JP7518779B2 - Electrophotographic photoreceptor and image forming apparatus - Google Patents

Description

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

The electrophotographic photoreceptor used in the image forming apparatus has a structure in which a multi-layered surface coating layer made of amorphous silicon (hereinafter also referred to as "a-Si") and various dopants, including a photoconductive layer, is laminated on the outer peripheral surface, which is the outer surface of a cylindrical conductive substrate, such as a hollow aluminum cylinder.

There are two types of electrophotographic photoreceptors: positively charged electrophotographic photoreceptors, which have a positive surface potential, and negatively charged electrophotographic photoreceptors, which have a negative surface potential. In digital and full-color electrophotographic devices, negatively charged electrophotographic photoreceptors are increasingly being used to improve the quality of output images.

As described in Patent Document 1, for example, a negatively charged electrophotographic photoreceptor has a light-receiving layer laminated on an aluminum substrate, and this light-receiving layer includes a lower charge injection blocking layer, a photoconductive layer, an upper charge injection blocking layer, and a surface protection layer.

JP 2003-15335 A

Some electrophotographic photoreceptors have a photoconductive layer whose thickness increases from one end to the other in the axial direction (rotation axis direction). This causes variation in the surface potential of the electrophotographic photoreceptor when it is charged by a charging device.

The electrophotographic photoreceptor of the present disclosure comprises a conductive cylindrical substrate and
a surface coating layer that coats 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 protection layer located outside the upper charge injection blocking layer,
the photoconductive layer has a first portion whose thickness gradually increases along an axial direction of the cylindrical body,
The upper charge injection blocking layer includes amorphous silicon as a base material and at least one of nitrogen and oxygen as a dopant, and the dopant concentration in the amorphous silicon varies depending on the thickness of the first portion of the photoconductive layer.

The image forming apparatus disclosed herein also includes the electrophotographic photoreceptor.

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

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

FIG. 2A is a partial cross-sectional view of an electrophotographic photoreceptor according to an embodiment, and FIG. 2B is a cross-sectional view showing the configuration of a surface coating layer. FIG. 2 is a schematic diagram illustrating a manufacturing apparatus for an electrophotographic photoreceptor. 1 is a structural diagram showing, in partial cross section, a configuration of an image forming apparatus according to an embodiment; 4 is a graph showing the dopant concentration in the upper charge injection blocking layer and the surface potential of the electrophotographic photoreceptor in the examples. 4 is a graph showing the dopant concentration in an upper charge injection blocking layer and the surface potential of an electrophotographic photoreceptor in a comparative example.

The following describes an embodiment of the present disclosure, an electrophotographic photoreceptor, and an image forming apparatus equipped with the same, with reference to the drawings.

The electrophotographic photoreceptor 10 of the embodiment is used by being incorporated into 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 laminated so as to cover the outer peripheral surface 1a of the conductive cylindrical substrate 1.

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

The 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. 1(a), it has an outer peripheral surface 1a, which is the outer surface, an inner peripheral surface 1b, and substrate end surfaces 1c at both ends in the tube length direction.

The cylindrical substrate 1 is formed as a conductive body made of, for example, a metal material such as aluminum (Al), stainless steel (SUS), zinc (Zn), copper (Cu), or iron (Fe), or an alloy containing these metal materials. The cylindrical substrate 1 may also be made of a non-conductive material such as ceramics, coated on its surface with a conductive film made of the metal materials listed above or a conductive material such as ITO (Indium Tin Oxide).

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

The electrophotographic photoreceptor 10 of the embodiment is a negatively charged electrophotographic photoreceptor, and as the surface coating layer 2 on the cylindrical substrate 1, as shown in FIG. 1(b), 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 this order from the outermost surface side (the upper side in the figure), which is the outer side of the photoreceptor.

In addition, in Figure 1(b), the thickness of each layer or film is exaggerated, so the layer thicknesses and layer thickness ratios, etc., differ from the actual ones.

