U.S. patent application number 12/400431 was filed with the patent office on 2009-07-02 for moisture barrier coatings.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Moses M. David, Raghunath Padiyath.
Application Number | 20090169770 12/400431 |
Document ID | / |
Family ID | 37311881 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090169770 |
Kind Code |
A1 |
Padiyath; Raghunath ; et
al. |
July 2, 2009 |
MOISTURE BARRIER COATINGS
Abstract
A barrier assembly having a flexible or rigid substrate
overcoated with an all polymer multilayer stack. A multilayer on
the substrate includes alternating diamond-like glass or carbon
layers with polymer layers. Another multilayer includes alternating
polymer layers using different types of polymers. The barrier
layers can be used to mount, cover, encapsulate or form composite
assemblies for protection of moisture or oxygen sensitive
articles
Inventors: |
Padiyath; Raghunath;
(Woodbury, MN) ; David; Moses M.; (Woodbury,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
37311881 |
Appl. No.: |
12/400431 |
Filed: |
March 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11185078 |
Jul 20, 2005 |
|
|
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12400431 |
|
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Current U.S.
Class: |
427/577 |
Current CPC
Class: |
H01L 51/5243 20130101;
H01L 51/448 20130101; C08J 7/046 20200101; H01L 51/5256 20130101;
C08J 7/048 20200101; Y02E 10/549 20130101; Y10T 428/31504 20150401;
B05D 1/62 20130101; B05D 7/58 20130101; C23C 16/545 20130101; C08J
7/123 20130101; B05D 7/546 20130101; C08J 7/043 20200101; C23C
16/26 20130101; Y10T 428/26 20150115; Y10T 428/31935 20150401; C08J
7/0423 20200101; Y10T 428/30 20150115; Y10T 428/265 20150115 |
Class at
Publication: |
427/577 |
International
Class: |
C23C 16/513 20060101
C23C016/513 |
Claims
1. A process for fabricating a composite assembly for protection of
a moisture or oxygen sensitive article, comprising: providing a
substrate; placing the substrate on an electrode in a chamber;
introducing a plasma into the chamber; biasing the substrate using
the electrode; overcoating a polymer layer on the substrate using
the plasma; and overcoating a diamond-like glass layer on the
polymer layer using the plasma, wherein the diamond-like glass
layer comprises an at least substantially amorphous glass including
carbon and silicon and has an oxygen to silicon ratio less than
1.5.
2. The process of claim 1, wherein during the overcoating steps the
pressure in the chamber is less than 50 mTorr.
3. The process of claim 1 wherein, during the overcoating steps the
bias of the substrate is greater than 500 V.
4. The process of claim 1, wherein the diamond-like glass layer
further comprises nitrogen.
5. A process for fabricating a composite assembly for protection of
a moisture or oxygen sensitive article, comprising: providing a
substrate; placing the substrate on an electrode in a chamber;
introducing a plasma into the chamber; biasing the substrate using
the electrode; overcoating a polymer layer on the substrate using
the plasma; overcoating a diamond-like glass layer on the polymer
layer using the plasma; and overcoating an inorganic barrier layer
on the diamond-like glass layer, wherein the diamond-like glass
layer comprises an at least substantially amorphous glass including
carbon and silicon.
6. The process of claim 5, wherein the diamond-like glass layer has
an oxygen to silicon ratio less than 1.5.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No.
11/185,078, filed Jul. 20, 2005, which is pending, the disclosure
of which is incorporated by reference in its entirety herein.
FIELD OF INVENTION
[0002] The present invention relates to barrier films for
protection of moisture or oxygen sensitive articles.
BACKGROUND
[0003] Organic light emitting devices (OLEDs) can suffer reduced
output or premature failure when exposed to water vapor or oxygen.
Metals and glasses have been used to encapsulate and prolong the
life of OLED devices, but metals typically lack transparency and
glass lacks flexibility. Intense efforts are underway to find
alternative encapsulation materials for OLEDs and other electronic
devices. Examples include various types of vacuum processes are
described in the patent and technical literature for the formation
of barrier coatings. These methods span the range of e-beam
evaporation, thermal evaporation, electron-cyclotron resonance
plasma-enhanced chemical vapor deposition (PECVD), magnetically
enhanced PECVD, reactive sputtering, and others. Barrier
performance of the coatings deposited by these methods typically
results in a moisture vapor transmission rate (MVTR) in the range
from 0.1-5 g/m.sup.2 day, depending on the specific processes.
Graff (WO0036665) demonstrates the importance of separating
multiple inorganic oxide coatings with vapor deposited highly
cross-linked polymer layers to achieve barrier performance
necessary for OLED device substrates.
[0004] It is commonly accepted that multiple inorganic layers
separated by polymer coatings are needed to achieve superior
barrier performance. U.S. Pat. No. 5,320,875 teaches the importance
of a plasma polymerized siloxane monomer and an adhesion promoter
in addition to generating the plasma in an "oxygen excessive" mode
and depositing the coatings in the "plasma reaction zone" to obtain
improved barrier performance. The best barrier coatings made by
this process still have an MVTR of 0.23 g/m.sup.2 day. Da Silva
Sobrinho et al. (Surface and Coatings Technology, 116-119, p 1204,
1999) report a microwave and radio frequency combined process for
depositing barrier coatings. In U.S. Pat. No. 6,146,225, Sheats et
al. claim that a high density plasma with low bias voltage results
in superior quality barrier coatings.
[0005] References relating to flexible barrier films include U.S.
Pat. No. 5,440,446 (Shaw et. al.), U.S. Pat. No. 5,530,581 (Cogan),
U.S. Pat. No. 5,681,666 (Treger et al.), U.S. Pat. No. 5,686,360
(Harvey, III et al.), U.S. Pat. No. 5,736,207 (Walther et al.),
U.S. Pat. No. 6,004,660 (Topolski et al.), U.S. Pat. No. 6,083,628
(Yializis), U.S. Pat. No. 6,146,225 (Sheats et al.), U.S. Pat. No.
6,214,422 (Yializis), U.S. Pat. No. 6,268,695 (Affinito), U.S. Pat.
No. 6,358,570 (Affinito), U.S. Pat. No. 6,413,645 (Graff et al.),
U.S. Pat. No. 6,492,026 (Graff et al.), U.S. Pat. No. 6,497,598
(Affinito), U.S. Pat. No. 6,497,598 (Affinito), U.S. Pat. No.
6,623,861 (Martin et al.), U.S. Pat. No. 6,570,325 (Graff et al.),
U.S. Pat. No. 5,757,126, U.S. Patent Application No. 2002/0125822
A1 (Graff et al.), and PCT Published Application No. WO 97/16053
(Robert Bosch GmbH).
SUMMARY OF INVENTION
[0006] A first composite assembly for protection of a moisture or
oxygen sensitive article includes a substrate, a first polymer
layer overcoated on the substrate, and a second polymer layer
overcoated on the first polymer layer. In this assembly, the first
polymer layer is composed of a first polymer and the second polymer
layer is composed of a second polymer different from the first
polymer, and the second polymer comprises a plasma polymer.
