Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
n
F~ eld of the Inv~tl on
This lnven~ion r~lates to coati~g c~>mposltions
particularl~ to coalting co~pos:Ltions containing ~lu~inum
flake, more part:icularly to an lmproYe~e~t in these coatirlg
CODI~O~ t~ons .
Prior Art
__
Pollution prol~leras caused by conve~tional p~int~
uhieh utili~e org~nlc ~olv~nts are forclr~g the manufacturing
10 indu~trles, such ~s th~ automo~ile and ~ruck manu~a~turing
industri es 9 to tur~ to
(1) dry pos~der coating co~LpositlonsJ
( 2 ~ water-based co~t i ng compos ~tions
t~at contain only ~all amount~ of organic
~olYents, or
( 3 ) high solid~ coating compos ~ tlons, 1 . e~,
a composltion that cont~ins very littleJ if any~
liquid c~Lrr 1 er.
Alumi~um flake h~ been utllized in conventiQr~al
20 solvent-ba~ed coakin~s co~positions to provide high quality
~i3nishe~ with ~n ~xceptio~al glamor ~ppearance. "~L~mor"
i8 a terrn used in the coating art to indica~ that property
o~ a metallic plgmented coating which cau~e~ the inten~ity
o~ light re~lected from lthe coat~d sub~rate to vary
markedly acc~rdi2lg tv ~he ~ngle from ~hich lt is ob~erved, as
well a~, providing sparkle ~Lnd an illu~ion o~ ~epth in the
coa~ing. However7 standard, i. e., untreated aluminum flake,
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pro~ides poor glamor appearance in dry powder and high
solids coating compositions, and is unstable in water-based
coating compositions.
When standard aluminum flake is added to a dry
powder coating composition, the coating prepared is usually
poor in appearance and exhibits a salt and pepper e~fect
due to inefec~ive mixing. Additionally~ in both dry
powder and high solids coating compositions, any in-
compatible material will float to the surface~ This
diminishes the ~lamor e~fect. In those coati~gs where
the flake is not properly aligned, it will also break
~hrough the surface of the coating.
In water-based coating compositions, standard
aluminum ~lake will both react with water in the compo-
sition to form hydrogen gas, particularly at elevated
temperatures~ creating a safety hazard, and te~ to settle
to form a hard cake in the w~ter-basedcoating composition.
The improved coating composition of this in~
vention overcomes these aforementioned problems o~ the art.
SUMMARY OF THE INVENTION
According to the present invention, there is
provided an improvement in coating compositions containing
aluminum flake; the improvement prior to placing the
flake into the coating composition comprises:
coating the aluminum flake with mono-ethyleni-
cally unsaturated silane and reacting the silane coated
flake with acrylic monomers having functiona~ groups to
form an acrylic polymer topcoat on the flake.
DETAILED DESCRIPTION OF THE INVENTIO~
The improved coating composition of this in-
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~ention utilizes a treated aluminum flake. The treat-
ment of the aluminum flake
(1) coated the Elake,
(2) prevents undesired reactions between
flake or its impurities with the remainder of
the composition,
(3) removes incompatible materials from
the surface of the flake, and
(4) provides an acrylic topcoating on
the flake with organo functional groups on
the surEace which can react a polymer used
in the coating composition.
This treatment prevents all of the previously mentioned
problems and produces a coating having an excellent appear-
ance.
Coating compositions containing aluminum flake
are well known in the art, as evidenced by the following
patent and patent applications:
Armour, Canadian Patent 880,950, issued 1971-09-14;
Pettit, U.S. Patent 3 998 768, issued 1976-12-21;
Fang, Belgian Patent 806 641, issued 1974-04-29;
Fang, U.S. Patent 3,839 254, issued 1974-10-01.
These coating compositions are applied to substrates
according to conventional coating techniques; techniques
in which, for example, the coating composition is sprayed,
brush coated, flow coated, dip coated, or electrocoated onto
a substrate. The substrate can be, for example, a primed or
non-primed metal, glass, plastic or fiber reinforced plastic,
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plastic such as st~rene, co?ol~mers o~ st~rene, polypropyl-
ene, and the like. These co~ing compositions are espe-
cially suited for use as ext~ior finishes o~ automobile-or
truck bodies.
Aluminum flake useful in this invention can be
as dry particles or as a paste in which the aluminum
particles are dispersed in an organic solvent Usuall~
the aluminum 1ake is in a paste, as it is most easily
obtained commercially in that form~ The percentage by
weight of aluminum flake to total wei ~ t of paste is
usuaLly ~rom 30-80%.
Aluminum ~lake itself is generally flat in shape
and has an a~erage largest dimension length greater than
about L0 microns. Usually the particles will have a
largest dimension from about 20 to 50 mi~rons with some
particles being as small as 1 to 5 microns in length.
While it is preferred to use initial flaXe particles
having an av~rage largest dL~ension from 20 to 50 micron~,
larger particles can be used~ up to 100 microns in length.
