JP4135596B2 - Organic photoreceptor, process cartridge, image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an organic photoreceptor, a process cartridge, an image forming apparatus, and an image forming method used for electrophotographic image formation. More specifically, the present invention relates to an organic photoconductor used for electrophotographic image formation used in the field of copying machines and printers. The present invention relates to a photoconductor (hereinafter also simply referred to as a photoconductor), a process cartridge, an image forming apparatus, and an image forming method.

  Organic photoconductors have great advantages such as wide selection of materials, excellent environmental suitability and low production costs compared to inorganic photoconductors such as selenium photoconductors and amorphous silicon photoconductors. In recent years, electrophotographic photoreceptors have become the mainstream in place of inorganic photoreceptors.

  On the other hand, in the image forming method based on the Carlson method, a charged, electrostatic latent image is formed on an electrophotographic photosensitive member, and a toner image is formed. Then, the toner image is transferred to a transfer paper, fixed, and finally processed. An image is formed.

  A corona discharger is the best known charging member that has been used as a member of the charging means. The corona discharger has an advantage that stable charging can be performed. However, since a high voltage must be applied to the corona discharger, a large amount of ionized oxygen, ozone, moisture, nitric oxide compound, etc. is generated, which causes deterioration of the organic photoreceptor (hereinafter also referred to as a photoreceptor). Or have problems such as adversely affecting the human body.

  Therefore, in recent years, use of a contact charging method that does not use a corona discharger has been studied. Specifically, a voltage is applied to a magnetic brush or a conductive roller that is a charging member to bring it into contact with a photosensitive member that is a member to be charged, and the surface of the photosensitive member is charged to a predetermined potential. If such a contact charging method is used, the voltage can be lowered and the amount of ozone generated can be reduced as compared with a non-contact charging method using a corona discharger.

In the contact charging method, a direct current or a direct current on which an alternating current is superimposed is applied to a charging member having a resistance of about 10 ² to 10 ¹⁰ Ω · cm on the photosensitive member, and the photosensitive member is pressed and brought into contact with the photosensitive member to apply a charge. Is the way. Since this charging method is performed by discharging from the charging member to the member to be charged in accordance with Paschen's law, charging is started by applying a voltage equal to or higher than a certain threshold value. In this contact charging method, compared to the corona charging method, the voltage applied to the charging member is lowered, and the generation amount of ozone and nitrogen oxides is reduced.

  However, if the surface of the organic photoreceptor is repeatedly charged by direct contact with a charging roller or the like, small unevenness or contamination occurs on the surface of the organic photoreceptor due to contact wear. Electric charges are concentrated on the surface, causing image defects such as dielectric breakdown and black spots, and image blurring. In particular, these problems are likely to occur under severe conditions such as high temperature and high humidity and low temperature and low humidity.

  Further, a cleaningless image forming apparatus that does not use a cleaning blade that removes residual toner on the photosensitive member together with the contact charging has been disclosed (Patent Document 1). The image forming apparatus includes an auxiliary charging unit in addition to the charging unit, and the auxiliary charging unit has an action of charging the residual toner and increasing the recovery efficiency of the residual toner in the developing unit. By providing the auxiliary charging means, the aforementioned dielectric breakdown and black spots are likely to occur.

  In order to prevent the occurrence of image defects such as dielectric breakdown and black spots as described above, the surface of the aluminum substrate of the conductive support is anodized to increase the resistance to charge leakage of the organic photoconductor, for example in the photosensitive layer. It has been proposed to prevent charge leakage from the conductive support even if unevenness, contamination, etc. occur (Patent Document 2).

However, organophotoreceptors using anodized aluminum substrates have the problem that the alumite layer is altered by slight changes in anodizing and subsequent aging conditions, and the above-described effect of preventing charge leakage is difficult to obtain stably. In addition, a charge trap site is easily formed between the alumite layer and the photosensitive layer, and a residual potential tends to be gradually accumulated over a long period of use.
JP 2000-199990 A Japanese Patent Laid-Open No. 5-80567

  The present invention relates to an organic photoreceptor, a process cartridge, an image forming apparatus, and an image which can perform stable image formation over a long period of time by using a charging method with low generation amount of ozone and nitrogen oxide and low power. It is to provide a forming method.

  Another object of the present invention is to prevent deterioration of electrophotographic characteristics (sensitivity, residual potential, etc.) that are likely to occur during repeated use in an organic photoreceptor used in a contact charging type image forming apparatus, and to prevent dielectric breakdown or blackness. An organic photoreceptor capable of preventing image defects such as spots and forming a long-term stable image with good sharpness, a process cartridge, an image forming apparatus and an image forming method using the organic photoreceptor Is to provide.

As a result of intensive studies, the present inventors have determined that the dielectric breakdown and image blur that are likely to occur in an image forming apparatus having both a contact charging unit and particularly a contact charging unit and a contact charging auxiliary unit are the contact charging unit and the contact charging auxiliary unit. As a result of contact with the organic photoreceptor, the present inventors have found that charge leakage generated in the organic photoreceptor and diffusion of charges in the lateral direction have been found. That is, the organic photoreceptor used in the image forming apparatus of the present invention has found that it is important to prevent the injection of free carriers from the conductive support and not to increase the thickness of the photosensitive layer, thereby completing the present invention. did. That is, the object of the present invention is achieved by adopting one of the following configurations.
(Claim 1)
Charging means for charging by bringing a charging member into contact with the organic photoreceptor, exposure means for forming an electrostatic latent image on the organic photoreceptor, developing means for developing the electrostatic latent image into a toner image, the toner image In an organic photoconductor used in an image forming apparatus having at least one auxiliary charging unit that is located upstream of the charging unit and charges toner on the surface of the organic photoconductor And having at least an intermediate layer, a charge generation layer, and a charge transport layer on the conductive support, the intermediate layer containing anatase-type titanium oxide pigment containing niobium element at 100 ppm to 2.0 mass%, and having a film thickness An organic photoreceptor having a thickness of 5 to 25 μm and a charge transport layer thickness of 5 to 20 μm.
(Claim 2)
The organophotoreceptor according to claim 1, wherein the number average primary particles of the anatase-type titanium oxide pigment are 5 to 400 nm .
(Claim 3)
3. The organic photoreceptor according to claim 1, wherein the intermediate layer contains a polyamide resin having a heat of fusion of 0 to 40 J / g and a water absorption of 5% by mass or less .
(Claim 4)
The organic photoreceptor according to claim 1, wherein the intermediate layer has a volume resistance of 10 ⁸ Ω · cm or more .
(Claim 5)
The organic photoreceptor according to claim 1, wherein the intermediate layer has a thickness of 7 to 15 μm .
(Claim 6)
Charging means for charging by bringing a charging member into contact with the organic photoreceptor, exposure means for forming an electrostatic latent image on the organic photoreceptor, developing means for developing the electrostatic latent image into a toner image, the toner image In a process cartridge used in an image forming apparatus having at least one auxiliary charging unit that is located upstream of the charging unit and charges the toner on the surface of the organic photoreceptor, The conductive support has at least an intermediate layer, a charge generation layer, and a charge transport layer. The intermediate layer contains an anatase-type titanium oxide pigment containing niobium element in an amount of 100 ppm to 2.0 mass%, and has a thickness of 5 An organic photoreceptor having a thickness of ˜25 μm, an intermediate layer thickness of 5-25 μm, and a charge transport layer thickness of 5-20 μm is integrated with at least one of the charging means, developing means, transfer means, and auxiliary charging means. Is lifting, the process cartridge characterized in that it is detachably attached to the image forming apparatus main body.
(Claim 7)
Charging means for charging by bringing a charging member into contact with the organic photoreceptor, exposure means for forming an electrostatic latent image on the organic photoreceptor, developing means for developing the electrostatic latent image into a toner image, the toner image In an image forming apparatus having at least one auxiliary charging unit that is located upstream of the charging unit and charges toner on the surface of the organic photosensitive member, the organic photosensitive member The conductive support has at least an intermediate layer, a charge generation layer, and a charge transport layer. The intermediate layer contains an anatase-type titanium oxide pigment containing niobium element in an amount of 100 ppm to 2.0 mass%, and has a thickness of 5 An image forming apparatus having a thickness of ˜25 μm and a charge transport layer thickness of 5˜20 μm.
(Claim 8)
An image forming method comprising forming an electrophotographic image using the image forming apparatus according to claim 7.

