JPH06149010A - Electrifying method, electrifying device and electrophotographic device provided with the device - Google Patents

Abstract

PURPOSE:To increase electrification capability as much as an electrifying device and also to reduce environmental fluctuation dependency by providing such a process that an auxiliary member for electrifying is abutted on a body to be electrified so that charged particles imparted to the body are destaticized. CONSTITUTION:An electrification auxiliary member 4 is constituted of a conductive shaft 4a, a semiconductive resin layer 4b and an insulating resin layer 4c, and the member 4 is abutted on a photosensitive body 1 by the appropriate press-contact force so as to follow with the photosensitive body 1 in a direction shown by an illustrated arrow. A constant current supply 3 is applied on the conductive shaft 4a of the electrification auxiliary member 4, and also, it is provided with an optical destaticizer 5. Also (d1) denotes a closest distance between the member 2 and the photosensitive body 1, and (d2) denotes the closest distance between the member 2 and the member 4. The electrification capability equivalent to that in a roller electrifying method for impressing the DC voltage and the AC voltage is obtained only by impressing the DC voltage on the member 2 and the member 4 without impressing the AC voltage on the members 2 and 4, and also the need of the AC supply is eliminated, so that the device can be miniaturized and also the occurrence of a trouble such as a vibration noise due to an ac electrical field is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging method for charging an object to be charged, a charging device, and an electrophotographic apparatus equipped with the charging device.

[0002]

2. Description of the Related Art A charging device in an electrophotographic apparatus, in which an object to be charged is a photoconductor, will be described as an example.

Charging devices intended to uniformly charge the surface of a photoconductor to a desired potential are roughly classified as follows.
It is divided into non-contact type and contact type.

The non-contact type charging device has been studied for a long time and put into practical use. Representative examples thereof include corotron and scorotron.

The corotron has a structure in which a conductive wire such as tank dust having a diameter of about 50 to 100 μm is surrounded by a conductive flat plate (hereinafter referred to as a housing) having an opening only on the surface facing the photoconductor. By applying a high voltage of about 4 to 10 kV to the conductive wire to form a stable electric field between the housing and the wire, a uniform potential can be applied to the surface of the photoconductor. There is a scorotron as a charging device which is an improved version of this corotron. The scorotron has a structure in which a mesh-shaped grid electrode, which is electrically insulated from the house swing, is provided on the open housing surface of the corotron, and by applying a bias voltage to the grid electrode, the photosensitive electrode is exposed. The charging device has an effect of controlling the surface potential of the body.

The above-mentioned corotron or scorotron has a simple structure and is advantageous in terms of manufacturing and cost, but it makes the discharge non-uniform due to dirt due to toner adhesion to the conductive wire, and when cleaning the wire. A charging device that has many problems such as the possibility of wire breakage, abnormal current concentration on the pinhole of the photoconductor (generation of spark discharge), and deterioration of the photoconductor due to active molecules such as ozone generated by corona discharge. Is.

As a charging device for solving the above-mentioned problems of the non-contact type charging device, a DC voltage and an AC voltage are applied to a roller-shaped charging member whose surface is covered with an insulating resin to bring it into contact with a photosensitive member. A contact-type charging device for electrically charging by means of a device has been devised and put into practical use (Japanese Patent Publication No. 3-52058). In the charging device, the gap between the charging roller and the photoconductor is very small (about several microns), and therefore the amount of corona current required for charging is small, and the amount of ozone generated is 1/10 of that of corotron and scorotron. Since it is suppressed to about 1/100, the photoreceptor and peripheral members are less likely to deteriorate. Also, since the surface of the charging roller is covered with an insulating resin with high resistance, even if the roller comes into contact with the pinhole of the photoconductor, the amount of current flowing in the roller surface toward the pinhole in the longitudinal direction of the roller. Is a small amount, and it is possible to prevent abnormal current concentration on the pinhole. For the charging roller,
Since the DC voltage and the AC voltage are superposed, decharging is repeated between the photoconductor and the roller, and further, the DC voltage applied at the part where the photoconductor and the roller are separated converges to less uneven charging and environmental fluctuations. Also few.

[0008]

The main drawbacks of the conventional charging device for charging the photosensitive member by applying only the DC voltage to the charging roller without applying the AC voltage to the charging roller are as described below.

1. Contamination of the surface of the photoconductor due to the deposition of the internal additive material that imparts conductivity from the charging roller.To make the charging roller softly contact the photoreceptor with a proper nip width, the charging roller material should be a resin material such as rubber. Need to be However, many rubber materials contaminate the photoconductor with the material internally added at the time of production, and the photoconductor with the conductive material internally added to impart conductivity (especially when a conductive salt is used). Surface resistance decreases, and after the charging process, the electrostatic latent image drawn by image exposure collapses and appears as an image blur on the image.

