JP2013054397A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which can rapidly heat a heating member and also easily maintain temperature of the heating member to fixing temperature.SOLUTION: A fixing device 100 comprises: a heating element (a halogen lamp 120) which generates heat; a heating member (a nip plate 130) heated by the heating element so as to be fixing temperature for thermal fixing of a developer image on a recording sheet (paper P); and a backup member (a pressure roller 150) which conveys a recording sheet while sandwiching the recording sheet between the heating member and the backup member. A specific heat change member 170 is disposed in contact with the heating member and has higher specific heat at the fixing temperature than specific heat at temperature lower than transition temperature by performing phase transition at transition temperature near the fixing temperature.

Description

  The present invention relates to a fixing device that thermally fixes a developer image transferred to a recording sheet, and an image forming apparatus including the fixing device.

  As a fixing device used in an electrophotographic image forming apparatus, a nip plate that forms a nip portion between a cylindrical fixing film, a heater disposed in the fixing film, and a pressure roller via the fixing film (Heating member) is known (for example, refer to Patent Document 1). In this fixing device, the developer image on the paper is thermally fixed while conveying the paper (recording sheet) between the fixing film supported by the nip plate and the pressure roller (nip portion).

JP 2008-233886 A

  Incidentally, in the above-described fixing device, it is desirable to reduce the heat capacity (specific heat × mass) of the nip plate in order to quickly heat the nip plate. However, if a member having a small specific heat is simply used as the nip plate, there is a problem that it becomes difficult to control because the temperature change becomes too sensitive when it is desired to maintain the temperature of the nip plate at the fixing temperature.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and an image forming apparatus that can quickly heat a heating member and easily maintain the temperature of the heating member at a fixing temperature.

  The present invention that solves the above problems includes a heating element that generates heat, a heating member that is heated by the heating element so as to have a fixing temperature for thermally fixing a developer image on a recording sheet, and the heating member. And a backup member that sandwiches and conveys the recording sheet between the heating member and the heating member, wherein the heating member causes a phase transition between substantially solid phases at a transition temperature near the fixing temperature. Thus, a specific heat change member having a specific heat larger at the fixing temperature than at a temperature lower than the transition temperature is arranged in contact.

  Here, “carrying and conveying the recording sheet between the heating member and (backup member)” includes a mode in which only the recording sheet is sandwiched between the heating member and the backup member to convey the recording sheet. A mode in which the recording sheet and the fixing film are sandwiched between the heating member and the backup member and the recording sheet is conveyed together with the fixing film is also included.

  According to the present invention, since the specific heat of the specific heat change member provided on the heating member is small until the heating member is heated to the vicinity of the fixing temperature by the heating element, the temperature of the heating member is quickly increased together with the temperature of the specific heat change member. Rise to near the fixing temperature. When the temperature of the heating member and the specific heat change member rises to near the fixing temperature, the specific heat of the specific heat change member changes and increases, so that the temperature of the heating member and the specific heat change member hardly changes, and the heating member and the specific heat change change. The temperature of the member can be easily maintained at a temperature near the fixing temperature.

  According to the present invention, the heating member can be heated quickly, and the temperature of the heating member can be easily maintained at the fixing temperature.

1 is a diagram illustrating a schematic configuration of a laser printer including a fixing device according to an embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. It is a perspective view of a halogen lamp, a nip plate, a reflecting plate, a stay, and a specific heat change member. It is the figure which looked at the nip plate, the reflecting plate, and the stay from the conveyance direction. It is a graph which shows the characteristic of a specific heat change member. It is a graph which shows the temperature change of the nip board at the time of printing control. It is a figure which shows the modification of a heating member.

  Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, the schematic configuration of the laser printer 1 (image forming apparatus) including the fixing device 100 according to the embodiment of the present invention will be described first, and then the detailed configuration of the fixing device 100 will be described.

<Schematic configuration of laser printer>
As shown in FIG. 1, the laser printer 1 includes a main body housing 2 in which a paper sheet 3 as an example of a recording sheet is fed, an exposure device 4, and a toner image (developer) on the paper P. And the fixing device 100 for thermally fixing the toner image on the paper P.

