JPH043182A - charging device - Google Patents

Abstract

PURPOSE:To allow the good electrifying processing of the surface of a body to be electrified by a contact electrifying system by using a conductive member of a wire and roughly flattening the surface of a resistance member in contact with the body to be electrified. CONSTITUTION:A photosensitive drum 1 consists of a drum base body 1b made of aluminum and a photosensitive body layer 1a formed on the outer peripheral surface of the base body 1b. A fine conductive wire or conductive sheet material of, for example, 5 to 1,000mum diameter, width or thickness is used as a conductive member for impressing the voltage of a contact electrifying member. This conductive wire is pressed in its body part to the surface of the body to be electrified directly or via a resistance member or the edge part of the conductive sheet material is pressed directly or via the resistance member to the above- mentioned surface and is relatively moved. The electrifying sound generated with the electrifying device of the contact electrifying system is decreased or substantially eliminated in this way and the good electrifying characteristic is assured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a method of charging the surface of a charged object to a predetermined potential by bringing a charging member to which a voltage is applied into contact with a charged object (including static elimination processing). The present invention relates to a contact charging device (the same applies hereinafter).

(Conventional technique #r) For example, in image forming devices such as electrophotographic devices (copying machines, laser beam printers, etc.) and #electronic recording devices, an image is formed as a charged body such as a photoreceptor or dielectric. A corona discharge device has been widely used as a means for charging the surface of a carrier.

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. but,
This method requires a high-voltage power source and has problems in that a relatively large amount of undesirable ozone is generated due to corona discharge.

In contrast to such a corona discharge device, a contact charging device, which charges the surface of the charged object by bringing a charging member to which a voltage is applied as described above into contact with the charged object, can reduce the voltage of the power source, and
Since it has the advantage that ozone generation is extremely rare, for example, it is used in image forming apparatuses to charge the surface of image carriers such as photoreceptors and dielectrics, and other objects to be charged.
It has attracted attention as an alternative device to corona discharge devices, and research on its practical use is progressing (Japanese Patent Application Laid-Open No. 17826-1983).
7・56-104351・58-40566・58-1
39156/58-150975, etc.).

The present applicant also applied two voltages to the charging member, one being a DC voltage and the other being the charging start voltage of the object to be charged, for the purpose of uniform charging.
Many proposals have been made for contact charging methods and devices that are based on applying an oscillating voltage (a voltage whose voltage value changes periodically over time) with a peak-to-peak voltage that is more than twice as high as the peak-to-peak voltage. -149668・149689
Publications, etc.).

The charging member generally has a roller type or plate type configuration.

FIG. 5 shows a schematic configuration of an example of an image forming apparatus using a roller type contact charging member as a charging processing means for an image carrier. The image forming apparatus in this example is a transfer type electrophotographic apparatus (copying machine, laser beam printer, etc.).

1 is a rotating drum-type electrophotographic photoreceptor (
(hereinafter referred to as a photosensitive drum), which is rotated clockwise as indicated by an arrow at a predetermined circumferential speed (process speed).

2 is a charging roller as a contact charging member, and is made of iron, copper,
A four-conductor core metal 23 made of aluminum, stainless steel (SUS), etc., a low resistance layer 2b made of carphone-containing EPDM, urethane, etc., whose outer periphery is coated in a roller shape, and a trace thin layer 2b made of EPDM, urethane, etc. The casting roller 2 presses both ends of the core metal 23 with pressure means such as springs (not shown) to apply a predetermined pressing force to the entire length of the roller against the surface of the photosensitive drum. In this example, the photosensitive tram 1 rotates as the photosensitive tram 1 rotates.

9 is an external power source that applies voltage to the charging roller 2;
f set for the charging roller 2 by the power source 9;
A superimposed voltage of a DC voltage and an oscillating voltage with a peak-to-peak voltage that is more than twice the charging start voltage of the photoconductor is applied to the contact spring 8 and the core bar 2a.
By applying the electric potential through the electric potential, the outer circumferential surface of the rotationally driven photosensitive tram 1 is charged to a predetermined electric potential.

Next, the charged surface of the photosensitive tram 1 is subjected to image exposure 3, such as imaging exposure of the original image or scanning exposure with a laser beam modulated in accordance with printed information, by an exposure means (not shown). Electrostatic latent images corresponding to image information are sequentially formed on one surface of the photosensitive drum.

Next, toner is supplied to the surface of the photosensitive drum from a developing sleeve 4 of a developing device, and the latent image formed on the surface of the photosensitive drum is sequentially developed as a toner image.

