JP2007057657A - Electrophotographic image forming apparatus, tandem type image forming apparatus, electrophotographic photoreceptor and image forming unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic image forming apparatus which causes neither occurrence of voids in a solid image nor clearing in the midsection of a character image, and continuously gives high density and high sharpness toner images, and to provide a tandem type image forming method, an electrophotographic photoreceptor and an image forming unit. <P>SOLUTION: The electrophotographic image forming apparatus has, around an electrophotographic photoreceptor, a charging device, an exposure device, a developing device for development with a toner-containing liquid developer, a primary transfer device for primarily transferring a toner image on the electrophotographic photoreceptor formed with the developing device onto an intermediate transfer member, and a secondary transfer device for transferring the toner image on the intermediate transfer member onto a recording medium, wherein the electrophotographic photoreceptor contains particles having a number average primary particle diameter of 1-200 nm in its surface layer, and a light source used in the exposure device is a semiconductor laser or a light emitting diode having an oscillation wavelength of 350-500 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, a tandem type image forming apparatus, an electrophotographic photosensitive member, and an image forming unit.

  In recent years, digital image forming methods have become mainstream as a result of progress in digital technology. A digital image forming method is required to visualize a small dot image of one pixel such as 1200 dpi (dpi in the present invention represents the number of dots per inch, that is, 2.54 cm). In some cases, there is a demand for high image quality technology that faithfully reproduces such a small dot image. In particular, in recent years, there has been an increasing demand for miniaturization, high resolution, and full color copying machines, and in the case of printers, stable creation of high-quality images comparable to printing. In order to stably obtain a high-quality toner image, a higher image quality enhancement technique is required.

  In order to obtain high-quality images, development means and electrophotographic photoreceptors have been studied.

  The developing means in the electrophotographic technology is roughly divided into two types: a dry developing means and a liquid developing means.

  The dry developing means is a method using a toner made of powder, and further, a dry two-component type in which the developer is composed of toner, carrier and other additives, and a dry one-component type in which the carrier is not included and is composed of toner and other additives. It is divided into two.

  On the other hand, the liquid developing means is a developing method using a liquid developer in which toner is dispersed in a carrier liquid. Liquid developer means have advantages such as finer toner particle size and higher toner transparency compared to dry developer means, and high quality toner images can be obtained regardless of analog, digital, monochrome, or color. And an energy-saving image forming apparatus can be obtained (see, for example, Patent Documents 1, 2, 3, and 4).

In addition, as an electrophotographic photosensitive member for obtaining a large number of high-quality toner images, proposals have been made to include fine particles in the surface layer (see, for example, Patent Documents 5 and 6).
JP 2000-35697 A JP 2003-177777 A JP 2002-126077 A JP 2002-21063 A JP 2005-43623 A JP 2004-94037 A

  However, if an image forming apparatus using a liquid developer as a developing means is loaded with an electrophotographic photosensitive member containing fine particles in the surface layer and a large number of sheets are printed, black spots, fogging, and missing characters occur. Further, since the image density is lowered or the sharpness is lowered, a high-quality toner image cannot be continuously obtained, and further improvement has been desired.

  The object of the present invention is to obtain a solid image or a blank image even when a toner image formed with a liquid developer on an electrophotographic photosensitive member is transferred to a recording medium via an intermediate transfer member. It is an object to provide an electrophotographic image forming apparatus, a tandem type image forming method, an electrophotographic photosensitive member, and an image forming unit that can continuously obtain a toner image having a high density and a high sharpness.

  The object of the present invention is achieved by adopting the following configuration.

(1)
On the electrophotographic photosensitive member, a charging unit, an exposing unit, a developing unit that develops with a liquid developer containing toner, and a primary transfer unit that primarily transfers the toner image on the electrophotographic photosensitive member formed by the developing unit onto the intermediate transfer member. In an electrophotographic image forming apparatus having a secondary transfer means for transferring a toner image on an intermediate transfer member to a recording medium,
The electrophotographic photoreceptor contains particles having a number average primary particle size of 1 to 200 nm on the surface layer thereof,
An electrophotographic image forming apparatus, wherein a light source used in the exposure means is a semiconductor laser or a light emitting diode having an oscillation wavelength of 350 to 500 nm.

(2)
The electrophotographic image forming apparatus according to (1), wherein the particles include at least inorganic particles and organic particles.

(3)
The electrophotographic image forming apparatus according to (1) or (2), wherein the inorganic particles are selected from silica particles, alumina particles, titanium dioxide particles, and strontium titanate particles.

(4)
The organic particles are selected from fluorine atom-containing resin particles, silicon atom-containing resin particles, polyolefin resin particles, and polyester resin particles, as described in (1) or (2) above Electrophotographic image forming apparatus.

(5)
The electrophotographic image forming apparatus according to any one of (1) to (4), wherein the surface layer of the electrophotographic photosensitive member is a protective layer.

(6)
On the electrophotographic photosensitive member, a plurality of image forming units having a developing unit that forms a toner image by developing with a charging unit, an exposing unit, and a liquid developer containing toner,
Primary transfer means for primary transfer of each color toner image formed by using differently colored toner for each image forming unit onto an intermediate transfer body, and secondary transfer means for transferring the toner image on the intermediate transfer body to a recording medium In a tandem type image forming apparatus having
The electrophotographic photoreceptor contains particles having a number average primary particle size of 1 to 200 on the surface layer thereof,
A tandem type image forming apparatus, wherein the light source used in the exposure means is a semiconductor laser or a light emitting diode having an oscillation wavelength of 350 to 500 nm.

(7)
The diameter of the electrophotographic photosensitive member used for the black toner image forming unit of the tandem type image forming apparatus is 60 to 250 mm, which is larger than the diameter of the electrophotographic photosensitive member used for the color toner image forming unit. (6) The tandem type image forming apparatus.

(8)
The electrophotographic photoreceptor used in the electrophotographic image forming apparatus according to any one of (1) to (5) and the tandem type image forming apparatus according to (6) or (7). .

(9)
The electrophotographic photosensitive member according to (8),
The electrophotographic image forming apparatus according to any one of (1) to (5), wherein at least one unit selected from a charging unit, an exposure unit, a developing unit, a transfer unit, and a cleaning unit is combined. 6. An image forming unit, wherein the image forming unit is formed so as to be able to be taken in and out of the main body of the tandem type image forming apparatus according to 6) or 7).

  An electrophotographic image forming apparatus (hereinafter also simply referred to as an image forming apparatus), a tandem type image forming apparatus, an electrophotographic photoreceptor (hereinafter also simply referred to as a photoreceptor), and an image forming unit according to the present invention are liquid-developed on the photoreceptor. Even if the toner image formed by the agent is transferred to the recording medium via the intermediate transfer member, there is no solid image blanking or character image blanking, and a high density and high sharpness toner image continues. It has an excellent effect obtained.

  The inventors of the present invention have made it possible to continuously obtain a high-quality toner image even when a toner image formed with a liquid developer on a photoreceptor is repeatedly transferred to a recording medium via an intermediate transfer member. The device was examined.

  As a result of various studies, it has been found that a photoreceptor and an exposure light source are important points for continuously obtaining a high-quality toner image.

