U.S. patent application number 14/199350 was filed with the patent office on 2014-07-03 for light-weight strengthened, low-emittance vacuum-insulated glass (vig) windows.
This patent application is currently assigned to Corning Incorporated. The applicant listed for this patent is Corning Incorporated. Invention is credited to Richard Robert Grzybowski, Michael S. Pambianchi, Alexander Mikhailovich Streltsov.
Application Number | 20140186557 14/199350 |
Document ID | / |
Family ID | 45931020 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140186557 |
Kind Code |
A1 |
Grzybowski; Richard Robert ;
et al. |
July 3, 2014 |
LIGHT-WEIGHT STRENGTHENED, LOW-EMITTANCE VACUUM-INSULATED GLASS
(VIG) WINDOWS
Abstract
Vacuum-insulated glass windows include two or more glass panes,
and glass-bump spacers formed in a surface of one of the panes. The
glass-bump spacers consist of the glass material from the body
portion of the glass pane. At least one of the glass panes
comprises chemically-strengthened glass. Methods of forming VIG
windows include forming the glass-bump spacers by irradiating a
glass pane with a focused beam from a laser. Heating effects in the
glass cause the glass to locally expand, thereby forming a
glass-bump spacer. In embodiments where the glass-bump spacers are
formed in a chemically-strengthened glass pane, the glass-bump
spacers may be formed before or after the chemical strengthening. A
second glass pane is brought into contact with the glass-bump
spacers, and the edges sealed. The resulting sealed interior region
is evacuated to a pressure of less than one atmosphere.
Inventors: |
Grzybowski; Richard Robert;
(Corning, NY) ; Pambianchi; Michael S.; (Corning,
NY) ; Streltsov; Alexander Mikhailovich; (Corning,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Assignee: |
Corning Incorporated
Corning
NY
|
Family ID: |
45931020 |
Appl. No.: |
14/199350 |
Filed: |
March 6, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13074599 |
Mar 29, 2011 |
8679599 |
|
|
14199350 |
|
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Current U.S.
Class: |
428/34 |
Current CPC
Class: |
C03B 2215/414 20130101;
C03C 17/366 20130101; C03B 23/02 20130101; C03C 21/002 20130101;
Y10T 428/315 20150115; E06B 3/6733 20130101; E06B 3/66304 20130101;
E06B 3/6775 20130101; C03C 23/005 20130101; E06B 3/663 20130101;
E06B 3/6612 20130101 |
Class at
Publication: |
428/34 |
International
Class: |
E06B 3/66 20060101
E06B003/66; E06B 3/663 20060101 E06B003/663 |
Claims
1. A vacuum-insulated glass (VIG) window, comprising: a first glass
pane having a first outer edge; a second glass pane spaced apart
from and disposed substantially parallel to the first glass pane at
a first distance, the second glass pane having a second outer edge;
a first edge seal formed around at least respective portions of the
first and second outer edges to define a first sealed interior
region between the first and second glass panes, wherein the first
sealed interior region has a vacuum pressure of less than one
atmosphere; a first plurality of glass-bump spacers integrally
formed from a first surface of the first glass pane and consisting
of glass material from the first glass pane, and a first optical
coating formed over both the first plurality of glass-bump spacers
and the first surface in which the first plurality of glass-bump
spacers are formed, wherein at least one of the first glass pane
and the second glass pane comprises a chemically-strengthened glass
material, the optical coating comprises a polymer layer or a
dielectric layer, and the first plurality of coated glass-bump
spacers contact the second glass pane so as to maintain said spaced
apart first distance.
2. The VIG window of claim 1, wherein the second glass pane
comprises a chemically-strengthened glass material.
3. The VIG window of claim 1, wherein the first glass-bump spacers
have a bump height H defined by 75 .mu.m.ltoreq.H.ltoreq.225
.mu.m.
4. The VIG window of claim 1, wherein the first and second glass
panes have respective thicknesses of less than 1 mm.
5. The VIG window of claim 1, wherein the window is substantially
flat.
6. The VIG window of claim 1, wherein the window is shaped.
7. The VIG window of claim 1, further comprising: a third glass
pane spaced apart from and disposed substantially parallel to the
first glass pane at a side opposite the second glass pane and at a
second distance, the third glass pane having a third outer edge; a
second plurality of glass-bump spacers integrally formed from a
second surface of the first glass pane opposite the first surface,
the second plurality of glass-bump spacers consisting of glass
material from the first glass pane; a second optical coating formed
over both the second plurality of glass-bump spacers and the second
surface, wherein the second plurality of coated glass-bump spacers
contact the third glass pane so as to maintain said spaced apart
second distance, and either a) the first edge seal further
surrounds at least a portion of the third outer edge to further
define, between the first and third glass panes, a second sealed
interior region having a vacuum pressure of less than one
atmosphere, or b) a second edge seal surrounds at least respective
portions of the first and third outer edges to further define,
between the first and third glass panes, a second sealed interior
region having a vacuum pressure of less than one atmosphere.
8. The VIG window of claim 7, wherein the third glass pane
comprises a chemically-strengthened glass material.
9. The VIG window of claim 7, wherein the first, second and third
glass panes each comprise a chemically-strengthened glass
material.
10. The VIG window of claim 7, wherein the second plurality of
glass-bump spacers are formed substantially opposed to respective
ones of the first plurality of glass-bump spacers.
11. The VIG window of claim 7, wherein the second plurality of
glass-bump spacers are formed offset from the first plurality of
glass-bump spacers.
12. The VIG window of claim 7, wherein the first, second and third
glass panes have respective thicknesses of less than 1 mm.
13. The VIG window of claim 7, wherein the window is substantially
flat.
14. The VIG window of claim 7, wherein the window is shaped.
15. The VIG window of claim 1, further comprising: a third glass
pane spaced apart from and disposed substantially parallel to the
first glass pane at a side opposite the second glass pane and at a
second distance, the third glass pane having a third outer edge; a
second plurality of glass-bump spacers integrally formed from a
third surface of the third glass pane and consisting of glass
material from the third glass pane; a second optical coating formed
over both the second glass-bump spacers and the third surface,
wherein the second plurality of coated glass-bump spacers contact
the first glass pane so as to maintain said spaced apart second
distance, and either a) the first edge seal further surrounds at
least a portion of the third outer edge to further define, between
the first and third glass panes, a second sealed interior region
having a vacuum pressure of less than one atmosphere, or b) a
second edge seal surrounds at least respective portions of the
first and third outer edges to further define, between the first
and third glass panes, a second sealed interior region having a
vacuum pressure of less than one atmosphere.
16. The VIG window of claim 1, further comprising: a third glass
pane spaced apart from and disposed substantially parallel to the
second glass pane at a side opposite the first glass pane and at a
second distance, the third glass pane having a third outer edge; a
second plurality of glass-bump spacers integrally formed from a
third surface of the third glass pane and consisting of glass
material from the third glass pane; a second optical coating formed
over both the second glass-bump spacers and the third surface,
wherein the second plurality of coated glass-bump spacers contact
the second glass pane so as to maintain said spaced apart second
distance, and either a) the first edge seal further surrounds at
least a portion of the third outer edge to further define, between
the first and third glass panes, a second sealed interior region
having a vacuum pressure of less than one atmosphere, or b) a
second edge seal surrounds at least respective portions of the
first and third outer edges to further define, between the first
and third glass panes, a second sealed interior region having a
vacuum pressure of less than one atmosphere.
17. A vacuum-insulated glass (VIG) window assembly, comprising: a
first glass pane; a second glass pane spaced apart from and
disposed substantially parallel to the first glass pane at a first
distance; a plurality of glass-bump spacers integrally formed from
a first surface of the first glass pane, and an optical coating
formed over both the glass-bump spacers and the first surface in
which the first glass-bump spacers are formed, wherein at least one
of the first glass pane and the second glass pane comprises a
chemically-strengthened glass material, the optical coating
comprises a polymer layer or a dielectric layer, and the plurality
of coated glass-bump spacers contact the second glass pane so as to
maintain said spaced apart first distance.
18. The VIG window of claim 17, wherein the second glass pane
comprises a chemically-strengthened glass material.
Description
RELATED APPLICATIONS
[0001] The present disclosure is a continuation application and
claims the priority benefit of U.S. patent application Ser. No.
