JP6172925B2 - Fixing device - Google Patents

Description

The present invention relates to a fixing device used in an image forming apparatus employing an image forming process such as an electrophotographic system or an electrostatic recording system, such as a copying machine or an LBP. Examples of such a fixing device include a device that heats and fixes an unfixed toner image formed on a recording material as a fixed image, and an increase in glossiness that increases the glossiness of the image by heating the image fixed on the recording material. An apparatus etc. can be mentioned.

  Conventionally, an image forming apparatus is directly applied to the surface of a recording material (paper, printing paper, transfer material sheet, OHT sheet, glossy paper, glossy film, etc.) by an image forming process such as electrophotography, electrostatic recording, and magnetic recording. Alternatively, an unfixed toner image corresponding to image information is formed by an indirect (transfer) method. A fixing device as an image heating device fixes the unfixed toner image as a fixed image on the recording material surface.

  As a fixing device, a heat fixing method in which an unfixed toner image formed on a recording material is heated and melted and fixed on the recording material is widely used. An on-demand fixing device (Patent Documents 1 and 2) is known.

  In the on-demand fixing device, for example, an image heating device is constituted by a thin and long substrate-like ceramic heater and a fixing belt that is a rotatable belt member that heats the ceramic heater by contacting the inner surface thereof. In addition, it has a pressure mechanism that presses the ceramic heater against an opposing member such as a pressure roller, and as a result, a fixing nip that is a pressure contact area formed between the fixing belt and the pressure roller is provided on the transfer material. The toner image is fixed. In such an on-demand fixing device, since the heat capacity of the device can be reduced as compared with the heat roller fixing device, the wait time, which is the time required for the temperature rise, can be shortened.

  In recent years, a color on-demand fixing device that is provided with an elastic layer on a fixing belt and can also fix a color image has been widely adopted. In addition, the diameter of the fixing belt is being reduced in order to reduce the size of the apparatus and further reduce the wait time.

JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878

  Here, when the diameter of the fixing belt of the on-demand fixing device is reduced to reduce the size and the wait time, the following problems relating to the pressure stay occur. This will be described with reference to FIG.

  In FIG. 15, a fixing belt 130 as a heating body having a ceramic heater 131 as a heat generating portion needs to be pressed with a strong force against an opposing member such as a pressure roller 201 in order to secure a necessary nip width. . For this reason, the pressure stay 300 is provided as a highly rigid skeleton member that can withstand the applied pressure and the force received from the opposing member, and plays a role of evenly distributing the applied pressure in the longitudinal direction. The pressurizing stay 300 is often used by bending a steel plate into a U shape or a U shape.

  In the figure, reference numeral 301 denotes a heater holder as a backup member, which is formed of a heat resistant resin that holds the ceramic heater 131 and at the same time transmits the pressure applied from the pressure stay 300 to the ceramic heater 131.

  Here, when the diameter of the fixing belt 130 as a flexible belt member is reduced, the height of the top surface portion 302 of the pressure stay 300 is avoided in order to avoid contact between the inner surface of the fixing belt 130 and the pressure stay 300. It is necessary to reduce the size of the pressure stay 300, for example, to reduce the pressure. As a result, there arises a problem that the strength is lowered and the bending of the pressure stay 300 is increased.

  When the bending of the pressure stay 300 increases due to the decrease in strength, the applied pressure cannot be uniformly distributed in the longitudinal direction, and the contact nip width in the conveying direction between the fixing belt 130 and the pressure roller 201 becomes the end in the longitudinal direction. It becomes non-uniform, such as thick in the partial region and thin in the central region in the longitudinal direction. As a result, unevenness occurs in the melted state of the toner, and as a result, uneven glossiness of the image is likely to occur, poor fixing due to insufficient melting of the toner, and hot offset due to excessive melting of the toner.

  Further, the top surface portion 302 of the pressure stay 300 approaches the inner surface of the fixing belt 130 in the central region in the longitudinal direction where the amount of displacement (the amount of jump) due to the bending of the pressure stay 300 due to the decrease in strength is the largest. There is a problem that the fixing belt 130 is deprived of heat. If the height of the pressure stay 300 is further lowered in order to avoid this contact, the bending will eventually be further deteriorated.

  On the other hand, it is conceivable to increase the thickness of the pressure stay 300 as a whole so as to increase the strength against bending even in a state in which the pressure stay 300 is downsized. However, the following problem also occurs in this case. . That is, in order to prevent contact with the fixing belt 130, it is necessary to increase the thickness of the top surface portion of the pressure stay 300 to the inside. As a result, the height of the space inside the pressure stay 300 (in the drawing) G) becomes low.

  In the space inside the pressure stay 300, there is housed a pressure stay built-in member 303 including elements such as a thermistor and a thermo switch for detecting the temperature of the ceramic heater 131, and the accommodation space is insufficient. Problems occur. At the stage of reducing the diameter of the fixing belt 130, the height of the space inside the pressure stay 300 (G in the figure) has already decreased, and there is no room for the storage of the pressure stay built-in member 303. Further, when the thickness is further reduced, it becomes difficult to store a built-in member having a height.

The object of the present invention is to reduce the unevenness of the image by reducing the deflection of the reinforcing member even when the diameter of the cylindrical belt is reduced, and to suppress the interference between the reinforcing member and the cylindrical belt or the reinforcing member built-in member. It is an object of the present invention to provide a fixing device that can perform the above operation.

