JPH07134476A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of fog by electrifying a photoreceptor by means of a pre-electrifier before electrifying it by means of a magnetic brush. CONSTITUTION:A developing device 16 is arranged in the vicinity of the photoreceptor 12, and the pre-electrifier 28 is provided in contact with the surface of the photoreceptor 12, upstream in the developing device 16. A development bias voltage is applied to a developing sleeve 22, and an electrification voltage is applied to the pre-electrifier 28. After the photoreceptor 12 is electrified by the pre-electrifier 28, the magnetic brush 34 composed of developer in which insulated toner and semiconductive, magnetic carrier are mixed comes into contact with the surface of the photoreceptor 12, thereby re-electrifying the photoreceptor 12 by the development bias voltage via the semiconductive, magnetic carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus using a so-called charge injection type electrophotographic process which can perform processes such as charging, exposure, development and cleaning almost at the same time.

[0002]

2. Description of the Related Art A conventional image forming apparatus of this type has been proposed in, for example, Japanese Patent Application Laid-Open No. 58-153957. FIG. 1 is an illustrative view showing an example of this conventional image forming apparatus. The conventional image forming apparatus 1 includes a developing device 3 arranged above the outer peripheral surface of the photosensitive drum 2, a transfer device 4 arranged below the outer peripheral portion, and an LE arranged inside the photosensitive drum.
A D array head 5 is included. The photoreceptor 2 includes a cylindrical transparent support substrate 2a made of glass, and a transparent electrode 2b and a photoconductive layer 2c are laminated on the outer periphery of the substrate 2a. Transparent electrode 2b
A voltage (V) of about 20 V is applied as a developing bias between the magnetic pole roller 6 and the magnetic pole roller 6 that constitutes the developing device 3.
The conductive magnetic toner 7 is adsorbed around the developing sleeve 8 covered on the outer circumference of the magnetic pole roller 6, thereby forming a so-called magnetic brush 9, and the tip of the magnetic brush 9 is almost on the outer peripheral surface of the photoconductive layer 2c. Contact. Therefore, the conductive magnetic toner 7 is applied to the photoconductive layer 2 from the developing bias.
Charge injection into c occurs, and the photoconductive layer 2c is charged to approximately the same potential as the developing bias.

On the other hand, the light image projected from the LED array head 5 is applied to the photoconductive layer 2 from the inside of the cylindrical transparent support substrate 2a.
Then, the electrostatic latent image is formed on the photoconductive layer 2c.
At this time, the toner 7 is adsorbed on the surface of the photoconductive layer 2b from the magnetic brush 9 to form a toner image. The toner image is transferred onto the recording paper by the transfer device 4. Then, the residual toner on the surface of the photosensitive drum 2 is removed by the scraping force of the developing device 3 and the magnetic force of the magnetic pole roller 6. Therefore, charging, exposure, development on the photoconductor drum 2,
And the cleaning process is performed by the developing device 3 and the LED.
The array head 5 and the array head 5 perform the operations substantially at the same time, which greatly simplifies the configuration of the image forming apparatus and the image forming process.

As described above, in the method using the conductive magnetic toner in the charge injection type electrophotographic process, in the case of the so-called direct transfer type in which the toner image is directly transferred onto the recording paper,
There is a problem in that plain paper cannot be used because high-resistance recording paper with a special coating on plain paper is required. Further, in the case of a so-called indirect transfer type in which a toner image is transferred onto a recording paper via an intermediate medium, there is an advantage that plain paper can be used, but a toner image on a photoconductor is transferred to the recording paper, for example, a transfer belt. An intermediate medium is needed. Therefore, such a transfer belt cooling device, a cleaning device for residual toner on the transfer belt, and a meandering prevention device for the transfer belt are required, which is disadvantageous in that the image forming apparatus becomes large and the driving system becomes complicated.

Therefore, for example, in Japanese Patent Publication No. 5-38950, a toner image is formed on plain paper by using a developer in which a conductive carrier and an insulating toner are mixed at a predetermined ratio in a charge injection type electrophotographic process. We are proposing a technology that can directly transfer.

[0006]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 5-38950
In the conventional technique disclosed in Japanese Patent Laid-Open Publication No. 2003-242242, a so-called fog phenomenon occurs because all the charge amount required for development is injected into the photoconductor via the developer. That is, in this conventional technique,
Insulating toner first adheres to the photoconductor, and as a result, the photoconductor is less likely to be charged, and thus a potential difference occurs between the photoconductor and the magnetic sleeve. Therefore, a so-called fogging phenomenon occurs in which the insulating toner remains attached to the surface of the non-image portion.

