U.S. patent application number 11/478957 was filed with the patent office on 2007-04-05 for uv-curable adhesion promoter, laminated structures using same and methods for fabricating such laminated structures.
This patent application is currently assigned to ROCKWELL SCIENTIFIC LICENSING, LLC. Invention is credited to Young J. Chung.
Application Number | 20070077372 11/478957 |
Document ID | / |
Family ID | 37901542 |
Filed Date | 2007-04-05 |
United States Patent
Application |
20070077372 |
Kind Code |
A1 |
Chung; Young J. |
April 5, 2007 |
UV-curable adhesion promoter, laminated structures using same and
methods for fabricating such laminated structures
Abstract
An adhesion promoter for enhancing the bond between adjacent
layers of a multilayer structure to prevent delamination thereof is
disclosed. The adhesion promoter comprises an aromatic
polyimide-based UV-cured acrylate. Also disclosed are laminated
structures including liquid crystal displays and bonded missile
domes that utilize an adhesion promoter of the invention, and
methods for fabricating such structures.
Inventors: |
Chung; Young J.; (Calabasas,
CA) |
Correspondence
Address: |
KOPPEL, PATRICK & HEYBL
555 ST. CHARLES DRIVE
SUITE 107
THOUSANDS OAKS
CA
91360
US
|
Assignee: |
ROCKWELL SCIENTIFIC LICENSING,
LLC
|
Family ID: |
37901542 |
Appl. No.: |
11/478957 |
Filed: |
June 29, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11434641 |
May 15, 2006 |
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11478957 |
Jun 29, 2006 |
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11241070 |
Sep 30, 2005 |
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11434641 |
May 15, 2006 |
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Current U.S.
Class: |
428/1.5 ;
525/178 |
Current CPC
Class: |
C09K 2323/05 20200801;
G02B 5/3016 20130101; Y10T 428/31507 20150401; C09K 2323/059
20200801; G02F 1/133634 20130101 |
Class at
Publication: |
428/001.5 ;
525/178 |
International
Class: |
C09K 19/00 20060101
C09K019/00 |
Claims
1. An adhesion promoter comprising an aromatic polyimide-based
UV-cured acrylate.
2. An adhesion promoter comprising as constituents: (a) an aromatic
polyimide; and (b) a UV-cured resin, wherein the proportions by
weight of the constituents (a) and (b) are effective to enhance the
bond between adjacent layers of a laminated structure.
3. The adhesion promoter of claim 2 wherein: the relative
proportions, by weight, of said constituents (a) and (b) are from
20% to 60% of (a), and from 40% to 80% of (b) for a total of 100
parts of (a) and (b).
4. The adhesion promoter of claim 2 wherein: the relative
proportions, by weight, of said constituents (a) and (b) are from
30% to 50% of (a), and from 50% to 70% of (b) for a total of 100
parts of (a) and (b).
5. The adhesion promoter of claim 2 wherein: the relative
proportions, by weight, of said constituents (a) and (b) are from
35% to 45% of (a), and from 55% to 65% of (b) for a total of 100
parts of (a) and (b).
6. A mixture for producing an adhesion promoter, the mixture
comprising as constituents: (a) an aromatic polyimide; (b) a
UV-curable resin; and (c) a solvent comprising: (1) ethyl
L-lactate; and (2) isopropanol, wherein the percentages by weight
of the constituents (a), (b) and (c) are effective to produce an
adhesion promoter for enhancing a bond between adjacent layers of a
laminated structure.
7. The mixture of claim 6 wherein: the relative proportions, by
weight, of said constituents (a), (b) and (c) are from 0.2% to 0.6%
of (a), from 0.4% to 0.8% of (b), from 55% to 64% of (c) (1), and
from 35% to 44% of (c) (2), for a total of 100 parts of (a), (b)
and (c).