In order to prevent the surface deposition of the substance internally added to the roller material as described above, it is necessary to cover the surface of the charging roller with a resin layer. In this case, the resin covering the surface is required to contain no internal additive substance, in which case,
Since many resins alone have high resistance, the surface of the charging roller is covered with an insulating resin.

When another resin layer is coated on the semiconductive resin layer, wrinkles occur in the coated resin layer and the surface roughness increases. When a DC voltage is applied to a roller with a high surface roughness to charge the photoconductor, the size of the gap due to the unevenness of the charge roller in the nip portion between the charge roller and the photoconductor causes a difference in discharge start voltage between the charge roller and the photoconductor. The difference appears, and as a result, large charging unevenness occurs.

2. Releasing property of the charging roller surface When the charging roller is brought into contact with the photosensitive member, uneven charging due to toner remaining on the photosensitive member adhering to the charging roller surface becomes a problem. For that purpose, it is necessary to provide a cleaning member on the charging roller or to improve the surface releasability of the charging roller. When the charging roller is provided with a cleaning member, the cleaning member wears the roller, and the torque applied to the charging roller increases to increase the photosensitive member drive torque.
Etc. becomes a problem and is not practical. Therefore, it is required to cover the surface of the charging roller with a resin layer having good releasability.
Also in this case, when the roller is coated with the resin layer as described above, wrinkles are generated, the surface roughness of the roller is increased, and as a result, large charging unevenness is caused.

3. Poor charging due to scratches on the surface of the roller When the toner etc. is caught in the nip between the charging roller and the photoconductor, the charging roller surface is scratched. When the roller surface is scratched, the gap between the roller and the photoconductor becomes large only at the scratched portion in the nip portion, and as a result, the discharge start voltage is increased, which causes charging failure.

4. Environmental Change Due to the environmental change, the volume resistance of the roller material changes, and the voltage drop of the applied DC voltage inside the roller changes accordingly, which causes environmental change of the charging device.

The main drawbacks of the conventional charging device for charging the photosensitive member by applying only the DC voltage to the charging roller are the above-mentioned four points, but as described above, the DC voltage and the AC voltage are applied to the charging roller. The charging device for applying a voltage has solved the above-mentioned four problems that the conventional technique had.

However, since the AC voltage is applied to the charging roller, the voltage source becomes large in size, which causes a problem in that the charging device as a whole becomes large in size. Further, since an oscillating electric field is formed in the nip portion between the photoconductor and the charging roller, there is a problem that vibration noise is generated due to the gap in the nip portion.

In view of the above-mentioned problems, the present invention uses only a DC power supply without using an AC voltage, and uses a roller whose surface is covered with an insulating resin as an auxiliary charging member. The present invention provides a charging method, a charging device, which has a charging ability as high as that of a charging device for applying a DC voltage and an AC voltage, and which is less dependent on environmental changes, and an electrophotographic apparatus equipped with the charging device.

[0018]

In order to solve the above problems, a charging method, a charging device, and an electrophotographic apparatus including the same according to the present invention have the following configurations.

The process of charging the charging assisting member and the charged member that are in contact with the charged member, and the charging assisting member is in contact with the charged member, and the charging assist member is applied to the charged member. And a step of neutralizing and smoothing the discharged charged particles.

The surface potential of the charged body immediately before the charging assisting member reaches the process of neutralizing and leveling the charged particles on the charged body by V
_1, the auxiliary charging member and the discharge starting voltage V _{T H} between the member to be charged, the minimum voltage arc discharge is generated between the auxiliary charging member and the object to be charged when the V _ARC, | V ₁ |> ｜ V _TH
|, And | V _ARC |> | V ₁ |.

The above charging method, wherein the surface of the charging assisting member is covered with an insulating resin.

The charging member is provided with a charging auxiliary member that is in contact with the member to be charged and has a region where the distance from the member to be charged is gradually reduced, and a charging member in which the discharging portion is set in the region. Charging the charged body and the charging assisting member, the charging assisting member abutting the charged body, and the charging assisting member discharging and leveling the charged particles applied to the charged body. Charging device characterized by.

The surface potential of the charged body immediately before the charge assisting member reaches the process of removing and leveling the charged particles on the charged body by V
_1, the auxiliary charging member and the discharge starting voltage V _{T H} between the member to be charged, the minimum voltage arc discharge is generated between the auxiliary charging member and the object to be charged when the V _ARC, | V ₁ |> ｜ V _TH
| And | V _ARC |> | V ₁ |.

The above charging device, wherein the surface of the charging assisting member is covered with an insulating resin.

The above charging device, wherein the charging member has a plurality of needle-like tips. The above-mentioned charging device, wherein the current applied to the charging member is controlled to a constant current.

The above charging device, wherein the insulating resin covering the surface of the charging assisting member is a fluororesin.

The charging device described in the above item 4, wherein the insulating resin covering the surface of the charging assisting member is a urethane resin internally added with hydrophobic silica.

