JPH08129296A - Developing device and image forming device - Google Patents

Abstract

PURPOSE: To provide a developing device and an image forming device having a high developing performance free from the occurrence of fogging even on a background part even in the case of using toner of small-sized grain as developer, and also capable of developing with a high density and high image quality free from the occurrence of the mixture of colors even in the case of overlap- developing multicolor toner images. CONSTITUTION: The device is provided with a developing roller 41 equipped with a fixed magnet body 42, a plate-shaped member 43 equipped with an electrode part 44, a supply roller 45, a member for controlling the carried developer amount 46, a scraper 47 functioning as a developer scraping member, a stirring roller 48, a casing 49 for the developing device, two-component developer 50, power sources 51 and 52 as bias impressing means, and a photoreceptor drum 10 having a photosensitive layer 12 formed on a conductive substrate 11, the developing roller 41 is a cylinder made of non-magnetic and also conductive metal such as aluminum and stainless steel, etc., and having a radius of 2.5 to 15mm, and the roller 41 is machined so as to have the surface roughness (Rz) of 1 to 30μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device and an image forming apparatus for developing a latent image on an image forming body to form an image by using an electrophotographic system, and more specifically to an image forming body and a developing device. A plate-like member having an electrode portion is provided on the upstream side of the developing area in which the developer transport body faces the developer transport body moving direction, a DC voltage is applied to the electrode portion, and a DC component is applied to the developer transport body. And a developing device for developing a latent image on the image forming body by flying a toner under an oscillating electric field by applying a superimposed voltage of an AC component, and a plurality of the developing devices are provided, and the developing device is provided on the image forming body. The present invention relates to an image forming apparatus for forming a multicolor image by repeating a step of forming a latent image and a step of developing the latent image a plurality of times.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus for developing a latent image on an image forming body to form a multi-color image by using an electrophotographic system, each process of charging, exposing, developing and transferring is performed plural times. There is an image forming apparatus that repeatedly forms a plurality of toner images on a transfer material to form a multicolor image. In this image forming apparatus, since the toner image is transferred onto the transfer material each time the development of each color is completed, it is necessary to provide a mechanism for holding the transfer material inside the apparatus, and there is a disadvantage that the apparatus becomes large. .

On the other hand, the steps of charging, exposing and developing are repeated a plurality of times to superimpose and develop a plurality of toner images on the same image forming body to collectively form a plurality of toner images on the image forming body. There is an image forming apparatus that forms a multicolor image by transferring the image onto a transfer material. Since this image forming apparatus employs a so-called overlay development / collective transfer method, there is no need to provide a mechanism for holding the transfer material inside the apparatus, and there is an advantage that the apparatus is downsized.

In such an image forming apparatus, for example, the developer layer on the developer carrying body and the image forming body are not in contact with each other, and an alternating voltage having a direct current component is applied to the developer carrying body to apply an oscillating electric field. Since a developing device for developing the latent image on the image forming body by flying the toner underneath is used and is non-contact,
This is preferable in that a large amount of the former toner that has already adhered to the image forming body does not mix into the latter developing device that contains toners of different colors.

However, in such a superposition development, since the latent image on the image forming body is developed in a non-contact manner, it is difficult to reproduce delicate lines or dots or a difference in shade, and it is difficult to obtain a high image quality. . Further, since the toner is made to fly under the oscillating electric field and developed on the image forming body on which the toner image has already been formed, the so-called color mixing occurs in which the toner of the subsequent stage is unnecessarily adhered to the toner image of the preceding stage. There is also.

Generally, in order to obtain a high quality image, it is effective to atomize the toner, but in the case of trying to atomize the toner in the above-mentioned superposition development, in order to obtain a sufficient image density. Is required to increase the AC voltage applied to the developer carrier. On the other hand, when the AC voltage is increased, more color mixture as described above occurs and the fog toner adheres to the background part, and eventually, in the overlapping development. It has been difficult to atomize the toner to obtain high image quality.

Therefore, for example, Japanese Patent Laid-Open No. 59-223467.
In the publication, a wire-shaped control electrode for controlling the flight of toner is provided in the gap between the image forming body and the developer layer on the developer transport body, and at least one of the control electrode and the developer transport body is provided. A developing method is disclosed in which an alternating voltage is applied to form an oscillating electric field, and toner is caused to fly to perform development. It is described in the above-mentioned publication that fine particles can be used as the toner of the two-component developer, fogging is prevented, and clear high image quality can be obtained.

However, when the developing method described in the above publication is used, since a plurality of wire-shaped control electrodes are provided in the developing area where the toner flies, the wire-shaped control electrodes are contaminated by the toner as they are used, or There is a problem that the toner is clogged between the wire-shaped control electrodes and the initial developability cannot be stably obtained. Further, in an actual device, it is difficult to accurately provide a plurality of wires in a narrow gap.

Therefore, for example, in Japanese Unexamined Patent Publication No. 5-346736, a plate-shaped member having an electrode in the upstream portion of the developing area where the image forming body and the developer transport body face each other is brought into contact with the developer transport body. Is provided between the electrode and the developer transport body.
A developing device is disclosed in which a second oscillating electric field is formed between the image forming body and the developer carrying body to cause the toner to fly and develop. According to the above publication, high image quality can be obtained even by using a toner having a small particle diameter with an average particle diameter of 10 μm or less, and color mixing does not occur even in an image forming apparatus adopting a superposition developing / collective transfer method, resulting in a high developing efficiency. It is described that high and uniform development can be performed.

[0010]

However, even when the developing device described in the above publication is used, the position where the plate-like member having the electrode is provided, the bias voltage applied to the electrode or the developer carrier, and the image forming body. Depending on the surface potential of the toner, the average charge amount and the average particle diameter of the toner used, sufficient developability may not be obtained, fogging may occur in the background portion, or color mixture may occur during overlay development. There is a problem that high image quality cannot always be obtained.

The object of the present invention is to solve the above-mentioned problems, and even when a toner having a small particle size is used as a developer, the developability is high, no fog is generated in the background portion, and a multicolor toner image is obtained. It is an object of the present invention to provide a developing device capable of performing excellent development in which color mixing does not occur even in the overlapping development of.

Another object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality multicolor image having high density and no color mixture even when the superposing development / collective transfer system is adopted. Is.

[0013]

As a result of repeated studies in order to achieve the above object, an electrode portion is provided on the upstream side in the moving direction of the developer transport body in the developing area where the image forming body and the developer transport body face each other. A plate-shaped member having the same, a direct current voltage is applied to the electrode portion, a superimposed voltage of a direct current component and an alternating current component is applied to the developer transport body, and the toner is caused to fly under an oscillating electric field to cause the image forming body. A developing device for developing the above latent image, and a plurality of such developing devices are provided, and the step of forming a latent image on the image forming body and the step of developing the latent image are repeated a plurality of times to obtain a multicolor image. Regarding the image forming apparatus to be formed, (A) When the oscillating electric field formed in the gap between the electrode portion and the developer transport body is strengthened, generation of a toner cloud is promoted and high developability can be obtained. A) On the other hand, the image forming body and the developer carrying body When the oscillating electric field formed in the gap is increased, fogging is generated in the background portion, and color mixture at the time of superposition development is also increased. (C) The DC electric field in the gap between the electrode portion and the developer transport body causes toner When acting as a force to be pressed against the developer transport body, if the DC electric field is strengthened, generation of a toner cloud is suppressed, fogging of the background portion and color mixing at the time of overlay development are suppressed, but high developability can be obtained. No, (d) On the contrary, when the DC electric field acts as a force for accelerating the toner, when the DC electric field is increased, the plate-shaped member having the electrode portion is provided at the end portion on the downstream side in the developer transporting body moving direction. The moving speed of the toner becomes faster, and high developability can be obtained in the solid part, but fog occurs in the background part and color mixing also increases.
(E) If the oscillating electric field in the gap between the electrode portion and the developer transport body is weaker than the DC electric field in the gap, and the DC electric field acts as a force for pressing the toner toward the developer transport body, the toner is Since the generation of a toner cloud is suppressed by being pressed against the developer transport body side, high developability cannot be obtained. In (f) superposition development, the image formation body and the developer transport in each developing step When the oscillating electric field in the gap with the body is made stronger than the oscillating electric field in the developing process in the former stage, the toner image in the former stage is disturbed in the developing process in the latter stage, and color mixing increases,
(G) When the width of the latent image formed on the image forming body in the direction orthogonal to the moving direction of the developer transport body is narrower than the width of the latent image formed in the direction orthogonal to the moving direction of the developer transport body. Since there is no electrode portion at both ends of the latent image, the developability of this portion is lowered and the image density is lowered. (H) Development carried on the developer transport body beyond the width of the latent image When the width of the developer layer in the direction orthogonal to the moving direction of the developer transport body is narrow, the developer is not supplied to both ends of the latent image, so that the toner is not developed. When the width of the plate-shaped member in the direction orthogonal to the moving direction of the developer transport body is narrow, it is actually impossible that the width of the electrode portion is larger than the width of the plate-shaped member. (5) At least the above-mentioned problems occur. When the width is narrow, since there is no developer layer at both ends of the electrode part, discharge easily occurs at this part between the electrode part and the developer transport body. , The developing bias is not applied, and even when the power is not down, the oscillating electric field between the electrode section and the developer transport body is weakened, the developability is lowered, and the image density is lowered. ) When the width of the plate-shaped member is narrower than the width of the developer layer, since there is no plate-shaped member that is also a developer layer pressing member at both ends of the developer layer, the height of the spikes of the developer layer at this portion is high. Is higher than the height of the ears of the developer layer at the portion pressed by the plate-shaped member, the ears come into contact with the image forming body, and color mixing occurs, or the developer layer is formed at the end of the plate-shaped member. It is said that the edges of the image will be cut off and carrier adhesion will be more likely to occur on the image forming body. Stop, which resulted in the completion of the present invention.

The above-mentioned object is to provide a plate-like member having an electrode portion on the upstream side in the moving direction of the developer transport body in the developing area where the image forming body and the developer transport body face each other, and to the electrode portion, a DC voltage is applied. And a superimposed voltage of a direct current component and an alternating current component is applied to the developer transport body to cause the toner to fly under an oscillating electric field to develop the latent image on the image forming body. The amplitude of the AC component applied to the carrier is V
_{When AC} [V], DC component is _VDC [V], and DC voltage applied to the electrode portion is V _DEN [V], V _AC > | V _DEN | − | V _DC | The closest distance between the developer transport body and D ₁ [mm], the closest distance between the electrode portion and the developer transport body is D ₂ [mm], and the average charge amount of the toner is Q _t [μ].
C / g] and the average particle diameter is d _t [μm], 10 · | Q _t | · d _t · D ₁ > _VAC > 5 · | Q _t | · d _t ·
D ₂ is a developing device.

Further, in the developing device of the present invention, the frequency of the AC component applied to the developer transport body is f _AC [Hz], the moving speed of the developer transport body is V _r [mm / sec], and the electrode portion is The width of the developer transport body in the moving direction is L ₁ [mm]
Then, f _AC ≧ 10 · V _r / L ₁ is characterized.

Further, the closest distances between the downstream end and the upstream end of the electrode portion in the moving direction of the developer transport body and the closest distance to the developer transport body are D ₄ [mm] and D ₅ [m], respectively.
m], the thickness of the developer layer at the position where the plate-shaped member is in contact with the developer on the developer transport body is H ₁ [mm]
Then, it is characterized in that D ₄ > D ₂ = D ₅ > H ₁ .

Further, the closest distance between the downstream end of the plate-shaped member in the moving direction of the developer transport body and the developer transport body is D ₃ [mm], the image forming body and the developer transport body are The thickness of the developer layer at the position closest to H ₂ [m
m], D ₄ ≧ D ₃ > H ₂ and 0.6 · D ₁ ≧ D ₃ ≧ 0.2 · D ₁ .

