JP2005070677A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and general purpose developing device which effectively prevents fogging or toner clouding, is hardly influenced by an environmental change or deterioration over time by improving electrostatic transferability and color aptitude which cause problems when conventional conductive toner is used. <P>SOLUTION: A toner feeding member 7 facing a toner carrier 4 and feeding conductive toner 3 to the toner carrier 4 is provided. A change injection electric field which is larger then the developing electric field, is made to act on between the toner carrier 4 and the toner feeding member 7 to thereby inject charge to the conductive toner 3, and charge injected conductive toner 3 is carried by the toner carrier 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer to which an electrophotographic system is applied, and in particular, a developing device that visualizes an electrostatic latent image with charged conductive toner. About.

JP-A-10-111604 Japanese Patent Publication No.58-26026 Japanese Patent Publication No. 63-10426 JP-A 63-159870 JP-A-6-95518

  Conventionally, in an image forming apparatus such as a copying machine or a printer to which this type of electrophotographic method is applied, an insulating property is used as a developer for developing an electrostatic latent image formed on an image carrier such as a photosensitive drum. In general, a method of developing a latent electrostatic image by applying a predetermined polarity by triboelectrically charging the insulating toner and applying a predetermined polarity to the insulating toner is widely used. Here, as a method of charging the insulating toner, the friction charging characteristic of the toner is controlled in advance by appropriately combining a binder resin and an additive in the toner, and the toner is stirred in the developing device. Many methods are used to charge toner by friction between the toner and a substance that easily causes triboelectric charging by rubbing the toners by agitating operation or conveying operation of the toner in the middle of the conveyance path during conveyance. .

  In such a toner charging method, since the frictional state of the toner varies depending on individual toner particles, a certain amount of charge distribution inevitably exists in the charge amount of the toner charged by friction. Therefore, the toner often includes a low-charged toner with a small charge amount or a reverse polarity toner charged to a polarity opposite to the charge polarity of the whole toner. Among these, the low-charge toner tends to be a so-called toner cloud that floats in the image forming apparatus apart from a toner carrier such as a developing roll in the developing apparatus, and this toner cloud causes various defects in the image forming apparatus. It has a problem that causes it.

  Further, the reverse polarity toner is electrostatically attracted to a background portion where the toner is not originally attached to the electrostatic latent image on the image carrier, and causes a so-called fogging that is a uniform stain on the background portion. have.

  Furthermore, this type of triboelectric charging method is susceptible to environmental changes such as temperature and humidity, and changes over time associated with the use of a developing device, and changes in the surface state of the triboelectric charging mechanism such as toner and stirring members. As a result, there is a problem that the charged state of the toner tends to become unstable as a result.

  Therefore, in order to solve such problems, a method of using a conductive toner instead of an insulating toner, specifically, charging a conductive toner by injecting a charge and using it for development. The method is known.

  This method using conductive toner has various advantages because it does not use frictional charging. In particular, the conductive toner easily moves the charge and can give the toner a uniform charge. Therefore, it is possible to prevent the occurrence of fog and toner cloud, and it is difficult to be affected by environmental changes and deterioration over time. This is the biggest feature. In addition, since the method using the conductive toner does not require a frictional charging mechanism, the structure of the developing device is simple, and the size and cost can be reduced.

  However, the above prior art has the following problems. That is, when the conductive toner is used, if a general-purpose electrostatic transfer system such as a corotron or a bias roll is used, when the recording paper absorbs moisture, it becomes difficult to transfer the toner image onto the recording paper. Has the problem. In addition, when forming a color image, it is necessary to reproduce various colors by superimposing color toners of different color materials. However, in the case of conductive toners, the toners cannot be superimposed and are colored. It also has a problem that it cannot cope with.

  The cause of this problem is that the toner charge is transferred between the recording paper and the toner that have absorbed moisture and become low resistance because the toner is conductive, and the electrostatic attraction force to the toner is reduced. It is to be lost. As another technical problem, since conductive toner easily injects electric charge, if the potential of the electrostatic latent image becomes unstable, a small potential difference (cleaning) between the developing bias and the background portion of the electrostatic latent image. (Referred to as “potential”), a charge of reverse polarity is injected into the toner, which is likely to cause fogging.

  In order to solve such technical problems, conventionally, Japanese Patent Laid-Open No. 10-111604, Japanese Patent Publication No. 58-26026, Japanese Patent Publication No. 63-10426, Japanese Patent Publication No. 63-159870 are conventionally used. Various techniques disclosed in Japanese Laid-Open Patent Publication No. 6-95518 and the like have already been proposed.

  The technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 10-111604 has a characteristic that the toner is easily charged to one of the positive and negative polarities and is difficult to be charged to the other polarity after being charged to the polarity. In other words, the present invention relates to a toner material that is easy to inject charges but does not leak easily.

  Further, the technique disclosed in the above Japanese Patent Publication No. 58-26026 is a recording paper (transfer medium) having a predetermined volume specific resistance value coated with a predetermined amount of an insulating medium on at least one surface of a substrate. Is used to make the charge retention of the paper stable and uniform.

  Further, the technique disclosed in the above Japanese Patent Publication No. 63-10426 reduces the image portion potential of the electrostatic latent image to a predetermined level of the image portion potential of the developed image after development and prior to transfer, thereby preventing toner scattering. It is to suppress.

  Further, the technique disclosed in the above Japanese Patent Application Laid-Open No. 63-159870 is a mixture of a conductive toner and an insulating toner, and at the time of transfer, charges are injected from the paper into the conductive toner. ) To prevent the conductive toner and paper from coming into contact with each other, thereby maintaining the charge retention of the conductive toner.

  Further, the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-95518 is such that the conductive toner on the image carrier is heated and softened and melted, and the adhesive force of the softened and melted toner is used. The present invention relates to a non-electrostatic transfer technique that maintains good transferability from an image carrier to a recording material.

  However, the prior art disclosed in JP-A-10-111604, JP-B-58-26026, JP-B-63-10426, JP-A-63-159870, JP-A-6-95518, etc. In the case of the technology, not only the transferability equivalent to that of the insulating toner cannot be obtained, but also, for example, in the technology disclosed in Japanese Patent Application Laid-Open Nos. 10-11604 and 63-159870. In this case, a special material must be used, and in the technique disclosed in Japanese Patent Publication No. 58-26026, a special recording paper must be used. In the techniques disclosed in Japanese Patent Laid-Open No. 63-10426 and Japanese Patent Laid-Open No. 6-95518, a special image forming process is indispensable. , There is a concern that significant loss versatility, it is fact is not put to practical use at this stage.

  Therefore, the present invention has been made to solve the above-described problems of the prior art, and the object is to improve electrostatic transferability, which is a problem when using a conventional conductive toner, An object of the present invention is to provide a simple and versatile developing device that can improve color suitability, effectively prevent fogging and toner clouding, is less susceptible to environmental changes and deterioration over time.

  In order to solve the above-mentioned problems, the invention described in claim 1 is configured such that, as shown in FIG. 1 (a), an electrically conductive material disposed opposite to an image carrier 2 carrying an electrostatic latent image 1 and charged. A developing electric field is formed between the toner carrying member 4 carrying and transporting the toner 3, and the toner carrying member 4 and the image carrying member 2, and the electrostatic latent image on the image carrier 2 is formed in this developing electric field region. A development electric field forming means 5 for developing with the conductive toner 3 is provided, and the conductive toner 3 has a resistance variable portion 6 that changes to a high resistance in the development electric field and changes to a low resistance in a charge injection electric field larger than the development electric field. (See FIG. 2), a developing device provided with a toner supply member 7 that faces the toner carrier 4 and supplies the conductive toner 3 to the toner carrier 4 is provided. Between member 7 and larger than development electric field By the action of the charge injection electric field, as well as charge injection to the conductive toner 3, the conductive toner 3 which is the charge injection, a developing device, characterized in that to be supported on the toner carrying member 4.

  The invention described in claim 2 is the developing device according to claim 1, wherein the toner supply member is made of a conductive foam roll.

  Furthermore, the invention described in claim 3 is the developing device according to claim 1, wherein the toner supply member is composed of a conductive roll having a polished surface formed on a surface thereof.

