JP2010072102A - Method for evaluating electrostatic latent image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating electrostatic latent images, by which the charge distribution of a dielectric is measured with a high resolution of μm order, so that the latent image forming ability of an electrostatic latent image in an electrophotographic process can be evaluated with high accuracy, which up to now evaluation has been very difficult in conventional techniques. <P>SOLUTION: Optical fatigue is given to a photoreceptor sample 2 in a vacuum chamber 8, by irradiating the photoreceptor sample with a light by a light-irradiating means 4, while charging it by an electron beam irradiating means 3, and the photoreceptor sample 2 is irradiated with a light having photoreceptor sensitivity by a charge-eliminating means 5, in a light quantity which is larger than exposure energy density necessary for the photoreceptor for eliminating electrified charges. In this state, the photoreceptor sample 2 is subjected to charged particle beam scanning by the electron beam irradiating means 3, and the electrons obtained by the scanning are detected by an electron detector 9, and thereby residual charges produced on the photoreceptor sample are evaluated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention has an electrostatic latent image evaluation method for a photoreceptor, an evaluation apparatus for carrying out the evaluation method, an electrophotographic photoreceptor produced based on the evaluation result, and the electrophotographic photoreceptor. The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, and a multifunction machine including at least one of them.
The present invention can be applied to an optical scanning device, a device for measuring electrostatic characteristics of a photoconductor, a device for measuring charge distribution, and a device for evaluating residual charge.

Conventionally, as a method for measuring the surface potential, a method is known in which a sensor head is brought close to a sample having a potential distribution, and electrostatic attraction and induced current that occur as an interaction at that time are measured and converted into a potential distribution. Yes. However, with this method, the resolution is as low as several millimeters in principle, and a resolution of 1 micron cannot be obtained.
Moreover, as an evaluation of LSI chips, a method of measuring an electric potential on the order of 1 micron using an electron beam has been conventionally known. However, the evaluation is for a conductive part through which LSI electricity flows, and the electric potential is The potential is as low as about +5 V at most, and the potential is limited, and it is not possible to cope with negative charges of several hundred to several thousand V in the photoconductor that is the subject of the present invention.
As a method for observing an electrostatic latent image using an electron beam, there is a method described in Patent Document 1, but the sample is limited to an LSI chip or a sample that can store and hold an electrostatic latent image.
That is, a normal photoconductor that causes dark decay cannot be measured.

Since a normal dielectric can hold a charge semipermanently, even if measurement is performed over time after forming a charge distribution, the measurement result is not affected. However, in the case of a photoconductor, since the resistance value is not infinite, the charge cannot be held for a long time, dark decay occurs, and the surface potential decreases with time.
The time that the photoconductor can hold the charge is at most 10 to 60 seconds even in the dark room. Therefore, even if an attempt is made to observe in an electron microscope (SEM) after charging and exposure, the electrostatic latent image disappears at the preparation stage. After the latent image is formed, it must be measured within a few seconds at the latest.

In the apparatus described in Patent Document 2, the X-ray is used and the wavelength used is completely different, and the charging potential in the electrophotographic process cannot be set to −500 to −1000 V, and an environment equivalent to that of an actual electrophotographic machine is obtained. The goal of reproduction cannot be achieved.
Accordingly, the present applicant has devised a method for measuring an electrostatic latent image even for a photoconductor sample having dark decay (see Patent Documents 3, 4, 5, and 6).

Japanese Patent Laid-Open No. 3-049143 Japanese Patent Laid-Open No. 3-200100 JP 2003-295696 A JP 2003-305881 A JP 2005-166542 A JP 2006-84434 A JP-A-3-53178

By the way, as shown in FIG. 22, the general structure of the photosensitive member includes a base (Sub) as a conductive layer, an undercoat layer (UL), a charge generation layer (CGL), and a charge transport layer (CTL). . The UL is provided for the purpose of preventing leakage of charge injection from the substrate side.
The organic photoreceptor (OPC) has a phenomenon that the image is disturbed as the number of output images increases. This reason is due to deterioration due to fatigue of the photoreceptor. One of the causes of deterioration is an increase in residual charge.
In the case of a normal product, carriers in which charges are generated in the CGL due to light irradiation cancel out the charged charges generated on the surface. However, even if sufficient light irradiation is performed, there is a charge that remains in the photoconductor as shown in FIG. This is the residual charge. As the number of images increases, as the residual charge increases, the difference between the charged potential and the exposure potential decreases, and a good image cannot be obtained.

Evaluation of this residual charge is important in realizing high image quality and high durability of the photoreceptor, and using a fatigue tester such as the OPC drum test apparatus described in Patent Document 7, the vibration capacity method It is known to measure the potential due to residual charges.
However, the conventional vibration capacity method generally used for surface potential measurement has a poor spatial resolution of about several millimeters and can only be evaluated macroscopically. For this reason, when evaluating an output image, it is necessary to go through a transfer / fixing process, and the characteristics of the photoreceptor alone cannot be evaluated.
In addition, when an attempt was made to observe in a vacuum apparatus after performing a fatigue test in the atmosphere using the conventional technique, the fatigue was recovered with the lapse of working time during that time, and a proper evaluation could not be performed.
If the residual charge can only be grasped macroscopically, it is difficult to optimize the design for high image quality, and it has been desired to measure the microscopic state on the micron scale.

