Image forming apparatus

Abstract

The present invention provides an image forming apparatus that can suppress image defects such as image fogging by suppressing contact charging between fluorine particles and toner due to the embedding of fluorine particles in the drum recesses, and contact charging between the toner and the drum recesses. [Solution] The image forming apparatus comprises an image carrier having a conductive substrate and a photosensitive layer laminated on the surface of the conductive substrate, a charging device, an exposure device, and a developing device. The developing device contains a non-magnetic one-component developer consisting only of toner and supplies the toner to the image carrier on which an electrostatic latent image has been formed. The toner comprises toner matrix particles and fluororesin particles with a number-average primary particle diameter of 100 nm to 300 nm that are externally added to the surface of the toner matrix particles. The amount of fluororesin particles added per 100 parts by mass of toner matrix particles is 1.2 parts by mass or less, and the number-average primary particle diameter r of the fluororesin particles and the arithmetic mean roughness Ra of the surface of the photosensitive layer satisfy r > Ra.

Description

Technical Field

[0001] The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine thereof, and particularly to an image forming apparatus using a non-magnetic one-component developing method using a non-magnetic toner as a non-magnetic one-component developer.

Background Art

[0002] Conventionally, as a toner applied to the electrophotographic method, after mixing a colorant, a charge control agent, a release agent, a magnetic material, etc. with a binder resin such as a thermoplastic resin, kneading, pulverizing, and classifying are performed to obtain toner particles (toner mother particles) having an average particle size of 5 μm or more and 10 μm or less. And for the purpose of imparting fluidity to the toner, imparting suitable charging performance to the toner, or improving the cleaning property of the toner from the photoreceptor drum, inorganic fine powders such as silica and titanium oxide are externally added to the toner mother particles.

[0003] In order to improve the fluidity and charging property of the toner, extensive studies have been conducted on external additives. Generally, external additives are roughly classified into inorganic fine particles and resin fine particles, and the combined use of inorganic fine particles and resin fine particles has been studied for the purpose of suppressing image fogging and image unevenness.

[0004] Patent Document 1 discloses that the binder resin of toner mother particles contains a polyester resin, and as an external additive, the average particle size is 200 to 2000 nm, and the electrical resistivity is 1 × 10 15 A positive-charged toner for non-magnetic one-component development containing negative-charged resin fine particles of Ω·cm or less, silica having an average particle size of 50 to 300 nm, silica having an average particle size of 5 nm or more and less than 50 nm, and polytetrafluoroethylene fine particles having an average particle size of 100 to 1000 nm is disclosed.

[0005] According to the configuration of Patent Document 1, the desorption of silica from the toner mother particles is suppressed by the triboelectric charging of fluorine fine particles and silica, image fogging at the initial stage of photoreceptor use is suppressed, and good solid following property can be maintained even during printing.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-180910 [Overview of the project] [Problems that the invention aims to solve]

[0007] The method described in Patent Document 1 had a problem in that when the fluorine particles were smaller than the surface roughness Ra of the drum, the fluorine particles and the recesses of the photoreceptor drum became triboelectrically charged, worsening the charge distribution and causing image defects such as fogging.

[0008] In view of the above problems, the present invention aims to provide an image forming apparatus that can suppress image defects such as image fogging by suppressing contact charging between fluorine particles and toner due to the embedding of fluorine particles in recesses of the photoreceptor, and contact charging between the toner and recesses of the photoreceptor. [Means for solving the problem]

[0009] To achieve the above objective, the first configuration of the present invention is an image forming apparatus comprising an image carrier, a charging device, an exposure device, and a developing device. The image carrier has a conductive substrate and a photosensitive layer laminated on the surface of the conductive substrate. The charging device charges the surface of the image carrier. The exposure device exposes the surface of the image carrier charged by the charging device to form an electrostatic latent image with reduced charge. The developing device has a developing container that contains a non-magnetic one-component developer consisting only of toner, a developer carrier that is pressed against the image carrier with a predetermined pressing force and forms a toner layer on its outer peripheral surface by supporting toner, and a regulating blade that contacts the outer peripheral surface of the developer carrier and regulates the thickness of the toner layer formed on the outer peripheral surface of the developer carrier, and supplies toner to the image carrier on which the electrostatic latent image has been formed. The toner has toner matrix particles and fluororesin particles with a number mean primary particle diameter of 100 nm or more and 300 nm or less that are externally added to the surface of the toner matrix particles. The amount of fluororesin particles added per 100 parts by mass of toner matrix particles is 1.2 parts by mass or less, and the number-average primary particle diameter r of the fluororesin particles and the arithmetic mean roughness Ra of the photosensitive layer surface satisfy r > Ra. [Effects of the Invention]

[0010] According to the first configuration of the present invention, the embedding of fluororesin particles into recesses on the surface of the photosensitive layer can be suppressed. As a result, since triboelectric charging between the fluororesin particles on the surface of the image carrier and the toner, or triboelectric charging between the recesses on the surface of the image carrier and the toner is suppressed, image fogging caused by the toner becoming reverse-charged can be effectively suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] Schematic diagram of an image forming apparatus 1 according to one embodiment of the present invention. [Figure 2] A side cross-sectional view showing the schematic configuration of the image forming unit 30, including the developing unit 33, in Figure 1. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below. Unless otherwise specified, the evaluation results (values ​​indicating shape or physical properties, etc.) for the powder (more specifically, toner core particles, toner mother particles, external additives, or toner, etc.) are the number average values ​​of the values ​​measured for each of the average particles selected from the powder. Unless otherwise specified, the number average particle diameter of the powder is the number average value of the equivalent circle diameter (the diameter of a circle having the same area as the projected area of ​​the particle) of the primary particles measured using a microscope. Unless otherwise specified, the measured value of the median volume diameter (D50) of the powder is the value measured using a laser diffraction / scattering particle size distribution analyzer ("LA-750" manufactured by Horiba, Ltd.). Unless otherwise specified, the measured values ​​of the acid value and hydroxyl value are the values ​​measured according to "JIS (Japanese Industrial Standards) K0070-1992". Furthermore, unless otherwise specified, the measured values ​​for number-average molecular weight (Mn) and mass-average molecular weight (Mw) are those obtained using gel permeation chromatography.

[0013] The softening point (Tm), unless otherwise specified, is the value measured using a high-temperature flow tester (Shimadzu Corporation "CFT-500D"). In the S-curve (horizontal axis: temperature, vertical axis: stroke) measured by the high-temperature flow tester, the temperature at which "(baseline stroke value + maximum stroke value / 2)" corresponds to Tm (softening point). The melting point (Mp), unless otherwise specified, is the temperature of the maximum endothermic peak in the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured using a differential scanning calorimeter (Seiko Instruments Inc. "DSC-6220"). This endothermic peak is due to the melting of the crystallized portion. It appears as follows. Unless otherwise specified, the glass transition temperature (Tg) is the value measured using a differential scanning calorimeter (Seiko Instruments Inc. "DSC-6220") in accordance with "JIS (Japanese Industrial Standards) K7121-2012". In the endothermic curve measured by the differential scanning calorimeter (vertical axis: heat flow (DSC signal), horizontal axis: temperature), the temperature at the inflection point due to the glass transition (more specifically, the temperature at the intersection of the baseline extrapolation line and the falling line extrapolation line) corresponds to Tg (glass transition temperature).

[0014] In the following, the compound name may be followed by "system" to comprehensively refer to the compound and its derivatives. When "system" is followed by a compound name to represent a polymer name, it means that the repeating unit of the polymer originates from the compound or its derivative. Also, acrylic and methacrylic may be comprehensively referred to as "(meth)acrylic". Furthermore, acryloyl (CH) 2 =CH-CO-) and methacryloyl (CH 2 =C(CH 3 The terms )-CO-) are sometimes collectively referred to as "(meth)acryloyl".

