What’s Plastic Bonding?

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Plastic bonding has become more common as the number and variety of bonded plastic materials has increased in recent years. Today, bonded plastic materials are all around us and new applications are being invented as the properties of plastics continue to improve. Plastic bonding is used in the manufacturing of countless items, such as digital video discs (DVDs), medical supplies, automobile parts, packaging components, and many more.

Bonding plastic is most often accomplished using an adhesive. A variety of adhesives are available, depending on the specific material properties required. Because adhesives can be distributed evenly between layers, they create a strong bond that creates a seal and helps distribute the forces applied to the bonded material evenly. These adhesives are generally lightweight, can be used with dissimilar materials, and are generally easy to apply to irregular shapes and surfaces.

Bonding plastics often requires surface preparation to ensure a high degree of bond strength between the adhesive and the plastic. Surface preparation can be as simple as cleaning to remove oils and other contaminants or it can involve the use of chemical primers or chemical etching. Many adhesives require curing time after application to reach their full strength and holding power. Curing of the adhesive is most often achieved with time, heat, ultraviolet and visible light, or a combination of methods.

The selection of the right adhesive for bonding plastics usually depends on the materials to be joined and the properties that the bonded material must have. There are several categories of adhesives used to bond plastics, such as acrylics, epoxies, and cyanoacrylates. Each category offers a unique set of material properties and performance characteristics. Within each category, many different adhesives are available to suit a wide variety of bonding applications. Some examples of different adhesive properties are flexibility, moisture resistance, curing time, and heat resistance.

Some plastic combinations are more difficult to bond than others. Adhesive joints can fail due to inadequate surface preparation, poor joint design, or the use of an adhesive that is not compatible with the plastic or operating environment. A good rule of thumb for bonding plastics is to maximize the area to be joined and incorporate mechanical locking into the joint design with the adhesive to increase bond strength.

Bonding of plastics can also be accomplished by a method commonly referred to as ultrasonic or plastic welding. This process uses an ultrasonic device that generates high-frequency vibrations to heat and melt plastic components. Ultrasonic bonding is commonly used in the manufacturing of automotive parts, packaging supplies, and toys. This method is usually limited to larger plastic parts or materials that are difficult to bond with adhesive methods.

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