JPH07175276A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic device forming a distinct image without causing image flowing and fogging as an electro-photographic device performing uniform electrostatic charging to a photoreceptor,, including a discharge phenomenon. CONSTITUTION:This electrophotographic device is equipped with an electrostatic charging means performing the uniform electrostatic charging by corona discharge or by the electrostatic charging means such as an electrostatic charging roller or the like, and exposing and developing means forming the image by reversal development. A photoreceptive layer is formed of an a-Si layer whose film thickness is <=25mum and the surface potential Vo of the photoreceptor generated by the discharge phenomenon is set to <= about 360V.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an invention applied to an electrophotographic apparatus using a-Si drum, such as a printer, a copying machine, a facsimile, etc., and particularly to an electronic apparatus for uniformly charging a photosensitive member including a discharge phenomenon. Regarding photographic equipment.

[0002]

2. Description of the Related Art Conventionally, process means for exposing, developing, transferring, cleaning (removing residual toner), discharging, and charging are arranged on the outer peripheral surface of a photosensitive drum, and an image is formed by a predetermined electrophotographic process. Electrophotographic devices based on the so-called Carlson process are well known.

In this type of electrophotographic apparatus, generally, corona discharge is used to charge the surface of the photosensitive member, but the corona discharge is generally 4 to 8 KV.
It is necessary to apply the above high voltage to the wire, so that ozone or nitrogen oxide or ammonium salt which is a discharge product thereof is generated by the corona discharge, and these are easily adsorbed on the surface of the photoconductor to cause image deletion. Become. The image deletion is remarkable in a high humidity environment. On the other hand, some photosensitive drums used in electrophotographic apparatuses use a-Si drums in recent years in order to improve durability and achieve free maintenance. However, a-Si is compared to OPC and other organic semiconductors. Since the water absorption is high, the image flow is a-
Most likely to occur on Si drums. Therefore, in the prior art, a sheet heater or other heating body is arranged on the back side of the photosensitive drum to heat the photosensitive drum to prevent the image deletion. In addition, since the surface of the nitrogen oxide is slightly scraped off by a rubbing of a cleaning blade that removes residual toner after transfer on a soft drum such as an OPC drum, the problem is less likely to be manifested. Since the drum is hard, the above-mentioned defects are likely to be revealed. Therefore, in the a-Si drum, the surface of the photoconductor drum is polished by using a polishing blade or a polishing roller to remove the above-mentioned products and prevent the occurrence of image deletion.

[0004]

As mentioned above, a-S
Although the i-drum is harder and has excellent durability as compared with the organic semiconductor drum, it is necessary to provide the above-mentioned heater or polishing means in order to achieve durability and free maintenance. The configuration becomes extremely complicated. In order to solve such a drawback, a roller charging method is configured in which a conductive roller is brought into contact with the photosensitive drum, and a DC voltage is applied to the conductive roller to perform contact charging of the photosensitive drum in a dark place. Exists. However, even in such a charging method, since there is a minute wedge-shaped void between the photosensitive drum and the charging roller, a slight discharge phenomenon occurs at that portion, and ozone generation is recognized. I don't get it. In order to solve such a drawback, a technique using a particle charging means as the charging means is also disclosed, but the particle charging means must store the particles in a charging container in a state where the photosensitive member side is opened. Not only is the handling complicated, but since particles are uniformly rubbed against the photosensitive member and are uniformly charged, fatigue of the particles easily occurs and durability is also poor.

In view of the drawbacks of the prior art, the present invention has
-A clear image can be obtained without causing image deletion or fog in an electrophotographic apparatus in which a photoconductor is uniformly charged by including a discharge phenomenon, such as a corona discharger, a charging roller, and a charging brush, using a Si drum. An object is to provide an electrophotographic apparatus that can be formed.

Another object of the present invention is that, in an electrophotographic apparatus using an a-Si drum, fogging and image deletion may occur due to environmental changes such as temperature while considering simplification and safety. An object of the present invention is to provide an electrophotographic apparatus capable of forming a clear image without any trouble.

