Conventionally "hard" rollers for commercial printing presses have consisted of cylindrical metal cores over which are secured plastic sleeves for example of polyethylene or Nylon (trade mark). Such rollers are conventionally made at the present time by various processes including the heating of the metal core and the placing of that core in a fluid bath of powdered plastic (e.g. Nylon or polyethylene), or by electrostatic spraying of the plastic material onto the metal core. The plastic coating is then machined to ensure proper symmetry thereof and proper size (outer diameter). The achievable thickness of the plastic sleeve is limited when using the fluid bath coating process. Both the fluid bath coating and electrostatic spray processes require relatively expensive apparatus.
Securing the plastic sleeve in place on the metal core by means of an adhesive substance is not a preferred process for making hard rollers, since conventional adhesives used in this process have a tendency to loosen under the rigorous conditions of usage of such hard rollers.
U.S. Pat. No. 4,198,739 of Dudinger et al issued Apr. 22, 1980 is representative of a process of securing such a plastic sleeve to a metal core by means of an adhesive.
U.S. Pat. Nos. 4,250,605 and 4,325,998, both of Chapman, issued respectively Feb. 17, 1981 and Apr. 20, 1982, describe and illustrate a method for providing a polymer sleeve for a process roller, which method uses a biaxially heat shrinkable sleeve, for example made of polyvinyl chloride. The sleeve is placed over a cylinder into a tight fitting relationship and then heat is applied to the sleeve to shrink it into secured position on the cylinder. This process requires usage of either a normally biaxially heat shrinkable polymer or, in the case of polyvinyl chloride, pretreating the polyvinyl chloride by biaxially expanding it in both radial and axial directions beyond its room temperature elastic limits. Such biaxially heat shrinkable polymers are relatively expensive and consequently may be impractical for general use in making hard rollers for commercial printing presses.
It is an object of the present invention to provide a simple, inexpensive method of making such hard rollers, using conventional polymer materials.