Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-08-09
2001-10-30
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S432000, C428S697000, C428S213000, C428S334000
Reexamination Certificate
active
06309753
ABSTRACT:
TECHNICAL FIELD
This invention relates to a glass substrate having a coating thereon. The coating strongly absorbs ultraviolet radiation. In one embodiment, the glasses also absorb ultraviolet radiation.
BACKGROUND OF THE INVENTION
When optical systems use high power lamp light sources, there can be a significant radiative proportion of the light emitting in the ultraviolet region. When organic materials are in the light path, there will be a degradation of this material over time. Ultraviolet radiation also causes degradation and discoloration in such items as paints, fabrics and plastics. Specifically, electromagnetic energy in the ultraviolet spectrum (i.e., between ~100 and ~400 nanometers), causes paints and dyes to fade, causes rubber to crack, and plastics to crumble with time. Therefore, strong ultraviolet absorption by architectural glazing materials is beneficial.
The sun is not the only light source that emits ultraviolet radiation. Various artificial lighting sources like Hg or Xe ARC and other discharge lamps emit ultraviolet radiation. Ultraviolet absorbing glasses can be used that block the entire range of the ultraviolet emission of these sources. However, as a result of the absorption, with prolonged usage, many glasses tend to solarize or darken with time, especially from the absorption of the shorter wavelength, higher energy portion of the ultraviolet region.
Ultraviolet absorbing glass trademarked Pyrex-UV-Plus™ (available from Corning Incorporated), has applications such as fiber optic distributed lighting, Liquid Crystal Projection and other projection technologies. These lighting or projection systems use high intensity discharge light sources which contain radiated output in the ultraviolet spectrum. The Pyrex-UV-Plus™ glass has a very sharp band edge near 400 nm (ultraviolet—visible boundary) which is useful in protecting organic components that degrade under ultraviolet fluence, while providing maximum visible radiation transparency throughout the visible part of the spectrum (400-760 mm). However, some customer and internal testing has shown that certain metal halide lamps which have output in the range of 250-280 nm can cause the absorbing Pyrex-UV-Plus™ glass to photodarken in the visible spectrum. Using glass pre-filters that have cutoffs ≧280 nm can prevent the photodarkening of the Pyrex-UV-Plus™ glass. However, adding two more glass surfaces would reduce the visible transmission. Most of the Pyrex-UV-Plus™ glass applications in fact use anti-reflection coatings applied to the glass surfaces to improve the visible lumen output.
Co-assigned U.S. Pat. No. 5,925,468, by Stewart, titled Solarization Resistant and UV Blocking Glass, filed Apr. 1, 1997, and herein incorporated by reference discloses ultraviolet-absorbing glass combined with a solarization resistant glass article to provide a substantially complete UV spectral blocking filter.
While these glasses provide a substantial improvement in ultraviolet absorbing glasses, there continues to be a need for improved systems. Accordingly, it is the object of the present invention to provide an improved UV-blocking glass.
SUMMARY OF THE INVENTION
We have found that the object of the invention can be attained by use of certain antireflective, hot mirror or heat rejection coatings which absorb radiation when applied to a glass surface. Briefly, the invention relates to a glass substrate having a multilayer coating thereon. The coating absorbs ultraviolet radiation at wavelengths ranging from ~230 to ~300 nm while providing high transmission throughout a region of visible wavelengths. Preferably, the coating consists essentially of three layers, wherein the first layer adjacent the substrate is a mixture of SiO
2
and TiO
2
, the second layer is TiO
2
and the third layer farthest from the substrate is SiO
2
. The coatings are preferably applied by a sol-gel dip method. Titania is an ultraviolet radiation absorber which absorbs photodarkening wavelengths to offer protection for the Pyrex-UV-Plus™ glass and other UV-absorbing glasses.
We ran solarization tests on coated and uncoated glasses using a 1000 watt Hg-Xe lamp, and compared transmission at 500 nm before and after several hours of exposure. A sample with a three-layer sol-gel dip coating consisting of TiO
2
and SiO
2
was tested along with another that had a deposited MgF
2
anti-reflection coating thereon, both versus a non-coated Pyrex-UV-Plus™ glass.
