JP7572999B2 - Process cartridge - Google Patents

Description

The present invention relates to a process cartridge used in copying machines and printers that use electrophotographic or electrostatic recording methods.

In recent years, there has been a widespread demand for electrophotographic image forming apparatuses with higher process speeds and longer life spans.
In an electrophotographic image forming apparatus that is becoming faster, the time required for each step in the electrophotographic process, such as charging and development, is becoming shorter. Therefore, in order to maintain the quality of electrophotographic images, it is necessary to develop a technology that can instantly charge toner and keep the charge of the toner stable for a long period of time under any usage environment.
In order to instantly charge the toner, there is a method of adding an external additive having a certain resistance value to the toner, as described in Japanese Patent Application Laid-Open No. 2003-233666.
In addition, as disclosed in JP-A-2003-133999, there is a method of maintaining stable electrical characteristics by incorporating niobium atom-containing titanium oxide particles in the protective layer of an electrophotographic photosensitive member.

JP 2001-125302 A JP 2009-229495 A

In Patent Document 1, it was found that there was a certain effect on the charge rise property of the toner, but in faster electrophotographic image forming devices, the charge rise property was insufficient, and the density of solid images immediately after starting up the device was found to be poor. It was also confirmed that in faster electrophotographic image forming devices, the density uniformity of halftone images was insufficient in process cartridges that had been used for a long time. The inventors speculate that the reason for this is as follows.

Toner that has an external additive with a certain resistance value is regulated by a blade or the like and frictionally charged before the nip where it is developed from the developer carrier to the electrophotographic photoreceptor. However, in faster electrophotographic image forming devices, the time for frictional charging is insufficient, and it is believed that charging is insufficient in solid images, which consume a lot of toner. In addition, the external additives are small and have a shape that makes them easy to embed in the toner, and the embedded parts charge up locally, making it difficult to maintain their effectiveness over long periods of use.

In addition, in Patent Document 2, the charge build-up immediately after starting up the electrophotographic image forming apparatus and the density uniformity of halftone images after long-term use were not sufficiently improved. The inventors speculate that the reason for this is as follows.

By including niobium atom-containing titanium oxide particles in the surface protective layer of the electrophotographic photoreceptor, the charge of the surface protective layer is less likely to change, but there is no mechanism for imparting a charge to the toner, and it is thought that this has no effect on improving the chargeability of the toner.

Therefore, the object of the present invention is to provide a process cartridge for a faster electrophotographic image forming apparatus, which has excellent charge build-up characteristics immediately after the apparatus is started up, and excellent density uniformity of halftone images over a long period of time from when the process cartridge is first used until after sufficient use. Hereinafter, the period immediately after the electrophotographic image forming apparatus is started up may be referred to as "initial period." Also, the period after the process cartridge has been used sufficiently may be referred to as "after durability."

A process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus,
The process cartridge comprises:
An electrophotographic photoreceptor;
Toner;
a developing means for storing the toner and supplying the toner to the surface of the electrophotographic photoreceptor;
having
The toner has toner particles and an external additive A,
The external additive A satisfies the following requirements (i) to (iii):
(i) the major axis is 100 nm or more and 3000 nm or less;
(ii) an aspect ratio of 5.0 or more;
(iii) Specific resistance is 1×10 ⁵ Ω・cm or more and 1×10 ⁸ Ω・cm or less,
the ratio of toner particles having the external additive A present on the surface to the total number of toner particles in the toner is 30% or more;
The electrophotographic photoreceptor has a conductive support, a photosensitive layer formed on the conductive support, and a surface protective layer formed on the surface of the electrophotographic photoreceptor,
The surface protective layer contains conductive particles,
the content of the conductive particles in the surface protective layer is 5% by volume or more and 70% by volume or less,
the volume resistivity of the surface protective layer is 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less;
The present invention provides a process cartridge.

The process cartridge of the present invention has excellent toner charge build-up immediately after starting up the electrophotographic image forming apparatus, and also has excellent charge stability over a long period of time, from when the process cartridge is first used until after it has been used for a long period of time. In other words, it is possible to provide a process cartridge that achieves both good solid images immediately after starting up the electrophotographic image forming apparatus, and halftones with excellent density uniformity over a long period of time.

1 shows an example of a schematic configuration of an electrophotographic photosensitive member. 1 shows an example of a schematic configuration of an electrophotographic image forming apparatus having a process cartridge equipped with an electrophotographic photosensitive member. FIG. 2 is an STEM image of an example of niobium-containing titanium oxide particles used in the present examples. FIG. 2 is a schematic diagram of an example of niobium-containing titanium oxide particles used in the present examples.

The expressions "XX to YY" and "XX to YY" representing a numerical range mean a numerical range including the endpoints, that is, the lower limit and the upper limit, unless otherwise specified.
When numerical ranges are stated in stages, the upper and lower limits of each numerical range can be combined in any way.

The structure of the process cartridge of the present invention will now be described.
The process cartridge of the present invention is a process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus,
The process cartridge comprises:
An electrophotographic photoreceptor;
Toner;
a developing means for storing the toner and supplying the toner to the surface of the electrophotographic photoreceptor;
having
The toner has toner particles and an external additive A,
The external additive A satisfies the following requirements (i) to (iii):
(i) the major axis is 100 nm or more and 3000 nm or less;
(ii) an aspect ratio of 5.0 or more;
(iii) Specific resistance is 1×10 ⁵ Ω・cm or more and 1×10 ⁸ Ω・cm or less,
the ratio of toner particles having the external additive A present on the surface to the total number of toner particles in the toner is 30% or more;
The electrophotographic photoreceptor has a conductive support, a photosensitive layer formed on the conductive support, and a surface protective layer formed on the surface of the electrophotographic photoreceptor,
The surface protective layer contains conductive particles,
the content of the conductive particles in the surface protective layer is 5% by volume or more and 70% by volume or less,
The surface protective layer has a volume resistivity of 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less.

In response to the above problem, the inventors have investigated a method of injecting a charge from the electrophotographic photoreceptor into the toner as the toner moves from the developer carrier to the nip where it is developed onto the electrophotographic photoreceptor. Generally, toner is regulated by the developer carrier and charged by friction. However, the inventors have hypothesized that, in addition to charging from friction, by injecting a charge from the electrophotographic photoreceptor into the toner as it moves into the development nip, stable toner charging performance can be achieved even in high-speed electrophotographic image forming apparatuses, immediately after the apparatus is started up.

As a result of the inventors' repeated investigations based on the above considerations, they discovered that by providing an external additive A with a specific volume resistivity and an irregular shape with a large surface area on the surface layer of the toner particles, charge is injected from the electrophotographic photoreceptor to the toner through the external additive A. Furthermore, they discovered that the unexpected effect of maintaining this charge injection property even after durability can be obtained. With this configuration, they have been able to provide a process cartridge that has excellent charge start-up properties immediately after starting up the electrophotographic image forming apparatus and excellent density uniformity over long-term use.

The electrophotographic photoreceptor of the present invention has a conductive support, and a photosensitive layer and a surface protective layer formed on the conductive support in this order.

The surface protective layer contains conductive particles, and the content of the conductive particles is 5 volume % or more and 70 volume % or less of the surface protective layer. The volume resistivity of the surface protective layer is 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less. This volume resistivity is measured in an atmosphere with a temperature of 23° C. and a humidity of 50 RH%. By being in this range, the volume resistivity is maintained relatively high despite the surface protective layer containing a large amount of conductive particles, so that it is possible to inject charge into the toner via the conductive particles while ensuring charge retention.

From the viewpoint of optimizing the charge injection property and improving the concentration uniformity of the process cartridge immediately after starting up the electrophotographic image forming apparatus and over a long period of time from the start of use to after sufficient use, the content ratio of the conductive particles in the surface protective layer is more preferably 20% by volume or more and 70% by volume or less, and even more preferably 40% by volume or more and 70% by volume or less. From the same viewpoint, the volume resistivity of the surface protective layer is more preferably 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less, and more preferably 1.0×10 ¹⁰ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less. The volume resistivity of the surface protective layer can be controlled, for example, by the particle diameter of the conductive particles.

The conductive particles contained in the surface protective layer include particles of metal oxides such as titanium oxide, zinc oxide, tin oxide, and indium oxide. When metal oxides are used as the conductive particles, the metal oxides may be doped with elements such as niobium, phosphorus, and aluminum, or oxides thereof.

The conductive particles in the electrophotographic photoreceptor of the present invention are preferably titanium oxide particles. The titanium oxide particles are produced by a known method. For example, see JP-A-7-242422.

From the viewpoint of moisture adsorption amount and particle dispersibility, the particle diameter of the conductive particles is preferably 5 nm or more and 300 nm or less, more preferably 40 nm or more and 300 nm or less, and even more preferably 100 nm or more and 250 nm or less, in terms of number average particle diameter.

Particularly preferred conductive particles are titanium oxide particles containing niobium and having a configuration in which niobium is unevenly distributed near the particle surface. This is because the uneven distribution of niobium near the surface allows for efficient transfer of electric charges. More specifically, titanium oxide particles in which the concentration ratio calculated as "niobium atomic concentration/titanium atomic concentration" at 5% inside the maximum diameter from the surface of the particle is 2.0 times or more than the concentration ratio calculated as "niobium atomic concentration/titanium atomic concentration" at the center of the particle. By making the concentration ratio at 5% inside the maximum primary particle diameter from the surface 2.0 times or more compared to the concentration ratio at the center, electric charges can be easily moved within the protective layer, and the charge injection from the electrophotographic photoreceptor to the toner can be improved. The niobium atomic concentration and titanium atomic concentration are obtained by a scanning transmission electron microscope (STEM) connected to an EDS analyzer (energy dispersive X-ray analyzer). FIG. 3 shows an STEM image of an example (X1) of titanium oxide particles used in the examples of the present invention. 3 is shown in FIG. 4. The details will be described later, but the niobium-containing titanium oxide particles used in the present embodiment are prepared by coating the titanium oxide particles as the core material with niobium-containing titanium oxide and then firing the coated titanium oxide. Therefore, it is considered that the coated niobium-containing titanium oxide grows as niobium-doped titanium oxide along the crystals of the titanium oxide core material by so-called epitaxial growth. The niobium-containing titanium oxide prepared in this manner has a lower density in the surface vicinity 32 compared to the density in the particle center 31 as shown in FIG. 3, and it can be seen that it has a core-shell-like form. In addition, in the EDS analysis by STEM, X-rays penetrate the entire particle, so that the EDS analysis by X-rays analyzing the inside of 5% of the primary particle diameter shown by 34 is more influenced by the surface vicinity 32 than the EDS analysis by X-rays that penetrate the particle center 31 shown by 33 as shown in FIG. 4. In other words, in the above-mentioned niobium-containing titanium oxide particles, the niobium/titanium atomic concentration ratio at 5% inside the particle from the surface to the maximum diameter is 2.0 times or more compared to the niobium/titanium atomic concentration ratio at the center of the particle, and niobium atoms are unevenly distributed near the surface. In the analysis using STEM connected to EDS, the niobium/titanium ratio is measured by EDS after observation with a transmission electron microscope. In addition, the electrophotographic photosensitive member can be directly measured by cutting it into thin slices using a microtome, Ar milling, FIB, or other means.

The titanium oxide particles containing niobium atoms are preferably anatase or rutile titanium oxide particles, and more preferably anatase titanium oxide particles. By using anatase titanium oxide, charge transfer within the surface protective layer becomes smooth, resulting in good charge injection. More preferably, the conductive particles are anatase titanium oxide particles in which niobium atoms are unevenly distributed near the surface. By using anatase titanium oxide particles as the core material and coating the surface with titanium oxide containing niobium atoms, charge can be easily transferred within the surface protective layer, and at the same time, charge injection into the toner can be improved. In addition, a decrease in the volume resistivity of the surface protective layer can be suppressed.

For the purpose of uniformly charging the electrophotographic photoreceptor, the conductive particles preferably have an atomic concentration ratio of Nb atoms to Ti atoms within 5% of the maximum diameter from the surface of 0.02 to 0.20. In addition, the amount of niobium atoms is preferably 2.6% by mass to 10.0% by mass relative to the mass of the titanium oxide particles.

The external additive A is less likely to be embedded in the toner, has a large surface area, and efficiently injects and charges the external additive. Therefore, preferred examples of its shape are as follows. That is, the external additive A is preferably a shape other than a sphere, and is preferably a shape that is long in one axial direction in a three-dimensional structure (the axis is called the long axis). The shape of a cross section obtained by cutting the external additive A perpendicularly to the long axis direction does not matter, and may be a circle, a square, a triangle, a polygon, or a combination thereof. In addition, the cross-sectional area of the cross section may be substantially the same in the entire long axis direction, or may vary, and the cross-sectional area may be small or large at both ends in the long axis direction, or the cross-sectional area of one end in the long axis direction may be smaller than the cross-sectional area of the other end. That is, the shape of the external additive A can be a cylinder (cylinder, square cylinder, triangular cylinder, polygonal cylinder), a cylinder with a thick center, a cylinder with a thin center, or a pyramid (cone, square pyramid, triangular pyramid, polygonal pyramid), a cut part of these, a needle shape (a cylinder or pyramid whose major axis is sufficiently longer than its minor axis), a rod shape, a mixture of these, etc. The major axis of the external additive A is the length of the major axis of the external additive, and the minor axis is the equivalent circle diameter of the cross section perpendicular to the major axis at the position where the cross-sectional area is maximum, and the number average value is used as the representative value for each.

