Electronic photography photosensitive member and image forming device including the same

Abstract

To provide a electronic photography photoreceptor using a known titanyl phthalocyanine addition product of 2, 3-butanediol as a charge generating material, the radiation photoreceptor capable of maintaining stable image characteristics without deteriorating chargeability even in long-term repetitive energization fatigue throughout the product life, and to provide an image forming apparatus including the radiation photoreceptor.SOLUTION: The electronic photography photoreceptor includes at least a laminated photosensitive layer in which a charge generation layer and a charge transport layer are laminated in this order on a substrate, wherein the electronic photography photoreceptor is characterized in that the charge generation layer contains, as a charge generation material, a titanyl phthalocyanine addition product to which butanediol is added and which has a specific particle size distribution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electrophotographic photoreceptor and an image forming apparatus including the same. [Background technology]

[0002] Electrophotographic image forming apparatuses that form images using electrophotographic technology are widely used in copying machines, printers, facsimile machines, and the like. An electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") used in an electrophotographic process is configured by laminating a photosensitive layer containing a photoconductive material on a substrate. Currently, research and development of photoreceptors with photosensitive layers whose main component is organic photoconductive materials (also called "organic photoreceptors") is progressing, and they now account for the mainstream of photoreceptors.

[0003] Proposed organic photoreceptors include a structure having a single-layer photoreceptor layer on a substrate (also called an "electrically conductive support") in which a charge generation substance and a charge transport substance (also called a "charge transfer substance") are dispersed in a binder resin (also called a "binder resin" or "binder resin"), and a structure having a multilayer photoreceptor layer in which a charge generation layer in which a charge generation substance is dispersed in a binder resin and a charge transport layer in which a charge transport substance is dispersed in a binder resin are laminated in that order. Of these, the latter function-separated photoreceptor is widely used because it has excellent electrophotographic properties and durability, allows a high degree of freedom in material selection, and is easy to design various photoreceptor properties.

[0004] Among these, Y-type titanyl phthalocyanine, a specific crystalline form, is widely used as a charge-generating material due to its highly sensitive electrical properties. However, it is known that the dissociation of carriers from Y-type titanyl phthalocyanine is promoted by moisture in the air, and fluctuations in the humidity of the external environment cause changes in sensitivity characteristics, which has been an issue. For example, if a photosensitive material is left in an image forming device in a humid environment overnight, such as during the rainy season, and the room is dehumidified the next day on a sunny day or with air conditioning, a difference in sensitivity characteristics may occur between the part of the photosensitive material that is open to the external environment and the part that is sealed off from the external environment, such as a developing tank, resulting in poor image quality.This problem has become more serious as demand for higher image quality increases.

[0005] To solve this humidity dependency of sensitivity characteristics, a titanyl phthalocyanine adduct of 2,3-butanediol has been proposed as a charge-generating material (JP 2011-186118 A: Patent Document 1). The titanyl phthalocyanine adduct is obtained by adding butanediol, which has a polar hydroxyl group, to Y-type titanyl phthalocyanine in place of the water in the crystal. Photoconductors using this as a charge-generating material are not affected by the external humidity environment in sensitivity characteristics like Y-type titanyl phthalocyanine without the adduct, and the influence of humidity on sensitivity characteristics is reduced.

[0006] However, it is known that during crystallization, the polar groups of the titanyl phthalocyanine adduct aggregate due to intermolecular forces, forming a crystalline structure in which the butanediol adduct is included within the titanyl phthalocyanine, and that this crystalline structure has a strong cohesion. In order to bring out the inherent properties of the titanyl phthalocyanine adduct, the aggregates must be disintegrated. However, the disintegration process is likely to cause lattice defects on the fracture surface of the titanyl phthalocyanine adduct, and these lattice defects have an adverse effect on the sensitivity characteristics of the photoreceptor.

[0007] To solve the problem of such lattice defects, studies are being conducted on the synthesis of pigments with a large BET specific surface area that are more easily crushed than in a crystalline state, as disclosed in JP-A-2004-125818 (Patent Document 2). However, if the particle size distribution of the titanyl phthalocyanine adduct is too small, the interaction between the titanyl phthalocyanine adducts will be strengthened, resulting in a decrease in dispersion stability and an increase in lattice defects due to dispersion. Furthermore, when the processes of charging, exposure, development, transfer, and static elimination are repeatedly performed, electrical fatigue or light fatigue due to static elimination light will have an effect, and with repeated use, the charging potential at the first rotation will not rise to a predetermined potential, resulting in a difference in surface potential between the area of ​​the photoreceptor at the first rotation and the area at the second rotation or later in the first copy image, which will cause uneven image density and background fogging, resulting in a decrease in image quality. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-186118 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-125818 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the present disclosure aims to provide an electrophotographic photoreceptor that uses a titanyl phthalocyanine adduct of 2,3-butanediol, which is known as a charge-generating substance, and that is capable of maintaining stable image characteristics without a decrease in charging ability even after repeated energization over a long period of time throughout the product life, and an image forming apparatus equipped with the same. [Means for solving the problem]

[0010] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found that, in a photoreceptor using a titanyl phthalocyanine adduct of 2,3-butanediol as a charge-generating material, controlling the particle size distribution of the titanyl phthalocyanine adduct in the charge-generating layer within a specific range can solve the above-mentioned problems and improve the stability of the electrical properties of the photoreceptor. In other words, even when fatigue is caused by repeated current application, the difference in charging potential between the first rotation and the second rotation can be reduced, and non-uniformity in image density on the first sheet can be eliminated, thereby completing the present invention.

[0011] Thus, according to the present disclosure, there is provided an electrophotographic photoreceptor comprising at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a substrate, the charge generation layer contains, as a charge generation material, at least one selected from a titanyl phthalocyanine adduct to which (2R,3R)-2,3-butanediol is added and a titanyl phthalocyanine adduct to which (2S,3S)-2,3-butanediol is added; The surface layer including the charge transport layer of the electrophotographic photosensitive member was peeled off, and a scanning electron microscope image of the surface of the charge generation layer was obtained. 2 When 100 particles are randomly extracted as primary particles of the titanyl phthalocyanine adduct from the region and the particle size distribution is observed, the average Feret diameter of the titanyl phthalocyanine adduct is 0.20 μm or more and 0.30 μm or less, the standard deviation thereof is 0.07 μm or more and 0.13 μm or less, and the skewness of the particle size distribution of the titanyl phthalocyanine adduct is 0.50 or more and 1.20 or less. An electrophotographic photoreceptor characterized by the above-mentioned is provided.

[0012] Furthermore, according to the present disclosure, there is provided an image forming apparatus comprising at least the above-mentioned electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, exposure means for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, developing means for developing the electrostatic latent image to form a toner image, and transfer means for transferring the toner image onto a recording medium. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide an electrophotographic photoreceptor that uses a titanyl phthalocyanine adduct of 2,3-butanediol, which is known as a charge-generating substance, and that is capable of maintaining stable image characteristics without a decrease in charging ability even after repeated energization over a long period of time throughout the product life, and an image forming apparatus equipped with the same. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the configuration of a main part of a photoreceptor (multilayer photoreceptor) F01 according to the present disclosure. [Figure 2] 1 is a schematic side view showing the configuration of a main part of an image forming apparatus 100 of the present disclosure. [Figure 3] 1 shows SEM images of the surface of the charge generation layer of the photoreceptor of (a) Example 1 and (b) Comparative Example 1 of the present disclosure. [Figure 4] FIG. 2 is a diagram showing the spectral absorption spectrum of the photosensitive layer of the photoreceptor according to Example 1 of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] The photoreceptor of the present disclosure is an electrophotographic photoreceptor including at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a substrate, the charge generation layer contains, as a charge generation material, at least one selected from a titanyl phthalocyanine adduct to which (2R,3R)-2,3-butanediol is added and a titanyl phthalocyanine adduct to which (2S,3S)-2,3-butanediol is added; The surface layer including the charge transport layer of the electrophotographic photosensitive member was peeled off, and a scanning electron microscope image of the surface of the charge generation layer was obtained. 2When 100 particles are randomly extracted as primary particles of the titanyl phthalocyanine adduct from the region and the particle size distribution is observed, the average Feret diameter of the titanyl phthalocyanine adduct is 0.20 μm or more and 0.30 μm or less, the standard deviation thereof is 0.07 μm or more and 0.13 μm or less, and the skewness of the particle size distribution of the titanyl phthalocyanine adduct is 0.50 or more and 1.20 or less. It is characterized by: Below, we will explain the constituent features that characterize the photoreceptor of the present disclosure, and then we will explain (1) the photoreceptor and (2) the image forming apparatus equipped with the same. Note that the embodiments and examples described below are merely specific examples of the present invention, and the present invention is not limited thereto.

[0016] The (2R,3R)-2,3-butanediol-added titanyl phthalocyanine and (2S,3S)-2,3-butanediol-added titanyl phthalocyanine of the present disclosure (hereinafter collectively referred to as "titanyl phthalocyanine adducts") are Y-type titanyl phthalocyanine charge-generating materials to which a certain proportion of the polar group 2,3-butanediol has been added. Due to the introduction of this polar group, photoreceptors using the titanyl phthalocyanine adducts are less susceptible to the effects of external humidity environments, unlike Y-type titanyl phthalocyanine, and the adverse effects of humidity on sensitivity characteristics are reduced.

[0017] However, the polar groups aggregate due to intermolecular forces, forming a crystalline structure in which the butanediol of the titanyl phthalocyanine adduct is enclosed within, and the strong aggregating force makes it difficult to disintegrate, which is a problem. In order to bring out the inherent properties of the titanyl phthalocyanine adduct as a charge-generating substance in a photoreceptor, it is necessary to disintegrate the aggregates. However, if the aggregates are disintegrated too much and the amount of small-particle-sized charge-generating substance increases too much, re-aggregation occurs due to the intermolecular forces between polar groups, which reduces the stability of the coating liquid for the charge-generating layer and causes the properties of the resulting photoreceptor to deteriorate. Furthermore, excessive stress is applied during the process of disintegrating the aggregates, such as during the dispersion treatment of the coating liquid, and lattice defects are likely to occur on the fracture surface of the charge-generating substance, and these lattice defects affect the charging stability during long-term current fatigue.

