JPH1069100A - Elecrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate a flow of a toner on a surface of an electrophotographic photoreceptor and to suppress a sticking of a toner on a non-image area. SOLUTION: An electric charge injection layer 1A contg. a fluororesin-contg. binder and electrically conductive particles dispersed in the binder is formed on the surface of an electrophotographic photoreceptor 1 and the surface energy of the electric charge injection layer (surface layer) 1A is regulated to <=30dyn/ cm. The flow of a toner on the surface of the layer 1A is facilitated and the sticking of the toner on the surface can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member used for an image forming apparatus of a back exposure type.

[0002]

2. Description of the Related Art Conventionally, as a means for obtaining a hard copy in a copying apparatus, a computer, or the like, an image forming apparatus employing an electrophotographic system has been widely used. This image forming apparatus is generally configured by arranging a large number of apparatuses for forming an image around an electrophotographic photosensitive member (hereinafter simply referred to as a “photosensitive member”). That is, around the photoreceptor,
A charging device, an exposure device, a developing device, a transfer device, a cleaning device, and the like are arranged. In such an electrophotographic image forming process, a photoconductor is charged and exposed to form an electrostatic latent image on the photoconductor, toner is attached to the electrostatic latent image, developed, and developed. The toner image is transferred onto the transfer, and then the toner image is fixed on a transfer material to finally obtain a print image.

A print image obtained in this way has higher resolution and higher contrast than print images obtained by other hard copy means, for example, a thermal transfer method, an ink jet method, an impact printing method and the like. As a whole, high image quality can be obtained.

However, since the image forming process by the electrophotographic method requires a large number of devices as described above, the configuration of the entire device tends to be large and complicated, and it is difficult to make the device compact and simple. Was.

[0005] For this reason, several methods have been proposed in which processes such as charging, exposure and development are combined while using the same electrophotographic method (hereinafter referred to as "simplification process" as appropriate), and these are performed almost simultaneously at almost the same position. Representative examples thereof are disclosed in, for example, JP-A-58-153957 and JP-A-62-209470. These generally use a conductive toner, or a conductive carrier and an insulating toner, and are used for (1) cleaning of transfer residual toner at the time of previous image formation, (2) contact charging, (3) image exposure from the back side to the photoreceptor, ( 4) A step of performing a series of processes of contact development. Then, the above steps are performed in a developing nip between the photoconductor and a magnetic brush roller which is in contact with the photoconductor surface while facing the photoconductor back exposure position.

More specifically, as shown in FIG. 3, first, cleaning is performed by scraping off the transfer residual toner on the upstream side in the developing nip N between the magnetic brush roller formed by the developing sleeve 22 and the photosensitive member 1. Do. At this time, the toner to be used is the magnetic toner T, and since the fixed magnet 23 is disposed inside the developing sleeve 22, the cleaning effect can be enhanced by the magnetic force. Next, the surface of the photoreceptor 1 is charged by rubbing the surface of the photoreceptor 1 with a conductive magnetic brush (conductive toner or conductive carrier) and injecting charges. This is because charging is performed by trapping charges at impurity levels on the surface of the photoreceptor 1. Therefore, a necessary charging is not performed unless a charging member having a sufficiently low resistance value is used and the charging time is long. For this reason, it is necessary to use a material capable of holding electric charges well near the surface as the photoconductor 1, and amorphous silicon (hereinafter referred to as “a-Si”), selenium, or the like is preferably used. The cleaning and charging described above are performed at the back exposure position A in the development nip N.
This is performed simultaneously in the cleaning / charging area N _C on the upstream side (described next). The charged potential of the photoconductor 1 due to the rubbing of the magnetic brush is substantially equal to the applied voltage.

Next, exposure is performed from the back of the photoreceptor 1. As the light source (exposure means) 3, an LED array 3a or the like is used, and a predetermined position (backside exposure position) A in the development nip N formed by the development sleeve 22 and the photoconductor 1
Is exposed. This exposure forms a latent image on the photoconductor 1.

[0008] The latent image is developed in the developing area N _D of the back exposure position A downstream side of the developing nip N. In the case of using the conductive toner, the charge electrostatically induced by the latent image formed on the photoreceptor 1 is injected into the toner at the tip of the spike through the toner spike, and a coulomb acting between the charge and the latent image charge The toner is separated from the spikes by force to perform development.

Further, in the case where development is carried out with a magnetic conductive carrier and an insulating toner using a two-component developer in the same configuration, the spikes of the conductive carrier serve as proximity electrodes, and the photosensitive member 1 and the developing sleeve 22 are provided. A sufficient electric field can be applied to the development even if the voltage applied between them is low, so that the development of the insulating toner can be performed at a low voltage.

