JP2014115511A - Fixing device and image forming apparatus including the fixing device - Google Patents

Abstract

The present invention provides a fixing device capable of satisfying both good fixability during intermittent paper feeding and productivity of small-size paper during continuous paper feeding.
A heating source, a cylindrical heating rotator that rotates while being in contact with the heating source, and a fixing rotator that forms a heating nip portion N2 with the heating rotator together with the heating source. And a backup member 50 that forms a fixing nip portion N1 together with the fixing rotator, heats the fixing rotator at the heating nip portion, and carries an unfixed toner image T at the fixing nip portion. In the fixing device for fixing the unfixed toner image on the recording material by heating while conveying P, the backup member is a member having a predetermined thermal conductivity, and the radiant heat generated by the heating rotator is directed toward the heating rotator. The radiant heat reflecting member 70 is reflected at least at a part around the heating rotator in the longitudinal direction perpendicular to the recording material conveyance direction.
[Selection] Figure 2

Description

  The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer, and an image forming apparatus including the fixing device.

  As a fixing device mounted on an electrophotographic copying machine or printer, an external heating type fixing device is known. Patent Document 1 describes this type of fixing device. This type of fixing device includes a fixing roller, a pressure roller that contacts the fixing roller to form a fixing nip portion, and a heating member that contacts the fixing roller to form a heating nip portion. As the heating member, a rotatable endless belt that moves while being in contact with a ceramic heater, a rotatable heating roller including a halogen heater, or the like is used. The recording material carrying the unfixed toner image is heated while being nipped and conveyed at the fixing nip portion of the fixing device, whereby the toner image on the recording material is heated and fixed on the recording material.

  In the external heating type fixing device, since the elastic layer of the fixing roller is thick, the fixing roller easily follows the unevenness of the recording material. Therefore, there is a merit for image quality improvement such as high gloss.

JP 2010-134054 A

  However, in recent years, as the paper passing speed and throughput of copiers and printers have increased, the external heating type fixing device has good fixability during intermittent paper passing and small size paper during continuous paper passing. It may be difficult to achieve a balance with productivity. Here, “intermittent paper feeding” refers to a printing operation condition that stops instantaneously every time one sheet is printed. Continuous paper passing means a printing operation condition in which continuous printing is performed and no instantaneous pause is performed for each sheet.

  When intermittent paper feeding is performed, a high temperature offset may occur at the center of the recording material in the longitudinal direction perpendicular to the recording material conveyance direction, and a low temperature offset may occur at both ends of the recording material. This is considered to be due to heat dissipation.

  The external heating type fixing device is a component of a component as compared with an internal heating type fixing device having a fixing roller including a heating member and a pressure roller that contacts the fixing roller to form a nip portion. Large surface area and heat capacity. When the surface area of the fixing roller or pressure roller that maintains a high temperature is increased, heat is likely to be radiated, so that the temperature at the end portion in the longitudinal direction of the fixing roller or pressure roller having the end surface is lower than the central portion in the longitudinal direction. As a result, in the longitudinal direction of the fixing roller and the pressure roller, a high temperature offset at the center of the image of the recording material and a low temperature offset at the end of the image occur simultaneously, resulting in an image defect. This phenomenon is prominent when the fixing roller and the pressure roller are kept at a high temperature and the heat is dissipated for a long time, that is, during intermittent paper feeding.

  On the other hand, the productivity of small-size paper may be reduced during continuous paper feeding. When the small-size paper is passed, the temperature of the area where the small-size paper of the fixing roller is not passed (hereinafter referred to as a non-paper passing portion) rises. In the non-sheet passing portion, the amount of heat is not absorbed by the small size paper, and therefore the temperature rises (non-sheet passing portion temperature rise). Since the fixing roller may be damaged if the temperature of the non-sheet passing part is excessively high, measures are taken to reduce the temperature rise of the non-sheet passing part by reducing productivity (throughput). Impairs sex.

  The temperature rise of the non-sheet passing portion tends to increase as the throughput increases. This is because the amount of heat necessary for the area through which the paper is passed increases and the amount of heat given to the non-sheet passing portion also increases. The temperature rise of the non-sheet passing portion is higher as the longitudinal thermal conductivity of the fixing roller or the pressure roller is larger. However, for the elastic layer of the fixing roller and pressure roller, silicone rubber is often selected from the viewpoint of heat resistance and durability, and the thermal conductivity of silicone rubber is sufficient to alleviate the temperature rise at the non-sheet passing portion. Not.

  In order to improve the productivity of small size paper, if high thermal conductivity filler is added to the silicone rubber of the pressure roller to increase the thermal conductivity, high temperature offset and low temperature offset will occur at the same time during intermittent paper feeding. To do. In other words, there is a trade-off relationship between the productivity of small-size paper during continuous paper feeding and the good fixability during intermittent paper feeding.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that can achieve both good fixability during intermittent paper feeding and productivity of small-size paper during continuous paper feeding, and an image forming apparatus including the fixing device. There is.

In order to achieve the above object, the configuration of the fixing device according to the present invention is as follows.
(1): A fixing device used in an image forming apparatus that forms an image on a recording material, the heating source, a cylindrical heating rotating body that rotates while being in contact with the heating source, and the heating together with the heating source A fixing rotator that forms a heating nip portion with the rotator interposed therebetween, and a backup member that forms a fixing nip portion together with the fixing rotator, and the fixing rotator is heated at the heating nip portion, and the fixing In a fixing device that fixes a non-fixed toner image on a recording material by heating while conveying a recording material carrying an unfixed toner image in a nip portion, the backup member is a member having a predetermined thermal conductivity, and the heating rotation A radiant heat reflecting member that reflects radiant heat generated by a body toward the heating rotator is provided at least at a part around the heating rotator in a longitudinal direction perpendicular to the recording material conveyance direction. To.

The configuration of the image forming apparatus according to the present invention for achieving the above object is as follows:
(2): In an image forming apparatus having an image forming unit that forms an image on a recording material and a fixing unit that fixes an image formed on the recording material to the recording material, the fixing unit is described in (1) above. The fixing device is provided.

  According to the present invention, it is possible to provide a fixing device that can achieve both good fixability during intermittent paper feeding and productivity of small-size paper during continuous paper feeding, and an image forming apparatus including the fixing device. realizable.