The major axis of the external additive A is 100 nm or more and 3000 nm or less, preferably 500 nm or more and 2000 nm or less, and more preferably 800 nm or more and 1700 nm or less. When the major axis of the external additive A is in this range, the efficiency of the injection charge from the electrophotographic photoreceptor is increased and the embedding of the external additive A into the toner particles is suppressed, so that the uniformity of the solid image is improved over a long period of use. The reason for the improvement in the uniformity of the solid image is thought to be that the external additive A touches the electrophotographic photoreceptor momentarily before the nip where development is performed from the developer carrier to the electrophotographic photoreceptor, and the injection charge to the toner occurs starting from the contact point.

The aspect ratio of the external additive A, i.e., the major axis/minor axis, is 5.0 or more, preferably 6.0 or more, and more preferably 8.0 or more. When the aspect ratio of the external additive A is in this range, the injection charge from the electrophotographic photoreceptor to the toner is made efficient, and the solid density immediately after starting up the electrophotographic image forming apparatus and the density uniformity over a sufficient period of use are improved. There is no particular upper limit for the aspect ratio, but from the viewpoint of facilitating the production of particles with a suitable particle size, a value of 20.0 or less, and more preferably 16.0 or less, is preferred.

The resistivity of the external additive A is from 1.0× ¹⁰ Ω·cm to 1.0× ¹⁰ Ω·cm, preferably from 1.0× ¹⁰ Ω·cm to 5.0× ¹⁰ Ω·cm. Within this range, charging can be efficiently injected into the toner, charge leakage is small, and both the charge rise immediately after start-up of the electrophotographic image forming apparatus and the charge uniformity even after endurance testing can be achieved.

In the toner, the percentage of toner particles on whose surface the external additive A can be confirmed is 30% by number or more, more preferably 40% by number or more, and even more preferably 50% by number or more. As long as the objective of injecting charge into the toner is met, there is no particular upper limit to the percentage, but from the viewpoint of preventing the toner from becoming too negatively charged, it is preferably 95% by number or less, and even more preferably 90% by number or less.

The presence of the external additive A on the surface means that one or more particles of the external additive A can be confirmed on the surface of the toner particle. The presence of the external additive A on the surface can be confirmed by observing the toner using a scanning microscope.

The material of the external additive A is not limited as long as it satisfies the above-mentioned range of physical properties, but it is preferable that the external additive A is an inorganic particle such as titanium oxide particle or aluminum oxide particle.
It is particularly preferable that the external additive A contains titanium oxide particles. When the external additive A contains titanium oxide particles, the resistance value can be easily set within a desired range, and half-tone unevenness after durability testing can be effectively suppressed.

It is further preferred that the external additive A contains rutile-type titanium oxide particles. By containing rutile-type titanium oxide particles, the charge injected from the surface of the electrophotographic photoreceptor is not leaked to the outside, and the toner can be charged efficiently.

In the present invention, the toner particles preferably contain boric acid. By containing boric acid in the toner particles, the toner has improved ability to retain the charge injected into it, improving image quality over a sufficient period of use.

It is preferable that boric acid is present near the toner surface. Whether or not boric acid in a toner particle is present near the toner surface can be confirmed by ATR-IR analysis using germanium; that is, when boric acid is detected in ATR-IR analysis using germanium, it means that boric acid is present near the toner surface. By having boric acid present near the toner surface, the charge of the toner charged by injection charging is maintained, and image quality can be improved over a sufficient period of use.

There are no particular limitations on the means by which boric acid is incorporated into toner particles. For example, boric acid can be incorporated into toner particles by adding it internally to the toner particles or using it as an aggregating agent in an aggregating method. Adding boric acid as an aggregating agent makes it easier to introduce boric acid near the surface of the toner particles. Raw materials for boric acid include organic boric acid, borate salts, borate esters, and the like. When toner particles are produced in an aqueous medium, it is preferable to add it as a borate salt from the viewpoint of reactivity and production stability. Specific examples include sodium tetraborate and ammonium borate, and borax is particularly preferred.

Borax is represented by the _decahydrate of sodium _{tetraborate Na2B4O7 ,} and changes to boric acid in an acidic aqueous solution, so borax is preferably used when used in an aqueous medium under an acidic environment. Borax is preferably contained in the toner particles in an amount of 0.1% by mass to 10% by mass.

The constitution of the toner in the present invention will be described below.
<Binder resin>
The toner particles contain a binder resin. The content of the binder resin is preferably 50% by mass or more of the total amount of the resin components in the toner particles.
The binder resin is not particularly limited as long as it contains a resin having an ester bond, and a known resin can be used. Styrene acrylic resin and polyester resin are preferred. Polyester resin is more preferred.

The polyester resin is obtained by selecting and combining suitable polycarboxylic acids, polyols, hydroxycarboxylic acids, etc., and synthesizing them using a known method such as an ester exchange method or a polycondensation method. The polyester resin preferably contains a condensation polymer of a dicarboxylic acid and a diol.

Polycarboxylic acids are compounds that contain two or more carboxy groups in one molecule. Of these, dicarboxylic acids are compounds that contain two carboxy groups in one molecule and are preferably used.

Examples of dicarboxylic acids include oxalic acid, succinic acid, glutaric acid, maleic acid, adipic acid, β-methyladipic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, fumaric acid, citraconic acid, diglycolic acid, cyclohexane-3,5-diene-1,2-carboxylic acid, hexahydroterephthalic acid, malonic acid, pimelic acid, suberic acid, phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carboxyphenylacetic acid, p-phenylenediacetic acid, m-phenylenediacetic acid, o-phenylenediacetic acid, diphenylacetic acid, diphenyl-p,p'-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, anthracenedicarboxylic acid, and cyclohexanedicarboxylic acid.

Examples of polycarboxylic acids other than the dicarboxylic acids include trimellitic acid, trimesic acid, pyromellitic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, pyrene tricarboxylic acid, pyrene tetracarboxylic acid, itaconic acid, glutaconic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, isododecyl succinic acid, isododecenyl succinic acid, n-octyl succinic acid, and n-octenyl succinic acid. These may be used alone or in combination of two or more.

Polyols are compounds that contain two or more hydroxyl groups in one molecule. Of these, diols are compounds that contain two hydroxyl groups in one molecule and are preferably used.

Specific examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,14-eicosapentaenoic acid. These include butyl ether glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-butenediol, neopentyl glycol, polytetramethylene glycol, hydrogenated bisphenol A, bisphenol A, bisphenol F, bisphenol S, and alkylene oxide (ethylene oxide, propylene oxide, butylene oxide, etc.) adducts of the above bisphenols.

（式（Ａ）中、Ｒは、それぞれ独立してエチレン基又はプロピレン基であり、ｘ及びｙはそれぞれ０以上の整数であり、かつ、ｘ＋ｙの平均値は０以上１０以下である。） Among these, preferred are alkylene oxide adducts of alkylene glycols having from 2 to 12 carbon atoms and bisphenols, and particularly preferred is a combination of an alkylene oxide adduct of a bisphenol and an alkylene glycol having from 2 to 12 carbon atoms. Examples of the alkylene oxide adducts of bisphenol A include the compounds represented by the following formula (A).

(In formula (A), each R is independently an ethylene group or a propylene group, each of x and y is an integer of 0 or more, and the average value of x+y is 0 or more and 10 or less.)

The alkylene oxide adduct of bisphenol A is preferably a propylene oxide adduct and/or an ethylene oxide adduct of bisphenol A. More preferably, it is a propylene oxide adduct. In addition, the average value of x+y is preferably 1 or more and 5 or less.

Examples of trihydric or higher alcohols include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, hexamethylolmelamine, hexaethylolmelamine, tetramethylolbenzoguanamine, tetraethylolbenzoguanamine, sorbitol, trisphenol PA, phenol novolac, cresol novolac, and alkylene oxide adducts of the above trihydric or higher alcohols. These may be used alone or in combination of two or more.

Examples of the styrene-acrylic resin include homopolymers made of the following polymerizable monomers, copolymers obtained by combining two or more of these, and mixtures thereof.
Styrenic monomers such as styrene, α-methylstyrene, β-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene and p-phenylstyrene may be mentioned.
Examples of (meth)acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, iso-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-amyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, dimethyl phosphate ethyl (meth)acrylate, diethyl phosphate ethyl (meth)acrylate, dibutyl phosphate ethyl (meth)acrylate, and 2-benzoyloxyethyl (meth)acrylate, (meth)acrylonitrile, 2-hydroxyethyl (meth)acrylate, (meth)acrylic acid, and maleic acid.
Examples of the monomer include vinyl ether monomers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketone monomers such as vinyl methyl ketone, vinyl ethyl ketone and vinyl isopropenyl ketone; and polyolefin monomers such as ethylene, propylene and butadiene.

The styrene acrylic resin may contain a polyfunctional polymerizable monomer as required. Examples of the polyfunctional polymerizable monomer include diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 2,2'-bis(4-((meth)acryloxydiethoxy)phenyl)propane, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, divinylbenzene, divinylnaphthalene, and divinyl ether.
In order to control the degree of polymerization, it is also possible to further add a known chain transfer agent and polymerization inhibitor.

Examples of the polymerization initiator for obtaining the styrene-acrylic resin include organic peroxide-based initiators and azo-based polymerization initiators.
Examples of the organic peroxide initiator include benzoyl peroxide, lauroyl peroxide, di-α-cumyl peroxide, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, bis(4-t-butylcyclohexyl)peroxydicarbonate, 1,1-bis(t-butylperoxy)cyclododecane, t-butylperoxymaleic acid, bis(t-butylperoxy)isophthalate, methyl ethyl ketone peroxide, tert-butylperoxy-2-ethylhexanoate, diisopropyl peroxycarbonate, cumene hydroperoxide, 2,4-dichlorobenzoyl peroxide, and tert-butylperoxypivalate.
Examples of the azo polymerization initiator include 2,2'-azobis-(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, azobismethylbutyronitrile, and 2,2'-azobis-(methyl isobutyrate).

Furthermore, a redox initiator, which is a combination of an oxidizing substance and a reducing substance, can also be used as the polymerization initiator.
Oxidizing substances include inorganic peroxides such as hydrogen peroxide, persulfates (sodium, potassium and ammonium salts) and oxidizing metal salts such as tetravalent cerium salts.
Examples of reducing substances include reducing metal salts (divalent iron salts, monovalent copper salts, and trivalent chromium salts), ammonia, lower amines (amines having from 1 to 6 carbon atoms, such as methylamine and ethylamine), amino compounds such as hydroxylamine, reducing sulfur compounds such as sodium thiosulfate, sodium hydrosulfite, sodium hydrogensulfite, sodium sulfite, and sodium formaldehyde sulfoxylate, lower alcohols (having from 1 to 6 carbon atoms), ascorbic acid or a salt thereof, and lower aldehydes (having from 1 to 6 carbon atoms).

Polymerization initiators are selected with reference to their 10-hour half-life temperatures and are used alone or in combination. The amount of polymerization initiator added varies depending on the desired degree of polymerization, but generally 0.5 to 20.0 parts by mass are added per 100.0 parts by mass of polymerizable monomer.

<Release Agent>
In the toner of the present invention, a known wax may be used as a releasing agent.
Specific examples include petroleum waxes and derivatives thereof, such as paraffin wax, microcrystalline wax, and petroleum waxes represented by petrolactam, montan wax and derivatives thereof, hydrocarbon waxes produced by the Fischer-Tropsch process and derivatives thereof, polyolefin waxes and derivatives thereof, such as polyethylene, natural waxes and derivatives thereof, such as carnauba wax and candelilla wax, and derivatives thereof. Derivatives also include oxides, block copolymers with vinyl monomers, and graft modified products.

Other examples include alcohols such as higher aliphatic alcohols, fatty acids such as stearic acid and palmitic acid or their acid amides, esters, ketones, hydrogenated castor oil and its derivatives, vegetable waxes, and animal waxes. These can be used alone or in combination.

Among these, polyolefins, Fischer-Tropsch hydrocarbon waxes, and petroleum waxes are preferred because their use tends to improve developability and transferability. In addition, antioxidants may be added to these waxes to the extent that the toner does not affect the effects of the present invention.

In terms of phase separation with respect to the binder resin or crystallization temperature, preferred examples include higher fatty acid esters such as behenyl behenate and dibehenyl sebacate.

When a release agent is used, its content is preferably 1.0 part by mass or more and 30.0 parts by mass or less per 100.0 parts by mass of the binder resin.

The melting point of the release agent is preferably 30°C or higher and 120°C or lower, and more preferably 60°C or higher and 100°C or lower.

By using a release agent that exhibits the thermal properties described above, the release effect is efficiently achieved and a wider fixing area is ensured.

<Plasticizer>
In the toner of the present invention, it is preferable to use a crystalline plasticizer in order to improve the sharp melting property. The plasticizer is not particularly limited, and any of the known plasticizers used in toners such as those described below can be used.

Specifically, esters of monohydric alcohols and aliphatic carboxylic acids such as behenyl behenate, stearyl stearate, and palmityl palmitate, esters of monohydric carboxylic acids and aliphatic alcohols, esters of dihydric alcohols and aliphatic carboxylic acids such as ethylene glycol distearate, dibehenyl sebacate, and hexanediol dibehenate, esters of dihydric carboxylic acids and aliphatic alcohols, esters of trihydric alcohols and aliphatic carboxylic acids such as glycerin tribehenate, esters of trihydric carboxylic acids and aliphatic alcohols, pentaerythritol tetrastearate, pentaerythritol tetrastearate, Examples of the ester include esters of tetrahydric alcohols and aliphatic carboxylic acids such as trapalmitate, esters of tetrahydric carboxylic acids and aliphatic alcohols, esters of hexahydric alcohols and aliphatic carboxylic acids such as dipentaerythritol hexastearate and dipentaerythritol hexapalmitate, esters of hexahydric carboxylic acids and aliphatic alcohols, esters of polyhydric alcohols and aliphatic carboxylic acids such as polyglycerin behenate, esters of polyhydric carboxylic acids and aliphatic alcohols, and natural ester waxes such as carnauba wax and rice wax, which can be used alone or in combination.