Furthermore, the distance between the end of the electrode portion on the downstream side in the moving direction of the developer transport body and the end of the plate-shaped member on the downstream side in the moving direction of the developer transport body, that is, the eaves of the plate-like member. Is L ₂ [mm], and the distance between the position where the plate-shaped member is in contact with the developer on the developer transport body and the end of the plate-shaped member on the downstream side in the developer transport body movement direction. To L ₃
When [mm] is set, L ₃ > L ₁ > L ₂ is characterized.

The radius of curvature in the developing area of the developer transport body is r [mm], and the position where the image forming body and the developer transport body are closest to each other with respect to the center of curvature of the developer transport body. And θ [°] between the position where the plate-shaped member is in contact with the developer on the developer transport body and θ [°], r · (1-cos θ) ≧ D ₁ and r · sin θ ≧ L It is characterized in that it is ₃ · cos θ.

Further, the plate-shaped member has an electrode portion and a coating layer formed on an insulating substrate material, and the width of the coating layer in the moving direction of the developer transport body is L ₄ [mm]. Then, it is characterized in that L ₃ > L ₄ ≧ L ₁ + L ₂ .

Further, the above-mentioned object is to provide a plate-like member having an electrode portion on the upstream side in the moving direction of the developer transport body in the developing area where the image forming body and the developer transport body are opposed to each other, and the electrode portion is provided with a direct current. In the developing device, which applies a voltage and applies a superimposed voltage of a direct current component and an alternating current component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image forming body, The amplitude of the AC component applied to the agent carrier is V _AC
[V], the direct current component is V _DC [V], and the direct current voltage applied to the electrode part is V _DEN [V], then V _AC > | V _DEN | − | V _DC | The closest distance of the developer transport body is D ₁ [mm], and the closest distance between the downstream end of the plate-shaped member in the developer transport body moving direction and the developer transport body is D ₃
[Mm], latent image potential V _L of the solid portion on the image forming body
[V], when the latent image potential of the background portion is a V _{H (V), | V H |> | V} DC |> | V L | and _{| V DC | + | V DC} -V L | · D 3 / D ₁ ＞ ｜ V _DEN ｜ ＞ ｜ V
_DC | - | characterized in that it is a _{· (1-D 3 / D} 1) | V H -V DC.

In the developing device of the present invention, the frequency of the AC component applied to the developer carrier is f _AC [Hz], the moving speed of the developer carrier is V _r [mm / sec], and the electrode is The width in the moving direction of the developer transport body is L ₁ [mm]
Then, f _AC ≧ 10 · V _r / L ₁ is characterized.

Further, the closest distance between the electrode portion and the developer transport body is D ₂ [mm], and the downstream end portion and the upstream end portion in the moving direction of the developer transport body of the electrode portion and the developing portion. The closest distances to the developer transport body are D ₄ [mm] and D ₅ [mm], respectively, and the thickness of the developer layer at the position where the plate member is in contact with the developer on the developer transport body is H. ₁
When [mm] is set, D ₄ > D ₂ = D ₅ > H ₁ is characterized.

Further, the thickness of the developer layer at the position where the image forming body and the developer carrying body are closest to each other is H
_{When 2} [mm], it is characterized in that D ₄ ≧ D ₃ > H ₂ and 0.6 · D ₁ ≧ D ₃ ≧ 0.2 · D ₁ .

Furthermore, the distance between the end of the electrode portion on the downstream side in the moving direction of the developer transport body and the end of the plate-shaped member on the downstream side in the moving direction of the developer transport body, that is, the eaves of the plate-like member. Is L ₂ [mm], and the distance between the position where the plate-shaped member is in contact with the developer on the developer transport body and the end of the plate-shaped member on the downstream side in the developer transport body movement direction. To L ₃
When [mm] is set, L ₃ > L ₁ > L ₂ is characterized.

The radius of curvature in the developing area of the developer transport body is r [mm], and the position where the image forming body and the developer transport body are closest to the center of curvature of the developer transport body. When the angle formed by the position of the plate-shaped member in contact with the developer on the developer transport body is θ [°], r · (1-cos θ) ≧ D ₁ and r · sin θ ≧ L It is characterized in that it is ₃ · cos θ.

Further, the plate-shaped member has an electrode portion and a coating layer formed on an insulating substrate material, and the width of the coating layer in the moving direction of the developer transport body is L ₄ [mm]. Then, it is characterized in that L ₃ > L ₄ ≧ L ₁ + L ₂ .

Further, the above object is to provide a plate-like member having an electrode portion on the upstream side in the moving direction of the developer carrying body in the developing area where the image forming body and the developer carrying body are opposed to each other, and the direct current is provided to the electrode part. A plurality of developing devices are provided for applying a voltage and applying a superimposed voltage of a direct current component and an alternating current component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image forming body. In the image forming apparatus for forming a multi-color image by repeating the step of forming a latent image on the image forming body and the step of developing the latent image a plurality of times, the developing agent is applied to the developer carrying body in each developing step. The amplitude of the alternating current component is V _AC [V], the direct current component is V _DC [V], and the direct current voltage applied to the electrode part is V
_DEN [V], the closest distance between the image forming body and the developer transport body is D ₁ [mm], the closest distance between the electrode portion and the developer transport body is D ₂ [mm], the average of the toner When the charge amount is Q _t [μC / g] and the average particle size is d _t [μm], V _AC > | V _DEN | − | V _DC | and 10 · | Q _t | · d _t · D ₁ > V _AC > 5 ・ ｜ Q _t ｜ ・ d _t・
D ₂ and the strength of the oscillating electric field in the gap between the image forming body and the developer carrying body in each developing step, and the strength of the oscillating electric field in the gap between the image forming body and the developer carrying body in the preceding developing step. This is achieved by an image forming apparatus characterized by making the strength of an oscillating electric field equal or weaker.

Still another object of the present invention is to provide a plate-shaped member having an electrode portion on the upstream side in the developing region moving direction of the developing area where the image forming body and the developer conveying body face each other, and the electrode portion is provided. A plurality of developing devices are provided for applying a DC voltage and applying a superimposed voltage of a DC component and an AC component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image forming body. In an image forming apparatus for forming a multi-color image by repeating the step of forming a latent image on the image forming body and the step of developing the latent image a plurality of times, the developing agent is transferred to the developer carrying body at each developing step. The amplitude of the applied AC component is V _AC [V], the DC component is V _DC [V], the DC voltage applied to the electrode portion is V _DEN [V], and the closest distance between the image forming body and the developer transport body. The distance is D ₁ [mm], and the downstream side in the moving direction of the developer transport body of the plate-shaped member The closest distance between the end of the image carrier and the developer transport body is D ₃ [mm], the latent image potential of the solid portion on the image forming body is V _L [V], and the latent image potential of the background portion is V _H [V]. ] and the _{time, V AC> | V DEN |} - | V DC | and _{| V H |> | V DC} |> | V L | and _{| V DC | + | V DC} -V L | · D 3 / D ₁ ＞ ｜ V _DEN ｜ ＞ ｜ V
_DC | − | V _H −V _DC | · (1-D ₃ / D ₁ ), and the strength of the oscillating electric field in the gap between the image forming body and the developer carrying body in each developing step is set to The image forming apparatus is characterized in that the strength of the oscillating electric field in the gap between the image forming body and the developer carrying body in the developing step is made equal to or weaker.

Further, the above object is to provide a plate-like member having an electrode portion on the upstream side in the moving direction of the developer transport body in the developing area where the image forming body and the developer transport body face each other, and the electrode portion is provided with a direct current. In the developing device for applying a voltage and applying a superimposed voltage of a direct current component and an alternating current component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image forming body, The width of the strip-shaped member in the direction orthogonal to the moving direction of the developer transport body is W ₁ [mm], and the width of the electrode portion in the direction orthogonal to the moving direction of the developer transport body is W ₂ [mm], the developer The width of the developer layer conveyed on the conveying body in the direction orthogonal to the moving direction of the developer conveying body is W ₃ [mm] and the moving direction of the developer conveying body of the latent image formed on the image forming body. When the width in the direction orthogonal to is W ₄ [mm], W ₁ > W ₃ > W ₂ > W ₄ is achieved by the developing device.

[0031]

In the present invention, the amplitude V _AC [V] of the _AC component applied to the developer carrier, the DC component V _DC [V], and the DC voltage V _DEN [V] applied to the electrode portion are V _AC >. The amplitude V _{AC of the AC} component, the DC component V _DC , and the DC voltage V _DEN are set so as to satisfy the relationship of | V _DEN | − | V _DC |. That is,
Since the oscillating electric field is made stronger than the DC electric field in the gap between the electrode portion and the developer transport body, the toner is not pressed to the developer transport body side, and the generation of the toner cloud is promoted.

In the present invention, the amplitude V _AC [V] of the _AC component applied to the developer transport body, the closest distance D ₁ [mm] between the image forming body and the developer transport body, and the electrode portion The closest distance D ₂ [mm] of the developer carrier, the average charge amount Q _t [μC / g] of the toner, and the average particle size d _t [μm] are 10 · | Q _t | · d _t · D ₁ ＞ _VAC ＞ 5 ・ ｜ Q _t ｜ ・ d _t・
So as to satisfy the relationship of D _2, the amplitude V _AC of the AC component, the closest distance D ₁ and D _2, sets the average charge amount Q _t and the average particle diameter d _t. That is, in the gap between the electrode portion and the developer conveying _{member, V AC / D 2> 5} · | Q t | to satisfy the relation · d _t, also the image forming body and said developer transport member In the gap of, the relationship of 10 · | Q _t | · d _t > _VAC / D ₁ is satisfied. The former is a condition of an oscillating electric field in the gap for promoting generation of a toner cloud in the gap between the electrode portion and the developer transport body, and the latter is a condition between the image forming body and the developer transport body. It is a condition of an oscillating electric field in the gap for suppressing generation of a toner cloud in the gap. By satisfying both of them, high developability can be obtained, and at the same time, fogging of the background portion and occurrence of color mixture can be suppressed.

Further, in the present invention, a DC component V _DC [V] applied to the developer carrying member, a DC voltage V _DEN [V] applied to the electrode portion, and the image forming member and the developer carrying member. The closest distance D ₁ [mm], the closest distance D ₃ [mm] between the developer transporter and the end of the plate member having the electrode portion on the downstream side in the moving direction of the developer transporter, and the image forming body. The latent image potential V _L [V] of the solid portion formed above and the latent image portion V _H [V] of the background portion are | V _H |> | V _DC |> | V _L | and | V _DC | + | V _DC -V _L ｜ ・ D ₃ / D ₁ ＞ ｜ V _DEN ｜> ｜ V
_DC | − | V _H −V _DC | · (1-D ₃ / D ₁ ), the DC component V _DC , the DC voltage V _DEN , the closest distances D ₁ and D ₃ , and the above setting the latent image potential V _L and the latent image potential V _H of the background portion of the solid portion. That is, in the solid part, the relationship of | V _DC |> | V _L | and | V _DC −V _L | / D ₁ > | V _DEN −V _DC | / D ₃ is satisfied, and in the background part, | V _H | > | V _DC | and _{| V H -V DC | / D} 1> | V DC -V DEN | / to satisfy following (D ₁ -D _3). The former is a condition for moving the toner pressed against the developer transport body side in the gap between the electrode portion and the developer transport body onto the image forming body by the latent image electric field of the solid portion, The latter is a condition that the toner accelerated in the gap between the electrode portion and the developer transport body receives a deceleration force by the latent image electric field in the background portion and does not reach the image forming body. By satisfying both of them, high developability is obtained in the solid portion, and generation of fogging and color mixture is suppressed in the background portion.

