JP2003140466A - Developing device and image forming apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that prevents problems, for example, fusion on a roller which is caused by a fact that a developer is repetitiously rubbed on the surface of a developer carrier and deteriorated as a result and to provide an image forming apparatus having the developing device. SOLUTION: The device has a corona discharger 17 that is disposed in contact with or near to a developing roller 8 and that changes the polarity of toner remaining on the developing roller 8 after development to the opposite polarity of the normal polarity. The device also has a supply bias power source 15 that generates between the developing roller 8 and a supply roller 9 an electric field in the direction in which the toner electrified to the opposite polarity by the corona discharger 17 is pulled back and transferred to the supply roller 9 from the developing roller 8.

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 printer, a copying machine, and a facsimile apparatus adopting an electrophotographic method, and an image forming apparatus including the developing device.

[0002]

2. Description of the Related Art Conventionally, as a developing device for visualizing a latent image formed on a latent image carrier with a toner as a developer, a one-component developing system or a two-component developing system is known.

Such a developing device is provided with a rotatable developer carrying member which is arranged in contact with or close to the latent image carrying member and carries toner, and the toner layer or the two components is provided on the developer carrying member. While forming a magnetic brush made of a developer, the toner is conveyed to a development area which is a contact area or a proximity area to the latent image carrier. Then, a developing bias voltage is applied between the developer carrier and the latent image carrier to form an electric field, and the toner is transferred to the latent image on the latent image carrier.

In such a developing device, in order to favorably transfer the toner to the latent image on the latent image carrier in the developing area, it is necessary to give the toner a predetermined charge amount. The two-component development type developing device imparts an electric charge to the toner by mixing and stirring the toner with a carrier separated in the triboelectric charging sequence, but the charge control agent externally added to the toner is released. May contaminate the carrier surface. Therefore, if the carrier is used for a long period of time, it becomes impossible to apply an electric charge to the toner due to these influences, and there is a drawback that the developer needs to be replaced. Further, a toner concentration control device or a developer stirring device for keeping the mixing ratio of the toner and the carrier constant, or a magnet in the developer carrying body for carrying the magnetic carrier may be required. Therefore, there is a drawback that the device becomes complicated.

On the other hand, the one-component developing system is widely used as a device capable of overcoming the drawbacks of the two-component developing system.

FIG. 5 is a schematic diagram of an image forming apparatus using a non-magnetic one-component toner.

As shown in FIG. 5, conventionally, in this type of image forming apparatus, a charging roller 1 as a primary charging device is provided around a photosensitive drum 100, which is a latent image carrier rotating in the X direction in the figure.
01, a developing device 103 as a developing device, a transfer roller 104 as a transfer charger, a cleaning member 105 for cleaning the surface of the photosensitive drum 100, and the like are provided.

The developing device 103 is arranged in contact with the photosensitive drum 100 and rotates in the Y direction in the figure to apply a developer to the photosensitive drum 100.
7. A supply roller 108, which is a developer supply member that supplies the non-magnetic toner T ′ to the developing roller 107 while rotating in the Z direction in the figure, and the toner T ′ on the developing roller 107 to a predetermined application amount and charge amount. The developing blade 110, which is a developer regulating member that regulates the toner, and the stirring member 10 that supplies the toner T ′ to the supply roller 108 and agitates the non-magnetic one-component toner.
9 and the like. The developing roller 107 and the supply roller 108 have a developing bias power source 111 and a developing bias power source 111, respectively.
The supply bias power source 112 is connected.

Next, the image forming operation of the conventional image forming apparatus will be described.

First, the photosensitive drum 100 starts to rotate in the direction of arrow X by a print signal from the outside, and the photosensitive drum 1
00 is uniformly charged by the charging roller 101. The charging roller 101 has a roller shape, and rotates in the arrow W direction by a driving force (not shown).

Next, exposure 10 by an exposure device (not shown)
2 forms an electrostatic latent image on the photosensitive drum 100,
When the photosensitive drum 100 rotates, the electrostatic latent image is developed on the developing device 10.
Reach the contact point with 3.

The developing device 103 performs the following operation in conjunction with the above operation.

The toner T'agitated by the agitating member 109 rubs the developing roller 107 rotating in the Y direction and the supplying roller 108 rotating in the Z direction, and the developing bias roller 112 supplies the developing roller 107 and the supplying roller 108. And the electric field formed between the developing roller 107 and the developing roller 107. The toner T ′ on the developing roller 107 is carried on the developing roller 107 after a desired charge amount is applied by the developing blade 110 and the toner amount is regulated. The toner in the developing device 103 is agitated by the agitating member 109 and conveyed to the supply roller 108.

When the toner carried on the developing roller 107 reaches the portion where the toner comes in contact with the photosensitive drum 100, the developing bias power source 111 causes the developing drum power source 111 and the developing roller 10 to move.
By applying a DC developing bias between 7 and
The electrostatic latent image formed on the surface of the photosensitive drum 100 is developed with the toner T ′ carried on the surface of the developing roller 107 to be visualized as a toner image.

