JPH0413164A - Developing device - Google Patents

Abstract

PURPOSE:To prevent the degradation of the image quality of a visual image and to improve the reproducibility of a half-tone image by applying a pulse bias voltage on a toner carrier, and setting frequency, peak-to-peak values whose minimum voltage value is subtracted from the maximum voltage value, and a duty ratio within a specific range. CONSTITUTION:As the toner carrier, a fine closing electric field is formed in the vicinity of the surface of the carrier by selectively holding a charge on the surface, and the toner carrier 5 attracting electrifying toner 4 by a closing electric field and carrying it is used. The pulse bias voltage is applied on the toner carrier 5, its frequency is set at 200Hz <= 700Hz, and the peak-to-peak values whose minimum voltage value is subtracted from its maximum voltage value is set at 200V <= 500V. When its high potential part time and one-cycle time are defined as B and T, respectively. B/T is set at 0.5 <= 0.9. Therefore, the occurrence of the leakage of the charge so as to disturb an electrostatic latent image on a photosensitive body 1 between the photosensitive body 1 and a developing roller 5 is prevented. Thus, the degradation of the image quality of the visual image is prevented, and the reproducibility of the half-tone image is improved.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention supplies toner to a toner carrier that is driven once, carries the toner on the surface of the carrier, and conveys the toner to the latent image carrier. The present invention relates to a developing device in which an electrostatic latent image formed on a latent image carrier is visualized by toner carried on the toner carrier in a development area where the toner carriers face each other.

[Conventional technology]

In an image forming apparatus such as an electronic copying machine, a laser printer, or a facsimile machine that obtains a recorded image by visualizing an electrostatic latent image formed on a latent image carrier, a toner to which an adjuvant is externally added as necessary, i.e. - It has been well known to employ a developing device of the above type using a component-based developer.

This type of developing device has the advantage that maintenance and management of the device can be simplified and the structure of the device can be made smaller, compared to a developing device using a two-component developer containing a carrier.

By the way, in a developing device using a -component developer,
In order to form a high-quality visible image with a predetermined density, it is necessary to transport a large amount of sufficiently charged toner to a development area and to convert the latent image into a visible image using the toner.

However, with conventional developing devices of this type, it has not been easy to satisfy this requirement. That is, in a developing device using a conventional one-component developer, the amount of toner that can be deposited on the toner carrier is usually 0.
In contrast, in the case of black toner, it is necessary to deposit approximately 0.4 to 0.5 .mu./d on the transfer paper, resulting in a shortage of toner. Furthermore, when color toner is used, it is necessary to deposit approximately 0.6 to 1.2 .mu./J of toner on the toner carrier, and the shortage of toner becomes even more significant.

Therefore, in the past, the speed of the toner carrier was increased, and the linear velocity of its surface was set to about 3 to 4 times the linear velocity of the surface of the latent image carrier, thereby increasing the amount of toner conveyed to the development area. This prevented a decrease in image density.

However, with this configuration, only the rear end side of the solid image formed on the latent image carrier in the direction of movement of the latent image carrier has an abnormally high density compared to other parts, which is called "back edge toner side". A phenomenon has occurred.

Its image quality deteriorates. This trailing edge toner bias phenomenon is.

In the case of a color image, parts where the image density is abnormally high appear as different colors from other parts, which is a particularly serious problem in the case of color development.

A developing device has also been proposed in which unevenness is formed on the surface of a toner carrier, and toner is filled and carried in these unevenness to increase the amount of toner conveyed to a developing area. Although the amount of toner that can be transported increases, the transported toner still contains a large amount of toner that is insufficiently charged.

This may reduce the quality of the visible image formed.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device which eliminates the above-mentioned conventional drawbacks and which has excellent reproducibility of halftone images.

[Means to solve the problem]

In order to achieve the above object, the present invention uses a developing device of the type described at the beginning, in which a toner carrier is used as a toner carrier, and a minute electric field is formed near the surface of the carrier by selectively retaining an electric charge on the surface of the carrier. .

Using a toner carrier that attracts and carries charged toner using this closed field, a pulse bias voltage is applied to the toner carrier.

The frequency is 200Hz or more and 700Hz or less, the peak-to-peak value obtained by subtracting the minimum voltage value from the maximum voltage value is 200V or more and 500V or less, and the high potential part time and 1 cycle time are B, respectively.

