JP2015169865A - Charging device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging device capable of suppressing a driven failure to an image holding body of a charging member and the generation of foreign substance adhesion to the image holding body due to the press-contact of a charging member.SOLUTION: A charging device is equipped with a charging member 120 made by implanting conductive fibers 122 on an outer peripheral surface of a cylindrical film base material 121. The charging member 120 is supported by a supporting member 123 so as to contact with a surface of a photoreceptor drum 11 and driven-rotate. On the conductive fibers 123 of the charging member 120, charging voltage is applied by a charging high-pressure power source 125. The charging voltage applied on the charging member 120 is different in an image area and a non-image area of the photoreceptor drum 11. The applied voltage of the image area is set to be higher than that of the non-image area, thereby suppressing a driven failure to the photoreceptor drum 11 of the charging member 120 and foreign substance adhesion on the surface of the photoreceptor drum 11.

Description

  The present invention relates to a charging device and an image forming apparatus.

  As a technique related to the charging device, for example, those disclosed in Patent Documents 1 to 3 have already been proposed. Patent Document 1 is a charging device including a plurality of rollers made of a conductive member and an endless charging belt having a multi-layer structure suspended on the plurality of rollers and having conductivity and specific resistance. A part is brought into contact with the image forming surface and a voltage is applied to the endless charging belt.

  Patent Document 2 is provided with a charging electrode in which a flexible semiconductive film-like member is formed in a substantially cylindrical shape, and the charged surface of the charged object is charged by bringing the peripheral surface of the charging electrode into contact with the charged object. The charging electrode is configured to move around by an electrostatic force acting between the electrodes.

  Patent Document 3 includes a charging brush belt constituted by an endless conductive belt in which an inner surface is stretched as a charging member by a plurality of support members, moves endlessly, and conductive fibers are planted on the outer surface. One of the supporting members applies a charging voltage from the voltage applying means to the charging brush belt, and the charging brush belt is cleaned by the cleaning member at a position not facing the voltage application supporting member.

Japanese Patent Laid-Open No. 06-194926 Japanese Patent Laid-Open No. 10-239946 JP 2006-221091 A

  SUMMARY OF THE INVENTION An object of the present invention is to suppress the following failure of the charging member with respect to the image carrier and the occurrence of foreign matter adhesion to the image carrier due to the pressure member being pressed.

The invention described in claim 1 is a charging member formed by flocking conductive fibers on the outer peripheral surface of an endless film substrate;
A support member that supports the charging member so that the charging member rotates in contact with the surface of the image carrier;
Voltage applying means for applying a charging voltage to the conductive fibers of the charging member,
The voltage applying unit applies a different charging voltage between an image area and a non-image area of the image carrier, and the applied voltage of the image area is higher than that of the non-image area.

  The invention described in claim 2 is characterized in that the charging member is formed by electrostatically flocking the conductive fibers through a conductive adhesive on an outer peripheral surface of the film base made of an insulating material. The charging device according to claim 1.

  According to a third aspect of the present invention, the voltage applying means includes a power supply member that contacts the surface of the charging member along the longitudinal direction of the image carrier. The charging device according to (1).

  The invention described in claim 4 is characterized in that the conductive fibers are planted in a state where the tip thereof is inclined toward the upstream side along the rotation direction of the charging member. 4. The charging device according to any one of 3 above.

The invention described in claim 5 includes an image holding body for holding an electrostatic latent image;
Charging means for charging the surface of the image carrier,
An image forming apparatus using the charging device according to claim 1 as the charging unit.

  According to the first aspect of the present invention, compared to the case without this configuration, the charging member is not driven properly with respect to the image holding member, and foreign matter adheres to the image holding member due to the pressure member being pressed. Can be suppressed.

  According to the second aspect of the present invention, the image carrier can be uniformly charged by the charging member as compared with the case where this configuration is not provided.

  According to the third aspect of the present invention, the charging voltage can be applied uniformly along the longitudinal direction of the charging member as compared with the case where the present configuration is not provided.

  According to the invention described in claim 4, it is possible to suppress unevenness in the charged potential when the conductive fiber is separated from the surface of the image carrier, as compared with the case where this configuration is not provided. Can do.

  According to the fifth aspect of the present invention, compared to the case where the present configuration is not provided, the charging member is not driven properly with respect to the image holding member, and the foreign matter adheres to the image holding member due to the pressure member pressing. Therefore, the image quality can be improved.

