JP2022117736A - Electrophotographic photoreceptor and image forming device - Google Patents

Abstract

To reduce variations in a surface potential in the axial direction during the electrification of a photoreceptor drum.SOLUTION: An electrophotographic photoreceptor 10 includes, in order from the outermost surface side, a surface protective layer 21, an upper charge injection blocking layer 22, a photoconductive layer 23 and a lower charge injection blocking layer 24 which are formed as a surface coating layer 2 on a cylindrical base body 1. The thickness of the photoconductive layer 23 has a first portion 23a, the thickness of which gradually becomes thicker along the axial direction of the cylindrical base body 1. The dopant concentration in an amorphous silicon of the upper charge injection blocking layer 22 varies depending on the thickness of the first portion 23a of the photoconductive layer 23.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrophotographic photoreceptor and an image forming apparatus.

An electrophotographic photosensitive member used in an image forming apparatus includes an amorphous silicon (hereinafter referred to as "a- It has a structure in which a multi-layered surface coating layer composed of various dopants is laminated.

As the electrophotographic photosensitive member, there are a positive charging electrophotographic photosensitive member having a positive surface potential and a negative charging electrophotographic photosensitive member having a negative surface potential. In order to improve the image quality of output images, negatively charged electrophotographic photoreceptors are often used.

A negative charging electrophotographic photoreceptor comprises, for example, a photoreceptor layer laminated on an aluminum substrate, as described in Patent Document 1. This photoreceptor layer comprises a lower charge injection blocking layer, a photoconductive layer , an upper charge injection blocking layer, and a surface protective layer.

Japanese Patent Application Laid-Open No. 2003-15335

In some electrophotographic photosensitive members, the thickness of the photoconductive layer increases from one end to the other end in the axial direction (rotational axis direction). As a result, when the electrophotographic photosensitive member is charged by the charging device, the surface potential of the electrophotographic photosensitive member varies.

The electrophotographic photoreceptor of the present disclosure comprises a conductive cylindrical substrate,
a surface coating layer that covers the outer surface of the cylindrical substrate,
The surface coating layer is
a lower charge injection blocking layer;
a photoconductive layer located outside the lower charge injection blocking layer;
an upper charge injection blocking layer located outside the photoconductive layer;
a surface protective layer located outside the upper charge injection blocking layer,
the photoconductive layer has a first portion whose thickness gradually increases along the axial direction of the cylindrical substrate;
The upper charge injection blocking layer includes amorphous silicon as a base material and at least one of nitrogen and oxygen as dopants. different concentrations.

Further, an image forming apparatus of the present disclosure includes the above electrophotographic photoreceptor.

According to the present disclosure, it is possible to provide an electrophotographic photoreceptor with reduced variations in surface potential.

Further, according to the present disclosure, it is possible to provide an image forming apparatus capable of forming a high-quality image by including the electrophotographic photoreceptor.

1A is a partial cross-sectional view of an electrophotographic photoreceptor according to an embodiment, and FIG. 1B is a cross-sectional view showing the structure of a surface coating layer; FIG. 1 is a schematic diagram showing a manufacturing apparatus for an electrophotographic photoreceptor; FIG. 1 is a structural diagram showing a partial cross-section of the configuration of an image forming apparatus according to an exemplary embodiment; FIG. 4 is a graph showing the dopant concentration in the upper charge injection blocking layer and the surface potential of the electrophotographic photoreceptor in Examples. 4 is a graph showing the dopant concentration in the upper charge injection blocking layer and the surface potential of the electrophotographic photoreceptor of Comparative Example.

An electrophotographic photoreceptor and an image forming apparatus having the same according to embodiments of the present disclosure will be described below with reference to the drawings.

The electrophotographic photoreceptor 10 of the embodiment is used by being incorporated in the image forming apparatus 100 shown in FIG. 3 as an electrophotographic photoreceptor alone or as an electrophotographic photoreceptor unit. As shown in FIG. 1(a), the electrophotographic photoreceptor 10 has a multi-layered surface coating layer 2 so as to cover the outer peripheral surface 1a of a conductive cylindrical substrate 1. As shown in FIG.