[0007]

First, the cause of image deletion will be described. The developing method used in electrophotographic devices is the same as the developing method used in copying machines, in which an electric charge having a polarity opposite to the surface potential of the photosensitive drum is injected into the magnetic toner to uniformly charge the image on the photosensitive drum. After exposing the background area, the surface potential of the photoconductor drum is different from that of the normal development method in which magnetic toner is applied with an electric charge of opposite polarity to the unexposed latent image area and the development method used in printers. After exposing the image background of the photoconductor drum that has been uniformly charged by injecting it into the magnetic toner that has the opposite polarity, the positive polarity that attaches the opposite polarity to the magnetic toner is applied to the unexposed latent image area. Similar to the transfer developing method and the developing method used in printers, charges having the same polarity as the surface potential of the photosensitive drum are injected into the magnetic toner, and the image is exposed on the uniformly charged photosensitive drum to remove the charges. Diving After the formation of the,
There is a reversal development method in which a magnetic toner having a charge of the same polarity is attached to the latent image by utilizing a development bias.

In the reversal development method, in particular, as shown in FIG. 1 (A), after a surface potential Vo having a predetermined potential is uniformly charged on the photosensitive member, the latent image having the inverse normal distribution is formed by exposing. The image potential distribution is formed, and the toner is attached to the portion where the distribution is lower than the threshold level V _B. That is, in the reversal development, the toner dot diameter D is determined by the threshold level V _B.

On the other hand, in the a-Si photosensitive member, ozone is generated due to the discharge phenomenon at the time of charging and the discharge product adheres to the drum, so that the surface of the photosensitive member has a high hygroscopic property and the surface resistance of the drum is lowered in a high humidity environment. , The surface potential Vo ′ decreases. As described above, since the toner dot diameter D is determined by the threshold level V _B , when the surface potential Vo ′ decreases, the dot diameter D ′ of the corresponding latent image potential distribution increases, resulting in a blurred image, that is, image deletion. Is likely to occur. Therefore, in order to prevent image deletion, the amount of decrease in surface potential (Vo-Vo ') due to hygroscopicity should be reduced. Further, it is necessary to sharpen the latent image potential distribution and prevent the dot diameter from increasing even if the surface potential Vo ′ decreases.

Therefore, in the present invention, the relationship between the drum film thickness and the line width is examined in FIG. 2, and the line width when the photoconductor film thickness is 40 μm or less is thicker than the line width when it is 25 μm or less. It is understood that the sharpness and the resolution are reduced accordingly. Further, when the thickness is 25 μm or less, the sharpness and the resolution are almost the same, and it is understood that there is no significant difference. Moreover, as is clear from FIG.
The depth of focus is 370 μm for m and 15 μm, which means that the depth of focus is slightly more than doubled, and the larger depth of focus means that the sharpness is maintained even when the surface potential Vo ′ decreases. Indicates that you can.

From this, as shown in FIG. 1 (B),
The thickness of the photoreceptor is 25 μm or less, preferably 20 μm or less,
More preferably, if it is set to 15 μm or less, the latent image potential distribution becomes sharp, the toner dot diameter D determined by the threshold level V _B becomes small, and the fluctuation of the dot diameter D becomes small due to the decrease of the surface potential Vo ′. Occurrence also decreases.

Therefore, when the photoconductor is formed of an a-Si material, the predetermined surface potential Vo 'can be obtained with a small light output by reducing the film thickness, but the lower limit is about 2.
It is preferably set to μm. The reason is that, when used for an exposure means such as an LED having a wavelength of about 700 nm, for example, the film thickness of the a-Si: H material until 90% of incident light is absorbed is about 2.2 μm. , Its lower limit is 2μ
It is better to set to m.

The amount of decrease in surface potential (V
In order to lower the (o−Vo ′), the charged surface potential V _O itself may be lowered, and as can be understood from FIG. 5, the surface potential Vo ′ caused by the temperature fluctuation is reduced as the drum film thickness is reduced.
Was found to be small, and in the photosensitive drum having a drum film thickness of 40 μm, the potential change amount of 10 to 40 ° C. was 80 V (2.7 V / ° C.),
In the case of 25 μm and 15 μm photosensitive drums, the temperature dependence is greatly reduced, and the potential change amount of 10 to 40 ° C. is 30 V (1.0 V / ° C.) for the former and 15 V (0.5 V / 0.5 V for the latter).
℃). On the other hand, in the case of the a-Si photoconductor, the withstand film thickness is 12 to 15 v / μm. Therefore, when the film thickness is set to 25 μm or less, the surface potential Vo is set to 360 V or less to prevent the blurred image and It is possible to prevent film thickness deterioration due to long-term use.

The environment in which a copying machine or a printer is usually installed is set in an office where air conditioning is performed in the summer and heating in the winter so that the staff can work comfortably. Therefore, there is no temperature difference in the office as much as the outside air, and the temperature difference is around 30 ° C at most even when the air conditioning and heating in the morning are not sufficiently effective. Therefore, for example, when the surface potential Vo of the photosensitive drum is set to approximately 300 V, the permissible range of fogging due to long-term use is ± 2.
Since it is 5 V, it can be understood that it can be used without a drum heater if the film thickness is 25 μm or less.

Therefore, according to the present invention, fogging does not occur even when an image is formed without using a heater.
In addition to drastically reducing the power consumption, the heater, thermistor for detecting the drum surface temperature, the reduction of electric components such as the heater control circuit based on the temperature detected by the thermistor, and the simplification of the circuit configuration are made, and the heater is not used. Therefore, the warming up time becomes unnecessary, and the equipment startup time can be greatly reduced.

Further, according to the present invention, the effect is further enhanced by setting the exposure wavelength to 700 nm or more. That is, as is apparent from FIG. 3, the half-sensitivity (exposure potential is reduced to 1/2 of the surface potential Vo) by using a photosensitive drum having a film thickness of 25 μm or less and a conventional photosensitive drum having a film thickness of 40 μm. Exposure energy density required to achieve the half-sensitivity decreases in proportion to the film thickness.
The sensitivity of 740 nm is lower than that of m, and only the central light amount is picked up without picking up the light amount of the optical aberration caused by the imaging error and the like, and a high-quality dot image with high image contrast and sharpness is obtained. Can be formed.

Thus, the present invention is applied to an electrophotographic apparatus comprising a charging unit for uniformly charging the discharge by corona discharge or a charging roller and other discharge phenomena, and an exposing and developing unit for forming an image by reversal development. The characteristic is that the photoconductor layer is formed of an a-Si layer having a film thickness of 25 μm or less, and the surface potential Vo of the photoconductor generated by the charging is set to approximately 360 V or less. I have set it. In this case, preferably the photosensitive layer is 2
It is preferable to set the surface potential Vo of the photosensitive member to approximately 20 V or less and approximately 300 V or less. Further, it is preferable to simplify the structure for performing image formation under the ambient temperature of the apparatus and shorten the start-up time without incorporating a heater in the substrate supporting the photoconductor layer.

Further, by setting the center exposure wavelength of the exposing means for forming the exposure image to 700 nm or more, it is possible to form a clear image without further fog or image deletion. That is, it is understood that when the exposure wavelength is 740 nm, as shown in FIG. 2, when the film thickness is 25 μm or less, the image resolution and the line drawing sharpness are also significantly improved as compared with the case where the film thickness is 40 μm. it can.

Further, even when an LED is used as the exposure means, the fact that the emission wavelength of the LED can be set to 700 nm or more is extremely advantageous in terms of LED manufacturing. That is, it is sufficient that the emission wavelength is 700 nm.
It is possible to form the film by reducing the mixing ratio of phosphorus P when the film formation is performed. This is compared with the case where the film formation time is 7.5 hours and 680 nm when manufacturing an LED of 740 nm, for example. It can be greatly shortened, and not only the manufacturing cost but also the manufacturing variation can be significantly reduced.

[0020]

Embodiments of the present invention will now be illustratively described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely examples, unless otherwise specified. Not too much. Figure 6
Shows an electrophotographic apparatus to which the present invention is applied, and an optical system including an LED head 2 for exposure and a SELFOC lens 3 along the rotation direction around an a-Si photosensitive drum 1 which rotates clockwise in the figure. A two-component developing unit 4, a transfer roller 5, a cleaning blade 6, a charge eliminating lamp 7, and a charging unit 8 are provided.

