JP2024067575A - Fixing device - Google Patents

Abstract

To solve the problem in which when a film support member has a shape extending from the downstream side to the upstream side in a recording material conveyance direction, if a fixing film is largely deformed during fixing, the fixing film and the film support member are brought into contact in a wide range, which deprives a large amount of heat of the fixing film and may cause problems such as local fixing failure and uneven glossiness.SOLUTION: When seen in a generatrix direction of a fixing film, a film deformation prevention member projects to the downstream side in a recording material conveyance direction beyond ribs of a film guide on the downstream side in the recording material conveyance direction. When a virtual line is drawn which passes through a rotation center axis of a pressure roller and is perpendicular to a surface of a heater facing the pressure roller, the film deformation prevention member is shorter in length in a rotation direction of the film deformation prevention member in a portion on the upstream side of the virtual line than a portion on the downstream side of the virtual line.SELECTED DRAWING: Figure 8

Description

The present invention relates to a fixing device used in image forming devices such as electrophotographic copying machines and laser printers.

Film heating type fixing devices have been known for some time as fixing devices used in electrophotographic image forming apparatuses. A film heating type fixing device has a heater with a resistance heating element on a ceramic substrate, a fixing film that is heated and rotates while in contact with the heater, and a pressure roller that forms a nip with the heater via the fixing film. A recording material carrying an unfixed toner image is heated while being sandwiched and transported in this nip, and the toner image on the recording material is fixed to the recording material.

In a fixing device that uses a film heating method, when narrow recording material (small-sized paper) is continuously transported relative to the maximum paper feed width, slack may occur in the center of the upstream longitudinal direction of the fixing film. This slack occurs when the flexible fixing film bends in a bow shape toward the upstream side in the transport direction of the recording material.

There is concern that the shape of the fixing film when it rotates may cause paper wrinkles, and in order to prevent such paper wrinkles, in Patent Document 1, a protrusion for supporting the fixing film from the inside is installed on the film guide downstream in the transport direction and in the longitudinal center.

However, in the configuration described in Patent Document 1, there is a concern that the sliding properties of the fixing film may deteriorate because the fixing film constantly rubs against the protruding portions while contacting them. For this reason, a method of suppressing deformation can be considered, as described in Patent Document 2, by providing a film support member that supports the inside of the fixing film when the fixing film is deformed and does not come into contact with the fixing film when the fixing film is not deformed.

Patent Publication No. 2007-79507 Patent Publication 2005-215390

The film support member in Patent Document 2 extends from downstream to upstream in the recording material transport direction. Therefore, if the fixing film is significantly deformed during fixing, the fixing film and the film support member come into contact over a wide area, which can take away a lot of heat from the fixing film, resulting in problems such as localized fixing failure and uneven gloss.

The purpose of the present invention is to minimize the area of contact between the film and the film support member when the film is deformed, thereby minimizing the loss of heat from the film and suppressing poor fixing and uneven gloss.

In order to solve the above problems, the present invention relates to
A cylindrical film that rotates while in contact with a recording material;
a heater disposed in an internal space of the film for heating a recording material;
a rotatable pressure roller that forms a nip portion with a heater via the film;
a guide member disposed in an internal space of the film and guiding a rotation of the film, the guide member having a plurality of ribs arranged along the generatrix direction at each of an upstream portion and a downstream portion of the heater in a recording material transport direction;
a stay member arranged in an internal space of the film and parallel to a generatrix direction of the film, the stay member reinforcing the guide member;
a film deformation suppressing member that is engaged with the stay member and that suppresses deformation of the film when the inner side of the film comes into contact with the stay member due to deformation of the film;
a fixing device for fixing a toner image on a recording material by heating the toner image on the recording material at the nip portion,
When viewed in the generating line direction, the film deformation suppressing member protrudes downstream in the recording material conveying direction further than the rib downstream in the recording material conveying direction,
The film deformation suppression member is characterized in that, when an imaginary line is drawn passing through the central axis of rotation of the pressure roller and perpendicular to the surface of the heater facing the pressure roller, the length of the film deformation suppression member in the rotational direction is shorter in the upstream portion of the imaginary line than in the downstream portion of the imaginary line.

According to the present invention, by minimizing the area of contact between the film and the film support member when the film is deformed, heat is not taken away from the film as much as possible, and poor fixing and uneven gloss can be suppressed.