The present invention is a static that can measure the latent image forming capability of an electrostatic latent image occurring in an electrophotographic process with high accuracy by measuring the charge distribution of a dielectric with high resolution on the order of microns, which has been extremely difficult with the prior art. The main purpose is to provide a method for evaluating an electrostatic latent image.
The charge includes not only electrons but also ions. Further, there may be a state in which there is a conductive portion on the surface and a voltage is applied to the conductive portion, thereby causing a potential distribution on the surface of the sample or in the vicinity thereof.

In order to achieve the above object, according to the first aspect of the present invention, a charged particle beam is irradiated to a photoconductor sample having a charge distribution, and the electrostatic latent image of the photoconductor sample is detected by a detection signal obtained by the irradiation. In a method of measuring an image,
The charged photoconductor sample is charged in a state in which the charged charge is removed by irradiating light in a vacuum with light having photoconductor sensitivity and irradiating a light amount larger than the required exposure energy density of the photoconductor. The electrostatic latent image evaluation method is characterized in that the residual charge generated on the photosensitive member sample is evaluated by scanning the particle beam and detecting electrons obtained by the scanning.

According to a second aspect of the present invention, in the method for evaluating an electrostatic latent image according to the first aspect, light fatigue is given to the photosensitive member by irradiating light while irradiating an electron beam. .
According to a third aspect of the invention, in the method for evaluating an electrostatic latent image according to the second aspect, in the process of irradiating light while irradiating an electron beam, the amplification factor of the electron detector is smaller than that during observation. It is characterized by setting.
According to a fourth aspect of the present invention, in the method for evaluating an electrostatic latent image according to the second or third aspect, the light fatigue state is controlled by changing a current of an electron beam applied to the photosensitive member sample. .

According to a fifth aspect of the present invention, in the method for evaluating an electrostatic latent image according to any one of the first to fourth aspects, the electric field strength to the photosensitive member sample is in the range of 10 ^ 4 V / cm to 10 ^ 6 V / cm. It is characterized by setting to.
According to a sixth aspect of the present invention, in the method for evaluating an electrostatic latent image according to any one of the first to fifth aspects, visible light having a wavelength of 400 to 800 nm is used as light having photoconductor sensitivity, and the photosensitive system is exposed by an optical system. Irradiating a predetermined region of the body sample.
According to a seventh aspect of the present invention, in the method for evaluating an electrostatic latent image according to any one of the first to sixth aspects, the light irradiation is performed with a semiconductor laser, and the amount of the semiconductor laser is changed to change the substrate of the photoreceptor sample. It controls the amount of current flowing through the.

According to an eighth aspect of the present invention, in the method for evaluating an electrostatic latent image according to any one of the first to seventh aspects, there is a condition that there is a region where the velocity vector in the sample vertical direction of the incident charged particle is reversed. The residual potential is measured by applying a voltage to the back surface of the sample to change the potential potential of the sample surface.
According to the ninth aspect of the present invention, there is provided a device for irradiating a photosensitive sample having a charge distribution with a charged particle beam and measuring an electrostatic latent image of the sample by a detection signal obtained by the irradiation. , Means for charging the sample by electron beam irradiation, means for irradiating the photoconductor with light having photosensitivity, and means for removing photocharge and leaving residual charge. The apparatus for evaluating an electrostatic latent image is characterized by evaluating a residual charge of a photoreceptor sample by scanning a charged particle beam and detecting electrons obtained by the scanning.

According to a tenth aspect of the present invention, in the apparatus for evaluating an electrostatic latent image according to the ninth aspect, one of the means for imparting light fatigue and the means for leaving the residual charge also serves as the other. .
In the invention described in claim 11, when the residual charge is evaluated using the evaluation method and the evaluation apparatus according to any one of claims 1 to 10, the average residual potential is larger than −50 V and the observation range is 200 μm or less. An electrophotographic photoreceptor having a maximum-minimum residual potential of 20 V or less was obtained.
According to a twelfth aspect of the present invention, in the image forming apparatus, a latent image is formed using the electrophotographic photosensitive member according to the eleventh aspect, and is developed and visualized.

According to the present invention, it is possible to evaluate the residual charge generated on the photoreceptor sample on a micron scale, and it is possible to evaluate the latent image forming ability of the electrostatic latent image occurring in the electrophotographic process with high accuracy. .
By irradiating light while irradiating an electron beam, it is possible to give light fatigue to the photoreceptor. Since it is generated in a vacuum, it is not significantly affected by exposure to Nox gas as in the fatigue experiment in the atmosphere. Simultaneous irradiation of electron beam irradiation and light irradiation is possible, and fatigue can be carried out efficiently.
By simultaneously performing charging and exposure, light fatigue can be efficiently applied in a short time.
By setting the amplification factor of the electron detector to be smaller than that at the time of observation, the process during light fatigue can be monitored without damaging or degrading the electron detector.
Conventionally, in corona charging and scorotron charging, since discharge in the air is used, it has been difficult to control the amount of electrons irradiated to the photoreceptor sample even though the passing current flowing through the substrate can be controlled. In the present invention, the electron beam can be irradiated and charged in the vacuum apparatus, and the electron irradiation current density that directly affects the light fatigue can be controlled, so that the light fatigue can be efficiently given.

