The Best Bonding Solution for Low Surface Energy Substrates
A material's surface energy is a critical component to the bonding process. If you are struggling to achieve a strong bond between an adhesive tape and a surface, or find that the bond fails days, weeks, or even months after application, the material’s surface energy could be the culprit. Materials with low surface energy are notoriously hard to bond without overcoming the surface characteristics of the material via welding or using some type of mechanical fastener (see how PSA tapes perform better than mechanical fasteners and welds).
Struggling to create a strong bond? Working with a low surface energy material? Learn more about the challenges of bonding LSE materials and what PSA tapes are the best for the job.
What is Low Surface Energy?
The surface energy of a substrate, as it relates to bonding, is how quickly the adhesive will spread out across the surface in order to adhere to it (a process known as wetting). High surface energy substrates are much easier to bond to, while low surface energy (LSE) substrates pose certain challenges. This is because low surface energy substrates have a weaker molecular attraction than those with high surface energy (metals, acrylics, glass/porcelain, etc.).
Surface energy is measured in dynes per centimeter, with higher numbers denoting higher surface energy. Materials like metal and glass can measure in the 1,000s of dynes/cm, while LSE materials typically measure below 36 dynes/cm.
Note: medium surface energy substrates (which include wood, stone, concrete, and some engineered plastics like Acrylonitrile Butadiene Styrene (ABS) and Polystyrene, can have a surface energy between 36 and 300 dynes/cm.
Learn more about surface energy and see some breakdowns of surface energy measurements on the 3M™ website.
What Materials Have Low Surface Energy?
Examples of LSE materials include:
Polyethylene
Polyolefin plastics
Surface with powder coated paints
Polypropylene
Ultra High Molecular Weight Polyethylene (UHMW)
“Non-stick” surfaces like polytetrafluorethylene (PTFE)
The Challenges of Bonding Low Surface Energy Materials
The largest challenge of bonding low surface energy materials is the weak attraction that the molecules of the material have, even to liquid adhesives and pressure sensitive adhesive (PSA) tapes. This is generally due to the materials being chemically inert. The second challenge is the poor wetting of the adhesives applied to the substrate—the adhesive does not uniformly spread out across the surface.
An analogy that is normally used to demonstrate poor wetting is the surface of a car. When the surface is not waxed, it has a high surface energy. This means that water droplets will puddle on the surface. When the car is waxed, it has a low surface energy, resulting in the water beading up on the surface.
The Advantages of Using PSA Tapes to Bond Low Surface Energy Materials
Historically, primers or chemical etching treatments were used on LSE materials in order to prepare the surface for bonding. Some manufacturers also took extra steps to prepare the surface, such as flame treatment, corona treatment, abrasion, etc.
Today, manufacturers like 3M have lines of PSA tapes that are specifically designed to create a strong bond to LSE materials. These adhesives tapes have added “tackifiers” that increase the tack of the adhesive softening the adhesive resin system and allowing it to wet out more effectively on LSE substrates. These tapes offer high bond strength and good initial tack, allowing them to quickly bond well even to hard-to-bond plastics, powder coated paints, and lightly oily metals.
Low Surface Energy Tape Options
Thin rubber-based PSA tapes provide excellent initial tack with an immediate bond strength that adheres to many types of substrates. They quickly stick to most surfaces and have full strength adhesion immediately with pressure. While bonding very well, they do not provide long term durability in harsh environments. These include:
3M LSE acrylic tape products are specially designed for low surface energy substrate adhesion. They have a good level of initial tack and achieve full bond strength in about 72 hours after placement, and best of all, can withstand challenging environmental conditions. These include:
Other 3M tape options can be combined with 3M’s Primer 94, which promotes adhesion to polyethylene, polypropylene, UHMW, powder coated paints blends and other substrates that are difficult to adhere to. This primer allows you to gain the benefits of using certain types of PSA tapes while increasing their adhesion to LSE substrates. These tapes include:
There are also other general purpose acrylic tapes from 3M, Tesa, Avery Dennison, and others that work well with LSE substrates. These include products like 3M’s 950 adhesive transfer tape, Tesa’s 4970 double sided tape, and Avery Dennison’s FBA 8950: