JP2003107759A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device equipped with a single-layer type photoreceptor drum the sensitivity deterioration of which is restrained even in the case exposure is small when a photoreceptive layer becomes a thin film, made excellent in gradation expression over a long term and capable of forming a high-quality image free from the lowering of image density. SOLUTION: This image forming device is provided with the organic photoreceptor drum on which an electrostatic latent image is formed, and at least an electrifying means for electrifying the surface of the organic photoreceptor drum to be positive, an exposure means, a reversal developing means and a transfer means on the outer periphery of the photoreceptor drum. In the device, the exposure means has a driving circuit for multi-valued modulation equal to or above the binary one, and the photoreceptor drum is equipped with a single photoreceptive layer consisting of binder resin incorporating at least a charge generating agent, a Hall transporting agent and an electron transporting agent on conductive base substance, and the weight ratio of the electron transporting agent to the Hall transporting agent is >=0.7.

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 such as a copying machine, a printer or a facsimile, which uses a single-layer type organic photosensitive drum. More specifically, the present invention relates to a reversal development type digital image forming apparatus using a single-layer organic photosensitive drum.

[0002]

2. Description of the Related Art In the above digital image forming apparatus,
Various photoconductors having sensitivity in the light source wavelength region of the exposure means used in the apparatus are used. One is an inorganic photoreceptor using an inorganic material such as selenium in the photosensitive layer, and the other is an organic photoreceptor using an organic material in the photosensitive layer (OP
C). Of these, organic photoreceptors are easier to manufacture than inorganic photoreceptors, and there are a wide range of choices for photoreceptor materials such as charge transport agents, charge generators, binder resins, etc., and high flexibility in functional design. Therefore, extensive research has been advanced in recent years.

The organic photoreceptor has a so-called laminated type photoreceptor having a laminated structure of a charge generating layer containing a charge generating agent and a charge transporting layer containing a charge transferring agent, a charge generating agent and a charge transferring agent. Is a single-layer type photoconductor in which is dispersed in a single photosensitive layer. The multilayer photoreceptor is a negative charging type in which a charge generation layer and a charge transport layer are sequentially laminated on a conductive substrate, and the single-layer photoreceptor is generally used as a positive charging type.
Laminated photoreceptors occupy a wide market size.

However, the single-layer type photoconductor has a simple layer structure and is excellent in productivity, can suppress the occurrence of film defects in the photosensitive layer, and has a small number of interfaces between layers, so that the optical characteristics can be improved. High resolution is possible, often used with positive charging, less ozone is generated in the image forming device,
Due to such advantages, the market is expanding due to rapid research and development, which is in the spotlight.

On the other hand, as the exposure means of the digital image forming apparatus, a light emitting element array having a plurality of LED elements, which can be reduced in cost, power consumption, and space, as compared with a semiconductor laser, is used. Things are being reviewed. Further, in digital image formation, reproduction of halftones by controlling the exposure amount of the exposure means is an important issue. In particular, with respect to a color image forming apparatus, in recent years, high image quality including color reproduction has been desired, and various halftone printing methods have been developed.

The halftone printing method includes, for example, an energy gradation method and an area gradation method. The energy gradation method is a method of expressing gradation by controlling the amount of energy according to the current value applied to the light emitting element and its time, and changing the size of the printing pixel. The print data of bits is given to the light emitting element. Further, in the case of controlling the current value, the number of constant current power supplies according to the number of gradations is provided.

The area gradation method is a method in which one pixel is composed of a plurality of printing dots and gradation is expressed by controlling the number of printing dots, and binary printing data is given to a light emitting element. For example, in the case of expressing with 16 gradations, in the case of forming a matrix of 4 in the main scanning direction × 4 in the sub scanning direction, 16-bit printing data is required. Also,
As one type of such area gradation method, there is also a method of expressing gradation by changing only the number of printing dots in the sub-scanning direction. Such a method is used in the case of expressing a smooth curve (smoothing). Are suitable.

[0008]

As an example, a tandem full-color image forming apparatus can be cited as a reversal developing type digital image forming apparatus. For example, specifically, multiple LEDs (light emitting diodes) driven by image signals
A light emitting element array having a light emitting element such as an element, a photoconductor that receives light from the light emitting element array, a developing device that develops an electrostatic latent image formed on the photoconductor that receives light from the light emitting element array, and For example, yellow (Y), magenta (M), cyan (C), and black are constituent elements for performing a single-color image forming operation such as a transfer device that transfers a toner image formed by development onto a predetermined recording paper. The color image forming apparatus is provided for each color image signal of (K) and repeatedly performs the operations from the formation of the electrostatic latent image to at least the transfer for each color. When a positively charged single-layer type photoreceptor is used in the color image forming apparatus of the above example, in order to reproduce halftones, for example, when the light amount of the light emitting element is controlled to be small by the gradation method as described above, It was found from the study by the present inventors that the image density is likely to decrease with the increase.

3 and 4, each exposure amount (0.5, 1.0 μ
The relationship between the photosensitive layer average film thickness of the single-layer type photoreceptor at J / cm ² ) and the post-exposure potential is shown. As is clear from the figure, especially when the exposure amount is small, the post-exposure potential increases with a small film thickness (the film thickness dependency is large), and the sensitivity tends to deteriorate.

