JP4249751B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a tandem type electrophotographic image forming apparatus equipped with a negatively charged photosensitive member made of an amorphous silicon photoconductive layer.

As a color printer that has already been commercialized, there is an image forming apparatus of a tandem type electrophotographic system, and a photoconductor mounted thereon is constituted by a negatively charged OPC. Since the charging ability of the OPC photosensitive member can be increased to about -800 V, the color toner can be easily attached (see Japanese Patent Laid-Open Nos. H4-287075 and H7-306624).
JP-A-4-287075 Japanese Patent Laid-Open No. 7-306624

  However, when an image forming apparatus equipped with the OPC photosensitive member is applied to high-speed color printing, the OPC photosensitive member is not suitable because of poor wear and durability.

  Therefore, an amorphous silicon photoconductor that has already been commercialized (hereinafter abbreviated as a-Si) was used in place of the OPC photoconductor for at least a photoconductor using a black toner image. The charging performance and photosensitivity were lower than those of the photoconductor, and satisfactory print performance could not be achieved. The reason will be described below.

The a-Si photoreceptor is suitable for positive charging, and has a layer structure in which an a-Si charge injection blocking layer and an a-Si photoconductive layer are sequentially laminated on a conductive substrate by glow discharge decomposition.
Then, a potential barrier against electrons is formed by doping the group 13 element of the periodic table in the a-Si charge injection blocking layer, thereby preventing injection of electrons from the conductive substrate and positively charging electrophotography. A photoreceptor is obtained.

On the other hand, a potential barrier for holes is formed by doping the charge injection blocking layer with Group 15 elements of the Periodic Table instead of Group 13 elements of the Periodic Table, thereby injecting holes from the conductive substrate. In order to prevent this, a negatively charged electrophotographic photoreceptor is expected to replace the conventional OPC photoreceptor, but has not yet been put into practical use.

The present inventor has made various studies on the problems that cannot be put into practical use as described above. As a result, the group 13 elements of the periodic table (hereinafter abbreviated as group 13 elements) are compared with existing positively charged electrophotographic photoreceptors. the doping of the charge injection blocking layer of the periodic table group 15 element if only was replaced with (hereinafter, abbreviated as group 15 elements), although negatively charged, also the positive charged I understood.

  Therefore, when such an electrophotographic photosensitive member is mounted on a printer (image forming apparatus) and an image is formed by using a negatively charged toner, the toner is transferred to the paper, resulting in the positive chargeability. The transfer bias voltage was canceled and the image characteristics deteriorated.

Moreover, phosphine (PH3), a gas used to dope Group 15 elements, is highly toxic and has a negative effect on the human body even at low concentrations. Therefore, it is necessary to pay close attention to safety management. As a result, there is a problem that the cost increases. Furthermore, in order to use such a doping gas with high accuracy as required, and to reduce variations in electrophotographic characteristics, it is necessary to considerably increase production control, which also increases production costs. .

  Moreover, in general, in the case of a color printer in which a plurality of photoconductors are arranged for one image forming apparatus, if the photoconductors having different photoconductive layers are arranged, coloring as required due to the difference in performance between the photoconductors. There is a problem that cannot be obtained.

The present inventor made intensive studies in view of the above circumstances. In a tandem type electrophotographic color printer, not only color printing is actually performed, but also monochrome (black) printing is frequently performed. Focusing on the fact that monochrome printing may be used more frequently than color printing, and therefore a photoconductor mounted on an image forming element for forming a black toner image is formed of an a-Si photoconductive layer. Further, in the infrared absorption spectrum of the a-Si photoconductive layer, by defining the relationship between the intensity Ia at a wave number of 2000 cm ⁻¹ and the intensity Ib at a wave number of 2100 cm ⁻¹ , the film quality is improved, thereby providing excellent negative chargeability. In addition, the difference in charging and sensitivity characteristics between the image forming element on which the OPC photoreceptor is mounted to form a colored toner image other than the black toner image is reduced. By enhanced degree, it is mounted photoreceptor heterologous was found that the image forming apparatus has sufficient practicality as a color printer.

