JP2011081159A - Heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect film breakage in a color on-demand fixing device.
A conductive member (plate, roller, brush) is brought into contact with the inner surface of the film near the nip, and a current flowing through the conductive pressure roller is detected from the film fracture surface. Example of halogen heater (radiation surface heating configuration) and ceramic heater.
[Selection] Figure 1

Description

  The present invention relates to a heating device (fixing device) used for fixing a toner image in an electrophotographic image forming apparatus.

  A problem that has recently become more important in electrophotographic image forming apparatuses used in copying machines, printers, fax machines, and the like is to respond to so-called demands for energy saving. Since the conventional toner image fixing device uses a method in which the toner is melted and fixed to the paper, power is directly consumed as thermal energy, and this power consumes a large amount of power used by the entire apparatus main body. Occupies part.

  In a heating device using a heating roller, a temperature detection element connected in series with a heat source (for example, a halogen lamp) as a safety element in contact with or close to the surface of the heating roller in order to ensure safety when the device runs away. Is used. In general, a thermostat, a thermo switch, a thermal fuse, or the like is used as the temperature detection element. When the halogen lamp is turned on due to a failure and the heating roller becomes an abnormally high temperature, the temperature detection element is cut off at the set temperature, and power supply to the halogen lamps connected in series is cut off. This prevents serious accidents that lead to ignition.

  On the other hand, as one direction for reducing the power consumption of the fixing device, on-demand (normally, no current flows through the heater, for example, real-time when the heater is turned on only during image formation) can be achieved. ing. Specifically, by making the fixing member into a thin roller, thin belt or film, the heat capacity is significantly reduced compared to the conventional thick heating roller, and at the same time the start-up of the device is accelerated. Power consumption is reduced. By achieving on-demand, when a print signal is received, printing starts immediately with almost no waiting time, so fixing is possible even during non-printing, as with conventional heating rollers. It is not necessary to keep the member at a high temperature around the printing temperature, and it is sufficient to keep the member at room temperature at most moderately low temperature. The heat dissipation during the heat retention of the fixing device increases in proportion to the temperature difference between the environmental temperature and the set temperature of the fixing member. However, such heat dissipation always consumes electric power even when printing is not performed. Therefore, in a moving situation where printing is repeated intermittently, a very large power saving effect is brought about by making the fixing device on demand.

  Furthermore, the present inventors have applied for a fixing device in which an elastic layer is provided on the film and heat is transferred by high-speed radiation. According to the invention, the infrared rays generated from the heat source are transmitted or semi-transmitted through the low heat capacity film base layer and the elastic layer, and then generate heat in the absorption layer provided in the vicinity of the film surface. Good thermal responsiveness is obtained without being greatly affected by the thickness, and the fixing property in a color image is improved by sufficient elasticity of the film surface.

JP-A-4-44075

  In a heating device using the above thin roller, film, or belt as a heating member, a part of the film belt is caused by contamination of foreign matters during paper passing, scratches or destruction during jam processing, and wear or fatigue during durability. Therefore, it is necessary to safely stop the apparatus even when a rupture, crack or the like occurs in a portion not facing the safety element using temperature detection.

  Therefore, this invention solves the said subject and aims at stopping a heating apparatus safely.

  The above object is achieved by the present invention described below. That is, the first invention in the present application includes a heating member that is rotatable at substantially the same speed as the material to be heated and includes a heat source inside, and a pressure member that pressurizes the heating member from the outside. In the heating device that forms a pressure nip between the heating member and the pressure member, and heats the material to be heated at the nip portion, a voltage is applied to at least a part between the heating member and the pressure member. A voltage applying means and a current detecting means for detecting a current from the voltage applying means are provided, and a current leaking from the inside of the heating member can be detected.

  A second invention according to the present application is characterized in that the heating member is a flexible film or belt, and is a heating member that may cause partial breakage, cracks, or the like. It is possible to detect a current leaking from the inside of the.

  A third invention according to the present application is characterized in that when the current detecting means detects a current, the power supply to the heat generating source is stopped, and the current leaked from the heating member is detected. Failures such as breaks and cracks can be determined earlier than the detecting method, and the apparatus can be safely stopped.

  A fourth invention according to the present application is characterized in that the voltage applying means is formed of a thin metal plate, and is pressed against the pressure member via the rotatable heating member to form a nip. It is possible to detect the breakage of the film over the entire nip from the light detection element having a leakage current of 3 to safely stop the apparatus.

  A fifth invention according to the present application is characterized in that the voltage applying member is formed of a conductive brush, and even if the voltage applying member is disposed outside the nip, the film breakage is detected throughout the nip, and safety is ensured. The device can be stopped.

  A sixth invention according to the present application is characterized in that the voltage applying means is a conductive roller that is pressed against the pressure member via the rotatable heating member to form at least a part of the nip, By reducing the friction between the voltage applying means and the heating member, it is possible to reduce the noise of the detection current caused by the frictional charging and improve the detection accuracy of the current detection element.

