JPH09114233A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device constituted so that not only a development with sufficient density and without fogging can be executed without soiling the inside of a machine or soiling an image caused by the splash of toner but also the toner which can form the excellent image without developing density irregularity even when developer whose fluidity is bad is used and which is charged to have identical polarity to the electrostatic charge of an image carrier is splashed from a developer layer on a developer carrier and attached to an electrostatic latent image on the image carrier. SOLUTION: This device is constituted so that a linear electrode 43 is laid between the image carrier and the developer carrier 41 and the toner charged to the identical polarity to the electrostatic charge of the image carrier is splashed from the developer layer which is not brought into contact with the image carrier on the carrier 41 and stuck to the electrostatic latent image on the image carrier under a vibration electric field. At this time, one linear electrode 43 is used and a voltage obtained by superimposing an AC component and a DC component whose polarity is identical to the electrostatic charge of the toner is respectively impressed on the electrode 43 and the carrier 41 so that the frequency of at least the AC component is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image on an image carrier used in an electrophotographic system, and more particularly, to a line in the gap between the image carrier and the developer carrier. -Shaped electrode is stretched, and the toner charged to the same polarity as that of the image carrier is ejected from the developer layer which is not in contact with the image carrier on the developer carrier under the oscillating electric field to fly the toner on the image carrier. The present invention relates to a developing device that adheres to an electrostatic latent image.

[0002]

2. Description of the Related Art As an image forming apparatus for developing an electrostatic latent image on an image carrier using an electrophotographic method to form a multicolor image, charging, exposing, developing and transferring steps are repeated a plurality of times. There is an image forming apparatus that forms a multicolor image by superposing a plurality of toner images on a transfer material. This image forming apparatus transfers a toner image to the same transfer material each time the development of each color is completed, so it is necessary to provide a mechanism for holding the transfer material inside the apparatus so as not to cause positional displacement, and the apparatus is large. It has the drawback of becoming

On the other hand, the steps of charging, exposing, and developing are repeated a plurality of times to superimpose a plurality of toner images on the image carrier, thereby transferring the color image formed on the image carrier to a transfer material. There is an image forming apparatus that forms a multicolor image. This image forming apparatus does not require a mechanism for holding the transfer material inside the apparatus, and has an advantage that the apparatus can be downsized. In this image forming apparatus, the developer layer on the developer carrier is brought into non-contact with the image carrier, and a superimposed voltage of a DC component and an AC voltage is applied to the developer carrier to fly the toner under an oscillating electric field. A developing device is used which allows the electrostatic latent image on the image carrier to adhere to the electrostatic latent image. In this developing device, since the developer layer of the developer transporting body is not in contact with the image carrier, the toner of the preceding developing device which has adhered to the image carrier does not contain toner of different colors. There is an advantage that a large amount does not mix in the developing device in the subsequent stage.

Also in the above-mentioned image forming apparatus, the image exposure from the original document is made incident on the charged surface of the image carrier through the color separation filter, and the electrostatic latent image formed thereby has a polarity opposite to that of the charge of the image carrier. A copying device that attaches charged toner, image exposure of dots from a laser beam scanner, a light emitting element array, etc., is made incident on the charged surface of an image carrier based on color-coded image signals from a document reading means, a computer, etc. There are two types of recording devices that perform so-called reversal development in which the electrostatic latent image formed by the above is attached with toner charged to the same polarity as the charge of the image carrier. 2. Description of the Related Art Recording devices have become mainstream in that different color toners are unlikely to be mixed in and stable and clear color images can be formed.

In the above-mentioned copying machine, since the image carrier and the toner are charged with opposite polarities, the developing density is easily increased, but the toner is liable to be adhered to the non-image portion, so that the toner is applied to the developer carrier. The DC component of the developing bias is set to a voltage having a polarity opposite to that of the toner charge for preventing the fog. However, if the fog is eliminated, the developing density is lowered and a different color toner is easily mixed in the developing device. There is a problem. On the other hand, in the recording apparatus, since the image carrier and the toner are charged with the same polarity, the DC component of the developing bias applied to the developer carrier to attach the toner to the image carrier is applied to the image carrier. It is necessary to set the voltage to the same polarity as the charge of the toner to be transferred, so that it is unlikely that different color toner will mix in the developing device and stable and clear color images can be formed, but on the other hand, sufficient development density without causing fog That is, if it is attempted to obtain a high-quality image in which the image density is obtained to reproduce delicate lines, dots, or shade differences, the charging potential of the image carrier and the DC component voltage value of the developing bias (the absolute value is obvious) In this case, the voltage is also simply increased), so that there is a problem in that in-machine contamination is likely to occur due to toner scattering from the developing area.

On the other hand, in order to obtain a high quality image, it is generally effective to atomize the toner. Therefore, when the toner used for the reversal development of the above-described recording apparatus is made into fine particles, in order to obtain a sufficient image density without causing fog, it is necessary to increase the AC voltage applied to the developer transport body. Therefore, in-apparatus contamination due to toner scattering is more likely to occur, and different-color toners are more likely to be mixed in the developing device, so that different-color toners are less likely to be mixed in the developing device for reverse reversal development, and a stable and clear color image can be formed. Therefore, it is difficult to obtain the high image quality by making the toner for reversal development into fine particles.

