JPH10239983A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a density irregularity and an increase in the cost of a power source device by disposing a developer supply member in contact with a developer carrier, and generating an alternating electric field between the developer carrier and developer supply member. SOLUTION: The supply roller 43 and the developing roller 45 are arranged opposite each other in contact with each other, a specific potential difference is made between the supply roller 43 and developing roller 45 by a bias application means, and such an electrostatic force as to transfer toner electrified to a desired polarity is transferred to the developing roller 45 is produced by the potential difference. That is, between the developing roller 45 and supply roller 43, the bias application means is provided for applying voltages by which an alternating electric field for transferring and attaching the toner, electrified to the desired polarity on the supply roller 43, to the developing roller 45 is applied to the developing roller 45 and supply roller 43. An alternating electric field generated between the photoreceptor 1 and developing roller 45 is made smaller in magnitude than the alternating electric field between the developing roller 45 and supply roller 43.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for an image forming apparatus such as a copying machine, a facsimile, a printer, etc., which uses an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art Conventionally, in a dry developing apparatus used for electrophotography and electrostatic recording, a developing apparatus using a one-component developer is advantageous in terms of miniaturization, low cost, high reliability, and the like. It is. Further, in a developing device using a one-component magnetic developer containing a magnetic material in a toner, the developer can be moved by using a magnetic force, and the developer can be stably conveyed.

As a developing method using a toner as a one-component developer, a toner charged to a desired polarity is carried on a surface by a developer supply member and conveyed, and the toner is transferred from the developer supply member to the developer. There is known a developing method in which the toner is transferred and adhered to a carrier by an electric force, and toner is transported to a developing unit by the developer carrier (for example, see Japanese Patent Application Laid-Open No. 61-34557). According to this method, only the toner charged to the desired polarity can be transported to the developing unit, and the occurrence of background contamination or image omission due to the oppositely charged toner can be prevented.

FIG. 5 is a schematic diagram showing an example of the developing device. The developing device 4 includes a toner storage section 41 as a developer storage section that stores a magnetic toner (hereinafter, referred to as toner) T as a one-component developer, a supply roller 43 as a developer supply member, Developing blade 44 as a developer regulating member for regulating the developer on the roller surface
And a developing roller 45 as a developer carrier, and an agitator 47 as a stirring member that supplies the toner T to the surface of the supply roller 43 while stirring the toner in the toner storage unit 41. .

[0005] In the developing device 4, the toner T stored in the toner storage section 41 is transferred to the agitator 4.
While being stirred by 7, it is supplied to the surface of the supply roller 43 having a magnetic pole inside, is attracted by a magnetic force, and is carried by the supply roller. Then, the toner T is thinned by the developing blade 44 in contact with the supply roller 43 and is triboelectrically charged to a desired polarity. Then, the toner T is conveyed to a portion facing the developing roller 45 by the rotation of the supply roller 43 in the direction of the arrow. A predetermined potential difference is formed between the supply roller 43 and the developing roller 45 by a bias applying unit (not shown).
The potential difference generates an electrostatic force that transfers the toner charged to the desired polarity to the developing roller 45. The toner T on the surface of the supply roller 43 is transferred to the surface of the developing roller 45 by the electrostatic force. At this time, no electrostatic force that causes the toner to be transferred to the developing roller 45 acts on the toner charged to the opposite polarity to the desired polarity, that is, the oppositely charged toner. Therefore, only the toner charged to the desired polarity is transferred to the surface of the developing roller 45, and the occurrence of an abnormal image due to the use of the oppositely charged toner for development can be prevented. Then, the toner transferred to the surface of the developing roller 45 is conveyed to a portion facing the photoconductor 1 as a latent image carrier by rotation of the developing roller 45 in the direction of the arrow, and the electrostatic latent image on the surface of the photoconductor 1 is Is developed.