A seventh invention according to the present application is characterized in that the electric resistance of the pressure member is 10 ⁴ to 10 ⁸ Ω, and the detection current is ensured, the detection accuracy is improved, and good fixability is ensured. Can do.

  The eighth invention according to the present application is characterized in that the voltage applied to the voltage applying member is a voltage having the same polarity as the electrode resistance of the toner image as the heated member, and when the film is broken, The detection current is stabilized and the detection accuracy is improved by preventing toner contamination of the voltage applying member at the rupture site.

A ninth invention according to the present application is characterized in that the heating member has a resistance layer having an electric resistance of at least 10 ¹⁰ Ω or more, and reduces the amount of current in a steady state and improves detection accuracy.

  According to a tenth aspect of the present invention, an elastic body containing at least silicone rubber is used as the resistance layer, and a resistance layer having excellent heat resistance and insulation can be formed. Can be obtained.

  According to the present invention, the heating member includes a heating member that is rotatable at substantially the same speed as the material to be heated and includes a heat source inside, and a pressing member that pressurizes the heating member from the outside. In the heating device that forms a pressure nip with the pressure member and heats the heated material at the nip portion, voltage applying means for applying a voltage to at least a part between the heating member and the pressure member; A current detecting means for detecting the current from the voltage applying means is provided, the current leaking from the inside of the heating member is detected, and the power supply to the fixing device is stopped. It became possible to ensure the sex.

  The heating member is a flexible film or belt, and detects a current leaking from the inside of the heating member to a heating member that may cause partial breakage, cracks, or the like. can do.

  When the current detection means detects a current, the power supply to the heat generation source is stopped, and since the current leaking from the heating member is detected, the breakage and the crack are faster than the method of detecting the temperature. And the like, and the apparatus can be safely stopped.

  The voltage applying means is formed of a thin metal plate, and press-contacts with the pressure member via the rotatable heating member to form a nip. It is possible to detect film breaks and to stop the apparatus safely.

  The voltage applying member is formed of a conductive brush. Even when the voltage applying member is disposed outside the nip, the film can be detected over the entire nip and the apparatus can be safely stopped.

  The voltage applying means is a conductive roller that is pressed against the pressure member via the rotatable heating member to form at least a part of a nip, and is provided between the voltage applying means and the heating member. By reducing the friction, it is possible to reduce the noise of the detection current caused by the frictional charging and improve the detection accuracy of the current detection element.

The pressure member has an electric resistance of 10 ⁴ to 10 ⁸ Ω, which can ensure a detection current, improve detection accuracy, and ensure good fixability.

  The voltage applied to the voltage applying member is a voltage having the same polarity as the electrode resistance of the toner image that is a member to be heated, and when the film breaks, the toner on the voltage applying member at the broken portion is stained. By preventing it, the detection current is stabilized and the detection accuracy is improved.

The heating member has at least a resistance layer having an electric resistance of 10 ¹⁰ Ω or more, and reduces the amount of current in a steady state and improves detection accuracy.

  An elastic body containing at least silicone rubber is used as the resistance layer, and a resistance layer having excellent heat resistance and insulation can be formed, so that stable detection accuracy can be obtained over a long period of time.

Sectional drawing of the heating apparatus configuration in the first embodiment Front view of a heating device configuration in the first embodiment Sectional drawing of the heating apparatus configuration in the second embodiment Explanatory drawing of the effect of radiation and heat on the fixing belt in the second embodiment Sectional drawing of the structure of the heating apparatus in the third embodiment Front view of a voltage applying member in the third embodiment Overall schematic view of an image forming apparatus using the present invention

(First embodiment)
First, an image forming apparatus using the heating device of the present invention will be described.

  FIG. 7 is a cross-sectional view of a color image forming apparatus provided with a fixing device as a heating device of the present invention.

  In FIG. 7, reference numeral 28 denotes a photosensitive drum, which can be configured by applying a photoconductor such as an organic photoreceptor (OPC) or amorphous silicon to the outer peripheral surface of an aluminum cylinder.

  The photosensitive drum 28 is driven at a predetermined speed (eg, 50 to 300 [mm / sec]) in the direction of the arrow by a driving unit (not shown), and the surface of the photosensitive drum 28 is darkened by the charger 29 (eg, −700 [V]). Is charged.

  Next, the exposure device 30 exposes the photosensitive drum 28 in accordance with the magenta image pattern, and the electrostatic potential image is formed by lowering the surface potential of only the image portion to the bright portion potential (eg, −150 [V]).

  The developing devices 21a, 21b, 21c, and 21d supported by the rotating support 30 include magenta, cyan, yellow, and black developer materials, respectively. Here, each color developer is a negatively chargeable toner having a weight average diameter of 6 μm which is synthesized by a suspension polymerization method and has a spherical shape and high development / transfer efficiency.