  By using the organophotoreceptor, process cartridge, image forming apparatus, and image forming method of the present invention, low temperature and low humidity, which are likely to occur in the contact charging method, increase in residual potential at high temperature and high humidity and fluctuation of the charged potential are prevented, In addition, dielectric breakdown and image defects can be prevented, and an electrophotographic image having good image density, fog, and sharpness can be provided.

The organophotoreceptor of the present invention comprises at least an intermediate layer, a charge generation layer, and a charge transport layer on a conductive support, and the intermediate layer contains anatase-type titanium oxide pigment containing 100 ppm to 2.0% by mass of niobium element. And the film thickness is 5 to 25 μm, and the film thickness of the charge transport layer is 5 to 20 μm.

  The organophotoreceptor of the present invention has the structure described above, so that even when used in an image forming apparatus having a contact charging means and an auxiliary charging means, an electrophotography having excellent sharpness can be prevented from causing dielectric breakdown and black spots. Images can be provided.

  As described above, the organic photoreceptor used in the contact charging method tends to concentrate electric charges on the small unevenness or contamination generated on the organic photoreceptor, and as a result, the occurrence of image defects such as dielectric breakdown and black spots. It is easy to cause, and it is easy to generate image blur. In order to prevent the concentration of electric charges peculiar to contact charging, the electric field intensity per unit film thickness of the photosensitive layer is reduced, and charge leakage is prevented even if small irregularities or contamination occurs on the surface of the photosensitive member. is important. In the present invention, in order to reduce the electric field strength per unit film thickness of the photosensitive layer, the organic photoreceptor is configured to have at least an intermediate layer, a charge generation layer, and a charge transport layer on a conductive support, and the film thickness of the intermediate layer By reducing the electric field strength of the photosensitive layer, particularly the charge transport layer, the dielectric breakdown and black spots can be prevented, and the residual potential can be reduced. In addition, it is possible to provide an organic photoreceptor having a stable charge potential and good sharpness.

  If the film thickness of the intermediate layer is less than 5 μm, dielectric breakdown and black spots are likely to occur, and if it exceeds 25 μm, image blur tends to occur and sharpness tends to deteriorate. On the other hand, when the thickness of the charge transport layer is less than 5 μm, dielectric breakdown and black spots are likely to occur, and when it exceeds 20 μm, image blur is likely to occur and sharpness is likely to deteriorate. The thickness of the intermediate layer is more preferably 7 to 15 μm. The thickness of the charge transport layer is more preferably 8 to 18 μm.

The intermediate layer of the present invention preferably contains metal oxide particles. Examples of the metal oxide particles include cerium oxide, chromium oxide, aluminum oxide, magnesium oxide, silicon oxide, tin oxide, zirconium oxide, iron oxide, and titanium oxide. Among these, titanium oxide (TiO ₂ ), zinc oxide (ZnO), aluminum oxide (Al ₂ O ₃ ), and zirconium oxide (ZrO ₂ ) are preferable, and titanium oxide is particularly preferably used.

  These metal oxide particles are preferably those hydrophobized with a hydrophobizing agent such as a titanium coupling agent, a silane coupling agent, a polymer fatty acid, or a metal salt thereof.

  By including these metal oxide particles in the intermediate layer, an organic photoreceptor having long-term stable performance is prevented by preventing the occurrence of dielectric defects, image defects such as black spots, and image blur that are likely to occur due to contact charging. Can be provided.

  The metal oxide particles are preferably fine particles having a number average primary particle diameter in the range of 5 to 400 nm. In particular, 10 nm to 200 nm is preferable. The number average primary particle diameter is a measured value as the average diameter in the ferret direction by image analysis by magnifying fine particles 10,000 times by transmission electron microscope observation, randomly observing 100 particles as primary particles.

  The titanium oxide particles include anatase, rutile, brookite, and amorphous forms as crystal forms. Among them, anatase form titanium oxide pigment is most preferable as the particles of the present invention.

The present invention is contained anatase type titanium oxide pigment containing 100ppm~2.0 wt% niobium in the intermediate layer. By including the niobium element in the above range in the anatase-type titanium oxide pigment, the rectification characteristics of the anatase-type titanium oxide pigment are stably demonstrated even during long-term use of the photoreceptor, and dielectric breakdown and black spots are generated. Even if the environmental conditions of temperature and humidity change, the change in charging characteristics and sensitivity characteristics is small.

  The content of niobium element in the anatase titanium oxide pigment is more preferably 300 ppm to 1.8% by mass.

  The concentration of niobium element in the whole anatase-type titanium oxide particles of the present invention can be analyzed by quantitative analysis by ICP (inductively coupled plasma emission spectrometry).

  The anatase-type titanium oxide pigment of the present invention can be produced by a known sulfuric acid method. That is, it is obtained by heating and hydrolyzing a solution containing titanium sulfate and titanyl sulfate to produce a hydrous titanium dioxide slurry, and dehydrating and firing the titanium dioxide slurry. Hereinafter, the manufacturing method of the anatase type titanium oxide pigment containing a niobium element is described.

  First, niobium sulfate (water-soluble niobium compound) is added to a hydrous titanium dioxide slurry obtained by hydrolyzing a titanyl sulfate aqueous solution. The addition amount is suitably 0.15 to 5 mass% niobium sulfate as niobium ions with respect to the amount of titanium in the slurry (in terms of titanium dioxide). Specifically, (i) hydrous titanium dioxide slurry obtained by hydrolyzing 0.15 to 5% by mass of niobium sulfate as niobium ion to titanyl sulfate aqueous solution, or (ii) hydrolyzing titanyl sulfate aqueous solution A slurry obtained by adding 0.15 to 5% by mass of niobium sulfate as niobium ions to the hydrous titanium dioxide slurry obtained as described above can be used.

  The hydrous titanium dioxide slurry containing the niobium ions and the like is dehydrated and fired. In general, the firing temperature is suitably 850 to 1100 ° C. When the firing temperature is less than 850 ° C., firing is not sufficiently performed. On the other hand, if the temperature exceeds 1100 ° C., the particles are sintered and the dispersibility of the pigment is significantly impaired. Niobium ions added to the slurry are segregated on the particle surface during firing, and are contained in the surface layer in a large amount as niobium oxide. By this production method, an anatase-type titanium oxide pigment having an average primary particle diameter of 0.01 to 10 μm and containing 100 ppm to 2 mass% of niobium element can be obtained.