  In the following description, the direction will be described with reference to the user who uses the laser printer. That is, the right side in FIG. 1 is “front”, the left side is “rear”, the front side is “left”, and the back side is “right”. Also, the vertical direction in FIG.

  The paper feed unit 3 is provided in the lower part of the main body housing 2, and includes a paper feed tray 31 that accommodates the paper P, a paper pressing plate 32 that lifts the front side of the paper P, a paper feed roller 33, and a paper feed pad 34. And paper dust removing rollers 35 and 36 and a registration roller 37 are mainly provided. The paper P in the paper feed tray 31 is brought close to the paper feed roller 33 by the paper pressing plate 32 and separated one by one by the paper feed roller 33 and the paper feed pad 34, and the paper dust removing rollers 35, 36 and the registration roller 37. Then, it is conveyed toward the process cartridge 5.

  The exposure apparatus 4 is arranged at the upper part in the main body housing 2 and mainly includes a laser light emitting unit (not shown), a polygon mirror 41 that is rotationally driven, lenses 42 and 43, and reflecting mirrors 44, 45, and 46. In preparation. In the exposure apparatus 4, the laser light (see the chain line) based on the image data emitted from the laser light emitting part is reflected or passed through the polygon mirror 41, the lens 42, the reflecting mirrors 44 and 45, the lens 43 and the reflecting mirror 46 in this order. The surface of the photosensitive drum 61 is scanned at high speed.

  The process cartridge 5 is disposed below the exposure apparatus 4 and is detachably mounted on the main body housing 2 through an opening formed when the front cover 21 provided on the main body housing 2 is opened. Yes. The process cartridge 5 includes a drum unit 6 and a developing unit 7.

  The drum unit 6 mainly includes a photosensitive drum 61, a charger 62, and a transfer roller 63. The developing unit 7 is configured to be detachably attached to the drum unit 6, and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, and a toner that contains toner (developer). The housing part 74 is mainly provided.

  In the process cartridge 5, the surface of the photosensitive drum 61 is uniformly charged by the charger 62 and then exposed by high-speed scanning of the laser light from the exposure device 4, whereby image data is transferred onto the photosensitive drum 61. An electrostatic latent image based on is formed. Further, the toner in the toner container 74 is supplied to the developing roller 71 via the supply roller 72 and enters between the developing roller 71 and the layer thickness regulating blade 73 to form a thin layer of a certain thickness on the developing roller 71. It is carried on.

  The toner carried on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photosensitive drum 61. As a result, the electrostatic latent image is visualized and a toner image is formed on the photosensitive drum 61. Thereafter, the paper P is conveyed between the photosensitive drum 61 and the transfer roller 63, whereby the toner image on the photosensitive drum 61 is transferred onto the paper P.

  The fixing device 100 is provided behind the process cartridge 5. The toner image (toner) transferred onto the paper P is thermally fixed onto the paper P by passing through the fixing device 100. The paper P on which the toner image is thermally fixed is discharged onto the paper discharge tray 22 by the transport rollers 23 and 24.

<Detailed configuration of fixing device>
As shown in FIG. 2, the fixing device 100 includes a fixing film 110, a halogen lamp 120 as an example of a heating element, a nip plate 130 as an example of a nip member (heating member), a reflection plate 140, and a backup member. A pressure roller 150 as an example, a stay 160 as an example of a support member, and a specific heat change member 170.

  The fixing film 110 is an endless (cylindrical) film having heat resistance and flexibility, and both ends of the fixing film 110 are guided by a guide member (not shown).

  The halogen lamp 120 is a known heating element that heats the toner on the paper P by heating the nip plate 130 and the fixing film 110. Inside the fixing film 110, a predetermined amount of heat is supplied from the inner surfaces of the fixing film 110 and the nip plate 130. They are arranged at intervals.