Therefore, a main object of the present invention is to provide an image forming apparatus which can directly transfer a toner image onto plain paper in an electric charge injection type electrophotographic process and is free from fogging.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a photoconductor including a substrate and a photoconductive layer laminated thereon, a photoconductive layer provided near the photoconductive layer surface of the photoconductor, and having an insulating toner and a semiconductive magnetic material. Storage means for storing the developer mixed with the carrier, developing means for charging the photoreceptor by contacting the developer stored in the storage means with the photoconductor, and a portion of the photoconductor to which the developer is contacted by the developing means With an exposure means for irradiating the photoconductive layer with exposure light, a developing bias means for applying a predetermined developing bias voltage between the developing means and the photoconductive layer, and a photoconductor on the upstream side of the developing means when viewed from the photoconductor. The image forming apparatus includes a pre-charging unit that applies a predetermined charging voltage to the photoconductor before the photoconductor is substantially contacted and charged by the developing unit.

[0009]

The photosensitive member is formed, for example, by a pre-charging means such as a conductive sheet or a conductive blade.
It receives a charge of 500 to -600V. When the area of the photoreceptor charged by the precharging means is brought to the developing means, the photoreceptor is mediated by the semiconductive magnetic carrier contained in the developer by the developing bias voltage applied to the developing means, for example, the developing sleeve. , For example, charged to −400V. At this time, the uneven charging due to the pre-charging means is made uniform. Then, when the photoconductor is charged by the developing means, the exposure light is applied to the area by the exposing means. Therefore, a toner image is formed on the photoconductor.

The area where the photoreceptor is charged by the pre-charging means holds a predetermined charging voltage until it is recharged by the developing means. Therefore, since a large potential difference does not occur between the photoconductor and the insulating toner contained in the developer, the insulating toner does not adhere to the non-exposed portion, that is, the non-image portion. That is, fogging does not occur.

[0011]

According to the present invention, since the toner image is formed only by the insulating toner, the toner image can be directly transferred onto the plain paper. Further, since the pre-charging means is provided so as to charge the photoconductor with a predetermined bias voltage in advance before the photoconductor is charged by the developing means, fogging does not occur.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the detailed description of the embodiments below with reference to the drawings.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming apparatus 10 of the embodiment shown in FIG.
The photoconductor 12 is the same as the photoconductor 2 of the conventional image forming apparatus 1 described above. The photoconductor 12 includes a transparent supporting substrate 12a made of cylindrical glass or the like, a transparent electrode 12b and a photoconductive layer 12c which are laminated on the outer periphery of the substrate 12a to a predetermined thickness. The photoconductor 12 is rotated clockwise, that is, in the direction of arrow A, by the driving force of a main motor (not shown). The substrate 12 is provided inside the photoconductor 12.
An optical writing head 14 including, for example, an LED array head for irradiating the photoconductive layer 12c with exposure light through a and the transparent electrode 12b is arranged.

A developing device 16 is provided near the surface of the photoconductive layer 12c of the photoconductor 12, and the developing device 16 contains a toner 18 containing a developer 18 in which an insulating toner 18a and a semiconductive magnetic carrier 18b are mixed. Includes box 20. A developing sleeve 22 including a magnetic roller 24 is arranged at the lower end opening of the toner box 20. The developing sleeve 22 is, for example, a non-magnetic cylinder made of aluminum, stainless steel, or the like, and a magnetic roller 24 is fixedly arranged therein. For example, eight magnetic poles N and S are alternately formed on the surface of the magnetic roller 24. The developing sleeve 22 is rotated counterclockwise, that is, in the direction of arrow B by a drive mechanism (not shown). This developing sleeve 22
Is arranged at a position facing the optical writing head 14 with the photoconductor 12 interposed therebetween.

The upper end opening of the toner box 20 is closed by a lid 26. Therefore, the replenishment of the insulating toner 18a to the toner box 20 is performed by opening and closing the lid 26. That is, the toner mixing ratio of the developer 18 in the toner box 20 decreases with the number of image forming processes, that is, the number of printed sheets, and when the mixing ratio becomes a predetermined value or less, the image density decreases. When the user determines that the image density has decreased, the user opens the lid 26 and replenishes the insulating toner by a predetermined amount. In this case, instead of the user's judgment, a sensor may detect a decrease in the mixing ratio, or a decrease in the mixing ratio may be detected from the developing current.

