US3658631A

US3658631A - Transparent non-wettable surface

Info

Publication number: US3658631A
Authority: US
Inventors: Robert H Shaw; Jerrold Zimmerman
Original assignee: Itek Corp
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1969-09-19
Filing date: 1969-09-19
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25

Abstract

An optical laminate structure is disclosed comprising a transparent substrate and a transparent layer of a non-wettable material bonded to said substrate and formed from a refractory metal oxide. These laminates are particularly useful in applications where it is important to maintain clear vision through the optical surface after it has been subjected to water such as with automobile windshields, periscopes and eyeglasses.

Description

United States Patent Shaw et a1.

[451 Apr. 25, 1972 [54] TRANSPARENT NON-WETTABLE SURFACE [72] Inventors: Robert H. Shaw, Concord; Jerrold Zimmerman, Randolph, both of Mass.

[58] Field ofSearch.... 161/1, 2, 4,182,164, 225,

[56] References Cited UNlTED STATES PATENTS 3,508,982 4/1970 Shearin ..161/2 3,510,371 5/1970 Frankson ..16l/2 X 1124,9313 2/1961 Ryan et a1. ...16l/408 X 2,628,927 2/1953 Colbert et a1. ...l6l/409 X 2,793,148 5/1957 West ...16l/408 X 3,406,085 10/1968 Brown et a1... ...161/408 X 3,498,775 3/1970 Simmons ..161/1 X 3,516,720 6/1970 Mauer ..16l/408 X Primary Examiner-Harold Ansher Attorney-Homer 0. Blair, Robert L. Nathans, W. Gary Goodson and David E. Brook [57] ABSTRACT An optical laminate structure is disclosed comprising a transparent substrate and a transparent layer of a non-wettable material bonded to said substrate and formed from a refractory metal oxide. These laminates are particularly useful in applications where it is important to maintain clear vision through the optical surface after it has been subjected to water such as with automobile Windshields, periscopes and eyeglasses.

6 Claims, 4 Drawing Figures TRANSPARENT NON -WETTABLE SURFACE CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation in part of Shaw et al., U.S. Ser. No. 717,550, filed on Apr. 1, 1968 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to water repellant materials and, more especially, to a transparent non-wettable abrasion resistant surface useful for optical windows, lenses, reflectors and similar elements.

2. Description of the Prior Art Compositions, methods and apparatus to render transparent materials non-wettable are described in detail in U.S. Pat. Nos. 1,275,975; 1,290,476; 2,777,772; 2,923,633; 2,962,390; 3,111,570; 3,244,541; and 3,303,049. In the aforesaid U.S. Pat. Nos. 3,1 1 1,570 and 1,275,975, there are disclosed optical instruments with heating means for removing water from the external portion of the optical system upon removal of the optical instrument from a water environment. For example, U.S. Pat. No. 1,275,975 describes heating coils in heating relationship to the optical elements of a periscope to prevent condensation of moisture on the optical elements. On the other hand U.S. Pat. No. 3,] 11,570 describes a laminated glass structure in which a series of thin wire electrically conductive elements are located between the glass laminations. U.S. Pat. Nos. 2,777,772; 2,923,633; 3,303,049; and 3,244,541 describe water-repellant compositions formed of organic compounds. For example, U.S. Pat. No. 2,777,772 describes a polysilicone composition in admixture with an adhesion-promoting agent such as carbon black and rouge; U.S. Pat. No. 3,244,541 describes a water-repellant film forming composition of an acid in alkylalkoxy silanes; U.S. Pat. No. 2,777,772 describes a substituted polysilicane composition; and U.S. Pat. No. 2,962,390 describes a non-wettable film composition of a clear non-wettable film of a hydrocarbon wax, a polyamide resin and a long-chain aliphalic amide. It is apparent then that maintenance of clear vision through optical windows which have been subjected to water, moisture, or a water spray has been a problem for a long time. Visibility is greatly impaired by the retention of water on an optical surface such as Windshields of automobiles, locomotives, boats, planes and lenses and reflectors of periscopes, binoculors and similar optical equipment. The various coating and methods for their application above mentioned have had disadvantages of one type or another arising from the severe requirements imposed on them. The important requirements for such surfaces are that they be nonwettab1e; durable, including abrasion resistant;

transparent in the visible region; have a homogeneous index ofrefraction; be capable of being worked to an optical surface; and remain optically clear and substantially inert under severe environmental conditions.

