Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED AIRCRAFT TRANSPARENCY
This application is a division of application Serial
No. 2,214,594 filed September 22, 1997.
15 BACKGROUND
Field of the Invention
The present invention relates to an aircraft
transparency having a polyurethane protective liner over an
electroconductive metal oxide coating over a rigid plastic
substrate, and more specifically to the use of a primer for
adhering the metal oxide coating to the substrate and/or a
primer for adhering the polyurethane protective liner to the
metal oxide coating.
Description of the Relatp~ Art
Today's aircraft window, usually referred to as an
aircraft transparency, has developed far from its earliest
stages of development of a single pane of common glass. The
current art includes a selection of base materials comprising
several types of glass and plastics. Glass base materials
include chemically tempered glass and thermally tempered
glass. Plastic base materials include cast acrylics,
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stretched acrylics, and polycarbo~ates, among others. Also
included are laminates which include multiple layers of glass,
plastic or both.
For example, aircraft transparencies may include
interlayers for joining base materials together selected from
materials including polyvinyl butyral, urethanes and
silicones. Aircraft transparencies may also include
protective liners, generally selected from polyurethanes,
which overlay the surfaces of the base materials isolate the
plastic from the environment to protect the plastic surfaces
from abrasion and crazing, and extend the serviceability of
the transparencies. Conductive coatings of metals or metal
oxides, including tin oxide or indium tin oxide may be
included between the interlayers of the transparency and,
among other things, energized with electric current to melt
ice and remove moisture from the outer surface of the
transparency. Sealing systems, attachment systems and
protection against electromagnetic interference and
electromagnetic pulses all form a part of the advanced
technology of today's aircraft transparency.
For those aircraft transparencies which include a
plastic base material, efforts have been made to adhere
various materials to the base material.
U.S. Patent No. 4,335,187 to Rukavina et al.
discloses a metal retainer, e.g. a stainless steel retainer,
for mounting a transparency to the aircraft body, which
retainer is bonded to polycarbonate, e.g. the polycarbonate
inboard ply of the transparency, by a polyurethane adhesive.
The polyurethane adhesive includes an isocyanate-terminated
polyester urethane crosslinked with a trifunctional compound
such as triisopropanolamine. The adhesive provides high
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strength flexible bonding between the metal retainer and the
inboard ply.
U.S. Patent No. 4,435,450 to Coleman discloses
applying abrasion resistant thin polyurethane coatings to
polycarbonate based aircraft transparencies with crosslinked
aliphatic polycarbonate urethane coatings applied from
solutions of a prepolymer and a crosslinking agent which are
flow or dip coated onto the substrate.
U.S. Patent Nos. 4,554,318; 4,609,703 and 4,670,350
to Rukavina disclose copolymers of acrylic acid and
cyanoethylacrylate for bonding indium oxide films to acrylic
substrates. Also disclosed is a terpolymer of
cyanoethylacrylate, acrylic acid and hydroxyethylacrylate for
the same purpose.
U.S. Patent No. 4,725,501 to Rukavina discloses a
silicate/titanate copolymer for use as a primer to adhere a
vinyl interlayer to stretched acrylic or indium/tin oxide
coated stretched acrylic substrate.
Other combinations of metal oxides and methods for
applying them to a substrate are described in U.S. Patent Nos.
4,094,763; 4,113,599; 4,434,284; 4,610,771; 4,622,120;
4,904,526 and 5,178,966.
While various approaches and compositions to
satisfactorily adhere a number of materials to the base
materials of aircraft transparencies are disclosed and are
acceptable, there are limitations, particularly for those
transparencies which include metal oxide coatings and/or
polyurethane protective liners. More particularly, separation
of the metal oxide coating from the substrate may be caused by
poor adhesion and/or the stress of unequal expansion and
contraction of the metal oxide coating with respect to either
the substrate itself and/or to the polyurethane protective
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liner. Even minor separation can result in rejection of the
aircraft transparency.
Further, it is important that where the aircraft
transparency includes a polyurethane protective liner to,
among other things, protect the metal oxide coating from
impingement damage, abrasion or chemical attack that the liner
remain strongly adhered to fully protect the metal oxide
coating.
As can be appreciated from the foregoing, it would
be advantageous to provide an aircraft transparency that is a
laminate having improved adhesion between the layers by
providing primers) for use in adhering an electroconductive
metal oxide coating to a substrate and/or adhering a
polyurethane protective liner to electroconductive metal oxide
coating which reduces or eliminates any separation between the
metal oxide coating and either the substrate and/or the
polyurethane protective liner.
The present invention relates to an improved
aircraft transparency; the aircraft transparency improved by
the practice of the invention is of the type which includes a
plastic substrate and an electroconductive metal oxide coating
disposed over the plastic substrate. The improvement of the
invention is the inclusion of a primer hereinafter the "metal
oxide primer" for adhering the metal oxide coating over the
substrate. The metal oxide primer includes a carbonate diol-
based crosslinked polyurethane that preferably is a reaction
product of a carbonate diol, a low molecular weight polyol and
polymeric methylene diisocyanate (hereinafter "MDI°). The
metal oxide primer of the instant invention imparts
flexibility which reduces or inhibits the effects of stress on
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the electroconductive metal oxide coating, provides good
adhesion of the metal oxide coating to the substrate without
undesirable distortion of light, and has a low coefficient of
expansion. In one embodiment of the invention, the index of
refraction of the metal oxide primer matches that of
substrate, to eliminate the undesirable optical effect of
scratches, minor surface irregularities and the like on the
substrate surface. When the aircraft laminate includes a
polyurethane protective liner which liner is applied as an
uncrosslinked polymer dissolved in a solvent whereupon the
solvent is removed and crosslinking occurs to form the liner,
the metal oxide primer of the instant invention also resists
swelling due to contact with the polyurethane protective
liner's solvent. This solvent can contact the metal oxide
primer by passing through defects in the metal oxide coating.
The metal oxide primer of the instant invention may also be
used to adhere metals such as gold, metal nitrides such as
titanium nitride, and/or the metal oxide coatings, to a
plastic substrate, however the discussion herein is directed
to its use with metal oxide coatings, particularly indium/tin
oxide coatings, e.g. those having a ratio of indium oxide to
tin oxide of about 9:1.
The present invention further includes a primer for
adhering a polyurethane protective liner over a metal oxide
coating (hereinafter the "polyurethane primer"). The
polyurethane primer is selected from the group consisting of:
a crosslinked copolymer of acrylic acid and substituted
acrylates such as 2-ethylhexylacrylate; a crosslinked
copolymer of cyanoethylacrylate and acrylic acid; and a
~rosslinked terpolymer of cyanoethylacrylate;
2-ethylhexylacrylate and acrylic acid. The polyurethane
primer of the present invention exhibits, among other things,
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improved bonding of the polyurethane protective liner to the
metal oxide coating and provides a shear absorbing layer which
reduces shear stress on the electroconductive metal oxide
coating caused by the differing coefficients of expansion
between the metal oxide coating and the polyurethane
protective liner.
As will be appreciated, the present invention
contemplates the use of metal oxide primer and polyurethane
protective liner primer together or separately. The invention
also includes a method of making aircraft transparencies of
the type discussed above.
DESCRT_PTION OF THE DRAWING
Fig. 1 is a side elevational view of an aircraft
transparency illustrating the metal oxide primer of the
present invention adhering a metal oxide coating to a
substrate.
Fig. 2 is a view similar to the view of Fig. 1
illustrating polyurethane primer of the present invention
adhering a polyurethane protective liner to a metal oxide
coating.
Fig. 3 is a view similar to Fig. 1 showing the metal
oxide primer of the present invention adhering the metal oxide
coating to the substrate and the polyurethane primer of the
present invention adhering the polyurethane protective liner
to the metal oxide coating.
Fig. 4 is view similar to Fig. 3, showing an
additional polyurethane protective liner bonded to the inboard
surface of the aircraft transparency.
_
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DESGR_TPmTON OF THE PREFER~RD EMB~nTt~~rra
The present invention is directed to an improved
aircraft transparency and method for making an improved
aircraft transparency of the type having a plastic substrate,
an electroconductive metal oxide coating disposed over the
substrate and/or a polyurethane protective liner disposed over
the electroconductive metal oxide coating. While the
following discussion is directed to metal oxide coatings for
the sake of brevity, as may be appreciated, the primers of the
present invention may be used to adhere other coatings
including but not limited to metal coatings such as gold and
metal nitride coatings such as titanium nitride in addition to
the metal oxide coatings discussed below. The improvement is
directed to the inclusion of a metal oxide primer of the
instant invention for improving the adhesion of the metal
oxide coating to the surface of the substrate, and/or the
inclusion of the polyurethane primer of the instant invention
for improving adhesion of the polyurethane protective liner to
the metal oxide coating. As will be appreciated, the aircraft
transparencies made in accordance with the present invention
are not limited to the configuration comprising a
substrate/metal oxide primer/ metal oxide coating/
polyurethane primer/polyurethane protective liner, but may
further include interlayers, other liners, primer, coatings
and the like and/or may exclude one of the primers.