Toner remaining on the surface of the developing roller 107 after development, which does not contribute to the development, is collected in the developing device 103 via the supply roller 108.

The toner image on the photosensitive drum 100 reaches the facing portion of the transfer roller 104 by the rotation of the photosensitive drum 100, and is transferred onto the transfer paper P'by the transfer roller 104. The transfer paper P ′ having received the transfer of the toner image is the fixing device 1
The toner image is heat-melted by being heated and pressurized by 06 to become a permanent image.

The toner T ′ remaining on the photosensitive drum 100 without being transferred onto the transfer paper P ′ by the transfer roller 104 is removed by the cleaning means.

[0018]

However, in the above-described conventional one-component developing system developing device, the supply roller 108 supplies the toner to the developing roller 107 and the toner not contributing to the development on the developing roller 107. The following problem arises because it performs the two roles of stripping off.

The toner is supplied from the supply roller 108 to the developing roller 107 by friction charging between the supplying roller 108 and the developing roller 107, which rotate counter to each other, and by being attracted to the developing roller 107 by electrostatic force. .

The toner that has not contributed to the development is stripped from the developing roller 107 by the scraping of the toner by the wall surface of the supply roller 108 formed of sponge that forms the holes, that is, by the mechanical force. Is.

However, since the toner that has not contributed to the development is stripped from the developing roller 107 by relying on the mechanical force, the stripping residue is inevitable. The toner remaining on the developing roller 107 without being stripped off by the supply roller 108 is further rubbed by the developing blade 110. That is, the toner that has been rubbed a second time (toner that has not been peeled off) has a larger amount of charge than the toner that has been rubbed the first time (toner newly carried on the developing roller). The toner that has been rubbed for the first time adheres more strongly to the developing roller 107.

As a result, when the toner does not contribute to the development again and returns to the supply roller 108, it is more difficult to be peeled off. Therefore, the mechanical force of the supply roller 108 cannot remove the toner, and the same toner is not removed. The developing roller 107 will be rubbed many times.

The toner remaining on the developing roller 107 and rubbed many times causes "roller fusion" in which the toner is melted on the developing roller 107 due to frictional heat. When the “roller fusion” occurs, the toner contacting that portion cannot be triboelectrically charged, so that the toner cannot be carried on the developing roller 107 or the toner cannot be regulated by the developing blade 110, and the toner from the developing device 103 cannot be collected. Problems such as blowing out occur.

As a means for preventing the "roller fusion", a potential difference may be provided between the developing roller 107 and the supply roller 108.

When a potential difference is provided between the developing roller 107 and the supplying roller 108 to strip the negatively charged toner having the normal polarity to the supplying roller side, it does not contribute to the developing and returns to the developing device 103 again. It is possible to peel off the received toner to the supply roller side. However, due to the friction between the developing roller 107 and the supply roller 108, the toner that was originally supposed to be carried on the developing roller 107 will be stripped off due to frictional charging. Therefore, the amount of toner on the developing roller 107 decreases, and the desired image density cannot be obtained.

Further, among the toners in the developing device 103, the toner charged to the opposite polarity to the normal polarity (hereinafter referred to as reverse toner) is carried on the developing roller 107, so that the output image Toner adheres to non-image areas,
So-called "reverse fog" occurs.

When a potential difference for supplying the negatively charged toner to the developing roller side is provided between the developing roller 107 and the supplying roller 108, the toner supplying amount to the developing roller 107 is satisfied, but the supplying roller is satisfied. The toner stripped from the developing roller 107 by 108 is again carried on the developing roller 107 by the electric field. Further, since the force of mechanically stripping is the same as that described above, if long-term durability is performed, "roller fusion" will occur as described above.

When an alternating electric field is provided between the developing roller 107 and the supply roller 108, negatively charged toner flows back and forth between the developing roller 107 and the supply roller 108. However, although it is possible to mix the toner in the developing device 103 with the toner that has already been carried on the developing roller 107 by the alternating electric field and has not contributed to the development, some of the mixed toner is again generated in the developing roller 107. Will be carried by. As a result, "roller fusion" occurs as described above.

As described above, in the conventional one-component developing system, it is possible to prevent the occurrence of "roller fusion" which occurs when the toner carried on the developing roller is rubbed many times. could not.

Therefore, the present invention is provided with a developing device and a developing device capable of preventing the occurrence of problems such as roller fusion caused by the developer being repeatedly rubbed and deteriorated on the developer carrying member. An object is to provide an image forming apparatus.

