Plastic bonding has become more common as the number and variety of combined plastic materials have 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 manufacture of countless items, such as digital video discs (DVDs), medical supplies, automotive parts, packaging components, and many more.
Plastic bonding is most often accomplished using an adhesive. A variety of adhesives are available, depending upon the specific material properties required. Since adhesives can be spread evenly between layers, they create a strong bond that makes a seal and helps to distribute applied forces evenly across the bonded material. These adhesives are usually light-weight, can be used with dissimilar materials, and are generally easy to apply on irregular surfaces and shapes.
Plastic bonding often requires surface preparation to ensure that there is a high degree of bond strength between the adhesive and plastic. Surface preparation may be as simple as cleaning to remove oils and other contaminants, or may involve the use of chemical primers or chemical etching. Many adhesives require curing time after application to reach their full strength and holding power. Adhesive curing is most often accomplished with time, heat, ultraviolet and visible light, or a combination of methods.
Selecting the right adhesive for plastic bonding usually depends on the materials being joined, and the properties that the bonded material must exhibit. There are several different 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, there are many different adhesives available to meet a wide range of bonding applications. Some examples of different adhesive properties are flexibility, moisture resistance, curing time, and thermal resistance.
Certain combinations of plastics are more difficult to bond than others. Adhesive joints can fail due to inadequate surface preparation, poor joint design, or use of an adhesive that is not compatible with the plastic or operating environment. A good general rule for plastic bonding is to maximize the area to be joined, and incorporate mechanical locking in the joint design with the adhesive to increase bond strength.
Plastic bonding 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 vibration to heat and melt plastic components together. Ultrasonic bonding is commonly used in the manufacture of automotive components, packaging supplies, and toys. This method is usually limited to larger plastic parts or materials that are difficult to bond using adhesive methods.