CA2378851A1 - Acyloxy silane treatments for metals - Google Patents
Acyloxy silane treatments for metals Download PDFInfo
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- CA2378851A1 CA2378851A1 CA002378851A CA2378851A CA2378851A1 CA 2378851 A1 CA2378851 A1 CA 2378851A1 CA 002378851 A CA002378851 A CA 002378851A CA 2378851 A CA2378851 A CA 2378851A CA 2378851 A1 CA2378851 A1 CA 2378851A1
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
- C23C2222/20—Use of solutions containing silanes
Abstract
A method of treating a metal surface by application of a solution containing at least one acyloxy silane and at least one basic compound. A composition having at least one acyloxy silane and at least one basic compound is also provided, along with a silane coated metal surface.
Description
ACYLOXY S LANE TREATMENTS FOR METALS
l3ackaround of the Invention Field of the Invention The present invention relates to silane coatings for metals. More particularly, the present invention provides coatings which include an acyloxy silane, and are particularly useful for preventing corrosion andlor promoting adhesion between a metal substrate and a polymer layer applied to the treated metal substrate_ Solutions for applying such coatings, compositions as well as methods of treating metal surfaces, are also provided.
pescription of Related Art Most metals are susceptible to corrosion, including the formation of various types of rust. Such corrosion will significantly affect the quality of such metals, as well as that of the products produced therefrom. Although rust and the like may often be removed, such steps are costly and may further diminish the strength of the metal. In addition, when polymer coatings such as paints, adhesives or rubbers are applied to the metals, corrosion may cause a loss of adhesion between the polymer coating and the metal.
By way of example, metallic coated steel sheet such as galvanized steel is used in many industries, including the automotive, construction and appliance industries. In most cases, the galvani2ed steel is painted or otherwise coated with a polymer layer to achieve a durable and aesthetically-pleasing product.
Galvanized steel, particularly hot-dipped galvanized steel, however, often develops "white rust" during storage and shipment.
White rust (also called "wet-storage stain") is typically caused by moisture condensation on the surtace of galvanized steel which reacts with the zinc coanng_ On products such as GALVALUME~, the wet-storage stain is black in color ("black rust"). White rust (as well as black rust) is aesthetically unappealing and impairs the ability of the galvanized steel to be painted or otherwise coated with a polymer. Thus, prior to such coating, the surface of the galvanized steel must be pretreated in order to remove the white rust and prevent its reformation beneath the polymer layer. various metnoas are currently employed to not only prevent the formation of white rust during shipment and storage, but also to prevent the formation of white rust beneath a polymer coating (e.g., paint)-(n order to prevent white rust on hot-dipped galvanized steel during storage and shipping, the surtace of the steel is often passivated by forming a thin chromate film an the surface of the steel- Wh~le such chromate coatings do promde resistance to the formation of white rust, chromium is h~gmy toxic aria environmentally undesirable. It is also known to employ a phosphate conversion coating in conjunction with a chromate rinse in order to improve paint adherence and provide corrosion protection. It ~s belevec7 tnat the cnrvma~e rinse cwe~
a the pores in the phosphate coating, thereby improving the corrosion resistance and adhesion performance. Once again, however, it is highly desiraple to eliminate the use of chromate altogether. Unfortunately, however, the phosphate conversion coating ~s generally not very effective without the chromate rinse.
Recently, various techniques for eliminating the use of chromate have been proposed. l~hese include coating the galvanized steel with an inorganic silicate followed by treating the silicate coating mth an organofunct~onal silane (U.S. Patent No. 5,108,793).
U.S. Patent No. 5,292,549 teaches the rinsing of metallic coated steel sheet with a solution containing an organofunctional silane and a crosslmkW g agent.
U_S. Patent No. 6,071,566 relates to a method of treating a metal substrate to provide permanent corrosion resistance. The method comprises applying a solution containing one or more mnyl silanes ~n admixture with one or more multi-silyl-functional silanes to a metal substrate in order to form a coating.
l3ackaround of the Invention Field of the Invention The present invention relates to silane coatings for metals. More particularly, the present invention provides coatings which include an acyloxy silane, and are particularly useful for preventing corrosion andlor promoting adhesion between a metal substrate and a polymer layer applied to the treated metal substrate_ Solutions for applying such coatings, compositions as well as methods of treating metal surfaces, are also provided.
pescription of Related Art Most metals are susceptible to corrosion, including the formation of various types of rust. Such corrosion will significantly affect the quality of such metals, as well as that of the products produced therefrom. Although rust and the like may often be removed, such steps are costly and may further diminish the strength of the metal. In addition, when polymer coatings such as paints, adhesives or rubbers are applied to the metals, corrosion may cause a loss of adhesion between the polymer coating and the metal.
By way of example, metallic coated steel sheet such as galvanized steel is used in many industries, including the automotive, construction and appliance industries. In most cases, the galvani2ed steel is painted or otherwise coated with a polymer layer to achieve a durable and aesthetically-pleasing product.
Galvanized steel, particularly hot-dipped galvanized steel, however, often develops "white rust" during storage and shipment.