In addition, it has also been found that the negative polarity can be charged satisfactorily without doping a group 15 element in the a-Si charge injection blocking layer, and the production cost can be reduced by not using phosphine gas.

  Therefore, the present invention has been completed based on the above knowledge, and an object thereof is to provide an image forming apparatus suitable for high-speed color printing.

  Another object of the present invention is to improve durability against monochrome printing, so that the overall printing performance can be maintained over a long period of time even when used separately with color printing, thereby enabling long-term reliable image formation. To provide an apparatus.

  Furthermore, another object of the present invention is to provide an image forming apparatus capable of reducing the production cost by using no phosphine gas.

A tandem electrophotographic image forming apparatus according to the present invention includes a photoconductor, a charging unit that applies a charge to the photoconductor, and an exposure unit that irradiates light to a charged region of the photoconductor. Developing means for developing an electrostatic latent image formed on the photoreceptor by the charging means and the exposure means with toner to form a toner image; and transfer means for transferring the toner image to a transfer material; A plurality of image forming elements, each of which includes a cleaning unit that removes toner remaining on the photoconductor and a static elimination unit that removes a residual electrostatic latent image remaining on the photoconductor, are arranged. One of the forming elements is used for forming a black toner image, and the charging unit is configured to apply a negative charge to the photoreceptor, and is used for forming the black toner image. Mounted on image forming elements The photosensitive member is an amorphous silicon that satisfies the strength Ia at wavenumber 2000 cm ^-1 in the infrared absorption spectrum, the intensity Ib at wavenumber 2100 cm ^-1 is 0.22 ≦ Ib / (Ia + Ib ) ≦ 0.35 in relation to a photoconductive layer, element of group 13 in periodic table and periodic table group 15 element is characterized by having the amorphous silicon charge injection blocking layer ing and contain oxygen and nitrogen Ri Oh without doping. In the image forming apparatus according to the present invention, a charging difference between an image forming element other than the black toner image forming image forming element and the black toner image forming image forming element among the plurality of image forming elements is 200 V or less. Preferably there is. In the image forming apparatus according to the present invention, it is preferable that the photoconductor mounted on an image forming element other than the image forming element for forming the black toner image among the plurality of image forming elements is an OPC photoconductor. The Group 15 element of the periodic table in the photoreceptor of the image forming apparatus according to the present invention is P.

  According to the image forming apparatus of the present invention, compared with the charging of the image forming element on which the OPC photosensitive member is mounted so as to form a colored toner image other than the black toner image, a charging difference of 200 V or less can be achieved, and the photosensitivity is further increased. As a result, a high-performance color printer suitable for high-speed color printing could be provided.

  Moreover, according to the present invention, there is provided a long-term reliable image forming apparatus that can be used properly with color printing by enhancing durability against monochrome printing, and can maintain the overall printing performance over a long period of time. I was able to provide it.

Furthermore, according to the present invention, even if the a-Si charge injection blocking layer is not doped with a group 15 element, the negative polarity can be satisfactorily charged, and the production cost can be reduced by not using phosphine gas or the like. It was.

FIG. 2 shows the layer structure of the photoreceptor 1 according to the image forming element for forming the black toner image of the present invention. The photosensitive layer 3 made of a-Si or the like is vacuum-deposited on the conductive substrate 2. The film is formed by a method, an active reaction vapor deposition method, an ion plating method, an RF sputtering method, a DC sputtering method, an RF magnetron sputtering method, a DC magnetron sputtering method, a thermal CVD method, a plasma CVD method, or the like. The photosensitive layer 3 is formed, for example, by sequentially laminating a charge injection blocking layer 4, a photoconductive layer 5, and a surface protective layer 6.

  The substrate 2 is made of a metal conductor such as copper, brass, SUS, Al, or Ni, or has a surface of an insulator such as glass or ceramic covered with a conductive thin film. The substrate 2 may be a sheet-like, belt-like or web-like flexible conductive sheet, such as a metal sheet such as SUS, Al, Ni, or a polymer resin film such as polyester, nylon, polyimide, etc. In addition, a metal such as Al or Ni, or a transparent conductive material such as tin oxide, indium tin oxide (ITO), or an organic conductive material coated by vapor deposition is used.