<Coloring Agent>
The toner particles may contain a colorant. Known pigments and dyes can be used as the colorant. Pigments are preferred as the colorant because they have excellent weather resistance.

Examples of cyan colorants include copper phthalocyanine compounds and derivatives thereof, anthraquinone compounds, and basic dye lake compounds.
Specific examples include C.I. Pigment Blue 1, C.I. Pigment Blue 7, C.I. Pigment Blue 15, C.I. Pigment Blue 15:1, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I. Pigment Blue 60, C.I. Pigment Blue 62 and C.I. Pigment Blue 66.

Examples of magenta colorants include condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds.
Specific examples include the following: 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 Violet 19, C.I. Pigment Red 23, C.I. Pigment Red 48:2, C.I. Pigment Red 48:3, C.I. Pigment Red 48:4, C.I. Pigment Red 57:1, C.I. Pigment Red 81:1, C.I. Pigment Red 122, C.I. Pigment Red 144, C.I. Pigment Red 146, C.I. Pigment Red 150, C.I. Pigment Red 166, C.I. C.I. Pigment Red 169, C.I. Pigment Red 177, C.I. Pigment Red 184, C.I. Pigment Red 185, C.I. Pigment Red 202, C.I. Pigment Red 206, C.I. Pigment Red 220, C.I. Pigment Red 221 and C.I. Pigment Red 254, and C.I. Pigment Violet 19.

Examples of yellow colorants include condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and allylamide compounds.
Specific examples include the following: 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 62, C.I. Pigment Yellow 74, C.I. Pigment Yellow 83, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 95, C.I. Pigment Yellow 97, C.I. Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 111, C.I. Pigment Yellow 120, C.I. Pigment Yellow 127, C.I. Pigment Yellow 128, C.I. Pigment Yellow 129, C.I. Pigment Yellow 147, C.I. Pigment Yellow 151, C.I. Pigment Yellow 154, C.I. Pigment Yellow 155, C.I. Pigment Yellow 168, C.I. Pigment Yellow 174, C.I. Pigment Yellow 175, C.I. Pigment Yellow 176, C.I. Pigment Yellow 180, C.I. Pigment Yellow 181, C.I. Pigment Yellow 185, C.I. Pigment Yellow 191 and C.I. Pigment Yellow 194.

Black colorants include carbon black and those toned to black using the above-mentioned yellow, magenta, and cyan colorants.

These colorants can be used alone or in mixtures, or further in the form of a solid solution.
When a colorant is used, it is preferable to use the colorant in an amount of 1.0 part by mass or more and 20.0 parts by mass or less per 100.0 parts by mass of the binder resin.

<Charge control agent and charge control resin>
The toner particles may contain a charge control agent or resin.
As the charge control agent, a known one can be used, and a charge control agent that has a high triboelectric charging speed and can stably maintain a constant triboelectric charge amount is particularly preferred. Furthermore, when the toner particles are produced by a suspension polymerization method, a charge control agent that has low polymerization inhibition properties and is substantially free of solubilized matter in an aqueous medium is particularly preferred.

Examples of substances that control the toner to be negatively charged include monoazo metal compounds, acetylacetone metal compounds, aromatic oxycarboxylic acids, aromatic dicarboxylic acids, oxycarboxylic and dicarboxylic acid-based metal compounds, aromatic oxycarboxylic acids, aromatic mono- and polycarboxylic acids and their metal salts, anhydrides, esters, phenol derivatives such as bisphenol, urea derivatives, metal-containing salicylic acid compounds, metal-containing naphthoic acid compounds, boron compounds, quaternary ammonium salts, calixarenes, and charge control resins.

The charge control resin may be a polymer or copolymer having a structure of sulfonic acid, a sulfonate salt, or a sulfonate ester. As a polymer having a structure of sulfonic acid, a sulfonate salt, or a sulfonate ester, the following polymers are particularly preferred. That is, a polymer containing 2% by mass or more of a sulfonate group-containing acrylamide monomer or a sulfonate group-containing methacrylamide monomer in a copolymerization ratio is preferred, and a polymer containing 5% by mass or more is more preferred.

The charge control resin preferably has a glass transition temperature (Tg) of 35° C. or more and 90° C. or less, a peak molecular weight (Mp) of 10,000 or more and 30,000 or less, and a weight average molecular weight (Mw) of 25,000 or more and 50,000 or less. When used, it can impart preferable triboelectric charging properties without affecting the thermal properties required for the toner particles. Furthermore, since the charge control resin contains a sulfonic acid structure, for example, the dispersibility of the charge control resin itself in the polymerizable monomer composition and the dispersibility of colorants and the like are improved, and the coloring power, transparency, and triboelectric charging properties can be further improved.
These charge control agents or charge control resins may be added alone or in combination of two or more kinds.

When a charge control agent or charge control resin is used, the amount added is preferably 0.01 parts by weight or more and 20.0 parts by weight or less, and more preferably 0.5 parts by weight or more and 10.0 parts by weight or less, per 100.0 parts by weight of the binder resin.

<External Additives>
The toner contains external additive A and may also contain other external additives.
The external additive A has a major axis (maximum diameter) of 100 nm or more and 3000 nm or less, preferably 500 nm or more and 2000 nm or less, and more preferably 800 nm or more and 1700 nm or less, an aspect ratio of 5.0 or more, preferably 6.0 or more, and more preferably 8.0 or more, and a specific resistance of 1.0×10 ⁵ Ω·cm or more and 1.0×10 ⁸ Ω·cm or less, and preferably 1.0×10 ⁶ Ω·cm or more and 5.0×10 ⁷ or less. The material of the external additive A is not limited as long as it satisfies the above-mentioned physical property ranges, but it is preferable that the external additive A is an inorganic particle such as titanium oxide particles or aluminum oxide particles.

It is particularly preferable that the external additive A contains titanium oxide particles. When the external additive A contains titanium oxide particles, the resistance value can be easily set within a desired range, and half-tone unevenness after durability testing can be effectively suppressed.
It is more preferable that the external additive A contains rutile-type titanium oxide particles. When the external additive A contains rutile-type titanium oxide particles, the charge injected from the surface of the electrophotographic photoreceptor is not leaked to the outside, and the toner can be efficiently charged.

The external additive A can be obtained, for example, by adding an aqueous NaOH solution to metatitanic acid, and then heating, cooling, neutralizing, etc. to produce fine rutile-type titanium oxide particles, which are then mixed, fired, and washed appropriately using a ball mill or the like.
Furthermore, examples of external additives other than external additive A include particulate silica particles, vinyl resins, polyester resins, silicone resins, titanium oxide particles, and aluminum oxide particles that do not have the above aspect ratio.

<Toner Manufacturing Method>
The toner of the present invention is not particularly limited in its manufacturing method, and may be manufactured by a known method such as a pulverization method, a suspension polymerization method, a dissolution suspension method, an emulsion aggregation method, or a dispersion polymerization method, and is preferably manufactured by the emulsion aggregation method. The following mainly describes the emulsion aggregation method.
The 50% particle size (D50) based on volume distribution of the binder resin particles in the aqueous dispersion of resin particles is preferably 0.05 μm or more and 1.0 μm or less, and more preferably 0.05 μm or more and 0.4 μm or less. By adjusting the 50% particle size (D50) based on volume distribution to the above range, it becomes easy to obtain toner particles with a volume average particle size of 3 μm or more and 10 μm or less, which is an appropriate size for toner particles.
The 50% particle size (D50) based on volume distribution can be measured using a dynamic light scattering particle size distribution analyzer Nanotrac UPA-EX150 (manufactured by Nikkiso Co., Ltd.).

<Colorant particle dispersion>
If necessary, a colorant particle dispersion is used. The colorant particle dispersion can be prepared by the following known methods, but is not limited to these methods.
The colorant particle dispersion can be prepared by mixing the colorant, the aqueous medium, and the dispersant with a known mixer such as a stirrer, an emulsifier, or a disperser. The dispersant used here can be a known one such as a surfactant or a polymer dispersant.

Although both the surfactant and the polymer dispersant can be removed in the washing step described below, from the viewpoint of washing efficiency, the surfactant is preferably used as the dispersant.
Examples of the surfactant include anionic surfactants such as sulfate ester salts, sulfonate salts, phosphate esters, and soap-based surfactants, cationic surfactants such as amine salts and quaternary ammonium salts, and nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyhydric alcohols.
Among these, nonionic surfactants or anionic surfactants are preferred. A nonionic surfactant and an anionic surfactant may be used in combination. The surfactant may be used alone or in combination of two or more. When a surfactant is used, its concentration in the aqueous medium is preferably 0.5% by mass or more and 5% by mass or less.

The content of the colorant particles in the colorant particle dispersion is not particularly limited, but is preferably from 1% by mass to 30% by mass based on the total mass of the colorant particle dispersion.
From the viewpoint of dispersibility of the colorant in the toner finally obtained, the dispersed particle size of the colorant fine particles in the aqueous dispersion of the colorant is preferably 0.5 μm or less in terms of the 50% particle size (D50) based on volume distribution. For the same reason, it is preferable that the 90% particle size (D90) based on volume distribution is 2 μm or less. The dispersed particle size of the colorant fine particles dispersed in the aqueous medium can be measured with a dynamic light scattering particle size distribution meter (Nanotrac UPA-EX150, manufactured by Nikkiso).

Known mixers such as stirrers, emulsifiers, and dispersers used when dispersing a colorant in an aqueous medium include ultrasonic homogenizers, jet mills, pressure homogenizers, colloid mills, ball mills, sand mills, and paint shakers. These may be used alone or in combination.

<Release agent (aliphatic hydrocarbon compound) fine particle dispersion>
If necessary, a dispersion of releasing agent particles may be used. The dispersion of releasing agent particles can be prepared by the following known methods, but is not limited to these methods.
The release agent microparticle dispersion can be prepared by adding the release agent to an aqueous medium containing a surfactant, heating the mixture to above the melting point of the release agent, dispersing the mixture into particles using a homogenizer or pressure discharge type disperser having a strong shearing ability, and then cooling the mixture to below the melting point. An example of the homogenizer is the "Clearmix W Motion" manufactured by M Technique Co., Ltd. An example of the pressure discharge type disperser is the "Gorin Homogenizer" manufactured by Gorin Co., Ltd.

The particle size of the release agent microparticle dispersion in the aqueous dispersion of the release agent is preferably 50% particle size (D50) based on volume distribution of 0.03 μm to 1.0 μm, and more preferably 0.1 μm to 0.5 μm. It is also preferable that no coarse particles of 1 μm or more are present.

By having the dispersed particle size of the release agent microparticle dispersion within the above range, it is possible to have the release agent finely dispersed in the toner, maximizing the seepage effect during fixing and achieving good separation properties. The dispersed particle size of the release agent microparticle dispersion dispersed in the aqueous medium can be measured using a dynamic light scattering particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso).

<Mixing step>
In the mixing step, a mixture is prepared by mixing the resin particle dispersion with at least one of a release agent particle dispersion and a colorant particle dispersion, if necessary. This can be carried out using a known mixing device such as a homogenizer or a mixer.

<Step of forming aggregate particles (aggregation step)>
In the aggregating step, for example, the fine particles contained in the mixed liquid prepared in the mixing step are aggregated to form aggregates having a desired particle size. At this time, an aggregating agent is added and mixed, and at least one of heating and mechanical power is appropriately applied as necessary, so that aggregates in which the resin fine particles and at least one of the release agent fine particles and the colorant fine particles are aggregated as necessary can be formed.

Examples of the flocculant include organic flocculants such as quaternary salt cationic surfactants, polyethyleneimine, and the like, inorganic flocculants such as inorganic metal salts such as sodium sulfate, sodium nitrate, sodium chloride, calcium chloride, and calcium nitrate, inorganic ammonium salts such as ammonium sulfate, ammonium chloride, and ammonium nitrate, and divalent or higher metal complexes.
It is also possible to add an acid to lower the pH and cause soft flocculation, for example sulfuric acid or nitric acid.

The flocculant may be added in the form of either a dry powder or an aqueous solution in which it is dissolved in an aqueous medium. In order to induce uniform flocculation, it is preferable to add the flocculant in the form of an aqueous solution.
The addition and mixing of the aggregating agent is preferably carried out at a temperature equal to or lower than the glass transition temperature or melting point of the resin contained in the mixed liquid. By carrying out the mixing under this temperature condition, the aggregation proceeds relatively uniformly. The mixing of the aggregating agent into the mixed liquid can be carried out using a known mixing device such as a homogenizer or a mixer. In the aggregation process, aggregates of the toner particle size are formed in the aqueous medium. The volume average particle size of the aggregates produced in the aggregation process is preferably 3 μm or more and 10 μm or less. The volume average particle size can be measured using a particle size distribution analyzer (Coulter Multisizer III, manufactured by Coulter) by the Coulter method.

<Step of Obtaining Dispersion Liquid Containing Toner Particles (Fusion Step)>
In the coalescence step, first, the aggregation of the dispersion containing the aggregates obtained in the aggregation step is stopped under stirring in the same manner as in the aggregation step.
The aggregation is stopped by adding an aggregation stopper such as a base capable of adjusting the pH, a chelating compound, or an inorganic salt compound such as sodium chloride.
After the dispersion state of the aggregated particles in the dispersion liquid is stabilized by the action of the aggregation terminator, the dispersion liquid is heated to a temperature equal to or higher than the glass transition temperature or melting point of the binder resin to fuse the aggregated particles and adjust the particle size to a desired size. The 50% particle size (D50) based on the volume distribution of the toner particles is preferably 3 μm or more and 10 μm or less.

