JP5701094B2 - Image heating apparatus and image forming apparatus - Google Patents

Description

  An image heating apparatus that preheats a recording material carrying a toner image using a heat pump before heat treatment, and more specifically, a heat exchanger that increases heating efficiency by the heat pump and reduces power consumption required for preheating the recording material. This relates to the arrangement configuration.

  2. Description of the Related Art Image forming apparatuses that transfer a toner image onto a recording material and then convey the recording material while heating and pressing it with a fixing device to fix the image on the recording material are widely used. Also, post-processing apparatuses that convey a recording material carrying a fixed toner image or a semi-fixed toner image while heating and pressurizing to give a desired surface state and glossiness have been put into practical use. The image heating device is a device name including a fixing device and a finishing device.

  Patent Document 1 proposes an image forming apparatus equipped with a roller fixing device heated by a heat pump. Here, the toner image is fixed on the recording material by bringing a heating roller heated using a one-stage or two-stage heat pump into contact with the image surface of the recording material.

  Patent Document 2 proposes a fixing system in which a recording material is preheated by a heat pump in a process in which a toner image is transferred to a recording material and conveyed to a fixing device. Here, the high-temperature refrigerant pressurized by the heat pump undergoes heat exchange with the roller fixing device and is guided to the preheating roller for heat exchange with the recording material in a state where the temperature is slightly lowered. As a result, the total power consumption required for fixing the toner image is reduced by utilizing the output of the heat pump in two stages of heating and preheating.

JP 2005-258003 A JP 2009-133848 A

  As described in Patent Document 1, a heat pump can theoretically generate a heat quantity several to several tens times as large as the input electric power, and thus a fixing device with low power consumption and high output can be expected. However, the efficiency of the heat pump decreases as the temperature difference between the heat absorption source and the heat dissipation source increases. For this reason, when trying to obtain a high temperature of 100 ° C. or higher at which the toner can be melted practically, it cannot be said that it is very efficient, and it is possible to consume less power by direct heating with a lamp heater or electromagnetic heating. There is also. That is, it is not possible to obtain an effect of reducing power consumption commensurate with the mounting of a large compressor and compressor noise.

  For this reason, the total power consumption including preheating and heating can be reduced by using a heat pump for preheating of about 60 degrees and performing intensive heating using electromagnetic heating after preheating. was suggested.

  However, in a normal heat pump, heating is mainly performed using the latent heat of the refrigerant, and therefore only heating up to the refrigerant condensation temperature at the compressor outlet pressure (or the outlet pressure of the condenser) can be performed. For this reason, the effect of reducing the power consumption of heating after preheating has been limited.

  The present invention provides an image heating apparatus that can preheat a recording material to a temperature exceeding the condensation temperature of the refrigerant without increasing the power consumption of the heat pump, and can effectively reduce the power consumption required for the heating after the preheating. The purpose is that.

  The image heating apparatus of the present invention includes a heating unit that heats a recording material carrying a toner image in a pressurized state, and preheats the recording material using a heat pump and transfers the recording material to the heating unit. And using the 1st heat exchange part which heats a recording material using the sensible heat of the refrigerant | coolant of the superheated vapor | steam which was compressed and heated with the compressor of the said heat pump, and the refrigerant | coolant thermally radiated by the said 1st heat exchange part A second heat exchange unit that heats the recording material at a lower heating temperature than the first heat exchange unit, and a recording material heated by the second heat exchange unit is conveyed to the first heat exchange unit. And a conveying means for delivering the recording material heated by the first heat exchange unit to the heating unit.

  In the image heating apparatus of the present invention, the heat exchange means performs two-stage preheating. First, heat is exchanged with the wet steam refrigerant condensed by the heat pump, and a large amount of heat at a constant temperature is transferred to the recording material to ensure that the temperature of the recording material is close to the condensation temperature of the refrigerant (humid steam temperature). . Thereafter, heat is exchanged with the refrigerant of the dry steam pressurized by the heat pump, and the recording material is heated to a temperature exceeding the condensation temperature of the refrigerant using the sensible heat of the dry steam.

  Therefore, the recording material can be preheated to a temperature exceeding the condensation temperature of the refrigerant and delivered to the heating unit. Without increasing the power consumption of the heat pump, the recording material is preheated to a temperature exceeding the condensation temperature of the refrigerant, and the power consumption required for heating after the preheating can be effectively reduced.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of the preheating apparatus of Example 1. FIG. It is explanatory drawing of a structure of a heat pump. It is a vapor diagram of a refrigerant. It is explanatory drawing of the thermal radiation process of a heat pump cycle. It is explanatory drawing of the relationship between the number of sheets processed per minute, and preheating performance. It is explanatory drawing of the heat exchange temperature distribution of a belt heat exchanger. It is a flowchart of control of a preheating apparatus. It is explanatory drawing of the power consumption reduction effect of the fixing | fixed part by preheating. It is explanatory drawing of a structure of the preheating apparatus of Example 2. FIG. It is explanatory drawing of the heat exchange temperature distribution of the belt heat exchanger in Example 2. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention can be implemented in another embodiment in which a part or all of the configuration of the embodiment is replaced with the alternative configuration as long as the recording material is preheated using a heat pump.

  Therefore, any image heating device that heats the toner image is not limited to the fixing device, the gloss processing device, the post-processing device, and the like that are provided in the image forming device, and can be implemented by a stand-alone image heating device. The configuration of the heating unit is not limited to the roller / roller system, and can be implemented by a roller / belt system.

  The image forming apparatus may use either a two-component developer or a one-component developer, and can be implemented without distinction between a tandem type / one drum type, an intermediate transfer type / a recording material conveyance type / a direct transfer type, and a monochrome / full color type. . In this embodiment, only main parts related to toner image formation / fixing will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In addition, about the general matter of the fixing device and image forming apparatus which are shown by patent document 1, 2, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. As shown in FIG. 1, the image forming apparatus 1 is a tandem intermediate transfer type full-color printer in which yellow, magenta, cyan, and black image forming portions Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 8. is there.

  In the image forming portion Pa, a yellow toner image is formed on the photosensitive drum 2 a and transferred to the intermediate transfer belt 8. In the image forming portion Pb, a magenta toner image is formed on the photosensitive drum 2 b and transferred to the intermediate transfer belt 8. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 2c and 2d and transferred to the intermediate transfer belt 8. The four color toner images transferred onto the intermediate transfer belt 8 are conveyed to the secondary transfer portion T2 and secondarily transferred to the recording material P.

  The intermediate transfer belt 8 is supported around a tension roller 11, a driving roller 10, and a counter roller 21, and is driven by the driving roller 10 to rotate in the direction of arrow R2 at a predetermined process speed. The secondary transfer roller 22 abuts on the intermediate transfer belt 8 whose inner surface is supported by the counter roller 21 to form a secondary transfer portion T2.

