JPH0431879A - Developing device - Google Patents

Abstract

PURPOSE:To carry the necessary quantity of toner having high electrostatically charged amount to a developing area and to form the visible image of desired density by selectively adding a charge to the surface of a toner carrier by a charge adding means and carrying the toner with the aid of fine closed electric fields which are formed. CONSTITUTION:A carrier whose surface has charge holding ability is used as the toner carrier 5, and the charge adding means 34 is constituted of a corona discharger 51 opposed to the surface of the carrier 5, and a grid electrode 34 which is arranged between the charge wire 54 of the discharger and the surface of the carrier 5 and provided with plural through holes 37 where corona ions from the charge wire 54 pass. Then, the charge is selectively added to the surface of the toner carrier 5 and a large number of fine closed electric fields are formed near the surface. Thus, the necessary quantity of toner to form the visible image of the desired density and high quality is carried to a developing area.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention supplies toner to a rotationally driven toner carrier, carries the toner on the surface of the carrier, and transports the toner to form a latent image carrier. The present invention relates to a developing device that visualizes an electrostatic latent image formed on a latent image carrier in a development area where the toner carriers face each other using toner carried on the toner carrier.

[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.

However, in conventional developing devices that use -component developers, it is difficult to transport a sufficient amount of toner to the developing area to form a high-quality visible image with a predetermined density. .

Therefore, a developing device has been proposed in which an uneven surface is formed on the surface of a toner carrier, and toner is filled and carried on the uneven surface to increase the amount of toner conveyed to a developing area. However, although this configuration increases the amount of toner that can be transported, the transported toner contains a large amount of undercharged toner, which may reduce the quality of the visible image formed. There is.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that eliminates the above-mentioned conventional drawbacks.

[Means to solve the problem]

In order to achieve the above object, the present invention uses, as a toner carrier, a carrier having charge retention property on one surface in the developing device described at the beginning, and selectively charges the surface of the toner carrier. a corona discharger facing the surface of the toner carrier, a charge wire of the discharger, and the toner. It is characterized by comprising a grid electrode provided with a plurality of through holes, which are disposed between the electrode and the surface of the carrier, through which corona ions from the charge wire pass.

〔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 drum-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. A high-resistance toner is used as the toner, and its specific volume resistivity is, for example, about 10 7 to 10 12 Ω·1. A developing roller 5 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 is rotated clockwise in FIG. 1 facing the photoreceptor 1. Ru. 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 the roller 6 is driven to rotate, for example, in a counterclockwise direction while contacting 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 triboelectrically 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. (See Figure 2). The configuration and operation related to this will be explained in detail later.

The toner supplied and supported on the circumferential 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 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. In FIG. 1, reference numeral 70 denotes a charger that charges the photoreceptor 1, 71 a light image that exposes the surface of the photoreceptor after charging, and 72 a visible image formed on the surface of the photoreceptor. This is a transfer charger that transfers images onto transfer paper.

The developing roller 5 and the toner supply roller 6 are simply grounded, or a bias voltage is applied to them by a power source 50, 1.50, and the conductive support supporting the photosensitive layer of the photoreceptor 1 is grounded. ing.

The above-mentioned configuration itself is no different from a conventional developing device.5 In such a conventional developing device, a predetermined amount of sufficiently charged toner required to form a high-quality visible image is transported to a developing area. was difficult. In order to eliminate such drawbacks, the illustrated developing device is constructed as follows.

First, as shown in an enlarged view in FIG. 2, the developing roller 5 has a conductive base body made of a conductive roller 10 made of, for example, aluminum or other metal, and a dielectric material 32 laminated over its entire surface. . On the other hand, on the upstream side of the toner supply roller 6 in the rotational direction of the developing roller 5 and downstream of the developing area 9, there is provided a conductive static eliminating roller 33 which is an example of static eliminating means.
The charge applying means 34 are sequentially arranged in the rotational direction of the developing roller 5.

The static eliminating roller 33 rotates while contacting the developing roller 5,
AC voltage is applied by the AC type g35, and the developing area 9
The surface of the developing roller 5 that has passed through the toner is neutralized and residual toner is scraped off. The static eliminating roller 33 is made of, for example, conductive foam or conductive rubber.

Or it is made of metal. Instead of the roller 33, a static eliminator consisting of a blade or the like may be used, an alternating current voltage may be applied to this, and the blade may be brought into contact with the surface of the developing roller 5.