That is, as the number of printed sheets increases, the surface of the photosensitive layer is gradually scraped off and thinned by a cleaning blade for removing untransferred toner remaining on the surface of the photosensitive member, and the exposure amount is reduced to reproduce halftone. In case,
It is considered that the deterioration of the sensitivity became remarkable and the image density decreased. As described above, the image density is lowered due to the deterioration of the sensitivity of the photoconductor, and it is difficult to obtain a high-quality color image even when used in an image forming apparatus of a system excellent in gradation reproduction.

Therefore, an object of the present invention is to provide a single-layer type photosensitive drum which has a small sensitivity deterioration even when the exposure amount is small when the film is thinned, that is, the film thickness dependence is small, and can express a gradation for a long period of time. An object of the present invention is to provide an image forming apparatus capable of forming a high-quality image that is excellent and does not cause a reduction in image density.

[0012]

DISCLOSURE OF THE INVENTION The present inventors have found that an organic photoconductor drum for forming an electrostatic latent image and a charging means for positively charging at least the surface of the organic photoconductor on the outer periphery of the organic photoconductor drum. And an exposure unit, a reversal developing unit, and a transfer unit, the exposure unit is
The organic photosensitive drum has a multi-value modulation driving circuit of three or more values, and the organic photosensitive drum is composed of a single binder resin containing at least a charge generating agent, a hole transferring material, and an electron transferring material on a conductive substrate. An image forming apparatus comprising a photosensitive layer and having a weight ratio of an electron transporting agent to a hole transporting agent of 0.7 or more is excellent in gradation expression for a long period of time.
Moreover, they have found that it is possible to provide a high-quality image without a decrease in image density.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The image forming apparatus of the present invention comprises an organic photoconductor drum for forming an electrostatic latent image and a charging means for positively charging at least the surface of the organic photoconductor on the outer periphery of the organic photoconductor drum. And an exposure unit, a reversal developing unit, and a transfer unit, the exposure unit includes a multi-value modulation driving circuit of three or more values.

As described above, typical halftone printing methods include the energy gradation method and the area gradation method. In the color image forming apparatus of the present invention, in addition, an arbitrary halftone printing method such as a density pattern method, a dither method, an error diffusion method, an FM screening method, a CNN halftone reproduction method can be used. Further, these halftone printing methods can be used alone or in combination of two or more methods.

On the other hand, the single-layer type organic photoconductor used in the image forming apparatus of the present invention is a positive charging type and has at least a charge generating agent, a hole transporting agent and an electron transporting agent on a conductive substrate. And a weight ratio of the electron transfer agent to the hole transfer agent is 0.7 or more.

In the positively charged single-layer type photoconductor, the electrons and holes generated in the vicinity of the surface of the photosensitive layer by exposure are hopping-conducted between the molecules of the hole transfer agent, and the electrons are transferred to the side of the conductive substrate. Hopping conduction occurs between the molecules to move to the surface of the photosensitive layer, and electrons cancel the positive charge on the surface of the photosensitive layer to form an electrostatic latent image. And
When the movement of holes and electrons is rate-determining, the sensitivity of the photoconductor deteriorates.

When the thickness of the photosensitive layer is large, electrons and holes are generated in the vicinity of the surface of the photosensitive layer as described above, so that the electron moving distance is shorter than the hole moving distance. Generally, the mobility of the electron transfer material is very small as compared with the mobility of the hole transfer material, but sufficient sensitivity is exhibited due to the short electron transfer distance as described above. However, if the photosensitive layer is shaved and thinned, the distance traveled by the holes and the distance traveled by the electrons gradually become equal.
By increasing the content of the electron transfer agent, the distance between the electron transfer agent molecules dispersed in the binder resin is shortened,
It is necessary to promote the movement of electrons.

Therefore, it is considered that the smaller the weight ratio of the electron transfer agent to the hole transfer agent is, the more the sensitivity tends to be deteriorated when the exposure amount is small when the photosensitive layer is scraped and thinned.

The mobility of the electron transfer material of the single-layer type organic photoreceptor used in the image forming apparatus of the present invention is 1.0 × 10 ^-8 c.
m ² / V / sec or more (electric field strength: 5 × 10 ⁵ V / cm)
Is preferred. This is because the photosensitive layer is thinned,
This is because, when the electron moving distance and the hole moving distance are gradually equalized, the sensitivity deterioration is reduced by increasing the mobility of the electron transferring material in addition to increasing the content of the electron transferring material.

The solid content concentration of the binder resin of the single-layer organic photoreceptor used in the image forming apparatus of the present invention is preferably 50 wt% or more and 70 wt% or less of the total solid content concentration. This is because the wear resistance of the photosensitive layer is improved as the solid content concentration of the charge transport agent is smaller, that is, the solid content concentration of the binder resin is larger, and a high-quality color image can be obtained for a long period of time. Further, by using the electron transfer agent having high mobility as described above, the sensitivity deterioration is lessened even if the solid content concentration of the binder resin is reduced.

Further, the binder resin preferably contains a polycarbonate resin represented by the general formula [1] or the general formula [2] as a main component. The polycarbonate resin is effective in improving the abrasion resistance of the photosensitive layer.

