JP4872625B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Conventionally, in an image forming apparatus using an electrophotographic method, as a developing method of an electrostatic latent image formed on an image carrier, a one-component developing method using only toner as a developer and a two-component using a toner and a carrier Development methods are known.

  In the one-component development method, a predetermined charge amount is generally obtained by using a toner carrier and a regulation plate pressed toward the toner carrier, and regulating the film thickness while pressing the toner on the toner carrier with the regulation plate. A thin toner layer can be formed. With this toner thin layer, the electrostatic latent image on the image carrier is developed. This method is excellent in dot reproducibility and is a method in which a uniform image with little image unevenness can be easily obtained. In addition, it is considered advantageous in terms of simplification, miniaturization, and cost reduction of the apparatus. However, in order to give a strong stress to the toner in the restricting portion, the toner surface is denatured, or toner or an external additive adheres to the surface of the toner restricting member or the toner carrying member, and the charge amount of the toner is reduced. This causes problems such as fogging on the image and dirt in the aircraft due to scattering. As a result, there is a problem that the life of the developing device is shortened.

  On the other hand, in the two-component development system, the toner is charged by frictional charging by mixing with the carrier, so that the stress is small and it is advantageous for the deterioration of the toner. Furthermore, since the carrier as a charge imparting member to the toner has a large surface area, it is relatively resistant to contamination by the toner and external additives, and is advantageous for extending the life.

  However, even when a two-component developer is used, the surface of the carrier is contaminated by toner and external additives, and the toner charge amount is reduced by long-term use, such as fogging and toner scattering. Problems arise and their lifetime is by no means sufficient, and a longer lifetime is desired.

  As a method for extending the life of a two-component developer, Patent Document 1 discloses that a carrier is supplied in small amounts together with toner or alone, and accordingly, a deteriorated developer having reduced chargeability is discharged and the carrier is replaced. A developing device is disclosed that suppresses the ratio of deteriorated carriers. In this apparatus, since the carrier is replaced, it is possible to suppress a decrease in toner charge amount due to carrier deterioration at a certain level, which is advantageous in extending the service life.

  Patent Document 2 discloses a two-component developer comprising a toner and a carrier externally added with reverse polarity particles having chargeability opposite to the toner charge polarity, and a developing method using the same. The reverse polarity particles in this development method act as abrasives and spacer particles, and the effect of suppressing carrier deterioration is shown by the effect of removing spent matter on the carrier surface.

Patent Document 3 discloses a so-called hybrid development system in which a latent image on an image carrier is developed using a toner carrier that carries only toner from a two-component developer. The hybrid development system does not cause uneven brushing of images with a magnetic brush, excels in dot reproducibility and image uniformity, and the image carrier and the magnetic brush are not in direct contact with each other, so that carrier transfer to the image carrier (carrier consumption) ) Also does not occur. In the hybrid development system, the toner is charged by frictional charging with the carrier. Therefore, maintaining the charge imparting performance of the carrier is important for stabilizing the chargeability of the toner and maintaining the image quality over a long period of time.
JP 59-1000047 A JP 2003-215855 A JP-A-9-185247

  However, in Patent Document 1, there is a problem in terms of cost and environment because a mechanism for collecting the discharged carrier is necessary and the carrier becomes a consumable item. Further, it is necessary to repeat a predetermined amount of printing until the new and old ratio of the carrier is stabilized, and the initial characteristics cannot always be maintained. Further, in Patent Document 2, when the area ratio (image area ratio) of the image portion of the output image is small, the opposite polarity particles to the non-image portion are compared with the toner consumption amount to the image portion on the image carrier. The amount of reverse polarity particles in the developing device decreases when a large amount of images with a small image area ratio are printed. As a result, there is a problem that the effect of the reverse polarity particles for suppressing carrier deterioration cannot be sufficiently exhibited, the toner charge amount is reduced, and image deterioration is caused. Also. In Patent Document 3, there is a problem that the carrier surface is contaminated with toner, a post-treatment agent, and the like together with the number of printed sheets, and the charge imparting performance of the carrier is lowered.

  Even when a large amount of images with a small image area ratio is printed, the present invention suppresses consumption of reverse polarity particles, suppresses a decrease in toner charge amount due to carrier deterioration, and forms a high-quality image over a long period of time. It is an object of the present invention to provide an image forming apparatus that can be used.

