JP7180175B2 - Image forming apparatus and image forming method - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming method.

Electrophotographic image forming apparatuses (for example, printers and multi-function peripherals) include an electrophotographic photoreceptor as an image carrier. An electrophotographic photoreceptor has a photosensitive layer. Electrophotographic photoreceptors include, for example, single-layer electrophotographic photoreceptors and laminated electrophotographic photoreceptors. A single-layer electrophotographic photoreceptor includes a single-layer photosensitive layer having a charge generation function and a charge transport function. A laminated electrophotographic photoreceptor includes a photosensitive layer including a charge generation layer having a charge generation function and a charge transport layer having a charge transport function.

The electrophotographic photoreceptor included in the image forming apparatus described in Patent Document 1 has a photosensitive layer containing an electron transport agent having a certain or higher electron mobility.

JP 2012-155202 A

However, the inventors of the present invention have found that the image forming apparatus described in Patent Document 1 has room for improvement in terms of the charging characteristics and sensitivity characteristics of the electrophotographic photosensitive member and the suppression of image ghosts caused by transfer memory. found.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus and an image forming method which are equipped with an electrophotographic photoreceptor having excellent charging characteristics and sensitivity characteristics and which can suppress image ghosts caused by transfer memory. is to provide

An image forming apparatus according to the present invention includes an image carrier, a charging unit that positively charges a surface of the image carrier, and an exposure unit that exposes the charged surface of the image carrier to expose the image carrier. An exposure unit that forms an electrostatic latent image on a surface, a development unit that supplies toner to the electrostatic latent image and develops the electrostatic latent image into a toner image, and a toner image on the image carrier. and a transfer unit for transferring onto a transfer body. The image carrier is a positively charged single-layer electrophotographic photoreceptor comprising a conductive substrate and a single-layered photosensitive layer, wherein the photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent and Contains a binder resin. The content of the charge generating agent in the photosensitive layer is 0.50% by mass or more and 1.50% by mass or less. Under the conditions of a temperature of 23° C. and an electric field strength of 1.5×10 ⁵ V/cm, the xerographic gain in the photosensitive layer is 32.0% or more, and the hole mobility in the photosensitive layer μ _h and electron mobility μ _e are both 1.0×10 ⁻⁷ cm ² /V/sec or more, and the ratio of the electron mobility μ _e to the hole mobility μ _h (μ _e /μ _h ) is 1/50.0 or more and 1/1.0 or less.

An image forming method of the present invention is an image forming method using the image forming apparatus described above. The image forming apparatus further includes a neutralization section that neutralizes the surface of the image carrier after the toner image has been transferred onto the transfer material. The image forming method of the present invention includes a charging step of positively charging the surface of the image carrier, and exposing the charged surface of the image carrier to an electrostatic charge on the surface of the image carrier. an exposure step of forming a latent image; a developing step of supplying toner to the electrostatic latent image to develop the electrostatic latent image into a toner image; and a discharging step of discharging the surface of the image bearing member after transferring the toner image onto the transfer receiving member. The time from when a predetermined portion of the surface of the image carrier is neutralized in the neutralization step until it is charged in the charging step is 200 milliseconds or less.

The image forming apparatus of the present invention includes an electrophotographic photoreceptor having excellent charging characteristics and sensitivity characteristics, and can suppress image ghosts caused by transfer memory. In the image forming method of the present invention, the electrophotographic photoreceptor to be used has excellent charging characteristics and sensitivity characteristics, and image ghosts caused by transfer memory can be suppressed.

1 is a partial cross-sectional view showing an example of the structure of a positive charging single-layer electrophotographic photosensitive member provided in the image forming apparatus according to the first exemplary embodiment of the present invention; FIG. 1 is a partial cross-sectional view showing an example of the structure of a positive charging single-layer electrophotographic photosensitive member provided in the image forming apparatus according to the first exemplary embodiment of the present invention; FIG. 1 is a partial cross-sectional view showing an example of the structure of a positive charging single-layer electrophotographic photosensitive member provided in the image forming apparatus according to the first exemplary embodiment of the present invention; FIG. 1 is a diagram showing an example of an image forming apparatus according to a first embodiment of the invention; FIG. FIG. 10 is a diagram showing an image in which an image ghost has occurred; 4 is a graph showing the relationship between the charge generating agent content measured in Examples and the xerographic gain. 4 is a graph showing the relationship between the xerographic gain measured in Examples and the post-exposure potential. 4 is a graph showing the relationship between the charge generating agent content measured in Examples and the charge potential. 4 is a graph showing the relationship between the process time measured in Examples and the charging potential. 4 is a graph showing the relationship between the process time measured in Examples and the charging potential. 4 is a graph showing post-exposure potentials measured in Examples. 4 is a graph showing post-exposure potentials measured in Examples.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is by no means limited to the following embodiments. The present invention can be implemented with appropriate modifications within the scope of the purpose of the present invention. It should be noted that descriptions of overlapping descriptions may be omitted as appropriate, but the gist of the invention is not limited.

Hereinafter, compounds and derivatives thereof may be collectively referred to by adding "system" to the name of the compound. In addition, when the name of a polymer is expressed by adding "system" to the name of a compound, it means that the repeating unit of the polymer is derived from the compound or its derivative.

Hereinafter, halogen atoms, alkyl groups having 1 to 8 carbon atoms, alkyl groups having 1 to 5 carbon atoms, alkyl groups having 1 to 4 carbon atoms, and alkoxy groups having 1 to 4 carbon atoms are , unless otherwise specified, have the following meanings.

Halogen atoms (halogen groups) include, for example, fluorine atoms (fluoro groups), chlorine atoms (chloro groups), bromine atoms (bromo groups) and iodine atoms (iodo groups).

The alkyl group having 1 to 8 carbon atoms, the alkyl group having 1 to 5 carbon atoms, or the alkyl group having 1 to 4 carbon atoms is each linear or branched and unsubstituted. Examples of alkyl groups having 1 to 8 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group and isopentyl. group, neopentyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, linear or branched hexyl group, linear or branched heptyl group, and linear or A branched octyl group is mentioned. Examples of alkyl groups having 1 to 5 carbon atoms or alkyl groups having 1 to 4 carbon atoms are groups having 1 to 5 carbon atoms among the groups described as examples of alkyl groups having 1 to 8 carbon atoms. They are the following groups or groups having 1 to 4 carbon atoms.

An alkoxy group having from 1 to 4 carbon atoms is linear or branched and unsubstituted. Examples of alkoxy groups having 1 to 4 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, and tert-butoxy groups.

<First Embodiment: Image Forming Apparatus>
The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that positively charges the surface of the image carrier, and exposes the charged surface of the image carrier to expose the surface of the image carrier to static electricity. An exposure unit that forms an electrostatic latent image, a development unit that supplies toner to the electrostatic latent image and develops the electrostatic latent image into a toner image, and a transfer unit that transfers the toner image from the image carrier to the transfer medium. and The image carrier is a positively charged single-layer electrophotographic photoreceptor (hereinafter sometimes referred to as a photoreceptor) including a conductive substrate and a photosensitive layer. The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent and a binder resin. The content of the charge generating agent in the photosensitive layer is 0.50% by mass or more and 1.50% by mass or less. Under the conditions of a temperature of 23° C. and an electric field strength of 1.5×10 ⁵ V/cm, the xerographic gain in the photosensitive layer is 32.0% or more, and the hole mobility μ _h and electron are all 1.0×10 ⁻⁷ cm ² /V/sec or more, and the ratio of the electron mobility _{μ e to} the hole mobility μ _h (μ _e /μ _h ) is 1/50.0 or more and 1/1.0 or less.

[Positive charging single-layer electrophotographic photoreceptor]
First, the photoreceptor provided as an image carrier in the image forming apparatus according to this embodiment will be described. 1, 2 and 3 are partial cross-sectional views showing the structure of the photoreceptor 1. FIG.

As shown in FIG. 1, the photoreceptor 1 includes, for example, a conductive substrate 2 and a photosensitive layer 3. As shown in FIG. The photosensitive layer 3 is a single layer (one layer). The photoreceptor 1 is a positively charged single-layer electrophotographic photoreceptor having a single photosensitive layer 3 .

As shown in FIG. 2, the photoreceptor 1 may include a conductive substrate 2, a photosensitive layer 3, and an intermediate layer 4 (undercoat layer). An intermediate layer 4 is provided between the conductive substrate 2 and the photosensitive layer 3 . The photosensitive layer 3 may be provided directly on the conductive substrate 2, as shown in FIG. Alternatively, as shown in FIG. 2, the photosensitive layer 3 may be provided on the conductive substrate 2 with the intermediate layer 4 interposed therebetween. The intermediate layer 4 may be a single layer or multiple layers.

As shown in FIG. 3, the photoreceptor 1 may comprise a conductive substrate 2, a photosensitive layer 3, and a protective layer 5. As shown in FIG. A protective layer 5 is provided on the photosensitive layer 3 . The protective layer 5 may be a single layer or multiple layers.

The thickness of the photosensitive layer 3 is not particularly limited as long as the function as the photosensitive layer 3 can be fully exhibited. The thickness of the photosensitive layer 3 is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 50 μm or less.

The structure of the photoreceptor 1 has been described above with reference to FIGS. 1 to 3. FIG. The photoreceptor will be described in more detail below.

[Conductive substrate]
The conductive substrate is not particularly limited as long as it can be used as the conductive substrate of the photoreceptor. At least the surface portion of the conductive substrate may be made of a conductive material. An example of the conductive substrate is a conductive substrate made of a conductive material. Another example of a conductive substrate is a conductive substrate coated with a material having electrical conductivity. Examples of electrically conductive materials include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass. These conductive materials may be used alone, or two or more of them may be used in combination (for example, as an alloy). Among these conductive materials, aluminum or an aluminum alloy is preferable because charge transfer from the photosensitive layer to the conductive substrate is favorable.

