Electrophotographic apparatus and belt fixing device with non-uniform nip pressure

A belt fixing device comprising:

• an endless fixing belt;
• a plurality of belt transport rollers for rotatably supporting said fixing belt;
• a heat source for applying heat to a sheet on which an image is to be fixed;
• and
• a pressure roller resiliently mounted for pressing said sheet against said fixing belt,
• wherein the area of contact between said fixing belt and said pressure roller includes, sequentially in a direction of sheet transport:
• a first contact portion in which toner on the sheet is heated and fused by said heat source;
• a second contact portion in which the fused toner is cooled;
• and
• a third contact portion in which said fixing belt and said pressure roller are kept in contact with each other;
• wherein a pressure in said first contact portion is greater than a pressure applied to the toner and the sheet in each of said second and third contact portions.

A belt fixing device comprising:

• an endless fixing belt;
• a plurality of belt transport rollers for rotatably supporting said fixing belt;
• a heat source for applying heat to a sheet on which an image is to be fixed;
• and
• a pressure roller mounted for pressing the sheet against said fixing belt,
• wherein the area of contact between said fixing belt and said pressure roller includes, sequentially in the direction of sheet transport:
• a first contact portion in which toner on the sheet is heated and fused by said heat source;
• a second contact portion in which the fused toner is cooled;
• and
• a third contact portion in which said fixing belt and said pressure roller are kept in contact with each other;
• wherein a pressure in said first contact portion is greater than a pressure applied to the toner and the sheet in each of said second and third contact portions;
• and
• wherein said fixing belt contains at least 90% nickel, and a sheet-contact surface of said fixing belt is coated with silicone rubber.

An electrophotographic apparatus including a photosensitive member, an exposure device for projecting light corresponding to image information onto said photosensitive member to form an electrostatic latent image thereon, a plurality of developers for developing the electrostatic latent image by employing toners corresponding to colors of the electrostatic latent image, a transfer device for transferring a developed toner image to a sheet, and a fixing device through which said sheet is passed for fixing the toner to the sheet,

• said fixing device comprising:
• an endless fixing belt;
• a plurality of belt transport rollers for rotatably supporting said fixing belt;
• a heat source for applying heat to the sheet, said heat source being provided inside one belt transport roller of said plurality of belt transport rollers, said one belt transport roller being disposed at a sheet entrance of the belt fixing device;
• and
• a pressure roller mounted for pressing the sheet against said fixing belt,
• wherein said belt transport rollers are disposed in contact with an external circumference of said pressure roller with said fixing belt being interposed, and a pressure between said pressure roller and said one belt transport roller is larger than a pressure between said pressure roller and another belt transport roller which is disposed downstream of said one belt transport roller in a direction of sheet transport.