The data indicates that the TiO
2
containing coating absorbed the ultraviolet radiation to lessen the photodarkening by a factor of 10 (using the loss of transmission at 500 nm). Other embodiments of the coating which should improve the photodarkening resistance of the glass may be made by inclusion of other ultraviolet absorbers such as ZnO, CeO
2
, VO
2
, Ta
2
O
5
or Nb
2
O
5
.
BEST MODE OF CARRYING OUT INVENTION
A preferred embodiment of this invention is a glass substrate having a multilayer coating thereon wherein the coating absorbs ultraviolet radiation at wavelengths ranging from ~230 to ~300 nm while providing high transmission throughout a region of visible wavelengths. The coating consists essentially of three layers, wherein the first layer adjacent the substrate is a mixture of SiO
2
and TiO
2
, the second layer is a TiO
2
rich mixed layer, and the third layer farthest from the substrate is SiO
2
. The first layer of the coating consists essentially of 25 to 75 weight percent SiO
2
and 25 to 75 weight percent TiO
2
. In a more preferred embodiment, the first layer of the coating consists essentially of 50 weight percent SiO
2
and 50 weight percent TiO
2
. The first layer may also be essentially pure SiO
2
or essentially pure TiO
2
. Although the preffered method of coating application is by sol-gel dip method, other methods such as PVD or CVD may also be employed.
The layers of the coating have a sufficient thickness to absorb ultraviolet radiation at wavelengths ranging from ~230 to ~300 nm while providing high transmission throughout a region of visible wavelengths. Generally, the coating has a thickness ranging from 1500 to 3500 Angstroms. Generally, the first layer has a thickness ranging from 300 to 1200 Angstroms, the second layer has a thickness ranging from 300 to 1200 Angstroms, and the third layer has a thickness ranging from 300 to 1200 Angstroms.
Generally, the glass substrate is capable of absorbing ultraviolet radiation at wavelengths in the 4-400 nm region, while providing high transmission throughout the visible region. More specifically, this glass transmits wavelengths in the visible and near infra red regions, while absorbing UV wavelengths in the 4 to 400 nm region. A particularly useful example of such ultraviolet blocking glass is the non-photochromic (no photodarkening under solar air mass on exposure) R
2
O—B
2
O
3
—SiO
2
glass of U.S. Pat. No. 5,322,819 (herein incorporated by reference), which contains a precipitated cuprous or cuprous-cadmium halide crystal phase and has a sharp spectral cutoff at about 400 nm. The '819 glass composition consists essentially of, in cation percent, 35-73% SiO
2
, 15-45% B
2
O
3
, 0-12% Al
2
O
3
, the Al
2
O
3
being less than 10% when the SiO
2
is over 55%, 0-12% Li
2
O, 0-20%, Na
2
O, 0-12% K
2
O, the Li
2
O+Na
2
O+K
2
O being 4.75-20%, 0-5% CaO+BaO+SrO, 0.125-1.0% Cu
2
O, 0-1% CdO, 0-5% ZrO
2
, 0-0.75% SnO
2
, 0-1% As
2
O
3
, and/or Sb
2
O
3
, the glass containing 0-1.25% Cl, 0-1.0% Br, 0.25-2.0% Cl+Br, and 0-2% F by weight, and having an R-value, calculated in mole percent, of about 0.15-0.45, the R-value not exceeding 0.30, except as the glass composition meets at least one condition selected from the group: up to 12 cation % Li
2
O, less than 10 cation % Al
2
O
3
, at least 0.3 cation % Cu
2
O and 0.50-2.0 wgt. % Cl+Br where
R
=
M
2
O
+
2
MO
-
Al
2
O
2
B
2
O
3
where
the
glass
oxide
values
are
in
cation
%
.
where the g
Grossman David G.
Stewart Ronald L.
Corning Incorporated
Gheorghiu Anca C.
Jones Deborah
Kung Vincent T.
Stein Stephen
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