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06/09/2011
BUSHNEL Patent
06/09/2011
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United States Patent |
6,542,302 |
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Cross |
April 1, 2003 |
Lens coating to reduce external fogging of scope lenses
Abstract
A coated lens for use in a riflescope, telescope, spotting scope, binoculars, or the like is provided. The coating on the lens comprises two layers, an anti-reflective layer adjacent the lens and a hydrophobic layer disposed on the anti-reflective layer. The hydrophobic layer preferably includes an organosilane compound. Advantageously, the coating does not significantly reduce light transmission through the lens.
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Inventors: |
Cross; John W. (Overland Park, KS) |
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Assignee: |
Bushnell Corporation (Overland Park, KS) |
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Appl. No.: |
961750 |
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Filed: |
September 24, 2001 |
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Current U.S. Class: |
359/581;
359/507; 359/582 |
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Intern'l Class: |
G02B 001/10 |
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Field of Search: |
359/581,582,507,407,399
33/507 351/163 |
References Cited [Referenced By]
U.S. Patent Documents
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Aug., 1956 |
Auwarter |
351/163. |
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Feb., 1977 |
French et al. |
351/163. |
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Dec., 1977 |
Laurin |
351/166. |
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Jun., 1983 |
Tani |
350/164. |
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Oct., 1985 |
Burzynski et al. |
106/287. |
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Feb., 1988 |
Kimura et al. |
350/164. |
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Aug., 1988 |
Taniguchi |
351/163. |
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Nov., 1988 |
Akatsuka et al. |
350/166. |
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Jan., 1992 |
Singh. |
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Apr., 1992 |
Loving |
42/119. |
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Apr., 1993 |
Singh. |
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Jun., 1993 |
Singh. |
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Feb., 1995 |
Wilson |
359/422. |
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Dec., 1995 |
Floch |
427/164. |
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Jun., 1998 |
Singh. |
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Apr., 1999 |
Singh. |
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Jun., 1999 |
Parker et al. |
351/163. |
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Nov., 2000 |
Singh. |
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Jan., 2001 |
Singh. |
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Jan., 2001 |
Belleville et al. |
427/162. |
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Mar., 2001 |
Singh. |
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Other References
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Primary Examiner: Phan; James
Assistant Examiner: Pritchett; Joshua
Attorney, Agent or Firm: Hovey Williams LLP
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part of application, Ser. No. 09/451,787,
filed Dec. 1, 1999, now abandoned.
Claims
What is claimed is:
1. A lens coating for a lens presenting a front face and a back face, said
coating comprising:
an anti-reflective layer on the front face of the lens; and
a hydrophobic layer on said anti-reflective layer, said coating permitting at
least 99% light transmission through the lens, said coating further retaining
at least 95% of a hydrophobic characteristic after an abrasion test comprising
the steps of rubbing an eraser for at least 20 strokes along the same line
using 2.5 pounds of pressure on the eraser, said hydrophobic characteristic
being selected from the group consisting of contact angles and stain removal
using adhesive tape.
2. The lens coating of claim 1, said anti-reflective layer being located
between the lens and said hydrophobic layer.
3. The lens coating of claim 1, said anti-reflective layer comprising a
plurality of sublayers, each of said sublayers comprising an anti-reflective
composition.
4. The lens coating of claim 3, said composition of each of said plurality of
sublayers being individually and respectively selected from the group
consisting of Al2O3, ZrO3, MgF2, SiO2, cryolite, LiF, ThF4, CeF3, PbF2, ZnS,
ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3, SiO, HfO2, ZrO2, CeO2, Nb2O5, Ta2O5
and TiO2.
5. The lens coating of claim 1, said hydrophobic layer being bonded to said
anti-reflective layer such that none of the hydrophobic layer is removed during
an adhesive tape test performed according to a test selected from the group
consisting of MIL-C-675C, MIL-F-48616, MIL-M-13508, and combinations thereof.
6. The lens coating of claim 1, said anti-reflective layer composition being
selected from the group consisting of Al2O3; ZrO3, MgF2, SiO2, cryolite, LiF,
ThF4, CeF3, PbF2, ZnS, ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3, SiO, HfO2,
ZrO2, CeO2, Nb2O5, Ta2O5 and TiO2.
7. The lens coating of claim 1, said hydrophobic layer comprising an
organosilane compound.
8. The lens coating of claim 1, said coating retaining at least 97% of said
hydrophobic characteristic.
9. The lens coating of claim 8, said coating retaining at least 98.5% of said
hydrophobic charateristic.
10. The lens coating of claim 9, said coating retaining at least 99.5% of said
hydrophobic characteristic.
11. The lens coating of claim 1, said coating further comprising said
anti-reflective layer and said hydrophobic layer being disposed on the back
face of said lens.
12. A lens coating for a lens presenting a front face and a back face, said
coating comprising:
an anti-reflective layer on the front face of the lens; and
a hydrophobic coating on said anti-reflective layer, said lens coating
retaining at least 95% of a hydrophobic characteristic after being rubbed by an
eraser under 2.5 pounds of pressure for 20 strokes along the same line, said
hydrophobic characteristic being selected from the group consisting of contact
angles and stain removal using adhesive tape.
13. The lens coating of claim 12, said anti-reflective layer being located
between the lens and said hydrophobic layer.
14. The lens coating of claim 12, said anti-reflective layer comprising a
plurality of sublayers, each of said sublayers comprising an anti-reflective
composition.