The lower charge injection blocking layer 24 on the inside (lower side in the figure) of the photoconductive layer 23 is a layer that suppresses the injection of charges (electrons) from the cylindrical substrate 1 side, and is formed, for example, from an a-Si material. This lower charge injection blocking layer 24 is formed, for example, from 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 the layers located inside the surface protective layer 21, such as the upper charge injection blocking layer 22 and the photoconductive layer 23. The surface protective layer 21 may be made of an a-Si material such as amorphous silicon carbide (a-SiC) or amorphous silicon nitride (a-SiN), or amorphous carbon (a-C), or may have a multi-layer structure thereof. In the embodiment, a-C is used, for example, 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 irradiation with light such as laser light. The photoconductive layer 23 is formed of, for example, an a-Si-based material or an amorphous selenium (a-Se)-based material such as Se-Te or _As2Se3 . The photoconductive layer 23 of the embodiment is formed of a- _Si or an a-Si-based material in which carbon (C), nitrogen (N), oxygen (O), or the like is added to a-Si, and may contain boron (B) or phosphorus (P) as a dopant.

The thickness of the photoconductive layer 23 may be appropriately set depending on the photoconductive material used and the desired electrophotographic properties. When the photoconductive layer 23 is formed using an a-Si material, the thickness is, for example, about 5 to 100 μm. The thickness of the photoconductive layer 23 in this embodiment has a first portion 23a whose thickness gradually increases along the axial direction of the cylindrical body 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 thickness gradually increases means that the thickness of the first portion 23a gradually increases from the thinnest portion to the thickest portion, and the difference between the thinnest and thickest portions 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 thickness of the photoconductive layer 23 is due to the characteristics of the equipment used to manufacture the electrophotographic photoreceptor 10, and is not an intentional change in thickness.

Since the thickness of the photoconductive layer 23 is not constant, the surface potential of the electrophotographic photoreceptor 10 varies when the electrophotographic photoreceptor 10 is charged. The surface potential is the potential on the surface of the electrophotographic photoreceptor 10 when a predetermined amount of charge is supplied to the electrophotographic photoreceptor 10 using a charging device or the like to charge the electrophotographic photoreceptor 10. In this embodiment, the upper charge injection blocking layer 22 reduces such variation in the surface potential of the electrophotographic photoreceptor 10. The upper charge injection blocking layer 22 is a layer that has the role of blocking the injection of charge (electrons) from the surface protection layer 21 side, and has an amorphous silicon (a-Si)-based material as a base material, for example. The upper charge injection blocking layer 22 is composed of a-Si, for example, containing boron (B) as a dopant and nitrogen (N) or oxygen (O) or both as a dopant in the a-Si base material.

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

The upper charge injection blocking layer 22 has a dopant concentration in the amorphous silicon that varies depending on the thickness of the first portion 23a 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, the dopant concentration is varied in accordance with the thickness of each position of the first portion 23a directly below, for example, in a range of 1 to 30% concentration, so that the dopant concentration is low in the thick portion and high in the thin portion. It is preferable that the change in the dopant concentration is gradually varied according to the change in the film thickness of the photoconductive layer 23. This can reduce the variation in the surface potential caused by the first portion 23a of the photoconductive layer 23.

As described above, the dopants in the upper charge injection blocking layer 22 are, for example, boron (B) and nitrogen (N) or oxygen (O), or both. The dopants whose concentrations are made different depending on the thickness of the first portion 23a of the photoconductive layer 23 may be all dopants or some dopants. In the example of this embodiment, the concentrations of all dopants, boron (B), nitrogen (N) and oxygen (O), contained in the amorphous silicon in the upper charge injection blocking layer 22 may be made different depending on the thickness of the first portion 23a of the photoconductive layer 23. In addition, the concentrations of nitrogen (N) and oxygen (O), which are part of the boron (B), nitrogen (N) and oxygen (O) contained in the amorphous silicon, may be made different depending on the thickness of the first portion 23a of the photoconductive layer 23. In this case, the remaining dopant, boron (B), may 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 dopant concentration that decreases 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 gradually changes, and the dopant concentration of the upper charge injection blocking layer 22 also gradually varies accordingly. This can further reduce the variation in the surface potential of the electrophotographic photoreceptor 10.

