JPH0134205Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a heating mechanism for a photoreceptor drum used in an image forming apparatus using an amorphous silicon photoconductor layer as a photoreceptor, and more particularly to a heating mechanism for effectively preventing image deletion. Amorphous silicon-based photoconductor layers have high surface hardness, are sensitive to light on the long wavelength side, and have good sensitivity, so they are attracting attention as photoreceptors for electrophotography. However, in electrophotographic devices using such amorphous silicon-based photoconductor layers, repeated use makes the surface of the photoreceptor sensitive to humidity and easily absorbs moisture, resulting in a decrease in surface resistance. It has the disadvantage that the charge moves laterally, causing so-called image deletion. In order to prevent such image blurring, it has been proposed to provide a protective layer such as a-Six, C1 _- x, a-SiNx, etc. on the surface of the photoreceptor. However, the current situation is that it has not been possible to completely prevent image deletion. The present inventors have proposed that when repeating the steps of charging, image exposure, development, and transfer in an electrophotographic device using an amorphous silicon-based photoconductive layer, for example, an image forming device such as a laser printer or a copier,
It has been found that the above image deletion can be completely prevented by heating the surface of the photoreceptor. That is, the purpose of the present invention is to provide an image forming apparatus using an amorphous silicon-based photoconductive layer as a photoreceptor,
An object of the present invention is to provide a heating mechanism for effectively solving the problem of image blurring. According to the present invention, there is provided a hollow rotating photoreceptor drum having an amorphous silicon-based photoconductor on a conductive substrate, and hot air from a heat fixing area is blown into the inner space of the photoreceptor drum to coat the photoconductive layer. The photoreceptor drum includes a hot air blowing mechanism for heating the drum to a temperature of 35 to 40°C, and a drive motor for rotating the drum by transmitting a drive from a drive motor to one circumferential edge of the photoreceptor drum. The hot air blowing mechanism has a hollow shaft extending longitudinally through approximately the center of the hollow space of the photoreceptor drum, and one end of the shaft is connected to a heat fixing member. and the other end communicates with a suction attachment, the hollow shaft has a large number of small holes on the circumferential surface, and the hollow part of the shaft is partitioned. A heating mechanism for a photoreceptor drum is provided. The present invention will be described in detail below based on a specific example (a copying machine as a typical image forming apparatus) shown in the accompanying drawings. Referring to FIG. 1 which simply shows the structure of the entire copying machine, an amorphous silicon-based photoconductor layer 2 is provided on the surface of a metal drum 1 that is driven and rotated.
Around this drum, a main charging corona charger 3; a lamp 4, a document support transparent plate 5, and an optical system 6 are provided.
An image exposure mechanism consisting of; a developing mechanism 8 having toner 7; a corona charger 9 for toner transfer; a corona charger 10 for paper separation; a static elimination lamp 11; and a cleaning mechanism 12 are provided in this order. First, the photoconductor layer 2 is charged with a constant polarity using the corona charger 3. Next, the original 13 to be copied is illuminated by the lamp 4, and the photoconductor layer 2 is exposed to a light beam image of the original through the optical system 6, thereby forming an electrostatic latent image corresponding to the original image. This electrostatic latent image is developed with toner 7 by a developing mechanism 8. The transfer paper 14 is supplied so as to be in contact with the drum surface at the position of the toner transfer charger 9, and corona charge with the same polarity as the electrostatic image is performed from the back side of the transfer paper 14 to transfer the toner image onto the transfer paper 14. . The transfer paper 14 on which the toner image has been transferred is electrostatically peeled off from the drum by the separation corona charger 10 and sent to the thermal fixing device 15 . The heat fixing device 15 is, for example, an oven heater type having heaters 16, 16 . The photoconductor layer 2 after toner transfer is a static elimination lamp 11
The residual charge is erased by the front exposure, and then the residual toner is removed by the cleaning mechanism 12. An important feature of the present invention is the heat fixing device 15.
The purpose is to blow hot air into the inner space of the drum 1 to heat the photoconductor layer 2. In other words, a photoreceptor having an amorphous silicon-based photoconductor layer on a conductive substrate adsorbs moisture on the surface by repeating a copying process such as charging, image exposure, development, and transfer, and the surface resistance decreases. This has the disadvantage that the surface charge decreases and the surface charge moves in the lateral direction, causing image deletion, and this tendency is particularly noticeable when the humidity is high. The cause of this image blurring is still not clear, but the inventors believe that it is due to changes in the bonding structure of the silicon due to corona discharge exposure on the surface of the amorphous silicon photosensitive layer during repeated use. I'm guessing. That is, in the amorphous silicon-based photoreceptor normally used in electrostatic copying devices, the long range order deposited on the substrate is lost due to glow discharge, and only short range order is deposited on the substrate. It is composed of interatomic bonds in silicon, and there are many dangling bonds.
dangling bonds). Therefore, the localized level density in the energy gap increases due to the existence of this dangling bond, so this dangling bond is usually blocked with hydrogen atoms and amorphous hydrogenated silicon (a-Si :H)
This makes doping effects of boron, phosphorus, etc. more likely to occur. If this amorphous hydrogenated silicon photosensitive layer is used repeatedly using existing electrophotographic processes, it will be exposed to corona discharge during each process such as charging and transfer.
