JP4904754B2 - Developing device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a printing apparatus, and more particularly to an improvement of a developing device using a one-component developer and an image forming apparatus using the developing device.

  As a developing device used in an image forming apparatus such as a conventional electrophotographic system, a one-component developing system using a one-component developer (toner) made only of toner and a two-component developer using a toner and a carrier are used. Component development methods are known. Among them, the one-component development type developing device does not require mixing with the carrier, stirring, and toner concentration control, so the device can be reduced in size and cost, and further, the developer can be replaced. Since it is unnecessary, it is increasingly used mainly in printers that require maintenance-free operation.

Conventionally, in the one-component development system, as a system for forming a toner layer having a predetermined toner amount and toner charge amount on a development roll, a film member is pressed against the development roll, and the inside of the nip region formed by this pressing force is used. Thus, a method of regulating the toner layer thickness on the developing roll and simultaneously performing frictional charging is employed (see Patent Documents 1 and 2).
For example, according to the prior art described in Patent Document 1, a film is pasted to a support frame disposed in the vicinity of the developing roll, and the film is pressed against the developing roll based on the tension of the film. Regulation and triboelectric charging.
Further, according to the prior art described in Patent Document 2, a voltage is applied to the film in accordance with the toner adhesion amount and the charge amount on the surface of the developing roll, and the film is electrostatically adsorbed to the developing roll. The toner layer thickness can be regulated and frictional charging can be performed.

  Furthermore, as a charging method, in addition to the friction charging method, it is also possible to incorporate a method of electrostatically charging the toner layer by bringing a film member into contact with the toner layer and applying a DC electric field. For example, when the toner is charged to a negative polarity, there is a technique in which a potential difference is applied between the film member and the developing roll so that the film member side has a negative polarity.

JP 63-1555065 A (Means for Solving Problems, FIG. 1) Japanese Patent No. 2982384 (Example, FIG. 2)

However, in such a system, if the reverse polarity toner charged to the opposite polarity to the toner polarity that should originally be obtained adheres to and accumulates on the surface of the film member, a new contact between the film member and the developing roll will occur. Since the toner entering in between does not come into contact with the surface of the film member, a desired toner layer thickness and charge amount cannot be obtained.
In addition, if reverse polarity toner is present on the developing roll due to charging failure, the reverse polarity toner is transferred to the non-image portion on the photoconductor when the toner is electrostatically transferred to the photoconductor drum. As a result, there is a problem that a fog phenomenon occurs in the image.

  The present invention has been made to solve the above technical problem, and removes the developer deposited and deposited on the surface of the charging member, and the developer layer has a desired layer thickness and charge amount. A developing device capable of being regulated and an image forming apparatus using the same are provided.

That is, as shown in FIG. 1, the basic structure of the present invention is a developer carrying body 2 that faces the image carrying body 1 carrying an electrostatic latent image and is rotatable and carries a developer G on the surface. A developing device including a charging member 4 that regulates charging of the developer G in contact with or in proximity to the developer G on the developer carrier 2 and a bias power source 5 that applies a predetermined bias to the charging member 4. in the bias power source 5 is, the polarity of the charging bias to a predetermined similar between charged during the image forming member 4 and the developer carrying member 2 is applied, the charge polarity which is determined in advance in accordance with the discharge by the charging bias AC to DC component of the opposite polarity to the charge bias applying means 6 for the developer G on the developing agent carrying member 2 for charging, and the charging bias are similar between the charging member 4 and the developer carrying member 2 at the time of non-image formation as neutralization via superimposed components There is applied, this in accordance with the discharge by discharging bias to adhere to the charging member 4 and the predetermined charging polarity and charge eliminating bias applying means (7) for neutralization with the discharge developer G oppositely charged polarity The connection between the charging bias applying means 6 and the discharging bias applying means 7 is switched so that one of the charging bias applying means 6 and the discharging bias applying means 7 acts between the charging member 4 and the developer carrier 2. Bias switching means 8 is provided.

In such technical means, the developer carrier 2 may be any material as long as it can carry the developer G. The developer carrier 2 includes a drum shape and a belt shape. Is preferably in contact with each other, but may be non-contact.
Further, the developer carrier 2 may be an elastic body or a rigid body, and may be a flexible tube, for example.
Further, the charging member 4 may be appropriately selected from a roll shape, a film sheet shape, a tube shape, a plate shape, a brush shape, etc. In the present invention, as described later, a film member and a flexible rotating body are used. Used .

Further, the charging bias applying means 6 may be appropriately selected as long as it can apply a charging bias for charging the developer to a predetermined charge amount between the charging member 4 and the developer carrier 2 during image formation. .
Further, the reverse polarity attached to the charging member 4 by applying a reverse polarity bias, for example, to the charging bias applying unit 6 between the charging member 4 and the developer carrier 2 at the time of non-image formation. Any toner can be appropriately selected as long as the toner can be neutralized or charged to a normal polarity.
Furthermore, the bias switching means 8 may be appropriately selected, for example, a type capable of switching between positive and negative with respect to a single DC power source, or a switch type which switches the connection of two wires, for example.
Further, the bias power source 5 is a single unit that can be used as the charging bias applying unit 6 and the neutralizing bias applying unit 7 if the bias switching unit 8 is of a type that can switch between positive and negative with respect to a single DC power source, for example. One application unit may be provided, or a plurality of application units each provided with the charging bias application unit 6 and the neutralization bias application unit 7 may be provided.

