JPH07175230A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image forming device excellent in the reproducibility of a highlight part by making the area of a laser beam on the surface of a photoreceptor equal to or under the half of the area of a basic picture element unit in the case of forming an electrostatic latent image by using the laser beam. CONSTITUTION:In this image forming device, an electrostatic latent image is formed on the photoreceptor 1 containing conductive metallic powder whose primary particle size is <=0.3mum or fluororesin in the surface layer of a photoreceptive layer on a conductive supporting body by using the laser beam. When it is assumed that the area of the basic picture element unit is S and the area of the laser beam on the surface of the photoreceptor is S', S'/S<1/2 holds. Since it is thought that the faulty reproducibility of the highlight part on the image is caused by the scattering of the laser light transmitted through a surface layer, the particulate whose particle size is shorter than the wavelength of the laser beam is contained in the surface layer in order to restrain the scattering of the laser light transmitted through the surface layer, and the beam diameter suitable for the diameter of the impalpable powder is set. Thus, the highlight part is vividly reproduced in image gradation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art FIG. 7 shows an example of a color image forming apparatus for forming a full color image.

In this example, in a color image forming apparatus, a photosensitive drum 101, which is an image carrier, is rotatably supported in the arrow direction, and the corona charger 1 is provided around the photosensitive drum 101.
02, optical system 103, developing device 104, transfer device 10
5, the cleaning device 106 is arranged.

The optical system 103 is, for example, a laser beam exposure apparatus shown in the figure, which is composed of a document scanning section and a color separation filter, and irradiates the photosensitive drum 101 with a color-separated optical image or an optical image E corresponding thereto.

The photosensitive drum 101 uniformly charged by the charger 102 is irradiated with a light image E for each separated color to form a latent image. The developing device 104 is a rotary developing device, and four developing devices, that is, a black developing device 104Bk, a cyan developing device 104c, a magenta developing device 104m, and a yellow developing device 104y are arranged around a central axis 104b, and a predetermined developing device is provided. To a developing position facing the photosensitive drum 101 to develop the latent image on the photosensitive drum 101.
An image is formed on the surface of No. 01 by toner using resin as a base.

Further, the toner image on the photosensitive drum 101 is supplied from the recording material cassette 107 via the conveying system and the transfer device 5 to a position facing the photosensitive drum 101 (according to the paper path shown by the dotted line in the figure). It is transferred to the recording material. The transfer device 105 includes a transfer drum 105a,
Adsorption roller 1 facing the transfer corona charger 105b and the adsorption corona charger 105c for electrostatically adsorbing the recording material.
05g, an inner corona charger 105d, and an outer corona charger 105e. A recording material carrying sheet 105f made of a dielectric material is cylindrical in the peripheral opening area of the transfer drum 105a which is rotatably driven. It is stretched integrally.

As the transfer drum 105a rotates, the toner image on the photosensitive drum is transferred onto the recording material carried on the recording material carrying sheet 105f by the transfer charger 105b.

A desired number of color images are transferred to the recording material sucked and conveyed by the recording material carrying sheet 105f, and a full color image is formed.

When the transfer of the desired number of toner images is completed in this way, the recording material is separated from the transfer drum 105a by the separating means 1.
The sheet is separated by 08 and discharged to the tray 110 via the heat roller fixing device.

On the other hand, after the transfer, the photosensitive drum 101 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 106.

The photoconductor is required to have predetermined sensitivity, electrical characteristics, and optical characteristics according to the electrophotographic process as described above. The surface layer of the photoconductor, that is, the layer most distant from the substrate, is directly exposed to external electrical and mechanical forces such as corona charging, toner development, transfer to paper, and cleaning, so durability against them is required. To be done.

Specifically, durability is required against abrasion and scratches on the surface due to rubbing, and deterioration of the surface due to ozone generated during corona charging under high humidity. On the other hand, there is a problem that the toner adheres to the surface layer due to repeated development and cleaning of the toner, and it is required to improve the cleaning property of the surface layer.

Various methods have been studied in order to satisfy the properties required for the surface layer as described above. Among them, a conductive metal powder or a curable resin in which a fluorine resin is dispersed is used as the surface layer. The means of using is effective. As the curable resin, thermosetting resins such as polyurethane resin, epoxy resin, melamine resin, or guanamine resin and photocurable resins typified by polyacrylates are used.