[0015] [1. Overall configuration of the image forming apparatus] Figure 1 is a schematic cross-sectional view of an image forming apparatus 1 according to one embodiment of the present invention. In Figure 1, the right side is the front side of the image forming apparatus 1, and the left side is the rear side.

[0016] The image forming apparatus 1 (here referred to as a monochrome printer) includes a main housing 10 having a roughly rectangular prism-shaped enclosure structure, a paper feeding unit 20 housed within the main housing 10, an image forming unit 30, and a fuser unit 40. The main housing 10 is provided with a front cover 11 on the front side and a rear cover 12 on the rear side. Each unit of the image forming unit 30 can be inserted into and removed from the rear side of the main housing 10 by opening the rear cover 12. The top surface of the main housing 10 is provided with a paper discharge unit 13 from which the image-formed sheet is discharged. In the following description, the term "sheet" refers to copy paper, coated paper, OHP sheets, cardboard, postcards, tracing paper, and other sheet materials that undergo image forming processing.

[0017] The paper feeding unit 20 includes a paper feeding cassette 21 that houses sheets to be subjected to image forming processing. A part of the paper feeding cassette 21 protrudes further forward from the front surface of the main body housing 10. The upper surface of the portion of the paper feeding cassette 21 housed within the main body housing 10 is covered by a paper feeding cassette top plate 21U. The paper feeding cassette 21 is provided with a paper storage space for storing a bundle of sheets, a lift plate for lifting up the bundle of sheets for paper feeding, and the like. A paper feeding portion 21A is provided at the upper part on the rear end side of the paper feeding cassette 21. A paper feeding roller 21B for feeding out one sheet at a time from the uppermost layer of the sheet bundle in the paper feeding cassette 21 is arranged at the paper feeding portion 21A.

[0018] The image forming unit 30 performs an image forming operation of forming a toner image (developer image) on the sheet fed out from the paper feeding unit 20. The image forming unit 30 includes a photosensitive drum 31, and a charging unit 32, an exposure unit 35, a developing unit 33, and a transfer roller 34 that are arranged around the photosensitive drum 31.

[0019] The photosensitive drum 31 (image carrier) includes a rotation axis (not shown), a conductive substrate 31a that rotates around the rotation axis, and a photosensitive layer 31b laminated on the surface of the conductive substrate 31a. The photosensitive layer 31b is a known organic (OPC) photosensitive layer containing, for example, a charge generating agent, a charge transporting agent, and the like. After being uniformly charged by the charging unit 32 described later, the photosensitive layer 31b is irradiated with light by the exposure unit 35 to form an electrostatic latent image with the charge attenuation, and the toner image obtained by visualizing the electrostatic latent image is carried by the developing unit 33.

[0020] The charging unit 32 (charging device) is arranged at a predetermined interval with respect to the outer peripheral surface of the photosensitive drum 31, and uniformly charges the photosensitive layer 31b of the photosensitive drum 31 in a non-contact state. Specifically, the charging unit 32 has a charge wire 321 and a grid electrode 322 (both are shown in FIG. 2). The charge wire 321 is a linear electrode extending in the rotation axis direction of the photosensitive drum 31, and generates corona discharge between the charge wire 321 and the photosensitive drum 31. The grid electrode 322 is a grid-shaped electrode extending in the rotation axis direction of the photosensitive drum 31, and is disposed between the charge wire 321 and the photosensitive drum 31. The charging unit 32 generates corona discharge by flowing a current with a predetermined current value through the charge wire 321, and uniformly charges the outer peripheral surface of the photosensitive drum 31 facing the grid electrode 322 to a predetermined surface potential by applying a predetermined voltage to the grid electrode 322.

[0021] The exposure unit 35 (exposure device) has a laser light source and optical system devices such as mirrors and lenses, and irradiates the outer peripheral surface of the photosensitive drum 31 with light modulated based on image data given from an external device such as a personal computer. Thereby, the exposure unit 35 forms an electrostatic latent image corresponding to the image based on the image data on the photosensitive layer 31b of the photosensitive drum 31.

[0022] The developing unit 33 (developing device) is detachable from the main body housing 10, and develops the electrostatic latent image formed on the photosensitive layer 31b of the photosensitive drum 31 by supplying a non-magnetic one-component toner (developer) to the outer peripheral surface of the photosensitive drum 31. Developing the electrostatic latent image means forming a toner image (developer image) in which the electrostatic latent image is visualized. The detailed configuration of the developing unit 33 will be described later.

[0023] The transfer roller 34 is a roller for transferring the toner image formed on the outer surface of the photoreceptor drum 31 onto the sheet. Specifically, the transfer roller 34 rotates around an axis and has an outer surface that faces the outer surface of the photoreceptor drum 31 at a position downstream of the developing roller 331 in the rotational direction of the photoreceptor drum 31. The transfer roller 34 transfers the toner image carried on the outer surface of the photoreceptor drum 31 to the sheet through the nip between the transfer roller 34 and the outer surface of the photoreceptor drum 31. During this transfer, a transfer voltage with the opposite polarity to the toner is applied to the transfer roller 34.

[0024] The fixing unit 40 performs a fixing process to fix the toner image transferred to the sheet onto the sheet. The fixing unit 40 has a fixing roller 41 and a pressure roller 42. The fixing roller 41 has a heating source inside and heats the toner transferred to the sheet to a predetermined temperature. The pressure roller 42 is pressed against the fixing roller 41, forming a fixing nip between the two. When the sheet on which the toner image has been transferred is passed through the fixing nip, the toner image is fixed onto the sheet by heating by the fixing roller 41 and pressurizing by the pressure roller 42.

[0025] The main housing 10 is equipped with a main transport path 22F and a reverse transport path 22B for transporting sheets. The main transport path 22F extends from the paper feeding section 21A of the paper feeding section 20, through the image forming section 30 and the fixing section 40, to the paper discharge port 14 located on the upper surface of the main housing 10, opposite the paper discharge section 13. The reverse transport path 22B is a transport path for returning the single-sided printed sheet to the upstream side of the image forming section 30 in the main transport path 22F when double-sided printing is performed on the sheet.

[0026] [2. Configuration of the image forming unit 30] Figure 2 is a cross-sectional view of the image forming section 30 in the image forming apparatus 1 of this embodiment. As shown in Figure 2, the developing section 33 includes a developing housing 330 (developing container), a developing roller 331 (developer carrier), a supply roller 332, a stirring paddle 333, and a regulating blade 334.

[0027] The developing housing 330 houses a non-magnetic, one-component developer consisting only of toner, as well as a developing roller 331, a supply roller 332, a regulating blade 334, and the like. The developing housing 330 is equipped with a stirring chamber 335 that houses the agitated developer (toner). A stirring paddle 333 is placed in the stirring chamber 335. The stirring paddle 333 agitates the toner in the stirring chamber 335.

[0028] The developing roller 331 comprises a rotating shaft 331a and a roller section 331b. The rotating shaft 331a is rotatably supported by a bearing section (not shown) of the developing housing 330. The roller section 331b is a cylindrical member laminated on the outer circumferential surface of the rotating shaft 331a (conductive substrate), and has a structure in which a coating layer (urethane layer) is laminated on the surface of a base rubber (silicone rubber layer) using a coating material with irregularities such as urethane. The roller section 331b rotates integrally with the rotating shaft 331a as the rotating shaft 331a rotates. A toner layer (developer layer) of a predetermined thickness is formed on the surface of the roller section 331b. The thickness of the toner layer is regulated (uniformly adjusted to a predetermined thickness) by a regulating blade 334, which will be described later. The toner layer is charged by static electricity generated by the contact (friction) between the regulating blade 334 and the roller section 331b.