  The recording material P drawn from the recording material cassette 17 is separated one by one by the separation roller 19 and sent to the registration roller 16. The registration roller 16 receives and waits for the recording material P in a stopped state, and sends the recording material P to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 8. A full color toner image is recorded from the intermediate transfer belt 8 by applying a positive DC voltage to the secondary transfer roller 22 in the process in which the recording material P is nipped and conveyed by the secondary transfer portion T2 while being superimposed on the toner image. Secondary transfer to the material P is performed. The untransferred toner remaining on the surface of the intermediate transfer belt 8 without being transferred is collected by the belt cleaning device 12.

  The recording material P on which the four-color toner images have been secondarily transferred is separated from the intermediate transfer belt 8 by the curvature, conveyed to the conveying belt 102, and sent to the fixing device 26, where it is heated and pressurized to form a toner image on the surface. After fixing, it is discharged outside the aircraft.

  The image forming portions Pa, Pb, Pc, and Pd are configured substantially the same except that the color of toner used in the developing devices 7a, 7b, 7c, and 7d is different from yellow, magenta, cyan, and black. In the following, the yellow image forming portion Pa will be described, and the other image forming portions Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals attached to the constituent members being described with “b”, “c”, and “d”. Shall be.

  Further, during double-sided printing, the recording material P that has passed through the fixing device 26 and the paper discharge roller 24 is guided in the direction of the double-side reversing path 27, and reversely conveyed in the reverse direction, and is conveyed to the double-sided path 28. The recording material P that has passed through the double-sided pass 28 passes through the vertical pass roller 20 again, forms the image on the second side, transfers, and fixes the same as the first side, and is discharged.

  In the image forming portion Pa, a corona charger 3a, an exposure device 5a, a developing device 7a, a transfer blade 6a, and a drum cleaning device 4a are arranged around the photosensitive drum 2a. The photosensitive drum 2a has a negatively charged photosensitive layer and rotates in the arrow direction at a predetermined process speed. The corona charger 3a uniformly charges the surface of the photosensitive drum 2a to the negative dark portion potential VD. The exposure device 5a scans the scanning line image data obtained by developing the yellow separated color image with a rotating mirror, and writes an electrostatic image of the image on the surface of the photosensitive drum 2a.

  The developing device 7a reversely develops the electrostatic image formed on the photosensitive drum 2a to form a toner image. The transfer blade 6 a presses the inner surface of the intermediate transfer belt 8 to form a primary transfer portion between the photosensitive drum 2 a and the intermediate transfer belt 8. By applying a positive voltage to the transfer blade 6a, the toner image carried on the photosensitive drum 2a is primarily transferred to the intermediate transfer belt 8. The drum cleaning device 4a collects the transfer residual toner remaining on the photosensitive drum 2a by escaping from the primary transfer to the intermediate transfer belt 8.

<Fixing device>
The fixing device 26, which is an example of a heating unit, conveys the recording material P carrying a toner image while heating and pressing. The fixing device 26 is in contact with a heating roller that is heated from the center by a halogen lamp heater and contacts the image surface of the recording material P, and a pressure roller that is heated from the center by the halogen lamp heater and contacts the back surface of the recording material P. Configured.

  The fixing device 26 applies heat and pressure to the recording material P to which the toner image G has been transferred and fixes it at a nip portion formed by a heating roller and a pressure roller. The rotation operation of the heating roller and the pressure roller is adjusted by a rotation driving means.

  The outer diameter of the heating roller is 51 mm, a rubber layer having a thickness of 500 μm is provided on an aluminum core, and a PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin having a thickness of 25 μm is further provided on the rubber layer. ) Or the like is coated. The pressure roller has the same configuration.

  By the way, the fixing device applies a heat and pressure to an unfixed toner image formed on the surface of the recording material using a toner (developer) made of a heat-meltable resin or the like, so that it is permanently applied to the surface of the recording material. Secure.

  When a halogen heater, an infrared lamp, or an induction heating method is employed as a heat source for the fixing device, the heat conversion efficiency does not exceed 1 because Joule heat generated by current is used. For this reason, heating exceeding the wattage supplied cannot be performed, and it has been difficult to save energy.

  In order to solve this problem, in the above-described image forming apparatuses of Patent Document 1 and Patent Document 2, a heat conversion device using a vapor compression reverse refrigeration cycle (heat pump cycle) having a heat pump function is used for the fixing device. The heat conversion device absorbs heat of the recording material after fixing, supplies the absorbed heat to a heating source of the fixing device, and heats it, thereby improving heat conversion efficiency and saving energy. The fixing unit of the fixing device is heated by the amount of heat radiated from the condenser of the heat pump, and heat of the fixing unit is applied to the recording material to heat it.

  However, at present, in order to melt and fix unfixed toner, it is necessary to heat to at least 100 ° C. or higher. Generally, when a heat pump is used as a heat source, the amount of heat at the time of condensation of the refrigerant is used, so in order to raise the condensation temperature to about 100 ° C, a special heat pump that can withstand high pressure and has a large compressor output is required. Power consumption will also increase. When such a special heat pump is used as the heat source of the fixing device, the power consumption is not much smaller than the power consumption of the fixing device using a halogen heater, an infrared lamp, or an induction heating method as the heat source.

  For example, in Patent Document 2, since a refrigerant is circulated through a heating roller that has a large heat capacity and requires heating capability, and then circulates through a preheating roller, a heat pump with a large compressor output is required. . In this case, since the power consumption of the heat pump is determined by the heating capability of the heating roller, the power consumption of the heat pump is not reduced even if the preheating roller is used.

  In a heat pump with low power consumption that has been put into practical use, the temperature of the high temperature part is about 60 ° C. to 70 ° C. For this reason, it is desired to use a heat pump as a preheating source for a recording material immediately before fixing, instead of using only the heat pump as a heat source of the fixing device as in Patent Document 1 and Patent Document 2. Since the heat conversion efficiency (COP; heating capacity / power consumption) of such a heat pump is considered to be about 5 to 6, a heat pump having a power consumption of about 200 W has a heating capacity of 1000 W or more. By utilizing this, it is possible to preheat the recording material from 60 ° C. to about 70 ° C. Then, by using a halogen heater, an infrared lamp, or induction heating having a lower wattage than conventional ones, it is possible to perform heating to a finally required temperature and control a fixing temperature.

  By increasing the temperature of the recording material before entering the fixing device by preheating, it is possible to lower the temperature of the fixing device or shorten the nip passage time, thereby reducing the power consumption of the fixing device and simultaneously increasing the processing speed. . By using a heat pump as a preliminary heating source, the power consumption used for fixing can be reduced and energy saving can be achieved.

