JP2002072796A - Apparatus and method for forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for image formation which can speedily stabilize the potential of a photosensitive body and immediately start forming an image. SOLUTION: This image forming apparatus which carries out an image formation preparation stage for stabilizing the potential of the photosensitive body 1 at a specific potential prior to the start of image formation performs light irradiation by a 2nd electrostatic discharging light source 11 having longer light emission center wavelength than a main electrostatic discharging light source 8 in the starting one round of the rotation of a photosensitive body 1 in the image formation preparation stage and then switches the light source to the main electrostatic discharging light source 8 to immediately stabilize the potential of the photosensitive body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electrophotographic image forming apparatus and an image forming method suitably applicable to such an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus, a transferable image is formed and carried on a first image carrier by an appropriate image forming process, and the transferable image is formed on a second image carrier.
In general, an apparatus having a system and a structure in which the image is transferred onto the image carrier and the first image carrier is repeatedly used for image formation is used.

For example, a general configuration of an image forming apparatus such as a copying machine or a laser beam printer of this type is as follows.
A rotating photoconductor such as a rotating drum as a first image carrier;
Charging means for uniformly charging the surface of the rotating photoreceptor to a predetermined polarity / potential; image exposing means for forming an electrostatic latent image on the charged surface of the rotating photoreceptor; Developing means for developing the image as an image, transfer means for transferring the toner image from the surface of the rotating photoreceptor to transfer paper as a second image carrier (recording medium), and a permanent fixed image of the toner image transferred to the transfer paper side And a photoreceptor cleaning unit (cleaner) for removing transfer residual toner remaining on the surface of the rotating photoreceptor without being transferred onto the transfer paper and cleaning the surface of the rotating photoreceptor.

The transfer paper subjected to the image fixing process by the fixing means is discharged as an image formed product (copy, print). The photoreceptor surface cleaned by the cleaning means is repeatedly used for image formation.

[0005] Selenium-based photoconductors, amorphous silicon (hereinafter a-Si) photoconductors, organic photoconductors and the like have been put into practical use as photoconductors used in conventional electrophotographic or electrostatic recording type image forming apparatuses. However, among them, it is known that the a-Si photosensitive member is particularly excellent in stability and durability.

Although the surface of the a-Si photoreceptor has a high hardness, the surface of the photoreceptor is sensitive to humidity and easily adsorbs moisture due to the influence of corona products generated by ozone generated from the charging means. It has the drawback of causing lateral flow of charges on the surface of the photoreceptor and deteriorating image quality, which is called image flow.

In order to prevent such image deletion, a method of heating with a heater as described in Japanese Utility Model Publication No. 1-305205, and a magnet roller and a magnetic toner as described in Japanese Patent Publication No. 2-38956 are used. A method for removing corona products by rubbing the surface of a photoreceptor with a brush formed from a brush, and a method for removing corona products by rubbing the surface of a photoreceptor with an elastic roller as described in JP-A-61-100780 Etc. are used.

On the other hand, as a charging method of the charging means, a contact charging method has been put into practical use instead of a corona charging method. In this method, a conductive contact charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type, or a blade type is brought into contact with a photoreceptor to be charged, and a predetermined charging bias is applied to the contact charging member. Is applied to charge the photoreceptor surface to a predetermined polarity and potential.A contact charger employing this type of method has a lower ozone and a lower ozone than a corona charger.
There are advantages such as low power.

The charging mechanism (charging mechanism, charging principle) of the contact charging system includes two types, a corona charging system and a contact injection charging system.
Types are mixed, and each characteristic appears depending on which is dominant.

The corona charging system uses a discharge phenomenon such as corona discharge generated in a minute gap between the contact charging member and the member to be charged, and charges the member to be charged with the discharge product. This corona charging system generates a very small amount of ozone, though much less than the corona charger.

The contact injection charging system is a system in which the surface of a member to be charged is charged by directly injecting charge from the contact charging member to the member to be charged. It is also called direct charging or injection charging.

Japanese Patent Application Laid-Open No. 6-3921 and the like disclose a charging roller, a fur brush, and conductive magnetic particles on a charge holding member such as conductive levels of a trap level or a charge injection layer on the surface of a photoreceptor. A method has been proposed in which charge is injected by a contact charging member such as a constrained magnetic brush to perform contact injection charging.

Since contact injection charging does not use a discharge phenomenon,
Only the portion where the member to be charged contacts the contact charging member is charged. For this reason, in order to perform good charging without uneven charging, the contact charging member and the member to be charged may have a peripheral speed difference, or the moving directions may be different from each other, and the contact probability between the member to be charged and the member to be contacted may be different. Should be high enough.

