JP2014119503A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that includes a toner carrier and a toner supply member that rotate so that respective surfaces move in the same direction at a nip part and can suppress fogging, a process cartridge, and an image forming apparatus.SOLUTION: A developing device includes a container that accommodates a toner, a toner carrier that carries a toner to develop an electrostatic latent image, and a toner supply member that is arranged to form a nip part with the toner carrier to supply a toner to the toner carrier. The toner carrier and the toner supply member rotate so that respective surfaces move in the same direction at the nip part; and a resistance value of the toner carrier measured when a voltage applied to the toner carrier is changed to 10 V to 50 V is set to fall within a range of 1×10^5 Ω to 5×10^8 Ω.

Description

  The present invention relates to a developing device, a process cartridge, and an image forming apparatus used in an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus using an electrophotographic method or an electrostatic recording method.

  As a developing device used in an image forming apparatus using an electrophotographic system or the like, there is a developing device that develops (visualizes) an electrostatic latent image using a non-magnetic one-component developer (toner). The developing device generally includes a developing roller as a toner carrying member that carries and conveys toner, and a supply roller as a toner supply member that is disposed around the developing roller and supplies toner to the developing roller.

  In such a developing device, toner is supplied to the developing roller while being frictionally charged by mechanical friction between the supply roller and the developing roller. The toner supplied to the developing roller is regulated to have a constant layer thickness on the developing roller by a regulating blade as a toner regulating member. Thereafter, the toner on the developing roller is conveyed to a developing area that is in the vicinity of the photosensitive drum as an image carrier, and is supplied to the photosensitive drum in accordance with the electrostatic latent image. Is developed (visualized) as a toner image. Toner (development residual toner) that is not used for development in the development area and remains on the development roller is scraped off from the development roller by mechanical friction at a contact portion (nip portion) between the development roller and the supply roller. . At the same time, toner is supplied from the supply roller to the developing roller. On the other hand, the toner scraped off from the developing roller is mixed with toner inside and around the supply roller.

  The developing roller and the supply roller are configured so that their surfaces move with a relative peripheral speed ratio so that both the supply capability of the toner to the development roller and the scraping performance of the residual toner can be achieved. Sometimes.

For example, in Patent Document 1, the developing roller and the supply roller rotate so that their surfaces move in the same direction at the nip portion. Then, the ratio of the circumferential speed _{V SP} peripheral speed _{V DR} and the supply roller of the developing roller is _{| V SP / V DR | ≦} 0.5 or _{1.5 ≦ | V SP / V DR} | ≦ 4 in a developing device Has been proposed. Further, Patent Document 1 proposes that the amount of biting X of the supply roller into the developing roller is 0 <X <1.8 <d (d is the thickness of the elastic layer of the supply roller).

JP 2006-208619 A

  However, in the developing device in which the toner carrier and the toner supply member are rotated so that the surfaces of the toner carrier and the toner supply member move in the same direction at the nip portion, the so-called “fogging” in which toner adheres to the non-image portion. In some cases, density unevenness of the image may occur.

  In the configuration in which the toner carrier and the toner supply member rotate so that their surfaces move in the same direction at the nip portion, in particular, the force that scrapes off the development residual toner on the toner carrier by the toner supply member is weak, The same toner continues to be held without being scraped off from the toner carrier. If the same toner is continuously held on the toner carrying member, a phenomenon in which electric charges escape from the toner to the toner carrying member and a phenomenon in which electric charges having a polarity opposite to the normal charging polarity are injected into the toner are repeated. A large amount of toner having a charge amount of zero or a toner having a charge of opposite polarity is generated, and fogging is considered to be remarkable.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a developing device capable of suppressing fog and density unevenness in a developing device in which a toner carrier and a toner supply member rotate so that their surfaces move in the same direction at a nip portion. , A process cartridge, and an image forming apparatus.

  In order to achieve the above object, a first developing device according to the present invention includes a container that contains toner, a toner carrier that carries the toner and develops an electrostatic latent image, and the toner carrier and a nip portion. And a toner supply member that supplies the toner to the toner carrier, wherein the toner carrier and the toner supply member have surfaces of each other at the nip portion. The resistance value of the toner carrier measured when rotating to move in the same direction and changing the voltage applied to the toner carrier from 10V to 50V is in the range of 1 × 10 ^ 5Ω to 5 × 10 ^ 8Ω. A developing device characterized in that the developing device fits inside.

  According to the present invention, in the developing device in which the toner carrier and the toner supply member rotate so that their surfaces move in the same direction at the nip portion, the developing device capable of suppressing fogging and density unevenness, A process cartridge and an image forming apparatus can be provided.

1 is a schematic longitudinal sectional view of an image forming apparatus according to a first embodiment. 1 is a schematic longitudinal sectional view of a developing device according to a first embodiment. It is a schematic diagram of a resistance measurement system of the developing roller. 3 is a resistance value measurement result of a developing roller used in Example 1. 10 is a measurement result of resistance value of a developing roller used in Example 2.

  Hereinafter, a developing device and an image forming apparatus according to the present invention will be described in more detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

(First embodiment)
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic longitudinal sectional view showing an overall schematic configuration of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 includes a drum-shaped electrophotographic photosensitive member (photosensitive member) as an image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure. Around the photosensitive drum 1, the following units are arranged in order along the rotation direction of the photosensitive drum 1. First, the charging roller 2 is a roller-shaped charging member as a charging unit that uniformly charges the surface of the photosensitive drum 1. Next, there is an exposure apparatus 3 as an exposure unit that forms an electrostatic latent image by irradiating (exposing) the photosensitive drum 1 with a laser beam or the like modulated based on image information. Next, there is a developing device 4 as a developing unit that develops an electrostatic latent image (electrostatic image) formed on the photosensitive drum 1 to form a toner image. Next, there is a transfer device 5 for transferring the toner image formed on the photosensitive drum 1 onto a transfer material P such as paper or a plastic sheet. Next, a cleaning device 6 is provided as a cleaning unit that removes toner remaining on the photosensitive drum 1 after transfer.

