JPH07325459A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent quality image without a defect in image quality such as a black streak caused by toner passing through a blade over a long period by electrifying residual toner to the same polarity as that of electrification with the blade in the part of an image carrier being on the upstream side of the blade used for electrifying and cleaning. CONSTITUTION:A negative DC voltage of about 600-1500V is applied to the electrode part 26 of the blade used for electrifying and cleaning 20 from a voltage applying means 22. On the other hand, a corona electrifier 21 is provided in the fixed part of a photoreceptor 1 being on the upstream side of the blade 20 and a negative DC voltage of about 3-5kV is applied to the corona wire of the electrifier 21 from a voltage applying means 23. The toner 9 remaining on the photoreceptor 1 is electrified to the negative polarity by the electrifier 21 and then, scraped by the blade 20. Moreover, even if the negatively electrified toner reaching the blade 20 passes therethrough, the toner is never stuck to the electrode part 26 to which the voltage of the negative polarity is applied.

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 applied to a copying machine, a printer or the like to which an electrophotographic process is applied.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, as shown in FIGS. 6 and 7, as a charging device b for charging a photoconductor (charge receptor) a, a conductive member such as a roll or a brush is used. By charging c with the photoreceptor a and applying a direct current or a superimposed voltage d of direct current and alternating current to discharge in a minute gap formed in the vicinity of the contact portion between the conductive member and the photoreceptor, the photoreceptor is charged. A contact type charging device is known. In FIG. 6, e is a cleaning device, f is an exposure device, g is a developing device, h is a recording sheet, i in FIG. 7 is a cleaning blade of the cleaning device, j is the same sealing member, and k is toner. Shown respectively.

For example, the roll type contact type charging device b is
As shown in FIG. 7, in order to perform uniform charging, it is necessary to improve the adhesion to the photoconductor and form stable microvoids.
Therefore, for example, a method of reducing the hardness of the rubber of the roll c is adopted. In this case, a large amount of process oil must be contained in the rubber material in order to reduce the rubber hardness, and as a result, the oil is liable to transfer to the photoreceptor side and adversely affect the image quality. There is also a method of increasing the outer shape accuracy of the roll, but in this case, it is difficult to improve the outer shape accuracy of an elastic body such as rubber, and there is a problem in that the yield is reduced and the cost is increased.

On the other hand, for example, Japanese Patent Laid-Open No. 60-147.
No. 756 and Japanese Patent Laid-Open No. 1-93760 propose blade-type contact charging devices. this is,
An electrostatic blade that applies a specified voltage is brought into contact with the photoconductor, and the photoconductor is charged by discharging in a wedge-shaped microvoid formed between the blade and the photoconductor. It has a feature that it can be stably formed and is inexpensive. Further, since the blade is brought into contact with the photoconductor, there is an advantage that a cleaning function can be expected together with the cleaning blade in the cleaning device.

When such a blade type contact type charging device has a cleaning function in addition to a charging function, a method of directly using a conductive rubber or the like as a blade can be considered. In that case, the strength of the blade is There is a problem that it is difficult to set conditions for exhibiting the cleaning function while ensuring physical properties such as elasticity and elastic modulus.

Therefore, as a technique for solving the above-mentioned problems, as shown in FIG. 8, a urethane blade c used as a conventional cleaning blade has a surface facing the photosensitive member a for discharging. A charging / cleaning blade having a structure provided with an electrode portion (resistor) m has been proposed (for example, JP-A-3-203754).

When this charging / cleaning blade is used, the charging function and the cleaning function can be substantially compatible if the position, shape, and electrical characteristics of the electrode portion are appropriate. However, when such a charging / cleaning blade is used for a long period of time while applying a DC voltage in particular, the surface of the electrode portion m is gradually contaminated by the toner k that slips through the blade little by little, so that the photoreceptor is not charged. There is a problem that it becomes uniform and eventually causes image quality defects such as uneven density and black streaks.

