JPH04194891A - Picture forming device - Google Patents

Abstract

PURPOSE:To prevent a toner from sticking at the time of inversion developing by forming an insulating layer of specific thickness or more, anodizing a surface of a material pipe, or an insulating layer, formed of a synthetic resin-made film, on a roll contact part of a sensitized drum. CONSTITUTION:An insulating layer 12 of 15mum or more thickness is formed by anodizing a surface of a material pipe 10 on at least a roll contact part 1b of a sensitized drum 1. Consequently, a charge is prevented from easily escaping at the time of charging, and surface potential of the contact part 1b is prevented from decreasing to a limit potential or less of sticking a toner. Since the insulating layer 12 is integrally formed by anodizing a surface of metal for constituting the material pipe 10, large mechanical strength is provided in addition to a large film thickness to hold a space between the sensitized drum 1 and a developing roller 2 without wearing for a long period. On the other hand, in the case of forming the insulating layer 12, formed of a synthetic resin-made film, on the contact part 1b, the charge is prevented from easily escaping at charging time, and the surface potential of the contact part 1b is prevented from decreasing to the limit potential or less. The insulating layer 12, provided with large mechanical strength, endures use for a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an image forming apparatus such as an electrostatic copying machine or a racer beam printer.

<Prior Art> In the above image forming apparatus, as a means for visualizing an electrostatic latent image corresponding to an original image formed on the surface of a photoreceptor drum using toner, the photoreceptor drum is generally used. A developing roller is used which is disposed facing and separated from the developing roller by a predetermined distance. This developing roller holds a developer containing toner and rotates in accordance with the rotation of the photoreceptor drum to supply the developer to the photoreceptor drum, thereby allowing the electrostatic latent image to be developed by the toner. It is the one that carries out the transformation.

In the image forming apparatus using the above-mentioned developing roller, if the distance between the photosensitive drum and the developing roller changes, the amount of developer supplied to the photosensitive drum changes, causing image defects such as density unevenness in the formed image. Therefore, it is necessary to always maintain a constant distance between the two.

As a means for keeping the distance between the developing roller and the photoreceptor drum constant, for example, as shown in FIG. used. This spacer roller 93.93 has a diameter slightly larger than that of the developing roller 9, and maintains the distance between the photoreceptor tram 92 and the developing roller 91 at a dimension corresponding to half of the difference in diameter. It is something.

The photosensitive tram 92 is made by laminating a photosensitive layer on which an electrostatic latent image is formed on the surface of a metal tube such as aluminum, and prevents the photosensitive layer from peeling off due to friction with spacer rollers 93, 93, etc. In order to prevent this, normally, as shown in the same figure, roller contact portions 92b, 92b on which no photosensitive layer is formed are provided adjacent to the photosensitive portion 92a on which a photosensitive layer is formed, and the roller contact portions 92b are , 92b are brought into contact with spacer rollers 93, 93. Therefore, in the roller contact portions 92b, 92b, the surface of the raw pipe or
The base layer formed as necessary between the photosensitive layer and the raw tube is exposed.

<Problem to be solved by the invention> Is there usually a photoconductive anodized film formed on the surface of the tube in order to stabilize the flow of charge from the photosensitive layer? Since the tube is thin at 5 μm or less, if the surface of the tube is exposed at the roller contact portions 92b, 92b, charges are likely to escape when the photoreceptor tram 92 is charged. Therefore, the surface potential of the roller contact portions 92b, 92b during charging is significantly lower than the surface potential of the photosensitive portion 92a.

In the case of reversal development, on the part of the surface of the photosensitive area g2B where the surface potential has decreased to a specific set value due to exposure,
Since toner is attached to the rollers, the surface potential of the roller contact portions c+2b and 92b decreases significantly.
When the above set value is approached, there is a problem that toner floating around the boundary between the photosensitive portion 92a and the roller contact portions 92b, 92b may adhere to the roller contact portions 92b, 92b.

When toner adheres to the roller contact parts 92b, 92b, the roller contact parts 92b, 92b and the spacer roller 93
．． Since the toner will be caught between the photosensitive drum 92 and the developing roller 93, the distance between the photosensitive drum 92 and the developing roller 91 will be distorted.

Further, the attached toner may scatter again, causing image defects such as toner scattering and fog in the formed image.

On the other hand, if the base layer is exposed at the roller contact portions 92b, 92b, the base layer is mainly an insulator such as a vapor-deposited film of metal oxide.
Charge is difficult to escape when charged.

