Electrophotographic photoreceptor and electrophotographic image forming apparatus

Abstract

The object of the present invention is to provide an electrophotographic photoreceptor and an electrophotographic image forming apparatus that can obtain sufficient image quality and durability even in a positively charged image forming apparatus. [Solution] An electrophotographic photoreceptor used in an image forming apparatus having a positively charged charging means, wherein the electrophotographic photoreceptor has a photosensitive layer and a protective layer, the protective layer is a cured film containing metal oxide particles and formed from a cured polymerizable compound, and the volume resistivity of the protective layer is 10 9 ~10 15 An electrophotographic photoreceptor characterized in that the polymerizable compound is within the range of Ω·cm, the polymerizable compound is either an acrylic monomer or a methacrylic monomer, or a mixture thereof, and the hydroxyl value of the polymerizable compound is within the range of 10 to 200 mgKOH / g.

Description

[Technical Field]

[0001] This invention relates to an electrophotographic photoreceptor and an electrophotographic image forming apparatus. More specifically, it relates to an electrophotographic photoreceptor that can obtain sufficient image quality and durability even in a positively charged image forming apparatus. [Background technology]

[0002] In recent years, the layer structure of electrophotographic photoreceptors used in electrophotographic image forming apparatuses has mostly consisted of a charge generation layer and a charge transport layer stacked in that order on a conductive support. Furthermore, electrophotographic image forming apparatuses with such a layer structure have a charging means equipped with a negatively charged photoreceptor.

[0003] Hereinafter, "an electrophotographic image forming apparatus having a charging means equipped with a negatively charged photoreceptor" will also be simply referred to as "a negatively charged image forming apparatus," and "a charging means equipped with a negatively charged photoreceptor" will also be simply referred to as "a negatively charged charging means." Furthermore, "an electrophotographic image forming apparatus having a charging means equipped with a positively charged photoreceptor" will also be simply referred to as "a positively charged image forming apparatus," and "a charging means equipped with a positively charged photoreceptor" will also be simply referred to as "a positively charged charging means."

[0004] Reasons why an electrophotographic image forming apparatus has a charging means equipped with a negatively charged photoreceptor include, for example, the following (1) and (2). (1) The organic compounds included in electrophotographic photoreceptors are required to exhibit high charge mobility that does not cause problems even in recent high-speed printing processes, and the design of the compound is more flexible and versatile if the charge transport material is hole transport rather than electron transport. (2) In order to achieve high durability, an electrophotographic photoreceptor with the charge transport layer located on the surface side is advantageous, and considering the reasons in (1) as well, it is necessary to form the charge transport layer using a hole-transporting charge transport material.

[0005] For reasons (1) and (2), in terms of the operating principle, most of the photoreceptors included in the charging means of commercially available electrophotographic image forming apparatuses are limited to the negative charging type.

[0006] Here, generally corona discharge is used as the charging means, and in the negative charging type charging means as described above, negative corona discharge is performed. However, this negative corona discharge is unstable and contributes to an increase in the cost of the charging member and a shortening of its lifespan.

[0007] In addition, negative corona discharge has a problem that more compounds such as ozone and NOx are generated compared to the case of positive corona discharge, and the surface of the electrophotographic photoreceptor is chemically deteriorated.

[0008] On the other hand, the positive charging type image forming apparatus has no such problems and has advantages in reducing the product cost and extending the lifespan of each member.

[0009] In Patent Document 1, a technique related to a single-layer type photoreceptor having metal oxide particles surface-treated with a polymerizable compound and a protective layer formed by a polymerization reaction between the polymerizable compounds is disclosed. Further, in Patent Document 2, a technique related to a single-layer type photoreceptor having a protective layer with a volume resistivity smaller than that of the photosensitive layer is disclosed.

[0010] However, there is still room for improvement in the above techniques related to photoreceptors.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] As the photoreceptor provided in the positively charged charging means, for example, the photoreceptors as in the following (i) and (ii) are known. (i) A single-layer photoreceptor containing a charge generating substance and a charge transporting substance in the same layer (ii) A reverse-layer laminated photoreceptor having a laminated order opposite to that of a so-called normal photoreceptor, in which a charge transporting layer and a charge generating layer are laminated in this order on a conductive support

[0013] The photoreceptors of (i) and (ii), that is, the positively charged photoreceptors, are both disadvantageous in terms of durability compared to the negatively charged photoreceptors in which the charge transporting layer can be provided on the surface side, and it becomes substantially essential to provide a protective layer on the outermost surface of the positively charged photoreceptor.

[0014] When a protective layer is provided on the outermost surface of the positively charged photoreceptor as described above, excessive wear is likely to occur on the surface of the photoreceptor compared to the outermost surface of the negatively charged photoreceptor. As a result, when cleaning the photoreceptor, toner leakage of the cleaning blade occurs, and problems such as poor cleaning occur.

[0015] The aforementioned Patent Document 1 discloses a technology related to the above positively charged photoreceptor, and improves durability while suppressing black spots and image blurring that are likely to occur in a single-layer photoreceptor.

[0016] However, in the technology disclosed above, the volume resistivity of the protective layer and the hydroxyl value of the constituent material are not defined, and there is room for improvement in suppressing excessive wear that occurs in the positively charged photoreceptor and the accompanying poor cleaning.

[0017] Further, Patent Document 2 discloses a single-layer photoreceptor in which the volume resistivity of the protective layer is made smaller than the volume resistivity of the photosensitive layer in the technology related to the above positively charged photoreceptor, and aims to achieve both charging performance and memory suppression during repeated printing.

[0018] However, the focus has primarily been on improving exposure performance, light responsiveness, and surface charge retention capabilities, and has not adequately addressed the aspect of suppressing excessive wear of the photoreceptor in positively charged image forming apparatuses.

[0019] A unique challenge in positively charged image forming apparatuses is that, because the photoreceptor has a positive charge, components with a negative charge sequence in the developer, as well as n-type semiconductor components, are strongly adsorbed electrostatically onto the photoreceptor surface. Examples of these components include external additives such as titania, silica, and carriers.

[0020] When the above-mentioned components strongly adhere to the surface of the photoreceptor electrostatically, there is a problem in that the photoreceptor is excessively polished and worn down by rubbing with a cleaning blade or the like.

[0021] This problem is more pronounced in positively charged image forming apparatuses compared to negatively charged image forming apparatuses.

[0022] This invention has been made in view of the above-mentioned problems and circumstances, and its objective is to provide an electrophotographic photoreceptor and an electrophotographic image forming apparatus that can obtain sufficient image quality and durability even in a positively charged image forming apparatus. [Means for solving the problem]

[0023] The inventors of the present invention have found that the above problems can be solved by setting the volume resistivity of the protective layer of a positively charged photoreceptor within a certain range, limiting the types of polymerizable compounds contained in the protective layer, and setting the hydroxyl value within a certain range, thereby arriving at the present invention. In other words, the above-mentioned problems according to the present invention are solved by the following means.

[0024] 1. An electrophotographic photoreceptor used in an image forming apparatus having a positively charged charging means, The electrophotographic photoreceptor has a photosensitive layer and a protective layer, The protective layer is a cured film containing metal oxide particles and formed from a cured polymerizable compound. The volume resistivity of the aforementioned protective layer, 10 9 ~10 15 It is within the range of Ω·cm, The polymerizable compound is either an acrylic monomer or a methacrylic monomer, or a mixture thereof. The hydroxyl value of the polymerizable compound is in the range of 10 to 200 mg KOH / g. An electrophotographic photoreceptor characterized by the following features.

[0025] 2. The hydroxyl value of the polymerizable compound is in the range of 50 to 160 mg KOH / g. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0026] 3. The polymerizable compound has three or more polymerizable functional groups. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0027] 4. The volume resistivity of the metal oxide particles is 10 6 ~10 10 It is within the range of Ω·cm. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0028] 5. The metal oxide particles are either titanium oxide or tin oxide, or a mixture thereof. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0029] 6. The content of the metal oxide particles is within the range of 25 to 65% by mass relative to the protective layer. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0030] 7. The protective layer is a cured film containing either resin particles or inorganic particles, or a mixture thereof. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0031] 8. The resin particles are one type of resin particle selected from acrylic resin particles, urethane resin particles, melamine resin particles, and epoxy resin particles, or a mixture of two or more types of resin particles. The electrophotographic photoreceptor according to paragraph 7, characterized in that...

[0032] 9. The inorganic particles are silica particles. The electrophotographic photoreceptor according to paragraph 7, characterized in that...

[0033] 10. The content of the resin particles and inorganic particles is within the range of 1 to 25% by mass relative to the protective layer. The electrophotographic photoreceptor according to paragraph 7, characterized in that...

[0034] 11. The thickness of the protective layer is within the range of 1 to 10 μm. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0035] 12. The photosensitive layer is a single-layer photosensitive layer containing a charge generating material, a charge transporting material, and a resin in the same layer. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0036] 13. The photosensitive layer is a laminated type photosensitive layer in which a charge transport layer and a charge generation layer are stacked in that order, and the protective layer and the charge generation layer are formed adjacent to each other. The electrophotographic photoreceptor according to the first paragraph, characterized in that...