<Cooling process>
If necessary, in the cooling step, the temperature of the dispersion liquid containing the toner particles obtained in the fusion step can be cooled to a temperature lower than at least one of the crystallization temperature and the glass transition temperature of the binder resin. By cooling to a temperature lower than at least one of the crystallization temperature and the glass transition temperature, the occurrence of depressions on the toner surface can be suppressed, and the shape factors SF1 and SF2 can be set to 125 or less. When the cooling step is performed, the specific cooling rate is 0.5° C./sec or more, preferably 2° C./sec or more, and more preferably 4° C./sec or more.

<Post-treatment process>
In the toner manufacturing method of the present embodiment, post-treatment steps such as a washing step, a solid-liquid separation step, and a drying step may be further performed. By performing the post-treatment steps, for example, toner particles in a dry state can be obtained.

<External Addition Process>
In the external addition step, the toner particles obtained in the drying step are subjected to external addition treatment. Specifically, the above-mentioned external additive A and, if necessary, other external additives such as inorganic fine particles such as silica and resin fine particles such as vinyl resin, polyester resin, and silicone resin are added by applying a shear force in a dry state.

The configuration of the electrophotographic photoreceptor in the present invention will be described below.
The electrophotographic photoreceptor in the present invention has a conductive support, and a photosensitive layer and a surface protective layer formed on the conductive support in this order. Fig. 1 shows an electrophotographic photoreceptor having a laminated type photosensitive layer as an example of the electrophotographic photoreceptor. In Fig. 1, an undercoat layer 22, a charge generating layer 23, a charge transport layer 24, and a surface protective layer 25 are laminated on a support 21.

<Surface protective layer>
The surface protective layer may contain a polymer of a compound having a polymerizable functional group and a resin. Examples of the polymerizable functional group or structure include an isocyanate group, a blocked isocyanate group, a methylol group, an alkylated methylol group, an epoxy group, a metal alkoxide structure, a hydroxyl group, an amino group, a carboxyl group, a thiol group, a carboxylic anhydride structure, a carbon-carbon double bond, an alkoxysilyl group, and a silanol group. A monomer having a charge transporting ability may be used as the compound having a polymerizable functional group. The compound having a polymerizable functional group may have a charge transporting structure in addition to a chain polymerizable functional group.

Examples of the resin include polyester resin, acrylic resin, phenoxy resin, polycarbonate resin, polystyrene resin, phenol resin, melamine resin, and epoxy resin. Among them, polycarbonate resin, polyester resin, and acrylic resin are preferable. The surface protective layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of the reaction include thermal polymerization reaction, photopolymerization reaction, and radiation polymerization reaction. Examples of the polymerizable functional group possessed by the monomer having a polymerizable functional group include an acryloyl group and a methacryloyl group. A material having a charge transport function may be used as the monomer having a polymerizable functional group.

The surface protective layer can be formed by preparing a coating solution for the surface protective layer containing conductive particles, the above-mentioned materials, and a solvent, forming this coating film on the photosensitive layer, and drying and/or curing it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

The surface protective layer may contain additives such as antioxidants, UV absorbers, plasticizers, leveling agents, slippage agents, and abrasion resistance improvers. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

The average thickness of the surface protection layer is preferably 0.2 μm or more and 5 μm or less, and more preferably 0.5 μm or more and 3 μm or less.

The titanium oxide particles containing niobium atoms used as the conductive particles contained in the surface protective layer can be of various shapes, such as spherical, polyhedral, ellipsoidal, flaky, and needle-like. Among these, from the viewpoint of reducing image defects such as black spots, spherical, polyhedral, and ellipsoidal shapes are preferred. The titanium oxide particles containing niobium atoms preferably used in the present invention are more preferably spherical or polyhedral close to spherical.

The titanium oxide particles containing niobium atoms are preferably anatase or rutile titanium oxide particles, and more preferably titanium oxide particles having an anatase degree of nearly 100%. By using anatase titanium oxide, charge transfer in the surface protective layer becomes smooth, and the injection chargeability becomes good. The anatase titanium oxide particles having an anatase degree of nearly 100% used in one embodiment of the present invention can be produced by a known sulfuric acid method. That is, a solution containing titanium sulfate and titanyl sulfate is heated and hydrolyzed to produce a hydrous titanium dioxide slurry, and the titanium dioxide slurry is dehydrated and fired to obtain the anatase titanium oxide particles. The anatase titanium oxide particles used in one embodiment of the present invention preferably have an anatase degree of 90 to 100%. In addition, the intermediate layer containing anatase titanium oxide containing niobium atoms in this range achieves good and stable rectification, and the above-mentioned effects are well achieved.
Here, the degree of anatase is a value calculated by measuring the intensity IA of the strongest interference ray (plane index 101) of anatase and the intensity IR of the strongest interference ray (plane index 110) of rutile in powder X-ray diffraction of titanium oxide, and using the following formula:
Anatase degree (%)=100/(1+1.265×IR/IA)
To produce titanium oxide with an anatase degree in the range of 90% to 100%, a solution containing titanium sulfate and titanyl sulfate as titanium compounds is heated and hydrolyzed in the production of titanium oxide. This method produces an anatase type titanium oxide with an anatase degree of nearly 100%. Also, if an aqueous titanium tetrachloride solution is neutralized with an alkali, an anatase type titanium oxide with a high anatase degree can be obtained.

The conductive particles contained in the surface protective layer of the electrophotographic photoreceptor in the present invention are more preferably anatase type titanium oxide particles with niobium atoms unevenly distributed near the surface. By using anatase type titanium oxide particles as the core material and coating the surface with titanium oxide containing niobium atoms, charges are easily injected from a charging member in contact with the surface of the conductive particles and are easily moved within the surface protective layer. In addition, a decrease in resistivity that would cause image deletion is suppressed.

The conductive particles contained in the surface protective layer of the electrophotographic photoreceptor in the present invention preferably have a number-average particle diameter of 40 nm or more and 150 nm or less. If the number-average particle diameter of the conductive particles is less than 40 nm, the specific surface area of the conductive particles increases, and moisture adsorption increases near the conductive particles on the surface of the surface protective layer, reducing the resistance of the surface of the surface protective layer and making image deletion more likely. If the diameter exceeds 150 nm, the dispersibility of the particles in the surface protective layer decreases and the area of the interface with the binder resin decreases, increasing the resistance at the interface and reducing the injection charging property due to the movement of charges.

<Support>
In the present invention, the support is preferably a conductive support having electrical conductivity. The shape of the support may be a cylinder, a belt, a sheet, or the like. Among them, a cylindrical support is preferable. The surface of the support may be subjected to electrochemical treatment such as anodization, blasting, cutting, or the like.
The support is preferably made of a metal, a resin, or a glass.
Examples of the metal include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among these, an aluminum support using aluminum is preferred.
In addition, it is preferable to impart electrical conductivity to the resin or glass by a process such as mixing with or coating with an electrically conductive material.

<Conductive Layer>
In the electrophotographic photoreceptor used in the present invention, a conductive layer may be provided on the support. By providing the conductive layer, scratches and unevenness on the support surface can be concealed and light reflection on the support surface can be controlled. The conductive layer preferably contains conductive particles and a resin.

Examples of the material of the conductive particles contained in the conductive layer include metal oxides, metals, and carbon black.
Examples of metal oxides include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, etc. Examples of metals include aluminum, nickel, iron, nichrome, copper, zinc, silver, etc.
Among these, it is preferable to use metal oxides as the conductive particles, and it is particularly preferable to use titanium oxide, tin oxide, or zinc oxide.
When a metal oxide is used as the conductive particles, the surface of the metal oxide may be treated with a silane coupling agent or the like, or the metal oxide may be doped with an element such as phosphorus or aluminum or an oxide thereof.
The conductive particles are preferably titanium oxide particles, barium sulfate particles, or zinc oxide particles, and preferably have niobium atoms distributed on or near the surface. When a metal oxide is used as the conductive particles, the number-average particle size is preferably 1 nm or more and 500 nm or less, and more preferably 3 nm or more and 400 nm or less.

Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, and alkyd resin.
The conductive layer may further contain silicone oil, resin particles, a masking agent such as titanium oxide, and the like.

The conductive layer can be formed by preparing a coating solution for the conductive layer containing the above-mentioned materials and solvent, forming this coating film on a support, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Examples of dispersion methods for dispersing the conductive particles in the coating solution for the conductive layer include methods using a paint shaker, a sand mill, a ball mill, and a liquid collision type high-speed disperser.

If a conductive layer is present, its average thickness is preferably 1 μm or more and 40 μm or less, and particularly preferably 3 μm or more and 30 μm or less.

<Undercoat layer>
In the present invention, an undercoat layer may be provided on the support or the conductive layer. By providing an undercoat layer, the adhesion between layers can be improved and a charge injection blocking function can be imparted.

The undercoat layer preferably contains a resin. Alternatively, the undercoat layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group.
Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, polyvinyl phenol resin, alkyd resin, polyvinyl alcohol resin, polyethylene oxide resin, polypropylene oxide resin, polyamide resin, polyamic acid resin, polyimide resin, polyamideimide resin, and cellulose resin.
Examples of the polymerizable functional group or structure possessed by the monomer having a polymerizable functional group include an isocyanate group, a blocked isocyanate group, a methylol group, an alkylated methylol group, an epoxy group, a metal alkoxide structure, a hydroxyl group, an amino group, a carboxyl group, a thiol group, a carboxylic anhydride structure, and a carbon-carbon double bond.

For the purpose of improving electrical properties, the undercoat layer may further contain an electron transporting material, a metal oxide, a metal, a conductive polymer, etc. Among these, it is preferable to use an electron transporting material or a metal oxide.
Examples of the electron transport substance contained in the undercoat layer include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, aryl halide compounds, silole compounds, boron-containing compounds, etc. An electron transport substance having a polymerizable functional group may be used as the electron transport substance, and the undercoat layer may be formed as a cured film by copolymerizing it with the monomer having the above-mentioned polymerizable functional group.
Examples of metal oxides include indium tin oxide, tin oxide, indium oxide, titanium oxide, zinc oxide, aluminum oxide, silicon dioxide, etc. Examples of metals include gold, silver, aluminum, etc.

The metal oxide particles contained in the undercoat layer may be surface-treated using a surface treatment agent such as a silane coupling agent. The method for surface-treating the metal oxide particles may be a general method, such as a dry method or a wet method.
In the dry method, metal oxide particles are stirred in a mixer capable of high-speed stirring, such as a Henschel mixer, while an alcohol aqueous solution, an organic solvent solution, or an aqueous solution containing a surface treatment agent is added to the metal oxide particles to uniformly disperse them, and then the particles are dried.
In the wet method, the metal oxide particles and the surface treatment agent are stirred in a solvent or dispersed in a sand mill using glass beads or the like, and the solvent is removed by filtration or distillation under reduced pressure. After the solvent is removed, it is preferable to further perform baking at 100° C. or higher.

The undercoat layer may further contain additives, such as metal powders such as aluminum, conductive materials such as carbon black, charge transport materials, metal chelate compounds, and organometallic compounds.

Examples of charge transport substances contained in the undercoat layer include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, aryl halide compounds, silole compounds, and boron-containing compounds. A charge transport substance having a polymerizable functional group may be used as the charge transport substance, and the undercoat layer may be formed as a cured film by copolymerizing it with the monomer having the above-mentioned polymerizable functional group.

The undercoat layer can be formed by preparing a coating solution for the undercoat layer containing the above-mentioned materials and a solvent, forming a coating film of this on a support or a conductive layer, and drying and/or curing the coating film.
Examples of the solvent used in the coating solution for the undercoat layer include organic solvents such as alcohols, sulfoxides, ketones, ethers, esters, halogenated aliphatic hydrocarbons, aromatic compounds, etc. In the present invention, it is preferable to use alcohol-based and ketone-based solvents.
Examples of a dispersion method for preparing a coating solution for the undercoat layer include methods using a homogenizer, an ultrasonic disperser, a ball mill, a sand mill, a roll mill, a vibration mill, an attritor, and a liquid collision type high-speed disperser.

If an undercoat layer is provided, its average thickness is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.1 μm or more and 5 μm or less.

<Photosensitive layer>
The photosensitive layer of the electrophotographic photoreceptor is mainly classified into (1) a laminated type photosensitive layer and (2) a single-layer type photosensitive layer, and either of them may be used. (1) The laminated type photosensitive layer is a photosensitive layer having a charge generating layer containing a charge generating material and a charge transport layer containing a charge transport material. (2) The single-layer type photosensitive layer is a photosensitive layer containing both a charge generating material and a charge transport material.

(1) Multi-Layer Photosensitive Layer The multi-layer photosensitive layer has a charge generating layer and a charge transport layer.

(1-1) Charge Generation Layer The charge generation layer preferably contains a charge generation material and a resin.

Examples of the charge generating material include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Among phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred.
The content of the charge generating material in the charge generating layer is preferably from 40% by weight to 85% by weight, and more preferably from 60% by weight to 80% by weight, based on the total weight of the charge generating layer.

Examples of resins include polyester resin, polycarbonate resin, polyvinyl acetal resin, polyvinyl butyral resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, polyvinyl alcohol resin, cellulose resin, polystyrene resin, polyvinyl acetate resin, polyvinyl chloride resin, etc. Among these, polyvinyl butyral resin is more preferable.

The charge generating layer may further contain additives such as antioxidants and ultraviolet absorbers. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, and benzophenone compounds.

The charge generation layer can be formed by preparing a coating solution for the charge generation layer containing the above-mentioned materials and solvent, forming this coating film on a lower layer such as an undercoat layer, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

The average thickness of the charge generating layer is preferably 0.1 μm or more and 1 μm or less, and more preferably 0.15 μm or more and 0.4 μm or less.