The contact injection charging does not have a threshold voltage for starting charging, the voltage required for charging is only the desired photoconductor surface potential, and is a low power and ozoneless charging system.

As a member to be charged which can be charged by contact injection, for example, in the case of an organic photoreceptor, it is necessary to provide a charge injection layer in which conductive fine particles are dispersed as a charge holding member on the surface of the photosensitive layer. In the case of an inorganic photoreceptor such as an a-Si photoreceptor, many trap levels based on crystal defects are present on the surface without newly providing a charge injection layer, and injected charges are held at the trap levels. Injection charging becomes possible.

Since contact discharge charging does not generate any discharge products, when the a-Si photosensitive member is combined with the contact injection charge, the image deletion which is a disadvantage of the a-Si photosensitive member can be fundamentally solved. There are advantages. Therefore, a
It is not necessary to constantly heat the Si photoreceptor with a heater or to provide a means for rubbing the photoreceptor surface with magnetic particles or an elastic member, so that power consumption can be saved and the apparatus can be simplified.

As a characteristic of the a-Si photosensitive member, when the light irradiation area and the dark area are simultaneously charged, the potential of the light irradiation area is extremely large in the dark area (dark decay), and the optical memory (afterimage phenomenon). Is liable to occur.

That is, the a-Si-based photoreceptor has many tangling bonds (unbonded bonds), which become localized levels to capture a part of the photocarriers and reduce its traveling property. Or reduce the probability of recombination of optical carriers. Therefore, in the image forming step, a part of the photocarrier generated by the exposure is a-
When an electric field is applied to the Si photoreceptor, the localized level is released at the same time as the electric field is applied, and a difference occurs in the surface potential of the a-Si type photoreceptor between the exposed portion and the non-exposed portion. Appears as.

Therefore, after the toner image is transferred onto the transfer paper, the photoreceptor is uniformly exposed to light by a light-elimination light source so that the number of photocarriers latent in the a-Si photoreceptor is increased so that the entire surface becomes uniform. Generally, erasing an optical memory is performed. At this time, the light amount of the neutralizing light emitted from the neutralizing light source is increased, or the wavelength of the neutralizing light is set to a
-The spectral sensitivity peak of the Si photoreceptor (about 600 to 700 n
By approaching m), it is possible to erase the optical memory more effectively.

Further, a-Si cannot be neglected due to dark decay due to heat-generated carriers, and the potential tends to fluctuate depending on the temperature. For this reason, in addition to the temperature control of the photoreceptor, the use of a potential stabilization method as described below prevents image deterioration due to environmental fluctuations.

That is, the potential of the photoreceptor latent image is measured by a potential sensor, the density of an image obtained by developing the electrostatic latent image is detected, and the detection signal is fed back to the charging means and the image exposure means in the image forming step. For example, US Pat. No. 2,956,487 describes a method for stabilizing an electrophotographic image by controlling a desired potential. Such an image stabilizing means is generally performed when the power of the apparatus is turned on, at the start of the image forming process, or at the end thereof.

[0022]

However, in the case of the above-described prior art, the following problems have occurred.

The effect of the static elimination light as a means for reducing the optical memory varies depending on the amount of light and the center wavelength of the light emission. Generally, when the light amount is increased, the effect of reducing the optical memory is also increased. In addition, the emission center wavelength is effective when the wavelength is shorter than the spectral sensitivity peak of the photoconductor. In order to obtain the same effect on the optical memory when the wavelength of the charge removing light is shortened, a larger amount of light is required.

This is because, in the case of static elimination light having a wavelength close to the sensitivity peak wavelength, compared with static elimination light having a shorter wavelength, light reaches deep into the photosensitive layer of the photosensitive member, so that photocarriers can be generated efficiently. On the other hand, with static elimination light having a short wavelength, photocarriers are generated near the surface of the photosensitive layer, and the probability that the photocarriers recombine and disappear is increased.

However, at wavelengths near the sensitivity peak, the amount of residual photocarriers is large, so that dark decay also increases, and the chargeability tends to be lower than that of static elimination light having a shorter wavelength.

Therefore, a light source having an emission center wavelength appropriately shorter than the spectral sensitivity peak of the photosensitive member is used as the charge removing light.

However, in the case of an a-Si photosensitive member having a large number of localized levels acting as an electron trap, the accumulation of photocarriers due to static elimination light progresses after the start of image formation. Occurs.