In the initial state, the developer 18 is fully loaded (without a gap) in the toner box 20. When the image forming process is repeatedly performed in this state, the insulating toner 18a of the developer 18 is consumed, the volume of the developer 18 in the toner box 20 is reduced, and a gap is formed in the upper portion inside the toner box 20. When the toner replenishment timing as described above is detected, the user replenishes the insulating toner until the gap of the toner box 20 is filled with the replenished insulating toner 18a. Therefore, it is possible to always replenish the optimum amount of toner without the user supplying too much replenishment toner. Even if the user does not replenish the toner until the upper space of the toner box 20 is full, the next toner replenishment time will be earlier and no particular problem will occur.

In the image forming apparatus 10 of the embodiment shown in FIG. 2, the photoconductive layer 1 of the photoconductor 12 is located at a position apart from the developing device 16 upstream of the photoconductor 12 by a predetermined distance D1.
The pre-charging device 28 is arranged so as to contact the surface of 2c. The pre-charging device 28 is formed of a conductive film in this embodiment, and its main surface contacts the outer peripheral surface of the photoconductor 12. The pre-charging device 28 is provided with a charging power source 30
For example, a predetermined negative charging voltage is applied. Also,
The developing sleeve 22 has a predetermined developing bias voltage (eg,
-400V) is applied. In this embodiment, the pre-charging device 28 is provided with a charging power source 30 so that the developing device 16
Above the developing bias voltage (-400V)
A negative charging voltage of about 900 to -1000V is applied,
As a result, the surface potential of the photoconductor 12 by the pre-charging device 28 becomes about -500 to -600V.

It is desirable that the voltage applied to the pre-charging device 28 is a voltage that can obtain the charging potential (surface potential) of the photoconductor 12 that is equal to or larger than the developing bias voltage. Any material can be used as a material for forming the substrate 12a of the photoconductor 12 as long as it is a material having excellent light transmittance and no optical distortion, such as soda glass and borosilicate glass. Glass, resin such as acrylic and polycarbonate may be used. Furthermore, the transparent electrode 1
As 2b, for example, indium tin oxide (IT
O), tin oxide, etc. can be used. Then, in order to form the transparent electrode 12b, a vacuum vapor deposition method, a sputtering method, a coating method, a dipping method or the like can be used. Furthermore, as the photoconductive layer 12c, a selenium-based, amorphous silicon-based, or organic-based photoconductive material can be used.

Further, the thickness of the substrate 12a may be 0.1 mm or more, and if the thickness is in a range of 0.1 mm to 1 mm and has some elasticity, the straightness (cylindricity) of the substrate 12a. Even when the accuracy is low, the magnetic roller 24 is pressed to force it into a desired shape. In such an image forming apparatus 10, the photoconductor 12 is charged to a voltage near the developing bias by the charging device 28, the photoconductor 12 is rotated, and the area charged by the pre-charging device 28 is developed while holding the voltage. It is brought into a position facing the device 16.

On the other hand, when the developing sleeve 22 is rotated,
The semiconductive magnetic carrier 18b attracted to the S pole and N pole of the magnetic roller 24 by the magnetic force moves as the developing sleeve 22 rotates. The insulating toner 18a, which is coupled to the semiconductive magnetic carrier 18b by Coulomb force or the like, is also pulled out from the lower end opening of the toner box 20 as the developing sleeve 22 rotates, and the photoconductive layer 12c of the photoconductor 12 is removed. Opposite the surface.

In more detail with reference to FIG. 3, semi-conductivity is provided along magnetic lines F between N and S poles formed alternately on the outer peripheral surface of the magnetic roller 24 of the developing device 16 in the circumferential direction. Brush 34 of developer 18 composed of a conductive magnetic carrier 18b and an insulating toner 18a attached to the semiconductive magnetic carrier 18b by a partial Coulomb force generated by frictional charging of the semiconductive magnetic carrier 18b.
Is formed. Then, the magnetic brush 3 on the developing device 16
4, a conductive path (chain of carriers 18b) is formed by the semiconductive magnetic carrier 18b, and the developing bias voltage source 32 develops on the surface of the photoreceptor 12 while it is in contact with the magnetic brush 34. Charges are injected until the potential becomes equal to the bias voltage. As a result, the surface of the photoconductor 12 and the developing sleeve 22 have the same potential and the same polarity, and the Coulomb force acting on the insulating toner 18a becomes zero. Therefore, the electric force for adhering the insulating toner 18a to the photoconductor 12 is reduced. Cease to exist.