Figs. 1-4 illustrate the placement of each of the
layers of an aircraft transparency according to the instant
invention and are not a representation of the relative
thickness of each layer. With reference to Fig. 1, there is
illustrated a cross section of an aircraft transparency 10
including the metal oxide primer 14 of the instant invention
interposed between and adhering together a substrate 12 and a
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metal oxide coating 16. Although not limited to the
invention, a polyurethane protective liner 18 is adhered to
the metal oxide coating 16 in any convenient manner.
Referring now to Fig. 2, there is shown a cross
section of an aircraft transparency 20 of the present
invention including a metal oxide coating 16 deposited on the
substrate 12 and a polyurethane primer 22 incorporating
features of the invention interposed between and adhering
together the metal oxide coating 16 and the polyurethane
protective liner 18.
Referring now to Fig. 3, there is shown a cross
section of an aircraft transparency 30 of the present
invention including the metal oxide primer 14 interposed
between and adhering together the substrate 12 and the metal
oxide coating 16, and the polyurethane primer 22 of the
instant invention interposed between and adhering together the
metal oxide coating 16 and the polyurethane protective liner
18.
Referring now to Fig. 4, there is shown a cross
section of an aircraft transparency 40 of the present
invention including the metal oxide primer 14 interposed
between and adhering together substrate 12 and the metal oxide
coating 16, and the polyurethane primer 22 interposed between
and adhering together the metal oxide coating 16 and the
polyurethane protective liner 18. Polyurethane protective
liner 24 is disposed over and adhered in any convenient manner
to the substrate 12 on surface 26 of substrate 12 opposite the
surface 28 of substrate 12 having the metal oxide primer 14
adhered thereto. The polyurethane protective liner 24 is
disposed over the surface 26 of substrate 12 corresponding to
the inboard surface of the aircraft transparency of the
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present invention, i.e. the surface of the transparency facing
the interior of the aircraft.
The substrate 12, metal oxide primer 14, metal oxide
coating 16, polyurethane protective liner primer 22 and
polyurethane protective liners 18 and 24 are discussed in
detail below.
I. THE SUBSTRATE:
The substrate of the present invention is
preferably, but not limited to, a monolithic plastic or a
laminate which has a plastic surface. The substrate may be
rigid or flexible, transparent or opaque. In the instance
when the end product is a transparency e.g. a window, the
substrate is preferably transparent. Rigid substrates are
generally preferred for aircraft transparencies. In the
following discussion, the invention will be discussed with
reference to a plastic substrate; however, as can be
appreciated, the invention is not limited thereto and in the
practice of the invention it is preferred to use a substrate
that is either plastic or if not plastic has a plastic
surface. The substrate is preferably either a polycarbonate,
cast acrylics, a biaxially oriented crosslinked
polymethylmethacrylate, also known as a stretched acrylic or a
polyurethane among others. The preferred substrate is a
polycarbonate.
Examples of polycarbonate substrates that may be
used in the practice of the invention include, but are not
limited to, polycarbonate polyurethanes, bisphenol A
polycarbonate and polyether polycarbonates made from monomers
such as those available under the trademark" CR-39" from PPG
Industries, Inc. of Pittsburgh, PA.
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As may be appreciated., the thickness of the
substrate may vary over a broad range depending upon its ,
application. Typically for an aircraft transparency which
includes only a stretched acrylic substrate (as opposed to a
laminate of more than one substrate material) the stretched
acrylic substrate has a thickness of about 0:125 to 1 inch
(about 3 to 25 millimeters). An aircraft transparency that
includes only polycarbonate typically has a thickness of about
.001 inch to 1 inch (.025 to 25 mm). As can now be
appreciated, the invention is not limited to the thickness of
the substrate and the substrate may be of any thickness.
II ~ THE MR?'AD OXIDE PRIMER
In accordance with the present invention, the metal
oxide primer preferably has:
(1) a coefficient of expansion in the range between
the coefficient of expansion of the substrate and the
coefficient of expansion of the metal oxide coating to prevent
buckling of the metal oxide coating in compressive stress;
(2) an elastic modulus that is higher than the
elastic modulus of the substrate to prevent buckling and
cracking of the primer with the expansion and contraction of
the substrate;
(3) good adhesion to the substrate;
(4) good adhesion to the metal oxide coating;
(5) a refractive index that is within ~2% of the
refractive index of the substrate. When the refractive index
of the metal oxide primer is within that range as the metal
oxide primer fills surface irregularities (e. g. surface
scratches present on the surface of the substrate) during its
application, the filled surface irregularities are rendered no
longer visible rendering acceptable a substrate which might
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otherwise be optically objectionable due to the presence of
such surface irregularities; and
(6) sufficient adhesion to maintain the metal oxide
coating on the substrate when the transparency is subjected to
temperature ranges of -65°F to 230°F (-53.9°C to
110°C) and when
the transparency is subjected to moist/wet conditions (e.g, a
30-day 105°F (40.6°C) 100% humidity Cleveland Condensing
Cabinet Humidity Test, which is discussed in more detail
below.
The metal oxide primer should permit the metal oxide
coating to survive strains of up to 1.0% which include the
total of applied bending strains plus thermally induced
expansion or compression strains. The preferred method of
measuring strain is discussed in detail below. The invention
will be discussed using the metal oxide primer disclosed
below. As will be appreciated, the invention is not limited
thereto and other metal oxide primers to provide the
transparency of the instant invention may be used.
The metal oxide primer preferably used in the
practice of the invention is a thermoset high modulus polymer
which is a good film former, and is transparent and colorless.
Preferably, the metal oxide primer of the present invention is
a carbonate diol-based crosslinked aromatic polyurethane. It
is a reaction product of a carbonate diol, a low molecular
weight polyol and an isocyanate composition. Low molecular
weight polyol is defined herein as a polyol having a molecular
weight of less than about 300 g/mole. These reactants are
combined in a solvent. The reaction mixture may also include
in addition to the foregoing, a catalyst and/or a surfactant.
.The reaction mixture is referred to hereinafter as "the metal
oxide primer composition". Each of the components of the
metal oxide primer composition is discussed in detail below.
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II.A. THE CA_RgONATU nrnr..
The carbonate diol preferred in the practice of the
invention is a high molecular weight polyol, having a
molecular weight of about 1000 g/mole and functions to extend
the length of crosslinks formed in the metal oxide primer
which in turn imports more flexibility to the metal oxide
primer to allow the absorption of more shear stress to prevent
the metal oxide coating from buckling or cracking. The
carbonate diol may include either a hexanediol-
cyclohexanedimethanol-based carbonate diol or may simply
include a hexanediol-based carbonate diol. The carbonate diol
of the present invention may have the general formula:
HO(ROCOO)aROH (Formula 1)
where a is an integer from 2 to 9, preferably 4, and where
each R group in Formula 1 is independently -(CH2)b-, where b is
an integer from 2 to 8, preferably 6, or
-CH~~CH= -
A suitable hexanediol-cyclohexandimethanol-based
carbonate diol includes KM-10-1667 available from Stahl, Inc.
of Boston, MA, having the following formula:
HO (H2C CHZOCOO) ~ (CH2CH2CHzCH2CH2CHzOCOO) dCH2 CH20H
(Formula 2)
where c and d are independently integers from 1-6, and c and d
are preferably each 3.
- Where a more flexible primer is desired, some or all
of the carbonate diol may be a hexanediol-based carbonate diol
instead of one which includes the cyclohexane-based groups. A
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suitable hexanediol-based carbonate_diol is one having the
formula:
HO(CHZCHZCHZCH2CHZCH20C00)eCHzCH2CH2CH2CH2CH20H (Formula 3)
where a is an integer from 2 to 13, preferably.6.