White rust (also called "wet-storage stain") is typically caused by moisture condensation on the surtace of galvanized steel which reacts with the zinc coanng_ On products such as GALVALUME~, the wet-storage stain is black in color ("black rust"). White rust (as well as black rust) is aesthetically unappealing and impairs the ability of the galvanized steel to be painted or otherwise coated with a polymer. Thus, prior to such coating, the surface of the galvanized steel must be pretreated in order to remove the white rust and prevent its reformation beneath the polymer layer. various metnoas are currently employed to not only prevent the formation of white rust during shipment and storage, but also to prevent the formation of white rust beneath a polymer coating (e.g., paint)-(n order to prevent white rust on hot-dipped galvanized steel during storage and shipping, the surtace of the steel is often passivated by forming a thin chromate film an the surface of the steel- Wh~le such chromate coatings do promde resistance to the formation of white rust, chromium is h~gmy toxic aria environmentally undesirable. It is also known to employ a phosphate conversion coating in conjunction with a chromate rinse in order to improve paint adherence and provide corrosion protection. It ~s belevec7 tnat the cnrvma~e rinse cwe~
a the pores in the phosphate coating, thereby improving the corrosion resistance and adhesion performance. Once again, however, it is highly desiraple to eliminate the use of chromate altogether. Unfortunately, however, the phosphate conversion coating ~s generally not very effective without the chromate rinse.
Recently, various techniques for eliminating the use of chromate have been proposed. l~hese include coating the galvanized steel with an inorganic silicate followed by treating the silicate coating mth an organofunct~onal silane (U.S. Patent No. 5,108,793).
U.S. Patent No. 5,292,549 teaches the rinsing of metallic coated steel sheet with a solution containing an organofunctional silane and a crosslmkW g agent.
U_S. Patent No. 6,071,566 relates to a method of treating a metal substrate to provide permanent corrosion resistance. The method comprises applying a solution containing one or more mnyl silanes ~n admixture with one or more multi-silyl-functional silanes to a metal substrate in order to form a coating.
Various other techniques for preventing the formation of white rust on galvanized steel, as well as preventing corrosion on other types of metals, have also been proposed. Many of the proposed techniques described in the prior arc are, however, ineffective, or require time-consuming, energy-inefficient, multi-step processes. Thus, there is a need for a simple, low-cost technique for preventing corrosion on the surtace of metal A particular problem associated with the silane treatments of the prior art ~s the rate of hydrolysis of the silane compounds. Such compounds are generally hydrolysed in water, at a specific pH, prior to application of the solution to the substrate to be treated. The rate of hydrolysis varies between silanes, and the degree of hydrolysis is a priori not known. Generally, it has to be guessed when the solution is ready for application When the solution has turned cloudy, this indicates that condensation of the silanes has occurred and the effectmeness of the treatment solution is reduced A further problem with the prior art techniques is the inherent insolubility in aqueous media of some of the silanes employed in the metal treatments. To overcome this problem it is commonplace to dissolve the silane with the aid of an organic solvent, for example, alcohols Thus a final treatment solution commonly contains up to 60% alcohol- The use of many volatile organic compounds (VOCs), including solvents, ~s highly undesirable from an economic, aswell as an environmental perspective. Apart from the cost of such organic solvents, including the cost of their disposal and methods of treatment solution preparation, such compounds present a threat to the environment and are a hazzard to the premises and personnel handling the materials.
A further problem is that the silane systems used in treatment solutions have to have their pH maintained in specific ranges by the initial and continuous addition of adds or bases.
It would therefore be desirable to provide an effectme treatment method for metal surfaces, especially to prevent corrosion, and/or improve adhesion.
It would also be desirable to provide a treatment solution useful in preventing corrosion, andlor adhesion promotion of metal surtaces, for example, steel, aluminium, aluminium alloys, zinc, zinc alloys, magnesium, magnesium alloys, copper, copper alloys, tin and tin alloys, particularly zinc, zinc alloys, and other metals having a zinc-containing coating thereon It would additionally be desirable to promde a metal surface hamng improved corrosion resistance and/or improved adhesion characteristics.
Summary of the Invention The present invention provides a method of treating a metal surface, comprising the steps of:
(a) promdmg a metal substrate; and (b) applying a solution to said metal substrate, said solution compnsmg (i) at least one acyloxy silane which comprises at least one acyloxy group, wherein said silane has been at least partially hydrolysed; and (ii) at least one basic compound;
wherein the acyloxy silane and the basic compound are present in concentrations to provide a solution pH of between about 3 and about 10, more preferably between about 4 and about 8, most preferably 4 to 5 and wherein the solution is substantially free of acid other than acid produced upon hydrolysis of the acyfoxy silane.
The present invention also provides a composition comprising at least one acyloxy silane and at least one basic compound, wherein the at least one acyloxy silane ~s at least partially hydrolyzed. A metal surface having improved corrosion resistance andlor adhesion and a composition concentrate is also provided.
Detailed Description of the Invention The acyloxy silane(s) utilised in the present invention may comprise one or more s~lyl groups and the solution may contain a mixture of acyloxy silanes S
Where the acyloxy silane comprises a single silyl group the silicon atom is tetrasubstituted, wherein the substituents are mdimdually selected from the group consisting of alKyl, alkenyl, alkynyl, aryl, alkaryl, aralkyl, vinyl, amino, ure~do, glycidoxy, epoxy, hydroxy, alKoxy, aryloxy and acyloxy, or any of the group alkyl, alkenyl, alkynyl, aryl, alkaryl and aralkyl substituted by a group selected from the group consisting of vinyl, amine, ureido, glycidoxy, epoxy, hydroxy and alkoxy, v~rith the proviso that at least one of the substituents on the silicon atom is an acyloxy group.
Where more than one acyloxy group is attached to the silicon atom of the syn group, the acyloxy groups are preferably all the same. The acyloxy groups) are preferably selected from the group consisting of Cz_,2 alkanoyloxy, C3_~Z alkenoyloxy, C3_,2 alkynoyloxy and C~_~e arenoyloxy, preferably C2_6 alkanoyloxy, C3~ alkenoyloxy, C3~ alkynoyloxy and Cy_,Z arenoyloxy. Most preferably the acyloxy groups are all the same and are ethanoyloxy (acetoxy) or methanoyloxy groups.