~rger fLake particles, however, may cause problems with
surface distortion of the coa~ing. GeneralLy the amount
of flake particles required to give any desired appear-
ance effect depends on the density of the flake and its
geometry. The important geometrical factor is the ratio
of length to thickness (aspect ratio). Generally an in-
crease in ~spect ratio will result in a decrease in flake
concentration in order to obtain the same appearance. The
aluminum~flake is usually present in a dry powder or a
high solids coating composition at a concentration of about
0.05 to 10% and preferably in the range of about 0.1 to ~O
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by weight of the composition. For conventional and aqueous
coating compositions, the flake concentration will nor~
mally be in the range of 0.1 to 4%.
Mono-ethylenically unsaturated silanes used
to treat the aluminum flake have the formula RSiX3 wherein
R is a mono-ethylenically unsaturated group attached to
the silicone atom in a thermally and hydrolytically
stable manner and ~ is a hydrolyzable group. The R
group can be separated from the silicone atom by an
alkyl chain.
Silanes are applied onto the aluminum flake
surface by means of dilute liquid solutions, i.e., solutions
containing about 0.2 to 5.0~ by weight of silane. Solubility
and stability of the silane in the solution becomes an im~ortant
consideration since silanes represent a variety of different
chemical molecules, it is not surprising that solubilities
also differ.
The following are general statements concerning
silanes:
1. Of the factors which determine hydrolysis
rate of silanes, solution pH is generally the strongest.
For most silanes, ma~imum hydrolysis rate is achieved
at a pH of three to five. Some silanes carry their own
catalyst in the form of by-products of hydrolysis.
2. In time, all aqueous silane solutions will
reach equilibrium levels of homopol~vmer (silane monomers
which have reacted together through the silicon-
functional groups to form a siloxane polymer).
~30
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catalyst r
RSi(OH)3 ~ -0-Si-O ~ H20
O
-o-si-o-
R
The following conditions effect this equilibrium:
a. pH (a range of four to ~ive generall~ ~avors
maximum monomer content) and
b. Silane concentrations.
Some of these homopolymers quickly lose water solubility as
the degree of polymerization is increased. Weak polymeric
gels which are insoluble may result. It is generally
desirable to retain the silane as monomer or dimer, in order
to preserve its coupling functionality.
The preferred silanes used to treat aluminum
flake are:
(1) vinyltrimethoxysilane
CH2=CH Si(OCH3)3
(2) vinyltrichlorosilane
CH2=~H Si(CL)3
(3) vinyltriethoxysilane
CH2=CH Si(OC2Hs)3
(4) vinyl tris(betamethoxyethoxy)silane
CH2=C~ Si(OCH2~H2oCH3)2
(5) gamm~-methacryloxypropyl-trimethoxysilane
CH3 O
.,
CH2=C - C - (CH2)3 Si(OCH3)3
.
.
The preferred silanes is #5 above.
It is believed that this invention improves
the appearance o~ coating compositions because the
coated aluminum flake has on the acrylic coating surface
pendant ~unctional ~roups of amine, hydroxy, or epoxy.
These pendant ~unctional groups are capable of being
reacted with the polymer of the coating composition.
The monoethylenically unsaturated silane, such
as gamma-methacryloxypropyl-trimethoxysilane, forms a
siloxane coating with pendent ethylenically unsaturated
on the aluminum flake surface. A mixture of acrylic
monomers, initiator, and chain transfer agents are added
to the silane treated ~lake such that the monomers can
react at the surface of the aluminum flake producing
an acrylic coating. The types of monomers are varied so
as to provide the desired type of reactive group at the surface.
Acrylic monomers which can be used along with
acrylic monomers that provide amine, hydroxy or epoxy
groups are alkyl acrylates and alkyl methacrylates
ha~in~ 1-12 carbon atoms in the alkyl groups. Typical
alkyl acrylates and alkyl methacrylates are methyl
methacrylate, ethyl methacrylate, propyl methacrylate
isopropyl methacrylate, butyl methacrylate pentyl metha-
crylate, hexyl methacrylate, 2-ethylhexyl methacrylate,
nonyl methacrylate, lauryl methacrylate, ethyl acrylate,
propyl acrylate, butyl acrylate, pentyl acrylate, hexyl
acrylate, octyl acrylate, nonyl acrylate lauryl acrylate
and the like.
Typical acrylic monomers that pro~ide hydroxyl
groups are hydroxyalkyl acrylates and hydroxyalkyl
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methacrylates such as hydroxyethyl acrylate, hydroxy~ropyl
acrylate, hydroxybutyl acrylate, hydroxyethyl methacylate,
hydroxypropyl methacrylate, hydroxybutyl methacrylate and
the like.
Glycidyl acrylate and glycidyl methacrylate are
acrylic monomers that provide epoxy groups.
Typical monomers that provide amine groups are
alkylaminoalkyl acrylates and methacrylates such as
diethyaminoethyl methacrylate, dimethylaminoethyl metha-
crylate, diethylaminoethyl acrylate, dimethylaminoethyl
acrylate, dipropylaminoethyl methacrylate, methylethylamino-
ethyl methacrylate, butylaminoethyl methacrylate, tertiary
butylaminoethyl methacrylate and the like.