[0031]

According to the present application, the above object is to provide a developer carrying member which carries a developer and which is disposed in contact with or in proximity to a latent image carrying member carrying a latent image, and the developing device. A developer which is arranged in contact with or close to the developer carrier to regulate the layer thickness of the developer on the developer carrier to a predetermined amount and to frictionally charge the developer on the developer carrier to a regular polarity. An amount regulating member and a developer supply member which is disposed in contact with or in proximity to the developer carrier and supplies the developer to the developer carrier while holding the developer, and the developer is supplied from the developer carrier. In a developing device which visualizes the latent image as a developer image by being applied to the latent image carrier, a developer which is disposed in contact with or close to the developer carrier and remains on the developer carrier after development. Reverse the polarity of the normal polarity to the opposite polarity A polarity reversing member, and an electric field in a direction in which the developer charged to the opposite polarity by the polarity reversing member is transferred back from the developer carrying member to the developer supplying member are transferred between the developer carrying member and the developer supplying member. It is achieved by the first invention that an electric field forming means is formed between them.

According to the present application, the above object can also be achieved by the second invention of the first invention, in which the polarity reversal member is disposed in contact with the developer carrying member.

Further, according to the present application, the above-mentioned object is, in the first invention or the second invention, that the polarity reversing member is 1e.
It is also achieved by the third invention, which is formed of a resin or an elastic body having a resistance value of ³ Ω or more and 1e ⁷ Ω or less.

Further, according to the present invention, in the above-mentioned object, in any one of the first to third inventions, the polarity reversing member is a developer whose constant current is controlled to a predetermined current value. It is also achieved by the fourth invention in which the voltage is applied between the carrier and the carrier.

Further, according to the present application, in the fourth aspect, the above-mentioned object is provided between the polarity reversing member and the developer carrying member in accordance with the amount of the developer remaining on the developer carrying member after the development. It is also achieved by the fifth aspect of the present invention, which comprises control means for controlling the control variable value for constant current control of the applied voltage.

Further, according to the present application, in the above-mentioned object, in any one of the first invention to the sixth invention, the electric field forming means is a DC voltage between the developer supply member and the developer carrier,
Alternatively, it is also achieved by the sixth invention that an electric field is formed between the developer carrying member and the developer supply member by applying a bias voltage in which a DC voltage and an AC voltage are superimposed. It

Further, according to the present application, the above-mentioned object is the developer according to any one of the first to sixth inventions,
The shape factor SF ₁ is 100 or more and 160 or less, and
It is also achieved by the seventh invention in which the shape factor SF ₂ is 100 or more and 140 or less.

Further, according to the present application, the above object is an image forming apparatus for recording an image formed by a series of image forming processes on a recording material, which is one of the first invention to the seventh invention. It is also achieved by the eighth invention including the developing device.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to this embodiment.

In such an image forming apparatus, the primary charger 2 uniformly charges the photosensitive drum 1 which is a latent image carrier rotating in the X direction as shown in FIG. Then, the photosensitive drum 1 is exposed by a light emitting element 3 such as a laser according to an information signal to form an electrostatic latent image. The electrostatic latent image is visualized as a toner image on the photosensitive drum carrying the electrostatic latent image by applying the toner T by the developing device 4 which is a developing device. Next, the toner image is transferred to the transfer paper P which is a recording material by the transfer charger 5, and further fixed on the transfer paper P by the fixing device 7 to become a permanent image. On the other hand, the toner remaining on the photosensitive drum 1 without being transferred is removed by the cleaning member 6.

In FIG. 1, the photosensitive drum 1 rotates in the arrow X direction at a rotation speed Vx. In the present embodiment, V
x was set to 48 mm / sec.

The primary charger 2 is a contact charging roller that contacts the photosensitive drum 1 to charge it, and is rotationally driven in the direction of arrow W at the same speed as the photosensitive drum 1. A charging bias power source 12 is connected to the primary charger 2 so as to uniformly charge the surface of the photosensitive drum 1, and during the image forming operation, the charging bias power source 12 is set to about −11.
00V is applied to the primary charger 2 to uniformly charge the surface of the photosensitive drum 1 to about -500V.

Next, the surface of the photosensitive drum 1 is exposed and scanned by a light emitting element 3 such as a laser or an LED, and exposure is performed according to an information signal to form an electrostatic latent image on the surface of the photosensitive drum 1. In the present embodiment, a so-called reversal development system for forming a toner image on the exposed portion of the photosensitive drum 1 with negatively charged toner will be described.

Developing device 4 containing non-magnetic one-component toner T
Has a developing roller 8 as a developer carrying member which is in contact with the photosensitive drum 1 and rotates in the arrow Y direction at a rotation speed Vy. Further, the developing device 4 includes the developing blade 1 which is a developer amount regulating member.
0, a supply roller 9 that is a developer supply member that rotates in the direction of arrow U, and a stirring member 11 that stirs the non-magnetic one-component toner T. Here, the relationship between the rotational speeds of the photosensitive drum 1 and the developing roller 8 is Vy> Vx. Where Vy is 81
It is rotating at mm / sec.

