JP2002244406A - Electrifier and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrifier capable of preventing toner and carrier, etc., regarded as a foreign matter from sticking onto the electrifier itself, preventing the occurrence of a filming phenomenon on an image carrier such as a photoreceptor drum, etc., and stably electrifying the surface of the image carrier over a long period. SOLUTION: The electrifier is provided with a cylindrical rotating film which is brought into contact with the image carrier for forming a toner image, and also, on which a prescribed electrifying bias is applied, and a driving means for driving the rotating film at a prescribed circumferential velocity, and on condition that the surface of the image carrier is uniformly electrified by the electrifier, and provided that the circumferential velocity of the image carrier is expressed by V1 and the circumferential velocity of the rotating film is expressed by V2, the relation of 1.01<(V2/V1)<=1.10 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, which charges a surface of an image carrier such as a photosensitive drum on which a toner image is formed to a uniform potential. More specifically, the present invention relates to an improvement for keeping the surface of the image bearing member and the surface of the charging device in a clean state for a long period of time.

[0002]

2. Description of the Related Art In an electrophotographic copying machine or a laser beam printer, the surface of an image carrier such as a photosensitive drum is uniformly charged, and then the surface of the photosensitive drum is exposed according to image information. An electrostatic latent image is formed, and the electrostatic latent image is developed with toner to form a toner image as a visible image. Finally, the toner image is transferred to an image receptor such as an intermediate transfer member or a recording sheet. To form a recorded image. Here, as a charging device for uniformly charging the surface of the photoreceptor drum, a non-contact type corona discharge device has been frequently used, but ozone generated by corona discharge adversely affects the environment and the human body. In recent years,
The replacement with a charging device that is used in direct contact with the image carrier is rapidly progressing.

Conventionally, as a contact-type charging device of this type, a conductive shaft core member is covered with a conductive rubber, and the conductive rubber is brought into contact with the surface of the photosensitive drum with a predetermined pressing force. 2. Description of the Related Art There is known a charging roll configured to perform the charging. In the charging roll having such a structure, a minute gap is formed between the conductive rubber and the photosensitive drum, and electric charges are given to the photosensitive drum by the discharge generated in the minute gap. However, with this charging roll, it is difficult to make uniform contact with the photoconductor drum because the conductive rubber layer is deformed by the pressing force, and uneven charging of the photoconductor drum is caused by non-uniform contact. There is a disadvantage that it occurs.

Therefore, Japanese Patent Application Laid-Open Nos. Hei 4-232977 and Hei 5-72869 disclose a charging device in which a rotating film formed in a cylindrical shape is brought into contact with a photosensitive drum. . Specifically, a rotating film having a predetermined resistance value is brought into contact with the photoconductor drum, and a conductive shaft member for supplying power to the rotating film is disposed through the rotating film, and the rotating shaft film has a predetermined resistance. To apply a DC bias voltage. According to such a configuration, the rotating film flexibly adapts to the outer peripheral surface of the photosensitive drum, and further, the rotating film itself is electrostatically attracted to the outer peripheral surface of the photosensitive drum by supplying a bias voltage. Thus, the rotating film and the photosensitive drum can be uniformly contacted, and the photosensitive drum can be charged evenly as compared with the conventional case in which the conductive rubber layer is pressed.

In the charging device disclosed in Japanese Patent Application Laid-Open No. H11-125596, a conductive foam layer is provided around a conductive shaft member, and a rotating film is adhered around the foam layer. By setting the hardness of the foam layer to be extremely soft, the rotating film comes into flexible contact with the photosensitive drum. Therefore, even in the charging device disclosed in this publication, it is possible to uniformly charge the photosensitive drum by applying a predetermined magnitude of bias voltage to the shaft core member.

[0006]

In an electrophotographic copying machine or the like using this type of charging device, an electrostatic latent image formed on the surface of a photosensitive drum is developed with toner, and the toner image is developed. Because it is transferred to the image receptor,
Residual toner, paper powder, and the like that cannot be transferred to the photosensitive drum easily adhere to the surface of the photosensitive drum. Fine particles such as silica and alumina are added to the toner to adjust the triboelectric charge and fluidity. When a toner image is formed on the photosensitive drum, these external additives adhere to the photosensitive drum. Resulting in. Further, when a two-component developer in which a toner and a carrier are mixed is used as a developer for an electrostatic latent image,
The carrier may adhere to the surface of the photosensitive drum.

For this reason, on the surface of the charging device which is in direct contact with the photosensitive drum, these foreign substances are easily transferred from the photosensitive drum, and if toner or the like adheres to the surface of the charging device, only the portion where the toner adheres to the surface. The discharge becomes abnormal, and the surface potential of the photosensitive drum tends to increase. In addition, when a foreign substance having a relatively large particle diameter such as a carrier adheres, poor charging of the photosensitive drum occurs. That is, unevenness occurs in the surface potential of the photosensitive drum, resulting in a difference in the amount of development. Therefore, especially when a halftone image is developed, unevenness in density becomes conspicuous.