FIG. 4 is a graph showing the charging voltage of the photoconductor 12 before contact with the magnetic brush 34 and after contact with the magnetic brush 34. After the photoconductor 12 is charged by the pre-charging device 28 to a voltage near the developing bias, the photoconductor 12 is brought into contact with the magnetic brush 34, so that the photoconductor 12 is moved to the developing device 1.
It is charged to substantially the same potential as the developing bias voltage of 6 (-400 V in this embodiment). That is, the charging potential of the photoconductor 12 converges on the developing bias voltage. Therefore, the charging unevenness of the pre-charging device 28 is made uniform by the injection of the electric charge from the magnetic brush 34, so that no special control is required during the charging by the pre-charging device 28.

In this way, when the photoconductor 12 is charged to the developing voltage, that is, the potential of the developer 18 is almost the same,
Since no electrical attractive force is generated between the developer 18 and the photoconductor 12, the developer 18 does not adhere to the surface of the photoconductive layer 12c of the photoconductor 12. That is, if the charging potential of the photoconductor after contacting the magnetic brush 34 is substantially the same as or higher than the developing bias voltage, the insulating toner 18a does not adhere to the surface of the photoconductor 12, so that the pre-charging device 28 is used.
The charging potential of the photoconductor 12 can be set in a wider range than in the usual electrophotographic process. That is, even when the charging potential of the photoconductor 12 by the pre-charging device 28 is lower than the developing bias voltage, if the charging voltage and the developing bias voltage have a certain potential difference, the charge injection from the magnetic brush 34 is performed. As a result, the charging potential of the photoconductor 12 becomes substantially the same as the developing bias voltage, so that fog does not occur. Further, when the charging potential of the photoconductor 12 by the pre-charging device 28 is higher than the developing bias voltage, naturally, fog does not occur.

The photoconductor 12 thus charged is exposed by the optical writing head 14. Optical writing head 14
By the exposure light from, the potential of the area receiving the exposure light is lowered, and a potential difference is generated between the photoconductor 12 and the developer 18 in that portion, and therefore an electric force is generated in that portion to develop. The insulating toner 18a of the agent 18 adheres to the photoconductor 10. At that time, since the semiconductive magnetic carrier 18b is hardly charged, an electric force generated between the semiconductive magnetic carrier 18b and the surface of the photoconductor 12 is weaker than a magnetic force generated between the semiconductive magnetic carrier 18b and the developing sleeve 22. The semi-conductive magnetic carrier 18b remains on the developing sleeve 22.

On the other hand, the insulating toner 18a is charged to a predetermined polarity, for example, a negative polarity by friction with the semiconductive magnetic carrier 18b.
A sufficiently large electric force is generated between the
As a result, the insulating toner 18a overcomes the Coulomb force and the like between the insulating toner 18a and the semiconductive magnetic carrier 18b, and the photoconductor 12
Moved to the area where the potential dropped due to the exposure light exposure,
Adhere to. That is, a toner image is formed on the photoconductor 12 only by the insulating toner 18 a contained in the developer 18.

Then, as shown in FIG. 2, the toner image formed on the photoconductor 12 is transferred to a transfer position facing the transfer roller 36 and transferred onto the recording paper 38 fed by the paper feed roller 40. To be done. At the transfer position, the insulating toner 18a attached on the photoconductor 12 is transferred onto the recording paper 38 by the electric force of the transfer roller 36 to which a transfer bias voltage of, for example, + 500V having a polarity opposite to the charging polarity is applied. Transcribed. Then, after that, the fixing roller 42
And the toner image on the recording paper 38 is fixed.

The photoconductor 12 is further rotated. When the residual toner remaining on the surface of the photoconductor 12 through the transfer process reaches the position of the pre-charging device 28, the pre-charging device 28 receives the physical force of the residual toner and disturbs it.
The electrostatic adhesion of the residual toner is reduced by the charging of the pre-charging device 28. Therefore, the residual toner and the photosensitive member 1
The adhesion with 2 is weakened. After that, when the photoconductor 12 is further rotated and the residual toner reaches the position of the developing device 16, the adhesive force between the residual toner and the photoconductor 12 is weakened. The magnetic carrier 18b is sucked and eventually collected by the developing device 16 (cleaning step). That is, the pre-charging device 28 functions as a residual toner peeling member.

With respect to the resistivity and the average particle diameter of the semi-conductive magnetic carrier 18b, which is one of the characteristics of the above-mentioned embodiment, suitable ranges were confirmed as shown in Tables 1 and 2, respectively.