Figure 2 is a schematic diagram showing an electrophotographic photoreceptor manufacturing apparatus, and shows the schematic configuration of a film-forming apparatus that applies the RF-CVD (radio-frequency Chemical Vapor Deposition) method, which is one of the P-CVD methods. First, a cylindrical aluminum base tube (cylindrical substrate) 1 is placed in a vacuum chamber 101. Next, while exhausting with a vacuum pump 102, a raw material gas 103 is introduced into the vacuum chamber 101 at a predetermined mixture ratio via a gas control device 104. Next, a high frequency is applied to the vacuum chamber 101 by a high frequency generator 105 and a matching device 106 to generate a plasma between the base tube 11, and a film is formed on the surface of the base tube 11 while rotating the base tube 11 around the rotation axis. By changing the type and mixture ratio of the raw material gas 103 and adjusting the film-forming conditions, each of the layers, the surface protection layer 21, the upper charge injection blocking layer 22, the photoconductive layer 23, and the lower charge injection blocking layer 24, can be formed.

In such a manufacturing apparatus, it may be unavoidable that the film thickness differs between the upper and lower sides of the blank tube 11 depending on the components of the raw material gas 103, the introduction position and exhaust position of the raw material gas 103, etc. In particular, the thicker the photoconductive layer 23, the greater the film thickness distribution. To deal with this, the dopant concentration of the upper charge injection blocking layer 22 is made different, and this is made possible by controlling the introduction position and exhaust position of the raw material gas 103, the timing of switching the raw material gas 103, the supply amount of the raw material gas 103, etc.

An example of the configuration of an image forming device 100 incorporating the electrophotographic photoreceptor 10 described above will be described with reference to FIG. 3.

The image forming apparatus 100 according to the embodiment employs the Carlson method as an image forming method, and includes the electrophotographic photoreceptor 10 described above, a charger 111, an exposure unit 112, a developing unit 113 including a developing roller 113A, a transfer unit 114, a pair of fixing rollers 115A and 115B that constitute the fixing unit 115, a cleaning unit 116 including a cleaning roller 116B and a cleaning blade 116A that contact the electrophotographic photoreceptor 10, and a static eliminator 117. Note that the arrow along the recording medium P in the figure indicates the direction of movement of the paper, which is the recording medium P.

The charger (charging roller) 111 has a role of charging the surface of the electrophotographic photoreceptor 10, which is negatively charged, to a negative polarity. In this embodiment, the charger 111 is a contact type charger. In addition to a charging roller, the charger 111 may be a corotron (corona charger) or a scorotron (a corona charger with a grid electrode added). The exposure unit 112 forms an electrostatic latent image on the electrophotographic photoreceptor 10, which has a uniform negative charge on its surface, by charging it. In this embodiment, the exposure unit 112 employs a light-emitting diode (LED) head. The developing unit 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 unit 113 is equipped with a developing roller 113A that magnetically holds a developer (hereinafter, toner) T.

The developing roller 113A conveys the toner T, which has been frictionally charged in the developing device 113, to the surface of the electrophotographic photoreceptor 10 in the form of a magnetic brush adjusted to a fixed spike length. The transfer device 114 includes a transfer charger 114A and a separation charger 114B that transfer the toner image of the electrophotographic photoreceptor 10 to the recording medium P supplied to the transfer area between the electrophotographic photoreceptor 10 and the transfer device 114. The fixing device 115 includes a pair of fixing rollers 115A, 115B that fix the toner image transferred to the recording medium P to the recording medium P.

