Silicone Laminating resin

Silicone laminates are used principally in electrical applications such as printed circuit boards, transformers, and slot wedges in electric motors, particularly class H motors. Compression-molding powders based on silicone resins are available and have been used in the molding of switch parts, brush ring holders, and other electrical applications that need to withstand high temperatures. 

The most common thermosetting laminating resins are phenolics, melamines, epoxies, polyesters, silicones, and polyimides. Thermoplastic resins used in making laminates include polysulfone, polyphenylene sulfide, polyetheretherketone, polyamide-imide, polybutylene terephthalate, nylon 6, and polypropylene. 

Silicone laminates are useful from cryogenic temperatures to about 260°C. The dielectric properties of silicones are particularly useful. Both dissipation factor and dielectric constant are low at room temperature and remain relatively constant up to 150°C. Because of the presence of the silicon atom, silicone laminates have good arc- and track resistance. The physical properties of silicones are not greatly influenced by aging, but compared with laminates that are based on other resins, the flexural and tensile strengths of silicones are not unusually high. Silicone laminates are used in electronics, heaters, rocket components, slot wedges, ablation shields, coil forms, and terminal board. 

Silicone polymers are available in the form of hquids, gels, elastomers, and brittle solids. The resinous polymers, when combined with glass fabrics, constitute the silicone laminate used mostly in the electrical and electronics industry. When... 

Polyvinyl Chloride Copolymers Nonrigid—Electrical Polyvinyl Chloride Copolymers Rigid—Normal Impact Silicone Woven Glass Fabric/ Silicone Laminate ABS Resins Molded, Extruded Low temperature impact 0.07—0.10 0.07—0.10 0.075—0.125 0.08—0.14... 

Silicone resins can also be used with glass reinforcement to produce laminates which are electrically superior to phenolic resin and amino resin based laminates but are mechanically weaker than other thermosets. Silicone laminates are used where very good electrical properties are required under high humidity conditions. 

Fig. 48. Effect of voltage stress on dissipation factor of A, paper-phenolic resin, laminate at 23° after 1 wk at 90% rh and B, after 1 wk at 50% rh C, dry glass-cloth-silicone laminate.

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

There are now commercially available a large range of laminated plastics materials. Resins used include the phenolics, the aminoplastics, polyesters, epoxies, silicones and the furane resins, whilst reinforcements may be of paper, cotton fibre, other organic fibres, asbestos, carbon fibre or glass fibre. Of these the phenolics were the first to achieve commercial significance and they are still of considerable importance. 

Because of their favourable price, polyesters are preferred to epoxide and furane resins for general purpose laminates and account for at least 95% of the low-pressure laminates produced. The epoxide resins find specialised uses for chemical, electrical and heat-resistant applications and for optimum mechanical properties. The furane resins have a limited use in chemical plant. The use of high-pressure laminates from phenolic, aminoplastic and silicone resins is discussed elsewhere in this book. 

Figure 29.4. Influence of resin content on the flexural strength of glass-cloth laminates made with two silicone resins A and B. (After Gale " )...

In recent years the dominance of shellac in mica-based laminates has met an increasing challenge from the silicone resins. 

Uses of silicone resins laminates, moulding compositions ... 

In addition to the polymer substrate, a series of binding resins made from polyamide and polyimide, polyphenylsulfide (PPS), polyether sulfone (PES) and/or silicone resin are necessary for applying the coating. Such substances like laminating agents (lithium polysilicate, aluminum phosphate and phosphoric acid) and various additives are also used. Included in these additives are emulsifiers and further processing aids (e.g. silicone oil). 

A schematic view of a microdielectrometer sensor is shown in Fig. 8 and illustrates the electrode array, the field-effect transistors and a silicon diode temperature indicator 15) which functions as a moderate accuracy ( 2 °C) thermometer between room temperature and 250 °C. The sensor is used either by placing a small sample of resin over the electrodes, or by embedding the sensor in a reaction vessel or laminate. Since all dielectric and conductivity properties are temperature dependent, the ability to make a temperature measurement at the same point as the dielectric measurement is a useful feature of this technique. 

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