JP2010127967A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus including a plurality of fixing means for fixing requiring a great amount of heat, reducing occurrence of paper blisters to obtain high-quality fixing without any high-temperature offset or separability problem, and performing efficient fixing with relatively low energy. <P>SOLUTION: The image forming apparatus includes a heating and pressing means and a noncontact heating means as fixing means, and an exhaust flow passage for letting exhaust air from the noncontact heating means, which generates more heat, flow toward the heating and pressing means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a heating and pressing unit and a non-contact heating unit as a fixing unit for fixing a toner image formed on a recording medium.

  2. Description of the Related Art An electrophotographic image forming apparatus that forms an electrostatic latent image on a photoreceptor (photosensitive drum), develops it with toner, and transfers and fixes the toner image onto paper or the like is widely used.

  As a developing method for developing an electrostatic latent image using a dry developer, a one-component developing method using only a toner and a two-component developing method using a toner and a carrier are known.

  The one-component development method is generally advantageous in terms of simplification, miniaturization, and cost reduction of the apparatus, but the life of the development apparatus is short. The two-component development method is advantageous for long life, but has problems such as generation of magnetic brush marks on the developed image.

  In recent years, a wet development method using a liquid developer having a small toner particle diameter and hardly disturbing a toner image has been used.

  As the liquid developer, it is common to use a liquid developer in which toner is dispersed at a high concentration in a “carrier liquid” as a solvent.

  The method of developing the latent image on the photoconductor differs between a dry development method using a one-component developer or a two-component developer and a wet development method using a liquid developer, but both are developed on the photoconductor by development. A toner image as an image is formed.

  This toner image is transferred to a recording medium. Alternatively, the toner image is first temporarily transferred to an intermediate transfer member or the like and then secondarily transferred to a recording medium.

  The toner image transferred to the recording medium is fixed on the recording medium, which is usually paper, by being pressurized and heated by a fixing device.

  As a general fixing unit, a heating and pressurizing unit that heats while pressing at a nip portion of a recording medium with a heated roller or the like is used like a roller fixing unit.

  Further, in order to avoid contact pressure at the nip portion, a non-contact heating means may be used in which a heat source such as a heater is disposed at a position not in contact with the recording medium and is heated and fixed by radiant heat or the like.

  In any case, fixing the toner image requires a large amount of heat energy for fusing the toner, and it is necessary to appropriately control the fixing temperature in order to ensure the fixing quality.

  In particular, in the case of a toner image developed using a liquid developer, a solvent (hereinafter also referred to as a carrier liquid) is contained between the toners of the toner images and between the toner papers, and the fixing is usually performed only by fusing the toners. More energy input is required.

  In addition, the carrier liquid may cause problems such as a decrease in toner image fixability, collapse or disorder of the image during pressure fixing, and acceleration of back-faced display where the toner image on the front surface can be seen through.

  In general, in order to supply a large amount of heat energy by the heating and pressurizing means, more heat energy can be added by expanding the nip, but the fixing device tends to be large. If the nip time is increased, a blistering phenomenon called blister tends to occur in the case of coated paper. There may also be problems with high temperature offset and separability.

  In addition, for the liquid developer, a problem of efficiently removing the liquid developer by volatilizing the solvent (carrier liquid) from the recording medium having the unfixed toner image at the time of fixing has been studied.

  On the other hand, a plurality of fixing means (heating and pressing means) are used to form a multi-stage fixing (for example, refer to Patent Documents 1 and 3), or non-contact heating means is provided (for example, refer to Patent Document 2). ) Fixing technology has been developed.

According to the technique described in Patent Document 1, the nip is divided by a plurality of roller fixing devices (heating and pressing means), and the fixing temperature is set so that the fixing device on the most downstream side becomes the highest, thereby generating blisters. It is preventing. Further, according to Patent Document 2, after preheating by a plate-like heating element (non-contact heating means), fixing is performed by a pressure heating means similarly heated by a plate-like heating element, thereby saving power and shortening the warm-up time. Technology has been advocated. According to Patent Document 3, two roller fixing devices (heating and pressing means) are arranged in multiple stages, and the exhaust heat path from the first fixing device is configured to pass through the second fixing device, so that the energy can be used efficiently. The technology to plan is proposed.
JP-A-11-202675 JP-A-10-133506 JP 2006-58646 A

  As described above, in the case of fixing that requires a large amount of heat, for example, volatilization of a solvent from a recording medium, it is a problem that fixing quality is not caused, and fixing is performed efficiently with low energy.

