JP2005221720A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a photoreceptor having surface smoothness, wear resistance and high-quality image characteristics without scattering of light even when laser light of a short wavelength is used. <P>SOLUTION: In the image forming apparatus equipped with a photoreceptor and a semiconductor laser having the oscillation wavelength of a 370 to 500 nm range as an exposure light source for the photoreceptor, the photoreceptor has a surface layer constituting the outermost surface in which a lubricant is dispersed by ≤1.3 mg per 1 mm<SP>2</SP>×(film thickness of the surface layer). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus used for electrophotography and electrostatic recording apparatuses.

In electrophotographic image formation, the surface of the photosensitive member is uniformly charged, exposed to a laser beam or the like to form an electrostatic latent image, and the toner is developed on the electrostatic latent image, and the toner image is recorded on the recording medium. It is carried out by using an electrophotographic process of transferring to an image. That is, when a uniformly charged photoconductor is exposed, the potential on the surface of the photoconductor is brightly attenuated, and an electrostatic latent image is formed on the exposed portion. When a developing bias is applied between the photosensitive member on which the electrostatic latent image is formed and the developer carrying member, the toner is developed on the electrostatic latent image by the potential difference between the potential after exposure and the developing bias potential. Therefore, an image is formed on the recording medium by transferring the toner image thus formed to the recording medium.
Here, when exposure of the photoreceptor after uniform charging is performed by a laser beam (hereinafter referred to as laser light), red laser light (about 630 to 780 nm) is generally used.

  In recent years, in order to improve the image quality of an output image of an electrophotographic apparatus, its resolution has been accelerated. The response on the device for this purpose is relatively easy from an optical point of view. That is, increasing the resolution is achieved by narrowing the spot diameter of the laser beam and increasing the writing density. However, with a semiconductor laser having an oscillation wavelength of about 630 to 780 nm used for a conventional light source, it is difficult to obtain a clear spot contour even if the beam diameter is reduced by operating the optical system. The cause is the diffraction limit of the laser beam, because the lower limit of the spot diameter D is a function that is directly proportional to the wavelength λ of the laser beam and is expressed by the following formula (1).

D = 1.22λ / NA (1)
(Here, “NA” represents the lens numerical aperture.)

  As is clear from the above formula (1), the red laser light generally used in the electrophotographic process has a long wavelength of about 630 to 780 nm. Therefore, the beam diameter can be reduced to a small diameter. Have difficulty. For this reason, there is a problem that the recording density on the photoreceptor cannot be increased more than a certain degree. In order to improve this problem, it is necessary to shorten the oscillation wavelength of the semiconductor laser.

There are several methods for shortening the laser oscillation wavelength.
One is to use a non-linear optical material and halve the wavelength of the laser beam by using second harmonic generation (SHG) (see, for example, Patent Documents 1 to 3). Since this system can use a GaAs laser diode (LD) or YAG laser that has already established technology and can output high power as a primary light source, it is possible to extend the life and increase the output.

  The other uses a wide gap semiconductor, and the size of the apparatus can be reduced as compared with a device using SHG. LDs using ZnSe-based semiconductors (for example, see Patent Documents 4 and 5) and GaN-based semiconductors (for example, see Patent Documents 6 and 7) have been the subject of much research from the past because of their high luminous efficiency. ing. However, these LDs are difficult to optimize the device structure, crystal growth conditions, electrodes, etc., and are difficult to oscillate at room temperature, which is essential for practical use, due to defects in the crystal.

  In response to this, technological innovations such as the foundation have progressed. In October 1997, Nichia Chemical Co., Ltd. proposed a 1150-hour continuous oscillation (50 ° C condition) in an LD using a GaN-based semiconductor. Has been on sale.

  On the other hand, an electrophotographic photoreceptor undergoes repeated processes of charging, exposure, development, transfer, cleaning, and charge removal in the image forming process. The electrostatic latent image formed by charging and exposure becomes a toner image by a fine particle developer called toner. Further, the toner image is transferred to a transfer material such as paper in the transfer process, but 100% of the toner is not transferred, and a part of the toner image remains on the photoreceptor. If this residual toner is not removed, a high-quality image free from stains cannot be obtained in the repeated process. Therefore, a residual toner cleaning process is required. The cleaning process typically uses a fur brush, a magnetic brush, a blade, or the like, but blade cleaning is generally selected in terms of cleaning accuracy, apparatus configuration, and the like.

