JP2020020906A - Image forming apparatus and image forming method - Google Patents

Abstract

To provide an image forming apparatus that comprises an electrophotographic photoreceptor excellent in charging characteristics and sensitivity characteristics and can prevent image ghost caused by transfer memory.SOLUTION: An image forming apparatus of the present invention comprises: an image carrier; a charging unit that charges a surface of the image carrier in a positive polarity; 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 a toner to the electrostatic latent image to develop the electrostatic latent image as a toner image; and a transfer unit that transfers the toner image from the image carrier to a transfer target body. The image carrier is a photoreceptor including a conductive substrate and a photosensitive layer. The photosensitive layer contains a charge generating agent, a hole transport agent, an electron transport agent, and a binder resin. In the photosensitive layer, the content ratio of the charge generating agent is 0.50 mass% or more and 1.50 mass% or less; the xerographic gain is 32.0% or more; the mobility μof a hole and the mobility μof an electron are 1.00×10cm/V/sec or more; the ratio (μ/μ) is 1/50.0 or more and 1/1.0 or less.SELECTED DRAWING: Figure 1

Description

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

  2. Description of the Related Art An electrophotographic image forming apparatus (for example, a printer and a multifunction peripheral) includes an electrophotographic photosensitive member as an image carrier. The electrophotographic photoreceptor includes a photosensitive layer. Examples of the electrophotographic photoconductor include a single-layer electrophotographic photoconductor and a laminated electrophotographic photoconductor. The single-layer type electrophotographic photoreceptor includes a single-layer photosensitive layer having a charge generation function and a charge transport function. The layered 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 provided in the image forming apparatus described in Patent Literature 1 has a photosensitive layer containing an electron transporting agent having a certain or higher electron mobility.

JP 2012-155202 A

  However, according to studies by the present inventors, the image forming apparatus described in Patent Document 1 has room for improvement in charging characteristics and sensitivity characteristics of an electrophotographic photosensitive member, and suppression of image ghost caused by a 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 that include an electrophotographic photosensitive member having excellent charging characteristics and sensitivity characteristics and that can suppress an image ghost caused by a transfer memory. It is to provide.

The image forming apparatus according to the present invention includes an image carrier, a charging unit configured to positively charge the surface of the image carrier, and exposing the charged surface of the image carrier to expose the surface of the image carrier. An exposure section for forming an electrostatic latent image on a surface; a developing section for supplying toner to the electrostatic latent image to develop the electrostatic latent image as a toner image; and a developing section for applying the toner image from the image carrier. And a transfer unit for transferring to a transfer body. The image carrier is a positively charged single-layer type electrophotographic photoreceptor including a conductive substrate and a single-layer photosensitive layer, wherein the photosensitive layer includes a charge generating agent, a hole transporting agent, an electron transporting agent, Contains binder resin. The content ratio of the charge generating agent in the photosensitive layer is from 0.50% by mass to 1.50% by mass. In the measurement under the conditions of a temperature of 23 ° C. and an electric field intensity of 1.5 × 10 ⁵ V / cm, the xerographic gain in the photosensitive layer was 32.0% or more, and the mobility μ _{h of} holes in the photosensitive layer. And the electron mobility μ _e are each 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 according to the present invention is an image forming method using the above-described image forming apparatus. The image forming apparatus further includes a charge removing unit that removes the charge on the surface of the image carrier after transferring the toner image to the transfer target. The image forming method according to the present invention includes a charging step of charging the surface of the image carrier to a positive polarity, and exposing the charged surface of the image carrier to electrostatically charge 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 and developing the electrostatic latent image as a toner image, and transferring the toner image from the image carrier to a transfer target And a charge removing step of removing the charge on the surface of the image carrier after transferring the toner image to the transfer target. The time from when the predetermined portion of the surface of the image bearing member is neutralized in the neutralization step to when it is charged in the charging step is 200 milliseconds or less.

  The image forming apparatus of the present invention includes an electrophotographic photosensitive member having excellent charging characteristics and sensitivity characteristics, and can suppress image ghost caused by a transfer memory. The image forming method of the present invention has excellent charging characteristics and sensitivity characteristics of the electrophotographic photoreceptor used and can suppress image ghost caused by the transfer memory.

FIG. 2 is a partial cross-sectional view illustrating an example of a structure of a positively charged single-layer type electrophotographic photoconductor provided in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a partial cross-sectional view illustrating an example of a structure of a positively charged single-layer type electrophotographic photoconductor provided in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a partial cross-sectional view illustrating an example of a structure of a positively charged single-layer type electrophotographic photoconductor provided in the image forming apparatus according to the first embodiment of the present invention. FIG. 1 is a diagram illustrating an example of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a diagram illustrating an image in which an image ghost has occurred. 4 is a graph showing the relationship between the content ratio of a charge generating agent measured in an example and xerographic gain. 4 is a graph showing the relationship between the xerographic gain measured in the example and the potential after exposure. 4 is a graph showing the relationship between the charge generating agent content ratio measured in the examples and the charging potential. 4 is a graph showing a relationship between a process time measured in an example and a charging potential. 4 is a graph showing a relationship between a process time measured in an example and a charging potential. 4 is a graph showing a post-exposure potential measured in an example. 4 is a graph showing a post-exposure potential measured in an example.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. The present invention can be implemented with appropriate modifications within the scope of the present invention. In addition, although the description may be omitted as appropriate for portions where the description is duplicated, the gist of the invention is not limited.

  Hereinafter, a compound and its derivative may be generically referred to by adding “system” after the compound name. Further, when a polymer name is indicated by adding “system” after the compound name, it means that the repeating unit of the polymer is derived from the compound or its derivative.

  Hereinafter, a halogen atom, an alkyl group having 1 to 8 carbon atoms, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4 carbon atoms are Unless otherwise specified, each has the following meaning.

  Examples of the halogen atom (halogen group) include a fluorine atom (fluoro group), a chlorine atom (chloro group), a bromine atom (bromo group), and an iodine atom (iodo group).

  The alkyl group having 1 to 8 carbon atoms, the alkyl group having 1 to 5 carbon atoms, and the alkyl group having 1 to 4 carbon atoms are linear or branched and unsubstituted, respectively. Examples of the alkyl group having 1 to 8 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, 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 And branched octyl groups. Examples of the alkyl group having 1 or more and 5 or less carbon atoms or the alkyl group having 1 or more and 4 or less carbon atoms are the groups described as examples of the alkyl group having 1 or more and 8 or less carbon atoms. The following groups or groups having 1 to 4 carbon atoms.

  The alkoxy group having 1 to 4 carbon atoms is straight-chain or branched and unsubstituted. Examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a sec-butoxy group, and a tert-butoxy group.

<First Embodiment: Image Forming Apparatus>
The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier to a positive polarity, and a surface of the charged image carrier that is exposed to light, and the surface of the image carrier is statically exposed. An exposure section for forming an electrostatic latent image, a developing section for supplying toner to the electrostatic latent image and developing the electrostatic latent image as a toner image, and a transfer section for transferring the toner image from the image carrier to the transfer target And The image bearing member is a positively charged single-layer type electrophotographic photosensitive member including a conductive substrate and a photosensitive layer (hereinafter, may be referred to as a photosensitive member). The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent, and a binder resin. The content ratio of the charge generating agent in the photosensitive layer is from 0.50% by mass to 1.50% by mass. In the measurement of the condition of a temperature 23 ° C. and the electric field strength 1.5 × 10 ⁵ V / cm, xerographic gain in the photosensitive layer is 32.0% or more, of holes in the light-sensitive layer mobility mu _h and electronic Has a mobility μ _e of 1.0 × 10 ⁻⁷ cm ² / V / sec or more, and a ratio of the electron mobility μ _{e to} the hole mobility μ _h (μ _e / μ _h ). Is not less than 1 / 50.0 and not more than 1 / 1.0.