In general, it is difficult to transfer the toner image on the photoreceptor 1 to the transfer material P using an electric field with the conductive toner. Therefore, the latter two-component development using an insulating toner is preferable. Have been.

As a photoreceptor, a function-separated type OPC photoreceptor, which has been dominant in recent years, has been poorly used for the image forming apparatus having the above configuration because of its poor charge injection property. It has been confirmed that by newly forming a charge injection layer on the surface of the photoconductor, the charge injection property is improved and good chargeability can be secured.

[0012]

However, according to the simplification process of the prior art, there is a problem that fogging occurs in a non-image portion. In the simplification process, since the inverted contrast set by a normal electrophotographic process cannot be obtained due to its configuration, the non-image portion is inherently easily fogged.

Specifically, FIG. 3 shows that actually 10 ³ Ω ·
When a voltage of +60 V was applied to the developing sleeve of a photoconductor having a silicon carbide layer provided on an a-Si photoconductor using conductive particles having a volume resistance value of cm, an image was formed by the apparatus shown in FIG. , the charge potential V _D to + 55V, the exposed portion potential V _L became + 5V. When development is performed on the photosensitive member potential in the latter half of the development area in the development nip, the potentials are set as follows: non-image portion potential V _D = + 55 V, image portion potential V _L = + 5 V, development potential V _DC = + 50V,
With this setting, the positive toner is developed in reverse.

As can be seen from this potential setting, the development contrast is 50 V, but there is no inversion contrast.
In the non-image area, the voltage is more toward the developing side by about 5 V.
Actually, the magnetism in the developing sleeve exerts a restraining force on the magnetic toner, so that development on non-image areas is suppressed. However, it can be seen that the process is very easy to fog.

As described above, although the simplification process has a simple structure, there is a problem that the image stability is poor in terms of fog.

It is known that when the toner easily moves on the surface of the photoreceptor, fog is reduced.

Accordingly, it is an object of the present invention to provide an electrophotographic photosensitive member which facilitates the movement of toner on the surface of the electrophotographic photosensitive member.

[0018]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and in an electrophotographic photosensitive member having a photosensitive layer provided on a conductive substrate, at least fluorine is used as a surface layer of the photosensitive layer. A charge injection layer having an insulating binder containing a resin and conductive particles dispersed in the binder and having a surface energy of 30 dyne / cm or less is provided.

[Operation] The main operation based on the above configuration (operation based on claim 1) is as follows.

By setting the surface energy of the photoreceptor to 30 dyne / cm or less, the releasability of the photoreceptor surface is improved.
Excessive adhesion can be prevented.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> In this embodiment, FIG.
In the photoreceptor backside exposure, cleaning, charging, and developing simultaneous process (simplified process) as shown in (1), a positively chargeable amorphous silicon drum (a-
(Si drum).

First, the outline of the image forming apparatus used in the embodiment shown in FIG. 2 will be described.

Electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum" as appropriate)
That. 1) is obtained by laminating a photosensitive layer on a transparent glass cylinder having a diameter of 30 mm. Heat-resistant glass is used for the cylinder, and I
A TO layer is applied to a thickness of about 1 μm. A functional layer is laminated thereon.

In order from the lower layer, an amorphous silicon carbide layer, an amorphous silicon photosensitive layer, and an amorphous silicon carbide protective layer were sequentially deposited as a layer for preventing injection of negative charges from the substrate to obtain a photosensitive member. Although the amorphous silicon carbide protective layer is generally used for a-Si photoconductors, in this embodiment, in order to form photoconductor surfaces having different surface energies, the degree of amorphization (crystallinity) and atomic composition are changed. in different ones of the ratio (the value of Si _X C _1-X of x) was performed three prototypes. When the degree of amorphization is increased, the material tends to be in a stable direction, so that the surface energy is reduced.

The photoreceptor 1 thus prepared is
When the surface energy (surface tension) value of the sample was measured, sample 1 was 33 dyne / cm, sample 2 was 30 dyne / cm,
Sample 3 was 28 dyne / cm.

For comparison, a selenium photoreceptor was also prepared as Sample 4, and the surface energy of the selenium photoreceptor sample 4 used in the present embodiment was measured by the same method. As a result, the value was 35 dyne / cm. Was.

The surface energy value used here is:
The value of surface tension is used in place of JIS K6768-1.
The test was performed based on the “wetting test method for polyethylene and polypropylene films” specified by N.971 and the energy value was determined by applying a wetting index standard solution having different values.

