JPH10198132A - Electrifying method and device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uniform electrification at one time, to suppress the total discharge without reducing a potential and to minimize the deterioration of the surface of an electrified means by providing a preexposure means for clearing the potential on the electrified means on the upstream side in the moving direction of the means to be electrified of an electrifying means and specifying the moving speed of the electrified means. SOLUTION: This image forming device has the preexposure means 3 provided in a position nearer to the upstream side in the moving direction of the means 1 to be electrified than the electrifying means 2. When the distance between the most downstream point of a preexposure irradiation region and the electrification starting point of the means 2 is defined as 1(mm), the moving speed of the means 1 is defined as v(mm/sec) and the life of a photocarrier generated in the electrified means 1 by preexposure is defined as t(sec), 1/v>t is satisfied. Thus, the potential of the surface of the photoreceptor drum 1 is increased up to a prescribed one by an electric discharge in a gap on the upstream side formed by the drum 1 and the electrifying roller 2. After that, the potential of the surface is kept almost constant up to the contact part, of the drum 1 with the electrifying roller 2, the gap on the downstream side and further, the completion of electrification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus for forming an image by a charging method and a charging device for charging a surface of a member to be charged and an image forming process means including a step of charging the member to be charged by the charging device. The present invention relates to an image forming apparatus such as a copying machine, a printer, and the like, and an electrostatic recording device.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
2. Description of the Related Art A corona charging method using corona discharge has been widely used as a charging device for charging a photosensitive member, a dielectric, or the like serving as an image carrier, which is a charged member. However, the corona charging method using corona discharge generates a large amount of undesired ozone at the time of discharge and requires a high voltage power supply. And high cost. For this reason, in recent years, low power consumption has been achieved, and a contact charging method that generates very little ozone has been put to practical use.

In this contact charging system, a charging means is disposed in direct contact with or in proximity to a charged object, and a voltage is applied to the charging means to change the surface of a roller-shaped photosensitive member as an image carrier. This is a method of performing a charging process (including a static elimination process).

In this case, there are a method of applying only a DC voltage to the charging roller (DC charging method) and a method of applying an AC voltage or an oscillating voltage obtained by superimposing a DC voltage on an AC voltage (AC charging method). In particular, the latter AC charging method is preferably used because it has better charging uniformity and provides a beautiful image than the DC charging method.

The charging means does not necessarily need to be in contact with the charged means, and as long as a dischargeable area determined by the gap voltage and the corrected Paschen curve between the charging means and the charged means is reliably guaranteed. And non-contact (proximity), which is also included in the category of contact charging.

In the above-described DC charging method and AC charging method, a roller-shaped charging member (hereinafter, referred to as a charging means) is used as a charging means.
It is known that when a charging roller is used, charging is performed by corona discharge in a minute gap on both sides of the contact position between the photosensitive member and the charging member. However, as described above, with respect to the photoconductor moving direction, when charging is performed at both the upstream and downstream minute gaps from the contact position of the charging roller, the potential difference between the charging roller and the photoconductor surface is not sufficient, Since the discharge is not stable, a part where the discharge is weak partially occurs, and small white stripes having a width of about 2 to 10 mm and a width of about 0.5 mm or less are generated in a direction perpendicular to the moving direction of the photoconductor.

Therefore, conventionally, in order to solve this problem, a method has been proposed and put into practical use in which the charge caused by the above-mentioned upstream charging is removed and only the downstream charging is used.

FIG. 5 is a schematic cross-sectional view around a photosensitive member of an image forming apparatus using such a charging device. The photosensitive member 1 and the charging roller 2 are formed on the upstream side with respect to the moving direction b of the photosensitive member. The light of the pre-exposure light source 3 is applied to the reflection
Irradiation is performed via the. 5 is an image exposure unit, 6 is a development unit, 7 is a transfer unit, and 8 is a cleaning unit.

[0009]

However, the above conventional example has the following problems.

That is, in order to completely remove the charging in the minute gap on the upstream side with respect to the moving direction of the photosensitive member, it is necessary to accurately irradiate a large amount of light to the minute gap on the upstream side. In addition, the mounting accuracy of the reflector 51 must be strictly controlled.

In order to obtain a sufficient amount of light, it is necessary to emit light more than in the normal pre-exposure 3. Therefore, since the light is irradiated to the charging roller 2 itself, the light emitted from the pre-exposure 3 is emitted. The heat gradually accumulates and raises the temperature inside the apparatus, adversely affecting the toner of the developing unit 6 or changing the resistance value of the charging roller 2.

Further, since the pre-exposure 3 irradiates the minute gap immediately before the nip formed by the photoreceptor 1 and the charging roller 2, the photocarriers in the photoreceptor 1 generated by the pre-exposure remain after passing through the nip. In some cases, the charge in the downstream gap may also be removed, resulting in poor charging efficiency and non-uniform charging potential.