The layers 21 to 24 constituting the surface coating layer 2 and the conductive cylindrical substrate 1 will be described with reference to FIG. 1(b).

A conductive cylindrical substrate 1 serves as a support for the surface coating layer 2 . At least the surface of the cylindrical substrate 1 is conductive, and as shown in FIG. have.

The cylindrical substrate 1 is made of a metal material such as aluminum (Al), stainless steel (SUS), zinc (Zn), copper (Cu), iron (Fe), or an alloy containing these metal materials. is formed as having conductivity. Alternatively, the cylindrical substrate 1 may be formed by coating the surface of a non-conductive material such as ceramics with a conductive film made of the exemplified metal material or a conductive material such as ITO (Indium Tin Oxide).

The cylindrical substrate 1 of the embodiment is made of, for example, an aluminum-based material. The aluminum-based material is lightweight and low-cost, and when forming a layer mainly composed of amorphous silicon (a-Si)-based material on the outer peripheral surface 1a, between those layers and the cylindrical substrate 1 high adhesion.

The electrophotographic photoreceptor 10 of the embodiment is an electrophotographic photoreceptor for negative charging, and as the surface coating layer 2 on the cylindrical substrate 1, as shown in FIG. A surface protective layer 21, an upper charge injection blocking layer 22, a photoconductive layer 23 and a lower charge injection blocking layer 24 are formed in order from the surface side (upper side in the drawing).

In addition, since the thickness of each layer or each film is emphasized in FIG.

The lower charge injection blocking layer 24 on the inner side (lower side in the drawing) of the photoconductive layer 23 is a layer that suppresses the injection of charges (electrons) from the cylindrical substrate 1 side, and is made of, for example, an a-Si material. there is The lower charge injection blocking layer 24 is formed of, for example, a-Si containing nitrogen (N) and oxygen (O) as dopants, and has a thickness of, for example, 2 to 10 μm.

The surface protective layer 21 protects each layer such as the upper charge injection blocking layer 22 and the photoconductive layer 23 located inside the surface protective layer 21 . The surface protective layer 21 is formed of an a-Si material such as amorphous silicon carbide (a-SiC) or amorphous silicon nitride (a-SiN), amorphous carbon (aC), or a multilayer structure thereof. do it. In embodiments, for example, aC is used from the viewpoint of wear resistance. The thickness of the surface protective layer 21 is, for example, about 0.1 to 2 μm.

The photoconductive layer 23 is a layer having a function of generating carriers by light irradiation such as laser light. The photoconductive layer 23 is made of, for example, an a-Si material or an amorphous selenium (a-Se) material such as Se-Te or As ₂ Se ₃ . The photoconductive layer 23 of the embodiment is formed of a-Si and a-Si-based material obtained by adding carbon (C), nitrogen (N), oxygen (O), or the like to a-Si, and as a dopant, It may contain boron (B) or phosphorus (P).

The thickness of the photoconductive layer 23 may be appropriately set according to the photoconductive material used and the desired electrophotographic properties. is. The thickness of the photoconductive layer 23 of this embodiment has a first portion 23 a whose thickness gradually increases along the axial direction of the cylindrical substrate 1 . The entire photoconductive layer 23 may be the first portion 23a, or, for example, the central portion excluding the ends may be the first portion 23a. The gradual increase in thickness means that in the first portion 23a, the thickness gradually increases from the thinnest portion to the thickest portion, and the difference between the thinnest portion and the thickest portion is It is about 10% of the film thickness of the photoconductive layer 23, for example, about 0.5 to 10 μm. Here, the thickness of the photoconductive layer 23 is the distance from the interface with the lower charge injection blocking layer 24 to the interface with the upper charge injection blocking layer 22 . The gradual increase in the thickness of the photoconductive layer 23 is due to the characteristics of equipment such as the manufacturing apparatus of the electrophotographic photosensitive member 10, and the thickness is not intentionally changed.

