JP2014041232A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device that employs so-called a transverse direction conduction method, suppresses a reduction in temperature of an end of a heating member while exhibiting a suppression effect of temperature rise in a non-paper feed part, and can suppress an increase in power supply to the end of the heating member.SOLUTION: An image heating member (20) has a heating member (60) that heats a toner image on a recording material, and a pressure member (70) that contacts the heating member to form a nip part, and hold and conveys the recording material carrying the toner image with the nip part to heat the toner image. The heating member (60) has a resistance heating element (620); and a pair of electrodes (621a, 621b) that is connected to the resistance heating element at both ends while extending along both ends in a width direction perpendicular to a recording material conveyance direction of the resistance heating element so as to be electrically conducted with the resistance heating element. The pressure member (70) is brought into pressure contact with the heating member (60) while a length in the width direction is equal to or less than a length in a width direction of the resistance heating element (620), and the entire area in the width direction is directed opposite to the resistance heating element.

Description

  The present invention relates to an image heating apparatus such as a fixing apparatus that heats an image formed on a recording material.

  Conventionally, a heat roller system is often used as an image heating apparatus such as an electrophotographic fixing apparatus which is mounted on an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a combination of these, and can form an image on a recording material. It was. In recent years, film heating type image heating apparatuses have been put into practical use from the viewpoint of quick start and energy saving.

  In the film heating type fixing device, the heat capacity of the film is smaller than that of the heat roller type fixing device. For this reason, there is a problem of the temperature rise of the non-sheet passing portion during continuous feeding of a recording material (hereinafter referred to as small size paper) having a width smaller than the recording material having the maximum paper passing size width (hereinafter referred to as maximum size paper). There is.

  The following countermeasure methods are known as countermeasures against such a temperature increase in the non-sheet passing portion of the fixing device. First, a plurality of resistance heating elements for heating the cylindrical film are provided, the distribution of heat generation in the longitudinal direction is made different, and the energization ratio to the plurality of resistance heating elements can be switched according to the width in the longitudinal direction of the recording material used. A technique provided with a control means has been proposed (see Patent Document 1).

  In addition, a technique has been proposed in which a cooling air blowing member that cools a predetermined region of the heating member is arranged to cool the non-sheet passing portion temperature rising portion (see Patent Document 2).

  Further, a technique in which power supply portions of the resistance heating element are provided along the longitudinal direction of the heating element on both longitudinal sides of the resistance heating element whose longitudinal direction is a direction orthogonal to the moving direction of the rotation axis of the film (hereinafter referred to as a short side). (Referred to as Patent Document 3).

Japanese Patent Laid-Open No. 10-177319 JP 2007-079033 A Japanese Patent Laid-Open No. 5-19652

  However, the above-described technique has the following problems. That is, with the technique described in Patent Document 1, it is difficult to cope with various recording material sizes. Moreover, in the technique of patent document 2, since a heating member is cooled with cooling air, an energy loss will generate | occur | produce and it is not suitable for energy saving. Furthermore, in patent document 2, since it is necessary to provide the ventilation member which cools pressure members, such as a pressurization rotary body, separately, the enlargement of an apparatus will be caused.

  On the other hand, in the technique described in Patent Document 3, the resistance value changes depending on the temperature distribution of the heating element, and the heat generation distribution is switched so that the temperature distribution in the longitudinal direction does not occur.

  By the way, the pressurization member used for the heating apparatus of the conventional film heating system is comprised so that it may become longer than the heat_generation | fever width. This is because if the heating element side heating element has a pressurized part and a non-pressurized part that are not pressurized, the temperature difference between the pressurized part and the non-pressurized part increases. This is to prevent a problem that the non-pressurized portion is excessively heated when controlling the temperature of the pressurized portion on the heating member side.

  In other words, in the pressurizing part pressurized by the pressurizing member, the heat generation energy from the heating element can be moved to the pressurizing member side, but in the non-pressurized part that is not pressurized, heat is transferred. It is overheated because it is hardly done.

  Here, in the conventional film heating method, the heat capacity of the heating member is small, particularly susceptible to heat radiation at the end, or the heat transfer to the pressure member side is large, The temperature of the heating member is lowered at the outer end of the opposing position. In order to prevent this, it is common to adopt a method of increasing the amount of heat generated at the end or controlling the energization ratio to a plurality of heating elements.

However, in the so-called short direction energization type film heating method such as the technique described in Patent Document 3, when a pressure member longer than the heat generation width is used as described above, the following (1), (2 ) May cause new problems.
(1). When using a heater that has almost the same TCR characteristics in the longitudinal direction of the resistance heating element (characteristic showing the temperature change and resistance value change of the heating element) The amount of power supplied to the section increases.
(2). In order to solve the problem (1), if a heater having a large calorific value at the end portion is used, the effect of suppressing the temperature rise in the non-sheet passing portion of the so-called short direction energization method becomes small.

  In other words, heat escapes from the end of the heater with a large amount of heat generation via the pressurizing member and its support, and the supply of electric power further increases to compensate for this.

  The present invention is a so-called short-direction energization type image heating apparatus that suppresses a decrease in the end temperature of the heating member while exhibiting the effect of suppressing the temperature rise in the non-sheet passing portion, and is applied to the end of the heating member. An object of the present invention is to provide an image heating apparatus capable of suppressing an increase in power supply.

  The present invention includes a heating member that heats a toner image on a recording material, and a pressure member that contacts the heating member to form a nip portion, and the recording material that carries the toner image is formed in the nip portion. In the image heating apparatus that heats a toner image while nipping and conveying, the heating member includes a resistance heating element and both side edges in the width direction orthogonal to the recording material conveyance direction of the resistance heating element to energize the resistance heating element A pair of electrodes connected to the side edges in a state of extending along the portion, and the pressure member has a width in the width direction of the resistance heating element. In the following, it is characterized in that it is pressed against the heating member in a state where the entire region in the width direction is opposed to the resistance heating element.