[0018] Therefore, in order to improve the charging stability of the photoreceptor, the following two measures are required for the titanyl phthalocyanine adduct as the charge generating substance. (1) Crushing the charge generating material in a state where stress on the charge generating material is reduced during the dispersion process of the coating liquid for the charge generating layer. (2) In order to reduce excessive stress on the small particle size charge generating material that is crushed during the dispersion process, coarse particles are allowed to remain to the extent that they do not adversely affect the dispersion stability of the coating liquid. According to the findings of the inventors, the stronger the load on the particles of the charge-generating material during the dispersion process, the greater the damage to the charge-generating material and the more likely it is that lattice defects will occur on the fractured surfaces; furthermore, the longer the dispersion process time, the more stress is applied to the charge-generating material that has already been crushed, resulting in an increase in the occurrence of lattice defects and a deterioration in the photosensitive material characteristics. It is believed that the charging stability of a photoreceptor is greatly affected by how efficiently the carriers generated in the charge generation layer by exposure can be separated and transported to the photoreceptor surface or substrate, and by whether a structure can be formed that can deactivate excess carriers from an excited state to the ground state. Therefore, in the photoreceptor of the present disclosure, it has been discovered that the charging stability of the photoreceptor can be improved against fatigue caused by long-term electrical conduction by reducing lattice defects in the charge generation layer as much as possible and adopting a structure that makes it easy to quickly deactivate excess carriers to the ground state.

[0019] The titanyl phthalocyanine adduct of the present disclosure is present in the charge generation layer with the particle size distribution as described above when the surface of the charge generation layer is observed with a scanning electron microscope as described above. A specific method for image analysis of the particle size distribution on the surface of the charge generating layer will be described in the examples.

[0020] <Average Feret diameter and its standard deviation of particle size distribution of titanyl phthalocyanine adduct> The average Feret diameter (also referred to as "unidirectional diameter") of the titanyl phthalocyanine adduct of the present disclosure is 0.20 μm or more and 0.30 μm or less, and the standard deviation is 0.07 μm or more and 0.13 μm or less. The "Féret diameter" is one of the statistical average diameters measured in a fixed direction across a field of view, assuming that particles are randomly oriented within the field of view. It is the fixed tangential diameter defined as the distance between two parallel lines that sandwich the particle. If the average Feret diameter is less than 0.20 μm or its standard deviation is less than 0.07 μm, there is a high possibility that excessive stress is being applied to the particles on the smaller particle size side, which may result in a deterioration in the charge stability of the photoreceptor, and therefore a deterioration in the charge stability of the photoreceptor. On the other hand, if the average Feret diameter exceeds 0.30 μm or its standard deviation exceeds 0.13 μm, there will be a large amount of residual coarse particles, which may result in a deterioration in the stability of the charge generating layer coating liquid over long-term storage, and therefore a deterioration in the charge stability of the photoreceptor. Therefore, the average Feret diameter of the preferred titanyl phthalocyanine adduct of the present disclosure is 0.23 μm or more and 0.30 μm or less, and the standard deviation is 0.08 μm or more and 0.11 μm or less.

[0021] <Skewness of particle size distribution of titanyl phthalocyanine> The skewness of the particle size distribution of the titanyl phthalocyanine adduct of the present disclosure is 0.50 or more and 1.20 or less. "Skewness" is a statistical quantity that indicates the degree to which a particle size distribution is distorted from a normal distribution, in other words, it is a statistical quantity that indicates the degree of skewness of a distribution, such that only one tail is extended, and is an index of symmetry around the integral distribution D50. Skewness can be calculated using the following formula (1), where n is the number of samples, x is the mean value of each data xi (i=1,2...,n), and s is the standard deviation. A positive value is indicated when the distribution is "right-tailed," "skewed to the right," or "biased to the left," and a negative value is indicated when the opposite is true. For a symmetrical distribution such as a normal distribution, skewness is 0.

[0022]

number

[0023] The particle size distribution of the titanyl phthalocyanine adduct of the present disclosure is small from D10 to D50 on the small particle size side of the integral distribution, and there is no problem even if coarse particles remain as long as they do not adversely affect the dispersion stability of the coating liquid for the charge generating layer. If the skewness is less than 0.50, there will be no coarse particles and the particles will be uniformly pulverized, but there is a high possibility that excessive stress will be applied to the crushed particles on the smaller particle size side, which may cause a deterioration in the charge stability of the photoreceptor, and ultimately a deterioration in the charge stability of the photoreceptor.On the other hand, if the skewness is more than 1.20, there will be a large amount of coarse particles remaining, which may cause a deterioration in the stability of the charge generating layer coating liquid over long-term storage, and ultimately a deterioration in the charge stability of the photoreceptor. Therefore, the skewness of the particle size distribution of the preferred titanyl phthalocyanine adduct of the present disclosure is 0.85 or more and 1.0 or less.

[0024] <Coarse particles in the particle size distribution of titanyl phthalocyanine> In the particle size distribution of the titanyl phthalocyanine adduct of the present disclosure, it is preferable that there are three or more agglomerates of the titanyl phthalocyanine adduct (hereinafter also referred to as "coarse particles") having a Feret diameter of 0.4 μm or more and 0.7 μm or less. As described above, the particle size distribution of the titanyl phthalocyanine adduct of the present disclosure does not pose a problem even if coarse particles remain within a range that does not adversely affect the dispersion stability of the coating liquid for the charge generating layer. The presence of residual coarse particles is an indicator of the dispersion treatment in the preparation of the coating liquid for the charge generating layer, and if the number of coarse particles is less than 3, the dispersion treatment is likely to have progressed a little too far, and excessive stress is likely to be applied to the particles on the smaller particle size side, which may result in a deterioration in the charge stability of the photoreceptor, and ultimately in a deterioration in the charge stability of the photoreceptor. On the other hand, if the number of coarse particles is too large, the dispersion treatment becomes insufficient, the particle size distribution of the titanyl phthalocyanine adduct of the present disclosure is not obtained, and the charge stability of the photoreceptor of the present disclosure may be reduced or not obtained at all, so it is more preferable that the number of coarse particles is 8 or less.

[0025] <Kurtosis of titanyl phthalocyanine particle size distribution> The kurtosis of the particle size distribution of the titanyl phthalocyanine adduct of the present disclosure is preferably 0.70 or more and 1.20 or less. "Kurtosis" is a statistical quantity that indicates how sharp a particle size distribution is from a normal distribution, that is, a statistical quantity that indicates the degree of peakedness of the particle size distribution, and is an index of the degree of peakedness and the degree of broadness of the tail of the particle size distribution. Kurtosis can be calculated using the following formula (2), where n is the number of samples, x is the mean value of each data xi (i=1,2...,n), and s is the standard deviation. When the normal distribution is peaked, that is, when the data is concentrated around the mean and the distribution has heavy tails, it shows a positive value, and when the distribution is flatter than the normal distribution, that is, when the data is scattered around the mean and the distribution has light tails, it shows a negative value. In the case of a normal distribution, kurtosis is 0.

[0026]

number

[0027] The particle size distribution of the titanyl phthalocyanine adduct of the present disclosure preferably has a heavy tail on the coarse particle side compared to a normal distribution, and is somewhat sharp, which is presumably a state in which the particles are evenly sheared. When the kurtosis is less than 0.70, the share of particles on the small particle size side around D10 is large, and there is concern that the deterioration of charging stability due to current fatigue of the photoreceptor may occur. On the other hand, when the kurtosis exceeds 1.20, most of the values ​​are concentrated at the median value, but the long, thick tail increases the possibility that pigments that have been subjected to extremely excessive shear may remain, which may lead to a deterioration of charging stability. More preferably, the kurtosis of the particle size distribution of the titanyl phthalocyanine adduct of the present disclosure is 0.85 or more and 1.10 or less.

[0028] <Binder Resin of Charge Generation Layer and Its Calculated Molecular Weight> The charge generating layer of the photoreceptor of the present disclosure contains a polyvinyl acetal resin as a binder resin, and the calculated molecular weight (g / mol) of the polyvinyl acetal resin is 5.0×10 4 It is preferable that this is equal to or greater than this. Titanyl phthalocyanine, the charge generating material of the present disclosure, has strong cohesive force. It has been found that, in preparing a coating solution for a charge generating layer, a binder resin with a low molecular weight and low viscosity can ensure wettability, improving the dispersibility of titanyl phthalocyanine. On the other hand, as the calculated molecular weight of the binder resin decreases, the glass transition temperature Tg also decreases, and the amount of elution from the charge generating layer to the charge transport layer increases. In other words, the highly water-absorbent polyvinyl acetal resin elutes into the charge generating layer, which can lead to charge trapping in a high-humidity environment, leading to problems such as a deterioration in the sensitivity of the photoreceptor and an increase in residual potential. Therefore, the calculated molecular weight of the polyvinyl acetal resin used as the binder resin is set to 5.0 × 10 4 Furthermore, if the calculated molecular weight is too large, the viscosity of the coating liquid for the charge generating layer increases and the dispersibility decreases, so that when forming a dispersed state of the titanyl phthalocyanine adduct in the charge generating layer of the photoreceptor of the present disclosure, a long dispersion time is required in preparing the coating liquid for the charge generating layer, and as a result, there is an increased possibility that excessive dispersion shear is applied to the charge generating substance, which may lead to deterioration of the properties of the photoreceptor, and the upper limit thereof is 20.0 × 10 4 Approximately, preferably 10.0 x 10 4 That's about it. Specific methods for measuring the calculated molecular weight and the amount of hydroxyl groups of the polyvinyl butyral resin will be described in the Examples.

[0029] <Amount of Hydroxyl Groups in the Binder Resin of the Charge Generating Layer> The amount of hydroxyl groups in the polyvinyl acetal resin is preferably 16% by mass or more and 22% by mass or less. The titanyl phthalocyanine adduct as the charge generation material of the present disclosure has a polar group inside thereof, and therefore has high affinity, particularly when the amount of hydroxyl groups is large. This has the advantage that the particles of the titanyl phthalocyanine adduct can be made fine in a short time when preparing a coating liquid for a charge generation layer to be used when forming a charge generation layer by a coating method described below. On the other hand, if the amount of hydroxyl groups in the binder resin increases, if the polyvinyl acetal resin elutes into the charge transport material in a high-humidity environment, there is a higher risk of charge trapping in the charge transport layer. Therefore, the risk of this problem occurring can be reduced by limiting the amount of hydroxyl groups in the binder resin to 22% by mass or less in advance. On the other hand, if the amount of hydroxyl groups in the binder resin is less than 16% by mass, the dispersibility of the titanyl phthalocyanine adduct decreases significantly, making it necessary to extend the dispersion time in preparing the coating liquid for the charge generation layer, which increases the dispersion stress of the charge transport material and may lead to deterioration of the properties of the photoreceptor. The amount of hydroxyl groups in the binder resin is more preferably 18% by mass or more and 22% by mass or less.