8. The mixture of claim 6 wherein: the relative proportions, by
weight, of said constituents (a), (b) and (c) are from 0.3% to 0.5%
of (a), from 0.5% to 0.7% of (b), from 57% to 62% of (c) (1), and
from 37% to 42% of (c) (2), for a total of 100 parts of (a), (b)
and (c).
9. The mixture of claim 6 wherein: the relative proportions, by
weight, of said constituents (a), (b) and (c) are from 0.35% to
0.45% of (a), from 0.55% to 0.65% of (b), from 59% to 60% of (c)
(1), and from 39% to 40% of (c) (2) , for a total of 100 parts of
(a), (b) and (c).
10. A layered structure comprising: a first layer having a surface;
a second layer having a surface confronting the surface of the
first layer; and an adhesion promoter layer joining the confronting
surfaces of the first and second layers, the adhesion promoter
comprising an aromatic polyimide-based UV-cured acrylate.
11. The structure of claim 10 wherein: the first layer comprises a
material selected from the group consisting of an inorganic
material and an organic material; and the second layer comprising a
material selected from the group consisting of an inorganic
material and an organic material.
12. The structure of claim 10 wherein: the adhesion promoter layer
comprises as constituents: (a) an aromatic polyimide; and (b) a
UV-cured resin, wherein the percentages by weight of the
constituents (a) and (b) are effective to enhance the bond between
adjacent layers of a laminated structure.
13. The structure of claim 12 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 20% to 60% of
(a), and from 40% to 80% of (b) for a total of 100 parts of (a) and
(b).
14. The structure of claim 13 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 30% to 50% of
(a), and from 50% to 70% of (b) for a total of 100 parts of (a) and
(b).
15. The structure of claim 13 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 35% to 45% of
(a), and from 55% to 65% of (b) for a total of 100 parts of (a) and
(b).
16. The structure of claim 10 wherein: The adhesion promoter layer
has a thickness in the range of 0.05 to 0.15 .mu.m.
17. A liquid crystal display comprising: a pair of optically
transparent substrates defining a liquid crystal cell, each
substrate of the pair of substrates having an outer surface
carrying an adhesion promoter layer comprising an aromatic
polyimide-based UV-cured acrylate; and an optical layer coated on
the adhesion promoter layer.
18. The display of claim 17 wherein: the adhesion promoter
comprises as constituents: (a) an aromatic polyimide; and (b) a
UV-cured resin, wherein the percentages by weight of the
constituents (a) and (b) are effective to enhance the bond between
adjacent layers of a laminated structure.
19. The display of claim 18 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 20% to 60% of
(a), and from 40% to 80% of, (b) for a total of 100 parts of (a)
and (b).
20. The display of claim 18 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 30% to 50% of
(a), and from 50% to 70% of (b) for a total of 100 parts of (a) and
(b).
21. The display of claim 18 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 35% to 45% of
(a), and from 55% to 65% of (b) for a total of 100 parts of (a) and
(b).
22. The display of claim 17 wherein: the optical layer comprises a
compensator.
23. The display of claim 17 wherein: the optical layer comprises a
polarizer.
24. The display of claim 17 wherein: The adhesion promoter coating
has a thickness in the range of 0.05 to 0.15 .mu.m.
25. A liquid crystal display comprising: a pair of optically
transparent substrates defining a liquid crystal cell, each
substrate of the pair of substrates having an outer surface
carrying a multilayer structure comprising in sequence from said
outer surface an adhesive promoter layer, a pressure sensitive
adhesive layer, a second adhesion promoter layer and an optical
layer, each of said adhesive promoter layers comprising an aromatic
polyimide-based UV-cured acrylate.
26. The display of claim 25 wherein: each of said adhesive promoter
layers comprises as constituents: (a) an aromatic polyimide; and
(b) a UV-cured resin, wherein the percentages by weight of the
constituents (a) and (b) are effective to enhance the bond between
adjacent layers of a laminated structure.