  In order to solve the above problems, the present invention has the following features.

An image forming apparatus according to an aspect of the present invention is an image forming apparatus that uses a developer including a toner, a carrier for charging the toner, and reverse polarity particles that are charged with a polarity opposite to the charging polarity of the toner. there are, a developer carrying member for bearing and conveying a current image agent to the surface, and the toner carrying member which carries and conveys the toner separated from the developer on the developer carrying member faces the current image carrying member , is disposed opposite to the preparative toner carrying member, an AC superimposed between an image bearing member for bearing an electrostatic latent image is developed with toner carrying the toner carrying member surface, the toner carrying member and the image bearing member an image forming apparatus comprising: a voltage applying means for applying a bias voltage, the AC superimposed bias voltage, Ri vibration waveform der the vibration waveform including a trapezoidal wave, Ru waveform der having a slope at the start of the trapezoidal wave It is characterized by that.

  According to the image forming apparatus of the present invention, a developer including toner, a carrier for charging the toner, a reverse polarity particle charged to a polarity opposite to the charging polarity of the toner, and the developer on the surface. A developer carrier that carries and conveys, a toner carrier that carries and separates the toner separated from the developer on the developer carrier that faces the developer carrier, and that faces the toner carrier. And an image carrier that carries an electrostatic latent image developed with the toner carried by the toner carrier, and a voltage application that applies an AC bias voltage between the toner carrier and the image carrier. And the AC superimposed bias voltage has a vibration waveform including a trapezoidal wave. Therefore, even when a large number of images with a small image area ratio are printed, the image carrier. The consumption of reverse polarity particles Abrogated toner charge amount decreases due to carrier deterioration, it is possible to form a high quality image over a long period of time.

  Embodiments of the present invention will now be described with reference to the drawings.

  FIG. 1 shows a main part of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus is a printer that forms an image by transferring a toner image formed on an image carrier 1 to a transfer medium P such as paper by an electrophotographic method. This image forming apparatus has an image carrier 1 for carrying an image. Around the image carrier 1, a charging means 3 for charging the image carrier 1 and a static on the image carrier 1 are provided. A developing device 2 that develops an electrostatic latent image, a transfer roller 4 for transferring a toner image on the image carrier 1, and a cleaning blade 5 for removing residual toner on the image carrier 1 rotate the image carrier 1. They are arranged in order along the direction A.

  The image carrier 1 is charged by the charging means 3 and then exposed by an exposure means (not shown) at the position of point E in the drawing to form an electrostatic latent image on the surface thereof. The developing device 2 develops the electrostatic latent image into a toner image. The transfer roller 4 transfers the toner image on the image carrier 1 to the transfer medium P, and then discharges it in the direction of arrow C in the figure. The cleaning blade 5 removes the residual toner on the image carrier 1 after the transfer with its mechanical force. As the image carrier 1, the charging unit 3, the exposure unit, the transfer roller 4, the cleaning blade 5 and the like used in the image forming apparatus, a well-known electrophotographic technique may be arbitrarily used. For example, although a charging roller is shown in the drawing as the charging means, a charging device that is not in contact with the image carrier 1 may be used. Further, for example, there may be no cleaning blade.

  In the present embodiment, the developing device 2 includes a developer tank 16 that contains the developer 24, a developer carrier 11 that carries the developer 24 supplied from the developer tank on the surface thereof, and the developer carrier. A toner carrier 25 for separating the toner from the developer on the body is provided.

  In the present embodiment, the developer 24 includes toner, a carrier for charging the toner, and reverse polarity particles.

  The toner carrier 25 is provided between the developer carrier 11 and the image carrier 1. An electric field is formed between the toner carrier 25 and the developer carrier 11 so that the toner is separated from the developer on the developer carrier 11 and moved to the toner carrier side. At this time, the reverse polarity particles in the developer move to the developer carrier 11 side due to the force of the electric field and are returned to the developing tank 16, but some of the reverse polarity particles strongly adhered to the toner together with the toner. Move to the toner carrier 25 side.

  Further, between the toner carrier 25 and the image carrier 1, a power source that is a voltage applying unit is used so that the toner on the toner carrier 25 develops the image portion of the electrostatic latent image on the image carrier 1. An electric field is formed by 52. The power source 52 applies an AC superimposed bias voltage in which an alternating current is superimposed on a direct current between the toner carrier 25 and the image carrier 1, and the vibration waveform of the AC superimposed bias voltage has a trapezoidal shape as shown in FIG. Contains waves. By applying such an AC superimposed bias voltage including a trapezoidal wave, the toner that can move even with a weak electric field moves in the process of gradually increasing the electric field.