1 is a schematic configuration diagram illustrating an image forming apparatus to which a charging device according to Embodiment 1 of the present invention is applied. It is a block diagram which shows an image formation part. It is a block diagram which shows the charging device which concerns on Embodiment 1 of this invention. It is a block diagram which shows the flocked state of a charging member. 2 is a block diagram illustrating a control circuit of the image forming apparatus. FIG. It is explanatory drawing which shows the switching timing of the applied voltage to a charging member. It is a chart which shows the result of an example of an experiment. It is a graph which shows the result of an example of an experiment. It is a graph which shows the result of an Example. It is a schematic diagram which shows the contact state of the conductive fiber of a charging member. It is a block diagram which shows the charging device which concerns on embodiment of this invention. It is a block diagram which shows the other example of an electric power feeding member.

  Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1]
1 and 2 show an outline of the entire image forming apparatus to which the charging device according to the first embodiment is applied. FIG. 1 shows an outline of the entire image forming apparatus, and FIG. 2 shows an enlarged main part (image forming apparatus, etc.) in the image forming apparatus.

<Overall Configuration of Image Forming Apparatus>
The image forming apparatus 1 according to the first embodiment is configured as a monochrome copying machine, for example. The image forming apparatus 1 includes an image reading device 3 that reads an image of a document, and an image forming unit 2 as an example of an image forming unit that forms an image on a recording medium based on image data. The image reading device 3 is disposed on the upper portion of the apparatus main body 1 a that houses the image forming unit 2.

  The image forming unit 2 transfers an image forming device 10 that forms a toner image to be developed with toner constituting the developer, and a toner image formed by the image forming device 10 to a recording sheet 5 as an example of a recording medium. The transfer device 20, the paper supply device 50 that accommodates and transports the recording paper 5 as an example of a required recording medium to be supplied to the transfer position of the transfer device 20, and the recording paper 5 transferred by the transfer device 15 A fixing device 40 for fixing the toner image is provided. The apparatus main body 1a is formed of a support structure member, an exterior cover, and the like.

  The image forming apparatus 10 is composed of one image forming apparatus that exclusively forms a black (K) toner image. The image forming apparatus 10 is disposed at a required position in the internal space of the apparatus main body 1a.

  As shown in FIG. 1, the image forming apparatus 10 includes a photosensitive drum 11 as an example of a rotating image carrier, and the following apparatuses are mainly disposed around the photosensitive drum 11. Has been placed. The main devices are a charging device 12 that charges a peripheral surface (image holding surface) on the photosensitive drum 11 on which an image can be formed to a required potential, and image information (on the charged peripheral surface of the photosensitive drum 11). The exposure device 13 as an electrostatic latent image forming means for forming an electrostatic latent image having a potential difference (for each color) by irradiating the light LB based on the signal), and the electrostatic latent image of black (K) A developing device 14 as a developing means that develops toner with a developer toner to form a toner image, and drum cleaning that removes and adheres toner and other adhering matter remaining on the image holding surface of the photosensitive drum 11 after transfer. Device 15 or the like.

  The photosensitive drum 11 is formed by forming an image holding surface having a photoconductive layer (photosensitive layer) made of a photosensitive material on the peripheral surface of a cylindrical or columnar base material to be grounded. The photosensitive drum 11 is supported so as to rotate in a direction indicated by an arrow A when power is transmitted from a rotation driving device (not shown).

  The charging device 12 is configured by a contact-type charging member that is disposed in contact with the photosensitive drum 11. A charging voltage is supplied to the charging device 12. As the charging voltage, when the developing device 14 performs reversal development, a voltage or current having the same polarity as the charging polarity of the toner supplied from the developing device 14 is supplied. The configuration of the charging device 12 will be described later.

  The exposure device 13 forms an electrostatic latent image by irradiating the charged surface of the photosensitive drum 11 with light LB configured according to image information input to the image forming device 1. To do. When a latent image is formed, the exposure device 13 is input to the image forming device 1 by any means, and transmits information (signal) of an image that has been subjected to image processing by an image processing device described later.