[0037] 14. An electrophotographic photoreceptor as described in any one of paragraphs 1 through 13, A positive charging means for charging the electrophotographic photoreceptor to a positive potential, An exposure means for forming an electrostatic latent image on the electrophotographic photoreceptor, Developing means for forming a toner image on the electrophotographic photoreceptor, A transfer means for moving a toner image formed on the electrophotographic photoreceptor to a transfer medium, It includes a cleaning means for collecting toner that remains on the photoreceptor without being transferred using a cleaning blade. An electrophotographic image forming apparatus characterized by the following: [Effects of the Invention]

[0038] The above means of the present invention makes it possible to provide an electrophotographic photoreceptor and an electrophotographic image forming apparatus that can obtain sufficient image quality and durability even in a positively charged image forming apparatus. Although the mechanism by which the effects of this invention manifest or the mechanism of action are not yet clear, we speculate as follows.

[0039] The electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor used in an image forming apparatus having a positively charged charging means, wherein the electrophotographic photoreceptor has a photosensitive layer and a protective layer, the protective layer is a cured film containing metal oxide particles and formed from a cured polymerizable compound, and the volume resistivity of the protective layer is 10 9 ~10 15 The polymerizable compound is within the range of Ω·cm, and is characterized in that the polymerizable compound is either an acrylic monomer or a methacrylic monomer, or a mixture thereof, and the hydroxyl value of the polymerizable compound is within the range of 10 to 200 mgKOH / g.

[0040] Problems caused by the adsorption of negative charge sequence components or n-type semiconductor components in the developer tend to become more pronounced as the volume resistivity of the protective layer applied to the photoreceptor increases. This is thought to be because the increased retention of positive charges leads to increased electrostatic adhesion of the developer components.

[0041] On the other hand, if the volume resistivity of the protective layer is too low, the retention of the electrostatic latent image decreases, and the image quality deteriorates due to excessive diffusion of the electrostatic latent image.

[0042] Therefore, the volume resistivity of the protective layer provided on the positively charged photoreceptor is set to 10 9 ~10 15It is within the range of

[0043] By doing this, while suppressing significant diffusion of the electrostatic latent image, the charges are appropriately diffused, the adhesion force of the developer components is reduced, and excessive wear of the photoreceptor can be suppressed.

[0044] Furthermore, it is presumed that by suppressing excessive wear of the photoreceptor, the occurrence of problems such as cleaning failures due to toner leakage from the cleaning blade can also be suppressed.

Brief Description of the Drawings

[0045] [Figure 1] Cross-sectional view showing an example of the layer structure of an electrophotographic photoreceptor having a single-layer type photosensitive layer [Figure 2] Cross-sectional view showing an example of the layer structure of an electrophotographic photoreceptor having an inverse layer type photosensitive layer [Figure 3] An example of a cross-sectional configuration diagram of an image forming apparatus according to the present invention [Figure 4] Schematic diagram showing a halftone image and the paper passing direction during printing [Figure 5] Schematic diagram showing an evaluation image and the paper passing direction

Embodiments for Carrying Out the Invention

[0046] The electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor used in an image forming apparatus having a positive charging type charging means, the electrophotographic photoreceptor has a photosensitive layer and a protective layer, the protective layer contains metal oxide particles and is a cured film formed from a cured product of a polymerizable compound, the volume resistivity of the protective layer is within the range of 10 9 ~10 15 Ω·cm, the polymerizable compound is either an acrylic monomer or a methacrylic monomer, or a mixture thereof, and the hydroxyl value of the polymerizable compound is within the range of 10 to 200 mgKOH / g. This feature is a technical feature common to or corresponding to each of the embodiments (appearances) described below.

[0047] In embodiments of the present invention, it is preferable that the hydroxyl value of the polymerizable compound is in the range of 50 to 160 mgKOH / g, as this allows for a more appropriate amount of water to be adsorbed on the protective layer and further enhances the effects of the present invention.

[0048] From the viewpoint of improving the durability of the protective layer, it is preferable that the polymerizable compound has three or more polymerizable functional groups.

[0049] The volume resistivity of the metal oxide particles is 10 6 ~10 10 The fact that the volume resistivity of the protective layer is within the range of Ω·cm is 10 9 ~10 15 This is preferable from the standpoint of making it easier to design within the range of Ω·cm.

[0050] Since the volume resistivity of titanium dioxide and the volume resistivity of tin oxide are within a favorable range for the present invention, it is preferable that the metal oxide particles are either titanium dioxide or tin oxide, or a mixture thereof. Furthermore, the fact that the metal oxide particles are either titanium dioxide or tin oxide, or a mixture thereof, provides excellent uniform dispersion in the protective layer film.

[0051] The content of the metal oxide particles is within the range of 25 to 65% by mass relative to the protective layer, which ensures that the volume resistivity of the protective layer is 10 9 ~10 15 This is preferable because it makes it easier to design within the range of Ω·cm and also improves the durability of the protective layer.

[0052] From the viewpoint of adjusting the volume resistivity of the protective layer and further improving its durability, it is preferable that the protective layer is a cured film containing either resin particles or inorganic particles, or a mixture thereof.

[0053] Preferably, the resin particles are one type of resin particle selected from acrylic resin particles, urethane resin particles, melamine resin particles, and epoxy resin particles, or a mixture of two or more types of resin particles. This allows for adjustment of the volume resistivity of the protective layer, further improving its durability.

[0054] It is more preferable that the inorganic particles are silica particles, from the viewpoint that this can adjust the volume resistivity of the protective layer and further improve its durability.

[0055] It is even more preferable, from the viewpoint of adjusting the volume resistivity of the protective layer and further improving its durability, that the content of the resin particles and inorganic particles is within the range of 1 to 25% by mass relative to the protective layer.

[0056] From the viewpoint of reducing the likelihood of problems such as image blurring due to the diffusion of electrostatic latent images occurring, it is preferable that the thickness of the protective layer be within the range of 1 to 10 μm.

[0057] The effects of the present invention can also be obtained in a single-layer photosensitive layer in which a charge generating material, a charge transporting material, and a resin are contained in the same layer.

[0058] Even if the photosensitive layer is a laminated type photosensitive layer in which a charge transport layer and a charge generation layer are stacked in that order, and the protective layer and the charge generation layer are formed adjacent to each other, the same effect as the single-layer type photosensitive layer can be obtained.

[0059] The electrophotographic photoreceptor of the present invention can be suitably used in an electrophotographic image forming apparatus having a positive charging means for charging the electrophotographic photoreceptor to a positive potential, an exposure means for forming an electrostatic latent image on the electrophotographic photoreceptor, a developing means for forming a toner image on the electrophotographic photoreceptor, a transfer means for moving the toner image formed on the electrophotographic photoreceptor to a transfer medium, and a cleaning means for recovering toner remaining on the photoreceptor that has not been transferred using a cleaning blade.

[0060] The present invention, its components, and embodiments and models for carrying out the present invention will be described in detail below. In this application, "~" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0061] While the advantages and features provided by one or more embodiments of the present invention will be better understood from the following detailed description and accompanying drawings, these drawings are for illustrative purposes only and are not intended to define any limitations of the present invention.

[0062] [I. Electrophotographic photoreceptor] 1. Overview The electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor used in an image forming apparatus having a positively charged charging means, wherein the electrophotographic photoreceptor has a photosensitive layer and a protective layer, the protective layer is a cured film containing metal oxide particles and formed from a cured polymerizable compound, and the volume resistivity of the protective layer is 10 9 ~10 15 The polymerizable compound is within the range of Ω·cm, and is characterized in that the polymerizable compound is either an acrylic monomer or a methacrylic monomer, or a mixture thereof, and the hydroxyl value of the polymerizable compound is within the range of 10 to 200 mgKOH / g.

[0063] The electrophotographic photoreceptor of the present invention is an organic photoreceptor. "Organic photoreceptor" means an electrophotographic photoreceptor in which at least one of the charge generation function and charge transport function, which are essential for the structure of an electrophotographic photoreceptor, is expressed by an organic compound. Furthermore, the meaning of "electrophotographic photoreceptor" includes photoreceptors composed of known organic charge-generating substances or organic charge-transporting substances, and photoreceptors in which the charge generation function and charge transport function are composed of polymer complexes.

[0064] (1.1) Positively charged charging means As a positive charging method for charging the surface of the photoreceptor to a positive potential, generally known charging methods can be applied. For example, corona discharge-based corotron charging and roller charging can be used as such charging methods.

[0065] (1.2) Composition of the photosensitive layer The photosensitive layer according to the present invention will be described as a photosensitive material in which a photosensitive layer is laminated on a conductive support.

[0066] The photosensitive layer according to the present invention can be (1) a single-layer photosensitive layer containing a charge generating material, a charge transporting material, and a resin in the same layer, or (2) a so-called reverse-layer laminated photosensitive layer formed by laminating a charge transporting layer and a charge generating layer in that order.