  The nip plate 130 is a plate-like member that receives radiant heat emitted from the halogen lamp 120, and is heated by the halogen lamp 120 to a predetermined fixing temperature (temperature for thermally fixing the toner image on the paper P). It has become. In the present embodiment, the temperature of the nip plate 130 is controlled by the control device 200 (see FIG. 1) by controlling the halogen lamp 120 according to the printing conditions, so that two types of fixing temperatures (FIG. 6) are obtained. The first fixing temperature T1 and the second fixing temperature T2) shown in FIG.

  Here, “switching according to printing conditions (control)” means, for example, control according to the type of paper P (paper size, thickness, etc.), the type of image quality, the type of color to be printed in the case of a color printer, and the like. Is mentioned. In other words, for example, the control is such that the first fixing temperature T1 is set when the paper P is A4 size, and the second fixing temperature T2 is set when the paper P is postcard size.

  The nip plate 130 is disposed so as to be in sliding contact with the inner surface of the cylindrical fixing film 110 and transmits radiant heat received from the halogen lamp 120 to the toner on the paper P through the fixing film 110.

  The nip plate 130 has a thermal conductivity higher than that of a steel stay 160, which will be described later. For example, the nip plate 130 is formed by bending an aluminum plate or the like into a substantially U shape in sectional view. More specifically, the nip plate 130 is bent toward the base portion 131 extending in the front-rear direction (the conveyance direction of the paper P) and upward (the direction from the pressure roller 150 toward the nip plate 130) in a cross-sectional view. The bent portion 132 is mainly included.

  As shown in FIG. 3, the nip plate 130 further includes an insertion portion 133 that extends in a flat plate shape from the right end portion of the base portion 131, and an engagement portion 134 that is formed at the left end portion of the base portion 131. The engaging portion 134 is formed in a U shape in a side view, and an engaging hole 134B is provided in a side wall portion 134A formed by bending upward.

  The specific heat changing member 170 is arranged so as to contact the inner surface 131A (the surface on the halogen lamp 120 side) of the nip plate 130 (base portion 131). The specific heat change member 170 will be described in detail later.

  As shown in FIG. 2, the reflector 140 reflects radiant heat from the halogen lamp 120 (mainly radiated heat radiated in the front-rear direction or upward direction) toward the nip plate 130 (the inner surface 131A of the base portion 131). This member is disposed at a predetermined interval from the halogen lamp 120 so as to surround the halogen lamp 120 inside the fixing film 110.

  By collecting the radiant heat from the halogen lamp 120 on the nip plate 130 with such a reflector 140, the radiant heat from the halogen lamp 120 can be used efficiently, and the nip plate 130 and the specific heat change member 170 are quickly heated. It is possible.

  The reflection plate 140 is formed by curving an aluminum plate or the like in a substantially U shape in cross section, for example, having a high infrared and far infrared reflectance. More specifically, the reflecting plate 140 mainly includes a reflecting portion 141 having a curved shape (substantially U-shaped in cross section) and a flange portion 142 extending from both ends of the reflecting portion 141 along the outer side in the front-rear direction. . In order to increase the thermal reflectance, the reflection plate 140 may be formed using a mirror-finished aluminum plate or the like.

  As shown in FIG. 3, a total of four flange-like locking portions 143 are formed at both ends of the reflection plate 140 in the left-right direction (the width direction of the paper P) (only three are shown). The locking portion 143 is located above the flange portion 142. As shown in FIG. 4, when the nip plate 130, the reflecting plate 140, and the stay 160 are assembled, a plurality of contact portions 163 of the stay 160 described later are provided. It arrange | positions so that it may pinch | interpose (adjacent to the outermost contact part 163A in the left-right direction).

  As a result, even if the reflection plate 140 tries to move left and right due to vibrations when the fixing device 100 is driven, the position of the reflection plate 140 in the left-right direction is restricted by the locking portion 143 coming into contact with the contact portion 163A. The As a result, it is possible to suppress the displacement of the reflecting plate 140 in the left-right direction.

  As shown in FIG. 2, the pressure roller 150 is an elastically deformable member and is disposed below the nip plate 130. The pressure roller 150 forms a nip portion with the fixing film 110 by sandwiching the fixing film 110 with the nip plate 130 in an elastically deformed state.