  According to the present invention, in a so-called short direction energization type image heating apparatus, while suppressing the temperature rise of the non-sheet-passing portion, the decrease in the end temperature of the heating member is suppressed, and the end portion of the heating member It is possible to suppress an increase in power supply to the power source.

1 is a schematic cross-sectional view schematically showing an overall configuration of an image forming apparatus according to the present invention. FIG. 2 is an explanatory diagram schematically showing a fixing device as an image heating device according to the present invention. FIG. 2 is an enlarged cross-sectional view of a fixing nip portion and its vicinity of the fixing device according to the first embodiment of the present invention. FIG. 3 is a plan view (top view) in the longitudinal direction of the nip portion of the fixing device according to the first embodiment. The figure which shows typically the relationship of the heater longitudinal direction width | variety in 1st Embodiment, a pressure roller longitudinal direction width | variety, and longitudinal input electric power. The longitudinal direction detail drawing of the heat generating body width | variety in 2nd Embodiment which concerns on this invention, and a pressure roller width | variety. The schematic diagram of the heater resistance in 2nd Embodiment. FIG. 5 is a detailed view of the nip portion in the longitudinal direction in Comparative Example 1. The figure which shows typically the relationship between the longitudinal direction width | variety of the heater in the comparative example 2, the longitudinal direction width | variety of a pressure roller, and longitudinal input electric power.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. The following embodiments are examples of the best embodiment of the present invention, but the present invention is not limited to these embodiments. In the present embodiment, the image heating device is described as a configuration applied to a fixing device that fixes an unfixed toner image on a recording material. However, the present invention uses a recording material carrying a fixed image or a semi-fixed image. It can also be implemented as a heat treatment apparatus that adjusts the surface properties of an image by heating.

<First Embodiment>
"Image forming part"
FIG. 1 is a schematic longitudinal sectional view showing a schematic configuration of an electrophotographic full-color printer (hereinafter referred to as a printer) which is an image forming apparatus equipped with a fixing device as an image heating device according to the present invention. First, an outline of the image forming unit will be described.

  The printer 26 has a printer main body 26a as an apparatus main body. The printer main body 26a has a control unit 110 such as a CPU. The printer 26 performs an image forming operation according to input image information from an external host device (not shown) that is communicably connected to the control unit 110, and forms and outputs a full color image on a recording material. The external host device means a computer, an image reader, or the like.

  The control unit 110 comprehensively controls each part of the apparatus, exchanges signals with the external host device, and exchanges signals with various image forming devices, and controls image forming sequence control.

  The printer main body 26a includes image forming units 1Y to 1Bk provided on the upper side of the main body, a paper feeding unit 28 provided on the lower side of the main body, a conveying unit 29, a paper discharge tray 23 provided on the upper side of the main body, and a main body side. And a manual feed tray (multipurpose tray) 17 provided in the section.

  An endless and flexible intermediate transfer belt 8 is disposed above the image forming portions 1Y, 1M, 1C, and 1Bk. The intermediate transfer belt 8 is stretched between the secondary transfer counter roller 9 and the tension roller 10 and is rotated at a predetermined speed in the direction of arrow E (counterclockwise direction) by driving the secondary transfer counter roller 9. Driven.

  A secondary transfer roller 11 is disposed opposite to the secondary transfer counter roller 9. A secondary transfer portion 25 is formed by a contact portion (nip portion) between the intermediate transfer belt 8 wound around the secondary transfer counter roller 9 and the secondary transfer roller 11 in pressure contact therewith.

  The image forming units 1Y, 1M, 1C, and 1Bk are arranged in a line at a predetermined interval along the belt moving direction on the lower side of the intermediate transfer belt 8. Each of the image forming units 1Y to 1Bk is composed of a laser exposure type electrophotographic process mechanism. Each of these image forming units 1Y to 1Bk has a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 2 as an image carrier that is rotationally driven at a predetermined speed in the clockwise direction of an arrow. .

  Around each photosensitive drum 2, a primary charger 3, a developing device 4, a primary transfer roller 5 as a transfer means, and a drum cleaner device 6 are arranged.

  Each primary transfer roller 5 is disposed inside the intermediate transfer belt 8 and is in pressure contact with the opposing photosensitive drum 2 via a downward belt portion of the intermediate transfer belt 8. A primary transfer portion 27 is configured by a contact portion between each photosensitive drum 2 and the intermediate transfer belt 8.

  Below the image forming units 1Y, 1M, 1C, and 1Bk, a laser exposure device 7 corresponding to the photosensitive drum 2 of each image forming unit is disposed. The laser exposure device 7 is composed of laser light emitting means for emitting light corresponding to time-series electric digital pixel signals of given image information, a polygon mirror, a reflection mirror, and the like. Reference numeral 12 denotes a belt cleaning device.

  The paper feeding unit 28 is arranged corresponding to each of the upper and lower multi-stage paper feeding cassettes 13A, 13B, and 13C and the paper feeding cassettes 13A, 13B, and 13C, each of which accommodates and accommodates recording materials P of various large and small width sizes. A paper feed roller 14.

  The control unit 110 described above causes each of the image forming units 1Y, 1M, 1C, and 1Bk to perform an image forming operation based on the color separation image signal input from the external host device. Thus, in the image forming units 1Y, 1M, 1C, and 1Bk, yellow, magenta, cyan, and black color toner images are formed at predetermined control timings on the surfaces of the rotating photosensitive drums 2, respectively. The electrophotographic image forming principle and process for forming a toner image on the photosensitive drum 2 are well-known and will not be described here.

  The toner images formed on the surface of the photoconductive drum 2 of each image forming unit are respectively rotated in the rotation direction and forward direction of the photoconductive drum 2 and the rotation speed of the photoconductive drum 2 in the primary transfer unit. The images are sequentially superimposed and transferred onto the outer surface of the intermediate transfer belt 8 that is rotationally driven at a corresponding speed. As a result, an unfixed full-color toner image is synthesized and formed on the surface of the intermediate transfer belt 8 by superimposing the four toner images.