[0008] Since the external additive is extremely small compared to the toner and the carrier, even if the external additive slightly adheres to the surface of the charging device, the external additive alone does not significantly affect the charging performance itself. When the charging device repeatedly rotates while both are attached to the surface of the charging device,
The toner tends to adhere to the surface of the charging device with the external additive as a nucleus, and the adhered toner is transferred to the surface of the photosensitive drum in a streak form, and finally spreads in a thin film form on the surface of the photosensitive drum. Would. Such adhesion of the toner to the charging device and the photosensitive drum is called a so-called filming phenomenon. When this filming phenomenon occurs, density unevenness and streaks occur in the formed image, and the image quality is significantly reduced.

In order to avoid such a problem, in a conventional copying machine, printer, or the like, a cleaner for cleaning the surface of the photosensitive drum is provided between the toner image transfer section and the charging device, and the photosensitive drum is provided with a cleaner. In general, foreign matter such as toner and carrier adhered to the charging device is collected in front of the charging device. However, the cleaner removes foreign substances such as toner from the surface of the photosensitive drum and also scrapes off the photosensitive layer on the surface of the photosensitive drum, thereby shortening the life of the photosensitive drum. In particular, this problem is remarkable in a type of cleaner in which the cleaning blade is pressed against the surface of the photosensitive drum. Further, when a cleaner is provided for the photosensitive drum, if the capacity of the collection box of the waste toner collected by the cleaner is set to be large, the image forming apparatus itself becomes large, and in particular, each color of yellow, magenta, cyan, and black is used. In a so-called tandem-type full-color copying machine having a photosensitive drum for each toner, there is a great problem. Particularly, in recent years, a photosensitive drum having a small diameter has been adopted for the purpose of downsizing a full-color laser printer, and a space around the photosensitive drum has been remarkably narrowed. Further, improvement of toner for improving transfer efficiency of a toner image is also progressing. For example, spherical toner described below is the case, and it is difficult to remove this toner from the photosensitive drum by simply providing a cleaning blade. Accordingly, there is a growing need for a so-called cleaner-less structure in which a cleaner is not provided for the photosensitive drum, and the adhesion of toner and the like to the charging device and the occurrence of a filming phenomenon are extremely important in realizing a cleaner-less image forming apparatus. This is an important problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the adhesion of foreign substances such as toner and carrier to the charging device itself, and the filling of an image carrier such as a photosensitive drum with an image carrier. It is an object of the present invention to provide a charging device capable of preventing occurrence of a ming phenomenon and stably charging the surface of such an image carrier over a long period of time.

[0011]

That is, the present invention provides a cylindrical rotating film which contacts an image bearing member on which a toner image is formed and to which a predetermined charging bias is applied, and which rotates the rotating film in a predetermined circumferential direction. And a driving device for driving the image carrier at a high speed, and assuming a charging device for uniformly charging the surface of the image carrier. When the peripheral speed of the image carrier is V1 and the peripheral speed of the rotating film is V2, .01 <(V2 / V1) ≦ 1.10.

Foreign matters such as toner and carrier adhering to the charging device originally adhered to an image carrier such as a photosensitive drum during development of an electrostatic latent image. Is transferred to the charging device in the contact area of. For this reason, if a speed difference is provided between the image carrier that rotates while contacting each other and the rotating film of the charging device, the speed difference between the foreign matter that adheres to the image carrier and proceeds and the rotating film is increased. The presence of such foreign matter makes it difficult for the foreign matter to adhere to the rotating film. Further, even when the carrier or the like has adhered to the rotating film, the adhered portion passes through the contact area with the image carrier again, so that the adhered foreign matter is washed off from the surface of the rotating film. In addition, it is possible to prevent the continuous attachment of foreign matter to the rotating film as much as possible. The present inventors have conducted experiments and confirmed that the peripheral speed V1 of the rotating film with respect to the peripheral speed V1 of the image carrier.
If the speed of Step 2 is greater than + 1%, adhesion of foreign matter to the surface of the rotating film was suppressed, and a good recorded image free of image stains on spots could be obtained.

On the other hand, if the difference between the two speeds is too large, a large shear stress acts on the toner sandwiched between the image bearing member and the rotating film. Easily adheres to the surface. The inventors of the present application have also confirmed through experiments that if the speed of the peripheral speed V2 of the rotating film with respect to the peripheral speed V1 of the image bearing member is + 10% or less, the toner on the surface of the image bearing member or the rotating film can be removed. The occurrence of sticking, that is, the occurrence of a filming phenomenon was suppressed, and a good recorded image without unevenness in image quality could be formed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a charging device of the present invention and an image forming apparatus using the same will be described in detail with reference to the accompanying drawings. FIG. 1 shows a full-color laser beam printer provided with the charging device of the present invention. In addition, the arrow in FIG. 1 has shown the rotation direction of each rotating member.