[0067] The above configurations (1) and (2) are generally known for positively charged photoreceptors, but in the photoreceptor of the present invention, the problem of excessive wear, which is characteristic of positively charged photoreceptors, can be suppressed in either configuration.

[0068] (1.3) Layer structure of the photoreceptor The photoreceptor of the present invention has a photosensitive layer and a protective layer, and the layer configuration when the photosensitive layer is a single layer is as follows. ·Conductive support / photosensitive layer / protective layer ·Conductive support / intermediate layer / photosensitive layer / protective layer

[0069] The photoreceptor of the present invention has a photosensitive layer and a protective layer, and the layer configuration when the photosensitive layer is of the reverse layer type is as follows. In the layer configuration below, the "charge transport layer / charge generation layer" is the portion of the photosensitive layer. • Conductive support / Charge transport layer / Charge generation layer / Protective layer • Conductive support / intermediate layer / charge transport layer / charge generation layer / protective layer

[0070] As mentioned above, the photosensitive layer according to the present invention may be a single-layer type or an inverse-layer type. However, since the structure of the protective layer is important for obtaining the effects of the present invention, the same effects can be obtained whether the photosensitive layer is a single-layer type or an inverse-layer type.

[0071] The protective layer, which is an important component of the electrophotographic photoreceptor of the present invention, will be described first, followed by the photosensitive layer, conductive support, and intermediate layer. Note that the protective layer, intermediate layer, and conductive support are not included in the term "photosensitive layer."

[0072] 2.Protective layer The purpose of providing a protective layer to a photoreceptor is to improve its durability. Therefore, a cured film formed from a cured polymerizable compound is selected as the protective layer.

[0073] Various generally known curing methods can be selected for forming the cured film. Examples of such curing methods include thermal curing, ultraviolet curing, and electron beam curing.

[0074] From the viewpoints of the speed of the curing reaction of polymerizable compounds, the simplicity of the curing apparatus configuration, and cost reduction, ultraviolet curing is preferred as the curing method.

[0075] (2.1) Inclusions (2.1.1) Polymerizable compounds The protective layer according to the present invention is a cured film formed from a cured polymerizable compound. The polymerizable compound improves the durability of the protective layer. The polymerizable compound is selected from either acrylic monomer or methacrylic monomer, or a mixture thereof. These are selected because of their fast curing reaction rate, the diversity of molecular designs such as hydroxyl value, and the minimal adverse effect on the electrical properties of the photosensitive layer.

[0076] (Hydroxyl value) The hydroxyl value of the polymerizable compound according to the present invention is in the range of 10 to 200 mg KOH / g. This ensures that the amount of water adsorbed on the protective layer is appropriate, allowing for moderate diffusion of the electrostatic latent image charge and reducing the likelihood of problems such as image blurring.

[0077] If the hydroxyl value is less than 10 mg KOH / g, the amount of water adsorbed is small, and adequate charge diffusion cannot occur. If the hydroxyl value exceeds 200 mg KOH / g, excessive water adsorption causes the electrostatic latent image to diffuse too much, making it prone to problems such as image blurring.

[0078] The hydroxyl value mentioned above is preferably within the range of 50 to 160 mg KOH / g. This allows for a more appropriate amount of moisture to be adsorbed onto the protective layer, thereby further enhancing the above-mentioned effects.

[0079] The hydroxyl value of the polymerizable compound according to the present invention can be measured by generally known measurement methods, for example, by potentiometric titration.

[0080] (Functional groups possessed by polymerizable compounds) To improve the durability of the protective layer, it is preferable that the polymerizable compound has three or more polymerizable functional groups. This allows the polymerizable compounds to be crosslinked three-dimensionally during the curing reaction, significantly improving the durability of the protective layer compared to the linear structure when the polymerizable compound has only two polymerizable functional groups.

[0081] (2.1.2) Metal oxide particles The metal oxide particles contained in the protective layer according to the present invention can be made from generally known materials. By making the protective layer highly durable through nanocomposite construction, and by adjusting the volume resistivity (powder resistance) and amount of the particle material added, it becomes possible to design the volume resistivity and hardness of the protective layer.

[0082] (Volume resistivity of metal oxide particles contained in the protective layer) The volume resistivity of the metal oxide particles contained in the protective layer according to the present invention is 10 6 ~10 10 It is preferable that it be within the range of Ω·cm. This makes the volume resistivity of the protective layer 10 9 ~10 15 This makes it easier to design within the range of Ω·cm.

[0083] In this specification, "volume resistivity of metal oxide particles" strictly refers to the volume resistivity of the metal oxide particles as a powder. Therefore, this volume resistivity is determined by the following process.

[0084] For example, in the formation of a protective layer according to the present invention, there is a process of dispersing metal oxide particles in a prepared solution containing metal oxide particles as a material using a sand mill. The volume resistivity of the metal oxide particles as raw materials before dispersion in this process is referred to as the volume resistivity of the metal oxide particles in this specification.

[0085] The volume resistivity [Ω·cm] of metal oxide particles can be determined as follows. Electrical resistance is generally used as a measure of the conductivity of a material. The value obtained by expressing this resistance per unit volume (1cm × 1cm × 1cm) is the volume resistivity.

[0086] That is, cross-sectional area S[cm²] 2 By passing a constant current I[A] through the electrode and measuring the potential difference V[V] between electrodes separated by a distance L[cm], the volume resistivity [Ω·cm] can be determined by the following formula. In the following formula, R is the resistance, and R = V / I. Volume resistivity = V × R = (S / L) × (V / I)

[0087] The volume resistivity [Ω·cm] of the metal oxide particles according to the present invention was determined by filling a container having electrodes arranged parallel to each other at a distance of 2 mm with metal oxide particles, and measuring the DC resistance at a potential difference of 500 V between the two electrodes using a Yokogawa Hewlett-Packard 4329A High Resistance Meter.

[0088] (kinds) The metal oxide particles contained in the protective layer according to the present invention are preferably titanium oxide, tin oxide, or a mixture thereof. The reasons for this preference are that the volume resistivity of titanium oxide and tin oxide are within a range that is favorable for the present invention, and that they exhibit excellent uniform dispersion in the protective layer film.

[0089] (Content of metal oxide particles in the protective layer) The content of metal oxide particles in the protective layer according to the present invention is preferably in the range of 25 to 65% by mass relative to the total solid content of the protective layer. This increases the volume resistivity of the protective layer to 10 9 ~10 15 This makes it easier to design within the Ω·cm range. Furthermore, it is also preferable from the standpoint of improving the durability of the protective layer.

[0090] In the protective layer according to the present invention, if the content of metal oxide particles is 25% by mass or more relative to the total solid content of the protective layer, the effect of improving durability is greatly enhanced, and if it is 65% by mass or less, the brittleness of the cured film can be suppressed.

[0091] (2.1.3) Resin particles and inorganic particles The protective layer according to the present invention is preferably a cured film containing either resin particles or inorganic particles, or a mixture thereof. The term "inorganic particles" here refers to particles containing inorganic elements other than metallic elements, and the term "metal" here does not include amphoteric metals such as silicon and aluminum. Furthermore, the inorganic particles include oxide particles of amphoteric metals such as silicon and aluminum. In this specification, the term "inorganic particles" does not include the aforementioned "metal oxide particles."

[0092] The resin and inorganic particles described above are insulating because they do not contain metal elements. The presence of these insulating particles allows for adjustment of the volume resistivity of the protective layer, thereby enhancing the desired effect. Furthermore, the addition of these particles can further improve the durability of the protective layer.

[0093] As the resin particles mentioned above, generally known resin particles can be used, but it is preferable that they be one type of resin particle selected from acrylic resin particles, urethane resin particles, melamine resin particles, and epoxy resin particles, or a mixture of two or more types of resin particles.

[0094] While generally known inorganic particles can be used as the inorganic particles mentioned above, it is preferable that the inorganic particles are silica particles.

[0095] It is preferable that the total amount of the above-mentioned resin particles, inorganic particles, and mixtures thereof added is within the range of 1 to 25% by mass relative to the total solid content in the protective layer.

[0096] When the total amount of additives mentioned above is 1% by mass or more, the effect obtained is greater, and when it is 25% by mass or less, the volume resistivity of the protective layer is increased by 10 9 ~10 15 It becomes easier to adjust the strength within the range of Ω·cm. Furthermore, it becomes easier to suppress the decrease in durability caused by the hardening film becoming brittle.

[0097] (2.2) Volume resistivity of the protective layer The protective layer according to the present invention has a volume resistivity of 10 9 ~10 15 It is within the range of Ω·cm. The volume resistivity is 10 9 If the volume resistivity is less than Ω·cm, the charge transport function of the protective layer deteriorates, making it more prone to malfunctions in image memory and other components. Also, if the volume resistivity is less than 10 15 When the value exceeds Ω·cm, the electrostatic latent image diffuses too much, making it more prone to problems such as image blurring.

[0098] The volume resistivity of the protective layer according to the present invention can be determined by measuring it using a known apparatus under conditions of 25°C and 50% relative humidity with an applied voltage of 100V (for 1 minute). An example of such a known apparatus is the High Resta-UP (MCP-450) from Dia Instruments Co., Ltd.