  The electrostatic latent image is first provided with a gap of 300 [μm] so that the magenta developing unit 21a faces the photosensitive drum 28. For example, AC2 [kVpp] is superimposed on DC-500 [V]. The toner is developed by the developing bias and visualized as a magenta toner image.

The visualized magenta toner image on the photosensitive drum 28 is supplied from an unillustrated transfer power source to an intermediate transfer drum 23 made of a medium resistance member such as PVdF subjected to a conductive treatment of 10 ⁶ to 10 ⁹ [Ω]. Transfer is performed with a transfer bias (+0.5 to 2 [kV]).

  When a magenta image for one A4 size page is transferred onto the intermediate transfer drum, the rotary support 22 rotates, and the above process is sequentially performed for each color of cyan, yellow, and black, and a plurality of color toner images are formed on the intermediate transfer drum 23. Form.

  On the other hand, the pickup roller 24 feeds the transfer paper P from the transfer paper cassette 25 in synchronization with the black toner image. By applying a secondary transfer bias (+1 to 2 [kV]) to the transfer roller 31, the toner image on the intermediate transfer drum is transferred to the transfer paper P and is carried into the fixing device 26.

  The transfer material P onto which the color image has been transferred is conveyed to the fixing device 26 by the conveying means and fixed, discharged as a color printed matter outside the apparatus, and stacked on the paper discharge tray 20.

  The transfer residual toner on the intermediate transfer drum is charged to a positive polarity by the charger 38 and then collected on the photosensitive drum 28 and cleaned by the cleaning device 27 in the same manner as the transfer residual toner on the photosensitive drum 28.

  Hereinafter, a fixing device as a heating device in this embodiment will be described with reference to FIG. FIG. 1 is a schematic sectional view seen from the side of the fixing device. FIG. 2 is a schematic front view seen from the front of the fixing device.

  In FIG. 1, a heating film 3 as a heating member includes a halogen lamp 1 having an output of 500 to 1200 [W], which is a heating element, and is pressed against a pressure roller by a support stay 6 to form a fixing nip. It is also possible to use a xenon lamp or the like in addition to the halogen lamp.

  The heating film 3 is a flexible film based on metal or resin, and has a release layer on the surface layer. Moreover, an elastic layer can be provided between the release layer.

  The base layer may be made of a metal such as nickel, iron, SUS, or nickel-cobalt alloy, or a resin such as polyimide. The thickness is preferably 10 to 100 μm.

  The elastic layer is made of silicone rubber, fluorine rubber, fluorosilicone rubber or the like, which has good heat resistance and good thermal conductivity.

The thickness t _s of the elastic layer is preferably 50 ≦ t _s ≦ 1000 [μm]. This elastic layer has a thickness necessary to guarantee the fixed image quality. When a color image is printed, a solid image is formed over a large area on the heated material P, particularly in a photographic image. In this case, if the heating surface (release layer) cannot follow the unevenness of the recording material or the unevenness of the toner layer, heating unevenness occurs, and gloss unevenness occurs in the image where the heat transfer amount is large and small. A portion with a large amount of heat transfer has a high glossiness and a portion with a small amount of heat transfer has a low glossiness. If the thickness of the elastic layer is 50 μm or less, the unevenness of the recording material or the toner layer cannot be followed and unevenness in image gloss occurs. On the other hand, when the elastic layer is 1000 μm or more, the thermal resistance of the elastic layer increases and the temperature response decreases. More preferably the thickness _{t s} of the elastic layer should preferably be _{100 ≦ t s ≦ 500 [μm} ].

  If the hardness of the elastic layer is too high, unevenness in image gloss will occur because it cannot follow the unevenness of the recording material or toner layer. Therefore, the hardness of the elastic layer is preferably 50 ° (JIS-A) or less.

  The thermal conductivity λ of the elastic layer is preferably 0.25 to 0.84 [W / m · ° C.]. When the thermal conductivity λ is smaller than 0.25 [W / m · ° C.], the thermal resistance is large, and the temperature rise in the surface layer (release layer) of the heating film is slow. When the thermal conductivity λ is larger than 0.84 [W / m · ° C.], the hardness becomes too high, or the compression set is deteriorated. Therefore, the thermal conductivity λ is preferably 0.25 to 0.84 [W / m · ° C.]. More preferably, 0.33 to 0.63 [W / m · ° C.] is preferable.

  For the release layer, a material having good release properties and heat resistance such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, and FEP can be selected.

The release layer is insulative with a surface resistance of 10 ¹¹ [Ω / cm ² ] or more.