Where the acyloxy s~lane comprises a single silyl group, preferably three of the substituents on the silyl group are acyloxy groups and the fourth substituent is preferably selected from a the group consisting of vinyl or vinyl substituted group, amine or amine substituted group, ureido or ureido substrtuted group and glycidoxy or glycidoxy substituted group.
In a particularly preferred embodiment, the acyloxy silane is selected from the group consisting of H
OCOR OCOR
~X-S''OCOR HzN-Y'Si-ocoR
H OCOR OCOR
OII OCOR O OCOR
H2N~N~Z-S~-OCOR ~W'S~-OCOR
OCOR OCOR
wherein W, X, Y and Z are selected from the group consisting of a C-Si bond, substituted aliphatic groups, unsubstituted aliphatic groups, substituted aromatic groups and unsubstituted aromatic groups; and R is selected from methyl, ethyl and propyl, preferably ethyl.
The acyloxy silane may comprises more than one silyl group. Although the term acyloxy silane generically refers to such a compound, it may be referred to as a multi-silyl-acyloxy silane. More than one multi-silyl-acyloxy s~lane may be employed in a mixture with one or more other mule-silyl-acyloxy silanes or one or more acyloxy silanes containing a s~ngie silyl group as described above.
The acyloxy groups bound to the silicon atoms of the s~lyl groups of the multi-silyl-acyloxy silane are preferably all the same and are preferably selectea from the group consisting of C2.,2 alkanoyloxy, C9_,z alkenoyloxy, C3.,2 alkynoyloxy and Cz_,e arenoyloxy, preferably C2~ alkanoyloxy, C3_6 a~kenoyloxy, C3_6 alkynoyloxy and C~.,2 arenoyloxy. Most preferably the acyloxy groups are all the same and are ethanoyloxy or methanoyloxy groups.
Preferably the multi-silyl-acyloxy silane utilised in the present invention has the structure Q Si - OC OR 1 wherein Q is selected from the group consisting of either a bond, an aliphatic or aromatic group; and R' is selected from methyl, ethyl and propyl.
Preferably Q is selected from the group consisting of a bond, C,-C6 alkylene, Cz-CB alkenylene, C,-C6 alkylgne subst~tutea mth at least one amino group, CZ-C6 alkenylene substituted with at least one amino group, C,-C6 alkylene substituted with at least one sulfide group containing 1 to 6 sulfur atoms, C2-Cs alkenylene substituted with at least one sulfide group containing 1 to 6 sulfur atoms, arylene and alkylarylene. In the case where Q is a bona, the multi-functional silane comprises two trisubstituted silyl groups which are bonded directly to one another. Preferred multi-silyl-acyloxy silane are bis-(triacetoxysilyl)alkane, bls-(triacetoxysilylalkyl)amine and bis-(triacetoxysilylalkyl)tetrasulfide, most preferably bis-(triacetoxysilyl)ethane, bas-(triacetoxysilylpropyl)amine and bis-(triacetoxysilylpropyl)tetrasulfide.
In an especially preferred embodiment, the acyloxy silane utilised in the present mvent~on is vinyltriacetoxysilane.
Acyloxy silanes utilised in the present invention generally dissolve and hydrolyze readily and completely in water to produce organic acids. For example, where an acetoxy silane is used, acetic acid is produced. Unlike the analogous alkoxy silanes commonly utilised in the prior art which produce alcohols upon hydrolysis, the acyloxy silanes utilised m the present invention produce substantially none or small amounts of VOCs depending on the level of non-acyloxy group substitution in the silanes_ Depending on the level of substitution of acyloxy groups in the silanes utilised in the present invention, the pH of the resultant solution can be predetermined and manipulated. Commonly, high degrees of acyloxy group substitution are present, for example ~ 100% substitution, and this can result in a pH as low as 1 or 2 At these low levels of pH, the hydrolysed acylvxysilanes tend to condense, therefore reducing their efficacy. It ~s therefore necessary to add a base to maintain the pH in an optimal range.
Preferably, where a single silyl group-containing silane is used as the acyloxy silane, 3 of the groups attached to the silicon atom of the silyl group are acyloxy groups, preferably methanoyloxy or acetoxy.
Preferably, where a multi-silyl-acyloxy silane is used, 3 of the groups attached to the each silicon atom of each silyl group are acyloxy groups, preferably methanoyloxy or acetoxy.
The pH of the silane mixture is between about 3 and about 10, more preferably between about 4 and about 8, most preferably 4 to 5 and should be maintained. The pH may be adjusted by the addition of one or more basic compounds or addition of acyloxy silane(s).
During preparation of the treatment solution, a pH of above 2, more preferably above 3, most preferably between 4 and 5 should be maintained.
In order to maintain an optimal pH during preparation of the treatment solution, a basic compound is applied to the treatment solution. The identity of the bask compounds) is not critical but it is highly beneficial to provide a compound which complements the acyloxy silane. °Complements" means that the basic compound aids, or at least does not substantially detract from the formation of the silane coating on the metal substrate or from the coatings effectiveness in improving corrosion resistance andlor adhesion promotion.
To maintain the pH in the preferred range, the acyloxy s~lane and the basic compound are preferably mixed together prior to the addition of water and subsequently dissolved in water. Exemplary basic compounds include the carbonates, hydrogen carbonates and hydroxides of the alkali and alkaline earth metals, organic amines, ammonia, amides and the like. A rn~xture of different basic compounds may be added to the treatment composition In a preferred embodiment, the basic compound is a basic s~lane compound. For example, amino silanes are particularly preferred. In one embodiment, ammo silanes which may be employed m the present invention each have a single trisubst~tuted silyl group in addition to the basic amine moiety, wherein at least on of the substituents is an alkoxy group. Thus, the amino silanes which maybe used in the present invention have the general structure oR2 ,N-x'-s.-o~
R~ oR2 Rz is chosen from the group consisting of hydrogen and C,-C2, alkyl, preferably C,-C6 alkyl and each RZ may be the same or different. Preferably RZ is individually chosen from the group consisting of hydrogen, ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl and ter-butyl.