General formula [1];

[Chemical 3] (In the general formula [1], R ¹⁰ and R ¹¹ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.
R ^12, R ¹³ are the same or different and are hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group, R ^14, R
¹⁵ is the same or different and represents an alkyl group having 1 to 3 carbon atoms, a phenyl group, or a cycloalkylidene group which may form a ring and may have a substituent. However, 0.05 ≦
m / [m + n] ≦ 0.4)

General formula [2];

[Chemical 4] (In the general formula [2], R ²⁰ and R ²¹ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.)

Next, a specific embodiment of the present invention will be described. <Image forming apparatus> The image forming apparatus of the present invention is
As described above, an organic photoconductor drum that forms an electrostatic latent image, a charging unit that positively charges at least the surface of the organic photoconductor to the outer periphery of the organic photoconductor drum, an exposure unit, a reversal developing unit, and a transfer. In the image forming apparatus having the means, the exposing means has a multi-value modulation driving circuit of three values or more.

Further, the exposing means includes a light emitting element array in which a plurality of light emitting elements (for example, LEDs) are linearly arranged, and three or more values for controlling energy given to the light emitting elements according to print data. The present invention is effective in the case of having the multi-valued modulation driving circuit. As described above, the light emitting element array using LEDs as the exposure means has various advantages as compared with the semiconductor laser, but conversely, the exposure amount becomes small and the exposure wavelength shifts to the short wavelength side. There is a tendency. For this reason, for example, when a single-layer type photoconductor using a phthalocyanine pigment as a charge generating agent, which will be described later, is mounted on an image forming apparatus having an LED as an exposure means, when the exposure amount is small, the photosensitive layer is scraped and thinned. In this case, it is expected that there will be a problem that the sensitivity will become more prominent.

As an example, FIG. 1 is a side view showing a tandem full-color image forming apparatus 19 embodying the present invention, and FIG. 2 is a front view seen from the X direction in FIG. The color image forming apparatus 19 is an apparatus that adopts a tandem system that forms a color image of four colors of Y (yellow), M (magenta), C (cyan), and K (black), and roughly four emission lights. Anode-side circuit board 1 on which element arrays (3Y, 3M, 3C, 3K) are arranged, cathode-side circuit board 2, lens array 4, first holder 5, four single-layer organic photosensitive drums (9Y) , 9M, 9C, 9K), 4 developing devices (10Y, 10M, 10C, 10K), transfer belt 11, 4 cleanings (14Y, 14M, 14)
C, 14K), four chargers (15Y, 15M, 15
C, 15K) and the second holder 17 are included.

Each light emitting element row (3Y, 3M, 3C, 3K)
Is formed by arranging a plurality of LED array chips, each of which is composed of a plurality of linearly arranged LED elements, in a line, and is driven by a color image signal of each color. On the single circuit board 1, each light emitting element row (3Y, 3M, 3C, 3
K) are arranged parallel to each other at a predetermined distance. For example,
The distance between adjacent light emitting element rows is 50 mm to 100 mm
The arrangement direction of the four light emitting element rows, that is, FIG.
The length of the circuit board 1 along the left-right direction on the paper surface is about 2
It is selected from 00 mm to 400 mm. On the circuit board 1,
The circuit board 2 is arranged so as to sandwich the light emitting element rows (3Y, 3M, 3C, 3K).

Each light emitting element row (3Y, 3M, 3C, 3K)
The light from is emitted to each of the photoconductor drums (9Y, 9M, 9C, 9K) via the lens array 4. The lens array 4 includes, for example, a plurality of lenses 4a respectively arranged on the optical axis of the LED element, and is formed by integrally forming these lenses 4a. The lens array 4 is not limited to the lens 4a integrally formed and may be an individual lens.

The circuit boards 1 and 2 and the lens array 4
Are held by the first holder 5. Here, the light irradiation direction of the light emitting element rows (3Y, 3M, 3C, 3K) and the optical axis direction of the lens 4a of the lens array 4 are aligned so as to substantially coincide with each other. The first holder 5 also
As shown in FIG. 2, each LDE array (3Y, 3M, 3
For each of (C, 3K), a partition plate 6 for shielding light from an adjacent LED element and a spacer 7 provided with a roller 8 for abutting the single-layer type organic photosensitive drum at the tip thereof are provided. By the spacer 7, each light emitting element row (3Y, 3Y
M, 3C, 3K) and single-layer type organic photoconductor drums (9Y, 9)
M, 9C, 9K) can be kept substantially constant.

Further, the light emitting element rows (3Y, 3M, 3C, 3
K) and I for individually selectively controlling the light emission of the light emitting elements
A multi-valued modulation drive circuit, which comprises a C chip, has a plurality of stages of shift registers and a plurality of switching elements in the IC chip, and controls the energy given to the light emitting element according to the print data for energy gradation. And a binary modulation drive circuit which uses a part of the shift register and the switching element of the multi-value modulation drive circuit and turns on / off the light emitting element according to the print data for area gradation.

According to the above structure, the light emitting element of the light emitting section is
Light is emitted by the energy according to the print data for energy gradation, and thus, the printing by the energy gradation method can be realized. Further, the light emitting element is turned on / off according to the printing data for area gradation, and thus, the printing by the area gradation method can be realized. One drive circuit for controlling the energy to be applied to the element in accordance with such multivalued energy gradation and binary area printing data for area gradation
Since it can be provided on the C chip, it is possible to reduce the size of the exposure apparatus.

