Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2.~04~ RD-14529
This invention relates to improved resinous
articles of manufacture, and more particularly to articles
containing an abrasion-resistant coating with improved
adhesion and resistance to light-induced degradation.
Various industrial resins are in wide use for
molding of structural articles and also, in transparent
sheet form, as shatterproof substitutes for glass. Aromatic
polycarbonates are examples of such industrial resins.
One of the problems with their use is susceptibility to
damage by solvent action and abrasion.
This problem is typically overcome by coating the
surface of the resin with an abrasion-resistant coating,
sometimes referred to hereinafter as a "hardcoat". Many of
such hardcoats are polysiloxane resins containing colloidal
silica; they are frequently designated hereinafter as
"silicone hardcoats". While silicone and other hardcoats
serve this purpose quite well, their adhesion to the base
resin is frequently inadequate, necessitating the use of an
adherent primer coating between the base resin and the
2C hardcoat.
A second problem which frequently arises is the
tendency of the base resin to degrade and discolor upon
exposure to light. Such degradation is generally accepted
as being the result of exposure of the resin to ultraviolet
radiation. It is frequently suppressed by a compound which
serves as an ultraviolet screening agent or similar ultra-
violet degradation inhibitor. Such compound may be incor-
porated in or coated on the base resin or incorporated in
the primer coating or hardcoat.
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Unfortunately, the use of such screening agents,
especially as part of the primer or hardcoat, introduces
still other problems. Among these are decreased adhesion of
the hardcoat even when a primer is used, loss of abrasion
resistance in the hardcoat, cracking of the hardcoat, and
the presence of a pink color in the hardcoat after curing.
It is believed that some of these problems arise from the
presence of the screening agent in the hardcoat, either
originally or as the result of diffusion from the primer.
The pink color is most often observed when the screening
agent is originally present in the hardcoat.
A principal object of the present invention,
therefore, is to provide improved resinous articles charac-
terized by resistance to abrasion and to ultraviolet degra-
dation.
A further object is to provide resinous articleswith an abrasion-resistant hardcoat whose adhesion is
promoted by an improved primer containing an ultraviolet
screening agent permanently incorporated therein.
A further object is to provide improved polycar-
bonate articles containing silicone hardcoats characterized
by excellent adhesion and resistance to discoloration and
ultraviolet degradation.
A still further object is to provide articles as
described hereinabove containing an improved acrylic primer
coating between the base resin and the hardcoat layer.
Other objects will in part be obvious and will in
part appear hereinafter.
The present invention is based on the discovery
that certain polymerizable ultraviolet screening agents may
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be copolymerized with primer-producing monomers to form a
polymeric primer which provides excellent adhesion of the
hardcoat to the base resin as well as excellent resistance
to ultraviolet degradation. At the same time, it has
unexpectedly been found that the screening moieties in the
primer layer prevent discoloration of the hardcoat even when
a screening agent is also present therein.
In its broadest sense, therefore, the subject
matter of the present invention is a solid article of
manufacture comprising (A) a resin base; (B) an abrasion-re-
sistant surface coating on said resin base; and (C) a primer
coating between said resin base and said surface coating,
said primer coating comprising an addition copolymer of a
monomer mixture comprising (C-l) a major proportion of at
least one acrylic monomer and (C-2) a minor proportion of at
least one ethylenically unsaturated monomer having the
formula
(I) CH2=C-Z-Xl,
R
wherein Rl is hydrogen or methyl, Z is a substantially inert
linking group, and Xl is an ultraviolet degradation-inhibit-
ing moiety.
The articles of manufacture of the present inven-
tion may be formed in conventional manners such as injection
molding, extrusion, casting, cold forming, vacuum orming,
blow molding, compression molding or transfer molding. They
include both finished articles and stock material, the
latter being exemplified by sheets and films. Transparent
articles are preferred and are most often provided in sheet
form.
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Component A, the resin base, can comprise any
suitable industrial resin. Illustrative resins are the
aromatic polycarbonates, polyphenylene oxides, acrylics,
thermoplastic polyesters, polyamides, polyimides, acrylo-
nitrile-styrene copolymers, acrylonitrile-butadiene-styrene
terpolymers, polyethylene and polyvinyl chloride. The
invention is particularly applicable to polycarbonates and
freguent reference will be made to them hereinafter.
However, it should be understood that other suitable indus-
trial resins may be substituted for polycarbonates whenappropriate.
The polycarbonates are well known in the art; they
are ordinarily prepared by reacting a polyhydroxyaromatic
compound with a carbonate precursor such as phosgene, a
haloformate or a carbonate ester. A dihydroxyaromatic
compound may be used, whereupon a linear polymer containing
units of the formula
01
-0-A-0-C- ,
;
wherein A is an aromatic radical derived from the dihydroxy-
aromatic compound, is obtained. Alternatively, a combina-
tion of dihydroxyaromatic and trihydroxyaromatic or other
polyfunctional compounds may be used whereupon the resin may
be branched or crosslinked.