  On the other hand, at a predetermined paper feed timing, the paper feed roller 14 corresponding to the selected paper feed cassette among the paper feed cassettes 13A, 13B, 13C is driven to rotate. As a result, the recording material P loaded and stored in the paper feed cassette at that level is separated and fed one by one, and conveyed to the registration roller 16 through the vertical conveyance path 15 of the conveyance unit 29.

  When manual sheet feeding is selected, the sheet feeding roller 18 disposed corresponding to the manual tray 17 is driven. As a result, the recording materials stacked and set on the manual feed tray 17 are separated and fed one by one and conveyed to the registration rollers 16 through the vertical conveyance path 15.

  The registration roller 16 adjusts the recording material so that the leading end of the recording material P reaches the secondary transfer unit 25 in synchronization with the timing at which the leading end of the full-color toner image on the rotating intermediate transfer belt 8 reaches the secondary transfer unit. P is transported in timing. As a result, the full-color toner image t (see FIG. 2) on the intermediate transfer belt 8 is secondarily transferred sequentially onto the surface of the recording material P at the secondary transfer unit 25.

  The recording material P that has exited the secondary transfer section 25 is separated from the surface of the intermediate transfer belt 8, guided by the vertical guide 19 of the transport section 29, and introduced into the fixing nip section (nip section) N of the fixing device 20. (See FIG. 2). The fixing device 20 melts and mixes the full-color toner image t and fixes it as a fixed image on the surface of the recording material P. Then, the recording material P exiting the fixing device 20 passes through the transport path 21 as a full-color image formed product, and is discharged onto the paper discharge tray 23 by the paper discharge roller 22.

  The surface of the intermediate transfer belt 8 after the recording material P is separated by the secondary transfer unit 25 is used to remove residual adhering matters such as secondary transfer residual toner by a belt cleaning device 12 disposed opposite to the tension roller 10. Received, cleaned, and repeatedly used for image formation.

  In the mono black print mode, only the image forming unit Bk that forms a black toner image is controlled by the control unit 110 to perform an image forming operation. When the duplex printing mode is selected, the recording material printed on the first side is sent out onto the paper discharge tray 23 by the paper discharge roller 22 and immediately before the rear end portion passes through the paper discharge roller 22. Thus, the rotation of the paper discharge roller 22 is converted to reverse rotation.

  As a result, the recording material P is switched back and introduced into the re-conveying path 24 of the conveying unit 29. Then, the paper is turned upside down and conveyed to the registration roller 16 again. Thereafter, similarly to the first side printing, the sheet is conveyed to the secondary transfer unit 25 and the fixing device 20 and is discharged onto the paper discharge tray 23 as a double-sided printed image formed product.

"Fixing device"
Next, the fixing device 20 as the image heating device of the present invention will be described in detail with reference to FIG. FIG. 2 is a schematic diagram illustrating a schematic configuration of the fixing device 20.

  The fixing device 20 includes a heater unit 60 that heats the toner image on the recording material, and a pressure roller 70 that contacts the heater unit 60 to form a fixing nip portion N. The fixing device 20 transfers the recording material P to the fixing nip portion N. Constitutes an image heating apparatus that heats the toner image t while being nipped and conveyed.

  That is, as shown in FIG. 2, the fixing device 20 includes a heater unit 60 as a heating member and a pressure roller 70 as a pressure member supported by a fixing device frame (not shown) so as to be in pressure contact with each other. Have. In addition, the heater unit 60 includes a fixing heater unit 600, a heater holder (film guide, heater stay) 660 having a semicircular cross section as a support for supporting the fixing heater unit 600, an inverted U-shaped supply sheet metal 670, and a fixing unit. Belt 650. The fixing belt 650 is made of an endless cylindrical heat resistant film. The replenishment sheet metal 670 prevents the heater unit 60 from being deformed when pressed by the pressure roller 70.

  The fixing heater unit 600 includes an insulating substrate 610 having insulation, heat resistance, and low heat capacity with a width direction perpendicular to the conveyance direction of the recording material P as a longitudinal direction, a heater 620 as a resistance heating element, and temperature detection means. Thermistor 630. The fixing heater unit 600 is fixedly supported by the heater holder 660.

  The insulating substrate 610 has a polyimide layer having a thickness of about 10 μm as a sliding layer on the contact surface side with the fixing belt 650. The polyimide layer reduces the frictional resistance between the fixing belt 650 and the fixing heater unit 600, thereby reducing the driving torque and preventing the inner surface of the fixing belt 650 from being worn.

  In the fixing belt 650, a silicone rubber layer (elastic layer) having a thickness of, for example, about 300 μm is formed by a ring coating method on a base material formed of stainless steel in a cylindrical shape having a thickness of, for example, 30 μm. Furthermore, a PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) resin tube having a thickness of, for example, 20 μm is coated on the silicone rubber layer as the outermost surface layer.

  The pressure roller 70 disposed below the heater unit 60 includes a cylindrical cored bar 71, an elastic layer 72 made of silicone rubber formed on the cored bar 71, and an elastic layer 72. And a surface layer 73 made of a fluorine-based resin.

  In other words, the pressure roller 70 includes, for example, a stainless steel core 71, an elastic layer 72 made of silicone rubber having a thickness of about 3 mm, and a PFA resin surface layer (tube) having a thickness of about 40 μm on the elastic layer 72, for example. ) 73 in order. Both ends of the metal core 71 of the pressure roller 70 are rotatably supported by bearings between a back plate and a front plate of a fixing device frame (not shown).