Cross-sectional view showing schematic configuration of image forming apparatus 1 is a cross-sectional view illustrating a schematic configuration of a fixing device according to a first embodiment. 1 is a cross-sectional view illustrating a schematic configuration of a ceramic heater used in a fixing device according to a first embodiment. Explanatory drawing showing a ceramic heater and an energization control system used in the fixing device according to the first embodiment. Explanatory drawing showing the time change of the temperature of the fixing roller of the fixing device according to the first embodiment. Explanatory drawing showing the positional relationship of the fixing cover and reflecting plate of the fixing device which concerns on Example 1 in the longitudinal direction. Cross-sectional view showing schematic configuration of comparative fixing device FIG. 6 is a diagram illustrating the relationship between the temperature difference between the center and end portions of the fixing roller of the fixing device according to the first embodiment and the productivity of small size paper. FIG. 6 is a diagram illustrating the relationship between the heat capacity of the pressure plate of the fixing device according to the first embodiment and the temperature difference between the center and the end of the fixing roller. FIG. 6 is a diagram illustrating the relationship between the thermal conductivity of the pressure plate of the fixing device according to the first embodiment and the temperature difference between the center and the end of the fixing roller. FIG. 6 is a diagram illustrating the relationship between the longitudinal width of the reflector of the fixing device according to the first embodiment and the temperature difference between the center and the end of the fixing roller. FIG. 7 is a cross-sectional view illustrating a schematic configuration of a fixing device according to the second embodiment.

[Example 1]
(1) Example of Image Forming Apparatus FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus equipped with a fixing device according to the present invention. This image forming apparatus is an electrophotographic laser beam printer. The recording material conveyance mode of this image forming apparatus is a central conveyance standard for conveying the recording material by aligning the center of the recording material with the center of the recording material conveyance path in the longitudinal direction orthogonal to the recording material conveyance direction of the image forming apparatus. (Central paper feed standard).

  The image forming apparatus shown in the present embodiment includes an image forming unit A that forms an image on a recording material, and a fixing unit (hereinafter referred to as a fixing device) B that fixes an image formed on the recording material to the recording material. doing.

  The image forming unit A uses first, fourth, and fourth image forming stations Pa, Pb, Pc, and Pd that form toner images using cyan, magenta, yellow, and black toners as developers in predetermined directions. This is an in-line device arranged in a line. Each of the image forming stations Pa, Pb, Pc, and Pd has a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 117 as an image carrier.

  In each of the image forming stations Pa to Pd, a drum charger 119 as a charging member and a scanning exposure device 107 as an exposure unit are provided around the outer peripheral surface (surface) of the photosensitive drum 117. A developing device 120 as a developing unit and a drum cleaner 122 are provided around the surface of the photosensitive drum 117. An intermediate transfer belt 123 as a conveying member is provided so as to straddle the photosensitive drum 117. The intermediate transfer belt 123 is wound around a driving roller 125a and a secondary transfer counter roller 125b.

  A primary transfer roller 124 as a first transfer member is provided on the inner peripheral surface (inner surface) side of the intermediate transfer belt 123 so as to sandwich each photosensitive drum 117 and the intermediate transfer belt 123. On the outer peripheral surface (front surface) side of the intermediate transfer belt 123, a secondary transfer roller 121 as a second transfer member is provided so as to sandwich the secondary transfer counter roller 125b and the intermediate transfer belt 123.

  In the image forming apparatus according to the present exemplary embodiment, the control unit 101 executes a predetermined image forming sequence in response to a print command output from an external device (not shown) such as a host computer, a network terminal, or an external scanner. The control unit 101 includes a CPU and a memory such as a ROM and a RAM. The memory stores an image formation sequence, various programs necessary for image formation, and the like.

  The image forming operation of the image forming apparatus of this embodiment will be described with reference to FIG. The control unit 101 sequentially drives the image forming stations Pa, Pb, Pc, and Pd of the image forming unit A according to an image forming sequence that is executed in response to a print command. First, each photosensitive drum 117 is rotated in the arrow direction at a predetermined peripheral speed (process speed), and the intermediate transfer belt 123 is driven in the arrow direction at a peripheral speed corresponding to the rotational peripheral speed of each photosensitive drum 117 by the driving roller 125a. It is rotated.

  In the cyan image forming station Pa for the first color, the surface of the photosensitive drum 117 is uniformly charged to a predetermined polarity and potential by the drum charger 119. Next, the scanning exposure device 107 scans and exposes the charged surface of the photosensitive drum 117 with laser light corresponding to image data (image information) output from the external device. As a result, an electrostatic latent image (electrostatic image) corresponding to the image data is formed on the charged surface of the photosensitive drum 117. The electrostatic latent image is developed by the developing device 120 using cyan toner. As a result, a cyan toner image (development image) is formed on the surface of the photosensitive drum 117.

  The same steps of charging, exposing, and developing are also performed at the second color magenta image forming station Pb, the third color cyan yellow image forming station Pc, and the fourth color black image forming station Pd. Each color toner image formed on the surface of each photosensitive drum 117 is sequentially transferred onto the surface of the intermediate transfer belt 123 by the primary transfer roller 124 at a primary transfer nip portion between the surface of the photosensitive drum 117 and the surface of the intermediate transfer belt 123. Is done. As a result, a full-color toner image is carried on the surface of the intermediate transfer belt 123.

  The toner remaining on the surface of the photosensitive drum 117 is removed by the drum cleaner 122 on the surface of the photosensitive drum 117 after the toner image is transferred, and is used for the next image formation.

  On the other hand, a recording material P (hereinafter referred to as a sheet) P such as recording paper is fed from the feeding cassette 102 one by one by a feeding roller 105 and conveyed to a registration roller 106. The sheet P is conveyed by the registration roller 106 to a secondary transfer nip portion between the surface of the intermediate transfer belt 123 and the outer peripheral surface (front surface) of the secondary transfer roller 121. In this conveying process, the toner image on the surface of the intermediate transfer belt 123 is transferred onto the sheet P by the secondary transfer roller 121. As a result, an unfixed full-color unfixed toner image is carried on the sheet P.

  The sheet P carrying the full-color unfixed toner image is introduced into a fixing nip portion N1 (described later) of the fixing device B. Then, heat and nip pressure are applied to the unfixed toner image while the sheet P is nipped and conveyed at the fixing nip portion N1, whereby the unfixed toner image on the sheet P is heated and fixed to the sheet P. The sheet P exiting the fixing nip portion N1 is discharged onto the discharge tray 112 by the discharge roller 111.

(2) Fixing device (fixing unit) B
In the following description, regarding the fixing device and the members constituting the fixing device, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. The longitudinal width is a dimension in the longitudinal direction. The short width is a dimension in the short direction.

  FIG. 2 is a cross-sectional view illustrating a schematic configuration of the fixing device B according to the present exemplary embodiment. FIG. 3 is a cross-sectional view showing a schematic configuration of the ceramic heater 15 used in the identification deposition apparatus B. FIG. 4 is an explanatory diagram showing the ceramic heater 15 and the energization control system. The fixing device 109 is an external heating type fixing device.

  The fixing device 109 shown in this embodiment includes a fixing roller (fixing rotator) 30, a heating unit (heating member) 10, and a pressure unit (backup member) 50. Further, it includes a fixing cover (heating rotator cover) 60, a radiant heat reflecting plate (radiant heat reflecting member (hereinafter referred to as a reflecting plate)) 70, and the like.