The supply roller 9 was rotated with a speed Vz with respect to the developing roller 8 in a width rotation (rotation direction arrow U). The rotation speed is the same as that of the developing roller and Vz is 81 mm /
sec. As the material of the supply roller 9, known materials such as foamed urethane rubber and foamed EPDM rubber are used. In this embodiment, the supply roller 9 made of foamed urethane rubber is used. The reason why the foamed rubber is used is that there are holes on the rubber surface to increase the toner carrying force, and the rubber hardness is suppressed to a low level, so that toner deterioration is less likely to occur. As the roller resistance of the supply roller 9, it is possible to use an actual resistance of 1e ⁴ Ω or more and 1e ⁸ Ω or less. If it is 1e ⁴ Ω or less, an overcurrent flows in at the time of leakage, which is not preferable. On the other hand, if it exceeds 1e ⁸ Ω, an electric field sufficient for toner transfer cannot be obtained, which is not preferable.

Further, a supply assisting member 19 for assisting the supply of toner is arranged upstream of the contact portion of the supply roller 9 with the developing roller 8 in the rotational direction. The supply assisting member 19 has a function of imparting a slight electric charge to the toner on the surface of the supply roller 9 by rubbing the toner on the surface of the supply roller 9 in order to supply the toner to the developing roller 8, and a reverse polarity described later. It plays a role of returning the charging polarity of the undeveloped residual toner charged to (positive polarity) to the normal polarity (negative polarity). As the supply assisting member 19, a metal member such as stainless steel and a resin member such as urethane rubber or silicone rubber are brought into contact with the supply roller 9 so as to slightly bite into the supply roller 9.

A supply bias power source 15, which is an electric field forming means, is connected to the supply roller 9, and a DC voltage of about −460 V is applied to energize the negatively charged toner from the supply roller 9 to the developing roller 8. To do.

The toner applied to the developing roller 8 by the supply roller 9 is then regulated by the developing blade 10 in the toner amount and tribo imparted by friction. The developing blade 10 is a thin plate (about 0.1 mmt) made of stainless steel and is bent at a position of about 2 mm from the tip end portion in the direction opposite to the rotation direction of the developing roller, and the bent portion slightly bites into the developing roller 8. Arrange in contact with each other.

Further, the developing bias power source 1 is applied to the developing roller 8.
3 is connected, while the photosensitive drum 1 is grounded.

The developing bias power source is a negative polarity DC power source, and in the present embodiment, it is -35 at the time of image formation.
A potential of 0V is applied. The toner charged by the developing blade 10 and carried on the developing roller 8 is supplied onto the photosensitive drum 1 by the developing bias to visualize the electrostatic latent image.

When the transfer sheet P conveyed by the paper cassette (not shown) and the conveying roller (not shown) reaches the transfer portion, the image formed on the surface of the photosensitive drum 1 is transferred by the transfer charger 5 to the transfer sheet P. Transfer to P. In this embodiment, it is a roller type transfer charger, and a transfer bias power source 14 is connected to the transfer charger 5. A voltage of about +2 to 5 kV is applied to the transfer bias power source 14 during image transfer.

The application timing of the charging bias power source 12, the developing bias power source 13, the supply bias power source 15, and the transfer bias power source 14 is controlled by the controller 16.

The transfer paper P on which the image has been transferred is heat-melted and fixed by the fixing device 7.

The toner remaining on the developing roller 8 without contributing to the development (hereinafter, referred to as the undeveloped toner) is disposed between the contact portion with the photosensitive drum 1 and the contact portion with the supply roller 9. It receives the discharge of the corona discharger 17, which is a polarity reversing member. In the corona discharger 17, the corona discharge power supply 18 gives a positive charge having a polarity opposite to the charge polarity of the toner. The corona discharger 17 performs constant current control to control the discharge current to the developing roller side to about 6 μA.

The reason why the discharge current is controlled to be constant current is that a constant amount of electric charge is constantly supplied onto the developing roller 8. When increasing the peripheral speed of the developing roller, it is preferable to increase the discharge current.

The toner whose polarity is reversed by the corona discharger 17 reaches the contact portion with the supply roller 9. As shown in FIG. 2, the undeveloped toner carried on the developing roller 8 is returned to the supplying roller 9 by the electric field urged toward the supplying roller side at the contact portion between the developing roller 8 and the supplying roller 9 and in the vicinity thereof. Are transferred. On the other hand, the regular toner carried on the supply roller 9 forms an electric field urged toward the developing roller. As a result, the supply roller 9
The regular toner present on the developing roller 8 is carried on the developing roller 8 side, and the reversal toner which is the undeveloped toner remaining on the developing roller 8 is pulled back to the supplying roller 9 and collected. The regular toner and the reverse toner are exchanged in the vicinity of the contact portion with the roller 9.

That is, the supply of the regular toner and the recovery of the toner remaining after development are collectively performed. In this way
Due to the electric field between the supply roller 9 and the developing roller 8, the undeveloped toner can be collected without relying on mechanical force. Further, since the toner carried on the developing roller 8 is only the negative toner due to the electric field, it is possible to prevent "reverse fogging" in which the toner adheres to the non-image portion of the photosensitive drum 1 during development.

