JP2001005282A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device constituted in such a way that the unstabilizing of developing potential caused by the electrification of a dielectric layer can be suppressed while sufficiently achieving the compatibility of the excellent reproducibility of a fine line and the excellent reproducibility of gradation at a solid part by arranging the dielectric layer as the developing device provided with a toner carrier having the dielectric layer. SOLUTION: This developing device 1 is constituted so that an electrostatic latent image held at the surface of a photoreceptor drum 30 is developed with toner. Besides, it is provided with a developing roller 2 for developing the electrostatic latent image by carrying the toner 7 to the drum 30 while holding it at the surface and a toner layer thickness regulation member 4 electrifying the toner 7 on the roller 2 in a contact state and regulating the thickness thereof so as to make it into the desired thickness layer. Then, the roller 2 is provided with an elastic conductive base material 22 and the dielectric layer 23 formed so as to cover the base material 22. Besides, the thickness A of the layer 23 is set so as to obtain the expression of 2×R<=A<=10×R when the volume average grain diameter of the toner is defined as R.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile, etc., using an electrophotographic process, and more particularly to a developing device using a non-magnetic one-component toner. .

[0002]

2. Description of the Related Art A developing device using a one-component toner that does not use a carrier has the advantages of a simple structure, an inexpensive device, and a reduction in size. In addition, it has an advantage in terms of cost maintenance. In particular, a developing device using a non-magnetic one-component toner that does not use a magnetic toner has advantages that a clear image can be obtained because it is small and inexpensive because a magnet roller is not used.

In a non-magnetic one-component developing apparatus, a roller or a belt made of conductive or semiconductive rubber is generally used as a toner carrier. However,
When such a toner carrier is used, the development γ characteristic (change in the amount of the developed toner with respect to the change in the development potential) in the development process becomes very steep. Therefore, it is advantageous for forming isolated fine lines and dots, but it is difficult to obtain good tone reproducibility in a solid (solid black) portion.

In order to steepen the development γ characteristic in isolated fine lines and dots and to moderate the development γ characteristic in a solid portion, a toner carrier having a dielectric layer provided on a conductive base material is used. A method to be used (disclosed in Japanese Patent Publication No. Hei 7-31452 and Japanese Patent Publication No. Hei 7-31453) has been considered. Also, a technique using a toner carrier having a minute floating electrode provided on the surface of a dielectric layer on a substrate (Japanese Patent Laid-Open No.
-72968).

[0005] In these techniques, a counter electrode of a developer carrier is formed on a conductive part by providing a dielectric layer on a conductive base material or by providing microelectrodes on the surface of the dielectric layer. The electric field component applied to the toner layer is reduced by the dielectric layer arrangement, and the development γ characteristic becomes gentle with respect to the change in the development potential difference. However, in the case of isolated fine lines and dots, the edge electric field enhancement effect of the electrostatic latent image is reduced. Then, a sufficient developing toner amount can be obtained, so that a steep developing γ characteristic can be maintained.

[0006]

However, when the dielectric layer is disposed, the dielectric layer is charged by contact with the toner layer regulating member, the latent image carrier, and the toner, and the dielectric layer may be charged due to continuous use or environmental fluctuation. It has been found that the charging state fluctuates, and a problem that a stable developing potential cannot be obtained in the developing step often occurs. This problem is particularly remarkable when the dielectric layer is thick.

On the other hand, if the thickness of the dielectric layer is too small, the effect of achieving both the steep development γ characteristic in isolated fine lines and dots as described above and the gentle development γ characteristic in the solid portion can be achieved. Not enough.

Further, when the dielectric layer is unavoidably charged by using a toner carrier having a dielectric layer provided on a conductive base, the charged dielectric layer is forcibly discharged. The method is disclosed in JP-A-59-171.

However, even in this method, the thickness of the dielectric layer is not set to an appropriate value. For example, JP
In Japanese Patent Application Laid-Open No. 9-171, the thickness of the dielectric layer is set to 400 to 10
The average particle diameter of the toner is about 9 μm, and the thickness of the dielectric layer is as thick as tens of times or more the average particle diameter of the toner.
Therefore, there arises a problem that a stable development potential as described above cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a developing apparatus having a toner carrier having a dielectric layer, whereby a fine fine line can be reproduced by disposing the dielectric layer. Device capable of suppressing instability of development potential due to charging of a dielectric layer while sufficiently achieving both compatibility (sharpness of fine lines) and good gradation reproducibility in a solid portion. Is to do.

[0011]

According to the present invention, there is provided a developing device for developing an electrostatic latent image held on a surface of an image carrier with toner to solve the above-mentioned problems. A toner carrier for transporting the toner onto the image carrier for development while holding the toner on the surface thereof, and contacting the toner on the toner carrier with the toner. A toner layer thickness regulating member that regulates the thickness, the toner carrier includes a conductive base having elasticity, and a dielectric layer provided so as to cover the conductive base. A is the thickness, and R is the volume average particle size of the toner.
Where the thickness of the dielectric layer is set so as to satisfy 2 × R ≦ A ≦ 10 × R.

According to the above configuration, by setting the thickness of the dielectric layer to 2 to 10 times the volume average particle diameter of the toner, the thickness of the dielectric layer can be set to an optimum value. By arranging the layers, it is possible to sufficiently achieve both the steep development γ characteristic in isolated fine lines and dots, the gradual development γ characteristic in the solid part, and the maximum density, while maintaining the development potential due to the charging of the dielectric layer. Stabilization can be suppressed.

In order to solve the above-mentioned problems, the developing device of the present invention preferably further includes a charge removing member that contacts the surface of the toner carrier after development to remove the charge of the toner carrier.

According to the above configuration, even when the dielectric layer is charged, the dielectric layer can be discharged, and a stable developing potential can be applied to the toner carrier.

In the developing device according to the present invention, in order to solve the above-mentioned problems, preferably, the charge removing member includes an aggregate of conductive fibers that comes into contact with the surface of the toner carrier.

According to the above configuration, the contact state between the charge eliminating member and the dielectric layer can be obtained even when there is a variation in the thickness of the toner layer or the like, by using the charge eliminating member provided with an aggregate of conductive fibers such as a brush. Of the dielectric layer can be effectively removed by the charge removing member. Therefore, even if the dielectric layer is charged,
The dielectric layer can be sufficiently discharged, and a stable development potential can be applied to the toner carrier.

In order to solve the above-mentioned problems, the developing device of the present invention preferably further includes voltage applying means for applying a voltage containing at least an AC component to the charge removing member.

Even if the dielectric layer is neutralized with a neutralization brush as described in Japanese Patent Application Laid-Open No. Sho 59-171 or the like, the static elimination effect cannot be obtained unless the voltage applied to the neutralization brush is properly set. It does not work effectively, but rather increases the instability of the potential of the dielectric layer due to frictional charging or the like by the charge removing member.

According to the above configuration, by applying a voltage including an AC component to the charge removing member, the contact interface resistance between the charge removing member and the toner carrier can be reduced, and the charge removing efficiency by charge injection can be improved. Can be. therefore,
Even when the dielectric layer is charged, the dielectric layer can be sufficiently discharged, and a more stable developing potential can be applied to the toner carrier.

In order to solve the above problems, the developing device of the present invention preferably further comprises a voltage applying means for applying a voltage to the charge eliminating member, and the voltage applied to the charge eliminating member is applied to the charge eliminating member. Assuming that the voltage to be applied is Ve, the desired surface potential of the toner carrier is Vd, and the discharge starting voltage between the toner carrier and the charge removing member is Vth, Ve = Vd + Vth is set.