The cleaning device 116 is equipped with a cleaning roller 116B and a cleaning blade 116A that remove the toner T remaining on the surface of the electrophotographic photoreceptor 10. The charge remover 117 uses a device capable of emitting light of a specific wavelength (e.g., 630 nm or more) to remove the surface charge of the electrophotographic photoreceptor 10.

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

Electrophotographic photoreceptors of Examples and Comparative Examples were produced, with the materials of each layer and cylindrical substrate of the electrophotographic photoreceptor being as follows:
Surface protection layer: amorphous silicon carbide Upper charge injection blocking layer: amorphous silicon (dopants: B, N, O)
Photoconductive layer: amorphous silicon (no dopant)
Lower charge injection blocking layer: amorphous silicon (dopants: N, O)
Cylindrical base: Aluminum

In the examples, the concentration of boron (B) was constant in the upper charge injection blocking layer. The concentrations of nitrogen (N) and oxygen (O) were set to be lower as the thickness of the photoconductive layer increased. In the comparative examples, the concentrations of boron (B), nitrogen (N) and oxygen (O) were constant in the upper charge injection blocking layer. The surface potential of the examples and comparative examples prepared under these conditions was measured, and the variation was evaluated. In both the examples and comparative examples, the thickness of the photoconductive layer gradually increased along the axial direction of the cylindrical substrate, and the difference between the thinnest and thickest parts within the measurement range was 2 μm.

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

The atomic concentration was measured using an X-ray photoelectron spectrometer (PHI5000 VersaProbe2, manufactured by ULVAC-PHI, Inc.) by irradiating the electrophotographic photoreceptors of the examples and comparative examples with Ar ions at an accelerating voltage of 4 kV and measuring the energy spectrum of the emitted photoelectrons.

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

The graph shows the measurement results of the N/O content (%) and surface potential (V) at each measurement position. Figure 4 shows the measurement results of the example, and Figure 5 shows the measurement results of the comparative example. In both the example and the comparative example, the photoconductive layer thickness is 32 μm at the 30 mm position, 31 μm at the 185 mm position, and 30 μm at the 360 mm position. As in the comparative example shown in Figure 5, when the N/O content of the upper charge injection blocking layer was constant, the surface potential varied depending on the thickness of the photoconductive layer. In contrast, as in the example shown in Figure 4, by varying the N/O content of the upper charge injection blocking layer depending on the thickness of the photoconductive layer, the surface potential became almost the same, and the variation could be reduced.

The present invention is not limited to the above-mentioned embodiments and examples, and can be improved or modified without departing from the spirit and scope of the present invention.

1 Cylindrical substrate (element tube)
1a Outer peripheral surface 1b Inner peripheral surface 1c End surface of substrate 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 Matching 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 Discharger P Recording medium T Developer (toner)

Claims (5)

A conductive cylindrical substrate;
a surface coating layer that coats 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 protection layer located outside the upper charge injection blocking layer,
the photoconductive layer has a first portion whose thickness gradually increases along an axial direction of the cylindrical body,
an upper charge injection blocking layer that includes amorphous silicon as a base material and at least one of nitrogen and oxygen as a dopant, and a dopant concentration in the amorphous silicon varies depending on a thickness of the first portion of the photoconductive layer; The electrophotographic photoreceptor according to claim 1, wherein the upper charge injection blocking layer further contains boron as a dopant. The electrophotographic photoreceptor according to claim 1 or 2, wherein the upper charge injection blocking layer has a lower dopant concentration in the amorphous silicon as the thickness of the first portion of the photoconductive layer increases. The electrophotographic photoreceptor according to any one of claims 1 to 3, wherein the upper charge injection blocking layer has a constant thickness along the axial direction of the cylindrical substrate. An image forming apparatus comprising an electrophotographic photoreceptor according to any one of claims 1 to 4.