The shape of the conductive substrate is appropriately selected according to the structure of the image forming apparatus. Examples of the shape of the conductive substrate include a sheet shape and a drum shape. Moreover, the thickness of the conductive substrate is appropriately selected according to the shape of the conductive substrate.

[Photosensitive layer]
The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent and a binder resin. The photosensitive layer may further contain other components such as additives as optional components.

The present inventors set the content ratio of the charge generating agent in the photosensitive layer of the photoreceptor to a certain range, set the hole mobility μ _h and the electron mobility μ _e to a certain level or more, and set the electron mobility μ _e and By balancing the hole mobility _μh and keeping the xerographic gain at a certain level or higher, the charges (holes and electrons) generated in the photosensitive layer are efficiently transported and the residual charge is reduced. I found The inventors of the present invention have found that such a photoreceptor has excellent charging characteristics and sensitivity characteristics, and can suppress image ghosts caused by transfer memory by using it as an image carrier of an image forming apparatus.

More specifically, as described in the above-mentioned Patent Document 1, conventionally, in improving the function of the photosensitive layer, the charge mobility of the charge transport agent alone (the hole mobility of the hole transport agent and the electron The electron mobility of the transport agent) has attracted attention. Here, in the photoreceptor, electric charge is generated by exposure relatively near the surface of the photoreceptor layer. Of the generated charges, holes need to travel a relatively long distance to the conductive substrate, whereas electrons need only travel a relatively short distance to the surface of the photosensitive layer. Further, the hole mobility of the hole transport agent (for example, 1.0×10 ⁻⁵ (cm ² /V/sec) or more) tends to be higher than the electron mobility of the electron transport agent. Therefore, according to conventional knowledge, it is preferable to define the electron mobility of the electron transport agent to be significantly lower than the hole mobility of the hole transport material (for example, 1/20,000 times or more 1 /10 times or less).

However, as a result of intensive studies, the present inventors have found that the important factor in improving the charging characteristics of the photoreceptor, the suppression performance of transfer memory, and the sensitivity characteristics is not the charge mobility of the charge transport agent itself, but the hole transport. It has been found that the mobility of holes and electrons in a photosensitive layer in which the agent and the electron transport agent are mixed to form a system in which the two interact. The inventors have also found that of particular importance is the balance of hole and electron mobility throughout the photosensitive layer. The inventors have found that the hole mobility of the hole-transporting material need not be significantly higher than the electron mobility of the electron-transporting material, as in the prior art. In particular, in image forming apparatuses, there is a tendency to shorten the process time from static elimination to charging in the image forming process in order to meet demands for speeding up and space saving. Therefore, in the image forming apparatus, both the holes and electrons generated by photoexcitation in the charge removing process are sufficiently removed from the photosensitive layer (that is, they are transported to the surface of the photosensitive layer or the conductive substrate) before the next charging process. ) is important. This is because if either the holes or the electrons remain in the photosensitive layer, the remaining carriers inhibit charging in the next step. Therefore, the photoreceptor is required to set the mobility of holes and electrons in the photosensitive layer.

In addition, the inventors have found that it is important to control the content of the charge generating agent in order to reduce the residual charge. The reason is shown below. In the photosensitive layer of a single-layer type photoreceptor, the charge generating agent generates charges by exposure, temporarily traps the movement of the generated charges, and then detraps them, thereby inhibiting charging of the surface of the photosensitive layer. There is In order to suppress charging inhibition of the surface of the photosensitive layer by such a charge-generating agent, it is important to reduce the content of the charge-generating agent in the photosensitive layer as much as possible. However, when the content of the charge generating agent in the photosensitive layer is reduced, the sensitivity characteristics of the photoreceptor are lowered. Therefore, it is important to reduce the content of the charge generating agent within a range in which a constant quantum efficiency (xerographic gain) can be maintained. The present inventors have completed the present invention in consideration of the above.

From the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghosts caused by transfer memory, measurements were made under conditions of a temperature of 23° C. and an electric field strength of 1.5×10 ⁵ V/cm. The hole mobility _μh in the photosensitive layer is preferably 4.0×10 ⁻⁷ cm ² /V/sec or more. From the same point of view, the hole mobility μ _h in the photosensitive layer is preferably 1.0×10 ⁻⁵ cm ² /V/sec or less, and 1.0×10 ⁻⁶ cm ² /V/sec or less. more preferred.

The hole mobility μ _h in the photosensitive layer can be adjusted mainly by the type and content of the hole transport agent. Specifically, increasing the content of the hole transport agent tends to increase the hole mobility μ _h . In addition, the use of a hole transport agent having excellent hole transport efficiency tends to increase the hole mobility μ _h .

From the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghosts caused by transfer memory, measurements were made under conditions of a temperature of 23° C. and an electric field strength of 1.5×10 ⁵ V/cm. The electron mobility μ _e in the photosensitive layer to be coated is preferably 1.5×10 ⁻⁷ cm ² /V/sec or more. From the same point of view, the electron mobility μ _e in the photosensitive layer is preferably 1.0×10 ⁻⁵ cm ² /V/sec or less, more preferably 1.0×10 ⁻⁶ cm ² /V/sec or less. It is preferably 3.0×10 ⁻⁷ cm ² /V/sec or less, more preferably 3.0×10 −7 cm 2 /V/sec or less.

The electron mobility μ _e in the photosensitive layer can be adjusted mainly by the type and content of the electron transport agent. Specifically, increasing the content of the electron transport agent tends to increase the electron mobility μ _e . In addition, the use of an electron transport agent having excellent electron transport efficiency tends to increase the electron mobility μ _e .

From the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghosts caused by transfer memory, the temperature was 23° C. and the electric field strength was 1.5×10 ⁵ V/cm. In the measurement, the ratio (μ _e /μ _h ) of the electron mobility _{μ e} to the hole mobility μ h in the photosensitive layer is preferably 1.0/10.0 or more and 1.0/1.0 or less. , 1.0/7.0 or more and 1.0/1.0 or less.

The mobility of electrons and holes in the photosensitive layer can be measured by the following method. First, a sample coating liquid containing a binder resin, a hole transport agent, an electron transport agent and a solvent is applied onto an aluminum substrate to form a sample layer (for example, a film thickness of 5 μm). The types of the binder resin, the hole transport agent and the electron transport agent in the sample coating liquid are the same as those of the photosensitive layer to be measured. Further, the sample coating liquid does not contain other components such as charge generating agents and additives. Furthermore, the content of the hole transport agent and the electron transport agent in the sample coating solution is such that the content ratio (% by mass) of the hole transport agent and the electron transport agent in the formed sample layer is the same as that of the photosensitive layer to be measured. Adjust so that That is, the sample layer formed from the sample coating liquid has the same binder resin type, electron transport agent and hole transport agent types and content ratios as compared with the photosensitive layer to be measured. The difference is that the agents and additives are replaced with the same amount of binder resin. Then, a sandwich cell is produced by forming a semi-transparent gold electrode on the obtained sample layer by a vacuum deposition method. Next, the obtained sandwich cell was subjected to a TOF method (time of flight) under the conditions of a temperature of 23° C. and an electric field strength of 1.5×10 ⁵ V/cm to measure hole mobility μ _h and electron Mobility μ _e can be measured.

The charge-generating agent, hole-transporting agent, electron-transporting agent, binder resin, and optional additives are described below.

(Charge generating agent)
The charge-generating agent is not particularly limited as long as it is a charge-generating agent for photoreceptors. Examples of charge generating agents include phthalocyanine pigments, perylene pigments, bisazo pigments, trisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaline pigments, indigo pigments, azulenium pigments, cyanine pigments, Pigments, powders of inorganic photoconductive materials (e.g. selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide or amorphous silicon), pyrylium pigments, anthanthrone-based pigments, triphenylmethane-based pigments, threne-based pigments, toluidine-based pigments, Examples include pyrazoline-based pigments and quinacridone-based pigments. The charge generating agent may be used singly or in combination of two or more.

Examples of phthalocyanine pigments include metal-free phthalocyanines and metal phthalocyanines. Metal phthalocyanines include, for example, titanyl phthalocyanine, hydroxygallium phthalocyanine and chlorogallium phthalocyanine. Titanyl phthalocyanine is represented by the following chemical formula (CGM-1). Examples of metal-free phthalocyanines include compounds represented by the following chemical formula (CGM-2). The phthalocyanine pigment may be crystalline or amorphous. The crystal shape of the phthalocyanine-based pigment (for example, α-type, β-type, Y-type, V-type, or II-type) is not particularly limited, and phthalocyanine-based pigments having various crystal shapes are used. The charge generating agent preferably contains a compound represented by the following chemical formula (CGM-1).

Examples of metal-free phthalocyanine crystals include X-type crystals of metal-free phthalocyanine (hereinafter sometimes referred to as X-type metal-free phthalocyanine). Examples of titanyl phthalocyanine crystals include α-type, β-type and Y-type crystals of titanyl phthalocyanine (hereinafter sometimes referred to as α-type, β-type and Y-type titanyl phthalocyanine).

For example, it is preferable to use a photoreceptor having sensitivity in a wavelength region of 700 nm or more for a digital optical image forming apparatus (for example, a laser beam printer or facsimile using a light source such as a semiconductor laser). As the charge generating agent, a phthalocyanine pigment is preferable, a metal-free phthalocyanine or titanyl phthalocyanine is more preferable, and an X-type metal-free phthalocyanine or a Y-type titanyl phthalocyanine is even more preferable, because it has a high quantum yield in a wavelength region of 700 nm or more. , Y-type titanyl phthalocyanines are particularly preferred.

