Vinyl Extrusion Explained
Vinyl extrusion is the process of manufacturing vinyl profiles used for fencing, patio covers and gates.
In basic terms, the raw “cake mix” (in blended powder form or in chip or pellet form) which includes PVC resin, impact modifiers, UV stabilizers, heat stabilizers, and flow agents are melted and forced through a heated screw and barrel that forces the melted compound through shaping dies, downstream tooling, and cooling baths to obtain the final rigid profile.
Vinyl profiles are run continuously and are cut as they come “off the line” by a sliding saw. The skill and equipment required to create high quality profiles that are consistent and meet specifications is significant.
Many of the important properties of these vinyl profiles are determined by the characteristics of the PVC compound from which the pipe is extruded. Larger extrusions companies blend their own proprietary compounds from resins and other micro-ingredients. Smaller extrusion companies (and many who make caps and accessories using the injection molding method) often use compound that has already been blended by major resin manufacturers.
There are two primary categories of vinyl extrusion: Mono-extrusion and Co-extrusion.
- Mono-extrusion has one layer of product all the way across the section of the profile (end view).
- Co-extrusion has both a substrate (inside of the profile) and cap-stock (outside of the profile). When properly extruded, these two layers are molecularly bonded as they are in a state of melt when extruded, and thus they will not delaminate.
There are good and bad examples of both mono-extruded and co-extruded vinyl products on the market.
When properly manufactured, co-extruded product can be favorably compared with mono-extruded product, and usually costs a little less.
The cost for setting up co-extrusion tooling is higher, because two extrusion machines are required along with more complex tooling, but the end result is a product that can be run faster and more cost effectively. The required ingredients are concentrated in the layer where they are most required. The UV stabilizers, which are most expensive, can be concentrated in the capstock, or outer layer where they are most useful and the impact modifiers and strengthening agents can be used in the substrate where it important and performs better.
Typically a mono-extrusion is only required is when significant portions of the substrate (inside) of the extrusion is to be regularly exposed to outside elements and UV rays.