Electrical properties resins

Insulation Applications Resin electrical properties become critical for insulation apphcations (the compound in direct contact with the metal conductor). Resins need to be specially manufacmred in order to minimize residual initiators, catalysts, and contaminants, which can negatively impact electrical properties. One of the ways this is accomplished is by carrying out the suspension resin polymerization process in deionized water and minimizing residual surfactant. Mass resins have found use in this application in the past due to the fact they do not require electrically deleterious surfactants agents in their manufacture. In order to minimize raw material inventory, many wire and cable manufacmrers who compound their own PVC formulations attempt to use the same resin for both jacket and insulation compounds. Because of this, resins with a T-value around 70 also predominate in insulation applications. 

Electrical properties of acetal resin are collected in Table 3. The dielectric constant is constant over the temperature range of most interest (—40 to 50°C). Table 3. Electrical Properties of Acetal Resins... 

Many grades of acetal resins are Hsted in Underwriters Eaboratories (UL) Kecogni d Component Directory. UL assigns temperature index ratings indicating expected continuous-use retention of mechanical and electrical properties. UL also classifies materials on the basis of flammability characteristics homopolymer and copolymer are both classified 94HB. 

Phenol—formaldehyde resins are used as mol ding compounds (see Phenolic resins). Their thermal and electrical properties allow use in electrical, automotive, and kitchen parts. Other uses for phenol—formaldehyde resins include phenoHc foam insulation, foundry mold binders, decorative and industrial laminates, and binders for insulating materials. 

Electrical Properties. Due to the comparatively low content of polar groups, most commercial ionomers ate very good insulating resins. Typical electrical properties (6) for a zinc ionomer are as foUows ... 

Nylon Cloth Grade with Phenolic Resin Binder. Grade N-1 has excellent electrical properties under high humidity conditions and good impact strength, but is subject to flow or creep under load, especially at temperatures higher than normal. 

Electrical Properties. AH polyolefins have low dielectric constants and can be used as insulators in particular, PMP has the lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and alow dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon). These properties remain nearly constant over a wide temperature range. The dielectric characteristics of poly(vinylcyclohexane) are especially attractive its dielectric loss remains constant between —180 and 160°C, which makes it a prospective high frequency dielectric material of high thermal stabiUty. 

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. 

An all aromatic polyetherimide is made by Du Pont from reaction of pyromelUtic dianhydride and 4,4 -oxydianiline and is sold as Kapton. It possesses excellent thermal stabiUty, mechanical characteristics, and electrical properties, as indicated in Table 3. The high heat-deflection temperature of the resin limits its processibiUty. Kapton is available as general-purpose film and used in appHcations such as washers and gaskets. Often the resin is not used directly rather, the more tractable polyamide acid intermediate is appHed in solution to a surface and then is thermally imidi2ed as the solvent evaporates. 

Electrical Properties. Polysulfones offer excellent electrical insulative capabiUties and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GH2 (microwave) frequency range. This performance is retained over a wide temperature range and has permitted appHcations such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic appHcations. 

Aniline—formaldehyde resins were once quite important because of their excellent electrical properties, but their markets have been taken over by newer thermoplastic materials. Nevertheless, some aniline resins are stiU. used as modifiers for other resins. Acrylamide (qv) occupies a unique position in the amino resins field since it not only contains a formaldehyde reactive site, but also a polymerizable double bond. Thus it forms a bridge between the formaldehyde condensation polymers and the versatile vinyl polymers and copolymers. 

Natural resins have been collected by hand throughout recorded history and used with minimal processing. They are reported to have been used in the arts, both in paints and for polishing sculptures, as early as 350 BC. Amber, the hardest of these resins, has been used as a gemstone from early Greek history to modem times. The electrical properties of amber were first recorded about 300 BC. Following is a description of commercial natural resins that are available in the United States. 

See Insulation, electric-properties and matbrials Resins, natural. 

The modem interest in composite materials can be traced to the development of BakeHte, or phenoHc resin, in 1906. BakeHte was a hard, brittle material that had few if any mechanical appHcations on its own. However, the addition of a filler— the eadiest appHcations used short cellulose fibers (2)—yielded BakeHte mol ding compounds that were strong and tough and found eady appHcations in mass-produced automobile components. The wood dour additive improved BakeHte s processibiHty and physical, chemical, and electrical properties, as weU as reducing its cost (3,4). 

For a part to exhibit stmctural stiffness, flexural moduH should be above 2000 N/mm (290,000 psi). Notched l2od impact values should be deterrnined at different thicknesses. Some plastics exhibit different notch sensitivities. For example, PC, 3.2 mm thick, has a notched l2od impact of 800 J/m (15 fdbf/in.) which drops to 100 J/m (1.9 fflbf/in.) at 6.4-mm thickness. On the other hand, one bisphenol A phthalate-based polyarylate resin maintains a 250-J /m (4.7-fdbf/in.) notched l2od impact at both thicknesses. Toughness depends on the stmcture of the part under consideration as well as the plastic employed to make the part. Mechanical properties, like electrical properties, ate also subject to thermal and water-content changes. 

Although these resins have been on the market for a number of years, volumes and appHcations remain low in spite of favorable properties including high temperature resistance, excellent wear and friction properties, good electrical properties, chemical inertness, and inherent nonflammability. ProcessibiHty and price may be the limiting factors. 

The bisphenol A-derived epoxy resins are most frequendy cured with anhydrides, aUphatic amines, or polyamides, depending on desired end properties. Some of the outstanding properties are superior electrical properties, chemical resistance, heat resistance, and adhesion. Conventional epoxy resins range from low viscosity Hquids to soHd resins. 

Although the general electrical properties of the polycarbonates are less impressive than those observed with polyethylene they are more than adequate for many purposes. These properties, coupled with the heat and flame resistance, transparency and toughness, have led to the extensive use of these resins in electrical applications. 

Electrical properties, which are initially similar to those of urea-formaldehyde resins, are maintained better in damp conditions tmd at elevated temperatures. 

The polyester alkyd resins are lower in cost than the DAP resins but are weaker mechanically, have a lower resistance to cracking round inserts and do not maintain their electrical properties so well under severe humid conditions. Fast-curing grades are available which will cure in as little as 20 seconds. 

A number of different resins are available and the ultimate choice will depend on the end use and proposed method of fabrication. For example, one resin will be recommended for maximum strength and fastest cures whilst another will have the best electrical properties. Some may be suitable for low-pressure laminating whilst others will require a moulding pressure of lOOOlbf/in (7 MPa). 

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