To achieve the above object, a fixing device according to the present invention forms a nip portion together with a cylindrical belt, a nip portion forming member that contacts an inner surface of the belt, and the nip portion forming member via the belt. A roller and a cross section perpendicular to the longitudinal direction of the belt is U-shaped, and is a reinforcing member made of metal that is long in the longitudinal direction of the belt and forms the U-shaped opening. A leg portion and a top surface portion that is in a region farther from the nip portion than the two leg portions and is continuous with the two leg portions, and the nip portion forming member is supported by the two leg portions. A fixing member that heats the recording material on which the image is formed at the nip portion while heating the recording material, and fixes the image on the recording material. The nip portion forming member heats the belt. A heating member, said At least the other hand the thickness of the two legs of the strong member may be thicker than the thickness of the top surface portion.

According to the present invention, even when the diameter of the cylindrical belt is reduced, the deflection of the reinforcing member is reduced to suppress uneven gloss of the image, and the interference between the reinforcing member and the cylindrical belt or the reinforcing member built-in member is suppressed. It is possible to provide a fixing device that can perform the above operation.

1 is a schematic configuration diagram of a fixing device as an image heating device according to a first embodiment of the present invention. 1 is a schematic configuration diagram of an image forming apparatus equipped with an image heating apparatus according to a first embodiment of the present invention. FIG. 3 is a schematic configuration diagram of the fixing device according to the first embodiment viewed from the upstream side in the conveyance direction. It is a schematic block diagram of the comparative example with respect to 1st Embodiment. It is a schematic block diagram of the fixing device which concerns on other embodiment. It is a schematic block diagram of the fixing device which concerns on other embodiment. It is a schematic block diagram of the fixing device which concerns on other embodiment. It is a schematic block diagram of the fixing device which concerns on other embodiment. It is a schematic block diagram of the fixing device which concerns on other embodiment. FIG. 5 is a schematic configuration diagram of a fixing device according to a second embodiment of the present invention. FIG. 6 is a schematic configuration diagram when a fixing device according to a second embodiment is viewed from an upstream side in a conveyance direction. FIG. 10 is a perspective view illustrating a schematic configuration of a pressure receiving portion of a pressure stay in a fixing device according to a second embodiment. It is a schematic block diagram of the fixing device which concerns on other embodiment. It is a figure which shows the longitudinal shape at the time of seeing the auxiliary | assistant pressurization stay in the 3rd Embodiment of this invention from the conveyance direction upstream. It is a schematic block diagram of the fixing device in the conventional example.

<< First Embodiment >>
(Image forming device)
FIG. 2 is a schematic configuration diagram of an image forming apparatus equipped with the image heating apparatus according to the embodiment of the present invention. This image forming apparatus is an electrophotographic color image forming apparatus employing a tandem method that is particularly excellent in terms of high speed. In FIG. 2, Y, M, C, and K are toner image forming units for yellow, magenta, cyan, and black, respectively. Each unit includes an electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier, a charging device 2, a laser exposure optical system 3, a developing device 4, a cleaning device 5, and the like. It consists of a photographic process mechanism.

  The photosensitive drum 1 is rotationally driven in the direction of the arrow at a predetermined peripheral speed, and a toner image corresponding to each color is formed on the surface of the photosensitive drum by a known electrophotographic image forming process.

  A transfer belt 6 is stretched between the driving roller 7 and the turn roller 8 and is arranged below all the units Y to K so as to extend over all the units. The transfer belt 6 is rotationally driven in a counterclockwise direction indicated by an arrow at a peripheral speed corresponding to the peripheral speed of the photosensitive drum 1.

  Reference numeral 9 denotes a transfer roller, and in each of units Y, M, C, and K, a transfer nip portion is formed by being pressed against the lower surface of the photosensitive drum 1 with the transfer belt 6 interposed therebetween. Reference numeral 10 denotes a registration roller, and a sheet-like recording material (transfer material, paper) P separated and fed from a paper feeding mechanism unit (not shown) is placed on the end of the transfer belt 6 on the first unit Y side. Feed at a predetermined control timing. The fed recording material P is electrostatically attached to the surface of the transfer belt 6 by the electrode roller 11.

  The transfer belt 6 holds the recording material P and sequentially conveys it to the transfer nips of the first to fourth units Y, M, C, and K. V 11 is a bias application power source for the electrode roller 11. V 9 is a power supply for applying a transfer bias to each transfer roller 9.

  As a result, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image are sequentially superimposed and transferred in the aligned state on the surface of the same recording material P, and an unfixed full-color toner image is synthesized and formed. .

  The recording material P transported and passed through the transfer nip portion of the fourth unit K is separated from the transfer belt 6, introduced into the fixing device F, subjected to a heat fixing process for an unfixed toner image, and discharged as a full color image formed product. Be transported.

(Image heating device)
Next, the configuration of the fixing device as the image heating device in the present embodiment will be described. The fixing device of the present embodiment employs an on-demand method. FIG. 1 shows a schematic cross-sectional configuration in the transport direction when the fixing device of the present embodiment is cut along a plane perpendicular to the longitudinal axis. FIG. 3 shows a schematic configuration diagram of the fixing device when viewed from the upstream side in the recording material conveyance direction.

  In FIG. 1, reference numeral 200 denotes a heating unit, which includes a fixing belt 130 that is a rotatable flexible belt member, which will be described in detail below, and a ceramic heater 131 that is also a heating source for heating the fixing belt 130 on the inner peripheral surface side thereof. I have. Heat is transferred by bringing the ceramic heater 131 into contact with the inner peripheral surface of the fixing belt 130, and the fixing belt 130 is heated.

  A backup member 132 is provided on the inner peripheral side of the fixing belt 130 and is provided on the outer peripheral side of the fixing belt 130 so as to face the pressure roller 201 which is a pressure member. The recording material carrying the image is nipped and conveyed to the fixing nip portion 101 formed between the fixing belt 130 and the pressure roller 201 to heat the image.