  The counter-type contact method, which is a commonly used cleaning method, simultaneously increases the contact pressure of the cleaning blade to the electrophotographic photosensitive member, causing an increase in the frictional force between them. As a result, problems such as a decrease in durability due to an increase in the amount of abrasion of the electrophotographic photosensitive member, generation of scratches on the electrophotographic photosensitive member, occurrence of cleaning failure due to reversal of the cleaning blade, and stoppage of the apparatus occur. It is known that it is effective to reduce the coefficient of friction of the photoconductor in order to solve the problems related to the cleaning of the photoconductor, in particular, the photoconductor scraping, scratches and blade reversal.

  It is known that lowering the coefficient of friction of the photoreceptor is also effective in increasing transfer efficiency. Conventionally, many methods for incorporating a lubricant into the surface layer of a photoconductor have been proposed as a method for reducing the friction coefficient of the photoconductor (see, for example, Patent Documents 8 and 9).

  Known lubricants include fluorine atom-containing resins such as polytetrafluoroethylene, spherical powders such as acrylic resins and polyethylene resins, metal oxide powders such as silicon oxide and aluminum oxide, and the like. In particular, the fluorine atom-containing resin powder containing a large amount of fluorine atoms has a significant effect as a lubricant because the surface energy is extremely small. Such a fluorine atom-containing resin powder is used as a crystalline powder, and after being dispersed in a binder resin such as an acrylic resin, polyester, polyurethane, or polycarbonate, a film is formed as a surface layer of the photoreceptor. Patent Documents 8 and 9 disclose that the surface layer needs to contain a fluorine atom-containing resin powder so that the surface layer exhibits a sufficient decrease in the friction coefficient.

However, in a system in which a lubricant is added to the surface layer of the photoreceptor in order to reduce the friction coefficient of the photoreceptor, a blue system having an oscillation wavelength of about 370 to 500 nm as typified by the laser using the GaN-based semiconductor described above. When a semiconductor laser is used as the exposure means, the electrostatic latent image becomes broad due to the scattering of exposure light by the lubricant added to the photoconductor, the writing density cannot be increased, and the laser by shortening the oscillation signal wavelength. There is a problem that the effect of reducing the beam diameter cannot be obtained.
JP-A-9-275242 JP-A-9-189930 JP-A-5-313033 Japanese Patent Laid-Open No. 7-321409 JP-A-6-334272 JP-A-8-088441 JP 7-335975 A JP 52-117134 A JP-A-53-107841

  The present invention has been made in view of the above circumstances, and a surface layer constituting the outermost surface of a photoreceptor even when a laser beam with a shorter oscillation wavelength is used as an exposure light source for the photoreceptor. It is an object of the present invention to provide an image forming apparatus in which exposure light is not scattered by the lubricant dispersed in.

In an image forming apparatus using a semiconductor laser having an oscillation wavelength in the range of 370 to 500 nm as an exposure light source for the photoreceptor, the surface layer constituting the outermost surface of the photoreceptor is lubricated to reduce the friction coefficient of the photoreceptor. It was found that an image forming apparatus free from scattering of exposure light caused by the lubricant can be obtained by adding a specific amount of lubricant contained in the surface layer of the photoreceptor when the agent is added.
That is, the present invention is as follows.
(1) In an image forming apparatus comprising a photoconductor and a semiconductor laser having an oscillation wavelength in the range of 370 to 500 nm as an exposure light source for the photoconductor.
The photoreceptor has a surface layer constituting an outermost surface, and a lubricant is dispersed in the surface layer, and the content of the lubricant is 1.3 mg or less in the surface layer thickness × 1 mm ^2. An image forming apparatus, comprising:
(2) The image forming apparatus according to (1), wherein the surface layer is a charge transport layer.
(3) The image forming apparatus according to (1), wherein the surface layer is a protective layer.
(4) The image forming apparatus according to (1), wherein the surface layer is a charge generation layer.
(5) The image forming apparatus according to any one of (1) to (4), wherein the lubricant is fluorine atom-containing resin fine particles.