  There is also a method of forming a titanium oxide pigment by gas sintering using titanium tetrachloride. In this case, unless other metal halogen components are brought into the raw gas component, other metal elements such as niobium are used. An anatase titanium oxide pigment having a content of zero (substantially not contained) can also be produced.

  The anatase-type titanium oxide of the present invention preferably has an anatase degree of 90 to 100%. By the above method, anatase-type titanium oxide having an anatase degree of almost 100% can be produced. Further, the intermediate layer of the present invention containing the anatase-type titanium oxide containing niobium element in this range has a good rectifying property and is stably achieved, and the above-described effects of the present invention are well achieved.

Here, the anatase degree is determined by measuring the intensity IA of the strongest interference line of anatase (plane index 101) and the intensity IR of the strongest interference line of rutile (plane index 110) in powder X-ray diffraction of titanium oxide, It is a value obtained by the following formula.
Degree of anataseization (%) = 100 / (1 + 1.265 × IR / IA)
In order to prepare the anatase degree in the range of 90 to 100%, in the preparation of titanium oxide, an anatase having an anatase degree of almost 100% is obtained by heating and hydrolyzing a solution containing titanium sulfate and titanyl sulfate as a titanium compound. A shaped titanium oxide is obtained. Further, when an aqueous solution of titanium tetrachloride is neutralized with an alkali, anatase-type titanium oxide having a high degree of anatase formation can be obtained.

  The anatase titanium oxide pigment is preferably subjected to a surface treatment with a reactive organosilicon compound. The surface treatment of the anatase titanium oxide pigment with the reactive organosilicon compound can be performed by the following wet method. The surface treatment of the reactive organosilicon compound means that a reactive organosilicon compound is used for the treatment liquid.

  That is, the anatase-type titanium oxide pigment is added to a solution obtained by dissolving or suspending the reactive organosilicon compound in an organic solvent or water, and this mixed solution is dispersed in a medium for several minutes to one day. And depending on the case, after heat-processing a liquid mixture, it passes through processes, such as filtration, It dries, and the anatase type titanium oxide pigment which coat | covered the surface with the organosilicon compound is obtained. Note that the reactive organosilicon compound may be added to a suspension in which titanium oxide is 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 mass of the reactive organosilicon compound with respect to 100 parts by mass of the anatase-type titanium oxide pigment in the amount charged in the surface treatment. More preferably, 0.1 to 5 parts by mass is used. When the surface treatment amount is less than the above range, the surface treatment effect is not sufficiently imparted, and the rectifying action and dispersibility of the titanium oxide particles in the intermediate layer are deteriorated. Further, when the surface treatment amount exceeds the above range, the electrophotographic characteristics are deteriorated, and as a result, the residual potential is increased and the charged potential is decreased.

  Examples of the reactive organosilicon compound used in the present invention include an organosilicon compound represented by the following general formula (1), and any compound that undergoes a condensation reaction with a reactive group such as a hydroxyl group on the titanium oxide surface, It is not limited to the following compounds.

General formula (1)
(R) _n -Si- (X) _4-n
(In the formula, Si represents a silicon atom, R represents an organic group in which carbon is directly bonded to the silicon atom, X 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 includes alkyl such as methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and dodecyl. Group, aryl group such as phenyl, tolyl, naphthyl, biphenyl, epoxy-containing group such as γ-glycidoxypropyl, β- (3,4-epoxycyclohexyl) ethyl, γ-acryloxypropyl, γ-methacryloxypropyl (Meth) acryloyl group, hydroxyl group such as γ-hydroxypropyl and 2,3-dihydroxypropyloxypropyl, vinyl 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, , 1,1-tri fluoroalkyl propyl, nonafluorohexyl, halogen-containing groups such as perfluorooctylethyl, other nitro, and cyano-substituted alkyl group. Examples of the hydrolyzable group for X 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.

  Moreover, in the specific compound of the organosilicon compound represented by the general formula (1), when n is 2 or more, a plurality of R may be the same or different. Similarly, when n is 2 or less, the plurality of Xs may be the same or different. Moreover, when using 2 or more types of organosilicon compounds represented by General formula (1), R and X may be the same between each compound, and may differ.

  Moreover, a polysiloxane compound is mentioned as a preferable reactive organosilicon compound. In particular, methyl hydrogen polysiloxane is preferred. The polysiloxane compound having a molecular weight of 1000 to 20000 is generally easily available, and has a good function to prevent occurrence of black spots.

  Another surface treatment of the titanium oxide of the present invention is titanium oxide particles that have been surface treated with an organosilicon compound having a fluorine atom. It is preferable to perform the surface treatment with the organosilicon compound having a fluorine atom and the wet method described above.

  In the present invention, the surface of the titanium oxide particles is coated with a reactive organosilicon compound because photoelectron spectroscopy (ESCA), Auger electron spectroscopy (Auger), secondary ion mass spectrometry (SIMS), and diffuse reflection. This is confirmed by combining surface analysis techniques such as FI-IR.

  Another one of the surface treatments of the anatase-type titanium oxide pigment includes at least one kind of surface treatment selected from alumina, silica, and zirconia.

  The alumina treatment, silica treatment, and zirconia treatment are treatments for precipitating alumina, silica, or zirconia on the surface of anatase-type titanium oxide. The alumina, silica, and zirconia deposited on these surfaces are water of alumina, silica, zirconia Japanese products are also included.

  The treatment of alumina and silica may be performed simultaneously, but it is particularly preferable to perform the alumina treatment first and then the silica treatment. Further, the amount of treatment of alumina and silica when treating alumina and silica is preferably higher than that of alumina.

  The surface treatment of anatase titanium oxide with a metal oxide such as alumina, silica, and zirconia can be performed by a wet method. For example, anatase-type titanium oxide subjected to surface treatment of silica or alumina can be produced as follows.

  When anatase type titanium oxide is used, titanium oxide particles (number average primary particle size: 50 nm) are dispersed in water at a concentration of 50 to 350 g / L to form an aqueous slurry. Add aluminum compound. Thereafter, alkali or acid is added for neutralization, and silica or alumina is precipitated on the surface of the titanium oxide particles. Subsequently, filtration, washing, and drying are performed to obtain the target surface-treated titanium oxide. When sodium silicate is used as the water-soluble silicate, it can be neutralized with an acid such as sulfuric acid, nitric acid or hydrochloric acid. On the other hand, when aluminum sulfate is used as the water-soluble aluminum compound, it can be neutralized with an alkali such as sodium hydroxide or potassium hydroxide.

  In addition, the amount of the metal oxide used for the surface treatment is 0.1 to 50 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the titanium oxide particles in the amount charged in the surface treatment. These metal oxides are used. In the case of using alumina and silica as described above, for example, in the case of anatase-type titanium oxide particles, it is preferable to use 1 to 10 parts by mass with respect to 100 parts by mass of titanium oxide particles, and the amount of silica is larger than that of alumina. Is preferred.

Moreover, it is preferable that the intermediate layer of the present invention is an insulating layer substantially. Here, the insulating layer has a volume resistance of 1 × 10 ⁸ or more. The volume resistance of the intermediate layer and the protective layer of the present invention is preferably 1 × 10 ⁸ to 10 ¹⁵ Ω · cm, more preferably 1 × 10 ⁹ to 10 ¹⁴ Ω · cm, and further preferably 2 × 10 ⁹ to 1 ×. 10 ¹³ Ω · cm. The volume resistance can be measured as follows.