  The pressure roller 150 is configured to be driven to rotate by a driving force transmitted from a motor (not shown) provided in the main body housing 2. Therefore, the pressure roller 150 sandwiches the fixing film 110 and the paper P between the nip plate 130 and sends them to the rear, whereby the fixing film 110 rotates the pressure roller 150. Accordingly, the paper P is rotated backward and the paper P is conveyed backward.

  Then, the sheet P is conveyed between the pressure roller 150 and the heated nip plate 130 (specifically, the fixing film 110), so that the toner image transferred onto the sheet P is thermally fixed. It has become.

  The stay 160 is a member that secures the rigidity of the nip plate 130 by supporting both end portions 131B of the nip plate 130 (base portion 131) in the front-rear direction via the flange portion 142 of the reflection plate 140. The stay 160 has a shape (substantially U shape in cross section) along the outer surface shape of the reflecting plate 140 (reflecting portion 141) and is disposed so as to cover the reflecting plate 140. Such a stay 160 has relatively high rigidity, for example, is formed by bending a steel plate or the like into a substantially U shape in cross-sectional view.

  At the lower ends of the front wall 161 and the rear wall 162 of the stay 160, as shown in FIG. 3, a plurality of contact portions 163 formed in a substantially comb shape are provided.

  Further, a substantially L-shaped locking portion 165 extending downward and further toward the left is provided at the right end portions of the front wall 161 and the rear wall 162 of the stay 160. Further, a holding portion 167 is provided at the left end of the stay 160 and extends leftward from the upper wall 166 and is bent into a substantially U shape in a side view. Engagement bosses 167B (only one is shown) projecting inward are provided on the inner surfaces of the side wall portions 167A of the holding portion 167.

  As shown in FIGS. 2 and 3, a total of four abutting bosses 168 projecting inward are provided at both ends in the left-right direction of the inner surfaces of the front wall 161 and the rear wall 162 of the stay 160. The abutting boss 168 abuts on the reflecting plate 140 (reflecting portion 141) in the front-rear direction. As a result, even if the reflection plate 140 tries to move back and forth due to vibrations when the fixing device 100 is driven, the position of the reflection plate 140 in the front-rear direction is restricted by contacting the contact boss 168. As a result, it is possible to suppress the displacement of the reflector plate 140 in the front-rear direction.

  When the reflecting plate 140 and the nip plate 130 are assembled to the stay 160 described above, the reflecting plate 140 is first attached to the stay 160 so as to be fitted. Since the abutting boss 168 is provided on the inner surfaces of the front wall 161 and the rear wall 162 of the stay 160, the reflecting plate 140 is temporarily held by the stay 160 when the abutting boss 168 contacts the reflecting plate 140. The

  Thereafter, as shown in FIG. 4, the insertion portion 133 of the nip plate 130 is inserted between the locking portions 165 of the stay 160 to engage the base portion 131 (both end portions 131B) with the locking portions 165, and then Then, the engaging portion 134 (engaging hole 134B) of the nip plate 130 and the holding portion 167 (engaging boss 167B) of the stay 160 are engaged.

  Thereby, the both ends 131 </ b> B of the base portion 131 are supported by the locking portion 165 and the engaging portion 134 is held by the holding portion 167, so that the nip plate 130 is held by the stay 160. The reflecting plate 140 is held by the stay 160 in a state where the flange portion 142 is sandwiched between the nip plate 130 and the stay 160.

  As a result, even if the reflection plate 140 tries to move up and down due to vibrations when the fixing device 100 is driven, the flange portion 142 is sandwiched between the nip plate 130 and the stay 160 so that the reflection plate 140 is moved in the vertical direction. The position of is regulated. As a result, it is possible to suppress the positional deviation of the reflecting plate 140 in the vertical direction and to fix the position of the reflecting plate 140 with respect to the nip plate 130.