Furthermore, in the present invention, the step of forming a latent image on the image forming body and the step of developing the latent image are repeated a plurality of times, and the image forming body and the developer carrying body in each developing step are repeated. The strength of the oscillating electric field is set so that the strength of the oscillating electric field in the gap is equal to or weaker than the strength of the oscillating electric field in the gap between the image forming body and the developer transporting body in the preceding developing step. . This allows
The toner image formed on the image forming body in the former developing step is not disturbed in the latter developing step,
The toner in the subsequent stage is not mixed in the toner image.

Furthermore, in the present invention, the width of the plate member in the direction orthogonal to the moving direction of the developer transport body is W.
₁ [mm], the width of the electrode portion in the direction orthogonal to the moving direction of the developer transport body is W ₂ [mm], the moving direction of the developer transport body of the developer layer transported on the developer transport body when the width in the direction perpendicular to the developer conveying member movement direction orthogonal latent image formed in the direction of width W ₃ (mm) and the image forming body on was W ₄ [mm] in, W ₁ The width W ₁ of the plate member, the width W _{2 of the} electrode portion, the width W ₃ of the developer layer, and the width W _{4 of the} latent image are set so as to satisfy the relationship of> W ₃ > W ₂ > W _4. Set. That is, since the width W _{2 of the} electrode portion is set to be wider than the width W _{4 of} the latent image, the developability at both ends of the latent image does not decrease and the image density does not decrease. Since the width W ₃ of the developer layer is set to be wider than the width W _{2 of} the electrode portion, discharge is generated at both ends of the electrode portion to reduce the developing bias, and The vibrating electric field with the body is not weakened so that the developing property is not lowered and the image density is not lowered, and further, the width W _{1 of the} plate member is wider than the width W ₃ of the developer layer. In order to set, the ears of the developer layer come into contact with the image forming body at both ends of the developer layer, and color mixing occurs, or the ears of the developer layer are cut off at the end portions of the plate-shaped member to form an image on the image forming body. No carrier adhesion occurs.

As described above, even when a toner having a small particle diameter is used, the developing property is high, the fog does not occur in the background portion, and the color mixture does not occur even in the superimposing development. You can Further, even in the case of adopting the overlay development / collective transfer method, it is possible to obtain a high-density multicolor image having high density and no color mixture.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an example of the developing device according to the present invention, and FIG. 2 is an enlarged sectional view of the main part of the developing device. In these figures, 41 is a developing roller which is a developer carrying body having a fixed magnet body 42 therein, and 43 is an electrode portion 44.
A plate-like member having a roller, 45 a supply roller as a developer supply member, 46 a restriction rod as a developer transport amount restriction member, 47
Is a scraper that is a developer scraping member, 48 is a stirring roller that is a developer stirring member, 49 is a casing of the developing device, 50 is a two-component developer including toner T and carrier C, and 51 and 52 are bias applying means, respectively. As a power source, 10 is a photosensitive drum that is an image forming body in which a photosensitive layer 12 is formed on a conductive substrate 11, D ₁ is the closest distance between the photosensitive drum 10 and the developing roller 41, and D ₂ is the electrode. The closest distance between the portion 44 and the developing roller 41, D ₃ indicates the closest distance between the end portion of the plate member 43 and the developing roller 41. The arrows in the figure indicate the rotation directions of the photosensitive drum 10 and the developing roller 41.

The developing roller 41 is made of a non-magnetic and conductive metal such as aluminum or stainless steel and has a radius of 2.
It is a cylinder of 5 to 15 mm and has a surface roughness (Rz) of 1 to 3.
It is processed to be 0 μm. The developing roller 4
1, the magnetic field on the surface of the developing roller 41 is 500
A cylindrical magnet body 42 having 4 to 12 magnetic poles magnetized to have N poles or S poles so as to have ˜1,200 gauss is fixedly disposed, and the developing roller 41 is the magnet. It is rotatable with respect to the body 42.

The plate member 43 is made of an insulating organic substrate material or inorganic substrate material such as polyimide resin, epoxy resin, glass fiber reinforced epoxy resin, ceramics, etc. and has a thickness of 0.05 to 0.5 mm and is a single layer or a multilayer. And a thickness of 0.005 to 0.1 m made of a conductive material such as copper foil on the top surface or inside of the plate member 43.
An electrode portion 44 having a width of m and a width of 0.1 to 1 mm is formed.

The casing 49 is a casing made of an insulating resin such as acrylic or polycarbonate, and the casing 49 has a developing roller 41, a supply roller 45, and a scraper 47 which include the fixed magnet body 42 therein.
And a stirring roller 48 are arranged and the casing 49
A restriction rod 46 is disposed at the outlet of the plate-shaped member 4 having the electrode portion 44 at the upper end of the casing 49.
3 is arranged with one end fixed.

A two-component developer 50 composed of toner T and carrier C is stored inside the casing 49. The two-component developer 50 is agitated and mixed by the agitating roller 48, and is supplied by the supply roller 45 and adheres onto the developing roller 41 to form a magnetic brush. The magnetic brush is conveyed while the conveying amount is regulated by the regulating rod 46 as the developing roller 41 rotates.

The developing roller 41 receives a superimposed voltage of a DC component and an AC component from the power source 51, and the plate member 4
A DC voltage is applied to the third electrode portion 44 from the power source 52, and a strong oscillating electric field is generated in the gap between the developing roller 41 and the electrode portion 44 and the gap between the developing roller 41 and the photosensitive drum 10. A weak oscillating electric field is formed. The strong oscillating electric field causes the toner T to fly away from the carrier C and generate a toner cloud. The toner cloud causes the photosensitive drum 1 to move due to the weak oscillating electric field.
The toner image is formed on the photoconductor drum 10 by being assisted in the flight toward the latent image on 0.

FIG. 3 is a block diagram showing an example of the image forming apparatus of the present invention. In the figure, 10 is a photosensitive drum which is an image forming body, 20 is a scorotron charger which is a charging means,
Reference numeral 25 is an image reading unit, 30 is an image writing unit using a laser beam as an exposure unit, 40A, 40B, 40.
C and 40D are the developing devices shown in FIG. 1 containing two-component developers of different colors, and 60 is the first paper feed roller 60.
And a sheet feeding unit including the second sheet feeding roller 62, 70 is a transfer corona charger that is a transfer unit, 75 is a separating corona charger that is a separating unit, 80 is a transport unit, 85 is a fixing unit, and 9 is a fixing unit.
Reference numeral 0 represents a cleaning device having a cleaning blade 91, and 95 represents a pre-charge exposure lamp. The arrow in the figure indicates the rotation direction of the photosensitive drum 10.

In the basic operation of the multicolor image forming process according to this embodiment, first, a copy start command is sent from an operation unit (not shown) to a control unit (not shown), and the photosensitive drum 10 starts rotating. As the photosensitive drum 10 rotates, its peripheral surface is uniformly charged by the scorotron charger 20. Further, the image reading unit 25 converts the optical information from the document into an electric signal, and the electric signal is subjected to image processing and then input to the image writing unit 30. An image writing unit 30 irradiates a laser beam onto the charged photoconductor drum 10 to form a latent image on the photoconductor drum 10. The latent image on the photosensitive drum 10 is
It is developed by any of the developing devices 40A, 40B, 40C or 40D, and a toner image is formed on the photosensitive drum 10.

Photosensitive drum 1 on which the toner image is formed
0 is uniformly charged again by the scorotron charger 20, and a laser beam is emitted by the image writing device 30 to form the next latent image. The latent image on the photoconductor drum 10 is the developing device 40A, 40B, 40.
After being developed by either C or 40D, the next toner image is superposed on the photoconductor drum 10.

In this embodiment, the latent image forming step as described above,
The developing process is repeated four times, and toner images of four colors are superposed on the photosensitive drum 10.

A recording sheet, which is a transfer material, is stored in the sheet feeding section 60, and is synchronized with the toner image superposed on the photosensitive drum 10 by the first sheet feeding roller 60 and the second sheet feeding roller 62. And is delivered to the transfer corona charger 70. The toner images superposed on the photosensitive drum 10 are transferred onto the recording paper by the transfer corona charger 70, and the recording paper is separated from the photosensitive drum 10 by the separating corona charger 75. The recording paper on which the toner image has been transferred is conveyed to the fixing unit 85 via the conveying unit 80, melted and pressure-fixed, and then discharged to the outside of the apparatus.

On the other hand, the toner remaining on the photoconductor drum 10 without being transferred to the recording paper is pressure-contacted to the photoconductor drum 10 at a timing.
It is scraped off by a cleaning device 90 equipped with 1.
After the residual potential is removed by the pre-charge exposure lamp 95,
Enter the next image forming process.

Now, the requirements of the present invention will be described.

In the present invention, the amplitude V _AC [V] of the _AC component applied to the developing roller 41, the DC component V _DC [V],
DC voltage V applied to the electrode portion 44 of the plate member 43
It is required that _DEN [V] satisfies the relationship of V _AC > | V _DEN | − | V _DC |.

By satisfying the above relationship, the toner T is generated in the gap between the electrode portion 44 and the developing roller 41.
Since the oscillating electric field for causing the toner to fly away from the carrier C to generate the toner cloud is stronger than the DC electric field for pressing the toner T to the developing roller 41 side, the generation of the toner cloud is promoted.

When V _AC , V _DC and V _DEN do not satisfy the above relationship, and V _AC ≤│V _DEN │- _{│V DC} │, the toner T becomes the developing roller 41.
Since it is pressed to the side, generation of toner cloud is suppressed, and high developability cannot be obtained.

Further, in the present invention, the developing roller 4
Amplitude V _AC [V] of the _AC component applied to the unit 1, the closest distance D ₁ [mm] between the photosensitive drum 10 and the developing roller 41,
The closest distance D ₂ between the electrode portion 44 and the developing roller 41
[Mm], the average charge amount of the toner T Q _t [μC /
g] and the average particle diameter d _t [μm] is 10 · | Q _t | · d _t · D ₁ > _VAC > 5 · | Q _t | · d _t ·
Satisfying the relationship of D ₂ is another requirement.

The above requirements will be described with reference to FIG.

FIG. 4 shows the photosensitive drum 10 and the developing roller 41.
FIG. 6 is a model diagram for considering an oscillating electric field formed in a gap between the electrode portion 44 and the developing roller 41 and a gap between the electrode portion 44 and the developing roller 41. In the figure, 10 is a photosensitive drum, 41 is a developing roller, 44 is an electrode portion, D ₁ is the photosensitive drum 10
Is the closest distance between the developing roller 41 and D ₂ , and D ₂ is the closest distance between the electrode portion 44 and the developing roller 41. An AC voltage V _AC is applied to the developing roller 41, and oscillating electric fields E ₁ and E ₂ are respectively applied to the gap between the photosensitive drum 10 and the developing roller 41 and the gap between the electrode portion 44 and the developing roller 41. Are formed.

In order to obtain high developability and to suppress fog and color mixture in the background part, a toner cloud is generated only in the gap between the electrode part 44 and the developing roller 41, and the photosensitive drum 10 and the developing part are developed. A toner cloud may not be generated in the gap between the roller 41 and the balance of the forces acting on the toner T is determined by the oscillating electric field E ₂ in the gap between the electrode portion 44 and the developing roller 41. The force F ₂ is set to be larger than the mirror image force F _i acting on the toner, and in the gap between the photoconductor drum 10 and the developing roller 41, the force F ₁ due to the oscillating electric field E ₁ is the mirror image force F _{i. It} may be set to be smaller than _i .

First, the gap between the photosensitive drum 10 and the developing roller 41 will be considered.

Force F ₁ due to the oscillating electric field E _{1 in the} gap
, When the average charge amount of the toner T and q _t, F ₁ = | a _{· V AC / D 1 (1} ) | q t.

Further, the image force F _i acting on the toner T is F _i = βq _t │ ² / (4π) where q _t is the average charge amount of the toner T and d _t is the average particle size. ε ₀ · d _t ² ) given by (2).