  The developing device 14 agitates the developer, a developing roll 141 that holds the developer and transports it to a developing region facing the photosensitive drum 11 inside a housing in which an opening and a developer storage chamber are formed. Two stirring agitators 142 and 143 such as a screw auger that convey the developing roll 141 while passing therethrough, and a layer thickness regulating member 144 that regulates the amount (layer thickness) of the developer held on the developing roll 141 are arranged. It is configured as follows. A developing voltage is supplied to the developing device 14 from a power supply device (not shown) between the developing roll 141 and the photosensitive drum 11. Further, the developing roll 141 and the agitating / conveying members 142 and 143 are rotated in a required direction by receiving power from a rotation driving device (not shown). Further, as the developer, a two-component developer containing a nonmagnetic toner and a magnetic carrier is used. In FIG. 1, reference numeral 145 denotes a developer container that contains a developer containing at least toner to be supplied to the developing device 14, and 146 denotes that the developer contained in the developer container 145 is replenished to the developing device 14. Each of the developer replenishing devices is shown.

  The transfer device 20 is a belt-type transfer device that rotates in contact with the peripheral surface of the photosensitive drum 11 and is supplied with a transfer voltage. This belt-type transfer device 20 is disposed inside a transfer belt 23 that is stretched between a drive roll 21 and a driven roll 22, and is disposed inside the transfer belt 23. And a transfer roll 24 that rotates in contact with the peripheral surface. A transfer voltage is applied to the transfer roll 24. As the transfer voltage, a DC voltage having a polarity opposite to the charging polarity of the toner is supplied from a power supply device (not shown).

  The drum cleaning device 15 is disposed so as to be in contact with the peripheral surface of the photosensitive drum 11 after the primary transfer with the container-shaped main body 150 that is partially opened, and removes adhered matters such as residual toner, and is cleaned. A cleaning plate 151 to be rotated, a rotating brush roll 152 disposed so as to rotate in contact with the peripheral surface of the photosensitive drum 11 on the upstream side in the rotation direction of the photosensitive drum 11 with respect to the cleaning plate 151, recovered residual toner, and the like The transporting auger 153 and the like for discharging the attached matter to the outside.

  The fixing device 40 is in contact with a rotating rotator 41 in the form of a roll or belt heated by heating means so that the surface temperature is maintained at a predetermined temperature, and the rotating rotator 41 for heating at a required pressure. And a pressurizing rotating body 42 in the form of a roll that rotates. In the fixing device 40, a contact portion where the heating rotator 41 and the pressing rotator 42 come into contact becomes a fixing processing unit that performs a required fixing process (heating and pressing).

  The paper feeding device 50 is arranged so as to exist at a position below the device housing 1a. The paper feeding device 50 includes a plurality (or a single number) of paper storage bodies 51a, 51b, 51c, 51d for storing recording paper 5 having a desired size and type, and paper storage bodies 51a, 51b, 51c. , 51d, and feeding devices 52, 53 that send out the recording paper 5 one by one. The paper containers 51a, 51b, 51c, 51d are attached so that they can be pulled out, for example, to the front side (side surface on which the user faces during operation) of the housing 1a.

  Between the sheet feeding device 50 and the transfer device 15, a plurality of sheet conveyance roll pairs 54, 55, and 56 that convey the recording sheet 5 delivered from the sheet feeding device 50 to the transfer position and a conveyance guide material are provided. A paper transport path 57 is provided. The pair of paper transport rollers 56 disposed at the position immediately before the transfer position in the paper feed transport path 57 is configured, for example, as a roll (registration roll) that adjusts the transport timing of the recording paper 5. Further, on the downstream side of the fixing device 40 along the paper conveyance direction, a switching member (not shown) that switches the conveyance direction of the recording paper 5 and the recording paper 5 whose conveyance direction is switched to one (right side in the figure) by the switching member. A pair of discharge rolls 72 for discharging the recording sheet 5 to the discharge container 71, a pair of reversing rolls 73 for reversing the front and back of the recording paper 5 whose transport direction is switched to the other (downward in the figure) by the switching member, and the front and back are reversed A plurality of paper conveyance roll pairs 74 for conveying the recording paper 5 to the paper conveyance path 57 and a double-sided paper conveyance path 75 constituted by a conveyance guide material are arranged.

<Basic operation of image forming apparatus>
Hereinafter, a basic image forming operation by the image forming apparatus 1 will be described.

  An image forming operation when a monochrome image composed of a black (K) toner image is formed using the image forming apparatus 10 will be described.