Next, each component will be described.
The photoconductor drum 1 includes a photoconductor layer 1b on a conductive support 1a,
And the surface layer 1c are laminated, and the support 1a is generally made of an aluminum cylinder. However, an inorganic material such as glass having a conductive film deposited on the surface thereof or a transparent material such as epoxy is used. It is made of resin or the like and has a wall thickness of 2 in this embodiment.
Set the outer diameter to 30 mm in mm and set 3 in the axial direction.
An aluminum cylinder having a length of 00 mm is used.

The a-Si type photoreceptor layer 1b and the surface layer 1c are formed by glow discharge decomposition method, sputtering method and EC.
A film is formed by R method, vapor deposition method, etc.
An element for terminating the dangling bond, such as (H) or halogen, is added in an amount of 5 to 40 wt. % Should be included. That is, the photoconductor layer 1b uses a photoconductor made of a-Si: H, and when the developing bias is positive, it contains a non-doped or Va group element in order to increase the mobility of electrons. In the case of a negative value, IIIa
It is preferable to include a group element. If necessary, elements such as C, O and N may be contained in order to obtain desired characteristics such as electrical characteristics such as dark conductivity and photoconductivity and optical bandgap.

The overall film thickness of the photoconductor layer 1b is
The thickness is preferably about 2 to 25 μm in order to secure the necessary charging and dielectric strength, absorb the exposed light, and suppress the above-mentioned residual potential.

The surface layer 1c is made of α-SiC, α-Si.
A of O, α-SiN, α-SiON, α-SiCON, etc.
It is preferable to use an organic insulating material such as -Si-based inorganic high resistance or insulating material, polyethylene terephthalate, parylene, polytetrafluoroethylene, polyimide, polyfluorinated ethylene propylene, especially when using a high resistance a-SiC layer. Characteristics such as dielectric strength, abrasion resistance, and environment resistance are improved. The value _x of a-Si _1-x C _x is set to 0.3 ≤ x <1.0, preferably 0.5 ≤ x ≤ 0.95 so that 10 ¹² to 10 10 can be obtained.
^It is possible to obtain high humidity resistance with a resistance value in the range of ¹³ Ω · cm, and in this case, the C content may have a gradient in the layer. Further, by containing N, O and Ge at the same time as C, the moisture resistance can be further enhanced.

The thickness of the surface layer 1c is 0.05 to 5 μm, preferably 0.1 to 3 μm, and the thickness of the surface layer 1c is set to 10 ¹² to 10 ¹³ Ω · cm.

In this embodiment, the a-S photoconductor layers 1b and a-S are formed by using a capacitively coupled glow discharge decomposition apparatus.
The SiC surface layer 1c and the SiC surface layer 1c are sequentially laminated, and the layer thickness of the photoconductor is 7, 10, 15, 20, 25, 40 μm, respectively, as described later.
A photoconductor drum 1 having a m-thick film layer was produced. In this case, the thickness of the surface layer 1c is set to 3 μm or less at the maximum and approximately 5% or less of the total layer thickness. At this time, in the case of the film having a thickness of 40 μm, the roundness was not obtained in the aluminum cylinder having a thickness of 2 mm, and therefore the film was formed again, but the result was not good. Therefore, in this embodiment, when the film was formed again using an aluminum tube having a thickness of 4 mm, the roundness could be obtained. Therefore, reducing the film thickness is
That is, it is possible to make the aluminum cylindrical body thin, and this achieves weight reduction.

The exposure LED head 2 has an exposure wavelength of 6
Using a head array of 85 nm and 740 nm, this is dynamically driven and 64 bits x 40 for each scanning line.
It is exposed in divided times.

The developing unit 4 comprises a developing container 41 containing a multi-component developer consisting of a carrier and toner, and a developing roller 42 containing a fixed magnet assembly 43. A direct-current developing bias power source 44, which can be arbitrarily set by, is connected to perform development.

The carrier has an average particle size of 70 μm.
However, the carrier is not limited to the ferrite carrier, and a carrier such as iron powder or magnetite or a magnetic resin carrier may be used.

