U.S. patent application number 17/181135 was filed with the patent office on 2021-06-10 for strengthened thin glass-polymer laminates.
The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Kiat Chyai Kang, Govindarajan Natarajan, Yu Xiao.
Application Number | 20210170722 17/181135 |
Document ID | / |
Family ID | 1000005407688 |
Filed Date | 2021-06-10 |
United States Patent
Application |
20210170722 |
Kind Code |
A1 |
Kang; Kiat Chyai ; et
al. |
June 10, 2021 |
STRENGTHENED THIN GLASS-POLYMER LAMINATES
Abstract
A glass-polymer laminate structure includes a flexible glass
substrate having a thickness of no more than about 0.3 mm. A
polymer layer is laminated to a surface of the flexible glass
substrate having a coefficient of thermal expansion (CTE) that is
at least about 2 times a CTE of the flexible glass substrate. The
polymer layer is laminated to the surface of the flexible glass
substrate after thermally expanding the polymer layer to provide
the flexible glass substrate with an in-plane compressive stress of
at least about 30 MPa along a thickness of the flexible glass
substrate.
Inventors: |
Kang; Kiat Chyai; (Painted
Post, NY) ; Natarajan; Govindarajan; (Poughkeepsie,
NY) ; Xiao; Yu; (Pittsford, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
Corning |
NY |
US |
|
|
Family ID: |
1000005407688 |
Appl. No.: |
17/181135 |
Filed: |
February 22, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14423956 |
Feb 25, 2015 |
10953633 |
|
|
PCT/US2013/056755 |
Aug 27, 2013 |
|
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17181135 |
|
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61695781 |
Aug 31, 2012 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29K 2909/08 20130101;
B29K 2105/0097 20130101; B29C 65/54 20130101; B32B 17/101 20130101;
B32B 27/308 20130101; B32B 2457/00 20130101; B29C 66/7465 20130101;
B32B 17/10752 20130101; B29L 2009/00 20130101; B32B 17/10018
20130101; Y10T 428/266 20150115; Y10T 428/24628 20150115; B29K
2833/12 20130101; B32B 2255/10 20130101; B29K 2105/253 20130101;
B32B 17/06 20130101; B32B 7/12 20130101; B32B 2250/02 20130101;
B32B 17/10036 20130101; B32B 27/06 20130101; B29C 65/02 20130101;
B29L 2031/3412 20130101; B29K 2995/0026 20130101; B32B 17/10743
20130101 |
International
Class: |
B32B 17/06 20060101
B32B017/06; B29C 65/00 20060101 B29C065/00; B32B 17/10 20060101
B32B017/10; B29C 65/02 20060101 B29C065/02; B32B 27/30 20060101
B32B027/30; B32B 7/12 20060101 B32B007/12; B29C 65/54 20060101
B29C065/54; B32B 27/06 20060101 B32B027/06 |
Claims
1. A method of forming a flexible glass-polymer laminate structure,
the method comprising: heating a polymer layer of the flexible
glass-polymer laminate structure to an elevated temperature of
greater than 20.degree. C., the polymer layer having a coefficient
of thermal expansion (CTE) that is at least 2 times a CTE of a
flexible glass substrate of the flexible glass-polymer laminate
structure, or having a coefficient of thermal expansion (CTE) that
is at least about 3 ppm/.degree. C. greater than a CTE of the
flexible glass substrate of the flexible glass-polymer laminate
structure; laminating the polymer layer at the elevated temperature
to the flexible glass substrate; and cooling the polymer layer
below the elevated temperature to introduce a compressive stress of
at least about 30 MPa across a thickness of the flexible glass
substrate.
2. The method of claim 1, wherein the flexible glass substrate has
a compressive stress of at least about 80 MPa across a thickness of
the flexible glass substrate.
3. The method of claim 1, wherein the polymer layer has a CTE that
is at least about 10 times the CTE of the flexible glass
substrate.
4. The method of claim 1, comprising expanding the polymer layer
relative to the flexible glass substrate as the polymer layer is
heated to the elevated temperature.
5. The method of claim 1, further comprising applying an adhesive
layer between the flexible glass substrate and the polymer layer
that laminates the polymer layer to the flexible glass
substrate.
6. The method of claim 1, further comprising cooling the polymer
layer below the elevated temperature to bend the flexible glass
substrate while simultaneously providing a compressive stress
across at least a portion of thickness of the flexible glass
substrate.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/423,956 filed on Feb. 25, 2015, which claims the
benefit of priority under 35 U.S.C. .sctn. 371 of International
Application No. PCT/US2013/056755, filed on Aug. 27, 2013, which
claims the benefit of priority under 35 U.S.C. .sctn. 119 of U.S.
Provisional Application Ser. No. 61/695,781 filed on Aug. 31, 2012
the content of each of which is relied upon and incorporated herein
by reference in its entirety.
FIELD
[0002] The present invention relates to glass-polymer laminate
structures and, more particularly, to strengthened thin
glass-polymer laminate structures.
BACKGROUND
[0003] Flexible polymer substrates are manufactured using a polymer
base material laminated with one or more polymer films. These
laminated substrate stacks are commonly used in flexible packaging
associated with PV, OLED, LCDs and patterned Thin Film Transistor
(TFT) electronics because of their low cost and demonstrated
performance.
[0004] In order to promote flexible glass structures as an
alternate technology selection, the real and perceived limitations
of mechanical reliability performance associated with glass, a
brittle material, must be overcome and demonstrated. Flexible glass
substrates offer several technical advantages over flexible polymer
technology. One technical advantage is the ability of the glass to
serve as a moisture or gas barrier, a primary degradation mechanism
in outdoor electronics. A second advantage is in its potential to
reduce overall package size (thickness) and weight through the
reduction or elimination of one or more package substrate layers.
Another advantage is having excellent surface qualities associated
with glass that can be cleaned easily. Thus, if the real and
perceived limitations of mechanical reliability performance
associated with glass can be overcome, the use of flexible glass
structures can be advanced.
SUMMARY
[0005] One technique to improve the mechanical reliability of bare
flexible glass is to laminate the flexible glass substrate with one
or more thin film polymers. Depending on the mechanical strength
requirements and the expected bending stresses and direction of the
end application, according to the concepts disclosed herein, a
flexible glass-polymer laminate substrate can be designed to meet
mechanical requirements. When used properly, the laminated
structure will offer improved mechanical reliability performance
over a flexible un-laminated (bare glass) structure.
[0006] Additional features and advantages will be set forth in the
detailed description which follows, and in part will be readily
apparent to those skilled in the art from the description or
recognized by practicing the invention as exemplified in the
written description and the appended drawings. It is to be
understood that both the foregoing general description and the
following detailed description are merely exemplary of the
invention, and are intended to provide an overview or framework to
understanding the nature and character of the invention as it is
claimed.