As the charging step is repeated, the trapped photocarriers enter a steady state, and the potential stabilizes. The state in which the potential is stabilized means that the balance between the generation and accumulation of photocarriers due to static elimination light and the disappearance of photocarriers due to the release of trapped photocarriers due to recombination or charging of photocarriers is in a steady state, Light intensity of static elimination light,
It depends on the wavelength or charging voltage.

Therefore, when the power is turned on or before the start of the image forming process, the photoreceptor is uniformly exposed to static elimination light to bring the photocarrier of the photoreceptor into a steady state, and the charging voltage of the charging means is controlled to an optimum value. In general, an image forming preparation step for stabilizing the photoconductor potential is performed.

However, the potential control process cannot be started while the potential of the photoreceptor is being reduced by the exposure to the neutralizing light, and this is the first copy time (after the image formation start command is issued and the image This increases the length of time before the formation process is started.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to quickly stabilize the potential of a photoreceptor and to immediately start image formation. An object of the present invention is to provide a forming apparatus and an image forming method.

[0032]

According to the present invention, there is provided an image bearing member, charging means for charging the image bearing member to a predetermined potential, and irradiating the image bearing member with light. An exposure unit for forming an image, and an erasing light irradiating unit for uniformly exposing the image carrier to erase an optical memory, and stabilizing the potential of the image carrier at a predetermined potential prior to the start of an image forming process. In the image forming apparatus having an image forming preparation step, the static elimination light irradiating unit exposes the image carrier also at the time of the image forming preparation step, and at the time of the exposure, the light sensitivity to the image carrier than at the time of the image forming step. It is characterized by irradiating high light.

The image carrier is provided endlessly,
The discharging light irradiating means may expose at least one round of the image carrier with the light having high photosensitivity.

Further, it is preferable that the discharging light irradiating means has a plurality of light emitting means for emitting light having different photosensitivity to the image carrier.

The light emitting means has a light emission center wavelength of 50.
An LED of 0 to 800 nm is preferable.

It is preferable that the surface layer of the image carrier has amorphous silicon.

It is preferable that the charging means has a conductive charging member, and the charging member is brought into contact with the image carrier to charge the image carrier.

Further, the charging means may be a corona charger.

Further, according to the present invention, there is provided an image carrier,
Charging means for charging the image carrier to a predetermined potential; exposure means for irradiating the image carrier with light to form an image; and discharging light irradiating means for uniformly exposing the image carrier to erase an optical memory; And an image forming apparatus having an image forming preparation step of stabilizing the potential of the image carrier to a predetermined potential prior to the start of the image forming step. And irradiating light having a longer emission center wavelength than during the image forming step during the exposure.

The image carrier is provided endlessly,
The discharging light irradiating means may expose at least one round of the image carrier with light having a long emission center wavelength.

Further, it is preferable that the discharging light irradiating means has a plurality of light emitting means having different emission center wavelengths.

The light emitting means has a light emission center wavelength of 50.
An LED of 0 to 800 nm is preferable.

Further, it is preferable that the surface layer of the image carrier has amorphous silicon.

Further, it is preferable that the charging means has a conductive charging member, and the charging member is brought into contact with the image carrier to charge the image carrier.

The charging means may be a corona charger.

Further, in the image forming method of the present invention, a first exposure step of exposing the image carrier to form an image on the image carrier, and a step of erasing an optical memory of the image carrier are performed. A second exposure step of exposing the image carrier, and a third exposure step of exposing the image carrier with light having higher photosensitivity to the image carrier than the second exposure step. It is characterized by.

Further, in the image forming method of the present invention, a first exposure step of exposing the image carrier to form an image on the image carrier, and a step of erasing an optical memory of the image carrier. A second exposure step of exposing the image carrier, and a third exposure step of exposing the image carrier with light having a longer emission center wavelength than the exposure light in the second exposure step. Features.

The third exposure step is preferably a step performed prior to the start of the image forming step.

Further, the third exposure step is preferably a step performed over at least one rotation cycle of the image carrier.

[0050]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The materials, shapes, relative arrangements, and the like are not intended to limit the scope of the present invention only to them unless otherwise specified.

(First Embodiment) An image forming apparatus according to a first embodiment will be described with reference to FIGS.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment, FIG. 2 is a diagram illustrating an image forming method of the image forming apparatus according to the present embodiment, and FIG. FIG. 4 is a graph showing a change in potential, and FIG. 4 is a schematic diagram of a cross section of a photoconductor of the image forming apparatus according to the present embodiment.

First, the configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG.