As shown in FIG. 1, this full-color printer has photosensitive drums (image carriers) 11, 12, and 13 for cyan (C), magenta (M), yellow (Y), and black (K). Forming units 1, 2, 3, 4 having photoconductor drums 11, 12, 1
Charging devices 21 and 2 for primary charging that come in contact with 3, 14
2, 23, 24, and laser beams 31, 32 of cyan (C), magenta (M), yellow (Y), and black (K).
A laser optical unit (exposure device) (not shown) for irradiating 32, 33, 34, and developing devices 41, 42, 43, 44
And a first primary intermediate transfer drum (intermediate transfer member) 51 contacting two of the four photosensitive drums 11, 12, 13, 14 and the other two photosensitive drums A second primary intermediate transfer drum (intermediate transfer body) 52 that contacts the first and second primary intermediate transfer drums 51 and 52; The main part is constituted by a final transfer roll (transfer member) 60 that comes into contact with the secondary intermediate transfer drum 53.

The photosensitive drums 11, 12, 13, 14 are
They are arranged at regular intervals so as to have a common tangent plane M. In addition, the first primary intermediate transfer drum 51 and the second primary intermediate transfer drum 52 have surfaces whose rotation axes are parallel to the photosensitive drums 11, 12, 13, and 14 and whose predetermined target surface is a boundary. They are arranged so as to be in an object relationship. Further, the secondary intermediate transfer drum 53 is disposed so that the rotation axis is parallel to the photosensitive drums 11, 12, 13, and 14.

A signal corresponding to image information for each color is rasterized by an image processing unit (not shown) and input to a laser optical unit (not shown). In this laser optical unit, laser light 31 of each color of cyan (C), magenta (M), yellow (Y), and black (K) is used.
32, 33, and 34 are modulated and irradiated onto the photosensitive drums 11, 12, 13, and 14 of corresponding colors.

Each of the photosensitive drums 11, 12, 13, 1
Around 4, an image forming process for each color is performed by a known electrophotographic method. First, the photosensitive drum 1
Photoreceptor drums using OPC photoreceptors having a diameter of 20 mm are used as 1, 12, 13, and 14, and these photoreceptor drums 11, 12, 13, and 14 are 95 mm / sec (V
It is driven to rotate at the rotation speed of 1). The photosensitive drum 1
As shown in FIG. 1, the surface of each of the charging devices 12, 22, 32, and 42 has a DC voltage of about -800 V applied thereto.
By applying a voltage, it is uniformly charged to, for example, about -300V. In this embodiment, only the DC component is applied to the charging device.
It can also be configured to overlap the C component.

On the surfaces of the photosensitive drums 11, 12, 13, and 14 having a uniform surface potential as described above, cyan (C), magenta (M), and yellow ( Laser light 31, 32, 33, 3 corresponding to each color of Y) and black (K)
4, and an electrostatic latent image corresponding to the input image information for each color is formed. When the electrostatic latent image is written by the laser optical unit, the photosensitive drums 11, 12, 13, 1
The surface potential of the image-exposed portion 4 is discharged to about -60 V or less.

The photosensitive drums 11, 12,
The electrostatic latent images corresponding to each color of cyan (C), magenta (M), yellow (Y), and black (K) formed on the surfaces of 13 and 14 are developed by developing devices 41 and 42 of corresponding colors.
The photosensitive drums 11 and 1 are developed by 43 and 44, respectively.
The image is visualized as a toner image of each color of cyan (C), magenta (M), yellow (Y), and black (K) on 2, 13, and 14. In this embodiment, the developing devices 41, 42,
A magnetic brush contact type two-component developing system is adopted as 43 and 44, and the developing devices 41, 42, 43 and 44 respectively provide cyan (C), magenta (M) and yellow ( Y), a developer composed of black (K) toner and a carrier is filled. When the developing devices 41, 42, 43, and 44 are supplied with toner from a toner supply device (not shown), the supplied toner is sufficiently stirred with the carrier by the auger 404 and is triboelectrically charged. Inside the developing roll 401, a magnet roll (not shown) in which a plurality of magnetic poles are arranged at a predetermined angle
Are arranged in a fixed state. This developing roll 40
The amount of the developer transported to the vicinity of the surface of the developing roll 401 by the paddle 403 that transports the developer to the developing roller 1 is regulated by the developer amount regulating member 402. In this embodiment, the amount of the developer is 30 to 5
0 g / m ^2, and the charge amount of the toner present on the developing roll 401 at this time is approximately −20 to −35 μC /
g.

