Note: Descriptions are shown in the official language in which they were submitted.
~ ~5 3~3
- ` 8CS 237
SUMMARY OF THE INVENTION
This invention relates to a method of applying a uniform,
adherent, hard, abrasion and organic solvent resistant thin glass
; coating on a polycarbonate substrate. The method comprises first
priming the polycarbonate substrate with a primer layer comprised
of the photoreaction products of certain polyfunctlonal acrylate
monomer and thereafter vapor depositing on said primed substrate
a thin layer of glass, said glass being evaporated by means of
radio frequency induction heating.
10BACKGROUND OF THE INVENTION
Polycarbonate resins are well known,commercially available
materials possessing excellent physical and chemical properties
which are useful in a wide variety of applications. Such polymers
or resins, since they are less dense and more breakage resistant
than glass, have been especially useful as substitutes for glass,
as for example, in the manufacture of tail lights and stop light
lenses, protective shields for fluorescent street lights, safety
shields in inspection windows, windshields, windows, and the like.
However, these resins have relatively low mar and chemical solvent
resistance.
In order to overcome this relatively low mar and chernical
solvent resistance, polycarbonate articles have been coated with
various organic and inorganic protective layers which increase the
mar resistarlce of said polycarhonate articles. One type of
inorganic protective layer is comprised of glass which has been
vapor deposited onto the polycarbonate su~strate. Thus, for
example, French Patent Specification No. 1,520,125 and the corres-
ponding ~ritish Specification No. 1,144,099 teach that the surfaces
of polycarbonates can be improved, especially rendered more
scratch resistant, by vapor depositing an SiO2 layer of at least
~3~3~
~CS 2378
lu thickness onto ~he polycarbonate. This vapor deposition is
accomplished by evaporating SiO2 with an electron beam evaporator
source in a high vacuum in the presence of oxygen while regularly
moving the polycarbonate article to be coated in the vapor jet and/
or the electron beam evaporator source in such a manner that at
least 50 successive layers are evaporated onto the surface of the
polycarbonate article.
~ owever, this electron beam vapor deposition method suffers
from several disadvantages. One of these is due to the electron
10 beam source being, in effect, a point source of SiOx molecules. ;~
Thus, the area of the substrate immediately above the electron
beam receives a thicker coating of glass than do the cross peri-
pheral to the point of impingement of the SiOx molecules. Conse-
quently, to provde a glass coating of uniform thickness a plurality
of electron beam sources need be used or, alternately, the single
electron beam qource must be rapidly oscillated along the width
oi the substrate. Thus, it is generally difficult to obtain a
glass layer of uniform thickness on large substrates utilizing an
electron beam evaporator device.
Furthermore, the articles thus prepared have been found to be
not entirely satisfactory since, under high stress or temperature
ahanges, the SiO2 protective layer tends to crack and~or separate
from the polycarbonate article. In order to overcome this crack-
:iny ancl separa tion of the protective silicate glass layer, various
modifications of the basic vapor deposition process have been
proposed. Thus, British Patent 1,313,866 teaches a polycarbonate
having a vapor deposited protective layer consisting of SiO2 and
5 to 10~ zirconium oxide. Similarly, U.S. Patent No. 3,645,779
teaches a synthetic polymer provided with a hard, abrasion-
res~stant surface free of fine hairline cracks by vapor depositing
~3~ 8CS 2378
under vacuum onto the sur~ace of said polymer a B203-SiO2 glass
containing less than S percent by weight of Na20. U.S. Patent No.
3,713,369 teaches disposing an in-termediate layer between the
plastic substrate and the vapor deposi-ted glass layer for the
purpose of improving the adherence of said glass layer. ~his
intermediate layer comprises a polymerization layer which is
formed by subjecting low-molecular organic vapors to a glow dis-
charge operation and depositing the polymerization products on the
substrate. The organic vapors are provided by organic compositions
such as acetylene, xylol, and those compounds which contain Si,
preferably in an SiO bond, such as silicate acid methyl or silicic
acid ethy].ester, and low boiling siloxanes.
By the method of the instant invention it is possible to
obtain vapor deposited glass coatings of uniform thickness and
good adhesion on large substrates. By utillzing the method of the
presen-t invention it is possible to produce a polycarbonate article
having a protective top layer of vapor deposited glass which is
free of cracks, is of a uniform thickness and is tenaciously and
durably adhered to the polycarbonate substrate. The advantages
~0 of the instant invention include the fact that~the glass used to
fo~m the protective layer need not be of any special composition,
as is the case in the afore-mentioned U.S. Patent 3,645,779 and
~3ritish Patent 1,313,866; that the intermediate primer layer aids
in providing solvent protection for the polycarbonate substrate;
and that the article produced by the instant method, since the
polycarbonate substrate is already coated with the intermediate
layer before it is exposed to the vapor deposition process, is
relatively easy and simple to manufacture, i.e., the conditions
existent during vapor deposition can be more variable than if there
30 were no intermediate layer and if radio frequency induction evapora- ;
tion were not used.
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8CS 2378
In one aspect of this invention there is provided a method
applying a thin relatively uniform protective glass coating on a poly-
carbonate article by vapor depositing a thin layer of glass on said
polycarbonate substrate using radio frequency induction heating to
vapori2e the glass. In another preferred aspect of this invention the ~-~
method of priming the polycarbonate by ~i) applying to the polycarbonate
substrate an ultraviolet light curable primer composition containing ;~
at least one certain polyfunctional acrylate monomer and a photo-
initiator; (ii) curing said primer composition by exposure to ultra-
violet light for a period of time effective to form a primer layer
comprised of the photoreaction products of said polyfunctional acrylate.
In a still further aspect of the invention there is provided
non-opaque polycarbonate articles having improved mar, abrasion, scratch
and solvent resistance which may be suitably formed in accordance witl
the preferred method above.
In the practice of this invention, any of the aromatic poly-
carbonates can be employed herein. These are homopolymers and copolymers
and mixtures thereof that are prepared by reacting a dihydric phenol
with a carbonate precursor. Typical of some of the dihydric phenols
that may be employed in the practice of this invention are bisphenol-A
(2,2-bis(4-hydroxyphenyl)propane), bis(4-hydroxyphenyl)methane, 2,2-
bis(4-hydroxy-3-methylphenyl) propane, 3,3-bis(4-hydroxyphenyl)pentane,
2,2-bis~3,5 dichloro-4-hydroxyphenyl)propane, 2,2-bis(4-3,5-dibromo-4-
hydroxyphenyl) propane, bis(3-chloro-4-hydroxyphenyl)methane. Other
dihydric phenols of the bisphenol type are also available and are
disclosed in U.S. Patents 2,999,835 issued September 2, 1961, 3,028,365
issued April 3, 1972 and 3,334,154 issued August 1, 1967. ~ -
It is, of course, possible to employ two or more different
dihydric phenols or a copolymer of a dihydric phenol with a blycol
or with hydroxy or acid terminated polyester, or with a dibasic
acid in the event a carbonate copolymer or interpolymer rather
~ ~ 8CS 2378
than a homopolymer is desired for use in the preparation of the
aromatic carbonate polymers of this invention. Also employed in
the practice of this invention may be blends of any of the above
materials to provide the aromatic carbonate polymer.
The carbonate precursor may be either a carbonyl halide, a
carbonate ester or a haloormate. The carbonyl halides which can
be employed herein are carbonyl bromide, carbonyl chloride and
mixtures thereof. Typical of the carbonate esters which may be
employed herein are diphenyl carbonate, di-(halophenyl) carbonates
such as di-(chlorophenyl) carbonate, di-(bromophenyl) carbonate,
di-(trichlorophenyl) carbonate, di-(tribromophenyl) carbonate,
etc., di-(alkylphenyl) carbonate such as di(tolyl) carbonate,
etc., di-(naphthyl) carbonate, di-(chloronaphthyl) carbonate,
phenyl tolyl carbonate, chlorophenyl chloronaphthyl carbonate,
etc., or mixtures thereof. The haloformates suitable for use
herein include bis-haloformates of dihydric phenols (bischloro-
formates of hydroquinone, etc.) or glycols (bishaloformates of
ethylene glycol, neopentyl glycol, polyethylene glycol, etc.).
While other carbonate;precursors will occur to those skilled in
the art, carbonyl chloride, also known as phosgene, is preferred.
Also included are the polymeric derivatives of a dihydric
phenol, a dicarboxylic acid and carbonlc acid~. These are dis-
closed in U.S. Patent 3,169,121 which igsued February 9, 1~65 ~ ;
E. P. Goldberg.
The aromatic carbonate polymers of this invention may be pre-
pared by employing a molecular weight regulator, an acid acceptor
and a catalyst. The molecular weight regulators which can be
employed in carrying out the process of this invention include
monohydric phenols such as phenol, chroman-I, para-tertiary-butyl-
phenol, para-bromophenol, prlmary and secondary amines, etc.
Preferably, phenol is employed as the molecular weight regulator.
~ 5 -
8CS 2378
A suitable acid acceptor may be either an organic or an
inorganic acid acceptor. A suitable organic acid acceptor is a
tertiary amine and includes such materials as pyridine, triethyl-
amine, dimethylaniline, tributylamine, etc. The inorganic acid
acceptor may be one which can be either a hydroxide, a carbonate,
a bicarbonate, or a phosphate of an alkali or alkaline earth
metal.
The catalysts which are employed herein can be any of the
suitable catalysts that aid the polymerization of bisphenol-A
with phosgene. Suitable catalysts include tertiary amines such
as, for example, triethylamine, tripropylamine, N,N-dimethyl-
aniline, quaternary ammonium compounds such as, for example,
tetraethylammonium bromide, cetyl triethyl ammonium bromide,
tetra-n-heptyl-ammonium iodide, tetra-n-propyl ammonium bromide,
tetramethyl ammonium chloride, tetramethyl ammonium hydroxide,
tetra-n~butyl-ammonium iodide, benzyltrimethylammonium chloride
and quaternary phosphonium compounds such as, for example,
n-butyltriphenyl phosphonium bromide and methyltriphenyl phos-
phonium bromide. ~`
Also included herein are branched polycarbonates wherein a
polyfunc~ional aromatic compound is reacted with the dihydric
phenol and carbonate precursor to provide a thermoplastic randomly
branched polycarbonate.
These polyfunctional aromatic compounds contain at least
three functional groups with are carboxyl, carboxylic anhydride,
haloformyl or mixtures thereof. Examples of these polyfunctional
aromatic compounds which may be employed in the practice of this
invention include: trimellitic ahhydride, trimellitic acid,
trimellityl trichloride, 4-chloroformyl phthalic anhydride, pyro-
mellitic acid, pyromellitic dianhydride, mellitic acia, mellitic
8CS 2378
~,3~
anhydride, trimesic acid, benzophenonetetracarboxylic acid,
benzophenonetetracarboxylic anhydride and the like. The preferred
polyfunctional aromatic compounds are trimellitic anhydride or
trimellitic acid, or their haloformyl derivativesO
S Also included herein are blends of a linear polycarbonate
and a branched polycarbonate.
The intermediate primer layer is formed by ~ust applying a
coating composition containing at least one polyfunctional acrylic
acid ester monomer onto ~he polycarbonate substrate and thereafter
exposing said polycarbonate substrate with the coating composition
thereon to ultraviolet light to cure said composition, thereby
forming the intermediate primer layer which contains the polymer-
ized photoreaction products of the polyfunctional acrylic acid
ester monomer or monomers which are present in the photocurable `
coating composition.
The polyfunctional acrylic ester monomers of the present ~
invention are represented by the general formula ~ `
I. [H2C = C - C - O 3 R
n
wherein n is an integer from 2 to 8, preferably from 2 to 6, and
more preferab].y from 2 to 4; and R is an n valent hydrocarbon
radical, an n valent substituted hydrocarbon radical, an n valent
hydrocarbon radical containing at least one ether linkage, and an
n valent substituted hydrocarbon radical containing at least one
ether linkage. ~`
Preferred n valent hydrocarbon radicals are the n valent
aliphatic, preferably saturated aliphatic, hydrocarbon radicals
containing from 1 to about 20 carbon atoms and the n valent
aromatic hydrocarbon radicals containing from 6 to about 10 carbon
atoms.
: . .
~ 8CS 2378
Preferred n valent hydrocarbon radicals containing at least
one ether linkage are the n valent aliphatic hydrocarhon radicals,
preferably saturated aliphatic hydrocarbon radicals, containing
from 1 to about 5 ether linkages and from 2 to about 20 carbon
atoms.
