subsequent edges that are not contaminated are By uniformly leveling out the non-uniformly charged surface by the charging process, it becomes possible to stably perform and maintain the uniform charging process on the surface of the charged object over a long period of time.

When 0.199 parts is brought into contact with the surface of the charged object in the counter direction, it has a great effect of wiping away the adhering dirt on the surface of the charged object. Therefore, by bringing the plurality of edge portions into contact with the surface of the object to be charged in the counter direction, the above-mentioned effects can be further improved.

In particular, it is appropriate that the edge portion on the most upstream side be brought into contact with the surface of the object to be charged in a counter direction.

(Embodiments) <Embodiment 1> (FIG. 1) FIG. 1(A) is a perspective view showing a schematic configuration of an embodiment of a charging device according to the present invention.

3 is a charged body, in this example, a rotating drum type electrophotographic OPC photosensitive member (organic semiconductor, hereinafter referred to as photosensitive drum).
shall be. This photosensitive tram 3 is driven to rotate in the clockwise direction of the arrow at a predetermined process speed (peripheral speed).

Reference numeral 4 denotes a conductive member as a charging member disposed in contact with the surface of the photosensitive tram 3.

The conductive member 4 is a horizontally elongated member whose longitudinal direction is the generatrix direction of the photosensitive tram 3, and includes a metal plate 40 that serves as a supporting member and an electrode;
It consists of a charging plate part 41 made of conductive urethane rubber formed on the body along the length of the lower side of this sheet metal, and this charging plate part 41 has two plate parts 41a and 41b in front and back on the tip side. This is a branched form.

Such a conductive member 4 can be obtained, for example, by injecting a liquid conductive urethane rubber material into a mold into which a metal plate 40 is attached and molding the charging plate portion 41 . Adhesion between the sheet metal 40 and the molded charging plate portion 41 (
Integrity) can be improved by forming a brimer layer on the 40 sides of the sheet metal in advance.

In order to impart electrical conductivity to urethane rubber, 10 to 50 wt % of particles of a conductive substance such as carbon or metal powder may be dispersed in the urethane rubber material.

In addition, a conductivity imparting substance such as a surfactant may be added. In addition to urethane rubber, elastic materials such as silicone rubber can be used.

First and second two branch plate parts 41a, 41, b
The resistance (conductivity) of the charging plate portion 41 including the electrification plate portion 41 is normally adjusted to a range of 10 3 to 10 6 Ω·cm 2 . If it is lower than 103Ω・Cm, if there is a defect such as a hole on the surface of the photosensitive tram 3 as the charged object, and the charging plate corresponds to the defect, the charging current will be concentrated on the defect. This makes it easier for leaks to occur. Furthermore, if the resistance is high, such as 10<6>Ω·Cm or more, the amount of charging current flowing from the charging plate side to the surface of the photosensitive drum as a charged object will be small, and charging defects will easily occur.

FIG. 1(B) is a side view of the conductive member 4 in a free state where it is not in contact with the photosensitive drum surface.

This conductive member 4 is connected to the first and second branch plate portions 41.
The tip edge portions of a and 41b are brought into contact with the surface of the photosensitive drum 3, and the plate portions 41a and 41b are bent appropriately against the elasticity of the plate portions 41a and 41b. By firmly fixing and supporting the photosensitive tram 3 (shown in the figure), the photosensitive tram 3 is disposed substantially parallel to and opposed to the photosensitive tram 3. FIG. 1(A) shows this arrangement.

In this embodiment, the edge portion of the first branching blade portion 41a and the edge portion of the second branching blade portion 41b are respectively positioned and contacted with the surface of the photosensitive drum 3 in order on the upstream side and the downstream side in the drum surface movement direction. In addition, the edge portion of the first branch plate portion 41a is in contact with the direction of surface movement of the photosensitive tram 3 in a counter direction, and the second branch plate portion 41b is in contact in a forward direction.

42 is a source for applying a bias voltage to the conductive member 4 as a charging member. By applying a predetermined voltage from this power source 42 to the sheet metal 40 of the conductive member 4, the first and second branch blade portions 4 which are in contact with the surface of the photosensitive drum 3, respectively.
A charging current flows from the charging plate section 41 having the sections 1a and 41b to the surface of the photosensitive drum 3. The surface of the rotating photosensitive drum 3 is charged to a predetermined polarity and potential by a contact charging method by contact with the conductive member 4 to which this voltage is applied.