  The pressure roller 70 is pressed against the heater unit 60 by a pressure mechanism (not shown) with a total pressure of 90 to 320 N, for example, and receives the driving force of a drive system (not shown) to receive the recording material P. 2 is rotated in the counterclockwise direction in FIG. As a result, the fixing belt 650 rotates along with the rotation of the pressure roller 70 and rotates around the heater holder 660 while closely sliding on the surface of the heating element of the fixing heater unit 600.

  The fixing heater unit 600 is disposed so as to extend in parallel with the pressure roller 70 with the fixing heater unit side facing downward. The fixing heater unit 600 is fixed to the lower surface of the heater holder 660 along the longitudinal direction of the heater holder 660, and the heating surface is configured to be slidable with the fixing belt 650. The fixing belt 650 is loosely fitted on the heater holder 660.

  The heater holder 660 is formed of a liquid crystal polymer resin having high heat resistance, and plays a role of holding the fixing heater portion 600 and guiding the fixing belt 650. In this example, Zenite 7755 (trade name) manufactured by DuPont was used as the liquid crystal polymer.

  The both ends of the heater holder 660 are moved in the axial direction of the pressure roller 70 with a force of 156.8 N (16 kgf) and a total pressure of 313.6 N (32 kgf), for example, by a pressure mechanism (not shown) different from the above. Is being energized. As a result, the lower surface (heating surface) of the fixing heater unit 600 is pressed against the elastic layer of the pressure roller 70 via the fixing belt 650 with a predetermined pressing force, and a fixing nip having a predetermined width necessary for fixing. Part N is formed. The length relationship between the pressure roller 70 and the fixing heater unit 600 in the longitudinal direction will be described in detail later.

  A plurality of thermistors 630 as temperature detecting means are installed on the back surface (the surface opposite to the heating surface) of the fixing heater unit 600 that is a heat source, and detects the temperature of the entire fixing heater unit 600 including the heater 620. It has a function to do. The plurality of thermistors 630 are each connected to a control unit (CPU) 110 via an A / D converter (not shown).

  The control unit 110 samples the output from each thermistor 630 at a predetermined cycle, and reflects the temperature information thus obtained in the temperature control. That is, the control unit 110 determines the temperature control content of the fixing heater unit 600 based on the output of the thermistor 630 and controls the energization of the fixing heater unit 600 by the heater drive circuit 51 that is a power supply unit. Reference numeral 30 denotes an AC power source.

  The pressure roller 70 is driven to rotate at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow. The fixing belt 650 that is in pressure contact with the fixing belt 650 rotates with a predetermined speed (driven rotation) as the pressure roller 70 rotates. At this time, the inner surface of the fixing belt 650 comes into close contact with the lower surface of the fixing heater portion 600 and slides while the outer periphery of the heater holder 660 is driven to rotate in the clockwise direction indicated by the arrow. By applying grease to the inner surface of the fixing belt 650, the slidability between the heater holder 660 and the inner surface of the fixing belt 650 is ensured.

  When the fixing belt 650 is driven to rotate in accordance with the rotation of the pressure roller 70, the fixing heater unit 600 is energized under the control of the control unit 110. Then, in a state where the temperature of the fixing heater unit 600 is adjusted to the set temperature, the recording material P carrying the unfixed toner image t is guided along the entrance guide 38 and introduced into the fixing nip portion N. .

  In the fixing nip portion N, the recording material P moves with the fixing belt 650 while the toner image carrying surface side is in close contact with the outer surface of the fixing belt 650. In the process of nipping and conveying the recording material P at the fixing nip N, heat from the fixing heater unit 600 is applied to the recording material P via the fixing belt 650, and the unfixed toner image t is melted and fixed on the recording material P. Is done. The recording material P that has passed through the fixing nip N is separated from the fixing belt 650 and discharged.

  Next, the configuration of the fixing nip portion N of the fixing device 20 and the vicinity thereof will be described with reference to FIGS. 3 is an enlarged cross-sectional view of the fixing nip portion N and the vicinity thereof in the fixing device 20, and FIG. 4 is a plan view (top view) showing the fixing heater portion 600 and the like in the fixing device 20. In FIG. 4, the thermistor 630 is not shown.

The insulating substrate 610 shown in FIGS. 3 and 4 has a thickness of about 0.5 mm to 1.0 mm, has heat resistance and electrical insulation, and high thermal conductivity, such as alumina (Al ₂ O ₃ ), nitriding It consists of a flat strip-shaped substrate made of a highly rigid ceramic such as aluminum (AlN). The insulating substrate 610 has a long rectangular shape extending along the longitudinal direction of the heater unit 60 (left and right direction in FIG. 4). A fixing nip portion N is formed by the fixing belt 650 supported from the inner surface by the insulating substrate 610 and the pressure roller 70 in pressure contact therewith.

  On the insulating substrate 610, a long rectangular heater 620 extending along the longitudinal direction (the left-right direction in FIG. 4) is disposed. On both sides in the longitudinal direction of the heater 620, wiring electrodes 621a and 621b as electrodes of the present invention, which are formed in parallel with the heater 620 and made of a material having a silver content of 90 wt% or more, are provided. ing.

  At the end portion of the wiring electrode (electrode) 621a on the insulating substrate 610, a power feeding portion 622a made of a silver-based good conductor film is connected to the wiring electrode 621a. In addition, on the end of the wiring electrode 621b on the insulating substrate 610 opposite to the power feeding unit 622a, a power feeding unit 622b made of the same material as the power feeding unit 622a is connected to the wiring electrode 621b. In addition, the heater drive circuit 51 and the AC power supply 30 are connected between the power feeding unit 622a and the power feeding unit 622b.

  The same material as the wiring electrodes (electrodes) 621a and 621b may be used for the power feeding units 622a and 622b. The power feeding units 622a and 622b and the wiring electrodes 621a and 621b can be integrally formed and fixed to the insulating substrate 610 by applying a conductive paste on the insulating substrate 610 and baking the conductive paste. Note that the power supply units 622a and 622b and the wiring electrodes 621a and 621b in the present embodiment can have a thickness of, for example, 10 μm and a sheet resistance of, for example, 10 mΩ / □.