By setting the electric field strength to the photosensitive member sample in the range of 10 4 V / cm or more and 10 6 V / cm or less, carriers can be generated efficiently and photo fatigue can be given.
By using an optical system that irradiates a predetermined area of the photoreceptor sample, uniform illumination can be performed on an area that directly affects photoreceptor fatigue.
By changing the injection current of the semiconductor laser and controlling the light irradiation amount and time that directly affect the photoreceptor fatigue, it is possible to grasp the latent image characteristics of the photoreceptor in the fatigued state.
The residual potential is measured by applying a voltage to the back of the sample in order to change the potential potential of the sample surface by measuring under conditions where there is a region where the velocity vector of the incident charged particles in the sample vertical direction is reversed. It is possible to measure with a scale.
In addition, it is possible to realize an apparatus for quantitatively evaluating the latent image forming ability of an electrostatic latent image formed on an electrophotographic photosensitive member, which has not been possible conventionally.
It is possible to provide an electrophotographic photosensitive member excellent in high image quality, high durability, high stability, and energy saving by dot scale evaluation of charge distribution variation, which is often overlooked in conventional macro evaluation.
By evaluating the residual charge on a micro scale, it can be fed back to the design, and the process quality of each process is improved, providing an electrophotographic photoreceptor excellent in high image quality, high durability, high stability, and energy saving. can do.
A high-quality, high-durability, high-stability, energy-saving latent image carrier and scanning optical system can be provided. By developing and visualizing, a high-density, high-quality, high-durability image forming apparatus Can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an apparatus for evaluating an electrostatic latent image according to this embodiment. FIG. 1A shows the evaluation apparatus from a side as a residual charge generation means, and FIG. 1B shows a side as a residual charge detection means.
The configuration of the residual charge generating means is shown in FIG. The residual charge generating means charges the photoconductor sample 2 as a photoconductor, and provides an electron beam irradiation means 3 and a light irradiation means 4 for giving light fatigue, a charge erasing means 5 for erasing the charged charges, It has the ammeter 7 as a means to measure the weak electric current which flows into the electroconductive support body 6 as a sample installation part, and the vacuum chamber 8 which accommodates these.
As the electron beam irradiation means 3, electrons emitted from an electron gun having tungsten or Lab6 as a cathode may be directly irradiated without scanning, but scanning may be performed to uniformly irradiate each scanning region. .

As shown in FIG. 22, the photoconductor is composed of an undercoat layer (UL), a charge generation layer (CGL), and a charge transport layer (CTL) layer on a conductive support (conductive layer). When exposed with the surface charge being charged, the CGL charge generation material (CGM) absorbs light and generates positive and negative charge carriers. One of these carriers (for example, positive carrier) is moved by the electric field to the CTL surface by the electric field, and the carrier injected into the CTL is combined with the charge on the surface of the photoreceptor to be erased. The other (eg, negative carrier) reaches the conductive support. Normally, the carrier moves in this way, but if the light irradiation continues for a long time or for a long time, the photoconductor is fatigued and trapped by the photoconductor to become a residual charge as shown in FIG.
FIG. 24 shows the relationship between the electric field strength applied to the photoconductor sample and the quantum efficiency of the amount of generated carriers generated when the CGL is irradiated with light. Electric field strength E on the photosensitive member sample = charge potential / photosensitive member film thickness.
CGM is a phthalocyanine-based (Y-TiOPc) and has a light source wavelength of 780 nm. The photoreceptor film thickness is about 30 μm. The higher the electric field strength, the higher the quantum efficiency, and the quantum efficiency converges to 1 at 10 ^ 6 V / cm. When the electric field strength decreases, the quantum efficiency decreases, and when it is 10 ^ 4 V / cm or less, the quantum efficiency is almost zero, and even when light is irradiated, carriers are hardly generated.

Therefore, in order to give light fatigue by irradiating light, it is desirable to set the electric field strength to the photosensitive member sample in the range of 10 ^ 4 V / cm or more and 10 ^ 6 V / cm or less.
The electric field strength can be realized by changing the acceleration voltage of incident electrons.
By setting the acceleration voltage to an acceleration voltage higher than the acceleration voltage at which the secondary electron emission ratio is 1, the amount of incident electrons exceeds the amount of emitted electrons, so that electrons are accumulated in the sample and charge up occurs (FIG. 6). ). As a result, the sample can be negatively charged uniformly.
There is a correlation as shown in FIG. 7 between the acceleration voltage and the charging potential. By appropriately performing the acceleration voltage and the irradiation time, the same charging potential as that of an actual machine in electrophotography can be formed.

As an illumination method for giving light fatigue, a method of using a light emitting diode (LED) and irradiating the entire sample with divergent light without using a lens may be used. By adjusting the amount of current supplied to the LED, the light irradiation light density can be set appropriately.
You may expose only a required wavelength through a filter. Further, in the case of a semiconductor laser (LD), the exposure amount can be appropriately adjusted by controlling the injection current.
In the simplest configuration, it is possible to give light fatigue even if light is emitted and emitted without using a lens. Further, it is more preferable that an optical system such as a lens or an aperture is arranged so as to give an appropriate amount of light to a necessary light irradiation region.