That is, in the cleaning device e,
The cleaning efficiency of the cleaning blade i is close to 100%, but a slight vibration is generated during the cleaning operation of the blade i, so that the toner k accumulated at the edge of the blade passes through the blade though it is small. However, the amount of the toner that slips through the cleaning blade in this manner is much smaller than that of the toner that slips through the blade in the state of so-called cleaning failure, and thus is generally collected by the developing device g or It does not cause any particular problem even if it slightly adheres to the background portion of the print sample.

Although the toner is less likely to slip through the cleaning blade in the initial stage, it becomes more and more noticeable when the number of prints increases and the blade edge wears or a minute crosstalk occurs. Tends to become. In addition, when some kind of impact is applied when the operation of the apparatus is stopped, the toner at the tip of the blade edge may be separated from the edge by the vibration, and the contact state of the edge with the photoconductor may be slightly changed. In such a case, the contact state of the grade edge is restored from the next start, and some toner may slip through the blade edge in a very short time until the blade is stably cleaned.

By the way, the charge polarity of the residual toner on the photoconductor reaching the cleaning blade is often opposite to the charge polarity of the toner required for the system, or almost not charged. Although this is not a serious problem in a general cleaning device, it causes the following problems in the charging / cleaning blade c.

That is, assuming that a negative DC voltage is applied to the charging / cleaning blade and the toner having passed through the cleaning blade has a reverse polarity, that is, a positive polarity in this case, the charging will be described. Since a negative voltage is applied to the electrode portion of the cleaning / cleaning blade, the electric field generated by the applied voltage attracts the toner to the electrode portion. In addition, a part of the toner that is hardly charged is gradually attached to the electrode portion. Then, such toner adhesion to the electrode portion progresses from the lower portion to the upper portion of the electrode portion as the number of prints increases, and eventually the surface (discharge area) of the electrode portion is covered with the toner. As a result, in such a state, the photoconductor cannot be normally charged in the portion of the electrode portion covered with the toner, so that the charge potential of the photoconductor becomes lower than the predetermined value, and as a result, the image quality is reduced. Black streaks occur on the top.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned various problems, and it is of a high quality that does not have image defects such as black streaks caused by blade slip-through toner for a long period of time. An object of the present invention is to provide an image forming apparatus capable of obtaining an image.

[0013]

The image forming apparatus of the present invention is a charging / charging device that elastically contacts the peripheral surface of an image carrier to remove residual toner on the image carrier and to charge the image carrier. In an image forming apparatus having a cleaning / combining blade, a charging device for charging the residual toner to the same polarity as the charging polarity by the blade is provided at the portion of the image carrier on the upstream side of the charging / cleaning blade. It is a thing.

As the above-mentioned charger, any charger can be used as long as it can charge the residual toner to the same polarity as the charging polarity by the charging / cleaning blade. For example, a corona charger or the like can be used. A non-contact type charger such as the above, a contact type charger using a semiconductive film, or the like can be used. From the viewpoint that ozone is not generated and a low applied voltage is sufficient, it is desirable to use a contact type charger using a semiconductive film.

[0015]

In the image forming apparatus according to the present invention, charging and
Toner that reaches the cleaning blade is always charged to the same polarity as the charging polarity of the blade by the charger before it reaches the cleaning blade, so not only for the blade itself but also for the electrode part provided on the blade. The image carrier does not adhere to it, and as a result, the image carrier can be uniformly charged to a predetermined potential.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples.

Embodiment 1 FIGS. 1 and 2 show a first embodiment of the present invention.
2 is a schematic configuration diagram of an electrophotographic process type image forming apparatus to which the present invention is applied, and FIG. 2 is an explanatory diagram of a main part of the apparatus of the present invention. In FIG. 1, reference numeral 1 denotes a photoconductor as an image carrier, and a charging / cleaning device 2, an exposure device 3, a developing device 4, and a transfer charging device 5 are sequentially arranged around the photoconductor 1. There is. Further, in the figure, 6 is a paper cassette, 7 is a paper, and 8 is a fixing device.