The heater 620 is manufactured as follows. That is, a resistor paste such as ruthenium oxide (RuO ₂ ) or tantalum nitride (Ta ₂ N) having a relatively high resistance value is placed between the wiring electrodes 621a and 621b on the insulating insulating substrate 610 in the longitudinal direction of the plate. Along with screen printing. Thereafter, the resistor paste is baked at a high temperature to obtain a heater 620 which is a wide resistance heating element having a predetermined resistance value and a thickness of about 10 μm. The sheet resistance of the heater 620 can be set to, for example, 1000Ω / □ according to the relationship between the heater 620 width and the pressure roller 70 width.

  Next, the relationship between the longitudinal width of the heater 620 as a resistance heating element and the longitudinal width of the pressure roller 70, which is one of the features of the present invention, will be described in contrast to Comparative Examples 1 and 2. FIG. 5 is a diagram schematically illustrating the relationship between the longitudinal width of the heater 620, the longitudinal width of the pressure roller 70, and the longitudinal input power in the present embodiment. FIG. 8 is a detailed view of the longitudinal direction of the nip portion in Comparative Example 1, and FIG. 9 schematically shows the relationship between the longitudinal width of the heater 1020, the longitudinal width of the pressure roller 70, and the longitudinal input power in Comparative Example 2. FIG.

  First, a case where the fixing operation is performed using a so-called longitudinal energization type heater in Comparative Example 1 shown in FIG. 8 will be described.

  That is, as shown in FIG. 8, in the heater unit 90 of Comparative Example 1, a long heater 920 is formed on the insulating substrate 910 along the longitudinal direction thereof. Power supply units 922a and 922b are connected to both ends of the heater 920, respectively. The heater drive circuit 51 and the AC power supply 30 are connected between the power supply unit 922a and the power supply unit 922b.

As in the case of the so-called short direction energization method, the following can be used as the insulating substrate 910 in such a so-called longitudinal direction energization method. That is, a high-rigidity ceramic such as alumina (Al ₂ O ₃ ) or aluminum nitride (AlN) having heat resistance and electrical insulation with a thickness of about 0.5 to 1.0 mm and high thermal conductivity, for example. It is possible to use a flat strip-shaped substrate made of the like.

  The power feeding portions 922a and 922b are power feeding electrodes each made of a silver-based good conductive film. The conductive paste is applied on the insulating substrate 910 and then fired to be integrally formed and fixed on the insulating substrate 910. To do. Note that the power feeding portions 922a and 922b in Comparative Example 1 can have a thickness of, for example, 10 μm and a sheet resistance of, for example, 10 mΩ / □.

  The heater 920 is formed in parallel along the longitudinal direction on the insulating substrate 910 between the power feeding units 922a and 922b. The heater 920 is a resistance heating element having a film thickness of about 20 μm having a predetermined resistance value after screen-printing a paste obtained by mixing glass powder or the like with an electric resistance material such as Ag / Pd (silver palladium). It is. In addition, the heater 920 in the comparative example 1 can have a thickness of, for example, 20 μm and a sheet resistance of, for example, 1000Ω / □.

  In the fixing device of Comparative Example 1 having the heater unit 90 configured as described above, the maximum width in the direction perpendicular to the conveyance direction of the recording material that is introduced into the fixing nip portion, nipped, conveyed, and fixed, and image conditions are the maximum. The paper passing size width was 320 mm, and the image guarantee area was 316 mm. At this time, the width of the pressure roller necessary for stabilizing the conveyance of the recording material needs to be about 325 mm with respect to the maximum sheet passing size width of 320 mm in consideration of the fluctuation width of the conveyance.

  However, the heat generation width of the heater 920 required to satisfy the image guarantee area 316 mm is about 340 mm in consideration of the influence of heat dissipation.

  In such a fixing device of Comparative Example 1 using the so-called longitudinal energization method, when the pressure roller is shorter than the heat generation width (longitudinal width) of the heater 920, the heater heating element of the portion that is not in contact with the pressure roller Since the heat transfer to the fixing belt that comes into contact with the fixing unit is not performed, the temperature of the unit increases excessively. Further, in the fixing device of Comparative Example 1 using the so-called longitudinal energization method under the recording material width and image conditions, the longitudinal width of the heater 920 is only 340 mm, for example, and the longitudinal width of the pressure roller is only 345 mm, for example. turn into.

  Next, a case where the fixing operation is performed using a so-called short-direction energization heater in Comparative Example 2 will be described with reference to FIG.

  That is, as shown in FIG. 9, in the heater unit 100 of Comparative Example 2, a long heater 1020 is formed on the insulating substrate 1010 along the longitudinal direction thereof. Wiring electrodes 1021a and 1021b extending in parallel along the heater 1020 are arranged on both sides of the heater 1020 in the longitudinal direction. At the end of the wiring electrode 1021a, a power feeding unit 1022a for power feeding is arranged connected to the wiring electrode 1021a, and at the end of the wiring electrode 1021b, the feeding unit 1022b is arranged connected to the wiring electrode 1021b. .

  According to the second comparative example, as in the case of using the fixing device 20 of the so-called short direction energization method as described in the present embodiment, the temperature increase of the non-sheet passing portion is markedly higher than that of the so-called longitudinal direction energization method. To be improved. This is because, as described in the background art, when the so-called short direction energization method is used, the resistance value changes depending on the temperature distribution of the heating element, and the heat generation distribution is switched so that the temperature distribution in the longitudinal direction does not occur. is there. That is, with respect to the resistance heating element width of the heater, the portion of the resistance heating element that is not passed through increases the temperature because there is less movement of the amount of heat, and the resistance value of the resistance heating element increases as the temperature rises. This is because it becomes difficult to input power, and the heat generation of the resistance heating element itself can be suppressed.