The thickness t _R of the release layer is preferably 10 ≦ t _R ≦ 100 [μm]. When the thickness of the release layer is less than 10 [μm], there arises a problem that a part having low release properties is formed due to coating unevenness of the coating film, or durability is insufficient. In addition, when the release layer exceeds 100 [μm], there is a problem that the heat conduction is lowered. In particular, in the case of a resin release layer, the hardness becomes too high, and the effect of the elastic layer is lost. More preferably, the thickness t _R is 10 ≦ t _R ≦ 50 [μm]. Further, the release layer may be previously formed into a tube shape.

Here, in order to obtain the effect of the present invention, the electric resistance of the heating member needs to be high. The electric resistance of the heating film, which is a heating member, is preferably 10 ¹⁰ Ω or more, and if it is 10 ⁹ Ω or less, the detection current at the steady state is increased and the detection accuracy is lowered. Here, the electrical resistance of the heating film was measured using a high resistance meter between the support stay and the pressure roller in a state where a low resistance aluminum roller was used as the pressure roller in the fixing device.

  The heating film 3 is driven to rotate by a pressure roller 5 driven by a motor (not shown), and rotates at the same speed as the pressure roller and paper as a transfer material. The heating film 3 has both end surfaces in the longitudinal direction in contact with or in proximity to the regulating member 47 shown in FIG. 2 to prevent the film from being biased due to rotation.

  The pressure roller 5 is formed by providing a silicone rubber layer having a thickness of 1 to 20 [mm] on a metal core such as aluminum, stainless steel, or iron, and the surface layer is a fluororesin for preventing toner contamination. Has a layer. Further, it is also possible to use a silicone sponge layer as the pressure roller 5 instead of the silicone rubber layer.

Here, in order to obtain the effect of the present invention, the pressure member needs to be conductive. Preferably the electrical resistance of a pressure member pressure roller is 10 ⁴ to 10 ⁸ Omega, the 10 ⁸ Omega or decreased is smaller becomes the detection accuracy detection current and the transfer paper is 10 ⁴ Omega less Charges leaked and the toner image was disturbed. Here, the electrical resistance of the pressure roller was measured by applying 100 V between the support stay and the pressure roller in the present fixing device without a heating film.

  In this example, two guide members 4 are disposed inside the heating film 3, and the heating film provides straightness to suppress meandering and prevent the heating film from contacting the halogen lamp 1. The guide member 4 is made of a metal sleeve such as aluminum or stainless steel, and is arranged in parallel with the axis over the entire region in the film axial direction. Here, the guide member 4 is made of a metal member, so that excellent thermal conductivity suppresses temperature unevenness in the axial direction of the heating film, particularly temperature rise when fixing small size paper, and enables stable image formation. .

  The surface temperature of the heated film is detected by the thermistor 6, and the halogen lamp is turned on / off by a fixing power source (not shown) so as to reach a predetermined temperature (160 to 190 ° C.), and the temperature is controlled.

  The support stay 2 is formed from a thin plate of a metal material such as aluminum, stainless steel, iron, or copper having a thickness of 0.3 to 2 [mm] so as to satisfy heat resistance, mechanical strength, and low heat capacity. The support stay 6 is formed with a bottom plate portion for forming a nip and an edge portion for guiding a film by pressing a thin metal plate.

  Here, in order to improve the slidability between the support stay and the inner surface of the film, various lubricants such as fluorine grease, silicone grease, and silicone oil can be applied to the inner surface of the film. The lubricant reduces the friction between the support stay and the film, and provides an effect of keeping the rotation speed of the film constant regardless of the environment.

  As shown in FIG. 2, it is also possible to use the present invention and a conventional safety element based on temperature detection. When the temperature rises abnormally, the thermistor 6 and the thermo switch 8 supply power to the halogen heater. Stop and prevent the fixing device from igniting and smoking.

  The thermo switch 8 is installed in contact with the heating film 3 or in a non-contact manner in the vicinity thereof. When the heating film 3 is above a certain temperature (for example, 200 ° C.), the thermoswitch 8 cuts off the voltage from the supply power source Vss, and the relay circuit 11 is cut off by turning off the exciting coil of the relay circuit 11. In this way, the power supply from the fixing power supply is forcibly stopped by shutting off the relay circuit 11 when the temperature rises abnormally.

  The thermistor 6 detects the temperature, controls the solid state relay 7 through the CPU 13, and controls the fixing power source 12 such as PID to set the heating film at an appropriate temperature. In the unlikely event that the heated film is abnormally heated above the set temperature, the Enable signal is turned off and the relay circuit 11 is cut off through the NAND circuit 10. In addition to abnormal temperature rise, the CPU 13 turns off the relay circuit 11 and stops the supply of power to the halogen heater even when the temperature does not rise even when energized, such as when a thermistor malfunctions or poor contact occurs.

  The NAND circuit 10 turns on the relay circuit 11 and energizes the halogen heater only when the heating film temperature is appropriate and the heating film is not broken or cracked.

  Next, a current detection mechanism for detecting the occurrence of breakage and cracks in the heating film, which is a feature of the present invention, will be described.