The charging member is provided with a charging assisting member which is in contact with the member to be charged and has a region where the distance to the member to be charged is gradually reduced, and a charging member in which a discharging portion is set in the region. Charging the charged body and the charging assisting member, the charging assisting member abutting the charged body, and the charging assisting member discharging and leveling the charged particles applied to the charged body. Thus, the electrophotographic apparatus is provided with a charging device that charges the charged body to a desired potential.

The surface potential of the charged body immediately before the charging assisting member reaches the process of removing and leveling the charged particles on the charged body by V
_1, the auxiliary charging member and the discharge starting voltage V _{T H} between the member to be charged, the minimum voltage arc discharge is generated between the auxiliary charging member and the object to be charged when the V _ARC, | V ₁ |> ｜ V _TH
The electrophotographic apparatus described above, further comprising a charging device having | and | V _ARC |> | V ₁ |.

The above electrophotographic apparatus comprising a charging device in which the surface of the charging assisting member is covered with an insulating resin.

The above-described electrophotographic apparatus, wherein the charging member comprises a charging device having a plurality of needle-shaped tips.

The above electrophotographic apparatus comprising a charging device in which the current applied to the charging member is controlled to a constant current.

The above-described electrophotographic apparatus comprising a charging device in which the insulating resin covering the surface of the charging assisting member is a fluororesin.

The above-described electrophotographic apparatus comprising a charging device in which the insulating resin covering the surface of the charging assisting member is a urethane resin internally added with hydrophobic silica.

[0035]

According to the present invention, the charging member having the above-mentioned structure is provided.
Also, since the charging auxiliary member has the same charging ability as that of the roller charging method of applying the DC voltage and the AC voltage by applying only the DC voltage without applying the AC voltage to the charging auxiliary member, and does not use the AC power supply, The present invention provides a charging method, a charging device, and an electrophotographic apparatus equipped with the charging device, which does not cause the problem of vibration noise due to an AC electric field.

The main functions of the present invention will be described below. 1. Charging that is not easily affected by the surface roughness of the roller The inventors studied a roller in which a semiconductive rubber layer is covered with a thin insulating tube from the viewpoint of durability and prevention of photoreceptor contamination. When a thin insulating tube was coated on the semi-conductive rubber layer, wrinkles were generated on the surface, and as described above, when a DC voltage was applied to this roller, uneven charging occurred.
The inventors have found from experiments that when a roller is used for the purpose of charging a dielectric (photoreceptor in this case) once within a certain potential range and then removing the charge on the dielectric given by the charging process. Found that static elimination is realized, which is less affected by the surface roughness of the roller.

It is affected by the surface roughness of the roller as described above.
A charging device including a static elimination step is a charging device of the present invention.
Is. In the charging device of the present invention, the charging member is previously charged.
The body within a suitable potential range (below) higher than the desired potential
Charging assistance that charges the electric potential and at the same time plays the role of static elimination
The members are also charged. Here, if the charging auxiliary member is charged,
When the body to be charged and the charging auxiliary member come into contact with each other, the charging auxiliary member
The charge imparted on the charged body is made more uniform, that is,
Eliminates almost no effect of surface irregularities (surface roughness)
It has the effect of working like an electric power. Higher than desired potential
The object to be charged is contacted with the auxiliary charging member and charged.
Discharge starting voltage V between the auxiliary member and the body to be charged _THAnd charging assistance
The surface potential of the member is added to the potential to be uniformly removed.
It Here, in order to control the surface potential of the charged body,
Applying a DC voltage to the charging auxiliary member, the surface of the charging auxiliary member
It suffices to change the potential. The above process, that is, the charging unit
The material keeps the charged body within the appropriate potential range, which is higher than the desired potential.
At the same time as charging, the charging auxiliary member is also charged, and
The nip portion where the power auxiliary member abuts
The charge corresponding to the potential higher than the desired
Through the process that the auxiliary member uniformly removes electricity, the charged body
Has a desired electric power that is hardly affected by the surface roughness of the roller.
Evenly charged.

The appropriate potential range when the charging member charges the body to be charged is the range described below. In the nip portion where the charged member to be charged and the charging auxiliary member are in contact with each other, in order for the charging auxiliary member to eliminate the charge on the charged member, the potential difference between the charged member and the charging auxiliary member is different from that of the charged member. It must be higher than the discharge start voltage V _TH between the charging assisting members. That is, if the surface potential of the photoconductor immediately before the charge assisting member comes into contact with the charged object charged by the charging member and the charge assisting member starts to be V ₁ , | V ₁ |> | V _TH | is there. If the potential difference between the member to be charged and the charging auxiliary member becomes too large, an arc discharge (spark discharge) occurs, and the charges given to the member to be charged are simultaneously removed by the charging auxiliary member, causing a charging failure. . Therefore, the minimum voltage at which arc discharge (spark discharge) occurs between the member to be charged and the auxiliary charging member is V
_{For ARC} , | V ₁ | <| V _ARC |. That is, the above-mentioned appropriate potential range in which the charging member charges the body to be charged means | V _TH | <| V ₁ | <| V _ARC | At the same time as charging the charged body, the charging assisting member is also charged, and the charging assisting member uniformly removes the charge on the charged body at the nip portion where the charged body and the charging assisting member contact each other. The roller is uniformly charged to a desired potential with almost no influence of the surface roughness of the roller.

