Image-forming machine fixing device with a nipping region having a pressure distribution

A fixing device comprising a thermally fixing roller, an endless belt, and pushing means which pushes said belt toward the thermally fixing roller from the side of the inner peripheral surface of said belt such that part of the region in the circumferential direction on the outer peripheral surface of said belt is pushed onto part of the region in the circumferential direction on the outer peripheral surface of the thermally fixing roller,

• wherein a nipping region is formed between said part of the region of said belt and said part of the region of the thermally fixing roller that come in contact with each other, and said belt is driven when the thermally fixing roller is driven to rotate,
• wherein said part of the region of said belt is pushed by pushing means onto said part of the region of the thermally fixing roller in a manner that a pressure distribution is established in the circumferential direction of said nipping region, said pressure distribution producing a maximum pressure in an upstream end region of the thermally fixing roller in the direction of rotation in said nipping region, another maximum pressure in a downstream end region thereof in the direction of rotation in said nipping region, and a pressure in an intermediate region of said nipping region between said upstream end region and said downstream end region, which pressure is not higher than said maximum pressure in said upstream end region and not higher than said another maximum pressure in said downstream end region,
• wherein provision is made of a parting member for parting the paper conveyed through said nipping region from the outer peripheral surface of the thermally fixing roller, the parting member being made of a piece of metal plate extending in the axial direction of the thermally fixing roller, and having a parting portion linearly extending toward the outer peripheral surface of the thermally fixing roller from the outer side in the radial direction of the thermally fixing roller and toward the upstream from the downstream in the direction of rotation when the thermally fixing roller is viewed in the axial direction, and the tip of the parting portion is positioned maintaining a gap of 0.5 mm to 2.0 mm with respect to the outer peripheral surface on the paper-passing region of the thermally fixing roller, and
• wherein, when the thermally fixing roller is viewed in the axial direction and when a time from when a point on the outer peripheral surface of the thermally fixing roller has separated away from said nipping region until when it arrives at a point where a straight line in agreement with the outer surface of the parting portion of the parting member intersects the outer peripheral surface on the paper-passing region of the thermally fixing roller, is regarded to be a parting time T (seconds), the parting time T (seconds) is defined to be within 60% to 100% of the nipping time S (seconds).