  According to a fourth aspect of the present invention, there is provided the developing device according to the first aspect, wherein the toner carrier and the toner supply member are opposed to each other through contact or a minute gap.

  Further, in the invention described in claim 5, as shown in FIG. 1B, the charged conductive toner 3 is carried and conveyed so as to face the image carrier 2 carrying the electrostatic latent image 1. Development in which a developing electric field is formed between the toner carrier 4 and the toner carrier and the image carrier, and the electrostatic latent image on the image carrier 2 is developed with the conductive toner 3 in the development electric field region. And the conductive toner 3 is provided with a variable resistance portion 6 (see FIG. 2) that changes to a high resistance in a developing electric field and changes to a low resistance in a charge injection electric field larger than the developing electric field. The developing device includes a charge injection member 8 disposed opposite to the toner carrier 4, and the toner injection with the toner carrier 4 sandwiching the conductive toner 3 carried on the surface of the toner carrier 4. Charge larger than the developing electric field between the member 8 By the action of incident electric field, a developing device, characterized in that the charge injection into the conductive toner 3.

  According to a sixth aspect of the present invention, in the developing device according to the fifth aspect, the toner carrier comprises a roll having a polished surface formed on the surface thereof.

  Furthermore, the invention described in claim 7 is the developing device according to claim 5, wherein the charge injection member is made of a conductive roll.

  The invention described in claim 8 is the developing device according to claim 5, wherein the charge injection member comprises a conductive plate to which conductive rubber is adhered.

  Furthermore, the invention described in claim 9 is the developing device according to claim 1 or 5, wherein the toner carrier is formed of a conductive roll having an insulated surface.

  In such technical means, the developing method for handling the conductive toner 3 may be any developing method such as a one-component developing method or a two-component developing method.

  Further, the developing electric field forming means 5 includes a wide range of devices that form a developing electric field between the image carrier 2 and the toner carrier 4, and the developing electric field here includes only a DC electric field or an alternating electric field. You may select suitably the superimposed DC electric field etc.

  The resistance variable portion 6 (see FIG. 2) of the conductive toner 3 is appropriately selected as long as it changes to a high resistance in the developing electric field and changes to a low resistance in the charge injection electric field larger than the developing electric field. It does not matter. As long as the resistance variable portion 6 is provided on the conductive toner 3 side, the resistance variable portion 6 may be configured at an arbitrary position such as the surface or inside of the conductive toner 3.

  Here, as a typical aspect of the resistance variable portion 6, for example, a conductive toner 3 main body is covered with an insulating coating, and a concave portion where the conductive toner main body is exposed is formed on a part of the insulating coating layer. Can be mentioned. In this aspect, the resistance variable portion can adjust the resistance of the conductive toner according to the magnitude of the electric field by adjusting the exposure ratio of the conductive toner main body. Another aspect of the variable resistance portion is one in which the periphery of the conductive toner body is covered with an insulating or semiconductive coating layer, and the resistance is set by adjusting the thickness of the coating layer. According to this aspect, by adjusting the thickness of the variable resistance portion, the variable resistance portion can adjust the resistance of the conductive toner according to the magnitude of the electric field.

  In other words, the variable resistance portion 6 provided in the conductive toner 3 is a film that has an insulating property in a developing electric field and has a conductive property in a charge injection electric field larger than the developing electric field. Can do. The variable resistance portion 6 may change from insulating to conductive or from conductive to insulating depending on the presence or absence of light irradiation, regardless of the magnitude of the electric field.

  Further, as a typical aspect of the resistance change of the resistance variable portion, a high resistance from a low resistance to an electric field that is larger than the developing electric field formed by the image portion potential of the electrostatic latent image and the developing bias potential and smaller than the charge injection electric field. A mode in which switching (resistance change) is performed. According to this aspect, since the variable resistance portion switches from a high resistance to a low resistance in the intermediate electric field between the development electric field and the charge injection electric field, the variable resistance portion is maintained at a high resistance in the development electric field. There is no charge transfer between the toners, and the conductive toner can maintain a constant charge. On the other hand, in the electric charge injection electric field, the resistance variable portion changes to a low resistance, so that electric charge is easily injected into the conductive toner.

  Further, as a preferable aspect of the resistance change of the resistance variable portion, for example, an electric field that is larger than the cleaning electric field formed by the background potential of the electrostatic latent image and the developing bias potential and smaller than the charge injection electric field, Examples of switching to low resistance (resistance change). According to this aspect, since the variable resistance portion switches from a high resistance to a low resistance in the intermediate electric field between the cleaning electric field and the charge injection electric field, the variable resistance portion is maintained at a high resistance in the working region of the cleaning electric field. In other words, a charge having a reverse polarity is not induced in the conductive toner at the tip on the toner carrier. For this reason, a so-called fog phenomenon in which a reverse polarity charge is induced in the conductive toner on the toner carrying member and adheres to the background portion of the electrostatic latent image is effectively suppressed.

  Furthermore, as a preferable aspect of the resistance change of the resistance variable portion, there is an aspect in which switching from high resistance to low resistance is performed with an electric field larger than the transfer electric field formed at the time of transfer and smaller than the charge injection electric field. According to this aspect, since the variable resistance portion is switched from high resistance to low resistance in the intermediate electric field between the transfer electric field and the charge injection charge, the variable resistance portion is kept high in the transfer electric field application region. In other words, during transfer, there is no movement of electric charge between the conductive toner 3 and the recording paper, and the electric charge of the conductive toner 3 is retained even with respect to, for example, highly water-containing paper. Transfer performance can be obtained.

Further, as a preferable resistance condition of the variable resistance portion, for example, the volume resistance of the conductive toner may be set to 10 ¹⁰ Ω · cm or less in the charge injection electric field and set to 10 ¹¹ Ω · cm or more in the developing electric field. If the resistance condition is set in such a range, the charge injection operation in the charge injection electric field application region and the charge holding operation in the development electric field application region are performed extremely well.

  In the present invention, the conductive toner includes the variable resistance portion as described above. To inject charges efficiently into this type of conductive toner 3, for example, the following charge injection is performed. Means may be provided.

  That is, it has a charge injection member disposed opposite to the toner carrier, and a charge injection electric field larger than the development electric field acts between the toner carrier and the charge injection member to inject the charge into the conductive toner and to inject the charge. A charge injection member for supporting the conductive toner on the toner carrier may be provided.

  Here, the charge injection member 8 is a member arranged to face the toner carrier 4 and may be any member that functions as an electrode for applying a charge injection electric field between the toner carriers 4. The shape or the shape of a braid can be selected as appropriate. The material of the charge injection member 8 is preferably aluminum or the like, but is not limited thereto and may be selected as appropriate. As the charge injection means, a normal power supply (not shown) is used as an element for generating a charge injection electric field larger than the development electric field between the toner carrier 4 and the charge injection member 8. The power source is not limited to one that generates a DC electric field, and may be selected weekly such as one that generates a DC electric field on which an alternating electric field is superimposed.

  Next, the operation of the developing device according to the present invention will be described.

  In the present invention, as shown in FIG. 2B, the conductive toner 3 is charged in the region where the charge injection electric field is higher than the development electric field by the charge injection means 7 having the charge injection member 8, for example. Injected and moved to the toner carrier (charge injection step). At this time, as shown in FIG. 2A, in the electric charge injection electric field, the resistance variable portion 6 changes to a low resistance or acts as a conductive film, and electric charge is easily injected into the conductive toner 3. Is done. In addition, the charge injection into the conductive toner 3 is performed such that after the conductive toner 3 is carried on the surface of the toner carrier, the charge is injected into the conductive toner 3 carried on the surface of the toner carrier. It may be configured.

  Thereafter, as shown in FIG. 2B, the conductive toner 3 carried on the toner carrier 4 is conveyed to a development area between the image carrier 2 and the toner carrier 4 to form a development electric field. It enters into the region where the developing electric field is applied by the means and moves to the image carrier 2 to visualize the electrostatic latent image 1 on the image carrier 2 (visualization step). At this time, as shown in FIG. 2A, in the developing electric field, the resistance variable portion 6 changes to a high resistance, so that it acts as an insulating film, and it becomes difficult for electric charge to be injected into the conductive toner. Accordingly, the conductive toner maintains a state where electric charge is held, and no charge is transferred between the conductive toners 3 and the like.