In the figure, reference numeral 1 denotes a cylindrical a-Si photosensitive member (image carrier) which rotates at 150 mm / sec in the direction of the arrow in the figure. Reference numeral 2 denotes a magnetic brush charger (charging unit) of a charge injection type using a magnetic brush, and 3 denotes an electrostatic latent image formed on the photoreceptor 1 by irradiating a laser beam L from an exposure unit (not shown). A developing device 4 for forming a toner image, a transfer roller 4 for electrostatically transferring the toner image formed on the photoconductor 1 to a transfer material P, and a cleaner 5 for collecting transfer residual toner remaining on the photoconductor 1 after the transfer process Reference numeral 6 denotes a fixing unit that thermally fixes the toner on the transfer material P, and reference numeral 7 denotes a potential sensor that detects a potential on the photoconductor 1.

Reference numeral 8 denotes a main static elimination light source for erasing the potential (optical memory) remaining on the photoconductor 1 after transfer. Numeral 11 denotes a light source that emits light having higher photosensitivity to the photoconductor 1 than the main static elimination light source 8. This is the second static elimination light source. 9 is a control device for selectively emitting light from the main static elimination light source 8 and the second static elimination light source 11,
Here, the main static elimination light source 8, the second static elimination light source 11, and the control device 9 constitute a static elimination light irradiation unit.

S1 is a power supply for applying a charging voltage to the magnetic brush charger 2, S2 is a power supply for applying a developing bias, 10
Is a control device that changes the output values of S1 and S2 based on the measurement value of the potential sensor 7.

In the above configuration, charging, exposure, development, and development are performed based on a well-known electrophotographic process.
Image formation is performed continuously by repeating the steps of transfer, fixing, and cleaning.

Hereinafter, the configuration of each part of the image forming apparatus according to the present embodiment will be described in more detail.

The developing device 3 used in the present embodiment has a rotatable sleeve 15 enclosing a fixed magnet roll 14, and the developer in a developing container 17 is thinned by a blade 18. The layer is coated on the sleeve 15 and transported to the developing section. The distance between the nip between the sleeve 15 and the photosensitive member 1 is 500 μm, and the amount of developer carried on the sleeve 15 is set to 40 mg / cm ² . At this time, the sleeve 15 is rotating at a peripheral speed of 150 mm / sec in the direction of the arrow.

The developer used in the present embodiment is a two-component developer, having a negatively chargeable toner of 8 μm and a positively chargeable toner of 50 μm.
μm magnetic carrier at a toner concentration of 5% by weight. The toner density is controlled by an optical toner density sensor (not shown), and the toner in the toner hopper 20 is supplied by the supply roller 23. The developer in the developing container 17 is uniformly stirred by the stirring members 21 and 22.

The sleeve 15 receives 2 kVp from the power source S2.
A developing bias in which a variable DC voltage Vdc is superimposed on an alternating electric field of p, 2 kHz is applied. The developer coated in a thin layer and conveyed to the developing unit contributes to the development of the electrostatic latent image on the photoconductor 1 by the electric field by the AC + DC voltage.

The magnetic brush charger 2 includes a rotatable sleeve 31 and a magnet roller 3 fixed in the sleeve 31.
0, a voltage obtained by superimposing an alternating electric field of 400 Vpp and 1 kHz on a variable DC voltage Vc from a power supply S1 is applied to the sleeve 31 during image formation. The application of an alternating electric field as a charging bias is effective in improving the charging ability and preventing a positive ghost.

The magnetic particles are held on the sleeve 31 by the magnetic constraining force of the magnet roller 30, and the thickness of the magnetic particles is regulated by the blade 32 having an interval set to 700 μm. Do.

The sleeve 31 is 200 mm / s in the direction of the arrow.
It rotates at a peripheral speed of ec. The amount of magnetic particles carried on the sleeve 31 when the photosensitive member 1 is not in contact with the photosensitive member 1 is 170 mg / cm ^2.
Met. The gap between the photoconductor 1 and the sleeve 31 in the nip is 500 μm, and the magnetic flux density by the magnet on the sleeve 31 of the charging unit is 800 × 10 ⁻⁴ T. As the magnetic particles of the magnetic brush, the average particle size is 25 μm, the resistance value is 5 × 10 ⁶ Ω · cm (5 × 10 ⁴ Ωm), and the saturation magnetization is 2 μm.
The one having a value of 00 emu / cm ³ (about 0.251 Wb / m ² ) was used.