The toner supplied onto the developing roll 401 is in the form of a magnetic brush composed of carrier and toner by the magnetic force of the magnet roll, and this magnetic brush is used as the photosensitive drums 11, 12, 13, and 14. Is in contact with By applying an AC + DC developing bias voltage to the developing roll 401 to develop the toner on the developing roll 401 into an electrostatic latent image formed on the photosensitive drums 11, 12, 13, and 14, a toner image is formed. It is formed. In this embodiment, the developing bias voltage is 4 kHz AC.
z, 1.5 kVpp, and DC is about -230V.

As the toner, a so-called "spherical toner" having a substantially spherical shape is used.
It is about μm. Here, the “spherical toner” refers to, for example, a scanning electron microscope FE-SEM (S
= 800), 100 toner images magnified at a magnification of 500 times are randomly sampled, and the image information is introduced into an image analyzer, for example, manufactured by Nicole, via an interface, and analyzed. The shape coefficient value MLS2 defined as a value obtained by calculation from the equation is 100 to 1
It has a value of 40. The shape of the toner produced by the ordinary kneading and pulverizing method is irregular, and the MLS2 is 14
It is about 0 to 160. MLS2 = {(absolute maximum length of toner particles) × 2} /
{(Projected area of toner particles) × π × １ ／ × 100}

Such a spherical toner has good releasability from the photosensitive drum, and can increase the transfer efficiency in the primary transfer of a toner image described later. In particular,
A toner having a spherical coefficient of 130 or less is optimal for realizing a so-called cleaner-less structure in which a cleaner is not provided for a photosensitive drum.

Next, each of the photosensitive drums 11, 12, 1
The toner images of each color of cyan (C), magenta (M), yellow (Y), and black (K) formed on the first and second primary intermediate transfer drums 51 and 52 are formed on the first and second primary intermediate transfer drums 51 and 52, respectively. The first transfer is electrostatically performed on the reference numeral 52. The cyan (C) and magenta (M) toner images formed on the photoconductor drums 11 and 12 are formed on the first primary intermediate transfer drum 51 by yellow (C) and magenta (M) toner images formed on the photoconductor drums 13 and 14, respectively. The toner images of Y) and black (K) are respectively transferred onto the second primary intermediate transfer drum 52. Accordingly, on the first primary intermediate transfer drum 51, the monochrome image transferred from either of the photosensitive drums 11 and 12 and the two-color toner image transferred from both of the photosensitive drums 11 and 12 are superimposed. A double-color image is formed. Further, on the second primary intermediate transfer drum 52, a similar single-color image and a similar double-color image are formed from the photosensitive drums 13 and 14.

The first and second primary intermediate transfer drums 5
The surface potential required for electrostatically transferring the toner image from the photosensitive drums 11, 12, 13, 14 onto the first and second photosensitive drums 52 is
+250 to 500V. The optimal surface potential varies depending on the toner charging state, ambient temperature, and humidity,
When the charge amount of the toner is in the range of −20 to −35 μC / g and in a normal temperature and normal humidity environment, the surface potential of the first and second primary intermediate transfer drums 51 and 52 is +380
V is desirable. Each of the first and second primary intermediate transfer drums 51 and 52 has an outer diameter of 42 mm and a resistance value of about 10 ⁸ Ω. Resistance elastic layer (R = 10 ²
It is formed by coating with ~10 ³ Ω). Further, on the surface of the low resistance elastic layer, a high release layer having a thickness of 3 to 100 μm is formed.
m of a fluororubber layer is provided and bonded with a silane coupling agent-based adhesive (primer). Incidentally, the resistance value of the high release layer is about R = 10 ⁵ to 10 ⁹ Ω.

Thereafter, the single-color or double-color toner images formed on the first and second primary intermediate transfer drums 51 and 52 are electrostatically secondary-transferred onto the secondary intermediate transfer drum 53. You. Therefore, on the secondary intermediate transfer drum 53, a final toner image from a single color image to a quadruple color image of cyan (C), magenta (M), yellow (Y), and black (K) is formed. Will be.

The surface potential required for electrostatically transferring a toner image from the first and second primary intermediate transfer drums 51 and 52 onto the secondary intermediate transfer drum 53 is +600 to 1
It is about 200V. The optimum surface potential varies depending on the charged state of the toner, the ambient temperature, and the humidity as in the case of the primary transfer. Further, what is necessary for the transfer is the potential difference between the first and second primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53, so that the transfer of the first and second primary intermediate transfer drums 51 and 52 is performed. It is necessary to set a value according to the surface potential. As described above, the toner charge amount is −20.
−35 C / g in a normal temperature and normal humidity environment, and the first and second primary intermediate transfer drums 51 and 52.
Is about +380 V, the surface potential of the secondary intermediate transfer drum 53 is about +880 V, that is, the first
It is desirable that the potential difference between the second primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53 be set to about + 500V.

