Today, adhesives are satisfying demands in the auto and medical arenas by enabling smaller, stronger, and lighter-weight assemblies. Estimates show that the industry will reach over $59 billion by 2020, according to Markets and Markets.com. One current trend making waves across these arenas is advanced thin-film adhesives, but other trends and advanced procedures are also enhancing both vehicle and driver applications.
The fundamental science of adhesives pertains to surface area and wettability. The more surface area an object can adhere to is obviously understood, but wettability is more involved. Wettability refers to surface-free energy (SFE). Materials with low surface energy, such as plastics and powder-coated metals, are difficult when it comes to bonding.
In general, to “stick,” an adhesive must have a lower SFE than the material it’s being applied to. This implies that adhesive should have minimal beading on the surface of a substrate. Beading can be minimized with additives that lower the adhesive’s SFE. Degreasing, sanding, and heat treatments can increase a material’s SFE, making it easier to create strong bonds with adhesives.
Companies use adhesives to make assemblies less complex, thus saving time and money. Adhesive can reduce the number of manufacturing processes, such as drilling and installing fasteners. Also, eliminating drilling or altering parts for fasteners keeps warranties from being voided.
Companies have teamed with adhesive firms to produce precut liners that address vibration and noise concerns. A recent trend is to have pre-impregnated adhesive in a matrix or thin films backing precut shapes. Pre-cut layered adhesive films can save time in assembly. “A vehicle can use thin laminated adhesives that are cut to size, which can free a designer to create a custom part that reduces weight, gives aesthetically pleasing results, and lets devices be thinner,” says Joe, senior account representative at 3M. “The industry trend across most markets is to go thin and lightweight; laminated adhesives accommodate for that challenge.”
Currently, there’s a trend of using reclaimed waste materials. In addition, composites and new polymers are being altered and developed for new applications. Consequently, an adhesive company must keep up with new material trends to ensure that it has a compatible product. The metals, plastics, foams, and fabrics that go into today’s vehicles have different rates of thermal expansion, SFE, and other properties that create challenges when developing automotive adhesives. Automotive materials must also withstand temperature fluctuation, oils, and fuels in its operating environment.
Engineers are finding ways to overcome these hurdles, though. For example, foam blocks are attached to metal components to reduce vibration and noise. The challenge was to find cost-effective adhesives that can bond to both materials. Designers at Fabrico developed a laminated film as a solution. The first film was selected to stick to metal and a piece of aluminum foil. On the other side of the foil, engineers added a different film capable of sticking to the aluminum foil and a foam block.
Foam tapes are used to attach accessories to a vehicle, such as interior and exterior trim. Using foam tapes save time and money by eliminating the need to drill holes, apply rustproofing, and installing fasteners. Trim provides a relatively large surface area that works well for applying adhesives, and tape makes for quick and easy assembly. Foam tape lets the trim follow the curves of the vehicle while providing looser tolerances on the trim by filling in small gaps that might occur between the trim and vehicle.
Adhesives are also critical in making sure labels stay where they belong. Warnings, maintenance, and even the appropriate operating pressure of your car’s tires are on labels. If the environments or time loosens these labels, it can inconvenience the owner, mechanic, and car company.
The medical industry has its own list of challenges. For instance, adhesives might touch the patient or be inside the body, making biocompatibility and non-toxic adhesives key areas to address. Trends in these types of adhesive products often stem from regulations and standards, such as the USP Class VI testing and ISO cytotoxicity standards.
Another key is that companies don’t want to complicate processing. A device manufacturer may prefer an adhesive with a paste-like viscosity for better control when applying it to a product. A medical silicone might have this consistency naturally, but the viscosity for other adhesives may need to be altered to fit demands. One-part epoxies can be altered easily to deliver a wide range of viscosities. Two-part epoxies offer strengths, but add complexity to processing because mixing of the parts must be precise, which can add cost to a production line.
Adhesive firms are working to improve medical tapes and films, which are often used to hold bandages over wounds and stitches, attach drug-delivering patches to the skin, and support sore joints. Such adhesives need to keep germs out, be permeable to let the skin can breathe, and stick to skin not medical products, such as stitches.
“Wearables are a rapidly growing area of the medical-device market,” says Craig McClenachan, director of marketing at Fabrico. “One of the critical components in body-worn devices are skin-friendly, stick-to-skin adhesives. These monitoring and drug-delivery devices need to be able to stick to the patient, in some cases up to seven days, and then come off without causing skin irritation.”
Adhesives and materials can that biodegrade or dissolve into the body are being developed to deliver drugs. However, drug delivery and wearables might only be a start for adhesives. Researchers at the U.S. Defense Advanced Research Projects Agency (DARPA) are even looking at using implantable silicone chips that dissolve once their task is finished. They could even be used to provide electrical stimulation that speeds recovery or reduces infection. That said, the adhesive industry may need to alter formulas to incorporate innovative drugs and microchips into the design in order to stay on the leading edge of the medical market.
Researchers are also using photopolymers as a medical adhesive. In one animal study, the Wyss Institute used a photopolymer adhesive patch to fix a hole in the heart. Infants sometimes require serious open-heart surgery to repair holes in the septum. In this new process, a catheter was snaked into the heart and through the hole in the septum. The tip of the catheter then retracts to deploy two balloons, one on either side of the hole. Then they’re inflated, which pushes a photopolymer adhesive patch over the hole. A UV light on the catheter cures the patch in place. The balloons are subsequently deflated and removed with the catheter. This adhesive patch will dissolve over time as tissue grows over the patch.