Optical device having low visual light transmission and low visual light reflection

Abstract

A solar control film having low visible light transmittance and low visible light reflectance is comprised of two or more transparent substrates each bearing a thin, transparent, discontinuous, incoherent film of metal having low visible light reflectance and a degree of visible light blocking capacity, the substrates being so assembled and laminated into a composite that the visible light blocking capacities of the metal films are effectively combined to provide a composite having low visible light transmittance. Performance characteristics are enhanced by providing on one or more of the substrates a transparent coating of high refractive index underlying the metal film. The material of high refractive index is preferably a synthetic high oxygen content oxide of bismuth, which facilitates efficient and economical production of the solar control film.

Description

FIELD OF THE INVENTION

The present invention relates to optical devices, such as solar energy control window films, having low visual light transmission and low visual light reflection, and to methods of making the same.

BACKGROUND

The glass tinting industry desires a class of solar energy control coatings or films with a visual light transmission (VLT) clear glass gold, silver, nickel and chromium and, nickel-chromium alloys of the same, and stainless steel. Sputtering of these metals is very straight forward and readily and quickly achieved, particularly in view of the thinness of the film, i.e., 1-20 nm. The metal is preferably sputtered in an inert gas partial pressure atmosphere introduced into the substantially enclosed station 58 via the inlet 43.

The materials of high refractive index customarily employed in optical films are slower and more difficult to deposit, especially titanium oxide which is the material of highest index. In order to enhance the rate of deposition of the oxide to keep pace with the rate of deposition of the metal film, it may prove necessary to add more magnetron cathodes at station 56 and/or to add another oxide deposition station intermediate the stations 56 and 58. As is known, the compound of high refractive index may itself comprise the target 56c, or a target of the metal per se may be reactively sputtered in the presence of a partial pressure atmosphere of reactive gas, e.g. oxygen and/or nitrogen, introduced to the station(s) 56 via the inlet 42. Even so, because the deposition of TiO₂ onto a substrate is such a slow and tedious process and the resultant product is so expensive, economies of production may dictate use of a different oxide or nitride, even though the refractive index is significantly less than desired.

Bismuth oxide Bi₂ O₃, though referenced in the literature for use in the far infrared range, is not considered an optical material in the visual range because it is highly absorbing in the visual spectrum, and therefore has not found application in the commercial solar film market.

The present invention is predicated in part upon the discovery that formation of a synthesized BiO_x having a high level of oxidation (x=>1.7) produces a thin film that is not highly absorbing, and that provides a very high index of refraction comparable to that of TiO₂. More importantly, in the context of the process of the invention, the synthetic BiO_x has a rate of deposition that is 25 or more times faster than that of TiO₂, thereby eliminating the economic impediment of TiO₂ and producing a better performing and more acceptable product.

Deposition of the BiO_x film may be accomplished by reactive sputter deposition, actuated reactive evaporation deposition and vacuum arcing deposition, but reactive sputter deposition, as illustrated in FIG. 7, is presently preferred. Specifically, the target 56c is comprised of bismuth and is sputtered within a partial pressure atmosphere of oxygen, the oxygen partial pressure being variable to produce a layer of synthetic bismuth oxide having an atomic ratio of oxygen to bismuth of from at least 1.7 up to about 2.5, i.e., BiO_x (x=1.7-2.5).

The thickness of the synthesized BiO_x (x=1.7-2.5) film deposited on the substrate 50 may be varied from about 0.1 to about 50 nm (10-500 Å) depending upon the performance characteristics desired. The recommended thickness range is from 0.1 to 10 nm for solar films having a VLT=>35%, and from 10-50 nm for solar films having a VLT=<35%. The rate of production will generally vary from about 20 feet per minute (fpm) for thicker films up to about 50 fpm for thinner films. For most applications contemplated by the present invention, a film thickness of about 40 nm applied at a substrate speed of about 50 fpm will produce a very acceptable product.

However, the desired extent of oxidation of the bismuth will also enter into the production equation. FIG. 8 comprises a graphic correlation of the rate of reactive sputter deposition of synthesized oxides of bismuth, BiO_x, the atomic ratio of oxygen to bismuth in the oxide, and the oxygen partial pressure within the sputter deposition vacuum chamber. In FIG. 8, the oxygen partial pressure (OPP) is plotted along the abscissa, the dynamic deposition rate (DDR) along the left hand ordinate and the atomic ratio (AR) along the right hand ordinate. The descending curve comprises the DDR and the ascending curve the AR. The DDR was calculated from two test runs. The AR was determined by Helium Ion Beam Rutherford Back Scattering measurements and Auger Electron Spectroscopy profiles, calibrated against commercial bulk Bi₂ O₃. For reasons not presently known, Auger profiles have consistently yielded higher AR values than Rutherford Back Scattering measurements, especially at higher AR values. Nevertheless, it is noted as a general observation that as the OPP increases, the AR rises and the film becomes clear when the AR equals or exceeds 1.7.

