JP2007322491A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where the original function of an image carrier is developed, and the life of the image carrier is prolonged. <P>SOLUTION: The image forming apparatus includes: a secondary transfer unit 60 for secondarily transferring a toner image carried on an intermediate transfer belt 40 to a recording medium in feeding; a fixing unit 80 for permanently fixing the toner image by heating the toner image transferred on the recording medium; a secondary transfer roller 41 that stretches the intermediate transfer belt 40 in contact with the inner peripheral surface of the intermediate transfer belt 40; a secondary transfer backup roller 61 arranged so as to sandwich the intermediate transfer belt 40 together with the secondary transfer roller 41; a preheater 70 provided in the secondary transfer roller 41, for preheating the toner image on the intermediate transfer belt 40; a center fixing heater 82 and an end fixing heater 83 provided in the fixing unit 80, used for thermal fixation. The diameter of the secondary transfer roller 41 is set so as to be the largest among a plurality of rollers that stretch the intermediate transfer belt 40. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, the latent image formed on the image carrier is developed by a developing device, transferred from the image carrier to the intermediate transfer belt at the transfer position of the primary transfer portion, and transferred from the intermediate transfer belt to the transfer position of the secondary transfer portion. The present invention relates to an image forming apparatus for transferring to a recording medium and further permanently fixing an image on the recording medium by a fixing unit, and particularly has a feature in a two-transfer transfer unit and a fixing unit in such an electrophotographic process. . The present invention is also applicable to an image forming apparatus of a general dry electrophotographic process, and is particularly suitable for a liquid developing type image forming apparatus using a liquid developer.

  At present, powder toner particles having an average particle diameter of about 7 to 10 μm are used in image forming apparatuses. However, it is considered to reduce the average particle diameter of the powder toner particles to improve the image quality. Has been. In particular, a liquid development type image forming apparatus that develops a latent image using a high-viscosity liquid developer in which a toner composed of a solid component is dispersed in a liquid solvent and visualizes the electrostatic latent image is formed of powder toner particles. When making the average particle diameter smaller, it is considered to be an important development method.

  When the average particle diameter of the toner particles is made smaller, the target is to have an average particle diameter of about 5 μm in the image forming apparatus of the dry electrophotographic process, and 1 μm in the image forming apparatus of the liquid developing system using the liquid developer. The goal is to be about. In a liquid development type image forming apparatus, toner particles are suspended in an electrically insulating organic solvent (carrier liquid) made of silicon oil, mineral oil, edible oil, or the like. By using this, it is possible to handle very fine toner particles having a particle diameter of 1 μm. That is, in the liquid development method, the carrier liquid constituting the developer has a function of making the toner particles charged and further uniformly dispersed in addition to preventing the scattering of toner particles having a particle diameter of about 1 μm. In the transfer process, the toner particles also have a role to make it easy to move by electric field action.

  By the way, when the surface of the recording medium is observed microscopically, there are irregularities on the surface of the medium, but the irregularities undulation is considerably larger than the average particle diameter of the toner, and the average particle diameter of the toner particles is further reduced. As a result, the toner particles are not completely contacted with the recording medium. Therefore, it has been proposed to improve the adhesion to the recording medium by increasing the temperature of the toner particles in advance before the fixing unit to reduce the viscosity.

  For example, Patent Document 1 (Japanese Patent No. 3042414) discloses an image forming apparatus that transfers toner images of a plurality of colors developed on an image carrier onto an intermediate transfer belt, and transfers and fixes the toner images collectively on a recording medium. The intermediate transfer belt is composed of an endless belt-like member, and the endless belt is heated to 1.5 to 2.5 times the softening point temperature of the toner to melt and transfer and fix the toner image. It is described that the nip passage time is set so that the temperature is lower than the softening point of the toner at the exit of the transfer / fixing nip.

  In Patent Document 2 (Japanese Patent Laid-Open No. 2001-296745), a plurality of color liquid developer toner images developed on an image carrier are transferred to an intermediate transfer belt, and the toner images are collectively recorded on a recording medium. The intermediate transfer belt is composed of an endless belt-like member, and the endless belt is heated to about 65 ° C. lower than the melting point temperature of the toner, or about 100 ° C. to 110 ° C. higher than the melting point or higher than the melting point temperature. The toner image is secondarily transferred to the recording medium by applying a bias. When the heating temperature of the endless belt is about 65 ° C., which is lower than the melting point temperature of the toner, the toner image is melted on the recording medium. Since it is not the next transfer, a fixing process is installed after this secondary transfer process to fix the secondary transferred toner image to the recording medium. When the heating temperature is about 100 ° C. to 110 ° C. above the melting point temperature of the toner or higher than the melting point temperature, the toner image is secondarily transferred and fixed on the recording medium in a molten state. An image forming apparatus is described that does not require a fixing process to be installed later.

Further, in Patent Document 3 (Japanese Patent Application Laid-Open No. 11-202675), a plurality of stages of fixing devices are arranged, and the heating temperature of the fixing device on the downstream side is set to the highest temperature, whereby the moisture contained in the recording medium is gradually increased. The heating temperature of the upstream fixing unit is determined by the water vapor pressure that could not be discharged to the outside due to the evaporation of moisture from the recording medium. Blister resulting from the phenomenon of scattering or misalignment: The heating temperature is set at a level that does not cause image disturbance called blistering, and the toner image is assumed to be attached to the recording medium (when sufficient fixing is not achieved) There is described an image forming apparatus which then proceeds to a fixing device on the downstream side to complete full-scale fixing.
Japanese Patent No. 3042414 JP 2001-296745 A JP-A-11-202675

  The technique described in Patent Document 1 is an effective technique for batch-transferring and fixing a toner image on a recording medium, but the endless belt is 1.5 times or more and 2.5 times the softening point temperature of the toner. The temperature of the endless belt reaching the next primary transfer portion from the transfer / fixing nip portion is also low, even if the heat capacity of the endless belt is minimal, since the toner image is melted by the following heating. Since the image carrier is in contact with the image carrier while maintaining a temperature corresponding to the heating temperature, the image carrier is not only unable to exhibit its original image carrier function under the influence of the heat, but also has a defect that shortens its life.

  In the technique described in Patent Document 2, when the endless belt is heated to about 65 ° C., which is lower than the melting point temperature of the toner, and a secondary transfer is performed by applying a bias, the endless belt having a minimum heat capacity is subjected to the secondary transfer. The temperature of the endless belt that reaches the next primary transfer portion from the nip portion is in contact with the image carrier in a state where heat is dissipated in the movement path. Although it does not impair the function and is not affected by the shortening of the service life, it is possible to fix the secondary transferred toner image on the recording medium by installing a fixing process after the secondary transfer process. It is essential. However, this heating transfer and fixing process is not preferable as a recent energy-saving product demanded from the market because the heating means is arranged over the two processes, so that the thermal energy efficiency is poor. On the other hand, when the heating temperature of the endless belt is about 100 ° C. to 110 ° C. above the melting point temperature of the toner or higher than the melting point temperature, the toner image is secondarily transferred and fixed on the recording medium in a molten state. Although it is not necessary to install a fixing step after the transfer / fixing step, it has an adverse effect on the image carrier similar to the invention described in Patent Document 1 described above.

  The technique described in Patent Document 3 is effective as a measure for preventing image disturbance called blister: blister, but it is assumed that it is worn by the first stage fixing device and complete fixing is completed by the downstream fixing device. However, the conventional energy consumption of the fixing device is increased, which is not preferable as an energy-saving product demanded recently. In addition, in the configuration in which the toner image is assumed to be attached by the first-stage fixing device and the full-scale fixing is completed by the downstream-side fixing device, the toner image is melted by the first-stage fixing device and the toner image that has been supposedly attached is downstream Since the toner image is melted and fixed again by the fixing device, the toner image may be thickened (for example, the line becomes thicker than the initial state), and a preferable image may not be obtained, and the fixing rate can be improved. However, the image quality may be deteriorated.