A transfer roller 5 is brought into pressure contact with the photosensitive drum 1 on the downstream side of the developing sleeve 4 in the rotational direction of the photosensitive drum, and transfers the transfer material 7 from a paper feed section (not shown) to the pressure contact portion (transfer) between the photosensitive tram 1 and the transfer roller 5. With respect to part), when the leading edge of the toner image on the surface of the photosensitive drum 1 reaches the pressure contact part, the leading edge of the transfer material 7 also reaches the pressure contact part, and the transfer material 7 is supplied in a period synchronized with the rotation of the photosensitive drum. .

A transfer bias is applied to the transfer roller 5 from a power source, and as the transfer material 7 passes through the pressure contact section, the toner image on the surface of the photosensitive drum is sequentially transferred to the transfer material 7 side (transfer).
do.

After the toner image is transferred, one surface of the photosensitive tram is cleaned by a cleaning device 6.
It is rolled, cleaned to remove residual toner, and is repeatedly used for image formation.

(Problems to be Solved by the Invention) However, the above conventional example has the following problems.

1) Rubber layer 2 of the charging roller as a charging member due to durability
From b and 2c, the iT plastic of the rubber oozed out and adhered or fused to the surface of the photosensitive tram 1, which was the object to be charged, causing image deletion.

2) The axial length of the charging roller 2 for A3 size also increases accordingly, and the charging roller 2 is pressed against the photosensitive tram 1 parallel to the tram bus line by pressing both ends of the charging roller 2 with a pressure means such as a spring. When the roller is applied, the center of the roller or the surface of the photosensitive tram 1 is lifted, resulting in charging failure in that area.

3) For models with high process speeds, in order to prevent charging failures, it is necessary to increase the primary power frequency applied to the charging roller 2 according to the process speed, or to change the frequency of the photosensitive tram l and the charging roller 2 accordingly. The charged layer generated by vibration becomes larger.

If the charging layer is lowered to a practically acceptable range by reducing the peak-to-peak voltage of the bias applied to the charging roller, it becomes difficult for the necessary current to flow, resulting in charging failure.

The present invention makes it possible to satisfactorily charge the surface of an object to be charged, such as a photosensitive drum, by a contact charging method without the problems described in t.

(Means for Solving the Problems) The present invention is a contact-type charging device that charges the surface of a charged object by bringing a conductive member to which a voltage is applied into contact with the charged object via a resistive member, The conductive member is a wire rod, and the surface of the surface resistance member that comes into contact with the charged object is approximately flat.
The gist of this invention is a charging device characterized by the following.

(Function) (1) As a conductive member that applies the voltage of the contact charging member.
Using a thin conductive wire or conductive thin plate material with a diameter, width, or thickness of, for example, 5 to 1000 μm, the conductive wire is brought into contact with the surface of the object to be charged, either directly or through a resistance member. or by bringing the edges of the conductive thin plate into contact with each other directly or through a resistive member and moving them relative to each other,
In the same way as a contact charging roller or a contact charging broad, contact charging processing can be performed on the surface of the object to be charged.

(2) Unlike contact charging rollers and contact charging plates, this case does not have a charging layer made of rubber or the like, so the plasticizer seeping through the rubber charging layer may adhere to the surface of the charged object. This technology was developed to prevent problems such as fusion and resulting image blurring in image forming apparatuses.

(3) If the contact charging member is in the form of a wire or plate as mentioned in (1), the entire length of the wire or the edge of the thin plate is covered with appropriate holding means or supporting means. Even if it is easy to hold each part in contact with the surface of the charged object without floating, it will solve the problem of floating of the power supply part due to leakage and poor charging caused by the floating. It becomes possible.

(4) By making the conductive member to which the voltage of the contact charging member is applied a wire rod or thin plate material having a small diameter, width, or thickness, the generation of a charged layer is reduced to a range that does not cause any practical problems, or I was able to virtually eliminate it.

The reason for this is that when an external bias is applied to the charging roller, the roller begins to vibrate, and a charged layer is generated due to the flow of air caught between the roller and the charged object. By using a wire as the conductive member as described above, there is almost no air trapped between the contact charging member and the charged object, so even if the conductive wire vibrates, the charged layer will deteriorate or substantially It is thought that it will disappear.

(5) When charging the surface of the charged object by bringing the conductive wire into contact with the charged object through a resistance member, there may be surface defects such as holes on the charged object, resulting in charging failure in the entire lti region. It becomes possible to make it rainproof.

That is, is it possible to use a bare metal wire or an uncoated conductive wire as the contact charging member? (stains, foreign matter, etc.)
If a pinhole is generated in a contact charging member or an uncoated conductive wire, when the hole portion moves to the charging area where the charging member and the photosensitive drum are in contact, a pinhole will be formed between the charging member and the photosensitive drum. A leak may occur between the two and the voltage of the power supply section will drop significantly.

