Image reproducing apparatus with high-speed transfer mechanism

Claim 1

An image reproducing apparatus comprising a driven toner image retaining member, an endless transfer belt moving with said toner image retaining member to allow the toner image to be transferred thereto when said transfer belt is brought into contact with the surface of said toner image retaining member, means pressing said belt into contact with said image retaining member, a belt supporting mechanism including a cylindrical roller about whose outer surface the inner surface of said transfer belt is wrapped through an angle of contact θ, determined by the following formula: θ=a×V/R×(C×r)/k×d.sup.2 wherein: a is a positive integer V is the moving speed of the belt in cm/sec. R is the radius of the cylindrical roller in cm. C is the specific heat of the belt in calories/gram °C. r is the mean specific gravity of the belt k is the thermal conductivity of the belt in calories/cm sec. d is the thickness of the belt in cm., transfer sheet material, a pressure roller first urging said transfer sheet material against said transfer belt approximately adjacent the point where the belt departs the outer surface of said cylindrical roller, and means heating said cylindrical roller to a temperature at which the surface of said belt is substantially equal to the softening point of the toner at said point, whereby the toner image on said transfer belt is gradually heated by said cylindrical roller throughout said angle of contact and is transferred to the transfer sheet material fed between said pressure roller and said belt.