Further, since charging is performed in both the upstream gap and the downstream gap, and discharging is performed simultaneously with charging on the upstream side, a discharge current always flows, and the photosensitive member 1 is charged.
There are problems such as promoting the deterioration of the surface of the photoconductor 1 and shortening the life of the photoconductor 1.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and provides a charging method and a charging device capable of uniformly and efficiently charging and extending the durable life of a charged member. As a first object.

Another object of the present invention is to provide an image forming apparatus capable of prolonging the durable life of a charged member, performing uniform and efficient charging, and producing a high-quality image without white stripes or the like. This is the purpose of 2.

[0016]

According to a first aspect of the present invention, there is provided a charging method according to the invention, wherein the charging means is disposed in contact with or in proximity to a moving charged means and has a relative movement relationship with the charged means. Power supply means for applying a voltage to the charging means, and a pre-exposure means provided upstream of the charging means in the moving direction of the charged means so as to perform pre-exposure for removing charges on the charged means. The distance between the most downstream point of the pre-exposure irradiation area and the charging start point of the charging unit is 1 (mm), the moving speed of the charged unit is v (mm / sec), and the charged unit is charged by the pre-exposure. When the life of the photocarrier of the photo generated at the time t is t (sec), 1 / v> = t is satisfied.

According to a second aspect of the present invention, there is provided a charging device which is disposed in contact with or close to a moving charged device and which has a relative moving relationship with the charged device; A power supply unit for applying a voltage; and a pre-exposure unit provided upstream of the charging unit in the moving direction of the charged unit so as to perform pre-exposure for removing charges on the charged unit. The distance between the most downstream point of the irradiation area and the charging start point of the charging unit is 1 (mm), the moving speed of the charging unit is v (mm / sec), and the photocarrier generated on the charging unit by the pre-exposure is When the life is t (sec), 1 / v> = t is satisfied.

The charging device according to the third aspect of the invention is characterized in that the voltage applied to the charging means is a DC voltage or an oscillating voltage obtained by superimposing a DC voltage on an AC voltage.

According to a fourth aspect of the present invention, in the charging device, a light shielding member is provided between a most downstream point of the pre-exposure irradiation area and a charging start point of the charged member.

According to a fifth aspect of the present invention, the charging device is characterized in that the charging means is pressed against the charged means with a constant pressing force.

According to a sixth aspect of the present invention, the charging means of the charging device comprises a metal core to which a voltage is to be applied, a conductive layer formed on the surface of the metal core, and a resistance layer formed on the surface. It is characterized by the following.

The charging device according to the present invention is characterized in that one or both of the charged means and the charging means are relatively moved.

According to an eighth aspect of the present invention, there is provided an image forming apparatus for forming an image on a charging device according to any one of the second to fifth aspects and a surface of a member to be charged. And an image forming process unit.

The image forming process means of the image forming apparatus according to the present invention has an image exposing means, a developing means, a transferring means, a cleaning means, and a pre-exposing means.
The pre-exposure unit is provided on the downstream side of the transfer unit in the moving direction of the charged unit and above the transfer unit that receives an image transfer from the charged unit by the transfer unit.

In the image forming apparatus according to the present invention, the exposure amount of the pre-exposure means for irradiating the nip portion between the charged means and the transfer means is 2 to 15 times the image exposure amount. It is characterized by.

According to the eleventh aspect of the present invention, the charged member of the image forming apparatus is an image carrier for forming an image.

An image carrier of an image forming apparatus according to the present invention comprises a charge generating layer formed on the surface of a base and a charge transport layer formed on the surface of the charge generating layer. It is characterized by the following.

According to a thirteenth aspect of the present invention, the image carrier of the image forming apparatus has an endless belt shape.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 is a cross-sectional view schematically showing the vicinity of an image forming unit of an image forming apparatus that best illustrates the features of the present invention.
Reference numeral 1 denotes a photosensitive member on a drum serving as an image carrier serving as a charging means (hereinafter, referred to as a photosensitive drum). 2 denotes a roller-shaped charging member serving as a charging member serving as a charging means (hereinafter, referred to as a charging roller). Reference numeral 3 denotes a pre-exposure illumination lamp as a pre-exposure light source as pre-exposure means, and 4 denotes a photosensitive drum 1 immediately before charging.
A light-shielding member for preventing irradiation of pre-exposure to the image, 5 is an image exposure as an image exposure means, 6 is a developing device as a development means
Reference numeral 7 denotes a transfer device as transfer means, and reference numeral 8 denotes a cleaning device.

The photosensitive drum 1 is a drum-type drum having a layered conductive polymer material, that is, a conductive base layer made of aluminum or the like and a photoconductive layer (charged surface) formed on the outer periphery thereof as a basic constituent layer. The photosensitive drum 1 is driven to rotate around a support shaft (not shown) at a predetermined peripheral speed v in the direction of arrow b.

