JP2860104B2 - Developing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a developing device, and more particularly, to a developing device in which a developer is conveyed to a development area by a developer carrier to form a static image formed on a latent image carrier. The present invention relates to a developing device that performs development by supplying toner to an electrostatic latent image.

(Prior Art) In general, in a magnetic brush developing apparatus using a two-component developer installed in an electrophotographic copying machine or the like, a developer in a developing tank is sprung on a developer carrier to form a magnetic brush. Is formed, and the magnetic brush is conveyed to the developing area, and the end of the brush is brought into sliding contact with the latent image carrier, whereby the electrostatic latent image is developed and visualized.
The developer is composed of a magnetic carrier and a toner, and selectively charges a toner charged so as to have a fixed polarity relationship with respect to the electrostatic latent image in a predetermined potential state to the electrostatic latent image side. The development is performed by shifting to.

On the developer carrier side, a developing bias having a predetermined relationship with the charged state of the electrostatic latent image and the toner is applied, and this developing bias prevents the toner from being stained on the background portion. Thus, the toner is selectively transferred favorably.

FIG. 7 is a schematic diagram showing an example of an electric field intensity distribution based on a solid latent image potential. As shown in this figure, in the solid image area, a developing electric field for attracting toner from the developer carrier side to the latent image carrier side is formed, and the other background area, in particular, the solid image area A reverse electric field in the direction of pushing the toner toward the developer carrying member is formed in the peripheral portion. The strength of these electric fields is determined by the value of the developing bias.

FIG. 8 shows a state in which toner particles in the magnetic brush 3 are moved toward the latent image carrier 1 when a developing electric field is applied between the latent image carrier 1 and the developer carrier 2. FIG. As shown in this figure, the developing electric field causes the toner particles 3a to move from the developer carrier 2 toward the spike ends of the carrier particles 3b that have been spiked. As a result, the toner particles 3a become latent. It is favorably transferred to the image carrier 1 side.

(Problems to be Solved by the Invention) On the other hand, FIG. 9 shows a case where a reverse electric field is applied between the latent image carrier 1 and the developer carrier 2. Such a reverse electric field is formed around the background portion and the solid image portion as described above. This reverse electric field causes the toner particles 3a to move toward the developer carrier 2, that is, toward the root of the carrier particles 3b that have been raised, and as a result, the toner particles 3a are reduced at the ends of the carrier particles 3b. . In particular, in the peripheral portion of the solid image portion where a strong reverse electric field is formed,
The toner particles 3a may not be present at the end of the carrier particles 3b.

As described above, when the magnetic brush 3 enters the developing area in a state where the toner particles are reduced or absent at the end of the spike and comes into contact with the electrostatic latent image, a good developing action is not performed, and the density is reduced. , Or a so-called white spot occurs in the image. Further, since the carrier particles are charged in the opposite polarity to the toner particles, when the spikes of the carrier particles come into contact with the developed image portion, the toner in the image portion may be taken back to the carrier side. . In this case, if a predetermined amount of toner is attached to the carrier side, the electric lines of force generated between the carrier and the toner form a closed system, and no electric force acts on the outside. . However, when the amount of toner is reduced due to the above-described reverse electric field force, the force of the charge of the carrier acts externally. Such a tendency becomes stronger as the resistance value or the dielectric constant of the carrier increases, and depends on the discharge time constant τ (= ρε) of the carrier.

In order to solve the above-described problems, means for narrowing the developing gap and reducing the resistance of the developer have been considered. However, neither of these methods can sufficiently reduce white spots, and the developing characteristics are fluctuated when the developing gap is narrowed, and stable against environmental fluctuations when the resistance of the developer is reduced. There is a problem that the performance is reduced.

Accordingly, the present invention provides a development capable of satisfactorily eliminating a white spot phenomenon occurring in a background portion, particularly a peripheral portion of a solid image with a simple structure, and stably obtaining a high quality image. The purpose is to do.

(Means for Solving the Problems) In order to achieve the above object, according to the first aspect of the present invention, a developer carrying member is provided so as to be close to a latent image carrying member, and the developing member is provided at a portion opposed to these two members. A first step of forming a developing area by a magnetic brush on the developer carrier, causing the developer carrier to transport a developer including toner and carrier to the developing area, and applying a developing bias voltage to the developer carrier; A bias application means for supplying the toner from the developer carrier to the electrostatic latent image formed on the latent image carrier by the developing bias voltage, and developing the electrostatic latent image. A second bias for applying a bias voltage to attract the toner in the developer on the developer carrier to the surface portion of the magnetic brush on the electrode plate; An application unit is provided, and a control unit for controlling an output of the first and second developing bias application units is provided.