Since the thickness of the photoconductive layer 23 is not uniform, the surface potential of the electrophotographic photosensitive member 10 varies during charging. The surface potential is the potential on the surface of the electrophotographic photoreceptor 10 when the electrophotographic photoreceptor 10 is charged by supplying a predetermined amount of electric charge to the electrophotographic photoreceptor 10 using a charging device or the like. In this embodiment, such variations in surface potential of the electrophotographic photosensitive member 10 are reduced by the upper charge injection blocking layer 22 . The upper charge injection blocking layer 22 is a layer that has a role of blocking injection of charges (electrons) from the surface protection layer 21 side, and is made of, for example, an amorphous silicon (a-Si)-based material as a base material. The upper charge injection blocking layer 22 is composed of, for example, a-Si containing boron (B) as a dopant and nitrogen (N) or oxygen (O) or both of them in the base a-Si. be done.

The thickness of the upper charge injection blocking layer 22 is, for example, 0.1 to 10 μm from the viewpoint of desired electrophotographic properties. The thickness of the upper charge injection blocking layer 22 is constant along the axial direction of the cylindrical substrate 1 . The constant thickness means that the difference between the thinnest portion and the thickest portion of the upper charge injection blocking layer 22 is less than 10% of the film thickness, for example, less than 1 μm at maximum.

The upper charge injection blocking layer 22 has different dopant concentrations in amorphous silicon depending on the thickness of the first portion 23 a of the photoconductive layer 23 . The upper charge injection blocking layer 22 is located outside the photoconductive layer 23 and covers at least the first portion 23a of the photoconductive layer 23 . In the upper charge injection blocking layer 22, corresponding to the thickness of each position of the first portion 23a immediately below, for example, the dopant concentration is low in the thick portion and the thickness is in the range of 1 to 30%. The dopant concentration is varied so that the dopant concentration is higher in the thin portion. It is preferable that the dopant concentration is changed gradually according to the change in the film thickness of the photoconductive layer 23 . As a result, variations in surface potential caused by the first portion 23a of the photoconductive layer 23 can be reduced.

As previously mentioned, dopants in upper charge injection blocking layer 22 are, for example, boron (B) and nitrogen (N) and/or oxygen (O). All or part of the dopants may have different concentrations according to the thickness of the first portion 23a of the photoconductive layer 23 . In the example of the present embodiment, in the upper charge injection blocking layer 22, the concentration of all dopants of boron (B), nitrogen (N) and oxygen (O) contained in the amorphous silicon is adjusted to the first concentration of the photoconductive layer 23. It may be varied according to the thickness of the portion 23a. Further, the concentrations of nitrogen (N) and oxygen (O), which are part of boron (B), nitrogen (N) and oxygen (O) contained in amorphous silicon, are measured in the first portion of the photoconductive layer 23 . It may be varied according to the thickness of 23a. In this case, the remaining dopant, boron (B), should be contained in the amorphous silicon at a constant concentration regardless of the thickness of the first portion 23a of the photoconductive layer 23 .

In this embodiment, the upper charge injection blocking layer 22 has a lower dopant concentration as the thickness of the first portion 23a of the photoconductive layer 23 increases. The thickness of the first portion 23a of the photoconductive layer 23 is gradually changed, and the dopant concentration of the upper charge injection blocking layer 22 is also gradually changed accordingly. As a result, variations in the surface potential of the electrophotographic photoreceptor 10 can be further reduced.

FIG. 2 is a schematic diagram showing a manufacturing apparatus for an electrophotographic photosensitive member, showing a schematic configuration of a film forming apparatus to which RF-CVD (radio-frequency Chemical Vapor Deposition) method among P-CVD methods is applied. is. First, a cylindrical blank tube (cylindrical substrate) 1 made of aluminum is placed in a vacuum chamber 101 . Next, a raw material gas 103 is introduced into the vacuum chamber 101 through a gas control device 104 at a predetermined mixing ratio while the vacuum pump 102 is evacuating the chamber. Next, a high frequency wave is applied to the vacuum chamber 101 by the high frequency generator 105 and the matching device 106 to generate plasma between the tube 11 and the tube 11, and while rotating the tube 11 around the rotation axis, to form a film. The surface protective layer 21, the upper charge injection blocking layer 22, the photoconductive layer 23, and the lower charge injection blocking layer 24 are formed by changing the type and mixing ratio of the raw material gas 103 and adjusting the film formation conditions. can be done.