Therefore, when this leak occurs, the entire longitudinal direction of the contact between the contact charging member and the photosensitive drum becomes defective in charging, and in the actual image, image unevenness appears in the form of a black band in the case of a reversal phenomenon, and as a white band in the case of a normal phenomenon. This occurs every rotation period, and the image quality deteriorates significantly.

On the other hand, the volume resistivity of the resistance member can be increased by carrying out the charging process on the surface of the object to be charged in such a manner that a conductive wire to which a voltage is applied as a contact charging member is brought into contact with the object to be charged through the resistance member. Since it is larger than the conductive wire, the current that flows through the resistive member into surface defects such as holes on the charged object side is small, so even if a surface defect such as a hole occurs on the charged object, contact charging will not occur in that area. Leakage with parts (
It is possible to prevent a voltage drop in the power supply section due to excessive current flow. Therefore, even if there are holes or the like on the surface of the object to be charged, it is possible to prevent charging defects in the entire area where the contact charging member is in contact with the object to be charged. In the image forming apparatus, the above-mentioned problem of image quality deterioration is solved. Moreover,
Since sufficient voltage is applied to the charged object without increasing the supply voltage, it is possible to prevent charging defects and uneven charging due to insufficient AC voltage.

(6) The smaller the diameter, width, or thickness of the wire as the conductive member to which voltage is applied, that is, the width of the part of the conductive wire facing the charged object, the smaller the charging noise generated will be within the practical range. It can be made smaller or virtually eliminated.

However, as the above-mentioned width is made smaller, the charging width of the contact charging member becomes smaller, and as a result, the resistance of the charging section increases, making it difficult for current to flow and causing charging failures to occur more easily.

For example, as schematically shown in FIG.
A conductive wire 10a with a round cross section is used as a conductive member.
The outer circumferential surface of the conductive wire is coated with a resistive material 10b (resistive member), and this is pressed against a member 1, for example, a photosensitive drum 1 as an object to be charged.
1 and the pressing member 12, the entire effective length of the photosensitive drum is brought into pressure contact with the surface of the photosensitive drum substantially parallel to the drum generatrix;
In the case of a configuration in which a voltage is applied from the power source 9 to the conductive wire IOa to perform contact charging processing on one surface of the photosensitive drum, note that the width of the portion of the conductive wire foa of the contact charging member 10 facing the photosensitive tram 1 (=diameter of the wire 10a) is d, and the charging width is L, the charging width is the width d.
If the width d is made smaller in order to reduce the generated charging noise, the charging width becomes smaller and smaller, and charging defects are more likely to occur.

The charging width can be determined as follows. The conductive wire 1 is heated for several minutes with the photosensitive drum 1 stopped.
A bias is applied to 0a from the power supply 9. Next, this tram 1 is developed at a halftone potential and transferred to a transfer material. Then, the developed charged memory image is transferred onto the transfer material.

The width of this charging memory image is the charging width.

Note that t indicates the charging limit, which is the separation limit at which charging is no longer possible if the surface of the contact charging member 10 separates from the surface of the photosensitive drum 1 by more than t. This is determined by Paschen's law, and in a normal environment, the separation limit is approximately several tens of microns. be.

Therefore, in such a system, there is a certain limit to reducing the width d in order to reduce the generated charging noise due to the trade-off with ensuring a sufficient charging width.

As described above, the present invention is characterized in that the portion of the resistance member that contacts the charged object is approximately flat, and in this way, as schematically shown in FIG. The charging range expands.

The contact charging member 10 in FIG. 1 is a conductive member (wire) 1
A conductive wire with a round cross section is used as the conductive wire 0a, and this is attached to the lower surface of the horizontally long cushioning material 10c such as Moltplane. A rigid pressing plate 10d is provided on the upper surface of the cushioning material 10c on the opposite side to the covering layer 10b.

The coating layer 10b is a resistive member, and the surface that comes into contact with the charged object 1 is approximately flat.

The contact charging member 10 is held with the coating layer 10b, which is a resistive member, facing the surface of the photosensitive drum, which is the object to be charged, and is appropriately pressed against the elasticity of the cushion material 10c. A voltage is applied to the wire 10a to contact charge the surface of the photosensitive drum.

In this case, as mentioned above, the charging width increases with respect to the width d, so the width d is set small and the magnitude of the generated charging noise is reduced by 1
This makes it possible to maintain stable and sufficient charging at all times by suppressing or substantially increasing the amount of charging within a minute, and by ensuring a sufficient charging width.

The effect described in F is particularly effective in a contact charging method in which the peak-to-peak voltage of the AC voltage applied to the contact charging member is more than twice the charging start voltage for charging the charged object when only DC voltage is applied. be.

