JP2010271425A - Pre-transfer charging device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pre-transfer charging device capable of uniformly charging a toner image on an intermediate transfer member before transferring it to material to be transferred in an ozone-less state and stably transferring it to the material to be transferred. <P>SOLUTION: The pre-transfer charging device 3 includes: an electron emitter 30 having an electron acceleration layer 303 held between an electrode substrate 301 and a thin film electrode 302; a first power supply V1 applying voltage between the electrode substrate 301 and the thin film electrode 302 so as to accelerate electron in the electron acceleration layer 303 and emit it from the thin film electrode 302; and a second power supply V2 applying voltage between the thin film electrode 302 and an intermediate transfer belt 21. The thin film electrode 302 is arranged to be opposed to the intermediate transfer belt 21, and the electron acceleration layer 303 includes a particulate layer containing insulation particulates. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pre-transfer charging device used in an image forming apparatus that transfers a toner image on an intermediate transfer member to a transfer material.

  Conventionally, as an image forming apparatus using an intermediate transfer member, a toner image formed on an image carrier is transferred to an intermediate transfer member, and the toner image on the intermediate transfer member is transferred to a transfer material (sheet material). Things are known. In this image forming apparatus, a toner image charged on a predetermined polarity formed on an image carrier is transferred to an intermediate transfer member using electrostatic force, and then the toner image on the intermediate transfer member is electrostatically charged. Transfer onto the transfer material using force.

  In particular, an image forming apparatus using an intermediate transfer member can superimpose a toner image formed on an image carrier on the intermediate transfer member, so that a color image forming apparatus that forms a color image on a transfer material is used. Widely applied. In such a color image forming apparatus, the toner images of the respective colors formed on the image carrier are transferred onto the intermediate transfer member, and the transferred toner image is collectively transferred to a transfer material using electrostatic force. To do.

  In the conventional image forming apparatus using the intermediate transfer member, the transfer condition for transferring the toner image on the intermediate transfer member to the transfer material is usually such that the transfer rate to the transfer material is a predetermined value or more. It is set to be approximately the center of the transfer range. It can be said that the transfer property is better as the efficiency of the transferred toner is higher and there is no transfer unevenness.

  Here, if the toner image after passing through the primary transfer portion for transferring the toner image from the image carrier to the intermediate transfer member includes a portion having a different toner adhesion amount, the charge amount in the toner image on the intermediate transfer member Variation occurs. In addition, the variation in the charge amount may occur due to a peeling discharge that occurs on the downstream side adjacent to the primary transfer portion in the surface movement direction of the intermediate transfer member.

  When there is a variation in the charge amount in the toner image on the intermediate transfer member, portions having different transfer characteristics exist in the same toner image, resulting in unevenness in the image and deterioration of the image. Such a phenomenon of image unevenness and image deterioration also occurs when the charge amount in the toner image on the intermediate transfer member is reduced and transfer efficiency is deteriorated.

  Therefore, even when there is a variation in the charge amount in the toner image on the intermediate transfer member transferred from the image carrier or the charge amount in the toner image on the intermediate transfer member is small, the toner image is transferred to the transfer material. An image forming apparatus that can stably transfer a toner image to a transfer material without causing a decrease in transfer efficiency or uneven transfer during transfer is desired.

  For example, Patent Document 1 discloses an image forming apparatus that transfers a toner image formed on an image carrier to an intermediate transfer member and transfers the toner image on the intermediate transfer member to a transfer material. A technique is disclosed in which a pre-transfer charger is provided as a pre-transfer charging unit that charges a toner image on an intermediate transfer body before being transferred to a transfer material. With this pre-transfer charger, the toner image can be stably transferred to the transfer material even if there is a variation in the charge amount in the toner image on the intermediate transfer member.

JP 10-274892 A (released on October 13, 1998)

  However, when corona discharge is performed by a pre-transfer charger as the pre-transfer charging means disclosed in Patent Document 1, a large amount of ozone is generated. Since ozone is harmful to the human body and oxidizes various things with its strong oxidizing power, there is a problem of damaging the surrounding members of the pre-transfer charging means. Has a restriction that a material having high ozone resistance must be used.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and its object is to uniformly charge a toner image on an intermediate transfer member without transferring to an ozone-less material before transfer to the material to be transferred, and stably onto the material to be transferred. An object is to provide a pre-transfer charging device and an image forming apparatus capable of transferring.

  In order to solve the above problems, the pre-transfer charging device of the present invention transfers an intermediate transfer unit that transfers a toner image on an image carrier to an intermediate transfer member, and transfers the toner image on the intermediate transfer member to a transfer material. An image forming apparatus comprising: a transfer unit that precharges a toner image on the intermediate transfer body before being transferred to the transfer material; an electrode substrate, a thin film electrode, and the electrode substrate; An electron-emitting device having an electron acceleration layer sandwiched between the thin-film electrodes, and the electrode substrate and the thin-film electrode so that electrons are accelerated in the electron acceleration layers and the electrons are emitted from the thin-film electrodes. First voltage applying means for applying a voltage therebetween, and second voltage applying means for applying a voltage between the thin film electrode and the intermediate transfer member, wherein the thin film electrode is opposed to the intermediate transfer member. The electron acceleration layer is composed of insulating fine particles. It is characterized by comprising a fine particle layer containing.

  According to the above configuration, the electron-emitting device emits electrons from the thin film electrode, and the toner image on the intermediate transfer member is charged by the electrons. This electron-emitting device has a configuration including an electron acceleration layer composed of a fine particle layer containing insulating fine particles, and does not generate harmful substances such as ozone and NOx. Therefore, in an intermediate transfer type image forming apparatus, even when there is a variation in the charge amount in the toner image on the intermediate transfer member, or even when the charge amount in the toner image on the intermediate transfer member is small, the electron emission having the above configuration is performed. By using a pre-transfer charging device including an element, it is possible to uniformly charge the toner image on the intermediate transfer member without using ozone. Therefore, the pre-transfer charging device of the present invention can stably and safely transfer the toner image to the transfer material without causing a decrease in transfer efficiency or transfer unevenness when the toner image is transferred to the transfer material.

  Here, in the pre-transfer charging device of the present invention, since the electron acceleration layer is composed of a fine particle layer containing insulating fine particles, the average particle diameter of the insulating fine particles and the number of particles of the insulating fine particles (electron acceleration layer) A device capable of emitting a stable and good amount of electrons can be easily obtained by a simple method of controlling the film thickness. In addition, since the structure is composed of a fine particle layer containing insulating fine particles, for example, the electron acceleration layer can be easily formed by a simple manufacturing process of applying a fine particle dispersion. Furthermore, in the pre-transfer charging device of the present invention, the electron emission element can control the electron emission characteristics by the average particle diameter of the insulating fine particles and the number of particles of the insulating fine particles (the film thickness of the electron acceleration layer). is there.

  Although the electron emission mechanism of the electron-emitting device in the pre-transfer charging device of the present invention is not clear, in a so-called MIM type electron-emitting device in which an insulator layer is inserted between two conductor films. It is considered similar to the operating mechanism. In the MIM type electron-emitting device, when an electric field is applied to the insulator layer, a general mechanism for forming a current path is as follows: a) diffusion of electrode material into the insulator layer, b) insulator material C) formation of a conductive path called a filament, d) stoichiometric deviation of the insulator material, e) trapping of electrons due to defects in the insulator material, and local formation of the trapped electrons Various theories such as a strong electric field region have been considered, but have not yet been clarified. For any reason, according to the above configuration of the present invention, when an electric field is applied to an electron acceleration layer composed of a fine particle layer containing insulating fine particles corresponding to the insulating layer, the formation of such a current path and the current As a result of acceleration of a part of the electron beam by the electric field, it becomes ballistic electrons, and when electrons pass through the thin film electrode which is one of the electrode substrate and the thin film electrode corresponding to the two conductor films, Conceivable.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the insulating fine particles may have an average particle size of 7 to 1000 nm. In this case, the dispersion state of the particle diameter may be broad with respect to the average particle diameter. For example, fine particles having an average particle diameter of 50 nm may have a particle diameter distribution in the region of 20 to 100 nm. If the particle size of the insulating fine particles is too small, the force acting between the particles is strong, so that the particles are likely to aggregate and difficult to disperse. In addition, if the particle size of the insulating fine particles is too large, the dispersibility is good, but it is difficult to adjust the thickness of the electron acceleration layer and the mixing ratio of the surface conductive material for resistance adjustment. Moreover, when the average particle diameter of the insulating fine particles is within the above range, the resistance value in the electron acceleration layer can be easily adjusted.

In the pre-transfer charging device of the present invention, in addition to the above configuration, the insulating fine particles may contain at least one of SiO ₂ , Al ₂ O ₃ , and TiO ₂ , or may contain an organic polymer. Good.

If the insulating fine particles contain at least one of SiO ₂ , Al ₂ O ₃ , and TiO ₂ , or contain an organic polymer, the insulating properties of these substances are high, so that the electron acceleration layer The resistance value can be adjusted to an arbitrary range. As the resistance value increases, it becomes difficult for the current in the electron-emitting device to flow, and the amount of electron emission decreases. On the other hand, as the resistance decreases, electrons are conducted without accelerating and the amount of emitted electrons is reduced. Therefore, by adjusting the resistance value, it is possible to control the current and electron acceleration in the electron-emitting device, and to control the electron emission amount. In addition, when an oxide (SiO ₂ , Al ₂ O ₃ , and TiO ₂ ) is used as the insulating fine particles, it is difficult to cause element deterioration due to oxidation by oxygen in the atmosphere. It can be operated stably even at atmospheric pressure.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the insulator fine particles may be surface-treated. Here, the surface treatment may be a treatment with a silanol or a silyl group.