  When the heat pump is used as a heat source for preheating, the high temperature zone in which the refrigerant is superheated steam cannot be used because of its small amount of heat, and it is difficult to heat the recording material to a temperature higher than the condensation temperature of the refrigerant. If the temperature of the recording material reaches the condensing temperature of the refrigerant during the preheating, the temperature of the recording material cannot be further increased, and there is a limit to the power consumption reduction of the fixing device.

  In the following embodiments, the recording material can be heated to a temperature higher than the condensation temperature of the refrigerant. As a result, since the vapor compression reverse refrigeration cycle with improved energy saving effect can be used as a preheating source without increasing the power consumption of the heat pump more than necessary, the power consumption of the fixing device is reduced. Since the recording material is heated using the amount of heat of the superheated steam higher than the condensation temperature together with the amount of heat at the time of refrigerant condensation, the recording material can be heated above the condensation temperature, so that the power consumption of the fixing device can be further reduced.

<Example 1>
FIG. 2 is an explanatory diagram of the configuration of the preheating device according to the first embodiment. FIG. 3 is an explanatory diagram of the structure of the heat pump. FIG. 4 is a vapor diagram (Mollier diagram) of the refrigerant. FIG. 5 is an explanatory diagram of the heat dissipation process of the heat pump cycle. FIG. 6 is an explanatory diagram of the relationship between the number of processed sheets per minute and the preheating performance. FIG. 7 is an explanatory diagram of the heat exchange temperature distribution of the belt heat exchanger. FIG. 8 is a flowchart of control of the preheating device. FIG. 9 is an explanatory diagram of the effect of reducing power consumption of the fixing unit by preheating.

  As shown in FIG. 1, the image forming portions Pa, Pb, Pc, Pd and the intermediate transfer belt 8 which are examples of the image forming unit form a toner image and transfer it to the recording material P.

  The fixing device 26 as an example of a heating unit heats the recording material P carrying a toner image in a pressurized state. The fixing device 26 heats and presses the recording material P onto which the toner image has been transferred to fix the toner image on the recording material P. The fixing device 26 heats the recording material P carrying the toner image in a pressurized state using a heating nip N that is electrically heated and temperature-controlled.

  The preheating device 100, which is an example of a preheating unit, preheats the recording material P using the heat pump 101 and delivers it to the fixing device 26. The preheating device 100 preheats and heats the recording material P carrying the toner image from the opposite surface of the toner image to a temperature lower than the heating nip N using the heat pump 101 while conveying the recording material P without applying pressure. Delivered to nip N.

  The evaporator 107 of the heat pump 101 evaporates the refrigerant using the exhaust heat of the heating unit, heats it to dry steam, and supplies it to the compressor 104 of the heat pump 101.

  As shown in FIG. 2, the conveyance belt 102, which is an example of a conveyance unit, conveys the recording material P heated by the condenser 105a to the condenser 105b, and then the recording material P heated by the condenser 105b. Transfer to the fixing device 26. The conveyance belt 102 is configured by an endless belt member that rotates by sliding the back side of the recording material P carrying surface against the heat radiation surface of the condenser 105b and the heat radiation surface of the condenser 105a. The recording material P is heated by the condenser 105a and the condenser 105b through the conveyance belt 102.

  The preheating device 100 is configured by incorporating a heat pump 101 into a belt heat exchanger 109. The conveying means for the recording material P includes a conveying belt 102 and a conveying roller 103. The conveyance belt 102 conveys the recording material P on which the four color toner images G are transferred to the fixing device 26.

  The preheating device 100 carries the recording material P on a conveyance belt 102 stretched between a pair of conveyance rollers 103 and conveys the recording material P. The conveyor belt 102 has a multilayer structure in which a conductive layer and a release layer (resistive layer) in units of several μm are sequentially coated on a film surface of several to several tens of μm formed endlessly of polyimide resin.

  A small hole for sucking the recording material P is formed in the transport belt 102, and a suction mechanism for sucking the recording material P through the transport belt 102 is provided inside the transport belt 102. The suction mechanism forms a plurality of air suction holes in the condenser (heat radiating plate) 105, and sucks air from the air suction holes of the heat radiating plate with a suction fan arranged below the air suction holes. As a result, the recording material P is attracted to the transport belt 102 and is transported on the heat radiating plate.

  Note that the contact method between the recording material P and the conveying belt 102 may be electrostatic. In that case, the conveying means includes a conveying unit in which the conveying belt 102 is wound around the conveying roller 103, a charging device (not shown) for electrostatically adsorbing the recording material P, and a heat radiating plate. The conductive layer of the conveying belt 102 is dropped to the ground by electrical connection (not shown), and the recording material P is applied by applying a charge to the release layer that is also an insulating layer, or to the recording material P that is further thereon. It is electrostatically attracted and can be transported on the heat sink.

  A condenser (heat radiating plate) 105 is disposed so as to be in close contact with the inner surface of the conveyor belt 102. The conveyance belt 102 conveys the recording material P from the refrigerant outlet side of the condenser 105 to the refrigerant inlet side. In the course of the conveyance, the recording material P is heated to the condensation temperature by exchanging heat with the condenser 105, and then heated to the condensation temperature T0 or higher in the superheated steam portion at the end of the conveyance.

  As shown in FIG. 3, the preheating device 100 preheats the recording material P using a heat pump 101 of a vapor compression reverse refrigeration cycle (heat pump cycle) as a heating source. The heat pump 101 causes the refrigerant that has been compressed and heated by the compressor 104 to dissipate heat by the condenser 105 and condense to the supercooled liquid. The expansion valve 106 reduces the pressure of the refrigerant, and the evaporator 107 removes ambient heat and vaporizes the refrigerant. The vaporized refrigerant is compressed by the compressor 104 to constitute a heat pump cycle.

  As shown in FIG. 4, the heat pump 101 executes the cycle of the closed curve ABCD in the Ph diagram of the pressure P and the enthalpy h. The refrigerant superheated steam A is compressed by the compressor 104 to a pressure equal to or higher than the saturated vapor pressure with respect to a desired temperature to be converted into superheated steam B and sent to the condenser 105. The high-temperature superheated steam B is cooled by dissipating the amount of heat Q1 in the condenser 105 and condensed / liquefied to become the supercooled liquid C.

  The supercooled liquid C is sent to the expansion valve 106, isententically expanded by the expansion valve 106, becomes a low-temperature wet steam D, and is sent to the evaporator 107. The low-temperature wet steam D is vaporized by obtaining the amount of heat Q2 from the surroundings in the evaporator 107, and becomes superheated steam A to complete one cycle. The superheated steam A is compressed again by the compressor 104 to become a high temperature superheated steam B, and the heat cycle is repeated.