FIG. 15 shows a layout of an illumination optical system as another embodiment for uniformly illuminating the photoconductor sample. In order to avoid interference between the electron beam and the optical system, the light beam is incident from an angle θ (FIG. 14).
A light beam emitted from a semiconductor laser or a light emitting diode 17 having a wavelength of 400 to 800 nm is converted into a parallel light beam by a collimating lens 18, and the diameter of the light beam is regulated by an aperture 19 to irradiate the aperture mask 20. The light beam that has passed through the aperture mask 20 forms an image on the image plane by the action of the imaging lens 210. The “image plane” is a “uniformly charged surface” of a photoconductive sample SP such as a photoconductor mounted on the sample mounting table 28.
In this way, the photoconductive sample SP is exposed, and the region corresponding to the opening mask 20 can be illuminated almost uniformly.
The opening mask 20 may be a rectangle as shown in FIG. 16A, a circle as shown in FIG. 16B, or a more complicated pattern.

As shown in FIG. 15, when the object distance of the aperture mask 20 in the imaging lens 210 is L1 and the image distance is L2, the imaging magnification of the imaging lens 210 in the “perpendicular direction to the optical axis”: β = L2 / L1, and a mask pattern image corresponding to this magnification is formed.
The imaging lens 210 is arranged so that the aperture mask 20 and the surface of the photoconductive sample are conjugated. Imaging magnification: Since β and the size of the mask pattern are known in advance, the illumination area imaged on the surface of the photoconductive sample can be calculated, and exposure in an exposure means that can form a desired pattern on the photoconductive sample The optical axis of the imaging lens 210 is a uniformly charged surface of the photoconductive sample in order to set the optical path for the “outside the region through which the charged particle beam that performs two-dimensional scanning of the photoconductive sample passes”. Inclined with respect to the normal
Accordingly, the mask 20 is also tilted with respect to the optical axis of the imaging lens 210 as shown in FIG. 15 so that the “mask pattern image” by the imaging lens 20 matches the surface of the photoconductive sample. Has been. The “inclination angles with respect to the optical axis of the imaging lens 210: α, θ” of the mask 20 and the photoconductive sample surface are α = θ = 45 degrees in the embodiment being described, and this is the imaging magnification. This is because it is the same magnification (L1 = L2).
For this reason, the mask pattern image formed on the surface of the photoconductive sample is √2 times in the plane parallel to the drawing with respect to the direction orthogonal to the drawing of FIG. To design a mask pattern.
In a general case where the imaging magnification is other than equal magnification, if the object distance is L1 and the image distance is L2, the relationship between these distances L1 and L2 and the inclination angles α and θ is L1. tanα = L2 · tanθ
Holds.
If the area illuminated by the optical system is S (mm) and the light output on the image plane is Pi (mW), the light irradiation light density can be expressed by Pi / S (mW / mm 2). By using such an optical system, it is possible to irradiate a predetermined region of the photoreceptor sample.

FIG. 17 shows the relationship between the LD drive current and the optical output. Raising the drive current to a threshold current or higher causes LD light emission. The light output can be controlled by changing the amount of current under conditions equal to or higher than the threshold current, and the amount of image plane light can be adjusted in proportion to the amount of light, and an appropriate light irradiation light amount density can be set.
The light irradiation means 4 for giving light fatigue and the light source and the optical system (charging erasing means 5) for erasing the charged charges can be used in common. In this way, it is possible to realize simplification and cost reduction of the configuration of the electrostatic latent image evaluation apparatus.
By applying photo fatigue using such a configuration and erasing the charged charges, for example, residual charges trapped inside the photoreceptor can be generated as shown in FIG.

The configuration of the residual charge detection means is shown in FIG. The residual charge detecting means includes means for scanning an electron beam (electron beam irradiation means 3) and an electron detector 9 for detecting a signal obtained by scanning electrons. The conductive support 6 may be GND, but may be configured to accurately measure the potential by applying an applied voltage described later.
In other words, the electrostatic latent image evaluation apparatus includes a charged particle irradiation unit that irradiates a charged particle beam, an exposure unit, a sample setting unit, a detection unit such as primary inversion charged particles and secondary electrons.
As used herein, charged particles refer to particles that are affected by an electric or magnetic field, such as an electron beam or an ion beam.

Hereinafter, an embodiment in which an electron beam is irradiated by scanning will be described with reference to FIG.
The electron beam irradiation unit (electron beam irradiation means 3) controls the electron gun 30 for generating an electron beam, the suppressor electrode 31, the extraction electrode 32 for controlling the electron beam, and the energy of the electron beam. Accelerating electrode 33, condenser lens 34 for focusing the electron beam generated from the electron gun 30, beam blanker (beam blanking electrode) 35 for turning on / off the electron beam, and electron beam irradiation current An aperture (charged particle optical system movable diaphragm) 36 for controlling the beam, a stigmator (astigmatism correction) 37, a scanning lens (deflection electrode) 38 for scanning the electron beam that has passed through the beam blanker 35, and scanning It consists of an objective lens 39 for condensing the lens again. A driving power source (not shown) is connected to each lens.
In the case of an ion beam, a liquid metal ion gun or the like is used instead of an electron gun.