On the other hand, as shown in FIGS. 1 and 3, the charge applying means 34 includes a corona discharger 51 and a grid electrode 52, which are arranged opposite to each other at a predetermined distance from the surface of the developing roller 5. ing.

The corona discharger 51 includes a casing 53 having a substantially U-shaped cross section with an opening facing the developing roller 5, and a casing 53 having an approximately U-shaped cross section.
The casing 5 is placed in a space surrounded on three sides by the casing 5.
It has a charge wire 54 extending in the longitudinal direction of three. The charge wire 54 is made of tungsten, for example.
The casing 53 is made of a conductor such as stainless steel, and both are electrically insulated from each other.

Although the casing 53 is grounded, a high voltage is applied to the charge wire 54 by a high voltage power source 55. As is known, a voltage may be applied to the casing 53 if necessary. The corona discharger 51 configured in this manner is disposed along the axial direction X of the developing roller 5, and is immovably supported by, for example, the toner container 3.

The grid electrode 52 is disposed between the charge wire 54 of the corona discharger 51 and the surface of the developing roller 5, and in the illustrated example covers the entire opening of the casing 53.
It is fixed to the casing 53 while being electrically insulated from the charge wire 54 and the casing 53. The grid electrode is made of a conductor such as a metal sheet, and is connected to a power source 56.
A voltage is applied by. In addition, this grid electrode 52
For example, the diameter is 25 mm as shown enlarged in Fig. 3a.
A plurality of circular through holes 57 having a pitch of 0 μm and an interval of 250 μm are arranged in an array along the axial direction X of the developing roller 5. These through holes 57 can be formed in the grid electrode 52 by etching, for example.

The polarity of the voltage applied to the charge wire 54 by the high-voltage power supply 55 may be the same polarity as the charging polarity of the toner or a different polarity, but in this example, it will be described as a negative polarity opposite to the charging polarity of the toner.

Similarly, the description will be made assuming that a pulsed alternating voltage having the same polarity as the voltage applied to the charge wire 54 is applied to the grid electrode 52 by a power source 56, as illustrated in FIG. 4(a).

With the above-described configuration, the portion of the developing roller that has been subjected to the static eliminating action by the static eliminating roller 33 and from which residual toner has been removed faces the corona discharger 51 .

Since a high voltage is applied to the charge wire 54, a corona discharge is generated from the wire 54.

At this time, since an alternating voltage is applied to the grid electrode 52, the corona ion flow selectively heads toward the developing roller 5 through each through hole 57, and the dielectric 32 on the surface is polarized to a predetermined polarity, in this example, a negative polarity. to be sexually charged. At this time,
Since the roller 51 is rotating and the corona ions selectively pass through each through hole 57 of the grid electrode 52, the surface of the developing roller 5 that has passed through the corona discharger 51 has a fifth
As shown by broken lines in the figure, an infinite number of negative charges are applied in the form of dots corresponding to the shape of each through hole 57. In this way, the charge applying means 34.

Electric charges are selectively applied to the surface of the developing roller 5. Here, if the surface portion of the developing roller 5 that is charged is represented by Xl, and the portion that is substantially uncharged is represented by Innumerable charge patterns X1 are formed.

Therefore, in the vicinity of the surface of the developing roller, a large number of small electric fields (microfields) are generated between the adjacent portions XI and X2 having different potentials. That is, as schematically shown in FIG. 6, in the space near the surface of the developing roller 5,
An electric force ME represented by a number of arcuate lines is formed between the charged developing roller portion X1 and the substantially uncharged portion X2. At this time, since the charged portion X1 and the uncharged portion X2 are adjacent to each other in a small area, the strength of each small electric field becomes very strong due to the edge effect or peripheral electric field effect. In this way, an electric field with a large electric field gradient is formed near the surface of the developing roller 5.

On the other hand, as described above, the toner 4 supplied to the developing roller 5 by the toner supply roller 6 is given a predetermined polarity (in this example, positive polarity) due to friction with both rollers 5 and 6, as schematically shown in FIG. is strongly triboelectrically charged. The illustrated 1-car supply roller 6 is made up of a core member 14 to which a voltage is applied by a power source 150 as described above, and a foam 15 of, for example, urethane resin laminated around the core member 14, but instead of the foam 15, For example, a fur brush or the like can also be used.