Y-type titanyl phthalocyanine has a main peak at, for example, a Bragg angle (2θ±0.2°) of 27.2° in its CuKα characteristic X-ray diffraction spectrum. The main peak in the CuKα characteristic X-ray diffraction spectrum is the peak having the first or second highest intensity in the range where the Bragg angle (2θ±0.2°) is 3° or more and 40° or less.

An example of the method for measuring the CuKα characteristic X-ray diffraction spectrum will be described. A sample (titanyl phthalocyanine) is filled in a sample holder of an X-ray diffraction device (for example, "RINT (registered trademark) 1100" manufactured by Rigaku Co., Ltd.), and an X-ray tube Cu, tube voltage 40 kV, tube current 30 mA, and CuKα An X-ray diffraction spectrum is measured under the condition of a characteristic X-ray wavelength of 1.542 Å. The measurement range (2θ) is, for example, 3° or more and 40° or less (start angle: 3°, stop angle: 40°), and the scanning speed is, for example, 10°/min.

Y-type titanyl phthalocyanines are classified into, for example, the following three types (A) to (C) according to their thermal properties in differential scanning calorimetry (DSC) spectra.
(A) A Y-type titanyl phthalocyanine having a differential scanning calorimetry spectrum having peaks in the range of 50° C. or higher and 270° C. or lower in addition to peaks associated with vaporization of adsorbed water.
(B) A Y-type titanyl phthalocyanine having no peaks in the range of 50° C. to 400° C. other than peaks associated with vaporization of adsorbed water in its differential scanning calorimetry spectrum.
(C) Y-type titanyl phthalocyanine having no peak in the range of 50° C. or higher and 270° C. or lower in the differential scanning calorimetry spectrum other than the peak associated with vaporization of adsorbed water, and having a peak in the range of 270° C. or higher and 400° C. or lower .

Y-type titanyl phthalocyanine has no peak in the range of 50° C. or higher and 270° C. or lower other than the peak associated with vaporization of adsorbed water in the differential scanning calorimetry spectrum, and has a peak in the range of 270° C. or higher and 400° C. or lower. is more preferred. As the Y-type titanyl phthalocyanine having such a peak, one having one peak in the range of 270°C to 400°C is preferable, and one having one peak at 296°C is more preferable.

An example of a method for measuring a differential scanning calorimetry spectrum will be described. A sample (titanyl phthalocyanine) is placed on a sample pan, and a differential scanning calorimetry spectrum is measured using a differential scanning calorimeter (eg, "TAS-200 model DSC8230D" manufactured by Rigaku Corporation). The measurement range is, for example, 40° C. or higher and 400° C. or lower. The heating rate is, for example, 20° C./min.

Anthanthrone-based pigments are preferably used as charge generating agents in photoreceptors applied to image forming apparatuses using short-wavelength laser light sources (for example, laser light sources having a wavelength of 350 nm or more and 550 nm or less).

The content of the charge generating agent in the photosensitive layer is preferably 0.70% by mass or more and 1.20% by mass or less.

The content of the charge generating agent in the photosensitive layer is preferably 0.5 parts by mass or more and 20 parts by mass or less, more preferably 1.0 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the binder resin. 5 parts by mass or more and 4.0 parts by mass or less is particularly preferable.

From the viewpoint of further improving the electrical properties of the photoreceptor, the xerographic gain of the photoreceptor measured under conditions of a temperature of 23° C. and an electric field strength of 1.5×10 ⁵ V/cm is preferably 35.0% or more. Further, the above xerographic gain is preferably 41.0% or less, more preferably 38.0% or less. By setting the xerographic gain to 35.0% or more, the sensitivity characteristics of the photoreceptor can be further improved. By setting the xerographic gain to 41.0% or less, it is possible to further improve the charging characteristics of the photoreceptor and more effectively suppress image ghosts caused by transfer memory.

Here, the xerographic gain is defined as the number of photons irradiated in the charged photosensitive layer is _Np , and the number of surface charges neutralized by movement of the charges generated by irradiation to the surface is _Nq . Sometimes it means the ratio of the number of neutralized surface charges Nq to the number _{Np of} photons striking the photosensitive layer.

The xerographic gain in the photosensitive layer can be measured by the following method. First, the photosensitive member is charged at a temperature of 23° C. while controlling the inflow current so as to achieve a predetermined charging potential (a range including a predetermined electric field strength between 100 V and 1000 V). Next, the charged photoreceptor is exposed for 1 second, and the charging potential during exposure is measured at regular intervals (for example, every 1 msec). The exposure light irradiation conditions are a wavelength (λ) of 780 nm and a light intensity (I ₀ ) of 1.0 μW/cm ² . The charging potential measurement result is time-differentiated, the maximum decay rate obtained is ΔVmax, the surface potential when ΔVmax is measured is SPmax, the film thickness of the photoreceptor is D, and the following equations (α) and The relationship between the xerographic gain and the electric field intensity E is obtained from (β). From the obtained relationship between the xerographic gain and the electric field strength E, the xerographic gain at the electric field strength of 1.5×10 ⁵ V/cm is calculated. In the following formula (α), εr indicates relative permittivity, ε0 indicates vacuum permittivity, e indicates elementary charge, h indicates Planck's constant, and c indicates light velocity. The xerographic gain of the photosensitive layer can also be measured by the same method for a photoreceptor having a protective layer on the photosensitive layer.
Xerographic gain=(ΔVmax×εr×ε0×λ)/(D×e×I ₀ ×h×c) (α)
E=SPmax/D (β)

(Hole transport agent)
Examples of hole transport agents include nitrogen-containing cyclic compounds and condensed polycyclic compounds. Nitrogen-containing cyclic compounds and condensed polycyclic compounds include, for example, triphenylamine derivatives; diamine derivatives (more specifically, N,N,N',N'-tetraphenylbenzidine derivatives, N,N,N ',N'-tetraphenylphenylenediamine derivatives, N,N,N',N'-tetraphenylnaphthylenediamine derivatives, di(aminophenylethenyl)benzene derivatives, N,N,N',N'-tetraphenyl phenanthrylenediamine derivatives, etc.); oxadiazole compounds (more specifically, 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole, etc.); styryl compounds (more Specifically, 9-(4-diethylaminostyryl) anthracene, etc.); carbazole compounds (more specifically, polyvinylcarbazole, etc.); organic polysilane compounds; pyrazoline compounds (more specifically, 1-phenyl- 3-(p-dimethylaminophenyl) pyrazoline, etc.); hydrazone compounds; indole compounds; oxazole compounds; isoxazole compounds; thiazole compounds; mentioned. These hole transport agents may be used singly or in combination of two or more.

The hole transport agent is a compound represented by the following general formula (10) (hereinafter referred to as , which may be described as a hole transport agent (10)).

In general formula (10), R ¹⁶ to R ¹⁸ each independently represent an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms. m and n each independently represent an integer of 1 or more and 3 or less. p and r each independently represent 0 or 1; q represents an integer of 0 or more and 2 or less.

In general formula (10), R ¹⁷ is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an n-butyl group.

In general formula (10), p and r preferably each represent 0. In general formula (10), q preferably represents 1.

In general formula (10), n and m preferably each independently represent 1 or 2, more preferably 2.

As the hole transport agent (10), a compound represented by the following chemical formula (HTM-1) (hereinafter sometimes referred to as hole transport agent (HTM-1)) is preferable.

The content of the hole transport agent in the photosensitive layer is preferably 10.0% by mass or more and 40.0% by mass or less, more preferably 15.0% by mass or more and 30.0% by mass or less.

The content of the hole transport agent in the photosensitive layer is preferably 20 parts by mass or more and 150 parts by mass or less, more preferably 35 parts by mass or more and 120 parts by mass or less, and 45 parts by mass or more and 70 parts by mass, based on 100 parts by mass of the binder resin. Part by mass or less is more preferable.

(Electron transport agent)
Examples of electron transport agents include quinone compounds, diimide compounds, hydrazone compounds, malononitrile compounds, thiopyran compounds, trinitrothioxanthone compounds, 3,4,5,7-tetranitro-9-fluorenone compounds, dinitroanthracene compounds, dinitroacridine compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride and dibromomaleic anhydride. Examples of quinone compounds include diphenoquinone compounds, azoquinone compounds, anthraquinone compounds, naphthoquinone compounds, nitroanthraquinone compounds and dinitroanthraquinone compounds. These electron transport agents may be used singly or in combination of two or more (for example, two).

The electron transport agent is represented by the following general formula (1), (2) or (3) from the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghosts caused by transfer memory. (hereinafter sometimes referred to as electron transfer agents (1) to (3)).

In general formulas (1) to (3), R ¹ to R ⁴ and R ⁹ to R ¹² each independently represent an alkyl group having 1 to 8 carbon atoms. Each of R ⁵ to R ⁸ independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a halogen atom.

In general formulas (1) to (3), the alkyl group represented by R ¹ to R ⁴ and R ⁹ to R ¹² is preferably an alkyl group having 1 to 5 carbon atoms, such as methyl group, tert-butyl or a 1,1-dimethylpropyl group are more preferred.

In general formulas (1) to (3), hydrogen atoms are preferred as R ⁵ to R ⁸ .

As the electron transport agents (1) to (3), the following chemical formula (ETM-1 ) to (ETM-3) (hereinafter sometimes referred to as electron transfer agents (ETM-1) to (ETM-3), respectively) are preferable. A preferred example of the electron transport agent (1) is the electron transport agent (ETM-1). A suitable example of the electron transport agent (2) is the electron transport agent (ETM-3). A suitable example of the electron transport agent (3) is the electron transport agent (ETM-2).