  Further, it is preferable that the charging bias applying means 6 applies a DC constant current. In addition to such a constant current control method, a constant voltage control method may be adopted. However, constant current control allows a constant current to be applied at all times. Even when the value fluctuates, a constant charge amount can be applied, and the developer G can be charged more stably than in the voltage control.

  Further, it is preferable that the bias switching unit 8 switches the connection to the static elimination bias applying unit 7 during a predetermined period during non-image formation. In this case, the bias switching means 8 appropriately switches to the neutralization bias at the time of non-image formation between the recording materials, when the power is turned on, and at the time of non-image formation such as the end mode, and reverse polarity developer attached to the charging member 4 is removed. Remove static electricity.

Furthermore, discharging bias applying means 7 which applies a discharge bias obtained by superimposing a direct current to alternating current to the charge polarity opposite to the polarity of the developer G is used. As a result, the developer G adhering to the charging member 4 can be effectively neutralized, and aggregation of the developers G when the developer G is recovered can be eliminated electrostatically. A thin layer can be formed even when the agent G is used.

Here, as a technique that approximates the present invention, a charging member that uniformly charges the surface of an electrostatic latent image carrier (for example, a photoconductor) uses a charging roll as the charging member, and when the image is formed on the charging roll. There has already been proposed a prior art in which a DC voltage is applied while a DC voltage or an AC voltage having a polarity opposite to that of the DC voltage is applied during non-image formation (see, for example, JP-A-2002-328508).
However, this type of prior art performs charging by ionic conduction, so that the ions involved in ionic conduction are applied to the inner side of the charging roll by applying a DC voltage or AC voltage having a polarity opposite to the bias at the time of image formation. Alternatively, the problem of being biased outward is prevented, and an increase in the resistance value of the charging roll is suppressed. Further, a pad-type cleaner that contacts the charging roll is disposed, and the toner adhering to the surface of the charging roll is cleaned by pressing the cleaner against the surface of the charging roll. It can be said that the bias applied during image formation does not exert a cleaning action on the toner adhering to the surface of the charging roll.
On the other hand, the present invention regulates the charge on the toner on the developer carrier 2 and further exerts a cleaning action on the reverse polarity developer reversely transferred to the charging member 4 by applying a neutralizing bias. Is.
Therefore, the technical problem to be solved and the means for solving the problem are completely different from the prior art, and the present invention cannot be conceived based on the prior art.

Further, it is preferable that a developer supply member 3 that is disposed opposite to the upstream side of the charging member 4 in the periphery of the developer carrier 2 and that supplies the developer G to the developer carrier 2 is preferably provided.
As long as the developer supply member 3 can carry and convey the developer G, a roll-shaped member or the like may be appropriately selected, and the developer supply member 2 may be in contact or non-contact.
Further, the developer supply member 3 is spaced apart from the developer carrier 2, and a supply bias is applied between the developer carrier 2 and the developer carrier 2 to promote the developer supply to the developer carrier 2, and is carried on the surface. It is preferable to supply the developed developer G to the developer carrier 2. As a result, it is possible to prevent the developer G from being rubbed and charged at the time of supply, and to supply the developer G stably.
Furthermore, the developer supply member 3 is preferably in the form of a rigid roll that can maintain a stable gap from the viewpoint that the developer supply member 3 is spaced from the developer carrier 2.
Further, the rotation directions of the developer carrier 2 and the developer supply member 3 may be different from each other (Against direction) or in the same direction (With direction) at the opposed portions.

The charging member 4 is preferably disposed with a contact pressure with the developer carrier 2 of 20 g / cm or less. As a result, the stress exerted on the developer G by the charging member 4 can be reduced, whereby the fixing phenomenon of the developer G to the charging member 4 and cracking of the developer G can be eliminated, and the performance of the developing device can be maintained over a long period of time. . Further, a soft developer G that can be fixed at low temperature can be used, and the energy consumption of an image forming apparatus using such a developing device can be reduced.
Further, the charging member 4 is preferably disposed with a nip width of 3 mm or more with respect to the developer carrier 2. Thereby, a sufficient contact time for charging the developer G can be secured.

Furthermore, the first aspect of the charging member 4 of the present invention is a film member that has a fixed end on the upstream side in the rotation direction of the developer carrier 2 and is arranged so that the downstream side in the rotation direction is a free end. Thus, charging of the developer G is regulated in contact with or in proximity to the developer G on the developer carrier 2. In this case, it is preferable to separately provide a layer thickness regulating member for regulating the layer thickness of the developer G on the developer carrier 2 to a constant thickness. Thus, by using the film member, not only can the layer thickness regulation and charging regulation to the developer G be performed at the same time, but also the stress applied to the developer G is reduced, so that soft development capable of low-temperature fixing is possible. The agent G can be used, and the energy consumption of the image forming apparatus can be reduced.
Further, the first aspect of the charging member 4 is a developer carrying member that rotates in the same direction as the developer carrying member 2 at the portion facing the developer carrying member 2 and has a flexible peripheral surface. The charging of the developer G is regulated in contact with or in proximity to the developer G on the body 2 .

  Furthermore, the present invention is not limited to the above-described developing device, but also targets an image forming apparatus using the same.