15. The lens coating of claim 12, said hydrophobic layer being bonded to said
anti-reflective layer such that none of the hydrophobic layer is removed during
an adhesive tape test performed according to a test selected from the group
consisting of MIL-C-675C, MIL-F-48616, MIL-M-13508, and combinations thereof.
16. The lens coating of claim 12, said composition of said anti-reflective
layer being selected from the group consisting of Al2O3, ZrO3, MgF2, SiO2,
cryolite, LiF, ThF4, CeF3, PbF2, ZnS, ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3,
SiO, HfO2, ZrO2, CeO2, Nb2O5, Ta2O5 and TiO2.
17. The lens coating of claim 14, said composition of each of said plurality of
sublayers being individually and respectively selected from the group
consisting of Al2O3, ZrO3, MgF2, SiO2, cryolite, LiF, ThF4, CeF3, PbF2, ZnS,
ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3, SiO, HfO2, ZrO2, CeO2, Nb2O5, Ta2O5
and TiO2.
18. The lens coating of claim 12, said hydrophobic layer comprising an organosilane
compound.
19. The lens coating of claim 18, said organosilane compound comprising
PERMASEAL.
20. The lens coating of claim 12, said coating retaining at least 97% of said
hydrophobic characteristic.
21. The lens coating of claim 20, said coating retaining at least 98.5% of said
hydrophobic characteristic.
22. The lens coating of claim 21, said coating retaining at least 99.5% of said
hydrophobic characteristic.
23. The lens coating of claim 12, said coating further comprising said anti-reflective
layer and said hydrophobic layer being disposed on the back face of said lens.
24. A lens presenting a front face and an opposed back face and said lens
comprising:
an anti-reflective layer disposed on at least one of said front face and said
back face; and
a hydrophobic layer disposed on said anti-reflective layer, said coating
retaining at least 95% of a hydrophobic characteristic after an abrasion test
comprising the steps of rubbing an eraser for at least 20 strokes along the
same line using 2.5 pounds of pressure on the eraser, said hydrophobic
characteristic being selected from the group consisting of contact angles and
stain removal using adhesive tape.
25. The lens of claim 24, said anti-reflective layer disposed on said front
face and said back face.
26. The lens of claims 25, said hydrophobic layer only being disposed on the
anti-reflective layer on said lens front face.
27. The lens of claim 24, said hydrophobic layer comprising an organosilane
compound.
28. The lens of claim 24, said lens permitting at least 99% light transmission
therethrough.
29. The lens of claim 28, said light transmission being at least 99.5%.
30. The lens of claim 24, said anti-reflective layer being located between the
lens and said hydrophobic layer.
31. The lens of claim 24, said anti-reflective layer comprising a plurality of
sublayers, each of said sublayers comprising an anti-reflective composition.
32. The lens of claim 31, the composition of each of said plurality of
sublayers being individually and respectively selected from the group
consisting of Al2O3, ZrO3, MgF2, SiO2, cryolite, LiF, ThF4, CeF3, PbF2, ZnS,
ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3, SiO, HfO2, ZrO2, CeO2, Nb2O5, Ta2O5
and TiO2.
33. The lens of claim 24, said hydrophobic layer being bonded to said
anti-reflective layer such that none of the hydrophobic layer is removed during
an adhesive tape test performed according to a test selected from the group
consisting of MIL-C-675C, MIL-F-48616, MIL-M-13508, and combinations thereof.
34. The lens of claim 24, said anti-reflective layer comprising a composition
being selected from the group consisting of Al2O3, ZrO3, MgF2, SiO2, cryolite,
LiF, ThF4, CeF3, PbF2, ZnS, ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3, SiO,
HfO2, ZrO2, CeO2, Nb2O5, Ta2O5 and TiO2.
35. The lens of claim 24, said coating retaining at least 97% of said
hydrophobic characteristic.
36. The lens of claim 35, said coating retaining at least 98.5% of said
hydrophobic charateristic.
37. The lens of claim 36, said coating retaining at least 99.5% of said
hydrophobic characteristic.
38. A scope presenting a first end and an opposed second end, said scope
comprising:
a first lens, said first lens being located adjacent said first end of said
scope and presenting a first face and an opposed second face with at least one
of said first and said second faces having a coating, said coating comprising
an anti-reflective layer disposed on said face and a hydrophobic layer disposed
on said anti-reflective layer wherein said coating permits at least 99% of the
light entering said lens second face to be transmitted through said lens first
face; and
a plurality of lenses located between said first lens and said second end of
said scope, each of said plurality of lenses presenting a first lens surface
and an opposed second lens surface, with certain of said lens surfaces
containing an anti-reflective layer disposed thereon, said coating retaining at
least 95% of a hydrophobic characteristic after an abrasion test comprising the
steps of rubbing an eraser for at least 20 strokes along the same line using
2.5 pounds of pressure on the eraser, said hydrophobic characteristic being
selected from the group consisting of contact angles and stain removal using
adhesive tape.
39. The scope of claim 38, said scope permitting at least 95% of the light
entering said scope second end to be transmitted through said plurality of
lenses and exit said scope through said first lens.
40. The scope of claim 38, said plurality of lenses being between 3 and 6.
41. The scope of claim 38, each of said plurality of lenses including an
anti-reflective layer on each of said first and second lens surfaces.
42. The scope of claim 38, said anti-reflective layer being
located between said first lens and said hydrophobic layer.
43. The scope of claim 38, said anti-reflective layer comprising a plurality of
sublayers, each of said sublayers comprising an anti-reflective composition.