[0007] The accompanying drawings are included to provide a further
understanding of principles of the invention, and are incorporated
in and constitute a part of this specification. The drawings
illustrate one or more embodiment(s), and together with the
description serve to explain, by way of example, principles and
operation of the invention. It is to be understood that various
features of the invention disclosed in this specification and in
the drawings can be used in any and all combinations. By way of
non-limiting example the various features of the invention may be
combined with one another according to the following aspects.
[0008] According to a first aspect, there is provided a
glass-polymer laminate structure comprising:
[0009] a flexible glass substrate having a thickness of no more
than about 0.3 mm; and
[0010] a polymer layer laminated to a surface of the flexible glass
substrate having a coefficient of thermal expansion (CTE) that is
at least about 2 times a CTE of the flexible glass substrate, the
polymer layer laminated to the surface of the flexible glass
substrate after thermally expanding the polymer layer to provide
the flexible glass substrate with a compressive stress of at least
about 30 MPa across a thickness of the flexible glass
substrate.
[0011] According to a second aspect, a glass-polymer laminate
structure comprising:
[0012] a flexible glass substrate having a thickness of no more
than about 0.3 mm; and
[0013] a polymer layer laminated to a surface of the flexible glass
substrate having a coefficient of thermal expansion (CTE) that is
at least about 3 ppm/.degree. C. greater than a CTE of the flexible
glass substrate, the polymer layer laminated to the surface of the
flexible glass substrate after thermally expanding the polymer
layer to provide the flexible glass substrate with a compressive
stress of at least about 30 MPa across a thickness of the flexible
glass substrate.
[0014] According to a third aspect, there is provided the laminate
structure of aspect 1 or aspect 2, wherein the flexible glass
substrate has an in-plane compressive stress of at least about 80
MPa across the thickness of the flexible glass substrate.
[0015] According to a fourth aspect, there is provided the laminate
of any one of aspects 1 to 3, wherein the polymer layer has a CTE
that is at least about 10 times the CTE of the flexible glass
substrate.
[0016] According to a fifth aspect, there is provided the laminate
of any one of aspects 1 to 4, further comprising an adhesive layer
that laminates the polymer layer to the flexible glass
substrate.
[0017] According to a sixth aspect, there is provided the laminate
of aspect 5, wherein the adhesive layer is heat activated, having
an activation temperature of greater than about 50.degree. C.
[0018] According to a seventh aspect, there is provided the
laminate of aspect 5, wherein the adhesive layer is a pressure
sensitive adhesive.
[0019] According to an eighth aspect, there is provided the
laminate of aspect 5, wherein the adhesive layer is UV
activated.
[0020] According to a ninth aspect, there is provided the laminate
of aspect 1 to 8, wherein the flexible glass substrate is a first
flexible glass substrate, the laminate structure further comprising
a second flexible glass substrate laminated to the polymer layer,
the polymer layer being between the first and second flexible glass
substrates.
[0021] According to a tenth aspect, there is provided the laminate
of aspect 9, wherein the polymer layer is formed of a liquid
polymer.
[0022] According to an eleventh aspect, there is provided the
laminate of aspect 10, wherein the polymer layer extends beyond an
outer edge of at least one of the first and second flexible glass
substrates.
[0023] According to a twelfth aspect, there is provided the
laminate of aspect 1 to 11, wherein the polymer layer is a first
polymer layer, the laminate structure further comprising a second
polymer layer laminated to the flexible glass substrate, the
flexible glass substrate being between the first and second polymer
layers.
[0024] According to a thirteenth aspect, there is provided a method
of forming a flexible glass-polymer laminate structure, the method
comprising:
[0025] heating a polymer layer of the flexible glass-polymer
laminate structure to an elevated temperature of greater than
20.degree. C., the polymer layer having a coefficient of thermal
expansion (CTE) that is at least 2 times a CTE of a flexible glass
substrate of the flexible glass-polymer laminate structure;
[0026] laminating the polymer layer at the elevated temperature to
the flexible glass substrate; and
[0027] cooling the polymer layer below the elevated temperature to
introduce a compressive stress of at least about 30 MPa across a
thickness of the flexible glass substrate.
[0028] According to a fourteenth aspect, a method of forming a
flexible glass-polymer laminate structure, comprising:
[0029] heating a polymer layer of the flexible glass-polymer
laminate structure to an elevated temperature of greater than
20.degree. C., the polymer layer having a coefficient of thermal
expansion (CTE) that is at least about 3 ppm/.degree. C. greater
than a CTE of a flexible glass substrate of the flexible
glass-polymer laminate structure;
[0030] laminating the polymer layer at the elevated temperature to
the flexible glass substrate; and
[0031] cooling the polymer layer below the elevated temperature to
introduce a compressive stress of at least about 30 MPa across a
thickness of the flexible glass substrate.
[0032] According to a fifteenth aspect, there is provided the
method of aspect 12 or aspect 13, wherein the flexible glass
substrate has an in-plane compressive stress of at least about 80
MPa across the thickness of the flexible glass substrate.
[0033] According to a sixteenth aspect, there is provided the
method of aspect 13 to 15, wherein the polymer layer has a CTE that
is at least about 10 times the CTE of the flexible glass
substrate.
[0034] According to a seventeenth aspect, there is provided the
method of aspect 11 to 13, comprising expanding the polymer layer
relative to the flexible glass substrate as the polymer layer is
heated to the elevated temperature.
[0035] According to an eighteenth aspect, there is provided the
method of aspect 13 to 17, further comprising applying an adhesive
layer between the flexible glass substrate and the polymer layer
that laminates the polymer layer to the flexible glass
substrate.
[0036] According to a nineteenth aspect, there is provided the
method of aspect 18, comprising heat activating the adhesive layer
after the polymer layer reaches the elevated temperature.
[0037] According to a twentieth aspect, there is provided the
method of aspect 18, comprising pressure activating the adhesive
layer after the polymer layer reaches the elevated temperature.
[0038] According to a twenty-first aspect, there is provided the
method of aspect 18, comprising UV activating the adhesive layer
after the polymer layer reaches the elevated temperature.
[0039] According to a twenty-second aspect, there is provided a
method of forming a flexible glass-polymer laminate structure, the
method comprising:
[0040] heating a polymer layer of the flexible glass-polymer
laminate structure to an elevated temperature of greater than
20.degree. C., the polymer layer having a coefficient of thermal
expansion (CTE) that is at least about 3 ppm/.degree. C. greater
than a CTE of a flexible glass substrate of the flexible
glass-polymer laminate structure;
[0041] laminating the polymer layer at the elevated temperature to
the flexible glass substrate; and
[0042] cooling the polymer layer below the elevated temperature to
bend the flexible glass substrate while simultaneously providing a
compressive stress across a thickness of the flexible glass
substrate.
