JP7794655B2 - Image forming apparatus and image forming method using the same - Google Patents

Description

The present invention relates to an image forming apparatus equipped with an electrophotographic photoreceptor that can suppress the occurrence of stress cracks and achieve stable image characteristics over the long term, and an image forming method using the same.

In recent years, with the remarkable development of office automation equipment, image forming apparatuses using electrophotography, such as digital copiers, printers, and facsimile machines, have become widespread, and organic photoreceptors using organic photoconductive materials are widely used as the electrophotographic photoreceptors (hereinafter also referred to as "photoreceptors") used in these processes. However, due to the nature of organic materials, organic photoreceptors have the disadvantage that their surfaces are easily worn away by contact with surrounding cleaning blades and the like.
Furthermore, with the recent increase in contact charging methods using roller charging and the trend toward longer life, smaller size and higher speed of image forming apparatuses, the organic photoreceptor is exposed to harsh conditions where its surface is more susceptible to wear.

To address this issue of wear on the surface of the photoreceptor, a technique has been proposed in which inorganic compound fine particles such as silica particles, alumina particles, or titanium dioxide particles are added as a filler to the surface layer of the photoreceptor, and a technique in which inorganic compound fine particles such as silica particles are added as a filler to a cured protective layer (surface protective layer) formed on the charge transport layer.
For example, Japanese Patent Laid-Open Publication No. 2017-049519 (Patent Document 1) discloses a laminated electrophotographic photoreceptor that includes a photosensitive layer including a charge generation layer containing a charge generation agent (charge generation substance) and a charge transport layer containing a charge transport agent (charge transport substance), a binder resin, a phthalocyanine pigment, and silica particles, wherein the charge transport layer is a single layer and is disposed as the outermost layer, the content of the silica particles is 0.5 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the binder resin, and the average primary particle diameter of the silica particles is 50 nm or more and 150 nm or less.

However, while dispersing fillers within the photosensitive layer can improve printing durability and achieve a long life, problems caused by contact with surrounding components, such as poor cleaning, are a hindrance, and the current situation poses significant practical challenges. These challenges tend to be more pronounced when small particle size fillers are used, and occur when repeated electrical fatigue and the accumulation of mechanical fatigue from the cleaning process lead to the formation of an aggregated structure of the small particle size filler, which then causes stress cracks to form from this aggregated structure.

As a technique for optimizing friction between the photoreceptor surface and surrounding components (contact components), Japanese Patent Application Laid-Open No. 2010-134459 (Patent Document 2) discloses a technique for forming linear scratches on the surface of the photosensitive layer, while International Publication No. WO2016/121231 (Patent Document 3) discloses a technique for controlling the surface properties of a high-pressure-durability photoreceptor using amorphous silicon.

In addition, Japanese Patent Laid-Open No. 2020-140113 (Patent Document 4) discloses an image forming apparatus in which a cleaning blade for removing toner in the image forming apparatus includes an elastic member having a substrate and a surface layer made of a cured product of a curable composition, the surface layer containing a siloxane-based compound, the Martens hardness HM measured using a nanoindenter having a hardness gradient that decreases from the surface toward the underside of the substrate in the film thickness direction, the average film thickness of the surface layer being 10 to 500 μm or less, the creep CIT of the surface layer measured using a nanoindenter having a gradient that decreases from the surface toward the underside of the substrate in the film thickness direction, and the creep CIT being 3.0 to 13.5% in the range from near the surface (load 1 μN) to the deepest part in the film thickness direction (load 1000 μN), and it also discloses that the external additive in the toner may be a fatty acid metal salt such as zinc stearate.

Japanese Patent Application Laid-Open No. 2017-049519 JP 2010-134459 A International Publication No. WO2016/121231 Japanese Patent Application Laid-Open No. 2020-140113

However, even if inorganic compound fine particles are contained in the surface layer of the photosensitive layer as in the above-mentioned prior art, it is difficult to achieve both improved abrasion resistance and stable image formation over a long period of time.
When inorganic compound microparticles are contained in the surface layer of the photosensitive layer, aggregates of the inorganic compound microparticles are formed inside the photosensitive layer due to insufficient dispersibility of the inorganic compound microparticles, and if the slipperiness of the photosensitive body surface is impaired due to electrical fatigue caused by roller charging or sliding of the cleaning blade (a process in which toner remaining on the outer peripheral surface of the photosensitive body is peeled off by the cleaning blade), the frictional resistance between the photosensitive body surface and the cleaning blade increases.
Furthermore, when inorganic compound particles are incorporated into a photosensitive layer, the binder resin has a larger thermal expansion coefficient than the inorganic compound particles, which causes shear stress at the interface between the inorganic compound particles and the binder resin. This stress concentrates around the aggregates of inorganic compound particles, leading to the problem of stress cracks. This phenomenon becomes more serious when the inorganic compound particles are insufficiently dispersible and when the frictional resistance between the photoreceptor surface and the cleaning blade increases with long-term use. Therefore, improving the dispersibility of inorganic compound particles in the photosensitive layer, the smoothness of the photosensitive layer surface, and the mechanical strength of the photosensitive layer have been issues.

The present invention was made in light of the above circumstances, and its purpose is to provide an image forming apparatus equipped with an electrophotographic photoreceptor that can suppress the occurrence of stress cracks and achieve stable image characteristics over the long term, as well as an image forming method using the same.

As a result of extensive research to solve the above problems, the inventors discovered that by improving the mechanical strength of the surface layer, improving the uniformity of dispersion of silica particles in the surface layer, and increasing and controlling the creep value of the surface layer to make it more flexible, and by externally adding an optimized amount of lubricant such as a fatty acid metal salt to the toner, it is possible to improve the lubricity between the photoreceptor and cleaning member and thereby improve the stress crack resistance of the photoreceptor, thereby completing the present invention.

Thus, according to the present invention, there is provided an electrophotographic image forming apparatus comprising at least an electrophotographic photosensitive member, a charging means for charging the electrophotographic photosensitive member, an exposure means for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, a developing means for developing the electrostatic latent image to form a toner image with toner, and a transfer means for transferring the toner image onto a recording medium,
the electrophotographic photoreceptor comprises at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a conductive support,
the charge transport layer contains at least a charge transport material, a binder resin, and silica particles;
the silica particles are contained in the charge transport layer in an amount of 7 to 25% by mass,
the charge transport layer has a surface layer with a ten-point surface roughness Rz of 0.08 to 1.2 μm as defined in JIS-B-0601 (1994),
the charge transport layer has a surface layer having a creep value C of 3.8 to 5.0% as measured by applying a maximum load of 30 mN for 5 seconds using a Vickers square pyramid diamond indenter with an opposing angle of 136° under an environment of a temperature of 25°C and a relative humidity of 50%,
The image forming apparatus is characterized in that the toner is externally added with two or more kinds of external additives including fatty acid metal salt particles.

According to the present invention, there is also provided an image forming method using the image forming apparatus described above, comprising:
The image forming method includes at least a charging step of charging the electrophotographic photosensitive member, an exposure step of exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, a development step of developing the electrostatic latent image to form a toner image with toner, and a transfer step of transferring the toner image onto a recording medium.

The present invention provides an image forming apparatus equipped with an electrophotographic photoreceptor that can suppress the occurrence of stress cracks and achieve stable image characteristics over the long term, as well as an image forming method using the same.

1 is a schematic cross-sectional view showing the configuration of a main part of a photoreceptor 1 of the present invention. 1 is a schematic cross-sectional view showing the configuration of a main part of a photoreceptor 2 of the present invention. 1 is a schematic side view illustrating a configuration of a main part of an image forming apparatus according to the present invention.

The image forming apparatus of the present invention comprises at least an electrophotographic photosensitive member, a charging unit for charging the electrophotographic photosensitive member, an exposure unit for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, a developing unit for developing the electrostatic latent image to form a toner image with toner, and a transfer unit for transferring the toner image onto a recording medium,
the electrophotographic photoreceptor comprises at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a conductive support,
the charge transport layer contains at least a charge transport material, a binder resin, and silica particles;
the silica particles are contained in the charge transport layer in an amount of 7 to 25% by mass,
the charge transport layer has a surface layer with a ten-point surface roughness Rz of 0.08 to 1.2 μm as defined in JIS-B-0601 (1994),
the charge transport layer has a surface layer having a creep value C of 3.8 to 5.0% as measured by applying a maximum load of 30 mN for 5 seconds using a Vickers square pyramid diamond indenter with an opposing angle of 136° under an environment of a temperature of 25°C and a relative humidity of 50%,
The toner is characterized in that two or more kinds of external additives including fatty acid metal salt particles are added externally.

As described above, the image forming apparatus of the present invention has a combination of a specific photoreceptor and a specific toner. The following describes the configuration and features of (1) the electrophotographic photoreceptor, (2) the toner, (3) the image forming apparatus equipped with them, and (4) the image forming method, in that order; however, the present invention is not limited to these descriptions.

(1) Electrophotographic Photoreceptor The photoreceptor used in the image forming apparatus of the present invention comprises at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a conductive support,
the charge transport layer contains at least a charge transport material, a binder resin, and silica particles;
the charge transport layer contains silica particles in an amount of 7 to 25% by mass,
the charge transport layer has a surface layer with a ten-point surface roughness Rz of 0.08 to 1.2 μm as defined in JIS-B-0601 (1994);
The charge transport layer has a surface layer having a creep value C of 3.8 to 5.0% as measured by applying a maximum load of 30 mN for 5 seconds using a Vickers square pyramid diamond indenter with an opposing angle of 136° in an environment of a temperature of 25°C and a relative humidity of 50%.

FIG. 1 is a schematic cross-sectional view showing the configuration of a main part of a photoreceptor 1, which is an example of the photoreceptor of the present invention.
Photoreceptor 10 is a laminated photoreceptor having a photosensitive layer (laminated photosensitive layer) 17 having a laminated structure in which an undercoat layer 12 is provided on a conductive support 11, a charge generation layer 13 containing a charge generation material thereon, and a charge transport layer 14 containing a charge transport material, a binder resin for binding the charge transport material, and silica particles 18 are laminated in this order from conductive support 11 outward. Each component and its features will be described below.

[Conductive support 11]
The conductive support has a function as an electrode of the photoreceptor and a function as a support member, and the material constituting the conductive support 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, 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 are particularly preferred.
The shape of the conductive support is not limited to a cylindrical (drum) shape as shown in FIG. 3, but may be a sheet shape, a columnar shape, an endless belt shape, or the like.
Furthermore, the surface of the conductive support may be subjected to anodizing film treatment, surface treatment with chemicals or hot water, coloring treatment, or diffuse reflection treatment such as surface roughening, as needed, to prevent interference fringes caused by laser light, within a range that does not affect image quality.

[Undercoat layer (also called "intermediate layer") 12]
The photoreceptor of the present invention preferably has an undercoat layer 12 between the conductive support 11 and the laminated photosensitive layer 17 .
The undercoat layer generally covers and smooths the irregularities on the surface of the conductive support, improves the film-forming properties of the laminated photosensitive layer, here the charge generating layer, suppresses peeling of the laminated photosensitive layer from the conductive support, and improves the adhesion between the conductive support and the laminated photosensitive layer. Specifically, it prevents charge injection from the conductive support into the laminated photosensitive layer, prevents a decrease in the chargeability of the laminated photosensitive layer, and can prevent image fogging (so-called black spots), thereby maintaining good electrophotographic properties such as chargeability throughout the life of the electrophotographic image forming apparatus.

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 conductive support, and then drying to remove the organic solvent.

Examples of binder resins include the same binder resins as those contained in the laminated photosensitive layer described below, as well as natural polymer materials such as casein, gelatin, polyvinyl alcohol, and ethyl cellulose, and one or more of these can be used.
The binder resin is required to have properties such as not dissolving or swelling in the solvent used when forming the photosensitive layer on the undercoat layer, having excellent adhesion to the conductive support, and having flexibility. Therefore, among the above binder resins, polyamide resins are preferred, and alcohol-soluble nylon resins 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 resins obtained by chemically modifying nylons such as N-alkoxymethyl-modified nylons.

Solvents for dissolving or dispersing resin materials include, for example, water; alcohols such as methanol, ethanol, and butanol; glymes such as methyl carbitol and butyl carbitol; chlorinated solvents such as dichloroethane, chloroform, and trichloroethane; acetone; dioxolane; and mixed solvents of two or more of these solvents. Among these solvents, non-halogenated organic solvents are preferred due to considerations for the global environment.

The coating solution for the undercoat layer may also contain inorganic compound fine particles. The inorganic compound fine particles of the undercoat layer have a different purpose from the inorganic compound fine particles of the outermost layer, and may be the same compound or different compounds.
The inorganic compound fine particles can easily adjust the volume resistivity of the undercoat layer, can further suppress the injection of charges into the laminated photosensitive layer, and can maintain the electrical properties of the photoreceptor under various environments.
Examples of inorganic compound fine particles include titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide.
The ratio (C/D) of the total mass C of the binder resin and inorganic compound particles to the mass D of the solvent in the coating liquid for the undercoat layer is preferably 1/99 to 40/60, particularly preferably 2/98 to 30/70.
The ratio E/F of the mass E of the binder resin to the mass F of the inorganic compound fine particles is preferably 90/10 to 1/99, and particularly preferably 70/30 to 5/95.