2. Stabilizing Effect of Discharge by Charging Aid Member Since the charging member of the present invention needs to charge the body to be charged within an appropriate potential range, a stable electric field is formed between the charging member and the body to be charged, and Controllability must be improved.
Therefore, a stable electric field can be formed between the charging member and the auxiliary charging member, and the electric field from the charging member toward the body to be charged can be stabilized. This is similar to the housing effect of (s) corotron. A high voltage is applied to the wire to generate a corona discharge. (S) In a corotron, the corona discharge of the wire is extremely unstable, so the wire periphery is covered with a conductive member (housing). By forming a stable electric field, the electric field toward the photoconductor is stabilized. By covering the wire periphery with a housing, the electric field toward the photoconductor is stabilized,
Besides achieving uniform charging, it also has the effect of preventing abnormal current concentration (spark discharge) on pinholes on the photoconductor. Corresponding member to the housing of this (Su) Corotron,
It is the charging auxiliary member of the present invention. By causing a discharge between the charging member and the charging auxiliary member, the electric field from the charging member to the body to be charged is stabilized, and the controllability of the charging member is enhanced.
It becomes easy to charge the body to be charged within the above-mentioned appropriate potential range. Further, it is possible to prevent abnormal current concentration (spark discharge) from the charging member to the pinhole of the photoconductor.

3. Stable Charging by Applying Constant Current to Charging Member In the configuration of the present invention, the charging member provided upstream of the charging assisting member in contact with the member to be charged charges the member to be charged and simultaneously charges the charging assisting member. At this time, even if the discharge between the charging member and the member to be charged and between the charging member and the auxiliary charging member is unstable, the charging member applies a constant current, so that the current flows from the charging member to the member to be charged. The sum of the current and the current flowing from the charging member to the charging auxiliary member is always constant. Therefore, even when a large amount of current flows from the charging member to the charging auxiliary member, the large amount of the current is canceled by the small amount of current flowing from the charging member to the charged member, and the charging auxiliary member and the charged member come into contact with each other. At the nip portion, the constant current applied to the charging member is always supplied. On the contrary, even when a small amount of current flows from the charging member to the charging auxiliary member, a constant current is supplied to the nip portion by the same mechanism as above. In this way, by applying a constant current to the charging member that charges the member to be charged and the charging auxiliary member at the same time, even if the discharge of the charging member becomes unstable, it is always applied to both the member to be charged and the charging auxiliary member. The generated charge is constant, and therefore stable charging can be performed.

4. Environmental Stability of Charging Aid Member In the configuration of the present invention, the electric current flowing through the charging auxiliary member is lower than the current due to self-discharge of the electric charge directly discharged from the needle charging member and the desired potential V ₀ due to the needle charging member. It is the sum of the overcharged current and the potential equivalent of V ₁ -V ₀ . The current value, by adjusting the voltage applied to the needle charging member decreases as closer to the V ₁ to V _0. By the way, the environmental change of roller charging mainly occurs because the volume resistance value of the material of the roller changes due to the environmental change, so that the voltage drop of the voltage applied to the roller changes inside the roller. Therefore, this voltage drop decreases as the current flowing through the roller decreases, and the environmental fluctuation also decreases as the current flowing through the roller decreases. Here, comparing the case where a roller made of the same material is used as the charging member and the case where the roller is used as the charging assisting member in the present invention, when the roller is used as the charging roller, the charged body is charged to a desired potential. While it is necessary to pass a current corresponding to the electric charge required for the charging roller to the charging roller, when used as a charging assisting member in the present invention, a member that slightly charges the body to be charged slightly more than a desired potential is used. The current flowing through the charging assisting member is the needle charging member, and is the sum of the current corresponding to V ₁ -V ₀ and the current component due to the charge directly applied to the charging assisting member from the needle charging member. _The current value corresponding to ₁ -V ₀ can be reduced by adjusting the voltage applied to the needle charging member, and the current due to the charge directly applied from the latter needle charging member to the charging auxiliary member. Is the body to be charged Can be set to be smaller than the current required to be charged to a desired potential. Therefore, the current flowing through the charging assisting member according to the configuration of the present invention is extremely smaller than the current flowing when the charging assisting member is used as a charging roller.
The fluctuation of the surface potential of the charging assisting member due to the fluctuation of the volume resistance value of the roller material due to the environmental fluctuation, that is, the fluctuation of the surface potential of the charged body is suppressed to be extremely small as compared with the charging method in which a DC voltage is applied to the charging roller. You can Like this
The charging method of the present invention has an advantage that it is not easily affected by the environment.