In order to solve the above-mentioned problem of reversal development, for example, Japanese Patent Laid-Open No. 59-223467 discloses a wire for controlling the flight of toner in the gap between the image carrier and the developer layer on the developer carrier. There is disclosed a developing method in which a control electrode is provided, and an alternating voltage is applied to at least one of the control electrode and the developer transport body to form an oscillating electric field, and the toner is ejected to perform development. According to the publication, the fine particle toner can be used as the toner of the two-component developer, and furthermore, the fog is prevented and a clear high image quality can be obtained. However, even when the developing method described in this publication is used, toner adheres to and accumulates on the linear electrodes to cause image contamination, and when fine particle toner is used, the fluidity of the developer is deteriorated and the developing density is reduced. There is a problem that high quality may not be obtained due to unevenness.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is possible to perform good development with sufficient density and without causing fog inside the machine or image stain due to toner scattering. Not only can it be performed, but a good image with no development density unevenness can be formed even when a developer with poor fluidity is used. Toner charged to the same polarity as that of the image carrier is charged on the developer carrier. An object of the present invention is to provide a developing device which is made to fly from a developer layer and adhere to an electrostatic latent image on an image carrier.

[0009]

In order to achieve the above object, the inventors of the present invention provided a linear electrode in the gap between the image carrier and the developer transport body, and provided the linear electrode and the developer transport body respectively. AC voltage and DC voltage of the same polarity as the toner charge are superimposed and applied, and the toner flies from the developer layer on the developer carrier under the oscillating electric field, and the charged surface of the image carrier has the same polarity as the toner. As a result of an examination of a developing device for adhering an electrostatic latent image composed of a distribution of low-potential dots formed on the above, the following facts were clarified.

(1) AC component and DC component of the developing bias applied to the linear electrode and the developer carrier, respectively. The frequency f ₁ [Hz] of the AC component applied to the linear electrode and the developer carrier are applied. AC component frequency f ₂ [Hz]
If they are the same, they will resonate, resulting in an image with unevenness.

Frequency f of the AC component applied to the linear electrode
_{When 1} and the frequency f _{2 of the} AC component applied to the developer transport body are different from each other, it is possible to prevent the toner from accumulating and accumulating on the linear electrode without resonating, and particularly 0.1f ₂ <f ₁ <f ₂ <3
A good image is obtained when the condition of f ₁ is satisfied.

DC component voltage V applied to the linear electrode
_DC1 [V] is the voltage V of the DC component applied to the developer carrier.
If it is smaller than _DC2 [V], the image is not discharged from the linear electrode to the image carrier, and an image without density unevenness can be obtained. Especially, the condition of V _DC2 / 2 ≦ V _DC1 <V _DC2 is satisfied. Advanced images are obtained when satisfied.

(2) Relationship between linear electrode and developer layer in the gap between the image carrier and the developer carrier When the linear electrode is completely separated from the surface of the developer layer on the developer carrier, or vice versa. In particular, when the developer is too close to the surface of the developer carrier and completely buried in the developer layer, the developability is low.

The closest distance between the linear electrode and the developer carrier is approximately equal to the thickness of the developer layer on the developer carrier, or the linear electrode is developed on the developer carrier without being completely buried. When it is in contact with the agent layer, the developability is high.

Even if the above conditions are satisfied, the developability deteriorates as the distance from the image carrier to the developer layer, and hence the distance from the image carrier to the linear electrodes, increases.

The closest distance between the linear electrode and the developer carrier is X ₁ [mm], and the closest distance between the linear electrode and the image carrier is X.
₂ [mm], the diameter of the linear electrode is d [mm], and the height of the developer layer on the surface of the developer transport body relative to the linear electrode without a linear electrode is h [mm], X ₁ ≧ X ₂ , X ₁ + d ≧
If the positional relationship between the linear carrier and the developer carrier or the image carrier and the relationship between the thickness of the developer layer on the developer carrier are set so as to satisfy h ≧ X ₁ ≧ h / 2, the developability is particularly improved. Is improved.

(3) Position and number of linear electrodes from the re-proximity position between the developer carrier and the image carrier: The linear electrode is gradually developed as the distance from the closest position between the developer carrier and the image carrier is increased. The developing property deteriorates sharply at a certain point, and the developer layer on the developer carrier moves from the closest position between the developer carrier and the image carrier to the upstream side and the downstream side. Comparing the rates of decrease in developability, the downstream side is slightly larger, the closest distance between the image carrier and the developer carrier is X ₀ [mm], and the closest position between the image carrier and the developer carrier is the development. The radius of curvature of the agent carrier is r [mm], and the angle θ ° formed by the straight line connecting the center of curvature of the agent carrier to the center of curvature of the image carrier and the straight line connecting the center of curvature of the linear electrode is developed by the center of curvature of the linear electrode. The developer on the developer carrier rather than the straight line connecting the center of curvature of the developer carrier and the center of curvature of the image carrier As + when in the upstream side of the movement, is stretched position of the linear electrode

[0018]

(Equation 2)

If the above condition is satisfied, high developability can be obtained.

When one linear electrode is installed at the closest position between the developer carrier and the image carrier, the developing property is greatly improved as compared with the case where the developer carrier and the image carrier are not installed, and the linear carrier of the developer carrier and the image carrier is improved. The developability is further improved by arranging a plurality of them in parallel in a direction away from the closest position at a right angle, but the rate of improvement in the developability is small.

When a plurality of linear electrodes are arranged in parallel in a direction away from the closest position of the developer carrier and the image carrier at a right angle, uneven image density at the rear end of the solid image portion is emphasized.

(4) Developer A single-component developer having an average particle diameter of toner of 10 μm or more can be used, but stability to obtain a high quality image is poor as compared with a two-component developer in which toner and carrier are mixed. .

When the average particle diameter of the toner is 10 μm or more in the conventional two-component developer, density unevenness does not occur on the image even if the AC component is not applied to the linear electrode.

