Fixing device

1 . A fixing device for fixing a toner image formed on a recording medium to the recording medium, the fixing device comprising:

a film unit including a tubular film that is configured to rotate while being in contact with the recording medium;

a roller configured to be in contact with an outer surface of the tubular film, wherein the roller and the film unit form a fixing nip portion configured to pinch and convey the recording medium on which the toner image is formed; and

a frame that includes a first side frame configured to hold one end portion of the film unit in a longitudinal direction of the fixing device and includes a second side frame configured to hold the other end portion of the film unit in the longitudinal direction,

wherein at least one of the first side frame and the second side frame includes a first plate configured to hold at least one of the film unit and the roller, and a second plate disposed substantially parallel to the first plate and having a surface facing the film unit,

wherein the first plate is fixed to the second plate on a surface facing the other side frame of the second plate, and

wherein as seen in the longitudinal direction, an area of the first plate is smaller than that of the second plate.

2 . The fixing device according to claim 1 , wherein each of the first plate and the second plate has U-shaped fitting portion configured to hold at least one of the film unit and the roller.

3 . The fixing device according to claim 1 , wherein a gear shaft of a gear configured to apply a power to the roller is fixed to the second plate.

4 . The fixing device according to claim 1 ,

wherein the second plate includes a first area that is in contact with the first plate and includes a second area that is substantially parallel to the first plate and is separated from the first plate in the longitudinal direction, and

wherein an air gap is provided between the first plate and the second plate by the second area.

5 . The fixing device according to claim 1 , further comprising a spring configured to urge the film unit in a direction toward the roller,

wherein the first plate holds the film unit and the roller, and

wherein the first plate and the second plate are fixed by a plurality of fixing portions, and the plurality of fixing portions is disposed at a position where the film unit is positioned in an urging direction of the spring.

6 . The fixing device according to claim 5 , wherein the plurality of fixing portions is a portion where the first plate and the second plate are fixed by welding.

7 . The fixing device according to claim 1 ,

wherein the film unit includes restriction portions,

wherein each of the restriction portions (i) is configured to restrict an offset movement of the tubular film in the longitudinal direction, (ii) faces, at positions, a different one of both end portions of the tubular film in the longitudinal direction, and (iii) is attached to the first plate.

8 . The fixing device according to claim 1 , wherein, in an internal space of the film unit, an elongated heater is provided along the longitudinal direction, and the tubular film is held between the elongated heater and the roller.