The magnetic brush injection charging is a charging method in which conductive magnetic particles are brought into contact with a member to be charged, and charges are directly injected. Compared with corona charging or roller charging using a discharge phenomenon, the injection charging system has no advantage in that no discharge occurs, and thus has the advantage that the resistance change of the photoconductor surface due to the discharge product does not occur. The a-Si photoreceptor is liable to change in surface resistance particularly due to a discharge product, and in a high humidity environment, blurring or flow of an electrostatic latent image due to a decrease in surface resistance is likely to occur. For this reason, it is necessary to provide a heater in the cylinder of the photoreceptor and to suppress this phenomenon by heating. When the injection charging method is used for such a photoreceptor, the dependence on the heater can be reduced because there is no influence by a discharge product.

In the case of using the injection charging method, it is necessary to provide a charge injection site by dispersing conductive particles such as tin oxide in the surface layer of a photosensitive member using an organic semiconductor. Has sufficient charge injection sites on the surface without giving any special prescription, and has very excellent charging characteristics.

Therefore, in this embodiment, an a-Si photosensitive member is used as the photosensitive member 1. FIG. 4 shows a schematic diagram of a cross section of the photoconductor used in the present embodiment.

The photosensitive member 1 used in this embodiment has a diameter of φ60.
And a charge injection blocking layer, a photoconductive layer and a surface layer sequentially laminated on the surface of the conductive support. Here, the charge injection blocking layer is for preventing charge injection from the conductive support into the photoconductive layer, and the photoconductive layer is made of an amorphous material containing silicon atoms as a main raw material. Is shown. Further, the surface layer contains silicon atoms and carbon atoms, and is responsible for holding an electron latent image formed on the surface and improving the durability of the film.

The a-Si photosensitive member has a very high surface hardness,
It shows high sensitivity to long wavelengths such as semiconductor lasers, and hardly shows any deterioration due to repeated use, so that it is suitable as a photoconductor for electrophotography.

The cleaner 5 includes a cleaning blade 33
And a screw 34 for transporting the toner removed from the photosensitive member 1 to a waste toner container (not shown).
Consists of

In the above configuration, when the image forming step is started, the photosensitive member 1 is uniformly charged to a predetermined potential by the magnetic brush charger 2, and then is exposed to an image by the exposure means (not shown). The laser beam L is irradiated (first
Exposure step), an electrostatic latent image is formed on the surface. The electrostatic latent image is visualized as a toner image by a developing device 3 carrying charged toner particles, and the toner image is electrostatically transferred to a transfer material P by a transfer roller 4 to form an image formed product.

Further, after the transfer of the toner image, the main charge removing light source 8
After the photoreceptor 1 is uniformly exposed to light and the optical memory on the photoreceptor 1 is erased (second exposure step), the transfer residual toner remaining on the photoreceptor 1 is collected by the cleaner 5. The photoreceptor 1 cleaned by the cleaner 5 is continuously provided for image formation by repeating the above operation.

In order to form a stable and high-quality image in the image forming step, the charging applied to the magnetic brush charger 2 based on the photoconductor potential measured by the potential sensor 7 prior to the start of the image forming step. An image forming preparation step of controlling voltage and the like is executed. In the present embodiment, initial potential control for setting a charging potential and a developing potential is performed when the power of the apparatus is turned on, and a potential fluctuation due to a change in the temperature in the apparatus during standby is corrected before the image forming process is started. Potential correction is performed.

A method for controlling the initial potential will be described. The charging voltage is set to predetermined voltage values Vh and Vl, and two types of image exposures L ₀₀ and L _FF are performed at each charging voltage, thereby measuring four types of photosensitive member potentials. Photoreceptor potential relative L ₀₀ exposure for charge voltage Vh and the charging voltage Vl
L ₀₀ obtains the L ₀₀ curves from the photosensitive member potential to the exposure time, obtaining the L _FF curve from the photosensitive member potential to the L _FF exposed in the same manner. L ₀₀ the curve obtained by subtracting a predetermined constant from the curve L
_The charging voltage value and the developing DC voltage value are calculated from the difference between the L _cont curve and the L _FF curve so that an appropriate contrast potential V _FF −V _cont is obtained.

In the potential correction, the photoconductor potential at the time of the initial potential control is compared with the photoconductor potential at the time of receiving the image formation start command, and the charging voltage is corrected based on the difference.

Next, an image forming method of the image forming apparatus according to the present embodiment will be described with reference to FIG. In the figure, the hatched portions indicate that the motor, the ramp, or the bias is operating.

When the power switch of the apparatus is turned on, heating of the fixing device 6 is started, and at the same time, an image forming preparation step at the time of power-on is executed. As shown, the drum motor and the developing motor are driven to drive the photosensitive member 1 and the developing device 3.
Is turned on to turn on the charging bias and the static elimination light source.

