Method for making a wide optical polarizer using extrusion

Abstract

The invention is directed to a method for preparing wide strip optical polarizers by extruding glass and stretching the extruded glass to thereby elongate the polarizing metals or metal salts within the glass. The invention enables one to form a optical polarizers that have a width of 300 mm or larger depending on the size of the die used. The stretching system using two set of rollers as described herein is particularly useful for making larger sizes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a glass bar that has been stretched according to prior art methods and shown an unstretched top and bottom part of the bar and the stretched middle part of the bar that forms the polarizing glass.

FIG. 1B is a side-by-side comparison of a wide polarizing strip according to the invention (upper strip) versus a narrow strip from a glass stretched according to the prior art (lower strip).

FIG. 2 illustrates the furnace, load cell and glass bar suspended in the furnace that are used to form the polarizer illustrated in FIG. 1.

FIG. 3 illustrates the mathematics and the “conservation of volume” of the drawing (stretching) process.

FIG. 4 illustrates an embodiment of the invention in which sets of rollers operating at different speeds are used to stretch a glass bar while minimizing the width reduction of the bar.

FIG. 5 illustrates an embodiment of the invention in which in place of one set of rollers an extruder is used to extrude and deliver a glass bar to a set of rollers that that rotates at a speed sufficient to reduce the thickness of the glass by stretching of the glass and the particles therein to produce the polarizing effect while maintaining or substantially maintaining the width of the glass.

FIG. 6 illustrates an embodiment of the invention in which glass is stretched directly from an extruded using a “gripper” to grip and pull one end of the glass to thereby elongate the particles within the glass.

FIG. 7 is an illustration of the extrusion set-up and a glass bar or ribbon exiting the die.

FIG. 8 is a picture of showing the main components of the extruder system.

FIG. 9 is a spectrum obtained using a first polarizing glass produced using the extrusion/draw system of the invention.

FIG. 10 is a spectrum obtained using a second polarizing glass produced using the extrusion/draw system of the invention.

Claims

1. A method of making a glass optical polarizers, said method comprising the steps of: preparing a glass melt batch containing a polarizing metal as the salt or metal(0) species and casting melt into boule;placing the boule or a form made from the boule into an extruder;heating the boule to a temperature at which the glass has a viscosity of at least 107 poise;extruding the glass through a heated die and grabbing the end of the glass extruded from the die;stretching the extruded glass into a ribbon having the width or substantially the width of the glass as it was extruded from the die;treating the glass ribbon containing the polarizing metal salt in a reducing atmosphere at temperature below the softening point of the glass for a time in the range of 4-40 hours to produce a polarizing metal(0) layer in the glass; andpolishing the ribbon; andcutting the ribbon to the desired size to thereby form an optical polarizer.

2. The method according to claim 1, wherein the polarizing metal salt is selected from at least one of the group consisting of a non-fluorine halide of silver, copper and cadmium, including mixtures thereof.

3. The method according to claim 1, wherein the metal salt is a silver salt and the silver concentration is in the range of 0.05-1.0 wt. %

4. The method according to claim 1, wherein the polarizer is capable of polarizing light in a region selected from the group consisting of the visible, infrared and ultraviolet regions.

5. The method according to claim 1, wherein, before drawing, the glass is subjected to an etching step or a thermal treatment step, or both, to remove and/or heal surface defects.

6. The method according to claim 1, wherein after passing through the die, the glass is grabbed by a first set of rollers operating at a first rotational speed and after passing through the first set of rollers the glass is picked up by a second set of rollers operating at a second rotational speed that is greater then the first rotational speed, the difference between the two rotational speed being sufficient to pull and elongate the glass and particles therein to thereby provide a ribbon having the width or substantially the width of the glass as it was extruded from the die.

7. The method according to claim 1, wherein after passing through the die, the glass is grabbed by a single set of rollers operating at a rotational speed greater than the rate at which the glass is extruded from the die to thereby pull and elongate the glass and particles therein to provide a ribbon having the width or substantially the width of the glass as it was extruded from the die.

8. The method according to claim 1, wherein after passing through the die, the glass is grabbed by a movable gripper, the gripper moving at a rate sufficient to pull and elongate the glass and particles therein to provide a ribbon having the width or substantially the width of the glass as it was extruded from the die.

9. A method for making a silver-containing visible light glass polarizer, the method consisting of the steps: melting a glass batch containing a source of silver and a halogen other than fluorine, and forming a glass body from a melt;heat treating the glass body at a temperature above the glass strain point to generate halide crystals having a size in the range of 500-2000 Angstroms;stressing the crystal-containing glass body at a temperature above the glass annealing point to elongate the body and thereby elongate and orient the crystals; andexposing the elongated body to a reducing atmosphere at a temperature above 250° C. to develop a reduced surface layer on the body that contains metal particles with an aspect ration of at least 2:1;wherein the stressing is carried out at a temperature above the annealing point of the glass using two sets of rollers, the glass being fed into a first set of rollers operating a first rotational speed and after passing through the first set of rollers the glass is picked up by a second set of rollers operating at a second rotational speed that is sufficiently greater than the first rotational speed so that sufficient is generated to elongate the silver particles.

10. A polarizer made according to claim 1, wherein said polarizer is capable of polarizing light in a region one selected from the group consisting of the visible, infrared and ultraviolet regions.

11. A silver containing polarizer according to claim 9, wherein the polarizer is capable of polarizing light in a region selected from the group consisting of the visible, infrared and ultraviolet regions, said polarizer having a silver content in the range of 0.5-1.0 wt. %.