The voltage applied to the conductive member 4 may be as high as a DC voltage, but an oscillating voltage (DC voltage) having a strike voltage that is at least twice the charging start voltage of the charged object when the DC voltage is applied is used. By applying a superimposed voltage with an alternating current voltage/pulsating current voltage (a voltage whose voltage value changes periodically over an hour), the uniformity of charging is improved compared to the case where only a direct current voltage is applied. Static electricity can be removed by applying an AC voltage.

The charging process for the surface of the rotating photosensitive drum 3 is carried out by charging the first and second conductive members 4, which are in contact with the surface of the photosensitive drum 3 in order in the front and back of the direction of movement of the drum surface, and to which a voltage is applied.
This is performed at each edge portion of the branch plate portions 41a and 41b.

Even if dirt substances such as developer that has not been removed by cleaning exist on the surface of the rotating photosensitive drum 3 and are carried to the position of the conductive member 4 as a charging member, the dirt substances are transferred to the second branch plate of the conductive member. It is wiped by the edge portion of the first branching blade portion 41a located upstream of the portion 41b in the direction of movement of the photosensitive drum surface and is not carried to the second branching blade portion 41b. Plate portion 41b is protected from dirt.

In this embodiment, since the first branch plate part 41a is brought into contact with its edge part in a counter direction with respect to the moving direction of the photosensitive drum surface, the effect of wiping off the adhered dirt on the photosensitive drum surface is good. The second branch plate portion 41b can be well protected from dirt.

Therefore, even if the edge portion of the first branching blade portion 41a is contaminated with dirt substances wiped from the surface of the photosensitive drum 3, uneven charging may occur in the charging process of the photosensitive drum surface by the first branching plate portion 41a. The unevenly charged surface of the photosensitive drum is well leveled by uniform charging processing by the edge portion of the second branch plate portion 41b that is protected from dirt, and the surface of the photosensitive drum 3 is uniformly charged. The uniform charging process can be stably performed over a long period of time.

<Example 2> (Fig. 2) Sheet metal 4 as an electrode part of a conductive member 4 as a charging member
In the case of a design configuration in which the 0 portion and the tram contact portion of the charging plate portion 41 (edge portions of the first and second branch plate portions 41a and 41b) are considerably separated, in order to prevent charging failure from occurring, , first and second branch blade portions 41a
・Resistance value (conductivity) of charging plate portion 41 including 41b
It is necessary to set it quite low within the above-mentioned range of 10 3 to 10 6 Ω·cm so that charging current can be sufficiently supplied to the three surfaces of the photosensitive drum.

However, if a large amount of conductive particles such as carbon or metal powder is added to the elastic material such as urethane rubber that constitutes the charging blade section 41 in order to lower the resistance value of the charging blade 41, the physical properties such as elasticity will decrease and the durability will deteriorate. descend.

Therefore, in this embodiment, as shown in FIGS. 2(A) and 2(B), a conductive film layer 43 made of aluminum, copper, etc. is formed on the surface of the charging plate 41 by means of vapor deposition or the like so as to be electrically connected to the sheet metal 40. .

This conductive film layer 43 serves as an auxiliary electrode, and the same effect as when the distance between the sheet metal 40 portion and the drum contact portion of the charging blade 41 is substantially reduced can be obtained, and the resistance of the charging plate portion 41 can be reduced within the above-mentioned range. The charging blade may be set to a higher value to ensure durability of the charging blade.

<Embodiment 3> The charging plate 41 is further provided with third, fourth, etc. branch plate portions, and these are brought into contact with the photosensitive drum surface in order in the direction of movement of the drum surface to carry out charging. It can also be configured.

Further, the conductive member is formed into a plurality of separate members each having an edge portion that comes into contact with the surface of the photosensitive drum as an object to be charged, and each member is brought into contact with the photosensitive drum surface sequentially in the direction of movement of the photosensitive drum surface. It is also possible to adopt a configuration in which charging is performed by arranging the members and applying a voltage to each member.

