JP2006058905A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can stably realize high printing quality, even if the image forming speed is high. <P>SOLUTION: In the image forming apparatus forming an electrostatic latent image on the surface of a photosensitive body, by exposing the charged photosensitive body, developing the latent image using a toner to form a toner image, and transferring the toner image to an image-holding body, the photosensitive body is formed of a base material, consisting of arsenic triselenide or amorphous silicon, and the wavelength λ<SB>0</SB>of the writing light used for the exposure and the wavelength λ<SB>1</SB>of a destaticizing light for destaticizing the photoreceptor where after the development the relation λ<SB>0</SB>-100 nm≤λ<SB>1</SB>≤680 nm exists. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine and a printer, and more particularly to an image forming apparatus using a reversal developing system.

The reversal development method is one of the most well-known development methods used for printers and the like. Known photoreceptors used in this electrophotographic system include pure Se photoreceptors, SeTe photoreceptors, arsenic triselenide (As ₂ Se ₃ ) photoreceptors, OPCs, amorphous silicon photoreceptors, and the like. .

In recent years, with an increase in the amount of information to be processed, printers (especially line printers) are desired to have a higher printing capability and to have high image quality and high definition. By the way, in high-speed printing, an As ₂ Se ₃ type photoconductor (Vickers hardness: Hv≈150) whose photoconductor wear is large and the photoconductor has a high film hardness due to friction with paper and a developer is being frequently used. . Amorphous silicon-based photoconductors have a very high surface hardness of Hv≈1200 and excellent wear resistance, but their manufacturing costs are more than 10 times that of other photoconductors, so they are used only in a few models. ing.

As for an image forming apparatus using an amorphous silicon photoconductor, for example, the following patent documents can be cited.
JP-A-2-210358 JP-A-4-352161 Japanese Patent Publication No. 6-079192

However, As ₂ Se ₃ photoconductors and amorphous silicon photoconductors have a small volume resistance of 1 × 10 ¹¹ (Ω · cm), so that the surface charge retention capability is other pure Se photoconductors, It is inferior to SeTe photoreceptors and OPCs. As a result, the latent image pattern at the development or transfer portion is disturbed (a sufficient contrast potential cannot be maintained), and image quality such as resolution is likely to deteriorate.

  In particular, recently, in order to reduce the size and cost of the exposure light source unit, it is strongly desired to employ a semiconductor laser or LED as the exposure light source. However, current semiconductor lasers and LEDs have a smaller light output than gas lasers, and the present situation is that the wavelength of light can be employed only at a long wavelength of about 600 nm or more for use in an exposure light source such as a printer. When these long-wavelength light (red light, usually about 630 nm or more) is used as an exposure light source, the long-wavelength light (red light) is likely to develop afterimage development because the penetration distance into the photoreceptor is deep. In order to prevent this, light of the same wavelength is used for the static elimination light. As a result, the photo fatigue that the photoconductor receives increases, and the charge retention of the photoconductor further decreases.

Further, when a low resistance developer is used as the developer, there has been a problem that the surface charge of the photoreceptor leaks to the developer and the latent image is disturbed. Further, the As ₂ Se ₃ photoconductor and the amorphous silicon photoconductor having high surface hardness are formed on the surface of the photoconductor with use because the photoconductor itself is hardly scraped by friction in each image forming process. Deterioration layer due to ozone remains as it is, causing functional deterioration. Furthermore, the surface of the photoreceptor is roughened by the deteriorated layer, and in many cases, a developer or paper powder adheres to the surface of the photoreceptor and causes a filming phenomenon.

  As a countermeasure against this, it is effective to increase the cleaning efficiency by roughening the surface of the photoreceptor in advance and increasing the frictional force with the cleaning member (cleaning brush or cleaning blade). However, the photoreceptor having a large surface area due to the roughening has a large charge leakage toward the surface, and the disturbance of the latent image becomes more remarkable. This leakage of the surface charge of the photosensitive member becomes a problem particularly when an image is formed with a resolution of 600 dpi or more.

  An object of the present invention is to provide an image forming apparatus capable of stably realizing high print quality even when the image forming speed is high.

In order to achieve the above object, the present invention exposes a charged photoconductor to form an electrostatic latent image on the surface of the photoconductor, visualizes the latent image with toner, and uses the toner image as an image carrier. In the image forming apparatus to transfer,
The photoconductor is a photoconductor based on arsenic triselenide or amorphous silicon,
The wavelength λ _{0 of the} writing light used for the exposure and the wavelength λ _{1 of the} neutralizing light for neutralizing the photoconductor after development have the following relationship.

λ ₀ -100 nm ≦ λ ₁ ≦ 680 nm

  The present invention is configured as described above, and high-quality printing can be stably performed.

As will be described later, the present invention is suitable for an As ₂ Se ₃ photoconductor or an amorphous silicon photoconductor with the image forming process (charging, exposure, development, transfer, charge removal, cleaning) disposed around the photoconductor. Furthermore, by optimizing the characteristics (impurity addition amount, film thickness, surface roughness, etc.) of the photoreceptor itself, high print quality can be stably realized.

Specifically, stable charging of As ₂ Se ₃ photoconductors and amorphous silicon photoconductors is realized, variation in charging is reduced, and the latent image formed in the exposure process is disturbed until the transfer process. Hold without. Further, the charge eliminating process for removing the latent image is to completely remove the latent image and to minimize the fatigue applied to the photoreceptor.

  As for the surface roughness of the photoreceptor, the center line average roughness (Ra) defined in JIS is in the range of 0.125 to 1.5 μm, preferably in the range of 0.2 to 0.75 μm. When the surface roughness is smaller than 0.125 μm, the frictional force of the cleaning part is not sufficient, and it is difficult to improve the cleaning efficiency, and filming may occur. On the other hand, when the surface roughness of the photosensitive member is larger than 1.5 μm, the surface potential varies, and the image quality such as fog noise is likely to be deteriorated. This surface roughness condition is effective when the image forming process speed is as high as 500 mm / second to 2000 mm / second.

A corotron or scorotron is used as the charger, and the charger width is set so that the time required for the photosensitive member to pass through the charger is 50 milliseconds or longer, preferably 55 milliseconds or longer. Since the As ₂ Se ₃ photoconductor and the amorphous silicon photoconductor have a small charging ability, when the charging time is less than 50 msec, the variation in charging becomes large, and the dark attenuation is extremely reduced. In addition, a combination of soft charging by scorotron and corotron charging is effective as a means for reducing variation in charging in a high-speed process.

The wavelength of the exposure light source (writing light source) for forming an image is preferably a short wavelength in consideration of light fatigue of the photoconductor and image resolution. Recently, however, small and low-cost LEDs and LDs are often used as the light source. In consideration of the spectral sensitivity characteristics and the light wavelength characteristics of the As ₂ Se ₃ photoconductor and the amorphous silicon photoconductor, the wavelength λ _{0 of the} writing light may be in the range of λ ₀ ≦ 780 nm, preferably λ ₀ ≦ 680 nm. desirable. In the case of λ ₀ > 780 nm, the photosensitivity of the photoconductor becomes small, so that it is difficult to form a latent image, and because of the long wavelength light, the photoconductor is greatly damaged, resulting in a decrease in charging ability and resolution.