13/074,599, entitled "Light-Weight Strengthened, Low-Emittance
Vacuum-Insulated Glass (VIG) Windows," filed Mar. 29, 2011, the
entirety of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present disclosure relates generally to low-emittance
(low-E) vacuum-insulated glass (VIG) windows, and more particularly
to vacuum-insulated glass windows that include at least one
chemically-strengthened pane of glass and which comprise glass-bump
spacers formed in one or more of the glass panes.
BACKGROUND
[0003] Vacuum-insulated glass (VIG) windows typically include two
or more glass panes with an evacuated space (i.e., vacuum) located
between the panes. The overall construction provides improved
thermal and noise insulating properties compared to ordinary glass
windows. To prevent sagging and contact between adjacent glass
panes, discrete spacers can be placed between adjacent glass panes.
The spacers can be made of aluminum, plastic, ceramic, or glass and
are conventionally distinct from the glass panes, i.e., they are
separate, discrete elements disposed and fixed between the glass
panes.
[0004] While conventional spacers are effective in separating the
panes, they tend to be visible when looking through the window,
thereby making the window unsightly. Moreover, in vacuum-insulated
glass windows that comprise low emissivity coatings, conventional
spacers can abrade the low-E coating, particularly when exposed to
a thermal gradient where differential thermal expansion between the
indoor and out door panes can cause relative movement of the glass
panes and the spacers. Abraded or otherwise damaged low-E coatings
non-uniformly reflect incident light, which manifests as so-called
"starlight emission" which is an undesired optical effect in window
glass. In addition, the need to dispose the discrete spacers
between the panes and then fix the spacers to the panes adds cost
and complexity to the VIG window manufacturing process.
[0005] In view of the foregoing, there is a need for economical
low-E vacuum-insulated glass windows as well as the attendant
methods for making such windows.
SUMMARY
[0006] The present disclosure relates to low-emittance VIG windows
as well as to methods of forming such windows. According to an
embodiment, a vacuum-insulated glass window comprises a first glass
pane having a first body formed from a first glass material and
having first opposite surfaces and a first outer edge, a second
glass pane spaced apart from and disposed substantially parallel to
the first glass pane at a first distance and having a second body
formed from a second glass material and having second opposite
surfaces and a second outer edge, and a first edge seal formed
around at least respective portions of the first and second outer
edges so as to define a first sealed interior region between the
first and second glass panes, wherein the first sealed interior
region has a vacuum pressure of less than one atmosphere. A first
plurality of glass-bump spacers are integrally formed in one of the
first surfaces of the first glass pane and consist of the first
glass material from the first body portion. A first optical coating
is formed over both the first glass-bump spacers and the first
surface in which the first glass-bump spacers are formed. In the
assembled window, the plurality of coated glass-bump spacers
contact the second glass pane so as to maintain said spaced apart
first distance. At least one of the first glass pane and the second
glass pane comprises a chemically-strengthened glass material. In
further embodiments, the VIG window comprises a third pane.
[0007] An example method of forming a VIG window includes providing
a first glass pane having a first body portion with a first surface
and a first edge and comprising a first glass material, and
integrally forming in the first surface a first plurality of
glass-bump spacers consisting of the first glass material from the
first body portion. A first optical coating is formed over both the
first surface and the first plurality of glass-bump spacers. The
plurality of coated glass-bump spacers of the first glass pane are
brought into contact with a chemically-strengthened second glass
pane having a second surface and a second edge so that the first
and second glass panes are spaced apart by a first distance between
the first and second surfaces. The first and second edges are
sealed to define an interior region between the first and second
glass panes, and a vacuum pressure of less than one atmosphere is
formed in the interior region. In embodiments, the glass-bump
spacers can be formed in a first glass pane that is
chemically-strengthened. The chemical strengthening is typically
done before forming the glass-bump spacers.
[0008] Additional aspects, features and advantages are set forth in
the detailed description that follows and, in part, will be readily
apparent to those skilled in the art from that description or
recognized by practicing the invention as described herein,
including the detailed description that follows, the claims, as
well as the appended drawings.
[0009] It is to be understood that both the foregoing general
description and the following detailed description and are intended
to provide an overview or framework for understanding the nature
and character of the invention as it is claimed. The accompanying
drawings are included to provide a further understanding and are
incorporated in and constitute a part of this specification. The
drawings illustrate various embodiments and, together with the
description, serve to explain the principles and operations of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a front-on view of an example two-pane VIG window
according to embodiments;
[0011] FIG. 2 is a cross-sectional view of the VIG window of FIG. 1
as viewed in the direction CS-CS;
[0012] FIG. 3 is a close-up cross-sectional view of an example
glass-bump spacer;
[0013] FIG. 4A is a cross-sectional view similar to FIG. 2 and that
illustrates an example embodiment of a three-pane VIG window having
a middle glass pane with glass-bump spacers formed in both surfaces
of the middle pane;
[0014] FIG. 4B is similar to FIG. 4A, except that the second set of
glass-bump spacers are formed in the back glass pane rather than
the middle glass pane;
[0015] FIG. 4C is similar to FIG. 4A, except that the first and
second sets of glass-bump spacers are formed in the front and back
glass panes rather than the middle glass pane;
[0016] FIG. 5A and FIG. 5B illustrate typical transmission curves
(transmission (%) vs. wavelength (nm)) in the UV and visible
wavelength spectrums for transparent alkaline earth aluminosilicate
glasses (FIG. 5A) and transparent soda-lime glasses (FIG. 5B);
[0017] FIG. 6 is a schematic diagram of an example laser-based
glass-bump-forming apparatus used to form glass-bump spacers in a
glass pane in the process of forming a VIG window;
[0018] FIG. 7 is a schematic diagram of an example embodiment of a
laser light beam as formed from light pulses from a pulsed
laser;
[0019] FIG. 8 is a bar graph that plots the laser power P (W), the
distance D.sub.F, and the glass-bump-spacer height H for a
soda-lime glass pane;
[0020] FIG. 9 is a three-dimensional image of a glass-bump spacer
formed in a 3-mm soda-lime glass pane sample;
[0021] FIG. 10 is a line scan of the glass-bump spacer of FIG. 9,
revealing a substantially hemispherical bump profile;
[0022] FIG. 11 is a three-dimensional image of a glass-bump spacer
similar to that shown in FIG. 9, except that the glass-bump spacer
has a substantially flat top portion;
[0023] FIG. 12 is a schematic side view of an example glass pane
having an infrared-reflective coating;
[0024] FIG. 13 is a close-up, cross-sectional view of an uncoated
glass-bump spacer formed in the glass pane of FIG. 12;
[0025] FIG. 14 is a close-up, cross-sectional view of a coated
glass-bump spacer formed in the glass pane of FIG. 12;
[0026] FIG. 15 is a cross-sectional view of the glass pane assembly
in a VIG window according to one embodiment;
[0027] FIG. 16 is a cross-sectional view of the glass pane assembly
in a VIG window according to a further embodiment; and
[0028] FIG. 17 is a cross-sectional view of the glass pane assembly
in a VIG window according to yet a further embodiment.
DETAILED DESCRIPTION
[0029] A vacuum-insulated glass (VIG) window comprises a first
glass pane, a second glass pane spaced apart from and disposed
substantially parallel to the first glass pane at a first distance,
a plurality of glass-bump spacers integrally formed in a first
surface of the first glass pane, and a first optical coating formed
over both the glass-bump spacers and the first surface in which the
first glass-bump spacers are formed, wherein at least one of the
first glass pane and the second glass pane comprises a
chemically-strengthened glass material, and the plurality of coated
glass-bump spacers contact the second glass pane so as to maintain
said spaced apart first distance. Two or more glass panes may be
incorporated into a VIG window that comprises an evacuated region
between adjacent glass panes. Aspects of forming glass-bump
spacers, chemically-strengthened glass panes and optical coatings
such as low-emittance (low-E) coatings are described below.
[0030] As disclosed herein, glass-bump spacers are "formed in" a
glass pane. "Formed in" means that the glass-bump spacers grow out
of the body portion of the glass pane and are formed from the glass
material making up the glass pane, so as to outwardly protrude in a
convex manner from an otherwise substantially flat glass-pane
surface. Glass-bump spacers can be formed in a glass pane via
photo-induced absorption.