The configuration of the electron detector 9 is shown in FIG. It consists of a scintillator to which a pull-in voltage of about 10 kV is applied and a photomultiplier tube. Photoelectrons emitted from the photocathode of the photomultiplier tube are guided to the electron lens system, collide with the first dynode, and emit (seconds) secondary electrons (FIG. 4). The secondary electrons are further multiplied by subsequent dynodes, and when they reach the anode, they are amplified by 10 ^ 4 to 7 times.
The secondary electron emission ratio δ per dynode is δ = A × Vdi ^ α if the applied voltage between dynodes is Vdi.
It is represented by α depends on the shape and material of the dynode, and is usually 0.7 to 0.8.
Here, when a voltage Vall is applied between the cathode and anode of a photomultiplier tube having n stages of dynodes, the gain μ is μ = K · Vall ^ (αn)
It becomes.
FIG. 5 shows the relationship between the gain voltage (cathode-anode voltage) and the gain. A large gain can be obtained with a slight voltage difference.

A photoconductor sample having a charge distribution is scanned with an electron beam, secondary electrons emitted are detected with a scintillator, converted into an electrical signal, and a contrast image is observed.
When the sample has a charge distribution, an electric field distribution corresponding to the charge distribution is formed in the space. In a portion where the negative charge density is relatively higher than that of the periphery, an accelerating electric field is generated and secondary electrons reach the electron detector 9.
In a portion where the negative charge density is relatively lower than that of the periphery, a deceleration electric field is generated, and secondary electrons are pulled back to the sample. As a result, the amount of electrons reaching the detector 9 changes, and a contrast image corresponding to the charge distribution can be obtained.
FIG. 10A illustrates the potential distribution in the space between the electron detector 9 and the sample surface in an explanatory manner with contour lines. FIG. 10B shows a relative charge distribution, and Q3 is a portion where the charge density is lower than Q1 and Q2. el1, el2, and el3 indicate electron trajectories.
For example, if the intensity of the secondary electrons to be captured is expressed by “brightness and weakness”, the coarse charge portion is dark and the dense charge portion is bright and contrasted, and is expressed (output) as a bright and dark image corresponding to the charge distribution. be able to.
In addition, although described as secondary electrons in the above description, it also includes detection of tertiary electrons or more electrons generated when the secondary electrons hit a member in the apparatus.
In this way, the charge distribution depending on the presence / absence of the residual charge can also be evaluated based on the above phenomenon.

FIG. 8 shows a flow of residual charge analysis, and FIG. 9 shows a timing chart of residual charge measurement.
Time: 0 to t1 is a process in which both the electron beam and the light are irradiated. In addition, even if it is said that there is a process in which both the electron beam and the light are irradiated, there may be a state in which one of them is not irradiated temporarily.
By irradiating the electron beam with the irradiation current density EB1 (C / mm ² ), the electric field strength is given, and by irradiating the light with the light amount P1 (W / mm ² ), a large number of carriers can be generated. Thereby, light fatigue can be given.
By appropriately setting the light irradiation amount or the electron beam irradiation current density, the passing current density I0 (A / m ² ) flowing through the conductive support can be appropriately controlled.
In the method of rotating the photosensitive drum as in the prior art, both the charging unit and the exposure unit are arranged at different locations, and therefore both cannot be irradiated simultaneously. Since the present invention enables both irradiations, light fatigue can be efficiently applied in a short time.

Time: t1 to t3 are processes for charge erasing.
After completion of light fatigue, the electron beam irradiation current density is once turned off. Even if it is not OFF, if it is as weak as about 1/100 or less, it is hardly charged, so the same effect can be obtained.
At this time, by performing light irradiation with the amount of light P2, the surface charge is erased and the passing current flowing through the substrate also decreases, and becomes almost zero at t2 (<t3). The light irradiation amount at this time may be the same P1 as that during light fatigue, but it is important that the light irradiation amount is larger than the required exposure energy density of the photoreceptor.
The exposure energy of normal OPC is several to tens of mJ / m ² . It can be said that it is sufficiently large if an exposure energy density of 10 times is given.

FIG. 25 shows an example of light attenuation characteristics of a phthalocyanine photoconductor (film thickness: 30 μm). It exceeds 4 mJ / ^{m 2} since it substantially constant, necessary exposure energy in this case is 4 mJ / ^{m 2,} if the light irradiation 40 mJ / ^{m 2} equivalent, sufficient to erase the charge It can be said that the amount of light.
Thereby, the charged charge on the surface is erased. This process can leave only residual charge.
Time: t4 to t5 are processes for measurement.
By scanning with the electron beam, the residual charge can be observed by detecting the signal obtained by the scanning with the electron detector. In order to increase the S / N ratio, it is better that the beam irradiation current is high, but in this case, charging occurs again and the distinction cannot be made. For this reason, it is preferable to scan with a weak electron beam irradiation current of about 1 to 20 pA for observation.

