JPH0553354A - Image forming device - Google Patents

Abstract

PURPOSE:To suppress ozone generation and to uniformize electrification of a photosensitive means. CONSTITUTION:The device is provided with a positive electrification type photosensitive means 1 to form an electrostatic latent image, an electrification means 2 to positively electrify the photosensitive means 1, a developing means 3 to carry out reversal development of the electrostatic latent image formed on the photosensitive means 1 with the supply of positively electrified toner 28, a negatively electrifying transfer means 4 to transfer a toner image developed by the developing means 3 to the image forming paper 5 by abutting the toner image to a surface of the image forming paper on the side not facing to the photosensitive means 1.

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 utilizing reversal development.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 3, in a negative charging reversal development method, a photosensitive surface 21 is provided around a photosensitive drum 20.
And a developing roller 25 for reversing and developing the electrostatic latent image formed by exposure.
And a transfer electrode 26 for transferring the developed toner image to the image forming paper 5 and the like. The charging electrode 22 and the developing roller 25 are connected to charging devices 23 and 24 for negative charging, and the transfer electrode 26 is connected to a charging device 27 for positive charging.

Explaining the principle of the system, first, the photosensitive drum 2 rotating in the arrow direction by the charging electrode 22.
The photosensitive surface 21 of 0 is negatively charged. Next, when the original image is exposed on the charged photosensitive surface 21, the electric charge of the light-exposed portion is neutralized to be in an uncharged state, and the negative electric charge remains in the non-exposed portion. Then, an electrostatic latent image is formed on the photosensitive surface 21. The developing roller 25 is attached to the electrostatic latent image.
When the negatively charged toner 28 is brought close to, the toner 28 receives a repulsive force from the negative charge on the photosensitive surface 21,
Only attaches to uncharged parts. That is, the toner 28 adheres to the exposed area to form a toner image.

Next, in order to transfer the toner image onto the image forming paper 5, the transfer electrode 26 is positively charged to positively charge the image forming paper 5, and the electrostatic force causes the toner image to form on the photosensitive surface 21. It is attached to the forming paper 5.

[0005]

The method using the charging electrode 22 that is negatively charged as described above has a problem that the amount of ozone generated is large due to the negative charging. Since ozone harms the human body and oxidizes the photoconductor, it is harmful to the environment and the durability of the image forming apparatus. In order to solve this, there is a method in which a charging roller or a charging brush is brought into contact with the photosensitive surface 21 instead of the charging electrode 22 to charge the photosensitive surface 21. The method using the charging roller is inferior in terms of material uniformity, product management, cost and stability in order to uniformly charge, and requires a complicated auxiliary means such as AC bias. Moreover, since the charging brush has low durability, it is difficult to be practically used.

In view of such problems of the conventional image forming apparatus, it is an object of the present invention to provide an image forming apparatus capable of suppressing the amount of ozone generation and uniformly charging the photosensitive means. To do.

[0007]

SUMMARY OF THE INVENTION The present invention is a positive charging type photosensitive means for forming an electrostatic latent image, a charging means for positively charging the photosensitive means, and a static means formed on the photosensitive means. The toner image developed by the developing means by bringing the latent image into reversal development by supplying positively charged toner and the surface of the image forming sheet that does not face the photosensitive means. For transferring to the image forming paper,
The image forming apparatus includes a transfer unit that is negatively charged.

[0008]

According to the present invention, the charging means positively charges the positive charging type photosensitive means, and the developing means reversely develops the electrostatic latent image formed on the photosensitive means by supplying the positively charged toner. Then, the transfer means makes contact with the surface of the image forming paper that does not face the photosensitive means to transfer the toner image onto the image forming paper.

[0009]

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

FIG. 1 is a side view of an image forming apparatus according to an embodiment of the present invention. That is, the optical unit 15 that forms the image light of the original read by the reader and sends the image light to the lower part on the upper part of the main body of the image forming apparatus.
Is provided.

Below the optical unit 15, a photosensitive drum 20 having a conductive substrate having a photosensitive surface 1 which is a photosensitive layer sensitive to the image light is provided so as to rotate in the direction of the arrow. ing. The photosensitive surface 1 and the photosensitive drum 20 constitute a photosensitive means. Around the photosensitive drum 20, a charging electrode 2 for performing corona discharge is arranged in order to positively and primaryly charge the photosensitive surface 1 upstream of a portion of the document exposed to the image light, and the charging electrode 2 is the charging electrode 2. Is connected to a first charging device 6 for positively charging.