Preferred n valent substituted hydrocarbon radicals are the
n valent aliphatic hydrocarbon radicals, preferably the saturated
aliphatic hydrocarbon radicals, contalning from 1 to about 20
carbon atoms, and the n valent aromatic hydrocarbon radicals con-
taining from 6 to about 10 carbon atoms which contain substituent
groups such as the halogens, i.e , fluorine, chlorine, bromine and
iodine, hydroxyl, -COOH, and -COOR' groups wherein Rl represents
alkyl groups containlng from 1 to about 6 carbon atoms. `
Preferred n valent substituted hydrocarbon radicals containing
at least one ether linkage are the n valent aliphatic 7 preferably
saturated aliphatic, hydrocarbon radicals containing from 2 to
about 20 carbon atoms and from 1 to about 5 ether linkages which ; ~
contain substituent groups such as the halogen hydroxyl, -COOH, i
and -COOR' groups wherein R' is as defined above.
It is to be understood that where substltuent groups are
present, they should be such that they do not unduly hinder or
interfere with the photocure of the polyfunctional acrylic monomers~
The more preferred polyfunctional acrylic monomers are those
represented by foxmula I wherein R is selected from the group
consisting of an n valent saturated aliphatic hydrocarbon radical
containing from 1 to about 20 carbon atoms, a hydroxyl substituted
n valent saturated aliphatlc hydrocarbon radlcal containing from
l to about 20 carbon atoms, an n valent saturated aliphatic hydro-
carbon radical containing from 2 to about 20 carbon atoms and from
1 to about 5 either linkages, and a hydroxyl substituted n valent
~ 8 -
~ 8CS 2378
saturated aliphatic hydroca.rbon radical containing from 2 to about
20 carbon atoms and from l to about 5 e-ther linkages.
The preferred polyfunctional acrylate ester monomers are
those wherein R is an alkyl, ether or.polyether group, with those
5 monomers wherein R is an alkyl group being more preferred.
More particularly, the difunctional acrylic monomers, or di-
acrylates, are represented by ormula I wherein n is 2; the tri- . ;
functional acrylic monomers, or triacrylates, are represented by ~ ~
formula I wherein n is 3; and the tetra-functional acrylic mono- ~ `
mers, or tetraacrylates, are represented by formula I wherein n is
4.
Illustrative of suitable polyfunctional acrylate ester mono- ;
mers of formula I are those listed below in TABLE I.
TABLE I
Diacry~ates of Formula I
1. CH2=CHCOO-CH2--OOCCH--CH2 ~,
2. CH2=CHCOO-CH2-CH2-OOCCH=CH2
3. CH2=CHCOO-CH2-CHOHCH2-OOCCH=CH2 ~ .
4. CH2=CHCOO-(CH2)6-OOCCH-CH2
20 5. CH2=CHCOO-CH2-CH2-CH-CH3
OOCCH=CH2
6- CH2=CHCOO-CH2CH2OCH2CH2-OOCCH=CH2
2 C O CH2cH2ocE~2cH2ocH2cH2ocH2cH2-ooccH=cH2
fH3 ~
8. CEl2=CHCOO-CH2-f-OOCCH=CH2
CH3 - :
CIH2OH : ~
9. CH2=CHCoO-CH2-f-cH20cH2cH2-OOccH=cH2 ~'
CH3
~ 8CS 2378
fH2H
10. CH2=CHCOO~CH2-C-OOCCH=CH2
CH3
fH2E~ ~
11. CH2=CHCOO-CH2-f-OOCCH=CH2
CH20H
Triacrylates of E'ormula 1
IOOCCH=CH2
10 12. CH2=CHCOO-CH2CH2CHCEI-OOCCH=CH2 ~ ~
CH2=cHcoo-fH2
13. CH2=CHCOO-CH2-f~CH2-CEI3
CH2=CHCOO-CH2
fH2H
15 14- CH2=cHcoo-cH2-7-cH2-ooccH=cH2
CH2 -OOCCH=CH2
fH2H
15. CH2=CHCOO-CH2CH2-O-CH2-f-OOCCH=CH2 ~;
CH2-OOCCH=CH2 ::,
Tetraacrylates of Form_la I ~
CH2=CHCOO-fEI2
16. CH2=CHCOO-CH2-f-CEI2-OOCCH=CH2
CH2-CHCOO-CH2
17. CH2=CHCOO-CH2-1CH-fH-CH2-OOCCH=CH2 ~ .
CH2=CHCOO-~H2CH2-OOCCH=CH2
IOH ' ~`'
CH2 CHCOO-CH2THCH-CH2fEI-ooCCH=CH2
CH2=CHCOO-CH2 CH2-00CCH=cH2
These polyacrylate esters and thei.r production are well known
to those skilled in -the art. One method of producing the di-, tri-,
:
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~ 8CS 2378
and tetraacrylate esters involves reacting acrylic acid with a
di-, tri-, or te~rahydroxyl compound to produce the diester,
triester or -tetraester. Thus, for example, acrylic acid can be
reacted with ethylene glycol to produce ethylene glycol diacrylate
(compound 2 in Table I).