  FIG. 3 shows the result of measuring the transient current flowing through the image carrier 1 when the toner moves from the surface of the toner carrier 25 to the surface of the image carrier 1 when a rectangular wave voltage is applied as the vibration waveform. Show. FIG. 4 shows a measurement result of the transient current flowing in the image carrier 1 when two trapezoidal waves A and B are applied as vibration waveforms. At this time, the distance between the toner carrier 25 and the image carrier 1 was set to 0.2 μm. Further, in order to obtain a current when the toner moves, the components other than the image carrier 1 and the toner carrier 25 having a toner layer formed on the surface are removed and a voltage is applied in a stationary state. In addition, the amount of toner adhered on the image carrier 1 after application was almost the same. From this result, it can be seen that by using the trapezoidal wave, most of the moving toner moves at the initial rising slope. That is, by moving before the electric field strength between the toner carrier 25 and the image carrier 1 reaches the peak, the collision force when the toner reaches the surface of the image carrier 1 is more trapezoidal than rectangular. Can be seen to be weakened.

  By thus weakening the collision force of the toner, it is possible to prevent separation of the reverse polarity particles from the toner. If the reverse polarity particles are not separated from the toner, the reverse polarity particles originally try to adhere to the non-image area on the image carrier 1, but the adhesion force (Van der Waals force + Coulomb force) with the toner is not strongly separated. Therefore, it is possible to prevent the reverse polarity particles from adhering to the non-image area. As a result, consumption of reverse polarity particles from the developing device 2 can be prevented, and even when a large amount of images with a small image area ratio is printed, reverse polarity particles are excessively consumed from the development device 2. Absent. Further, the consumption of the reverse polarity particles attached to the toner developed in the image area can be supplied to the developing device 2 based on a signal from a toner sensor or the like, with replenishment toner externally added with the reverse polarity particles beforehand. . Thus, the reversal of the reverse polarity particles corresponding to the consumption of the toner depending on the area ratio of the image to be printed can be appropriately performed, and even when the image area ratio is extremely small, the amount of the reverse polarity particles in the developing device can be reduced. Absent. By maintaining the amount of the reverse polarity particles in the developing device in this manner, the reverse polarity particles can compensate for the toner charging ability of the carrier that gradually deteriorates with each printing, and the toner charge amount can be maintained over a long period of time. A stable and high-quality image can be formed.

  Further, the trapezoidal wave of the AC superimposed bias voltage by the power supply 52 is more effective in a shape having a slope at the rising portion as shown in FIG. By adopting a configuration in which the voltage at the time of rising is gradually increased, the force with which more toner collides with the surfaces of the image carrier 1 and the toner carrier 25 can be weakened.

  The reverse polarity particles can be charged to a polarity opposite to the charged polarity of the toner by frictional charging with the carrier used. For example, when the toner is negatively charged by the carrier, the opposite polarity particles are positively charged particles that are positively charged in the developer. Also, for example, when the toner is positively charged by the carrier, the reverse polarity particles are negatively charged particles that are negatively charged in the developer. By incorporating reverse polarity particles in the two-component developer and accumulating the reverse polarity particles in the developer with durability by the separating means, the chargeability of the carrier can be increased by spending the toner or the post-treatment agent on the carrier. Even if it decreases, the reverse polarity particles can also charge the toner to the normal polarity, so that the chargeability of the carrier can be effectively compensated, and as a result, the deterioration of the carrier can be suppressed.

  The reverse polarity particles used in the present invention are appropriately selected depending on the charging polarity of the toner. When a negatively chargeable toner is used as the toner, fine particles having positive chargeability are used as the reverse polarity particles. For example, inorganic fine particles such as strontium titanate, barium titanate, and alumina, acrylic resin, benzoguanamine resin, and nylon resin are used. Fine particles composed of thermoplastic resin such as polyimide resin and polyamide resin or thermosetting resin can be used, and a positive charge control agent imparting positive charge property can be contained in the resin, or a nitrogen-containing monomer You may make it comprise the copolymer of these. Here, as the positive charge control agent, for example, a nigrosine dye, a quaternary ammonium salt, or the like can be used, and as the nitrogen-containing monomer, 2-dimethylaminoethyl acrylate, 2-acrylic acid 2- Diethylaminoethyl, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinyl pyridine, N-vinyl carbazole, vinyl imidazole and the like can be used.

