Optical element having a water repellant coating constructed...

Details Optical element having a water repellant coating constructed... Optical element having a water repellant coating constructed...

2001-02-05

2002-05-07

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Physical dimension specified

C359S582000, C359S586000

Reexamination Certificate

active

06383629

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 89116427, filed Aug. 15, 2000.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an optically coated element. More particularly, the present invention relates to an optical element having a water repellant coating constructed from a composite material of CaF
2
and TiO
2
.
2. Description of Related Art
Most optical-electrical/optical coated elements have a plurality of organic or inorganic coatings on an organic (for example, acrylic resin, epoxy resin, polymer resin or polycarbonate resin) or inorganic (for example, ceramic, glass or metal) substrate to attain a specified optoelectronic/optical property. In some situations, the optically coated element needs to be water repellant with suitable hardness and environmental stability aside from the specified optoelectronic/optical property. To be water repellant, the optical element is usually coated with a Teflon material such as polytetrafluoroethylene, PTFE, [—CF
2
—CF
2
]
n
or polychlorotrifluoroethylene PCTFE, [—CF
2
—CFCl—]
n
(refer to U.S. Pat. No. 4,869,922 by R D'Agositno et al, titled “Method of Coating with Polyfluorocarbons”, U.S. Pat. No. 4,410,563 by H. P. Richter and E. J. Dibble, titled “Repellant Coatings for Optical Surface’, and an article written by J. R. Hollahan et. al, titled “Combination Moisture Resistant and Antireflection Plasma Polymerized thin Films for Optical Coatings” in Applied Opt. 13, 1844-1849 (1974)). When a drop of water is dropped onto a polytetrafluoroethylene or polychlorotrifluoroethylene coated surface, the water droplet forms a high contact angle of 109°. By comparison, the same drop of water on a cleaned glass surface, magnesium fluoride (MgF
2
) and indium-tin oxide (ITO), the contact angles are 15°, 28.5° and 37.2° respectively. A Teflon coating has a low refractive index (n=1.46, &lgr;=500 nm) besides water repellant (refer to the article by Z. Seres et al, titled “Optical Transmission of Mylar and Teflon Films”, in Opt. Eng. 33, 3031‥3032 (1994)). Hence, a Teflon coating is often formed on an optical element to serve as a single anti-reflection layer (refer to the article by J. R. Hollahan et al, titled “Combination Moisture Resistant and Antireflection Plasma Polymerized Thin Films for Optical Coatings, in Applied Opt. 13, 1844-1849 (1974)). However, because Teflon material will absorb light in the upper visible (that is, lower than 500 nm), the ultraviolet (refer to the article by Z. Seres et. al, titled “Optical Transmission of Mylar and Teflon Films”, in Opt. Eng. 33, 3031-3032 (1994)) and in the infrared region between 6 &mgr;m to 8 &mgr;m (refer to the article by J. R. Hollahan et al, titled “Combination Moisture Resistant and Antireflection Plasma Polymerized Thin Films for Optical Coatings, in Applied Opt. 13, 1844-1849 (1974)), the use of Teflon coating for transmitting light within these regions is restricted. On the other hand, most optical coatings on an optical element consist of a stack of alternately deposited high and low refractive index layers in order to obtain a specified optical function (refer to the article by H. A. Macleod, titled “Thin-Film Optical Filters” in 2
nd
ed., Adam Hilger Ltd., 1986). However, organic optical coating layer having a high refractive index is quite rare. Therefore, it is difficult to make a fully organic multilayer optical coating. Hence, the use of Teflon as an optical coating material is further limited. Consequently, finding a water repellant inorganic coating material that has suitable hardness and environmental stability to replace Teflon is an important preoccupation in the optical coating industry.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide an optical element having a water repellant composite layer composed of the materials CaF
2
and TiO
2
. The optical element includes a substrate and a composite layer formed from a material having a chemical formula (100-X)CaF
2
—(X)TiO
2
. The composite layer is formed over the substrate, where X is the molar percentage of TiO
2
.
A second object of the invention is to provide an optical element having a water repellant surface layer formed from a composite material including CaF
2
and TiO
2
. The optical element includes a substrate, at least one optical coating and a composite surface layer having a chemical formula (100-X)CaF
2
—(X)TiO
2
. The optical coating and the composite surface layer are separately formed over the substrate. The X on the chemical formula (100-X)CaF
2
—(X)TiO
2
of the composite surface layer represents the molar percentage of TiO
2
. The optical coating can be a composite layer having a chemical formula of (100-Y)CaF
2
—(Y)TiO
2
, where Y on the chemical formula (100-Y)CaF
2
—(Y)TiO
2
represents the molar percentage of TiO
2
and X≠Y.
The addition of some TiO
2
material into a CaF
2
film on the substrate to form the (100-X)CaF
2
—(X)TiO
2
composite surface layer helps to increase surface smoothness, adhesion and hardness of the composite layer without causing any change to water repellant capability. The (100-X)CaF
2
—(X)TiO
2
composite layer has superior water-resistant property. Ranging from a TiO
2
content X of 2% to 100%, the layer has a contact angle of over 100° for water drop comparable to that of Teflon. The refractive index of the composite layer varies according to its composition. In general, the refractive index is between 1.23 (for 2% TiO
2
) and 2.3 (for pure TiO
2
) for light having a wavelength of 600 nm. Beside having a superior water resistance property, the composite layer can be coated on the surface of an optoelectronic/optical element to increase transparency to light (or anti-reflection) or forming other optical film with specified requirement.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.


REFERENCES:
patent: 3895155 (1975-07-01), Shukuri et al.
patent: 4410563 (1983-10-01), Richter
patent: 4450201 (1984-05-01), Brill et al.
patent: 4869922 (1989-09-01), D'Agostino
patent: 5208101 (1993-05-01), Boulos et al.
patent: 5688608 (1997-11-01), Tsai et al.
patent: 5808715 (1998-09-01), Tsai et al.
patent: 6066401 (2000-05-01), Stilburn
“Optical Transmission of Mylar and Teflon Films”, By Zoltan Seres Et Al Optical Engineering/Sep. 1994/ vol. 33 No. 9/ pp. 3031-3033.
“Combination Moisture Resistant and Antireflection Plasma Polymerized Thin Films For Optical Coatings” By Jjohn R. Hollahan Et Al. Applied Optics / vol. 13, No. 8 / Aug. 1974 / p. 1844-1849.

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