However, the configuration of Comparative Example 2 has the following problems. That is, as already mentioned above,
(A). In the case of using a heater having substantially the same TCR characteristics (characteristics indicating the temperature change and resistance value change of the heating element) in the longitudinal direction of the resistance heating element, The amount of power supplied to the end will increase.
(I). In order to solve the problem (a), when a heater having a large calorific value at the end portion is used, the effect of suppressing the temperature rise in the non-sheet passing portion of the so-called short direction energization method is reduced.

  When considering the movement of the amount of heat, the amount of heat from the resistance heating element moves to the pressure roller side when the sheet is not passed (for example, during startup or between sheets). Since heat is also transferred within the pressure roller, when the pressure roller is longer than the resistance heating element width, the resistance heating element is in contact with the pressure roller outside the resistance heating element width. The amount of heat applied to the pressure roller located on the end side of the part moves to the outside.

  Accordingly, the temperature on the end side of the pressure roller is lower than that of the central portion. Under the influence of the temperature drop at the end of the pressure roller, the temperature of the resistance heating element also decreases, the resistance value of the resistance heating element decreases, and this part has more power than the central part. Is inserted.

  Regarding the above phenomenon, FIG. 9 schematically shows the relationship between the resistance heating element width, the pressure roller longitudinal direction width (pressure roller width), and the input power in the longitudinal direction. FIG. 9A shows a configuration of a so-called short-direction energization type heater 1020 in which the longitudinal width (resistance heating element width) of the resistance heating element of Comparative Example 2 is 340 mm. FIG. 9b shows a configuration of a pressure roller having a width of 345 mm capable of pressing the entire region of the resistance heating element width of the heater of Comparative Example 2. FIG. 9c shows a graph of the power consumed (input) until the recording material is passed through the fixing device after the image forming operation is started using the heater and the pressure roller in FIG. In addition, the arrow D in a figure shows the moving direction of the heat generated from the heater 1020 as a resistance heating element.

  In the configuration of Comparative Example 2 described above, when paper is not being passed, the amount of heat generated by the resistance heating element is moved to the end of the pressure roller that is not involved in the fixing operation, thereby wasting power. .

  In contrast to the comparative example 2, in the present embodiment, in order to solve the above problem, in the fixing device 20 of the so-called short-direction energization method, the pressure roller 70 is provided with a heater (resistance heating) over the entire longitudinal direction. Body) 620 is configured to be in pressure-contact with 620.

  The configuration of this embodiment is schematically shown in FIG. In FIG. 5, in the so-called short-side energization method, the power consumed until the recording material is passed through the fixing device 20 when a configuration in which the entire width in the longitudinal direction of the pressure roller is pressed against the heater 620 is used. Indicates.

  FIG. 5 a shows a configuration of a so-called short-direction energization type heater 620 having a resistance heating element width of 340 mm used in the first embodiment. FIG. 5b shows the configuration of the pressure roller having a longitudinal width of 325 mm used in the first embodiment. FIG. 5c shows a graph of power consumed (input) until the recording material is passed through the fixing device 20 after the image forming operation is started using the heater 620 and the pressure roller 70 in FIG. . An arrow D in the figure indicates the direction of movement of heat generated from the heater 620 as a resistance heating element.

  In this embodiment, the width of the recording material to be introduced and nipped and transported to the fixing device 20 and fixed, and the image conditions are set to a maximum sheet passing width of 320 mm and an image guarantee area of 316 mm.

  The longitudinal width of the heater 620 (resistance heating element width) was 340 mm, whereas the longitudinal width of the pressure roller 70 was set to 325 mm. As described above, the resistance heating element width 340 mm is a heat generation width necessary for satisfying the image fixing property and image quality within the image guarantee region 316 mm. On the other hand, the longitudinal width (pressure roller width) 325 mm of the pressure roller 70 is a width necessary for stably transporting a recording material having a maximum sheet passing size width of 320 mm.

  Here, the pressure roller width is 325 mm shorter than the resistance heating element width 340 mm, but the heater 620 in this embodiment uses a so-called short-direction energization method. Therefore, the portion of the heater 620 that is not in contact with the pressure roller 70 has PTC characteristics, and the resistance value of the heating element itself rises even if the temperature rises without moving the amount of heat. Is difficult to be introduced. Therefore, an excessive temperature rise is not caused as in the case of the so-called longitudinal energization method. The PTC characteristic is a positive resistance temperature characteristic (a self-temperature control characteristic in which the resistance value increases as the temperature rises).

  As can be seen from FIG. 5, the amount of heat generated from the short direction energization direction moves to the pressure roller 70 side as indicated by the arrow D, but the entire pressure roller 70 is pressurized to the heater 620 side. The heat transfer to the pressure roller end side as described in FIG. 9 does not occur. As a result, the temperature of the heating element itself does not decrease due to the temperature decrease of the pressure roller 70, and the bias of input power in the longitudinal direction of the heater 620 does not occur.

  Here, the amount of electric power input until the unfixed image formed on the recording material can be sufficiently fixed is actually compared between the configuration of Comparative Example 2 and the configuration of the present embodiment. Using the configuration, it was found that there was a power reduction effect of about 60 W compared to Comparative Example 2.

  As described above, by using the configuration of the present exemplary embodiment, even when heat transfer to the pressure roller 70 is performed, for example, when the fixing device 20 is started up while preventing the temperature increase of the non-sheet passing portion. Thus, it is possible to provide a configuration that saves power without wasting power (see Table 1). Specifically, with the configuration of the present embodiment, it is possible to obtain a power reduction effect of about 60 W at startup.

  As for the power effect during start-up in Comparative Example 1, since energization in the longitudinal direction is performed, even if the temperature at the end of the pressure roller decreases, the same power is supplied in the longitudinal direction, and there is no reduction effect itself. In Table 1, it is indicated by Δ.