  In the technique described in Patent Document 1, the increase in the fixing temperature is suppressed by a plurality of roller fixing devices, and blistering prevention is performed. However, particularly when a large amount of heat is required such as volatilization of a solvent, heat supply is insufficient. It is. In addition, a plurality of heating and pressurizing means are arranged, and the problems of high temperature offset and separability due to the plurality of nip portions are not sufficiently solved.

  In the technique described in Patent Document 2, pre-heating is performed by a plate-like heating element, but this is a non-contact heating method, and if it is left as it is, a large amount of heat is diffused by radiation and thermal efficiency is not good.

  In the technique described in Patent Document 3, the heat exhaust path from the roller fixing device is routed through another roller fixing device. However, all of them are fixed by pressing the roller as heating and pressing means. The amount of exhaust heat is not so large, and improvement in thermal efficiency cannot be expected. Further, the volatilization promotion of the solvent is insufficient, and the problems of high temperature offset and separability due to a plurality of nip portions are not sufficiently solved.

  The present invention has been made in view of the above technical problems. An object of the present invention is to obtain a high-quality fixing by suppressing the occurrence of paper blisters in an image forming apparatus having a plurality of fixing means for fixing that requires a large amount of heat, without causing problems with high-temperature offset and separability. And an image forming apparatus capable of fixing efficiently with relatively low energy.

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

  1. As a fixing means for fixing the toner image formed on the recording medium, a heating / pressurizing means for bringing a heated member into contact with the recording medium and heating while pressing, and the recording medium as a non-contact heat source An image forming apparatus comprising: a non-contact heating unit that heats by heat radiation from the non-contact heating unit, wherein the image forming apparatus includes an exhaust passage for flowing exhaust from the non-contact heating unit toward the heating and pressurizing unit. An image forming apparatus.

  2. 2. The image forming apparatus according to 1, wherein the exhaust flow path includes a flow path changing unit for preventing the exhaust from the non-contact heating unit from flowing toward the heating and pressurizing unit.

  3. 3. The image forming apparatus according to 2, wherein the flow path changing unit changes the flow path according to the temperature of the heating and pressurizing unit.

  4). 4. The image forming apparatus according to claim 1, wherein the non-contact heating unit is disposed downstream of the heating and pressurizing unit in the recording medium passing direction.

  5. The image forming apparatus according to any one of 1 to 4, wherein the toner image on the recording medium is developed using a liquid developer.

  In the image forming apparatus according to the present invention, for fixing that requires a large amount of heat, the heating and pressurizing unit and the non-contact heating unit are used as the fixing unit, and the exhaust from the non-contact heating unit that generates more heat. Has an exhaust passage for flowing toward the heating and pressurizing means. As a result, there is no problem in high temperature offset and separability, generation of paper blisters can be suppressed, high quality fixing can be obtained, and fixing can be performed efficiently with relatively low energy.

  An image forming apparatus according to an embodiment of the invention will be described with reference to the drawings.

  Liquid development using a liquid developer is used in image forming apparatuses such as copying machines, simple printing machines, and printers. In general, an electrophotographic image forming process is commonly used for these. First, the electrophotographic wet image forming unit will be described with reference to FIG. 1, and a fixing device that heats and fixes a pre-fixed toner image that has been developed using a liquid developer and transferred to a recording medium. The configuration and functional operation will be described.

(Configuration of image forming unit and functional operation)
An example of the configuration and operation of the toner image forming unit in the image forming apparatus of this embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view illustrating a schematic configuration example of a toner image forming unit, a transfer device, and a fixing device in a wet image forming apparatus.

  In FIG. 1, reference numeral 1 denotes a photosensitive drum, which functions as an image carrier. The toner image forming unit 10 has a charging device 2 for uniformly charging the surface of the photosensitive drum 1 disposed around the photosensitive drum 1 around the photosensitive drum 1, and an LED or a laser on the charged photosensitive drum 1. An exposure device 3 for irradiating a beam to form an electrostatic latent image; a liquid developing device 4 for developing the electrostatic latent image using a liquid developer; an intermediate transfer member 5 to which the developed toner image is transferred; A cleaning device 6 for removing the liquid developer remaining on the surface of the photosensitive drum 1 after the transfer is provided.