[Positively charged single-layer type electrophotographic photoreceptor]
First, a photoconductor provided as an image carrier in the image forming apparatus according to the present embodiment will be described. 1, 2 and 3 are partial cross-sectional views showing the structure of the photoconductor 1.

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

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

  As shown in FIG. 3, the photoconductor 1 may include a conductive base 2, a photosensitive layer 3, and a protective layer 5. The protective layer 5 is provided on the photosensitive layer 3. The protective layer 5 may be a single layer or a plurality of layers.

  The thickness of the photosensitive layer 3 is not particularly limited as long as the function as the photosensitive layer 3 can be sufficiently 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 photoconductor 1 has been described above with reference to FIGS. Hereinafter, the photoconductor will be described in more detail.

(Conductive substrate)
The conductive substrate is not particularly limited as long as it can be used as a conductive substrate of the photoreceptor. The conductive substrate only needs to be formed of a material having conductivity at least on its surface. As an example of the conductive substrate, a conductive substrate formed using a conductive material can be given. Another example of the conductive substrate is a conductive substrate coated with a material having conductivity. Examples of the conductive material 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 in combination of two or more (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 good.

  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. Further, 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 value or more, respectively, and set the electron mobility μ _e and By balancing the hole mobility μ _h and keeping the xerographic gain above a certain level, the charges (holes and electrons) generated in the photosensitive layer are efficiently transported and the residual charges are reduced. Was found. The present inventors have found that such a photoreceptor has excellent charging characteristics and sensitivity characteristics and can suppress an image ghost caused by a transfer memory when used as an image carrier of an image forming apparatus.

More specifically, as described in Patent Document 1 described above, conventionally, in improving the function of the photosensitive layer, the mobility of the charge of the charge transporting agent alone (the mobility of the hole of the hole transporting agent and the electron mobility). Attention has been focused on the electron mobility of the transport agent). Here, in the photoreceptor, charge generation due to exposure occurs relatively near the surface of the photosensitive layer. Then, among the generated charges, holes need to move a relatively long distance to the conductive substrate, whereas electrons need only move 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 larger than the electron mobility of the electron transport agent. Therefore, according to conventional knowledge, it is preferable that the electron mobility of the electron transporting agent is specified to be much smaller than the hole mobility of the hole transporting material (for example, 1 / 20000-fold or more and 1-fold). / 10 times or less).

  However, as a result of intensive studies, the present inventors have found that what is important in improving the charging characteristics of the photoconductor, the suppression performance of the transfer memory, and the sensitivity characteristics is not the charge mobility of the charge transporting agent alone but the hole transporting property. It has been found that the mobility of holes and electrons in the photosensitive layer in which the agent and the electron transporting agent are mixed to form a system in which the two interact. In addition, the present inventors have found that what is particularly important is the balance of hole and electron mobilities in the entire photosensitive layer. Then, the present inventors have found that the hole mobility of the hole transport material does not need to be much larger than the electron mobility of the electron transport material as in the related art. In particular, in an image forming apparatus, in order to meet demands for high speed and space saving, a process time from charge removal to charging in an image forming process tends to be shortened. Therefore, in the image forming apparatus, both holes and electrons generated by photoexcitation in the charge removal step are sufficiently removed from the photosensitive layer by the next charging step (that is, transported to the photosensitive layer surface or the conductive substrate). Is important. This is because if one of the holes and the electrons remains in the photosensitive layer, the remaining carriers hinder the charging in the next step. Therefore, the photoconductor is required to set the mobility of holes and electrons in the photosensitive layer.

  In addition, the present inventors have found that it is important to adjust 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 photoreceptor, the charge generating agent generates charges upon exposure, while temporarily trapping the movement of the generated charges and subsequently detrapping, thereby inhibiting the charging of the photosensitive layer surface. There is. In order to suppress the charge inhibition on the photosensitive layer surface by such a charge generating agent, it is important to minimize the content of the charge generating agent in the photosensitive layer. However, when the content of the charge generating agent in the photosensitive layer is reduced, the sensitivity characteristics of the photoreceptor deteriorate. Therefore, it is important to reduce the content of the charge generating agent within a range where a certain quantum efficiency (xerographic gain) can be maintained. The present inventors have completed the present invention in consideration of the above.

Measured at a temperature of 23 ° C. and an electric field strength of 1.5 × 10 ⁵ V / cm from the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghost caused by the transfer memory. The mobility μ _h of holes in the photosensitive layer to be formed is preferably 4.0 × 10 ⁻⁷ cm ² / V / sec or more. From the same viewpoint, the mobility μ _h of holes in the photosensitive layer is preferably equal to or less than 1.0 × 10 ⁻⁵ cm ² / V / sec, and is equal to or less than 1.0 × 10 ⁻⁶ cm ² / V / sec. 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. More specifically, there is a tendency that by increasing the content of the hole transfer agent mobility mu _h of holes is increased. Further, there is a tendency that the use of the hole transporting material excellent in hole-transport efficiency mobility mu _h of holes is increased.

Measured at a temperature of 23 ° C. and an electric field strength of 1.5 × 10 ⁵ V / cm from the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghost caused by the transfer memory. The electron mobility μ _e in the photosensitive layer to be formed is preferably 1.5 × 10 ⁻⁷ cm ² / V / sec or more. From the same viewpoint, the electron mobility μ _e in the photosensitive layer is preferably equal to or less than 1.0 × 10 ⁻⁵ cm ² / V / sec, and more preferably equal to or less than 1.0 × 10 ⁻⁶ cm ² / V / sec. It is 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 transporting agent. Specifically, when the content of the electron transporting agent is increased, the electron mobility μ _e tends to increase. Also, when an electron transporting agent having excellent electron transport efficiency is used, the electron mobility μ _e tends to increase.

From the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghost caused by the transfer memory, the temperature and the electric field strength are set at 23 ° C. and 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 from 1.0 / 10.0 to 1.0 / 1.0. , 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 solution containing a binder resin, a hole transporting agent, an electron transporting agent, and a solvent is applied on an aluminum substrate to form a sample layer (for example, a film thickness of 5 μm). The types of the binder resin, the hole transporting agent and the electron transporting agent in the sample coating liquid are the same as those of the photosensitive layer to be measured. Further, other components such as a charge generating agent and an additive are not contained in the sample coating solution. Further, the content of the hole transporting agent and the electron transporting agent in the sample coating solution is such that the content ratio (% by mass) of the hole transporting agent and the electron transporting agent in the formed sample layer is the same as that of the photosensitive layer to be measured. Adjust as follows. That is, the sample layer formed by the sample coating solution has the same type of binder resin and the same type and content of the electron transporting agent and the hole transporting agent as compared with the photosensitive layer to be measured, and the charge generation. The difference is that the agents and additives are replaced with the same amount of binder resin. Then, a sandwich cell is manufactured by forming a translucent gold electrode on the obtained sample layer by a vacuum evaporation method. Next, the resultant sandwich cell, the temperature 23 ° C., TOF method under the conditions of electric field strength 1.5 × 10 ⁵ V / cm by performing (Time of Flight) hole mobility μ of _h and electrons The mobility μ _e can be measured.

  Hereinafter, the charge generating agent, the hole transporting agent, the electron transporting agent, the binder resin, and the optional additive will be described.