  That is, after the transfer process is completed, a recording material (not shown) on which an unfixed toner image is placed is conveyed from the right side to the left side in the drawing and guided to the fixing nip 101. The toner is melted and fixed on the transfer material by the pressure applied at the fixing nip portion 101 and the heat transmitted from the fixing belt or the ceramic heater.

  Here, the left-right direction in FIG. 1 is expressed as a conveyance direction, and the right side in the drawing is expressed as an upstream side in the conveyance direction, and the left side is expressed as a downstream side in the conveyance direction.

(Flexible belt member)
The fixing belt 130 as a flexible belt member is provided with a 200 μm thick silicone rubber layer as an elastic layer on a base layer made of a cylindrical polyimide resin having a thickness of 60 μm, an inner diameter of 18 mm, and a length of 240 mm. Further, a release layer made of PFA resin having a thickness of 30 μm is formed on the outer side by coating.

  As the base layer of the fixing belt 130, other heat-resistant resin materials or other metal materials such as nickel and SUS can be used. The release layer can also be provided by covering a tube made of a fluororesin such as PFA. Although the elastic layer can be omitted, in particular, in the case of an on-demand fixing device used in a color image forming apparatus as in the present embodiment, it is not omitted in order to prevent uneven glossiness of the output image. desirable.

  When the elastic layer is thickened, the effect of preventing uneven glossiness of the image due to the unevenness of the surface of the recording material is enhanced, while the heat transfer efficiency from the ceramic heater to the belt surface is reduced. Furthermore, since the heat capacity of the fixing belt itself increases, the temperature rise time on the surface of the fixing belt is delayed. According to the study by the inventors, the balance between gloss unevenness and temperature rise is good when the thickness of the elastic layer is 50 to 1000 μm, preferably around 100 to 500 μm. At this time, the heat capacity (per 1 cm 2) of the fixing belt was approximately 4.19 × 10 2 -J / cm 2 · K to 4.19 J / cm 2 · K.

  Increasing the thermal conductivity of the base layer and the elastic layer is also effective for shortening the temperature rise time of the fixing belt 130 and improving the fixing ability. Therefore, in the present embodiment, a material having a high thermal conductivity of 1.0 w / m · K or higher is used for both the base layer and the elastic layer.

  Since the fixing belt 130 is in close contact with the ceramic heater 131 and the heater holder 132 in the fixing nip 101 (FIG. 1) and has a flat shape, the locus of the fixing belt during rotational driving is compressed in the vertical direction as shown in FIG. The shape spreads in the left-right direction. In order to reduce the frictional force generated between the fixing belt 130 and the ceramic heater 131 during rotational driving, heat-resistant grease as a lubricant is interposed between the two. As the heat resistant grease, for example, a mixture of fluorine oil and fluorine resin can be used. In this embodiment, HP-300 grease manufactured by Dow Cornig Asia Co., Ltd. was used as the lubricant. The amount used was 400 mg.

(Ceramic heater)
The ceramic heater 131 as a heating source is formed by forming a resistance heating element pattern on a substrate surface made of alumina, aluminum nitride or the like formed to a length of 270 mm, a width of 7.5 mm, and a thickness of 0.7 mm. In the present embodiment, a resistance heating pattern is formed on the surface of the alumina substrate on the fixing belt side by printing, and an insulating heat-resistant glass protective layer having a thickness of 60 μm is provided thereon. In order to control the temperature of the ceramic heater 131 to a target value, a thermistor (not shown) is provided in contact with the non-contact surface of the ceramic heater with the fixing belt. The calorific value (input power) of the ceramic heater 131 is controlled in accordance with the temperature detection result by the thermistor. A plurality of thermistors are often arranged in the longitudinal direction.

(Backup material)
The heater holder 132 as a backup member is made of a heat-resistant resin (liquid crystal polymer or the like), holds the ceramic heater 131, and also partially contacts the fixing belt 130 and also plays a role of guiding the running.

(Pressure roller)
The pressure roller 201 is provided with a silicone rubber elastic layer 141 having a thickness of 4 mm on a stainless steel core 140 having an outer diameter of 14 mm, and a surface layer (non-coated) formed by a PFA resin having a thickness of 50 μm thereon as a release layer. The one provided was used. Therefore, the outer diameter of the pressure roller 201 is about 22 mm. More specifically, the outer diameter of the pressure roller 201 has an inverted crown shape in which the outer diameter of the end portion is 120 μm larger than the longitudinal center portion. This is to prevent wrinkling of the recording material during the fixing process.

  The product hardness of the pressure roller 201 was 55 degrees (ASKER-C load 1 kg). The width of the contact nip portion 101 (hereinafter referred to as the fixing nip) 101 between the fixing belt 130 and the pressure roller 201, which is formed by the elastic layer 141 being deformed by the pressure applied from the ceramic heater 131, is approximately 8 mm. In this embodiment, the pressure roller 201 is driven by a drive motor (not shown). The operation of the drive motor is controlled by a control unit (not shown) in terms of drive, stop, and rotation speed.

  The fixing belt 130 is driven by the pressure roller 201 by a frictional force acting on the fixing nip 101, and is rotationally driven in the direction of the arrow at substantially the same peripheral speed as the pressure roller while sliding against the ceramic heater 131 and part of the heater holder 132. Is done.

During normal image formation in which an image is formed on a recording material such as plain paper having a basis weight of 60 to 100 g / m ² , the pressure roller is driven at a peripheral speed of 200 mm / s and the temperature of the fixing belt 130 is increased. The energization to the ceramic heater is adjusted to 180 ° C.