(Example) In FIG. 1, 1 is a photosensitive drum as a charged body in the image forming apparatus shown in FIG. The formed photoreceptor layer Ia (in this example, an organic photoreceptor (
OPC)), has an outer diameter of 30φ in this embodiment, and is driven to rotate at a predetermined speed in the clockwise direction of the arrow.

10 is the contact charging member mentioned above. Specifically, the details are as follows.

Conductive wire 10a: tungsten wire with diameter d=60 μm.

Resistance member 10b = carbon fluorine resin with volume resistivity controlled to IQIOΩcm (product: Emlaron, Nippon Asison Co., Ltd.), thickness 25 μm
0 In the case of this contact charging member 10, the charging width was 200 μm with respect to the diameter d of the conductive wire 10a: 60 μm.

It should be noted that the resistance material coating 10b (thickness 2
Tungsten wire 1 with diameter d = 60 μm
The charging width in the case of the contact charging member IO having the form 0a was as small as 40 μm.

In this embodiment, with the above configuration, the photosensitive drum 1 is moved at a circumferential speed of 4.
Rotate at 0 mm/sec and charge wire 1
When a DC voltage of -700 V and an AC voltage with a peak-to-peak voltage of 1,800 Vpp and a frequency of 250 Hz were applied to the power source 9, the surface of the photoreceptor 18 was uniformly charged to about -700 V, causing abnormal images due to holes and charging noise. There was no occurrence or very small occurrence, and a good image was output.

In the case of this embodiment, the presence of the cushion member 10c has the effect of further reducing the generation of charging noise.

In addition, unlike in the case of charging rollers and charging blades, there was no occurrence of image deletion due to stains from the conductive rubber layer due to plasticizer, or occurrence of partial charging defects due to floating of the charging member.

This embodiment is particularly applicable when the peak-to-peak voltage of the AC voltage/E applied to the charging member 10 is set to 1-2 times the charging start voltage that charges the wave-charged body when only the DC voltage is applied. The effect is great.

In this example, the charging start voltage when only DC voltage was applied was -560V.

The conductive member 10a is not limited to tungsten, but may be made of any conductive material such as iron, copper, aluminum, or SUS.

The cross-sectional shape of the conductive member 10a is limited to a circular shape, but the cross-sectional shape may be any rectangular (rectangular) square, triangular, square (rectangular), or elliptical shape as in the example shown in FIG.

The coating layer 10b as a resistance member generally has a thickness of 10 to 1000
The layer thickness is assumed to be μm. Other constituent materials include N-
Resins such as methoxymethylated nylon (trade name: Torezin: Teikoku Kagaku Sangyo ■), polyvinyl butyral resin, polyurethane resin, ethylene/vinyl acetate resin, styrene-butadiene resin, regenerated cellulose, as well as epichlorohydrin, urethane, CR, and NBR-based resins. rubber, etc. can be used. Furthermore, it is also possible to use a heat shrink tube.

The waveform of the oscillating voltage is not limited to a sine wave, but may be a rectangular wave, a square wave, or a pulse wave. Furthermore, it is possible to charge the object to be charged with the same amount of DC voltage.

The number of 4+1 wires 10a is not limited to one, but by using two or more wires, more reliable charging performance can be obtained than in the case of one wire. Even if a foreign object adheres to one charging wire or the wire is broken, charging can be reliably continued using the remaining charging wires.

As shown in the cross-sectional diagrams of the conductive wire FOA in FIGS.
It can also be an integrally molded body embedded within the wall thickness of 0b, which has the advantage of being mass-producible and reducing costs.

(Effects of the Invention) As described below, according to the present invention, the charging noise generated in a contact charging type charging device is reduced or substantially eliminated,
In addition, it is possible to ensure good charging properties, and other
Previous problems have been resolved and the intended objectives have been successfully achieved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional model diagram of the device of the first embodiment. FIG. 3 is the same view of the second embodiment device of FIG. 2; 3 (A> and (B) are the same views as above of the third embodiment apparatus. FIG. 4 is the same view of the comparative example apparatus. FIG. 5 is a schematic view of an example of an image forming apparatus using a charging roller. Reference numeral 1 denotes a photosensitive tram as an object to be charged, 10. a contact charging member, 10a a conductive member, 10b a resistive member, and 9 an external power source.

Claims (1)

[Claims] (1) A contact-type charging device that charges the surface of the charged object by bringing a conductive member to which a voltage is applied into contact with the charged object via a resistive member, the conductive member being a wire, and the resistor A charging device characterized in that a surface of the member that comes into contact with an object to be charged is substantially flat.