[0007] A second composite assembly for protection of a moisture or
oxygen sensitive article includes a substrate, a polymer layer
overcoated on the substrate, and a diamond-like carbon layer
overcoated on the polymer layer.
[0008] A third composite assembly for protection of a moisture or
oxygen sensitive article includes a substrate, a polymer layer
overcoated on the substrate, and a diamond-like glass layer
overcoated on the polymer glass layer.
[0009] Processes include any method of fabricating these
assemblies.
[0010] The words of orientation such as "atop", "on", "uppermost"
and the like for the location of various layers in the barrier
assemblies or devices refer to the relative position of one or more
layers with respect to a horizontal support layer. We do not intend
that the barrier assemblies or devices should have any particular
orientation in space during or after their manufacture.
[0011] The term "overcoated" to describe the position of a layer
with respect to a substrate or other element of a barrier assembly,
refers to the layer as being atop the substrate or other element,
but not necessarily contiguous to either the substrate or the other
element.
[0012] The term "polymer" refers to homopolymers and copolymers, as
well as homopolymers or copolymers that may be formed in a miscible
blend, e.g., by coextrusion or by reaction, including, e.g.,
transesterification. The term "polymer" also includes plasma
deposited polymers. The term "copolymer" includes both random and
block copolymers. The term "curable polymer" includes both
crosslinked and uncrosslinked polymers. The term "crosslinked"
polymer refers to a polymer whose polymer chains are joined
together by covalent chemical bonds, usually via crosslinking
molecules or groups, to form a network polymer. A crosslinked
polymer is generally characterized by insolubility, but may be
swellable in the presence of an appropriate solvent.
[0013] The term a "visible light-transmissive" support, layer,
assembly or device means that the support, layer, assembly or
device has an average transmission over the visible portion of the
spectrum, T.sub.vis of at least about 20%, measured along the
normal axis.
[0014] The term "diamond-like glass" (DLG) refers to substantially
or completely amorphous glass including carbon and silicon, and
optionally including one or more additional components selected
from the group including hydrogen, nitrogen, oxygen, fluorine,
sulfur, titanium, and copper. Other elements may be present in
certain embodiments. The amorphous diamond-like glass films may
contain clustering of atoms to give it a short-range order but are
essentially void of medium and long range ordering that lead to
micro or macro crystallinity which can adversely scatter radiation
having wavelengths of from 180 nanometers (nm) to 800 nm.
[0015] The term "diamond-like carbon" (DLC) refers to an amorphous
film or coating comprising approximately 50 to 90 atomic percent
carbon and approximately 10 to 50 atomic percent hydrogen, with a
gram atom density of between approximately 0.20 and approximately
0.28 gram atoms per cubic centimeter, and composed of approximately
50% to approximately 90% tetrahedral bonds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention may be more completely understood in the
following detailed description of various embodiments of the
invention in connection with the accompanying drawings, in
which:
[0017] FIG. 1 is a schematic view of a disclosed barrier
assembly;
[0018] FIG. 2 is a schematic view of a disclosed barrier assembly
having multiple layers made from alternating DLG or DLC layers and
polymer layers;
[0019] FIG. 3 is a schematic view of a disclosed laminated barrier
assembly having multiple layers made from polymers;
[0020] FIG. 4 is a schematic view of an apparatus for carrying out
a disclosed process for making barrier assemblies; and
[0021] FIG. 5 is a schematic cross-sectional view of an exemplary
OLED device that can incorporate the barrier assembly.
DETAILED DESCRIPTION
[0022] Embodiments consistent with the present invention include an
enhanced PECVD process that leads to coatings having superior
moisture vapor barrier performance. In one particular embodiment,
excellent barrier performance is achieved from a SiOCH film formed
on a web in intimate contact with a drum electrode utilizing radio
frequency (RF) plasma conditions that lead to an oxygen depleted
silicon oxide coating under significant energetic ion bombardment.
The MVTRs of barrier coatings deposited using this process were
less than 0.005 g/m.sup.2 day measured using ASTM F-1219 at
50.degree. C. According to certain embodiments, barrier coatings at
least 100 nm thick deposited under high self-bias and low pressures
(approximately 5-10 mTorr) result in superior moisture vapor
transmission rates. The coatings are deposited on a drum electrode
powered using an RF source operating at least 1000 W of forward
power. The vacuum chamber is configured such that these operating
conditions result in a very high (>500 V) negative potential on
the drum electrode. As a result of ion bombardment from having high
substrate bias, the coating formed has very low free volume. The
drum is typically water cooled. A silicon source such as tetra
methyl silane (TMS) and oxygen is introduced in quantities such
that the resulting coatings are oxygen depleted in certain
embodiments. Even though the coatings are deficient in oxygen, the
coatings have high optical transmission. Nitrogen may be introduced
in addition to oxygen to obtain a SiOCNH coating. The SiOCNH
coatings also have superior barrier properties.
[0023] Therefore, the process conditions that result in better
barrier coatings are as follows: (1) barrier coatings are made by
an RF PECVD process on a moving drum electrode under high
self-bias; (2) the CVD process is operated at a very low pressure
of less than 50 mTorr, preferably less than 25 mTorr, most
preferably less than 10 mTorr to avoid gas phase nucleation and
particle formation, and to prevent collisional quenching of ion
energy at higher pressures; and (3) the coatings are significantly
"oxygen depleted," meaning that for every Si atom there are less
than 1.5 oxygen atoms present in the coating (O/Si atomic
ratio<1.5).
[0024] The barrier coatings may be used for various types of
packaging applications. For example, electronics, medical,
pharmaceutical and foodstuffs packaging all have varying
requirements for protection from moisture and oxygen. For
pharmaceuticals, the barrier coatings may be used, for example, to
protect drugs from oxygen and moisture, helping to maintain their
purity and increase their shelf life by avoiding the adverse
effects of contaminants. For foodstuffs, the barrier coatings may
be used, for example, to protect food products from oxygen and
moisture, helping to preserve their flavor and increase their shelf
life. Another application involves using the coatings to
encapsulate phosphor particles including electroluminescent
phosphor particles such as zinc sulfide, organic electroluminescent
thin films, photovoltaic devices, and other such devices.
Substrates having the barrier coatings may be used in the
fabrication of flexible electronic devices such as OLEDs, organic
transistors, liquid crystal displays (LCD), and other devices. The
coatings can also be used to encapsulate the OLED devices directly,
and the barrier film could be used as a cover for encapsulating
glass or plastic substrate devices. Due to the superior barrier
performance of the coatings produced using the described PECVD
conditions, such devices could be produced at a lower cost with
better performance.
Exemplary Barrier Assembly Structures
[0025] FIG. 1 is a schematic view of a disclosed barrier assembly
having a coating 100 to reduce or prevent substantial transfer of
moisture and oxygen, or other contaminants, to an underlying
substrate 102. The assembly can represent any type of article
requiring or benefiting from protection from moisture or oxygen,
such as the examples provided above. For certain types of
electronic or display devices, for example, oxygen and moisture can
severely degrade their performance or lifetime, and thus the
coating 100 can provide significant advantages in device
performance.