In the above-described developing device, the toner image can faithfully reproduce the latent image and is excellent in gradation reproducibility and fine line reproducibility, but the developing roller 45 after development is easily affected by the developed image. That is, the portion corresponding to the all black image portion on the developing roller 45 after the development rotates in the direction of the arrow, and the toner amount (M / A) on the developing roller after the toner is supplied from the supply roller 43 and the developing roller The portion corresponding to the all-white image portion on 45 rotates in the direction of the arrow, causing a difference between the toner amount (M / A) on the developing roller after the supply roller 43 supplies the toner. Thus, the toner amount on the developing roller (M /
A) receives the history of the developed image. As a result, a difference also occurs in the charged state of the toner on the developing roller 45. Due to such a difference in toner on the developing roller, image density unevenness has occurred.

It is noted that such an abnormal image that density unevenness occurs due to a difference in toner on the developing roller is shown in FIG.
This can occur not only in the developing device in which the photoconductor and the developer carrier are in contact with each other, but also in the case where the photoconductor and the developer carrier are not in contact with each other.

In order to prevent this density unevenness, Japanese Unexamined Patent Publication No.
JP-A-36283 discloses that "a supply roller and a developing roller are arranged at a predetermined interval, and an AC power supply for applying an AC voltage to the developing roller to generate an alternating electric field between the supply roller and the developing roller is provided." A device has been proposed.

[0009]

However, Japanese Patent Application Laid-Open No.
In the developing device proposed in Japanese Patent Publication No. 36283, since the developer carrier and the developer supply member are arranged at a predetermined interval, a sufficient amount of toner is supplied from the developer supply member to the developer carrier. In order to prevent the concentration unevenness, a high-cost power supply device for applying a large alternating electric field is required.

The present invention has been made in view of the above background, and an object of the present invention is to provide a developing device capable of preventing the occurrence of the density unevenness and suppressing an increase in the cost of a power supply device. That is.

[0011]

In order to achieve the above object, according to the present invention, there is provided a developer carrier facing a latent image carrier, and a magnetic material for supplying a one-component magnetic developer to the developer carrier. A developer supply member, wherein the developer supply member is disposed so as to be in contact with the developer carrier, and is alternately provided between the developer carrier and the developer supply member. It is characterized in that an electric field is formed.

According to the first aspect of the present invention, the developer carrier and the developer supply member are in contact with each other at the opposing portion, and the developer is brought into contact with the developer carrier by forming an alternating electric field at the contact portion. Enhances the mobility in both directions between the agent supply members,
In the developer consuming portion corresponding to the all black image portion on the developer carrier, the developer is transferred and adhered, and in the non-consumed portion of the developer corresponding to the all white image portion, excessive transfer of the developer is prevented. The developer on the carrier is made uniform.

According to a second aspect of the present invention, in the developing device of the first aspect, both the space between the latent image carrier and the developer carrier and the space between the developer carrier and the developer supply member are provided. An alternating electric field is formed, and the magnitude (Vp-p) of the alternating electric field between the latent image carrier and the developer carrier varies between the developer carrier and the developer supply member. It is characterized by being smaller than the magnitude of the electric field (Vp-p).

According to the second aspect of the present invention, the alternating electric field formed between the latent image carrier and the developer carrier causes the movement of the developer in the opposed contact portion between the developer carrier and the developer supply member. Reduce the effects on gender. As a result, the developer is reliably transferred and adhered to the developer consuming area corresponding to the all black image area on the developer carrier, and excessive transfer of the developer is caused to the developer consuming area corresponding to the all white image area. Is prevented, and the developer on the developer carrying member is made uniform.

[0015] The invention of claim 3 is claim 1 or claim 2.
In the developing device, the alternating electric field between the developer carrying member and the developer supply member is obtained by superimposing an AC voltage on a DC voltage, and a lower limit V of the magnitude of the alternating electric field.
p (min) is characterized in that it is formed so as not to exceed GND (0 V).