(Charge generator)
The charge generator is not particularly limited as long as it is a charge generator for a photoreceptor. As the charge generator, for example, phthalocyanine pigments, perylene pigments, bisazo pigments, trisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, indigo pigments, azurenium pigments, cyanine Pigments, powders of inorganic photoconductive materials (for example, selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide or amorphous silicon), pyrylium pigments, ancesthrone-based pigments, triphenylmethane-based pigments, selenium-based pigments, toluidine-based pigments, Pyrazoline pigments and quinacridone pigments. One kind of the charge generating agent may be used alone, or two or more kinds may be used in combination.

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

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

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

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

  An example of a method for measuring a CuKα characteristic X-ray diffraction spectrum will be described. A sample (titanyl phthalocyanine) is filled in a sample holder of an X-ray diffractometer (for example, “RINT (registered trademark) 1100” manufactured by Rigaku Corporation), and an X-ray tube Cu, a tube voltage of 40 kV, a tube current of 30 mA, and CuKα are used. An X-ray diffraction spectrum is measured under the condition of a characteristic X-ray wavelength of 1.542 °. The measurement range (2θ) is, for example, not less than 3 ° and not more than 40 ° (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 thermal characteristics in a differential scanning calorimetry (DSC) spectrum.
(A) Y-type titanyl phthalocyanine having a peak in the range of 50 ° C. or more and 270 ° C. or less in a differential scanning calorimetric analysis spectrum, in addition to a peak associated with vaporization of absorbed water.
(B) Y-type titanyl phthalocyanine having no peak in the range of 50 ° C. or more and 400 ° C. or less in the differential scanning calorimetry spectrum other than the peak accompanying the vaporization of the adsorbed water.
(C) Y-type titanyl phthalocyanine having no peak in the range of 50 ° C. or more and 270 ° C. or less in the differential scanning calorimetric analysis spectrum other than the peak associated with the vaporization of the adsorbed water and having a peak in the range of 270 ° C. or more and 400 ° C. or less .

  As the Y-type titanyl phthalocyanine, in the differential scanning calorimetric analysis spectrum, it has no peak in the range of 50 ° C or more and 270 ° C or less except for the peak accompanying the vaporization of the adsorbed water, and has a peak in the range of 270 ° C or more and 400 ° C or less. Are more preferred. As the Y-type titanyl phthalocyanine having such a peak, one having one peak in the range of 270 ° C. or more and 400 ° C. or less 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 (for example, “TAS-200 DSC8230D” manufactured by Rigaku Corporation). The measurement range is, for example, 40 ° C. or more and 400 ° C. or less. The heating rate is, for example, 20 ° C./min.

  In a photoreceptor applied to an image forming apparatus using a short-wavelength laser light source (for example, a laser light source having a wavelength of 350 nm or more and 550 nm or less), an ensenzlon-based pigment is suitably used as a charge generating agent.

  The content ratio of the charge generating agent in the photosensitive layer is preferably from 0.70% by mass to 1.20% by mass.

  The content of the charge generating agent in the photosensitive layer is preferably from 0.5 to 20 parts by mass, more preferably from 1.0 to 10 parts by mass, based on 100 parts by mass of the binder resin. Particularly preferred is 5 parts by mass to 4.0 parts by mass.

From the viewpoint of further improving the electrical characteristics of the photoreceptor, the xerographic gain of the photosensitive layer measured at a temperature of 23 ° C. and an electric field strength of 1.5 × 10 ⁵ V / cm is preferably 35.0% or more. The above xerographic gain is preferably 41.0% or less, more preferably 38.0% or less. By setting the above-mentioned xerographic gain to 35.0% or more, the sensitivity characteristics of the photoconductor can be further improved. By setting the above-mentioned xerographic gain to 41.0% or less, the charging characteristics of the photoconductor can be further improved, and the image ghost caused by the transfer memory can be more effectively suppressed.

Here, the xerographic gain, the number of photons emitted in charged photosensitive layer and N _p, the number of the neutralized surface charge by charge generated is moved on the surface by irradiation was N _q Occasionally, it means the ratio of the number N _q of the neutralized surface charge to the number N _p of photons irradiated to the photosensitive layer.

The xerographic gain in the photosensitive layer can be measured by the following method. First, the photoreceptor is charged under a temperature condition of 23 ° C. while controlling the inflow current so as to have a predetermined charging potential (a range including a predetermined electric field strength between 100 V and 1000 V). Next, the charged photoconductor is exposed for 1 second, and the charged potential during the exposure is measured at regular intervals (for example, every 1 msec). The irradiation condition of the exposure light is such that the wavelength (λ) is 780 nm and the light intensity (I ₀ ) is 1.0 μW / cm ² . The measurement result of the charging potential is differentiated with time, the maximum value of the obtained decay rate is defined as ΔVmax, the surface potential when ΔVmax is measured is defined as SPmax, the film thickness of the photoconductor is defined as D, and the following formula (α) and The relationship between the xerographic gain and the electric field strength E is obtained from (β). 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 is calculated. In the following formula (α), εr indicates a relative dielectric constant, ε0 indicates a dielectric constant in a vacuum, e indicates an elementary charge, h indicates a Planck constant, and c indicates a light speed. It should be noted that the xerographic gain of the photosensitive layer can be measured by the same method for a photosensitive member having a protective layer provided 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 the hole transport agent include a nitrogen-containing cyclic compound and a condensed polycyclic compound. Examples of the nitrogen-containing cyclic compound and the condensed polycyclic compound include a triphenylamine derivative; a diamine derivative (more specifically, an N, N, N ′, N′-tetraphenylbenzidine derivative, N, N, N ', N'-tetraphenylphenylenediamine derivative, N, N, N', N'-tetraphenylnaphthylenediamine derivative, di (aminophenylethenyl) benzene derivative, N, N, N ', N'-tetraphenyl Oxadiazole-based compounds (more specifically, 2,5-di (4-methylaminophenyl) -1,3,4-oxadiazole and the like); styryl-based compounds (more Specifically, 9- (4-diethylaminostyryl) anthracene and the like); carbazole-based compounds (more specifically, polyvinyl carbazole and the like); Pyrazoline compounds (more specifically, 1-phenyl-3- (p-dimethylaminophenyl) pyrazolin and the like); hydrazone compounds; indole compounds; oxazole compounds; isoxazole compounds; thiazole compounds A thiadiazole compound; an imidazole compound; a pyrazole compound; and a triazole compound. One of these hole transporting agents may be used alone, or two or more thereof may be used in combination.

  The hole transport agent is a compound represented by the following general formula (10) (hereinafter referred to as a compound represented by the following general formula (10)) from the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghost caused by the transfer memory. , A hole transporting agent (10).)

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

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

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

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

  The content ratio of the hole transporting agent in the photosensitive layer is preferably from 10.0% by mass to 40.0% by mass, more preferably from 15.0% by mass to 30.0% by mass.

  The content of the hole transporting agent in the photosensitive layer is preferably from 20 parts by mass to 150 parts by mass, more preferably from 35 parts by mass to 120 parts by mass, and more preferably from 45 parts by mass to 70 parts by mass, per 100 parts by mass of the binder resin. It is more preferably at most part by mass.

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

  The electron transport agent has 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 ghost caused by the transfer memory. (Hereinafter, sometimes referred to as electron transporting agents (1) to (3), respectively).

In the 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. R ⁵ to R ⁸ each independently represent a hydrogen atom, 1 or more carbon atoms alkyl group of 4 or less, or a halogen atom.

In the 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 a methyl group and tert-butyl. Groups or 1,1-dimethylpropyl groups are more preferred.

In the general formulas (1) to (3), R ^{5 to} R ⁸ are preferably a hydrogen atom.