We propose a configuration in which B/T is set to 0.5 or more and 0.9 or less, where T is T.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a developing device according to the present invention, and first the overall structure and operation thereof will be explained.

In FIG. 1, a belt-shaped photoreceptor 1, which is an example of a latent image carrier, is driven in the direction of arrow A, and a developing device 2 is provided opposite to it. In the toner container 3 of the developing device 2, there is a non-magnetic toner 4 mixed with an auxiliary agent as needed.
That is, a non-magnetic one-component developer is accommodated therein. The specific volume resistivity of the toner is, for example, about 10' to 1012 Ω.

A developing roller 5 (see also FIG. 7) is supported on the front and rear side plates of the toner container 3 with a portion exposed from the opening of the container, and the roller 5 faces the photoreceptor 1 as shown in FIG. is rotated counterclockwise at .

Although the developing roller 5 constitutes an example of a configuration of a toner carrier, a belt-shaped toner carrier may be used instead of the roller 5. Further, a toner supply roller 6, which is an example of a toner supply member, is supported on the front and rear side plates of the toner container 3, and while the roller 6 is in contact with the developing roller 5,
At the contact portion, it is rotated in the opposite direction to the developing roller 5 at a surface linear velocity that is, for example, 0.5 times or more the surface linear velocity of the developing roller 5 .

The toner 4 in the toner container 3 is conveyed to a toner supply roller 6 while being stirred by an agitator rotating clockwise, and then supplied to a developing roller 5 by this roller 6. During this supply, the toner is frictionally charged to a predetermined polarity (in this example, a positive polarity opposite to the electrostatic latent image on the photoreceptor 1), electrostatically adheres to the surface of the developing roller 5, and is carried on the developing roller 5. Ru. The configuration and operation related to this will be explained in detail later.

The toner supplied and supported on the surface of the developing roller 5 as described above is conveyed by the rotation of the roller 5, and is leveled by the doctor blade 8, which is an example of a layer thickness regulating member.
Thickness is regulated. This toner is then conveyed to a developing area 9 where the photoreceptor 1 and the developing roller 5 face each other, where it is electrostatically transferred to the electrostatic latent image formed on the photoreceptor 1, converting the latent image into a visible image. become

The toner that has passed through the development area 9 without being subjected to development is returned to the toner supply roller 6 while being supported on the development roller 5. Further, the visible image formed on the photoreceptor 1 is transferred to a transfer paper (not shown), and fixed onto the transfer paper by a fixing device.

The above-mentioned configuration itself is the same as that of a conventional developing device, and in such a conventional developing device, it is difficult to convey a large amount of sufficiently charged toner to the developing area. 3 to 4 of the linear velocity of the surface of the photoreceptor
This was set to double, but this caused the problem shown earlier.

In the developing device shown therein, the developing roller 5
As shown schematically and enlarged in Figures 2 to 4, 1
A conductive base body made of a conductive roller 1o made of aluminum, for example, and a groove 100 formed on the surface of the roller 1o.
The surface of the developing roller 5 has a conductive surface 12 on the surface of the conductive roller and the surface of the dielectric 11 embedded in the groove 100 in a regular pattern as shown in FIG. (or irregularly) and its surface is smooth. Although the planar shape of the groove 100, that is, the surface shape of the dielectric 11 exposed to the outside and the surface shape of the conductive surface 12, can be set as appropriate, in the examples shown in FIGS. It extends in a grid pattern. The pitch P of the dielectric 11, that is, the groove 100 is, for example, 0°1 to 1,01 m, preferably 0.2
The distance is set to about 0.4 m, and the ratio of the total area of the conductive surface 12 to the total surface area of the developing roller 5 is, for example, about 20 to 80%, preferably about 30 to 60%.

The above-mentioned numerical values are appropriately selected each time so as to increase the electric field strength of the closed electric field, which will be described later, so that an optimum amount of toner can be deposited on the developing roller 5.

By dispersing and fixing on the surface of the conductive roller 10 a large number of fine conductor particles that are electrically conductive to the roller 10, the particles become part of the conductive roller 10, and a dielectric material is provided around these particles. It is also possible to use a developing roller or the like in which the surface of the dielectric material and the conductive surface of the surface of the conductive particles are exposed to the outside. In any case, on the surface of the developing roller 5, the surface of the dielectric 11 and the conductive surface 12 coexist in a small area.