  Specifically, by using a photoconductor provided with a surface layer containing particles having a number average primary particle size of 1 to 200 nm, a high-quality toner image obtained by developing a latent image on the photoconductor with a liquid developer is exposed. The present inventors have found that transfer can be carried out satisfactorily from the body to the intermediate transfer body.

  Further, by using a photoconductor in which a layer containing particles having a number average primary particle size of 1 to 200 nm is provided on the surface layer, a high-resolution image is generated on the photoconductor using a light source having an oscillation wavelength of 350 to 500 and a short wavelength. It has been found that a latent image can be formed, and a high-resolution toner image can be obtained by developing the latent image on the photoreceptor with a liquid developer.

  Furthermore, by using a photoconductor containing particles in the surface layer, even if a large number of prints are made, problems caused by abrasion or scratches caused by the intermediate transfer member or the cleaning blade can be suppressed, and continuously. It has been found that a good image can be obtained.

  The reason that the toner image obtained by liquid development can be satisfactorily transferred is presumed that the toner transfer rate can be improved by incorporating particles having high releasability in the surface layer of the photoreceptor. Yes.

  A high-resolution (high sharpness) toner image can be formed because the photoreceptor according to the present invention does not contain particles having a particle size that adversely affects a short-wavelength light source used as an exposure light source. It is estimated that.

  The reason that the surface of the photoconductor is not scratched and no longer wears is that the surface of the photoconductor is made of inorganic particles and organic particles so that the surface of the photoconductor has flexibility and wear resistance. I guess it was because I could have both.

  Hereinafter, the present invention will be described in detail.

〔particle〕
The particles used in the present invention have a number average primary particle size of 1 to 200 nm, preferably 10 to 150 nm.

  Here, the number average primary particle size is a value obtained by observing 100 particles as primary particles at random by 10000-fold observation with a transmission electron microscope and image analysis.

  Examples of the transmission electron microscope (TEM) include “H-9000NAR” (manufactured by Hitachi, Ltd.) and “JEM-200FX” (manufactured by JEOL Ltd.).

  The observation method using a transmission electron microscope is performed by a normal method performed when measuring the particle size of the particles. For example, the procedure is as follows. First, materials for observation are prepared. After sufficiently dispersing the particles in a room temperature curable epoxy resin, the particles are embedded and cured to produce a block. The prepared block is cut into a thin piece having a thickness of 80 to 200 nm using a microtome equipped with diamond teeth to prepare a measurement sample. Next, the particles are magnified 10,000 times using a transmission electron microscope (TEM), and the particles are photographed. Next, the image information of 100 inorganic particles photographed by the image processing apparatus “Luzex F” (manufactured by Nicole) is arithmetically processed to obtain the number average primary particle size.

  Particles having a number average primary particle size in the above range can be uniformly dispersed in the coating solution, so that formation of aggregated particles and generation of large irregularities on the surface can be prevented. In addition, it is possible to form a good toner image without generation of transfer memory and generation of black spots due to the large unevenness. Further, the particles are less likely to settle in the coating solution, and the dispersion stability of the solution is also excellent.

  In the present invention, the particles preferably include at least inorganic particles and organic particles.

  As for the ratio of an inorganic particle and an organic particle, 20-80 mass% of inorganic particles are preferable, and 30-70 mass is more preferable.

  Examples of the inorganic particles include those selected from silica particles, alumina particles, titanium dioxide particles, and strontium titanate particles. Of these, silica particles and alumina particles are preferred.

  The number average primary particle size of the inorganic particles is preferably 1 to 150 μm.

  The inorganic particles according to the present invention are preferably surface-treated from the viewpoint of improvement in dispersibility and stability of electrophotographic characteristics. For example, inorganic particles are added to a solution obtained by dissolving or suspending a reactive organosilicon compound in an organic solvent or water, and this solution is stirred for several minutes to about 1 hour. And depending on the case, after heat-processing this liquid, it passes through processes, such as filtration, and is dried, and the inorganic particle which coat | covered the surface with the organosilicon compound is obtained. A reactive organosilicon compound may be added to a suspension in which inorganic particles are dispersed in an organic solvent or water.

  The amount of the reactive organosilicon compound used for the surface treatment is 0.1 to 10 parts by weight of the reactive organosilicon compound with respect to 100 parts by mass of titanium oxide treated with the metal oxide in the charge amount during the surface treatment. 50 mass parts, More preferably, 1-10 mass parts is preferable. When the surface treatment amount is less than the above range, the surface treatment effect is not sufficiently imparted, and the dispersibility of the titanium oxide particles in the intermediate layer is deteriorated. Moreover, if the above range is exceeded, the electrical performance is deteriorated, resulting in an increase in residual potential and a decrease in charging potential.

  Examples of the reactive organosilicon compound include compounds represented by the following general formula (1), but the compound is not limited to the following compounds as long as it is a compound that undergoes a condensation reaction with a reactive group such as a hydroxyl group on the surface of the inorganic particles. .

General formula (1)
_{(R 1) n -Si- (X} 1) 4-n
(In the formula, Si represents a silicon atom, R ₁ represents an organic group in which carbon is directly bonded to the silicon atom, X ₁ represents a hydrolyzable group, and n represents an integer of 0 to 3.)
In the organosilicon compound represented by the general formula (1), the organic group in which carbon is directly bonded to the silicon represented by R ₁ includes methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, dodecyl and the like. Alkyl groups, aryl groups such as phenyl, tolyl, naphthyl, biphenyl, epoxy-containing groups such as γ-glycidoxypropyl, β- (3,4-epoxycyclohexyl) ethyl, γ-acryloxypropyl, γ-methacryloxy Propyl-containing (meth) acryloyl group, γ-hydroxypropyl, hydroxyl group such as 2,3-dihydroxypropyloxypropyl, vinyl-containing group such as vinyl and propenyl, mercapto group such as γ-mercaptopropyl, γ-aminopropyl Amino-containing groups such as N-β (aminoethyl) -γ-aminopropyl, γ-chloropropyl, Examples include halogen-containing groups such as 1,1,1-trifluoropropyl, nonafluorohexyl, perfluorooctylethyl, and other nitro and cyano-substituted alkyl groups. Examples of the hydrolyzable group for X ₁ include alkoxy groups such as methoxy and ethoxy, halogen groups, and acyloxy groups.

  Moreover, the organosilicon compound represented by the general formula (1) may be used alone or in combination of two or more.

Further, when n is 2 or more in the specific compound of the organosilicon compound represented by the general formula (1), a plurality of R ₁ may be the same or different. Similarly, when n is 2 or less, the plurality of X ₁ may be the same or different. Further, when the general formula (1) Organic silicon compound represented by the use of two or more, may be the same among R ₁ and X ₁ each compound may be different.

  Moreover, a hydrogenpolysiloxane compound is mentioned as a preferable reactive organosilicon compound used for surface treatment. The hydrogen polysiloxane compound having a molecular weight of 1000 to 20000 is generally easily available, and has a good function to prevent black spots. In particular, when methyl hydrogen polysiloxane is used, a good effect can be obtained.

  Another surface treatment of the inorganic particles according to the present invention is inorganic particles that have been surface treated with an organosilicon compound having a fluorine atom. The surface treatment with the organosilicon compound having a fluorine atom is preferably performed by the wet method described above.

  That is, an organic silicon compound having fluorine atoms in an organic solvent or water is dissolved or suspended, untreated inorganic particles are added thereto, and such a solution is stirred for several minutes to 1 hour and mixed. In some cases, after heat treatment, drying is performed through a process such as filtration, and the surfaces of the inorganic particles are coated with an organosilicon compound having a fluorine atom. The organosilicon compound having a fluorine atom may be added to a suspension in which inorganic particles are dispersed in an organic solvent or water.

Examples of the organosilicon compound having a fluorine atom used in the present invention include 3,3,4,4,5,5,6,6,6-nonafluorohexyltrichlorosilane, 3,3,3-trifluoropropyltrimethoxy. Silane, methyl-3,3,3-trifluoropropyldichlorosilane, dimethoxymethyl-3,3,3-trifluoropropylsilane, 3,3,4,4,5,5,6,6,6-nonafluoro Examples include hexylmethyldichlorosilane.

  Other specific reactive organic titanium compounds used for the surface treatment of the inorganic particles include metal alkoxide compounds such as tetrapropoxy titanium and tetrabutoxy titanium, diisopropoxy titanium bis (acetyl acetate), and diisopropoxy titanium bis. Examples thereof include metal chelate compounds such as (ethyl acetoacetate), diisopropoxytitanium bis (lactate), dibutoxytitanium bis (octylene glycolate), and diisopropoxytitanium bis (triethanolaminate). Examples of the reactive organic zirconium compound include metal alkoxide compounds and metal chelate compounds such as tetrabutoxyzirconium and butoxyzirconium tri (acetyl acetate).

  Examples of the organic particles include those selected from fluorine atom-containing particles, polyolefin particles, polyester particles, and silicon atom-containing particles. Among these, fluorine atom-containing particles and polyester particles are preferable.

  Examples of the fluorine atom-containing particles include ethylene tetrafluoride resin, ethylene trifluoride chloride resin, hexafluoroethylene propylene resin, vinyl fluoride resin, vinylidene fluoride resin, ethylene difluoride dichloride resin, and these It is preferable to appropriately select one or two or more types from among the copolymers, and particularly, a trifluoroethylene chloride resin, a tetrafluoroethylene resin, and a vinylidene fluoride resin are preferable.

  The number average primary particle size of the organic particles is preferably 20 to 200 μm.

〔light source〕
The light source used in the present invention is a semiconductor laser or light emitting diode having an oscillation wavelength of 350 to 500 nm.

  The kind of the semiconductor laser or the light emitting diode is not particularly limited, and any semiconductor laser or light emitting diode can be used as long as the oscillation wavelength is 350 to 500 nm.

  Using these light sources, the exposure dot diameter in the writing direction is narrowed down to 10 to 50 μm, and digital exposure is performed on the photosensitive member, so that it is higher than 600 dpi (dpi: the number of dots per 2.54 cm) to 2500 dpi. A resolution electrophotographic image can be obtained.

The exposure dot diameter refers to the length of the exposure beam along the main scanning direction (Ld: measured at the maximum position) in the region where the intensity of the exposure beam is 1 / e ² or more of the peak intensity.

The light beams used have a scanning optical system and LED solid scanner such as a semiconductor laser, there is a Gaussian distribution and Lorentz distribution, etc. also the light intensity distribution is in each 1 / e ² or more regions of peak intensity The exposure dot diameter is used.

[Photoconductor]
The photoreceptor used in the present invention contains particles having a number average primary particle diameter of 1 to 200 nm in the surface layer of the photoreceptor. The particles preferably contain at least inorganic particles and organic particles.

  The photoreceptor used in the present invention preferably has a layer structure in which at least an intermediate layer, a photosensitive layer and a protective layer are sequentially provided on a conductive support, and the surface layer is preferably a protective layer.

  The diameter of the photoreceptor used in the black image forming unit is preferably 60 to 250 mm, and is larger than the diameter of the photoreceptor in the color image forming unit.

<< Layer structure of photoconductor >>
The photoreceptor used in the present invention may contain particles having a number average primary particle size of 1 to 200 nm in the surface layer, and the layer structure is not particularly limited, and specifically, as shown below. Can be mentioned.

1) A structure in which a charge generation layer and a charge transport layer are sequentially laminated as a photosensitive layer on a conductive support;
2) A structure in which a charge generation layer, a charge transport layer, and a protective layer are sequentially laminated as a photosensitive layer on a conductive support;
3) A structure in which a single layer containing a charge transport material and a charge generation material is formed as a photosensitive layer on a conductive support;
4) A structure in which a single layer containing a charge transport material and a charge generation material and a protective layer are formed as a photosensitive layer on a conductive support;
5) A structure in which a charge transport layer and a charge generation layer are sequentially laminated as a photosensitive layer on a conductive support;
6) A structure in which a charge transport layer, a charge generation layer, and a protective layer are sequentially laminated as a photosensitive layer on a conductive support;
The photoreceptor of the present invention may be any of the above-described structures, but among them, those prepared by providing an intermediate layer, a charge generation layer, a charge transport layer, and a protective layer on a conductive substrate are preferable.

  In the present invention, an intermediate layer can be provided between the conductive support and the photosensitive layer for the purpose of improving electrical characteristics and adhesiveness.

  Here, the surface layer of the photoconductor is a layer in which the photoconductor is in contact with the air interface. When only a single-layer type photoconductive layer is formed on the conductive support, the photoconductive layer is a surface layer. In the case where a single layer type or laminated type photosensitive layer and a protective layer are laminated on a conductive support, the protective layer is a surface layer.

  FIG. 1 is a schematic diagram showing an example of a layer structure of a photoreceptor used in the present invention.

  FIG. 1A shows a photoreceptor whose surface layer is a charge transport layer, and FIG. 1B shows a photoreceptor whose surface layer is a protective layer.

  In FIG. 1, 100 is a conductive substrate, 200 is an intermediate layer, 210 is inorganic particles, 220 is a binder, 300 is a photosensitive layer, 400 is a charge generation layer, 500 is a charge transport layer, 600 is a protective layer, and 700 is inorganic particles. , 800 represents organic particles, and 900 represents a surface layer.

<< Production of photoconductor >>
The photoreceptor can be prepared by dip coating, circular amount regulation type coating, or a combination of dip coating and round amount regulation type coating, but is not limited thereto. The circular amount regulation type application is described in detail in, for example, Japanese Patent Application Laid-Open No. 58-189061.

  Next, members constituting the conductive substrate, the intermediate layer, the photosensitive layer, and the protective layer, and methods for forming each layer will be described.

<Conductive substrate>
The conductive substrate used in the present invention is preferably cylindrical and has a specific resistance of 10 ³ Ωcm or less. As a specific example, cylindrical aluminum whose surface has been cleaned after cutting can be mentioned.

<Intermediate layer>
The intermediate layer is formed by applying and drying an intermediate layer coating solution composed of a binder, a dispersion solvent, and the like on a conductive substrate.