Although the invention contemplates but is not
preferred in the practice of the invention, the cyclohexane-
based diol component may be replaced completely with an
aliphatic straight chained based carbonate diol. This is not
preferred because where the carbonate diol is comprised only
of aliphatic straight chained diols the metal oxide primer may
become too flexible and the coefficient of expansion of the
primer may substantially outstrip that of the metal oxide
coating causing the metal oxide coating bonded to the metal
oxide primer to crack as the metal oxide primer expands or
contracts. Preferably not more than half the carbonate diol
will be comprised of hexanediol-based carbonate diols.
2 0 I I . B . THE LOW MOLECULAR WEIGHT POr vnr .
The low molecular weight polyol is a compound of the
general formula:
CfH(2f+2-g) (OH)g (Formula 4)
having a molecular weight of less than about 300 grams per
mole, where f is an integer from 4-18, and g is an integer
independently selected from 3-12. Preferably f is an integer
from 5-7 and g is an integer from 3-6. The low molecular
wEight polyol may include an aliphatic triol having a
molecular weight of 100-300, however any low molecular weight
aliphatic polyol having more than two hydroxyl groups may be
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used. A preferred low molecular weight polyol is
trimethylolpropane. Pentaerythritol is a satisfactory ,
substitute for trimethylolpropane.
II. C. THB ISOCvANATE COMPOSTTTOh~~
Polymeric MDI exists in several isomers. Further,
polymeric MDI may include products which contain more than two
. aromatic rings in the molecule, such as 3- and higher ring
compounds. Thus polymeric MDI may be a mixture of many
chemical individuals, and consequently polymeric MDI is
offered commercially as a wide variety of products having a
wide variety of molecular weights ranging from polymers
including the pure 4,4'-two ringed product to products
including all of the MDI isomers.
The polymeric MDI preferably used in the present
invention may be represented more or less generically by the
following Formula 5:
NCO
CH2
OCN CH2
OCN CH2....
(Formula 5)
wherein the NCO groups and methylene groups,(-CH2-), may be in
any position on the phenyl ring, although as may be
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appreciated, an NCO group and a methylene group will not be in
the same position on the same phenyl ring.
The polymeric MDI of the present invention may
alternatively be described as an alternating polymer of the
series:
NCO NCO NCO
Ph - Me - Ph - Me - Ph - Me (Formula 6)
where Ph is phenyl and Me is methylene, and each of the phenyl
groups includes an NCO group bonded thereto. As with the
generic formula set forth above, each of the NCO groups and
methylene groups may be envisioned as being in any position on
the phenyl groups, although as may be appreciated, an NCO
group and a methylene group will not be in the same position
on the phenyl ring.
One polymeric MDI which may be used in the
preparation of the novel metal oxide primer of the present
invention is a product of Bayer Corporation of Pittsburgh, PA,
available under the trade name MONDUR MRTM
Typical molecular weights of polymeric MDI products
are generally at least about 460 grams per mole. Polymeric
MDI products having molecular weights of about 1000 grams per
mole are preferred.
II. D. THE SOLVENT:
In the practice of the invention, the solvent is
organic and does not cause visible degradation of the
substrate surface. Particularly when the substrate is a
bisphenol-A polycarbonate, a solvent can visibly degrade the
surface of the substrate by partial dissolution of the
substrate surface. The solvents of the instant invention are
selected in part, with solubility parameters which are
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different from those of the substrate, whereby the solvents of
the instant invention do not cause visible degradation of the
substrate surface. The solvent of the metal oxide primer of
the present invention is~preferably selected from tertiary
alcohols, ketones and ethers. Tertiary alcohols include
diacetone alcohol, t-butanol, and t-pentanol. Ketones include
cyclohexanone and cyclopentanone. Ethers include butylether.
Mixtures of these solvents are also contemplated by the
instant invention. The preferred solvent is diacetone
alcohol.
II. E. THE CATALYST~
Although not required but preferred in the practice
of the invention is the use of a catalyst to promote the
reaction of the isocyanate of the polymeric MDI with the
hydroxyl groups of the carbonate diol and the hydroxyl groups
of the low molecular weight polyol to yield a urethane.
Stannous octoate and butyl stannic acid are acceptable
catalysts. The preferred catalyst is dibutyltindilaurate.
I I . F . THE SURFACTArrr
Although not required but preferred in the practice
of the invention, a surfactant may be used which functions as
a flow control agent. When the metal oxide primer is applied
to a substrate, visible distortion may result in the
transparency from individual pockets of primer which are
formed by gradients in the surface tension of the primer. The
surfactant lowers the surface tension of the primer, allowing
the primer to flow together to form a uniform film on the
substrate surface. A suitable surfactant includes a
fluorinated nonionic surfactant manufactured by 3M Corporation
of St. Paul, MN, available under the trade name ~~FC430~~.
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Other suitable surfactants include surfactants sold under the
trade name "BYK300" or "BYK306" manufactured by Byk-Chemie of
Germany.
II . G. THE RA'~'TO~ OF THE COMP~~'.u'rQ
The ratios of the various components of the metal
oxide primer of the present invention are as follows.
The ranges in wt% of the carbonate diol, polyol and
polymeric MDI are set forth below in Table 1. These weight
percent ranges assume that the carbonate diol has an
equivalent weight of about 380 to 500 grams per equivalent.
Equivalent weight is defined as grams of polymer per
equivalent of hydroxyl groups present in the primer.
It is possible to use carbonate diols in the instant
invention which have equivalent weights above or below the
range of 380 to 500 grams per equivalent as defined and set
forth above. However, as will be appreciated by those skilled
in the art, other carbonate diol equivalent weights require a
minor adjustment in the weight percent ranges shown in Table
1, (namely an adjustment in the ratios of weight percents of
the polyol and carbonate diol) in order to obtain the metal
oxide primer of the instant invention having the same
thermomechanical properties such as glass transition
temperature, elastic modulus and coefficient of expansion as
is obtained from the carbonate diols having equivalent weights
of 380 to 500 grams per mole. For example, where the '
equivalent weight of carbonate diol is above 500 g per
equivalent, more polyol and less carbonate diol is required.
When the equivalent weight of carbonate diol is below 380,
more carbonate diol and less polyol will be required.
The weight percents shown in Table 1 are the solids
contents by weight percent for the three solid components,
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(namely the carbonate diol, the polyol and polymeric MDI) in
the metal oxide primer composition. The solids content is
defined as that portion of the metal oxide primer composition
other than the solvent or trace components (e. g. catalyst
and/or surfactant).
TABLE 1
SELECTED METAL OXIDE PRIMER WEIGHT % BASED PRIMER
COMPOSITION COMPONENT COMPOSITr~ ON ONTENT
N SOLTn.
Carbonate Diol 18.65 - 18.76wt%
Polyol 18.68 - 19.10wt%
Polymeric MDI 62.24 - 62.57wt%
With regard to the polymeric MDI, carbonate diol and
low molecular weight polyol, for each equivalent of polymeric
MDI, it is desirable to have about the same number of hydroxyl
groups (combined from the hydroxyl groups present in the
carbonate diol and low molecular weight polyol) as NCO groups
in the polymeric MDI, that is a ratio of about 1 ~0.1 NCO
groups to total hydroxyl groups in the metal oxide primer
composition. Therefore, in accordance with the present
invention, there is preferably for each equivalent of NCO
groups in the polymeric MDI, about 0.9 to 1.1 equivalents of a
combined total of hydroxyl groups in the metal oxide primer
composition comprised of the hydroxyl groups present in the
low molecular weight polyol and hydroxyl groups present in the
carbonate diol.
The individual equivalent of the low molecular
weight polyol's hydroxyl groups is preferably about 0.9
equivalents, preferably 0.9 ~0.1 equivalents, and the
individual equivalent of the carbonate diol's hydroxyl groups
is preferably at least 0.05 equivalents, preferably about 0.05
to 0.15 equivalents-, more preferably about 0.1 equivalents.
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Excess carbonate diol Zaill result in a metal oxide
primer which has an undesirably high coefficient of expansion
and an undesirably low glass transition temperature such that
when the primer expands or contracts, it does so at a rate
that is much faster than the metal oxide coating causing the
metal oxide coating to buckle or crack.
Insufficient carbonate diol will result in a metal
oxide primer that has an insufficient coefficient of expansion
resulting in high stress development in the primer as the
substrate expands or contracts at a rate exceeding that of the
primer which is transmitted to the metal oxide coating causing
the metal oxide coating to crack.
Excess polyol has the same effect as insufficient
carbonate diol on the primer. Insufficient polyol has the
same effect as excess carbonate diol on the primer.