According to the above configuration, by setting the voltage to the above-described value, the dielectric layer can be effectively neutralized by using a discharge phenomenon between the neutralizing member and the dielectric layer. The surface of the subsequent toner carrier can be set to a desired development potential. Therefore, a desired development potential can be more stably maintained.

In order to solve the above-mentioned problems, the developing device of the present invention preferably further comprises a voltage applying means for applying a superimposed voltage, which is obtained by superimposing an AC voltage on the DC voltage, to the discharging member, When the DC voltage is Vddc, the peak-to-peak voltage of the AC voltage is Vpp, the desired surface potential of the toner carrier is Vd, and the discharge start voltage between the toner carrier and the charge removing member is Vth, the AC voltage is Vddc +
(1/2) Difference between Vpp and Vd, and Vddc−
(1/2) At least one of the differences between Vpp and Vd is Vt
h.

According to the above configuration, by setting the DC voltage and the AC voltage to the above-described settings, the dielectric layer can be effectively neutralized by using a discharge phenomenon between the neutralizing member and the dielectric layer. The difference between the DC voltage and the potential of the toner carrier surface after static elimination can be reduced by making the DC voltage a value equal to or close to a desired development potential (the desired toner carrier potential). This makes it possible to bring the dielectric layer after static elimination closer to a desired development potential. As a result, the desired development potential can be stably maintained without being affected by charge injection due to aging or environmental fluctuation.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] An embodiment of the present invention will be described with reference to FIGS.
It is as follows.

As shown in FIG. 1, the developing device 1 of this embodiment is a developing device for developing an electrostatic latent image held on the surface of a photosensitive drum (image carrier) 30 with toner. A developing roller (toner carrier) 2 for carrying and developing the supplied toner 7 (hereinafter abbreviated as toner) on the photosensitive drum 30 while holding the toner 7 on the surface thereof; A toner layer thickness regulating member for regulating the thickness of the toner so as to form a layer having a desired thickness while contact-charging the toner.

In the present embodiment, a non-magnetic one-component toner having a resistivity in a pellet state of about 10 ¹⁰ Ω · cm, which is generally called a high-resistance toner, is used as the toner. The present invention is particularly effective for high-resistance toners, but is also effective for other toners. As the toner, those produced by the following method are preferable. That is, first, a polyester resin or a styrene-acryl copolymer (styrene- (meth) acrylate copolymer) 80 to 9 as a binder resin (base resin)
0 parts by weight and carbon black 4 to 10 as a colorant
Parts by weight are melt-kneaded, and if necessary, an appropriate amount of 5 parts by weight or less of a charge control agent (CCA) or a small amount of a vulcanization control agent is blended to obtain pellets. Next, the obtained pellets are pulverized, and the volume average particle diameter is adjusted by classification so that particles having a desired volume average particle diameter are obtained. Then, about 0.2 to 2 parts by weight of an external additive such as silica is added. Mix. The developing roller 2 includes
A developing bias voltage E1 is applied from a power supply 9 via a conductive shaft 21 (described later).

The developing roller 2 holds the supplied toner as a toner layer T on the surface thereof, and rotates at a different peripheral speed from the photosensitive drum 30 while making contact with the photosensitive drum 30 via the toner layer T. By doing so, the toner is conveyed onto the photosensitive drum 30.

As shown in FIG. 2, the developing roller 2 is formed by winding a conductive base material 22 having elasticity on a conductive shaft (core metal) 21 made of metal such as stainless steel or conductive resin. The dielectric layer 23 is formed thereon. The electric resistance of the conductive substrate 22 can be adjusted by a resistance adjusting material. In the present invention, the toner carrier is not limited to the developing roller 2 having the shape shown in FIG. 2 as long as a dielectric layer is provided on a conductive base material having elasticity. An endless belt having a dielectric layer formed on a conductive rubber sheet may be used.

The conductive substrate 22 has a volume resistivity of 10 ⁴ to 10 ⁴ .
It is preferable to use a conductive elastic member of about 10 ⁶ Ω · cm. Examples of the material forming the conductive base material 22 include elastic materials such as ethylene-propylene-diene copolymer (EPDM), urethane rubber, silicone rubber, nitrile butadiene rubber, and butadiene rubber; A dispersion-type resistance-adjusting resin in which fine particles and / or carbon are dispersed and mixed; at least one ionic conductive material (for example, an inorganic ionic conductive material such as sodium perchlorate, calcium perchlorate, sodium chloride, etc.) is used as an elastic material And an electric resistance adjusting resin dispersed therein. These resins may be foamed resins by foaming and mixing using a foaming agent. In this case, silicone resin such as polydialkylsiloxane or polysiloxane-polyalkylene oxide block copolymer is used as the foaming agent. It is preferable to use a system surfactant.

A toner replenishing roller 3 for supplying the toner in the toner tank 6 to the developing roller 2 and agitating the toner in the toner tank 6 and removing the toner after the development is pressed against the developing roller 2. . The toner replenishing roller 3 rotates in a direction opposite to the developing roller 2 at a portion facing the developing roller 2. Toner supply roller 3
Is made of a conductive elastic material similar to the conductive rubber forming the developing roller 2, and similarly to the developing roller 2, the electric resistance can be adjusted by a resistance adjusting material. The elastic material forming the toner supply roller 3 is
It is preferable that the material is foamed by using more foaming agent than the elastic material forming the developing roller 2 so that the elasticity is larger than the elastic material forming the developing roller 2.

A bias voltage E2 is applied to the toner supply roller 3 from a power supply 10, which is a bias power supply.
The bias voltage E2 is a bias voltage in a direction of electrically pushing the toner toward the developing roller 2, and is, for example,
In the case of a negative polarity toner, a larger bias voltage is applied to the negative electrode side.

The toner layer thickness regulating member 4 has a cantilever leaf spring structure having a free end on the upstream side in the rotation direction of the developing roller 2, and the leading end or the abdomen near the leading end is pressed against the developing roller 2. The toner layer thickness regulating member 4 is formed of a conductive plate-like elastic material made of stainless steel, conductive resin, or the like. The toner layer thickness regulating member 4 adjusts the pressure and the arrangement position of the pressure contact with the developing roller 2 so that the toner supplied to the developing roller 2 becomes a toner layer of a predetermined thickness having a predetermined charge amount. T can be regulated. A bias voltage E3 is applied to the toner layer regulating member 4 from the power supply 11.

At the lower portion of the developing device 1 facing the surface of the developing roller 2 after the developing process, a sheet-shaped discharging member 5 having a discharging function for discharging the developing roller 2 from a seal for preventing leakage of toner is provided. Is installed. The static elimination member 5
At least one surface is formed of a conductive material, and a power supply (voltage applying means) 12 applies a voltage E4 having the same potential as the supply voltage to the developing roller 2 or a polarity E4 in the direction of reducing the charged potential of the dielectric layer to the conductive voltage. By applying the material to the material and bringing the conductive material into contact with the developing roller 2, a charge removing function is provided. As the charge removing member 5, a member provided with an aluminum vapor-deposited film on a resin film made of polyethylene terephthalate or the like is preferable.

As described above, in the present embodiment, in order to reduce the number of members, the charge eliminating member is also provided with a function as a seal. However, it is also possible to provide the static elimination member and the seal independently. In some cases, the charge removing member can be omitted.