Secondary intermediate transfer drum 5 used in this embodiment
Reference numeral 3 denotes first and second primary intermediate transfer drums 51 and 5 having an outer diameter of 1st and 2nd.
2, and the resistance value is set to about 10 ¹¹ Ω. Similarly to the primary intermediate transfer drum, the secondary intermediate transfer drum 53 is formed by forming a metal pipe made of Fe, Al, or the like with a low-resistance elastic layer (R = 10 ² to 10 ³ Ω), and the surface of the low-resistance elastic layer has a thickness of 3 to 10
It is coated with a high release layer made of 0 μm fluororubber. Here, the resistance value of the secondary intermediate transfer drum 53 is
And higher than the second primary intermediate transfer drums 51 and 52. Otherwise, the secondary intermediate transfer drum 53 charges the first and second primary intermediate transfer drums 51 and 52, and the first and second primary intermediate transfer drums 5 and 52 are charged.
It becomes difficult to control the surface potentials of the first and second surfaces.

Finally, the final toner image from the single-color image to the quadruple-color image formed on the secondary intermediate transfer drum 53 is tertiarily transferred by a final transfer roll 60 onto a sheet passing through the sheet transport path P. Is done. This paper passes through a paper transport roll 90 through a paper feeding process (not shown), and is fed into a nip portion between the secondary intermediate transfer drum 53 and the final transfer roll 60. After this final transfer step, the final toner image formed on the paper is fixed by the fixing device 70, and a series of image forming processes is completed.

FIG. 2 shows the charging device 21 arranged in contact with the photosensitive drum 11. The charging device 21 includes a cylindrical rotating film 210 having electrical conductivity in contact with the photosensitive drum 11 and a film 2.
Shaft core member 211 made of conductive metal penetrating inside 10
And a conductive elastic body 212 provided to cover the periphery of the shaft core member 211 and press the film 210 against the photosensitive drum 11. Is adhered to the entire surface of the elastic body 212 to be integrated. A gear (not shown) is mounted on one end of the shaft core member 211, and the rotational driving force of a motor (not shown) is transmitted to the charging device 21 via the gear. In order to maintain the contact pressure of the rotating film 210 on the photosensitive drum 11 at a low level, the shaft member 211 is positioned at a fixed position without being urged against the photosensitive drum 11. As a result, the nip width of the rotating film 210 with respect to the photosensitive drum 11 is set to 0.5 to 1.5 mm, and the bite amount is set to 0.15 mm, and this state is maintained even during long-term use. Then, by applying a bias voltage to the shaft core member 211, the peripheral surface of the rotating film 210 and the photosensitive drum 11
A discharge occurs in the wedge-shaped minute gap formed by the peripheral surface of the photosensitive drum 11 and a desired surface potential can be given to the photosensitive drum 11.

Further, a temporary toner holding member 215 for temporarily holding the toner adhered to the surface of the photosensitive drum 11 is provided upstream of the charging device 21 with respect to the rotation direction of the photosensitive drum 11. This temporary toner holding member 215
Is constituted by a conductive brush, and by applying a bias voltage, the toner whose polarity has been inverted at each transfer portion is temporarily collected from the surface of the photosensitive drum 11 until a cleaning mode described later is started. Meanwhile, the toner is held. That is, the toner is charged to the (−) polarity in the developing device 41,
In each transfer step, the toner image is transferred in a direction of higher potential. However, when such a toner image repeatedly passes through the transfer portion of each transfer step,
Due to Paschen discharge or charge injection, a part of the (−) charged toner may be inverted to the opposite polarity, that is, (+) polarity, and may be charged. It is not transferred and flows backward to the upstream side. Finally, the toner is transferred to the photosensitive drum 11, and eventually adheres to the charging device 21. The temporary toner holding member 215 is provided in order to catch the toner whose polarity has been inverted before the charging device 21 and prevent the toner from being attached to the charging device 21. Therefore, at the time of forming a toner image, the surface potential of the photosensitive drum 11 −
A potential of −400 V, which is lower than 300 V, is applied to the temporary toner holding member 215. Further, in order to prevent the temporary toner holding member 215 from damaging the photosensitive drum 11, the tip of the brush rubs the photosensitive drum 11 in the same direction as the moving direction of the photosensitive drum 11. The bite amount of the brush outer diameter with respect to the photosensitive drum 11 is set to be extremely small at 0.65 mm or less.

In the above description, the charging device 21 and the toner temporary holding member 21 provided for the photosensitive drum 11 are provided.
5, the other photosensitive drums 12, 13,
14, charging devices 22, 23, and 24 and a toner temporary holding member (not shown) having the same structure are provided.