In a preferred embodiment, the novel primer of the
present invention is a urethane defined as having a molecular
weight per crosslink (designated "M~~~) of about 276 grams per
mole to 411 grams per mole, preferably about 340.3 grams per
mole and a weight percent of urethane of about 24 wt% to 32
wt%, preferably about 27.5 wt% based on one equivalent of
urethane group having an equivalent weight of 59 grams per
equivalent.
The amount of catalyst present is in the range of
about 0-600 ppm, preferably about 100 ppm of solids content in
the metal oxide primer composition. As may be appreciated by
those skilled in the art, the amount of surfactant necessary
to sufficiently reduce surface tension will vary with the
specific surfactant chosen. When the surfactant is FC430, it
is preferred that at least .05 weight percent by weight of the
metal oxide primer composition be used.
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II.H. THE MIXTNG OF THE L'-nMpnNRNTQ II A F.
The carbonate diol, low molecular weight polyol and
polymeric MDI are blended and mixed in the solvent in the
range of about 1 to 20 wt% solids content. A catalyst and/or
a surfactant may be added. The reactants are blended to form
the metal oxide primer composition. The components of the
metal oxide primer composition are permitted to react until
upon application to the substrate a clear polymeric film will
form which has acceptable optical properties. Typically this
reaction time is 2 hours at room temperature but can be
accelerated with increased catalyst, increased solids contents
or heat.
After the metal oxide primer composition is prepared
the metal oxide primer composition is applied to the substrate
surface as a solution by dip, spin, spray, flow or other
conventional application technique, after cleaning the
substrate surface with hexane and methanol as follows. First
hexane is wiped over the substrate with a soft lint free cloth
and the surface is then allowed to dry. Second, the surface
is similarly wiped with methanol, and is again allowed to dry.
Static may be removed from the surface of the substrate before
application of the metal oxide primer composition as for
example by the use of an antistatic gun.
After the metal oxide primer composition is applied
to the cleaned substrate, it is allowed to air dry at room
temperature until tack free. The solvent is then evaporated
and the primer, composition is cured at slightly elevated
temperature, that is, above ambient temperature whereupon
crosslinking will occur to form the crosslinked metal oxide
primer of the instant invention. A temperature in the range
of about 230°F-265°F (110°C - 129.4°C) for
approximately 1 to 2
hours, preferably two hours will suffice for curing.
CA 02363894 2001-12-12
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II . J. PROPERTIES OF TFIE ~~rnr OXIDE PRIMEu
The thickness of the metal oxide primer after cure
is preferably in the range of about 0.5 to 10 microns, more
preferably about 1.5 to 3 microns for optimum stress reduction
and adhesion of the electroconductive metal oxide coating.
The metal oxide primer has a glass transition temperature (Tg)
of at least 230°F (110°C), preferably about 248°F
(120°C). It
has a molecular weight per crosslink of 276 to 411 g/mole, and
a weight percent content of urethane of about 24 to 32 wt%.
It also has a refractive index of about 1.5555 to 1.6155,
preferably about 1.5855.
The metal oxide primer of the instant invention
mitigates the effects of stress on the electroconductive
coating caused by different coefficients of expansion between
the metal oxide coating and the substrate. More particularly,
the metal oxide primer acts as a shear-absorbing layer to
reduce shear stress on the metal oxide coating.
The metal oxide primer permits the metal oxide
coating to withstand strains of up to 1%. Strain may be
measured by any known techniques, but preferably is measured
as follows. A 1" x 6" bisphenol A polycarbonate substrate,
coated with the metal oxide primer of the instant invention
and a metal oxide coating, has laminated to the metal oxide
coating a pair of bus bars at opposite ends of the substrate.
The substrate is placed with the metal oxide coated
bus bar "front" surface facing downwardly, over a pair of end
supports located at opposite ends of the substrate, said
supports being positioned more or less under the bus bars. A
bending force is applied to the "backside" of the substrate by
applying a downward force perpendicular to the substrate near
. the midpoint of the backside of the substrate between the two
CA 02363894 2001-12-12
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end supports, to bend the substrate between the supports,
thereby inducing a radius of curvature in the substrate and
providing a bending strain.
The temperature of the coated substrate may be
raised or lowered during the bending process to induce a
thermal expansion or compression strain to determine the
ability of the metal oxide coating to withstand strain as a
function of temperature.
Force is applied until an increase in the resistance
between the bus bars of about 10% is obtained over the initial
resistance prior to bending. This 10% increase in resistance
has been found by the inventors to be indicative of the
formation of microcracks in the metal oxide coating.
From a measured or calibrated radius of curvature
corresponding to the amount of force applied, the temperature
and the coated substrate composition and thickness, the
strain may be calculated. Coatings are deemed to have
sufficient ability to withstand strain where they withstand
strains of up to about 1% total strain with less than a 10%
increase in resistance. Total strain includes bending strain
plus thermal compression or expansion strains.
The metal oxide primer of the present invention also
provides good water resistance and good adhesion of the
electroconductive layer to the substrate as determined by
subjecting samples to a 140°F (60°C) 100% humidity Cleveland
Condensing Cabinet Humidity Test for up to six months,
whereupon it was found by periodic scribe tape testing of
samples taken during the Cleveland Condensing Cabinet Humidity
Test, that no loss of adhesion was observed.
_ The Cleveland Condensing Cabinet Humidity Test
includes supporting samples on a rack-type system within a
Cleveland Condensing Cabinet manufactured by Q-panel
CA 02363894 2001-12-12
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Corporation of Cleveland, OH, wherein the humidity,
temperature and time of exposure to'the aforesaid humidity and
temperature can be controlled. Scribe tape testing includes
cutting a coating on a substrate into squares by scribing with
a razor knife followed by pressing a suitable adhesive tape
against the coating and pulling the adhesive tape at
approximately a 90° angle to the surface of the coating in an
effort to delaminate the coating from the substrate.' The
scribe tape test is described in ASTM D3359-93.
Further, in the preferred embodiment of the present
invention, the index of refraction of the metal oxide primer
matches that of a substrate, which permits the metal oxide
primer to fill surface irregularities in the substrate,
causing such surface irregularities to become invisible to the
optically unaided eye permitting the use of substrates which
are other than optically perfect.
Further, the metal oxide primer of the present
invention has an important advantage stemming from its ability
to resist solvents. More particularly, where a polyurethane
protective liner is applied over a metal oxide coating, the
solvent of the polyurethane protective liner can penetrate
through defects in the metal oxide coating and undesirably
swell certain metal oxide primers, resulting in cracking of
the metal oxide coating. The metal oxide primer of the
instant invention is able to withstand such polyurethane
protective liner solvent contact without deformation or
dimensional change and/or solvent-induced loss of adhesion of
the metal oxide coating or primer. The metal oxide primer of
the present invention is excellent at resisting such
polyurethane protective liner solvent-induced degradation.
CA 02363894 2001-12-12
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Further, the metal oxide primer of the present
invention may be used in a wider role as a barrier film (with
or without a metal oxide coating disposed thereon) to protect'
the substrate to which it is adhered from chemical attack from
any number of overlying materials or environmental sources.
For example, a polyvinyl butyral interlayer could be disposed
over the metal oxide primer, wherein the metal oxide primer
acts as a barrier film to block migration of plasticizer of
the polyvinyl butyral to the substrate, which plasticizer
l0 would otherwise damage a polycarbonate substrate over which
the metal oxide primer is disposed.
III. THEM. , _CTROCOND mrV Mg~r~n_T, OXTnF rnamT,,,~,
In addition to melting ice and removing moisture as
discussed above, the metal oxide coatings of the instant
invention can be used to absorb microwave energy for the
protection of the aircraft occupants and/or as an antistatic
coating to remove static electricity that may build up on the
aircraft during flight. Such static electricity can, upon
discharge, damage the aircraft transparency. Further, the
build up of static charge can operate to attract oppositely
charged particles of dirt and debris, causing such particles
to collect on the transparency hindering the pilot's and/or
other occupant's vision through the transparencies.
The electroconductive metal oxide coating may be
placed on the metal oxide primer by any conventional known
technique. Preferred techniques include magnetron sputtering
vacuum deposition (hereinafter "MSVD~~) and/or the cathode
sputtering methods of Gillery disclosed in U.S. Patent
4,094,763. See also U.S. Patents 4,113,599; 4,610,771;
4,622,120 and 5,178,966 for additional procedures which may be
CA 02363894 2001-12-12
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used to apply metal oxide, particularly indium/tin oxide
coatings or similar electroconductive coatings over the metal
oxide primer on a rigid plastic substrate. The metal oxide
primer of the present invention is particularly well suited to
adhere coatings of indium oxide, tin oxide, or mixtures
thereof and is particularly useful for metal oxide coatings
comprising a ratio of indium to tin oxide of about 9:1
commonly applied by MSVD.