However, when these resins are used alone in the surface layer, the surface resistivity is very high, and so on.
Residual charge accumulates, which causes the problem of increased durability and residual charge, and poor surface lubricity, resulting in poor cleaning performance. Therefore, a conductive metal powder or a fluorine-based resin is dispersed in these resins to reduce the amount of residual charges accumulated in the surface layer and its lower layer, improve surface lubricity, and form a surface layer satisfying the above characteristics. To do.

[0015]

However, in the above-mentioned conventional example, when a photoconductor having conductive metal powder or fluorine resin dispersed in the surface layer is used in an image forming apparatus using a laser beam, image gradation is reduced. In terms of sex, it was difficult to reproduce the highlight part.

In particular, a plurality of electrostatic latent images are visualized and superposed,
In a device for forming a color image, a solid image such as a photograph is often printed, and when the above-mentioned photoconductor is used, there is a problem that defective reproduction of a highlight portion is very conspicuous.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus having high reproducibility of highlight portions.

[0018]

In order to achieve the above object, in the present invention, a conductive metal powder or fluorine having a primary particle size of 0.3 μm or less is formed on the surface layer of a photosensitive layer on a conductive support. In an image forming apparatus that forms an electrostatic latent image on a photoconductor containing a resin based on a laser beam, the area of a basic pixel unit is S, and the laser beam area on the photoconductor surface is S ′. At this time, S ′ / S <1/2.

Further, a plurality of electrostatic latent images may be visualized by developing means and superposed to form a color image.

Further, the electrostatic latent image is visualized by developing means,
The development by the developing means may be reversal development.

[0021]

In the present invention having the above construction, the area of the basic pixel unit is S, and the laser beam area on the surface of the photoconductor is S '.
Then, by setting S ′ / S <1/2, it becomes possible to clearly reproduce the highlight portion in the image gradation.

The present inventors consider the factors that may cause the above phenomenon as follows. The poor reproduction of the highlighted portion on the image is caused by the scattering of the laser light that passes through the surface layer. Therefore, in order to reduce the scattering of laser light transmitted through the surface layer, the surface layer contains fine powder with a particle diameter shorter than the laser wavelength.A beam diameter suitable for the fine powder diameter determined above is set. It is necessary to set the conditions. The present invention has been empirically found to be a value satisfying the above conditions by repeating trials, and thus an image forming apparatus capable of clearly reproducing a highlight portion in image gradation can be completed. The present invention will be described in detail below.

The conductive metal powder applied to the present invention is a metal such as aluminum, copper, nickel or silver, zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, indium oxide doped with tin. ，
Metal oxides such as tin oxide and zirconium oxide doped with antimony and one or more thereof are appropriately selected, and the primary particles are preferably 0.3 μm or less.

Further, as the fluorine resin powder applied to the present invention, tetrafluoroethylene resin, trifluoroethylene chloride resin, tetrafluoroethylene hexafluoropropylene resin, vinyl fluoride resin, vinylidene fluoride resin, One or more kinds are appropriately selected from the difluorochloroethylene resin and their copolymers, especially in a low molecular weight clade,
Moreover, the primary particles are preferably 0.3 μm or less.

According to the above-mentioned conditions, this value should be shorter than the wavelength of the semiconductor laser beam, so it seems to be too short. However, in the practical system, secondary particles and tertiary particles are inevitably produced, and this is caused. As a result of conducting an experiment in consideration of the above, an appropriate value of the primary particle diameter is 0.3 μm or less.

The content of the conductive metal powder dispersed in the surface layer is appropriately 5 to 90% by weight, preferably 10 to 90% by weight, based on the weight of the solid content of the surface layer. Content rate is 5
If it is less than 10% by weight, the resistance value is too high and the residual charge becomes high.
If it exceeds 0% by weight, the surface layer has a low resistance, which lowers the charging ability and causes pinholes.

The content of the fluororesin powder dispersed in the surface layer is 1 to 50% by weight based on the weight of the solid content of the surface layer.
Is suitable, and particularly preferably 2 to 30% by weight. When the content is less than 1% by weight, the effect of modifying the surface layer by the fluororesin is not sufficient, while when it exceeds 50% by weight, the light transmittance is lowered and the carrier mobility is also lowered.

The binder resin for forming the surface layer may be a polymeric substance capable of forming a film. However, from the viewpoint that it has a certain degree of hardness when used alone and does not interfere with carrier transportation, Methacrylic acid ester, polystyrene, methacrylic acid ester / styrene copolymer,
Polycarbonate, polyester, polysulfone and the like are preferable.

The curable resin for forming the surface layer is a photocurable resin represented by thermosetting resins such as polyurethane resin, epoxy resin, melamine resin or guanamine resin and polyacrylates as described above. Resins are used.

When the electrophotographic photosensitive member used in the present invention is manufactured, the conductive support is a conductive material obtained by dispersing conductive particles in a suitable binder resin on a support such as metal such as aluminum and stainless steel, paper, plastic or the like. A cylindrical cylinder provided with layers or a film is used. However, when the support itself is conductive, the conductive support need not be provided with a conductive layer.

An undercoat layer (adhesive layer) having a barrier function and an undercoat function can be provided on these conductive supports.

The subbing layer improves the adhesion of the photosensitive layer, the coating property, the protection of the conductive support, the coating of defects on the conductive support, the improvement of the charge injection property from the conductive support, and the formation of the photosensitive layer. It is formed for protection against electric breakdown. Known materials for the subbing layer include polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, methyl cell source, ethylene-acrylic acid copolymer, casein, polyamide copolymerized nylon, glue and gelatin. These are dissolved in a solvent suitable for each and coated on the substrate. The film thickness is
It is about 0.2 μm to 2 μm. As the charge generating substance, a cyanine dye, an azulene dye, a squarylium dye, a pyrylium dye, a thycypyrylium dye, a phthalocyanine pigment, an anthanthrone pigment, a dibenzpyrenequinone pigment, a pyranthrone pigment, a monoazo pigment, a disazo Azo pigments such as pigments and trisazo pigments,
Indigo pigments, quinacridone pigments, asymmetric quinocyanines, quinocyanines and the like can be used. As the charge transport material, pyrene, N-ethylcarbazole, N
-Isopropylcarbazole, N-methyl-N-phenylhydrazino-3-methylidene-9-ethylcarbazole, N, N-diphenylhydrazino-3-methylidene-
9-ethylcarbazole, N, N-diphenylhydrazino-3-methylidene-10-ethylphenothiazine,
N, N-diphenylhydrazino-3-methylidene-10
-Ethylphenoxazine, p-diethylaminobenzaldehyde-N, N-diphenylhydrazone, p-diethylaminobenzaldehyde-N-α-naphthyl-N-phenylhydrazone, p-pyrrolidinobenzaldehyde-
Hydrazones such as N, N-diphenylhydrazone, 1,3,3-trimethylindolenine-ω-aldehyde-N, N-diphenylhydrazone, p-diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrazone, 2 , 5-bis (p-diethylaminophenyl)-
1,3,4-oxadiazole, 1-phenyl-3-
(P-Diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [quinolyl (2)]
-3- (p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [pyridyl (2)]-3- (p-diethylaminostyryl) -5-
(P-Diethylaminophenyl) pyrazoline, 1- [6
-Methoxypyridyl (2)]-3- (p-diethylaminostyryl) -5- (p-diethylaminophenylpyrazoline, 1- [pyridyl (3)]-3- (p-diethylaminostyryl) -5- (p- Diethylaminophenyl) pyrazoline, 1- [lepidyl (2)]-3- (p-
Diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [pyridyl (2)]-3-
(P-Diethylaminostyryl) -4-methyl-5-
(P-Diethylaminophenyl) pyrazoline, 1- [pyridyl (2)]-3- (α-methyl-p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1-phenyl-3- (p-diethylamino) Pyrazolines such as styryl) -4-methyl-5- (p-diethylaminophenyl) pyrazoline, 1-phenyl-3- (α-benzyl-p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, spiropyrazolin, 2- (p-diethylaminostyryl)-
Oxazole compounds such as 6-diethylaminobenzoxazole and 2- (p-diethylaminophenyl) -4- (p-dimethylaminophenyl) -5- (2-chlorophenyl) oxazole, 2- (p-diethylaminostyryl) -6- Thiazole compounds such as diethylaminobenzthiazole, bis (4-diethylamino-2)
-Methylphenyl) phenylmethane and other triarylmethane compounds, 1,1-bis (4-N, N-diethylamino-2-methylphenyl) heptane, 1,1,2,
Polyarylalkanes such as 2-tetrakis (4-N, N-dimethylamino-2-methylphenyl) ethane,
5- (4-diphenylaminobenzylidene) -5H dibenzo [a, d] cycloheptene, 1,2-benzo-3-
A stilbene compound such as (d-phenylstyryl) -9-n-butylcarbazole can be used.