(Operation) In the means having the configuration described in claim 1,
Until the magnetic brush is carried into the developing area or immediately after the magnetic brush is carried in, the toner particles in the magnetic brush are attracted to the end of the ear by the electrode plate, and the toner attracting action to the developer carrier by the reverse electric field force is exerted. It is being weakened.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a developing device 11 to which the present invention is applied. A toner hopper section 13 is provided at a rear end side (right end side in the figure) of the casing 12 containing the two-component developer, and a toner cartridge 14 is detachably attached to the toner hopper section 13. It is installed. In the toner cartridge 14, an agitator 15 for agitating the new toner stored therein is mounted, and a toner replenishing roller 16 is provided at an outlet provided below the toner hopper 13. Supported. And agitator 15
The toner sent out of the toner cartridge 14 by the stirring action of the toner is temporarily stored in the toner hopper section 13 and then intermittently driven by the toner replenishing roller 16 to a predetermined amount near the paddle wheel 17 provided in the casing 12. It is sent one by one.

On the front side (left side in the drawing) of the paddle wheel 17, a developing roller 18 as a developer carrier is disposed, and the developing roller 18 is stirred by the paddle wheel 17.
The developer composed of the toner and the carrier pumped up on the brush 18 is raised on the surface of the sleeve by a magnet 19 installed in the hollow sleeve of the developing roller 18 to form a magnetic brush 20. This magnetic brush 20
Is transported in the direction of the arrow, and a doctor blade 21 as a developer regulating member is disposed downstream of the transport direction. The doctor blade 21 has a function of regulating the height of the ears of the magnetic brush 20, that is, the amount of the developer. The surplus developer scraped off by the doctor blade 21 is returned to the paddle wheel 17 again while being laterally stirred by the separator 22 and the stirring screw 23 installed immediately after the doctor blade 21.

Further, the hollow sleeve forming the developing roller 18 is:
A portion of the front end outer surface side is exposed from the front end opening of the casing 12 so as to face the photosensitive drum 24 as a latent image carrier, and particularly, as shown in FIG. A developing region 25 is formed in a portion facing the photoconductor drum 24 and the photoconductor drum 24. Then, in the development area 25, the end of the magnetic brush 20 is brought into contact with the surface of the photosensitive drum 24, so that the development action is performed. In the present embodiment, together with the photosensitive drum 24 is rotated so as to be conveyed by V _p (mm / sec) in the direction of the arrow, the developing roller 18 in the direction of arrow v _s (mm / sec) are rotationally driven so as to be conveyed in, is set as the relationship between the two becomes v _s> v _p.

Further, an electrode plate 30 that attracts the toner in the developer forming the magnetic brush 20 to the surface layer of the magnetic brush 20 is provided at the upstream side of the developing region 25 in the magnetic brush transport direction. The electrode plate 30 is formed of a conductive thin plate member having a predetermined length in the rotation axis direction of the developing roller 18 and having a predetermined width in the transport direction of the magnetic brush 20. An insulating layer may be coated on the surface of the thin plate member. This electrode plate 30 is a magnetic brush
It is arranged so as to be in contact with or close to the end of the spike 20, and extends to the boundary of the development area 25. A bias voltage having a polarity opposite to the charged polarity of the toner is applied to such an electrode plate 30 by a power supply circuit 31, and the magnetic brush 20, that is, the toner in the developer is applied to the surface layer of the magnetic brush 20 by the bias voltage. It has been attracted to.

In such an embodiment, as shown in FIG. 3 in particular, until just before the magnetic brush 20 is carried into the developing area 25, the toner in the magnetic brush 20 is removed by the electric field force of the electrode plate 30. Therefore, the magnetic brush 20 is attracted to the surface layer of the magnetic brush 20 against the reverse electric field force. Therefore, a state in which the toner particles are reduced or absent at the end of the magnetic brush 20 is avoided, and the magnetic brush 20 enters the developing area 25 in a normal state and contacts the electrostatic latent image. As a result, a good developing action is performed. Therefore, unlike the related art, it is possible to prevent an image having only a low density from being obtained and to prevent a so-called white spot from occurring in the image.

Further, since the magnetic brush 20 is prevented from being in the state of only the carrier as described above, the spike consisting of only the carrier does not come into contact with the already developed image portion. Is prevented from being taken back to the carrier side. Further, by obtaining the magnetic brush 20 in which the toner is well distributed, the image density of the solid image portion is increased, and it is possible to form a more uniform image without white spots. The image density can be set to a desired value by adjusting a bias voltage value applied to the electrode plate 30.

Further, in the embodiment shown in FIG.
Are formed so as to be curved with a constant curvature, whereby the electrode plate 40 is arranged along the curvature of the developing roller 18. With such a configuration, the electrode plate 40 can be extended in a long shape without contacting the photosensitive drum 24 side, which is convenient.