[0030] <Maximum absorption wavelength of the spectral absorption spectrum> The titanyl phthalocyanine adduct of the present disclosure preferably has a maximum absorption in the wavelength range of 745 nm or more and 755 nm or less in the spectroscopic absorption spectrum. If the maximum absorption wavelength of the titanyl phthalocyanine adduct is less than 745 nm, the charging stability of the photoconductor may deteriorate, whereas if the maximum absorption wavelength of the titanyl phthalocyanine adduct is greater than 755 nm, the Vr of the photoconductor may increase due to fatigue caused by repeated energization, which may deteriorate the charging stability of the photoconductor. A specific method for measuring the spectroscopic absorption spectrum of titanyl phthalocyanine will be explained in the Examples.

[0031] The maximum absorption in the spectral absorption spectrum of titanyl phthalocyanine tends to be small if too much dispersion shear is applied during preparation of the coating liquid for the charge generating layer. On the other hand, when the coating solution for the charge generating layer is prepared by dispersing under conditions of low dispersion stress, such as using an ultrasonic cleaning bath, the maximum absorption tends to shift to the long wavelength side, which increases the standard deviation of the particle size distribution, increases the particle size variation, and causes uneven distribution of the charge generating material as a whole, which is presumed to result in a deterioration of the photoreceptor properties.

[0032] <Method for synthesizing titanyl phthalocyanine adduct> The titanyl phthalocyanine adduct of the present disclosure can be synthesized by heating and reacting titanyl phthalocyanine with (2R,3R)-2,3-butanediol or (2S,3S)-2,3-butanediol in various solvents, based on the method described in Japanese Patent No. 5609167.

[0033] The raw material titanyl phthalocyanine is represented by the following formula (A). [ka]

[0034] The oxotitanium phthalocyanine represented by formula (A) can be produced by known synthesis methods described, for example, in JP-A-6-293769, JP-A-2003-183534, JP-A-7-271073, and Moser, Frank H. and Arthur L. Thomas, Phthalocyanine Compounds, Reinhold Publishing Corp., New York, 1963.

[0035] Known synthesis methods may or may not use titanium halide as a starting material. However, the present inventors have confirmed that the excellent effects of the present disclosure can be obtained regardless of the synthesis starting material or synthesis method, as long as a titanyl phthalocyanine adduct of 2,3-butanediol having the above-mentioned spectral absorption spectrum characteristics can be synthesized. Since the presence of halogens such as chlorine in (2R,3R)-2,3-butanediol or (2S,3S)-2,3-butanediol can adversely affect the charging performance of photoreceptors, titanyl phthalocyanine derived from raw materials that do not contain halogens such as chlorine is preferred. However, if the uniformity of titanyl phthalocyanine can be improved by controlling the washing process, halogen-containing raw materials can also be used without any problems. The synthesis method is exemplified below, but this synthesis route is only an example and is not intended to be limiting.

[0036] Phthalonitrile and a titanium alkoxide such as tetrabutoxytitanium are reacted in the presence of urea at a temperature of 150°C for at least 5 hours with stirring. After the reaction is complete, the resulting titanyl phthalocyanine is filtered off. The resulting product is washed with a solvent, such as alcohols (e.g., methanol, ethanol, n-propanol, butanol), chlorinated hydrocarbons (e.g., dichloroethane, chloroform), ethers (e.g., dimethyl ether, diethyl ether, tetrahydrofuran), or ketones (e.g., acetone, methyl ethyl ketone), to obtain titanyl phthalocyanine. While titanyl phthalocyanine does not dissolve in these solvents, impurities adhering to titanyl phthalocyanine do. Repeated washing minimizes the amount of residual impurities.

[0037] Furthermore, oxotitanium phthalocyanine can be obtained by reacting isoindoline with titanium tetraalkoxide such as tetrabutoxytitanium in a suitable solvent such as N-methylpyrrolidone under heating. This titanyl phthalocyanine may contain a phthalocyanine derivative in which the hydrogen atoms on the benzene ring are substituted with substituents such as chlorine, fluorine, nitro, cyano, and sulfonic acid groups. The titanyl phthalocyanine thus obtained can be treated with a water-immiscible organic solvent such as dichloroethane in the presence of water to obtain crystalline titanyl phthalocyanine, which is a raw material for the titanyl phthalocyanine adduct used as the charge generating material in the present disclosure.

[0038] Examples of the treatment method (crystal conversion method) include a method in which titanyl phthalocyanine is swelled with water and then treated with an organic solvent, and a method in which water is added to an organic solvent and titanyl phthalocyanine powder is added thereto without performing the swelling treatment. For example, titanyl phthalocyanine can be swollen with water by dissolving it in 10 to 30 times concentrated sulfuric acid, removing any insoluble matter by filtration, and precipitating the resulting solution in cooled water. The resulting titanyl phthalocyanine is then filtered with ion-exchanged water to remove the acid, and washing is repeated until the solution becomes neutral to obtain a wet cake.

[0039] When titanyl phthalocyanine is swollen with water, it is washed using known stirring and dispersing equipment such as a homomixer, paint mixer, ball mill, or sand mill. If sulfuric acid remains in the wet cake, it will be difficult to proceed with the reaction with butanediol in the next step, so careful washing is necessary. After the washing process, the wet cake is filtered and dried to obtain amorphous titanyl phthalocyanine.

[0040] To the amorphous titanyl phthalocyanine obtained, butanediol is added in an amount of 1 to 3.5 times the molar equivalent. If the amount of butanediol is less than 1, it is not possible to obtain a spectral absorption spectrum within the range specified in the present disclosure, and the humidity dependency of sensitivity specific to titanyl phthalocyanine may be insufficient. On the other hand, if the amount of butanediol is more than 3.5 times, the amount of butanediol becomes excessive, making it difficult to remove unreacted butanediol, and it has been found that stability against repeated electrical fatigue is significantly reduced.

[0041] The organic solvent used here is not particularly limited as long as it can give the desired crystal form, and examples thereof include chlorobenzene, dichlorobenzene, anisole, chloronaphthalene, quinoline, and tetrahydrofuran. One or a mixture of two or more selected from these solvents may also be used. The synthesis of the titanyl phthalocyanine adduct of 2,3-butanediol used in the present disclosure can be easily optimized by appropriately selecting each production condition, such as the reaction molar ratio, reaction temperature, reaction time, selection of solvent type, and crystallization method.

[0042] (1) Electrophotographic photoreceptor The photoreceptor of the present disclosure includes at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a substrate. The photoreceptor of the present disclosure will be described below with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a schematic cross-sectional view showing the configuration of the main part of a photoreceptor (multilayer photoreceptor) F01 of the present disclosure. The multi-layer photoreceptor F01 has a multi-layer photosensitive layer in which an undercoat layer F21, a charge generation layer F22 containing a charge generation material, and a charge transport layer F23 containing a charge transport material are laminated in this order on a substrate F1. In the figure, Fa indicates the photoreceptor surface. The photoreceptor of the present disclosure may have a surface protective layer (protective layer) on the laminated photosensitive layer.

[0043] <Base F1> The substrate (also referred to as "conductive substrate" or "conductive support") functions as an electrode for the photoreceptor and as a support member, and its constituent material is not particularly limited as long as it is a material used in the relevant technical field. Specific examples include metal materials such as aluminum, aluminum alloys, copper, zinc, stainless steel, and titanium, as well as polymer materials such as polyethylene terephthalate, nylon, and polystyrene, whose surfaces are laminated with metal foil, subjected to metal vapor deposition, or vapor-deposited or coated with a layer of a conductive compound such as a conductive polymer, tin oxide, or indium oxide, as well as hard paper and glass. Among these, aluminum is preferred from the viewpoint of ease of processing, and aluminum alloys such as JIS 3003, JIS 5000, and JIS 6000 series are particularly preferred. The shape of the substrate is not limited to a cylindrical (drum) shape, but may be a sheet shape, a columnar shape, an endless belt shape, or the like. Furthermore, the surface of the substrate may be subjected to anodizing treatment, surface treatment with chemicals or hot water, coloring treatment, or diffuse reflection treatment such as surface roughening, as long as it does not affect the image quality, in order to prevent interference fringes caused by laser light.

[0044] <Undercoat layer F21> The photoreceptor of the present disclosure preferably includes an undercoat layer (also referred to as an "intermediate layer") between the substrate and the laminated photosensitive layer. The undercoat layer generally covers and smooths the surface irregularities of the substrate, improves the film-forming properties of the laminated photosensitive layer, suppresses peeling of the photosensitive layer from the substrate, and improves the adhesion between the substrate and the photosensitive layer. Specifically, it prevents charge injection from the substrate into the photosensitive layer, prevents a decrease in the chargeability of the photosensitive layer, and prevents image fogging (so-called black spots). The undercoat layer can be formed, for example, by dissolving a binder resin in a suitable solvent to prepare a coating liquid for the undercoat layer, applying this coating liquid to the surface of the substrate, and then drying to remove the organic solvent.

[0045] Examples of binder resins include acetal resins, polyamide resins, polyurethane resins, polyester resins, acrylic resins, epoxy resins, phenolic resins, melamine resins, urethane resins, etc. Binder resins are required to have properties such as not dissolving or swelling in the solvent used when forming the photoreceptor layer on the undercoat layer, excellent adhesion to the substrate, and flexibility. Therefore, among the above binder resins, polyamide resins are preferred, and alcohol-soluble nylon resins and polyamide resins containing piperazine compounds are particularly preferred. Examples of alcohol-soluble nylon resins include homopolymer or copolymer nylons such as 6-nylon, 66-nylon, 610-nylon, 11-nylon, and 12-nylon, and chemically modified nylons such as N-alkoxymethyl-modified nylons. A curing agent that crosslinks the binder resin may also be used to form a cured film. Blocked isocyanate is preferred as the curing agent from the viewpoint of storage stability and electrical properties of the coating liquid.

[0046] Examples of solvents include lower alcohols such as water, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, 2-butanol, and isobutanol, ketones such as acetone, cyclohexanone, and 2-butanone, ethers such as tetrahydrofuran, dioxane, ethylene glycol, and diethyl ether, and halogenated hydrocarbons such as methylene chloride and ethylene chloride. These solvents can be selected appropriately based on the solubility of the binder resin and the surface smoothness of the undercoat layer, and can be used alone or in combination of two or more. Among these solvents, for example, non-halogen organic solvents can be preferably used in consideration of the global environment.