44. The scope of claim 43, each of said plurality of sublayers being
individually and respectively selected from the group consisting of Al2O3,
ZrO3, MgF2, SiO2, cryolite, LiF, ThF4, CeF3, PbF2, ZnS, ZnSe, Si, Ge, Te, PbTe,
MgO, Y2O3, Sc2O3, SiO, HfO2, ZrO2, CeO2, Nb2O5, Ta2O5 and TiO2.
45. The scope of claim 38, said hydrophobic layer being bonded to said
anti-reflective layer such that none of the hydrophobic layer is removed during
an adhesive tape test performed according to a test selected from the group
consisting of MIL-C-675C, MIL-F-48616, MIL-M-13508, and combinations thereof.
46. The scope of claim 38, said anti-reflective layer being selected from the
group consisting of Al2O3, ZrO3, MgF2, SiO2, cryolite, LiF, ThF4, CeF3, PbF2,
ZnS, ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3, SiO, HfO2, ZrO2, CeO2, Nb2O5,
Ta2O5 and TiO2.
47. The scope of claim 38, said hydrophobic layer comprising an organosilane
compound.
48. The scope of claim 38, said coating retaining at least 97% of said
hydrophobic characteristic.
49. The scope of claim 48, said coating retaining at least 98.5% of said
hydrophobic charateristic.
50. The scope of claim 49, said coating retaining at least 99.5% of said
hydrophobic characteristic.
51. The scope of claim 38, said scope being selected from the group consisting
of riflescopes, binoculars, telescopes, and spotting scopes.
52. A lens coating for a glass telescope or glass riflescope lens presenting a
front face and a back face, said coating comprising:
an anti-reflective layer on the front face of the glass lens; and
a hydrophobic coating on said anti-reflective layer, said lens coating
retaining at least 95% of a hydrophobic characteristic after being rubbed by an
eraser under 2.5 pounds of pressure for 20 strokes along the same line, said
hydrophobic characteristic being selected from the group consisting of contact
angles and stain removal using adhesive tape.
53. The lens coating of claim 52, said anti-reflective layer being located
between the lens and said hydrophobic layer.
54. The lens coating of claim 52, said anti-reflective layer comprising a
plurality of sublayers, each of said sublayers comprising an anti-reflective
composition.
55. The lens coating of claim 54, said composition of each of said plurality of
sublayers being individually and respectively selected from the group
consisting of Al2O3, ZrO3, MgF2, SiO2, cryolite, LiF, ThF4, CeF3, PbF2, ZnS,
ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3, SiO, HfO2, ZrO2, CeO2, Nb2O5, Ta2O5
and TiO2.
56. The lens coating of claim 52, said hydrophobic layer being bonded to said
anti-reflective layer such that none of the hydrophobic layer is removed during
an adhesive tape test performed according to a test selected from the group
consisting of MIL-C-675C, MIL-F-48616, MIL-M-13508, and combinations thereof.
57. The lens coating of claim 52, said composition of said anti-reflective
layer being selected from the group consisting of Al2O3, ZrO3, MgF2, SiO2,
cryolite, LiF, ThF4, CeF3, PbF2, ZnS, ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3,
SiO, HfO2, ZrO2, CeO2, Nb2O5, Ta2O5 and TiO2.
58. The lens coating of claim 52, said hydrophobic layer comprising an
organosilane compound.
59. The lens coating of claim 58, said coating retaining at least 97% of said
hydrophobic characteristic.
60. The lens coating of claim 59, said coating retaining at least 98.5% of said
hydrophobic characteristic.
61. The lens coating of claim 60, said coating retaining at least 99.5% of said
hydrophobic characteristic.
62. The lens coating of claim 52, said coating further comprising said
anti-reflective layer and said hydrophobic layer being disposed on the back
face of said lens.
63. A lens for riflescopes or telescopes comprising:
a glass optic presenting a front face and a back face;
an anti-reflective layer disposed on at least one of said front face and said
back face; and
a hydrophobic layer disposed on said anti-reflective layer, said coating
retaining at least 95% of a hydrophobic characteristic after an abrasion test
comprising the steps of rubbing an eraser for at least 20 strokes along the
same line using 2.5 pounds of pressure on the eraser, said hydrophobic
characteristic being selected from the group consisting of contact angles and
stain removal using adhesive tape.
64. The lens of claim 63, said anti-reflective layer disposed on said front
face and said back face.
65. The lens of claim 64, said hydrophobic layer only being disposed on the
anti-reflective layer on said lens front face.
66. The lens of claim 63, said hydrophobic layer comprising an organosilane
compound.
67. The lens of claim 63, said lens permitting at least 99% light transmission
therethrough.
68. The lens of claim 67, said light transmission being at least 99.5%.
69. The lens of claim 63, said anti-reflective layer being located between the
lens and said hydrophobic layer.
70. The lens of claim 63, said anti-reflective layer comprising a plurality of
sublayers, each of said sublayers comprising an anti-reflective composition.
71. The lens of claim 70, the composition of each of said plurality of sublayers
being individually and respectively selected from the group consisting of
Al2O3, ZrO3, MgF2, SiO2, cryolite, LiF, ThF4, CeF3, PbF2, ZnS, ZnSe, Si, Ge,
Te, PbTe, MgO, Y2O3, Sc2O3, SiO, HfO2, ZrO2, CeO2, Nb2O5, Ta2O5 and TiO2.
72. The lens of claim 63, said hydrophobic layer being
bonded to said anti-reflective layer one of the hydrophobic layer is removed
during an adhesive tape test performed according elected from the group
consisting of MIL-C-675C, MIL-F-48616, MIL-M-13508, and combinations thereof.