  As shown in FIG. 5, in the process in which the refrigerant releases heat Q1 in the condenser 105, changes in the enthalpy and temperature of the refrigerant occur. In the sensible heat change from the superheated steam B state to the saturated steam B ′ state, the enthalpy slightly changes from hB to hB ′ while the temperature of the refrigerant decreases.

  Next, in the latent heat change from the state of the saturated vapor B ′ to the state of the saturated liquid C ′, the temperature is constant (condensation temperature), and the enthalpy changes greatly from hB ′ to hC. Thereafter, in the sensible heat change from the state of the saturated liquid C ′ to the state of the supercooled liquid C, the enthalpy slightly changes from hC ′ to hC while the temperature is lowered.

  The amount of heat released when the enthalpy changes from hB to hB ′ is Q1 ″, and the amount of heat released when the enthalpy changes from hB ′ to hC is Q1 ′.

  When the recording material P is heated using the heat quantity Q1 radiated from the condenser 105, first, the heat quantity Q1 ′ at the time of the latent heat change having a large enthalpy change and the sensible heat change at the time of supercooling (hB ′ → hC) is obtained. Utilizing this, heat exchange is performed with the recording material P. As a result, the temperature of the recording material P is raised to near the refrigerant condensation temperature T0.

  Thereafter, heat is exchanged with the recording material P by using the heat quantity Q1 ″ when the sensible heat change (hB → hB ′) of the superheated steam with a slight enthalpy change. As a result, the temperature of the recording material P is increased to a temperature T1 that is equal to or higher than the condensation temperature T0.

  Since the heat capacity of the recording material P is small, the temperature rises sufficiently even with the heat quantity Q1 ″ of the superheated steam with a slight enthalpy change, and the recording material P can be heated to a temperature equal to or higher than the condensation temperature T0. If it demonstrates numerically, when radiating heat amount Q1, the enthalpy of a refrigerant will change from hB to hC. At this time, the sensible heat change of the superheated steam changes from hB to hB ', and considering the ratio of enthalpy change, the heat quantity Q1 "is about 20% of the heat quantity Q1. When Q1 can be expected to be about 2500 W as the capability of the heat pump 101, the sensible heat change of the superheated steam is about 500W.

As shown in FIG. 6, let E be the amount of heat received by the recording material P that is continuously preheated at the amount of heat Q1 ″ when sensible heat changes (hB → hB ′). Assuming a state in which the toner is 10 μm thick on the recording material P having a paper basis weight of 105 g / m ² , a computer simulation was performed when the toner was transported at 85 ppm and 150 ppm and preheated.

  When the temperature range to be preheated by the heat pump 101 is increased, the amount of heat to be supplied to the recording material P is increased. When preheating 150 sheets (150 ppm) per minute, the temperature range that can be raised by the heat pump 101 is smaller than when preheating 85 sheets (85 ppm) per minute.

  It was confirmed that the temperature of the recording material P onto which the toner has been transferred can be further increased by about 30 ° C. at 85 ppm and about 18 ° C. even at 150 ppm when the heat quantity Q1 ″ equal to or higher than the condensation temperature is 500 W.

  As described above, the heat capacity of the recording material P onto which the toner has been transferred can sufficiently raise the temperature by using the heat amount of the superheated steam.

  As shown in FIG. 2, the heat pump 101 is provided with a pressure gauge 108, a fan 114, and an inverter control unit 115 in addition to the compressor 104, the condenser 105, the expansion valve 106, and the evaporator 107. A temperature sensor 116 for temperature measurement is provided. By operating the fan 114 attached to the evaporator 107, the evaporator 107 can recover heat from the surroundings with high efficiency.

  The pressure of the refrigerant in the condenser 105 can be grasped by the pressure gauge 108, and the condensation temperature of the refrigerant under the pressure can be known by referring to the vapor diagram of FIG. 4 with the measured pressure. The temperature sensor 116 is attached in the vicinity of the superheated steam B inlet side in the center of the heat sink. The inverter control unit 115 adjusts the frequency output to the compressor 104 from 30 Hz to 75 Hz, thereby changing the rotation speed of the compressor 104, controlling the refrigerant circulation amount, and adjusting the heat radiation amount of the condenser 105. .

  The condenser 105 is attached so as to be in close contact with the inner surface of the conveyance belt 102, and the recording material P onto which the toner images G are collectively transferred is heated by exchanging heat with the condenser 105 via the conveyance belt 102.

  As shown in FIG. 7A, the condenser 105 is a rectangular parallelepiped heat sink in which a copper tube 111 is meandered in an aluminum plate 112. However, the arrangement of the copper tubes 111 is not limited to the arrangement shown in the figure. As the contact area between the copper tube 111 and the aluminum plate 112 increases, the heat conversion efficiency between the refrigerant and the aluminum plate 112 may be increased.

  As shown in FIG. 7B, the aluminum plate 112 and the copper tube 111 are processed with high adhesion in order to improve heat transfer. Moreover, the copper pipe 111 is heat-insulated from the compressor 104 to the superheated steam inlet, and prevents the amount of heat (enthalpy) of the superheated steam from radiating to the surroundings. The surface of the aluminum plate 112 that is in contact with the conveyor belt 102 has a high degree of smoothness in order to improve adhesion to the conveyor belt 102 and is subjected to a plating treatment with Ti or the like in order to reduce wear due to friction. The back surface and four side surfaces of the aluminum plate 112 are heat-insulated with a heat-insulating material in order to prevent heat radiation to other than the conveyor belt 102.

  The refrigerant which has been compressed to a pressure equal to or higher than the saturated vapor pressure with respect to the desired temperature by the compressor 104 and has become the superheated steam B enters from the inlet side as the superheated steam B and condenses while passing through the copper pipe 111 arranged meandering. It flows to the exit side. At this time, the surface temperature of the heat radiating plate on which the copper tube 111 in which the refrigerant flows as superheated steam is arranged is equal to or higher than the condensation temperature of the refrigerant.

  As shown in FIG. 7C, the temperature distribution on the heat radiation surface, which is the contact surface of the condenser (heat radiation plate) 105 with the conveyor belt 102, becomes higher in the x direction. In the first embodiment, the first heat exchange unit and the second heat exchange unit are formed in an integrated condenser (heat radiating plate) 105 and are not thermally separated. The temperature distribution on the heat dissipation surface is continuous.