Although the coating compositions may contain only one of
said polyfunctional acrylate monomers, preferred coating composi-
tions contain a mixture of two polyfunctional monomers, preferably
a diacrylate and a triacrylate. When the coating compositions
contain a mixture of acrylate monomers, it is preferred that the
ratio, by weight, of the diacrylate to the triacrylate be from
about 30/70 to about 70/30. Exemplary mixtures of diacrylates
and triacrylates include mixtures of hexanediol diacrylate with
pentaerythritol triacrylate, hexanediol diacrylate with trimethyl-
olpropane triacrylater dlethyleneglycol diacrylate with pentaeryth-
ritol triacrylate, and diethyleneglycol diacrylate with trimethyl-
olpropane triacrylate.
Generally, the coating composition contains from about 70 to
about 99weight percent of the polyfunctional acrylate monomer or
mixtures of said monomers. ~he UV cured coating contains from
about 70 to about 99 weight percent of the photoreaction products
of the polyfunctional acrylate monomer or mixture of polyfunctional
acrylate monomers present in the coating composition,
The photocurable coating composition also contains a photo-
~ensitizing amoun-t of photosensitizer, i.e., an amount effective
to effect ~he photocure of the coating composition. Generally,
this amount is from about 0.01% to about 10% by weight r preferably
from about 0.1% to about 5% by weight of the photocurable coating
composition. These additives and the cure thereof are generally
well known in the art. Some nonlimiting examples of these UV
~ 11 -
3~ cs 2378
radiation photosensitizers include ketones, such as benzophenone,
acetophenone, benzil, benzyl methyl ketone; benzoins and substi-
tuted benzoins such as benzoin methyl ether, ~ -hydroxymethyl
benzoin isopropyl ether; halogen containing compounds such as
C~-bromoacetophenone, p-bromoacetophenone, ~-chloromethyl-
naphthalene, and the like.
The coating composition of the instant invention may also
optionally contain various flatting agents, surface-active agents,
thixotropic agents, and UV light absorbers. A11 of these addi-
tives and the use thereof are well known in the art and do notrequire extensive discussions. Therefore, only a limited number
will be referred to, it being understood that any compounds
possessing the ability to function in such a manner, i.e., as a
flatting agent, surface-active agent, UV light absorber, and the
like, can be used so long as they do not deleteriously affect the
photocuring of the coating compositions and do not adversely affect
the non-opaque character of the coating.
The various sur~ace-active agents, including anionic, cationic
and nonionic suriace-active agents are described in Kirk-Othmer
Encyclopedia of Chemical Technology, Vol. l9, Interscience Pub--
lishers, New York, 1969, pp. 507-593, and Encyclo~_i of Pol~mer
Science and Technology, Vol. 13, Interscience Publishers, New York,
1970, pp. 477--486, both of which are references.
In a preferred embodiment of the instant invention, the
25 coating compositions contain resorcinol monobenzoate. The resor-
cinol monobenzoate is present in an amount, based upon the weight
of the coating composition, exclusive of any additional solvent
which may optionally be present, of from about 1 to about 20
weight percent, preferably from about 3 to about 15 weight percent.
~3~3~ 8CS 2378
The preferred UV cured coating thus contains, in addition to the
afore-described photoreaction products of at least one polyfunc-
tional acry]ic monomer, from about 1 to about 20% by weight of the
photoreaction products of resorcinol monobenzoate, which products
are formed during the UV cure of the UV curable coating composition.
The glass coated polycarbonate articles having the preferred -;
intermediate primer layers, i.e., those intermediate primer layers
formed by the ultraviolet light cure of the intermediate coating
composition containing resorcinol monobenzoate, have superior
adhesion of the vapor deposited glass protective layer to the
polycarbonate substrate, especially after exposure to weathering, ;
~ompared to glass coated polycarbonate articles having intermediate
primer layers formed by the ultraviolet light cure of intermediate
coating compositions wlthout the resorcinol monobenzoate.