When the average particle diameter of the toner is smaller than 10 μm in the conventional two-component developer, the fluidity of the developer is deteriorated. In particular, when the average particle diameter of the toner is 8 μm or less, the fluidity is extremely deteriorated and uneven density occurs on the image.

When a developer having poor fluidity is used, including the above cases, when the superimposed voltage of the direct current component and the alternating current component as in the above (1) is applied to the linear electrode in the development gap, the density on the image is increased. The unevenness is eliminated.

The present invention has been made based on the above findings of the present inventors. A linear electrode is stretched in the gap between the image carrier and the developer carrier to develop the developer under an oscillating electric field. In a developing device in which a toner charged to the same polarity as the charging of the image carrier is ejected from a developer layer that is not in contact with the image carrier on the carrier and adheres to the electrostatic latent image on the image carrier, One electrode is used, and a superimposed voltage of an alternating current component and a direct current component having the same polarity as the charging of the toner is applied to the linear electrode and the developer carrier, respectively, and at least the frequencies of the alternating current components are changed. In the first aspect of the invention, or the closest distance between one linear electrode for applying a superimposed voltage of an AC component between the image carrier and the developer carrier and a DC component having the same polarity as the charging of the toner and the developer carrier. the X ₁ mm and the distance of closest approach linear electrode and the image carrier X ₂ mm and the line When the diameter of the electrode was d [mm], a height of the developer layer on the linear electrodes is not state of the developer carrying member surface to the linear electrode and the h _{[mm], X 1 ≧ X 2, X} 1 The object is achieved by the configuration of the second invention, in which the linear electrode is installed so as to satisfy + d ≧ h ≧ X ₁ ≧ h / 2.

[0027]

In the present invention, the number of linear electrodes is set to one, so that the area of the strong oscillating electric field formed by the linear electrodes is narrowed, and the area of the toner cloud formed by the oscillating electric field is narrowed. As a result, the area where the developing action is actually performed is narrowed, and it is possible to prevent the occurrence of image density unevenness seen behind the solid image portion. In the first aspect of the invention, since the superimposed voltage of the alternating current component and the direct current component having the same polarity as the charging of the toner is applied to the linear electrode and the developer transport body, respectively, at least the frequencies of these alternating current components are changed, so that the resonance occurs. It is possible to prevent toner from accumulating and accumulating on the linear electrode without doing so, and even if a developer with poor fluidity is used, even if a developer with poor fluidity is used, a high-quality image without uneven density can be obtained. Obtainable.

Further, in the second invention, the closest distance between the linear electrode applying the superimposed voltage of the alternating current component and the direct current component having the same polarity as the toner charging and the developer carrying member is X ₁ [mm], and the linear electrode is The closest distance of the image carrier is X ₂ [mm], the diameter of the linear electrode is d [mm], and the height of the developer layer on the surface of the developer carrier relative to the linear electrode without the linear electrode is As h [mm], the positional relationship between the developer carrier or the image carrier and the linear electrode and the developer carrier so that X ₁ ≧ X ₂ and X ₁ + d ≧ h ≧ X ₁ ≧ h / 2 are satisfied. Since the relationship with the thickness of the developer layer is set, the linear electrode exerts a strong vibration action on the toner near the surface of the developer layer to form a stable and highly dense toner cloud, and the toner cloud forms a linear electrode. Due to the action of a strong oscillating electric field, it is sufficiently supplied to the surface of the image carrier to obtain high developability.

[0029]

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 of the present invention, FIG. 2 is a block diagram showing an example of an image forming apparatus in which the developing device of the present invention is used, and FIG. 3 is a developing action before installation of linear electrodes. It is an explanatory view of a range measuring method.

In FIG. 1, 41 is a developing roller which is a developer transporting body having a fixed magnet body 42 therein, 43 is a linear electrode, 45 is a supply roller which is a developer supplying member, and 46.
Is a developer carrying amount regulating member, 47 is a scraper which is a developer scraping member, 48 is a stirring roller which is a developer stirring member, 49 is a casing of the developing device, and 50 is a mixture of toner and carrier. Two-component developer, 51 and 52 are power supplies as developing bias applying means,
Reference numeral 10 is a photosensitive drum which is an image carrier having a photosensitive layer 12 formed on a conductive substrate 11, X ₀ is the closest distance between the photosensitive drum 10 and the developing roller 41, and X ₁ is the linear electrode 43 and the developing roller 41. the closest distance, X ₂ is the distance of closest approach linear electrode 43 and the photosensitive drum 10, d is the diameter of the linear electrode 43, h is in the absence of the linear electrodes 43 at the installation position of the linear electrodes 43 It represents the height of the developer layer on 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 aluminum, for example.
Diameter 5 made of non-magnetic and conductive metal such as stainless steel
It is a cylinder of about 30 [mm] and has a surface roughness of 1 to 30 [μ
m] is processed. The developing roller 41 is
It rotates, but the magnetic field strength of its surface is 500 to 1,200.
A columnar fixed magnet body 42 having 4 to 12 N and S poles of [Gauss] is provided inside. Not limited to this, the magnet body 42 may rotate in the direction opposite to the rotation direction of the developing roller 41, or the magnet body 42 may rotate and the developing roller 41 may be fixed.

The linear electrode 43 is made of a conductive metal wire such as tungsten or stainless steel, and its surface is preferably covered with an insulating resin such as polyurethane or polyamide for preventing the occurrence of discharge between the developing roller 41 and the developing roller 41. It has a layer and is provided in a gap in which the photoconductor drum 10 and the developing roller 41 face each other in a direction parallel to the developing roller 41 at a right angle to the moving direction of the developer layer on the developing roller 41. .