  When the image forming apparatus 1 receives command information for requesting an image forming operation (printing), the image forming apparatus 10, the transfer apparatus 20, the fixing apparatus 40, and the like are started.

  In the image forming apparatus 10, first, the photosensitive drum 11 rotates in the direction indicated by the arrow A, and the charging device 12 sets the surface of the photosensitive drum 11 to a required polarity (negative polarity in the first embodiment) and a potential. Charge. Subsequently, the exposure device 13 irradiates the charged surface of the photosensitive drum 11 with the light LB emitted based on the image signal input to the image forming device 1, and the surface is irradiated with a required potential difference. An electrostatic latent image is formed.

  Subsequently, the developing device 14 supplies toner charged to a required polarity (minus polarity) to the electrostatic latent image formed on the photosensitive drum 11 and electrostatically attaches it to perform development. By this development, the electrostatic latent image formed on the photosensitive drum 11 is visualized as a toner image developed with toner.

  Subsequently, when the toner image formed on the photosensitive drum 11 of the image forming device 10 is conveyed to the transfer position, the transfer device 20 applies the toner image to the recording paper 5 conveyed by the transfer roll 24. Transfer.

  In the image forming apparatus 10 that has completed the transfer, the drum cleaning device 15 cleans the surface of the photosensitive drum 11 by removing the deposits such as toner remaining on the surface of the photosensitive drum 11 so as to scrape off. Thereby, the image forming apparatus 10 is brought into a state in which the next image forming operation can be performed.

  On the other hand, in the paper feeding device 50, the required recording paper 5 is sent out to the paper feeding conveyance path 57 in accordance with the image forming operation. In the paper feed conveyance path 57, a pair of paper conveyance rolls 56 as registration rolls feeds the recording paper 5 to the transfer position in accordance with the transfer timing.

  Subsequently, the recording paper 5 onto which the toner image has been transferred is conveyed to the fixing device 40 by the transfer belt 150. In the fixing device 40, a necessary fixing process (heating and pressing) is performed to fix the unfixed toner image on the paper 5. Finally, the recording paper 5 after the fixing is completed is, for example, in a discharge accommodating portion 71 installed outside the housing 1a by a paper discharge roll pair 72 via a switching member during a normal image forming operation. Discharged.

  In the image forming operation in the duplex mode, the recording sheet 5 after the fixing by the fixing device 40 is reversed by the pair of reversing rolls 73 via the switching member, and then the duplex sheet feeding conveyance path. The paper is conveyed to a transfer position via a paper feed conveyance path 57 by a pair of paper conveyance rollers 74 provided at 75. Then, the recording paper 5 on which the toner image is transferred to the back surface at the transfer position is subjected to a fixing process by the fixing device 40 and is discharged to the discharge accommodating portion 71 by the paper discharge roll pair 72 via the switching member.

  Through the above operation, the recording paper 5 on which a monochrome image is formed on one side or both sides is output.

<Configuration of charging device>
FIG. 3 is a block diagram showing a charging device according to this embodiment.

  As shown in FIG. 3, the charging device 12 includes a charging member 120 in which conductive fibers 122 are implanted on the outer peripheral surface of an endless film substrate 121, and a support member 123 that rotatably supports the charging member 120. And a power supply member 124 for applying a charging voltage to the conductive fibers 122 of the charging member 120. For example, the film base 121 is formed so that a free shape to which an external force does not act is a cylindrical shape, but if it exhibits an endless shape, it may be formed in another shape such as an oval shape or an elliptical shape. Also good. The film-like substrate 121 is not required to have conductivity, and a film-like member made of an insulating material can be used as it is. Examples of the material for the film-like substrate 121 include polyethylene terephthalate, polyamide, polyimide, polyamideimide, polyethylene, polycarbonate, polyurethane, polyvinylidene fluoride, polyethylene naphthalate, polyether ketone, polyether sulfone, polyphenylene sulfide, PFA, Examples thereof include synthetic resins such as fluorine resins such as PVdF, ETFE, and CTFE, and synthetic rubbers such as silicone rubber, ethylene propylene diene rubber, ethylene propylene rubber, butyl rubber, acrylic rubber, urethane rubber, and nitrile rubber. In this embodiment, a film made of polyethylene terephthalate is used as the film-like substrate.

