Materials Used

Published in Insulation Materials

PVC (Polyvinyl Chloride) (thermoplastic)
PVC formulations vary widely depending on the desired properties. Because it is relatively inexpensive, easy to extrude and exhibits many excellent mechanical and electrical properties, PVC has been used for many applications.

The maximum temperature range for the best PVC formulations is -55°C to 105°C with general purpose vinyls ranging -20°C to 80°C. PVC has excellent flame, moisture and abrasion resistance, as well as superb gasoline, alcohol, ozone, acids and solvent resistance.

PVC can be formulated with non-migrating plasticizers for special electrical or termination applications. It can be modified for medical and food preparation applications because PVC in general is odorless, tasteless, and non-toxic. PVC compounds exhibit high capacitance and attenuation loss due to their relatively high dielectric constant when used in wire and cable. In retractile cord applications, PVC has below average to average elastomeric properties. Additionally, at low temperatures, PVC should not be used when flexibility and flex life are required.

PVC can be used in thin and heavy wall applications as a primary wire insulation as well as a cable jacket insulation.

Semi Rigid PVC
Used as a very abrasion resistant primary PVC insulation. For 30-16 gauge, a 10 mil. wall meets UL style 1061, 80°C 300V.

Polyethylene (thermoplastic)
Polyethylene is the compound most widely used in coaxial and low capacitance cables due to its fine electrical properties. Although polyethylene is flammable, additives can be used to make the polyethylene flame retardant at the expense of the dielectric constant and power loss characteristics.

Usable temperature ranges from a low of -65°C to as high as 80°C. Polyethylene (in high, medium and low densities) is generally very hard and stiff, and these properties typically do not change over the usable temperature range. Polyethylene can be foamed to reduce the dielectric constant to 1.50, creating an economically attractive insulation for use in special application coaxials and ultra low capacitance transmission cable. Polyethylene can be used by for primary insulation as will as a cable jacketing compound.

Polyethylene—Based Variations

  • Foamed or Cellular Polyethylene—Foaming polyethylene reduces the dielectric constant to approximately 1.5, which makes this a very attractive insulation compound for cables requiring a high-speed transmission rate. Once foamed, the compound loses some of its tensile strength, elongation, and dielectric strength properties, although they are still acceptable for use in many applications.
  • Cross-linked Polyethylene—Rated at 150°C. Cross-linking changes polyethylene from a thermoplastic to a thermoset material, which creates a high resistance to stress cracking, cut-through, soldering, and many solvents.
  • Flame-retardant Polyethylene—Polyethylene is a very flammable material that can be controlled by the use of special flame-retardant additives. These additives, however adversely affect many of polyethylene's fine electrical properties, such as the dielectric constant, power factor, and dielectric strength.

Polypropylene (thermoplastic)
Polypropylene has properties almost identical to that of polyethylene and is used almost exclusively for thin wall primary insulations. Polypropylene can be rated for -30°C to 80°C. Polypropylene can be foamed for improved electrical properties.

Polyurethane in general has excellent low-temp flexibility, high tensile strength, and long flex-life. It exhibits excellent chemical, water, and abrasion resistance, as well as being extremely tough and cut-through resistant.

Plasticizers, which can migrate out to contaminate other compounds or cause embrittlement with aging, are not present in polyurethane.

Polyurethane is extremely flammable but can be offered in a flame-retardant version at the expense of tensile strength and surface finish.

One major disadvantage of polyurethane is its poor electrical qualities, which restrict its use to jackets. It does have excellent retractile cord characteristics, and is a good candidate for use in salt-spray and low-temperature military applications.

Hytrel* was developed by E. I. du Pont de Nemours and Company to be used for thin-wall applications. Hytrel* is similar to Nylon in its toughness, chemical resistance, flexibility, and resilience.
Some applications include primary insulation for retractile and telephone line cords, high flex-life cables, and cables requiring a tight bend radius.

Nylon* exhibits excellent jacket toughness, especially in thin-wall applications, and has excellent abrasion, cut-through, and chemical resistance. Its main application is to provide these qualities when extruded over softer insulation compounds. Nylon* has a very low coefficient of friction, making it a good choice for use in high flex applications.
Nylon* does absorb moisture, which somewhat degrades its electrical properties from their original state.

Surlyn*, an electrical grade ionomer from Dupont, has been used for application requiring excellent mechanical properties. Combining superb cut-through and stress cracking resistance with ultra low temperature flexibility and a brittleness temperature under -100°C, Surlyn* can be used to meet many of the stringent military requirements.

Thermoplastic Rubber was developed to act as a substitute in many applications for true thermoset rubber. Some advantages over thermoset material are: Colorability, higher processing speeds, and wide service temperature range. TPR has excellent heat, weathering, and aging resistance, and no curing is necessary.
Most commonly used in applications where cut-through resistance is not required, but other properties of rubber are still necessary.

KYNAR's advantages include: Exceptional chemical resistance, high tensile strength, abrasion resistance, cut through and UV resistance. Additionally, it is highly flame resistant and produces very little smoke in the presence of flame. For applications requiring increased flexibility and stress crack resistance, KYNAR FLEX® copolymers are recommended.
SOLEF® is a registered trademark of Soltex, which is a subsidiary of Solvay, a manufacturer of Vinylidene Fluoride-based resins. Solef has a number of grades which are widely being used in fiber and overall jacketing applications. It's properties are very similar to KYNAR's.
PFA possesses some of fluorocarbon's best properties. Its high temperature rating of 250°C, low temperature of -65°C and dissipation factor of .0002 equal or better most of the other fluorocarbons' properties. However, it does not possess the thermoset properties of TFE which limits it to a select group of applications. Although it can be processed in long lengths, PFA's high material cost has prevented it from gaining widespread use.
FEP is the most commonly used fluoropolymer currently because of its excellent processing characteristics and wide applications range. Although it is not a thermoset, this material does have high flame resistance. Hence, its usage in plenum cable and military applications has been steadily increased as pricing and processing improve. FEP can also be "foamed" for improved data transmission characteristics.
Although lacking many of FEP's excellent electrical properties, ECTFE and ETFE posses better flexibility and mechanical strength than either PFA or FEP. Additionally, ECTFE & ETFE can become thermoset by the irradiation method. ECTFE can also be "foamed" for improved data transmission characteristics and is frequently used for the purpose of weight reduction.

Read 10364 times Last modified on Friday, 08 May 2015 16:33
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