27. The display of claim 26 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 20% to 60% of
(a), and from 40% to 80% of (b) for a total of 100 parts of (a) and
(b).
28. The display of claim 26 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 30% to 50% of
(a), and from 50% to 70% of (b) for a total of 100 parts of (a) and
(b).
29. The display of claim 26 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 35% to 45% of
(a), and from 55% to 65% of (b) for a total of 100 parts of (a) and
(b).
30. The display of claim 25 wherein: the optical layer comprises a
compensator.
31. The display of claim 25 wherein: the optical layer comprises a
polarizer.
32. The display of claim 25 wherein: each of said adhesion promoter
layers has a thickness in the range of 0.05 to 0.15 .mu.m.
33. A laminated structure comprising: a first layer optically
transparent at selected wavelengths; a second layer optically
transparent at said selected wavelengths, a surface of said first
layer being in confronting relationship with a surface of said
second layer; an adhesive layer between said surfaces; a first
UV-cured adhesion promoter layer interposed between and joining the
surface of the first layer and the adhesive layer; and a second
UV-cured adhesion promoter layer interposed between and joining the
surface of the second layer and the adhesive layer.
34. The structure of claim 33 wherein: said first and second layers
are made of sapphire.
35. The structure of claim 33 wherein: each of the first and second
adhesion promoter layers comprises an aromatic polyimide-based
UV-cured acrylate.
36. The structure of claim 33 wherein: each of the adhesion
promoter layers comprises as constituents: (a) an aromatic
polyimide; and (b) a UV-cured resin, wherein the percentages by
weight of the constituents (a) and (b) are effective to enhance the
bond between adjacent layers of a laminated structure.
37. The structure of claim 36 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 20% to 60% of
(a), and from 40% to 80% of (b) for a total of 100 parts of (a) and
(b).
38. The structure of claim 36 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 30% to 50% of
(a), and from 50% to 70% of (b) for a total of 100 parts of (a) and
(b).
39. The structure of claim 36 wherein: the relative proportions, by
weight, of said constituents (a) and (b) are from 35% to 45% of
(a), and from 55% to 75% of (b) for a total of 100 parts of (a) and
(b).
40. The structure of claim 33 wherein: each of the adhesion
promoter layers has a thickness in the range of 0.05 to 0.15
.mu.m.
41. A method of fabricating a laminated, optically transparent
structure comprising: preparing a mixture by dissolving an aromatic
polyimide and a UV-curable resin in a solvent; stirring the
mixture; filtering the mixture; coating the mixture on a surface of
a substrate; air drying the coated mixture; and curing the coated
mixture using UV radiation, the cured coated mixture comprising an
adhesion promoter layer.
42. The method of claim 41 further comprising: applying an optical
layer over the cured adhesion promoter coating.
43. The method of claim 42 wherein: the optical layer comprises an
optical element selected from the group consisting of a compensator
and a polarizer.
44. The method of claim 41 wherein: the relative proportions, by
weight, of said aromatic polyimide, UV-curable resin and solvent
are, respectively, in the ranges of 0.35% to 0.45%; 0.55% to 0.65%;
and 98.9% to 99.1%, by weight.
45. The method of claim 41 wherein: the solvent comprises as
constituents ethyl L-lactate and isoproponal.
46. The method of claim 45 wherein: the relative proportions, by
weight, of the solvent constituents comprise 55% to 100% of ethyl
L-lactate and 0% to 45% of isoproponal, for a total of 100 parts of
the solvent.
47. The method of claim 41 wherein: the coated mixture has a
thickness in the range of 0.05 to 0.15 .mu.m.
48. The method of claim 41 further comprising: coating the mixture
on a surface of a second substrate; air drying the coated mixture
on the surface of the second substrate; curing the coated mixture
on the surface of the second substrate using UV radiation, the
cured coated mixture on the second substrate comprising an adhesion
promoter layer; and bonding the first and second substrates
together using an adhesive between the adhesion promoter layers on
the first and second substrates.
