Polyethylene films are well suited for use in disposable articles formed from plural layers of plastic material, but no suitable welding or sealing technique has heretofore been developed to enable polyethylene to be used where now only vinyl is being used. For instance, polyethylene film is well suited to uses in the medical field where vinyl is presently used, such as in the construction of disposable cholestomy collection bags and blood bags. The number of such uses is growing. Polyethylene, a non-polar material, is approved for use in cholestomy bags and blood bags, but its use therein is hindered by difficulties in fabrication. The articles constructed of polyethylene can be made of much thinner film than those constructed of vinyl, because of the superior resistance of polyethylene to permeation of fluids therethrough. Furthermore, because of the rising cost of petroleum for use as a chemical feedstock, the thinner polyethylene film affords a decided cost advantage over the thicker vinyl film. In this regard, it is noted that other non-polar materials such as acetate, do not require petroleum in their manufacture, and would also provide a cost advantage.
Unfortunately, because polyethelene is a non-polar material, it is unsuited for dielectric heating technique, and therefore, unlike vinyl or other polar materials, could not heretofore be sealed thermally by any conventional application of radio frequency (RF) current to the material. Thus, films of polyethylene or other non-polar thermoplastic materials have been difficult to employ in fabrication of the above-mentioned medical articles or other like articles.
USPTO Backgrounds
USPTO Backgrounds