When the photosensitive layer contains two or more electron transport agents, the photosensitive layer contains electron transport agents (ETM-1) and (ETM-2), or electron transport agents (ETM-1) and (ETM- 3) is preferably included. When the photosensitive layer contains two types of electron transport agents, it is preferable to contain two types of electron transport agents in approximately the same amount. Specifically, the ratio of the content of one electron transport agent to the content of the other electron transport agent in the photosensitive layer is preferably 40:60 or more and 60:40 or less.

The content of the electron transport agent in the photosensitive layer is preferably 10.0% by mass or more and 40.0% by mass or less, more preferably 20.0% by mass or more and 30.0% by mass or less.

The content of the electron transport agent in the photosensitive layer is preferably 15 parts by mass or more and 160 parts by mass or less, more preferably 30 parts by mass or more and 100 parts by mass or less, and 40 parts by mass or more and 60 parts by mass with respect to 100 parts by mass of the binder resin. Part or less is more preferable.

(binder resin)
Examples of binder resins include thermoplastic resins, thermosetting resins, and photocurable resins. Examples of thermoplastic resins include polycarbonate resins, polyarylate resins, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, acrylic acid polymers, styrene-acrylic acid copolymers, Polyethylene resin, ethylene-vinyl acetate copolymer, chlorinated polyethylene resin, polyvinyl chloride resin, polypropylene resin, ionomer resin, vinyl chloride-vinyl acetate copolymer, alkyd resin, polyamide resin, urethane resin, polysulfone resin, diallyl phthalate resins, ketone resins, polyvinyl butyral resins, polyester resins and polyether resins. Thermosetting resins include, for example, silicone resins, epoxy resins, phenolic resins, urea resins and melamine resins. Examples of photocurable resins include acrylic acid adducts of epoxy compounds and acrylic acid adducts of urethane compounds. The photosensitive layer may contain only one of these binder resins, or may contain two or more of them.

The binder resin is a polyarylate resin (hereinafter referred to as a polyarylate resin (PA)) having a repeating unit represented by the following general formula (20) (hereinafter sometimes referred to as a repeating unit (20)). is) is preferably included.

In general formula (20), R ²⁰ and R ²¹ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ²² and R ²³ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group. R ²² and R ²³ may combine with each other to represent a divalent group represented by the following general formula (W). Y represents a divalent group represented by the following chemical formula (Y1), (Y2), (Y3), (Y4), (Y5) or (Y6).

In general formula (W), t represents an integer of 1 or more and 3 or less. * represents a bond.

In general formula (20), R ²⁰ and R ²¹ are preferably alkyl groups having 1 to 4 carbon atoms, more preferably methyl groups.

In general formula (20), R ²² and R ²³ preferably combine with each other to represent a divalent group represented by general formula (W).

In general formula (20), Y is preferably a divalent group represented by chemical formula (Y1) or (Y3).

In general formula (W), 2 is preferable as t.

The polyarylate resin (PA) preferably has only repeating units (20), but may further have other repeating units. The ratio (molar fraction) of the amount of other repeating units to the total amount of repeating units in the polyarylate resin (PA) is preferably 0.20 or less, more preferably 0.10 or less, and 0.00. More preferred. The polyarylate resin (PA) may have one type of repeating unit (20), or may have two or more types (for example, two types).

In the specification of the present application, the substance amount of each repeating unit in the polyarylate resin (PA) is not the value obtained from one resin chain, but the entire polyarylate resin (PA) contained in the photosensitive layer (a plurality of resin chain). Further, the substance amount of each repeating unit can be calculated from the ¹ H-NMR spectrum obtained by measuring the ¹ H-NMR spectrum of the polyarylate resin (PA) using, for example, a proton nuclear magnetic resonance spectrometer. .

The polyarylate resin (PA) includes repeating units represented by the following chemical formulas (20-a) and (20-b) (hereinafter sometimes referred to as repeating units (20-a) or (20-b) ), more preferably both repeating units (20-a) and (20-b).

As the polyarylate resin (PA), for example, a resin having repeating units (20-a) and repeating units (20-b) can be used. In this case, the arrangement of repeating units (20-a) and (20-b) is not particularly limited. That is, the polyarylate resin (PA) having repeating units (20-a) and (20-b) is any of random copolymers, block copolymers, periodic copolymers and alternating copolymers. good too. In this case, it is preferable that the amounts of the repeating units (20-a) and the repeating units (20-b) in the polyarylate resin (PA) are approximately the same. Specifically, the ratio (molar fraction) between the substance amount of the repeating unit (20-a) and the substance amount of the repeating unit (20-b) in the polyarylate resin (PA) is 49:51 or more and 51 : 49 or less is preferable.

The polyarylate resin (PA) may have terminal groups represented by the following chemical formula (Z). In the following chemical formula (Z), * represents a bond. When the polyarylate resin (PA) has repeating units (20-a) and repeating units (20-b) and a terminal group represented by the following chemical formula (Z), the terminal group is a repeating unit (20-a ) and the repeating unit (20-b).

As the polyarylate resin (PA), a polyarylate resin having a main chain represented by the following chemical formula (PA-1a) and a terminal group represented by the chemical formula (Z) (hereinafter referred to as polyarylate resin (PA-1 ) is preferred. In the following chemical formula (PA-1a), the number attached to the lower right of the repeating unit is the amount of material of the repeating unit with the number with respect to the amount of material of all repeating units possessed by the polyarylate resin (PA-1). shows the ratio (molar fraction) of The polyarylate resin (PA-1) may be any of random copolymers, block copolymers, periodic copolymers and alternating copolymers.

The viscosity average molecular weight of the binder resin is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 30,000 or more. When the viscosity-average molecular weight of the binder resin is 10,000 or more, the wear resistance of the photoreceptor tends to be improved. On the other hand, the viscosity average molecular weight of the binder resin is preferably 80,000 or less, more preferably 70,000 or less. When the viscosity-average molecular weight of the binder resin is 80,000 or less, the binder resin tends to be easily dissolved in the solvent for forming the photosensitive layer, thereby facilitating the formation of the photosensitive layer.

(Additive)
Additives that are optional components include, for example, deterioration inhibitors (more specifically, antioxidants, radical scavengers, quenchers, ultraviolet absorbers, etc.), softeners, surface modifiers, extenders, extenders, Viscous agents, dispersion stabilizers, waxes, donors, surfactants, and leveling agents. Examples of leveling agents include silicone oil. When additives are added to the photosensitive layer, one of these additives may be used alone, or two or more thereof may be used in combination.

(combination)
Combinations of the hole transport agent and the electron transport agent in the photosensitive layer include:
a combination of a hole transport agent (HTM-1) and electron transport agents (ETM-1) and (ETM-2), or a hole transport agent (HTM-1) and an electron transport agent (ETM-1) and A combination with (ETM-3) is preferred.

Combinations of the charge-generating agent, the hole-transporting agent and the electron-transporting agent in the photosensitive layer include:
A combination of titanyl phthalocyanine, a hole transport agent (HTM-1), and electron transport agents (ETM-1) and (ETM-2), or titanyl phthalocyanine, a hole transport agent (HTM-1), and an electron Combinations with transport agents (ETM-1) and (ETM-3) are preferred.

[Intermediate layer]
As noted above, the photoreceptor may have an intermediate layer (eg, an undercoat layer). The intermediate layer contains, for example, inorganic particles and a resin used for the intermediate layer (an intermediate layer resin). Interposing the intermediate layer makes it possible to smoothen the flow of current generated when the photoreceptor is exposed to light while maintaining an insulating state capable of suppressing leakage, thereby suppressing an increase in electrical resistance.

Examples of inorganic particles include particles of metal (more specifically, aluminum, iron, copper, etc.), metal oxides (more specifically, titanium oxide, alumina, zirconium oxide, tin oxide, zinc oxide, etc.). and particles of non-metal oxides (more specifically, silica and the like). One of these inorganic particles may be used alone, or two or more thereof may be used in combination. In addition, the inorganic particles may be surface-treated.

The intermediate layer resin is not particularly limited as long as it can be used as a resin for forming the intermediate layer.

[Method for producing photoreceptor]
A photoreceptor is manufactured by, for example, applying a coating liquid for forming a photosensitive layer onto a conductive substrate and drying the coating liquid. The photosensitive layer-forming coating liquid is produced by dissolving or dispersing in a solvent a charge generating agent, a hole transporting agent, an electron transporting agent, a binder resin, and optionally added optional components.

The solvent contained in the coating liquid for forming the photosensitive layer is not particularly limited as long as it can dissolve or disperse each component contained in the coating liquid. Examples of solvents include alcohols (eg methanol, ethanol, isopropanol or butanol), aliphatic hydrocarbons (eg n-hexane, octane or cyclohexane), aromatic hydrocarbons (eg benzene, toluene or xylene), Halogenated hydrocarbons (e.g. dichloromethane, dichloroethane, carbon tetrachloride or chlorobenzene), ethers (e.g. dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether or propylene glycol monomethyl ether), ketones (e.g. acetone, methyl ethyl ketone or cyclohexanone), esters (eg ethyl acetate or methyl acetate), dimethylformaldehyde, dimethylformamide and dimethylsulfoxide. One type of these solvents may be used alone, or two or more types may be used in combination. It is preferable to use a non-halogen solvent (a solvent other than halogenated hydrocarbons) as the solvent in order to improve the workability during the production of the photoreceptor.

The photosensitive layer-forming coating liquid is prepared by mixing each component and dispersing the mixture in a solvent. For mixing or dispersing, for example, a bead mill, roll mill, ball mill, attritor, paint shaker or ultrasonic disperser can be used.