[0026] FIG. 2 is a schematic view of a disclosed laminated barrier
assembly 110 having multiple layers made from alternating DLG or
DLC layers 116, 120 and polymer layers 114, 118 protecting an
underlying substrate 112. FIG. 3 is a schematic view of a disclosed
laminated barrier assembly 130 having multiple layers made from
alternating different types of polymer layers, for example
alternating polymer layers 136, 140 and polymer layers 134, 138
protecting an underlying substrate 132. In this example, layers 136
and 140 are composed of a first type of polymer, and layers 134 and
138 are composed of a second type of polymer different from the
first type of polymer. Any highly crosslinked polymers may be used
for the layers, examples of which are provided below. Assembly 130,
in one embodiment, is thus an all polymer multilayer construction
of a barrier assembly, although it can also include other types of
layers. Each group of different polymers (e.g., 134 and 136), or
combinations of polymers including DLG or DLC (e.g., 114 and 116),
are referred to as a dyad, and the assembly can include any number
of dyads. It can also include various types of optional layers
between the dyads, examples of which are provided below.
[0027] Assemblies 110 and 130 can include any number of alternating
or other layers. Adding more layers may improve the lifetime of the
assemblies by increasing their imperviousness to oxygen, moisture,
or other contaminants. Use of more or multiple layers may also help
cover or encapsulate defects within the layers. The number of
layers can be optimized, or otherwise selected, based upon
particular implementations or other factors.
Substrate
[0028] Substrates having moisture barrier coatings can include any
type of substrate material for use in making a display or
electronic device. The substrate can be rigid, for example by using
glass or other materials. The substrate can also be curved or
flexible, for example by using plastics or other materials. The
substrate can be of any desired shape. Particularly preferred
supports are flexible plastic materials including thermoplastic
films such as polyesters (e.g., PET), polyacrylates (e.g.,
polymethyl methacrylate), polycarbonates, polypropylenes, high or
low density polyethylenes, polyethylene naphthalates, polysulfones,
polyether sulfones, polyurethanes, polyamides, polyvinyl butyral,
polyvinyl chloride, polyvinylidene difluoride and polyethylene
sulfide, and thermoset films such as cellulose derivatives,
polyimide, polyimide benzoxazole, and poly benzoxazole.
[0029] Other suitable materials for the substrate include
chlorotrifluoroethylene-vinylidene fluoride copolymer (CTFE/VDF),
ethylene-chlorotrifluoroethylene copolymer (ECTFE),
ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated
ethylene-propylene copolymer (FEP), polychlorotrifluoroethylene
(PCTFE), perfluoroalkyl-tetrafluoroethylene copolymer (PFA),
polytetrafluoroethyloene (PTFE), polyvinylidene fluoride (PVDF),
polyvinyl fluoride (PVF), tetrafluoroethylene-hexafluoropropylene
copolymer (TFE/HFP),
tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride
terpolymer (THV), polychlorotrifluoroethylene (PCTFE),
hexafluoropropylene-vinylidene fluoride copolymer (HFP/VDF),
tetrafluoroethylene-propylene copolymer (TFE/P), and
tetrafluoroethylene-perfluoromethylether copolymer (TFE/PFMe).
[0030] Alternative substrates include materials having a high glass
transition temperature (Tg) barrier, preferably being
heat-stabilized, using heat setting, annealing under tension, or
other techniques that will discourage shrinkage up to at least the
heat stabilization temperature when the support is not constrained.
If the support has not been heat stabilized, then it preferably has
a Tg greater than that of polymethyl methacrylate (PMMA,
Tg=105.degree. C.). More preferably the support has a Tg of at
least about 110.degree. C., yet more preferably at least about
120.degree. C., and most preferably at least about 128.degree. C.
In addition to heat-stabilized polyethylene terephthalate (HSPET),
other preferred supports include other heat-stabilized high Tg
polyesters, PMMA, styrene/acrylonitrile (SAN, Tg=110.degree. C.),
styrene/maleic anhydride (SMA, Tg=115.degree. C.), polyethylene
naphthalate (PEN, Tg=about 120.degree. C.), polyoxymethylene (POM,
Tg=about 125.degree. C.), polyvinylnaphthalene (PVN, Tg=about
135.degree. C.), polyetheretherketone (PEEK, Tg=about 145.degree.
C.), polyaryletherketone (PAEK, Tg=145.degree. C.), high Tg
fluoropolymers (e.g., DYNEON.TM. HTE terpolymer of
hexafluoropropylene, tetrafluoroethylene, and ethylene, Tg=about
149.degree. C.), polycarbonate (PC, Tg=about 150.degree. C.), poly
alpha-methyl styrene (Tg=about 175.degree. C.), polyarylate (PAR,
Tg=190.degree. C.), polysulfone (PSul, Tg=about 195.degree. C.),
polyphenylene oxide (PPO, Tg=about 200.degree. C.), polyetherimide
(PEI, Tg=about 218.degree. C.), polyarylsulfone (PAS,
Tg=220.degree. C.), poly ether sulfone (PES, Tg=about 225.degree.
C.), polyamideimide (PAI, Tg=about 275.degree. C.), polyimide
(Tg=about 300.degree. C.) and polyphthalamide (heat deflection temp
of 120.degree. C.). For applications where material costs are
important, supports made of HSPET and PEN are especially preferred.
For applications where barrier performance is paramount, supports
made of more expensive materials may be employed. Preferably the
substrate has a thickness of about 0.01 millimeters (mm) to about 1
mm, more preferably about 0.05 mm to about 0.25 mm.
DLG Layer
[0031] Diamond-like glass is an amorphous carbon system including a
substantial quantity of silicon and oxygen that exhibits
diamond-like properties. In these films, on a hydrogen-free basis,
there is at least 30% carbon, a substantial amount of silicon
(typically at least 25%) and no more than 45% oxygen. The unique
combination of a fairly high amount of silicon with a significant
amount of oxygen and a substantial amount of carbon makes these
films highly transparent and flexible (unlike glass).
[0032] Diamond-like glass thin films may have a variety of light
transmissive properties. Depending upon the composition, the thin
films may have increased transmissive properties at various
frequencies. However, in specific implementations the thin film
(when approximately one micron thick) is at least 70% transmissive
to radiation at substantially all wavelengths from about 250 nm to
about 800 nm and more preferably from about 400 nm to about 800 nm.
The extinction coefficient of DLG film is as follows: 70%
transmission for a one micron thick film corresponds to an
extinction coefficient (k) of less than 0.02 in the visible
wavelength range between 400 nm and 800 nm.
[0033] Diamond thin films, having significantly different
properties from the amorphous diamond-like glass film of the
present invention due to the arrangement and intermolecular bonds
of carbon atoms in the specific material, have previously been
deposited on substrates. The type and amount of intermolecular
bonds are determined by infrared (IR) and nuclear magnetic
resonance (NMR) spectra. Carbon deposits contain substantially two
types of carbon-carbon bonds: trigonal graphite bonds (sp.sup.2)
and tetrahedral diamond bonds (sp.sup.3). Diamond is composed of
virtually all tetrahedral bonds, while diamond-like films are
composed of approximately 50% to 90% tetrahedral bonds, and
graphite is composed of virtually all trigonal bonds.
