JP3581492B2 - Proximity charging device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charging device of an image forming apparatus using an electrophotographic process such as an electrostatic copying machine or a laser printer, and more particularly, to a method in which a charged surface of a charging member is brought into non-contact with a movable charged surface of a charged member. The present invention relates to a proximity charging device to be opposed.
[0002]
[Prior art]
As a charging device of an image forming apparatus, a corona charging device such as a scorotron has been conventionally used. In such a corona charging device, there are problems such as a large amount of generated ozone and a large applied voltage of, for example, 5 to 7 KV. A contact charging device that contacts and charges the surface of the member to be charged has also been used as a charging device of an image forming apparatus.
[0003]
FIG. 8 is a configuration diagram schematically showing an electrophotographic image forming apparatus provided with a conventional charging device. The photoconductor drum 1 is obtained by applying a photoconductor 1a to the surface of a cylindrical conductor 1b, and rotates in a direction indicated by an arrow in FIG. The charging member 2 contacts the photoconductor 1a of the photoconductor drum 1 and charges the surface of the photoconductor 1a to a predetermined potential.
[0004]
Next, the photosensitive member 1a is exposed by the electrostatic latent image forming means 6 to form an electrostatic latent image corresponding to a desired image, and the developing means 7 develops the electrostatic latent image with toner, and A visible toner image is formed thereon. The toner image on the photoreceptor 1a is transferred onto a transfer body 9 such as paper conveyed by a transfer unit (not shown) by a transfer unit 8, but is not transferred onto the transfer body 9 by the transfer unit 8 The toner remaining on 1a is cleaned by cleaning means 10. The transfer body 9 to which the toner image has been transferred by the transfer unit 8 is conveyed to a fixing unit (not shown), and the toner is heated and fixed on the transfer body 9.
[0005]
During the above process, since the photosensitive drum 1 is rotating in the direction indicated by the arrow, a desired image is formed on the transfer body 9 by repeating the above procedure. In FIG. 8, even if the charging member 2 is replaced with a corona charging device, the image forming process in the image forming apparatus is exactly the same.
[0006]
FIG. 9 is a sectional view of a main part showing an example of a conventional contact charging device. The charging member 2 is formed by forming an elastic layer 2a on a roller-shaped conductor 2b having a diameter of 5 to 20 mm and a length of approximately 300 mm. The photosensitive drum 1 is a cylindrical member having a diameter of 30 to 80 mm and a length of approximately 300 mm. The photoconductor 1a is formed on the conductor 1b. The charging member 2 rotates in contact with the photosensitive drum 1 rotating clockwise, and rotates counterclockwise.
[0007]
The elastic layer 2a of the charging member 2 is made of a material having a resistivity of 10 ⁷ to 10 ⁹ Ωcm, and a voltage is applied to the charging member 2 by a power supply 4 to charge the photosensitive member 1a. The applied voltage at this time is -1.5 to -2 KV in direct current.
Such a contact charging device has advantages in that almost no ozone is generated and an applied voltage is small as compared with a corona charging device.
[0008]
However, in such a contact charging device, the charging member is in direct contact with the photoconductor, so that the toner or the like on the photoconductor adheres to the charging member, thereby lowering the charging performance or constituting the charging member. There are problems such as adhesion of the substance to the photoreceptor and permanent deformation of the charging member that occurs when the photoreceptor is stopped for a long time.
[0009]
As a method of solving such a problem of the contact charging device, a proximity charging device has been developed in which a charging member is brought into close contact with a photoconductor in a non-contact manner. In this proximity charging device, the charging member is charged by applying a voltage to the charging member with the charging member facing the photosensitive member so that the distance to the photosensitive member is 0.005 to 0.3 mm at the nearest part. Things.
[0010]
In such a proximity charging device, since the charging member and the photoconductor are not in contact with each other, one of the above-described problems of the contact charging device is that the material constituting the charging member adheres to the photoconductor, The problem of permanent deformation of the charging member that occurs when the charging member is stopped for a long period of time has been solved, and the problem of deterioration in charging performance due to the adhesion of toner and the like on the photoconductor to the charging member has also been reduced. It is clear that such a proximity charging device is superior.