  Examples of the binder for the intermediate layer include polyamide resins, vinyl chloride resins, vinyl acetate resins, and copolymer resins containing two or more of these resin repeating units. Among these resins, a polyamide resin is preferable because it can reduce a residual potential increase due to repeated use.

  As the solvent for preparing the intermediate layer coating solution, a solvent in which inorganic particles are well dispersed and the polyamide resin is dissolved is preferable. Specifically, alcohols having 2 to 4 carbon atoms such as ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, t-butanol, sec-butanol and the like are excellent in solubility and coating performance of the polyamide resin. These solvents are 30 to 100% by mass, preferably 40 to 100% by mass, and more preferably 50 to 100% by mass in the total solvent. Examples of co-solvents that can be used in combination with the above-mentioned solvent to obtain preferable effects include methanol, benzyl alcohol, toluene, methylene chloride, cyclohexanone, and tetrahydrofuran.

  The thickness of the intermediate layer is preferably 0.2 to 40 μm, and more preferably 0.3 to 20 μm.

<Photosensitive layer>
The photosensitive layer may have a single layer structure in which a charge generation function and a charge transport function are provided in one layer, but more preferably the function of the photosensitive layer is separated into a charge generation layer (CGL) and a charge transport layer (CTL). It is more preferable to take a layer structure. By adopting a configuration in which the functions are separated, an increase in residual potential due to repeated use can be controlled to be small, and other electrophotographic characteristics can be easily controlled according to the purpose. In the negatively charged photoreceptor, a charge generation layer (CGL) is formed on the intermediate layer, and a charge transport layer (CTL) is formed thereon. In the positively charged photoconductor, the order of the layer configuration is opposite to that in the negatively charged photoconductor. A preferred layer structure of the photosensitive layer is a negatively charged photoreceptor having the function separation structure.

  Hereinafter, each layer of the photosensitive layer of the function-separated negatively charged photoreceptor will be described.

(Charge generation layer)
The charge generation layer contains a charge generation material (CGM). Other substances may contain a binder resin and other additives as necessary.

  A known charge generation material (CGM) can be used as the charge generation material (CGM). For example, a phthalocyanine pigment, an azo pigment, a perylene pigment, an azulenium pigment, or the like can be used. Among these, the CGM that can minimize the increase in residual potential due to repeated use has a three-dimensional and potential structure that can form a stable aggregate structure among a plurality of molecules. Specifically, a phthalocyanine having a specific crystal structure. CGM of pigments and perylene pigments. For example, CGM such as titanyl phthalocyanine having a maximum peak at a Bragg angle 2θ of 27.2 ° with respect to the Cu—Kα ray and benzimidazole perylene having a maximum peak at 2θ of 12.4 ° has almost no deterioration due to repeated use. The increase in residual potential can be reduced.

  When a binder is used as a CGM dispersion medium in the charge generation layer, a known resin can be used as the binder, but the most preferable resins include formal resin, butyral resin, silicon resin, silicon-modified butyral resin, phenoxy resin, and the like. Can be mentioned. The ratio of the binder resin to the charge generating material is preferably 20 to 600 parts by mass with respect to 100 parts by mass of the binder resin. By using these resins, the increase in residual potential associated with repeated use can be minimized. The thickness of the charge generation layer is preferably from 0.01 to 2 μm.

(Charge transport layer)
When the charge transport layer is the uppermost layer, it contains particles (resin particles and inorganic particles) according to the present invention, a charge transport material (CTM), and a binder resin. Other substances may contain an antioxidant, a dispersant and the like as necessary.

  The thickness of the charge transport layer is preferably 0.2 to 40 μm, and more preferably 3 to 20 μm.

  5-50 mass% is preferable with respect to the whole charge transport layer, and, as for content of the particle | grain in a charge transport layer, 10-30 mass% is more preferable.

  Moreover, 20-80 mass% is preferable and, as for the ratio of the inorganic particle to the whole particle | grain, 30-70 mass% is more preferable.

  A known charge transport material (CTM) can be used as the charge transport material (CTM). For example, a triphenylamine derivative, a hydrazone compound, a styryl compound, a benzidine compound, a butadiene compound, or the like can be used. These charge transport materials are usually dissolved in a suitable binder resin to form a layer.

  Examples of the resin used for the charge transport layer (CTL) include polystyrene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, polyvinyl butyral resin, epoxy resin, polyurethane resin, phenol resin, polyester resin, alkyd resin, and polycarbonate. Resin, silicon resin, melamine resin, and copolymer resin containing two or more of repeating units of these resins. In addition to these insulating resins, polymer organic semiconductors such as poly-N-vinylcarbazole can be used.

  Most preferred as a binder for these CTLs is a polycarbonate resin. The polycarbonate resin is most preferable in improving the dispersibility and electrophotographic characteristics of CTM. The ratio of the binder resin to the charge transport material is preferably 10 to 200 parts by mass with respect to 100 parts by mass of the binder resin. The thickness of the charge transport layer is preferably 10 to 40 μm.

  As the antioxidant, a known compound can be used, and specifically, “Irganox 1010” (manufactured by Ciba Geigy Japan) can be mentioned.

<Protective layer>
The protective layer contains particles (resin particles and inorganic particles) according to the present invention and a binder resin. Other materials may contain a charge transport material, an antioxidant, a dispersant and the like as necessary.

  As the binder resin, a resin having abrasion resistance is preferable. Specifically, a silica atom having a small environmental fluctuation in the resistance of the protective layer and excellent in the dispersibility of particles and the stability after dispersion is used. Examples thereof include resins containing, fluorine-containing resins, polycarbonate resins, acrylic resins, phenol resins, epoxy resins, urethane resins, and siloxane resins.

  Specific examples of the binder resin for the protective layer include those having the following structural units.

  Binder resin containing structural formula 1 below as a structural unit

(In Structural Formula 1, R ¹ and R ² represent a hydrogen atom, an alkyl group, and an aryl group, R ³ and R ⁴ represent a hydrogen atom, a halogen atom, an alkyl group, and an aryl group, and X ² represents an F atom-containing group. To express.)
Binder resin structural unit represented by Structural Formula 1

  Binder resin containing structural formula 1 below as a structural unit

Binder resin structural unit represented by Structural Formula 2 (In Structural Formula 1, R ⁵ and R ⁶ represent a hydrogen atom, an alkyl group, and an aryl group, and R ⁷ and R ⁸ represent a hydrogen atom, a halogen atom, an alkyl group, X ¹ representing an aryl group represents a Si atom-containing group.

  5-50 mass% is preferable with respect to the whole protective layer, and, as for the ratio of the particle | grains (inorganic particle | grains and organic particle) which occupy in a protective layer, 10-30 mass% is more preferable.

  Moreover, 20-80 mass% is preferable and, as for the ratio of the inorganic particle to the whole particle | grain, 30-70 mass% is more preferable.

  By mixing and using inorganic particles and organic particles in the above ratio, it is more preferable that both surface characteristics and abrasion resistance of the surface can be satisfied.

[Development means]
The developer used for the developing means is a liquid developer having at least a toner and a carrier liquid.

  The toner concentration of the liquid developer is preferably 10% by mass or more, and more preferably 20 to 60% by mass with respect to 100 parts by mass of the carrier liquid.