In order to disperse the inorganic compound particles in the coating liquid for the undercoat layer, known devices such as a ball mill, a sand mill, an attritor, a vibration mill, an ultrasonic disperser, and a paint shaker may be used.
The coating method for the undercoat layer coating liquid may be appropriately selected from among the methods most suitable for the coating liquid, taking into consideration the physical properties of the coating liquid, productivity, and the like. Examples of the 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.

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 less than 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 about 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 laminated photosensitive layer described below and other treatments.

The thickness of the undercoat layer is not particularly limited, but is preferably 0.01 to 20 μm, more preferably 0.05 to 10 μm.
If the thickness of the undercoat layer is less than 0.01 μm, the undercoat layer will not substantially function as an undercoat layer, and it will be impossible to cover defects in the conductive support to obtain a uniform surface, and it may become impossible to prevent injection of charges from the conductive support into the laminated photosensitive layer. On the other hand, if the thickness of the undercoat layer is more than 20 μm, it will be difficult to form a uniform undercoat layer, and the sensitivity of the photoreceptor may also decrease.
When the conductive support is made of aluminum, a layer containing alumite (alumite layer) can be formed as an undercoat layer.

[Charge Generation Layer 13]
The charge generation layer has the function of generating charges by absorbing light irradiated by a semiconductor laser beam or the like in an image forming apparatus, and contains a charge generation substance as a main component and, if necessary, a binder resin and additives.

The charge-generating substance may be a compound used in the art, specifically, azo pigments such as monoazo pigments, bisazo pigments, and trisazo pigments; indigo pigments such as indigo and thioindigo; perylene pigments such as peryleneimide and perylene acid anhydride; polycyclic quinone pigments such as anthraquinone and pyrenequinone; phthalocyanine pigments such as metal phthalocyanines and metal-free phthalocyanines, including titanyl phthalocyanine; organic photoconductive materials such as squarylium dyes, pyrylium salts, thiopyrylium salts, and triphenylmethane dyes; and inorganic photoconductive materials such as selenium and amorphous silicon, among others. These charge-generating substances may be used singly or in combination of two or more.
Among these charge generating materials, those represented by the following general formula (A):

(wherein X ¹ , X ² , X ³ and X ⁴ are the same or different and each represents a halogen atom, an alkyl group or an alkoxy group; and r, s, y and z are the same or different and each represents an integer of 0 to 4.)
It is preferable to use titanyl phthalocyanine represented by the following formula:
Titanyl phthalocyanine is a charge-generating material that has high charge generation and charge injection efficiencies in the emission wavelength range (near-infrared light) of currently commonly used laser light and LED light. It generates a large amount of charge by absorbing light and can efficiently inject the generated charge into a charge-transporting material without accumulating it internally.

The titanyl phthalocyanine represented by the general formula (A) can be produced by a known production method, for example, the method described in Phthalocyanine Compounds by Moser, Frank H. and Arthur L. Thomas, Reinhold Publishing Corp., New York, 1963.
For example, among the titanyl phthalocyanine compounds represented by general formula (A), in the case of an unsubstituted titanyl phthalocyanine in which r, s, y, and z are 0, it can be obtained by synthesizing dichlorotitanyl phthalocyanine by heating and melting phthalonitrile and titanium tetrachloride or by heating and reacting them in a suitable solvent such as α-chloronaphthalene, and then hydrolyzing the resultant with a base or water.
Alternatively, a titanyl phthalocyanine composition can be produced by reacting isoindoline with a titanium tetraalkoxide such as tetrabutoxytitanium under heating in a suitable solvent such as N-methylpyrrolidone.

Methods for forming a charge generation layer include vacuum deposition of a charge generation material onto a conductive support, and coating a coating liquid for a charge generation layer obtained by dispersing a charge generation material in a solvent onto a conductive support. Of these, a preferred method is to disperse a charge generation material in a binder resin solution obtained by mixing a binder resin in a solvent using a conventionally known method, and then coat the coating liquid for a charge generation layer onto a conductive support. This method is described below.

The binder resin is not particularly limited, and any resin known in the art can be used, such as polyester, polystyrene, polyurethane, phenolic resin, alkyd resin, melamine resin, epoxy resin, silicone resin, acrylic resin, methacrylic resin, polycarbonate, polyarylate, polyphenoxy, polyvinyl butyral, and polyvinyl formal, as well as 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 resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, and acrylonitrile-styrene copolymer resin. These resins can be used alone or in combination of two or more.

Examples of solvents 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 (THF) 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.

The compounding ratio of the charge generating material to the binder resin is preferably such that the proportion of the charge generating material is in the range of 10 to 99% by mass.
If the proportion of the charge generating substance is less than 10% by mass, the sensitivity may decrease. On the other hand, if the proportion of the charge generating substance exceeds 99% by mass, not only the film strength of the charge generating layer decreases, but also the dispersibility of the charge generating substance decreases, resulting in an increase in coarse particles, which may reduce the surface charge in areas other than those that should be erased by exposure, resulting in image defects, particularly image fogging called black spots, in which toner adheres to a white background and forms tiny black spots.

Before dispersing the charge-generating material in the binder resin solution, the charge-generating material may be pulverized in advance using a pulverizer such as a ball mill, a sand mill, an attritor, a vibration mill, or an ultrasonic disperser.
Examples of dispersing machines used to disperse the charge generating material in the binder resin solution include a paint shaker, a ball mill, a sand mill, etc. Dispersion conditions at this time should be selected appropriately so as to prevent the incorporation of impurities due to wear of the container and components of the dispersing machine.
The coating liquid for the charge generating layer may be applied by the same method as the coating liquid for the undercoat layer, and a dip coating method is particularly preferred.

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 may decrease, and the sensitivity of the photoreceptor may decrease. 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 may become the rate-limiting step in the process of erasing the charge on the surface of the laminated photosensitive layer, and the sensitivity of the photoreceptor may decrease.

[Charge transport layer 14]
The charge transport layer has the function of receiving the charges generated by the charge generating material and transporting them to the surface of the photoreceptor, and contains at least a charge transport material, a binder resin, and silica particles, and may contain additives as needed within the range that does not impair the effects of the present invention.

In the present invention, the "silica" in "silica particles" refers to silicon dioxide (SiO ₂ ). Silica particles used in the present invention include particles synthesized by a dry method and a wet method. Dry method silica includes fumed silica obtained by burning silicon tetrachloride, and arc method silica, in which silica is microparticulated in the gas phase using high energy such as plasma. Wet method silica includes precipitation method silica particles synthesized under alkaline conditions using an aqueous sodium silicate solution as a raw material, and gel method silica particles synthesized under acidic conditions. Other examples include colloidal silica particles obtained by polymerizing acidic silicic acid in an alkaline state, and sol-gel method silica particles obtained by hydrolysis of an organosilane compound.

Examples of silica particles used in the charge transport layer include dry silica particles and wet silica particles.
Examples of dry silica particles include combustion silica (fumed silica) obtained by burning a silane compound, and deflagration silica obtained by explosively burning metallic silicon powder.
Examples of wet silica particles include wet silica particles obtained by a neutralization reaction between sodium silicate and a mineral acid (precipitation silica synthesized and agglomerated under alkaline conditions, and gel silica particles synthesized and agglomerated under acidic conditions), colloidal silica particles (silica sol particles) obtained by polymerizing acidic silicic acid in an alkaline state, and sol-gel silica particles obtained by hydrolysis of an organic silane compound (e.g., alkoxysilane).
Among these, from the viewpoint of suppressing image defects due to the generation of residual potential and other deterioration of electrical properties (suppressing deterioration of fine line reproducibility), combustion method silica particles having a low silanol group content on the surface and a low porosity structure are preferred.
Furthermore, silica particles can exhibit the best electrophotographic properties when they are treated with dimethyldichlorosilane or hexamethyldisilazane.
The physical properties of the charge transport layer containing such silica particles are greatly affected by the content and dispersion state of the silica particles.

<Silica particle content>
The silica particles are dispersed in the charge transport layer, which is the surface layer of the photoreceptor, at a ratio of 7 to 25% by weight, ie, 7 to 25% by weight based on the total solid content of the charge transport layer.
If the silica particle content is less than 7% by mass, the effect of improving the printing durability of the photoreceptor may be reduced, whereas if the silica particle content is more than 25% by mass, silica aggregates may be easily formed in the surface layer, increasing the risk of stress cracking.
The preferred silica content is 10 to 15% by mass.

<Surface Rz of Charge Transport Layer and Its Variation>
The charge transport layer has a surface layer with a ten-point surface roughness Rz of 0.08 to 1.2 μm as defined in JIS-B-0601 (1994).
This is achieved by aggregating small silica particles in a moderate and uniform manner. Generally, the larger the particle size of silica particles, the higher the abrasion resistance, but this can cause chipping of the cleaning blade edge. Therefore, by aggregating relatively small silica particles in a moderate manner, larger particles are created, improving abrasion resistance. When the cleaning blade chips, the small silica particles peel off, making it less likely that partial damage will occur.

Surface roughness Rz is an index of the state of aggregation of silica particles (dispersion state of silica particles) in the charge transport layer of a photoreceptor. The ten-point average roughness Rz, as defined in JIS-B-0601 (1994), is the difference in μm between the average elevation of the top five highest peaks and the average elevation of the bottom five deepest valleys, measured in a reference length from a line parallel to the average line but not intersecting the cross-sectional curve, in a direction perpendicular to the average line. The measurement method is explained in the examples.

A ten-point mean roughness Rz of the charge transport layer of less than 0.08 μm means that the particle size of the silica particles is small or the content thereof is low, and under these conditions, the silica particles may not be expected to improve the mechanical strength of the charge transport layer. On the other hand, if the ten-point mean roughness Rz of the charge transport layer of more than 1.2 μm, the dispersion state of the silica particles in the charge transport layer becomes insufficient, and stress cracks may easily occur due to long-term friction with the cleaning blade.
The ten-point average roughness Rz of the charge transport layer is preferably 0.1 to 0.3 μm.

When the ten-point surface roughness of a 4 mm wide area at the center A and edge B of the charged area in the axial direction of the photoreceptor in the charge transport layer is RzA and RzB, respectively, the following formula is obtained:
1≦RzB/RzA≦1.3
It is preferable that the following relationship is satisfied.
Because the coating liquid for a charge transport layer containing silica particles has a high viscosity, it is difficult to form a uniform film, and the ten-point mean roughness Rz tends to be higher at the lower end of the coating than at the center in the axial direction of the photoreceptor. If the ten-point mean roughness Rz varies in the axial direction of the photoreceptor, the load from the cleaning blade is likely to be applied to points with high Rz, making stress cracks likely to occur starting from these points. Therefore, it is necessary to minimize the variation in the ten-point mean roughness Rz in the axial direction of the photoreceptor and control it within the range of the above formula.
A more preferable numerical range is 1≦RzB/RzA≦1.1.

<Creep Value C of Surface Layer of Charge Transport Layer>
The charge transport layer also has a surface layer with a creep value C of 3.8 to 5.0% as measured by applying a maximum load of 30 mN for 5 seconds using a Vickers square pyramid diamond indenter with an opposing angle of 136° in an environment of a temperature of 25°C and a relative humidity of 50%.

The creep value C is a parameter that evaluates the change in the amount of indentation by an indenter when a desired load is applied to the surface of the photosensitive member for a certain period of time, i.e., the degree of relaxation of the surface film of the photosensitive member against the indentation load.
In general, solid materials exhibit a gradual and continuous deformation phenomenon, known as creep, as the load is maintained for a certain period of time, even when the load is relatively low. Creep is particularly pronounced in organic polymeric materials. The creep value C is roughly divided into a delayed elastic deformation component and a plastic deformation component, and is used as an index of the flexibility of a material.
The creep value C (%) can be calculated using the following formula from the indentation depth h1 at the time when the maximum load of 30 mN is reached and the indentation depth h2 at the time when the maximum load of 30 mN is maintained. The measurement method will be explained in the Examples.
C (%) = 100 x (h2-h1)/h1

When the charge transport layer contains silica particles, the mechanical durability of the surface improves, but the flexibility is lost and the creep value decreases. In addition, the binder resin of the charge transport layer chemically deteriorates due to electrical fatigue, causing the surface layer to lose flexibility, the creep value decreases, and the risk of stress cracking increases.
That is, the surface of the photoreceptor is deformed by the energy given when pressed against a cleaning member, etc., and it was found that the inclusion of silica reduces the creep value and reduces the flexibility of the photosensitive layer. Furthermore, when the creep value of a photosensitive layer containing silica is low, the risk of stress cracks originating from the silica increases due to the addition of external mechanical, chemical, and electrical fatigue caused by repeated use.
In the present invention, by setting the creep value, which is an index showing the flexibility of the surface layer (film) of the charge transport layer, to 3.8 to 5.0%, the internal energy due to deformation is alleviated (dispersed), the progress of wear is suppressed, the occurrence of stress cracks is reduced, and the stress crack resistance of the photoreceptor can be improved.
If the creep value C is less than 3.8%, the flexibility of the photoreceptor surface is poor, stress crack resistance is reduced, and the photoreceptor life may be shortened. On the other hand, if the creep value C is more than 5.0%, the photoreceptor surface is too flexible, and for example, the amount of deformation caused by the cleaning member when rubbed increases, and a sufficient cleaning effect may not be obtained.
The creep value C of the surface of the charge transport layer is more preferably 4.0 to 4.5%.