  According to the developing device of the present invention, the resistance variable portion whose resistance is changed by the applied electric field with respect to the conductive toner is provided, and the resistance of the variable resistance portion is reduced by a charge injection electric field larger than the developing electric field. Since the resistance of the variable resistance portion is increased, the charge can be easily injected into the conductive toner by lowering the resistance of the variable resistance portion when the charge is injected into the conductive toner. In addition, when developing, the charge retention of the conductive toner can be improved by increasing the resistance of the resistance variable portion.

  Accordingly, it is possible to achieve both the charge injection property for the conductive toner and the charge retention property for the injected toner, while maintaining a good charge injection property for the conductive toner, The reverse polarity toner is rarely generated, fog and toner cloud can be effectively prevented, and the development performance for the conductive toner can be kept good.

  Further, according to the present invention, since the variable resistance portion that changes resistance by the applied electric field is provided for the conductive toner, for example, by increasing the resistance of the variable resistance portion in the transfer electric field action region, The charge retention of the conductive toner at the time can be kept good. For this reason, it is possible to effectively prevent the electric charge held in the conductive toner from moving between the moisture-absorbing recording paper and the toner, and the electrostatic attraction force to the toner can be maintained. Therefore, it is possible to transfer a toner image onto a highly water-containing paper or the like, and it is also possible to form a color image by superimposing color toners. Therefore, it is possible to easily realize a good transfer performance for conductive toner. .

As described above, according to the developing device of the present invention, it is possible to effectively prevent fogging and toner cloud by improving electrostatic transferability and color suitability, which are problems in using conventional conductive toner. In addition, it is possible to provide a simple and versatile developing device that is not easily affected by environmental changes and deterioration over time.

  Further, according to the developing device of the present invention, the conductive toner is supplied to the toner carrier by the toner supply member, and a charge injection larger than the developing electric field is injected between the toner carrier and the toner supply member. By applying an electric field, electric charge is injected into the conductive toner, and the charged electric conductive toner is carried on the toner carrier, so that the toner carrier carries the static toner carried on the image carrier. The electrostatic latent image can be developed satisfactorily.

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

Embodiment 1
FIG. 3 shows an image forming apparatus to which the developing device according to Embodiment 1 of the present invention is applied.

  As shown in FIG. 3, the image forming apparatus according to the first embodiment has a photosensitive drum 10 as an image carrier that is rotationally driven at a predetermined speed in the direction of the arrow. Around the drum 10, a charging device 11 that charges the surface of the photosensitive drum 10 to a predetermined potential, and an exposure device as a latent image writing unit that forms an electrostatic latent image Z on the photosensitive drum 10. 12, a developing device 13 that visualizes the electrostatic latent image Z formed on the photosensitive drum 10, and a recording paper 18 that uses the toner image visualized on the photosensitive drum 10 as a recording medium. A transfer device 14 serving as transfer means for transferring the toner to the surface of the photosensitive drum 10 and a cleaning device 15 for cleaning the toner remaining on the surface of the photosensitive drum 10 are sequentially provided.

  By the way, the developing device according to the first embodiment is arranged to face an image carrier carrying an electrostatic latent image and carries a charged conductive toner, and the toner carrier and the image carrier. And a developing electric field forming means for developing an electrostatic latent image on the image bearing member with the conductive toner in the developing electric field region. In a developing device provided with a variable resistance portion that changes to a high resistance in an electric field and changes to a low resistance in a charge injection electric field larger than the developing electric field, the conductive toner is supplied to the toner carrier facing the toner carrier. A toner supply member is provided, and a charge injection electric field larger than a developing electric field is applied between the toner carrier and the toner supply member to inject charge into the conductive toner, and the charge is injected. The conductive toner is configured to be supported on the toner carrying member.

  That is, the developing device 13 according to this embodiment includes a developing device housing 131 as shown in FIG. 3, and the developer G including the conductive toner 20 is accommodated in the developing device housing 131. Has been. The developer G may be a one-component developer composed only of the conductive toner 20 or a two-component developer composed of the conductive toner and a carrier. In the first embodiment, a one-component developer G composed only of the conductive toner 20 is used. The developing device housing 131 is provided with a developing opening 132 at a position facing the photosensitive drum 10, and a developing roll 133 as a toner carrier is disposed in the developing opening 132. Has been. A predetermined developing bias voltage is applied to the developing roll 133 so that a developing electric field acts on the developing area between the photosensitive drum 10 and the developing roll 133. Further, a toner supply roll 134 as a toner supply member / charge injection member is provided inside the development housing 131 on the back side of the development roll 133 so as to face the development roll 133.

  Here, in the first embodiment, the conductive toner 20 includes a spherical conductive core 201 made of a conductive material, as shown in FIG. The periphery of 201 is covered with an insulating coating layer (for example, an insulating resin layer) 202, and an appropriate number of resistance variable portions are provided in the insulating coating layer 202 so that a part of the conductive core 201 is exposed. What provided the recessed part 203 is used. In this recess 203, the insulating coating layer 202 is not formed and the conductive core 201 is completely exposed, or the insulating coating layer 202 is formed to be significantly thinner than the other portions. As a result, a recess may be formed.

  In the first embodiment, the conductive toner 20 can be prepared by a polymerization method or various known encapsulation techniques.

  Such a conductive toner 20 tends to rapidly decrease in resistance when a high electric field is applied. The magnitude of the electric field that lowers the resistance depends mainly on the occupation ratio of the concave portion 203 of the conductive toner 20 or the thickness of the insulating coating layer 202.

  With respect to this mechanism, since the conductive core 201 is covered with the insulating coating layer 202, the conductive core 201 does not directly contact the toner, the conductive member, or the like. As a result, it is presumed that, when a high electric field is applied, for example, conduction (reduction in resistance) is caused by a tunnel effect or the like.

This conductive core 201 is made by dispersing a conductive agent such as conductive carbon black, magnetic powder, transparent conductive powder such as ITO / TiO ₂ / SnO ₂ in polyester or styrene acrylic resin, or from polyester or styrene acrylic resin. It is produced by covering the particle surface with the conductive agent.

  Further, in the first embodiment, the conductive toner 20 is formed by coating the conductive core 201 with the insulating coating layer 202 as shown in FIG. However, the present invention is not limited to this. For example, as shown in FIG. 4B, the conductive core 201 is variable in resistance such as insulating or semiconductive. A mode in which the resistance of the conductive toner 20 can be adjusted by covering with the coating layer 204 as a portion and adjusting the thickness of the coating layer 204 as appropriate may be selected.

At this time, the semiconductive coating layer 204 may itself be made of a semiconductive material. For example, a metal oxide such as SiO ₂ or TiO ₂ or conductive carbon is added to the insulating resin. You may make it use the semiconductive resin made to contain a trace amount.

  The toner supply roll 134 (see FIG. 3) as the toner supply member / charge injection member acts on the conductive toner 20 by applying a charge injection electric field larger than the development electric field outside the development region to the conductive toner 20. Charge injection is performed with the resistance of 20 lowered.

  As the toner supply roll 134, a foamed urethane foam roll itself imparted with conductivity, a roll coated with a urethane foam imparted with conductivity, or the surface is polished or blasted. A conductive roll made of metal or the like is used. In addition, the toner supply roll 134 is disposed in contact with the developing roll 133 or opposed to the toner supply roll 134 through a minute gap so as to improve the charge injection property to the conductive toner 20.

  As the developing roll 133, for example, a conductive roll having an insulating surface with a thickness of about 5 μm to 100 μm or a semiconductive roll is used. The developing roll 133 is composed of, for example, an aluminum roll whose surface is anodized, a conductive roll whose surface is covered with an insulating tube, or an elastic roll. Further, the developing roll 133 is rotationally driven or driven in a direction in which the surface moves in the same direction as the moving direction of the surface of the photosensitive drum 10. On the other hand, the toner supply roll 134 in this embodiment is rotationally driven or driven in a direction in which the surface moves in the direction opposite to the moving direction of the surface of the developing roll 133.