1 is a cross-sectional view of an image forming apparatus according to a first embodiment of the present invention; 1 is a schematic cross-sectional view of a fixing device according to a first embodiment of the present invention; FIG. 1 is a schematic diagram for explaining a crown shape of a heater holder in the first embodiment; FIG. 1 is an explanatory diagram of a heater holder in the first embodiment. FIG. 1 is an explanatory diagram of a film deformation suppressing member in Example 1. FIG. 1 is a diagram for explaining the positional relationship between a film deformation suppressing member and a rib of a heater holder in the first embodiment; FIG. 1 is an explanatory diagram of the attachment of a film deformation suppressing member in the first embodiment. FIG. 1 is a diagram for explaining the effects of the first embodiment. FIG. 13 is a diagram for explaining the position of a film deformation suppressing member in the second embodiment; FIG. 13 is a diagram for explaining the effects of the second embodiment. An explanatory diagram of a heater holder in a conventional configuration

[Example 1]
A first embodiment of the present invention will be described below. First, the main body structure of an image forming apparatus in this embodiment will be described, and then the fixing device will be described in detail.

(Image forming apparatus)
An example of an image forming apparatus used in this embodiment will be described with reference to the schematic diagram shown in FIG. 1. The image forming apparatus 50 in this embodiment is an electrophotographic image forming apparatus that transfers a toner image on a photosensitive drum 1 directly onto a recording material P. On the peripheral surface of the photosensitive drum 1, which is an image carrier, a charger 2, an exposure device 3 that irradiates the photosensitive drum 1 with a laser beam L, a developing device 5, a transfer roller 10, and a photosensitive drum cleaner 16 are arranged in this order along the rotation direction (arrow R1 direction). First, the surface of the photosensitive drum 1 is negatively charged by the charger 2. Next, an electrostatic latent image is formed on the surface of the charged photosensitive drum 1 by the laser beam L of the exposure device 3. The toner in this embodiment is negatively charged, and the toner is attached only to the electrostatic latent image portion on the photosensitive drum 1 by the developing device 5 containing black toner, and a toner image T is formed on the photosensitive drum 1. When the recording material P is fed by the feed roller 4, the recording material P is conveyed to the transfer nip Ntr by the conveying roller 6. A transfer bias of positive polarity, which is opposite to the polarity of the toner, is applied to the transfer roller 10 from a power source (not shown), and the toner image T on the photosensitive drum 1 is transferred onto the recording material P at the transfer nip Ntr. After transfer, residual toner on the surface of the photosensitive drum 1 is removed by a photosensitive drum cleaner 16 having an elastic blade. The recording material P bearing the toner image T is transported to a fixing device 100, where the toner image T on the surface is heated and fixed.

(Fixing device)
The fixing device 100 of this embodiment will be outlined below. The fixing device 100 of this embodiment is a film heating type fixing device aimed at shortening warm-up time and reducing power consumption. Fig. 2(a) is a cross-sectional view of the fixing device 100 in this embodiment near the longitudinal center, and Fig. 2(b) is a cross-sectional view in the longitudinal direction near the longitudinal end. In the following description, the recording material conveying direction is A, the heater holder longitudinal direction is B, and the heater sliding surface perpendicular direction is C.

In this embodiment, the fixing film 112 has an inner diameter of Φ18 mm in a cylindrical state without deformation, and has a multi-layer structure in the thickness direction. The layer structure of the fixing film 112 consists of at least a base layer to maintain the strength of the film and a release layer to reduce dirt adhesion to the surface. The material of the base layer needs to be heat-resistant to receive the heat of the heater 113, and also needs to be strong to slide against the heater 113, so it is recommended to use metals such as stainless steel or nickel, or heat-resistant resins such as polyimide. In this embodiment, polyimide is used as the material of the base layer of the fixing film 112, and a carbon-based filler is added to improve thermal conductivity and strength. The thinner the thickness of the base layer, the easier it is to transmit the heat of the heater 113 to the surface of the recording material P, but the strength decreases, so it is preferable that the thickness is about 15 μm to 100 μm, and in this embodiment, it is 60 μm.