[0029]

[Table 1]

[0030]

[Table 2]

In the experiment of Table 1, the resistivity of the carrier was changed within the range of 10 ¹ -10 ¹⁰ Ω · cm, and five evaluation items (1) non-image portion potential change amount, (2) image density, ( We evaluated 3) image quality, (4) pinhole effect, and (5) charge injection. The amount of change in the potential of the non-image portion was evaluated by the amount of change in the potential of the non-image portion on the photoconductor 12. That is, as described above, the photoconductor 1 is contacted by the contact between the pre-charge device 28 and the photoconductor 12.
When 2 is charged, charging unevenness occurs, but this charging unevenness is eliminated by charge injection due to contact between the magnetic brush 34 of the developer 18 and the photoconductor 12. To what extent the charge unevenness of the pre-charging device 28 was made uniform by the charge injection was evaluated by the potential change amount of the non-exposed portion, that is, the non-image portion. If the uniformizing effect of charge injection by carriers is small, a streak pattern is generated in the non-image area. Table 1 shows that when the resistivity of the carrier is 10 ¹⁰ Ω · cm or more, there is no homogenizing effect and the carrier cannot be used.

The image density was evaluated by the toner image density of the image area. In Table 1, the carrier resistivity is 10 ¹⁰ Ω.
When it is more than cm, the image density is remarkably reduced, and the carrier cannot be used. The image quality was evaluated by the sharpness and fringe at the edge of the image. In Table 1, the carrier resistivity is 10 ² Ω · cm.
The following cases show that the image quality is significantly deteriorated and the carrier cannot be used.

With respect to the pinhole effect, when a pinhole was generated in the photoconductive layer 12c of the photoconductor 12, how the resistivity of the carrier affected the pinhole was evaluated. When the pinhole exists in the photoconductive layer 12c, the carrier comes into contact with the pinhole, the electric charge leaks from the pinhole through the carrier, and the potential of the non-image portion decreases as if the exposure light was irradiated. Toner may adhere to the surface of the photoconductor 12, or a streak pattern may be generated in the axial direction of the photoconductor 12 in some cases. Table 1 shows that when the resistivity of the carrier is 10 ² Ω · cm or less, the leakage of charges is too large and the carrier cannot be used.

The charge injection was evaluated by the charge injection amount of carriers. In Table 1, the carrier resistivity is 10 ¹⁰ Ω.
At cm or more, the charge injection amount is too small, indicating that the carrier cannot be used. As a result of comprehensively evaluating the above-mentioned evaluation items, as shown in Table 1, the resistivity of the semiconductive magnetic carrier 18b of the present invention is 10 ⁴ -10 ⁸ Ω ·
cm, particularly preferably 10 ⁵ -10 ⁷ Ω ・
It turned out to be cm.

Furthermore, in the experiment of Table 2, the resistivity of the carrier was set to 10 ⁶ Ω · cm, and the average particle diameter of the carrier was changed in the range of 15 to 100 μm.
We evaluated (1) charge injection, (2) image quality, and (3) carrier subtraction. The charge injection was evaluated by the charge injection amount of carriers. Table 2 shows that when the average particle diameter of the carrier is 60 μm or more, the charge injection amount decreases, which is not preferable.

The image quality was evaluated by the sharpness and fringe at the edge portion of the image. Table 2 shows that when the average particle diameter of the carrier is 100 μm or more, the image quality is deteriorated, which is not preferable. Career pulling is
The evaluation was made according to how much the carrier was pulled by the photoreceptor 12. When the carrier is attracted to the photoconductor, the mixing ratio of the toner and the carrier in the developer changes, which is not preferable. Table 2 shows that when the average particle size of the carrier is 15 μm, the carrier pulling is large and the carrier cannot be used.

As a result of comprehensive evaluation of the above-mentioned evaluation items, as shown in Table 2, the semiconductive magnetic carrier 18 of the present invention is obtained.
It was found that the average particle size of b should be 20-50 μm. However, the resistivity of the carrier shown in Table 1 is 10 ⁴ −1.
The average particle size in the range of 0 ⁸ Ω · cm that is preferable, has been confirmed by experiments. In addition, the semiconductive magnetic carrier 18b used for the developer 18 and the insulating toner 1
The mixing ratio with 8a must be determined after comprehensively considering the charging characteristics of the photoconductor 12 and the image forming speed.

That is, since the insulating toner 18a contributes to the development in the image forming apparatus 10 of the embodiment, if the ratio is too small, the amount of the toner adhering to the image area on the photoconductor 12 becomes small, Sufficient image density cannot be obtained. On the other hand, if the proportion of the insulating toner 18a is too large, the conductive path (FIG. 3) by the semiconductive magnetic carrier 18b is hard to be formed, and the charging efficiency of the photoconductor 12 is lowered. Therefore, the semiconductive magnetic carrier 18
It is desirable that the weight ratio of the insulating toner 18a to the developer 18 including b and the insulating toner 18a is in the range of 5 to 95%.