On the other hand, the printer of this embodiment does not have a cleaner for cleaning the surfaces of the photosensitive drums 11, 12, 13, and 14 after the primary transfer of the toner image, and employs a so-called cleaner-less structure. Although the primary transfer efficiency of the toner image has been improved by the use of spherical toner, etc., it is difficult to always achieve 100% transfer efficiency because the transfer efficiency is affected by environmental fluctuations such as temperature and humidity. It is. For this reason, residual toner not transferred to the primary intermediate transfer drums 51 and 52 is transferred to the photosensitive drums 11, 12 and 1.
The photosensitive drums 11 and 1 remain attached to the photosensitive drums 3 and 14.
2, 13, and 14 and the charging devices 21, 22, 23, and 24, and the charging device 21,
It adheres to the surfaces of 22, 23 and 24.

Therefore, in the printer of this embodiment, the toner is prevented from adhering to the charging devices 21, 22, 23, and 24, and the toner whose polarity has been inverted is collected from the toner temporary holding member 215. Before printing operation,
After the printing operation, the following cleaning operation is performed at a predetermined timing such as every predetermined number of sheets during continuous printing.

In this cleaning operation, first,
Charging devices 21, 22, 23, 24, toner temporary holding member 2
15, the photosensitive drums 11, 12, 13, 14; the first and second primary intermediate transfer drums 51 and 52; the secondary intermediate transfer drum 53; A voltage having a potential gradient is applied in order to increase the voltage, so that the (+) charged toner of the opposite polarity collected and held by the temporary toner holding member 215 during the printing operation is sequentially transferred to the final transfer roll 60. Each transfer is performed, and the toner is collected by a cleaning device 80 provided in contact with the final transfer roll 60.
Therefore, when such a cleaning operation is started,
The (+) charged toner temporarily held by the toner temporary holding member 215 is removed from the photosensitive drums 11, 12, 13, and 1.
4, the toner temporary holding member 215 returns to a clean state.

When the cleaning of the (+) charged toner is completed in this manner, the same potential as that at the time of forming the toner image is applied to the charging devices 21, 22, 23, 24, the temporary toner holding member 215, and the photosensitive drum 11. , 12, 13, 14, 1st
And the second primary intermediate transfer drums 51 and 52, the secondary intermediate transfer drum 53, and the final transfer roll 60, and the charging devices 21, 22, 23, and 24, and the photosensitive drum 11,
The cleaning of the (−) charged toner adhered to 12, 13, and 14 is performed. That is, by applying the same potential as that at the time of image formation, the (-) charged toner whose polarity has not been inverted is transferred to the primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53 in the same manner as in the normal toner image transfer. After reaching the final transfer roll 60, it is collected by the cleaning device 80.

By periodically performing such a cleaning operation, the photosensitive drums 11, 12, 13, 1
4 and the toner adhering to the charging devices 21, 22, 23 and 24 are collected by the cleaning device 80 regardless of the polarity, and the photosensitive drums 11, 12, 13 and
14 and the charging devices 21, 22, 23, and 24 can be cleaned.

However, even if such a cleaning operation is performed periodically, the residual toner that has not been transferred to the primary intermediate transfer drums 51 and 52 during the toner image forming operation is small, , 12,13,14
And the charging device 21, 22, 23, 24. Further, even during the cleaning operation, the temporary toner holding member 215 transfers the photosensitive drums 11, 12, 13,
14, the (+) charged toner discharged to the charging device 21,
The transfer to the primary intermediate transfer drums 51 and 52 is made through the contact portions with the intermediate transfer drums 22, 23 and 24. And
When these toners adhere to the charging devices 21, 22, 23, and 24, the photosensitive drums 11, 12, 13, and 14
Charging unevenness occurs, and image quality defects such as image omission and density unevenness occur. The toner is charged by the charging devices 21 and
2, 23, 24 and the photosensitive drums 11, 12, 1, 1
When the toner is crushed at the contact portions with the toner particles 3, 14, the toner adheres to the charging devices 21, 22, 23, 24 and the photosensitive drums 11, 12, 13, 14 to cause a filming phenomenon. Body drums 11, 12, 1
Since the charging unevenness occurs in the toner images 3 and 14, the image quality of the formed toner image is deteriorated.

Therefore, in the printer of the present embodiment, the rotating film 210 constituting the charging devices 21, 22, 23, 24 is provided.
And the elastic body 2 covered with the rotating film 210
Twelve configurations are set as follows.

First, the rotating film 210 is made of a material having a small surface energy in order to prevent toner and external additives added thereto from adhering. Specifically, PVdF (water contact angle θ: about 90 degrees)
A conductive agent was dispersed in the mixture, the surface resistance was adjusted to 10 ⁶ Ω / □, and a thin film having a thickness of 45 μm was used. In addition, polyamide, polyimide, polyetherimide, elastomer PVdF, polyester, polycarbonate, polyolefin, PEN, PEK, P
A material obtained by dispersing a conductive agent in ES, PPS, PFA, ETFE, CTFE, or the like and forming it into a thin film can be used.