As graphically portrayed in FIG. 8, BiO_x with an AR of 1.8 may be deposited at an oxygen partial pressure of about 7.5 E-5T (7.5×10-5 Torr.) and a DDR of about 3.5 nm×cm**2/j (thickness in nm times area in sq. cm. divided by energy in Joules); and BiO_x with an AR of 2.5 may be produced at an OPP of 12E-5T and a DDR of about 2.5 nm×cm**2/j. In contrast, the DDR for reactive sputtering of TiO₂ is typically about 0.1 nm×cm**2/j. Thus, the synthetic BiO_x (x=>1.7) provided by the invention may be deposited 25 to 35 times faster than TiO₂, which is a very significant economic advantage, especially in view of the fact that the refractive indices are essentially the same. Moreover, the enhanced speed of deposition of BiO_x facilitates deposition of the oxide at the same web speed as deposition of the metal, thereby to provide for very economical production of the solar control films of the invention.

Taking into consideration production speed and the quality of coating desired, a preferred AR will fall within the range of 1.8 to 2.2.

Auger profile measurements establish that the thin BiO_x coating on the substrate is very uniform. Scanning electron microscope (SEM) photographs at a magnification of 50,000 times further reveal that as the OPP is increased to produce a BiO_x film having an AR of 1.7 or greater, the surface of the coating becomes extremely smooth and uniform, thereby significantly reducing absorption and providing a film of high refractive index ideal for practice of the invention.

The invention thus provides for economical mass production of highly durable solar control films having low visual light transmission and low visual light reflection.

The objects and advantages of the invention have therefore been shown to be attained in a convenient, economical and practical manner.

While preferred embodiments of the invention have been herein illustrated and described, it is to be appreciated that various changes, rearrangements and modifications may be made therein without departing from the scope of the invention, as defined by the appended claims.

Claims

1. A solar control film having low visible light transmittance and low visible light reflectance comprising .

a first sheet of transparent substrate material having thereon a thin, incoherent, transparent film of metal effective to partially block visible light transmittance and having a preselected low visible light reflectance,

a second sheet of transparent substrate material having thereon a thin, incoherent, transparent film of metal effective to partially block visible light transmittance and having a preselected low visible light reflectance, and

a layer of adhesive bonding said first and second sheets to one another with the films of metal facing one another and separated and optically decoupled from one another,

the bonded sheets forming a composite film having a combined visible light transmittance blocking effect equal approximately to the sum of the blocking effects of the incoherent films and visible light reflectance substantially equal to the visible light reflectance of just one of the incoherent films, the visible light reflectance of each incoherent film being such that the visible light reflectance of the composite film on clear glass does not exceed about 12% when visible light transmittance is within the range of from about 35% up to about 50% or less, and does not exceed about 15% when visible light transmittance is about 35% or less and does not exceed about 20% when visible light transmittance is about 25% or less.

2. A solar control film as set forth in claim 1 wherein at least one of said sheets of substrate material bears a layer of material of high refractive index between the substrate and the incoherent film of metal for further controlling the visible light transmittance and visible light reflectance of the composite film.

3. A solar control film as set forth in claim 2 wherein the material of high refractive index is selected from silicon nitride, the oxides of chromium, niobium and titanium, and a synthesized oxide of bismuth having an atomic ratio of oxygen to bismuth of from about 1.7 to about 2.5.

4. A solar control film as set forth in claim 1 wherein the thin incoherent metal film is selected from gold, silver, nickel, chromium and nickel-chromium alloys thereof and stainless steel.

5. A solar control film as set forth in claim 1 including a third sheet of transparent substrate material having thereon a thin, incoherent, transparent film of metal effective to partially block visible light transmittance and having substantially the same low visible light reflectance as the other incoherent films, said third sheet being sandwiched between and physically bonded to said first and second sheets with the incoherent film of metal thereon separated from and optically decoupled from the incoherent films of metal on said first and second sheets.

6. A solar control film as set forth in claim 5 wherein one, two or all of said sheets of substrate material bears a layer of material of high refractive index between the substrate and the incoherent film of metal for further controlling the visible light transmittance and visible light reflectance of the composite film.

7. A solar control film as set forth in claim 1 including a layer of pressure sensitive adhesive on one side of the composite film for bonding the same to a window and a protective coating on the other side of the composite film for protecting the film from damage.