Since F _i > F ₁ in the gap, β · | q _t | ² / (4 · π · ε ₀ · d _t ² )> | q _t | · _VAC
/ D ₁ , and rearranging this equation gives β · | q _t | · D ₁ / (4 · π · ε ₀ · d _t ² )> _VAC (3).

[0062] On the other hand, the average charge amount q _t of the toner T is the average charge amount Q _t, when the density _{ρ t, q t = Q t} · ρ t · (4/3) · π · (d since _t / 2) is ³ (4), (4) a (3) assignment to be and β · ρ _t · organized _{| Q t | · d t ·} D 1 / (24 · ε 0)> V _AC (5) is obtained.

In the equations (2) to (5), β is the toner T
And a coefficient relating to the dielectric constant of carrier C, which is described in the literature (M.
H. Davis, Amer. J. Physics, 3
7, 26 (1969). ), Β = 2. ε ₀ is the dielectric constant of vacuum, and ε ₀ = 8.85 × 10 ⁻¹² [F / m]
Is. Further, the density ρ _{t of the} toner T is ρ _t = 1.1 [g / cm ³ ] for a normal non-magnetic toner. Substituting these numerical values into the equation (5), the units of Q _t , d _t , D ₁ and V _AC are Q _t [μC / g] and d _t [μ, respectively.
m], D ₁ [mm], and V _AC [V], 10 · | Q _t | · d _t · D ₁ > _VAC (6) is obtained.

The expression (6) is a condition for suppressing the generation of the toner cloud in the gap and preventing the fog and the color mixture of the background portion.

Next, the gap between the electrode portion 44 and the developing roller 41 will be considered.

Force F ₂ due to the oscillating electric field E _{2 in the} gap
Is F ₂ = | q _t | · _VAC / D ₂ (7).

The image force F _i acting on the toner T is given by F _i = β│q _t │ ² / (4πε ₀ d _t ² ) (2), and in the gap, F ₂ >. Since it is F _i , | q _t | · _VAC / D ₂ > β · | q _t | ² / (4 · π · ε ₀ ·
d _t ² ) and rearranging this equation yields V _AC > β · | q _t | · D ₂ / (4 · π · ε ₀ · d _t ² ) (8).

Similar to the above, the equation (4) is substituted into the equation (8) for rearranging, and β = 2 and ε ₀ = 8.85 × 10.
^-12 [F / m], ρ _t = 1.1 [g / cm ³ ] is substituted,
The units of _VAC , Q _t , d _t and D ₂ are V
_AC [V], Q _t [μC / g], d _t [μm], D ₂ [m
m], V _AC > 10 · | _Qt | · _dt · D ₂ (9) is obtained.

When the equation (9) is derived, the electrode portion 4
The oscillating electric field E _{2 in the} gap was calculated assuming that there is no dielectric other than air in the gap between the developing roller 41 and the developing roller 41.
Due to the presence of the component developer 50, the oscillating electric field E ₂ is strengthened.

Considering this, the equation (9) is as follows.

V _AC > 5 · | _Qt | · _dt · D ₂ (10) The expression (10) is a condition for promoting generation of a toner cloud in the gap and obtaining high developability.

Combining the equations (6) and (10), we obtain 10 · | Q _t | · d _t · D ₁ > _VAC > 5 · | Q _t | · d _t · D ₂ (11) , The requirements of the present invention are derived.

Actually, the toner T having the average charge amount Q _t [μC / g] and the average particle size d _t [μm] is used, and the developing roller 41 is used.
Amplitude V _AC [V] of _AC component applied to the photoconductor drum 1
0 and the closest distance D ₁ [mm] between the developing roller 41 and the closest distance D ₂ [mm] between the electrode portion 44 of the plate-like member 43 and the developing roller 41 so as to satisfy the relationship of the equation (11). When set, the image density is high, background fog,
It is possible to obtain a high-quality image with no color mixture.

On the other hand, V does not satisfy the relationship of the above equation (11).
_{When AC} is 10 · | _Qt | · _dt · D ₁ or more, the toner adheres to the latent image or toner image of the background portion formed on the photoconductor drum 10 to cause fog, resulting in color mixture. Conversely, V
_{If the AC} is 5 · | Q _t | · d _t · D ₂ or less, the image density of the solid portion becomes low and the line width becomes thin, and a good image cannot be obtained in any case.

Further, in the present invention, the developing roller 41
DC component V _DC [V] applied to the plate member 43, DC voltage V _DEN [V] applied to the electrode portion 44 of the plate member 43, and the closest distance D ₁ [m] between the photosensitive drum 10 and the developing roller 41.
m], the closest distance D ₃ [mm] between the developing roller 41 and the downstream end of the plate-like member 43 in the moving direction of the developing roller 41 (hereinafter referred to as the downstream end of the plate-like member 43),
The latent image potential V _L of the solid portion formed on the photosensitive drum 10 V, the latent image potential V _H of the background portion V, | V _H |> | V _DC |> | V _L | and | _{V DC | + | V DC -V} L | · D 3 / D 1> | V DEN |> | V
Another requirement is to satisfy the relationship of _DC | − | V _H −V _DC | · (1-D ₃ / D ₁ ).

The above requirements will be described with reference to FIG.

FIG. 5 shows the photosensitive drum 10 and the developing roller 41.
6A and 6B are model diagrams for considering the flying of toner in a developing area where and are opposed to each other. FIG. 7A is a case where a latent image of a solid portion is formed on the photoconductor drum, and FIG. This is the case where the latent image or toner image of the background portion is formed on the drum 10. In the figure, 10 is a photosensitive drum, 41 is a developing roller, 43 is a plate-shaped member having an electrode portion 44, D ₁ is the closest distance between the photosensitive drum 10 and the developing roller 41, and D ₃ is the plate-shaped member. It is the closest distance between the downstream end of 43 and the developing roller 41.

First, referring to FIG. 5A, the photosensitive drum 1
Consider the case where the latent image of the solid portion is formed on 0.

A DC voltage V is applied to the electrode portion of the plate member 43.
_DEN , a DC voltage V _DC is applied to the developing roller 41, and a DC electric field E ₃ is formed in the gap between the plate-like member 43 having the electrode portion 44 and the developing roller 41.
Further, a latent image of a solid portion having a latent image potential V _L is formed on the photoconductor drum 10, and a DC electric field E ₄ is also formed in the gap between the photoconductor drum 10 and the developing roller 41. .

Now, the toner T is present at the downstream end of the plate-like member 43, and from the balance of the forces acting on the toner T, the conditions for obtaining high developability in the solid portion will be obtained.

[0081] In order to move the toner T to the latent image on the photosensitive drum 10, the force F ₃ to be impose the toner T to the developing roller 41 side by the DC electric field E ₃
It is necessary that the force F ₄ for moving the toner T to the latent image on the photoconductor drum 10 by the DC electric field E ₄ is larger than that, that is, F ₄ > F ₃ .

The force F _{3 for} pressing the toner T toward the developing roller 41 and the force F ₄ for moving the toner T to the latent image on the photosensitive drum 10 are:
When the average charge amount q _t of the toner T, the distance between the downstream end of the electrode portion 44 and the developing roller 41 is D ₄ , and the closest distance between the photosensitive drum 10 and the developing roller 41 is D _1. each _{F 3 = | q t | ·} E 3 = | q t | · | V DEN -V DC | / D 4 (12) and _{F 4 = | q t | ·} E 4 = | q t | · | V _DC −V _L | / D ₁ (13) Therefore, the condition for obtaining high developability in the solid part is | q _t | · | V _DC −V _L | / D ₁ > | q _t |
· | A _{/ D 4 | V DEN -V DC} . If | q _t | is deleted from both sides and rearranged, it becomes | V _DC | + | V _DC −V _L | · D ₄ / D ₁ > | V _DEN |, and since D ₃ ≧ D ₄ , | V _DC | _{+ | V DC -V L | ·} D 3 / D 1> | V DEN | (14) is obtained.

Formula (14) is a condition for obtaining high developability in the solid part.

Next, referring to FIG. 5B, the photosensitive drum 10
Consider a case where a latent image or a toner image of the background portion is formed on the background.

A DC voltage V _DEN is applied to the electrode portion of the plate member 43, and a DC voltage V _DC is applied to the developing roller 41,
A DC electric field E ₅ is formed in the gap between the plate-like member 43 having the electrode portion 44 and the developing roller 41. A latent image or toner image of the background portion of the latent image potential V _H is formed on the photosensitive drum 10, and the photosensitive drum 10 is formed.
A DC electric field E ₆ is also formed in the gap between the developing roller 41 and the developing roller 41.

The toner T currently on the developing roller 41
Receives the force F ₅ from the DC electric field E ₅ and moves to the downstream end of the plate member 43 while increasing the speed, and then the toner T that has passed the downstream end of the plate member 43. This time, it is assumed that the speed is gradually decreased by receiving the force F _{6 in the} opposite direction due to the DC electric field E _6, and the condition for preventing fog and color mixture in the background portion is obtained.

In the process in which the toner T on the developing roller 41 moves to the downstream end portion of the plate-like member 43, the mass of the toner T is m _t , the acceleration acting on the toner T is α ₁ , and the acceleration acting on the toner T is α ₁ . The time required for the toner T to move from the developing roller 41 to the downstream end of the plate member 43 is t ₁ , and the toner T at the downstream end of the plate member 43 is t ₁ .
The velocity v _1, wherein said developing roller 41 plate-like member 43
When the distance of the downstream end and the _{D 3, F 5 = m t} · α 1 (15) v 1 = α 1 · t 1 (16) D 3 = α 1 · t 1 2/2 (17) The relational expression of is established.

In the process in which the toner T passing through the downstream end of the plate-like member 43 at the speed v ₁ receives the force in the direction opposite to the advancing direction and finally the speed becomes 0,
The negative acceleration acting on the toner T is α ₂ , the time until the speed of the toner T becomes 0 is t ₂ , the position where the speed of the toner T becomes 0, and the downstream end of the plate member 43. when the distance was set to _{x 1, F 6 = m t} · α 2 (18) 0 = v 1 -α 2 · t 2 (19) x 1 = v 1 · t 2 -α 2 · t 2 2/2 The relational expression (20) holds.

From equations (15) to (20), m _t , α ₁ , t
Eliminating ₁ , v ₁ , α ₂ , and t ₂ gives x ₁ = F ₅ · D ₃ / F ₆ (21).

The condition that the fog and the color mixture of the background portion do not occur is that the toner T does not reach the latent image or the toner image of the background portion on the photosensitive drum 10, so the condition of x _{1 in} the equation (21) is , said closest distance D ₁ of the developing roller 41 the photosensitive drum 10, when the closest distance downstream end and the developing roller 41 of the plate-like member 43 was set to D _3, D ₁ -D ₃ > X ₁ (22).

[0091] On the other hand, the force F ₆ by the force F ₅ and a DC electric field E ₆ by a DC electric field E ₅ is the average charge amount q _t of the toner, the closest distance D of the developing roller 41 and the photosensitive drum 10 ₁ , where D ₄ is the closest distance between the developing roller 41 and the downstream end of the electrode portion 44, F ₅ = | q _t | · E ₅ = | q _t | · | V _DC −V _DEN | / D ₄ (23) and F ₆ = | q _t | · E ₆ = | q _t | · | V _H −V _DC | / D ₁ (24).

Substituting equations (21), (23) and (24) into equation (22) and rearranging: | V _H −V _DC | · (D ₁ −D ₃ ) / D ₁ > | V _DC- V _DEN ｜
· D ₃ / D _4, and the because the _{D 3 ≧ D 4, | V} H -V DC | · (D 1 -D 3) / D 1> | V DC -V DEN | become. When this is arranged, | V _DEN |> | V _DC |-| V _H -V _DC | · (1-D ₃ / D ₁ ) (25) is obtained.