  According to the present invention, there is provided an image forming apparatus provided with an electrophotographic photoreceptor having surface slipperiness and wear resistance and having high-quality image characteristics without light scattering even when a short wavelength laser is used. can do.

The image forming apparatus of the present invention uses a semiconductor laser whose exposure light source has an oscillation wavelength in the range of 370 to 500 nm, and the photoreceptor used in the image forming apparatus has a lubricant of the surface layer thickness × 1 mm. ² having a surface layer constituting the outermost surface dispersed so as to be 1.3 mg or less.
In the present invention, the “surface layer” refers to a layer constituting the outermost surface of the photoreceptor. Usually, the photoreceptor has a photosensitive layer on a conductive support. The photosensitive layer may be a single layer type in which the charge transport material and the charge generation material are contained in the same layer, or may be a laminated type in which the charge transport layer and the charge generation layer are separated. In the present invention, the surface layer of the photoreceptor may be formed as a surface layer in the case of a single layer type, or as a part of the photosensitive layer in the case of a laminated type (for example, as a charge transport layer or a charge generation layer). ) It may be formed on the surface or as a protective layer on the photosensitive layer.

The protective layer is usually a thin layer compared to the photosensitive layer. In the present invention, when the charge transport layer is a surface layer, a lubricant is contained in the charge transport layer in order to reduce the coefficient of friction of the photoreceptor in the transfer process and the cleaning process. Note that if the charge transport layer is a surface layer compared to the case where a thin protective layer is a surface layer, the film thickness is large, so the content of the lubricant should be limited in order to suppress exposure light scattering by the lubricant. Is preferred.
However, even if the amount of lubricant in the charge transport layer is limited, sensitivity deterioration due to light scattering occurs when the total thickness of the photosensitive layer is large, especially when photocarriers are generated mainly on the conductive support side of the photosensitive layer. The image uniformity is significantly reduced. The reason is that a charge transport layer containing a lubricant is laminated on the charge generation layer, so that the charge transport layer becomes a light scattering layer, and particularly when photocarriers are generated mainly on the support side of the photosensitive layer, This is because the farther the carrier generation portion is from the light scattering layer, that is, the thicker the charge transport layer, the longer the optical path length in the light scattering layer, and the greater the influence of light scattering.

  On the other hand, even if the photosensitive layer is too thin, the thickness of the photosensitive layer is 5 to 30 [mu] m, preferably 10 to 20 [mu] m. The thickness of the charge generation layer in the photosensitive layer is 0.01 to 1.0 μm, preferably 0.05 to 0.5 μm, and the thickness of the charge transport layer is 5.0 to 30.0 μm, preferably Is 10.0 to 30.0 μm. Further, it is preferable that the lubricant contained in the photoreceptor is as small as possible. Specifically, the content of the lubricant in the charge transport layer is 5 to 10% by mass, preferably 5 to 8% by mass.

Further, when a protective layer as a surface layer constituting the outermost surface is provided on the photosensitive layer, the content of the lubricant capable of effectively reducing the coefficient of friction on the surface of the photoreceptor is 5 to 20 mass in the protective layer. %, Preferably 5 to 10% by mass, and the thickness of the protective layer is 0.05 to 6.0 μm, preferably 0.5 to 4 μm.
In addition, in order to “disperse the lubricant so that the surface layer thickness is 1 mg ² or less to 1.3 mg”, the surface layer thickness obtained during the production of the photoreceptor and the surface layer coating solution are dispersed. Adjust the amount of lubricant to be applied.