  The fixing roller 30 is a member that is long in the longitudinal direction, and has a longitudinal width of 225 mm and an outer diameter of 18 mm. The fixing roller 30 has a round shaft-shaped cored bar 30A made of a metal material such as iron, SUS, or aluminum. An elastic layer 30B mainly composed of silicone rubber or the like is formed on the outer peripheral surface between the shaft portions at both ends in the longitudinal direction of the core metal 30A, and PTFE, PFA, FEP or the like is formed on the outer peripheral surface of the elastic layer 30B. A release layer 30C as a main component is formed.

  The fixing roller 30 has shafts at both ends in the longitudinal direction of the core metal 30A supported rotatably on side plates (not shown) on both sides in the longitudinal direction of an apparatus frame (not shown) via bearings (not shown). . Accordingly, the fixing roller 30 has the elastic layer 30B on the cored bar side (rotational center axis side) of the cored bar 30A that serves as the rotational center axis of the fixing roller 30.

  The heating unit 10 includes a ceramic heater (heating source (hereinafter referred to as a heater)) 15, a cylindrical heating film (heating rotating body) 16, a heating film guide (rotating holding member for heating rotating body) 19, and the like. doing. The heater 15, the heating film 16, and the heating film guide 19 are all members that are long in the longitudinal direction.

  The heating film guide 19 is formed in a substantially concave shape in cross section using a predetermined heat resistant material. In this embodiment, LCP is used as the heat resistant material. Then, both ends in the longitudinal direction of the heating film guide 19 are supported by side plates on both sides in the longitudinal direction of the apparatus frame. The heating film guide 19 is configured to guide the rotation of the heating film 16 with arcuate guides 19B provided on both sides in the short direction.

  The heater 15 is supported by a groove 19A provided along the longitudinal direction at the center of the lower surface of the heating film guide 19 in the short direction. The heating film 16 is loosely fitted on the heating film guide 19 supporting the heater 15 without tension. The heating film guide 19 is configured to guide the rotation of the heating film 16 with arcuate guides 19B provided on both sides in the short direction.

  As shown in FIG. 3, the heater 15 has a thin heater substrate 15 </ b> A mainly composed of ceramic such as alumina or aluminum nitride. On the substrate surface of the heater substrate 15A on the heating film 16 side, an energization heating resistor 15B mainly composed of silver, palladium or the like is provided along the longitudinal direction of the heater substrate 15A. In addition, a protective layer 15C mainly composed of a heat-resistant resin such as glass, fluorine resin, or polyimide is provided on the surface of the substrate 15A so as to cover the energization heating resistor 15B.

  The heating film 16 has a heating film 16 having a longitudinal width of 235 mm and an outer diameter of 18 mm. As a layer structure of the heating film 16, a two-layer structure is adopted in which the outer peripheral surface of an endless belt-like film base layer mainly composed of polyimide is covered with an endless belt-shaped surface layer mainly composed of PFA.

  The heating unit 10 is disposed in parallel with the fixing roller 30 above the fixing roller 30. Then, both end portions in the longitudinal direction of the heating film guide 19 are urged by a pressure spring (not shown) in a vertical direction perpendicular to the generatrix direction of the fixing roller 30, and the heating film 16 is applied to the outer surface of the protective layer 15 </ b> C of the heater 15. The outer peripheral surface (surface) of the fixing roller 30 is brought into contact (contacted) in a pressurized state. As a result, the elastic layer 30B of the fixing roller 30 is crushed and elastically deformed at a position corresponding to the outer surface of the protective layer 15C of the heater 15, and the surface of the fixing roller 30 and the outer peripheral surface (surface) of the heating film 16 have a predetermined short side. A heating nip portion N2 having a width is formed.

  The pressure unit 50 includes a cylindrical pressure film (pressure rotator) 51, a pressure film guide (rotation holding member for pressure rotator) 52, a pressure plate (pressure member) 53, and the like. ing. The pressure film guide 52 is formed in a substantially inverted concave shape in cross section using a predetermined heat resistant material. In this embodiment, LCP is used as the heat resistant material. Then, both end portions in the longitudinal direction of the pressure film guide 52 are supported by side plates on both sides in the longitudinal direction of the apparatus frame. The pressure film guide 52 guides the rotation of the pressure film 51 by arcuate guides 52B provided on both sides in the short direction.

  The pressure plate 53 is formed in a plate shape from a predetermined high heat conductive material. The pressure plate 53 is supported by a groove 52A provided along the longitudinal direction at the center of the upper surface of the pressure film guide 52 in the short direction. The pressure film 51 is loosely fitted on the pressure film guide 52 that supports the pressure plate 53 without tension.

  The pressure plate 53, the pressure film 51, and the pressure film guide 52 are all members that are long in the longitudinal direction.

  The pressurizing film 51 has a longitudinal width of 235 mm and an outer diameter of 18 mm. As the layer configuration of the pressure film 51, a two-layer structure is adopted in which the outer peripheral surface of an endless belt-shaped film base layer mainly composed of polyimide is covered with an endless belt-shaped surface layer mainly composed of PFA.

  The pressure plate 53 is formed of a high heat conductive member such as aluminum having a longitudinal width of 240 mm, a short width of 10 mm, and a thickness of 1 mm. The material is preferably a material having a low heat capacity and a high thermal conductivity.

  The pressure unit 50 is disposed below the fixing roller 30 in parallel with the fixing roller 30. Then, both ends in the longitudinal direction of the pressure film guide 52 are urged by a pressure spring (not shown) in the vertical direction perpendicular to the generatrix direction of the fixing roller 30, and the pressure film 51 is fixed on the flat surface of the pressure plate 53. The surface of the roller 30 is brought into contact (contact) in a pressurized state. As a result, the elastic layer 30B of the fixing roller 30 is crushed and elastically deformed at a position corresponding to the flat surface of the pressure plate 53, and the surface of the fixing roller 30 and the outer peripheral surface (surface) of the pressure film 51 have a predetermined short width. A fixing nip portion N1 is formed.

  As shown in FIG. 6, the fixing cover 60 is a member that is long in the longitudinal direction. The longitudinal width of the fixing cover 60 is 235 mm which is the same as that of the heating film 16. The fixing cover 60 is formed in a substantially inverted concave shape in cross section having a height larger than the outer diameter of the heating film 16 (see FIG. 2), and covers the entire longitudinal area of the surface of the heating film 16. The fixing cover 60 covers the entire longitudinal area of the surface of the heating film 16, and device frame support portions (not shown) provided outside both longitudinal ends of the fixing cover 60 have both longitudinal sides of the apparatus frame. Is supported by the side plate. The material of the fixing cover 60 is a heat resistant resin.

