Coextrusion of multilayer articles using protective boundary layers and apparatus therefor

Claim 2

A process for the coextrusion of a multilayer polymeric reflective body comprising the steps of: providing at least a first stream and a second stream of heat plastified extrudable thermoplastic polymeric material, dividing each of the stream into a plurality of first substreams and a plurality of second substreams, respectively, combining the substreams to form a composite stream having said first substreams and second substreams interdigitated, providing a third stream of heat plastified thermoplastic polymeric material to the exterior surfaces of said composite stream to form protective boundary layers to prevent breakup of the layers of said first and second thermoplastic polymeric materials during layer manipulation and multiplication, said third stream of thermoplastic polymeric material having a viscosity which is equal to or less than that of either said first or second streams of thermoplastic polymeric material and is supplied at a volumetric flow rate which is from about 1-12.5% of the total volume of said composite stream, forming a manipulated stream by mechanically manipulating said composite stream having said protective boundary layers to provide an increased number of layers, and shaping the manipulated stream into a multilayer polymeric reflective body having a sufficient number of alternating layers of said first and second thermoplastic polymeric materials such that at least 30% of light incident on said body is reflected and wherein said first and second thermoplastic polymeric materials differ from each other in refractive index by at least about 0.03 to produce a reflective polymeric body, said layers being generally parallel to one another.

Claim 3

A process as claimed in claim 1 in which said multilayer body has from about 500 to about 5000 layers.

Claim 4

A process as claimed in claim 1 in which said first polymeric material is a polycarbonate and said second polymeric material is polymethyl methacrylate.

Claim 5

A process as claimed in claim 3 in which said third polymeric material is a polycarbonate.

Claim 6

A process as claimed in claim 1 including the step of providing protective skin layers to the exterior surfaces of said manipulated stream prior to shaping said manipulated stream into said multilayer polymeric body.

Claim 7

A process for he coextrusion of a multilayer polymeric reflective body comprising the steps of: providing at least a first stream and a second stream of heat plastified extrudable thermoplastic polymeric material, dividing each of the streams into a plurality of first substreams and a plurality of second substreams, respectively, combining the substreams to form a composite stream having said first substreams and second substreams interdigitated, forming a manipulated stream by mechanically manipulating said composite stream to provide an increased number of layers, providing a third stream of heat plastified thermoplastic polymeric material to the exterior surfaces of said manipulated stream to form protective boundary layers to prevent breakup of the layers of said first and second thermoplastic polymeric materials during layer manipulation and multiplication, said third stream of thermoplastic material having a viscosity which is equal to or less than that of either said first or second streams of thermoplastic material and is supplied at a volumetric flow rate which is from about 1-12.5% of the total volume of said manipulated stream, further mechanically manipulating said manipulated stream having said protective boundary layers to provide an increased number of layers, and shaping said manipulated stream into a multilayer polymeric reflective body having a sufficient number of alternating layers of said first and second thermoplastic polymeric materials such that at least 30% of light incident on said body is reflected and wherein said first and second polymeric materials differ from each other in refractive index by at least about 0.03 to produce a reflective polymeric body having layers which are generally parallel to one another.

Claim 8

A process for he coextrusion of a multilayer polymeric reflective body comprising the steps of: providing at least a first stream and a second stream of heat plastified extrudable thermoplastic polymeric material, dividing each of the streams into a plurality of first substreams and a plurality of second substreams, respectively, combining the substreams to form a composite stream having said first substreams and second substreams interdigitated, forming a manipulated stream by mechanically manipulating said composite stream to provide an increased number of layers, providing a third stream of heat plastified thermoplastic polymeric material to the exterior surfaces of said manipulated stream to form protective boundary layers to prevent breakup of the layers of said first and second thermoplastic polymeric materials during layer manipulation and multiplication, said third stream of thermoplastic material having a viscosity which is equal to or less than that of either said first or second streams of thermoplastic material and is supplied at a volumetric flow rate which is from about 1-12.5% of the total volume of said manipulated stream, further mechanically manipulating said manipulated stream having said protective boundary layers to provide an increased number of layers, and shaping said manipulated stream into a multilayer polymeric reflective body having a sufficient number of alternating layers of said first and second thermoplastic polymeric materials such that at least 30% of light incident on said body is reflected and wherein said first and second polymeric materials differ from each other in refractive index by at least about 0.03 to produce a reflective polymeric body having layers which are generally parallel to one another.