  On the other hand, in the case of using a positively chargeable toner, fine particles having negative chargeability are used as the reverse polarity particles. For example, in addition to inorganic fine particles such as silica and titanium oxide, fluorine resin, polyolefin resin, silicone resin, polyester resin Fine particles composed of thermoplastic resins such as thermoplastic resins or thermosetting resins can be used, and a negative charge control agent that imparts negative chargeability to the resin can be contained, or fluorine-containing acrylic monomers and fluorine-containing methacrylates can be used. You may make it comprise the copolymer of a system monomer. Here, as said negative charge control agent, a salicylic acid type, a naphthol type chromium complex, an aluminum complex, an iron complex, a zinc complex etc. can be used, for example.

  In order to control the chargeability and hydrophobicity of the reverse polarity particles, the surface of the inorganic fine particles may be surface-treated with a silane coupling agent, a titanium coupling agent, silicone oil, etc. When imparting positive chargeability, surface treatment with an amino group-containing coupling agent is preferred, and when imparting negative chargeability, surface treatment with a fluorine group-containing coupling agent is preferred.

  The toner used in the present invention is not particularly limited, and a commonly used known toner can be used. A colorant in the binder resin and, if necessary, a charge control agent, a release agent, etc. It is possible to use those which are contained and treated with external additives. The toner particle diameter is not limited to this, but is preferably about 3 to 15 μm.

  In manufacturing such a toner, it can be manufactured by a publicly known method, for example, a pulverization method, an emulsion polymerization method, a suspension polymerization method, or the like.

  Also, as the above external additives, publicly known ones can be used, and fluidity improvement, for example, inorganic fine particles such as silica, titanium oxide, aluminum oxide, acrylic resin, styrene resin, silicone resin In addition, resin fine particles such as a fluororesin can be used, and it is particularly preferable to use a resin that has been hydrophobized with a silane coupling agent, a titanium coupling agent, silicon oil or the like. Such a fluidizing agent is added at a ratio of 0.1 to 5 parts by mass with respect to 100 parts by mass of the toner.

  The carrier used in the present invention is not particularly limited, and a known carrier that is generally used can be used, and a binder type carrier, a coat type carrier, and the like can be used. Although it is not limited to this as a carrier particle size, 15-100 micrometers is preferable.

  On the other hand, a coated carrier is a carrier in which a carrier core particle made of a magnetic material is coated with a resin, and in a coated carrier, similarly to a binder-type carrier, positive or negatively chargeable fine particles are fixed to the carrier surface. it can. The charging characteristics such as the polarity of the coated carrier can be controlled by the type of the surface coating layer and the chargeable fine particles.

  The charging polarity of the toner and the reverse polarity particles by the combination of the reverse polarity particles, the toner and the carrier is obtained by mixing and stirring each to form a developer, and then using the apparatus as shown in FIG. It can be easily found from the direction of the electric field when separating. FIG. 5 is a schematic view of an apparatus for measuring the charge amount of charged particles such as toner.

  That is, in the apparatus shown in FIG. 5, the developer composed of toner, carrier, and reverse polarity particles is placed uniformly on the entire surface of the conductive sleeve 31, and the magnet roll 32 provided in the conductive sleeve 31 is mounted. The rotational speed is set to 1000 rpm, a bias voltage of 2 kV is applied from the bias power source 33 to the same polarity as the charging potential of the toner, the conductive sleeve 31 is rotated for 15 seconds, and the conductive sleeve 31 is stopped. The potential Vm at the cylindrical electrode 34 is read, and the mass of the toner adhering to the cylindrical electrode 34 is measured with a precision balance to obtain the charge amount of the toner.

  Further, the polarity of the particles to be added other than the toner and the carrier can be determined by the polarity of the bias voltage applied from the bias power source 33. That is, when the bias voltage applied from the bias power source 33 is applied with a polarity opposite to the charging potential of the toner, the particles adhering to the cylindrical electrode 34 are opposite to the charging polarity of the toner, that is, are opposite polarity particles.

  The mixing ratio of the toner and the carrier may be adjusted so as to obtain a desired toner charge amount. The toner ratio is 3 to 50% by mass, preferably 6 to 30% by mass with respect to the total amount of the toner and the carrier. ing.