The photosensitive layer-forming coating liquid may contain, for example, a surfactant in order to improve the dispersibility of each component.

The method for applying the photosensitive layer-forming coating liquid is not particularly limited as long as it is a method capable of uniformly applying the coating liquid onto the conductive substrate. Examples of coating methods include blade coating, dip coating, spray coating, spin coating and bar coating.

The method for drying the photosensitive layer-forming coating solution is not particularly limited as long as the solvent in the coating solution can be evaporated. be done. The heat treatment temperature is, for example, 40° C. or higher and 150° C. or lower. The heat treatment time is, for example, 3 minutes or more and 120 minutes or less.

The photoreceptor manufacturing method may further include one or both of the step of forming an intermediate layer and the step of forming a protective layer, if necessary. A known method is appropriately selected for the step of forming the intermediate layer and the step of forming the protective layer.

[Tandem Color Image Forming Apparatus]
One aspect of the image forming apparatus according to the present embodiment will be described below by taking a tandem color image forming apparatus as an example. FIG. 4 is a diagram showing an example of an image forming apparatus according to this embodiment. The image forming apparatus 100 according to this embodiment includes an image carrier 30 , a charging section 42 , an exposure section 44 , a developing section 46 and a transfer section 48 . The image carrier 30 is the photoreceptor 1 described above. The charging section 42 charges the surface of the image carrier 30 . The charging polarity of the charging section 42 is positive. The exposure unit 44 exposes the charged surface of the image carrier 30 to form an electrostatic latent image on the surface of the image carrier 30 . The developing unit 46 supplies toner to the electrostatic latent image to develop the electrostatic latent image into a toner image. The transfer unit 48 transfers the toner image from the image carrier 30 to the recording medium P while bringing the surface of the image carrier 30 and the recording medium P (transfer target) into contact with each other. The outline of the image forming apparatus 100 according to the present embodiment has been described above.

The image forming apparatus 100 according to this embodiment includes the photoreceptor 1 having excellent charging performance and sensitivity characteristics, and can suppress image ghosts caused by transfer memory. The reason why the image forming apparatus 100 can suppress the image ghost caused by the transfer memory is presumed as follows. That is, the photoreceptor 1 can suppress transfer memory as described above. Therefore, the image forming apparatus 100 according to the present embodiment can suppress image defects such as image ghosts, which will be described later. Image ghosts caused by transfer memory will be described below.

When transfer memory occurs in the image forming process, the non-exposed area around the reference circumference (any one rotation when images are formed continuously) on the surface of the image carrier 30 becomes the exposed area around the reference circumference. , the potential tends to decrease during charging in the next round of the reference round. For this reason, the non-exposed area of the reference circumference more easily attracts the positively charged toner than in the normal state in the development process of the next circumference. As a result, an image reflecting the non-image portion (non-exposure area) of the reference circumference is likely to be formed in the next rotation of the reference circumference. An image defect in which an image reflecting the non-image portion of the reference rotation is formed in the next rotation is an image ghost caused by transfer memory.

Image ghosts will be described with reference to FIG. FIG. 5 is a diagram showing an image 60 in which an image ghost has occurred. Image 60 includes area 62 and area 64 . A region 62 corresponds to one round of the image carrier (one round of the reference round), and an area 64 also corresponds to one round of the image carrier (one round of the next round of the reference round). Region 62 contains image 66 . The image 66 consists of a square solid image. Region 64 includes image 68 and image 69 . Image 68 is a square halftone image. Image 69 is a halftone image of the area excluding image 68 in area 64 . The design image of the area 64 is a uniform halftone image. As shown in FIG. 5, image 69 has a higher image density than image 68 . Image 69 is an image defect (image ghost) that reflects the unexposed area of area 62 and is darker than the designed image density.

Hereinafter, each unit of the image forming apparatus 100 will be described in detail with reference to FIG. 4 again.

The image forming apparatus 100 employs a direct transfer method. That is, in the image forming apparatus 100, the transfer section 48 transfers the toner image onto the recording medium P while the surface of the image carrier 30 and the recording medium P are in contact with each other. Generally, in an image forming apparatus that employs a direct transfer method, transfer memory is likely to occur because the image bearing member is susceptible to the transfer bias. However, since the image forming apparatus 100 according to the present embodiment includes the photoreceptor 1 as the image carrier 30, transfer memory can be effectively suppressed. As described above, since the photosensitive member 1 is provided as the image carrier 30, image ghosts caused by transfer memory are suppressed even in the image forming apparatus 100 that employs the direct transfer method.

The image forming apparatus 100 includes image forming units 40 a , 40 b , 40 c and 40 d , a transfer belt 50 and a fixing section 54 . Hereinafter, each of the image forming units 40a, 40b, 40c, and 40d will be referred to as the image forming unit 40 when there is no need to distinguish between them.

The image forming unit 40 includes an image carrier 30 , a charging section 42 , an exposure section 44 , a developing section 46 , a transfer section 48 , and a cleaning section 52 that cleans the surface of the image carrier 30 . The cleaning portion 52 is a cleaning blade. Generally, in an image forming apparatus having a cleaning blade, the image carrier tends to be triboelectrically charged due to contact between the image carrier and the cleaning blade. Therefore, in an image forming apparatus equipped with a cleaning blade, transfer memory is likely to occur due to the charge generated by triboelectrification remaining in the image carrier. However, the image forming apparatus 100 according to this embodiment includes the photoreceptor 1 described above as the image carrier 30 . Photoreceptor 1 can suppress transfer memory. Therefore, by providing the above-described photoreceptor 1 as the image carrier 30, even in the image forming apparatus 100 having a cleaning blade, it is possible to effectively suppress image ghosts caused by transfer memory.

The image carrier 30 is provided at the center position of the image forming unit 40 so as to be rotatable in the arrow direction (counterclockwise). Around the image carrier 30, a charging unit 42, an exposure unit 44, a developing unit 46, a transfer unit 48, and a cleaning unit 52 are provided in this order from the upstream side in the rotational direction of the image carrier 30 with respect to the charging unit 42. be done. It is preferable that the image forming unit 40 is further provided with a neutralizing section (not shown) that neutralizes the surface of the image carrier 30 after the toner image has been transferred onto the transfer material. In this case, the time (process time from static elimination to charging) from when a predetermined portion of the surface of the image carrier 30 is statically eliminated by the static elimination unit until it is charged again by the charging unit 42 is preferably 200 milliseconds or less. . By setting the process time from static elimination to charging to 200 milliseconds or less in this manner, the image forming apparatus 100 can be made faster and smaller. The predetermined location is, for example, one location (for example, one point) on the surface of the image carrier 30 . On the other hand, in the conventional image forming apparatus, if the process time from static elimination to charging is shortened, it tends to become difficult to charge the surface of the image carrier to a desired potential. However, the image forming apparatus 100 according to this embodiment includes the photoreceptor 1 described above as the image carrier 30 . The photoreceptor 1 has excellent charging characteristics. Therefore, the image forming apparatus 100 according to the present embodiment includes the photoreceptor 1 described above as the image carrier 30, so that the image carrier 30 can be used as desired even if the process time from static elimination to charging is set to 200 milliseconds or less. It can be charged to an electric potential. The process time from static elimination to charging is preferably 160 milliseconds or less, more preferably 120 milliseconds or less. The process time from static elimination to charging is preferably 30 milliseconds or longer, more preferably 80 milliseconds or longer.

Each of the image forming units 40a to 40d sequentially superposes toner images of a plurality of colors (for example, four colors of black, cyan, magenta, and yellow) on the recording medium P on the transfer belt 50 .

The charging unit 42 is a charging roller. The charging roller charges the surface of the image carrier 30 while contacting the surface of the image carrier 30 . In addition, as another contact charging type charging unit, for example, a charging brush can be used. Also, the charging unit may be of a non-contact type. Examples of non-contact charging units include a corotron charging unit and a scorotron charging unit.

A voltage applied by the charging unit 42 is not particularly limited. The voltage applied by the charging section 42 includes a DC voltage, an AC voltage, and a superimposed voltage (a voltage in which an AC voltage is superimposed on a DC voltage), and more preferably a DC voltage. DC voltage has the following advantages over AC voltage and superimposed voltage. When the charging unit 42 applies only a DC voltage, the voltage value applied to the image carrier 30 is constant, so that the surface of the image carrier 30 can be uniformly charged to a constant potential. Also, when the charging unit 42 applies only a DC voltage, the abrasion amount of the photosensitive layer tends to decrease. As a result, good images can be formed. The charging section 42 is in contact with the image carrier 30 and can apply a DC voltage to the image carrier 30 .

The exposure unit 44 exposes the charged surface of the image carrier 30 . Thereby, an electrostatic latent image is formed on the surface of the image carrier 30 . The electrostatic latent image is formed based on image data input to image forming apparatus 100 .

The developing unit 46 supplies toner to the surface of the image carrier 30 and develops the electrostatic latent image into a toner image. As the developing section 46 , for example, a developing section that develops an electrostatic latent image into a toner image while being in contact with the surface of the image carrier 30 can be employed.

The transfer belt 50 conveys the recording medium P between the image carrier 30 and the transfer section 48 . The transfer belt 50 is an endless belt. The transfer belt 50 is rotatable in the arrow direction (clockwise).

The transfer section 48 transfers the toner image developed by the developing section 46 from the surface of the image carrier 30 to the recording medium P. As shown in FIG. The image carrier 30 is in contact with the recording medium P when the toner image is transferred from the image carrier 30 to the recording medium P. As shown in FIG. Examples of the transfer unit 48 include a transfer roller.