  Further, a charge injection bias voltage that forms a high electric field for injecting charges into the conductive toner 20 is applied between the toner supply roll 134 and the developing roll 133 by a power supply for charge injection. . As the charge injection bias voltage, for example, a voltage corresponding to the charging polarity of the toner (for example, a negative polarity) and a voltage of about 100 V to 1000 V is used.

  In the first embodiment, as shown in FIG. 3, the transfer device 14 is provided with a transfer roll (not shown) facing the photosensitive drum 10, for example, and a transfer bias voltage is applied to the transfer roll. When applied, a transfer electric field acts between the photosensitive drum 10 and the transfer roll, and the toner image on the photosensitive drum 10 is electrostatically transferred to the recording paper 18 as a recording medium.

  Next, the operation of the image forming apparatus according to this embodiment will be described.

  Now, when the image forming process is started, the surface of the photosensitive drum 10 is first charged by the charging device 11, and then the exposure device 12 writes the electrostatic latent image Z on the charged photosensitive drum 10, The developing device 13 visualizes the electrostatic latent image Z.

  Thereafter, the toner image on the photosensitive drum 10 is conveyed to a transfer portion and electrostatically transferred onto a recording paper 18 as a recording medium by the transfer device 14. Thereafter, the recording paper 18 is peeled off from the surface of the photosensitive drum 10 and fixed with heat and pressure by a fixing device (not shown). The toner remaining on the photosensitive drum 10 is removed by the cleaning device 15.

  FIG. 5 shows the configuration of the developing device 13 more specifically.

  As shown in FIG. 5, the developing device 13 includes a developing device housing 131 formed of synthetic resin or the like, and a developing opening is provided at a position facing the photosensitive drum 10 of the developing device housing 131. A portion 132 is provided. In the developing opening 132, a developing roll 133 as a toner carrier is disposed so as to be rotatable along the arrow direction. For example, a conductive roll having an insulating surface is used as the developing roll 133 in order to prevent leakage from occurring with the toner supply roll 134. Further, as the developing roll 133, a semiconductive roll may be used. As the developing roll 133, for example, as described above, an aluminum roll whose surface is anodized is used.

  In addition, a predetermined developing bias voltage is applied to the developing roll 133 by a developing bias power source 135 as a developing electric field forming unit, and a developing electric field is formed between the developing roll 133 and the photosensitive drum 10. The electrostatic latent image on the photosensitive drum 10 is developed with the conductive toner 20 in the developing electric field region.

  Further, a toner supply roll 134 as a toner supply member / charge injection member is disposed on the back side of the developing roll 133 so as to face the developing roll 133 so as to be rotatable along the arrow direction. . As the toner supply roll 134, a conductive foam roll or a conductive roll having a polished surface is used, and the toner supply roll 134 is in contact with the developing roll 133 or opposed to each other through a minute gap. It is arranged. As the toner supply roll 134, for example, a urethane foam roll itself imparted with conductivity, a roll coated with a urethane foam imparted with conductivity, or the surface is polished or blasted. An aluminum roll in which minute irregularities are formed is used.

  A charge injection power source 136 is connected between the toner supply roll 134 and the developing roll 133 for applying a charge injection electric field larger than the developing electric field. The voltage of the charge injection power source 136 is appropriately set to, for example, a value of about −100 V to −1000 V (−600 V in this embodiment).

  Further, a toner layer forming member 137 for forming a toner layer on the surface of the toner supply roll 134 is provided on the surface of the toner supply roll 134. As the toner layer forming member 137, for example, a metal blade with a rubber material adhered to the tip portion thereof is used, and the rubber material of the toner layer forming member 137 is in pressure contact with the surface of the toner supply roll 134. Thus, a toner layer having a predetermined layer thickness is formed. As the toner layer forming member 137, for example, a material obtained by vulcanizing and bonding Si rubber or EPDM rubber to a stainless steel plate spring having a thickness of about 0.03 to 0.3 mm is used. One end of the toner layer forming member 137 is in light contact with the surface of the toner supply roll 134, and the other end is supported by a part of the developing device housing 131.

  Further, a toner storage unit 138 that stores the conductive toner 20 is provided on the back side of the toner supply roll 134, and a predetermined height is provided between the toner storage unit 138 and the toner supply roll 134. The partition member 139 has a partition. An agitator 140 that agitates the conductive toner 20 accommodated in the toner accommodating portion 138 and supplies it to the toner supply roll 134 is provided at a predetermined timing inside the toner accommodating portion 138. It is arrange | positioned so that it may be rotationally driven.

  In the above-described configuration, the developing device according to the first embodiment improves the electrostatic transferability and the color suitability, which are problems in using the conventional conductive toner, as follows. In addition, the toner cloud can be effectively prevented, is not easily affected by environmental changes and deterioration over time, and is simple and versatile.

  That is, in the developing device 13 according to the first embodiment, as shown in FIG. 5, the conductive toner 20 accommodated in the toner accommodating portion 138 of the developing device housing 131 is agitated by the agitating member 140 at a predetermined timing. While being supplied, the toner is supplied to the toner supply roll 134.

  Next, the conductive toner 20 supplied to the toner supply roll 134 adheres to the surface of the toner supply roll 134 due to unevenness on the surface of the toner supply roll 134 or physical adhesion (van der Waals force). However, the toner layer forming member 137 is formed with a predetermined layer thickness. The thin layer of the conductive toner 20 formed on the surface of the toner supply roll 134 is conveyed to a region facing the developing roll 133 as the toner supply roll 134 rotates.

  Meanwhile, an electric field for charge injection is formed by a charge injection power source 136 in a region where the toner supply roll 134 and the developing roll 133 are opposed to each other. This electric field for charge injection is larger than the developing electric field, and the conductive toner 20 has a low resistance due to the presence of the concave portion 203 as a variable resistance portion. Therefore, the conductive toner 20 has a negative polarity from the toner supply roll 134. Is injected, and a predetermined amount of charge is uniformly injected. As a result, the conductive toner 20 carried on the surface of the toner supply roll 134 is in a state of being charged substantially uniformly with a predetermined amount of charge injected uniformly.

  The conductive toner 20 carried on the surface of the toner supply roll 134 and charged substantially uniformly is charged by the charge of the conductive toner 20 and the charge injection voltage applied to the developing roll 133. In the state as it is, it transfers to the surface of the developing roll 133 by electrostatic attraction. When the conductive toner 20 transferred to the surface of the developing roll 133 passes through a region where a charge injection electric field acts opposite to the toner supply roll 134, the resistance is increased, so that the charge injected into the conductive toner 20 is reduced. There is no movement.

  The conductive toner 20 transferred to the surface of the developing roll 133 is conveyed to a developing area facing the surface of the photosensitive drum 10 as the developing roll 133 rotates, and a developing electric field formed in the developing area. Thus, the electrostatic latent image formed on the surface of the photosensitive drum 10 is developed.

  At that time, the developing electric field is smaller than the electric field for charge injection, and the conductive toner 20 has a high resistance due to the presence of the concave portion 203 as the variable resistance portion. Will not move involuntarily.

  As shown in FIG. 3, the conductive toner 20 developed on the photosensitive drum 10 moves to a transfer position as the photosensitive drum 10 rotates, and is transferred by a transfer electric field formed by the transfer device 14. And transferred onto the recording paper 18.

  At that time, the transfer electric field is smaller than the electric field for charge injection, and the conductive toner 20 has a high resistance due to the presence of the concave portion 203 as the variable resistance portion. Even when the paper 18 absorbs moisture and has a low resistance, the electric charge of the conductive toner 20 does not move unintentionally and is transferred onto the recording paper 18 satisfactorily.

  Then, the toner image made of the conductive toner 20 that is satisfactorily transferred onto the recording paper 18 is fixed with heat and pressure by a fixing device (not shown) to form a desired image. The conductive toner 20 remaining on the photosensitive drum 10 is removed by the cleaning device 15 to prepare for the next image forming process.