  Measurement conditions: According to JIS: C2318-1975.

Measuring instrument: Hiresta IP manufactured by Mitsubishi Yuka
Measurement conditions: Measurement probe HRS
Applied voltage: 500V
Measurement environment: 30 ± 2 ℃, 80 ± 5RH%
If the volume resistance is less than 1 × 10 ⁸ , the charge blocking property of the intermediate layer decreases, the occurrence of black spots increases, the potential holding property of the organic photoreceptor deteriorates, and good image quality cannot be obtained. On the other hand, if it is greater than 10 ¹⁵ Ω · cm, the residual potential tends to increase in repeated image formation, and good image quality cannot be obtained.

  The intermediate layer coating solution prepared for forming the intermediate layer of the present invention is composed of metal oxide particles such as surface-treated titanium oxide, a binder resin, a dispersion solvent, and the like.

  The intermediate layer of the present invention contains 10 to 10,000 parts by mass, preferably 50 to 1,000 parts by mass of metal oxide particles with respect to 100 parts by mass of the binder resin. By using the metal oxide particles in this range, the dispersibility of the metal oxide particles can be kept good, no dielectric breakdown or black spots occur, and a good intermediate layer with little potential fluctuation is formed. be able to.

  On the other hand, the binder resin in which these particles are dispersed to form the layer structure of the intermediate layer is preferably a polyamide resin in order to obtain good dispersibility of the particles, but the polyamide resin shown below is particularly preferable.

  That is, the intermediate layer of the present invention is preferably a polyamide resin having a heat of fusion of 0 to 40 J / g and a water absorption of 5% by mass or less. The heat of fusion is more preferably 0 to 30 J / g, and most preferably 0 to 20 J / g. On the other hand, when the water absorption rate exceeds 5% by mass, the moisture content in the intermediate layer increases, dielectric breakdown and black spots are likely to occur, and electrophotographic characteristics such as increased residual potential and fogging are also likely to deteriorate. . The water absorption is more preferably 4% by mass or less.

  The heat of fusion of the resin is measured by DSC (Differential Scanning Calorimetry). However, if the same measurement value as the DSC measurement value is obtained, the DSC measurement method is not particular. The heat of fusion is determined from the endothermic peak area when the DSC temperature rises.

  On the other hand, the water absorption rate of the resin is determined by mass change by the water immersion method or by the Karl Fischer method.

  The binder resin for the intermediate layer of the present invention is preferably an alcohol-soluble polyamide resin. As the binder resin for the intermediate layer of the organic photoreceptor, a resin having excellent solvent solubility is required in order to form the intermediate layer with a uniform film thickness. As such an alcohol-soluble polyamide resin, a copolymerized polyamide resin or a methoxymethylated polyamide resin composed of a chemical structure with few carbon chains between amide bonds such as 6-nylon described above is known. This resin has a high water absorption rate, and the intermediate layer using such a polyamide tends to be highly environment-dependent. As a result, for example, charging characteristics and sensitivity under high temperature and high humidity and low temperature and low humidity are likely to change. Dielectric breakdown and black spots are also likely to occur.

  The alcohol-soluble polyamide resin of the present invention improves the above-described drawbacks, and gives the characteristics of a heat of fusion of 0 to 40 J / g and a water absorption of 5% by mass or less. Thus, even if the external environment changes or the organic photoreceptor is used continuously for a long time, a good electrophotographic image can be obtained.

  Hereinafter, the alcohol-soluble polyamide resin having a heat of fusion of 0 to 40 J / g and a water absorption of 5% by mass or less will be described.

  The alcohol-soluble polyamide resin is preferably a polyamide resin containing a repeating unit structure having 7 to 30 carbon atoms between amide bonds in an amount of 40 to 100 mol% of the entire repeating unit structure.

  Here, a repeating unit structure having 7 to 30 carbon atoms between amide bonds will be described. The repeating unit structure means an amide bond unit forming a polyamide resin. This is because a polyamide resin (type A) formed by condensation of a compound having a repeating unit structure having both an amino group and a carboxylic acid group, and a polyamide resin (type B) formed by condensation of a diamino compound and a dicarboxylic acid compound. ) In both examples.

  That is, the repeating unit structure of type A is represented by the general formula (2), and the carbon number contained in X is the carbon number of the amide bond unit in the repeating unit structure. On the other hand, the type B repeating unit structure is represented by the general formula (3), and the number of carbon atoms contained in Y and the number of carbon atoms contained in Z are the carbon number of the amide bond unit in the repeating unit structure.

In general formula (2), R ₁ is a hydrogen atom, a substituted or unsubstituted alkyl group, X is a substituted or unsubstituted alkylene group, a group containing a divalent cycloalkane, a divalent aromatic group, and these A mixed structure is shown, and l is a natural number.

In general formula (3), R ₂ and R ₃ are each hydrogen atom, a substituted or unsubstituted alkyl group, Y and Z are each substituted or unsubstituted alkylene group, a group containing a divalent cycloalkane, and a divalent group. And m and n are natural numbers.

  As described above, the repeating unit structure having 7 to 30 carbon atoms includes a substituted or unsubstituted alkylene group, a group containing a divalent cycloalkane, a divalent aromatic group, and a chemical structure having a mixed structure thereof. Among them, a chemical structure having a group containing a divalent cycloalkane is preferable.

  The polyamide resin of the present invention has 7 to 30 carbon atoms between amide bonds in the repeating unit structure, preferably 9 to 25, more preferably 11 to 20. The proportion of the repeating unit structure having 7 to 30 carbon atoms between amide bonds in the entire repeating unit structure is 40 to 100 mol%, preferably 60 to 100 mol%, more preferably 80 to 100 mol%.

  When the carbon number is less than 7, the hygroscopicity of the polyamide resin is large, the electrophotographic characteristics, particularly the humidity dependency of the potential during repeated use is large, and image defects such as black spots are likely to occur. If it is larger than 30, the dissolution of the polyamide resin in the coating solvent becomes worse, and it is not suitable for forming a coating film of the intermediate layer.

  Further, when the ratio of the repeating unit structure having 7 to 30 carbon atoms between amide bonds to the entire repeating unit structure is smaller than 40 mol%, the above effect is reduced.

  A preferable polyamide resin of the present invention includes a polyamide having a repeating unit structure represented by the following general formula (4).

In General Formula (4), Y ₁ is a group containing a divalent alkyl-substituted cycloalkane, Z ₁ is a methylene group, m is 1 to 3, and n is 3 to 20.

In the general formula (4), the group containing a divalent alkyl-substituted cycloalkane of Y ₁ preferably has the following chemical structure. That is, the polyamide resin of the present invention in which Y ₁ has the following chemical structure has a remarkable effect of improving black spots.

In the above chemical structure, A represents a single bond and an alkylene group having 1 to 4 carbon atoms, R ₄ represents a substituent, represents an alkyl group, and p represents a natural number of 1 to 5. However, the plurality of R ₄ may be the same or different.

  Specific examples of the polyamide resin of the present invention include the following examples.

  In the above specific examples, “%” in parentheses indicates the ratio (mol%) of the repeating unit structure having 7 or more carbon atoms between amide bonds in the repeating unit structure.

