Importance

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Abstract

A method and apparatus for producing highly-oriented polyester sheet comprises a two-stage drawing process. The first drawing stage is performed within a zero-gap milling and stretching roller assembly comprising a pair of opposed rollers defining a nip therebetween and wherein the rollers are rotated in opposite directions at different lineal surface velocities such that a predetermined draw ratio is defined therebetween. Amorphous polyester sheet is conducted through the nip of the opposed rollers, and as a result of the simultaneous milling and stretching of the polyester sheet, the amorphous polyester is transformed into crystalline polyester as a result of orientation-induced crystallization. The crystalline polyester sheet is heated above the glass transition temperature (T.sub.g) immediately downstream of the nip defined between the pair of opposed rollers, and an exit bridle assembly is disposed downstream of the pair of opposed rollers. The rollers of the bridle assembly are rotated at lineal surface velocities which are greater than the lineal surface velocity of the downstream one of the pair of opposed rollers such that a second draw ratio is defined with respect to such downstream one of the pair of opposed rollers. The heating of the crystalline polyester sheet facilitates the additional stretching thereof within the second drawing stage of the apparatus, the overall drawing ratio being approximately 6:1. Highly oriented polyester, having tensile strength values of approximately 100,000 psi, and modulus values of approximately 3,000,000-5,000,000, is achieved.

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First Claim