(Pressure stay as frame member (reinforcement member) )
Reference numeral 151 in FIG. 1 denotes a pressure stay as a skeleton member that supports the heater holder 132 in the longitudinal direction intersecting the transport direction. Further explaining with reference to FIG. 3, the pressure stay 151 is directed toward the pressure roller 201 applied by the pressure mechanism via the pressure spring 180 at the pressure receiving portions 181 provided at both ends in the longitudinal direction. Receive the pressure. In the present embodiment, the total applied pressure is 226 N, and the distance between the fulcrums of the pressure receiving portions at both ends (L in the figure) is 254 mm. In the figure, reference numeral 183 denotes a pressure spring holder that relays the delivery of the applied pressure between the pressure spring 180 and the pressure receiving portion 181.

  The applied pressure received by the pressure stay 151 as the skeleton member via the pressure spring 180 is transmitted to the heater holder 132 so as to be uniform in the longitudinal direction, and further transmitted to the ceramic heater 131. As a result, the ceramic heater 131 can press the fixing belt 130 against the pressure roller 201.

  In FIG. 1, of the contact surfaces between the pressure stay 151 and the heater holder 132 for transmitting the pressurizing force, the pressure stay side surface 182 is referred to as a pressure transmission surface, and the heater holder side surface 160 is referred to as a pressure receiving surface. . In this embodiment, the length of the pressure transmission surface 182 (M in FIG. 3) is 240 mm. Of the contact surfaces of the ceramic heater 131 and the heater holder 132, the surface 161 on the heater holder side is referred to as a heater holding surface.

(Pressure stay side deflection)
When pressure is applied to the pressure receiving portion 181 (FIG. 3) of the pressure stay 151, the pressure stay 151 is a longitudinal region of 225 mm corresponding to the pressure roller surface length with which the pressure roller 201, which is an opposing member, contacts (FIG. The reaction force is received in W) of 3. As a result, the pressure stay 151 jumps up and bows in the longitudinal direction.

  In order to keep such bending to a minimum, the pressure stay 151 is required to have high rigidity. In the present embodiment, a steel one is used. The heater holder 132 only needs to have a strength in the short direction so as not to bend greatly when a pressure is applied from the pressure stay 151, and the strength as high as the pressure stay 151 is not necessary. In the case of the heater holder 132, it is preferable that the heater holder 132 is made of a member having a lower heat capacity and a lower thermal conductivity so as not to take away excessive heat from the ceramic heater 131 and the fixing belt 130 that are in contact. A resin member was used.

(Pressure roller side deflection)
In addition to the pressure stay 151, the bending at the time of pressurization also occurs on the opposite pressure roller 201 side. As a result, the thickness between the pressure receiving surface 160 of the heater holder 132 and the heater holding surface 161 is thick at the center in the longitudinal direction in order to prevent the applied pressure and the nip width from becoming non-uniform in the longitudinal direction. A thickness shape is provided to compensate for the amount of bending, such that the thickness is reduced at the end.

  Specifically, while the pressure receiving surface 160 of the heater holder 132 is a flat surface, the heater holding surface 161 has an arc shape protruding toward the pressure roller, and the thickness of the longitudinal end portion of the pressure roller is The thickness of the central part in the longitudinal direction was increased to 450 μm. Such a thickness shape may be provided on the pressure receiving surface 160 side, or may be provided on both the pressure receiving surface 160 and the heater holding surface 161. The thickness shape may be another curved shape.

  In the following, the shape in which the central portion in the longitudinal direction is thicker than the end portion in the longitudinal direction is referred to as a crown shape, and the amount obtained by increasing the thickness of the central portion relative to the end portion is referred to as the crown amount. . In other words, in this embodiment, it can be said that a 450 μm crown shape is provided in the thickness of the heater holder 132 as a backup member.

(Built-in pressure stay)
Also in this embodiment, various built-in members are arranged in the space between the pressure stay 151 and the ceramic heater 131 or the heater holder 132 as follows, and the state is particularly small in the height direction. ing. For example, reference numeral 170 in FIG. 1 denotes a thermo switch. The thermo switch 170 is provided on the non-contact surface side of the ceramic heater 131 with the fixing belt 130 and plays a role of detecting an abnormal rise in the temperature of the ceramic heater 131 to cut off power and stop heat generation. A thermal fuse or the like can also be used.

  Elements such as the thermo switch 170 may be disposed in contact with the ceramic heater 131, but in the present embodiment, the element is disposed between the ceramic heater 131 via a resin spacer member 171. This is because, when a member having a large heat capacity such as the thermo switch 170 is brought into direct contact with the ceramic heater 131, the heat of the ceramic heater 131 may be taken and temperature unevenness may be caused.

  When the ceramic heater 131 is abnormally heated, the spacer member 171 is melted and the heat sensitive part of the thermo switch 170 is in close contact with the ceramic heater 131. In order to improve the adhesion at that time, the thermo switch 170 is pressed in the direction of the ceramic heater 131 by the biasing spring 172. In this embodiment, the applied pressure is 4.9N.

  In FIG. 1, reference numeral 173 denotes a thermo switch holder member that holds the thermo switch 170 and the urging spring 172. Reference numeral 174 denotes a heat-resistant power cable for connecting the thermo switch 170 in series in a current path through which the ceramic heater 131 is energized. The power cable 174 has a specification that can withstand a maximum current of 10 A and the highest temperature of 250 ° C., and is connected to terminals provided on both sides of the thermoswitch 170 in the longitudinal direction. One of them is arranged so as to be folded over the thermoswitch holder in this way.

  In addition to the built-in members, the pressurizing mechanism for bringing the thermistor into close contact with the ceramic heater, the holding member, the signal line of the thermistor, the holding member for holding the signal line and the power cable, etc. are different from this cross-sectional view. It is also arranged in the longitudinal position.