According to a twenty-third aspect, there is provided the method of
aspect 22, wherein the step of heating the polymer layer comprises
heating the polymer layer to a temperature of at least about
50.degree. C. before laminating the polymer layer to the flexible
glass substrate.
[0043] According to a twenty-fourth aspect, a flexible
glass-polymer laminate structure, comprising:
[0044] a flexible glass substrate having a thickness of no more
than about 0.3 mm; and
[0045] a polymer layer laminated to a surface of the flexible glass
substrate having a coefficient of thermal expansion (CTE) that is
at least about 3 ppm/.degree. C. greater than a CTE of the flexible
glass substrate, the polymer layer laminated to the surface of the
flexible glass substrate after thermally expanding the polymer
layer providing the flexible glass substrate with a bent
configuration while simultaneously providing a compressive stress
along at least a portion of a thickness of the flexible glass.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a schematic illustration of an embodiment of a
symmetric flexible glass-polymer laminate structure;
[0047] FIG. 2 is a schematic illustration of another embodiment of
a symmetric flexible glass-polymer laminate structure;
[0048] FIG. 3 is a schematic illustration of another embodiment of
a flexible glass-polymer laminate structure having edge protection
features;
[0049] FIG. 4 illustrates schematically another embodiment of a
flexible glass-polymer laminate structure having an asymmetric
configuration;
[0050] FIG. 5 is a schematic drawing of a piece of glass having a
neutral bending axis;
[0051] FIG. 6 illustrates a tensile stress reduction in an
exemplary thermally bent laminate;
[0052] FIG. 7 is a schematic illustration of another embodiment of
a flexible glass-polymer laminate structure; and
[0053] FIG. 8 is a schematic illustration of another embodiment of
a flexible glass-polymer laminate structure.
DETAILED DESCRIPTION
[0054] In the following detailed description, for purposes of
explanation and not limitation, example embodiments disclosing
specific details are set forth to provide a thorough understanding
of various principles of the present invention. However, it will be
apparent to one having ordinary skill in the art, having had the
benefit of the present disclosure, that the present invention may
be practiced in other embodiments that depart from the specific
details disclosed herein. Moreover, descriptions of well-known
devices, methods and materials may be omitted so as not to obscure
the description of various principles of the present invention.
Finally, wherever applicable, like reference numerals refer to like
elements.
[0055] Ranges can be expressed herein as from "about" one
particular value, and/or to "about" another particular value. When
such a range is expressed, another embodiment includes 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 embodiment. 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.
[0056] Directional terms as used herein--for example up, down,
right, left, front, back, top, bottom--are made only with reference
to the figures as drawn and are not intended to imply absolute
orientation.
[0057] Although glass is an inherently strong material, its
strength (reliability) is a function of its surface defect or flaw
size density distribution and the cumulative exposure of stress to
the material over time. During the entire product life cycle, a
flexible glass-polymer laminate will be subjected to various kinds
of static and dynamic mechanical stresses. Embodiments described
herein generally relate to flexible glass substrates that are
strengthened using a polymer layer. A relatively large coefficient
of thermal expansion (CTE) mismatch between the polymer layer and
the flexible glass substrate is utilized by laminating the polymer
layer to the flexible glass substrate at an elevated temperature
followed by a slow cooling. Such an elevated temperature lamination
approach can create a uniformly distributed compressive residual
stress across the thickness of the flexible glass substrate once
the laminate structure is cooled.
[0058] Referring to FIGS. 1 and 2, two exemplary flexible
glass-polymer laminate structures 10 and 40 are illustrated along
with their corresponding stress diagrams 12 and 42. Referring first
to FIG. 1, the flexible glass-polymer laminate structure 10
includes a first outermost glass layer 14 that is formed by a first
flexible glass substrate 16 (having Eg, Vg, .alpha., t.sub.g/2), a
second outermost glass layer 18 that is formed by a second flexible
glass substrate 20 (having Eg, Vg, .alpha., t.sub.g/2) and a
polymer layer 22 (having Ep, Vp, .alpha..sub.p, t.sub.p) that is
sandwiched between and laminated to the first and second flexible
glass substrates 16 and 20. Adhesive layers 24 and 26 may be used
to laminate the first and second flexible glass substrates 16 and
20 to the polymer layer 22 at the interfaces between their
respective broad surfaces 28, 30 and 32, 34.
[0059] While FIG. 1 illustrates outermost glass layers 14 and 18,
FIG. 2 illustrates an alternative embodiment with a flexible glass
substrate 44 (having Eg, Vg, .alpha., t.sub.g) that is sandwiched
between outermost polymer layers 50 and 52 (each having Ep, Vp,
.alpha..sub.p, t.sub.p/2). Again, adhesive layers 54 and 56 may be
used to laminate the first and second polymer layers 50 and 52 to
the flexible glass substrate 44 at the interfaces between their
respective broad surfaces 58, 60 and 62, 64.
[0060] The stress diagrams 12 and 42 of FIGS. 1 and 2 illustrate
that residual, in-plane compressive stresses are generated across
the thicknesses of the flexible glass substrates 16 and 20 of the
flexible glass-polymer laminate structure 10 and the flexible glass
substrate 44 of flexible glass-polymer laminate structure 40, which
are compensated by tensile stresses in the polymer layer 22 of the
flexible glass-polymer laminate structure 10 and polymer layers 50
and 52 of the flexible glass-polymer laminate structure 40.
Referring first to FIG. 1, the residual compressive stresses in the
flexible glass substrates 16 and 20 of the flexible glass-polymer
laminate structure 10 can be substantially uniformly distributed
across the thicknesses of the flexible glass substrates 16 and 20
and generated by laminating the polymer layer 22 to the flexible
glass substrates 16 and 20 at an elevated temperature and then
cooling to room temperature. Similarly, referring to FIG. 2, the
residual compressive stresses in the flexible glass substrate 44 of
the flexible glass-polymer laminate structure 40 can be
substantially uniformly distributed across the thickness of the
flexible glass substrate 44 and generated by laminating the polymer
layers 50 and 52 to the flexible glass substrate 44 at an elevated
temperature and then cooling to room temperature, which will be
described in greater detail below. Further, while tri-layer
laminate structures are illustrated by FIGS. 1 and 2, the number of
layers can be greater or less than three layers and selected
depending on, for example, the end use and processing requirements.
Various other layered laminate examples will be described
herein.
[0061] The flexible glass substrates 16, 20 and 44 may be
"ultra-thin" having a thickness t.sub.g of about 0.3 mm or less
including but not limited to thicknesses of, for example, about
0.01-0.05 mm, about 0.05-0.1 mm, about 0.1-0.15 mm and about
0.15-0.3 mm. The flexible glass substrates 16, 20 and 44 may be
formed of glass, a glass ceramic, a ceramic material or composites
thereof. A fusion process (e.g., downdraw process) that forms high
quality thin glass sheets can be used in a variety of devices such
as flat panel displays. Glass sheets produced in a fusion process
have surfaces with superior flatness and smoothness when compared
to glass sheets produced by other methods. The fusion process is
described in U.S. Pat. Nos. 3,338,696 and 3,682,609. Other suitable
glass sheet forming methods include a float process, updraw and
slot draw methods.