49. The method of claim 48 wherein: the first and second substrates
comprise sapphire.
50. A method of using an aromatic polyimide-based UV-curable
acrylate, the method comprising: depositing a coating of said
aromatic polyimide-based UV-curable acrylate on the surface of a
first layer; curing said coating using UV radiation; and applying a
second layer on the UV-cured coating, said coating preventing
separation of said layers.
51. The method of claim 50 wherein: the first layer comprises a
material selected from the group consisting of an inorganic
material and an organic material; and the second layer comprises a
material selected from the group consisting of an inorganic
material and an organic material.
52. The method of claim 50 wherein: the coating of said aromatic
polyimide-based UV-curable acrylate has a thickness in the range of
0.05 to 0.15 .mu.m.
53. A mixture for producing an adhesion promoter, the mixture
comprising: (a) an aromatic polyimide; (b) a UV-curable resin; and
(c) a solvent, wherein: (a) is present in an amount from 0.2% to
0.6% of the mixture by weight; (b) is present in an amount from
0.4% to 0.8% of the mixture by weight, and wherein (c) comprises
the remainder of the mixture and comprises from 55% to 100%, by
weight, of ethyl L-lactate and from 0% to 45%, by weight, of
isopropanol.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 11/434,641, filed May 15, 2006, titled "UV
Curable Alignment Material for Fabrication of Monolithic
Compensators for Liquid Crystal Displays", which in turn is a
continuation-in-part of U.S. patent application Ser. No.
11/241,070, filed Sep. 30, 2005 and titled "New Low Temperature Low
Cost Liquid Crystal Alignment Material"; both of the foregoing
applications are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to laminated optical
apparatus and particularly to the prevention of the delamination of
such apparatus.
BACKGROUND OF THE INVENTION
[0003] One example of a laminated optical apparatus is a thin film
flat panel display such as a liquid crystal display (LCD). LCDs
exist in a multitude of embodiments depending upon the specific
type of liquid crystal material and the configuration of the
polarizers and electrodes. In its simplest form, a typical LCD
comprises a liquid crystal cell situated between a pair of
optically transparent substrates each of which has an outer surface
that may be coated with a polarizer layer.
[0004] Many LCDs exhibit optical performance that is highly
sensitive to the angle at which the display is viewed. Optical
compensation layers, also referred to as compensators or retarders,
are commonly used to mitigate the viewing angle effects in LCDs.
Such a compensator or retarder layer may be applied directly to the
outer surface of each substrate so as to be situated between the
substrate and an associated polarizer layer.
[0005] Delamination of a coated layer such as a compensator or
polarizer layer often occurs in LCDs. To improve the interfacial
adhesive forces between the coated layer and the substrate, the
layer-receiving surface of the substrate may be treated before
coating by, for example, plasma or corona discharge surface
treatment, acid/base etching, or the like. These treatments are
usually time-consuming and not always effective, particularly for
certain substrates such as fluorinated compounds.
[0006] As an alternative to the foregoing surface treatments,
adhesion promoters such as acrylic polymers (an example of which is
General Electric's SHP401 primer) applied to the layer-receiving
surface of the substrate have been used in an effort to prevent
delamination. However, the interfacial forces provided by such
adhesion promoters have often been inadequate to prevent
delamination.
[0007] Another example of a laminated optical apparatus subject to
delamination is the window or dome structure that houses the
optical sensors carried by a missile. Such a dome structure may
comprise a pair of adhesively bonded optically transparent sapphire
substrates or layers. The severe operating environment of the
missile subjects the dome structure to high temperatures and
mechanical stresses often causing separation of the dome layers
along the adhesive bond.