73. The lens of claim 63, said anti-reflective layer comprising a composition
being selected from the group consisting of Al2O3, ZrO3, MgF2, SiO2, cryolite,
LiF, ThF4, CeF3, PbF2, ZnS, ZnSe, Si, Ge, Te, PbTe, MgO, Y2O3, Sc2O3, SiO,
HfO2, ZrO2, CeO2, Nb2O5, Ta2O5 and TiO2.
74. The lens of claim 63, said coating retaining at least 97% of said
hydrophobic characteristic.
75. The lens of claim 74, said coating retaining at least 98.5% of said
hydrophobic characteristic.
76. The lens of claim 75, said coating retaining at least 99.5% of said
hydrophobic characteristic.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present application is directed toward a coating for an exterior surface of
a telescope lens, especially a riflescope, a spotting scope, or a binocular to
reduce the likelihood of fogging or distortion due to the collection of
moisture on the lens without significantly reducing light transmission through
the lens in the visible range. More particularly, the present invention is
directed toward such coatings that are durable. Still more particularly, such
coatings may include two layers with the first layer being an anti-reflective
(AR) coating which has either a single layer or multiple layers such that light
transmission in the visible range is not significantly reduced and the second
coating is a durable hydrophobic coating over the AR coating. Still more
particularly, the present invention provides a coating which is not easily
scratched or worn away undergoing standard durability and abrasion testing.
2. Description of the Prior Art
Scopes used by sportsmen, military and the like, have improved significantly
over the years. However, much of this improvement is lost on cold days or rainy
days due to collection of moisture or fogging on the lens which then
significantly distorts the image. For example, a hunter on a cold day will
often bring the gun to his face to aim through a scope at a target, and in
doing so often breathes on the scope's lens. The hunter's breath then fogs the
lens. On days when it is raining or drizzling, the moisture from the rain can
likewise collect on the lens and distort the image. While the interior face of
the lens can be protected against the elements by placement of a moisture free
gas within the interior of the scope, the exterior face of the lens is
invariably exposed to the elements and incurs the fogging and moisture
collection noted above.
Various treatments have been previously utilized that apply hydrophobic materials
to various articles, such as sunglasses and automobile windshields, to produce
beading of water droplets/or the quick sloughing of moisture, so that the
moisture is not retained and spread unevenly on the article due to surface
tension so as to produce distortion. However, such treatments reduce the
transmissions of light through the article. Typically this reduction in
transmission occurs even if the treatment is essentially clear or see through,
since the index of refraction of the treatment is different in comparison to
the index of refraction of the article causing some amount of reflection to
occur. The light that is reflected is then not seen by the viewer which reduces
the quality of the image. In articles such as windshields and sunglasses, the amount
of reduction in light transmission is not critical, and therefore, a loss of a
small amount is not considered to be extremely important.
However, in riflescopes and other telescopic devices, it is extremely important
to maintain light transmission in the visible range near 100 percent of
incident light in order to ensure that the best possible quality image is seen
through the scope. Conventional treatments for rendering articles hydrophobic
reduce the transmission of light in certain visible ranges sufficiently to make
use of such treatments unacceptable.
Anti-reflective treatments are used on various materials to decrease reflection
and increase transmission of light, especially in certain wavelengths.
Anti-reflective treatments have been previously used in the prior art for
various types of devices, including lenses. Anti-reflective treatments have
been especially used where lenses with multiple components are joined together
in a side-by-side (or layered) relationship. However, hydrophobic polymers that
naturally reduce transmission of light do not adhere to most of the components
of anti-reflective treatments that increase transmission of light. Even if the
hydrophobic polymer will adhere to an anti-reflective, it has been found
through testing that the hydrophobic polymer can often easily be removed by
rubbing or just general wear over time.
Consequently, it is desirable to provide an overall coating for an exterior
face of a riflescope lens or the like, which includes an externally located hydrophobic
polymer that transmits light in the visible range and causes quick beading and
sloughing of moisture from the lens. Furthermore, the hydrophobic polymer
requires an anti-reflective component that is designed to allow almost one
hundred percent of visible light at selected wavelengths to be transmitted
through the lens and the hydrophobic polymer. Still furthermore, it is
important that the hydrophobic coating be strongly adhered to the lens and not
easily removed by rubbing or wear over time. Additionally, what is needed is a
hydrophobic lens coating having a certain hardness or durability which provides
a certain degree of protection for the lens or any AR layers located on the
lens such that the coating is not easily scratched. In this respect, it is
desirable that the hydrophobic lens coating be of sufficient hardness and
durability to undergo conventional testing without significant damage to the
hydrophobic coating, any AR coating, or the lens itself.
SUMMARY OF THE INVENTION
The present invention overcomes the problems inherent in the prior art and
provides a distinct advance in the state of the art. A coating is provided for
lenses to render the exterior face or surface of the lens hydrophobic to reduce
the likelihood of fogging and to reduce the likelihood of distortion of images
passing through the lens by collection of water thereon. The coating comprises
two layers; the first layer being an anti-reflective treatment and the second
layer being a light transmitting hydrophobic polymer treatment.
The anti-reflective layer includes multiple sublayers, the material of
construction of which and the thickness of which are chosen to provide the best
transmission of selected wavelengths through the lens in conjunction with the
particular hydrophobic polymer utilized. The number of sublayers in the
anti-reflective layer may vary in accordance with design techniques and
typically range from three to seven in number. Preferably, the anti-reflective
layer has four sublayers.