[0034] The crystallinity and the nature of the bonding of the
carbon system determine the physical and chemical properties of the
deposit. Diamond is crystalline whereas the diamond-like glass is a
non-crystalline amorphous material, as determined by x-ray
diffraction. Diamond is essentially pure carbon, whereas
diamond-like glass contains a substantial amount of non-carbon
components, including silicon.
[0035] Diamond has the highest packing density, or gram atom
density (GAD) of any material at ambient pressure. Its GAD is 0.28
gram atoms/cc. Amorphous diamond-like films have a GAD ranging from
about 0.20 to 0.28 gram atoms/cc. In contrast, graphite has a GAD
of 0.18 gram atoms/cc. The high packing density of diamond-like
glass affords excellent resistance to diffusion of liquid or
gaseous materials. Gram atom density is calculated from
measurements of the weight and thickness of a material. The term
"gram atom" refers to the atomic weight of a material expressed in
grams.
[0036] Amorphous diamond-like glass is diamond-like because, in
addition to the foregoing physical properties that are similar to
diamond, it has many of the desirable performance properties of
diamond such as extreme hardness (typically 1000 to 2000
kg/mm.sup.2), high electrical resistivity (often 109 to 1013
ohm-cm), a low coefficient of friction (for example, 0.1), and
optical transparency over a wide range of wavelengths (a typical
extinction coefficient of about between 0.01 and 0.02 in the 400 nm
to 800 nm range).
[0037] Diamond films also have some properties which, in many
applications, make them less beneficial than amorphous diamond-like
glass films. Diamond films usually have grain structures, as
determined by electron microscopy. The grain boundaries are a path
for chemical attack and degradation of the substrates, and also
cause scattering of actinic radiation. Amorphous diamond-like glass
does not have a grain structure, as determined by electron
microscopy, and is thus well suited to applications wherein actinic
radiation will pass through the film. The polycrystalline structure
of diamond films causes light scattering from the grain
boundaries.
[0038] In creating a diamond-like glass film, various additional
components can be incorporated into the basic carbon or carbon and
hydrogen composition. These additional components can be used to
alter and enhance the properties that the diamond-like glass film
imparts to the substrate. For example, it may be desirable to
further enhance the barrier and surface properties.
[0039] The additional components may include one or more of
hydrogen (if not already incorporated), nitrogen, fluorine, sulfur,
titanium, or copper. Other additional components may also be of
benefit. The addition of hydrogen promotes the formation of
tetrahedral bonds. The addition of fluorine is particularly useful
in enhancing barrier and surface properties of the diamond-like
glass film, including the ability to be dispersed in an
incompatible matrix. The addition of nitrogen may be used to
enhance resistance to oxidation and to increase electrical
conductivity. The addition of sulfur can enhance adhesion. The
addition of titanium tends to enhance adhesion as well as diffusion
and barrier properties.
[0040] These diamond-like materials may be considered as a form of
plasma polymers, which can be deposited on the assembly using, for
example, a vapor source. The term "plasma polymer" is applied to a
class of materials synthesized from a plasma by using precursor
monomers in the gas phase at low temperatures. Precursor molecules
are broken down by energetic electrons present in the plasma to
form free radical species. These free radical species react at the
substrate surface and lead to polymeric thin film growth. Due to
the non-specificity of the reaction processes in both the gas phase
and the substrate, the resulting polymer films are highly
cross-linked and amorphous in nature. This class of materials has
been researched and summarized in publications such as the
following: H. Yasuda, "Plasma Polymerization," Academic Press Inc.,
New York (1985); R.d'Agostino (Ed), "Plasma Deposition, Treatment
& Etching of Polymers," Academic Press, New York (1990); and H.
Biederman and Y. Osada, "Plasma Polymerization Processes," Elsever,
New York (1992).
[0041] Typically, these polymers have an organic nature to them due
to the presence of hydrocarbon and carbonaceous functional groups
such as CH.sub.3, CH.sub.2, CH, Si--C, Si--CH.sub.3, Al--C,
Si--O--CH.sub.3, etc. The presence of these functional groups may
be ascertained by analytical techniques such as IR, nuclear
magnetic resonance (NMR) and secondary ion mass (SIMS)
spectroscopies. The carbon content in the film may be quantified by
electron spectroscopy for chemical analysis (ESCA).
[0042] Not all plasma deposition processes lead to plasma polymers.
Inorganic thin films are frequently deposited by PECVD at elevated
substrate temperatures to produce thin inorganic films such as
amorphous silicon, silicon oxide, silicon nitride, aluminum
nitride, etc. Lower temperature processes may be used with
inorganic precursors such as silane (SiH.sub.4) and ammonia
(NH.sub.3). In some cases, the organic component present in the
precursors is removed in the plasma by feeding the precursor
mixture with an excess flow of oxygen. Silicon rich films are
produced frequently from tetramethyldisiloxane (TMDSO)-oxygen
mixtures where the oxygen flow rate is ten times that of the TMDSO
flow. Films produced in these cases have an oxygen to silicon ratio
of about 2, which is near that of silicon dioxide.
[0043] The plasma polymer layer of this invention is differentiated
from other inorganic plasma deposited thin films by the oxygen to
silicon ratio in the films and by the amount of carbon present in
the films. When a surface analytic technique such as ESCA is used
for the analysis, the elemental atomic composition of the film may
be obtained on a hydrogen-free basis. Plasma polymer films of the
present invention are substantially sub-stoichiometric in their
inorganic component and substantially carbon-rich, depicting their
organic nature. In films containing silicon for example, the oxygen
to silicon ratio is preferably below 1.8 (silicon dioxide has a
ratio of 2.0), and most preferably below 1.5 as in the case of DLG,
and the carbon content is at least about 10%. Preferably, the
carbon content is at least about 20% and most preferably at least
about 25%. Furthermore, the organic siloxane structure of the films
may be detected by IR spectra of the film with the presence of
Si--CH.sub.3 groups at 1250 cm.sup.-1 and 800 cm.sup.-1, and by
secondary ion mass spectroscopy (SIMS).
[0044] One advantage of DLG coatings or films is their resistance
to cracking in comparison to other films. DLG coatings are
inherently resistant to cracking either under applied stress or
inherent stresses arising from manufacture of the film. This
property was determined by cutting 75 mm.times.10 mm strips of
sample #2 prepared according to the process conditions in Table 2
of Example 1 below (175 nm thick DLG coating) and sample #1
prepared according to the conditions described in Table 3 of
Example 1 below (60 nm thick sputtered SiOx film). The strips were
attached to the jaws of a home-made vise. The extent of travel of
the jaws was determined by a digital micrometer attached to the
vise. The sample strips were stretched by opening the jaws by 1.5
mm thus producing a 2% elongation in the coated samples. The
stretched samples were placed under a microscope and number of
cracks in the coating were counted. The results are provided in
Table 1. It can be seen that the number of cracks is substantially
lower for the DLG film even though its thickness is almost three
times that of the sputtered SiOx film, contrary to the generally
expected result that a thicker film would result in a greater
tendency to crack.