  In general, the liquid developing device 4 carries a thin layer of a liquid developer on its surface, a developing roller 41 for developing a latent image on the photosensitive drum 1 as an image carrier, and a liquid developer 8 on its surface. Developer tank 44 and the like.

  In some cases, before and after the liquid developing device 4, a device for applying or collecting a part of the liquid developer in advance is provided. Here, a squeeze device 61 for removing excess liquid developer from the developed toner image is provided after the liquid developing device 4.

  The developed toner image on the photosensitive drum 1 may be transferred directly to the recording medium 7 such as a recording sheet instead of the intermediate transfer member 5. In the present embodiment, the toner image primarily transferred to the intermediate transfer member 5 is transferred to the recording medium 7 again (secondary transfer) using the transfer roller 51. Normal paper is used as the recording medium 7, and in the following description, the recording medium 7 will be described as recording paper (hereinafter referred to as recording paper 7).

  In FIG. 1, only one set of toner image forming units 10 is arranged, but a plurality of sets may be arranged around the intermediate transfer body 5 for forming a color image. The color development method, the presence / absence of intermediate transfer, and the like may be set arbitrarily, and an arbitrary arrangement according to it can be taken.

  The photosensitive drum 1 rotates in the direction of arrow A shown in FIG. 1, and the charging device 2 charges the surface of the rotating photosensitive drum 1 to about several hundred volts by corona discharge or the like. On the downstream side of the charging device 2 in the rotation direction of the photosensitive drum, an electrostatic latent image whose surface potential is lowered to about 100 V or less is formed by the laser beam emitted from the exposure device 3.

  A liquid developing device 4 is disposed further downstream of the exposure device 3, and the electrostatic latent image formed on the photosensitive drum 1 is developed using the liquid developer 8.

  In the liquid developing device 4, a liquid developer 8 in which toner is dispersed in an insulating solvent (hereinafter also referred to as carrier liquid) is accommodated in a developer tank 44, and the liquid developer is provided on the surface of the developing roller 41. 8 is supplied, and a thin layer of the liquid developer 8 is carried on the developing roller 41.

  Further, due to the potential difference between the developing roller 41 and the electrostatic latent image on the photosensitive drum 1, the toner particles in the thin layer of the liquid developer 8 carried on the developing roller 41 become an electrostatic latent image on the photosensitive drum 1. Moving, the electrostatic latent image is developed.

  The developed toner image on the photosensitive drum 1 contains a liquid developer 8, that is, toner and carrier liquid. The squeeze device 61 is, for example, a squeeze roller, and removes excess carrier liquid from the developed toner image. The carrier liquid on the squeeze roller is removed by the blade 62.

  The intermediate transfer member 5 rotates in the direction of arrow B shown in FIG. 1 and is applied with a bias voltage at the nip portion with the photosensitive drum 1 that similarly rotates in contact with the intermediate transfer member 5, thereby developing the developed toner on the photosensitive drum 1. The image is primarily transferred onto the intermediate transfer member 5.

  When a plurality of sets of toner image forming units 10 are arranged around the intermediate transfer member 5 for color image formation, the toner images of the respective colors developed in the toner image forming units are superimposed on the intermediate transfer member 5. In each case, primary transfer is performed.

  In the toner image forming unit 10, a cleaning device 6 (for example, a cleaner blade) that removes the liquid developer 8 remaining on the surface of the photosensitive drum 1 after the primary transfer is disposed on the downstream side of the intermediate transfer member 5. ing. The cleaning device 6 removes the liquid developer 8 remaining on the photosensitive drum 1.

  The toner image primarily transferred onto the intermediate transfer member 5 is sandwiched between the recording paper 7 conveyed in the direction of arrow C in FIG. 1 at the same speed as the peripheral speed of the intermediate transfer member 5 at the nip portion with the transfer roller 51, By applying a bias voltage, the image is secondarily transferred onto the recording paper 7.

  The recording paper 7 onto which the toner image has been transferred by the transfer roller 51 is conveyed to the fixing device 9 and is discharged after being heated and fixed.

  Details of the heating means of the toner image at the time of fixing and the volatilization and fixing of the carrier liquid thereby will be described later as an embodiment of the fixing device 9.

(Developer composition)
The liquid developer 8 used for development will be described. In the liquid developer 8, colored toner particles are dispersed at a high concentration in a carrier liquid as a solvent. In addition, additives such as a dispersant and a charge control agent may be appropriately selected and added to the liquid developer 8.