Since the occurrence of the filming phenomenon is closely related to the magnitude of the shearing stress acting on the toner, the charging device 2 is required to prevent such occurrence.
1, 2, 23, 24 photosensitive drums 11, 12, 1
It is very important to reduce the contact pressure on 3,14. From this, the charging devices 21 and 2 of the present embodiment are
2, 23, and 24, the hardness is 50 ° on an Asker-F scale as an elastic body 212 that presses the rotating film 210 against the photosensitive drums 11, 12, 13, and 14.
The following were used. Specifically, the hardness is Asker-
A foamed polyester having an F scale of 30 ° was used. As the elastic body 212, various kinds of elastic bodies can be used as long as they have conductivity. Among them, the foam can easily realize the above hardness by adjusting the size and number of cells. .

Further, the hardness of such an elastic layer 212 is extremely soft, and in order to achieve the above hardness by using a foam as the elastic layer 212, it is necessary to set the cells in the foam to be large. Become. For this reason, if the thickness of the rotating film 210 is extremely thin, irregularities corresponding to the locations of the cells are generated on the surface of the film 210, and even if the smoothness of the film surface is increased as described above, Is wasted. For this reason, in this embodiment, the thickness of the rotating film 210 is set to 45 μm.

On the other hand, in order to prevent the filming phenomenon from occurring, it is necessary to positively prevent foreign substances such as toner and carriers from adhering to the rotating film 210. For this reason, in the printer of this embodiment, the rotating film 210 is formed by using the material having a small surface energy as described above, and the toner and the carrier are transferred from the photosensitive drums 11, 12, 13, and 14 to the rotating film 210. In order to positively prevent the rotation, the peripheral speed V2 of the rotating film 210 is set to be slightly higher than the peripheral speed V1 of the photosensitive drum. Table 1 below shows the evaluation of the occurrence of filming on the photoreceptor and the image quality of the recorded image actually formed on the recording sheet at different speed ratios of V2 to V1 (V2 / V1). . As the experimental conditions, 2,000 recording sheets were continuously run by the above-described printer under an environment of a temperature of 10 ° C. and a humidity of 15% RH, and a band-shaped solid image with 90% image coverage was formed on each recording sheet. This condition is much harsher than that in which a printer of the above configuration would normally be used, in order to accurately detect the occurrence of the phenomenon and to search for an extremely reliable configuration.

[0044]

[Table 1]

In this experimental result, the speed ratio was -1.3.
In the case of%, 0% and 1%, spots are formed at regular intervals in the band-shaped solid image actually formed on the recording sheet. It is assumed that each time the toner or carrier attached to the surface of the film 210 comes into contact with the photoconductor drum, uneven charging of the photoconductor drum occurs. However,
When the speed ratio is + 1%, spots are also formed at regular intervals, but the initial frequency decreases compared to the cases of -1.3% and 0%, suggesting an improvement tendency.

When the speed ratio is equal to or more than + 3%, even if spots appear in the solid band image, they are not repeatedly formed at a constant pitch, and only one point appears and disappears immediately. Was. From this, the speed ratio is +
When the content is 3% or more, it is clear that the toner and the carrier can be prevented from continuously adhering to the rotating film 210, and the charging failure and the charging unevenness of the photosensitive drum can be prevented as much as possible. Was.

On the other hand, when the speed ratio becomes + 10%, it is evident that partial fogging starts to occur on the surface of the photosensitive drum, and that the toner has begun to adhere to the surface of the photosensitive drum.
This is because, as the speed ratio increases, a greater shear stress acts on the toner existing between the photosensitive drum and the rotating film. When the speed ratio was + 10%, the filming phenomenon started to occur slightly, but there was no problem with the band-shaped solid image formed on the recording sheet. A filming phenomenon was observed, and density unevenness was also observed in a band-like solid image actually formed. Therefore, from the viewpoint of preventing the occurrence of the filming phenomenon,
The speed ratio needs to be suppressed to + 10% or less.

That is, the rotating film 2 of the charging device 21
From the viewpoint of preventing toner and carrier from adhering to the belt 10, the speed ratio (V2 / V1) between the peripheral speed V1 of the photosensitive drum and the peripheral speed V2 of the rotating film 210 needs to be larger than + 1% (> + 1%). From the viewpoint of preventing the occurrence of the filming phenomenon on the photosensitive drum, the speed ratio (V2 / V1) is not more than + 10% (≦ + 10%).
%). Actually the above speed ratio is 3%
When the printing was repeated by setting the two types of printing, that is, 5% and 5%, in each case, a toner image of good image quality could be obtained even with about 20,000 prints.

