Raw materials. All vinyl products are made from a unique combination of vinyl resin and various additives which give these products their particular properties. For more information on the vinyl resin process, see general vinyl section. Every formulation is different, and most are proprietary. Some of the additives commonly used in vinyl roofing membrane include:
•Plasticizers, which give vinyl roofing membranes flexibility to ensure long-term durability, weldability and reparability. Plasticizers are selected for their stability and resistance to degradation by UV light. Tests have shown that 20-year-old applications of vinyl roofing membranes have retained 80 to 90 percent of their original plasticizer content.
•Stabilizers, commonly used in reinforced vinyl roofing membranes to improve heat and UV light stability.
•Pigments, which, added during the manufacturing process, give vinyl a range of colors.
Processing/fabricating. Once the additives have been combined with the resin, the resulting material is called vinyl compound, and is in liquid, pellet or powder form. The nature of the vinyl compound allows versatility in the production process, enabling manufacturers to meet many of the unique performance requirements of buildings. In the next stage of manufacturing, vinyl roofing membrane is created through one of two different processes:
•Spread coating process. Vinyl compound in a liquid form known as plastisol is mixed and uniformly applied onto the reinforcement layer. This layer may consist of either a non-woven glass mat or a polyester fabric, and is fused at high temperatures. There are no pressure rollers used to form the sheet in this application method.
•Calendering and extrusion processes. These processes use rollers to create a vinyl membrane under heat and pressure. The materials' reinforcement is incorporated by laminating two calendered or extruded films around a polyester or fiberglass scrim.
The sheets are typically manufactured in widths from 4' to 6-1/2' and in lengths from 65' feet to 100'. These sheets can also be found in a variety of thicknesses, such as 36 mil, 48 mil, 60 mil, 72 mil, 80 mil and 96 mil. Increasing the thickness of the sheet typically improves the weathering properties as well as tensile strength, tear resistance and puncture resistance. Finished sheets of vinyl roofing membrane are wound onto rolls, ready to be shipped to the construction site.