Further, in the embodiment shown in FIG. 5, a bias applying device 51 is attached to the electrode plate 50, and the bias applying device 51 includes a control device 52 for performing output control based on image forming timing. It is attached. When the developer contacts the non-image area, the control device 52 switches the bias voltage generated from the bias application device 51 to the same polarity as the toner. According to such an embodiment, when the developing operation is not performed, the toner particles are moved to the developing roller 18 side,
As a result, the toner attached to the electrode plate 50 is removed, and the toner is prevented from sticking, so that inconveniences such as generation of oppositely charged toner due to friction between the toners can be avoided. A control device 54 that performs output control based on image forming timing is also provided for the bias application device 53 that applies a developing bias to the developing roller 18. By controlling the output of the developing bias by such a control device 54, the above-described operation of removing the adhered toner on the electrode plate 50 can be performed more effectively. Each of the bias applying devices 51 and 53 is configured to output two or more different bias values. .

Furthermore, in the embodiment shown in FIG.
The electrode plate 60 is provided so as to cover a part of the development area. In such an embodiment, the same operation and effect as those of the above embodiments can be obtained. In the present embodiment, a portion of the electrode plate 60 that is in contact with the photosensitive drum 24 is insulated so that leakage of the electrostatic latent image is prevented. As the insulation treatment, it is possible to adopt, for example, vapor deposition of aluminum on polyethylene terephthalate (PET).

In each of the above embodiments, if an alternating current is superimposed on a bias applied to the electrode plate, a similar effect such as improvement of white spots can be obtained, and at the same time, toner adhesion to the electrode plate is prevented by the action of the AC voltage. It is also possible and convenient.

The present invention is applicable regardless of normal development or reversal development.

(Effect of the Invention) As described above, in the developing device according to the first aspect of the present invention, the toner in the magnetic brush enters the deep layer portion due to the reverse electric field generated in the background portion, particularly in the peripheral portion of the solid image portion. In order to prevent such a situation, an electrode plate for attracting toner to the surface layer of the magnetic brush is provided on the upstream side of the developing area, and the control means controls the bias output based on the image forming timing. The toner particles can be maintained in a good distribution state against the reverse electric field, and the toner attached to the electrode plate can be removed by appropriately controlling the bias voltage according to the image forming area to prevent the toner from sticking. In addition to this, the AC component is superimposed on the bias voltage applied to the electrode plate, preventing the toner from adhering to the electrode plate and preventing the generation of reversely charged toner due to the adhered toner. Since it is possible to prevent the occurrence of reversely charged toner due to friction between toners, it is possible to satisfactorily reduce the white spot phenomenon that has conventionally been apt to occur in the background, particularly in the periphery of a solid image, with a simple structure. At the same time, the image density of the solid image portion can be further increased, and a high-quality image can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an enlarged part of a developing device in one embodiment of the present invention, FIG. 2 is a schematic longitudinal sectional view showing the entire developing device, and FIG. FIG. 4 is a schematic explanatory view showing a part of the developing device in another embodiment of the present invention in an enlarged manner, and FIGS. 5 and 6 are further explanatory diagrams of the present invention. FIG. 7 is a schematic explanatory diagram showing a part of a developing device in another embodiment, FIG. 7 is a schematic distribution diagram showing an example of an electric field intensity distribution formed by a solid latent image potential, and FIG. FIG. 9 is a schematic explanatory view showing a state in which a developing electric field is applied between the body and the developer carrying member;
The figure is a schematic explanatory view showing a state in which a reverse electric field is applied between the latent image carrier and the developer carrier. 11 developing device, 18 developing roller, 24 photosensitive drum, 25 developing area, 30, 40, 50, 60 electrode plate.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hidetoshi Yano 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Junichi Terai 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Tomoko Ogawa 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-57-177170 (JP, A) JP-A-53- 110844 (JP, A) JP-A-53-116844 (JP, A) JP-A-58-70258 (JP, A) JP-A-58-70259 (JP, A) JP-A-58-156973 (JP, A) JP-A-1-186986 (JP, A) JP-A-1-186987 (JP, A) JP-A 61-42552 (JP, U) JP-A 62-177095 (JP, U) (58) Fields investigated (Int.Cl. ⁶ , DB name) G03G 15/06-15/095

Claims (1)

(57) [Claims] A developer carrier is provided so as to be close to a latent image carrier, and a developing area by a magnetic brush on the developer carrier is formed in a portion opposed to the two members,
A first bias applying unit is provided for transferring a developer including a toner and a carrier to a developing area by the developer carrier, and applying a developing bias voltage to the developer carrier. A developing device for supplying toner from the developer carrier to the electrostatic latent image formed on the body to perform development, wherein an electrode plate is provided in an upstream portion of the developing area in the developer transport direction, A second bias voltage is applied to this electrode plate to attract toner in the developer on the developer carrier to the surface layer of the magnetic brush.
And a control means for controlling the output of the first and second developing bias applying means, wherein the second bias applying means has a bias in which an AC component is superimposed on the electrode plate. A developing device, wherein a voltage is applied, and the control unit controls an output of the first bias applying unit or the second bias applying unit based on an image forming timing.