(1-2) Charge Transport Layer The charge transport layer preferably contains a charge transport material and a resin.

Examples of the charge transport material contained in the charge transport layer include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, resins having groups derived from these substances, etc. Among these, triarylamine compounds and benzidine compounds are preferred.
The content of the charge transport material in the charge transport layer is preferably from 25% by weight to 70% by weight, and more preferably from 30% by weight to 55% by weight, based on the total weight of the charge transport layer.

Examples of the resin include polyester resin, polycarbonate resin, acrylic resin, polystyrene resin, etc. Among these, polycarbonate resin and polyester resin are preferable. As the polyester resin, polyarylate resin is particularly preferable.
The content ratio (mass ratio) of the charge transport material to the resin is preferably from 4:10 to 20:10, and more preferably from 5:10 to 12:10.

The charge transport layer may also contain additives such as antioxidants, UV absorbers, plasticizers, leveling agents, slippage agents, and abrasion resistance improvers. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

The charge transport layer can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned materials and solvent, forming this coating film on the charge generation layer, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Among these solvents, ether-based solvents and aromatic hydrocarbon-based solvents are preferred.

The average thickness of the charge transport layer is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, and particularly preferably 10 μm or more and 30 μm or less.

(2) Single-layer type photosensitive layer The single-layer type photosensitive layer can be formed by preparing a coating solution for the photosensitive layer containing a charge generating material, a charge transporting material, a resin and a solvent, forming this coating film on a lower layer such as an undercoat layer, and drying it. The charge generating material, charge transporting material and resin contained in the single-layer type photosensitive layer are the same as those in the above "(1) laminated type photosensitive layer".

[Process Cartridge]
The process cartridge of the present invention integrally supports the electrophotographic photosensitive member and developing means described above, and may further include charging means, transfer means, and cleaning means. The process cartridge of the present invention is characterized in that it is detachably mountable to the main body of an electrophotographic image forming apparatus. The main body of an electrophotographic image forming apparatus refers to the parts of the electrophotographic image forming apparatus other than the process cartridge.
Furthermore, as one embodiment, the present invention provides an electrophotographic image forming apparatus including a process cartridge, the electrophotographic image forming apparatus being characterized by having the electrophotographic photosensitive member, charging means, exposure means, developing means and transfer means described above.

FIG. 2 shows an example of a schematic configuration of an electrophotographic image forming apparatus having a process cartridge equipped with an electrophotographic photosensitive member.
A cylindrical (drum-shaped) electrophotographic photoreceptor 1 rotates around an axis 2 in the direction of the arrow at a predetermined peripheral speed (process speed). The surface of the electrophotographic photoreceptor 1 is charged to a predetermined positive or negative potential by a charging means 3 during the rotation process. Although FIG. 2 shows a roller charging method using a roller-type charging member, a corona charging method, a proximity charging method, an injection charging method, or other charging methods may be adopted. Exposure light 4 is irradiated from an exposure means (not shown) onto the charged surface of the electrophotographic photoreceptor 1, and an electrostatic latent image corresponding to the target image information is formed. The exposure light 4 is light whose intensity is modulated in response to a time-series electric digital image signal of the target image information, and is output from an image exposure means such as a slit exposure or a laser beam scanning exposure. The electrostatic latent image formed on the surface of the electrophotographic photoreceptor 1 is developed (normal development or reversal development) by supplying toner contained in a toner container in the developing means 5, and a toner image is formed on the surface of the electrophotographic photoreceptor 1. The toner image formed on the surface of the electrophotographic photoreceptor 1 is transferred to a transfer material 7 by a transfer means 6. At this time, a bias voltage of a polarity opposite to that of the charge held by the toner is applied to the transfer means 6 from a bias power source (not shown). When the transfer material 7 is paper, the transfer material 7 is taken out from a paper feeder (not shown) and fed between the electrophotographic photoreceptor 1 and the transfer means 6 in synchronization with the rotation of the electrophotographic photoreceptor 1. The transfer material 7 onto which the toner image has been transferred from the electrophotographic photoreceptor 1 is separated from the surface of the electrophotographic photoreceptor and conveyed to a fixing means 8, where the toner image is fixed, and the image is printed out as an image formed product (print, copy) outside the electrophotographic image forming apparatus. The electrophotographic image forming apparatus may have a cleaning means 9 for removing deposits such as toner remaining on the surface of the electrophotographic photoreceptor after transfer. Alternatively, a so-called cleanerless system may be used in which the cleaning means 9 is not provided and the deposits are removed by the developing means 5 or the like. In the present invention, a process cartridge is formed by placing a plurality of components selected from the electrophotographic photoreceptor 1, the charging means 3, the developing means 5, and the cleaning means 9 in a container and supporting them integrally. The process cartridge can be configured to be detachably mounted to the main body of the electrophotographic image forming apparatus. For example, the process cartridge is configured as follows. At least one selected from the charging means 3, the developing means 5, and the cleaning means 9 is integrally supported together with the electrophotographic photosensitive member 1 to form a cartridge. This can be made into a process cartridge 11 that is detachably mounted to the main body of the electrophotographic image forming apparatus using a guide means 12 such as a rail of the main body of the electrophotographic image forming apparatus. The electrophotographic image forming apparatus may have a charge removing mechanism that removes charge from the surface of the electrophotographic photosensitive member 1 by a pre-exposure light 10 from a pre-exposure means (not shown). In addition, a guide means 12 such as a rail may be provided to attach and detach the process cartridge 11 to the main body of the electrophotographic image forming apparatus. The electrophotographic image forming apparatus in the present invention may have the electrophotographic photosensitive member 1, and at least one means selected from the group consisting of the charging means 3, the exposure means, the developing means 5, and the transfer means 6.
The process cartridge of the present invention can be used in laser beam printers, LED printers, copiers, facsimiles, and multifunction machines thereof.

Next, the following describes the measurement methods that have been used or are preferred for the physical properties of the external additive A, the surface protective layer of the photoreceptor, and the conductive particles contained in the surface protective layer. However, the following description is an example, and the measurement methods are not limited to this.

<Method of measuring major axis, minor axis and aspect ratio of external additive A>
The major axis (maximum diameter) and aspect ratio of external additive A are measured using a scanning electron microscope (for example, scanning electron microscope "S-4800" (product name; manufactured by Hitachi, Ltd.)). The toner to which external additive A has been added is observed in a field of view magnified up to 50,000 times, and the major axis and minor axis of 100 primary particles of external additive A selected at random are measured. Here, the aspect ratio of external additive A is calculated by the following formula. The observation magnification is appropriately adjusted depending on the size of external additive A.
Aspect ratio of external additive A = major axis of external additive A / minor axis of external additive A The major axis and minor axis were averaged over 100 particles and used as representative values. The aspect ratio was calculated by dividing the average major axis of the 100 particles by the average minor axis.

<Method for measuring the proportion of toner particles having the external additive A present on the surface>
The proportion of toner particles having external additive A present on the surface was measured using a scanning electron microscope (for example, scanning electron microscope "S-4800" (product name; manufactured by Hitachi, Ltd.)). 50 toner particles to which external additive A was added were randomly observed in a field of view magnified about 3000 times so that 10 to 30 toner particles could be observed in one field of view. The proportion of toner particles having one or more external additives A present among the 50 toner particles was calculated, and this was taken as the proportion of toner particles for which the presence of external additive A was confirmed on the surface. The observation magnification was appropriately adjusted depending on the size of the toner and the size of external additive A.

<Calculation of primary particle size of conductive particles>
First, the entire electrophotographic photoreceptor was immersed in methyl ethyl ketone (MEK) in a graduated cylinder and irradiated with ultrasonic waves to peel off the resin layer, and then the support of the electrophotographic photoreceptor was taken out. Next, the insoluble matter (photosensitive layer and surface protective layer containing conductive particles) that does not dissolve in MEK was filtered, the filtrate was collected, and dried in a vacuum dryer. Furthermore, the obtained solid was suspended in a mixed solvent of tetrahydrofuran (THF)/methylal at a volume ratio of 1:1, the insoluble matter was filtered, and the filtrate was collected and dried in a vacuum dryer. This operation obtained conductive particles and the resin of the surface protective layer. Furthermore, the filtrate was heated to 500°C in an electric furnace so that the solid was only the conductive particles, and the conductive particles were collected. In order to ensure the necessary amount of conductive particles for measurement, the same treatment was performed on multiple electrophotographic photoreceptors.
A part of the collected conductive particles was dispersed in isopropanol (IPA), and the dispersion was dropped onto a grid mesh with a support film (Cu150J, manufactured by JEOL Co., Ltd.), and the conductive particles were observed in the STEM mode of a scanning transmission electron microscope (JEM2800, manufactured by JEOL Co., Ltd.). The observation was performed at a magnification of 500,000 to 1.2 million times to easily calculate the particle diameter of the conductive particles, and STEM images of 100 conductive particles were taken. At this time, the acceleration voltage was set to 200 kV, the probe size was set to 1 nm, and the image size was set to 1024 x 1024 pixels. Using the obtained STEM image, the primary particle diameter was measured using the image processing software "Image-Pro Plus (manufactured by Media Cybernetics Co., Ltd.)". The measurement method was as follows. First, the straight line tool (Straight Line) on the toolbar was used to select the scale bar displayed at the bottom of the STEM image. In this state, when Set Scale is selected from the Analyze menu, a new window opens and the pixel distance of the selected line is entered in the Distance in Pixels field. The value of the scale bar (e.g., 100) is entered in the Known Distance field of the window, the unit of the scale bar (e.g., nm) is entered in the Unit of Measurement field, and the scale setting is completed by clicking OK. Next, a straight line is drawn using a straight line tool so as to be the maximum diameter of the conductive particles, and the particle diameter is calculated. This operation is performed for 100 conductive particles, and the number average value of the obtained value (maximum diameter) is taken as the primary particle diameter of the conductive particles.

<Calculation of Niobium Atom/Titanium Atom Concentration Ratio>
A sample piece of 5 mm square was cut from the photoreceptor, and cut to a thickness of 200 nm at a cutting speed of 0.6 mm/s using an ultrasonic ultramicrotome (Leica, UC7) to prepare a thin sample. This thin sample was observed at a magnification of 500,000 to 1.2 million times using a scanning transmission electron microscope (JEOL, JEM2800) in STEM mode connected to an EDS analyzer (energy dispersive X-ray analyzer).
Among the cross sections of the observed conductive particles, the cross sections of the conductive particles having a maximum diameter of approximately 0.9 to 1.1 times the primary particle diameter calculated above were visually selected. Then, the constituent elements of the cross sections of the selected conductive particles were collected using an EDS analyzer to prepare EDS mapping images. The collection and analysis of the spectra were performed using an NSS (Thermo Fischer Scientific). The collection conditions were an acceleration voltage of 200 kV, a probe size of 1.0 nm or 1.5 nm was appropriately selected so that the dead time was 15 to 30, the mapping resolution was 256 x 256, and the number of frames was 300. The EDS mapping images were obtained for 100 cross sections of the conductive particles.
By analyzing the EDS mapping image thus obtained, the ratio of the niobium atomic concentration (atomic %) to the titanium atomic concentration (atomic %) at the center of the particle and within 5% of the maximum diameter of the measured particle from the particle surface was calculated. Specifically, the following method was used. First, the "line extraction" button of the NSS was pressed, a straight line was drawn to represent the maximum diameter of the particle, and information on the atomic concentration (atomic %) on the straight line from one surface through the particle part to the other surface was obtained. If the maximum diameter of the particle obtained at this time is in the range of less than 0.9 times or more than 1.1 times the primary particle diameter calculated above, it is excluded from the subsequent analysis. (The analysis shown below was performed only on particles having a maximum diameter in the range of 0.9 times or more and less than 1.1 times the primary particle diameter.) Next, the niobium atomic concentration (atomic %) at the particle surface on both sides within 5% of the maximum diameter of the measured particle from the particle surface was read. In the same manner, the "titanium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface" was obtained. Next, using these values, the "concentration ratios of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" on both particle surfaces are calculated according to the following formula.
The concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface =
(Niobium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface)/(Titanium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface)
Of the two concentration ratios obtained, the smaller value is adopted as "the concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" in the present invention.
Also, the niobium atom concentration (atomic %) and titanium atom concentration (atomic %) are read at the position on the straight line that is the midpoint of the maximum diameter. Using these values, the "concentration ratio of niobium atoms to titanium atoms at the center of the particle" is calculated using the following formula.
Concentration ratio of niobium atoms to titanium atoms in the particle center =
(Niobium atom concentration (atomic %) at the center of the particle)/(Titanium atom concentration (atomic %) at the center of the particle)
The "concentration ratio calculated as niobium atomic concentration/titanium atomic concentration at a portion within 5% of the maximum diameter of the measured particle from the particle surface to the concentration ratio calculated as niobium atomic concentration/titanium atomic concentration at the particle center" is calculated by the following formula.
(concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface)/(concentration ratio of niobium atoms to titanium atoms in the particle center)

Next, four sample pieces of 5 mm square were cut out from the photoreceptor, and the surface protective layer was three-dimensionalized to 2 μm × 2 μm × 2 μm using Slice & View of FIB-SEM. The content of conductive particles in the total volume of the surface protective layer was calculated from the difference in contrast of Slice & View of FIB-SEM. In the following examples, the conditions of Slice & View were as follows.
Analytical sample processing: FIB method Processing and observation equipment: SII/Zeiss, NVision 40
Slice interval: 10 nm
Observation conditions Acceleration voltage: 1.0 kV
Sample tilt: 54°
WD: 5mm
Detector: BSE detector Aperture: 60 μm, high current
ABC:ON
Image resolution: 1.25 nm/pixel

The analysis area is 2 μm long x 2 μm wide, and the information for each cross section is integrated to obtain the volume V of the specimen per 2 μm long x 2 μm wide x 2 μm thick (8 μm3). The measurement environment was a temperature of 23° C. and a pressure of 1×10−4 Pa. As a processing and observation device, a Strata 400S (sample inclination 52°) manufactured by FEI can also be used. The information for each cross section was obtained by image analysis of the area of the specified conductive particles. The image analysis was performed using image processing software (Image-Pro Plus manufactured by Media Cybernetics).
Based on the obtained information, the volume V of the conductive particles in a volume of 2 μm × 2 μm × 2 μm (unit volume 8 μm ³ ) was obtained for each of the four sample pieces. Then, (V μm ³ /8 μm ³ × 100) was calculated. The average value of the (V μm ³ /8 μm ³ × 100) values for the four sample pieces was taken as the content [volume %] of the conductive particles in the surface protective layer relative to the total volume of the surface protective layer.
Furthermore, for all four sample pieces, the thickness of the surface protective layer was measured by processing up to the boundary between the surface protective layer and the lower layer, and the value was used to calculate the volume resistivity ρv in the <Method for measuring the volume resistivity of the protective layer of a photoconductor> described below.