In the charge injection blocking layer 4, a-Si is not doped with a group 13 element and / or a group 15 element as a valence electron control impurity, and even if it is non-doped, the photoconductive layer 5 by setting the intensity Ia at wave number 2000 cm ^-1 in the infrared absorption spectrum of the intensity Ib of wavenumber 2100 cm ^-1 so as to satisfy 0.22 ≦ Ib / (Ia + Ib ) ≦ 0.35 relational expression, Excellent negative charging ability was obtained.

  In other words, in the present invention, non-doped a-Si is weak n-type due to structural defects in the bond network formed during film formation, so P is doped using phosphine (PH3) gas or the like. Even if it was not, it was an unexpected effect that an excellent negative charging ability was obtained by defining the film quality of the photoconductive layer 5.

Specifically, when the photoconductive layer 5 is formed by the plasma CVD method, the value of the high frequency power to be applied is changed, or the film formation speed is changed, thereby combining the Si atoms and the H atoms [SiH bond. ] And [(SiH2) n bond] can be defined, but when this is expressed by an infrared absorption spectrum, the relationship between the intensity Ia at a wave number of 2000 cm ^-1 and the intensity Ib at a wave number of 2100 cm ^-1 is When the IR ratio shown is expressed as Ib / (Ia + Ib) and satisfies the relational expression of 0.22 ≦ IR ratio ≦ 0.35, preferably 0.25 ≦ IR ratio ≦ 0.34, excellent negative charging ability is obtained. In addition, the difference in charging and sensitivity characteristics between the image forming element on which the OPC photoconductor is mounted to form a colored toner image other than the black toner image is reduced, and the photosensitivity is increased. It became suitable for color printing. Furthermore, the photosensitivity is improved over short wavelength visible light to near infrared light (long wavelength light), that is, with respect to irradiation light having a wavelength peak of 520 to 820 nm. As a result, various light sources having a wide wavelength peak in laser light, LED, etc. can be used in the printer.

  In addition, the charge injection blocking layer 4 can contain oxygen or nitrogen to increase the forbidden band width, thereby increasing the barrier in terms of the function of blocking charge injection, and by containing oxygen, The adhesion of is improved. However, since oxygen alone tends to react with the silane gas and cause an explosion, inert nitrogen should be coexisted. Nitrogen monoxide (NO) gas or the like is actually used.

  The surface protective layer 6 is made of a-Si, amorphous silicon carbide, amorphous silicon nitride, amorphous silicon oxide, selenium, glow discharge decomposition method, vacuum deposition method, active reaction deposition method, ion plating method, RF sputtering method, A film is formed by a DC sputtering method, an RF magnetron sputtering method, a DC magnetron sputtering method, a thermal CVD method, or the like. When an organic material is used, the film is formed by coating or the like.

  According to the photoconductor 1 having the above-described configuration, the film quality is improved by defining the IR ratio with respect to the photoconductive layer 5 as described above, whereby excellent negative chargeability is obtained, and further, a colored toner image other than the black toner image is obtained. The difference in charging and sensitivity characteristics between the image forming element on which the OPC photoconductor is mounted to reduce the size of the image forming element is small, and the photosensitivity is increased, so that it is sufficient as a color printer even if a different type of photoconductor is mounted. The image forming apparatus has practical utility.

In addition, it has also been found that the negative polarity can be charged satisfactorily without doping a group 15 element in the a-Si charge injection blocking layer, and the production cost can be reduced by not using phosphine gas.