  As shown in FIG. 3, the specific heat changing member 170 has a transition temperature Tt in the vicinity of the higher (highest) first fixing temperature T1 of the two types of fixing temperatures T1 and T2, more specifically as shown in FIG. It is made of a material that undergoes a phase transition at a transition temperature Tt between the first fixing temperature T1 and the second fixing temperature T2. Here, the “temperature near the first fixing temperature T1” is, for example, preferably a temperature within a range of ± 20 ° C. from the first fixing temperature T1, more preferably a range of ± 15 ° C., and further a range of ± 10 ° C. preferable.

  The specific heat change member 170 undergoes a phase transition, so that the specific heat at the first fixing temperature T1 is larger than that at the temperature lower than the transition temperature Tt. That is, the specific heat change member 170 has a specific heat that is small in the room temperature region (at room temperature) and is much larger than the specific heat at the room temperature when the first fixing temperature T1 is much higher than that at the room temperature. In other words, the specific heat change member 170 is formed of a material whose specific heat change rate (inclination) becomes abrupt near the transition temperature Tt.

  As a result, as shown in FIG. 6, when the temperature is lower than the transition temperature Tt, the nip plate 130 rises rapidly together with the specific heat change member 170, and the specific heat of the specific heat change member 170 rapidly exceeds the transition temperature Tt. As the temperature increases, the temperature rise of the specific heat change member 170 and the nip plate 130 in contact with the specific heat change member 170 becomes moderate. That is, since the temperature change of the nip plate 130 becomes dull, it becomes easy to maintain the nip plate 130 at the first fixing temperature T1.

  Further, since the transition temperature Tt is higher than the second fixing temperature T2, the temperature of the nip plate 130 can be rapidly heated to the second fixing temperature T2.

  In the present embodiment, the first fixing temperature T1 is set to 145 ° C., and the second fixing temperature T2 is set to 130 ° C. Further, as the specific heat changing member 170, a polycarbonate that undergoes a glass transition in the vicinity of 140 ° C. and whose specific heat changes due to the glass transition is adopted.

  Further, as shown in FIG. 3, the specific heat changing member 170 is provided separately from the stay 160, and is disposed at a portion (a central portion in the left-right direction) of the nip plate 130 that is not supported by the stay 160. . Therefore, even when the specific heat change member 170 is phase-transitioned and softened, the support of the nip plate 130 by the stay 160 can be maintained.

  Further, the specific heat changing member 170 is provided at a portion (inner surface 131 </ b> A) that is not in contact with the pressure roller 150. Therefore, even when the specific heat change member 170 is phase-transformed and softened, it is possible to prevent the specific heat change member 170 from being crushed between the nip plate 130 and the pressure roller 150.

  The specific heat change member 170 is formed of a material (transparent polycarbonate) that can transmit light (electromagnetic waves) emitted from the halogen lamp 120. As a result, the nip plate 130 can be efficiently heated by the halogen lamp 120.

  Furthermore, the specific heat change member 170 is provided on a part of the inner surface 131A so that the inner surface 131A of the nip plate 130 is exposed. As a result, a portion of the nip plate 130 where the specific heat changing member 170 is not provided can be directly heated by the halogen lamp 120.

  In particular, in the present embodiment, the specific heat change member 170 is formed in a lattice shape having a plurality of openings 171 exposing the inner surface 131A of the nip plate 130. Accordingly, the nip plate 130 can be directly heated from the opening 171 by the halogen lamp 120, and the specific heat change member 170 is formed to be large over the entire area of the inner surface 131A of the nip plate 130 so that the effect of the specific heat change member 170 is sufficiently exhibited. It is possible.

  The specific heat change member 170 may be fixed to the nip plate 130 by any method, for example, fixed with an adhesive having a property close to the specific heat change member 170 (a property in which the specific heat changes in substantially the same manner). Alternatively, the specific heat change member 170 may be melted and fixed directly to the nip plate 130. Further, a part of the specific heat change member may be fitted and fixed in the hole formed in the nip plate.