SUMMARY OF THE INVENTION
[0008] In accordance with one aspect of the invention, there is
provided an adhesion promoter for enhancing the bond between
adjacent layers of a multilayer structure to prevent delamination
thereof. Examples of multilayer structures that may advantageously
utilize the adhesion promoter of the invention include, without
limitation, liquid crystal displays and bonded missile domes.
[0009] Broadly, the adhesion promoter of the invention comprises an
aromatic polyimide-based UV-cured acrylate. More specifically but
without limitation, the adhesion promoter comprises an aromatic
polyimide and a UV-cured resin, wherein the proportions by weight
of the constituents are effective to enhance the bond between
adjacent layers of a laminated structure. Preferably, the relative
proportions, by weight, of the constituents are from 20% to 60% of
the aromatic polyimide and from 40% to 80% of the UV-cured resin
for a total of 100 parts of the constituents.
[0010] Pursuant to another aspect of the invention there is
provided a mixture for producing an adhesion promoter, the mixture
comprising (a) an aromatic polyimide; (b) a UV-curable resin; and
(c) a solvent comprising (1) ethyl L-lactate and (2) isopropanol
wherein the percentages by weight of the constituents (a), (b) and
(c) are effective to produce an adhesion promoter for enhancing a
bond between adjacent layers of a laminated structure. Preferably,
the relative proportions, by weight, of the constituents (a), (b)
and (c) are from 0.2% to 0.6% of (a), from 0.4% to 0.8% of (b),
from 55% to 64% of (c) (1) , and from 35% to 44% of (c) (2), for a
total of 100 parts of (a), (b) and (c).
[0011] In accordance with a specific exemplary embodiment, there is
provided a liquid crystal display comprising a pair of optically
transparent substrates defining a liquid crystal cell, each
substrate of the pair of substrates having an outer surface
carrying a multilayer structure comprising in sequence from the
outer surface an adhesive promoter layer, a pressure sensitive
adhesive layer, a second adhesion promoter layer and an optical
layer, each of the adhesive promoter layers comprising an aromatic
polyimide-based UV-cured acrylate.
[0012] In accordance with another specific exemplary embodiment,
there is provided a laminated structure comprising a first
substrate and a second substrate, the substrates being optically
transparent at selected wavelengths. A surface of the first
substrate is in confronting relationship with a surface of the
second substrate, and an adhesive layer is disposed between the
surfaces. A first UV-cured adhesion promoter layer joins the
surface of the first substrate and the adhesive layer, and a second
UV-cured adhesion promoter layer joins the surface of the second
substrate and the adhesive layer. In one form of this embodiment,
the first and second layers are made of sapphire. In another form,
each of the first and second adhesion promoter layers comprises an
aromatic polyimide-based UV-cured acrylate. Preferably, each of the
adhesion promoter layers comprises an aromatic polyimide and a
UV-cured resin, wherein the percentages by weight of the
constituents are effective to enhance the bond between the surface
of the associated substrate and the adhesive layer.
[0013] Pursuant to another specific, exemplary embodiment of the
invention, there is provided a method of fabricating a laminated,
optically transparent structure comprising preparing a mixture by
dissolving an aromatic polyimide and a UV-curable resin in a
solvent, stirring the mixture, filtering the mixture, coating the
mixture on a surface of a substrate, air drying the coated mixture,
and curing the coated mixture using UV radiation, the cured coated
mixture comprising an adhesion promoter layer. The method may
further comprise applying an optical layer such as a compensator or
polarizer over the cured adhesion promoter coating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Further objects, features and advantages of the invention
will become apparent from the detailed description, below, when
read in conjunction with the accompanying drawings in which:
[0015] FIG. 1 is a schematic, cross section view of a portion of a
laminated optical apparatus in the form of an LCD in accordance
with a specific, exemplary embodiment of the present invention;
[0016] FIG. 2 is a schematic, cross section view of a portion of a
laminated optical apparatus in the form of a missile dome in
accordance with another specific, exemplary embodiment of the
present invention;
[0017] FIG. 3 is a flow chart showing an example of a process in
accordance with an aspect of the present invention for fabricating
the apparatus of FIG. 1; and
[0018] FIG. 4 is a flow chart showing an example of a process in
accordance with an aspect of the present invention for fabricating
the apparatus of FIG. 2.