  The liquid developer preferably has a high viscosity of 100 mPa · s or higher. The viscosity can be measured with a B-type viscometer at 60 rpm.

  The carrier liquid is preferably a volatile solution or a non-volatile solution, which can increase the viscosity of the developer and can contain toner at a high concentration.

  As the volatile solution used as the carrier liquid, a non-aqueous solution having a high insulating property and a low dielectric constant is used. Specific examples include trichlorotrifluoroethane, hexane, cyclohexane, and Isopar H.

Non-volatile solution used as the carrier liquid, highly insulating, non-aqueous solution of a low dielectric constant is used, the viscosity in particular is 10 to 100 mm ² / s, preferably include silicone oil 20 to 50 mm ² / s It is done.

The toner is mainly composed of a heat-melting resin and a colorant, and preferably has a median particle diameter (D ₅₀ ) of 0.4 to 2 μm, more preferably 0.7 to 1.5 μm, based on the number.

  The particle size of the toner can be measured by “Cole-Turter Multisizer Type III” (manufactured by Beckman Coulter, Inc.).

  As the resin used for the toner, for example, alkyd resin, rosin-modified phenol formaldehyde resin, polyhydric alcohol ester of hydrogenated rosin, polyacrylic ester, polymethacrylic ester resin, styrene resin, chlorinated rubber or the like is used.

  Examples of the colorant used in the toner include carbon black, phthalocyanine blue, phthalocyanine green, sky blue, rhodamine lake, malachite green lake, methyl violet lake, peacock blue lake, naphthol green B, naphthol green Y, naphthol yellow S, and risol first. Yellow 2G, permanent red 4R, brilliant first scarlet, Hansa yellow, benzidine yellow, resol red, lake red, lake red D, brilliant carmine 6B, permanent red F5R, pigment scarlet 3B, Bordeaux 10B, naphthol red, etc. are used.

  When the electrostatic latent image on the photoconductor according to the present invention is developed using this liquid developer, a high-resolution toner image can be formed on the photoconductor. This toner image can be satisfactorily transferred to the intermediate transfer member, and finally a high-resolution toner image can be formed on the recording medium.

[Image forming apparatus]
The image forming apparatus of the present invention has the following charging means, exposure means, developing means, and transfer means, and further includes a fixing means and a cleaning means as necessary.

<Charging means>
In the charging means, wire discharge or a roller charging device is used in order to apply a charge to the photoreceptor according to the present invention.

<< Exposure means >>
In the exposure means, a semiconductor laser or light emitting diode having an oscillation wavelength of 350 to 500 nm is used as a light source in order to form an electrostatic latent image on the photoreceptor.

<Development means>
In the developing means, each color developing device is used to form each color toner image from the electrostatic latent image formed on the photoreceptor using a liquid developer.

<Transfer means>
The transfer unit uses a transfer device that sequentially transfers the toner images of the respective colors formed on the photosensitive member to the intermediate transfer member, and a transfer device that collectively transfers the toner images on the intermediate transfer member to the recording medium.

《Fixing means》
The fixing unit uses a thermal fixing device to fix the toner image formed on the recording medium to the recording medium.

《Cleaning means》
The cleaning unit uses a blade cleaning device to clean the transfer residual toner on the photosensitive member or the transfer residual toner on the intermediate transfer member.

[Tandem type image forming apparatus]
The tandem type image forming apparatus is a transfer in which a plurality of image forming units are arranged, and each color toner image formed using each color toner changed in color for each image forming unit is sequentially transferred to an intermediate transfer member to form a toner image. And a transfer means for collectively transferring the toner image formed by transferring to the intermediate transfer body onto the recording medium.

  The image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 2 shows an image forming apparatus in which an electrostatic latent image formed on a photoconductor is formed into a toner image by a liquid developing unit, and the toner image is transferred to a recording medium by an intermediate transfer unit using an intermediate transfer member. It is a schematic cross section which shows an example.

  This image forming apparatus is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, an endless transfer belt unit 7, a paper feeding / conveying means, and a heating and pressing type fixing. Device 24. A document image reading device SC is disposed on the upper part of the main body A of the image forming apparatus.

  An image forming unit 10Y for forming a yellow image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a primary transfer unit disposed around a drum-shaped photoconductor 1Y as a first image carrier. It has a primary transfer roll 5Y and a cleaning means 6Y. The image forming unit 10M for forming a magenta image includes a drum-shaped photosensitive member 1M as a first image carrier, a charging unit 2M, an exposure unit 3M, a developing unit 4M, a primary transfer roll 5M as a primary transfer unit, It has a cleaning means 6M. An image forming unit 10C for forming a cyan image includes a drum-shaped photoconductor 1C as a first image carrier, a charging unit 2C, an exposure unit 3C, a developing unit 4C, a primary transfer roll 5C as a primary transfer unit, It has cleaning means 6C. The image forming unit 10K for forming a black image includes a drum-shaped photosensitive member 1K as a first image carrier, a charging unit 2K, an exposure unit 3K, a developing unit 4K, a primary transfer roll 5K as a primary transfer unit, and a cleaning unit. 6K.

  The endless transfer belt unit 7 is wound by a plurality of rolls 71, 72, 73, 74, 76, and is endless transfer as a semiconductive endless belt-like second image carrier that is rotatably supported. A belt 70 is provided.

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred onto the rotating endless transfer belt 70 by the primary transfer rolls 5Y, 5M, 5C, and 5K, and the combined color. An image is formed. The recording medium P accommodated in the paper feeding cassette 20 is fed by the paper feeding means 21 and is conveyed to the secondary transfer means 5A through a plurality of intermediate rolls 22A, 22B, 22C, 22D and a registration roll 23, A color image is collectively transferred onto the recording medium P. The recording medium P onto which the color image has been transferred is fixed by the heat and pressure type fixing device 24, is contact-conveyed (for example, niped) by the conveying member 25, and is placed on a paper discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the recording medium P by the secondary transfer means 5A, the residual toner is removed by the cleaning means 6A from the endless transfer belt 70 from which the recording medium P is separated by curvature.

  During the image forming process, the primary transfer roll 5K is always in pressure contact with the photoreceptor 1K. The other primary transfer rolls 5Y, 5M, and 5C are in pressure contact with the corresponding photoreceptors 1Y, 1M, and 1C, respectively, only during color image formation.

  The secondary transfer means 5A is in pressure contact with the endless transfer belt 70 only when the recording medium P passes through the secondary transfer means 5A.

  In this way, a toner image is formed on the photoconductor by charging, exposure, and development, and each color is superimposed on the transfer belt, transferred onto a recording medium as a recording medium, and added by a heat and pressure type fixing device. It is fixed by heat and pressure. The heat-fixed support is contacted and conveyed by a conveying member and discharged out of the system. After the toner image is transferred to the recording medium, the photosensitive member and the transfer belt enter the next image forming cycle after cleaning the toner remaining in the cleaning device.

  FIG. 3 shows an image forming apparatus that forms a toner image from an electrostatic latent image formed on a photoreceptor by a liquid developing unit and transfers the toner image to a recording medium by an intermediate transfer unit using an intermediate transfer member. It is a schematic cross section which shows an example.