According to the present invention, a bias power source including a charging bias applying unit, a neutralizing bias applying unit, and a bias switching unit is provided, and a charging bias having a predetermined polarity is provided between the charging member and the developer carrier during image formation. is applied, switches the connection to the charging bias application means for the developer carrying member of the developer Ru is charged so that the charge polarity which is determined in advance in accordance with the discharge by the charging bias, whereas, at the time of non-image formation charging member And a charge eliminating bias in which an AC component is superimposed on a DC component having a polarity opposite to the charging bias is applied between the developer carrying member and the developer with the opposite polarity attached to the charging member is discharged due to the discharge due to the charge eliminating bias. since to switch the connection to the bias applying means, the opposite polarity developer deposited adhering to the surface of the charging member is removed, the surface of the charging member To provide a developing device that can be kept clean at all times, and that can regulate the developer on the developer carrying member to a desired developer layer thickness and charge amount, and an image forming apparatus using the same. Can do.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 shows an image forming apparatus according to the first embodiment to which the present invention is applied.
In FIG. 1, the image forming apparatus according to the present embodiment includes an image forming engine 20 that forms a toner image on a recording material 28 and a fixing device 50 that fixes an unfixed toner image on the recording material 28. Yes.
The image forming engine 20 includes a photosensitive drum 21 as an image carrier that rotates in a predetermined direction. Around the photosensitive drum 21, a charging device 22 that charges the photosensitive drum 21 and the photosensitive member are provided. For example, an exposure device 23 as a latent image writing device that forms an electrostatic latent image on the drum 21, a developing device 30 that visualizes the electrostatic latent image formed on the photosensitive drum 21, and a photoconductor A transfer device 26 that transfers a toner image visualized on the drum 21 to a recording material 28 that is a recording medium, and a cleaning device 29 that cleans residual toner on the photosensitive drum 21 are sequentially arranged. is there.

Here, as the charging device 22, for example, a charging roll is used, but a charging device such as a corotron may be used.
Further, the exposure device 23 only needs to be able to write an image on the photosensitive drum 21 with light. In this example, for example, a print head using LEDs is used, but the present invention is not limited to this. The print head used may be selected as appropriate, such as a scanner that scans a laser beam with a polygon mirror.
Furthermore, the cleaning device 29 removes the toner remaining on the photosensitive drum 21 after the transfer. For example, a doctor blade type is adopted.
Further, the transfer device 26 is composed of, for example, a transfer roll disposed in contact with the photoconductive drum 21, and a transfer bias in a direction in which a toner image developed on the photoconductive drum 21 is attracted by a bias power source 27 is applied. The toner image on the photosensitive drum 21 is transferred to the recording material 28.

  On the other hand, the fixing device 50 includes a heating roll 51 whose surface is heated by a heating source and rotates so as to be drivable, and a heating roller 51 that is press-contacted with the heating roll 51 and that conveys the recording material 28 between the heating roll 51. A pressure roll 52 is provided, and the toner image is fixed on the recording material 28 by passing the recording material 28 between the heating roll 51 and the pressure roll 52.

Further, the developing device 30 which is a characteristic point of the present embodiment will be described in detail with reference to FIG.
In the drawing, a developing device 30 has a developing housing 31 in which toner which is a one-component developer is accommodated. In the developing housing 31, a developing opening is opened facing the photosensitive drum 21. A developing roll 32 as a developer carrying member is disposed in the developing opening, and a toner supply roll 34 that supplies toner to the developing roll 32 facing the developing roll 32 is provided in the developing housing 31. It is.
A developing bias in which an AC voltage is superimposed on a DC voltage is applied to the developing roll 32 from a bias power source 33, thereby causing a developing electric field to act on the developing area between the photosensitive drum 21 and the developing roll 32. ing.

As the developing roll 32 in the present embodiment, a roll made of metal such as stainless steel (SUS), for example, whose surface has an arithmetic average roughness of 0.7 μm or less is used.
In this way, by setting the arithmetic average roughness of the developing roll 32 to 0.7 μm or less, the residual toner on the developing roll 32 can be easily peeled off, so that the development history can be eliminated. Further, by reducing the surface roughness of the developing roll 32, when supplying toner from the toner supply roll 34, there is also an effect of preventing excessive friction between the toners on the developing roll 32. It is possible to reduce the generation amount of the reverse polarity toner.

Further, for example, a toner supply roll 34 made of a SUS roll having a mirror-finished surface is used as the toner supply roll 34, and the toner supply roll 34 is in the same direction (With) at a portion facing the developing roll 32. Direction).
The toner supply roll 34 is not limited to this, and may be a belt-like form as long as it can supply toner to the developing roll 32.

Further, a bias power source 35 is connected between the toner supply roll 34 and the developing roll 32 so that a supply bias for supplying toner from the toner supply roll 34 to the developing roll 32 is applied.
Further, a toner hopper 36 for containing toner is provided behind the toner supply roll 34, and the toner is stirred by an agitator (not shown), for example, so that the toner is conveyed to the toner supply roll 34 side. Reference numeral 37 in the figure denotes a scraping member for scraping off the toner on the toner supply roll 34.