  Reference numeral 40 in FIG. 2 denotes a DC power source, which applies a DC voltage to the support stay 2 which is a voltage applying member in this embodiment. Since the support stay 2 forms a contact nip with the conductive pressure roller 5 via the insulating heating film 3, when the heating film breaks, cracks, etc., the heating film The support stay 2 and the pressure roller come into contact with each other through the fracture surface, and a current flows from the DC power supply 40 to the support member 2.

The current detection circuit 9 sends an Enable signal to the NAND circuit 10 in a normal state, but turns the Enable signal off when the current flowing through the support stay 2 exceeds a certain value. As an example of the current detection circuit, a part of a current-voltage conversion circuit using an operational amplifier or the like can be used. By detecting the current between the conductive support stay and the pressure roller in this way, it is possible to detect the occurrence of cracks and cracks in the heated film that is insulative or high resistance (10 ¹⁰ Ω or more) over the length of the film. I can do it now.

  The Enable output signal of the current detection circuit is constantly monitored, and when a leakage current is generated from the heating film, the relay circuit 11 is cut off through the negative AND circuit 10 and the power supply to the halogen lamp is stopped.

  Here, the absolute value of the voltage applied to the supporting member, which is a voltage applying member, is preferably 10 to 1000 V, and provides good detection accuracy in the pressure roller having the above-described electrical resistance. If the absolute value of the supporting member applied voltage is less than 10V, current detection at the time of breakage becomes difficult, and if it is more than 1000V, problems such as an increase in cost for securing insulation from the surroundings occur.

  Furthermore, it is preferable that the voltage applied to the supporting member that is a voltage applying member is a voltage having the same polarity as the charging polarity of the toner image that is the material to be heated. In this embodiment, since negatively chargeable toner is used, by applying −100 V as a negative polarity to the support member, when the paper having the toner image enters the nip at the time of film breakage or immediately after breakage, the support at the fracture surface is supported. It is possible to prevent the contact surface of the member from being contaminated with toner and increasing its resistance, and to improve the detection system. Furthermore, by making the applied voltage of the support member the same polarity as the toner, an electrostatic field is created in the nip other than when the film is broken, so that the toner is prevented from adhering to the heated film (so-called offset), and good for a long time It becomes possible to obtain a fixed image quality.

  That is, according to the present embodiment, the fixing member nip is formed by forming the supporting member of the heating member from a metal member and pressing the pressure roller, so that the heating film interposed with a simple configuration is driven by the pressure roller. It is possible to reduce the heat capacity of the fixing device and to quickly start it up. Furthermore, by applying a voltage to the support member and detecting a current flowing in the fixing nip, it is possible to detect breakage and cracks of the heating film with a simple configuration.

(Second Embodiment)
Hereinafter, a fixing device as a heating device in this embodiment will be described. FIG. 3 is a schematic cross-sectional view seen from the side of the fixing device.

  In this embodiment, a conductive roller is used as a voltage applying means to prevent the inner surface of the heating film from being worn and to improve the accuracy of film breakage detection in the present invention. Furthermore, in this embodiment, an elastic film having infrared transparency is used as the heating film, so that the vicinity of the surface of the heating film can be heated at high speed, and high-speed and high-quality image output is possible.

  Next, the configuration of the fixing device in this embodiment will be described.

  Reference numeral 43 in FIG. 3 denotes a heating film, which includes a halogen lamp 1 having an output of 500 to 1200 [W], which is a heating element. Here, the radiation light source can be of any type as long as it efficiently radiates infrared rays at high speed. A xenon lamp or the like can be used in addition to the halogen lamp, but the halogen lamp 1 in this example has a wavelength of 0.8 μm. It is possible to radiate the above infrared rays with a high efficiency of 85% or more of the input power, and to radiate by heating a tungsten filament with a small heat capacity, so that it is possible to obtain a fast start-up and responsiveness. To do.

  The coil of the heating element in the halogen lamp is wound almost evenly and installed over the entire image area without segmentation. Therefore, a decrease in the amount of radiant light in the non-coil portion generated between the coils when the heating element is segmented is prevented, and the occurrence of the heating element coil trace (gross unevenness, fixing unevenness) in the longitudinal direction in the fixed image is prevented. . The heating film 43 is provided with a thermistor 6 which is a temperature detecting means. Electric power is supplied to the halogen lamp 1 according to the surface temperature of the heating film 43 detected by the thermistor, and about 90% of the input power is in the infrared region. Is emitted as output light.

  Around the halogen lamp 1, three metal support rollers 42a, 42b, and 42c are disposed as film holding members. The heating film 43 is rotatably supported by the support roller 42 and is in pressure contact with the pressure roller 5.