Most often, the polycarbonate is prepared exclu-
sively from one or more dihydroxyaromatic compounds.
Suitable compounds of this type which may be used for the
preparation of polycarbonates are disclosed in a large
number of U.S. patents including the following
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3,161,615 3,666,614
3,220,973 3,875,256
3,312,659 3,989,672
3,312,660 4,377,662.
3,313,777
From the standpoint of the present invention, the preferred
polycarbonates are those prepared from 2,2-bis(4-hydroxy-
phenyl)propane, referred to hereinafter as "bisphenol A".
Other examples of suitable base resins are the
polyester-polycarbonates of the type obtained by the reac-
tion of at least one polyhydroxyaromatic compound with a
mixture of phosgene and a dicarboxylic acid chloride such as
isophthaloyl chloride. Such polyester-polycarbonates are
alsc known in the art and are disclosed in a number of
patents and publications.
The molecular weight of the base resin is not
critical, and those skilled in the art will easily be able
to determine suitable molecular weight ranges. In the case
of polycarbonates, for example, satisfactory molecular
weights are generally represented by intrinsic viscosities
within the range of about 0.3-1.0, preferably about
0.4-0.65, as measured in methylene chloride at 25C.
Component B, the abrasion-resistant surface
coating or hardcoat, is often adhered to the entire surface
of the base resin article. It is within the scope of the
invention, however, for the hardcoat to be adhered to only a
portion of said surface, as, for example, to only one
surface of a transparent sheet.
A variety of hardcoats may be used as component B;
included are silicone hardcoats, various organic coatings,
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RD-14529
glass coatings, metal oxide coatings and evaporative or
"sputtered" coatings. Silicone hardcoats are preferred, and
reference to them will fre~uently by made hereinafter;
however, it should be understood that other types of hard-
coats may be substituted for silicone hardcoats when appro-
priate.
Typical coating compositions for producing sili-
cone hardcoats comprise aqueous alcohol solutions of partial
condensates of silanols of the formula RSi(OH)3, wherein R
is an alkyl radical containing 1-3 carbon atoms or an aryl
radical. Colloidal silica is usually also present in
dispersion. Typically, such compositions are prepared by
adding an aqueous dispersion of colloidal silica to a
solution in aqueous alkanol of an alkyl- or aryltrialkoxy-
silane which contains a small proportion of an acetoxyreagent such as acetic acid or an alkyltriacetoxysilane. A
two-phase system is initially formed; upon standing for
about 6-8 hours at a temperature in the range of about
20-40C, a single phase forms. During this time and upon
further hydrolysis, typically for a period of about 24-48
hours depending on the desired final viscosity, the tri-
alkoxysilane is hydrolyzed and partially condensed to form
siloxanols. The degree of condensation and the viscosity of
the coating composition vary with time and with the pH of
the original composition, which, for maximum shelf life,
should be maintained within the range of about 3-8 with the
exact value dependent to some degree on the chemical nature
of the composition.
The coating composition may optionally contain
other ingredients. For example, polysiloxane polyether
copolymers are effective as flow control agents, and func-
tionally terminated oligosiloxanes wherein the end groups
are hydroxy, alkoxy or amino react with the siloxanols upon
curing improve the crack resistance of ~he hardcoat. Also
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contemplated are ultraviolet screening agents known in the
art, which typically contain functional groups of the type
disclosed hereinafter.
Silicone hardcoat-forming compositions as des-
cribed hereinabove are known in the art and are disclosed,
for example, in the following U.S. patents:
3,986,997 4,368,235
4,239,798 4,368,236
4,278,804 4,410,594
Other ar~-recognized variations of said coating
compositions may be employed in the present invention.
_
Component C, the primer coating, is produced by
polymerization of a monomer mixture comprising two essential
reagents. Reagent C-l, present in major proportion, is at
least one acrylic monomer. The term "acrylic monomer" as
used herein includes acrylic and methacrylic acids and their
derivatives, chiefly esters and amides. Acrylamide, methyl
acrylate, ethyl acrylate, methyl methacrylate and ethyl
methacrylate are illustrative, and of these the esters
(especially of alkanols containing 1-4 carbon atoms) are
preferred; the methacrylate esters are most preferred
because their polymers exhibit particularly high weather
resistance. The preparation and use of acrylic primers is
disclosed in the aforementioned U.S. Patent 4,239,798.