<Measurement of Volume Resistivity of Surface Protective Layer>
A pA (picoampere) meter was used to measure the volume resistivity of the surface protective layer. First, a comb-shaped gold electrode with an interelectrode distance (D) of 180 μm and a length (L) of 5.9 cm was prepared by vapor deposition on a PET film, and a surface protective layer with a thickness (T1) of 2 μm was provided thereon. Next, a direct current (I) was measured when a direct current voltage (V) of 100 V was applied between the comb-shaped electrodes in an environment of a temperature of 23° C. and a humidity of 50% RH. The volume resistivity A (temperature 23° C./humidity 50% RH) was obtained by the following formula (7). The measurement results using this method are not described in the present specification.
Volume resistivity ρv (Ω cm) = V (V) × T1 (cm) × L (cm) / {I (A) × D (cm)} (7)

When it is difficult to identify the composition of the conductive particles and binder resin of the surface protective layer, the surface resistivity of the surface of the electrophotographic photoreceptor is measured and converted into volume resistivity. When measuring the volume resistivity of the surface protective layer in a state where it is applied to the surface of the photoreceptor, rather than the surface protective layer alone, it is preferable to measure the surface resistivity of the surface protective layer and convert it into volume resistivity. By measuring the direct current when a comb-shaped electrode is gold-deposited on the surface protective layer in a state where it is applied to the photoreceptor, and applying a constant direct current voltage, the surface resistivity ρs can be calculated from the following formula (8). The results shown in the following examples were obtained using this measurement method.
ρv = ρs × t (8)
(t is the thickness of the charge injection layer)

In this measurement, since a minute amount of current is measured, it is preferable to use a device capable of measuring minute current as the resistance measurement device. An example of the resistance measurement device is a picoammeter 4140B manufactured by Hewlett-Packard. It is preferable to select the interdigital electrodes to be used and the voltage to be applied so as to obtain an appropriate S/N ratio depending on the material and resistance value of the charge injection layer.
In the present invention, comb-shaped gold electrodes having an interelectrode distance (D) of 120 μm and a length (L) of 2.0 cm are formed on the surface of the electrophotographic photoreceptor by deposition. Next, a direct current (I) is measured when a direct current voltage (V) of 1000 V is applied between the comb-shaped electrodes in an environment of a temperature of 23° C. and a humidity of 50% RH, and the surface resistivity ρs (temperature 23° C./humidity 50% RH) is obtained.
Furthermore, the thickness T1 (cm) of the surface protective layer was measured by the above-mentioned <Analysis of Cross Section of Surface Protective Layer of Electrophotographic Photoreceptor>. The volume resistivity ρv (temperature 23° C./humidity 50% RH) was calculated by the above formula in which the surface resistivity ρs was multiplied by the thickness T1.

<Method for Analyzing Niobium Atom Content in Conductive Particles>
The niobium atom content in the conductive particles used in the present invention is measured as follows.
The conductive particles collected from the photoconductor in the above <Calculation of the primary particle diameter of the conductive particles> are pelletized by the press molding described below to prepare a sample. The prepared sample is measured with an X-ray fluorescence analyzer (XRF) and the niobium atom content of the entire conductive particles is quantified by the FP method.
Specifically, the amount of niobium pentoxide is determined and converted into the content of niobium atoms.
(i) Example of equipment used: X-ray fluorescence analyzer 3080 (Rigaku Denki Co., Ltd.)
(ii) Sample Preparation Samples are prepared using a sample press molding machine, MAEKAWA Testing Machine (manufactured by MFG Co, Ltd.) 0.5 g of conductive particles are placed in an aluminum ring (model number: 3481E1), and the load is set to 5.0 tons, and the sample is pressed for 1 minute to form a pellet.
(iii) Measurement conditions Measurement diameter: 10φ
Measurement potential, voltage: 50 kV, 50-70 mA
2θ angle 25.12°
Crystal plate LiF
Measurement time: 60 seconds

<Powder X-ray diffraction measurement of conductive particles>
A method for determining whether the conductive particles used in the electrophotographic photoreceptor of the present invention contain anatase type titanium oxide or rutile type titanium oxide will be described below.
Identification is performed using the inorganic materials database (AtomWork) of the National Institute for Materials Science (NIMS) from a chart obtained by powder X-ray diffraction using CuKα X-rays. The conductive particles contained in the protective layer of the electrophotographic photoreceptor of the present invention are subjected to the above-mentioned process (quantitative determination of niobium atoms contained in the conductive particles) as an example.
The powder X-ray diffraction measurement can be carried out under the following conditions.
Measuring equipment used: X-ray diffraction device RINT-TTRII (manufactured by Rigaku Denki Co., Ltd.)
X-ray tube: Cu
Tube voltage: 50 kV
Tube current: 300mA
Scanning method: 2θ/θ scanning Scanning speed: 4.0°/min
Sampling interval: 0.02°
Start angle (2θ): 5.0°
Stop angle (2θ): 40.0°
Attachment: Standard sample holder Filter: Not used Incident monochrome: Used Counter monochromator: Not used Divergence slit: Open Divergence vertical limit slit: 10.00 mm
Scattering slit: open Receiving slit: open Flat plate monochromator: Counter used: Scintillation counter

The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited in any way by the following examples, so long as it does not deviate from the gist of the invention. In the following description of the examples, when "parts" is simply written, it means parts by mass unless otherwise specified.

<Production Example of Toner Particle 1>
"Synthesis of polyester resin 1"
Bisphenol A ethylene oxide 2 mole adduct 9 mol Bisphenol A propylene oxide 2 mole adduct 95 mol Terephthalic acid 50 mol Fumaric acid 30 mol Dodecenyl succinic acid 25 mol The above monomers were charged into a flask equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a distillation column, and the temperature was raised to 195 ° C. in 1 hour, and it was confirmed that the reaction system was stirred uniformly. 1.0 part of tin distearate was added to 100 parts of these monomers. The temperature was raised from 195 ° C. to 250 ° C. over 5 hours while distilling off the water produced, and a dehydration condensation reaction was carried out at 250 ° C. for another 2 hours.
As a result, polyester resin 1 having a glass transition temperature of 60.2° C., an acid value of 16.8 mgKOH/g, a hydroxyl value of 28.2 mgKOH/g, a weight average molecular weight of 11,200 and a number average molecular weight of 4,100 was obtained.

"Synthesis of polyester resin 2"
Bisphenol A-ethylene oxide 2-mol adduct 48 mol parts Bisphenol A-propylene oxide 2-mol adduct 48 mol parts Terephthalic acid 65 mol parts Dodecenyl succinic acid 30 mol parts The above monomers were charged into a flask equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a rectification column, and the temperature was raised to 195 ° C. in 1 hour, and it was confirmed that the reaction system was uniformly stirred. 0.7 parts of tin distearate were charged per 100 parts of these monomers. The temperature was raised from 195 ° C. to 240 ° C. over 5 hours while distilling off the water produced, and a dehydration condensation reaction was carried out at 240 ° C. for another 2 hours. Next, the temperature was lowered to 190 ° C., and 5 mol parts of trimellitic anhydride were gradually charged, and the reaction was continued at 190 ° C. for 1 hour.
As a result, polyester resin 2 having a glass transition temperature of 55.2° C., an acid value of 14.3 mgKOH/g, a hydroxyl value of 24.1 mgKOH/g, a weight average molecular weight of 43,600 and a number average molecular weight of 6,200 was obtained.

"Preparation of Resin Particle Dispersion 1"
Polyester resin 1 100 parts Methyl ethyl ketone 50 parts Isopropyl alcohol 20 parts Methyl ethyl ketone and isopropyl alcohol were added to the container. Then, the above materials were gradually added, stirred, and completely dissolved to obtain a polyester resin 1 solution. The container containing this polyester resin 1 solution was set to 65°C, and while stirring, 10% ammonia aqueous solution was gradually dropped to a total of 5 parts, and 230 parts of ion-exchanged water was gradually dropped at a rate of 10 ml/min to cause phase inversion emulsification. The pressure was further reduced with an evaporator to remove the solvent, and a resin particle dispersion 1 of polyester resin 1 was obtained. The volume average particle size of this resin particle was 135 nm. In addition, the resin particle solid content was adjusted to 20% with ion-exchanged water.

"Preparation of Resin Particle Dispersion 2"
Polyester resin 2 100 parts Methyl ethyl ketone 50 parts Isopropyl alcohol 20 parts Methyl ethyl ketone and isopropyl alcohol were added to the container. Then, the above materials were gradually added, stirred, and completely dissolved to obtain a polyester resin 2 solution. The container containing this polyester resin 2 solution was set to 40°C, and while stirring, 10% ammonia aqueous solution was gradually dropped to a total of 3.5 parts, and 230 parts of ion-exchanged water were gradually dropped at a rate of 10 ml/min to cause phase inversion emulsification. The pressure was further reduced to remove the solvent, and a resin particle dispersion 2 of polyester resin 2 was obtained. The volume average particle size of the resin particles was 155 nm. The resin particle solid content was adjusted to 20% with ion-exchanged water.

"Preparation of colorant particle dispersion"
Copper phthalocyanine (pigment blue 15:3) 45 parts Ionic surfactant Neogen RK (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 5 parts Ion-exchanged water 190 parts The above was mixed and dispersed with a homogenizer for 10 minutes, and then dispersed with an ultimizer at a pressure of 250 MPa for 20 minutes to obtain a colorant particle dispersion liquid with a volume average particle size of 120 nm and a solid content of 20%. The homogenizer used was an Ultra Turrax manufactured by IKA. The ultimizer used was a counter-impingement type wet grinder manufactured by Sugino Machine Co., Ltd.

"Preparation of release agent particle dispersion"
Release agent (hydrocarbon wax, melting point 79° C.) 15 parts Ionic surfactant NEOGEN RK (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 2 parts Ion-exchanged water 240 parts The above was heated to 100° C. and thoroughly dispersed using an Ultra-Turrax T50 manufactured by IKA. The mixture was then heated to 115° C. using a pressure discharge type Gaulin homogenizer and subjected to a dispersion treatment for 1 hour, thereby obtaining a release agent particle dispersion having a volume average particle size of 160 nm and a solid content of 20%.

"Production of toner particles 1"
Resin particle dispersion 1 500 parts Resin particle dispersion 2 400 parts Colorant particle dispersion 50 parts Release agent particle dispersion 80 parts First, as the core formation process, the above materials were put into a round stainless steel flask and mixed. Then, using a homogenizer Ultra Turrax T50 (manufactured by IKA), the mixture was dispersed at 5000 r/min for 10 minutes. After adding a 1.0% nitric acid aqueous solution and adjusting the pH to 3.0, the mixture was heated to 58°C in a heating water bath using a stirring blade while appropriately adjusting the rotation speed so that the mixture was stirred. The volume average particle size of the formed aggregated particles was appropriately confirmed using a Coulter Multisizer III, and when aggregated particles (cores) of 5.0 μm were formed, the following materials were put in as the shell formation process and further stirred for 1 hour to form a shell.
Resin particle dispersion 1 40 parts Ion-exchanged water 300 parts 10.0% by mass borax aqueous solution 19 parts (borax; sodium tetraborate decahydrate, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
Thereafter, the pH was adjusted to 9.0 using a 5% aqueous sodium hydroxide solution, and the mixture was heated to 89° C. while continuing to stir.
When the desired surface shape was obtained, the heating was stopped, the mixture was cooled to 25° C., filtered and separated into solid and liquid, and then washed with ion-exchanged water. After washing, the mixture was dried using a vacuum dryer to obtain toner particles 1. The obtained toner particles 1 had a boron-derived fluorescent X-ray intensity of 0.15 and a weight average particle size of 6.5 μm.

"Production of toner particles 2"
Resin particle dispersion 1 500 parts Resin particle dispersion 2 400 parts Colorant particle dispersion 50 parts Release agent particle dispersion 80 parts First, as the core formation process, the above materials were put into a round stainless steel flask and mixed. Then, using a homogenizer Ultra Turrax T50 (manufactured by IKA), the mixture was dispersed at 5000 r/min for 10 minutes. After adding a 1.0% nitric acid aqueous solution and adjusting the pH to 3.0, the mixture was heated to 58°C in a heating water bath using a stirring blade while appropriately adjusting the rotation speed so that the mixture was stirred. The volume average particle size of the formed aggregated particles was appropriately confirmed using a Coulter Multisizer III, and when aggregated particles (cores) of 5.0 μm were formed, the following materials were put in as the shell formation process and further stirred for 1 hour to form a shell.
Resin particle dispersion 1 40 parts Ion-exchanged water 300 parts Thereafter, the pH was adjusted to 9.0 using a 5% aqueous sodium hydroxide solution, and the mixture was heated to 89° C. while continuing to stir.
When the desired surface shape was obtained, the heating was stopped, the mixture was cooled to 25° C., filtered and separated into solid and liquid, and then washed with ion-exchanged water. After washing, the mixture was dried using a vacuum dryer to obtain toner particles 2. The weight average particle size of the obtained toner particles 2 was 6.6 μm.

