CA1144823A - Treatment of aluminum flake with unsaturated silane and acrylic monomers - Google Patents
Treatment of aluminum flake with unsaturated silane and acrylic monomersInfo
- Publication number
- CA1144823A CA1144823A CA000338812A CA338812A CA1144823A CA 1144823 A CA1144823 A CA 1144823A CA 000338812 A CA000338812 A CA 000338812A CA 338812 A CA338812 A CA 338812A CA 1144823 A CA1144823 A CA 1144823A
- Authority
- CA
- Canada
- Prior art keywords
- silane
- flake
- alkyl
- aluminum flake
- improvement
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE
An improvement in coating compositions containing aluminum flake is provided. The improvement is coating the aluminum flake with a mono-ethylenically unsaturated silane and then reacting the silane coated flake with acrylic monomers having amine hydroxyl or epoxy groups to form an acrylic coating prior to placing the aluminum flake into the coating composition.
An improvement in coating compositions containing aluminum flake is provided. The improvement is coating the aluminum flake with a mono-ethylenically unsaturated silane and then reacting the silane coated flake with acrylic monomers having amine hydroxyl or epoxy groups to form an acrylic coating prior to placing the aluminum flake into the coating composition.
Description
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, .
- - ~
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-- . .
- ~ ~
;d 3 ~ention utilizes a treated aluminum flake. The treat-ment of the aluminum flake (1) coated the Elake,
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, .
- - ~
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-- . .
- ~ ~
;d 3 ~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, ~ .
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
-8~23 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 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
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, ~ .
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
-8~23 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 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 ., 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 .:: .
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 ' - , .
.' ~ ~ ~ ... . .
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-. ,~ .
~ . ~
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-'' ~' ' ' ~ ... .
- : ~
' 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 . . ~
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 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 ..
, ,3 steel substrates and baked using conventional procedures.
In each case a finish resulted that had a good appearance and excellent metallic glamour.
.
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 .:: .
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 ' - , .
.' ~ ~ ~ ... . .
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-. ,~ .
~ . ~
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-'' ~' ' ' ~ ... .
- : ~
' 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 . . ~
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 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 ..
, ,3 steel substrates and baked using conventional procedures.
In each case a finish resulted that had a good appearance and excellent metallic glamour.
Claims (10)
1. An improvement in a coating composition containing aluminum flake, the improvement comprising:
coating the aluminum flake with a mono-ethylenically unsaturated silane and reacting the coated flake with acrylic monomers having functional groups to form an acrylic topcoat on the flake prior to placing the aluminum flake into the coating composition, wherein the silane is a compound having the structure RSiX3 wherein R is a group containing mono-ethylenical unsaturation and X is a hydrolyzable group and the functional groups of the acrylic monomers are amine, hydroxyl or epoxide.
coating the aluminum flake with a mono-ethylenically unsaturated silane and reacting the coated flake with acrylic monomers having functional groups to form an acrylic topcoat on the flake prior to placing the aluminum flake into the coating composition, wherein the silane is a compound having the structure RSiX3 wherein R is a group containing mono-ethylenical unsaturation and X is a hydrolyzable group and the functional groups of the acrylic monomers are amine, hydroxyl or epoxide.
2. The improvement of claim 1 wherein the R
is separated from the silicone atom by an alkyl group.
is separated from the silicone atom by an alkyl group.
3. The improvement of claim 1 wherein the silane is vinyltrimethoxysilane vinyltriethoxysilane vinyltris(beta-methoxyethoxysilane) or gamma-methacryloxypropyl-trimethoxysilane.
4. The improvement of claim 1 wherein the silane is gamma-methacryloxypropyl-trimethoxysilane.
5. The improvement of claim 1 wherein the aluminum flake has a surface area of 1-10 meter2/gram of aluminum flake, the silane has a minimum surface area average of 200-500 meter2/gram of silane, and silane is present in a concentration of 200-1000% based on the minumum amount of silane required to form a monolayer on the alumlnum flake.
6. The improvement of claim l in whicn the acrylic monomers are an alkyl acrylate or an alkyl metha-crylate or mixtures thereof in combination with a glycidyl acrylate, glycidyl methacrylate, hydroxy alkyl acrylate, a hydroxy alkyl methacrylate, an alkyl amino alkyl acrylate or an alkyl amino alkyl methacrylate.
7. A process for coating aluminum flake comprising (1) coating the aluminum flake with a mono-ethylenically unsaturated silane wherein the silane is R SiX3 wherein R is a group contalning mono-ethylenical unsaturation and X is a hydrolyzable group;
(2) reacting the silane coated aluminum flake with acrylic monomers having an amine, hydroxy, or epoxy group to form an acrylic polymer topcoating on the flake.
(2) reacting the silane coated aluminum flake with acrylic monomers having an amine, hydroxy, or epoxy group to form an acrylic polymer topcoating on the flake.
8. The process of claim 7 in wherein the silane is vinyltrimethoxysilane vinyltriethoxysilane vinyltris(beta-methoxyethoxysilane) or gamma-methacryloxypropyl-trimethoxy silane.
9. The process of claim 7 in which the silane is gamma-methacryloxypropyl trimethoxy silane.
10. The process of claim 9 in which the acrylic monomers are alkyl acrylate or an alkyl methacrylate or mixtures thereof in combination with a glycidyl acrylate, a glycidyl methacrylate, a hydroxyalkyl acrylate, a hydroxy-alkyl methacrylate, an alkyl amino alkyl acrylate, or an alkyl amino alkyl methacrylate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000338812A CA1144823A (en) | 1979-10-31 | 1979-10-31 | Treatment of aluminum flake with unsaturated silane and acrylic monomers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000338812A CA1144823A (en) | 1979-10-31 | 1979-10-31 | Treatment of aluminum flake with unsaturated silane and acrylic monomers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1144823A true CA1144823A (en) | 1983-04-19 |
Family
ID=4115481
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000338812A Expired CA1144823A (en) | 1979-10-31 | 1979-10-31 | Treatment of aluminum flake with unsaturated silane and acrylic monomers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1144823A (en) |
-
1979
- 1979-10-31 CA CA000338812A patent/CA1144823A/en not_active Expired
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