  In order to solve the above-mentioned problems, the invention according to claim 1 is directed to subjecting the toner image to a secondary transfer to a recording medium fed so as to be in contact with the toner image carried on the intermediate transfer member. A secondary transfer section, a fixing section that heats and permanently fixes the toner image transferred on the recording medium by the secondary transfer section, and an inner peripheral surface of the intermediate transfer member that is provided in the secondary transfer section A secondary transfer roller that stretches the intermediate transfer member as described above, and a secondary transfer backup roller that is provided in the secondary transfer portion and is disposed so as to sandwich the intermediate transfer member together with the secondary transfer roller; An image forming apparatus comprising: a preheating heater provided on the secondary transfer roller for preheating a toner image on the intermediate transfer member; and a fixing heater provided on the fixing unit for fixing heating. The transfer body is stretched by multiple rollers. The secondary transfer roller is equal to or largest after in the plurality of rollers.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the secondary transfer roller is a drive roller that drives the intermediate transfer member.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the winding amount of the intermediate transfer member around the secondary transfer roller is equal to or greater than a half circumference of the secondary transfer roller. It is characterized by being.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the image forming process is a dry electrophotographic process, and the volume average particle diameter of the toner particles is 2 μm. The above is 5 μm or less.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the image forming process is a liquid developing type electrophotographic process, and the volume average particle diameter of the toner particles is It is 0.5 μm or more and 2 μm or less.

  The invention according to claim 6 is the image forming apparatus according to any one of claims 1 to 5, wherein there are a plurality of the fixing heaters, and the length of the preheating heater is the length of the fixing heater. It is longer than any one of the plurality of heaters.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the length of the preheating heater is the widest of the recording media handled by the image forming apparatus. It is more than the width of the thing.

  The invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 7, wherein the intermediate transfer member has an outer peripheral surface of an endless belt base material coated with a fluorine resin. It has a surface layer.

  The invention according to claim 9 is the image forming apparatus according to any one of claims 1 to 8, wherein the secondary transfer roller has a fluororesin coated on the outer peripheral surface of the core metal substrate. It has a surface layer.

  According to the present invention, the temperature increase of the intermediate transfer member in contact with the image bearing member is suppressed as much as possible to reduce the thermal effect on the image bearing member, so that the original function of the image bearing member is exhibited, and the life of the image bearing member is improved. An image forming apparatus can be provided. In the present invention, an efficient thermal energy consumption form is formed to provide an image forming apparatus that is preferable as an energy saving product to meet recent market needs and to fix a fixed image without image deterioration such as blisters. Can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting the image forming apparatus according to the embodiment of the present invention. The embodiment of the present invention will be described by taking a liquid developing type image forming apparatus as an example, but the present invention can also be applied to an image forming apparatus of a dry electrophotographic process. In particular, the effect of the present invention can be expected when the toner particles have a volume average particle diameter of 2 μm or more and 5 μm or less.

  Development units 30Y, 30M, 30C, and 30K are arranged at the lower part of the image forming apparatus, and the intermediate transfer belt 40 and the secondary transfer unit 60 are arranged for the image forming unit of each color arranged in the center of the image forming apparatus. Arranged at the top of the image forming apparatus.

  The image forming unit includes image carriers 10Y, 10M, 10C, and 10K, charging rollers 11Y, 11M, 11C, and 11K, and exposure units 12Y, 12M, 12C, and 12K (not shown). The exposure units 12Y, 12M, 12C, and 12K have an optical system such as a semiconductor laser, a polygon mirror, and an F-θ lens. The image bearing members 10Y, 10M, 10C, and 10K are provided by charging rollers 11Y, 11M, 11C, and 11K. Are uniformly charged and irradiated with a modulated laser beam based on the input image signal by the exposure units 12Y, 12M, 12C, and 12K, and charged image carriers 10Y, 10M, 10C, and 10K. An electrostatic latent image is formed thereon.

  The developing units 30Y, 30M, 30C, and 30K generally include liquid developers of respective colors including the developing rollers 20Y, 20M, 20C, and 20K, yellow (Y), magenta (M), cyan (C), and black (K). Developer containers (reservoirs) 31Y, 31M, 31C, 31K to be stored, and developer supply rollers for supplying liquid developers of these colors from the developer containers 31Y, 31M, 31C, 31K to the developing rollers 20Y, 20M, 20C, 20K 32Y, 32M, 32C, 32K and the like, and the electrostatic latent images formed on the image carriers 10Y, 10M, 10C, and 10K are developed with liquid developers of respective colors.

  The intermediate transfer belt 40 is an endless belt, is stretched between the secondary transfer roller 41 and the tension roller 42, and has image transfer members 10Y, 10M, 10C, and 10K at the primary transfer portions 50Y, 50M, 50C, and 50K. And is driven to rotate by a secondary transfer roller 41 which is a driving roller. In the primary transfer portions 50Y, 50M, 50C, and 50K, the primary transfer backup rollers 51Y, 51M, 51C, and 51K are disposed opposite to each other with the image transfer bodies 10Y, 10M, 10C, and 10K interposed between the intermediate transfer belt 40 and the image support 10Y. 10M, 10C, and 10K are used as transfer positions, and the developed toner images of the respective colors on the image carriers 10Y, 10M, 10C, and 10K are sequentially transferred onto the intermediate transfer belt 40 and transferred. A toner image is formed.

  The intermediate transfer belt 40 of the present embodiment is made of a fluorine resin such as PFA having a thickness of about 2 μm to 10 μm on the surface of an endless polyimide belt material formed with a thickness of 30 μm to 120 μm, or a fluorine rubber. The surface layer is formed by means such as coating to improve the releasability of the developer at the time of secondary transfer, and has a very small heat capacity.

  In the secondary transfer unit 60, a secondary transfer backup roller 61 is disposed opposite to the secondary transfer roller 41 with the intermediate transfer belt 40 interposed therebetween, and a cleaning device including a secondary transfer roller cleaning blade 62 and a developer recovery unit 63 is provided. Be placed. Then, at the transfer position where the secondary transfer backup roller 61 is disposed, paper, film, cloth, etc., on which the monochromatic toner image or full color toner image formed on the intermediate transfer belt 40 is conveyed by the recording medium conveyance path L Transfer to a recording medium. The secondary transfer roller 41 has a configuration in which an elastic layer is disposed on the surface of the roller core bar, and drives the intermediate transfer belt 40 by a driving force from a driving source (not shown) and also preheats a halogen lamp or the like. A heater 70 is built in along the axial direction of the secondary transfer roller 41. The preheating heater 70 is used for preheating in the previous stage where the toner image on the recording medium is fixed by the fixing unit 80. Further, the length of the preheating heater 70 in the roller axis direction is configured to be equal to or greater than the width of the widest recording medium handled by the image forming apparatus. In the present invention, since the secondary transfer unit 60 is provided with such preliminary heating, “secondary transfer” may be referred to as “heated secondary transfer” or the like. Details of the secondary heating transfer of the present invention will be described later.

  A fixing unit 80 is disposed in front of the recording medium conveyance path L, and a single-color toner image or a full-color toner image transferred onto a recording medium such as paper is fused and fixed on the recording medium such as paper. The fixing unit 80 includes a fixing roller 81 that heats the recording medium that passes therethrough, and a pressure unit that presses the recording medium toward the fixing roller 81. The fixing roller 81 is formed of a roller core having an elastic layer on the surface, and includes a central heater 82 for heating the axial central portion of the fixing roller 81 and both axial end portions. And an end heater 83 for heating the heater. The pressure unit includes a first pressure roller 84, a second pressure roller 85, and a fixing belt 86 stretched between these two rollers. The recording medium is fixed to the fixing belt 86 as shown in the figure. The structure is sufficiently heated by passing through a relatively long nip region formed between the roller 81 and the roller 81.