Strengthening Symmetric Flexible Glass-Polymer Laminates
[0062] A process is developed for strengthening flexible glass
substrates that utilizes a large CTE mismatch (e.g., about 2 times
or more, such as about 5 times or more, such as about 10 times or
more) between the polymer layer and the flexible glass substrate by
laminating the polymer layer and the flexible glass substrate
(e.g., as shown in FIGS. 1 and 2) at an elevated temperature and
then slowly cooling to create a residual compressive stress across
the thickness of the flexible glass substrate. In some embodiments,
the CTE mismatch may be at least about 3 ppm/.degree. C. or more,
such as about 6 ppm/.degree. C. or more, such as about 9
ppm/.degree. C. or more, such as about 12 ppm/.degree. C. or more,
such as about 15 ppm/.degree. C. or more, such as about 20
ppm/.degree. C. or more, such as about 27 ppm/.degree. C. or more,
such as about 50 ppm/.degree. C. or more. The flexible
glass-polymer laminates may be classified as symmetric and
asymmetric. A symmetric laminate structure is constructed such that
the layers below a central plane C (FIGS. 1 and 2) of the laminate
structure form a mirror image of the layers above the central plane
C and asymmetric laminates do not have such a mirror image about
their central planes. For symmetric flexible glass-polymer
laminates formed of two different materials and having three or
more layers with different CTE laminated at an elevated
temperature, the compressive stress across the thickness of the
flexible glass substrate at room temperature (assuming bi-axial
deformation) is given by:
.sigma. g = - E g ( 1 - v g ) + E g t g ( 1 - v p ) / E p t p (
.alpha. p - .alpha. g ) ( T lamination - T r o o m )
##EQU00001##
[0063] wherein: [0064] E is Young's modulus, a is linear thermal
expansion coefficient, t is total thicknesses of one type of
material, v is Poisson's ratio, and the subscripts "g" and "p"
refer to "glass" and "polymer", respectively. T.sub.lamination
refers to the curing temperature of the adhesive used in the
lamination process. Thus, the compressive stress in the flexible
glass substrate can be increased by one or more of [0065] 1.
reducing the glass layer thickness; [0066] 2. increasing the
Young's modulus of the flexible glass substrate; [0067] 3.
increasing the Young's modulus of the polymer layer; [0068] 4.
increasing the thickness polymer layer; [0069] 5. increasing the
thermal expansion coefficient difference between the flexible glass
substrate and the polymer layer; and [0070] 6. increasing the
lamination temperature.
[0071] While larger compressive stresses (e.g., 30 MPa or more,
such as 50 MPa or more, such as 60 MPA or more, such as about 70
MPa or more such as about 80 MPa or more, such as about 90 MPA or
more, such as about 100 MPa or more, such as about 110 MPa or more)
are desired across the thickness of the flexible glass substrates,
there are limits on the amount of compressive stress that can be
introduced. For example, to achieve large compressive stresses in
the flexible glass substrate, one approach is to set the lamination
temperature as high as possible. However, the upper end of this
lamination temperature should not exceed limits set by specific
properties of the flexible glass-polymer laminate materials, such
as the working temperature limit of any adhesive used. Material and
structural integrity should be considered in insuring product
reliability. Thus, various limits may affect the amount of
compressive stress that can be introduced to the flexible glass
substrate.
Forming Strengthened Flexible Glass-Polymer Laminates
[0072] Any number of lamination processes may be used to achieve
the desired high compressive stresses in the flexible glass
substrates. Importantly, the polymer layer should be allowed to
thermally expand, at least to some degree, relative to the flexible
glass substrate due to the large CTE mismatch between the flexible
glass substrate and the polymer layer before laminating the polymer
layer to the flexible glass substrate. Once laminated, the flexible
glass-polymer laminate structure may be allowed to controllably
cool (e.g., about 1-2.degree. C./min or less) back down to room
temperature, which introduces the compressive stress into the
flexible glass substrate.
[0073] Examples of laminating at an increased temperature for
generating a compressive stress due to a large CTE mismatch between
a polymer layer and a flexible glass substrate are described below.
These examples are exemplary in nature and are not meant to be
limiting. For example, while a polymer layer of polymethyl
methacrylate (PMMA) may be used in many of the examples discussed
below, a polymer layer of polycarbonate may be used, as well as a
number of other polymer materials, which are discussed below,
having a relatively large CTE mismatch with the flexible glass
substrate. PMMA and polycarbonate polymer materials may be
desirable where transparency in the end use of the flexible
glass-polymer laminate is preferred.
Example 1: UV Sensitive Adhesive
[0074] A flexible glass-polymer laminate structure as shown in FIG.
1 was formed using two flexible glass substrates 0.1 mm in
thickness and a polymer layer formed of polymethyl methacrylate
(PMMA), a transparent thermoplastic, having a thickness of 1.3 mm.
A UV sensitive adhesive (NOA 68 commercially available from Norland
Products) was applied about 20 nm in thickness between the polymer
layer and the flexible glass substrate layers. The flexible
glass-polymer laminate structure was placed on a thermoelectric
hotplate and heated from one side maintained at 80.degree. C.,
which was below the UV sensitive adhesive's working limit of
90.degree. C. The UV sensitive adhesive was then cured using UV
light applied to the UV sensitive adhesive from a side of the
flexible glass-polymer laminate structure opposite the
thermoelectric hotplate to bond the polymer layer at an elevated
temperature to the flexible glass substrate layers and allowed to
cool at a rate of 3.degree. C./min. About a 110 MPa compressive
stress in the flexible glass substrate was confirmed using
birefringence measurements (FSM). Table I below highlights material
properties for this exemplary flexible glass-polymer laminate
structure and Table II below illustrates stress estimates using the
compressive stress formula set forth above.
TABLE-US-00001 TABLE I Materials Coefficient Lamination Young's of
Thermal Temp/ Modulus Poisson's Expansion Thickness Room Material
(GPa) Ratio (10.sup.-6/.degree. C.) (mm) Temp (.degree. C.) PMMA
2.5 0.37 90 1.3 80/20 Glass 73.6 0.23 3.17 0.1 (0.2 Substrate
total)
TABLE-US-00002 TABLE II Stress Estimates Compressive Residual
Stress Tensile Residual Stress in in Glass Substrate (MPa) PMMA
(MPa) Estimate 105.8 16.3
Example 2: Heat Sensitive Adhesive
[0075] A flexible glass-polymer laminate structure as shown in FIG.