  In particular, in the present exemplary embodiment, the charging sheet 41 is disposed on the downstream side in the toner conveyance direction at the position facing the developing roll 32 and the toner supply roll 34 at a position facing the developing roll 32. The charging sheet 41 performs layer thickness regulation and charging regulation on the toner on the developing roll 32, and includes a film member 41a formed of a resin layer using an ion conductive material as a conductive agent. As a result, the electric field applied to the toner during charging can be made uniform, and a more stable charge amount can be imparted to the toner.

  The charging sheet 41 according to the present embodiment is obtained by fixing a part of the film member 41 a to a conductive support 41 b fixed to the developing housing 31, and the free end side of the film member 41 a is the rotation direction of the developing roll 32. The developing roller 32 is brought into contact with the downstream side. At this time, the contact nip width (peripheral length direction of the developing roll 32) between the developing roll 32 and the film member 41a is set to 3 mm or more, and the contact pressure is set to 20 g / cm or less. As described above, by setting the nip width between the developing roll 32 and the film member 41a to 3 mm or more and setting the contact pressure to 20 g / cm or less, it is possible to reduce the stress on the toner, thereby the toner on the film member 41a. Fixing phenomenon and toner breakage can be eliminated, and the performance of the developing device can be maintained over a long period of time. Furthermore, a soft toner that can be fixed at a low temperature can be used, and energy consumption of the image forming apparatus can be reduced. In addition, a sufficient time for charging the toner can be secured with a sufficient nip width.

Further, in the present embodiment, a bias power source 43 is connected between the conductive support 41b of the charging sheet 41 and the developing roll 32 so that a charging bias and a discharging bias are applied.
In particular, as shown in FIG. 3B, the bias power source 43 includes a charging bias power source 432 having a DC voltage 434 having one polarity, for example, a negative polarity, and a DC voltage 435 and an AC voltage having the other polarity, for example, a positive polarity. And a changeover switch 431 for switching the connection between the charging bias power source 432 and the neutralizing bias power source 433.
The changeover switch 431 selectively switches between a contact point a provided in the wiring on the charging bias power source 432 side and a contact point b provided in the wiring on the neutralization bias power source 433 side.

The charging bias power source 432 is connected as an image creation mode at the time of image formation, and is subjected to constant current control in order to charge the toner on the developing roll 32 uniformly. According to such constant current control, for example, even when the electrical resistance value of the charging member fluctuates due to environmental fluctuations, the charge amount given to the toner can be kept constant, or the toner charge quantity can be set to a desired value due to environmental fluctuations, When the value is increased / decreased, the constant current value is changed to increase / decrease the charge amount of the toner to return it to a desired value.
The charging bias power source 432 does not always need to apply a bias while the developing roll 32 is rotating, and at least the toner layer corresponding to the image portion of the photosensitive drum 21 has the film member 41a, the photosensitive drum 21, and the like. A bias may be applied when it is between.

On the other hand, the neutralizing bias power source 433 is connected as a cleaning mode only during a predetermined period during non-image formation, such as when the power is turned on, when the print job is finished, or when non-image formation between the recording materials 28 is performed during continuous printing. It is .
Further, in the present embodiment, the bias power source 43 is not limited to such a mode. If the changeover switch 431 is of a type that switches between positive and negative with respect to one power source, the charging bias power source is used. It is also possible to use a power source that can be used as both the power source 432 and the neutralizing bias power source 433.

Further, the supply bias applied between the toner supply roll 34 and the developing roll 32 in the present embodiment will be described.
FIG. 4 shows an example of the voltage waveform of the supply bias in the present embodiment. The operation time (corresponding to the operation region) in which the trapezoidal wave (rectangular wave) has a large voltage fluctuation and the subsequent non-zero voltage zero are shown. The voltage waveform forms one cycle with the action time (corresponding to the non-action area). The bias power supply 35 is configured so that this voltage waveform is applied. The toner supply roll 34 is applied with a waveform superimposed on the developing bias applied to the developing roll 32.
In other words, in the present embodiment, toner flying from the toner supply roll 34 to the developing roll 32 is performed during an action time with a large fluctuation of the trapezoidal wave, and development is performed by changing the ratio (duty ratio) of the action time in one cycle. The amount of toner supplied to the roll 32 can be controlled. Further, the toner is not charged unnecessarily. If this operation time is continued, the amount of toner to be supplied becomes too large, and it becomes difficult to control to a predetermined supply amount.
A toner supply amount and a toner layer surface potential of the toner layer supplied onto the developing roll when the supply bias duty ratio is changed will be described in Example 2 described later.

In order to apply such a bias, for example, a waveform generation circuit based on a CPU or the like is used, a development bias in which a DC component and an AC component are superimposed is applied to the bias power source 33, and a supply bias is shown in FIG. After the waveform is synthesized, it may be applied to the bias power source 35.
The supply bias is not limited to the trapezoidal wave (rectangular wave) shown in FIG. 4 and may be, for example, a sine wave or a triangular wave as long as it has an operation time and a non-operation time.
Further, in order to suppress the charge amount of the toner layer on the developing roll 32 (reduce the surface potential), for example, the toner on the toner supply roll 34 may be neutralized.

Next, the operation of the present embodiment will be described with reference to FIG.
In the drawing, the toner stirred by an agitator (not shown) in the toner hopper 36 is supplied to the toner supply roll 34.
Then, when the toner adhering to the toner supply roll 34 reaches the facing gap between the toner supply roll 34 and the developing roll 32, the toner is transferred to the developing roll 32 by the supply bias from the bias power source 35.

