Electrical properties dielectric strength

Electrical, electronic, and technical appHcations use polycarbonates for a variety of purposes. The woddwide market is about 156,000 t aimuaHy. Because of exceHent electrical properties (dielectric strength, volume resistivity), and resistance to heat and humidity, polycarbonate is used for electrical connectors (qv), telephone network devices, oudet boxes, etc. Polycarbonate had been popular for use in computer and business machine housings, but the use of neat resin has been largely supplanted by blends of polycarbonate with ABS. OveraH, however, the total use of polycarbonate continues to increase. 

Electrical properties Dielectric strength Dielectric constant 60 Hz 10 Hz 10 Hz... 

Polysulfone is UL listed for continuous service at 320F, although it will withstand higher temperatures intermittently. It offers a good combination of electrical properties dielectric strength and volume resistivities are high, while dielectric constant and dissipation factor are low. 

Electrical Properties Dielectric Strength (V/Mil) Dielectric Constant ( 1 MC dry) Dissipation Factor ( 1 MC dry)... 

We can define the principal electrical properties of polymers in terms of four characteristics electrical resistance, capacitive properties, dielectric strength, and arc resistance. We can change the surface characteristics of a polymer by subjecting it to a corona discharge generated by a strong electrical field. Lastly, we must also consider the influence of other physical properties on the application of polymers in electrical applications. 

The insulating property of materials breaks down in strong electrical fields. This breakdown strength, called the electric or dielectric strength (DS) is the voltage where material electrical failure occurs. The DS is often related to material thickness, L, as shown in the following equation ... 

Electrical properties — dielectric constant (e), representing polarization dissipation factor (tan 8), representing relaxation phenomena dielectric strength (EB), representing breakdown phenomena and resistivity (pv), an inverse of conductivity — are compared with other polymers in Table 5.14.74 The low dielectric loss and high electrical resistivity coupled with low water absorption and retention of these properties in harsh environments are major advantages of fluorosilicone elastomers over other polymeric materials.74... 

Electrical. The dielectric strength of laminates will decrease with increasing thickness and is highly dependent upon the direction of the electric field stress. This property will show higher when tested across the sample s thickness whereas end-to-end testing will show lower values. Laminates with higher resin content will show better electrical properties but poorer physical properties than laminates with lower resin content. 

Subsequently, the specimens are removed from the oven and should be tested after 24 hours. The tests selected should relate to a property relevant to actual service application, and standardized test methods should be utilized in order to allow for comparisons. If a specific application has not been defined, it is recommended to utilize a slow (tensile strength) and a rapid (impact tensile strength) tensile loading or electric loading (dielectric strength), respectively. ISO 11403-3 [103] lists tensile strength and/or tensile energy absorption as criteria. 

Electrica.1 Properties. The bulk electrical properties of the parylenes make them excellent candidates for use in electronic constmction. The dielectric constants and dielectric losses are low and unaffected by absorption of atmospheric water. The dielectric strength is quoted for specimens of 25 p.m thickness because substantially thicker specimens cannot be prepared by VDP. If the value appears to be high in comparison with other materials, however, it should be noted that the usual thickness for such a measurement is 3.18 mm. Dielectric strength declines with the square root of increasing... 

Electrical Resistance—Conductivity. Most fillers are composed of nonconducting substances that should, therefore, provide electrical resistance properties comparable to the plastics in which they are used. However, some fillers contain adsorbed water or other conductive species that can gready reduce their electrical resistance. Standard tests for electrical resistance of filled plastics include dielectric strength, dielectric constant, arc resistance, and d-c resistance. 

Electrical Properties. The low polarizabiHty of perfluorinated Hquids makes them exceUent insulators. Theh dielectric strengths are about 40 kV (ASTM D877) dissipation factors are about 0.0001 at 1 MH2 dielectric constants are about 1.8 volume resistivities are about 1 x 10 ohm-cm (ASTM D257) (17). 

Electrical Properties. Polytetrafluoroethylene is an excellent electrical insulator because of its mechanical strength and chemical and thermal stabihty as well as excellent electrical properties (Table 6). It does not absorb water and volume resistivity remains unchanged even after prolonged soaking. The dielectric constant remains constant at 2.1 for a temperature range of —40 to 250°C and a frequency range of 5 Hz to 10 GHz. 

Electrical Insulation. The substitution of a gas for part of a soHd polymer usuaUy results in large changes in the electrical properties of the resulting material. The dielectric constant, dissipation factor, and dielectric strength are aU generaUy lowered in amounts roughly proportional to the amount of gas in the foam. 

The most important electrical properties of insulation are dielectric strength, insulation resistance, dielectric constant, and power factor. Corona resistance, although not stricdy an electrical property, is usually considered also (10). 

Commonly used materials for cable insulation are poly(vinyl chloride) (PVC) compounds, polyamides, polyethylenes, polypropylenes, polyurethanes, and fluoropolymers. PVC compounds possess high dielectric and mechanical strength, flexibiUty, and resistance to flame, water, and abrasion. Polyethylene and polypropylene are used for high speed appHcations that require a low dielectric constant and low loss tangent. At low temperatures, these materials are stiff but bendable without breaking. They are also resistant to moisture, chemical attack, heat, and abrasion. Table 14 gives the mechanical and electrical properties of materials used for cable insulation. 

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