[0011]
FIG. 10 is a cross-sectional view of a main part showing an example of a proximity charging device that has been conventionally considered. The charging member 2 is formed by forming a resistance layer 2a on a roller-shaped conductor 2b having a diameter of 5 to 20 mm and a length of approximately 300 mm, and may or may not rotate itself. On the other hand, the photoconductor drum 1 is formed by forming a photoconductor 1a on a cylindrical conductor 1b having a diameter of 30 to 80 mm and a length of approximately 300 mm. The charging member 2 is disposed at a position where the distance D at the closest point between the charging member 2 and the photosensitive drum 1 rotating in the direction of the arrow becomes 0.005 to 0.3 mm. The resistance layer 2 a of the charging member 2 is made of a material having a resistivity of 10 ⁷ to 10 ⁹ Ωcm, and a DC voltage of −2 to −5 KV is applied to the charging member 2 by a power source 4 to apply a direct current to the photosensitive member 1 a. Is charged.
[0012]
[Problems to be solved by the invention]
However, even in such a conventional proximity charging device, although small in comparison with the contact charging device, it is inevitable that toner or the like adheres to the surface of the charging member due to long-term use. When the photosensitive member is charged in a state where the surface of the charging member is contaminated with toner or the like, a decrease in the potential at the time of charging or uneven charging occurs. Is non-uniform, and the toner adheres to a white background portion during reversal development, or a portion where the toner adheres little to a black background portion appears.
[0013]
As a method of preventing the influence of the surface contamination of the charging member, a method of charging the photosensitive member while moving the surface of the charging member by, for example, rotating a charging roller has been proposed. As a result, the surface area of the charging member can be substantially increased, and the attached toner can be dispersed to reduce the influence of the contamination of the charging member. Further, a method has been proposed in which a toner, which is a cleaning member, is slid in contact with the surface of a moving charging member to remove toner adhered to the surface of the charging member (see JP-A-6-149020).
[0014]
On the other hand, in such a charging device that charges the photosensitive member while moving the surface of the charging member, uneven charging occurs compared to a charging device in which the charging member is stopped and the photosensitive member is charged. There is a problem that it is easy. Here, the uneven charging means a state in which the photosensitive member is not uniformly charged, and a state in which the surface potential of the photosensitive member is higher or lower depending on the location.
[0015]
Since the charging unevenness appearing in the proximity charging device has a small pitch (spatial period) of about 0.1 to 1 mm, a general surface voltmeter having a spatial resolution of about 5 mm is averaged and detected. At first glance, the photoreceptor appears to be uniformly charged. However, when an image is actually formed on the photoreceptor in this state, spot-like charging unevenness appears on the image, and the above-described inconvenience occurs.
The present invention has been made in view of the above points, and an object of the present invention is to provide a proximity charging device that can prevent the occurrence of uneven charging while moving the surface of a charging member.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the present invention makes the moving surface of the member to be charged face the moving surface of the charging member in a non-contact manner such that the closest distance of the moving member becomes 0.1 mm or more, By applying a voltage to the charging member, in a proximity charging device that discharges between the charging surface and the surface to be charged and charges the surface to be charged, the proximity member is defined by the resistivity × dielectric constant of the charging member. that the time constant tau, when one point on the charging surface is the time required to pass through the discharge region between the member to be charged and the charging member and t, t / τ> 10 satisfies the ^second condition The present invention is to provide a proximity charging device.
In addition, the moving surface of the charging member is brought into contact with the moving surface of the charging member in a non-contact manner such that the closest distance is 0.1 mm or more, and a voltage is applied to the charging member. Thereby, in the proximity charging device that discharges between the charging surface and the charged surface to charge the charged surface, the charging member is constituted by a plurality of layers, and the capacitance × resistance of the charging member in the time constant defined tau, when one point on the charging surface is the time required to pass through the discharge region between the member to be charged and the charging member and t, t / τ> 10 ² of A proximity charging device satisfying the conditions is also provided.
And these charging members may have to the roller shape, the charged surface of the belt conductive member, even better when sliding contact cleaning member of the charging surface.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. The same reference numerals are given to portions corresponding to FIGS. 8 to 10, and description of those portions will be omitted.
FIG. 1 is a sectional view of a main part showing a first embodiment of the present invention.
FIG. 1 is substantially the same as FIG. 10 described above, but differs from the conventional example shown in FIG. 10 in the following three points. That is, the distance D between the charging member 2 and the photoconductor (surface to be charged) 1a of the photoconductor drum 1 is 0.1 mm or more even at the smallest point, and the charging surface 3 forming the surface of the charging member 2 moves. Τ, a time constant defined by the resistivity × dielectric constant of the charging member 2 is τ, and one point on the charging surface 3 passes through an area where discharge occurs between the charging member and the photoconductor 1 due to the movement of the charging surface 3. when the time required is t to a three points satisfying t / tau> 10 ² relationship.