  The transfer device 5 includes an endless belt-shaped intermediate transfer belt 51 as an intermediate transfer member. The intermediate transfer belt 51 is stretched by a plurality of stretching rollers, and is driven to rotate in the direction of arrow R2 in the drawing. On the inner peripheral surface side of the intermediate transfer belt 51, a primary transfer roller 52, which is a roller-shaped transfer member serving as a primary transfer unit, is disposed at a position facing the photosensitive drum 1. The primary transfer roller 52 is pressed against the photosensitive drum 1 via the intermediate transfer belt 51 to form a primary transfer portion (primary transfer nip) where the intermediate transfer belt 51 and the photosensitive drum 1 are in contact with each other. Further, on the outer peripheral surface side of the intermediate transfer belt 51, a secondary transfer roller 8 that is a roller-shaped transfer member as a secondary transfer unit is disposed at a position facing one of the stretching rollers of the intermediate transfer belt 51. Yes. The secondary transfer roller 8 is pressed against the stretching roller via the intermediate transfer belt 51 to form a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 51 and the secondary transfer roller 8 are in contact with each other. doing.

  The image forming apparatus 100 also includes a transfer material supply device (not shown) that supplies the transfer material P from a paper feed tray, a registration roller pair 7 that conveys the transfer material P in synchronization with the rotation of the photosensitive drum 1, and a transfer material. A fixing device (not shown) for fixing the toner image on P is provided.

  At the time of image formation, the surface of the photosensitive drum 1 that rotates in the direction of the arrow R1 in the drawing is uniformly charged by the charging roller 2 to a predetermined charging potential Vc that is positive or negative (in this embodiment, negative). Thereafter, a laser beam modulated based on the image information is scanned and irradiated in the direction of the rotation axis of the photosensitive drum 1. As a result, an electrostatic latent image is formed on the photosensitive drum 1.

  The electrostatic latent image formed on the photosensitive drum 1 is developed with a normal charging polarity (electrostatic latent image is developed by the developing device 4 in a developing region where the photosensitive drum 1 and a developing roller 42 described later of the developing device 4 face each other. In this embodiment, since the negative electrostatic latent image is reversely developed, the charged toner is attached to the toner so that the toner image is developed. In the present embodiment, toner charged to the same polarity as the charged polarity of the photosensitive drum 1 is attached to an exposed portion (image portion) in which the absolute value of the potential is reduced by being exposed after being uniformly charged. Thus, the electrostatic latent image is developed.

  Thereafter, the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 51 (primary transfer) by supplying a charge having a polarity opposite to the charged polarity of the toner to the intermediate transfer belt 51 by the primary transfer roller 52. Is done.

  On the other hand, the transfer material P supplied from a transfer material supply device (not shown) is conveyed by a pair of registration rollers 7 to the secondary transfer portion N2 where the intermediate transfer belt 51 and the secondary transfer roller 8 face each other at a predetermined timing. . The toner image on the intermediate transfer belt 51 is transferred (secondary transfer) to the transfer material P by applying a charge having a polarity opposite to the toner charge polarity of the toner image to the secondary transfer roller 8.

  The transfer material P onto which the toner image has been transferred is separated from the intermediate transfer belt 51 and sent to a fixing device (not shown). The transfer material P is discharged to the outside of the main body of the image forming apparatus 100 after the toner image is fixed by the fixing device.

  Further, the toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 after the toner image transfer process to the intermediate transfer belt 51 is cleaned by the cleaning device 6. The cleaning device 6 removes the transfer residual toner from the rotating photosensitive drum 1 by a cleaning blade 61 as a cleaning member, and collects the toner in a recovery toner container 62.

2. Next, the overall configuration of the developing device 4 in the present embodiment will be described. In the present embodiment, the developing device 4 is in the form of a cartridge that can be attached to and detached from the image forming apparatus main body (apparatus main body) of the image forming apparatus 100. The cartridge may be a developing cartridge in which the developing device 4 is detachably attached to the apparatus main body alone, or may be a process cartridge in which the developing apparatus 4 is detachable from the apparatus main body together with other process means. . In general, a process cartridge is formed by integrally forming a photosensitive member and at least one of a charging unit, a developing unit, and a cleaning unit serving as a processing unit that acts on the photosensitive unit with a frame body, so that the image forming apparatus includes: It is detachable from the apparatus main body. In the present invention, the process cartridge has at least a developing device. These cartridges can be attached to and detached from the apparatus main body via mounting means such as a positioning section and a mounting guide section provided in the apparatus main body. Further, as is well known to those skilled in the art, these cartridges, when mounted at predetermined positions on the apparatus main body, transmit driving force and voltage via couplings and contacts provided on the cartridge and the apparatus main body. Can be applied. In the present embodiment, it is assumed that the developing device 4 is a developing cartridge that can be detachably attached to the apparatus main body.

  FIG. 2 is a schematic longitudinal sectional view showing a schematic configuration of the developing device 4 in the present embodiment. As shown in FIG. 2, the developing device 4 includes a container 47 for storing toner, a developing roller 42 as a toner carrier, a supply roller 43 as a toner supply member, a restriction blade 44 as a toner restriction member, And a blowout prevention sheet 46 as a toner leakage prevention member. The container 47 has a developing chamber 41 and a toner storage chamber 40.