Further, when the toner formed on the developing roll 32 is conveyed to the charging sheet 41 as the developing roll 32 rotates, the layer thickness is regulated by the charging sheet 41 and a charging bias is applied to make the toner negative. Charge.
Then, when the toner is conveyed to a portion facing the photosensitive drum 21 and a developing bias is applied by the bias power source 33, the toner is transferred to the photosensitive drum 21 side and the electrostatic on the photosensitive drum 21 is also transferred. The latent image is visualized.
Further, the toner that has not been consumed by the development remains on the downstream side of the portion of the developing roll 32 facing the photosensitive drum 21. This is because the toner layer uniformly formed on the developing roll 32 is developed along the electrostatic latent image on the photosensitive drum 21 side, while the toner is not transferred to the non-image portion on the photosensitive drum 21. This is because the toner consumption varies from place to place.

Then, the toner remaining on the developing roll 32 is conveyed as it is with the rotation of the developing roll 32 and reaches the gap facing the toner supply roll 34. In the present embodiment, since the surface roughness of the developing roll 32 is reduced, the residual toner on the developing roll 32 is peeled off by the toner flying between the gap between the developing roll 32 and the toner supply roll 34.
The toner that has not been supplied to the developing roll 32 side on the toner supply roll 34 is scraped off by the scraping member 37 and collected by the toner hopper 36.

In particular, in the present embodiment, since the bias power source 43 can switch between the charging bias and the neutralizing bias, the toner charging property is extremely good.
That is, as shown in FIG. 5, in the present embodiment, the changeover switch 431 is connected to the charging bias power supply 432 side in the image creation mode, and the changeover switch 431 is connected to the neutralization bias power supply 433 side in the cleaning mode. Connected. At this time, the charging process is performed when the changeover switch 431 is connected to the charging bias power supply 432 side, while the discharging process is performed when the changeover switch 431 is connected to the discharging bias power supply 433 side.

If it is now in the image creation mode, the changeover switch 431 is connected to the charging bias power source 432 side, and the toner layer supplied onto the developing roll 32 is regulated by the charging sheet 41 and the charging bias is applied. As a result, a predetermined charge amount can be obtained.
That is, in this case, as shown in FIG. 6A, when the toner layer corresponding to the image forming region passes through the portion facing the film member 41a, a negative DC constant current is applied to the conductive portion of the charging sheet 41. Applied. At this time, in the nip region between the film member 41a and the developing roll 32, there are a positive charge 60 and a negative charge 61 that are ionized by molecules in the air due to discharge. Among these, the negative charge 61 moves to the developing roll 32 side by an electric field, and adheres to the toner on the surface side of the developing roll 32, thereby negatively charging the toner.
The negatively charged toner adheres to the developing roll 32 due to a mirror image force, and is used for development in a developing area which is a portion where the photosensitive drum 21 and the developing roll 32 are opposed to each other.

On the other hand, the positive charge 60 adheres to the toner particles on the film member 41a side and charges the toner to positive polarity (reverse polarity). The positively charged reverse polarity toner adheres to and accumulates on the film member 41a due to a mirror image force.
Therefore, in the present embodiment, as the cleaning mode, by connecting the changeover switch 431 to the neutralization bias power source 433 side, a neutralization bias is applied, and the accumulated reverse polarity toner attached to the film member 41a is removed. Can do.
That is, as shown in FIG. 6B, a voltage equal to or higher than the discharge start voltage is applied to the conductive portion of the charging sheet 41, and an electric field acts on the negative charge of the molecules in the air ionized by the discharge. The electric charge 61 moves to the film member 41a side, adheres to the reverse polarity (positive polarity) toner adhering to the film member 41a, and discharges the positive polarity toner. The discharged toner is peeled off from the film member 41 a by the vibration action of the alternating electric field component and the rubbing force with the developing roll 32.

Furthermore, some toner is negatively charged by the negative charge 61 and may adhere again to the film member 41a side. However, the toner is peeled off from the film member 41a by applying a negative constant current in the image forming mode. Is done.
On the other hand, the positively charged ionized 60 adheres to the toner particles on the developing roll 32 side, so that a part of the toner is charged to a positive polarity with a reverse polarity. The positively charged toner adheres to the developing roll 32 due to a mirror image force, and is peeled off by the toner flying at a portion facing the toner supply roll 34.
In order to suppress the charge amount of the reverse polarity toner on the developing roll 32 side, it is preferable to set the current value of the DC component to a low value of about +4 μA, for example.

Next, the developing bias in the cleaning mode will be described in detail.
As described above, the toner transferred onto the developing roll 32 in the cleaning mode passes through the developing area while having a positive charge 60 or zero charge having a reverse polarity, and is collected by the toner supply unit (toner supply roll 34). The At this time, it is necessary to apply a developing bias to a portion of the developing roll 32 facing the photosensitive drum 21 so that toner having a positive charge 60 or near zero charge does not transfer to the photosensitive drum 21 side.
That is, in the present embodiment, assuming that the surface of the photosensitive drum 21 rotates uniformly while holding a non-image area charged to, for example, −600 V, the toner collected from the film member 41a is developed. When passing through, waste toner can be held on the developing roll 32 side by applying a developing bias having a larger absolute value than −600 V, for example, −750 V, as the developing bias to the developing roll 32. On the other hand, at other timings, the negatively charged toner that is normally charged becomes non-image on the photosensitive drum 21 by applying a developing bias having an absolute value smaller than −600 V, for example, −300 V. The fog phenomenon can be prevented without transferring to the formation portion.