  As shown in FIG. 7A, the preheating device 100 conveys the recording material P, onto which the toner image G has been transferred, by the conveyance belt 102, and the recording material P is fed with a condenser (heat radiating plate) 105 during conveyance. It is heated by exchanging heat with. The recording material P onto which the toner image G has been transferred is conveyed from the outlet side of the copper tube 111 on the low temperature side of the condenser (heat radiating plate) 105 to the inlet side of the superheated steam B on the high temperature side. Heated to above the condensation temperature of the refrigerant. Since the recording material P to which the toner image G has been transferred has a small heat capacity, when the heat is exchanged with the refrigerant by the condenser (heat radiating plate) 105, the temperature of the superheated steam is small but the amount of heat is high. It is because it can raise.

<Control of heat pump>
As shown in FIG. 8 with reference to FIG. 2, the compressor 104 of the heat pump 101 of the preheating device 100 compresses the refrigerant with a variable output, and keeps the refrigerant in the condenser 105b at a predetermined temperature exceeding the condensation temperature. The output of the compressor 104 is controlled.

  When the image forming apparatus (1: FIG. 1) is started, the compressor 104 is driven to start warming up of the condenser (heat radiating plate) 105 (S101). At the same time, power is supplied to the heat source of the fixing device 26 and the warming up of the heating roller 26a is started (S102). Simultaneously with the start of warming up, the temperature of the heating roller 26a is measured by the temperature sensor 26s, and it is determined whether or not the fixing start temperature has been reached (S103).

  If the fixing start temperature has not been reached (NO in S103), warm-up is continued, and if it has reached (YES in S103), the process proceeds to the standby mode (S104). In the standby mode, electric power is supplied to the heat source so that the temperature of the heating roller 26a maintains the fixing start temperature (S104).

  Next, simultaneously with the start of warming up of the condenser (heat radiating plate) 105, the temperature of the heat radiating plate is measured by the temperature sensor 116, and it is determined whether the preheating temperature necessary for fixing has been reached (S105). If the preheating temperature necessary for fixing has not been reached (NO in S105), the warming-up is continued, and if it has reached (YES in S105), the process proceeds to the standby mode (S106). In the standby mode, the compressor is maintained at a rotational speed sufficient to maintain the preheating temperature necessary for fixing the condenser (heat radiating plate) 105 (S106).

  Thereafter, a printing operation is executed (S107). When the printing operation is executed, the recording material P is deprived of heat, and the refrigerant pressure in the condenser 105 decreases. The inverter control unit 115 measures the pressure at the outlet of the condenser 105 with the pressure gauge 108 (S108), and calculates the condensation temperature of the refrigerant with reference to the Ph diagram of FIG. 4 with the measured pressure (S109).

  The inverter control unit 115 measures the temperature of the condenser (heat radiating plate) 105 by the temperature sensor 116 of the condenser (heat radiating plate) 105, and determines whether the heat radiating plate temperature is equal to or higher than the calculated condensation temperature (S109). (S110).

  Inverter control part 115 performs control which raises the frequency outputted to compressor 104 and raises the number of rotations, when it is not more than condensation temperature (S111). As the rotational speed increases, the amount of refrigerant circulation increases, and the amount of heat radiated from the condenser (heat radiating plate) 105 increases. As a result, a predetermined heat pump cycle as shown in the Ph diagram of FIG. 4 is maintained.

  When the temperature is equal to or higher than the condensation temperature, the inverter control unit 115 determines whether the printing operation is finished (S112). In the case where the printing operation is continued without being finished, in S112, the process returns to step S103, and S103 to S112 are repeated until the printing operation is finished. However, when the printing operation is completed (YES in S112), the heat pump is stopped (S113), the power supply to the heating source of the heating roller 26a is stopped (S114), and the image forming apparatus (1: FIG. 1) is stopped. To do.

  The heat radiating surface size of the aluminum plate heat radiating plate which is the condenser 105 of the heat pump used in Example 1 is 320 mm × 400 mm. The copper pipe is meandering about 5 m in the heat sink, and the temperature on the superheated steam inlet side of the heat dissipating surface is about 70 ° C. which is necessary for fixing in about 120 seconds after the compressor is operated. The amount of refrigerant in the heat pump 101 was adjusted so that

  As the refrigerant used, R134a (registered trademark) of alternative chlorofluorocarbon (hydrofluorocarbon) which is a kind of general alternative chlorofluorocarbon (hydrofluorocarbon) was used. The heat pump 101 was operated at 75 Hz, which is the maximum frequency of the compressor 104. When the temperature on the refrigerant inlet side of the heat radiating surface reached 70 ° C., the heat radiating surface temperature was maintained while adjusting the frequency of the compressor 104.

  As the recording material P, A4 size plain paper having a thickness of 100 μm was used. The recording material P was started to be continuously conveyed at a conveyance speed of 400 mm / sec, and it was possible to fix in advance, and a permanent image was obtained through the fixing device 26 on standby. Since the length of the heat radiating surface of the condenser (heat radiating plate) 105 in the transport direction is 400 mm, the heating time of the recording material was 1 second.

  At this time, the power consumption of the heat pump was about 280 W by the above control. And the measured value of the pressure gauge 108 attached between the condenser 105 and the expansion valve 106 was 1.6 MPa, and the condensation temperature shown in FIG. The temperature of the condenser (heat radiating plate) 105 was 68 ° C. on the refrigerant inlet side and higher than the condensation temperature of 60 ° C. The recording material P is conveyed from the refrigerant outlet side of the condenser (heat radiating plate) 105 to the refrigerant inlet side by the conveying belt 102, and the toner surface temperature on the recording material P has increased from 25 ° C. to 63 ° C. . The recording material P is heated to the temperature of the condenser (heat radiating plate) 105 that is substantially the same as the condensing temperature while being conveyed to the vicinity of the center of the condenser (heat radiating plate) 105, and the condenser (heat radiating plate) 105 refrigerant. The temperature rose further in the second half of the conveyance near the entrance.

  The recording material P having a small heat capacity heated by exchanging heat with the condenser (heat radiating plate) 105 can be heated also on the refrigerant inlet side of the heat radiating plate through which superheated steam with a small amount of heat flows. The temperature of the recording material P on which the toner was transferred could be raised. During continuous conveyance of the recording material P, the pressure gauge 108 in the condensing part attached between the condenser 105 and the expansion valve 106 was stably maintained at 1.6 MPa, and the power consumption of the heat pump was constant at 280 W.

  According to the control of the first embodiment, a large amount of heat can be transferred to the recording material P in the first heat exchange unit that uses the sensible heat of the dry steam refrigerant. For this reason, insufficient heat dissipation of the condenser 105 is reduced, and a stable reverse refrigeration cycle can be maintained, so that preheating can be performed without increasing the power consumption of the compressor 104 more than necessary, and the energy saving effect is increased.