Further, as will be described later, a bias voltage of a pulse or a pulse with superimposed direct current is applied to the conductive roller 10 of the developing roller 5.

In this example, a material that is triboelectrically charged to a polarity opposite to that of the toner, that is, a negative polarity, is selected as the dielectric material 11. Moreover, the toner supply roller 6 in contact with the developing roller 5 is in contact with the dielectric material 11 of the developing roller 5,
It is made of a material that triboelectrically charges this to a polarity opposite to that of the toner (negative polarity) and triboelectrically charges the toner to a positive polarity. In the example shown in FIGS. 1 and 2.

The toner supply roller 6 is composed of a conductive core member 14 and a cylindrical foam 15 laminated around the core member 14, and the foam 15 is pressed against the developing roller 5 while being elastically deformed.

When such a toner supply roller 6 is used, 1 foam 1
5 may be made of a material that galvanizes the dielectric 11 to a negative polarity as described above. Instead of the foam 15,
For example, a known per se such as a fur brush can also be used.

A more detailed explanation of the operation of the above configuration is as follows.

As previously explained with reference to FIG. 1, the portion of the developer roller that has passed through the development area 9 moves to and comes into contact with the toner supply roller 6.

Here, the toner carried on the developing roller 5 that has not been subjected to development is mechanically and electrically scraped off by the toner supply roller 6. At the same time, the dielectric 1 of the developing roller 5
1 comes into contact with the toner supply roller 6 and is charged to a negative polarity opposite to that of the toner due to the friction. At this time, even if an electrostatic afterimage remains on the dielectric 11 on the peripheral surface of the developing roller that has passed through the developing area 9 due to the influence of the electrostatic latent image on the photoreceptor 1, due to friction with the toner supply roller 6, Since the dielectric material 11 is charged almost to a saturated state and the amount of charge becomes uniform, there is no afterimage and the developing roller 5 is initialized.

On the other hand, as schematically shown in FIG. 2, the toner 4 conveyed to the developing roller 5 while contacting the surface of the toner supply roller 6 is triboelectrically charged to a positive polarity due to friction with the toner supply roller 6, and the developing roller At this time, due to the friction between the developing roller 5 and the dielectric material 11, the developing roller 5 is triboelectrically charged more strongly to a positive polarity, and electrostatically adheres to the circumferential surface of the developing roller 5.

At this time, the dielectric body 11 of the developing roller 5 is negatively charged due to friction with the toner supply roller 6, and a large number of conductive surfaces 12 with minute areas are present adjacent to this dielectric body 11. 12 and the surface of the dielectric 11 coexist. In this state, negative charges are selectively held on the dielectric 11 on the surface of the developing roller 5.

Therefore, as shown in FIG.
A large potential difference is created between the surfaces of 1, and a closed electric field is formed between them. That is, countless minute closed electric fields (microfields) are formed near the surface of the developing roller 5. To explain in more detail, when considering electric lines of force that represent the state of the electric field, there is an electric force Is! in the space near the surface of the developing roller 5, as shown by many arcuate lines in FIG. E is formed, and its electric lines of force are connected to the developing roller 5.
and returns to the same developing roller 5, forming a closed electric field near the surface of the roller 5. In this way, an electric field with a large electric field gradient is formed near the surface of the developing roller.

Since the surface of the dielectric 11 and the conductive surface 12 are adjacent to each other in a small area, the strength of each small closed electric field becomes very strong due to the so-called edge effect or fringing effect (marginal electric field effect). Due to this closed electric field, the positively charged toner is strongly attracted to the surface of the dielectric 11 and held on the developing roller 5 in a large amount in a state where it is difficult to separate. At this time, the toner is strongly triboelectrically charged due to the friction between the toner supply roller 6 and the developing roller 5, and is held by the action of a strong minute closed electric field on the surface of the developing roller 5, so that a high electric charge is placed on the developing roller 5. A large amount of toner with . Moreover, when the layer thickness of the toner carried on the developing roller 5 is regulated by a doctor blade 8 made of urethane, for example, the sufficiently charged toner is strongly held on the surface of the developing roller 5 by a minute closed electric field. Even if the toner contains toner with a small amount of charge, this
In the end, only toner with a large amount of charge is transported to the developing area 9 in a larger amount than in the past.
The electrostatic latent image is visualized as described above. The electric field between the developing roller 5 and the photoreceptor 1 in the developing area 9 has a large electrode effect, and the toner on the developing roller 5 tends to adhere to the photoreceptor 1, so that the developing operation is performed efficiently. .