The material of the release layer of the fixing film 112 is preferably a fluororesin such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polytetrafluoroethylene (PTFE), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). In this embodiment, PFA, which has excellent release properties and heat resistance among fluororesins, is used. The release layer may be a tube covered or a surface coated with paint. In this embodiment, the release layer is molded by a coat that is excellent for thin-wall molding. The thinner the release layer, the easier it is to transmit the heat of the heater 113 to the surface of the fixing film 112, but if it is too thin, durability will deteriorate, so a thickness of about 5 μm to 30 μm is preferable, and in this embodiment, it is 10 μm. In addition, although not used in this embodiment, an elastic layer can be provided between the base layer and the release layer. In that case, silicone rubber, fluororubber, etc. are used as the material of the elastic layer.

A heater holder 130 is provided in the internal space of the fixing film 112. The heater holder 130 has a cross section that is approximately semicircular and gutter-shaped, and is made of a highly heat-resistant liquid crystal polymer to meet heat resistance and rigidity requirements. In this embodiment, Sumikasuper (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. is used as the liquid crystal polymer. The heater holder 130 holds the heater 113, but also serves as a guide member that guides the rotation of the fixing film 112 by loosely fitting the fixing film 112 onto the heater holder 130. The heater holder 130 will be described in detail later.

The stay member 119 is disposed parallel to the heater holder 130 along the longitudinal direction of the heater holder 130. The stay member 119 is made of highly rigid sheet metal such as stainless steel that has been bent to apply uniform pressure to the heater holder 130 in the longitudinal direction, reinforcing the heater holder 130.

The film deformation suppression member 134 is engaged with the stay member 119. The film deformation suppression member 134 will be described in detail later.

In this embodiment, the pressure roller 110 has an outer diameter of Φ20 mm, and is formed with a Φ14 mm iron core 117 and an elastic layer 116 with a thickness of 3.0 mm. The material of the elastic layer 116 is solid rubber or foamed rubber. Foamed rubber has a low heat capacity and low thermal conductivity, and the heat on the surface of the pressure roller 110 is not easily absorbed into the inside, so the surface temperature is easily raised, and the fixing start-up time can be shortened. In this embodiment, foamed rubber made by foaming silicone rubber is used. On the elastic layer 116, a release layer 118 made of PFA is formed as a release layer for the toner. The release layer 118 may be covered with a tube or coated with paint, as with the release layer of the fixing film 112, but in this embodiment, a tube with excellent durability was used. The lower the surface hardness of the pressure roller 110, the lighter the pressure pressure and the wider the fixing nip Nf can be obtained, but it is necessary to determine the surface hardness taking durability into consideration. In this example, we used a 50° Asker-C hardness (4.9 N load).

The heater 113 in this embodiment is a typical heater used in a fixing device that uses a film heating method, and is equipped with a resistance heating element on a ceramic substrate. The heater 113 is made of an alumina substrate with a width of 6 mm and a thickness of 1 mm in the recording material conveying direction, coated with an Ag/Pd (silver palladium) resistance heating element by screen printing to a thickness of several tens of μm, and then covered with glass to a thickness of 60 μm to protect the heating element and ensure sliding properties. The temperature of the heater 113 is adjusted by appropriately controlling the current flowing through the resistance heating element in response to a signal from a temperature detection element (not shown) that detects the temperature of the ceramic substrate or the fixing film 112. The heater 113 is fixed and supported by being fitted into a groove portion provided in the heater holder 130. In this embodiment, the center of the heater 113 in the recording material conveying direction is located 0.2 mm upstream of the center of the pressure roller 110 in the conveying direction.

As shown in FIG. 2(b), the left and right flanges 120 are fitted to the left and right outward extension arms 119a of the stay member 119, respectively. The film unit 101 is arranged approximately parallel to the upper side of the pressure roller 110 with the heater 113 side facing downward, and is disposed between the left and right side plates 136 of the device frame 135. The core metal shaft portion 117a of the pressure roller 110 is installed on the bearing member 137 engaged with the left and right side plates 136 of the device frame 135. The left and right flanges 120 each have a vertical groove portion that engages with the vertical edge portion of a vertical guide slit provided in the left and right side plates 136, respectively. In this embodiment, a liquid crystal polymer is used as the material for the flanges 120.