According to the third aspect of the present invention, in order to form an alternating electric field for equalizing the developer on the developer carrying member at a contact facing portion between the developer carrying member and the developer supply member, the polarity of the DC voltage is changed. It is possible to use a bias application power supply that superposes an AC voltage in a range that does not change.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a laser printer (hereinafter, referred to as a printer) as an image forming apparatus will be described below. FIG. 1 is a front view showing a schematic configuration of the printer according to the present embodiment. First, an outline of the printer will be described. The printer shown in FIG.
A charging device 2 having a charging roller 21 for contacting the photosensitive member 1 and charging the surface thereof around a photosensitive member 1 as a rotating body rotating in the direction of the arrow, and an exposure device 3 having a laser
And a transfer device having a transfer device 71 for transferring a toner image on the surface of the photoconductor 1 onto a transfer paper P, and a developing device 4 for converting the electrostatic latent image on the photoconductor 1 into a toner image by supplying toner. 7 and a cleaning device 5 for removing residual toner from the surface of the photoconductor 1 are provided, and these devices form an image forming unit.

A case 8 disposed on the left side of the image forming section
Inside, electronic devices and control devices such as a power supply 81 and a printed board 82 are housed.
3 are also stored. Further, above the case 8, a paper discharge tray 9 for storing the transfer paper P after the toner image is fixed is provided, and the paper discharge tray 9 can correspond to the size of the transfer paper P to be discharged. As shown in FIG.
It can be moved in the direction of. An operation surface having an operation panel 6 is disposed on the right side of the image forming unit.

Further, below the image forming section, a paper cassette 11 for storing the stacked transfer papers P is detachably disposed in the direction of arrow b, and the uppermost paper of the stacked transfer papers P is placed in the cassette. Arm 11 by the force of a spring (not shown)
1 is pressed against a sheet feed roller 113 via an intermediate plate 112 pushed up.

In the printer shown in FIG. 1, a paper feed tray 14 for feeding the transfer paper P to the image forming section with priority over the paper cassette 11 is provided at a position adjacent to the operation surface. It is provided in. This paper feed tray 1
4 is rotatably attached by a pin 141. When the paper feed tray 14 is used, the paper feed tray 14 is turned around the pin 141 and set at the position shown in the figure.

When an image is formed by the printer having the above-described configuration, the laser beam L from the exposure device 3 is incident on the surface of the photosensitive member 1 and is charged by the charging device 2 uniformly. The surface is exposed to form an electrostatic latent image thereon. Then, this electrostatic latent image is formed into a toner image by the toner supplied by the developing device 4 to become a toner image.

On the other hand, an instruction for feeding paper from the paper cassette 11 is issued by a control unit (not shown), and the uppermost sheet pressed against the feed roller 113 is the feed roller 1.
The sheet 13 is fed one by one while being prevented from being double fed by the separation pad 114 with the rotation of 13, and is conveyed to the registration roller pair 115. Then, the toner is conveyed toward the transfer device 7 provided with the transfer roller 71 at an accurate timing coincident with the toner image on the photoconductor 1.

The transfer paper P conveyed to the transfer device 70 is separated from the photoconductor 1 after the toner image on the photoconductor 1 is transferred, and is conveyed to the fixing device 12. And the heater 12
The toner image is fixed when the toner image passes between a fixing roller 121 having a built-in 1a and a pressure roller 122 which rotates by pressing against the fixing roller 121. Is discharged.

FIG. 2 is a schematic configuration diagram of the developing device 4 of the printer according to the present embodiment and the toner cartridge 100 that stores toner to be supplied to the toner storage portion 41 of the developing device 4. Since the basic configuration and operation of the developing device 4 are the same as those of the developing device of FIG. 5 described above, the same components as those of FIG.

The toner cartridge 100 is provided so as to be detachable from the developing device 4 and receives an agitator 101 for agitating the toner for replenishment therein, a toner agitated by the agitator 101, and removes the toner. A magnetic roller 103 and the like for supplying toner from the supply port 102 to the toner storage section 41 are provided. Then, the toner for replenishment is sent to the magnetic roller 103 by the stirring operation of the agitator 101, and the toner for replenishment is supplied by the rib B provided close to the surface of the magnetic roller by the movement of the surface of the magnetic roller. The toner is scraped off and supplied to the toner storage section 41 from the supply port. Thus, toner supply from the toner cartridge is performed.