  As described above, in the developing device 13, as shown in FIG. 5, the conductive toner 20 that develops the electrostatic latent image formed on the photosensitive drum 10 changes to a high resistance in the developing electric field and the developing electric field is developed. Since the resistance variable section 203 that changes to a low resistance in a larger electric charge injection electric field is provided, when the toner image is transferred onto the recording paper 18 at the transfer position, the resistance of the recording paper 18 is reduced. Even in such a case, since the transfer electric field is smaller than the electric charge injection electric field, the conductive toner 20 has a high resistance and maintains a predetermined electric charge, and can be satisfactorily recorded on the recording paper 18. It becomes possible to transfer to.

  Further, since the conductive toner 20 used for development in the developing device 13 changes to a high resistance in the developing electric field, the electrostatic latent image on the photosensitive drum 10 is developed by the action of the developing electric field. In addition, it is effective that fogging and toner cloud are generated without being charged in reverse polarity by the cleaning electric field due to the potential difference between the developing bias voltage formed on the electrostatic latent image on the photosensitive drum 10 and the surface potential. Can be prevented.

  Further, since the conductive toner 20 used for development in the developing device 13 changes to a low resistance in a charge injection electric field larger than the development electric field, it is hardly affected by environmental changes and deterioration with time, and is always in a good development state. Can be maintained.

  Further, since the developing device 13 performs charge injection while supplying the conductive toner 20 to the surface of the developing roll 133 by the toner supply roll 134, the toner supply roll 134 has the transportability of the conductive toner 20. On the other hand, it is sufficient to use a conductive roll capable of injecting electric charge into the conductive toner, and it is not necessary to consider the triboelectric charging property of the toner, and it is simple and versatile.

  In such an image forming process, the operating conditions required for the developing device 13 and the transfer device 14 are examined.

  First, when the developing device 13 shown in FIG. 3 is modeled, it can be expressed as shown in FIG. 6, for example.

  In FIG. 6, reference numeral 21 denotes a charge injection plate (toner supply plate) which is one element of the charge injection member 134, and is constituted by, for example, an aluminum plate. A charge injection power source 25 is connected to the charge injection plate 21 and a charge injection bias Vl is applied.

  Reference numeral 22 denotes a toner carrying roll corresponding to the developing roll 133 of the developing device 13, and is constituted by, for example, an aluminum pipe whose surface is anodized. A developing bias power source 26 is connected to the toner carrying roll 22 and a developing bias V2 is applied.

  Further, reference numeral 23 denotes an image carrying plate corresponding to the photosensitive drum 10, which is composed of, for example, an aluminum plate having a 55 μm thick PET film attached to the surface thereof, with a predetermined gap with respect to the toner carrying roll 22. And move in a substantially horizontal direction. The image carrying plate 23 is connected to an image carrying bias power source 27, and a predetermined image carrying bias V3 is applied thereto.

  In such a developing device model, about one layer of conductive toner 20 (for example, the embodiment shown in FIG. 4A) is applied on the charge injection plate 21, and is slid rightward in FIG. At this time, due to the charge injection bias Vl applied to the charge injection plate 21 and the developing bias V2 applied to the toner carrying roll 22, a charge injection electric field A is generated between the charge injection plate 21 and the toner carrying roll 22. The electric charge is injected into the conductive toner 20 on the charge injection plate 21 by the electric charge injection electric field A, and the conductive toner 20 moves to the toner carrying roll 22 by electrostatic attraction force. Next, when the conductive toner 20 moved to the toner carrying roll 22 is conveyed to the development region by the rotation of the toner carrying roll 22, it is applied to the image carrying bias V 3 applied to the image carrying plate 23 and the toner carrying roll 22. The developing electric field B is formed by the developing bias V 2, and the conductive toner 20 moves to the image carrying plate 23 by the developing electric field B.

  In such a developing operation process, in order to keep the developing performance of the developing device 13 favorable, the charge injection electric field A is higher than the development electric field B, and is higher than the intermediate electric field between the charge injection electric field A and the development electric field B. It was confirmed that the resistance of the conductive toner 20 needs to be switched from a high resistance to a low resistance in a high electric field. This is supported by the examples described later.

  Further, in the case of a monochromatic image forming process that does not require the movement of a multilayer toner image, only toner adhesion to the background portion of the photosensitive drum 10 may be prevented. At this time, due to the influence of an electric field (cleaning electric field) formed by the potential difference between the developing roll 134 and the background portion, a charge of reverse polarity is induced in the toner at the tip on the developing roll 134, which causes the fogging to adhere to the background portion. There is a possibility.

  Therefore, in this case, as a characteristic of the conductive toner 20, the electrical resistance may be switched from a high resistance to a low resistance when the electric field is larger than the cleaning electric field and less than or equal to the charge injection electric field A so as to satisfy a predetermined range of electric resistance. . In general, since the cleaning electric field is smaller than the developing electric field B, the conductive toner (the characteristic that the resistance is switched from a high resistance to a low resistance at a high electric field equal to or higher than the intermediate electric field between the charge injection electric field A and the developing electric field B). 20) can be used as it is.

  Further, when the transfer device 14 is modeled, it can be expressed as shown in FIG.

  In FIG. 7, reference numeral 31 denotes a charge injection plate (toner supply plate) which is one element of the charge injection member 134, and is constituted by, for example, an aluminum plate. The charge injection plate 31 is connected with a charge injection power source 35 and applied with a charge injection bias V4.

  Reference numeral 32 denotes an image carrying roll corresponding to the photosensitive drum 10, and is constituted by, for example, an aluminum pipe having a 55 μm thick PET film attached to the surface thereof. An image carrying bias power source 36 is connected to the image carrying roll 32, and an image carrying bias V5 is applied.

  Further, reference numeral 33 denotes a recording medium plate corresponding to an electrode member such as a transfer roll of the transfer device 14, and is constituted by an aluminum plate having a recording medium 34 (for example, equivalent to the recording paper 18 in FIG. 3) attached to the surface. Is done. The recording medium plate 33 is connected to a transfer bias power source 37 and applied with a transfer bias V6.

  In such a transfer device model, about one layer of conductive toner 20 (for example, the embodiment shown in FIG. 4A) is spread on the charge injection plate 31 and is slid rightward in FIG. At this time, a charge injection electric field A is formed between the charge injection plate 31 and the image carrier roll 32 by the charge injection bias V4 applied to the charge injection plate 31 and the image carrier bias V5 applied to the image carrier roll 32. The electric charge is injected into the conductive toner 20 on the charge injection plate 31 by the electric charge injection electric field A, and the conductive toner 20 moves to the image carrying roll 32 by electrostatic attraction force. Next, when the conductive toner 20 that has moved to the image carrying roll 32 is conveyed to the transfer region by the rotation of the image carrying roll 32, it is applied to the transfer bias V 6 applied to the recording medium plate 33 and the image carrying roll 32. A transfer electric field C is formed by the image bearing bias V 5, and the conductive toner 20 moves to the recording medium plate 33 by the transfer electric field C.

  In such a transfer operation process, in order to keep the transfer performance of the transfer device 14 good, the charge injection electric field A is higher than the transfer electric field C and is higher than the intermediate electric field between the charge injection electric field A and the transfer electric field C. It was confirmed that the resistance of the conductive toner 20 needs to be switched from a high resistance to a low resistance in a high electric field. This is supported by the examples described later.

Embodiment 2
FIG. 8 is a diagram showing the configuration of a color image forming apparatus to which the developing device according to Embodiment 2 of the present invention is applied.

  In the figure, the color image forming apparatus is a so-called tandem type, and a reading unit 41 for reading a document is disposed above the apparatus main body 40, while the four color components (this) In the embodiment, Y: yellow, M: magenta, C: cyan, K: black) image forming engines 42 (specifically 42a to 42d) are arranged in the horizontal direction, and below each image forming engine. An intermediate transfer belt 43 that is circulated and conveyed along the arrangement direction of 42 is disposed, and an image on the intermediate transfer belt 43 is transferred to, for example, a recording sheet 44 as a recording medium. A secondary transfer device 45 is disposed, and further, a supply cassette 46 for storing the recording paper 44 is disposed below the apparatus main body 40, and the recording paper 44 from the supply cassette 46 is transferred to the secondary transfer device. 5 is obtained by configured to direct to the fixing device 47 via the.