<Number average primary particle diameter of silica particles>
The silica particles contained in the charge transport layer preferably have a number average primary particle size of 10 to 50 nm.
If the number average primary particle diameter of the silica particles is less than 10 nm, the anchoring effect at the surface layer of the silica particles may not be obtained, and if it is less than 7 nm in particular, the silica particles have a strong cohesion force, are difficult to disintegrate, and their dispersibility may decrease.On the other hand, if the number average primary particle diameter of the silica particles is more than 50 nm, the silica particles themselves are large, so that when they form aggregates, damage is large, and the risk of affecting stress crack resistance may increase.
The number average primary particle size of the silica particles is preferably 10 to 20 nm.
The number average primary particle diameter is a measurement value of the Feret's mean diameter obtained by observing silica particles under a scanning electron microscope at a magnification of 30,000 to 300,000 times, for example, 100,000 times, randomly selecting 100 particles as primary particles, and analyzing the image. The measurement method will be described in the Examples.

The charge 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 charge transport materials can be used alone or in combination of two or more.
Among these various charge transport materials, stilbene derivatives, butadiene derivatives, enamine derivatives and compounds in which a plurality of these compounds are bonded are preferred in terms of electrical properties, durability and chemical stability, with stilbene derivatives being more preferred.

A preferred method for forming the charge transport layer is to disperse the charge transport material and silica particles in a binder resin solution obtained by mixing a binder resin in a solvent using a conventionally known method, and then apply the charge transport layer coating liquid onto the charge generation layer. This method is described below.

The binder resin is not particularly limited, and resins having binding properties that are used in the art can be used, and those having excellent compatibility with the charge transport material are preferred.
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, resins with a polyarylate skeleton (polyarylate resins) are particularly preferred because they have good silica particle dispersibility, are resistant to electrical and chemical fatigue, can maintain a high initial creep value throughout the product's life without impairing the flexibility of the photosensitive layer surface, and can reduce the risk of adverse effects on stress crack resistance. However, as long as the resin can control the dispersion state, surface properties, and creep value of the silica particles of the present invention, it is not limited to polyarylate resins, and may also be resins with a polycarbonate skeleton (polycarbonate resins) or polyester skeletons (polyester resins).

Solvents include aromatic hydrocarbons such as benzene, toluene, xylene, and monochlorobenzene; halogenated hydrocarbons such as dichloromethane and dichloroethane; 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 of two or more. Among these solvents, non-halogenated organic solvents, for example, are preferred in consideration of the global environment.

The ratio (G/H) of the mass G of the charge transport material to the mass H of the binder resin is preferably, for example, about 10/12 to 10/30.
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.

[Second charge transport layer 16]
FIG. 2 is a schematic cross-sectional view showing the configuration of a main part of a photoreceptor 20, which is an example of the photoreceptor of the present invention.
2, the charge transport layer of the photoreceptor of the present invention may be a first charge transport layer 15 and a second charge transport layer 16 sequentially laminated on a charge generating layer, with the first charge transport layer 15 containing a charge transport material and a binder resin, and the second charge transport layer 16 containing a charge transport material, a binder resin, and silica particles 18. That is, the charge transport layer may be composed of two layers, with the second charge transport layer 16, which is the outermost layer of the photoreceptor, containing silica particles 18.
This allows for functional separation between the layers, and by containing silica only in the second charge transport layer and forming the outermost layer as a hardened film, the printing durability of the entire photosensitive layer can be improved.

The charge transport material, binder resin, and silica particles may be those described in the previous section [Charge Transport Layer 14].
The first charge transport layer 15 and the second charge transport layer 16 are formed, for example, in the same manner as in the formation of the charge generation layer 13 and the charge transport layer 14, by dissolving or dispersing the components in an appropriate solvent to prepare a coating liquid for the first charge transport layer and a coating liquid for the second charge transport layer, respectively, and then applying the coating liquids onto the charge generation layer 13 and the first charge transport layer 15, respectively, by a method such as spraying, bar coating, roll coating, blade coating, ring coating, or dip coating. Of these coating methods, the dip coating method is particularly advantageous in various respects as described above, and is therefore widely used when forming these layers.

The thickness of the first charge transport layer is not particularly limited, but is preferably 15 to 50 μm, and more preferably 25 to 40 μm.
The thickness of the second charge transport layer is not particularly limited, but is preferably 5 to 20 μm, and more preferably 5 to 10 μm.
Photoreceptors intended for long-term, repeated use are designed to be highly mechanically durable and resistant to wear. However, in actual equipment, ozone and NOx gases are generated from charging members and adhere to the surface of the photoreceptor, causing image deletion. To prevent this image deletion, the laminated photosensitive layer must be worn at a certain rate or faster. Considering long-term, repeated use, the second charge transport layer preferably has a thickness of at least 1.0 μm. Furthermore, if the thickness of the second charge transport layer exceeds 8.0 μm, problems such as an increase in residual potential and a decrease in fine dot reproducibility may occur.

(2) Toner The toner used in the image forming apparatus of the present invention is externally added with two or more kinds of external additives including fatty acid metal salt particles.
When toner is externally added with inorganic compound particles such as silica particles, that is, when the surface layer of the toner contains silica particles, although the mechanical strength is high due to excessive electrical fatigue and chemical fatigue, image defects due to stress cracks have been an issue. However, by externally adding fatty acid metal salts to the toner together with silica particles, the load on stress cracks is reduced.

[Fatty metal salt particles]
Since it is important that the fatty acid metal salt be present in the nip between the drum and the cleaning blade, it is necessary to adhere it relatively weakly and control the content of the fatty acid metal salt so that an appropriate amount of fatty acid metal salt is supplied between the photosensitive layer surface and the cleaning blade.
Examples of the aliphatic metal salt of the aliphatic metal salt particles include zinc stearate, magnesium stearate, lithium stearate, calcium stearate, and aluminum stearate. Among these, zinc stearate and magnesium stearate are preferred, with zinc stearate being particularly preferred, as they are highly effective in enhancing the lubricity of the photoreceptor surface.

<External Addition Ratio of Fatty Acid Metal Salt Particles>
The fatty acid metal salt particles are preferably added externally to the toner in a proportion of 0.05 to 0.5% by mass.
If the proportion of the fatty acid metal salt particles added externally is less than 0.05% by mass, a sufficient amount of fatty acid metal salt particles cannot be supplied to the image forming section, and the effect of stress crack resistance may not be obtained. On the other hand, if the proportion of the fatty acid metal salt particles added externally exceeds 0.5 parts by mass, the amount of fatty acid metal salt particles liberated in the developing tank increases, and the toner charge amount decreases, making it difficult for the toner to mix with the developer, resulting in a deterioration in developability and making it more likely that image defects such as roughness will occur.
The proportion of the fatty acid metal salt particles added externally is more preferably 0.05 to 0.3% by mass, and even more preferably 0.1 to 0.25% by mass.

<Average primary particle size of fatty acid metal salt particles>
The fatty acid metal salt particles preferably have an average primary particle size of 1.5 μm or less.
The fatty acid metal salt particles preferably have an average primary particle size of 0.3 μm or more.
If the average primary particle diameter of the fatty acid metal salt is less than 0.3 μm, the toner can be uniformly applied to the surface of the photoreceptor, but the fatty acid metal salt particles reach the image area of the recording medium (paper) together with the toner base particles, resulting in insufficient supply of the fatty acid metal salt particles to the surface of the photoreceptor, and the stress crack suppression effect of the toner may be reduced. On the other hand, if the average primary particle diameter of the fatty acid metal salt exceeds 1.5 μm, although stress crack resistance is maintained, the fatty acid metal salt functions as a lubricant, which is likely to be liberated independently as particles having opposite charge polarity, resulting in significant slippage of external additives, causing non-uniformity in the amount of stearic acid applied on the surface of the photoreceptor, and reducing cleaning resistance.
More preferably, the average primary particle size of the fatty acid metal salt is 0.5 to 1.0 μm.

<Adhesion strength of fatty acid metal salt particles>
The fatty acid metal salt particles preferably have an adhesion strength such that they detach from the toner at a ratio of 0.02 to 0.4 mass % when subjected to an external adhesion strength test in which 2.0 g of toner is added to 40 ml of a 0.2 mass % aqueous polyoxyethylene octylphenyl ether solution and stirred for 1 minute, the resulting aqueous solution is irradiated with ultrasound at an output of 40 μA for 3 minutes, and then the solution is left to stand for 3 hours to separate the toner and the liberated external additives. After removing the supernatant, about 50 ml of pure water is added to the precipitate and the mixture is stirred for 5 minutes, and the mixture is suction filtered using a membrane filter with a pore size of 1 μm. The toner remaining on the membrane filter is vacuum dried overnight to obtain a toner after external additive removal treatment.
The external adhesive strength test will be explained in the examples.

If the proportion of fatty acid metal salt particles detached from the toner is less than 0.02% by mass, the amount of fatty acid metal salt supplied to the image forming section will be insufficient to obtain the effect of stress crack resistance, or the adhesive strength of the fatty acid metal salt will be too strong, causing the fatty acid metal salt to migrate onto the recording medium (paper), and when the toner and fatty acid metal salt melt and fix together, low-temperature fixability may deteriorate. On the other hand, if the detachment proportion exceeds 0.4% by mass, the adhesive strength will be too weak, increasing the amount supplied to the image forming section, causing too much detachment of the fatty acid metal salt in the developer tank, causing aggregation of the fatty acid metal salt and toner aggregation, increasing the risk of causing deterioration in developability, and making it difficult to uniformly apply the fatty acid metal salt to the photoreceptor surface, which may reduce cleaning resistance.
The preferred desorbed ratio is 0.05 to 0.2 mass %.

[External additives other than fatty acid metal salt particles]
Among the two or more external additives, examples of the external additive other than the fatty acid metal salt particles include silica, alumina, and titanium oxide. Among these, silica is particularly preferred in terms of appropriately improving the fluidity of the toner base particles.

[Small particle size silica particles]
The toner of the present invention preferably contains, as an external additive, small particle size silica particles having a number average primary particle size of 15 nm or less, together with a fatty acid metal salt.
By incorporating small particle size silica, the fluidity of the toner base particles can be appropriately improved, and optimum external adhesive strength can be easily obtained.
The small particle size silica particles are silica particles having a number average primary particle size of 5 nm or less, and are derived from the same raw material as the silica particles contained in the charge transport layer of the photoreceptor.

[Large particle size silica particles]
The toner of the present invention is preferably prepared by externally adding large silica particles having a number average primary particle diameter of 50 to 200 nm together with the fatty acid metal salt as an external additive, and the fatty acid metal salt particles are preferably added after the large silica particles have been externally added.
By externally adding the large silica particles and the fatty acid metal salt particles in this order, it becomes easier to obtain the optimum adhesive strength.On the other hand, if they are added simultaneously or the fatty acid metal salt particles are added before the large silica particles, the charge polarities of the two particles are usually opposite, which makes it easier for aggregates to form and makes it difficult to obtain the optimum adhesive strength.

The large particle size silica particles have a number average primary particle size of 50 to 200 nm, and are derived from the same raw material as the silica particles contained in the charge transport layer of the photoreceptor.
Generally, the method for controlling nucleus growth involves controlling the nucleation and growth stages. When the amount of raw material in the particle generation field is constant, many particles are produced in the nucleus growth stage, so the raw material is consumed in generating "nuclei," and less raw material is used for nucleus growth, making it possible to reduce particle size. On the other hand, if the concentration during nucleation is reduced, more raw material is available in the growth stage, making the particles larger. For these reasons, particle size can be controlled by setting the amount and concentration of raw material charged.
By such a control method, large silica particles having a desired number average particle size can be obtained. More specific preparation of large silica particles will be described in the Examples.

[Negatively charged toner base particles]
The toner of the present invention may be either a positively charged toner or a negatively charged toner, but when zinc stearate is added externally as in the present invention, a negatively charged toner is preferred in that the adhesive strength can be easily controlled.
The toner base particles contained in the toner contain at least a binder resin, a colorant, a release agent, and a charge control agent, and may contain known additives as necessary within a range that does not impair the effects of the present invention.