[0031] The term "photo-induced absorption" is broadly understood to
mean a local change of the absorption spectrum of a glass pane
resulting from locally exposing (irradiating) the glass pane with
radiation. Photo-induced absorption may involve a change in
absorption at a wavelength or a range of wavelengths, including,
but not limited to, ultra-violet, near ultra-violet, visible,
near-infrared, and/or infrared wavelengths. Examples of
photo-induced absorption in a transparent glass pane include, for
example and without limitation, color-center formation, transient
glass defect formation, and permanent glass defect formation.
[0032] A window as defined herein is an article comprising two or
more glass panes that are at least partially transparent to
electromagnetic (EM) radiation, including EM radiation having
ultra-violet, near ultra-violet, visible, near-infrared, and/or
infrared wavelengths.
VIG Windows with Integrally Formed Glass-Bump Spacers
[0033] FIG. 1 is a front-on view of an example embodiment of a
two-pane VIG window 10. FIG. 2 is a cross-sectional view of the
example VIG window 10 of FIG. 1 as viewed in the direction CS-CS.
Cartesian coordinates are shown for reference. VIG window 10
includes two glass panes 20, namely a front glass pane 20F and a
back glass pane 20B disposed opposite to and substantially parallel
to one another. Front glass pane 20F has a body portion 23F made of
a first glass material and has outer and inner surfaces 22F and 24F
and an outer edge 28F. Likewise, back glass pane 20B has a body
portion 23B made of a second glass material and has outer and inner
surfaces 22B and 24B and an outer edge 28B. In an example
embodiment, the first and second glass materials making up body
portions 23F and 23B are the same. In a further example embodiment,
either or both of the first and second glass materials making up
body portions 23F and 23B can comprise chemically-strengthened
glass.
[0034] Front and back glass panes 20F and 20B are separated by a
distance D.sub.G as measured from their respective inner surfaces
24F and 24B. An edge seal 30 is provided at respective outer edges
28F and 28B to surround at least a portion of each outer edge to
provide a hermetic seal. Edge seal 30 and front and back glass pane
inner surfaces 24F and 24B define a sealed interior region 40.
Sealed interior region 40 is preferably at least partially
evacuated so that it has a vacuum pressure of less than one
atmosphere, which provides VIG window 10 with desirable thermal and
acoustic insulation properties.
[0035] VIG window 10 further includes a plurality of glass-bump
spacers 50 integrally formed in inner surface 24B of back glass
pane 20B. FIG. 3 is a close-up view of an example glass-bump spacer
50. Note that glass-bump spacers 50 are integrally formed in back
glass pane 20B and are not added as separate or discrete elements
to VIG window 10. Thus, glass-bumps 50 are formed from (and thus
consist of) the same material as back glass pane 20B, and in fact
are extensions of body portion 23B. Example methods of forming
glass-bumps 50 are discussed in detail below.
[0036] In an example embodiment, glass-bump spacers 50 are
regularly spaced with respect to one another. Because glass-bump
spacers 50 are integrally formed in body portion 23B, they are
substantially invisible when the VIG window 10 is viewed at regular
(i.e., substantially normally incident) viewing angles.
Consequently, glass-bumps 50 are shown in phantom in FIG. 1.
Glass-bump 50 has a "tip" or "top portion" 51, as shown in FIG. 3.
As discussed below, top portion 51 need not be rounded as is shown
in FIG. 3. Glass-bump spacers 50 contact front pane inner surface
24F and serve to maintain the separation distance D.sub.G between
front and back glass panes 20F and 20B.
[0037] In an example embodiment, glass panes 20F and 20B are formed
from soda-lime glass or an alkali aluminosilicate glass, which in a
further example embodiment have a respective thickness T.sub.G
between 0.5 mm and 3 mm (e.g., 0.5, 0.7, 1, 1.5, 2, 2.5 or 3 mm).
In an example embodiment, glass-bump spacers 50 have a height
("bump height") H in the range from 50 .mu.m to 200 .mu.m, more
preferably in the range from 75 .mu.m to 150 .mu.m, and even more
preferably in the range from 100 .mu.m to 120 .mu.m. In an example
embodiment, glass panes 20F and 20B have substantially the same
thickness T.sub.G (see FIG. 6).
[0038] FIG. 4A is a cross-sectional view similar to FIG. 2 and
illustrates an example embodiment of a three-pane VIG window 10
that includes a middle glass pane 20M sandwiched between front pane
20F and back pane 20B. Middle glass pane 20M has a body portion 23M
of a third glass material and has a front side 22M, a back side 24M
and an edge 28M. First and second sets of glass-bump spacers 50 are
respectively formed in both the front and back sides 22M and 24M of
middle pane 20M and respectively serve to maintain distance
D.sub.GA between middle glass pane 20M and front pane 20F, and
distance D.sub.GB between the middle pane and back pane 20B. In the
example embodiment shown in FIG. 4A, a single edge seal 30 serves
to seal edges 28F, 28M and 28B. In another example embodiment,
multiple edge seals 30 are used, where one edge seal serves to seal
at least respective portions of edges 28F and 28M, and the other
edge seal serves to seal at least respective portions of edges 28M
and 28B (see FIG. 4B).
[0039] Edge seal 30 and glass pane surfaces 24F and 22M define a
first sealed interior region 40A, while edge seal 30 and glass pane
surfaces 24M and 24B define a second sealed interior region 40B.
Sealed interior regions 40A and 40B are preferably evacuated so
that they each have a vacuum pressure of less than one atmosphere,
which provides triple-pane VIG window 10 with desirable thermal
insulation and acoustic properties, and in particular with about
twice the insulation of a two-pane VIG window 10 such as shown in
FIG. 1 and FIG. 2.
[0040] FIG. 4B is similar to FIG. 4A, and illustrates an alternate
example embodiment of a three-pane VIG window 10, wherein the
second set of glass-bump spacers 50 are formed in inner surface 24B
of back glass pane 20B rather than in the middle glass pane 20M.
FIG. 4B also illustrates an example embodiment where multiple edge
seals 30 are used, as described above.
[0041] FIG. 4C is similar to FIG. 4B, and illustrates yet another
alternate example embodiment of a three-pane VIG window 10, wherein
the first set of glass-bump spacers 50 are formed in inner surface
24F of front glass pane 20F rather than in the middle glass pane
20M. Thus, in the embodiment illustrated in FIG. 4C, the glass-bump
spacers are formed in the inner and outer panes, while in the
embodiment illustrated in FIG. 4A, the glass-bump spacers are
formed in the middle pane.
[0042] As disclosed in further detail below, one or more optical
coatings such as low-emissivity coatings, can be formed over the
glass-bump spacers as well as over the surface in which the
glass-bump spacers are formed. For the sake of clarity, the optical
coating(s) have been omitted from the illustrated embodiments shown
in FIGS. 1, 2 and 4.
[0043] In an example embodiment, middle glass pane 20M is formed
from soda-lime glass or an alkali aluminosilicate glass, and in a
further example embodiment has a thickness T.sub.G between 0.5 mm
and 3 mm. In various embodiments, the first, second, and third
glass materials making up body portions 23F, 23B and 23M can
independently or in any combination comprise
chemically-strengthened glass. In an example embodiment, the front,
middle and back glass pane body portions 23F, 23M and 23B are made
of the same glass material.
[0044] While soda-lime glass is the most common window glass, the
VIG window disclosed herein can be applied to any type of glass in
which integral glass-bump spacers 50 can be formed using the
methods described in detail below. For example, the VIG window
disclosed herein applies to low-iron ("ultra-clear") window
glasses, as well as to the other glasses introduced and discussed
below.
Glass-Bump Spacer Formation
[0045] Available transparent glasses used for window panes tend to
have very little absorption at wavelengths where high-power lasers
are available, such as the near-infrared (NIR) band between about
800 .mu.m and 1600 .mu.m, or the ultraviolet (UV) band between
about 340 nm and about 380 nm. For example, alkaline earth
aluminosilicate glasses and sodium aluminosilicate glasses (e.g.,
glass such as Eagle.sup.2000.RTM. glass, EagleXG.TM. glass, 1317
glass, and Gorilla.TM. glass, all available from Corning
Incorporated, Corning, N.Y.) typically have a transmission spectra
as shown in FIG. 5A, and soda-lime glass typically has a
transmission spectra as shown in FIG. 5B. As evident from FIG. 5A
and FIG. 5B, the transmission of alkaline earth aluminosilicate and
soda-lime glasses is more than about 85% (including Fresnel losses
due to reflection at the glass/air interface) at a wavelength of
355 nm, which poses a challenge for heating even small volumes of
glass to temperatures close to a working point (.about.10.sup.5
Poise) unless lasers with several hundred watts of available output
power are used.
