General Types of Electrical Insulation Materials

Films are a common type of material used in this category. Films are thin sheets with excellent flexibility. Films are non-porous. This characteristic is excellent for some applications, but not beneficial in other applications. Films are excellent when the application requires a non-porous barrier in the device. But by being non-porous, these products can restrict passage of impregnating resins or varnishes. Being non-porous may also cause some processing problems in designs which need to have air removed from the windings to maximize the penetration of impregnating resins. Common chemistries used in electrical grade films are Polyethyleneteraphthlate [PET]. Polyethylenenaphthalate [PEN], and Polyimide [PI].
Fibrous Papers / Sheets offer the ability of impregnating resins to penetrate the fibers and form a more rigid total product when cured. Fibrous sheets offer increased performance when used with an impregnating resin or varnish. The impregnating resins, or varnishes, fills the voids between the fibers and solidifies the total isolative construction.

Composite / Laminated Sheets are constructed with two or more layers of materials bonded to each other by an adhesive or by heating. Common constructions are polyester mat (fibers) bonded to polyester film. The adhesive or bonding material is one of the critical components of any composite sheet. The adhesive / resin can provide an oxygen inhibiting layer which can greatly extend the life at elevated temperatures compared to the life of the polyester film without the adhesive component being part of the total construction.
Tape is a material which is shaped into a long strip for application. Any construction which is many times longer than wide can be described as being a tape. There are no specified proportions between width and length for this word.
Pressure Sensitive Adhesive Tape refers to a tape with an adhesive applied. The adhesive applied may be selected to provide easier application and/or possible increased electrical insulation characteristics.
Pressboards are made from electrical grade papers processed to a thickness to give rigidity. Presspaper refers to thicknesses which are still flexible, while pressboard refers to thicknesses which are inflexible. As the layers of presspaper are bonded or processed together to form pressboard, the bonding may be due to the natural intertwining of the fibers, by heat bonding, or by use of binding resins.


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