Joining two surfaces together doesn’t sound complicated. Yet, depending on the substrates and the performance demanded of an adhesive bond, choosing the wrong adhesive could create a huge mess.
Modern materials have started replacing mechanical fasteners and welds, so we’ve decided to share what we know and our experience using different types of adhesive bonding materials.
Once you’ve learned more about the alternatives, you’ll be able to decide which bonding solution is right for your future product.
The 5 Types of Adhesive Bonding Materials
Historically, mechanical fasteners— rivets, brackets, bolts, screws, retaining rings — have been used to “permanently” bond two substrates. Unfortunately, mechanical fasteners tend to look unsightly, and their weight and likelihood of corrosion increase the possibility of bond failure.
Rather than using mechanical fasteners, we’ve spent over three decades working with low profile industrial bonding adhesive alternatives like acrylic foam tapes, which evenly distribute pressure along the substrates.
When looking at adhesive bonding materials, applications, and technology, it’s important to remember that each material offers specific advantages. For instance, liquid adhesives, like glue or epoxy, can fill gaps by flowing and conforming to the shape of the bond area.
Let’s explore the adhesive bonding materials that might suit your project needs. Then, we’ll take a closer look at how to choose a material based on your substrates.
1. EPOXY
Generally, epoxies are hard and durable adhesives that successfully bond many substrates.
Epoxies are usually a 2-part system that can be formulated for many applications, cure speeds, and perform in extreme environments. Because of their strength and toughness, epoxies are often used to join structural materials, for instance, plywood.
Unfortunately, epoxies can be challenging to apply, so automated machines are standard yet can also be expensive. During manual application, liquid adhesives are difficult to apply and control. The assembly process must factor in curing, which is often an additional step.
2. GLUE
In the past glues created relatively weak bonds, yet 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. The properties of glue allow it to act as an adhesive and sealant simultaneously.
Similar to epoxy, glue 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 or weathering.
3. SPRAY ADHESIVE
As a 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.
The application of spray adhesives can be challenging. It’s essential to apply in a well-ventilated room using a specialized applicator, either manual or automatic. The spray adhesive solvent must completely evaporate before bonding, after which repositioning your substrate will be impossible.
4. ADHESIVE FILM
Adhesive films are a thin layer of high-performing bonding agent on a backing material that creates a strong bond.
While some adhesive films are moisture-activated or heat-activated, films are typically pressure-sensitive adhesives. Adhesive films also contain no liquids, allowing them to be stored indefinitely.
Modern bonding innovations have enabled glues and weak adhesive films to transform into durable, trusted materials. Yet, similar to epoxies, most films now use self-curing adhesives. These bonds are strong yet require extra curing time.
5. ADHESIVE TAPE
Adhesive tape is customizable into various sizes, shapes, and formats. Once die cut, adhesive parts fit seamlessly into automated or manual assembly processes. In addition, they create secure coverage that can function as a seal.
The difference between adhesive film and adhesive tape is that tape tends to have more adhesive and a thicker construction. Adhesive tape tends to have a higher holding power for more structural stability.
Force on a bond is evenly distributed when a strip of pressure sensitive adhesive tape connects the two substrates along the entire bond. Fewer concentrated stress points decrease stress and failure while increasing the shear strength.
One of the biggest advantages of adhesive tape bonding is versatility because it allows you to bind a wide range of dissimilar surfaces and objects.
In addition to increased shear strength, adhesive tape is also one of the most aesthetically pleasing bonding options. Adhesive bonding tape creates a tight, low-profile connection without adding unsightly bulk to the components.
Lastly, automatic adhesive dispensing, typically using a robotic system, makes assembly accurate, efficient, and consistent.
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, using tape with reliable holding properties that can be removed or repositioned easily is vital. These are often called “temporary bonding tape,” “removable tape,” or “repositionable tape.”
What Should I Know About Bonding Before Choosing My Materials?
Any bonding material selection aims to help you create your solution while manufacturing products in efficient, effective, and innovative ways.
Adhesive bonding materials offer the following advantages:
- The lack of 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
However, certain materials lend themselves to production better than others and offer more versatility for a wider range of applications.
SUBSTRATES ARE CRITICAL TO CHOOSING YOUR ADHESIVE
In our blog series on thin bonding, we explored how substrates' high and low surface energy affect adhesion. High surface energy offers strong molecular attraction, while low surface energy offers weak attraction.
High surface energy substrates: metal, glass, epoxy paint, PVC rigid, nylon, and polyester.
Strong, durable, cost-effective, and easily machined metals are typically easy to bond if the surface has been prepared appropriately. Bonding metals enhance the advantages of many bonding adhesives: gap-filling and isolation of substrates.
Glass, ceramic, concrete, and natural materials like wood, textiles, leather, and stone are traditional materials with medium surface energies, making them easy to bond. A converter will help determine the specific adhesive to bond each material.
Engineered plastics such as polycarbonate, acrylonitrile butadiene styrene (ABS), urethane foam, and many coatings, are strong and stiff plastics. While they perform well at high temperatures and are easy to bond, they cost more than other options.
Low surface energy substrates: composites, powders and coatings, acetal, polystyrene, polypropylene, PVA, polyethylene, and other plastics.
The adhesive selection process is essential for plastics with low surface energy (LSE): polypropylene, polystyrene, polyethylene, and many powder-coated paints.
You might have difficulty sourcing materials when joining substrates with low surface energies. A flexible material converter could have the right experience and supplier connections to guide you in the right direction.
What Role Do Converters Play in Choosing a Bonding Material?
Trusted materials are always needed, but on their own, they’re inadequate.
If you’re new to the process, you might not know how much of a role adhesive selection and product design play in determining how much you spend on part manufacturing. A full-service converter helps you determine adhesive bonding materials for each product based on design manufacturability.
Preparing for your adhesive design phase can be challenging, but a converter can help you define a strategy and production process to build the most effective parts while avoiding common errors:
Suppose you’re new to working with a converter or have doubts about the process. In that case, you can further the search for the right adhesive bonding materials by reading our Flexible Material Converting Q&A Guide, where we’ll answer questions we’ve been asked as flexible material converters.