[0046] Unexpectedly, for certain transparent glass panes, including
those formed from alkaline earth aluminosilicate glasses (e.g., LCD
glasses such as the aforementioned Eagle 2000.TM. glass and Eagle
XG.TM. glass), soda-lime glasses and sodium aluminosilicate glasses
(e.g., the aforementioned 1317 glass and Gorilla.TM. glass), it has
been found that absorption at the laser wavelength can be raised to
a sufficient level by transmitting an intense UV laser beam through
the transparent glass pane. In particular, a high repetition-rate,
nanosecond-pulse-width UV laser was found to be the most effective.
On the order of a second or two of exposure with such a pulsed UV
laser beam was found to result in photo-induced absorption in the
otherwise relatively low-absorption transparent glass. This induced
glass absorption significantly increases at the UV wavelength,
making it possible to locally heat the glass pane to its working
temperature (using the same laser or a separate laser) and enables
the formation of glass-bumps 50. The UV-generated absorption fades
over a short period of time (e.g., a few seconds) once the
irradiation is terminated.
[0047] Other types of lasers, such as mid-infrared-wavelength
lasers, can be used instead of a UV laser for most transparent
glass materials. An example mid-infrared-wavelength laser generates
a laser beam having a wavelength of about 2.7 .mu.m. For the sake
of illustration, a UV laser is described and considered below in
connection with the apparatus used to form the VIG windows
disclosed herein.
[0048] FIG. 6 is a schematic diagram of an example laser-based
apparatus ("apparatus") 100 used to form glass-bump spacers 50 in a
glass pane 20 in the process of forming VIG window 10. Apparatus
100 includes a laser 110 arranged along an optical axis A1. Laser
110 emits a laser beam 112 having power P along the optical axis.
In an example embodiment, laser 110 operates in the ultraviolet
(UV) region of the electromagnetic spectrum.
[0049] With reference also to FIG. 7, in a particular example
embodiment, laser 110 is a pulsed laser that generates light pulses
112P that constitute laser beam 112, wherein the light pulses have
a UV wavelength (e.g., about 355 nm) and a nanosecond-scale
temporal pulse width .tau..sub.P. In an example embodiment, light
pulses 112P have a temporal pulse width .tau..sub.P in the range 20
ns.ltoreq..tau..sub.P.ltoreq.80 ns, and a repetition rate R in the
range 50 kHz.ltoreq.R.ltoreq.200 kHz. Further in the example
embodiment, laser 110 is a 20 Watt laser (i.e., P=20 W). In an
example embodiment, laser 110 comprises a third-harmonic Nd-based
laser. As shown in FIG. 7, light pulses 112P are spaced apart in
time by an amount .DELTA.t, thereby defining the repetition rate as
R=1/.DELTA.t.
[0050] Apparatus 110 also includes a focusing optical system 120
that is arranged along optical axis A1 and defines a focal plane
P.sub.F that includes a focal point FP. In an example embodiment,
focusing optical system 120 includes, along optical axis A1 in
order from laser 110: a combination of a defocusing lens 124 and a
first focusing lens 130 (which combination forms a beam expander),
and a second focusing lens 132. In an example embodiment,
defocusing lens 124 has a focal length f.sub.D=-5 cm, first
focusing lens 130 has a focal length f.sub.C1=20 cm, and second
focusing lens 132 has a focal length f.sub.C2=3 cm and a numerical
aperture NA.sub.C2=0.3. In an example embodiment, defocusing lens
124 and first and second focusing lenses 130 and 132 are made of
fused silica and include anti-reflection (AR) coatings. Alternate
example embodiments of focusing optical system 120 include mirrors
or combinations of mirrors and lens elements configured to produce
focused laser beam 112F from laser beam 112.
[0051] Apparatus 100 also includes a controller 150, such as a
laser controller, a microcontroller, computer, microcomputer or the
like, electrically connected to laser 110 and adapted to control
the operation of the laser. In an example embodiment, a shutter 160
is provided in the path of laser beam 112 and is electrically
connected to controller 150 so that the laser beam can be
selectively blocked to turn the laser beam "ON" and "OFF" using a
shutter control signal SS rather than turning laser 110 "ON" and
"OFF" with a laser control signal SL.
[0052] Prior to initiating the operation of apparatus 100, glass
pane 20 having a body portion 23 with a front surface 22 and back
surface 24, is disposed relative to the apparatus. Specifically,
glass pane 20 is disposed along optical axis A1 so that front and
back glass pane surfaces 22 and 24 are substantially perpendicular
to the optical axis and so that back glass pane surface 24 is
slightly axially displaced from focal plane P.sub.F in the
direction towards laser 110 (i.e., in the +Z direction) by a
distance D.sub.F. In an example embodiment, glass pane 20 has a
thickness T.sub.G in the range 0.5 mm.ltoreq.T.sub.G.ltoreq.6 mm.
Also in an example embodiment, 0.5 mm.ltoreq.D.sub.F.ltoreq.2 mm.
In this arrangement, glass-bump spacers are to be formed in glass
pane surface 24, which corresponds to surface 24B of back glass
pane 20B of FIG. 2.
[0053] Laser 110 is then activated via control signal SL from
controller 150 to generate laser beam 112. If shutter 160 is used,
then after laser 110 is activated, the shutter is activated and
placed in the "ON" position via shutter control signal SS from
controller 150 so that the shutter passes laser beam 112. Laser
beam 112 is then received by focusing optical system 120, and
defocusing lens 124 therein causes the laser beam to diverge to
form a defocused laser beam 112D. Defocused laser beam 112D is then
received by first focusing lens 130, which is arranged to form an
expanded collimated laser beam 112C from the defocused laser beam.
Collimated laser beam 112C is then received by second focusing lens
132, which forms a focused laser beam 112F. Focused laser beam 112F
passes through glass pane 20 and forms a focus spot S along optical
axis A1 at focal point FP, which, as mentioned above, is at
distance D.sub.F from glass pane back surface 24 and thus resides
outside of body portion 23. It is noted here that glass pane 20
slightly affects the position of focal point FP of optical system
20 because focused laser beam 112F converges as it passes through
the glass pane. However, the thickness T.sub.G of glass pane 20 is
typically sufficiently thin so that this focus-shifting effect can
be ignored.
[0054] A portion of focused laser beam 112F is absorbed as it
passes through glass pane 20 due to the aforementioned
photo-induced absorption in the glass pane. This serves to locally
heat glass pane 20. The amount of photo-induced absorption is
relatively low, e.g., about 3% to about 4%. When focused light beam
112F is locally absorbed in glass pane 20, a limited expansion zone
is created within body portion 23 in which a rapid temperature
change induces an expansion of the glass. Since the expansion zone
is constrained by unheated (and therefore unexpanded) regions of
glass surrounding the expansion zone, the glass within the
expansion zone is compelled to relieve internal stresses by
deforming upward, thereby forming a glass-bump spacer 50. As shown
in the inset of FIG. 6, glass-bump spacer 50 has a peak 51
corresponding to the location of the highest beam intensity. In an
example embodiment, glass-bump spacer 50 is fixed by rapidly
cooling the heated region of the glass. This fixing can be
accomplished by terminating the exposure with (i.e., the
irradiation by) focused laser beam 112F.
[0055] If focused light beam 112F has a circularly symmetric
cross-sectional intensity distribution, such as a Gaussian
distribution, then the local heating and the attendant glass
expansion occurs over a circular region in glass pane body 23, and
the resulting glass-bump spacer 50 is substantially circularly
symmetric.
[0056] The process can be repeated at different locations in the
glass pane to form a plurality (e.g., an array) of glass-bump
spacers 50 in glass pane 20. After formation of the glass-bump
spacers, the glass pane can optionally be processed further and
then incorporated into VIG window 10. In an example embodiment,
apparatus 100 includes an X-Y-Z stage 170 electrically connected to
controller 150 and configured to move glass pane 20 relative to
focused laser beam 112F in the X, Y and Z directions, as indicated
by large arrows 172. This allows for a plurality of glass-bump
spacers 50 to be formed by selectively translating stage 170 via a
stage control signal ST from controller 150 and irradiating
different locations in glass pane 20.