  When the electron acceleration layer is produced, when the insulating fine particles are dispersed in an organic solvent and applied to the electrode substrate, the surface of the particles is treated with silanol and silyl groups, so that the insulating fine particles are added to the organic solvent. An electron acceleration layer in which dispersibility is improved and the insulating fine particles are uniformly dispersed can be easily obtained. Further, since the insulating fine particles are uniformly dispersed, an electron acceleration layer having a thin layer thickness and high surface smoothness can be formed, and a thin film electrode thereon can be formed thin. The thinner the thin film electrode is, the more efficient it is to emit electrons.

  The fine particle layer may contain at least one of conductive fine particles and a basic dispersant.

  According to the above configuration, the electron acceleration layer is provided between the electrode substrate and the thin-film electrode, the electron acceleration layer including a fine particle layer mainly containing insulating fine particles and containing at least one of conductive fine particles and a basic dispersant. Yes.

  In the configuration including the conductive fine particles, the electron acceleration layer is a layer in which the insulating fine particles and the conductive fine particles are densely assembled, and has semiconductivity. When a voltage is applied to the semiconductive electron acceleration layer, a current flows in the electron acceleration layer, and a part thereof is emitted as ballistic electrons by the strong electric field formed by the applied voltage.

  On the other hand, in the configuration containing the basic dispersant, the mechanism of electron emission has not been clearly analyzed, but by applying a voltage between the electrode substrate and the thin film electrode, a current flows in the electron acceleration layer, Part of it becomes ballistic electrons by the strong electric field formed by the applied voltage, and is emitted from the thin film electrode side. Here, it is presumed that electrons are emitted from the electron-emitting device because an electron-pair donor that donates an electron pair possessed by the basic dispersant is acting. That is, the basic dispersant has an electron pair donor that donates an electron pair, and the electron pair donor ionizes after donating the electron pair. It is considered that the ionized electron pair donor transfers charges on the surface of the attached insulating fine particles, and electrical conduction is possible on the surface of the insulating fine particles.

  In addition, since the function of fine particles such as metals is assigned to the dispersant, which can be said to be an essential element in dispersing the insulating fine particles in the solvent, the effect of reducing the manufacturing process and material costs can be expected. .

  Further, in the pre-transfer charging device of the present invention, in addition to the above configuration, when the fine particle layer contains the insulating fine particles and at least the conductive fine particles, the conductive fine particles are conductors having high antioxidation power. It may be. Here, the high antioxidant power means that the oxide forming reaction is low. In general, the larger the negative value ΔG [kJ / mol] value of the oxide formation free energy obtained by thermodynamic calculation, the easier the oxide formation reaction occurs. In the present invention, a metal element corresponding to ΔG> −450 [kJ / mol] or more corresponds to conductive fine particles having a high antioxidant power. In addition, the conductive fine particles in a state in which an oxide generation reaction is more difficult to occur by attaching or coating an insulating material smaller than the size of the conductive fine particles around the corresponding conductive fine particles have anti-oxidation power. Included in high conductive particles.

  The electron acceleration layer is a thin film layer in which insulating fine particles and conductive fine particles having high antioxidation power are densely assembled, and has semiconductivity. When a voltage is applied to the semiconductive electron acceleration layer, a current flows in the electron acceleration layer, and a part thereof is emitted as ballistic electrons by the strong electric field formed by the applied voltage.

  According to the above configuration, since the conductive material having high antioxidation power is used as the conductive fine particles, it is difficult for the device to deteriorate due to oxidation by oxygen in the atmosphere, so that the electron-emitting device can be operated stably even at atmospheric pressure. it can. Therefore, the life of the pre-transfer charging device can be extended, and continuous operation can be performed for a long time even in the atmosphere.

  In the pre-transfer charging apparatus of the present invention, in addition to the above configuration, the conductive fine particles may be a noble metal. Thus, since the conductor which comprises the said conductive fine particle is a noble metal, element deterioration including the oxidation of the conductive fine particle by the oxygen in air | atmosphere etc. can be prevented. Therefore, the lifetime of the pre-transfer charging device can be extended.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the conductive fine particles may contain at least one of gold, silver, platinum, palladium, and nickel.

  Since the tunnel effect is hindered when the oxide film of the conductive fine particles becomes thick, the conductor constituting the conductive fine particles needs to be a metal that is difficult to oxidize. Therefore, when the conductive fine particles contain at least one of gold, silver, platinum, nickel, and palladium, oxidation by oxygen in the atmosphere can be more effectively prevented. Therefore, the lifetime of the pre-transfer charging device can be extended more effectively.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the conductive fine particles preferably have an average particle size of 3 to 10 nm. Thus, when the average particle diameter of the conductive fine particles is preferably 3 to 10 nm, a conductive path is not formed by the conductive fine particles in the electron acceleration layer, and dielectric breakdown does not easily occur in the electron acceleration layer. Become. Although there are many unclear points in principle, ballistic electrons are efficiently generated by using conductive fine particles having an average particle diameter within the above range.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, a small insulator material that is an insulator material smaller than the size of the conductive fine particles may be present around the conductive fine particles. Thus, the presence of a small insulator around the above-mentioned electro fine particles contributes to the improvement of the dispersibility of the conductive fine particles in the dispersion at the time of creating the electron-emitting device, and the conductive fine particles in the atmosphere. Degradation of the electron-emitting device such as oxidation by oxygen can be prevented more effectively. Therefore, the lifetime of the pre-transfer charging device can be extended more effectively.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the small insulator material may include at least one of alcoholate, fatty acid, and alkanethiol. If the small insulator material contains at least one of an alcoholate, a fatty acid, and an alkanethiol, it contributes to improving the dispersibility of the conductive fine particles in the dispersion at the time of forming the electron-emitting device. In addition to making it difficult for the current collector to form an abnormal current path, the composition of the particles due to the oxidation of the conductive fine particles themselves around the insulating fine particles themselves does not change, so the electron emission characteristics are not affected. . Therefore, the lifetime of the pre-transfer charging device can be extended more effectively.

  Here, in the pre-transfer charging device of the present invention, the small insulator substance adheres to the surface of the conductive fine particles and exists as an attached substance, and the attached substance is smaller than the average particle diameter of the conductive fine particles. The conductive fine particle surface may be coated as an aggregate of shapes. As described above, the surface of the conductive fine particles is coated on the surface of the conductive fine particles or as an aggregate having a shape smaller than the average particle diameter of the conductive fine particles. In order to contribute to improving the dispersibility of the conductive fine particles in the dispersion liquid at the time, the aggregate of the conductive fine particles makes it difficult to form an abnormal current path, and the conductive fine particles existing around the insulating fine particles themselves Since the composition change of the particles accompanying oxidation does not occur, the electron emission characteristics are not affected. As a result, it is possible to further effectively extend the life of the pre-transfer charging device.

  Further, in the pre-transfer charging device of the present invention, in addition to the above configuration, when the fine particle layer contains the insulating fine particles and at least a basic dispersant, the basic dispersant has a steric repulsion effect. Thus, an electron pair donor for donating an electron pair may be introduced as a substituent into the polymer in which the insulating fine particles are dispersed.

  By having the polymer that disperses the insulating fine particles by the steric repulsion effect, the dispersibility of the insulating fine particles can be improved, and a uniform fine particle layer can be formed as the electron acceleration layer. Thereby, the production variation in an electron-emitting device can be suppressed few.

  However, there is an optimum value for the addition amount of such a basic dispersant, and when the addition amount is too large, the resistance component of the polymer portion of the basic dispersant makes it difficult for the current in the device to flow. As a result, there is a risk that electron emission from the electron-emitting device is reduced. On the other hand, if the addition amount is too small, a sufficient amount of current flowing through the electron acceleration layer cannot be obtained, and electron emission from the electron-emitting device cannot be obtained at all. The optimum addition amount of the basic dispersant is a design matter in relation to the insulating fine particles. By appropriately controlling this addition amount, sufficient electron emission from the electron-emitting device can be obtained.

  In order to solve the above problems, the pre-transfer charging device of the present invention includes an intermediate transfer unit that transfers a toner image on an image carrier to an intermediate transfer member, and a toner image on the intermediate transfer member. An image forming apparatus comprising: a transfer unit configured to transfer a toner image on the intermediate transfer body before transfer to the transfer material; and an electrode substrate, a thin film electrode, and the electrode An electron-emitting device having an electron acceleration layer sandwiched between a substrate and the thin-film electrode, and the electrode substrate and the thin-film electrode so that electrons are accelerated in the electron-acceleration layer and the electrons are emitted from the thin-film electrode A first voltage applying means for applying a voltage between the thin film electrode and a second voltage applying means for applying a voltage between the thin film electrode and the intermediate transfer body. The electron acceleration layer is arranged in a layered manner Consist formed insulator material, the insulator material has a plurality of openings through the thickness direction of the layer, it is characterized in that the opening conducting particles is accommodated.

  According to the above configuration, the electron-emitting device emits electrons from the thin film electrode, and the toner image on the intermediate transfer member is charged by the electrons. The electron-emitting device is composed of an insulating material formed in a layer shape, and the insulating material has a plurality of openings that penetrate in the thickness direction of the layer, and conductive fine particles are accommodated in the openings. It does not generate harmful substances such as ozone and NOx. Therefore, in an intermediate transfer type image forming apparatus, even when there is a variation in the charge amount in the toner image on the intermediate transfer member, or even when the charge amount in the toner image on the intermediate transfer member is small, the electron emission having the above configuration is performed. By using a pre-transfer charging device including an element, it is possible to uniformly charge the toner image on the intermediate transfer member without using ozone. Therefore, the pre-transfer charging device of the present invention can stably and safely transfer the toner image to the transfer material without causing a decrease in transfer efficiency or transfer unevenness when the toner image is transferred to the transfer material.

  Here, since the insulating substance formed in a layer form exists as a solid lump rather than an aggregate of fine particles, it functions as an insulator through which no current flows. On the other hand, in the portion where the conductive fine particles are accommodated in the opening, the surface resistance is lowered and the current easily flows only in that portion. Therefore, when a voltage is applied to the electron acceleration layer, electron emission occurs only in the portion where the conductive fine particles are accommodated in the opening. Further, in order to form this structure, it is not necessary to uniformly apply a dispersion in which fine particles are dispersed, so that an electron-emitting device having a larger area can be easily formed.