  The support roller 42a is a metal roller such as stainless steel or aluminum, and may be a hollow sleeve having a wall thickness of about 0.3 to 2 [mm] in order to realize higher-speed startup. The support roller 42a is used for downstream pressure, and is pressed toward the center of the pressure roller at 98 to 490 [N]. Further, the support roller 42b is for upstream pressure, and is pressed toward the center of the pressure roller at 9.8 to 300 [N] so as to realize a contact pressure lower than that of the downstream pressure roller 42a. The support roller 42c is for film control. By tensioning the pressure film 3, the tension between the support rollers 42a and 42b is generated, and the heating film 43 is brought into close contact with the pressure roller to form a stable fixing nip. is doing. Further, since the heating film position can be moved in the axial direction by moving one end of the supporting roller 42c up and down by a cam (not shown), the supporting roller 42c is adapted according to information from a film position detecting means (not shown). Can be moved to suppress the meandering and displacement of the film.

  The support roller 42a is driven at the same speed as the pressure roller by a drive motor (not shown), and similarly rotates the heating film 43 at the same speed as the pressure roller 5 driven by the drive motor (not shown).

  The pressure roller 5 is formed by providing a silicone rubber layer having a thickness of 1 to 10 [mm] on a metal core such as aluminum, stainless steel, or iron, and the surface layer is a fluororesin for preventing toner contamination. Has a layer.

  Even in the configuration in which the heating film has the support roller as described above, it is possible to obtain the same effect as that of the embodiment.

  In the present embodiment, three support rollers are used as the film holding member. However, the present invention is not limited to this, and the same pressure distribution can be provided using two or four or more support rollers. It is possible to obtain an effect.

  Next, the structure of the other heating film 3 is demonstrated using FIG.

  The heating film 43 has an excellent heat resistance and slidability, a heat resistant base layer 43a having a thickness of 20 to 200 [μm], an elastic layer 43b having a thickness of 50 to 1000 [μm], and an infrared ray having a thickness of 5 to 50 [μm]. It is a seamless film provided with an absorbent layer 43c.

  As the film base layer 43a, a heat resistant resin such as polyimide, polyamideimide, or aramid can be used. In particular, the polyimide film has excellent mechanical strength and heat resistance, and transmits infrared light with a wavelength of 3 [μm] or less emitted from a halogen lamp at 80 [%] or more, so that the effect of surface heating in the present invention is more effective. Can be obtained.

  As the elastic layer 43b, various silicone rubbers such as LTV, HTV, and RTV, or rubbers or sponges having high heat resistance such as fluorine rubber are formed, and those that are soft and have a small permanent strain are used. Here, the hardness of the elastic layer is preferably 50 ° or less in terms of JIS-A hardness in order to obtain flexibility corresponding to the unevenness of the toner surface. Further, the elastic layer made of silicone rubber can also transmit infrared light having a wavelength of 3 [μm] or less at 80 [%] or more, thereby realizing efficient surface heating.

  The silicone rubber layer 43b provided on the polyimide base layer 43a of the heating film 43 is formed with a thickness of 50 to 1000 [μm] so that a uniform pressure can be applied to a thick toner layer in a color image. Is set. In color image formation using a hard roller or film that does not have an elastic layer as a heating member, if a multicolor toner layer and a single color toner layer are present in the vicinity of a fixed image, the single color toner layer is sufficiently pressurized. In the heating film provided with the elastic layer in this embodiment, both the multicolor toner layer and the single color toner layer are used to cope with the unevenness of the toner layer. Therefore, even in a color fixed image, uniform fixing property and high transparency in OHP were obtained.

  Further, fine particles may be appropriately dispersed in the elastic layer 43b in order to adjust mechanical strength, electrical resistance and thermal conductivity, and by dispersing fine particles such as silica, tin oxide, titanium oxide and zinc oxide, the rubber layer Compression set can be reduced. By suppressing the scattering of the radiation light, the amount of radiation can be suppressed, and the particle diameter of the filler fine particles in the elastic layer in the present invention is preferably less than or equal to the wavelength of transmitted infrared rays, more preferably 0. It is preferable that it is 3 [μm] or less.

  Further, in order to transfer heat in the elastic layer mainly by radiation rather than heat conduction, an infrared absorption layer 43c is provided on the surface of the heating member to generate heat on the surface of the heating film.

As the absorption layer 43c, carbon-based particles such as carbon black and graphite, which are infrared absorbing materials, or various metal oxide particles such as iron oxide are dispersed in a release layer made of a conventional fluororesin such as PFA or PTFE. Therefore, infrared light can be absorbed well. Moreover, the electrical resistance of the surface can be lowered by using a conductor such as carbon black as an infrared absorbing material, and electrostatic offset can be prevented by controlling it to about 10 ⁶ to 10 ¹⁴ [Ω / cm]. It is also possible to do.