8. A solar control film having low visible light transmittance and low visible light reflectance comprising

a first sheet of transparent substrate material bearing thereon a thin transparent layer of a material of high refractive index and a thin, transparent, incoherent coating of metal overlying the material of high refractive index, the metal film being effective to partially block visible light transmittance through the coated substrate and having a preselected low visible light reflectance,

a second sheet of transparent substrate material bearing thereon a thin transparent layer of a material of high refractive index and a thin, transparent, incoherent coating of metal overlying the material of high refractive index, the metal film being effective to partially block visible light transmittance through the coated substrate and having a preselected low visible light reflectance, and

a layer of adhesive bonding said first and second sheets to one another with the films of metal facing one another and optically decoupled and separated from one another,

the bonded sheets forming a composite film having a combined visible light transmittance blocking effect equal approximately to the sum of the blocking effects of the incoherent films and low visible light reflectance substantially equal to the visible light reflectance of just one of the incoherent films, the visible light reflectance of each incoherent film being such that the visible light reflectance of the composite film does not exceed about 20% when visible light transmittance is no greater than about 25%, on clear glass does not exceed about 15% when visible light transmittance is no greater than about 35% and does not exceed about 12% when visible light transmittance is within the range of from about 35% up to about 50%.

9. A solar control film as set forth in claim 8 including a third sheet of transparent substrate material bearing thereon a thin, incoherent, transparent coating of metal effective to partially block visible light transmittance through the coated substrate and having substantially the same low visible light reflectance as the other incoherent films, said third sheet being sandwiched between and physically bonded to said first and second sheets with the incoherent film of metal thereon separated and optically decoupled from the incoherent films of metal on said first and second sheets.

10. A solar control film as set forth in claim 8 wherein the material of high refractive index comprises a synthesized oxide of bismuth reactively sputter deposited on the substrate material and having an atomic ratio of oxygen to bismuth of from 1.7 to 2.5.

11. A solar control film as set forth in claim 8 wherein the material of high refractive index is selected from the oxides of chromium, niobium and titanium and silicon nitride.

12. A method of making solar control films having low visible light transmittance and low visible light reflectance comprising the steps of

depositing onto a transparent substrate a thin, incoherent, transparent coating of metal that is effective to partially block visible light transmittance through the coated substrate and that is sufficiently thin and incoherent as to have a preselected low visible light reflectance,

assembling into a composite film a plurality of the coated substrates such that the incoherent metal coatings face one another internally of the composite film and are separated and optically decoupled from one another and such that the metal coatings together provide a combined visible light blocking effect sufficient to provide a preselected low level of visible light transmittance through the composite film, and

laminating the coated substrates to one another to provide a composite film having a combined visible light transmittance blocking effect equal approximately to the sum of the blocking effects of the incoherent metal coatings and low visible light reflectance substantially equal to the visible light reflectance of just one of the incoherent metal coatings, the visible light reflectance of each incoherent metal coating being such that the visible light reflectance of the composite film does not exceed about 20% when visible light transmittance is no greater than about 25%, on clear glass does not exceed about 15% when visible light transmittance is no greater than about 35% and does not exceed about 12% when visible light. transmittance is within the range of from about 35% up to about 50%.

13. A method as set forth in claim 12 wherein the coated substrates are laminated to one another and are separated and optically decoupled from one another by means of one or more interleaved layers of adhesive.

14. A method as set forth in claim 12 including the step of first depositing onto the substrate a thin transparent layer of material of high refractive index and then depositing the metal coating onto the material of high refractive index.

15. A method as set forth in claim 14 wherein the material of high refractive index has a refractive index of at least 2∅

16. A method as set forth in claim 12 including the step of reactively sputter depositing onto the substrate a synthesized oxide of bismuth having an atomic ratio of oxygen to bismuth of from 1.7 to 2.5, and then sputter depositing the thin coating of metal onto the synthesized bismuth oxide. 17. A method as set forth in claim 12 wherein the metal deposited on each substrate comprises chromium, a nickel-chromium alloy or stainless steel.18. A method as set forth in claim 17 wherein the metal is sputter deposited onto the substrate.19. A solar control film as set forth in claim 1 wherein the metal deposited on each substrate comprises chromium, a nickel-chromium alloy or stainless steel sputter deposited onto the substrate.20. A solar control film as set forth in claim 1 wherein the visible light transmission of the composite film lies within

the range of from about 20% to about 50%.21. A solar control film having low visible light transmittance and low visible light reflectance comprising

a first sheet of transparent substrate material having thereon a thin, incoherent, transparent film of metal effective to partially block visible light transmittance and having a preselected low visible light reflectance,

a second sheet of transparent substrate material having thereon a thin incoherent, transparent film of metal effective to partially block visible light transmittance and having a preselected low visible light reflectance, and

a layer of adhesive bonding said first and second sheets to one another with the films of metal facing one another and separated and optically decoupled from one another,

the bonded sheets forming a composite film having a combined visible light transmittance blocking effect equal approximately to the sum of the blocking effects of the incoherent films and visible light reflectance substantially equal to the visible light reflectance of just one of the incoherent films, the composite film having on clear glass a visible light transmittance within the range of 20% to 50% and a visible light reflectance no greater than 15% when visible light transmittance is within the range of 20% to 35% and no greater than 12% when visible light transmittance is within the range of 35% to 50%.