Plastics and other low surface energy materials such as polypropylene (PP) and polyethylene (PE or HDPE) and polytetrafluorethylene (PTFE) are known to present challenges when bonding to other surfaces. Due to the low melting point of these materials, it can be difficult to find a bonding adhesive solution that doesn’t compromise the material itself.
While many manufacturers take to mechanical bonding techniques or welding, these can also present unfavorable obstacles including the use of hazardous chemicals.
Of course, plastics have become integrated into most all aspects of peoples’ lives and therefore, have become an essential material for many manufacturing operations. While the prevalence of plastics in manufacturing is generally industry-agnostic, surface energies for different types of plastics can range from 18-43 mN/m, meaning that each application warrants a very specific bonding strategy.
Fortunately, recent innovations in manufacturing and technology have uncovered solutions for bonding LSE materials in a way that omits many of these historic challenges. While the surface energy of these materials is always important to consider, technical tape and adhesive options have given manufacturers more liberties in the realm of product design, stress distribution and overall material diversification. In this article, we’ll highlight several solutions to bonding LSE materials with adhesives.
Types of Adhesives
Adhesive materials are classified in a variety of ways, some based on their chemical composition, such as acrylic, epoxy or urethane. Others are classified by the function they serve, such as pressure sensitive or heat curable adhesives. The following three adhesive bonding methods are some of the most commonly used by manufacturers:
To ensure that a bond is structurally sound, many manufacturers take to structural adhesives. As the name suggests, this method is particularly well-suited for applications that must maintain a reliable structure when bonding takes place. By definition, structural adhesives form bonds that are capable of withstanding great amounts of weight or pressure.
The adhesive should be so reliable that it attains a similar yield point as the materials being bonded. The strength and durability of structural adhesives have many benefits, particularly when used for applications in the automotive or aerospace industry. As structural adhesives are designed to be as strong as the materials they bond together, using a structural adhesive in place of a mechanical bond makes for a cost-efficient, light-weight bonding solution.
Hot Melt Adhesives
While this adhesive method is frequented in manufacturing applications, many people have had hands-on experience with hot melt adhesives (Think: arts and crafts in primary school). Ring a bell? Glue guns are one type of hot melt adhesive which, in manufacturing applications, are typically used for packaging, page-to-spine bonding for books, textiles, and even some electronic applications.
A hot-melt adhesive is typically stored as a solid at room temperature and then activated with heat, at which point it liquefies and can then wet the surface of the materials being bonded. Once the adhesive is set in place, it cools and solidifies to create a structurally sound adhesive. One unique benefit of hot melt adhesives is that they can be heated more than once to re-bond materials.
The adhesive can also be removed and replaced, making for efficient swapping of other parts and materials within the application and minimizing waste during the manufacturing process.
Of course, this means that the application itself should not be susceptible to temperatures that surpass the melting point of the adhesive to ensure optimal bonding strength. Similarly, hot melt adhesives are not suitable for applications that bear heavyweight, for which their structural adhesive counterparts should be considered.
Pressure Sensitive Adhesives
One of the easiest material bonding techniques is known as pressure-sensitive adhesion. Formulated from different types of rubber-like compounds, pressure-sensitive adhesives are sometimes known as self-stick adhesives for their ability to activate without a chemical reaction taking place. While other techniques are reliant on a solvent, water or heat to activate, PSAs form bonds simply using applied pressure.
They are typically viscous and remain malleable, making them a rapid bonding solution conducive to detachment and reapplication. This versatility is highly valuable for manufacturing applications, temporarily holding parts in place per the manufacturer’s preference.
When applying pressure-sensitive adhesives to an application, there are many techniques used depending on the specific use case. Pressure-sensitive adhesives are not solid nor liquid, so it’s important to be mindful of whether the technique being used will impact the adhesive’s functionality. Techniques, where heat is involved, can weaken the bond. Similarly, when PSAs undergo high amounts of pressure, they may shift, although the bond will strengthen over time.
Still searching for an adhesive bonding solution?
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