Then, the pressure spring 122 is compressed between the pressure portion 120b of the left and right flanges 120 and the pressure spring support portion 121. As a result, the heater 113 is pressed against the upper surface of the pressure roller 110 with a predetermined pressing force, sandwiching the fixing film 112 through the left and right flanges 120, the stay member 119, and the heater holder 130. In this embodiment, the pressure of the pressure spring 122 is set so that the pressing force between the fixing film 112 and the pressure roller 110 is 15 kg. In the fixing nip portion Nf, the fixing film 112 is sandwiched between the heater 113 and the pressure roller 110 and bent according to the flat surface of the lower surface of the heater 113, and the inner surface of the fixing film 112 is in close contact with the flat surface of the lower surface of the heater 113. The fixing film regulating portion 120a of the flange 120 is shaped to be located 0.5 mm upstream in the conveying direction, based on a shape that follows the natural shape formed when the fixing film 112 is pressed at the fixing nip portion Nf. By regulating the inner surfaces of both ends of the fixing film 112 on the upstream side, the trajectory of the fixing film 112 when it is rotated is stabilized.

Then, a rotational force is transmitted from a drive mechanism (not shown) to the drive gear G of the pressure roller 110, and the pressure roller 110 is rotated at a predetermined speed in the direction of the arrow R2 in FIG. 2(a). As the pressure roller 110 rotates, a rotational force acts on the fixing film 112 due to the frictional force between the pressure roller 110 and the fixing film 112 in the fixing nip portion Nf. As a result, the inner surface of the fixing film 112 slides in close contact with the lower surface of the heater 113 while the outer circumference of the heater holder 130 rotates in the direction of the arrow R3 in FIG. 2(a) following the rotation of the pressure roller 110. The pressure roller 110 rotates at a surface movement speed of 200 mm/sec. A heat-resistant lubricant is applied to the inner surface of the fixing film 112, thereby ensuring the sliding properties between the heater 113 and the heater holder 130 and the inner surface of the fixing film 112. In this embodiment, fluorine-based grease is used as the lubricant. Specifically, perfluoropolyether (PFPE) oil was used as the base oil, and grease mixed with polytetrafluoroethylene (PTFE) powder was used as the adjuster.

(Heater holder)
The shape of the heater holder 130 will be described in detail. As shown in the schematic diagram of FIG. 3, the heater holder 130 has a crown shape in which the longitudinal center of the seating surface supporting the heater 113 protrudes toward the pressure roller 110 compared to the longitudinal ends. The heater 113 is attached to the heater holder seating surface at both ends by a heater power supply unit 138 and a heater clip 139. The crown shape is a gentle quadratic curve shape in a region CR with a longitudinal width of 225 mm corresponding to the position facing the pressure roller 110, and the longitudinal center protrudes 0.4 mm compared to the longitudinal ends. By providing this crown shape, when the stay member 119 and the core metal 117 are bent and deformed when pressure is applied, a fixing nip Nf of uniform width can be formed in the longitudinal direction. As described above, the width of the fixing nip Nf in the recording material conveying direction in this embodiment is 6.2 mm in the longitudinal direction.

Figure 4(a) is a cross-sectional view of the heater 113 and heater holder 130 near the fixing nip Nf in the longitudinal center. The heater holder 130 has an upstream protrusion 131 that protrudes toward the pressure roller 110 from the seat surface S1 of the heater 113, upstream of the heater 113 in the recording material conveying direction. The protrusion height H of the upstream protrusion 131 from the heater sliding surface S2 needs to be a certain height to regulate the trajectory of the fixing film 112 and prevent the fixing film 112 from contacting the edge of the heater 113. However, if it is too high, it will be a factor that prevents the recording material P from entering the fixing nip, so a height of about 0.1 to 1.0 is desirable. In this embodiment, the height H of the upstream protrusion 131 from the heater sliding surface S2 is 0.2 mm.

The heater holder 130 has a downstream protrusion 132 that protrudes toward the pressure roller 110 from the seat surface S1 of the heater 113 downstream in the recording material conveyance direction. In the longitudinal region where the recording material P is conveyed, the heater 113 is positioned in the conveyance direction by positioning portions provided at both longitudinal ends of the heater holder 130, and the downstream protrusion 132 is formed after leaving a gap of 0.05 mm from the downstream end position of the heater 113.

The downstream protrusion 132 has an R section 132a in the portion close to the heater 113, a flat section 132b following the R section 132a, and an inclined section 132c continuing from the flat section 132b and sloping toward the opposite side of the pressure roller 110. In this embodiment, the R section 132a is a curved surface with a radius of 0.3 mm. It is desirable that the height of the flat section 132b be approximately the same as the heater sliding surface S2, and in this embodiment, the height of the flat section 132b from the seating surface S1 is 1.0 mm.