  The amount of the reverse polarity particles contained in the initial developer is not particularly limited as long as the object of the present invention is achieved. For example, 0.01 to 5.00% by mass, particularly 0.01 to 2% with respect to the carrier. 0.000% by mass is preferred.

  The developer is preferably adjusted by externally adding reverse polarity particles to the toner in advance and then mixing with a carrier.

  The developer carrying member 11 includes a magnet roller 13 that is fixedly arranged, and a rotatable sleeve roller 12 that contains the magnet roller 13. The magnet roller 13 has five magnetic poles N1, S1, N3, N2, and S2 along the rotation direction B of the sleeve roller 12. Of these magnetic poles, the main magnetic pole N1 is disposed at the position of the developing region 6 facing the image carrier 1 and generates a repulsive magnetic field for peeling off the developer 24 on the sleeve roller 12. The pole portions N3 and N2 are arranged at positions facing the inside of the developing tank 16.

  The developer tank 16 is formed of a casing 18 and normally contains a bucket roller 17 for supplying developer to the developer carrier 11 therein. An ATDC (Automatic Toner Density Control) sensor 20 for detecting toner concentration is preferably disposed at a position facing the bucket roller 17 of the casing 18.

  The developing device 2 normally has a replenishment section 7 for replenishing toner in the developer tank 16 for the amount of toner consumed in the development area 6 and a developer thin film for regulating the amount of developer on the developer carrier 11. It has a regulating member (regulating blade) 15 for stratification. The supply unit 7 includes a hopper 21 that stores supply toner 23 and a supply roller 19 for supplying toner into the developer tank 16.

  As the replenishing toner 23, a toner obtained by externally adding reverse polarity particles is used. By using the toner to which the reverse polarity particles are externally added, it becomes possible to effectively assist the decrease in the chargeability of the carrier that gradually deteriorates due to durability. The external addition amount of the reverse polarity particles in the replenishing toner 23 is preferably 0.1 to 10.0% by mass, particularly preferably 0.5 to 5.0% by mass with respect to the toner.

  The toner separation bias voltage for separating the toner from the developer on the developer carrier 11 applied to the toner carrier 25 and the developer carrier 11 by the power source 51 to the toner carrier 25 side varies depending on the charging polarity of the toner. That is, when the toner is negatively charged, the average value of the potential of the toner carrier 25 is higher than the average value of the potential of the developer carrier 11, and when the toner is positively charged, the developer carrier 11 It is applied so that the average value of the potential of the toner carrier 25 is lower than the average value of the potential. Even when the toner is charged to a positive or negative polarity, the difference between the average potentials of the toner carrier 25 and the developer carrier 11 is 20 to 500 V, particularly 50 to 300 V. preferable. If the potential difference is too small, it is difficult to sufficiently separate the toner. On the other hand, if the potential difference is too large, the carriers held by the magnetic force on the developer carrier are separated by the electric field, and the original developing function may be impaired in the developing region.

In the developing device 2, it is further preferable that an alternating electric field is formed between the toner carrier 25 and the developer carrier 11. By forming an alternating electric field, the toner reciprocally vibrates, so that the toner can be effectively separated. At that time, an electric field of 2.5 × 10 ⁶ V / m or more is preferably formed. By forming an electric field of 2.5 × 10 ⁶ V / m or more, it becomes possible to separate the toner from the developer carrier even by the electric field, and it is possible to further improve the toner separation property. Become.

In the present specification, an electric field formed between the toner carrier 25 and the developer carrier 11 is referred to as a toner separation electric field. It is desirable to form a toner separation electric field using an alternating voltage applied to the toner carrier 25. At this time, the toner separation electric field may be an electric field having a maximum absolute value of 2.5 × 10 ⁶ V / m or more.

  The toner carrier 25 may be made of any material as long as a voltage can be applied. For example, an aluminum roller subjected to a surface treatment may be used. In addition, on a conductive substrate such as aluminum, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate You may use what gave resin coatings, such as resin, a silicone resin, a fluororesin, and rubber coatings, such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. The coating material is not limited to this. Further, a conductive agent may be added to the bulk or surface of the coating. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent. Examples of the electronic conductive agent include carbon black such as kettin black, acetylene black, and furnace black, metal powder, and metal oxide fine particles, but are not limited thereto. Examples of the ionic conductive agent include cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials. Furthermore, a conductive roller made of a metal material such as aluminum may be used.