In the photosensitive drum 30, an underlayer (underlayer) is formed on a drum-shaped conductive substrate made of metal or conductive resin, and a carrier generation layer (C) is formed on the underlayer.
A carrier transport layer (GL) is formed, and a carrier transport layer (CTL) using polycarbonate as a binder resin as a main component is formed as an outermost layer on the carrier generation layer. Each of the above layers is formed by being applied, and has a thin film shape.

The image bearing member to which the present invention is applied is not limited to the photosensitive drum 30 having the above-described structure as long as it can hold an electrostatic latent image. Therefore, an image carrier having another shape such as a sheet-shaped photoconductor may be used, or an image carrier having another layer configuration such as a photoconductor provided with a protective layer in addition to the above layers may be used. Is also good. Further, another resin, for example, polyester or methacrylic resin may be used as the binder resin of the carrier transport layer.

Next, the operation of toner transport and image formation by the developing device 1 having the above configuration will be described.

First, the toner stored in the toner tank (hopper) 6 is conveyed to the vicinity of the toner supply roller 3 by the agitator 8 or the screw. Next, the toner conveyed to the vicinity of the toner replenishing roller 3 is frictionally charged (preliminarily charged) by the toner replenishing roller 3, and is applied to the surface of the developing roller 2 by a bias voltage between the toner replenishing roller 3 and the developing roller 2. Applied. The toner supplied to the developing roller 2 is conveyed to the position of the toner layer thickness regulating member 4 by the rotation operation of the developing roller 2. The toner supplied to the developing roller 2 is regulated by the toner layer thickness regulating member 4 so as to have a prescribed charge amount and a prescribed thickness (that is, a prescribed amount of adhered toner). ), And is used in a developing step described later.

Developing roller 2 not used in developing step
The upper undeveloped toner returns to the developing device 1 from the developing area by the rotation of the developing roller 2. After that, the undeveloped toner is charged by the charge removing member 5 on the developing roller 2 installed in front of the toner replenishing roller 3, and then the toner replenishing roller 3 is brought into contact with the toner replenishing roller 3 at the entrance of the contact portion. And is recovered by the toner tank 6 and reused.

On the other hand, before the developing step, an electrostatic latent image is formed on the surface of the photosensitive drum 30 as follows. That is, first, the surface of the photosensitive drum 30 is uniformly charged to a desired potential in advance by a charger (corona charger or contact roller charger) not shown. Thereafter, the uniformly charged charged potential (charge) on the surface of the photosensitive drum 30 is exposed to a desired pattern by a separately provided exposure device (not shown). As a result, carriers are generated from the carrier generation layer at the exposed positions of the photosensitive drum 30, and the charged potential is canceled. As a result, an electrostatic potential pattern, that is, an electrostatic latent image is formed on the surface of the photosensitive drum 30. In the exposure, lamp light is used in an analog machine, while laser light is generally used in a digital machine.

Next, the electrostatic latent image formed on the photosensitive drum 30 is transferred to the developing roller 2 by rotation of the photosensitive drum 30.
Is transported to a region (developing region) facing the developing device, and a developing process is performed. In the developing step, the electrostatic latent image is subjected to contact reversal development using toner. That is, when the photosensitive drum 30 on which the electrostatic latent image is formed is pressed by the developing roller 2 in the developing area, the toner, which has been controlled to a predetermined charge amount and thickness in advance as described above, It moves to the photosensitive drum 30 according to the latent image. Thus, the electrostatic latent image is visualized (developed) to form a toner image.

The toner image formed on the photosensitive drum 30 in the developing step is conveyed to a transfer area where a transfer device (not shown) is installed by rotation of the photosensitive drum 30. In synchronization with this, a recording medium such as paper supplied by a paper feeding device (not shown) is conveyed to the transfer area.
As a result, the recording medium comes into contact with the toner image on the photosensitive drum 30 in synchronization. Then, by applying a voltage in the polarity direction on the side of moving the toner on the photosensitive drum 30 to the recording medium by the transfer device to the transfer area, the toner image on the photosensitive drum 30 moves on the recording medium, that is, Transcribed. The transfer device includes a charger type and a contact roller type provided with a high-voltage power supply, and any type may be used.

Thereafter, the recording medium to which the toner image has been transferred is generally melted and fixed on the recording medium by a heat fixing device (not shown), and discharged by a discharge device (not shown).

On the other hand, untransferred toner remaining on the photosensitive drum 30 after passing through the transfer area is removed from the photosensitive drum 30 by a cleaner (not shown). Also,
The surface of the photosensitive drum 30 from which the untransferred toner has been removed is refreshed in potential by a light discharging lamp or contact discharging means for erasing (removing) residual charges, and is reused for the first charging by the charger.

Next, the dielectric layer 23 having an optimum thickness, which is a feature of the present invention, will be described.

The dielectric layer 23 has a volume resistivity of 10 ¹⁰ -1.
It is preferable that the resistivity is 0 ¹⁵ Ω · cm and the relative dielectric constant is about 3 to 10. Further, as a dielectric for forming the dielectric layer 23, an ethylene-tetrafluoroethylene copolymer (ETF) is used.
E), fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are preferred, and polyvinylidene fluoride (PVDF) is particularly preferred.

When the thickness of the dielectric layer 23 is A and the volume average particle diameter of the toner is R, the following equation is obtained: 2 × R ≦ A ≦ 10 × R (1) It is set to meet. This allows both fine line reproducibility and solid portion gradation reproducibility to be compatible,
A change in development potential due to charging of the dielectric layer 23 can be suppressed, and image uniformity can be improved.

In order to adjust the thickness of the dielectric layer 23 so as to satisfy the expression (1), the dielectric layer 23 may be formed by spray-coating the above dielectric substance a plurality of times.

Embodiment 2 Another embodiment of the present invention will be described below with reference to FIGS. 3 and 4. For the sake of convenience, members having the same functions as those described in the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

By the way, in the first embodiment,
Although the developing potential did not fluctuate much due to the charging of the dielectric layer 23 of the developing roller 2, in rare cases, the sheet-like static eliminator 5 as in the first embodiment is replaced with the sheet-like neutralizer 5.
In some cases, it is difficult to maintain a good contact state between the dielectric layer 23 of the developing roller 2 and the charge removing member 5 over the entire area of the developing roller 2 due to undulation or variation in the thickness of the intervening toner layer T.

In such a case, static elimination of the dielectric layer 23 by the static elimination member 5 is not effectively performed, and it becomes difficult to apply a stable developing potential. If the contact pressure of the charge removing member 5 with respect to the developing roller 2 is increased, the contact state can be improved. However, in this case, damage to the developing roller 2 and adhesion of toner to the charge removing member 5 tend to occur. Not a very good technique.

Therefore, in the developing device 31 of the present embodiment, as shown in FIG. 3, in the developing device 1 of the first embodiment, the conductive brush 16 made of an aggregate of conductive fibers is used instead of the charge removing member 5. Is disposed, and the seal is made independent as the seal 18. The aggregate of the conductive fibers is fixed by being planted on the surface of a band-shaped base fabric made of insulating fibers such as rayon and polyester fibers. As the conductive fiber, a dispersion of carbon in rayon (trade name “REC” manufactured by Unitika Ltd.),
An example in which a nylon film is formed on a conductive yarn (manufactured by Kanebo Co., Ltd., trade name "Beltron") is exemplified. Also,
As shown in FIG. 4, the conductive brush 16 is provided on a plate-shaped conductive base material 17 made of metal or conductive resin so that electrical conduction can be obtained. Further, a voltage equal to a desired surface potential (development potential) of the developing roller 2 is applied to the conductive substrate 17.