  As the electron transporting agents (1) to (3), from the viewpoint of further improving the charging characteristics and sensitivity characteristics of the photoreceptor and more effectively suppressing image ghost caused by the transfer memory, the following chemical formula (ETM-1) ) To (ETM-3) (hereinafter sometimes referred to as electron transporting agents (ETM-1) to (ETM-3), respectively) are preferred. A preferred example of the electron transporting agent (1) is an electron transporting agent (ETM-1). A preferred example of the electron transport agent (2) is an electron transport agent (ETM-3). A preferred example of the electron transport agent (3) is an electron transport agent (ETM-2).

  When the photosensitive layer contains two or more electron transporting agents, the photosensitive layer contains the electron transporting agents (ETM-1) and (ETM-2), or the electron transporting agents (ETM-1) and (ETM- Preferably, 3) is included. When the photosensitive layer contains two types of electron transporting agents, it is preferable that the two types of electron transporting agents are contained in substantially equal amounts. 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 from 40:60 to 60:40.

  The content ratio of the electron transport agent in the photosensitive layer is preferably from 10.0% by mass to 40.0% by mass, more preferably from 20.0% by mass to 30.0% by mass.

  The content of the electron transporting agent in the photosensitive layer is preferably from 15 parts by mass to 160 parts by mass, more preferably from 30 parts by mass to 100 parts by mass, and more preferably from 40 parts by mass to 60 parts by mass, per 100 parts by mass of the binder resin. Parts or less is more preferable.

(Binder resin)
Examples of the binder resin include a thermoplastic resin, a thermosetting resin, and a photocurable resin. As the thermoplastic resin, for example, polycarbonate resin, polyarylate resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, acrylic acid polymer, styrene-acrylic acid copolymer, 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 are exemplified. Examples of the thermosetting resin include a silicone resin, an epoxy resin, a phenol resin, a urea resin, and a melamine resin. Examples of the photocurable resin include an acrylic acid adduct of an epoxy compound and an acrylic acid adduct of a urethane compound. The photosensitive layer may contain only one kind of these binder resins, or may contain two or more kinds.

  The binder resin may be described as a polyarylate resin (hereinafter, polyarylate resin (PA)) having a repeating unit represented by the following general formula (20) (hereinafter, sometimes referred to as a repeating unit (20)). Is preferable.

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 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.

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

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

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

  In the general formula (W), t is preferably 2.

  The polyarylate resin (PA) preferably has only the repeating unit (20), but may further have another repeating unit. 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 the 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 a value obtained from one resin chain, but the entire polyarylate resin (PA) contained in the photosensitive layer (a plurality of substances). (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) may be described as a repeating unit represented by the following chemical formulas (20-a) and (20-b) (hereinafter, referred to as a repeating unit (20-a) or (20-b), respectively). ), And more preferably both repeating units (20-a) and (20-b).

  As the polyarylate resin (PA), for example, a resin having a repeating unit (20-a) and a repeating unit (20-b) can be used. In this case, the arrangement of the repeating units (20-a) and (20-b) is not particularly limited. That is, the polyarylate resin (PA) having the repeating units (20-a) and (20-b) is any of a random copolymer, a block copolymer, a periodic copolymer, and an alternating copolymer. Is also good. In this case, the amount of each of the repeating unit (20-a) and the repeating unit (20-b) of the polyarylate resin (PA) is preferably substantially the same. Specifically, the ratio (molar fraction) between the amount of the repeating unit (20-a) and the amount of the repeating unit (20-b) in the polyarylate resin (PA) is 49:51 or more and 51:51 or more. : 49 or less is preferable.

  The polyarylate resin (PA) may have a terminal group represented by the following chemical formula (Z). In the following chemical formula (Z), * represents a bond. When the polyarylate resin (PA) has a repeating unit (20-a) and a repeating unit (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 addition, in the following chemical formula (PA-1a), the number attached to the lower right of the repeating unit is the substance amount of the numbered repeating unit with respect to the substance amount of all the repeating units of the polyarylate resin (PA-1). Is shown (molar fraction). The polyarylate resin (PA-1) may be any of a random copolymer, a block copolymer, a periodic copolymer, and an alternating copolymer.

  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 abrasion resistance of the photoconductor 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 is easily dissolved in the solvent for forming the photosensitive layer, and the formation of the photosensitive layer tends to be facilitated.

(Additive)
Examples of the additive as an optional component include, for example, a deterioration inhibitor (more specifically, an antioxidant, a radical scavenger, a quencher, and an ultraviolet absorber), a softener, a surface modifier, a bulking agent, and a bulking agent. Examples include thickeners, dispersion stabilizers, waxes, donors, surfactants, and leveling agents. Examples of the leveling agent include silicone oil. When additives are added to the photosensitive layer, one kind of these additives may be used alone, or two or more kinds may be used in combination.

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

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

(Intermediate layer)
As described above, the photoconductor may have an intermediate layer (for example, an undercoat layer). The intermediate layer contains, for example, inorganic particles and a resin used for the intermediate layer (a resin for the intermediate layer). When an intermediate layer is interposed, the flow of current generated when exposing the photosensitive member is smoothed, and the rise in electric resistance can be suppressed while maintaining an insulating state that can suppress leakage.

  Examples of the inorganic particles include metal (more specifically, aluminum, iron, copper, etc.) particles and metal oxides (more specifically, titanium oxide, alumina, zirconium oxide, tin oxide, zinc oxide, etc.). And particles of a nonmetal oxide (more specifically, silica or the like). One type of these inorganic particles may be used alone, or two or more types may be used in combination. The inorganic particles may have been subjected to a surface treatment.

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

(Method of manufacturing photoconductor)
The photoreceptor is manufactured, for example, by applying a coating solution for forming a photosensitive layer on a conductive substrate and drying the coating. The coating solution for forming a photosensitive layer is produced by dissolving or dispersing a charge generating agent, a hole transporting agent, an electron transporting agent, a binder resin, and optional components added as necessary in a solvent.

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

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

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

  The method for applying the coating solution for forming a photosensitive layer is not particularly limited as long as the coating solution can be uniformly applied on the conductive substrate. Examples of the coating method include a blade coating method, a dip coating method, a spray coating method, a spin coating method, and a bar coating method.

  The method of drying the coating solution for forming a photosensitive layer is not particularly limited, as long as the solvent in the coating solution can be evaporated, and examples thereof include a method of performing heat treatment (hot air drying) using a high-temperature dryer or a reduced-pressure dryer. Can be The heat treatment temperature is, for example, 40 ° C. or more and 150 ° C. or less. The heat treatment time is, for example, not less than 3 minutes and not more than 120 minutes.

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

[Tandem type color image forming apparatus]
Hereinafter, one aspect of the image forming apparatus according to the present embodiment will be described using a tandem type color image forming apparatus as an example. FIG. 4 is a diagram illustrating an example of the image forming apparatus according to the present embodiment. The image forming apparatus 100 according to the present embodiment includes the image carrier 30, a charging unit 42, an exposure unit 44, a developing unit 46, and a transfer unit 48. The image carrier 30 is the photoconductor 1 described above. The charging section 42 charges the surface of the image carrier 30. The charging polarity of the charging unit 42 is positive. The exposure section 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 and develops the electrostatic latent image as 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 into contact with the recording medium P (transfer medium). The outline of the image forming apparatus 100 according to the present embodiment has been described above.

  The image forming apparatus 100 according to the present embodiment includes the photosensitive member 1 having excellent charging performance and sensitivity characteristics, and can suppress image ghost caused by the 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 photoconductor 1 can suppress the transfer memory as described above. Therefore, the image forming apparatus 100 according to the present embodiment can suppress an image defect such as an image ghost described later. Hereinafter, an image ghost caused by the transfer memory will be described.