  Here, the amount of radiation (solid line) and the temperature distribution (broken line) in the heating film will be described with reference to FIG. The vertical axis in FIG. 4B represents the position y in the thickness direction in the film cross section, and the horizontal axis represents the amount of radiated light (solid line) and the temperature T (broken line). Radiation light irradiated by the halogen lamp inside the heating film is not attenuated so much in the film base layer 43a and the elastic layer 43b, but 70% or more of it is absorbed in the release layer 43c on the surface of the heating film. Therefore, the film surface side is heated at high speed (A).

  On the other hand, when a similar film is heated by heat conduction in a conventional fixing nip, in order to obtain a temperature equivalent to A on the film surface, the inner surface of the film is considerably higher than the surface temperature as shown in B (20 to 50 [° C. ]) It was necessary to set.

  Therefore, by adopting this configuration, it becomes possible to lower the film inner surface temperature, and the amount of heat required to heat the surface of the heating member to the fixing temperature is lower than that of the conventional fixing device using heat conduction, and energy saving is achieved. In addition, the life of the heating member, particularly the elastic layer, can be extended.

  Furthermore, the elastic layer 43b in the heating film has a low thermal conductivity and rather provides a heat insulating effect. Therefore, the temperature of the support roller 42 constituting the nip does not need to be positively increased from the inner surface of the heating film, and the toner and the transfer material are sufficiently heated by the amount of heat stored on the film surface, so that good fixing is possible even during continuous printing. Sex is realized.

  Although the heating film has a three-layer structure including a base layer, an elastic layer, and a release layer, for example, a conductive primer layer or an adhesive layer may be inserted in the middle to obtain the effect of the present embodiment even when the structure is four or more layers. Can do.

  By using the heated film with this configuration, a highly insulating film base layer and elastic layer are used, so that high insulation can be ensured in the fixing nip at normal times when there is no film breakage, and good detection of film breakage is also possible.

  Further, in the present invention, since it is sufficient that good insulation is obtained between the voltage applying means and the pressure member when the heating film is present, for example, even if a conductive layer as described above is provided on the elastic layer, the detection accuracy is extremely lowered. It never happened.

  Here, the film breakage detection in the present embodiment will be described. In this embodiment, the support roller 42a is used as a voltage applying member, and -300V is supplied as a detection bias from the DC power supply 13 to the rotating support roller 42a via a graphite contact (not shown).

On the other hand, the pressure roller 5 is made conductive as in the above-described embodiment. In this embodiment, a roller having a resistance of 10 ⁷ Ω is used as an example.

  The pressure roller 5 is grounded via a current detection circuit 44. When a part or the whole of the insulating or high resistance film is broken, a detection bias flows as a current. .

  In principle, the current detection circuit 44 sends an Enable signal to the heater control circuit so that the temperature of the film can be controlled in the situation where the film does not break as in the case of the first embodiment. When a detection current flows to 44, the Enable signal is cut off and all heaters are turned off.

  Here, it is possible to place the current detection circuit 44 on the hot side of the DC power supply as in the first embodiment, but it is possible to reduce the withstand voltage of the current detection circuit and reduce the cost by placing it on the ground side. Become. However, in the configuration of this embodiment, in addition to the detection bias, there is a risk of being affected by the charged charge of the paper that has entered the fixing nip as a material to be heated. Therefore, the detection of film breakage when there is no paper in the fixing nip such as between papers. By performing this, the detection accuracy can be improved.

  In this embodiment, since the conductive support roller is used as the voltage applying member, the friction between the voltage applying member and the heating film is reduced, and the heating film has a longer life because the heating film reduces abrasion. Insulating abrasion powder generated by abrasion is prevented from accumulating between the voltage applying member and the heating film to increase the resistance, so that a detection current at the time of film breakage can be secured stably over a long period of time.

  Furthermore, by using a conductive support roller as the voltage application member, it is no longer necessary to apply a lubricant such as grease to the inner surface of the heating film as in the prior art, so it is not affected by the electrical resistance of the grease and stable over a long period of time. The detection current can be secured.

(Third embodiment)
Hereinafter, a fixing device as a heating device in this embodiment will be described. In this embodiment, it is possible to provide a voltage applying member in addition to the fixing nip by using a conductive brush as a voltage applying means, and even when an insulating heat source such as a ceramic heater is disposed in the nip portion, film breakage or It is a thing that made it possible to detect cracks.

  FIG. 5 is a schematic cross-sectional view seen from the side of the fixing device.

  In the present embodiment, a ceramic heater 14 is used as a heat source and is heated in direct contact with the heating film 3 similar to that in the first embodiment. As the ceramic heater 14, for example, an insulating and high thermal conductive substrate such as alumina or aluminum nitride provided with an energization heating resistance layer such as silver palladium and a glass protective layer can be used.

  A thermistor 15 is brought into contact with the back surface of the ceramic heater 14 to detect the temperature of the ceramic heater. The detection signal of the thermistor 15 is connected to a fixing power supply circuit (not shown) as in the previous embodiment, and the temperature of the ceramic heater is controlled to 160 to 200 ° C.

