Co-extrusion and mono-extrusion are the processes normally used in the production of all types of PVC/Vinyl Fence. The American Society for Testing and Materials (ASTM) has specifications for each product line. The buyer should be aware of which specifications are being used by the extruder. Some say Mono-Extrusion is better, some say Co-Extrusion. Take a look at the argument below and you decide.
Monoextrusion is the original way fence and even siding is made. Mono-extrusion is a process that injects a U.V. protector in the entire profile, having 100% coverage. Now most fence companies use co-extrusion because of cost, which is extruded with a capstock (the outer layer) and a substrate (the inner layer). Using co-extrusion causes the profile to have ONLY 20% coverage of U.V. protection, which is the capstock and is only paper-thin. It is easy to understand the differences if you think of mono-extrusion as being solid gold and co-extrusion as being plated gold, in time the outer layer will wear off and the fence profiles will begin to become brittle, crake and peal.
Co-extrusion is the newest technology used for shaping PVC products. Two or more layers areproduced. The outer layer (or cap stock) is similarto a “skin”. It contains a denser concentration of the essential elements (including UV inhibitors) and protects like a sunscreen when exposed to harmful UV rays. ASTM’s specification for rigid PVC exterior profiles used for fencing (F964- 94) requires the cap stock layer to be a minimum of 0.015 inches thick and a maximum of 20% of the profile wall overall thickness.
One popular misconception is that the co-extrusion process is inferior to mono-extrusion. Co-extrusion is the newer, more expensive technology and supports concentration of the essential materials, resulting in a stronger, more durable product-the customer receives more value per dollar. (Manufacturers who cannot afford retooling or do not support this new generation of advanced processing may make claims of the inferiority of high-tech co-extrusion.) Thirdly, there are claims that the layers in co-extruded products may delaminate. Co-extrusion isnot a lamination. Lamination is a process whereby adhesives or reheating are used to bond two ormore layers together. Co-extrusion is a homogenous process accomplished at high pressure and temperature in a sealed environment where moisture and air cannot be trapped. Co-extrusion produces superior product without the use of adhesives, making separation of the layer virtually impossible.