A developing device 30 and a developing roller 3 built in the developing device 30 for supplying the toner 28 to the electrostatic latent image formed on the photosensitive surface 1 are arranged downstream of the portion where the image light strikes. A second charging device 7 for positively charging the developing roller 3 is connected to the developing roller 3, and a toner hopper 31 for replenishing the toner 28 is attached to the developing device 30.

A registration roller 34 for supplying the image forming paper 5 is arranged downstream of the developing roller 30.
A paper feed cassette 32 and a paper feed roller 33 for replenishing the image forming paper 5 are provided on the right side of the registration roller 34 in the drawing.

Further downstream of the registration roller 34,
A transfer roller 4 for transferring the toner image onto the image forming paper 5 is arranged so that it can come into contact with the surface of the image forming paper 5 that does not face the photosensitive surface 1, and the transfer roller 4 is attached to the transfer roller 4. A third charging device 8 for negatively charging is connected.

The photosensitive surface 1 is provided on the downstream side of the transfer roller 4.
Cleaning unit 3 for removing residual toner of
6 is arranged, and on the left side of the transfer roller 4 in the drawing, a conveyor belt 35 for conveying the transferred sheet is arranged.
On the left side of the transport belt 35, a fixing device 37 for fixing the toner transferred to the image forming paper 5 is provided.

As the photosensitive means, any photosensitive body can be used as long as it is a positive charging type photosensitive body having a photosensitive layer provided on a conductive substrate.

Examples of the conductive substrate include simple metals such as aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, titanium, nickel, palladium and indium, alloys such as stainless steel and brass, or the above. Examples thereof include insulating materials such as plastics and glass, in which metal and aluminum iodide, tin oxide, ITO, etc. are conductively coated by vapor deposition, coating, laminating method or the like.

The conductive substrate may be in the form of a sheet, a drum, or the like, as long as the substrate itself has conductivity or the surface of the substrate has conductivity. Also,
The substrate preferably has sufficient mechanical strength when used.

As the photosensitive layer, any photosensitive member such as selenium, selenium-tellurium, selenium-arsenic, amorphous silicon, cadmium sulfide, phthalocyanine, etc. can be used as long as it is a positive charging type photosensitive member, but sensitivity, stability, From the viewpoints of harmlessness and cost, the positively charged organic photoreceptor is most suitable.

The photosensitive layer of the positive charging type organic photoreceptor is formed of a resin layer containing a charge generating material which absorbs light to generate charge carriers and a charge transporting material which moves the generated charge carriers. ..

Next, metal-free phthalocyanine is used as the charge generating material, and the following formula (2) is used as the electron transferring material of the charge transferring material.
An example of a method for producing a photoreceptor using the diphenoquinone compound represented by

[0022]

[Chemical 2]

Example 1 (Single-layer type photosensitive layer) (Component) (Part) Metal-free phthalocyanine 1 Binder resin Polycarbonate 100 Diphenoquinone compound 60 N, N, N ', N' represented by the above formula (2) -Tetrakis (3-methylphenyl) -1,3-diaminobenzene 40 Each of these components was added to a predetermined amount of dichloromethane and dispersed for 2 hours with a paint shaker using stainless beads (2 mm diameter). The obtained dispersion liquid is 40 mm in diameter,
It was dip coated on an aluminum cylinder having a length of 250 mm and dried at 60 ° C. for 1 hour to form a photosensitive layer of 20 μm, thereby obtaining a single-layer type electrophotographic photosensitive member.

Next, the operation of the above embodiment will be described.

When copying is started by the image forming apparatus, the photosensitive drum 20 rotates in the direction of the arrow as shown in FIG. The charging electrode 2 is positively charged by the charging devices 6 and 7, and the charging electrode 2 uniformly charges the photosensitive surface 1 positively (for example, the surface potential is +680 V) by corona discharge. Photosensitive drum 2
When 0 rotates to the exposure position of the image signal, the photosensitive surface 1
In the area exposed to the light, the photocharged carriers neutralize the positive charge and become almost non-charged, and the positive charge in the area not exposed to the light is directly charged on the photosensitive surface 1.

In this way, a negative electrostatic latent image having a positive charge is formed on the surface of the photosensitive surface 1 which is not exposed to light,
The photosensitive drum 20 rotates toward the developing roller 3. On the other hand, the toner 28 on the developing roller 3 is positively charged by friction with the developing blade 9, and the developing roller 3 has a positive AC voltage lower than that of the charging electrode 2 (for example, the upper limit is +600 volts, the lower limit is +100 volts, the duty ratio is 50%, and the frequency is 50%). 1k
The toner 28 positively charged by the AC bias of a rectangular wave of Hz is caused to fly between the photosensitive drum 20 and the developing roller 3 and supplied to the photosensitive surface 1 on which the electrostatic latent image is formed. Since the toner 28 has the same polarity as that of the positively charged portion of the photosensitive surface 1, it is repelled by the repulsive force and is repelled from the photosensitive surface 1, and a part thereof is in the uncharged portion of the photosensitive surface 1 exposed to light. Adhere to.