  In the fixing device of the present embodiment, the portion where the thermo switch 170 shown in FIG. Particularly, the space in the height direction is small, and the space margin (B shown in FIG. 1) between the power cable 174 at the highest position of the built-in member and the top surface portion of the pressure stay 151 is only 0.2 mm. This space margin is also a space margin required for dimensional tolerance of parts. That is, in the present embodiment, it is impossible to increase the strength by increasing the thickness of the ceiling portion of the pressure stay 151.

(Pressure stay shape)
In the present embodiment, regarding the cross-sectional shape of the pressure stay that is a skeleton member that supplies pressure to the backup member, the thickness of the upstream side surface portion on the upstream side in the conveyance direction and the downstream side surface portion on the downstream side in the conveyance direction of the recording material It is characterized by being thicker than the thickness of the top surface portion connecting the side surface portions.

In FIG. 1, the pressure stay 151 has a cross-sectional shape bent into a U-shape or a U-shape. In the following description, of the cross-sectional shape of the pressure stay, the portion 175 is referred to as the top surface portion of the pressure stay, and the portions (leg portions) extending downward in the figure are the upstream side surface portion 176 of the pressure stay, respectively. And the downstream side surface portion 177. The lower end surfaces of the upstream side surface portion 176 and the downstream side surface portion 177 in the drawing are the pressure transmission surfaces 182 already described in FIG.

  Here, in the present embodiment, the cross-sectional shape of the pressure stay 151 is configured as follows using the fact that the trajectory of the fixing belt 130 is compressed in the vertical direction and becomes a shape that expands in the horizontal direction (that is, the conveyance direction). did. That is, by utilizing the fact that a space is easily created between the fixing belt 130 and the pressure stay 151 on the upstream side and the downstream side in the transport direction, the upstream side surface portion 176, the thickness of the top surface portion 175 of the pressure stay 151 is determined. And the thickness of the downstream side surface part 177 was increased. Specifically, the thickness of the top surface portion was 1.6 mm, whereas the thickness of the side surface portion was 3.2 mm.

  The thick portion of the side surface portion of the pressure stay 151 was obtained by adding a separate steel plate to a steel plate having a uniform thickness by welding or the like and integrating them. More specifically, the steel plate was welded to the portion corresponding to the side surface portion in the state of the flat plate before bending the steel plate, and then the portion corresponding to the top surface portion was bent and formed. On the contrary, the steel plate may be bent and formed into a U shape having a uniform thickness, and then the steel plate may be welded and formed. Although spot welding is used as the welding method, other welding methods may be used.

  The height (A in the figure) of the pressurizing stay 151 is 11 mm, the width in the left and right direction (D in the figure) is 14 mm, and the height (C in the figure) of the portion where the thickness of the side surface is increased is 7 mm. It is said. In FIG. 3 showing the shape in the longitudinal direction, the thickened side portion of the pressure stay 151 is a region colored and displayed in gray. The length in the longitudinal direction is 240 mm (M shown in FIG. 3) which is the same as the width of the pressure transmission surface 182.

(Comparative example)
Next, the effect of the present embodiment will be described in comparison with a comparative example that employs a conventional pressure stay having a uniform thickness. FIG. 4 shows a cross-sectional shape of a conventional pressure stay 190 in the comparative example. The thickness of the top surface portion and the upstream and downstream side portions are uniform at 1.6 mm, the height in the vertical direction (E in the figure) is 11 mm as in the first embodiment, and the width in the left and right direction (F in the figure). The inside dimension of the stay side face was aligned and 10.8 mm.

  Here, it is generally known that the amount of deflection h of a member when a load is applied is inversely proportional to the cross-sectional secondary moment I (N / mm ^ 4) of the member. Specifically, in the case of a pressure stay of a fixing device, it is known that the deflection amount h is given by the following equation.

h = F × L ^ 3 / ((48 + 29 × W / I) × E × I)
E is the elastic coefficient (N / mm ^ 2) of the steel member, F is the applied pressure (N), L is the length between the fulcrums, that is, the length 254 between the fulcrums of the pressure receiving portion shown in FIG. (Mm), W is the length of the region where the reaction force of the pressing force is applied by the opposing member, that is, the pressure roller surface length 225 (mm).

  When the amount of bending of the pressure stay in the present embodiment and the comparative example when the applied pressure F was 226 N was determined, they were 460 μm and 600 μm, respectively. The amount of bending of the pressure stay in this embodiment is 460 μm, which is the same as the amount of crown that is provided at the thickness between the pressure receiving surface 160 (FIG. 1) of the heater holder 132 and the heater holding surface 161 (FIG. 1). Degree. Therefore, it can be considered that the amount of bending is offset by the crown shape of the heater holder, and a substantially uniform pressure is obtained in the longitudinal direction.

  On the other hand, in the case of the comparative example, unless the crown amount of the heater holder 191 shown in FIG.

  Table 1 shown below is a comparison between the present embodiment and the comparative example in which the problems described in the problem explanation section of the conventional fixing device occur. Specifically, the results of a comparison of gloss unevenness that occurs when the fixing nip width is not uniform in the longitudinal direction and the presence or absence of contact between the top surface portion 175 of the pressure stay and the inner peripheral surface of the fixing belt 130 are shown. Show. As for the comparative example, the case of using the same 450 μm crown holder as in the present embodiment (Comparative Example A) and the case of increasing the crown amount of the heater holder to 600 μm in accordance with the deflection of the pressure stay (Comparative Example B) The results are shown for each.