The casing 49 is made of an insulative resin such as acrylic or polycarbonate.
A developing roller 41 including the above-mentioned magnet body 42, a supply roller 45, a scraper 47, and a stirring roller 48 are arranged inside, and a regulation rod 46 is arranged at the outlet of the casing 49. Fixing pins are planted on the outer surfaces of both side plates (not shown) of the casing 49, and one end of the linear electrode 43 is directly attached to the fixing pins and the other end is attached via a tension spring. .

A two-component developer 50 composed of toner and carrier is stored inside the casing 49, and the two-component developer 50 is agitated and mixed by an agitating roller 48 to make the toner have the same polarity as the charging polarity of the photosensitive drum 10. In addition to being triboelectrically charged, it is supplied onto the developing roller 41 by the supply roller 45, adheres to the developing roller 41, and is conveyed to form a developer layer. The layer thickness of the developer layer on the developing roller 41 is regulated by the regulating rod 46, and the developing roller 41 is conveyed to the developing area facing the photoconductor drum 10.

On the developing roller 41, a superimposed voltage of a direct current component voltage V _DC2 [V] having the same polarity as that of the charging of the photosensitive drum 10 and an alternating current component of a frequency f ₂ [Hz] is applied to the developing roller 41, and the linear electrode 43. DC voltage V of the same polarity from the power source 51
Although superimposed voltage of the AC component of _DC1 [V] and the frequency f ₁ (Hz) is applied, the frequency f ₁ of the AC component applied from the frequency f ₂ and the power supply 51 of an AC component applied from the power source 52 to each other Use different frequencies. The frequencies f ₁ and f ₂ preferably satisfy the condition of 0.1f ₂ <f ₁ <f ₂ <3f ₁ . In addition, the DC component voltage V applied from the power source 52
DC component voltage V _DC1 applied from _DC2 and power supply 51 is V
It is preferable that the condition of _DC2 / 2 ≦ V _DC1 <V _DC2 is satisfied. As a result, the strong oscillating electric field generated in the gap between the developing roller 41 and the linear electrode 43 causes the toner to separate from the carrier to form a toner cloud, which toner cloud forms in the gap between the linear electrode 43 and the photoconductor drum 10. Thus, a toner image having a sufficient density is formed by the developing bias from the developing roller 41 toward the electrostatic latent image on the photoconductor drum 10 from the developing roller 41 in particular.

The image forming apparatus shown in FIG. 2 is a recording apparatus for performing copying. 20 is a charging means using a scorotron charger for uniformly charging the photosensitive drum 10 rotating in the direction of the arrow, and 25 is an image reading device. And 30 are image writing units of image exposure means using a laser beam, 40A, 4
0B, 40C and 40D are developing devices similar to those shown in FIG. 1 using yellow, magenta, cyan and black toners as developers, and 60 is provided with a first paper feed roller 61 and a second paper feed roller 62. A sheet feeding unit, 70 a transfer unit using a corona charger, 75 a separating unit using a corona charger, 80 a transport unit, 85 a fixing unit, 90 a cleaning device equipped with a cleaning blade 91, and 95 The pre-charging static elimination means using an exposure lamp is shown.

In the basic operation of the multicolor image forming process in this image forming apparatus, 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 charging means 20.
In the image reading unit 25, optical information from the document is converted into an electric signal. The electric signal is subjected to image processing and then input to the image writing unit 30. The image writing unit 30 outputs a laser beam onto the charged photoconductor drum 10 to form an electrostatic latent image having a distribution of low potential dots. This electrostatic latent image is developed by the developing devices 40A, 40B, 40.
A yellow toner image is developed by, for example, 40A of C and 40D.

The surface of the photosensitive drum 10 on which the yellow toner image has been formed is again uniformly charged by the charging means 20 and the laser beam is made incident by the image writing section 30 to form the next electrostatic latent image. The electrostatic latent image is developed into a magenta toner image by, for example, 40B of the developing devices 40B, 40C and 40D, whereby a two-color image of yellow and magenta is formed on the photoconductor drum 10. Further, the latent image forming step and the developing step as described above are repeated twice to form a color image on the photoconductor drum 10 by superposing toner images of four colors.

A recording sheet, which is a transfer material, is stored in the sheet feeding section 60, and the recording sheet is synchronized with the color image on the photosensitive drum 10 by the first sheet feeding roller 61 and the second sheet feeding roller 62. It is sent to the transfer means 70. The color image on the photoconductor drum 10 is transferred onto the recording paper by the transfer unit 70, the recording paper is separated from the photoconductor drum 10 by the separating unit 75, and is sent to the fixing unit 85 by the conveying unit 80.
The color image is melted and pressure-fixed by the fixing unit 85, and then discharged out of the apparatus.

On the other hand, the photosensitive drum 1 after the color image transfer
The surface 0 is scraped of residual toner by a cleaning device 90 equipped with a cleaning blade 91 which is pressure-bonded to the surface at a certain timing, and the residual potential is removed by the pre-charging static elimination means 95, and then the next image forming process is performed. Be offered.

In the above-described developing device of the present invention used as described above, since only one linear electrode 43 is provided in the developing area where the developing roller 41 faces the photosensitive drum 10, the linear electrode 43 is provided. The area of the strong oscillating electric field formed by 43 is narrowed, the area of the toner cloud formed by the oscillating electric field is narrowed, and the area where the developing action is performed is narrowed. It is possible to prevent the occurrence of image density unevenness. On the other hand, when the number of the linear electrodes 43 is plural, the space in which the toner cloud is formed becomes wider and thus the developability is improved, but the image density unevenness seen on the rear end side of the solid image portion occurs. In some cases, image density unevenness increases and toner scattering from the developing area also increases.

