JP2017009892A - Fixation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device capable of suppressing occurence of a fixing failure even on acceleration of printing speed.SOLUTION: The fixation device comprises: a slide member with which an inner peripheral surface of a rotatable endless belt is slid; and a holding member including a groove in which the slide member is fitted and holding the slide member so as to be in contact with the inner peripheral surface of the endless belt in the state in which gaps on the upstream side and the downstream side are formed between the slide member and itself in a recording material conveyance direction and fitting the slide member therein. The holding member is constituted such that the gaps in a recording material conveyance region satisfy both of GUc<GDc and WGUc<WGDc and the gaps in a recording material non-conveyance region satisfy both of GUe>GDe and WGUe>WGUe.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer.

  As a fixing device for fixing a toner (developer) image used in an electrophotographic system, a heat roller system, a film heating system, and the like are conventionally known. The film heating type fixing device (Patent Document 1) uses a film (endless belt) having a small heat capacity as a fixing member as compared with the heat roller of the heat roller type heating device, so that the fixing member is raised to a predetermined temperature. Can be shortened. Further, since the rise time is short, it is not necessary to warm the fixing member during standby, and power consumption can be suppressed as low as possible.

  As a fixing film material in a film heating type fixing device, a metal material such as SUS or nickel may be used, or a heat resistant resin material such as polyimide may be used. Metal materials can be made thinner because they are stronger than resin materials, and because they have high thermal conductivity, they can cope with higher speed and longer life. On the other hand, since the specific gravity of resin materials is smaller than that of metals, there is an advantage that the heat capacity is small and the resin materials are easily heated. In addition, the resin material has a feature that it can be molded at low cost because a thin film can be molded by coating.

  A general film heating type fixing device is shown in FIG. A heater 113 as a heating member (heat generating member) is held by a heater holder 119 (holding member), and a rotatable cylindrical fixing film 112 (rotating body, endless belt) having flexibility is provided around the heater 113. It becomes the composition. The pressure roller 110 (pressure member) is in pressure contact with the heater 113 so as to sandwich the fixing film 112.

  The heater 113 is in contact with the inner surface (inner peripheral surface) of the fixing film 112 to form an inner surface nip Nk. The heat of the heater 113 is transferred to the fixing film 112 at the inner surface nip Nk, and the fixing film 112 is heated. The surface (outer peripheral surface) of the fixing film 112 is in contact with the surface of the pressure roller 110 to form a fixing nip portion N.

  When the pressure roller 110 is driven in the direction of arrow R1 in the figure, the fixing film 112 receives power from the pressure roller 110 at the fixing nip portion N and is driven to rotate in the direction of arrow R2. At this time, the heat of the fixing film 112 heated by the heater 113 at the fixing nip portion N is transferred to the pressure roller, and the pressure roller 110 is also heated. When the recording material P onto which the unfixed toner image T has been transferred is conveyed from the direction of arrow A1 to the fixing nip N in the figure, the heat of the fixing film 112 and the pressure roller 110 heated in the fixing nip N is recorded. Heat is transferred to the material P and the toner image T, and the toner image T is fixed to the recording material P.

  In the case where a resin material is used for the fixing film 112 by the film heating method, when the recording material with the adhering foreign matter to the fixing nip portion N or the staple is conveyed, the fixing film 112 is torn or perforated. Damage may occur. This will be described below.

  The heater 113 is held by being fitted into a slot provided in the heater holder 119. Since the heater 113 is fitted into the slot of the heater holder 119, the width Wh of the slot provided in the heater holder 119 is set wider than the width Wk of the heater 113 in relation to the width in the recording material conveyance direction. Here, each of the heater 113 and the heater holder 119 is thermally expanded when the heater 113 is heated to a high temperature. Even in the case of thermal expansion, it is necessary to set the width Wh of the slot of the heater holder 119 so that the heater 113 can be accommodated in the heater holder 119.

  If the width Wh of the slot of the heater holder 119 is narrow and thermally expands, if the heater 113 is stressed, the heater 113 may break. In general, the heater 113 is configured to generate heat by energizing a heating resistance layer provided on a substrate. However, if the heating heater 113 breaks due to thermal expansion during heating as described above, the heating resistance layer Short circuit may cause abnormal heat generation.

  Therefore, the heater 113 needs to be configured so as not to break in any case. Specifically, even when the heater 113 becomes hotter than expected and the thermal expansion amount of the heater 113 and the heater holder 119 is larger than usual, the following is performed. That is, the width Wh of the slot of the heater holder 119 is set so that the heater 113 fits in the slot of the heater holder 119 and the heater 113 does not break.

  Thus, the gap G is formed between the heater 113 and the heater holder 119 in order to set the width Wh of the slot of the heater holder 119 sufficiently wider than the width Wk of the heater 113. The heater 113 and the heater holder 119 may be bonded with an adhesive, but in many cases, they are not bonded from the viewpoint of improving assemblability and cost reduction. When the heater 113 and the heater holder 119 are not bonded, the heater 113 receives a frictional force in the downstream direction at the inner surface nip portion Nk due to the rotation of the fixing film 112, so that the heater 113 has a groove in the heater holder 119. It hits the downstream side.

  Therefore, the gap G can be made upstream of the heater 113. If the gap G is on the upstream side of the heater 113, the fixing film may be damaged when foreign matter is mixed into the fixing nip portion N or the recording material P with staples is conveyed. In order to explain this, an enlarged schematic view of the gap G is shown in FIG.

  When foreign matter is mixed into the fixing nip portion N or the recording material P with staples is conveyed, as shown in the schematic diagram of FIG. 6A, foreign matter and staples S enter the gap G, and foreign matter and staples. S may catch on the upstream edge portion E of the heater 113. If foreign matter or staples S are caught on the upstream edge E of the heater 113, the fixing film 112 may be damaged, such as a hole.

  When perforation occurs in the fixing film 112, particularly when an image with a high printing rate is output, image defects such as “white spots” and “black spots” occur on the fixed image at the cycle of the fixing film 112. There is. Further, when the size of the hole in the fixing film is increased, the fixing film is torn, and in some cases, the recording material may not be conveyed.