In the pre-transfer charging device of the present invention, in addition to the above configuration, the fine insulating material may contain at least one of SiO ₂ , Al ₂ O ₃ , and TiO ₂ , or may contain an organic polymer. . Alternatively, in the pre-transfer charging device of the present invention, in addition to the above configuration, the insulator substance may include at least one of SiO ₂ , Al ₂ O ₃ , and TiO ₂ , or may include an organic polymer. Good.

If the insulator material contains at least one of SiO ₂ , Al ₂ O ₃ , and TiO ₂ , or contains an organic polymer, the insulating properties of these materials are high. The resistance value can be adjusted to an arbitrary range. As the resistance value increases, it becomes difficult for the current in the electron-emitting device to flow, and the amount of electron emission decreases. On the other hand, as the resistance decreases, electrons are conducted without accelerating and the amount of emitted electrons is reduced. Therefore, by adjusting the resistance value, it is possible to control the current and electron acceleration in the electron-emitting device, and to control the electron emission amount. In addition, when an oxide (SiO ₂ , Al ₂ O ₃ , and TiO ₂ ) is used as the insulator material, it is difficult to cause element deterioration due to oxidation by oxygen in the atmosphere. It can be operated stably even at atmospheric pressure.

  Further, in the pre-transfer charging device of the present invention, in addition to the above-described configuration, when the electron acceleration layer includes at least the conductive fine particles, the conductive fine particles may be a conductor having high anti-oxidation power. Good. Here, the high antioxidant power means that the oxide forming reaction is low. In general, the larger the negative value ΔG [kJ / mol] value of the oxide formation free energy obtained by thermodynamic calculation, the easier the oxide formation reaction occurs. In the present invention, a metal element corresponding to ΔG> −450 [kJ / mol] or more corresponds to conductive fine particles having a high antioxidant power. In addition, the conductive fine particles in a state in which an oxide generation reaction is more difficult to occur by attaching or coating an insulating material smaller than the size of the conductive fine particles around the corresponding conductive fine particles have anti-oxidation power. Included in high conductive particles.

  The electron acceleration layer is a thin film layer in which an insulating substance and conductive fine particles having high antioxidation power are densely assembled, and has semiconductivity. When a voltage is applied to the semiconductive electron acceleration layer, a current flows in the electron acceleration layer, and a part thereof is emitted as ballistic electrons by the strong electric field formed by the applied voltage.

  According to the above configuration, since the conductive material having high antioxidation power is used as the conductive fine particles, it is difficult for the device to deteriorate due to oxidation by oxygen in the atmosphere, so that the electron-emitting device can be operated stably even at atmospheric pressure. it can. Therefore, the life of the pre-transfer charging device can be extended, and continuous operation can be performed for a long time even in the atmosphere.

  In the pre-transfer charging apparatus of the present invention, in addition to the above configuration, the conductive fine particles may be a noble metal. Thus, since the conductor which comprises the said conductive fine particle is a noble metal, element deterioration including the oxidation of the conductive fine particle by the oxygen in air | atmosphere etc. can be prevented. Therefore, the lifetime of the pre-transfer charging device can be extended.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the conductive fine particles may contain at least one of gold, silver, platinum, palladium, and nickel.

  Since the tunnel effect is hindered when the oxide film of the conductive fine particles becomes thick, the conductor constituting the conductive fine particles needs to be a metal that is difficult to oxidize. Therefore, when the conductive fine particles contain at least one of gold, silver, platinum, nickel, and palladium, oxidation by oxygen in the atmosphere can be more effectively prevented. Therefore, the lifetime of the pre-transfer charging device can be extended more effectively.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, a small insulator material that is an insulator material smaller than the size of the conductive fine particles may be present around the conductive fine particles. Thus, the presence of a small insulator around the above-mentioned electro fine particles contributes to the improvement of the dispersibility of the conductive fine particles in the dispersion at the time of creating the electron-emitting device, and the conductive fine particles in the atmosphere. Degradation of the electron-emitting device such as oxidation by oxygen can be prevented more effectively. Therefore, the lifetime of the pre-transfer charging device can be extended more effectively.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the small insulator material may include at least one of alcoholate, fatty acid, and alkanethiol. If the small insulator material contains at least one of an alcoholate, a fatty acid, and an alkanethiol, it contributes to improving the dispersibility of the conductive fine particles in the dispersion at the time of forming the electron-emitting device. In addition to making it difficult for the current collector to form an abnormal current path, the composition of the particles due to the oxidation of the conductive fine particles existing around the insulator material does not change, so the electron emission characteristics are not affected. . Therefore, the lifetime of the pre-transfer charging device can be extended more effectively.

  Here, in the pre-transfer charging device of the present invention, the small insulator substance adheres to the surface of the conductive fine particles and exists as an attached substance, and the attached substance is smaller than the average particle diameter of the conductive fine particles. The conductive fine particle surface may be coated as an aggregate of shapes. As described above, the surface of the conductive fine particles is coated on the surface of the conductive fine particles or as an aggregate having a shape smaller than the average particle diameter of the conductive fine particles. In order to contribute to improving the dispersibility of the conductive fine particles in the dispersion liquid at the time, the aggregate of the conductive fine particles makes it difficult to form an abnormal current path based on the original, and the conductive fine particles existing around the insulator substance itself Since the composition change of the particles accompanying oxidation does not occur, the electron emission characteristics are not affected. As a result, it is possible to further effectively extend the life of the pre-transfer charging device.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the conductive fine particles preferably have an average particle size of 3 to 10 nm. Thus, when the average particle diameter of the conductive fine particles is preferably 3 to 10 nm, a conductive path is not formed by the conductive fine particles in the electron acceleration layer, and dielectric breakdown does not easily occur in the electron acceleration layer. Become. Although there are many unclear points in principle, ballistic electrons are efficiently generated by using conductive fine particles having an average particle diameter within the above range.

  In the pre-transfer charging device of the present invention, in addition to the above configuration, the thin film electrode may contain at least one of gold, silver, carbon, tungsten, titanium, aluminum, and palladium. By including at least one of gold, silver, carbon, tungsten, titanium, aluminum, and palladium in the thin film electrode, these materials have a low work function, so that electrons generated in the electron acceleration layer are efficiently tunneled. More high-energy electrons can be emitted outside the electron-emitting device.

In order to solve the above problems, an image processing apparatus according to the present invention includes an intermediate transfer unit that transfers a toner image on an image carrier to an intermediate transfer member;
Transfer means for transferring the toner image on the intermediate transfer member to a transfer material; and any one pre-transfer charging device for charging the toner image on the intermediate transfer member before being transferred to the transfer material; It is characterized by having.

  According to the above configuration, since the toner image on the intermediate transfer member is charged by the pre-transfer charging device of the present invention, it can be uniformly charged without ozone, and can be stably transferred onto the transfer material. An image forming apparatus capable of obtaining a quality image can be provided.

  As described above, the pre-transfer charging device according to the present invention includes an electrode substrate, a thin film electrode, an electron acceleration layer sandwiched between the electrode substrate and the thin film electrode, and the electron acceleration layer. The first voltage applying means for applying a voltage between the electrode substrate and the thin film electrode so that the electrons are accelerated and emitted from the thin film electrode, and between the thin film electrode and the intermediate transfer body. And a second voltage applying means for applying a voltage to the thin film electrode, the thin film electrode being arranged to face the intermediate transfer member, and the electron acceleration layer comprising a fine particle layer containing insulating fine particles.

  According to the above configuration, the electron-emitting device emits electrons from the thin film electrode, and the toner image on the intermediate transfer member is charged by the electrons. This electron-emitting device has a configuration including an electron acceleration layer composed of a fine particle layer containing insulating fine particles, and does not generate harmful substances such as ozone and NOx. Therefore, in an intermediate transfer type image forming apparatus, even when there is a variation in the charge amount in the toner image on the intermediate transfer member, or even when the charge amount in the toner image on the intermediate transfer member is small, the electron emission having the above configuration is performed. By using a pre-transfer charging device including an element, it is possible to uniformly charge the toner image on the intermediate transfer member without using ozone. Therefore, the pre-transfer charging device of the present invention can stably and safely transfer the toner image to the transfer material without causing a decrease in transfer efficiency or transfer unevenness when the toner image is transferred to the transfer material.

  Here, in the pre-transfer charging device of the present invention, since the electron acceleration layer is composed of a fine particle layer containing insulating fine particles, the average particle diameter of the insulating fine particles and the number of particles of the insulating fine particles (electron acceleration layer) A device capable of emitting a stable and good amount of electrons can be easily obtained by a simple method of controlling the film thickness. In addition, since the structure is composed of a fine particle layer containing insulating fine particles, for example, the electron acceleration layer can be easily formed by a simple manufacturing process of applying a fine particle dispersion. Furthermore, in the pre-transfer charging device of the present invention, the electron emission element can control the electron emission characteristics by the average particle diameter of the insulating fine particles and the number of particles of the insulating fine particles (the film thickness of the electron acceleration layer). is there.

  In addition, as described above, the pre-transfer charging device of the present invention includes an electron emission element having an electrode substrate, a thin film electrode, and an electron acceleration layer sandwiched between the electrode substrate and the thin film electrode, and the electron acceleration layer. The first voltage applying means for applying a voltage between the electrode substrate and the thin film electrode so that the electrons are accelerated and emitted from the thin film electrode, and the thin film electrode and the intermediate transfer body A second voltage applying means for applying a voltage therebetween, wherein the thin film electrode is disposed to face the intermediate transfer body, and the electron acceleration layer is made of an insulating material formed in a layer shape, The insulator substance has a plurality of openings penetrating in the thickness direction of the layer, and conductive fine particles are accommodated in the openings.