[Binder resin]
As the binder resin contained in the toner of the present invention, a polyester resin can be suitably used, and it is preferable that the binder resin contains at least a non-crystalline polyester resin and a crystalline polyester resin.
It is generally known that crystalline polyester resins can lower the softening temperature and melt viscosity of toners, and that their combined use with amorphous polyester resins can improve the low-temperature fixability of toners. Furthermore, when the raw materials of the amorphous polyester resins and the crystalline polyester resins used in combination are different, specifically, when the main components of the dicarboxylic acid monomer and polyhydric alcohol are different, the compatibility of the two resins can be more reliably suppressed, and a greater improvement in low-temperature fixability can be expected. However, suppressing the compatibility of the two resins makes the crystalline polyester resin more likely to separate from the amorphous polyester resin and more likely to be fixed to the developing roller together with the filler component.

In the present invention, amorphous resins and crystalline resins are distinguished by their crystallinity index, with resins having a crystallinity index in the range of 0.6 to 1.5 being crystalline resins, and resins having a crystallinity index of less than 0.6 or more than 1.5 being amorphous resins. That is, resins having a crystallinity index of more than 1.5 are amorphous, while resins having a crystallinity index of less than 0.6 have low crystallinity and a large amount of amorphous portions.
The crystallinity index is a physical property that indicates the degree of crystallization of a resin, and is defined as the ratio of the softening temperature to the highest endothermic peak temperature (softening temperature/highest endothermic peak temperature). Here, the highest endothermic peak temperature refers to the temperature of the highest endothermic peak observed. For crystalline polyester resins, the highest peak temperature is the melting point (Tmp), and for amorphous polyester resins, the highest peak temperature is the glass transition temperature (Tg).
The degree of crystallization can be controlled by adjusting the types and ratios of raw material monomers, as well as production conditions (for example, reaction temperature, reaction time, cooling rate), and the like.

The amorphous polyester resin is not particularly limited, but can be obtained, for example, by a polycondensation reaction between a carboxylic acid monomer containing terephthalic acid or isophthalic acid as a main component and a polyhydric alcohol containing ethylene glycol as a main component.
The reaction conditions are the same as those for producing ordinary polyester resins, and an amorphous polyester resin can be obtained, for example, by reacting a dicarboxylic acid monomer with a polyhydric alcohol in a nitrogen gas atmosphere, optionally in the presence of an esterification catalyst, at a temperature of 190 to 240° C. The reaction ratio of the polyhydric alcohol to the carboxylic acid monomer is preferably 1.3:1 to 1:1.2 in terms of the equivalent ratio of hydroxyl groups to carboxyl groups [OH]:[COOH].

The molar content of terephthalic acid or isophthalic acid in the dicarboxylic acid monomer is preferably 70 to 100%, more preferably 80 to 100%.
The dicarboxylic acid monomer may also include aromatic dicarboxylic acids such as fumaric acid, adipic acid, sebacic acid, succinic acid, and the like, and may also include ester-forming derivatives of terephthalic acid or isophthalic acid, ester-forming derivatives of aromatic dicarboxylic acids, ester-forming derivatives of aliphatic dicarboxylic acids, and acid anhydrides or alkyl esters of these carboxylic acids.
Furthermore, the dicarboxylic acid monomer may be used in combination with a polycarboxylic acid having three or more valences, such as trimellitic acid or pyromellitic acid, or an ester-forming derivative thereof.
The above dicarboxylic acid monomers and polycarboxylic acid monomers may be used alone or in combination of two or more.

The molar content of ethylene glycol in the polyhydric alcohol is preferably 70 to 100%, more preferably 80 to 100%.
The polyhydric alcohol may include other polyhydric alcohols such as 1,3-propylene glycol and 1,4-butanediol.
The above polyhydric alcohols can be used alone or in combination of two or more.

From the viewpoint of the fixability, storage stability, and durability of the toner, the amorphous polyester resin preferably has a glass transition temperature (Tg) of 50 to 70°C. If the glass transition temperature is outside this range, the balance among the fixability, storage stability, and durability of the toner may be lost.
Furthermore, from the viewpoint of achieving both low temperature fixability and hot offset resistance of the toner, the amorphous polyester resin preferably has a softening point (Tm) of 100 to 150°C. If the softening point is outside this range, the balance between the low temperature fixability and hot offset resistance of the toner may be lost.

From the viewpoint of achieving a balance between the heat resistance, thermal storage stability, and low-temperature fixability of the toner, the amorphous polyester resin preferably has a peak top molecular weight Mp of 3,000 to 10,500. If the peak top molecular weight is outside this range, the balance between the heat resistance, thermal storage stability, and low-temperature fixability of the toner may be lost.
Here, the peak top molecular weight Mp means the molecular weight showing the maximum peak height of the tetrahydrofuran (THF) soluble matter in gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the mobile phase and polystyrene as the standard substance.

In addition, from the viewpoint of the toner's charging characteristics, the amorphous polyester resin preferably has an acid value of 0 to 60 mgKOH/g, and from the viewpoint of the toner's hot offset resistance, a hydroxyl value of 0 to 50 mgKOH/g. If the acid value exceeds 60 mgKOH/g, the toner's charging performance may decrease, and if the hydroxyl value exceeds 50 mgKOH/g, the toner's hot offset resistance may become insufficient.

The amorphous polyester resin preferably has an SP value (solubility parameter) of 10.5 to 12.5. If the SP value is less than 10.5, the compatibility with the crystalline resin may be excessive, which may impair the blocking resistance and hot offset resistance of the toner. On the other hand, if the SP value is more than 12.5, the compatibility with the crystalline resin may be excessively reduced, which may result in insufficient low-temperature fixing properties.
The SP value will be described in detail in the Examples.

The crystalline polyester resin is not particularly limited, but is preferably composed of a linear saturated aliphatic polyester unit obtained by a polycondensation reaction between a carboxylic acid monomer containing, as a main component, an aliphatic dicarboxylic acid having 9 to 22 carbon atoms and a polyhydric alcohol containing, as a main component, an aliphatic diol having 2 to 10 carbon atoms.
The reaction conditions are the same as those for producing ordinary polyester resins, and for example, a crystalline polyester resin can be obtained by reacting a dicarboxylic acid monomer with a polyhydric alcohol in a nitrogen gas atmosphere, optionally in the presence of an esterification catalyst, at a temperature of 190 to 240° C. From the viewpoint of toner storage stability, the reaction ratio of the polyhydric alcohol to the carboxylic acid monomer is preferably an equivalent ratio of hydroxyl groups to carboxyl groups [OH]:[COOH] of 0.83:1 to 1.3:1.

The molar content of dicarboxylic acid in the carboxylic acid monomer is preferably 90 to 100%. If the molar content of dicarboxylic acid is low, the rate and speed of crystallization may decrease, resulting in insufficient toner aggregation resistance.
Examples of the aliphatic dicarboxylic acid having 9 to 22 carbon atoms include azelaic acid, zebaic acid, 1,10-decanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, etc. The carboxylic acid monomer and polycarboxylic acid monomer may contain an ester-forming derivative of these aliphatic dicarboxylic acids.
Furthermore, the carboxylic acid monomer may be used in combination with a polycarboxylic acid having three or more valences, such as trimellitic acid or pyromellitic acid, or an ester-forming derivative thereof.
The above carboxylic acid monomers may be used alone or in combination of two or more.

The molar content of the aliphatic diol having 2 to 10 carbon atoms in the polyhydric alcohol is preferably 80 to 100%.
Examples of the aliphatic diol having 2 to 10 carbon atoms include ethylene glycol, 1,4-butanediol, and 1,6-hexanediol.
Furthermore, examples of polyhydric alcohols that can be used in combination with the above aliphatic diols include trihydric or higher alcohols such as glycerin and trimethylolpropane.
The above polyhydric alcohols can be used alone or in combination of two or more.

From the viewpoint of the fixability, storage stability, and durability of the toner, the crystalline polyester resin preferably has a melting point (Tmp) of 40 to 90°C. If the melting point is less than 40°C, the durability of the toner may be insufficient. On the other hand, if the melting point is more than 90°C, the fixability of the toner may be insufficient. A more preferred melting point is 60 to 90°C.
Furthermore, from the viewpoint of low-temperature fixability and blocking resistance of the toner, the crystalline polyester resin preferably has a softening point (Tm) of 65 to 110°C. If the softening point is outside this range, the low-temperature fixability and blocking resistance of the toner may become insufficient.
Furthermore, from the viewpoint of crystallization rate and blocking resistance, the crystalline polyester resin preferably has a softening point (Tm) to melting point (Tmp) ratio (Tm/Tmp) of 1.0 to 1.4. On the other hand, if the softening point to melting point ratio is outside this range, the crystallization rate and blocking resistance may become insufficient.

From the standpoint of toner storage stability and low-temperature fixability, the crystalline polyester resin preferably has a peak top molecular weight Mp of 10,000 to 90,000. If the peak top molecular weight is outside this range, the toner storage stability and low-temperature fixability may be insufficient.

In addition, from the viewpoint of the toner's charging characteristics, the crystalline polyester resin preferably has an acid value of 0 to 60 mgKOH/g, and from the viewpoint of the toner's hot offset resistance, a hydroxyl value of 0 to 40 mgKOH/g. If the acid value exceeds 60 mgKOH/g, the toner's charging performance may decrease, and if the hydroxyl value exceeds 40 mgKOH/g, the toner's hot offset resistance may become insufficient.

It is preferable that the crystalline polyester resin has an SP value of 9.3 to 10.0. If the SP value is less than 9.3, compatibility with the amorphous polyester resin will be too low, and the toner's durability may be insufficient. On the other hand, if the SP value exceeds 10.0, the Tg of the binder resin will decrease, and the toner's blocking resistance may decrease.

The content of the binder resin in the toner of the present invention is not particularly limited, but is preferably 60 to 90% by weight, and particularly preferably 70 to 85% by weight.
The contents of the amorphous polyester resin and the crystalline polyester resin in the toner of the present invention are not particularly limited, but are preferably 50 to 80% by weight and 10 to 30% by weight, respectively, in the toner.
The weight ratio of the crystalline polyester resin to the amorphous polyester resin in the binder resin of the toner of the present invention is not particularly limited and can be adjusted as needed, but from the viewpoint of achieving both low-temperature fixability and hot offset resistance of the toner, it is preferably 3:97 to 20:80. If the weight ratio of the crystalline polyester resin is less than 3%, the low-temperature fixability of the toner is improved but the low-temperature fixability may be impaired. On the other hand, if the weight ratio of the crystalline polyester resin exceeds 20%, the low-temperature fixability of the toner is improved but the hot offset resistance may be impaired.

[Colorant]
As the colorant contained in the toner of the present invention, various types and colors of organic and inorganic pigments and dyes commonly used in the art can be used, including, for example, black, white, yellow, orange, red, purple, blue and green colorants.
Examples of black colorants include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, non-magnetic ferrite, magnetic ferrite, and magnetite. Examples of white colorants include zinc oxide, titanium oxide, antimony white, and zinc sulfide.

Examples of yellow colorants include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, tartrazine lake, C.I. pigment yellow 12, C.I. pigment yellow 13, C.I. pigment yellow 14, C.I. pigment yellow 15, C.I. pigment yellow 17, C.I. pigment yellow 74, C.I. pigment yellow 93, C.I. pigment yellow 94, C.I. pigment yellow 138, C.I. pigment yellow 181, C.I. pigment yellow 185, and the like.
Examples of orange colorants include red lead yellow, molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan orange, induthrene brilliant orange RK, benzidine orange G, induthrene brilliant orange GK, C.I. pigment orange 31, and C.I. pigment orange 43.

Examples of red colorants include red iron oxide, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, lithol red, pyrazolone red, watching red, calcium salt, lake red C, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B, C.I. pigment red 2, C.I. pigment red 3, C.I. pigment red 5, C.I. pigment red 6, C.I. pigment red 7, C.I. pigment red 15, C.I. pigment red 16, C.I. pigment red 48:1, C.I. pigment red 53:1, C.I. pigment red 57:1, C.I. Examples of pigments that can be used include C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 149, C.I. Pigment Red 166, C.I. Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 222, C.I. Pigment Red 269, and the like.
Examples of purple colorants include manganese violet, fast violet B, and methyl violet lake.

Examples of blue colorants include Prussian blue, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, fast sky blue, indanthrene blue BC, C.I. pigment blue 15, C.I. pigment blue 15:2, C.I. pigment blue 15:3, C.I. pigment blue 15:4, C.I. pigment blue 16, C.I. pigment blue 60, and the like.
Examples of green colorants include chrome green, chromium oxide, pigment green B, micalite green lake, final yellow green G, C.I. pigment green 7, and C.I. pigment green 36.