The frequency f ₁ [Hz] of the AC component applied to the linear electrode 43 and the frequency f ₂ [Hz] of the AC component applied to the developing roller 41 are set to different values, more preferably 0.1 f. By satisfying ₂ <f ₁ <f ₂ <3f ₁ , the toner cloud can be stably formed to have a high density and can be held in the narrow region described above. On the other hand, if the frequencies f ₁ and f ₂ are the same, it becomes difficult to form a high density toner cloud due to resonance, and f ₁ and f ₂
However, if f ₁ > f ₂ the toner cloud is insufficiently generated, and if 0.1f ₂ > f ₁ it is difficult to hold the toner cloud in a narrow area, and if f ₂ > 3f _{1 the} toner cloud is difficult to hold. Is easily scattered from the developing area.

Further, the DC component voltage V _DC1 [V] having the same polarity as the toner charging applied to the linear electrode 43 and the developing roller 4 are used.
DC component voltage V _DC2 [V] applied to 1 is V _DC2 / 2 ≦ V
It is preferable to satisfy _DC1 ≦ V _DC2 , whereby the toner can be stably and sufficiently adhered to the electrostatic latent image on the photoconductor drum 10 without accumulating toner on the linear electrode 43. . On the other hand, V _DC1 <V _DC2 / 2
In the case of V _DC1 > V _DC2 , the toner easily adheres to the linear electrodes 43 and the development unevenness easily occurs. When V _DC1 > V _DC2 , the linear electrodes 43 are discharged to the photosensitive drum 10 and the image is easily disturbed.

The closest distance between the linear electrode 43 and the developing roller 41 is X ₁ [mm], the closest distance between the linear electrode 43 and the photosensitive drum 10 is X ₂ [mm], and the diameter of the linear electrode 43 is Is d [mm], and the height of the developer layer without the linear electrode 43 at the position where the linear electrode 43 is installed is h [mm], X
_The linear electrode 43 is installed in the developing area so as to satisfy ₁ ≧ X ₂ , X ₁ + d ≧ h ≧ X ₁ ≧ h / 2. And the linear electrode 43
By applying a developing bias composed of an AC voltage and a DC voltage having the same polarity as that of the toner and the charging of the photosensitive drum 10 to each other, stable and sufficient density development can be performed. In this case, the AC component does not have to be superposed on the developing bias applied to the developing roller 41. However, it is preferable to superimpose the AC component as described above.

When X ₁ <X ₂ is satisfied with respect to the above conditions, it becomes difficult to hold the high density toner cloud by the linear electrode 43, the developing density is lowered, and fog occurs. Easier to do. Also, h <X ₁ ,
When X ₁ <h / 2, it becomes difficult to form a high-density toner cloud by the linear electrode 43, and the development density decreases.

Further, the photosensitive drum 10 and the developing roller 41
Is the closest distance to X ₀ [mm], the radius of curvature of the developing roller 41 is r [mm], the straight line connecting the center of curvature of the developing roller 41 and the center of curvature of the photosensitive drum 10, the center of curvature of the linear electrode 43, and the development. When the angle formed by the straight line connecting the centers of curvature of the rollers 41 is θ ° and the upstream side in the moving direction of the developer layer on the developing roller 41 is the + direction,

[0048]

(Equation 3)

It is preferable to install the linear electrode 43 so as to satisfy the above condition. This will be described with reference to FIG.

In the non-contact reversal development method in which the linear electrode 43 is not installed, the developing action is greatest at the closest position between the photosensitive drum 10 and the developing roller 41, and from the closest position to the developing roller 41. The developing action becomes smaller toward the upstream side and the downstream side in the developer layer conveying direction, and eventually the developing action is not performed at all. This is because the photosensitive drum 10 and the developing roller 41 are separated from each other. The range from the closest position of the photosensitive drum 10 and the developing roller 41 to the circumferential direction of the developing roller 41 was measured by the following method.

In the gap between the photoconductor drum 10 and the developing roller 41, a plate-like shielding member is installed on the upstream side in the developer layer conveying direction, which is sufficiently separated from the closest position of the photoconductor drum 10 and the developing roller 41. Then, the installed shielding member is gradually moved toward the closest position between the photoconductor drum 10 and the developing roller 41, and the position and developing property of the shielding member at that time are measured.
The same measurement is performed from the closest position of the photosensitive drum 10 and the developing roller 41 to the downstream side in the developer layer conveying direction.

As a result of the above measurement, the following was found.

On the upstream side in the developer layer conveying direction from the closest position of the photosensitive drum 10 and the developing roller 41, the shielding member is located closer to the photosensitive drum 10 and the developing roller 41 than the point Q on the developing roller 41 in FIG. When it comes close to the contact position, the developability starts to decrease.

On the other hand, on the downstream side of the conveyance of the developer layer, the shielding member is located at the photosensitive drum 10 from the point Q'on the developing roller in FIG.
When the position is close to the closest position of the developing roller 41, the developing property starts to deteriorate.

When the relationship between the distance from the points Q and Q'to the photosensitive drum 10 and the closest distance X ₀ between the photosensitive drum 10 and the developing roller 41 is examined, they are 1.2 times and 1.1 times, respectively. I found out.

Therefore, the photosensitive drum 10 and the developing roller 41
The closest contact point on the developing roller 41 at the closest position of P is the angle formed by P, the straight line connecting the rotation center of the developing roller 41 with P, and the straight line connecting Q with the rotation center of the developing roller 41.
[°], the angle between P and the straight line connecting the rotation center of the developing roller 41 and Q ′ and the straight line connecting the rotation center of the developing roller 41 is α ′ [°], and the developer layer on the developing roller 41 moves. Assuming that the upstream side in the direction is the + direction, the radius of the photosensitive drum 10 is sufficiently larger than the radius of the developing roller 41, and the surface of the photosensitive drum 10 is a flat surface,

[0057]

(Equation 4)

Therefore, it was found that the developing action was performed in the region represented by this.