According to the above, the following effects can be obtained in the present embodiment.
Since the specific heat changing member 170 whose specific heat changes greatly in the vicinity of the first fixing temperature T1 is provided so as to come into contact with the nip plate 130, the nip plate 130 can be rapidly heated to the first fixing temperature T1, and the nip plate It becomes easy to maintain the temperature of 130 at the first fixing temperature T1.

  Since the specific heat change member 170 is provided separately from the stay 160 and is disposed in a portion of the nip plate 130 that is not supported by the stay 160, the stay 160 is not affected even if the specific heat change member 170 undergoes phase transition and becomes soft. Therefore, the support of the nip plate 130 can be maintained.

  Since the specific heat change member 170 is provided in a portion that is not in contact with the pressure roller 150, even if the specific heat change member 170 is softened by phase transition, the specific heat change between the nip plate 130 and the pressure roller 150. It is possible to prevent the member 170 from being crushed.

  Since the specific heat change member 170 is provided on the inner surface 131A of the nip plate 130 and is formed of a material that can transmit light emitted from the halogen lamp 120, the nip plate 130 can be efficiently heated by the halogen lamp 120. .

  Since the specific heat changing member 170 is provided on a part of the inner surface 131A so that the inner surface 131A of the nip plate 130 is exposed, a portion of the nip plate 130 where the specific heat changing member 170 is not provided is directly connected by the halogen lamp 120. The temperature of the nip plate 130 can be quickly raised.

  Since the specific heat change member 170 is formed in a lattice shape having a plurality of openings 171 that expose the inner surface 131A of the nip plate 130, the nip plate 130 can be directly heated by the halogen lamp 120 from the openings 171 and the specific heat change member. 170 can be formed over the entire area of the inner surface 131 </ b> A of the nip plate 130 so that the effect of the specific heat change member 170 can be sufficiently exerted.

  Since the transition temperature Tt of the specific heat change member 170 is a temperature around the first fixing temperature T1 (that is, the highest fixing temperature of the two types of fixing temperatures) higher than the second fixing temperature T2, the nip plate 130 has the highest temperature. It is possible to quickly heat up to the first fixing temperature T1.

In addition, this invention is not limited to the said embodiment, It can utilize with various forms so that it may illustrate below.
In the above embodiment, the specific heat change member 170 is provided on the nip plate 130. However, the present invention is not limited to this, and any specific heat change member may be provided on any heating member that is heated by a heating element. Good. For example, as shown in FIG. 7, the specific heat changing member 270 may be provided on the inner peripheral surface 231 of the cylindrical heating roller 230. Here, the heating roller 230 is a component formed in a hollow cylindrical shape, and is formed of, for example, aluminum.

  The heating roller 230 includes the halogen lamp 120 as in the above-described embodiment, and is heated by the halogen lamp 120. As the specific heat changing member 270, a member formed in a lattice shape as in the above-described embodiment and provided over the entire inner peripheral surface of the heating roller 230 can be employed. Even if it is this form, the effect similar to the said embodiment can be acquired.

  In the form in which the heating roller 230 is adopted, examples of the support member include a bearing that supports both ends of the heating roller 230.

  Further, the heating members such as the inner peripheral surface 231 of the heating roller 230 and the inner surface 131A of the nip plate 130 of the above-described embodiment are coated with black or a heat absorbing member different from the specific heat changing members 170 and 270 is used. It may be provided. According to this, the radiant heat from the halogen lamp 120 can be efficiently absorbed by the heating member.

  In the above embodiment, polycarbonate is adopted as the specific heat change member, but the present invention is not limited to this, and any material such as other resin or metal may be used as long as it has a transition temperature corresponding to the fixing temperature. Good. Moreover, as long as specific heat changes, the kind of phase transition is not ask | required.

  In the embodiment, the specific heat change member 170 is provided on the inner surface 131A of the nip plate 130. However, the present invention is not limited to this, and for example, the specific heat change is applied to a portion of the outer surface (lower surface) of the nip plate outside the nip portion. A member may be provided. Further, when the specific heat change member is formed of a material that does not soften while it is maintained at the maximum fixing temperature, it is between the support member (stay 160) and the nip plate or between the nip plate and the pressure roller. A specific heat changing member may be provided.