  When a transfer memory is generated in the image forming process, the non-exposure area around the reference circumference (one arbitrary round when an image is continuously formed) on the surface of the image carrier 30 becomes the exposure area around the reference circumference. , The electric potential tends to decrease at the time of charging next round of the reference round. For this reason, the non-exposure area of the reference circumference is more likely to attract the positively charged toner in the next round of the development process than in the normal state. As a result, an image reflecting the non-image portion (non-exposed area) of the reference rotation is likely to be formed in the next rotation of the reference rotation. The image defect in which the image reflecting the non-image portion of the reference circumference is formed in the next rotation is an image ghost generated due to the transfer memory.

  The image ghost will be described with reference to FIG. FIG. 5 is a diagram illustrating an image 60 in which an image ghost has occurred. Image 60 includes region 62 and region 64. The region 62 is a region corresponding to one rotation of the image carrier (one rotation of the reference rotation), and the region 64 is also a region corresponding to one rotation of the image carrier (one rotation of the next rotation of the reference rotation). Region 62 includes image 66. The image 66 is composed of a square solid image. The area 64 includes an image 68 and an image 69. The image 68 is a square halftone image. The image 69 is a halftone image of a region other than the image 68 in the region 64. The design image of the region 64 is a uniform halftone image over the entire surface. As shown in FIG. 5, the image 69 has a higher image density than the image 68. The image 69 is an image defect (image ghost) that reflects the non-exposed area of the area 62 and is darker than the design image density.

  Hereinafter, each part 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 unit 48 transfers the toner image to the recording medium P while bringing the surface of the image carrier 30 into contact with the recording medium P. Usually, in an image forming apparatus employing a direct transfer method, a transfer memory is easily generated because the image carrier is easily affected by a transfer bias. However, since the image forming apparatus 100 according to the present embodiment includes the above-described photoconductor 1 as the image carrier 30, the transfer memory can be effectively suppressed. As described above, since the photoconductor 1 is provided as the image carrier 30, the image ghost caused by the transfer memory is suppressed even in the image forming apparatus 100 employing the direct transfer method.

  The image forming apparatus 100 includes image forming units 40a, 40b, 40c, and 40d, a transfer belt 50, and a fixing unit 54. Hereinafter, each of the image forming units 40a, 40b, 40c, and 40d will be referred to as an image forming unit 40 unless it is necessary to distinguish them.

  The image forming unit 40 includes 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 for cleaning the surface of the image carrier 30. The cleaning unit 52 is a cleaning blade. Normally, in an image forming apparatus provided with a cleaning blade, the image carrier is likely to be triboelectrically charged due to the contact between the image carrier and the cleaning blade. For this reason, in an image forming apparatus provided with a cleaning blade, a transfer memory is likely to occur due to charges generated by frictional charging remaining in the image carrier. However, the image forming apparatus 100 according to the present embodiment includes the above-described photoconductor 1 as the image carrier 30. The photoconductor 1 can suppress transfer memory. Therefore, by providing the above-described photoconductor 1 as the image carrier 30, even in the image forming apparatus 100 including the cleaning blade, image ghost caused by the transfer memory can be effectively suppressed.

  The image carrier 30 is provided rotatably in the arrow direction (counterclockwise) at the center position of the image forming unit 40. 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 rotation direction of the image carrier 30 with respect to the charging unit 42. Can be It is preferable that the image forming unit 40 further includes a charge removing unit (not shown) that removes the charge on the surface of the image carrier 30 after the toner image is transferred to the transfer target. In this case, the time from the time when the predetermined portion on the surface of the image carrier 30 is neutralized by the neutralization unit to the time when it is charged again by the charging unit 42 (the process time from the neutralization to the charging) is preferably 200 milliseconds or less. . By setting the process time from charge elimination to charging to 200 milliseconds or less, the speed and size of the image forming apparatus 100 can be reduced. The predetermined location is, for example, one location (for example, one location) on the surface of the image carrier 30. On the other hand, in the conventional image forming apparatus, if the process time from charge removal to charging is shortened, it tends to be difficult to charge the surface of the image carrier to a desired potential. However, the image forming apparatus 100 according to the present embodiment includes the above-described photoconductor 1 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 above-described photoconductor 1 as the image carrier 30, so that even if the process time from the charge elimination to the charging is set to 200 milliseconds or less, the image carrier 30 can be a desired image carrier. It can be charged to a potential. The process time from static elimination to charging is preferably 160 milliseconds or less, more preferably 120 milliseconds or less. Further, the process time from charge elimination to charging is preferably 30 milliseconds or more, more preferably 80 milliseconds or more.

  By each of the image forming units 40a to 40d, toner images of a plurality of colors (for example, four colors of black, cyan, magenta, and yellow) are sequentially superimposed 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. An example of another contact charging type charging unit is a charging brush. Further, the charging unit may be a non-contact type. Examples of the non-contact charging unit include a corotron charging unit and a scorotron charging unit.

  The voltage applied by the charging unit 42 is not particularly limited. Examples of the voltage applied by the charging unit 42 include a DC voltage, an AC voltage, and a superimposed voltage (a voltage obtained by superimposing an AC voltage 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 the DC voltage, the voltage applied to the image carrier 30 is constant, so that the surface of the image carrier 30 is easily charged uniformly to a constant potential. When the charging unit 42 applies only the DC voltage, the wear amount of the photosensitive layer tends to decrease. As a result, a good image can be formed. The charging unit 42 can apply a DC voltage to the image carrier 30 by contacting the image carrier 30.

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

  The developing unit 46 supplies toner to the surface of the image carrier 30, and develops the electrostatic latent image as a toner image. As the developing unit 46, for example, a developing unit that develops the electrostatic latent image as a toner image while contacting 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 unit 48. The transfer belt 50 is an endless belt. The transfer belt 50 is provided so as to be rotatable in the arrow direction (clockwise).

  The transfer unit 48 transfers the toner image developed by the developing unit 46 from the surface of the image carrier 30 to the recording medium P. When the toner image is transferred from the image carrier 30 to the recording medium P, the image carrier 30 is in contact with the recording medium P. The transfer unit 48 includes, for example, a transfer roller.

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

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

<Second embodiment: image forming method>
The image forming method according to the present embodiment is an image forming method using the image forming apparatus according to the first embodiment. The image forming apparatus further includes a charge removing unit that removes the charge on the surface of the image carrier after transferring the toner image to the transfer target. The image forming method according to this embodiment includes a charging step of charging the surface of the image carrier to a positive polarity, and exposing the charged surface of the image carrier to form an electrostatic latent image on the surface of the image carrier. Exposing, supplying toner to the electrostatic latent image, developing the electrostatic latent image as a toner image, transferring the toner image from the image carrier to the transfer target, and transferring the toner image And a charge removing step of removing the charge on the surface of the image carrier after the image is transferred to the transfer target. The time from the neutralization of the predetermined portion on the surface of the image carrier in the neutralization step to the charging in the charging step (process time from neutralization to charging) 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. Further, the process time from charge elimination to charging is preferably 30 milliseconds or more, more preferably 80 milliseconds or more. For details of the charging step, the exposing step, the developing step, the transferring step, and the discharging step, for example, the functions of the charging section, the exposing section, the developing section, the transferring section, and the discharging section of the image forming apparatus according to the first embodiment are described. Can be referenced. The image forming method according to the present embodiment has excellent charging characteristics and sensitivity characteristics of an electrophotographic photosensitive member to be used, and can suppress image ghost caused by a transfer memory.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the invention is not at all limited to the scope of the examples.