The charging roller 2 comes into contact with the surface to be charged of the photosensitive drum 1, and uniformly charges (including a charge removing process) the photosensitive drum 1 to a predetermined polarity and potential. This charging roller 2
The basic structure includes a central metal core 2a, a conductive layer 2b formed on the outer periphery thereof, and a resistance layer 2c formed on the outer periphery thereof.

The charging roller 2 is rotatably supported at both ends in a longitudinal direction (a direction along the metal core) of the metal core 2 a by a bearing member (not shown). And pressing means (not shown)
As a result, the photosensitive drum 1 is pressed against the charged surface of the photosensitive drum 1 with a predetermined pressing force, and is driven to rotate in the direction of arrow c with the rotation of the photosensitive drum 1 in the direction of arrow b.

A power supply sliding contact (not shown) is in contact with the metal core 2a of the charging roller 2, and a DC voltage or an oscillating voltage is applied from a power supply (not shown) via the contact.
As a result, the charged surface 1 of the photosensitive drum 1 is contact-charged to a predetermined polarity and potential.

The charging roller 2 may be driven to rotate as described above, or may be positively driven at a predetermined peripheral speed in the forward or reverse direction with respect to the rotation direction of the charged surface of the photosensitive drum 1. May be driven to rotate. Further, the charging member 2 can be fixedly disposed without rotating, and the charging member 2 can be arranged along the fixed planar photosensitive member surface.
Can also be moved.

The photosensitive drum surface uniformly charged by the charging roller 2 is subjected to image exposure 5 (laser beam scanning exposure, slit exposure of a document image, etc.) of target information. In this embodiment, slit exposure of the document image is performed. Is performed, an electrostatic latent image corresponding to the target information can be formed on the charged surface of the photosensitive drum. The electrostatic latent image is developed with a toner in the developing device 6 and is sequentially visualized as a toner image.

This toner image is then transferred to the transfer paper 9 by the transfer device 7. The transfer device 7 includes a rotatable transfer roller 7 and a transfer power supply (not shown), and charges the toner on the photosensitive drum 1 from the back side of the transfer paper 9 by the transfer power supply. The images are sequentially transferred onto the upper surface of the transfer paper 9. Here, the transfer paper 9 is transported from a transport device (not shown) to a transfer section between the photosensitive drum 1 and the transfer device 7 at an appropriate timing synchronized with the rotation of the photosensitive drum 1. is there.

The transfer paper 9 to which the toner image has been transferred is subsequently separated from the photosensitive drum 1 and conveyed to a fixing device (not shown) where the toner image is fixed. Or, for example, if an image is also formed on the back surface, it is conveyed to a re-conveying unit to the transfer unit.

After the transfer of the photosensitive drum 1 from which the toner image has been removed, the contaminants such as residual toner are removed by the cleaning blade of the cleaning device 8, and then the charge is removed by the pre-exposure device 3 to perform the copying process. Of 1
The cycle ends.

A light-shielding plate 4 is provided between the pre-exposure light source 3 and the charging roller 2, and a distance l between an irradiation position of the pre-exposure and a contact portion between the charging roller 2 and the photosensitive drum 1 is set. During this time, the surface of the photosensitive drum 1 is not irradiated with light. That is, light is irradiated by the pre-exposure light source 3,
After the photocarriers are generated in the photoconductor drum and the charge on the photoconductor drum surface is removed, the photocarriers in the photoconductor drum are darkened by the light shielding plate 4 as the photoconductor drum 1 rotates. All the photo carriers disappear, and the adjacent portion d (charging area) between the charging roller 2 and the photosensitive drum 1
Then, the surface of the photosensitive drum 1 is charged by the charging roller 2 in a state where the charge is removed and there is no photocarrier of the photosensitive drum. The charging ends.

That is, when the pre-exposure is applied to the vicinity of the upstream side gap or to the upstream side gap, if the light is completely irradiated into the gap, the charge on the upstream side is eliminated, and furthermore, the light is applied to the gap side. The generated photocarrier remains even after passing through the contact portion between the photosensitive drum 1 and the charging roller 2, and partially removes the charge caused by the discharge between the charging roller 2 and the photosensitive drum 1 in the downstream gap. As a result, the discharge current is wastefully removed, so that the charging efficiency is low with respect to the discharge current, and the damage to the photosensitive drum due to the discharge is increased.

When light is irradiated to the vicinity of the gap region without irradiating the light in the gap on the upstream side, the photocarrier sufficiently remains in the charged region d. Is done. Further, the photosensitive drum 1
The surface potential of the photosensitive drum 1 gradually decreases between the charging roller 2 and the charging roller 2 due to the influence of the photocarrier. If discharge and charging are performed in the gap between the photosensitive drum 1 and the charging roller 2 on the downstream side in this state, the potential difference between the charging roller 2 and the surface of the photosensitive drum 1 is not sufficient, and the discharge is not stable. In this case, a weak discharge portion is formed, which causes white stripes and the like.