  In the second embodiment, the image forming engine 42 includes, for example, a photoconductive drum 51, and a charger 52 that charges the photoconductive drum 51 around the photoconductive drum 51, on the charged photoconductive drum 51. An image writing device 53 such as a laser device for writing an electrostatic latent image on the surface, and a developing device 54 (specifically, 54a to 54d) that visualizes the electrostatic latent image on the photosensitive drum 51 with each color component toner. A primary transfer device 55 that primarily transfers a toner image on the photosensitive drum 51 to the intermediate transfer belt 43 and a drum cleaner 56 that removes residual toner on the photosensitive drum 51 are sequentially arranged.

  On the other hand, the intermediate transfer belt 43 is stretched over a plurality (four in this example) of stretching rolls 71 to 74, the stretching roll 71 is a driving roll, and the other stretching rolls 72 to 74 are driven rolls. It is supposed to function.

  Next, the developing device 54 used in the second embodiment will be described.

  The developing device according to the second embodiment is disposed opposite to an image carrier carrying an electrostatic latent image, and carries a toner carrier carrying and conveying a charged conductive toner, and the toner carrier and the image carrier. And a developing electric field forming means for developing the electrostatic latent image on the image carrier with the conductive toner in the developing electric field region. A developing device having a variable resistance portion that changes to a high resistance and changes to a low resistance in a charge injection electric field larger than a developing electric field, and has a charge injection member disposed to face the toner carrier, and the toner carrier An electric charge injection electric field larger than a developing electric field is applied between the toner carrier and the charge injection member with the conductive toner carried on the surface of the toner in between, and the electric charge is injected into the conductive toner. The That.

  That is, the developing device 54 according to the second embodiment includes a developing device housing 131 formed of synthetic resin or the like as shown in FIG. 9 and faces the photosensitive drum 51 of the developing device housing 131. An opening 132 for development is provided at the position. In the developing opening 132, a developing roll 133 as a toner carrier is disposed so as to be rotatable along the arrow direction. As the developing roll 133, for example, a conductive roll having an insulating surface is used in order to prevent leakage between the developing roll 133 and the toner supply roll 134. Further, as the developing roll 133, a semiconductive roll may be used. As the developing roll 133, for example, a roll having a polished surface on the surface to improve toner transportability is used.

  Further, a predetermined developing bias voltage is applied to the developing roll 133 by a developing bias power source 135 as a developing electric field forming means, and a developing electric field is formed between the developing roll 133 and the photosensitive drum 51. The electrostatic latent image on the photosensitive drum 51 is developed with the conductive toner 20 in the developing electric field region.

  Further, a toner supply roll 134 as a toner supply member / refresh roll is disposed on the rear side of the developing roll 133 so as to face the developing roll 133 so as to be rotatable along the arrow direction. The toner supply roll 134 is disposed so as to come into contact with the developing roll 133, and supplies the new conductive toner 20 while temporarily removing the conductive toner 20 attached to the surface of the developing roll 133 (development). The roll surface is refreshed). As the toner supply roll 134, for example, a urethane foam roll itself imparted with conductivity, a roll coated with a urethane foam imparted with conductivity, or the surface is polished or blasted. A metal roll on which minute irregularities are formed is used.

  Further, on the surface of the developing roll 133, a charge injection member that injects charges into the conductive toner 20 supplied to the surface of the developing roll 133 by the toner supply roll 134 on the downstream side of the toner supply roll 134 in the rotation direction. 141 is disposed. The charge injection member 141 is formed by a conductive plate having a conductive roll or conductive rubber bonded to the surface thereof, and is arranged in a state of rotating or fixed along the direction of the arrow while being in contact with the surface of the developing roll 133. Has been.

  The charge injection member 141 is connected between the developing roll 133 and the toner supply roll 134 with a power injection power source 136 for applying a charge injection electric field larger than the developing electric field. The voltage of the charge injection power source 136 is appropriately set to a value of about −100 V to 1000 V, for example.

  Further, a toner layer forming member 137 for forming a toner layer on the surface of the toner supply roll 134 is provided on the surface of the toner supply roll 134. As the toner layer forming member 137, for example, a metal blade with a rubber material adhered to the tip thereof is used, and the rubber material of the toner layer forming member 137 is in pressure contact with the surface of the toner supply roll 134. Thus, a toner layer having a predetermined layer thickness is formed.

  Further, a toner storage portion 138 for storing the conductive toner 20 is provided on the back side of the toner supply roll 134, and a predetermined height is provided between the toner storage portion 138 and the toner supply roll 134. It is partitioned by a partition member 139. An agitator 140 that agitates the conductive toner 20 accommodated in the toner accommodating portion 138 and supplies it to the toner supply roll 134 is provided at a predetermined timing inside the toner accommodating portion 138. It is arrange | positioned so that it may be rotationally driven.

  In the above-described configuration, the developing device according to the second embodiment improves the electrostatic transferability and the color suitability, which are defects when using the conventional conductive toner, as follows. And toner cloud can be effectively prevented, are not easily affected by environmental changes and deterioration over time, and are simple and versatile.

  That is, in the developing device 54 according to the second embodiment, as shown in FIG. 9, the conductive toner 20 accommodated in the accommodating portion 138 of the developing device housing 131 is agitated by the agitating member 140 at a predetermined timing. While being supplied to the toner supply roll 134.

  Next, the conductive toner 20 supplied to the toner supply roll 134 adheres to the surface of the toner supply roll 134 due to irregularities on the surface of the toner supply roll 134 or physical adhesion (van der Waals force). However, the toner layer forming member 137 is formed with a predetermined layer thickness. The thin layer of the conductive toner 20 formed on the surface of the toner supply roll 134 is conveyed to a region facing the developing roll 133 as the toner supply roll 134 rotates.

  Note that the thin layer of the conductive toner 20 formed on the surface of the toner supply roll 134 is slightly charged (about several μC) by frictional charging, and in the region facing the developing roll 133, Electrostatic transfer to the surface. The thin layer of the conductive toner 20 transferred to the surface of the developing roll 133 is injected with a charge by a charge injection member 141 made of a conductive roll or the like.

  Meanwhile, an electric field for charge injection is formed by a charge injection power source 136 in a region where the charge injection member 141 and the developing roll 133 face each other. This electric field for charge injection is larger than the electric field for development, and the conductive toner 20 has a low resistance due to the presence of the concave portion 203 as a variable resistance portion. Polar charge is injected, and a predetermined amount of charge is uniformly injected. As a result, the conductive toner 20 carried on the surface of the developing roll 133 is in a state of being charged substantially uniformly with a predetermined amount of charge injected uniformly.

  The conductive toner 20 charged on the surface of the developing roll 133 is conveyed to a developing area facing the surface of the photosensitive drum 51 as the developing roll 133 rotates, and a developing electric field formed in the developing area. Thus, the electrostatic latent image formed on the surface of the photosensitive drum 51 is developed with a predetermined amount of toner.

  At that time, the developing electric field is smaller than the electric field for charge injection, and the conductive toner 20 has a high resistance due to the presence of the concave portion 203 as the variable resistance portion. Will not move involuntarily.

  As shown in FIG. 3, the conductive toner 20 developed on the photosensitive drum 10 moves to the transfer position as the photosensitive drum 51 rotates, and is transferred by the transfer electric field formed by the transfer device 14. Then, it is transferred onto the recording paper 44.

  At that time, the transfer electric field is smaller than the electric field for charge injection, and the conductive toner 20 has a high resistance due to the presence of the concave portion 203 as the variable resistance portion. Even when the transfer belt 43 has a low resistance, the electric charge of the conductive toner 20 is transferred onto the intermediate transfer belt 43 satisfactorily without moving to an unintentional position.

  As described above, in the developing device 54, as shown in FIG. 9, the conductive toner 20 that develops the electrostatic latent image formed on the photosensitive drum 51 changes to a high resistance in the developing electric field and the developing electric field. Since the resistance variable section 203 that changes to a low resistance in a larger electric charge injection electric field is provided, when the toner image is transferred onto the intermediate transfer belt 43 at the transfer position, the resistance of the intermediate transfer belt 43 is reduced. Even in this case, since the transfer electric field is small compared to the electric charge injection electric field, the conductive toner 20 has a high resistance and maintains a predetermined charge, so that the intermediate transfer is satisfactorily performed. It becomes possible to transfer onto the belt 43.