Equation (25) is a condition for preventing fog and color mixture in the background portion.

Combining the equations (14) and (25), it is: | V _DC | + | V _DC -V _L | .D ₃ / D ₁ > | V _DEN |> | V _DC |-| V _H -V _DC | · (1-D ₃ / D ₁ ) (26) is obtained, and the requirements of the present invention are derived.

The DC component V _DC [V] actually applied to the developing roller 41, the DC voltage V _DEN [V] applied to the electrode portion 44 of the plate member 43, and the solid portion on the photosensitive drum 10 The latent image potential V _L , the latent image potential V _H of the background portion on the photoconductor drum 10, the distance D ₃ between the downstream end of the plate-like member 43 and the developing roller 41, the photoconductor drum 10 and the developing unit. Set the closest distance D ₁ of the roller 41 to (2
By setting so as to satisfy the relationship of the expression (6), it is possible to obtain a high-quality image having a high image density and free from background fog and color mixture.

On the other hand, the relationship of the above equation (26) is not satisfied |
If V _DEN | is too large, the image density of the solid part will be low and the line width will be thin, and conversely, if | V _DEN | is too small, the latent image or toner of the background part formed on the photosensitive drum 10 will be formed. The toner adheres to the image as well, causing fog and color mixture, and in any case, a good image cannot be obtained.

Furthermore, in the present invention, the step of forming a latent image on the photoconductor drum 10 and the step of developing the latent image are repeated a plurality of times, and the photoconductor drum 10 and the developing roller 41 in each development step are The strength of the oscillating electric field in the gap of the photosensitive drum 1
Another requirement is to set the strength of the oscillating electric field so as to be equal to or weaker than the strength of the oscillating electric field in the gap between 0 and the developing roller 41.

That is, the amplitude of the AC component applied to the developing roller 41 of the developing device that has developed the latent image in the preceding developing step is V _AC (n-1), and the closest distance between the developing roller 41 and the photosensitive drum 10 is Is D ₁ (n−1), and the amplitude of the AC component applied to the developing roller 41 ′ of the developing device for developing the latent image in the subsequent developing step is V _AC (n), the developing roller 41 ′ and the photosensitive member. When the closest distance of the drum 10 is D ₁ (n), V _AC (n-1) / D ₁ (n-1) ≧ V _AC (n) / D
V _AC (n-1) in the developing process of the first stage so that it becomes ₁ (n).
And D ₁ (n-1) and V in the subsequent developing process.
Set _AC (n) and D ₁ (n).

With this setting, the toner image formed on the photosensitive drum 10 in the former developing process is not disturbed in the latter developing process, and the latter toner image is mixed with the latter toner image. In addition, it is possible to obtain a high-quality multicolor image.

On the contrary, when the oscillating electric field in the latter developing process is made stronger than the oscillating electric field in the former developing process, the toner image of the former stage is disturbed and the toner of the latter stage is mixed with the toner image, resulting in unclear and low image quality. It becomes a multicolored image.

Further, in the present invention, the width of the plate member 43 in the direction orthogonal to the moving direction of the developing roller 41 is W ₁ [m
m], the width of the electrode portion 44 in the direction orthogonal to the moving direction of the developing roller 41 is W ₂ [mm], and the width of the developer layer 50 conveyed on the developing roller 41 in the direction orthogonal to the moving direction of the roller 41. The width is W ₃ [mm] and the photoconductor drum 10
When the width of the latent image formed above in the direction orthogonal to the moving direction of the developing roller 41 is W ₄ [mm], it is required that the relationship of W ₁ > W ₃ > W ₂ > W ₄ is satisfied. .

The above requirements will be described with reference to FIG.

FIG. 6 shows the photosensitive drum 10 and the developing roller 41.
And the developing roller 41 in each part in the developing area where
It is a top view which shows the width of the direction orthogonal to a moving direction. In the figure, 10 is a photosensitive drum, 41 is a developing roller, and 43.
Is a plate member having the electrode portion 44, 50 is a developer layer, W ₁ is the width of the plate member 43 in the direction orthogonal to the moving direction of the developing roller 41, and W ₂ is the developing portion of the electrode portion 44. the width in the direction perpendicular to the roller 41 moving direction, W ₃ is the latent image width in the direction perpendicular to the developing roller 41 a moving direction of the developer layer 50, W ₄ is formed on the photosensitive drum 10 The width in the direction orthogonal to the moving direction of the developing roller 41 is shown.

First, the condition of the latent image width W ₄ will be described.

The width W _{2 of the} electrode portion 44 is larger than the width W _{4 of the} latent image.
When the value is set to be narrow, the electrode portion 44 is not provided in the portion facing both ends of the latent image, so that the generation of the toner cloud in this portion is not promoted, the developability is lowered, and the image density is lowered. I will end up. Further, when the width W ₃ of the developer layer 50 is set to be narrower than the width W _{4 of the} latent image, the developer 50 is not supplied to the portions facing the both ends of the latent image. The latent image is not developed and no image is formed. Further, the width W _{1 of the} plate member 43 is larger than the width W _{4 of the} latent image.
When N is set to be narrow, the width W of the electrode portion 44 is inevitably
_{Since 2} also becomes narrower than the width W _{4 of the} latent image, at least the above problems occur. Therefore, W ₁ , W ₂ , W ₃ > W ₄ is obtained as the condition for the latent image width W ₄ .

Next, the condition of the width W ₂ of the electrode portion 44 will be described.

When the width W ₃ of the developer layer 50 is set narrower than the width W _{2 of the} electrode portion 44, the electrode portion 44
There is no developer layer 50 on both ends of the
Since the plate-shaped member 43 having 4 and the developing roller 41 are in direct contact with each other, discharge easily occurs between the electrode portion 44 and the developing roller 41 at this portion. When the discharge occurs, the power is turned off and the developing bias is not applied. Even when the power is not turned off, the oscillating electric field formed between the electrode portion 44 and the developing roller 41 is weakened and the toner is not applied. The generation of cloud is not promoted, the developability is lowered, and the image density is lowered. In addition, it is practically impossible that the width W ₂ of the electrode portion 44 is wider than the width W ₁ of the plate member 43. Therefore, as the condition of the width W ₂ of the electrode portion 44, W ₁ , W ₃ > W ₂ is obtained, and in combination with the condition of the width W ₄ of the latent image, W ₁ , W ₃ > W ₂ > W ₄ is obtained. .

Further, the condition of the width W ₃ of the developer layer 50 will be described.

When the width W ₁ of the plate-like member 43 is set narrower than the width W ₃ of the developer layer 50, the plate-like member 43
Does not come into contact with the developer layer conveyed to both ends of the developing roller 41, so that the height of the ear of the developer layer at this portion is the ear of the developer layer at the portion where the plate-like member 43 abuts. Is higher than the height of the plate, and the ears come into contact with the photoconductor drum 10 to cause color mixing, or the developer layer 50 is cut off at the end of the plate-like member 43 to attach the carrier onto the photoconductor drum 10. Will occur. Therefore, as a condition of the width W ₃ of the developer layer 50, W ₁ > W ₃ is obtained, and W ₁ > W ₃ > when combined with the conditions of the latent image width W ₄ and the electrode portion 44 width W _2. W ₂ > W ₄ is obtained.

When the width W ₁ of the plate-like member 43, the width W _{2 of the} electrode portion, the width W ₃ of the developer layer 50 and the width W _{4 of the} latent image are set in this manner, the developability is improved. An excellent image without any color mixture can be obtained.

On the other hand, any of the width W ₁ of the plate member 43, the width W _{2 of the} electrode portion, the width W ₃ of the developer layer 50, and the width W ₄ of the latent image does not satisfy the above conditions. In this case, the above-mentioned problems occur and a good image cannot be obtained.

Next, other conditions relating to the present invention will be described.

First, the plate member 43 having the electrode portion 44 and the arrangement of the members will be described.

The plate-like member 43 having the electrode portion 44 is provided on the upstream side in the moving direction of the developing roller 41 in the developing area where the photosensitive drum 10 and the developing roller 41 face each other, and the electrode portion 44 and the developing roller 41 are provided. A toner cloud is generated by forming an oscillating electric field in the gap between and.

The plate-like member 43 having the electrode portion 44 has the structure shown in FIGS. 7A to 7F, for example. (A) is an electrode part made of a conductive material such as copper foil at the downstream end of the upper surface of an insulating organic substrate material or inorganic substrate material such as polyimide resin, epoxy resin, glass fiber reinforced epoxy resin, or ceramic. 44 (b), in which (b) an eaves portion is provided at the downstream end of the plate-like member 43 and the electrode portion 44 is formed slightly upstream of the downstream end of the plate-like member 43. Is. Also (c)
And (d) are the electrode parts 4 of (a) and (b), respectively.
4 and the eaves part, for example, polyimide resin, epoxy resin,
A multilayer structure is formed by coating an insulating material such as glass fiber reinforced epoxy resin, and (e) and (f) are multilayers obtained by coating the entire upper surfaces of (a) and (b) with an insulating material. It is configured.

Of the above, (d) and (f) are particularly preferably used. The eaves are provided at the downstream end of the plate-like member 43, and the electrode 44 is covered with an insulating material. As a result, the toner T wraps around the downstream end of the plate-like member 43 and the upper surface of the plate-like member 43, especially the electrode portion 4
4 can be prevented.

The plate-like member 43 having the electrode portion 44 can be attached to the developing device by fixing one end of the plate-like member 43 to the upper end of the casing 49 of the developing device as shown in FIG. The lower surface of the member 43 is brought into contact with the two-component developer 50 on the developing roller 41 with a predetermined contact pressure.

Next, regarding the size of each portion of the plate-like member 43 having the electrode portion 44 in contact with the developer layer on the developing roller 41 and the arrangement with other members, an enlarged view in the vicinity of the developing area in FIG. Will be explained.

In FIG. 8, L ₁ is the width of the electrode portion 44 of the plate-like member 43 in the moving direction of the developing roller 41, L ₂ is the width of the eave portion of the plate-like member 43 in the moving direction of the developing roller 41, L 2 ₃ is the distance between the position P where the plate-shaped member 43 is in contact with the developer on the developing roller 41 (hereinafter referred to as contact point) and the downstream end of the plate-shaped member 43, and L ₄ is the electrode part 44. 7 (c) or 7 (d), the width of the coating layer in the moving direction of the developing roller 41, D ₁ is the photosensitive drum 10 and the developing roller. closest distance 41, D ₂ is the plate-like member 43
The closest distance between the electrode portion 44 and the developing roller 41, D ₃
Is the downstream end of the plate-like member 43 and the developing roller 41.
Is the closest distance, D ₄ is the closest distance between the downstream end of the electrode portion 44 and the developing roller 41, and D ₅ is the electrode portion 44.
The closest distance between the upstream end of the developing roller 41 and the developing roller 41, H ₁
Is the thickness of the developer layer at the contact point, H ₂ is the thickness of the developer layer or the height of the magnetic brush at the position where the photosensitive drum 10 and the developing roller 41 are closest to each other, and H ₃ is the electrode The thickness of the layer below the electrode portion 44 of the plate-like member 43 having the portion 44, that is, on the side closer to the developing roller 41, H ₄ is greater than the electrode portion 44 of the plate-like member 43 having the electrode portion 44. The thickness of the layer on the upper side, that is, the side closer to the photosensitive drum 10, r is the developing roller 4
1 is the radius of curvature in the developing area, θ is the developing roller 41
Is an angle (hereinafter referred to as an abutment point angle) formed by the abutment point and a position where the photoconductor drum 10 and the developing roller 41 are closest to the center of curvature.

The width L ₁ of the electrode portion 44 of the plate member 43 is usually about 0.2 to 3 mm, preferably 0.3 to ₁ mm, and the eave width L ₂ of the plate member 43 is usually 0 to 0 mm. 1 mm
The distance L ₃ between the contact point and the downstream end of the plate-like member 43 is usually 1 or so.
It is about 5 mm.