  The distance between the inner surface of the fixing cover 60 on the heating film 16 side and the surface of the heating film 16 is about 5 to 15 mm. The emissivity (reflectance) of the inner surface of the fixing cover 60 is preferably greater than 0.9. The technical meaning of the emissivity of the fixing cover 60 will be described in detail in (5) below.

  A reflection plate 70 is attached to the inner surface of the fixing cover 60 so as to cover the periphery of both ends 16 a in the longitudinal direction of the surface of the heating film 16. The reflection plate 70 has a longitudinal width of 50 mm and is formed of an aluminum thin film or thin plate. FIG. 6 shows the positional relationship between the fixing cover 60 and the reflecting plate 70 in the longitudinal direction.

  As shown in FIG. 6, the reflecting plate 70 occupies two left and right regions of 67.5 to 117.5 mm from the position of the longitudinal center of the fixing cover 60 toward the end in the longitudinal direction. The two regions on the left and right are regions that face the longitudinal end 16a of the heating film 16 in the radial direction of the heating film 16, respectively. That is, the reflecting plate 70 is disposed so as to face at least a part around the heating film 16 in the longitudinal direction of the heating film 16, that is, the both longitudinal ends 16 a of the heating film 16 in the radial direction of the heating film 16. .

  The left and right reflectors 70 reflect the radiant heat generated by the heating film 16 toward the corresponding longitudinal end 16a of the surface of the heating film 16. The reflector 70 preferably has an emissivity (reflectance) smaller than 0.1. The technical meaning of the emissivity of the reflecting plate 70 will be described in detail in the section (5) described later.

  The heating and fixing operation of the fixing device B will be described with reference to FIGS.

  The control unit 101 rotationally drives a drive motor (not shown) as a drive source in accordance with an image forming sequence executed in response to a print command. The rotation of the output shaft of the drive motor is transmitted to the core metal 30A of the fixing roller 30 through a predetermined gear train (not shown). As a result, the fixing roller 30 rotates in the arrow direction at a peripheral speed (process speed) of 200 mm / sec.

  The rotation of the fixing roller 30 is transmitted to the pressure film 51 by the frictional force between the surface of the fixing roller 30 and the surface of the pressure film 51 at the fixing nip portion N1. As a result, the pressure film 51 rotates in the direction of the arrow following the rotation of the fixing roller 30 while the inner peripheral surface (inner surface) of the pressure film 51 is in contact with the flat surface of the pressure plate 53.

  The rotation of the fixing roller 30 is transmitted to the heating film 16 by the frictional force between the surface of the fixing roller 30 and the surface of the heating film 16 at the heating nip portion N2. As a result, the heating film 16 rotates in the direction of the arrow following the rotation of the fixing roller 30 while the inner peripheral surface (inner surface) of the heating film 16 is in contact with the outer surface of the protective layer 15C of the heater 15.

  The control unit 101 turns on the triac 20 as an energization control unit in accordance with the image forming sequence. The triac 20 controls the power applied from the AC power source 21 and starts energizing the energization heating resistor 15B of the heater 15. By this energization, the energization heating resistor 15B generates heat, and the heater 15 rapidly rises in temperature to heat the heating film 16. The temperature of the heater 15 is detected by a thermistor 18 as a temperature detection member provided on the substrate surface of the heater substrate 15A on the heating film guide 19 side.

  The control unit 101 takes in an output signal (temperature detection signal) from the thermistor 18 via the A / D conversion circuit 22 and maintains the heater 15 at a predetermined fixing temperature (target temperature) based on this output signal. The TRIAC 20 is controlled. As a result, the heater 15 is adjusted to a predetermined fixing temperature.

  The surface of the fixing roller 30 that is rotating is heated by the heater 15 through the heating film 16 at the heating nip N2. As a result, a necessary and sufficient amount of heat is applied to the surface of the fixing roller 30 in order to heat and fix the unfixed toner image T carried by the sheet P at the fixing nip portion N1. In a state where the drive motor is driven to rotate and the heater 15 is temperature-controlled, the sheet P carrying the unfixed toner image T is introduced (passed through) into the fixing nip portion N1 with the toner image carrying surface facing upward. .

  The sheet P is nipped between the surface of the fixing roller 30 and the surface of the pressure film 51 at the fixing nip portion N1, and is conveyed (nipped and conveyed) to that state. In this conveyance process, the unfixed toner image T is heated and melted on the surface of the fixing roller 30 and a nip pressure by the fixing nip portion N1 is applied to the melted toner image T. Fixed on the surface.

(3) Description of high temperature offset and low temperature offset In this embodiment, both good fixability during intermittent paper feeding and productivity of small size paper during continuous paper feeding are achieved. First, a description is given of good fixability during intermittent paper feeding.

  The toner image T is fixed on the sheet P by being given a predetermined amount of heat at the fixing nip portion N1. However, when the amount of heat given to the toner image T is insufficient, a low temperature offset occurs. When the amount of heat given to the toner image T is excessive, a high temperature offset occurs.

  The amount of heat applied to the toner image T is determined by the short width of the fixing nip portion N1 (hereinafter referred to as the fixing nip portion N1 width) and the temperature of the fixing roller 30. In general, since the fixing nip portion N1 has a substantially uniform width in the longitudinal direction, temperature variations of the fixing roller 30 in the longitudinal direction (hereinafter referred to as longitudinal variations) lead to variations in the amount of heat applied to the toner image T.

  The toner used in this embodiment causes high temperature offset and low temperature offset in one sheet P when the longitudinal variation in temperature of the fixing roller 30 becomes 15 ° C. or more. The greater the longitudinal variation in the temperature of the fixing roller 30, the greater the difference between the high temperature offset level and the low temperature offset level. On the contrary, when the longitudinal variation in the temperature of the fixing roller 30 is smaller than 15 ° C., the toner image T is fixed over and over the entire length of the sheet P. The temperature of the fixing roller 30 is a temperature that can be measured by bringing a thermocouple into contact with the surface of the fixing roller 30.

  FIG. 5 schematically shows a temporal change in the temperature of the fixing roller 30 after the start of printing in this embodiment. For printing, letter-size paper was used, and two consecutive sheets were repeatedly passed at intervals of 1 minute. A solid line indicates the temperature at the center of the fixing roller 30 in the longitudinal direction, and a broken line indicates the temperature at the end of the fixing roller 30 in the longitudinal direction. It can be seen that the temperature difference between the central portion in the longitudinal direction and the end portion in the longitudinal direction of the fixing roller 30 (hereinafter referred to as the center-end portion temperature difference) increases with time. The center-edge temperature difference increases with time, but finally reaches an equilibrium state at a substantially constant value.

  As a comparative study, the final temperature of the center-end temperature difference was confirmed. Further, when the temperature difference between the center and the end was smaller than 15 ° C., it was confirmed how many ° C. there was a margin for obtaining good fixability. The temperature of the fixing roller 30 is measured by arranging a thermocouple at a position of 100 mm from the longitudinal center to the longitudinal end of the fixing roller 30 on the upstream side of the fixing nip N1 in the recording material conveyance direction. The temperature at the center part in the longitudinal direction and the temperature at the end part in the longitudinal direction were used.