  In order to prevent the fixing film from being damaged, the upstream portion of the fixing nip N of the heater holder 119 is made higher than the sliding surface of the heater 113 with the fixing film 112 as shown in FIG. Proposed (heater holder upstream projection H). This prevents foreign matter and staples S from being caught on the upstream edge portion E by the heater 113 and prevents damage to the fixing film.

Japanese Patent Laid-Open No. 04-044075

  In recent years, a further increase in printing speed has been demanded, and it is necessary to improve the fixing performance by increasing the heat transfer efficiency and increasing the pressure by reducing the thickness of the fixing film. Here, in a film heating type fixing device, if a thin fixing film is used or the applied pressure is increased, the rigidity of the film becomes weak, or foreign matter and staples strongly press against the upstream edge E of the heater 113. It is done. For this reason, the fixing film may be damaged by the above-described foreign matters and staples.

  Therefore, if the heater holder upstream convex portion H is set higher in order to suppress damage to the fixing film as described above as the fixing film is thinned and the pressurizing force is increased, the fixing film can be prevented from being damaged. It becomes difficult for the inner surface of the film 113 to come into contact with the heater 113. For this reason, the inner surface nip portion Nk is narrowed, and the heat of the heater 113 is hardly transmitted to the fixing film 113.

  For this reason, it is difficult to supply heat from the fixing film to the toner T on the recording material P, and the recording material P of the toner T is increased despite the fact that the fixing film is thinned and the pressing force is increased to improve the fixing performance. It will lead to deterioration of fixing property.

  An object of the present invention is to provide a fixing device that can suppress the occurrence of fixing failure even when the printing speed is increased.

In order to achieve the above object, a fixing device according to the present invention includes a rotatable endless belt, a sliding member on which an inner circumferential surface of the endless belt slides when the endless belt rotates, and the sliding member. In contact with the inner peripheral surface of the endless belt in a state in which an upstream and downstream gap is formed between the groove and the sliding member in the recording material conveying direction. A holding member that holds the sliding member, and a facing member that forms a nip portion that is opposed to the sliding member via the endless belt and that conveys the recording material between the outer peripheral surface of the endless belt. The GUc on the upstream side, the GDc on the downstream side, and the length in the longitudinal direction intersecting the recording material conveyance direction in which the GUc is formed with respect to the gap in the recording material conveyance region The GDc is shaped When the WGDc the length of the longitudinal direction is,
GUc <GDc
WGUc <WGDc
In the recording material non-conveying area, the upstream side is GUe, the downstream side is GDe, the length in the longitudinal direction where the GUe is formed is WGUe, and the longitudinal direction where the GDe is formed. When the length in the direction is WGDe,
GUe> GDe
WGUe> WGUe
The holding member is configured to satisfy both of the above.

  According to the present invention, it is possible to provide a fixing device that can suppress the occurrence of fixing failure even when the printing speed is increased.

1 is a cross-sectional view illustrating an outline of a fixing device according to a first embodiment of the present invention. It is a figure which shows the slot shape of the heater holder in the fixing device which concerns on 1st Embodiment. 1 is a cross-sectional view illustrating an outline of an entire image forming apparatus including a fixing device according to an embodiment of the present invention. FIG. 5 is a schematic diagram of a recording material used for a perforation test of a fixing film. It is a figure which shows the slot shape of the heater holder in 2nd Embodiment. FIG. 3 is a cross-sectional view of the fixing nip portion upstream side. It is sectional drawing which shows the outline of the conventional heating apparatus. It is a figure which shows the slot shape of the conventional heater holder.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<< First Embodiment >>
(Image forming device)
An example of an image forming apparatus equipped with a film heating type fixing device according to this embodiment will be described with reference to a schematic diagram shown in FIG. The image forming apparatus 50 forms a single image by sequentially transferring toner images of four colors of yellow, magenta, cyan, and black onto the recording material P carried on the recording material conveyance belt 9. is there.

  On the peripheral surface of the photosensitive drum 1 as an image carrier, a charger 2, an exposure device 3 for irradiating the photosensitive drum 1 with laser light, and a developing device 5 are arranged in this order along the rotation direction (arrow R1 direction). Yes. Further, a transfer roller 10 and a photosensitive drum cleaner 16 are disposed via the recording material conveyance belt 9.

  Here, the surface of the photosensitive drum 1 is charged to negative polarity by the charger 2. Next, an electrostatic latent image is formed on the surface of the charged photosensitive drum 1 by the exposure L of the exposure means 3 (the surface potential of the exposed portion is increased). The toner of this embodiment is charged with negative polarity for each color. First, the negative toner is attached only to the electrostatic latent image portion on the photosensitive drum 1 by the developing device 5 containing yellow toner of the first color, and the photosensitive drum. A yellow toner image is formed on 1.

  On the other hand, the recording material transport belt 9 is supported by two support shafts (drive roller 12 and tension roller 14), and is rotated in the direction of arrow R3 by the drive roller 12 rotating in the direction of arrow R4 in the drawing. When the recording material P is fed by the paper feed roller 4, the recording material P is charged by the suction roller 6 to which a positive polarity bias is applied, and is electrostatically attracted and transported onto the recording material transport belt 9.

  When the recording material P is conveyed to the transfer nip N1, a positive transfer bias having a polarity opposite to the polarity of the toner is applied from a power source (not shown) to the transfer roller 10 driven to rotate by the recording material conveyance belt 9. The Then, the yellow toner image on the photosensitive drum 1 is transferred onto the recording material P at the transfer nip portion N1. The transfer residual toner on the surface of the photosensitive drum 1 after the transfer is removed by a photosensitive drum cleaner 16 having an elastic blade.

  The above-described series of image forming processes of charging, exposure, development, transfer, and cleaning is sequentially performed for each developing cartridge of the second color magenta M30, the third color cyan C30, and the fourth color black K30, and recording on the recording material transport belt 9 Four color toner images are formed on the material P. The recording material P carrying the four color toner images is conveyed to the heating device 100, where the toner image on the surface is heated and fixed.