1 was formed using two flexible glass substrates 0.1 mm in
thickness and a polymer layer formed of PMMA having a thickness of
1.3 mm. A heat sensitive adhesive (NOA 68H commercially available
from Norland Products) was applied about 20 nm in thickness between
the polymer layer and the flexible glass substrate layers. The
flexible glass-polymer laminate structure was heated in a
convection oven to a lamination temperature (cure at 100.degree. C.
for 3 hours, 3.degree. C./min ramp-up rate, 1.degree. C./min
cooling rate, aged at 50.degree. C. for 12 hours before cooling
down to room temperature), which was below the softening
temperature of the PMMA (91.degree. C. to 115.degree. C.), allowing
the polymer layer to expand as the lamination temperature was
reached to bond the polymer layer at an elevated temperature to the
flexible glass substrate layers.
Example 3: Pressure Sensitive Adhesive
[0076] A flexible glass-polymer laminate structure as shown in FIG.
1 was formed using two flexible glass substrates 0.1 mm in
thickness and a polymer layer formed of PMMA having a thickness of
1.3 mm. A pressure sensitive adhesive (8211 OCA commercially
available from 3M) was applied (about 50 .mu.m thick) between the
polymer layer and the flexible glass substrate layers. The flexible
glass-polymer laminate structure was heated in an autoclave to a
lamination temperature, which was below the softening temperature
of the PMMA (91.degree. C. to 115.degree. C.), allowing the polymer
layer to expand as the lamination temperature was reached to bond
the polymer layer at an elevated temperature to the flexible glass
substrate layers (cured at 90 psi and 85.degree. C. for 1 hour,
3.degree. F./min ramp up and cooling rate).
[0077] While the above examples utilize an intermediate adhesive
layer to bond the polymer layer and flexible glass substrate, other
embodiments may include the polymer layer bonded directly to the
flexible glass substrate without any use of an intermediate
adhesive layer. For example, a polymer layer may be heated to a
temperature above the plastic softening temperature (glass
transition temperature), but below the melting temperature for the
polymer. For PMMA, for example, the softening temperature is
91.degree. C. to 115.degree. C. and the melting temperature is
160.degree. C. A combination of heat and pressure may be utilized
(e.g., using an autoclave) to heat the polymer layer to a
temperature between the softening temperature and the melting
temperature. In some instances, the heated temperature may be held
for a preselected period of time and then the flexible
glass-polymer laminate structure may be cooled at a predetermined
rate (e.g., less than about 3.degree. F./min).
[0078] As another example of a polymer layer, a liquid polymer
solution may be injected into a space between flexible glass
substrates. Referring briefly to FIG. 3, at an elevated
temperature, a flexible glass-polymer laminate 70 may be formed by
separating flexible glass substrates 72 and 74, for example, using
spacers (represented by dotted lines 76). The liquid polymer
solution 78 may be injected into a space 80 formed between the
flexible glass substrates 72 and 74. Lamination of the polymer
layer 82 to the flexible glass substrates 72 and 74 may be
completed through polymer solidification (curing for example) and a
controlled cooling step. Capillary forces, viscous flow and
expansion of the liquid polymer solution 78 during heating may
force the liquid polymer solution 78 beyond outer edges 84 and 86
of the flexible glass substrates 72 and 74, which can lead to
encapsulating and covering the outer edges 84 and 86. This
encapsulation of the outer edges 84 and 86 can provide an edge
protection feature 88 for the flexible glass substrates 72 and 74
once the polymer layer 82 is formed. Such edge protection can be
advantageous as the compressive stress at the edges of the flexible
substrates 72 and 74 may be relatively low or even not present,
even after formation of the polymer layer 82 and the edges may have
a relatively low strength compared to the bulk glass. To facilitate
bonding, adhesive promoters may be added to the polymer solution
78. Physical bonding, and in some instances chemical bonding,
occurs between the polymer layer 82 and the flexible glass
substrates 72 and 74.
[0079] In addition to the above-mentioned heaters and ovens,
non-contact heaters, such as radiative heaters (and microwave
heating) can be used to heat the polymer layers discussed herein.
Radiative heaters emit infrared radiation, which can be absorbed by
materials resulting in heat transfer to the heated body. Radiative
heating can be efficient and rapid compared to convective or
conductive heating, and does not require contact with the surface
of the heated body. As one alternative to the heating of Example 1,
the flexible glass-polymer laminate structure may be passed between
a UV light source and a radiative heater, such that UV curing of
the adhesive material is obtained at the desired temperature, which
can be maintained by the radiative heating. Further, as a variation
of Example 2, the convection oven may be replaced by two radiative
heaters, one on either side of the flexible glass-polymer laminate
structure. The process can be continuous by controlling the feed
rate and power of the heaters to achieve heating, the lamination
temperature and cooling. Multiple radiative heaters may be used to
control heating, dwell and cooling rates.
Asymmetric Flexible Glass-Polymer Laminates
[0080] Lamination processes may also be used to manipulate or
affect stress profiles in asymmetric flexible glass-polymer
laminate structures. In these embodiments, the polymer layer is
allowed to thermally expand relative to the flexible glass
substrate due to the large CTE mismatch between the flexible glass
substrate and the polymer layer before laminating the polymer layer
to the flexible glass substrate. However, due to the asymmetric
nature of the flexible glass-polymer laminate structures, bending,
uniaxial or biaxial, may be introduced in the flexible glass
substrate and the polymer layer.
[0081] Referring to FIG. 4, a uniaxial bending curvature induced by
a CTE mismatch in an asymmetric flexible glass-polymer laminate
structure 90 is given by (assuming plane stress and the flexible
glass substrate 96 and polymer layer 98 have the same width and
length dimensions):
.kappa. = 6 ( .alpha. p - .alpha. g ) ( T laminaton - T r o o m ) t
g t p ( t g + t p ) E g t g 4 / E p + 4 t g 3 t p + 6 t g 2 t p 2 +
4 t g t p 3 + E p t p 4 / E g ##EQU00002##
[0082] wherein: [0083] .kappa. is bending curvature, E is Young's
modulus, a is linear thermal expansion coefficient, t is total
thicknesses of one type of material, and the subscripts "g" and "p"
refer to "glass" and "polymer", respectively. T.sub.lamination
refers to the curing temperature of the adhesive used in the
lamination process. Bending curvature .kappa. is related to the
radius R measured from center C to the neutral axis A by:
[0083] R=1/.kappa.
and is also related to an angle .theta. measured between ends 92
and 94 of the flexible glass-polymer laminate structure 90 by:
.theta.=L/R=.kappa.L.