In this embodiment, the brush-like charge removing member 1 is used.
By using No. 5, compared to Embodiment 1 using sheet-like static elimination member 5, even if toner layer T is interposed or a relatively small contact pressure, a good contact state is maintained. be able to. In other words, the conductive fibers pass through the gap between the toner and come into contact with the developing roller 2, and a static elimination effect is obtained near the contact portion. Furthermore, since it is fibrous, its flexibility allows the fiber tip to move relatively freely. Therefore, the surface of the developing roller 2 can be uniformly discharged. Therefore, a uniform charge eliminating effect can be obtained over the entire area of the developing roller 2 without toner adhesion or damage to the developing roller 2, and stable development potential can be applied.

[Third Embodiment] The following will describe another embodiment of the present invention. Note that, for convenience of description, a description of members having the same functions as the members described in the first and second embodiments will be omitted.

Incidentally, depending on the combination of other members (toner layer thickness regulating member 4, toner replenishing roller 3, photosensitive drum 30, etc.) which come into contact with dielectric layer 23, dielectric layer 2
In some cases, charging of No. 3 becomes large. In such a case,
According to the study by the inventors of the present application, a sufficient static electricity removing effect cannot be obtained only by applying a DC voltage having the same potential as a desired developing potential to the static electricity removing members 5 and 15 as in the first and second embodiments. It has been found.

The reason is considered as follows. That is, under a condition where the potential difference between the charge removing members 5 and 15 and the dielectric layer 23 is relatively small, a charge removing effect is obtained by utilizing the phenomenon of charge injection from the charge removing members 5 and 15. The charge removal effect due to the charge injection decreases as the contact interface resistance increases. In this case, the dielectric layer 23 of the developing roller 2
Has a very high resistance, and the static elimination members 5 and 15 and the dielectric layer 2
3, the charge removal effect by charge injection is low, and the charge removal efficiency is poor.

Therefore, in the present embodiment, in each of the first and second embodiments, a voltage including an AC component is applied to the charge eliminating members 5 and 15 instead of a DC voltage.

As a result, the contact interface resistance (impedance) is reduced by an amount corresponding to 1 / Cω (ω = 2πf, where f is the frequency of the AC voltage and C indicates the capacitance of the contact interface). As a result, the charge removal effect by charge injection can be improved, and the dielectric layer 23 can be charge removed efficiently. That is, the charge of the dielectric layer 23 can be reduced by using the AC voltage. Therefore, the development potential can be made closer to a desired potential.

[Fourth Embodiment] The following will describe another embodiment of the present invention. Note that, for convenience of description, a description of members having the same functions as the members described in the first and second embodiments will be omitted.

Incidentally, depending on the combination of other members (toner layer thickness regulating member 4, toner replenishing roller 3, photosensitive drum 30, etc.) that come into contact with dielectric layer 23, dielectric layer 2
In some cases, charging of No. 3 becomes large. In such a case,
According to the study by the inventors of the present application, a sufficient static electricity removing effect cannot be obtained only by applying a DC voltage having the same potential as a desired developing potential to the static electricity removing members 5 and 15 as in the first and second embodiments. It has been found.

The reason is considered as follows. That is, under a condition where the potential difference between the charge removing members 5 and 15 and the dielectric layer 23 is relatively small, a charge removing effect is obtained by utilizing the phenomenon of charge injection from the charge removing members 5 and 15. The charge removal effect due to the charge injection decreases as the contact interface resistance increases. In this case, the dielectric layer 23 of the developing roller 2
Has a very high resistance, and the static elimination members 5 and 15 and the dielectric layer 2
3, the charge removal effect by charge injection is low, and the charge removal efficiency is poor.

Therefore, in the present embodiment, a discharge phenomenon, specifically, a Paschen discharge in a minute gap is used as an action for obtaining a charge eliminating effect.

That is, in this embodiment, in Embodiments 1 and 2, the voltage value applied to the charge eliminating members 5 and 15 is Ve, the desired surface potential of the developing roller 2 is Vd, and the developing roller 2 and the charge eliminating member The voltage was set so that Ve = Vd + Vth when the discharge starting voltage between the two in the atmosphere surrounding 5.15 was Vth. Thereby, a favorable static elimination effect was obtained.

Here, the discharge starting voltage Vth is a value measured as follows. That is, first, the developing roller 2 and the charge removing member 5
In this state, a voltage is applied between the developing roller 2 and the charge removing members 5 and 15, and the applied voltage is changed to measure a change in the surface potential on the developing roller 2. FIG. 5 shows the relationship between the applied voltage and the surface potential of the developing roller 2. Here, a dielectric layer 2 having a thickness of 20 μm and a relative dielectric constant of about 3 is used.
3 shows an example in which a brush-like static elimination member 15 is used.

The value of the applied voltage when the rate of change (gradient) of the surface potential on the developing roller 2 changes discontinuously is defined as a discharge starting voltage Vth. That is, in FIG.
Although two linear relationships are recognized at a certain voltage, in the region where the applied voltage is low (region where the gradient is small), the dielectric layer 23 is charged by charge injection, and the region where the applied voltage is high (region where the gradient is large). In (), it is considered that the dielectric layer 23 is charged by Paschen discharge. Therefore, the voltage value at the intersection of the two straight lines is considered to be the applied voltage at which Paschen discharge occurs for the first time. Therefore, the voltage value at the intersection of these two straight lines is defined as the discharge start voltage Vth.

FIG. 5 shows a discharge start voltage Vth on the positive polarity side (hereinafter referred to as a positive discharge start voltage Vth ₊ ).
It is. Although not shown, the discharge start voltage Vth when changing the applied voltage to the negative polarity side (hereinafter, a negative discharge start voltage Vth _- hereinafter) is, in the present embodiment, the above discharge start voltage Vth ₊ Although the sign was different, the magnitude was almost equal to the positive discharge starting voltage Vth ₊ . Therefore, when the charge potential Vc of the dielectric layer 23 is positive, Ve = Vd + Vth _- when charge potential Vc of the dielectric layer 23 is negative, the Ve to satisfy Ve = Vd + Vth ₊ is set .

Next, the effect of the present embodiment will be described in the case where a voltage Ve = Vd + Vth ₊ is applied to the charge removing member 15 in a state where the desired developing potential Vd is negative and the charging potential Vc of the dielectric layer 23 is negative. Consider using FIG.

In this case, in the initial state, as shown in FIG. 6, the surface potential of the developing roller 2 is Vd + Vc. Therefore, the potential difference between the developing roller 2 and the charge removing member 15 (the difference between the surface potential of the developing roller 2 and the voltage applied to the charge removing member 15) is Ve− (Vd + Vc) = Vth ₊ −Vc,
Since the voltage becomes higher than the positive discharge start voltage Vth ₊ , Paschen discharge occurs. This discharge continues until the potential difference between the developing roller 2 and the charge removing member 15 becomes equal to or less than the positive discharge start voltage Vth ₊ . That is, the surface potential of the developing roller 2 at the time the discharge is finished, Ve = Vd + Vth _- become. Therefore, the electric potential of the developing roller 2 can be rapidly eliminated by the Paschen discharge until the electric potential of the developing roller 2 reaches a desired electric potential Vd of the developing roller 2. Therefore, a desired development potential can be more stably maintained.