  Among the above specific examples, N-1 to N-4 polyamide resins having a repeating unit structure of the general formula (4) are particularly preferable.

  The molecular weight of the polyamide resin of the present invention is preferably 5,000 to 80,000 in terms of number average molecular weight, and more preferably 10,000 to 60,000. When the number average molecular weight is 5,000 or less, the uniformity of the film thickness of the intermediate layer is deteriorated, and the effects of the present invention are not sufficiently exhibited. On the other hand, if it is larger than 80,000, the solvent solubility of the resin tends to be lowered, and an aggregated resin is likely to be generated in the intermediate layer, and image defects such as black spots are likely to occur.

  A part of the polyamide resin of the present invention is already on the market. For example, it is sold under the trade name such as Vestamelt X1010, X4585 manufactured by Daicel Degussa Co., Ltd., and is prepared by a general polyamide synthesis method. An example of synthesis is given below.

Synthesis of exemplified polyamide resin (N-1) 215 parts by mass of lauryl lactam, 3-aminomethyl-3,5,5-trimethylcyclohexylamine in a polymerization kettle equipped with a stirrer, nitrogen, nitrogen introduction tube, thermometer, dehydration tube, etc. 112 parts by mass, 153 parts by mass of 1,12-dodecanedicarboxylic acid and 2 parts by mass of water were mixed and reacted for 9 hours while distilling water under heating and pressure. When the polymer was taken out and the copolymer composition was determined by C ¹³ -NMR, it coincided with the composition of N-1. The melt flow index (MFI) of the synthesized copolymer was 5 g / 10 min under the condition of (230 ° C./2.16 kg).

  Solvents for dissolving the polyamide resin of the present invention to prepare a coating solution include alcohols having 2 to 4 carbon atoms such as ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, t-butanol, sec-butanol and the like. Preferably, it is excellent in the solubility of polyamide and the applicability of the prepared coating solution. 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.

  On the other hand, the structure of the charge transport layer can be obtained using a known structure. It is necessary to select the charge transport material and binder appropriately to form the charge transport layer.

  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 in combination. 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, silicone resin, melamine resin, and copolymer resin containing two or more of repeating unit structures of these resins. In addition to these insulating resins, high molecular 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 charge transport layer preferably contains an antioxidant. Typical examples of the antioxidants are those that prevent the action of oxygen under conditions of light, heat, discharge, etc. on auto-oxidizing substances present in the organic photoreceptor or on the surface of the organic photoreceptor, It is a substance that has the property of inhibiting.

  Next, the layer structure of the organic photoreceptor having the above intermediate layer and charge transport layer will be described.

  The organic photoconductor of the present invention means an electrophotographic photoconductor constituted by giving an organic compound at least one of a charge generation function and a charge transport function indispensable for the constitution of the electrophotographic photoconductor. It contains all known organic electrophotographic photoreceptors such as a photoreceptor composed of an organic charge generating material or an organic charge transport material, a photoreceptor composed of a polymer complex with a charge generating function and a charge transport function.

  The constitution of the organic photoreceptor used in the present invention is described below.

Conductive Support The conductive support used for the photoreceptor may be either a sheet or a cylinder, but a cylindrical conductive support is preferred for designing an image forming apparatus compactly. .

  Cylindrical conductive support means a cylindrical support necessary for forming an endless image by rotating. Conductivity is within a range of 0.1 mm or less in straightness and 0.1 mm or less in deflection. A support is preferred. Exceeding the range of straightness and shake makes it difficult to form a good image.

As the conductive material, a metal drum such as aluminum or nickel, a plastic drum deposited with aluminum, tin oxide, indium oxide or the like, or a paper / plastic drum coated with a conductive substance can be used. The conductive support preferably has a specific resistance of 10 ³ Ωcm or less at room temperature.

  As the conductive support used in the present invention, one having an alumite film that has been sealed on the surface thereof may be used.

Intermediate Layer In the present invention, an intermediate layer having the barrier function is provided between the conductive support and the photosensitive layer.

Photosensitive layer The photosensitive layer configuration of the photoreceptor of the present invention may be a single-layer photosensitive layer configuration in which the intermediate layer has a charge generation function and a charge transport function in one layer, but more preferably the function of the photosensitive layer. The charge generation layer (CGL) and the charge transport layer (CTL) may be separated from each other. By adopting a configuration in which the functions are separated, an increase in the 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 photoconductor, it is preferable that 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 the reverse of that in the negatively charged photoconductor. The most preferred photosensitive layer structure of the present invention is a negatively charged photoreceptor structure having the function separation structure.

  The structure of the photosensitive layer of the function-separated negatively charged photoreceptor will be described below.

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, CGM which can minimize the increase in residual potential due to repeated use has a crystal structure capable of taking a stable aggregate structure among a plurality of molecules, specifically, a phthalocyanine pigment having a specific crystal structure, CGM of a perylene pigment is mentioned. For example, titanyl phthalocyanine having a maximum peak at a Bragg angle 2θ of 27.2 ° with respect to the Cu—Kα ray, titanyl phthalocyanine having remarkable diffraction peaks at 7.5 ° and 28.7 ° of the same 2θ, and 12.2 of the same 2θ. CGM such as benzimidazole perylene having a maximum peak at 4 has almost no deterioration due to repeated use, and the residual potential can be increased and decreased.

  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 preferred resins include formal resin, butyral resin, silicone resin, silicone-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 0.01 μm to 1 μm. If the thickness is less than 0.01 μm, sufficient sensitivity characteristics cannot be obtained, and the residual potential tends to increase. On the other hand, if it exceeds 1 μm, dielectric breakdown and black spots are likely to occur.

Charge transport layer The charge transport layer of the present invention is a charge transport layer having a film thickness of 5 to 20 μm. If the film thickness is less than 5 μm, dielectric breakdown, black spots, etc. are likely to occur, and if it exceeds 20 μm, the image tends to be blurred and sharpness tends to deteriorate.

  In the above, the most preferable layer structure of the photoreceptor of the present invention is exemplified, but in the present invention, a photoreceptor layer structure other than the above may be used.

  Solvents or dispersion media used to form layers such as intermediate layers, charge generation layers, and charge transport layers include n-butylamine, diethylamine, ethylenediamine, isopropanolamine, triethanolamine, triethylenediamine, N, N-dimethylformamide, acetone , Methyl ethyl ketone, methyl isopropyl ketone, cyclohexanone, benzene, toluene, xylene, chloroform, dichloromethane, 1,2-dichloroethane, 1,2-dichloropropane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, trichloroethylene, Tetrachloroethane, tetrahydrofuran, dioxolane, dioxane, methanol, ethanol, butanol, isopropanol, ethyl acetate, butyl acetate, dimethyl sulfoxide, methyl cello Lube, and the like. Although this invention is not limited to these, Dichloromethane, 1, 2- dichloroethane, methyl ethyl ketone, etc. are used preferably. These solvents may be used alone or as a mixed solvent of two or more.

  Further, the coating solution for each layer is preferably filtered with a metal filter, a membrane filter or the like in order to remove foreign matters and aggregates in the coating solution before entering the coating step. For example, it is preferable to select a pleat type (HDC), a depth type (profile), a semi-depth type (profile star), etc., manufactured by Nippon Pole Co., Ltd. according to the characteristics of the coating solution and perform filtration.