  The gloss unevenness was evaluated by visually evaluating the difference in gloss between the central portion and the end portion in the longitudinal direction when a solid image was fixed. Regarding the contact between the pressure stay and the inner peripheral surface of the fixing belt, when contact is observed even during image fixing operation, the fixing belt temperature is rising while the fixing belt temperature is rising before the image fixing operation. A symbol △ indicates that the contact is made only while the rotation is slightly unstable, and a symbol ◯ indicates that the contact is not always made.

  Since the base layer of the fixing belt 130 employed in this embodiment has a low resistance because carbon filler is added to improve the thermal conductivity, the presence or absence of contact is the resistance between the pressure stay and the base layer of the fixing belt. It was performed by measuring.

  According to the results of Table 1, in the comparative example, even when the crown amount of the pressure stay is adjusted, uneven gloss and interference between the pressure stay and the fixing belt are not compatible with each other. We were able to achieve both without problems.

  As described above, in this embodiment, when the fixing belt is used in a shape that is widened in the transport direction, the strength of the pressure stay 151 is increased using the space in the fixing belt that is created upstream and downstream in the transport direction. Reinforced. That is, by increasing the thickness of the upstream side surface portion 176 and the downstream side surface portion 177 from the thickness of the top surface portion 175 of the pressure stay 151, the pressurization is performed while maintaining the storage space for the built-in items of the pressure stay 151. The bending of the stay 151 could be reduced. As a result, the occurrence of uneven glossiness of the image and the interference between the pressure stay 151 and the inner peripheral surface of the fixing belt 130 can be prevented.

<< Second Embodiment >>
In the present embodiment, unlike the first embodiment, as shown in FIG. 10, the pressure stay is formed by combining a plurality of members 350, 351, and 352. In the total thickness of the pressure stays in which the plurality of members are combined, the thickness of the upstream side surface portion and the downstream side surface portion of the pressure stay is greater than the thickness of the top surface portion.

  That is, in this embodiment, the thickened portions in the first embodiment are arranged as auxiliary pressure stays 351 and 352 of separate members on the upstream and downstream side portions of the pressure stay main body 350, respectively. The pressure stay was formed by combining a plurality of members (the pressure stay main body 350 and the auxiliary pressure stays 351 and 352). The material of the auxiliary pressure stays 351 and 352 is also the same steel as the material of the pressure stay main body 350.

  Unlike the first embodiment, since the auxiliary pressure stays 351 and 352 are independent of the pressure stay main body 350, the strength of the pressure stay main body 350 cannot be improved. However, as will be described in detail below, a part of the load applied to the pressure stay main body 350 is handled by the auxiliary pressure stays 351 and 352, thereby reducing the load applied to the pressure stay main body 350 and reducing the deflection amount. Can be made. In FIG. 10, 215 is a pressure transmission surface of the pressure stay main body 350, and 216 is a pressure transmission surface of the auxiliary pressure stay 352 on the downstream side.

  In the present embodiment, the combined cross-sectional shape of the pressure stay and the auxiliary pressure stay is the same as that of the first embodiment. The pressure stay main body 350 has a height of 11 mm, a width of 10.8 mm, and a thickness of 1.6 mm for both the top surface portion and the side surface portion. The auxiliary pressure stays 351 and 352 have a thickness of 1.6 mm and a height of 7 mm.

  FIG. 11 shows the longitudinal shape of the pressure stay main body 350 and the auxiliary pressure stay 351 (only the upstream side auxiliary pressure stay is shown in the drawing) as viewed from the upstream side in the transport direction. In order to take part of the pressure applied to the pressure stay main body 350, both longitudinal end portions of the auxiliary pressure stay 351 are provided with pressure receiving portions 354. The pressure receiving portion 354 receives the pressure applied by the pressure spring 180 via the pressure spring holder 355 together with the pressure receiving portion 353 of the pressure stay main body 350 (which overlaps the back side of the 354 in FIG. 11). ing.

  FIG. 12 is a perspective view showing a state around the pressure receiving portion of the pressure stay. The pressure spring holder 355 also plays a role of bundling the auxiliary pressure stay 351, which is a separate member, and the pressure stay main body 350. In FIG. 12, the pressure receiving portion 354 of the auxiliary pressure stay 351 and the pressure receiving portion 353 of the pressure stay main body are bundled by the pressure spring holder 355, and the auxiliary pressure stay 351 does not fall down and the pressure stay main body. A state of being held in close contact with 350 is shown.

  In addition, in order to hold the auxiliary pressure stays 351 and 352 along the pressure stay main body 350 even in the central region in the longitudinal direction, as shown in FIG. A plurality of 357 are provided to regulate the position of the auxiliary pressure stay. In the pressurization stay configuration of the present embodiment, the amount of deflection of the pressurization stay main body 350 when a pressurizing force of 226 N was applied was obtained in the same manner as in the first embodiment, and was 530 μm.

  Similarly to the first embodiment, the results of examining the nip shape in the longitudinal direction, the occurrence of gloss unevenness, and the presence or absence of contact between the pressure stay and the fixing belt are shown in Table 2 below. The comparative example is the same as that of the first embodiment.

  From the above results, it was found that although the deflection amount of the pressure stay main body 350 is larger than the result of the first embodiment, the uneven glossiness and the contact between the fixing belt and the pressure stay can be compatible. The reason why the amount of deflection in the present embodiment is greater than that of the first embodiment is that the auxiliary pressure stay is a separate member, so that the total value of the secondary moments of the cross section between the auxiliary pressure stay and the pressure stay body is the first. This is because it is lower than the case of integration as in the first embodiment. On the other hand, in the present embodiment, welding of the pressure stay can be omitted, and there is an advantage that it can be realized more easily.