[0057] In an example embodiment, glass-bump spacers 50 are formed
in a regular array such as shown in FIG. 1. In an example
embodiment, the spacing between adjacent glass-bump spacers 50 is
between about 2 inches (i.e., about 5 cm) and 6 inches (i.e., about
15 cm). Also in an example embodiment, glass-bump spacer formation
is controlled using a feedback device or system that tracks the
growth of glass-bump spacers 50 so that the glass-bump spacers can
be formed to have a select height H that is substantially uniform
over the set of glass-bump spacers.
[0058] In one example embodiment, glass-bump spacer formation is
tracked by measuring the transmission T of focused laser beam 112F
through glass pane 20. In an example embodiment, this is
accomplished by arranging a photodetector 180 along axis A1 at the
output side of glass pane 20 and electrically connecting the
photodetector to controller 150. The transmission T of focused
laser beam 112F rapidly decreases when a glass-bump 50 is formed.
Accordingly, this rapid drop in transmission can be detected by a
change in an electrical detector signal SD generated by
photodetector 180 in response to detecting transmitted light in
focused laser beam 112F. Terminating the irradiation (exposure)
with focused laser beam 112F (e.g., via the operation of controller
150 using control signals SL or SS as described above) stops the
localized heating and fixes glass-bump spacer 50. In an example
embodiment, the measured transmission T is used to control the
irradiation dose.
[0059] In an alternate example embodiment, photodetector 180 is
arranged adjacent the input side of glass pane 20 and detects
fluorescence from glass pane body 23 during the irradiation
process. A threshold change in detected fluorescence can then be
used to terminate the exposure or to adjust the irradiation
dose.
[0060] In another example embodiment, a feedback sub-system can be
used to control the bump height of each glass-bump spacer by
controlling the irradiating. For example, a feedback sub-system can
be implemented to control the irradiating by monitoring one or more
of a transmission intensity of the focused laser beam through the
first glass pane, a temperature of each respective glass-bump
spacer, a fluorescence intensity emanating from each respective
glass-bump spacer, and a bump height of each respective glass-bump
spacer, and terminating the irradiating when a predetermined value
of the monitored variable is measured.
[0061] In another example embodiment, focusing optical system 120
is adapted for scanning so that focused laser beam 112F can be
selectively directed to locations in glass pane 20 where glass-bump
spacers 50 are to be formed.
[0062] Bump height H depends on several factors, which include the
laser power P, the repetition rate R, the focusing conditions, and
the glass material making up glass pane 20. FIG. 8 is a bar graph
that plots the laser power (W) in focused laser beam 112F, distance
D.sub.F between focal plane P.sub.F and back glass pane surface 24,
and bump height H for a glass pane made of soda-lime glass having a
thickness T.sub.G=3 mm. The bar graph of FIG. 8 is based in
experimental data and provides an example range of operating
parameters for forming glass-bump spacers 50 using apparatus 100
for the particular type of glass pane 20. The exposure
(irradiation) time used ranged between 2 to 2.5 sec and it was
observed that this variation did not significantly affect the bump
height H. The optimum repetition rate of the UV laser was found to
be R=150 kHz. The bump height H ranged from about 75 .mu.m for
D.sub.F of about 0.6 mm and a laser power P of about 9 W to about
170 .mu.m for D.sub.F of about 1.1 mm and a laser power of about 13
W.
[0063] Note that if bump heights H are too small, it could result
in a reduction in the amount of vacuum that can be applied to
interior region 40, leading to reduced insulation properties with
too small a gap between adjacent glass panes 20. The smaller
interior region volume that results also translates into reduced
insulation properties. In addition, small bump heights H can give
rise to the appearance of "Newton's rings" due to light
interference between closely arranged glass surfaces. It is
estimated that a bump height H.gtoreq.100 .mu.m is sufficient to
overcome these two potential problems for most VIG windows 10.
[0064] FIG. 9 is a three-dimensional image of a glass-bump spacer
50 formed in a soda-lime glass pane having a thickness T.sub.G=3
mm. FIG. 10 is a line-scan of glass-bump spacer 50 of FIG. 9. The
line scan reveals that glass-bump spacer 50 has a substantially
hemispherical shape, a bump height H of about 75 .mu.m and a base
diameter D.sub.B of about 250 .mu.m. In an embodiment, by providing
glass-bump spacers 50 having a small and curved point of contact
with an opposing glass pane, abrasion of the optical coating can be
minimized. Moreover, by minimizing the contact area between each
glass-bump spacer and the opposing glass pane, thermal transfer via
the glass-bump spacers can be minimized while achieving a
mechanically robust VIG window.
[0065] FIG. 11 is a three dimensional image of a glass-bump spacer
50 similar to that shown in FIG. 9, except that a growth-limiting
surface in the form of a glass plate was placed adjacent glass pane
surface 24 and then the glass pane irradiated as per above. The
resulting glass-bump spacer 50 grew to a certain bump height H and
then this growth was limited by the adjacent glass plate. The
result was a glass-bump spacer 50 having a substantially flat top
portion 51 with a diameter D.sub.T. In this way, the area, height
and shape of glass-bumps 50 can be controlled, and in particular
the diameter D.sub.T (and thus the surface area) of substantially
flat top portion 51 can be controlled. In an example embodiment,
substantially flat top portion 51 has a substantially circular
shape so that its surface area SA is approximated by the
relationship SA=.pi.[D.sub.T/2].sup.2. The total contact area
SA.sub.T presented by a set of n glass-bump spacers 50 is
approximated by SA.sub.T=.pi.n[D.sub.T/2].sup.2.
[0066] The size, shape and height of glass-bump spacers 50 can be
more accurately controlled by using more complicated
growth-limiting configurations or by altering the cross-sectional
shape of focused laser beam 112F. An advantage of controlling bump
height H is that it mitigates the variability in bump heights due
to glass non-uniformity and minor laser instability. Another
advantage of substantially flat-top glass-bump spacers 50 is the
reduction (including the minimization) of mechanical stresses at
the contact point between tip portions 51 and glass 20F.
[0067] In an example embodiment of VIG window 10, the total contact
area SA.sub.T is selected to increase and preferably optimize the
thermal insulation. It is estimated that for glass-bump spacers 50
having a base diameter D.sub.B in the range from about 300 .mu.m to
about 700 .mu.m, the substantially flat top portion 51 preferably
has a "top" diameter D.sub.T.ltoreq.100 .mu.m, more preferably
D.sub.T.ltoreq.75 .mu.m, and even more preferably D.sub.T.ltoreq.50
.mu.m.
[0068] Apparatus 100 enables glass-bump spacers 50 to have a
hemispherical shape largely because the swelling of the glass that
causes bump formation is controlled by the surface tension of the
molten glass. This effect is exploited by using a focused laser
beam 112F having a circularly symmetric cross-section. A rounded
profile for glass-bump spacers 50 is advantageous in that it
provides minimal total contact area S.sub.AT between the glass-bump
spacers and the adjacent glass pane, thereby reducing the heat
conductivity between the two glass panes. It is important to reduce
(and preferably minimize) this heat transfer mechanism in VIG
windows 10 because thermal insulation diminishes with increased
total contact area SA.sub.T. On the other hand, a very small
contact area SA per glass-bump spacer 50 may lead to local stress
concentration and can potentially damage the adjacent glass pane 20
and/or optical coatings 210.
[0069] To assess the visibility of laser-grown glass-bump spacers
50 in VIG window 10 versus that of discrete spacers used in
conventional VIG windows, several photos were taken at different
tilt angles relative to the surface normal of the VIG window. While
glass-bump spacers 50 were visible when viewed at glazing incident
angles, they became practically invisible at the more usual
near-incident viewing angles. The photos of VIG window 10 were then
compared to photos taken under virtually identical conditions for a
commercial window pane having discrete ceramic spacers. The
discrete ceramic spacers were much more visible, particularly at
the usual, near-incident viewing angles.
[0070] As shown in FIG. 4A, in an example embodiment, glass-bump
spacers 50 are formed in both sides 22M and 24M of middle glass
pane 20M to form triple-pane VIG window 10. Double-side glass-bump
spacers 50 are formed in one example embodiment by altering the
irradiation conditions as compared with forming single-side bumps.
By way of example, in one approach glass-bump spacers 50 are formed
in one side 22M of glass pane 20M, and then the glass pane is
turned over and more glass-bumps are formed in the other side 24M.
