Guidelines for Tape Design, Construction and SelectionThursday, May 1st, 2008
Adhesive tape applications range from the obvious, such as wound care and bandages, to the more obscure, such as diagnostic strips used in pregnancy tests and other point-of-care diagnostic devices. Selecting the appropriate adhesive tape for any application is critical to a new-product development project’s success. It requires a detailed understanding of performance requirements, analysis of available options and their performance attributes, and insight into the manufacturability of various tape, adhesive, and substrate combinations.
A number of variables—such as the suitability of the adhesive tape for the application, material compatibility, adhesive performance properties, environmental factors, sterilization methods, and material cost targets—must be investigated and taken into consideration. See the sidebar for a detailed list of products that use adhesive tape.
The specific composition of adhesive tapes can vary widely, but understanding the common components of construction provides an excellent framework for identifying the optimal product for any application.
Nearly every adhesive tape used in a medical application comprises three primary components: a face stock, a release liner, and an adhesive. Whether the final product is a simple short-term-use bandage or a complex multimillion-dollar medical device, the adhesive tape requirements must be assessed in terms of the same three elements.
Face Stock. The face stock is the base carrier material onto which an adhesive is applied. Face stock can consist of a number of materials, including film, foam, foil, paper, and woven and nonwoven materials. Face stock can also vary in thickness and weight to improve conformability and manufacturability, multiplying the available configuration possibilities significantly. The composition of the face stock helps determine the elongation or stretching characteristics of the adhesive tape, the tape’s conformability to a structure such as a part of the human body, and the tape’s anchorage, tear strength, moisture-vapor transmission rate (MVTR), and cost.
Adhesives. The composition of adhesives varies as well, with each variation offering unique characteristics. Cost-effective rubber-based adhesives deliver a high initial tack, but are limited by a relatively low maximum temperature. Rubber-based adhesives can be unreliable at temperatures above 140°F and could fail at high temperatures.
Acrylic polymer–based adhesives, on the other hand, can be used at relatively high temperatures (up to approximately 250°F) and resist environmental factors. Acrylic polymer adhesives are limited by low initial-tack characteristics, but have excellent long-term aging characteristics. Although these adhesives can be modified to increase tack, doing so reduces the adhesive’s resistance to solvents and high temperatures.
Hydrocolloid adhesives are specifically designed for wound-care applications. Hydrocolloid is hypoallergenic and has a high MVTR. The material is engineered to maintain moisture in the wound bed and absorb exudates, making it ideal for long-term wear of up to 7 days. Most hydrocolloids combine with wound exudate to form a gel-like covering, which protects the wound bed and maintains a moist wound environment. In addition, hydrocolloid is comfortable on the skin, conformable to the body, and easy to remove, all desired characteristics for wound-care applications.
The thickness of an adhesive also affects its strength and performance. If the substrate to be bonded is not uniform or has a deep cellular structure, a thick adhesive may be desirable. A thick adhesive more readily adapts to the irregularities of a substrate, effectively seeping into the “nooks and crannies” and adhering to the cell structure, making a strong and durable bond. A thick adhesive also tends to be very flexible. Such flexibility is desired for applications in which expansion and contraction are a concern, such as if temperature fluctuations are prevalent.
Very-high-strength super-cross-linked adhesives (e.g., VHB and UHA) are also available. These have very high bond strength for particular applications but are not typically used for wound-care applications. They are, however, suitable for box builds and other applications that do not require skin contact.
On occasion, an adhesive is coated onto both sides of a carrier (or scrim) in a double-coated-tape format. This can involve the use of the same adhesive on both sides, or two different adhesives with different and distinct properties for each particular application. The carrier in the middle gives the final product greater structural integrity, reduces stretching, and aids in lamination, slitting, and die-cutting. Typical materials for the scrim in medical tape are paper, film, tissue, or a nonwoven component. Hydrogel sheet materials often use a scrim to provide structure and integrity.