Therefore, the surface potential of the roller contact portions 92b, 92b during charging does not decrease much, and toner adhesion does not occur during reversal development. However, the base layer has a spacer roller of 93.9
Since it is easily worn out by friction with 3, it cannot withstand long-term use; however, in a short period of time, the surface of the raw tube becomes exposed, causing the above-mentioned problem due to toner adhesion.

According to studies conducted by the present inventors, when the surface potential of the roller contact portion exceeds a certain value higher potential (hereinafter referred to as "limit potential") than the set value for reversal development, the roller It has been found that toner does not adhere to the roller contact portion, or that toner adheres to the roller contact portion when the surface potential of the roller contact portion falls below the above-mentioned limit potential and approaches the set value. For example, if the charging potential of the photosensitive area during reversal development is -600 to -900V, the set value is -I C1OV.
, the above limit potential is -170 to -200V
If the surface potential of the roller contact portion is close to this limit potential or higher, toner adhesion will not occur, or if the surface potential of the roller contact portion falls below the limit potential and approaches -100V, toner adhesion will not occur. It happens.

The present invention has been made in view of the above circumstances, and
It is an object of the present invention to provide an image forming apparatus in which no toner adheres to the roller contact portion of a photoreceptor drum during reversal development, and there is no risk of the above-mentioned problem caused by toner adhesion.

<Means for Solving the Problems> In order to solve the above problems, an image forming apparatus of the present invention has the following features:
The photosensitive drum is characterized in that an insulating layer with a thickness of 15 μm or more is formed by anodizing the surface of a raw tube at least on the roller contact portion.

Further, according to another aspect of the present invention, the roller contact portion includes:
An image forming apparatus is provided in which an insulating layer made of a synthetic resin film is formed.

<Function> According to the image forming apparatus of the present invention having the above configuration, an insulating layer with a thickness of 15 square meters or more formed by anodizing the surface of the raw tube is provided on at least the roller contact portion of the photosensitive drum. is formed, so it is difficult for charges to escape when charged. Therefore, the surface potential of the roller contact portion does not fall below the above-mentioned limit potential for toner adhesion. In addition, the above-mentioned insulating layer is created by anodizing the surface of the metal that makes up the tube.
Because it is formed integrally with the base pipe, the mechanical strength is strong due to the thick coating, and even after long-term use,
It does not wear out easily like traditional underlayers.

On the other hand, according to another aspect of the present invention, the roller contact portion includes:
Since an insulating layer made of a synthetic resin film is formed, charges are difficult to escape when charged.

Therefore, the surface potential of the roller contact portion does not drop below the limit potential. Furthermore, since the insulating layer is made of synthetic resin and has higher mechanical strength than the base layer, which is a vapor-deposited film, it will not wear out as easily as the base layer, even if used for a long period of time. Moreover, when the film is worn out, a new film can be applied to the roller contact area.

<Embodiment> An image forming apparatus of the present invention will be described below with reference to drawings showing a laser beam printer as an embodiment.

As shown in FIG. 3, in the laser beam printer of this embodiment, the photoreceptor drum 1 is
A charger T1 for charging the surface of the photoreceptor tram 1, a laser beam optical system (not shown) that exposes the surface of the photoreceptor tram 1 as shown by the dotted chain arrow in the figure, and a laser beam optical system (not shown) that exposes the surface of the photoreceptor tram 1 to A developing device that develops the formed electrostatic latent image, a transfer charger T2 that transfers the toner image formed on the photoreceptor drum 1 by development onto a sheet of paper, and a transfer charger T2 that transfers the toner image and the sheet onto the photoreceptor tram 1. A separation charger T3 that separates the toner from the photosensitive drum 1 and a cleaning device C that removes the toner remaining on the photosensitive drum 1 are provided.

Then, the surface of the photoreceptor drum 1 rotating at a constant speed is uniformly charged by a charging charger T1, exposed to light by a laser beam optical system to form an electrostatic latent image, and the electrostatic latent image is converted into a toner image by a developing device. After the toner image is visualized as a toner image, a transfer charger T2 transfers this toner image onto a sheet of paper that has been conveyed through a paper conveyance path R1. By removing and cleaning the toner remaining on the surface of the body drum 1 by the cleaning device C,
One cycle of image formation is completed.

Further, the paper peeled off from the photoreceptor drum 1 is guided to the fixing device F via the paper conveyance path R2, and after the toner image is fixed thereon, it is discharged from the apparatus.