In the practice of the invention the metal oxide
coating is indium/tin oxide, preferably has at least
3 ohms/sq. resistance and preferably is less than about
13,OOOA thick. A preferred metal oxide coating has a
resistance of about 3 to 40,000 ohms/sq. and a thickness about
1400 to 13,OOOA . A particularly preferred metal oxide
coating has a resistance of about 10 ohms/sq. and a thickness
of about 7500A to maintain the metal oxide coating on the
substrate through temperature ranges of about -65°F to +230°F
(-53.9°C to 110°C).
IV. THE POT.vrraFT nNrz pgOTECTT~rQ
LINER D17TMR17
In a preferred aircraft transparency of the present
invention, the electroconductive metal oxide coating is
protected with a polyurethane protective liner. The
protective liner is adhered to the metal oxide coating by
interposing a novel primer of the instant invention between
the metal oxide coating and the polyurethane protective liner,
the primer being referred to hereinafter as "the polyurethane
primer". The polyurethane primer improves the adhesion of
the polyurethane protective liner to the metal oxide coating.
The invention will be discussed using the polyurethane primer
disclosed below. As will be appreciated, the invention is not
CA 02363894 2001-12-12
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limited thereto and other polyurethane primers to provide the
transparency of the invention may be used.
In one embodiment, the polyurethane primer of the
instant invention is a crosslinked copolymer of acrylic acid
(hereinafter "AA") and substituted acrylates such as 2
ethylhexylacrylate (hereinafter "EHA"). In an alternative
embodiment of the present invention the primer is a
crosslinked copolymer of cyanoethylacrylate (hereinafter
"CEA") and AA. In still another embodiment of the present
invention, the primer is a terpolymer of CEA/EHA/AA.
These copolymers and terpolymer are prepared by
polymerizing the respective monomers in an appropriate solvent
using a free radical initiator. It is a three step process in
which the copolymer or terpolymer is formed in a first step,
followed by formation of an uncrosslinked polyurethane primer
composition in a second step, followed by a third step of
applying the primer composition over the metal oxide coating
and curing of the primer composition to cause the primer
composition to crosslink, thereby forming the polyurethane
primer of the instant invention on the metal oxide coating.
The polyurethane primer is then overcoated with the
polyurethane protective liner. The polyurethane primer has
good adhesion to the metal oxide coating and to the
polyurethane protective liner.
IV. A. MONOMERS AND RATIn~
Where the polyurethane primer is an EHA/AA
copolymer, the mole ratio of EHA to AA in the polyurethane
primer of the present invention may vary from 3:1 to 1:3.
Where the polyurethane primer is a CEA/AA copolymer, the mole
ratio may vary from 3:1 to 1:3. Where the polyurethane primer
CA 02363894 2001-12-12
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is a CEA/EHA/AA terpolymer, the mole ratio may vary from 1:2:1
to 0.5:0.5:3.
Increasing the mole ratio of AA beyond the specified
mole ratio increases the solvent resistance of the
polyurethane primer, but at the expense of raising the glass
transition temperature of the primer. Increasing the mole
ratio of CEA beyond the specified mole ratio increases the
water absorption and reduces the humidity resistance.
Increasing the mole ratio of EHA beyond the specified ratio
lowers the glass transition temperature but simultaneously
lowers the polyurethane primer's ability to withstand exposure
to solvents that may be present in the polyurethane protective
liner as the polyurethane protective liner is applied in
liquid form over the polyurethane primer.
It is preferred that the polyurethane primer exhibit
as low a glass transition temperature and as high a solvent
resistance as possible. This is so because it is preferred to
cure the polyurethane primer composition at a temperature
above the glass transition temperature of the polyurethane
primer itself, (to reduce thermally induced stresses and to
obtain a complete cure of the polyurethane primer composition)
and yet remain below a temperature that would cause thermal
stress in the metal oxide coating. Where the polyurethane
primer has a glass transition temperature after crosslinking
of less than 180°F (82.2°C), the polyurethane primer
composition can be fully cured but without developing
thermally induced stresses in the metal oxide coating,
(particularly an indium/tin metal oxide coating), which could
occur with a glass transition temperature above 180°F (82.2°C).
- For a metal oxide coating comprising indium/tin
oxide having a 10 ohm/square resistance, over which a
polyurethane primer having.the preferred EHA/AA copolymer is
CA 02363894 2001-12-12
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deposited, the optimum ratio of EHA.to AA in the copolymer is
2:1. This ratio will provide a desirably low starting glass
transition temperature in the EHA/AA copolymer prior to
crosslinking of about -30°F (-34°C) which results in a
desirable glass transition temperature after crosslinking of
about 131°F (55°C), well below the 180°F (82.2°C)
threshold
discussed above. The EHA/AA copolymer has a desirable
crosslinking density which resists solvent degradation by
solvents of the polyurethane protective liner. (The starting
glass transition temperature of the polyurethane primer
composition prior to crosslinking directly affects the final
glass transition temperature of the polyurethane primer after
crosslinking.) This ratio of 2:1 of EHA to AA is also
preferred because it provides a sufficient number of hydroxyl
groups in the polyurethane primer after reaction of the AA
with a crosslinker as discussed below, which hydroxyl groups
are necessary for adhesion of the polyurethane primer to the
metal oxide coating.
The molecular weight range of the EHA/AA copolymer,
CEA/AA copolymer or CEA/EHA/AA terpolymer of the present
invention prior to crosslinking is about 10,000 to 100,000,
preferably 25;000 to 50,000 grams per mole.
IV. B. SOLVENT
More particularly, the copolymers or terpolymer of
the instant invention are formed in a first step by adding the
respective monomers to an appropriate solvent, such as 1-
methoxy-2-propanol where the monomers comprise 10 to 80
wt%,-preferably 40 to 60 wt% of the monomer/solvent solution.
The monomer/solvent solution is stirred until thoroughly
blended. The solution is sparged with dry nitrogen for about
CA 02363894 2001-12-12
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20 minutes to displace any oxygen~in the solution which oxygen
would terminate free radical polymerization. ,
IV. C. FREE R_anl~nr. INITIpTn~
Next, a free radical initiator is added and mixed at
about room temperature until dissolved. Appropriate free
radical initiators include azobisisobutyronitrile (hereinafter
"AIBN"). Weight percents of initiator can be varied from .O1
wt% to 2.0 wt% but are preferably about 0.10 to 1.0 wt% by
weight of the monomers present in the monomer/solvent
solution.
IV . D . FOR_MA'rTON OF COPOL~R
TERPOL~~
Upon addition of the free radical initiator,
polymerization of the monomers commences when the temperature
of the solution is raised to about 147.2°F (64°C). Stirring is
continued during the polymerization process. Total reaction
time is generally about 12 hours to obtain high conversion of
monomers to the respective copolymers or terpolymer. Percent
conversion preferably ranges from about 94 to 99%. A nitrogen
blanket is kept over the solution throughout the
polymerization to prevent oxygen inhibition of the free
radical polymerization.
At the end of the polymerization process, the
resulting product is a clear viscous liquid with a slight
amber cast.
IV. E.
In a second step, at least a portion of the
copolymer or terpolymer formed in the first step is blended
with additional components to form a polyurethane primer
composition. More particularly, the copolymer or terpolymer
CA 02363894 2001-12-12
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described above is blended with a'crosslinker, an optional
catalyst, an optional surfactant, and an optional additional
higher boiling solvent to form a polyurethane primer
composition. The polyurethane primer composition has a solids
content of about 10% to 50%, preferably 20% to 40% solids by
weight of polyurethane primer composition. The individual
components of the primer composition are discussed as follows.
IV.E.l. rROBSLINKING AGENT
The crosslinking agent of the polyurethane primer
composition includes cycloaliphatic compounds, including
cycloaliphatic diepoxides, and still further including
compounds of the general formula:
O O
CH20C ( ( CHz ) hCOCH2 J i
O O
(Formula 7)
where h is an integer from 0 or 1 and i is an integer from 2
to 6.
Two particular cycloaliphatic diepoxides useful with
the present invention are available under the trade names are
ERL-4221 and ERL-4299 from Union Carbon of Danbury, CT.