In the process of irradiating light while irradiating with an electron beam, the amount of secondary electron emission becomes enormous, and the scintillator may be damaged when the amplification factor of the electron detector is in a normal observation state. . When monitoring the light fatigue state while preventing breakage, it is better to set the amplification factor (gain) G2 of the electron detector to a smaller condition than the observation amplification factor G1. In order to lower the amplification factor, the voltage between the cathode and the anode is preferably lowered.
As shown in FIGS. 18A and 18B, the amount of electrons passing through the pinhole can be adjusted by changing the voltage applied to the condenser lens of the electron beam.
The amount of electrons can be easily measured by converting the amount of electrons into a current at the sample position using a Faraday cup.
In corona charging and scorotron charging, since discharge in the air is used, it is difficult to control the amount of electrons irradiated to the photoreceptor sample even though the passing current flowing through the substrate can be controlled.
One feature of the present invention is that it can be charged by irradiating with an electron beam in a vacuum apparatus, and an electron beam current that directly affects light fatigue can be controlled, thereby efficiently giving light fatigue. be able to.

The amount of light was adjusted so that the passing current was 830 pA / mm ² at a charging potential of −800 V and an electron beam irradiation current of 1.8 nC / mm ² per ^second, and light fatigue was performed for 30 minutes. Thereafter, light irradiation was performed for 30 seconds to irradiate a light amount 10 times or more of ⁴ mJ / m ² which is the required exposure energy of the photosensitive member, to remove the charged charge, and to detect the residual charge.
Samples A, B, and C used for evaluation have the same CTL film thickness of about 30 μm, but have different UL prescriptions.
When the average residual potential VR in a region of 2 mm square or more was measured in advance, the absolute value of VR was -50 V or more for sample A, about -30 V for sample B, and -10 V or less for sample C.
The measurement results are shown in FIG. Sample A with a large residual charge has a large detection signal, and sample C with a small residual charge has a small detection signal and is displayed dark. In sample B, light and dark are mixed locally.
It shows that the residual charge remains locally. This indicates that the dispersibility of the material of the photoconductor formulation such as UL is not good.
The luminance signal of the measurement cross section is shown in FIG. The conventional macro average residual potential is good in the order of C, B, and A. The bias potential increase can be adjusted by the development bias potential or the like, but the local variation cannot be corrected and is output as a deteriorated image.
Considering the dot scale, if the PV value is 20 V in the range of 200 μm, for example, the dot reproducibility of a 600 dpi 2 by 2 image deteriorates.
Therefore, as shown in FIG. 13, the electrophotographic photoreceptor desirably has a residual potential PV value of 20 V or less in a range of 200 μm or less. Thus, it became possible to evaluate the spatial residual potential fluctuation in the micro region.
As a result, it has become possible to directly evaluate characteristic values by improving the image quality.

By measuring the profile of the surface charge distribution and the surface potential distribution, it is possible to measure with higher accuracy.
FIG. 19 is a diagram showing another embodiment of the surface potential distribution measuring apparatus (electrostatic latent image evaluation apparatus) of the present invention.
A voltage application unit capable of applying a voltage ± Vsub is connected to the sample installation part below the sample.
Further, the upper portion of the sample has a configuration in which a grid is arranged in order to suppress the incident electron beam from being affected by the sample charge.
FIG. 20 is a diagram showing the relationship between incident electrons and a sample. FIG. 4A shows the case where the acceleration voltage is larger than the surface potential potential, and FIG. 4B shows the case where the acceleration voltage is smaller than the surface potential potential.
There is a region where a state where the velocity vector of the incident charged particles in the sample vertical direction is reversed before reaching the sample, and the primary incident charged particles are detected.
The acceleration voltage is generally expressed as positive, but the applied voltage Vacc of the acceleration voltage is negative, and in order to have a physical meaning as a potential potential, it is more preferable to express it as negative. Here, the acceleration voltage is expressed as negative (Vacc <0).
The acceleration potential of the electron beam is Vacc (<0), and the potential potential of the sample is Vp (<0).
A potential is an electrical potential energy possessed by a unit charge. Therefore, the incident electrons move at a speed corresponding to the acceleration voltage Vacc at the potential 0 (V). That is, assuming that the charge amount of electrons is e and the mass of electrons is m, the initial velocity of electrons v0 is
mv02 / 2 = e × | Vacc |
It is represented by In vacuum, due to the law of conservation of energy, it moves at a constant speed in the region where the acceleration voltage does not work, and as it approaches the sample surface, the potential increases, and the velocity decreases due to the influence of Coulomb repulsion of the sample charge.

Therefore, the following phenomenon generally occurs.
In FIG. 9A, since | Vacc | ≧ | Vp |, the electron reaches the sample although the speed is reduced.
In FIG. 4B, in the case of | Vacc | <| Vp |, the velocity of the incident electrons is gradually decelerated by the influence of the potential potential of the sample, and the velocity becomes zero before reaching the sample. And go in the opposite direction. In a vacuum without air resistance, the energy conservation law is almost completely established.
Therefore, the surface potential can be measured by measuring a condition in which the energy on the sample surface, that is, the landing energy when the energy of the incident electrons is changed, is almost zero. Here, primary inversion charged particles, particularly electrons, are referred to as primary inversion electrons. The secondary electrons generated when the sample reaches the sample and the primary inversion charged particles differ greatly in the amount reaching the detector, so that they can be identified from the boundary of contrast between light and dark.