In FIG. 6, the case where the charging potential of the dielectric layer 23 is negative has been described.
The same effect can be obtained when the is charged to the positive polarity. Desired surface potential Vd of the developing roller 2 is negative, while the charge potential Vc is positive dielectric layer 23, the voltage Ve = Vd + Vth the neutralizing member 15 _- in the case of applying the, consider the effect.

In this case, in the initial state, the surface potential of the developing roller 2 is Vd + Vc. Therefore, the potential difference between the developing roller 2 and the charge removing member 15 is (Vd + Vc) −Ve =
−Vth ₋ + Vc, the absolute value of which becomes higher than the negative discharge starting voltage Vth ₋ , Paschen discharge occurs. The discharge firing voltage potential difference is negative between the developing roller 2 and the charge removing member 15 Vth _- continues until below. That is, the surface potential of the developing roller 2 at the time when the discharge ends is Ve−Vth ₋ = Vd. Therefore, the electric potential of the developing roller 2 can be rapidly eliminated by the Paschen discharge until the electric potential of the developing roller 2 reaches a desired electric potential Vd of the developing roller 2. Therefore, a desired development potential can be more stably maintained.

[Fifth Embodiment] Another embodiment of the present invention will be described below. Note that, for convenience of description, a description of members having the same functions as the members described in the first and second embodiments will be omitted.

In the fourth embodiment, when the potential difference between the charge removing members 5 and 15 and the developing roller 2 becomes the discharge starting voltage Vth due to the discharge, the charge between the charge removing members 5 and 15 and the developing roller 2 is reduced. Has been almost eliminated, and it has been described that the surface potential of the developing roller 2 becomes the desired surface potential Vd of the developing roller 2.

However, an increase in the potential of the dielectric layer 23 caused when a DC voltage equal to or lower than the discharge starting voltage Vth is applied to the charge removing members 5 and 15, that is, an amount of change in the potential (charge) of the surface of the developing roller 2 due to charge injection. As shown in FIG. 7, the amount of injection may increase due to environmental fluctuations such as a high-humidity environment or a temporal change of the dielectric layer 23. Therefore, when the charge injection amount increases due to the environmental change and the aging of the dielectric layer 23 as described above, even if the discharge is completed, the charge injection phenomenon due to the potential difference of the discharge start voltage Vth as shown in FIG. , The potential on the developing roller 2 is
15 may approach the DC component (Ve) of the applied voltage. Therefore, as in the fourth embodiment, the static elimination member 5
If the difference between the DC component voltage value Ve of the voltage applied to 15 and the potential of the surface of the developing roller 2 is large, the dielectric layer 23
The potential change due to the charge injection is likely to increase due to the change over time and the environmental change.

Therefore, in the present embodiment, in Embodiments 1 and 2, a superimposed voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charge eliminating members 5 and 15, and the DC voltage is Vddc, and the AC voltage is Where Vpp is the peak-to-peak voltage, Vd is the desired surface potential of the developing roller 2, and Vth is the discharge starting voltage between the two in the atmosphere surrounding the developing roller 2 and the neutralizing members 5.15.
The difference between Vd and at least one of (1/2) Vpp and Vddc- (1/2) Vpp is set to Vth or more. Further, the voltage value Vddc of the DC component of the voltage applied to the charge removing members 5 and 15 is set such that the difference from the desired surface potential Vd of the developing roller 2 is smaller than when only the DC voltage is applied. ing.

As a result, the difference between the voltage value Vddc of the DC component of the voltage applied to the charge removing members 5 and 15 and the potential of the surface of the developing roller 2 is reduced, and the potential change due to the aging of the dielectric layer 23 and environmental fluctuation is reduced. Can be suppressed.

Next, the effect of the present embodiment will be discussed with reference to FIG. 9 in the case where the desired surface potential Vd of the developing roller 2 is negative and the charging potential Vc of the dielectric layer 23 is negative. In the initial state, as shown in FIG. 9, the surface potential of the developing roller 2 is Vd + Vc.

Then, (Vd
(dc + Vpp / 2) -Vd> Vth is applied so that the potential difference between the charge removing members 5.15 and the developing roller 2 is set to be larger than the discharge starting voltage Vth.

By applying such a voltage to the charge removing members 5 and 15, the voltage applied to the charge removing members 5 and 15 increases to the positive polarity side, and the surface potential of the developing roller 2 and the charge removing members 5 and 15 are increased.
The discharge is started when the potential difference from 15 becomes equal to or higher than the discharge start voltage Vth, and the surface potential of the developing roller 2 becomes Vd.
The static elimination by discharging is performed until dc + Vpp / 2−Vth. Thereafter, when the voltage value applied to the charge removing members 5 and 15 passes the peak on the positive polarity side, the potential difference between the surface potential of the developing roller 2 and the charge removing members 5 and 15 decreases and falls below the discharge start voltage Vth. Therefore, the discharge stops. Thereafter, by the voltage of the AC component, charges are exchanged between the surface of the developing roller 2 and the charge removing members 5 and 15 by charge injection, and the potential of the surface of the developing roller 2 is made uniform while repeatedly increasing and decreasing finely. Then, the voltage approaches a desired value between the surface potential Vd of the developing roller 2 and the voltage value Vddc of the DC component of the voltage applied to the charge removing members 5 and 15.

In this case, the difference between the surface potential of the developing roller 2 after the end of the discharge and the voltage value of the DC component to the charge removing members 5 and 15 is very small. Even if the charge injection amount changes due to the influence of the environment, the change has little effect on the surface potential of the developing roller 2. Therefore, it is possible to suppress a change in the surface potential of the developing roller 2 due to an influence of an environment such as a temporal change of the dielectric layer 23 and humidity, and to apply a stable developing potential to the developing roller 2.

[0080]

EXAMPLES [Examples 1 to 6 and Comparative Examples 1 to 6] The developing device 1 described in the first embodiment will be described in more detail based on specific examples. The device configuration and various conditions in this example and comparative examples are described below.

As the toner, 80 to 90 parts by weight of a polyester resin as a binder resin is added with carbon black 4
A negatively charged non-magnetic one-component toner to which 10 to 10 parts by weight and 5 parts by weight of a charge control agent (CCA) were added was used.

The developing roller 2 is a roller having a diameter of 34 mm, and has a peripheral speed Vb = 130 mm / in the direction of the arrow shown in FIG.
Spinning at s. The developing roller 2 has a nip width W
Is in contact with the photosensitive drum 30 via the toner layer so that the distance is 2 mm. The developing bias voltage E1 applied from the power supply 9 to the developing roller 2 was set to -300V.

The conductive shaft 21 of the developing roller 2 has a diameter of 10 mm and is made of metal such as stainless steel. As the conductive substrate 22, an elastic member having a volume resistivity of about 10 ⁴ to 10 ⁶ Ω · cm in which carbon is dispersed in urethane rubber is used. As the dielectric layer 23, polyvinylidene fluoride (PVDF) is spray-coated on the conductive base layer 102 a plurality of times, and a desired layer thickness, preferably 1
What was formed to 150 μm was used.

The toner supply roller 3 has a volume resistivity of about 10
A roller having a diameter of 20 mm made of conductive urethane foam having a resistance of ⁵ Ω · cm and a cell density of about 3 to 4 cells / mm.
It rotates at a peripheral speed Vc = 160 mm / s in the direction of the arrow shown in FIG. A power supply 10 is connected to the toner supply roller 3 via a conductive shaft such as stainless steel or conductive resin.
, A supply bias voltage E2 = −400 V was applied.