Next, each component used in the present invention will be described.

The developing roller 8 comprises a rubber elastic single layer formed of a known material such as silicone rubber, urethane rubber or hydrin rubber on a stainless cored bar, and a polyamide resin, silicone resin, urethane resin or fluorine on the rubber surface. A developing roller having a multi-layer structure coated with a resin or the like can be used. The surface roughness of the developing roller 8 depends on the particle size of the toner to be used, but is 10-point average roughness Rz of 3
It is preferably not less than μm and not more than 15 μm. If the toner particle size used is 6 μm in average volume particle size, it is preferable to use 10-point average roughness Rz of 5 μm or more and 12 μm or less. When the toner particle size is smaller, it is preferable to make the ten-point average roughness Rz slightly smaller. If the ten-point average roughness Rz is 3 μm or less, a sufficient toner conveying force cannot be obtained and the density becomes insufficient, resulting in 1
This is because if the thickness is 5 μm or more, the toner cannot be sufficiently charged. Ten-point average roughness Rz is JIS B06
The surface roughness tester “SE-30H” manufactured by Kosaka Laboratory was used for the measurement using the definition shown in 01.

As the roller resistance of the developing roller 8, it is possible to use an actual resistance of 1e ⁴ Ω or more and 1e ¹¹ Ω or less. If it is 1e ⁴ Ω or less, an overcurrent flows in at the time of leakage, which is not preferable. On the other hand, when it is 1e ¹¹ Ω or more, discharge charges due to corona discharge are accumulated on the developing roller 8 and hinder the toner conveyance, which is not preferable.

Developing blade 10 as a toner regulating member
Is a thin plate (about 0.1 mmt) made of stainless steel and bent at a position of about 2 mm from the tip end in the direction opposite to the developing roller, and the bent portion comes into contact with the developing roller 8 in a state of slightly biting.

The toner according to the present invention has a shape factor SF ₁ measured by an image analyzer of 100 to 160,
The shape factor SF _{2 has} a value of preferably 100 to 140, the shape factor SF _{1 has} a value of 100 to 140, and the shape factor SF _{2 has} a value of 100 to 120. Further, the above conditions are satisfied and (SF ₂ ) / (S
By setting the value of F ₁ ) to 1.0 or less, not only the characteristics of the toner but also the matching with the image analysis device becomes extremely good.

S indicating the shape factor used in the present invention
The F _1, SF _2, Hitachi FE-SEM (S-80
0) randomly sample 100 toner images magnified 500 times, and the image information is image analysis device (Luzex3) manufactured by Nicolet Co., Ltd. via an interface.
In the present invention, the shape factors SF ₁ and SF ₂ are defined as the values obtained by the following equations, which are calculated by the following equation.

SF ₁ = ((MXLNG) ² / AREA) ×
(Π / 4) × 100 SF ₂ = ((PERI) ² / AREA) × (1 / 4π) ×
100 AREA: toner projected area, MXLNG: absolute maximum length,
PERI: Perimeter toner shape factor SF ₁ indicates the degree of roundness of toner particles, gradually changing from spherical to irregular.

SF ₂ represents the degree of unevenness of the toner particles, and the unevenness of the toner surface becomes remarkable.

If the shape factor SF ₁ exceeds 160, the shape of the toner becomes irregular. Therefore, the charge amount distribution of the toner becomes broad, and it becomes difficult to locally replace the toner at the supply roller 9 when the toner is replaced.

Further, in order to enhance the replacement of the toner on the supply roller 9, the shape factor SF ₂ of the toner particles is 1
The value of (SF ₂ ) / (SF ₁ ) is 1.
It should be 0 or less. The shape factor SF ₂ of the toner particles is larger than 140, and the value of (SF ₂ ) / (SF ₁ ) is 1.0.
If it exceeds, the surface of the toner particles is not smooth,
Since the toner particles have many irregularities, the fluidity of the toner tends to decrease. That is, it becomes difficult to transfer all the undeveloped toner to the supply roller 9.

Therefore, as described above, according to the present embodiment, the toner that does not contribute to the development and is collected in the developing device is charged to a polarity opposite to the normal charging polarity, and the developing roller and the supply roller are separated from each other. By supplying the toner to the developing roller in the contact area and collecting the returned toner that does not contribute to the development by the electric field at the same time, it is possible to prevent problems such as roller fusion without causing toner deterioration due to mechanical force. .

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted.

In the above-described first embodiment, the corona discharger is used as the polarity reversal member. However, according to the corona discharger, a large amount of discharge products are generated, so that the developing roller 8
It was found that the strength of the resin was weakened. Further, since a large amount of ozone is generated in corona discharge, a filter device such as an ozone filter is required, which leads to an increase in cost.

Therefore, in the present embodiment, a reversal charge is applied to the undeveloped toner by using a charging blade that is a polarity reversal member, and the toner is collected and supplied collectively at the contact portion between the supply roller and the development roller. Is.