A scanning electron microscope or the like has a backscattered electron detector. In this case, the backscattered electrons are generally reflected (scattered) on the rear back surface due to the interaction with the material of the sample, and the sample. It refers to the electrons that jump out of the surface. The energy of the reflected electrons is comparable to the energy of the incident electrons. It is said that the intensity of the reflected electrons increases as the atomic number of the sample increases, and this is a detection method for understanding the difference in composition of the sample and unevenness.
In contrast, primary inversion electrons are electrons that are inverted before reaching the sample surface under the influence of the potential distribution on the sample surface, and are completely different phenomena.

FIG. 21 is a diagram showing an example of a latent image depth measurement result.
If the difference between the acceleration voltage Vacc and the sample lower applied voltage Vsub is Vth (= Vacc−Vsub) at each scanning position (x, y), Vth (x, y) when the landing energy becomes almost zero. Can be measured to measure the potential distribution V (x, y).
Vth (x, y) has a unique correspondence with the potential distribution V (x, y). If Vth (x, y) is a gentle charge distribution, the potential distribution V (x , Y).
The upper curve in FIG. 21 shows an example of the surface potential distribution generated by the charge distribution on the sample surface. The acceleration voltage of the electron gun for two-dimensional scanning was set to −1800V. The potential at the center (horizontal axis coordinate = 0) is about -600V, the potential increases in the negative direction as it goes from the center to the outside, and the potential in the peripheral region whose radius exceeds 75 μm from the center is about -850V. ing. The oval in the middle of the figure is an image of the detector output when the back surface of the sample is set to Vsub = −1150V.
At this time, Vth = Vacc−Vsub = −650V. The oval in the lower part of the figure is an image of the detector output obtained under the same conditions as above except that Vsub = −1100V. At this time, Vth is -700V.
Therefore, the surface potential information of the sample can be measured by scanning the sample surface with electrons while changing the acceleration voltage Vacc or the applied voltage Vsub and measuring the Vth distribution.
By using this method, it is possible to visualize the latent image profile on the micron order, which has been difficult in the past.

In the method of measuring the latent image profile with primary inversion electrons, the energy of incident electrons changes drastically, causing the trajectory of the incident electrons to shift, resulting in a change in scanning magnification and distortion. Will be.
In that case, the electrostatic field environment and the electron trajectory can be calculated in advance, and correction can be performed based on the calculation, thereby making it possible to measure with higher accuracy.
It is desirable that the photosensitive member for electrophotography has an average residual potential greater than -50V in the observation range of 2 mm or more and a maximum value-minimum value of the residual potential in the observation range of 200 μm or less of 20V or less.
It is desirable that the residual potential is inherently low. However, it becomes a factor of high cost. In addition, the residual potential can be lowered by setting the resistance of UL low, but the insulation resistance is lowered, which causes soiling.
It was found that the spatial variation affects the reproducibility of 1 dot or 2 dots when the maximum value-minimum value of the residual potential is 20 V or more in a region with a high spatial frequency such as an observation range of 200 μm or less than the average potential. .
Therefore, for example, even if the average potential in the region where the observation range is 2 mm or more is slightly larger than the absolute value of −50 V, the maximum value of the residual potential in the observation range of 200 μm or less can be obtained by selecting a material with high UL dispersibility. It is desirable that the minimum value be 20V or less.

Hereinafter, an embodiment of the image forming apparatus of the present invention will be described. FIG. 26 schematically shows the laser printer according to the first embodiment. The laser printer 100 has a “cylindrical photoconductive photosensitive member” as the image carrier 111. Around the image carrier 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are provided. In this embodiment, a contact-type charging roller 112 that generates less ozone is used as the “charging means”, but a corona charger that uses corona discharge can also be used as the charging means.
Further, an optical scanning device 117 is provided to perform “exposure by optical scanning of the laser beam LB” between the charging roller 112 and the developing device 113. In FIG. 26, reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a registration roller pair, reference numeral 120 denotes a paper feed roller, reference numeral 121 denotes a conveyance path, reference numeral 122 denotes a discharge roller pair, and reference numeral 123 denotes a tray. Yes.

When forming an image, the image carrier 111, which is a photoconductive photosensitive member, is rotated at a constant speed in the clockwise direction, and the surface thereof is uniformly charged by the charging roller 112. An electrostatic latent image is formed by the exposure by engraving. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the image carrier 111.
The cassette 118 storing the transfer paper is detachable from the main body of the image forming apparatus 100, and the uppermost sheet of the stored transfer paper is fed by the paper feeding roller 120 in the state of being mounted as shown in the figure. The transferred transfer paper is fed to the registration roller pair 119 at the leading end. The registration roller pair 119 feeds the transfer paper to the transfer unit at the same timing as the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114.
The transfer paper on which the toner image is transferred is fixed on the toner image by the fixing device 116, passes through the conveyance path 21, and is discharged onto the tray 123 by the discharge roller pair 122. After the toner image is transferred, the surface of the image carrier 111 is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like.