  Further, since the conductive toner 20 used for development in the developing device 54 changes to a high resistance in the developing electric field, the electrostatic latent image on the photosensitive drum 51 is developed by the action of the developing electric field. In addition, it is effective that fogging and toner cloud are generated without being charged in reverse polarity by the cleaning electric field due to the potential difference between the developing bias voltage formed on the electrostatic latent image on the photosensitive drum 51 and the surface potential. Can be prevented.

  Further, since the conductive toner 20 used for development in the developing device 54 changes to a low resistance in a charge injection electric field larger than the development electric field, it is hardly affected by environmental changes and deterioration with time, and is always in a good development state. Can be maintained.

  Further, the developing device 54 supplies the conductive toner 20 to the surface of the developing roll 133 by the toner supply roll 134, and the charge injection into the conductive toner 20 is performed by the charge injection member 141. The roll 134 may be formed of a member having the transportability of the conductive toner 20, and it is not necessary to consider the triboelectric chargeability of the toner. Charge injection into the conductive toner 20 is effectively performed by the charge injection member 141. It is easy and versatile.

  As shown in FIG. 9, the developing device 54 according to the second embodiment is opened facing the photosensitive drum 51 and contains therein a developer G containing the same conductive toner 20 as in the first embodiment. A developing device housing 131, a developing roller 133 facing the photosensitive drum 51 facing the opening of the developing device housing 131, and a toner supply roller 134 for supplying the conductive toner 20 to the developing roller 133. A charge injection member 141 for injecting charges into the conductive toner on the developing roll 133, a toner layer forming member 137 for forming a thin layer of the conductive toner 20 on the surface of the toner supply roll 134, and the developing device housing 131. And an agitator 140 that is a stirring member that is provided on the back side of the toner supply roller 134 and stirs the conductive toner 20.

  In the second embodiment, a developing bias from the developing bias power source 135 is applied to the developing roll 133, while a charge injecting bias from the charge injecting power source 136 is applied to the charge injecting member 141. As a result, a developing electric field acts between the photosensitive drum 51 and the developing roll 133, and a charge injection electric field acts between the developing roll 133 and the charge injecting member 141.

  Next, since a voltage having a polarity opposite to that of the toner is applied to the primary transfer device 55 at a position where the photosensitive drum 51 and the intermediate transfer belt 43 are in contact with each other, an unfixed toner formed on the photosensitive drum 51 is used. The image is transferred to the intermediate transfer belt 43 (see FIG. 8). Further, the toner image primarily transferred to the intermediate transfer belt 43 is conveyed to the secondary transfer device 45 as the intermediate transfer belt 43 rotates, and the recording paper 44 conveyed from the supply cassette 46 is The intermediate transfer belt 43 and the secondary transfer device 45 are conveyed to a contact area.

  At this time, the toner image on the intermediate transfer belt 43 is electrostatically attracted to the recording paper 44 by applying a voltage having a polarity opposite to the charging polarity of the toner to the secondary transfer device 45, and then the toner image is transferred. The recording paper 44 is fixed by a fixing device 47.

  In particular, in this embodiment, the conductive toner 20 has the same characteristics as in the first embodiment.

  That is, since the conductive toner 20 is changed to a low resistance by applying a charge injection electric field (high electric field) in the charge injection region, the charge injection into the conductive toner 20 is easily performed. On the other hand, the conductive toner 20 changes to a high resistance in the development area and the transfer area by applying a development electric field and a transfer electric field (low electric field). Therefore, no movement of charge causing fogging occurs in the cleaning electric field, and no movement of charge occurs between the recording paper 44 and the toner. The toner image can be transferred, and a color image can be formed by overlapping color toners.

  In the second embodiment, the configuration of the tandem type image forming apparatus having a plurality of photosensitive drums has been described as an example. However, the configuration is not limited to this example. Each developing device or rotary developing device is provided to form a one-color toner image for each cycle and sequentially transfer it to the intermediate transfer member. By transferring multiple color component toner images in multiple cycles, a color image can be obtained. The same applies to the mode of formation. Further, the present invention can be similarly applied to a paper conveyance transfer system in which a paper is held on a recording paper conveyance body, conveyed, and transferred. In this embodiment, the color machine has been described, but it is needless to say that the present invention can be similarly applied to a monochrome machine.

Embodiment 3
FIG. 10 shows Embodiment 3 in which the present invention is applied to an image forming apparatus that does not use an electrostatic transfer system.

  In the image forming apparatus according to the third embodiment, as shown in FIG. 10, a charging device 81 that charges the photosensitive drum 80 around the photosensitive drum 80, and each color on the charged photosensitive drum 80. An exposure device 82 that writes an electrostatic latent image of components (yellow, magenta, cyan, and black in this example), and development that visualizes each color component latent image formed on the photosensitive drum 80 with each color component toner. An apparatus 83, an adhesive intermediate transfer roll 84 for transferring a toner image on the photosensitive drum 80, and a cleaning apparatus 85 for cleaning residual toner on the photosensitive drum 80 are provided. A secondary transfer roll 86 having a heating source is disposed below the adhesive intermediate transfer roll 84. Reference numeral 88 denotes a recording paper supply device for sending out the recording paper 87, and 89 denotes a conveyance belt for conveying the fixed recording paper 87.

  In the third embodiment, since the adhesive intermediate transfer roll 84 is made of an elastic material such as silicone rubber, for example, between the photosensitive drum 80 and the adhesive intermediate transfer roll 84 and the secondary transfer. The roll 86 and the adhesive intermediate transfer roll 84 are in elastic contact with a predetermined nip area. Further, the developing device 83 and the conductive toner in the third embodiment are the same as those used in the first embodiment, and other devices may be appropriately selected.

  Next, the operation of the image forming apparatus according to the third embodiment will be described.

  In the third embodiment, the electrostatic latent image carried on the photosensitive drum 80 is superimposed with toner images of different color components for each rotation of the photosensitive drum 80 by the developing device 83 as shown in FIG. It is done. When the superimposed toner images are pressed onto the adhesive intermediate transfer roll 84, the toner images are collectively transferred onto the adhesive intermediate transfer roll 84 by the adhesive force of the adhesive intermediate transfer roll 84. At that time, the toner image transferred onto the adhesive intermediate transfer roll 84 is heated by the secondary transfer roll 86, the releasability of the adhesive intermediate transfer roll 84 is improved, and the toner image is also heated. Viscosify. As a result, the toner image is retransferred to the recording paper 87 between the adhesive intermediate transfer roll 84 and the secondary transfer roll 86, and fixing is completed at the same time.

  In such an image forming process, the characteristics of the conductive toner used in Embodiment 3 are larger than the developing electric field formed by the image portion of the electrostatic latent image and the developing bias, and the electric resistance is below the electric charge injection electric field. Is switched from high resistance to low resistance, so that the conductive toner into which the charge is injected visualizes the electrostatic latent image on the photosensitive drum 80 in a state where the resistance is increased in the developing electric field action region. Thus, it is possible to superimpose toner images on the photosensitive drum 80.

  As a result, it is possible to prevent fogging and toner clouding, to be hardly affected by environmental changes and deterioration over time, to achieve an image forming apparatus that does not use an electrostatic transfer method, has a simple structure, and can be reduced in size and cost. Can do. In addition, an image forming apparatus that does not use an electrostatic transfer method, and a monochrome-only machine that does not need to form a color image, it is only necessary to form a single toner layer, so that the toner adheres to the background. Only need to prevent. At this time, the electric field (cleaning electric field) formed by the developing bias and the potential difference between the background portion induces a charge of reverse polarity to the toner on the tip of the developing roll, thereby preventing the fogging from adhering to the background portion. Therefore, it is sufficient that the electrical resistance can be switched from a high resistance to a low resistance as a characteristic of the conductive toner when the electric field is larger than the cleaning electric field and below the charge injection electric field.

Example 1
FIG. 11 shows the conductivity of the developing device model (see FIG. 5) according to the first embodiment when an electric field is applied to the conductive toner 20 (see FIG. 4A) used in the first embodiment. 5 shows the result of measuring the volume resistivity change of the toner 20.

