JPH0134206Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Detailed description of the invention] The present invention relates to a heating mechanism for a photoreceptor drum used in an image forming apparatus using an amorphous silicon-based photoconductor layer as a photoreceptor, and more specifically, to a heating mechanism for effectively preventing image deletion. This invention relates to a heating mechanism for heating. An amorphous silicon-based photoconductor layer has high surface hardness, is sensitive to light on the long wavelength side, and has good sensitivity itself, so it is attracting attention as a photoreceptor 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・Cπ _1- x, a-SixN _1- x, etc. on the surface of the photoreceptor. At present, even if processing is performed, image deletion cannot be completely prevented. The inventors of the present invention have proposed that in an electrophotographic device using an amorphous silicon-based photoconductive layer, the above-mentioned image deletion can be prevented by heating the surface of the photoreceptor when repeating the steps of charging, image exposure, development, and transfer. We have found that it can be completely prevented. 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, a hollow rotating photoreceptor drum having an amorphous silicon-based photoconductive layer on a conductive substrate and a space inside the drum are heated so that the photoconductive layer is
The drum consists of a heating mechanism for heating the drum to a temperature of 40°C to 40°C, and both sides of the drum are sealed by a flange having an opening in the center, and a drive motor is connected to the circumferential edge of the flange on one side. The heating mechanism is provided at a position of a drum rotation axis connecting both openings of the flange without being involved in the rotation of the drum. Additionally, there is provided a heating device for a photoconductor drum in an image forming apparatus, characterized in that the temperature of the photoconductor layer is controlled by a temperature sensor provided near the surface of the photoconductor drum. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings using an example in which the present invention is applied to a copying machine, which is a typical image forming apparatus. FIG. 1 shows the overall configuration of the 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 are a main charging corona charger 3; an image exposure mechanism consisting of a lamp 4, a document support transparent plate 5, and an optical system 6; a developing mechanism 8 having toner 7; a toner transfer corona charger 9; and a paper separation corona charger 10. ; 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 . This heat fixing device 15 has a heater 1 inside, for example.
It is an oven heater type having heaters 6, 16, . . . , and thermal fixing is performed by heat radiation from the heater 16. The photoconductor layer 2 after toner transfer is a static elimination lamp 11
The residual charge is erased by full-surface exposure, and then the residual toner is removed by the cleaning mechanism 12. An important feature of the present invention is that the inner space of the drum 1 is heated and the photoconductor layer 2 is heated. 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 caused by changes in the bonding structure of the silicon due to corona discharge when the surface of the amorphous silicon photosensitive layer is repeatedly used. It is estimated that 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 such that there are many 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. When this amorphous hydrogenated silicon photosensitive layer is used repeatedly using existing electrophotographic processes, it is 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.
Si-OH or Si-O- which is more stable than Si-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 based on 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 that Si-O bonds are detected on the surface of the photosensitive layer where image blurring occurs. 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, when performing electrostatic copying by heating the inner space of the drum 1, heating the photoconductor layer 2, and keeping it at a constant temperature at all times, as shown in the example described later, image fading may occur. The surprising effect is achieved that no . That is, since the aforementioned adsorption phenomenon between the water molecule adsorption medium on the surface of the photosensitive layer and water molecules in the atmosphere is an adsorption/desorption phenomenon that depends on temperature and humidity, the photoconductor layer 2
By heating , it becomes possible to maintain the equilibrium on the desorption side. Referring to FIGS. 2 and 3 for explaining the heating device of the present invention, in this heating device, flanges 21 and 21' having openings 20 and 20' in the center are formed on both sides of the drum 1. By providing a gear portion 22 on the circumferential edge of one flange 21 for transmitting the drive from the drive motor to the drum 1, the drum rotation shaft 23 itself is not directly involved in the rotational drive, and this For example, a heater 24 can be provided as a heating mechanism at the position to heat the inside of the drum 1 and maintain the photosensitive layer 2 at a predetermined temperature. That is, the flanges 21, 21' are attached to both sides of the drum 1 by a plurality of rod members 25 having male threads at both ends. The center portions of the flanges 21, 21' have protrusions 26, 26' that protrude outward, and openings 20, 22' are formed in the centers.
0'. Further, a gear portion 22 is provided on the circumferential edge of one flange 21, and a drive from a drive motor (not shown) of the copying machine main body is transmitted to the drum 1 to this gear 22. When the photosensitive drum 28 having the above structure is attached to the main body of the copying machine, the protrusions 26, 2
6' is fitted into bearings 27, 27' and held in a drum holder (not shown) of the main body of the copying machine. At this time, the photosensitive drum 28 can be set in the copying machine main body in a rotatable state by threading the gear portion 22 with the drive gear of the copying machine main body. Next, installation of the heating mechanism will be explained. The photosensitive drum 28 set in the main body of the copying machine includes
Since the openings 20, 20' are provided and the drive is transmitted through the gear 22 of the flange 21, an axis connecting the centers of the openings 20, 20';
In other words, the rotating shaft itself has a structure that does not participate in rotation. Therefore, for example, a rod-shaped heater 24 can be used as a heat source from either of the openings 20 and 20'.
Insert it and fix it with the heater electrode sockets 30, 30' attached to the main body of the copying machine, and then turn on the power supply 31.
It is now possible to apply more voltage. In this aspect of the invention, both flanges 21 and 2 are designed to facilitate insertion of the heater 24.
It is also possible to appropriately provide a hollow pipe 32 or the like over 1'. The temperature of the photosensitive layer 2 by this heating mechanism is controlled by a temperature sensor 33 attached near the surface of the photosensitive layer 2, and a heater circuit controlled by a control unit 34 which receives a signal from the sensor 33 and sets the temperature to a predetermined temperature. This can be done by turning the switch 35 ON and OFF. As another aspect of mounting the heating mechanism of the present invention, as shown in FIG.
Bearings 40, 4 are further inserted into the openings 20, 20' of 1'.
0' and attach the heater 24 to the center hole of this bearing via the fixing members 41, 41'.
The heater 24 may also be attached before the photosensitive drum 28 is set in the main body of the copying machine. In this embodiment, only one of the heater electrodes and socket (42, 43 in the figure) can be used, and connection to the power source 31 is facilitated. In the present invention, heating is performed so that the photoconductor layer 2 is
The temperature is between 40°C and 40°C. 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 amount of charge on the photoconductor layer 2 will decrease. It should be noted that heating the photoconductive layer 2 should be maintained at the above-mentioned temperature even when the copying machine is stopped, that is, when it is not being used at night, to more completely prevent image blurring immediately after the copying machine is started to be used. This is desirable from the standpoint of preventing. 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 a Group or Group element 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 charged positively or negatively depending on the doping species, and the voltage applied to the corona charger is 5 to 5.
8KV range is common. As mentioned above, in the present invention, amorphous silicon-based light is produced 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 conductive layers. In addition to the above-mentioned copying machine, a laser printer can be used as an image forming apparatus to which the present invention is applied. 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) as a photoreceptor drum was continuously applied to a copying machine having the photoreceptor drum heating mechanism shown in Figures 1 to 3. After 50,000 repetitions, an a-Si:H drum with Si-O bonds formed on its surface due to exposure to corona discharge was attached, and the temperature around the drum was changed to produce 100 sheets in an atmosphere with relative humidity of 75% and 85%. Performed continuous copying. The results are shown in Table 1.