FIG. 2 shows how the surface potential of the photosensitive drum 1 changes near the charging roller 2 when the irradiation position of the pre-exposure is changed. In FIG. 2, the vertical axis indicates the charging potential. The horizontal axis represents the relative position between the photosensitive drum 1 and the charging roller 2. In the figure, a solid line 21 indicates a transition of charging in the first embodiment according to the present invention,
Represents the transition of the charging in the conventional charging in which the pre-exposure is irradiated to the vicinity of the upstream gap, and the dotted line 23 represents the transition of the charging in the case where the pre-exposure is irradiated to the inside of the upstream gap.

A dashed line 22 indicates a transition of the charging when the pre-exposure is irradiated to the vicinity of the upstream gap and the charging is performed by the charging roller 2 in a state where the photocarriers sufficiently remain in the photosensitive drum 1. In the upstream side gap, although receiving the charge by the discharge, a part of the charge is continuously removed by the photocarrier, and the charge is gradually attenuated also in the contact portion between the photosensitive drum 1 and the charging roller 2.

Then, in the downstream gap, discharge starts between the photosensitive drum 1 and the charging roller 2 to be charged. However, since the difference between the surface potential of the photosensitive drum 1 and the potential of the charging roller 2 is small, the discharge is unstable. , Partial discharge unevenness occurs, charging ripples of about 30 to 50 V are generated, appear as white stripes and black stripes, and the uniformity of charging is poor. Further, since the removal of the charged charges and the recharging are repeatedly performed, the discharge current amount increases, and the deterioration of the photosensitive drum is accelerated accordingly.

The dotted line 23 shows the transition of the charging when the pre-exposure is irradiated to the inside of the upstream gap. In the upstream gap, the discharge between the photosensitive drum 1 and the charging roller 2 is performed. Since static elimination is performed, the charged potential on the surface of the photosensitive drum 1 remains almost 0,
In this state, the toner passes through the contact portion between the photosensitive drum 1 and the charging roller 2, and charging is started by discharge in the downstream gap. In this case, since the photocarrier is still sufficiently present, a part of the charge on the surface of the photoreceptor is continuously removed, so that the charged potential is separated from the downstream gap without increasing sufficiently.

Accordingly, since there is no discharge or charging phenomenon in a state where the potential difference is small, the occurrence of white stripes or the like due to unstable charging is prevented, but the upstream gap between the photosensitive drum 1 and the charging roller 2 is prevented. Since the discharge is always performed once or more in the downstream gap in the section, the discharge current amount with respect to the charging potential is very large, and the deterioration of the photosensitive drum is promoted.

On the other hand, the solid line 21 according to the first embodiment
Since the photocarriers on the photosensitive drum 1 have disappeared at the start of charging, the potential on the surface of the photosensitive drum 1 is reduced to a predetermined potential by discharging in the upstream gap formed by the photosensitive drum 1 and the charging roller 2. After that, the potential of the surface is kept substantially constant until the contact portion between the photosensitive drum 1 and the charging roller 2 and the gap on the downstream side and until the end of charging.

In this case, since the discharge is performed only in a part of the upstream gap, the charge can be efficiently performed with a small amount of discharge, and an extremely uniform charge can be obtained. Further, since the discharge amount is small and the efficiency can be increased, the deterioration of the photosensitive drum 1 can be suppressed to a small extent.

Therefore, the same potential difference between the photosensitive drum 1 and the charging roller 2 can be obtained as compared with the conventional method in which the upstream gap indicated by the dotted line 23 is irradiated with the pre-exposure to suppress the occurrence of white stripes and the like. In this case, since the charging is performed only in the substantially upstream gap, the discharge current is reduced to about １ ／, and the scraping amount of the photosensitive drum 1 is reduced to about に 対 し て for the same durable number.
Has the effect of becoming

When the same charging potential is applied to the photosensitive drum 1, when the nip exposure is applied to the upstream gap, it is necessary to increase the potential difference between the photosensitive drum 1 and the charging roller 2. Yes, instantaneous discharge power increases. For this reason, the deterioration of the surface of the photosensitive drum 1 is further accelerated, and the shaving amount increases. On the other hand, in the configuration of the first embodiment, the shaving amount can be reduced to 1/3 to 1/4.

Further, as the discharge power increases, the deterioration of the photoconductive property of the photosensitive drum 1 and the deterioration of the sensitivity (increase in vs1) are promoted. In the charging method and the charging device according to the first embodiment, a predetermined charging potential can be obtained with a small discharge power, so that the sensitivity of the photosensitive drum 1 hardly deteriorates. Therefore, there is an effect that a good image can be obtained for a long time.