FIG. 3 is a schematic configuration diagram of the image forming apparatus according to the present embodiment.

In this embodiment, the developing roller 22 is
An elastic rubber is used on the core metal as in the first embodiment described above.
An elastic developing roller is used. However, in this embodiment
Since contact charging is performed, an appropriate discharge voltage can be obtained.
Thus, the resistance of the developing roller 22 is adjusted. Development low
La roller resistance is 1e in actual resistance⁸Ω or more 1e^{1 1}
Ω or less is desirable. More preferably development
La has a two-layer structure of a lower elastic layer and a surface resistance layer,
Sexual layer 1e^FiveΩ or more 1e⁷Ω or less
And is desirable. So that the discharge voltage can be obtained by the resistance layer
By doing so, the voltage drop due to the elastic layer can be prevented.
is there.

The charging blade 20, which is a polarity reversing member, is counter-arranged in the rotation direction of the developing roller 22 downstream of the developing area and upstream of the contact portion with the supply roller 9. This is to prevent negative contact with another member and then negative charge again after the discharge is generated. A discharge power source 21 is connected to the charging blade 20 and a positive voltage is applied as in the first embodiment.
In this embodiment, constant current control is used.

Further, in the constant current control in the present embodiment, the constant current control value is made variable by the controller 16 as the control means.

As the variable, about +6 μA to 10 μA was set according to the residual toner amount, and the current amount was increased as the residual toner amount was decreased. The reason is that as the toner is developed, the amount of residual toner remaining after development decreases, and as a result, the developing roller 22 is prevented from being discharged due to the occurrence of a portion in direct contact with the charging blade 20. The amount of undeveloped toner can be detected by the pixel density of the image formed.

The resistance of the charging blade 20 is 500
It is desirable that it is about 1e ³ Ω to 1e ⁷ Ω when V is applied.

This is because if it is less than 1e ³ Ω, an overcurrent will flow when a discharge voltage is applied, or a required discharge voltage will not be obtained. This is also because discharge variation occurs at 1e ⁷ Ω or more. In order to measure the resistance, instead of the developing roller 22, a metal cylinder having the same diameter was brought into contact with the metal cylinder, and a voltage was applied between the metal cylinder and the charging blade. In this embodiment, a charging blade having a resistance of about 6e ⁴ Ω is used.

Further, it is also possible to coat the surface layer of the charging blade with a material such as a fluororesin which imparts a positive charge to the toner by friction.

Now, the operation of the developing device of this embodiment will be described.

Toner is carried from the supply roller 9 to the developing roller 22 in the same manner as in the first embodiment described above, and the toner is developed from the developing roller 22 to the photosensitive drum 1 at the contact portion with the photosensitive drum 1. The undeveloped toner passes through the contact portion and reaches the contact portion with the charging blade 20. Then, in the minute space immediately after passing through the charging blade 20, the positive polarity discharge is received, and the negative polarity toner is inverted to the positive polarity.

As for the reversed toner, in the vicinity of the contact portion with the supply roller 9, the undeveloped toner is moved to the supply roller side and the negative polarity toner carried on the supply roller 9 is discharged in the same manner as in the first embodiment. An electric field is formed to urge the developing roller side. By forming this electric field, it is possible to collect the transfer residual toner and supply new toner at the same time. Then, by using the charging blade, the ozone filter is not required, and the cost is reduced.

Therefore, as described above, according to this embodiment, the toner that does not contribute to the development and is collected in the developing device is charged by the charging blade to a polarity opposite to the normal charging polarity,
At the contact portion between the developing roller and the supply roller, the electric field collectively collects the toner supplied to the developing roller and the toner returned without contributing to the development. Defects such as roller fusion can be prevented without causing deterioration.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment or the second embodiment described above are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, a case will be described in which a bias in which alternating current and direct current are superposed is used as a developing bias in the case of performing non-contact developing.

FIG. 4 is a schematic configuration diagram of the image forming apparatus according to the present embodiment.

In this embodiment, the developing roller 23, which is a developer carrier, is a rigid roller having a stainless pipe surface coated with a resistance layer of about 9e ⁹ Ω. A developing blade 26, which is a developer amount regulating member having a contact portion made of elastic rubber, is brought into contact with the developing roller 23, and imparts a charge to the toner and regulates the toner carrying amount. Developing roller 23
A developing bias power source 24 is connected to the developing roller 23, and a voltage in which alternating current and direct current are superimposed is applied to the developing roller 23. AC value is 160 in Vpp (peak to Peak)
0V, frequency 1800Hz, DC value is -350V
Was applied.

A voltage in which alternating current and direct current are superposed is applied to the charging blade 20 so that the developing roller 23 always has the same potential difference. AC value is 1600V in Vpp,
Frequency 1800Hz, no phase difference with developing bias,
As the DC value, + 1200V was applied. Therefore, there is always a potential difference of about 1550V with the developing bias.