In the vicinity of the surface of the developing roller 5 that has passed the toner supply roller 6, there are two cases in which only a *11X closed electric field is formed over the entire area as schematically shown in No. 5@, and a case where an electric field other than a closed electric field is formed. It is conceivable that the electric field may be mixed with the electric field, but in any case, since a large number of minute closed electric fields exist, the strength of the electric field is increased and a large amount of toner can be supported. For example, in order to prevent background smearing and increase the sharpness of a visible image, a 0.6 to 2.0 q/d, preferably 0.8 to 1.2 q/d, charged to about 8 to 15 μc/g is used. A large amount of toner can be conveyed to the developing area 9.

As described above, since a large amount of sufficiently charged toner can be carried on the developing roller 5 and transported to the developing area 9, the insufficient amount of toner in the developing area 9 can be prevented without increasing the surface linear velocity of the developing roller as in the conventional case. This can be prevented, and the occurrence of the above-mentioned trailing edge toner deviation phenomenon can also be substantially prevented.

In the example shown in FIG. 1, contact development is performed in the development area 9, but the latent image may be visualized by a non-contact development method. Further, in the above-mentioned example, the dielectric 11 was charged to the opposite polarity to that of the toner, but it is also possible to charge the dielectric 11 to the same polarity as that of the toner, so that a large amount of toner adheres to the conductive surface 12 in particular. .

As mentioned above, the conventional drawbacks can be avoided by forming a large number of minute electric fields near the surface of the developing roller and carrying the toner on the developing roller by the action. If exposed, the reproducibility of halftone images may deteriorate as described below.

The photoreceptor 1 shown in FIG. 1 is irradiated with a light image of an original image (not shown), or a laser beam corresponding to an image signal obtained by reading the original image is irradiated onto the surface of the photoreceptor 1. An electrostatic latent image is formed, which is made into a visible image as described above. The former method of irradiating a light image is generally called an analog method, and the latter method of laser light irradiation is called a digital method.

FIG. 6 shows an example of the relationship between the original image density when the analog method is adopted and the copy image density obtained thereby, and a curve γ□ representing these relationships.

γ2 is generally referred to as a 7-curve. Here, in order to faithfully reproduce the original image with intermediate image density, that is, the halftone image, as a copy image, the angle α of the seven curves should be 45°, that is, the angle of the curve γ shown by the solid line, or a curve close to this. It is necessary to make it happen. However, when the conductive surface 12 is exposed on the surface like the developing roller 5 shown in FIG. may decrease.

This is because digital image forming apparatuses can process image signals electrically.

Generally speaking, this is not a major problem, but in analog systems, the image quality of the copied images deteriorates, and this cannot be ignored.

Therefore, in the developing bag M2 shown in FIG. 1, a pulse bias voltage as illustrated in FIG. 6a is applied to the conductive roller 10 of the developing roller 5 by the power source 101. When a pulse bias voltage is applied to the developing roller 5 in this way, compared to when this is not applied, it is possible to change the 7 curves and perform development with the characteristics shown by γ□ in Figure 6, or characteristics close to these. Therefore, the reproducibility of halftone images can be improved.

As described above, by applying a pulse bias voltage to the developing roller 5 in which a minute electric field is formed, it is possible to prevent a decrease in the density of a visible image and improve the reproducibility of a halftone image. A new problem arises with the application of pulsed bias voltages. That is, there is a conductive surface 12 on the surface.
If a pulse bias voltage with a high peak value is applied to the exposed developing roller 5, the developing area 9
In this case, charge leakage occurs between the developing roller 5 and the photoreceptor 1, which disturbs the electrostatic latent image on the photoreceptor 1, and there is a possibility that the quality of the visible image may deteriorate.

Therefore, in the configuration according to the present invention, in order to prevent the occurrence of this leakage phenomenon, the frequency of the pulse bias voltage applied to the conductive roller 10 of the developing roller 5 is set to 70 Hz or more.
The value shall be within the range of 00Hz or less.