(Fixing device)
Next, the fixing device 100 of this embodiment will be described below. The fixing device 100 according to the present embodiment is a film heating method for the purpose of shortening the startup time and reducing power consumption as described above. FIG. 1 is a cross-sectional view of a fixing device 100 according to the present embodiment, and the basic configuration is the same as that of the fixing device of FIG. 7 described in the background art.

  A heater 113 as a sliding member is held by a heater holder 130 as a holding member, and a fixing film 112 that is a cylindrical endless belt having flexibility is provided around the heater. The heater 113 contacts the inner surface of the fixing film 112 to form an inner surface nip Nk, and heats the fixing film 112 from the inside. A pressure roller 110 as an opposing member forms a fixing nip portion N so as to face the heater 113 so as to sandwich the fixing film 112.

  When the pressure roller 110 is driven in the direction of arrow R1 in the figure, the fixing film 112 receives power from the pressure roller 110 at the fixing nip portion N and is driven to rotate in the direction of arrow R2. When the recording material P to which the unfixed toner image T has been transferred is conveyed from the direction of arrow A1 to the fixing nip N in the drawing, the toner image T is fixed to the recording material P.

(Fixing film)
The heater holder 130 holding the heater 113 is supported from the opposite side of the heater 113 by an iron stay 120 to give strength, and a flexible cylindrical fixing film 112 is provided around the heater holder 130. It has a configuration. The fixing film 112 of the present embodiment has an outer diameter of φ20 mm in a cylindrical state that is not deformed, and has a multilayer structure in the thickness direction. The layer structure of the fixing film 112 includes a base layer 126 for maintaining the strength of the film and a release layer 127 for reducing the adhesion of dirt to the surface.

  The material of the base layer 126 needs heat resistance because it receives heat from the heater 113, and needs strength because it slides on the heater 113. For this reason, it is good to use metals, such as SUS (Stainless Used Steel: Stainless steel) and nickel, and heat resistant resins, such as a polyimide. Since the metal is stronger than the resin, it can be thinned and has a high thermal conductivity. Therefore, the heat of the heater 113 is easily transmitted to the surface of the fixing film 112.

  On the other hand, since the specific gravity of the resin is smaller than that of the metal, there is an advantage that the heat capacity is small and the resin is easily heated. In addition, the resin can be molded at low cost because a thin film can be formed by coating. In this embodiment, a polyimide resin is used as the material of the base layer 126 of the fixing film 112, and a carbon-based filler is added to improve the thermal conductivity and strength. The thinner the base layer 126 is, the easier it is to transfer the heat of the heater 113 to the surface of the fixing roller 110, but the strength is reduced. Therefore, the base layer 126 is preferably about 15 μm to 100 μm, and in this embodiment, 50 μm.

  The material of the release layer 127 of the fixing film 112 is preferably a fluororesin such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP). In this embodiment, PFA which is excellent in releasability and heat resistance among fluororesins is used.

  The release layer 127 may be a tube-coated one, but may be one whose surface is coated with a paint, and in this embodiment, the release layer 127 is formed by a coating excellent in thin-wall molding. The thinner the release layer 127 is, the easier it is to transfer the heat of the heater 113 to the surface of the fixing film 112. However, if the release layer 127 is too thin, the durability deteriorates, and is preferably about 5 to 30 μm.

(Pressure roller)
The pressure roller 110 of this embodiment has an outer diameter of φ20 mm, and an elastic layer 116 (foamed rubber) having a thickness of 4 mm formed by foaming silicone rubber on an iron core metal 117 of φ12 mm. When the pressure roller 110 has a large heat capacity and a high thermal conductivity, the heat on the surface of the pressure roller 110 is easily absorbed into the inside, and the surface temperature of the pressure roller 110 is unlikely to rise.

  That is, the rise time of the surface temperature of the pressure roller 110 can be shortened with a material having a low heat capacity, a low thermal conductivity, and a high heat insulating effect. The thermal conductivity of foamed rubber obtained by foaming the silicone rubber is 0.11 to 0.16 W / m · K, which is lower than that of solid rubber of about 0.25 to 0.29 W / m · K. The specific gravity related to the heat capacity is about 1.05 to 1.30 for solid rubber, and about 0.75 to 0.85 for foamed rubber, which is also a low heat capacity. Therefore, this foamed rubber can shorten the rise time of the pressure roller 110 surface temperature.

  If the outer diameter of the pressure roller 110 is smaller, the heat capacity can be suppressed. However, if the pressure roller 110 is too small, the width of the fixing nip N is narrowed, so that an appropriate diameter is required. In this embodiment, the outer diameter is set to φ20 mm. As for the thickness of the elastic layer 116, if it is too thin, heat escapes to the metal core, so an appropriate thickness is required. In this embodiment, the thickness of the elastic layer 116 is 4 mm.

  A release layer 118 made of perfluoroalkoxy resin (PFA) is formed on the elastic layer 116 as a toner release layer. Like the release layer 127 of the fixing film 112, the release layer 118 may be a tube coated or a surface coated with a paint, but in this embodiment, a tube having excellent durability is used.

  As a material for the release layer 118, in addition to PFA, a fluororesin such as PTFE or FEP, a fluororubber having good releasability, a silicone rubber, or the like may be used. As the surface hardness of the pressure roller 110 is lower, the width of the fixing nip N can be obtained with a light pressure. However, if the surface hardness is too low, the durability deteriorates. In this embodiment, the Asker-C hardness (4.9 N load) is used. 40 °. The pressure roller 110 is rotated by a rotating means (not shown) in the direction of arrow R1 in the drawing at a surface moving speed of 200 mm / sec.

(Heating heater)
The heater 113 has a rectangular parallelepiped shape with a width Wh = 6 mm in the recording material conveyance direction and a width 270 mm in the longitudinal direction, and an Ag / Pd (silver palladium) energization heating resistance layer is formed on the surface of the alumina substrate by screen printing. Apply 10 μm. And what covered glass by the thickness of 50 micrometers as a heat generating body protective layer on it was used.

  The maximum recording material width of the image forming apparatus equipped with the fixing device of the present embodiment is a letter size, and the longitudinal width of the energized heating resistor layer is larger than the letter size so that the letter size longitudinal width 216 mm can be sufficiently heated. It is 218 mm long by 1 mm on the left and right.