As shown in FIG. 2, the charging / cleaning combined device 2 comprises a charging / cleaning combined blade 20,
A corona charger 21 as a charger, voltage applying means 22 connected to the blade 20 and the charger 21, respectively.
23 and 23 form the main part. The charging / cleaning blade 20 is composed of an elastic blade main body 25 whose one end is fixed to a supporting member 24 such as a metal plate, and an electrode portion 26 provided on the surface of the main body facing the photoconductor. A negative DC voltage of about 600 to 1500 V is applied from the voltage applying means 22 to the electrode portion 26 of the blade 21. On the other hand, the corona charger 21 has the blade 2
0 is provided at a predetermined portion of the photoconductor 1 on the upstream side, and the corona wire has three to three voltage applying means 23 to
A negative DC voltage of about 5 kV is applied. In the figure, 9 is toner and 27 is a film seal member for preventing toner scattering.

Image formation by the apparatus of this embodiment is performed as follows. That is, after the photosensitive member 1 is charged to a predetermined potential by the blade 20 in the charging / cleaning device 2, the charged surface of the photosensitive member 1 is exposed by the exposure means according to image information (laser beam exposure). Etc.) to form an electrostatic latent image. Toner is attached to the electrostatic latent image by the developing device 4 to form a toner image. The toner image on the photoconductor 1 is transferred from the paper cassette 6 onto the paper 7 superposed on the photoconductor 1 by the electrostatic action of the transfer charging device 5 or the like. The toner image transferred onto the sheet 7 is fixed on the sheet by the fixing device 8, and thus a fixed image is obtained.

In the apparatus of this embodiment, the toner remaining on the photoconductor 1 is removed and cleaned by the charging / cleaning device 2. That is, the residual toner 9 is negatively charged by the corona charger 21 and then scraped off by the blade 20. Further, even if the negatively charged toner that reaches the blade 20 slips through the blade, it does not adhere to the electrode portion 26 to which the negative voltage is applied.

When an image was formed by the apparatus of this embodiment, black streaks did not occur on the image even if the number of prints increased, and a good image could be obtained.

Example 2 and Comparative Example FIG. 3 shows a second example of the present invention. The apparatus of this example has the same configuration as that of Example 1 except that a semiconductive film charger 28 is applied instead of the corona charger 21 of Example 1 as the charger in the charging / cleaning device 2. is there.

In the semiconductive film charger 28, the tip of the flexible semiconductive film having a volume resistivity of 10 ³ to 10 ¹⁰ Ω · cm is brought into contact with the photoconductor 1 to form the sealing member in the first embodiment. It is provided in substantially the same form as 27. As the semi-conductive film, polyester, polyamide, polyethylene, polycarbonate, polyolefin, polyurethane, fluororesin and other synthetic resin film material, by dispersing a powdery conductive substance such as conductive carbon black, the volume resistivity A film molded so as to be used is used. In consideration of direct contact with the photoconductor 1, the semiconductive film preferably has a thickness of about 50 to 500 μm and a tensile elastic modulus of about 10 to 280 kg / mm ² .

The film of the semiconductive film charger 28 is applied to the film by the voltage applying means 23, for example, 0.6 to 1.5 k.
A negative DC voltage of about V is applied. In this case, the residual toner 9 on the photoconductor 1 is charged to a negative polarity by the discharge between the semiconductive film of the charger 28 and the photoconductor. The charge amount at that time is about 4 to 6 μC / g.

Also in the apparatus of this embodiment, good image formation can be performed in the same manner as in the first embodiment. And the photoconductor 1
The toner 9 remaining on the top is charged by the charger 28 and then removed by the blade 20. Further, even if the toner after charging passes through the blade 20, it does not adhere to the electrode portion 26 of the blade 20 as in the first embodiment.

Next, in order to confirm the image forming performance (image quality maintaining property) in the apparatus of the second embodiment, the following test was conducted.