DETAILED DESCRIPTION
[0019] The following description is of a best mode presently
contemplated for practicing the invention. This description is not
to be taken in a limiting sense but is made merely for the purpose
of describing the general principles of the invention whose scope
may be ascertained by referring to the appended claims.
[0020] FIG. 1 is a schematic illustration of a portion of a
laminated or layered optical apparatus in the form of an LCD 10
incorporating features of the invention.
[0021] The LCD 10 comprises a liquid crystal cell 12 illuminated by
a rear illumination source 14. The liquid crystal cell may comprise
a twisted nematic liquid crystal material 16 encapsulated between
two optically transparent plates or substrates 18 and 20 of, for
example, glass. The substrates 18 and 20 carry typical LCD features
(not shown) including, for example, color filters, thin film
transistor multiplex drive electronics, transparent electrodes and
liquid crystal alignment films on the source and viewer sides.
Applied to an outer surface 22 of the rear or source side liquid
crystal cell substrate 18 is a multilayer structure 23 comprising
an adhesive promoter layer 24, a pressure sensitive adhesive (PSA)
layer 26, a second adhesive promoter layer 28 and, finally, a rear
polarizer layer 30 adjacent to the rear illumination source 14. The
PSA layer 26 may comprise any of a variety of commercially
available optically transparent PSA products from such suppliers as
3M, Sumitomo Chemical, Nitto Denko Corp., and so forth. The rear
polarizer layer 30 may comprise, by way of example, a thin sheet of
stretched polyvinyl alcohol (PVA) stained with iodine.
[0022] In accordance with an aspect of the invention, the adhesion
promoter layers 24 and 28 are preferably fabricated of an aromatic
polyimide-based UV-cured acrylate. The adhesion promoter layers 24
and 28 provide strong interfacial bonds between the PSA layer 26
and the rear polarizer layer 30, and between the PSA layer 26 and
the surface 22 of the rear or source side liquid crystal cell
substrate 18 preventing delamination of the PSA and polarizer
layers 26 and 30.
[0023] The PSA layer 26 may have a thickness in the range of, for
example, 1 to 2 .mu.m. Each of the adhesion promoter layers 24 and
28 is very thin (for example, less than 0.2 .mu.m thick such as in
the range of 0.05 to 0.15 .mu.m) so as not to attenuate or
otherwise affect light transmitted through the liquid crystal cell
12.
[0024] Overlying an outer surface 32 of the front or viewer side
liquid crystal cell substrate 20 is a multilayer structure 34 like
the structure 23 on the source side of the cell 12. The multilayer
structure 34 comprises an adhesive promoter layer 36, a PSA layer
38, a second adhesive promoter layer 40, and a front polarizer
layer 42 (commonly referred to as the analyzer layer). The
materials, thicknesses, and so forth of the front side layers are
preferably the same or substantially the same as those of the rear
side layers.
[0025] Each of the adhesion promoter layers 24, 28, 36 and 40 may
comprise, as constituents, an aromatic polyimide and a UV-cured
resin, the percentages by weight of the constituents being
effective to enhance the bond between adjacent layers of the LCD
structure. By way of example, the relative proportions of the
constituents may preferably comprise, by weight, from 20% to 60% of
aromatic polyimide, and from 40% to 80% of UW-cured resin for a
total of 100 parts. More preferably, the relative proportions of
the constituents may comprise, by weight, from 30% to 50% of
aromatic polyimide and from 50% to 70% of UV-curable resin for a
total of 100 parts. Most preferably, the relative proportions of
the constituents may comprise, by weight, from 35% to 45% and from
55% to 65%, respectively, for a total of 100 parts.