The developing device includes a casing D1 containing a developer therein.
, a developing roller 2 rotatably disposed in an opening D2 formed in a portion of the casing D1 facing the photoreceptor drum 1, and a reservoir for stirring the developer rotatably disposed inside the casing D1. stirring blade D3 and this stirring blade D
The toner hopper D4 is provided above the toner hopper D4 for replenishing toner consumed during image formation.

As shown in FIG. 1, the photosensitive drum 1 includes a raw tube 10 made of metal such as aluminum, and a photosensitive portion 1a on which a photosensitive layer 11 is formed is provided on the surface of the raw tube 10. Roller abutments Nlb, 1b on which the photosensitive layer 11 is not formed are provided adjacent to both sides of the photosensitive portion 1a. The roller contact parts 1b, 1b are formed by forming an insulating layer 12 on the surface of the raw tube 10, and the insulating layer 12 is formed by anodizing the surface of the raw tube 10 and has a thickness of 15 μm or more. or a synthetic resin film.

The insulating layer 12 formed by anodizing the surface of the tube 10 may be formed only on the roller contact portions 1b and lb, or may be formed in order to stabilize the flow of charge from the photosensitive layer 11. In addition, like the conventional anodized film, the raw tube
It may be formed throughout. The insulating layer 12 is connected to the raw pipe 10
When forming the entire insulating layer 12, the entire insulating layer 12 is
In addition to having a thickness of 15 .mu.w or more, the photosensitive portion 1a of the insulating layer 12 may have a thickness of about 5 .mu.m as in the prior art, and only the roller contact portions 1b, 1b may have a thickness of 15 .mu.m or more.

The reason why the thickness of the insulating layer 12 is limited to 15 μm or more is as follows. That is, the thickness of the insulating layer]2 or 1
If it is less than 5 mm, the potential tends to escape when the photoreceptor tram unit is charged, and the roller contact portion]b.

The surface potential during charging of 1b has decreased significantly and is below the limit potential during reversal development, causing toner to be floating mainly around the boundary between the photosensitive area]a and the roller contact areas 1b and lb. It becomes easier to attach the shield to the roller contact portions 1b, 1b. On the other hand, if the thickness of the insulating layer 12 is 15 μm or more, the surface potential of the roller contact portions 1b, lb during charging will not be lower than the above-mentioned limit potential. There is no risk of it sticking.

The upper limit of the thickness of the insulating layer 12 is not particularly limited, or if the insulating layer 12 is formed over the entire tube 10 and the thickness of the entire insulating layer 12 is 15 μm or more, the upper limit of the thickness of the insulating layer 12 is not particularly limited.
The thickness is preferably 30μ0 or less. When the thickness of the insulating layer 12 exceeds 30 μm, the electric charge of the exposed portion is transferred from the photosensitive layer 11 to the base tube 10 during exposure.
There is a risk that the electrostatic latent image will not be able to be formed.

On the other hand, when forming the insulating layer 12 only on the roller contact parts 1b, 1b, or forming the insulating layer 12 on the entire tube 10, only the roller contact parts 1b, 1b have a thickness of 15 μm.
When the thickness is greater than or equal to m, the thickness of the insulating layer 12 of the roller contact portions 1b and lb is preferably 50 μm or less. If the thickness of the insulating layer 12 exceeds 50 μI, there will be problems in manufacturing.

The insulating layer 12 made of a synthetic resin film is formed by adhering the synthetic resin film to the roller contact portions 1b, lb. Various conventionally known synthetic resin films can be used, especially ultra-thin electrical insulating tape made of polyethylene terephthalate, which has excellent insulation properties, mechanical strength, heat resistance, etc., and has a constant thickness. Moreover, it has a small expansion and contraction rate due to heat, so it is suitably used.

When providing the insulating layer 12 made of the above-mentioned synthetic resin film, in order to stabilize the flow of charge from the photosensitive layer 11, an anodized film similar to the conventional one is formed on the entire surface of the tube 10, Although it is preferable to form the insulating layer 12 by pasting a synthetic resin film thereon, the anodized film may be formed only on the photosensitive area 1a.

As shown in FIG. 2, the photosensitive drum 1 includes a blank tube 10
It is attached to a shaft 14 rotatably supported by the main body of the copying machine via flange members 13, 13 fitted in openings at both ends of the copying machine.

As shown in FIGS. 1 and 2, the developing roller 2 is attached to a shaft 3, and by rotatably supporting the shaft 3 on a cane D1 of the developing device, an opening D2 of the cane D1 is opened. is rotatably arranged.