  In the present example, the center-end temperature difference finally became 12 ° C. At this time, the high temperature offset at the center in the longitudinal direction and the low temperature offset at the end in the longitudinal direction are compatible, and the margin is 3 ° C.

  As Comparative Example 1, the same measurement was performed with a configuration in which the longitudinal width of the reflecting plate 70 was 25 mm. As for the longitudinal positional relationship, the reflector 70 occupies a region of 92.5 to 117.5 mm from the longitudinal center position of the fixing cover toward the left and right end portions. Other configurations are the same as those of the present embodiment. The center-end temperature difference was finally 18 ° C. The high temperature offset at the center in the longitudinal direction and the low temperature offset at the end in the longitudinal direction are compatible, but there is no margin.

  As Comparative Example 2, the same measurement was performed with a configuration in which the longitudinal width of the reflecting plate 70 was 0 mm, that is, the reflecting plate 70 was removed. Other configurations are the same as those of the present embodiment. The center-to-end temperature difference was finally 24 ° C. The high temperature offset at the longitudinal center and the low temperature offset at the longitudinal end are not compatible.

  As Comparative Example 3, the reflection plate 70 is removed, the thickness of the pressure plate 53 is 0.5 mm, and a plate having a thickness of 0.5 mm between the pressure plate 53 and the pressure film guide 52 (the material is the pressure film guide 52). The same measurement was performed with the configuration to which Other configurations are the same as those of the present embodiment. The center-end temperature difference was finally 18 ° C. The high temperature offset at the center in the longitudinal direction and the low temperature offset at the end in the longitudinal direction are compatible, but there is no margin.

  As Comparative Example 4, the reflection plate 70 was removed, the thickness of the pressure plate 53 was 1.0 mm, and the same measurement was performed with the same material as the pressure film guide 52. Other configurations are the same as those of the present embodiment. The center-end temperature difference was finally 5 ° C. The high temperature offset at the center in the longitudinal direction and the low temperature offset at the end in the longitudinal direction are compatible, and the margin is 10 ° C.

  As Comparative Example 5, the reflection plate 70 is removed, the thickness of the pressure plate 53 is set to 0.3 mm, the material is changed to SUS, and the thickness between the pressure plate 50 and the pressure film guide 52 is 0.7 mm. The same measurement was performed with a configuration in which a plate (the material is the same as that of the pressure film guide 52) was added. Other configurations are the same as those of the present embodiment. The center-edge temperature difference was 7 ° C. at the maximum. The high temperature offset at the center in the longitudinal direction and the low temperature offset at the end in the longitudinal direction are compatible, and the margin is 8 ° C.

  As Comparative Example 6, the same measurement was performed with a configuration in which the thickness of the pressure plate 53 was 1.0 mm and the material was the same as that of the pressure film guide 52. Other configurations are the same as in this embodiment (the reflector 70 is present). The center-end temperature difference was finally -5 ° C. That is, a low temperature offset is more likely to occur at the longitudinal center than at the longitudinal end. In this case, the low-temperature offset at the center in the longitudinal direction and the high-temperature offset at the end in the longitudinal direction are compatible, and the margin is 10 ° C.

  FIG. 7 is a cross-sectional view illustrating a schematic configuration of the fixing device of Comparative Example 7. The fixing device of Comparative Example 7 removes the reflection plate 70 and uses a pressure roller 90 instead of the pressure unit 50. The pressure roller 90 has a round shaft-shaped cored bar 90A (Φ18 mm) whose main component is a metal material such as aluminum. An elastic layer 90B (thickness 2.5 mm) mainly composed of silicone rubber or the like is formed on the outer peripheral surface of the core metal 90A, and PTFE, PFA, FEP or the like is provided as the outermost layer on the outer peripheral surface of the elastic layer 90B. A release layer 90C (thickness 50 μm) as a main component is formed. In Comparative Example 7, the center-end temperature difference finally became 18 ° C. The high temperature offset at the center in the longitudinal direction and the low temperature offset at the end in the longitudinal direction are compatible, but there is no margin.

(4) Description of productivity of small size paper Next, productivity of small size paper will be described. When small-size paper (for example, B5 size) is continuously passed, the non-sheet passing portion temperature of the fixing roller 30 becomes higher than the sheet passing area. This is because, in the sheet passing area, the heat amount is absorbed by small-size paper, whereas the non-sheet passing portion does not collect the heat amount and accumulates it. If the temperature of the non-sheet passing portion of the fixing roller 30 exceeds 230 ° C., the fixing roller 30 may be damaged. This is because the heat resistance temperature of the silicone rubber used for the fixing roller 30 is exceeded.

  In order to compare the productivity of small size paper, the following comparative study was conducted. The temperature of the thermistor 18 was adjusted to 220 ° C., 100 sheets of B5 size paper were passed at a throughput of 30 ppm, and it was confirmed whether the fixing roller 30 was damaged after 100 sheets. Further, it was confirmed what temperature of the fixing roller 30 was when the tenth sheet was passed. The higher the temperature of the fixing roller 30 when the tenth sheet is passed, the higher the possibility that the fixing roller 30 is damaged.

  The temperature of the fixing roller 30 was measured by placing a thermocouple at a position of 100 mm from the longitudinal center of the fixing roller 30 to the end side on the upstream side of the fixing nip portion N1 in the recording material conveyance direction. The results are shown below.

  In this embodiment, the temperature of the fixing roller 30 when the tenth sheet was passed was 200 ° C. There was no problem such as damage to the fixing roller 30 after 100 sheets were passed.

  In Comparative Example 1, the same confirmation was performed. The temperature of the fixing roller 30 when the tenth sheet was passed was 198 ° C. There was no problem such as damage to the fixing roller 30 after 100 sheets were passed.

  In Comparative Example 2, the same confirmation was performed. The temperature of the fixing roller 30 when the tenth sheet was passed was 195 ° C. There was no problem such as damage to the fixing roller 30 after 100 sheets were passed.

  In Comparative Example 3, the same confirmation was performed. The temperature of the fixing roller 30 when the tenth sheet was passed was 210 ° C. The fixing roller 30 after passing 100 sheets had a problem that the release layer 30C was peeled off.

  In Comparative Example 4, the same confirmation was performed. The temperature of the fixing roller 30 when the 10th sheet was passed was 230 ° C. A problem occurred that the release layer 30C of the fixing roller 30 was peeled after 50 sheets were passed, and the passing of the paper was stopped.

  In Comparative Example 5, the same confirmation was performed. When the tenth sheet was passed, the temperature of the fixing roller 30 was 225 ° C. After 70 sheets were passed, there was a problem that the release layer 30C of the fixing roller 30 was peeled off, and the sheet passing was stopped.