In this embodiment, it may be necessary to slightly displace the
two sets of glass-bump spacers 50 formed in the respective sides of
middle glass pane 20M to avoid irradiating the previously formed
glass-bump spacers. The amount of this displacement is, for
example, equal to or up to about twice the base diameter D.sub.B,
which is typically in the order of 200 .mu.m to 700 .mu.m and is
thus quite small when compared to the size of a typical VIG window
10.
[0071] It is anticipated that the use of integrally formed
glass-bump spacers 50 for VIG windows 10 will be more cost
effective than disposing and fixing discrete (i.e., non-integral)
spacers to a glass pane. This is largely because the disclosed
approach obviates the need for equipment and processes for placing
discrete spacers in precise positions and keeping them in place
while assembling the VIG window. Because of the smaller and
controllable contact area SA between the tip portion 51 of
glass-bump 50 and adjacent glass pane 20, heat transfer through VIG
window 10 via thermal conduction is reduced (and preferably
minimized) relative to the use of discrete spacers. Cost advantages
become even more evident in the case of manufacturing a triple-pane
VIG window, where handling and placement of the discrete spacers
can be quite challenging.
[0072] Example embodiments of VIG window 10 employ glass panes 20
having different material compositions. For example, one glass pane
20 (e.g., back glass pane 20B in FIG. 2) is formed from a first
glass type and another glass pane (e.g., front glass pane 20F) is
formed from a second glass type. For example, the first glass type
is soda-lime window glass while the second glass type is an
ion-exchanged sodium aluminosilicate glass (e.g., 1317, 2317, and
others), or vice versa. Furthermore, in embodiments where a
chemically-strengthened (e.g., ion-exchanged) glass pane is used,
the chemically-strengthened pane can be thinner (e.g., 0.5-2 mm)
than conventional (e.g., 2-4 mm soda-lime) glass panes, which can
reduce the total thickness and weight of a VIG window 10 while
maintaining comparable or superior mechanical properties.
[0073] Glass-bump formation experiments conducted in sodium
aluminosilicate glass 1317 ("1317 glass") revealed a high degree of
swelling capability, with bump heights H of 155 .mu.m formed in a
sample having a thickness T.sub.G=1.3 mm. It is noted here that
soda-lime window glass and 1317 glass have similar coefficients of
thermal expansion (CTEs) of about 9 ppm/.degree. C.
[0074] In experiments conducted in "ultra-white" window glass panes
20 that have a very low iron content (and thus do not have a
greenish tint), glass-bump spacers 50 with bump heights H of about
212 .mu.m were formed using the above methods. Thus, in an example
embodiment, glass-bump spacers 50 formed in low-iron content
glasses have a bump height H in the range from 75 .mu.m to 225
.mu.m, more preferably in the range from 100 .mu.m to 225 .mu.m,
and even more preferably in the range from 150 .mu.m to 225
.mu.m.
[0075] Glass panes for use in VIG windows can be made using a
variety of glass sheet forming methods. Example glass sheet forming
methods include fusion draw and slot draw processes, which are each
examples of a down-draw process, as well as float processes. The
fusion draw process uses a drawing tank that has a channel for
accepting molten glass raw material. The channel has weirs that are
open at the top along the length of the channel on both sides of
the channel. When the channel fills with molten material, the
molten glass overflows the weirs. Due to gravity, the molten glass
flows down the outside surfaces of the drawing tank. These outside
surfaces extend down and inwardly so that they join at an edge
below the drawing tank. The two flowing glass surfaces join at this
edge to fuse and form a single flowing sheet. The fusion draw
method offers the advantage that, because the two glass films
flowing over the channel fuse together, neither outside surface of
the resulting glass sheet comes in contact with any part of the
apparatus. Thus, the surface properties of the fusion drawn glass
sheet are not affected by such contact.
[0076] The slot draw method is distinct from the fusion draw
method. Here the molten raw material glass is provided to a drawing
tank. The bottom of the drawing tank has an open slot with a nozzle
that extends the length of the slot. The molten glass flows through
the slot/nozzle and is drawn downward as a continuous sheet and
into an annealing region. The slot draw process can provide a
thinner sheet than the fusion draw process because only a single
sheet is drawn through the slot, rather than two sheets being fused
together.
[0077] Down-draw processes produce surfaces that are relatively
pristine. Because the strength of the glass surface is controlled
by the amount and size of surface flaws, a pristine surface that
has had minimal contact has a higher initial strength. When this
high strength glass is then chemically strengthened, the resultant
strength can be higher than that of a surface that has been a
lapped and polished. Down-drawn glass may be drawn to a thickness
of less than about 2 mm. In addition, down drawn glass has a very
flat, smooth surface that can be used in its final application
without costly grinding and polishing.
[0078] In the float glass method, a sheet of glass that may be
characterized by smooth surfaces and uniform thickness is made by
floating molten glass on a bed of molten metal, typically tin. In
an example process, molten glass that is fed onto the surface of
the molten tin bed forms a floating ribbon. As the glass ribbon
flows along the tin bath, the temperature is gradually decreased
until a solid glass sheet can be lifted from the tin onto rollers.
Once off the bath, the glass sheet can be cooled further and
annealed to reduce internal stress. Glass sheets, once formed, can
be cut and shaped as desired to form a window pane for
incorporation into a VIG window.
[0079] The glass window can be substantially flat or shaped for
certain applications. For instance, the windows can be formed as
bent or shaped parts for use as windshields or cover plates. The
structure of a shaped VIG window may be simple or complex. In
certain embodiments, a shaped VIG window may have a simple
curvature. In certain embodiments, a shaped VIG window may have a
complex curvature where the glass panes have a distinct radius of
curvature in two independent directions. Such shaped or curved
glass panes may thus be characterized as having "cross curvature,"
where the glass is curved along an axis that is parallel to a given
dimension and also curved along an axis that is perpendicular to
the same dimension. An automobile sunroof, for example, typically
measures about 0.5 m by 1.0 m and has a radius of curvature of 2 to
2.5 m along the minor axis, and a radius of curvature of 4 to 5 m
along the major axis.
[0080] Shaped VIG windows according to certain embodiments can be
defined by a bend factor, where the bend factor for a given part is
equal to the radius of curvature along a given axis divided by the
length of that axis. Thus, for the example automotive sunroof
having radii of curvature of 2 m and 4 m along respective axes of
0.5 m and 1.0 m, the bend factor along each axis is 4. Shaped glass
windows can have a bend factor ranging from 2 to 8 (e.g., 2, 3, 4,
5, 6, 7, or 8).
[0081] Methods for bending and/or shaping glass panes can include
gravity bending, press bending and methods that are hybrids
thereof.
[0082] In a traditional method of gravity bending thin, flat sheets
of glass into curved shapes such as automobile windshields, cold,
pre-cut single or multiple glass sheets are placed onto the rigid,
pre-shaped, peripheral metal support surface of a bending fixture.
Prior to bending, the glass typically is supported only at a few
contact points. The glass is heated, usually by exposure to
elevated temperatures in a lehr, which softens the glass allowing
gravity to sag or slump the glass into conformance with the
peripheral support surface. Substantially the entire support
surface generally will then be in contact with the periphery of the
glass.
[0083] A related technique is press bending where flat glass sheets
are heated to a temperature corresponding substantially to the
softening point of the glass. The heated sheets are then pressed or
shaped to a desired curvature between male and female mold members
having complementary shaping surfaces.
[0084] A thickness of the assembled VIG window can range from about
2 mm to 4 mm, where the individual glass panes can have a thickness
of from 0.5 to 2 mm (e.g., 0.1, 0.2, 0.3, 0.5, 0.7, 1, 1.4, 1.7, or
2 mm). In embodiments, a chemically-strengthened glass sheet can
have a thickness of less than 1.4 mm or less than 1.0 mm.
Chemically-Strengthened Glass Sheets
[0085] As noted above, the vacuum insulated glass windows disclosed
herein comprise one or more chemically-strengthened glass sheets.
Due to chemical strengthening, one or both of the surfaces of the
chemically-strengthened panes that are incorporated into the VIG
windows are under compression. In order for flaws to propagate and
failure of the glass to occur, the tensile stress from an impact
must exceed the surface compressive stress. In embodiments, the
high compressive stress and high depth of layer of
chemically-strengthened glass sheets enable the use of thinner
glass than in the case of non-chemically-strengthened glass.