Embodiment 4 (FIGS. 3 and 4) This embodiment is an example of an image forming apparatus in which the charging device of Embodiment 1 (FIG. 1) is used as a primary charging means for an image carrier.

FIG. 3 is a schematic configuration diagram of the image forming apparatus. This example is a laser beam printer using a transfer type electrophotographic process.

A laser beam modulated according to an image signal is scanned and outputted from a scanner unit 1 including a laser and a polygon mirror correction lens system, reflected by a folding mirror 2, and irradiated onto a photosensitive tram 3 as an image carrier. The photosensitive tram 3 is placed in contact with the surface of the photosensitive drum 3 as shown in FIG. 1(A), and is uniformly charged by a conductive member 4 to which a voltage is applied, and an electrostatic latent image is formed by irradiation with laser light. do. The electrostatic latent image is developed with toner 5a in the developing device 5 to form a toner image.

On the other hand, a recording material 7 such as paper or plastic film stored in the cassette 7a is fed by a paper feed roller P to a registration roller R in synchronization with the formation of a latent image on the photosensitive tram 3. The recording material 7 is a registration roller r
The latent image formed on the photosensitive tram 3 is conveyed to a transfer charger 6, which is a corona discharger, in synchronization with the leading edge of the latent image formed on the photosensitive tram 3, and the toner image is transferred onto a recording material 7 by the transfer charger 6. The recording material 7 onto which the toner image has been transferred is conveyed along the conveying kite g, permanently fixed by the fixing device 8, and discharged to the outside of the apparatus.

The photosensitive drum 3, the conductive member 4, the developing device 5, the cleaning device 9, and the cover 10 are physically formed as an image forming unit (hereinafter referred to as a cartridge) K, which is attached to and detached from the image forming mounting main body. The cover 10 has the function of blocking light and preventing rubber from adhering to the photosensitive drum 3 when the cartridge K is removed from the main body of the image forming apparatus.

The photosensitive drum 3 is an OPC photosensitive member, and by applying a superimposed voltage of DC component -600V and AC component -2KV to the conductive member 4, the surface of the photosensitive drum 3 becomes 600V.
It was charged evenly and without charging defects, and good images were output stably over a long period of time.

The relationship between the voltage applied to the conductive member 4 and the charging current is shown in FIG. 4, and the charging start voltage Vo is approximately 5.
The voltage is between 00 and 600 V, and the charging voltage is approximately the same as the DC component of the applied voltage.

The applied voltage may be higher than the DC voltage or 1 V to 4
By superimposing KV AC voltage (waveform is triangular wave, rectangular wave, etc.), it prevents minute charging defects that tend to occur when only DC voltage is used, and the resulting fogging on the output image. can.

(Effects of the Invention) As described above, according to the present invention, it is possible to stably perform and maintain a uniform charging process on the surface of a charged object over a long period of time in a contact charging type charging device.

[Brief explanation of the drawing]

FIG. 1(A) is a perspective view showing the configuration of the apparatus of the embodiment, and FIG. 1(B) is a cross-sectional side view of the four-electroconductor member in its free state before being pressure-contacted with the photosensitive tram. FIG. 2(A) is a side view of another embodiment of the apparatus, and FIG. 2(B) is a cross-sectional side view of the conductive member in its free state before being pressure-contacted with the photosensitive tram. FIG. 3 is a schematic configuration diagram of an example of an image forming apparatus using the charging device of FIG. 1(A). FIG. 4 is a graph showing the relationship between the voltage applied to the conductive member and the charging current. 3 is a photosensitive drum as an object to be charged, 4 is a conductive member as a charging member, 40 is a sheet metal, 41 is a charging plate portion, 4
1a and 41b are first and second branch plate parts, 42 is a bias application power source, and 43 is a metal film layer as an auxiliary electrode. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] (1) In a charging device that charges the surface of the object to be charged by bringing a conductive member into contact with the surface of the object to be charged and moving the two relatively, the conductive members are placed in order in the direction of relative movement and are placed on the surface of the object to be charged, respectively. a member having a plurality of contacting edge portions;
or a plurality of members having edge portions that contact the surface of the charged object, and at least one edge portion of the members having the edge portions, or at least one member of the plurality of members having edge portions, is connected to the surface of the charged object. A charging device characterized by being brought into contact with the counter in the counter direction.