As described above, the positively charged toner 4 is transferred to the developing roller 5.
At this time, as described above, a large number of minute electric charge patterns are formed on the surface of the developing roller 5, and as a result, countless minute electric fields are formed. It is attracted and carried upwards. As described above, the strength of this electric field is strong and the toner is also strongly charged, so a large amount of highly charged toner is carried on the developing roller 5.

The toner supported in this way passes through a doctor blade 8 made of, for example, urethane resin, and its layer thickness is regulated, but in this process, even if toner with a small amount of charge is mixed in the supported toner, , such toner is removed by the contact pressure with the doctor blade 8, and in the end, only the toner with a large amount of charge is strongly held by the minute electric field and is conveyed in large quantities to the developing area 9, where the electrostatic latent occurs as described above. Visualize the image. For example, to prevent background smudges on visible images,
And in order to increase the sharpness, 8 to 15μc/
It is possible to convey to the development area 9 a large amount of toner charged to about 0.6 to 2.0 g/d, preferably 0.8 to 1.2 .mu./d. Therefore, even if the toner is black or another chromatic color, the quality of the visible image can be improved. In the development area 9,
The electric lines of force from the developing roller 5 move toward the electrostatic latent image on the photoreceptor 1, and the force of holding the toner on the developing roller weakens.
A latent image can be effectively visualized.

The surface of the developing roller 5 that has passed through the developing area 9 is again neutralized by the neutralizing roller 33, and then charged again by the electric charge applying means 34 in a continuous manner, and conveys the toner to the developing area 9 while carrying the toner.

If each charge applying means 34 is configured to always apply a charge to the same portion of the developing roller, it is possible to omit the charge removing means such as the charge removing roller 33.

The principle of how corona ions from the charge wire 54 selectively pass through the through holes 57 by applying a voltage as illustrated in FIG. 4(a) to the grid electrode 52 is known per se, but this This will be briefly explained below for understanding of the invention.

To simplify the explanation, the conductive roller 1 of the developing roller 5
It is assumed that no voltage is applied to 0 and that this is grounded, and that a charge pattern X1 of -500V is formed on the dielectric 32 on the surface of the developing roller. Here, a voltage of, for example, -5 KV is applied to the charge wire 54 by a power source 55. On the other hand, the upper limit peak value VO (FIG. 4(a)) is set to -500 by the power supply 56 on the grid electrode 52.
An alternating voltage of V is applied.

When the lower limit peak value of the alternating electric field (Ov here) is applied to the grid electrode 52, this electrode 52 is exactly grounded, so the corona ions from the charge wire 54 are transferred to the casing 53 and the grid electrode. 52 and does not pass through the through hole 57.

On the other hand, the upper limit peak value of the alternating electric field V0 (-500V)
is applied to the grid electrode 52 , an electric field is formed between the electrode 52 and the uncharged developing roller 5 , so the corona ions from the charge wire 54 pass through the through hole 57 and reach the developing roller 5 . The dielectric layer 32 is negatively charged. When the surface potential of the dielectric 32 reaches 1,500 square meters, the electric field between the surface and the grid electrode 52 disappears, and the flow of corona ions through the first through hole 57 stops.

The above-mentioned operations are performed continuously, and since the developing roller 5 is rotating at this time, a dot-shaped charge pattern X1 is formed on its surface as shown in FIG.

Such an effect occurs even when a voltage is applied to the conductive roller 1o of the developing roller 5, or when a direct current is superimposed on the alternating voltage applied to the grid electrode 52, as illustrated in FIG. 4(b). Basically, there is no difference, and it is possible to form a charge pattern with a potential difference on the surface of the developing roller, and to form a large number of minute closed electric fields with high intensity.

The charged portion X1 of the developing roller 5, that is, the size, shape, and pitch of the charge pattern can be set as appropriate in consideration of the amount of toner to be conveyed to the developing area and other conditions, as shown in FIG. Its diameter and pitch P,
PL is, for example, about 100 μm to 500 μm. Such a value is.

The voltage applied to the charge wire 54, the distance between the wire 54 and the surface of the developing roller, the pitch and size of the through holes 57 of the grid electrode 52, the voltage application time Tl of the alternating voltage applied to the grid electrode 52 (Fig. 4(a) )), and can be determined by appropriately setting the surface linear velocity (peripheral velocity) of the developing roller 5.