  In Comparative Example 6, the same confirmation was performed. The temperature of the fixing roller 30 when the tenth sheet was passed was 250 ° C. A problem occurred that the release layer 30C of the fixing roller 30 was peeled after 15 sheets were passed, and the sheet passing was stopped.

  In Comparative Example 7, the same confirmation was performed. The temperature of the fixing roller 30 was 215 ° C. when the tenth sheet was passed. The fixing roller 30 after passing 100 sheets had a problem that the release layer 30C was peeled off.

(5) Coexistence of good fixability during intermittent sheet feeding and productivity of small-size sheets during continuous sheeting Table 1 summarizes the results described above. In Table 1, ◯ of the fixing property is good, Δ is slightly good, and x is poor. A broken circle indicates that the fixing roller is not broken, and a cross indicates that the fixing roller is broken. Further, FIG. 8 shows the relationship between the temperature difference between the center and the edge during intermittent passage of letter size paper and the temperature reached by the fixing roller 30 in the 10th continuous B5 size paper.

  The comparison between the present embodiment and Comparative Examples 1 and 2, and the comparison between Comparative Example 4 and Comparative Example 6 show changes when the longitudinal width of the reflecting plate 70 is changed.

  From the comparison between this embodiment and Comparative Example 1 to Comparative Example 2, the change in the longitudinal width of the reflecting plate 70 has a large influence on the temperature difference between the center and the end of the fixing roller 30 and the influence on the productivity of small size paper. Is small. This relationship means that the temperature difference between the center and the end of the fixing roller 30 can be reduced without significantly reducing the productivity of small size paper. The comparison between Comparative Example 4 and Comparative Example 6 will be described later.

  Comparison between Comparative Example 2 and Comparative Example 5 shows changes when the heat conductivity and heat capacity of the pressure plate 53 are changed.

  From the comparison between Comparative Example 2 and Comparative Example 5, the change of the pressure plate 53 greatly affects both the center-end temperature difference of the fixing roller 30 and the productivity of small-size paper. This relationship means that reducing the center-edge difference of the fixing roller 30 affects the productivity of small-size paper.

  Comparative Example 7 shows the performance of a conventional fixing device, and shows that a configuration with a smaller center-to-end temperature difference and higher productivity of small-size paper than Comparative Example 2 is a configuration suitable for the purpose.

  The details of these results are compared below.

  As described above, Comparative Example 2 to Comparative Example 5 have a correlation between the temperature difference between the center and the end of the fixing roller 30 and the productivity of small size paper. First, paying attention to the temperature difference between the center and the end, the difference between Comparative Example 2 and Comparative Example 5 will be considered. In Comparative Examples 2 to 5, the configuration of the pressure plate 53 is changed. Since the change of the pressure plate 53 is accompanied by the change of the thermal conductivity and the heat capacity, it was confirmed which of them has a correlation with the center-end temperature difference of the fixing roller 30. Comparative example 7 was also compared in the same manner.

  The heat capacity and thermal conductivity of the pressure plate 53 were calculated from the physical properties corresponding to the type of sliding plate (pressure plate) and the cross-sectional area and volume of the pressure plate (cross-sectional area multiplied by 240 mm). The heat capacity of the pressure plate 53 is obtained by multiplying the specific heat, specific gravity, and volume of physical properties. The thermal conductivity of the pressure plate 53 is obtained by multiplying the thermal conductivity of the physical property value by the cross-sectional area of the pressure plate. In addition, when the pressure plate 53 is composed of a plurality of plates, the sum of the thermal conductivity and heat capacity of each is used as the heat conductivity and heat capacity of the pressure plate. Regarding Comparative Example 2 to Comparative Example 5, the heat capacity of the pressure film guide 52 (volume is 10 times that of the pressure plate 53) was taken into consideration and ignored because the heat conductivity was very small. Since the pressure film 51 is very thin, the thermal conductivity and heat capacity of the pressure film 51 were ignored.

  In Comparative Example 7, instead of the pressure plate 53, the heat capacity and thermal conductivity of the silicone rubber portion of the pressure roller 90 were used. The thermal conductivity of the silicone rubber part was measured using QTM-500 (Kyoto Electronics Industry Co., Ltd.) when the thermal conductivity was less than 10 W / mK. Those having a thermal conductivity of 10 W / mK or more were measured using LFA-502 (Kyoto Electronics Industry). The error was about ± 10% after 10 measurements.

  Table 2 summarizes the heat capacity and thermal conductivity. The thermal conductivity of the pressure plate 53 is converted into the amount of heat per unit time passing through the cross-sectional area of the pressure plate 53 when there is a temperature difference of 1 ° C. per 1 mm longitudinal width (per unit length) of the pressure plate 53. ing.

  Based on the values in Table 2, the relationship between the heat capacity of the pressure plate 53 and the temperature difference between the center and the end of the fixing roller 30 is shown in FIG.

  In Comparative Examples 2 to 5, although the heat capacities of the pressure plates 53 are substantially equal, the center-end temperature difference of the fixing roller 30 is greatly different. That is, it cannot be said that there is a correlation between the heat capacity of the pressure plate 53 and the center-end temperature difference of the fixing roller 30. The reason is as follows. The temperature of each member when the center-end temperature difference becomes maximum reaches a substantially equilibrium state, and the temperature change is small. For this reason, it is considered that the influence of the heat capacity is reduced.

  On the other hand, Comparative Example 7 can be viewed as the heat capacity affecting the center-end temperature difference. The pressure roller 90 having a large heat capacity is unlikely to decrease in temperature. Although the temperature of the center part in the longitudinal direction of the pressure roller 90 is kept high, the temperature at the end part in the longitudinal direction of the pressure roller 90 is also large to dissipate heat to keep a certain level of high temperature. As a result, it is considered that the pressure roller 90 is likely to generate a temperature difference between the longitudinal center portion and the longitudinal end portion of the pressure roller 90.

  Further, based on the values shown in Table 2, FIG. 10 shows the relationship between the thermal conductivity of the pressure plate 53 and the center-end temperature difference of the fixing roller 30.

  For Comparative Examples 2 to 5, it was found that the thermal conductivity of the pressure plate 53 and the temperature difference at the center end of the fixing roller 30 have a strong correlation. The reason may be the effect of heat dissipation. Basically, the temperature at the end in the longitudinal direction of the fixing roller 30 is affected by heat radiation. The higher the thermal conductivity of the pressure plate 53, the greater the influence of heat dissipation on the longitudinal end temperature of the fixing roller 30.