Reagent C-2 is characterized by formula I in which
Rl may be hydrogen or methyl. The Z value is a linking
group which is substantially inert under prevailing colldi-
tions of use. Suitable linking groups will be apparent to
those skilled in the art; illustrative moieties which may be
~ ~3C~
RD-14529
present therein are hydrocarbon radicals free from ethylenic
and acetylenic unsaturation, oxygen atoms, NH and NR3 groups
wherein R3 is a hydrocarbon radical free from ethylenic and
acetylenic unsaturation, carbonyl groups and sulfone groups.
Examples of suitable Z values are the following:
Alkylene, especially lower alkylene ~the term
"lower" denoting up to 7 carbon atoms) and most especially
methylene.
Radicals of the formula
(II) -C-0-R - ,
wherein R2 is an alkylene radical, especially ethylene or
propylene and most especially ethylene.
Radicals of the formula
0 O
Il 2 ;~
(III) -C-0-R -NHC- ,
wherein R2 is as defined above.
Especially preferred as Z are -CH2- and groups
having formula II wherein R2 is ethylene and is attached to
Xl.
The Xl value is an ultraviolet degradation-inhib-
iting moiety. Many of such moieties are known in the art,
and any of them are useful according to the present inven-
tion. Examples are hydroxybenzophenone, hydroxyarylbenzo-
triazole, benzoate ester, phenyl salicylate, benzylidenemal-
onate and aryl-substituted 2-cyanoacrylate and 2-cyanocro-
tonate moieties. A large number of moieties of these types
are disclosed in the aforementioned U.S. Patent 4,410,594
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RD-14S29
and in ~ _ _f_Pol~mer Science and Techno~y, Vol.
14, pp. 125-148, especially Table 4 at pp. 140-141.
Particularly preferred as the Xl moiety according
to this invention are radicals of the formula
x GH
X3 ~ 1~ ~ -
wherein each of x2 and X3 is hydrogen or hydroxy. Prefer-
ably, each of x2 and X3 is hydrogen. Also included, how-
ever, are polyhydroxy compounds such as those in which X or
both x2 and X3 are hydroxy.
Suitable compounds of formula I may be prepared by
known reaction sequences starting from precursors containing
the appropriate ultraviolet degradation-inhibiting moieties.
Examples of suitable reactions are esterification, reaction
with ethylene oxide followed by esterification, and the
like. A number of such compounds are known in the art;
examples are 2-hydroxy-4-acryloxyethoxybenzophenone, 2-hy-
droxy-4-methacyloxyethoxybenzophenone, 2-hydroxy-4-al-
lyloxybenzophenone and 2-hydroxy-4-(2-hydroxy-3-methacryl-
oxypropyl)benzophenone. These compounds and similar ones,
and methods for their preparation, are disclosed in the
following U.S. patents:
3,215,665
3,313,866
4,310,650.
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Other monomers may also be present in the monomer
mixture for component C, typically in amounts up to about
25% by weight based on reagent C-l. Examples are ethylenic-
ally unsaturated silane monomers, including such materials
S as vinylsilanes and ~-methacryloxypropyltrimethoxysilane,
and polyfunctional acrylates as described hereinafter when
the primer coating is produced by polymerization of a
deposited monomer layer.
The composition from which the primer coating is
deposited is typically a solution in a substantially inert
organic liguid of an addition copolymer prepared by polymer-
izing a mixture containing about 5-35% by weight of reagent
C-2, with the balance being reagent C-1 or a combination
thereof with any other monomers present. Organic liquids
which may be employed include alcohols, ethers, esters and
the like; examples thereof are ethylene glycol, ethylene
glycol monomethyl ether, ethylene glycol dimethyl ether,
ethylene glycol monobutyl ether, diethylene glycol and
ethers thereof, butyl acetate, ethylene glycol diacetate,
and mixtures of the foregoing. Copolymer emulsions or
suspensions may also be used. The total monomer concentra-
tion in the solution, emulsion, suspension or the like is
typically about 5-50% by weight.
Polymerization is usually initiated by the action
of one or more free radical polymerization initiators such
as benzoyl peroxide, tertiary butyl hydroperoxide, acety~
peroxide, hydrogen peroxide, azobisisobutyronitrile, per-
sulfate-bisulfite, persulfate-sodium formaldehyde sulfox-
ylate, chlorate-sulfite and the like. Polymerization by
techniques such as ultraviolet, electron beam or plasma
irradiation is also contemplated. Chain transfer agents,
typically mercaptans such as butanethiol or dodecanethiol,
may be present in the solution. Polymerization most often
precedes deposi.tion of the primer on the base resin, but
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deposition followed by polymerization is also possible. In
the latter case, crosslinking monomers such as polyfunc-
tional acrylates may be present in m~nor amounts, typically
up to about 5% by weight of the monomer mixture. The primer
coating composition may additionally contain such materials
as antioxidants, flow control agents, quenchers, dyes,
pigments, surfactants, flatting agents and the like.