Here, while the photoconductor 1 makes one rotation (one rotation) immediately after the start of the image forming preparation process, only the second static elimination light source 11 that emits light having higher photosensitivity to the photoconductor 1 than the main static elimination light source 8 is used. Is emitted (third exposure step). Then, after the photoconductor 1 makes one round, the controller 9 switches from the second static elimination light source 11 to the main static elimination light source 8 and starts the above-described initial potential control.

As described above, by switching and using the static elimination light source, the photocarriers can be saturated at once and the surface potential of the photosensitive member 1 can be immediately stabilized, and the potential control can be quickly and accurately performed. It becomes possible.

When the initial potential control is completed, the main discharging light source 8 and the charging bias are turned off. Further, when the fixing device 6 reaches a predetermined temperature, the drum motor and the developing motor are also turned off.
F, the image forming apparatus enters a standby state.

When an image formation start instruction is received,
An image forming preparation step is performed before the image forming step. As in the image forming preparation process at the time of turning on the power, only the second static elimination light source 11 emits light for the first round of the photoconductor 1 to stabilize the surface potential of the photoconductor 1, and then the same as in the image forming process. Switching to the main static elimination light source 8 to light it up and perform potential correction. The image forming process is started in a state where the photoconductor potential and the development contrast are controlled appropriately.

Next, referring to FIG. 3, the static elimination light irradiation means and the potential control step of the image forming apparatus according to the present embodiment will be described in more detail.

FIG. 3 is a graph schematically showing a change in the surface potential of the photosensitive member.
That is, the drum motor, static elimination light source, and charging bias are turned on.
The vertical axis indicates the surface potential of the photoconductor 1 detected by the potential sensor 7. A graph (a) indicated by a solid line indicates a change in surface potential in the image forming apparatus according to the present embodiment, and a graph (b) indicated by a dotted line indicates an image forming apparatus according to the related art (light irradiation only by the main static elimination light source 8). Of the surface potential change in the prior art).

In order to perform high-precision potential control in a potential control step such as initial potential control or potential correction, first, the surface potential of the photosensitive member must be in a stable state.
However, in the case of a photoconductor such as an a-Si photoconductor, which contains many electron traps in the photoconductive layer, photocarriers gradually accumulate by light irradiation of only the main static elimination light source 8, so that the dotted line (b) in FIG. Shows the initial charging characteristics shown in FIG.

In the conventional example (b), it can be seen that it takes about 15 to 20 seconds from when the charging bias is turned on to when the photosensitive member potential is stabilized. After receiving the image formation command,
It is preferable that the image be output earlier,
When a photoconductor such as a-Si is used, it is not possible to immediately proceed to the potential control step for such a reason, and the first copy time becomes long.

Therefore, as described above, in the present embodiment, the image forming command is received, and the photosensitivity of the photoconductor 1 to the photoconductor 1 is higher than that of the main static elimination light source 8 over the first rotation cycle after the photoconductor 1 starts rotating. By irradiating light with the second static elimination light source 11 that emits high light and then switching to the main static elimination light source 8, the potential of the photoconductor is immediately stabilized. The graph showing the change in the photoconductor surface potential in this case is shown by the solid line (a) in FIG. 3, and it can be seen that the photoconductor surface potential is immediately stabilized, unlike in (b). Therefore, photoconductor 1
After one round, the process can immediately proceed to the potential control step.

The a-Si photosensitive member has a large dark decay, and it is desirable that the light amount of the main static elimination light source 8 be as small as possible in order to efficiently obtain the required potential. On the other hand, the optical memory using the residual photocarriers due to the image exposure tends to be improved as the amount of light of the main charge removing light source 8 increases, so
Is preferably set to the minimum light amount at which the optical memory reaches an allowable level. Further, as described above, the wavelength of the main charge removing light source 8 is desirably a light source having a light emission center wavelength appropriately shorter than the spectral sensitivity peak of the photoconductor 1.

On the other hand, the second static elimination light source 11 is a light source that emits light having higher photosensitivity to the photosensitive member 1 than the main static elimination light source 8 so that the photocarriers of the photosensitive member 1 can be immediately saturated. There must be.

From the above conditions, an LED having a light emission center wavelength of 500 to 800 nm is preferable as the charge removing light source. The main static elimination light source 8 used in the present embodiment has an emission center wavelength of 610.
The LED emits light at 10 lx · s with respect to the photoconductor 1 rotating at 150 mm / sec. Further, as the second neutralization light source 11, a light source having a longer emission center wavelength than the main neutralization light source 8 and emitting light in a wavelength region close to the spectral sensitivity peak of the photoreceptor 1 is used.
1 for the photosensitive drum rotating at 150 mm / sec.
It was provided to emit light at 2 lx · s.