In the toner of the present invention, the above colorants can be used alone or in combination of two kinds, and the combination may be of different colors or the same color.
Two or more colorants may be used in the form of composite particles. The composite particles can be produced, for example, by adding an appropriate amount of water, a lower alcohol, etc. to two or more colorants, granulating the mixture using a general granulator such as a high-speed mill, and drying the mixture. Furthermore, in order to uniformly disperse the colorant in the binder resin, the colorant may be used in the form of a masterbatch. The composite particles and masterbatch are mixed into the toner composition during dry mixing.

The content of the colorant in the toner of the present invention is not particularly limited, but is preferably 2.5 to 7.5% by mass, and more preferably 3.0 to 6.5% by mass.
If the content of the colorant is within the above range, it is possible to form an image having a high image density and excellent image quality without impairing various physical properties of the toner.

[Release agent]
As the release agent contained in the toner of the present invention, any release agent commonly used in the art can be used.
Examples include petroleum-based waxes such as paraffin wax and microcrystalline wax and derivatives thereof; hydrocarbon-based synthetic waxes such as Fischer-Tropsch wax, polyolefin wax (polyethylene wax, polypropylene wax, etc.), low-molecular-weight polypropylene wax and polyolefin-based polymer wax (low-molecular-weight polyethylene wax, etc.) and derivatives thereof; plant-based waxes such as carnauba wax, rice wax, candelilla wax and derivatives thereof, and Japan wax; animal-based waxes such as beeswax and spermaceti; oil-based synthetic waxes such as fatty acid amides and phenol fatty acid esters; long-chain carboxylic acids and derivatives thereof; long-chain alcohols and derivatives thereof; silicone-based polymers; and higher fatty acids. Of these, hydrocarbon-based waxes are preferred.
The derivatives include oxides, block copolymers of vinyl monomers and wax, and graft modified products of vinyl monomers and wax.
In the present invention, the above-mentioned release agents can be used alone or in combination of two or more.

The release agent preferably has a melting point of 70°C or less in order to achieve both low-temperature fixability and hot offset resistance of the toner in a belt fixing device, particularly from the perspective of low-temperature fixability. The lower limit of the melting point is approximately 60°C.

The content of the release agent in the toner of the present invention is not particularly limited, but is preferably 2.0 to 7.0% by mass, and more preferably 3.0 to 5.0% by mass.
If the content of the release agent is within the above range, it is possible to form an image having a high image density and excellent image quality without impairing various physical properties of the toner.

[Charge control agent]
As the charge control agent contained in the toner of the present invention, a charge control agent for negative charge control commonly used in the art can be used.
Examples of charge control agents for negative charge control include oil-soluble dyes such as oil black and Spiron black, metal-containing azo compounds, azo complex dyes, metal naphthenate salts, metal complexes and metal salts of salicylic acid and its derivatives (metals include chromium, zinc, zirconium, etc.), boron compounds, fatty acid soaps, long-chain alkyl carboxylate salts, and resin acid soaps.
In the toner of the present invention, the above-mentioned charge control agents can be used alone or in combination of two or more.

The content of the charge control agent in the toner of the present invention is not particularly limited, but is preferably 0.5 to 2.0% by mass, and more preferably 0.7 to 1.5% by mass.
If the content of the charge control agent is within the above range, it is possible to form an image having a high image density and excellent image quality without impairing various physical properties of the toner.

[Physical Properties of Toner]
[Average primary particle diameter of toner]
The toner of the present invention preferably has an average primary particle size of 4 to 10 μm.
If the average primary particle diameter is less than 4 μm, the particle diameter of the toner base particles becomes too small, which may result in high charge and poor fluidity. This high charge and poor fluidity may prevent the toner from being stably supplied to the photoreceptor, which may result in background fogging and reduced image density. On the other hand, if the average primary particle diameter exceeds 10 μm, the particle diameter of the toner base particles becomes large, resulting in a thicker image layer with a significantly grainier appearance, making it difficult to obtain a high-resolution image, which is undesirable. Furthermore, the large particle diameter of the toner base particles reduces the specific surface area and the charge amount of the toner. If the charge amount of the toner is low, the toner may not be stably supplied to the photoreceptor, which may result in contamination inside the machine due to toner scattering. A preferred average primary particle diameter is 5 to 8 μm.

[Method of manufacturing toner base particles]
The toner base particles used in the present invention can be produced by a known method using a known device commonly used in the technical field, for example, by a mixing step of mixing a filler with a coarsely pulverized molten kneaded product containing at least a binder resin, a colorant, and a release agent, a fine pulverization step of finely pulverizing the mixture obtained in the mixing step, a classification step of classifying the finely pulverized product obtained in the fine pulverization step, and a spheronization treatment step of spheronizing the classified product obtained in the classification step with hot air.
Dry methods are preferred in that they require fewer steps and require less equipment cost than wet methods, and among these, pulverization is particularly preferred.
The conditions for each of the following steps may be appropriately set depending on the target material and the desired physical properties.

[Method of Adding External Additive to Toner]
An externally-added toner can be obtained by adding and mixing an external additive with the toner base particles, and performing an external addition step of externally adding the external additive to the toner base particles.
The adding and mixing operations can be carried out using known devices commonly used in the technical field, and the conditions in the process, such as the order of adding multiple external additives and the processing time (mixing time), may be appropriately set depending on the target material and the desired physical properties.

[Developer (two-component developer)]
The developer of the present invention contains the toner of the present invention and a carrier.
[Career]
The toner of the present invention can be used in the form of either a one-component developer or a two-component developer, and when used as a two-component developer, a carrier is further blended in addition to the external additive.
As the carrier, carriers commonly used in the art can be used, such as simple or composite ferrites made of iron, copper, zinc, nickel, cobalt, manganese, chromium, etc., and carrier core particles surface-coated with known coating materials.
The average particle size of the carrier is preferably from 10 to 100 μm, more preferably from 20 to 50 μm.
The amount of the carrier to be mixed is not particularly limited, but is preferably 4 to 15 parts by weight, and more preferably 5 to 10 parts by weight, per 100 parts by weight of the toner base particles.

(3) Image Forming Device The image forming device of the present invention comprises at least the photosensitive member of the present invention described in (1) above, 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 (visible image) with toner, and a transfer means for transferring the toner image onto a recording medium, and may also comprise means selected from a fixing means for fixing the transferred toner image onto the recording medium to form an image, a cleaning means for removing and recovering toner remaining on the photosensitive member, and a discharging means for discharging surface charges remaining on the photosensitive member.
The image forming apparatus of the present invention and its operation will be described below with reference to the drawings, but the present invention is not limited to the following description.

FIG. 3 is a schematic side view showing the configuration of the main part of the image forming apparatus 100 of the present invention.
The image forming apparatus (laser printer) 100 in Figure 3 is configured to include the photoreceptor 1 of the present invention (corresponding to numbers 10 and 20 in Figure 2), exposure means (semiconductor laser) 31, charging means (charger) 32, developing means (developer) 33, transfer means (transfer charger) 34, a conveyor belt (not shown), fixing means (fixer) 35, and cleaning means (cleaner) 36. Reference numeral 51 denotes a recording medium (recording paper or transfer paper).

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 a drive means (not shown). The drive means, which may include, for example, an electric motor and a reduction gear, transmits its driving force to the conductive support that forms the core of photoreceptor 1, thereby driving photoreceptor 1 to rotate at a predetermined peripheral speed. Charging means (charger) 32, exposure means 31, developing means (developer) 33, transfer means (transfer charger) 34, and cleaning means (cleaner) 36 are arranged in this order along the outer surface of photoreceptor 1, from upstream to downstream in the direction of rotation of photoreceptor 1, as indicated by arrow 41.

The charger 32 is a charging device that uniformly charges the outer surface of the photoreceptor 1 to a predetermined potential. Examples of charging devices include non-contact charging methods such as corona charging using a charger, and contact charging methods using a charging roller or charging brush.

The exposure unit 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 of light output from the light source, thereby exposing the charged outer surface of the photoreceptor 1 according to the image information. The light is repeatedly scanned in the main scanning direction, which is the direction of the rotation axis 44 of the photoreceptor 1, and these light beams are focused to sequentially form electrostatic latent images on the surface of the photoreceptor 1. In other words, the charge amount of the photoreceptor 1, which is uniformly charged by the charger 32, differs depending on whether or not it is irradiated with the laser beam, forming an electrostatic latent image.

The developing unit 33 is a developing means that uses developer (toner) to develop the electrostatic latent image formed on the surface of the photoreceptor 1 by exposure. It is provided facing the photoreceptor 1 and includes a developing roller 33a that supplies toner to the outer peripheral surface of the photoreceptor 1, and a casing 33b that rotatably supports the developing roller 33a about an axis of rotation parallel to the axis of rotation 44 of the photoreceptor 1 and contains developer containing toner in its internal space.

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

The cleaner 36 is a cleaning device that removes and collects toner remaining on the outer surface of the photoreceptor 1 after the transfer operation by the transfer charger 34. It is equipped with a cleaning blade 36a that removes toner remaining on the outer surface of the photoreceptor 1, and a collection casing 36b that contains the toner removed by the cleaning blade 36a. The cleaner 36 is also provided with a static elimination lamp (not shown).

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 for accommodating the above-mentioned means of the image forming apparatus.

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 configured such that multiple electrophotographic photosensitive elements, on which toner images are respectively formed, are arranged side by side in a predetermined direction (for example, the horizontal direction H or approximately the horizontal direction H). The image forming apparatus 100 may also be another color image forming apparatus, a copier, a multifunction machine, or a facsimile machine.

(4) Image Forming Method The image forming method of the present invention comprises at least an electrophotographic photosensitive member, a charging unit for charging the electrophotographic photosensitive member, an exposure unit for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, a developing unit for developing the electrostatic latent image to form a toner image with toner, and a transfer unit for transferring the toner image onto a recording medium,
the electrophotographic photoreceptor comprises at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a conductive support,
the charge transport layer contains at least a charge transport material, a binder resin, and silica particles;
the silica particles are contained in the charge transport layer in an amount of 7 to 25% by mass,
the charge transport layer has a surface layer with a ten-point surface roughness Rz of 0.08 to 1.2 μm as defined in JIS-B-0601 (1994),
the charge transport layer has a surface layer having a creep value C of 3.8 to 5.0% as measured by applying a maximum load of 30 mN for 5 seconds using a Vickers square pyramid diamond indenter with an opposing angle of 136° under an environment of a temperature of 25°C and a relative humidity of 50%,
an image forming method using an image forming apparatus in which the toner is externally added with two or more kinds of external additives including fatty acid metal salt particles,
The method is characterized by including at least a charging step of charging the electrophotographic photosensitive member, an exposure step of exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, a development step of developing the electrostatic latent image to form a toner image with toner, and a transfer step of transferring the toner image onto a recording medium.
The image forming apparatus is as described in (3) Image Forming Apparatus, the electrophotographic photosensitive member provided therein is as described in (1) Electrophotographic Photosensitive Member, and the toner used therein is as described in (2) Toner. Below, the image forming operation will be explained.

The image forming method of the present invention is not particularly limited as long as it has the above-mentioned constituent elements. For example, the image forming operation by the image forming apparatus 100 in FIG. 3 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 the exposure means 32 onto the surface of the photoreceptor 1. This exposure removes surface charge from the areas of the 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.

In synchronization with the exposure of the photosensitive member 1, a transfer paper 51 is supplied between the photosensitive member 1 and the transfer charger 34. The transfer charger 34 imparts a charge of the opposite polarity to that of the toner to the supplied transfer paper 51, and the toner image formed on the surface of the photosensitive member 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 pressed 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 then ejected to the outside of the image forming apparatus 100 by the transport means.

Meanwhile, any toner remaining on the surface of photoreceptor 1 after the toner image has been transferred by transfer charger 34 is removed from the surface of photoreceptor 1 and collected 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. Photoreceptor 1 is then rotated again, and the series of operations starting with charging are repeated again, forming images continuously.

The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.
The physical properties of the photoreceptors and toners obtained in the examples and comparative examples, as well as the physical properties of their raw materials, were measured by the following methods.

(1) Number Average Primary Particle Diameter of Silica Particles Using a scanning electron microscope (SEM, manufactured by Hitachi High-Technologies Corporation, Model: S-4800), silica particles are photographed at a magnification of 30,000 to 300,000 times, for example, 100,000 times, and 100 silica particles are arbitrarily selected from the obtained image and observed as primary particles. The average particle diameter (major axis) in the Feret's direction is calculated by image analysis, and this is defined as the number average primary particle diameter.

(2) Ten-point surface roughness Rz of the surface layer of the photoreceptor
Using a surface roughness measuring device (Tokyo Seimitsu Co., Ltd., model: Surfcom 1400D), the ten-point surface roughness RzA (μm) of a 4 mm wide area at the center of the charged area in the axial direction of the surface layer (charge transport layer) of the photosensitive member is measured using a method with a reference length of 0.8 mm, a cutoff wavelength of 0.8 mm, a measurement speed of 0.1 mm/sec, and a Gaussian cutoff type.
This Rz corresponds to the ten-point surface roughness Rz defined in JIS-B-0601 (1994).
Also, the ten-point surface roughness RzB (μm) of a 4 mm wide area at the end of the charged area in the axial direction of the surface layer (charge transport layer) of the photosensitive member is measured, and RzB/RzA is calculated.