[0026] FIG. 2 is a schematic illustration of a portion of another
example of a laminated or layered optical apparatus utilizing
features of the present invention. The apparatus of FIG. 2 is in
the form of a high strength, bonded, optically transparent dome 50
forming part of a missile and incorporating features of the
invention. The dome 50 may enclose one or more of a variety of
optical sensors for performing such tasks as missile guidance and
target acquisition. The dome 50 comprises an inner substrate or
layer 52 and an outer substrate or layer 54, each of the layers 52
and 54 being formed of a high strength, heat resistant material
such as sapphire having the desired optical, mechanical and thermal
properties.
[0027] The dome layers 52 and 54 are joined along confronting faces
56 and 58 by means of an adhesive layer 60 comprising, for example,
a UV cure clear silicone elastomer such as that supplied by Gelest,
Inc., under the trademark ZIPCONE.TM. UE. The adhesive layer 60 may
be 1 to 2 .mu.m thick and optically transparent to the wavelengths
of interest, for example, 3-5 .mu.m. Interposed between the face 56
of the inner dome layer 52 and the adhesive layer 60 is a UV-cured
adhesion promoter layer 62. A similar UV-cured adhesion promoter
layer 64 is interposed between the face 58 of the outer dome layer
54 and the adhesive layer 60. In accordance with an aspect of the
invention, each of the adhesion promoter layers 62 and 64 comprises
an aromatic polyimide-based UV-cured acrylate providing high
resistance to delamination of the dome layers 52 and 54. Each of
the adhesion promoter layers 62 and 64 is sufficiently thin, for
example, less than 0.2 .mu.m thick (such as in the range of 0.05 to
0.15 .mu.m) so as not to attenuate or otherwise affect the
transmitted or received optical is preferably the same as that
described above in connection with FIG. 1.
[0028] The following are non-limiting examples of materials and
fabrication processes that may be employed in practicing the
invention.
[0029] The adhesion promoter of the invention preferably comprises
a UV curable composition basically comprising a mixture of an
aromatic polyimide, such as a segmented, rigid-rod aromatic
polyimide, and a UV-curable acrylate photopolymer. In accordance
with one, specific exemplary embodiment, the adhesion promoter may
be fabricated from the following materials: [0030] Aromatic
polyimide: PYRALIN.TM. PI4700 (DuPont) [0031] UV curable resin:
Norland Optical Adhesive 68 (NOA 68) (Norland) [0032] Solvent:
Ethyl L-lactate (Spectrum) and Isopropanol (Aldrich)
EXAMPLE 1
[0033] FIG. 3 is a flow chart showing preferred steps for
fabricating laminated or layered structures utilizing aspects of
the present invention. For example, an adhesion promoter mixture
was prepared by dissolving (step 70) 0.4 g of aromatic polyimide
and 0.6 g of UV curable resin in a solvent comprising 59.4 g of
ethyl L-lactate and 39.6 g of isopropanol, for a total of 100 g.
The mixture was stirred (step 71) for about 2 hours using a
magnetic stirrer. The mixture was then filtered (step 72) through a
filter membrane having a 0.45 .mu.m pore size. The mixture was
coated (step 73) on a surface of a glass substrate by spin-coating
at a speed of 1,500 rpm for 30 seconds. Alternatively, the mixture
may be coated on the surface of the substrate by, for example,
dipping, spraying or brushing. The coating was air-dried (step 74)
at a temperature of 50.degree. C. for 10 minutes, and then UV-cured
(step 75) in a nitrogen atmosphere by means of a UV fusion lamp
conveyor system with the conveyor moving at a speed of 10 fpm, to
form the final adhesion promoter layer.