In the above-described embodiment, the developer 18 is stored on the upstream side with respect to the rotation direction of the photoconductor 12 as shown in FIG. 2, but this storage amount is the developing nip width, that is, the photoconductor 12. The contact width between the magnetic brush 34 and the magnetic brush 34 (Fig. 3) is 4 mm to 1
It is desirable to adjust it to 5 mm. If the developing nip width is 4 mm or less, the charge injection by the developer 18 becomes insufficient, and it becomes difficult to uniformly charge the photoconductor 12, so that fogging due to uneven charging occurs. When the developing nip width is 15 mm or more, the upper layer portion of the stored developer 18 comes into contact with the surface of the photoconductor 12 before the charge injection, so that the precharge device 28 has a portion of the photoconductor having a low charging potential. Then, since the magnetic force of the magnetic roller 24 against the stored developer 18 is weak, the insulating toner 18a in the upper layer portion of the stored developer 18 adheres to the photoconductor 12. At this time, if the amount of the adhered toner is large, the surface of the photoconductor 12 may not be cleaned while passing through the developing nip portion, and therefore fogging also occurs in this case. This fogging can be effectively prevented by the other embodiments shown in FIGS.

Next, another embodiment of the present invention will be described with reference to FIGS. As described above, the N poles and the S poles are alternately arranged on the surface of the magnetic roller 24. The N1 pole exists at the minimum distance between the photoconductor 12 and the developing sleeve 22, that is, at the downstream side of the straight line OO ′ connecting the centers of the photoconductor 12 and the developing sleeve 22,
The S1 pole exists on the upstream side. Here, the developing sleeve 22
The angle formed by the straight line OO ′ connecting the center O of the developing sleeve 20 and the magnetic pole N1 is θ1, and the center O of the developing sleeve 20 and the magnetic pole S
If the angle between the straight line connecting 1 and the straight line OO ′ is θ2, in this embodiment, the magnetic poles N1 and S1 are arranged so that θ1 ≦ θ2. In the embodiment, θ1 is 18
And θ2 is 27 °.

The position of the magnetic pole means the position on the surface of the developing sleeve of the magnetic pole where the magnetic flux density in the normal direction of the surface is maximized. Further, in this embodiment, the position of the pre-charging device 28 for charging the photoconductor 12 is different from that in the previous embodiment, as is clear from comparison between FIGS. 6 and 2. That is, in the previous embodiment, the position of the pre-charging device 28 and the position where the magnetic brush 34 is in contact with the photoconductor 12 are largely separated by the distance D1. It is arranged at a position of a distance D2 from. However, D1> D2. Therefore, the pre-charging device 28 is brought very close to its contact area. As a result, the fog generated in the embodiment of FIG. 2 can be eliminated.

That is, in the embodiment of FIG. 2, when the charging power source 30 and the developing bias power source 32 are commonly used to apply the charging voltage and the developing bias voltage at the same timing, the pre-charging device 28 causes the magnetic brush 34 to operate. When the area of the photoconductor 12 charged by the pre-charging device 28 comes into contact with the magnetic brush 34, the photoconductor 12 is charged only by the developing bias voltage 32 and is not developed. To be done. Therefore, fogging occurs and toner adheres to this portion. When the toner adheres to the photoconductor 12, there arises a problem that the transfer roller 36 becomes dirty, or the backside of the recording paper is caused by the dirt. However, by bringing the pre-charging device 28 very close to the magnetic brush 34 as in this embodiment, the pre-charging device 2
The position where the charging by 8 is performed and the position where the charging is performed by the magnetic brush 34 can be set to substantially the same position, and the fog described above does not occur.

Further, in order to dispose the pre-charging device 28 close to the developing device 16, that is, the magnetic brush 34, in this embodiment, as shown in FIG. 6, the pre-charging device 28 is located at the upper left end of the developer box 20. It is fixed to 20a. In this way, by fixing the pre-charging device 28 to the upper left end of the developer box 20, the scattering preventing function (described later) of the pre-charging device 28 is surely exhibited.