  According to the above configuration, the electron-emitting device emits electrons from the thin film electrode, and the toner image on the intermediate transfer member is charged by the electrons. The electron-emitting device is composed of an insulating material formed in a layer shape, and the insulating material has a plurality of openings that penetrate in the thickness direction of the layer, and conductive fine particles are accommodated in the openings. It does not generate harmful substances such as ozone and NOx. Therefore, in an intermediate transfer type image forming apparatus, even when there is a variation in the charge amount in the toner image on the intermediate transfer member, or even when the charge amount in the toner image on the intermediate transfer member is small, the electron emission having the above configuration is performed. By using a pre-transfer charging device including an element, it is possible to uniformly charge the toner image on the intermediate transfer member without using ozone. Therefore, the pre-transfer charging device of the present invention can stably and safely transfer the toner image to the transfer material without causing a decrease in transfer efficiency or transfer unevenness when the toner image is transferred to the transfer material.

  Here, since the insulating substance formed in a layer form exists as a solid lump rather than an aggregate of fine particles, it functions as an insulator through which no current flows. On the other hand, in the portion where the conductive fine particles are accommodated in the opening, the surface resistance is lowered and the current easily flows only in that portion. Therefore, when a voltage is applied to the electron acceleration layer, electron emission occurs only in the portion where the conductive fine particles are accommodated in the opening. Further, in order to form this structure, it is not necessary to uniformly apply a dispersion in which fine particles are dispersed, so that an electron-emitting device having a larger area can be easily formed.

1 is a schematic diagram illustrating a partial configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration of a pre-transfer charging device provided in the image forming apparatus. It is a perspective sectional view of an electron-emitting device provided in the pre-transfer charging device. It is an enlarged view of the electron acceleration layer of the electron-emitting device of one Embodiment of this invention. It is an enlarged view of the electron acceleration layer of the electron-emitting device of another embodiment of this invention. It is an enlarged view of the electron acceleration layer of the electron-emitting device of further another embodiment of this invention.

  Embodiments of the present invention will be described below with reference to FIGS. Note that the embodiments and examples described below are merely specific examples of the present invention, and the present invention is not limited thereto.

(Configuration of image forming apparatus)
FIG. 1 is a cross-sectional view schematically showing a configuration in the vicinity of an intermediate transfer belt (intermediate transfer member) 21 of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 is a so-called tandem type and intermediate transfer type printer, and can form a full-color or monochrome image on a sheet material (transfer material) P in accordance with transmitted image information. The image forming apparatus 10 may be a multifunction machine having both a copying function, a printer function, and a facsimile function. In this case, the image forming apparatus 10 has three types of printing modes, ie, a copier mode (copy mode), a printer mode, and a FAX mode, and an operation input from an operation unit (not shown), a personal computer, a portable terminal device, and information One of the print modes is selected by a control unit (not shown) in response to reception of a print job from an external device using a recording storage medium or a memory device.

  The image forming apparatus 10 includes a toner image forming unit 1 and a transfer unit having a primary transfer unit 4 and a secondary transfer unit 2. In addition, the image forming apparatus 10 includes an optical system unit, a paper feed unit, and the like, and further includes a housing that accommodates these members, but a description thereof is omitted.

  Four toner image forming units 1 are provided to correspond to the image information of each color of black (b), cyan (c), magenta (m), and yellow (y) included in the color image information. Each of the four toner image forming units 1 includes a photoreceptor 11, a charging unit 12, a developing unit 13, and a cleaning unit 14. Each developing unit 13 accommodates toner of each color of black, cyan, magenta, and yellow. In this embodiment, a negatively charged minus toner is used as the toner. Note that the charging unit 12 may be configured to include the electron-emitting device 30 as in the pre-transfer charging device 3 described later.

  The transfer unit is disposed above the photosensitive member 11, and includes an intermediate transfer belt (intermediate transfer member) 21, a drive roller (transfer unit) 22, a drive roller 23, a primary transfer roller (intermediate transfer unit) 24, and a transfer belt cleaning unit 25. And a secondary transfer roller (transfer means) 26. A region where the toner image is transferred to the intermediate transfer belt 21 by the primary transfer roller 24 is the primary transfer unit 4, and a region where the toner image is transferred to the sheet material P by the secondary transfer roller 26 is the secondary transfer unit 2. . As shown in FIG. 2, a pre-transfer charging device 3 having an electron emitting element 30 for charging the toner image T on the intermediate transfer belt 21 is provided on the upstream side of the secondary transfer unit 2 in the sheet material conveyance direction. ing. The pre-transfer charging device 3 will be described in detail later.

  The intermediate transfer belt 21 is an endless belt-like member that is stretched by driving rollers 22 and 23 to form a loop-like movement path. The intermediate transfer belt 21 is rotationally driven in the direction of arrow A in FIG. The intermediate transfer belt 21 is semiconductive. There are no particular limitations on the intermediate transfer belt 21, and a semiconductive intermediate transfer belt used in a general image forming apparatus can be used. As the intermediate transfer belt 21, for example, a polyimide film or a polycarbonate film containing carbon black as a conductive agent can be used.

  The image forming process by the image forming apparatus 10 is as follows. First, after the charging unit 12 uniformly charges the surface of the photoconductor 11, an optical system unit (not shown) exposes the surface of the charged photoconductor 11 with a laser according to image information to form an electrostatic latent image. Subsequently, the developing means 13 develops the electrostatic latent image on the photoconductor 11 with toner, and the primary transfer roller 24 to which a bias voltage having a polarity opposite to that of the toner is applied is obtained by developing the toner image. Transfer is performed on the intermediate transfer belt 21. As a result, the respective toner images of black, cyan, magenta, and yellow are transferred onto the intermediate transfer belt 21.

  Thereafter, the toner image T on the intermediate transfer belt 21 is uniformly charged by the pre-transfer charging device 3 and further conveyed to the secondary transfer unit 2 and separately fed from a sheet feeding unit (not shown). Are collectively transferred.

  Further, a fixing device (not shown) is provided downstream of the secondary transfer unit 2, and the toner image T is fixed to the sheet material P. Alternatively, at least one of the driving roller 22 and the secondary transfer roller 26 may have a heat source, and the secondary transfer unit 2 may perform secondary transfer and fixing at the same time. Thereafter, the sheet material P on which the toner image T is transferred and fixed is discharged to the outside. Thus, the image forming process is completed.

(Pre-transfer charging device)
Next, the pre-transfer charging device 3 will be described. FIG. 2 is a cross-sectional view schematically showing the configuration of the pre-transfer charging device 3. The pre-transfer charging device 3 includes an electron-emitting device 30 including an electrode substrate 301, a thin film electrode 302, and an electron acceleration layer 303, a first power source (first voltage applying unit) V1, and a second power source (second voltage applying unit). ) V2. The electron acceleration layer 303 exists between the electrode substrate 301 and the thin film electrode 302. The first power source V1 applies a voltage between the electrode substrate 301 and the thin film electrode 302, accelerates electrons in the electron acceleration layer 303 of the electron emitter 30 and emits electrons from the thin film electrode 302. Used for. The second power source V2 applies a voltage between the thin film electrode 302 and the intermediate transfer belt 21, and is used to apply electrons emitted from the thin film electrode 302 to the toner image on the intermediate transfer belt 21. .

  Here, as shown in FIG. 2, in the present embodiment, the electron-emitting device 30 is provided 5 mm below (away from) the intermediate transfer belt 21. That is, the electron emission surface of the thin film electrode 302 is disposed to face the toner image forming surface of the intermediate transfer belt 21.

  FIG. 3 is a perspective sectional view of the electron-emitting device 30 provided in the pre-transfer charging device 3. FIG. 4 is an enlarged schematic view of the electron acceleration layer 303 of the electron emitter 30. The electron acceleration layer 303 is composed of a fine particle layer including insulator fine particles 306. In the electron-emitting device 30 a according to another embodiment of the present invention, as shown in FIG. 5, the electron acceleration layer 303 a includes a fine particle layer including insulating fine particles 306, and the fine particle layer may include conductive fine particles 307. Good. In the electron-emitting device 30b according to still another embodiment of the present invention, as shown in FIG. 6, the electron acceleration layer 303b is composed of a fine particle layer containing insulating fine particles 306, and this fine particle layer is composed of a basic dispersant 60. May be included. Further, the fine particle layer including the insulating fine particles 306 may include the conductive fine particles 307 and the basic dispersant 60.

  As shown in FIG. 2, the electron-emitting device 30 (30a and 30b and below are omitted) causes a current to flow between the electrode substrate 301 and the thin-film electrode 302, that is, the electron acceleration layer 303, by the first power source V1. The thin film electrode 302 is transmitted or emitted from the gap between the thin film electrodes 302 as ballistic electrons by a strong electric field formed by an applied voltage. Then, electrons emitted by the voltage applied from the second power source V2 are attracted to the intermediate transfer belt 21 side.

  The applied voltage from the first power source V1 is not limited as long as electrons are stably emitted from the electron-emitting device 30 and has a charging effect, and the amount of electron emission depends on the process speed of the image forming apparatus and the second power source V2. Control may be performed in accordance with the applied voltage from.

  The applied voltage from the second power source V2 is set in accordance with the potential of the toner surface layer of the toner image formed on the intermediate transfer belt 21. Here, when the electron-emitting device 30 is disposed, the distance between the intermediate transfer belt 21 and the thin film electrode 302 is particularly a distance that allows electrons emitted from the thin film electrode 302 to be applied to the intermediate transfer belt 21. Not limited. However, it is preferable that the distance is small to increase the electric field strength between the intermediate transfer belt 21 and the thin film electrode 302. For example, the distance is preferably 5 to 10 mm.