X' is a group selected from the group consisting of a bond, a substituted or unsubstituted aliphatic or aromatic group. Preferably X' is selected from the group cons~stmg of a bond, C,-C6 alkylene, CZ-Cg alkenylene, C,-C6 alkylene substituted with at least one amino group, CZ-C6 alkenylene substituted with at least one amino group, C6-,e arylene and C~-C,e alkylarylene;
R3 is a group indwidually selected from the group consisting of hydrogen, C,-alKyl, C2-C6 alkenyl, C,-C6 alkyl substituted with at least one amino group, alkenyl substituted with at least one amino group, arylene and afkylarylene_ Preferably R3 ~s individually selected from the group consisting of hydrogen, ethyl, methyl, propyl, ~so-propyl, butyl, iso-butyl, sec-butyl ter-putyl and acetyl.
Particular preferred ammo silanes employed in the method of the present mvent~on are y-ammopropyltriethoxysilane and y-aminopropyl trimethoxysilane.
In another embodiment, the amino silane may be a bis-silyl am~nosilane(s). Such a compound comprises an aminosilane having two tnsubst~tuted silyl groups, wherein the substituents are individually selected from the group consisting of hydroxy and alkoxy. Preferably, the bis-silyl aminosilane compnses_ OR° OR°
R°O- ~ i R5 XZ RS- ~ ~-OR°
R4 ~ R°
wherein each Rq is individually selected from the group consisting of:
hydrogen and C, - C24 alkyl;
each RS is individually selected from the group consisting of: substituted aliphatic groups, unsubstituted aliphatic groups, substituted aromatic groups, and unsubstituted aromatic groups; and Xz ~s either:
Rs Ra Rs or ~N~R~ N-wnerein each RB is individually selected from the group consisting of:
hydrogen, substituted and unsubstituted aliphatic groups, and substituted and unsubstituted aromatic groups; and R' is selected from the group consisting of: substituted and unsubstituted aliphatic groups, and substituted and unsubstituted aromatic groups Particularly preferred bis-silt' aminosilanes which may be used in the present invention include:
bis-(trimethoxysilylpropyl)amine (which is sold under the tradename A-1170 by Witco):
CH30--SI-CjH6-N--C3H6-SI-OC H3 OCH3 OCHg bis-(triethoxysilylpropyl)amme:
OC2Hs H OC2H5 C2H50-~I-C3H6-N-C3H6-Si-OC2H5 OC2Hs OCzHs and bis-(triethoxysilylpropyl)ethylene d~amine:
I I I I
CH30-SI-C3H6-N-C2Hp-N-C3H6-SI-OCH3 Particularly preferred combinations of acyloxy silanes and basic compounds are:
vinyltriacetoxysilane and bis-(trimethoxysilylpropyl)amine;
1,2-bis-(tri~thoxysilyl)ethane and bis-(tnmethoxysilylpropyl)amme;
v~nyltriacetoxysilane and aminopropyltriethoxysilane;
vinyltriacetoxysilane and bas-(triethoxysilylpropyl)amine;
1,2-bis-(triethoxysilyl)ethane and bis-(triethoxysilylpropyl)amine;
vinyltriacetoxysilane and am~nopropyltrimethoxysilane.
Where basic silanes are used as the basic compound, additional basic compounds may be used, for example, the inorganic bases referred to above.
The solutions and methods of the present invention may be used on a vanety of metals, including steel, aluminium, aluminium alloys, zinc, zinc alloys, magnesium, magnesium alloys, copper, copper alloys, tin and tin alloys. In particular, the present method is particularly useful on zinc, zinc alloy, and metals having a zinc-containing coating thereon, as well as aluminium or aluminium containing substrates. For example, the treatment solutions and methods of the present invention are useful in preventing corrosion of steel having a zinc-containing coating, such as: galvanized steel (especially not dipped galvanized steel), GALVALUME~ (a 55%-AI/43.4%-Zn/1.6% - Si alloy coated sheet steel manufactured and sold, for example, by Bethlehem Steel Corp), GALFAN~ (a 5%-Al/95%-Zn alloy coated sheet steel manufactured and sold by Weirton Steel Corp., of Weirton, WV), galvanneal (annealed hot dipped galvanized steel) and similar types of coated steel. Zinc and zinc alloys are also particularly amenable to application of the treatment solutions and methods of the present invention. Exemplary zinc and zinc alloy materials include:
titanium-zinc (zinc which has a very small amount of titanium added thereto), zinc-nickel alloy (typically about 5% to about 13% nickel content), and zinc-cobalt alloy (typically about 1 % cobalt).
The solutions of the present invention may be applied to the metal prior to shipment to the end-user, and provide corrosion protection during shipment and storage (including the prevention of wet-storage stain such as white rust).
If a paint or other polymer coating is desired, the end user may merely apply the paint or polymer (e.g., such as adhesives, plastics, or rubber coatings) directly on top of the silane coating provided by the present invention. The silane coatings of the present invention not only provide excellent corrosion protection even without paint, but also provide superior adhesion of paint, rubber or other polymer layers. Thus, unlike many of the currently-employed treatment techniques, the silane coatings of the present invention need not be removed prior to painting (or applying other types of polymer coatings such as rubber).