[0042]

EXAMPLES A charging device used in an electrophotographic apparatus according to an example of the present invention will be described below with reference to the drawings in comparison with a comparative example.

(First Embodiment) FIG. 1 is a block diagram of a charging device used in an electrophotographic apparatus according to the first embodiment of the present invention.

Reference numeral 1 is a photosensitive member, 1a is a grounded conductive support, and 1b is a photosensitive layer. In FIG. 1, a negative charging type photoconductor is assumed, but a positive charging type photoconductor may be used. Photoconductor 1
Rotates at a constant speed in the direction of the arrow in the figure. Reference numeral 2 is a needle charging member having a plurality of needle-shaped tips. 3 is a constant current source. Four
Is a charging assisting member, 4a is a conductive mandrel, 4b is a semiconductive resin layer, and 4c is an insulating resin layer. The charging assisting member 4 contacts the photoconductor 1 with an appropriate pressure contact force, and follows the photoconductor 1 in the direction of the arrow in the figure. The constant current source 3 is a charging auxiliary member 4
To the conductive mandrel 4a. Reference numeral 5 is an optical static eliminator. d
₁ is the closest distance between the charging member 2 and the photosensitive member, and d ₂ is the closest distance between the charging member and the auxiliary charging member.

FIG. 2 is a front view of the needle charging member 2, where h is the height of the needle-like tip and a is the distance between the needle-like tips. FIG. 3 is a front view of the charging auxiliary member 4, 6 is a conductive mandrel, and 7 is a semiconductive resin layer coated with an insulating resin.

Experiments were conducted under the following conditions and materials with the configurations shown in FIGS. 1, 2 and 3. A drum-shaped aluminum base tube having a diameter of 30 mm was used as the conductive support 1 a of the photoconductor 1. The photosensitive layer 1b was formed by stacking a charge generation layer and a charge transport layer in this order on the conductive support 1a, and the charge generation layer was prepared by dispersing τ-type metal-free phthalocyanine as a charge generation substance in a melamine-modified thermosetting resin. The charge transport layer used was a tetraphenyl butadiene derivative, which is a charge transport material, dispersed in a polycarbonate resin. The thickness of the charge generation layer is about 0.2 μm, and the thickness of the charge transport layer is about 20 μm.
m. The peripheral speed of the photoconductor 1 was 25 mm / sec during the experiment.
It turned in.

A negative current of 10 μA was applied from a constant current source by setting d ₁ = d ₂ = 4 mm. As the conductive mandrel 4a of the charging assisting member 4, an aluminum mandrel having a diameter of 5 mm was used and grounded. For the semiconductive resin layer 4b, a urethane resin in which a Li salt that promotes ion conduction generated by using water molecules as a medium is uniformly added is used. With urethane resin alone, the volume resistivity at room temperature and humidity is approximately 10 ¹² Ω ・
The volume resistivity was about 10 ⁷ Ω · cm by uniformly internally adding the Li salt as described above. The semiconductive resin layer 4b was covered with a fluororesin film having a thickness of about 5 μm, which was used as an insulating resin layer 4c. The surface roughness of the charging auxiliary member 4 thus created is Ra = 0.94 μ.
m, Rz = 6.2 μm, and Rmax = 9.1 μm. Under normal temperature and normal humidity environment, the volume resistivity of the fluororesin used for the insulating resin layer 4c is about 10 ¹⁵ Ω · cm. The diameter of the charging assisting member 4 including the conductive mandrel 4a was 12 mm. The pressure contact force of the charging assisting member 4 against the photoconductor 1 is 500 at both end values of the conductive mandrel 4 a of the charging assisting member 4.
It was set to g.

(Second Embodiment) FIG. 4 is a block diagram of a charging device used in an electrophotographic apparatus according to the second embodiment of the present invention.

Reference numeral 8 denotes a photoconductor, which rotates at a constant speed in the direction of the arrow in the figure. Reference numeral 8a is a grounded conductive support, and 8b is a photosensitive layer. 9 is a charging roller, 9a is a conductive mandrel, 9
Reference numeral b is a semiconductive resin layer, and 9c is an insulating resin layer. 10
Is an AC voltage source, 11 is a DC voltage source, and AC voltage source 1
0 and the DC voltage source 11 are applied in series to the conductive mandrel 8a of the charging roller 9. Reference numeral 12 is an optical static eliminator.

As the photoconductor 8, the same one as in the first embodiment was used. The charging roller 9 is the charging auxiliary member 4 in the first embodiment.
The same roller used as was used. For the charging roller 9, an AC voltage source 10 and a DC voltage source 11 are used,
An AC voltage having a peak-to-peak voltage of 2.0 kV was superposed on a DC voltage of 0V.