[0029] When the developing roller 331 is positioned opposite the photoreceptor drum 31, it rotates in a direction from upstream to downstream (counterclockwise in Figure 2) in the direction of rotation of the photoreceptor drum 31 (clockwise in Figure 2). In other words, when the developing roller 331 is positioned opposite the photoreceptor drum 31, it rotates in the same direction as the photoreceptor drum 31.

[0030] The supply roller 332 is positioned opposite the developing roller 331. The supply roller 332 holds the developer contained in the agitation chamber 335 on its outer surface. The supply roller 332 also supplies the developer held on its outer surface to the developing roller 331.

[0031] The supply roller 332, when facing the developing roller 331, rotates from downstream to upstream in the direction of rotation of the developing roller 331 (counterclockwise in Figure 2). In other words, when facing the developing roller 331, the supply roller 332 rotates in the opposite direction to the developing roller 331. A predetermined supply voltage (DC voltage) is applied to the supply roller 332 in order to move the toner from the supply roller 332 to the developing roller 331.

[0032] The developing roller 331 receives developer from the supply roller 332 and holds a toner layer on its outer surface. The developing roller 331 then supplies developer to the photoreceptor drum 31. The axial lengths (directions perpendicular to the plane of the paper in Figure 2) of the developing roller 331 and the supply roller 332 are approximately the same as the axial length of the photoreceptor drum 31. A predetermined developing voltage (DC voltage) is applied to the developing roller 331 in order to move the toner from the developing roller 331 to the photoreceptor drum 31.

[0033] The regulating blade 334 is a thin, plate-like member made of metal (for example, stainless steel). The regulating blade 334 is configured such that its base end 334a is fixed to the developing housing 330 and its tip end 334b ​​is a free end. The regulating blade 334 contacts the outer circumferential surface of the developing roller 331 at a position upstream in the rotational direction of the developing roller 331 from the position where the photoreceptor drum 31 and the developing roller 331 face each other.

[0034] Since the regulating blade 334 contacts the developing roller 331 with a constant regulating pressure (contact linear pressure), the toner layer supported on the outer surface of the developing roller 331 is adjusted to a uniform thickness. In this way, the regulating blade 334 regulates the amount of toner on the outer surface of the developing roller 331. The regulating blade 334 also charges the toner by friction with the toner supported on the outer surface of the developing roller 331. The contact linear pressure of the regulating blade 334 against the developing roller 331 is the contact pressure per unit length of the regulating blade 334 at the contact point between the regulating blade 334 and the outer surface of the developing roller 331. The regulating pressure of the regulating blade 334 is preferably 15 to 40 [N / m]. If the regulating pressure is less than 15 [N / m], the toner cannot be regulated, and if it is more than 40 [N / m], the frictional force on the toner becomes strong, and the toner layer becomes thinner.

[0035] [3. Toner Configuration] The non-magnetic one-component developing toner (hereinafter also simply referred to as toner) used in the image forming apparatus 1 of the present invention comprises at least toner matrix particles and an external additive attached to the surface of the toner matrix particles. The structure of the toner and the materials of the toner will be described below.

[0036] [3-1. Toner matrix particles] The toner matrix particles contain at least a binder resin and a colorant. They may also contain, if necessary, a release agent, a charge control agent, etc. Furthermore, the toner matrix particles may consist of toner core particles and a shell layer formed on the surface of the toner core particles. If no shell layer is formed, the toner core particles themselves become the toner matrix particles.

[0037] (Binding resin) The toner core particles constituting the toner of the present invention contain a binder resin. The binder resin that can be contained in the toner core particles is not particularly limited as long as it is a resin that has been conventionally used as a binder resin for toner. Specific examples of binder resins include thermoplastic resins such as styrene resins, acrylic resins, styrene-acrylic resins, polyethylene resins, polypropylene resins, vinyl chloride resins, polyester resins, polyamide resins, polyurethane resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. Among these resins, polystyrene resins and polyester resins are preferred in terms of the dispersibility of the colorant in the binder resin, the electrostatic properties of the toner, and the fixation to paper. Polystyrene resins and polyester resins will be described below.

[0038] Polystyrene resins may be homopolymers of styrene or copolymers of styrene with other copolymerizable monomers. Specific examples of other copolymerizable monomers with styrene include: p-chlorostyrene; vinylnaphthalene; ethylene-unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, and vinyl fluoride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dothoyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, and phenyl acrylate. Examples include (meth)acrylic acid esters such as methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate; other acrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, and methyl isopropenyl ketone; and N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidene. Two or more of these copolymer monomers can be copolymerized with styrene monomers.

[0039] Polyester resins can be obtained by condensation polymerization or copolymerization of a divalent or trivalent or higher alcohol component with a divalent or trivalent or higher carboxylic acid component. The following alcohol and carboxylic acid components are examples of components used in the synthesis of polyester resins.

[0040] Specific examples of divalent or trivalent or higher alcohol components include diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A, hydrogenated bisphenol A, and polyoxyethylene Examples include bisphenols such as bisphenol A and polyoxypropylene bisphenol A; and trivalent or higher alcohols such as sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

[0041] Specific examples of divalent or trivalent or higher carboxylic acid components include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebatic acid, azelaic acid, malonic acid, or divalent alkyl or alkenyl succinic acids such as n-butylsuccinic acid, n-butenylsuccinic acid, isobutylsuccinic acid, isobutenylsuccinic acid, n-octylsuccinic acid, n-octenylsuccinic acid, n-dodecylsuccinic acid, n-dodecenylsuccinic acid, isododecylsuccinic acid, and isododecenylsuccinic acid. Carboxylic acids include trivalent or higher carboxylic acids such as 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalentricarboxylic acid, 1,2,4-naphthalentricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empol trimeric acid. These divalent or trivalent or higher carboxylic acid components may be used as ester-forming derivatives such as acid halides, acid anhydrides, and lower alkyl esters. Here, "lower alkyl" means an alkyl group having 1 to 6 carbon atoms.

[0042] When the binder resin is a polyester resin, the softening point of the polyester resin is preferably 70°C to 130°C, and more preferably 80°C to 120°C. To improve the strength of the toner core and the fixation of the toner, the number-average molecular weight (Mn) of the polyester resin is preferably 1000 to 2000. The molecular weight distribution of the polyester resin (ratio of mass-average molecular weight (Mw) to number-average molecular weight (Mn) Mw / Mn) is preferably 9 to 21.

[0043] As the binder resin, it is preferable to use a thermoplastic resin because it has good adhesion to paper. However, thermoplastic resins can be used alone, or crosslinking agents or thermosetting resins can be added to the thermoplastic resin. By adding crosslinking agents or thermosetting resins and introducing a partially crosslinked structure into the binder resin, the heat resistance, storage properties, and durability of the toner can be improved without reducing the toner's adhesion. When using a thermosetting resin, the amount of crosslinked portion (gel amount) of the binder resin extracted using a Soxhlet extractor is preferably 10% by mass or less, and more preferably 0.1% by mass or more and 10% by mass or less, relative to the mass of the binder resin.

[0044] Epoxy resins and cyanate resins are preferred thermosetting resins that can be used with thermoplastic resins. Specific examples of suitable thermosetting resins include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, cyclic aliphatic type epoxy resins, and cyanate resins. Two or more of these thermosetting resins can be used in combination.

[0045] The glass transition temperature (Tg) of the binder resin is preferably between 40°C and 70°C. If the glass transition temperature is too high, the low-temperature fixability of the toner tends to decrease. If the glass transition temperature is too low, the heat resistance of the toner tends to decrease.

[0046] The glass transition point of a binder resin can be determined from the point of change in the specific heat of the binder resin using a differential scanning calorimeter (DSC). More specifically, the glass transition point of the binder resin can be determined by measuring the endothermic curve of the binder resin using a Seiko Instruments Inc. DSC-6200 differential scanning calorimeter as the measuring device. A 10 mg sample is placed in an aluminum pan, and an empty aluminum pan is used as a reference. The glass transition point of the binder resin can be determined from the endothermic curve obtained by measuring the binder resin at room temperature and humidity with a temperature range of 25°C to 200°C and a heating rate of 10°C / min.