The fixing section 54 heats and/or presses the unfixed toner image transferred onto the recording medium P by the transfer section 48 . The fixing section 54 is, for example, a heating roller and/or a pressure roller. The toner image is fixed on the recording medium P by heating and/or pressing the toner image. As a result, an image is formed on the recording medium P. FIG.

An example of the image forming apparatus according to the present embodiment has been described above, but the image forming apparatus according to the present embodiment is not limited to the image forming apparatus 100 described above. For example, the image forming apparatus 100 described above is a tandem image forming apparatus, but the image forming apparatus according to the present embodiment is not limited to this, and may be, for example, a rotary image forming apparatus. Also, the image forming apparatus according to the present embodiment may be a monochrome image forming apparatus. In this case, the image forming apparatus may have, for example, only one image forming unit. Further, the image forming apparatus according to this embodiment may employ an intermediate transfer method. When the image forming apparatus according to this embodiment employs an intermediate transfer method, the transfer target corresponds to an intermediate transfer belt.

<Second Embodiment: Image Forming Method>
The image forming method according to this embodiment is an image forming method using the image forming apparatus according to the first embodiment. This image forming apparatus further includes a neutralization unit that neutralizes the surface of the image carrier after the toner image has been transferred onto the transfer material. The image forming method according to the present embodiment comprises a charging step of positively charging the surface of the image carrier, and exposing the charged surface of the image carrier to form an electrostatic latent image on the surface of the image carrier. a developing step of supplying toner to the electrostatic latent image to develop the electrostatic latent image into a toner image; a transferring step of transferring the toner image from the image bearing member to the transferred member; and a charge removing step of removing charges from the surface of the image bearing member after transferring onto the transfer receiving member. The time (process time from static elimination to charging) from when a predetermined portion of the surface of the image carrier is statically eliminated in the static elimination process to charged in the charging process is 200 milliseconds or less. The process time from static elimination to charging is preferably 160 milliseconds or less, more preferably 120 milliseconds or less. The process time from static elimination to charging is preferably 30 milliseconds or longer, more preferably 80 milliseconds or longer. For details of the charging process, the exposure process, the development process, the transfer process, and the static elimination process, for example, the functions of the charging section, the exposure section, the development section, the transfer section, and the static elimination section of the image forming apparatus according to the above-described first embodiment are described. You can refer to it. In the image forming method according to the present embodiment, the electrophotographic photosensitive member used has excellent charging characteristics and sensitivity characteristics, and image ghosts caused by transfer memory can be suppressed.

EXAMPLES Hereinafter, the present invention will be described more specifically using examples. However, the present invention is in no way limited to the scope of the examples.

<Material for Forming Photosensitive Layer>
As materials for forming the photosensitive layer of the photoreceptor, the following charge-generating agent, hole-transporting agent, electron-transporting agent and binder resin were prepared.

(Charge generating agent)
Y-type titanyl phthalocyanine and metal-free phthalocyanine were prepared as charge generating agents (hereinafter sometimes referred to as charge generating agents (CGM-1) and (CGM-2), respectively). The charge generating agent (CGM-1) was titanyl phthalocyanine represented by the chemical formula (CGM-1) described in the embodiment and having a Y-type crystal structure. In the differential scanning calorimetry spectrum, this Y-type titanyl phthalocyanine does not have a peak in the range of 50° C. or higher and 270° C. or lower other than the peak associated with the vaporization of adsorbed water, and has a peak in the range of 270° C. or higher and 400° C. or lower. (Specifically, it had one peak at 296°C). The charge generating agent (CGM-2) was a compound represented by the chemical formula (CGM-2) described in the embodiment and having an X-type crystal structure.

(Hole transport agent)
As a hole transport agent, the hole transport agent (HTM-1) described in the embodiment was prepared.

(Electron transport agent)
As electron transport agents, the electron transport agents (ETM-1) to (ETM-3) described in the embodiment were prepared.

(binder resin)
As a binder resin, the polyarylate resin (PA-1) described in the embodiment was prepared. The viscosity average molecular weight of the polyarylate resin (PA-1) was 60,000.

<Relationship between type and content of charge generating agent and xerographic gain>
Photoreceptors (a-1) to (a-8) and (b-1) to (b-6) were used to examine the relationship between the type and content of the charge generating agent in the photosensitive layer of the photoreceptor and the xerographic gain. manufactured.

[Production of photoreceptor]
Charge generation agent, hole transport agent (10-1) 65 parts by mass, electron transport agent (ETM-1) 33.5 parts by mass, electron transport agent (ETM-3) 33.5 parts by mass, binder 138 parts by mass of polyarylate resin (PA-1) as a resin and a solvent (tetrahydrofuran) were added. Thus, a coating liquid for forming a photosensitive layer was obtained. The type and content of the charge generating agent contained in the coating solution for forming the photosensitive layer were as shown in Table 1 below. In Table 1 below, "wt %" indicates the content ratio (% by mass) in the solid content (charge generating agent, hole transport agent, electron transport agent and binder resin) of the photosensitive layer forming coating liquid. The same applies to "wt%" in Tables 2 to 4 below. A coating liquid for forming a photosensitive layer was applied onto an aluminum drum-shaped support (diameter: 30 mm, total length: 247.5 mm) as a conductive substrate by dip coating to form a coating film. The coating film was dried with hot air at 100° C. for 40 minutes. As a result, a single-layered photosensitive layer (thickness: 30 μm) was formed on the conductive substrate. As a result, photoconductors (a-1) to (a-8) and (b-1) to (b-6) were obtained.

The type and content of the charge generating agent in the formed photosensitive layer were as shown in Table 1 below.

[Measurement of xerographic gain]
For each of the photoreceptors (a-1) to (a-8) and (b-1) to (b-6), a drum sensitivity tester (manufactured by Gentec Co., Ltd.) is used to perform xerographic tests on the photosensitive layer. Gain was measured. First, each photoreceptor was charged at a temperature of 23° C. while controlling an inflow current so as to obtain a predetermined charging potential (100 to 1000 V). Each charged photoreceptor was exposed for 1 second, and the charging potential during exposure was measured at regular intervals (every 1 millisecond). The exposure light irradiation conditions were a wavelength (λ) of 780 nm and a light intensity (I ₀ ) of 1.0 μW/cm ² . The charging potential measurement result is time-differentiated, the maximum decay rate obtained is ΔVmax, the surface potential when ΔVmax is measured is SPmax, the film thickness of the photoreceptor is D, and the following equations (α) and The relationship between the xerographic gain and the electric field strength E was obtained from (β). For this measurement, the above procedure was repeated while varying the charging potential to include a field strength of 1.5×10 ⁵ V/cm. From the obtained relationship between the xerographic gain and the electric field intensity E, the xerographic gain at an electric field intensity of 1.5×10 ⁵ V/cm was calculated. The measurement results are shown in Table 1 below and FIG. In the following formula (α), εr indicates relative permittivity, ε0 indicates vacuum permittivity, e indicates elementary charge, h indicates Planck's constant, and c indicates light velocity.
Xerographic gain=(ΔVmax×εr×ε0×λ)/(D×e×I ₀ ×h×c) (α)
E=SPmax/D (β)

In FIG. 6, CGM (wt %) indicates the content ratio (mass %) of the charge generating agent.

As shown in Table 1 and FIG. 6, in the photosensitive layer of each photoreceptor, it was confirmed that the xerographic gain increased as the content of the charge generating agent increased. Photoreceptors (a-1) to (a-8) using the charge generating agent (CGM-1) are photoreceptors (b-1) to (b-) using the charge generating agent (CGM-2). Compared to 6), it was confirmed that the xerographic gain per content ratio of the charge generating agent was high. From this, the charge generation agent (CGM-1) has higher charge generation efficiency than the charge generation agent (CGM-2), and can generate more charge even if the content ratio is the same. is judged.

<Relationship between xerographic gain and sensitivity characteristics>
Next, in order to examine the relationship between the xerographic gain and the sensitivity characteristics in the photosensitive layer of the photoreceptor, photoreceptors (c-1) to (c-6) were produced and their sensitivity characteristics were measured.

[Production of Photoreceptor and Measurement of Xerographic Gain]
The photoreceptor ( Production of c-1) to (c-6) and measurement of xerographic gain were carried out. In the production of the photoreceptors (a-1) to (a-8) and (b-1) to (b-6), the type and content of the charge generating agent were as shown in Table 1, but the photoreceptor (c -1) to (c-6) were manufactured as shown in Table 2 below. Table 2 below and FIG. 7 show the measurement results of the xerographic gain in the photosensitive layers of the photoreceptors (c-1) to (c-6).

[Measurement of sensitivity characteristics]
The sensitivity characteristics of the photoreceptor (post-exposure potential V _L ) were measured in an environment of a temperature of 23° C. and a relative humidity of 50% RH. As an evaluation machine, a color image forming apparatus (“Task alfa 356ci” manufactured by Kyocera Document Solutions Inc.) was used. This image forming apparatus was equipped with a contact-type charging roller that applies a DC voltage.

In the measurement of the post-exposure potential _VL , the photoreceptor was first mounted on the evaluation machine, and the photoreceptor was charged so that the surface potential (non-exposed area) was +500 V ± 10 V by adjusting the voltage applied to the charging roller. rice field. Then, the photosensitive member was exposed using a laser diode mounted on the evaluation machine as an irradiation light source. The exposure conditions were a wavelength of 670 nm and an exposure energy of 1.16 μJ/cm ² . After exposure, the surface potential of the photoreceptor was measured at the position of the developing portion, and this was defined as post-exposure potential V _L (unit: +V). The smaller the absolute value of the post-exposure potential, the better the sensitivity characteristics of the photoreceptor. The evaluation results are shown in Table 2 below and FIG.