The outer layer of the anti-reflective layer, that is the layer opposite the
lens and adjacent the hydrophobic layer is constructed of silicon dioxide. The
anti-reflective layer is applied in ways well known in the art. However, in
order to make the hydrophobic polymer layer wear resistant, it is best to heat
the anti-reflective layer above ambient temperature. Preferably the
anti-reflective layer is heated to a temperature in the range of
250-300.degree. centigrade provided that the lens is constructed of glass that
can withstand such temperatures. In alternative methods, the anti-reflective
coating is applied to a lens using vapor deposition or sputtering.
Alternatively, the outer layer of the anti-reflective layer
can be formed of any conventional AR coating and it is desirable to select each
AR layer based upon the desired AR characteristics of the final product. Of
course, this is also true for single-layer AR coatings.
While the anti-reflective layers may be constructed of numerous types of
materials, one particular preferred embodiment includes 70 nanometers of
aluminum oxide (Al.sub.2 O.sub.3), 70 nanometers of ZrO.sub.3, 225 nanometers
of MgF.sub.2 and 140 nanometers of SiO.sub.2 where it is desired that the
wavelength of visible light at 550 nanometers be most clearly and completely
transmitted through the lens.
One preferred method of applying this coating (including both an AR layer and a
hydrophobic coating) generally includes the steps of applying an AR coating to
a lens under vacuum in a first chamber and then having the hydrophobic coating
applied to the AR-coated lens applied using vapor deposition in a second vacuum
chamber. Another preferred method applies the AR coating to a lens using
sputtering with the final layer being sputtered on being the hydrophobic coating.
This process is especially adapted for AR coatings which do not incorporate
silicon dioxide as the layer occurring just beneath the hydrophobic coating as
any AR layer could be used.
In one aspect of the present invention, a coating is applied to a lens which
has an AR coating thereon. In other words, the lens has at least two layers on
one of the surfaces. The first layer is the AR layer and the second layer is
the hydrophobic coating. The AR layer can be of any AR material and may be
comprised of several layers of different AR materials. On top of this AR layer,
the hydrophobic coating is applied. This hydrophobic coating is preferably a
coating which does not significantly affect light transmission and which
provides a durable outer layer which is not easily scratched or marred. The
hydrophobic coating should also adhere to the underlying AR layer such that it
is not easily removed. The hydrophobic coating is preferably an organosilane
compound. Preferred organosilane compounds applied to lenses will retain at
least 95% of its hydrophobic characteristics after undergoing a standard eraser
test. Still more preferably, the hydrophobic coating will retain at least 97%
(and even more preferably at least 98.5%) of its hydrophobic characteristics
after undergoing a standard eraser test. Most preferably, the hydrophobic
coating will retain at least 99.5% of its hydrophobic characteristics after
undergoing a standard eraser test. One method of testing the hydrophobic
characteristics would include measuring the contact angle of a water drop both
before and after the eraser test. Furthermore, when undergoing a standard
adhesive tape test, the coating should retain less than 5% of the applied stain
with the remaining 95% being removed by the adhesive tape. Still more
preferably, the hydrophobic coating will permit removal of at least 97% (and
even more preferably at least 98.5%) of the stain undergoing a standard
adhesive tape test. Most preferably, the hydrophobic coating will permit
removal of at least 99.5% of the applied stain after undergoing a standard
adhesive tape test. With respect to light transmission, the hydrophobic coating
should have little to no effect and riflescopes containing a plurality of
lenses therein should exhibit less than a 5% loss of light through the lenses.
Preferably, any one lens having an AR coating on each side of the lens and a
hydrophobic coating applied to at least one of the sides of the lens should
have at least 99% light transmission therethrough. A particularly preferred organosilane
compound is PERMASEAL (Nanofilms, Inc., Valley View, Ohio).
Therefore the principle objects of the present invention are: to provide a
telescope lens having an external face that is treated with a coating to resist
accumulation of water on the lens to reduce the likelihood of fogging and to
reduce the likelihood of distortion due to collection of moisture acting under
surface tension thereon; to provide such a lens having a high percentage of
transmission of light in the visible range; to provide such a lens wherein the
coating comprises a anti-reflective layer and a hydrophobic polymer layer on
the surface of the lens; to provide such a lens wherein the anti-reflective
layer has a sublayer of silicon dioxide that is adjacent to the hydrophobic layer;
to provide such a lens wherein the anti-reflective layer is heated during
manufacturing and while on the lens to a temperature above ambient temperature
and preferably to a temperature in the range of 250-300.degree. centigrade; to
provide such a lens that has very close to 100% transmission of light over a
very wide spectrum of visible light; to provide a lens having an AR layer and a
hydrophobic coating on top of the AR layer wherein the hydrophobic coating
provides increased durability while having little to no effect on light
transmission; and to provide such a lens which is relatively easy to construct,
inexpensive to produce and especially well suited for the intended usage
thereof.
Other objects and advantages of this invention will become apparent from the
following description taken in conjunction with the accompanying drawings
wherein are set forth, by way of illustration and example, certain embodiments
of this invention.
The drawings constitute a part of this specification and include exemplary
embodiments of the present invention and illustrate various objects and
features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a hunter utilizing a rifle with a riflescope
having a lens treated in accordance with the present invention;
FIG. 2 is a fragmentary side elevational view of the riflescope, with portions
broken away to show placement of the lens therein;
FIG. 3 is a fragmentary and very highly enlarged cross-sectional view of the
lens and various coating layers on the surface of the lens;
FIG. 4 is a graphical representation of light transmission
through the lens at various wavelengths; and
FIG. 5 is a graph illustrating the light transmission through a riflescope in
accordance with the present invention in comparison to other riflescopes.