First, the apparatus of this embodiment was constructed by setting the charging / cleaning apparatus 2 and the like under the following conditions (see FIG. 4). <Blade body 25> -Material: Urethane rubber (hardness 70 °) -Free length L: 7.5 mm-Thickness t: 2 mm-Setting angle SA: 22 ° -Bite amount N: 1.2 mm-Working angle WA: 10 ° ・ Contact pressure NF: 3.4gf / mm ・ Nip width I: 60μm

<Electrode part 26> -Coating film thickness T: 10 μm-Volume resistivity of the conductive layer 26a: 10 ⁰ Ωcm-Volume resistivity of the conductive layer 26b: 10 ⁶ Ωcm-The tip position E of the electrode part : 0.1 from the blade edge tip
5mm ・ Applied voltage: DC-1.1kV <Charger 28> ・ Film material: Fluorine resin ・ Thickness: 0.1mm ・ Volume resistivity: 10 ⁴ Ω ・ cm ・ Tensile modulus: 130kg / mm ²・ Applied voltage : DC-900V

<Photoreceptor 1> • Organic photoreceptor drum • Drum diameter: 30 mm <Toner> • Average particle size: 7 μm • Charging polarity: Negative

For comparison, the device shown in FIG. 5 was used.
That is, the device as a comparative example has the same configuration as that of the second embodiment except that the seal member 27 (material: urethane) of the first embodiment is provided in place of the semiconductive film charger 28 of the second embodiment. Is.

When an image forming test was carried out by the apparatus of this embodiment and the apparatus of the comparative example under such a condition, an extremely thin black streak was confirmed in the reference apparatus when the number of printed sheets was about 1000, and a stage of 5000 sheets was confirmed. In contrast, black streaks of a level that can be visually confirmed were generated, whereas in the apparatus of this example, black streaks were hardly seen even at the printing stage of 5000 sheets, and it was confirmed that good image quality was obtained.

[0032]

As described above, according to the present invention,
Since the residual toner on the image carrier does not adhere to the charging / cleaning blade especially to the electrode part thereof, the image carrier can always be uniformly charged to a predetermined potential, and therefore black stripes and the like can be maintained for a long time. It is possible to stably form a high-quality image with no image defects.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus to which the present invention is applied.

FIG. 2 is an explanatory diagram showing an example (embodiment 1) of a main part of the device of the present invention in FIG.

FIG. 3 is an explanatory view showing another example (embodiment 2) of the main part of the device of the present invention in FIG.

4A and 4B are reference views showing the contents of setting conditions of the apparatus of FIG. 3, FIG. 4A is an overall view of a charging / cleaning blade, and FIG. 4B is an enlarged view of part B of FIG. 4A.

FIG. 5 is an explanatory diagram showing a main part of a comparative example device.

FIG. 6 is a schematic configuration diagram showing a conventional image forming apparatus.

7 is an explanatory diagram showing an example of a main part of the apparatus shown in FIG.

8 is an explanatory diagram showing another example of the main part of the apparatus of FIG.

[Explanation of symbols]

1 ... Image bearing member (photoreceptor), 9 ... Toner, 20 ... Charging / cleaning blade, 21, 28 ... Charger, 22,
23 ... Voltage applying means.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location G03G 15/22 101 Z 21/10 21/06 (72) Inventor Yuka Nakayama 2274 Hongo, Ebina City, Kanagawa Prefecture Address inside Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. An image forming apparatus having a charging / cleaning blade for elastically contacting a peripheral surface of an image carrier to remove residual toner on the image carrier and to charge the image carrier. An image forming apparatus characterized in that a charging device for charging the residual toner to the same polarity as the charging polarity of the blade is provided at the upstream side of the cleaning / cleaning blade. 2. The apparatus according to claim 1, wherein the charger has a flexible volume resistivity of 10 ³ to 10 ¹⁰ Ω · cm.
The image forming apparatus is a semi-conductive film of. 3. The image forming apparatus according to claim 2, wherein the semiconductive film is provided in a form that functions as a seal member for preventing toner contamination.