  In the developing chamber 41, a developing roller 42 is provided to face the photosensitive drum 1 with a part of the peripheral surface exposed from the opening of the container 47. The developing chamber 41 is provided with a supply roller 43 and a regulating blade 44 so as to come into contact with the developing roller 42 around the developing roller 42. Further, at the edge of the opening of the developing chamber 41 on the side opposite to the side where the regulating blade 44 is provided, toner is prevented from leaking from between the developing roller 42 and the frame of the developing device. A blowout prevention sheet 46 is provided as a toner leakage prevention member.

  The toner storage chamber 40 stores a nonmagnetic one-component developer (toner) as a developer. Further, an agitator 45 as a toner transport member is provided in the toner storage chamber 40.

3. Next, the operation of the developing device 4 in this embodiment will be described. In the developing device 4, the toner stored in the toner storage chamber 40 is pumped by the agitator 45 to the developing chamber 41 where the developing roller 42 is disposed. The pumped toner is stored on the upper side in the gravity direction of the nip portion (contact portion) N3 between the developing roller 42 and the supply roller 43, and the nip portion between the developing roller 42 and the supply roller 43 as the supply roller 43 rotates. N3 is mechanically rubbed. The toner is frictionally charged by this rubbing and is supplied so as to be carried on the developing roller 42.

  The toner supplied to the developing roller 42 is thinned to an appropriate layer thickness by a regulating blade 44 that is in contact with the developing roller 42 via the toner. At the same time, the toner supplied to the developing roller 42 is sandwiched between the developing roller 42 and the regulating blade 44, so that the toner is slid on the surface of the developing roller 42 and the regulating blade 44 to have a desired polarity ( In this embodiment, it is triboelectrically charged (negative polarity). Then, the toner supplied to the developing roller 42 is conveyed to a developing area which is a portion facing the photosensitive drum 1 by the rotation of the developing roller 42 in the direction of arrow R3 in the drawing.

  In the developing area, the toner in the toner layer on the developing roller 42 is transferred to the photosensitive drum 1 according to the electrostatic latent image on the photosensitive drum 1 by a developing electric field formed between the developing roller 42 and the photosensitive drum 1. Is done. As a result, the electrostatic latent image on the photosensitive drum 1 is developed (visualized) as a toner image. The development electric field is formed by a development voltage (development bias) applied to the development roller 42 by a development power source 50 as a voltage application unit (bias application unit).

  Toner that is not used for development in the development region and remains on the developing roller 42 (development residual toner) is rubbed by the supply roller 43 at the nip portion N3 between the development roller 42 and the supply roller 43 and scraped from the development roller 42. Is taken and mixed with the toner in the developing chamber 41. At the same time, toner is newly supplied onto the developing roller 42 by the rotation of the supply roller 43.

  On the other hand, a part of the development residual toner rubbed by the supply roller 43 and mixed with the toner in the development chamber 41 is returned to the toner storage chamber 40 below the development chamber 41 by the rotation of the supply roller 43 and is agitated. The toner is agitated by 45 and mixed with the toner in the toner storage chamber 40.

4). Next, the configuration of each part of the developing device 4 in the present embodiment will be described in more detail.

  As the toner, a negatively chargeable toner, which is a non-magnetic one-component developer, in which silica fine particles are externally added as an external additive is used. In this embodiment, silica fine particles were externally added in the range of 0.5 wt% to 2.0 wt% as the external addition ratio (number of external addition parts) when the weight of the resin toner particles was 100 wt%. In addition to silica fine particles, fine particles such as titanium oxide, aluminum oxide, zinc oxide, cerium oxide, tin oxide, or strontium titanate can be used as the external additive. As the toner, a toner having an aggregation degree of 5% to 50% in an initial state (unused state of the developing device 4) can be used.

The degree of toner aggregation was measured as follows. As a measuring apparatus, a powder tester (manufactured by Hosokawa Micron Co., Ltd.) having a digital vibrometer (manufactured by DEGITAL VIBLATIONMETER MODEL 1332 SHOWA SOKKI CORPORATION) was used. As a measuring method, 390 mesh, 200 mesh, and 100 mesh sieves are placed on the shaking table in the order of narrow opening, that is, 390 mesh, 200 mesh, and 100 mesh sieves are stacked so that the 100 mesh sieve comes to the top. I set it. Add 5 g of accurately weighed sample (toner) to the set 100 mesh sieve, adjust the displacement value of the digital vibrometer to 0.60 mm (peak-to-peak), and apply vibration for 15 seconds. It was. Thereafter, the mass of the sample remaining on each sieve was measured, and the degree of aggregation was obtained based on the following formula.
Aggregation degree (%) = (residual sample mass on 100 mesh sieve / 5 g) × 100 + (residual sample mass on 200 mesh sieve / 5 g) × 60 + (residual sample mass on 390 mesh sieve / 5 g) × 20
The samples used for this measurement were previously left for 24 hours in an environment of 23 ° C. and 60% RH, and the measurement was performed in an environment of 23 ° C. and 60% RH.

  As the developing roller 42, a roller having a diameter of 15 mm and having a silicone rubber base layer and a urethane rubber surface layer (elastic layer) formed on a conductive core metal having a diameter of 6 mm was used. The rubber length in the axial direction of the elastic layer is 240 mm. As the developing roller 42, those having a surface hardness of 30 ° to 75 ° in Asker-C can be suitably used. Further, in the silicone rubber and the urethane rubber, for example, carbon black (trade name: MA230, manufactured by Mitsubishi Chemical Corporation) is appropriately added as conductive fine particles, and a developing roller having a desired resistance is obtained by stirring and mixing. Can do. In addition to carbon black, the resistance can be adjusted by adding and dispersing an ion conductive agent such as lithium perchlorate or quaternary ammonium salt in the rubber.