[0018]
In the first embodiment, the charging member 2 is, for example, a roller having a diameter of 15 mm and a length of 300 mm, and a charging member 2a having a thickness of 3 mm formed on a conductor 2b. It is made of a material having conductivity by adding a compound (ionic compound), and its resistivity is adjusted to 10 ⁸ Ωcm.
[0019]
In addition, in addition to the above-mentioned materials, the charging member 2 may be made of an ionic conductive material obtained by adding an ionic compound to a polymer material such as various rubbers and resins, or an ionic compound. Instead, an electronic conductive material in which carbon is dispersed in a polymer material, or a medium resistivity of, for example, 10 ⁷ to 10 ⁹ Ωcm for preventing the occurrence of charging unevenness and charging the photoreceptor 1a. Any material or the like may be used, and metal oxides such as ceramics may be used.
[0020]
The materials constituting these charging members are adjusted to have a dielectric constant of 1/10 ¹⁰ F / m, and regarding this dielectric constant, the materials that can be used as the charging member are limited to only the above-mentioned materials. is not.
In the first embodiment, the time constant τ of the charging member 2 is as follows.
[0021]
^{Resistivity: 10 8 Ω m ~10 6 Ω} m
Dielectric constant: 1/10 ¹⁰ F / m
Time constant: 10 ⁶ Ωm × 1/10 ¹⁰ F / m = 1/10 ⁴ sec
The time constant 1/10 ⁴ sec has a different value when the type of the material of the charging member 2 is changed.
[0022]
The charging member 2 shown in FIG. 1 is rotated in a direction indicated by an arrow A by a driving source (not shown), and its rotation speed is adjusted such that a moving speed of one point on the charging surface 3 becomes, for example, 15 mm / sec. is there. At this time, the rotating direction of the charging member 2 may be either the opposite direction or the same direction as shown in FIG. 1, and the moving speed of the surface of the charging member 2 is not necessarily 15 mm / sec. However, it is necessary to satisfy the conditional expression t / τ> 10 ² described above.
[0023]
In the proximity charging device shown in FIG. 1, when a DC voltage of −2 to −5 KV is applied to the charging member 2, a discharge occurs between the charging member 2 and the photoconductor 1 a to charge the photoconductor 1 a. The region has a width W in the direction in which the surface of the charging member 2 moves as shown in FIG. The width W is determined by the diameter of the charging member 2, the diameter of the photosensitive drum 1, the magnitude of the applied voltage, and the closest distance D between the charging member 2 and the photosensitive member 1a.
[0024]
In this embodiment, the diameter of the charging member 2 is 15 mm, the diameter of the photosensitive drum 1 is 30 mm, the applied voltage is -2 KV, the distance D at the nearest part is 0.1 mm, and the width W of the discharge region is 1. 5 mm. Therefore, the time t required for one point on the charged surface 3 to pass through the width W of the discharge region with the movement of the charged surface is:
The speed at which one point on the charged surface moves: 15 mm / sec
Discharge area width W: 1.5 mm
Time required to pass t: 1/10 sec
It becomes.
Therefore, t / τ = 10 ³ from the above values of t and τ, which satisfies the conditional expression t / τ> 10 ² sufficiently.
[0025]
FIG. 3 shows the results of an investigation on the relationship between the speed at which the surface of the charging member 2 moves and the state of occurrence of charging unevenness in the first embodiment. The horizontal axis indicates the surface of the charging member 2. The moving speed and the vertical axis show the ratio of the area where the uneven charging occurs on the image. As can be seen from FIG. 3, as a result of the experiment, when the surface moving speed of the charging member 2 exceeds 45 mm / sec, uneven charging occurs. This is a point corresponding to t / τ = 3 × 10 ² .
[0026]
The reason why the occurrence of charging unevenness largely depends on the moving speed of the surface of the charging member 2 can be considered as follows.
The potential of the portion of the surface of the charging member 2 that depends on the region where the discharge occurs should be lower than the applied potential. This is because, when charges are originally accumulated on the surface of the charging member 2, the charges should escape to the base portion of the charging member 2 according to the time constant τ of the charging member 2.