In such a manufacturing apparatus, depending on the composition of the raw material gas 103, the introduction position of the raw material gas 103, the exhaust position, etc., it may be unavoidable that the film thickness is different between the upper side and the lower side of the blank pipe 11. In particular, the thicker the photoconductive layer 23, the greater the distribution of the film thickness. In order to cope with this, the dopant concentration of the upper charge injection blocking layer 22 is varied, and the introduction position and exhaust position of the raw material gas 103, the switching timing of the raw material gas 103, the supply amount of the raw material gas 103, and the like are controlled. is possible.

A configuration example of an image forming apparatus 100 incorporating the electrophotographic photoreceptor 10 as described above will be described with reference to FIG.

The image forming apparatus 100 according to the embodiment employs the Carlson method as an image forming method, and includes the electrophotographic photosensitive member 10 described above, the charging device 111, the exposure device 112, the developing device 113 including the developing roller 113A, and the transfer device. 114, a pair of fixing rollers 115A and 115B as a fixing device 115, a cleaning device 116 including a cleaning roller 116B and a cleaning blade 116A in contact with the electrophotographic photosensitive member 10, a static eliminator 117, and the like. The arrow along the recording medium P in the drawing indicates the moving direction of the paper, which is the recording medium P. As shown in FIG.

The charger (charging roller) 111 has a role of negatively charging the surface of the negatively charged electrophotographic photosensitive member 10, for example. In this embodiment, the charger 111 is a contact charger. As the charger 111, a corotron (corona charger) or a scorotron (a corona charger with a grid electrode) may be used instead of the charging roller. The exposing device 112 forms an electrostatic latent image on the electrophotographic photosensitive member 10 having a uniform negative charge on its surface by charging. In this embodiment, the exposure unit 112 employs a light emitting diode (LED) head. The developing device 113 develops the electrostatic latent image on the electrophotographic photoreceptor 10 to form a toner image on the surface of the electrophotographic photoreceptor 10 . The developing device 113 includes a developing roller 113A that magnetically holds developer (hereinafter referred to as toner) T. As shown in FIG.

The developing roller 113A conveys the toner T triboelectrically charged in the developing device 113 to the surface of the electrophotographic photosensitive member 10 in the form of a magnetic brush adjusted to have a constant brush length. The transfer device 114 includes a transfer charger 114A and a separation charger 114B for transferring the toner image of the electrophotographic photoreceptor 10 onto the recording medium P supplied to the transfer area between the electrophotographic photoreceptor 10 and the transfer device 114. Prepare. The fixing device 115 includes a pair of fixing rollers 115A and 115B for fixing the toner image transferred onto the recording medium P onto the recording medium P. As shown in FIG.

The cleaning device 116 includes a cleaning roller 116B and a cleaning blade 116A for removing toner T remaining on the surface of the electrophotographic photoreceptor 10 . A device capable of emitting light of a specific wavelength (for example, 630 nm or more) is used as the static eliminator 117 to remove the surface charge of the electrophotographic photosensitive member 10 .

In the embodiment, the base material of the upper charge injection blocking layer 22 is amorphous silicon (a-Si), and the amorphous silicon contains boron (B) and both nitrogen (N) and oxygen (O) as dopants. rice field.

Electrophotographic photoreceptors of Examples and Comparative Examples were prepared. Materials for each layer of the electrophotographic photosensitive member and the cylindrical substrate were as follows.
Surface protective layer: amorphous silicon carbide Upper charge injection blocking layer: amorphous silicon (dopants: B, N, O)
Photoconductive layer: amorphous silicon (no dopants)
Lower charge injection blocking layer: amorphous silicon (dopants: N, O)
Cylindrical substrate: aluminum

In the examples, the concentration of boron (B) was kept constant in the upper charge injection blocking layer. The concentrations of nitrogen (N) and oxygen (O) were made lower as the thickness of the photoconductive layer increased. In the comparative example, the concentrations of boron (B), nitrogen (N) and oxygen (O) were kept constant in the upper charge injection blocking layer. The surface potentials of Examples and Comparative Examples fabricated under these conditions were measured to evaluate variations. In both Examples and Comparative Examples, the thickness of the photoconductive layer gradually increased along the axial direction of the cylindrical substrate. difference was 2 μm.