The preparation of primer coating compositions
useful according to this invention is illustrated by the
following examples. All parts, percentages and other
proportions in the examples herein are by weight unless
otherwise indicated.
EXAMPLES 1-3
Solutions of 50 grams of a mixture of ethyl
methacrylate and reagent C-2, 0.25 gram of azobisisobutyro-
nitrile and 0.15 gram of dodecanethiol in 200 ml. of toluene
were heated at 80C under nitrogen for 18 hours, with
stirring. An additional 0.125 gram of azobisisobutyro-
nitrile was then added and heating was continued for four
hours. The solutions were poured into methanol, the precip-
itated amorphous copolymers were removed by filtration and 6
parts of each was dissolved in 94 parts of a solvent mixture
consisting of 80% ethylene glycol monobutyl ether and 20%
ethylene glycol diacetate. The constitutions of the compo-
sitions thus obtained are listed in Table I.
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TABLE I
Reagent C-2
Exam~le Percent of
monomer mixture Identitv
2-Hydroxy-4-acryloxy-
1 ethoxybenzophenone
2-Hydroxy-4-methacryl-
2 oxyethoxybenzophenone
2-Hydroxy-4-allyloxy-
3 benzophenone
In the practice of the present invention, the
primer coating is first formed on the base resin article by
methods which may include conventional coating operations
such as flowina, spraying, dipping, brushing, roller coat-
ing, spin coating, drawing down or the like followed by
removal of any solvent or other inert liquid by evaporation
and then by drying, typically at a temperature within the
range of about 20-150C and preferably 50-150C. The thick-
ness of the primer coating thus applied is typically sub-
stantially uniform and is about 0.002-1.0 mil, most often
about 0.01-0.1 and preferably about 0.02-0.08 mil.
The hardcoat is then applied to the pri~ed
article, ordinarily by one of the coating operations pre-
viously recited, and is subsequently cured by heating at a
temperature within the range of about 75-150C, optionally
in the presence of a condensation catalyst. The thickness
of the hardcoat is usually about 0.1-0.7 mil, preferably
about 0.2-0.3 mil. The product of these operations is an
article according to the present invention; its appearance
and color are substantially those of the base resin and it
is protected from ultraviolet degradation and discoloration
and from damage from abrasion, solvent action and the like.
~2~3~ RD- 14529
The preparation and testing of articles of this
invention is illustrated by the following examples.
EXAMPLE 4
Primer coating compositions prepared according to
Examples 1-3 were flow-coated on bisphenol A polycarbonate
panels, drained for 15 minutes and dried at 130C for lS
minutes. The primed panels were then flow-coated with
commercial silicone hardcoat coating compositions prepared
as follows:
Hardcoat I: A suspension in 2-methyl-1-propanol
of 2 parts of methyltrimethoxysilane and 1 part of an
aqueous colloidal silica suspension, in an amount to provide
20% solids after standing for several hours.
Hardcoat II: A combination of Hardcoat I and
10-15% (based on solids content) of a silanated derivative
of 2,4-dihydroxybenzophenone of the type disclosed in the
aforementioned U.S. Patent 4,278,804.
The coated panels were drained for 30 minutes and
cured at 130C for 90 minutes. They were then subjected to
consecutive 8-hour cycles of exposure to fluorescent ultra-
violet light at 70C and 4-hour cycles of high humidity at
50C. The adhesion of the hardcoats was tested by scribing
with a crosshatch cutter, applying pressure-sensitive tape
to the crosshatched area and rapidly removing the tape.
Primer thicknesses were determined by etching away the
primer with sulfuric acid and tracing across the etched area
with a thickness-measuring instrument.
The results are given in Table II. The control
was similarly prepared using as the primer an ethyl meth-
acrylate homopolymer solution. Adhesion ratings are given
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in hours to failure; i.e., to the point when hardcoat was
removed upon removal of the pressure-sensitive tape.
TA~LE II
Primer thickness, Failure time,
5 Identity mils Hardcoat hrs.
Ex. 1 0.02 I 570
Control 1 0.02 I 170
Ex. 1 0.02 II '3930
Ex. 2 0.07 II '3690
Ex. 3 0.02 II 2903
Control 2 0.04 II 640
EXAMPLE 5
A test panel similar to those of Example 4 was
prepared using the primer coating composition of Example 2,
and a silicone hardcoat solution identical to Hardcoat I t
except that it additionally contained 4% (based on solids
- content) of 2,4-dihydroxybenzophenone. The resulting panel
was transparent and colorless. A control panel, prepared
identically except that the primer was a solution of 5 parts
of an ethyl methacrylate homopolymer and 10 parts of 2,4-hy-
droxybenzophenone in 85 parts of ethylene glycol monobutyl
ether, was a distinctly pink color.
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