The wavelength λ _{1 of the} static elimination light is also preferably a short wavelength in consideration of the light fatigue and image resolution of the photoreceptor, but recently, a light source is frequently used as a light source with a small and low-cost LED or LD, and the light wavelength is 600 nm or more. It becomes red light (600 to 720 nm). Since long-wavelength light (red light) has a long penetration distance into the photoconductor and an afterimage phenomenon is likely to occur, the wavelength λ _{1 of the} static elimination light is λ ₁ ≦ 680 nm (however, the amount of light is more than four times that of the writing light) ) Is desirable. On the other hand, in the case of λ ₁ <λ ₀ -100 nm, the influence of the latent image of the previous process affects the next process, and an afterimage phenomenon is likely to occur. On the other hand, when λ ₁ > 680 nm, light fatigue of the photosensitive member due to static elimination light increases, resulting in a decrease in charging ability and resolution. A preferable range of λ ₁ is 450 to 660 nm. Thus the relationship of the wavelength lambda ₁ of the discharging light wavelength lambda ₀ of the exposure light source, a _{λ 0 -100nm ≦ λ 1 ≦ 680nm} .

Process time from latent image formation exposure to development start: T ₁ needs to be 70 ≦ T ₁ ≦ 300 msec, and particularly preferably 100 ≦ T ₁ ≦ 250 msec. When 70 ms> T ₁ , the photoresponsiveness of the As ₂ Se ₃ photoconductor and the amorphous silicon photoconductor is poor (the mobility of the optical carrier is about one digit smaller than that of the SeTe photoconductor), so that the developing portion Insufficient image formation in (cannot secure sufficient contrast potential for development). Further, at T ₁ > 300 ms, the charge holding ability of the As ₂ Se ₃ photoconductor and the amorphous silicon photoconductor is small (the dark decay is large), so the contrast potential (the surface of the photoconductor on the toner adhering portion and the non-adhering portion). (Potential difference) decreases.

Development time: T ₂ (contact time between the photoreceptor and the developing brush) needs to be 50 ms ≦ T ₂ ≦ 200 ms, and preferably 60 ms ≦ T ₂ ≦ 100 ms. When 50 ms> T ₂ , the developing time is short, so it is difficult to obtain a sufficient image density (1.4D or more). On the other hand, when T ₂ > 200 ms, the friction caused by the developing brush increases. It tends to cause image quality deterioration such as fogging.

In order to satisfy the development conditions (development time) in the high-speed printing process, it is desirable to take measures such as a multi-stage development method and an increase in the diameter of the development roll. Further, in the case of the multi-stage development method, it is desirable that the developing bias voltage applied to the developing roll is set so as to decrease toward the downstream side in the photosensitive member rotation direction. This is because the As ₂ Se ₃ photoconductor and the amorphous silicon photoconductor have a large dark decay of the surface potential, so that the contrast potential of the photoconductor gradually decreases during the development process.

For the same reason, when an As ₂ Se ₃ photoconductor or an amorphous silicon photoconductor is adopted, it is necessary to pay attention to the contrast potential of the transfer portion. At that time, the contrast potential immediately before the transfer portion is 300 V or more, preferably 350 to 500. When the contrast potential immediately before the transfer portion is smaller than 300 V, the force for electrostatically confining the toner adhering to the photoreceptor is weakened, and the toner image is disturbed by electrostatic attraction during transfer or friction with the paper, There is a risk that image quality degradation such as image resolution degradation is likely to occur.

  The frequency of the AC current applied to the AC corona charger for toner neutralization installed behind the transfer unit: ν needs to be 500 Hz ≦ ν ≦ 7,000 Hz, and particularly 500 Hz ≦ ν ≦ 2,000 Hz is desirable. It is. When ν <500 Hz, the influence on the photosensitive member is large, and the potential variation on the non-charging side becomes large. In addition, when ν> 7,000 Hz, the current flowing into the charger shield becomes large, and the charge removal effect of the toner tends to be lowered, so that the cleaning efficiency is lowered.

The film thickness of the photoreceptor using As ₂ Se ₃ or amorphous silicon as a base material is 40 μm or more and 80 μm or less, preferably 50 μm or more and 75 μm or less. When the thickness of the photosensitive member is less than 40 μm, it is difficult to obtain the initial surface potential of the photosensitive member, and problems such as dielectric breakdown of the photosensitive member are likely to occur (As ₂ Se ₃ photosensitive member has a withstand voltage of about 15 V / It is about μm). On the other hand, when the film thickness is greater than 80 μm, problems such as an increase in residual potential, a decrease in light response, and a decrease in resolution are likely to occur.

  In the high-speed printing process, it is effective to add impurities of a halogen element such as iodine or chlorine to the photoreceptor, and the addition amount is preferably 1 ppm or more and 500 ppm or less. If the addition amount is less than 1 ppm, the effect of impurity addition is small, the photoresponsiveness is poor, and it is difficult to obtain a sufficient development contrast potential in a high-speed process (the time between exposure and development is about 100 milliseconds or less). The effect appears particularly at low temperatures. On the other hand, when the addition amount is more than 500 ppm, the film resistance (volume resistance value) of the photoreceptor is extremely lowered, and the charging ability and dark attenuation characteristics are lowered.

  In the image forming apparatus according to the present invention, an electrostatic latent image is formed on the photosensitive drum by electrostatic application and exposure. As a specific electrostatic application method, a relatively uniform charge is held on the surface of the photoreceptor by a charging method (corotron or scorotron) using corona discharge.

  Next, an image to be formed is drawn on the surface of the photoreceptor by an exposure light source. At that time, the surface charge of the photosensitive member in the portion irradiated with light is canceled by electrons (or holes) generated by the photoelectric effect in the photosensitive layer, and an electrostatic latent image is formed on the surface of the photosensitive member after exposure. It is formed. Thereafter, the electrostatic latent image is made visible by electrostatic toner adhesion in the developing unit. This visible image is transferred onto the paper in the subsequent transfer section. The toner and the electrostatic latent image left on the surface of the photoconductor are removed by a subsequent static elimination and cleaning process, and the photoconductor is ready for charging for the next printing.