Suitable polymer coatings include various types of paints, adhesives (such as epoxy automotive adhesives), and peroxide-cured rubbers (e.g., peroxide-cured natural, NBR, SBR, nitrite or silicone rubbers). Suitable paints include polyesters, polyurethanes and epoxy-based paints. Plastic coatings are also suitable including acrylic, polyester, polyurethane, polyethylene, polyimide, polyphenylene oxide, polycarbonate, polyamide, epoxy, phenolic, acrylonitrile-butadiene-styrene, and acetal plastics. Thus, not only do the coatings of the present invention prevent corrosion, they may also be employed as primers and/or adhesive coatings for other polymer layers.
Tne solutions of the present invention do not require the use or addition of silicates-The compositions may optionally comprise other silane compounds to the acyloxy silanes or the basic silanes disclosed herein.
The treatm~nt solution is aqueous, and may optionally include one or more compatible solvents (such as ethanol, methanol, propanol or isopropanol) although their presence is not normally required. Where an organic solvent is required, ethanol is preferred. Preferably, solutions of the present invention are substantially free of organic solvents and VOCs.
As mentioned above, the silane(s) in the solution of the present invention are at least partially, and preferably are substantially fully hydrolyzed in order to facilitate the bonding of the silanes to the metal surface and to each other.
During hydrolysis, the alkoxy groups in the case of the non-acyloxy silanes and the acyloxy in the case of the acyloxy silanes are replaced by hydroxyl groups.
Hydrolysis of the silanes may be accomplished, for example, by merely mixing the silanes in water, and optionally including a solvent (such as an alcohol) in order to improve silane solubility and solution stability.
In order to accelerate silane hydrolysis and avoid silane condensation during hydrolysis, the pH may be maintained below about 8, more preferably between about 4 and about 6, and even more preferably between about 4 and about 5.
It should be noted that the various s~lane concentrations discussed and claimed herein are all defined in terms of the ratio between the amount (by volume) of unhydrolyZed silane(s) employed to prepare the treatment solution (i.e., prior to hydrolyzation), and the total volume of treatment solution components (i.e., acyloxy silanes, basic compound, water, and optional solvents- In the case of acyloxy silane(s), the concentrations herein (unless otherwise specified) refer to the total amount of unhydrolyzed acyloxy sifanes employed, since multiple acyloxy silanes may optionally be present. The basic compounds concentrations herein are defined in the same manner.
As for the concentration of hydrolyzed silanes in the treatment solution, beneficial results will be obtained overawide range of silane concentrations and ratios It is preferred, however, that the solution have at least about 0.1 acyloxy silanes by volume, more preferably at least about 1 % acyloxy silanes by volume, most preferably between about 2% and about 5% by volume. Lower vinyl silane concentrations generally provide less corrosion protection.
Higher concentrations of acyloxy sifanes (greater than about 10%) should also be avoided for economic reasons, and to avoid silane condensation (which may limit storage stability).
The concentration of the basic compound required in the treatment solution varies strongly with the type of acyloxy silane employed and the type of basic compound. Obviously, a strongly acidic solution produced by a highly acyloxy group-substituted acyloxy silane will require an appropriate amount of basic compound to result in a treatment solution with a pH in the pre-determined range. Once the pH of the acyloxy silane in solution is known, an appropriate amount of a basic compound (with a known pN value in solution) can be added to the solution. The relative acidity and basicity of the acyloxy silane and the basic compound may be established before the solution is made up and are commonly presented in standard tables reciting physical properties of known compounds. However, the concentration of the basic compound is generally in the range of about 0.1 °~ and about 10% by volume.
Where a basic silane is used as the basic compound, the solution should have at least about 0.1 % basic silanes by volume, more preferably at least about 1 % basic s~lane by volume, more preferably between about 2% and about 10%, most preferably between about 2% and about 5% by volume.
As for the ratio of acyloxy silanes to basic compound, a wide range of ratios may be employed, and the present invention is not limited to any particular range of silane ratios.
The mixture of the acyloxy and basic compound may be provided to the user m a pre-mixed, unhydrolysed form which improves shelf life as ~ 0 condensation of the siiane is limiteo. Sucn a mixture can then be made up into a treatment solution as defined herein Such a pre-mixed, unhydrolysed compositions should preferably be substantially free of water but may include one or more organic solvents (such as alcohols). The composition may also include other components such as stabilizers, pigments, desiccants, and the like.
Such a pre-mixed composition can be made up with a pre-determined amount of acyloxy silane and bask compound so that the addition of the mixture to water results in a pH within the preferred range. Such pre-mixing prevents or Imits a drop in pH, due to the acyloxy silane alone being present in solution, to levels which promote condensation of the silanes in solution- However, the composition can be presented in a "two-pack" kit, wherein one part of the kit comprises the acyloxy silane, while another part of the kit provides the basic compound.
In ether of the above presentation embodiments, the acyloxy silane and basic compound, along with the other components of the composition are provided in a concentrated form as a powder or liquid mixture. In either case, the concentrate is substantially free of water and may be presented in a hermetically sealed container or kit. Preferably, substantially no organic solvent ~s present in the composition.
The concentration of the acyloxy silane and basic compound in the pre-mixed concentrate composition is generally in the range 10-100%, preferably 15-80%, most preferably 25-70%. The concentrate may contain numerous additional components such as stabilisers, pigments, anti-oxidants, basic pH
adjusters, desiccants, adhesion promoters, corrosion inhibitors and the like.
The treatment method itself is very simple. Where the solution is to be made up of separately presented components, the unhydrolyzed acyloxy silane, water, basic compound, solvent (~f desired), are combined with one another.