DETAILED DESCRIPTION OF THE INVENTION
As required, detailed embodiments of the present invention are disclosed
herein; however, it is to be understood that the disclosed embodiments are
merely exemplary of the invention, which may be embodied in various forms.
Therefore, specific structural and functional details disclosed herein are not
to be interpreted as limiting, but merely as a basis for the claims and as a
representative basis for teaching one skilled in the art to variously employ
the present invention in virtually any appropriately detailed structure.
The reference numeral 1 generally indicates a lens in accordance with the
present invention mounted in a riflescope 4 that is in turn mounted on a rifle
5 that is illustrated as being aimed by a user 6 in FIG. 1.
The scope 4 is of a type conventionally used on rifles by sportsmen and the
like, although it is foreseen that many types of telescope systems such as
binoculars, spotting scopes and the like may be treated with the present
invention. The scope 4 may include multiple internal lenses and related
internal components which are quite conventional and are not illustrated in
detail or highly described herein. The invention is specifically directed to the
lens 1 which has an external face 10 that is exposed to the ambient
environment, especially rain and the breath of the user.
The lens face 10 is positioned during use in front of an eye 11 of the user 6
and in doing so, the user 6 often exhales a breath 12 that is supersaturated
with moisture from the lungs of the user 6. The user's breath 12, as well as
falling or driven rain or mist, engages the lens external face 10. Under
typical circumstances, the breath 12 upon striking the lens face 10 or rain or mist
on the lens face 10 will cause the lens 1 to fog or the images seen
therethrough to become distorted due to surface tension acting on the moisture
on the lens 1.
Consequently, in accordance with the present invention, the lens face 10 is
covered with a coating 15 that reduces surface tension and causes beading of
moisture, thereby significantly reducing the likelihood of image distortion
through the lens 1 due to moisture collecting thereon. The coating 15 is very
thin in thickness and does not show as a separate layer in FIG. 2 for this
reason. The coating 15 is best illustrated in FIG. 3 which is highly enlarged
fragmentary view of a portion of the lens 1 and coating 15. The entire
thickness of the coating 15 will typically be less than 1000 nanometers (nm).
In order to not affect light transmission, the coating must be very thin as
compared to the wavelength of light of interest. For example for a wavelength
of 550 nm, the coating must be much thinner than 550 nm. Preferably, the
coating is less than 50 nm thick. The coating 15 includes an anti-reflective
layer 18 and a hydrophobic layer 19.
The anti-reflective layer 18 is best specifically designed or engineered for
the particular lens 1 and hydrophobic layer 19 utilized therewith. Design of
anti-reflective layers, such as layer 18, is somewhat both an art and a
science. Conventionally there have been many different types of anti-reflective
layers that have been developed for various lenses and for various purposes.
The typical anti-reflective layers include multiple sub-layers which are each
made of materials which are different from adjacent sub-layers and which are
typically deposited in thicknesses wherein the thickness of each sub layer is
related to an even whole number division of the wavelength of light that is
most preferred to be transmitted through the lens 1.
For example, light that has a wavelength of 550 nm and is approximately in the
middle of the visible range is typically considered to be an important
wavelength to be transmitted through the lens 1. Therefore, the sub-layers of
the anti-reflective layer 18 may be chosen to be deposited in proportion to the
550 nm wavelength. As an example, a common coating that is three sub-layers in
thickness is often deposited in layers that are 1/4, 1/2 and 1/4 of the length
of the wave of the wavelength or 140 nm, 220 nm, and 140 nm in thickness. The
art associated with production of anti-reflective coatings and how to deposit
such coatings on articles is well known to those having ordinary kills in the
art. In particular, the art of designing and depositing anti-reflective layers
on objects can be found in such references as the Handbook of Optics by McGraw
Hill, 2.sup.nd Ed., in Chapter 42, Dealing with Optical Properties of Films and
Coatings, Design of Optical Interference Coatings by McGraw Hill Book Company
in Chapter 4 on Anti-Reflection Coatings, as well as in issued U.S. Pat. No.
4,726,654 to Kimura et al., Akatuska et al., U.S. Pat. No. 4,784,467 and Tani,
U.S. Pat. No. 4,387,960, which are all included here in reference.
Anti-reflective coatings may include sublayers of many
different materials, some of which are as follows: Al.sub.2 O.sub.3, ZrO.sub.3,
MgF.sub.2, SiO.sub.2, cryolite, LiF, ThF.sub.4, CeF.sub.3, PbF.sub.2, ZnS,
ZnSe, Si, Ge, Te, PObTe, MgO, Y.sub.2 O.sub.3, Sc.sub.2 O.sub.3, SiO,
HfO.sub.2, ZrO.sub.2, CeO.sub.2, CeO.sub.2, Nb.sub.2 O.sub.3, Ta.sub.2 O.sub.5,
and TiO.sub.2. These different compositions are chosen by those having skill in
the art to best mate and match with the other materials used in the
construction of the lens 1 so as to provide the transmission of light at
selected advantageous wavelengths. Preferably, for the present invention, it is
desired to have the transmission of light be as close as possible to 100% of
the incident light across the entire spectrum of visible light, but especially
in the center of the spectrum.