In recent years, OPC, which is excellent in manufacturing cost, is becoming mainstream as a photoreceptor material used for an electrostatic application method. However, some high-speed printers such as line printers and high-speed copying machines employ As ₂ Se ₃ photoconductors. This is because the surface hardness of the As ₂ Se ₃ photoconductor is large and has a single-layer structure, so that it has good wear resistance and environmental resistance characteristics (especially high temperature characteristics) against paper and developer in a high-speed printing process. It is. Amorphous silicon photoconductors are also being used. However, As ₂ Se ₃ photoconductors and amorphous silicon photoconductors, which are excellent in wear resistance, have a volume resistance of 2 to 4 digits smaller than that of OPC or SeTe photoconductors (As ₂ Se ₃ photoconductors). body ^{≒ 1 × 10 11 Ω · cm} ) for a low charge retention capability of the photoreceptor (easy surface charge of photoreceptor leaks), also there is a problem that larger dark decay of the surface potential. That is, the contrast potential at which the latent image can be held before the electrostatic latent image generated in the exposure unit reaches the transfer unit through the development process is reduced. As a result, the electric field for confining the electrostatically adhered toner to the low potential portion of the electrostatic latent image is reduced, and the toner image is likely to be disturbed. In other words, the resolution of the image at the transfer portion is likely to decrease. Hereinafter, the case of an As ₂ Se ₃ photoconductor will be described as an example.

  FIG. 1 is an example of a schematic diagram of an image forming apparatus according to the present invention. In the figure, reference numeral 1 denotes a photosensitive drum having a diameter of 150 to 400 mm, which rotates at a peripheral speed (process speed: vP) of 500 to 2,000 mm / sec. Around the photosensitive drum 1, a charger 2, a developing device 3, a transfer device 4, an AC static eliminator 5, an erase lamp 6, and a cleaning device 7 such as a cleaning brush, a blade, and a blower are disposed. As shown in the figure, a cleaning device 7 is interposed between the charger 2 and the erase lamp 6.

  A paper feed retractor 8 is disposed below the transfer device 4, and a paper discharge retractor 9 is disposed above. On the upper right side of the photosensitive drum 1 in the figure, an exposure light source of any one of a semiconductor laser, an LED, and a gas laser, and a scanner unit 10 including a polygon mirror and a lens are disposed.

The charging time of the As ₂ Se ₃ photoconductor or the amorphous silicon photoconductor is 50 msec to 300 msec, preferably 50 msec to 200 msec. As a result, the amount of dark decay after charging can be suppressed and the size of a practical charger can be obtained.

  Image light X is irradiated from the scanner unit 10 to the photosensitive drum 1 uniformly charged by the charger 2, and an electrostatic latent image is formed on the photosensitive drum 1. The electrostatic latent image moves toward the developing device 3 as the photosensitive drum 1 rotates, and is supplied with toner by the developing device 3 to be visualized as a toner image. The toner image on the photosensitive drum 1 is transferred onto the paper 11 by the transfer device 4. The paper 11 is conveyed toward the transfer device 4 and the photosensitive drum 1 by the paper feed retractor 8, and the paper 11 after the transfer is sent to the fixing device (not shown) by the paper discharge retractor 9, and the toner image is a permanent image. As established.

After the transfer, the photosensitive drum 1 has its surface charge removed by the erase lamp 6 and then the residual toner is removed by the cleaning device 7 to prepare for the next image formation. The arrangement of the erase lamp 6 may be between the transfer unit 4 and the AC static eliminator 5, and this is preferable in order to suppress the occurrence of the afterimage phenomenon. The wavelength λ _{1 of the} erase light is λ ₁ ≦ 780 nm, preferably λ ₁ ≦ 680 nm, for the As ₂ Se ₃ photoconductor and amorphous silicon photoconductor, and for the wavelength λ _{0 of the} write light. When λ ₀ −100 nm ≦ λ ₁ ≦ λ ₀ +50 nm, it is preferable for suppressing the afterimage phenomenon and light fatigue, and particularly effective when 600 nm ≦ λ ₀ ≦ 680 nm.

  In the drawing, 3a is a first developing roll, 3b is a second developing roll, 3c is a third developing roll, and the first developing roll 3a and the second developing roll from the upstream side to the downstream side in the rotation direction of the photosensitive drum 1. 3b and the third developing roll 3c are arranged in this order. Reference numeral 12 denotes toner, and 13, 14, 15, and 16 denote potential sensors arranged at predetermined positions.

FIG. 2 shows changes in the surface potential of the As ₂ Se ₃ photosensitive drum 1 in this image forming process. In the figure, the horizontal axis represents the image forming process of charging, exposure, development, recharging, and transfer, and the vertical axis represents the surface potential of the photosensitive drum. The solid line in the figure indicates the surface potential in the non-exposed area, and the dotted line indicates the surface potential in the exposed area. The difference in surface potential between the non-exposed area and the exposed area during development is the development contrast potential. The surface potential difference of the part is the toner image contrast potential.

  As can be seen from the change in the potential of the non-exposed portion of the solid line, the surface potential of the photosensitive member after charging decreases exponentially, and a potential drop of about 400 V occurs in about 0.5 seconds from charging to transfer. The contrast potential, which was about 700 V immediately after exposure, becomes about 300 V immediately before transfer, and dark decay is large, so that the latent image is destroyed.

  3A and 3B are diagrams showing the relationship between the collapse of the latent image and the toner image. FIG. 3A shows a state where the latent image is not destroyed immediately after development, and FIG. 3B shows the state where the latent image is destroyed immediately before transfer. Show. In the state where the latent image is not collapsed as shown in FIG. 5A, the height H of the electrostatic wall that prevents the disturbance of the toner image attached to the electrostatic latent image is high, but the dark decay of the photosensitive drum is reduced. Because of its large size, the latent image collapses when the height H of the wall rapidly decreases as shown in FIG. Therefore, when the toner image is transferred to the paper, the toner is likely to be scattered due to rubbing with the paper, and the image quality is deteriorated such as a reduction in resolution.

  Furthermore, when red light (long wavelength light) such as a semiconductor laser or LED is used for the latent image writing light source or the neutralization light source, the charge holding power of the photoreceptor is further reduced. This is because long-wavelength light has a deep penetration distance into the photoconductor, and the photocarrier generated in the photoconductive layer is deep, so that the generated light carrier remains in the photoconductor in a short process time such as high-speed printing. It is because it is easy to do.

As one of the measures for preventing this resolution reduction, it is conceivable to sufficiently increase the initial contrast potential at the time of exposure. However, using an As ₂ Se ₃ photoconductor with a small volume resistance and a low charging ability at a high speed and having a large contrast potential increases the burden on the charging process. Problems such as breakdown voltage also occur (the breakdown voltage of the As ₂ Se ₃ photoreceptor is about 15 V / μm).

Therefore, in the present invention, even if an As ₂ Se ₃ photoconductor or an amorphous silicon photoconductor that is excellent in printing resistance and can be expected to have a long life is used at a high speed, it does not cause fogging or a reduction in resolution, and is stably high quality An object of the present invention is to provide an image forming apparatus in which charging conditions, development conditions, exposure / static discharge conditions, and photoconductor specifications are optimized for the purpose of printing. In other words, the dark decay characteristics and variations of the photoreceptor potential were improved by optimizing the charging time under the charging conditions, and both image density and fogging were achieved by optimizing the developing time and developing bias under the developing conditions. Furthermore, in order to reduce photo fatigue (afterimage phenomenon, dark decay reduction) of the photoconductor, the writing light / static discharge light conditions were optimized.