  A temperature detection element 115 for detecting the temperature of the ceramic base material (substrate) raised in response to the heat generated by the energization heat generation resistance layer is provided on the back surface of the heater 113, which is a ceramic heater whose base material (substrate) is made of ceramic. Is arranged. The temperature of the heater 113 is adjusted by appropriately controlling the current flowing from the electrode portion (not shown) at the end portion in the longitudinal direction to the energization heating resistor layer in accordance with the signal of the temperature detection element 115.

  On the other hand, on the back surface of the heater 113, an energization interruption element 140 that interrupts energization under predetermined conditions shown below is also arranged. This is to prevent abnormal heat generation due to cracking of the heater when the temperature detection element 115 fails and the heater 113 continues to be energized and the temperature rises abnormally. The energization cut-off element 140 of this embodiment is a general thermoswitch, and is connected in series to a conducting wire that energizes the heater 113. When the temperature of the energization interrupting element 140 (the back surface temperature of the heater 113) reaches 270 ° C., the energization to the heater 113 is interrupted by the deformation of the bimetal.

  Even if the temperature detecting element 115 fails, when the temperature on the back surface of the heater 113 reaches 270 ° C., the heater 113 stops heating due to the energization interruption of the energization interruption element 140, and abnormal heat generation due to cracking of the heater can be prevented.

  The heat of the heater 113 whose temperature is adjusted and heated by the temperature detection element 115 is transmitted from the inner surface of the fixing film 112 to the surface, and heats the surface of the pressure roller 110 via the fixing nip N. When the recording material P onto which the unfixed toner image T has been transferred as described above is conveyed to the fixing nip N, the heat of the fixing film 112 and the pressure roller 110 is transmitted to the unfixed toner image T and the recording material P. The toner image T is fixed on the recording material P.

(Heater holder)
Next, the heater holder 130 that is a feature of the present invention will be described. As shown in FIG. 1, the heater 113 as a sliding member on which the inner peripheral surface of the fixing film 112 slides is fitted and held in a slot (groove portion) 130 g provided in the heater holder 130. The heater holder 130 is preferably made of a material having a low heat capacity so that the heat of the heater 113 is not easily removed. In the present embodiment, a liquid crystal polymer (LCP) which is a heat resistant resin is used.

  The heater holder 130 is supported from the side opposite to the heater 113 by an iron stay 120 to give strength. The stay 120 is pressed from both ends in the longitudinal direction (direction intersecting the recording material conveyance direction) by a pressing spring 114 in the direction of arrow A2 in the figure.

  First, the shape of the conventional heater holder 119 will be described for comparison. FIG. 8 shows a schematic diagram of the heater 113 fitted into the slot of the heater holder 119 as viewed from the direction of the arrow A3 in FIG. FIG. 8A is a diagram at normal temperature, and FIG. 8B is a diagram when the heater and the heater holder are heated to a high temperature (abnormal temperature rise) and thermally expanded. The slot of the conventional heater holder 119 has a rectangular shape.

  Since the heater 113 is not bonded to the heater holder, the heater 113 hits the downstream GD of the heater holder by the rotation of the fixing film 112 as described above, and is in the state of FIG. An upstream gap GU is formed at Since the slot of the conventional heater holder 119 has a rectangular shape, the upstream gap GU can be as long as the heater width Wks = 270 mm in the longitudinal direction (WGU in FIG. 2). The width Wh in the conveying direction of the slot of the heater holder 119 is such that the heater 113 is not cracked due to thermal expansion even when the heater 113 is hotter than expected (abnormally heated). Widely set for Wk.

  Even if the temperature rises abnormally, when the energization interrupting element reaches the operating temperature of 270 ° C., the energization is interrupted and the temperature rise is stopped. However, the width Wh of the heater holder slot is more than the operating temperature of the energization cutoff element. That is, the heater 113 is set to fit in the slot of the heater holder 119 even if the heater and the heater holder are thermally expanded to about 300 ° C.

  The alumina heater 113 thermally expands by about 0.1 to 0.2 mm in the recording material conveyance direction at about 300 ° C., and the liquid crystal polymer (LCP) heater holder 119 has a groove Wh of 0.1 to 0. Assume 2 mm narrower. Therefore, the width Wh of the slot of the heater holder 119 is set to be 0.4 mm wider than the width Wk = 6.0 mm of the heater 113.

  Therefore, even when the heater 113 and the heater holder 119 are abnormally heated and thermally expanded as shown in FIG. 8B, the heater 113 is received in the groove of the heater holder 119 without the upstream gap GU becoming zero, The heater 113 does not break. However, when the toner is fixed to the recording material P by heating, the temperature of the heater 113 is controlled only to about 150 to 200 ° C. For this reason, the thermal expansion of the heater 113 and the heater holder 119 is smaller than that at the time of abnormal temperature rise, and the recording material P is heated and fixed in a state where the upstream gap GU is about 0.2 to 0.3 mm. Become.

  Thus, if the upstream gap is large, foreign matter and staples are likely to be caught by the upstream edge portion E of the heater 113. For this reason, in the conventional heater holder 119, the upstream portion of the fixing nip N of the heater holder 119 is 0.3 mm higher than the sliding surface of the heater 113 with the fixing film 112 (FIG. 4 (b). H) This prevents foreign matter and staples from being caught on the upstream edge portion E of the heater 113.

(Shape of heater holder 130)
Next, the shape of the heater holder 130 of this embodiment will be described. FIG. 2 shows a schematic view of the heater 113 as seen from the direction of arrow A3 in FIG.

  In the present embodiment, the heater holder 130 is configured as follows regarding the gap between the heater holder 130 and the heater 113 in the recording material conveyance region. That is, when the upstream side is GUc, the downstream side is GDc, the length in the longitudinal direction where the GUc is formed is WGUc, and the length in the longitudinal direction where the GDc is formed is WGDc, both of the following expressions are satisfied.