The solution is then stirred at room temperature in order to hydrolyze the silanes. The solution generally goes clear when hydrolyses is complete In this embodiment it is beneficial to maintain the pH of the solution above 2 to limit any condensation of the silanes in solution, particularly the acyloxy silanes_ Where the composition is presented as a pre-mixed kit, the composition is simply added to a pre-determined amount of water and mixed until the solution is substantially clear.
The metal surface to be coated with the solution of the present invention may be solvent and/or alkaline cleaned by techniques well-known to those skilled in the art prior to application of the treatment solution of the present invention. The silane solution is then applied to the metal surface (i.e., the sheet is coated wrth the silane solution) by, for example, dipping the metal into the solution (also referred to as "rinsing''), spraying the solution onto the surtace of the metal, or even brushing or wiping the solution onto the metal surface.
Various other application techniques well-known to those skilled in the art may also be used When the preferred application method of dipping is employed, the duration of dipping is not critical, as it generally does not significantly affect the resulting film thickness. It is merely preferred that whatever application method is used, the contact time should be sufficient to ensure complete coating of the metal. For most methods of application, a contact time of at least about 2 seconds, and more preferably at least about 5 seconds, will help to ensure complete coating of the metal.
As the treatment solution is used up, the acyloxy silane concentration is reduced and the acetic acid concentration remains approximately constant as long as no further acyloxy silane is added to the solution. As further acyloxy silane is added to maintain their concentration, acetic acid is built up in the solution. To maintain the pH in the preferred range pH adjusters may be added such as basic compounds as hereinbefore described, buffers and the like. In one embodiment, a basic compound may be added along with the addiuonat acyloxy silane which forms a salt with the acid m solution This may form an insoluble salt which can be removed from the process.
The treatment solution may also be heated when applying the treatment solution. Where the treatment solution is heated, the temperature of the treatment solution is generally in the range 20°C to 80°C, preferably 30°C to 50°C .
After coating with the treatment solution of the present mvenuon, the metal sheet may be air-dried at room temperature, or, more preferably, placed into an oven for heat drying. Preferable heated drying conditions include temperatures between about 20°C and about 200 °C with drying times of between about 30 seconds and about 60 minutes (higher temperatures allow far shorter drying times) More preferably, heated drying is performed at a temperature of at least about 90°C, for a time sufficient to allow the silane coating to dry. While heated drying vs not necessary to achieve satisfactory results, it will reduce the drying time thereby lessening the likelihood of the formation of white rust during drying. Once dried, the treated metal may be shipped to an end-user, or stored for later use.
The examples below demonstrate some of the superior and unexpected results obtained by employing the methods of the present invention.
Exameles Example 1 Salt Spray test (SST)(Lakebluff) was carried out on A1170Ninyltriacetoxysilane (1/1, 5°r6, natural pH--4) treated AA5005 panels.
Alkaline cleaned blank and chromated AA5005 panels were chosen as controls The treated panels were cured at 100°C for 10 min, and then exposed to SST for 29 days, along with the control panels. Four replicates were made for each treatment The results are presented in Fig. 1.
1. A1170MAS treated panels showed original surface after 29 days of exposure to SST, i.e. no corrosion occurred during testing.
2. The blank panels corroded heavily, white the chramated ones pitted apparently.
Example 2 Salt Spray test (Lakebluff) was carried out on A1170/VTAS (1.511.5%, natural pH=4) treated A12024-T3 panels. Alkaline cleaned blank and chromated A12024-T3 panels were chosen as controls. The treated panels were cured at 100°C far 10 min, and then exposed to SST for 7 days, along with the control panels. Three replicates were made for each treatment. The results are presented in Fig. 2.
3. A1170NTAS treated panels showed almost original surface after 7 days of exposure to SST, ~.e , only slight edge corrosion occurred during testing.
4. The blank panels corroded heavily, while the chromated ones pitted slightly.
Example 3 In order to investigate the paintability of A1170IVTAS water-based silane film on metal substrates, A1170IVTAS (1.5/1,2%, pH'-5) water-based silane film was applied on A12023-T3 and HDG, respectively. The treated panels were then powder-painted at Lakebluff with Polyester and Polyurethane powder paints. After that, the panels were put into salt spray chamber for some times, along with the control panels, the blank and the chromated. Three replicates were made for each treatment The results are shown in Fig. 3 1. As for A12024-T3 painted with both powder paints (1000hrs in SST), the corrosion performance and paint adhesion improved significantly, which was equal to the chromated and much better than the blank.
2. As for powder-painted HDG (336 hrs in SST), the corrosion performance improved apparently, compared with the chromated is and the clank. The paint adhesion improved somewhat, which was better that the control panels-
A further problem is that the silane systems used in treatment solutions have to have their pH maintained in specific ranges by the initial and continuous addition of adds or bases.
It would therefore be desirable to provide an effectme treatment method for metal surfaces, especially to prevent corrosion, and/or improve adhesion.
It would also be desirable to provide a treatment solution useful in preventing corrosion, andlor adhesion promotion of metal surtaces, for example, steel, aluminium, aluminium alloys, zinc, zinc alloys, magnesium, magnesium alloys, copper, copper alloys, tin and tin alloys, particularly zinc, zinc alloys, and other metals having a zinc-containing coating thereon It would additionally be desirable to promde a metal surface hamng improved corrosion resistance and/or improved adhesion characteristics.
Summary of the Invention The present invention provides a method of treating a metal surface, comprising the steps of:
(a) promdmg a metal substrate; and (b) applying a solution to said metal substrate, said solution compnsmg (i) at least one acyloxy silane which comprises at least one acyloxy group, wherein said silane has been at least partially hydrolysed; and (ii) at least one basic compound;
wherein the acyloxy silane and the basic compound are present in concentrations to provide a solution pH of between about 3 and about 10, more preferably between about 4 and about 8, most preferably 4 to 5 and wherein the solution is substantially free of acid other than acid produced upon hydrolysis of the acyfoxy silane.