Height h to the neutral axis can be determined by:
h = R ( 1 - cos ( .theta. 2 ) ) = 1 .kappa. ( 1 - cos ( .kappa.L 2
) ) . ##EQU00003##
Thus, bending characteristics of an asymmetric flexible
glass-polymer laminate structure can be determined where the
material properties and lamination temperatures are known. For
example, for a 100 .mu.m/500 .mu.m/100 .mu.m
glass/polycarbonate/glass laminate, where polycarbonate has a
Young's modulus E of 2.377 GPa, a CTE a of
67.5.times.10.sup.-6/.degree. C. and a lamination temperature
T.sub.lamination of 80.degree. C., the height h, once cooled to
room temperature, is about 11.3 mm.
[0084] Referring to FIG. 5, when an uncoated piece of glass 100
(either a sheet or ribbon of glass) is bent into a curve of radius
R (such as when the glass is held in a device or bends around a
roller during processing), there is created a stress in the glass.
When the piece of glass 100 is subject to a bending moment, so that
the glass achieves a bending radius R, the stress at a location (y)
relative to the x-axis (neutral axis) can be calculated by:
.sigma. = E g y R ( 1 - .nu. g 2 ) ( plain strain ) ##EQU00004## or
##EQU00004.2## .sigma. = E g y R ( plain stress ) ##EQU00004.3##
[0085] wherein: [0086] .sigma. is the stress; [0087] E.sub.g is the
Young's modulus of the glass; [0088] v.sub.g is the Poisson's ratio
of the glass; [0089] y is the position in the y-axis direction at
which the stress 6 is calculated; [0090] R is the bending radius of
the glass.
[0091] The maximum tensile stress occurs on either side of the
glass 100, and will be either surface 102 or surface 104 depending
on the bending direction. That is, if the glass 100 is bent so that
surface 102 is convex, the maximum tensile stress will be on
surface 102, whereas if the glass 100 is bent so that surface 104
is convex, the maximum tensile stress will be on surface 104. In
either case, by substituting 1/2 tg for y, the absolute value of
the maximum stress .sigma..sub.max is defined by:
.sigma. max = E g t g 2 R ( 1 - .nu. g 2 ) ( plain strain )
##EQU00005## or ##EQU00005.2## .sigma. max = E g t g 2 R ( plain
stress ) ##EQU00005.3##
[0092] Laminating the polymer layer 98 at an elevated temperature
to the flexible glass substrate 96 as shown in FIG. 4, for example,
allows for manipulation of the stress profile, compared to the
uncoated glass of FIG. 5. In particular, laminating the polymer
layer 98 having the high CTE mismatch with the flexible glass
substrate 96 to cause bending and introduce compressive stress in
the flexible glass substrate can reduce or even eliminate the
tensile stress that would be expected in a bent glass and can serve
to strengthen the overall bent flexible glass laminate structure 90
(FIG. 4).
[0093] The following discussion illustrates the reduction in
tensile stress in the flexible glass substrate in the
flexible-glass polymer laminate. For an asymmetric flexible
glass-polymer laminate formed of two different materials, the
curvature induced by CTE mismatch (assuming uniaxial plane stress
bending) is (as noted above):
.kappa. 0 = 6 ( .alpha. p - .alpha. g ) ( T lamination - T r o o m
) t g t p ( t g + t p ) E g t g 4 / E p + 4 t g 3 t p + 6 t g 2 t p
2 + 4 t g t p 3 + E p t p 4 / E g ##EQU00006## [0094] the neutral
axis is given by:
[0094] y 0 = .alpha. p ( E p t p 4 / E g + 6 t p 3 t g + 9 t p 2 t
g 2 + 4 t p t g 3 ) + .alpha. g ( E g t g 4 / E p - 3 t g 2 t p 2 -
2 t g t p 3 ) 6 ( .alpha. p - .alpha. g ) t g t p ( t g + t p )
##EQU00007##
[0095] and the bending stress across the thickness of the flexible
glass substrate at room temperature is given by:
.sigma.=E.sub.g(.kappa..sub.0(y-y.sub.0)+.alpha..sub.g(T.sub.lamination--
T.sub.room))
[0096] The bending stress at the top surface of the flexible glass
substrate is given by:
.sigma. glass _ top = ( .alpha. p - .alpha. g ) ( T lamination - T
r o o m ) t p ( 2 E g t g 3 + 3 E g t g 2 t p - E p t p 3 ) E g t g
4 / E p + 4 t g 3 t p + 6 t g 2 t p 2 + 4 t g t p 3 + E p t p 4 / E
g ##EQU00008## [0097] and the bending stress at the bottom surface
(i.e., the interfacial surface with the polymer layer) is given
by:
[0097] .sigma. glass _ bottom = - ( .alpha. p - .alpha. g ) ( T
lamination - T r o o m ) t p ( 4 E g t g 3 + 3 E g t g 2 t p + E p
t p 3 ) E g t g 4 / E p + 4 t g 3 t p + 6 t g 2 t p 2 + 4 t g t p 3
+ E p t p 4 / E g ##EQU00009## [0098] wherein: [0099] E.sub.g,
V.sub.g are the Young's modulus and Poisson's ratio of the flexible
glass substrate; [0100] E.sub.p, v.sub.p are the Young's modulus
and Poisson's ratio of the polymer layer; [0101] t.sub.g is the
thickness of the flexible glass substrate; [0102] t.sub.p is the
thickness of the plastic layer; [0103] .alpha..sub.g is the
coefficient of thermal expansion of the flexible glass substrate;
[0104] .alpha..sub.p is the coefficient of thermal expansion of the
polymer layer; [0105] T.sub.lamination is the lamination
temperature; [0106] T.sub.room is room temperature; [0107]
.kappa..sub.0 is the bending curvature induced by the CTE mismatch;
[0108] .sigma. is the bending stress; and [0109] y.sub.0 is the
neutral axis of the bent laminates.
[0110] Referring to FIG. 6 and the above equations particularly for
bending stress, it can be seen that tensile stress inside a
thermally bent, flexible glass substrate is much less than a
mechanically bent flexible glass substrate. This reduction in the
tensile stress can be seen throughout the thickness of the flexible
glass substrate from the bottom side to the top side. It should be
noted, however, that the stress across the entire thickness of the
flexible glass substrate is not uniform as depicted in FIGS. 1 and
2 due to the bending of the flexible glass substrate. In this
embodiment, only a portion of the thickness of the flexible glass
is at or above 30 MPa nearer the bottom side of the flexible glass
substrate.
General Considerations
[0111] The polymer layers for use in the laminate structures
described herein may include various polymers, for example, any one
or more of polyethylene teraphthalate (PET), polyethylene
Naphthalate (PEN), ethylene tetrafluoroethylene (ETFE), or
thermopolymer polyolefin (TPO.TM.--polymer/filler blends of
polyethylene, polypropylene, block copolymer polypropylene (BCPP),
or rubber), polyesters, polycarbonate, polyvinylbuterate, polyvinyl
chloride, polyethylene and substituted polyethylenes,
polyhydroxybutyrates, polyhydroxyvinylbutyrates, polyetherimides,
polyamides, polyethylenenaphalate, polyimides, polyethers,
polysulphones, polyvinylacetylenes, transparent thermoplastics,
transparent polybutadienes, polycyanoacrylates, cellulose-based
polymers, polyacrylates and polymethacrylates, polyvinylalcohol,
polysulphides, polyvinyl butyral, polymethyl methacrylate and
polysiloxanes. It is also possible to use polymers which can be
deposited/coated as pre-polymers or pre-compounds and then
converted, such as epoxy-resins, polyurethanes, phenol-formaldehyde
resins, and melamine-formaldehyde resins. Many display and
electrical applications may prefer acrylic based polymers,
silicones and such structural aiding layers, for example,
commercially available SentryGlas.RTM. from BuPont. The polymer
layers may be transparent for some applications, but need not be
for other applications.
[0112] Non-limiting examples of adhesive materials for laminating
the polymer layers to the flexible glass substrates at elevated
temperatures include UV curable optical adhesives or optical
cements such as those manufactured by Norland.TM. Optical Adhesives
(NOA60, NOA61, NOA63, NOA65, NOA68, NOA68T, NOA71, NOA72, NOA73,
NOA74, NOA75, NOA76, NOA78, NOA81, NOA84, NOA88, NOA89), Dow
Corning.TM. (Sylgard 184 and other thermally curing silicones),
Dymax.TM., and others. For heat-activated adhesive materials (e.g.,
NOA83H), adhesive materials with activation temperatures of greater
than a preselected temperature (e.g., about 50.degree. C. or more,
such as about 70.degree. C. or more, such as 80.degree. C. or more,
such as 100.degree. C. or more) may be used to allow the polymer
layer an opportunity to expand relative to the flexible glass
substrate prior to its lamination thereto.
[0113] Additionally, each of the polymer layers may itself be a
laminated or composite structure made of different types of polymer
having different Young's moduli, different Poisson's Ratios, and/or
layer thicknesses. In this case, one of skill in the art would be
able to homogenize the compound layer to find effective values for
the overall layer, including an effective thickness, an effective
Young's modulus, and an effective Poisson's Ratio that may be used
as described herein to beneficially configure a glass-polymer
laminate. The composites, for example, may be formed of any
combinations of the above materials and/or metals, such as
stainless steel, nickel, copper, noble metals, metal oxides,
etc.
[0114] The glass-polymer laminates described herein may be used as
a substrate for mounting device-functional layers, or may be used
as an encapsulant layer or barrier layer within the device. The
device may be an electronic device, for example, a display screen
(including a Liquid Crystal Display, a Plasma Display, an Organic
Light Emitting Diode display, flat panel display, for example), a
lighting-emitting device, or a solar cell module. The functional
layers may include, for example, thin film transistors (TFTs),
diodes, photodiodes, triodes, photovoltaic cells, photocouplers,
transparent electrodes, color filter, or an electroconductive
layer. The glass-polymer laminate may be used as a cover laminated
onto the display screens. The glass-polymer laminate may be used as
a substrate/encapsulant not only for OLEDs (small molecule
fluorescence (SMF) and (LEP) light emitting polymers) but for other
devices including an electrically active layer e.g. organic
photo-detectors, organic solar-cells, thin-film-transistor (TFT)
arrays and TFTs for OLEDs. Another use is for LEP products such as
un-patterned backlights and other light sources or patterned
devices such as signs, alpha-numeric displays or dot-matrix and
other high-resolution displays.
[0115] The glass-polymer laminate may be a substantially
transparent formable and/or flexible structure for use as a
protective element in an electronic device, wherein the
glass-polymer laminate is a composite structure comprising a layer
of glass of a thickness from 5 to 300 microns, and a layer of
polymer ranging in thickness from 50 microns to 1 cm or more. In
this connection, the formability of the glass-polymer laminate
allows it to deviate from full planarity by bending and/or twisting
so it can adapt to the shape or form of some other object. Its
flexibility allows it to be bent without detrimentally affecting
its barrier properties.
[0116] The glass-polymer laminate can constitute a substrate for an
electronic device and, as such, can be coated with a transparent
electrode layer. The layer may be the anode and may be indium tin
oxide or silver based conductors. As alternatives, the
glass-polymer laminate may constitute an encapsulation film for
light-emitting, or other electronic device.
[0117] The electronic device with the glass-polymer laminate can be
manufactured in a sequence of integrated steps which include the
construction of the glass-polymer laminate, deposition of the
transparent electrode layer, deposition of the or each electrically
active layer and deposition of the second electrode layer. A batch,
semi-continuous or continuous process can be considered for the
manufacture of the complete device. A further encapsulation layer
on the second electrode layer can be provided. Various techniques
for manufacturing the glass-polymer laminate are possible in
accordance with different embodiments.
[0118] According to one embodiment, a polymer layer carrying a
coating of a first transparent electrode (e.g. ITO) is provided.
Then, at least one layer of an electrically active, e.g.
electroluminescent, organic material is deposited followed by the
second electrode layer. The complete structure is then laminated to
the glass layer. According to another embodiment, the polymer and
glass layers are exchanged in the preceding sequence. According to
a further embodiment, the glass-polymer laminate is prefabricated
and is then used as the basis for deposition of the first electrode
layer, the at least one layer of an electrically active material
and the second electrode layer.
[0119] The glass and polymer layers can be provided in sheet form
according to a batch process. Alternatively, the glass layer can be
provided in sheet form and the polymer layer from a continuous
roll. As a further possibility, both glass and polymer layers are
from continuous rolls. The composite structure can be formed by
lamination of the glass and polymer layers, e.g. according to a
batch process, a continuous roll-to-roll process or a
semi-continuous process whereby the polymer layer is a continuous
film and the glass layer is in sheet form.
[0120] For the polymer layer, it is possible to use polymers which
can be deposited/coated as pre-polymers or pre-compounds and then
converted, such as epoxy-resins, polyurethanes, phenol-formaldehyde
resins, and melamine-formaldehyde resins. The lamination of the
glass and polymer layers can be with glue/adhesive in between the
layers. In that case, adhesive can be pre-coated onto one of the
two or on both substrates; or supplied during the lamination
process, at room or elevated temperature and with or without
pressure. UV-cured glues are also suitable. The polymer layer can
be in the form of polymer sheets which are pre-coated with a
heat-seal glue. Lamination and/or deposition of the polymer layer
onto the glass layer can be integrated in the fabrication process
of the glass, i.e. glass comes off the fabrication line and is then
(still hot or warm or cold) coated with the polymer.