  FIG. 6 schematically shows the configuration of the image carrier 1.

  The image bearing member (photosensitive member) 1 is obtained by sequentially forming an undercoat layer 102 and a photosensitive layer 103 on an aluminum cylindrical substrate (conductive support) 101. The photosensitive layer 103 is a charge generation layer, followed by charge transport. Even if it is a function separation type consisting of layers, a single layer structure in which a charge generation material and a charge transport material are dispersed in a resin may be used. The function separation type image carrier 1 will be described below.

  First, a charge generation layer is formed on a conductive support. The charge generation layer is formed by vacuum-depositing the charge generation material, applying the charge generation material dissolved in an amine solvent and drying, or dissolving the charge generation material in an appropriate solvent or, if necessary, a binder resin. It is formed by applying and drying a coating solution prepared by dispersing in the solution. The thickness of the charge generation layer is 0.01 to 5 μm, preferably 0.1 to 2 μm.

  As the conductive support 101, a cold drawn (ED tube) after extrusion, an extruded aluminum pipe is cut after extrusion, and the outer surface is cut using a cutting tool such as a diamond bite. Finished by cutting to about 0.2 to 0.3 mm (cutting tube), impact processing of an aluminum disc into a cup shape, and finishing the outer surface by ironing (EI tube), aluminum circle For example, after deep drawing the plate, the outer surface is finished by ironing (DI pipe). Further, those obtained by further cutting these surfaces, those subjected to anodization treatment, or those subjected to sealing treatment after anodization treatment may be used.

  Prior to the formation of the charge generation layer, an undercoat layer 102 may be formed on the conductive support 101 for the purpose of preventing charge injection from the conductive support. When the undercoat layer is provided, the material is dispersed in water or alcohol-soluble resin such as polyamide, polyvinyl alcohol or copolymer nylon, curable resin such as polyurethane or epoxy resin, or low resistance compound such as tin oxide or indium oxide. The ones made are suitable. In this case, the thickness of the undercoat layer is desirably 1 μm or less.

  Examples of the charge generation material include bisazo pigments, pyrylium dyes, azo dyes, perylene pigments, squarylium pigments, phthalocyanine pigments, and the like. When the charge generation layer has the charge generation material dispersed in the binder resin, the content of the charge generation material in the layer is 10 to 400 parts by mass, preferably 50 to 100 parts by mass with respect to 100 parts by mass of the binder resin. 250 parts by weight is preferred. In this case, examples of the binder resin include thermoplastic resins such as butyral resin (polyvinyl butyral) and polyester resin, and thermosetting resins such as epoxy resin, alkyd resin, urethane resin, silicone resin, and phenol resin. It is done.

  A charge transport layer is then formed. The charge transport layer is formed by applying a coating liquid containing at least a charge transport material, a binder resin and an organic solvent on the charge generation layer and drying it. The thickness of the charge transport layer is 4 to 50 μm, preferably 10 to 30 μm.

  Examples of the charge transport material that can be used for forming the charge transport layer include hydrazone compounds, styryl compounds, stilbene compounds, triphenylamine compounds, and tetraphenylbenzidine compounds. It can be used alone or in combination of two or more. The content of the charge transport material is 2 to 200 parts by mass, preferably 50 to 120 parts by mass, with respect to 100 parts by mass of the binder resin. Examples of the binder resin used for forming the charge transport layer include a polycarbonate resin, a polyester resin, and a polyarylate resin. From the viewpoint of suppressing durability deterioration, it is preferable to add a phenol-based or amine-based antioxidant.

  The toner used in the present invention is described below.

  For 100 parts by mass of toner base material having a particle size of about 6.5 μm prepared by wet granulation method, 0.2 parts by mass of first hydrophobic silica, 0.5 parts by mass of second hydrophobic silica, and hydrophobicity A 0.5 part by mass of titanium oxide was subjected to a surface treatment using a Henschel mixer (manufactured by Mitsui Kinzoku Mining Co., Ltd.) at a speed of 40 m / s for 3 minutes for external addition.