  In the present invention, it is important to maintain the preheating in the heating secondary transfer process up to the fixing process as much as possible. Therefore, the distance from the nip region outlet of the secondary transfer unit 60 to the nip region inlet of the fixing unit 80. Is set to such a distance that preheating in the heating secondary transfer process of the present embodiment, which will be described in detail later, does not decrease. When the recording medium is conveyed from the nip area exit of the secondary transfer unit 60 to the nip area entrance of the fixing unit 80, the recording medium comes into contact with a recording medium conveying means such as a conveying belt or a conveying roller. , The recording medium and the developer are deprived of heat. Therefore, in the present embodiment, the distance from the nip area exit of the secondary transfer unit 60 to the nip area entrance of the fixing unit 80 is shorter than the length in the conveyance direction of the minimum size recording medium handled by the image forming apparatus. The arrangement relationship. With this setting, for example, even a recording medium of the minimum size handled by the image forming apparatus is transported from the secondary transfer unit 60 to the fixing unit 80 without being in contact with the recording medium transporting means as described above, and heated by the second heating unit. The pre-heating in the next transfer process is not lost. Note that a postcard is often set as the minimum-size recording medium handled by the image forming apparatus, and its length in the transport direction is 148 mm.

  On the side of the tension roller 42 that stretches the secondary transfer unit 60 together with the secondary transfer roller 41, a cleaning device including an intermediate transfer belt cleaning blade 46 and a developer recovery unit 47 is disposed along the outer periphery thereof.

  Next, the image forming unit and the developing unit will be described. FIG. 2 is a cross-sectional view showing main components of the image forming unit and the developing unit. Since the configurations of the image forming unit and the developing unit for each color are the same, the following description will be made based on the yellow (Y) image forming unit and the developing unit.

  The image forming unit includes a cleaning device including a latent image eraser 16Y, an image carrier cleaning blade 17Y, and a developer recovery unit 18Y along the rotation direction of the outer periphery of the image carrier 10Y, a charging roller 11Y, an exposure unit 12Y, and a development unit. A cleaning device including a developing roller 20Y of 30Y, an image carrier squeeze roller 13Y, an image carrier squeeze roller cleaning blade 14Y, and a developer recovery unit 15Y, which are associated with the development roller 20Y, is provided. In the developing unit 30Y, a cleaning blade 21Y, a developer supply roller 32Y using an anilox roller, and a developer compression roller 22Y are arranged on the outer periphery of the developing roller 20Y, and the liquid developer agitation is placed in the liquid developer container 31Y. A roller 34Y and a developer supply roller 32Y are accommodated. A primary transfer roller 51Y of the primary transfer portion is disposed along the intermediate transfer belt 40 at a position facing the image carrier 10Y, and an intermediate transfer belt squeeze roller 53Y, a backup roller 54Y, an intermediate transfer belt are disposed downstream of the moving direction. An intermediate transfer belt squeeze device 52Y including a belt squeeze roller cleaning blade 55Y and a developer recovery unit 56Y is disposed.

  The image carrier 10Y is a photosensitive drum made of a cylindrical member that is wider than the developing roller 20Y and has a photosensitive layer formed on the outer peripheral surface thereof. For example, the image carrier 10Y rotates in a clockwise direction as shown in FIG. The photosensitive layer of the image carrier 10Y is composed of an organic image carrier or an amorphous silicon image carrier. The charging roller 11Y is disposed upstream of the nip portion between the image carrier 10Y and the developing roller 20Y in the rotation direction of the image carrier 10Y, and a bias having the same polarity as the toner charging polarity is applied from a power supply device (not shown) to The carrier 10Y is charged. The exposure unit 12Y irradiates laser light onto the image carrier 10Y charged by the charging roller 11Y on the downstream side in the rotation direction of the image carrier 10Y with respect to the charging roller 11Y, thereby forming a latent image on the image carrier 10Y. To do.

  The developing unit 30Y includes a developer compression roller 22Y, a developer container 31Y that stores a liquid developer in which toner is dispersed in a carrier at a weight ratio of approximately 25%, a developing roller 20Y that carries the liquid developer, a liquid The developer supply roller 32Y, the regulating blade 33Y, the stirring roller 34Y, and the liquid developer carried on the developing roller 20Y for maintaining the developer in a uniform dispersed state by stirring the developer are brought into a compacted state. And a developing roller cleaning blade 21Y for cleaning the developing roller 22Y and the developing roller 20Y.

  The liquid developer accommodated in the developer container 31Y is a low concentration (about 1 to 2 wt%) and low viscosity with Isopar (trademark: exon) as a carrier, which is generally used, and is volatile at room temperature. It is not a volatile liquid developer having a property, but a non-volatile liquid developer having a high concentration and a high viscosity and having a non-volatile property at room temperature. That is, the liquid developer in the present invention contains toner particles having a volume average particle diameter of 0.5 μm or more and 2 μm or less in which a colorant such as a pigment is dispersed in a thermoplastic resin, an organic solvent, silicon oil, mineral oil or It is a liquid developer having a high viscosity (about 30 to 10,000 mPa · s) which is added together with a dispersant to a liquid solvent such as edible oil and has a toner solid content concentration of about 25 wt%. Using such a developer, in order to exhibit a desirable secondary transfer function and a fixing function at a stage where an image is formed through various process steps and then transferred to a final recording medium and then transferred to a fixing step. It is desirable that the liquid developer is in a dispersion state of approximately 40% to 60% in approximate toner weight ratio.

  In the image forming process using a liquid developer, in the process of transferring the developer to a recording medium such as development, primary transfer, and secondary transfer, the developer is dispersed with the carrier by applying a bias as a means for transferring toner particles. Particle migration takes place. Accordingly, when the toner particles are transferred, the transfer function is enhanced as the amount of the carrier is increased. On the other hand, when the developer is thermally fixed on the recording medium, the carrier becomes a requirement for inhibiting the fixing property. That is, the carrier interposed between the recording medium and the toner weakens the fixing force of the toner particles to the recording medium, and the carrier interposed between the toner particles weakens the binding force between the toner particles. Therefore, in order to increase the secondary transfer efficiency and improve the fixing rate of the toner to the recording medium, the secondary transfer is performed while maintaining the corresponding carrier amount in the secondary transfer stage, and this carrier is used in the fixing stage. It is desirable to fix the toner particles separately from the toner particles.

  As a result of repeated experiments by the inventors in order to establish this contradictory phenomenon, the carrier is dispersed in the carrier because the viscosity is lowered and the fluidity is improved when heated in the same manner as a general liquid. In addition to speeding up the movement of the toner particles, for example, when the recording medium is composed of fibers such as paper, the carrier is found to increase the speed of penetration into the fibers. The present inventors have conceived a configuration relating to a heating secondary transfer process which is a characteristic configuration of the present invention.

  The developer supply roller 32Y is a cylindrical member that rotates in a clockwise direction as shown in FIG. 2, for example, and has a fine and uniform spiral groove on the surface so that the developer can be easily carried on the surface. It is an anilox roller which formed the uneven surface by. The groove dimensions are such that the groove pitch is about 130 μm and the groove depth is about 30 μm. The developer supply roller 32Y supplies the liquid developer from the developer container 31Y to the developing roller 20Y. The stirring roller 34Y and the developer supply roller 32Y may be in sliding contact with each other, but may be arranged in a distant relationship.

