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Thermal Management Properties of Urethane and Acrylic

( 07/07/2021 ) Written by: Mekiyah Bailey

Consumer demands have driven manufacturers to design more powerful and smaller products, contributing to increased power consumption and heat generation. High heat generation can adversely affect the product’s reliability and performance, making thermal management a necessity for all electronics products.

We’ve developed an in-depth five-part educational webinar series for those who want to learn more about thermal management. The first four webinars include Introduction to Thermal Management, Understanding Technical Terms, Silicone Properties, and Epoxy Properties. Our final webinar focuses on acrylic and urethane chemistries offered by Parker LORD. For a recap of this webinar, continue reading below.

What are Acrylics and Where are They Used? 

Acrylics, while often in the form of structural adhesives, can be found everywhere—from fiber optic cables to cars, signs, roofs, plexiglass and more. Acrylic adhesives offer great adhesion to metals, composites and thermoplastics. They are impact and chemical resistant, perform well in high and low temperatures, cure quickly and provide an excellent bond with minimum surface preparation. They also have a strong odor and are not repairable unless paired with one of our LokRelease products.

Properties of Acrylic Adhesives

Glass transition temperature (Tg) is the temperature at which a material transitions from firm to glassy. Tg is one of the most important properties to consider when selecting an adhesive or thermal management solution. Tg can be influenced by cure temperature. Most acrylics are room temperature cured but your Tg can be customized to your specific application by adding a post-bake. Crossing over the Tg in an operation leads to changing properties—becoming more rigid when below the Tg and more rubbery when above it. 

Tg is closely tied to the coefficient of thermal expansion (CTE) which refers to the relationship between the fractional change in size and in temperature. CTE is the leading cause of acrylic failures especially when bonding dissimilar substrates which have different CTEs. These different CTEs lead to a different rate of expansion which results in delamination from the substrates. 
Acrylics are used to bond two surfaces together. There are two categories of LORD acrylic adhesive solutions—UV (ultraviolet) Cure and General Purpose/Thermally Conductive. 

UV Cure Acrylic Adhesives

What makes UV cure possible and why can’t all adhesives be UV cured? UV cured solutions contain a small amount of photoinitiator that, when exposed to high-intensity UV light, triggers a crosslinking reaction change from a liquid to solid-state. Our one-component (1K) UV curable acrylic, LORD® AC-902 LC, provides excellent adhesion to plastics and metals, is optimized to cure within seconds, and fluoresces under high-intensity UV light. 

Thermally Conductive Acrylic Adhesives

Our thermally conductive 2K product, CoolTherm® TC-2002, is a two-in-one adhesive acting as a thermal link while also providing a structural bond. This product can be used in battery packs where the cells are bonded to the cooling plate and where there are high discharge and recharge rates that can raise the battery’s temperature. Thermal conductivity helps remove the heat and extend the life of the product. CoolTherm TC-2002 is often found in battery packs placed in electric vehicles, aircraft, and energy storage units. It also performs well in bonding structural joints.
We also offer a range of non-thermally conductive 2K acrylics including LORD 5206/55GB, and the Maxlok™ and LORD 800 series.

When to Consider Using a Urethane

Urethanes are very diverse chemistries that can be hard or soft, have short pot lives, and have low viscosity (at room temperature). They also cure quickly and operate best at lower temperatures. 
In addition, urethanes offer good adhesion to most substrates without requiring a primer and some can act as a sealant, providing an excellent water barrier. Urethanes, in general, are moisture sensitive which should be considered when storing and applying. 

Because our urethane products can be either soft or hard, there will be a range of Tg values. If your operation will go through various temperature changes, alterations within the urethane properties will occur—becoming more rigid below Tg and rubbery above Tg, as seen with acrylic adhesives mentioned above. A larger CTE will occur when the urethane is soft which helps avoid cracking during thermal cycling and shock. Conversely, hard urethanes can crack and delaminate due to changing dimensions in the materials. 

Non-thermal urethanes can be used as structural adhesives when bonding and sealing are your top priorities. We offer a wide range of non-thermally conductive products. Urethanes materials are offered as potting and encapsulants, gap fillers, or adhesives. Thermal urethanes make excellent gap fillers allowing heat transfer between substrates making them a great alternative to traditional gap pads. 
Our urethane product lines offer a wide range of classifications and properties including viscosity, hardness, and working life, making them the ideal solution for many different projects. 

No matter what your application needs may be, Parker LORD is your one-stop-shop for thermal management, adhesive, coating, and specialty chemical solutions.  
To check out our other in-depth webinars in the educational series please visit our Thermal Management Virtual Academy page. And, if you need help with your project, please contact us via our website or by phone at 1-877-ASK LORD.
 

ABOUT THE AUTHOR MORE BY THIS AUTHOR
Mekiyah Bailey Mekiyah Bailey is an application engineer in the electronic materials group and has been with Parker LORD for over 2 years. Her expertise is in silicone and urethane materials and she runs thermal testing in our electronic materials labs. Her primary focus is finding solutions and communicating results based on a customer’s needs. She also holds a bachelors degree from University of North Carolina Greensboro and a Masters degree in Chemistry from the University of North Carolina Wilmington.

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