Next, each single-layer type organic photoconductor drum (9Y,
9M, 9C, 9K), each light emitting element row (3Y,
3M, 3C, 3K), the electrostatic latent image forming position where the electrostatic latent image is formed is set. The diameter of each single-layer organic photosensitive drum (9Y, 9M, 9C, 9K) is selected to be, for example, 16 mm to 30 mm.

Each single layer type organic photoconductor drum (9Y, 9M,
9C and 9K), the developing device (10
Y, 10M, 10C, 10K), the transfer belt 11, the cleaning (14Y, 14M, 14C, 14K) and the charger (15Y, 15M, 15C, 15K), respectively. The transfer belt 11 is commonly provided for the four single-layer organic photosensitive drums (9Y, 9M, 9C, 9K).

The single-layer type organic photosensitive drum (9Y, 9
M, 9C, 9K) is held by the second holder 17. Specifically, the second holder 17 has four engaging pieces 18 which are respectively engaged with the rotary shafts 16 of the single-layer organic photosensitive drums (9Y, 9M, 9C, 9K). The second holder 17 is also fixed to the first holder 5. Here, each single-layer organic photoconductor drum (9Y, 9M, 9C, 9Y
K) rotation axis direction and each light emitting element row (3Y, 3M, 3).
The LEDs are aligned so that the arrangement directions of the LED elements (C, 3K) substantially coincide with each other.

A color image is formed in the order of Y, M, C and K. First, the single layer type organic photosensitive drum 9 which is positively charged (for example, +400 V) by the charger 15Y.
The outer peripheral surface of Y is irradiated with the light from the first light emitting element array 3Y controlled as described above to form an electrostatic latent image. The electrostatic latent image is developed with the Y toner by the developing device 10Y to form a toner image. The toner image is transferred by the roller 13 to the transfer belt 11 that is in contact with the single-layer organic photosensitive drum 9Y.

Next, an electrostatic latent image is formed on the outer peripheral surface of the single-layer type organic photosensitive drum 9M positively charged by the charger 15M by the light from the second light emitting element array 3M controlled as described above. Is formed and is developed with the toner of M by the developing device 10M to form a toner image.
Transferred to 1. Similarly, the C and K toner images are transferred to the transfer belt 11. The toner image transferred to the transfer belt 11 is further transferred and fixed on a predetermined recording paper 24 to form a color image.

After the transfer is completed, the single-layer type organic photosensitive drum 9 is formed.
Excessive toner attached to Y, 9M, 9C and 9K is removed by cleaners 14Y, 14M, 14C and 14K, and is again positively charged by chargers 15Y, 15M, 15C and 15K.

<Single Layer Type Organic Photoreceptor> The present invention comprises a single photosensitive layer comprising a binder resin containing at least a charge generating agent, a hole transfer agent and an electron transfer agent on a conductive substrate. An image forming apparatus using a single-layer type organic photosensitive drum, characterized in that a weight ratio of the electron transferring material to the hole transferring material is 0.7 or more. The constituent materials of the single-layer organic photosensitive drum used in the image forming apparatus of the present invention will be described in detail below.

[Binder Resin] As the binder resin of the single-layer type organic photoreceptor, a conventionally known binder resin can be used. For example, polycarbonate resin, polyester resin, polyarylate resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, acrylic copolymer, styrene-acrylic acid copolymer, polyethylene ,
Ethylene-vinyl acetate copolymer, chlorinated polyethylene,
Polyvinyl chloride, polypropylene, ionomer, vinyl chloride-vinyl acetate copolymer, alkyd resin, polyamide, polyurethane, polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, thermoplastic resin such as polyether resin, silicone resin, epoxy Resins such as resins, phenolic resins, urea resins, melamine resins, other crosslinkable thermosetting resins, and photocurable resins such as epoxy acrylate and urethane-acrylate can be used.

Further, as described above, the solid content concentration of the binder resin is 50 wt% or more and 70 w of the total solid content concentration.
It is preferably t% or less. Assuming that the single-layer type photoconductor is composed of only the charge generating agent, the hole transporting agent, the electron transporting agent, and the binder resin, the solid content concentration of the binder resin is calculated by the following equation.

[Solid content of binder resin (wt
%)] = [Binder resin content] / [(charge generating agent content) + (hole transport agent content) + (electron transport agent content) + (binder resin content)] × 100

In the above formula, the contents of the hole transfer material and the electron transfer material have a great influence on the abrasion resistance of the photosensitive layer. That is, these low molecular weight compounds act as a plasticizer in the binder resin, and the wear resistance of the photosensitive layer deteriorates as the content increases. For example, when the binder resin content is 100 parts by weight and the charge generating agent content is 2.5 parts by weight, the sum of the hole transfer agent content and the electron transfer agent content is approximately 40 parts by weight or more and 95 parts by weight or less. The following are preferred.

As described above, the binder resin preferably contains a polycarbonate resin represented by the general formula [1] or the general formula [2] as a main component.

In order to prevent blade squeaking and blade curling up, for example, a binder resin having the following repeating structural unit may be contained in the range of 0.05 to 10 wt%.

[Chemical 5]

All of the binder resins exemplified above can be used alone or by blending or copolymerizing two or more kinds. The weight average molecular weight of all of the above binder resins is 10,000 to 400,000, more preferably 30,000.
˜200,000 is preferable.