TABLE-US-00001 TABLE 1 Number of cracks/mm after Thickness 2%
stretch DLG film 175 nm 52 Sputtered film 60 nm 84
DLC Layer
[0045] Diamond and DLC differ significantly due to the arrangement
of carbon atoms in the specific material. Carbon coatings contain
substantially two types of carbon-carbon bonds: trigonal graphite
bonds (sp.sup.2) and tetrahedral diamond bonds (sp.sup.3). Diamond
is composed of virtually all tetrahedral bonds, DLC is composed of
approximately 50% to 90% tetrahedral bonds, and graphite is
composed of virtually all trigonal bonds. The type and amount of
bonds are determined from IR and nuclear magnetic resonance (NMR)
spectra.
[0046] The crystallinity and the nature of the bonding of the
carbon determine the physical and chemical properties of the
coating. Diamond is crystalline whereas DLC is a non-crystalline
amorphous material, as determined by x-ray diffraction. DLC
contains a substantial amount of hydrogen (from 10 to 50 atomic
percent), unlike diamond which is essentially pure carbon. Atomic
percentages are determined by combustion analysis.
[0047] Diamond has the highest packing, or gram atom, density (GAD)
of any material at ambient pressure. Its GAD is 0.28 gram atoms/cc.
Diamond-like carbon has a GAD ranging from about 0.20 to 0.28 gram
atoms/cc. In contrast, graphite has a GAD of 0.18 gram atoms/cc.
The high packing density of DLC affords it excellent resistance to
diffusion of liquid or gaseous materials.
[0048] DLC coatings are diamond-like because, in addition to the
foregoing physical properties that are similar to diamond, they
have many of the desirable properties of diamond such as extreme
hardness (1000 to 2000 kg/mm.sup.2), high electrical resistivity
(109 to 1013 ohm-cm), a low coefficient of friction (0.1), and
optical transparency over a wide range of wavelengths (extinction
coefficient of less than 0.1 in the 400 to 800 nanometer
range).
[0049] However, diamond coatings have some properties which, in
some applications, make them less beneficial as a coating than DLC.
Diamond coatings are comprised of a grain structures, as determined
by electron microscopy. The grain boundaries are a path for
chemical attack and degradation of underlying sensitive materials,
via transmission of water or oxygen. The amorphous DLC coatings do
not have a grain structure, as determined by electron
microscopy.
[0050] Diamond and DLC also have different light absorption
characteristics. For example, diamond has no intrinsic fundamental
absorption in the blue light range because its optical band gap is
5.56 eV and it is transmissive well into the ultraviolet region.
DLC, on the other hand, contains small amounts of unsaturated bonds
due to carbon-carbon double bonding, which causes an optical
absorption band in the blue region of the electromagnetic
spectrum.
[0051] Various additives to the DLC coating can be used. These
additives may comprise one or more of nitrogen, oxygen, fluorine,
or silicon. The addition of fluorine is particularly useful in
enhancing barrier and surface properties, including dispersibility,
of the DLC coating. Sources of fluorine include compounds such as
carbon tetrafluoride (CF.sub.4), sulfur hexafluoride (SF.sub.6),
C.sub.2F.sub.6, C.sub.3F.sub.8, and C.sub.4F.sub.10. The addition
of silicon and oxygen to the DLC coating tend to improve the
optical transparency and thermal stability of the coating. The
addition of nitrogen may be used to enhance resistance to oxidation
and to increase electrical conductivity. Sources of oxygen include
oxygen gas (O.sub.2), water vapor, ethanol, and hydrogen peroxide.
Sources of silicon preferably include silanes such as SiH.sub.4,
Si.sub.2H.sub.6, and hexamethyldisiloxane. Sources of nitrogen
include nitrogen gas (N.sub.2), ammonia (NH.sub.3), and hydrazine
(N.sub.2H.sub.6).
[0052] The additives may be incorporated into the diamond-like
matrix or attached to the surface atomic layer. If the additives
are incorporated into the diamond-like matrix they may cause
perturbations in the density and/or structure, but the resulting
material is essentially a densely packed network with diamond-like
carbon characteristics (chemical inertness, hardness, barrier
properties, etc.). If the additive concentration is large, greater
than 50 atomic percent relative to the carbon concentration, the
density will be affected and the beneficial properties of the
diamond-like carbon network will be lost. If the additives are
attached to the surface atomic layers they will alter only the
surface structure and properties. The bulk properties of the
diamond-like carbon network will be preserved.
Polymer Layers
[0053] The polymer layers used in the multilayer stack of the
barrier assemblies are preferably crosslinkable. The crosslinked
polymeric layer lies atop the substrate or other layers, and it can
be formed from a variety of materials. Preferably the polymeric
layer is crosslinked in situ atop the underlying layer. If desired,
the polymeric layer can be applied using conventional coating
methods such as roll coating (e.g., gravure roll coating) or spray
coating (e.g., electrostatic spray coating), then crosslinked
using, for example, ultraviolet (UV) radiation. Most preferably the
polymeric layer is formed by flash evaporation, vapor deposition
and crosslinking of a monomer as described above. Volatilizable
(meth)acrylate monomers are preferred for use in such a process,
with volatilizable acrylate monomers being especially preferred.
Preferred (meth)acrylates have a molecular weight in the range of
about 150 to about 600, more preferably about 200 to about 400.
Other preferred (meth)acrylates have a value of the ratio of the
molecular weight to the number of acrylate functional groups per
molecule in the range of about 150 to about 600
g/mole/(meth)acrylate group, more preferably about 200 to about 400
g/mole/(meth)acrylate group. Fluorinated (meth)acrylates can be
used at higher molecular weight ranges or ratios, e.g., about 400
to about 3000 molecular weight or about 400 to about 3000
g/mole/(meth)acrylate group. Coating efficiency can be improved by
cooling the support. Particularly preferred monomers include
multifunctional (meth)acrylates, used alone or in combination with
other multifunctional or mono functional (meth)acrylates, such as
hexanediol diacrylate, ethoxyethyl acrylate, phenoxyethyl acrylate,
cyanoethyl (mono)acrylate, isobornyl acrylate, isobornyl
methacrylate, octadecyl acrylate, isodecyl acrylate, lauryl
acrylate, beta-carboxyethyl acrylate, tetrahydrofurfuryl acrylate,
dinitrile acrylate, pentafluorophenyl acrylate, nitrophenyl
acrylate, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate,
2,2,2-trifluoromethyl (meth)acrylate, diethylene glycol diacrylate,
triethylene glycol diacrylate, triethylene glycol dimethacrylate,
tripropylene glycol diacrylate, tetraethylene glycol diacrylate,
neopentyl glycol diacrylate, propoxylated neopentyl glycol
diacrylate, polyethylene glycol diacrylate, tetraethylene glycol
diacrylate, bisphenol A epoxy diacrylate, 1,6-hexanediol
dimethacrylate, trimethylol propane triacrylate, ethoxylated
trimethylol propane triacrylate, propylated trimethylol propane
triacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate,
pentaerythritol triacrylate, phenylthioethyl acrylate,
naphthloxyethyl acrylate, IRR-214 cyclic diacrylate from UCB
Chemicals, epoxy acrylate RDX80095 from Rad-Cure Corporation, and
mixtures thereof. A variety of other curable materials can be
included in the crosslinked polymeric layer, e.g., vinyl ethers,
vinyl naphthylene, acrylonitrile, and mixtures thereof.