  This image forming apparatus is called a tandem type color image forming apparatus as in FIG. 2, and is the same as FIG. 2 except that the diameter of the photosensitive member 1K in FIG.

  The recording medium used in the present invention is a support for holding a toner image, and is usually called an image support, a recording material or a transfer paper. Specific examples include various types of recording materials such as plain paper from thin paper to thick paper, coated printing paper such as art paper and coated paper, commercially available Japanese paper and postcard paper, plastic films for OHP, and cloth. However, it is not limited to these.

  Examples according to the present invention will be described below, but the present invention is not limited to the following examples.

<< Production of photoconductor >>
<Preparation of Photoreceptor 1>
(Conductive substrate)
As the conductive substrate, a cylindrical aluminum substrate whose surface was cleaned after cutting (processing to JISB-0601 standard 10-point surface roughness Rz: 0.81 μm) was prepared.

(Formation of intermediate layer)
An intermediate layer coating solution was prepared by dissolving the following resin components.

Intermediate layer coating solution Polyamide resin (N-9) 1 part by mass Solvent 10 parts by mass
(Ethanol / n-propyl alcohol / tetrahydrofuran
= Mass ratio 5/2/3)

  The intermediate layer coating solution was adjusted to a penetration depth of the dip coating, applied from the upper end of the conductive substrate to 15 mm, and dried to form an intermediate layer coating film.

  Thereafter, the intermediate layer coating film from the lower end of the conductive substrate to 15 mm is removed with a tape impregnated with a solvent (ethanol / n-propyl alcohol / tetrahydrofura (mass ratio 5/2/3)) to remove the lower end of the conductive substrate. After the exposure, heat treatment was performed at 120 ° C. for 30 minutes to form an intermediate layer having a thickness of 3.0 μm. The film thickness is a value measured using an eddy current type film thickness measuring device “EDDY560C” (manufactured by HELMUT FISCHER).

(Formation of charge generation layer)
A liquid in which the following components were mixed was dispersed using a sand mill disperser to prepare a charge generation layer coating liquid.

Charge generation layer coating liquid Y-type oxytitanyl phthalocyanine (X-ray diffraction spectrum by Cu-Kα characteristic X-ray, titanyl phthalosine pigment having a maximum diffraction peak at a Bragg angle (2θ ± 0.2 °) of 27.3 °) 20 parts by mass Silicon-modified polyvinyl butyral 10 parts by mass 4-methoxy-4-methyl-2-pentanone 700 parts by mass t-butyl acetate 300 parts by mass The penetration depth of the dip coating was adjusted, and an intermediate layer was provided. A charge generation layer was formed by applying and drying 13 mm from the upper end of the conductive substrate.

  Thereafter, the charge generation layer coating film from the lower end of the substrate to 13 mm was removed with a tape impregnated with a solvent (4-methoxy-4-methyl-2-pentanone / t-butyl acetate (mass ratio 7/3)) to remove the lower end of the substrate. And a charge generation layer having a thickness of 0.3 μm was formed on the intermediate layer. The film thickness is a value measured using an eddy current type film thickness measuring device “EDDY560C” (manufactured by HELMUT FISCHER GMBTE CO).

(Formation of charge transport layer)
A liquid in which the following components are mixed is dispersed for 10 hours using a batch type sand mill disperser, and then filtered (filter; rigesh mesh filter manufactured by Nihon Pall Co., Ltd., nominal filtration accuracy: 5 μm, pressure: 50 kPa) and applied to a charge transport layer. A liquid was prepared.

Charge transport layer coating solution 4-methoxy-4 '-(4-methyl-α-phenylstyryl) triphenylamine
70 parts by mass Bisphenol Z-type polycarbonate “Iupilon-Z300” (manufactured by Mitsubishi Gas Chemical Company) 100 parts by mass Inorganic particles “titanium dioxide” (number average primary particle size 33 nm) 30 parts by mass Organic particles “polyester resin” (number average primary particles Diameter 70 nm) 45 parts by mass Antioxidant “Irganox 1010” (manufactured by Nippon Ciba-Geigy) 8 parts by mass Solvent (tetrahydrofuran / toluene (mass ratio 8/2)) 750 parts by mass The charge transport layer was formed by applying and drying 10 mm from the upper end of the conductive substrate provided with the charge generation layer.

  Thereafter, the charge transport layer coating film from the lower end of the substrate to 10 mm is removed with a tape impregnated with a solvent (tetrahydrofuran / toluene (mass ratio 8/2)) to expose the lower end of the substrate, and the film thickness is formed on the charge generation layer. A 25 μm charge transport layer was formed. The film thickness is a value measured using an eddy current type film thickness measuring device “EDDY560C” (manufactured by HELMUT FISCHER GMBTE CO).

(Formation of protective layer)
A liquid in which the following components are mixed is dispersed for 10 hours using a batch-type sand mill disperser, and then filtered (filter; rigesh mesh filter made by Nihon Pall Co., Ltd., nominal filtration accuracy: 5 μm, pressure: 50 kPa), and a protective layer coating liquid Was prepared.

Protective layer coating solution 4-methoxy-4 '-(4-methyl-α-phenylstyryl) triphenylamine
10 parts by mass Si atom-containing binder resin (Example 1) 27 parts by mass Toluylene diisocyanate (TDI) (manufactured by Nippon Polyurethanes) 3 parts by mass Sanol LS2626 (manufactured by Sankyo Co., Ltd.) 1 part by mass 1,2-dichloroethane 150 parts by mass Inorganic particles “Titanium dioxide” (number average primary particle size 33 nm) 10 parts by mass Organic particle “polyester resin” (number average primary particle size 70 nm) 15 parts by mass The above-mentioned protective layer coating solution is applied to the surface of the charge transport layer in a circular amount-regulating type. By applying and drying with an apparatus, a 6 μm-thick protective layer coating film was formed to produce “Photoreceptor 1” (corresponding to (b) of FIG. 1).

<Production of photoconductors 2 to 5 and 7 to 9>
The “inorganic particles” and “organic particles” used in the preparation of the charge transport layer and the protective layer of the “photoreceptor 1” were changed as shown in Table 1, and the same method as the production method of the “photoreceptor 1” was used. “Photosensitive members 2 to 5, 7, and 8” were produced (corresponding to (b) of FIG. 1).

<Preparation of Photoreceptor 6>
In “Preparation of Photoreceptor 1”, “Photoreceptor 6” was prepared in the same manner except that the charge transport layer was formed, the protective layer was not formed thereon, and the charge transport layer was the surface layer (FIG. 1). (Corresponding to (a)).

  Table 1 shows the layer structure of “photosensitive members 1 to 9”, the types of inorganic particles and organic particle particles used in the preparation of the charge transport layer and the protective layer, the number average primary particle diameter, and the ratio of the inorganic particles.

<Production of liquid developer>
(Preparation of liquid developer 1)
Add 0.90 kg of sodium n-dodecyl sulfate and 10 L of pure water and dissolve with stirring. With stirring, 1.2 kg of Legal 330R (Carbot Black manufactured by Cabot) was gradually added to this liquid, and then continuously dispersed for 20 hours using a sand grinder (medium disperser). After dispersion, the particle size of the dispersion was measured using an electrophoretic light scattering photometer ELS-800 manufactured by Otsuka Electronics Co., Ltd. As a result, the mass average particle size was 122 nm.