[0121] As an alternative to formation by lamination, the polymer
layer of the composite is coated onto the glass layer by a batch or
continuous process. Coating of the polymer onto the glass can be by
dip, spray, solution-spin, solution-blade, meniscus coating, or by
coating of a molten polymer onto the glass layer. That is, it is
possible to consider the different situations (i) where polymer
exists already as film and is laminated to the glass and (ii) where
polymer is not in film form but is coated onto the glass by dip,
spray, etc. etc. The pre-polymers mentioned above, for example, are
amenable to case (ii). However, also several of the other polymers
mentioned above can be coated for case (ii). In this instance the
polymers can be coated onto the glass principally by: coating from
solution, from a melt or as pre-polymer.
[0122] In manufacture of an electronic device, it is usually
necessary to subject some or all of the layers to processing steps.
For example, if there is present an electroluminescent organic
material that is a semiconductive conjugated polymer such as
poly(phenylene vinylene) (PPV) then the deposition of that layer
would normally take place by depositing a precursor to the polymer
in a solvent, for example by spin-coating, and then subjecting that
layer to a subsequent processing step to convert the precursor to
the final polymer. Thus, the underlying glass-polymer laminate, if
present during these processing steps, must be able to withstand
the solvents used for spin-coating the precursor layer and the
subsequent temperatures used for driving off the solvent and
converting the precursor to the polymer. Thus, the polymer layer of
the glass-polymer laminate needs to be of appropriate qualities.
For example, if the glass-polymer laminate is to be subjected to
high temperatures, then the glass-transition temperature of the
polymer layer (and the working temperature of any adhesive used)
should be above those temperatures. For example, a temperature of
in excess of 150.degree. C. is possible. Moreover, in certain
situations, the polymer layer should be resistant to the solvent
layers used for the polymers, such as mixed xylene, THF, used for
soluble conjugated polymers such as MEH PPV.
[0123] The glass-polymer laminate can comprise more than two or
three layers. Referring to FIG. 7, a flexible glass-polymer
laminate structure 120 includes more than three layers, in this
case, seven layers 122, 124, 126, 128, 130, 132 and 134 with layers
122 and 134 labeled Glass 1, layers 126 and 130 labeled Glass 2,
layers 124 and 132 labeled Polymer 2 and layer 128 labeled Polymer
1. Here, the glass layers 122 and 134 form the outermost layers.
Glass 1 and Glass 2 may have the same or different glass
compositions (including Eg, Vg, .alpha., t.sub.g) and may each be a
single homogeneous sheet, or be glass laminates. Polymer 1 and
Polymer 2 may be the same or of different materials (including Ep,
Vp, .alpha..sub.p, t.sub.p) and can be either a single homogeneous
polymer sheet or be laminates of different polymers.
[0124] Referring to FIG. 8, another flexible glass-polymer laminate
structure 140 includes seven layers 142, 144, 146, 148, 150, 152
and 154 with layers 142 and 154 labeled Polymer 2, layers 146 and
150 labeled Polymer 1, layers 144 and 152 labeled Glass 2 and layer
148 labeled Glass 1. Here, the polymer layers 142 and 154 form the
outermost layers (having Ep2, Vp2, .alpha..sub.p2, t.sub.p2/2).
Glass 1 and Glass 2 (including: Eg1, Vg1, .alpha..sub.g1, t.sub.g1;
and E.sub.g2, V.sub.g2, .alpha..sub.g2, t.sub.g2/2, respectively)
may have the same or different glass compositions and may each be a
single homogeneous sheet, or be glass laminates. Polymer 1 and
Polymer 2 (including: Ep1, Vp1, .alpha..sub.p1, t.sub.p1/2; and
Ep2, Vp2, .alpha..sub.p2, t.sub.p2/2, respectively) may be the same
or of different materials and can be either a single homogeneous
polymer sheet or be laminates of different polymers.
[0125] The above-described flexible glass-polymer laminate
structures provide increased strength to ultra-thin flexible glass
substrates. Nearly constant uniform compressive stress can be
provided through the glass thickness for symmetric laminate
structures. The polymer layers can provide breakage protection and
hold the flexible glass substrates together in the event of any
breakage. The flexible glass-polymer laminate structures can
provide touch and cover glass, which could be used to replace
chemically strengthened glass. Curved display glass, such as that
discussed above in connection with asymmetric flexible
glass-polymer laminate structures can be provided. The flexible
glass-polymer laminate structures can provide a barrier layer for
thin film PV, such as BIPV applications and provide improved impact
protection for PV modules. The flexible glass substrates can also
act as a moisture barrier and block undesired UV light. A potential
application is as an encapsulant for OLEDs.
[0126] Additional functionality can be incorporated into polymer
layers. For example, the polymer layer can comprise a polymer
polarizer sheet, a contrast-enhancing filter-laminate, have
anti-reflective properties, color filter properties or color
conversion properties. For example, it would be possible to have a
device in which the light emitting layer emits blue light and in
which the laminate contains, for example, red or green fluorescent
molecules which absorb the blue and re-emit in the red or green.
Alternatively or additionally, the polymer layer can be designed to
block undesired ambient light and/or have scattering particles so
that wave guiding is reduced and the brightness of the device is
increased. Such additional functionalities could be incorporated in
the glass layer. Where a third polymer layer is provided in the
composite structure, this allows the possibility of two different
types of polymer layers, providing the possibility for
incorporating different additional functionalities into the
different layers.
[0127] In addition to electronic devices, the above-described
flexible glass-polymer laminate structures may be used in other
areas, such as architectural surface decoration, protective
coatings, electrochromatic windows, fire resistant surfaces and in
various configurations of multi-stack structures required to meet
ballistic glazing requirements. Similarly, the flexible
glass-polymer laminate structures could act as a barrier material
to protect films, structures and/or devices from oxygen and
moisture ingress/permeation for applications such as organic/thin
film, PV, OLED display and lighting.
[0128] The flexible glass-polymer laminate structures can take
advantage of attributes from two classes of material (organic and
inorganic). Polymer materials are easily scratched, degrade from
environmental elements including sunlight exposure and provide poor
moisture/oxygen barrier properties. Glass, on the other hand, is
scratch resistant, durable and is known for excellent
moisture/oxygen barrier properties. However, glass has higher
density compared to polymer and is a brittle material where
strength of glass is dictated by defects and flaws. The above
described flexible glass-polymer laminate structures and methods of
making them take advantage of these two classes of materials and
combining into one laminate structure having improved barrier
properties, lightweight and higher mechanical reliability compared
to a bare thin glass stack.
CONCLUSION
[0129] It should be emphasized that the above-described embodiments
of the present invention, particularly any "preferred" embodiments,
are merely possible examples of implementations, merely set forth
for a clear understanding of various principles of the invention.
Many variations and modifications may be made to the
above-described embodiments of the invention without departing
substantially from the spirit and various principles of the
invention. All such modifications and variations are intended to be
included herein within the scope of this disclosure and the present
invention and protected by the following claims.
* * * * *