Sullivan says engineers are asking for more adhesives with multiple functions such as resistance to chemicals, corrosion, humidity, and extreme temperatures. "We're also getting more inquiries for bonding solutions, not always structural, in robotics, medical, aerospace, and military applications." Medical and military/aerospace applications also need these characteristics, as well as more chemical resistance.
Pressure-sensitive adhesives also help reduce VOCs -- a requirement of many plant managers, according to Sullivan.
"We did some work with an aerospace company that used a liquid adhesive to bond two surfaces together in the cockpit of a plane. We went in with a pressure-sensitive adhesive, eliminating the need to use a liquid bonding adhesive," he said. "This also eliminated the time needed to process the liquid bonding, so they got better throughput in their internal processes."
Throughput and cost are also reduced when fasteners are replaced by laminating. Using adhesives often can be as fast as a single laminating step.
PennEngineering's PEM self-clinching fasteners speed assembly by reducing
the number of steps required and by producing a permanent bond.
Doughty says adhesives that are resistant to temperature extremes also come into play in automotive and aerospace applications. Automobile interiors are hot environments, and an aircraft exterior gets very cold at high elevations. However, most applications involve temperatures below 225F. Most adhesives can handle temperatures up to 225F without compromising their characteristics, and many perform well even above that.
"We're finding that corrosion and rust are really a big factor for raw steel," Doughty says. Often an adhesive can protect a substrate against corrosion, because it protects so well against water and other liquids. "So as long as the adhesive sticks to the underlying steel, there's no corrosion problem unless the underlying steel itself is already corroded."
Chemical exposure also affects adhesives. Many factories use hydraulic fluids, machine oil, and various paints or coatings. Some chemical dips used before paint processes can compromise paints that are not tough enough to resist them. There are also solvents and cleaners like acetone and methyl ethyl ketone that can harm adhesives.
Today plant managers are demanding adhesives that are easier to handle, easier to apply, and faster to use, according to Doughty. "For example, they want operators to be able to use them with applicator guns. This is occurring mostly because of pressure to reduce throughput times."