  The electrode substrate 301 serves as a support for the electron-emitting device. Therefore, any material can be used without particular limitation as long as it has a certain degree of strength, has good adhesion to a directly contacting substance, and has appropriate conductivity. Examples thereof include metal substrates such as SUS, Ti, and Cu, semiconductor substrates such as Si, Ge, and GaAs, insulator substrates such as glass substrates, and plastic substrates. For example, if an insulator substrate such as a glass substrate is used, it can be used as an electrode substrate by attaching a conductive material such as a metal to the interface with the electron acceleration layer 303 as an electrode. The conductive material is not particularly limited as long as a noble metal material excellent in conductivity can be formed into a thin film using magnetron sputtering or the like. An ITO thin film widely used for transparent electrodes is also useful as an oxide conductive material. In addition, for example, a metal thin film in which a Ti film having a thickness of 200 nm is formed on the surface of a glass substrate and a Cu film having a thickness of 1000 nm may be used may be used because a tough thin film can be formed. However, it is not limited to these materials and numerical values.

  The thin film electrode 302 applies a voltage in the electron acceleration layer 303. Therefore, any material that can be applied with voltage can be used without particular limitation. However, from the viewpoint of transmitting electrons that have been accelerated and become high energy in the electron acceleration layer 303 with as little energy loss as possible, if the material has a low work function and can form a thin film, it is higher. The effect can be expected. Examples of such a material include gold, silver, carbon, tungsten, titanium, aluminum, palladium, and the like whose work function corresponds to 4 to 5 eV. In particular, assuming operation at atmospheric pressure, gold without oxide and sulfide formation reaction is the best material. In addition, silver, palladium, tungsten, and the like, which have a relatively small oxide formation reaction, are materials that can withstand actual use without problems.

  The film thickness of the thin film electrode 302 is important as a condition for efficiently emitting electrons from the electron-emitting device 30 to the outside, and is preferably in the range of 10 to 100 nm. The minimum film thickness for causing the thin film electrode 302 to function as a planar electrode is 10 nm. If the film thickness is less than this, electrical conduction cannot be ensured. On the other hand, the maximum film thickness for emitting electrons from the electron-emitting device 30 to the outside is 100 nm. When the film thickness exceeds this value, no ballistic electrons are transmitted, and the thin-film electrode 302 absorbs ballistic electrons or the thin-film electrode 302. As a result, a phenomenon occurs in which the ballistic electrons are reflected and recaptured in the electron acceleration layer 303.

  The electron emission mechanism of the electron-emitting device 30 provided in the pre-transfer charging device 3 of the present invention is considered to be similar to the operation mechanism in a so-called MIM type electron-emitting device in which an insulator layer is inserted between two conductor films. It is done. In the MIM type electron-emitting device, when an electric field is applied to the insulator layer, a general mechanism for forming a current path is as follows: a) diffusion of electrode material into the insulator layer, b) insulator material C) formation of a conductive path called a filament, d) stoichiometric deviation of the insulator material, e) trapping of electrons due to defects in the insulator material, and local formation of the trapped electrons Various theories such as a strong electric field region have been considered, but are not clear. For any reason, according to the configuration of the electron-emitting device 30 provided in the pre-transfer charging device 3 of the present invention, an electric field is applied to the electron acceleration layer 303 formed of a fine particle layer including the insulating fine particles 306 corresponding to the insulating layer. As a result of the formation of such a current path and a part of the current accelerated by an electric field, ballistic electrons are formed, and a thin film which is one of the electrode substrate 301 and the thin film electrode 302 corresponding to two conductor films. It is considered that electrons pass through the electrode 302 and are emitted out of the device.

  Further, in the electron acceleration layers 303a and 303b of the electron-emitting devices 30a and 30b in which at least one of the conductive fine particles 307 and the basic dispersant 60 is included in the fine particle layer shown in FIGS. It is thought that when an electric field is applied to the acceleration layers 303a and 303b, a current path is formed by the following mechanism.

  The electron acceleration layer 303a including the conductive fine particles 307 is a thin film layer in which the insulating fine particles 306 and the conductive fine particles 307 are densely assembled, and has semiconductivity. When a voltage is applied to the semiconductive electron acceleration layer 303a, a current flows in the electron acceleration layer 303a, and a part thereof is emitted as ballistic electrons by the strong electric field formed by the applied voltage.

  On the other hand, in the electron acceleration layer 303b configured to include the basic dispersant 60, the mechanism of electron emission has not been clearly analyzed, but by applying a voltage between the electrode substrate 301 and the thin film electrode 302, the electron emission layer 303b A current flows in the acceleration layer 303b, and a part of the current becomes ballistic electrons due to a strong electric field formed by the applied voltage, and is emitted from the thin film electrode 302 side. Here, it is presumed that electrons are emitted from the electron-emitting device 30b because an electron-pair donor that donates an electron pair included in the basic dispersant 60 is acting. That is, the basic dispersant 60 has an electron pair donor that donates an electron pair, and the electron pair donor ionizes after donating the electron pair. It is considered that this ionized electron pair donor transfers charges on the surface of the attached insulating fine particles 306, and electrical conduction is possible on the surface of the insulating fine particles 306.

  Hereinafter, the configuration of the electron acceleration layers 303, 303a, and 303b will be described.

(Electron acceleration layer 1)
As shown in FIG. 4, the electron acceleration layer 303 is formed of a fine particle layer including insulator fine particles 306.

The insulator fine particles 306 can be used without any particular limitation as long as the material has insulating properties. Materials of the insulating fine particles _{306, SiO 2, Al 2 O 3} , things like TiO ₂ becomes practical. However, using small-sized silica particles with surface treatment increases the surface area of the silica particles in the solvent and increases the solution viscosity compared to using spherical silica particles with a larger particle diameter. Therefore, the thickness of the electron acceleration layer 303 tends to increase slightly. Further, as the insulating fine particles 306, fine particles made of an organic polymer may be used. As fine particles made of organic polymer, for example, highly crosslinked fine particles (SX8743) made of styrene / divinylbenzene manufactured and sold by JSR Corporation, and fine sphere series of styrene / acrylic fine particles produced and sold by Nippon Paint Co., Ltd. can be used. is there. Further, as the insulating fine particles 306, two or more kinds of particles having different materials may be used, or particles having different particle size peaks may be used. Further, as the insulating fine particles 306, single particles having a broad particle size distribution may be used.

  The average particle diameter of the insulating fine particles 306 is preferably 7 to 400 nm when the electron acceleration layer 303 includes the insulating fine particles 306 and does not include conductive fine particles. As described later, the thickness of the electron acceleration layer 303 is preferably 1000 nm or less. However, when the average particle diameter of the insulating fine particles 306 is larger than 400 nm, the layer thickness of the electron acceleration layer 303 is controlled to an appropriate thickness. Difficult to do. Therefore, the average particle diameter of the insulating fine particles 306 is preferably within the above range. In this case, the dispersion state of the particle diameter may be broad with respect to the average particle diameter. For example, fine particles having an average particle diameter of 50 nm may have a particle diameter distribution in the region of 20 to 100 nm. Absent.

  The insulating fine particles 306 may be surface-treated. This surface treatment may be a treatment with silanol or silyl group. When the electron acceleration layer 303 is produced, when the insulating fine particles 306 are dispersed in an organic solvent and applied to the electrode substrate, the surface of the particles is treated with silanol and silyl groups, so that the dispersibility in the organic solvent is improved. Thus, the electron acceleration layer 303 in which the insulating fine particles 306 are uniformly dispersed can be easily obtained. Further, since the insulating fine particles 306 are uniformly dispersed, an electron acceleration layer having a thin layer thickness and high surface smoothness can be formed, and a thin film electrode thereon can be formed thin. As described above, the thinner the thin film electrode 302 can secure electric conduction, the more efficiently electrons can be emitted.

  When the electron acceleration layer 303 includes the insulating fine particles 306 and does not include the conductive fine particles, the thickness of the electron acceleration layer 303 is preferably not less than the average particle diameter of the insulating fine particles 306 and not more than 1000 nm. . The thinner the electron acceleration layer 303 is, the easier it is for current to flow, but since the insulator fine particles 306 of the electron acceleration layer 303 do not overlap and are evenly spread on the electrode substrate 301, it is the minimum. The minimum layer thickness of the electron acceleration layer 303 is the average particle diameter of the insulating fine particles 306 constituting the electron acceleration layer 303. When the layer thickness of the electron acceleration layer 303 is smaller than the average particle diameter of the insulator fine particles 306, it means that there is a portion in the electron acceleration layer 303 where the insulator fine particles 306 are not present, and functions as an electron acceleration layer. do not do. Therefore, the above range is preferable as the lower limit value of the thickness of the electron acceleration layer 303. A more preferable value of the lower limit layer thickness of the electron acceleration layer 303 is considered to be a state in which two to three or more insulator fine particles are stacked. The reason is that if the electron acceleration layer 303 has a thickness equivalent to one constituent particle, the amount of current flowing through the electron acceleration layer 303 increases, but the leakage current increases and the electric field applied to the electron acceleration layer 303 becomes weak. This is because electrons cannot be efficiently emitted. On the other hand, if the thickness is larger than 1000 nm, the resistance of the electron acceleration layer 303 increases, and a sufficient current does not flow, so that a sufficient electron emission amount cannot be obtained.

  Note that the layer thickness of the electron acceleration layer 303 is controlled by the particle size of the insulating fine particles 306 and the concentration (viscosity) of the dispersion liquid in which the insulating fine particles 306 are dispersed in a solvent. .

  The electron emission mechanism of the electron-emitting device 30 having the electron acceleration layer 303 including the insulating fine particles 306 and not including the conductive fine particles will be described. Although the electron emission mechanism of the electron-emitting device 30 is not clear, it can be explained as follows by using the interpretation of e) above, for example, from the above-described five conductive path formation mechanisms a) to e). . When a voltage is applied between the electrode substrate 301 and the thin film electrode 302, electrons move from the electrode substrate 301 to the surface of the insulating fine particles 306. Since the inside of the insulating fine particles 306 has a high resistance, electrons are conducted through the surface of the insulating fine particles 306. At this time, electrons are trapped at impurities on the surface of the insulating fine particles 306, oxygen defects that may be generated when the insulating fine particles 306 are oxides, or contacts between the insulating fine particles 306. The trapped electrons work as fixed charges. As a result, in the vicinity of the thin film electrode 302 of the electron acceleration layer 303, the applied voltage and the electric field created by the trapped electrons are combined to form a high electric field region locally, and the high electric field accelerates the electrons. It is thought that electrons are emitted.

