Questions to Ask When Choosing a PSA Tape for Your Substrate
When choosing a pressure sensitive adhesive (PSA) tape for your application, it’s vital to study the substrates (surfaces) of the materials you are bonding together. It’s one of the most crucial questions to ask, as the level of adhesion and bond strength will vary depending on the substrates being bonded and the type of PSA tape you use. Different tapes are ideal for different surfaces, depending on their qualities. What are the materials made of? Are you bonding together two similar or dissimilar surfaces? These are all important to consider, along with a few other key questions.
How Rough is the Surface Texture?
Standard pieces of tape simply lie over the surface of a material, failing to form a secure bond if one or more of the substrates has a rough or uneven surface. PSA tapes are coated with viscoelastic adhesives that flow into the smallest valleys of a surface. The “flow” of the adhesive, given ample dwell time, is enough to securely form a bond between two rough surfaces.
The adhesive tape you choose depends on the roughness of the surface. Smoother surfaces can be easily bonded with a thinner adhesive, but rougher surfaces require a thicker adhesive that has a better flow. Choosing the right thickness of your adhesive is a matter of testing it out on the surfaces being bonded to see which tape provides the longest and strongest bond.
What is the Contour of the Surface?
The contour of the surface directly impacts the type of tape that will be most effective. Specifically, it decides the thickness and firmness of the tape that should be used. Running a piece of pressure sensitive adhesive tape along a flat surface differs greatly from running it along a contoured surface. The greater the curve, the more flexible the piece of tape will need to be in order to correctly bond to the surface. If the tape is too thin or firm, it can cause internal stress on the tape (resulting in tearing) and flagging (lifting at the edges). A thicker, more flexible piece of tape with a softer adhesive allows for maximum surface contact and bond strength.
What is the Surface Energy of the Substrate?
A substrate’s surface energy is a relative measurement of the excess energy on the surface of a material, and its importance in the bonding process cannot be understated. The surface energy of a particular material mainly affects the “wetting” of the adhesive on PSA tape, which is how quickly the adhesive spreads out, affecting the strength of the attraction. The higher the surface energy, the greater the attraction, meaning the surface is easy to adhere to. High surface energy materials include that have an excellent adhesive wet-out include:
Aluminum
Copper
Stainless Steel
Tin
Glass
Porcelain
Medium surface energy materials, including a range of plastics and paints, typically demonstrate very good adhesive wet-out such as the following:
PVC
Acrylic
Nylon
Polyester
Polyurethane or epoxy paints
Kapton (polyimide film)
Phenolic
ABS
On the other hand, surfaces with a low surface energy are harder to adhere to because the attraction is not as strong. Low surface energy materials that have poor adhesive wet-out include:
Polystyrene
Polyvinyl acetate
Acetyl
EVA
Powder paints
Polyethylene
Polypropylene
UHMW
Tedlar (PVF)
Teflon
In order to bond surfaces together that have low surface energies, it’s often best to use a very high bonding acrylic foam tape like the 3M™ VHB™ Tape LSE Series or 3M LSE thin bonding tapes.
What is the Operating Environment?
The environment where your substrates need to be bonded is just as important as the substrates themselves. Different environmental conditions create problems for certain adhesive tapes, often resulting in weaker bonds and shorter bonding times. It’s important to ask what conditions your PSA tape will be exposed to, including:
Solvents and chemicals: can cause adhesive tapes to swell, soften, and even dissolve. If your substrates are often exposed to chemicals, it’s best to consider acrylic adhesive tapes, which have a high cohesive strength that makes them resistant to many solvents for extended periods.
Plasticizers: can cause adhesive tapes to soften, turn stringy, or become discolored over time. Choose a tape that is resistant to plasticizer migration, which prevents the tape from softening. Acrylic adhesive tapes are better than rubber tapes in this application.
UV light: exposure to excessive sunlight causes PSA tapes to become discolored and brittle over time, and it can also cause chemical degradation and a failure of the adhesive. Different PSA tapes have different levels of UV light resistance.
Low temperatures: cold air causes some adhesive tapes to harden and become brittle. This not only reduces the adhesive tack, it can also lessen their resistance to impact shocks. Cold temperature performing PSA tapes are ideal for low temperatures.
High temperatures: hot air causes adhesive softening and reduces the shear and cohesive strength of the tape. If you are bonding surfaces that are exposed to heat or high temperatures, use PSA tapes that can perform well in this environment (like silicone foam tapes).
Is There Surface Contamination?
Keep in mind that solid and liquid contaminants can cause a poor bond to be formed between the PSA tape and the substrate. Contaminants like grease, oil, and moisture can form a barrier between the surface and the adhesive on the tape, causing the bond to fail. Particles like dust, talc, and fibers can impact the tackiness of the PSA tape and reduce the contact surface area, which will also cause the bond to fail over time. Always make sure to clean your surface of contaminants before applying a PSA tape.