The operation of the developing device of this embodiment will be described below.

As in the first embodiment described above, toner is carried from the supply roller 9 to the developing roller 23, and the toner is developed from the developing roller 23 to the photosensitive drum 1 at the portion facing the photosensitive drum 1. The undeveloped toner passes through the contact portion and reaches the contact portion with the charging blade 20. Then, in the minute space immediately after passing through the charging blade 20, the positive polarity discharge is received, and the negative polarity toner is inverted to the positive polarity.

The reversed toner approaches the contact group between the developing roller 23 and the supply roller 9 as the developing roller 23 turns around. Here, an alternating electric field is generated between the supply roller 9 and the developing roller 23. Therefore, the undeveloped toner and the negative polarity toner carried on the supply roller 9 are
While moving back and forth between 3 and the supply roller 9, the DC component urges the undeveloped toner to the supply roller side and the negative polarity toner to the developing roller side. In this way, even if the alternating current is superposed, the polarity of the development residual toner is different from that of the newly carried toner, so that it is possible to collectively collect the development residual toner and supply the negative polarity toner unlike the conventional example. . Further, since the applied voltage is increased by superposing the AC voltage, it becomes possible to collect even the toner having a large amount of electric charge locally from the developing roller.

Therefore, as described above, according to the present embodiment, the toner that does not contribute to the development and is collected in the developing device is charged to a polarity opposite to the normal charging polarity, and the developing roller and the supply roller are separated from each other. By supplying the toner to the developing roller at the contact portion and collecting the returned toner without contributing to the development by the electric field at the same time, it is possible to prevent problems such as roller fusion without causing toner deterioration due to mechanical force. .

[0095]

As described above, according to the first invention of the present application, the polarity reversing member causes the polarity of the developer remaining on the developer carrier after development to be opposite to the regular polarity. And the electric field forming means causes an electric field in a direction in which the developer charged in the opposite polarity by the polarity reversing member is transferred back from the developer carrying member to the developer supplying member and transferred to the developer carrying member and the developer. Since it is formed between the developer supply member and the supply member, it is possible to prevent problems such as roller fusion caused by the developer being repeatedly rubbed and deteriorated on the developer carrier.

According to the second invention of the present application,
The polarity reversing member reverses the polarity of the developer remaining on the developer carrier after development while contacting the developer carrier to a polarity opposite to the regular polarity, and the electric field forming means reverses the polarity by the polarity reversing member. Since the electric field in the direction of pulling back and transferring the polar-charged developer from the developer carrying member to the developer supplying member is formed between the developer carrying member and the developer supplying member, While preventing the generation of discharge products such as ozone to prolong the life and cost of the developer carrier, roller melting due to the deterioration of the developer by repeated rubbing on the developer carrier. It is possible to prevent problems such as wearing.

Further, according to the third invention of the present application, the polarity reversing member whose resistance value is optimized makes the polarity of the developer remaining on the developer carrying member after development the normal polarity. Is reversed to the opposite polarity, and the electric field forming means applies an electric field in the direction of pulling back and transferring the developer charged in the opposite polarity by the polarity reversing member from the developer carrying member to the developer supplying member. Since it is formed between the developer supply member and the developer supply member, it is possible to stably generate a problem such as roller fusion due to deterioration of the developer by being repeatedly rubbed on the developer carrier. Can be prevented.

According to the fourth invention of the present application,
The polarity reversing member applies a constant-current-controlled voltage between the polarity reversing member and the developer carrying member so that the polarity of the developer remaining on the developer carrying member after development is opposite to the normal polarity. The polarity is reversed, and the electric field forming means applies an electric field in a direction in which the developer charged in the opposite polarity by the polarity reversing member is pulled back from the developer carrying member to the developer supplying member and transferred to the developer carrying member and the developing member. Since it is formed between the developer supply member and the developer supply member, it is possible to stably prevent the occurrence of problems such as roller fusion due to the deterioration and deterioration of the developer on the developer carrier many times. be able to.

Further, according to the fifth invention of the present application, the polarity reversing member applies a constant current controlled voltage corresponding to the amount of the developer remaining on the developer carrying member after development to the polarity reversing member. And the developer carrying member, the polarity of the developer remaining on the developer carrying member after development is reversed to the polarity opposite to the normal polarity, and the electric field forming means reverses the polarity by the polarity reversing member. Since the electric field in the direction of pulling back and transferring the polar-charged developer from the developer carrying member to the developer supplying member is formed between the developer carrying member and the developer supplying member, It is possible to stably prevent the occurrence of problems such as roller fusion caused by the developer being repeatedly rubbed and deteriorated on the developer carrier.