[0054] The physical thickness of the crosslinked polymeric layer
will depend in part upon its refractive index and in part upon the
desired optical characteristics of the film (e.g., on whether the
film should contain a Fabry-Perot stack). For use in an
infrared-rejecting Fabry-Perot stack, the crosslinked polymeric
spacing layer typically will have a refractive index of about 1.3
to about 1.7, and preferably will have an optical thickness of
about 75 nm to about 200 nm, more preferably about 100 nm to about
150 nm and a corresponding physical thickness of about 50 nm to
about 130 nm, more preferably about 65 nm to about 100 nm.
[0055] Alternative materials for the polymer layers include
materials having a Tg greater than or equal to that of HSPET. A
variety of alternative polymer materials can be employed.
Volatilizable monomers that form suitably high Tg polymers are
especially preferred. Preferably the alternative polymer layer has
a Tg greater than that of PMMA, more preferably a Tg of at least
about 110.degree. C., yet more preferably at least about
150.degree. C., and most preferably at least about 200.degree. C.
Especially preferred monomers that can be used to form this layer
include urethane acrylates (e.g., CN-968, Tg=about 84.degree. C.
and CN-983, Tg=about 90.degree. C., both commercially available
from Sartomer Co.), isobornyl acrylate (e.g., SR-506, commercially
available from Sartomer Co., Tg=about 88.degree. C.),
dipentaerythritol pentaacrylates (e.g., SR-399, commercially
available from Sartomer Co., Tg=about 90.degree. C.), epoxy
acrylates blended with styrene (e.g., CN-120S80, commercially
available from Sartomer Co., Tg=about 95.degree. C.),
di-trimethylolpropane tetraacrylates (e.g., SR-355, commercially
available from Sartomer Co., Tg=about 98.degree. C.), diethylene
glycol diacrylates (e.g., SR-230, commercially available from
Sartomer Co., Tg=about 100.degree. C.), 1,3-butylene glycol
diacrylate (e.g., SR-212, commercially available from Sartomer Co.,
Tg=about 101.degree. C.), pentaacrylate esters (e.g., SR-9041,
commercially available from Sartomer Co., Tg=about 102.degree. C.),
pentaerythritol tetraacrylates (e.g., SR-295, commercially
available from Sartomer Co., Tg=about 103.degree. C.),
pentaerythritol triacrylates (e.g., SR-444, commercially available
from Sartomer Co., Tg=about 103.degree. C.), ethoxylated (3)
trimethylolpropane triacrylates (e.g., SR-454, commercially
available from Sartomer Co., Tg=about 103.degree. C.), ethoxylated
(3) trimethylolpropane triacrylates (e.g., SR-454HP, commercially
available from Sartomer Co., Tg=about 103.degree. C.), alkoxylated
trifunctional acrylate esters (e.g., SR-9008, commercially
available from Sartomer Co., Tg=about 103.degree. C.), dipropylene
glycol diacrylates (e.g., SR-508, commercially available from
Sartomer Co., Tg=about 104.degree. C.), neopentyl glycol
diacrylates (e.g., SR-247, commercially available from Sartomer
Co., Tg=about 107.degree. C.), ethoxylated (4) bisphenol a
dimethacrylates (e.g., CD-450, commercially available from Sartomer
Co., Tg=about 108.degree. C.), cyclohexane dimethanol diacrylate
esters (e.g., CD-406, commercially available from Sartomer Co.,
Tg=about 110.degree. C.), isobornyl methacrylate (e.g., SR-423,
commercially available from Sartomer Co., Tg=about 110.degree. C.),
cyclic diacrylates (e.g., IRR-214, commercially available from UCB
Chemicals, Tg=about 208.degree. C.) and tris (2-hydroxy ethyl)
isocyanurate triacrylate (e.g., SR-368, commercially available from
Sartomer Co., Tg=about 272.degree. C.), acrylates of the foregoing
methacrylates and methacrylates of the foregoing acrylates.
Other Optional Layers, Coatings, and Treatments
[0056] Various functional layers or coatings can be added to the
barrier assemblies to alter or improve their physical or chemical
properties, particularly at the surface of the barrier film. Such
layers or coatings can include, for example, visible
light-transmissive conductive layers or electrodes (e.g., of indium
tin oxide); antistatic coatings or films; flame retardants; UV
stabilizers; abrasion resistant or hardcoat materials; optical
coatings; anti-fogging materials; magnetic or magneto-optic
coatings or films; photographic emulsions; prismatic films;
holographic films or images; adhesives such as pressure sensitive
adhesives or hot melt adhesives; primers to promote adhesion to
adjacent layers; and low adhesion backsize materials for use when
the barrier assembly is to be used in adhesive roll form. These
functional components can be incorporated into one or more of the
outermost layers of the barrier assembly or can be applied as a
separate film or coating.
[0057] Optional layers can also include "getter" or "desiccant"
layers functionally incorporated within or adjacent to the barrier
coating; examples of such layers are described in copending U.S.
patent application Ser. Nos. 10/948,013 and 10/948,011, which are
incorporated herein by reference as if fully set forth. Getter
layers include layers with materials that absorb or deactivate
oxygen, and desiccant layers include layers with materials that
absorb or deactivate water.
[0058] Other optional layers include one or more inorganic barrier
layers. The inorganic barrier layers, when multiple such layers are
used, do not have to be the same. A variety of inorganic barrier
materials can be employed. Preferred inorganic barrier materials
include metal oxides, metal nitrides, metal carbides, metal
oxynitrides, metal oxyborides, and combinations thereof, e.g.,
silicon oxides such as silica, aluminum oxides such as alumina,
titanium oxides such as titania, indium oxides, tin oxides, indium
tin oxide ("ITO"), tantalum oxide, zirconium oxide, niobium oxide,
boron carbide, tungsten carbide, silicon carbide, aluminum nitride,
silicon nitride, boron nitride, aluminum oxynitride, silicon
oxynitride, boron oxynitride, zirconium oxyboride, titanium
oxyboride, and combinations thereof. Indium tin oxide, silicon
oxide, aluminum oxide and combinations thereof are especially
preferred inorganic barrier materials. ITO is an example of a
special class of ceramic materials that can become electrically
conducting with the proper selection of the relative proportions of
each elemental constituent. The inorganic barrier layers, when
incorporated into the assembly, preferably are formed using
techniques employed in the film metallizing art such as sputtering
(e.g., cathode or planar magnetron sputtering), evaporation (e.g.,
resistive or electron beam evaporation), chemical vapor deposition,
plating and the like. Most preferably the inorganic barrier layers
are formed using sputtering, e.g., reactive sputtering. Enhanced
barrier properties have been observed when the inorganic layer is
formed by a high energy deposition technique such as sputtering
compared to lower energy techniques such as conventional chemical
vapor deposition processes. Without being bound by theory, it is
believed that the enhanced properties are due to the condensing
species arriving at the substrate with greater kinetic energy,
leading to a lower void fraction as a result of compaction. The
smoothness and continuity of each inorganic barrier layer and its
adhesion to the underlying layer can be enhanced by pretreatments
(e.g., plasma pretreatment) such as those described above.