  As described above, in this embodiment as well, in the same manner as in the first embodiment, the space on the inner peripheral side of the fixing belt 130 that is born upstream and downstream in the transport direction is used to The total thickness of the side portions on the upstream side and the downstream side was increased from the thickness. As a result, the bending of the pressure stay can be reduced while maintaining the storage space for the built-in pressure stay. As a result, it was possible to prevent occurrence of uneven glossiness of the image and contact between the pressure stay and the inner surface of the fixing belt.

  Further, in the present embodiment, the pressurization stay is further reinforced by the auxiliary pressurization stay which is a separate member, so that complicated processing such as welding is not required, and the same effect can be obtained with a simpler configuration. Could get.

  In the present embodiment, the auxiliary pressure stays 351 and 352 are separate members, and the pressure spring holder 355 is used to bundle them with the pressure stay main body 350. However, the present invention is not limited to this. That is, as shown in FIG. 13, the auxiliary pressure stays 353 are connected in the vicinity of the pressure receiving portion 354 at the end, and an integrated auxiliary pressure stay may be used. In this case, the auxiliary pressure stay can be placed along the pressure stay body without being bundled by the pressure spring holder.

<< Third Embodiment >>
In this embodiment, as in the second embodiment, the pressure stay, which is a skeleton member, is formed by combining a plurality of members. That is, an auxiliary pressure stay, which is a separate member, is arranged on the portion where the thickness of the side surface portions located upstream and downstream in the transport direction is increased, and a part of the load applied to the pressure stay main body is supplemented. It is the structure which reduces the bending amount of a pressurization stay main body by taking charge in a pressure stay.

  This embodiment is different from the second embodiment in that the longitudinal shape of the pressure transmission surface of at least one member among the plurality of members forming the pressure stay is different from that of the pressure stay. The pressure transmission surface is different from the shape in the longitudinal direction. In other words, the shape of the pressure transmission surface contacting the heater holder of the auxiliary pressure stay corresponding to 215 in FIG. 10 and the shape of the pressure transmission surface of the pressure stay main body corresponding to 216 are changed. . Specifically, the pressure transmission surface of the pressure stay main body has a planar shape, whereas the pressure transmission surface of the auxiliary pressure stay has a crown shape in the longitudinal direction.

  The cross-sectional shape of the pressure stay in this embodiment is the same as that in FIG. 10 in the second embodiment. FIG. 14 shows the shape in the longitudinal direction when the auxiliary pressure stay 360 in this embodiment is viewed from the upstream side in the conveyance direction. Although viewed from the same direction as in FIG. 11 of the second embodiment, components other than the auxiliary pressurizing stay are omitted here.

  In this embodiment, the crown amount provided on the pressure transmission surface 361 (FIG. 14) of the auxiliary pressure stay 360 is 500 μm. That is, the pressure transmission surface 361 of the auxiliary pressure stay 360 is formed in an arc shape, and the pressure transmission surface of the longitudinal central portion 363 is 500 μm apart from the position 362 corresponding to the end of the pressure roller in the longitudinal direction. It was made to have a convex shape protruding to the side. The member shape and dimensions other than the shape of the auxiliary pressure stay 360 are the same as those of the second embodiment (auxiliary pressure stays 351 and 352). Since the heater holder 132 is provided with a 450 μm crown shape as in the first and second embodiments, the total crown amount is 950 μm.

  In this embodiment, as in the second embodiment, the pressure stay body and the auxiliary pressure stay press the same pressure receiving surface 160 (FIG. 10) of the heater holder. Therefore, in the pressurized state, the pressure transmission surface 215 of the pressure stay body and the transmission surface 216 of the auxiliary pressure stay have the same bending shape. That is, if the shape of both pressure transmission surfaces is the same, the deflection amount of the entire pressure stay body and the deflection amount of the entire auxiliary pressure stay are the same. As a result, the pressurizing force at the central portion in the longitudinal direction is applied to the pressurizing stay main body and the auxiliary pressurizing stay by an amount proportional to the product of the respective elastic modulus and the secondary moment of section.

  In this embodiment, the pressure transmission surface of the auxiliary pressure stay is provided with a crown shape opposite to the bending direction. As a result, even if both pressure transmission surfaces in the pressurized state have the same bending shape, the amount of bending of the entire auxiliary pressure stay is greater than the amount of bending of the entire pressure stay body by the crown shape. Can do. Since the amount of bending is proportional to the applied pressure, the ratio of the applied pressure at the longitudinal center of the auxiliary pressurizing stay can be increased. As a result, the load applied to the pressurizing stay main body 350 is reduced, and the pressurizing stay main body is reduced. Can be reduced.

  When the crown amount is increased, if the pressure stay main body 350 is used, the top surface portion of the longitudinal center portion becomes high, and the possibility of contact with the inner surface of the fixing belt 130 increases. However, in the case of the auxiliary pressurizing stay 360, there is no problem because the space (364 in FIG. 10) above the auxiliary pressurizing stay that absorbs the bending has a sufficient margin.

  In the pressurization stay configuration of the present embodiment, the amount of deflection of the pressurization stay main body 350 when a pressurizing force of 226 N was applied was obtained in the same manner as in the first embodiment, and was 450 μm. That is, the amount of bending is reduced from that of the second embodiment, which is the same as that of the first embodiment, and the applied pressure is uniformly corrected by the crown amount of the heater holder.

  The results of examining the longitudinal nip shape, the occurrence of gloss unevenness, and the presence or absence of interference between the pressure stay and the sleeve are the same as those in the first embodiment shown in Table 1, preventing gloss unevenness and fixing. It was found that contact prevention between the belt and the pressure stay is compatible.