  On the other hand, in Comparative Example 7, even when the thermal conductivity of the pressure roller 90 is approximately the same as that of Comparative Example 4 and Comparative Example 5, the temperature difference between the center and the end of the fixing roller 30 is large and the tendency is different. The reason is considered to be the influence of the heat capacity described above. That is, as the thermal conductivity of the pressure plate 53 is increased, the temperature at the end portion in the longitudinal direction of the fixing roller 30 tends to decrease. Since the heat capacity of the pressure roller 90 is large, the temperature at the end portion of the fixing roller 30 is Go down.

  As can be seen so far, the productivity of small-size paper can be improved by increasing the thermal conductivity of the pressure plate 53, but the center-end temperature of the fixing roller 30 is increased. That is, it is difficult to achieve both good fixability at the time of intermittent paper feeding and productivity of small size paper at continuous paper passing only by increasing the thermal conductivity of the pressure plate 53.

  Next, the influence of the reflecting plate 70 will be described by comparing the present embodiment with Comparative Examples 1 and 2 and comparing Comparative Example 4 and Comparative Example 6.

  First, the center-edge temperature difference of the fixing roller 30 will be described. FIG. 11 shows the relationship between the longitudinal width of the reflector 70 and the center-end temperature difference of the fixing roller 30.

  As the longitudinal width of the reflecting plate 70 is increased, the temperature difference between the center and the end of the fixing roller 30 is reduced. This is the effect of reheating by the reflector 70 and heat retention.

  The emissivity of the reflecting plate 70 is 0.05, and the emissivity of the portion where the reflecting plate 70 is not disposed (fixing cover 60) is 0.95. This means that the reflection plate 70 can reflect 95% and the fixing cover 60 can reflect 5% of the heat radiated from the heating film 16 and the fixing roller 30. Therefore, the larger the longitudinal width of the reflecting plate 70, the more heat radiated from the heating film 16 and the fixing roller 30 can be reflected.

  During the passage of paper, both the longitudinal ends of the surface of the heating film 16 can be reheated by reflecting the heat radiated from the heating film 16 having a particularly high temperature by the reflecting plate 70. Further, during the intermittent standby, both longitudinal ends of the surface of the heating film 16 can be kept warm. In other words, since the heat radiation at both ends in the longitudinal direction on the surface of the heating film 16 can always be suppressed during the paper passing and intermittent standby, the temperature difference between the center and the end of the fixing roller 30 can be reduced.

  In Comparative Example 6, the temperature at the end portion in the longitudinal direction of the fixing roller 30 is higher than that at the center portion in the longitudinal direction, and a high temperature offset occurs at the end portion in the longitudinal direction.

  Considering the purpose of reducing the temperature difference between the center and the end of the fixing roller 30, it is preferable that the reflection plate 70 be on both ends in the longitudinal direction of the fixing roller 30, and it is not preferable to cover the entire region of the fixing roller 30 in the longitudinal direction. . If the longitudinal width of the reflecting plate 70 is increased more than necessary, the temperature rises near the longitudinal end of the fixing roller 30 and a high temperature offset may occur near the end.

  Next, the influence of the longitudinal width of the reflecting plate 70 on the productivity of small size paper will be described. As can be seen from FIG. 8, in the present example and Comparative Examples 1 to 2, the longitudinal width of the reflecting plate 70 has little influence on the productivity of small size paper. On the other hand, in Comparative Example 4 and Comparative Example 6, the influence of the longitudinal width of the reflecting plate 70 on the productivity of small-size paper is relatively large. The influence of the longitudinal width of the reflecting plate 70 on the productivity of small-size paper varies depending on the amount of heat that can be mitigated by the pressure plate 53. Details are described below.

The amount of heat released by thermal radiation from the object D having the emissivity ε ₂ of the surface area A ₂ of the absolute temperature Ts can be expressed by the following equation. σ is the Stefan-Boltzmann constant. (Surface wall surface area A ₁ , emissivity ε ₁ , temperature Ta)

Assuming A ₁ is very large and the heat spreads far away,

This represents the amount of heat released by the object D when the surrounding walls do not reflect thermal radiation.

In the case where reflection is not taken into consideration from the formulas [Equation 1] and [Equation 2], the amount of heat lost by radiating from the outer peripheral surface of the heating film 51 per 1 mm of the longitudinal width is estimated. The temperature of the heating film 16 is 215 ° C., and the temperature of the surrounding walls is 80 ° C. The temperature of the heating film 16 and the temperature of the surrounding wall were set to values close to the actual temperature. The emissivity of the heating film 16 is 0.95. The surface area of the heating film 16 is 0.000057 (m ² ). This assumes a heating film 16 having an outer diameter of Φ18 mm and a longitudinal width of 1 mm.

  When calculated from these conditions, the amount of heat radiated from the outer peripheral surface of the heating film 16 per 1 mm of the longitudinal width is 0.126 W. If the surrounding walls absorb all of the heat radiated from the heating film 16, the heating film 16 loses 0.126 W of heat per 1 mm of the longitudinal width. Conversely, if the surrounding walls reflect all of the heat radiated from the heating film 16, the heating film 16 does not lose its heat. In other words, the portion having the reflecting plate 70 around the heating film 16 can reflect the heat amount of the theoretical maximum value 0.126 W to the heating film 16 as compared with the portion where the reflecting plate 70 is not provided.

  However, the radiant heat that can be reflected by the reflecting plate 70 with respect to the heating film 16 per 1 mm longitudinal width under actual conditions is smaller than 0.126W. The reason for this is as follows. For example, the emissivity of the reflecting plate 70 cannot be reduced to 0, and all of the radiant heat radiated from the heating film 16 cannot be reflected toward the heating film 16.

  The amount of heat absorbed by the fixing cover 60 from the heating film 16 is also smaller than 0.126W. The reason for this is as follows. The emissivity of the fixing cover 60 is about 0.95, and about 5% of the radiant heat radiated from the heating film 16 is reflected.

  In consideration of these, the portion around the heating film 16 where the reflecting plate 70 is located is supplied with an amount of heat of about 0.08 W to 0.1 W around the heating film 16 than the portion where the fixing cover 60 is located.

  The thermal conductivity of the pressure plate 53 in this embodiment is 2.36 W / mm · K. This means that the amount of heat passing through the cross-sectional area of the pressure plate 53 is 2.36 W when there is a temperature difference of 1 ° C. at both ends of the sliding plate having a longitudinal width of 1 mm. This is much larger than 0.08 W to 0.1 W, which is radiant heat reflected by the reflecting plate 70 on the heating film 16 per 1 mm length. Therefore, if the thermal conductivity of the pressure plate 53 is 200 W / mK or more, the influence on the productivity of small-size paper during continuous paper feeding by the reflection plate 70 is small.

  On the other hand, the thermal conductivity of the pressure plate 53 in Comparative Example 4 is 0.005 W / mm · ° C., and the radiant heat reflected by the reflective plate 70 on the heating film 16 per 1 mm in the longitudinal width cannot be sufficiently relaxed. For this reason, the influence on the productivity of small-size paper during continuous paper feeding by the reflecting plate 70 becomes large. That is, the larger the thermal conductivity of the pressure plate 53, the smaller the influence of the reflector 70 on the productivity of small size paper.

