Cyclic Olefin Co-polymers (COC) are a relatively new class of polymers that have seen significant growth and penetration into the medical device and diagnostics markets. Chemically COC are generally comprised of a rigid ring structure and optionally varying amounts of ethylene and are polymerized using a metallocene catalyst. The most common ring structures are based on norbornene with various substituent groups to tailor properties. There are also commercial resins based on more complex ring structures that lead to higher Tg values.
Figure 1. Representative Structure of COC
Ticona was the highest volume COC producer but sold the business to Daicel Chemical Industries and Polyplastics Co., Ltd who markets under the original trade name TOPAS™. Injection molding and extrusion grade are also marketed as Zeonor™ by Zeon Chemicals, and Apel™ by Mitsui Chemical.
Distinguishing characteristics of COC resins are based on their amorphous character, moderate to high Tg, very high optical clarity, low birefringence and excellent moisture barrier properties. The barrier properties of COC are quite remarkable as shown in the figure below:
Figure 2. Oxygen and Moisture Barrier Properties of Selected Polymers.
The combination of high optical clarity and high moisture resistance has let to these materials being used extensively in the development of barrier packaging products (primarily film based), medical devices and a wide array of microfluidic and diagnostic products.
Injection molding and extrusion of COC can be carried out on standard equipment, however it should be recognized that those grades of materials which do not have antioxidant or stabilizer packages can be prone to discoloration or gel formation and may require an inert gas (usually nitrogen) blanked or purge.
Because the COC is a completely saturated hydrocarbon structure they have very low surface energy and can present specific challenges if one wants to bond to them. For example, most acrylic or EVA type adhesives will form little or no bond to COC. COC are also incompatible with most all polymer, however there are know examples of limited compatability with certain grades of polyethylene or polypropylene.
In a number of applications using COC, it is necessary to not only bond to it but to produce a hermetic seal, for example; sealing a COC based 96-well-plate. In several applications is even desirable to produce such a seal in the presence of liquid water.
A number of commercial heat seal films have been evaluated for use with COC and found to either bond poorly or to not be hermetic. Also, if based on polypropylene their activation temperature may be so high as to damage either the COC substrate on some component of the device.
Bay Materials has developed a four layer hermetic heat seal film for use with cyclic olefin copolymers, designated SF 47. This film utilizes a pierceable aluminum backing to provide a fully hermetic seal and a proprietary heat seal layer that readily bonds to COC. A diagram of the film is shown in Figure 3.
Figure 3. Construction of SF 47 Hermetic Seal Film for COC.
Thermal analysis was conducted on the heat seal layer to facilitate selection of bonding conditions. The TMA softening curve (Figure 4) shows a softening onset of 65 C and a maximum at about 80 C. Accordingly, this film can be sealed at temperature that will not damage devices which may contain water or biological samples.
This particular film was developed for use with Topas 8007, the most common COC for injection molding and extrusion. However, it works equally well on other COC resins with Tg values similar to 8007. Bay can readily provide modified films with different properties to meet your specific needs.
For additional information on heat seal films for cyclic olefin copolymers contact Ray Stewart at Bay Materials, LLC.
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