The switching of the static elimination light source by the controller 9 is performed based on a signal detected by a photoconductor position detecting means (not shown). At this time, if the charge elimination light source is switched before the photosensitive member 1 makes one complete rotation, a potential ripple may occur, and care must be taken.

In the potential control of this embodiment, the development contrast potential V _FF -V _cont is set to be controlled to 200 V, and Vc at that time is approximately 750 V, Vdc.
Is about 250V.

Note that the image forming preparation step and the potential control step described in the present embodiment are merely examples, for example, a-Si
Depending on the characteristics of the photoconductor and the rotation speed of the photoconductor, the appropriate light emission amount and wavelength of the main static elimination light source 8 or the second static elimination light source 11 are not limited to those described in the present embodiment.

The same effect can be obtained by causing the second charge removing light source 11 to emit light not only for one rotation of the photosensitive member but also for two or more rotations.

As described above, in the image forming apparatus of the present embodiment, in the image forming preparation step, the emission center wavelength is longer than that of the main static elimination light source 8 before the potential control is started.
By causing the second static elimination light source 11 that emits light in a wavelength range close to the photoconductor sensitivity peak to emit light, it is possible to stabilize the photoconductor surface potential quickly and immediately perform potential control, thereby shortening the first copy time. Was completed.

(Second Embodiment) FIG. 5 shows a second embodiment. In the first embodiment,
Although the magnetic brush charger is used as the charging unit, the present embodiment is characterized in that a conductive fur brush is used.

The other configuration and operation are the same as those of the first embodiment, so that the same components are denoted by the same reference characters and description thereof is omitted.

The fur brush 40 used in this embodiment has a core bar having an outer diameter of 7 mm, a bristle length of 3 mm, and a flock density of 100,000 / inch ² (about 15,500 / c).
m ² ), a cylindrical material having a total outer diameter of 13 mm in which conductive fibers having a resistance value of 1 × 10 ⁶ Ω were planted.

The nip width with the photosensitive member 1 is about 3 mm.
The rotation direction is the counter direction with respect to the photoconductor 1, and the rotation speed is 150 mm / sec.
0 rotates at 150 mm / sec. A voltage is applied to the fur brush 40 from the power supply S3, and the voltage is variable by the control device 10.

The injection charging can be performed by adjusting the electric resistance of the fur brush 40. There is a disadvantage that the contact density is small and the charging uniformity is inferior to that of the magnetic brush injection charging, but it is used because the device configuration is simple.

Also in the present embodiment, in the image forming preparation process, before the potential control is performed, the second neutralization having a longer emission center wavelength than the main neutralization light source 8 and emitting light in a wavelength region close to the photosensitive member sensitivity peak is performed. By causing the light source 11 to emit light,
As a result, the surface potential of the photoreceptor can be quickly stabilized and the potential can be controlled immediately, and the first copy time can be reduced.

(Third Embodiment) FIG. 6 shows a third embodiment. In the first embodiment,
Although the magnetic brush charger is used as the charging means, the present embodiment is characterized in that a corona charger is used. A heater for heating the photoconductor and a control device for controlling the temperature of the photoconductor are provided in the photoconductor 1 (not shown).

The other configuration and operation are the same as those of the first embodiment, so that the same components are denoted by the same reference characters and description thereof is omitted.

The discharge wire 45 has a voltage of -10 from the power source S4.
A charging bias by a constant current control of 00 μA is applied. The grid 46 is a power source S5 that can control the applied bias.
The grid application bias is changed during initial potential control and potential correction.

The corona charging method has disadvantages such as the necessity of heating the photoreceptor 1 under the influence of a discharge product such as ozone. However, the corona charging method is widely used because of its simple structure and high durability. I have.

Also in the charging method in which charge is applied to the photosensitive member 1 in a non-contact manner as in the present embodiment, in the image forming preparation step, the emission center wavelength is longer than that of the main charge removing light source 8 before the potential control is started. By causing the second static elimination light source 11 that emits light in a wavelength range close to the body sensitivity peak to emit light, the surface potential of the photoreceptor can be quickly stabilized and the potential can be immediately controlled, and the first copy time can be reduced. did it.

[0106]

As described above, according to the present invention,
When the static elimination light irradiating unit irradiates the image carrier during the image forming preparation process with light having higher photosensitivity to the image carrier than during the image forming process, more light carriers are generated on the image carrier. In addition, the potential of the image carrier can be quickly stabilized by accumulation, and the potential control of the charging unit can be immediately performed, so that the first copy time can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an image forming method of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a graph showing a change in photoconductor surface potential.