The material constituting the toner supply roller 3 is 5 parts by weight or more per 100 parts by weight of polyurethane.
After mixing 5 parts by weight or less (in some cases, about 70 parts by weight) of carbon black and stirring and whipping with a whipping machine,
A conductive sponge which was heated and blown to form a sponge around a metal shaft of a cored bar was used. As carbon black, the nitrogen adsorption specific surface area is 20 m ² / g or more and 130 m ² / g or more.
m ² / g or less, DBP oil absorption 60 ml / 100 g or more 1
20 ml / g or less of carbon black, for example, ISA
F (semi-wear resistance), HAF (high wear resistance), GPF (general-purpose properties), SRF (medium reinforcement properties), etc. were used. As the polyurethane, a flexible polyurethane foam or a polyurethane elastomer is suitable. Further, the electric resistance of the conductive sponge is preferably 10 ⁵ Ω · cm or less. In this embodiment, the conductive sponge has a thickness of 6
mm, a sponge having a cell density of about 3 to 4 cells / mm, a sponge density of 0.1 g / cm ³ , and a hardness of 68 degrees (Asker F) (“E” manufactured by Bridgestone Corporation, a commercial product)
PT urethane conductive sponge ") was used.

Both the developing roller 2 and the toner replenishing roller 3 have been finished so as to have desired surface properties and outer dimensions by polishing the outer diameter with a grindstone after injection and heat molding. .

The toner layer regulating member 4 is a leaf spring made of stainless steel having a thickness of 0.1 mm. The bias voltage E3 applied from the power supply 11 to the toner layer regulating member 4 is:
It was set to -350V.

As the charge removing member 5, a 0.1 mm thick polyethylene terephthalate (PET) film provided with an aluminum vapor-deposited film was used, and the vapor-deposited surface of the aluminum vapor-deposited film was in contact with the developing roller 2. The voltage E4 supplied from the power supply 12 to the deposition surface of the aluminum deposition film was set to -300V.

The photosensitive drum 30 is a negatively charged photosensitive drum having a diameter of 55 mm and a surface potential charged to -700 V, and a peripheral speed Vp = 100 mm / in the direction of the arrow shown in FIG. Spinning at s.

In the present embodiment and the comparative example, the thickness of the toner layer formed on the developing roller 2 was adjusted so that the thickness of the toner layer was about twice the particle diameter of the toner.

In this example and the comparative example, as shown in Table 1, the volume average particle size (hereinafter, simply referred to as the particle size) was 4 μm.
In the case of using two kinds of toners, i.e., a toner having a particle diameter of 10 μm and a toner having a particle diameter of 4 μm, the thickness of the dielectric layer 23 of the developing roller 2 is set to 2 μm, 4 μm,
m, 20 μm, 40 μm, and 80 μm,
For an example using a toner having a particle size of 10 μm, the thickness of the dielectric layer 23 of the developing roller 2 is set to 5 μm, 10 μm, and 20 μm.
m, 50 μm, 100 μm, and 200 μm.

Table 1 summarizes the experimental conditions. Also,
Table 1 shows the results of evaluating whether or not the reproducibility of fine line reproducibility and the tone reproducibility of a solid portion can be achieved satisfactorily by ○ (good) and × (poor).

[0093]

[Table 1]

Then, development was performed under each condition, and development characteristics of isolated fine lines and dots and development characteristics of a solid pattern (solid portion) were measured. The image density of the solid portion is determined by X-write (X-Rite).
310 (manufactured by X-rite). On the other hand,
The image density of the dots was determined by taking in image data using an image processing apparatus (“VH-7000” manufactured by Keyence Corporation) and performing processing with a personal computer.

FIG. 10 shows the results when the toner having a particle size of 4 μm was used (Examples 1 to 3 and Comparative Examples 1 to 3).
FIG. 10 shows the values of the maximum density of the solid portion as thin lines and thin lines.
The maximum values of the dot densities are matched and shown as relative values.

As can be seen from the broken lines in FIG. 10, the development γ characteristics of the isolated fine lines and dots did not change significantly in each case, and the sharpness of the fine lines and dots was good. In contrast, as can be seen from the solid line in FIG. 10, the development γ characteristic in the solid portion greatly changed depending on the thickness of the dielectric layer 23.

That is, when the thickness of the dielectric layer 23 is less than twice the particle diameter of the toner (Comparative Examples 1 and 2), the development γ characteristic of the solid portion is almost the same as that of an isolated fine line or dot pattern, and Was inferior.

On the other hand, the condition that the thickness of the dielectric layer 23 is twice or more the toner particle size (Examples 1 to 3 and Comparative Example 3)
In, the development γ characteristic of the solid portion showed a gradual change, and good gradation was obtained.

However, if the thickness of the dielectric layer 23 is too large (Comparative Example 3), the developing γ characteristic in the solid portion becomes too gentle, and the developing potential at which fog does not increase (in this case, -450 V or less) As a result, a problem that the maximum density cannot be obtained occurs. It has been found that this problem occurs when the thickness of the dielectric layer 23 is greater than 10 times the particle size of the toner. Further, when the thickness of the dielectric layer 23 is larger than 10 times the particle diameter of the toner,
A change in the developing potential due to the charging of the toner image appeared, and the uniformity of the image deteriorated.

When a toner having a particle size of 10 μm was used (Examples 4 to 6 and Comparative Examples 4 to 6), the toner having a particle size of 4 μm was used.
(Examples 1 to 3 and Comparative Examples 1 to 3)
The same result as in 3) was obtained.

Therefore, when these results are summarized,
When the thickness of the dielectric layer 23 is less than twice the particle size of the toner (Comparative Examples 1, 2, 4, and 5) or when the thickness of the dielectric layer 23 exceeds 10 times the particle size of the toner (Comparative Example) In 3.6), as shown in Table 1, the reproducibility of fine lines (sharpness of fine lines) and the gradation reproducibility of solid portions cannot be compatible. Further, when the thickness of the dielectric layer 23 exceeds 10 times the particle diameter of the toner (Comparative Examples 3 and 6), the uniformity of the image deteriorates. On the other hand, in the present invention, as in Examples 1 to 6, the thickness of the dielectric layer 23 is set to be twice or more and 10 times or less of the particle diameter of the toner, so that the fine line reproducibility and the tone reproduction of the solid portion are reproduced. , And a change in development potential due to charging of the dielectric layer 23 can be suppressed, and the uniformity of an image can be improved.

The reason for obtaining such a result is that the thickness of the dielectric layer 23 changes the width of the region where the edge emphasizing electric field acts to change the fine line reproducibility. It is considered that even if the thickness of the dielectric layer 23 is small, the effect of the dielectric layer 23 may be exhibited.

Therefore, when the thickness of the dielectric layer 23 is A and the particle size of the toner is R, the A / R is in the range of 2 to 10, that is, 2 × R ≦ A ≦ 10 × It has been found that by setting the thickness of the dielectric layer so as to satisfy R, it is possible to achieve both fine line reproducibility and solid portion gradation reproducibility and improve the uniformity of the image.

[Embodiment 7] With respect to the developing device 31 described in the second embodiment, the result of confirming the effect of the specific example will be described below. Note that the device configuration and various conditions in this embodiment are the same as those in Embodiments 1 to 6 except that a static elimination member 15 and a seal 18 are used instead of the static elimination member 5.

