Kynar^®  PVDF Resin
Processing Guidelines

PIPE EXTRUSION

Kynar^® 740 resin and Kynar^® 1000 resin are the primary grades used in chemical pipe applications. Kynar^® 740-02 resin contains a smoke suppressant package and is primarily used for waste drainage pipe and fittings. Kynar Flex^® 2850 copolymer can be used for applications requiring higher impact and stress crack resistance.

Standard metering screws with an L/D ratio of 24/1 and a compression ratio of 3/1 are commonly used. The screw should have an even flight distribution between the feed, transition and metering zones. Better temperature and output stability can be achieved by using a barrier-type screw. Maddox and spiral mixers are also acceptable, but pin type mixers are not recommended. Good temperature control of the extruder and tooling is required for optimal processing.

It is important to eliminate areas of slow-flow, or hang-up points, to prevent Kynar^® resin from discoloring. Common areas of melt accumulation include behind the breaker plate, at undercuts and in any other stagnant areas. In-line spider dies are commonly used for producing Kynar^® pipe. The design should minimize material inventory in the head and be streamlined to eliminate material hang-up. Spiral dies should be designed similarly and can provide better weld line strength.

The draw down ratio (DDR) for tip and die selection generally ranges from 1.3-2.1 (area DDR), or 1.05-1.5 (OD DDR), but varies based on the dimensions of the finished pipe. The optimum land length will vary based on pipe size, process conditions and material grade. Extrusion temperatures range between 200°-240°C (392°-464°F), but vary depending on material grade, as well as pipe and tooling size. Lower melt temperatures provide a “stronger” melt and are used when product whiteness is of primary concern.

Pipe is typically sized using a vacuum calibration system equipped with either a solid brass or a brass disk caliper, which is oversized to accommodate material shrinkage. See Table XII for common pipe processing temperatures.

RECOMMENDED SAFETY PRECAUTIONS FOR MELT PROCESSING

Kynar^® resins are relatively nontoxic and non-hazardous under typical handling conditions. Mechanical malfunctions or human error, however, may lead to thermal decomposition with evolution of hydrogen fluoride (HF). Precautions must be taken to prevent excessive inhalation and physical contact with hydrogen fluoride should decomposition take place. Unlike PVC, Kynar^® resins will stop decomposing when the heat source is removed and the temperature of the melt is allowed to fall to normal processing temperature.

Additives, such as mica, asbestos, glass fibers, certain formulations of titanium dioxide, and very finely divided metals, may catalyze thermal de- composition rates during processing and should be used with caution. It is strongly recommended that the fabricator consult with the local Fluoropolymer Sales Representative before using any additives.