According to the sixth invention of the present application,
The polarity reversing member reverses the polarity of the developer remaining on the developer carrier after development to a polarity opposite to the regular polarity, and the electric field forming means applies a direct current between the developer supply member and the developer carrier. Voltage or a bias voltage in which a DC voltage and an AC voltage are superposed is applied to pull back and transfer the developer charged in the opposite polarity by the polarity reversing member from the developer carrying member to the developer supplying member. Since an electric field is formed between the developer carrying member and the developer supplying member, roller fusion or the like due to the developer being repeatedly rubbed and deteriorated on the developer carrying member. It is possible to prevent the occurrence of problems.

Further, according to the seventh invention of the present application, the polarity reversing member reverses the polarity of the developer remaining on the developer carrying member after development to a polarity opposite to the regular polarity, thereby forming an electric field. The means draws an electric field in a direction in which the developer charged in the opposite polarity by the polarity reversing member is transferred back from the developer carrying member to the developer supplying member between the developer carrying member and the developer supplying member. Since it is formed, it is possible to prevent the occurrence of problems such as roller fusion due to the developer being repeatedly rubbed and deteriorated on the developer carrier.

According to the eighth invention of the present application,
The polarity reversing member reverses the polarity of the developer remaining on the developer carrier after development to a polarity opposite to the regular polarity, and the electric field forming means removes the developer charged to the reverse polarity by the polarity reversing member. Since an electric field in the direction in which the developer carrying member pulls back and transfers to the developer supplying member is formed between the developer carrying member and the developer supplying member,
It is possible to prevent the occurrence of problems such as roller fusion due to the developer being repeatedly rubbed and deteriorated on the developer carrier.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the behavior of the developer between the developer carrier and the developer supply member in the first embodiment of the present invention.

FIG. 3 is a schematic diagram showing a schematic configuration of an image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing a schematic configuration of an image forming apparatus according to a third embodiment of the present invention.

FIG. 5 is a schematic diagram showing a schematic configuration of a conventional image forming apparatus.

[Explanation of symbols]

1 Photosensitive drum (latent image carrier) 4 Developer (Developer) 8 Development roller (developer carrier) 9 Supply roller (developer supply member) 10 Development blade (developer amount control member) 15 Supply bias power supply (electric field forming means) 16 Controller (control means) 17 Corona discharger (polarity reversal member) 20 Charging blade (polarity reversal member) 22 Development roller (developer carrier) 23 Developing Roller (Developer Carrier) 26 Development Blade (Developer Amount Controlling Member)

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H005 AA15 FA07                 2H073 BA02 BA04 BA11 BA13 CA02                 2H077 AB04 AB14 AB15 AC04 AC16                       AD06 AD13 AD23 AD31 AD35                       AD36 AE03 AE08 AE09 CA02                       CA09 EA14 EA15 EA16 GA03

Claims (8)

[Claims] 1. A developer carrying member, which is arranged in contact with or close to a latent image carrying member carrying a latent image and carries a developer,
It is arranged in contact with or close to the developer carrying member to regulate the layer thickness of the developer on the developer carrying member to a predetermined amount and to frictionally charge the developer on the developer carrying member to a regular polarity. A developer amount control member and a developer supply member that is disposed in contact with or in proximity to the developer carrier and supplies the developer to the developer carrier while holding the developer, wherein the developer is the developer carrier. In a developing device which visualizes the latent image as a developer image by being applied to the latent image carrier from the body, it is disposed in contact with or close to the developer carrier and remains on the developer carrier after development. A polarity reversing member for reversing the polarity of the developer to a polarity opposite to the normal polarity, and a direction for pulling back and transferring the developer charged by the polarity reversing member to the opposite polarity from the developer carrying member to the developer supplying member. Electric field above the developer Developing apparatus is characterized by comprising electric field forming means for forming between the lifting member and the developer supplying member. 2. The developing device according to claim 1, wherein the polarity reversing member is arranged in contact with the developer carrying member. 3. The developing device according to claim 1, wherein the polarity reversing member is formed of a resin or an elastic body having a resistance value of 1e ³ Ω or more and 1e ⁷ Ω or less. 4. The polarity reversing member is configured such that a voltage whose constant current is controlled so as to have a predetermined current value is applied between the polarity reversing member and the developer carrying member.
The developing device according to any one of 1. 5. A control variable value for constant current control of a voltage applied between the polarity reversing member and the developer carrier according to the amount of the developer remaining on the developer carrier after development is controlled. The developing device according to claim 4, further comprising: 6. The electric field forming means applies a DC voltage, or a bias voltage in which a DC voltage and an AC voltage are superimposed, between the developer supply member and the developer carrying member, thereby applying the bias voltage to the developer carrying member and the developer carrying member. The developing device according to any one of claims 1 to 5, wherein the developing device is configured to form an electric field between the developer supply member and the developer supply member. 7. The developer according to claim 1, wherein the shape factor SF ₁ is 100 or more and 160 or less, and the shape factor SF ₂ is 100 or more and 140 or less. The developing device described. 8. An image forming apparatus for recording an image formed by a series of image forming processes on a recording material, comprising the developing device according to any one of claims 1 to 7. Image forming apparatus.