  The first hydrophobic silica used here is obtained by subjecting silica having an average primary particle size of 16 nm (# 130: manufactured by Nippon Aerosil Co., Ltd.) to surface treatment with hexamethyldisilazane (HMDS) as a hydrophobizing agent. . The second hydrophobic silica is obtained by surface-treating silica (# 90G: manufactured by Nippon Aerosil Co., Ltd.) having an average primary particle size of 20 nm with HMDS. Hydrophobic titanium oxide is an anatase-type titanium oxide having an average primary particle size of 30 nm and surface-treated with isobutyltrimethoxysilane as a hydrophobizing agent in an aqueous wet process.

Subsequently, strontium titanate having an average primary particle size of 350 nm as reverse polarity particles was externally added for 3 minutes at a speed of 40 m / s using a Henschel mixer at 2 parts by mass with respect to 100 parts by mass of toner base particles. Obtained.
Example 1
The photoconductor used in Example 1 is described below.

  After cutting the surface of a JIS5657 cylindrical aluminum alloy (outer diameter 30 mm, thickness 1 mm) with a cutting tool using natural diamond as a cutting blade, it is degreased and washed with running water, and then anodized. An anodized layer having a thickness of 8 μm was formed. This was washed with running water with pure water, and then sealed with a sealing agent containing nickel acetate. Thus, a photoreceptor substrate having the anodized layer sealed was obtained. Formation of the photosensitive layer was performed as follows.

  1 part of butyral resin (manufactured by Sekisui Chemical Co., Ltd .: ESREC BX-1) and 1 part of m-type titanyl phthalocyanine (manufactured by Toyo Ink Co., Ltd .: am-TiOPc) are added to 100 parts of tetrahydrofuran, and these are dispersed in a sand mill for 5 hours. Thus, a charge generation layer coating solution was prepared, and this charge generation layer coating solution was dip-coated on the support to form a charge generation layer having a thickness of 0.2 μm. For 100 parts of tetrahydrofuran, 100 parts of a polycarbonate resin (manufactured by Teijin Chemicals Ltd .: Panlite TS-2020), 70 parts of a styryl compound as a charge transport material, and 8 parts of a phenol compound butylhydroxytoluene are dissolved to form a charge transport layer. A coating solution was prepared, and this charge transport layer coating solution was dip-coated on the charge generation layer, and this was blown and dried to form a charge transport layer having a thickness of 20 μm.

The developing device shown in FIG. 1 was used, and a carrier for bizhub C350 (particle size of about 33 μm) manufactured by Konica Minolta was used as the developer. The toner ratio in the developer was 8% by mass. A DC voltage of −400 V was applied to the developer carrying member. A trapezoidal developing bias having an amplitude of 1.6 kV, a DC component of −300 V, a duty ratio of 50%, and a frequency of 2 kHz was applied to the toner carrier. FIG. 7 shows the shape of the trapezoidal wave. The average potential of the toner carrier has a potential difference of 100V with respect to the potential of the developer carrier, and the maximum potential difference is 900V. An aluminum roller having an alumite treatment on the surface was used for the toner carrier, and the gap at the closest part between the developer carrier and the toner carrier was 0.3 mm. The background potential of the electrostatic latent image formed on the image carrier 1 is −550V, the image portion potential is −60V, and the gap at the closest portion between the image carrier 1 and the toner carrier 25 is 0.15 mm. It was. The maximum value of the absolute value of the toner separation electric field formed between the toner carrier 25 and the developer carrier 11 was 900 V / 0.3 mm = 3.0 × 10 ⁶ V / m.
(Example 2)
Example 2 was performed in the same manner as Example 1 except that a trapezoidal vibration bias shown in FIG. 8 was applied to the toner carrier with an amplitude of 1600 V, a duty ratio of 50%, and a frequency of 2000 Hz.
(Example 3)
In Example 3, the same procedure as in Example 1 was performed except that a trapezoidal vibration bias shown in FIG. 9 was applied to the toner carrier at an amplitude of 1600 V, a duty ratio of 50%, and a frequency of 2000 Hz.
(Comparative Example 1)
In Comparative Example 1, the same procedure as in Example 1 was performed, except that a rectangular wave vibration bias shown in FIG. 10 was applied to the toner carrier with an amplitude of 1600 V, a duty ratio of 50%, and a frequency of 2000 Hz.
(Evaluation 1)
In both the above examples and comparative examples, 10 sheets of A4 side with an image area ratio of 0% (blank paper) are printed, and the operation is forcibly stopped during the formation of an image with an area ratio of 0% on the 11th sheet. Later, four opposite polarity particles adhered to the image carrier 1 before transfer were observed with a SEM and compared. Table 1 shows the observation results. In the observation, the surface of the image carrier 1 was enlarged by a magnification of 20,000 with an SEM, and the number of reverse polarity particles per screen was compared.