A method of measuring the resistance value of the developing roller 42 is shown in FIG. In an environment of 25 ° C./55% RH, the developing roller 42 is brought into contact with the aluminum cylindrical conductor 48 having a diameter of 30 mm from above. At that time, a load of 500 gf is applied to both ends of the developing roller 42 to press the developing roller 42 against the aluminum cylindrical conductor 48. At the same time, in order to make the intrusion amount between the aluminum cylindrical conductor 48 and the developing roller 42 constant at 50 μm, the intrusion amount holding member having a cylindrical shape whose outer diameter is smaller than the outer diameter of the developing roller 42 at both ends of the developing roller 42. Fit. Then, an electric resistance R _{0 of} about 10 KΩ is provided on the ground side, the aluminum cylindrical conductor 48 is rotated at 60 rpm, and the developing roller 42 is driven with respect to the aluminum cylindrical conductor 48. The resistance of the developing roller 42 was calculated by applying a measurement voltage to the core of the developing roller 42 with the measurement system as described above, measuring the voltage across the resistor _R0 provided on the ground side, and calculating the current. . When the applied voltage is increased and the value of the current flowing through the measurement system is increased, the resistance _R0 provided on the ground side is appropriately reduced to about 0.1 KΩ according to the applied voltage. Thereby, the resistance value of the developing roller 42 can be measured accurately. Details of the resistance value of the developing roller 42 used in the embodiment will be described later.

  As the supply roller 43, one having a diameter of 15 mm and a flexible foamed polyurethane layer (elastic layer) formed on a conductive core metal having a diameter of 6 mm was used. As the supply roller 43, one having a surface hardness of 50 ° to 80 ° in Asker-F can be suitably used. Further, the intrusion amount of the supply roller 43 with respect to the developing roller 42 is preferably 0.25 mm to 1.8 mm in order to suppress toner deterioration, and is set to 1.0 mm in this embodiment. Here, the intrusion amount is represented by a value obtained by subtracting the distance between the rotation centers of the developing roller 42 and the supply roller 43 from the value obtained by adding the radius of the developing roller 42 and the radius of the supply roller 43.

Further, as the supply roller 43, a roller having a volume resistance of 10 ⁴ to 10 ⁸ Ω can be suitably used. The volume resistance of the supply roller 43 is measured by a measurement method substantially similar to the measurement method of the developing roller 42. In the case of the supply roller 43, the amount of penetration between the aluminum cylindrical conductor and the developing roller 42 is set to 1. Measurements were taken at 0 mm.

  The regulation blade 44 has its tip (free end) facing upstream with respect to the rotation direction of the developing roller 42, and its tip is in contact with the developing roller 42 (counter contact). The contact portion of the regulating blade 44 with the developing roller 42 is located downstream of the nip portion N3 between the developing roller 42 and the supply roller 43 in the rotation direction of the developing roller 42. In the present embodiment, the regulation blade 44 is arranged so that the tip thereof faces upward. The regulating blade 44 contacts the developing roller 42 over its entire length in the longitudinal direction. More specifically, the regulating blade 44 is formed on the peripheral surface of the developing roller 42 at the edge portion on the leading end (free end) side and / or the surface on the developing roller 42 side in a predetermined range from the edge portion to the base end portion side. Contact. In addition, the material of the regulation blade 44 may be any of metal, resin, and the like. Specific examples include metals such as stainless steel (SUS), phosphor bronze, and aluminum, and resins such as polyethylene terephthalate, acrylic, polyethylene, and polyester. Such a resin can be made conductive by adding a conductive agent such as carbon black or an ionic conductive agent. The regulating blade 44 can be a flat plate or a curved plate that is curved.

  In this embodiment, a contact development method is used in which development is performed in a state where the photosensitive drum 1 and the developing roller 42 are in contact with each other. The photosensitive drum 1 and the developing roller 42 are rotationally driven so that the surfaces of the photosensitive drum 1 and the developing roller 42 move in the same direction at the contact portion. The rotation peripheral speed ratio (ratio of the peripheral speed of the developing roller 42 to the peripheral speed of the photosensitive drum 1) is preferably 110% or more in order to satisfy the image density. On the other hand, if it is 180% or more, the mechanical stress at the contact portion increases and toner deterioration becomes remarkable. From the above, the peripheral speed ratio is preferably 110 to 180%, and is set to 130% in the present embodiment. In this embodiment, the rotation speed of the developing roller 42 is 200 rpm.

  The supply roller 43 rotates in the direction opposite to the developing roller 42 as indicated by an arrow R4 in the drawing. That is, the developing roller 42 and the supply roller 43 are rotationally driven so that the surfaces thereof move in the same direction at the nip portion N3 between the developing roller 42 and the supply roller 43. The ratio (peripheral speed ratio) of the peripheral speed V2 of the supply roller to the peripheral speed V1 of the developing roller 42, that is, (V2 / V1) × 100 [%] is preferably 100% to 200%. If it is 100% or less, the toner supply amount to the developing roller 42 may be insufficient, and if it is 200% or more, the mechanical rubbing force between the developing roller 42 and the supply roller 43 is high, and toner deterioration may be remarkable. . From the above, in this embodiment, it was set to 160%.