Figure 4(b) is an oblique view of the heater holder 130. Figure 4(c) is a cross-sectional view of the film unit 101, taken at a longitudinal position where there is an upstream rib 133a, which is a rib located upstream in the transport direction, and a downstream rib 133b, which is a rib located downstream in the transport direction, provided on the heater holder 130. The shape of the fixing film 112 in Figure 4(c) represents the shape of the fixing film 112 rotating steadily.

In this embodiment, ten upstream ribs 133a and ten downstream ribs 133b are arranged at a predetermined interval in the longitudinal direction within the paper passing area. The upstream ribs 133a and downstream ribs 133b are shaped to provide a predetermined gap from the fixing film 112, which is rotating steadily. The reason they are provided with a gap between them and the fixing film 112 is to prevent heat from being lost from the fixing film 112 by contact with the upstream ribs 133a and downstream ribs 133b.

When the fixing film 112 is subjected to a large deformation due to an external force, the upstream rib 133a and the downstream rib 133b back up the inner surface of the fixing film 112 to prevent the fixing film 112 from being damaged. For example, the fixing film 112 may be significantly deformed during a jam clearance operation in which the user manually removes the recording material P caught in the fixing nip Nf. In this embodiment, as shown in FIG. 4(c), a gap of G1 = 0.8 mm is provided between the inner surface of the fixing film 112 and the tip of the upstream rib 133a, and a gap of G2 = 0.8 mm is provided between the inner surface of the fixing film 112 and the tip of the downstream rib 133b.

(Film deformation suppression member)
5A is a cross-sectional view of the film unit 101 at the longitudinal center, and FIG. 5B is a diagram for explaining the positional relationship with the heater holder and the inner surface of the fixing film. FIG. 5C is a diagram showing the longitudinal arrangement of the stay member 119, the heater holder 130, and the film deformation suppressing member 134 in the film unit 101. In this embodiment, the film deformation suppressing member 134 is attached to the stay member 119. The attachment method may be appropriately selected, and may be double-sided tape or adhesive, but in this embodiment, the film deformation suppressing member 134 is fixed by inserting a claw portion (not shown) provided on the film deformation suppressing member 134 into a through hole provided in the stay member 119. The film deformation suppressing member 134 is formed of the same liquid crystal polymer as the heater holder 130 in order to satisfy heat resistance and dimensional accuracy. In addition, the film deformation suppressing member 134 has a rib shape with three protrusions on the surface in order to minimize the heat taken from the fixing film 112 when it comes into contact with the fixing film 112.

The film deformation suppression member 134 is shaped to continuously cover the stay member 119 from the downstream side in the transport direction to the top surface of the stay member 119. In FIG. 5(b), the downstream rib 133b and the film deformation suppression member 134 are drawn overlapping in the longitudinal direction to explain the positional relationship with the heater holder and the inner surface of the fixing film. The shape of the fixing film 112 in FIG. 5(b) represents the shape of the fixing film 112 during steady rotation.

The film deformation suppression member 134 protrudes from the downstream rib 133b downstream in the transport direction by D1 = 0.5 mm, and is positioned to provide a gap of D3 = 0.3 mm with the fixing film 112 rotating steadily. In addition, the film deformation suppression member 134 is formed in a position that ensures a gap of at least 0.3 mm with the fixing film rotating steadily from the downstream side in the transport direction to the upper surface.

If an imaginary line LC is drawn that passes through the central axis of rotation of the pressure roller and is perpendicular to the surface of the heater facing the pressure roller, the imaginary line LC becomes a line that is approximately in the center of the fixing film when the fixing film is viewed in the generatrix direction. As shown in FIG. 5(a), the length of the film deformation suppression member 134 in the rotation direction is shorter on the upstream side of the imaginary line LC than on the downstream side.

It is desirable to provide at least one film deformation suppression member 134 in the longitudinal direction of the stay member 119 within the minimum paper passing width of the paper size that can be printed. In this embodiment, the film deformation suppression member 134 is located at the longitudinal center of the paper passing area and between the downstream ribs 133b of the heater holder, as shown in FIG. 5(c).