  The regulating blade 33Y is composed of an elastic blade whose surface is covered with an elastic body, a rubber portion made of urethane rubber or the like that contacts the surface of the developer supply roller 32Y, and a metal plate or the like that supports the rubber portion. The Then, the film thickness and amount of the liquid developer carried and conveyed by the developer supply roller 32Y composed of an anilox roller are regulated and adjusted, and the amount of liquid developer supplied to the developing roller 20Y is adjusted. Note that the rotation direction of the developer supply roller 32Y may be the opposite direction instead of the arrow direction shown in FIG. 2, and the regulating blade 33Y at that time requires an arrangement corresponding to the rotation direction.

  The developing roller 20Y is a cylindrical member, and rotates counterclockwise around the rotation axis as shown in FIG. The developing roller 20Y is provided with an elastic layer made of polyurethane rubber, silicon rubber, NBR or the like on the outer periphery of an inner core made of metal such as iron. The developing roller cleaning blade 21Y is made of rubber or the like that comes into contact with the surface of the developing roller 20Y. The developing roller 20Y is arranged downstream of the developing nip portion where the developing roller 20Y comes into contact with the image carrier 10Y in the rotation direction of the developing roller 20Y. The liquid developer remaining on the developing roller 20Y is scraped off and removed.

  The developer compression roller 22Y is a cylindrical member having a structure in which a conductive resin layer or a rubber layer is provided on the surface layer of a metal roller base. For example, as shown in FIG. Rotate around. The developer compression roller 22Y has means for increasing the charging bias on the surface of the development roller 20Y, and the developer conveyed by the development roller 20Y is brought into sliding contact with the developer compression roller 22Y as shown in FIG. An electric field is applied from the developer compression roller 22Y side toward the developing roller 20Y at a compaction site to be formed. The electric field applying means for compaction may be corona discharge from a corona discharger instead of the roller shown in FIG. Some of the toner that has not been compacted by the developer compression roller 22Y is scraped off by the developer compression roller cleaning blade 23Y, merged with the developer in the reservoir 31Y, and reused.

  The image carrier squeeze device is disposed on the downstream side of the developing device 20Y so as to face the image carrier 10Y and collects the excess developer of the toner image developed on the image carrier 10Y, as shown in FIG. As described above, the image carrier squeeze roller 13Y made of an elastic roller member that is slidably contacted with the image carrier 10Y, the cleaning blade 14Y that presses and slidably contacts the image carrier squeeze roller 13Y, and the surface of the developer collecting unit 15Y. It consists of.

  In the primary transfer unit 50Y, the developer image developed on the image carrier 10Y is transferred to the intermediate transfer belt 40 by the primary transfer roller 51Y. Here, the image carrier 10Y and the intermediate transfer belt 40 are configured to move at a constant speed, reducing the driving load of rotation and movement, and suppressing the disturbance effect on the visible toner image of the image carrier 10Y. Yes. The primary transfer portion 50Y for the first color does not cause a color mixing phenomenon because it is the first primary transfer, but since the second and subsequent colors transfer different color toner images onto the already transferred primary toner image portions, the intermediate transfer belt 40 is overlapped. Due to the so-called reverse transfer phenomenon in which the toner moves from the image carrier 10 (M, C, K) to the image carrier 10 (M, C, K), the reverse transfer toner and the untransferred toner are mixed and are carried on the image carrier 10 (M, C, K) together with the surplus carrier. Moved from the image carrier by the action of the cleaning blade 17 (M, C, K) and pooled.

  The intermediate transfer belt squeeze device 52Y is disposed on the downstream side of the primary transfer unit 50Y, and removes excess carrier liquid from the intermediate transfer belt 40 to increase the toner particle ratio in the visible image. In the stage where the carrier amount of the developer (toner dispersed in the carrier) transferred to the intermediate transfer belt 40 by the transfer unit 50Y is secondarily transferred to the above-described final recording medium and proceeds to the fixing step (not shown). In order to exhibit a preferable secondary transfer function and fixing function, excess carrier is further removed from the intermediate transfer belt 40 when the approximate toner weight ratio of the desired dispersion state of the liquid developer has not reached about 40% to 60%. It is provided as a means. Similar to the image carrier squeeze device 52Y, the intermediate transfer belt squeeze device 52Y includes an intermediate transfer belt squeeze roller 53Y composed of an elastic roller member that is covered with an elastic body and is in sliding contact with the image carrier 40, and the image carrier 40. A backup roller 54Y disposed opposite to the intermediate transfer belt squeeze roller 53Y, a cleaning blade 55Y for pressing and slidingly contacting the intermediate transfer belt squeeze roller 53Y, and a developer collecting unit 56Y. The developer recovery unit 56Y also serves as a recovery mechanism for the carrier liquid recovered by the magenta image carrier squeeze roller cleaning blade 14M disposed on the downstream side thereof.

  The surplus carrier collecting ability can be set to a desired collecting ability according to the rotational direction of the intermediate transfer belt squeeze roller 53Y and the relative peripheral speed difference of the surface of the intermediate transfer belt squeeze roller 53Y with respect to the moving speed of the intermediate transfer belt 40. Thus, when the intermediate transfer belt 40 is rotated in the counter direction, the recovery capability is increased, and even if the peripheral speed difference is set to be large, the recovery capability is increased, and this synergistic action is also possible. In this embodiment, as an example, the intermediate transfer belt squeeze roller 53Y rotates with the intermediate transfer belt 40 at substantially the same peripheral speed, and a weight ratio of about 5 to 10% from the developer primarily transferred to the intermediate transfer belt 40 is obtained. The excess carrier and fog toner are collected to reduce both rotational driving loads and to suppress the disturbance effect on the toner image of the intermediate transfer belt 40.

  Next, the secondary transfer unit 60 will be described in more detail. FIG. 3 is a diagram showing a cross section of main components of the secondary transfer unit according to the embodiment of the present invention. The toner images that are primarily transferred from the plurality of image carriers 10Y, 10M, 10C, and 10K and overlaid with color are carried on an intermediate transfer belt 40 as an intermediate transfer member and conveyed to a secondary transfer portion. The intermediate transfer belt 40 is driven and conveyed by a secondary transfer roller 41, and the other side of the secondary transfer roller 41 is supported by at least one tension roller 42 that applies tension to the intermediate transfer belt 40 and stretches it. . The moving speed of the intermediate transfer belt 40 is synchronized with the moving speed of each image carrier.

  The intermediate transfer belt 40 of the present embodiment is not particularly limited as long as it has good heat resistance, but in the present embodiment, carbon that imparts conductivity to a polyimide resin material excellent in heat resistance and mechanical strength. A substrate in which a fine powder having excellent thermal conductivity such as black was dispersed in an endless belt was used as a base material. The fine powder excellent in thermal conductivity imparting conductivity is not limited to carbon black, and is a fine powder excellent in thermal conductivity such as magnesium oxide, silica, alumina, silicon nitride, zinc oxide, and the like. Also good.

  Thickness of 2 μm to 10 μm by imparting conductivity to the material having good heat resistance and releasability such as PFA and PTFE such as PFA and PTFE on the outer peripheral surface of the endless belt base material having the above structure by the same means as described above. Thus, the surface layer is covered by means such as coating to increase the transfer efficiency for transferring the developer in the heat transfer nip to the recording medium.

  Although it is desirable that the intermediate transfer belt 40 has a small heat capacity as much as possible in order to increase the preheating efficiency of the carried developer, in this embodiment, the thickness including the surface layer is set to 80 μm in consideration of mechanical strength. . The intermediate transfer belt 40 may be configured to have a thickness of 30 μm or less as long as the intermediate transfer belt 40 has a regulation configuration in which stress is not generated at the end in the meandering control of the intermediate transfer belt 40. For example, it may be configured with a thickness of 120 μm or more, but it is not very advantageous in consideration of cost.