According to the present embodiment, since the waste toner collected from the charged sheet 41 has been neutralized, aggregation of the toner is eliminated. Therefore, unevenness in the formation of a thin layer of toner that may occur when the collected toner is supplied again to the developing roll 32 can be eliminated, the toner charge amount can be stabilized, and high image quality can be obtained. It becomes possible.
Furthermore, as the charging member, the use of the charging sheet 41 that exerts a small stress on the toner can reduce the stress on the toner, so that a soft toner can be used. Thus, if soft toner can be used, low-temperature fixing can be achieved, leading to reduction of energy consumption of the image forming apparatus.

Further, in the present embodiment, the reverse polarity toner attached to the surface of the film member 41a and the toner close to zero charge are always removed and collected, so that the film member 41a can always maintain a refreshed state. Further, according to the present embodiment, a uniform toner layer having excellent toner supply property is formed, and the film member 41a can maintain a refreshed state, so that a more stable toner layer can be formed. Furthermore, since the toner on the developing roll 32 is surely in contact with the film member 41a, it is possible to obtain a normal toner charging polarity regardless of the period of use and frequency of use.
Furthermore, according to the present embodiment, the reverse polarity toner and the zero charged toner are not deposited on the surface of the film member 41a, and the resistance value of the film member 41a is not changed. Even if is adopted, it is possible to maintain a constant current. Therefore, it is also possible to employ a constant voltage control bias application method.

In this embodiment, since a specific supply bias is applied, toner supply performance can be kept extremely good.
That is, normally, when the toner particles are rubbed against the inner wall of the toner hopper 36 or the agitator, the toner has a bipolar charge, so that some toner particles adhere to the developing roll 32 side due to the alternating electric field effect of the supply bias. Become. At this time, as a result of the reciprocal vibration of the toner particles between the gaps due to the alternating electric field having a small supply bias, the toner adhering to the developing roll 32 forms a uniform thin layer. Further, since the duty ratio of the supply bias is small and the non-operation time is long, the charge amount of the toner attached on the developing roll 32 can be reduced.

If only a DC electric field is applied as the supply bias, the toner layer formed on the developing roll 32 has a large amount of charge, and a non-uniform layer with large thickness unevenness is formed.
That is, a predetermined amount of toner with a small charge amount is supplied to the developing roll 32 by a supply bias applied between the developing roll 32 and the toner supply roll 34, and the toner is uniform and has a small surface potential on the developing roll 32. A layer is formed.

Embodiment 2
FIG. 7 shows an outline of the developing device 30 according to the second embodiment to which the present invention is applied. In this figure, the present embodiment is configured in substantially the same manner as the developing device 30 (see FIG. 3) of the first embodiment, but a charging roll 42 is used instead of the charging sheet 41 of the first embodiment as a charging member. Different points are used. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

The charging roll 42 in the present embodiment is, for example, a flexible tube in which a conductive layer is provided on the inner surface of the PVDF tube, and a rotary support for fixing the tube is provided on the inner surface of the tube. The surface is in contact with or close to the developing roll 32.
Further, the charging roll 42 is rotated in the same direction (within the direction) at the facing portion with a peripheral speed ratio of 0.5, for example, with respect to the peripheral speed of the developing roll 32.

Also in this embodiment, the same effects as those of the first embodiment are obtained.
In the present embodiment, the charging roll 42 is configured to cover the flexible tube with the hollow body. However, the present invention is not limited to this, and the flexible tube is attached to the circular support plate provided inside the both ends of the flexible tube. The circular support plates at both ends are connected by a rod-shaped member having an outer diameter sufficiently smaller than the inner diameter of the flexible tube, and the other ends of the flexible tube are in contact with or close to the developing roll 32. May be. As described above, even if the flexible tube is pressed against the developing roll 32, since it is flexible, the stress applied to the toner is reduced, and the nip area during charging is widened (developing roll 32). (Peripheral length direction) can be maintained, and stable charge control becomes possible.
Further, although not provided in this example, as shown by a phantom line in FIG. 7, in order to improve the cleaning property of the surface of the charging roll 42, the charging roll 42 is disposed on the opposite side of the charging roll 42 from the developing roll 32. A scraping member 44 made of, for example, a PET (polyester) sheet may be provided to scrape off the attached toner.

Example 1
In this example, the developing device model according to the first embodiment is embodied, and the performance of the developing device model according to the present embodiment was confirmed. In order to compare the performance of the present embodiment, a comparative example of a static elimination bias non-application method (comprising only a charging bias power source) was used, and the toner adhesion amount and the charge amount at that time were examined.
In this embodiment and the comparative example, as shown in FIGS. 8A and 8B, the developing roll 100 carrying and transporting the toner, the toner roll is disposed opposite to the developing roll 100, and the toner is charged with the layer thickness. The charging sheet 101 is disposed, and the toner on the developing roll 100 is regulated in layer thickness by the film member 101a of the charging sheet 101. Then, the potential difference between the film member 101a and the developing roll 100 is zero in a quiet state. The film member 101a was pulled apart, and the characteristics of the toner layer on each member in the nip portion were measured.