  Next, as a coating processing method for manufacturing the organic photoreceptor, a coating processing method such as dip coating, spray coating, circular amount regulation type coating or the like is used. It is most preferable to use the circular amount regulation type coating method for the protective layer. The circular amount regulation type coating is described in detail in, for example, Japanese Patent Application Laid-Open No. 58-189061.

  Next, an image forming apparatus using the contact charging method of the present invention will be described.

  FIG. 1 is a schematic cross-sectional view of an image forming apparatus 1 using a contact charging method according to the present invention. The image forming apparatus 1 includes a photosensitive cartridge 2, a developing cartridge 3, an exposure device 4 that emits a laser beam modulated based on an image signal from the outside while deflecting, a paper feeding device 5 that supplies recording paper, A transfer roller 6, a fixing device 7 and a paper discharge tray 8 are provided.

  The photoconductor cartridge 2 includes a photoconductor 21 formed by forming a thin film layer of an organic photoconductive material on the outer peripheral surface of a cylindrical body, a charging brush 22 and the like. The developing cartridge 3 includes a developing sleeve (not shown), a stirring roller, and a toner tank in which toner and a carrier are accommodated. A developing bias is applied to the developing sleeve from a developing power source (not shown). Both cartridges are closed when inserted into the image forming apparatus 1 in order to prevent problems caused by mechanical contact when the cartridge is attached to or detached from the image forming apparatus 1, and are removed from the image forming apparatus 1. A protective cover (not shown) that is sometimes opened is provided.

  Since the image forming process is well known, only a brief description will be given below. First, the surface of the photoreceptor 21 is uniformly charged with a predetermined voltage by the charging brush 22. The exposure device 4 generates a modulated laser beam (indicated by a broken arrow in the figure), deflects the laser beam by a polygon mirror (not shown), deflects and scans the surface of the photosensitive member 21, and applies it to the charged surface. An electrostatic latent image corresponding to image information is sequentially formed. The toner in the toner tank is stirred by a stirring roller and then supplied onto the developing sleeve to form a toner image corresponding to the electrostatic latent image at a portion facing the photoreceptor 21. At the same time, residual toner existing in a portion (non-image portion) that has not been exposed on the surface of the photoconductor 21 is developed using the potential difference between the developing bias voltage applied to the developing sleeve and the surface potential of the photoconductor 21. The cartridge is recovered by electrostatic force. On the other hand, the toner image is electrostatically transferred onto the recording paper by the transfer roller 6 disposed facing the photoconductor 21. Note that the recording paper is conveyed from the paper feeding device 5 along a conveyance path indicated by a solid line arrow in the figure. Next, the recording paper is conveyed to the fixing device 7 where the unfixed toner image is heat-fixed on the recording paper. Finally, the recording paper on which a desired image is formed is discharged from the paper discharge tray 8. By repeating the above-described series of processes, a large amount of original can be duplicated at high speed.

  On the upstream side of the charging brush 22, a pre-charge film 24 (sheet-like member, member for uniformizing charging unevenness on the photosensitive member, and simultaneously charging the residual toner on the photosensitive member with the same polarity as the charging polarity of the photosensitive member at the same time) Residual toner is also charged: auxiliary charging means for charging the toner of the present invention, charging leveling members 25 and 26 (sponge-like members, members for equalizing uneven charging on the photosensitive member, and residual toner are also simultaneously charged: Auxiliary charging means for charging the toner of the present invention is provided, and the charging brush, pre-charging film, and charging leveling member are in contact with the photoreceptor. Further, the charging brush mechanically agitates the residual toner sent to the contact portion with the photosensitive member by the rotation of the photosensitive member, and diffuses it on the surface of the photosensitive member until it becomes unreadable. The charging brush electrostatically adsorbs and collects residual toner having the opposite polarity (reverse polarity) to the charging polarity of the photoconductor, and charges it to the same polarity (regular polarity) as the charging polarity of the photoconductor. Discharge onto the surface of the photoreceptor.

  FIG. 2 is a schematic cross-sectional view of a photosensitive cartridge 2 that is detachable from the image forming apparatus 1. The photosensitive member cartridge 2 includes a photosensitive member 21 as an image carrier, a charging brush 22 disposed in contact with the photosensitive member 21, and a charging brush 22 in a casing 28 with a protective cover that can be opened and closed (not shown). A power connection member 23 for applying a predetermined voltage, a pre-charge film 24, charging leveling members (sponge-like charging members) 25 and 26, and a power connection member 27 are accommodated. The casing 28 with a protective cover has a mechanism in which the protective cover is opened when attached to an exposure light incident window, a developing means attachment port, and an image forming apparatus (not shown), and the photosensitive member and the transfer means come close to or contact each other.

  The photosensitive member 21 is rotated in the direction of the arrow in the drawing by a driving device (not shown). The charging brush 22 is obtained by implanting conductive yarn made of hairy fibers on a brush support. The charging brush 22 is in contact with the surface of the photosensitive member 21 and is rotated in the same direction as the rotational direction of the photosensitive member 21 in the direction of the arrow in the drawing, that is, in the contact portion with the photosensitive member 21 by a driving device (not shown). . During image formation, a voltage is applied to the charging brush 22 from a charging power source (not shown), thereby charging the surface of the photoconductor 21 uniformly to a predetermined polarity. On the other hand, at the time of non-image formation, a voltage having a polarity opposite to that at the time of image formation is applied to the charging brush 22 from the charging power source. The charging polarity of the toner is the same as the polarity of the charging voltage at the time of image formation. Therefore, at the time of non-image formation, the toner accumulated in the charging brush 22 can be ejected onto the photoreceptor 21 by electrostatic repulsion.

  The pre-charge film 24 is provided to give a normal polarity to the residual toner on the photoreceptor so that it can be easily collected by the developing means. The charge leveling members 25 and 26 have the same function as that of the precharge film, but at the same time, have a function of diffusing residual toner on the photoconductor and a function of compensating for charging unevenness on the photoconductor by the charging brush 22. Yes.

  The image forming apparatus is a monochrome laser printer, but can be similarly applied to a color laser printer or a copy.

  The image forming apparatus is exemplified by a cleanerless image forming apparatus as a preferred example, that is, a cleaning apparatus having a main function for removing or collecting residual toner on the photosensitive member, or a cleaning member (for example, Although a cleanerless image forming apparatus having no cleaning blade or the like has been exemplified, an image forming apparatus including a dedicated cleaning device for collecting residual toner may be used. That is, the present invention can also be applied to an image forming apparatus that is not a cleanerless type.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this. However, “part” in the following text indicates “part by mass”.

  A photoreceptor used for evaluation was produced as follows.

Preparation of photoreceptor 1 Intermediate layer 1
The following intermediate layer coating solution was applied by a dip coating method onto a washed cylindrical aluminum substrate (processed to a surface roughness Rz: 1.0 μm by cutting) to form an intermediate layer 1 having a dry film thickness of 10 μm.

  The following intermediate layer dispersion was diluted twice with the same mixed solvent, and allowed to stand overnight, then filtered (filter; rigesh mesh filter made by Nihon Pall Corporation, nominal filtration accuracy: 5 microns, pressure: 50 kPa), and the intermediate layer coating solution was Produced.

(Preparation of intermediate layer dispersion)
Binder resin: (Exemplary polyamide N-1) 1 part Anatase type titanium oxide A1 containing 0.5% by mass of niobium element (primary particle size 35 nm; surface treatment is treated with methyl hydrogen polysiloxane ) 3.0 parts Isopropyl alcohol 10 parts The above components were mixed and dispersed in a batch system for 10 hours using a sand mill disperser to prepare an intermediate layer dispersion.