[0047] The coating solution for the undercoat layer may contain metal oxide particles, which can easily adjust the volume resistivity of the undercoat layer, further suppress charge injection into the charge generating layer, and maintain the electrical properties of the photoreceptor under various environments. Materials that can be used for the metal oxide particles include, for example, titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide. The ratio (A / B) of the total mass A of the binder resin and metal oxide particles to the mass B of the solvent in the coating liquid for forming the undercoat layer is, for example, preferably about 1 / 99 to 30 / 70, and particularly preferably about 2 / 98 to 40 / 60. The ratio (C / D) of the mass C of the binder resin to the mass D of the metal oxide particles is preferably, for example, about 1 / 99 to 90 / 10, and particularly preferably about 5 / 95 to 70 / 30.

[0048] The coating method for the undercoat layer coating liquid may be appropriately selected from the most suitable methods taking into consideration the physical properties of the coating liquid, productivity, and the like. Examples of the coating method include spraying, bar coating, roll coating, blade coating, ring coating, and dip coating. Among these, the dip coating method is a method in which a substrate is immersed in a coating tank filled with a coating liquid and then pulled up at a constant speed or a gradually changing speed to form a layer on the surface of the substrate, and is relatively simple and excellent in terms of productivity and cost, so it can be suitably used for manufacturing photoreceptors. The apparatus used for the dip coating method may be provided with a coating liquid dispersion device, typified by an ultrasonic generator, in order to stabilize the dispersibility of the coating liquid.

[0049] The solvent in the coating film may be removed by natural drying, or the solvent in the coating film may be removed forcibly by heating. The temperature in such a drying step is not particularly limited as long as it is a temperature at which the solvent used can be removed, but a temperature of about 50 to 140°C is appropriate, and a temperature of about 80 to 130°C is particularly preferred. If the drying temperature is below 50°C, the drying time may be long and the solvent may not evaporate sufficiently and remain in the photoreceptor layer.If the drying temperature exceeds approximately 140°C, the electrical characteristics of the photoreceptor may deteriorate during repeated use, resulting in poor quality of the resulting image. Such temperature conditions are common not only to the formation of the undercoat layer but also to the formation of layers such as the photosensitive layer, which will be described later, and other processes.

[0050] The thickness of the undercoat layer is not particularly limited, but is preferably 0.01 to 20 μm, and more preferably 0.05 to 10 μm. If the thickness of the undercoat layer is less than 0.01 μm, it may not be possible to obtain sufficient blocking effect against electron injection from the conductive substrate side and sufficient effect against interference fringes due to light scattering.On the other hand, if the thickness of the undercoat layer is more than 20 μm, the sensitivity may change significantly during continuous printing, which may result in large changes in image density.

[0051] <Charge generation layer F22> The charge generation layer has the function of generating charges by absorbing light irradiated by a light emitting device such as a semiconductor laser light beam in an electrophotographic device such as an image forming device, and contains a charge generation substance as a main component and, if necessary, a binder resin and / or additives.

[0052] As the charge generation substance, at least one selected from the above-mentioned titanyl phthalocyanine adduct to which (2R,3R)-2,3-butanediol is added and the titanyl phthalocyanine adduct to which (2S,3S)-2,3-butanediol is added is used, and other charge generation substances known in the art may be used in combination to the extent that the effect of the titanyl phthalocyanine adduct is not impaired. However, since the properties of the photoreceptor of the present disclosure are improved depending on the content of the titanyl phthalocyanine adduct, the higher the content, the better, and it is preferable that the content be at least 60% or more, and preferably 80% or more.

[0053] A preferred method for forming the charge generating layer is to disperse a charge generating material in a binder resin solution obtained by mixing a binder resin in a solvent by a conventionally known method, and then apply a coating liquid for the charge generating layer onto the undercoat layer. This method is described below.

[0054] The binder resin is not particularly limited, and resins having binding properties used in the art and binder resins exemplified for the undercoat layer above can be used, and those having excellent compatibility with the charge generating material are preferred. Specific examples include polyacetal resins, polyester resins, polystyrene resins, polyurethane resins, phenolic resins, alkyd resins, melamine resins, epoxy resins, silicone resins, acrylic resins, methacrylic resins, polycarbonate resins, polyarylate resins, phenoxy resins, polyvinyl formal resins, and copolymer resins containing two or more of the repeating units constituting these resins. Examples of copolymer resins include insulating resins such as vinyl chloride-vinyl acetate copolymer resins, vinyl chloride-vinyl acetate-maleic anhydride copolymer resins, and acrylonitrile-styrene copolymer resins. These binder resins can be used alone or in combination of two or more.

[0055] In the photoreceptor of the present disclosure, among the above binder resins, a polyvinyl acetal resin obtained by an acetalization reaction between two or more types of aldehyde and polyvinyl alcohol is preferred, and its calculated molecular weight is 5.0 × 10 4 It is preferable that this is equal to or greater than this. The amount of hydroxyl groups in the polyvinyl acetal resin is preferably 16% by mass or more and 22% by mass or less.

[0056] Examples of the solvent include halogenated hydrocarbons such as dichloromethane and dichloroethane; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as tetrahydrofuran and dioxane; alkyl ethers of ethylene glycol such as 1,2-dimethoxyethane; aromatic hydrocarbons such as benzene, toluene, and xylene; and aprotic polar solvents such as N,N-dimethylformamide and N,N-dimethylacetamide. These solvents can be used alone or in combination of two or more. Among these solvents, for example, non-halogen organic solvents can be preferably used in consideration of the global environment.

[0057] As with the undercoat layer, a dispersing machine such as a paint shaker, ball mill, sand mill, high-pressure homogenizer, or ultrasonic bath can be used to dissolve or disperse the charge generating material in the binder resin solution. In this case, it is preferable to appropriately set the dispersing conditions so that impurities generated by wear or the like from the components constituting the container and dispersing machine are not mixed into the coating solution.

[0058] In the photoreceptor of the present disclosure, the dispersion state of the titanyl phthalocyanine adduct as the charge generating material in the charge generating layer is important. Therefore, in order to obtain the excellent effects of the photoreceptor of the present disclosure, the dispersion treatment in the preparation of the coating liquid for the charge generating layer, in addition to the selection of the binder resin as described above, is important. In the dispersion process using the ball mill described above, the material and diameter (particle size) of the dispersion media affect the grinding efficiency. Also, in media-less dispersion processes using the high-pressure homogenizers and ultrasonic baths described above, which do not use dispersion media, excessive dispersion stress may be applied to the particles depending on the specifications and conditions, which may have a negative impact on the properties of the photoreceptor. To achieve a dispersed state of the charge generating material in the photoreceptor of the present disclosure, a dispersing machine and optimal dispersing conditions may be selected.

[0059] For example, in a dispersion treatment using a ball mill, the dispersion media diameter (particle size) is preferably 0.1 to 3.0 mm, and more preferably 0.1 to 2.0 mm, and spherical media are preferred, and it is preferable to reduce the shear applied to the particles as much as possible. Furthermore, glass beads with a low specific gravity are preferred as the material for the dispersion media. If the media diameter exceeds 3.0 mm, the shear force acting on the particles increases, the collision frequency decreases, and the pulverization efficiency decreases, making it impossible to adjust the spectral absorption spectrum within the range specified in the present disclosure, and extending the dispersion time may result in excessive shear acting on the particles, deteriorating the properties of the photoreceptor, and the particle diameter may not decrease, leading to adverse effects such as the formation of aggregates.On the other hand, if the media diameter is less than 0.1 mm, the shear force acting on the particles is too weak, making it impossible to obtain a pulverization effect, and if a long dispersion process is required, the amount of contamination from the dispersion media increases, which may adversely affect charge generation. Alumina beads used as dispersion media have a higher specific gravity than glass beads, and even when long-term dispersion processing is required, the amount of contamination from the media is reduced, there is little adverse effect on charge generation, and adverse effects such as an increase in VL due to electrical fatigue can be suppressed.

[0060] It is preferable to form the charge generating layer by applying a coating liquid for the charge generating layer. The ratio (E / F) of the mass E of the charge generating substance to the mass F of the binder resin is preferably, for example, about 55 / 45 to 80 / 20. If the ratio (E / F) is less than 55 / 45, i.e., if the mass E of the charge generating substance is small, the charge generation efficiency may decrease and the sensitivity may deteriorate. On the other hand, if the ratio (E / F) exceeds 80 / 20, i.e., if the mass E of the charge generating substance is large, there may be too much charge generating substance, which may result in poor dispersion stability in the binder resin. A more preferable ratio is about 60 / 40 to 70 / 30.

[0061] The thickness of the charge generating layer is not particularly limited, but is preferably 0.05 to 5 μm, and more preferably 0.1 to 1 μm. If the thickness of the charge generating layer is less than 0.05 μm, the efficiency of light absorption will decrease, which may result in a decrease in the sensitivity of the photoreceptor. On the other hand, if the thickness of the charge generating layer is more than 5 μm, the charge transfer within the charge generating layer will become the rate-limiting step in the process of erasing the charge on the surface of the photoreceptor, which may result in a decrease in the sensitivity of the photoreceptor.

[0062] <Charge transport layer F23> The charge transport layer has the function of receiving the charges generated by the charge generation substance and transporting them to the surface of the photoreceptor (Fa in FIG. 1), and contains a charge transport substance, a binder resin, and, if necessary, additives. The charge transport layer of the photoreceptor of the present disclosure may contain an electron transport material, which is described separately from the hole transport material, which also transports charges.

[0063] The hole transport material is not particularly limited, and any compound used in the art can be used. Specific examples include carbazole derivatives, pyrene derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, polycyclic aromatic compounds, indole derivatives, pyrazoline derivatives, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, triarylmethane derivatives, phenylenediamine derivatives, stilbene derivatives, enamine derivatives, benzidine derivatives, polymers having groups derived from these compounds in the main chain or side chain (such as poly-N-vinylcarbazole, poly-1-vinylpyrene, ethylcarbazole-formaldehyde resin, triphenylmethane polymer, poly-9-vinylanthracene), and polysilanes. These hole transporting materials can be used alone or in combination of two or more.