  Further, the thickness of the film base 121 is not particularly limited, and it is desirable that the film base 121 has a flexibility that can rotate following the rotation of the photosensitive drum 11 as an image holding member. Even if the film base 121 is formed in a cylindrical shape and does not have flexibility, the film base 121 cannot be deformed into a bent shape when contacting the surface of the photosensitive drum 11, and the photosensitive drum 11 Undesirable contact with the surface may be insufficient. The thickness of the film-like substrate 121 is set to about 10 to 500 μm, for example. In this embodiment, a film substrate 121 having a thickness of 100 μm formed in a cylindrical shape having an outer diameter of 10 to 12 mm is used.

Conductive fibers 122 are densely planted on the outer peripheral surface of the film substrate 121. As the conductive fibers 122, for example, synthetic resin fibers whose volume resistivity is adjusted by spinning a synthetic resin such as nylon, rayon, or polyester in which a conductive material such as carbon black is dispersed are used. . In this embodiment, nylon fibers in which carbon black is dispersed are used. The volume resistivity of the conductive fiber 122 is set to, for example, 10 ³ to 10 ¹⁰ Ω · cm. When the volume resistivity is 10 ² or less, spark discharge is likely to occur, and when the volume resistivity is 10 ¹¹ or more, dot-like charging failure is likely to occur. In this embodiment, the volume resistivity of the conductive fiber is set to about 10 ⁶ to 10 ⁷ Ω · cm.

Moreover, the length of the conductive fiber 122 is set to about 0.5 to 2.0 mm, for example. The thickness of the conductive fiber 122 is set to about 0.5 to 10d, for example. In this embodiment, conductive fibers 122 having a thickness of 2d are used. Moreover, although the flocking density of the conductive fiber 122 is set to 200,000 / inch ² , for example, it is not limited to this.

  As shown in FIG. 4, the conductive fiber 122 is substantially uniform by electrostatic flocking in a state where a conductive adhesive 125 such as acrylic, urethane, or epoxy is applied to the outer peripheral surface of the film base 121. It is flocked to a density. The conductive fibers 122 may be planted substantially perpendicularly to the outer peripheral surface of the film base 121, but the tip 122a of the conductive fibers 122 is inclined toward the upstream side along the rotation direction B of the charging member. It is desirable to plant. The reason is that the conductive fibers 122 are implanted in a state where the conductive fibers 122 are substantially perpendicular to the outer peripheral surface of the film base 121 or the tip 122a of the conductive fibers 122 is inclined toward the downstream side in the rotation direction B of the charging member 120. In this case, after the conductive fibers 122 are brought into contact with the surface of the photoconductive drum 11 and then separated from the surface of the photoconductive drum 11, the leading end 122a of the conductive fibers 122 is the surface of the photoconductive drum 11. This is because variations in charging potential are likely to occur.

  The conductive fiber 122 may be directly planted with the tip 122a inclined toward the upstream side along the rotation direction B of the charging member, but the conductive fiber 122 may be implanted on the outer peripheral surface of the film base 121. After the hair is implanted substantially perpendicularly, a mechanical force and / or heat is applied so that the tip 122a is inclined toward the upstream side along the rotation direction B of the charging member. good.

  As shown in FIG. 3, the support member 123 is configured by a columnar or cylindrical member that is inserted into the charging member 120 so as to penetrate along the longitudinal direction. As the supporting member 123, for example, a member made of a metal such as stainless steel or aluminum, or a synthetic resin is used. In this embodiment, a cylindrical member having a diameter of 4 mm made of a metal such as stainless steel is used as the support member 123. The support member 123 is not required to be a conductive material.

  On the surface of the charging member 120, a power supply member 124 constituting a part of voltage applying means for applying a charging voltage to the charging member 120 is disposed so as to be in contact with substantially the entire length of the charging member 120. The power supply member 124 may have any shape as long as it can apply a charging voltage to the charging member 120. For example, the power supply member 124 has various shapes such as a rod shape, a plate shape, a loop shape, a brush shape, and a foam shape. Is used. The power supply member 124 may be made of a material having a volume resistivity lower than that of the conductive fiber 133 of the charging member 120. For example, the power supply member 124 may be a synthetic resin, a synthetic rubber, a synthetic foam, or a synthetic foam to which metal or conductivity is imparted. It can be formed from a body or the like.

  A required charging voltage having the same polarity (negative polarity) as the charging polarity of the toner is applied to the power supply member 124 by a charging high-voltage power source 125 as an example of a voltage applying unit. Note that the power supply member 124 may be configured to apply a DC voltage on which an AC voltage is superimposed.