Ordinary high-resistance or insulating toner is used as the toner. For example, a binder resin, a colorant, a charge control agent, an offset preventing agent, etc., to which a magnetic substance is added, has an average central particle size of 5 to 15 μm. The front and rear magnetic toners are constituted and the proper mixing ratio of the carrier and the toner is set to, for example, 85 to 90:15 to 10% by weight. As the transfer roller 5, a conductive roller is used in order to increase transfer efficiency, a transfer bias having a polarity opposite to the charging potential of the toner is applied, and the transfer roller 5 is uniformly pressed against the peripheral surface of the photosensitive drum 1 to synchronize with the drum 1. And make it rotatable.

The charging unit 8 was uniformly charged on the photosensitive member by a known corotron charging device.
In the figure, 81 is a corona discharge line, 82 is a control grid, 83 is a discharge bias, and 84 is a charge control bias.

In this embodiment, the charge control bias is set to 1
By applying a high-voltage discharge bias in a state where the bias is appropriately set between about 50 V and 450 V, the surface potential Vo of the photosensitive drum 1 is charged to the following set value, and then a predetermined latent voltage is set by the exposure head 2. After exposing the image, a toner image is attached to the latent image by the developing unit 4,
Transfer to the transfer roller 5. Next, the following experiment was conducted by using the above-mentioned apparatus and using the photosensitive drums 1 having different film thicknesses.

The surface potential Vo of the photosensitive drum 1 is 20.
After adjusting the charging control bias etc. to 0V, 7
Using an LED head having an exposure wavelength of 40 nm, the energy level for forming an image on the photosensitive drum 1 is 1.0 μ.
After adjusting the output of the exposure head 2 so as to be J / cm ² , the drum film thickness and the line width when the exposure image of the energy level is written on the photoconductor drums 1 having different film thicknesses. The relationship with is shown in FIG. As you can see from this figure,
In both cases of horizontal lines and vertical lines, the photoconductor film thickness is 40μ
The line width in the case of m or less is thicker than the line width in the case of 25 μm or less, and the sharpness and the resolution are reduced accordingly, and as a result, as shown in FIG. It is understood that it is spreading. Further, in the case of 25 μm or less, the sharpness and the resolution are almost the same and sharp, and as a result, it is understood that the latent image potential distribution width is narrowed as shown in FIG. 1 (B).

Further, FIG. 3 shows an LED having an exposure wavelength of 685 nm after adjusting the charging control bias and the like so that the surface potential Vo of the photosensitive drum 1 becomes 200V.
For each of the head and the LED head having an exposure wavelength of 740 nm, the photoconductor drum having a film thickness of 7, 10, 15, 20, 25 μm and the conventional photoconductor drum having a film thickness of 40 μm are halved. The sensitivity (exposure energy density required to reduce the exposure potential to 1/2 of the surface potential Vo) was examined.
The half-sensitivity is significantly lower than that of a photoconductor drum having a film thickness of m, so that the latent image potential distribution width is narrowed, and
As shown in (A), even if the latent image potential distribution slightly expands due to a decrease in the surface potential Vo ′, only the central light amount is picked up without picking up the light amount at the periphery of the distribution, and high-quality dots with high image contrast and sharpness are obtained. It is possible to form an image. The effect is further enhanced at 740 nm as compared to the wavelength of 685 nm.

Further, FIG. 4 shows the relationship between the depth of focus and the drum sensitivity when the surface potential Vo was charged at 450 V and the exposure was performed at an exposure wavelength of 740 nm and an energy density of 0.2 μJ / cm ^2. In comparison with the case where the film thickness is 40 μm, the depth of focus is 370 μ when the thickness is 7 μm or 15 μm.
m, the depth of focus is slightly more than doubled, and the depth of focus becomes large, as shown in FIG. 1 (B). The occurrence of blurring is also reduced.