The method for adjusting the electrophotographic photosensitive member of the present invention will be described by taking the case of the function-separated type photosensitive member in which the charge transport layer is laminated on the charge generating layer as an example.

The above charge generating substance is used together with 0.3 to 10 times the amount of the binder resin and the solvent, a homogenizer, ultrasonic waves,
Disperse well by methods such as ball mill, vibration ball mill, sand mill, attritor, and roll mill. This dispersion was applied onto the substrate coated with the undercoat layer and dried to give 0.1
A coating film of about 1 μm is formed.

In this example, since the surface layer serves as a charge transport layer, the fluororesin powder is dispersed therein.

That is, the binder resin and the fluororesin powder are dispersed together with a solvent by a homogenizer, ultrasonic wave, ball mill, sand mill, attritor, roll mill or the like, and a solution of the charge transporting substance and the binder resin is added to this to obtain the desired mixture. The charge transport layer liquid is prepared.

The mixing ratio of the charge transport material and the binder resin is about 2: 1 to 1: 4.

As the solvent, aromatic hydrocarbons such as toluene and xylene, chlorine-based hydrocarbons such as dichloromethane, chlorobenzene, chloroform and carbon tetrachloride are used. When applying this solution, for example, a coating method such as a dip coating method, a spray coating method, a spinner coating method, a bead coating method, a blade coating method or a curtain coating method can be used, and drying is performed at 10 to 200 ° C. It can be carried out at a temperature in the range of 20 to 150 ° C. for 5 minutes to 5 hours, preferably for 10 minutes to 2 hours under blast drying or static drying. The thickness of the formed charge transport layer is about 10 to 30 μm.

Further, in the case of a photoreceptor in which the charge generating layer is coated on the charge transporting layer, the charge generating layer serves as the surface layer, and therefore the dispersion-stabilized fluorine resin powder is contained therein. This charge generation layer dispersion is prepared by adding and mixing the dispersion prepared by dispersing the fluororesin powder in the binder resin used for the charge generation layer to the charge generation dispersion prepared as described above. This dispersion can be applied onto the charge transport layer to obtain the photoreceptor of the present invention.

When the photosensitive layer has a protective layer, the protective layer serves as a surface layer of the photosensitive layer, and the dispersion-stabilized fluororesin powder is contained in the protective layer. This protective layer can be obtained by applying a dispersion liquid of the fluorine-based resin powder dispersion-stabilized in the resin forming the protective layer onto the photosensitive layer as described above.

In the present invention, when the basic pixel area is S and the laser beam area on the surface of the photoconductor is S ', the following method is used to satisfy S' / S <1/2.

By using InGaAsP for the semiconductor laser, the wavelength of the laser light is shortened, the diffracting power is reduced, the beam waist is narrowed, and the beam diameter on the drum surface is reduced.

By controlling the laser light diverged from the laser oscillator from parallel light to divergent light convergent light by a variable focus lens, the beam waist of the laser is accurately aligned on the drum surface, and the beam is blurred on the drum surface. Instead, the beam diameter on the drum surface was reduced.

[0044]

【Example】

[First Embodiment] (First Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic sectional view of a color image forming apparatus according to an embodiment of the present invention.

This example has a digital color image reader section in the upper part and a digital color image printer section in the lower part.

In the reader unit, the original 30 is placed on the original table glass 31 and exposed and scanned by the exposure lamp 32, so that the reflected light image from the original 30 is condensed by the lens 33 on the full color sensor 34, and the color color is obtained. Obtain a decomposed image signal. The color-separated image signal passes through an amplifier circuit (not shown), is processed by a video processing unit (not shown), and is sent to the printer section.

In the printer section, the photosensitive drum 1, which is an image bearing member, is a photosensitive member having a surface layer as will be described later, and is rotatably carried in the direction of the arrow. A pre-exposure lamp 11 and a corona are provided around the photosensitive member 1. Charging device 2, laser exposure optical system 3, potential sensor 12, four developing devices 4y, 4 having different colors
c, 4m, 4Bk, the on-drum light amount detection means 13, the transfer device 5, and the cleaning device 6 are arranged.