[0099] (2.3) Thickness of the protective layer There are no particular limitations on the thickness of the protective layer according to the present invention, but it is preferable that the thickness of the protective layer is in the range of 1 to 10 μm.

[0100] By keeping the thickness of the protective layer within the above range, the volume resistivity of the protective layer is set to 10 9 ~10 15 Even if the Ω·cm range is maintained and the hydroxyl value of the polymerizable compound is adjusted to the range of 10-200 mgKOH / g, problems such as image blurring due to the diffusion of the electrostatic latent image will be less likely to occur. The effect of the hydroxyl value of the polymerizable compound on the present invention will be described later.

[0101] The reason why the above-mentioned problems occur is thought to be that the diffusion of the electrostatic latent image occurs not only horizontally but also in the depth direction.

[0102] If the protective layer thickness is 1 μm or more, stable film formation becomes easier due to manufacturing issues, and the lifespan of the photoreceptor is extended due to wear of the protective layer. Furthermore, if the protective layer thickness is 10 μm or less, problems such as image blurring due to the diffusion of the electrostatic latent image mentioned above are less likely to occur, and the amount of energy required to cure the protective layer is reduced, improving productivity.

[0103] (2.5) Method for forming a protective layer The protective layer according to the present invention is formed by preparing a protective layer-forming composition, applying it to a photosensitive layer, drying it, and curing it.

[0104] "Protective layer-forming composition" refers to a composition containing metal oxide particles, resin particles, inorganic particles, polymerizable monomers, and polymerization initiators used in forming a protective layer. However, in this specification, the above-mentioned "protective layer-forming composition" does not include a solvent. Furthermore, the "protective layer-forming coating solution" described later refers to the above-mentioned "protective layer-forming composition" including a "solvent."

[0105] (Polymerization initiator) The polymerization initiator is appropriately selected depending on the type of polymerizable compound contained in the protective layer-forming composition. In the present invention, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator, but a photopolymerization initiator is preferred. In particular, a radical polymerization initiator is preferred.

[0106] There are no particular limitations on the radical polymerization initiators, and any known ones can be used. Examples include alkylphenone compounds and phosphine oxide compounds.

[0107] Among these, compounds having an α-aminoalkylphenone structure or an acylphosphine oxide structure are preferred, and compounds having an acylphosphine oxide structure are more preferred.

[0108] An example of a compound having an acylphosphine oxide structure is "Omnirad819" (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, manufactured by IGM Resins BV).

[0109] Polymerization initiators may be used alone or in combination of two or more types.

[0110] The amount of polymerization initiator in the protective layer-forming composition is preferably in the range of 0.1 to 20 parts by mass, and more preferably in the range of 0.5 to 10 parts by mass, per 100 parts by mass of the total amount of charge transport material and polymerizable compound.

[0111] (Other ingredients) The protective layer-forming composition may contain other components. Examples of other components include antioxidants, stabilizers, and silicone oils. For antioxidants, those disclosed in Japanese Patent Publication No. 2000-305291 are preferred.

[0112] Antioxidants, stabilizers, silicone oils, etc., can each be used in a range of preferably 0.01 to 50 parts by mass, more preferably 0.01 to 40 parts by mass, per 100 parts by mass of the total amount of polymerizable compounds.

[0113] 3.Photosensitive layer First, as a photosensitive layer according to the present invention, a single-layer type photosensitive layer containing a charge generating material, a charge transporting material, and a resin in the same layer will be described.

[0114] (3.1) Single-layer photosensitive layer Figure 1 is a cross-sectional view showing an example of the layer structure of an electrophotographic photoreceptor having a single-layer photosensitive layer. In the electrophotographic photoreceptor 1 shown in Figure 1, an intermediate layer 12, a photosensitive layer 13, and a protective layer 14 are sequentially laminated on a conductive support 11. The photosensitive layer 106 also includes two functions: a charge generation function and a charge transport function.

[0115] A "single-layer photosensitive layer" is essentially a single photosensitive layer that achieves both charge generation and charge transport functions within that single layer. The following describes the charge generation and charge transport materials used in single-layer photosensitive layers.

[0116] (3.1.1) Charge-generating materials As the charge-generating material, known charge-generating materials can be used. Preferably, examples include phthalocyanine pigments, polycyclic quinone pigments, perylene-based pigments, and bis-azo pigments. As phthalocyanine-based pigments, metal-free phthalocyanine, vanadium phthalocyanine, oxotitanium phthalocyanine, and gallium phthalocyanine are preferably used. Among these, polycyclic quinone pigments and titanyl phthalocyanine pigments are preferred. Furthermore, these charge-generating materials may be used individually or in combination of two or more.

[0117] (3.1.2) Charge transport material As the charge transport material, known charge transport materials can be used. Preferably, a combination of a hole-transporting charge transport material and an electron-transporting charge transport material is preferred.

[0118] (Hole-transporting charge-transporting material) Examples of hole-transporting charge-transporting substances include carbazole derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolon derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, pyrazoline compounds, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, phenylenediamine derivatives, stilbene derivatives, benzidine derivatives, poly-N-vinylcarbazole, poly-1-vinylpyrene, and poly-9-vinylanthracene, triphenylamine derivatives, and two or more of these may be used in combination.

[0119] (electron-transporting charge-transporting substance) Examples of electron-transporting charge-transporting materials include 2-nitro-9-fluorenone, 2,7-dinitro-9-fluorenone, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2-nitrobenzothiophene, 2,4,8-trinitrothioxanthone, dinitroanthracene, dinitroacridine, dinitroanthraquinone, naphthoquinones, and 3,5-dimethyl-3′,5′-di-t-butyldiphenoquinone.

[0120] (3.1.3) Resin Various resins can be used as the binding resin for charge-generating and charge-transporting materials. The "binding resin for charge-generating and charge-transporting materials" is a resin that serves as a medium or matrix (base) for dispersing charge-generating and charge-transporting materials.

[0121] Examples of the binder resins mentioned above include various polymers such as styrene polymers, acrylic polymers, styrene-acrylic polymers, ethylene-vinyl acetate copolymers, polypropylene, olefin polymers such as ionomers, polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, polyesters, alkyd resins, polyamides, polyurethanes, epoxy resins, polycarbonates, polyarylates, polysulfones, diallyl phthalate resins, silicone resins, ketone resins, polyvinyl butyral resins, polyether resins, phenolic resins, and photocurable resins such as epoxy acrylates. These can be used individually or in combination of two or more. Among these, styrene polymers, acrylic polymers, styrene-acrylic polymers, polyester resins, alkyd resins, polycarbonates, and polyarylates are preferred.

[0122] (3.1.4) Content of each component In a single-layer photoreceptor, the content of the charge-generating substance is in the range of 0.1 to 50 parts by mass, preferably 0.5 to 30 parts by mass, per 100 parts by mass of the binder resin.

[0123] The content of the hole-transporting charge-transporting substance is in the range of 5 to 500 parts by mass, preferably 25 to 200 parts by mass, per 100 parts by mass of the binder resin.

[0124] The content of the electron-transporting charge-transporting substance is in the range of 5 to 100 parts by mass, preferably 10 to 80 parts by mass, per 100 parts by mass of the binder resin.

[0125] The total content of hole-transporting charge-transporting material and electron-transporting charge-transporting material is preferably in the range of 20 to 500 parts by mass, more preferably in the range of 30 to 200 parts by mass, per 100 parts by mass of binder resin.

[0126] When an electron-accepting compound is included in a single-layer photosensitive layer, the content of the electron-accepting compound is preferably in the range of 0.1 to 40 parts by mass, more preferably in the range of 0.5 to 20 parts by mass, per 100 parts by mass of the binder resin.

[0127] (3.1.5) Thickness of the photosensitive layer The thickness of the single-layer photosensitive layer is generally preferable in the range of 5 to 100 μm in terms of electrophotographic properties. It is more preferable in the range of 10 to 50 μm.

[0128] (3.2) Reverse-layer photosensitive layer An inverse-layer photosensitive layer is formed by stacking a charge transport layer and a charge generation layer in that order. Figure 2 is a cross-sectional view showing an example of the layer structure of an electrophotographic photoreceptor having an inverse-layer photosensitive layer. In the electrophotographic photoreceptor 2 shown in Figure 2, an intermediate layer 22, a photosensitive layer 23, and a protective layer 24 are sequentially stacked on a conductive support 21. The photosensitive layer 23 includes a charge transport layer 23a and a charge generation layer 23b, and is formed by stacking the charge transport layer 23a and the charge generation layer 23b in that order.

[0129] (3.2.1) Charge transport layer The charge transport layer according to the present invention is a layer containing a charge transport material and a binder resin. When the charge transport layer also serves as a charge generating layer, the charge transport layer contains the aforementioned charge generating material.

[0130] As the charge transport material, the same material as that contained in the single-layer photosensitive layer described above can be used. The amount of charge transport material in the charge transport layer is preferably in the range of 10 to 500 parts by mass, and more preferably in the range of 20 to 250 parts by mass, per 100 parts by mass of the binder resin for the charge transport layer.