(3) Creep Value of Photoreceptor Using a microhardness tester (manufactured by Fischer Instruments, model: Fischerscope (registered trademark) H100V), a Vickers square pyramid diamond indenter with an opposing angle of 136° is used to apply a maximum indentation load of 30 mN for 5 seconds in an environment of 25°C and 50% relative humidity, and the creep value C (%) is measured.
The creep value C (%) is calculated from the indentation depth h1 when the maximum load of 30 mN is reached and the indentation depth h2 when the maximum load of 30 mN is maintained, using the following formula.
C (%) = 100 x (h2-h1)/h1

(4) Volume Average Primary Particle Diameter of Toner Particles 20 mg of a sample and 1 ml of sodium alkyl ether sulfate are added to 50 ml of an electrolyte (manufactured by Beckman Coulter, Inc., product name: ISOTON-II), and the mixture is dispersed using an ultrasonic disperser (manufactured by AS ONE Corporation, tabletop dual-frequency ultrasonic cleaner, model: VS-D100) at a frequency of 20 kHz for 3 minutes to obtain a measurement sample. The obtained measurement sample is measured using a particle size distribution measuring device (manufactured by Beckman Coulter, Inc., model: Multisizer 3) under conditions of an aperture diameter of 100 μm and a measurement particle count of 50,000, and the volume average primary particle diameter (μm) is determined from the volume particle size distribution of the sample particles.

(5) Adhesion Strength of External Additives to Toner The toner is subjected to an external adhesion strength test according to the following procedure to obtain a toner after the external additive removal treatment.
(1) 2.0 g of toner is added to 40 ml of a 0.2% by weight aqueous solution of polyoxyethylene octylphenyl ether (Rohm & Haas (now Dow Chemical Company), product name: Triton (registered trademark)) and stirred for 1 minute.
(2) Using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., model: US-300T), the resulting aqueous solution is irradiated with ultrasonic waves at an output of 40 μA for 3 minutes.
(3) After that, the mixture is left for 3 hours, and the toner and the free external additives are separated.
(4) After removing the supernatant, add approximately 50 ml of purified water to the precipitate and stir for 5 minutes.
(5) The solution is filtered by suction using a membrane filter (manufactured by Advantec) with a pore size of 1 μm.
(6) The toner remaining on the membrane filter is vacuum dried overnight to obtain the toner after the external additive removal treatment.

The obtained toner after the external additive removal treatment and the toner before the external additive removal treatment were analyzed for the intensities of elements (Zn, Mg) in the external additives of 1 g of toner using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, model: ZSX Primus II), and the mass ratio in the toner of the external additives made of fatty acid metal salts that had been detached from the toner in the external adhesion strength test was determined from the difference between these intensities.
Additionally, the amount of ultrafine powder in the externally added toner, the amount of ultrafine powder in the toner after the external additive adhesion strength test, the non-adhesion rate and strong adhesion rate of the aliphatic metal salt fine particles, and the non-adhesion rate and strong adhesion rate of silica (total of large particle size silica and small particle size silica) are also calculated.

(Example 1-1: Preparation of Photoreceptor 1)
Three parts by mass of titanium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., product name: TYPAQUE (registered trademark) TTO-D-1) and two parts by mass of copolymer polyamide (nylon) (manufactured by Toray Industries, Inc., product name: AMILAN (registered trademark) CM8000) were added to 25 parts by mass of methyl alcohol, and the mixture was dispersed for eight hours using a paint shaker to prepare three liters of a coating solution for an 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, serving as the conductive support 11, was immersed therein and then removed. The obtained coating film was allowed to dry naturally, thereby forming an undercoat layer 12 with a thickness of 1 μm on the conductive support.

Oxotitanyl phthalocyanine, represented by the following structural formula, was prepared in advance for use as a charge-generating material.

29.2 g of diiminoisoindoline and 200 ml of sulfolane were mixed, and 17.0 g of titanium tetraisopropoxide was added, followed by reaction for 2 hours at 140° C. under a nitrogen atmosphere. 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 washed successively with water and methanol, and dried to obtain 25.5 g of blue-purple crystals.
Chemical analysis of the resulting compound confirmed that it was the oxotitanyl phthalocyanine represented by the above structural formula (yield: 88.5%).

One part by weight of the obtained titanyl phthalocyanine and one part by weight of butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BM-2) were added to 98 parts by weight of methyl ethyl ketone, and the mixture was dispersed for two hours using a paint shaker to prepare 3 liters of a coating liquid for the charge generating layer.
The obtained coating liquid for the charge generating layer was applied onto the undercoat layer 12 by the same dipping method as in the case of forming the undercoat layer, and the obtained coating film was allowed to dry naturally to form a charge generating layer with a film thickness of 0.3 μm.

Next, 6.9 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were added to 24.6 g of tetrahydrofuran, and the mixture was stirred for 5 hours using a stirrer (manufactured by Shinto Chemical Co., Ltd., model: BL300) and an inclined paddle-type stirring blade (with a blade diameter of 40 mm, manufactured by Shinto Chemical Co., Ltd.).
18.0 g of tetrahydrofuran was added to the obtained silica particle (silica filler) suspension, and the mixture was degassed for 4 minutes using a rotation-revolution mixer (Thinky Corporation, Awatori Rentaro atmospheric pressure type, model: ARE-310).

A stilbene compound represented by the following structural formula to be used as a charge transport material was prepared in advance according to the method described in Japanese Patent No. 3272257.

To the obtained silica filler suspension, 16 g of the obtained stilbene compound, 30.4 g of polyarylate (manufactured by Mitsubishi Chemical Corporation, product name: E2-400) as a binder resin, and 158.1 g of tetrahydrofuran were added and mixed, and the mixture was stirred in a ball mill for 30 hours.
The resulting mixture was subjected to 4-pass dispersion treatment using a particle dispersion device (Microfluidics, model: Microfluidizer M-110P) to prepare 254.1 g of a charge transport coating liquid, which was then allowed to stand at 20° C. for 1 week.

The resulting charge transport layer coating liquid was applied to the charge generation layer 13 using the same immersion method as used to form the undercoat layer, and the resulting coating was dried at 115°C for 1.5 hours to form a charge transport layer with a thickness of 35 μm, producing the photoreceptor 1 shown in Figure 1.

(Example 1-2: Preparation of photoreceptor 2)
Photoreceptor 2 was produced in the same manner as in Example 1-1, except that in the preparation of the coating liquid for the charge transport layer, the amount of silica particles was changed from 6.9 g to 5.04 g, and the amount of tetrahydrofuran was changed from 24.6 g to 17.9 g, and a stirring treatment was performed; the amount of tetrahydrofuran in the obtained silica filler suspension was changed from 18.0 g to 13.1 g, and a degassing treatment was performed; and the amount of the stilbene compound as the charge transport material was changed from 16 g to 20 g, the amount of polyarylate was changed from 30.4 g to 38 g, and the amount of tetrahydrofuran was changed from 158.1 g to 206.2 g, and a stirring treatment was performed.

(Example 1-3: Preparation of photoreceptor 3)
Photoreceptor 3 was produced in the same manner as in Example 1-1, except that in the preparation of the coating liquid for the charge transport layer, the amount of silica particles was changed from 6.9 g to 12.8 g, and the amount of tetrahydrofuran was changed from 24.6 g to 45.5 g, and a stirring treatment was performed; the amount of tetrahydrofuran in the obtained silica filler suspension was changed from 18.0 g to 33.3 g, and a degassing treatment was performed; and the amount of the stilbene compound as the charge transport material was changed from 16 g to 14 g, the amount of polyarylate was changed from 30.4 g to 26.6 g, and the amount of tetrahydrofuran was changed from 158.1 g to 122.3 g, and a stirring treatment was performed.

(Example 1-4: Preparation of photoreceptor 4)
Photoreceptor 4 was produced in the same manner as in Example 1-1, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were changed to silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment).

(Example 1-5: Preparation of Photoreceptor 5)
Photoreceptor 5 was produced in the same manner as in Example 1-3, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were changed to silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment).

(Example 1-6: Preparation of photoreceptor 6)
In preparing the charge transport layer coating liquid, 6.9 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were replaced with 4.37 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment), and 24.6 g of tetrahydrofuran were changed to 15.5 g, and a stirring treatment was performed. The obtained silica filler suspension was changed from 18.0 g to 11.3 g of tetrahydrofuran and a degassing treatment was performed. The charge transport material was changed from 16 g to 20 g of stilbene compound, from 30.4 g to 38 g of polyarylate, and from 158.1 g to 207.9 g of tetrahydrofuran, and a stirring treatment was performed. Photoreceptor 6 was produced in the same manner as in Example 1-1.

(Example 1-7: Preparation of photoreceptor 7)
Photoreceptor 7 was produced in the same manner as in Example 1-1, except that in the preparation of the coating liquid for the charge transport layer, 6.9 g of silica particles were changed to 5.96 g, and 24.6 g of tetrahydrofuran were changed to 21.1 g, and a stirring treatment was performed; 24.6 g of tetrahydrofuran was changed to 15.5 g of the obtained silica filler suspension, and a degassing treatment was performed; and 30.4 g of polyarylate (manufactured by Mitsubishi Chemical Corporation, product name: E2-400) was changed to 23.9 g of polycarbonate resin (Teijin Chemical Co., Ltd., product name: Panlite (registered trademark) TS2050), and 158.1 g of tetrahydrofuran was changed to 135.8 g, and a stirring treatment was performed.

(Example 1-8: Preparation of photoreceptor 8)
Photoreceptor 8 was produced in the same manner as in Example 1-1, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were changed to silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) RX50, number average primary particle diameter 40 nm, hexamethyldisilazane surface treatment).

(Example 1-9: Preparation of Photoreceptor 9)
Photoreceptor 9 was produced in the same manner as in Example 1-1, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were changed to silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) RX40S, number average primary particle diameter 80 to 100 nm, hexamethyldisilazane surface treatment).

(Example 1-10: Preparation of photoreceptor 10)
Photoreceptor 10 was produced in the same manner as in Example 1-1, except that in the preparation of the coating liquid for the charge transport layer, 158.1 g of tetrahydrofuran was changed to 200.5 g.

(Example 1-11: Preparation of photoreceptor 11)
Photoreceptor 11 was produced in the same manner as in Example 1-1, except that in the preparation of the coating liquid for the charge transport layer, 158.1 g of tetrahydrofuran was changed to 217.9 g.

(Comparative Example 1-1: Preparation of Comparative Photoreceptor 1)
Comparative photoreceptor 1 was produced in the same manner as in Example 1-1, except that in the preparation of the charge transport layer coating liquid, 6.9 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were replaced with 6.63 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment), and 24.6 g of tetrahydrofuran were changed to 23.5 g, and a stirring treatment was performed; the amount of tetrahydrofuran of the obtained silica filler suspension was changed from 18.0 g to 17.2 g, and a degassing treatment was performed; and the charge transport material was changed from 16 g to 42 g of a stilbene compound, from 30.4 g to 84 g of polyarylate (manufactured by Mitsubishi Chemical Corporation, product name: E2-400), and from 158.1 g to 458.2 g of tetrahydrofuran, and a stirring treatment was performed.

(Comparative Example 1-2: Preparation of Comparative Photoreceptor 2)
In preparing the coating liquid for the charge transport layer, 6.9 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) was replaced with 11.10 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972, number average primary particle diameter 16 nm, dimethyldichlorosilane surface treatment), and 24.6 g of tetrahydrofuran was replaced with 39.3 g, followed by stirring. Comparative photoreceptor 2 was produced in the same manner as in Example 1-1, except that the amount of tetrahydrofuran in the suspension was changed from 18.0 g to 28.8 g, and a degassing treatment was performed; the amount of a stilbene compound as a charge transport material was changed from 16 g to 10 g, the amount of polyarylate (manufactured by Mitsubishi Chemical Corporation, product name: E2-400) was changed from 30.4 g to 20 g of polycarbonate resin (manufactured by Teijin Chemical Co., Ltd., product name: Panlite (registered trademark) TS2050) and the amount of tetrahydrofuran was changed from 158.1 g to 86.4 g, and a stirring treatment was performed.

(Comparative Example 1-3: Preparation of Comparative Photoreceptor 3)
Comparative photoreceptor 3 was produced in the same manner as in Example 1-1, except that in the preparation of the charge transport layer coating liquid, 6.9 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were replaced with 4.64 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment), and 24.6 g of tetrahydrofuran were changed to 16.5 g, and a stirring treatment was performed; the amount of tetrahydrofuran of the obtained silica filler suspension was changed from 18.0 g to 12.1 g, and a degassing treatment was performed; and the charge transport material was changed from 16 g to 20 g of a stilbene compound, from 30.4 g to 41.7 g of polyarylate, and from 158.1 g to 220.9 g of tetrahydrofuran, and a stirring treatment was performed.