In the laser exposure optical system 3, the image signal from the reader section is converted into an optical signal for image scan exposure by a laser output section (not shown), and the converted laser beam is reflected by the polygon mirror 3a. It is projected onto the surface of the photosensitive drum 1 through the lens 3b and the mirror 3c.

When forming an image on the printer section, the photosensitive drum 1
Is rotated in the direction of the arrow, and the photosensitive drum 1 after the charge is removed by the pre-exposure lamp 11 is uniformly charged negatively by the charger 2, and the light image E is emitted for each separated color to form a latent image. .

Next, the predetermined developing device is operated to develop the latent image on the photosensitive drum 1, and a toner image is formed on the photosensitive drum 1 with a negative toner having a resin base. The developing device is adapted to selectively approach the photosensitive drum 1 according to each separated color by the operation of the eccentric cams 24y, 24c, 24m and 24Bk.

Further, the toner image on the photosensitive drum 1 is
The recording material is transferred onto the recording material supplied from the recording material cassette 7 to the position facing the photosensitive drum 1 via the transport system and the transfer device 5. In this example, the transfer device 5 includes a transfer drum 5a, a transfer charger 5b, and an attraction charger 5c for electrostatically attracting a recording material.
A recording material carrying sheet 5f made of a dielectric material in the peripheral opening area of a transfer drum 5a which has a suction roller 5g, an inner charging device 5d, and an outer charging device 5e which face each other. Is integrally stretched in a cylindrical shape. The recording material carrying sheet 5f uses a dielectric sheet such as a polycarbonate film.

As the transfer device in the form of a drum, that is, the transfer drum 5a is rotated, the toner image on the photosensitive drum is transferred onto the recording material carried on the recording material carrying sheet 5f by the transfer charger 5b.

In this way, a desired number of color images are transferred to the recording material that is adsorbed and conveyed to the recording material carrying sheet 5f to form a full color image.

In the case of forming a full-color image, when the transfer of the four color toner images is completed in this way, the recording material is separated from the transfer drum 5a by the action of the separation claw 8a, the separation push-up roller 8b and the separation charger 5h, and the heat is generated. The sheet is discharged onto the tray 10 via the roller fixing device 9.

On the other hand, after the transfer, the photosensitive drum 1 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 6.

When images are formed on both sides of the recording material,
Immediately after the fixing device 9 is discharged, the transport path switching guide 19 is driven, and after being guided to the reversing path 21 via the transport vertical path 20, the reverse end of the reversing roller 21b causes the trailing end when fed to be the leading end. Then, it is withdrawn in the direction opposite to the direction in which it was fed and is stored in the intermediate tray 22. After that, an image is formed on the other surface by the above-described image forming step.

Further, in order to prevent the powder from being scattered on the recording material-carrying sheet 5f of the transfer drum 5a and the oil from being adhered to the recording material, the brush is interposed via the fur brush 14 and the recording material-carrying sheet 5f. 14, a backup brush 15 facing the sheet 14, an oil removing roller 16 and a recording material carrying sheet 5
Cleaning is performed by the action of the backup brush 17 that faces the roller 16 via f. Such cleaning should be done before or after image formation, or jam (paper jam)
When it occurs, it will be done as needed.

Further, in this example, the eccentric cam 25 is operated at a desired timing and the cam follower 5i integrated with the transfer drum 5a is operated, so that the gap between the recording material carrying sheet 5f and the photosensitive drum 1 is reduced. The configuration can be set arbitrarily. For example, during standby or when the power is off, the transfer drum and the photosensitive drum are separated from each other.

FIG. 2 is a block diagram of the image processing unit 40, and the same portions as those in FIG. 1 are designated by the same reference numerals.

The digital image data 42 is the D / A converter 4
It is converted into an analog image signal 403 by 02 and is input to one terminal of the comparator 411. A timing signal generation circuit 407 inputs the reference clock signal 43 and creates and outputs the pixel clock 404 and the screen clock 408 to the pattern signal generator 409. The pattern signal generator 409 outputs the pattern signal 410 based on the screen clock 408, and inputs it to the other terminal of the comparator 411.

The digital image data 42 is the pixel clock 4
04, and the D / A converter 402 outputs the analog image signal 403 in synchronization with the pixel clock 404. Screen clock 408 is pixel clock 404
The clock signal is obtained by multiplying the cycle of the above by an integer, and defines the cycle of the pattern signal 410, which is, for example, a triangular wave.