Then, in this embodiment, when the magnetic brush 34 comes into contact with the surface of the photoconductor 10, charges are injected into the photoconductor 12 by the developing bias voltage. At this time, since θ1 ≦ θ2, the center position of the magnetic poles N1 and S1 where the developer 18 is most dense, that is, the magnetic flux density on the surface of the developing sleeve 22 in the normal direction of the surface becomes zero. Since the position is on the upstream side of the straight line OO ', the conductive path for charging the photoconductor 12 is dense, and the charge is efficiently and uniformly injected into the photoconductor 12, and thus the photoconductor 12 is charged. Is uniformly and uniformly charged.

FIG. 7 is a graph showing the relationship between the position of the magnetic pole N1 and the fog. The position of the magnetic pole N1 is represented by an angle θ1. It can be seen that fogging is small in the range where the angle θ1 is from 0 ° to + 22.5 °, that is, the position where θ1 ≦ θ2. Further, when a magnetic pole is arranged in this developer supply portion, the fluidity of the developer in this portion deteriorates, and the developer is stored upstream along the surface of the photoconductor 10. The magnetic restraining force of the magnetic roller 24 on the stored developer is weakened, and the developer 30 is easily scattered. Therefore, in this embodiment, the pre-charging device 28 is arranged in close contact with the upper part of the developer reservoir.
Since the pre-charging device 28 includes the conductive film as described above, the pre-charging device 28 can be flexibly displaced in response to an increase or decrease in the developer storage amount. Therefore, in this embodiment, the pre-charging device 28 functions to prevent the developer from scattering.

Although the above-mentioned embodiment describes the back side exposure recording system, it is also applicable to a system of exposing from the outside of the photoconductor. That is, in the type in which light is exposed from the outside of the photoconductor 12 between the pre-charging device 28 and the developing device 16, the charging voltage of the pre-charging device 28 and the developing bias voltage of the developing device 16 are increased, and the developing device 16 By eliminating the uneven charging due to the pre-charging device 28 by the magnetic brush 34, the fogging can be reduced. At this time, the charge potential performed by the magnetic brush 34 of the developing device 16 raises the charging potential of the photoconductor 12 after exposure. However, the developing voltage, that is, the developing bias voltage and the charging voltage of the photoconductor 12 after exposure, increase. If the difference is increased, the charging voltage of the photoconductor 12 after exposure can be made lower than the developing bias voltage, and therefore toner development is possible.

The image forming apparatus 10 of the embodiment shown in FIG. 8 includes a conductive brush as the precharging device 28. The conductive brush is attached to the upper end 20b of the developer box 20. In this embodiment, since the pre-charging device 28 is composed of a conductive brush, the residual toner peeling function described above can be further exerted. That is, when the residual toner attached to the photoconductor 12 passes through the pre-charging device 28, that is, the conductive brush, the residual toner is disturbed by the conductive brush. Therefore, the residual toner can be more reliably collected by the magnetic brush 34.

In the embodiment shown in FIG. 9, the pre-charging device 28 is formed of a conductive blade, and the pre-charging device 28 made of this conductive blade is covered by the upper end 20c of the developer box 20. That is, in this embodiment, the pre-charging device 28 is housed in the developer box 20. By housing the pre-charging device 28 in the developer box 20 in this manner, the scattering of the developer can be prevented and the residual toner can be collected more reliably.

The embodiment shown in FIG. 10 is the same as the embodiment shown in FIG. 9 except that the pre-charging device 28 is formed of a conductive plate. In the embodiment shown in FIG. 11, the partition wall 20d is arranged in the developer box 20, and the partition wall 2
The toner supply portion 20e is formed by 0d. And
An agitator 44 is arranged at the lower end opening of the toner supply unit 20e. Therefore, the insulating toner replenished to the toner replenishing section 20 e is scraped out by the rotation of the agitator 44 and brought to the developing sleeve 22.

[Brief description of drawings]

FIG. 1 is an illustrative view showing an example of a conventional image forming apparatus using a charge injection type electrophotographic process.

FIG. 2 is an illustrative view showing one embodiment of the present invention.

FIG. 3 is an illustrative view showing each process of charge injection, exposure and development in the embodiment in FIG.

FIG. 4 is a graph showing the charging voltage of the photoconductor before and after passing through the developing area in the embodiment of FIG.

FIG. 5 is an illustrative view showing a main part of another embodiment of the present invention.

FIG. 6 is an illustrative view showing another embodiment of the present invention.

FIG. 7 is a graph showing the relationship between magnetic pole position and charging voltage in the embodiment of FIG.

FIG. 8 is an illustrative view showing another embodiment of the present invention.

FIG. 9 is an illustrative view showing another embodiment of the present invention.

FIG. 10 is an illustrative view showing another embodiment of the present invention.

