Adhesives are basically made from natural and synthetic rubbers, resin tackifiers, fillers, anti-fungicides, colors (if needed) and anti-oxidents (to combat aging). These are all classified as solids. These solids must be put into solution for application whether it be for Knife-Over-Roll, Reverse Roll or Calender coating. The solutions used to accomplish this are solvents and water. There are also some thermoplastic adhesives which can be applied by heat extrusion. Thermoplastic adhesives are used because they soften under high heat (during application) and are soluble in selected solvents which allows the coating to be spread evenly on the surface of the cloth.

Coating Procedures

Advances made in technology and machinery make Knife-Over-Roll coating procedures every bit as expensive as Calender coating from initial set-up to day by day operation. In many cases now, Knife-Over-Roll coaters produce their own adhesives because of advances in construction of totally enclosed coating heads, and the restriction placed on the transporting of adhesives and chemicals.

Knife-Over-Roll coaters actually pump the adhesive from holding tanks (which are part of the machinery) directly to the coating surface subjecting not one gram of adhesive to the atmosphere. This is required by environmental regulations both in Canada and the United States. All bi-products of the adhesive formula are destroyed via incineration which is also controlled by government regulation.

Every gram of adhesive produced must be accounted for. One kilogram of adhesive, for example , is made up of 50% solids and 50% solvents. The coated fabric passes through a long oven at controlled speeds removing 100% of the solvent blend to destruction. Only 100% of the rubber and tackifying resins (the solids) are remaining. Computers monitor the destruction of the solvent and adjust the line speeds so as to ensure 100% evaporation and provide quality assurance. This ensures environmental safety by destroying all traces of solvent that is not incorporated into our product.

Calender coating uses more adhesive mass, and that usually means more evaporation into the atmosphere.

The product that is produced, whether it be by Knife-Over-Roll, Calender or other method of coating procedure still depends on quality of concerned workers and testing procedures within the coating facilities.