Electrical properties of laminates, especially moulded premix parts prepared from polyester resins, can be significantly improved by the judicious selection of inert fillers to be incorporated into the system. In general, the electrical properties will improve as the filler content of a product is increased. Therefore, it is most practical to use the highest possible amount of fillers of the proper type, not only for optimum electrical properties, but also for low compound cost.
The limit of the amount of filler which can be loaded, depends upon other physical properties. For example, Calcium carbonate offers the highest practical filler loadings because of their very low resin absorption values, but it leads to reduced flame retardance and is not recommended where maximum flame retardance is required. Various clays are quite suitable for standard applications, while Alumina Trihydrate is highly recommended to obtain maximum arc and track resistance.
Another important application of Chlorendic Anhydride in the electrical/electronic industry is its use as a hardener for Epoxy Resins, and offers:
(a) High heat distortion temperatures up to 200°C on clear castings.
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(b) Excellent strength and stiffness at high temperatures. High power factors and stable dielectric constants at high temperatures.
(c) Permanent flame retardance.
(d) Excellent mechanical and Physical properties.
Conventionally, Phthalic Anhydride is used industrially as a hardener for epoxy resins. Laboratory data shows that Chlorendic Anhydride as compared to Phthalic Anhydride, confers more rapid hardening, high heat distortion temperatures, fire resistance, increased hardeners and easier handling as compared to other commonly used hardener’s to obtain good heat resistance such as metaphenylene diamine. Chlorendic Anhydride in addition to earlier referred properties, offers better thermal properties of plastic laminate, no dermatitis or staining and is economical.
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This unusual combination of physical and electrical properties has expanded the use of Epoxy Resins and significant improvements can be made in the following field of applications:
(i) Glass Reinforced laminates flat sheets and rolled tubes.
(ii) Casting resins for potting and encapsulation of electrical systems.
(iii) Plastic tools and dies which require heat resistance, potential applications are moulds for polyesters, metal forming dies and plastic.
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(iv) Heat and fire resistant adhesives.
(v) Protective coating requiring heat or fire resistance as well as varnishes for electrical equipment.
Resins suitable for casting and potting are made by mixing Chlorendic Anhydride and preferably the liquid type epoxy resins at about 100°C. This gives a 100% resin mixture. On the other hand, plastic laminates are best prepared by dissolving the Chlorendic Anhydride and Epoxy Resin in a suitable solvent which is used to impregnate glass cloth. Removal of solvent at moderate temperature will leave a dry film and several layers of cloth can then be pressed together under heat and pressure to form a laminate.
Casting compositions are prepared by stirring the appropriate amount of Chlorendic Anhydride into a liquid epoxy resin at a temperature where rapid solution occurs. The resin is heated at about 120°C. The Chlorendic Anhydride is added and the mixture stirred at 100°C until a solution is formed. This liquid is formed into a mould coated with a release agent. The mould is then heated in an oil bath or even until the desired cure has been obtained.
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Glass Cloth Laminates:
Excellent laminates may be prepared from Chlorendic Anhydride and epoxy resins by using dry lay-up type techniques. In this method, the resin is dissolved in a suitable solvent with which glass-cloth is impregnated and partially cured to non-tacky condition.
This treated cloth is then pressed or rolled to form laminates at the desired curing schedules. Fabrication of impregnated cloth into laminates should be done as soon as possible since its shelf life may be limited.