Next, the developing device 2 will be described. The developing device 2 includes a developing container 21 for storing the developer D,
The developing sleeve 22 includes a rotatable developing sleeve 22 of 0 mm and a fixed magnet 23 disposed inside the developing sleeve 22. The developing sleeve 22 is in the same direction as the photosensitive drum 1 rotating in the direction of arrow R1 (the photosensitive drum in the developing nip N). (The movement direction between the first surface and the surface of the developing sleeve 22 is the same) and is rotated in the direction of arrow R2 at a peripheral speed six times as high.

In this embodiment, since the process speed is 50 mm / sec at the peripheral speed of the photosensitive drum, the peripheral speed of the developing sleeve 22 is 300 mm / sec. The magnetic poles of the fixed magnet 23 are arranged at eight equal poles, one of which is located at the peak position of the photosensitive drum 1 and the developing sleeve 2.
It is arranged to be on a straight line connecting the centers of each other,
The magnetic flux density on the developing sleeve 22 at the peak position is 800
Set to Gaussian.

The developer D is composed of two components, and is a combination of a magnetic conductive carrier C (hereinafter, simply referred to as "carrier") and a magnetic insulating toner T (hereinafter, simply referred to as "toner").

The magnetic conductive carrier C contributes to cleaning of the transfer residual toner, charging of the photosensitive drum surface, and conveyance of the toner. The carrier has a particle size of 25 μm and a resistance value of 10 ³ Ω · cm, and is a resin carrier in which magnetite is dispersed in a polyethylene resin and carbon black is dispersed for conductivity.

The magnetic insulating toner T is a negative toner and has a particle diameter of 7 μm and a resistance value of 10 ¹⁴ Ω · cm.

The toner and the carrier are used in a T / D ratio of 15%.
(The weight ratio of the toner T to the total amount of the developer D), and is stored in the developing container 21. In the developing container 21, a metal plate blade 24 for regulating the coat thickness of the toner on the surface of the developing sleeve 22 is opposed to the developing sleeve 22, and the layer thickness of the toner is about 1 mm. The developing sleeve 22 and the photosensitive drum 1 are held at an interval of 0.5 mm by an end contact roller (not shown). In this state, when the photosensitive drum 1 and the developing sleeve 22 are rotated at a predetermined speed, the developing nip N of both is set to be 7 mm.

The voltage applied between the developing sleeve 22 and the photosensitive drum 1 is +60 V, and reversal development is performed in combination with the negative toner.

The exposure means 3 has an LED array 3 and is inserted inside the photosensitive drum 1 so as to make a back surface at an exposure irradiation position A of the developing nip N. The exposure irradiation position A is performed at a position 2 mm from the most downstream side in the development nip N. If this position is too close to the upstream, the latent image formed by the exposure is recharged by the conductive carrier, and the latent image contrast is reduced, so that the image density does not increase. Conversely, if it is too far downstream from the predetermined position, the area contributing to development becomes short, and similarly, there is a problem that the image density does not increase.

The toner image thus developed is transferred onto the transfer material P by the transfer roller 5. The transfer roller 5 used in this embodiment had a resistance of 5 × 10 ⁷ Ω and an applied bias of +500 V. The toner not transferred in the transfer portion is scraped off on the upstream side in the development nip N at the time of the next image formation, so that the next image formation is not affected.

An example in which an image is actually formed using the above-described apparatus will be described.

First, on the upstream side of the developing nip N formed by the photosensitive drum 1 and the developing sleeve 22, the toner remaining on the photosensitive drum at the time of the previous image formation is scraped off by the magnetic brush which has been advanced. . At the same time, when the conductive carrier and the photosensitive drum 1 come into contact with each other, electric charges are injected into the conductive powder of the charge injection layer 1A of the photosensitive drum 1 and charging is performed. In this embodiment, when a voltage of +60 V is applied to the developing sleeve 22, a potential of +55 V is obtained. Then, at the exposure irradiation position A, the exposure portion potential (bright portion potential) is reduced to +5 V by performing LED exposure from the inner surface of the photosensitive drum. Development nip N after exposure
Then, contact development by an electric field is performed.

Samples 1 to 3 used in this embodiment
−Si photosensitive drums have a development potential of +60 V and a dark area potential of +
55 V, bright part potential +5 V. Therefore, although the development contrast is 50 V, the development contrast is 5 V even in the non-image area, so that the inversion contrast cannot be obtained as in a normal electrophotographic process. Tends to occur.

In the simplification process, the developing contrast voltage is as small as several tens of volts. However, since the ears formed by the conductive carrier are almost in contact with the photosensitive drum 1, the developing electric field applied to the toner is very large. Can be higher. Each of a used in the present embodiment
As a result of density measurement using a Macbeth reflection densitometer using a -Si photosensitive drum, a density of about 1.3 was obtained.