[0034] The relative proportions by weight of the adhesion promoter
constituents are preferably in the range of 0.2-0.6% of aromatic
polyimide, 0.4-0.8% of UV curable resin, 55-64% of ethyl L-lactate
and 35-44% isopropanol for 100% of the mixture of the four
constituents. More preferably, the relative proportions by weight
may be 0.3-0.5% aromatic polyimide, 0.5-0.7% UV curable resin,
57-62% ethyl L-lactate and 37-42% isopropanol for 100% of the
mixture, and most preferably the relative proportions by weight may
be 0.35-0.45% aromatic polyimide, 0.55-0.65% UV curable resin,
59-60% ethyl L-lactate and 39-40% isopropanol for 100% of the
mixture.
[0035] In accordance with one exemplary application of the
foregoing process, an optical layer (not shown) such as a polarizer
or an optical compensator of, for example, a thin sheet of
stretched PVA, may be applied over the adhesion promoter layer
prepared in steps 70-75 to provide a strong, delamination-resistant
bond between the substrate and the overlying optical layer.
[0036] Alternatively, as further shown in FIG. 3, an LCD such as
that illustrated in FIG. 1 was fabricated by applying (step 76) a
PSA layer to the adhesion promoter layer formed in steps 70-75,
coating an acrylate mixture as prepared in steps 70-72 on a
polarizer layer (step 77), followed by air-drying and UV-curing of
the coating (steps 78 and 79) to form a second adhesion promoter
layer in the manner described in steps 74 and 75, and applying the
coated polarizer layer (step 80) to the PSA layer.
[0037] Alternatively, for the percentage ranges of aromatic
polyimide and isopropanol specified above, the solvent may comprise
from 55% to 100%, by weight, of ethyl L-lactate and from 0% to 45%,
by weight, of isopropanol for 100 parts of the solvent.
EXAMPLE 2
[0038] FIG. 4 is a flow chart showing the steps of a preferred
process for fabricating a laminated or layered optical structure
such as that shown in FIG. 2. An adhesion promoter mixture of
aromatic polymide, UV-durable resin and solvent was prepared by
dissolving (step 82), stirring (step 84) the mixture and filtering
(step 86) as in Example 1. The mixture was coated (step 88) on the
surfaces of the first and second sapphire substrates as in Example
1. The coatings on the substrates were air-dried (step 90) and
UV-cured (step 92) as in Example 1 to form an adhesive promoter
layer on each substrate. The substrates were then bonded (step 94)
by applying a layer of an optically transparent adhesive such as
ZIPCONE.TM. UE mentioned above on the adhesion promoter layer on
one of the sapphire substrates and the two sapphire substrates were
then joined to form the structure depicted in FIG. 2. The relative
proportions by weight of the adhesion promoter constituents were
the same as those set forth in Example 1.
[0039] By way of example and not by way of limitation, the adhesion
promoter of the present invention may be used to enhance adhesion
between:
[0040] 1. an organic substrate and an organic thin film;
[0041] 2. an organic substrate and an inorganic thin film;
[0042] 3. an organic substrate and an organic substrate;
[0043] 4. an inorganic substrate and an inorganic thin film;
and
[0044] 5. an inorganic substrate and an inorganic substrate.
[0045] Examples of organic materials include, but are not limited
to, polycarbonate, polypropylene, polyimide and fluorocarbon.
Examples of inorganic materials include, but are not limited to,
oxide, fluoride and sulfide materials.
[0046] While several illustrative embodiments of the invention have
been disclosed herein, still further variations and alternative
embodiments will occur to those skilled in the art. Thus, the
adhesive promoter forming one aspect of the invention is useful
wherever the prevention of film delamination is an important goal
and accordingly is amenable to a broad range of applications
including, besides those described above, the adhesive bonding
between a window pane and a UV or IR protective film, or between a
polycarbonate headlight lens and an abrasion resistant hardcoat.
Such variations and alternative embodiments are contemplated, and
can be made without departing from the spirit and scope of the
invention as defined in the appended claims.
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