(Comparative Examples 1-4: Preparation of Comparative Photoreceptor 4)
Comparative photoreceptor 4 was produced in the same manner as in Example 1-1, except that in the preparation of the charge transport layer coating liquid, 6.9 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were replaced with 4.03 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment), and 24.6 g of tetrahydrofuran were changed to 14.3 g, and the stirring treatment was carried out for 6 hours; the obtained silica filler suspension was changed from 18.0 g to 10.5 g of tetrahydrofuran, and a degassing treatment was carried out; and 16 g of a stilbene compound as the charge transport material was changed to 30.4 g of polyarylate (manufactured by Mitsubishi Chemical Corporation, product name: E2-400), and 158.1 g of tetrahydrofuran was changed to 165.0 g, and the stirring treatment was carried out.

(Comparative Examples 1-5: Preparation of Comparative Photoreceptor 5)
Comparative photoreceptor 5 was produced in the same manner as in Examples 1-3, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974, number average primary particle diameter 12 nm, dimethyldichlorosilane surface treatment) were changed to silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) NX130, number average primary particle diameter 16 nm, hexamethyldisilazane surface treatment) and the degassing treatment time was changed from 4 minutes to 2 minutes.

(Comparative Example 1-6: Preparation of Comparative Photoreceptor 6)
Comparative photoreceptor 6 was produced in the same manner as in Example 1-3, except that in the preparation of the coating solution for the charge transport layer, 16 g of a stilbene compound was used as the charge transport material, and polyarylate (manufactured by Mitsubishi Chemical Corporation, product name: E2-400) was replaced with polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2040), and stirring was performed.

(Production Example 1: Preparation of amorphous polyester resin A)
A 5 L reaction vessel was charged with 440 g (2.7 mol) of terephthalic acid, 235 g (1.4 mol) of isophthalic acid, 7 g (0.05 mol) of adipic acid, 554 g (8.9 mol) of ethylene glycol, and 0.5 g of tetrabutoxy titanate as a polymerization catalyst, and the mixture was reacted at 210°C under a nitrogen stream for 5 hours while distilling off the produced water and ethylene glycol, and then the mixture was reacted under a reduced pressure of 5 to 20 mmHg for 1 hour.
Next, 103 g (0.54 mol) of trimellitic anhydride was added, and the mixture was allowed to react under normal pressure for 1 hour. After that, the mixture was allowed to react under a reduced pressure of 20 to 40 mmHg, and the resin was taken out at a predetermined softening point. 219 g (3.5 mol) of ethylene glycol was recovered. The obtained resin was cooled to room temperature and then pulverized into particles. This was designated amorphous polyester resin A.
The amorphous polyester resin A had a glass transition temperature Tg of 56° C., a softening point Tm of 135° C., an SP value of 11.0, an acid value of 37 mgKOH/g, and a hydroxyl value of 50 mgKOH/g.

(Production Example 2: Preparation of Crystalline Polyester Resin C)
A 5 L reaction vessel was charged with 132 g (1.12 mol) of 1,6-hexanediol, 230 g (1.0 mol) of 1,10-decanedicarboxylic acid, and 3 g of tetrabutoxy titanate as a polymerization catalyst, and the mixture was reacted at 210°C under atmospheric pressure for 5 hours while distilling off the water produced. The reaction was then continued under a reduced pressure of 5 to 20 mmHg, and the resin was removed when the acid value reached 2 mgKOH/g or less. The resulting resin was cooled to room temperature and then pulverized into particles. This was designated crystalline polyester resin C.
Crystalline polyester resin C had a melting point Tmp of 80° C., a softening point Tm of 88° C. (Tm/Tmp=1.1), and an SP value of 9.5.

(Production Example 3: Preparation of large particle size silica S1)
Next, a silica sol was prepared by the sol-gel method, and the obtained silica sol was subjected to a hydrophobic treatment with hexamethyldisilazane (HMDS) to obtain hydrophobic large particle silica S1 having an average primary particle diameter of 100 nm.

(Production Example 4: Preparation of large particle size silica S2)
Hydrophobic large particle size silica S2 was obtained in the same manner as in Production Example 3, except that nucleus growth was controlled so that the average primary particle size of the silica particles would be 200 nm.

(Production Example 5: Preparation of large particle size silica S3)
Hydrophobic large particle size silica S3 was obtained in the same manner as in Production Example 3, except that nucleus growth was controlled so that the average primary particle size of the silica particles would be 50 nm.

(Production Example 6: Preparation of resin-coated carrier)
0.375 parts by mass of coating resin 1 (silicone-based, manufactured by Shin-Etsu Chemical Co., Ltd., product name: room temperature drying type methyl-based resin KR-240) and 0.375 parts by mass of coating resin 2 (manufactured by Shin-Etsu Chemical Co., Ltd., product name: room temperature drying type methyl-based resin KR-251) were dissolved in 12 parts by mass of toluene, and 0.0375 parts by mass of conductive particles (conductive carbon black, manufactured by Cabot Corporation, product name: VULCAN XC-72) and 0.0225 parts by mass of a coupling agent (manufactured by Dow Corning Toray Co., Ltd., product name: AY43-059) were further added internally or dispersed to prepare 12.8 g of coating resin liquid.
The surface of 100 parts by mass of a ferrite carrier core material having a volume average particle size of 40 μm was coated with 12.8 parts by mass of the coating resin liquid by a dipping method, and then subjected to a curing process at a curing temperature of 200° C. for 1 hour, followed by sieving with an opening of 150 μm to prepare a resin-coated carrier.

(Example 2-1: Preparation of Toner 1)
[Material mixing, kneading, pulverization, and classification processes]
Binder resin: amorphous polyester resin A (Production Example 1) 80% by mass
Crystalline polyester resin C (Production Example 2) 8% by mass
Colorant: Colorant (CI Pigment Blue 15:3, manufactured by DIC Corporation) 6% by mass
Release agent: monoester wax (NOF Corporation, product name: WEP-3) 5% by mass
Charge control agent: salicylic acid compound (Orient Chemical Industry Co., Ltd., product name: Bontron E-84) 1% by mass

The above materials were premixed for 5 minutes using an airflow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke and Engineering Co., Ltd.), model: FM20C), and then melt-kneaded using an open-roll type continuous kneader (manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke and Engineering Co., Ltd.), model: MOS320-1800) to obtain a molten kneaded product.
The open roll conditions were as follows: the heating roll had a supply side temperature of 130°C, a discharge side temperature of 100°C, and the cooling roll had a supply side temperature of 40°C, and a discharge side temperature of 25°C. The heating roll and cooling roll both had a diameter of 320 mm and an effective length of 1550 mm, and the gap between the rolls on the supply side and the discharge side was 0.3 mm. The heating roll rotation speed was 75 rpm, the cooling roll rotation speed was 65 rpm, and the toner raw material supply rate was 5.0 kg/h.

The resulting melt-kneaded product was cooled on a cooling belt and then coarsely pulverized using a speed mill equipped with a φ2 mm screen.
The obtained coarsely pulverized product was finely pulverized using a jet pulverizer (manufactured by Nippon Pneumatic Mfg. Co., Ltd., model: IDS-2) to obtain a finely pulverized product [fine pulverization step].
Next, the resulting finely pulverized product was classified using an elbow jet classifier (manufactured by Nittetsu Mining Co., Ltd., model: EJ-LABO) to obtain toner base particles [classification step].
The average primary particle diameter of the obtained toner base particles was 6.7 μm, and the amount of ultrafine powder was 5% by mass .

[External addition process]
100 parts by mass of the obtained toner base particles, 1.0 part by mass of the large particle diameter silica S1 obtained in Production Example 1 as the large particle diameter silica, and 1.0 part by mass of silica particles as the small particle diameter silica (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment) were charged into an air flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke and Engineering Co., Ltd.), model: FM20C), and stirred for 4 minutes with the tip speed of the stirring blade set to 40 m/sec.
Next, 0.2 parts by mass of zinc stearate fine particles (average primary particle diameter 0.7 μm, manufactured by NOF Corporation, product name: Nissan Electol (registered trademark) MZ-2) as aliphatic metal salt particles were added to the air flow mixer, and the tip speed of the stirring blade was set to 40 m/sec, followed by stirring for 2 minutes to obtain an externally added toner.
The amount of ultrafine powder in the obtained toner containing external additives was 20%, and the amount of ultrafine powder in the toner after the external additive adhesion strength test was 5%. Furthermore, the non-adhesion rate of zinc stearate microparticles was 60%, and the strong adhesion rate was 10%, and the non-adhesion rate of silica (total of large particle size silica and small particle size silica) was 3%, and the strong adhesion rate was 65%.

[Developer manufacturing process]
The obtained externally added toner and the resin-coated carrier obtained in Production Example 6 were mixed so that the concentration of the externally added toner relative to the total amount of the two-component developer was 7% by mass, thereby obtaining a two-component developer (toner 1) with a toner concentration of 7%.
Hereinafter, the two-component developers obtained in the examples and comparative examples will be referred to as "toner X" and "comparative toner Y," respectively, with the suffix numbers X and Y of the examples and comparative examples.

(Examples 2-2 and 2-3: Preparation of Toners 2 and 3)
Toners 2 and 3 were obtained in the same manner as in Example 2-1, except that in the external addition step, the amount of zinc stearate fine particles was changed from 0.2 parts by mass to 0.07 parts by mass and 0.5 parts by mass, respectively.

(Example 2-4: Preparation of Toner 4)
Toner 4 was obtained in the same manner as in Example 2-1, except that in the external addition step, the zinc stearate fine particles were changed to magnesium stearate fine particles (average primary particle diameter 2.0 μm, manufactured by NOF Corporation, product name: MM-2).

(Examples 2-5 and 2-6: Preparation of Toners 5 and 6)
Toners 5 and 6 were obtained in the same manner as in Example 2-1, except that in the external addition step, the amount of zinc stearate fine particles was changed from 0.2 parts by mass to 0.04 parts by mass and 0.05 parts by mass, respectively.

(Example 2-7: Preparation of Toner 7)
Toner 7 was obtained in the same manner as in Example 2-1, except that in the external addition step, the stirring (external addition) time in the air flow mixer was changed from 4 minutes and 2 minutes to 2 minutes and 4 minutes, respectively.

(Example 2-8: Preparation of Toner 8)
Toner 8 was obtained in the same manner as in Example 2-1, except that in the external addition step, the stirring (external addition) time in the air flow mixer was changed from 4 minutes and 2 minutes to 5.5 minutes and 0.5 minutes, respectively.

(Example 2-9: Preparation of Toner 9)
Toner 9 was obtained in the same manner as in Example 2-1, except that in the external addition step, only small particle silica was added to the obtained toner base particles and stirred for 4 minutes in an air flow mixer, and then large particle silica and zinc stearate microparticles were added simultaneously and stirred for 2 minutes in an air flow mixer.

(Example 2-11: Preparation of Toner 11)
Toner 11 was obtained in the same manner as in Example 2-1, except that in the external addition step, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R976, number average primary particle diameter 7 nm, dimethyldichlorosilane surface treatment) used as small particle diameter silica were changed to silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) NAX50, number average primary particle diameter 30 nm, hexamethyldisilazane surface treatment).

(Examples 2-11 and 2-12: Preparation of Toners 11 and 12)
Toners 11 and 12 were obtained in the same manner as in Example 2-1, except that in the external addition step, the large particle diameter silica S1 obtained in Production Example 1 was changed to the large particle diameter silica S3 and S2 obtained in Production Examples 3 and 2, respectively.

(Comparative Example 2-1: Preparation of Comparative Toner 1)
Comparative toner 1 was obtained in the same manner as in Example 2-1, except that in the external addition step, zinc stearate fine particles were not used as the aliphatic metal salt particles, and the 2-minute stirring in the air flow mixer was not carried out.

[evaluation]
The prepared photoreceptors 1 to 11 of Examples 1-1 to 1-11 and comparative photoreceptors 1 to 3 of Comparative Examples 1-1 to 1-3 were combined with toners 1 to 13 of Examples 2-1 to 2-13 and comparative toners 1 and 2 of Comparative Examples 2-1 to 2-2 as shown in Table 1, and the photoreceptors were evaluated for (1) printing durability, (2) stress crack resistance, and (3) cleaning resistance. These were designated Examples 1 to 23 and Comparative Examples 1 to 7, respectively.
The photosensitive member was mounted in a unit of a digital copier (Model: MX-4151, manufactured by Sharp Corporation), a developing unit was attached, and the pressure at which the cleaning blade of the cleaning unit contacts the photosensitive member, i.e., the cleaning blade pressure, was adjusted to 25 gf/cm (2.05 × 10 ⁻¹ N/cm: initial linear pressure), and the machine was modified into a durability tester for printing durability, stress crack resistance, and cleaning resistance.