First, regarding the charging conditions, the relationship between the charging time and the drum potential holding ratio is shown in FIG. In this test, an LED having a wavelength of 600 nm (light quantity: 300 is μW / cm ² ) is used as an erase light source, and an As ₂ Se ₃ photoconductor added with 20 ppm of iodine is used as a photoconductor. The potential retention of was measured. For example, when the charging time is 55 msec, the drum potential is charged at a drum potential of 800 V (V ₀ ) for 55 msec, and after 300 msec elapse, the drum potential (V ₁ ) is measured and V ₁ / V This is a numerical value obtained by ₀ × 100 (in this case, the drum potential holding ratio is 70%).

As is clear from the figure, when the charging time is shorter than 50 milliseconds, the potential holding ratio of the drum is drastically decreased. On the other hand, when the charging time is longer than 55 milliseconds, the drum potential holding ratio is substantially constant. The upper limit of the charging time is about 200 milliseconds due to the device configuration. This tendency was almost the same in conditions such as the shape of the charger, charging current, erase conditions, and the amount of impurity added to the photoreceptor (1 to 500 ppm). As described above, the As ₂ Se ₃ photoconductor has a relatively large dark decay. Therefore, by setting the drum potential holding ratio after 70 msec from charging to 70% or more, the resolution can be maintained and the fog can be reduced. .

FIG. 5 shows the relationship between the wavelength of the writing light and the static elimination light and the afterimage phenomenon. In this test, the amount of writing light was 4 times the half-exposure amount of the photoconductor (As ₂ Se ₃ ), and the amount of charge removal light was 16 times the half-exposure amount. Evaluation of the afterimage phenomenon was carried out by printing a 1-inch solid black image, printing horizontal line images at intervals of one line, and visually checking for the presence of the afterimage phenomenon.

In the figure, white circles indicate that no afterimage phenomenon has occurred, and black circles indicate that an afterimage phenomenon has occurred. As can be seen from the figure, the afterimage phenomenon can be prevented when the relationship between the wavelength of the writing light: λ ₀ and the wavelength of the static elimination light: λ ₁ is λ ₁ ≧ λ ₀ -100 nm.

  FIG. 6 shows the relationship between the wavelength of the static elimination light and the potential holding ratio of the drum. The drum potential holding ratio in this test is the ratio of the drum potential VA immediately after exposure measured by the potential sensor 13 in FIG. 1 and the drum potential VB immediately after development measured by the potential sensor 14 (VB / (VA × 100). The process time between the potential sensor 13 and the potential sensor 14 is about 300 milliseconds.

  As is clear from this figure, the drum potential holding ratio decreases as the wavelength of the static elimination light increases, and the drum potential holding ratio decreases below 50% when the wavelength exceeds 680 nm. It becomes difficult to maintain about 300V). Accordingly, it is necessary to use a charge elimination light having a wavelength of 680 nm or less.

  Next, as the photoreceptor conditions, FIG. 7 shows the relationship between the film thickness of the photoreceptor, the residual potential, and the limit drum surface potential. In this test, the residual potential and the drum potential were measured by the potential sensor 14 in FIG. The black circles in the figure indicate the residual potential, and the black triangles indicate the limit drum surface potential.

  As is apparent from the figure, the residual potential and the limit drum potential increase as the thickness of the photosensitive member increases. Here, since an increase in the residual potential causes a decrease in image density, the residual potential is generally good at 100 V or less, so that the film thickness of the photoreceptor needs to be regulated to 80 μm or less. The limit drum surface potential is a surface potential that can be stably used without causing dielectric breakdown such as pinholes. Therefore, it can be seen that the film thickness of the photoreceptor needs to be 40 μm or more in order to obtain a sufficient contrast potential (about 400 V or more at the developing portion). This relationship is the same even when an amorphous silicon photoconductor is used. Therefore, it is necessary to regulate the film thickness of the photosensitive member in the range of 40 to 80 μm, preferably 50 to 75 μm.

For the As ₂ Se ₃ photoconductor used in the high-speed process, it is effective to add a halogen element such as iodine or chlorine in order to improve the photoresponse characteristics. FIG. 8 shows the relationship between the amount of iodine added and the electrophotographic characteristics (initial potential, residual potential, potential holding ratio, photoresponse time) of the photoreceptor.

  As is clear from this figure, the addition of a small amount of iodine (1 ppm or more) significantly increases the photoresponse time, but the charging ability and voltage holding ratio decrease as the addition amount increases. When the amount of iodine exceeds 500 ppm, the voltage holding ratio of the drum becomes 50% or less, and it becomes difficult to maintain a sufficient contrast potential. This tendency also appears in other halogen elements such as chlorine. Therefore, it is necessary to regulate the addition amount of the halogen element in the range of 1 to 500 ppm.

FIG. 9 shows the dark decay curve (A) of the non-exposed portion and the light decay curve (B) of the exposed portion of the As ₂ Se ₃ photoconductor. Measurement conditions were a writing light wavelength: 680 nm (light quantity: 7 mW / cm ² ), and an exposure output was set to 7 mW on the surface of the photosensitive drum 1. As the photoconductor, an As ₂ Se ₃ photoconductor added with 50 ppm iodine was used.

From the light attenuation curve (B) in the figure, it can be seen that a time of 70 milliseconds or more after exposure is required for the residual potential to become almost stable (the residual potential is about 100 V or less). On the other hand, if the time after exposure exceeds 800 milliseconds, the drum potential of the non-exposed part becomes 400 V or less due to dark decay of the surface potential, and a sufficient contrast potential cannot be obtained. Therefore, the process time T ₁ from exposure to the start of development needs to be 70 ms or more.

FIG. 10 shows the relationship between the time from exposure to the start of development and the limit resolution. In this test, an As ₂ Se ₃ photoconductor was used, a semiconductor laser having a wavelength of 680 nm was used as a writing light source, and an LED (light amount: 300 μW / cm ² ) was used as an erase light source. The developing conditions were a developing machine equipped with three developing rolls, a two-component developer was used as the developer, and a styrene acrylic toner having an average particle diameter of 11 μm was used as the toner. The photosensitive member surface potential is about 800 V immediately before the developing machine and a development contrast potential of 300 V. As the photoconductor, an As ₂ Se ₃ photoconductor added with 20 ppm and 500 ppm of iodine and an additive-free As ₂ Se ₃ photoconductor were used, and the surface roughness of the photoconductor was 0.75 μm.

The resolution was evaluated by evaluating dot reproducibility by measuring MF (Modulation Function). Here, MF evaluates the contrast of an image by the degree of modulation. The image density of a 1 dot on 1 dot off image is measured with a microdensitometer, and a high density value and a low density value are based on the average density. The average values _Dmax and _Dmin were calculated and calculated by the following formula.

