In this interview, AZoM talks to Robert Michaels, Vice President of Technical Sales at Masterbond about the benefits and applications of toughened epoxies.
Could you please provide a brief introduction to the industry that Master Bond Inc. works within and outline the key drivers?
Master Bond Inc. was founded in 1976. Our focus has been on developing the best in epoxies, silicones, polyurethanes, polysulfides, UV cures and other specialty adhesive systems. We formulate the highest quality products and offer unmatched technical advice and customer support. Our product line consists of advanced adhesives, sealants, coatings, potting/encapsulation compounds and impregnation resins. Each compound is designed to meet specific application needs and requirements.
Master Bond manufactures over 3,000 grades of specially designed formulations. We also offer replacements for competitors’ discontinued products.
Why is flexibility considered a desirable property for adhesives, sealants and coatings?
When comparing a toughened and conventional epoxy, the mechanical property difference that jumps off the data sheets is elongation. Whereas a traditional epoxy will have elongation of less than 5 percent, toughened epoxies typically have elongation that fall within the range of 50 to 80 percent.
This elongation improvement represents a huge increase in ductility, which allows the adhesive to withstand impacts and "flex" under cyclic loads caused by fatigue or temperature swings. The extra measure of ductility also facilitates the joining of dissimilar substrates in ways that a brittle adhesive cannot--this is because ductile adhesives can better absorb the stresses caused by coefficient of thermal expansion (CTE) differences between the two substrates.
Lastly, toughened compounds tend to cure with lower residual stresses than their more rigid counterparts. Unlike conventional epoxies, toughened compounds often have residual stresses approaching zero.
Are there any trade-offs?
With toughened compounds, ductility does come with a small trade-off related to maximum service temperature. While high temperature epoxies can withstand intermittent temperatures above 300°C, toughened products top out at about 200°C intermittent. Reductions in typical continuous use temperatures are similarly about 100°C. This loss of thermal properties, though seemingly significant, does not have widespread practical implications since the vast majority of bonding, potting and coating applications do not require anywhere near the maximum temperature resistance offered by the epoxy family.
This loss of thermal properties comes into play only at the top end of the service temperature range. At very low temperatures, which tend to magnify any ductility issues an adhesive might have, toughening actually imparts a performance advantage. Nearly all cryogenically serviceable epoxies, some of which have to withstand temperatures as low as 4K, have some sort of toughening agent.
How are toughened epoxies formulated?
Toughened epoxy compounds can be created in a variety of ways. Toughening sometimes involves the incorporation of ductile rubber or thermoplastic materials into epoxy's normally rigid molecular backbone. These ductile materials may remain in the epoxy compound as distinct phases, absorbing shear or impact forces. Carboxyl terminated butadiene-acrylonitrile (CTBN) copolymers are one family of ductile materials that Master Bond has used to great advantage in a variety of toughened compounds.
Other toughening methods rely on specific diluents or other reactive elements to change the epoxy's molecular structure in ways that make it more flexible. For example, by reducing the crosslink density or by shortening molecular chains. Heat cure schedules can also be manipulated to improve epoxy ductility.
What are the advantages and/or disadvantages of these different toughening methods?
Every toughening method has its advantages and disadvantages, but they all address the chief shortcoming of epoxy compounds. For all their first-rate mechanical, thermal and chemical properties, conventional epoxies can sometimes be too rigid for use in structural applications subject to extremely heavy fatigue, impact or thermal shock loads.
Toughened epoxies have no such Achilles Heel. They can be used in scores of electrical, optical and medical applications where rigidity might otherwise prohibit epoxy usage.
What are some key applications where toughened epoxies would be an asset?
Because they stand up to challenging cyclic loads and cure with low residual stresses, toughened epoxies are used to bond, seal or encapsulate a wide variety of electronic, optical and medical components. Among them are:
- Coils and potentiometers
- Flexible circuits
- Piezoelectric and micro-machined sensors
- Surface mount components
- Heat sinks
- Optoelectronic transceiver modules
- Cable joints and terminations
- Guide wires and catheter balloons
- Transformers and inductors
- Chip scale packages
- Boroscopes and doublets
- Heating elements
- Low-force gaskets
- Flexible substrates and connectors
- Semiconductors, capacitors and resistors for hybrid circuit fabrication
- Cast cable connectors and wiring harnesses
- Cyrogenically serviceable components
If an engineer has an application that must resist vibration, impact and shock, as well as thermal cycling while also offering high peel and shear strength, what would you recommend?
We have many different grades of epoxies, both one and two component, with a wide range of properties including service temperature ranges from cryogenic to 500°F, electrical conductivity, NASA low outgassing, optical clarity and more. For the specifications required above, we offer Supreme 10HTFL, an easy to use one component epoxy with high temperature resistance and a fast cure schedule. It has the ability to survive exposure to repeated thermal cycling, vibration and shock. It is also serviceable at cryogenic temperatures, has a consistent viscosity and outstanding peel and shear strength.
Our technical experts are available to provide individual service to determine the best adhesive for your application and will work with you throughout the design, prototyping and manufacturing processes. They can be reached at [email protected] or at +1.201.343.8983.
How do you see the field of adhesive manufacturing developing over the next decade?
Continuous research is being performed in order to improve the temperature and chemical resistance properties of the toughened and flexible epoxy systems. These improvements would make these adhesives suitable for use in many more advanced applications in various industries like aerospace, electronics, and medical. Some other areas of research are: shortening the cure times further to decrease the production time even more, convenient adhesive packaging options with more controlled application techniques, improving energy efficiency, and formulating more environmentally friendly adhesives.
About Robert Michaels
As an integral part of the foundation of Master Bond, Robert Michaels has served as the Vice President of Technical Sales for over 25 years.
Master Bond is a leading manufacturer of high performance adhesives, sealants, coatings, potting and encapsulation compounds and impregnation resins. Their line of products consists of:
- Epoxy Systems
- Silicone Systems
- UV Curable Systems
Master Bond custom formulates products with specific performance properties designed for unique applications. These compounds exhibit the advanced properties required for a number of different industries, including the aerospace, medical, optical, electrical, electronic and other manufacturing industries.
Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of AZoM.com Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.