  On the other hand, the refrigerant inlet and the refrigerant outlet of the condenser (heat radiating plate) 105 are reversed, and the recording material P is conveyed from the refrigerant inlet side of the condenser (heat radiating plate) 105 to the refrigerant outlet side and delivered to the fixing device 26. The experiment was conducted. As a result, the surface temperature of the toner 109 on the recording material P increased only from 25 ° C. to 58 ° C. This is because the condenser (heat radiating plate) 105 on the refrigerant inlet side through which the superheated steam flows is cooled by the unheated recording material P. Therefore, the superheated steam with a small amount of heat cannot maintain a high temperature, and the condenser (heat radiating plate) 105. This is because the temperature of the temperature dropped to 60 ° C., which is almost the same as the condensation temperature.

  If the temperature of the recording material P reaches the condensing temperature during the preheating, the recording material P cannot obtain any more heat radiated from the condenser 105 of the heat pump 101, and this state is maintained for a long time. If this is continued, insufficient heat dissipation of the condenser 105 will be caused.

  As a result, the refrigerant is liquefied by the condenser 105 and depressurized by the expansion valve 106 without being supercooled, so that a stable heat pump cycle cannot be maintained, and the operating pressure of the compressor 104 becomes high. Then, since the operating pressure of the compressor 104 and the power consumption are in a substantially proportional relationship, the power consumption of the heat pump 101 is increased.

  From the above, the conveying direction of the recording material P is from the refrigerant outlet side that is the low temperature side of the condenser (heat radiating plate) 105 to the refrigerant inlet side that is the high temperature side, that is, the condenser ( It is necessary to convey from the low temperature side of the heat sink 105) to the high temperature side.

<Effect of Example 1>
As shown in FIG. 9, the relationship between the temperature of the recording material P carrying the toner image G preliminarily heated and delivered to the fixing device 26 and the amount of power consumed by the fixing device 26 was examined by computer simulation. The fixing conditions used in the calculation are as follows in addition to the above conditions of Example 1.

The peripheral speed of the heating roller 26a is 360 mm / sec, the average nip pressure is 2.2 kgf / cm ² , and the nip width is 8 mm. The heating roller 26a is heated and maintained at a regulated surface temperature of 180 ° C. by radiation energy from a heating source of a halogen lamp heater disposed at the center. The recording material P has a paper basis weight of 105 g / m ² , and a toner image G is placed thereon with a thickness of 10 μm.

  As shown in FIG. 9, when the toner image G and the recording material P are about 25 ° C., which is about room temperature, the power consumption of the fixing device 26 is about 1000 W. As the temperature rises due to preheating, the power consumption of the fixing device 26 is reduced. By raising the temperature by about 10 ° C., power consumption of about 100 W can be reduced.

  Therefore, the temperature of the recording material P is increased as much as possible without increasing the power consumption of the heat pump 101 more than necessary by the preheating device 100 including the conveyance belt 102, and used for fixing when forming a permanent image. Power consumption can be reduced.

  In Example 1, since the surface temperature of the toner image G on the recording material P was increased from 25 ° C. to 63 ° C., the power consumption of the fixing device 26 could be reduced by about 400 W from the relationship of FIG. It will be. Even considering the heat pump power consumption of 280 W, the total power consumption was reduced by 120 W.

<Example 2>
FIG. 10 is an explanatory diagram of the configuration of the preheating device according to the second embodiment. FIG. 11 is an explanatory diagram of the heat exchange temperature distribution of the belt heat exchanger in the second embodiment.

  As illustrated in FIG. 2, the preheating device 100 according to the second embodiment transports the recording material P by the transport belt 102 and preheats the heat pump 101 similarly to the first embodiment. The difference from the first embodiment is that the first heat exchange part and the second heat exchange part of the condenser (heat radiating plate) 105 are thermally separated.

  As shown in FIG. 10, the condenser 105b and the condenser 105a are thermally separated, and the mass of the heat exchange part of the condenser 105b is smaller than the mass of the heat exchange part of the condenser 105b.

  The condenser 105a which is an example of the second heat exchange unit heats the recording material at a heating temperature lower than that of the condenser 105b using the refrigerant radiated by the condenser 105b. The condenser 105a heats the recording material using the latent heat of the refrigerant cooled to the condensation temperature of the refrigerant by the condenser 105b. In the condenser 105a, the recording material P is heated to the condensation temperature of the refrigerant.

  The condenser 105b, which is an example of the first heat exchange unit, heats the recording material P using the sensible heat of the superheated steam refrigerant compressed and heated by the compressor 104 of the heat pump 101. The condenser 105b heats the recording material using the sensible heat of the refrigerant heated to a temperature exceeding the condensation temperature of the refrigerant. In the condenser 105b, the recording material P is heated to a temperature exceeding the refrigerant condensation temperature. In the condenser 105b, the heating temperature on the fixing device 26 side which is an example of the heating unit side is higher than the heating temperature on the condenser 105a side which is an example of the second heat exchange unit side.

  As shown to (a) of FIG. 11, the preheating apparatus 100 of Example 2 has the condenser (radiation board) 105a which the refrigerant | coolant condenses and becomes wet steam, and the condenser (heat dissipation) which becomes superheated steam. Plate) 105b is thermally separated. The heat radiation surface, which is the contact surface with the conveyor belt 102 of the condenser 105a, and the heat radiation surface, which is the contact surface with the conveyor belt 102, of the condenser 105b are adiabatically separated.

  The heat radiating surface size of the condenser (heat radiating plate) 105b of the heat pump 101 was 320 mm × 80 mm, and the heat radiating surface size of the condenser (heat radiating plate) 105a was 320 mm × 320 mm, which were separated by about 5 mm. The total length of the copper tubes meandering in the two heat sinks was about 5 m, and the amount of refrigerant in the heat pump was the same as in Example 1.

  As shown in FIG. 11 (b), the condenser 105a through which the wet steam flows and the condenser 105b through which the superheated steam flow are separated, and the respective heat radiation surfaces, which are the contact surfaces with the conveyor belt 102, are adiabatically separated. . As a result, the condenser (heat radiating plate) 105b on the fixing device side can be set to a temperature higher than the temperature of the saturated vapor B 'inlet of the condenser (heat radiating plate) 105a on the paper feeding side.

  As shown in FIG. 11 (c), the temperature distribution of the condenser (heat radiating plate) 105a and the condenser (heat radiating plate) 105b which are adiabatic and separated is discontinuous. Since the temperature of the condenser (heat radiating plate) 105b is higher than that of the saturated vapor B ′ inlet side of the condenser (heat radiating plate) 105a, the temperature of the recording material P is higher than that of Example 1 shown in FIG. Can be raised.