  As described above, by increasing the thermal conductivity of the pressure plate 53, it is possible to improve the productivity of small-size paper during continuous paper feeding, and to offset the adverse effects of the reflecting plate 70. In addition, by disposing the reflection plate 70, it is possible to offset the adverse effects caused by increasing the thermal conductivity of the pressure plate 53, and to obtain good fixability during intermittent paper feeding. That is, by using the pressure plate 53 and the reflection plate 70 in combination, it is possible to achieve both good fixability during intermittent paper feeding and productivity of small size paper during continuous paper feeding.

[Example 2]
Another embodiment of the fixing device will be described. In this embodiment, the same members as those of the fixing device B of Embodiment 1 are denoted by the same reference numerals, and the description of the members is omitted.

  FIG. 12 is a cross-sectional view illustrating a schematic configuration of the fixing device B according to the present embodiment. The fixing device B of the present embodiment has the same configuration as the fixing device B of the first embodiment, except that a pressure roller 90 is used instead of the pressure unit 50. The pressure roller 90 is a member that is long in the longitudinal direction.

  The pressure roller 90 has a round shaft-shaped cored bar 90A (Φ18 mm) whose main component is a metal material such as aluminum. An elastic layer 90B (thickness: 2.5 mm) mainly composed of silicone rubber containing a high thermal conductive filler such as carbon nanotube is formed on the outer peripheral surface between the shafts at both ends in the longitudinal direction of the core metal 90A. . A release layer 90C (thickness: 50 μm) mainly composed of PTFE, PFA, FEP or the like is formed as the outermost layer on the outer peripheral surface of the elastic layer 90B. The pressure roller 90 has shafts at both ends in the longitudinal direction of the metal core 90A supported rotatably on side plates (not shown) on both sides in the longitudinal direction of an apparatus frame (not shown) via bearings (not shown). Yes.

  The pressure roller 90 is disposed below the fixing roller 30 in parallel with the fixing roller 30. The bearings are urged in the vertical direction perpendicular to the generatrix direction of the fixing roller 30 by pressure springs (not shown) at both longitudinal ends of the core metal 90A of the pressure roller 90, and the outer peripheral surface ( The surface) is brought into contact (contact) with the surface of the fixing roller 30 in a pressurized state. As a result, the elastic layer 30B of the fixing roller 30 and the elastic layer 90B of the pressure roller 90 are crushed and elastically deformed at positions corresponding to the contact position between the surface of the fixing roller and the surface of the pressure roller, respectively. A fixing nip portion N1 having a predetermined short width is formed with the pressure roller surface. Accordingly, the fixing roller 30 forms a fixing nip portion N1 together with the pressure roller 90.

  In this example, the temperature difference between the center and the edge during intermittent passage of letter-size paper and the temperature reached by the fixing roller 30 on the 10th continuous B5-size paper were confirmed. The results are shown in Table 3. In Table 3, ○ of the fixing property is good, and × is bad. A broken circle indicates that the fixing roller is not broken, and a cross indicates that the fixing roller is broken.

  Table 4 shows the heat capacity and thermal conductivity of the elastic layer 90B of the pressure roller 90.

  As can be seen from the comparison between Example 2 and Comparative Example 7 in Tables 3 and 4, the size of the elastic layer 90B of the pressure roller 90 is increased (300 W / mK) to reduce the size during continuous paper feeding. The productivity of the paper can be improved, and the adverse effects of the reflector 70 can be offset. Further, by disposing the reflecting plate 70, it is possible to cancel the adverse effects caused by increasing the thermal conductivity of the elastic layer 90B of the pressure roller 90, and to obtain good fixability during intermittent paper feeding. That is, by using the pressure roller 90 and the reflection plate 70 in combination, it is possible to achieve both good fixability during intermittent paper feeding and productivity of small-size paper during continuous paper feeding.

[Other embodiments]
The longitudinal width of the reflecting plate 70 varies depending on the longitudinal width of the fixing roller 30 and is not limited to the longitudinal width of this embodiment.

  The heating unit 10 is not limited to the one described in the first embodiment, and the same effect can be obtained even when a cylindrical rotatable heating roller including a halogen heater is used.

15: Ceramic heater, 16: Heated film, 16a: Longitudinal end of the heated film, 30: Fixing roller, 50: Pressurizing unit, 60: Fixing cover, 70: Reflecting plate, N2: Heating nip, N1: Fixing Nip part, P: recording material, T: unfixed toner image

Claims (8)

A fixing device used in an image forming apparatus for forming an image on a recording material, comprising a heating source, a cylindrical heating rotating body that rotates while being in contact with the heating source, and the heating rotating body sandwiched between the heating source and the heating source A fixing rotator that forms a heating nip portion, and a backup member that forms a fixing nip portion together with the fixing rotator. The fixing rotator is heated by the heating nip portion, and the fixing nip portion is undetermined at the fixing nip portion. In a fixing device for fixing a non-fixed toner image on a recording material by heating while conveying a recording material carrying a contact toner image,
The backup member is a member having a predetermined thermal conductivity. A fixing device having at least a part around the body.   The fixing device according to claim 1, wherein the backup member is a pressure roller having an elastic layer having a predetermined thermal conductivity.   The backup member includes a pressure member having a predetermined thermal conductivity, and a cylindrical pressure rotator that rotates while contacting the pressure member, and the fixing rotator and the pressure member. The fixing device according to claim 1, wherein the fixing nip portion is formed with the pressure rotator interposed therebetween.   The fixing device according to claim 3, wherein the pressure member has a thermal conductivity of 200 W / mK or more.   A heating rotator cover that covers the periphery of the heating rotator in the entire longitudinal direction orthogonal to the recording material conveyance direction of the heating rotator, and that reflects the radiant heat generated by the heating rotator toward the heating rotator. 5. The radiant heat reflecting member is provided between the heating rotator cover and the heating rotator, and the radiant heat reflecting member is disposed between the heating rotator cover and the heating rotator. Fixing device.   The emissivity at which the radiant heat reflecting member reflects the radiant heat toward the heating rotator is less than 0.1, and the emissivity at which the heating rotator cover reflects the radiant heat toward the heating rotator is 0.9. The fixing device according to claim 5, wherein the fixing device is larger than the fixing device.   6. The radiant heat reflecting member is disposed at two positions opposite to each other in the radial direction of the heating rotator and both ends of the heating rotator in the longitudinal direction perpendicular to the recording material conveyance direction. The fixing device according to 1. In an image forming apparatus having an image forming unit that forms an image on a recording material, and a fixing unit that fixes an image formed on the recording material to the recording material.
An image forming apparatus comprising the fixing device according to claim 1, wherein the fixing unit includes the fixing device according to claim 1.