Epoxides electrical properties

The basic role of gas in the electric properties of plastic foams postulated by Domkin has been confirmed by Giessner in a study on the electric properties of epoxide foams, the cells of which were filled with a electronegative gas, sulfur hexafluoride (SFg). The introduction of SFg results in very good dielectric properties over a wide temperature interval, including high Ebr corona resistance (Fig. 21). Previously, Palmer established that Ebr in the case of SFg is by 3.5 times higher than for air. 

The effect of moisture on the electrical properties of epoxide foams is shown in Fig. 24. These data are, to a certain extent, in contrast to the above mentioned values. 

Generally these compositions contain an epoxy-novolac, a hardener, a catalyst, silica fillers, and an internal lubricant/mold release compound. Brom-inated epoxies and antimony trioxide are included to provide the required flame retardant characteristics. Other, unspecified additives are used to promote adhesion or to reduce corrosion rates. Because of their superior thermal capabilities and electrical properties, epoxidized novolacs are preferred over epoxy homopolymers. Near stoichiometric amounts of hardeners such as novolacs (Equation 1), anhydrides, and primary amines can be used to cure the resins in the presence of a catalyst. The linkages which are formed include ethers, esters, or secondary amines, respectively. 

There is a wide variety of chemicals that can be used to modify specific properties of the resin, such as resistance to mechanical or thermal shock, increase elongation, and higher impact strength and flexibility. Usually this will involve a trade-off of some other property, such as physical strength, electrical properties, resistance to chemicals or solvents, and/or performance at elevated temperatures. For epoxies, there are DER-type flexible resins and monofunctional epoxide compounds, such as epoxidized cashew nut oil flexibilizer. Typically 30% or less by weight of these can be used, they can also be used at ratios of 1 1 to obtain a flexible and rubbery cured composition. The additives are also shelf-stable when blended with the resin. 

Cured epoxy-anhydride systems exhibit excellent thermal, mechanical, and electrical properties, and are used in filament-wound epoxy pipe, PCB laminates, mineral-filled composites, and electrical casting and encapsidation applications. Anhydride-cin-ed epoxies also have better aqueous acid resistance than similar amine-cured systems. Anhydrides are the principal curing agents for cycloaliphatic and epoxidized olefin resins in electrical casting and potting. Some... 

The epoxide resins are a class of materials that possess all the properties required to make them useful for a wide range of applications throughout the electronics industry. They have good electrical properties, low shrinkage, good adhesion and resistance to thermal and mechanical shock, whilst also possessing resistance to moisture, solvents and general chemical attack. 

Burhans reported a high performance cycloaliphatic epoxide system for electrical apparatus which provided a unique balance of high heat distortion temperature, thermal shock resistance and high temperature electrical properties. All of the formulations were based upon the cycloaliphatic epoxide ... 

This complex has negligible reactivity at room temperature (good latency) but at around 90°C it begins to dissociate and react with the epoxide. The complex is normally used in concentrations of around 3 parts per hundred of resin and a typical cure would be 2 h at 105°C, with a post-cure of 4 h at ITSX. The cured products are very hard, strong and brittle, and have good to average electrical properties. Care should be exercised in the use of these materials with certain metals or sensitive devices, since the liberated BF3 may cause corrosion. 

The calcined clays are considerably harder than their hydrated counterparts but they impart better electrical properties to both thermosetting compounds and thermoplastics. Clay is also of particular use in fibre-filled epoxides, where its plate-like structure and viscosity increasing properties prevent fibres blooming or appearing at the moulded surface. Calcined clay is used to increase volume resistivity in the formulation of electrical laminate type compounds. A hydrophobic surface treated version of calcined clay is available for applications where enhanced electrical properties are required even under humid conditions. 

For many uses of epoxide resin systems, a low viscosity product is required and the role of the diluent is usually to reduce the viscosity of the formulated compound. Diluents can also be used to tailor other characteristics of the epoxide, such as the chemical resistance, electrical properties, thermal expansion coefficient and glass transition temperature. They may be conveniently divided into two groups, the reactive diluents and the non-reactive diluents. 

The electrical properties of a CTBN-containing epoxide may also be altered somewhat from those of the base material, but for most applications the effect is negligible. The dielectric constant of the cured compound will tend to be slightly higher and may show a greater dependence upon temperature than the unmodified compound, whUst the volume resistivity will tend to fall. The veu-iation of electrical properties of a filled low density amine cured epoxide suitable for electrical applications is shown in Table 10.2 for both the standard and CTBN-modified materials. 

Variation of Electrical Properties for CTBN Modified and Standard Riled Low Density Amine Cured Epoxide ... 

The Effects of Silane Treatment upon the Flexural Strength and Electrical Properties of a Quartz-Filled Anhydride Cured Epoxide ... 

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