[Charge Generating Agent] Examples of the charge generating agent include phthalocyanine-based pigments such as metal-free phthalocyanine, oxotitanyl phthalocyanine, and hydroxygallium phthalocyanine, perylene-based pigments, bisazo pigments, dioketopyrrolopyrrole pigments, and metal-free naphthalocyanines. Pigments,
Organics such as metal naphthalocyanine pigments, squaraine pigments, trisazo pigments, indigo pigments, azurenium pigments, cyanine pigments, pyrylium pigments, anthanthrone pigments, triphenylmethane pigments, threne pigments, toluidine pigments, pyrazoline pigments, quinacridone pigments Known charge generating agents such as photoconductors and inorganic photoconductive materials such as selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, and amorphous silicon can be used. The charge generating agents exemplified above may be used alone or in combination of two or more so as to have an absorption wavelength in a desired region.

Since the image forming apparatus of the present invention is a reversal developing system, it is preferably a digital optical system. Among the charge generating agents exemplified above, particularly in an image forming apparatus of a digital optical system using a light source such as an LED element or a semiconductor laser, a photoreceptor having sensitivity in a wavelength region of 600 nm or more is required. Phthalocinin-based pigments such as metal-free phthalocyanine, oxotitanyl phthalocyanine, and hydroxygallium phthalocyanine are preferably used. The crystal type of the phthalocyanine-based pigment is not particularly limited, and various types can be used.

The charge generating agent is 0.1 to 50 wt% or more and 70 wt% or less with respect to the total weight of the binder resin, and further 0.1.
It is preferable to contain 5 to 10 wt%.

[Charge Transporting Agent] The single-layer type organic photoreceptor used in the color image forming apparatus of the present invention comprises a single photosensitive material composed of a binder resin containing a charge generating agent, a hole transporting agent and an electron transporting agent. A layer is provided, and the weight ratio of the electron transfer material to the hole transfer material is 0.7 or more. When the weight ratio of the electron transfer material is smaller than 0.7, as described above, when the exposure amount is small, the movement of electrons is rate-determining and the sensitivity is largely deteriorated as the photosensitive layer is scraped and the film thickness is reduced. Become.

[Hole Transport Agent] As the hole transport agent,
Conventionally known hole transport agents can be used, for example,
N, N, N ', N'-tetraphenylbenzidine derivative, N, N, N', N'-tetraphenylphenylenediamine derivative, N, N, N ', N'-tetraphenylnaphthylenediamine derivative, N, N, N ', N'-tetraphenylphenanthrylenediamine derivatives, oxadiazole compounds such as 2,5-di (4-methylaminophenyl) -1,3,4-oxadiazole, 9- (4 -Diethylaminostyryl) anthracene and other styryl compounds, polyvinylcarbazole and other carbazole compounds, organic polysilane compounds, 1-phenyl-3- (p-
Including pyrazoline compounds such as dimethylaminophenyl) pyrazolin, hydrazone compounds, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, triazole compounds, etc. Examples include nitrogen cyclic compounds and condensed polycyclic compounds.

In particular, it is preferable that the hole transport material contains a compound represented by the general formula [3], the general formula [4], the general formula [5] or the general formula [6].

General formula [3];

[Chemical 6] (In the general formula [3], R ³⁰ , R ³¹ , R ^32, and R ³³ are the same or different and each represents an alkyl group, an alkoxy group, an aryl group, an aralkyl group, or a halogen atom;
n, p and q are the same or different and each represents an integer of 0 to 3. R ³⁴ and R ³⁵ are the same or different and each represents a hydrogen atom or an alkyl group. Also, -X- is

[Chemical 7] Or

[Chemical 8] Indicates. )

General formula [4];

[Chemical 9] (In the general formula [4], R ⁴⁰ and R ⁴² are the same or different and each represents an alkyl group which may have a substituent, and R ⁴¹ and R ^42
43 is the same or different and represents a hydrogen atom or an alkyl group which may have a substituent. )

General formula [5];

[Chemical 10] (In the general formula [5], R ⁵⁰ , R ⁵¹ , R ⁵² , R ⁵³ and R ^53
54 is the same or different and is a hydrogen atom, a halogen atom,
An alkyl group or an alkoxy group which may have a substituent is shown. )

General formula [6];

[Chemical 11] (In the general formula [6], R ⁶⁰ , R ⁶¹ , R ⁶² and R ⁶³ are the same or different and may have a halogen atom or a substituent,
An alkyl group, an alkoxy group or an aryl group is shown.
a, b, c and d are the same or different and each represents an integer of 0-5. When a, b, c or d is 2 or more, each R
⁶⁰ , R ⁶¹ , R ⁶² and R ⁶³ may be different. )

The hole-transporting agents represented by the general formulas [3] to [6] are effective in improving the sensitivity of the photoconductor because they efficiently transport holes, and show sufficient practical sensitivity even with a small content. .

In the present invention, all the hole-transporting agents exemplified above may be used alone or in combination of two or more.