As shown in Table 2 and FIG. 7, the higher the xerographic gain in the photosensitive layer, the lower the absolute value of the post-exposure potential of the photoreceptor and the better the sensitivity characteristics. Here, in order to form a good image, the post-exposure potential of the photosensitive member is preferably 150 V or less in absolute value. This is because if the post-exposure potential of the photoreceptor is 150 V or more, a sufficient developing electric field cannot be obtained, and an image with good density cannot be formed. It should be noted that even with a photoreceptor having a post-exposure potential exceeding 150 V in absolute value measured under the above conditions, it is possible to form an image of good density by increasing the intensity of the exposure light, but this increases the cost of the exposure unit. It is not preferable because it leads to ups. From the above, it is judged that the xerographic gain in the photosensitive layer of the photoreceptor should be 32.0% or more.

Here, from each photoreceptor in FIG. 6, the content ratio of the charge generating agent required to obtain a xerographic gain of 32.0% or more will be confirmed. As is clear from the photoreceptors (a-1) to (a-8), when the charge generating agent (CGM-1) is used, the xerographic gain of 32 can be obtained by setting the content ratio to 0.50% by mass or more. 0% or more. Further, as is clear from the photoreceptors (b-1) to (b-6), when the charge generating agent (CGM-2) is used, the xerographic gain can be can be 32.0% or more.

However, as described above, in the photosensitive layer of a single-layer electrophotographic photoreceptor in which a charge-generating agent, an electron-transporting agent, and a hole-transporting agent are mixed, the charge-generating agent acts as a trap site and lowers charging performance. It is judged that it is preferable to reduce the content ratio as much as possible. Further tests were performed to confirm this.

<Content ratio of charge generating agent and charging performance>
In order to investigate the relationship between the charge generating agent content in the photosensitive layer of the photoreceptor and the charging performance, photoreceptors (d-1) to (d-10) were produced and their charging performance was measured.

[Production of photoreceptor]
Photoreceptors (d-1) to (d-1) to (b-6) are manufactured in the same manner as the photoreceptors (a-1) to (a-8) and (b-1) to (b-6), except that the following points are changed. d-10) was produced. In the production of the photoreceptors (a-1) to (a-8) and (b-1) to (b-6), the type and content of the charge generating agent were as shown in Table 1, but the photoreceptor (d -1) to (d-10) were manufactured as shown in Table 3 below.

[Measurement of charging performance]
In the measurement of the charging performance (charging potential V ₀ ), each photoreceptor was first mounted on an evaluation device ("CYNTHIA30M" manufactured by Gentec Co., Ltd.). The evaluation device includes a charging roller as a charging unit and an LED lamp as a static elimination unit. It was a device that eliminates static electricity with A transparent probe for measuring the surface potential of the photoreceptor was attached to the exposure position of the evaluation device. In the evaluation, the charge potential V ₀ (unit: +V) of the photoreceptor was maintained while the surface charge density of the photoreceptor was kept constant (6×10 ⁻⁴ C/m ² ) by appropriately adjusting the voltage applied to the charging roller. was measured. Various conditions were as follows. The temperature and relative humidity were 25° C. and 40% RH. The process speed (peripheral speed of the photosensitive member) was 215 mm/sec. The process time from when a predetermined portion of the surface of the photoreceptor was neutralized by the neutralizer to when it was charged by the charging roller (length: 232 mm) was 180 milliseconds. The smaller the absolute value of the charging potential V ₀ , the better the charging characteristics of the photoreceptor. The measurement results are shown in Table 3 below and FIG.

As is clear from Table 3 and FIG. 8, the charging performance of the photoreceptor is generally constant as long as the content of the charge generating agent in the photosensitive layer is within the range of 0.50% by mass or more and 1.50% by mass or less. However, when the content of the charge-generating agent exceeded 1.50% by mass, it tended to decrease. Thus, when the charge generating agent is excessively present in the photosensitive layer, it impedes charge transport and lowers the charging performance of the photoreceptor. Therefore, from the viewpoint of charging performance of the photoreceptor, the content of the charge generating agent in the photoreceptor layer is determined to be preferably 1.50% by mass or less.

In summary, in order to achieve both sensitivity characteristics and charging performance in the photoreceptor, the content of the charge generating agent in the photoreceptor layer should be 0.50% by mass or more and 1.50% by mass or less, and measurement should be performed under the above conditions. It is determined that the xerographic gain applied should be 32.0% or greater. Further evaluation was performed using an image forming apparatus.

<Evaluation of Image Forming Apparatus>
[Production of photoreceptor]
Photoreceptors (A-1) to (A-1) to ( A-9) and (B-1) to (B-8) were produced. In the production of the photoreceptors (a-1) to (a-8) and (b-1) to (b-6), the types and contents of the charge generating agent, electron transport agent and hole transport agent are as described above. However, in the production of photoreceptors (A-1) to (A-9) and (B-1) to (B-8), the types and content ratios shown in Table 4 below were used.

[Measurement of mobility]
The hole mobility μ _h and the electron mobility μ _e in the photosensitive layer of each photoreceptor were measured. First, as a sample for measurement, a sample layer corresponding to a layer having the same composition as the photosensitive layer of each photoreceptor except that the same amount of binder resin was used as the charge generating agent was formed. A sample coating solution containing only a hole transport agent, an electron transport agent, a binder resin and a solvent was used to form this sample layer. Each sample coating liquid and the photosensitive layer-forming coating liquid used to form the corresponding photoreceptor had the same binder resin, hole transport agent, and electron transport agent. On the other hand, each sample coating solution contained no charge-generating agent as compared with the photosensitive-layer-forming coating solution used to form the corresponding photoreceptor. The difference was that the content of the binder resin was increased by only one.

A thin film (sample layer) was formed by applying the sample coating liquid to an aluminum substrate using a wire bar so as to have a film thickness of 5 μm and then drying. After that, a semi-transparent gold electrode was vacuum-deposited on this thin film to fabricate a sandwich cell. The resulting sandwich cell was measured for hole mobility μh and electron mobility _μh by a conventional TOF method (time of flight) under conditions of a temperature of 23° C. and an electric field strength of 1.5×10 ⁵ V/cm. We measured _e . The hole mobility μ _h and electron mobility _{μ e} measured with this sandwich cell were defined as the hole mobility μ _h and electron mobility μ _e in the photosensitive layer of each photoreceptor.

In the measurement of the hole mobility μ _h and the electron mobility μ _e by the TOF method, half The thin film was irradiated with pulsed light (wavelength: 337 nm) through the transparent gold electrode. A nitrogen laser generator (“ULC-50” manufactured by Usho Co., Ltd.) was used as a pulsed light source. The change over time of the current generated by the irradiation of the pulsed light was measured with a storage scope ("TS-8123" manufactured by Iwasaki Tsushinki Co., Ltd.). The change in current over time was represented by a log-log graph, and the transit time (tr, unit: seconds) was obtained based on the change in slope. The film thickness (L), transit time (tr), and voltage (V) of the thin film were substituted into the following relational expression (μ) to calculate the charge mobility. The measurement results are shown in Table 4 below.
Charge mobility = (L/tr)/(V/L) (μ)

[Measurement of charging potential for each process time]
Photoreceptors (A-1) to (A-9) and (B-3) were measured in the same manner as the charging potentials of photoreceptors (d-1) to (d-10), except that the following points were changed. ), (B-4), (B-7) and (B-8) were _measured . In the measurement of the charging potential of the photoreceptors (d-1) to (d-10), the process time from static elimination to charging was constant. On the other hand, in the measurement of the charging potential V ₀ of the photosensitive members (A-1) to (A-9), (B-3), (B-4), (B-7) and (B-8), The process time until charging was 100 ms, 150 ms, 180 ms, 200 ms, 250 ms or 300 ms. In addition, in measuring the charging potential V ₀ of the photoreceptors (A-1) to (A-9), (B-3), (B-4), (B-7) and (B-8), the photoreceptor was constant at 6.00×10 ⁻⁴ (C/m ² ). The charging characteristics of the photosensitive member were evaluated as good (A) when the charging potential V ₀ was 490 V or more when the process time was 200 milliseconds, and not good (B) when the charging potential V 0 was less than 490 V. The measurement results are shown in Table 5, FIGS. 9 and 10.

Incidentally, the photoreceptors (B-1), (B-2), (B-5) and (B-6) did not have good sensitivity characteristics as will be described later, so the charging potential measurement was omitted.

[Measurement of post-exposure potential]
Photoreceptors (A-1) to (A-9) and (B-1) to (B-8) were measured in the same manner as the post-exposure potential V ₀ of photoreceptors (c-1) to (c-6). ) was _measured after exposure. The post-exposure potential V ₀ of the photosensitive member was evaluated as good (A) when the absolute value was 150 V or less, and not good (B) when the absolute value exceeded 150 V. The measurement results are shown in Table 5 below, FIGS. 11 and 12.

[Evaluation of Image Ghost Caused by Transfer Memory]
It was evaluated whether or not each photoreceptor could suppress image ghost caused by transfer memory. First, the photoreceptors (A-1) to (A-9), (B-3), (B-4), (B-7) and (B-8) were evaluated using an evaluation machine (manufactured by Kyocera Document Solutions Co., Ltd. TASKalfa 356ci", process time from static elimination to charging is about 180 mm) as an image bearing member to obtain an image forming apparatus. This evaluation machine was provided with a scorotron charging device as a charging section and a static elimination lamp as a static elimination section. The charge potential of the image bearing member was set to +500V. The transfer bias of the image carrier was set to -10 μA. Using this image forming apparatus, the presence or absence of image ghost caused by transfer memory was evaluated. The evaluation was performed under an environment of temperature 10° C. and relative humidity 20% RH.