FM value = (D _max −D _min ) / (D _max + D _min ) × 100 (%)
Accordingly, the larger the MF value, the better the dot reproducibility, and this time, an MF value of 50% or more was set as a pass value. The target value of resolution is 600 dpi.

  From FIG. 10, it can be seen that the longer the exposure-development time, the smaller the limit resolution obtained. This is because the latent image of the dots formed on the photoconductor collapses over time and the reproducibility decreases. It can also be seen that the limit resolution in the same exposure-development time decreases as the amount of halogen element (iodine here) added to the photoreceptor increases. This is because the material resistance of the photoreceptor is lowered by the addition of the halogen element, and the latent image is easily broken. From the results shown in FIG. 10, it can be seen that the exposure-development time must be set within 300 milliseconds in order to achieve the target resolution of 600 dpi.

  FIG. 11 shows the relationship between the development time (when there are a plurality of development rolls, the total thereof), the image density, and the fog density. In the figure, black circles indicate the relationship between development time and image density, and black triangles indicate the relationship between development time and fog density. The image density is evaluated by measuring the reflection density of an image of a solid black print sample (measuring device: Graphcs Microsystems Inc., product name: Macbeth reflection densitometer). The evaluation was performed (measuring instrument: Hunter Associates Laboratory Inc., trade name Hunter densitometer).

  As shown in the figure, when the development time is 50 ms or more and the image density is about 1.4 (D) or more, the fog density increases as the development time becomes longer, and when the development time exceeds 200 ms. The fog density is about 0.8% or more. Therefore, it is necessary to regulate the development time in the range of 50 to 200 milliseconds, preferably 60 to 100 milliseconds.

  FIG. 12 shows the relationship between the developing bias condition, the image density, and the fog density. In this test, as shown in FIG. 1, a developing machine having three developing rolls 3a to 3c, a two-component developer was used as a developer, and a styrene acrylic toner having an average particle diameter of 11 μm was used as a toner. . The surface potential of the photoreceptor is about 750 V just before the developing machine.

  As shown in the figure, as a result of examining the image density and the fog density when the development bias voltages applied to the three development rolls (first roll, second roll, and third roll) are variously changed, the development bias voltage is determined as follows. It has been found that the fog can be reduced by decreasing the size toward the downstream side in the rotation direction of the photosensitive member.

  FIG. 13 shows the relationship between the contrast potential of the transfer portion and the line width of one dot line. This measurement was performed with the apparatus shown in FIG. 1, and the contrast potential was measured with the potential sensor 15 in FIG. The spot diameter of the writing light on the drum surface was about 100 μm, and an optical system equivalent to 240 dpi was used.

  As can be seen from the figure, the line width increases as the contrast potential of the transfer portion decreases, and the resolution decreases. Since a slight line thickening occurs depending on development conditions and the like, it can be seen that when the limit line width is set to 120 μm, the contrast potential of the transfer portion is 300 V or more and the line width of one dot line is 120 μm or less.

  FIG. 14 shows the relationship between the frequency of the AC static eliminator, the variation in drum potential, and the cleaning efficiency. In this test, the applied voltage of the AC static eliminator was about 5 kV as an execution value, and the variation in potential was measured by the potential sensor 16 in FIG. The black circles in the figure indicate the relationship between the frequency of the AC static eliminator and the variation in drum potential, and the black triangles indicate the relationship between the frequency of the AC static eliminator and the cleaning efficiency.

  As is clear from the figure, when the frequency of the AC static eliminator is smaller than 500 Hz, the variation in drum potential increases rapidly, resulting in a variation in potential of 100 V or more. Further, it can be seen that the cleaning efficiency gradually decreases as the frequency increases, and that the cleaning efficiency becomes 85% or less when the frequency exceeds 7,000 Hz. This tendency was almost the same when the applied voltage was in the range of 2 kV to 7 kV. For these reasons, the frequency of the AC static eliminator is in the range of 500 to 7,000 Hz, preferably in the range of 500 to 2,000 Hz.

Next, specific examples of the present invention will be described.
Example 1
In the image forming apparatus shown in FIG. 1, an InGaAlP / GaAs semiconductor laser (wavelength 680 nm) was used as a writing exposure light source of the scanner unit 10, and an exposure output was set to about 6 mW on the surface of the photosensitive drum 1. As the photosensitive drum 1, an As ₂ Se ₃ photosensitive body (shape: outer diameter 262 mm × length 430 mm, film thickness: 60 μm) to which 20 ppm of iodine was added was used to improve photoresponsiveness. The rotational speed of the photosensitive drum 1 is 60 rpm, and the process time between the exposure unit and the developing machine 3 is about 180 milliseconds.

  Image formation according to the present invention was performed as follows. First, a surface potential of about +800 V is charged to the photosensitive drum 1 by applying a voltage of about +7.5 kV to the charger 2. The diameter of the corona wire of the charger 2 was 70 μm, the distance between each wire and the distance between the drum and the wire was about 10 mm, and the width of the charger 2 in the circumferential direction of the drum was 80 mm.

  Next, image exposure is performed by the scanner unit 10 to form a latent image on the surface of the photosensitive drum 1. Here, in this embodiment, the laser exposure spot diameter is about 70 μm and the resolution is 480 dpi. As the developing machine 3, a multistage developing machine provided with three developing rolls 3a to 3c was used. Each developing roll had a diameter of 50 mm and a developing time of about 90 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 11 μm. The developing bias voltage was set to 400 V / 350 V / 300 V from the upstream side to the downstream side in the rotation direction of the photosensitive drum 1.

The toner image visualized by the developing device 3 is transferred to the paper 11 by the transfer device 4. The transfer voltage was about -6.0 kV. The untransferred residual toner is neutralized by a subsequent AC static eliminator 5 (AC frequency: 500 Hz, applied voltage: 5 kV), and the electrostatic latent image on the photosensitive drum 1 is erased by an erase lamp 6 (a 15 W white fluorescent lamp is red). It is neutralized through a filter with a wavelength of about 660 nm and a light quantity of 300 μW / cm ² (red light). Thereafter, the surface of the photosensitive drum 1 is cleaned by a cleaning device 7 (in this embodiment, a fur brush is used for cleaning) and is prepared for the next image formation.

  Reference numerals 13, 14, and 15 denote surface potential sensors. The sensor 13 was installed immediately after exposure, the sensor 14 was installed immediately after the developing machine, and the sensor 15 was installed immediately before transfer, and the surface potential value of the photosensitive drum 1 was detected. The drum potential according to the image forming conditions is non-exposed portion potential: V0 / exposed portion potential: VR = 800 V / 90 V at the position of sensor 13, 630 V / 105 V at the position of sensor 14, and 500 V / 100 V at the position of sensor 15. It was. The voltage holding ratio at 70 milliseconds after charging was 70%, and the residual potential was 85V.