That is, a linear electrode 43 for applying a developing bias composed of a superposition of a DC component and an AC component having the same polarity as the charging of the toner and the photoconductor drum 10 is provided in the area represented by α and α '. As a result, a highly vibrating electric field formed by the linear electrode 43 can generate a high density toner cloud and hold it in the developing area, so that high developability can be obtained.
Also in this case, it is preferable that the developing bias applied to the developing roller 41 has the AC component as described above superimposed.
It is not necessary to include the AC component.

When the linear electrodes 43 are provided outside α and α ′ under the above conditions, the toner cloud is formed outside the area where the developing action is performed, so that sufficient developability is obtained. In addition, the toner scattering outside the developing area is increased, and the inside of the machine is likely to be contaminated.

The closest distance X ₀ between the photoconductor drum 10 and the developing roller 41 is preferably 0.2 to 1 from the viewpoint that it is relatively easy to set conditions such as a developing bias for good development by non-contact reversal development. When set in the range of [mm], the height h of the developer layer before the linear electrode 43 is installed is 0.1 to
0.5 [mm], the closest distance X ₁ between the developing roller 41 and the linear electrode 43 is 0.05 to 0.35 [mm], the linear electrode 4
3 is the closest distance X ₂ between the photosensitive drum 10 and 0.05
0.3 [mm], the diameter d of the linear electrode 43 is 0.02
In the range of 0.25 [mm], X ₁ + d + X ₂ ≈
It is preferable to set the values to satisfy X ₀ , X ₁ ≧ X ₂ , and X ₁ + d ≧ h ≧ X ₁ ≧ h / 2.

For example, in the case of non-contact reversal development using a negatively charged photosensitive drum 10 and a negatively charged toner developer, the photosensitive member is charged to -800 [V] to form an electrostatic latent image. When formed, the developing roller 41 has -700.
DC bias voltage of [V] and frequency 5 to 20 [KHz]
Then, the superimposed voltage of the AC bias voltage of the peak-to-peak voltage of 600 to 2000 [Vpp] is applied, and -70 is applied to the linear electrode 43.
0 [V] (DC bias voltage applied to developing roller 41) to 0 [V], preferably -200 to -600 [V], and frequency 1 to 20 [kHz], preferably 1 to 10 [kHz] The peak-to-peak voltage is 0 to 1000 [V
It is preferable to apply a superimposed voltage of the AC bias voltage of [pp].

To describe other preferable conditions and configurations relating to the present invention, the linear electrode 43 is attached to the developing device by, for example, fixing one end to a fixing pin planted on the outer surface of the casing 49 of the developing device. The other end is fixed to a fixing pin planted in the casing 49 via a tension spring. Positioning of the linear electrode 43 is performed by stretching it over a positioning member that is fixedly provided on both ends of the rotation shaft of the developing roller 41 so as not to hinder the rotation of the developing roller 41, and the closest distance to the developing roller 41. Also, the distance from the closest position between the photosensitive drum 10 and the developing roller 41 is determined. The erection tension of the linear electrode 43 is set by the tension spring,
The size thereof is determined in consideration of the allowable load determined by the material and the diameter, the allowable deflection amount, the relationship between the frequency of the AC voltage applied to the developing roller 41 and the natural frequency of the linear electrode 43, and the like. For example, when the tungsten wire having a diameter d of 30 to 300 [μm] and the length of the portion facing the developing roller 41 is 200 to 350 [mm], the tension is 200 to 150.
0 [g] is suitable.

When the vibration of the linear electrode 43 poses a problem, it is advisable to bring the anti-vibration member into contact with the inside of the positioning member to absorb the vibration. It is preferable to use a highly elastic material for the vibration isolator.

Explaining the developer, a one-component developer can be used as mentioned above, but a two-component developer is preferably used. Generally, when the average particle diameter of the toner becomes large, the roughness of the image becomes noticeable.
In order to obtain the resolution of fine wires arranged at a pitch of about 0 [lines / mm], there is no problem even if the average particle size is about 20 [μm]. However, the average particle diameter of the toner is preferably 10 [μm] or less, and particularly preferably 4 to 6 [μm], in order to further improve the resolution and obtain a clear high-quality image in which the tone difference is faithfully reproduced. The average particle size of this toner is about 2
A suspension obtained by adding about 1 mg of a sample and a surfactant to 00 [ml] and dispersing with an ultrasonic disperser for about 1 minute is a particle size distribution measuring device "Coulter Counter TA-II type".
(Aperture 100 [μm] manufactured by Coulter Inc.) is a value obtained by measuring the volume average particle size distribution.

When the average charge amount of the toner increases, it is necessary to increase the electric field required to fly the toner.
Electric discharge easily occurs in the gap between the linear electrode 43 and the developing roller 41. On the other hand, when the average charge amount of the toner is too small, the toner easily scatters from the developing device. The average charge amount of the toner is usually in the range of 5 to 40 [μC / g] in absolute value. The average charge amount of this toner is 2 [cm] × 5
A developing roller 4 having a diameter of 20 mm and a conductive plate of [cm].
The developing roller 41 is rotated at 200 [rpm] so as to form a developer layer on the surface of the developing roller 41 and convey the developing roller 41, and the developing roller 41 is conveyed. For example, DC component V _DC2 = −1000
[V] and AC component f ₂ = 8000 [Hz], V _AC2 = 15
By applying a superimposed voltage of 00 [Vpp], the toner flies from the developer layer on the developing roller 41 onto the conductive plate to be attached, and then the conductive plate with the toner attached is connected to a Faraday cage. It is obtained by blowing off the toner and measuring the charge amount and the weight of the toner blown off at this time.

