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About Welding of Thin
Polymeric Films For Medical Applications
Nearly all thermoplastics can be
used in film form as thin, soft, flexible, elastomeric materials
that can be folded or creased without damage. In selecting films
for medical devices. The factors to be considered include cost,
biocompatibility, sterilizability, mechanical toughness,
elasticity, optical clarity, leachability, barrier properties,
drug interaction, and sealing and assembly characteristics.
Films most commonly used in the
medical industry include high- and low-density polyethylene and
polypropylenes , plasticized PVC, polyurethane elastomers, and
breathable specialty films such as polyester. A clear
understanding is required not only of a material’s properties, but
also of how a particular welding process will affect it.
The weldability of plastics is
affected by various factors, including type of polymer; resin
grade; presence of plasticizers, lubricants, and other additives;
and moisture content. Thermal properties, molecular
characteristics, and crystallinity of a polymer affect processing
and film properties; additives influence extrusion and orientation
processes and improve film properties; and reductions in the
thickness of a film can lower costs and increase the area obtained
from a given weight of polymer yield per square meter.
In the 1970s, PVC became the
material of choice for Band-Aids, and later the use of polymeric
film patches in surgical draping became popular, replacing latex
films. In the 1990s, the use of organ bags, drug-delivery patches,
and breathable films for wound care increased dramatically, making
films much in demand in the medical industry. However, health and
environmental concerns about PVC and latex films have driven the
development of alternative materials for these applications.
Thermoplastic polyurethane, is well
suited for use in flexible medical products such as storage and
collection bags and other types of flexible containers and similar
articles.
Polyurethane films offer some
important advantages over other films, including PVC. They have
similar welding characteristics to PVC, provide strength equal to
PVC in a thinner film, contain no plasticizers, are sterilizable
by either EtO or gamma radiation, and have good alcohol
resistance. Polyurethane films also can be readily sealed using
radio frequency (RF) welding techniques.
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