  The charging device 12 configured as described above applies a charging voltage to the conductive fiber 122 of the charging member 120 via the power supply member 124 by the charging high-voltage power source 125, thereby electrostatically forming the surface of the film substrate 121. The implanted conductive fibers 122 are electrostatically attracted to the surface of the photosensitive drum 11 by electrostatic force, and are rotated following the movement of the surface of the photosensitive drum 11. At that time, the charging member 120 causes the surface of the photosensitive drum 11 to be exposed to a minute discharge generated in a minute gap formed on the upstream side and the downstream side of the contact region where the charging member 120 and the surface of the photosensitive drum 11 are in contact with each other. Charge to the required potential.

  By the way, the charging device 12 is driven along the arrow direction A along with the rotation of the photosensitive drum 11 by the attractive force that the conductive fibers 122 of the charging member 120 electrostatically attracts to the surface of the photosensitive drum 11. Rotate. For this reason, if the attracting force acting between the conductive fiber 122 of the charging member 120 and the surface of the photosensitive drum 11 is insufficient, the charging member 120 may be driven poorly and charged to the surface potential of the photosensitive drum 11. Unevenness or the like occurs, causing a reduction in image quality.

  More specifically, if the adsorbing force acting between the conductive fiber 122 of the charging member 120 and the surface of the photosensitive drum 11 is insufficient, the conductive fiber 122 is strained (see FIG. 10B). The conductive fibers 122 are not sufficiently in contact with the surface of the photosensitive drum 11 due to the repulsive force due to the (rigid) force, and a gap is formed between the film base 121 and the photosensitive drum 11, and the charging member 120 and the photosensitive drum 11. Adhesiveness with the surface is lowered, and a follow-up failure of the charging member 120 is likely to occur.

  On the other hand, when the charging voltage applied to the charging member 120 is set relatively high in order to increase the adsorption force acting between the conductive fiber 122 of the charging member 120 and the surface of the photosensitive drum 11, the charging member The electrostatic adsorption force acting between the conductive fiber 122 of 120 and the surface of the photosensitive drum 11 becomes excessive, and the toner that has passed through the drum cleaning device 15 and the external additive of toner such as silica and titanium are charged by the charging member 120. As a result, the film is pressed against the surface of the photosensitive drum 11, and filming may occur in which an external additive such as toner or silica adheres to the surface of the photosensitive drum 11 in the form of a film. In particular, filming due to such external additives as toner and silica occurs remarkably in the image forming apparatus 1 adopting a cleaner-less system that does not include the drum cleaning device 15.

  Therefore, in this embodiment, the transfer voltage applied to the energizing member 124 by the charging high-voltage power supply 125 is made different between the image area and the non-image area of the photosensitive drum 11, and the applied voltage of the image area is the non-image area. Is set to be higher than the applied voltage.

  FIG. 5 is a block diagram showing a control device of the image forming apparatus according to this embodiment.

  The control device 100 includes a CPU 101 that controls the operation of the image forming apparatus 1, a hard disk drive (HDD) 102 that stores programs executed by the CPU 101, image data, and the like, an interface unit 103, and the like. The control device 100 also receives image data of a document read by the image reading device 3, image data sent from an external device such as a personal computer (not shown), or image data transferred via a telephone line. Etc. are entered.

  The control device 100 is a non-image area such as an image area or an inter-image area located between pages among the image data recorded on the recording paper 5 based on a page sync signal or the like at the time of image formation. Is determined.

  Then, the control device 100 controls the charging high-voltage power supply 125 so that the voltage applied to the charging device 12 is set to a first voltage value corresponding to the image region and a second voltage value corresponding to the non-image region. Switch to.

<Operation of Characteristic Part of Image Forming Apparatus>
As described above, when the image forming apparatus 1 receives command information for requesting an image forming operation (printing), the image forming apparatus 10, the transfer apparatus 15, the fixing apparatus 40, and the like are started.

  In the image forming apparatus 10, first, the photosensitive drum 11 rotates in the direction indicated by the arrow A, and the charging device 12 sets the surface of the photosensitive drum 11 to a required polarity (negative polarity in the first embodiment) and a potential. Charges up.