The present invention also provides a composition comprising at least one acyloxy silane and at least one basic compound, wherein the at least one acyloxy silane ~s at least partially hydrolyzed. A metal surface having improved corrosion resistance andlor adhesion and a composition concentrate is also provided.
Detailed Description of the Invention The acyloxy silane(s) utilised in the present invention may comprise one or more s~lyl groups and the solution may contain a mixture of acyloxy silanes S
Where the acyloxy silane comprises a single silyl group the silicon atom is tetrasubstituted, wherein the substituents are mdimdually selected from the group consisting of alKyl, alkenyl, alkynyl, aryl, alkaryl, aralkyl, vinyl, amino, ure~do, glycidoxy, epoxy, hydroxy, alKoxy, aryloxy and acyloxy, or any of the group alkyl, alkenyl, alkynyl, aryl, alkaryl and aralkyl substituted by a group selected from the group consisting of vinyl, amine, ureido, glycidoxy, epoxy, hydroxy and alkoxy, v~rith the proviso that at least one of the substituents on the silicon atom is an acyloxy group.
Where more than one acyloxy group is attached to the silicon atom of the syn group, the acyloxy groups are preferably all the same. The acyloxy groups) are preferably selected from the group consisting of Cz_,2 alkanoyloxy, C3_~Z alkenoyloxy, C3_,2 alkynoyloxy and C~_~e arenoyloxy, preferably C2_6 alkanoyloxy, C3~ alkenoyloxy, C3~ alkynoyloxy and Cy_,Z arenoyloxy. Most preferably the acyloxy groups are all the same and are ethanoyloxy (acetoxy) or methanoyloxy groups.
Where the acyloxy s~lane comprises a single silyl group, preferably three of the substituents on the silyl group are acyloxy groups and the fourth substituent is preferably selected from a the group consisting of vinyl or vinyl substituted group, amine or amine substituted group, ureido or ureido substrtuted group and glycidoxy or glycidoxy substituted group.
In a particularly preferred embodiment, the acyloxy silane is selected from the group consisting of H
OCOR OCOR
~X-S''OCOR HzN-Y'Si-ocoR
H OCOR OCOR
OII OCOR O OCOR
H2N~N~Z-S~-OCOR ~W'S~-OCOR
OCOR OCOR
wherein W, X, Y and Z are selected from the group consisting of a C-Si bond, substituted aliphatic groups, unsubstituted aliphatic groups, substituted aromatic groups and unsubstituted aromatic groups; and R is selected from methyl, ethyl and propyl, preferably ethyl.
The acyloxy silane may comprises more than one silyl group. Although the term acyloxy silane generically refers to such a compound, it may be referred to as a multi-silyl-acyloxy silane. More than one multi-silyl-acyloxy s~lane may be employed in a mixture with one or more other mule-silyl-acyloxy silanes or one or more acyloxy silanes containing a s~ngie silyl group as described above.
The acyloxy groups bound to the silicon atoms of the s~lyl groups of the multi-silyl-acyloxy silane are preferably all the same and are preferably selectea from the group consisting of C2.,2 alkanoyloxy, C9_,z alkenoyloxy, C3.,2 alkynoyloxy and Cz_,e arenoyloxy, preferably C2~ alkanoyloxy, C3_6 a~kenoyloxy, C3_6 alkynoyloxy and C~.,2 arenoyloxy. Most preferably the acyloxy groups are all the same and are ethanoyloxy or methanoyloxy groups.
Preferably the multi-silyl-acyloxy silane utilised in the present invention has the structure Q Si - OC OR 1 wherein Q is selected from the group consisting of either a bond, an aliphatic or aromatic group; and R' is selected from methyl, ethyl and propyl.
Preferably Q is selected from the group consisting of a bond, C,-C6 alkylene, Cz-CB alkenylene, C,-C6 alkylgne subst~tutea mth at least one amino group, CZ-C6 alkenylene substituted with at least one amino group, C,-C6 alkylene substituted with at least one sulfide group containing 1 to 6 sulfur atoms, C2-Cs alkenylene substituted with at least one sulfide group containing 1 to 6 sulfur atoms, arylene and alkylarylene. In the case where Q is a bona, the multi-functional silane comprises two trisubstituted silyl groups which are bonded directly to one another. Preferred multi-silyl-acyloxy silane are bis-(triacetoxysilyl)alkane, bls-(triacetoxysilylalkyl)amine and bis-(triacetoxysilylalkyl)tetrasulfide, most preferably bis-(triacetoxysilyl)ethane, bas-(triacetoxysilylpropyl)amine and bis-(triacetoxysilylpropyl)tetrasulfide.
In an especially preferred embodiment, the acyloxy silane utilised in the present mvent~on is vinyltriacetoxysilane.
Acyloxy silanes utilised in the present invention generally dissolve and hydrolyze readily and completely in water to produce organic acids. For example, where an acetoxy silane is used, acetic acid is produced. Unlike the analogous alkoxy silanes commonly utilised in the prior art which produce alcohols upon hydrolysis, the acyloxy silanes utilised m the present invention produce substantially none or small amounts of VOCs depending on the level of non-acyloxy group substitution in the silanes_ Depending on the level of substitution of acyloxy groups in the silanes utilised in the present invention, the pH of the resultant solution can be predetermined and manipulated. Commonly, high degrees of acyloxy group substitution are present, for example ~ 100% substitution, and this can result in a pH as low as 1 or 2 At these low levels of pH, the hydrolysed acylvxysilanes tend to condense, therefore reducing their efficacy. It ~s therefore necessary to add a base to maintain the pH in an optimal range.