As shown in Figures 6(a) and (b), when the fixing film is viewed from the upstream side in the generatrix direction or the recording material transport direction, there is a gap of length Da between the upstream rib 133a and the film deformation suppression member 134 so that they do not overlap. As shown in Figures 6(c) and (d), when the fixing film is viewed from the downstream side in the generatrix direction or the recording material transport direction, the downstream rib 133b and the film deformation suppression member 134 overlap by a length Db.

Figure 7 shows a perspective view of the film deformation suppression member 134 installed on the stay member 119. The maximum paper passing width of the fixing device in this invention is 216 mm, and the minimum paper passing width is 100 mm.

(Effects of this embodiment)
The behavior of the fixing film 112 will be described when large size paper is passed through and when small size paper is passed continuously. The behavior of the fixing device will be described when small size paper, which is narrower than A4, is passed continuously when LTR or A4 size recording material is used as the large size paper.

When small-sized paper is continuously fed through the longitudinal center position, the temperature of the fixing film 112, pressure roller 110, etc. rises in the non-paper-passing areas at both longitudinal ends. This causes the elastic layer 116 of the pressure roller to thermally expand, and the outer diameter of the non-paper-passing areas increases. As a result, since the fixing film 112 is rotated by the pressure roller 110, the conveying speeds Vr and Vl of the fixing film 112 at the longitudinal ends are greater than the speed Vc of the fixing film 112 at the longitudinal center, as shown in Figure 8(a).

Before describing the rotation shape of the fixing film 112 in this embodiment, the shape of the fixing film 112 during rotation when small size paper is passed using a film unit 101 that does not have a film deformation suppression member 134 will be described. FIG. 11(a) is a diagram illustrating the shape of the longitudinal center of the fixing film 112 during small size paper passing in a conventional fixing device 100. When small size paper is passed, the fixing film 112 near the longitudinal center moves upstream in the recording material P conveying direction relative to the heater holder 130, and the gap with the downstream rib 133b decreases. This is related to the temperature rise of the non-paper passing portion of the pressure roller 110 when small size paper is passed as described above. When small size paper is passed continuously, the fixing film 112 moves upstream (arrow E side) in the recording material P conveying direction A as shown in FIG. 11(a) because the conveying speed of the longitudinal center decreases relatively to both ends in the longitudinal direction B. This is because the fixing film 112 receives a force from the recording material P in the fixing nip Nf in the direction opposite to the conveying direction.

Next, the longitudinal shape of the fixing film 112 will be described with reference to FIG. 11(b). Both longitudinal ends of the heater holder 130 are restricted by flanges 120 fixed between the left and right side plates 134 of the device frame 135, and therefore cannot move upstream. Therefore, when small-sized paper is being fed through, the fixing film 112 bends in a bow shape toward the upstream side in the transport direction of the recording material P, unlike when large-sized paper is being fed through.

Figure 8 (b) shows the behavior of the fixing film 112 when small size paper is continuously passed through the fixing device in this embodiment. In this embodiment, the inner surface of the fixing film 112 that is rotating at a steady speed is provided with a film deformation suppression member 134, so when small size paper is continuously passed through, the fixing film 112 in the longitudinal center tends to bend upstream (toward the arrow E) as shown in Figure 8 (b). In this embodiment, the inner surface of the fixing film 112 is provided with a film deformation suppression member 134. Therefore, when the fixing film 112 tends to bend upstream, it is continuously held by the film deformation suppression member 134 from the downstream side of the inner surface of the fixing film 112 in the conveying direction to the upper surface side of the stay member 119 on the opposite side to the fixing nip Nf. As a result, it is possible to suppress slackening of the fixing film 112 in the conveying direction upstream of the longitudinal center. Therefore, even when small size paper is continuously passed through, it is possible to prevent the occurrence of paper wrinkles caused by slackening of the fixing film 112.

On the other hand, when large-sized paper is passed through, the slack in the fixing film 112 as described above does not occur, and the fixing film 112 rotates in approximately the same shape as when it is rotating steadily without the recording material P being passed through as shown in Figure 5 (b). When large-sized paper is passed through, a predetermined gap is provided between the inner surface of the fixing film 112 and the film deformation suppression member 134, so localized temperature drops in the fixing film 112 are unlikely to occur, and fixing failures are unlikely to occur. Since the inner surface of the fixing film 112 can be continuously backed up only when small-sized paper is passed through continuously, paper wrinkles that occur when small-sized paper is passed through continuously can be prevented.