Thus it is desirable to provide an optical surface which fullfills these requirements.

It is also desirable to provide an optical surface which fullfills the requirements and which may be easily applied to various transparent or reflective substrates and other optical surfaces.

Other desirable features will in part be obvious and will in part appear hereinafter.

SUMMARY OF THE INVENTION It has now been unexpectedly found that the above-mentioned requirements are met and that markedly improved water-repellant characteristics are achieved when a nonwettable surface is formed from a layer of a refractory metal oxide. Therefore the present invention comprises a transparent non-wettable surface which is formed from a layer of a refractory metal oxide used in combination with a transparent substrate to form an optically transparent non-wettable laminate.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and features of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein like reference characters refer to like element and wherein:

FIG. 1 is a diagrammatic schematic cross sectional view of an embodiment of the present invention.

FIG. 2 is a diagrammatic schematic cross sectional view of an alternate embodiment of the present invention.

FIG. 3 is a modified form of FlG.2 embodying the invention.

FIG. 4 is a diagrammatic schematic cross sectional view of an optical reflector prepared in accordance with teachings of the present invention. 1

FIG. 5 is a fragmentary diagrammatic schematic cross sectional view of an embodiment of the present invention as applied to a periscope.

The invention may be made by forming the non-wettable surface from a layer of a refractory metal oxide. Where the optical surface is to subject to abrasion of various kinds, it is preferable that the refractory metal oxide have a hardness in excess of 7 as determined by the Moh scale of hardness or in excess of 820 as determinedby the Knoop scale of hardness. While it is desirable that the refractory oxide be substantially completely free of impurities, freedom from impurities is not essential. The main requirement is that the impurities be sufficiently low so as not to affect the optical properties. Thus, sapphire, either natural or synthetic, has been found especially useful for this invention.

Exemplary of the refractory metal oxides suitable for carrying out of the present invention are the oxides of Aluminum, Titanium, Zirconium, Chromium, Tantalum, Noibium, Vanadium, Molybdenum, Hafnium and mixtures thereof.

In a preferred embodiment of the present invention, the refractory metal oxide layer is formed of aluminum oxide. The aluminum oxide layer can be prepared by the techniques described in U.S. Pat. No. 1,004,505 granted to Verneuil, Sept. 26, 19 11. Other techniques for forming the refractory metal oxide layer include the vacuum vapor deposition of the metal oxides onto a heated substrate or sputtering by the ion beam or radio frequency techniques which are all well known in the art.

In cases where the refractory metal oxide layer is crystalline, it is especially preferred, although not required, to have a single crystal layer. This eliminates the boundaries between individual crystals in polycrystalline layers at which water droplets can form.

In accordance with the present invention reference being bad to FIG. 1 of the drawing there is illustrated at 2 an optical window formed completely of a refractory metal oxide and having optically polished

surfaces

4 and 6.

Referring now to FIG. 2 there is illustrated an alternate embodiment of the present invention comprising a transparent substrate 8 and an outer surface or layer of a refractory metal oxide 10 secured to said substrate 8 by a transparent optical cement 12. In this embodiment of the invention the substrate 8 can be formed of a solid material such as glass or various plastics. The optical cement can be formed from the combination of an epoxy resin and a suitable hardener. An example of one such suitable combination is the liquid epoxy resin sold under the trade name Epikote 815 and the polyamide hardener known in the trade as No. 951". Other commercially available optical cements are the methacrylate cements. The main requirements of the cement being that it be optically clear over the range of wave lengths of light to be transmitted, should not appreciably reduce the light transmitted therethrough, have a compatible refractive index, and be substantially stable to changes in environment.