  Any carrier liquid can be used without particular limitation as long as it is generally used as an electrophotographic developer. In consideration of safety, an insulating, non-volatile solvent at room temperature is used. Examples of the non-volatile solvent include silicon oil, mineral oil, paraffin oil, mineral oil, and the like.

  The toner particles are mainly composed of a resin and a pigment or dye for coloring. The resin has a function of uniformly dispersing pigments and dyes in the resin and a function as a binder when being fixed to the recording material.

  Examples of the resin that can be used include thermoplastic resins such as polystyrene resin, styrene-acrylic resin, acrylic resin, polyester resin, epoxy resin, polyamide resin, polyimide resin, and polyurethane resin. A plurality of these resins may be mixed and used.

  Commonly commercially available pigments and dyes used for coloring the toner can also be used. For example, carbon black, bengara, titanium oxide, silica, phthalocyanine blue, phthalocyanine green, sky blue, benzidine yellow, lake red D, etc. can be used as the pigment. Solvent red 27, acid blue 9, or the like can be used as the dye.

  As a method for adjusting the liquid developer, it can be adjusted based on a commonly used technique. For example, the resin and the pigment are melt kneaded using a pressure kneader, a roll mill or the like at a predetermined blending ratio and uniformly dispersed, and the obtained dispersion is finely pulverized by, for example, a jet mill. Further, by classifying the obtained fine powder with, for example, an air classifier, a colored toner having a predetermined particle diameter can be obtained.

  Subsequently, the obtained toner is mixed with an insulating liquid as a carrier liquid at a predetermined blending ratio. This mixture can be uniformly dispersed by a dispersing means such as a ball mill to obtain a liquid developer.

  The volume average particle diameter of the toner is suitably in the range of 0.1 μm or more and 5 μm or less. When the average particle diameter of the toner is less than 0.1 μm, the developability is greatly lowered. On the other hand, when the average particle diameter exceeds 5 μm, the quality of the image is degraded.

  An appropriate ratio of the toner particles to the liquid developer is about 10 to 50% by mass. When the amount is less than 10% by mass, the toner particles are liable to settle, and there is a problem in stability over time during long-term storage. Further, in order to obtain a required image density, it is necessary to supply a large amount of developer, the carrier liquid adhering to the paper increases, and it must be dried at the time of fixing, and steam is generated, resulting in environmental problems. If it exceeds 50% by mass, the viscosity of the liquid developer becomes too high, making it difficult to manufacture and handle.

  The viscosity of the liquid developer is preferably from 0.1 mPa · s to 10,000 mPa · s at 25 ° C. When it is 10,000 mPa · s or more, it becomes difficult to stir the carrier liquid and the toner, and the burden on the apparatus surface for obtaining a uniform liquid developer is large.

(Fixing device configuration and functional operation)
FIG. 2 shows a schematic configuration example of the fixing device in the image forming apparatus of FIG. A configuration example and functional operation of the fixing device will be described with reference to FIG.

  The fixing device 9 has a plurality of heating means for fixing. A roller fixing device 101 as a heating and pressing unit and a non-contact heater 102 as a non-contact heating unit. Each of the heating means includes a non-contact heating means (non-contact heating means) on the downstream side in the sheet passing direction of the recording paper 7 after the recording paper 7 carrying the unfixed toner image passes through the heating and pressurizing means (roller fixing device 101). It is arranged to receive the thermal radiation of the contact heater 102). That is, it is arranged so as to be a multi-stage fixing method, and each temperature control is performed accordingly.

<Roller fixing device>
The roller fixing device 101 which is a heating and pressing unit will be described.

  91a is a fixing roller, and 91b is a pressure roller. As shown in the drawing, the fixing roller 91a and the pressure roller 91b are arranged so that the rotation shafts are parallel to each other in the vertical direction, and both ends in the axial direction are rotatably supported by bearing members (not shown). Further, the pressure roller 91b is urged in the direction of the fixing roller 91a with a predetermined pressure contact force by a pressure mechanism (not shown) using a spring or the like, and a pressure nip portion is formed on the lower surface portion of the fixing roller 91a. .

  The pressure roller 91b is rotationally driven at a predetermined peripheral speed in the direction of the arrow by a drive mechanism (not shown). The fixing roller 91a is rotated by the rotation of the pressure roller 91b by the pressure frictional force with the pressure roller 91b at the pressure nip portion. The fixing roller 91a may be driven to rotate, and the pressure roller 91b may be driven to rotate.

