Joining two surfaces together.
It doesn’t sound that difficult. Yet, depending on the substrates and the performance demanded of that adhesive bond, it can be pretty tricky.
Historically, mechanical fasteners of all kinds — rivets, brackets, bolts, screws, retaining rings — have been used to “permanently” bond two substrates. But, these are not low-profile, plus their weight and likelihood to corrode increases the possibility of bond failure.
Many industrial bonding adhesives are low profile, including 3M™ VHB™ and acrylic foam tapes, which evenly distribute pressure along the substrates and enhance aesthetics.
That’s just one example. More and more, modern materials are replacing mechanical fasteners and welds. In fact, there are so many; we decided to write this article to examine 5 low-profile adhesive bonding materials.
Examining Adhesive Bonding Materials and Substrates
The goal of any bonding solution is to help customers manufacture products in efficient, effective, and innovative ways. Some materials do that better than others, offering versatility for a wide range of applications and substrates.
Advantages that nearly all low-profile adhesive bonding materials offer include:
- No drilling/holes reduces labor costs
- Thin, light materials reduce weight and energy use
- Stress is distributed evenly across the bond
- Easier to bond dissimilar materials
- Seal and bond simultaneously
- Vibration is reduced in the final product
In a recent blog series on thin bonding, we explored how the surface energy — both low surface energy and high surface energy — of substrates affects adhesion (high surface energy offers strong molecular attraction; low surface energy offers weak attraction).
Substrates with high surface energy: metal, glass, epoxy paint, PVC rigid, nylon, polyester. Substrates with low surface energy: composites, powders and coatings, acetal, polystyrene, polypropylene, PVA, polyethylene, and other plastics.
Understanding Substrates is Critical
• Strong, durable, cost-effective, and easily machined metals are typically easy to bond as long as the surface is appropriately prepared. Bonding metals enhances the advantages of many bonding adhesives: gap-filling and isolation of substrates.
• Glass, ceramic, concrete, and natural materials such as wood, textiles, leather, and stone. These traditional materials have medium surface energies, so they’re easy to bond. A converter will help determine the specific adhesive to bond each material.
• Engineered plastics — polycarbonate, acrylonitrile butadiene styrene (ABS), urethane foam, and some coatings, for example — are strong, stiff plastics. While they perform well at high temperatures and are easy to bond, they cost more than many other options.
• The adhesive selection process is much more critical for plastics with low surface energy (LSE). Examples: polypropylene, polystyrene, polyethylene, and many powder-coated paints.
The 5 Best Low-Profile Adhesive Bonding Materials
Now that we’ve covered substrates let’s explore the top 5 materials that offer low-profile adhesive bonding of these substrates.
When looking at adhesive bonding materials, applications, and technology, it’s important to remember that each offers specific advantages. For example, liquid adhesives (#1 and #2 below) can fill gaps by flowing and conforming to the shape of the bond area.
In general, epoxies are very hard, durable adhesives that successfully bond many substrates. Usually a 2-part system, epoxy can be formulated for many applications, many cure speeds, and to perform in many extreme environments. Because of their strength and toughness, epoxies are often used to join structural materials, for instance, plywood.
Epoxies can be challenging to apply, so automated machines are standard yet can also be expensive. During manual application, liquid adhesives are challenging to apply and difficult to control. Either way, the assembly process must take into account curing, usually an extra step.
In the past, glues created relatively weak bonds, although recent innovations with self-curing adhesives now make glue a preferred material for joining many applications. Many types of glue are now carbon-based petrochemical derivatives, so bonding metal to dissimilar materials is more effective. Glues’ properties mean they form both an adhesive and sealant simultaneously.
Similar to epoxy above, application can be tricky. Expensive machinery is often the preferred application method. In addition, glue bonds may fail when the bond is exposed to prolonged heat and/or weathering.
3. Spray Adhesive
A type of contact adhesive, spray adhesives are typically used to bond paper, fabrics, foam, and felt. Specialty contact adhesives are used for more demanding projects: metal, plastic sheet laminates, and wood. Achieving a uniform thickness across the entire surface can be difficult.
Application of spray adhesives can be challenging. It’s essential to apply in a well-ventilated room using a specialized applicator, for both manual and automatic. The solvent needs to completely evaporate before bonding, after which repositioning substrates is not possible.
4. Adhesive Film
A layer of high-performing bonding agent on a backing material, an adhesive film is thin and creates a strong bond. While some adhesive films are moisture-activated or pressure-sensitive activated, these films are typically heat-activated adhesives. Plus, adhesive films contain no liquids, allowing them to be stored indefinitely.
Similar to how glues have reached high-performance levels in recent years, weak adhesive films are now a durable, trusted material thanks to bonding innovations. Yet, like epoxies, most modern films now use self-curing adhesives. These bonds are strong, yet require extra curing time.
5. Adhesive Tape
Spoiler alert: this is our favorite. Pressure sensitive adhesive tape (PSAs) are some of the most trusted low-profile bonding solutions. Smaller, smoother, better looking … modern PSA solutions provide unlimited design opportunities for engineers. Let’s explore more about adhesive tape.
Benefits of Adhesive Tape
• Stress Distribution — Yes, we mentioned this in the “advantages list” for low-profile adhesive bonding materials earlier, yet it demands an additional mention. Force on a bond is evenly distributed when a strip of adhesive tape connects the two substrates along the entire bond. Fewer concentrated stress points, less stress, less failure, more shear strength.
• Strong Protective Seal — Mechanical fasteners were never exceptional at creating a physical seal between components. Adhesive tapes are. They create secure coverage that works like a seal.
• Ability to Convert — Converting adhesive tape to custom sizes, shapes, and formats is a huge advantage. Once die cut, adhesive parts fit seamlessly into assembly processes, whether automated or manually applied.
• Improved Appearance — Aesthetics are more important than ever. Adhesive bonding tape creates a tight, low-profile connection without adding unsightly bulk to the components.
• Versatility — One of the most powerful advantages of adhesive bonding is its versatility, allowing for bonding of a wide range of items and between surfaces that are not exactly the same
• Virtually Future-Proof — Automatic adhesive dispensing, typically using a robotic system, makes assembly accurate, efficient, and consistent. As low-profile bonding applications become more in demand, adhesive tape becomes the preferred option.
Temporary or Permanent?
Not all adhesive bonding options are permanent, especially low-profile solutions. Think of reclosable packaging, changeable gaskets, and other removable material. Since the goal isn’t always the strongest bond, it’s vital to use tape with reliable holding properties that can be removed or repositioned easily. These are often called “temporary bonding tape,” “removable tape,” or “repositionable tape.”
The Crucial Role of Converters
Trusted materials are always needed. Yet, on their own, they’re less than adequate. That’s why it’s crucial to work with a trusted converting partner. A full-service converter helps determine specific low-profile adhesive bonding materials (and carriers, if needed) for each product, plus the format required for that application. PSAs are converted into rolls or sheets, depending on the application and how they’re applied.
Continue your search for the right adhesive bonding materials by reading our Flexible Material Converting Q&A Guide. We answer many common questions asked of adhesive converters. Need immediate help? Give Strouse a call today (800)-410-8273, or you can ask an engineer!