[0059] For some applications, it may be desirable to alter the
appearance or performance of the barrier assembly, such as by
laminating a dyed film layer to the barrier assembly, applying a
pigmented coating to the surface of the barrier assembly, or
including a dye or pigment in one or more of the materials used to
make the barrier assembly. The dye or pigment can absorb in one or
more selected regions of the spectrum, including portions of the
infrared, ultraviolet or visible spectrum. The dye or pigment can
be used to complement the properties of the barrier assembly,
particularly where the barrier assembly transmits some frequencies
while reflecting others.
[0060] The barrier assembly can be treated with, for example, inks
or other printed indicia such as those used to display product
identification, orientation information, advertisements, warnings,
decoration, or other information. Various techniques can be used to
print on the barrier assembly, such as, for example, screen
printing, inkjet printing, thermal transfer printing, letterpress
printing, offset printing, flexographic printing, stipple printing,
laser printing, and so forth, and various types of ink can be used,
including one and two component inks, oxidatively drying and
UV-drying inks, dissolved inks, dispersed inks, and 100% ink
systems.
[0061] The barrier assemblies can also have a protective polymer
topcoat. If desired, the topcoat polymer layer can be applied using
conventional coating methods such as roll coating (e.g., gravure
roll coating) or spray coating (e.g., electrostatic spray coating),
then crosslinked using, for example, UV radiation. A pretreatment
(e.g., plasma pretreatment) may be used prior to formation of the
topcoat polymer layer. The desired chemical composition and
thickness of the topcoat polymer layer will depend in part on the
nature and surface topography of the underlying layer(s), the
hazards to which the barrier assembly might be exposed, and
applicable device requirements. The topcoat polymer layer thickness
preferably is sufficient to provide a smooth, defect-free surface
that will protect the underlying layers from ordinary hazards.
General Techniques for Coating of Layers
[0062] The polymer layers can be formed by applying a layer of a
monomer or oligomer to the substrate and crosslinking the layer to
form the polymer in situ, e.g., by flash evaporation and vapor
deposition of a radiation-crosslinkable monomer, followed by
crosslinking using, for example, an electron beam apparatus, UV
light source, electrical discharge apparatus or other suitable
device. Coating efficiency can be improved by cooling the support.
The monomer or oligomer can also be applied to the substrate using
conventional coating methods such as roll coating (e.g., gravure
roll coating) or spray coating (e.g., electrostatic spray coating),
then crosslinked as set out above. The polymer layers can also be
formed by applying a layer containing an oligomer or polymer in
solvent and drying the thus-applied layer to remove the solvent.
Plasma polymerization may also be employed if it will provide a
polymeric layer having a glassy state at an elevated temperature,
with a glass transition temperature greater than or equal to that
of HSPET. Most preferably, the polymer layers are formed by flash
evaporation and vapor deposition followed by crosslinking in situ,
e.g., as described in U.S. Pat. No. 4,696,719 (Bischoff), U.S. Pat.
No. 4,722,515 (Ham), U.S. Pat. No. 4,842,893 (Yializis et al.),
U.S. Pat. No. 4,954,371 (Yializis), U.S. Pat. No. 5,018,048 (Shaw
et al.), U.S. Pat. No. 5,032,461 (Shaw et al.), U.S. Pat. No.
5,097,800 (Shaw et al.), U.S. Pat. No. 5,125,138 (Shaw et al.),
U.S. Pat. No. 5,440,446 (Shaw et al.), U.S. Pat. No. 5,547,908
(Furuzawa et al.), U.S. Pat. No. 6,045,864 (Lyons et al.), U.S.
Pat. No. 6,231,939 (Shaw et al.) and U.S. Pat. No. 6,214,422
(Yializis); in published PCT Application No. WO 00/26973 (Delta V
Technologies, Inc.); in D. G. Shaw and M. G. Langlois, "A New Vapor
Deposition Process for Coating Paper and Polymer Webs", 6th
International Vacuum Coating Conference (1992); in D. G. Shaw and
M. G. Langlois, "A New High Speed Process for Vapor Depositing
Acrylate Thin Films: An Update", Society of Vacuum Coaters 36th
Annual Technical Conference Proceedings (1993); in D. G. Shaw and
M. G. Langlois, "Use of Vapor Deposited Acrylate Coatings to
Improve the Barrier Properties of Metallized Film", Society of
Vacuum Coaters 37th Annual Technical Conference Proceedings (1994);
in D. G. Shaw, M. Roehrig, M. G. Langlois and C. Sheehan, "Use of
Evaporated Acrylate Coatings to Smooth the Surface of Polyester and
Polypropylene Film Substrates", RadTech (1996); in J. Affinito, P.
Martin, M. Gross, C. Coronado and E. Greenwell, "Vacuum deposited
polymer/metal multilayer films for optical application", Thin Solid
Films 270, 43-48 (1995); and in J. D. Affinito, M. E. Gross, C. A.
Coronado, G. L. Graff, E. N. Greenwell and P. M. Martin,
"Polymer-Oxide Transparent Barrier Layers", Society of Vacuum
Coaters 39th Annual Technical Conference Proceedings (1996).
Manufacturing Process
[0063] FIG. 4 illustrates a preferred apparatus 180 that can be
used for roll-to-roll manufacture of barrier assemblies on the
invention, such as those shown in FIGS. 1-3 and described above. A
more detailed diagram and description of a vacuum system used to
make the barrier coatings is shown in U.S. Pat. No. 5,888,594,
incorporated herein by reference. Powered rolls 181a and 181b move
supporting web 182 back and forth through apparatus 180.
Temperature-controlled rotating drums 183a and 183b, and idler
rolls 184a, 184b, 184c, 184d and 184e carry web 182 past metal
sputtering applicator 185, plasma pretreater 186, monomer
evaporator 187 and E-beam crosslinking device 188. Liquid material
189 is supplied to evaporator 187 from reservoir 190. Successive
layers or pairs of layers can be applied to web 182 using multiple
passes through apparatus 180. Additional applicators, pretreaters,
evaporators and crosslinking devices can be added to apparatus 180,
for example along the periphery of drums 183a and 183b, to enable
sequential deposition of several pairs of layers. A power source
191 can provide the appropriate bias to drum 183a. Apparatus 180
can be enclosed in a suitable chamber (as represented by the box
enclosing it) and maintained under vacuum or supplied with a
suitable inert atmosphere in order to discourage oxygen, water
vapor, dust and other atmospheric contaminants from interfering
with the various pretreatment, monomer coating, crosslinking and
sputtering steps. Also, apparatus 180 can alternatively use only
one drum 183 a for coating web 182, along the appropriate elements
for applying layers to the web.