The toner is, for example, a resin such as a styrene resin, a vinyl resin, an acrylic resin, a polyamide resin, a silicone resin, a polyester resin, a fluororesin or an epoxy resin, and carbon black or a coloring component such as a color pigment or a color dye. And a charge control agent are added, and the toner particles can be produced by the same method as a conventionally known method for producing toner particles. Further, if necessary, a fluidizing agent for increasing the fluidity of particles and a cleaning agent for cleaning the surface of the photosensitive drum 10 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 constituting the two-component developer 50 together with the toner includes metals such as iron, chromium, nickel, cobalt, zinc and copper, or their compounds and alloys such as γ-ferric oxide and dioxide. Chromium, manganese oxide, spherical particles of ferromagnetic or paramagnetic material such as ferrite, or the surface of these magnetic particles is styrene resin, vinyl resin, ethylene resin, acrylic resin,
Particles obtained by coating with a resin such as polyamide resin or polyester, or by forming spherical particles of resin or fatty acid wax containing magnetic fine particles dispersed therein are used. The average particle size is 70 [μm] or less, preferably 30
Those having a thickness of about 50 [μm] are preferably used. This average particle diameter is a value obtained in the same manner as the average particle diameter of the toner.

Specific examples of the present invention will be shown below together with comparative examples.

(Developing device) As the developing device shown in FIG. 1, a full-color copying machine "Konica 9028" (manufactured by Konica)
For yellow (Y), magenta (M), cyan (C),
The casing 49 of each of four types of developing devices containing black (K) developers is modified to have the linear electrodes 43 stretched, and the linear electrodes are stretched for comparison. Use the one that does not.

(Image Forming Apparatus) As the image forming apparatus shown in FIG. 2, a full-color copying machine "Konica 9028" (manufactured by Konica Corporation) is used to develop yellow (Y), magenta (M), cyan (C), and black (K). The developing device of FIG. 1 is replaced by the developing device 40A, 40B, 40C and 40D, and the developing device without the linear electrode stretched for comparison is used as the developing device 40A, 40B, 40C and 40D.
The one designated as D is used. Power supplies 51 and 52 for applying a superimposed voltage of a DC component and an AC component are provided to the developing roller 41 and the linear electrode 43 of each developing device, respectively. The timing of applying the developing bias to the developing roller 41 and the linear electrode 43 of each developing device is from a predetermined time before the start of image exposure for forming an electrostatic latent image to be developed to a predetermined time after the end of image exposure. The rotation timing of the roller 41 was also the same.

(Experimental Example 1) Radius 90 of photosensitive drum 10
mm, moving speed of the photoconductor drum 10 in the direction of arrow 140 mm
/ Sec, charging potential of the photoconductor drum −800
[V], diameter of writing laser beam 62 [μm], potential of electrostatic latent image low potential dot −50 [V], photoconductor drum 4
0 and the developing roller 41 closest distance X ₀ 0.70 [m
m], the radius 10 of the developing roller 41 mm and an arrow direction movement velocity 350 [mm / sec of the developing roller 41], the DC voltage V _DC2 -700 applied to the developing roller 41 V,
AC voltage applied to developing roller 41 V _AC2 1000 [V
pp], AC frequency f ₂ 8 to be applied to the developing roller 41
[KHz], AC waveform rectangular wave applied to developing roller 41, average toner particle size 5.5 [μm], average toner charge amount -20 [μC / g], toner concentration 7.0 [wt]
%], The average particle diameter of the carrier is 46 [μm], and the layer thickness h of the developer layer is 0.4 mm when there is no linear electrode. Diameter d0.0 of linear electrode 43 using a developing device in which a linear electrode is stretched
96 [mm], the gap X between the linear electrode 43 and the developing roller 41
₁ 0.35 [mm], linear electrode 43 and photosensitive drum 10
Gap X ₂ 0.26 mm and the DC voltage V _DC1 -400 [V] applied to the linear electrodes 43, the AC voltage V _AC1 500 applied to the linear electrodes 43 [Vpp], applied to the linear electrodes 43 The AC waveform is a rectangular wave and the AC voltage f ₁ applied to the linear electrode 43 is changed to three types of 0.8, ₄ and 12 [kHz]. An electrostatic latent image with a dot area ratio of 74% and 37% is developed in a single-color mode, transferred to recording paper and fixed, and toner is attached per unit area of the image recording portion of the recording paper due to the increase in weight of the recording paper due to image recording The amounts M ₁ and M ₂ are calculated, and are proportional to the difference between the toner adhesion amount per unit area of the low-potential dot and the toner adhesion amount per unit area of the white background portion (M ₁ −M ₂ ) =
The values of M (M is larger as the toner adhesion amount of low-potential dots is larger and the amount of fog is smaller) are compared.

As a result, assuming that M is 1 when there is no linear electrode, the AC frequency f ₁ applied to the linear electrode 43 is 0.8.
The M of [kHz] was 1.01, the M of f ₁ of 4 [kHz] was 1.28, and the M of f ₁ of 12 [kHz] was 1.02. That is, it was found that when the condition of 0.1f ₂ <f ₁ <f ₂ <3f ₁ is satisfied, a clear image is formed with a large amount of toner attached to the low-potential dots and less fog.