<Material for forming photosensitive layer>
The following charge generating agent, hole transporting agent, electron transporting agent, and binder resin were prepared as materials for forming the photosensitive layer of the photoreceptor.

(Charge generator)
As the charge generator, Y-type titanyl phthalocyanine and metal-free phthalocyanine were prepared (hereinafter sometimes referred to as charge generators (CGM-1) and (CGM-2), respectively). The charge generator (CGM-1) was titanyl phthalocyanine represented by the chemical formula (CGM-1) described in the embodiment and having a Y-type crystal structure. This Y-type titanyl phthalocyanine has no peak in the range of 50 ° C. or more and 270 ° C. or less in the differential scanning calorimetric analysis spectrum other than the peak accompanying the vaporization of the adsorbed water, and has a peak in the range of 270 ° C. or more and 400 ° C. or less. (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)
The hole transporting agent (HTM-1) described in the embodiment was prepared as the hole transporting agent.

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

(Binder resin)
As the 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>
Photoconductors (a-1) to (a-8) and (b-1) to (b-6) in order to investigate the relationship between the type and content ratio of the charge generating agent in the photosensitive layer of the photoconductor and the xerographic gain. Was manufactured.

[Manufacture of photoconductor]
In a container, 65 parts by mass of a charge generating agent, a hole transporting agent (10-1), 33.5 parts by mass of an electron transporting agent (ETM-1), 33.5 parts by mass of an electron transporting agent (ETM-3), and a binder 138 parts by mass of a polyarylate resin (PA-1) as a resin and a solvent (tetrahydrofuran) were charged. Thus, a coating solution for forming a photosensitive layer was obtained. The type and content ratio of the charge generating agent contained in the coating solution for forming a 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 generator, hole transport agent, electron transport agent, and binder resin) of the coating solution for forming a photosensitive layer. The same applies to “wt%” in Tables 2 to 4 described below. A coating solution for forming a photosensitive layer was applied by a dip coating method on an aluminum drum-shaped support (diameter 30 mm, total length 247.5 mm) as a conductive substrate to form a coating film. The coating film was dried with hot air at 100 ° C. for 40 minutes. Thus, a single 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 ratio 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 photoconductors (a-1) to (a-8) and (b-1) to (b-6), a xerographic image was formed on the photosensitive layer by using a drum sensitivity tester (Gentec Corporation). The gain was measured. First, each photoreceptor was charged under a temperature condition of 23 ° C. while controlling a current flowing into the photoreceptor so as to have a predetermined charging potential (100 to 1000 V). Each charged photoreceptor was exposed for 1 second, and the charged potential during the exposure was measured at regular intervals (every millisecond). The irradiation conditions of the exposure light were such that the wavelength (λ) was 780 nm and the light intensity (I ₀ ) was 1.0 μW / cm ² . The measurement result of the charging potential is differentiated with time, the maximum value of the obtained decay rate is defined as ΔVmax, the surface potential when ΔVmax is measured is defined as SPmax, the film thickness of the photoconductor is defined as D, and the following formula (α) and From (β), the relationship between the xerographic gain and the electric field strength E was determined. In this measurement, the above procedure was repeated while changing the charging potential so as to include an electric field intensity of 1.5 × 10 ⁵ V / cm. From the relationship between the obtained xerographic gain and the electric field strength E, the xerographic gain at an electric field strength 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 a relative dielectric constant, ε0 indicates a dielectric constant in a vacuum, e indicates an elementary charge, h indicates a Planck constant, and c indicates a light speed.
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 (% by mass) of the charge generating agent.

  As shown in Table 1 and FIG. 6, in the photosensitive layer of each photosensitive member, it was confirmed that the xerographic gain increased as the content ratio of the charge generating agent increased. The photoconductors (a-1) to (a-8) using the charge generator (CGM-1) are the photoconductors (b-1) to (b-) using the charge generator (CGM-2). Compared with 6), it was confirmed that the xerographic gain per content ratio of the charge generating agent was higher. For this reason, the charge generation agent (CGM-1) has a higher charge generation efficiency than the charge generation agent (CGM-2) and can generate more charges even if the content ratio is the same. Is determined.

<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 photosensitive member, photosensitive members (c-1) to (c-6) were manufactured, and the sensitivity characteristics were measured.

[Production of photoreceptor and measurement of xerographic gain]
Except for the following changes, the photoconductors (a-1) to (a-8) and (b-1) to (b-6) were manufactured in the same manner as in the production and measurement of the xerographic gain. Production of c-1) to (c-6) and measurement of xerographic gain were performed. In the production of the photoconductors (a-1) to (a-8) and (b-1) to (b-6), the types and the content ratios of the charge generators were as shown in Table 1. In the production of -1) to (c-6), the results are shown in Table 2 below. The measurement results of the xerographic gain in the photosensitive layers of the photoconductors (c-1) to (c-6) are shown in Table 2 below and FIG.

[Measurement of sensitivity characteristics]
The sensitivity characteristics (potential after exposure _VL ) of the photoreceptor were measured in an environment at a temperature of 23 ° C. and a relative humidity of 50% RH. A color image forming apparatus ("Task alpha 356ci" manufactured by Kyocera Document Solutions Inc.) was used as an evaluation machine. This image forming apparatus was provided with a contact type charging roller for applying a DC voltage.

In the measurement of the post-exposure potential V _L, the photoreceptor is first mounted on an evaluation machine, and the photoreceptor is charged so that the surface potential (non-exposed portion) becomes +500 V ± 10 V by adjusting the voltage applied to the charging roller. Was. Next, the photoconductor 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 the exposure, the surface potential of the photoreceptor at the developing part position was measured, and this was defined as the post-exposure potential V _L (unit: + V). The smaller the absolute value of the post-exposure potential, the better the sensitivity characteristics of the photoconductor. The evaluation results are shown in Table 2 below and FIG.

  As shown in Table 2 and FIG. 7, the photosensitive member was superior in sensitivity characteristics as the xerographic gain in the photosensitive layer was higher, as the absolute value of the post-exposure potential was lower. Here, in order to form a good image, it is preferable that the post-exposure potential of the photoconductor be 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 having a good density cannot be formed. It should be noted that even for a photoreceptor whose absolute value after exposure, measured under the above-described conditions, exceeds 150 V in absolute value, it is possible to form an image having a good density by increasing the intensity of the exposure light. It is not preferable because it leads to up. From the above, it is determined that the xerographic gain in the photosensitive layer of the photosensitive member needs to be 32.0% or more.

  Here, the content ratio of the charge generating agent necessary for setting the xerographic gain to 32.0% or more from each photoconductor of FIG. 6 will be confirmed. As is clear from the photoconductors (a-1) to (a-8), when the charge generating agent (CGM-1) is used, the xerographic gain is set to 32 by setting the content ratio to 0.50% by mass or more. 0.0% or more. Further, as is apparent from the photoconductors (b-1) to (b-6), when the charge generating agent (CGM-2) is used, the content ratio of the charge generating agent is set to 1.50% by mass or more so that the xerographic gain can be reduced. Can be set to 32.0% or more.

  However, as described above, in the photosensitive layer of the single-layer type electrophotographic photosensitive member in which the charge generating agent, the electron transporting agent, and the hole transporting agent are mixed, the charge generating agent acts as a trap site to lower the charging performance. It is determined 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>
Photoconductors (d-1) to (d-10) were manufactured and the charging performance was measured in order to investigate the relationship between the charge generating agent content ratio in the photosensitive layer of the photoconductor and charging performance.

