Patent ID: 7266339

Claim:
An image-forming device comprising: an image-forming portion that forms a visible image on an A4-size recording paper by using developer, the recording paper having four sides, the four sides including a pair of opposite first sides and a pair of opposite second sides that are longer than the first sides; and a fixing portion, the fixing portion including: a heating roller having a central axis and a rigid peripheral surface around the central axis, the peripheral surface being heated to a temperature T HR (° C.); and a pressure roller having a central axis and a resilient layer around the central axis, the central axis of the pressure roller being parallel to the central axis of the heating roller, the pressure roller having a diameter D PR (mm), the pressure roller being pressed against the heating roller to allow the resilient layer to be compressed by the rigid surface of the heating roller, thereby causing the resilient layer of the pressure roller to deform and follow the shape of the surface of the heating roller, a nip part being defined as an area of contact between the heating roller and the pressure roller, the heating roller and the pressure roller rotating to convey the recording paper in a recording paper conveying direction through the nip part, the nip part having an upstream end and a downstream end in the recording paper conveying direction, the heating roller and the pressure roller conveying the recording paper through the nip part from the upstream end to the downstream end with a leading edge of the recording paper being one of the first sides, thereby causing the visible image to be fixed on the recording paper, the heating roller and the pressure roller discharging the recording paper fixed with the visible image from the downstream end of the nip part in a discharging direction, the heating roller having a width W NIP (mm) at the nip part between the upstream end and the downstream end, an angle of separation θ (°) being defined within a plane orthogonal to the central axis of the heating roller and being formed between the discharging direction and a tangent to the heating roller at the downstream end of the nip part, the temperature T HR (° C.), the angle of separation θ (°), the diameter D PR (mm), and the width W NIP (mm) satisfying the following inequality: 114≦0.55 T HR −2.36θ−1.59 D PR +8.62 W NIP ≦144.