[Electron Transfer Agent] As the electron transfer agent, conventionally known electron transfer agents can be used, and examples thereof include diphenoquinone derivatives, benzoquinone derivatives, azoquinone derivatives, monoquinone derivatives, dinaphthylquinone derivatives, and the like.
Tetracarboxylic acid diimide derivative, carboxylic acid imide derivative, stilbenquinone derivative, anthraquinone derivative, malononitrile derivative, thiopyran derivative, trinitrothioxanthone derivative, 3,4,5,7-tetranitro-9-fluorenone derivative, dinitroanthracene derivative, dinitroacridine Derivatives, nitroanthraquinone derivatives, dinitroanthraquinone derivatives, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, dibromo Examples thereof include various compounds having an electron accepting property such as maleic anhydride.

In particular, the electron transfer agent is represented by the general formula [7], the general formula [8], the general formula [9], the general formula [10], the general formula [1].
1], the general formula [12], the general formula [13] or the general formula [14] is preferably contained.
These electron transfer agents have a mobility of 1.0 × 10 ⁻⁸ cm ² / V / sec or more at an electric field strength of 5 × 10 ⁵ V / cm, and are effective in improving sensitivity.

General formula [7];

[Chemical 12] (In the general formula [7], R ⁷⁰ and R ⁷¹ are the same or different and each represents an alkyl group which may have a substituent.)

General formula [8];

[Chemical 13] (In the general formula [8], R ⁸⁰ and R ⁸¹ are the same or different and each represents a monovalent hydrocarbon group which may have a substituent.)

General formula [9];

[Chemical 14] (In the general formula [9], R ⁹⁰ represents a halogen atom, an alkyl group or an aryl group which may have a substituent, and R ⁹¹ represents an alkyl group or an aryl group which may have a substituent, or a group: .R ^91a showing a -O-R ^91a represents an alkyl group or an aryl group which may have a substituent.)

General formula [10];

[Chemical 15] (In the general formula [10], R ¹⁰⁰ , R ¹⁰¹ , R ¹⁰² , and R ¹⁰³ are
The same or different alkyl groups which may have a substituent are shown. )

General formula [11];

[Chemical 16] (In the general formula [11], R ¹¹⁰ and R ¹¹¹ are the same or different and each is a hydrogen atom, an alkyl group having 1 to 12 carbons, or a carbon number 1
To 12 are an alkoxy group, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent and a halogenated alkyl group. The substituent is a halogen atom, an alkoxy group having 1 to 6 carbon atoms, a water acidic group, a cyano group, an amino group, a nitro group or a halogenated alkyl group. )

General formula [12];

[Chemical 17] (In the general formula [12], R ^{120 to} R ¹²³ are the same or different and each is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or 1 carbon atom.
To 12 are an alkoxy group, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent and a halogenated alkyl group. The substituent is a halogen atom, an alkoxy group having 1 to 6 carbon atoms, a water acidic group, a cyano group, an amino group, a nitro group or a halogenated alkyl group. )

General formula [13];

[Chemical 18] (In the general formula [13], R ¹³⁰ and R ¹³¹ are the same or different and each is a hydrogen atom, an alkyl group having 1 to 12 carbons, or a carbon number 1
To 12 are an alkoxy group, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent and a halogenated alkyl group. R ^{132 to} R ¹³⁶ are
Identical or different, hydrogen atom, halogen atom, carbon number 1
~ 12 alkyl groups, C 1-12 alkoxy groups,
It represents an aralkyl group which may have a substituent, a phenoxy group which may have a substituent, or a halogenated alkyl group, and two or more groups may be bonded to form a ring. The substituent is a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a water acidic group, a cyano group, an amino group, a nitro group, or a halogenated alkyl group. )

General formula [14];

[Chemical 19] (In the general formula [14], R ^{140 to} R ¹⁴³ are the same or different and each is a hydrogen atom, an alkyl group having 1 to 12 carbons, or 1 carbon atom.
To 12 are an alkoxy group, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent and a halogenated alkyl group. R ¹⁴⁴ and R ¹⁴⁵ are
The same or different, a hydrogen atom and a C1-C12 alkyl group are shown. R ^{146 to} R ¹⁵³ are the same or different and each is a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group which may have a substituent, a halogenated alkyl group. Indicates. The substituent is a halogen atom, an alkyl group having 1 to 6 carbon atoms, or 1 to 6 carbon atoms.
Represents an alkoxy group, a water acidic group, a cyano group, an amino group, a nitro group, and a halogenated alkyl group. )

In the present invention, all the electron transfer agents exemplified above may be used alone or in combination of two or more.

[Photoreceptor Drum] The initial photosensitive layer thickness of the single-layer type photoreceptor is preferably 5 to 100 μm, more preferably 25 to 50 μm.

In the photosensitive layer, in addition to the above-mentioned components, various conventionally known additives such as an antioxidant, a radical scavenger, a singlet quencher, etc. may be added as long as the electrophotographic characteristics are not adversely affected. Deterioration inhibitors such as UV absorbers, softeners,
A plasticizer, a surface modifier, a bulking agent, a thickener, a dispersion stabilizer, a wax, an acceptor, a donor and the like can be added. In order to improve the sensitivity of the photosensitive layer, for example,
Known sensitizers such as terphenyl, halonaphthoquinones, and acenaphthylene may be used in combination with the charge generating agent.

A barrier layer may be formed between the support and the photosensitive layer as long as the characteristics of the photosensitive member are not impaired.