  Moreover, the solid content concentration of the dispersion measured by a mass method by standing drying was 16.6% by mass. This dispersion is referred to as “colorant dispersion 1”.

  0.055 kg of sodium dodecylbenzenesulfonate is mixed with 4 L of ion-exchanged water and dissolved by stirring at room temperature. This is designated as anionic surfactant solution A.

  0.014 kg of nonylphenol alkyl ether is mixed with 12 L of ion-exchanged water, and dissolved under stirring at room temperature. This is called initiator solution A.

  In a 100 liter reaction kettle equipped with a temperature sensor, a cooling pipe, and a nitrogen introducing device, 3.41 kg of a polypropylene emulsion having a number average molecular weight (Mn) of 3500, an anionic surfactant solution A, and a nonionic surfactant solution are added and stirred. Start. Next, 44 L of ion exchange water is added.

  Heating is started, and when the liquid temperature reaches 75 ° C., the whole amount of the initiator solution A is added. Thereafter, 12.1 kg of styrene, 2.88 kg of n-butyl acrylate, 1.04 kg of methacrylic acid, and 548 g of t-dodecyl mercaptan are charged while controlling the liquid temperature to 75 ± 1 ° C.

  Further, the liquid temperature was lowered to 80 ° C. ± 1 ° C., and the mixture was heated and stirred for 6 hours. Cool the liquid temperature below 40 ° C and stop stirring. It filtered with the pole filter and this was set as latex A1.

  The glass transition temperature of the resin particles in the latex A1 was 57 ° C., the softening point 121 ° C., the molecular weight distribution was 12,700 in weight average molecular weight, and the mass average particle size was 120 nm.

  200.7 g of potassium persulfate is mixed with 12 L of ion-exchanged water and dissolved by stirring at room temperature. This is designated initiator solution B.

  A nonionic surfactant solution is put into a 100 L reaction kettle equipped with a temperature sensor, a cooling pipe, a nitrogen introduction pipe, and a comb baffle, and stirring is started. Next, 44L of ion exchange water is added.

  Heating is started, and when the liquid temperature reaches 70 ° C., the initiator solution B is added. At this time, a solution prepared by previously mixing 11 kg of styrene, 4 kg of n-butyl acrylate, 1.04 kg of methacrylic acid, and 9.02 g of t-dodecyl mercaptan is added.

  Thereafter, the liquid temperature was controlled to 72 ± 2 ° C., and the mixture was heated and stirred for 6 hours. Furthermore, the liquid temperature was raised to 80 ± 2 ° C., and stirring was carried out for 12 hours. Next, the liquid temperature is cooled to 40 ° C. or lower, and stirring is stopped. It filtered with the pole filter and this filtrate was set to latex B1. The glass transition temperature of the latex B1 resin particles was 58 ° C., the softening point was 132 ° C., the molecular weight distribution was 245,000, and the mass average particle size was 110 nm.

  5.36 kg of sodium chloride as a salting-out agent and 20 L of ion-exchanged water are added and dissolved by stirring. This is designated as sodium chloride solution A.

  Latex A1, 20 kg, latex B1, 5.2 kg and colorant dispersion 1 prepared in a 100 L SUS reaction kettle (stirring blade is an anchor blade) equipped with a temperature sensor, a cooling pipe, a nitrogen introducing device, and a comb baffle , 0.4 kg and 20 kg of ion exchange water are added and stirred. Then warm to 35 ° C. and add sodium chloride solution A. Then, after standing for 5 minutes, temperature increase is started, and the liquid temperature is increased to 85 ° C. in 5 minutes (temperature increase rate 10 ° C./min). Heat and stir at a liquid temperature of 85 ± 2 ° C. for 6 hours to salt out and fuse. Thereafter, it is cooled to 30 ° C. or lower, and stirring is stopped. The mixture is filtered through a sieve having an opening of 45 μm, and this filtrate is designated as an associated liquid (1). Next, using a centrifugal separator, wet cake-like non-spherical particles were collected from the associated liquid (1) by filtration. Thereafter, it was washed with ion exchange water.

  The wet cake-like colored particles having been washed as described above were dried with hot air at 40 ° C. to obtain colored particles. The number average particle diameter of the colored particles was 2.5 μm. Further, 100 g of the colored particles were mixed with 250 g of an IP solvent 1620 solution of 0.25% by mass of petroleum sulfonic acid barium salt (sulfur Ba-30N) and uniformly dispersed with a sand grinder, and further 0.25% by mass of 3150 g of an IP solvent 1620 solution of petroleum sulfonic acid barium salt (sulfur Ba-30N) was added and diluted to prepare “Liquid Developer 1” having a number average particle diameter of 2.5 μm.

(Preparation of liquid developer 2)
“Liquid developer 2” was produced in the same manner except that the carbon black used in the production of liquid developer 1 was changed to paphthalocyanine blue.

(Preparation of liquid developer 3)
“Liquid developer 3” was produced in the same manner except that the carbon black used in the production of liquid developer 1 was changed to naphthol yellow S.

(Preparation of liquid developer 4)
“Liquid developer 4” was produced in the same manner except that the carbon black used in the production of liquid developer 1 was changed to permanent red F5R.

<Image forming apparatus>
The image forming apparatus shown in FIG. 3 was used as an evaluation apparatus under the following conditions.

Photoconductor: large diameter (diameter 60 mm) mounted on black image forming unit: small diameter (diameter 30 mm) mounted on color (Y, M, C) image forming unit Charging means: sawtooth electrode, uniform charge of -400 V Exposure Means: Semiconductor laser Developing means: mounting liquid developers 1 to 4 Transfer means: using an intermediate transfer belt Cleaning means: using a cleaning blade Fixing means: heat fixing Process speed: 100 mm / sec
<Evaluation image forming apparatus>
As an image forming apparatus for evaluation, an image forming apparatus loaded with the “liquid developers 1 to 4” prepared above was prepared.

  The evaluation was performed by sequentially loading the photoconductor and the light source of the exposure unit in the image forming apparatus for evaluation as shown in Table 2.

《Image evaluation》
In the image evaluation, a character image (3 point, 5 point character) with a pixel rate of 7%, a human face photo (dot image including a halftone), a solid white image, and a solid black image are each divided into ¼ equal parts. The original image was printed with a printed image obtained by printing on neutral paper (64 g / m ² ) of A4 size.

(Blank image)
The original document was printed in a high temperature and high humidity (30 ° C., 85% RH) environment.

  The evaluation of the white spot of the solid image was determined by how many white spots having a major axis of 0.4 mm or more per A4 paper in the solid image portion. Incidentally, the hollow major axis was measured with a microscope equipped with a video printer.

Evaluation Criteria A: White spot frequency of 0.4 mm or more: All copied images are 3 / A4 or less. ○: White spot frequency of 0.4 mm or more: 4 / A4 or more, 19 / A4 or less occurs. ×: White spot frequency of 0.4 mm or more: One or more of 20 / A4 or more occurred.