The development conditions in this example are as follows.
Developing roll: SUS roll, diameter 30 mm, mirror finish (arithmetic average roughness = 0.145 μm, maximum height = 1.801 μm, ten-point average roughness = 1.118 μm), peripheral speed 220 mm / sec
Toner supply roll: SUS roll, diameter 20 mm, mirror finish (same specifications as developing roll), peripheral speed 440 mm / sec
Arrangement of developing roll and toner supply roll: gap 100 μm, rotating in the same direction (with direction) at opposite parts. Charged sheet: polyvinylidene fluoride (PVDF) film member (volume resistivity 1 × 10 ¹⁰ Ω · cm , 50μm thickness)
-Contact nip between the developing roll and the film member: width (perimeter direction of the developing roll) of about 10 mm, contact pressure of 10 g / cm
・ Charging bias: DC constant current value -10μA
-Static elimination bias: DC constant current value + 4 μA + AC voltage (frequency 2 kHz, peak-to-peak voltage Vpp 500 V)
The surface roughness of the developing roll was measured in accordance with JIS B0601-1994, with a measurement length of 1.5 mm and a cutoff wavelength of 0.25 mm along the circumferential direction of the roll using Surfcom 1400A manufactured by Tokyo Seimitsu Co., Ltd. The measurement speed was 0.3 mm / sec.

In the comparative example, as shown in the operation diagram of FIG. 8A, sufficient layer thickness regulation and charging regulation can be performed on the toner on the developing roll 100 by the deposited toner 102 attached to the film member 101 a. There wasn't.
That is, the toner amount of the deposited toner 102 on the film member 101a side was about 2 mg / cm ² per unit area (the value obtained by measuring the toner weight attached to the entire film and dividing by the area where the toner is attached). . The amount of toner on the developing roll 100 in the nip area was about 1.9 mg / cm ^{2 as} measured with a book tape. On the other hand, the toner amount on the developing roll 100 after passing through the nip region was 0.83 mg / cm ² .
Thus, according to the comparative example, while the nip region exists in the toner is ^{2mg / cm 2 + 1.9mg / cm} 2 = about 3.9 mg / cm ^2, the toner amount after nip pass is 0.83mg / Cm ² , and it was confirmed that the toner after passing through the nip region was present only about a quarter of the amount of toner in the nip region.

Further, when the toner charge amount (specific charge amount) was measured using a Trek q / M meter, the toner charge amount of the deposited toner 102 adhering to the film member 101a side was +7 μC / g. The toner charge amount on the developing roll 100 in the nip area was −2.6 μC / g. Further, the toner charge amount on the developing roll 100 after passing through the nip region was −9.6 μC / g.
As described above, according to the comparative example, the toner conveyed to the nip area does not come into contact with the film member 101a when the toner layer passes through the nip due to the presence of the accumulated toner 102 attached to the surface of the film member 101a. It was confirmed that the desired charge amount could not be obtained.

On the other hand, as shown in the operation diagram of FIG. 8B, the toner amount of the present embodiment hardly deposits the deposited toner 102 attached to the film member 101a, and obtains a good toner amount and toner charge amount. I was able to.
That is, the amount of toner adhering to the film member 101a side is a very small amount of about 0.01 mg / cm ² , and the amount of toner on the developing roll 100 in the nip area is 0.7 mg / cm ² , while the developing roll after passing through the nip area The toner amount on 100 was 0.6 mg / cm ² .
Further, when the toner charge amount was measured, the amount of toner adhering to the film member 101a side was too small to be measured. The charge amount of the toner on the developing roll 100 was −32 μC / g.

  From the above, according to the present embodiment, the reverse polarity toner or the toner close to zero charge that has adhered to the surface of the film member due to the neutralization bias is always neutralized and collected, so that the surface of the film member is always refreshed. confirmed. As a result, it was confirmed that stable layer thickness regulation was performed on the toner and that the toner was stably charged by the charging bias.

Example 2
In this embodiment, the toner supply amount and the toner layer surface potential of the toner layer supplied onto the developing roll when the duty ratio of the supply bias is changed are measured with the same configuration as in the first embodiment.
The supply bias applied between the developing roll and the toner supply roll was adjusted so that the peak-to-peak voltage Vpp was 1.5 kV and the frequency was 2 kHz in the voltage waveform of FIG.

As a result, as shown in FIG. 9, it was confirmed that the toner supply amount tends to increase in proportion to the duty ratio. The toner layer surface potential was about 0 to 5 V until the duty ratio was about 0.6. However, when the toner layer surface potential was exceeded, the toner layer surface potential changed rapidly, and the toner layer surface potential (absolute value) tended to increase. It was.
In this embodiment, no positive frictional force was applied to the toner when the toner was supplied, and the charge amount of the toner was estimated to be quite small, and the result also reflected this.
From this result, when the toner supply amount (corresponding to the toner adhesion amount) on the developing roll is made as thin as about 6 to 14 g / m ² , the toner layer surface potential becomes as small as about 0 to +5 V. It was confirmed that by supplying such a thin toner layer, the supplied toner can be judged to be at an almost uncharged level. Further, when the toner supply amount exceeds 14 g / m ² , the toner layer surface potential (absolute value) suddenly increases due to the increase in the toner layer thickness, and there is a concern about the influence on charging. Become.

