Understanding Composite Materials: Tapes

At first thought tapes sound like a simple concept; a long, narrow piece of material that is sticky on one side and used to hold things together. However, in the world of advanced flexible materials, a more detailed definition is necessary in order to capture the technical attributes of tape which enable functionality across a wide array of applications.  

Tape is a substrate that is coated on one or two sides with an adhesive. This definition broadens and simplifies the traditional understanding of a tape, which allows us to include all of the sophisticated materials that are used in technical markets such as aerospace, advanced wound care, biopharmaceutical manufacturing, and medical device manufacturing. Tapes that are used in these markets have much more complex designs that drive specific performance characteristics.

In this technical brief, we will discuss three main aspects of tapes that will help sourcing teams, product development groups, and R&D staff who are searching and selecting materials for a new project.

Substrates

One of the important elements of tapes to understand is the substrate, or base material, that the adhesive will eventually be applied to. The substrate provides the structure for the adhesive and can impact many of the overall functions of the tape composite. All of the core material types in the Sourcebook™ material sourcing platform can be used as a tape substrate, although some of the most commonly used materials are films, foams, and nonwovens.

The material type and composition of a substrate will significantly affect many properties including; air permeability, moisture vapor transmission rate, tensile strength, elongation, conductivity, shielding effectiveness, and so on.

An example of the impact of a substrate's functionality can be taken from the advanced wound care market where silicone adhesives are now commonly used to cover the skin-contact side of a dressing.  These adhesives are frequently applied to a film substrate with a foam material, then laminated to the top - from skin contact up - the materials are adhesive, film, and then foam.

In this example, the purpose of the foam is to extract exudate (moisture) from the wound so the film substrate holding the adhesive layer must have some liquid permeability. In this application, an apertured or perforated film could be an ideal solution. The ability for the exudate to transfer into the foam would increase depending on the pore size of the apertured film. It may even be possible to match the pore size in the apertured film to the expected size of the exudate molecules.

Adhesive Composition

The composition of the adhesive layer is likely the most important consideration for a tape composite because it is most directly related to the key function of adherence. Common adhesive types used in technical markets are variations of acrylic, silicone, rubber, and hydrogels. When selecting an adhesive the fixation surface dictates the first set of decisions. For adhesives that will come in contact with skin, the composition should be silicone or a hydrogel, and some newly designed low tack acrylics. For high tack fixation applications, in particular non-skin surfaces, acrylic and rubber adhesives are most appropriate. There are also conductive acrylic adhesives used in many electronic applications.

In medical applications, an important consideration is the sterilization method of the finished product, which carries potential impacts for each raw material inside the device. The four most common sterilization methods are:

• Gamma Irradiation
• Ethylene Oxide
• E-Beam
• Steam

Two common sterilization methods in the medical market are gamma irradiation and ethylene oxide. Gamma sterilization is less expensive and less time-consuming but is limited by the low number of adhesives and polymers that can withstand the process without becoming degraded. Ethylene Oxide is gentler on materials but has an extended validation period, and therefore a greater expense associated with it.

Using our previous example, silicone adhesives are popular in advanced wound care due to their gentle release. Unfortunately, silicone gels degrade when they undergo gamma irradiation, so ethylene oxide must be used. The cost of ethylene oxide sterilization and silicone adhesive is significant and has to be carefully considered early on in a project so as to avoid pitfalls throughout the commercialization process.  

Watch our video series about biomedical innovation.

Coating Characteristics

Tape substrates can be coated on one or two sides, which lends flexibility in the final assembly of many products. Double-sided tapes can help facilitate the lamination of two components that must be joined together but have different fixation surface requirements or manufacturing challenges.   

Double coated adhesives provide great design benefits if mechanical bonding is not an option, or is very difficult. In the aerospace industry, it is becoming more common for components of aircrafts to be secured together using a high tack adhesive. This has decreased the weight of air crafts, which decreases the fuel costs of the plane, as well as the overall cost of assembling the aircraft.

Double coated tapes can also have differential coatings in order to facilitate different fixation requirements. This is especially useful in medical device manufacturing where it may require that one side of a tape sticks to a patient's skin, while the other side of the tape adheres to the device itself.  

Conclusion

Tapes are an important part of advanced flexible materials markets, and they provide us with a wide range of functionality that goes far beyond our traditional understanding of tape. With the multitude of options for each component of the composite, there are limitless combinations of products that can be manufactured. Understanding how these many combinations interact and how the components complement one another is essential in creating the optimal product functionality. 

A number of flexible materials manufacturers produce composite tapes and have extensive capabilities to customize their products and facilitate new and innovative concepts. Engaging manufacturers on development projects frequently yields great results and drives innovation through the commercialization of new technologies.