Method for producing a laminated high strength sheet
First Claim
1. Method for producing a laminated high strength sheet comprising the steps of attenuating while extruding each of at least two layers of at least a blend of two or more polymers containing not more than about 85% of any one of such polymer and at least about 15% of one or more different polymer, the polymers in said blend being sufficiently incompatible as to form upon extrusion of the blend a microscopically visible grain and impart upon solidification a pronounced direction of splittability, before or after solidification of said layers uniting the layers into a common sheet with the grain direction of adjacent layers herein extending in criss-crossing relationship while forming a generally weak bond between said layers, solidifying if not already solid and finally biaxially orienting the solid laminated sheet thus obtained in at least two separate steps each of which is essentially unidirectional with the directions crossing one another at a temperature sufficiently low for maintaining a significant splittability in each layer.
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Abstract
A high-strength laminate comprising generally weakly adhered biaxially oriented films, each formed of a blend which exhibits a distinct fibrous morphology with the fibres forming a distinct unidirectional grain when measured on a macro-scale but with the fibre-portions strongly deflected from this direction as seen on a micro-scale and with the unidirectional grain in at least two of the films criss-crossing each other. Producing this laminate by melt attenuating the blend(s) while extruding the latter to films, cross-laminating the layers before or after solidification while they are still in molecularly unoriented state -- except for the weak orientation produced by the melt-attenuation -- and finally strongly biaxially orienting the laminate by stretching in several steps, whereby the stretching is generally uniaxial during each step.
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Citations
24 Claims
- 1. Method for producing a laminated high strength sheet comprising the steps of attenuating while extruding each of at least two layers of at least a blend of two or more polymers containing not more than about 85% of any one of such polymer and at least about 15% of one or more different polymer, the polymers in said blend being sufficiently incompatible as to form upon extrusion of the blend a microscopically visible grain and impart upon solidification a pronounced direction of splittability, before or after solidification of said layers uniting the layers into a common sheet with the grain direction of adjacent layers herein extending in criss-crossing relationship while forming a generally weak bond between said layers, solidifying if not already solid and finally biaxially orienting the solid laminated sheet thus obtained in at least two separate steps each of which is essentially unidirectional with the directions crossing one another at a temperature sufficiently low for maintaining a significant splittability in each layer.
Specification