  The developing roller 42 is rotatably supported by the frame of the developing device 4 via a conductive support, and the main body of the image forming apparatus 100 via a conductive contact (not shown) with respect to the conductive support. Is connected to a developing power source 50 as a voltage applying means. The supply roller 43 is rotatably supported by the frame of the developing device 4 via a conductive support, and the image forming apparatus 100 includes a conductive contact (not shown) with respect to the conductive support. A power supply 49 as a voltage applying means provided on the apparatus main body 10 side is connected. Further, the regulating blade 44 is supported on the frame of the developing device via a conductive support, and is provided in the apparatus main body of the image forming apparatus 100 via a conductive contact (not shown) with respect to the conductive support. The regulated power supply 51 is connected as a voltage application means. The developing roller 42, the supply roller 43, and the regulation blade 44 can be applied with different predetermined voltages by the development power source 50, the supply power source 49, and the regulation power source 51.

  In this embodiment, regarding the potential difference (hereinafter referred to as Vback) between the voltage applied to the developing roller 42 and the surface potential of the white portion of the photosensitive drum 1 (the potential of the unexposed portion), Will be described in detail.

5. Fog “Fog” refers to a state in which a small amount of toner has been developed on the non-printing portion (white portion that should not be printed) of the white transfer material P. This phenomenon is white in the transfer material P after passing through the image forming apparatus and passing through the printing process from the reflection density (unit:%) of the white portion of the transfer material P in the unused (unrecorded) state. It can be quantified by subtracting the reflection density (unit:%) of the power part (white part). In a normal developing device, when this “fogging” is 2.5% or more, it seems that a portion that should be white when viewed by human eyes is colored. This “fogging” is caused by the fact that toner having a charge opposite to the original polarity (regular charging polarity) or toner having a zero charge amount is carried on the developing roller 42.

  When a developing device in which the developing roller 42 and the supply roller 43 rotate so that their surfaces move in the same direction at the nip portion N3 as in this embodiment is used, the toner is less likely to deteriorate, but “fogging” occurs. It's easy to do. On the other hand, if the developing roller 42 and the supply roller 43 are commonly used developing devices in which the surfaces of the developing roller 42 and the supply roller 43 move in opposite directions at the nip portion N3, the “fogging” hardly occurs but the toner deteriorates. It's easy to do.

  Here, as a result of examining the above “fogging”, the following phenomenon is likely to occur in the developing device in which the developing roller and the supply roller rotate so that their surfaces move in the same direction at the nip portion N3. I found out. That is, it has been found that a phenomenon in which the charge of the toner carried on the developing roller 42 escapes through the developing roller and a phenomenon in which charges having a reverse polarity are injected from the developing roller side are likely to occur.

  This phenomenon is caused by the fact that the supply toner 43 keeps the same toner without being scraped off from the D roller due to the weak force of scraping the development residual toner on the developing roller 42 by the mechanical rubbing force. It was prominent. If the same toner continues to be held on the developing roller 42, the phenomenon of charge escaping and the phenomenon of injecting a reverse polarity charge are repeated for the same toner. It is considered that a lot of toner is generated and “fogging” becomes remarkable.

  In order to solve this problem, the mechanical rubbing force by the supply roller is increased and the development residual toner is sufficiently scraped with the configuration in which the surfaces of the development roller 42 and the supply roller 43 move in the same direction at the nip portion N3. Measures can be taken to ensure that they are taken.

  However, for example, when the peripheral speed ratio of the supply roller with respect to the developing roller is increased, or when the amount of penetration of the supply roller with respect to the developing roller is set to be large, toner deterioration, that is, free and buried external additives on the toner surface. Promoted. As a result, there is a risk of increasing the degree of aggregation of the toner and reducing the charging performance of the toner. For this reason, problems such as toner filming in which the toner is fused on the developing roller may occur, which may hinder the extension of the service life.

  In this way, even if the scraping force of the toner from the developing roller is relatively small such that the surfaces of the developing roller and the supply roller move in the same direction at the nip portion, the “fogging” is suppressed. It is hoped that.

  That is, it is desired to form a high-quality image over a long period from the beginning of use of the developing device to the end of use by suppressing both toner deterioration and “fogging”.

  Accordingly, in Example 1, as a configuration for achieving both suppression of toner deterioration and suppression of “fogging”, the resistance value when the resistance of the developing roller 42 is measured in the range of applied voltage of 10 V to 50 V is 1 × 10 ^. A developing roller that falls within the range of 5Ω to 5 × 10 ^ 8Ω is used.

  In addition to satisfying the resistance value of the first embodiment, the second embodiment has the following characteristics. A potential difference Vback between the potential Vdc of the developing roller 42 during development and the surface potential of the white portion of the photosensitive drum 1 (surface potential Vc of the photosensitive drum charged on the charging roller (non-image portion potential not exposed to the exposure means)). = Vdc-Vc) is the applied voltage when measuring the resistance of the developing roller. Even if Vback is increased by using a developing roller having a resistance value of 1 × 10 ^ 4Ω or more at that time, “fogging” can be suppressed.

6). Experiment 1
In the developing device in which the developing roller and the supply roller rotate so that the surfaces of the developing roller and the supply roller move in the same direction at the nip portion N3, Example 1 capable of suppressing “fogging” is based on experiments together with Comparative Example 1. explain.
First, four developing rollers having different resistance values were produced, and the resistance values of the four developing rollers were measured in the range of applied voltage of 10 to 100V. The results are shown in FIG.

  Using these developing rollers in the image forming apparatus of the above-described embodiment, Vback was set to 100 V, 20,000 sheets were continuously printed on A4 paper, and the “fogging” level was compared. The “fogging” was measured every 2000 sheets printed, and the most prominent “fogging” value is shown in Table 1. Further, the density unevenness of the halftone image generated during this evaluation was evaluated as being invisible (O) and being visible (X). In this experiment, the surface roughness on the developing roller 42 and the contact position between the regulating blade 44 and the developing roller 42 are made equal, and the amount of toner carried on the developing roller 42 when not developed is adjusted to be the same. did. In this way, it is possible to compare only the relationship between the resistance value of the developing roller and the “fogging”.

