Apparatus for forming a uniform liquid film on a roller

Claim 1

A fixing apparatus for thermally fixing toner images onto a support medium, comprising a first roller, a second roller arranged parallel and adjacent to the first roller so that rotation of at least one of the first and second rollers will feed the support medium between the first and second rollers, a layer of releasing material formed on the circumference of the first roller, a heater to heat the layer, a transfer roller arranged parallel to the first roller and in contact with the layer, and an applicator to apply a lubricant onto the circumference of the transfer roller to be transferred therefrom onto the circumference of the first roller, the applicator comprising a reservoir containing the lubricant, a porous member partially immersed in the lubricant, a porous cloth contacting the porous member and the circumference of the transfer roller, and biasing means to urge the porous cloth against the circumference of the transfer roller, the compositions of the first roller, the transfer roller, the porous cloth and the lubricant being selected so that the coefficient of friction between the first roller and the transfer roller is greater than the coefficient of friction between the transfer roller and the porous cloth when the thickness of the lubricant is less than a predetermined value, and the coefficient of friction between the first roller and the transfer roller is less than the coefficient of friction between the transfer roller and the porous cloth when the thickness of the lubricant on the first roller is greater than the predetermined value such that when the thickness is less than the predetermined value the transfer roller is rotated by the first roller to pick up lubricant from the porous cloth and transfer the same to the first roller, and when the thickness slightly exceeds the predetermined value the transfer roller will be prevented from rotating by the porous cloth until the thickness drops slightly below the predetermined value, whereby a uniform film of lubricant of substantially constant thickness is applied onto the circumference of the first roller.