In addition, the film deformation suppression member 134 has a shorter length in the rotation direction on the upstream side than on the downstream side in the recording material transport direction, so it is possible to suppress the loss of heat from the film on the upstream side, thereby suppressing poor fixing and uneven gloss.

In this embodiment, one film deformation suppression member 134 is provided in the longitudinal center, but this is not limited to this, and multiple film deformation suppression members 134 may be provided. It is desirable to provide at least one film deformation suppression member 134 within the minimum paper passing width, but it is also effective to provide film deformation suppression members 134 in at least the central region divided into three parts of the maximum paper passing width.

[Example 2]
A second embodiment of the present invention will be described below. The second embodiment differs from the first embodiment only in the number and position of the film deformation suppressing members in the longitudinal direction. Other configurations are the same as those of the first embodiment, so detailed configurations of the image forming apparatus and the fixing device will not be described.

(Features of this embodiment)
The longitudinal position of the film deformation suppressing member 134, which is a feature of this embodiment, will be described with reference to Fig. 9. In the first embodiment, the film deformation suppressing member 134 is provided in only one place at the longitudinal center, whereas in this embodiment, two are provided at positions symmetrical with respect to the longitudinal center. The distance from the longitudinal center to the center position of the film holding member 134 is 26 mm.

(Effects of this embodiment)
Further effects of this embodiment will be described. In the first embodiment, since only one film deformation suppressing member 134 is provided in the longitudinal center, when small size paper is continuously passed through and the inner surface of the fixing film 112 is supported by the film deformation suppressing member 134, the fixing film 112 is supported at one point as shown in FIG. 10A, and therefore comes into contact with the film deformation suppressing member 134 with a relatively strong force. Depending on the conditions such as the rigidity of the fixing film 112, the fixing film 112 may be locally deformed near the contact point, which may affect the conveyance of the recording material P. On the other hand, in this embodiment, since two film deformation suppressing members 134 are provided, the inner surface of the fixing film 112 is supported at two points as shown in FIG. 10B when small size paper is continuously passed through. Therefore, the force applied to the inner surface of the fixing film 112 is dispersed, and local deformation of the fixing film 112 is less likely to occur. As a result, the rotation shape of the fixing film 112 is more stable, and the occurrence of paper wrinkles can be prevented.

In this embodiment, two film deformation suppression members 134 are provided, but three or more may be provided.

[Additional Notes]
The above embodiments disclose at least the following recording device.

(Item 1)
A cylindrical film that rotates while in contact with a recording material;
a heater disposed in an internal space of the film for heating a recording material;
a rotatable pressure roller that forms a nip portion with a heater via the film;
a guide member disposed in an internal space of the film and guiding the rotation of the film, the guide member having a plurality of ribs arranged along a generatrix direction of the film on both an upstream side portion and a downstream side portion of the heater in a recording material transport direction;
a stay member arranged in an internal space of the film and parallel to a generatrix direction of the film, the stay member reinforcing the guide member;
a film deformation suppressing member that is engaged with the stay member and that suppresses deformation of the film when the inner side of the film comes into contact with the stay member due to deformation of the film;
a fixing device for fixing a toner image on a recording material by heating the toner image on the recording material at the nip portion,
When viewed in the generating line direction, the film deformation suppressing member protrudes downstream in the recording material conveying direction further than the rib downstream in the recording material conveying direction,
A fixing device characterized in that, when an imaginary line is drawn passing through the central axis of rotation of the pressure roller and perpendicular to the surface of the heater facing the pressure roller, the length of the film deformation suppression member in the rotation direction is shorter in the upstream portion of the imaginary line than in the downstream portion of the imaginary line.

(Item 2)
Item 2. The fixing device according to item 1,
The fixing device according to claim 1, wherein the film deformation suppressing member does not overlap with the upstream rib when viewed in the generatrix direction.

(Item 3)
3. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the film deformation suppressing member overlaps with the rib on the downstream side when viewed in the generatrix direction.

(Item 4)
4. The fixing device according to any one of claims 1 to 3,
the fixing device comprising a plurality of the film deformation suppressing members, each of which is engaged with the stay member so as to be aligned in the generatrix direction.