(1) Printing durability A printing durability test was carried out by printing a character test chart (ISO19752) on 300,000 sheets of recording paper in a normal temperature/high humidity environment of 25° C./75% humidity.
The thickness of the photosensitive layer at the start of the printing durability test and after 300,000 images were formed was measured using a film thickness measuring device (Filmetrics, Model: F-20-EXR).
The amount of abrasion (amount of film reduction) per 100,000 rotations of the photosensitive drum was calculated from the difference between the film thickness at the start of the printing durability test and the film thickness after forming 300,000 images, and the printing durability was evaluated based on the obtained amount of abrasion according to the following criteria.
The greater the amount of scraping, the worse the printing durability was evaluated to be.

<Judgment criteria>
VG: Amount of scraping < 0.50 μm/100,000 revolutions Can be used without problems in multifunction devices or printers that require a long life G: 0.50 μm/100,000 revolutions≦amount of scraping < 0.70 μm/100,000 revolutions Although the amount of scraping is somewhat large, it can be used without problems unless it is a multifunction device or printer that requires a long life NB: 0.70 μm/100,000 revolutions≦amount of scraping < 0.85 μm/100,000 revolutions Although the amount of scraping is large, it can be used without problems in inexpensive multifunction devices or printers B: 0.85 μm/100,000 revolutions≦amount of scraping There is a large amount of scraping, which causes problems in practical use

(2) Stress crack resistance The level of stress cracking defects on the photoreceptor was confirmed by visually observing the output image during the printing test. The presence or absence of stress cracking on the image was confirmed, and if stress cracking occurred, the number of sheets on which it occurred was confirmed. From the results obtained, stress crack resistance was evaluated according to the following criteria.

<Judgment criteria>
VG: No occurrence G: Although not visible on the image, stress cracks were confirmed on the photoreceptor surface after the printing test was completed B: Image defects caused by stress cracks were confirmed before 300,000 sheets were printed

(3) Cleaning resistance (effective against uneven density caused by external additives slipping through)
In order to confirm the occurrence level of cleaning defects of the photoreceptor after the printing durability test, the photoreceptor after 300,000 images were formed was attached to a unit of a test digital copier (manufactured by Sharp Corporation, model: MX-B455W), and one untransferred image of 100% density was output onto an A4 sheet of paper. Immediately after that, the copier was forcibly stopped, and the surface of the photoreceptor was visually observed, and the cleaning ability was evaluated according to the following criteria.

<Judgment criteria>
VG: No cleaning defects G: One clear cleaning defect present Can be used without problems with devices other than multifunction devices and printers that do not require high image quality NB: 2 to 5 clear cleaning defects present Can be used without problems with inexpensive multifunction devices and printers B: Many (6 or more) cleaning defects present Problems with practical use

(4) Overall Evaluation Based on the results of the above evaluations, the photoreceptors were overall evaluated according to the following criteria.
VG: VG rating in all items, very good G: Some items were rated G, but all items were rated G or better Can be used without problems in devices other than long-life, high-image-quality multifunction devices or printers NB: Some items were rated C, but all items were rated NB or better Can be used without problems in devices other than inexpensive multifunction devices or printers B: Some items were rated B, not suitable for practical use The raw materials and physical properties of the photoconductor are shown in Table 1, the raw materials and physical properties of the toner are shown in Table 2, and the evaluation results of the toner are shown in Table 3.

The results in Tables 1 to 3 reveal the following: (1) The image forming apparatuses (Examples 1 to 23) equipped with the photoreceptor and toner of the present invention can provide an image forming apparatus equipped with an electrophotographic photoreceptor that can suppress the occurrence of stress cracks and obtain stable image characteristics over a long period of time, compared to the case where a photoreceptor having a silica particle content (solid content) in the charge transport layer of the photoreceptor outside the range (Comparative Examples 1 and 2), a photoreceptor having a surface layer creep value outside the range (Comparative Examples 3 and 8), a photoreceptor having a ten-point surface roughness Rz outside the range of the photoreceptor surface (Comparative Examples 6 and 7), or a toner to which no fatty acid metal salt is externally added (Comparative Examples 4 and 5) is used.

(2) The average primary particle diameter of the fatty acid metal salt externally added to the toner base particles as an external additive is preferably 1.5 μm or less. Toners with an external additive of a fatty acid metal salt exceeding this diameter (Example 9) exhibit stress crack resistance and cleaning resistance, but the fatty acid metal salt tends to separate from the toner base particles, resulting in significant slippage (detachment) of the external additive, which reduces the uniformity of the amount of fatty acid metal salt applied to the photoreceptor surface and results in insufficient effectiveness.

(3) The non-adhered mass of fatty acid metal salt particles contained as an external additive in the toner, as calculated by an external adhesion strength test, significantly affects the printing durability, stress crack resistance, and cleaning resistance of a photoreceptor containing silica particles. Furthermore, if the fatty acid metal salt particle content exceeds 0.4% by mass (Example 15), the adhesion strength is too weak, resulting in an increased supply to the image forming unit. This results in excessive detachment of the fatty acid metal salt in the developer tank, which can cause aggregation of the fatty acid metal salt particles and toner aggregation, increasing the risk of poor developability. It also makes it difficult to uniformly apply the fatty acid metal salt particles to the photoreceptor surface, thereby preventing sufficient stress crack resistance and cleaning resistance. On the other hand, if the fatty acid metal salt particle content is less than 0.02% by mass, the amount of fatty acid metal salt particles supplied to the image forming unit is insufficient, resulting in insufficient stress crack resistance, and the fatty acid metal salt particles' adhesion strength is too strong, causing the fatty acid metal salt particles to migrate to the paper, increasing the risk of poor low-temperature fixability when the toner and fatty acid metal salt melt and fuse together.

(4) By incorporating small-particle silica with a number-average primary particle diameter of 15 nm or less as an external additive to the toner in addition to large-particle silica, the fluidity of the toner base particles can be appropriately improved, making it easier to achieve optimal external adhesion strength. Furthermore, by externally adding large-particle silica and then fatty acid metal salt particles in that order, optimal adhesion strength can be easily achieved, allowing the amount of fatty acid metal salt particles supplied to the image forming unit to be optimized (Comparison between Example 1 and Examples 14, 16-18).

(5) By using a resin with a polyarylate skeleton as the binder resin constituting the charge transport layer on the surface of the photoreceptor, it is easier to set a high creep value, the resin is more resistant to electrical and mechanical fatigue, and the effects of stress crack resistance and cleaning resistance are improved (comparison of Example 1 and Example 19). This is not limited to a polyarylate skeleton, and similar effects can be obtained with other skeletons as long as they are within the scope specified in this invention.

(6) The smaller the number-average primary particle size of the silica contained in the charge transport layer on the surface of the photoreceptor, the better for stress crack resistance. It is preferable that the number-average primary particle size is 10 to 50 nm, and more preferably 10 to 20 nm (comparison between Examples 1, 20, and 21).

(7) It has been found that a uniform ten-point surface roughness Rz of a photoreceptor in the axial direction is advantageous in terms of stress crack resistance. This is even better when the ten-point surface roughness RzA and RzB of the central and end portions of the charged area of the photoreceptor in an image forming device satisfy the relationship "1≦RzB/RzA≦1.3" (Example 1). However, when there is a difference in the ten-point surface roughness Rz in the axial direction, stress is more likely to be applied to the photoreceptor surface in areas with higher Rz, increasing the risk of stress cracks and poor cleanability (Examples 22 and 23).

1, 10, 20 Electrophotographic photoreceptor 11 Conductive support 12 Undercoat layer (intermediate layer)
13 Charge generation layer 14 Charge transport layer 15 First charge transport layer 16 Second charge transport layer 17 Photosensitive layer (laminated photosensitive layer)
18 Silica particles

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 Collection casing 37 Separation means 38 Housing 41, 42 Arrows 44 Rotation axis 51 Recording medium (recording paper or transfer paper)
100 Image forming device (laser printer)

Claims (9)

an electrophotographic photosensitive member; a charging unit for charging the electrophotographic photosensitive member; an exposure unit for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image; a developing unit for developing the electrostatic latent image to form a toner image with toner; and a transfer unit for transferring the toner image onto a recording medium;
the electrophotographic photoreceptor comprises at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a conductive support,
the charge transport layer contains at least a charge transport material, a binder resin, and silica particles;
the silica particles have a number average primary particle diameter of 10 to 20 nm and are contained in the charge transport layer in an amount of 7 to 25% by mass,
the charge transport layer has a surface layer with a ten-point surface roughness Rz of 0.1 to 0.3 μm as defined in JIS-B-0601 (1994),
the charge transport layer has a surface layer having a creep value C of 3.8 to 5.0% as measured by applying a maximum load of 30 mN for 5 seconds using a Vickers square pyramid diamond indenter with an opposing angle of 136° under an environment of a temperature of 25°C and a relative humidity of 50%,
the toner is externally added with two or more kinds of external additives including fatty acid metal salt particles,
The fatty acid metal salt particles have an adhesion strength such that they detach from the toner at a ratio of 0.05 to 0.2% by mass when subjected to an external adhesion strength test in which 2.0 g of the toner is added to 40 ml of a 0.2% by mass aqueous solution of polyoxyethylene octylphenyl ether and stirred for 1 minute, the resulting aqueous solution is irradiated with ultrasonic waves at an output of 40 μA for 3 minutes, and then the solution is left to stand for 3 hours to separate the toner and the liberated external additives, the supernatant is removed, and then about 50 ml of pure water is added to the precipitate and the mixture is stirred for 5 minutes. The mixture is suction filtered using a membrane filter with a pore size of 1 μm, and the toner remaining on the membrane filter is vacuum dried overnight to obtain a toner after external additive removal treatment.
An image forming apparatus characterized by: The image forming apparatus according to claim 1, wherein the fatty acid metal salt particles are externally added to the toner at a ratio of 0.05 to 0.5% by mass. The image forming apparatus according to claim 1 or 2, wherein the fatty acid metal salt particles have an average primary particle diameter of 1.5 μm or less. The image forming apparatus according to any one of claims 1 to 3, wherein the fatty acid metal salt particles are particles of a compound selected from zinc stearate and magnesium stearate. 5. The image forming apparatus according to claim 1 , wherein the toner contains, as an external additive, small-particle silica particles having a number-average primary particle size of 15 nm or less, together with the fatty acid metal salt. 6. The image forming apparatus according to claim 1, wherein the toner comprises large silica particles having a number average primary particle diameter of 50 to 200 nm externally added together with the fatty acid metal salt as an external additive, and the fatty acid metal salt particles are externally added after the large silica particles have been externally added. 7. The image forming apparatus according to claim 1, wherein the binder resin of the charge transport layer is a resin having a polyarylate skeleton. When the ten-point surface roughnesses of a 4 mm wide region at the center A and end B of the charged region in the axial direction of the electrophotographic photosensitive member in the charge transport layer are RzA and RzB, respectively, the following formula is obtained:
1≦RzB/RzA≦1.3
8. The image forming apparatus according to claim 1, wherein the following relationship is satisfied: an electrophotographic photosensitive member; a charging unit for charging the electrophotographic photosensitive member; an exposure unit for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image; a developing unit for developing the electrostatic latent image to form a toner image with toner; and a transfer unit for transferring the toner image onto a recording medium;
the electrophotographic photoreceptor comprises at least a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on a conductive support,
the charge transport layer contains at least a charge transport material, a binder resin, and silica particles;
the silica particles have a number average primary particle diameter of 10 to 20 nm and are contained in the charge transport layer in an amount of 7 to 25% by mass,
the charge transport layer has a surface layer with a ten-point surface roughness Rz of 0.1 to 1.3 μm as defined in JIS-B-0601 (1994),
the charge transport layer has a surface layer having a creep value C of 3.8 to 5.0% as measured by applying a maximum load of 30 mN for 5 seconds using a Vickers square pyramid diamond indenter with an opposing angle of 136° under an environment of a temperature of 25°C and a relative humidity of 50%,
the toner is externally added with two or more kinds of external additives including fatty acid metal salt particles,
the fatty acid metal salt particles have an adhesion strength such that they detach from the toner in a proportion of 0.05 to 0.2 mass % of the toner when subjected to an external adhesion strength test in which 2.0 g of the toner is added to 40 ml of a 0.2 mass % aqueous solution of polyoxyethylene octylphenyl ether and stirred for 1 minute, the resulting aqueous solution is irradiated with ultrasonic waves at an output of 40 μA for 3 minutes, and then the solution is left to stand for 3 hours to separate the toner and the liberated external additives, the supernatant is removed, and then about 50 ml of pure water is added to the precipitate and the mixture is stirred for 5 minutes, and the mixture is suction filtered using a membrane filter with a pore size of 1 μm, and the toner remaining on the membrane filter is vacuum dried overnight to obtain a toner after external additive removal treatment ,
An image forming method comprising at least a charging step of charging the electrophotographic photosensitive member, an exposure step of exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, a development step of developing the electrostatic latent image to form a toner image with toner, and a transfer step of transferring the toner image onto a recording medium.