A hydrogen atom is removed and a dangling bond is formed again. This silicon dangling bond is attacked by ozone generated by corona discharge, and the silicon
-Si-OH or Si-O- which is more stable than -H bond
Silicon and oxygen bonds in Si occur. Since the oxygen atoms present on the surface of the photosensitive layer are hydrophilic in nature, as exposure due to corona discharge progresses and the silicon-oxygen bond concentration increases, they tend to adsorb water molecules in the atmosphere near the surface of the photosensitive layer. As a result, the photoreceptor becomes sensitive to humidity, which is thought to induce image deletion. This fact is due to the fact that Si-O bonds are detected when the surface of the photosensitive layer where image blurring occurs is analyzed using XPS (Xray Photoelectron Spectroscopy), and the surface of the photosensitive layer where image blurring occurs is detected. This can also be confirmed by the fact that image deletion is no longer caused by thinly scraping off the surface layer in which Si--O bonds have formed by plasma etching. However, in the present invention, by blowing hot air from the heat fixing device 15 to heat the photoconductor layer 2, the surprising effect that no image deletion occurs is achieved, as shown in the example described later. be. That is, since the aforementioned adsorption phenomenon between the water molecule adsorption medium on the surface of the photosensitive layer and the water molecules in the atmosphere is a temperature-dependent adsorption/desorption phenomenon, heating the photoconductor layer 2 causes the equilibrium to be released. It is possible to keep it on the side. Referring to FIGS. 2 and 3 for explaining the heating mechanism of the present invention, in this heating mechanism, a hollow shaft 20 extending through the center of the drum 1 is shown.
A heat fixing device 15 blows hot air into the shaft 20 to heat the photoconductor layer 2 from the substrate side. That is, this hollow shaft 20 has one end connected to the blower pipe 21,
21' to the inside of the heat fixing device 15, and the other end is connected to an exhaust fan 23 via a blow pipe 22.
is connected to. Further, a large number of small holes 24 are formed in this hollow shaft 20, and a rubber plug 25 or the like is provided in the hollow portion of the shaft 20, and the space is divided into two. Therefore, by operating the exhaust fan 23, the hot air from the heat fixing device 15 is introduced into the hollow shaft 20, fills the inner space of the drum 1 through the small hole 24, and then flows through the small hole 24. Hollow shaft 20
It is discharged to the outside of the copying machine by the exhaust fan 23 through the exhaust fan 23. In this way, the photoconductive layer 2 is heated by the hot air from the heat fixing device 15, and image deletion is effectively prevented. In the present invention, in order to penetrate the hollow shaft 20 into the drum 1, flanges 31 and 3 having openings 30 and 30' in the center are provided on both sides of the drum 1.
1', and the openings 30, 30' have protrusions 32, 32' on the outside, and the protrusions 32, 32' are fitted into the bearings 33, 33' to attach the bearings. It is configured to be supported by a drum holder (not shown) of the machine body. In this configuration, the drum 1 is driven by a gear 34 provided on the flange 31 on one side of the drum 1, in which drive from a drive motor (not shown) is transmitted, and the drum 1 is rotated. In addition, with this configuration, the openings 30, 30'
The drum 1 has a sealed structure, except for the drum 1, which prevents outside air from flowing into the space inside the drum 1, thereby efficiently heating the photoconductive layer 2 with hot air, and allowing the heat fixing device 15 to It is also easy to blow hot air. Further, both ends of the hollow shaft 20 are connected to the flanges 3
1 and 31' in such a manner that they cover the openings 30 and 30', and are connected to the inside of the air pipes 21 and 2.
2 pass through the openings 30 and 30', respectively, to the hollow shaft 2.
It is oriented towards space within 0. In this case, the blower pipes 21, 22 are fixed to the flanges 31, 31' via bearings 35, 36. Therefore, when the drum 1 is driven to rotate, the hollow shaft 20 rotates together with the drum 1, but the blower pipes 21 and 22 remain fixed in position. Since the heating mechanism of the present invention uses the heat fixing device 15 as a heat source, there is no need to provide a separate heat source.Moreover, instead of blowing hot air from outside the photoconductive layer 2, hot air is blown inside the drum 1. Since the heating is carried out in a heated manner, heating is carried out extremely efficiently without being affected by airflow or the like. In the present invention, heating with hot air is preferably performed continuously at all times, but may be performed intermittently as long as the surface temperature of the photoconductive layer 2 is within the range described below. Further, in the present invention, heating with hot air is carried out so that the surface temperature of the photoconductive layer 2 is in the range of 35 to 40°C, as will be clear from the examples described later. If the temperature is lower than the above, the desired effect will not be achieved, and if the temperature is higher than the above, the photoconductor layer 2
This results in a decrease in the amount of charge. For example, a temperature sensor may be provided near the surface of the photoconductive layer 2, and the temperature may be adjusted by stopping the operation of the exhaust fan 23 when the temperature exceeds a predetermined temperature. As the amorphous silicon-based photoconductor layer used in the present invention, any known material can be used. For example, amorphous silicon deposited on a substrate by plasma decomposition of silane gas is used. Things are doped with hydrogen, halogen, etc.
