The Role of Heat-Seal Coating in Seal-Peel Medical Packaging

Originally Published MDDI August 2004

Packaging  

Selection of a seal-peel packaging construction is influenced by how well the adhesive coating satisfies the basic functional needs of sealing, protecting, and opening. Following is an overview of selection criteria to be considered when planning an overall heat-seal coating for gas-sterilized device packaging.

Sealing Features. The first consideration is for coating uniformity. It is essential that the coating be free of voids or defects that can cause channels in the seal area. Control in the coating process and converting stages is critical to the quality of the product. The packagers, too, should check quality with visual aids, such as colored coating, or with fluorescence under ultraviolet light.

The adhesive also should seal over a wide range of temperature, pressure, and dwell conditions. It must be functional on a variety of heat-sealing equipment such as rotary, platen, or impulse. It should seal well within the tolerance limits of the substrate and the blister or film. Tyvek, for example, must be sealed at contact temperatures below 275F.

It is also desirable for a single coating to adhere to as many packaging materials as possible. For example, a typical seal-peel coating can adhere to a range of plastics. Finally, the adhesive must have sufficient hot strength immediate-ly after sealing to withstand stresses in the package—on or off the packaging line—while the seal is cooling.

Protective Features. These basic protection features must be carefully considered when selecting an adhesive:

•The coating should not significantly alter the porosity of the substrate because gases must have rapid entry and release during the sterilization cycle. Gurley porosity values of less than 100 seconds are desired.
•The adhesive must be resistant to creep when subjected to the elevated temperatures of sterilization and the stress relief encountered in some blister pack operations.
•Aging stability must be ensured for both pre- and postsealing.
•Sealed packages must be able to withstand shipping abuse over a range of temperature conditions without opening. Adhesives should retain flexibility at low temperatures to maintain package security.
•Properly packaged, the adhesive coating must also remain usable for periods of at least two years under ambient warehouse conditions. Sealed packages should retain their integrity and functionality indefinitely under normal storage condi-tions. The adhesive should not 
impart odor, taste, or color to products in the package. The adhesive must also be nontoxic, nonallergenic, and nonpyrogenic.

Opening Features. Two additional concepts are critical when selecting an adhesive: its ability to peel easily, and its resistance to tampering. A seal-peel bond should be controlled to optimize both the security and the convenience of opening.

A peel strength of 1.0–2.5 lb/in. (approximately 453–1150 g) is generally considered desirable. The adhesive should also peel away from the substrate without generating loose fibers or adhesive particles.

The advantage of a coated material is its ability to provide fairly uniform bond strengths over a range of sealing conditions. When a seal is opened, it should not be resealable by simple pressure. This precaution minimizes potential contamination if a seal is broken accidentally or tampered with.

The selection of an adhesive-coated material for sterile packaging can require months of testing and screening. Systematic application of these criteria can help speed the process and ensure the most appropriate selection.  

Copyright ©2004 Medical Device & Diagnostic Industry