[0131] Known resins can be used as the binder resin contained in the charge transport layer, such as polycarbonate, polyacrylate, polyester, polystyrene, styrene-acrylonitrile copolymer, polymethacrylate ester, and styrene-methacrylate ester copolymer. Among these, polycarbonate is preferred.

[0132] Furthermore, polycarbonate resins of the BPA (bisphenol A) type, BPZ (bisphenol Z) type, dimethyl BPA type, and BPA-dimethyl BPA copolymer type are preferred in terms of crack resistance, abrasion resistance, and electrostatic properties.

[0133] The charge transport layer may contain other components such as antioxidants, electronically conductive agents, stabilizers, and silicone oil. For antioxidants, those disclosed in Japanese Patent Publication No. 2000-305291 are preferred, and for electronically conductive agents, those disclosed in Japanese Patent Publication Nos. 50-137543 and 58-76483 are preferred.

[0134] The thickness of the charge transport layer varies depending on the properties of the charge transport material, the properties and content ratio of the binder resin for the charge transport layer, etc., but is preferably in the range of 5 to 40 μm, and more preferably in the range of 10 to 30 μm.

[0135] (3.2.2) Charge generation layer The charge generating layer is a layer containing a charge generating substance and a binder resin.

[0136] As the charge generating material, the same material as that contained in the single-layer photosensitive layer described above can be used. The amount of charge generating material in the charge generating layer is preferably in the range of 1 to 600 parts by mass, and more preferably in the range of 50 to 500 parts by mass, per 100 parts by mass of the binder resin for the charge generating layer.

[0137] As the binder resin for the charge generation layer, known resins can be used, for example, polystyrene resin, polyethylene resin, polypropylene resin, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, polyvinyl butyral resin, epoxy resin, polyurethane resin, phenolic resin, polyester resin, alkyd resin, polycarbonate resin, silicone resin, melamine resin, and copolymer resins containing two or more of these resins (for example, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin), poly-vinylcarbazole resin, etc., but are not limited to these. Among these, polyvinyl butyral resin is preferred.

[0138] The thickness of the charge generation layer varies depending on the properties of the charge generation material, the properties and content ratio of the binder resin for the charge generation layer, etc., but is preferably in the range of 0.01 to 5 μm, and more preferably in the range of 0.05 to 3 μm.

[0139] (3.3) Method for forming a photosensitive layer In the case of the single-layer type photosensitive layer according to the present invention, the photosensitive layer is formed by applying a photosensitive layer-forming coating solution to a conductive support or an intermediate layer formed on a conductive support, drying it, and curing it. The photosensitive layer-forming coating solution contains a charge generating substance, a charge transporting substance, and a binder resin, etc.

[0140] When the photosensitive layer according to the present invention is of the reverse layer type described above, a coating solution for forming a charge transport layer and a coating solution for forming a charge generation layer are prepared, applied sequentially, dried, and cured. In addition, a charge transport layer is first formed on the conductive support or on an intermediate layer formed on the conductive support, and then a charge generation layer is formed on the charge transport layer.

[0141] 4. Conductive support As conductive supports, for example, metals such as aluminum, copper, chromium, nickel, zinc, and stainless steel can be formed into drums or sheets, or metal foils such as aluminum or copper can be laminated onto a plastic film. Alternatively, materials such as aluminum, indium oxide, and tin oxide can be vapor-deposited onto a plastic film, or metals, plastic films, and paper can be used to provide a conductive layer by coating a conductive substance alone or together with a binder resin.

[0142] 5. Middle class An intermediate layer having barrier and adhesive functions may be provided between the conductive support and the photosensitive layer.

[0143] The intermediate layer can be formed by dissolving binder resins such as casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide, polyurethane, and gelatin in a known solvent and applying them by immersion coating or the like. Among these, alcohol-soluble polyamide resins are preferred.

[0144] Furthermore, various conductive fine particles and metal oxide particles can be included to adjust the resistance of the intermediate layer. For example, various metal oxide particles such as alumina, zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, and bismuth oxide can be used. In addition, ultrafine particles such as tin-doped indium oxide, antimony-doped tin oxide, and zirconium oxide can be used.

[0145] These metal oxide particles may be used individually or in a mixture of two or more types. When two or more types are mixed, they may take the form of a solid solution or fusion. The average particle size of such metal oxide particles is preferably 0.3 μm or less, more preferably 0.1 μm or less.

[0146] As the solvent used for the intermediate layer, it is preferable to use one that can well disperse various conductive fine particles and metal oxide particles and dissolve the polyamide resin. Specifically, C2-C4 alcohols such as ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, t-butanol, and sec-butanol are preferred because they have excellent solubility and coating performance for polyamide resins. In addition, as cosolvents that can be used in combination with the above solvent to improve storage properties and particle dispersibility and obtain desirable effects, methanol, benzyl alcohol, toluene, methylene chloride, cyclohexanone, and tetrahydrofuran are examples of such solvents.

[0147] The concentration of the binder resin is selected appropriately according to the thickness of the intermediate layer and the production speed.

[0148] When conductive fine particles or metal oxide particles are dispersed in a binder resin, the mixing ratio of these particles to the binder resin is preferably in the range of 20 to 400 parts by mass per 100 parts by mass of the binder resin, and more preferably in the range of 50 to 200 parts by mass.

[0149] Dispersion methods that can be used include, but are not limited to, ultrasonic dispersers, ball mills, sand grinders, and homomixers.

[0150] The drying method for the intermediate layer can be appropriately selected depending on the type of solvent and film thickness, but heat drying is preferred.

[0151] The thickness of the intermediate layer is preferably in the range of 0.1 to 15 μm, and more preferably in the range of 0.3 to 10 μm.

[0152] [II. Electrophotographic Image Forming Apparatus] The electrophotographic image forming apparatus of the present invention is characterized by comprising: an electrophotographic photoreceptor of the present invention; a positive charging means for charging the electrophotographic photoreceptor to a positive potential; an exposure means for forming an electrostatic latent image on the electrophotographic photoreceptor; a developing means for forming a toner image on the electrophotographic photoreceptor; a transfer means for moving the toner image formed on the electrophotographic photoreceptor to a transfer medium; and a cleaning means for collecting toner remaining on the photoreceptor that has not been transferred using a cleaning blade.

[0153] The positively charged electrophotographic photoreceptor of the present invention is applicable to generally known positively charged electrophotographic image forming apparatuses. The electrophotographic photoreceptor exhibits particularly excellent effects in image forming apparatuses having a cleaning means for recovering toner remaining on the photoreceptor without being transferred using a cleaning blade. This is because excessive wear of the photoreceptor occurs when developer components adhering to the surface of the photoreceptor are rubbed off by the cleaning blade.

[0154] As an electrophotographic image forming apparatus, for example, the one described in Japanese Patent Publication No. 2011-242574 can be used.

[0155] Figure 3 is an example of a cross-sectional view of the image forming apparatus according to the present invention.

[0156] This image forming apparatus is called a tandem-type color image forming apparatus and consists of four sets of image forming sections (image forming units) 10Y, 10M, 10C, and 10Bk, an endless belt-shaped intermediate transfer unit 7, a paper feeding and transporting means 21, and a fixing means 24. An original image reading device SC is located on the upper part of the main body A of the image forming apparatus.

[0157] The image forming unit 10Y, which forms a yellow image, includes a charging means 2Y, an exposure means 3Y, a developing means 4Y, a primary transfer roller 5Y as a primary transfer means, and a cleaning means 6Y, all arranged around a drum-shaped photoreceptor 1Y as a first image carrier.

[0158] The image forming unit 10M, which forms a magenta-colored image, includes a drum-shaped photoreceptor 1M as a first image carrier, a charging means 2M, an exposure means 3M, a developing means 4M, a primary transfer roller 5M as a primary transfer means, and a cleaning means 6M.

[0159] The image forming unit 10C, which forms a cyan image, includes a drum-shaped photoreceptor 1C as a first image carrier, a charging means 2C, an exposure means 3C, a developing means 4C, a primary transfer roller 5C as a primary transfer means, and a cleaning means 6C.

[0160] The image forming unit 10Bk that forms the black image includes a drum-shaped photoreceptor 1Bk as a first image carrier, a charging means 2Bk, an exposure means 3Bk, a developing means 4Bk, a primary transfer roller 5Bk as a primary transfer means, and a cleaning means 6Bk.

[0161] The four image forming units described above consist of a photoreceptor drum, a rotating charging means, an image exposure means, a rotating developing means, and a cleaning means for cleaning the photoreceptor drum.

[0162] The image forming units 10Y, 10M, 10C, and 10Bk have the same configuration, differing only in the color of the toner image formed on the photoreceptors 1Y, 1M, 1C, and 1Bk, respectively. The image forming unit 10Y will be explained in detail as an example.

[0163] The image forming unit 10Y arranges a charging means 2Y, an exposure means 3Y, a developing means 4Y, and a cleaning means 6Y around the photosensitive drum 1Y, which is the image forming body, to form a yellow (Y) toner image on the photosensitive drum 1Y.