  At this time, the charging voltage applied to the charging device 12 is controlled by the control device 100 via the charging high-voltage power source. As shown in FIG. 6, the control device 100 continuously forms images on the surface of the photosensitive drum 11 on a non-image area before image exposure corresponding to image data or on a plurality of recording sheets 5. If it is determined that it is a non-image region such as an inter-image corresponding to the recording paper 5 in the case, or a non-image region after an image is formed on the recording paper 5, it is applied to the charging device via a high-voltage power supply for charging. The voltage is switched to a second voltage value (for example, −750 V) that is a relatively low value.

  If the control device 100 determines that the surface of the photosensitive drum 11 is an image area that is subjected to image exposure according to image data, the voltage applied to the charging device via the charging high-voltage power supply is relatively high. The value is switched to the first voltage value (for example, −1050 V).

  As described above, in the above embodiment, in the case of an image region where an image is formed on the recording paper 5, the charging voltage applied to the charging device is switched to a relatively high first voltage value (for example, −1050 V). As a result, the electrostatic adsorption force acting between the charging member 120 of the charging device 12 and the surface of the photosensitive drum 11 can be increased, and the follow-up rate of the charging member 120 can be improved.

  More specifically, when the electrostatic adsorption force sufficiently acts between the conductive fiber 122 of the charging member 120 and the surface of the photosensitive drum 11, the conductive fiber 122 is sufficiently laid as shown in FIG. As a result, the adhesion between the conductive fiber 122 and the surface of the photosensitive drum 11 is increased, and the charging member 120 is driven and rotated with respect to the surface of the photosensitive drum 11.

  In the above embodiment, in the non-image region, the charging member 120 and the photosensitive member are switched by switching the charging voltage applied to the charging device to a relatively low second voltage value (for example, −750 V). It is possible to reduce the electrostatic attraction acting between the surface of the drum 11 and suppress the occurrence of filming.

Experimental Example Next, in order to confirm the effect of the image forming apparatus according to the above-described embodiment, the inventors made a prototype of a bench model including the image forming apparatus 10 as shown in FIG. An experiment was conducted to confirm the follow-up rate of the charging member 120 with respect to the surface of the photosensitive drum 11 and the state of filming generated on the surface of the photosensitive drum 11 when the charging voltage applied to is changed.

  The follow-up ratio of the charging member 120 to the surface of the photosensitive drum 11 is determined by attaching a reflecting member that reflects light to the surface of the charging member 120 and receiving the reflected light when the reflecting member is irradiated with light by the light receiving element. The rotation state of the charging member 120 is detected by converting it into an electrical signal.

  Further, the filming occurrence state was evaluated by observing the surface of the photosensitive drum 11 with an optical microscope and classifying the occurrence degree into five levels as follows. If it is grade 2 or less, it is considered that there is no problem in practical use. In addition, when it was judged as the intermediate level of each grade, it evaluated as grade 0.5.

G0: Not generated G1: Filming hardly occurs and no white spot occurs in the image quality G2: Filming slightly occurs, but the occurrence of white spot on the print is very small G3: Filming occurs and print G4: Filming is considerably generated, and white spots are generated in substantially half of the print. G5: Filming is wisely generated on almost the entire surface of the photosensitive drum. White spots occur on almost the entire surface of the print.

    7 and 8 are charts and graphs showing the results of the experimental example.

    As is apparent from FIGS. 7 and 8, when the charging voltage applied to the charging device 12 is increased from 500V, the follow-up rate gradually increases from 62%, and when the charging voltage reaches 900V. It was found that the follow-up rate exceeded 97%, which is no problem in image quality. However, if a charging voltage of 900 V or more is constantly applied to the charging device 12, the filming occurrence state becomes 2.5 or more and exceeds the allowable level of Grade 2, which causes a problem in practical use from the filming occurrence state. Is determined to occur at a level where

<Example>
Further, based on the results of the above experimental example, the present inventors set the voltage applied to the charging device 12 to −1050 V, which is the first voltage value in the image region, and to the first voltage value in the non-image region. It was configured to switch to -750 V, which is a voltage value of 2.

  FIG. 9 is a chart showing the results of the above example.

  As is apparent from FIG. 9, the charging voltage applied to the charging device 12 is switched to -1050 V, which is the first voltage value in the image area, and to -750 V, which is the second voltage value in the non-image area. The driven rate of the charging member 120 in the image area can be maintained at a significantly high value of 99%, and no print defect due to a driven failure has occurred.