In the practice of the present invention, the intermediate
photocurable coating compositions are first formulated by adding
together the polyfunctional acrylic monomer or mixtures thereof,
the UV photosensitizer, resorcinol monobenzoate, and, optionally, `
any of the other aforementioned additives. Additionally, if so
desired to reduce the viscosity of the coating formulation, an
organic solvent, such as an alcohol, may optionally be incorpora-
t~d into the fo.rmulation. Generally, the amount of solvent, if any,
present shouldbesuch that evaporation of the solvent occurs
before any deleterious effect on the substrate due to the aggres-
siveness (in the chemical etching sense) of the coating composition ~
develops. The various components are thoroughly mixed so as to ; ~;
form a generally homogeneous coating composition. A thin, uniform
coating of the coating solution is then applied onto the polycar~
bonate sllrface by any of the known means such as dipping, spraying,
roll-coating and the like. The coating is then cured in an inert,
:
- 13 -
~3~3~ 8CS 2378
e~g~, nitrogen~ atmosphere by irradiation with ultraviolet light
which can have a wavelength of from 1849 A. to 4000 A. The lamp
systems used to generate such radiation can consist of ultraviolet
lamps which can consist of discharg~ lamps, as for example, xenon,
metallic halide, metallic arc, such as low or high pressure mercury
vapor discharge lamp, etc., having operating pressures of frorn as
low as a few milli-torr up to about 10 atmospheres, can be employed.
By curing is meant both polymerization of the polyfunctional
acrylic monomers and cross-lin~ing of the polymers to form hard,
non-tacky intermediate primer coatings.
The cured intermediate primer layer has a thickness of from
about 0.1 mils to about 10 mils, preferably from about0O2 mils to
about 5 mils.
After the polycarbonate substrate has been primed by the
application thereon of the intermediate primer coating composition
and the cure of said coating composition by exposure to ultraviolet
light, a thin layer of glass is vapor deposited onto said primed
substrate using radio frequency induction heating to evaporate the
glass.
The glass which can be deposited by vapor deposition OIltO the
primed polycarbonate substrate generally consists mainly of SiO2.
0ther types of glass, however, can also be the protective top layer
in accordance with the present invention. Examples of these other
types o~ hard inoryanic glass include a glass consisting of SiO2,
25 B2O3~ A12O3 and N2O3; HfOX; ZrO2; and the like.
In describing the vapor deposition of the glass coating
reference will be made to the two FIGURES of the drawings which
illustrate in perspective and diagrammatically a preferred embodi-
rnent of the arrangement for practicing the method of the invention. -~
The primed polycarbonate substrate 11, in this case a poly- -~
carbonate panel with the cured primer layer 20 in one side thereof
- 14 -
;
~3~3~ 8CS 2378
is placed in a vacuum vessel 10. The vacuum vessel contains a
graphite crucible 12 demountably located in a ceramic receptacle
13 having radio frequency induction coils 14 mounted therein. The
material to be volatilized l9,e.~,quartz, is placed in the crui-
cible. The crucible is positioned so that its longitudinal axis `is transverse to the longitudinal axis and direction of travel of
the polycarbonate panel thereby enabling the volatilized quartz
material to be evenly deposited across the entire width of the
polycarbonate panel as it passes over the crucible. Preferably,
the crucible is positioned at a distance of about 10 inches below
the polycarbonate sheet. The coils 14 are connected by means of
power cells to a power supply service 16. The power supply source
is a commercially available unit sold by Applied Materials, Inc.,
California, under the tradename Pachydyne~ 50 Induction Heating
Power Supply rated at 50Kw/50 KHz. A vacuum system including a dif-
fusion oil pump, is connected to the vacuum vessel to provide the
necessary low pressures needed. Generally, these pressures are in
the range of from about 10-4 to about 10-6 mm Hg. The vacuum
vessel may optionally contain member 18 which may be in the shape
of a hollow cyclindrical member having a plurality of small open-
ings therein used for the introduction of oxygen into the vacuum
chamber during the vapor deposition of the glass coating on the ~ `
primed polycarbonate panel.