[0086] Glass sheets may be chemically strengthened by an ion
exchange process. In this process, typically by immersion of the
glass sheet into a molten salt bath for a predetermined period of
time, ions at or near the surface of the glass sheet are exchanged
for larger metal ions from the salt bath. The temperature of the
molten salt bath is typically about 400-500.degree. C. and the
predetermined time period can range from about two to ten hours.
The incorporation of the larger ions into the glass strengthens the
sheet by creating a compressive stress in a near surface region. A
corresponding tensile stress is induced within a central region of
the glass to balance the compressive stress.
[0087] Example ion-exchangeable glasses that are suitable for
forming glass panes are alkali aluminosilicate glasses or alkali
aluminoborosilicate glasses, though other glass compositions are
contemplated. As used herein, "ion exchangeable" means that a glass
is capable of exchanging cations located at or near the surface of
the glass with cations of the same valence that are either larger
or smaller in size. One example glass composition comprises
SiO.sub.2, B.sub.2O.sub.3 and Na.sub.2O, where
(SiO.sub.2+B.sub.2O.sub.3).gtoreq.66 mol %, and Na.sub.2O.gtoreq.9
mol %. In an embodiment, the glass sheets include at least 6 wt. %
aluminum oxide. In a further embodiment, a glass sheet includes one
or more alkaline earth oxides, such that a content of alkaline
earth oxides is at least 5 wt. %. Suitable glass compositions, in
some embodiments, further comprise at least one of K.sub.2O, MgO,
and CaO. In a particular embodiment, the glass can comprise 61-75
mol % SiO.sub.2; 7-15 mol % Al.sub.2O.sub.3; 0-12 mol %
B.sub.2O.sub.3; 9-21 mol % Na.sub.2O; 0-4 mol % K.sub.2O; 0-7 mol %
MgO; and 0-3 mol % CaO.
[0088] A further example glass composition suitable for forming
glass panes comprises: 60-70 mol % SiO.sub.2, 6-14 mol %
Al.sub.2O.sub.3, 0-15 mol % B.sub.2O.sub.3, 0-15 mol % Li.sub.2O,
0-20 mol % Na.sub.2O, 0-10 mol % K.sub.2O, 0-8 mol % MgO, 0-10 mol
% CaO, 0-5 mol % ZrO.sub.2, 0-1 mol % SnO.sub.2, 0-1 mol %
CeO.sub.2, less than 50 ppm As.sub.2O.sub.3, and less than 50 ppm
Sb.sub.2O.sub.3, where 12 mol
%.ltoreq.(Li.sub.2O+Na.sub.2O+K.sub.2O).ltoreq.20 mol % and 0 mol
%.ltoreq.(MgO+CaO) 10 mol %.
[0089] A still further example glass composition comprises:
63.5-66.5 mol % SiO.sub.2, 8-12 mol % Al.sub.2O.sub.3, 0-3 mol %
B.sub.2O.sub.3, 0-5 mol % Li.sub.2O, 8-18 mol % Na.sub.2O, 0-5 mol
% K.sub.20, 1-7 mol % MgO, 0-2.5 mol % CaO, 0-3 mol % ZrO.sub.2,
0.05-0.25 mol % SnO.sub.2, 0.05-0.5 mol % CeO.sub.2, less than 50
ppm As.sub.2O.sub.3, and less than 50 ppm Sb.sub.2O.sub.3, where 14
mol %.ltoreq.(Li.sub.2O+Na.sub.2O+K.sub.2O).ltoreq.18 mol % and 2
mol %.ltoreq.(MgO+CaO) 7 mol %.
[0090] In a particular embodiment, an alkali aluminosilicate glass
comprises alumina, at least one alkali metal and, in some
embodiments, greater than 50 mol % SiO.sub.2, in other embodiments
at least 58 mol % SiO.sub.2, and in still other embodiments at
least 60 mol % SiO.sub.2, wherein the ratio
Al 2 O 3 + B 2 O 3 modifiers > 1. ##EQU00001##
In the expressed ratio the components are expressed in mol % and
the modifiers are alkali metal oxides. Such a glass, in particular
embodiments, comprises, consists essentially of, or consists of:
58-72 mol % SiO.sub.2, 9-17 mol % Al.sub.2O.sub.3, 2-12 mol %
B.sub.2O.sub.3, 8-16 mol % Na.sub.2O, and 0-4 mol % K.sub.2O,
wherein the ratio
Al 2 O 3 + B 2 O 3 modifiers > 1. ##EQU00002##
[0091] In another embodiment, an alkali aluminosilicate glass
comprises, consists essentially of, or consists of: 61-75 mol %
SiO.sub.2, 7-15 mol % Al.sub.2O.sub.3, 0-12 mol % B.sub.2O.sub.3,
9-21 mol % Na.sub.2O, 0-4 mol % K.sub.2O, 0-7 mol % MgO, and 0-3
mol % CaO.
[0092] In yet another embodiment, an alkali aluminosilicate glass
substrate comprises, consists essentially of, or consists of: 60-70
mol % SiO.sub.2, 6-14 mol % Al.sub.2O.sub.3, 0-15 mol %
B.sub.2O.sub.3, 0-15 mol % Li.sub.2O, 0-20 mol % Na.sub.2O, 0-10
mol % K.sub.2O, 0-8 mol % MgO, 0-10 mol % CaO, 0-5 mol % ZrO.sub.2,
0-1 mol % SnO.sub.2, 0-1 mol % CeO.sub.2, less than 50 ppm
As.sub.2O.sub.3, and less than 50 ppm Sb.sub.2O.sub.3, wherein 12
mol %.ltoreq.Li.sub.2O+Na.sub.2O+K.sub.2O.ltoreq.20 mol % and 0 mol
%.ltoreq.MgO+CaO.ltoreq.10 mol %.
[0093] In still another embodiment, an alkali aluminosilicate glass
comprises, consists essentially of, or consists of: 64-68 mol %
SiO.sub.2, 12-16 mol % Na.sub.2O, 8-12 mol % Al.sub.2O.sub.3, 0-3
mol % B.sub.2O.sub.3, 2-5 mol % K.sub.2O, 4-6 mol % MgO, and 0-5
mol % CaO, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %,
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %, 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %,
(Na.sub.2O+B.sub.2O.sub.3)-Al.sub.2O.sub.3.ltoreq.2 mol %, 2 mol
%.ltoreq.Na.sub.2O-Al.sub.2O.sub.3.ltoreq.6 mol %, and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)-Al.sub.2O.sub.3.ltoreq.10 mol %.
[0094] The window glass, in some embodiments, is batched with 0-2
mol % of at least one fining agent selected from a group that
includes Na.sub.2SO.sub.4, NaCl, NaF, NaBr, K.sub.2SO.sub.4, KCl,
KF, KBr, and SnO.sub.2.
[0095] In one example embodiment, sodium ions in the glass can be
replaced by potassium ions from the molten bath, though other
alkali metal ions having a larger atomic radii, such as rubidium or
cesium, can replace smaller alkali metal ions in the glass.
According to particular embodiments, smaller alkali metal ions in
the glass can be replaced by Ag.sup.+ ions. Similarly, other alkali
metal salts such as, but not limited to, sulfates, halides, and the
like may be used in the ion exchange process.
[0096] The replacement of smaller ions by larger ions at a
temperature below that at which the glass network can relax
produces a distribution of ions across the surface of the glass
that results in a stress profile. The larger volume of the incoming
ion produces a compressive stress (CS) on the surface and tension
(central tension, or CT) in the center of the glass. The
compressive stress is related to the central tension by the
following relationship:
CS = CT ( t - 2 DOL DOL ) ##EQU00003##
where t is the total thickness of the glass sheet and DOL is the
depth of exchange, also referred to as depth of layer.
Optical Coatings
[0097] One or more optical coatings may be incorporated into a VIG
window. In embodiments, the optical coatings comprise one or more
polymer layers that may provide complimentary or distinct
functionality, including acoustic control, UV transmission control,
and/or IR transmission control.
[0098] Low-emissivity coatings typically include a layer of an
infrared-reflecting film and one or more optional layers of a
transparent dielectric film. The infrared-reflecting film, which
generally comprises a conductive metal such as silver, gold or
copper, reduces the transmission of heat through the coated pane. A
dielectric film can be used to anti-reflect the infrared-reflecting
film and to control other properties and characteristics of the
coating, such as color and durability. Commonly used dielectric
materials include oxides of zinc, tin, indium, bismuth, and
titanium, among others.
