Natural rubber was first used as an adhesive in the early nineteenth century. Since its creation, adhesives manufacturers have consistently developed their products, which have resulted in natural rubber adhesives (NRA) and synthetic rubber adhesives (SRA). Rubber adhesives are made from a variety of compound combinations including; resins, agents and additives. These compounds are added in order to boost certain characteristics. Rubber adhesives have many purposes; both in the home and manufacturing, and a multitude of types exist today. They can be used to bond a variety of elements, including glass, metal, leather and natural fibers.
Natural Rubber Adhesives
SRA is widely used for making electrical insulation tapes, packaging tapes, plasters and surgical tapes - this is due partly to its tack properties and partly to the easy and damage-free removal of these adhesives. Most adhesives, such as the well-known super-glue, do not provide both these qualities. The backing to these tapes can be made from a variety of materials depending on the application.
Synthetic Rubber Adhesives
Despite the good tack properties of SRA, it is not suitable for adverse environments or for structures that need to endure high loads. Subsequently, numerous polymers were developed to improve upon the NRA. Various resins and other compounding ingredients are mixed with the rubber adhesive in order to create the desirable property. These include flexibility, pressure sensitivity, water and ageing resistance and sealant. Rubber is a well-known adhesive due to its flexibility - a SRA adhesive known as styrene is commonly used in automobile manufacturing as it adapts well to pressure and temperature changes. However, rubber adhesives are generally flammable, so is not suited for bonding in high temperature situations.
Another favorable quality of rubber adhesive is its water resistance. As a result, it is often used where dampness is an issue, for example; it is often used to bond shoes, suitcases, handbags and similar items that are likely to come in to contact with rain and moisture. Polysulfide, another SRA is commonly used on boats and marine equipment that is submerged in water. It is flexible, chemically resistant and able to withstand water and is consequently used as a sealant. An additional bonus is that it can be applied quickly and is often carried on-board in emergency situations. A widely used SRA is polyurethane, which provides extremely strong bonding. The initial bond created, before the adhesive dries, is so strong that no clamp is required to secure the product in place. This provides a cheap and simple solution for many manufacturers. Polyurethane adhesives tend to be exceptionally flexible and durable, and provide good impact resistance. Furthermore, polyurethane can be used on an array of materials including plastic, metal and glass. Another noteworthy characteristic is its resistance to most acids, solvents and oils.
In a nutshell, rubber adhesives are responsible for bonding and sealing several of our day-to-day items. So next time you pop your shoes on, close your windows or drive to the supermarket - remember what's holding these items together!