FIG. 11 is an illustrative view showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 12 ... Photosensitive body 12a ... Translucent substrate 12c ... Photoconductive layer 14 ... Optical writing head 16 ... Developing device 18 ... Developer 18a ... Insulating toner 18b ... Semiconductive magnetic carrier 22 ... Development sleeve 24 ... Magnetic roller 28 ... Pre-charging device 30 ... Charging voltage power supply 32 ... Development bias power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 21/16 15/02 101 15/06 101 15/08 501 D 8530-2H 505 Z 8530-2H 507 B 8530-2H 15/09 Z 21/10 G03G 9/10 8909-2H 15/00 554 6605-2H 21/00 312 (72) Inventor Yoshinori Senoo 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Denki Co., Ltd. (72) Inventor Yoichiro Goto 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Denki Co., Ltd.

Claims (15)

[Claims] 1. A photoconductor including a substrate and a photoconductive layer laminated on the substrate, provided near the surface of the photoconductive layer of the photoconductor, wherein an insulating toner and a semiconductive magnetic carrier are mixed. Storage means for storing a developer; developing means for charging the photoconductor by bringing the developer stored in the storage means into contact with the photoconductor; and of the photoconductor with which the developer is brought into contact by the developing means. Exposure means for irradiating the photoconductive layer with exposure light at a portion, development bias means for applying a predetermined development bias voltage between the developing means and the photoconductive layer, and of the developing means as seen from the photoreceptor. An image forming apparatus comprising: a pre-charging unit that applies a predetermined charging voltage to the photoconductor before the photoconductor is charged by the developing unit while being substantially in contact with the photoconductor on the upstream side. 2. The image forming apparatus according to claim 1, wherein the substrate is a translucent substrate, and the exposing unit irradiates the photoconductive layer with exposure light through the translucent substrate. 3. The image forming apparatus according to claim 1, wherein the pre-charging means applies the predetermined charging voltage having an absolute value equal to or more than the absolute value of the developing bias voltage to the photoconductor. 4. The image forming apparatus according to claim 3, wherein the pre-charging means applies the predetermined charging voltage to the photoreceptor so that a photoreceptor charging potential equal to or higher than the developing bias voltage is obtained. 5. The photosensitive member includes a cylindrical photosensitive member, and the developing means includes a magnetic roller having first and second magnetic poles alternately arranged on an outer peripheral surface thereof, and a developing sleeve rotatably covered by the magnetic roller. The first magnetic pole and the second magnetic pole are vertically arranged with a first straight line connecting the center of the cylindrical photosensitive member and the center of the magnetic roller interposed therebetween, and the first magnetic pole and the magnetic roller. A second straight line connecting the center of the second magnetic pole and the first straight line forms a first angle with the first straight line, and a third straight line connecting the second magnetic pole and the center of the magnetic roller forms the first straight line. The image forming apparatus according to claim 1, wherein the image forming apparatus is larger than an angle. 6. The image forming apparatus according to claim 1, wherein the pre-charging unit is arranged at a position spaced apart from the developing unit by a first distance. 7. The pre-charging means includes the developing means and the first charging means.
Arranged at a second spaced position which is shorter than the spacing of
The image forming apparatus according to claim 1. 8. A flexibility in which a developer reservoir is formed between the developing device and the photoconductor on the upstream side of the developing device, and the pre-charging device is provided in contact with or close to the developer reservoir. 8. The image forming apparatus according to claim 7, further comprising a conductive member having, the conductive member functioning as a scattering prevention member for the developer. 9. The pre-charging means includes a conductive sheet, and the conductive sheet functions as a residual toner peeling member for peeling the toner remaining on the photoconductor from the photoconductor.
The image forming apparatus according to claim 1. 10. The pre-charging means includes a conductive blade, and the conductive blade functions as a residual toner peeling member for peeling the toner remaining on the photoconductor from the photoconductor. The image forming apparatus according to claim 1. 11. The pre-charging means includes a conductive brush,
8. The image forming apparatus according to claim 1, wherein the conductive brush functions as a residual toner peeling member that peels the toner remaining on the photoconductor from the photoconductor. 12. The image forming apparatus according to claim 1, wherein the developing unit includes a housing that houses the pre-charging unit. 13. The carrier is 10 ⁴ to 10 ⁸ Ω · cm.
The image forming apparatus according to claim 1, having the resistivity of. 14. The carrier is 10 ⁵ to 10 ⁷ Ω · cm
The image forming apparatus according to claim 13, having a resistivity of. 15. The image forming apparatus according to claim 1, wherein the carrier has an average particle diameter of 20 to 50 μm.