The developing device 4 includes a toner storage section 41, a supply roller 43 as a developer supply member, and a supply roller 43.
A developing blade 44 as a developer regulating member for regulating the toner on the surface; an elastic developing roller 45 as a developer carrier; and a toner supply roller 43 while stirring the toner in the toner storage section 41. Agitator 47 as a stirring member for supplying to the surface, toner transport auger 4
6 and the like.

In the developing device 4, the toner stored in the toner storage section 41 is the same as the agitator 47.
The toner is supplied to the surface of the supply roller 43 having a magnetic pole therein while being stirred by the toner transporting auger 46 and moved laterally by the toner transport auger 46, and is attracted and carried by the magnetic force. Then, the toner is thinned by the developing blade 44 in contact with the supply roller 43 and is triboelectrically charged to a desired polarity. The toner is supplied to the developing roller 4 by the rotation of the supply roller 43 in the direction of the arrow.
5 is conveyed. The supply roller 43 and the developing roller 45 are arranged so as to be in contact with each other at the facing portion, and between the supply roller 43 and the developing roller 45,
A predetermined potential difference is formed by a bias applying unit (not shown), and the potential difference generates an electrostatic force for transferring the toner charged to the desired polarity to the developing roller 45. The toner on the supply roller 43 is transferred to the surface of the developing roller 45 by the electrostatic force. Then, the toner transferred to the surface of the developing roller 45 is conveyed to a portion facing the photoconductor 1 as a latent image carrier by the rotation of the developing roller 45 in the arrow direction, and the electrostatic latent image on the surface of the photoconductor 1 is Is developed.

FIG. 3 is an explanatory view of a bias applying means for forming an alternating electric field between the developing roller 45 and the supply roller 43 in the developing device according to the present embodiment. In this developing device, an alternating electric field is formed between the developing roller 45 and the supply roller 43 so that a desired polarity on the supply roller 43, for example, negatively charged toner is transferred and adhered onto the development roller 45. A bias applying means for applying a voltage to the developing roller 45 and the supply roller 43 is provided. The bias applying means includes a DC developing bias power supply for applying Vm to the developing roller 45 and Vb for the supply roller, and a supply roller bias power supply for superimposing AC on DC. Then, Vm, for example, -350 V DC is applied to the developing roller by the developing bias power supply, and Vm is applied to the supply roller by the supply roller bias power supply.
b, for example, to -750V DC, the magnitude (Vp-p) 1.
A voltage obtained by superimposing an alternating current of 2 Kv and a frequency of 2 KHz is applied.

The bias applying means makes the developing roller 4
5 and the supply roller 43, and the developing roller bias Vm is, for example, DC-35.
A developing bias power supply for applying 0 V and a supply bias power supply for applying, for example, only -750 V DC are provided as the supply roller bias Vb.
The effect of the type of developed image on the amount of toner (M / A) on the developing roller after development was compared when no alternate electric field was formed between the developing device and No. 3. FIG. 4 shows the toner amount (M / A) on the developing roller 45 after the portion corresponding to the all black image portion on the developing roller 45 rotates in the direction of the arrow and toner is supplied from the supply roller 43. The upper portion corresponding to the all-white image portion rotates in the direction of the arrow, and indicates the toner amount (M / A) on the developing roller after the toner is supplied from the supply roller 43. When the alternating electric field is formed, the difference in the toner amount (M / A) on the developing roller due to the image history is smaller than when the alternating electric field is not formed, and it can be said that the toner on the developing roller can be made uniform.

In the developing device 4 of the above embodiment, when an alternating electric field is formed between the photosensitive member 1 and the developing roller 45, the magnitude of the alternating electric field between the photosensitive member 1 and the developing roller 45 ( When (Vp-p) is larger than the alternating electric field formed between the developing roller 45 and the supply roller 43, the result is that density unevenness is likely to occur. This is because the mobility of the toner on the developing roller between the developing roller 45 and the supply roller 43 is different from that of the supply roller 43 and the developing roller 4.
5 are in contact with each other at the opposing portion, so that they are easily affected by an alternating electric field formed between the photoconductor 1 and the developing roller 45, and as a result, the electric field is formed between the photoconductor 1 and the developing roller 45. It is considered that the alternating electric field may disturb the transfer adhesion of the toner in both directions. For this reason, the magnitude of the alternating electric field formed between the photosensitive member 1 and the developing roller 45 is made smaller than the magnitude of the alternating electric field formed between the developing roller 45 and the supply roller 43, and the magnitude of the alternating electric field formed between the supply roller 43 and the developing roller 45 is reduced. The effect on the mobility of the toner on the developing roller at the opposing contact portion with the roller 45 is reduced.