[0064] A preferred method for forming the charge transport layer is to disperse a hole transport material in a binder resin solution obtained by mixing a binder resin in a solvent by a conventionally known method, and then apply a coating liquid for the charge transport layer onto the charge generation layer. This method is described below. The binder resin is not particularly limited, and any resin having binding properties that is used in the relevant technical field can be used, and it is preferable that the resin has excellent compatibility with the hole transport material. Specific examples include vinyl polymer resins such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymer resins thereof, as well as resins such as polycarbonate, polyester, polyester carbonate, polysulfone, phenoxy resin, epoxy resin, silicone resin, polyarylate, polyamide, polyether, polyurethane, polyacrylamide, phenolic resin, and polyphenylene oxide, and thermosetting resins obtained by partially crosslinking these resins. These binder resins can be used alone or in combination of two or more. Among these, polystyrene, polycarbonate, polyarylate and polyphenylene oxide have a volume resistivity of 10 13 It is preferable because it has a hardness of Ω or more, is excellent in electrical insulation, and is also excellent in film-forming properties and potential characteristics, and polycarbonate is particularly preferable.

[0065] Examples of solvents include aromatic hydrocarbons such as benzene, toluene, and xylene; halogenated hydrocarbons such as dichloromethane, monochlorobenzene, dichloroethane, and monochlorobenzene; ethers such as tetrahydrofuran, dioxane, and dimethoxymethyl ether; and aprotic polar solvents such as N,N-dimethylformamide. If necessary, solvents such as alcohols, acetonitrile, or methyl ethyl ketone can also be added. These solvents can be used alone or in combination. Among these solvents, for example, non-halogen organic solvents can be preferably used in consideration of the global environment.

[0066] The ratio (G / H) of the mass G of the hole transport material to the mass H of the binder resin is preferably, for example, about 10 / 30 to 10 / 12. If the ratio G / H is less than 10 / 30 and the proportion of binder resin is high, the viscosity of the coating solution increases when the charge transport layer is formed by dip coating, resulting in a decrease in coating speed and significantly reduced productivity. Furthermore, if the amount of solvent in the coating solution is increased to suppress the increase in viscosity of the coating solution, blushing may occur, causing the formed charge transport layer to become cloudy. On the other hand, if the ratio G / H exceeds 10 / 12 and the proportion of binder resin is low, the printing durability may be reduced compared to when the proportion of binder resin is high, and the amount of wear of the photosensitive layer may increase.

[0067] The charge transport layer may contain additives as long as the effects of the present disclosure are not impaired. The additives include, for example, ultraviolet absorbers for improving light resistance, and specifically, perimidine compounds such as those used in the examples. However, the addition of an additive to the charge transport layer may form traps for charge transport, adversely affecting the properties of the photoreceptor, and the amount of additive added is about 1 to 10 parts by mass relative to the hole transport substance. Furthermore, the charge transport layer may contain inorganic fine particles such as silica or aluminum oxide to improve printing durability, or may contain fluorine-based resin fine particles to improve surface lubricity, within the range that does not impair the effects of the present disclosure.

[0068] The thickness of the charge transport layer is not particularly limited, but is preferably about 5 to 50 μm, and more preferably about 10 to 40 μm. If the thickness of the charge transport layer is less than 5 μm, the charge retention ability of the photoreceptor surface may decrease, whereas if the thickness of the charge transport layer is more than 50 μm, the resolution of the photoreceptor may decrease.

[0069] <Surface protection layer (not shown in Figure 1)> The photoreceptor F01 of the present disclosure may have a surface protective layer on the laminated photosensitive layer (charge transport layer F23). The surface protective layer has the function of improving the durability of the photoreceptor, and contains a binder resin and, if necessary, additives. The surface protective layer may contain the same one or more charge transport materials as those in the charge transport layer in order to stabilize the electrical characteristics. Examples of the binder resin include the binder resins exemplified for the charge transport layer, and among these, polycarbonate and polyarylate are particularly preferred in consideration of wear characteristics and electrical characteristics.

[0070] The thickness of the protective layer is not particularly limited, but is preferably about 3 to 7 μm, and more preferably about 4 to 6 μm. If the thickness of the protective layer is less than 3 μm, the effects on printing durability and scratch resistance may not be sufficient, whereas if the thickness of the protective layer is more than 7 μm, the electrical properties may deteriorate.

[0071] (2) Image forming apparatus 100 The image forming apparatus of the present disclosure is characterized by comprising at least the photosensitive member of the present disclosure, a charging means for charging the photosensitive member, an exposure means for exposing the charged photosensitive member to light to form an electrostatic latent image, a developing means for developing the electrostatic latent image to form a toner image (make it visible), and a transfer means for transferring the toner image onto a recording medium. The image forming apparatus of the present disclosure may include a fixing unit that fixes the transferred toner image onto a recording medium to form an image, a cleaning unit that removes and collects toner remaining on the photosensitive member, and a discharging unit that removes surface charge remaining on the photosensitive member. The image forming apparatus of the present disclosure and its operation will be described below with reference to the drawings, but the image forming apparatus of the present disclosure is not limited thereto.

[0072] FIG. 2 is a schematic side view showing the configuration of the main part of the image forming apparatus 100 of the present disclosure. The image forming apparatus (laser printer) 100 in Figure 2 includes a photoreceptor 1 (corresponding to F01 in Figure 1) of the present disclosure, an exposure means (semiconductor laser) 31, a charging means (charger) 32, a developing means (developer) 33, a transfer means (transfer charger) 34, a conveyor belt (not shown), a fixing means (fixer) 35, and a cleaning means (cleaner) 36. Reference numeral 51 denotes a recording medium (recording paper or transfer paper).

[0073] Photoreceptor 1 is rotatably supported on the main body of image forming apparatus 100 and is driven to rotate around rotation axis 44 in the direction of arrow 41 by driving means (not shown). The driving means includes, for example, an electric motor and a reduction gear, and transmits its driving force to a substrate that constitutes the core of photoreceptor 1, thereby driving photoreceptor 1 to rotate at a predetermined peripheral speed. Charging means 32, exposure means 31, developing means 33, transfer means 34, and cleaning means 36 are provided in this order along the outer circumferential surface of photoreceptor 1 from upstream to downstream in the direction of rotation of photoreceptor 1, as indicated by arrow 41.

[0074] The charger 32 is a charging means for uniformly charging the outer circumferential surface of the photosensitive member 1 to a predetermined potential. Examples of the charging means include a non-contact charging method such as a corona charging method using a charger, and a contact charging method using a charging roller or a charging brush.

[0075] The exposure means 31 has a semiconductor laser as a light source, and irradiates the surface of the photoreceptor 1 between the charger 32 and the developer 33 with a laser beam light output from the light source, thereby exposing the charged outer peripheral surface of the photoreceptor 1 according to image information. The light is repeatedly scanned in the main scanning direction, that is, the direction of extension of the rotation axis 44 of the photoreceptor 1, and these are focused to sequentially form electrostatic latent images on the surface of the photoreceptor 1. In other words, the amount of charge on the photoreceptor 1, which has been uniformly charged by the charger 32, differs depending on whether or not it is irradiated with the laser beam, thereby forming an electrostatic latent image.

[0076] The developing device 33 is a developing means that develops the electrostatic latent image formed on the surface of the photosensitive member 1 by exposure with a developer (toner), and is provided facing the photosensitive member 1 and includes a developing roller 33a that supplies toner to the outer peripheral surface of the photosensitive member 1, and a casing 33b that supports the developing roller 33a rotatably around a rotation axis parallel to the rotation axis 44 of the photosensitive member 1 and contains a developer containing toner in its internal space.

[0077] The transfer charger 34 is a transfer means that transfers a toner image, which is a visible image formed on the outer peripheral surface of the photosensitive member 1 by development, onto transfer paper 51, which is a recording medium that is supplied between the photosensitive member 1 and the transfer charger 34 from the direction of arrow 42 by a transport means (not shown). The transfer charger 34 is, for example, a contact-type transfer means that includes a charging means and transfers the toner image onto the transfer paper 51 by applying a charge of the opposite polarity to that of the toner to the transfer paper 51.

[0078] The cleaner 36 is a cleaning means that removes and collects toner remaining on the outer peripheral surface of the photoreceptor 1 after the transfer operation by the transfer charger 34, and includes a cleaning blade 36a that separates the toner remaining on the outer peripheral surface of the photoreceptor 1, and a collection casing 36b that contains the toner separated by the cleaning blade 36a. The cleaner 36 is also provided together with a static elimination lamp (not shown).

[0079] The image forming apparatus 100 is also provided with a fixing device 35, which is a fixing means for fixing the transferred image, downstream of the transport of the transfer paper 51 that has passed between the photoreceptor 1 and the transfer charger 34. The fixing device 35 is provided with a heating roller 35a having a heating means (not shown), and a pressure roller 35b that is provided opposite the heating roller 35a and is pressed against the heating roller 35a to form a contact portion. Reference numeral 37 denotes a separating means for separating the transfer paper from the photosensitive member, and reference numeral 38 denotes a housing (casing) that houses the various means of the image forming apparatus.

[0080] The image forming operation by this image forming apparatus 100 is performed as follows. First, when the photosensitive member 1 is rotated in the direction of arrow 41 by the driving means, the surface of the photosensitive member 1 is uniformly charged to a predetermined positive potential by the charger 32, which is located upstream of the image-forming point of the light by the exposure means 31 in the direction of rotation of the photosensitive member 1. Next, light corresponding to image information is irradiated from exposure means 32 onto the surface of photoreceptor 1. This exposure removes surface charge from the areas of photoreceptor 1 that have been irradiated with light, creating a difference in surface potential between the areas that have been irradiated with light and the areas that have not been irradiated with light, forming an electrostatic latent image. Toner is supplied from a developing device 33, which is located downstream in the rotational direction of the photosensitive member 1 from the point where light is focused by the exposure means 33, to the surface of the photosensitive member 1 on which the electrostatic latent image is formed, thereby developing the electrostatic latent image and forming a toner image.

[0081] In synchronization with the exposure of the photoreceptor 1, transfer paper 51 is supplied between the photoreceptor 1 and transfer charger 34. The transfer charger 34 imparts a charge of opposite polarity to that of the toner to the supplied transfer paper 51, and the toner image formed on the surface of the photoreceptor 1 is transferred onto the transfer paper 51. The transfer paper 51 onto which the toner image has been transferred is transported by the transport means to the fixing device 35, and is heated and pressurized as it passes through the contact area between the heating roller 35a and the pressure roller 35b of the fixing device 35, and the toner image is fixed onto the transfer paper 51 to form a solid image. The transfer paper 51 on which the image has been formed in this way is ejected to the outside of the image forming apparatus 100 by the transport means.