  Next, an embodiment of a method for manufacturing the electron-emitting device 30 having the electron acceleration layer 303 including the insulator fine particles 306 and not including the conductive fine particles will be described. First, an insulating fine particle dispersion A in which the insulating fine particles 306 are dispersed in a solvent is obtained. The solvent used here can be used without particular limitation as long as the insulating fine particles 306 can be dispersed and dried after coating. For example, toluene, benzene, xylene, hexane, methanol, ethanol, propanol or the like can be used. it can.

  Then, the insulating fine particle dispersion A prepared as described above is applied onto the electrode substrate 301 by using a spin coating method to form the electron acceleration layer 303. A predetermined film thickness can be obtained by repeating film formation and drying by a spin coating method a plurality of times. The electron acceleration layer 303 can be formed by a method such as a dropping method or a spray coating method in addition to the spin coating method.

  After the formation of the electron acceleration layer 303, a thin film electrode 302 is formed on the electron acceleration layer 303. For forming the thin film electrode 302, for example, a magnetron sputtering method may be used. Further, the thin film electrode 302 may be formed using, for example, an ink jet method, a spin coating method, a vapor deposition method, or the like.

(Electron acceleration layer 2)
As another form of the electron acceleration layer according to the present invention, FIG. 5 shows a schematic diagram of an electron acceleration layer 303 a including insulator fine particles 306 and conductive fine particles 307.

  As the material of the conductive fine particles 307, any conductor can be used on the principle of operation of generating ballistic electrons. However, if the conductor has a high anti-oxidation power, it is possible to avoid oxidative degradation when operated at atmospheric pressure. Here, the high antioxidant power means that the oxide forming reaction is low. In general, the larger the negative value ΔG [kJ / mol] value of the oxide formation free energy obtained by thermodynamic calculation, the easier the oxide formation reaction occurs. In the present invention, a metal element corresponding to ΔG> −450 [kJ / mol] or more corresponds to conductive fine particles having a high antioxidant power. In addition, the conductive fine particles in a state in which an oxide generation reaction is more difficult to occur by attaching or coating an insulating material smaller than the size of the conductive fine particles around the corresponding conductive fine particles have anti-oxidation power. Included in high conductive particles. The conductive fine particles having high anti-oxidation power can prevent device deterioration such as oxidation of the conductive fine particles by oxygen in the atmosphere. Therefore, the lifetime of the electron-emitting device can be extended.

  Examples of the conductive fine particles having high anti-oxidation power include materials such as noble metals such as gold, silver, platinum, palladium, and nickel. Such conductive fine particles 307 can be prepared using a known fine particle production technique such as sputtering or spray heating, and also use commercially available metal fine particle powders such as silver nanoparticles produced and sold by Applied Nano Laboratory. Is possible. The principle of ballistic electron generation will be described later.

  Here, the average particle diameter of the conductive fine particles 307 is more preferably 3 to 10 nm. As described above, by setting the average particle diameter of the conductive fine particles 307 to preferably 3 to 10 nm, the conductive path by the conductive fine particles 307 is not formed in the electron acceleration layer 303a, and the dielectric breakdown in the electron acceleration layer 303a is performed. Is less likely to occur. Although there are many unclear points in principle, ballistic electrons are efficiently generated by using the conductive fine particles 307 having an average particle diameter within the above range.

  The proportion of the conductive fine particles 307 in the entire electron acceleration layer 303a is preferably 0.5 to 30% by weight. When the amount is less than 0.5% by weight, the effect of increasing the current in the device as conductive fine particles is not exhibited, and when the amount is more than 30% by weight, aggregation of the conductive fine particles occurs. Especially, it is more preferable that it is 1 to 10 weight%.

  Note that a small insulator material that is an insulator material smaller than the size of the conductive fine particles 307 may exist around the conductive fine particles 307, and the small insulator material adheres to the surface of the conductive fine particles 307. The substance may be a substance, and the attached substance may be an insulating film that coats the surface of the conductive fine particles 307 as an aggregate having a shape smaller than the average particle diameter of the conductive fine particles 307. As the small insulator material, any insulator material can be used on the principle of operation of generating ballistic electrons. However, when the insulating material smaller than the size of the conductive fine particles 307 is an insulating film that coats the conductive fine particles 307, and the insulating film is covered by the oxide film of the conductive fine particles 307, the thickness of the oxide film due to oxidative degradation in the atmosphere. In order to avoid oxidative degradation when operated at atmospheric pressure, an insulating film made of an organic material is preferable. For example, materials such as alcoholate, fatty acid, and alkanethiol are listed. It is done. It can be said that the thinner the insulating coating, the more advantageous.

  In addition, the conductive fine particles 307 are preferably subjected to a surface treatment in order to improve dispersibility when preparing a dispersion of the conductive fine particles 307 in the manufacturing method described later, and the surface treatment is performed as described above. It may be to coat a substance.

  The configuration and the like of the insulator fine particles 306 may be the same as described above. However, when the electron acceleration layer 303a includes the insulator fine particles 306 and the conductive fine particles 307, the average particle size of the insulator fine particles 306 is 10 to 1000 nm. It is preferable that it is 12-110 nm.

  In addition, when the voltage applied between the electrode substrate 301 and the thin film electrode 302 is the same, a stronger electric field is applied to the electron acceleration layer 303a as the layer thickness is thinner. Therefore, by reducing the thickness of the electron acceleration layer 303a, electrons can be accelerated by applying a strong electric field while keeping the voltage applied between the electrode substrate 301 and the thin film electrode 302 low. On the other hand, the layer thickness of the electron acceleration layer 303a needs to be able to make the layer thickness uniform and to adjust the resistance of the acceleration layer in the layer thickness direction. In view of these, the thickness of the electron acceleration layer 303a is preferably 12 to 6000 nm, and more preferably 300 to 6000 nm.

  Note that when the electron acceleration layer 303a includes the conductive fine particles 307, the electrical conductivity of the surface of the insulator fine particles 306 by the conductive fine particles 307 is improved, and thus the conductivity of the element can be easily controlled.

  The principle of electron emission of the electron-emitting device 30a having such an electron acceleration layer 303a will be described with reference to FIG. As shown in FIG. 5, most of the fine particle layer constituting the electron acceleration layer 303a is composed of insulating fine particles 306, and conductive fine particles 307 are scattered in the gaps. The ratio between the insulating fine particles 306 and the conductive fine particles 307 is such that the weight ratio of the insulating fine particles 306 to the total weight of the insulating fine particles 306 and the conductive fine particles 307 corresponds to, for example, 80%.

  As described above, the electron acceleration layer 303a includes the insulating fine particles 306 and the small number of conductive fine particles 307, and thus has semiconductivity. Therefore, when a voltage is applied to the electron acceleration layer 303a, a very weak current flows. The voltage-current characteristic of the electron acceleration layer 303a shows a so-called varistor characteristic, and the current value is rapidly increased as the applied voltage increases. Part of this current becomes ballistic electrons due to a strong electric field in the electron acceleration layer 303a formed by the applied voltage, and is transmitted through the thin film electrode 302 or passed through the gap to be emitted to the outside of the electron-emitting device 30a. The formation process of ballistic electrons is thought to be due to electrons tunneling while being accelerated in the direction of the electric field, but it has not been determined.

  Next, an embodiment of a method for manufacturing the electron-emitting device 30a that enables electrical conduction on the surface of the insulating fine particles 306 with such conductive fine particles 307 will be described. First, a fine particle dispersion B in which insulating fine particles 306 and conductive fine particles 307 are dispersed on the electrode substrate 301 is obtained. Here, the solvent used in the dispersion can be used without particular limitation as long as the insulating fine particles 306 and the conductive fine particles 307 can be dispersed and dried after coating. For example, toluene, benzene, xylene, hexane, tetradecane, etc. Can be used. Further, for the purpose of improving the dispersibility of the conductive fine particles 307, an alcoholate treatment may be performed as a pretreatment.

  Then, the fine particle dispersion B prepared as described above is applied onto the electrode substrate 301 by using a spin coating method to form the electron acceleration layer 303a. A predetermined film thickness can be obtained by repeating film formation and drying by a spin coating method a plurality of times. The electron acceleration layer 303a can be formed by a method such as a dropping method or a spray coating method in addition to the spin coating method. Note that this method of manufacturing the electron acceleration layer is merely an embodiment, and may be manufactured by another method, for example, adding conductive fine particles on the insulating fine particle layer.

  After the formation of the electron acceleration layer 303a, a thin film electrode 302 is formed on the electron acceleration layer 303a. The film formation of the thin film electrode 302 is the same as described above.

(Electron acceleration layer 3)
As still another embodiment of the electron acceleration layer according to the present invention, FIG. 6 shows a schematic diagram of an electron acceleration layer 303b including insulating fine particles 306 and a basic dispersant 60.

  The basic dispersant 60 is for preventing the aggregation of the insulating fine particles 306 in the solvent and dispersing the insulating fine particles 306, but here, the dispersion of the insulating fine particles 306 which are easily aggregated in the solvent is good. Thus, it has an original function as a dispersant that realizes formation of a very smooth fine particle layer on the surface of the electrode substrate 301 and a further function that enables electrical conduction on the surface of the insulating fine particles 306.