1A and 1B are diagrams showing an apparatus for evaluating an electrostatic latent image according to an embodiment of the present invention, in which FIG. 1A is a schematic configuration diagram from a side surface as a residual charge generating unit, and FIG. It is a block diagram. It is a schematic block diagram of an electron beam irradiation means. It is a block diagram which shows the structure of an electron detector. It is a figure for demonstrating the function of the photomultiplier tube in an electron detector. It is a characteristic figure which shows the gain voltage of a photomultiplier tube and shows the relationship of a gain. It is a characteristic view which shows the relationship between an acceleration voltage and charging. It is a characteristic view which shows the relationship between an acceleration voltage and a charging potential. It is a flowchart of a residual charge measurement. It is a timing chart of residual charge measurement. It is a figure which shows the principle model of the charge distribution detection by a secondary electron. It is a figure which shows the measurement result of the residual charge according to sample. It is a characteristic view which shows the cross-sectional distribution evaluation result of the residual charge according to sample. It is a figure which shows the parameter | index of residual charge evaluation. It is a schematic block diagram of the illumination optical system in the evaluation apparatus for electrostatic latent images. It is a figure which shows the layout of an illumination optical system. It is a figure which shows the shape of the aperture mask in an illumination optical system. It is a characteristic view which shows the relationship between LD drive current and optical output. It is a figure for demonstrating the adjustment function of the amount of electrons from an electron gun. It is a figure which shows the other example of the evaluation apparatus of an electrostatic latent image. It is a characteristic view which shows the relationship between an incident electron and a photoreceptor sample. It is a figure which shows an example of a latent image depth measurement result. It is a schematic sectional drawing of a photoreceptor sample. It is a schematic sectional drawing of the photoreceptor sample which has a residual charge. It is a characteristic view which shows quantum efficiency. It is a characteristic view which shows the relationship between exposure energy density and surface potential. 1 is a schematic configuration diagram of an image forming apparatus.

Explanation of symbols

2 Photosensitive material sample 3 Electron beam irradiation means as means for charging the sample by electron beam irradiation 4 Light irradiation means as means for giving photo fatigue to the photoconductor 5 Charging as means for removing charged charges and leaving residual charges Erasing means

Claims (12)

In a method of irradiating a photoconductor sample having a charge distribution with a charged particle beam and measuring an electrostatic latent image of the photoconductor sample by a detection signal obtained by the irradiation,
The charged photoconductor sample is charged in a state in which the charged charge is removed by irradiating light in a vacuum with light having photoconductor sensitivity and irradiating a light amount larger than the required exposure energy density of the photoconductor. A method for evaluating an electrostatic latent image, comprising: scanning a particle beam and detecting electrons obtained by the scanning to evaluate a residual charge generated on a photoconductor sample. The method for evaluating an electrostatic latent image according to claim 1,
A method for evaluating an electrostatic latent image, characterized in that light fatigue is given to a photosensitive member by irradiating light while irradiating an electron beam. The method for evaluating an electrostatic latent image according to claim 2,
A method for evaluating an electrostatic latent image, characterized in that, in the process of irradiating light while irradiating an electron beam, the amplification factor of the electron detector is set to a condition smaller than that during observation. In the evaluation method of the electrostatic latent image according to claim 2 or 3,
A method for evaluating an electrostatic latent image, characterized by controlling a light fatigue state by changing a current of an electron beam applied to a photoconductor sample. In the evaluation method of the electrostatic latent image according to any one of claims 1 to 4,
A method for evaluating an electrostatic latent image, comprising setting an electric field strength to a photoreceptor sample in a range of 10 ^ 4 V / cm to 10 ^ 6 V / cm. In the evaluation method of the electrostatic latent image according to any one of claims 1 to 5,
A method for evaluating an electrostatic latent image, wherein visible light having a wavelength of 400 to 800 nm is used as light having photoconductor sensitivity, and a predetermined region of a photoconductor sample is irradiated by an optical system. In the evaluation method of the electrostatic latent image according to any one of claims 1 to 6,
A method for evaluating an electrostatic latent image, characterized in that light irradiation is performed by a semiconductor laser, and the amount of current of the semiconductor laser is changed to control the amount of current flowing through the substrate of the photoreceptor sample. In the evaluation method of the electrostatic latent image according to any one of claims 1 to 7,
Measure the residual potential by applying a voltage to the back of the sample in order to change the potential potential on the sample surface. A method for evaluating an electrostatic latent image, comprising: In an apparatus for irradiating a photosensitive sample having a charge distribution with a charged particle beam and measuring an electrostatic latent image of the sample by a detection signal obtained by the irradiation,
Means for charging the sample by electron beam irradiation in a vacuum;
Means for irradiating light having photoconductor sensitivity to give light fatigue to the photoconductor,
Means for removing the charged charge and leaving a residual charge;
With
An apparatus for evaluating an electrostatic latent image, characterized by evaluating a residual charge of a photosensitive member sample by scanning a charged particle beam and detecting electrons obtained by the scanning. The apparatus for evaluating an electrostatic latent image according to claim 9,
One of the means for giving light fatigue and the means for leaving the residual charge serves as the other. When the residual charge is evaluated using the evaluation method and the evaluation device according to claim 1,
An electrophotographic photosensitive member having an average residual potential greater than -50 V and a maximum-minimum value of residual potential of 20 V or less in an observation range of 200 μm or less.   12. An image forming apparatus, wherein a latent image is formed using the electrophotographic photosensitive member according to claim 11, and is developed and visualized.

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