The relationship between L ₁ , L ₂ and L ₃ is preferably L ₃ > L ₁ > L ₂ .

A plate-like member 43 having the electrode portion 44
Has a coating layer as shown in FIG. 7 (c) or (d), the width L _{4 of the} coating layer is usually 0.2 to 5 mm, and L ₄ is L ₃ > L ₄ ≧ L ₁ + L It is preferably ₂ .

The closest distance D ₁ between the photosensitive drum 10 and the developing roller 41 is usually about 0.2 to ₁ mm, and the plate-like member 43 is arranged in non-contact with the photosensitive drum 10. The closest distance D ₂ between the electrode portion 44 and the developing roller 41 is usually about 0.05 to 0.5 mm, and the closest distance D ₃ between the downstream end of the plate-like member 43 and the developing roller 41 is usually 0. The distance D ₄ between the downstream end of the electrode portion 44 and the developing roller 41 is normally 0.1 to 0.5 mm.
˜0.6 mm, and the closest distance D ₅ between the upstream end of the electrode portion 44 and the developing roller 41 is usually 0.05 to 0.5 m.
m.

D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , the thickness H ₁ of the developer layer at the contact point, and the developer layer at the closest position between the photosensitive drum 10 and the developing roller 41. The thickness H ₂ of the above is preferably D ₄ > D ₂ = D ₅ > H ₁ , and further D ₄ ≧ D ₃ > H ₂ and 0.6 · D ₁ ≧ D ₃ ≧ 0.2 · D It is preferably ₁ .

The thickness of the plate-like member 43 having the electrode portion 44 is such that the thickness H ₃ of the lower layer of the electrode portion 44 is usually 0.
The thickness H ₄ of the upper layer of the electrode portion 44 is usually about 0 to 0.5 mm.

[0126] relation of the H _3, H ₄ and D _{1 are, D 1/2 ≧ H 3} + is preferably set to H _4, also the plate-like member 43 having the electrode 44 FIG. 7 (c) ~ ( In the case of the multi-layer structure as in (f), a value obtained by dividing the thickness H ₃ of the lower layer of the electrode portion 44 by the relative dielectric constant of the layer is the thickness H ₄ of the upper layer of the electrode portion 44. It is preferably greater than the value divided by the relative permittivity of the layer.

The radius of curvature r in the developing area of the developing roller 41 is usually about 2.5 to 15 mm, and the contact point angle θ is usually 10 to 30 °.

R, θ, the contact point and the plate member 4
3 The relationship between the distance L ₃ at the downstream end and the closest distance D ₁ between the photosensitive drum 10 and the developing roller 41 is r · sin θ ≧ L ₃ · cos θ and r · (1-cos θ) ≧ D ₁ . It is preferable.

[0129] The moving speed V _r of the developing roller 41, wherein, when the moving speed of the photosensitive drum 10 was set to V _p, it is preferred that the V _r is 1-3 times the V _p, the developing roller 41 The moving direction of is in the same direction in the developing area facing the photoconductor drum 10.

Further, the thickness H ₁ of the developer layer at the contact point and the thickness H ₂ of the developer layer at the closest position between the photosensitive drum 10 and the developing roller 41 are preferably H ₂ > H _1. , 4H ₁ ≧ H ₂ ≧ 2H ₁ is particularly preferable.

In order to set the above H ₁ and H ₂ to the above relationship, the main magnetic pole of the magnet body 42 fixedly arranged inside the developing roller 41 is connected to the photosensitive drum 10 and the developing unit. It is preferable to dispose the roller 41 at a position closest to the roller 41 or between the position and the contact point.

In the above, the developing device 40 of the image forming apparatus of the present application.
As the plate-like member 43 having the electrode portion used for FIG.
However, it goes without saying that a plate-like member having a configuration derived from this can also be used in the image forming apparatus of the present invention.

Next, the superimposed voltage of the direct current component and the alternating current component applied to the developing roller 41 will be described.

The frequency of the AC component is the unit of the frequency f _AC [Hz], the unit of the width L ₁ of the electrode portion 44 of the plate member 43 in the moving direction of the developing roller 41 [mm], the developing roller 41. When the unit of the moving speed V _r of [mm / sec] is [mm / sec], it is preferable that f _AC ≧ 10 · V _r / L ₁ .

The waveform of the AC component may be a sine wave, a rectangular wave, a triangular wave, or the like, but the rectangular wave is preferable in order to efficiently generate the toner cloud.

Next, the toner T will be described.

Generally, when the average particle diameter d _t of the toner T becomes large, the roughness of the image becomes noticeable. Normally 10 / mm
In order to obtain the resolution of fine lines arranged at a certain pitch, there is no problem even if the average particle size d _t is about 20 μm, but in order to further improve the resolution and obtain a clear high-quality image in which the difference in shade is faithfully reproduced. It is preferable that the average particle diameter d _t of the toner T is smaller. The average particle diameter d _t of the toner T is 10 μm.
m or less is preferable, and 4 to 6 μm is particularly preferable.

The average particle diameter d _t of the toner T is obtained by adding about 1 mg of a sample and a surfactant to about 200 ml of an electrolytic aqueous solution and dispersing the suspension by an ultrasonic disperser for about 1 minute. Distribution measuring device "Coulter Counter TA-II type"
(Aperture 100 μm manufactured by Coulter, Inc.) is used to measure the volume average particle size distribution.

Further, when the absolute value of the average charge amount Q _t of the toner T becomes large, it is necessary to increase the electric field required to fly the toner, and discharge easily occurs in the gap between the electrode portion 44 and the developing roller 41. Become. On the contrary, if the absolute value of the average charge amount Q _t of the toner T is too small, the toner T is likely to be scattered from the developing device. The toner T
The average charge amount Q _t of which about 5~40μC / g in normal absolute values.

The average charge amount Q _t of the toner T is 2 cm.
A conductive plate of × 5 cm is made to face a developing roller having a diameter of 20 mm at a closest distance of 0.7 mm, a developer is supplied to the developing roller 41, and the developing roller 41 is rotated at 200 rpm. (For example, | V _DC | =
1000 [V], V _AC = 1500 [V], f _AC = 800
0 [Hz]) is applied to develop the toner T on the conductive plate, and then the conductive plate on which the toner T is developed is connected to a Faraday cage to blow away the toner T, which was blown off at this time. It is obtained by measuring the charge amount and the weight of the toner T.

In the developing device 40 used in the image forming apparatus of the present application, the toner T is a resin such as styrene resin, vinyl resin, acrylic resin, polyamide resin, silicon resin, polyester resin, fluorine resin, epoxy resin, or the like. In addition, a coloring component such as carbon black or a color pigment or a color dye, a charge control agent and the like are added, and the toner particles can be produced by the same method as a conventionally known method for producing toner particles. If necessary, a fluidizing agent for increasing the fluidity of particles and a cleaning agent for cleaning the surface of the image forming body can be mixed. As the fluidizing agent, colloidal silica, silicon varnish, metal soap, nonionic surface active agent and the like can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicon, fluorine and other surface active agents can be used. it can.

The carrier C is a metal such as iron, chromium, nickel, cobalt, zinc or copper, or a compound or alloy thereof, for example, a ferromagnetic material such as γ-ferric oxide, chromium dioxide, manganese oxide or ferrite. Or spherical particles of paramagnetic material, or the surfaces of these magnetic material particles are spherically coated with a resin such as styrene resin, vinyl resin, ethylene resin, acrylic resin, polyamide resin, polyester, or magnetic material. Particles obtained by forming spherical particles of a resin or fatty acid wax containing fine particles dispersed therein are used. An average particle size of 70 μm or less, preferably about 30 to 50 μm is suitably used.

Although the present invention has been described using the two-component developer, the present invention is not limited to this, and the same effect can be obtained even when the one-component developer is used.

The examples of the present invention will be described more specifically below.

[Developing device] Full-color copying machine "Koni"
ca 9028 "(made by Konica) yellow (Y),
The upper lids of the casings 49 of the four types of developing devices containing the magenta (M), cyan (C), and black (K) developers are respectively modified, and one end of a plate-like member described later is fixed to the end of the upper lid. The developing devices 40A, 40B, 40C and 40D of the present invention are used.

[Image forming apparatus] Full color copying machine "Ko
nica 9028 "(manufactured by Konica) in place of the yellow (Y), magenta (M), cyan (C), and black (K) developing devices, the developing devices 40A, 40B of the present invention,
The image forming apparatus of the present invention was prepared by mounting 40C and 40D and separately providing a power source for applying a voltage to the developing roller of each developing device and the electrode portion of the plate member. The timing of applying the DC voltage to each electrode portion and the timing of applying only the DC voltage to each developing roller are the same as the timing of charging the photosensitive drum, and the timing of applying the superimposed voltage of the DC component and the AC component to each developing roller. Is the same as the timing of driving each developing roller.

[Developer] Five kinds shown in Table 1 were used.

[0148]

[Table 1]

[Plate Member Having Electrode] 3 shown in Table 2
Used the type.

[0150]

[Table 2]

[Conditions Common to Each Embodiment] Table 3 shows the conditions common to each embodiment.

[0152]

[Table 3]

(Example 1-1) The developing device was set to the conditions shown in Table 4, and the DC voltage V _DEN applied to the electrode part was -75.
Amplitude V of AC component fixed to 0V and applied to the developing roller
_The image is output in the single color mode while changing the _AC, and the weight of the toner attached per unit area of the surface of the photosensitive drum corresponding to the solid portion (hereinafter, the primary attachment amount M / A [mg / mg /
cm ² ]) and the number of toner particles (hereinafter referred to as fog toner number N ₁ [units / mm ² ]) per unit area of the surface of the photoconductor drum corresponding to the background portion, and determined according to the following criteria. did.

Primary Adhesion Amount M / A [mg / cm ² ] Evaluation Criteria (When the Toner's Average Particle Diameter is d _t [μm]): ◯ ... d _t × 0.8 ≦ M / A Δ · ..D _t × 0.6 ≦ M / A <d _t × 0.8 × ... M / A <d _t × 0.6 Number of fog toner N ₁ [units / mm ² ] Evaluation standard: ○ ・・ N ₁ ≦ 10 Δ ・ ・ ・ 10 <N ₁ ≦ 20 × ... 20 <N ₁

[0155]

[Table 4]

The results are shown in Table 5.

[0157]

[Table 5]

(Embodiment 1-2) The developing device is used in Embodiment 1-1.
Set to the same conditions as, while the amplitude V _AC of the AC component applied to the developing roller by changing the DC voltage V _DEN applied to the electrode portion is fixed to 500V performs image reproduction in a monochromatic mode, the primary deposition amount M / A and the fog toner number N ₁ are measured,
It evaluated similarly to Example 1-1. The results are shown in Table 6.

[0159]

[Table 6]

(Example 2-1) The developing device was set to the conditions shown in Table 7, and the DC voltage V _DEN applied to the electrode part was -75.
Amplitude V of AC component fixed to 0V and applied to the developing roller
_An image is displayed in a single color mode while changing the _AC , and the primary adhesion amount M / A and the fog toner number N ₁ are measured.
It evaluated similarly to -1. Table 8 shows the results.

[0161]

[Table 7]

[0162]

[Table 8]

(Embodiment 2-2) A developing apparatus is used in Embodiment 2-1.
Under the same conditions as described above, the amplitude V _AC of the _AC component applied to the developing roller is fixed to 500 V, and the DC voltage V _DEN applied to the electrode part is changed to perform image output in the single color mode, and the primary adhesion amount M / A and the fog toner number N ₁ are measured,
It evaluated similarly to Example 1-1. The results are shown in Table 9.