(Cut out of text image)
The original document was printed in a low temperature and low humidity (10 ° C., 15% RH) environment.

  The three-point and five-point characters of the black character image were magnified and observed with a magnifying glass, and the occurrence of a void in the character image was visually evaluated.

Evaluation criteria ◎: Up to the 50,000th print, no 3 point or 5 point characters are missing. ○: Up to the 50,000th print, no 3 point characters are missing. ×: 50,000 sheets There is a noticeable dropout in the 3-point and 5-point characters printed on the eyes.

(Cover)
For fogging, the density of neutral paper (white paper) that has not been printed is measured at 20 locations and the absolute image density, the average value is taken as the white paper density, and then the white background portion of the neutral paper on which a solid image has been formed Similarly, measurement was performed at 20 positions at an absolute image density, and a value obtained by subtracting the white paper density from the average density was evaluated as a fog density. The measurement was performed using “RD-918” (Macbeth reflection densitometer).

Evaluation Criteria A: Good at 0.005 or less both at the initial stage and after printing 100,000 sheets ○: Level at 0.005 or less at the initial stage and 0.01 or less after printing 1,000,000 sheets No problem for practical use ×: Initial stage and 10 Both levels after printing 10,000 sheets are larger than 0.01 and cause practical problems.

(Black pot)
The black spots were evaluated after printing 100,000 sheets and printing 100 plain images. The evaluation was performed on the number of black spots per A4 plate that can be visually observed (diameter 0.4 mm or more) on the hard copy, where the periodicity of black spots coincides with the period of the photoreceptor.

Evaluation criteria ◎: Black hard spot occurrence frequency is 3 / A4 or less for all hard copies ○: Black stick occurrence frequency is 4 / A4 or higher and 10 / A4 or lower for all hard copies 1 or more occurs, but there is no practical problem. X: In all hard copies, the frequency of occurrence of black spots is 11 / A4 size or more, and there is a practical problem.

(Image density)
The image density was evaluated by the density of the solid black image portion of the print image. The image density was measured using “RD-918” (manufactured by Macbeth Co.), and the relative reflection density with the paper reflection density set to “0”.

Evaluation criteria ◎: Image density is 1.2 or higher in both initial and 1 million prints. ○: Initial image density is 1.2 or higher, and image density is 1.0 or higher after 1 million prints. Level where there is no problem ×: Image density is less than 1.0 both in the initial stage and after printing 1 million sheets.

(Sharpness)
The sharpness was evaluated by printing 1 million sheets, printing an original document, and observing a character image with a 10 × magnifier.

Evaluation criteria ◎: 3 points and 5 points are clear, easy to read and good ○: 3 points are partially unreadable, 5 points are clear, easily read and practically no problem ×: 3 The points are almost unreadable, and some or all of the 5 points are unreadable and practically problematic.

  Table 2 shows the evaluation results.

  From Table 2, it can be seen that "Examples 1 to 8" according to the present invention can obtain a high-quality toner image without any problem in any of the evaluation items. On the other hand, it is understood that “Comparative Examples 1 to 5” for comparison have a problem in any of the evaluation items.

FIG. 2 is a schematic diagram illustrating an example of a layer configuration of a photoreceptor according to the present invention. A schematic view showing an example of an image forming apparatus that forms a toner image from an electrostatic latent image formed on a photoreceptor by a liquid developing unit, and transfers the toner image to a recording medium by an intermediate transfer unit using an intermediate transfer member. It is sectional drawing. A schematic view showing an example of an image forming apparatus that forms a toner image from an electrostatic latent image formed on a photoreceptor by a liquid developing unit, and transfers the toner image to a recording medium by an intermediate transfer unit using an intermediate transfer member. It is sectional drawing.

Explanation of symbols

100 substrate 200 intermediate layer 300 photosensitive layer 400 charge generation layer 500 charge transport layer 600 protective layer 700 inorganic particle 800 organic particle 900 surface layer 1Y, 1M, 1C, 1K photoreceptor 2Y, 2M, 2C, 2K charging means 3Y, 3M, 3C, 3K Exposure means 4Y, 4M, 4C, 4K Development means 5Y, 5M, 5C, 5K Primary transfer roller as primary transfer means 5A Secondary transfer roller as secondary transfer means 6Y, 6M, 6C, 6K Cleaning means 7 Endless belt-shaped intermediate transfer body unit 10Y, 10M, 10C, 10K Image forming unit 11Y, 11M, 11C, 11K Liquid developer 24 Fixing device

Claims (9)

On the electrophotographic photosensitive member, a charging unit, an exposing unit, a developing unit that develops with a liquid developer containing toner, and a primary transfer unit that primarily transfers the toner image on the electrophotographic photosensitive member formed by the developing unit onto the intermediate transfer member. In an electrophotographic image forming apparatus having a secondary transfer means for transferring a toner image on an intermediate transfer member to a recording medium,
The electrophotographic photoreceptor contains particles having a number average primary particle size of 1 to 200 nm on the surface layer thereof,
An electrophotographic image forming apparatus, wherein a light source used in the exposure means is a semiconductor laser or a light emitting diode having an oscillation wavelength of 350 to 500 nm. The electrophotographic image forming apparatus according to claim 1, wherein the particles include at least inorganic particles and organic particles. The electrophotographic image forming apparatus according to claim 1, wherein the inorganic particles are selected from silica particles, alumina particles, titanium dioxide particles, and strontium titanate particles. 3. The electrophotographic image according to claim 1, wherein the organic particles are selected from fluorine atom-containing resin particles, silicon atom-containing resin particles, polyolefin resin particles, and polyester resin particles. Forming equipment. The electrophotographic image forming apparatus according to claim 1, wherein the surface layer of the electrophotographic photosensitive member is a protective layer. On the electrophotographic photosensitive member, a plurality of image forming units having a developing unit that forms a toner image by developing with a charging unit, an exposing unit, and a liquid developer containing toner,
Primary transfer means for primary transfer of each color toner image formed by using differently colored toner for each image forming unit onto an intermediate transfer body, and secondary transfer means for transferring the toner image on the intermediate transfer body to a recording medium In a tandem type image forming apparatus having
The electrophotographic photoreceptor contains particles having a number average primary particle size of 1 to 200 on the surface layer thereof,
A tandem type image forming apparatus, wherein the light source used in the exposure means is a semiconductor laser or a light emitting diode having an oscillation wavelength of 350 to 500 nm. The diameter of the electrophotographic photosensitive member used for the black toner image forming unit of the tandem type image forming apparatus is 60 to 250 mm, which is larger than the diameter of the electrophotographic photosensitive member used for the color toner image forming unit. Item 7. The tandem image forming apparatus according to Item 6. An electrophotographic photoreceptor used in the electrophotographic image forming apparatus according to any one of claims 1 to 5 and the tandem type image forming apparatus according to claim 6 or 7. The electrophotographic photosensitive member according to claim 8,
The electrophotographic image forming apparatus according to any one of claims 1 to 5, wherein at least one means selected from a charging means, an exposure means, a developing means, a transfer means, and a cleaning means is combined. An image forming unit, wherein the image forming unit is formed so as to be able to be inserted into and removed from the main body of the tandem type image forming apparatus described in 1.

Images