  The fixing roller 91a and the pressure roller 91b each include heater lamps 92a and 92b, and the surface temperature is controlled to a desired temperature by a control unit (not shown).

  The fixing roller 91a and the pressure roller 91b are provided on the outer periphery of a metal core having a good thermal conductivity such as aluminum, and a silicon rubber layer as an elastic layer for securing a nip width, in order to improve the surface releasability. And a release layer made of fluororesin such as PTFE or PFA having a thickness of 10 to 50 μm.

<Non-contact heater>
The non-contact heater 102 which is a non-contact heating means will be described.

  In the non-contact heater 102, a heater 94 is installed in a heat insulating cover 95. The surface temperature of the heater 94 is controlled to a desired temperature by control means (not shown). In the non-contact heater 102, the recording paper 7 is conveyed by a recording paper conveying means (not shown) arranged on the non-image surface side. The heater 94 may be a long-wavelength heater such as a ceramic heater in consideration of the difference in light absorption between black toner and yellow, magenta, cyan, and non-image portions.

  The surface temperature of the ceramic heater is about 500 to 700 ° C. The heat insulating cover 95 for keeping the inside of the non-contact heater 102 at a high temperature may be made of a highly heat insulating and heat resistant material such as ceramic fiber.

<Fixing operation>
The toner image and carrier liquid secondarily transferred from the intermediate transfer body 5 to the recording paper 7 reach the roller fixing device 101.

  The recording paper 7 on which the toner image and the carrier liquid are put is pressed and heated at the pressure nip portion of the roller fixing device 101, the toner is melted, a part of the carrier liquid is volatilized at the nip outlet, and a part is a fixing roller. It is removed by 91a. However, most of the carrier liquid transferred to the recording paper 7 remains in the toner image or the recording paper 7.

  When the recording paper 7 passes through the roller fixing device 101 which is a heating and pressurizing means, it is not necessary to secure sufficient fixing property yet. This is because the fixing device 9 is a two-stage fixing method, and the toner is melted and the carrier liquid is volatilized also in the non-contact heater 102 which is a non-contact heating means arranged downstream.

  When the recording paper 7 reaches under the heat radiation by the non-contact heater 102, the recording paper 7 on which the toner image and the carrier liquid are put is heated mainly by the heat radiation from the heater 94, and most of the remaining carrier liquid. Volatilizes.

  In order to volatilize efficiently, not only the temperature of the recording paper 7 (the temperature of the carrier liquid) is maintained at a high temperature, but also the saturated vapor pressure of the volatilized carrier liquid is increased to facilitate volatilization. The inside must also be kept at a high temperature.

  Further, since the volatilization of the vaporized carrier liquid stays inside the non-contact heater 102, new volatilization is suppressed. Therefore, it is necessary to move the vapor of the vaporized carrier liquid to the outside. Therefore, as will be described later, the air containing the steam in the non-contact heater 102 is exhausted.

(Effect of multi-stage fixing method)
As described above, the fixing device 9 is a two-stage fixing system including a heating and pressing unit (roller fixing device 101) and a non-contact heating unit (non-contact heater 102). The intent is not only to provide a sufficient amount of heat for fixing, but also to perform fixing with higher heat efficiency and to suppress the influence on the fixing quality due to an excessive amount of heat.

  As an example, prevention of occurrence of paper blisters will be described with reference to FIG. FIG. 3 is a graph showing the relationship between the heating time by the heating means and the temperature of the recording paper.

  In FIG. 3, L1 is heated only by the heating and pressing means (roller fixing device 101), L2 is heated only by the non-contact heating means (non-contact heater 102), and L3 is two-staged as in this embodiment. The relationship between the heating time and the temperature of the recording paper is shown for the fixing method.

  Since the L1 roller fixing device 101 is in pressure contact with the nip portion, the thermal efficiency of the recording paper is good, so that the temperature of the recording paper rises quickly. However, if the nip time is increased, the temperature becomes too high, and paper blisters may be generated particularly on the coated paper (point G in the figure). In addition, there is a concern that high temperature offset occurs and a problem occurs in separability.

  On the other hand, the non-contact heater 102 of L2 is advantageous to the paper blister because the temperature rise of the recording paper is moderate due to heating by non-contact heat radiation. However, the efficiency of supplying heat to the recording paper is poor, the heater must be maintained at a high temperature, and the heating time must be long, so that the required input energy becomes too large.