Analog image signal 403 and pattern signal 4
10 is compared by the comparator 411, and when the analog image signal 403 is larger, it is set to 0, and when it is smaller, the pulse width modulated binarized image data 41 is created and output.

FIG. 3 is a timing chart showing the timing of each part of FIG.

Here, the screen clock 408 is a clock having a cycle twice that of the pixel clock 404.
Digital image data 42 from hexadecimal 00 (white) to F
When changing to F (black) stepwise, the pattern signal 410
4 shows a pulse waveform of the binarized image data 41 pulse-width-modulated by. By changing the amplitude of the pattern signal 410 in this way, the relationship between the input level of the digital image data 42 and the pulse width of the binarized image data 41 can be changed.

FIG. 4 shows 8-bit digital image data 42.
When (256 data from 00 to FF) is input, almost continuous pulse width modulation is performed by the image processing unit 40, the binarized image data 41 is input to the image forming unit of the full-color copying machine, and laser light is input. It is a sensitometry showing the correspondence when the exposure by light is converted into the surface potential and the surface potential is converted into the concentration.

Since the image processing section 40 is intended to obtain an image output with good gradation, it is desirable that the relationship between the input level of the digital image data 42 and the density of the reproduced image is linear. However, as can be seen in FIG. 4, the linear part in the figure is from the Δ mark (50) to the ○ mark (5
It is the part up to 1). Therefore, by setting the input level of the portion of 50 to 00 and the input level of the portion of 51 to FF, it is possible to obtain good gradation for an 8-bit digital image.

The pulse width of the binarized image data 41 is made to correspond to the input level, and the white level (00) is set as shown in FIG.
Is PW0, and the pulse width for the black level (FF) is PW1. On the other hand, the surface potential measured by the potential sensor 12 of the photoconductor 1 is V0, and the potential corresponding to the black level is V1.

These potentials V0 and V1 are often different from the dark part potential (Vd) in the translucent state and the bright part potential (Vl) at the time of full lighting. However, the area used for image formation is the area from the triangle (50) to the circle (51).
V0 and V1 are brought close to the target value to stably form a high quality image.

FIG. 5 shows an electrostatic latent image formed on the photosensitive drum 1 at 200 line / inch by the laser exposure optical system 3 based on the binary image data 41. In the figure, the right diagonal line S
Is the area of a basic pixel unit, and the left diagonal line portion S ′ is the laser beam area on the surface of the photoconductor.

FIG. 6 is a diagram showing the relationship between S'and highlight reproduction of an image obtained by subjective evaluation. In the figure, highlight reproduction is good below the triangle mark, and defects are conspicuous above the triangle mark.

When the relationship between S and S'at 200 lines / inch was examined, the relationship was S '/ S <1/2, and the photosensitive drum 1 had S' / S <1/2. By setting the area of the upper laser beam, it was possible to always reproduce good highlights.

The pixel unit area in the sub-scanning direction of 200 line / inch and the main scanning direction of 400 line / inch is S = 8.0 × 10 ⁻³
a mm ^3, the laser spot diameter area in order to obtain good highlight reproducibility according to the present invention 1 / 2S = 4.0
The feature is that it is set to × 10 ⁻³ mm ³ .

In the present invention, a laser and its peripheral optical system as shown in the model diagram of FIG. 1 are applied. In the configuration shown in FIG. 1, the optical scanning operation is as follows.

The divergent light modulated according to the scanning information from the laser oscillator (InGaAsP semiconductor laser wavelength 675 mm) is made into parallel light or divergent light or convergent light by the collimator lens and propagates to the cylindrical lens, and only by the cylindrical lens in the sub-scanning direction. , A light deflector, that is, a rotary polygon mirror 3a is focused on a reflecting surface and irradiated with substantially parallel light in the scanning direction, and the laser beam flux reflected by the polygon mirror is refracted again by the scanning lens 3b. A beam waist is formed on the surface 11 to be irradiated, that is, on the surface of the photoconductor. At this time, the size of the laser beam spot on the surface of the photoconductor was 3 × 10 ⁻³ mm ² or less.

The method for producing the photoreceptor of the present invention will be described below.