  For measurement of “fogging”, DENSOMETER-TC6DS manufactured by Tokyo Denshoku was used. From the measured value of the white portion of the transfer material P in the unused (unrecorded) state, the value of the white portion (white portion) in the transfer material P after passing through the image forming apparatus and passing through the printing process (white portion) ( It was digitized by subtracting (unit:%).

  When the resistance value when the applied voltage was 10 to 50 V was the resistance value as shown in Examples 1-1 and 1-2, there was no image problem and “fogging” was good.

  On the other hand, in Comparative Example 1-1, the resistance value when 30 V was applied was 5.4 × 10 ^ 8Ω, and density unevenness occurred in the halftone image under evaluation. This is because when the developing roller 42 is rubbed by the supply roller 43 and the regulating blade 44, the developing potential is not stabilized and the density unevenness appears. When examined in detail, when the applied voltage may exceed 5 × 10 ^ 8Ω in the range of 10 to 50 V, such density unevenness occurred in the image.

  In Comparative Example 1-2, the resistance value when 50 V was applied was 9.7 × 10 4 Ω, and “fogging” was not good. Examining in detail the lower limit of the resistance value at which this “fogging” is unacceptable, the result of “fogging” exceeding 2.5% when the applied voltage may be less than 1 × 10 ^ 5Ω in the range of 10 to 50 V It became.

  From Experiment 1, the present inventor has found that it is important to measure the resistance value of the developing roller 42 to be considered in order to improve “fogging” with an applied voltage in the range of 10 to 50V. This will be further described.

  First, in the developing device of this embodiment, the preferable range of the charged charge of the toner on the developing roller 42 was −10 to −50 V as the surface potential. This is because the potential difference formed by the toner layer itself on the developing roller 42 during the image forming operation, that is, the absolute value range of the potential difference between the toner layer and the conductive core of the developing roller 42 is 10 to 50V. means.

  The phenomenon that the charged charge of the toner carried on the developing roller 42 escapes or the reverse polarity charge is injected may correlate with the potential difference between the toner layer and the conductive core of the developing roller 42. all right. This phenomenon becomes more prominent as the resistance value of the developing roller measured when a voltage corresponding to the absolute value of the surface potential is applied is lower.

  Further, for example, as shown in FIG. 4, there was almost no difference in the resistance value of the developing roller measured at an applied voltage of 100 V as shown in Japanese Patent No. 4416296 between Example 1-2 and Comparative Example 1-2. That is, depending on the resistance value when the applied voltage is 100 V, a suitable resistance value range for “fogging” cannot be obtained.

  Accordingly, when setting a suitable developing roller resistance value for “fogging”, a measuring method for measuring the resistance value by applying a voltage of 10 V to 50 V to the developing roller as a measuring method of the developing roller resistance value. Is effective.

  Next, it will be described that the surface potential formed by the toner layer on the developing roller 42 is preferably −10 to −50 V in the developing device of the present embodiment.

  First, in order to adjust the charge amount of the toner, a plurality of toners whose particle sizes and external addition amounts of silica fine particles as external additives are adjusted are prepared, and each of them is a developing roller at the same applied voltage and rotation speed as during image forming operation The surface potential on 42 was measured. For measurement of the surface potential, MODEL 344 manufactured by TREK was used.

  By removing the developing bias applied to the developing roller 42 from the measurement result of the surface potential, the surface potential formed by the toner layer was obtained. For each toner, as in the experiment of Table 1, continuous printing of 20,000 sheets on A4 paper was performed.

  As a result, when the surface potential is -10 V or less, the charge amount of the toner on the developing roller is low, or the toner charge amount on the developing roller is small even though the toner charge amount is appropriate, which is not practical. . For example, when the charge amount of the toner is low, the developing roller 42 cannot carry the toner, the toner is scattered from the developing roller 42, and the developing device and the image forming apparatus are contaminated with the toner. In addition, when the amount of toner carried is small (even if the charged charge of the toner is appropriate), a sufficient density cannot be obtained.

  On the other hand, when the surface potential of the toner on the developing roller is -50 V or more, the toner carrying amount on the developing roller cannot be kept constant during continuous printing of 20,000 sheets. In particular, such a tendency is shown in the configuration in which the same toner is easily carried on the developing roller 42 as in the present embodiment.

  This is because the developing device in which the developing roller and the supply roller rotate so that their surfaces move in the same direction at the nip portion is in the following state. That is, reverse polarity toner, that is, toner charged to positive polarity is likely to be generated, while the same toner is repeatedly charged to the negative polarity side by the supply roller 43 and the regulating blade 44. This is because it occurs. In such a case, there is a toner charged positively and a toner charged strongly negatively, and the charge distribution becomes wide.

  This negatively charged toner has very strong electrostatic adhesion on the developing roller 42 and cannot be completely regulated by the regulating blade 44. As a result, the balance between the supply by the supply roller 43 and the regulation by the regulation blade 44 is lost, and the phenomenon that the toner carrying amount on the developing roller is doubled and tripled occurs, and a stable image is printed. Became difficult.

  Further, the range of the surface potential described above is a range peculiar to the developing device in which the developing roller and the supply roller rotate so that their surfaces move in the same direction at the nip portion. When the setting of the developing device of this embodiment is changed so that the surfaces of the developing roller 42 and the supply roller 43 move in the opposite direction at the nip portion N3, even if the surface potential is −50V or more. This is because the amount of toner carried on the developing roller can be kept constant. This is because almost the same result was obtained when the above (V2 / V1) × 100 [%] was in the range of 100% to 200%, or when the amount of penetration of the supply roller 43 was changed.