  As the lubricant used in the photoreceptor in the present invention, fluorine atom-containing resin fine particles are preferably used, and specific examples include the following. Specifically, fluorine atom-containing resin fine particles include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polydichlorodifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer. Those composed of one or more selected from the group consisting of polymers, tetrafluoroethylene-ethylene copolymers and tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymers are preferably used. . For these, commercially available fluorine atom-containing resin fine particles can be used as they are. As the fluorine atom-containing resin fine particles, those having a molecular weight of 3,000 to 5,000,000 can be used, and those having a particle size of 0.01 to 10 μm, preferably 0.05 to 2.0 μm can be used. .

  FIG. 1 is a schematic sectional view showing an embodiment of the image forming apparatus of the present invention. The photoreceptor in the present invention is a laminate type photoreceptor in which a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material are laminated in this order, or a charge generation layer and a charge transport layer laminated in reverse. Laminated photoreceptor, single layer photoreceptor in which a charge generating material and a charge transport material are contained in a single layer, and a protective layer as a surface layer constituting the outermost surface of these laminated and monolayer photoreceptors A photosensitive member having the above is also preferably used.

  FIG. 2 shows an example of the layer structure of the photoreceptor in the present invention. On the conductive support 21, a charge generation layer 24 and a charge transport layer 25 are provided as photosensitive layers. As the conductive support 21, a metal or an alloy such as iron, copper, silver, aluminum, zinc, lead, tin, titanium, nickel, or an oxide of these metals, carbon, a conductive polymer molded product, or the like can be used. It is. In some cases, a non-conductive material such as paper, plastic or ceramic is subjected to a conductive treatment such as conductive paint or vapor deposition. The shape includes a drum shape such as a cylindrical shape and a columnar shape, a sheet shape, and a belt shape. A conductive layer 22 may be provided between the conductive support 21 and the photosensitive layer 27, or an intermediate layer 23 may be further provided for the purpose of improving the adhesion and electrical characteristics between the photosensitive layer 27 and the conductive layer 22.

  The conductive layer 22 functions as a charge injection control at the interface and as an adhesive layer. The conductive layer is mainly composed of a binder resin, but may contain the metal or alloy, or oxides, salts, or surfactants thereof. Examples of the binder resin that forms the conductive layer include polyester, polyurethane, polyarylate, polyethylene, polystyrene, polybutadiene, polycarbonate, polyamide, polypropylene, polyimide, phenol resin, acrylic resin, silicone resin, epoxy resin, urea resin, and allyl resin. Alkyd resin, polyamide-imide, polysulfone, polyallyl ether, polyacetal, butyral resin, and the like. The film thickness is preferably 0.05 to 7 μm, more preferably 0.1 to 2 μm.

  The intermediate layer 23 can be formed of casein, polyvinyl alcohol, nitrile cellulose, polyvinyl butyral, polyester, polyurethane, gelatin, polyamide (nylon 6, nylon 66, nylon 610, copolymer nylon, alkoxymethylated nylon), aluminum oxide, or the like. The film thickness of the intermediate layer 23 is 0.1 to 10 μm, preferably 0.3 to 3.0 μm.

Examples of the charge generation material used for the charge generation layer 24 include phthalocyanine pigments, polycyclic quinone pigments, trisazo pigments, disazo pigments, azo pigments, perylene pigments, indigo pigments, quinacridone pigments, azulenium salt dyes, squalium dyes, cyanine dyes, and pyrylium dyes. Thiopyrylium dye, xanthene dye, triphenylmethane dye, styryl dye, selenium, selenium-tellurium alloy, amorphous silicon, cadmium sulfide and the like.
These pigment and dye type charge generation materials are generally dispersed in a binder resin and used as a paint. As the binder resin used for the charge generation layer, polyvinyl butyral, polyvinyl benzal, polyarylate, polycarbonate, polyester, polyester, polyurethane, phenoxy resin, acrylic resin, cellulose resin and the like are preferable.

  In addition to the charge generation material, various additives can be used for the charge generation layer in order to improve mechanical properties and durability. As such additives, antioxidants, ultraviolet absorbers, stabilizers, crosslinking agents, lubricants, conductivity control agents, and the like are used.