[0047] The mass-average molecular weight (Mw) of the binder resin is not particularly limited as long as it does not hinder the objectives of the present invention. Typically, the mass-average molecular weight (Mw) of the binder resin is preferably 20,000 to 300,000, and more preferably 30,000 to 2,000,000. The mass-average molecular weight of the binder resin can be determined by gel permeation chromatography (GPC) using a calibration curve prepared in advance using standard polystyrene resin.

[0048] Furthermore, when the binder resin is a polystyrene-based resin, it is preferable that the binder resin has peaks in both the low molecular weight region and the high molecular weight region on the molecular weight distribution measured by gel permeation chromatography or the like. Specifically, it is preferable that the peak in the low molecular weight region is in the range of 3,000 to 20,000 molecular weights, and the peak in the high molecular weight region is in the range of 300,000 to 1,500,000 molecular weights. In addition, for polystyrene-based resins with such a molecular weight distribution, the ratio of the number average molecular weight (Mn) to the mass average molecular weight (Mw) (Mw / Mn) is preferably 10 or more. By having peaks in both the low molecular weight region and the high molecular weight region in the molecular weight distribution of the binder resin, it is possible to obtain a toner that has excellent low-temperature fixation properties and can suppress high-temperature offset.

[0049] (Coloring agent) Toner core particles contain a colorant. The colorant that can be included in the toner core particles can be any known pigment or dye, depending on the color of the toner. Specific examples of suitable colorants that can be added to toner include: black pigments such as carbon black, acetylene black, lamp black, and aniline black; yellow pigments such as lead yellow, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, tartrazine lake, monoazo yellow, and diazo yellow; orange pigments such as red lead yellow, molybdenum orange, permanent orange GTR, pyrazolone orange, balkan orange, and induthrene brilliant orange GK; red iron oxide, cadmium red, red lead, mercury cadmium sulfide, permanent red 4R, lithol red, and pyrazolone. Examples of colorants include red pigments such as Lon Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B, and Monoazo Red; purple pigments such as Manganese Violet, Fast Violet B, and Methyl Violet Lake; blue pigments such as Prussian Blue, Cobalt Blue, Alkali Blue Lake, Victoria Blue Partial Chloride, Fast Sky Blue, Induthlene Blue BC, and Phthalocyanine Blue; green pigments such as Chrome Green, Chromium Oxide, Pigment Green B, Malachite Green Lake, and Final Yellow Green G; white pigments such as Zinc Oxide, Titanium Dioxide, Antimony White, and Zinc Sulfide; and extender pigments such as Barite Powder, Barium Carbonate, Clay, Silica, White Carbon, Talc, and Alumina White. Two or more of these colorants can also be used in combination to adjust the toner to a desired hue.

[0050] The amount of colorant used is not particularly limited as long as it does not hinder the objective of the present invention. Specifically, the amount of colorant used is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 7% by mass or less, relative to the total mass of the toner core particles.

[0051] Furthermore, a colorant can also be used as a masterbatch in which the colorant is pre-dispersed in a resin material such as a thermoplastic resin. When using a colorant as a masterbatch, it is preferable that the resin contained in the masterbatch is the same type of resin as the binder resin.

[0052] (Release agent) Toner core particles preferably contain a release agent to improve adhesion and offset resistance. The type of release agent that can be included in the toner core particles is not particularly limited as long as it does not hinder the objectives of the present invention. Wax is preferred as the release agent, and examples of waxes include carnauba wax, synthetic ester wax, polyethylene wax, polypropylene wax, fluororesin wax, Fischer-Tropsch wax, paraffin wax, montan wax, and rice wax. Two or more of these release agents can be used in combination. By adding such a release agent to the toner, the occurrence of offset and image smearing (smudges around the image when the image is rubbed) can be suppressed more efficiently.

[0053] When polyester resin is used as the binder resin, from the viewpoint of compatibility, one or more release agents selected from the group consisting of carnauba wax, synthetic ester wax, and polyethylene wax are preferably used as the release agent. Similarly, when polystyrene resin is used as the binder resin, from the viewpoint of compatibility, Fischer-Tropsch wax and / or paraffin wax are preferably used as the release agent.

[0054] Fischer-Tropsch wax is a straight-chain hydrocarbon compound with few iso-structure molecules or side chains, produced using the Fischer-Tropsch reaction, which is a catalytic hydrogenation reaction of carbon monoxide.

[0055] Among Fischer-Tropsch waxes, those with a mass-average molecular weight of 1,000 or more and whose endothermic peak bottom temperature observed by DSC measurement is in the range of 100°C to 120°C are more preferable. Examples of such Fischer-Tropsch waxes include Sazol wax C1 (endothermic peak bottom temperature: 106.5°C), Sazol wax C105 (endothermic peak bottom temperature: 102.1°C), and Sazol wax SPRAY (endothermic peak bottom temperature: 102.1°C), all available from Sazol.

[0056] The amount of release agent used is not particularly limited as long as it does not hinder the objectives of the present invention. Preferably, the amount of release agent used is 1% by mass or more and 10% by mass or less, relative to the total mass of the toner core particles. If the amount of release agent used is too little, the desired effect of suppressing offset and image smearing in the formed image may not be obtained, and if the amount of release agent used is too much, the heat resistance of the toner may decrease due to fusion of toners.

[0057] (Charge control agent) Toner core particles preferably contain a charge control agent to improve the charge level of the toner and the charge rise characteristics, which are indicators of whether or not it can be charged to a predetermined charge level in a short time, and to obtain a toner with excellent durability and stability. Since the toner of the present invention is positively charged, a positively charged charge control agent is used.

[0058] The types of charge control agents that can be contained in toner core particles are not particularly limited as long as they do not hinder the objectives of the present invention, and can be appropriately selected from charge control agents that have been conventionally used in toners. Specific examples of positively charged charge control agents include azine compounds such as pyridazine, pyrimidine, pyrazine, orthoxazine, metaoxazine, paraoxazine, orthothiaidine, metathiaidine, parathiaidine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline, and quinoxaline; azine compounds Examples include direct dyes consisting of azine compounds such as Stread FC, Azin Fast Red 12BK, Azin Violet BO, Azin Brown 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, and Azin Deep Black 3RL; nigrosine compounds such as nigrosine, nigrosine salts, and nigrosine derivatives; acid dyes consisting of nigrosine compounds such as nigrosine BK, nigrosine NB, and nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; and quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride. Among these positively charged charge control agents, nigrosine compounds are particularly preferred because they provide a faster charge rise. Two or more of these positively charged charge control agents can be used in combination.

[0059] Resins having quaternary ammonium salts, carboxylates, or carboxyl groups as functional groups can also be used as positively charged charge control agents. More specifically, examples include styrene resins having quaternary ammonium salts, acrylic resins having quaternary ammonium salts, styrene-acrylic resins having quaternary ammonium salts, polyester resins having quaternary ammonium salts, styrene resins having carboxylates, acrylic resins having carboxylates, styrene-acrylic resins having carboxylates, polyester resins having carboxylates, styrene resins having carboxyl groups, acrylic resins having carboxyl groups, styrene-acrylic resins having carboxyl groups, and polyester resins having carboxyl groups. The molecular weight of these resins is not particularly limited as long as it does not hinder the objectives of the present invention, and they may be oligomers or polymers.

[0060] Among resins that can be used as positively charged charge control agents, styrene-acrylic resins having quaternary ammonium salts as functional groups are more preferred because the amount of charge can be easily adjusted to a value within a desired range. Specific examples of preferred acrylic comonomers copolymerized with styrene units in styrene-acrylic resins having quaternary ammonium salts as functional groups include alkyl (meth)acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate.