  Since the power consumption of the fixing device 26 can be further reduced by further increasing the temperature of the recording material P, the energy saving effect is increased without increasing the power consumption of the compressor 104. As the temperature rises, the amount of heat exchanged from the condenser (heat radiating plate) 105b to the recording material P increases, so that the heat dissipation of the condenser (heat radiating plate) 105b is reduced and the heat pump cycle is stabilized.

<Control of heat pump>
As shown in FIG. 10, when the recording material P is heated by exchanging heat with the condensers 105 a and 105 b while being transported by the transport belt 102, the heat pump cycle shown in FIGS. 4 and 5 is stably maintained in the heat pump 101. Suppose that At this time, the condenser 105b on the side close to the fixing device 26 is maintained in a state from B to B ′ where the superheated steam in the heat pump cycle of FIG. 4 flows, and the condenser 105a on the side on which the recording material P is fed is The state is maintained from B ′ to C through which condensed wet steam and supercooled liquid flow.

  In this state, the recording material P radiates heat from the contact surface between the condenser (heat radiating plate) 105a and the conveying belt 102 and radiates heat from the contact surface between the condenser (heat radiating plate) 105b and the conveying belt 102. Is heated by the amount of heat Q1 ″.

  For this reason, the ratio of the amount of heat released between the respective heat sinks Q1 ′ and Q1 ″ (ratio of enthalpy change amount) is equal to the heat dissipation area of the condenser (heat sink) 105b on the side close to the fixing device 26 and the paper feed. It controls so that it may become the ratio of the thermal radiation area of the condenser (radiation board) 105a of the side. When the state of heat exchange between the condenser (heat radiating plate) 105 and the recording material P changes due to the difference in the recording material P or the conveyance speed, the heat pump cycle in FIGS. 4 and 5 changes, There is a possibility that the heat release amount ratio (the ratio of the enthalpy change amount) between Q1 ′ and Q1 ″ will change. In such a case, in order to maintain the heat pump cycle of FIGS. 4 and 5, the inverter control unit 115 adjusts the refrigerant circulation amount by controlling the rotational speed of the compressor 104.

  Specifically, the temperature sensor 116 is provided in the condenser (heat radiating plate) 105b on the fixing device 26 side, and the following flow is performed after step S108 of the flowchart shown in FIG.

  The inverter control unit 115 calculates the refrigerant condensing temperature T0 with reference to the Ph diagram of FIG. 4 based on the pressure measured by the pressure gauge 108 (S109).

  The inverter control unit 115 measures the temperature of the condenser (heat sink) 105b by the temperature sensor 116 of the condenser (heat sink) 105b. Then, it is determined whether the temperature of the condenser (heat radiating plate) 105 is equal to or higher than the condensation temperature T0 by comparing with the calculated temperature (S109) (S110).

  Inverter control part 115 performs control which raises the frequency of compressor 104 and raises the number of rotations, when it is not more than condensation temperature T0 (S111). As the rotational speed increases, the amount of refrigerant circulating increases, the amount of heat radiated from the condenser (heat radiating plate) 105 increases, and the heat pump cycle shown in the Ph diagram of FIG. 4 is maintained.

<Effect of Example 2>
Regarding Example 2, the reduction effect of the total power consumption of the fixing device 26 and the preheating device 100 was examined. The image forming apparatus used in the second embodiment is the same as that in the first embodiment, and the heat pump control accompanying the image forming process is the same as that in the first embodiment.

  When the heat pump 101 is operated at 75 Hz which is the maximum frequency of the compressor 104 and the temperature of the condenser 105b reaches 80 ° C. which is a preheating temperature necessary for fixing, the condenser 105b is adjusted while adjusting the frequency of the compressor 104. The temperature of was maintained.

  The recording material P was continuously transported at a transport speed of 400 mm / sec, and a permanent image was obtained by passing through the fixing device 26 which was able to be fixed in advance and was on standby. As the recording material P, A4 size plain paper having a thickness of 100 μm was used. At this time, the power consumption of the heat pump was about 280 W.

  The limit value of the pressure gauge 108 attached between the condenser 105a and the expansion valve 106 was 1.6 MPa, and the condensation temperature was 60 ° C. The temperature of the condenser (heat radiating plate) 105b was 75 ° C., which was higher than the condensation temperature of the refrigerant, and further higher than the temperature of the condenser (heat radiating plate) 105 of Example 1.

  The recording material P is conveyed by the conveying belt 102 from the refrigerant outlet side of the condenser 105a to the refrigerant inlet side of the condenser 105b, and the surface temperature on the recording material P has increased from 25 ° C. to 68 ° C. The recording material P is already heated to the vicinity of the condensation temperature while being conveyed on the condenser (heat radiating plate) 105a, and further conveyed on the condenser 105b having a temperature higher than that of the condenser 105 of the first embodiment. The temperature rose.

  As a result, the toner temperature on the recording material P could be further increased by 5 ° C. from Example 1. Further, during continuous conveyance of the recording material P, the limit value of the pressure gauge 108 attached between the condenser 105a and the expansion valve 106 is stably maintained at 1.6 MPa, and the power consumption of the compressor 104 is constant at 280W. It was.

  Since the relationship between the recording material heating temperature in FIG. 9 and the power consumption of the fixing device 26 is the same as that in the first embodiment, in Embodiment 2, the power consumption of the fixing device 26 can be reduced by about 450 W from FIG. Even considering the power consumption 280 W of the heat pump 101, the total power consumption was reduced by 170 W, which was further reduced by 50 W compared to Example 1. The power consumption used for fixing the toner image could be reduced from 1000 W to 830 W without increasing the power consumption of the heat pump 101 more than necessary.

  In the preheating device according to the second embodiment, the temperature of the recording material on which the toner is transferred is preheated to be equal to or higher than the condensation temperature of the refrigerant by using a vapor compression reverse refrigeration cycle (heat pump cycle) with improved energy saving effect as a preheating source. can do.

  Thereby, further energy saving of the fixing device 26 can be achieved. In addition, the heat exchange efficiency with the heat sink increases, so the lack of heat dissipation is reduced, and by maintaining a stable reverse refrigeration cycle, the recording material can be pre-heated without raising the power consumption of the compressor more than necessary, Furthermore, the energy saving effect is enhanced.

<Example 3>
In the first and second embodiments, the heat pump cycle in which the refrigerant includes a wet vapor phase in both the evaporation process and the condensation process has been described using a general alternative fluorocarbon (hydrofluorocarbon). However, according to the present invention, as long as the heat pump cycle is performed, the refrigerant is not limited to the alternative chlorofluorocarbon, and the condensation process is not limited to the wet vapor phase.

  For example, a carbon dioxide heat pump cycle that is widely used at present can be used. The heat pump cycle of carbon dioxide gas is characterized in that the evaporation process is performed in a wet vapor phase, but the condensation process is a phase transition from a superheated vapor phase to a direct liquid phase.