Generally polymerization initiators and chain
transfer agents are used to form the acrylic coating on
the flakes. Typical initiators are azo-bis~ gamma-
dimethylv~leronitrile), benzoyl peroxide, t-butylperoxy-
pivalate, azo-bis-isQbutyronitrile, and the like. Typical
chain transfer agents can be used to contr~ the molecular
20 weight, such as dodecyl mercaptan, and mercaptoethanol.
Mercaptoethanol is preferred to provide acrylic polymers
with terminal hydroxyl groups.
The reaction in which the silane is coated upon
the aluminum flake utilizes at least 100%, preferably
200-lO00~, more preferably 300-400~, of the quantity of
silane required to form a monolayer on the surface area
of the flake. The amount of silane required is determined
by first measuring the surface area of the aluminum flake
using conventional techniques, then determining the mini~
30 mum surface area coverage of the silane to be used using
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conventional techniques, and then using the percentage
desired of the minimum amount of silane required to
cover the aluminum flake.
The surface area of aluminum flake i5 usually
in ~he range of 1-10 meter 2/gram. The minimum surface
area coverage of silane is usualLy in the range of about
200-500 meter /gram of silane depending on the chemical
structure and molecular weight o~ the silane molecule.
The reaction is carried out for a period of
time and at a temperature sufficient to coat the aluminum
flake with the silane. Preferably, the temperature is
about 50-100C. and the period of time is 1-5 hours. The
lower the temperature, the longer the period of time re-
quired. Most preferably, the temperature is about 60C.
and the period of time is about 1 hour.
Conventional polymeri2ation times and temperatures
are used to from the acrylic coating on the flake. Generally
temperatures of 50-150C are used with a polymerization
time of 0.5-4 hours.
It has been found that other treatments for
aluminum flake improve the appearance of coating compo-
sitions containing the treated aluminum flake to varying
degrees.
Dispersing aluminum flake in polar solvents, e.g.,
butyl cellosolve, ethyl cellosolve, cellosolve acetate~ etc.,
has an effect in improving the appearance of both dry powder
and high solids coating compositions.
Treating aluminum flake with ammonium pkospilate
provides improved appearance in dry powder coatings over
formulations using conventional aluminum pastes. The treat-
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ment consists of displacing long chain organic acids which
are commonly used to treat aluminum flake with the phos-
phate ion. The treatment removes material from the alumi-
num flake surface which causes poorer appearance because
the material is incompatible with the vehicle system.
The following example illustrates the
invention.
E~AMPLE
Mix together, in a 3-liter round bottom resin
kettle (equipped with a Teflon~ stirrer, M2 inlet,
thermometer, reflux condenser, and additional funnel):
186.6 g. Aluminum flake paste
(Silhexline* SS-3199-A.R.,
sold by Silberline Manu-
facturing Company, Inc.)
which has been washed
with Cellosolve* acetate.
l,OOOg.
Stir the resultin~ mixture at 300 revolutions per minute
under a slow stream of N2 for 5-10 minutes until complete
dispersion is affected.
Add slowly to the mixture
15.92 g. Gamma-methacryloxypropyl-
trimethoxy silane (A-174
Silane* sold by Union
Carbide Corporation)
.002 g. Hydroquinone
Stir the resulting slurry at room temperature (300
revolutions per minute) for 20 minutes, then heat slowly
to 60C and maintain for 3 hours.
Add a solution of
0.014 g. Dimethylvaleronitrile
(VA~O~ 52 sold by E. I.
du Pont de Nemours and
Company).
*Denotes trade mark -11-
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10. ml. Methyl "Cellosolve" acetate
Then add dropwise over a period of 30 minutes, a solution of
4.11 g. Methyl methacrylate
1.39 g. Ethylhexyl acrylate
0.36 g. Hydroxyethyl acrylate
0.036 g. VA~O~ 52
25. ml. Methyl "Cellosolve" acetate
When the addition is complete, maintain a temperature of
60C. for 20 minutes. Cool to room temperature and wash
the flake paste several times with methyl cellosolve
acetate. The percent solids of the silane-coated aluminum
flaXe paste is 67.5 ~ O. 2%o
ESC~ analysis of the coated flake paste produces
the ~ollowing results:
Charge Corrected (C - 284~0) Bindinq Enerqies (e~)
Cls Cls ls Nls A12p A12p Si2p
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Hydro- Car-
carbon bonyl Amine Trivalent Metal Silane
284.0 287.7 531.6 399.5 73.3 70.6 101~0
~ormalize _ eak Intenslties (Coun_s,~Sec.)
C C O ~ Al Al Si
ls ls ls ls 2p 2p 2p
.
Hydro- Car-
carbon bonyl Amine Trivalent Metal Silane
15086 1650 8430 106 5017 3302 383
The resulting coated flake was used in water
based acrylic coating composi.tion, acrylic powder coating
composition and acrylic high solids coating composition.
Each of the above compositions was applied to primed
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steel substrates and baked using conventional procedures.
In each case a finish resulted that had a good appearance
and excellent metallic glamour.
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