FIG. 4 is a schematic sectional view of a photoconductor of the image forming apparatus according to the first embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of an image forming apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoreceptor 2 Magnetic brush charger 3 Developing device 4 Transfer roller 5 Cleaner 6 Fixing device 7 Potential sensor 8 Main static elimination light source 9 Control device 10 Control device 11 Second static elimination light source 30 Magnet roller 31 Sleeve 32 Blade 40 Fur brush 45 Discharge Wire 46 grid S1, S2, S3, S4, S5 power supply

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2H003 AA01 BB11 CC01 CC04 CC06 DD03 2H027 DA02 EA10 EC06 EC15 EC18 ED15 EE07 EF12 2H035 AA09 AA10 AB02 AC02 AC03 AC06 2H068 DA03 DA05 FA12 FB08

Claims (20)

[Claims] An image carrier, a charging unit for charging the image carrier to a predetermined potential, an exposure unit for irradiating the image carrier with light to form an image, and uniformly exposing the image carrier. An erasing light irradiating means for erasing an optical memory, wherein the erasing light irradiating means comprises: an image forming preparation step of stabilizing the potential of the image carrier to a predetermined potential prior to the start of the image forming step. An image forming apparatus comprising: exposing the image carrier during an image forming preparation step; and irradiating the image carrier with light having a higher photosensitivity than the image forming step during the exposure. 2. The image forming apparatus according to claim 1, wherein said image carrier is provided endlessly, and said discharging light irradiating means exposes at least one circumference of said image carrier with said light having high photosensitivity. 3. An image forming apparatus according to claim 1, wherein said discharging light irradiating means has a plurality of light emitting means for emitting light having different light sensitivities to said image carrier. 4. The light emitting means has a light emission center wavelength of 500-8.
The image forming apparatus according to claim 3, wherein the image forming apparatus is a 00 nm LED. 5. The image forming apparatus according to claim 1, wherein a surface layer of said image carrier has amorphous silicon. 6. The charging means has a conductive charging member,
The image forming apparatus according to any one of claims 1 to 5, wherein the charging member is charged by bringing the charging member into contact with the image carrier. 7. An image forming apparatus according to claim 1, wherein said charging means is a corona charger. 8. An image carrier, charging means for charging the image carrier to a predetermined potential, exposure means for irradiating the image carrier with light to form an image, and uniformly exposing the image carrier. An erasing light irradiating means for erasing an optical memory, wherein the erasing light irradiating means comprises: an image forming preparation step of stabilizing the potential of the image carrier to a predetermined potential prior to the start of the image forming step. An image forming apparatus comprising: exposing the image carrier also during an image forming preparation step; and irradiating light having a longer emission center wavelength than during the image forming step during the exposure. 9. The image forming apparatus according to claim 8, wherein said image carrier is provided endlessly, and said discharging light irradiating means exposes at least one circumference of said image carrier with light having a long emission center wavelength. . 10. An image forming apparatus according to claim 8, wherein said discharging light irradiating means has a plurality of light emitting means having different emission center wavelengths. 11. The light-emitting means has an emission center wavelength of 500 to 500.
The image forming apparatus according to claim 10, wherein the image forming apparatus is an 800 nm LED. 12. The image forming apparatus according to claim 8, wherein a surface layer of said image carrier has amorphous silicon. 13. The image forming apparatus according to claim 8, wherein said charging means has a conductive charging member, and charges said image carrier by bringing said charging member into contact with said image carrier. Image forming device. 14. An image forming apparatus according to claim 8, wherein said charging means is a corona charger. 15. A first exposure step of exposing the image carrier to form an image on the image carrier, and a second exposure step of exposing the image carrier to erase an optical memory of the image carrier. An image forming method, comprising: exposing the image carrier with light having higher photosensitivity to the image carrier than the second exposing step. 16. The image forming method according to claim 15, wherein said third exposure step is a step performed prior to the start of the image forming step. 17. The image forming method according to claim 15, wherein the third exposure step is a step performed over at least one rotation cycle of the image carrier. 18. A first exposure step of exposing the image carrier to form an image on the image carrier, and a second exposure step of exposing the image carrier to erase an optical memory of the image carrier. An image forming method, comprising: exposing the image carrier with light having a longer emission center wavelength than the exposure light in the second exposure step. 19. The image forming method according to claim 18, wherein the third exposure step is a step performed before the start of the image forming step. 20. The image forming method according to claim 18, wherein the third exposure step is a step performed over at least one rotation cycle of the image carrier.