In the above-described embodiment, the reflecting plate 140 and the stay 160 are provided. However, the present invention is not limited to this, and the reflecting plate and the stay may be omitted.
In the embodiment, the halogen lamp 120 (halogen heater) is exemplified as the heating element. However, the present invention is not limited to this, and may be, for example, an infrared heater or a carbon heater.

In the embodiment, the plate-shaped nip plate 130 is exemplified as the nip member. However, the present invention is not limited to this, and a thick member that is not plate-shaped may be employed.
In the embodiment, the pressure roller 150 is exemplified as the backup member. However, the present invention is not limited to this, and may be, for example, a belt-like pressure member.

In the embodiment, the paper P such as plain paper or postcard is exemplified as the recording sheet, but the present invention is not limited to this, and may be, for example, an OHP sheet.
In the above embodiment, the specific heat change member 170 has a lattice shape, but the present invention is not limited to this, and the shape and number can be arbitrarily set. Depending on the shape of the specific heat change member, for example, the specific heat change member may have a plate shape that covers substantially the entire surface of the nip plate.

  In the above embodiment, the laser printer 1 is exemplified as the image forming apparatus including the fixing device of the present invention. However, the present invention is not limited to this, and may be, for example, an LED printer that performs exposure using LEDs. A copying machine other than a printer or a multifunction machine may be used. In the above-described embodiment, an image forming apparatus that forms a monochrome image is exemplified. However, the present invention is not limited to this, and an image forming apparatus that forms a color image may be used.

DESCRIPTION OF SYMBOLS 100 Fixing device 120 Halogen lamp 130 Nip plate 131A Inner surface 150 Pressure roller 160 Stay 170 Specific heat change member 171 Opening portion T1 First fixing temperature T2 Second fixing temperature Tt Transition temperature

Claims (10)

A heating element that emits heat;
A heating member heated by the heating element so as to have a fixing temperature for thermally fixing the developer image on the recording sheet;
A fixing device comprising a backup member that sandwiches and conveys the recording sheet with the heating member,
In the heating member,
A specific heat change member that makes a specific heat larger at the fixing temperature than at a temperature lower than the transition temperature due to a phase transition between the substantially solid phases at a transition temperature near the fixing temperature. The fixing device is characterized in that the fixing device is arranged.   The fixing device according to claim 1, wherein the phase transition is a glass transition. A support member for supporting the heating member;
The said specific heat change member is provided separately from the said supporting member, and is arrange | positioned in the site | part which is not supported by the said supporting member among the said heating members, The Claim 1 or Claim 2 characterized by the above-mentioned. Fixing device.   The fixing device according to claim 1, wherein the specific heat change member is provided in a portion that is not in contact with the backup member.   The said specific heat change member is provided in the surface at the side of the said heat generating body of the said heating member, and is formed with the material which can permeate | transmit the electromagnetic waves emitted from the said heat generating body. The fixing device according to claim 1. The heating member is a cylindrical heating roller in which the heating element is disposed,
The fixing device according to claim 1, wherein the specific heat changing member is provided on an inner peripheral surface of the heating roller. The heating member is a nip member that sandwiches a cylindrical fixing film with the backup member,
The fixing device according to claim 1, wherein the specific heat change member is provided on a surface of the nip member on the heating element side.   The said specific heat change member is provided in a part of the said surface so that the surface by the side of the said heat generating body of the said heating member may be exposed, The said any one of Claims 5-7 characterized by the above-mentioned. Fixing device.   The fixing device according to claim 8, wherein the specific heat changing member is formed in a lattice shape having an opening that exposes a surface on the heating element side of the heating member. A fixing device according to any one of claims 1 to 9,
A control device that executes control for switching the temperature of the heating member between at least two types of fixing temperatures according to printing conditions,
The image forming apparatus according to claim 1, wherein a transition temperature of the specific heat change member is a temperature in the vicinity of the highest fixing temperature among at least two fixing temperatures.

Images