Charge generation layer The following components were mixed and dispersed using a sand mill disperser to prepare a charge generation layer coating solution. This coating solution was applied by a dip coating method to form a charge generation layer having a dry film thickness of 0.3 μm on the intermediate layer.

Form B oxytitanyl phthalocyanine (X-ray diffraction spectrum by Cu-Kα characteristic X-ray, titanyl phthalosine pigment having remarkable diffraction peaks at Bragg angles (2θ ± 0.2 °) of 7.5 ° and 28.7 °) ) 20 parts polyvinyl butyral (BX-1, manufactured by Sekisui Chemical Co., Ltd.) 10 parts methyl ethyl ketone 700 parts cyclohexanone 300 parts Charge transport layer The following components were mixed and dissolved to prepare a charge transport layer coating solution. This coating solution was applied onto the charge generation layer by a dip coating method to form a charge transport layer having a dry film thickness of 15 μm.

Charge transport material (4-methoxy-4 ′-(4-methyl-α-phenylstyryl) triphenylamine) 70 parts Polycarbonate resin “Iupilon-Z300” (manufactured by Mitsubishi Gas Chemical Company)
100 parts Antioxidant (compound A below) 2 parts Tetrahydrofuran / toluene (volume ratio 8/2) 750 parts Preparation of photoreceptors 2 to 18 Surface roughness Rz of aluminum substrate, particles of intermediate layer, binder resin, dry film thickness Photoconductors 2 to 18 were prepared in the same manner as the photoconductor 1 except that the charge transport material and the film thickness of the charge transport layer were changed as shown in Table 1.

At the same time as the production of the photoconductors 1 to 18, the intermediate layer coating solution was applied onto an aluminum-deposited polyethylene terephthalate support using the intermediate layer coating solution of each photoconductor. An intermediate layer having a dry film thickness of 10 μm was formed under the same conditions to prepare a volume resistance measurement sample, and the volume resistance of each intermediate layer was measured. As a result, the volume resistances of the intermediate layers of the photoreceptors 1 to 18 were all 1 × 10 ⁸ Ω · cm or more.

In the table,
A1 is anatase type titanium oxide containing 0.5% by mass of niobium element (degree of anatase conversion: 100%)
A2 is anatase-type titanium oxide containing 1.0% by mass of niobium element (anatase degree: 95%)
A3 is anatase titanium oxide containing 300 ppm of niobium element (degree of anatase conversion: 100%)
A4 is anatase-type titanium oxide containing 1.8% by mass of niobium element (degree of anatase conversion: 92%)
A5 is anatase-type titanium oxide containing no niobium element (degree of anatase conversion: 94%: niobium element content of 10 ppm or less)
Z is zinc oxide AL is alumina (Al ₂ O ₃ )
Zr is zirconium oxide (ZrO ₂ )
In the table, “surface treatment” refers to the substance used for the surface treatment applied to the surface of the particles.

  The heat of fusion and water absorption in the table were measured as follows.

Measurement conditions of heat of fusion Measuring machine: Measured using Shimadzu Corporation “Shimadzu heat flow rate differential scanning calorimeter DSC-50”.

  Measurement conditions: The measurement sample is set in the above-mentioned measuring machine, measurement is started from room temperature (24 ° C.), the temperature is raised to 200 ° C. at 5 ° C./min, and then cooled to room temperature at 5 ° C./min. This is repeated twice, and the heat of fusion is calculated from the endothermic peak area due to melting during the second temperature increase.

Measurement condition of water absorption rate The sample to be measured is sufficiently dried at 70 to 80 ° C. for 3 to 4 hours, and its mass is accurately weighed. Next, the sample is put into ion-exchanged water maintained at 20 ° C., and after a certain period of time, the sample surface is pulled up and wiped off with a clean cloth to measure the mass. The above operation was repeated until the increase in mass was saturated, and the value obtained by dividing the increased mass (increase) of the resulting sample by the initial mass was taken as the water absorption rate.

In the table, the ratio of the unit structure having 7 or more carbon atoms refers to the ratio (mol%) of the repeating unit structure having 7 or more carbon atoms between amide bonds in the repeating unit structure. N-12 is methoxymethylated nylon 6 (carbon number between amide bonds is 5, methoxymethylation degree is 25%)
Evaluation Each of the photoreceptors 1 to 18 obtained as described above is basically mounted on an EPSONLP-2400 (Epson Co., Ltd. sales: printer with 16 sheets of A4 paper / min) having the structure shown in FIGS. The evaluation items were changed in an environment of high temperature and high humidity (30 ° C., 80% RH) and low temperature and low humidity (10 ° C., 20% RH). The evaluation results are shown in Table 2.

Charging conditions Pre-charged film: 800-850V
Charge leveling member: 800-850V
Brush charging member: 800-850V
Exposure condition Exposure part potential target: Set to an exposure amount to be less than -50V.

  Exposure beam: Image exposure with a dot density of 600 dpi (dpi is the number of dots per 2.54 cm) was performed. The laser uses a 780 nm semiconductor laser.

  Development conditions: Reversal development using a non-magnetic one-component developer.

Evaluation item and evaluation method Evaluation item and evaluation criteria Evaluation of residual potential (change in potential of solid black image)
Under low-temperature and low-humidity (10 ° C., 20% RH) and high-temperature, high-humidity (HH: 30 ° C., 80% RH) environments, a character image with a pixel rate of 7%, a halftone image, a solid white image, and a solid black image are each 1 / An image in four equal portions was printed on 10,000 sheets in the single sheet intermittent mode at A4, and the potential change (| ΔV |) of the solid black image portion at the development position after the initial and 10,000 sheets was evaluated. The smaller the | ΔV |, the smaller the increase in the residual potential.

A: Potential change in solid black image portion | ΔV | is less than 50 V (good)
○: Potential change of solid black image portion | ΔV | is 50 V to 150 V (no problem in practical use)
×: The potential change | ΔV | of the solid black image portion is larger than 150 V (practically problematic)
Evaluation of charging potential (change in potential of solid white image)
Under low-temperature and low-humidity (10 ° C., 20% RH) and high-temperature, high-humidity (HH: 30 ° C., 80% RH) environments, a character image with a pixel rate of 7%, a halftone image, a solid white image, and a solid black image are each 1 / An image in four equal portions was printed on 10,000 sheets in the single sheet intermittent mode at A4, and the potential change (| ΔV |) of the solid white image portion at the development position after the initial and 10,000 sheets was evaluated. The smaller | ΔV | is, the smaller the change in charging potential is.

A: Potential change | ΔV | of solid white image portion is less than 50 V (good)
○: Potential change of solid white image portion | ΔV | is 50 V to 150 V (no problem in practical use)
×: The potential change | ΔV | of the solid white image portion is larger than 150 V (practically problematic)
Image density: Evaluation at low temperature and low humidity (LL: 10 ° C., 20% RH), high temperature and high humidity (HH: 30 ° C., 80% RH) Measured using Macbeth RD-918. The relative reflection density was measured with the paper reflection density set to “0”. As the residual potential increases on multiple copies, the image density decreases. Measurements were taken at the solid black image portion after 10,000 copies each.