It can be confirmed that the amount of reverse polarity particles attached to the image carrier 1 is smaller in Examples 1 to 3 than in Comparative Example 1. From this, it can be seen that applying an AC superimposed bias voltage including a trapezoidal wave between the toner carrier and the image carrier makes it difficult for reverse polarity particles to adhere to the non-image portion of the image carrier.
(Evaluation 2)
In both Examples 1 and 2 and Comparative Example 1 above, an endurance test of 50,000 sheets was performed with an image area ratio of 3%. Table 2 shows the toner charge amount before and after the endurance.

  While Comparative Example 1 shows a slight decrease, it can be confirmed that Examples 1 to 3 maintain the charging performance. Further, in Example 1 and 2, no fog was observed at all in comparison with Comparative Example 1 in which a slight fog was observed on the image after 50,000 sheets.

  As described above, by applying an AC superimposed bias voltage including a trapezoidal wave having an inclination at the time of rising between the toner carrier and the image carrier, the polarity is reversed even when a large amount of images with a low image area ratio is printed. The consumption of particles can be suppressed, so that the reverse polarity particles can compensate for the decrease in the toner charge amount accompanying the deterioration of the carrier. As a result, it has been possible to provide an image forming apparatus capable of forming a high-quality image over a long period of time.

1 is a diagram illustrating a main part of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the vibration waveform of the alternating current superimposed bias voltage containing the trapezoid wave applied to the toner carrier which concerns on this invention. FIG. 6 is a diagram illustrating a current flowing through an image carrier when an AC superimposed bias voltage including a rectangular wave is applied to the toner carrier. FIG. 6 is a diagram illustrating a current flowing through an image carrier when an AC superimposed bias voltage including a trapezoidal wave is applied to the toner carrier according to the present invention. It is the schematic of the apparatus which measures the charge amount of a charged particle. FIG. 3 is a diagram schematically showing a configuration of an image carrier according to the present invention. It is a figure which shows the vibration waveform of the alternating current superimposed bias voltage containing the trapezoid wave applied to the toner carrier which concerns on this invention. It is a figure which shows the vibration waveform of the alternating current superimposed bias voltage containing the trapezoid wave applied to the toner carrier which concerns on this invention. It is a figure which shows the vibration waveform of the alternating current superimposed bias voltage containing the trapezoid wave applied to the toner carrier which concerns on this invention. FIG. 4 is a diagram illustrating a vibration waveform of an AC superimposed bias voltage including a rectangular wave applied to a toner carrier.

Explanation of symbols

1 Image carrier (photosensitive drum)
DESCRIPTION OF SYMBOLS 2 Developing device 3 Charging device 4 Transfer roller 5 Cleaning blade 6 Development area 7 Toner replenishing device 11 Developer carrying member 12 Sleeve roller 13 Magnet roller 15 Restriction member (regulation blade)
16 Developer tank 17 Bucket roller 18 Casing 19 Supply roller 20 ATDC sensor 21 Hopper 23 Supply toner 24 Developer 25 Toner carrier 31 Conductive sleeve 32 Magnet roll 33 Bias power supply 34 Cylindrical electrode 101 Aluminum cylindrical substrate (conductive support)
102 Undercoat layer 103 Photosensitive layer 104 Overcoat layer

Claims (1)

An image forming apparatus using a developer including a toner, a carrier for charging the toner, and reverse polarity particles charged to a polarity opposite to the charging polarity of the toner ,
A developer carrying member for bearing and conveying a current image agent to the surface,
And the toner carrying member which carries and conveys the toner separated from the developer carrier opposed to the developer on the developer carrying member,
An image carrier that is disposed facing the toner carrier and carries an electrostatic latent image developed on the toner carried by the toner carrier on the surface;
In an image forming apparatus comprising: a voltage applying unit that applies an AC superimposed bias voltage between the toner carrier and the image carrier .
The AC superimposed bias voltage, Ri vibration waveform der the vibration waveform including a trapezoidal wave, the image forming apparatus according to claim waveform der Rukoto having a slope at the beginning portion of the trapezoidal wave.

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