In particular, when the toner supply amount is 10 g / m ² or less, the surface potential of the toner layer is kept small, uniform charge control at the time of charging is further possible, and stress on the toner can be further reduced. It is understood that it can be done.
Thereafter, when the same evaluation as described above was performed with the gap between the developing roll and the toner supply roll being 50 to 400 μm, it was confirmed that the same effect was obtained.
From the above, it has been understood that a sufficiently uniform toner layer is formed, the subsequent uniform charge control is possible, and the stress applied to the toner is small.

It is explanatory drawing which shows the outline | summary of the image development apparatus concerning this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram illustrating an image forming apparatus according to a first embodiment to which the present invention is applied. (A) is explanatory drawing which shows the developing device of Embodiment 1, (b) is explanatory drawing which shows a bias switching means. FIG. 6 is an explanatory diagram illustrating a waveform of a supply bias according to the first embodiment. FIG. 6 is an explanatory diagram illustrating a flowchart of bias switching processing according to the first embodiment. (A), (b) is explanatory drawing which shows the effect | action of the toner in the nip area | region of Embodiment 1. FIG. FIG. 10 is an explanatory diagram illustrating an overview of a developing device according to a second embodiment. (A) is explanatory drawing which shows the principal part of the developing apparatus of a comparative example, (b) is explanatory drawing which shows the principal part of the developing apparatus of an Example. FIG. 6 is an explanatory diagram showing the results of Example 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Developer carrier, 3 ... Developer supply member, 4 ... Charging member, 5 ... Bias power supply, 6 ... Charging bias application means, 7 ... Static elimination bias application means, 8 ... Bias switching means, G ... Developer

Claims (9)

A developer carrying member that faces the image carrier on which the electrostatic latent image is carried and is rotatable and carries a developer on the surface;
Consists film member and the downstream side in the rotational direction has a rotation direction upstream side to the fixed end of the developer carrying member is disposed so that the free end, in contact or in proximity to the developer on the developer carrying member the A charging member that regulates charging of the developer;
A bias power source for applying a predetermined bias to the charging member;
Bias power supply
A charging bias polarity predetermined Te between the charging member and the developer carrying member at the time of image formation is applied, developed on the developer carrying member so that the charge polarity which is determined in advance in accordance with the discharge by the charging bias Charging bias applying means for charging the agent;
The hand the charging bias between the charging member and the developer carrying member at the time of non-image forming discharge bias obtained by superimposing an AC component on a DC component of the opposite polarity is applied, to adhere to the charging member with the discharge by the discharging bias And a neutralizing bias applying means for neutralizing a developer charged to a polarity opposite to the predetermined charging polarity ;
And a bias switching means for switching the connection of the charging bias applying means and said discharge bias applying means so that one acts between the charging member and the developer carrying member of the charging bias applying means and charge eliminating bias application means A developing device comprising: A developer carrying member that faces the image carrier on which the electrostatic latent image is carried and is rotatable and carries a developer on the surface;
Rotating and the circumferential surface in the developer carrying member in the same direction in the opposing portion between the developer carrier from the rotating member having flexibility, contact or in proximity to the developer on the developer carrying member the developer A charging member that regulates charging,
A bias power source for applying a predetermined bias to the charging member;
Bias power supply
A charging bias polarity predetermined Te between the charging member and the developer carrying member at the time of image formation is applied, developed on the developer carrying member so that the charge polarity which is determined in advance in accordance with the discharge by the charging bias Charging bias applying means for charging the agent;
The hand the charging bias between the charging member and the developer carrying member at the time of non-image forming discharge bias obtained by superimposing an AC component on a DC component of the opposite polarity is applied, to adhere to the charging member with the discharge by the discharging bias And a neutralizing bias applying means for neutralizing a developer charged to a polarity opposite to the predetermined charging polarity ;
And a bias switching means for switching the connection of the charging bias applying means and said discharge bias applying means so that one acts between the charging member and the developer carrying member of the charging bias applying means and charge eliminating bias application means A developing device comprising: The developing device according to claim 1 or 2 ,
A developing device comprising a developer supply member that is disposed opposite to the upstream side of the charging member in the periphery of the developer carrier and that supplies the developer to the developer carrier. The developing device according to claim 1 or 2 ,
2. A developing device according to claim 1, wherein the bias switching means of the bias power source switches the connection to the static elimination bias applying means during a predetermined period during non-image formation. The developing device according to claim 1 or 2 ,
A developing device characterized in that the charging bias applying means of the bias power source applies a DC constant current. The developing device according to claim 1 or 2 ,
The developing device, wherein the charging member is disposed with a contact pressure with the developer carrying member of 20 g / cm or less. The developing device according to claim 1 or 2 ,
The developing device, wherein the charging member is disposed with a nip width of 3 mm or more with respect to the developer carrying member. The developing device according to claim 3 .
The developer supply member is spaced apart from the developer carrying member, and a supply bias for energizing the developer to the developer carrying member is applied between the developer carrying member and the developer carried on the surface. A developing device for supplying to a developer carrying member. Imaging of an image bearing member on which an electrostatic latent image is carried, characterized by comprising a developing device according to any one of claims 1 to 8 for developing an electrostatic latent image on the image carrier apparatus.

Images