In the present invention, it is desirable to have an anti-reflective layer 18
that functions well in cooperation with the hydrophobic layer 19 to provide
transmission of light through a wide range of wavelengths, especially light
having a wavelength of 550 nm. Consequently, preferred for this invention are
anti-reflective layer 18, sublayers 21 through 24 with sublayer 21 being
adjacent to the lens face 10 and with sublayer 24 being adjacent to the
hydrophobic layer 19. The preferred composition and thickness of the sublayers
is as follows: approximately 70 nm of Al.sub.2 O.sub.3 ; approximately 70 nm of
ZrO.sub.3 ; approximately 225 nm of MgF.sub.2, and finally approximately 140 nm
of SiO.sub.2. For embodiments of this particular invention where the AR layer
and the lens are heated to between 250-300.degree. C. before applying the
hydrophobic layer, it has been found that it is important to have the final
sublayer, in this case sublayer 24, be silicon dioxide to bind with the
hydrophobic layer. Most of the other components normally utilized in
anti-reflective layers are unsuitable for direct binding with the hydrophobic
layer 19; however, it is foreseen that there may be one or more compounds other
than silicon dioxide that may be used as the final sublayer, provided that such
a compound offers a suitable binding for the particular hydrophobic polymer
used. In embodiments where the AR layer and lens are not heated to between
250-300.degree. C., virtually any conventional AR compound can be adjacent the
hydrophobic coating.
Prior to deposition of the hydrophobic layer 19 during manufacturing the lens 1
with the anti-reflective layer 18 thereon is heat-treated above ambient
temperature. While different temperatures may be utilize for different lens
constructions, it has been found that heating the lens between 250-300.degree.
C. provides a very stable anti-reflective layer 18 which is not easily removed
by scratching, rubbing or normal wear. Such heat treating is not available for
any devices where the lens is constructed of plastic or of a composite material
that does not lend itself to application of heat.
Subsequent to the anti-reflective layer 18 being applied to the lens 1, the
hydrophobic layer 19 is applied. Typically, the hydrophobic layer generally
allows full transmission of light in the normal vision range (especially at a
wavelength of 550 nm) and is composed of a hydrophobic polymer. The hydrophobic
layer may be applied in a layer that is as little as several nm in thickness.
The hydrophobic layer 19 may be applied by dipping the lens 1 with the
anti-reflective layer 18 there into a liquid bath of the hydrophobic polymer
which then adheres to and binds with the silicon dioxide sublayer 24, through
vapor deposition or by other suitable methods. Various hydrophobic materials
may be utilized that are well known to those skilled in the art, but are
especially chosen by those having skill in the art in conjunction with the
materials of construction of the lenses, and the anti-reflective layer 18 to
function therewith so as to provide high light transmission.
Using another preferred method in accordance with the present invention, the
hydrophobic coating is applied to an AR-coated lens by loading an ampule
containing the hydrophobic coating into DAS Series (Denton Vacuum, Moorestown,
N.J.) vacuum system. Prior to loading the ampule, the DAS system was started
using the System Start button and the chamber walls where heated to operating
temperature (40-60.degree. C.). Once the walls are at the operating
temperature, the ampule was loaded into the heater/breaker assembly and the
screen above the assembly was replaced. The lenses were loaded into a basket in
the chamber and the chamber door closed before pressing the start button. The
door was held closed until the roughing valve opened. Once the roughing valve
opened, the mechanical pump evacuated the air from the chamber and the
isolation valve opened to connect the Granville Phillips vacuum relay to the
chamber. The ampule heater heated the ampule to the first set point
(140-170.degree. C.) where is was held until the vacuum set point was reached.
The roughing valve remained open until the vacuum set point (5.times.10.sup.-2
Torr) was reached and the LED on the Granville Phillips relay turned green.
Once the set point was reached, all valves closed and the deposition process
began. The ampule was heated to the second temperature set point (220.degree.
C.) whereupon the ampule was broken by the solenoid. The process is stopped for
two minutes at this point to allow the chemical reaction to take place at the
surface of the lenses. When the top of the ampule is broken off, the liquid in
the ampule has already been heated to vaporize and the chemical in the ampule
disperses throughout the chamber to deposit the hydrophobic coating on the
lenses. Once the deposition process is complete, the bypass valves open and the
chamber is evacuated through the acid neutralization trap for two minutes.
After this second pump down of the chamber, the bypass valves close and the
isolation valve opens. The vent valve then opens to vent the chamber to the
atmosphere whereupon the end indicator light flashes and an audible alarm
sounds to notify the operator that the process is complete.
Illustrated in FIG. 4 is a graphical representation of light
transmission as a percentage of incoming light through a lens that has been
treated with a coating 15 in accordance with the present invention. As can be
seen from the graph, light transmission over the range of from 430-730 nm is
within 1% of incident light. It is noted that the percentage of transmission
goes slightly above 100% over a small amount of the range due to expected small
amounts of error in testing(signal-to-noise problems which would disappear if
the data were collected at a slower rate).
FIG. 5 illustrates light transmission through a riflescope in accordance with
the present invention in comparison to other riflescopes of similar
construction but lacking the hydrophobic coating of the present invention. As
shown in this figure, over 95% of the light at 550 nm was transmitted through
the riflescope. This is a great improvement over the next highest performing
riflescope which permitted just over 94% of the light to be transmitted through
the riflescope.
Durability of a lens produced in accordance with the present invention
exhibited superior results in both the standard eraser test and in the standard
adhesive tape test. The standard eraser test was performed using an eraser
insert complying with military specification MIL-E-12397B. The eraser was
pressure fitted into the tester before performing the test. For the test, a
lens having a hydrophobic coating in accordance with the present invention was
tested by pressing the eraser against the lens at a pressure of 2.5 pounds.