However, when the fog of the non-image portion is measured,
Table 1 shows the case where each a-Si photosensitive drum is used.
And different values.

The measurement of the fogging amount is defined by a difference in reflectance between a printed transfer material and a non-printed transfer material using a photobolt meter.

FIG. 4 shows the fog amount when a test was carried out for each of the a-Si photosensitive drum and the selenium photosensitive drum while changing the voltage applied to the developing sleeve 22.

[0045]

[Table 1] It is apparent from Table 1 and FIG. 4 that the fogging of the non-image portion is determined not by the developing sleeve voltage but by the surface energy.

This is because, in the apparatus of the present embodiment, the developing force of the non-image portion given by the developing sleeve voltage and the dark portion potential and the magnetic restraining force on the toner by the fixed magnet 23 are almost balanced. This is because fogging is mainly caused by Van der Waals force acting between the photosensitive drum surfaces.

When the fog in a non-image portion at a level that is practically acceptable was examined by visual discrimination by a panel test,
If it is 4.0% or less, it turns out that it is not much bothersome.

Therefore, by setting the surface energy of the photosensitive drum to 30 dyne / cm or less of the sample 2,
It has been found that fogging can be made to a practically acceptable level.

<Embodiment 2> This embodiment is characterized in that a function-separated negatively-charged OPC is used for a photosensitive drum, and a charge injection layer whose surface energy is newly reduced is newly provided on the surface layer.

The charge injection layer is made by dispersing conductive particles in an insulating resin. The conductive layer is applied to a capacitor in which the photosensitive layer acts as a dielectric and the conductive particles act as minute float electrodes. Inject and charge with a magnetic brush.

For this reason, even if a photosensitive material such as OPC which cannot be used because there is no level for trapping charges on the surface of the photosensitive layer in the conventional simplified process cannot be used, good charging can be performed. And the room for selection of the photoconductor material is expanded.

If a charge injection layer is provided on the photosensitive drum, the surface of the photosensitive drum can be instantaneously charged even by using a magnetic brush having a high resistance value of about 10 ⁶ Ω, and the electric withstand voltage can be further reduced. When applied to a high OPC photosensitive drum, a voltage of several hundred volts is applied to the conductive magnetic brush instead of the a-Si photosensitive drum, which had a low electric breakdown voltage and could only apply several tens of volts in the past. A sufficient image density can be obtained.

In this embodiment, an apparatus having exactly the same configuration as that of the first embodiment is used, and only the configuration of the photosensitive drum is changed.
However, in the first embodiment, since the photosensitive drum is a positively charged photosensitive drum, in the present embodiment, development is performed by reflection development using a negatively charged photosensitive drum and negative toner.

Instead of a-Si, a photosensitive drum is used in which a polycarbonate is used as a binder on a normal OPC photosensitive member and a charge injection layer in which titanium dioxide is dispersed at a weight ratio of 120 wt% is used.

If the amount of the conductive filler dispersed in the charge injection layer is large, the surface resistance of the photosensitive drum is reduced particularly in a high-temperature and high-humidity environment, which may cause image deletion. There is a possibility that a charging area occupying the surface area of the drum is reduced and charging failure occurs. For this reason, the dispersion amount of titanium dioxide is preferably within the range of 5 to 250 wt%.
20% was adopted.

In this embodiment, fluorocarbon resin particles are further dispersed in a binder in order to reduce the surface energy of the photosensitive drum. The fluororesin particles were PTFE particles manufactured by DuPont, and had a particle size of about 0.5 μm. The surface energy of the PTFE resin itself is 2
Since it is extremely low at 1.5 dyne / cm, the surface energy of the photosensitive drum can be significantly reduced by dispersing it.

In this embodiment, PTFE is used for comparison.
Experiments were conducted on three types of samples: a sample 5 in which particles were dispersed at 5 wt% with respect to a binder, a sample 6 in which particles were dispersed in 10 wt%, and a sample 7 in which particles were not dispersed.

In a conventional electrophotographic process, the incorporation of such particles in a large amount on the surface of the photosensitive drum is limited because it hinders image exposure from the surface of the photosensitive drum.
In the present simplification process, since the inner surface exposure is performed, the surface of the photosensitive drum does not need to transmit light, and a large amount of light can be dispersed as in the present embodiment.

[0059]

[Table 2] The results are shown in Table 2. The sample having a lower photosensitive drum surface energy has less fog in the non-image area, and the dispersion of Teflon is 10% in order to satisfy the fog limit of 4.0%, which is practically no problem. As described above, the surface energy value is 30 dyne
/ Cm or less. This value was in good agreement with the value in the first embodiment, and a correlation between the fog and the surface energy value was confirmed.