GUc <GDc
WGUc <WGDc
On the other hand, regarding the gap in the recording material non-transport area, the gap between the heater holder 130 and the heater 113 is set as follows. That is, when the upstream side is GUe, the downstream side is GDe, the length in the longitudinal direction where GUe is formed is WGUe, and the length in the longitudinal direction where GDe is formed is WGDe, both of the following expressions are satisfied.

GUe> GDe
WGUe> WGUe
In the following, the validity of these equations will be described with a reason. The heater holder 130 according to the present embodiment has a shape in which the gap on the upstream side of the heater 113 is reduced in the recording material conveyance region, so that the fixing film is hardly damaged by foreign matter or staples.

  FIG. 2A is a diagram at normal temperature, and FIG. 2B is a diagram when the heater and the heater holder are heated to a high temperature (abnormal temperature rise) and thermally expanded. Similar to the conventional heater 113 shown in FIG. 8, the heater 113 in this embodiment hits the downstream side of the heater holder 130 by the rotation of the fixing film 112 and becomes the state of FIG.

  Here, the downstream butting surface GDe (FIG. 2A) of the heater 113 in the heater holder 130 of the present embodiment is provided only at both longitudinal ends of the recording material non-transport region. The central portion including the recording material conveyance area has a shape in which a downstream gap GDc is provided on the downstream side of the heater 113.

  Similar to the conventional heater holder 119, in this embodiment, even when the heater 113 and the heater holder 130 are abnormally heated and thermally expanded, the heater 113 is set to fit in the slot of the heater holder 130. That is, at any location in the longitudinal direction, the width Wh of the slot of the heater holder 130 in the recording material conveyance direction is 6.4 mm or more, which is 0.4 mm larger than the heater 113 width Wk = 6 mm. At both ends in the longitudinal direction of the recording material non-conveying area, since the heater 113 abuts the downstream surface GDe, there is no gap on the downstream side, and the upstream gap GUe can be 0.4 mm on the upstream side.

  Since the recording material non-conveying area (both ends in the longitudinal direction) is an area where the fixing nip portion N does not exist, no damage to the fixing film due to foreign matter or staples occurs even if there is a gap on the upstream side. On the other hand, in the recording material conveyance area (the central portion excluding both end portions in the longitudinal direction), the upstream gap GUc is made as narrow as possible in order to suppress damage to the fixing film due to foreign matter or staples. Since the upstream gap GUc is set narrower, the downstream gap GDc is provided wider to absorb thermal expansion during abnormal temperature rise.

  In this embodiment, the upstream gap GUc in the recording material conveyance area is set to 0.1 mm, and the downstream gap GDc is set to 0.3 mm. The narrower the upstream gap GUc, the more difficult it is for foreign matter and staples to be caught by the upstream edge of the heater 113, so the fixing film is less likely to break.

  However, the heater 113 and the heater holder 130 are slightly thermally expanded even when the toner is fixed to the normal recording material P by heating. If the upstream gap GUc is too narrow, stress may be applied to the heater 113 due to thermal expansion during normal heating and fixing, and the heater 113 may be cracked. In this embodiment, a gap is formed on the upstream side of the heater 113. It was set as the structure which provides GUc 0.1mm.

  In the heater holder 130 of the present embodiment, the upstream gap GUc becomes substantially zero due to slight thermal expansion during normal heating and fixing. Therefore, compared to the upstream gap GU = 0.2 to 0.3 mm during normal heating and fixing of the conventional heater holder 119, foreign matter and staples are less likely to catch on the upstream edge of the heater 113, and the fixing film is damaged. hard. The downstream gap GDc may be set to a gap amount that does not break the heater 113 when the temperature rises abnormally in consideration of thermal expansion at the time of abnormal temperature rise. In this embodiment, the downstream gap GDc is set to 0.3 mm.

  Even if a gap is formed on the downstream side of the heater 113, foreign matter and staples are not caught on the edge of the heater 113. Further, the downstream edge portion HDE (FIG. 2A) of the heater holder 130 is curved in the recording material conveyance direction so that the downstream edge portion of the heater holder 130 is not caught. Therefore, even if the gap GDc on the downstream side of the heater 113 is wide, the fixing film is hardly damaged by foreign matter or staples.

  The width WGUc in the longitudinal direction of the upstream gap GUc having a small gap amount is preferably equal to or larger than the maximum recording material width Wp of the image forming apparatus in consideration of damage to the fixing film due to staples attached to the recording material. In consideration of fixing film breakage due to foreign matters in the entire longitudinal direction of the fixing nip portion N, it is preferable to set the rubber length of the pressure roller 110 forming the fixing nip portion N or longer.

  The longitudinal rubber length of the pressure roller 110 of the present embodiment is 226 mm, and the longitudinal width WGUc of the upstream gap GUc of the present embodiment is WGUc = 230 mm, which is 2 mm larger than the rubber length of the pressure roller 110. did.

  On the other hand, the longitudinal width WGDc of the downstream gap GDc of the heater 113 is set wider than the longitudinal width WGUc of the upstream gap GUc. This is to prevent cracking of the heater due to changes in the shape of the heater 113 and the heater holder 130 when the temperature rises abnormally.

  The material of the heater holder 130 of this embodiment uses liquid crystal polymer (LCP), and when the temperature rises abnormally to 280 ° C. or higher, it begins to soften while thermally expanding. The heater holder 130 is sufficiently softer than the alumina heater 113 made of ceramic. For this reason, as shown in FIG. 2B, the thermal expansion of the heater 113 is absorbed by the heater downstream gap GDc in the recording material conveyance region, and the heat heater upstream gap GUe is heated at both ends of the recording material non-conveyance region. The heater holder 130 bends to absorb the expansion. Therefore, even when thermal expansion occurs due to abnormal temperature rise, the stress on the heater 113 is small and the heater 113 does not crack.

  Here, when thermal expansion occurs due to abnormal temperature rise, the interval between the narrowest portions of the slot of the heater holder 130 becomes Wmin with respect to the width Wk of the heater 113, and the heater 113 is likely to be stressed (see FIG. 3 (b)). However, regarding the interval Wmin between the narrowest portions, if the distance Wk of the heater 113 is equal to or greater than the distance obtained by adding the thermal expansion amount at the time of abnormal temperature rise of the heater 113 and the heater holder 130, the heating at the time of abnormal temperature rise is ensured. The stress on the heater 113 is kept low.