In the practice of the method of the present invention the
primed polycarbonate panel 11 is placed into the vacuum chamber 10
with the side of said panel containing the primer layer 20 disposed
facing the crucible 12 which contains a supply of quartz. The
chamber is then evacuated until a pressure of about 10-4 to about
10-6 mm of Hg is achieved. The coils 14 are then energized to melt
the quartz and the polycarbonate panel is transported over the
- 15 -
~ 3g~ 8CS 2378
crucible in the direction indicated by the arrow, i.e., a direc-
tion transverse to the longitudinal axis of the crucible. The
stream of vaporized Si x particles then impinges upon
and adheres to the primed polycarbonate panel. Oxygen can be in~
troduced into the vacuum chamber 10 by means of the hollow cylindri-
cal member 18 to insure conversion of the SiOx stream to Sio2. The
rate of movement of the poLycarbonate panel over the crucible can
be varied so as to achieve the desired thickness of the SiO2 coat-
ing thereon, i.e., the greater the rate of transport the thinner
the SiO2 layer, the lower the rate of transpor~ the thicker the
SiO2 layer. Generally, the thickness of the SiO2 layer ranges from
about 1 to about 10 microns, preferably from about 2 to about 7
microns.
PREFERRED EMBODIMENTS OF THE INVENTION
_ _
In order to more fully and clearly illustrate the present
invention, the following specific examples are presented. It is
intended that the examples be considered as illustrative of rather
than limiting the invention disclosed and claimed herein.
EXAMPLE 1
An aromatic polycarbonate is prepared by reacting 2,2-bis(4-
hydroxyphenyl)propane and phosgene in the presence of an acid
acceptor and a molecular weight reyulator and having an intrinsic
viscosity of 0.57. The product is then fed into an extruder,
whiah extruder is operated at about 265C and the extrudate is
comminuted into pellets.
EXAMPLE 2
An intermediate coating composition is prepared by blending
together 50 parts by weight of ethyleneglycol dlacrylate, 50 parts ~ -
by weight of pentaerythritol triacry:Late, 2 parts by weight of
~, ~-diethoxyacetophenone, 5 parts by weight of resorcinol
~ - 16
, -
~3~ 8CS 237~
monobenzoate, and 0.5 parts by weight of a silicone oil type
surface-active agent produced by Mallincrodt Chemical Co. of
New Jexsey under the designation, sYK-3oo. A film of about 12.5
microns thickness of this coating composition is applied to the
polycarbonate panels prepared substantially in accordance with
Example 1 using a wire-wound drawdown bar. The coated polycarbon~
ate panels are then passed through a Linde photocuring apparatus
(this consists of a variable speed conveyor running through a
chamber containing germicidal type mercury vapor lamps which emit
light mainly at 2537A, 3150A and 3605A operating in air) wherein
the nitrogen pressure is 25 psi nitrogen and the speed of the
conveyor is 50 ft/min. The resulting primer coating is hard and
tack~free.
I EXAMPLE 3
A polycarbonate test panel prepared substantially in accord-
ance with Example 1 is placed into a vacuum deposition chamber
containing a crucible about which is disposed a radio frequency
induction coil, said coil being connected to a power supply source.
The power supply source is a commercially available unit sold by
Applied Materials, Inc., California, under the tradename, Pachy-
dyne~ 50 Induction Heating Power Supply rated at 50 Kw 50 KHz.
This power supply source is operated at between 15-30 Kw. The
cruicible, to which quartz is added, is located at a distance of
10 inches below the polycarbonate sheet. The crucible is posi-
25 tioned so that its longitudinal axis is transverse to the longitu- ;
dinal axis and khe direction of travel of the polycarbonate test
panel thereby enabling the volatilized quartæ material to be
evenly deposited across the entire width of the test panel as it
passes over the cruicible. The vacuum deposition chamber is
maintained at a pressure of approximately 1 x 10-4 mm Hg and the
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polycarbonate test panel is transported across the crucible at a
rate of l foot per minute. A coating of silicon dioxide 3 microns
thick is evenly and uniformly deposited on the polycarbonate pa~el.
EXAMPEE 4
A polycarbonate test panel prepared substantially in accord~
ance with Example l and precoated substantially in accordance
with Example 3 is placed into a vacuum deposition chamb~r contain-
ing a cruicible about which is disposed a radio frequency induction
coil, said coil being connected to a Pachydyne~ 50 Induction
~eating Power Supply operating at between 15 30 Kw. The crucibler
which contains quartz, is located lO inches below the polycarbonate
test panel. The crucible~ is positioned so that its longitudinal
axis is transverse to the longitudinal axis and the direction of
travel of the polycarbonate test panel thereby enabling the vola-
tilized quartz stream to evenly impinge upon the side of the poly-
carbonate panel facing the crucible and resulting in a silicon
dioxide layer which is evenly and uniformly deposited across the
entire width of the test panel as it passes over the cruicible.