Examples of the charge transport material used for the charge transport layer 25 include pyrene compounds, N-alkylcarbazole compounds, hydrazone compounds, N, N-dialkylaniline compounds, diphenylamine compounds, triphenylamine compounds, triphenylmethane compounds, pyrazoline compounds, Examples include styryl compounds, stilbene compounds, polynitro compounds, and polycyano compounds.
These charge transport materials are generally dissolved in a binder resin and used as a paint. The binder resin used for the charge transport layer is polycarbonate, polyester, polyurethane, polysulfone, polyamide, polyarylate, polyacrylamide, polyvinyl butyral, phenoxy resin, acrylic resin, acrylonitrile resin, methacrylic resin, phenol resin, epoxy resin, alkyd resin. Etc.

As the photoreceptor used in the image forming apparatus of the present invention, it is also preferable to provide a protective layer 26 as shown in FIG. 3 as a surface layer constituting the outermost surface, if necessary.
The paint used when applying the protective layer is prepared by dispersing the fluorine atom-containing resin fine particles as a lubricant in a binder resin and a solvent. As a dispersion method, a ball mill, an ultrasonic wave, a paint shaker, a red devil, a sand mill, or the like is used.

As binder resin, polyester, polyurethane, polyarylate, polyethylene, polystyrene, polybutadiene, polycarbonate, polyamide, polypropylene, polyimide, phenol resin, acrylic resin, silicone resin, epoxy resin, urea resin, allyl resin, alkyd resin, polyamide-imide , Nylon, polysulfone, polyallyl ether, polyacetal, butyral resin and the like.

A photoreceptor having a surface layer containing a lubricant of 1.3 mg or less in a surface layer thickness × 1 mm ² used in the present invention can be obtained, for example, as follows.
For example, when the surface layer is a protective layer, the allowable amount of fluorine atom-containing resin fine particles is 40% by mass or less in the protective layer when the thickness of the protective layer is 5 μm. A fluorine atom-containing resin particle dispersion was 40 wt% in the coating solution of the protective layer, and a dip coating so as to have a desired thickness (in this case 5 [mu] m), 1 in the surface layer thickness × 1 mm ^2. A photoreceptor satisfying the condition of 3 mg or less is obtained.

  Examples of the charging means used for primary charging of the image forming apparatus of the present invention include a non-contact method using a corona charger and a contact method using a roller charger. As the developing unit, the transfer unit, the cleaning unit, etc., those used in a normal image forming apparatus are used, and there is no particular limitation in the present invention.

  The present invention will be described below with reference to examples, but the present invention is not limited thereto. In addition, all the parts used in an Example show a mass part.

(Photoconductor Production Example 1)
After mixing and dissolving 10 parts of nylon (trade name: M-4000, manufactured by Toray Industries, Inc.), 100 parts of methanol and 90 parts of isopropanol, on an aluminum cylinder having an outer diameter of 190 mm, a wall thickness of 1.5 mm, and a length of 363 mm. It was dip coated and dried at 90 ° C. for 20 minutes to form a 2.0 μm subbing layer.

  Next, 10 parts of a trisazo pigment, 5 parts of polycarbonate (bisphenol A type, Mn 20000) and 600 parts of cyclohexanone were dispersed in a sand mill to prepare a charge generation layer coating material. This paint was dip-coated on the undercoat layer and dried at 120 ° C. for 20 minutes to form a 0.15 μm charge generation layer. Next, 20 parts of a biphenyl compound, 20 parts of polycarbonate (bisphenol A type, Mn 20000), 2 parts of polytetrafluoroethylene fine particles (trade name: Lubron L-5, manufactured by Daikin Industries) and 800 parts of chlorobenzene are dispersed with a ball mill. Thus, a paint for the charge transport layer was prepared. This paint was dip coated on the charge generation layer and dried at 130 ° C. for 90 minutes to form an 18 μm charge transport layer, whereby Photoreceptor 1 was obtained.