  The secondary transfer roller 41 is configured to drive and convey the intermediate transfer belt 40 and includes a preheater heater 70 such as a halogen lamp inside as a heating unit, and the temperature is controlled by a control unit (not shown). The toner images that are primarily transferred from the plurality of image carriers 10Y, 10M, 10C, and 10K and overlaid with color are carried on the intermediate transfer belt 40 and conveyed to the secondary transfer site, and a preheater heater 70 is provided inside. Then, the secondary transfer roller 41 that is heated is wound around and heated.

  The secondary transfer roller 41 of the present embodiment is a heating source in which an elastic layer 72 having heat resistance and conductivity is formed on the outer periphery of a cored bar 71 made of a thin pipe material in order to reduce heat capacity. A preheating heater 70 such as a halogen lamp is built in, and is driven by a drive source (not shown) so as to be rotatable.

  The secondary transfer backup roller 61 is a structure that is disposed to face the secondary transfer roller 41 and presses it toward the secondary transfer roller 41 with a desired pressure. The secondary transfer roller 41 may be driven to rotate, or may be driven to rotate by a driving source (not shown).

  The secondary transfer roller 41 on which the elastic layer 72 is formed is configured to be driven by winding the intermediate transfer belt 40 around its outer periphery, and the elastic layer 72 has a corresponding frictional force in order to stabilize this drive. On the other hand, the intermediate transfer belt 40 that primarily transfers the toner images developed on the plurality of image carriers 10Y, 10M, 10C, and 10K and superimposes them in a predetermined relationship and conveys them in a moving direction. In order to perform regular regulation in the direction perpendicular to the movement, meandering is regulated by meandering regulation means (not shown). In order to achieve this meandering regulation mechanism, it is desirable that the frictional force of the secondary transfer roller 41 and the intermediate transfer belt 40 in the axial direction of the secondary transfer roller 41 is reduced as much as possible. Therefore, in this embodiment, in order to impart conductivity to the silicon rubber having excellent heat resistance for the elastic layer 72, carbon black fine powder is dispersed to form a desired conductivity. Since the tackiness is strong and the frictional force with the intermediate transfer belt becomes strong, which is not preferable for the above meandering regulation, the fluorine material that has high heat resistance and reduces frictional force such as fluororubber or fluororesin is further dispersed. Consists of materials. As a matter of course, the frictional force reducing measure is not limited to the method of dispersing the fluorine material in the silicon rubber, and for example, a conductive fluorine material that reduces the frictional force is coated on the outer periphery of the conductive silicon rubber or the like. The surface layer may be formed by covering the tube, or a lubricant such as heat-resistant conductive grease may be interposed between the contact surface of the conductive silicon rubber and the intermediate transfer belt.

In the above configuration, when a feeding trouble (common name: jam) of a recording medium to be fed to the nip in the secondary transfer unit 60 occurs, the recording medium is not interposed in the nip, so that the developer is a secondary transfer backup roller. Therefore, a secondary transfer roller cleaning blade 62 that is in sliding contact with the surface of the secondary transfer backup roller 61 is provided in order to remove this and prepare for the next secondary transfer. In order to effectively perform this cleaning function, it is desirable to have a structure in which the developer is easily peeled from the surface of the secondary transfer backup roller 61. The specific configuration of the secondary transfer backup roller 61 reduces the heat capacity. The outer periphery of the cored bar made of thin-walled pipe material is coated with a dispersion of fluorocarbon resin such as PFA resin that has heat resistance and conductivity and is excellent in developer release characteristics. It is preferable that the tube is covered. As described above, the secondary transfer backup roller 61 has a surface hardness higher than that of the elastic layer 72 of the secondary transfer roller 41 and is pressed toward the secondary transfer roller 41 and fed to the heated secondary transfer nip. A secondary transfer backup roller having a structure in which a heated secondary transfer nip is formed in which the elastic layer 72 of the secondary transfer roller 41 is recessed while the intruding recording medium and the intermediate transfer belt 40 are interposed. 61 has a higher elasticity than the elastic layer 72 of the secondary transfer roller 41 made of silicon rubber having heat resistance and conductivity at the outer peripheral portion of the cored bar made of a thin pipe material in order to reduce the heat capacity. The intermediate transfer belt 4 may be formed by coating or tube coating a carbon-dispersed PFA resin having excellent developer release characteristics on the surface on which the layer is formed. Forming effect a state in which modeled after the surface of the recording medium relative to the developer carried on the further improved.

  A state when the recording medium passes through the secondary transfer unit 60 configured as described above will be described. FIG. 4 is an enlarged view schematically showing a state of a cross section at the time of secondary transfer in the secondary transfer unit 60 according to the embodiment of the present invention.

  The secondary transfer backup roller 61 has a surface hardness higher than that of the elastic layer 72 of the secondary transfer roller 41. When the secondary transfer backup roller 61 is pressed toward the secondary transfer roller 41 side, the secondary transfer backup roller 61 is fed and enters the heated secondary transfer nip. As shown in FIG. 4 with the medium and the intermediate transfer belt interposed, a heated secondary transfer nip is formed in which the elastic layer 72 of the secondary transfer roller 41 is recessed. When the leading edge of the recording medium 100 is ejected from the heated secondary transfer nip in which the elastic layer 72 of the secondary transfer roller 41 is recessed, the elastic force of the recording medium 100 itself (commonly called the waist strength of the recording medium). ) And the deformation behavior of the recording medium 100, the leading edge of the recording medium 100 is smoothly separated without being wound around the intermediate transfer belt 40 to which the transfer bias is applied, and is discharged.

  Note that the secondary transfer backup roller 61 must have a conductive surface in order to make the transfer bias application effective, and is developed from the intermediate transfer belt 40 wound around the secondary transfer roller 41. In order to achieve a preferable transfer of the agent, the surface of the recording medium 100 is made as smooth as possible by utilizing the elasticity of the secondary transfer roller 41 with respect to the developer carried on the intermediate transfer belt 40. It is desirable to form a state that follows the surface. Specifically, it is preferable that the ten-point average roughness (Rz) is 0.5 to 10 times the volume average particle diameter of the toner particles 101.

  On the other hand, in the scene where the secondary transfer roller 41 forms a state in which the developer carried on the intermediate transfer belt 40 is made to follow the surface of the recording medium 100 using the elasticity of the secondary transfer roller 41 as described above. The hardness of the elastic layer 72 is more suitable for the purpose, but on the other hand, for the purpose of driving the intermediate transfer belt 40 regularly, the hardness of the elastic layer 72 is configured with a high hardness. At the same time, it is desirable that the thickness of the elastic layer 72 be made small in order to minimize the change in diameter due to thermal expansion. The specific configuration in the present embodiment is that the elastic layer 72 including the surface layer has a thickness of 0.4 mm and a hardness of JIS A 30 degrees, but a thickness of 0.3 mm and a hardness of JIS A 20 degrees level, or Even if the thickness is 1 mm and the hardness is JIS A 60 degree level, the purpose can be achieved.

  Next, the heaters in the secondary transfer unit 60 and the fixing unit 80 will be described. FIG. 5 is a diagram schematically showing axial sections of the secondary transfer unit 60 and the fixing roller 81 according to the embodiment of the present invention.