ERL-4221 is 3,4-epoxycyclohexylmethyl-3,4-epoxy-
cyclohexanecarboxylate whose chemical formula is shown below:
O
O COCH2
O
(Formula 8)
CA 02363894 2001-12-12
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ERL-4229 is bis(3,4-epoxycyclohexyl)adipate, whose
chemical formula is shown below:
CH20CCHZCH2CH2CH2COCH2
O O
(Formula 9)
The appropriate amount of crosslinker to be added to
the polyurethane primer composition is conveniently calculated
in terms of the epoxy group equivalents in the crosslinker
versus carboxylic acid group equivalents in the copolymer or
terpolymer. The epoxy group equivalents provided by the
crosslinker should be in excess of the carboxylic acid group
equivalents provided by the EHA/AA or CEA/AA copolymers, or
the CEA/EHA/AA terpolymer respectively. The ratio of
carboxylic acid group equivalents in the copolymer or
terpolymer to the epoxy group equivalents in the crosslinking
agent is known as the "R value", and is defined in Equation 1
as follows:
Rvalue = e~ivalents of carbo~y'1 ; r ate; ~7 groups ; r, rhP opal ~~ r nr rP,-
n~3,mer
2 0 equivalents of epoxy groups in the crosslinking agent
(Equation 1)
The R value must be adjusted to account for homopolymerization
of the epoxy groups while still reacting all of the carboxylic
acid groups. R values in accordance with the present
invention can vary from about 0.5 to 0.9 but are dependent on
the acid strength of the respective copolymer or terpolymer,
and the amount of catalyst added, as both can promote
homopolymerization~of the epoxy component of the crosslinking
CA 02363894 2001-12-12
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agent requiring more crosslinking agent in order to have
sufficient crosslinking agent in the polyurethane primer ,
composition to react all of the carboxylic acid groups. It
is particularly preferred to maintain R values of about 0.6 to
0.8, to assure that all the carboxylic acid groups are
reacted.
Failure to react all of the carboxylic acid groups
provided by the respective copolymer or terpolymer will result
in longer time requirements for curing the polyurethane
protective liner after it is applied over the polyurethane
primer, particularly at the polyurethane protective
liner/primer interface, where unreacted carboxylic acid groups
in the polyurethane primer will reduce the reactivity of the
polyurethane protective liner's reactive components.. This can
result in the polyurethane_.protective liner curing slowly on
the surface adjacent the polyurethane primer, but curing
rapidly on the surface opposite the surface adjacent the
polyurethane primer (hereinafter the 'outer surface"). If the
outer surface of the polyurethane protective liner cures
faster than the rest of the polyurethane protective liner,
surface wrinkling and streaking of the polyurethane protective
liner may result. Where polyurethane protective liner coating
compositions having relatively low viscosity, i.e. 500
centipoise, are used, this effect tends to be more pronounced;
high viscosity combined with lower cure temperatures will tend
to ameliorate the undesirable effects. Failure to react all
of the carboxylic acid groups in the polyurethane primer will
also result in reduced crosslink density (because all of the
carboxylic acid groups are not crosslinked) and reduced
solvent resistance in the polyurethane primer because of the
reduced crosslink density.
CA 02363894 2001-12-12
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IV.E.2. OPTT_ONAr~ HT_C-H8R BOTLTNG gOTh'T SOL NT
A higher boiling point solvent may be added to the
polyurethane primer composition to dilute the composition in
order to lower the solids content of the primer composition
and slow the rate of solvent evaporation, allowing the solvent
to remain in the polyurethane primer composition for
sufficient time before its eventual evaporation and slightly
delay the crosslinking reaction described below, so as to
permit the polyurethane primer composition to flow evenly upon
its application over the metal oxide coating, thereby forming
a uniform film having optimal optical qualities after
crosslinking. A preferred higher boiling point solvent is
diacetone alcohol. The higher boiling point solvent is added
from about 0 to 40 wt% of the polyurethane primer composition.
Exceeding about 40 wt% causes solvent to be trapped in the
polyurethane primer.
IV.E.3. SURFACTANT
A surfactant, which functions as a flow control
agent, may be added to the polyurethane primer composition to
improve the flow of the polyurethane primer composition. When
the polyurethane primer composition is applied over the metal
oxide coating, visible distortion may result from individual
pockets of primer which are formed by gradients in the surface
tension of the primer. The surfactant lowers the surface
tension of the primer, allowing the primer to flow together to
form a uniform film on the metal oxide coating. A preferred
surfactant is available under the trade name "BYK303" which is
a available from BYK Chemie of Germany. The amount of
surfactant is preferably at least about .05 wt% by weight of
the crosslinking solution.
CA 02363894 2001-12-12
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- 34 -
IV . 8 . 4 . np'r'TONAT~ CA'~'AT~YST _
An optional catalyst is included with the
polyurethane primer composition to promote the crosslinking
reaction, which can be a Lewis acid catalyst, such as
dibutytindilaurate, stannous octoate, or uranyl nitrate. The
catalyst may also be of the nucleophilic type such as
triphenylphosphine or triethylamine. Weight percents range
from 0.1% to 5.0% but preferably 0.5% to 2.0% by weight of
polymer and crosslinker present in the primer composition.
IV . E . 5 . BLE1~T.T~TIyT~'~ OF COMPONENTS IN A SOLVENT TO FORM
PnT.vrT~tRT~ArTR: PRIMER COMPOST_TT_ON
The EHA/AA copolymer, crosslinking agent, catalyst
(if present), surfactant (if present), and higher boiling
point solvent (if present) are combined in a solvent to form
the polyurethane primer composition. Suitable solvents
include alcohols and ketones. A preferred solvent is 1-
methoxy-2-propanol, available under the trade name "Dowanol
PM" from Dow Chemical of Midland, MI. The amount of solvent
in accordance with the present invention is about 40 to 90 wt%
of the polyurethane primer composition, preferably 60 to 70
wt%. About 90 wt% solvent causes poor adhesion of the
polyurethane protective liner to the polyurethane primer.
Falling below about 40 wt% solvent results in unacceptable
optics due to poor flow properties resulting in poor optical
properties in the polyurethane primer due to the increased
viscosity of the primer composition.
CA 02363894 2001-12-12
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IV.E.6. AppT T~ATTOh' OF THE POLSC~;JRETHAnr~ vRTHrxR CnMPOSITION
O~~R A ME't'AD OXIDE COATING AND CROSSLINKING TO FORM
T~a"'rs POLYD'RETHANE PRIMER OF THE INSTANT INVENTIQN
The polyurethane primer composition is preferably
applied over the metal oxide coating by conventional processes
including dipping, spraying or flow coating to a thickness of
about .25 mils to 3 mils. The polyurethane primer composition
is air dried at room temperature until the viscosity of the
polyurethane primer composition stabilizes. Air drying
generally requires 1/2 to 1 hour. The polyurethane primer
composition is then cured, generally at a temperature between
about 180°F to 230°F (82.2°C to 110°C), preferably
about 180°F
(82.2°C) resulting in crosslinking of the polyurethane primer
composition to form the polyurethane primer of the instant
invention. Curing will be generally satisfactory after 8
hours, but about 12 hours is recommended to assure complete
curing. Persons skilled in the art will alter the cure time
inversely with temperature according to the particular
circumstances and formulation used.
The polyurethane protective liner is then formulated
and applied over the polyurethane primer as follows.
V. '~'HE POLYURETH_A~ PROTECTIVE LINER
The polyurethane protective liner deposited on the
polyurethane primer of the present invention is preferably a
transparent layer which is a reaction product of an isocyanate
and a polyol such as a diisocyanate reacted with a
trifunctional polyol or a triisocyanate reacted with a
difunctional polyol.
- Preferred isocyanates include aliphatic
diisocyanates, aromatic diisocyanates and aromatic
' triisocyanates.
CA 02363894 2001-12-12
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The polyols can be pol~rcarbonates, polyesters or
polyethers or any combination of these polyols combined into a
urethane polyol. The polyols typically have number average
molecular weights from about 250 to about 6000, preferably
from 1000 to 2000. Preferred polyols include polycaprolactone
polyol, hexanediol carbonate polyol, cyclohexanedimethanol
carbonate polyol, phthalate ester polyol,
hexanediol/cyclohexanedimethanol carbonate polyol and mixtures
thereof.
The preferred polyurethane protective liner is a
crosslinked thermoset polycarbonate polyurethane.
The polyurethane protective liner is applied as an
about 80% solids solution over the polyurethane primer that
has been applied over the metal oxide coating as described
above. The thickness of the cured polyurethane protective
liner ranges from 1 mil to 5 mils. The thickness is critical
to the protection of the metal oxide coating because the
polyurethane protective liner is designed to protect the metal
oxide coating and the substrate from abrasion damage,
impingement damage and ultraviolet light damage. The thicker
the polyurethane protective liner the better the protection of
the underlying layers.