As the support on which the photosensitive layer is formed, various conductive materials can be used.
Iron, aluminum, copper, tin, platinum, silver, vanadium,
Molybdenum, chromium, cadmium, titanium, nickel,
Examples include simple metals such as palladium, indium, stainless steel, and brass, plastic materials obtained by vapor deposition or lamination of the above metals, and glass covered with aluminum iodide, tin oxide, indium oxide, or the like.

The shape of the support may be drum-like or sheet-like, and it is sufficient that the support itself has conductivity or the surface of the support has conductivity. In addition, the support preferably has sufficient mechanical strength when used.

When the photosensitive layer is formed by a coating method, the above-mentioned charge generating agent, charge transporting agent, binder resin and the like are used together with a suitable solvent by a known method, for example, a roll mill, a ball mill, an attritor, a paint coater. The dispersion may be prepared by dispersing and mixing using an acre, an ultrasonic disperser or the like, and the dispersion may be applied by a known means and dried.

As the solvent for preparing the above dispersion liquid, various organic solvents can be used. Examples thereof include alcohols such as methanol, ethanol, isopropanol and butanol, and aliphatic compounds such as n-hexane, octane and cyclohexane. Hydrocarbons, aromatic hydrocarbons such as benzene, toluene, xylene, halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, chlorobenzene, dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc. Ethers, acetone, ketones such as methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and methyl acetate, dimethylformaldehyde, dimethylformamide, dimethylsu Examples include luhoxide. These solvents may be used alone or in combination of two or more.

Further, in order to improve the dispersibility of the charge generating agent, the charge transporting agent and the like and the smoothness of the photosensitive layer surface, a surfactant, a leveling agent and the like may be used.

[0077]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to Examples and Comparative Examples. The following embodiments are examples of embodying the present invention, and do not limit the technical scope of the present invention.

<Production of Single Layer Type Photoreceptor> [Examples 1 to 3] [Comparative Examples 1 to 3] 2 parts by weight of a charge generating agent (X type metal-free phthalocyanine) and 60 parts by weight of a hole transferring material (HTM-1). Part, electron transfer agent (E
TM-1) 20 to 70 parts by weight, weight average molecular weight 100,
100 parts by weight of 000 binder resin (Resin-1) was dispersed or dissolved in a ball mill for 24 hours together with 700 parts by weight of tetrahydrofuran to prepare a single layer type photosensitive layer coating solution. Then, this coating solution is applied on an aluminum base tube as a support by a dip coating method, and hot air drying is performed at 120 ° C. for 40 minutes to obtain a photosensitive layer average film thickness of 40 μm, 35 μm, 30 μm, 25 μm, 20 μm.
m, 15 μm, and 12 μm single-layer type photoconductors were produced.

[HTM-1]

[Chemical 20]

[ETM-1]

[Chemical 21]

[Resin-1]

[Chemical formula 22]

<Sensitivity Evaluation Test> Gentec
Using an EC) drum sensitivity tester (trade name: Gentec Cynthia 30M), an applied voltage was applied to the single-layer type photoconductors of Examples and Comparative Examples to charge the surface thereof to + 800V.

Next, monochromatic light of a wavelength of 750 nm (half-width of 20 nm, light intensity of 20 μW) extracted from white light of a halogen lamp, which is an exposure light source of the above tester, using a bandpass filter was applied to the charged photoreceptor. Was exposed (exposure time: 40 msec) (exposure energy: 0.
5, 1.0 μJ / cm ² ).

Then, 500 msec from the start of exposure
The surface potential at the elapsed time was measured as the post-exposure potential (V). That is, the smaller the post-exposure potential, the higher the sensitivity of the photoreceptor.

The above evaluation results are shown in Tables 1 and 2.

[Table 1]

[0086]

[Table 2]

FIGS. 3 and 4 are graphs of the results of Tables 1 and 2 above, showing the respective exposure doses (0.5, 1.0 μJ /
3 is a graph showing the influence of the weight ratio of the electron transfer agent to the hole transfer agent (abbreviated as ETM / HTM weight ratio) on the sensitivity film thickness dependency in cm ² ).

5 and 6 show the respective exposure doses (0.5, 1.0 μ).
J / cm ² ), the rate of change in sensitivity when the average thickness of the photosensitive layer is decreased from 40 μm to 12 μm, and ETM / HT
It is a graph which shows the relationship with M weight ratio. The rate of change in sensitivity was calculated by the following formula, and 60% or less was acceptable and greater than 60% was not acceptable.

Sensitivity change rate [40 → 12 μm] (%) =
{[Residual potential (V) at photosensitive layer average film thickness 12 μm] −
[Residual potential (V) at average thickness of photosensitive layer of 40 μm]} ÷
[Residual potential (V) at average thickness of photosensitive layer of 40 μm] × 10
0

From FIGS. 3 and 4, the sensitivity film thickness dependency was large when the exposure amount was small, and the sensitivity became worse as the photosensitive layer film thickness became thinner.

From FIGS. 5 and 6, the sensitivity change rate was large when the exposure amount was small, and the sensitivity change rate was larger as the ETM / HTM weight ratio was smaller. However, when the ETM / HTM weight ratio is greater than 0.7, the exposure dose is 0.5 μJ / cm ²
However, the sensitivity change rate was 60% or less, and there was no problem.