(Experimental Example 2) The AC frequency f ₁ 4 [kHz] applied to the linear electrode 43 in the case of using the developing device having the linear electrode stretched in Experimental Example 1 was applied to the linear electrode 43. DC voltage V _DC1 -350, -400, -700 [V], except that the three types of electrostatic latent images were developed, transferred, and fixed in the same manner as in Experimental Example 1, and the value of M was determined. Were compared.

As a result, the DC voltage V _DC1 -350 applied to the linear electrode 43 is set to 1 in the case of no linear electrode.
The M of [V] 1.02, the M of V _DC1 -400 [V] 1.28, M of V _DC1 -700 [V] was 1.01. That is, it was found that when the condition of V _DC2 / 2 ≤V _DC1 <V _DC2 is satisfied, a clear image is formed with a large amount of toner adhered to the low potential dots and less fog.

(Experimental Example 3) When the developing device in which the linear electrode of Experimental Example 1 is stretched is used, the AC frequency f ₁ 4 [kHz] applied to the linear electrode 43 is set, and the linear electrode 43 and the developing roller are set. The gap X ₁ of 41 is 0.30, 0.35, 0.41 [m
m], and accordingly, the linear electrode 43 and the photoconductor drum 10
Gap X ₂ 0.36, 0.26, 0.20 [mm] 3
Two types of electrostatic latent images were developed, transferred, and fixed in the same manner as in Experimental Example 1 except that the conditions of the set were changed, and the values of M were compared.

As a result, when M without a linear electrode is 1, the gap X ₁ between the linear electrode 43 and the developing roller 41 is 0.
30, M when the gap X ₂ between the linear electrode 43 and the photosensitive drum 10 is 0.36 is 0.75, M when X ₁ is 0.35 and X ₂ is 0.26 is 1.28, When X ₁ was 0.41 and X ₂ was 0.20, M was 0.86. That is, X ₁ ≧
It has been found that when the conditions of X ₂ and X ₁ + d ≧ h ≧ X ₁ ≧ h / 2 are satisfied, a clear image is formed with a large amount of toner adhered to the low-potential dots and less fog.

[0078]

According to the non-contact reversal developing device of the present invention, good development can be performed with sufficient density and without fog, without causing in-machine stain and image stain due to toner scattering, and poor fluidity. It is possible to form a good image without unevenness in development density even when a developer is used.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram showing an example of an image forming apparatus in which the developing device of the present invention is used.

FIG. 3 is an explanatory view of a method for measuring a developing action range before installing a linear electrode.

[Explanation of symbols]

 10 Photoconductor Drum (Image Forming Body) 11 Conductive Substrate 12 Photosensitive Layer 20 Charging Means 25 Image Reading Section 30 Image Writing Section 40A, 40B, 40C, 40D Developing Device 41 Developing Roller (Developer Conveying Body) 42 Magnet Body 43 Wire Electrode 45 supply roller 46 regulation rod 47 scraper 48 stirring roller 49 casing 50 two-component developer 51, 52 power supply

Claims (5)

[Claims] 1. A linear electrode is stretched in a gap between an image carrier and a developer carrier, and a developer layer which is not in contact with the image carrier on the developer carrier under an oscillating electric field is removed from the image carrier. In a developing device in which toner charged with the same polarity as that of electric charges is caused to fly and adhere to an electrostatic latent image on an image carrier, the linear electrode is set as one, and alternating current is applied to the linear electrode and the developer carrier. A developing device characterized by applying a superimposed voltage of a DC component having the same polarity as that of the charge of the component and the toner, and changing at least the frequencies of the AC components. 2. A frequency f ₁ [Hz] of an AC component applied to the linear electrode, a voltage value V _DC1 [V] of a _DC component, and a frequency f ₂ [Hz] of an AC component applied to the developer carrier. ,
As a DC component voltage value V _DC2 [V], 0.1 f ₂ <f _1
2. The developing device according to claim 1, wherein the conditions of <f ₂ <3f ₁ and V _DC2 / 2 ≦ V _DC1 <V _DC2 are satisfied. 3. A linear electrode is stretched in a gap between the image carrier and the developer carrier, and a developer layer which is not in contact with the image carrier on the developer carrier under an oscillating electric field is removed from the image carrier. In a developing device in which a toner charged to the same polarity as that of a charge is ejected and adhered to an electrostatic latent image on an image carrier, one linear electrode is provided, and an AC component and a DC component having the same polarity as the toner charge are applied to the linear electrode. A superposed voltage is applied, the closest distance between the linear electrode and the developer carrying body is X ₁ [mm], the closest distance between the linear electrode and the image carrier is X ₂ [mm], and the linear shape is Set the diameter of the electrode to d [m
m], when the height of the developer layer on the surface of the developer carrier with respect to the linear electrode is h [mm], X ₁ ≧ X ₂ , X ₁ + d ≧ h ≧ X A developing device, wherein the linear electrode is installed so as to satisfy ₁ ≧ h / 2. 4. The closest distance between the image carrier and the developer carrier is X ₀ [mm], and the radius of curvature of the developer carrier at the closest position between the image carrier and the developer carrier is r [m
m], a straight line connecting the center of curvature of the developer carrier and the center of curvature of the image carrier at the position closest to the image carrier and the developer carrier, the center of curvature of the linear electrode, and the developer carrier The angle θ ° formed by the straight line connecting the center of curvature of the developer carrier is moved by the developer carrier more than the straight line connecting the center of curvature of the linear carrier and the center of curvature of the image carrier. When there is an upstream side of, as +, The developing device according to any one of claims 1 to 3, wherein the linear electrode is installed so as to satisfy the above condition. 5. The developer is a two-component developer comprising a mixture of toner and carrier, and the toner has an average particle size of 10 μm.
The developing device according to any one of claims 1 to 4, wherein the developing device has a thickness of m or less.