Tips on How to Choose between Peel-Plies and Release Films
Peel-plies and release films both serve the purpose of preventing foreign materials from becoming integrated into your finished part. The most obvious differences are peel-plies are typically considered to be woven fabrics while release films are thin plastic sheets. In an effort to narrow down your options, here are some issues to consider when selecting the appropriate material for your application.
Peel-ply is the best option if you want a finished surface requiring minimal preparation before secondary bonding as the resulting surface will be textured to the weave of the peel-ply selected. Most often peel-plies are porous allowing epoxy to bleed through them prior to cure. The bleeder (breather) material behind the peel-ply will absorb the epoxy that bleeds through the peel-ply. Teflon coated glass (TCG) is a type of peel-ply and usually more porous than traditional nylon or polyester peel-ply. To minimize weight, use TCG with a slow cure, low viscosity laminating epoxy and a bleeder. Vacuum bagging will allow uniform pressure to force the epoxy into the bleeder over a longer period of time resulting in a lighter finished part. TCG peels away easily when removed with the bleeder as one unit.
Release films are available in both porous (sometimes referred to as perforated) and non-porous films. Porous release films act much like the peel-ply discussed above except the finished surface will be much smoother. The amount of epoxy that bleeds off is dependent upon the type of perforations, epoxy system, bleeder and pressure used. Generally speaking, you will not bleed off as much epoxy with a release film as with TCG.
Non-porous release films are simply thin plastic sheets. The epoxy will cure to the smooth surface. Non-porous release films minimize the work required to prepare a part for final finish and painting. Release films can be used when patching or repairing a molded part by wetting out a piece of fiberglass (or carbon fiber etc.) then, while still wet and on the release film, the patch can be cut to shape and placed on the prepared damaged area. If appropriate, place a second piece of release film over the patch so any epoxy that oozes out around the edges will smooth out and bridge the layers. If desired, the repair can be vacuum bagged or simply weighted and left to cure. When cured, remove the release film(s) from the part, lightly sand the edges to fair in the repair and finish as desired. If curing directly on the damaged part is not possible, cure the patch on the release film and use an epoxy adhesive to bond the sanded patch to the repair needed. In all cases, the release film will peel cleanly away from the epoxy part.
In summary, make sure the release fabric or film will release from the type of resin system you are using. All CST release films and fabrics are intended for epoxy release and some work with other resin systems. Please give us a call if you need specifics. We have recently added a low cost Poly Release Film in the form of a 16” lay-flat tube. It can be cut open if you want to lay it flat as a single layer instead of doubled in the lay-flat tube. It is 2 mils thick, non-porous and transparent. Details including prices of all CST release fabrics or films can be found at www.cstsales.com/release-film.html
Tips on Repairs Using Peel-Plies & Release Films
Peel-plies and Release films are often used in molding and vacuum bagging but are very handy when doing repairs as well. Prepare the surface to be repaired by gluing the damaged structure together to assure proper alignment of the structure first. Make sure the damaged area is clean and lightly sanded taking away the glossy surface.
Teflon coated glass (TCG) is best for repairs when minimizing weight is important. Simply wet out the fabric with WEST SYSTEM or Pro-Set epoxy on release film and blot off the excess epoxy with a paper towel. After placing the wet epoxy patch on the prepared surface remove the release film. Cover the patch with a piece of TCG and bleeder material then apply pressure. Please another piece of release film over the bleeder before applying pressure. Five things effect the amount of epoxy left in the repair: the amount of epoxy initially in the fabric, the bleeder material used, the amount of pressure applied, the viscosity and pot life of the epoxy system used. When the epoxy is cured, remove the TCG and bleeder together as one unit. Lightly sand the finely textured patch and finish as necessary.
When weight is not as critical and a smooth surface is desired, the repair patch can be wet out on a release film where excess epoxy can be blotted off. Once wet out, it can be cut to shape then placed over the prepared damage. Another larger piece of release film can then be laid over the patch so any epoxy that seeps out around the edges can be faired into the surface. Apply uniform pressure over the entire area. When cured, peel away the release film, lightly sand the edges to fair in the repair and finish to match the original surface.
A third repair method is to cure the wet out fabric directly on the Mylar creating a cured fabric sheet. The side against the Mylar will be smooth. Lightly sand the exposed side removing the epoxy gloss. This material be it fiberglass or carbon fiber, can be bonded to the prepared damaged area using an epoxy adhesive such as WEST SYSTEM G-Flex.