[0082] Meanwhile, any toner remaining on the surface of photoreceptor 1 after the transfer of the toner image by transfer charger 34 is peeled off and collected from the surface of photoreceptor 1 by cleaner 36. The charge on the surface of photoreceptor 1 from which the toner has been removed in this way is removed by light from the discharging lamp, and the electrostatic latent image on the surface of photoreceptor 1 disappears. Thereafter, photoreceptor 1 is rotated again, and the series of operations starting with charging are repeated again to form images continuously.

[0083] The image forming apparatus 100 described above is a monochrome image forming apparatus (printer), but it may also be, for example, an intermediate transfer type color image forming apparatus capable of forming color images. Specifically, it may be a so-called tandem type full-color image forming apparatus having a configuration in which multiple electrophotographic photosensitive members on which toner images are respectively formed are arranged side by side in a predetermined direction (for example, horizontal direction H or approximately horizontal direction H). Furthermore, the image forming apparatus 100 may also be another color image forming apparatus, a copier, a multifunction machine, or a facsimile machine. [Example]

[0084] The present disclosure will be specifically explained below with reference to Production Examples, Comparative Production Examples, Examples, and Comparative Examples, but the present invention is not limited to the following Examples as long as it does not depart from the gist of the present invention. In the examples and comparative examples, a laminated photoreceptor having only a laminated photosensitive layer on the surface side of the photoreceptor was used, but similar results can be obtained by using a laminated photoreceptor that further has a surface protective layer on the laminated photosensitive layer. The materials used in the examples and comparative examples and the physical properties of the resulting photoreceptors were measured by the following methods.

[0085] [Calculated molecular weight of polyvinyl acetal resin] Based on JIS K6728:1977 (ASTM D1396-92), the degree of acetalization and the amount of residual hydroxyl groups of the polyvinyl acetal resin used as the binder resin in the charge generating layer were measured, and the calculated molecular weight of the binder resin was calculated from the degree of polymerization and the degree of acetalization of vinyl alcohol. When multiple resins were used, the calculated molecular weight was calculated from the mass ratio to the total amount of resin. In the following examples and comparative examples, S-LEC B (BL-1, BL-10, BM-2, BL-5Z, BM-SHZ, BX-1) manufactured by Sekisui Chemical Co., Ltd. was used as the polyvinyl acetal resin, and the amount of hydroxyl groups and calculated molecular weight in the charge generating layer were adjusted to compare the effect of the resin structure on the properties.

[0086] [Image analysis of particle size distribution of titanyl phthalocyanine adducts] The particle size distribution of the charge generating material in the charge generating layer of the photoreceptor was confirmed as follows. The center of the resulting photoreceptor was cut, and the entire photoreceptor was immersed in acetone for 20 minutes. After removal, the charge transport layer was peeled off one minute later, and the charge generation layer was then washed with acetone to prepare a sample for measuring the particle size distribution of the charge generation layer. Peeling at the interface between the charge transport layer and charge generation layer is possible because the low molecular weight components of the charge transport layer are soluble in acetone, while the high molecular weight components are insoluble. The surface of the obtained test piece was observed without deposition using a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, model: S-4800) at an acceleration voltage of 1 keV to observe the particle size distribution of the charge generation substance (titanyl phthalocyanine adduct) in the charge generation layer. One hundred titanyl phthalocyanine particles were randomly selected from the obtained image and observed as primary particles. Basic statistical analysis was performed using image analysis and Excel data analysis tools to calculate the mean Feret diameter, its standard deviation, and the skewness and kurtosis of the particle size distribution. FIG. 3 shows SEM images of the surfaces of the charge generating layers of the photoreceptors of (a) Example 1 and (b) Comparative Example 1 of the present disclosure, respectively.

[0087] [Absorption spectrum of titanyl phthalocyanine adduct] The photosensitive layer of the obtained photoreceptor was peeled off, and the spectral absorption spectrum of the titanyl phthalocyanine adduct of 2,3-butanediol in the photosensitive layer was measured in the wavelength range of 400 to 900 nm using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, UV-VIS SPECTROPHOTOMETER, model: UV-2450). FIG. 4 is a diagram showing the spectral absorption spectrum of the photosensitive layer of the photoreceptor of Example 1 of the present disclosure. FIG. 4 shows that the titanyl phthalocyanine in the laminated photosensitive layer of the photoreceptor of Example 1 has a maximum absorption in the wavelength range of 745 to 755 nm.

[0088] [Manufacturing Example 1] <Preparation of titanyl phthalocyanine> Titanyl phthalocyanine to which (2R,3R)-2,3-butanediol is added or titanyl phthalocyanine to which (2S,3S)-2,3-butanediol is added, represented by the following structural formula, used as a charge generating material, was prepared according to the method described in Japanese Patent No. 5609167 (Production Examples 1 to 3).

[0089] [ka]

[0090] 29.2 g of diiminoisoindoline and 200 ml of sulfolane were mixed, and 17.0 g of titanium tetraisopropoxide was added, followed by reaction under a nitrogen atmosphere at 140°C for 2 hours. The resulting reaction mixture was allowed to cool, and the precipitate was collected by filtration, washed successively with chloroform and a 2% aqueous solution of hydrochloric acid, and then with water and methanol, and dried to obtain 25.5 g (yield: 89%) of crude titanyl phthalocyanine as a blue-purple crystalline product.

[0091] Five parts by mass of the obtained crude titanyl phthalocyanine that had been washed with hot water was stirred in 100 parts by mass of sulfuric acid at 3 to 5°C, gradually dissolved, and filtered. If the reaction temperature exceeds 5°C, the phthalocyanine may decompose, so the temperature was strictly controlled to be 5°C or below. The resulting sulfuric acid solution was added dropwise to 3,500 parts by mass of ice water while stirring. The temperature of the ice water was maintained at 5°C or below during this process. The precipitated crystals were filtered and then repeatedly washed by suspension in a washing solution, yielding 250 g of the desired titanyl phthalocyanine wet cake. The pH of the washing solution was measured to be 6.8, confirming that deacidification washing had been successful. The obtained wet cake was spread to a uniform thickness on a flat tray and frozen while taking care to prevent uneven freezing over the entire surface, to obtain a frozen wet paste. The frozen wet paste was then thawed, filtered, washed with water, and filtered again. The process of washing the wet paste with water, spreading it, freezing it, and filtering was repeated, and after drying, it was confirmed that there were no localized lumps, and 23.1 g (yield: 80%) of amorphous titanyl phthalocyanine was obtained.

[0092] [Manufacturing Example 2] <Preparation of titanyl phthalocyanine adduct of (2R,3R)-2,3-butanediol> 10.0 g of the amorphous titanyl phthalocyanine wet cake obtained in Production Example 1 and 2.50 g of (2R,3R)-2,3-butanediol were mixed in 1000 ml of orthodichlorobenzene and heated and stirred at 45 to 65°C for 6.0 hours. After standing overnight, 1000 ml of water was added to the resulting reaction solution, and hydrolysis was carried out by heating and stirring at 45 to 65°C for 6.0 hours. Thereafter, the reaction solution was allowed to cool, methanol was added, and the resulting crystals were filtered. The filtered crystals were washed with methanol to obtain 11.2 g of a titanyl phthalocyanine adduct of (2R,3R)-2,3-butanediol. The X-ray diffraction spectrum of the resulting adduct was confirmed to have diffraction peaks at Bragg angles of 8.3°, 24.7°, 25.1°, and 26.5°. Furthermore, thermal analysis of the obtained adduct confirmed that there was a mass loss of approximately 11.0% at 300 to 410°C. Normally, the boiling point of 1,2-butanediol is 191°C, and it is presumed that the adduct incorporated into titanyl phthalocyanine was eliminated.

[0093] [Manufacturing Example 3] <Preparation of titanyl phthalocyanine adduct of (2S,3S)-2,3-butanediol> The same procedure as in Production Example 2 was carried out except that (2S,3S)-2,3-butanediol was used in place of (2R,3R)-2,3-butanediol in the amorphous titanyl phthalocyanine wet cake obtained in Production Example 1, to obtain 12.5 g of a titanyl phthalocyanine adduct of (2S,3S)-2,3-butanediol. The X-ray diffraction spectrum of the resulting adduct was confirmed to have diffraction peaks at Bragg angles of 8.3°, 24.7°, 25.1°, and 26.5°. Furthermore, thermal analysis of the obtained adduct confirmed that it lost approximately 9.1% of its mass at temperatures between 300 and 410°C.

[0094] [Comparative Manufacturing Example 1] To 10.0 g of the amorphous titanyl phthalocyanine wet cake obtained in Production Example 1, 200 g of tetrahydrofuran (THF) was added as a crystallization solvent. The mixture was stirred at room temperature at 500 rpm for 1 hour using a homomixer (manufactured by Kenis Co., Ltd., model: MARKf model) and then filtered. After washing with methanol, titanyl phthalocyanine was obtained. A second crystallization treatment was then carried out using a mixed solvent of THF:toluene = 5:5, and the mixture was dried under reduced pressure to obtain 8.9 g of titanyl phthalocyanine crystals of Comparative Production Example 1. In the X-ray diffraction spectrum of the obtained titanyl phthalocyanine crystal, it was confirmed that the crystal had diffraction peaks at Bragg angles of 7.3°, 9.4°, 11.6°, 24.2° and 27.3°.

[0095] [Example 1] (Formation of undercoat layer) Three parts by weight of titanium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., product name: TIPAEQ TTO-D-1) and two parts by weight of copolymer polyamide (nylon) (manufactured by Toray Industries, Inc., product name: Amilan (registered trademark), grade: CM8000) were added to 25 parts by weight of methyl alcohol, and the mixture was dispersed for eight hours using a paint shaker to prepare three liters of coating liquid for the undercoat layer. The obtained coating liquid for the undercoat layer was filled into a coating tank, and an aluminum drum-shaped support having a diameter of 30 mm and a length of 255 mm as the substrate F1 was immersed in it and then removed. The obtained coating film was allowed to dry naturally, forming an undercoat layer F21 having a thickness of 1 μm on the substrate F1.

[0096] (Formation of Charge Generation Layer) 3 parts by weight of the titanyl phthalocyanine adduct obtained in Production Example 2 as a charge generation material and 2 parts by weight of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product names: S-LEC BL-1 and BX-1, mass ratio BL-1 / BX-1 = 5 / 95) as a binder resin were added to 95 parts by weight of methyl ethyl ketone, and the mixture was dispersed using a commercially available bead mill disperser (mill capacity: 100 mL, manufactured by VMA-Getzmann, model: Dispermat vertical disperser CV3-PLUS) with 0.6 mm diameter glass beads at a rotation speed of 500 rpm for 5 hours to prepare 28 g of a charge generation layer coating solution. The obtained coating liquid for the charge generating layer was applied onto the undercoat layer F21 using the same immersion method as in the case of forming the undercoat layer, and the resulting coating film was allowed to dry naturally to form a charge generating layer F22 with a thickness of 0.3 μm.