In addition, the value obtained by subtracting the minimum voltage value from the maximum voltage value of the pulse voltage, that is, the peak-to-peak value (hereinafter referred to as P-P value), is set to a value in the range of 200 V or more and 500 V or less, as shown in Figure 6a. As shown, B/T (duty ratio) was set in the range of 0°5 or more and 0.9 or less, where B is the time of the high potential portion of the pulse voltage and T is the time of one cycle. By setting the frequency, P-P value, and duty ratio (B/T) within these ranges, the electrostatic latent image on the photoreceptor 1 is prevented from being disturbed between the photoreceptor 1 and the developing roller 5. It is possible to prevent the occurrence of charge leakage that would otherwise occur, and it is possible to form a high-quality visible image that accurately reproduces halftones at a predetermined density. These facts have been confirmed by numerous experiments.

Further, when a pulse bias voltage is applied to the developing roller 5, there is an advantage that the duty ratio (B/T) can be freely selected.

In the example shown in FIG. 1, as can be seen from FIG. 6a, the conductive roller 10 of the developing roller 5 is applied not only with a pulse bias voltage but also with a DC power source 102 of the same polarity as the electrostatic latent image. A DC bias voltage is also applied to suppress background smudges in the visible image. Similarly, a DC voltage is applied to the toner supply roller 6 by the power source 1.3.

By the way, as explained earlier, since a large amount of toner can be carried on the developing roller 5, the surface linear velocity of the roller can be lowered. When the surface linear velocity of body 1 is Vp.

Vp In particular, set to Vp, for example, set the surface linear velocity of the developing roller 5 to 170 +
+io/see, that of photoreceptor 1 at 120 m/s
If ee is set, the following advantages can be obtained.

That is, if vd/vp is suppressed to 1.5 or less.

The above-mentioned trailing edge toner deviation is hardly noticeable, and not only can this phenomenon be substantially prevented from occurring, but also toner scattering, early toner fatigue, and toner filming on the developing roller can be effectively suppressed. I can do it.

Further, when Va/Vp is set to 1.2 or more, especially 1.3 or more, a larger amount of toner adheres to the dielectric material 11 than the conductive surface 12.
However, even when a pattern appears regularly on the surface of the developing roller 5 as shown in FIG. 3, this pattern does not appear as a "mark" on the image plane of the visible image, and the image quality is affected. can be increased. Further, when vd/vp is set to 1.2 or 1.3 or more, the toner on the developing roller 5 exerts a scavenging effect on the background portion of the photoreceptor 1 in the developing area 9, causing background smearing. It also has the advantage of reducing

Next, for the purpose of understanding the present invention, a more specific example of a developing device including the above-described developing roller 5 will be shown below.

(1) Developing roller The diameter D1 of the developing roller 5 shown in FIG. 7 is 25°,
A groove 100 is formed on the surface by knurling,
The pitch of the grooves 100 is 0.4 m, and the depth is D2 (Figure 4).
is 0.1 m, the groove width Wl (Fig. 3) is 0.15 mm, and the angle θ of the groove 100 extending in a lattice pattern or the dielectric 11 with respect to the developing roller moving direction Y is 45''. The symbol X in the figure and No. 7 @ indicates the axial direction of the developing roller 5.

The area ratio of the dielectric 11 exposed on the surface of the developing roller is 61
%, and the conductive surface is 39%. The width of the conductive surface 12 is 0.15 mm.

(...) The foam material of the toner supply roller is treated with foamed polyurethane carbon, and its outer diameter is 14 m, and the amount of penetration into the photoreceptor l is 1.
mm, and the surface resistance of the foam 15 is 107Ω.

(■) Doctor blade A fluorine-based resin PTFE sheet (PTFE resin tape 200 μm, manufactured by Nichas C Co., Ltd.) is fixed to an elastic member made of phosphor bronze with a thickness of 0.1 mm.

(■) P-p value 500V to developing roller, wave number 250H
z, DC to pulse voltage with duty ratio (B/T) 0.7
-250V superimposed voltage is applied. DC to toner supply member ~
Apply voltage of 250v.

(V) Photoreceptor OPC photoreceptor 6 (■) Toner Non-magnetic styrene acrylic positive charge/toner polarity control agent: Nigrosine, external additive: Sj○21# powder 0.5wt
%.

Next, a method for manufacturing the developing roller 5 will be briefly described.

(Summer) First, as shown in FIG. 8(a), a metal roller (conductive roller 10) with square grooves formed on its surface is made.

The grid-like square grooves 100 are formed by square groove knurling, for example, with a pitch of 0.2 to 1.0 mm and a depth D of 0.1 mm.
0.5 to 0.5, and 30° to the circumferential direction of the developing roller.
Extend at an angle of 60° to 60°, especially 45°. By employing such a knurling method, it is possible to reduce costs and improve component precision.