  The basic dispersant 60 has a polymer and an electron pair donor introduced into a part of the polymer. The polymer imparts dispersibility due to the steric repulsion effect. In FIG. 6, reference numeral 15 indicates a region that is formed between the insulating fine particles 306 and becomes a steric hindrance. The electron pair donor serves as an anchor that is adsorbed to the insulating fine particles 306. Further, the electron pair donor becomes a positive ion by donating an electron pair, and enables ion conduction. The function that enables electrical conduction on the surface of the insulating fine particles 306 is considered to be because the portion of the basic dispersant 60 that enables ionic conduction is transferring charges. In addition, since the ion conductive portions of the basic dispersant 60 repel each other electrically, they contribute to the dispersibility of the insulating fine particles.

  The electron-pair donor moiety is a specific substituent composed of an electron-donating group, and examples of the substituent include a phenyl group, a vinyl group, an alkyl group, and an amino group that are π-electron systems.

  Examples of commercially available basic dispersant 60 that can be applied to the present invention include trade names such as Solsperse 9000, 13240, 13940, 20000, 24000, 24000GR, 24000SC, 26000, 28000, 32550, 34750, and 31845 manufactured by Avicia. Various Solsperse dispersants, trade names manufactured by Big Chemie: Dispersic 106, 112, 116, 142, 161, 162, 163, 164, 165, 166, 181, 182, 183, 184, 185, 191, 2000, 2001, Product names manufactured by Ajinomoto Fine Techno Co., Ltd .: Addisper PB711, PB411, PB111, PB821, PB822, product names manufactured by Efka Chemicals Co., Ltd .: EFKA-47, 4050, and the like.

  The content of the basic dispersant 60 in the electron acceleration layer 303b is related to the ease of flow of the current in the electron-emitting device 30b, which has a correlation with the amount of electron emission, and is important in controlling the amount of electron emission. It is one of the control factors.

  The addition of the basic dispersant 60 to the electron acceleration layer 303b is performed in the process of dispersing the insulator fine particles 306 constituting the electron acceleration layer 303b in a solvent. In other words, the surface of the insulating fine particles 306 is obtained by adding the insulating fine particles 306 to the dispersant-containing solvent in which a necessary amount of the basic dispersant 60 is added to the solvent to be used and dispersing, and sufficiently dispersing the insulating fine particles 306. The basic dispersant 60 is adhered to the surface. The amount of the dispersant attached to the surface of the insulating fine particles 306 can be controlled by manipulating the amount of the dispersant added to the solvent. However, there is a one-to-one relationship between the input amount of the dispersant and the ease of current flow in the electron acceleration layer 303b obtained after the addition of the dispersant. . When the addition amount is small, the number of electrons is small, so that the amount of current flowing through the electron acceleration layer 303b is naturally small. On the other hand, when the addition amount is too large, the polymer component of the basic dispersant acts strongly as a resistance component against the current flowing through the element, and the current value is reduced.

  As described above, the addition amount of the basic dispersant 60 has an optimum value, and is optimally set in view of the amount of current flowing in the element. When the amount of the basic dispersant 60 added to the solvent is defined under the conditions in which the dispersed dispersion is dropped and the electron acceleration layer 303b is formed by spin coating, the addition amount is preferably 0.4 to 10 wt%. More preferably, it is 1-5 wt% or less.

  If the amount added to the solvent is less than 0.4 wt%, the amount of current flowing through the electron acceleration layer 303b cannot be obtained sufficiently, and there is a possibility that electron emission from the electron-emitting device cannot be obtained at all. When the content is more preferably 1 wt% or more, electron emission from the electron-emitting device can be stably obtained. On the other hand, if it exceeds the upper limit of the amount of addition, if it exceeds 10%, the resistance component of the polymer portion of the basic dispersant 60 makes it difficult for the current in the device to flow, reducing the electron emission from the electron-emitting device There is a risk of causing it. By setting the lower limit of the addition amount to be more preferably 5 wt% or less, there is an effect that the electron emission from the electron-emitting device 30b can be obtained without decreasing.

  In the electron-emitting device 30b that enables electrical conduction on the surface of the insulating fine particles 306 with the basic dispersant 60, the electron acceleration layer 303b can be formed even if the electron acceleration layer 303b is formed by an inexpensive manufacturing method such as spin coating. Thus, it is possible to provide the electron-emitting device 30b which is free from the risk of dielectric breakdown. Moreover, in dispersing the insulating fine particles in the solvent, the dispersing agent, which can be said to be an essential member, has the function of the fine particles such as metal, so that the manufacturing process can be reduced and the material cost can be reduced.

  The configuration and the like of the insulator fine particles 306 may be the same as described above. However, when the electron acceleration layer 303b includes the insulator fine particles 306 and the basic dispersant 60, the average particle diameter of the insulator fine particles 306 is 10 to 10. 1000 nm is preferable, and 12 to 110 nm is more preferable.

  The layer thickness of the electron acceleration layer 303b is preferably 12 to 6000 nm, and more preferably 300 to 2000 nm, like the electron acceleration layer 303a.

  The principle of electron emission in the electron-emitting device 30b that enables electrical conduction on the surface of the insulating fine particles 306 with such a basic dispersant 60 will be described with reference to FIG.

  As shown in FIG. 6, most of the electron acceleration layer 303 b is composed of the insulating fine particles 306, and the basic dispersant 60 is attached to the surface of the insulating fine particles 306. Thereby, the steric hindrance region 15 made of the basic dispersant 60 is formed on the surface of the insulating fine particles 306, and the insulating fine particles 306 are favorably dispersed in the solvent. The insulating fine particles 306 are insulative, but the ion accelerating portion of the basic dispersant 60 attached to the surface transfers charges, so that the electron acceleration layer 303b has semiconductivity. Therefore, when a voltage is applied between the electrode substrate 301 and the thin film electrode 302, a very weak current flows in the electron acceleration layer 303b. The voltage-current characteristic of the electron acceleration layer 303b shows a so-called varistor characteristic, and the current value is rapidly increased as the applied voltage increases. A part of this current becomes ballistic electrons due to the strong electric field in the electron acceleration layer 303b formed by the applied voltage, and passes (transmits) through the thin film electrode 302 or has a hole (gap) in the thin film electrode 302. From the hole, it is discharged to the outside. The formation process of free electrons is thought to be due to electrons tunneling while being accelerated in the direction of the electric field, but it has not been determined.

  Next, an embodiment of a manufacturing method of the electron-emitting device 30b that enables electrical conduction on the surface of the insulating fine particles 306 with such a basic dispersant 60 will be described. The basic dispersant 60 is added to the dispersion solvent, and the basic dispersant 60 is dispersed through an ultrasonic disperser, and then the insulating fine particles 306 are added, and the insulating fine particles 306 are dispersed again through the ultrasonic disperser. To obtain an insulating fine particle dispersion C. The dispersion method is not particularly limited, and the dispersion method may be performed by a method other than the ultrasonic disperser.

  Here, any dispersion solvent can be used without particular limitation as long as it has good compatibility with the basic dispersant 60, can effectively disperse the insulating fine particles 306, and evaporates after application. As the dispersion solvent, for example, toluene, benzene, xylene, hexane, tetradecane and the like can be used.

  Then, the insulating fine particle dispersion C prepared as described above is applied onto the electrode substrate 301 to form the electron acceleration layer 303b. As a coating method, for example, a spin coating method can be used. The insulating fine particle dispersion C is dropped on the electrode substrate 301, and a thin film to be the electron acceleration layer 303b is formed by using a spin coating method. A predetermined film thickness can be obtained by repeating the dropping of the insulating fine particle dispersion C onto the electrode substrate 301, film formation by spin coating, and drying a plurality of times. In addition to the spin coating method, for example, a dropping method, a spray coating method, or the like can be used for forming the electron acceleration layer 303b. In addition, the manufacturing method of this electron acceleration layer is only one embodiment, For example, you may manufacture by other methods, such as adding a basic dispersing agent on an insulator fine particle layer.

  Then, after the formation of the electron acceleration layer 303b, a thin film electrode 302 is formed on the electron acceleration layer 303b. The film formation of the thin film electrode 302 is the same as described above.

  As described above, in the pre-transfer charging device 3 of the present embodiment, the electron-emitting device 30 (30a, 30b) emits electrons from the thin film electrode, and the toner image on the intermediate transfer member is charged by the electrons. The electron-emitting device 30 (30a, 30b) has a configuration including an electron acceleration layer 303 (303a, 303b) composed of a fine particle layer containing insulating fine particles, and does not generate harmful substances such as ozone and NOx. Therefore, in the intermediate transfer type image forming apparatus 10, even when there is a variation in the charge amount in the toner image on the intermediate transfer member or when the charge amount in the toner image on the intermediate transfer member is small, By using the pre-transfer charging device 3 provided with the emission elements 30 (30a, 30b), the toner image on the intermediate transfer member can be uniformly charged without any ozone. Therefore, the pre-transfer charging device 3 of the present embodiment can stably and safely transfer the toner image to the transfer material without causing a decrease in transfer efficiency or transfer unevenness when the toner image is transferred to the transfer material. it can.

  In addition, since the image forming apparatus 10 of the present embodiment includes the pre-transfer charging device 3, the image forming apparatus 10 can stably transfer onto the transfer material and obtain a high-quality image.

  Here, in the above description, the electron acceleration layer has been described as being composed of a fine particle layer containing insulating fine particles. However, instead of the fine particle layer containing insulating fine particles, the electron acceleration layer is an insulating substance formed in a layer shape. The insulator substance may have a plurality of openings penetrating in the thickness direction of the layer, and conductive fine particles may be accommodated in the openings. Here, as the insulating material formed in layers, for example, a sheet substrate made of an organic polymer may be used. However, the sheet-like substrate needs to have a plurality of fine holes penetrating in the thickness direction. As a material satisfying such requirements, for example, a membrane filter new clipper (manufactured by polycarbonate) manufactured and sold by Whatman Japan Co., Ltd. is useful.