[0061] Furthermore, as quaternary ammonium salts, dialkylaminoalkyl(meth)acrylates, dialkyl(meth)acrylamides, or units derived from dialkylaminoalkyl(meth)acrylamides through a quaternization process can be used. Specific examples of dialkylaminoalkyl(meth)acrylates include dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate, dipropylaminoethyl(meth)acrylate, and dibutylaminoethyl(meth)acrylate. Specific examples of dialkyl(meth)acrylamides include dimethylmethacrylamide, and specific examples of dialkylaminoalkyl(meth)acrylamides include dimethylaminopropylmethacrylamide. In addition, hydroxyl group-containing polymerizable monomers such as hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, and N-methylol(meth)acrylamide can be used in combination during polymerization.

[0062] The amount of charge control agent used is not particularly limited as long as it does not hinder the objectives of the present invention. Typically, the amount of charge control agent used is preferably 0.1% by mass or more and 10% by mass or less, relative to the total mass of the toner core particles. If the amount of charge control agent used is insufficient, it is difficult to stably charge the toner to a predetermined polarity, which may result in the image density of the formed image falling below the desired value or making it difficult to maintain the image density over a long period of time. In addition, because the charge control agent is difficult to disperse uniformly, the formed image is more prone to blurring, and contamination of the latent image-carrying area by toner components is more likely to occur. If the amount of charge control agent used is excessive, the environmental resistance deteriorates, making it easier for image defects in the formed image due to poor charging under high temperature and high humidity conditions, and contamination of the latent image-carrying area by toner components to occur.

[0063] (Shell material) Toner core particles may optionally have their surfaces coated with a shell layer. When a shell layer is formed on toner core particles, the shell layer is formed of resin fine particles. In order to give the shell layer an appropriate surface adsorption force, it is particularly preferable that the shell layer contains a resin film mainly composed of aggregates of resin particles with a glass transition temperature of 50°C to 100°C, the number-average circularity of the heat-resistant particles constituting the resin film is 0.55 to 0.75, the heat-resistant particles contain a resin containing one or more repeating units derived from styrene monomers, repeating units having alcoholic hydroxyl groups, and repeating units derived from nitrogen-containing vinyl compounds, and that the repeating unit having the highest mass proportion among the repeating units contained in the resin contained in the heat-resistant particles is the repeating unit derived from styrene monomers.

[0064] The shell layer constituting the toner of the present invention includes vinyl resin fine particles with a relatively small average particle diameter (first resin fine particles) and vinyl resin fine particles with a relatively large average particle diameter (second resin fine particles). The first resin fine particles form the sea-like regions of the shell layer. The second resin fine particles form the convex portions of the shell layer. The average particle diameter of the first resin fine particles is preferably about 10 nm to 40 nm. The average particle diameter of the second resin fine particles is preferably about 70 nm to 150 nm.

[0065] Regarding the shell layer described above (i.e., a resin film mainly composed of an aggregate of heat-resistant particles), in order to ensure sufficient heat resistance, fixability, and electrostatic properties of the toner, it is preferable that the thickness of the shell layer be between 10 nm and 35 nm. The thickness of the shell layer can be measured by analyzing a TEM (transmission electron microscope) image of the cross-section of the toner particle using commercially available image analysis software (for example, "WinROOF" manufactured by Mitani Corporation). If the thickness of the shell layer is not uniform in a single toner particle, the thickness of the shell layer is measured at four evenly spaced locations (specifically, two perpendicular lines are drawn at approximately the center of the cross-section of the toner particle, and the thickness of the shell layer is measured at four locations where these two lines intersect the shell layer), and the arithmetic mean of the four obtained measurements is taken as the evaluation value (shell layer thickness) of that toner particle. The boundary between the toner core particle and the shell layer can be confirmed, for example, by selectively staining only the shell layer among the toner core particle and the shell layer. If the boundary between the toner core particles and the shell layer is unclear in the TEM image, the boundary can be clarified by combining TEM and electron energy loss spectroscopy (EELS) to map characteristic elements contained in the shell layer within the TEM image.

[0066] Regarding the shell layer described above (i.e., a resin film mainly composed of an aggregate of heat-resistant particles), in order to ensure sufficient heat resistance, fixability, and electrostatic properties of the toner, it is preferable that the shell layer covers 50% to 80% of the surface area of ​​the toner core particles. The area ratio of the surface area of ​​the toner core particles covered by the shell layer can be measured by taking an image of the surface of the toner particles (for example, pre-stained toner particles) with an electron microscope and analyzing the resulting image using commercially available image analysis software.

[0067] [3-2. External Additives] The toner of the present invention is manufactured by treating toner matrix particles with an external additive. The external additive used in the toner of the present invention includes at least fluororesin particles.

[0068] (Fluororesin particles) The fluororesin particles contain fluororesin. The fluororesin content in the fluororesin particles is, for example, 90% by mass or more, and preferably 100% by mass. The fluororesin particles detach from the toner matrix particles as the toner particles pass through the contact area (regulating nip) between the developing roller 331 and the regulating blade 334, and adhere to and coat the regulating blade 334 or the developing roller 331.

[0069] Examples of fluororesins contained in fluororesin particles include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene, polyvinylidene fluoride, polydichlorodifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer. PTFE, PFA, or FEP are preferred as the fluororesin.

[0070] The number-average primary particle diameter of fluororesin particles is preferably 70 nm to 400 nm, and more preferably 100 nm to 300 nm. Setting the number-average primary particle diameter of fluororesin particles to 70 nm or more promotes the detachment of fluororesin particles from toner matrix particles when toner particles pass through the regulating nip. Setting the number-average primary particle diameter of fluororesin particles to 400 nm or less suppresses the detachment of fluororesin particles from toner matrix particles before toner particles pass through the regulating nip. The number-average primary particle diameter of fluororesin fine particles is calculated by number-averaging the particle diameters of primary particles measured from scanning electron microscope images.

[0071] The content of fluororesin particles in toner particles is preferably 0.1 parts by mass or more and 1.2 parts by mass or less, and more preferably 0.4 parts by mass or more and 1.0 part by mass or less, per 100 parts by mass of toner mother particles. By having a fluororesin particle content of 0.1 parts by mass or more, the detachment of fluororesin particles from toner mother particles can be promoted when toner particles pass through the regulating nip. By having a fluororesin particle content of 1.2 parts by mass or less, the detachment of fluororesin particles from toner mother particles before toner particles pass through the regulating nip can be suppressed.

[0072] In the present invention, preferred PTFE particles are those having a nearly spherical shape produced by emulsion polymerization. Examples of commercially available products include "KTL-500F" (manufactured by Kitamura Co., Ltd., average primary particle diameter 300 nm), "Lubron L2" (manufactured by Daikin Industries, Ltd., average primary particle diameter 300 nm), "Lubron L5" (manufactured by Daikin Industries, Ltd., average primary particle diameter 200 nm), and "Fluon Lubricant L170J" (manufactured by Asahi ICI Fluoropolymers Co., Ltd., average primary particle diameter 100 nm). Examples include "Fluon Lubricant L172J" (manufactured by Asahi ICI Fluoropolymers, average primary particle size 100nm), "MP-1100" (manufactured by Mitsui DuPont Fluorochemicals, average primary particle size 200nm), "MP-1200" (manufactured by Mitsui DuPont Fluorochemicals, average primary particle size 300nm), and "TLP-10F-1" (manufactured by Mitsui DuPont Fluorochemicals, average primary particle size 200nm).

[0073] (Inorganic particles) The toner of the present invention may contain inorganic particles in addition to fluororesin particles. Examples of inorganic particles include metal oxides such as silica, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate. Silica or titanium oxide are particularly preferred. These particles may be used individually or in combination of two or more. The average particle size of the inorganic particles is preferably between 10 nm and 100 nm.

