Polyamide imide enamels

Polyamide Imide Enamels. Aromatic polyamide imide insulations are made from aromatic acids and aromatic diamines. The polyamide imide polymers are primarily present in the form of polyamic acids in the Af-methyIpyrrolidone solutions. During the enameling process the polyamic acids undergo imidization and become essentially fully imidized. Whereas the polyester and polyester imide enamels contain cresylic acids as the major solvent, the polyamide imide enamels are mainly formulated with A/-methylpyrrolidone as solvent. 

These polyamide imide films have excellent thermal, mechanical, and electrical properties, and they are used to upgrade other enamel films. Other attractive features of polyamide imide film insulations are a low coefficient of friction and good solvent resistance. These enamels are rated for use at 200 °C. 

Dual Constructions. In addition to the "basic" magnet wire insulations in which the conductor wire is coated with a single enamel, there are a number of cases where two different enamels are used one overcoated over the other. Examples include polyurethane-base insulation overcoated with poly(vinyl butyral) or with nylon, or polyester-base insulation overcoated with nylon or with polyamide imide. 

Uses of polyamide-imides include pumps, valves, refrigeration plant accessories, and electronic components. The polymers have low coeflScient of friction, e.g., 0.2 (to steel), which is further reduced to as little as 0.02-0.08 by blending with graphite and Teflon. In solution form in N-methyl-2-pyrrolidone, Torlon has been used as a wire enamel, as a decorative finish for kitchen equipment, and as an adhesive and laminating resin in spacecraft... 

S. Kbnig, K. W. Lienert, and G. Schmidt. Polyamide-imide resin solution and the use thereof for producing wire enamels. US Patent 7 122 244, assigned to Altana Electrical Insulation GmbH (Wesel, DE), October 17,2006. 

Polyamide-imide polymers find application in hydraulic bushings and seals, mechanical parts for electronics, and engine components. The polymer in solution has application as a laminating resin for spacecraft, a decorative finish for kitchen equipment, and as wire enamel. Low coefficient of friction materials may be prepared by blending PAI... 

Following this wire enamel introduction, Amoco began development, in the mid-1970s, of melt processable polyamide-imide compounds for the injection molding and extrusion markets [6]. 

Also in this time frame, wire insulation producers began producing polyamide-imides using lower-cost isocyanate chemistry. This technology largely supplanted the acid chloride route for the wire enamel market. 

The other most popular method of synthesizing commercial PAI uses the so-called isocyanate route. This is the primary route to polyamide-imides which are then utilized as wire enamels or fibers. This PAI chemistry involves the reaction of a di-isocyanate, often -methylenediphenyldi-isocyanate (MDI) (Fig. 12.3) with trimellitic anhydride (TMA) (Fig. 12.4). To overcome the lower reactivity of the carboxylic acid functionality in... 

The polyamide-imide achieved at the end of this process is a high-molecular-weight, fully imidized polymer in solvent with no condensation by-products, since the carbon dioxide gas is easily removed. This convenient form makes it especially beneficial for the manufacturer where the primary end use is wire enamel or another coating application. The solution viscosity is thus controlled by stoichiometry, monofunctional reagents, and polymer solids. The typical polymer sohds level is 35 to 45% and it may be diluted further by the supplier or customer with diluents. 

The majority of isocyanate-produced polyamide-imide solutions are consumed within the wire enamel marketplace, where Altana AG and Hitachi are known. Other producers with polyamide-imide solution products include Bayer Material Science with Resistherm , while Huntsman has Rhodeftal . 

H. Kikuchi, H. Hanawa, Y. Honda, Development of polyamide-imide/silica nanocomposite enameled wire. Electron. Comm. Jpn. 96, 41-48 (2013)... 

---