(Comparative Example) An experiment was conducted under the same structure and conditions as in the first example except that d ₂ shown in FIG. 1 was set to 15 mm.

The operation of the charging device shown in the first embodiment in a normal temperature and normal humidity environment will be described. FIG. 5 shows the surface potential of the photoconductor 1 charged by the charging member 2 just before contacting the charging assisting member 4 and removing the charge.

The surface potential of the photoreceptor is -560V to -90.
Uneven charging up to 0 V was shown. Since the discharge starting voltage of the charging assisting member 4 and the photoconductor 1 is 520V and the minimum voltage for causing spark discharge is about 1100V, the charging is performed within an appropriate potential range. FIG. 6 shows the surface potential immediately after the photoconductor 1 passes through the nip portion with the charging auxiliary member.

It can be seen that the surface potential of the photosensitive member 1 is uniformly charged to −540V. The surface of the charging assisting member 4 is charged to about -90 V at the portion closest to the charging member 2,
Immediately after passing through the nip portion between the charging assisting member 4 and the photoconductor 1, the voltage was reduced to -20V. The discharge start voltage V _TH (520 V) between the photoconductor 1 and the charging assisting member 4 and the surface potential of the charging assisting member 4 at the nip portion between the photoconductor 1 and the charging assisting member 4 (−
The photoconductor 1 is uniformly charged to a value (-540V) obtained by adding 20V).

In the charging device shown in the first embodiment, no abnormal current concentration occurred on the pinhole of the photoconductor.
It is considered that this is because a stable discharge electric field was formed between the charging member and the auxiliary charging member.

In the charging device shown in the second embodiment, the surface of the photoconductor 1 immediately after passing through the nip portion between the photoconductor 8 and the charging roller 9 has a DC voltage value (-55) applied to the charging roller.
0V) and was uniformly charged to −540V.

In the charging device of the comparative example, since the charging member and the charging auxiliary member are installed separately from each other, the discharge between the charging member and the charging auxiliary member hardly occurs, and the charging member on the surface of the charging auxiliary member is not discharged. In the part that corresponds to the closest distance of, about -3
Only V was charged. FIG. 7 shows the surface potential of the photoconductor immediately before passing through the nip portion between the photoconductor and the charging auxiliary member.

The charging unevenness from −580V to −1400V was observed, but the charging unevenness was larger than that in FIG. 5 of the first embodiment. This is presumably because the distance between the charging member and the charging assisting member was large, so that stable discharge was not formed between the charging member and the charging assisting member, and the controllability of the charging member deteriorated. FIG. 8 shows the surface potential of the photoconductor immediately after passing through the nip portion between the charging assisting member and the photoconductor.

As shown in FIG. 8, a large charging unevenness was observed. This is because the surface potential of the photoconductor immediately before passing through the nip portion is the minimum voltage at which spark discharge occurs between the photoconductor and the charging auxiliary member. It is considered that since the value (1100 V) was exceeded, spark discharge occurred in the nip portion, and the charged particles on the photoconductor were simultaneously discharged by the charging auxiliary member. Also in the first embodiment, the same phenomenon occurs when the current value applied to the charging member 2 is increased and the surface potential of the photoconductor immediately before passing through the nip portion is increased.

In the charging device of the comparative example, abnormal current concentration (spark discharge) frequently occurred in the pinhole of the photoconductor. It is considered that this is also because the stable electric field is not formed between the charging member and the auxiliary charging member.

The charging unevenness (ripple) by the charging device shown in the first embodiment, the second embodiment and the comparative example is shown in Table 1.
Shown in.

[0062]

[Table 1]

As can be seen from Table 1, there is no significant difference in the charging unevenness between the first embodiment and the second embodiment, and a charging device with small charging unevenness was realized, but in the comparative example, the charging unevenness was large. , Is not suitable for practical use.

In the charging device shown in the first embodiment, a constant current is applied to the charging member 2, but instead of this,
-When a constant voltage of -2.7 kV is applied, charging unevenness is 20
It was V. From this, it can be seen that more stable charging can be performed by applying a constant current to the charging member 2 of the charging device having the configuration of the present invention than when a constant voltage is applied.

Table 2 shows the results of examining the environmental fluctuations of the charging device shown in the first and second embodiments.

[0066]

[Table 2]

The same roller was used as the charge eliminating roller in the first embodiment and as the charging roller in the second embodiment, but the current flowing through the roller in the first embodiment under normal temperature and normal humidity is While it was 3 μA, the current flowing through the roller in the second embodiment was 8 μA. Environmental fluctuations of rollers
This is mainly caused by the fluctuation of the voltage drop inside the roller due to the resistance change of the roller. Therefore, the smaller the amount of current flowing through the roller, the smaller the environmental fluctuation of the roller. The reason why the environmental fluctuation of the first embodiment is smaller than that of the second embodiment is considered to be that the amount of current flowing through the roller is small.