The laminate structure illustrated in FIG. 2 thus provides the advantages of a non-wettable surface having hardness and chemical stability-together with the strength and economy of a glass or plastic substrate.

In FIG. 3 there is shown a modified form of the embodiment of the invention illustrated in FIG. 2. In this embodiment of the invention the transparent substrate 8 is sandwiched between the refractory metal oxide layer 10 bonded to substrate 8 by the optical cement 12 and refractory oxide layer 16 bonded to substrate 8 by optical cement 14. This embodiment of the invention, in addition to providing the advantages mentioned above with respect to the embodiment of the invention illustrated in FIG. 2, is particularly useful in applications where the optical window may not only be subject to contact with water or rain on its outer surface but to humidity conditions by the condensing of moisture on its inner surface which results in fogging. I

Referring now to FIG. 4 there is illustrated an embodiment of the present invention as applied to optical reflectors. In this embodiment, a substrate 18 having a reflecting surface 20 has bonded thereto an aluminum oxide layer 10 by an optical cement 12.

A particular application of the teachings of the present invention to optical instruments is illustrated in FIG. 5 wherein 22 represents the housing of a periscope tube having an optical window, indicated generally by the numeral 24, and a reflector indicated generally by the numeral 26, employed therewith for reflecting downward through the tube 28 of the periscope. Preferably the optical window 24 is constructed in accordance with the embodiment of the invention disclosed with respect to FIG. 3. The reflector 26 is preferably constructed in accordance with the embodiment of the present invention disclosed with respect to FIG. 4.

The invention will now be described by way of thefollowing examples.

EXAMPLE 1'- In this example, an optical window formed of a single crystal of aluminum oxide optically polished to a flat surface on each side and having a diameter of 1 inch and a thickness of 0.1 inch was employed. The window was placed adjacent to an aperture in a wall and a camera was placed on one side of the window. A scene to be photographed was placed at a point distant from the opposite side of the window. The side of the window adjacent the scene was immersed in a salt water solution. The saltwater solution was then drained away from the window and simultaneously the camera was operated to photograph the scene through the window. The time required for the window to shed the salt water solution and provide a picture of the scene comparable to a picture of the scene when the window was dry was measured. This procedure was repeated. The average time required to shed the salt water was 1 second and did not exceed 2 seconds.

EXAMPLE 2 This example was similar to Example I in all respects except that the window was formed of fused quartz and was optically polished to a flat surface on each side. In this example the fused quartz window retained a thin film of water in addition to drops on the optical surface in contact with the salt water. Additionally the salt water which was shed required in excess of 4 seconds.

EXAMPLE 3 In this example the windows of Examples 1 and 2 were subjected to the tilting plate method of determining non-wettability. This method is well known to those skilled in the art and need not be described in detail. As briefly stated, the method comprises partially immersing the window in a fluid such as water and then rotating the window around its horizontal axis until the fluid surface at the point of contact exhibits no miniscus. The contact angle, which is the an le between the surface of the wmdow and the undisturbed uid surface, IS

EXAMPLE 4 An aluminum oxide layer was sputtered onto the surface of a borosilicate crown glass (517645) disc 2 inches in diameter and '18 inch thick. Sputtering was accomplished in an ion beam sputtering chamber operated at 10' Torr and 40 C. A beam of argon and oxygen was directed against the target. The ionization potential applied was 50 KeV. A target of a-aluminum oxide was used and the substrate disc was positioned approximately 1 foot from the target. Both the target and substrate disc were water cooled. A plasma neutralizer was introduced into the chamber at a point near the target to neutralize charges on the target surface.