(Photoconductor Production Example 2)
In Production Example 1 of the photoreceptor, polytetrafluoroethylene fine particles are not used in the charge transport layer, and the thickness of the charge transport layer is set to 15 μm. A layer, a charge generation layer, and a charge transport layer were formed. Subsequently, 1 part of polytetrafluoroethylene fine particles, 6 parts of the biphenyl compound, 12 parts of polycarbonate (bisphenol Z type, Mn 18000) and 1000 parts of dichloromethane were dispersed with a sand mill to prepare a coating material for a protective layer. This paint was dip-coated on the charge transport layer and dried at 120 ° C. for 30 minutes to form a 2.0 μm protective layer, whereby Photoreceptor 2 was prepared.

(Photoconductor Production Example 3)
Photoconductor Production Example 1 with the exception that polytetrafluoroethylene particles (trade name: Lubron L-5, manufactured by Daikin Industries, Ltd.) were not added and the charge transport layer coating material dispersed in a ball mill was used. Similarly, a photoreceptor 3 was prepared.

(Photoconductor Production Example 4)
Protection by adding 30 parts of polytetrafluoroethylene particles (trade name: Lubron L-5, manufactured by Daikin Industries, Ltd.) and dispersing in a ball mill apparatus without adding a fluorosurfactant having a perfluoroalkyl group A photoconductor 4 was prepared in the same manner as in Photoconductor Production Example 2 except that the layer coating material was used.

[Example 1]
1 is a modified machine of the image forming apparatus (CLC1100 (manufactured by Canon Inc.) shown in FIG. 1 using a semiconductor laser having an oscillation wavelength of 370 to 500 nm, and the oscillation of the semiconductor laser used in this example. The following evaluation was performed using a wavelength of 405 nm.

(Cleanability)
The evaluation was based on the presence or absence of toner passing through the cleaning blade with 20,000 continuous copies.
○: No slipping Δ: Although it is on the photoreceptor but not on the image ×: Present on the image (transferability)
The evaluation was made based on the transfer efficiency and the degree of scattering on the transfer paper (visual evaluation).
○: No problem Δ: Cannot be confirmed visually, but can be seen when enlarged ×: Can be confirmed visually (light scattering)
The evaluation was based on the reproduction size of one dot of 400 dpi on the photoreceptor (one dot one space image).
○: Completely isolated and reproduced △: Almost isolated but sometimes connected to the next dot ×: Connected to the next dot (durability) In order to avoid blade turning, the drum is artificially applied with toner. After mounting, evaluation was made by the amount of photoconductor shaving after 20,000 continuous color copies.
○: 0.1 μm or less Δ: 0.1 to 0.3 μm
X: 0.3 μm or more Evaluation results of these photoreceptors. The evaluation is a three-stage evaluation in the order of ◯>Δ> ×.

In each of the examples, it was possible to eliminate the influence of light scattering even when the wavelength of the exposure light source was 370 to 500 mm while maintaining the cleaning property and the transfer property.

1 is a schematic configuration diagram of an image forming apparatus used in an embodiment. FIG. 3 is a layer configuration diagram of a photoreceptor used in the image forming apparatus of the present invention. FIG. 3 is a layer configuration diagram of a photoreceptor used in the image forming apparatus of the present invention.

Explanation of symbols

1: Development unit 2: Primary charger 3: Light source for exposure 4: Cleaner 5: Transfer drum 6: Fixing device 7: Photoconductor 8: Document base 21: Support 22: Conductive layer 23: Intermediate layer 24: Charge generation layer 25: Charge transport layer 26: Protective layer 27: Photosensitive layer

Claims (5)

In an image forming apparatus comprising: a photoconductor; and a semiconductor laser having an oscillation wavelength in a range of 370 to 500 nm as an exposure light source for the photoconductor.
The photoreceptor has a surface layer constituting an outermost surface, and a lubricant is dispersed in the surface layer, and the content of the lubricant is 1.3 mg or less in the surface layer thickness × 1 mm ^2. An image forming apparatus, comprising: The image forming apparatus according to claim 1, wherein the surface layer is a charge transport layer. The image forming apparatus according to claim 1, wherein the surface layer is a protective layer. The image forming apparatus according to claim 1, wherein the surface layer is a charge generation layer. The image forming apparatus according to claim 1, wherein the lubricant is fluorine atom-containing resin fine particles.

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