The dopant concentration was measured at three positions of 30 mm, 185 mm, and 360 mm from the end face of the substrate along the axial direction of the cylindrical substrate having a length of 395 mm. The N/O content (%) was measured as the dopant concentration of the upper charge injection blocking layer. The N/O content (%) is the amount of each of nitrogen (N) and oxygen (O) obtained by measurement when the total amount of atoms (excluding hydrogen) constituting the upper charge injection blocking layer is taken as 100%. It is the average value of the content. In Examples and Comparative Examples, nitric oxide (NO) was used as a raw material gas during production, and in this case, the contents of nitrogen (N) and oxygen (O) were approximately the same.

The atomic concentration was measured by using an X-ray photoelectron spectrometer (PHI5000 VersaProbe2, manufactured by ULVAC-PHI, Inc.), irradiating the electrophotographic photoreceptors of Examples and Comparative Examples with Ar ions at an acceleration voltage of 4 kV, and measuring the number of emitted photoelectrons. Energy spectra were measured.

The surface potential was measured at three locations that were the same as the dopant concentration. The surface potential was determined by applying a constant charge to the electrophotographic photoreceptors of Examples and Comparative Examples using a scorotron charger, and using a measurement probe (Trek model 6000B-7C, Trek Japan) connected to a surface potential meter (Trek model 344, manufactured by Trek Japan Co., Ltd.). Co., Ltd.).

The graph shows the measurement results of the N/O content (%) and the surface potential (V) at each measurement position. FIG. 4 shows the measurement results of the example, and FIG. 5 shows the measurement results of the comparative example. In both Examples and Comparative Examples, the thickness of the photoconductive layer is 32 μm at the position of 30 mm, 31 μm at the position of 185 mm, and 30 μm at the position of 360 mm. As in the comparative example shown in FIG. 5, when the N/O content of the upper charge injection blocking layer was constant, the surface potential varied according to the thickness of the photoconductive layer. On the other hand, by varying the N/O content of the upper charge injection blocking layer according to the thickness of the photoconductive layer as in the embodiment shown in FIG. could be reduced.

The present invention is not limited to the above-described embodiments and examples, and improvements and modifications can be made without departing from the scope of the present invention.

1 Cylindrical base (base tube)
1a outer peripheral surface 1b inner peripheral surface 1c base end surface 2 surface coating layer 10 electrophotographic photoreceptor 21 surface protective layer 22 upper charge injection blocking layer 23 photoconductive layer 23a first portion 24 lower charge injection blocking layer 100 image forming apparatus 101 vacuum chamber 102 Vacuum pump 103 Source gas 104 Gas control device 105 High frequency generator 106 Alignment device 111 Charger 112 Exposure device 113 Developing device 113A Developing roller 114 Transfer device 114A Transfer charger 114B Separation charger 115 Fixing device 115A Fixing roller 116 Cleaning device 116A Cleaning blade 116B Cleaning roller 117 Eliminator P Recording medium T Developer (toner)

Claims (5)

an electrically conductive cylindrical substrate;
a surface coating layer that covers the outer surface of the cylindrical substrate,
The surface coating layer is
a lower charge injection blocking layer;
a photoconductive layer located outside the lower charge injection blocking layer;
an upper charge injection blocking layer located outside the photoconductive layer;
a surface protective layer located outside the upper charge injection blocking layer,
the photoconductive layer has a first portion whose thickness gradually increases along the axial direction of the cylindrical substrate;
The upper charge injection blocking layer includes amorphous silicon as a base material and at least one of nitrogen and oxygen as dopants. Electrophotographic photoreceptors with different densities. 2. The electrophotographic photoreceptor according to claim 1, wherein said upper charge injection blocking layer further comprises boron as a dopant. 3. The electrophotographic photoreceptor according to claim 1, wherein said upper charge injection blocking layer has a lower dopant concentration in amorphous silicon as said first portion of said photoconductive layer is thicker. 4. The electrophotographic photoreceptor according to claim 1, wherein said upper charge injection blocking layer has a constant thickness along the axial direction of said cylindrical substrate. An image forming apparatus comprising the electrophotographic photoreceptor according to any one of claims 1 to 4.

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