[0099] Example low-emissivity coatings include one or two silver
layers each sandwiched between two layers of a transparent
dielectric film. Increasing the number of silver layers can
increase the total infrared reflection, although additional silver
layers can also reduce the visible transmission through the window
and/or negatively impact the coating's color or durability.
[0100] Optical coatings may be applied using a conventional
film-forming process such as physical or chemical vapor deposition
or, for larger area glass panes, via lamination. During the
lamination process, a thin film of the coating material is
typically heated to a temperature effective to soften the coating
material, which promotes a conformal mating of the coating material
to a surface of a glass panes. Mobile polymer chains within the
coating material develop bonds with the glass surfaces, which
promote adhesion. Elevated temperatures also accelerate the
diffusion of residual air and/or moisture from the glass-coating
interface.
[0101] The application of pressure both promotes flow of the
coating material, and suppresses bubble formation that otherwise
could be induced by the combined vapor pressure of water and air
trapped at the interfaces. To suppress bubble formation, heat and
pressure are simultaneously applied to the assembly in an
autoclave.
[0102] FIG. 12 is a schematic side view of an example glass pane 20
that has an infrared-reflective coating 210 formed over back
surface 24. Such glass panes are useful in VIG windows because they
can attenuate the amount of transmitted (i.e., heat generating)
radiation.
[0103] FIG. 13 is a close-up cross-sectional view similar to that
of FIG. 12, but for the IR-reflective glass pane 20 of FIG. 12,
showing a glass-bump spacer 50 formed thereon. If the reflective
coating 210 is formed prior to forming the glass-bump spacer, since
the coating 210 has a much lower melting point than glass pane 20,
it melts away from the vicinity of glass-bump spacer 50, leaving it
uncoated. Any remnants of coating 210 are easily removed by
cleaning back surface 24 using standard glass cleaning
techniques.
[0104] In contrast, by incorporating the reflective coating 210
after formation of the glass-bump spacer 50, the reflective coating
210 forms a substantially conformal coating over the entire back
surface of the pane, including the glass-bump spacer 50. FIG. 14 is
a cross-sectional view of an IR-reflective pane 20 comprising a
reflective coating 210 formed over back surface 24 as well as over
glass-bump spacer 50 formed in the back surface.
VIG Window Formation
[0105] An embodiment of the disclosure relates to forming a VIG
window, such as VIG window 10. With reference to FIG. 14 and again
to FIG. 1 and FIG. 2, an example method of forming a VIG window 10
includes forming, in a first (back) glass pane 20B comprising a
first glass material, a plurality of glass-bump spacers 50
consisting of the first glass material from the first body portion
23. The method then includes forming an optical coating over both
the glass-bump spacers and the surface in which the glass bump
spacers are formed and bringing a second (front) glass pane 20F of
a second glass material in contact with the first plurality of
glass-bump spacers 50 so that the first and second glass panes are
spaced apart by first distance D.sub.G between respective surfaces
24F and 24B. The method then includes sealing at least respective
portions of the first and second edges 28F and 28B with edge seal
30 to define interior region 40 between front and back glass panes
20F and 20B. Interior region 40 is then at least partially
evacuated to form a vacuum pressure therein of less than one
atmosphere. In embodiments, one or both panes of glass can comprise
chemically-strengthened glass. In a particular example embodiment,
the second glass pane is a chemically-strengthened glass pane.
[0106] A method of forming a three-pane VIG window 10 is similar to
the formation of the two-pane VIG window and is now discussed with
reference to FIG. 4A, FIG. 4B and FIG. 4C. With reference first to
FIG. 4A, in an example embodiment the formation of three-pane VIG
window 10 involves forming two sets of glass-bump spacers in a
middle ("first") glass pane 20M that resides between front (second)
and back (third) glass panes 20F and 20B. Middle glass pane 20M
thus has first and second pluralities (sets) of glass-bump spacers
50 in respective surfaces 22M and 24M. Middle glass pane 20M also
has an outer edge 28M and is made up of a first glass material.
[0107] The method further includes forming an optical coating 210
over one or both of the surfaces of the middle glass pane, such
that each optical coating 210 is formed over both the glass-bump
spacers 50 and over the respective surface 22M and 24M in which the
glass bump spacers are formed. Then, the front and back glass panes
20F and 20B (made up of a second and third glass materials,
respectively) can be brought into respective contact with the first
and second plurality of glass-bump spacers 50 so that front, middle
and back glass panes 20F, 20M and 20B are spaced apart by a
distance D.sub.GA between surfaces 24F and 22M, and so that middle
and back glass panes 20M and 20B are spaced apart by a distances
D.sub.GB between surfaces 24M and 24B.
[0108] The method then includes sealing at least respective
portions of the front, middle and back edges 28F, 28M and 28B of
the three glass panes with one or more edge seals 30 (one edge seal
30 is shown in FIG. 4A). This serves to define first and second
interior regions 40A and 40B between the front and middle glass
panes 20F and 20M and the middle and back glass panes 20M and 20B,
respectively. Interior regions 40A and 40B are then at least
partially evacuated to form respective vacuum pressures therein of
less than one atmosphere. In embodiments, at least on the glass
panes is a chemically-strengthened glass pane. In a particular
example embodiment, the first and third glass panes are
chemically-strengthened glass panes. The configuration of the glass
panes showing conformal optical coatings formed over the middle
pane is shown schematically in FIG. 15.
[0109] In alternate embodiments that are illustrated with reference
to FIG. 4B and FIG. 4C, rather than forming both sets of glass-bump
spacers 50 in middle glass pane 20M, they can be formed, as
illustrated with reference to FIG. 4B and FIG. 16, in one surface
22M of the middle pane 20M and in inner surface 24B of back glass
pane 20B or, as shown as illustrate with reference to FIG. 4C and
FIG. 17, in inner surface 24F of the front glass pane 20F and in
inner surface 24B of back glass pane 20B. The optical coatings and
edge seals can be formed as described above. By way of example, as
shown in FIG. 4B, the method of forming triple-pane VIG window 10
can include using one edge seal 30 to seal at least respective
portions of edges 28F and 28M to form the vacuum seal for first
interior regions 40A, and another edge seal to seal at least
respective portions of edges 28M and 20B to form the vacuum seal
for second interior region 40B.
[0110] The foregoing low-E VIG windows can be used to provide
beneficial effects, including the attenuation of acoustic noise,
reduction of UV and/or IR light transmission, and/or enhancement of
the aesthetic appeal of a window opening in a light-weight,
mechanically-robust package.
[0111] As used herein, the singular forms "a," "an," and "the"
include plural referents unless the context clearly dictates
otherwise. Thus, for example, reference to a "metal" includes
examples having two or more such "metals" unless the context
clearly indicates otherwise.
[0112] Ranges can be expressed herein as from "about" one
particular value, and/or to "about" another particular value. When
such a range is expressed, examples include from the one particular
value and/or to the other particular value. Similarly, when values
are expressed as approximations, by use of the antecedent "about,"
it will be understood that the particular value forms another
aspect. It will be further understood that the endpoints of each of
the ranges are significant both in relation to the other endpoint,
and independently of the other endpoint.
[0113] Unless otherwise expressly stated, it is in no way intended
that any method set forth herein be construed as requiring that its
steps be performed in a specific order. Accordingly, where a method
claim does not actually recite an order to be followed by its steps
or it is not otherwise specifically stated in the claims or
descriptions that the steps are to be limited to a specific order,
it is no way intended that any particular order be inferred.
[0114] It is also noted that recitations herein refer to a
component of the present invention being "configured" or "adapted
to" function in a particular way. In this respect, such a component
is "configured" or "adapted to" embody a particular property, or
function in a particular manner, where such recitations are
structural recitations as opposed to recitations of intended use.
More specifically, the references herein to the manner in which a
component is "configured" or "adapted to" denotes an existing
physical condition of the component and, as such, is to be taken as
a definite recitation of the structural characteristics of the
component.
[0115] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Since
modifications combinations, sub-combinations and variations of the
disclosed embodiments incorporating the spirit and substance of the
invention may occur to persons skilled in the art, the invention
should be construed to include everything within the scope of the
appended claims and their equivalents.
* * * * *