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New Castable Urethane Adhesives

( 11/15/2021 ) Written by: Katherine

Castable urethanes have been around many years and can be found just about everywhere. Used in wheels, rollers, bumpers, mining and oilfield equipment and much more, they include two parts—a liquid prepolymer (A side) and a curative (B side).
Easy to use and process, castable urethanes offer abrasion, oil, and tear and cut resistance, and are high load bearing. At the same time, they do not perform especially well in wet or hot environments and are expensive. In addition, certain variables can affect a castable urethane’s performance such as stoichiometry (or index number), polyol chain length, multifunctional crosslinkers and additives.
The good news is that urethane manufacturers are producing better elastomers that can withstand extreme conditions and engineers are taking advantage of the high load bearing capabilities. They are also creating more complex parts to handle vibration, flexing and impact that can generate an internal temperature increase. If the heat is not dissipated correctly, the urethane or bond can fail.
Unfortunately, many castable urethane adhesives were not designed to perform at elevated temperatures or in hot or wet conditions. With manufacturers making better elastomers, adhesives must be improved. That’s why Parker LORD developed two new adhesives: Chemlok 701 and 701/702. 
Chemlok 701 is a primer for bonding both mainstream castable polyurethanes and tougher-to-bond, high-performance castable urethane products to metal. This primer was designed to perform well in tough environmental conditions like elevated temperatures and high humidity. In addition, the two-component system (701/702) can be used for extreme conditions like direct water exposure at elevated temperatures.

How we do it
The tools we use when developing new products include mechanical rotation where we look for the surface part that is abraded or grit blasted and bond to these imperfections. During the cure process we then crosslink the adhesive system and diffuse into the urethane and back. We then conduct hydrogen bonding to get that first “bite” into the urethane as well as rubber retention. In the post-cure phase, the polyurethane’s hard blocks align producing hydrogen bonding, rounding out the properties. When developing this kind of adhesive, each interface acts like a link in a chain. Knowing that chains fail at their weakest link, we design the adhesive to bond to the substrate and up into the urethane. When they are destructively tested, the weakest link will be in the urethane, resulting in rubber retention.

To determine the adhesive strength, we tested, using the ASTM International D429 Method B standard. In addition, we experimented under extreme environmental conditions including boiling water and hot tear in a hot box. 
After the success of our internal benchmarking tests and customer trials, we conducted a robustness study in which we focused on determining application ranges of variables (702 curative ratio, dry film thickness, prebake and elastomer type of bonding performance) to ensure the optimal performance of Chemlok 701. 
Chemlok castable urethane adhesives bond a variety of cast urethanes. They are available in one- and two-component systems, are stable, do not require prebake and are easy to apply. All you need to start your own casting operation is the proper PPE, an oven and a mold and Parker LORD is here to help. If you would like to learn more about Chemlok adhesives and see the test results, please check out our webinar, visit our website or call us at 1-877-ASK-LORD.

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