This pressure is indicated on the indicator rod of the body of the tester
containing the eraser insert. The surface of the lens was rubbed with 20 strokes
of the eraser wherein each stroke was about one inch in length. All strokes
were made on one path. The lens was then washed with acetone and inspected for
deterioration of the coating. No visible deterioration was detected after
placing a drop of water on the area of the lens which had been rubbed with the
eraser. Further testing of the contact angles of the water drop would confirm
that the lens with the coating retained at least 95% of its hydrophobic
characteristics after undergoing the test. Depending upon the method of
applying the hydrophobic coating, the coatings will retain between 95-100% of
their hydrophobic characteristics after undergoing the standard eraser test.
Another method of testing the retention of hydrophobic characteristics as well
as durability of the coating generally includes the step of performing the
standard eraser test (as described above) and marking the lens in a direction
transverse to the eraser strokes. The marking of the lens is generally done
with a marker whereupon a strip of adhesive tape is placed over the mark and
then removed. Preferably, at least 95% of the mark should be removed by the
tape and the present invention exceeds this benchmark.
A second test of durability is performed according to MIL-C-675C and MWL-F-48616.
For this test, a strip of tape approximately 1.5 inches in length has
approximately half of its length pressed onto the coated surface to be tested.
The other half of the tape is held at an angle away from the surface and the
pressed portion of the tape is pulled up quickly. The coating of the present
invention passed this test as no coating was removed after the tape was lifted.
Similarly, a second test was performed according to MIL-M-13508. For this test,
approximately one inch of tape was placed over a portion of the coated surface
such that the tape overlapped an edge of the object which was coated. The tape
was pressed down on the coated surface as well as over the edge and then slowly
removed. The coating of the present invention also passed this test as no
coating was removed after the tape was lifted.
A third test of durability tests for crosshatch adhesion of the anti-reflective
layer and the hydrophobic layer. To perform the test, a lens having an
anti-reflective layer and a hydrophobic layer in accordance with the present
invention was cleaned. A blade was used to make 6 incisions towards the edge of
the lens. Six additional incisions were then made perpendicular to the first 6
incisions so that the combination of the incisions resembled a grid pattern.
The dust and particles were removed from the grid with compressed air and the
lens was inspected to ensure that the grid contained no chips and that the
incisions were even. Adhesive tape (Scotch #600, 3M) was then applied over the
cross hatch pattern with one end of the tape extending past the edge of the
lens by at least 1/2 inches. The tape was pressed against the lens to remove
any air bubbles trapped between the lens and the tape. Within 90 seconds (+/-30
seconds), the adhesive tape was removed by holding the lens firmly, grasping
the extended end of the tape and pulling it rapidly to the other side of the
lens as close to an angle of 180.degree. as possible. The entire operation was
repeated two more times over a testing period of 24 hours for each of the 10
lenses tested.
Results were scored on a scale
of 1 to 5 in four categories after 8, 16 and 24 hours. The categories were:
crazing; delamination (interlayer detachment; delamination (complete coating
detachment); and crosshatching. For the crazing assessment, lenses having no
visible crazing received a score of A5, lenses having hairline crazing only
just visible points or cracks received a score of A4, if hairline crazing
covered up to 25% of the lens surface, a score of A3 was given, if hairline
crazing covered up to 75% of the lens surface, a score of A2 was given, if
hairline crazing covered the entire lens surface, a score of A1 was given, and
if any region of the lens had severe Fern-like or Matt-like crazing, a score of
A0 was given. Out of the 10 lenses tested, 8 lenses received a score of A4, 1
received a score of A3, and 1 received a score of A5. There were no changes in
the testing over the testing period (i.e. at 8, 16, and 24 hours).
In the interlayer delamination category, a score of B5 indicated no
delamination over the entire lens surface, B4 indicated partial delamination of
individual layers covering up to 25% of the lens surface, B3 indicated partial
delamination of individual layer covering up to 75% of the lens surface and B2
indicated total delamination of individual layer over the entire lens surface.
All lenses received a score of B5 in this test over the entire testing period.
In the delamination complete coating detachment category, a score of C5
indicated no delamination of all layers over the entire lens surface, C4
indicated partial delamination of all layers covering up to 25% of the lens
surface, C3 indicated partial delamination of all layers covering up to 75% of
the lens surface and C2 indicated total delamination of all layers over the
entire lens surface. All lenses received a score of C5 in this test over the
entire testing period.
Finally, in the crosshatch category, a score of D5 indicated that the edges of
the cuts were completely smooth and none of the squares of the cross hatched
area were detached, a score of D4 indicates that small flakes of the coating
are detached at the intersections of the squares and the area affected is less
than 5% of the total area, a score of D3 indicates that small flakes of the
coating are detached along the edges and at the intersections of the squares
and the area affected is between 5% and 15% of the total area, a score of D2
indicates that the coating has flaked along the edges and on parts of the
squares and the area affected is 5% to 15% of the total area, a score of D1
indicates that the coating has flaked along the edges of the cuts in large
ribbons and whole squares are detached and the area affected is 35-65% of the
total area, a score of D0 indicates worse flaking and detachment than a score
of D1. A lenses received a score of D5 in this test over the entire testing
period.
In summary, the coating 15 of the lens 1 is highly effective at providing a
surface coat of a hydrophobic polymer to produce beading of moisture on the
surface of lens 1 and reduce the effect of the moisture in distorting images
passing through the lens 1. The anti-reflective layer 18 cooperates with the
hydrophobic polymer layer to provide transmission of very close to 100% of the
light at the wavelengths associated with the normal field of vision that passes
through the scope 4, and therefore provides the user 6 with a very high quality
image as seen through the lens 1.
It is to be understood that while certain forms of the present invention have
been illustrated and described herein, it is not to be limited to the specific
forms or arrangement of parts described and shown.
* * * * *