Wire & Cable
Processing Guidelines
Kynar® and Kynar Flex® PVDF resins are readily extruded using standard melt processing equipment with few modifications.
Extrusion Guidelines for Kynar® PVDF Resin in Wire and Cable Applications
General Extrusion Guidelines
- Water temperature range:
up to 50°C (122°F), warmer temp. preferred - Line speed:
300 ft/min typical for jacket applications - Insulation thickness range:
0.005 in. – 0.060 in. (0.015 in. – 0.020 in. typical)
Extrusion Tip and Dye
- Typical area draw down ratio: 7 to 1
- Draw balance range from 1 - 1.02
- Land length: 0.25 in. typical
Extrusion Screw Design
- Barrier screw preferred
- Tube on extrusion suggested
Extrusion Equipment
Most Kynar® PVDF resins are processed using single screw extruders with an L/D ratio of 24/1 or higher. The extruder is most commonly outfitted with a general purpose, chrome plated 4140 stainless steel metering screw with a 3 to 1 compression ratio. Output fluctuations issues can be improved tremendously through the use of a barrier screw.
Extrusion Tooling
Kynar® and Kynar Flex® PVDF resins can typically be processed on standard wire and cable crossheads used for PVC and other materials considered moderately heat-sensitive. It is recommended that the tool design be free flowing and have limited flow restrictions. Kynar® PVDF resin is sensitive to burning and, if allowed to collect around undercuts or dead spots in the system, it will produce charred specks in the final extruded product. Kynar® PVDF resin is most often processed using tube-on tooling with an area draw down ratio between 7 to 1 and 10 to 1. It is very important to have the draw balance between 0.98 and 1.02 to reduce post-application shrinkback. Lower draw down ratios and higher process temperatures can also be used to reduce jacket shrinkback. Higher draw down ratios have been used for softer Kynar® PVDF resin grades that exhibit better melt stability under extensional deformation. Land lengths of approximately 0.250 inches are recommended, but lower land lengths can be used to reduce melt fracture. Double-angle dies with zero land length and a 15° taper, as well as higher die temperatures, can also be used.
Extrusion Processing Guidelines
All Kynar® and Kynar Flex® resin grades are processed between 220°C and 255°C (428°F - 491°F). An ascending melt temperature profile is typically used, with the metering section of the screw set at the desired melt temperature and the feed section set at 220°C (430°F). The transition section can be set at an intermediate temperature between the feed and melt temperature. The clamp, adapter and extrusion head are typically set at the desired melt temperature. If there is aparticular issue with burning, then lower temperatures in these areas are required. To smooth out the surface of the extrudate, higher die temperatures are sometimes used, with 260°C (500°F) being typical. This approach can only be used if the residence time of the material in the die is relatively short. Warm to hot water can be used in the cooling trough, as hotter water tends to reduce extrudate shrinkback. Typical cooling water temperatures range from 32°C to 43°C (90°F -110°F). Kynar® EX-AD 3000 is an extrusion aid specifically formulated to assist with the extrusion of Kynar® PVDF resins. It acts to provide lubricity for Kynar® and Kynar Flex® PVDF grades to increase smooth surface finish and/or reduce die build-up.
|
Barrel Section |
Temperature (C) |
Temperature (F) |
|
Feed |
210 - 230 |
410 – 450 |
|
Transition |
220 - 240 |
430 – 460 |
|
Metering |
230 – 250 |
450 - 480 |
|
Tooling |
230 – 240 |
450 - 470 |
Quick Tips:
- Higher melt temperatures is required to obtain smooth, shiny surface
- Die temperature often set at 250°C or above for smooth and shiny surface
- Extra care required when extruding Kynar® PVDF flame retarded products
Injection Molding Guidelines for Kynar® PVDF Resin in Wire and Cable Applications
Standard injection molding equipment and tooling can be used to process Kynar® resin. No specialty materials of construction are required, but chrome or nickel plating of polymer contact surfaces is recommended to prevent pitting.
Melt temperatures will vary based on the part geometry, tooling and resin grade. In general, lower melt and mold temperatures can be used effectively with low viscosity Kynar® copolymer grades.
Kynar® resin is best processed with a large sprue or edge gates. To produce the best quality parts, fill the sprue, runners and gates slowly and then ramp up the injection speed until the screw reaches its transfer position. Small pin or subgates can be used for smaller parts and will require faster injection speeds and higher melt temperatures to fill the part. If a process calls for use of a hot runner system, please contact a technical representative before committing to this practice.
Kynar® PVDF resin requires generous venting at the end of the filling process or a burning phenomenon known as dieseling can occur.
Kynar® PVDF resin is a highly crystalline material and will exhibit shrinkage. Shrinkage rate is a function of part thickness, flow direction (which is a function of gate type and location) and processing conditions.
Voiding can be a problem when molding Kynar® resin due to the polymer’s high crystallinity. Good part design practices are required to prevent voiding in thick sections of the part. See the table below for common injection molding temperatures.
Arkema technical service is available to discuss tooling and processing of Kynar® PVDF.
|
GRADE |
BARREL TEMPERATURE °C |
||||
|---|---|---|---|---|---|
|
|
REAR |
MIDDLE |
FRONT |
NOZZLE |
MOLD |
|
Kynar® 460 |
200 – 230 |
210 – 240 |
220 – 250 |
230 – 255 |
50 - 90 |
|
Kynar SuperFlex® 2500 |
170 – 220 |
170 – 220 |
170 – 245 |
170 – 245 |
50 - 90 |
|
Kynar Flex® 2750-01 |
200 – 220 |
210 – 230 |
210 – 245 |
210 – 245 |
50 - 90 |
|
Kynar Flex® 2800-20 |
200 – 220 |
210 – 230 |
210 – 245 |
210 – 245 |
50 - 90 |
|
Kynar Flex® 2850-04 |
190 – 210 |
200 – 220 |
200 – 240 |
200 – 240 |
50 - 90 |
|
Kynar Flex® 3120-10 |
190 – 210 |
200 – 220 |
200 – 240 |
200 – 240 |
50 - 90 |