  As a result of performing a print test of about 5,000 pages under the above conditions, the print sample has a solid image density of 1.45 (D), a fog density of 0.4%, and a high definition image quality equivalent to 480 dpi. Obtained. Moreover, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

(Example 2)
A red LED (wavelength 680 nm) was used as the writing exposure light source, and the exposure output was set to about 6 mW on the surface of the photosensitive drum 1. As the photosensitive drum 1, an As ₂ Se ₃ photosensitive body (shape: outer diameter 262 mm × length 430 mm) to which 300 ppm of iodine was added was used to improve photoresponsiveness, and the film thickness of the photosensitive body was set to 40 μm. The rotational speed of the photosensitive drum 1 is 60 rpm, and the process time between the exposure unit and the developing machine 3 is about 150 milliseconds. The width of the charger 2 was set to 110 mm, and the charging time of the photosensitive member was set to about 133 milliseconds. The LED exposure spot diameter was about 40 μm and the resolution was 600 dpi.

The developing machine 3 was the same as in Example 1, and the development time was about 95 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 7 μm. The development bias voltage was set to 400 V / 350 V / 300 V from the upstream side in the rotation direction of the photosensitive drum 1. As the erase lamp 6, a 660 nm LED (light quantity: 400 μW / cm ² ) was adopted.

  The other image forming conditions were the same as in Example 1, and a printing test of about 5,000 pages was performed. As a result, the drum potential at the position of the potential sensor 13 was non-exposed portion potential: V0 / exposed portion potential: VR = 800 V / 80 V, 630 V / 100 V at the position of the potential sensor 14, and 510 V / 100 V at the position of the potential sensor 15. The voltage holding ratio at 70 milliseconds after charging was 70%, and the residual potential was 75V. In addition, the printed sample had a high-definition image quality with a solid density of 1.45 (D), a fog density of 0.45%, and a resolution equivalent to 600 dpi. Moreover, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

(Example 3)
A HeNe laser (wavelength 635 nm) was used as the writing exposure light source, and the exposure output was set to about 6 mW on the surface of the photosensitive drum 1. As the photosensitive drum 1, an As ₂ Se ₃ photosensitive body (shape: outer diameter 262 mm × length 430 mm, film thickness: 60 μm) to which 10 ppm of iodine was added was used to improve photoresponsiveness. The rotational speed of the photosensitive drum 1 is 72 rpm, and the process time between the exposure unit and the developing machine 3 is about 125 milliseconds.

  Image formation according to this example was performed as follows. First, a surface potential of about +800 V is charged to the photosensitive drum 1 by applying a voltage of about +8.5 kV to the charger 2. The diameter of the corona wire of the charger 2 is 70 μm, the distance between each wire and the distance between the drum and the wire is about 10 mm, and the width of the charger 2 in the circumferential direction of the drum is 110 mm. Set with seconds.

  Next, image exposure is performed by the scanner unit 10 to form a latent image on the surface of the photosensitive drum 1. Here, in this embodiment, the laser exposure spot diameter is about 70 μm and the resolution is 480 dpi.

  As the developing machine 3, a multi-stage developing machine provided with three developing rolls was used, each developing roll diameter was 50 mm, and the developing time was about 80 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 11 μm. The developing bias voltage was set to 350 V / 300 V / 250 V from the upstream side to the downstream side in the rotation direction of the photosensitive drum 1.

The toner image visualized by the developing device 3 is transferred to the paper 11 by the transfer device 4. The transfer voltage was about -6.0 kV. The untransferred residual toner is neutralized by a subsequent AC static eliminator 5 (AC frequency: 5 kHz, applied voltage: 5 kV), and the electrostatic latent image on the photosensitive member is erased by a erase filter 6 (15 W white fluorescent lamp with a red filter). Through a red light having a wavelength of about 600 nm and a light quantity of 250 μW / cm ² .

  The drum potential according to the image forming conditions is as follows: non-exposed portion potential: V0 / exposed portion potential: VR = 800V / 85V at the position of the potential sensor 13, 680V / 105V at the position of the potential sensor 14, and 550V / at the position of the potential sensor 15. As a result of performing a printing test of about 5,000 pages at 100 V, the printed sample has a solid image density of 1.35 (D), a fog density of 0.4%, and a high definition image quality equivalent to 480 dpi. It was. Moreover, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

Example 4
An Ar laser (wavelength 488 nm) was used as a writing exposure light source, and the exposure output was set to about 8 mW on the surface of the photosensitive drum 1. As the photosensitive drum 1, an As ₂ Se ₃ photosensitive body (shape: outer diameter 262 mm × length 430 mm) to which 3 ppm of iodine was added was used to improve photoresponsiveness, and the film thickness of the photosensitive body was 50 μm. The rotational speed of the photosensitive drum 1 is 80 rpm, and the process time between the exposure unit and the developing machine 3 is about 120 milliseconds. The width of the charger 2 was set to 110 mm, and the charging time of the photosensitive member was set to about 100 milliseconds. The LED exposure spot diameter was about 40 μm and the resolution was 600 dpi.

As the developing machine 3, a multistage developing machine having four developing rolls was used, the developing roll diameter was 50 mm, and the developing time was about 90 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 7 μm. The development bias voltage was set to 400 V / 350 V / 300 V / 250 V from the upstream side to the downstream side in the rotation direction of the photosensitive drum. The erase lamp 6 was a 15 W white fluorescent lamp with a wavelength of about 450 nm and a light amount of 250 μW / cm ² through a blue filter (BPB45).

  When the other image forming conditions were the same as in Example 3 and a printing test of about 5,000 pages was performed, the drum potential at the position of the potential sensor 13 was non-exposed portion potential: V0 / exposed portion potential: VR = 800 V / 75 V, 700 V / 85 V at the position of the potential sensor 14, 610 V / 85 V at the position of the potential sensor 15, and the print sample has a solid density of 1.50 (D), a fog density of 0.3%, and a resolution equivalent to 600 dpi High-definition image quality was obtained. Moreover, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

(Example 5)
Four semiconductor lasers (wavelength 635 nm) were used in an array form as a writing exposure light source, and the exposure output was set to about 8 mW on the surface of the photosensitive drum 1. As the photosensitive drum 1, an As ₂ Se ₃ photosensitive body (shape: outer diameter 262 mm × length 430 mm) to which 50 ppm of chlorine was added was used to improve photoresponsiveness, and the film thickness of the photosensitive body was 45 μm. The rotational speed of the photosensitive drum 1 is 80 rpm, and the process time between the exposure unit and the developing machine 3 is about 120 milliseconds. The width of the charger 2 was set to 80 mm, and the charging time of the photosensitive member was set to about 73 milliseconds. The LED exposure spot diameter was about 40 μm and the resolution was 600 dpi.

As the developing machine 3, a multistage developing machine having four developing rolls was used, the developing roll diameter was 50 mm, and the developing time was about 90 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 7 μm. The developing bias voltage was set to 400 V / 350 V / 300 V / 250 V from the upstream side in the rotation direction of the photosensitive drum. As the erase lamp 6, an LED array having a wavelength of 600 nm (light quantity: 350 μW / cm ² ) was used.