  Table 1 shows each energization method, resistance heating element width, pressure roller width, maximum sheet passing width (maximum sheet passing size width), and image guarantee area used in the first embodiment, comparative example 1, and comparative example 2. Are also shown together.

  Table 1 shows the first embodiment and comparative example 1 regarding the maximum sheet passing size width, image guarantee area, energization method, resistance heating element width, pressure roller width, non-sheet passing portion temperature rise, and start-up power. The difference by each of the comparative example 2 is described.

  The maximum sheet passing size width and the image guarantee area are 320 mm and 316 mm in all of the first embodiment, Comparative Example 1 and Comparative Example 2. As for the energization method, a so-called short direction energization method is used in the first embodiment, a so-called longitudinal direction energization method in Comparative Example 1, and a so-called short direction energization method in Comparative Example 2. The resistance heating element width is 340 mm in all of the first embodiment, comparative example 1 and comparative example 2.

  The pressure roller width is 325 mm in the first embodiment, 345 mm in Comparative Example 1, and 345 mm in Comparative Example 2. The temperature increase of the non-sheet passing portion is effective in the first embodiment, ineffective in Comparative Example 1, and effective in Comparative Example 2. As for power at startup, the first embodiment has a power reduction effect, the comparative example 1 has no reduction effect itself, and the comparative example 2 has no power reduction effect.

  In the above-described embodiment, the pressure roller 70 is set so that the length in the width direction orthogonal to the recording material conveyance direction is shorter than the length in the width direction of the heater 620. However, the present invention is not limited to this. It is possible to include the case where it is set to be the same as the length. In that case, the same effect can be obtained. In other words, in the present embodiment, the heater unit 60 includes both sides of the heater 620 and the both sides of the heater 620 that extend along both sides of the heater 620 in the width direction perpendicular to the recording material conveyance direction. A pair of wiring electrodes 621a and 621b connected to each other. The pressure roller 70 is pressed against the heater unit 60 with the length in the width direction being equal to or less than the length in the width direction of the heater 620 and with the entire width direction facing the heater 620.

  Therefore, in the fixing device 20 of the so-called short direction energization method, while suppressing the temperature rise of the non-sheet passing portion, the lowering of the end temperature of the heater unit 60 is suppressed, It is possible to suppress an increase in power supply.

  In the present embodiment, the pressure roller 70 is set so that the length in the width direction is longer than the maximum sheet passing size width of the recording material P to be passed through the fixing nip N. However, the present invention is not limited to this. It is also possible to set the same value as that of the recording material P having the maximum sheet passing size width. In that case, the same effect can be obtained. That is, since the length in the width direction of the pressure roller 70 is the same as the recording material having the maximum sheet passing size width or longer than the maximum sheet passing size width, the effect of suppressing the temperature increase at the non-sheet passing portion and the temperature decrease at the end of the heater unit The effect of suppressing the increase in power supply to the end of the heater unit can be enhanced.

<Second Embodiment>
Next, a second embodiment in which the configuration of the heater unit 60 in the first embodiment is partially changed will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram showing in detail the longitudinal direction of the heating element width and pressure roller width of the heater 820 in the so-called short direction energization method in this embodiment, and FIG. 7 is a diagram schematically showing the heater resistance in this embodiment. It is. In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  That is, in this embodiment, the resistance heating element width of the heater 820 and the positional relationship in the longitudinal direction of the pressure roller 70 (see FIG. 5) are the same, but the power supply units 822a and 822b with respect to the wiring electrodes 821a and 821b of the heater 820. The feeding position is different. In this embodiment, as in the first embodiment, the width of the recording material introduced into the fixing device 20 and the image conditions are set to a maximum sheet passing size width of 320 mm and an image guarantee area of 316 mm.

  FIG. 6 shows the configuration of the heater unit 80, the longitudinal width of the heater 820 (resistance heating element width), the longitudinal width of the pressure roller 70 in pressure contact with the heater unit 80 (pressure roller width), and the maximum sheet passing capacity. The paper passing size width is also described.

  As shown in FIG. 6, a long rectangular heater 820 extending along the longitudinal direction (the left-right direction in FIG. 6) is disposed on the insulating substrate 810. On both sides of the heater 820 in the longitudinal direction, wiring electrodes (electrodes) 821a and 821b extending in parallel along the heater 820 are arranged. These wiring electrodes 821a and 821b are connected to both side edges in a state of extending along both side edges in the width direction perpendicular to the recording material conveyance direction of the heater 820 in order to energize the heater 820.

  At the end portion of the wiring electrode 821a on the insulating substrate 810, a power feeding portion 822a for power feeding is arranged in such a manner that the connection portion 822c is connected to a position closer to the center side from the edge of the wiring electrode 821a. Further, at the end portion of the wiring electrode 821b on the insulating substrate 810, a power feeding portion 822b for power feeding is arranged in such a manner that the connection portion 822d is connected to a position closer to the center side from the end edge of the wiring electrode 821b. Yes. In other words, the pair of power feeding units 822a and 822b that supply power to the pair of wiring electrodes 821a and 821b are connected to the wiring electrodes 821a and 821b, respectively, at the center side with respect to both ends of the heater 820 in the width direction.

  Further, the heater drive circuit 51 and the AC power supply 30 are connected between the power supply unit 822a and the power supply unit 822b. In addition, about the used material, thickness, etc., it is the same as that of the case of the heater unit 60 used in 1st Embodiment.

  In this embodiment, the position of the power supply to the wiring electrode of the heater and the resistance heating element is arranged so as to be inside the width of the pressure roller to be in contact. This avoids the inconvenience that it is difficult to supply power when the temperature of the wiring electrode in the portion not in contact with the pressure roller 70 is raised when the power feeding position is outside the both ends of the pressure roller 70. Because.

