Understanding Urethanes

Urethanes offer an array of benefits including flexibility, water white clarity, low temperature functionality, and elongation as well as abrasion resistance. Due to these properties, urethanes are at an advantage compared to other adhesives in devices that are undergoing stress due to discrepancies of component composition.

Numerous urethanes consist of low glass transition temperatures so they have the ability to protect components in consumer electronics which operate at a range of -40C to 105C. Several urethanes can also be used at temperatures of -70C and others as high as 130C.

Chemists can manipulate urethane formulations to have either an extremely quick gel time at room temperature or a slow gel time with low exotherms. In fact, urethanes can be created to a range of hardness from soft gels to high Shore D.

Generally, urethane chemistry consists of a two-component system; one side is polyol and the other side is isocyanate. When moisture is in the air, the isocyanate will react so it’s encouraged to protect unused materials with a layer of nitrogen gas during storage. This will remove an air that is in the container.

Polyurethane Adhesives

Commonly referred to as “elastic adhesives,” polyurethane adhesives are glues which consist of urethane polymers; these polymers contain chemical based of isocyanate group. Typically you’ll find polyurethane adhesives in the following application:

  • Encapsulation/Potting/Sealing
  • Medical grade adhesives
  • Automotive applications
  • Plastic bonding
  • Application that require low temperature capabilities
  • Applications that require strong water/moisture resistance
  • Applications that are exposed to the outside elements (weather/sun radiation)

Cured by polyaddition reactions, polyurethane adhesives take on a reticulated structure. This structure can be ridged or flexible, elastomer like, dependent on the level of crosslinking.

Advantages of Polyurethane Adhesives

Due to the hydroxyl functionality of the polyol portion of polyurethane these adhesives are completely water resistant. Additionally, polyurethane adhesives can be formulated to be at a low viscosity, cure within seconds, and cure to a pliable state at room temperature conditions. As an adhesive, the cure time is determined by the length of time required before the adhesive has bonded two materials together.

Three Types of Polyurethane Adhesives

  • Two component polyurethane adhesives
  • One component polyurethane adhesives cured by heat
  • One component polyurethane adhesives cured by moisture

Polyurethane Adhesive Applications

Resin Designs has urethanes products that cover the majority of the described applications:

  • Entex 51021: A general purpose electronic encapsulate with success in underwater applications. Features include low Tg (-65 °C) and medium hardness (Shore A90).
  • Nexus 52101: Clear encapsulate and plastic bonder, especially to polycarbonate. Features include medium hardness (Shore 45D) and good elongation (170%). Axis M-100N is the medical grade version of this product.
  • Entex 53051: Crystal clear, UV stable, adhesive with success in lens coating. This material is more ridge (Shore D75) than other urethane products.
  • Nexus 51031: Strong adhesive bonder. Works well with thermoplastics, wood, metal, ceramic, and stone. This adhesive has a fast work life (3 minutes) and is ridged (Shore D80).

If you need a custom urethane adhesive please contact us. We look forward to work with you to help deliver the product you need.