[0164] Furthermore, in this embodiment, at least the photoreceptor drum 1Y, charging means 2Y, developing means 4Y, and cleaning means 6Y of the image forming unit 10Y are integrated into one unit.

[0165] The charging means 2Y is a means of applying a uniform potential to the photoreceptor drum 1Y, and in this embodiment, a corona discharge type charging means 2Y is used for the photoreceptor drum 1Y.

[0166] The image exposure means 3Y is a means for exposing a photoreceptor drum 1Y, which is given a uniform potential by the charging means 2Y, based on an image signal (yellow), to form an electrostatic latent image corresponding to the yellow image.

[0167] The image exposure means 3Y may consist of an array of LEDs arranged in the axial direction of the photoreceptor drum 1Y and an imaging element (product name; CELFOC® lens), or a laser optical system.

[0168] In the image forming apparatus of the present invention, the above-mentioned photoreceptor and components such as a developer and a cleaning unit may be integrally combined as a process cartridge (image forming unit), and this image forming unit may be configured to be detachably attached to the main body of the image forming apparatus.

[0169] Alternatively, a process cartridge (image forming unit) may be formed by integrally supporting at least one of the charging means, image exposure unit, developer, transfer or separator, and cleaning unit together with the photoreceptor. Alternatively, a single image forming unit may be detachably attached to the main body of the image forming apparatus, and detachable using guide means such as rails on the main body of the image forming apparatus.

[0170] The endless belt-shaped intermediate transfer unit 7 has an endless belt-shaped intermediate transfer body 70 as a second image carrier, which is a semiconductive endless belt-shaped body that is wound around a plurality of rollers and rotatably supported.

[0171] The images of each color formed by the image forming units 10Y, 10M, 10C, and 10Bk are successively transferred onto a rotating endless belt-shaped intermediate transfer body 70 by primary transfer rollers 5Y, 5M, 5C, and 5Bk, which serve as primary transfer means, to form a combined color image.

[0172] The transfer material P, which is housed in the paper feed cassette 20 and serves as a support for holding the final fixed image (e.g., plain paper, transparent sheet, etc.), is fed by the paper feed means 21. Subsequently, it is transported through multiple intermediate rollers 22A, 22B, 22C, 22D and the registration roller 23 to the secondary transfer roller 5b, which serves as a secondary transfer means, and the color image is transferred onto the transfer material P in a single transfer.

[0173] The transfer material P onto which the color image has been transferred is fixed by the fixing means 24 and then held by the paper discharge roller 25 and placed on the paper discharge tray 26 outside the machine. Here, the transfer support for the toner image formed on the photoreceptor, such as the intermediate transfer body or transfer material, is collectively referred to as the transfer medium.

[0174] On the other hand, after the color image is transferred to the transfer material P by the secondary transfer roller 5b, which acts as a secondary transfer means, the endless belt-shaped intermediate transfer body 70, which is formed by curvature separation of the transfer material P, has residual toner removed by the cleaning means 6b.

[0175] During the image formation process, the primary transfer roller 5Bk is always in contact with the photoreceptor 1Bk. The other primary transfer rollers 5Y, 5M, and 5C are in contact with their respective photoreceptors 1Y, 1M, and 1C only when a color image is being formed.

[0176] The secondary transfer roller 5b contacts the endless belt-shaped intermediate transfer body 70 only when the transfer material P passes over it and secondary transfer is performed.

[0177] Furthermore, the housing 8 can be extended from the main body A of the image forming apparatus via support rails 82L and 82R.

[0178] The housing 8 consists of image forming units 10Y, 10M, 10C, and 10Bk, and an endless belt-shaped intermediate transfer unit 7.

[0179] The image forming units 10Y, 10M, 10C, and 10Bk are arranged in a vertical column. An endless belt-shaped intermediate transfer unit 7 is located to the left of the photoreceptors 1Y, 1M, 1C, and 1Bk in the diagram. The endless belt-shaped intermediate transfer unit 7 consists of an endless belt-shaped intermediate transfer body 70 that can be rotated by winding around rollers 71, 72, 73, and 74, primary transfer rollers 5Y, 5M, 5C, and 5Bk, and a cleaning means 6b. [Examples]

[0180] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the examples, the units "parts" or "%" are used, and unless otherwise specified, they represent "parts by mass" or "mass%". In the examples below, only photoreceptors having a single-layer photoreceptor are manufactured, but as mentioned above, the effects of the present invention can be similarly obtained with a reverse-layer photoreceptor.

[0181] A. Fabrication of the photoreceptor (A.1) Photoreceptor 1 (Preparation of conductive support) A conductive support [1] with a surface roughness Rz of 1.5 μm was prepared by machining the surface of a cylindrical aluminum support.

[0182] (Formation of the intermediate layer) The following materials were dispersed in the following quantities using a sand mill as a disperser in a batch manner for 10 hours to prepare the coating solution for forming the intermediate layer [1].

[0183] ·material Polyamide resin X1010 (manufactured by Daicel Degussa Co., Ltd.) 1 part by mass Titanium oxide SMT500SAS (manufactured by Teika Co., Ltd.) 1.1 parts by mass Ethanol 20 parts by mass

[0184] An intermediate layer [1] was formed on a conductive support [1] by immersion coating, applying an intermediate layer forming solution [1] to the intermediate layer so that the thickness of the intermediate layer after drying at 110°C for 20 minutes was 2 μm.

[0185] (Formation of the photosensitive layer) The following materials were mixed in the quantities specified below and mixed and dispersed in a ball mill for 50 hours to prepare a coating solution for photosensitive layer formation [1].

[0186] ·material Charge generating substance α 10 parts by mass 100 parts by mass of hole-transporting charge-transporting material CTM-A Electron-transporting charge-transporting substance CTM-H 50 parts by mass Polycarbonate Z300 (binding resin) 200 parts by mass Irganox1010 (antioxidant) 6 parts by mass Toluene / tetrahydrofuran = 1 / 4 volume % 1600 parts by mass Silicone oil "KF-54" 1 part by mass

[0187] The "charge-generating substance α" mentioned above is a titanyl phthalocyanine pigment that has a maximum diffraction peak at at least 27.3° in Cu-Kα characteristic X-ray diffraction spectrum measurements. The "polycarbonate Z300" mentioned above is manufactured by Mitsubishi Gas Chemical Company. The "Irganox 1010" mentioned above is manufactured by Ciba Japan. The silicone oil "KF-54" mentioned above is manufactured by Shin-Etsu Chemical Co., Ltd.

[0188] The structural formula of the hole-transporting charge transporter CTM-A is shown below. The electron-transporting charge transporter CTM-H is 3,5-dimethyl3′,5′-di-(t)butyldiphenoquinone.

[0189] [ka]

[0190] Using a circular volume-controlled coating apparatus, a photosensitive layer-forming coating solution [1] was applied onto the intermediate layer [1], and the photosensitive layer [1] was formed by drying at 110°C for 60 minutes. At this time, the total thickness of the intermediate layer [1] and the photosensitive layer [1] was set to 20 μm.

[0191] (Formation of a protective layer) Under light-shielding conditions, the following materials were mixed in the following quantities and dispersed for 5 hours using a sand mill as a disperser to obtain prepared solution [1].

[0192] ·material 66 parts by mass of the difunctional radical polymerizable compound "701A". Metal oxide particles [1] 24 parts by mass 2-Butanol (solvent 1) 400 parts by mass Tetrahydrofuran (solvent 2) 40 parts by mass

[0193] The above-mentioned difunctional radical polymerizable compound "701A" is 2-hydroxy-3-methacrylate manufactured by Shin Nakamura Chemical Industry Co., Ltd., with a hydroxyl value of 200 mgKOH / g. The above-mentioned metal oxide particles [1] are "FZO-50" manufactured by Ishihara Sangyo Co., Ltd., with a volume resistivity of 1.0 × 10⁻⁶. 5 These are zinc oxide particles with dimensions of Ω·cm.

[0194] Ten parts by mass of the polymerization initiator "IRGACURE819" were added to the prepared solution [1], and the mixture was stirred under light shielding to dissolve it and prepare the protective layer forming coating solution [1].

[0195] Using a circular slide hopper type coating machine, a protective layer forming coating liquid [1] was applied onto the photosensitive layer [1] to form a coating film, and the protective layer [1] was formed by drying by irradiating with ultraviolet light for 1 minute using a metal halide lamp. The thickness of the protective layer [1] was 11.0 μm.

[0196] Based on the above, a photoreceptor [1] was prepared.

[0197] (A.2) Photoconductor 2 Photoreceptor 2 was prepared in the same manner as photoreceptor 1, except that the bifunctional radical polymerizable compound "701A" was replaced with the polyfunctional radical polymerizable compound "PETIA" in the formation of the protective layer.

[0198] The polyfunctional radical polymerizable compound "PETIA" is a pentaerythritol (tri / tetra)acrylate manufactured by Daicel Ornex Corporation with a hydroxyl value of 170 mgKOH / g.

[0199] (A.3) Photoreceptor 3 The photoreceptor 3 was fabricated in the same manner as the photoreceptor 2, except that the metal oxide particles [1] were changed to metal oxide particles [2] in the formation of the protective layer.