The vacuum deposition chamber is maintained at a pressure of ap-
proximately l x 10-4 mm Hg and the polycarbonate test panel is
transported across the crucibLe at a rate of l foot per minute.
A coating of silicon dioxide 3 microns thick is evenly and uniform-
ly deposited on the precoated polycarbonate test panel.
The glass coated polycarbonate panels prepared in accordance
with Examples 3 and 4 are subjected to a series of tests to
determine the durability of adhesion of the glass coat, protection
a~forded the polycarbonate substrate by the glass coating against
attack by organic solvents, and the abrasion resistance of the
glass coating.
The test to determine the durability of the glass coating in- `
volves subjecting the glass coated samples to a humidity test.
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This humidity test involves subjecting the glass coated samples to ~.
a number of humidity oven cycles, and after each cycle subjecting
said samples to a scribed adhesion test. One humidity oven cycle
consists of placing the sample into a cabinet maintained at 99~
relative humidity and 80-85F, raising the ~emperature to 140F,
maintaining the temperature at 140F for 6 hours, and thereafter
lowering the temperature to 80-85~, at which time one cycle is
complete and the sample is removed and subjected to the scribed
adhesion test. The scribed adhesion test consists of using a
multiple blade tool to cut parallel grooves about 1 mm apart
through the coating into the polycarbonate substrate, rotating the
sample 90 and repeating the cutting process thereby forming a grid
pattern of 1 mm squares cut into the coating and substrate, and
applying an adhesive tape over the cross~hatched area and quickly
lS pulling said tape off. A sample fails the adhesion test if any of
the coating on any of the squares is pulled off. The results of
this test are set forth in Table II~ -
TABI,E II `
Humidity Test
No. oE cycles in humidity oven `
after which sample fails scribed
Example No. adhesion test
3 1
4 Passes adhesion test after 10
cycles
The determination of the protection afforded against solvent
attack of the polycarbonate substrate by the glass coating is
accomplished by stressing an uncoated sample and -the glass coated
~amples to about 1,000 psi, and thereafter contacting for a period
of 15 minutes the uncoated sample and the glass coated surface of
the coated samples with a solvent mixture comprised, in parts by
volume, of 100 parts methylene chloride, 100 parts chloroform,
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5 parts methylethyl ketone, and 25 parts benzyl alcohol. After the15 minute exposure to the solvent mixtures, the samples are air
dried and subjected to visual observation. The results are set
forth in Table III.
TABLE III
Example No. Results of Visual Observation
1 Extreme cloudiness of sample due
to etching and surface pitting as
a result of surface chemical at-
tack by solvent mixture.
3 Moderate cloudiness oE sample due
to etching and surface pitting as
a result of surface chemical at-
tack by solvent mixture.
15 4 Clear sample indicating no etching
or surface pitting of polycarbon-
ate substrate by solvent mixture.
The abrasion test is one wherein test panels having a 1/4
inch diameter hole cut in the center are subjected to a Taber
Abraser. The Taber Abraser is equipped with CS-lOF wheels which
are resurfaced every 200 cycles by abrading for 25 cycles on an
S-11 refacing disc. The weights used in combination with the
CS-lOF wheels are 500 gm. weights. Initial measurements of the
% Haze are made at follr places around -the future wear track of the
sample using a Gardner Hazemeter. The sample is abraded for 100
cycles, cleaned with isopropanol, and the % Haze is remeasured at
the same four places. The four differences in % Haze are calcu-
lated and averayed to give the a % Haze. The results are set
forth in Table IV.
T~sLE IV
Abrasion Resistance
Example No. ~ % Haze
,
1 34
3 4.1
35 4 3-5
. , .
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,
As can be seen from Table IV, the protection provided the pol~
carbonate substrate by a glass coating vapor deposited upon a
primed polycarbonate panel i5 substantially the same as that pro
vided by a glass coating vapor deposited on an unprimed polycar-
bonate panel. However, as seen from Tables II and III, the glasscoating which is vapor deposited on a polycarbonate panel primed
in accordance with the present invention results in a coating
having a much superior durability after exposure to humidity and
provides a much greater degree of solvent resistance than does a
glass coating which is vapor deposited on a polycarbonate panel
which is not primed. This results in a glass coated polycarbonate
panel which can be utilized successfully in many commercial ap-
plications.
Having now fully described the invention, it will be apparent
to one of ordinary skill in the art that many changes and modifi-
cations can be made thereto without departing from the spirit or
scope of the invention as set forth herein.
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