[0074] The amount of external additive used is not particularly limited as long as it does not hinder the objective of the present invention. Typically, the amount of external additive used is preferably 0.1% to 10% by mass, and more preferably 0.2% to 5% by mass, relative to the total mass of toner matrix particles. If the amount of external additive used is insufficient, the hydrophobicity of the toner tends to decrease. As a result, it becomes more susceptible to the influence of water molecules in the air under high temperature and high humidity environments, which can easily lead to problems such as a decrease in image density of the formed image due to an extreme decrease in the charge amount of the toner, and a decrease in toner fluidity. On the other hand, if the amount of external additive used is excessive, it may lead to a decrease in image density due to excessive toner charge buildup.

[0075] By adding silica particles and fluororesin particles as external additives to the toner matrix particles, the amount of toner charged and deposited on the developing roller 331 can be stabilized throughout the lifespan of the developing unit 33, thereby obtaining a desirable image.

[0076] [4. Configuration of the photoconductor drum] The photoreceptor drum 31 used in the image forming apparatus 1 of this embodiment is a positively charged single-layer photoreceptor in which an organic photosensitive layer (OPC) containing a charge generating agent, a charge transport agent, a binder resin, and a filler in the same layer is laminated on a conductive substrate (cylindrical body) such as aluminum. The conductive substrate and the photosensitive layer will be described in detail below.

[0077] [4-1. Conductive substrates] The conductive substrate is not particularly limited as long as it can be used as a conductive substrate for a positively charged single-layer photoreceptor. Specifically, examples include those in which at least the surface portion is made of a conductive material. For example, it may be made of a conductive material, or the surface of a plastic material or the like may be coated with a conductive material. Examples of conductive materials include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, brass, etc. Furthermore, one type of conductive material may be used, or two or more types may be combined and used, for example, as an alloy. Among the above, it is preferable to use aluminum or an aluminum alloy as the material for the conductive substrate, as it allows for good charge transfer from the photoreceptor layer to the conductive substrate.

[0078] [4-2. Photosensitive layer] The photosensitive layer of a positively charged single-layer photoreceptor is a single-layer photosensitive layer comprising a charge generating agent, a charge transporter, a filler, and a binder resin, and is not particularly limited as long as the filler contains one or more fine particles selected from the group consisting of silica fine particles and resin fine particles. The following describes the components constituting the photosensitive layer, namely the charge generating agent, charge transporter, filler, binder resin, and additives, as well as the method for manufacturing a positively charged single-layer photoreceptor.

[0079] (Charge-generating agent) The charge generating agent is not particularly limited as long as it can be used as a charge generating agent for a positively charged single-layer photoreceptor. Specifically, examples include phthalocyanine pigments, perylene pigments, bisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metallic naphthalocyanine pigments, squaline pigments, trisazo pigments, indigo pigments, azulenium pigments, cyanine pigments, powders of inorganic photoconductive materials such as selenium, selenium-tellurium, selenium-arsenide, cadmium sulfide, and amorphous silicon, pyrylium salts, anthensrone pigments, triphenylmethane pigments, surene pigments, toluidine pigments, pyrazoline pigments, and quinacridone pigments.

[0080] Furthermore, the charge generating agent may be used alone or in combination of two or more types, so as to have an absorption wavelength in a desired region. In addition, among the aforementioned charge generating agents, laser beam printers using light sources such as semiconductor lasers and digital optical system image forming devices such as facsimile machines require a positively charged single-layer electrophotographic photoreceptor that is sensitive to wavelengths of 700 nm or more. For this reason, phthalocyanine-based pigments such as metal-free phthalocyanine and oxotitanyl phthalocyanine are preferably used. The crystalline form of the above phthalocyanine-based pigment is not particularly limited, and various types can be used.

[0081] (Charge transport agent) The charge transport agent includes one or more materials selected from hole transport agents (HTMs) and electron transport agents (ETMs). The hole transport agent and electron transport agent will be described in detail below.

[0082] The hole transporter (HTM) is not particularly limited as long as it can be used as a hole transporter contained in the photosensitive layer of a positively charged monolayer photoreceptor. Specifically, examples include benzidine derivatives, oxadiazole compounds such as 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole, styryl compounds such as 9-(4-diethylaminostyryl)anthracene, carbazole compounds such as polyvinylcarbazole, organic polysilane compounds, pyrazoline compounds such as 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline, nitrogen-containing cyclic compounds such as hydrazone compounds, triphenylamine compounds, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds, triazole compounds, and condensed polycyclic compounds. Among these hole transporters, triphenylamine compounds having one or more triphenylamine skeletons in the molecule are more preferred. These hole transporters may be used alone or in combination of two or more.

[0083] The electron transport agent (ETM) is not particularly limited as long as it can be used as an electron transport agent contained in the photosensitive layer of a positively charged single-layer photoreceptor. Specifically, examples include quinone derivatives such as naphthoquinone derivatives, diphenoquinone derivatives, anthraquinone derivatives, azoquinone derivatives, nitroantaraquinone derivatives, and dinitroanthraquinone derivatives, malononitrile derivatives, thiopyran derivatives, trinitrothioxanthone derivatives, 3,4,5,7-tetranitro-9-fluorenone derivatives, dinitroanthracene derivatives, dinitroacridine derivatives, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. These electron transport agents may be used individually or in combination of two or more.

[0084] (Filler) The filler contains one or more fine particles selected from the group consisting of silica fine particles and resin fine particles. The volume-average particle size of the filler is between 5 nm and 5 μm. By including such a filler in the photosensitive layer, a positively charged single-layer photoreceptor with excellent abrasion resistance can be obtained.

[0085] The material of the resin microparticles is not particularly limited as long as it does not hinder the objectives of the present invention. Preferred examples of the material of the resin microparticles include silicone resins such as silicone rubber and organopolysiloxane, polyphenylene sulfide resins, and fluorine-containing resins such as polytetrafluoroethylene resins. Among silicone resins, polysilsesquioxane is preferred, and polymethylsilsesquioxane is more preferred.

[0086] Silica nanoparticles can be appropriately selected from well-known silica nanoparticles, as long as they do not hinder the objectives of the present invention. Silica nanoparticles treated with surface treatment agents such as silane coupling agents or silicone oils can also be used.

[0087] The volume-average particle size of the filler is 5 nm or more and 5 μm or less, more preferably 5 nm or more and 1 μm or less, and particularly preferably 5 nm or more and 0.1 μm or less. If the volume-average particle size of the filler is too large, the photoreceptor surface tends not to be charged well, making it difficult to obtain a positively charged single-layer photoreceptor with excellent electrical properties.

[0088] The filler may contain other types of fine particles besides silica fine particles and resin fine particles, to the extent that they do not hinder the objectives of the present invention. The other types of fine particles besides silica fine particles and resin fine particles are selected from, for example, metal oxide fine particles, inorganic metal salt fine particles, and organometallic salt fine particles, taking into consideration the performance of the resulting positively charged single-layer electrophotographic photoreceptor. When the filler contains other types of fine particles besides silica fine particles and resin fine particles, the total content of silica fine particles and resin fine particles in the filler is preferably 80% by mass or more, preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the mass of the filler.

[0089] (Binding resin) The binder resin is not particularly limited as long as it can be used as a binder resin included in the photosensitive layer of a positively charged single-layer electrophotographic photoreceptor. Specific examples of resins suitably used as binder resins include thermoplastic resins such as polycarbonate resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, styrene-acrylic acid copolymer, acrylic copolymer, polyethylene resin, ethylene-vinyl acetate copolymer, chlorinated polyethylene resin, polyvinyl chloride resin, polypropylene resin, ionomer, vinyl chloride-vinyl acetate copolymer, alkyd resin, polyamide resin, polyurethane resin, polyarylate resin, polysulfone resin, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, and polyester resin; thermosetting resins such as silicone resin, epoxy resin, phenolic resin, urea resin, melamine resin, and other crosslinkable thermosetting resins; and photocurable resins such as epoxy acrylate resin and urethane-acrylate copolymer resin. These resins may be used individually or in combination of two or more types.