Further, from the viewpoint of reducing the shear stress acting on the toner between the charging devices 21, 22, 23, 24 and the photosensitive drums 11, 12, 13, 14, from the viewpoint of preventing the occurrence of the filming phenomenon. Then, charging device 2
It is preferable that a low surface energy substance such as silicone oil is applied to the surfaces of 1, 2, 23, and 24 to reduce the friction coefficient of the surface of the rotating film 210. Silicone oil is applied to the surface of the rotating film 210 actually set to the speed ratio, and the charging devices 21, 22, 2
When a toner image was formed using 3,24, no filming phenomenon was observed even when printing was repeated up to about 30,000 sheets after passing 20,000 sheets.

The application of the low surface energy substance to the surfaces of the charging devices 21, 22, 23 and 24 may be performed periodically. Is preferably maintained over a long period of time. Amine-modified silicone oil has good coating retention properties when applied to an organic substance such as a resin film.By applying this during product assembly, the friction coefficient of the surface of the rotating film 210 is suppressed for a long time, It is possible to prevent the occurrence of the filming phenomenon.

Further, silica (SiO ₂ ) or the like is added as an external additive in an amount of about 1 wt% as an external additive for adjusting the triboelectric charge amount and the fluidity of the toner. If dimethyl silicone oil is applied to the surface of the external additive, the external additive adhered to the photosensitive drums 11, 12, 13, and 14 together with the toner during the development of the electrostatic latent image is charged by the charging devices 21, 22, Since the dimethyl silicone oil adheres to the surfaces of the charging films 21, 22, 23, and 24, that is, the surface of the rotating film 210, the dimethyl silicone oil can be constantly supplied. Therefore, no maintenance is required, and it is possible to continuously prevent toner from adhering to the charging devices 21, 22, 23, and 24 and occurrence of a filming phenomenon.

Although the full-color printer shown in FIG. 1 employs a so-called cleaner-less structure in which a cleaner is not provided for the photosensitive drum of each color, the charging roll of the present invention uses a cleaning blade for the photosensitive drum. Even in the case where a cleaner such as a cleaning brush or the like is provided, the occurrence of the filming phenomenon can be effectively prevented as in the above-described embodiment.

[0053]

As described above, according to the charging device of the present invention and the image forming apparatus using the same, the speed ratio between the peripheral speed V1 of the image carrier and the peripheral speed V2 of the rotating film of the charging device. Is set to 1.01 <(V2 / V1) ≦ 1.10. Therefore, it is possible to prevent foreign matters such as toner and carrier adhering to the image carrier from transferring to the charging device as much as possible. Thus, the surface of the image carrier can be stably charged for a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a full-color laser beam printer using a charging device of the present invention.

FIG. 2 is a sectional view showing a charging device to which the present invention is applied.

[Explanation of symbols]

11, 12, 13, 14 ... photosensitive drum (image carrier),
21, 22, 23, 24: charging device, 210: rotating film, 211: shaft member, 212: elastic body

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshihiko Mihashi 3-7-1, Fuchu, Iwatsuki-shi, Saitama, Fuji Xerox Co., Ltd. Iwatsuki Office (72) Inventor Satoru Hirosaki 3-7-1, Funai, Iwatsuki-shi, Saitama No. 1, inside Fuji Xerox Co., Ltd. Iwatsuki Office (72) Inventor Masahiro Sato 3-7-1, Fuwa, Iwatsuki City, Saitama Prefecture, inside Fuji Xerox Co., Ltd. Iwatsuki Office (72) Inventor Hiromitsu Koizumi, Iwatsuki City, Saitama Prefecture 3-7-1, Fuji Xerox Co., Ltd. Iwatsuki Office F-term (reference) 2H003 AA12 BB11 CC05 DD03 3J103 AA02 AA14 EA07 FA07 GA52 GA57 GA58 HA12 HA20

Claims (3)

[Claims] An image carrier on which a toner image is to be formed and a cylindrical rotating film to which a predetermined charging bias is applied; and driving means for driving the rotating film at a predetermined peripheral speed; In the charging device for uniformly charging the surface of the image carrier, when the peripheral speed of the image carrier is V1 and the peripheral speed of the rotating film is V2, 1.01 <(V2 / V1) ≦ 1.10. A charging device that satisfies the following relationship: 2. A shaft member penetrating through the rotating film is provided, and a periphery of the shaft member is adhered to an inner peripheral surface of the rotating film to press the rotating film toward the image carrier. 2. A charging device according to claim 1, wherein an elastic body is provided, and said driving means drives said rotary film via said shaft core member and said elastic body. 3. An image carrier, a charger for uniformly charging the surface of the image carrier, and writing means for forming an electrostatic latent image on the surface of the image carrier in accordance with image information; An image forming apparatus comprising: a developing device that develops the electrostatic latent image with toner; and a transfer unit that transfers a toner image developed by the developing device from an image carrier to an image receiving member. An image forming apparatus using the charging device according to claim 1.