[0027]
However, since the discharge occurs between the charging member 2 and the photosensitive drum 1 sequentially, it is considered that the state where the predetermined amount of charge is accumulated on the surface of the charging member 2 is balanced. On the other hand, the potential on the surface of the charging member in a region where discharge does not occur is the same as the applied potential. That is, no charge is accumulated.
[0028]
In the charging device that moves the surface of the charging member 2, the surface of the charging member 2 that has been in the non-discharged region sequentially moves into a region where a discharge occurs between the charging member 2 and the photoconductor drum 1, and the inside of the discharge region It is considered that the first discharge in the above, that is, the charge is accumulated on the surface, and the discharge until the charge reaches an equilibrium state causes uneven charging. In other words, the mode of discharge changes according to the state of charge accumulation on the surface of the charging member 2, uniform discharge occurs without charge unevenness in the state where charge is accumulated, and uneven charge occurs in the state where no charge is accumulated. It can be considered that non-uniform discharge accompanied by
[0029]
Therefore, the surface moving speed of the charging member 2 is high, that is, the time t required for one point on the surface of the charging member 2 to pass through the discharge region is small, or the time constant τ of the charging member 2 is large, and the charge accumulation is If the charging is not performed promptly, the influence of the discharge in a state where the above-mentioned electric charge is not accumulated becomes dominant, and uneven charging occurs.
[0030]
As is clear from the above, in order to avoid such a condition of uneven charging, in the present invention, by satisfying the condition of t / τ> 10 ² , the surface of the charging member 2 was moved and adhered to the surface. It is possible to effectively prevent the occurrence of uneven charging while reducing the influence of the toner.
[0031]
In the first embodiment, since the charging member is formed in a roller shape, its support and surface moving mechanism can be simplified.
[0032]
Next, FIG. 4 shows a second embodiment of the present invention in which the charging member of the charging member of the first embodiment is changed from a roller to a belt.
In the second embodiment, the charging member 12 is formed into an endless belt shape by forming a charging surface 13 by coating the surface of an NBR rubber 12a formed on a conductor 12b with a conductive material. The closest distance D between the charging surface 13 and the photoconductor 1a of the photoconductor drum 1 is set to 0.1 mm or more. The other configuration is the same as that of FIG. 1, and the operation and effect are similar to those of the first embodiment.
[0033]
FIG. 5 shows a third embodiment of the present invention. A plurality of layers 22b and 22a made of conductive materials having different resistivities are laminated and formed on a roller-shaped conductor 22c of the charging member 22, and the surface of the uppermost layer 22a is coated with a material having conductivity and charged. The surface 23 is formed, and the closest distance D between the charging surface 23 and the photoconductor 1a is set to 0.1 mm or more. The other configuration is the same as that of FIG.
[0034]
When the charging member 22 is composed of a plurality of layers as described above, the time constant τ of the charging member 22 cannot be calculated as dielectric constant × resistivity as in the first embodiment. Therefore, the charging member 22 is modeled by an electric circuit as shown in FIGS. 6A and 6B, and for example, by applying an AC voltage to the charging member 22 placed on the grounded metal plate P, The capacitance C and the resistance R are measured. From the values of C and R measured in this manner, the time constant τ can be obtained as τ = CR.
[0035]
The charging member 22 according to the third embodiment includes first and second coating layers 22b and 22a made of polyurethane resin on the surface of a conductor 22c made of NBR-based rubber having conductivity imparted similarly to the first embodiment. It was formed to a thickness of 30 μm, and the resistivity was adjusted to 10 ¹¹ Ωcm by adding an ionic compound.
[0036]
The above-mentioned coat layers 22b and 22a may be made of acrylic resin, fluorine-based resin or the like instead of polyurethane resin, and the film thickness is not necessarily limited to 30 μm, and the number of layers may be three or more. Absent. Further, in the third embodiment, points other than the configuration in which the charging member is composed of a plurality of layers, for example, the shape of the charging member, the point that the photosensitive member is charged while the surface of the charging member is moved, and the like are described in the first embodiment. Same as the form.
[0037]
As described above, by forming the charging member from a plurality of layers, it becomes possible to cause each layer to share a function role in addition to the effects of the first embodiment. Specifically, the control of the time constant of the charging member is performed by the charging member itself, and the surface of the charging member is coated with a material having excellent durability against discharge products such as ozone, thereby forming the charging member itself. Can be reduced.
[0038]
Next, FIG. 7 is a sectional view of a main part showing a fourth embodiment of the present invention.
