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Design & Tape Selection

For the complete guide on how to select the right tape, the tape thickness for the surface and the quantity of tape required to handle the stress involved are mentioned below.

How to select the Right Tape for the Surface

The molecular attraction between dissimilar materials is called Adhesion, which is similar to the magnetic force. The strength of the adhesion is determined by the surface energy of the material. The higher the surface energy, the stronger the bond and lower the surface energy, the weaker the force.

On high energy surfaces a tape or adhesive can flow or "wet out", which assures a stronger bond. Some of these surfaces include aluminum, steel and glass. On low surface energy surfaces most adhesives and tapes will resist flowing onto the surface, leaving poor surface contact and low adhesion.

Previously, substrates were categorized as having high or low surface energy based on how they were bonding with adhesives. With the increasing number of substrates and new adhesives that meet those requirements, it is common for substrates to have medium surface energy or even medium high or medium low surface energies.

With the surface energy defining a new level for the adhesives to get wet and bond to the surface the adhesive type can bond to surfaces with a particular or higher surface energy level.

Mentioned below is the list of Adhesive types and the corresponding 3M™ VHB™ Tape:

Multi-purpose Adhesive
3M Multi-purpose Adhesives bond to medium, medium high and high surface energy substrates. They are used with 4941, 4945 and 4622 (liner side) family tapes.

Modified Acrylic Adhesive
The Modified Acrylic Adhesives from 3M, bonds to medium low, medium, medium high and high surface energy substrates. They are used with 5952 family tapes.

General Purpose Adhesive
The General Purpose Adhesives bond to high surface energy substrates and some medium and medium high surface energy materials. They are used with 4950, 4910 and 4611 family tapes.

Low Temperature Appliable Adhesive
3M Low Temperature Applicable Adhesives, bond to high surface energy substrates and some medium and medium high surface energy materials. (Used on 4951 family tapes)

Low Surface Energy
The Low Surface Energy Adhesives from 3M bond to some low surface energy substrates and smooth surface in the other categories. They are used with the 4952 family tapes.


Listed below is the general classification of materials into surface energy categories. Note here that it should be treated only as a guideline, as many general plastic types (e.g. ABS) can have a wide range of surface energies depending on the additives. There is a significant shift in the surface energy with mold releases or surface oils. Also ensure that adhesion to a substrate should be confirmed through testing.

Surface Energy Chart

How to use the right thickness for the Surface
The thickness of the tape depends on the rigidity of the substrates and the flatness or irregularity. If the 3M™ VHB™ Tapes conform to some amount of irregularity, then they will not flow to fill gaps between materials.
• For bonding rigid materials with normal flatness, consider use of tapes with thickness of 45 mils (1.1 mm) or greater.
• As the substrate flexibility increases thinner tapes can be considered.
• Thinner tapes can be used to bond small rigid parts.
• Large parts where a higher degree of expansion and contraction is expected might need thicker tapes. 
• As a guideline, the 3M™ VHB™ Tapes can allow up to 3 times their thickness is differential substrate movement in the shear direction (300% shear strain).

Consider the use of conformable or very conformable foam types to increase the contact area and reliability on rigid substrates.

Consider the Environment of Use

Temperature
3M™ VHB™ Tapes should provide good performance in typical ambient temperatures from about 200 F down to -40 F and below, provided there is a good adhesive bond to the substrates. While we do not see low temperatures to be a limiting factor in most applications, we do suggest that a thorough evaluation be conducted by the end user at actual use conditions on applications where high impact stress is expected at low temperatures. Some tape types are suitable for longer periods of time at temperatures up to 300 F and are capable of handling temperatures up to 500 F for short periods of time such as could be experienced in a paint process.

Moisture
The 3M™ VHB™ Tapes maintain excellent performance in high humidity and high water contact conditions. Tape bonds showed excellent integrity and adhesion levels after submersion in water and salt water for 10 years. Long term submersion or exposure to moisture or water submersion can have the effect of making the polymer more resilient and tolerant of high elongation. Drying of the 3M™ VHB™ Tapes and bond lines will show this effect is reversible, and that the bond will return to the original dry stiffness and strength.

Solvent and Chemical
With excellent solvent and chemical resistance, 3M™ VHB™ Tapes provide an occasional splash contact for solvents and chemicals that have a more significant effect on the tape performance. The tapes withstand regular contact with solvents or chemicals and do not affect performance, nevertheless continuous submersion in solvents or chemical solutions is not recommended. If there is an effect in performance the areas exposed to the solvent will show swelling at the edges. Also ensure there is no contact with strong acids when the tape is bonded to metal substrates.

UV
3M™ VHB™ Tapes safeguard from the harmful UV rays. It provides excellent UV resistance.

How much is right?

3M™ VHB™ Tapes are viscoelastic by nature, making them durable and stiff. But, this depends on the amount of stress exerted on them. 3M™ VHB™ Tapes behave stronger with a faster rate of stress load (dynamic stresses) and will show signs of creeping with the stress load prolonging for a long period of time (static stresses).

Static Stresses
As a general guideline, four square inches (approx.) of tape should be used for each pound of weight supported in order to prevent excessive creeping (0.25 lb/in2 load factor), which also includes a general safety factor. The static load can include the dead load weight the tape is holding or recovery of one of the substrates if there is a "spring back" condition or if the fit is not ideal.

Dynamic Stresses
The data page provides the dynamic performance characteristics that are useful for general applications with appropriate safety factors. For panel to frame applications, a design strength of 60 lb/in2 is commonly used (45 lb/in2 for 5952 family), which is derived from the simulated 1 minute peak wind load. A safety factor of 3 to 5 is applied depending on the application.

Mechanical assistance (fasteners, setting a panel on a ledge or setting block) is sometimes included in the design to reduce or eliminate the static stress on the tapes while ensuring the advantage of excellent dynamic strength is still preserved. The effects of expansion/contraction allowance or dynamic strength should always be considered when designing.
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For full range of products on VHB™ Tapes visit our Product Catalogue