  As described above, in the present embodiment, a crown shape larger than the pressure stay main body 350 is provided on the pressure transmission surface of the auxiliary pressure stay 360 (FIG. 14). Thereby, even when the auxiliary pressurizing stay 360 is bent more largely than the pressurizing stay main body 350, the applied pressure can be transmitted to the heater holder 132 evenly. For this reason, the bending of the pressure stay can be further reduced as compared with the second embodiment while the storage space for the built-in pressure stay is maintained. As a result, it was possible to prevent the occurrence of uneven glossiness of the image and the interference between the pressure stay and the inner surface of the fixing belt.

  In the present embodiment, the shape of the pressure transmission surface 361 of the auxiliary pressure stay 360 is different from the shape of the pressure transmission surface 216 of the pressure stay main body 350. However, the shape may be as follows. it can. That is, the shape of the pressure receiving surface of the heater holder 132 that receives the auxiliary pressure stay 360 may be different from the shape of the pressure receiving surface of the portion that receives the pressure stay main body 350.

  In other words, the heater holder 132 has a plurality of pressure receiving surfaces that receive pressure from the plurality of members 350 and 351 forming the pressure stay, and the shape of the pressure receiving surfaces is at least one different. A featured configuration may be employed. For example, the same effect as that of the present embodiment can be obtained by providing a larger amount of crown than the pressure receiving surface receiving the pressure stay main body 350 for the pressure receiving surface receiving the auxiliary pressure stay 360 having a large deflection. it can.

(Other embodiments)
In the above-described embodiment, the pressure receiving surface 160 (FIG. 1) of the same height in the heater holder 132 is provided with the pressure transmission surface of the reinforcing portion with increased thickness and the pressure transmission surface of the pressure stay portion before reinforcement. The pressure receiving surfaces 210 and 211 having different heights may be used as shown in FIG. Such a configuration is particularly effective when the pressure receiving surface of the reinforcing portion and the fixing belt are close to each other and a space for providing the pressure receiving surface is insufficient.

  Further, as shown in FIG. 6, the portion 212 corresponding to the pressure transmission surface of the reinforcing portion may be floated without contacting the heater holder 132. In this case, it is not necessary to increase the surface accuracy of the end surface of the reinforcing portion to be welded, and the manufacture becomes easy.

  Further, instead of adding a steel plate as in the present embodiment to increase the thickness, it is also possible to use a steel plate that is originally thick and the top surface portion made thin by grinding to have a similar shape. Further, the pressure stay as in the present embodiment can be formed by a method such as casting.

  Further, as shown in FIG. 7, the thickness of the side surface portion may be increased by further folding back the upstream and downstream side surface portions of the pressure stay. In FIG. 7, the number of times of folding is one time, but the thickness may be increased by folding a plurality of times. In particular, when the diameter of the fixing belt is further reduced and it becomes necessary to further reduce the thickness of the top surface portion of the pressure stay, it is necessary to use a thin steel plate. In that case, since the folding process becomes easier, it is more effective to improve the strength of the side surface by such folding.

  Further, the thickness of the upstream side surface portion of the pressure stay 151 may be different from the thickness of the downstream side surface portion. In particular, when the heating unit is used while being shifted upstream or downstream as shown in FIG. 8, or when the heating unit is used as inclined as shown in FIG. 9, the load applied on the upstream side of the pressure stay 151 is applied. And a load applied to the downstream side is different.

  8 and 9, the load on the downstream side of the pressure stay 151 is increased. In such a case, it is possible to positively reinforce the more flexible one, such as increasing the thickness of the downstream side surface than the thickness of the upstream side surface of the pressure stay 151 in accordance with the difference in load. .

  The fixing belt 130 as the flexible belt member is not limited to the one heated by the heater described in the above-described embodiment, and the fixing belt 130 includes a current-carrying unit and generates heat, or the fixing belt 130 It may generate heat by electromagnetic induction.

  In the above-described embodiment, the pressure roller as the driving roller is used as the pressure member. However, when the fixing belt 130 as the flexible belt member can be spanned and rotated via another driving roller. In this case, a fixed pressure pad may be used as the pressure member.

  In the above-described embodiment, regarding the pressure stay as the skeleton member, the thickness of the upstream side surface portion and the thickness of the downstream side surface portion are larger than the thickness of the top surface portion. Only one of the thicknesses may be thicker than the thickness of the top surface portion.

130 ..Fusing belt (flexible belt member) 131 ..Ceramic heater (heating source) 132 ..Heater holder (backup member) 151 ..Pressure stay (frame member) 201. Pressure member)

Claims (5)

A cylindrical belt,
A nip forming member that contacts the inner surface of the belt;
A roller that forms a nip portion with the nip portion forming member via the belt;
A cross-section perpendicular to the longitudinal direction of the belt is U-shaped, and is a reinforcing member made of metal that is long in the longitudinal direction of the belt and that forms the U-shaped opening, and And a top surface portion that is located farther from the nip portion than the two leg portions and is continuous with the two leg portions, and that supports the nip portion forming member by the two leg portions. When,
Have
In the fixing device for fixing the image to the recording material by heating while conveying the recording material on which the image is formed in the nip portion,
The nip forming member is a heating member for heating the belt,
Wherein said at least hand the thickness of the two legs of the reinforcing member, a fixing device according to claim thicker than the thickness of the top surface portion.   The fixing device according to claim 1, wherein the reinforcing member is formed of a single plate material.   The fixing device according to claim 2, wherein the two leg portions are formed by bending two end portions of the plate material so as to overlap each other.   The fixing device according to claim 1, wherein the two leg portions are formed by overlapping separate plate materials.   The temperature detection member is provided on a surface of the nip portion forming member opposite to a surface in contact with the belt in a region surrounded by the nip portion forming member and the reinforcing member. The fixing device according to any one of 1 to 4.