[0090] Among these resins, polycarbonate resins such as bisphenol Z type polycarbonate resin, bisphenol ZC type polycarbonate resin, bisphenol C type polycarbonate resin, and bisphenol A type polycarbonate resin are more preferred because they provide a photosensitive layer with an excellent balance of processability, mechanical properties, optical properties, and abrasion resistance.

[0091] (Additives) The photosensitive layer of a positively charged single-layer photoreceptor may contain various additives in addition to the charge generating agent, hole transporter, electron transporter, filler, and binder resin described above, as long as they do not adversely affect the electrophotographic properties. Examples of additives that can be incorporated into the photosensitive layer include antioxidants, radical scavengers, singlet quenchers, UV absorbers and other degradation inhibitors, softeners, plasticizers, surface modifiers, bulking agents, thickening agents, dispersion stabilizers, waxes, acceptors, donors, surfactants, and leveling agents.

[0092] The above describes a positively charged single-layer photosensitive layer as an example of the photosensitive layer of the photosensitive drum 31, but the photosensitive layer is not limited to this. For example, a positively charged multilayer photosensitive layer can also be used, in which a charge generation layer is laminated on a conductive substrate, and a charge transport layer is laminated on the charge generation layer.

[0093] Furthermore, an intermediate layer (undercoat) may be laminated between the conductive substrate and the photosensitive layer. The intermediate layer may contain, for example, one or both of inorganic particles and organic particles, and a resin used for the intermediate layer (intermediate layer resin). The presence of the intermediate layer allows for a degree of insulation that can suppress leakage, while facilitating the flow of current generated when the photosensitive material is exposed, thereby suppressing an increase in resistance.

[0094] [5. Relationship between particle size of fluororesin particles and surface roughness of the photoreceptor drum] The following describes the relationship between the particle size of the fluororesin particles contained as an external additive in the toner and the surface roughness of the photoreceptor drum 31, which is a characteristic feature of the image forming apparatus 1 of this embodiment. As mentioned above, in a non-magnetic one-component development method, if the particle size of the fluororesin particles is less than or equal to the surface roughness (arithmetic mean roughness Ra) of the photoreceptor drum 31, the charge distribution of the toner deteriorates, which can cause image defects such as image fogging.

[0095] Specifically, fluororesin particles become embedded in the depressions on the surface of the photoreceptor drum 31, causing frictional charging (contact charging) between the fluororesin particles adhering to the surface of the photoreceptor drum and the toner, as well as frictional charging between the depressions on the surface of the photoreceptor drum 31 and the toner. As a result, the toner becomes charged with the opposite polarity (negative polarity) to its normal charge polarity (positive polarity in this embodiment). This reverse-charged toner (reverse-charged toner) adheres to the white areas of the photoreceptor drum 31, causing image fogging.

[0096] Therefore, in the image forming apparatus 1 of this embodiment, the relationship between the arithmetic mean roughness Ra of the surface of the photoreceptor drum 31 (hereinafter also simply referred to as surface roughness Ra) and the number mean primary particle diameter r of the fluororesin particles is set to r > Ra. Note that the surface roughness Ra of the photoreceptor drum 31 is the surface roughness Ra of the photosensitive layer 31b.

[0097] The surface roughness Ra of the photosensitive layer 31b can be adjusted by adjusting the surface roughness of the conductive substrate 31a. The surface roughness of the conductive substrate 31a and the photosensitive layer 31b can be measured using a surface roughness measuring instrument (SURFCOM1500DX, manufactured by Tokyo Seimitsu Co., Ltd.) and determined according to the JIS B0601-1994 standard.

[0098] By setting the relationship between surface roughness Ra and the number-average primary particle diameter r of the fluororesin particles to r > Ra, the embedding of fluororesin particles into depressions on the surface of the photoreceptor drum 31 can be suppressed. As a result, triboelectric charging between the fluororesin particles on the surface of the photoreceptor drum and the toner, or triboelectric charging between the depressions on the surface of the photoreceptor drum 31 and the toner, can be suppressed, thereby suppressing image defects such as image fogging.

[0099] Furthermore, if the surface roughness Ra of the photoreceptor drum 31 is less than 30 nm, the coefficient of friction between the photoreceptor drum 31 and the cleaning blade becomes large when the photoreceptor drum 31 is cleaned with the cleaning blade. As a result, the edge portion of the cleaning blade may be damaged, and vertical lines may appear on the image, as shown in the example described later. For this reason, it is preferable to set the surface roughness Ra of the photoreceptor drum 31 to 30 nm or more.

[0100] Furthermore, if the amount of fluororesin particles added per 100 parts by mass of toner base particles is less than 0.5 parts by mass, the spacer effect of the fluororesin particles becomes small, and there is a risk that vertical lines will appear on the half image due to the adhesion of silica particles to the regulating blade 334. On the other hand, if the amount of fluororesin particles added exceeds 1.5 parts by mass, the toner will be reverse-charged due to the triboelectric charging of the fluororesin particles, making image fogging more likely to occur. For this reason, as shown in the examples described later, it is preferable to add fluororesin particles per 100 parts by mass of toner base particles in an amount of 0.5 parts by mass or more and 1.5 parts by mass or less.

[0101] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, in the above embodiments, a monochrome printer equipped with a non-magnetic one-component developing unit 33 was described as the image forming apparatus 1, but the present invention is applicable to various image forming apparatuses using a non-magnetic one-component developing method, such as monochrome copiers, digital multifunction printers, color printers, and color copiers. The effects of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Examples]

[0102] [Manufacturing Example 1] (Manufacturing of toner matrix particles) 100 parts by mass of polyester resin as a binder, 5 parts by mass of carbon black (REGAL330R, manufactured by Cabot Corporation) as a coloring agent, 1 part by mass of carnauba wax (Carnauba No. 1, manufactured by Kato Yoko Co., Ltd.) as a release agent, and 3 parts by mass of quaternary ammonium salt compound (FCA210PS, manufactured by Fujikura Chemical Co., Ltd.) as a charge control agent were mixed using an FM mixer (FM-20B, manufactured by Nippon Coke Co., Ltd.). The resulting mixture was melt-kneaded at 150 °C using a twin-screw extruder (TEM45, manufactured by Toshiba Machine Co., Ltd.). The resulting kneaded material was cooled and coarsely ground using a pulverizer (Feather Mill 350 x 600 type, manufactured by Hosokawa Micron Corporation). The resulting coarsely ground material was finely ground using an air-jet pulverizer (Jet Mill IDS-2 type, manufactured by Nippon Pneumatic Mfg. Co., Ltd.). The resulting finely ground material was classified using an elbow jet classifier (Elbow Jet EJ-LABO type, manufactured by Nippon Steel Mining Co., Ltd.). This resulted in toner matrix particles with a median volume diameter (D50) of 8 μm. A particle size analyzer (Coulter Counter Multisizer 3, Beckman Coulter) was used to measure the median volume diameter.

[0103] (External addition process) 100 parts by mass of toner matrix particles obtained above, 2.0 parts by mass of hydrophobic silica particles (CAB-O-SIL TG-7120, manufactured by Cabot, number-average primary particle diameter 20 nm), and 1.0 part by mass of fluororesin particles (Fluorine Lubricant L170J, manufactured by Asahi ICI Fluoropolymers, number-average primary particle diameter 100 nm) were mixed using an FM mixer (FM-10B, manufactured by Nippon Coke Industries Co., Ltd.) at a rotation speed of 3,500 rpm for 25 minutes (external additive processing time). The resulting mixture was sieved using a 200-mesh sieve (mesh opening 75 μm). This yielded toner T1 comprising toner matrix particles and external additive particles (fluororesin particles and silica particles) adhering to the surface of the toner matrix particles.