  Further, with respect to filming on the surface of the photosensitive drum 11, filming slightly occurs, but the occurrence of white spots on the print is evaluated as grade 2 which is extremely small, and can be suppressed to a level where there is no problem in actual use. I understood.

  Thus, the charging member 120 is switched by switching the charging voltage applied to the charging device 12 to -1050 V, which is the first voltage value in the image area, and to -750 V, which is the second voltage value in the non-image area. As a matter of course, the non-image area can be switched to the second voltage value of −750 V, compared to the case where the first voltage value of −1050 V is always applied, It is possible to suppress the level of occurrence of filming to a grade 2 level that causes no problem in actual use.

  By suppressing the charging voltage applied to the charging device 12 to a voltage lower than the image area in the non-image area, it is possible to reduce the friction generated between the charging member 120 and the surface of the photosensitive drum 11. It is considered that the occurrence of filming could be suppressed.

<Comparative Example 1>
In Comparative Example 1, in the image forming apparatus 1, the voltage applied to the charging device 12 was always set to −1050 V, which is the first voltage value corresponding to the image area of the example.

  As is apparent from FIG. 9, in this comparative example 1, the driven rate of the charging member 120 can be maintained at a significantly high value of 99% as in the image area of the first example, and the print defect due to the driven failure has not been achieved. It was outbreak.

  Further, regarding filming on the surface of the photosensitive drum 11, filming occurs, and grade 3 in which white spots are partially streaked on the print, and filming occurs considerably, almost half of the print. It was judged as grade 3.5, which is the middle of grade 4 where white spots occur, and it was found that this was a level where image quality problems occurred.

<Comparative Example 2>
In Comparative Example 2, in the image forming apparatus 1, the voltage applied to the charging device 12 was always set to -750 V, which is the second voltage value corresponding to the non-image area of the example.

  As is apparent from FIG. 9, in Comparative Example 2, the driven rate of the charging member 120 was significantly low at 78%, and a print defect due to a driven failure occurred.

  On the other hand, with respect to filming on the surface of the photosensitive drum 11, grade 0, which is intermediate between grade 0 in which filming has not occurred and grade 1 in which filming has hardly occurred and white spots have not occurred in image quality. .5, and it was found that the image quality was satisfactory.

Embodiment 2
FIG. 11 is a block diagram showing Embodiment 2 of the charging device according to the present invention.

  In the second embodiment, as shown in FIG. 11, the charging member 12 is not supported by a support member inserted therein, but the outer periphery, ie, the upper surface and both side surfaces of the charging member 12 are covered and the lower end surface is opened. A support member 123 made of a frame having a rectangular cross section is used.

  Further, as the power supply member 124, a flat plate-like or foam-like member provided by means such as adhesion on the ceiling surface of a support member made of a frame having a rectangular cross section is used.

  As described above, by using a support member made of a frame having a rectangular cross section with an open lower end surface as the support member 123, the charging device 12 can be downsized.

  In the above-described embodiment, the case where the rod-shaped power supply member 124 is used has been described. However, as the power supply member 124, a flat plate-like or foam-like member may be used as shown in FIG.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 12 ... Charging apparatus 120 ... Charging member 121 ... Film base material 122 ... Conductive fiber

Claims (5)

A charging member formed by implanting conductive fibers on the outer peripheral surface of an endless film base;
A support member that supports the charging member so that the charging member rotates in contact with the surface of the image carrier;
Voltage applying means for applying a charging voltage to the conductive fibers of the charging member,
The charging device, wherein the voltage applying unit applies different charging voltages to an image area and a non-image area of the image carrier, and an applied voltage of the image area is higher than that of the non-image area.   The charging device according to claim 1, wherein the charging member is formed by electrostatically flocking the conductive fibers on a peripheral surface of the film base made of an insulating material via a conductive adhesive.   3. The charging device according to claim 1, wherein the voltage application unit includes a power supply member that contacts a surface of the charging member along a longitudinal direction of the image holding member.   The charging device according to any one of claims 1 to 3, wherein the conductive fibers are planted in a state in which a tip thereof is inclined toward an upstream side along a rotation direction of the charging member. An image carrier for holding an electrostatic latent image;
Charging means for charging the surface of the image carrier,
An image forming apparatus using the charging device according to claim 1 as the charging unit.

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