Fixing device including heating body and overtemperature protector, image forming apparatus and fixing device heating unit therewith

1. A fixing device, comprising:

an endless belt that supplies heat to a medium;

a heat diffusion member that stretches the endless belt;

a heating body that heats the heat diffusion member;

an overtemperature protector that is positioned to face the heating body; and

a support member that is positioned between the heating body and the overtemperature protector.

2. The fixing device according to claim 1 , wherein

the heat diffusion member includes an indented part that abuts the heating body; and

the indented part includes

an abutting part that abuts the heating body, and

a heat transfer part that faces the support member.

3. The fixing device according to claim 2 , wherein

the heating body is configured with a sheet heating body that is in a sheet shape,

a surface area of the support member is formed larger than a surface area of the sheet heating body, and

areas of the support member that project from the sheet heating body face the heat transfer part.

4. The fixing device according to claim 2 , wherein

the heating body is configured with a sheet heating body that is in a sheet shape,

a distance between the abutting part and the heat transfer part is smaller than a thickness of the sheet heating body.

5. The fixing device according to claim 2 , further comprising:

heat conductive grease that is applied between the heat transfer part and the support member.

6. The fixing device according to claim 1 , wherein

the support member is an aluminum plate having a heat capacity of 11.75 J/K or more and 24.2 J/K or less.

7. The fixing device according to claim 1 , wherein

the support member is a copper plate.

8. The fixing device according to claim 1 , wherein

the support member is a plate having a uniform thickness.

9. The fixing device according to claim 1 , wherein

the support member is formed in a U shape by folding edge parts of a plate of the support member.

10. The fixing device according to claim 1 , wherein

the support member is positioned in contacting edge parts to the heat diffusion member.

11. The fixing device according to claim 1 , wherein

the overtemperature protector is positioned in abutting the support member.

12. The fixing device according to claim 1 , wherein

a heat capacity of the support member is 30% or more and 62% or less of a heat capacity of the heat diffusion member.

13. The fixing device according to claim 1 , wherein

a thickness of the support member is 1 mm or more and 2 mm.

14. The fixing device according to claim 1 , wherein

an expression below is satisfied:

T 2max≧( C 1 ×T 1max)/( C 2×α)

where C 1 is a heat capacity of the heat diffusion member, C 2 is a heat capacity of the support member, T1max is a maximum reaching temperature of the endless belt, T2max is a maximum reaching temperature of the overtemperature protector, and α is a coefficient.

15. An image forming apparatus, comprising:

the fixing device according to claim 1 .

16. A fixing device heating unit, comprising:

a heat diffusion member that diffuses heat including a two-step indented part, the two-step indented part including a first indented section and a second indented section larger than the first indented section;

a heating body that heats the heat diffusion member and that has a first width, the heating body being fitted in the first indented section and including a first side facing the heat diffusion member and a resistance heating body being provided on the first side;

a support member that contacts the heating body and has a second width larger than the first width, the support member being fitted in the second indented section; and

heat transfer from the heating body to the heat diffusion member is faster than from the heating body to the support member.