For example, the frequency of the alternating voltage (or voltage obtained by superimposing direct current on this) applied to the grid electrode 52 is f (Hz), its period is T (see), the circumferential speed of the developing roller 5 is V,
(mm/5ee), the relationship between these and the pitch P (mm) of the charge pattern X1 in the developing roller moving direction is T (see) = P (Mn) / V (+w/
5ee) or P (+m+) = V (m/5ec) / f (1
/5ee), so for example, V = 100
(m/5ee), if you want to obtain a charge pattern X1 with a density of Pm2O3 (μm), apply an alternating voltage with a frequency of f = 100/ (400X103) = 250 (Hz) to the grid electrode 52. Bye. Similarly, when the pitch P is 200 μm, for example, f=600 (Hz).

Furthermore, in order to set P in the range of 0.1 m+ to 0.5 m, the frequency f of the dielectric voltage applied to the grid electrode 52 or the voltage obtained by superimposing direct current on this voltage is set to 2 (am)XV≦f≦1.
00 (m)xv.

In this way, the shape, pitch, and size of the charge pattern X1 can be set to desired values that meet the requirements of each developing device.

Further, as shown in FIGS. 4(a) and (b) for the grid electrode 52,
For example, a DC voltage is applied instead of an alternating voltage as shown in FIG.
can also be formed.

In each of the embodiments described above,! ! If the resistance value of the surface of the A-image roller 5 is low, the electric charge will easily leak, the electric charge will not be retained, and the electric field strength of the minute closed electric field will weaken.
Since the toner holding power decreases, it is desirable to set the volume resistivity of the dielectric material 32 on the surface of the developing roller to 10'' Ω·1 or more, which makes it difficult for charge leakage to occur.

Moreover, instead of the dielectric material 32 on the surface of the conductive roller 10,
A photosensitive layer (photoconductive layer) that exhibits insulation in the dark and exhibits conductivity when exposed to light may be laminated. Even when such a developing roller is used, charges can be selectively applied by the charge applying means 34. Further, as the static eliminating means for the developing roller, a lamp for irradiating light onto the photosensitive layer, a corona discharger, etc. can also be used.

In short, it is sufficient to use a developing roller whose five surfaces have charge retention properties, and the same applies when the toner carrier is a belt.

Further, in each of the above-mentioned embodiments, a developing device using a single-component non-magnetic toner developer particularly suitable for color development has been exemplified, but the present invention is constructed using a magnetic toner to which an auxiliary agent is externally added as necessary. It can also be applied to a developing device using a one-component developer.

Further, the charge applying means can selectively apply a charge having the same polarity as the charging polarity of the toner to the surface of the toner carrier, and the toner can be supported by a minute closed electric field formed thereby.

〔Effect of the invention〕

According to the present invention, a required amount of highly charged toner can be conveyed to the development area to form a visible image with a desired density. Furthermore, since the corona ion flow toward the toner carrier can be controlled by using a grid electrode, it is possible to form a charge pattern in a desired form on the toner carrier, and the charge imparting means can be used in a non-contact manner with respect to the toner carrier. Therefore, there is no risk of damaging the toner carrier.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing an example of a developing device, FIG. 2 is an explanatory view schematically showing toner particles in an enlarged manner, and FIG. 3 is a partially cutaway view of the charge applying means as seen from the developing roller side. 3rd a
The figure is an enlarged view of the part indicated by the symbol ■ in Figure 3, and Figure 4 (a
) and (b) are diagrams illustrating the voltage applied to the grid electrode, and FIG. 5 shows the relationship between the charge pattern formed on the developing roller and the grid electrode, and is an expanded view of the surface of the developing roller. FIG. 6 is an explanatory diagram showing lines of electric force of a minute closed electric field formed near the surface of the developing roller.
FIG. 7 is an explanatory diagram similar to FIG. 5, showing another example of a charge pattern. 2...Developing device 9...Developing area 5]...Corona discharger 54...Charge wire 4...Toner 34...Charge applying means 52...Grid electrode 57...Through hole Figure 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 in a developing area where the latent image carrier and the toner carrier face each other. , a developing device that visualizes an electrostatic latent image formed on a latent image carrier with toner carried on a toner carrier, using a carrier whose surface has charge retention properties as the toner carrier; , a charge applying means for selectively applying a charge to the surface of the toner carrier and forming a large number of minute closed electric fields in the vicinity of the surface is provided, and the charge imparting means is opposed to the surface of the toner carrier. The present invention is comprised of a corona discharger and a grid electrode disposed between a charge wire of the discharger and the surface of the toner carrier and provided with a plurality of through holes through which corona ions from the charge wire pass. Characteristic developing device.