  As described above, in the image forming apparatus according to this embodiment, the developing roller has a resistance value measured using an applied voltage in the range of 10 to 50 V within the range of 1 × 10 ^ 5 to 5 × 10 ^ 8Ω. Is used. In other words, a developing roller is used such that the resistance value of the developing roller measured when the voltage applied to the developing roller is changed to 10 to 50 V falls within the range of 1 × 10 ^ 5Ω to 5 × 10 ^ 8Ω. In other words, when the resistance value of the developing roller is measured by changing the applied voltage to 10 to 50 V, the developing roller whose resistance value falls within the range S of FIG. Use. As a result, in the developing device in which the developing roller and the supply roller rotate so that their surfaces move in the same direction at the nip portion, the developing device and process capable of suppressing “fogging” and image density unevenness A cartridge and an image forming apparatus can be provided.

7). Experiment 2
In Experiment 2, the configuration of Example 2 that can effectively suppress “fogging” according to Vback at the time of image formation will be described in comparison with Comparative Example 2.

  First, in order to clarify the range of the resistance value in the experiment, four developing rollers A to D different from the roller shown in FIG. The resistance values of these four developing rollers were measured in the range of applied voltage of 10 to 300V. The results are shown in FIG. As is clear from FIG. 5, for the four rollers used in this example, the resistance value in the applied voltage range of 10 to 50 V is B, C, and D, except that A exceeds the upper limit. In Example 1, the “fogging” was in a range showing good.

  Next, continuous printing of 20,000 sheets of A4 paper was performed for each developing roller with the settings of Vback 100 V, 200 V, and 300 V, and the “fogging” level was compared. The “fog” is measured every 2000 prints, and the most “fog” during printing up to 20,000 prints shows a remarkable value. Table 2 shows the results at Vback 100V, Table 3 shows the results at Vback 200V, and Table 4 shows the results at Vback 300V.

  The developing roller 42 used in the experiment changes the surface roughness on the developing roller 42 and the contact position between the regulating blade 44 and the developing roller 42 to change the toner carrying amount on the developing roller 42 when not developed. Were adjusted to be the same. By this experiment, it is possible to obtain the range of the resistance value of the developing roller in which “fogging” is good at each Vback setting.

In the case of Vback 100V Table 2 shows the experimental results when Vback is 100V.

  As shown in Table 2, “fogging” was good when the resistance value when the applied voltage was 100 V was the resistance value as shown in Example 2-1 to Example 2-3.

  On the other hand, in the developing roller A of Comparative Example 2-1, density unevenness occurred in the halftone image under evaluation. In the same manner as in the first embodiment, when the developing roller 42 is rubbed by the supply roller 43 and the regulating blade 44, the developing potential is not stabilized due to the charge-up, which appears as image density unevenness. This is because.

When Vback is 200V Table 3 shows the experimental results when Vback is 200V.

  When the resistance value when the applied voltage was 200 V was the resistance value as shown in Example 2-4 and Example 2-5, the fog was good.

  In the developing roller A of Comparative Example 2-2, the density unevenness occurred in the halftone image under evaluation, as in the case of 100V. Further, in the developing roller D corresponding to Comparative Example 2-3, the resistance value when 200 V was applied was lower than 1 × 10 4 Ω, and the result “fogging” was not good.

In the case of Vback 300V Table 4 shows the experimental results when Vback is 300V.

When the resistance value when the applied voltage was 300 V was the resistance value shown in Example 2-6, the fog was good.
In the developing roller A of Comparative Example 2-4, unevenness occurred in the halftone image under evaluation as in the case of 100V and 200V. In Comparative Example 2-5, as can be seen from FIG. 5, by increasing the applied voltage at the time of resistance measurement, the resistance value at the time of 300V application was 5.1 × 10 ^ 3Ω, and the fog was higher than that in Example 2-6. The result became remarkable. Further, in Comparative Example 2-5, “fogging” of an unfavorable level occurred, which was as low as 3.5 × 10 3 Ω.

  In Examples 2-4, 2-5, and 2-6, “fogging” could be suppressed while increasing Vback compared to Example 1. If Vback can be increased, effects such as improved γ characteristics and improved contamination of the charging roller can be obtained, and the degree of freedom in designing the image forming apparatus is increased. Further, for example, in the case of an image forming apparatus in which the developing device collects transfer residual toner on the photosensitive drum 1 without the cleaning blade 61, it is desirable that Vback can be set large. In that case, when collecting paper dust and transfer residual toner on the negatively charged photosensitive drum through the developing roller in contact with the photosensitive drum into the developing container, a large potential difference can be set, and the Coulomb force in the collecting direction is increased and collected. This is because it becomes easy.

Consider the mechanism by which the results shown in Tables 2 to 4 were obtained.
As described above, “fogging” occurs due to a phenomenon in which the charged charge of the toner on the developing roller 42 escapes or a phenomenon in which a charge having a reverse polarity is injected. It has been found by the inventors that this phenomenon has also occurred at the nip portion between the photosensitive drum 1 and the developing roller 42. Due to the potential difference of Vback at the nip portion between the photosensitive drum 1 and the developing roller 42, a minute current flows from the developing roller 42 toward the photosensitive drum 1, and the negative charge of the toner escapes. At the same time, a positive charge is injected into the toner from the developing roller side to generate a toner having a reverse polarity charge.

