Solution Prepreg

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 webs, paper, or unidirectional tows to make a tape.

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.

Copper Clad Laminates

A printed circuit board consists of layers of impregnated fiberglass and copper foil.  Litzler CCL machines help manufacture the fiberglass prepreg.  The CCL machines feature integrated web and tension control, precision metering rolls,  Opti-flow convection oven or patented Perfect Radiant oven, and Litzler Automation control system.

  • Traditional treaters with 6-12 meter tall ovens
  • Lightweight glass treaters with 3-9 meter tall oven
  • PTFE treaters with high temperature drying and sintering zones

Structural Composites

Structural composites are now part of our everyday life.  Beginning with the early high end aerospace applications,  prepreg is now widely used in sporting goods, industrial applications,  aerospace tooling, automotive,  aircraft interiors, as well as the traditional defense and aerospace applications.

The Solution prepreg machines for structural composites  integrated web and tension control, precision metering rolls,  Opti-flow convection ovens, precision compaction rolls and Litzler Automation control system.

Litzler started producing solution prepreg machines in 1959 and has significant experience with fabrics, UD tape, and tow applications.

Structural composites incorporate carbon fiber, fiberglass, aramids and other combinations of fibers to achieve the desired end-result.

Structural composites can be manufactured in multiple ways depending on the desired end-use and the customer preference.  The major processes include:

  • Woven Solution – vertical or horizontal ovens
  • UD Solution – horizontal arch oven

Solution Based Prepreg Machines

The heart of any solution based prepreg is the application of resin (coating/impregnation) and the removal of solvents (drying).  The other major components include the web handling/tension control and the overall control system including safety.

A complete system includes some or all of the following components:

  • Unwinds with precise tension control
  • Splice press for continuous operation
  • Accumulator for continuous operation
  • Tension isolation and control via loadcells, brakes, tension stands (s-wrap) and AC drives
  • Impregnation with precision metering rolls
  • Drying
  • Pollution control if necessary with solvent applications
  • Web guiding
  • Web cooling
  • Compaction Rolls
  • Poly liner unwinds and rewinds
  • Edge trim or slitting along with trim collection
  • Windup accumulator for safe continuous operation
  • Winding
  • Controls integration (drives, safety, temperature control, LHMI, data acquisition)
  • Solvent safety management

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.