[0097] (Formation of charge transport layer) 10 parts by mass of a stilbene derivative (compound (a)) represented by the following structural formula as a hole transport substance and 20 parts by mass of Z-type polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2020) as a binder resin were added to 104 parts by mass of tetrahydrofuran, and the mixture was stirred and mixed to prepare 30 g of a coating liquid for forming a charge transport layer. The stilbene derivative represented by the following structural formula was prepared in advance based on the method described in Japanese Patent No. 3272257.

[0098] [ka]

[0099] The obtained coating liquid for the charge transport layer was applied onto the charge generation layer F22 by the same immersion method as in the case of forming the undercoat layer, and the resulting coating film was dried at 120°C for 1 hour to form a charge transport layer F23 with a thickness of 30 μm, thereby obtaining the photoreceptor shown in Figure 2.

[0100] [Example 2] The photoreceptor of Example 2 was prepared in the same manner as in Example 1, except that in preparing the coating solution for the charge generating layer, the mass ratio of the polyvinyl butyral resins was changed to BL-1 / BX-1 = 40 / 60 and the dispersion treatment time in the bead mill disperser was changed to 7 hours.

[0101] [Example 3] The photoreceptor of Example 3 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product names: S-LEC BL-1 and BM-SHZ, mass ratio BL-1 / BM-SH = 25 / 75) was used as the binder resin and the dispersion treatment time in the bead mill disperser was changed to 7 hours.

[0102] [Example 4] A photoreceptor of Example 4 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, the dispersion treatment time in the bead mill disperser was changed to 10 hours.

[0103] [Example 5] A photoreceptor of Example 5 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, the dispersion treatment time in the bead mill disperser was changed to 3 hours.

[0104] [Example 6] The photoreceptor of Example 6 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, the rotation speed of the bead mill disperser was changed to 300 rpm and the dispersion treatment time was changed to 12 hours.

[0105] [Example 7] The photoreceptor of Example 7 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BL-1) was used as the binder resin, and an ultrasonic cleaning tank (tank capacity: 27 L, manufactured by AS ONE Corporation, model: MCS-27) was used instead of the bead mill disperser, and the dispersion treatment was carried out for 2 hours under conditions of a frequency of 40 kHz and an output of 500 W.

[0106] [Example 8] The photoreceptor of Example 8 was prepared in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, glass beads with a diameter of 0.4 mm were used and the dispersion treatment time in the bead mill disperser was changed to 5 hours.

[0107] [Example 9] The photoreceptor of Example 9 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product names: S-LEC BL-1 and BM-SHZ, mass ratio BL-1 / BM-SH = 5 / 95) was used as the binder resin and the dispersion treatment time in the bead mill disperser was changed to 9 hours.

[0108] [Example 10] The photoreceptor of Example 10 was prepared in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, the mass ratio of the polyvinyl butyral resin was changed to BL-1 / BX-1 = 40 / 60 (same as in Example 2) and the dispersion treatment time in the bead mill disperser was changed to 8 hours.

[0109] [Example 11] The photoreceptor of Example 11 was prepared in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BL-10) was used as the binder resin.

[0110] [Example 12] The photoreceptor of Example 12 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BX-1) was used as the binder resin and the dispersion treatment time in the bead mill disperser was changed to 12 hours.

[0111] [Example 13] The photoreceptor of Example 13 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product names: S-LEC BL-1 and BL-5Z, mass ratio BL-1 / BL-5Z = 5 / 95) was used as the binder resin, the rotation speed of the bead mill disperser was changed to 700 rpm, and the dispersion treatment time was changed to 12 hours.

[0112] [Example 14] The photoreceptor of Example 14 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BM-2) was used as the binder resin and the dispersion treatment time in the bead mill disperser was changed to 4 hours.

[0113] [Example 15] A photoreceptor of Example 15 was prepared in the same manner as in Example 1, except that the titanyl phthalocyanine adduct obtained in Production Example 3 was used as the charge generating substance in preparing the coating liquid for the charge generating layer.

[0114] [Comparative Example 1] The photoreceptor of Comparative Example 1 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BL-1) was used as the binder resin and the dispersion treatment time in the bead mill disperser was changed to 12 hours.

[0115] Comparative Example 2 The photoreceptor of Comparative Example 2 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BM-SHZ) was used as the binder resin and the dispersion treatment time in the bead mill disperser was changed to 12 hours.

[0116] Comparative Example 3 The photoreceptor of Comparative Example 3 was prepared in the same manner as in Example 1, except that in preparing the coating solution for the charge generating layer, the mass ratio of the polyvinyl butyral resins was changed to BL-1 / BX-1 = 40 / 60, glass beads with a diameter of 0.4 mm were used, and the dispersion treatment time in the bead mill disperser was changed to 7 hours.

[0117] Comparative Example 4 The photoreceptor of Comparative Example 4 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generating layer, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BL-5Z) was used as the binder resin and the dispersion treatment time in the bead mill disperser was changed to 20 hours.

[0118] Comparative Example 5 The photoreceptor of Comparative Example 5 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generation layer, the titanyl phthalocyanine crystals obtained in Comparative Production Example 1 were used as the charge generation material, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BX-1) was used as the binder resin, zirconia beads with a diameter of 0.5 mm were used, and the dispersion treatment time of the bead mill disperser was changed to 2 hours.

[0119] Comparative Example 6 The photoreceptor of Comparative Example 6 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generation layer, the titanyl phthalocyanine crystals obtained in Comparative Production Example 1 were used as the charge generation material, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BX-1) was used as the binder resin, zirconia beads with a diameter of 0.5 mm were used, and the dispersion treatment time of the bead mill disperser was changed to 3 hours.

[0120] Comparative Example 7 The photoreceptor of Comparative Example 7 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge generation layer, the titanyl phthalocyanine crystals obtained in Comparative Production Example 1 were used as the charge generation material, only polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BX-1) was used as the binder resin, zirconia beads with a diameter of 0.3 mm were used, and the dispersion treatment time in the bead mill disperser was changed to 3 hours at a rotation speed of 300 rpm.

[0121] [evaluation] The coating solutions for charge generating layers and the photoreceptors prepared in Examples 1 to 14 and Comparative Examples 1 to 7 were evaluated for the following items.

[0122] [Evaluation 1: Dispersion stability of coating liquid] The coating liquid for the charge generating layer prepared in the production of each photoreceptor was placed in a 50 mL screw cap bottle (storage bottle) immediately after preparation and stored stationary in a storage cabinet adjusted to a temperature of 20°C for 3 months. After storage, the state of aggregation and sedimentation of each coating liquid was visually observed, and the dispersion stability of the coating liquid was judged based on the results and the measurement results of the particle size distribution of the charge generating material in the charge generating layer according to the following criteria. VG: When the storage bottle is shaken 10 times, no sediment is found at the bottom of the storage bottle and the initial particle size distribution is maintained. G: When the storage bottle was shaken 10 times, sediment remained at the bottom of the bottle, but after shaking 20 times the sediment disappeared and the initial particle size distribution was maintained. NB: When the storage bottle was shaken 10 times, sediment remained at the bottom of the bottle, but after shaking it 20 times, the sediment disappeared. In particle size distribution measurement, although the average particle size of D50 was maintained, the particle size of D90 became slightly larger and aggregation of coarse particles was confirmed, but this did not affect the image characteristics. B: When the storage bottle is shaken 20 times, the presence of sediment can be confirmed.

[0123] [Evaluation 2: Sensitivity characteristics] The photoreceptor to be evaluated was mounted in a digital copier (Model MX-2600, manufactured by Sharp Corporation) that had been modified for the test. The developing unit was removed from the digital copier and a surface potential meter (Model 344, manufactured by Trek Japan) was attached to the developing section instead. Sensitivity potential VL in a low humidity (NL) environment (temperature 25°C / relative humidity 10%) and a high humidity (NH) environment (temperature 25°C / relative humidity 85%) NL (-V) and VL NH (-V) and calculate the difference between them as ΔVL NL-HH The sensitivity stability was evaluated based on the following criteria, and used as an index of the sensitivity fluctuation with humidity. Specifically, the "VL" of each criterion NL " and "ΔVL NL-HH " is judged as satisfying the two requirements of the above criteria, and if one requirement of a certain criterion is met and the other requirement is not met, the judgment is made based on the lower criterion that is met. VG: VL NL <200 and 0≦ΔVL NL-HH <10 Can be used without problems in high-speed multifunction devices or printers that require high sensitivity G: 200≦VL NL <220 and 10≦ΔVL NL-HH <25 Can be used without problems with medium to low speed multifunction devices or printers NB:220≦VL NL <240 and 25≦ΔVL NL-HH <35 Although the density is slightly low, it can be used without any problems on slow, inexpensive multifunction devices or printers. B: 240≦VL NL and 35≦ΔVL NL-HH Poor sensitivity results in low concentration, which is problematic for practical use

[0124] [Evaluation 3: Electrical fatigue test] The photoreceptor to be evaluated was attached to the unit of a digital copier (manufactured by Sharp Corporation, model: BP-40C26) that had been modified for the test, the developing unit was removed from the digital copier, and a surface potentiometer (manufactured by Trek Japan, model: MODEL 344) was attached to the developing section instead. The surface potential of the photoconductor after electrical fatigue was measured in an environment of 25°C temperature and 10% relative humidity, and the difference between the charge potential on the first rotation of the photoconductor and the charge potential on the second rotation was taken as ΔV0 (V). The electrical fatigue characteristics were judged based on the following criteria and used as an index of charging stability after repeated use. <Judgment criteria> VG: 0≦ΔV0<60 (very good) G: 60≦ΔV0<80 (good) NB: 80≦ΔV0<100 (fairly good) B :100≦ΔV0(defective)

[0125] In addition, under an environment of 35°C temperature and 85% relative humidity, the initial residual potential and the surface potential of the photoreceptor after electrical fatigue were measured, and the difference between these was taken as ΔVr (V). The sensitivity stability was judged based on the following criteria, and this was used as an index of sensitivity deterioration due to repeated use. <Judgment criteria> VG: 0≦ΔVr<60 (very good) G: 60≦ΔVr<80 (good) NB: 80≦ΔVr<100 (fairly good) B :100≦ΔVr(defective)

[0126] [comprehensive evaluation] Based on the results of the above evaluations 1 to 3, a comprehensive evaluation was made according to the following criteria. <Evaluation criteria> VG: VG rating in all categories, very good Can be used without problems in multifunction devices and printers that require long life and high image quality G: Some items may be rated G, but all items are rated G or higher Can be used without problems except for multifunction devices and printers that require long life and high image quality NB: Some items may be judged as NB, but all items may be judged as NB or better. If it is an inexpensive multifunction device or printer, it can be used without any problems. B: Any item has a B rating and cannot be used. Poor sensitivity results in low concentration, which is problematic for practical use

[0127] Table 1 shows the main constituent materials of the charge generating layer, their properties, and the dispersion conditions for the coating liquid for forming the layer. Table 2 shows the evaluation results of the coating liquid for the charge generating layer and the photoreceptor. The abbreviations in Table 1 have the following meanings. Coarse particles: Agglomerates of titanyl phthalocyanine with a maximum Feret diameter of 4 μm or more and 0.7 μm or less BMD: Bead mill dispersion USD: Ultrasonic dispersion GB: Glass beads ZB: Zirconia (zirconium oxide) beads Furthermore, the materials of the binder resin of the charge generating layer are expressed by their product names, and in the case of a single material, the ratio is expressed as "100", and in the case of a mixed material, the ratio is expressed when the total amount is 100.