Configuration of Image Forming Apparatus FIG. 1 shows an image forming apparatus according to the present invention. First, FIG. 3 shows the principle of a printer style image forming element 7 according to the present invention. Reference numeral 8 denotes a photoconductor. A corona charger 9 as a charging unit on the peripheral surface of the photoconductor 8, an LED head 10 as an exposure unit for irradiating light after the charging, and a toner image are formed on the surface of the photoconductor 8. A developing device 12 that is a developing means including a toner 11 for transferring, a transfer device 14 that is a transfer means for transferring the toner image to a transfer material 13, and a cleaning that removes residual toner on the surface of the photoreceptor after the transfer. A means 15 and a static eliminating means 16 for removing the residual electrostatic latent image after the transfer are provided. Reference numeral 17 denotes a fixing device for fixing the toner image transferred to the transfer material 13 by heat or pressure.

  This Carlson method repeats the following processes (1) to (6).

(1) The peripheral surface of the photoreceptor 8 is charged by the corona charger 9.

(2) An image is exposed by the LED head 10 to form an electrostatic latent image as a potential contrast on the surface of the photoreceptor 8.

(3) The electrostatic latent image is developed by the developing machine 12. By this development, the colored toner adheres to the surface of the photoreceptor due to electrostatic attraction with the electrostatic latent image and is visualized.

(4) The toner image on the surface of the photosensitive member is electrostatically transferred by applying an electric field having a polarity opposite to that of the toner from the back surface of the transfer material 13 such as paper.

(5) The residual toner on the surface of the photoreceptor is mechanically removed by the cleaning means 15.

(6) The entire surface of the photosensitive member is exposed with strong light, and the remaining electrostatic latent image is removed by the charge eliminating means 16.

  Next, in the image forming apparatus 18 of FIG. 1, 7a is an image forming element for black (indicated by K in the figure), 7b is an image forming element for yellow (indicated by Y in the figure), and 7c is for cyan. An image forming element (indicated by C in the figure) and 7d are magenta image forming elements (indicated by M in the figure). Then, the photoreceptor 1 is mounted on the image forming element 7a (K), and a known OPC photoreceptor is mounted on each of the other image forming elements 7b (Y), 7c (C), and 7d (M). Further, a sheet as the transfer material 13 is placed on the transport belt 19 and moved in the direction of the arrow.

  Thus, according to the image forming apparatus 18 configured as described above, the charging of the photoconductor A of the image forming element 7a (K) has a charging difference of 200 V or less compared to the OPC photoconductor, so that no printing unevenness occurs and a clear color image is formed. The resulting color image forming apparatus could be provided. In addition, by improving the durability performance of the photoreceptor A of the image forming element 7a (K), high-speed color printing can be performed, and even if the color printing and the monochrome printing are used separately, the overall quality is improved. Maintained for a period of time.

Example 1 The photoreceptor 1 of the image forming element 7a (K) was produced as follows. A photosensitive layer 2 is formed by plasma CVD on a cylindrical substrate 1 (outer diameter 180 mm, length 372 mm) made of Al having a purity of 99.9%. The photosensitive layer 2 was formed by sequentially laminating a charge injection blocking layer 4, a photoconductive layer 5, and a surface protective layer 6 under the film forming conditions shown in Table 1. For the surface protective layer 6, the flow rates of SiH4 and CH4 from the start to the end of film formation are gradually changed, and the film formation speed is also changed accordingly.

  For the other OPC photoreceptor, an undercoat layer (intermediate layer), a carrier generation layer having a thickness of 1 μm or less, and a carrier transport layer having a thickness of 15 to 40 μm are sequentially laminated on a cylindrical substrate made of Al. The undercoat layer is made of a water-soluble or alcohol-soluble resin, a thermosetting or photocurable resin, and the carrier generation layer is composed of a fine particle pigment dispersed in a resin binder. Further, the carrier transport layer is a layer having an electron donating property with a high hole mobility, in which a carrier transport material is dispersed and dissolved in a resin binder.

In forming the photoconductive layer 5, by changing the high frequency power as shown in Table 2, various IR ratios [Ib / (Ia + Ib)] are obtained, and the respective photoconductors are formed as image forming elements 7. And various image forming apparatuses 18 were produced.

  The print quality is classified into ○ and ×, where ○ indicates a case where excellent print quality without any practical problem is obtained, and × indicates a case where defective printing is recognized.