[0200] Furthermore, the volume resistivity of the metal oxide particles [2] is adjusted to 1.0 × 10⁻⁶ by adjusting the volume resistivity of the metal oxide particles [1]. 11 These are zinc oxide particles with a density of Ω·cm.

[0201] (A.4) Photoreceptor 4 The photoreceptor 4 was manufactured in the same manner as the photoreceptor 2, except that the metal oxide particles [1] were changed to metal oxide particles [3] in the formation of the protective layer.

[0202] Furthermore, the volume resistivity of the metal oxide particles [3] is adjusted to 1.0 × 10⁻⁶ by adjusting the volume resistivity of the metal oxide particles [1]. 9 These are zinc oxide particles with a density of Ω·cm.

[0203] (A.5) Photoreceptor 5 The photoreceptor 5 was manufactured in the same manner as the photoreceptor 2, except that the metal oxide particles [1] were changed to metal oxide particles [4] in the formation of the protective layer.

[0204] The above metal oxide particles [4] are tin(IV) nanopowder manufactured by Sigma-Aldrich, with a volume resistivity of 1.0 × 10⁻⁶. 9 These are tin oxide particles with a density of Ω·cm.

[0205] (A.6) Photoreceptor 6 The photoreceptor 6 was prepared in the same manner as the photoreceptor 5, except that the amount of metal oxide particles [4] added was changed from 24 parts by mass to 66 parts by mass in the formation of the protective layer.

[0206] (A.7) Photoconductor 7 The photoreceptor 7 was prepared in the same manner as the photoreceptor 5, except that the amount of metal oxide particles [4] added was changed from 24 parts by mass to 50 parts by mass in the formation of the protective layer.

[0207] (A.8) Photoreceptor 8 An intermediate layer and a photosensitive layer were formed on a conductive support in the same manner as in photoreceptor 1. In addition, a protective layer forming coating solution [8] was prepared as described below.

[0208] The following materials were mixed in the following quantities under light-shielding conditions and dispersed for 5 hours using a sand mill as a disperser to obtain the prepared solution [8]. ·material 14 parts by mass of the polyfunctional radical polymerizable compound "PETIA" Metal oxide particles [4] 50 parts by mass Acrylic resin particles "FS-107" 26 parts by mass 2-Butanol (solvent 1) 400 parts by mass Tetrahydrofuran (solvent 2) 40 parts by mass

[0209] The acrylic resin particles "FS-107" mentioned above are manufactured by Nippon Paint Industrial Coating Co., Ltd.

[0210] Ten parts by mass of the polymerization initiator "IRGACURE819" were added to the prepared solution [8], and the mixture was stirred under light shielding to dissolve it and prepare the coating solution for forming the protective layer [8].

[0211] The coating solution for forming the protective layer [8] was applied to the photosensitive layer, and the conditions for UV irradiation and drying were the same as for the photoreceptor 1, and a protective layer was formed on the photosensitive layer.

[0212] Based on the above, a photoreceptor [8] was prepared.

[0213] (A.9) Photoreceptor 9 The photoreceptor 9 was manufactured in the same manner as the photoreceptor 8, except that the acrylic resin particles "FS-107" were replaced with silica particles [1].

[0214] The silica particles [1] are AEROSIL OX50 silica particles manufactured by AEROSIL.

[0215] (A.10) Photoreceptor 10 The photoreceptor 10 was prepared in the same manner as the photoreceptor 8, except that the amount of acrylic resin particles "FS-107" added was changed from 26 parts by mass to 20 parts by mass.

[0216] (A.11) Photoreceptor 11 The acrylic resin particles "FS-107" were replaced with silica particles [1], the amount of silica particles [1] added was set to 20 parts by mass, and the conditions for coating the protective layer onto the photosensitive layer, as well as UV irradiation and drying treatment, were changed to make the thickness of the protective layer 5 μm. Otherwise, the photoreceptor 11 was prepared in the same manner as the photoreceptor 8.

[0217] (A.12) Photoreceptor 12 The photoreceptor 12 was prepared in the same manner as the photoreceptor 11, except that the polyfunctional radical polymerizable compound "PETIA" was changed to the polyfunctional radical polymerizable compound "PETRA" in the formation of the protective layer.

[0218] The polyfunctional radical polymerizable compound "PETRA" is a pentaerythritol (tri / tetra)acrylate manufactured by Daicel Ornex Corporation with a hydroxyl value of 115 mgKOH / g.

[0219] (A.13) Photoreceptor 13: Comparative Example 1 An intermediate layer and a photosensitive layer were formed on a conductive support in the same manner as in photoreceptor 1. In addition, the following materials were mixed in the following quantities and dispersed for 5 hours using a sand mill as a disperser to prepare a protective layer forming coating solution

[13] .

[0220] ·material Polycarbonate "Z300" (binding resin) 50 parts by mass Metal oxide particles [4] 50 parts by mass Tetrahydrofuran (solvent 1) 1600 parts by mass Toluene (solvent 2) 400 parts by mass

[0221] Using a circular slide hopper type coating machine, the protective layer forming coating liquid

[13] was applied onto the photosensitive layer to form a coating film, and then dried in a drying oven at 120°C for 1 hour to form a protective layer with a dry film thickness of 5.0 μm.

[0222] Based on the above, a photoreceptor

[13] was prepared.

[0223] (A.14) Photoreceptor 14: Comparative example 2 An intermediate layer and a photosensitive layer were formed on a conductive support in the same manner as in photoreceptor 1. In addition, a protective layer forming coating solution

[14] was prepared as described below.

[0224] The following materials were mixed in the following quantities under light shielding conditions, and the mixture was stirred for 5 hours using a sand mill as a disperser to obtain the prepared solution

[14] .

[0225] ·material Polyfunctional radical polymerizable compound "PETIA" 90 parts by mass 2-Butanol (solvent 1) 400 parts by mass Tetrahydrofuran (solvent 2) 40 parts by mass

[0226] Ten parts by mass of the polymerization initiator "IRGACURE819" were added to the prepared solution

[14] , and the mixture was stirred under light shielding to dissolve it, thereby preparing the protective layer forming coating solution

[14] .

[0227] The protective layer was formed on the photosensitive layer by changing the application of the protective layer-forming coating solution to the photosensitive layer, as well as the conditions such as UV irradiation and drying treatment, to achieve a thickness of 5 μm.

[0228] Based on the above, a photoreceptor

[14] was prepared.

[0229] (A.15) Photoreceptor 15: Comparative example 3 A photoreceptor 15 was prepared in the same manner as photoreceptor 2, except that metal oxide particles [1] were replaced with metal oxide particles [5], and the conditions for applying the protective layer-forming coating solution to the photoreceptor layer, as well as conditions such as ultraviolet irradiation and drying treatment, were changed to make the thickness of the protective layer 5 μm.

[0230] Note that the metal oxide particles [5] are tin oxide particles obtained by adjusting the volume resistivity of the metal oxide particles [4] to 1.0×10 12 Ω·cm.

[0231] (A.16) Photoreceptor 16: Comparative Example 4 The polyfunctional radically polymerizable compound "PETIA" was changed to the polymerizable compound "Desolite SCR701" manufactured by Nippon Special Coatings Co., Ltd., and the coating of the coating solution for forming the protective layer on the photosensitive layer and the conditions such as ultraviolet irradiation and drying treatment were changed to make the thickness of the protective layer 5 μm. Otherwise, the photoreceptor 16 was produced in the same manner as the photoreceptor 7.

[0232] Note that "Desolite SCR701" is a urethane acrylate manufactured by Nippon Special Coatings Co., Ltd.

[0233] (A.17) Photoreceptor 17: Comparative Example 5 The photoreceptor 17 was produced in the same manner as the photoreceptor 7, except that the polyfunctional radically polymerizable compound "PETIA" was changed to the polyfunctional polymerizable compound "TMPTA" manufactured by Daicel Ornex Co., Ltd. in the formation of the protective layer.

[0234] Note that "TMPTA" is trimethylolpropane triacrylate manufactured by Daicel Ornex Co., Ltd. with a hydroxyl value of 9 mgKOH / g.

[0235] B. Volume Resistivity of the Protective Layer of Each Photoreceptor The volume resistivity of the protective layer of each produced photoreceptor was measured at a temperature of 25 °C, a relative humidity of 50%, and an applied voltage of 100 V (for 1 minute). As the measuring device, the High Resistesta-UP (MCP-450) of Dia Instruments Co., Ltd. was used.

[0236] C. Summary of the Protective Layer of Each Photoreceptor As described above, the polymerizable compounds, contained particles, volume resistivity, and thickness in the protective layer of each produced photoreceptor were summarized in Table I.

[0237] [Table 1]

[0238] D. Rating All evaluations were conducted using an evaluation machine that was a modified full-color printing press (bizhub PRESS C1070, manufactured by Konica Minolta) converted into a positively charged electrophotographic image forming system.

[0239] (D.1) Abrasion resistance Each fabricated photoreceptor was assembled into a drum unit, and a durability test was conducted by printing 300,000 horizontal band images with a coverage rate of 10% on A3 size acid-free paper under conditions of 20°C and 50% RH.

