Thermoset Prepreg Systems
Litzler offers prepreg systems for manufacturing thermoset prepregs using two primary methods. One method uses a saturation process (solution dip); the other uses a film transfer (hot melt) process.
- The solution-dip systems use a solvent to dissolve the resin, reducing its viscosity and improving its wetting characteristics. After the fiber is soaked with the solution, the solvent is evaporated away and the resin is partially polymerized (B-stage), leaving only resin and fiber.
- The hot-melt systems utilize a resin film that is cast onto a carrier – typically a coated industrial paper. The fiber and film are passed through heated rollers which transfer the resin to the fiber and force partial impregnation of the resin into the fiber web.
Solution Prepreg Machines:
Solution prepreg is the basic process of coating (dipping) a composite web (glass, carbon, aramid, etc.) with a resin in order to impregnate the web and make prepreg. This process is used for Printed Circuit boards (Copper Clad Laminates – CCL) and Structural Composites (traditional prepreg). Solution prepreg can be for woven or non-woven webs, paper, or unidirectional tows to make tape. Solution machines primarily utilize organic solvents in the dip and require special safety systems for the processing and handling of solvents.
Litzler’s first solution prepreg machine was supplied in 1959 in Southern California. That vertical tower machine was active and operated into the 1990’s making prepreg.
- Solution machines can be vertical or horizontal depending on the requirements
- Fabric machines can be either vertical or horizontal
- UD solution machines are normally horizontal
Fabric Prepreg Treating
Woven fabric prepreg can start with Glass, Carbon, Aramid, and other textiles. Typical widths start at 12” (300 mm) and go up to 84” (2130 mm) based on available weave widths. The ovens can be vertical or horizontal depending on the space available for the customer.
UD solution Treating
UD fibers include Glass, Carbon, Aramid, Ceramic, and other fibers. Machine widths start at 12” (300 mm) and go up to 120” (3 meters wide). The fiber is typically supported on a carrier film or paper after the impregnation as it processes through a special arch oven to remove the solvents.
- Web Handling – unwinds (or creel), rewinds, tension control
- Unwinds and rewinds feature safety chucks for safe operation and precise tension control (unwind photo, closeup of safety chucks/package)
- Custom designed to accommodate the package sizes and desired speed and tension requirements
- Narrower machines often include cantilevered unwinds/rewinds
- Resin Application – Impregnation Station and Metering Rolls
- Resin applications is critical to apply the proper amount of resin on the fiber
Generally a dipping process followed by a set of precision TIR metering rolls. The metering rolls set a finite gap and remove the excess material to achieve the proper resin content weight.
Hot Melt Prepreg Machines:
Hot melt prepreg is a two-step process that eliminates the solvent coating and drying used in the solution style prepreg.
The fiber tow is impregnated with a hot melt resin that is normally precoated on a paper or film carrier on a separate off-line process (machine called a “filmer”).
The hot melt Prepreg process uses a combination of heat and pressure to transfer the film resin from the carrier paper into the fiber bundle. This is accomplished through precision Compaction Rolls. The Compaction Rolls can be operated in Nip configuration or S-wrap configuration.
The hot melt machine can produce UD Tape (unidirectional) or woven fabric prepreg depending on the machine configuration.
The hot melt process typically uses pre coated paper (film) – some customers prefer to introduce the resin in-line with the prepreg machine. Litzler offers this on-line filming option. For certain applications this can save the customer from having to install two machines – filmer and prepreg machine.