  As shown in FIG. 2, in Example 3, the fixing device 26 side portion of the condenser 105, which is an example of the first heat exchange unit, is compressed by the superheated steam carbonated by the compressor 104 of the heat pump 101 and heated. The recording material P is heated using the sensible heat of the gas. The secondary transfer portion (T2) side portion of the condenser 105, which is an example of the second heat exchange portion, uses the refrigerant that has radiated heat at the fixing device 26 side portion of the condenser 105, and thus the fixing device 26 side portion of the condenser 105. The recording material P is heated at a lower heating temperature. The conveying belt 102, which is an example of conveying means, conveys the recording material P heated at the secondary transfer portion (T2) side portion of the condenser 105 to the fixing device 26 side portion of the condenser 105. The recording material P heated at the fixing device 26 side portion 105 is delivered to the fixing device 26.

<Example 4>
In recent years, the power consumption of fixing devices has been reduced by lowering the melting point of toner. Moreover, the heating temperature of the heat pump cycle can be increased by a refrigerant that can be used at a high temperature such as a carbon dioxide cycle. Therefore, as shown in Patent Document 2, there is a possibility that the toner image is fixed only by heating by a heat pump cycle without having a heat source that directly heats with electric power in the fixing device.

  In this case, if the recording material P is heated and pressurized using sensible heat of the refrigerant, a toner image of a toner having a melting point higher than the condensation temperature of the refrigerant can be fixed. The toner image can be fixed only by heating by a heat pump cycle using a refrigerant having a condensation temperature lower than the melting point of the toner.

  However, when a toner image is fixed on a recording material, the energy actually used for heating and melting the toner image is very small, and most of the power consumption is much lower than the melting temperature of the toner of 100 ° C. It is used to heat to temperatures around 60 ° C. Therefore, such a simple heating of the recording material can sufficiently cope with the condensation temperature of the existing refrigerant. By utilizing a heat pump using an existing refrigerant, energy that is several to ten times the power consumption can be used for preheating the recording material.

  Moreover, when performing final heating and pressurization with a heat pump, it is not easy to accurately control the temperature of the heating nip. This is because a heat pump is interposed between the electrical control and the heating, and the responsiveness and adjustment accuracy are impaired.

  For example, when the rotational speed of the compressor of the heat pump is changed to change the temperature, a considerable delay time occurs until the temperature of the fixing nip changes due to the change of the condenser temperature of the heat pump. Further, when the rotation speed of the heat pump compressor is used for temperature control of the heating nip, fluctuations in the pressure of the condenser may cause the heat pump cycle to become unstable.

  Therefore, when a heat pump is used for the image heating apparatus, the final heating nip should be directly heated using radiation heating such as a halogen lamp heater, electromagnetic heating such as electromagnetic induction, or resistance heating such as a heater. Is desirable. This is because temperature control with a high response speed can be performed electrically. In addition, by preloading the heat pump with enormous energy supply for simply heating the recording material, it is possible to achieve significant power saving, precise temperature control, and downsizing for heating the fixing nip. .

  In Example 4, as shown in FIG. 2, the recording material P preheated using the heat pump 101 is heated to the final fixing temperature using a very simple fixing device 26. The fixing device 26 heats the recording material P carrying the toner image in a pressurized state using a heating nip N that is electrically heated and temperature-controlled.

  The preheating device 100 preheats the recording material P using the heat pump 101 and delivers it to the fixing device 26. The preheating device 100 preheats and heats the recording material P carrying the toner image from the opposite surface of the toner image to a temperature lower than the heating nip N using the heat pump 101 while conveying the recording material P without applying pressure. Delivered to nip N.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus, Pa, Pb, Pc, Pd Image forming part 8 Intermediate transfer belt, 17 Recording material cassette, 22 Secondary transfer roller 26 Fixing device, 101 Heat pump, 102 Conveying belt 103 Conveying roller, 104 Compressor, 105, 105a, 105b Condenser 106 Expansion valve, 107 Evaporator, 108 Pressure gauge, 111 Copper tube 112 Aluminum plate, 114 Fan, 115 Inverter controller 116 Temperature sensor P Recording material, G Toner image

Claims (7)

In an image heating apparatus comprising a heating unit that heats a recording material carrying a toner image in a pressurized state, and pre-heating the recording material using a heat pump and delivering it to the heating unit,
A first heat exchange unit that heats the recording material using the sensible heat of the superheated steam refrigerant compressed and heated by the compressor of the heat pump;
A second heat exchanging unit that heats the recording material at a heating temperature lower than that of the first heat exchanging unit using the refrigerant that has dissipated heat in the first heat exchanging unit;
Conveying means for conveying the recording material heated in the second heat exchanging section to the first heat exchanging section and delivering the recording material heated in the first heat exchanging section to the heating section; An image heating apparatus comprising: The first heat exchange unit heats the recording material using the sensible heat of the refrigerant heated to a temperature exceeding the condensation temperature of the refrigerant,
The second heat exchanging unit heats the recording material using the latent heat of the refrigerant cooled to the condensation temperature of the refrigerant in the first heat exchanging unit,
The image heating apparatus according to claim 1, wherein the first heat exchange unit has a heating temperature on the heating unit side higher than a heating temperature on the second heat exchange unit side.   The recording material is heated to a condensation temperature of the refrigerant in the second heat exchange unit, and the recording material is heated to a temperature exceeding the condensation temperature of the refrigerant in the first heat exchange unit. 2. The image heating apparatus according to 2.   The first heat exchange unit and the second heat exchange unit are thermally separated, and the mass of the first heat exchange unit is smaller than the mass of the first heat exchange unit. The image heating apparatus according to claim 3.   The compressor includes control means for compressing the refrigerant with a variable output and controlling the output of the compressor so as to keep the refrigerant in the first heat exchange section at a predetermined temperature exceeding the condensation temperature. The image heating apparatus according to claim 2. The conveying means is composed of an endless belt that rotates by sliding the back side of the recording material carrying surface against the heat radiating surface of the first heat exchanging portion and the heat radiating surface of the second heat exchanging portion , recording material an apparatus according to any one of claims 1 to 5, characterized in that it is heated by the said through an endless belt second heat exchanger and the first heat exchange section . Image forming means for forming a toner image and transferring it to a recording material;
An image heating apparatus according to any one of claims 1 to 6, wherein the recording material to which the toner image has been transferred is heated and pressed to fix the toner image on the recording material.
The image forming apparatus according to claim 1, wherein the evaporator of the heat pump evaporates the refrigerant using the exhaust heat of the heating unit, heats the refrigerant to dry steam, and supplies the dry vapor to the compressor of the heat pump.

Images