The magnitude of the alternating electric field (Vp) formed between the photosensitive member 1 and the developing roller 45 by the bias applying means
-P) is made larger than the alternating electric field formed between the developing roller 45 and the supply roller 43, and the magnitude of the alternating electric field formed between the photosensitive member 1 and the developing roller 45 (Vp -P) is changed to the developing roller 45 and the supply roller 43.
Is smaller than the alternating electric field formed between the developing roller and the developing roller, the type of the developed image is the toner amount (M
/ A) were compared. The magnitude of the alternating electric field formed between the photoconductor 1 and the developing roller 45 (Vp-p)
Is smaller than the alternating electric field formed between the developing roller 45 and the supply roller 43, the difference (M / A) in the amount of toner on the developing roller due to the image history is small, and the toner on the developing roller can be made uniform. It can be said that there is.

Further, as the supply roller bias Vb of the developing device of the above embodiment, the magnitude of the superimposed alternating current (Vp-p) when the direct current is -750 V is 1.5 Kv (750 kV).
V) The following supply roller bias power supply was provided. Also in this case, the difference in the amount of toner on the developing roller with respect to the image history was small, the toner on the developing roller could be made uniform, and an image without density unevenness was obtained. As described above, even when an alternating electric field is formed between the developing roller 45 and the supply roller 43 by using the supply roller bias power source with a low cost in a range where the DC polarity is not changed, the supply roller 43 and the development roller 45 face each other. Since the contact is made at the portions, efficient two-way adhesion transfer of the toner is performed, and the toner on the developing roller can be made uniform.

As described above, according to the present embodiment, the toner on the developing roller is made uniform, and a high-quality image without density unevenness due to the image history can be obtained.

In the above embodiment, the applied bias has been described as reversal development using a one-component magnetic toner having a negative polarity. However, the present invention can be applied to other developer charging polarity and developing polarity.

[0035]

According to the first to third aspects of the present invention, it is possible to provide a developing device capable of preventing the occurrence of density unevenness and suppressing the cost of the power supply device.

[Brief description of the drawings]

FIG. 1 is a front view illustrating a schematic configuration of a printer according to an embodiment.

FIG. 2 is a schematic configuration diagram of a developing device and a toner cartridge of the printer.

FIG. 3 is an explanatory diagram of a bias applying unit of the developing device of the printer.

FIG. 4 is a comparison diagram of the amount of toner on a developing roller based on the image history of the developing device of the printer.

FIG. 5 is a schematic configuration diagram illustrating an example of a conventional developing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 3 Exposure device 4 Developing device 41 Toner storage part 43 Supply roller 44 Developing blade 45 Developing roller 46 Toner transport auger 47 Agitator 100 Toner cartridge

Claims (3)

[Claims] 1. A developing device comprising: a developer carrier facing a latent image carrier; and a magnetic developer supply member for supplying a one-component magnetic developer to the developer carrier. Is arranged so as to be in contact with the developer carrier, and an alternating electric field is formed between the developer carrier and the developer supply member. 2. The developing device according to claim 1, wherein an alternating electric field is formed both between said latent image carrier and said developer carrier and between said developer carrier and said developer supply member. The magnitude of the alternating electric field (Vp-p) between the latent image carrier and the developer carrier is the magnitude of the alternating electric field between the developer carrier and the developer supply member (Vp-p). V
(p-p). 3. The developing device according to claim 1, wherein the alternating electric field between the developer carrier and the developer supply member superimposes an AC voltage on a DC voltage, and The lower limit Vp (min) of the magnitude of the alternating electric field is GN
A developing device, wherein the developing device is formed so as not to exceed D (0 V).