  As is apparent from the results shown in Table 2, printing failure did not occur at all in Samples C to F of the present invention, and excellent image characteristics were obtained. Incidentally, the charge of the photoreceptor A of these image forming elements 7a (K) was around -620V, the charge of the OPC photoreceptor was -800V, and the charge difference between them was about 180V. When color printing was performed on Sample C to Sample F of the present invention, an excellent color image was obtained at a printing speed of 12 sheets / minute.

  On the other hand, since the high frequency power is low in the sample A and the sample B, the discharge does not spread uniformly in the film forming apparatus, and particularly the film near the upper and lower ends becomes thin, thereby causing uneven film formation in the axial direction. Also, the film adhesion at both ends was inferior and sometimes peeled off. Further, the sample G generally has a thin black solid, and the sample H has a black solid.

  (Example 2) Next, a printing durability test (500,000 sheets) was performed using the image forming apparatus 18 on which the photoreceptors of Sample C to Sample F of the present invention were mounted. As a result, no scratches or the like were generated and a high quality image was obtained. On the other hand, when the conventional OPC photosensitive member is used as the photosensitive member of the image forming element 7a (K), the surface of the photosensitive member is damaged, and black stripes are generated on a white background in terms of image quality.

  In addition, this invention is not limited to the said embodiment, A various change, improvement, etc. do not interfere in the range which does not deviate from the summary of this invention. For example, in this embodiment, an LED head is used as the exposure means, but laser light, halogen light, or the like may be used instead.

1 is a schematic view of an image forming apparatus of the present invention. 2 is a partial cross-sectional view showing a layer structure of a photoreceptor according to an embodiment of the invention. 1 is a schematic diagram of an imaging element of the present invention.

Explanation of symbols

1 ... Photoconductor 2 ... Substrate
3 ... photosensitive layer 4 ... charge injection blocking layer 5 ... photoconductive layer 6 ... surface protection layer 7,7a, 7b, 7c, 7d ··· image forming elements 8 ... photoconductor DESCRIPTION OF SYMBOLS 9 ... Corona charger 10 ... LED head 11 ... Toner 12 ... Developing machine 13 ... Transfer material 14 ... Transfer device 15 ... Cleaning means 16 ... Static elimination means 17 ... Fixer 18 ... Image forming device 19 ... Conveying belt

Claims (4)

A photosensitive member; a charging unit that applies a charge to the photosensitive member; and an exposure unit that irradiates light to a charged region of the photosensitive member. The charging unit and the exposing unit form the photosensitive member. Developing means for developing the electrostatic latent image to be formed with toner, transfer means for transferring the toner image to a transfer material, cleaning means for removing the toner remaining on the photoreceptor, A plurality of image forming elements provided with a charge eliminating means for removing a residual electrostatic latent image remaining on the photosensitive member are arranged, and one of the plurality of image forming elements is used for forming a black toner image. A tandem type electrophotographic image forming apparatus,
The charging means is configured to give a negative charge to the photoconductor,
The photoreceptor mounted on the image forming element for forming the black toner image has an intensity Ia at a wave number of 2000 cm ⁻¹ and an intensity Ib at a wave number of 2100 cm ⁻¹ in an infrared absorption spectrum of 0.22 ≦ Ib / ( Ia + Ib) ≦ 0.35 and an amorphous silicon photoconductive layer satisfying a relational expression, the periodic table group 13 elements and the periodic table group 15 element is Ah Ri and oxygen and nitrogen comprise Na Ru amorphous silicon charge undoped An tandem type electrophotographic image forming apparatus comprising an injection blocking layer. The charge difference between an image forming element other than the image forming element for forming the black toner image and the image forming element for forming the black toner image among the plurality of image forming elements is 200 V or less . Tandem type electrophotographic image forming apparatus. 3. The tandem electrophotographic system according to claim 1, wherein the photoconductor mounted on an image forming element other than the image forming element for forming the black toner image among the plurality of image forming elements is an OPC photoconductor. Image forming apparatus. 4. The tandem electrophotographic image forming apparatus according to claim 1, wherein the Group 15 element of the periodic table is P. 5.

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