<Production Example of External Additive 1>
Additive 1, which is additive A, was produced as follows. Metatitanic acid obtained by the sulfuric acid method was added with 50%-NaOH aqueous solution in an amount of 4 times the molar amount of TiO ₂ as NaOH, and heated at 95°C for 2 hours. After thoroughly washing this, 31%-HCl was added so that HCl/TiO ₂ = 0.26, and heated at the boiling point for 1 hour. After cooling, it was neutralized to pH 7 with 1 mol/L-NaOH, washed and dried to produce fine rutile-type titanium oxide. The specific surface area of the obtained fine rutile-type titanium oxide was 115 g/m ^2. To 100 parts of this fine rutile-type titanium oxide, 100 parts of NaCl and 25 parts of Na ₂ P ₂ O _{7.10H 2} O were added, mixed in a vibration ball mill for 1 hour, and the mixture was fired in an electric furnace at 850°C for 2 hours. The obtained calcined product was placed in pure water and heated at 80° C. for 6 hours, and then washed to remove soluble salts. All particles obtained after drying were fine needle-shaped titanium oxide particles having a minor axis in the range of 0.03 to 0.07 μm and a major axis in the range of 0.4 to 0.8 μm. The physical properties of the external additive 1 thus obtained are shown in Table 1.

<Production Examples of External Additives 2 to 14>
External additives 2 to 14, which are external additives A, were obtained in the same manner as in the manufacturing example of external additive 1, except that the conditions were changed to those in Table 1. The physical properties of the obtained external additives 2 to 14 are shown in Table 1. For the specific external additives, the treatment agents shown in Table 1 were used.

<Production Example of External Additive 15>
External additive 15, which is an external additive not corresponding to external additive A, is silica particles, and was obtained by subjecting silica particles having a raw material BET specific surface area of 170 m ² /g to a hydrophobic treatment using hexamethyldisilazane.

<Production Example of Toner 1>
Toner particles 1 100.0 parts External additive 1 0.60 parts External additive 15 0.80 parts Using a Henschel mixer (manufactured by Nippon Coke Corporation), the above materials were mixed at 3000 rpm for 15 minutes to obtain toner 1. When the toner was observed using a scanning electron microscope, the proportion of toner particles on whose surfaces it was confirmed that external additive A was present was 70% by number or more.

<Production Examples of Toners 2 to 17>
Toners 2 to 17 were obtained in the same manner as in the production example of toner 1 except for changing the conditions in Table 2. The ratio of toner particles on whose surfaces the external additive was confirmed to be present was as shown in Table 2.

<Production Examples of Anatase-Type Titanium Oxide Particles 1, 2, 5, and 6>
A solution containing titanium sulfate and titanyl sulfate was heated and hydrolyzed to produce a hydrous titanium dioxide slurry, which was then dehydrated and fired. This resulted in anatase-type titanium oxide 1 with an anatase degree of nearly 100%. In the above method, anatase-type titanium oxide particles 2, 5, and 6 with an anatase degree of nearly 100% were produced by controlling the concentration of the titanyl sulfate solution. The physical properties of the resulting anatase-type titanium oxide particles are shown in Table 3.

<Production Examples of Anatase-Type Titanium Oxide Particles 3, 4, and 7>
Niobium sulfate (a water-soluble niobium compound) was added to a hydrous titanium dioxide slurry obtained by hydrolysis of an aqueous titanyl sulfate solution in an amount of 10.0 mass % in terms of niobium ions relative to the amount of titanium in the slurry (calculated as titanium dioxide).
Niobium sulfate was added to an aqueous titanyl sulfate solution at a ratio of 10.0 mass% in terms of niobium ions, and the resulting solution was hydrolyzed to obtain a hydrous titanium dioxide slurry. Next, the hydrous titanium dioxide slurry containing niobium ions and the like was dehydrated and fired at a firing temperature of 1000° C. In this way, anatase-type titanium dioxide particles 3 containing niobium atoms were obtained.
In the above-mentioned method, the amount of niobium sulfate added was controlled to obtain niobium atom-containing anatase type titanium oxide particles 4 and 7. The physical properties of the obtained anatase type titanium oxide particles are shown in Table 3.

<Production Examples of Conductive Particles 1, 2, 3, and 5> Niobium hydroxide (V) was dissolved in concentrated sulfuric acid and mixed with an aqueous titanium sulfate solution to prepare an acidic mixed solution of a niobium salt and a titanium salt (hereinafter referred to as a "titanium-niobium mixed solution").
100 parts of anatase type titanium oxide particles 1 were weighed out and dispersed in water as core particles to prepare a suspension, which was then heated to 670° C. while being stirred in 1000 parts of water suspension.
While maintaining the pH at 2.5, a titanium-niobium mixed solution containing 337 g/kg of Ti and 10.3 g/kg of Nb relative to the weight of anatase-type titanium oxide particles 1 and an aqueous sodium hydroxide solution were added simultaneously. In addition, a titanium niobium acid solution (the weight ratio of niobium atoms to titanium atoms in the solution is 1.0/20.0) was prepared by mixing a niobium solution in which 3 parts of niobium pentachloride (NbCl ₅ ) were dissolved in 100 parts of 11.4 mol/L hydrochloric acid and 200 parts of a titanium sulfate solution containing 12.0 parts of titanium. This titanium niobium acid solution and a 10.7 mol/L sodium hydroxide solution were simultaneously dropped (added in parallel) into the aqueous suspension over 3 hours so that the pH of the aqueous suspension was 2 to 3. After the dropwise addition was completed, the suspension was filtered, washed, and dried at 110° C. for 8 hours. This dried material was baked together with the organic material in a nitrogen atmosphere at 725° C. for 1 hour to obtain niobium atom-containing titanium oxide particles 1 in which niobium atoms were unevenly distributed near the surface.

以上を混合し、攪拌装置で４時間攪拌した後、ろ過、洗浄後、さらに１３０℃で３時間加熱処理を行って、導電性粒子１が得られた。
上記の方法において、表３に示す酸化チタンに対するニオブ原子の重量比になるように五塩化ニオブの量を制御することで、導電性粒子２、３、５を得た。得られた導電性粒子の表面の物性や粒子径を表３に示す。 next,
Niobium atom-containing titanium oxide particles 1 100.0 parts Surface treatment agent 1 6.0 parts Toluene 200.0 parts Surface treatment agent 1 is KBM-3033, a product name of Shin-Etsu Chemical Co., Ltd., and is represented by the following formula (S-1).

The above ingredients were mixed and stirred for 4 hours using a stirrer, then filtered, washed, and further heat-treated at 130° C. for 3 hours to obtain conductive particles 1.
In the above method, the amount of niobium pentachloride was controlled so as to obtain the weight ratio of niobium atoms to titanium oxide shown in Table 3, thereby obtaining conductive particles 2, 3, and 5. The surface properties and particle diameters of the obtained conductive particles are shown in Table 3.

(Production Example of Conductive Particle 4)
100 g of spherical anatase-type titanium oxide particles 4 with a number-average particle size of 190 nm were dispersed in water, and 1 L of the aqueous suspension was heated to 60° C. A titanic acid solution mixed with 600 mL of titanium sulfate solution containing 33.7 g of titanium and a 10.7 mol/L sodium hydroxide solution were simultaneously dropped (added in parallel) over a period of 3 hours so that the pH of the suspension became 2 to 3. After the dropwise addition was completed, the suspension was filtered, washed, and dried at 110° C. for 8 hours. The dried product was subjected to a heat treatment at 800° C. for 1 hour in an air atmosphere. As a result, conductive particles 4 were obtained, which were titanium oxide particles with niobium atoms unevenly distributed near the surface.

(Production Example of Conductive Particles 6)
Approximately spherical anatase type titanium oxide particles 6 having a number average particle size of 170 nm were used as the conductive particles 6. The physical properties of the conductive particles 6 are shown in Table 3.

これらを混合し、攪拌装置で４時間攪拌した後、ろ過及び洗浄を行い、その後、さらに１３０℃で３時間加熱処理を行って、表面処理をすることで導電性粒子７を得た。 (Production Example of Conductive Particles 7)
The following materials were prepared:
Tin oxide particles (product name: S-2000, manufactured by Mitsubishi Materials Corporation): 100.0 parts Surface treatment agent 2: 20.0 parts Toluene: 200.0 parts Surface treatment agent 2 is the product name KBM-3033 manufactured by Shin-Etsu Chemical Co., Ltd., represented by the following formula (S-2).

These were mixed and stirred for 4 hours with a stirrer, then filtered and washed, and then further heat-treated at 130° C. for 3 hours for surface treatment, thereby obtaining conductive particles 7.

(Production Example of Conductive Particles 8)
Conductive particles 8 were obtained in the same manner as in Conductive Particles 7, except that the tin oxide particles were changed to those having a number average particle size of 20 nm.

(Production Example of Conductive Particles 9)
Approximately spherical anatase type titanium oxide particles 7 having a number average particle size of 6 nm and a niobium atom content of 0.5% by mass were used as the conductive particles 9 .

表中、Ａは、「粒子表面から測定粒子の最大径の５％内部におけるニオブ原子とチタン原子との濃度比率」であり、Ｂは、「粒子中心部におけるニオブ原子とチタン原子との濃度比率」である。

In the table, A is the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface," and B is the "concentration ratio of niobium atoms to titanium atoms in the particle center."

<Production Example of Electrophotographic Photoreceptor 1>
An aluminum cylinder (JIS-A3003, aluminum alloy) having a diameter of 24 mm and a length of 257.5 mm was used as a support (conductive support).

(Conductive Layer Manufacturing Example 1)
Next, the following materials were prepared:
Titanium oxide (TiO ₂ ) particles (average primary particle diameter 230 nm) coated with oxygen-deficient tin oxide (SnO ₂ ) 214 parts Phenol resin (trade name: Plyofen J-325, manufactured by Dainippon Ink & Chemicals, Inc., resin solid content: 60% by mass) 132 parts 1-methoxy-2-propanol 98 parts These were placed in a sand mill using 450 parts of glass beads with a diameter of 0.8 mm, and dispersion treatment was carried out under conditions of a rotation speed of 2000 rpm, a dispersion treatment time of 4.5 hours, and a cooling water set temperature of 18°C, to obtain a dispersion. The glass beads were removed from this dispersion using a mesh (opening 150 μm). Silicone resin particles (trade name: Tospearl 120, manufactured by Momentive Performance Materials, Inc., average particle size 2 μm) were added to the obtained dispersion as a surface roughening agent. The amount of silicone resin particles added was 10% by mass based on the total mass of the metal oxide particles and the binder material in the dispersion after removing the glass beads. Silicone oil (product name: SH28PA, manufactured by Dow Corning Toray Co., Ltd.) was added as a leveling agent to the dispersion to be 0.01% by mass based on the total mass of the metal oxide particles and the binder material in the dispersion.
Next, a mixed solvent of methanol and 1-methoxy-2-propanol (mass ratio 1:1) was added to the dispersion so that the total mass of the metal oxide particles, the binder material, and the surface roughening agent in the dispersion (i.e., the mass of the solid content) was 67 mass% relative to the mass of the dispersion. The mixture was then stirred to prepare a coating liquid for a conductive layer. The coating liquid for a conductive layer was dip-coated on a support and heated at 140°C for 1 hour to form a conductive layer with a thickness of 30 μm.

以上を混合溶解して、下引き層用塗布液を調製した。この下引き層用塗布液を導電層上に浸漬塗布し、これを３０分間１７０℃で加熱することによって、膜厚が０．７μｍの下引き層を形成した。 (Preparation Example 1 of Undercoat Layer)
Next, the following materials were prepared:
Compound represented by the following formula E-1 as an electron transport material: 3.0 parts; Blocked isocyanate (product name: Duranate SBB-70P, manufactured by Asahi Kasei Chemicals Corporation) 6.5 parts; Styrene-acrylic resin (product name: UC-3920, manufactured by Toagosei Co., Ltd.) 0.4 parts; Silica slurry (product name: IPA-ST-UP, manufactured by Nissan Chemical Industries, Ltd., solids concentration 15 mass%, viscosity 9 mPa·s) 1.8 parts; 1-butanol 48 parts; Acetone 24 parts, where the electron transport material (formula E-1) is represented by the following formula:

The above ingredients were mixed and dissolved to prepare a coating solution for an undercoat layer. The conductive layer was dip-coated with this coating solution and heated at 170° C. for 30 minutes to form an undercoat layer with a thickness of 0.7 μm.