  That is, the interval Wmin of the narrowest portion of the slot portion of the heater holder 130 is the width in the recording material conveyance direction when the heater 113 is thermally expanded in a state where the temperature is higher than that when the heater 113 heats the recording material. By making it wider than the sum of the thermal expansion amount of the holding member, the problem can be solved.

  For this reason, in the present embodiment, the longitudinal width WGDc of the downstream gap GDc of the heater 113 is set to 234 mm longer by 2 mm to the left and right than the longitudinal width WGUc = 230 mm of the upstream gap GUc. As a result, the interval Wmin between the narrowest portions was set to about 6.4 mm (at room temperature). For this reason, even if the heater 113 and the heater holder 130 of this embodiment are thermally expanded due to abnormal temperature rise, the stress on the heater 113 is reduced and the heater 113 is not cracked.

  In the present embodiment, the longitudinal width WGDc of the heater heater downstream gap GDc in the recording material conveyance region is 234 mm with respect to the longitudinal width Wks = 270 mm of the heater 113. Therefore, the longitudinal width WGDe of the butting surface GDe is about 18 mm on the left and right sides of the heater 113 at both ends in the longitudinal direction of the recording material non-conveying area.

  On the other hand, on the upstream side, the longitudinal width WGUc of the heater heater upstream gap GUc in the recording material conveyance region is 230 mm with respect to the longitudinal width Wks = 270 mm of the heater 113. For this reason, the longitudinal width WGUe of the upstream gap GUe at both ends in the longitudinal direction of the recording material non-conveying region is about 20 mm on the left and right, and is 2 mm wider on the left and right than the longitudinal width WGDe of the downstream abutment surface GDe.

  As described above, the shape of the heater holder 130 according to the present embodiment is such that the gap on the upstream side of the heater can be narrowed in the central portion including the recording material conveyance area, and therefore, the shape of the heater holder 130 can be reduced by foreign matter or staples. The fixing film is hardly damaged. Therefore, in the heater holder 130 of the present embodiment, the upstream portion (the heater holder upstream convex portion H shown in FIG. 6) of the fixing nip portion N of the conventional heater holder 119 can be set low.

  If the heater holder upstream convex portion H (FIG. 6) can be lowered, the inner surface of the fixing film 113 is easily brought into contact with the heater 113, so that the inner surface nip Nk is widened and the heat of the heater 113 is easily transmitted to the fixing film 113. . Therefore, the fixability of the toner to the recording material P is improved. The lower the heater holder upstream convex portion H is, the wider the inner surface nip Nk becomes, so that the fixing property is improved. However, when the heater holder upstream convex portion H becomes lower than the sliding surface of the heater 113 with the fixing film 112, the upstream edge portion E of the heater 113 becomes lower. It will be in the state which protrudes with respect to the heater holder upstream convex part H. FIG. For this reason, the fixing film 112 is easily caught by the upstream edge portion E of the heater 113.

  Therefore, the heater holder upstream convex portion H (FIG. 6) is preferably about 0 ≦ H <0.3 mm, and in this embodiment, the heater holder upstream convex portion H is set to 0.05 mm. In this embodiment, since the gap on the upstream side of the heater is narrow, the fixing film is hardly damaged by foreign matter or staples, and the pressing force can be increased.

  In this embodiment, the fixing force is further increased by setting the pressing force in the direction of the arrow A2 in the drawing by the pressure spring 114 in FIG. 1 to be stronger than usual, and taking a wider width in the recording material conveyance direction of the fixing nip portion. Has improved. The stronger the applied pressure, the wider the fixing nip portion N and the better the fixability. However, the amount of rubber deformation of the elastic layer 116 of the pressure roller 110 increases, which may cause rubber breakage. . Therefore, the applied pressure is preferably 100 N or more, particularly about 100 N to 300 N, and is 245 N in this embodiment. At this time, the width of the fixing nip N is 10 mm, and the width of the inner surface nip Nk is 5 mm.

(Comparison result)
Here, using the configuration of the fixing device of this embodiment, the heater holder 130 of this embodiment and the conventional heater holder 119 were compared. Specifically, the fixing film base layer thickness was changed to 40 μm, 50 μm, 60 μm, and 70 μm, and the fixing property was compared with the presence or absence of image defects due to the perforation of the fixing film.

  The fixability is expressed by a density reduction rate and is calculated by the following method. The measuring instrument used was a Macbeth reflection densitometer RD914, and the halftone image fixed on the paper was rubbed 5 reciprocally at a load of 0.4 N / cm2 on 5 sheets of lens cleaning paper (Dusper K-3 manufactured by Ozu Sangyo). Measure the concentration before and after. In this embodiment, a halftone density having a density D1 before rubbing of about 0.7 is used. If the density after rubbing is D2, the density reduction rate is calculated by (D1-D2) / D1.

  Then, the temperature of the back surface of the heater 113 is controlled to be 200 ° C., a black halftone image is printed for each base film thickness of the fixing film, and the density reduction rate is measured to measure the fixing property. Evaluation was performed. A case where the density reduction rate was less than 10% was evaluated as good fixability. A case where the density reduction rate was 20% or more was evaluated as. Here, the fixing criteria are determined by the specifications of the device, and the required fixing properties can be determined appropriately by the device.

  In addition, the following procedure was used to evaluate the occurrence of image defects due to the perforation of the fixing film. A recording material is prepared in which staples as shown in FIG. 4 are fastened to a letter-size recording material having a basis weight of 90 g / cm 2. 4A is a cross-sectional view of the staple, and the staple is fastened to the recording material in such a direction that the “back” in FIG. 4A comes to the back side (non-printing ground side) of the normal recording material. In FIG. 4A, it has been found from prior investigation that when the “back” is conveyed to the fixing nip portion N in a direction in contact with the fixing film 112, a hole is easily formed in the fixing film.