Physical properties of the polyurethane protective
liner of the instant invention include a molecular weight per
crosslink of about 500 to 10,000 grams per mole, where 1000 to
6000 grams per mole is preferred, and more preferred still is
a molecular weight per crosslink of about 1909 grams per mole.
The polyurethane protective liner has a molecular weight
between branch points of about 1279 grams per mole. The
urethane content of the polyurethane protective liner can
range between 5 to 30%, with a preferred range of about 8 to
22% and a still more preferred urethane content of about 9.4%.
CA 02363894 2001-12-12
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The crosslink density and urethane content determine in part
the mechanical properties and weatherability of the
polyurethane protective liner of the present invention.
To the polyurethane protective liner composition may
be added additional compounds, including but not limited to
ultraviolet light absorbers, antioxidants, and/or hindered
amine light stabilizers.
Polyurethane compositions and reactants are
described in detail in the above cited references,
particularly U.S. Patents 4,335,187 and 4,435,450; see also
U.S. Patent 4,434,284..
The following are examples of the present invention;
however, as can be appreciated, the invention is not_limited
thereto.
In this example, a polycarbonate substrate was
primed with a metal oxide primer and coated with an indium/tin
oxide coating as follows. The metal oxide primer included
carbonate diol, a low molecular weight polyol and polymeric
MDI blended as shown in Table 2 below:
Hydroxyl Isocyanate Wt% by Weight
Cov~onent EcauivalentsH~uivalents Solids Content
Carbonate Diol
(KM-10-1667 - 0.1 0.0 18.73
molecular weight
of
about 1000 grams
per
mole)
Polyol
(trimethylolpropane)0.9 0.0 18.76
Polymeric MDI - 1.0 62.5
CA 02363894 2001-12-12
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Persons skilled in the art will appreciate that the.
ratio of components as shown in Table 2 is such that there is
one isocyanate equivalent of polymeric MDI for one hydroxyl
equivalent, with the hydroxyl equivalent representing the
total of the hydroxyl groups contributed by the KM-10-1667
carbonate diol and the hydroxyl groups contributed by the
trimethylolpropane low molecular weight polyol.
More particularly 18.73 grams of KM-10-1667
carbonate diol, 18.76 grams trimethylolpropane low molecular
weight polyol, and 62.5 grams polymeric MDI were blended and
mixed in 300 grams of diacetone alcohol solvent to form a 25%
solids content solution which was reacted for 2 hours. After
2 hours, 600 grams of diacetone alcohol was added to dilute to
a 10% solids content, along with .O1 grams dibutyltindilaurate
as a catalyst and .05 grams of FC430 as a surfactant were
blended until thoroughly mixed to form a metal oxide primer
composition.
A substrate of Lexan'~, a polycarbonate material
available from General Electric of Pittsfield, MA; measuring
about 6 feet in length by about 4 feet in width by about 1/2
inch thick was cleaned by wiping with hexane and a lint free
cloth followed by cleaning with methanol and wiping with a
lint free cloth. The metal oxide primer composition was flow-
coated to a thickness of about 2 microns onto the cleaned
LexanTM substrate and cured for two hours at 230°F (110°C)
in
air to form a metal oxide primer on the LexanT"" substrate. The
metal oxide primer had a molecular weight per crosslink of
340.3 g/mole, a molecular weight between branch points of 228
g/mole and a urethane content of 27.5% by weight. The
refractive index of the metal oxide primer was 1.5855 which
nearly matched the refractive index of the LexanT'" substrate
CA 02363894 2001-12-12
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which was about 1.5850. The metal oxide primer exhibited a
glass transition temperature of 248°F (120°C) as measured by a
Torsional Braid Analyzer manufactured by Plastics Instruments,
Inc. of Princeton, NJ.
A 10 ohms/square resistance coating of indium/tin
oxide was applied by magnetic sputtering vacuum deposition
(MSVD)to the primed substrate at a substrate temperature of
180°F (82.2°C). The thickness of the indium/tin oxide coating
was 7500 Angstroms.
The substrate/metal oxide primer/metal oxide coating
article thus formed was subjected to a 5-day 176°F (80°C) 100%
humidity Cleveland Condensing Cabinet Humidity Test and was
checked for cracking on a daily basis by cutting samples and
conducting visual and microscopic inspection of the samples.
No cracking of the metal oxide coating was observed during the
5-day 176°F (80°C) 100% humidity Cleveland Condensing Cabinet
Humidity Test, showing that the metal primer of the present
invention maintained the mechanical integrity and adhesion of
the metal oxide coating to the substrate.
The following Comparative Example 1 demonstrates
that where a substrate is coated with a metal oxide primer and
metal oxide coating, wherein the polymeric MDI of the metal
oxide primer of the instant invention is replaced entirely by
an all-aliphatic substitute (a known crosslinking agent, but
having an index of refraction which does not match the
refractive index of the substrate), the resultant comparative
metal oxide primer did not prevent the metal oxide coating
from buckling and cracking. The comparative metal oxide
primer results in cracking of the metal oxide coating as it
CA 02363894 2001-12-12
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cools to room temperature from the temperature at which the
metal oxide coating was applied of about 180°F (82.2°C)..
13.538 of KM-10-1667 carbonate diol was mixed with
13.558 trimethylolpropane low molecular weight polyol and
72.928 of an all-aliphatic substitute, namely triisocyanurate
of hexanediisocyanate available under the trade name DesmodurTM
3300 available from Bayer of Pittsburgh, PA. A 25% solids
content solution of the above carbonate diol, polyol and all-
aliphatic substitute was made in diacetone alcohol. 300 ppm
dibutyltindilaurate by weight of solids content in the
comparative primer composition was added as a catalyst. The
reactants were allowed to react for 2 hours at 230°F (110°C),
then the solution was diluted with diacetone alcohol to a 10%
solids content to form a comparative metal oxide primer
composition.
The comparative metal oxide primer composition was
flow coated onto a bisphenol A polycarbonate substrate and
cured for 2 hours at 230°F (110°C). An indium/tin oxide
coating was vacuum deposited onto the comparative metal oxide
primer composition at a thickness of 7500A with a resistance
of about 10 ohms/sq. and at a substrate temperature of about
180°F (82.2°C). The comparative metal oxide primer had a
weight % urethane content of 21.4% and a molecular weight per
crosslink of 438 grams per mole.
Four hours after cooling to room temperature the
indium/tin oxide coating cracked. The comparative metal oxide
primer is assumed to have had a coefficient of expansion which
was too high whereupon the rate of contraction of the metal
oxide primer upon cooling exceeded the strain limit of the
indium/tin oxide coating, causing the indium/tin oxide coating
to crack.
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AMPLE 2
In this example, an EHA/AA copolymer was formed (but
not crosslinked) as follows. 836.6 grams of EHA and 163.4
grams of AA were added to a 4 liter vessel along with 1000
grams of Dowanol PMTM (1-methoxy-2-propanol) solvent and
stirred. 1 gram of azobisisobutyronitrile (AIBN) free radical
initiator was added and mixed until all components were
dissolved.
The vessel was placed in a 149°F (65°C) water bath.
Nitrogen was applied above the vessel to prevent oxygen
inhibition of the free radical polymerization of the monomers
in the vessel. When the temperature in the vessel reached
149°F (65°C) the water bath was turned off and ice was added to
cool the bath as necessary to maintain the exothermic reaction
below 51.6°F (125°C). Stirring was continued during the
exothermic reaction. When the exotherm was complete, the
temperature dropped to 212°F (100°C), and the water bath was
turned back on to maintain the vessel contents at about 158°F
(70°C) to continue polymerization for a total of 12 hours, to
obtain high conversion of monomer to polymer. Nitrogen flow
was continued during the 12 hour polymerization time. The
resultant reaction product is a 50% solids content copolymer
of EHA/AA in Dowanol PM.
EXAMPLE 3
The copolymer of Example 2 was crosslinked and cured
to form a polyurethane primer as follows. To 500 grams of the
EHA/AA copolymer of Example 2, was added 114.6 grams Dowanol
PM, 156.28 grams diacetone alcohol and 1.74 grams BYK 306
surfactant. The components were mixed thoroughly with an
overhead stirrer. 97.25 grams of crosslinking agent ERL-4221
' was added and the solution was again stirred until the
CA 02363894 2001-12-12
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components were completely dissolved, to form a polyurethane
primer composition. No catalyst was added. The R value was
calculated to be 0.8.