<Image Evaluation Test> Single layer type photoconductors of Examples and Comparative Examples (drum samples having a photosensitive layer average film thickness of 12 μm)
1 was mounted on the tandem full-color image forming apparatus (with a sensitivity correction mechanism) shown in FIGS. 1 and 2, and a printing test of an image sample having a halftone was carried out, and the presence or absence of image density reduction was visually evaluated.

The results are shown in Table 3. Although the tandem full-color image forming apparatus has a sensitivity correction mechanism, the image density is lowered in the single-layer type photoconductors of Comparative Examples 1 to 3. This is because the sensitivity is so low that the sensitivity correction mechanism cannot handle it (photosensitive layer thickness 12 μm). On the other hand, with the single-layer type photoconductors of Examples 1 to 3, there was no reduction in image density, and high-quality color images could be obtained. That is, it is proved that the single-layer type photoconductors of Examples 1 to 3 do not have a decrease in image density even when the photosensitive layer has an average film thickness of 12 μm, and can form a high-quality color image for a long time. did.

[0094]

[Table 3]

[0095]

As described above, the organic photoconductor drum for forming an electrostatic latent image, the charging means for positively charging at least the surface of the organic photoconductor on the outer periphery of the organic photoconductor drum, the exposing means, and the reversal development. In the image forming apparatus having a transfer unit and a transfer unit, the exposure unit has a multi-value modulation driving circuit of three or more values, and the organic photoconductor drum has at least a charge generator and a hole transporter on a conductive substrate. An image forming apparatus comprising a single photosensitive layer made of a binder resin containing an agent and an electron transfer agent, wherein the weight ratio of the electron transfer agent to the hole transfer agent is 0.7 or more. As a result, it is possible to form a high-quality color image that is excellent in gradation expression and has no deterioration in image density.

[0096]

[Brief description of drawings]

FIG. 1 is a side view of a tandem full-color image forming apparatus embodying the present invention.

FIG. 2 is a front view seen from the X direction in FIG.

FIG. 3 is a graph showing the influence of the ETM / HTM weight ratio on the sensitivity film thickness dependency at an exposure dose of 0.5 μJ / cm ² .

FIG. 4 is a graph showing the effect of the ETM / HTM weight ratio on the sensitivity film thickness dependence at an exposure dose of 1.0 μJ / cm ² .

FIG. 5 is a graph showing the relationship between the sensitivity change rate and the ETM / HTM weight ratio when the photosensitive layer average film thickness is reduced from 40 μm to 12 μm at an exposure dose of 0.5 μJ / cm ² .

FIG. 6 is a graph showing the relationship between the sensitivity change rate and the ETM / HTM weight ratio when the average film thickness of the photosensitive layer is reduced from 40 μm to 12 μm at an exposure dose of 1.0 μJ / cm ² .

[0097]

[Explanation of symbols]

1, 2 circuit board 3Y, 3M, 3C, 3K Light emitting element array 9Y, 9M, 9C, 9K Single layer type organic photoconductor drum 10Y, 10M, 10C, 10K Developing device 19 Color image forming device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/043 F term (reference) 2H068 AA13 AA20 AA28 AA31 BA63 BA64 BB26 BB54 FA30 FB07 FB08 2H076 AB41 AB46 AB75

Claims (6)

[Claims] 1. An organic photosensitive drum for forming an electrostatic latent image,
In an image forming apparatus having, on the outer periphery of the organic photoconductor drum, at least a charging unit for positively charging the surface of the organic photoconductor, an exposing unit, a reversal developing unit, and a transferring unit, the exposing unit has a multivalue of three or more. The organic photosensitive drum has a value modulation drive circuit, and a single photosensitive layer made of a binder resin containing at least a charge generating agent, a hole transporting agent, and an electron transporting agent is provided on the conductive substrate.
The weight ratio of the electron transfer material to the hole transfer material is 0.7.
An image forming apparatus having the above. 2. The exposure means comprises a light emitting element array in which a plurality of light emitting elements are linearly arranged, and multi-valued modulation driving of three or more values for controlling energy applied to the light emitting elements according to print data. The image forming apparatus according to claim 1, further comprising a circuit. 3. The electric field strength of the electron transfer material is 5 × 10 ⁵ V
Mobility at 1.0 / cm is 1.0 × 10 ^-8 cm ² / V / s
The image forming apparatus according to claim 1, wherein the image forming apparatus has an ec or more. 4. The image forming apparatus according to claim 1, wherein the solid content concentration of the binder resin is 50 wt% or more and 70 wt% or less of the total solid content concentration. 5. The binder resin of the single-layer type photosensitive drum is mainly composed of a polycarbonate resin having a repeating structural unit represented by the general formula [1]. 4. The image forming apparatus according to item 4. General formula [1]; (In the general formula [1], R ¹⁰ and R ¹¹ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.
R ^12, R ¹³ are the same or different and are hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group, R ^14, R
¹⁵ is the same or different and represents an alkyl group having 1 to 3 carbon atoms, a phenyl group, or a cycloalkylidene group which may form a ring and may have a substituent. However, 0.05 ≦
m / [m + n] ≦ 0.4) 6. A polycarbonate having a repeating structural unit represented by the general formula [2] in place of the polycarbonate resin having the repeating structural unit represented by the general formula [1] as the binder resin of the single-layer type photosensitive drum. A resin as a main component, Claim 1, 2, 3 or 4.
The image forming apparatus described. General formula [2]; (In the general formula [2], R ²⁰ and R ²¹ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.)