Image heating apparatus

1. An image heating apparatus comprising:

a rotatable member;

a heater contactable to a surface of said rotatable member to heat said rotatable member; and

a back-up member cooperative with said rotatable member to form a nip for nipping and feeding a recording material carrying an image, wherein a position of a peak in a pressure distribution with respect to a rotational direction of said rotatable member is upstream, with respect to the rotational direction, of a central portion of a contact region between said rotatable member and said heater with respect to the rotational direction.

2. An apparatus according to claim 1 , wherein said heater includes a ceramic substrate and a heat generating resistor provided on said ceramic substrate.

3. An apparatus according to claim 1 , wherein said rotatable member is a roller having an elastic layer around a metal core.

4. An apparatus according to claim 3 , wherein said roller has a heat storage layer provided around said elastic layer, wherein the thermal conductivity of said elastic layer is no higher than 0.15 W/m·k and the specific gravity of said elastic layer is no higher than 0.85, and the thermal conductivity of said heat storage layer is 0.50 W/m·k-1.60 W/m·k and the specific gravity of said heat storage layer is 1.05-1.30.

5. An apparatus according to claim 4 , wherein said roller has a separation layer which is provided around said heat storage layer, and the material of which said separation layer is composed is a fluorinated resin.

6. An apparatus according to claim 5 , wherein said separation layer contains silicon carbide or graphite.

7. An apparatus according to claim 5 , wherein said roller is formed so that its surface hardness is in a range of 40°-45° in the Asker C scale, under a load of 4.9 N.

8. An apparatus according to claim 3 , wherein said heater is disposed such that in a contact area between said heater and said roller, a line L 1 which is perpendicular to a contact plane between said heater and said roller and which passes through a widthwise center of said heater is downstream, with respect to the rotational direction of said roller, of a line L 2 which is parallel with the widthwise center line L 1 and which passes through said metal core.

9. An apparatus according to claim 8 , wherein a portion of said heater at an entrance to the contact area is a curved surface.

10. An apparatus according to claim 1 , wherein said rotatable member is an endless belt stretched around a plurality of rollers, and one of the rollers and said back-up member sandwiches said endless belt to form said nip.

11. An apparatus according to claim 1 , further comprising a sliding member interposed between said heater and said rotatable member.

12. An apparatus according to claim 11 , wherein a micro hardness of a surface of said sliding member is higher than that of a surface of said rotatable member.

13. An apparatus according to claim 11 , wherein a surface of said sliding member which is in contact with said rotatable member is tilted so that the upstream edge of the surface of said sliding member, upstream with respect to the rotational direction, is closer to an axial line of said rotatable member than the downstream edge of the surface of said sliding member, downstream with respect to the rotational direction.

14. An apparatus according to claim 11 , wherein a surface of said sliding member which is in contact with said rotatable member has a bulge portion configured to create the peak in the pressure distribution.

15. An apparatus according to claim 1 , wherein the peak value in the pressure distribution is no higher than 9.8 N.

16. An apparatus according to claim 1 , wherein said heater is kept under pressure by a compression spring in a pressing direction toward said rotatable member, and wherein said heater is tilted so that a normal line relative to an interface between said heater and said rotatable member does not become parallel to the pressing direction by said compression spring.