  When the other image forming conditions were the same as in Example 4 and a printing test of about 5,000 pages was performed, the drum potential was the non-exposed portion potential: V0 / exposed portion potential: VR = 800 V / 85 V at the position (A). , (B) position is 660V / 100V, (C) position is 500V / 100V, the print sample has a solid density of 1.45 (D), fog density of 0.5%, resolution is high definition equivalent to 600 dpi The image quality of was obtained. In addition, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

(Example 6)
In the apparatus shown in FIG. 1, an nGaAlP / GaAs semiconductor laser (wavelength 680 nm) was used as a writing exposure light source in the scanner unit 10, and the exposure output was set to about 6 mW on the surface of the photosensitive drum 1. The photoreceptor drum 1 uses an As ₂ Se ₃ photoreceptor (shape: outer diameter 262 mm × length 430 mm, film thickness: 60 μm) to which 20 ppm of iodine is added to improve photoresponsiveness, and has a surface roughness of 0.375 μm. It was. The rotational speed of the photosensitive drum 1 is 60 rpm, and the process time between the exposure unit and the developing machine 3 is about 180 milliseconds.

  Image formation according to the present invention was performed as follows. First, a surface potential of about +800 V is charged to the photosensitive drum 1 by applying a voltage of about +7.5 kV to the charger 2. The diameter of the corona wire of the charger 2 was 70 μm, and the distance between each wire and the distance between the drum and the wire were about 10 mm. The width of the charger 2 in the drum circumferential direction was 80 mm.

  Next, image exposure is performed by the scanner unit 10 to form a latent image on the surface of the photosensitive drum 1. In this embodiment, the laser exposure spot diameter is about 45 μm and the resolution is 600 dpi. As the developing machine 3, a multistage type developing machine having three developing rolls was used, the developing roll diameter was 50 mm, and the developing time was about 90 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 11 μm. The developing bias voltage was set to 400 V / 350 V / 300 V from the upstream side to the downstream side in the rotation direction of the photosensitive drum.

The toner image visualized by the developing device 3 is transferred to the paper 11 by the transfer device 4. The transfer voltage was about -6.0 kV. The untransferred residual toner is neutralized by a subsequent AC static eliminator 5 (AC frequency: 500 Hz, applied voltage: 5 kV), and the electrostatic latent image on the photosensitive member is erased by a erase filter 6 (15 W white fluorescent lamp with a red filter). Then, the charge is eliminated with a wavelength of about 660 nm and a light quantity of 300 μW / cm ² (red light). Thereafter, the surface of the photosensitive drum 1 is cleaned by a cleaning device 7 (in this embodiment, a fur brush is used for cleaning) and is prepared for the next image formation.

  The drum potential according to the image forming conditions is as follows: non-exposed portion potential: V0 / exposed portion potential: VR = 800 V / 90 V at the position of the potential sensor 13, 630 V / 105 V at the position of the potential sensor 14, and 500 V / at the position of the potential sensor 15. 100V. The voltage holding ratio at 70 milliseconds after charging was 70%, and the residual potential was 85V.

  As a result of performing a printing test of about 5,000 pages under the above conditions, the printed sample has a solid density of 1.45 (D) and a fog density of 0.4% (fog density; N is a Hunter color difference densitometer. Measured and obtained by the following formula: N = γmax−γA, γmax: paper reflectance (maximum reflectance), γA: average reflectance in the measurement area A), MF value is 68%, resolution is equivalent to 600 dpi High definition image quality was obtained. Moreover, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

(Example 7)
A red LED (wavelength 780 nm) was used as a writing exposure light source, and the exposure output was set to about 6 mW on the surface of the photosensitive drum 1. The photosensitive drum 1 is an As ₂ Se ₃ photosensitive body (shape: outer diameter 262 mm × length 430 mm) to which 300 ppm of iodine is added in order to improve photoresponsiveness. The photosensitive body has a film thickness of 40 μm and a surface roughness of It was set to 0.75 μm. The rotational speed of the photosensitive drum 1 is 60 rpm, and the process time between the exposure unit and the developing machine 3 is about 70 milliseconds. The width of the charger 2 was set to 110 mm, and the charging time of the photosensitive member was set to about 133 milliseconds. The LED exposure spot diameter was about 40 μm and the resolution was 600 dpi.

The developing machine 3 was the same as in Example 6, and the development time was about 95 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 7 μm. The developing bias voltage was set to 400 V / 350 V / 300 V from the upstream side to the downstream side in the rotation direction of the photosensitive drum. As the erase lamp 6, a 660 nm LED (light quantity: 400 μW / cm ² ) was adopted.

  The other image forming conditions were the same as in Example 6, and a printing test of about 5,000 pages was performed. The drum potential at the position of the potential sensor 13 was non-exposed portion potential: V0 / exposed portion potential: VR = 800 V / 80 V, 630 V / 100 V at the position of the potential sensor 14, and 510 V / 100 V at the position of the potential sensor 15. The voltage holding ratio at 70 milliseconds after charging was 70%, and the residual potential was 75V. In addition, the print sample had a solid density of 1.45 (D), a fog density of 0.45%, an MF value of 60%, and a high definition image quality equivalent to 600 dpi. Moreover, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

(Example 8)
A HeNe laser (wavelength 635 nm) was used as the writing exposure light source, and the exposure output was set to about 6 mW on the surface of the photosensitive drum 1. As the photosensitive drum 1, an As ₂ Se ₃ photosensitive body (shape: outer diameter 262 mm × length 430 mm, film thickness: 60 μm) to which 10 ppm of iodine was added was used to improve photoresponsiveness. The surface roughness was 1.5 μm. The rotational speed of the photosensitive drum 1 is 72 rpm, and the process time between the exposure unit and the developing machine 3 is about 125 milliseconds.

  Image formation according to this example was performed as follows. First, a surface potential of about +800 V is charged to the photosensitive drum 1 by applying a voltage of about +8.5 kV to the charger 2. The diameter of the corona wire of the charger 2 was 70 μm, and the distance between each wire and the distance between the drum and the wire were about 10 mm. In addition, the charging time of the photosensitive member was set to about 111 milliseconds by setting the width of the charger 2 in the drum circumferential direction to 110 mm. Next, image exposure is performed by the scanner unit 10 to form a latent image on the surface of the photosensitive drum 1. Here, in this embodiment, the laser exposure spot diameter is about 35 μm and the resolution is 800 dpi.

  As the developing machine 3, a multistage developing machine having three developing rolls was used, the developing roll diameter was 50 mm, and the developing time was about 80 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 11 μm. The developing bias voltage was set to 350 V / 300 V / 250 V from the upstream side to the downstream side in the rotation direction of the photosensitive drum.