  Here, as apparent from FIG. 5, in the developing roller 42 provided with conductivity by this embodiment or an electronic conductive mechanism generally used for the developing roller, the resistance value generally increases as the applied voltage increases. Shows a downward trend. Therefore, the resistance value of the developing roller 42 during printing of the white portion correlates with Vback, that is, the potential difference between the surface potential of the photosensitive drum 1 and the cored bar portion of the developing roller 42. For this reason, the resistance value of the developing roller 42 when an applied voltage corresponding to Vback is applied correlates with the phenomenon that the charged charge of the toner escapes or the phenomenon that the charge of opposite polarity is injected, as shown in Table 2. It was a result.

  Further, regarding the developing roller A, the density unevenness of the halftone image occurred regardless of Vback. When examined in detail, the resistance value of the developing roller 42 at which density unevenness occurs in the image is correlated with the resistance value when a voltage of 10 to 50 V is applied. This is because the charge-up potential of the developing roller in which density unevenness occurs is 30 to 50V, and the developing roller resistance when a voltage of 10 to 50V is applied correlates with the escape of the charge. Therefore, the upper limit of the resistance of the developing roller preferably used in this embodiment is determined by the developing roller resistance when 10 to 50 V is applied.

  As described above, in Example 2, the resistance value of the developing roller measured when a voltage equal to the potential difference Vback (= Vdc−Vd) between the developing roller potential Vdc and the charging potential Vd during development is applied to the developing roller. However, a developing roller having 1 × 10 ^ 4Ω or more was used. Thereby, in the developing device in which the developing roller and the supply roller rotate so that their surfaces move in the same direction at the nip portion, in addition to the effect obtained in the first embodiment, “fogging” is effective according to Vback. The effect that it suppresses automatically can be acquired.

  Further, by making it possible to achieve both suppression of toner deterioration and suppression of “fogging”, it is possible to form a high-quality image over a long period from the initial use to the end of use of the developing device.

(Other embodiments)
The present invention is not limited to the above-described embodiment. For example, the effect of the present invention can be applied to a configuration using various toners generally used in electrophotography. For example, a toner containing a magnetic material (for example, Japanese Patent Application Laid-Open No. 2012-63574), or a toner using styrene acrylic or polyester resin as a binder may be used. Further, as an external additive, silica fine powder, or a toner to which fine particles such as titanium oxide, aluminum oxide, zinc oxide, cerium oxide, tin oxide, or strontium titanate are appropriately added can be used. Even when such a toner is used, the resistance range of the developing roller 42 in which the “fogging” is relatively good and the range of the applied voltage at the time of measurement are the same as the ranges shown in the above embodiments.

  For example, in the invention shown in Example 1, in the above-described embodiment, the example in the case of the contact development method in which the developing roller 42 and the photosensitive drum 1 are in contact during printing is used, but magnetic one-component non-contact development is used. The present invention is also applicable when the toner carrier and the photosensitive drum are not in contact with each other as in the system.

1 Photosensitive drum (image carrier)
2 Charging roller (charging member)
DESCRIPTION OF SYMBOLS 3 Exposure apparatus 4 Developing apparatus 42 Developing roller (toner carrier)
43 Supply roller (toner supply member)
47 containers

Claims (11)

A container that contains toner, a toner carrier that carries the toner and develops an electrostatic latent image, and a toner that is disposed so as to form a nip portion with the toner carrier and that supplies the toner to the toner carrier A developing device comprising a supply member,
The toner carrier and the toner supply member rotate so that their surfaces move in the same direction at the nip portion,
The development characterized in that the resistance value of the toner carrier measured when the voltage applied to the toner carrier is changed from 10V to 50V falls within the range of 1 × 10 ^ 5Ω to 5 × 10 ^ 8Ω. apparatus. An image carrier for carrying an electrostatic latent image;
A charging member that charges the surface of the image carrier to a potential Vc;
An exposure device that exposes the image carrier to form an electrostatic latent image;
A developing device according to claim 1, wherein the developing device is used in an image forming apparatus comprising:
The resistance value of the toner carrier measured when a voltage equal to the potential difference Vback (= Vdc−Vc) between the potential Vdc of the toner carrier and the potential Vc during development is applied to the toner carrier is 1 ×. A developing device characterized by being 10 ^ 4Ω or more.   3. The ratio (V2 / V1) × 100 [%] of the peripheral speed V2 of the toner supply member to the peripheral speed V1 of the toner carrier is 100% to 200%. The developing device according to 1.   The developing device according to claim 1, wherein the toner carrier has a surface hardness of 30 ° to 75 ° in Asker-C.   The developing device according to claim 1, wherein a surface hardness of the toner supply member is 50 ° to 80 ° in Asker-F.   The developing device according to claim 1, wherein an amount of penetration of the toner supply member with respect to the toner carrier is 0.25 mm to 1.8 mm. The developing device according to claim 1, wherein the toner supply member has a volume resistance of 10 ⁴ Ω to 10 ⁸ Ω.   The developing device according to claim 1, wherein the toner has a cohesion degree of 5% to 50%.   A process cartridge, comprising: the developing device according to claim 1; and an image carrier that carries an electrostatic latent image, wherein the process cartridge is detachable from the main body of the image forming apparatus.   The developing device according to claim 1, an image carrier that carries an electrostatic latent image, a charging member that charges the surface of the image carrier to a potential Vc, and the image carrier. An image forming apparatus comprising: an exposure device that exposes to form an electrostatic latent image.   A method of measuring a resistance value of a toner carrying member that carries toner and develops an electrostatic latent image, wherein the resistance value is measured by applying a voltage of 10 V to 50 V to the toner carrying member. Of measuring resistance value of toner carrier.