LIST OF SYMBOLS 1 Photosensitive drum 2 Charger for charging photosensitive drum 3 Exposure device for exposing charged photosensitive drum 4 Paper feed roller for feeding paper 5 Developing device for developing developer onto photosensitive drum 6 Transport roller for transporting recording material 10 Transfer roller for transferring developer on photosensitive drum onto recording material 16 Photosensitive drum cleaner for cleaning photosensitive drum 50 Image forming apparatus main body 100 Fixing device 110 Pressure roller for forming a fixing nip and rotating fixing film 112 Fixing film which is an endless belt 113 Heater 116 Elastic rubber layer of pressure roller 117 Core metal of pressure roller 118 Release layer of pressure roller made of fluororesin 119 Stay member 119a Outer extension arm of stay member 120 Flange 120a Film regulation portion of flange 120b Pressure portion of flange 121 Pressure spring support portion 122 Pressure spring 130 Heater holder for holding heater 131 Upstream protruding portion of heater holder 132 Downstream protruding portion of heater holder 132a R portion of downstream protruding portion 132b Flat portion of downstream protruding portion 132c Sloped portion of downstream protruding portion 133a Upstream rib of heater holder 133b Downstream rib of heater holder 134 Film deformation suppressing member 135 Device frame 136 Side plate 137 Bearing member 138 Heater power supply portion 139 Heater clip 140 Second protruding portion P Recording material L Laser light emitted from exposure device T Toner image Ntr Transfer nip Nf Fixing nip S1 Heater seating surface S2 Heater sliding surface G Pressure roller gear A Recording material transport direction B Longitudinal direction C Direction perpendicular to heater sliding surface CR Crown area R1 Drum rotation direction R2 Pressure roller rotation direction R3 Fixing film rotation direction L1 Width of flat portion 132b in the recording material transport direction L2 Width of flat portion 132b' at the longitudinal end in the recording material transport direction H Height of upstream protrusion 131 from heater sliding surface S2 D1 Protrusion amount of film deformation suppressing member 134 from downstream rib 133b of heater holder downstream in the transport direction D2 Coverage amount of film deformation suppressing member 134 in the upstream direction from the heater center line D3 Gap from film deformation suppressing member 134 to the inner surface of fixing film 112 downstream in the transport direction D4 Gap from film deformation suppressing member 134 to the inner surface of fixing film 112 on the upper surface of fixing film unit 112 D5 Gap from film deformation suppressing member 134 to the inner surface of fixing film 112 at a position between the downstream in the transport direction and the upper surface LC Approximately center line of fixing film Da Gap length between upstream rib 133a and film deformation suppressing member 134 Db Overlapping length between the upstream rib 133a and the film deformation suppressing member 134

Claims (4)

A cylindrical film that rotates while in contact with a recording material;
a heater disposed in an internal space of the film for heating a recording material;
a rotatable pressure roller that forms a nip portion with the heater via the film;
a guide member disposed in an internal space of the film and guiding the rotation of the film, the guide member having a plurality of ribs arranged along a generatrix direction of the film on both an upstream side portion and a downstream side portion of the heater in a recording material transport direction;
a stay member arranged in an internal space of the film and parallel to a generatrix direction of the film, the stay member reinforcing the guide member;
a film deformation suppressing member that is engaged with the stay member and that suppresses deformation of the film when the inner side of the film comes into contact with the stay member due to deformation of the film;
a fixing device for fixing a toner image on a recording material by heating the toner image on the recording material at the nip portion,
When viewed in the generating line direction, the film deformation suppressing member protrudes downstream in the recording material conveying direction further than the rib downstream in the recording material conveying direction,
A fixing device characterized in that, when an imaginary line is drawn passing through the central axis of rotation of the pressure roller and perpendicular to the surface of the heater facing the pressure roller, the length of the film deformation suppression member in the rotation direction is shorter in the upstream portion of the imaginary line than in the downstream portion of the imaginary line. The fixing device according to claim 1, characterized in that, when viewed in the generatrix direction, the film deformation suppression member does not overlap with the upstream rib. The fixing device according to claim 1, characterized in that, when viewed in the generatrix direction, the film deformation suppression member overlaps with the downstream rib. The fixing device according to any one of claims 1 to 3, characterized in that there are a plurality of the film deformation suppression members, each of which is engaged with the stay member so as to be aligned in the generatrix direction.

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