  As shown in the figure, the fixing roller 81 incorporates a heater including two halogen lamps along the axial direction of the fixing roller 81. These two heaters are a center heater 82 that heats the axial center of the fixing roller 81 and an end heater 83 that heats both ends in the axial direction, and when fixing a wide recording medium. When fixing a narrow recording medium by energizing both the central heater 82 and the end heater 83, the fixing roller 81 is heated by energizing only the central heater 82. Originally, it is more advantageous in terms of cost to configure a single heater in the fixing roller in the axial direction. However, in a configuration in which a single heater always heats the entire area in the axial direction of the fixing roller, fixing is performed. Overheating at both ends of the roller axis tends to occur. Therefore, in the fixing roller 81 of the present embodiment, when fixing a narrow recording medium, only the central heater 82 is energized to suppress the above-described overtemperature rise at both ends.

  As shown in FIG. 5, the secondary transfer roller 41 has a configuration in which an elastic layer is disposed on the surface of the roller core, and further, one preheating heater 70 is incorporated over the entire area in the axial direction of the secondary transfer roller 41. . The total length C of the preheating heater 70 of the secondary transfer roller 41 is longer than both the length A of the central heating heater 82 of the fixing roller 81 and the length 2B of both end portions of the end heating heater 83. To do. Further, the length C of the preheating heater 70 is configured to be longer than the width of the widest recording medium handled by the image forming apparatus. According to the preheating heater 70 configured as described above, since the secondary transfer roller 41 can be heated over the entire axial direction, even in the case of a wide recording medium, the moisture of the recording medium is efficiently transferred during the secondary transfer. It can be removed and blisters can be prevented. The efficient removal of moisture from the recording medium will be described in detail later.

  As described above, the heater built in the fixing roller 81 has a problem of excessive temperature rise at both ends of the roller. However, in the preheating heater 70 built in the secondary transfer roller 41, the secondary transfer roller 41 is set at room temperature or higher. Since the heating is performed to a temperature below the melting temperature of the toner particles (more specifically, about 50 ° C. if a temperature range is indicated), the problem of excessive temperature rise at both ends of the roller does not occur. Accordingly, the preheating heater 70 built in the secondary transfer roller 41 covers the entire axial direction of the secondary transfer roller 41 with one heater, and any one of the two heaters built in the fixing roller 81. Longer than that. Note that an elastic layer may be provided on the surface of the secondary transfer backup roller 61 or an elastic layer may not be provided.

  Next, the operation of the image forming apparatus of the present invention configured as described above will be described. In the secondary transfer process of the present embodiment, the movement of the toner particles dispersed in the carrier is speeded up by heating the developer carrier described above by the heating of the secondary transfer roller 41 by the preheating heater 70. This is based on the phenomenon that the penetration rate of the carrier improves into the fiber. However, the present invention is not limited to the liquid transfer type secondary transfer process, and the same effect as that of the toner and the recording medium can be obtained even when applied to the dry type electrophotographic secondary transfer process.

  The toner images that are primary-transferred from a plurality of image carriers 10Y, 10M, 10C, and 10K and overlaid are carried on the intermediate transfer belt 40, conveyed to the secondary transfer unit 60, and heated by the preheating heater 70. The secondary transfer roller 41 is wound around and heated. As described above, when the intermediate transfer belt 40 configured to have a very small heat capacity is wound around the secondary transfer roller 41, the intermediate transfer belt 40 is preheated together with the developer in a very short time due to the temperature of the heated secondary transfer roller 41. And proceeds to the secondary transfer nip portion.

  In FIG. 3, if the secondary transfer backup roller 61 is disposed immediately below the secondary transfer roller 41, the secondary transfer roller 61 enters the secondary transfer nip without the preheating. 41, the intermediate transfer belt 40 is disposed at a position shifted from the position where the intermediate transfer belt 40 starts to wind around the secondary transfer roller 41 to the secondary transfer nip entrance by an angle θa toward the downstream side, and can be sufficiently preheated. It is configured. FIG. 6 is a diagram illustrating a cross-section of main components of the secondary transfer unit 60 according to the comparative example. In the comparative example of FIG. 6, the secondary transfer backup roller 61 has a configuration closer to the winding start position of the secondary transfer roller 41 than the present embodiment, and the secondary transfer nip from the winding start position. The angle θb to the entrance is smaller than the angle θa of the present embodiment. In this case, the intermediate transfer belt 40 that has entered the winding start position has a short distance until it reaches the secondary transfer nip entrance, and the intermediate transfer belt 40 may not be sufficiently preheated. Then, the toner image on the intermediate transfer belt 40 is secondarily transferred to the recording medium at the secondary transfer nip with the secondary transfer backup roller 61 without sufficient preliminary heating. You may not be able to. Therefore, in the present embodiment, in particular, by setting θa ≧ 90 [deg], that is, as the distribution of the winding length of the winding portion of the intermediate transfer belt 40 with respect to the secondary transfer roller 41, the intermediate transfer member conveyance direction. The winding length from the upstream side (inlet side) to the center of the nip between the secondary transfer roller 41 and the secondary transfer backup roller 61 is from the center of this nip to the downstream side (outlet side) in the intermediate transfer member conveyance direction. By setting the length to be longer than the winding length, the toner image on the intermediate transfer belt 40 can be sufficiently preheated.

  In order to sufficiently preheat the toner image on the intermediate transfer belt 40, in order to increase the distance between the secondary transfer roller 41 and the intermediate transfer belt 40 until reaching the secondary transfer nip entrance, In the previous example, the angle θ from the winding start position to the secondary transfer nip entrance is increased. However, as another method, the secondary transfer roller 41 is extended by a plurality of rollers that stretch the intermediate transfer belt 40. It can be considered to set the largest of the rollers. FIG. 7 is a diagram showing main components of the image forming apparatus according to the embodiment of the present invention using the secondary transfer roller 41 having a large roller diameter. In this embodiment, as the secondary transfer roller 41, a roller having a larger warp than the tension roller 42 which is another roller on which the intermediate transfer belt 40 is stretched is used. In this case, the amount of winding of the intermediate transfer belt 40 with respect to the secondary transfer roller 41 is more than half of the roller length of the secondary transfer roller 41, and the winding length of the intermediate transfer belt 40 becomes longer due to the larger roller length. Accordingly, the distance that the secondary transfer roller 41 and the intermediate transfer belt 40 are in contact with each other can be increased. As a result, the toner image on the intermediate transfer belt 40 can be sufficiently preheated. In this example, the intermediate transfer belt 40 is stretched by two rollers, ie, a secondary transfer roller 41 and a tension roller 42, which are driving rollers. Even in the configuration in which the belt 40 is stretched, the secondary transfer roller 41 having the preheater heater 70 built therein has a larger roller length than the other rollers on which the intermediate transfer belt 40 is stretched. The distance that the next transfer roller 41 and the intermediate transfer belt 40 are in contact with each other can be increased, and a sufficient preheating effect can be expected.

  The heating secondary transfer process of the present embodiment does not completely fix the toner by the secondary transfer unit 60, but improves the secondary transfer efficiency and the fixing by the fixing unit 80 disposed on the downstream side. A heating temperature that improves the ability and achieves the object is sufficient.

  First, the preheating temperature will be described in detail with respect to the heating secondary transfer process of the present embodiment. By heating the carrier as described above, the movement of the toner particles dispersed in the carrier becomes faster and the carrier is made of fibrous material. The temperature at which the effect of increasing the penetration rate toward the inside is exhibited stably is the preheating temperature lower limit. As a result of repeated experiments, the present inventor has confirmed that a level of about 50 ° C. is preferable as the preheating temperature lower limit value. The upper limit of the preheating temperature is preferably set from the characteristic value (melting temperature) of the toner particles dispersed in the carrier. That is, in the heating secondary transfer process of the present embodiment, the secondary transfer roller 41 is heated by the preheating heater 70 to a temperature not lower than room temperature and not higher than the melting temperature of the toner particles. Of course, the temperature of the heating secondary transfer process is smaller than the temperature of the fixing process.