[Manufacture of photoconductor]
Except for the following changes, the photoconductors (d-1) to (d-1) to (a-1) to (a-8) and (b-1) to (b-6) were manufactured in the same manner as in the production of the photoconductors (d-1) to (b-6). d-10) was manufactured. In the production of the photoconductors (a-1) to (a-8) and (b-1) to (b-6), the types and the content ratios of the charge generators were as shown in Table 1. In the production of -1) to (d-10), the results are shown in Table 3 below.

[Measurement of charging performance]
In the measurement of the charging performance (charging potential V ₀ ), first, each photoconductor was mounted on an evaluation device (“CYNTHIA30M” manufactured by Gentec). The evaluation device includes a charging roller as a charging unit and an LED lamp as a charge removing unit. While rotating the photosensitive member, the surface of the photosensitive member is charged by the charging unit, and the charged surface of the photosensitive member is removed by the charge removing unit. It was a device to remove electricity. A transparent probe for measuring the surface potential of the photoconductor was attached to the exposure position of the evaluation device. In the evaluation, the charging potential V ₀ (unit: + V) of the photoconductor while maintaining the surface charge density of the photoconductor 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 photoconductor) was 215 mm / sec. The process time from when a predetermined portion of the surface of the photoreceptor was neutralized by the neutralization unit 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 photoconductor. 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 was substantially constant when the content ratio of the charge generating agent in the photosensitive layer was in the range of 0.50 to 1.50% by mass. However, when the content ratio of the charge generating agent exceeded 1.50% by mass, the content tended to decrease. As described above, the charge generating agent, when present in an excessive amount in the photosensitive layer, impedes charge transport and lowers the charging performance of the photoreceptor. Therefore, from the viewpoint of the charging performance of the photoconductor, it is determined that the content ratio of the charge generating agent in the photosensitive layer is desirably 1.50% by mass or less.

  In summary, in order to achieve both sensitivity characteristics and charging performance in the photoreceptor, the content ratio of the charge generating agent in the photosensitive layer is set to 0.50% by mass to 1.50% by mass and measured under the above conditions. It is determined that the required xerographic gain needs to be 32.0% or more. Hereinafter, further evaluation was performed using the image forming apparatus.

<Evaluation of image forming apparatus>
[Manufacture of photoconductor]
Except for the following changes, the photoconductors (A-1) to (A-1) to (a-8) and (b-1) to (b-6) are manufactured in the same manner as in the production of the photoconductors (A-1) to (b-6). A-9) and (B-1) to (B-8) were manufactured. In the production of the photoconductors (a-1) to (a-8) and (b-1) to (b-6), the types and content ratios of the charge generating agent, the electron transporting agent and the hole transporting agent are as described above. However, in the production of the photoconductors (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]
Hole mobility μ _h and 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 that of the photosensitive layer of each photosensitive member was formed by replacing the charge generating agent with the same amount of the binder resin, and otherwise forming the same layer. For the formation of this sample layer, a sample coating solution containing only a hole transporting agent, an electron transporting agent, a binder resin and a solvent was used. Each sample coating solution and the coating solution for forming the photosensitive layer used for forming the corresponding photoreceptor were the same with respect to the types of the binder resin, the hole transport agent, and the electron transport agent. On the other hand, each sample coating solution does not contain a charge generating agent, and instead has a mass part corresponding to the content of the charge generating agent, as compared with the photosensitive layer forming coating solution used for forming the corresponding photoreceptor. The only difference was that the content of the binder resin was increased.

The sample coating solution was applied to an aluminum substrate using a wire bar so as to have a thickness of 5 μm, and then dried to form a thin film (sample layer). Thereafter, a translucent gold electrode was vacuum-deposited on the thin film to produce a sandwich cell. The resulting sandwich cell, the temperature 23 ° C., the electric field strength 1.5 × 10 ⁵ V / cm normal TOF method under conditions of (Time of Flight) at the mobility of holes mu _h and electron mobility mu _e was measured. The mobility mu _h and electron mobility mu _e of holes was measured by sandwich cell was mobility mu _h and electron mobility mu _e of holes in the photosensitive layer of the photosensitive member.

In the measurement of the hole mobility μ _h and the electron mobility μ _e by the TOF method, half of the voltage was applied between the electrodes (semi-transparent gold electrode and aluminum substrate) of the sandwich cell while applying a voltage (75 V in absolute value). The thin film was irradiated with pulsed light (wavelength: 337 nm) via a transparent gold electrode. As a light source of the pulsed light, a nitrogen laser generator ("ULC-50" manufactured by Usho) was used. The change with time of the current generated by the irradiation of the pulsed light was measured with a storage scope (“TS-8123” manufactured by Iwasaki Communication Equipment Co., Ltd.). The temporal change of the current was represented by a log-logarithmic graph, and the transit time (tr, unit: second) was obtained based on the change in the slope. The charge mobility was calculated by substituting the film thickness (L), transit time (tr), and voltage (V) of the thin film into the following relational expression (μ). The measurement results are shown in Table 4 below.
Charge mobility = (L / tr) / (V / L) (μ)

[Measurement of charged potential for each process time]
Except for the following changes, the photoconductors (A-1) to (A-9) and (B-3) are measured in the same manner as the measurement of the charged potential of the photoconductors (d-1) to (d-10). ) was measured charge potential V ₀ (B-4), (B -7) and (B-8). In the measurement of the charging potential of the photoconductors (d-1) to (d-10), the process time from the charge elimination to the charging was fixed. On the other hand, in the measurement of the charged potential V ₀ of the photoconductors (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 the measurement of the charging potential V ₀ of the photoconductors (A-1) to (A-9), (B-3), (B-4), (B-7) and (B-8), Was made constant at 6.00 × 10 ⁻⁴ (C / m ² ). Charging characteristics of the photosensitive member, the charging potential V ₀ which when the process time is 200 milliseconds good if more than 490V (A), was evaluated as not good if less than 490V (B). The measurement results are shown in Table 5, FIG. 9 and FIG.

  As for the photoconductors (B-1), (B-2), (B-5) and (B-6), the measurement of the charging potential was omitted because the sensitivity characteristics were not good as described later.

[Measurement of post-exposure potential]
In the photosensitive member (c-1) ~ (c -6) the same way as the measurement of post-exposure potential V _0, a photoreceptor (A-1) ~ (A -9) and (B-1) ~ (B -8 The potential V ₀ after the exposure was measured. The post-exposure potential V ₀ of the photoreceptor was evaluated as good (A) when the absolute value was 150 V or less, and poor (B) when the absolute value exceeded 150 V. The measurement results are shown in Table 5 below, and FIGS. 11 and 12.

[Evaluation of image ghost caused by transfer memory]
It was evaluated whether or not each photoconductor can suppress image ghost caused by the transfer memory. First, the photoconductors (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 Inc.) An image forming apparatus was obtained by mounting the image carrier on TASKalfa 356ci "(process time from charge elimination to electrification of about 180 mm). This evaluation machine was provided with a scorotron charging device as a charging unit and a static elimination lamp as a static elimination unit. The charging potential of the image carrier was set to + 500V. The transfer bias of the image carrier was set to -10 μA. Using this image forming apparatus, the occurrence of image ghost caused by the transfer memory was evaluated. The evaluation was performed in an environment at a temperature of 10 ° C. and a relative humidity of 20% RH.

  First, 100 print patterns (print rate 5%) were printed on a recording medium (A4 size paper) at intervals of 2 seconds. Thereafter, an evaluation image was created.

  The evaluation image was composed of an area corresponding to one reference circumference of the photoreceptor (area A) and an area corresponding to the next circumference of the reference circumference (area B). The area A was composed of a solid image (image density 100%) and a white image (image density 0%) in the solid image area. That is, an image in which the white image is surrounded by the solid image is formed in the area A. In the region B, an entire halftone image (image density 40%) was formed.