Claim 9

A process as claimed in claim 6 in which said multilayer body has from about 500 to about 5000 layers.

Claim 10

A process as claimed in claim 6 in which said first polymeric material is a polycarbonate and said second polymeric material is polymethyl methacrylate.

Claim 11

A process as claimed in claim 8 in which said third polymeric material is a polycarbonate.

Claim 12

A process as claimed in claim 6 including the step of providing a protective skin layer to the exterior surfaces of said manipulated stream prior to shaping said manipulated stream into said multilayer polymeric body.

Claim 13

A process for preventing layer breakup in the coextrusion of a multilayer polymeric reflective body comprising the steps of: providing at least a first stream and a second stream of heat plastified extrudable thermoplastic polymeric material, dividing each of the streams into a plurality of first substreams and a plurality of second substreams, respectively, combining the substreams to form a composite stream having said first substreams and second substreams interdigitated, forming a manipulated stream by mechanically manipulating said composite stream by flowing portions of said composite stream through a plurality of conduits to provide an increased number of layers while preventing breakup of said layers, the prevention of layer breakup being accomplished by performing at least one of the following steps prior to or during the formation of said manipulated stream: a) reducing shear stress at the walls of said plurality of conduits, b) reducing shear rate at the walls of said plurality of conduits, c) increasing the layer thickness adjacent the walls of said plurality of conduits, and shaping the manipulated stream into a multilayer polymeric reflective body having a sufficient number of alternating layers of said first and second thermoplastic polymeric materials such that at least 30% of light incident on said body is reflected and wherein said first and second thermoplastic polymeric materials differ from each other in refractive index by at least about 0.03 to produce a reflective polymeric body, said layers being generally parallel to one another.

Claim 14

A process for preventing layer breakup in the coextrusion of a multilayer polymeric reflective body comprising the steps of: providing at least a first stream and a second stream of heat plastified extrudable thermoplastic polymeric material, dividing each of the streams into a plurality of first substreams and a plurality of second substreams, respectively, combining the substreams to form a composite stream having said first substreams and second substreams interdigitated, forming a manipulated stream by mechanically manipulating said composite stream by flowing portions of said composite stream through a plurality of conduits to provide an increased number of layers while preventing breakup of said layers, the prevention of layer breakup being accomplished by performing at least one of the following steps prior to or during the formation of said manipulated stream: a) reducing shear stress at the walls of said plurality of conduits, b) reducing shear rate at the walls of said plurality of conduits, c) increasing the layer thickness adjacent the walls of said plurality of conduits, and shaping the manipulated stream into a multilayer polymeric reflective body having a sufficient number of alternating layers of said first and second thermoplastic polymeric materials such that at least 30% of light incident on said body is reflected and wherein said first and second thermoplastic polymeric materials differ from each other in refractive index by at least about 0.03 to produce a reflective polymeric body, said layers being generally parallel to one another.

Claim 15

The process of claim 11 wherein the step of reducing shear stress at the walls of said plurality of conduits comprises coating the walls of said conduits with a low surface tension material.

Claim 16

The process of claim 12 wherein said low surface tension material comprises titanium nitride.

Claim 17

The process of claim 12 wherein the step of reducing shear stress at the walls of said plurality of conduits comprises incorporating a slip additive into said heat plastified extrudable thermoplastic material.

Claim 18

The process of claim 12 wherein the step of reducing shear stress at the walls of said plurality of conduits comprises lowering the viscosity of the layers adjacent the walls of said conduits.

Claim 21

The apparatus of claim 16 wherein said means for dividing said first composite stream into a plurality of individual inlets divided by splitting vanes, and said means for providing said third stream of heat plastified thermoplastic material includes shaped feed slots adjacent said individual inlets.

Claim 22

The apparatus of claim 16 wherein said means for providing said third stream of heat plastified thermoplastic material includes means for controlling the amount of said thermoplastic material fed to said feed slots.