Formable reflective multilayer body

• US 5,568,316 A
• Filed: 04/13/1995
• Issued: 10/22/1996
• Est. Priority Date: 10/29/1992
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: The Dow Chemical Company (Dow, Inc.)
• Inventors: Balazs, Conrad F., Arends, Charles B., Wheatley, John A., Lewis, Ray A., Schrenk, Walter J.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Schuberg, Darren E.
• Time in patent office: 558 Days
• Field of Search: 359/580, 359/582, 359/584, 359/586, 359/588
• US Class Current: 359/584
• CPC Class Codes: F21S 43/26 Refractors, transparent cover plates, light guides or filters not provided in groups F21S43/235 - F21S43/255
• CPC Class Codes: F21V 3/04 characterised by materials, surface treatments or coatings
• CPC Class Codes: G02B 5/0841 comprising organic materials, e.g. polymers
• CPC Class Codes: G02B 5/26 Reflecting filters G02B5/28 takes precedence
• CPC Class Codes: G02B 5/287 comprising at least one layer of organic material

Abstract

A formable multilayer reflective polymeric body which has a substantially uniform broad bandwidth reflectance over substantially the entire range of the visible spectrum to provide a substantially uniform reflective appearance is provided. The body includes at least first and second diverse polymeric materials, the body comprising a sufficient number of alternating layers of the first and second polymeric materials such that at least 40% of visible light incident on the body is reflected. A substantial majority of the individual layers of the body have optical thicknesses in the range where the sum of the optical thicknesses in a repeating unit of the polymeric materials is greater than about 190 nm, and the first and second polymeric materials differ from each other in refractive index by at least about 0.03.

Claims

1. A formable polymeric multilayer reflective body having a substantially uniform reflective appearance over substantially the entire range of the visible spectrum comprising:

at least first and second diverse polymeric materials, the body comprising a sufficient number of alternating layers of said first and second polymeric materials such that at least 40% of visible light incident on said body is reflected, a substantial majority of the individual layers of said body having optical thicknesses in the range where the sum of the optical thicknesses in a repeating unit of said polymeric materials is between about 190 nm and 1700 nm, wherein said first and second polymeric materials differ from each other in refractive index by at least about 0.03, wherein said layers have a gradient of optical layer repeat unit thicknesses through the thickness of said body which is sufficient to reflect substantially the entire range of visible light up to a predetermined maximum draw ratio ##EQU8## where MDR is the maximum draw ratio;

t_i is the initial thickness of the optically active layers in the multilayer stack;

t_f is the final thickness of the layers in the microlayer core in the thermoformed part at MDR;

(λ

₁)_max is the maximum reflecting wavelength in the body in nanometers;

the summation from i=1 to j of (N_i d_i)_max is the maximum optical repeat unit thickness in the body in nanometers;

N_i is the refractive index of the i^th layer in the repeat unit;

d_i is the physical layer thickness of the i^th layer in the repeat unit; and

the constant 680 nm is the upper wavelength limit of visible light.

2. The formable polymeric multilayer reflective body of claim 1 in which said polymeric materials are elastomers.

3. The formable polymeric multilayer reflective body of claim 1 in which said gradient of optical layer repeat unit thicknesses is a function which provides substantially continuous wavelength coverage spanning the range of from about 380 nm to about 2000 nm.

4. The formable polymeric multilayer reflective body of claim 1 in which said gradient of optical layer repeat unit thicknesses is a linear function.

5. The formable polymeric multilayer reflective body of claim 1 wherein the reflectance of said body changes upon the thinning of said layers.

6. The formable polymeric multilayer reflective body of claim 1 wherein said body has at least 1000 layers.

7. The formable polymeric multilayer reflective body of claim 1 wherein at least 80% of visible light incident on said body is reflected.

8. A formable polymeric multilayer reflective body having a substantially uniform reflective appearance over substantially the entire range of the visible spectrum comprising:

at least first and second diverse polymeric materials, the body comprising a sufficient number of alternating layers of said first and second polymeric materials such that at least 40% of visible light incident on said body is reflected, a substantial majority of the individual layers of said body having optical thicknesses in the range where the sum of the optical thicknesses in a repeating unit of said polymeric materials is between about 190 nm and 1700 nm, wherein said first and second polymeric materials differ from each other in refractive index by at least about 0.03, wherein said layers have a gradient of optical layer repeat unit thicknesses through the thickness of said body such that said gradient of optical layer repeat unit thicknesses provide continuous wavelength coverage over substantially the entire range of the visible spectrum for said body to maintain a substantially uniform reflective appearance when drawn, and wherein said gradient of optical layer repeat unit thicknesses is a quartic function.

9. The formable polymeric multilayer reflective body of claim 8 in which said quartic function which defines said gradient of optical layer repeat unit thicknesses is superimposed on a linear gradient.