  In the area B of the evaluation image, a portion corresponding to the white image in the area A was observed with the naked eye and a loupe (magnification: 10 times, manufactured by TRUSCO, TL-SL10K). When the transfer memory occurs, in the area B, the image density of the portion corresponding to the non-image portion (rectangular white image) on the reference circumference is larger than the image density of the portion corresponding to the image portion (solid image) of the reference circumference. Also darkens. Based on the following criteria, the presence or absence of an image ghost caused by the transfer memory was evaluated from the observation result of the evaluation image. The evaluation results are shown in Table 5 below. In addition, evaluation A was set to pass.

(Evaluation criteria for image ghost caused by transfer memory)
Evaluation A: The image ghost corresponding to the image A was not observed, or even if observed, it was at a level causing no practical problem.
Evaluation B: The image ghost corresponding to the image A was clearly observed, and was at a practically problematic level.

  The evaluation of the image ghost was omitted for the photoconductors (B-1), (B-2), (B-5) and (B-6) because the sensitivity characteristics were not good.

In the photoconductors (A-1) to (A-9), the content ratio of the charge generating agent in the photosensitive layer is 0.50% by mass to 1.50% by mass, 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 was 32.0% or more, and both the hole mobility μ _h and the electron mobility μ e were 1.00 × 10 ^−7. cm ² / V or more, and the ratio of the electron mobility μ _{e to} the hole mobility μ _h (μ _e / μ _h ) was 1 / 50.0 to 1 / 1.0. As a result, as is clear from Table 5, FIGS. 9 and 10, the photoconductors (A-1) to (A-9) had excellent charging characteristics. In particular, the photoconductors (A-1) to (A-9) exhibited excellent charging characteristics even when the process time from charge elimination to charging was short (for example, 200 milliseconds or less). Further, as is clear from Table 5, FIG. 11 and FIG. 12, the photoconductors (A-1) to (A-9) also had excellent sensitivity characteristics. Further, as is apparent from Table 5, the image forming apparatus using the photoconductors (A-1) to (A-9) was able to suppress the image ghost caused by the transfer memory.

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

In the photoconductors (B-3), (B-4), (B-7) and (B-8), the content ratio of the charge generating agent in the photosensitive layer was more than 1.50% by mass. As a result, as is clear from Table 5, FIGS. 9 and 10, the photoconductors (B-3), (B-4), (B-7) and (B-8) had poor 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 significantly reduced. Further, as is clear from Table 5, the photoconductors (B-3), (B-4), (B-7) and (B-8) cannot sufficiently suppress the image ghost caused by the transfer memory. Was.

From the above, according to the image forming apparatus and the image forming method of the present invention, the content ratio of the charge generating agent in the photosensitive layer is 0.50% by mass to 1.50% by mass, the temperature is 23 ° C., and the electric field strength is 1. In the measurement under the condition of 5 × 10 ⁵ V / cm, the xerographic gain in the photosensitive layer was 32.0% or more, and both the hole mobility μ _h and the electron mobility μe were 1.00 × 10 5. ^-7 cm ² / V or more, and a ratio of electron mobility μ _{e to} hole mobility μ _h (μ _e / μ _h ) of 1 / 50.0 or more and 1 / 1.0 or less. It has been confirmed that the use of the toner can improve the charging characteristics and the sensitivity characteristics of the photoreceptor and suppress image ghost caused by the transfer memory. Further, it was confirmed that the above-mentioned photoreceptor exhibited excellent charging characteristics even when the process time from charge elimination to charging was shortened.

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

Reference Signs List 1 photoconductor 2 conductive substrate 3 photosensitive layer 4 intermediate layer 5 protective layer 30 image carriers 40a, 40b, 40c: image forming unit 42 charging unit 44 exposure unit 46 development unit 48 transfer unit 50 transfer belt 52 cleaning unit 54 fixing unit 100 Image forming apparatus P recording medium

Claims (15)

An image carrier;
A charging unit that charges the surface of the image carrier to a positive polarity,
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;
A transfer unit for transferring the toner image from the image carrier to the transfer target, an image forming apparatus comprising:
The image carrier is a positively charged single-layer type electrophotographic photoreceptor including a conductive substrate and a single-layer photosensitive layer,
The photosensitive layer contains a charge generating agent, a hole transporting agent, an electron transporting agent and a binder resin,
The content ratio of the charge generating agent in the photosensitive layer is from 0.50% by mass to 1.50% by mass,
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 mobility μ _{h of} holes and the mobility μ _{e of} electrons in the photosensitive layer are 1.0 × 10 ⁻⁷ cm ² / V / sec or more,
The image forming apparatus, wherein a ratio of the electron mobility μ _{e to} the hole mobility μ _h (μ _e / μ _h ) is not less than 1 / 50.0 and not more than 1 / 1.0.   The image forming apparatus according to claim 1, wherein the charging unit contacts the image carrier and applies a DC voltage to the image carrier. The image forming apparatus according to claim 1, wherein the charge generating agent includes a compound represented by the following formula (CGM-1).

The ratio (μ _e / μ _h ) of the electron mobility μ _{e to} the hole mobility μ _h is not less than 1 / 10.0 and not more than 1 / 1.0. 2. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the xerographic gain in the photosensitive layer is 41.0% or less. The mobility μ _{h of the} holes and the mobility μ _{e of the} electrons in the photosensitive layer are both 1.0 × 10 ⁻⁵ cm ² / V / sec or less. Item 10. The image forming apparatus according to item 1. The image forming apparatus according to claim 1, wherein the electron transporting agent includes a compound represented by the following general formula (1), (2), or (3).

(In the 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,
R ⁵ to R ⁸ each independently represent a hydrogen atom, 1 or more carbon atoms alkyl group of 4 or less, or a halogen atom. ) The compound represented by the general formula (1) is represented by the following chemical formula (ETM-1),
The compound represented by the general formula (2) is represented by the following chemical formula (ETM-3),
The image forming apparatus according to claim 7, wherein the compound represented by the general formula (3) is represented by the following chemical formula (ETM-2).

The image forming apparatus according to claim 1, wherein the hole transporting agent includes a compound represented by the following general formula (10).

(In the 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. ) The image forming apparatus according to claim 9, wherein the compound represented by the general formula (10) is represented by the following chemical formula (HTM-1).

The image forming apparatus according to any one of claims 1 to 10, 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. )

The image forming apparatus according to claim 11, wherein the polyarylate resin has a main chain represented by the following chemical formula (PA-1a) and a terminal group represented by the following chemical formula (Z).

(In the chemical formula (Z), * represents a bond) For the total of the hole transporting agent, the electron transporting agent and the binder resin in the photosensitive layer,
The content ratio of the hole transporting agent is from 10.0% by mass to 40.0% by mass,
The image forming apparatus according to claim 1, wherein a content ratio of the electron transporting agent is 10.0% by mass or more and 40.0% by mass or less. The image forming apparatus further includes a static elimination unit configured to neutralize the surface of the image carrier after transferring the toner image to the transfer target body,
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, according to any one of claims 1 to 13, The image forming apparatus as described in the above. An image forming method using the image forming apparatus according to claim 1,
The image forming apparatus further includes a static elimination unit that neutralizes the surface of the image carrier after transferring the toner image to the transfer target body,
A charging step of charging the surface of the image carrier to a positive polarity,
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 the transfer target,
Removing the surface of the image carrier after transferring the toner image to the transfer object, and
An image forming method, wherein a time from when a predetermined portion on the surface of the image bearing member is neutralized in the neutralization step to when the predetermined part is charged in the charging step is 200 milliseconds or less.

Images