  In this embodiment, unlike the multi-stage toner image fixing configuration in which full-scale fixing is performed from the assumed arrival described in Patent Document 3, the fixing is completed only once and the invention described in Patent Document 3 is described. In this way, it is possible to achieve an energy-saving configuration without causing image deterioration, and at the heat transfer portion, the toner image carried on the intermediate transfer member can be secondarily transferred to the recording medium without melting. It is aimed. In other words, in this embodiment, when the intermediate transfer belt 40 having a very small heat capacity is wound around the secondary transfer roller 41 as described above, the temperature of the heated secondary transfer roller 41 and the developer are extremely short in a very short time. When the pre-heated state proceeds to the secondary transfer nip part, and joins the recording medium fed at a predetermined timing for heat transfer, a large amount of energy is applied to heat the recording medium at the heating transfer nip part. Therefore, the preheated developer temporarily drops in temperature.

  In this embodiment, the toner particles are set to a temperature at which the toner particles are not melted, including the preheated state and the state where the recording medium is further lowered from the temporary temperature drop state. Specifically, the melting point of the toner particles of the present embodiment is set. Is about 80 ° C., and the secondary transfer roller 41 is heated to about 80 ° C. When a recording medium containing moisture is fed in this configuration, at least the corresponding moisture is removed by heating, and the image disorder called blister: blister described in Patent Document 3 is described. Useful in preventing

  Next, the relationship between the heating of the secondary transfer roller 41 and the intermediate transfer belt 40 will be described. The toner images temporarily transferred from the plurality of image carriers 10Y, 10M, 10C, and 10K and overlaid with color are carried on the intermediate transfer belt 40 and conveyed to the secondary transfer portion, and the toner particles are brought to a temperature that does not melt. The preheated developer is secondarily transferred to the recording medium in the heated secondary transfer nip, and the intermediate transfer belt 40 is disposed on the other side of the secondary transfer roller 41 and is tensioned by applying tension to the intermediate transfer belt 40. It moves toward the tension roller 42.

  As described above, the intermediate transfer belt 40 is configured to have a very small heat capacity. Therefore, the intermediate transfer belt 40 moves away from the secondary transfer roller 41 having a heating source, passes through the tension roller 42, and reaches the first elephant carrier 10Y. Then, the image is cooled again and proceeds to the next image forming step. However, since the heating temperature at the secondary transfer roller 41 is low and sufficient cooling is performed in the moving path of the intermediate transfer belt 40, the image is transferred. There is no problem as described in Patent Document 1 in which the support is not only unable to exhibit its original image support function due to the influence of heat but also shortens its life. If the intermediate transfer belt 40 is not cooled sufficiently so as not to adversely affect the image carrier, cooling means such as a cooling fan may be provided in the moving path of the intermediate transfer belt 40. On the other hand, since the developer preheated to a temperature at which the toner particles are not melted is secondarily transferred to the recording medium at the heated secondary transfer portion of the present embodiment, the purpose of the preheating is to improve the secondary transfer efficiency. Therefore, this preheating temperature does not require severe temperature control as performed by a general fixing device. In this embodiment, the halogen lamp of the preheating heater 70 built in the secondary transfer roller 41 is used for the secondary transfer. The roller 41 is configured to have the same length as that of the secondary transfer roller 41 in the axial direction so as to uniformly heat the entire area of the secondary transfer roller 41, and is uniform with a configuration including one halogen lamp. It is possible to sufficiently perform functions such as temperature distribution.

  The secondary transfer roller 41 is heated uniformly over substantially the entire area in the axial direction, and the sufficiently cooled intermediate transfer belt 40 has a width substantially the same as the axial length of the secondary transfer roller 41 to form the secondary transfer roller 41. Since the transfer roller 41 is wound and driven over substantially the entire area, the amount of heat for preheating the intermediate transfer belt 40 carrying the developer is substantially uniform in the axial direction. On the other hand, the recording medium to be fed has various sizes and is heated in the heated secondary transfer nip, but enters the overheated secondary transfer nip opposite to the preheated developer in advance. Compared with the case where the developer is heated from the zero base stage, it is not necessary to consider the heating temperature response. Further, the secondary transfer backup roller 61 disposed so as to face the secondary transfer roller 41 with the intermediate transfer belt 40 interposed therebetween is configured to have substantially the same axial length as the secondary transfer roller 41 and the intermediate transfer belt 40. In addition, since the secondary transfer roller 41, the intermediate transfer belt 40, the halogen lamp of the preheating heater 70, and the secondary transfer backup roller 61 are arranged at substantially the opposite positions, the axial heat distribution at the heating secondary transfer site is Plays a uniform effect.

  Next, the heating secondary transfer resistance value and the bias application relationship will be described. The secondary transfer roller 41 of the present embodiment has a heat resistant and conductive elastic layer 72 formed on the outer periphery of a cored bar made of a thin pipe material in order to reduce the heat capacity, and a halogen as a heating source inside. A lamp (preheating heater 70) is built in, and is configured to be rotatable by being driven by a drive source (not shown). Then, in order to impart conductivity to the silicon rubber having excellent heat resistance, the elastic layer 72 has a desired conductivity by dispersing fine carbon black powder and the like, and the silicone rubber generally has tackiness. Since it is strong and the frictional force with the intermediate transfer belt 40 becomes strong and is not preferable for the above meandering regulation, it is a material in which a fluorine material that has high heat resistance and reduces frictional force such as fluororubber or fluororesin is further dispersed. It is configured and conductive.

In addition, as a measure for reducing the frictional force, the method is not limited to the method of dispersing the fluorine material in the silicone rubber. For example, the outer periphery of the conductive silicone rubber is coated with a conductive fluorine material or the like that reduces the frictional force or the tube is covered. The surface layer may be configured, or a lubricant such as heat-resistant conductive grease may be interposed on the contact surface between the conductive silicone rubber and the intermediate transfer belt. Including the volume resistance value of the portion in contact with the intermediate transfer belt 40 is a low resistance of 10 ⁵ Ω or less.

On the other hand, the intermediate transfer belt 40 is an endless belt formed by dispersing fine powder having excellent thermal conductivity such as carbon black imparting conductivity to a polyimide resin material having excellent heat resistance and mechanical strength. Constructed as a base material, a material having good heat resistance and releasability such as PFA and PTFE fluororesin on the outer peripheral surface of the endless belt base material is given conductivity by the same means as described above, and 2 μm The surface layer is coated with a means such as coating with a thickness of 10 μm to increase the transfer efficiency for transferring the developer in the heated secondary transfer nip to the recording medium, and the volume including the belt base material and the surface layer The resistance value is in the middle resistance range of 10 ⁶ Ω to ^{10 10} Ω, which is larger than the volume resistance value of the secondary transfer roller 41. The secondary transfer backup roller 61 is made of PFA resin having heat resistance and conductivity on the outer periphery of the cored bar made of a thin pipe material to reduce the heat capacity, and having excellent developer peeling characteristics. Carbon black fine powder powder or the like is dispersed or coated with a tube or the like, and the volume resistance value of the surface layer portion is a low resistance of 10 ⁵ Ω or less, which is smaller than the volume resistance value of the intermediate transfer belt 40. It is configured.

  In the relationship between the secondary transfer roller 41, the intermediate transfer belt 40, and the secondary transfer backup roller 61, when a secondary transfer bias is applied in such a direction that the toner particles move toward the recording medium that has entered the heating secondary transfer nip. As shown in FIG. 4, the developer that is substantially carried by the intermediate transfer belt 40 is conveyed to the toner particles 101 on the intermediate transfer belt 40 side. In the heated secondary transfer nip, the agglomerated toner particles 101 move to the recording medium 100 side, and good secondary transfer of the toner particles 101 can be obtained. On the other hand, a part of the carrier 102 moves to the recording medium 100 side, but most of the carrier 102 remains on the intermediate transfer belt 40 side and is transported to clean the intermediate transfer belt at the portion of the tension roller 42 disposed on the other side of the secondary transfer roller 41. It is removed by the blade 46.

