How to Choose the Right VHB Tape for your Application
In the world of pressure sensitive adhesive (PSA) tapes, there exists a subset of tapes known as high bonding tapes, also known by the ubiquitous 3M™ trade name, VHB™. These tapes are ideal bonding solutions in applications where metal fasteners, welds and other liquid adhesive solutions are typically specified. Because of their strength and durability, VHB tapes are a permanent bonding solution. They are ideal for a variety of applications and can be used with many different types of substrates. Because of their versatility, and the many types of VHB tapes available, you have a choice when it comes to the specific tape you use.
What factors should you consider when choosing a VHB tape for your application? Not sure if VHB tapes are even right for you? Find out more about these high-strength PSA tapes and how you can make the best decision for your adhesive tape needs.
What are VHB Tapes?
VHB tapes are industrial PSA tapes that are high performance adhesives laminated to either side of an acrylic foam core pressure sensitive adhesive. They are widely used because of their ease of application, clean aesthetic appeal, and their ability to withstand dynamic loads. Besides their impressive bonding strength, there are many reasons why VHB tapes can be the best bonding solution for your application (see some of the common applications of VHB tapes here):
Durability VHB tapes can withstand decades of extreme temperatures, high impacts and shock, water/moisture, vibration, and UV and humidity. They are ideal for use in many environments. With its natural viscoelasticity, VHB is able to absorb dynamic loads by distributing stress across the entire bond area, VHB tapes can withstand vibration, absorb impacts and compensate for thermal expansion and contraction of bonded parts.
Bond thinner, different substrates: VHB tapes can join materials ranging from aluminum and steel to glass, plastics, and even painted and powder-coated surfaces. Because the tapes are double-sided, they can also join dissimilar substrates with relative ease. This is particularly useful when trying to prevent corrosion between different types of metals. Unlike mechanical fasteners and welding, a specific substrate gauge is not required for use, so you can specify thinner lighter substrates.
Aesthetics: Without having to design around unsightly rivets and fasteners and expanding your substrate choices for material and gauge, designing beautiful products becomes easy.
Save costs: Eliminate labor time, redeploy highly skilled welders, and reduce production mess.
The Factors to Consider When Choosing VHB Tapes
As with any PSA tape, there are many things you should take into account when choosing among the many VHB tape options available to you.
The Joint Design and Bond Stress
There are many forces that can be placed on the bond and joint (see a breakdown of them here). It’s crucial to understand how the joint is positioned and which types of stress will be acting on it. Some questions to consider when designing a joint are:
What type and how much dead load and dynamic stresses with the bond see?
Are there opportunities to minimize dead load on the tape?
How can you minimize the most challenging forces like cleavage, peel stress
How can you design/change the joint to account for the required tensile strength or shear strength?
What is the surface area available for bonding?
The Substrates Being Bonded
Understanding how different adhesive tapes react with different substrates is crucial to the performance and longevity of your bond. While VHB tapes adhere well to everything from metals to glass and high surface energy materials, it’s important to know which specific VHB tapes to use with each substrate.
Consider the surface energy of your substrate. High surface energy materials include aluminum, steel, plastics, powder coated surfaces, etc. Medium surface energy materials include ABS, Polycarbonate and PVC. Low surface energy materials like Polyethylene and polypropylene Material Texture (smooth, grainy etc.)
For the best overall performance on metals, many paints, and medium surface energy plastics, it’s wise to test these tapes:
For more challenging powder-coated paint substrates it makes sense to evaluate the softer tapes:
If you are working with the most difficult to bond to substrates like polyethene and polypropylene you may choose to use one of the above tapes along with Primer 94 or instead, leverage an exciting new addition to the VHB tape family, 3M™ VHB™ LSE Tape Series.
The Thickness and Quantity of the VHB Tape
Tape thickness is highly dependent on the mismatch between the two surfaces being bonded. Thinner tapes can be used when one of the two substrates is thinner. As a general rule, the VHB tape should be target 50% of the thickness of the thinnest rigid substrate being bonded. If you are in between tape thicknesses, it is probably better to use the thicker tape. So, for example, if you have a 40 mil thick ABS plastic you are bonding, it will likely be a more robust bond using the 25-mil thick 3M VHB 4936 Acrylic Foam Tape instead of the 15-mil 3M VHB 4926 Acrylic Foam Tape. Using too thick a tape for the application can also degrade performance
It’s also important to consider the thermal expansion/contraction or movement in the joint. The expansion or movement of the joint should not exceed three times the thickness of the tape. Use thicker tapes if higher expansion/contraction or movement is predicted.
The size and weight of the parts being bonded together will determine how much tape needs to be used. Consider things like the shear stress that will be put on the tape (e.g., in applications that hold a panel or hanging sign). It is common to design four square inches of tape per pound of dead load to avoid tape creep. For dynamic loads, page four on the Technical Data Page is a useful reference. It’s important to use the right amount of tape to distribute the force more evenly over the entire bond.
What is the Operating Environment?
The environment of the application is just as important as the substrates being bonded. Many VHB tapes perform well in a wide range of environments, but understanding the environmental hazards the tape will be subjected to will allow you to choose a tape that can withstand them.
The general operating temperature of most VHB tapes is as high as 200°F, but there are tapes with special properties that allow them to perform outside of this range. For example, the 3M VHB GPH Series Tapes can operate in temperatures of 300°F and for the short term can go through bake cycles of 450°F. Some other environmental factors to consider include exposure to humidity, UV light, and chemicals, solvents, or plasticizers.
The Application Constraints
Many tapes are used on assembly lines; they aren’t being applied in a clean laboratory setting. Keep in mind that tapes need to be applied correctly in order to minimize the chances of application failure. Some of the things that can cause VHB tapes to fail include:
Surface contamination: heavy oils, greases, water, dirt, and other solvents can impact adhesion, so make sure the application surface is clean and completely dry.
Application temperatures: as noted above, most VHB tapes must be bonded in temperatures above 50°F and below 100°F. While it is generally best to control this application temperature range, some VHB products, like 3M VHB 4943 Acrylic Foam Tape and 3M VHB 4951 Acrylic Foam Tape may be bonded in temperatures as low as 32°F.
Rate of strength build up requirements: VHB tapes build up to 45% of their overall strength with good bond line pressure upon application. The bond increases over time over several days. Typically, within 72 hours the bond should be close to reaching maximum strength.