In the present embodiment, as the conductive fiber constituting the conductive brush 16 of the charge removing member 15, carbon fiber dispersed in rayon (trade name “R” manufactured by Unitika Ltd.)
EC ") was used. The thickness of the conductive fiber is 20-30μ
m, flocking density of conductive fiber is 100,000 / inch ²
The length of the conductive fiber was about 5 mm. The resistivity of the conductive fiber is such that when the metal electrode is pressed against the conductive brush 16 and a voltage of about 10 to 1000 V is applied to the metal electrode so as to have a bite amount of about 0.5 to 1 mm, Was set so that the resistance value of the sample was about 10 ³ to 10 ⁸ Ω. The same voltage as the desired development potential, that is, -300 V, was applied to the conductive substrate 17 of the charge removing member 15.

In this embodiment, the toner is fixed and the developing roller 2
It was confirmed that a uniform charge eliminating effect was obtained over the entire area of the developing roller 2 without any damage to the developing roller 2 and stable development potential application was possible.

[Embodiment 8] With respect to the developing device described in the third embodiment, the result of confirming the effect of the specific example will be described below. Note that the device configuration and various conditions in the present embodiment are the same as those in the first embodiment except that a static elimination member 15 and a seal 18 are used instead of the static elimination member 5.

In the first to sixth and seventh embodiments, a desired developing potential is applied to the charge eliminating members 5 and 15 as a DC voltage component, and a peak-to-peak voltage Vp is applied as an AC voltage component.
When a voltage of p = 400 V and a frequency of 1 kHz is applied, the development potential can be made closer to a desired potential as compared with a case where only a DC voltage component is applied (Examples 1 to 6 and Example 7). Admitted.

[Embodiment 9] In this embodiment, the thickness is 20 μm.
m, using a dielectric layer 23 having a relative dielectric constant of about 3, and using the same developing apparatus as in Example 7 except that the voltage applied to the charge removing member 15 was set as shown in Embodiment 3. The effect of mode 4 was confirmed.

In the present embodiment, the discharge starting voltage Vth ₊ when the applied voltage was changed to the positive polarity side was about 470 V as shown in FIG. Although not shown, the discharge starting voltage Vth when the applied voltage was changed to the negative polarity was of the opposite polarity and almost the same value.

In the developing device of this embodiment, the initial charging potential Vc of the dielectric layer 23 was -200V. Further, the desired development potential Vd was set to -300V. In this embodiment, Ve = Vd + Vth ₊ = − 300 is applied to the charge removing member 15.
An applied voltage of + 470 = + 170 V was applied.

As a result, the potential difference between the developing roller 2 and the charge removing member 15 in the initial state was 670 V, which was larger than the positive-side discharge starting voltage, so that Paschen discharge occurred. This discharge is performed when the potential difference between the developing roller 2 and the charge removing member 15 is changed to the discharge start voltage Vth ₊ (= 470) on the positive polarity side.
V). That is, the surface potential of the developing roller 2 at the end of the discharge is (voltage applied to the neutralizing member 15) − (positive discharge start voltage) = 170−
470 = −300, and a desired potential of the developing roller 2 was obtained.

Therefore, it is found that the potential of the developing roller 2 can be quickly eliminated by the Paschen discharge until the potential of the developing roller 2 reaches the desired potential Vd of the developing roller 2, and the desired developing potential can be maintained more stably. Was.

[Embodiment 10] In this embodiment, the dielectric layer 2
Example 9 except that the polarity of No. 3 was changed from negative polarity to positive polarity.
The effect of the fourth embodiment was confirmed using the same developing device as in the first embodiment.

[0115] That is, in this embodiment, in the same manner as in Example 9, the desired development potential Vd is -300 V, the discharge starting voltage of the negative polarity side Vth _- is -470V, the charging potential of the initial dielectric layer 23 Vc is + 200V. Therefore, the surface potential of the developing roller 2 in the initial state is -100V.
In the present embodiment, Ve = Vd + V
An applied voltage of th _- = _- 300-470 = -770 V was applied.

As a result, the potential difference between the developing roller 2 and the charge removing member 15 in the initial state was -670 V, which was higher than the discharge start voltage on the negative polarity side, and Paschen discharge occurred. This discharge is caused by the developing roller 2 and the neutralizing member 15.
And the potential difference between the discharge start voltage Vth ₋ (= −4)
70 V). That is, the surface potential of the developing roller 2 at the end of the discharge is (applied voltage to the charge removing member 15) − (discharge start voltage on the negative polarity side) =
−770 + 470 = −300, and a desired potential of the developing roller 2 was obtained.

Therefore, it can be seen that the Paschen discharge can quickly remove the potential of the developing roller 2 until the potential of the developing roller 2 reaches the desired potential Vd, and the desired developing potential can be maintained more stably. Was.

[Embodiment 11] In this embodiment, the charge removing member 5 is used.
Fifth Embodiment Using the same developing device as in the ninth embodiment except that the voltage applied to 15 is changed to a superimposed voltage described later,
The effect was confirmed.

In this embodiment, the effect of this embodiment is as follows.
The case where the desired developing potential Vd is -300 V and the charging potential Vc of the dielectric layer 23 is -200 V will be considered with reference to FIG. In the initial state, as shown in FIG.
Has a surface potential of Vd + Vc = −500 V. Further, the positive discharge starting voltage Vth ₊ of the charge removing members 5 and 15 is 470 V as in the case of the ninth and tenth embodiments.

Then, the DC voltage Vddc = −250 V and the peak-to-peak voltage Vpp are 9 with respect to the charge removing members 5 and 15.
A voltage on which an AC voltage of 00 V was superimposed was applied. As a result, the peak voltage Vddc + (1/2) Vpp (= −25)
0V + (1/2) 900V = + 200V) and Vd (= −
300 V) is +200 V − (− 300 V) = 5
Since the voltage becomes 00 V, there is a state where the voltage is higher than the positive discharge start voltage Vth ₊ .

When the voltage applied to the charge removing members 5 and 15 increases to the positive polarity side and the potential difference between the surface potential of the developing roller 2 and the charge removing members 5 and 15 becomes equal to or higher than the positive discharge starting voltage Vth ₊ , the discharge is performed. Was started, and the discharge was stopped when the voltage applied to the charge removing members 5 and 15 passed the peak on the positive polarity side. Thereafter, the surface potential Vd of the developing roller 2 was made uniform while the potential of the surface of the developing roller 2 repeatedly increased and decreased by the voltage of the AC component.

As described above, the charge removing member is set such that the difference between one of the voltage value obtained by adding the value of the DC voltage Vddc to の of the peak-to-peak voltage Vpp and the desired developing potential Vd is equal to or higher than the discharge starting voltage Vth. By applying the superimposed voltage of the DC voltage and the AC voltage to 5.15, the difference between the surface potential of the developing roller 2 and the voltage value of the DC component to the static elimination member 5.15 becomes smaller when only the DC voltage is applied. It became very small in comparison. Therefore, it was found that the surface potential of the developing roller 2 hardly fluctuated due to the influence of the environment such as the aging of the dielectric layer 23 and the humidity, and it became possible to stably apply the developing potential.

[0123]

As described above, the developing device of the present invention is a developing device for developing an electrostatic latent image held on the surface of an image carrier with toner, and holding the toner on the surface. A toner carrier for transporting the toner onto the image carrier and developing the toner, and a toner layer thickness regulator that contacts and charges the toner on the toner carrier and regulates the thickness of the toner to a desired thickness. And a member, wherein the toner carrier is
An elastic conductive layer and a dielectric layer provided so as to cover the conductive layer. When the thickness of the dielectric layer is A and the volume average particle diameter of the toner is R, 2 × R The thickness of the dielectric layer is set so as to satisfy ≦ A ≦ 10 × R.