  Therefore, two-stage fixing such as L3 is effective. First, the paper is passed through the roller fixing device 101, the temperature of the recording paper is efficiently raised, and a graph equivalent to L1 is drawn. However, of course, the roller temperature and the nip time are set below the temperature at which the paper blister is generated, pass through the roller fixing device 101, and reach the non-contact heater 102 on the downstream side.

  Thereafter, heating is applied by the non-contact heater 102 for a time necessary for reducing the carrier liquid. As a result, the input energy as a whole can be reduced without adversely affecting the fixing quality.

(Use of exhaust heat in non-contact heating means)
In the non-contact heater 102, if the vaporized carrier liquid vapor stays inside the non-contact heater 102, new volatilization is suppressed, so that it is necessary to move the vapor to the outside. Therefore, it has already been described that the air containing the steam in the non-contact heater 102 is exhausted.

  As described above, the non-contact heater 102 has low heat supply efficiency to the recording paper 7 due to heating by non-contact heat radiation, and the heater 94 must be maintained at a high temperature. The surface temperature of the roller fixing device 101 is about 250 ° C. or less because of heat resistance.

  That is, the heater 94 of the non-contact heating means (non-contact heater 102) is hotter than the heating and pressurizing means (roller fixing device 101), and therefore the exhaust of the non-contact heater 102 is higher than the ambient temperature of the roller fixing device 101. Becomes too hot.

<Exhaust flow path setting>
In order to further improve the thermal efficiency of the entire fixing device 9 using this high-temperature exhaust, in the image forming apparatus according to the present embodiment, the exhaust from the non-contact heating means (non-contact heater 102) is heated and pressurized ( An exhaust passage for flowing toward the roller fixing device 101) is provided.

  FIG. 4 is a schematic view showing an example in which an exhaust passage 103 is provided for flowing exhaust from the non-contact heating means (non-contact heater 102) around the heating and pressurizing means (roller fixing device 101).

  The paper passing direction of the recording paper 7 is indicated by an arrow C. The non-contact heating unit 102 is provided on the downstream side of the heating and pressing unit 101 in the sheet passing direction of the recording paper 7.

  Reference numeral 104 denotes an exhaust fan. The exhaust fan 104 exhausts the high-temperature exhaust gas from the non-contact heating unit 102 through the exhaust passage 103 and the vicinity of the heating and pressurizing unit 101 in the direction of arrow F.

  As a result, the temperature around the roller fixing device 101 can be kept higher, and as a result, the power consumption of the roller fixing device 101 can be reduced.

  This leads to lower power consumption of the roller fixing device 101 when the exhaust temperature of the non-contact heater 102 is higher than the ambient temperature of the roller fixing device 101 even during standby, as well as during paper passing. . For example, during the standby mode in which the print mode can be entered immediately, the heater 94 and the roller fixing device 101 of the non-contact heater 102 need to be maintained at a high temperature.

<Exhaust flow path configuration>
The exhaust passage for flowing the exhaust from the non-contact heating means (non-contact heater) toward the heating and pressurizing means (roller fixing device) can take various forms.

  FIG. 5 is a schematic view showing an example in which another form of the exhaust passage 203 is provided to flow the exhaust of the non-contact heating means (non-contact heater 202) around the heating and pressurizing means (roller fixing device 201).

  The paper passing direction of the recording paper 7 is indicated by an arrow C. It is the same that the non-contact heating unit 202 is provided on the downstream side of the heating and pressing unit 201 in the sheet passing direction of the recording paper 7.

  Reference numeral 204 denotes an exhaust fan. By the exhaust fan 204, the hot exhaust gas from the non-contact heating unit 202 passes through the exhaust passage 203 and is exhausted in the direction of arrow F through the periphery of the heating and pressurizing unit 201.

  The only difference is that the exhaust flow path 203 bends in a U-shape and passes through the periphery of the heating and pressurizing means 201 perpendicularly to the paper passing direction of the recording paper 7.

  As a result, the temperature around the roller fixing unit 201 can be kept higher, and the power consumption of the roller fixing unit 201 can be reduced.

  FIG. 6 is a schematic diagram showing an example in which a hot air supply device 305 is provided in addition to an exhaust flow path 303 for flowing the exhaust of the non-contact heating unit (non-contact heater 302) around the heating and pressurizing unit (roller fixing unit 301). It shows with.