[0164]

[Table 9]

(Example 3-1) The developing device was set to the conditions shown in Table 10, and the DC voltage V _DEN applied to the electrode part was -7.
While fixing the voltage to 50 V and changing the amplitude V _AC of the _AC component applied to the developing roller, an image was output in the single color mode, and the primary adhesion amount M / A and the fog toner number N ₁ were measured. It evaluated similarly. The results are shown in Table 11.

[0166]

[Table 10]

[0167]

[Table 11]

(Embodiment 3-2) A developing device is used in Embodiment 3-1.
Under the same conditions as described above, the amplitude V _AC of the _AC component applied to the developing roller is fixed to 500 V, and the DC voltage V _DEN applied to the electrode portion is changed to perform image output in the single color mode, and the primary adhesion amount M / A and the fog toner number N ₁ are measured,
It evaluated similarly to Example 1-1. The results are shown in Table 12.

[0169]

[Table 12]

(Example 4-1) The developing device was set to the conditions shown in Table 13, and the DC voltage V _DEN applied to the electrode part was -7.
While fixing the voltage to 50 V and changing the amplitude V _AC of the _AC component applied to the developing roller, an image was output in the single color mode, and the primary adhesion amount M / A and the fog toner number N ₁ were measured. It evaluated similarly. The results are shown in Table 14.

[0171]

[Table 13]

[0172]

[Table 14]

(Embodiment 4-2) A developing device is applied to Embodiment 4-1.
Under the same conditions as above, the amplitude V _AC of the _AC component applied to the developing roller is fixed at 600 V, and the DC voltage V _DEN applied to the electrode portion is changed to perform image output in the single color mode, and the primary adhesion amount M / A and the fog toner number N ₁ are measured,
It evaluated similarly to Example 1-1. The results are shown in Table 15.

[0174]

[Table 15]

(Example 5-1) The developing device was set to the conditions shown in Table 16, and the DC voltage V _DEN applied to the electrode part was -7.
While fixing the voltage to 50 V and changing the amplitude V _AC of the _AC component applied to the developing roller, an image was output in the single color mode, and the primary adhesion amount M / A and the fog toner number N ₁ were measured. It evaluated similarly. The results are shown in Table 17.

[0176]

[Table 16]

[0177]

[Table 17]

(Embodiment 5-2) A developing device is used in Embodiment 5-1.
Under the same conditions as above, the amplitude V _AC of the _AC component applied to the developing roller is fixed at 500 V, and the image is displayed in the single color mode while changing the absolute value V _DEN of the DC voltage applied to the electrode portion, and the primary adhesion is performed. The amount M / A and the fog toner number N ₁ were measured and evaluated in the same manner as in Example 1-1. The results are shown in Table 18.

[0179]

[Table 18]

10 in Examples 1-1 to 5-1.
_{· | Q t | · d t} · D 1 and 5, | Q _t | of-d _t · D ₂ values are shown in Table 19, 10-values of V _AC | Q _t | ·
By setting the range of d _t · D ₁ > V _AC > 5 · | Q _t | · d _t · D ₂ , good results can be obtained for both the primary adhesion amount M / A and the fog toner number N ₁ . On the other hand, when V _AC is too large, the number of fog toners N ₁ increases, and when V _AC is too small, the primary adhesion amount M / A becomes insufficient, and good results cannot be obtained in any case.

[0181]

[Table 19]

In addition, | V in Examples 1-2 to 5-2
_{DC | + | V DC -V L} | · D 3 / D 1 and | V _DC | - | V _H
The value of −V _DC | · (1-D ₃ / D ₁ ) is as shown in Table 20, and the value of | V _DEN | is | V _DC | + | V _DC + V _L | · D _{3
/ D 1> | V DEN |} > | V DC | - | V H -V DC | · (1-
When it is set within the range of D ₃ / D ₁ ), good results can be obtained for both the primary adhesion amount M / A and the fog toner number N ₁ . On the other hand, | V
_{If DEN} | is too large, the primary adhesion amount M / A will be insufficient,
On the other hand, if | V _DEN | is too small, the number of fog toners N ₁ increases, and good results cannot be obtained in any case.

[0183]

[Table 20]

(Embodiment 6) The developing devices of the image forming apparatus are set to the conditions shown in Table 4, Table 7, Table 10 and Table 13, respectively, and the DC voltage V _DEN applied to the electrode portion is different in each developing device. Is also set to -750 V, the amplitude V _AC of the _AC component applied to the developing roller of each developing device is set as shown in Table 19, and yellow → magenta → in full color mode.
The number of toners per unit area of other color toner adhered to each solid part of yellow, magenta, and cyan color toners (hereinafter referred to as the number of mixed color toners) N ₂ [pieces / m
m ² ]) was measured and judged according to the following criteria. The results are shown in Table 21.

Number of color-mixed toners N ₂ [number / mm ² ] Evaluation criteria: ◯ ... N ₂ ≦ 20 Δ ... 20 <N ₂ ≦ 40 × ... 40 <N ₂

[0186]

[Table 21]

In this embodiment, the closest distance D ₁ between the developing roller and the photosensitive drum is 0.
Since it is 5 mm, the strength of the oscillating electric field in the gap between the photosensitive drum and the developing roller in each developing step is determined by the value of the amplitude V _AC of the _AC component applied to the developing roller. As shown in Table 21, the values of _VAC applied to the yellow, magenta, cyan, and black developing rollers are _VAC (yellow) ≥ _VAC (magenta) ≥ _VAC (cyan) ≥ _VAC (black). If they are set smaller in order, a good multicolor image with no color mixture can be obtained. On the other hand, V
_If the value of _AC is set to be larger than the value of V _{AC in} the previous developing process, the toner developed in the previous developing process is mixed on the toner image at that time, and a good image cannot be obtained.

(Embodiment 7) [Developing device] Full-color copying machine "Konica 902"
8 "(manufactured by Konica), the upper lid of the casing 49 of the developing device for accommodating the black developer is modified so that one end of a plate-like member 43 described later is fixed to the end of the upper lid, and the developing device of the present invention or for comparison. 40E. The position of the main magnetic pole of the magnet body 42 of the developing device 40E is fixed so as to be the closest position to the photosensitive drum 10, and the developing roller 4 of the plate member 43 is fixed.
The position of the downstream end in the first moving direction is also set to the closest position between the developing roller 41 and the photosensitive drum 10. As a developer, a black developer for a full-color copying machine “Konica 9028” (manufactured by Konica Corporation) was used as it was at a carry amount of 15 mg / cm ² , and it was used between the both ends of the developing roller 41 of the developing device 40E and the upper lid. A urethane sponge was sandwiched in between to adjust the width of the developer layer conveyed on the developing roller 41. A high voltage power source for testing "HV-408" is used as a bias applying power source 51 or 52 for the developing roller 41 and the electrode portion 44 of the plate member 43, respectively.
(Nagano Aichi Denki Co., Ltd.) is connected, and in synchronization with the timing of driving the developing roller 41, V _DC = −750 V and V
The superimposed voltage or V _DEN = -750 V of DC voltage _AC = 350 V was applied.

[Plate-shaped member] An electrode portion made of copper foil is formed by etching on the upper surface of an insulating substrate material made of glass fiber reinforced epoxy resin having a thickness of 0.1 mm, and further, a 0.1 mm thick portion is formed thereon. A coating layer made of a polyimide resin was provided to obtain a plate-shaped member for this example and comparative example.
The size of each part of the plate member is as follows.

Width W _{2 of} electrode part 44 in the direction orthogonal to the moving direction of the developing roller: 250 mm or 300 mm Width of electrode part 44 in the moving direction of the developing roller L ₁ : 0.5 mm Eave width L ₂ : 0 mm Width of coating layer L _4: 2.0 mm plate-shaped member 43 of the developing roller movement direction orthogonal to the width W _1: cutting the plate-shaped member such that the width will be described later.

[Image forming apparatus] Full color copying machine "Ko
The developing device 40E was mounted instead of the developing device containing the black developer for "nica 9028" (manufactured by Konica). In addition, the full-color copying machine "Konica 902"
Video interface board (part number:
5060887180; manufactured by Konica), and a print controller "SKYBOX-5028A" is mounted on the board.
(Manufactured by Konica Business Machines Co., Ltd.) and a personal computer “PC9801 NS / R” (manufactured by NEC Corporation) were connected to complete the image forming apparatus according to the present embodiment and the comparative example.

In this image forming apparatus, since a latent image is formed on the photosensitive drum 10 according to the image data transmitted from the personal computer via the print controller, the latent image is formed by changing the image data. The width of the latent image formed on the photosensitive drum 10 was changed.
In this example and the comparative example, the width of the latent image is 297 mm.
Or 200 mm.

The other setting conditions in this example and the comparative example were the same as those of the full-color copying machine "Konica 9028" unless otherwise specified.

[0194] latent formed in the Print Test width W ₁ of the plate-like member 43, the width W ₂ of the electrode portion 44, the width W ₃ of the developer layer is conveyed on the developing roller 41 and the photosensitive drum 10 on The width W ₄ of the image is set to the conditions shown in Table 22 and continuous printing of A4 100 sheets is performed in the full color mode to evaluate the developability of the black solid portion, the color mixture of the black toner on the yellow solid portion, and the carrier adhesion. did.

The developability of the black solid portion is 5 mm, 75 mm, 145 mm and 215 from the front, with the longitudinal direction of A4 orthogonal to the moving direction of the developing roller 41.
mm solid positions and 285 mm positions, respectively, 5 black solid portions of 5 mm × 5 mm (width of latent image is 29 mm).
7 mm) or size 5 mm x 5 provided at 75 mm position, 145 position and 215 mm position, respectively.
The print density of each black solid portion was measured at three black solid portions of 3 mm (when the width of the latent image was 200 mm) using a printing accuracy evaluation system "RT-2000" (manufactured by Yerman).

For the color mixture, the longitudinal direction of A4 is the developing roller 41.
5mm from the front as a direction orthogonal to the moving direction, 7
5 mm position, 145 mm position, 215 mm position and 2
Five 5 mm x 5 mm yellow solid parts provided at 85 mm positions (when the latent image width is 297 mm) or 75 mm positions, 145 mm positions and 215
The number of black toners per unit area adhered on each yellow solid part is increased by 250 times at three yellow solid parts each having a size of 5 mm × 5 mm (when the width of the latent image is set to 200 mm). I expanded and counted.

For carrier adhesion, a carrier collecting magnet is provided on the downstream side of the developing device in the rotation direction of the photosensitive drum to collect the carrier adhered on the photosensitive member for each color developer, and after the printing test is completed. The carrier adhesion for the black developer was evaluated.

The results are shown in Table 22.

[0199]

[Table 22]

As shown in Table 22, the width W ₁ of the plate member>
When the width W ₃ of the developer layer> the width W _{2 of the} electrode portion> the width W _{4 of the} latent image, there is no particular problem and excellent images are obtained with excellent developability. On the other hand, the latent image width W ₄ > the electrode portion width W ₂
If the width W _{4 of the} latent image is greater than the width W ₃ of the developer layer, the both ends of the image are not developed and the width of the electrode portion is further decreased. When W ₂ > width of developer layer W ₃ , width of image area W ₂ > width of developer layer W ₃
In that case, ring marks are generated at both ends of the image due to discharge, and when the width W _{4 of the} latent image is greater than the width W ₁ of the plate-shaped member, color mixing and carrier adhesion occur at both ends of the image.
In either case, a good image cannot be obtained.

[0201]

As described above, according to the developing device and the image forming apparatus of the present invention, even when a toner having a small particle diameter is used as the developer, the developing property is high and the background portion is not fogged. Further, it is possible to provide a developing device capable of performing excellent development without causing color mixture even when superposed development of multicolor toner images. Further, in a color image forming apparatus of a system in which a multicolor toner image is superposed and developed on a photosensitive drum and then transferred in a batch, a high-density multicolor image with high density and no color mixture can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a developing device according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a main part of the developing device.