With this arrangement, it is possible to sufficiently achieve both the steep development γ characteristic in isolated fine lines and dots and the gradual development γ characteristic in the solid portion and the maximum density by disposing the dielectric layer. Instability of the developing potential due to the charging of the layer can be suppressed. Therefore, the above configuration
Suppressing instability of development potential due to charging of the dielectric layer, while achieving both good fine line reproducibility and good gradation reproducibility in the solid part by arranging the dielectric layer. This provides an effect that a developing device capable of performing the above-described operations can be provided.

As described above, the developing device of the present invention preferably further includes a charge removing member that contacts the surface of the toner carrier after development to remove the charge of the toner carrier.

Therefore, according to the above configuration, even when the dielectric layer is charged, the dielectric layer can be discharged.
There is an effect that a stable development potential can be applied to the toner carrier.

As described above, the developing device of the present invention is preferably configured such that the charge removing member includes an aggregate of conductive fibers that comes into contact with the surface of the toner carrier.

As a result, even if there is a variation in the thickness of the toner layer, the contact state between the charge removing member and the dielectric layer can be kept good. Therefore, the above configuration has an effect that even when the dielectric layer is charged, the dielectric layer can be sufficiently discharged, and a more stable development potential can be applied to the toner carrier. .

As described above, the developing device of the present invention preferably further includes a voltage applying means for applying a voltage containing at least an AC component to the charge removing member.

As a result, the contact interface resistance between the charge removing member and the toner carrier can be reduced, so that the charge removing efficiency by charge injection can be improved. therefore,
The configuration described above has an effect that even when the dielectric layer is charged, the dielectric layer can be sufficiently discharged, and a more stable developing potential can be applied to the toner carrier.

As described above, the developing device of the present invention preferably further includes voltage applying means for applying a voltage to the charge eliminating member. Ve, where Vd is the desired surface potential of the toner carrier and Vth is the discharge starting voltage between the toner carrier and the charge removing member, the configuration is such that Ve = Vd + Vth.

Thus, the dielectric layer can be effectively neutralized by using a discharge phenomenon between the neutralizing member and the dielectric layer, and the surface of the toner carrier after the neutralization is set to a desired development potential. be able to. Therefore, the above configuration has an effect that a desired development potential can be more stably maintained.

As described above, the developing device of the present invention preferably further includes voltage applying means for applying a superimposed voltage obtained by superimposing an AC voltage on a DC voltage to the charge eliminating member. When the DC voltage is Vddc, the peak-to-peak voltage of the AC voltage is Vpp, the desired surface potential of the toner carrier is Vd, and the discharge starting voltage between the toner carrier and the discharging member is Vth, Vddc + (1/2) ) Vp
The difference between p and Vd, and Vddc- (1/2) Vpp
And Vd is set so that at least one of the differences between Vd and Vd is equal to or higher than Vth.

As a result, the dielectric layer can be effectively neutralized by using a discharge phenomenon between the neutralizing member and the dielectric layer, and the potential of the toner carrier surface after the neutralization and the DC voltage can be reduced. The difference can be reduced, and the dielectric layer after static elimination can be brought close to a desired development potential. Therefore, the above configuration has an effect that a desired development potential can be stably maintained without being affected by charge injection due to aging or environmental change.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a developing device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically illustrating a developing roller provided in the developing device.

FIG. 3 is a cross-sectional view schematically showing a developing device according to another embodiment of the present invention.

FIG. 4 is a perspective view schematically showing a charge removing member provided in the developing device shown in FIG. 3;

FIG. 5 is a graph for explaining a charge injection and a discharge phenomenon between a developing roller and a charge removing member, and is a graph showing a change in a surface potential of the developing roller due to a change in a voltage applied to the charge removing member. .

FIG. 6 is a graph for explaining a static elimination effect using a discharge phenomenon, and is a graph showing a temporal change of a voltage applied to a static elimination member and a surface potential of a developing roller.

FIG. 7 is a graph for explaining changes in charge injection due to environmental changes and changes over time, and is a graph showing changes in the surface potential of the developing roller due to changes in the voltage applied to the charge removing member.

FIG. 8 is a graph for explaining a change in the static elimination effect due to an environmental change and a temporal change when only a DC voltage is applied, and shows a temporal change in a voltage applied to the static elimination member and a surface potential of the developing roller. It is a graph.

FIG. 9 is a graph for explaining a static elimination effect when the developing device of the fifth embodiment is applied, and is a graph showing a temporal change in a voltage applied to a static elimination member and a surface potential of a developing roller.

FIG. 10 is a graph showing the results of measuring the development γ characteristics (fine line reproducibility) of isolated fine lines and dots and the development γ characteristics (gradation characteristics) of a solid portion when the developing device of the first embodiment is applied. .

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 developing device 2 developing roller (toner carrier) 4 toner layer thickness regulating member 5 static elimination member 7 toner 12 power supply (voltage applying means) 15 static elimination member 16 conductive brush (aggregate of conductive fibers) 22 conductive base material 23 Dielectric layer 30 Photoreceptor drum (image carrier) 31 Developing device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H073 AA05 BA04 BA12 BA13 BA15 CA02 2H077 AC04 AD06 AD13 AD17 AD23 AD31 AD32 AD36 AE02 AE03 AE10 EA14 EA15 FA13 FA22 FA25 GA17

Claims (6)

[Claims] A developing device for developing an electrostatic latent image held on the surface of an image carrier with toner, wherein the developing device transports the electrostatic latent image onto the image carrier while holding the toner on the surface to perform development. And a toner layer thickness regulating member that regulates the thickness of the toner so as to form a layer having a desired thickness while contacting and charging the toner on the toner carrier. And a dielectric layer provided so as to cover the conductive substrate. When the thickness of the dielectric layer is A and the volume average particle diameter of the toner is R, 2 × R ≦ A developing device, wherein the thickness of the dielectric layer is set so as to satisfy A ≦ 10 × R. 2. The developing device according to claim 1, further comprising a charge removing member that contacts the surface of the toner carrier after development to remove the charge of the toner carrier. 3. The developing device according to claim 2, wherein said static elimination member includes an aggregate of conductive fibers in contact with the surface of the toner carrier. 4. The developing device according to claim 2, further comprising voltage applying means for applying a voltage including at least an AC component to the charge removing member. 5. A voltage applying means for applying a voltage to the charge eliminating member, wherein the voltage applied to the charge eliminating member is Ve, a voltage applied to the charge eliminating member, Vd is a desired surface potential of the toner carrier,
The discharge starting voltage between the toner carrier and the charge removing member is Vth
The developing device according to claim 2, wherein Ve = Vd + Vth. 6. A voltage applying means for applying a superimposed voltage, which is obtained by superimposing an AC voltage on a DC voltage, to the charge eliminating member, wherein the DC voltage and the AC voltage are DC voltage Vddc,
Assuming that the peak-to-peak voltage of the AC voltage is Vpp, the desired surface potential of the toner carrier is Vd, and the discharge starting voltage between the toner carrier and the charge removing member is Vth, Vddc + (1/2)
The difference between Vpp and Vd, and Vddc- (1/2) V
4. The developing device according to claim 2, wherein at least one of the difference between pp and Vd is set to be equal to or higher than Vth.