The minute gap (the width of the charging area d) formed between the photosensitive drum 1 and the charging roller 2 varies the curvature, resistance value, capacitance, etc. of the photosensitive drum 1 and the charging roller 2 and changes the photosensitive drum 1 And the electric field applied between the charging rollers 2. In order to know the width of the charging area d, a predetermined potential difference is applied between the photosensitive drum 1 and the charging roller 2.
By applying a pulse bias of １００100 μsec and observing the potential on the photosensitive drum, the charging area d and the charging start point can be known.

In the charging method and the charging apparatus according to the present invention, as a condition for eliminating photocarriers before charging, assuming that the life of the photocarrier is t, the photosensitive drum 1 and the charging roller are charged after the end of the pre-exposure. The distance to the upstream gap portion (upstream end of the charging area d) between the lasers 2 is 1,
When the peripheral speed of the photosensitive drum 1 is set to v, it is necessary that 1 / v> = t.

Since the life length of photocarriers generally has a distribution, it is preferable to set the life time of 100% of the photocarriers to disappear. In the case of the present invention, it is also included in the scope of the present invention that t is set to a range in which the charging potential is hardly affected, for example, 98% of all photocarriers disappear.

The life of the photocarrier of the photosensitive drum is
Although it is affected by the material, thickness, ambient temperature, humidity, and the like of the photoconductive layer, the blackout time may be set to be longer than the life of the photocarrier under actual use conditions. In addition, the influence of scattering of pre-exposure light on the surface of the photoreceptor drum, or particularly when light is irradiated to the upstream gap, the irradiation angle of the light becomes closer to the tangential direction of the photoreceptor. Does not proceed in the axial direction of the photoconductor drum, propagates along the surface layer of the photoconductor drum, is scattered by impurity defects on the surface of the photoconductor drum, is absorbed by the inside of the photoconductor drum, and is downstream from the light irradiation position. Photo carriers may also be formed on the side.

In this case, the time until the substantial disappearance of the photocarriers in consideration of the generation of such secondary photocarriers is referred to as the lifetime of the photocarriers rather than the physical lifetime of the photocarriers. It is the gist of the present invention to eliminate residual photocarriers.

In the first embodiment, the light shielding plate 4 is provided between the pre-exposure device 3 and the charging roller 2 to cut the exposure on the upstream side of the charging area. The pre-exposure is not directly applied to the surface of the charging roller, the temperature rise due to radiant heat is prevented, and the resistance value of the charging roller 2 changes due to the drying of the charging roller 2 and the deterioration of the rubber layer. Can be suppressed. Further, since the light along the surface layer of the photosensitive drum 1 is cut by the light shielding plate 4 and only the light in the normal direction to the photosensitive drum 1 is generated, the secondary generation of the photo carrier is prevented. There is an effect that good and efficient charging and image formation can be performed.

Second Embodiment In the first embodiment, a photosensitive member having a drum shape is used. However, a photosensitive member having another shape can be used. FIG.
The photoreceptor has an endless belt shape, and the same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

As in the second embodiment, by forming the photosensitive member into an endless belt shape, even if the light shielding member 4 is not provided immediately before the charging roller 2, the photosensitive member on the surface of the photosensitive member upstream of the charging roller 2 can be provided. It is possible to easily create a configuration that can prevent exposure irradiation.

Third Embodiment In the first and second embodiments, the position of the pre-exposure lamp is located upstream of the charging roller 2 and downstream of the cleaning member 8. If the photo carrier has disappeared before, the position is not limited to this position, and may be provided, for example, on the upstream side of the cleaning member 8.

FIG. 4 shows a third embodiment in this case, and the same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. An organic photoconductor (hereinafter, referred to as an OPC layer) is used as a photoreceptor, and contact charging and contact transfer (both having a roller shape) that generate less ozone are used as a charging / transfer process. 2-1578
No. 6 discloses a film fixing device 10 (a so-called SURF fixing device) pursuing energy saving.

In the OPC layer, if the charging potential and the post-transfer potential are set too high, a charging memory may be generated. Particularly, in the transfer portion, the post-transfer potential greatly differs depending on the presence or absence of the transfer paper 9. Since the post-transfer potential of a portion having no image (for example, a portion where the transfer paper 9 does not pass when a small-size transfer paper passes through the largest original) increases, the
There is a high possibility that the residual potential increases due to impurity defects in the layer, and the transfer voltage cannot be sufficiently increased.

As a result, since the transfer voltage is small, the recording paper 9 and the developer (toner) are not sufficiently adsorbed, and the SUR
The image on the recording paper may be disturbed by generation of water vapor due to rapid heating in the F fixing unit 10 and air flow due to expansion.