In this embodiment, a cleaning member 5 made of an elastic blade is slid on a charging surface 3 of a charging member 2 similar to that of FIG. The cleaning member 5 may be slidably contacted with the charging member 2 at all times, or may be slidably contacted at any time according to contamination on the surface of the charging member 2. The other configuration is the same as that of the first embodiment shown in FIG.
As a method of cleaning the surface of the charging member 2, for example, a brush roller, a sponge roller, a felt, or the like may be used in addition to the elastic blade, and a voltage may be applied to these cleaning members.
[0039]
According to such a configuration, the toner 6 adhering to the surface of the charging member 2 is removed by the cleaning member 5 as the surface of the charging member 2 moves in the direction of arrow A. Is maintained in a state in which no toner adheres, and it is possible to prevent non-uniform charging of the photoconductor due to toner contamination on the surface of the charging member.
[0040]
【The invention's effect】
As described above, the proximity charging device according to the present invention reduces the influence of toner contamination by satisfying the predetermined relationship between the time constant, which is the material characteristic of the charging member, and the moving speed of the charging member surface. Therefore, even if the surface of the charging member is moved, it is possible to prevent uneven charging. As a result, the effect of toner adhering on the surface of the charging member can be significantly reduced as compared with a conventional proximity charging device in which the surface of the charging member must be fixed to prevent charging unevenness. .
[0041]
Further, the charging member is constituted by a plurality of layers, and the relationship between the time constant, which is a material property of the charging member, and the moving speed of the charging member surface satisfies a predetermined condition. The function of each layer of the charging member can be shared, so that the deterioration can be reduced and the characteristic change for a long period can be prevented.
In these proximity charging devices, if the charging member is formed in a roller shape, the mechanism for supporting the charging member and moving the surface can be simplified in addition to the above-described effects.
[0042]
Further, in the above proximity charging device, when the cleaning member is slid on the charging surface of the charging member, the toner adhered to the charging surface is removed by the cleaning member as the surface of the charging member moves, and the charging surface is removed. It is always maintained in a state where no toner adheres. Therefore, there is no possibility that a problem such as the photosensitive member not being uniformly charged occurs, and a proximity charging device in which the charging performance is not deteriorated even when used for a long time can be obtained.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a main part of a first embodiment of the present invention.
FIG. 2 is an explanatory view schematically showing the discharge region.
FIG. 3 is an explanatory diagram showing the relationship between the moving speed of the surface of the charging member and the ratio of the uneven charging generation region.
FIG. 4 is a sectional view of a main part showing a second embodiment of the present invention.
FIG. 5 is a sectional view of a main part showing a third embodiment of the present invention.
FIG. 6 is an explanatory diagram showing a time constant measuring method.
FIG. 7 is a sectional view of a main part showing a fourth embodiment of the present invention.
FIG. 8 is a configuration diagram schematically showing a conventional image forming apparatus.
FIG. 9 is a sectional view of a main part showing an example of a conventional contact charging device.
FIG. 10 is a sectional view of a main part showing an example of a conventional proximity charging device.
[Explanation of symbols]
1: Photoconductor drum 1a: Photoconductors 2, 12, 22: Charging members 3, 13, 23: Charging surface 4: Power supply 5: Cleaning member 6: Toner

Claims (4)

With respect to the moving charged surface of the member to be charged, the moving charging surface of the charging member is opposed to the charging surface in a non-contact manner such that the closest distance is 0.1 mm or more, and by applying a voltage to the charging member, In a proximity charging device that discharges between the charged surface and the charged surface to charge the charged surface,
The time constant defined by the resistivity × dielectric constant of the charging member was τ, and the time required for one point on the charging surface to pass through a discharge region between the charged member and the charging member was t. when, t / τ> 10 proximity charging device and satisfies the ^second condition. By moving the charged surface of the charged member in a non-contact manner with the moving surface of the charging member so that the closest distance is 0.1 mm or more, and applying a voltage to the charging member, In a proximity charging device that discharges between the charged surface and the charged surface to charge the charged surface,
The charging member is composed of a plurality of layers, a time constant defined by the capacitance of the charging member × resistance is τ, and one point on the charging surface is a discharge area between the charged member and the charging member. A proximity charging device , wherein t / τ> 10 ² is satisfied , where t is a time required to pass through . 3. The proximity charging device according to claim 1, wherein the charging member has a roller shape . The proximity charging device according to any one of claims 1 to 3, wherein a cleaning member for the charging surface is slidably contacted with the charging surface of the charging member.

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