The toner image visualized by the developing device 3 is transferred to the paper 11 by the transfer device 4. The transfer voltage was about -6.0 kV. The untransferred residual toner is neutralized by a subsequent AC static eliminator 5 (AC frequency: 5 kHz, applied voltage: 5 kV), and the electrostatic latent image on the photosensitive member is erased by a erase filter 6 (15 W white fluorescent lamp with a red filter). Through a red light having a wavelength of about 600 nm and a light quantity of 250 μW / cm ² .

  The drum potential according to the image forming conditions is as follows: non-exposed portion potential: V0 / exposed portion potential: VR = 800V / 85V at the position of the potential sensor 13, 680V / 105V at the position of the potential sensor 14, and 550V / at the position of the potential sensor 15. As a result of performing a printing test of about 5,000 pages at 100 V, the printed sample has a high-definition image quality with a solid density of 1.35 (D), a fog density of 0.4%, and an MF value of 55% or more. was gotten. Moreover, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

Example 9
An Ar laser (wavelength 488 nm) was used as a writing exposure light source, and the exposure output was set to about 8 mW on the surface of the photosensitive drum 1. The photoconductor drum 1 uses an As ₂ Se ₃ photoconductor (shape: outer diameter 262 mm × length 430 mm, surface roughness: 0.75 μm) to which 3 ppm of iodine is added in order to improve photoresponsiveness. The thickness was 50 μm. The rotational speed of the photosensitive drum 1 is 80 rpm, and the process time between the exposure unit and the developing machine 3 is about 80 milliseconds. The width of the charger 2 was 110 mm. The Ar (argon) exposure spot diameter was about 40 μm and the resolution was 600 dpi.

As the developing machine 3, a multistage developing machine having four developing rolls was used, the developing roll diameter was 50 mm, and the developing time was about 90 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 7 μm. The development bias voltage was set to 400 V / 350 V / 300 V / 250 V from the upstream side to the downstream side in the rotation direction of the photosensitive drum. The erase lamp 6 was a 15 W white fluorescent lamp with a wavelength of about 450 nm and a light amount of 250 μW / cm ² through a blue filter (BPB45).

  The other image forming conditions were the same as in Example 8, and a printing test of about 5,000 pages was performed. As a result, the drum potential at the position of the potential sensor 13 was non-exposed portion potential: V0 / exposed portion potential: VR = 800 V / 75 V, 700 V / 85 V at the position of the potential sensor 14 and 610 V / 85 V at the position of the potential sensor 15. The print sample has a solid density of 1.50 (D), a fog density of 0.3%, and an MF value of 70. % High-definition image quality was obtained. Moreover, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

(Example 10)
Four semiconductor lasers (wavelength 635 nm) were used in an array form as a writing exposure light source, and the exposure output was set to about 8 mW on the surface of the photosensitive drum 1. As the photosensitive drum 1, an As ₂ Se ₃ type photosensitive body (shape: outer diameter 262 mm × length 430 mm) to which 50 ppm of chlorine is added to improve photoresponsiveness, the thickness of the photosensitive body is 45 μm, and the surface roughness is It was 0.375 μm. The rotational speed of the photosensitive drum 1 is 80 rpm, and the process time between the exposure unit and the developing machine 3 is about 200 milliseconds. The width of the charger 2 was set to 80 mm, and the charging time of the photosensitive member was set to about 73 milliseconds. The semiconductor laser exposure spot diameter was about 40 μm and the resolution was 600 dpi.

As the developing machine 3, a multistage developing machine having four developing rolls was used, the developing roll diameter was 50 mm, and the developing time was about 90 milliseconds. As the developer, a two-component developer was used, and the toner 12 was a styrene acrylic toner having an average particle diameter of 7 μm. The development bias voltage was set to 400 V / 350 V / 300 V / 250 V from the upstream side to the downstream side in the rotation direction of the photosensitive drum. As the erase lamp 6, an LED array having a wavelength of 600 nm (light quantity: 350 μW / cm ² ) was used.

  The other image forming conditions were the same as in Example 9, and a printing test of about 5,000 pages was performed. The drum potential at the position of the potential sensor 13 was non-exposed portion potential: V0 / exposed portion potential: VR = 800 V / 85 V, 660 V / 100 V at the position of the potential sensor 14, and 500 V / 100 V at the position of the potential sensor 15. The print sample has a solid density of 1.45 (D), a fog density of 0.5%, and an MF value of 65. % High-definition image quality was obtained. In addition, this could be maintained over a long period of time, and a practical image was obtained even when printing 3 million pages.

1 is a schematic configuration diagram of an image forming apparatus in an embodiment of the present invention. FIG. 6 is a characteristic diagram of drum potential in each image forming process. FIG. 6 is a diagram for explaining a collapse of a toner image immediately before transfer. FIG. 6 is a characteristic diagram showing a relationship between charging time and drum potential holding ratio. It is a characteristic view which shows the relationship between the wavelength of writing light, and the wavelength of static elimination light. It is a characteristic view showing the relationship between the wavelength of the charge removal light and the potential holding ratio of the drum. FIG. 6 is a characteristic diagram showing the relationship between the film thickness of the photoreceptor, the residual potential, and the limit drum surface potential. It is a characteristic view which shows the effect of iodine addition. It is a characteristic view which shows the change of the drum electric potential after exposure. It is a characteristic view which shows the relationship between exposure-development time and a limit resolution. FIG. 6 is a characteristic diagram showing the relationship between development time, image density, and fog density. FIG. 6 is a characteristic diagram illustrating a relationship between a developing bias voltage, an image density, and a fog density. FIG. 5 is a characteristic diagram illustrating a relationship between a contrast potential of a transfer portion and a line width. It is a characteristic view which shows the relationship between the frequency of AC static eliminator, and the variation in drum potential.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Developing machine 4 Transfer device 5 AC static eliminator 6 Erase lamp 7 Cleaning device 10 Scanner unit 11 Paper 12 Toner 13-16 Potential sensor

Claims (5)

In an image forming apparatus that exposes a charged photoreceptor to form an electrostatic latent image on the surface of the photoreceptor, visualizes the latent image with toner, and transfers the toner image to an image carrier.
The photoconductor is a photoconductor based on arsenic triselenide or amorphous silicon,
An image forming apparatus, wherein the wavelength λ _{0 of the} writing light used for the exposure and the wavelength λ _{1 of the} neutralizing light for neutralizing the photoconductor after development have the following relationship:
λ ₀ -100 nm ≦ λ ₁ ≦ 680 nm The image forming apparatus according to claim 1, wherein a wavelength λ _{0 of the} writing light is regulated in a range of 600 nm to 720 nm. 2. The image forming apparatus according to claim 1, wherein the light source for the writing light and the charge removing light is a semiconductor laser or an LED. 4. The image forming apparatus according to claim 1, wherein a plurality of laser beams are used for the writing light. 2. The image forming apparatus according to claim 1, wherein two or more developing rolls are provided in a developing machine for developing the electrostatic latent image, and the toner is supplied to the photosensitive member by the developing rolls. Image forming apparatus.

Images