In this way, a reversal developed toner image is formed on the photosensitive surface 1. At the same time when the photosensitive surface 1 further rotates, the image forming paper 5 is supplied from the registration roller 34 (see FIG. 1) between the photosensitive surface 1 and the transfer roller 4.
The transfer roller 4 is negatively charged (for example, -800 V) by the charging device 8 to press the paper 5 from the back surface of the toner image, and the positively charged toner 28 is transferred to the paper by electrostatic attraction. 5 Transfer to the surface. At this time,
The transfer roller 4 may be charged with a negative voltage smaller than that when a transfer electrode is used, and since corona discharge is not used, ozone is not generated at all.

Table 1 shows the case where the transfer roller 4 of the above embodiment is used, the case where the conventional transfer charger is used, and the case where the negative charging charger and the positive transfer charger using the conventional negative charging photoreceptor are used. And are the experimental results comparing the amount of ozone generated.

[0029]

[Table 1]

In the table, the photoconductor surface potential and the developing bias under the experimental conditions are the same. Regarding the transfer potential, the transfer roller applies a -800 volt bias potential, while the transfer charger applies -5.2 kV charge potential. As a result, the ozone generation amount is 0.4 ppm in the transfer roller, which is 1/5 of 2 ppm in the transfer charger. The 0.4 ppm of ozone is generated by corona discharge of the positive charging electrode.

Further, when the conventional negatively charged photoreceptor is used, ozone is generated at 4 ppm, and the amount of ozone generated is compared with that, and it is reduced to about 1/10.

Table 2 shows the experimental results for selecting the transfer potential of the transfer roller of the above embodiment.

[0033]

[Table 2]

In the table, the photoconductor surface potential and the developing bias under the experimental conditions are the same. When the transfer potential is changed, when the bias potential is deeper than -1000 V, the image density becomes low, and when the bias potential is shallower than -200 V, toner dust is generated, which is unsuitable.
As shown in the table, the bias potential is -1000 V to -2.
It may be set between 00 volts.

Although the transfer roller is used as the transfer means in the above-described embodiment, a belt to which a bias potential is applied may be contacted from the back surface of the sheet to transfer the transfer roller instead of the transfer roller.

Further, although the photosensitive layer in the above-mentioned embodiment is a single layer type photosensitive layer, it may be a laminated type photosensitive layer in which a charge generating layer and a charge transporting layer are laminated.

[0037]

As is apparent from the above description, the present invention has the advantage that the amount of ozone layer generated can be suppressed to a small level and the photosensitive means can be uniformly charged.

Further, the present invention has advantages that the amount of ozone generated is small and the reliability is high by using the positive charging type organic photoreceptor having excellent sensitivity and repetitive characteristics.

[Brief description of drawings]

FIG. 1 is a side view of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a schematic view of part of the embodiment.

FIG. 3 is a schematic view of part of a conventional image forming apparatus.

[Explanation of symbols]

 1 Photosensitive Surface 2 Charging Electrode 3 Developing Roller 4 Transfer Roller 5 Image Forming Paper 6 First Charging Device 7 Second Charging Device 8 Third Charging Device 10 Conductive Substrate 11 Photosensitive Layer 28 Toner 30 Developer

Claims (4)

[Claims] 1. A positive charging type photosensitive unit for forming an electrostatic latent image, a charging unit for positively charging the photosensitive unit, and an electrostatic latent image formed on the photosensitive unit are positively charged. The developing device for reversal development by supplying the toner charged to the surface of the image forming sheet and the surface of the image forming sheet on the side not facing the photosensitive device are brought into contact with each other to form the toner image developed by the developing device. An image forming apparatus comprising: a negatively-charged transfer unit for transferring to a sheet. 2. The image forming method according to claim 1, wherein the positive charging type photosensitive means is provided with a resin layer containing a charge generating material and a charge transport material as a photosensitive layer on a conductive substrate. apparatus. 3. The image forming apparatus according to claim 2, wherein the charge generating material is phthalocyanine. 4. The image forming apparatus according to claim 2, wherein the charge transport material contains a diphenoquinone derivative represented by the following formula (1) as an electron transport agent. [Chemical 1] (In the formula, R ^{1 to} R ⁶ represent hydrogen or an alkyl group, a substituted alkyl group, an alkoxy group, an aryl group, or a substituted aryl group.)