  Next, a fixing process in the fixing unit after the secondary heating transfer will be described. As described above, in the present embodiment, when a recording medium containing moisture is fed, at least the corresponding moisture is removed by heating and the recording medium that has passed through the heated secondary transfer nip is The developer is carried on the secondary transfer and maintained in a heated state up to the heated secondary transfer nip portion, proceeds to the fixing process, and proceeds to the fixing nip of the fixing unit 80. Therefore, blisters generated in the fixing nip: image disturbance called blistering is prevented, and the heated state is maintained and the fixing unit 80 proceeds to the fixing nip. Fixing heat efficiency is good instead of heating.

  Further, in order to prevent the above-described blistering caused by the evaporation of water contained in the recording medium, it is possible to construct and contain a nip pressure that can overcome the vapor pressure over the entire fixing nip. However, in the configuration of this embodiment, the recording medium that enters the fixing nip is heated in advance and the corresponding moisture is removed, so that the fixing nip pressure may be low.

  However, since the liquid developing type developer contains a carrier component in addition to the toner particles, the fixing unit 80 of this embodiment has a built-in heat source for the purpose of forming the fixing nip as long as possible to stabilize the fixing characteristics. A first pressure roller 84 and a second pressure roller 85 constituting a predetermined fixing nip pressure are provided opposite to the fixing roller 81, and these pressure rollers are made of, for example, a polyimide material having excellent heat resistance and stable strength. The formed endless belt (fixing belt 86) is wound around, and a tension roller is provided on the other side to apply tension to the endless belt and urge the endless belt to the fixing roller 81, thereby extending the fixing nip. It is formed.

The fixing nip of the fixing unit 80 having the above structure is adjusted to a temperature of about 190 ° C., and a recording medium in which the above-mentioned developer is supported on the secondary transfer and kept in the heated secondary transfer nip portion is maintained. When it penetrates, the moisture contained in the recording medium is reduced, so that it is possible to prevent image disturbance called blister: blister, and the toner particles are melted and fixed on the recording medium in the fixing nip. Therefore, image defects such as the toner image becoming thick or misaligned that occur in the invention described in Patent Document 3 do not occur in the present invention. In addition, since the relatively low temperature heating secondary transfer process and the main fixing process in the fixing unit 80 can be configured by efficiently sharing energy, an energy-saving product configuration is also possible.

1 is a diagram illustrating main components constituting an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating main components of an image forming unit and a developing unit. It is a figure which shows the cross section of the main components of the secondary transfer unit 60 which concerns on embodiment of this invention. It is the figure which expanded and showed the mode of the cross section at the time of the secondary transfer in the secondary transfer unit 60 which concerns on embodiment of this invention. FIG. 3 is a diagram schematically showing a cross section in the axial direction of each of a secondary transfer unit 60 and a fixing roller 81 according to an embodiment of the present invention. It is a figure which shows the cross section of the main components of the secondary transfer unit 60 which concerns on a comparative example. FIG. 3 is a diagram illustrating main components of an image forming apparatus according to an embodiment of the present invention using a secondary transfer roller 41 having a large roller diameter.

Explanation of symbols

10Y, 10M, 10C, 10K ... image carrier, 11Y, 11M, 11C, 11K ... charging roller, 12Y, 12M, 12C, 12K ... exposure unit, 13Y ... image carrier squeeze roller, 14Y: Image carrier squeeze roller cleaning blade, 15Y: Developer recovery unit, 16Y: Latent image eraser, 17Y: Image carrier cleaning blade, 18Y ... Developer recovery unit, 20Y, 20M, 20C, 20K ... developing roller, 21Y ... developing roller cleaning blade, 22Y ... developer compression roller, 23Y ... developer compression roller cleaning blade, 30Y, 30M, 30C, 30K ... Developing unit, 31Y, 31M, 31C, 31K ... Developer container, 32Y, 32M, 32C, 32K ... Image supply roller, 31Y, 31M, 31C, 31K ... developer container, 33Y ... regulating blade, 21Y, 34Y ... stirring roller, 40 ... intermediate transfer belt, 41 ... secondary transfer Roller, 42 ... tension roller, 46 ... intermediate transfer belt cleaning blade, 47 ... developer recovery unit, 50Y, 50M, 50C, 50K ... primary transfer unit, 51Y, 51M, 51C, 51K ..Primary transfer backup roller, 52Y, 52M, 52C, 52K ... intermediate transfer belt squeeze unit, 53Y ... intermediate transfer belt squeeze roller, 54Y ... intermediate transfer belt squeeze backup roller, 55Y ... intermediate transfer Belt squeeze roller cleaning blade, 56Y ... developer recovery unit, 60 ... secondary transfer unit 61 ... secondary transfer backup roller 62 ... secondary transfer backup roller cleaning blade 63 ... developer recovery part 70 ... preheating heater 71 ... core metal 72 ... Elastic layer, 80 ... Fixing unit, 81 ... Fixing roller, 82 ... Central heater, 83 ... End heater, 84 ... First pressure roller, 85 ..Second pressure roller, 86 ... fixing belt, 100 ... recording medium, 101 ... toner particles, 102 ... carrier

Claims (9)

A secondary transfer portion for secondary transfer of the toner image to a recording medium fed so as to be in contact with the toner image carried on the intermediate transfer member, and toner transferred on the recording medium by the secondary transfer portion; A fixing unit that heats and permanently fixes an image; a secondary transfer roller that is provided in the secondary transfer unit and stretches the intermediate transfer member so as to contact the inner peripheral surface of the intermediate transfer member; and the secondary transfer roller A secondary transfer backup roller provided in the transfer portion and arranged to sandwich the intermediate transfer member together with the secondary transfer roller, and a toner image on the intermediate transfer member provided in the secondary transfer roller is preheated In an image forming apparatus having a preheating heater and a fixing heater provided in the fixing unit and performing fixing heating,
The image forming apparatus, wherein the intermediate transfer member is stretched by a plurality of rollers, and the secondary transfer roller has the largest diameter among the plurality of rollers. The image forming apparatus according to claim 1, wherein the secondary transfer roller is a drive roller that drives the intermediate transfer member. 3. The image forming apparatus according to claim 1, wherein a winding amount of the intermediate transfer member around the secondary transfer roller is equal to or more than a half circumference of the secondary transfer roller. The image forming apparatus according to claim 1, wherein the image forming process is a dry electrophotographic process, and the volume average particle diameter of the toner particles is 2 μm or more and 5 μm or less. The image according to any one of claims 1 to 3, wherein the image forming process is an electrophotographic process of a liquid development system, and the volume average particle diameter of the toner particles is 0.5 µm or more and 2 µm or less. Forming equipment. 6. The fixing heater according to claim 1, wherein a plurality of the fixing heaters are provided, and the length of the preheating heater is longer than any of the plurality of heaters of the fixing heater. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 6, wherein the length of the preheating heater is equal to or greater than a width of the widest recording medium handled by the image forming apparatus. apparatus. 8. The image forming apparatus according to claim 1, wherein the intermediate transfer member has a surface layer in which a fluororesin is coated on an outer peripheral surface of an endless belt base material. 9. The image forming apparatus according to claim 1, wherein the secondary transfer roller has a surface layer coated with a fluororesin on an outer peripheral surface of a core metal substrate.

Images