There is also a method of controlling the exposure light amount, charging voltage and transfer voltage by detecting the thickness of the OPC layer. As a method of detecting the thickness of the OPC layer, the charging roller 2 and the photosensitive member 1 are controlled.
JP-A-5-30 discloses a method for detecting the amount of current flowing between
No. 7315.

However, in the method of detecting the amount of current flowing between the charging roller 2 and the photoconductor 1, the current flowing through the photoconductor 1 is determined by the amount of change in the surface potential of the photoconductor drum and the OPC
Since the thickness is determined by the thickness (capacity) of the layer, in order to know the thickness of the OPC layer accurately, it is necessary to keep the potential on the photoconductor before contact between the charging member 2 and the photoconductor 1 at a constant value. .

In general, pre-exposure is performed to keep the potential on the photosensitive drum constant. However, if provided between the charging member 2 and the cleaning member 8 as described above, miniaturization of the apparatus is hindered. This is a factor. When the photosensitive drum 1 has deteriorated and the light-potential portion has risen, the potential of the photosensitive member cannot be set to a predetermined value in the pre-exposure, and a residual potential remains. Since the amount is smaller than when there is no residual potential, the thickness of the photosensitive drum may not be known correctly.

Next, an image forming operation will be briefly described with reference to FIG. The photosensitive drum 1 is driven to rotate in a direction indicated by an arrow b by a driving unit (not shown). A DC voltage or an oscillating voltage is applied to the charging roller 2 from a power supply (not shown).
The surface of the photoreceptor drum 1 is contact-charged with a uniform potential. Subsequently, image exposure 5 is given by a known image exposure means (not shown), and an electrostatic latent image is formed on the photosensitive drum 1. The electrostatic latent image is formed into a head image by a toner of a known developing device 6, and the visualized toner image is transferred to a transfer paper 9 as a recording paper by a transfer roller to which a voltage is applied by a power supply (not shown). The transfer paper 9 carrying the transferred toner image is transported to a SURF fixing device 10 by a transport device (not shown), and is heated and pressed to be fixed. On the other hand, the photosensitive drum 1
The remaining toner is cleaned by the cleaning device 8 and used for the next image formation.

In the image forming apparatus according to the third embodiment, the illuminating device 3 is provided below the cleaning device 8, and the nip formed by the photosensitive drum 1 and the transfer roller 7 is located downstream of the photosensitive drum 1 in the rotation direction. Light is irradiated from the side to attenuate the surface potential of the photosensitive drum 1 immediately after transfer / separation.

Here, the relationship between the transfer strength (post-transfer potential) when there is no exposure after transfer, the image disturbance during fixing, and the transfer speed of the transfer paper will be described. The case where the photosensitive drum 1 is negatively charged, the developer (toner) is positive, and the transfer electric field is negative will be described as an example.

The surface potential of the photosensitive drum 1 after passing through the transfer roller 7 indicating the transfer strength (hereinafter, referred to as a post-transfer potential) is
Even if the same transfer electric field is applied, the potential varies depending on the type and presence or absence of the transfer paper 9, but the potential after transfer becomes highest when there is no transfer paper.

When a paper of 46 to 128 g / cm ² is used as the transfer paper and particles having an average particle diameter of about 6 to 11 μm and a charge amount of about +9 to 12 μc / g are used as the toner, the non-paper passing portion When the post-transfer potential of the entire white portion is -900 V or more, good transferability can be obtained. This value was the same even when the transfer speed of the transfer paper 9 was changed from 20 to 200 mm / sec. This means that the amount of charge for transferring the toner on the photosensitive drum 1 to the transfer paper 9 is substantially constant regardless of the speed.

When the fixing operation is performed by the film fixing device 10, there is a close relationship between the post-transfer potential, the transfer speed of the transfer paper, and the image disturbance during fixing. Here, the principle of image disturbance during fixing will be briefly described.

In the film fixing device 10, the film 10
a is heated intensively in the nip portion 10d formed by the heater 10b and the pressure roller 10c, so that the air around the transfer paper taken along by the transfer paper 9 and the air in the transfer paper are generated by the heat of the nip portion 10d. The expansion and the moisture in the transfer paper are vaporized and expanded by the heat of the nip 10d, so that the unfixed image on the transfer paper 9 is blown off at the entrance side of the nip, thereby causing image disturbance in fixing.

As a method of preventing the image disturbance in the fixing unit, a method of warming a paper feed cassette for the purpose of preventing the transfer paper 9 from absorbing moisture, a method of warming the transfer paper 9 and the air before the nip is inserted, for example, an entrance of the nip A method of preliminarily warming the pressure roller, the fixing film, etc. on the side, suppressing the rapid vaporization / expansion of air and moisture in the nip, a method of releasing the vaporized / expanded air, applying an electric field to the nip 10d, Has been proposed and put to practical use. However, each of these methods complicates the fixing device 10 and causes an increase in cost.