50 parts by weight of conductive titanium oxide powder coated with tin oxide containing 10% antimony oxide, 25 parts by weight of phenol resin, 20 parts by weight of methyl cellosolve, 5 parts by weight of methanol and silicone oil (polydimethylsiloxane poly 0.002 parts by weight of the oxyalkylene copolymer (number average molecular weight 3000) was dispersed for 2 hours in a sand mill using a φ1 mm glass beam to prepare a conductive coating material. Aluminum cylinder (φ180mm × 36
0) was coated with the above coating by dipping and dried at 140 ° C. for 30 minutes to form a conductive layer having a film thickness of 20 μm.

Next, 30 parts by weight of methoxymethylated nylon resin (number average molecular weight 32000) and 10 parts by weight of alcohol-soluble copolymerized nylon resin (number average molecular weight 29000) were added to a mixed solvent of 260 parts by weight of methanol and 40 parts by weight of butanol. The dissolved liquid was applied onto the conductive layer by a dipping coating machine to form an undercoat layer having a film thickness after drying of 1 μm.

Next, a disazo pigment represented by the following structural formula

[0080]

[Chemical 1] 4 parts by weight, benzal resin 2 parts by weight, and tetrahydrofuran 40 parts by weight were dispersed for 60 hours in a sand mill using φ1 mm glass beads, and then diluted with a cyclohexanone / tetrahydrofuran mixed solvent to prepare a charge generation layer coating material.

This coating solution was applied onto the above-mentioned undercoat layer by a dipping coating machine to form a charge generation layer having a thickness of 0.1 μm after drying.

Next, the following structural formula [Chemical formula 2]

[0083]

[Chemical 2] 10 parts by weight of the charge transport material and 10 parts by weight of a polycarbonate resin (number average molecular weight 25,000) were added to dichloromethane.
It was dissolved in a mixed solvent of 0 parts by weight and 40 parts by weight of monochlorobenzene, and this solution was dip-coated on the charge generation layer and dried at 120 ° C. for 60 minutes to form a charge transport layer having a thickness of 20 μm.

Next, 4 parts by weight of an acrylic monomer resin, 5 parts by weight of tin oxide (average primary particle size 0.3 μm), and 1 part by weight of a photopolymerization initiator were dispersed in a solvent of 30 parts by weight of ethanol,
Dissolve the solution, apply dip coating on the charge transport layer, and apply a metal halide lamp (560 mW / cm ² : 360
Illumination with a sensor having a central sensitivity of nm) was performed for 30 seconds. As a result, a surface protective layer having a film thickness of 3 μm was formed.

The electrophotographic photosensitive member thus manufactured was subjected to image formation and evaluation by a laser beam printer having the above-mentioned structure. Furthermore, in terms of image gradation, the highlight part could be reproduced clearly. It was also possible to confirm durability stability such as no scratches and a small amount of wear.

(Example 2) Tin oxide particles (average primary particle size of 0.1%) in the surface protective layer of the electrophotographic photosensitive member of Example 1 were used.
Example 1 except that 1 part by weight of 3 μm) is included.
Under the same conditions as above, the image formation evaluation of the prepared sample was performed in the same manner as in Example 1.

(Example 3) The same conditions as in Example 1 except that the acrylic monomer resin in the surface protective layer of the electrophotographic photosensitive member in Example 1 was an epoxy resin and 10 parts by weight of this was included. Image evaluation of the sample prepared in 1. was performed in the same manner as in Example 1.

(Comparative Example 1) The laser oscillator in Example 1 was GaAsP (wavelength 780 nm), and the size of the laser beam spot on the surface of the photoconductor was 4.3 × 10 ⁻³ mm ^2.
Images were evaluated under the same conditions as in Example 1 except that

(Comparative Example 2) Comparative Example 2 was the same as Example 2 except that there was no focus lens on the laser peripheral optical system and the size of the laser beam spot on the drum surface was 5.8 × 10 ⁻³ mm ^2. Image evaluation was performed under the same conditions.

(Comparative Example 3) The same conditions as in Example 1 except that the average primary particle size of the conductive metal powder in the surface protective layer of the electrophotographic photosensitive member of Example 1 was 0.6 μm. In the same manner as in Example 1, image evaluation of the prepared sample was performed.

(Comparative Example 4) A photosensitive member prepared under the same conditions as in Example 1 except that the surface protective layer of the electrophotographic photosensitive member of Example 1 was not provided and the charge transport layer had a thickness of 25 μm. The image output evaluation was performed in the same manner as in Example 1. The results are shown in Table 1. When a continuous durability test was conducted on this system, the surface of the photoreceptor was scraped 100 times that of the system of Example 1.