  In this case, the electron-emitting device is made of an insulating material formed in a layer shape, and the insulating material has a plurality of openings penetrating in the thickness direction of the layer, and conductive fine particles are accommodated in the openings. It is a structure and does not produce harmful substances such as ozone and NOx. Therefore, similarly to the above, it is possible to uniformly charge the toner image on the intermediate transfer member without using ozone. Therefore, the toner image can be stably and safely transferred to the transfer material without causing a decrease in transfer efficiency or transfer unevenness when the toner image is transferred to the transfer material.

  Examples and comparative examples according to the present invention are shown below.

(Example)
The electron-emitting device of the pre-transfer charging device of this example was manufactured as follows. SUS substrate as the electrode substrate 301, gold (Au) as the thin film electrode 302, silver nanoparticles (silver average particle diameter of 10 nm, of which the insulating coating alcoholate is 1 nm thickness) manufactured by Nanoparticle Laboratories as the conductive fine particles 307, and the insulating fine particles 306 Hydrophobic silica having an average particle size of 110 nm was used.

  Silver nanoparticles and hydrophobic silica were dispersed in toluene at a blending ratio of 1: 9 and a solid content of 20 wt%, and applied on a SUS substrate by spin coating to form an electron acceleration layer 303a. Here, a SUS substrate having a size of 10 mm × 50 mm square and a thickness of 1 mm was used. Further, the electron acceleration layer 303a was formed to have a layer thickness of 780 nm.

  After forming the electron acceleration layer 303a on the SUS substrate in this manner, the thin film electrode 302 was formed by sputtering gold so that the film thickness was 40 nm on the electron acceleration layer, and the electron-emitting device 30a was manufactured.

Six electron-emitting devices 30a obtained as described above were arranged 5 mm below (away from) the vertical direction of the intermediate transfer belt 21 in the width of the image area. A voltage of 15 V was applied to these electron-emitting devices 30a from the first power source V1, and the electron-emitting current amount was always set to 0.33 μA · cm ⁻² by constant current driving. All the electron-emitting devices 30a arranged were set so that the amount of electron emission current was 0.33 μA · cm ⁻² . In addition, a voltage of 100 V was applied between the thin film electrode 302 and the intermediate transfer belt 21 by the second power source V2. Here, the thin film electrode 302 is set to −100 V, and the intermediate transfer belt 21 is set to the ground (0 V). In this manner, an image forming apparatus provided with a pre-transfer charging device having an electron-emitting device was configured as the image forming apparatus of this example.

  The intermediate transfer belt 21 is a polyimide film containing carbon black having a thickness of 150 μm, and the belt width is 34 cm.

  In the image forming apparatus of this example, the toner image on the intermediate transfer belt 21 was charged by the electron-emitting device 30a, and then the toner image was transferred to the transfer material, and the transfer efficiency was measured. At this time, the process speed was set to 0.3 m / s (equivalent to 50 sheets machine). As a result of the measurement, the transfer efficiency was 95%, and no image unevenness occurred.

(Comparative Example 1)
In the image forming apparatus of Comparative Example 1, the toner image on the intermediate transfer belt is transferred to the transfer material with the same configuration as in Example 1 except that the pre-transfer charging device using the electron-emitting device was not installed. The transfer efficiency was measured. As a result, the transfer efficiency was 75% and image unevenness occurred.

(Comparative Example 2)
In the image forming apparatus of Comparative Example 2, the toner image on the intermediate transfer belt is transferred with the same configuration as in Example 1 except that a corona charging device is installed instead of the pre-transfer charging device using the electron-emitting device. The material was transferred to a material and the transfer efficiency was measured. As a result, the transfer efficiency was 90%, but ozone odor was generated. The installation and operating conditions of the corona charging device were the same as in Patent Document 1.

  From the above, it can be seen that the pre-transfer charging device of the present invention can uniformly charge without ozone and stably transfer the toner image on the intermediate transfer member onto the transfer material.

  The present invention is not limited to the embodiments and examples described above, and various modifications are possible within the scope of the claims. In other words, embodiments and examples obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

  Since the pre-transfer charging device according to the present invention can uniformly charge the toner image on the intermediate transfer body without ozone, the image forming apparatus including the same can stably transfer onto the transfer material. Therefore, the present invention can be suitably used for an image forming apparatus such as a copying machine, a printer, and a facsimile machine using an intermediate transfer member.

DESCRIPTION OF SYMBOLS 1 Toner image formation part 2 Secondary transfer part 3 Pre-transfer charging apparatus 4 Primary transfer part 10 Image forming apparatus 11 Photosensitive body (image carrier)
12 Charging means 13 Developing means 21 Intermediate transfer belt (intermediate transfer member)
22 Drive roller (transfer means)
23 Drive roller 24 Primary transfer roller (intermediate transfer means)
26 Secondary transfer roller (transfer means)
30, 30a, 30b Electron-emitting device 60 Basic dispersant 301 Electrode substrate 302 Thin film electrode 303, 303a, 303b Electron acceleration layer 306 Insulator fine particles 307 Conductive fine particles T Toner image P Sheet material (transfer material)
V1 1st power supply (1st voltage application means)
V2 Second power source (second voltage applying means)

Claims (23)

The above-mentioned transfer material of an image forming apparatus comprising: an intermediate transfer unit that transfers a toner image on an image carrier to an intermediate transfer member; and a transfer unit that transfers a toner image on the intermediate transfer member to a transfer material In the pre-transfer charging device for charging the toner image on the intermediate transfer body before being transferred to
An electron-emitting device having an electrode substrate, a thin film electrode, and an electron acceleration layer sandwiched between the electrode substrate and the thin film electrode;
First voltage applying means for applying a voltage between the electrode substrate and the thin film electrode so as to accelerate electrons in the electron acceleration layer and emit the electrons from the thin film electrode;
Second voltage applying means for applying a voltage between the thin film electrode and the intermediate transfer member;
With
The thin film electrode is disposed to face the intermediate transfer member,
The pre-transfer charging device, wherein the electron acceleration layer comprises a fine particle layer containing insulating fine particles.   The pre-transfer charging device according to claim 1, wherein the insulating fine particles have an average particle size of 7 to 1000 nm. The pre-transfer charging device according to claim 1, wherein the insulating fine particles contain at least one of SiO ₂ , Al ₂ O ₃ , and TiO ₂ , or contain an organic polymer. .   The pre-transfer charging device according to claim 1, wherein the insulating fine particles are surface-treated.   The pre-transfer charging device according to claim 4, wherein the surface treatment is a treatment with silanol or a silyl group.   The pre-transfer charging device according to claim 1, wherein the fine particle layer contains at least one of conductive fine particles and a basic dispersant.   7. The pre-transfer charging device according to claim 6, wherein the fine particle layer includes the insulating fine particles and at least the conductive fine particles, and the conductive fine particles are a conductor having a high anti-oxidation power.   The pre-transfer charging device according to claim 7, wherein the conductive fine particles are a noble metal.   The pre-transfer charging device according to claim 7 or 8, wherein the conductive fine particles contain at least one of gold, silver, platinum, palladium, and nickel.   The pre-transfer charging device according to claim 7, wherein the conductive fine particles have an average particle size of 3 to 10 nm.   11. The pre-transfer charging device according to claim 7, wherein a small insulator material, which is an insulator material smaller than the size of the conductive fine particles, is present around the conductive fine particles.   12. The pre-transfer charging device according to claim 11, wherein the small insulator material includes at least one of alcoholate, fatty acid, and alkanethiol. The fine particle layer contains the insulating fine particles and at least a basic dispersant,
7. The basic dispersing agent according to claim 6, wherein an electron pair donor that donates an electron pair is introduced as a substituent into a polymer that disperses the insulating fine particles by a steric repulsion effect. Pre-transfer charging device. The above-mentioned transfer material of an image forming apparatus comprising: an intermediate transfer unit that transfers a toner image on an image carrier to an intermediate transfer member; and a transfer unit that transfers a toner image on the intermediate transfer member to a transfer material In the pre-transfer charging device for charging the toner image on the intermediate transfer body before being transferred to
An electron-emitting device having an electrode substrate, a thin film electrode, and an electron acceleration layer sandwiched between the electrode substrate and the thin film electrode;
First voltage applying means for applying a voltage between the electrode substrate and the thin film electrode so as to accelerate electrons in the electron acceleration layer and emit the electrons from the thin film electrode;
Second voltage applying means for applying a voltage between the thin film electrode and the intermediate transfer member;
With
The thin film electrode is disposed to face the intermediate transfer member,
The electron acceleration layer is made of a layered insulator material, and the insulator material has a plurality of openings penetrating in the thickness direction of the layer, and conductive fine particles are accommodated in the openings. A pre-transfer charging device. The pre-transfer charging device according to claim 14, wherein the insulator material includes at least one of SiO ₂ , Al ₂ O ₃ , and TiO ₂ , or includes an organic polymer.   16. The pre-transfer charging device according to claim 14, wherein the conductive fine particles are a conductor having a high anti-oxidation power.   The pre-transfer charging device according to claim 14, wherein the conductive fine particles are a noble metal.   18. The pre-transfer charging device according to claim 14, wherein the conductive fine particles include at least one of gold, silver, platinum, palladium, and nickel.   19. The pre-transfer charging device according to claim 14, wherein a small insulator material, which is an insulator material smaller than the size of the conductive fine particles, is present around the conductive fine particles.   The pre-transfer charging device according to claim 19, wherein the small insulator material includes at least one of an alcoholate, a fatty acid, and an alkanethiol.   21. The pre-transfer charging device according to claim 14, wherein the conductive fine particles have an average particle size of 3 to 10 nm.   The pre-transfer charging device according to any one of claims 1 to 21, wherein the thin film electrode includes at least one of gold, silver, carbon, tungsten, titanium, aluminum, and palladium. Intermediate transfer means for transferring the toner image on the image bearing member to the intermediate transfer member;
Transfer means for transferring the toner image on the intermediate transfer member to a transfer material;
23. An image forming apparatus comprising: the pre-transfer charging device according to claim 1 that charges a toner image on the intermediate transfer body before being transferred to the transfer material. .

Images