[0128] [Table 1]

[0129] [Table 2]

[0130] Tables 1 and 2 reveal the following: (1) The photoreceptors (Examples 1 to 15) satisfying the constituent requirements of the present disclosure are excellent in the evaluation of the humidity fluctuation range of sensitivity, charging stability due to repeated fatigue, and fluctuation in residual potential, whereas the photoreceptors (Comparative Examples 1 to 7) not satisfying the constituent requirements of the present disclosure are inferior, and the coating liquid for forming the charge generating layer of the photoreceptor satisfying the constituent requirements of the present disclosure is excellent in dispersion stability. Specifically, by adjusting the average Feret diameter of titanyl phthalocyanine to 0.20 μm or more and 0.30 μm or less, its standard deviation to 0.07 μm or more and 0.13 μm or less, and the skewness of the particle size distribution of titanyl phthalocyanine to 0.50 or more and 1.20 or less, a balanced state of properties with few adverse effects can be achieved. Furthermore, by adjusting the average Feret diameter of titanyl phthalocyanine to 0.23 μm or more and 0.30 μm or less, its standard deviation to 0.08 μm or more and 0.11 μm or less, the skewness of the particle size distribution of titanyl phthalocyanine to 0.85 or more and 1.0 or less, and the kurtosis of the particle size distribution to 0.70 or more and 1.20 or less, a more optimized state can be achieved.

[0131] These differences are thought to be related to the dispersion state of titanyl phthalocyanine, which is the charge-generating substance in the charge-generating layer, and that when the dispersion stress of titanyl phthalocyanine is excessive, charging stability decreases, and when the dispersion stress is too low and excessive coarse particles remain, dispersion stability decreases. In other words, the photoreceptor of the present disclosure is believed to be able to obtain stable image characteristics over a long period of time by minimizing dispersion stress on the charge generating material within a range that ensures dispersion stability of the coating liquid for forming the charge generating layer.

[0132] (2) The photoreceptors of the present disclosure (Examples 1 to 15) using titanyl phthalocyanine adducts as charge-generating materials can significantly reduce the humidity fluctuation range of sensitivity, while the photoreceptors using conventional titanyl phthalocyanine (Comparative Examples 5 and 6) are presumed to improve sensitivity in high-humidity environments and worsen sensitivity in low-humidity environments because the water component in the air adheres to the charge-generating material, promoting charge generation. Furthermore, the photoconductor (Example 1) using titanyl phthalocyanine as the charge generating material, which has a maximum absorption in the wavelength range of 745 nm to 755 nm in the spectral absorption spectrum, is less susceptible to fatigue due to repeated energization than the photoconductors (Examples 6 and 7) using titanyl phthalocyanine with maximum absorption wavelengths of 743 nm and 762 nm, respectively. The maximum absorption on the long wavelength side is thought to be largely due to the selection of the dispersion method and the manufacturing method of the charge generating material.

[0133] (3) In the particle size distribution of the titanyl phthalocyanine adduct, the photoreceptor (Example 1) in which there are three or more agglomerates of the titanyl phthalocyanine adduct having a Feret diameter of 0.4 μm or more and 0.7 μm or less has improved charging stability against fatigue caused by repeated current application. On the other hand, in the photoreceptors with less than three agglomerates (Examples 4, 10, and 11), the charge reduction in the current fatigue test tended to be somewhat large, and in the photoreceptors with many agglomerates (Examples 12 and 13), the sensitivity of the photoreceptor decreased and the stability of the coating liquid for forming the charge generating layer tended to be somewhat poor.

[0134] (4) The charge generating layer contains a polyvinyl acetal resin as a binder resin, and the calculated molecular weight of the polyvinyl acetal resin is 5.0 × 10 4 When the above conditions are satisfied, the stability of the coating liquid for forming the charge generating layer is improved when the coating liquid is stored for a long period of time, and a photoreceptor (Example 9) having the above-mentioned excellent properties can be obtained. On the other hand, the calculated molecular weight of the binder resin is 5.0 × 10 4 If it is less than this, the amount of low molecular weight components in the coating liquid for forming the charge generating layer increases, the viscosity of the coating liquid decreases, and the charge generating material becomes easier to disintegrate and handle during dispersion, but it becomes difficult to maintain its stability, and the properties of the resulting photoreceptor (Example 3) tend to deteriorate. Furthermore, when the calculated molecular weight of the binder resin is too large (Example 12), the dispersion processing time of the coating liquid for forming the charge generating layer becomes long, and depending on the dispersion conditions, the dispersion share for the charge generating substance becomes large, lattice defects increase, and there is a tendency for the risk during dispersion, for example, a decrease in charging in an electrical fatigue test, to become somewhat large.

[0135] (5) Even if the calculated molecular weight of the binder resin in the charge generating layer is approximately the same, the greater the amount of hydroxyl groups, the better the dispersibility of the coating liquid for forming the charge generating layer when stored for a long period of time, and the better the dispersion stability, resulting in a photoreceptor with the above-mentioned excellent properties (Comparison between Examples 9 and 14 and Comparative Example 2). This is thought to be because the greater the amount of hydroxyl groups in the binder resin, the greater the affinity with polar groups in the charge generating material, and the greater the dispersibility and dispersion stability of the coating liquid for forming the charge generating layer. By using a binder resin with a large amount of hydroxyl groups, the polyvinyl acetal resin of the binder resin also has a high affinity with tetrahydrofuran and toluene, which are the coating liquid solvents for the upper layer, the charge transport layer, and therefore dissolves into the charge transport layer. This increases the risk of charge trapping in a high-humidity environment and the risk of sensitivity deterioration due to fatigue from repeated electrical current application. [Explanation of symbols]

[0136] F01 Multilayer electrophotographic photoreceptor (multilayer photoreceptor, photoreceptor) F1 Substrate (conductive support) F21 Undercoat layer (intermediate layer) F22 charge generation layer F23 charge transport layer Fa Photoconductor surface

[0137] 1 photoreceptor 31 Exposure means (semiconductor laser) 32 Charging means (charger) 33 Developing means (developer) 33a Developing roller 33b casing 34 Transfer means (transfer charger) 35 Fixing means (fixing device) 35a Heating roller 35b Pressure roller 36 Cleaning means (cleaner) 36a cleaning blade 36b Recovery casing 37 Separation means 38 Housing 41, 42 arrow mark 44 Rotation axis 51 Recording media (recording paper or transfer paper) 100 Image forming device (laser printer)

Claims

1. an electrophotographic photoreceptor comprising at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a substrate; the charge generation layer contains, as a charge generation material, at least one selected from a titanyl phthalocyanine adduct to which (2R,3R)-2,3-butanediol is added and a titanyl phthalocyanine adduct to which (2S,3S)-2,3-butanediol is added; The surface layer including the charge transport layer of the electrophotographic photosensitive member was peeled off, and a scanning electron microscope image of the surface of the charge generation layer was obtained. 2 When 100 particles are randomly extracted as primary particles of the titanyl phthalocyanine adduct from the region (a) to (c), and the particle size distribution is observed, the average Feret diameter of the titanyl phthalocyanine adduct is 0.20 μm or more and 0.30 μm or less, the standard deviation thereof is 0.07 μm or more and 0.13 μm or less, and the skewness of the particle size distribution of the titanyl phthalocyanine adduct is 0.50 or more and 1.20 or less. An electrophotographic photoreceptor characterized by the above-mentioned.

2. 2. The electrophotographic photoreceptor according to claim 1, wherein the titanyl phthalocyanine adduct has a maximum absorption in a wavelength range of 745 nm to 755 nm in a spectroscopic absorption spectrum.

3. 3. The electrophotographic photoreceptor according to claim 1, wherein the average Feret diameter of the titanyl phthalocyanine adduct is from 0.23 to 0.30 [mu]m, and the standard deviation thereof is from 0.08 to 0.11 [mu]m.

4. 3. The electrophotographic photoreceptor according to claim 1, wherein the skewness of the particle size distribution of the titanyl phthalocyanine adduct is 0.85 or more and 1.0 or less.

5. 3. The electrophotographic photosensitive member according to claim 1, wherein the particle size distribution of the titanyl phthalocyanine adduct contains three or more agglomerates of the titanyl phthalocyanine adduct having a Feret diameter of 0.4 [mu]m or more and 0.7 [mu]m or less.

6. 3. The electrophotographic photoreceptor according to claim 1, wherein the titanyl phthalocyanine adduct has a particle size distribution kurtosis of 0.70 or more and 1.20 or less.

7. The charge generating layer contains a polyvinyl acetal resin as a binder resin, and the calculated molecular weight of the polyvinyl acetal resin is 5.0×10 4 3. The electrophotographic photoreceptor according to claim 1, wherein the electrophotographic photoreceptor is a photosensitive member.

8. 8. The electrophotographic photoreceptor according to claim 7, wherein the polyvinyl acetal resin has a hydroxyl group content of 16% by mass or more and 22% by mass or less.

9. 3. An image forming apparatus comprising at least the electrophotographic photosensitive member according to claim 1 or 2, a charging unit that charges the electrophotographic photosensitive member, an exposure unit that exposes the charged electrophotographic photosensitive member to light to form an electrostatic latent image, a developing unit that develops the electrostatic latent image to form a toner image, and a transfer unit that transfers the toner image onto a recording medium.

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