  As in the above-described embodiment, the paper passing direction of the recording paper 7 is indicated by an arrow C. Similarly, the non-contact heating unit 302 is provided on the downstream side of the heating and pressing unit 301 in the sheet passing direction of the recording paper 7.

  Reference numeral 304 denotes an exhaust fan, and high-temperature exhaust from the non-contact heating unit 302 passes through the exhaust passage 303 and is exhausted in the direction of arrow F through the periphery of the heating and pressurizing unit 301.

  However, the point which provided the hot air supply device 305 for supplying a hot hot air to the non-contact heating means 302 differs from the form mentioned already.

  The hot air supply device 305 is provided to keep the periphery of the paper passing path of the non-contact heating means 302 at a higher temperature. In order to promote the volatilization of the carrier liquid from the recording paper 7, the temperature in the vicinity of the paper passing path is preferably 200 ° C. or higher.

  This configuration also makes it possible to maintain the temperature around the roller fixing device 301 at a higher temperature by using high-temperature exhaust, and further reduce the power consumption of the roller fixing device 301 and the non-contact heater 302. It becomes possible.

<Change of exhaust flow path>
The set temperature of the heating and pressing means (roller fixing device) may be changed depending on, for example, the basis weight of the recording paper and the paper type (coated paper, uncoated paper, etc.). Generally, the temperature of thin paper is set to a lower temperature. Accordingly, when the basis weight of the recording paper is changed from thick paper to thin paper, it is necessary to lower the temperature of the roller fixing device.

  In that case, it is better not to flow the exhaust of the non-contact heating means (non-contact heater) around the heating and pressurizing means (roller fixing device). This is to quickly lower the temperature of the roller fixing device.

  In FIG. 7, in addition to the first exhaust flow path 403a that flows the exhaust of the non-contact heating means (non-contact heater 402) around the heating and pressurizing means (roller fixing device 401), the heating and pressurizing means (roller fixing device) 401) A schematic view showing an example in which the second exhaust flow path 403b that does not flow around is branched and a flow path changing means (switch 406) is provided.

  As in the above-described embodiment, the paper passing direction of the recording paper 7 is indicated by an arrow C. Similarly, the non-contact heating unit 402 is provided on the downstream side of the heating and pressing unit 401 in the sheet passing direction of the recording paper 7.

  The first exhaust flow path 403a is provided with a first exhaust fan 404a, and the exhaust of the non-contact heating unit 402 is exhausted in the direction of the arrow Fa through the periphery of the heating and pressurizing unit 401.

  On the other hand, a second exhaust fan 404b is provided in the second exhaust passage 403b, and the exhaust of the non-contact heating unit 402 is exhausted in the direction of the arrow Fb without passing through the heating and pressurizing unit 401.

  The flow path changing means (switch 406) is provided at a branch point between the first exhaust flow path 403a and the second exhaust flow path 403b, and switches the exhaust flow path by a control means (not shown). The flow path changing means (switcher 406) may be switched by a normal valve.

  The procedure for changing the first and second exhaust flow paths will be described later.

  This configuration also makes it possible to keep the ambient temperature of the roller fixing device 401 at a higher temperature, respond quickly to changes in the set temperature, and efficiently use the power consumption of the roller fixing device 401. It becomes possible to do.

<Exhaust flow path change procedure>
As described above, when the basis weight of the recording paper, the paper type, or the like is changed, the temperature setting of the heating and pressing means (roller fixing device) is generally changed accordingly. Of course, the temperature of the roller fixing device is controlled according to the set temperature.

  That is, heating is controlled by the heater lamps 92a and 92b built in the fixing roller 91a and the pressure roller 91b, and at the same time, the exhaust of the non-contact heating means (non-contact heater) is heated and pressurized (roller fixing device). ) It is desirable to control whether to flow around or not.

  Specifically, in synchronization with the temperature control of the fixing roller, the first exhaust flow path 403a and the second exhaust flow path 403b are switched by the flow path changing means (switch 406).

  FIG. 8 is a flowchart showing an example of a procedure for changing the exhaust passage. The procedure for changing the exhaust flow path will be described with reference to FIG.

  In step S11 of FIG. 8, a fixing roller temperature T for controlling the roller fixing device 401 to a set temperature is detected.

  Next, in step S12, it is determined whether or not the fixing roller temperature T exceeds the set temperature.