In this embodiment, the particles having low surface energy are dispersed in the binder. However, it is also possible to use a material having low surface energy for the binder itself. In particular, as described above, since the charge injection layer on the surface of the photosensitive drum does not need to be light-transmitting, the range of choice of the binder is very wide.

As a specific example, as a binder, P
FA, DuPont's ZELEC E as conductive filler
CP (silica around the core, further coated with PTFE doped with tin oxide to reduce the resistance, particle size of about 1 to 10
If the charge injection layer in which the particles (μm particles) are dispersed is provided, the surface material of the photosensitive drum can be entirely made of fluororesin, and the surface energy can be greatly reduced.

<Embodiment 3> In the present embodiment, as a means for reducing the surface energy of the photosensitive drum, the surface of the photosensitive layer of the above-mentioned Embodiment 2 is made thinner to several angstroms to reduce the resistance, The coating is performed so that the potential is sufficiently small. A diamond-like thin film is formed as a coating material.

In the present embodiment, the conductive powder is dispersed in a binder having a low surface energy in order to achieve both low surface energy and chargeability of the photosensitive drum surface. The conductive powder is considerably exposed on the surface of the photosensitive drum.

Therefore, the effect of using a binder having a low surface energy may not be sufficiently obtained. In order to expect a further effect, it is sufficient to cover the surface with the binder, but this does not ensure the charging property.
In addition, even if the charging is performed, there is a problem that the residual potential increases when the image exposure is performed.

Therefore, in the present embodiment, a material having a low surface energy is thinned and coated on the surface of the photosensitive drum so that the charge can be moved by the tunnel effect so that both the charging property and the residual potential can be compatible.

In order to expect the charge to move by the tunnel effect, the film thickness needs to be several angstroms. Therefore, in this embodiment, a diamond-like thin film is formed by vapor deposition of carbon.

Specifically, according to the second embodiment, a charge injection layer in which titanium dioxide is dispersed at 120 wt% in a polycarbonate binder is laminated on a normal OPC photosensitive drum, and a diamond-like thin film is further formed thereon. Grew.

Actually, the photoreceptor sample 8 provided with only the charge injection layer and the sample 9 of the present embodiment having the diamond-like thin film grown thereon were tested with the apparatus shown in FIG. What showed 4.8% fog can be reduced to 3.6% in sample 9.

As described above, by performing a thin coating on the surface of the photosensitive drum with a material having a low surface energy,
High chargeability, low residual potential, and low image fog can be simultaneously satisfied.

[0070]

As described above, according to the present invention,
In an electrophotographic photoreceptor, a fluorine resin is contained in a photosensitive layer binder on the surface, and the surface energy of the photosensitive layer is reduced by 3%.
By controlling the density to 0 dyne / cm or less, the magnetic brush facing the surface of the electrophotographic photosensitive member can be sufficiently moved.

In particular, in the case of using the charge injection layer, since the selection range of the binder and the conductive filler constituting the charge injection layer is wide, it is easy to improve the charge holding ability of the photoreceptor and to lower the surface energy. In addition, the effect of increasing the degree of freedom in design was obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a developing unit of a conventional image forming apparatus.

FIG. 2 is a cross-sectional view schematically illustrating a developing unit of the image forming apparatus according to the first embodiment.

FIG. 3 is a diagram showing a charging potential of a developing unit.

FIG. 4 is a diagram showing a relationship between a developing sleeve applied voltage and a fog amount.

[Explanation of symbols]

 Reference Signs List 1 photoconductor (photosensitive drum) 1A charge injection layer 3 exposure means 3a LED array 11a conductive substrate (ITO layer) 12 photosensitive layer (a-Si layer) 22 magnetic brush roller (development sleeve) 22A sleeve 23A magnet roller D developer N Development nip P Transfer material

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04N 1/29 H04N 1/29 E G03G 15/00 115 (72) Inventor Harumi Kugo Ota-ku, Tokyo 3-30-2 Shimomaruko Canon Inc. (72) The inventor Junji Araya 3-30-2 Shimomaruko Ota-ku, Tokyo Inside Canon Inc.

Claims (1)

[Claims] 1. An electrophotographic photoreceptor having a photosensitive layer provided on a conductive substrate, wherein the surface layer of the photosensitive layer includes an insulating binder containing at least a fluororesin, and a conductive layer dispersed in the binder. Particles, and the surface energy is 30 dyne
An electrophotographic photoreceptor comprising a charge injection layer having a thickness of not more than / cm.