The polyurethane primer composition was deposited on
an indium/tin oxide coating which had been in turn deposited'
on a metal oxide primer of the instant invention which had in
turn been deposited on a bisphenol-A polycarbonate substrate
measuring about 6 foot in length by 4 foot in width by 1/2
inch in thickness (1.8m x 1.2m x 1.25cm). The polyurethane
primer composition was deposited by flow coating to a
thickness of about 2 mils, air dried for 30 minutes to 1 hour
and cured at 179.6°F (82°C) for about 8 hours to crosslink the
polyurethane primer composition and to form a polyurethane
primer over the indium/tin metal oxide coating.
The polyurethane primer was a tough and rubbery
polymer that had good adhesion to the indium/tin oxide
surface. A scribe tape test was performed on the primer as
described in ASTM D3359-93. No polyurethane primer adhesion
failure was observed. After exposing the coated composite to
a 3-day 140°F (60°C) 100% humidity Cleveland Condensing Cabinet
Humidity Test, visual inspection of the polyurethane primer
determined that no water pockets were seen at the polyurethane
primer/indium tin oxide coating interface. Water pockets,
similar in appearance to blisters will form at the metal oxide
coating/polyurethane primer interface in the presence of poor
adhesion between the metal oxide coating and the polyurethane
primer, allowing water to enter the interface and displace the
metal oxide coating/polyurethane primer bond.
The sample exposed to the 3-day 140°F (60°C) 100%
humidity Cleveland Condensing Cabinet Humidity Test was dried
for 2 hours at room temperature pursuant to ASTM D3359-93, and
the coated composite was again scribe tape tested for
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adhesion. 100% of the tape test area retained adhesion
demonstrating excellent adhesion of the polyurethane primer to
the metal oxide coating.
EXAMPLE 4
A polyurethane protective liner was formed and
applied over the polyurethane primer of Example 3, (thereby
forming a bisphenol -A polycarbonate substrate/metal oxide
primer/metal oxide coating/polyurethane primer/polyurethane
protective liner composite), as follows.
First, a polyurethane protective liner composition
was formed by adding solvent, catalyst, temporary catalyst
poison, antioxidant, hindered light amine, ultraviolet
stabilizer, polyol and isocyanate as follows. 881.4.grams of
cyclohexanone solvent was poured into a one gallon vessel.
36.7 grams of a 1% solution of dibutyltindilaurate in
cyclohexanone was added to function as a catalyst. 36.7 grams
of acetyl acetone was also added to function as a "temporary
catalyst poison" to extend the pot life of the composition in
the vessel. The acetyl acetone acted as a temporary catalyst
poison by reducing the catalytic activity of the
dibutyltindilaurate in the vessel, but evaporated off with the
solvent after application of the polyurethane protective liner
composition over the polyurethane primer as described below,
permitting the dibutyltindilaurate to resume normal catalytic
reactivity. 18.4 grams of an antioxidant available from Ciba
Geigy Inc., of Ardsley, NY, under the trade name Irganox'~M 1076
was added to the vessel. 36.7 grams of a hindered amine light
available from Ciba Geigy under the trade name TinuvinTM 440 was
added to the vessel. 55.0 grams of an ultraviolet light
stabilizer available from Sandoz, Inc., of Charlotte, NC under
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the trade name SandozT" 3206 was added to the vessel. The
mixture was stirred until complete solution was obtained. -
The polyol was added in two parts. First, 1500
grams of carbonate diol polyol available from Stahl, Inc. of
Boston, MA, under the trade name KM-10-1667 was melted at
about 176°F (80°C) and added in its melted state to the vessel
and mixed until a clear solution was obtained. Next, 1000
grams of carbonate diol polyol available from Stahl, Inc. of
Boston, MA, under the trade name IQ~i-10-1733 was melted at
about 176°F (80°C) and was added in its melded state to the
vessel and mixed until a clear solution was obtained. The KM-
10-1667 functioned to strengthen the polyurethane protective
liner, and the KM-10-1733 functioned to slightly soften the
polyurethane protective liner.
The above mixture was cooled to room temperature and
1172.35 grams of an isocyanate, specifically a triisocyanate
available from Bayer Inc., of Pittsburgh, Pennsylvania under
the trade name Desmodur 3390 was added to the vessel and mixed
until a clear solution was obtained having a viscosity at
about 77°F (25°C) of about 1200 centipoise, to forth a
polyurethane protective liner composition. The equivalent
weights of the polyols and isocyanate reactive components in
the polyurethane protective liner composition are as set forth
in Table 3 below:
Comy~onent Equ ivalent Wei,g
KM-10-1733 443.86 grams/equivalent
KM-10-1667 474.38 grams/equivalent
Desmodur 3390 216.5 grams/equivalent
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The polyurethane protective liner composition was
allowed to react for about 2 hours until the viscosity reached
about 1500 centipoise at room temperature.
The polyurethane protective liner composition was
applied over the polyurethane primer of Example 3. The
polyurethane protective liner composition was applied by flow
coating to a thickness of about 4 mils. The polyurethane
protective liner was allowed to air dry until tack free, which
was approximately 4 hours. The substrate coated as described,
hereinafter "the article" was then placed in an air
circulating oven and cured at 180°F (82.2°C) for approximately
4 hours to form a polyurethane protective liner over the
polyurethane primer.
A sample approximately 4" by 4" (10.16 cm. by 10.16
cm) of the article was cut, and abrasion resistance was
measured on a Taber Abraser. The Taber Abraser is a device
known in the art in which a turntable rotates beneath an
abrasive pad attached to a mechanical arm. A sample is placed
in the turntable and the table is caused to rotate causing the
abrasive pad to abrade the sample. One revolution of the
turntable is one cycle. The measurement revealed an increase
in haze after 1000 cycles of abrasion of about 7%. Haze was
measured by a Haze Gard, Model XL211, manufactured by Pacific
Scientific Corp. of Newport Beach, CA.
An additional sample of the article was subjected to
scribe tape test according to ASTM D3359-93. No coating
failure was observed.
A sample of the article was subjected to a 140°F
(60°C) 100% humidity Cleveland Condensing Cabinet Humidity Test
-for about 6 months. Visual inspection once a week for the 6
month period for water pockets at the polyurethane
primer/metal oxide coating interface showed none.
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A sample of the article subjected to the 6 month
140°F (60°C) 100% humidity Cleveland Condensing Cabinet
Humidity Test was dried for about 2 hours at room temperature,
and the scribe tape test for adhesion was again performed
pursuant to ASTM D3359-93. 80% of the tape test area retained
adhesion demonstrating the excellent adhesion of the
polyurethane protective liner to he polyurethane primer, and
excellent adhesion of the polyurethane primer to the metal
oxide coating.
The same polyurethane protective liner described in
Example 4 was applied to an article as described in Example 4,
except that the article of this comparative example did not
include a polyurethane primer, and therefore, the
polyurethane protective liner was applied directly over the
metal oxide coating.
A sample of the article of Comparative Example 2 was
subjected to the scribe tape test according to ASTM D3359-93,
which resulted in 100% removal of the polyurethane protective
liner from the scribed area demonstrating the poor adhesion of
the polyurethane protective liner to the metal oxide coating.
Another sample of the article of Comparative Example
2 was subjected to a 24 hour 140°F (60°C) 100% humidity
Cleveland Condensing Cabinet Humidity Test. Upon visual
inspection after testing, many undesirable water pockets were
visible at the polyurethane protective liner/metal oxide
coating interface, indicating poor polyurethane protective
liner adhesion to the metal oxide coating in the absence of
the polyurethane primer of the instant invention.
The sample subjected to the 24 hour 140°F (60°C)
100% humidity Cleveland Condensing Cabinet Humidity Test was
CA 02363894 2001-12-12
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dried for two hours at room temperature, and the article was
again subjected to the scribe tape test for adhesion as
described in ASTM D3359-93. The test results showed 100%
adhesion loss, demonstrating the efficacy of the polyurethane
primer.
Another sample of the article of Comparative Example
2 was tested on the Taber Abraser for abrasion resistance.
After 100 cycles, the test was stopped as the polyurethane
protective liner was completely removed from the metal oxide
coating, demonstrating the poor adhesion of the polyurethane
protective liner to the metal oxide coating in the absence of
the primer of the instant invention.
The above examples are offered to illustrate the
present invention and are not intended to limit the invention.
Various modifications are included within the scope of the
invention, which is defined by the following claims.