[0104] Toners T2 to T6 were obtained using the same method as described above, except that the particle size and amount of fluororesin particles were changed.

[0105] [Test to confirm the effectiveness of suppressing image defects] The effect of suppressing image defects was investigated when the relationship between the surface roughness Ra of the photoreceptor drum 31 and the particle size of the fluororesin particles, which are an external additive for the toner, was set as in this embodiment.

[0106] The test method involved mounting one of five photoreceptor drums, each with a positively charged organic photosensitive layer surface roughness Ra ranging from 25nm to 327nm, onto an image evaluation machine (PA2000, manufactured by Kyocera Document Solutions). One of the toners T1 to T6 obtained in Manufacturing Example 1 was then loaded into the evaluation machine, and 1500 test images with a print density of 5% were printed intermittently with a 400-second interval under normal temperature and humidity conditions (23°C / 50%RH). The following items were then evaluated.

[0107] (Image overlap) The fogging density (FD) of the white areas of the printed material was measured using a reflectance densitometer (R710, IHARA Corporation) after 1500 durable prints. The fogging density (FD) was calculated using the following formula (1). FD = (Reflectance density of the white area of ​​the printed paper) - (Reflectance density of the unprinted paper) The evaluation criteria are as follows. ○: FD≦0.01 ×: FD>0.01

[0108] (Drum filming capability) After performing 1500 durability prints, the presence or absence of fluororesin particles adhering to the surface of the photoreceptor drum was visually inspected. The criteria for drum filming performance are shown below. ○: No fluororesin particles were observed to be present upon visual inspection. ×: Fluororesin particles were observed to be present upon visual inspection.

[0109] (Image showing vertical lines due to a missing cleaning blade) After 1500 print runs, the occurrence of vertical streaks in the printed materials was visually evaluated. The evaluation criteria are as follows. ○: No vertical streaky image defects were observed. ×: A vertical streak-like image defect was observed.

[0110] (Image of half-vertical streaks caused by silica particle adhesion to the regulated blade) After performing 1500 durability prints, a halftone image was printed. The resulting halftone image was visually inspected for the presence or absence of vertical streaks. The evaluation criteria are shown below. ○: No vertical streaky image defects were observed in the halftone image. ×: Vertical streaks were observed in the halftone image.

[0111] Table 1 shows the evaluation results for image fogging, drum filming performance, vertical streaks in images due to damage to the cleaning blade, and half-vertical streaks in images due to silica particle adhesion to the regulating blade, along with the combination of surface roughness of the photoreceptor drum, particle size of fluororesin particles, and amount added.

[0112] [Table 1]

[0113] As shown in Table 1, in Inventions 1 to 9, where the number-average primary particle diameter r of the fluororesin particles is 100 nm to 300 nm, the relationship between the number-average primary particle diameter r of the fluororesin particles and the surface roughness Ra of the photoreceptor drum is r > Ra, and the amount of fluororesin particles added per 100 parts by mass of toner matrix particles is 1.0 part by mass or less, the fogging density (ID) was 0.01 or less in all cases, and no image fogging was observed. Furthermore, no adhesion of fluororesin particles to the surface of the photoreceptor drum was observed.

[0114] In particular, in Inventions 1-5 and 7-9, where the surface roughness Ra of the photoreceptor drum is 30 nm to 300 nm, no vertical streaks were observed due to defects in the cleaning blade. Furthermore, in Inventions 1-7 and 9, where the amount of fluororesin particles added is 0.5 parts by mass to 1.2 parts by mass, no half-vertical streaks were observed due to silica particle adhesion to the regulating blade.

[0115] In contrast, in Comparative Examples 1-3, where the relationship between the number-average primary particle diameter r of the fluororesin particles and the surface roughness Ra of the photoreceptor drum was r ≤ Ra, the fogging density (ID) exceeded 0.01 in all cases, indicating the occurrence of image fogging. Furthermore, adhesion of fluororesin particles to the surface of the photoreceptor drum was also observed. This is thought to be because the fluororesin particles become embedded in the depressions on the surface of the photoreceptor drum, leading to triboelectric charging between the fluororesin particles and the toner, and triboelectric charging between the photoreceptor drum and the toner, making it easy for reverse-charged toner to be generated.

[0116] On the other hand, in Comparative Example 4, where the amount of fluororesin particles added was 1.5 parts by mass per 100 parts by mass of toner matrix particles, no adhesion of fluororesin particles to the surface of the photoreceptor drum was observed, but image fogging occurred. This is thought to be because the amount of fluororesin particles adhering to the surface of the toner increased, making the toner more prone to reverse charging.

[0117] From the above results, it was confirmed that by setting the relationship between the number-average primary particle diameter r of the fluororesin particles and the surface roughness Ra of the photoreceptor drum to r > Ra, and by setting the amount of fluororesin particles added to 1.2 parts by mass or less per 100 parts by mass of toner matrix particles, it was confirmed that filming of fluororesin particles on the photoreceptor drum and image fogging can be effectively suppressed. Furthermore, it was confirmed that by setting the surface roughness Ra of the photoreceptor drum to 30 nm to 300 nm, and the amount of fluororesin particles added to 0.5 parts by mass to 1.0 part by mass, it was confirmed that vertical streaks in images caused by damage to the cleaning blade and vertical streaks in half images caused by the adhesion of silica particles to the regulating blade can also be suppressed. [Industrial applicability]

[0118] The present invention is applicable to electrophotographic image forming apparatuses. By using the present invention, it is possible to provide an image forming apparatus that can suppress image defects such as image fogging by suppressing contact charging between fluorine particles and toner due to the embedding of fluorine particles in the recesses of the photoreceptor, and contact charging between the toner and the recesses of the photoreceptor. [Explanation of Symbols]

[0119] 1. Image forming apparatus 30 Image forming unit 31. Photosensitive drum (image carrier) 31a Conductive substrate 31b Photosensitive layer 32. Charging section (charging device) 33. Developing section (developing device) 330 Developing housing (developing container) 331 Developing roller (developer carrier) 334 Regulatory Blade 35. Exposure section (exposure apparatus)

Claims

1. An image carrier having a conductive substrate and a photosensitive layer laminated on the surface of the conductive substrate, A charging device for charging the surface of the image carrier, An exposure apparatus that exposes the surface of the image carrier, which has been charged by the charging apparatus, to form an electrostatic latent image with reduced charge, A developing container containing a non-magnetic, one-component developer consisting only of toner, A developer carrier is pressed against the image carrier with a predetermined pressing force, and a toner layer is formed on its outer surface by carrying the toner; A restricting blade that contacts the outer surface of the developer carrier and restricts the thickness of the toner layer formed on the outer surface of the developer carrier, A developing apparatus having a toner that supplies the toner to the image carrier on which the electrostatic latent image is formed, In an image forming apparatus equipped with, The aforementioned toner is Toner matrix particles and Fluororesin particles having a number-average primary particle diameter of 100 nm or more and 300 nm or less, which are added to the surface of the toner matrix particles, It has, The amount of fluororesin particles added per 100 parts by mass of toner matrix particles is 1.2 parts by mass or less. An image forming apparatus characterized in that the number-average primary particle diameter r of the fluororesin particles and the arithmetic mean roughness Ra of the surface of the photosensitive layer satisfy r > Ra.

2. The image forming apparatus according to claim 1, characterized in that the arithmetic mean roughness Ra of the surface of the photosensitive layer is 30 nm or more and 300 nm or less.

3. Inorganic particles are added to the surface of the toner matrix particles together with the fluororesin particles. The image forming apparatus according to claim 1, characterized in that the amount of fluororesin particles added per 100 parts by mass of toner matrix particles is 0.5 parts by mass or more and 1.2 parts by mass or less.

Images