  The film guide 17 is made of a heat-resistant resin such as a liquid crystal polymer, and holds the ceramic heater 14 and is disposed along the inner surface of the heating film 3 so as to rotatably support the heating film.

  The support stay 16 is made of, for example, a metal member such as stainless steel or a steel plate, and supports the film guide 14 with pressure uniformly in the longitudinal direction.

  The conductive brush 18 which is a voltage applying member in the present embodiment is fixed to the support stay 16 and arranged so that the tip of the brush abuts along the heating film 3.

  Here, as the conductive brush, for example, a stainless steel brush, amorphous fiber, carbon fiber or the like having both conductivity and heat resistance can be applied.

As shown in FIG. 6, the conductive brush 18 is formed by implanting conductive fiber portions 18b and 18c on the conductive base material 18a. The electric resistance of the conductive fiber is preferably 10 ⁸ Ω or less in order to ensure an accurate detection current.

  Further, as shown in FIG. 6A, the conductive brush 18 may be subjected to flocking over the entire longitudinal direction to detect film breakage over the entire region, and also shown in FIG. 6B for cost reduction. In this way, detection may be performed by flocking only a portion where film breakage easily occurs, for example, both ends.

  A detection bias is supplied to the conductive brush 18 from the DC power source 40 as in the above embodiment. If the heating film breaks, the conductive brush on the broken surface comes into contact with the pressure roller 5 to detect the detection current. Will occur.

  The detection current is detected by the current detection circuit 19 and fed back to the fixing power supply circuit in the same manner as in the above embodiment, and when a current exceeding a certain level flows due to film breakage, the power supply to the ceramic heater 14 is stopped and image defects are detected. Prevent occurrence.

  Here, the position of the current detection circuit 19 is preferably connected to the ground side of the DC power supply, and is less affected by the charged charge of the paper or film compared to the connection to 19B in the figure, and the film breakage is accurately performed. It became possible to detect.

Further, as the heating film 3 in this embodiment, it is sufficient that the insulating property in the radial direction is high (> 10 ¹⁰ Ω) as in the first embodiment. For example, if the heat resistant resin having high resistance is used as a base, two layers having a release layer are provided. A three-layer film having a film or an elastic layer and a release layer can be obtained. Also, in the case of a heating film based on a conductive metal, it can be used in the present invention by providing an elastic layer having good heat resistance and high resistance such as silicone rubber, fluorine rubber, fluorosilicone rubber or the like. If a mechanism for applying a release material such as silicone oil to the surface of the heating film is provided, it is not necessary to provide a release layer on the heating film, and the effects of the present invention can be obtained.

  In this embodiment, a conductive brush as a voltage applying member is provided in a fixing device using a ceramic heater to detect film breakage. However, the effect of the present invention is not limited to this, and a halogen heater and magnetic induction heating are used as a heat source. In addition, the present invention can be applied to a configuration in which an insulating material such as a glass plate is disposed in the fixing nip portion, and film breakage can be detected.

DESCRIPTION OF SYMBOLS 1 Halogen lamp 2 Support stay 3 Heating film 4 Guide member 5 Pressure roller 6 Thermistor 7 Solid state relay 9 Current detection circuit 11 Relay circuit 12 Fixing power supply 13 DC power supply 43 Heating film

Claims (10)

A heating member that can rotate at a constant speed with the material to be heated and includes a heat source inside, and a pressurizing member that pressurizes the heating member from the outside, and press-contacting the heating member and the pressurizing member In a heating apparatus that forms a nip and heats the material to be heated at the nip portion,
A heating apparatus, comprising: a voltage applying unit that applies a voltage to at least a part between the heating member and the pressure member; and a current detecting unit that detects a current from the voltage applying unit.   The heating apparatus according to claim 1, wherein the heating member is a flexible film or belt.   3. The heating apparatus according to claim 1, wherein when the current detection unit detects a predetermined current or more, power supply to the heat generation source is stopped.   The heating apparatus according to claim 1, wherein the voltage applying means is formed of a thin metal plate and press-contacts with a pressure member via the rotatable heating member to form a nip.   The heating apparatus according to claim 4, wherein the voltage applying member is formed of a conductive brush.   6. The heating apparatus according to claim 1, wherein the voltage applying means is a conductive roller that is pressed against the pressure member via the rotatable heating member and forms at least a part of a nip. . The heating device according to any one of claims 1 to 6, wherein an electric resistance of the pressure member is 10 ⁴ to 10 ⁸ Ω.   8. A heating apparatus according to claim 1, wherein the voltage applied to the voltage applying member is a voltage having the same polarity as the electrode resistance of the toner image as the member to be heated. The heating apparatus according to claim 1, wherein the heating member has a resistance layer having at least an electric resistance of 10 ¹⁰ Ω or more.   The heating device according to claim 9, wherein an elastic body containing at least silicone rubber is used as the resistance layer.

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