(II) Next, as shown in FIG. 8(b), a dielectric material 11 made of, for example, fluorine resin (Lumiflon LF200 manufactured by Asahi Glass Co., Ltd., etc.)
, corner #lj! 100 is coated on the surface of the roller 10 and dried at 100° C. for about 30 minutes. The coating thickness is set so that the groove 100 is completely filled.

(III) Furthermore, the surface of the roller is cut or polished as shown in FIG.
The ratio should be between 0 and 80%.

In this way, a developing roller 5 having a substantially smooth surface is completed.

In the case of a belt-shaped toner carrier, FIG. 8(a)
), (b), and (c) instead of the conductive roller 1o shown in FIG. The method is not substantially different from that shown in FIG.

It is clear that various types of toner carriers in which the dielectric material and the conductive surface are exposed on the surface can be constructed using various other methods.

In the embodiment shown in FIGS. 1 and 2, the dielectric 1
1 to a predetermined polarity, a minute electric field is formed near the surface of the toner carrier, and the toner used for visualizing the latent image is attached to the toner carrier by the closed electric field. Although the supply roller 6 is used, any other suitable charging means known per se may be used, such as an independent frictional charging member, a corona discharger, or a member that injects charge in contact with the toner carrier.

Next, additional examples of the materials of the main components of the toner and the developing device will be given for reference.

Toners are generally based on resins such as polyester, BMA, polystyrene, epoxy, and phenol, and the charge polarity and amount of charge can be controlled by a polarity control agent that is added internally or externally to the toner.

Note that external addition refers to mixing an auxiliary agent such as a polarity control agent with toner particles, and internal addition refers to integrating an auxiliary agent such as a polarity control agent by kneading it into each toner particle itself.

Each member of the developing device also depends on the charging polarity of the toner.

In consideration of releasability from toner, durability, etc., for example, the following examples are used as appropriate.

Above, a developing device using a one-component developer of non-magnetic toner, which is particularly suitable for color development, has been exemplified. However, the present invention uses a one-component developer made of a magnetic toner to which an auxiliary agent is externally added as necessary. It can also be applied to a developing device using a.

〔Effect of the invention〕

According to the present invention, a large amount of sufficiently charged toner can be conveyed to the development area without rotating the toner carrier at high speed as in the past, and a visible image with a desired density can be formed, as well as a halftone image. It is possible to form a high-quality visible image by increasing the reproducibility of the electrostatic latent image and preventing disturbance of the electrostatic latent image due to charge leakage between the toner carrier and the latent image carrier.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of a developing device, FIG. 2 is an explanatory diagram schematically showing the dielectric of the developing roller and toner particles in an enlarged manner, and FIG. 3 is an enlarged plan view of the surface of the developing roller. , FIG. 4 is an enlarged cross-sectional view of the rV-mV line in FIG. Graph shown, No. 6a
The figure shows an example of a pulse bias voltage applied to the developing roller, FIG. 7 is a perspective view of the developing roller and schematically shows a part of the grooves enlarged, a),
(b) and (c) are schematic enlarged sectional views showing an example of a method for manufacturing a developing roller. 2...Development device 4...Toner 9...Development area 11...Dielectric 12...Conductive surface agent Patent attorney Norio Hoshino Figure 4 Figure 5 Figure 6 Original Fukuga f& J /i Figure 6α 1

Claims (1)

[Scope of Claims] Toner is supplied to a rotationally driven toner carrier, the toner is carried on the surface of the carrier, and the toner is conveyed to a developing area where the latent image carrier and the toner carrier face each other. In a developing device that visualizes an electrostatic latent image formed on a latent image carrier with toner carried on a toner carrier, the toner carrier selectively retains an electric charge on its surface. A minute closed electric field is formed near the surface of the carrier, and a toner carrier that attracts and carries the charged toner by this closed electric field is used. A pulse bias voltage is applied to the toner carrier, and its frequency is set to 200 Hz or more. 700
Hz or less, the peak-to-peak value obtained by subtracting the minimum voltage value from the maximum voltage value is 200V or more and 500V or less, and when the high potential part time and 1 cycle time are B and T, respectively, B/T is 0.5 A developing device characterized in that the above is set to 0.9 or less.