On both sides of the developing roller 2 on the shaft 3, there are photoreceptor drums 1.
A spacer roller 4.4 is provided in contact with the roller contact portions 1b, 1b to maintain a constant distance between the photoreceptor tram 1 and the developing roller 2. This spacer roller 4.4
is slightly larger in diameter than the developing roller 2, and the distance between the photoreceptor tram 1 and the developing roller 2 is maintained at a dimension corresponding to half of the difference in diameter.

In the image forming apparatus of this embodiment, which is composed of the above-mentioned parts, the roller contact part 1b of the photoreceptor drum 1;

An insulating layer 12 with a thickness of 15 μs or more, or an insulating layer 12 made of a synthetic resin film, is formed on the surface of the raw tube 10 exposed in step 1b by anodizing the surface of the raw tube 10. Therefore, it is difficult for potential to escape during charging, and the roller contact portion 1b.

There is no risk that the surface potential of 1b will drop significantly.

Therefore, during reversal development, the roller contact portion 1b.

Since toner does not adhere to 1b, the distance between the photoreceptor drum 1 and the developer roller 2 may be distorted, and the adhered toner may scatter again, causing image defects such as toner scattering and fogging on the formed image. It never happens.

Furthermore, since the former insulating layer 12 is formed integrally with the raw tube 10 by anodizing the surface of the metal constituting the raw tube 10, it has a thick film thickness. It has strong mechanical strength and does not wear out as easily as the base layer, even after long-term use. On the other hand, the latter insulating layer 12 is made of synthetic resin and has stronger mechanical strength than the base layer, so it does not wear out as easily as the base layer even if used for a long period of time. Another advantage is that when the film wears out, a new film can be applied to the roller contact area.

Experimental Example 1 The surface of a raw tube made entirely of aluminum and having a length of 344 mm and an outer diameter of 78 mm was anodized to form an insulating layer with a thickness of 15 μm on the entire surface of the raw tube. Next, leave 10 angles at both ends on the surface of this raw pipe,
A photosensitive layer coating solution was applied and dried to form a photosensitive layer with a width of 324 mm, and adjacent to the left and right sides of the photosensitive area,
A photoreceptor drum having a roller contact portion with a width of 10 mm on which no photoreceptor layer was formed was produced.

Experimental Example 2 A photoreceptor drum was produced in the same manner as in Experimental Example 1, except that the thickness of the insulating layer was 30 μm.

Experimental Example 3 The surface of the same raw tube as used in Experimental Example 1 above was anodized to form an anodized layer with a thickness of 5 μm over the entire surface of the raw tube. Next, a coating solution for a photosensitive layer is applied to the surface of this raw tube, leaving 10+ nm at both ends, and dried, forming a photosensitive area with a width of 324 mm on which a photosensitive layer is formed, and adjacent areas on the left and right sides of the photosensitive area. A roller abutting portion with a width of 10 mm on which no photosensitive layer was formed was formed. Then, an electrically insulating tape made of polyethylene terephthalate (trade name: "Polyester Tape" manufactured by Miki Kagaku Kogyo Co., Ltd., manufactured by Miki Kagaku Kogyo Co., Ltd.), which will serve as an insulating layer, is attached to the above-mentioned roller contact portion, and the photoreceptor drum is Created.

Experimental Example 4 Experimental Example 1 above except that the thickness of the insulating layer was 5 μm.
A photoreceptor drum was produced in the same manner.

Evaluation test The surface of the tungsten wire was plated with gold at a position 9 to 10 m+a from the surface of the photoreceptor drum to be attached.
A char 7 wire with a diameter of 60 μm is stretched parallel to the axis of the photoreceptor drum, and a tungsten wire with a diameter of 50 μm is placed in front of the charge wire at a position 1.5 degrees from the surface of the photoreceptor drum. The photoreceptor drums prepared in Experimental Examples 1 to 4 above were attached to a racer beam printer equipped with a charging device in which 20 grid wires were stretched parallel to the axis of the photoreceptor drum at intervals of 11111I. Then, by applying a voltage of 15 kV to the charge wire and 1700 V to the grid wire, the surface of the photoreceptor drum was charged to 1700 V using a scorotron method, and a probe for measuring the charged potential (manufactured by Monroe) was used. , on the boundary line between the photosensitive part and the roller contact part on the surface of the photoreceptor drum, from the boundary line to the roller contact part side +2.5+n+e and +
The charged potential was measured at a position of 5.0 mm, a position of -1 m+a and -10+ nm from the boundary line toward the photosensitive area. The results are shown in Figure 4. In addition, in the figure, -・-・- is Experimental Example 1, -muumu is Experimental Example 2, -△-△- is Experimental Example 3, -
0-O- indicates the results of Experimental Example 4.