First, 100 sheets of a print pattern (printing rate of 5%) were printed on a recording medium (A4 size paper) at intervals of 2 seconds. After that, images for evaluation were created.

The image for evaluation consisted of an area (area A) corresponding to one reference circumference of the photosensitive member and an area (area B) corresponding to one circumference next to the reference circumference. Area A was composed of a solid image (image density 100%) and a blank image (image density 0%) in the solid image area. That is, in the area A, an image in which a blank image is surrounded by a solid image is formed. In the region B, a full-surface halftone image (image density 40%) was formed.

In the area B of the evaluation image, the portion corresponding to the blank image of the area A was observed with the naked eye and with a magnifying glass (10 times magnification, TL-SL10K manufactured by TRUSCO). When transfer memory occurs, in area B, the image density at the portion corresponding to the non-image portion (rectangular blank image) on the reference circumference is lower than the image density at the portion corresponding to the image portion (solid image) on the reference circumference. becomes darker. Based on the following criteria, the presence or absence of image ghost caused by transfer memory was evaluated from the observation results of the image for evaluation. The evaluation results are shown in Table 5 below. In addition, evaluation A was set as the pass.

(Evaluation Criteria for Image Ghost Caused by Transfer Memory)
Evaluation A: Image ghost corresponding to image A was not observed, or was observed at a level of practically no problem.
Evaluation B: An image ghost corresponding to image A was clearly observed, and the level was practically problematic.

Photoreceptors (B-1), (B-2), (B-5) and (B-6) did not have good sensitivity characteristics, so evaluation of image ghost was omitted.

In the photoreceptors (A-1) to (A-9), the content of the charge generating agent in the photosensitive layer is 0.50% by mass or more and 1.50% by mass or less, and the temperature is 23° C. and the electric field strength is 1.5×. In the measurement under the condition of 10 ⁵ V/cm, the xerographic gain in the photosensitive layer is 32.0% or more, and the hole mobility _μh and the electron mobility μe are both 1.00×10 ^{−7 .} cm ² /V or more, and the ratio of electron mobility μ _e to hole mobility μ _h (μ _e /μ _h ) was 1/50.0 or more and 1/1.0 or less. As a result, as is clear from Table 5, FIGS. 9 and 10, the photoreceptors (A-1) to (A-9) were excellent in charging characteristics. In particular, photoreceptors (A-1) to (A-9) exhibited excellent charging properties even when the process time from static elimination to charging was short (for example, 200 milliseconds or less). Moreover, as is clear from Table 5, FIGS. 11 and 12, the photoreceptors (A-1) to (A-9) were also excellent in sensitivity characteristics. Furthermore, as is clear from Table 5, the image forming apparatuses using the photosensitive members (A-1) to (A-9) were able to suppress image ghosts caused by transfer memory.

On the other hand, photoreceptors (B-1), (B-2), (B-5) and (B-6) have a charge generating agent content of less than 0.50% by mass in the photosensitive layer and The xerographic gain in the photosensitive layer was less than 32.0% when measured at 23° C. and a field strength of 1.5×10 ⁵ V/cm. As a result, as is clear from Table 5, FIGS. 11 and 12, photoreceptors (B-1), (B-2), (B-5) and (B-6) did not have good sensitivity characteristics. rice field.

Photoreceptors (B-3), (B-4), (B-7) and (B-8) contained more than 1.50% by mass of the charge generating agent in the photosensitive layer. As a result, as is clear from Table 5, FIGS. 9 and 10, the photoreceptors (B-3), (B-4), (B-7) and (B-8) did not have good charging performance. In particular, when the process time from static elimination to charging was shortened (for example, 200 milliseconds or less), the charging potential V ₀ was remarkably lowered. In addition, as is clear from Table 5, photoreceptors (B-3), (B-4), (B-7) and (B-8) could not sufficiently suppress image ghost caused by transfer memory. rice field.

As described above, in the image forming apparatus and the image forming method of the present invention, the content of the charge generating agent in the photosensitive layer is 0.50% by mass or more and 1.50% by mass or less, the temperature is 23° C., and the electric field strength is 1.50% by mass. The xerographic gain in the photosensitive layer was 32.0% or more, and the hole mobility μ _h and electron mobility μ e were both 1.00×10 when measured under the condition of 5×10 ⁵ V/cm. ⁻⁷ cm ² /V or more, and the ratio of electron mobility μ _e to hole mobility μ _h (μ _e /μ _h ) is 1/50.0 or more and 1/1.0 or less. It was confirmed that the use of the toner can improve the charging characteristics and sensitivity characteristics of the photoreceptor and can suppress image ghosts caused by transfer memory. Further, it was confirmed that the photoreceptor described above exhibits excellent charging characteristics even if the process time from static elimination to charging is shortened.

The image forming apparatus and image forming method according to the present invention can be used for image formation.

1 Photoreceptor 2 Conductive substrate 3 Photosensitive layer 4 Intermediate layer 5 Protective layer 30 Image carriers 40a, 40b, 40c: Image forming unit 42 Charging section 44 Exposure section 46 Development section 48 Transfer section 50 Transfer belt 52 Cleaning section 54 Fixing section 100 image forming apparatus P recording medium

Claims (10)

an image carrier;
a charging unit that positively charges the surface of the image carrier;
an exposure unit that exposes the charged surface of the image carrier to form an electrostatic latent image on the surface of the image carrier;
a developing unit that supplies toner to the electrostatic latent image and develops the electrostatic latent image as a toner image;
An image forming apparatus comprising a transfer section for transferring the toner image from the image bearing member to a transfer receiving member,
The image carrier is a positively charged single-layer electrophotographic photoreceptor comprising a conductive substrate and a single-layer photosensitive layer,
The photosensitive layer contains a charge generating agent, a hole transport agent, an electron transport agent and a binder resin,
The content of the charge generating agent in the photosensitive layer is 0.50% by mass or more and 1.50% by mass or less,
In the measurement at a temperature of 23° C. and an electric field strength of 1.5×10 ⁵ V/cm,
The xerographic gain in the photosensitive layer is 32.0% or more;
Both the hole mobility μ _h and the electron mobility μ _e in the photosensitive layer are 1.0×10 ⁻⁷ cm ² /V/sec or more,
a ratio (μ _e /μ _h ) of the electron mobility μ _e to the hole mobility μ _h is 1/50.0 or more and 1/1.0 or less;
the charging unit is in contact with the image carrier and applies a DC voltage to the image carrier;
The electron transport agent includes a compound represented by the following chemical formula (ETM-1) and a compound represented by the following chemical formula (ETM-3),
The image forming apparatus , wherein the hole transport agent contains a compound represented by the following chemical formula (HTM-1) .

2. The image forming apparatus according to claim 1, wherein the charge generating agent contains a compound represented by the following formula (CGM-1).

3. The method according to claim 1, wherein a ratio (μ _e /μ _h ) of the electron mobility μ _e to the hole mobility μ _h is 1/10.0 or more and 1/1.0 or less. Image forming device. 4. The image forming apparatus according to claim 1, wherein the xerographic gain in said photosensitive layer is 41.0% or less. 5. The method according to claim 1, wherein both the hole mobility μ _h and the electron mobility μ _e in the photosensitive layer are 1.0×10 ⁻⁵ cm ² /V/sec or less. 10. The image forming apparatus according to claim 1. The image forming apparatus according to any one of claims 1 to 5 , wherein the binder resin includes a polyarylate resin having a repeating unit represented by the following general formula (20).

(In the general formula (20),
R ²⁰ and R ²¹ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms,
R ²² and R ²³ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group;
R ²² and R ²³ may combine with each other to represent a divalent group represented by the following general formula (W),
Y represents a divalent group represented by the following chemical formula (Y1), (Y2), (Y3), (Y4), (Y5) or (Y6). )

(In the general formula (W),
t represents an integer of 1 or more and 3 or less,
* represents a bond. )

7. The image forming apparatus according to claim 6 , wherein the polyarylate resin has a main chain represented by the following chemical formula (PA-1a) and terminal groups represented by the following chemical formula (Z).

(In the chemical formula (Z), * represents a bond.) With respect to the sum of the hole transport agent, the electron transport agent and the binder resin in the photosensitive layer,
The content of the hole transport agent is 10.0% by mass or more and 40.0% by mass or less,
The image forming apparatus according to any one of claims 1 to 7, wherein the content of the electron transport agent is 10.0% by mass or more and 40.0% by mass or less. further comprising a charge removing unit for removing charge from the surface of the image bearing member after the toner image has been transferred to the transfer receiving member;
9. The method according to any one of claims 1 to 8, wherein the time from when a predetermined portion of the surface of the image carrier is neutralized by the neutralization unit to when it is charged by the charging unit is 200 milliseconds or less. The described image forming apparatus. An image forming method using the image forming apparatus according to any one of claims 1 to 8 ,
The image forming apparatus further includes a charge removing section that removes charges from the surface of the image carrier after the toner image has been transferred to the transfer material,
a charging step of positively charging the surface of the image carrier;
an exposure step of exposing the surface of the charged image carrier to form an electrostatic latent image on the surface of the image carrier;
a developing step of supplying toner to the electrostatic latent image and developing the electrostatic latent image as a toner image;
a transfer step of transferring the toner image from the image carrier to a transfer target;
a charge removing step of removing charges from the surface of the image carrier after the toner image has been transferred to the transfer material;
The image forming method according to claim 1, wherein the time from when a predetermined portion of the surface of the image carrier is neutralized in the neutralization step until it is charged in the charging step is 200 milliseconds or less.

Images