  As can be seen from the figure, the conductive toner 20 rapidly decreases in resistance from a high resistance to a low resistance when a high electric field is applied.

Here, the relationship between the charge injection electric field A and the development electric field B and the electric resistance of the conductive toner 20 will be described. Generally, the electric field E applied to the conductive toner 20 is expressed as follows.
E = (V−VS) / εt (Dp + Dt + Dm + Dg)
Where V: potential of the counter electrode, VS: potential on the toner layer before movement, Dp to Dg: dielectric thickness of each layer forming the nip (Dp: dielectric thickness of the image carrier, Dt: dielectric thickness of the toner layer, Dm: toner carrier dielectric thickness, Dg: void layer dielectric thickness), εt: relative dielectric constant of toner.

Predicting from the above, under the above conditions, the electric field applied to the conductive toner 20 during charge injection is 5 × 10 ⁴ V / cm, and the electric field applied to the conductive toner 20 during development is 8 × 10 ³ V / cm. there were. At this time, as shown in FIG. 11, the volume resistivity of the conductive toner 20 is between 10 ¹³ Ω · cm and 10 ⁹ Ω · cm between 8 × 10 ³ V / cm and 5 × 10 ⁴ V / cm. It has changed to cm.

At this time, since the transit time of the charge injection electric field A region and the development electric field B region is about 0.01 seconds, the time constant is preferably 0.01 seconds or less in order to easily inject charges. The volume resistivity of the conductive toner 20 may be 10 ¹⁰ Ω · cm or less. Moreover, in order to hold the charged electric charge, it is necessary that no charge transfer or the like occurs within the time during which the developing electric field B is applied. The volume resistivity of the conductive toner 20 may be 10 ¹¹ Ω · cm or more. The volume resistivity of the conductive toner 20 was calculated by filling the toner in a φ30 mm cell, applying a voltage to the upper and lower surfaces, and measuring the flowing current.

Example 2
FIG. 12 shows the development toner amount (converted to the number of layers) with respect to a change in the image bearing bias of the image bearing bias power supply 27 in the developing device model according to the first embodiment (see FIG. 5). This is a result of comparative measurement between when the toner 20 is used and when the conductive toner 20 that does not have the insulating coating layer 202 (see FIG. 4) according to the comparative example is used. In Example 2, the development bias V2 was fixed at 0 V and the charge injection bias V1 was fixed at -600 V, and a series of image forming processes was repeated four times to perform multiple development on the image carrier plate 23.

  In Example 2, when the voltage of the image carrying plate 23 (image carrying bias V3) is changed to 50 to 150 V, the amount of developing toner (number of layers) using the conductive toner 20 increases. The amount of developing toner using such conductive toner (conductive toner not having the insulating coating layer 202) has hardly increased.

  As a result, when forming a color image, the conductive toner 20 can reproduce various colors by overlapping coloreners having different color materials, but it is understood that the conductive toner according to the comparative example cannot cope with colorization. Is done.

Example 3
FIG. 13 shows the results of measuring the relationship between the recording medium plate 33 voltage (transfer bias V6) and the transfer rate (%) in the transfer device model (see FIG. 7) according to the first embodiment.

In Example 3, as the recording medium 34 attached to the surface of the recording medium plate 33, an absolutely green paper and a semiconductive paper (5 × 10 ⁸ Ω · cm, high water content paper state) were used. Then, the image carrying roll 32 voltage (image carrying bias V5) is fixed to 0 V, the charge injection plate 31 voltage (charge injection bias V4) is set to −600 V, and the insulating coating layer 202 (FIG. 4) is applied to the semiconductive paper. In the comparative example using the conductive toner not coated with the insulation in the reference), it was also measured.

  According to the measurement results of Example 3, the conductive toner 20 according to Example 3 can achieve a transfer rate of 80% or more on insulating paper and semi-conductive paper (highly water-containing paper). It can be seen that the conductive toner can only obtain a transfer rate of about 30% on a semiconductive paper (highly water-containing paper), resulting in a transfer failure.

  As described above, the conductive toner 20 according to the third embodiment (switching in which resistance is changed from high resistance to low resistance at an intermediate electric field larger than the transfer electric field formed at the time of transfer and smaller than the electric charge injection electric field A is switched. If a variable resistance portion is used, high water content paper transfer and multiple transfer are possible.

1A and 1B are explanatory views showing an outline of a developing device according to the present invention. FIG. 2A is an explanatory diagram modeling the conductive toner according to the present invention, and FIG. 2B is an explanatory diagram of the developing device and the conductive toner according to the present invention. FIG. 3 is an explanatory view showing an outline of the image forming apparatus according to Embodiment 1 of the present invention. 4A and 4B are explanatory views showing a specific configuration example of the conductive toner used in Embodiment 1 of the present invention. FIG. 5 is a block diagram showing the developing device according to Embodiment 1 of the present invention. FIG. 6 is an explanatory diagram modeling the developing device according to Embodiment 1 of the present invention. FIG. 7 is an explanatory diagram modeling the transfer device according to the first embodiment of the present invention. 8 is a block diagram showing an image forming apparatus to which the developing device according to Embodiment 2 of the present invention is applied. FIG. 9 is a block diagram showing a developing device according to Embodiment 2 of the present invention. FIG. 10 is a block diagram showing an image forming apparatus to which a developing device according to Embodiment 3 of the present invention is applied. FIG. 11 is a graph showing a change in volume resistivity of the conductive toner with respect to the applied electric field in Example 1. FIG. 12 is a graph showing the developing toner amount with respect to the image carrier plate voltage change in the second embodiment. FIG. 13 is a graph showing a transfer rate with respect to a change in recording medium plate voltage in Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrostatic latent image, 2 ... Image carrier, 3 ... Conductive toner, 4 ... Toner carrier, 5 ... Development electric field formation means, 6 ... Variable resistance part, 7 ... Charge injection means, 8 ... Charge injection member

Claims (9)

A developing electric field is formed between the toner carrier, which is disposed opposite to the image carrier carrying the electrostatic latent image, and carries the charged conductive toner, and the toner carrier and the image carrier. A developing electric field forming means for developing the electrostatic latent image on the image bearing member with an electroconductive toner in an electric field region, and the electroconductive toner has a charge that changes to a high resistance in the developing electric field and is larger than the developing electric field. In a developing device having a resistance variable portion that changes to a low resistance in an injection electric field,
A toner supply member that faces the toner carrier and supplies conductive toner to the toner carrier is provided, and a charge injection electric field larger than a developing electric field acts between the toner carrier and the toner supply member. A developing device characterized in that charge is injected into the conductive toner and the charged toner is carried on the toner carrier. The developing device according to claim 1, wherein the toner supply member is made of a conductive foam roll. The developing device according to claim 1, wherein the toner supply member is made of a conductive roll having a polished surface formed on a surface thereof. The developing device according to claim 1, wherein the toner carrier and the toner supply member are opposed to each other through contact or a minute gap. A developing electric field is formed between the toner carrier, which is disposed opposite to the image carrier carrying the electrostatic latent image, and carries the charged conductive toner, and the toner carrier and the image carrier. A developing electric field forming means for developing the electrostatic latent image on the image bearing member with an electroconductive toner in an electric field region, and the electroconductive toner has a charge that changes to a high resistance in the developing electric field and is larger than the developing electric field. In a developing device having a resistance variable portion that changes to a low resistance in an injection electric field,
A charge injection member disposed opposite to the toner carrier, and a conductive toner carried on the surface of the toner carrier sandwiching the conductive toner between the toner carrier and the charge injection member; A developing device, wherein a large electric charge injection electric field is applied to inject electric charges into the conductive toner. 6. The developing device according to claim 5, wherein the toner carrying member comprises a roll having a polished surface formed on a surface thereof. The developing device according to claim 5, wherein the charge injection member is made of a conductive roll. 6. The developing device according to claim 5, wherein the charge injection member is made of a conductive plate to which conductive rubber is bonded. 6. The developing device according to claim 1, wherein the toner carrying member is made of a conductive roll whose surface is insulated.

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