Comparative Example 5 The laser oscillator in Comparative Example 4 is GaAsP (wavelength 780 nm), and the size of the laser beam spot on the drum surface is 4.3 × 10 ⁻³ mm ^2.
Images were evaluated under the same conditions as in Comparative Example 4 except that.

This system was also subjected to a continuous durability test,
The surface of the photoreceptor was scraped 100 times as much as that of the system of Example 1.

Example 4 In the same manner as in Example 1, a conductive layer, an undercoat layer, a charge generation layer and a charge transport layer were formed on an aluminum cylinder.

Next, 6 parts by weight of a polycarbonate resin (number average molecular weight 25,000), 3 parts by weight of the above charge transport material, and 1 part of polytetrafluoroethylene (average primary particle size 0.3 μm)
Part by weight is dissolved in a mixed solvent of 200 parts by weight of dichloromethane and 300 parts by weight of monochlorobenzene, and this solution is spray coated on the charge transport layer and dried at 120 ° C. for 60 minutes to form a surface protective layer having a thickness of 5 μm. A photoconductor was prepared in the same manner as in Example 1 except that the photoconductor was formed.

The electrophotographic photosensitive member thus manufactured was subjected to image evaluation by a laser beam printer having the above-mentioned structure. Furthermore, in terms of image gradation, the highlight part could be reproduced clearly. Further, even in a high humidity environment, durability stability including cleaning property could be confirmed.

(Example 5) The surface protection layer of the electrophotographic photosensitive member of Example 4 was not provided, and the polytetrafluoroethylene particles (average primary particle size 0.3 µm) were 10 in the charge transport layer.
%, Except under the same conditions as in Example 4,
The image output was evaluated.

Example 6 Under the same conditions as in Example 4, except that the average primary particle size of the polytetrafluoroethylene particles in the surface protective layer of the electrophotographic photosensitive member of Example 4 was 0.1 μm. The images were evaluated.

[Second Embodiment] The first embodiment is 200 li
I mentioned the case of ne / inch, but with a higher resolution of 40
Even at 0 line / inch and 600 line / inch, the same relationship was established for S and S ', and the highlight part was reproduced well.

[Third Embodiment] Contrary to the first and second embodiments, low resolution 100 line / inch, 133 line / inc.
Similarly, at h, S '/ S <1/2 was established and the highlight part was reproduced well.

[0101]

As described above, the photosensitive layer on the surface of the photosensitive layer on the conductive support contains a conductive metal powder having a primary particle diameter of 0.3 μm or less or a fluororesin on the photosensitive layer. In an image forming apparatus that forms an electrostatic latent image by using a laser beam, when the area of a basic pixel unit is S and the laser beam area on the surface of the photoconductor is S ′, S ′ / S <1/2
By so setting, the highlight part can be reproduced well in the image gradation.

[Brief description of drawings]

FIG. 1 is a sectional view of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of an image processing unit of the apparatus.

FIG. 3 is a timing chart of the image processing unit of the apparatus.

FIG. 4 is a diagram showing sensitometry of an image processing unit of the apparatus.

FIG. 5 is a diagram illustrating latent image formation at 200 lines / inch in the apparatus.

FIG. 6 is a graph showing the relationship between the number of lines, the laser beam area on the photosensitive drum, and the reproduction of the highlight portion in the same apparatus.

FIG. 7 is a diagram illustrating an example of a conventional image forming apparatus.

[Explanation of symbols]

 1 Photosensitive drum (photoreceptor)

Claims (3)

[Claims] 1. A laser beam is applied to a photosensitive body containing a conductive metal powder having a primary particle diameter of 0.3 μm or less or a fluorine-based resin in the surface layer of the photosensitive layer on the conductive support, using a laser beam. In an image forming apparatus for forming a latent image, when the area of a basic pixel unit is S and the laser beam area on the photoconductor surface is S ′, S ′ / S <1/2 Forming equipment. 2. The image forming apparatus according to claim 1, wherein a plurality of electrostatic latent images are visualized by a developing means and are superposed to form a color image. 3. The image forming apparatus according to claim 1, wherein the electrostatic latent image is visualized by developing means, and the developing by the developing means is reversal development.