  Further, it has been found that the fixing film 112 is likely to be perforated when the direction in which the staple is fastened is perpendicular to the recording material longitudinal direction or 45 degrees. For this reason, the recording material used in this test includes staples at four locations, two at the front end and the rear end of the recording material in the direction perpendicular to the longitudinal direction of the recording material and in the direction of 45 degrees as shown in FIG. What was fastened one by one was used.

  Then, the image forming apparatus is set so that the “back” side in FIG. 4A is in contact with the surface of the fixing film 112. One sheet of the recording material with the staples is conveyed, and then a solid black image is printed on the entire surface.

  When there was a hole in the fixing film, a “white spot” was generated on the solid black image. Therefore, when even one “white spot” occurred, it was evaluated as x. Further, when there was no hole in the fixing film and the surface was flawed, a flaw of the fixing film period was also generated on the solid black image. Therefore, the case where the flaw occurred on the image was evaluated as Δ. A case where there was no defect in the fixing film cycle on the image was evaluated as ◯. The fixing performance evaluation and the fixing film perforation test were all compared with the configuration of the fixing device of this embodiment, except for the difference in the heater holder.

  Table 1 shows a comparison result when the heater holder 130 of the present embodiment and the conventional heater holder 119 are used.

  In the conventional heater holder, the upstream gap at the time of heat fixing is as wide as 0.2 to 0.3 mm. Therefore, when the pressure is high as in the heating device of this embodiment, the base film thickness of the fixing film is 60 μm and the fixing film becomes a fixing film. Scratches are generated and perforations occur at 50 μm or less. In addition, since the heater holder upstream convex portion H is as high as 0.3 mm, the fixing layer density reduction rate could not be less than 10% unless the inner surface nip width is narrow and the base film thickness of the fixing film is 50 μm or less. .

  On the other hand, in the heater holder of this embodiment, since there is almost no upstream gap at the time of heating and fixing, even in the fixing device configuration of this embodiment having a high applied pressure, even if the fixing film thickness is reduced to 40 μm, it remains scratched. There was no hole. Further, since the heater holder upstream convex portion H is as low as 0.05 mm, the inner surface nip width is wide, and even when the film thickness of the fixing film is 60 μm or more, the density reduction rate of the fixing property can be less than 10%.

  By adopting a shape like the heater holder 130 of the present embodiment, the gap on the upstream side of the heater can be narrowed in the central portion including the recording material conveyance area. Is less likely to break. Therefore, it is possible to use a fixing film thinner than the conventional heater holder 119 and increase the pressure, and it is possible to cope with higher speed.

<< Second Embodiment >>
In the first embodiment, the downstream abutment portion of the heater 113 to the heater holder 130 is a surface (downstream abutment surface GDe), but is not limited to the surface. For example, as shown in the heater holder 150 in FIG. 5, the heater 113 may be abutted at a point where the abutting portion of the heater 113 downstream of the heater holder 130 is a convex portion PDe.

  In this case, the position of the downstream abutment protrusion PDe is set such that the longitudinal width WGDc of the downstream gap GDc of the heater 113 is wider than the longitudinal width WGUc of the upstream gap GUc. Then, the interval Wmin between the narrowest portions is set to be equal to or greater than the distance obtained by adding the amount of thermal expansion at the time of abnormal temperature rise of the heater 113 and the heater holder 130 to the width Wk of the heater 113. Thereby, the stress to the heater 113 can be kept low when the temperature rises abnormally.

  Note that the shape of the abutting portion downstream of the heater 113 to the heater holder 130 is not limited to that described in the first embodiment or the present embodiment.

(Modification)
Although the preferred embodiments of the present invention have been described in the above-described embodiments, the present invention is not limited to these embodiments, and various modifications are possible within the scope of the gist. In accordance with the recording material conveyance speed and fixability required depending on the specifications, optimization of settings such as rigidity of heater or sliding plate or heater holder, film thickness, pressure, etc. Addition is possible.

(Modification 1)
In the embodiment described above, the sliding member is a heat generating member (heater), and the endless belt is heated by the heater, but the present invention is not limited to this. The endless belt may be a heat generating belt provided with a heat generating layer, and the sliding member may be a temperature equalizing member that equalizes the temperature unevenness of the heat generating belt in the longitudinal direction.

(Modification 2)
In the above-described embodiment, the configuration in which the heater 113 made of alumina is fitted into the slot of the liquid crystal polymer heater holder 130 is described, but the present invention is not limited to this. The width of the heater and sliding member and the gap between the heater holders should be set in consideration of the amount of thermal expansion of each material so that the heater will not break under stress even if the heater is heated abnormally. It ’s fine. In addition, the height and pressure setting of the heater holder upstream convex portion is optimized according to the required printing speed and fixability, and according to the setting amount of the gap upstream of the heater and the strength and rigidity of the base layer of the fixing film. Good.

  Further, the configuration in which the heater is not bonded to the heater holder has been described, but the same effect can be obtained when the heater is bonded to the heater holder.

(Modification 3)
In the above-described embodiment, the configuration in which the heater holder 130 is more easily bent than the heater 113 by using a soft material for the heater holder 130 has been described, but the present invention is not necessarily limited thereto. The heater holder 130 receives the frictional force F from the fixing film 112 and bends and deforms in the downstream direction. However, the heater holder 130 can be easily bent by increasing the frictional force F between the heater holder 130 and the fixing film 112.

  For example, the inner surface of the fixing film 112 and the sliding surface of the heater holder 130 with the fixing film 112 may be roughened, or the pressure contact force of the pressure roller 110 may be increased. In this way, the frictional force F between the heater holder 130 and the fixing film 112 can be increased, and the heater holder 130 can be easily bent and deformed in the downstream direction.

(Modification 4)
In the above-described embodiment, the heater 113 uses an alumina substrate as the substrate, has a sufficiently higher rigidity than the heater holder 130, and the heater 113 is not easily bent by the frictional force F of the fixing film 112. However, the present invention is not limited to this.

  When the heater 113 does not have a sufficiently high rigidity, for example, a glass with higher smoothness is formed on the sliding surface between the fixing film 112 and the inner surface of the fixing film 112 in order to reduce the frictional force between the fixing film 112 and the heater 113. May be used. Or you may make it the structure which provides the layer of a fluorine layer (for example, PTFE or PFE) with a small friction coefficient. In this way, if the frictional force between the fixing film 112 and the heater 113 can be reduced, the heater 113 does not bend, and only the heater holder 130 can be bent and deformed.