In FIG. 5, the film thickness of the a-Si drum is 40 μm.
Surface potential V at a temperature of 30 ° C. using the photosensitive drum of
After adjusting the charge control bias etc. so that o becomes 320 V, in a state where the charge control bias is kept constant,
The machine temperature under medium humidity is 10 ℃, 20 ℃, 30 ℃ 4
15μm, 25μm, 40μ when changed to 3 ° C
The relationship between the a-Si photosensitive drum formed on m and the surface potential Vo is shown. As can be understood from this figure, in the photoconductor drum having a drum film thickness of 40 μm, the temperature dependency was high and the potential change amount of 80 V (2.7 V / ° C.) at 10 to 40 ° C. was 25 μm and 15 μm. In the case of the photosensitive drum of No. 3, the temperature dependency is significantly reduced, and the potential change amount of 10 to 40 ° C. is 30 V (1.0 V / ° C.) for the former and 15 V for the latter
(0.5 V / ° C.). From this fact, the fluctuation of the surface potential Vo due to the environmental fluctuation can be suppressed by thinning the photosensitive drum to 25 μm or less.

Next, the surface potential Vo of the photosensitive drum is set to 30.
With the developing bias set to 0V and the developing bias set to 210V, without attaching a heater to the photosensitive drum,
m and 15 μm photosensitive drums were printed at 180,000 sheets (approximately 300 hours) while changing the temperature inside the machine from 10 ° C. to 40 ° C. at a gradient of 10 ° C./hour under medium humidity. Even on the photoconductor drum, a clear image could be obtained without causing image fogging or fogging.

Next, the surface potential Vo of the photosensitive drum is set to 45
With the developing bias set to 0V and the developing bias set to 250V, 40 μ without attaching a heater to the photosensitive drum.
Similarly, with respect to the photoconductor drum of m, printing was performed while changing the in-machine temperature up and down at a gradient of 10 ° C./hour between 10 ° C. and 40 ° C., and image deletion occurred in a short time.

[0039]

As described above, according to the present invention, a
-A clear image can be obtained without causing image deletion or fogging in an electrophotographic apparatus that uses a Si drum and that uniformly charges a photoconductor including a discharge phenomenon, such as a corona discharger, a charging roller, and a charging brush. Can be formed.

Further, according to the present invention, in the electrophotographic apparatus using the a-Si drum, simplification of structure and safety are taken into consideration, and fog and image deletion do not occur due to environmental changes such as temperature. A clear image can be formed. It has various remarkable effects.

[Brief description of drawings]

FIG. 1A shows the relationship between the surface potential and the latent image potential distribution when the surface potential is lowered, and particularly shows the state where the toner dot diameter is increased (image deletion). (B) shows the relationship between the photoconductor film thickness and the latent image potential level.

FIG. 2 shows the relationship between drum film thickness and line width, (A) showing a horizontal line and (B) showing a vertical line.

FIG. 3 is a graph showing the relationship between drum film thickness and half-sensitivity.

FIG. 4 is a graph showing the relationship between drum sensitivity and depth of focus for each drum film thickness.

FIG. 5 shows the relationship between the film thickness of the a-Si photosensitive drum and the surface potential when the in-machine temperature is changed while the charge control bias is kept constant.

FIG. 6 is a schematic view showing an electrophotographic apparatus to which the present invention is applied.

[Explanation of symbols]

 1 Photoconductor drum 2 Exposure head 3 Optical system 4 Two-component developing unit 8 Charging device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G03G 15/02 102

Claims (4)

[Claims] 1. An electrophotographic apparatus for performing image formation by reversal development while uniformly writing an exposed image on a photoconductor layer supported on a substrate while including a discharge phenomenon, An electrophotographic apparatus characterized in that the photoreceptor layer is formed of an a-Si layer having a thickness of 25 μm or less, and the surface potential of the photoreceptor produced by the charging is set to about 360 V or less. 2. The electrophotographic apparatus according to claim 1, wherein the photoconductor layer is set to 2 to 20 μm, and the surface potential of the photoconductor is set to about 300 V or less. 3. An electrophotographic apparatus, wherein an image is formed at an internal environmental temperature of a machine without incorporating a heater in a substrate that supports the photosensitive layer. 4. The electrophotographic apparatus according to claim 1, wherein the center exposure wavelength of the exposing means for forming the exposure image is set to 700 nm or more.