Machine Components

Creels for UD machines
  • Creels are available in various levels of tension control – from basic friction tension holdback up to servo driven and load-cell controlled positions
  • Creels are designed to present the fiber sheet in a stable condition to the impregnation process
Fabric/Paper/Poly Unwinds
  • Unwinds (or Let-offs) are used throughout the machine for introduction of web materials (coated paper, fabric, scrims, and poly liners) into the process
  • All unwinds feature tension control through brakes or AC drives and are always loadcell controlled
  • For operator safety and convenience, unwinds feature heavy duty safety chucks and lightweight air shafts
  • Fixed, turret and guided versions are availalble
  • Turrets are controlled by Litzler Automation control system
Splice  Press
  • All fabric lines require a splice press for continuous operation
  • Splice presses feature heated platens to join the fabric using heat, pressure and splicing  tapes
  • In conjunction with the splice press, an accumulator allows the prepreg machine to operate in a continuous fashion
  • When a fabric roll is close to empty, the accumulator automatically fills with fabric, when the accumulator is full, the operator has several minutes to change to a new roll and make the splice
  • The impregnation process continues as the accumulator empties
  • Litzler accumulators feature low drag idler rolls, and specific controls to maintain tension control and are usually designed for 2-6 minutes of storage
Tension Control
  • Tension control and tension isolation are critical for high quality operations
  • Litzler machines isolate the unwind and rewind tension from the coating and drying tension for more flexibility and process control
  • Our design concept uses driven s-wrap stands – no running nips, which can damage delicate materials
  • The s-wrap rolls are either load cell or dancer controlled depending on the application
Impregnation (Metering Rolls)
  • Prepreg requires precise application of resin in order to control weight and / or thickness
  • The impregnation starts with submerging the fabric in a tank with 2-5 stainless steel rollers – the tank features recirculation controls and overflow weirs to maintain a constant level
  • Metering roll sets are machined to TIR ranging from 0.0002” to 0.00005” depending on the application
  • Special bearings and housings are used, and metering rolls are final ground in these bearings
  • Gap control is precise and repetitive using our proven gap setting design. Manual or Servo controls are available
  • The rolls are driven by individual servo drives to give precision RPM control
  • The complete system is designed to typically operate within the Class 1, Division 1 regulations (or CE/ATEX) for solvents and includes explosion proof designs and an enclosure with supply and exhaust fans, and LEL monitoring
  • Litzler ovens all feature our unique Opti-flow design for uniform temperature and airflow
  • Prepreg ovens can be vertical or horizontal depending on the application and space available
  • Litzler uses a proprietary Oven Sizing Computer Program to work with customer to determine the correct oven length to meet your production requirements
  • Vertical ovens are the most popular as it allows the prepreg to exit the metering rolls and enter the oven without touching any rolls
  • Horizontal ovens are used on occasion and feature a “spring” conveyor to support the prepreg during the drying and curing process
  • Ovens feature multiple zones  and variable speed drives for good process control and flexibility
  • Most ovens for solvents feature stainless steel interiors for easy cleaning and long life
  • Removable nozzle for cleaning
  • Makeup air and recirculation air filters are available
  • Heating can utilize waste heat from the pollution control or standalone direct or indirect heating with gas, electric, steam or oil coils depending on the utilities available at site
  • Vertical ovens feature driven turn around rolls that are water cooled to prevent pickoff
  • Turn around zone also features our exclusive Perfect Float flotation air bars for improved cooling heat transfer and increased web stability
  • Pollution control is integrated into the system as required to ensure clean air standards and operator  safety
Web Cooling
  • The prepreg requires cooling after the oven and this is accomplished two ways – convection or conduction
  • A Perfect Float convection system is available after the oven to blow cold air on the prepreg – this also helps to stabilize the prepreg after the long down pass in the oven
  • Cooling rolls are also used featuring conduction technology – cooling rolls also act as the lead drive and are part of the tension control system
Web Guiding
  • After the prepreg leaves the oven, typically an edge guider is provided to ensure that  the web is  properly aligned prior to winding
  • Guiders feature electo mechanical or pneumatic actuators to keep the web aligned
Compaction Rolls
  • Some processes include compaction rolls for further smoothing and impregnation of the resin into the woven fiber
  • Litzler compaction rolls feature exclusive designs including
    • 0002” TIR rolls
    • Large diameter rolls to minimize deflection
    • Precision gap setting mechanism
Edge Trim
  • To meet end-user clean edge requirements, shear or score edge slitters are incorporated
  • Center cuts and multiple-web slitting is also available
  • Web-following (guiding) systems are available to ensure consistent web width
Edge Trim Collection
  • Edge trim collection can feature Quickdraft pneumatic trim removal systems or trim winders
Windup accumulator
  • A windup accumulator is a smaller version of the unwind accumulator – 30 seconds to 2 minutes accumulation
  • The accumulator allows the operator to make the winder change safely by stopping the web and allowing the roll change to occur
  • 30 seconds is typically enough time for most process requirements
Poly unwinds
  • Unwinds and rewinds for poly liners, scrims, and paper liners are provided to maximize flexible processing potential
  • Each unwind features safety chucks and tension control
  • Some positions feature removable carts for loading and unloading
  • Drop spice designs are available
  • Web guiding is available
  • The winder is a critical part of the process and Litzler features multiple designs
    • Turret winders – 2-6 positions available – cantilever and safety chuck styles
    • Fixed winders
  • All winders feature AC drives and either loadcell or clutch control for taper or constant tension winding
  • Lay on or press rollers available
Controls and machine integration
  • See the Litzler Automation – Control Systems web page for additional details