In addition, after image formation was performed with the photosensitive drums of Experimental Examples 1 to 4 installed in the racer beam printer, the presence or absence of toner adhesion at the roller contact portions was visually observed.

From the results shown in the above figure, in Experimental Example 2.3, the surface potential at the roller contact portion was more than 100V higher than the set value of -100V for toner adhesion during exposure. Upon observation, no toner was observed to adhere to the roller contact portion.

In Experimental Example 1, +2.
At the 5mm position, the surface potential or the above setting value (-100
The potential was about 70V higher than V), or +5.0
At the mm position, the voltage exceeded the set value (-100V). However, by visual observation, no toner was observed to adhere to the roller contact portion. This is the side of the roller abutting part near the boundary line, or as mentioned above, it is 70° below the set value.
Since the toner has a surface potential as high as V, it is thought that the cause may be toner floating near the boundary line of the photosensitive area, or toner migrating to the roller contact area to prevent it from adhering.

On the other hand, in Experimental Example 4, the surface potential has already decreased to the above set value at a position +2.5 mm from the boundary line toward the roller contact area, and even when visually observed, the surface potential has already decreased to the above set value. Adhesion of toner was observed on t2.

<Effects of the Invention> The image forming apparatus of the present invention is configured as described above, and at least the roller contact portion of the photoreceptor drum has a material tube whose surface is anodized and has a thickness of 15 μm or more. According to another aspect of the present invention, an insulating layer made of a synthetic resin film is formed on the roller contact portion. Therefore, when charging, it is difficult for charges to escape, and the surface potential of the roller contact area does not fall below the limit potential for toner adhesion, so toner adhesion does not occur.
Due to the distance between the photoconductor tram and the developing roller due to toner adhesion, or the adhering toner scattering again.
Image defects such as toner scattering and fogging will not occur.

In addition, as mentioned above, the former insulating layer is formed integrally with the base tube by anodizing the surface of the metal that makes up the base tube, so this layer is thick. It has strong mechanical strength and does not wear out as easily as the base layer, even after long-term use. On the other hand, the latter insulating layer is made of synthetic resin and has stronger mechanical strength than the base layer, which is a vapor-deposited film, so it does not wear out as easily as the base layer, even after long-term use, and when it does wear out. new film,
It also has the advantage that it only needs to be pasted on the floor contact area.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a photosensitive drum and a developing roller, which are the main parts of a racer beam printer as an embodiment of the image forming apparatus of the present invention, and FIG. 2 is a plan view of the photosensitive drum and developing roller. , FIG. 3 is a schematic diagram showing the internal configuration of the laser beam printer of the above embodiment, and FIG. 4 is a surface potential near the boundary between the roller contact part and the photosensitive part in an experimental example for confirming the effects of the present invention. FIG. 5 is a plan view of a photosensitive drum and a developing roller in a conventional image forming apparatus. 1... Photosensitive drum, 1b... Roller contact portion, 10.
...Main tube, 11...Photosensitive layer, 12...Insulating layer, 2...Developing roller, 4...Spacer roller.

Claims (1)

[Scope of Claims] 1. A photoreceptor drum having a metal tube, a photosensitive layer laminated on the surface of the tube and on which an electrostatic latent image corresponding to a document image is formed, and the photoreceptor. A developing roller that supplies developer to the drum to visualize the electrostatic latent image contacts a roller abutting portion on the surface of the photosensitive drum on which no photosensitive layer is formed,
In an image forming apparatus equipped with a spacer roller that maintains a constant distance between the photosensitive drum and the developing roller, an insulating layer with a thickness of 15 μm or more, which is formed by anodizing the surface of the raw tube, is provided at least on the roller contact portion. An image forming apparatus characterized by forming: 2. A photoreceptor drum having a metal tube and a photosensitive layer laminated on the surface of the tube to form an electrostatic latent image corresponding to the original image, and supplying developer to the photoreceptor drum. The developing roller that visualizes the electrostatic latent image is brought into contact with the roller abutting portion on the surface of the photosensitive drum where no photosensitive layer is formed,
An image forming apparatus equipped with a spacer roller that maintains a constant distance between the photosensitive drum and the developing roller, characterized in that an insulating layer made of a synthetic resin film is formed on the roller contact portion. Device.