  In the so-called short direction energization method, when the temperature of the wiring electrode and the resistance heating element is increased, the resistance of the wiring electrode and the resistance heating element are increased and power cannot be input. However, in the case of the heater 620 shown in FIG. 4, the temperature rises at the electrode ends of the wiring electrodes 621a and 621b that are not in contact with the pressure roller 70 as compared with the contacted portions. .

  In particular, when the heater is used with a large heat generation amount, such as when a high temperature control temperature is required or when the input power needs to be increased for speeding up, there are the following possibilities. In other words, there is a possibility that the temperature of the wiring electrode and the heater in the portion not in contact with the pressure roller 70 becomes too high and the power is not turned on or the time until the fixing device is started up becomes long.

  In the case of the heater 820 shown in FIG. 6 used in the second embodiment, since the power feeding position is inside the pressure roller 70, the temperature rise at the electrode end as described above is more effectively suppressed and stable. Power supply can be made possible. This is because, in the present embodiment, the connection portions 822c and 822d, which are power supply positions by the power supply units 822a and 822b, are located inside the pressure roller width (for example, 325 mm), and thus the energization to the heater 820 is on the opposite side of the power supply unit 822a. This is performed with the power feeding unit 822b.

  When the temperature of the heater 820 is high, the resistance value becomes high due to PTC (self-temperature control) and power cannot be input. However, the current passing through the heater 820 from the inside of the pressure roller contact portion is directed to the end portion side. Is difficult to flow. This is because the resistance value of the heater 820 at the portion not in contact with the pressure roller 70 increases as the temperature rises.

  In this embodiment, the power feeding positions by the connecting portions 822c and 822d of the power feeding portions 822a and 822b are arranged so as to be inside the pressure roller width, but are set to be 161 mm from the heater center. ing. This is because it is arranged inside the pressure roller width (for example, 325 mm) and outside the maximum sheet passing width (for example, 320 mm). As described above, by arranging the power feeding position inside the width of the pressure roller (for example, 325 mm), the temperature of the wiring electrodes 821a and 821b and the heater 820 becomes too high, and a phenomenon in which power cannot be input, or the fixing device The phenomenon that the start-up of 20 becomes long can be prevented.

  The current from the connection part 822c of the power supply part 822a through the wiring electrode 821a to the power supply part 822b via the heater 820 and the reverse wiring electrode 821b and the connection part 822d is from the power supply position to the reverse power supply position. A large amount of current flows in a position where the apparent resistance value is the lowest.

  Here, regarding the heater 820 used in the present embodiment, the resistance from the power feeding position to the power feeding position on the opposite side can be schematically represented as shown in FIG.

  In FIG. 7, R1, R2, and R3 represent the resistance of the heater (resistance heating element) 820, and R1 = R2 = R3. R1, r2, r3, and r4 represent resistances of the wiring electrodes 821a and 821b, and r1 = r2 = r3 = r4.

At this time, assuming that the current flowing through the resistor R1 is i1 and the current flowing through the resistor R2 is i2, the current i1 and the current i2 flowing through the resistors R1 and R2 are expressed by the following relational expression (1) from Kirchhoff's law. Holds.
i2 = (R / (R + r)) × i1 (1)

  That is, the current flowing through the heater 820 connected to the power feeding units 822a and 822b is larger than that in the inner portion, and thus the amount of heat generation is also increased.

  As described above, the temperature at the power feeding portion is likely to be higher than that at other places, and there is a possibility of uneven gloss in this portion, but the power feeding position in this embodiment is not affected by temperature unevenness. The position is on the inner side of the pressure roller width and the outer side of the maximum sheet passing width.

  With the configuration of the present embodiment described above, electric power is wasted even when heat transfer to the pressure roller 70 is performed, such as when the fixing device 20 is started up, while preventing the temperature rise of the non-sheet passing portion. Therefore, a configuration that saves power can be provided. Further, even when the fixing device 20 is speeded up, stable power supply can be achieved.

  In the second embodiment as well, the pressure roller 70 is set so that the length in the width direction orthogonal to the recording material conveyance direction is longer than the maximum sheet passing size width of the recording material P to be passed. However, the present invention is not limited to this, and it is also possible to set the recording material having the maximum sheet passing width. In this case, the feeding positions of the connecting portions 822c and 822d are positions where the pressure roller width and the maximum sheet passing size width coincide with each other. However, it is possible to obtain substantially the same effect as that of the second embodiment. Is possible.

  20 ... Image heating device (fixing device), 60, 80 ... Heating member (heater unit), 70 ... Pressure member (pressure roller), 620, 820 ... Resistance heating element (heater), 621a, 621b, 821a, 821b ... a pair of electrodes (wiring electrodes), 622a, 622b, 822a, 822b ... a pair of power feeding parts, 822c, 822d ... a connection part, N ... a nip part (fixing nip part), P ... a recording material

Claims (3)

A heating member that heats the toner image on the recording material; and a pressure member that forms a nip portion in contact with the heating member, while the recording material carrying the toner image is nipped and conveyed by the nip portion. In an image heating apparatus for heating a toner image,
The heating member is
A pair of resistance heating elements connected to the side edges in a state of extending along both side edges in the width direction perpendicular to the recording material conveyance direction of the resistance heating elements to energize the resistance heating elements An electrode, and
The pressure member is
The length in the width direction is equal to or less than the length in the width direction of the resistance heating element, and is pressed against the heating member in a state where the entire area in the width direction is opposed to the resistance heating element.
An image heating apparatus. The pressure member is
The length in the width direction is longer than the maximum sheet passing size width of the recording material passed through the nip portion or the same as the maximum sheet passing size width.
The image heating apparatus according to claim 1. Having a pair of power feeding sections for supplying power to the pair of electrodes,
The pair of power feeding portions are respectively connected to the pair of electrodes on the center side with respect to both ends of the resistance heating element in the width direction.
The image heating apparatus according to claim 1, wherein the apparatus is an image heating apparatus.

Images