Table 3 shows the measurement results of the ozone amount generated by the charging devices shown in the first and second embodiments.

The measurement results of the ozone amount generated by the charging device shown in this embodiment are shown in Table 3 together with the conventional example and the comparative example.

[0070]

[Table 3]

The amount of ozone generated by corona discharge is approximately proportional to the amount of corona current. In the charging device of the first embodiment, the current flowing from the charging member 2 was 10 μA and the current flowing into the charging auxiliary member 4 was 3 μA, and it is considered that the ozone corresponding to the corona current of 13 μA in total was generated. In the charging device of the second embodiment, the current flowing through the charging roller was about 8 μA, and it is considered that the ozone corresponding to the corona current of 8 μA was generated.

As can be seen from Table 3, the charging device of the first embodiment generated twice as much ozone as the charging device of the second embodiment. By comparison, the amount of ozone generation is 1/10 to 1/100, and it can be said that the charging device is a low ozone generation device.

As described above, according to the charging device of the first embodiment, 1. Uniformly charge the photoconductor by once charging it to a desired potential or higher, and then removing the charge with a charge assisting member. 2. Stabilization of discharge to the photoconductor by the charging member due to a stable discharge electric field formed between the charging member and the charging auxiliary member, 3. Stable charging by applying a constant current to the charging member, 4. By using the roller as a static eliminator, it is possible to realize a charging device with less environmental fluctuation.

(Third Embodiment) The third embodiment of the present invention will be described below.

The surface layer 4c of the charging assisting member 4 in FIG.
The procedure is the same as that of the first embodiment except that a urethane resin internally added with hydrophobic silica is used. Urethane resin layer 4b internally added with Li salt
A urethane resin layer having hydrophobic silica internally added was formed on the above by the following method.

First, 30 parts by weight of hydrophobic silica was added to a coating solution prepared by dissolving 100 parts by weight of urethane elastomer in 1600 parts by weight of n-butyl alcohol and dispersed by ultrasonic dispersion to prepare a coating solution. This coating solution is dip-coated on the urethane resin 9b, heat-treated at 110 ° C. for 1 hour, and then cured.
An insulating surface layer 9c having a film thickness of about 5 μm was provided.

The urethane resin internally added with hydrophobic silica is excellent in water repellency and surface releasability. Table 4 shows pure water of the urethane resin containing no additives, the fluororesin used for the surface insulating layer of the charge assisting member of the first embodiment, and the urethane resin internally added with the hydrophobic silica used in this embodiment. The measured values of the contact angle with and the dynamic friction coefficient with a steel ball having a smooth surface are shown.

[0078]

[Table 4]

As can be seen from Table 4, the urethane resin internally added with the hydrophobic silica has excellent surface releasability equivalent to that of the fluororesin, but particularly has a very high water repellent surface. In a high humidity environment, the nip portion between the charging assisting member and the photoconductor in the configuration of the present invention may cause charge injection using water as a medium. Charging or charge elimination by charge injection causes uneven charge or charge elimination because water is not always adsorbed uniformly on the surface of the charging member, the charge eliminating member, or the photoconductor. Therefore, it is necessary to cover the surface of the charging assisting member, which is a member in contact with the photoconductor, with a material having extremely excellent water repellency as in the present embodiment, because of unstable electric charge using water as a medium in a high humidity environment. The injection phenomenon can be suppressed.

[0080]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a charging assisting member having a region whose surface is covered with an insulating resin and which is in contact with an object to be charged and whose distance from the object to be charged gradually decreases, A charging member provided in the region, the charging member charging the charging target member and the charging auxiliary member, and the charging auxiliary member at the nip portion where the charging auxiliary member and the charging target member contact each other. By undergoing a process of uniformly removing the above charge, uneven charging is small, the charging assisting member and irregularities on the surface of the member to be charged are widely absorbed, the amount of ozone generated is extremely small, and the charging is excellent in environmental stability. The device can be realized by operating only the DC power supply without using the AC power supply.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a charging device according to a first embodiment of the present invention.

FIG. 2 is a front view of a charging member in the embodiment.

FIG. 3 is a front view of the charging assisting member in the embodiment.

FIG. 4 is a configuration diagram of a charging device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing the surface potential of the photoconductor immediately before passing through the nip portion between the charging assisting member and the photoconductor when the photoconductor is charged by the charging device according to the first exemplary embodiment of the present invention.

FIG. 6 is a diagram showing the surface potential of the photoconductor immediately after passing through the nip portion between the charging assisting member and the photoconductor when the photoconductor is charged by the charging device according to the first exemplary embodiment of the present invention.

FIG. 7 is a diagram showing the surface potential of the photoconductor immediately before passing through the nip portion between the charging assisting member and the photoconductor when the photoconductor is charged by the charging device in the comparative example.