A: Black solid image is higher than 1.2 for both low temperature and low humidity and high temperature and high humidity (good)
○: Black solid image of 1.0 or more and 1.2 or less for both low temperature and low humidity and high temperature and high humidity (no problem in practical use)
×: Black solid image is less than 1.0 in either low temperature and low humidity or high temperature and high humidity (practical problem)
Fog: Evaluation at low temperature and low humidity (LL: 10 ° C., 20% RH), high temperature and high humidity (HH: 30 ° C., 80% RH) The fog density was measured by reflection density using a solid white image RD-918 manufactured by Macbeth. The reflection density was evaluated by a relative density (the density of A4 paper not printed is 0.000). Measurements were taken at the solid black image portion after 10,000 copies each.

A: Concentration is less than 0.010 (good) for both low temperature and low humidity and high temperature and high humidity
○: Concentration of 0.010 or more and 0.020 or less for both low temperature and low humidity and high temperature and high humidity (a level that causes no practical problems)
X: Concentration is higher than 0.020 at either low temperature and low humidity or high temperature and high humidity (a level that causes practical problems)
Dielectric breakdown: evaluated at low temperature and low humidity (LL: 10 ° C., 20% RH), high temperature and high humidity (30 ° C., 80% RH) ○: No dielectric breakdown of the photoconductor due to charge leakage at LL or HH.

  X: Dielectric breakdown of the photoreceptor due to charge leakage occurred at LL or HH.

Black pot (high temperature and high humidity (30 ° C 80% RH))
The periodicity coincided with the period of the photoconductor, and the number of visible black spots and black streak-like image defects per A4 size was determined.

A: Frequency of image defects of 0.4 mm or more: All printed images are 5 / A4 or less (good)
○: Frequency of image defects of 0.4 mm or more: 1 or more of 6 / A4 or more and 10 / A4 or less (no problem in practical use)
X: Frequency of image defects of 0.4 mm or more: 11 or more A4 or more occurred (practical problem)
Sharpness The sharpness of the image was evaluated by squashing characters by displaying images in both low temperature and low humidity (10 ° C., 20% RH) and high temperature, high humidity (30 ° C., 80% RH) environments. 3-point and 5-point character images were formed and evaluated according to the following criteria.

◎: No image blurring, 3 points and 5 points are clear and easy to read ○: Image blurring is minor, 3 points are partially unreadable, 5 points are clear and easy ×: Image blur occurs, 3 points are almost unreadable, 5 points are partially or completely unreadable

From Table 2, the organic photoreceptors of the present invention, that is, the organic photoreceptors 1 to 9 having a thickness of the intermediate layer of 5 to 25 μm and the thickness of the charge transport layer of 5 to 20 μm are high temperature and high humidity and low temperature and low humidity. In this case, the residual potential and the charging potential are stable, and the image density is sufficient and the fog density is small. In addition, dielectric breakdown does not occur, and the improvement effect such as black spots is remarkable, and as a result, an electrophotographic image having excellent sharpness is obtained. In particular, an anatase-type titanium oxide containing niobium element in the metal oxide particles in the intermediate layer and a polyamide resin having a heat absorption of 0 to 40 J / g and a water absorption of 5% by mass or less, the intermediate layer thickness is 7 to 18 μm, In addition, the photoreceptors 1 to 6 having a charge transport layer thickness of 8 to 18 μm have a remarkable improvement effect on each evaluation item. On the other hand, the photoconductor 15 having an intermediate layer thickness of 4 μm has a dielectric breakdown, black spots are often generated, and sharpness is also deteriorated. In the photoreceptor 16 having an intermediate layer thickness of 27 μm, the residual potential is greatly increased, the image density is lowered, and as a result, the sharpness is also lowered. The photoconductor 17 having a charge transport layer thickness of 4 μm has dielectric breakdown, black spots are often generated, and sharpness is also deteriorated. On the photoconductor 18 having a charge transport layer thickness of 22 μm, each dot image is unclear and sharpness is lowered.

1 is a schematic cross-sectional view of an image forming apparatus 1 using a contact charging method according to the present invention. 2 is a schematic cross-sectional view of a photosensitive cartridge 2 that is detachable from the image forming apparatus 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photoconductor cartridge 3 Developer cartridge 4 Exposure apparatus 5 Paper feeder 6 Transfer roller 7 Fixing device 8 Paper discharge tray 21 Photoconductor 22 Charging brush 23, 27 Power supply connection member 24 Pre-charge film 25, 26 Charging Element

Claims (8)

Charging means for charging by bringing a charging member into contact with the organic photoreceptor, exposure means for forming an electrostatic latent image on the organic photoreceptor, developing means for developing the electrostatic latent image into a toner image, the toner image In an organic photoconductor used in an image forming apparatus having at least one auxiliary charging unit that is located upstream of the charging unit and charges toner on the surface of the organic photoconductor And having at least an intermediate layer, a charge generation layer, and a charge transport layer on the conductive support, the intermediate layer containing anatase-type titanium oxide pigment containing niobium element at 100 ppm to 2.0 mass%, and having a film thickness An organic photoreceptor having a thickness of 5 to 25 μm and a charge transport layer thickness of 5 to 20 μm. The organophotoreceptor according to claim 1, wherein the number average primary particle of the anatase titanium oxide pigment is 5 to 400 nm . 3. The organic photoreceptor according to claim 1, wherein the intermediate layer contains a polyamide resin having a heat of fusion of 0 to 40 J / g and a water absorption of 5% by mass or less . The organophotoreceptor according to claim 1, wherein the intermediate layer has a volume resistance of 10 ⁸ Ω · cm or more . The organic photoreceptor according to claim 1, wherein the intermediate layer has a thickness of 7 to 15 μm . Charging means for charging by bringing a charging member into contact with the organic photoreceptor, exposure means for forming an electrostatic latent image on the organic photoreceptor, developing means for developing the electrostatic latent image into a toner image, the toner image In a process cartridge used in an image forming apparatus having at least one auxiliary charging unit that is located upstream of the charging unit and charges the toner on the surface of the organic photoreceptor, The conductive support has at least an intermediate layer, a charge generation layer, and a charge transport layer. The intermediate layer contains an anatase-type titanium oxide pigment containing niobium element in an amount of 100 ppm to 2.0 mass%, and has a thickness of 5 An organic photoreceptor having a thickness of ˜25 μm, an intermediate layer thickness of 5-25 μm, and a charge transport layer thickness of 5-20 μm is integrated with at least one of the charging means, developing means, transfer means, and auxiliary charging means. Is lifting, the process cartridge characterized in that it is detachably attached to the image forming apparatus main body. Charging means for charging by bringing a charging member into contact with the organic photoreceptor, exposure means for forming an electrostatic latent image on the organic photoreceptor, developing means for developing the electrostatic latent image into a toner image, the toner image In an image forming apparatus having at least one auxiliary charging unit that is located upstream of the charging unit and charges toner on the surface of the organic photosensitive member, the organic photosensitive member The conductive support has at least an intermediate layer, a charge generation layer, and a charge transport layer. The intermediate layer contains an anatase-type titanium oxide pigment containing niobium element in an amount of 100 ppm to 2.0 mass%, and has a thickness of 5 An image forming apparatus having a thickness of ˜25 μm and a charge transport layer thickness of 5˜20 μm. An image forming method comprising forming an electrophotographic image using the image forming apparatus according to claim 7.

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