Display Device with Barrier
[0064] FIG. 5 is a schematic cross-sectional view of a disclosed
OLED device. The barrier assemblies of the invention, such as those
shown in FIGS. 1-3 and described above, can be used to inhibit the
transmission of moisture vapor, oxygen or other gases in a variety
of applications. The barrier assemblies are especially useful for
encapsulating OLEDs, light valves such as LCDs, and other
electronic devices, aside from the other examples provided above. A
representative encapsulated OLED device 200 is shown in FIG. 5. The
front or light-emitting side of device 200 faces downward in FIG.
5. Device 200 includes a visible light-transmissive barrier
assembly 210 having an outer indium tin oxide layer (not shown in
FIG. 5, but oriented so that it would face upward) that serves as
an anode.
[0065] Light emitting structure 220 is formed on barrier assembly
210 in contact with the outer ITO layer. Structure 220 contains a
plurality of layers (not individually shown in FIG. 5) that
cooperate to emit light downward through barrier assembly 210 when
suitably electrically energized. Device 200 also includes
conductive cathode 230 and metallic foil surround 250. Foil
surround 250 is adhered to the back, sides and part of the front of
device 220 by adhesive 240. An opening 260 formed in adhesive 240
permits a portion 270 of foil 250 to be deformed into contact with
cathode 230. Another opening in foil 250 (not shown in FIG. 5)
permits contact to be made with the anode formed by the outer ITO
layer of barrier assembly 210. Metal foil 250 and barrier assembly
210 largely prevent water vapor and oxygen from reaching light
emitting structure 220.
[0066] The invention will now be described with reference to the
following non-limiting examples.
EXAMPLE 1
[0067] A UV-curable polymer solution was made containing 100 grams
of epoxy acrylate, commercially available from UCB Chemicals,
Smyrna, Ga. under the trade designation "Ebecryl 629"; 2 grams of
1-hydroxy-cyclohexyl-phenyl ketone, commercially available from
Ciba Specialty Chemicals, Tarrytown, N.Y. under the trade
designation "Irgacure184" dissolved in 1000 grams of methyl ethyl
ketone. The resulting solution was coated at a web speed of 20
ft/min on a 6.5 inch wide, 100 micron polyethylene terephthalate
("PET") liner commercially available from Teijin Corp., Japan under
the trade designation "HSPE 100" using a microgravure coater
commercially available from Yasui Seiki, Japan under the trade
designation "Model CAG150" fitted with a 90R knurl. The coating was
dried in-line at 70.degree. C. and cured under a nitrogen
atmosphere with UV lamp commercially available from Fusion UV
systems, Gaithersburg, Md. under the trade designation "F-600
Fusion D UV lamp" operating at 100% power, resulting in a dried
coating thickness of approximately 1.2 microns.
[0068] The polymer coated web described above was loaded into the
vacuum chamber of the coating system used to make DLG coating shown
in U.S. Pat. No. 5,888,594 and pumped down to approximately 1
mTorr. The reactive gases were introduced into the chamber and RF
power was applied to the drum. The web speed was adjusted to
achieve the desired coating thickness. A second polymer layer was
coated over the first DLG coating according to same conditions as
the first polymer layer except a 110R knurl was used which resulted
in the polymer layer thickness of approximately 0.7 microns. Table
2 describes the deposition conditions for DLG coating and the MVTR
of the resulting barrier coatings that were made in this
chamber.
[0069] Barrier coatings were also made using reactive sputtering
process for comparison purposes. PET web coated with the first
polymer layer was coated with SiOx coating deposited under
conditions shown in Table 3. A second polymer layer was coated over
the first SiOx layer and a second SiOx layer was then coated over
the second polymer layer. The deposition conditions and MVTR of
coatings made by the reactive sputtering process are listed in
Table 3.
TABLE-US-00002 TABLE 2 Deposition conditions used to make barrier
coatings and their MVTRs Deposition Substrate TMS O.sub.2 Time
Pressure Thickness Bias MVTR Sample # Sccm sccm seconds mTorr nm
Volts g/m.sup.2 day 1 180 200 51 6 100 -805 0.017 2 180 200 90 6
175 -805 <0.005* *MVTR @ 50.degree. C./100% RH = 0.008 g/m.sup.2
day
TABLE-US-00003 TABLE 3 Comparative example: Barrier films made
using reactive sputtering process Web Coating Target Argon O.sub.2
Speed Pressure Thickness Power Voltage MVTR Sample # Sccm sccm fpm
mTorr nm Watts Volts g/m.sup.2day 1 51 27 1.4 1 60 2000 -600 0.028
2 51 31 1.7 3 100 4000 -620 0.095
EXAMPLE 2
[0070] The effect of the diamond-like film deposition conditions
was established by depositing a two-dyad stack of solution coated
acrylate and a diamond-like film. In particular, referring to FIG.
2, the sample analyzed included a PET substrate 112, acrylate
layers 114 and 118, and DLG film layers 116 and 120. The process
for coating the acrylate layers is described in Example 1.
[0071] The primary variables explored in the study of the sample
were as follows: (1) tetramethylsilane (TMS)/oxygen ratio and
plasma power; (2) plasma power; and (3) deposition time (thickness)
of the DLG film.
[0072] Sixteen different conditions were studied as shown in Table
4 below, and the moisture barrier properties of these films was
measured for each of these conditions at 50.degree. C. The MVTR
values are shown in the last column in Table 4 below. From these
results, it may be seen that there were several conditions that
yield MVTR values that are at or below the detection limit of the
Mocon tester at 50.degree. C. Additional significant points were as
follows. For a fixed value of the TMS/O.sub.2 ratio and power, the
MVTR values decrease with increasing thickness of the diamond-like
film. For any fixed value of power, the MVTR values are lower at a
TMS/O.sub.2 ratio of 1.0 when compared to 0.25. This means that the
films with more organic content had improved barrier performance.
For any fixed value of TMS/O.sub.2 ratio and thickness, the MVTR
values were slightly higher for the 2000 watts compared to 1000
watts of plasma power.
TABLE-US-00004 TABLE 4 MVTR @ Pressure Power Time O.sub.2 TMS
50.degree. C. RunOrder TMS/O.sub.2 (mTorr) (W) (sec) sccm sccm DC
Bias V (g/(m.sup.2day)) 020-02 1 7 1000 30 200 200 -763 0.02 020-03
1 7 1000 60 200 200 -763 0.005 020-04 1 7 1000 90 200 200 -763
0.005 020-01 1 7 1000 120 200 200 -763 <0.005 020-06 0.25 7 1000
30 320 80 -748 0.043 020-07 0.25 7 1000 60 320 80 -748 0.025 020-08
0.25 7 1000 90 320 80 -748 0.016 020-05 0.25 7 1000 120 320 80 -748
0.005 020-10 1 7 2000 30 200 200 -1107 0.017 020-11 1 7 2000 60 200
200 -1107 0.005 020-12 1 7 2000 90 200 200 -1107 <0.005 020-09 1
7 2000 120 200 200 -1107 <0.005 020-14 0.25 7 2000 30 320 80
-1059 0.076 020-15 0.25 7 2000 60 320 80 -1059 0.062 020-16 0.25 7
2000 90 320 80 -1059 0.012 020-13 0.25 7 2000 120 320 80 -1059
<0.005
* * * * *