Tables 1 to 4 show the moisture absorption state of the transfer paper 9 and the transfer paper 9
Is a summary of the relationship between the transfer speed, the post-transfer potential (non-sheet passing portion) and the image disturbance.
Indicates that an image disorder has occurred.

[0076]

[Table 1]

[0077]

[Table 2]

[0078]

[Table 3]

[0079]

[Table 4] The film fixing device 10 is used for a copying machine FC2 manufactured by Canon Inc., and is performed at a temperature at which the toner can be satisfactorily fixed at each speed. According to experiments conducted by the applicants and the like, even if the speed of the image forming / transfer process is changed, if the post-transfer potential (non-sheet passing portion) is the same, the manner of occurrence of image disturbance is the same for each fixing speed. Met. This means that if the potential is the same after the transfer regardless of the transport speed of the transfer paper 9, the toner and the transfer paper 9 have the same suction force.

As can be seen from the table, the disorder of the image becomes worse as the transport speed of the transfer paper 9 increases and as the amount of water in the transfer paper 9 increases. This requires a certain amount of heat to fix the toner image, and the amount of air that expands due to the amount of heat is constant, so that a faster transport speed makes it more difficult for the expanded air to escape, resulting in image disturbance and moisture When the amount is large, it is considered that turbulence is likely to occur because the amount of vaporized vapor increases.

In this experiment, the potential after transfer (non-sheet passing portion) was 90
When the voltage is less than 0 V, the experiment was not performed because the transfer performance may not be sufficient. Further, the potential after transfer is -20.
When the voltage is 00 V or more, the applicant has omitted the experiment because the applied voltage may leak between the transfer roller 7 and the ground substrate of the photoconductor drum 1 in the photoconductor used. It is thought that if the post-transfer potential is further increased, the attraction force between the transfer paper 9 and the toner is increased, and even if the speed is further increased, the image is not disturbed.

However, in the conventional image forming apparatus, if the post-transfer potential is set to -1500 V or more, the injection of electric charge is promoted, and a charge memory, an increase in the residual potential and the like due to impurities and defects in the OPC layer are caused. Previously, it could not be used because of body deterioration.

According to the image forming apparatus of the third embodiment, however, the transfer roller 7 and the nip portion on the downstream side in the rotation direction of the photosensitive drum 1 are exposed to light. Since the attenuation is attenuated, the deterioration of the photosensitive drum due to the injection of electric charges or the like is substantially prevented, so that the transfer electric field can be increased, and the attraction force between the transfer paper 9 and the toner is increased. This has the effect of preventing image disturbance and the like.

Further, exposure is performed immediately after the transfer (in the third embodiment, about 5 times the image exposure amount, generally about 2 to 15 times the image exposure amount in order to completely attenuate the charging potential). If it is less than twice the image exposure amount, the light may not be sufficiently attenuated, and if it is more than 15 times, an optical memory may be generated.) Adhesion of residual toner is weakened,
The cleaning can be easily performed, the allowable setting range can be widened, and the cleaning pressure is set to a small value, so that the shaving amount of the photoconductor 1 can be further reduced, and the life of the photoconductor 1 can be reduced. Has the effect of extending.

Further, even if small-size paper is continuously passed, deterioration of the photosensitive potential (increase in residual potential) due to charge injection does not occur, so that the potential can be uniformly and stably attenuated.
The amount of current flowing between the charging roller 2 and one photoconductor is stabilized, and the thickness of the OPC layer of the photoconductor 1 can be accurately detected. Therefore, appropriate control can be performed by this detection value, and a higher-quality image can be provided. Further, the cleaning device 8 can also be used as the light shielding device 4.

[0086]

As described above, according to the present invention,
The following effects can be obtained. 1) A pre-exposure unit for clearing the potential on the charged unit is provided upstream of the charging unit in the moving direction of the charged unit, and a most downstream point of the pre-exposure irradiation area and a charging start point of the charging unit. 1 (mm) and the moving speed of the charged member is v (mm / sec).
c), and when the lifetime of the photocarrier generated on the charged member by the pre-exposure is t (sec), 1 / v
> = T, so that all charges of the charged member before charging are removed by pre-exposure irradiation, and the charged portion is charged at the time of charging in the upstream gap formed between the charged portion and the charging device. Since all the photocarriers in the means have disappeared, the charging is performed uniformly at one time, and the potential is not reduced, the total discharge can be suppressed, and the effect of minimizing the deterioration of the surface of the means to be charged is reduced. There is.

2) In addition to the above effects, there is an effect that an image forming apparatus capable of supplying a high-quality image and having a long life of the charged member can be provided.