FIG. 3 is a configuration diagram showing an example of an image forming apparatus of the present invention.

FIG. 4 is a model diagram for considering an oscillating electric field formed in a gap between a photosensitive drum, a developing roller, and an electrode portion.

FIG. 5 is a model diagram for considering toner flight in a developing area.

FIG. 6 is a plan view showing the width of each part in the developing area.

FIG. 7 is a cross-sectional view showing a configuration of a plate-shaped member having an electrode portion.

FIG. 8 is an enlarged view in the vicinity of a development area in which a plate-shaped member having an electrode portion is arranged.

[Explanation of symbols]

 10 Photoconductor Drum (Image Forming Body) 11 Conductive Substrate 12 Photosensitive Layer 20 Scorotron Charger 25 Image Reading Section 30 Image Writing Section 40A, 40B, 40C, 40D Developing Device 41 Developing Roller (Developer Conveying Body) 42 Magnet 43 Plate-shaped member 44 Electrode portion 45 Supply roller 46 Restriction rod 47 Scraper 48 Stirring roller 49 Casing 50 Two-component developer 51,52 Power source 60 Paper feeding portion 60 First paper feeding roller 62 Second paper feeding roller 70 Transfer corona charger 75 Separation Corona Charger 80 Conveying Section 85 Fixing Section 90 Cleaning Device 91 Cleaning Blade 95 Pre-charging Exposure Lamp

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayasu Onodera 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Inventor Yuuo Endo 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Inventor Hiroyuki Nomori 2970 Ishikawa-cho, Hachioji City, Tokyo Konica Stock Company

Claims (17)

[Claims] 1. A plate-shaped member having an electrode portion is provided on an upstream side of a developing area where an image forming body and a developer conveying body face each other in a moving direction of the developer conveying body, and a DC voltage is applied to the electrode portion. ,
In a developing device for applying a superimposed voltage of a direct current component and an alternating current component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image forming body, the developer transport body is applied. The amplitude of the alternating current component is V _AC [V], the direct current component is V _DC [V], and the direct current voltage applied to the electrode part is V
_{When DEN} [V], V _AC > | V _DEN | − | V _DC |, the closest distance between the image forming body and the developer transport body is D ₁ [mm], the electrode portion and the developer The closest distance of the carrier is D ₂ [mm], and the average charge amount of the toner is Q _t [μ].
C / g] and the average particle diameter is d _t [μm], 10 · | Q _t | · d _t · D ₁ > _VAC > 5 · | Q _t | · d _t ·
D ₂ is a developing device. 2. A frequency of an AC component applied to the developer transport body is f _AC [Hz], a moving speed of the developer transport body is V _r [mm / sec], and the developer transport body of the electrode portion is The developing device according to claim 1, wherein f _AC ≧ 10 · V _r / L ₁ when the width in the moving direction is L ₁ [mm]. 3. The closest distances between the downstream end and the upstream end of the electrode portion in the moving direction of the developer carrier and the closest distances to the developer carrier are D ₄ [mm] and D ₅ [m], respectively.
m], the thickness of the developer layer at the position where the plate-shaped member is in contact with the developer on the developer transport body is H ₁ [mm]
The developing device according to claim 1 or ₂ , wherein D ₄ > D ₂ = D ₅ > H ₁ . 4. The closest distance between the end of the plate-shaped member on the downstream side in the moving direction of the developer transport body and the developer transport body is D.
₃ [mm], where the thickness of the developer layer at the position where the image forming body and the developer transport body are closest to each other is H ₂ [mm], D ₄ ≧ D ₃ > H ₂ and 0.6 The developing device according to any one of claims 1 to _{3, wherein} D ₁ ≧ D ₃ ≧ 0.2 · D ₁ . 5. A distance between an end of the electrode portion on the downstream side in the moving direction of the developer transport body and an end of the plate-shaped member on the downstream side in the moving direction of the developer transport body, that is, the eaves of the plate-like member. The width is L ₂ [mm], and the distance between the position where the plate-shaped member is in contact with the developer on the developer transport body and the end of the plate-shaped member on the downstream side in the developer transport body moving direction is defined. L ₃ when a [mm], L _3> L _1> an apparatus according to any one of claims 1 to 4, characterized in that the L _2. 6. A position at which the image forming body and the developer transport body are closest to the center of curvature of the developer transport body with a radius of curvature of r [mm] in the developing area of the developer transport body. When the angle between the position where the plate-shaped member is in contact with the developer on the developer transport body is θ [°], r · (1-cos θ) ≧ D ₁ and r · sin θ ≧ L The developing device according to any one of claims 1 to 5, wherein the developing device has ₃ · cos θ. 7. The plate-shaped member has an electrode portion and a coating layer formed on an insulating substrate material, and the width of the coating layer in the moving direction of the developer transport body is L ₄ [mm]. At this time, L ₃ > L ₄ ≧ L ₁ + L ₂ is satisfied, and the developing device according to any one of claims 1 to 6. 8. A plate-shaped member having an electrode portion is provided on the upstream side in the moving direction of the developer transport body in the developing area where the image forming body and the developer transport body face each other, and a DC voltage is applied to the electrode portion. ,
In a developing device for applying a superimposed voltage of a direct current component and an alternating current component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image forming body, the developer transport body is applied. The amplitude of the alternating current component is V _AC [V], the direct current component is V _DC [V], and the direct current voltage applied to the electrode part is V
_{When DEN} [V], V _AC > | V _DEN |-| V _DC |, the closest distance between the image forming body and the developer transport body is D ₁ [mm], and the development of the plate-shaped member is performed. The closest distance between the downstream end of the developer transport body and the developer transport body is D ₃
[Mm], the latent image potential of the solid portion on the image forming body is V
_L [V] and the latent image potential of the background portion are V _H [V], then | V _H |> | V _DC |> | V _L | and | V _DC | + | V _DC −V _L | ₃ / D ₁ ＞ ｜ V _DEN ｜ ＞ ｜ V
_{DC | - | V H -V DC} | · (1-D 3 / D 1) and a developing device which is characterized in that. 9. A frequency of an AC component applied to the developer transport body is f _AC [Hz], a moving speed of the developer transport body is V _r [mm / sec], and the developer transport body of the electrode portion is 9. The developing device according to claim 8, wherein f _AC ≧ 10 · V _r / L ₁ when the width in the moving direction is L ₁ [mm]. 10. The closest distance between the electrode portion and the developer transport body is D ₂ [mm], and the developing portion and the downstream end portion of the electrode portion in the moving direction of the developer transport body are connected to the developing portion. The closest distances to the agent carrier are D ₄ [mm] and D _{5 respectively.}
[Mm], the thickness of the developer layer at the position where the plate-shaped member is in contact with the developer on the developer transport body is H ₁ [m
m], the developing device according to claim 8 or 9, wherein D ₄ > D ₂ = D ₅ > H ₁ . 11. The thickness of the developer layer at the position where the image forming body and the developer carrying body are closest to each other is H ₂ [m
m], D ₄ ≧ D ₃ > H ₂ and 0.6 · D ₁ ≧ D ₃ ≧ 0.2 · D ₁ are satisfied. The developing device according to 1. 12. A distance between an end of the electrode portion on the downstream side in the moving direction of the developer transport body and an end of the plate-shaped member on the downstream side in the moving direction of the developer transport body, that is, the eaves of the plate-like member. The width is L ₂ [mm], and the distance between the position where the plate-shaped member is in contact with the developer on the developer transport body and the end of the plate-shaped member on the downstream side in the developer transport body moving direction is defined. L ₃ [mm]
The developing device according to claim 8, wherein L ₃ > L ₁ > L ₂ is satisfied. 13. A position at which the image forming body and the developer transport body are closest to each other with respect to the center of curvature of the developer transport body, where the radius of curvature of the developer transport body in the developing area is r [mm]. When the angle formed by the position of the plate-shaped member in contact with the developer on the developer transport body is θ [°], r · (1-cos θ) ≧ D ₁ and r · sin θ ≧ L 13. The developing device according to claim 8, wherein the developing device has ₃ · cos θ. 14. The plate-shaped member has an electrode portion and a coating layer formed on an insulating substrate material, and the width of the coating layer in the moving direction of the developer transport body is L ₄ [mm]. At this time, L ₃ > L ₄ ≧ L ₁ + L ₂ is satisfied, and the developing device according to any one of claims 8 to 13. 15. A plate-shaped member having an electrode portion is provided on the upstream side in the moving direction of the developer transport body in the developing area where the image forming body and the developer transport body face each other, and a DC voltage is applied to the electrode portion. , A plurality of developing devices for applying a superimposed voltage of a direct current component and an alternating current component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image formation body, In an image forming apparatus that forms a multicolor image by repeating the step of forming a latent image and the step of developing the latent image a plurality of times, in each developing step, the AC component applied to the developer carrier is Amplitude is V _AC [V], DC component is V
_DC [V], DC voltage applied to the electrode part is V
_DEN [V], the closest distance between the image forming body and the developer transport body is D ₁ [mm], the closest distance between the electrode portion and the developer transport body is D ₂ [mm], the average of the toner When the charge amount is Q _t [μC / g] and the average particle size is d _t [μm], V _AC > | V _DEN | − | V _DC | and 10 · | Q _t | · d _t · D ₁ > V _AC > 5 ・ ｜ Q _t ｜ ・ d _t・
D ₂ and the strength of the oscillating electric field in the gap between the image forming body and the developer carrying body in each developing step, and the strength of the oscillating electric field in the gap between the image forming body and the developer carrying body in the preceding developing step. An image forming apparatus characterized by making the strength of an oscillating electric field equal or weaker. 16. A plate-shaped member having an electrode portion is provided on the upstream side in the moving direction of the developer transport body in the developing area where the image forming body and the developer transport body face each other, and a DC voltage is applied to the electrode portion. , A plurality of developing devices for applying a superimposed voltage of a direct current component and an alternating current component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image formation body, In an image forming apparatus that forms a multicolor image by repeating the step of forming a latent image and the step of developing the latent image a plurality of times, in each developing step, the AC component applied to the developer carrier is Amplitude is V _AC [V], DC component is V
_DC [V], DC voltage applied to the electrode part is V
_DEN [V], the closest distance between the image forming body and the developer transport body is D ₁ [mm], the downstream end of the plate-shaped member in the developer transport body moving direction and the developer transport body When the closest distance is D ₃ [mm], the latent image potential of the solid portion on the image forming body is V _L [V], and the latent image potential of the background portion is V _H [V], V _AC > | V _DEN |-| V _DC | and | V _H |> | V _DC |> | V _L | and | V _DC | + | V _DC -V _L | -D ₃ / D ₁ > | V _DEN |> | V
_DC | − | V _H −V _DC | · (1-D ₃ / D ₁ ), and the strength of the oscillating electric field in the gap between the image forming body and the developer carrying body in each developing step is set to The image forming apparatus is characterized in that the strength of the oscillating electric field in the gap between the image forming body and the developer carrying body in the developing step is made equal to or weaker. 17. A plate-shaped member having an electrode portion is provided on the upstream side in the moving direction of the developer transport body in the developing area where the image forming body and the developer transport body face each other, and a DC voltage is applied to the electrode portion. In a developing device for applying a superimposed voltage of a direct current component and an alternating current component to the developer transport body to fly toner under an oscillating electric field to develop a latent image on the image forming body, The width in the direction orthogonal to the moving direction of the developer transport body is W
₁ [mm], the width of the electrode portion in the direction orthogonal to the moving direction of the developer transport body is W ₂ [mm], the moving direction of the developer transport body of the developer layer transported on the developer transport body when the width in the direction perpendicular to the developer conveying member movement direction orthogonal latent image formed in the direction of width W ₃ (mm) and the image forming body on was W ₄ [mm] in, W ₁ > W ₃ > W ₂ > W _{4 The} developing device.