Furthermore, it may be doped with an element of Group 1 or Group 3 of the periodic table, such as boron or phosphorus. The physical properties of a typical amorphous silicon photoreceptor include dark conductivity of 10 ^-12 Ω ^-1 cm ^-1 , activation energy <0.85 eV, photoconductivity >10 ^-7 Ω ^-1 cm ^-1 , The optical bandgap is 1.7 to 1.9 eV, the amount of bonded hydrogen is 10 to 20 at%, and the dielectric constant of the film is 11.5 to 1.9 eV.
12.5. This amorphous silicon photoconductive layer can be positively charged or negatively charged depending on the doping species, and the voltage applied to the corona charger is 5 to 5.
8KV range is common. As mentioned above, the idea was to create an amorphous silicon-based photoconductive material by simply heating the photoreceptor surface from the substrate side, without using any troublesome means such as surface treatment of the photoreceptor surface. This eliminates the inherent drawbacks of the sexual layer. In the example shown in FIG. 1, an oven heater type device is used as the heat fixing device 15, but a heater roller type device may of course be used. The effects of the present invention will be explained with the following example. Example A process consisting of charging (positive charge), exposure (uniform white exposure over the entire surface), and neutralization (AC charge) was continuously applied to the photoconductor drum in a copying machine having the photoconductor drum heating mechanism shown in FIGS. 1 to 3. Repeated 30,000 times

[Table] ○ No blurring of characters or image blurring From Table 1, in an environment with a relative humidity of 75% and the temperature around the drum below 30°C, image blurring occurs after about a dozen copies, and this condition continues, but after 30 No image deletion occurred during continuous copying when the temperature was above .degree. In addition, under high humidity conditions of 85% relative humidity, 30℃,
In an environment where the ambient temperature of the drum was 32°C, there was a slight smearing of the letters, although this had little effect on the image. However, at temperatures above 35 degrees Celsius, no text blurring or image blurring occurred. However, under both 75% and 85% humidity conditions, when the ambient temperature of the drum was 45° C., a phenomenon occurred in which the image density of copies decreased. This is a general physical property of the a-Si:H drum as a semiconductor, and is a phenomenon that occurs as a result of the increase in charge mobility at high temperatures. For reference, FIG. 4 shows the relationship between drum ambient temperature and image density retention.
In addition, the retention rate in the figure is measured using a reflection densitometer (Tokyo Denshoku TC-
Image area (2 x 2 cm) measured with a 6D reflection densitometer
It is expressed as a percentage, with the reflection density of 1.3 (black solid area) as 100%. From the above results, when using the photoreceptor drum heating mechanism of the present invention, by setting the temperature near the photoreceptor surface to 30 to 40°C, a stable image with high density can be obtained without causing image deletion. When kept at a temperature of 35 to 40°C, the effect is achieved with no smearing of the characters even under humidity as high as 85%.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of a copying machine to which the present invention is applied. FIG. 2 is a perspective view for explaining the heating mechanism of the present invention. FIG. 3 is a sectional view of a drum having a heating mechanism according to the present invention. FIG. 4 is a graph showing the relationship between drum ambient temperature and image density retention rate. Reference number 1 is drum, 20 is hollow shaft, 21,2
2 is a blower pipe, 23 is an exhaust fan, 25 is a rubber stopper, and 31 and 31' are flanges, respectively.

Claims (1)

[Scope of utility model registration request] A hollow rotating photoreceptor drum having an amorphous silicon-based photoconductive layer on a conductive substrate is heated to a temperature of 35 to 40°C by blowing hot air from a heat fixing area into the inner space of the photoreceptor drum. The photoreceptor drum includes a hot air blowing mechanism for heating the photoreceptor drum to a temperature, and the photoreceptor drum has a drive transmission member on one circumferential edge of the drum for transmitting the drive from the drive motor to rotationally drive the drum. The hot air blowing mechanism has a hollow shaft extending longitudinally through approximately the center of the hollow space of the photoreceptor drum, one end of the shaft extends into the heat fixing area, and the other end extends through the heat fixing area. A photoreceptor drum in an image forming apparatus, wherein the hollow shaft is in communication with a suction device, the hollow shaft has a large number of small holes on the circumferential surface, and the hollow part of the shaft is partitioned. heating mechanism.