[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 keeping the temperature near the photoreceptor surface at 30 to 40°C, a stable image with high density can be obtained without causing image deletion. Especially 35 to 40
When kept at ℃, the effect is that the characters do not bleed at all even under high humidity conditions of 85%.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a copying machine to which the present invention is applied. FIG. 2 is a sectional view of a drum having a heating mechanism according to the present invention. FIG. 3 is a perspective view for explaining the heating device of the present invention. FIG. 4 is a sectional view showing an embodiment of the heating device of the present invention. FIG. 5 is a graph showing the relationship between drum ambient temperature and image density retention rate. Reference numeral 1 indicates a drum, 21 a flange, 24 a heater, 30 and 43 a socket, and 33 a temperature sensor.

Claims (1)

[Claims for Utility Model Registration] A hollow rotating photosensitive drum having an amorphous silicon-based photoconductive layer on a conductive substrate;
The drum consists of a heating mechanism for heating to a temperature of 40°C, and the drum is sealed on both sides by a flange having an opening in the center, and transmits the drive from the drive motor to the circumferential edge of the flange on one side. and a drive transmission member for rotationally driving the drum, and the heating mechanism is provided at a position of the drum rotation axis connecting both openings of the flange without being involved in the rotation of the drum. A heating device for a photoconductor drum in an image forming apparatus, wherein the temperature of the photoconductor layer is controlled by a temperature sensor provided near the surface of the photoconductor drum.