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Bonding dissimilar surfaces:
Why PSA tapes are better than metal fasteners

[Credit: Image courtesy of Engineered Materials]

 

 

By Engineered Materials engineering team

There are many reasons why pressure sensitive adhesive (PSA) tapes perform better than other attachment methods such as liquid adhesives and metal fasteners. These advantages are even more beneficial when working with two different substrates. Bonding of dissimilar surfaces can be a challenge to solve for multiple reasons, which can include thermal expansion differences, galvanic corrosion, or the roughness and porosity of the surfaces.

• Thermal expansion: The shape, volume, and area of many materials are not static and can change in reaction to variations in temperature known as thermal expansion. When bonding two surfaces of the same material, the expansion and contraction of the material as environmental temperatures change will coincide. However, as different materials expand and contract at different rates, bonding solutions, like rivets and fasteners, can be stressed. When temperatures change, the rigid bonds with specific stress points can fatigue, which ultimately results in a failed bond. To account for the movement of the materials, more flexible and uniform bonds are required to prevent failure.
• Galvanic corrosion: Different metals and alloys have different electrode potentials. When those materials encounter one another, a reaction known as galvanic corrosion occurs. The resulting reaction leads to the metals corroding quickly over time, even if they are coated with galvanized zinc (which can fade and chip away). In these cases, a metal fastener is not an ideal solution, since a resistant barrier must be introduced. A simpler alternative is to leverage an adhesive barrier that bonds and separates the materials.
• Stress fatigue: Whether bonding dissimilar or similar materials, bond lines often experience stress during the application life. Joints may experience peel, cleavage, sheer, or tensile forces. Mechanically fastened bonds with specific attachment points (like rivets, spot welds, or screws) may experience fatigue over time when exposed to these forces. This fatigue will lead to weaker bond strength or even failure. Viscoelastic PSA tapes, used over the entire bond, are able to absorb much of the energy caused by bond stress. The end result is a bond that can distribute force uniformly throughout the entire bond.

Use PSA tapes for maximum adhesive performance
PSA tapes offer characteristics that overcome the challenges of bonding dissimilar materials.

[Credit: Image courtesy of Engineered Materials]

 

 

• Viscoelastic: Can absorb the expansion and contraction of different materials caused by changing temperatures. Tapes and the adhesive applied to them are flexible and allow for much more movement than rigid fasteners, bolts/screws, and other bonding solutions.
• An ample barrier: Prevents galvanic corrosion and other reactions caused by dissimilar metals and materials that contact one another.
• Highly resistant and resilient: Choose from a wide range of PSA tapes, each with their own resistances to heat, flame, electrostatic discharges, chemicals, water/moisture, sound and vibrations, shock and impact, and much more.
• Able to act as seals and gaskets: Many types of PSA tapes can be used to fill gaps between two materials and can even act as a seal or gasket to block the flow of water, moisture, or gases.

Double-sided PSA tapes and VHB offer more versatility
Double-sided PSA tapes may use different pressure sensitive adhesives on each side of the tape to allow the adhesive choice that provides the strongest bond based on the different substrates. Meanwhile, the right adhesive transfer tapes chosen for specific applications bond and separate materials along the bond line. Both tape options account for different surface porosities, finishes, contours, surface energies, and much more.

[Credit: Image courtesy Engineered Materials]

 

 

Additionally, 3M™ VHB™ Tapes (Very High Bond) are high-strength, double-sided foam tapes that are highly viscoelastic and can be leveraged to replace mechanical fasteners in some of the most demanding applications. These tapes are versatile, highly resistant to environmental factors, and allow for stronger bonds in less time.

How to choose the right double-sided PSA tape
To select a PSA tape for an application, be sure to:

• Identify the application of the tape (where and how it will be used, the joint, etc.).
• Identify the two substrates to be bonded and how they differ from one another.
• Choose the right adhesive for the substrates based on their inherent qualities.
• Choose the right release liner and carrier material based on the application.
• Consider the specifications needed for each piece of tape. PSA tapes are available on rolls or can be die-cut into custom parts.

Other considerations to help choose the best PSA tape for specific applications include surface contour, surface energy, and the operational environment. Each of these parameters will dictate the needed tape characteristics, such as thickness and flexibility, wetting of the adhesive, and specific tape material. Before PSA tape application, it is critical that the bonding surfaces are free of grease, oil, moisture, particulates (dust talc or fibers), or other contaminates that can contribute to bond failure.

When bonding dissimilar materials, consider PSA tapes as the best alternative to metal fasteners or liquid adhesives for a simpler, faster, and cleaner result.

Engineered Materials converts and fabricates a wide variety of tapes and adhesives for the manufacturing industry to solve bonding and sealing challenges. Learn more at engineeredmaterialsinc.com.

Published October 2024

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