  Actually, only when the fixing roller temperature T is equal to or lower than the “set temperature + ripple”, the exhaust of the non-contact heating means (non-contact heater) is determined to flow around the heating and pressurizing means (roller fixing device). Good. As for the temperature ripple at each temperature setting, a value measured in advance according to the print mode, the operating environment, etc. may be stored in the memory.

  If the fixing roller temperature T is equal to or lower than “set temperature + ripple” in step S12 (step S12; YES), step S13 is executed, and the first exhaust passage 403a is selected as the exhaust passage.

  When the fixing roller temperature T exceeds “set temperature + ripple” in Step S12 (Step S12; NO), Step S14 is executed, and the second exhaust passage 403b is selected as the exhaust passage.

  In step S15, if it is necessary to change the exhaust flow path according to the selection in step S13 or step S14, the flow path changing means (switch 406) causes the first exhaust flow path 403a and the second exhaust flow to be changed. The path 403b is switched.

  In step S16, it is determined whether or not to end the temperature control. If the process is to be ended (step S16; YES), the procedure for changing the exhaust flow path is also ended.

  When the temperature control is not finished (step S16; NO), the process returns to step S11, and all steps are repeated from the detection of the fixing roller temperature T. The repetition is continued until the temperature control is finished in step S16.

  This is the end of the description of the procedure for changing the exhaust flow path.

  As described above, the image forming apparatus according to the present embodiment has a heating / pressurizing unit and a non-contact heating unit as a fixing unit to generate more heat for fixing that requires a large amount of heat. It has an exhaust passage for flowing the exhaust from the non-contact heating means toward the heating and pressurizing means. As a result, there is no problem in high temperature offset and separability, generation of paper blisters can be suppressed, high quality fixing can be obtained, and fixing can be performed efficiently with relatively low energy.

  Although the roller fixing device has been described as the heating and pressing means, any form such as an upper belt fixing device and a lower free belt fixing device may be used as long as the fixing device forms a pressure nip portion.

  Further, a fixing device may be added further downstream depending on a request for controlling fixing quality such as glossiness.

  The above-mentioned embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

FIG. 3 is a cross-sectional view illustrating a schematic configuration example of a toner image forming unit, a transfer device, and a fixing device in a wet image forming apparatus. FIG. 2 is a cross-sectional view illustrating a schematic configuration example of a fixing device in the image forming apparatus of FIG. 1. It is a graph which shows the relationship between the heating time by a heating means, and the temperature of a recording paper. It is a schematic diagram which shows the example which provided the exhaust flow path which flows the exhaust_gas | exhaustion of a non-contact heating means around a heating pressurization means periphery. It is a schematic diagram which shows the example which provided the exhaust flow path of another form. It is a schematic diagram which shows the example which provided the hot air supply device in addition to the exhaust flow path. It is a schematic diagram showing an example in which a second exhaust flow channel is branched in addition to the first exhaust flow channel and a flow channel changing means is provided. It is a flowchart which shows the example of the procedure which changes an exhaust flow path.

Explanation of symbols

1 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 2 Charging device 3 Exposure device 4 Liquid developing device 5 Intermediate transfer member 6 Cleaning device 7 Recording paper 8 Liquid developer 9 Fixing device 41 Developing roller (developer carrier)
44 Developer tank 51 Transfer roller 91a Fixing roller 91b Pressure roller 92a, 92b Lamp heater 94 Heater 95 Thermal insulation cover 101 Roller fixing device (pressure heating means)
102 Non-contact heater (non-contact heating means)
103 Exhaust flow path 104 Exhaust fan 305 Hot air supply device 406 Changeover device (flow path changing means)

Claims (5)

As fixing means for fixing the toner image formed on the recording medium,
A heating and pressurizing means for bringing the heated member into contact with the recording medium and heating while pressing;
Non-contact heating means for heating the recording medium by heat radiation from a non-contact heat source;
An image forming apparatus having
An image forming apparatus comprising an exhaust passage for allowing exhaust from the non-contact heating means to flow toward the heating and pressurizing means. The exhaust passage is
The image forming apparatus according to claim 1, further comprising a flow path changing unit configured to prevent exhaust from the non-contact heating unit from flowing toward the heating and pressurizing unit. The flow path changing means includes
The image forming apparatus according to claim 2, wherein the flow path is changed according to a temperature of the heating and pressurizing unit. The non-contact heating means includes
4. The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed downstream of the heating and pressurizing unit in the recording medium passage direction. 5. The image forming apparatus according to claim 1, wherein the toner image on the recording medium is developed using a liquid developer.

Images