Backup roll for heated fuser system

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG.
1, the fuser system includes a fuser roll couple comprised of a fuser roll 1 and a backup roll 2.
As is conventional, the rolls are mounted for rotation in opposite directions with the fuser roll in pressure contact with the backup roll and driven by suitable means shown at 3.
Sheets, such as paper 4, are fed into the nip between the rolls to fix the thermoplastic image thereto.
In construction, the fuser roll may include a thin substantially rigid cylindrical wall 5 made of good heat conductive material such as aluminum.
The surface of the cylindrical wall is provided with a smooth thin layer of silicone elastomer 6 such as General Electric RTV60 which is resistant to heat degradation and deformable under pressure engagement with the backup roll.
The fuser roll is heated by a heating element 7 extending axially through the interior of the roll.
In accordance with the teachings of the present invention, the backup roll 2 is constructed of a core member 8 having good heat conductive characteristics.
As shown, the core member is cylindrical in shape and has an internally vaned construction.
In the preferred embodiment of the invention, the core member is constructed of aluminum with a wall thickness of about 1/2 inch.
The outer cylindrical surface of the core member is coated with a heat insulative coating 9.
In the preferred construction, this coating covers the entire outer surface of the core member and is of polyurethane reinforced fluorinated ethylene propylene.
Such a coating material is manufactured by the Dupont Corporation as Dupont 958-200 Series Teflon-S.
The coating material is chosen for its heat transfer characteristics; and more particularly, in accordance with the teachings of the present invention, it is one that has heat transfer characteristics that are substantially the same as those of the paper copy sheets fed through the fuser couple.
In determining the necessary characteristics of the coating, the thermal properties of the paper and, in particular, its heat transfer characteristics in relation to the heated fuser roll and backup roll are first determined