  Here, in addition to the frictional force F caused by the rotation of the fixing film 112, there is a frictional force between the heater 113 and the heater holder 130. If the frictional force between the heater holder 130 and the heater 113 is high, the heater 113 may be bent and deformed together with the bending deformation of the heater holder 130. In such a case, it is preferable to reduce the frictional force between the heater holder 130 and the heater 113 by applying grease to the bottom surface of the slot of the heater holder 130 and the back surface of the heater 113.

  By doing in this way, the heater 113 cannot be bent easily, and only the heater holder 130 can be configured to be easily bent and deformed in the downstream direction.

  Further, the frictional force between the fixing film and the heater holder can be appropriately reduced by the rigidity of the heater and the heater holder, the surface property of the inner surface of the fixing film, the pressure contact force (pressing force) of the pressure roller, and the like. Alternatively, the frictional force between the fixing film and the heater and between the heater and the heater holder can be reduced. Accordingly, the heater can hardly be bent and deformed, and only the heater holder can be easily bent and deformed. As described above, even if the heater holder is not necessarily softer than the heater, it is possible to obtain the same effect as that shown in the above-described embodiment.

(Modification 5)
In the above-described embodiment, the fixing film which is a rotating body has a two-layer structure including the base layer 126 and the release layer 127. However, the present invention is not limited to this. An elastic layer may be provided between the base layer 126 and the release layer 127. By using a heat-resistant silicone rubber or the like as the elastic layer, the fixing film easily adheres to the unevenness of the recording material, so that the image quality is good. become. The thicker the elastic layer, the easier it is to adhere to the irregularities of the recording material and the better the image quality. However, if it is too thick, the heat of the heater is difficult to transfer to the recording material and the fixability deteriorates. preferable.

  Even when a fixing film having an elastic layer is used as described above, if the heater holder shape of the present invention is used, the gap on the upstream side of the heater can be narrowed, so that the fixing film is hardly damaged by foreign matter or staples.

(Modification 6)
In the above-described embodiment, the endless belt is provided on the first rotating body. However, the endless belt may be provided on the second rotating body facing the first rotating body. An endless belt may be provided on both the first rotating body and the second rotating body.

  In the above-described embodiment, the case where the rotating body (pressure roller) as the rotating body and the pressing body presses the fixing rotating body (fixing belt) is shown. However, the present invention is not limited to this, and the present invention can be similarly applied to a case where a rotating body as an opposing body is pressed from a fixing belt (film) as a fixing rotating body, not as a pressing body. Here, the opposing body is a member that faces the fixing rotator, presses against the fixing rotator, forms a fixing nip portion, and clamps the moving recording material at the fixing nip portion.

  In the above-described embodiment, the recording paper is described as the recording material. However, the recording material in the present invention is not limited to paper. Generally, a recording material is a sheet-like member on which a toner image is formed by an image forming apparatus. For example, regular or irregular plain paper, cardboard, thin paper, envelope, postcard, seal, resin sheet, OHP sheet, Includes glossy paper. In the above-described embodiment, for the sake of convenience, the recording material (sheet) P has been described using terms such as passing paper, paper passing portion, and non-paper passing portion. It is not limited.

  In the above-described embodiment, the fixing device that fixes an unfixed toner image on the sheet has been described as an example. However, the present invention is not limited to this, and the toner that is assumed on the sheet in order to improve the gloss of the image. The present invention can be similarly applied to a device that heats and presses an image (also a fixing device in this case).

110 ..Pressure roller, 112 ..Fixing film, 113 ..Heating heater, 130 ..Heater holder

Claims (11)

A rotatable endless belt,
A sliding member on which an inner peripheral surface of the endless belt slides during rotation of the endless belt;
The endless belt includes a groove for fitting the sliding member, and forms an upstream and downstream gap with the sliding member in the recording material conveying direction so as to fit the sliding member. A holding member that holds the sliding member in contact with the inner peripheral surface of
A facing member that forms a nip portion that is opposed to the sliding member via the endless belt and that transports a recording material between an outer peripheral surface of the endless belt;
A fixing device comprising:
Regarding the gap in the recording material conveyance area,
When the upstream side is GUc, the downstream side is GDc, the length in the longitudinal direction intersecting the recording material conveyance direction in which the GUc is formed is WGUc, and the length in the longitudinal direction in which the GDc is formed is WGDc.
GUc <GDc
WGUc <WGDc
Together, and
Regarding the gap in the recording material non-transport region,
When the upstream side is GUe, the downstream side is GDe, the length in the longitudinal direction where the GUe is formed is WGUe, and the length in the longitudinal direction where the GDe is formed is WGDe,
GUe> GDe
WGUe> WGUe
The fixing member is configured to satisfy both of the above.   The fixing device according to claim 1, wherein the sliding member has a rectangular parallelepiped shape that is long in the longitudinal direction.   The fixing device according to claim 1, wherein the sliding member is a heat generating member, and the endless belt is heated by the heat generating member.   The endless belt is a heat generating belt provided with a heat generating layer, and the sliding member is a temperature equalizing member that equalizes temperature unevenness of the heat generating belt in the longitudinal direction. The fixing device described.   The fixing device according to claim 3, wherein the heat generating member is a ceramic heater whose base material is ceramic.   The interval between the narrowest portions of the groove portions is the width in the recording material conveyance direction and the thermal expansion of the holding member during thermal expansion of the heating member in a state where the heating member is at a higher temperature than when the heating member heats the recording material. The fixing device according to claim 3, wherein the fixing device is wider than a sum of the amount.   The fixing device according to claim 1, wherein the GDe is zero.   The fixing device according to claim 1, wherein the holding member is made of a liquid crystal polymer.   The fixing device according to claim 1, wherein the endless belt is made of a heat resistant resin.   The fixing device according to claim 1, wherein the facing member is a pressure roller.   11. The fixing device according to claim 1, wherein the pressure of the press-contact forming the nip portion is 100 N or more.