Joining low-surface-energy plastics that are difficult to bond
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Low surface energy plastics, or LSE plastics, are often known by their initials and include such materials as polypropylene (PP), polyethylene (PE or HDPE), polystyrene, acetal, EVA (ethylene vinyl acetate) and powder-coated paints. They are generally soft and have a low melting point so they’re easy to process, even at high volumes, and they’re low-density, which helps with lightweighting. Because low surface energy is the primary characteristic of this group, they’re all more difficult to bond – there are adhesive and tape options that work well, but there are far fewer options to choose from and test.
LSE plastics are easily molded into a variety of shapes and are commonly used for single-use applications such as signage, decorative trim or packaging – plastic containers, but also plastic trays, protective buffers and wrapping films. Most applications don’t require a strong adhesive, but as a re-use market many recyclable plastics are shredded and turned into lightweight plastic lumber, which generally has the same bonding properties but may also require more adhesive strength.
These are some of the best adhesives and tapes to use for LSE plastics. Learn more about each featured technology using the links below.
Pressure-Sensitive Adhesive (PSA) bonding tapes are thin tapes with an adhesive on both sides. These tape constructions include adhesive transfer tapes and double-sided tapes. 3M has unique formulations that are designed for adhesion to LSE surfaces. They are ideal for smooth, flat surfaces and are often used for complicated flat shapes such as die cuts for smartphones, flat-screen TVs, gasketing, trim attachment and many packaging applications.
3M™ Scotch-Weld™ instant adhesives are high-strength liquid adhesives designed for tight-fitting joints. As little as one drop of instant adhesive per square inch can be enough to bond many substrates, including LSE plastics.
3M™ Scotch-Weld™ Structural Acrylic Adhesives are 2-component liquid adhesives that give designers the greatest strength for demanding applications. Many of these adhesives are a good choice for bonding LSE plastics. 3M™ Scotch-Weld™ Structural Acrylic adhesives provide impact resistance and high performance in a wide range of environmental conditions.
Polypropylene is a low-density plastic manufactured in very large volume and widely used as film, fiber and molded parts. It is often used for packaging as containers, absorbent pads and wrapping film as well as to create lightweight components for the automotive, appliance and medical industries.
Polystyrene is a clear, hard plastic; it can be brittle, but tougher versions known as high-impact polystyrene (HIPS) are available which have slightly different bonding properties. Some of the many applications that use polystyrene include foam peanuts, CD cases, clamshell containers, bottles, trays, cups and disposable cutlery. Polystyrene processes easily by molding, allowing for fine detail, as well as by vacuum forming to create foam panels.
Polyethylene is the most common plastic, produced in the largest volume. It is often made into wrapping film for packaging and molded into bottles or other containers. Polyethylene has relatively low strength and low temperature resistance but is easy to process and used for applications where those factors are less important.
Polyoxymethylene is an opaque white high-performance plastic with high strength, stiffness and rigidity plus good impact and temperature resistance and dimensional stability. It is often used in components like gear wheels, conveyor belts, eyeglass frames, fasteners and ski bindings.
Ethylene vinyl acetate is a rubber-like polymer with good toughness and crack resistance. It is often used as foam in footwear, particularly midsoles for tennis shoes and sandals, and for sports padding; it can also be a substitute for natural cork.
Traditional paints have a range of surface energies resulting in different bonding requirements. Powder-coat paints are a free-flowing dry powder which is applied and then heated to form a hard protective coating. Additives with low surface energy often flow to the surface when melted, which can make powder coats difficult to bond.
In determining which adhesive will perform best, it is very often helpful to consider the assembly type. The six assembly types shown below have different design characteristics that often determine the best adhesive or tape.