3) Since the light shielding means is provided between the most downstream point of the pre-exposure irradiation area and the charging start point of the charging means,
A substantial pre-exposure irradiation direction is restricted, and light in the tangential direction of the charged means incident on the upstream gap formed by the charged means and the charging roller can be reduced to zero, thereby increasing the charged area. The photo carrier can be extinguished in front. As a result,
There is an effect that more uniform and efficient charging can be performed, and an image forming apparatus having higher image quality and a long life of the charged member can be provided.

4) A charging means having an organic photoconductor as a photosensitive layer and supported endlessly and having a charging means, an image exposure means, a developing means, a transfer means, a cleaning means,
Pre-transfer pre-exposure means, comprising a fixing means for transferring the transferred toner image to the transfer-receiving means, and a post-transfer pre-exposure means downstream of the transfer position in the moving direction of the charged means and above the transfer-receiving means. Since the nip portion of the transfer unit and the charged unit is irradiated with an exposure amount of 2 to 15 times the image exposure amount, there is no image disturbance in the fixing unit, and the thickness of the surface layer of the charged unit is accurately determined. In addition, there is an effect that an image forming apparatus that can detect the image forming apparatus uniformly, obtain uniform charging, and extend the life of the charged member can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part of an image forming apparatus using a charging device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a change in the surface potential of a photosensitive drum near a contact portion between the photosensitive drum and a charging roller;

FIG. 3 is a schematic sectional view of a main part of an image forming apparatus using a charging device according to a second embodiment of the present invention.

FIG. 4 is a schematic sectional view of a main part of an image forming apparatus using a charging device according to a third embodiment of the present invention.

FIG. 5 is a sectional view of a main part of a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum (charged means) 2 charging roller (charging means) 3 pre-exposure light source (pre-exposure means) 4 light-shielding member (light-shielding means) 5 image exposure device (image exposure means) 6 developing device (developing means) 7 transfer Member (transfer means), 8 Cleaning device (cleaning means) 9 Transfer paper (transferred means)

Claims (13)

[Claims] A charging means disposed in contact with or in proximity to the moving charging means, and having a relative movement relationship with the charging means; a power supply means for applying a voltage to the charging means; A pre-exposure unit provided upstream of the charging unit in the moving direction of the charged unit so as to perform pre-exposure for removing charges, and a most downstream point of a pre-exposure irradiation area and charging of the charging unit. The distance from the start point is 1 (mm), the moving speed of the charged member is v (mm / sec), and the life of the photocarrier generated in the charged member by the pre-exposure is t (sec).
a charging method characterized by satisfying 1 / v> = t when c) is satisfied. 2. A charging means which is disposed in contact with or close to a moving charged object and has a relative moving relationship with the charged object, a power supply means for applying a voltage to the charging means, and a charging means. A pre-exposure unit provided upstream of the charging unit in the moving direction of the charged unit so as to perform pre-exposure for removing charges, and a most downstream point of a pre-exposure irradiation area and charging of the charging unit. The distance from the start point is 1 (mm), the moving speed of the charged member is v (mm / sec), and the life of the photocarrier generated in the charged member by the pre-exposure is t (sec).
A charging device characterized by satisfying 1 / v> = t when c) is satisfied. 3. The charging device according to claim 2, wherein the voltage applied to the charging unit is a DC voltage or an oscillating voltage obtained by superimposing a DC voltage on an AC voltage. 4. The charging device according to claim 2, wherein a light-blocking member is provided between a most downstream point of the pre-exposure irradiation area and a charging start point of the charged member. 5. The charging device according to claim 2, wherein the charging unit is pressed against the charging unit with a constant pressing force. 6. A charging device comprising: a core metal to which a voltage is to be applied;
The charging device according to any one of claims 2 to 4, comprising a conductive layer formed on the surface of the metal core and a resistance layer formed on the surface. 7. The charging device according to claim 2, wherein one or both of the charged unit and the charging unit are relatively moved. 8. A charging device according to claim 2, further comprising: an image forming process unit configured to execute image formation on a surface of the charged unit. Image forming apparatus. 9. The image forming process means has an image exposing means, a developing means, a transferring means, a cleaning means, and a pre-exposure means, and is located downstream of the transferring means in the moving direction of the charged means and by the transferring means. 9. The image forming apparatus according to claim 8, wherein the pre-exposure unit is provided above a transfer receiving unit that receives an image transfer from the charging unit. 10. The exposure amount of the pre-exposure means for irradiating the nip portion between the charged means and the transfer means is 2 to 15 times the image exposure amount.
The image forming apparatus according to claim 8, wherein the number is double. 11. The image forming apparatus according to claim 8, wherein the charged member is an image carrier for forming an image. 12. The image bearing member according to claim 11, wherein the charge generating layer formed on the surface of the base and the charge transport layer formed on the surface of the charge generating layer are used as basic components. Image forming apparatus. 13. The image forming apparatus according to claim 9, wherein the image carrier has an endless belt shape.