FIG. 8 is a diagram showing the surface potential of the photoconductor immediately after passing through the nip portion between the charging assisting member and the photoconductor when the photoconductor is charged by the charging device in the comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1a Conductive support constituting a photoconductor 1b Photosensitive layer constituting a photoconductor 2 Charging member having a plurality of needle-shaped tips 3 Constant current source 4a Conductive mandrel constituting a charge assisting member 4b Half constituting a charge assisting member Conductive resin layer 4c Insulating resin layer constituting charge assisting member 5 Optical static eliminator 6 Conductive assisting member or conductive mandrel constituting charging roller 7 Covering with charge assisting member or insulating resin layer constituting charge roller Semi-conductive resin layer 8a Conductive support member 8b constituting photosensitive member Photosensitive layer 9a constituting photosensitive member 9a Conductive mandrel constituting charging roller 9b Semi-conductive resin layer constituting charging roller 9c Constituting charging roller Insulating resin layer 10 AC voltage source 11 DC voltage source 12 Optical static eliminator

Claims (17)

[Claims] 1. A process of charging a charging assisting member that contacts an object to be charged and the member to be charged, and the charging assisting member contacts the member to be charged, and the charging assisting member causes the member to be charged. And a step of removing the electric charge of the charged particles applied to the surface and leveling them. 2. The surface potential of the charged body immediately before the charging assisting member reaches the process of neutralizing and leveling the charged particles on the charged body by V.
₁ , where V _TH is the discharge start voltage between the charging assisting member and the body to be charged and V _ARC is the minimum voltage at which arc discharge occurs between the charging assisting member and the body to be charged, | V ₁ |> | V _TH
|, And | V _ARC |> | V ₁ |. The charging method according to claim 1. 3. The charging method according to claim 1, wherein the surface of the charging assisting member is covered with an insulating resin. 4. A charging assisting member, which is in contact with a member to be charged and has a region where the distance to the member to be charged is gradually reduced, and a charging member in which a discharging portion is set in the region, A charging member charges the member to be charged and the auxiliary charging member, the auxiliary charging member contacts the member to be charged, and the auxiliary charging member discharges and evens the charged particles applied to the member to be charged. Charging device characterized by 5. The surface potential of the charged body immediately before the charge assisting member reaches the process of neutralizing and leveling the charged particles on the charged body by V.
₁ , where V _TH is the discharge starting voltage between the charging assisting member and the body to be charged and V _ARC is the minimum voltage at which arc discharge occurs between the charging assisting member and the body to be charged, | V ₁ |> | V _TH
The charging device according to claim 4, wherein | and | V _ARC |> | V ₁ |. 6. The charging device according to claim 4, wherein the surface of the charging assisting member is covered with an insulating resin. 7. The charging device according to claim 4, wherein the charging member has a plurality of needle-shaped tips. 8. The charging device according to claim 4, wherein the current applied to the charging member is controlled to a constant current. 9. The charging device according to claim 4, wherein the insulating resin covering the surface of the charging auxiliary member is a fluororesin. 10. The charging device according to claim 4, wherein the insulating resin covering the surface of the charging assisting member is a urethane resin internally added with hydrophobic silica. 11. A charging auxiliary member having a region that is in contact with a member to be charged and whose distance from the member to be charged is gradually reduced,
The discharging part comprises a charging member set in the region,
The charging member charges the body to be charged and the charging assisting member, the charging assisting member contacts the body to be charged, and the charging assisting member neutralizes charged particles applied to the body to be charged. An electrophotographic apparatus comprising a charging device that charges the body to be charged to a desired potential by leveling. 12. The surface potential of the charged body immediately before the charging assisting member reaches the process of neutralizing and leveling the charged particles on the charged body by V ₁ , and starting discharge between the charging assisting member and the charged body. | V ₁ |> | V, where V _TH is the voltage and V _ARC is the minimum voltage at which arc discharge occurs between the charging assisting member and the charged object.
_The electrophotographic apparatus according to claim 11, further comprising a charging device that satisfies _TH | and | V _ARC |> | V ₁ |. 13. The charging device according to claim 1, further comprising a charging device in which a surface of the charging auxiliary member is covered with an insulating resin.
1. The electrophotographic apparatus according to 1. 14. The electrophotographic apparatus according to claim 11, wherein the charging member includes a charging device having a plurality of needle-shaped tips. 15. A charging device comprising a charging device in which the current applied to the charging member is controlled to a constant current.
1. The electrophotographic apparatus according to 1. 16. The electrophotographic apparatus according to claim 11, further comprising a charging device in which the insulating resin covering the surface of the charging auxiliary member is a fluororesin. 17. The electrophotographic apparatus according to claim 11, further comprising a charging device in which the insulating resin covering the surface of the charging assisting member is a urethane resin internally added with hydrophobic silica.