Specimens having aluminum oxide layers of I70, 340, 510, and l,000 millimicrons were produced. Each of these specimens was submerged in water, and upon removal, no water was visible on the aluminum oxide surface. This indicates that the aluminum oxide layers deposited by sputtering were non-wettable.

. What is claimed is: I

1. An optical laminate structure consisting of a transparent substrate and an abrasion-resistant, non-wettable layer of an oxide of a refractory metal bonded to the substrate, said refractory metal being selected from the group consisting of aluminum, titanium, zirconium, chromium, tantalum, niobium, vanadium, molybdenum, hafnium and mixtures thereof, said non-wettable layer also having substantial transparency to visible radiation, a substantially homogeneous index of refraction, and a hardness in excess of seven on the Moh scale.

2. An optical laminate structure of claim I wherein said refractory metal oxide comprises aluminum oxide.

3. An optical laminate structure of claim 2 wherein said refractory metal oxide comprises sapphire.

4. An optical laminate structure consisting of a transparent substrate, a first transparent layer of an abrasion-resistant, non-wettable material bonded to one side of said substrate, a second transparent layer of an abrasion-resistant, non-wettable material bonded to the other side of said substrate, said transparent layers being formed from oxides of refractory metals individually selected from the group consisting of aluminum, titanium, zirconium, chromium, tantalum, niobium, vanadium, molybdenum, hafnium and mixtures thereof, and said layers having a substantially homogeneous index of refraction and a hardness in excess of seven on the Moh scale.

, 5. In an optical instrument containing an optical system of several elements including an outer optical window, the improvement which consists of having an outer optical window formed from a transparent, abrasion-resistant, non-wettable layer of an oxide of a refractory metal selected from the group consisting of aluminum, titanium, zirconium, chromium, tantalum, niobium, vanadium, molybdenum, hafnium and mixtures thereof, and said layer having a substantially homogeneous index of refraction and a hardness in excess of seven on the Moh scale.

6. A laminate structure consisting of a substrate having a reflective surface and a transparent layer of an abrasion-resistant, non-wettable material bonded to said surface, said transparent layer being formed from an oxide of a refractory metal selected from the group consisting of aluminum, titanium, zirconium, chromium, tantalum, niobium, vanadium, molybdenum, hafnium and mixtures thereof, and said layer having a substantially homogeneous index of refraction and a hardness in excess of seven on the Moh scale.

Claims

2. An optical laminate structure of claim 1 wherein said refractory metal oxide comprises aluminum oxide.
3. An optical laminate structure of claim 2 wherein said refractory metal oxide comprises sapphire.
4. An optical laminate structure consisting of a transparent substrate, a first transparent layer of an abrasion-resistant, non-wettable material bonded to one side of said substrate, a second transparent layer of an abrasion-resistant, non-wettable material bonded to the other side of said substrate, said transparent layers being formed from oxides of refractory metals individually selected from the group consisting of aluminum, titanium, zirconium, chromium, tantalum, niobium, vanadium, molybdenum, hafnium and mixtures thereof, and said layers having a substantially homogeneous index of refraction and a hardness in excess of seven on the Moh scale.
5. In an optical instrument containing an optical system of several elements including an outEr optical window, the improvement which consists of having an outer optical window formed from a transparent, abrasion-resistant, non-wettable layer of an oxide of a refractory metal selected from the group consisting of aluminum, titanium, zirconium, chromium, tantalum, niobium, vanadium, molybdenum, hafnium and mixtures thereof, and said layer having a substantially homogeneous index of refraction and a hardness in excess of seven on the Moh scale.
6. A laminate structure consisting of a substrate having a reflective surface and a transparent layer of an abrasion-resistant, non-wettable material bonded to said surface, said transparent layer being formed from an oxide of a refractory metal selected from the group consisting of aluminum, titanium, zirconium, chromium, tantalum, niobium, vanadium, molybdenum, hafnium and mixtures thereof, and said layer having a substantially homogeneous index of refraction and a hardness in excess of seven on the Moh scale.