[0240] At this time, the amount of wear on each photoreceptor from its initial state was measured, and the wearability of each photoreceptor was evaluated by ranking them according to the evaluation criteria below. The values ​​below represent ranks, with ranks 3, 4, and 5 being judged as having no practical problems, and ranks 1 and 2 being judged as having practical problems. The evaluation results are shown in Table II.

[0241] (Evaluation Criteria) 5: The amount of wear on the photoreceptor from its initial state is 0.05 μm or less (pass). 4: The amount of wear on the photoreceptor from its initial state is within the range of 0.05 to 0.1 μm (pass). 3: The amount of wear on the photoreceptor from its initial state is within the range of 0.1 to 0.3 μm (pass). 2: The amount of wear on the photoreceptor from its initial state is within the range of 0.3 to 0.5 μm (failure). 1: The amount of wear on the photoreceptor from its initial state is 0.5 μm or more (fail).

[0242] (D.2) Cleanability Each fabricated photoreceptor was incorporated into a drum unit, and 20,000 halftone images with 80% coverage, where the printed area was positioned towards the front of the paper in the paper transport direction and the white area towards the rear, were printed on A3 size acid-free paper under conditions of 10°C and 20% RH. Figure 4 is a simplified diagram showing the halftone image and paper transport direction during printing.

[0243] At this time, the degree of toner penetration was visually observed on the white areas, and the cleaning performance of each photoreceptor was evaluated by ranking them according to the evaluation criteria below. The numbers below represent ranks, with ranks 3, 4, and 5 being judged as having no practical problems, and ranks 1 and 2 being judged as having practical problems. The evaluation results are shown in Table II.

[0244] (Evaluation Criteria) 5: No stains were found (passed). 4: Short, streaky stains were present, but they were minor (acceptable). 3: Streaky stains were present, but they were minor (acceptable). 2: Obvious streaky stains appeared (failed). 1: Multiple obvious streaky stains were found (failed).

[0245] (D.3) Fine line reproducibility Each of the fabricated photoreceptors was assembled into a drum unit, and an image of fine lines with a width of 100 μm arranged in a grid was printed under conditions of 30°C and 80% RH.

[0246] At this time, the fine lines printed on the image were observed under a microscope and visually, and the fine line reproducibility of each photoreceptor was evaluated by ranking them according to the evaluation criteria below. The numbers below represent ranks, with ranks 2, 3, 4, and 5 being judged as acceptable for practical use, and rank 1 being judged as having practical problems. The evaluation results are shown in Table II.

[0247] (Evaluation Criteria) 5. Under microscopic observation, there is no toner scattering around the fine lines, no breaks in the fine lines, and fine lines with clear edges are formed (pass). 4: Under microscopic observation, there is no toner scattering around the fine lines or breaks in the fine lines, but fine lines with blurred edges are formed (pass). 3: Microscopic observation revealed no toner scattering around the fine lines or breaks in the fine lines, but clearly thinner fine lines were formed (pass). 2: In microscopic observation, although toner scattering around the fine line and some breaks in the fine line occur, the fine line can be visually confirmed (qualified). 1: In microscopic observation, a large amount of toner scattering around the fine line and breaks in the fine line occur, and thinning and breaks in the line width can also be confirmed visually (unqualified).

[0248] (D.4) Memory Each prepared photoreceptor was incorporated into the drum unit, and an evaluation image with a solid patch on the front side and a halftone on the rear side in the paper conveyance direction was printed on A3-sized neutral paper under the environment of 10°C and 20% RH. Figure 5 is a schematic diagram showing the evaluation image and the paper passing direction.

[0249] At this time, the memory occurring at the position after the second rotation of the photoreceptor was visually observed, ranked according to the following evaluation criteria, and the memory property of each photoreceptor was evaluated. The following numerical values are ranks. Ranks 2, 3, 4, and 5 were judged as evaluations without practical problems, and rank 1 was judged as an evaluation with practical problems. The evaluation results are shown in Table II.

[0250] (Evaluation Criteria) 5: No memory occurs (qualified). 4: Very fine memory of the solid patch occurs at the position of the second rotation of the photoreceptor (qualified). 3: Memory of the solid patch occurs at the position of the second rotation of the photoreceptor (qualified). 2: Memory of the solid patch clearly occurs at the position of the second rotation of the photoreceptor (qualified). 1: In addition to the position of the second rotation of the photoreceptor, memory of the solid patch also clearly occurs at the position of the third rotation (unqualified).

[0251]

Table 2

[0252] E. Overall Evaluation As is clear from Tables I and II, the examples are superior to the comparative examples in terms of wear resistance, cleanability, fine line reproduction, and memory evaluation of each photoreceptor, indicating that sufficient image quality and durability can be obtained even in positively charged image forming apparatuses.

[0253] Although embodiments of the present invention have been described and illustrated in detail above, the disclosed embodiments are illustrative and for illustrative purposes only and are not limiting. The scope of the present invention should be interpreted by the terms of the appended claims. [Explanation of symbols]

[0254] 1Y, 1M, 1C, 1Bk photoconductor 2Y, 2M, 2C, 2Bk Charging means 3Y, 3M, 3C, 3Bk exposure method 4Y, 4M, 4C, 4Bk developing means 5Y, 5M, 5C, 5Bk Primary Transfer Rollers 5b Secondary transfer roller 6Y, 6M, 6C, 6Bk Cleaning Methods 6b Cleaning method 7. Intermediate Transfer Unit 8 cabinets 10Y, 10M, 10C, 10Bk Image forming unit 20 Paper feed cassettes 21 Paper feeding and transporting means, paper feeding means 22A, 22B, 22C, 22D Intermediate Rollers 23 Resist Roller 24 Fixing means 25 Paper output roller 26 Paper output tray 70 Intermediate Transfer 71, 72, 73, 74 Rollers 82L, 82R support rails 100, 200 photoreceptor 101, 201 Conductive support 102, 202 Middle layer 103, 203 Photosensitive layer 203a Charge transport layer 203b Charge generation layer 104, 204 protective layer A Image forming apparatus main unit SC Document Image Reader P Transfer Material

Claims

1. An electrophotographic photoreceptor used in an image forming apparatus having a positively charged charging means, The electrophotographic photoreceptor has a photosensitive layer and a protective layer, The protective layer is a cured film containing metal oxide particles and formed from a cured polymerizable compound. The volume resistivity of the protective layer is 10 ９ ~10 １５ It is within the range of Ω·cm, The polymerizable compound is either an acrylic monomer or a methacrylic monomer, or a mixture thereof. The hydroxyl value of the polymerizable compound is in the range of 10 to 200 mg KOH / g. An electrophotographic photoreceptor characterized by the following features.

2. The hydroxyl value of the polymerizable compound is in the range of 50 to 160 mg KOH / g. The electrophotographic photoreceptor according to feature 1.

3. The polymerizable compound has three or more polymerizable functional groups. The electrophotographic photoreceptor according to feature 1.

4. The volume resistivity of the metal oxide particles is 10 ６ ~10 １０ It is within the range of Ω·cm. The electrophotographic photoreceptor according to feature 1.

5. The metal oxide particles are either titanium oxide or tin oxide, or a mixture thereof. The electrophotographic photoreceptor according to feature 1.

6. The content of the metal oxide particles is in the range of 25 to 65% by mass relative to the protective layer. The electrophotographic photoreceptor according to feature 1.

7. The protective layer is a cured film containing either resin particles or inorganic particles, or a mixture thereof. The electrophotographic photoreceptor according to feature 1.

8. The resin particles are one type of resin particle selected from acrylic resin particles, urethane resin particles, melamine resin particles, and epoxy resin particles, or a mixture of two or more types of resin particles. The electrophotographic photoreceptor according to feature 7.

9. The inorganic particles are silica particles. The electrophotographic photoreceptor according to feature 7.

10. The content of the resin particles and inorganic particles is within the range of 1 to 25% by mass relative to the protective layer. The electrophotographic photoreceptor according to feature 7.

11. The thickness of the protective layer is in the range of 1 to 10 μm. The electrophotographic photoreceptor according to feature 1.

12. The photosensitive layer is a single-layer photosensitive layer containing a charge generating material, a charge transporting material, and a resin in the same layer. The electrophotographic photoreceptor according to feature 1.

13. The photosensitive layer is a laminated type photosensitive layer in which a charge transport layer and a charge generation layer are stacked in that order, and the protective layer and the charge generation layer are formed adjacent to each other. The electrophotographic photoreceptor according to feature 1.

14. An electrophotographic photoreceptor according to any one of claims 1 to 13, A positive charging means for charging the electrophotographic photoreceptor to a positive potential, An exposure means for forming an electrostatic latent image on the electrophotographic photoreceptor, Developing means for forming a toner image on the electrophotographic photoreceptor, A transfer means for moving a toner image formed on the electrophotographic photoreceptor to a transfer medium, It includes a cleaning means for collecting toner that remains on the photoreceptor without being transferred using a cleaning blade. An electrophotographic image forming apparatus characterized by the following:

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