Use the Right Tape for the Surfaces Involved
Adhesion is the molecular attraction between unlike materials, similar to magnetic force. Strength of attraction is generally determined by the surface energy of the material. The higher the surface energy, the greater the attraction. The lower the surface energy, the weaker the attractive forces.
On high surface energy surfaces a tape or adhesive can flow or "wet out" to assure a stronger bond. These surfaces include aluminum, steel or glass. On low surface energy surfaces most adhesives and tapes will resist flowing onto the surface, leaving poor surface contact and low adhesion strength. Traditionally substrates have been categorized as having high surface energy or low surface energy as it relates to bonding with adhesives. With the increasing number of substrates and with new adhesives it is common to identify substrates as having medium surface energy or even medium high or medium low surface energy.
Because the surface energy defines a level at which the adhesive can wet and bond to the surface, generally an adhesive type can bond to surfaces with a particular surface energy level and higher. Following are guidelines for matching 3M™ VHB™ Tapes adhesive types with typical substrates.
Multi-purpose Adhesive
Bonds to medium, medium high and high surface energy substrates. (Used on 4941, 4945 and 4622 (liner side) family tapes)
Modified Acrylic Adhesive
Bonds to medium low, medium, medium high and high surface energy substrates (used on 5952 family tapes)
General Purpose Adhesive
Bonds to high surface energy substrates and some medium and medium high surface energy materials. (Used on 4950, 4910 and 4611 family tapes)
Low Temperature Appliable Adhesive
Bonds to high surface energy substrates and some medium and medium high surface energy materials. (Used on 4951 family tapes)
Low Surface Energy
Bonds to some low surface energy substrates and smooth surface in the other categories. (Used on 4952 family tapes)
Below are general groupings of materials into surface energy categories. Note that this 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. Mold releases or surface oils can also significantly shift the surface energy. Adhesion to a particular substrate type should always be confirmed through testing.
Use the right thickness of tape
The necessary thickness of tape depends on the rigidity of the substrates and their flatness or irregularity. While the 3M™ VHB™ Tapes will conform to a certain amount of irregularity, 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
The 3M™ VHB™ Tapes have excellent solvent and chemical resistance. For solvents and chemicals that have a more significant effect on tape performance occasional splash contact is generally suitable. The tapes can withstand regular contact with solvents or chemicals that have less effect on performance. Continuous submersion in solvent or chemical solutions is not recommended. When performance has been affected with solvent exposure the tape will show swelling at the edges. Contact with strong acids when the tape is bonded to metal substrates should be avoided.
UV
All 3M™ VHB™ Tapes have excellent UV resistance.
Use the right amount of tape
Because 3M™ VHB™ Tapes are viscoelastic by nature their strength and stiffness is a function of the rate at which they are stressed. 3M™ VHB™ Tapes behave stronger with relatively faster rate of stress load (dynamic stresses) and will tend to show creep behavior with stress load acting over a long period of time (static stresses).
Static Stresses
As a general guideline, approximately four square inches of tape should be used for each pound of weight to be supported in order to prevent excessive creep. (0.25 lb/in2 load factor). This includes a general safety factor. Static load can include dead load weight the tape is holding, or memory or recovery of one of the substrates if there is a "spring back" situation or if fit is less than ideal.
Dynamic Stresses
The dynamic performance characteristics provided in the data page should be useful for general applications, factoring in the appropriate safety factors. For panel to frame applications, design strength of 60 lb/in2 is commonly used (45 lb/in2 for 5952 family). This is derived from the simulated 1 minute peak wind load. A safety factor of 3 to 5 would typically be applied depending on the application.
Mechanical assistance (fasteners, setting a panel on a ledge or setting block) is sometimes included in a design to reduce or eliminate the static stress on the tape while taking advantage of excellent dynamic strength. The effects that this has on expansion/contraction allowance or dynamic strength should be considered when designing.