Next, 10 parts of hydroxygallium phthalocyanine in a crystalline form having peaks at 7.5° and 28.4° in a chart obtained by CuKα characteristic X-ray diffraction and 5 parts of polyvinyl butyral resin (product name: S-LEC BX-1, manufactured by Sekisui Chemical Co., Ltd.) were prepared. These were added to 200 parts of cyclohexanone and dispersed for 6 hours with a sand mill device using glass beads with a diameter of 0.9 mm.
This was further diluted with 150 parts of cyclohexanone and 350 parts of ethyl acetate to obtain a coating solution for a charge generating layer. The obtained coating solution was dip-coated on the undercoat layer and dried at 95° C. for 10 minutes to form a charge generating layer having a thickness of 0.20 μm.
The powder X-ray diffraction measurement was carried out under the following conditions.
Measuring equipment used: Rigaku Electric Co., Ltd., X-ray diffraction device RINT-TTRII
X-ray tube: Cu
Tube voltage: 50 kV
Tube current: 300mA
Scanning method: 2θ/θ scanning Scanning speed: 4.0°/min
Sampling interval: 0.02°
Start angle (2θ): 5.0°
Stop angle (2θ): 40.0°
Attachment: Standard sample holder Filter: Not used Incident monochrome: Used Counter monochromator: Not used Divergence slit: Open Divergence vertical limit slit: 10.00 mm
Scattering slit: open Receiving slit: open Flat plate monochromator: Counter used: Scintillation counter

(Photosensitive Layer Production Example 1)
Next, the following materials were prepared:
Charge transport material (hole transport material) represented by the following formula (C-1): 6.0 parts Charge transport material (hole transport material) represented by the following formula (C-2): 3.0 parts Charge transport material (hole transport material) represented by the following formula (C-3): 1.0 part Polycarbonate (product name: Iupilon Z400, manufactured by Mitsubishi Engineering Plastics Corporation): 10.0 parts Polycarbonate resin having copolymerized units represented by the following formula (C-4) and formula (C-5): (x/y=0.95/0.05, viscosity average molecular weight=20,000): 0.02 parts These were dissolved in a mixed solvent of 25 parts orthoxylene/25 parts methyl benzoate/25 parts dimethoxymethane to prepare a coating solution for the charge transport layer. This charge transport layer coating liquid was dip-coated onto the charge generating layer to form a coating film, and the coating film was dried at 120° C. for 30 minutes to form a charge transport layer having a thickness of 12 μm.

この表面保護層用塗布液１を電荷輸送層上に浸漬塗布して塗膜を形成し、得られた塗膜を６分間５０℃で乾燥させた。その後、窒素雰囲気下にて、加速電圧７０ｋＶ、ビーム電流５．０ｍＡの条件で支持体（被照射体）を３００ｒｐｍの速度で回転させながら、１．６秒間電子線を塗膜に照射した。表面保護層位置の線量は１５ｋＧｙであった。その後、窒素雰囲気下にて、塗膜の温度を１１７℃に昇温させた。電子線照射から、その後の加熱処理までの酸素濃度は１０ｐｐｍであった。
次に、大気中において塗膜の温度が２５℃になるまで自然冷却した後、塗膜の温度が１２０℃になる条件で１時間加熱処理を行い、膜厚２μｍの表面保護層を形成した。このようにして、導電性粒子１を含有する表面保護層を有する電子写真感光体１を製造した。感光体の表面保護層表面の物性について表４に示す。 (Surface protection layer manufacturing example 1)
Next, the following materials were prepared:
Conductive particles 1 76.0 parts, a compound represented by the following formula (O-1) as a binder resin 76.0 parts, 1-propanol (1-PA) 100.0 parts, and cyclohexane (CH) 100.0 parts were mixed and stirred with a stirrer for 6 hours to prepare a coating solution for a surface protective layer.

This surface protective layer coating solution 1 was applied by dip coating on the charge transport layer to form a coating film, and the obtained coating film was dried at 50°C for 6 minutes. Then, under a nitrogen atmosphere, the support (irradiated body) was rotated at a speed of 300 rpm under the conditions of an acceleration voltage of 70 kV and a beam current of 5.0 mA, and the coating film was irradiated with an electron beam for 1.6 seconds. The dose at the surface protective layer position was 15 kGy. Then, under a nitrogen atmosphere, the temperature of the coating film was raised to 117°C. The oxygen concentration from the electron beam irradiation to the subsequent heat treatment was 10 ppm.
Next, the coating film was naturally cooled in the atmosphere until the temperature reached 25° C., and then heat treatment was performed for 1 hour under conditions such that the temperature of the coating film reached 120° C., forming a surface protective layer with a thickness of 2 μm. In this manner, an electrophotographic photoreceptor 1 having a surface protective layer containing conductive particles 1 was produced. The physical properties of the surface of the surface protective layer of the photoreceptor are shown in Table 4.

(Production Examples of Electrophotographic Photoreceptors 2 to 4 and 6 to 15)
Electrophotographic photoreceptors 2 to 4 and 6 to 15 were produced in the same manner as in Example 1, except that in the production example of electrophotographic photoreceptor 1, changes were made as shown in Table 4. Table 4 shows the physical properties of the surface of the surface protective layer of the photoreceptor.

(Production Example of Electrophotographic Photoreceptor 5)
An electrophotographic photoreceptor 5 was obtained in the same manner as in the production example of the electrophotographic photoreceptor 1, except that (production example of the surface protective layer) was changed as follows.
A coating solution for a surface protective layer was prepared as follows.
First, the following materials were prepared:
Conductive particles 9: 10 parts Compound represented by the following formula (H-7): 10 parts Polymerization initiator (1-hydroxycyclohexyl(phenyl)methanone): 1 part These were mixed with 40 parts of n-propyl alcohol and dispersed in a sand mill for 2 hours to prepare a protective layer coating solution.
Except for using this protective layer coating liquid, electrophotographic photoreceptor 5 was produced in the same manner as in electrophotographic photoreceptor 1. The physical properties of electrophotographic photoreceptor 5 are shown in Table 4.

Example 1
The following actual machine evaluation was carried out using the toner 1 and the electrophotographic photoreceptor 1. The evaluation results are shown in Table 5.
For the actual machine evaluation, a modified Canon laser beam printer "LBP7600C" was used. The modification involved changing the gear and software of the evaluation machine body, setting the number of rotations of the developing roller to rotate at twice the peripheral speed relative to the drum, and setting the process speed to double. In addition, the pre-exposure device in the laser beam printer was removed. By making the above modifications, the mode becomes more severe in terms of evaluating the change in image density.
Next, the electrophotographic image forming apparatus and the unused electrophotographic photoreceptor 1 were left to stand for 24 hours or more in an environment of a temperature of 23.0° C. and a humidity of 50% RH, and then 70 g of the toner 1 and the electrophotographic photoreceptor 1 were mounted in a cartridge of the electrophotographic image forming apparatus.
The paper used was LETTER size Business 4200 (manufactured by XEROX Corporation, 75 g/m ² ), with left and right margins of 50 mm.

<Evaluation of Charge Start-up Property Immediately After Starting Up Electrophotographic Image Forming Apparatus>
The modified machine was placed in an environment of 23°C and 50% RH and 10 sheets of solid images were printed in a single color. Density measurements were performed at 20 random locations on the second and tenth images, and the solid image density was calculated from the average value of the 20 locations. The density was measured using an X-Rite color reflection densitometer (X-rite 500 Series, manufactured by X-rite Corporation). The difference in density between the second and tenth solid images was taken as the initial charge rise property and was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 5.
(Evaluation Criteria)
A: Initial charge rise property is less than 0.04 B: Initial charge rise property is 0.04 or more and less than 0.07 C: Initial charge rise property is 0.07 or more and less than 0.10 D: Initial charge rise property is 0.10 or more

<Evaluation of initial density uniformity and density uniformity after durability test>
The modified machine was placed in a 23°C, 50% RH environment, and one character image with a printing ratio of 1% was output as described above, followed by a halftone (40H) image. Then, 10,000 character images with a printing ratio of 1% were output, followed by a halftone (40H) image. The density uniformity of these halftone images was evaluated based on the following criteria. The 40H image is a halftone image in which 256 gradations are expressed in hexadecimal, with 00H being solid white (non-image) and FFH being solid black (full image).
The density uniformity was evaluated by measuring the density at 20 points and judging the difference between the maximum and minimum density values as the density uniformity. The density was measured using an X-Rite color reflection densitometer (X-rite 500 Series, manufactured by X-rite Corporation), and the initial density uniformity on the second sheet and the density uniformity after durability on the 10,000th sheet were evaluated according to the following evaluation criteria. The evaluation results are shown in Table 5.
(Evaluation Criteria)
A: Density uniformity is less than 0.04 B: Density uniformity is 0.04 or more and less than 0.07 C: Density uniformity is 0.07 or more and less than 0.10 D: Density uniformity is 0.10 or more

<Examples 2 to 23 and Comparative Examples 1 to 8>
Using toner particles 2 to 17, the same evaluation as in Example 1 was carried out. The evaluation results of Examples 2 to 23 and Comparative Examples 1 to 8 are shown in Table 5.

The embodiments of the present invention include the following configurations.
(Configuration 1)
A process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus,
The process cartridge comprises:
An electrophotographic photoreceptor;
Toner;
a developing means for storing the toner and supplying the toner to the surface of the electrophotographic photoreceptor;
having
The toner has toner particles and an external additive A,
The external additive A satisfies the following requirements (i) to (iii):
(i) the major axis is 100 nm or more and 3000 nm or less;
(ii) an aspect ratio of 5.0 or more;
(iii) a resistivity of 1×10 Ω cm or more and 1×10 Ω cm or less;
the ratio of toner particles having the external additive A present on the surface to the total number of toner particles in the toner is 30% or more;
The electrophotographic photoreceptor has a conductive support, a photosensitive layer formed on the conductive support, and a surface protective layer formed on the surface of the electrophotographic photoreceptor,
The surface protective layer contains conductive particles,
the content of the conductive particles in the surface protective layer is 5% by volume or more and 70% by volume or less,
The volume resistivity of the surface protective layer is 1.0×10 Ω cm or more and 1.0×10 Ω cm or less.
A process cartridge comprising:
(Configuration 2)
2. The process cartridge according to claim 1, wherein the external additive A is titanium oxide particles.
(Configuration 3)
3. The process cartridge according to claim 1, wherein the external additive A is rutile type titanium oxide particles.
(Configuration 4)
4. The process cartridge according to any one of claims 1 to 3, wherein the toner particles contain boric acid.
(Configuration 5)
5. The process cartridge according to any one of claims 1 to 4, wherein the conductive particles are titanium oxide particles.
(Configuration 6)
6. The process cartridge according to any one of claims 1 to 5, wherein the conductive particles are titanium oxide particles containing niobium atoms.
(Configuration 7)
The process cartridge according to Configuration 6, wherein the niobium-atom-containing titanium oxide particles have a concentration ratio calculated as niobium atom concentration/titanium atom concentration at a portion within 5% of the maximum diameter of the measured particle from the particle surface, which is 2.0 times or more, relative to a concentration ratio calculated as niobium atom concentration/titanium atom concentration at a center of the particle.
(Configuration 8)
The process cartridge according to Configuration 6 or 7, wherein the titanium oxide particles containing niobium atoms contain 2.6% by mass or more and 10.0% by mass or less of niobium atoms.
(Configuration 9)
the conductive particles account for 40% by volume or more and 70% by volume or less of the surface protective layer;
9. The process cartridge according to any one of Configurations 1 to 8, wherein the volume resistivity of the surface protective layer is 1.0×10 Ω·cm or more and 1.0×10 Ω·cm or less.

21 Support 22 Undercoat layer 23 Charge generating layer 24 Charge transport layer 25 Surface protective layer 1 Electrophotographic photosensitive member 2 Shaft 3 Charging means 4 Exposure light 5 Developing means 6 Transfer means 7 Transfer material 8 Fixing means 9 Cleaning means 10 Pre-exposure light 11 Process cartridge 12 Guide means 31 Center of conductive particle 32 Near the surface of conductive particle 33 X-ray analyzing center of conductive particle 34 X-ray analyzing 5% of the inside of the conductive particle from the surface

Claims (9)

A process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus,
The process cartridge comprises:
An electrophotographic photoreceptor;
Toner;
a developing means for storing the toner and supplying the toner to the surface of the electrophotographic photoreceptor;
having
The toner has toner particles and an external additive A,
The external additive A satisfies the following requirements (i) to (iii):
(i) the major axis is 100 nm or more and 3000 nm or less;
(ii) an aspect ratio of 5.0 or more;
(iii) Specific resistance is 1×10 ⁵ Ω・cm or more and 1×10 ⁸ Ω・cm or less,
the ratio of toner particles having the external additive A present on the surface to the total number of toner particles in the toner is 30% or more;
The electrophotographic photoreceptor has a conductive support, a photosensitive layer formed on the conductive support, and a surface protective layer formed on the surface of the electrophotographic photoreceptor,
The surface protective layer contains conductive particles,
the content of the conductive particles in the surface protective layer is 5% by volume or more and 70% by volume or less,
the volume resistivity of the surface protective layer is 1.0×10 ⁹ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less;
A process cartridge comprising: The process cartridge according to claim 1, characterized in that the external additive A is titanium oxide particles. The process cartridge according to claim 1, characterized in that the external additive A is rutile-type titanium oxide particles. The process cartridge according to claim 1, characterized in that the toner particles contain boric acid. The process cartridge according to claim 1, characterized in that the conductive particles are titanium oxide particles. The process cartridge according to claim 1, characterized in that the conductive particles are titanium oxide particles containing niobium atoms. The process cartridge according to claim 6, wherein the niobium atom-containing titanium oxide particles have a concentration ratio calculated as niobium atom concentration/titanium atom concentration at the center of the particle, the concentration ratio calculated as niobium atom concentration/titanium atom concentration at an area 5% inside the particle surface from the maximum diameter of the measured particle, which is 2.0 times or more. The process cartridge according to claim 6, wherein the titanium oxide particles containing niobium atoms contain 2.6% by mass or more and 10.0% by mass or less of niobium atoms. the conductive particles account for 40% by volume or more and 70% by volume or less of the surface protective layer;
9. The process cartridge according to claim 1, wherein the surface protective layer has a volume resistivity of 1.0×10 ¹⁰ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less.

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