Preferably, where a single silyl group-containing silane is used as the acyloxy silane, 3 of the groups attached to the silicon atom of the silyl group are acyloxy groups, preferably methanoyloxy or acetoxy.
Preferably, where a multi-silyl-acyloxy silane is used, 3 of the groups attached to the each silicon atom of each silyl group are acyloxy groups, preferably methanoyloxy or acetoxy.
The pH of the silane mixture is between about 3 and about 10, more preferably between about 4 and about 8, most preferably 4 to 5 and should be maintained. The pH may be adjusted by the addition of one or more basic compounds or addition of acyloxy silane(s).
During preparation of the treatment solution, a pH of above 2, more preferably above 3, most preferably between 4 and 5 should be maintained.
In order to maintain an optimal pH during preparation of the treatment solution, a basic compound is applied to the treatment solution. The identity of the bask compounds) is not critical but it is highly beneficial to provide a compound which complements the acyloxy silane. °Complements" means that the basic compound aids, or at least does not substantially detract from the formation of the silane coating on the metal substrate or from the coatings effectiveness in improving corrosion resistance andlor adhesion promotion.
To maintain the pH in the preferred range, the acyloxy s~lane and the basic compound are preferably mixed together prior to the addition of water and subsequently dissolved in water. Exemplary basic compounds include the carbonates, hydrogen carbonates and hydroxides of the alkali and alkaline earth metals, organic amines, ammonia, amides and the like. A rn~xture of different basic compounds may be added to the treatment composition In a preferred embodiment, the basic compound is a basic s~lane compound. For example, amino silanes are particularly preferred. In one embodiment, ammo silanes which may be employed m the present invention each have a single trisubst~tuted silyl group in addition to the basic amine moiety, wherein at least on of the substituents is an alkoxy group. Thus, the amino silanes which maybe used in the present invention have the general structure oR2 ,N-x'-s.-o~
R~ oR2 Rz is chosen from the group consisting of hydrogen and C,-C2, alkyl, preferably C,-C6 alkyl and each RZ may be the same or different. Preferably RZ is individually chosen from the group consisting of hydrogen, ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl and ter-butyl.
X' is a group selected from the group consisting of a bond, a substituted or unsubstituted aliphatic or aromatic group. Preferably X' is selected from the group cons~stmg of a bond, C,-C6 alkylene, CZ-Cg alkenylene, C,-C6 alkylene substituted with at least one amino group, CZ-C6 alkenylene substituted with at least one amino group, C6-,e arylene and C~-C,e alkylarylene;
R3 is a group indwidually selected from the group consisting of hydrogen, C,-alKyl, C2-C6 alkenyl, C,-C6 alkyl substituted with at least one amino group, alkenyl substituted with at least one amino group, arylene and afkylarylene_ Preferably R3 ~s individually selected from the group consisting of hydrogen, ethyl, methyl, propyl, ~so-propyl, butyl, iso-butyl, sec-butyl ter-putyl and acetyl.
Particular preferred ammo silanes employed in the method of the present mvent~on are y-ammopropyltriethoxysilane and y-aminopropyl trimethoxysilane.
In another embodiment, the amino silane may be a bis-silyl am~nosilane(s). Such a compound comprises an aminosilane having two tnsubst~tuted silyl groups, wherein the substituents are individually selected from the group consisting of hydroxy and alkoxy. Preferably, the bis-silyl aminosilane compnses_ OR° OR°
R°O- ~ i R5 XZ RS- ~ ~-OR°
R4 ~ R°
wherein each Rq is individually selected from the group consisting of:
hydrogen and C, - C24 alkyl;
each RS is individually selected from the group consisting of: substituted aliphatic groups, unsubstituted aliphatic groups, substituted aromatic groups, and unsubstituted aromatic groups; and Xz ~s either:
Rs Ra Rs or ~N~R~ N-wnerein each RB is individually selected from the group consisting of:
hydrogen, substituted and unsubstituted aliphatic groups, and substituted and unsubstituted aromatic groups; and R' is selected from the group consisting of: substituted and unsubstituted aliphatic groups, and substituted and unsubstituted aromatic groups Particularly preferred bis-silt' aminosilanes which may be used in the present invention include:
bis-(trimethoxysilylpropyl)amine (which is sold under the tradename A-1170 by Witco):
CH30--SI-CjH6-N--C3H6-SI-OC H3 OCH3 OCHg bis-(triethoxysilylpropyl)amme:
OC2Hs H OC2H5 C2H50-~I-C3H6-N-C3H6-Si-OC2H5 OC2Hs OCzHs and bis-(triethoxysilylpropyl)ethylene d~amine:
I I I I
CH30-SI-C3H6-N-C2Hp-N-C3H6-SI-OCH3 Particularly preferred combinations of acyloxy silanes and basic compounds are:
vinyltriacetoxysilane and bis-(trimethoxysilylpropyl)amine;
1,2-bis-(tri~thoxysilyl)ethane and bis-(tnmethoxysilylpropyl)amme;
v~nyltriacetoxysilane and aminopropyltriethoxysilane;
vinyltriacetoxysilane and bas-(triethoxysilylpropyl)amine;
1,2-bis-(triethoxysilyl)ethane and bis-(triethoxysilylpropyl)amine;
vinyltriacetoxysilane and am~nopropyltrimethoxysilane.
Where basic silanes are used as the basic compound, additional basic compounds may be used, for example, the inorganic bases referred to above.
The solutions and methods of the present invention may be used on a vanety of metals, including steel, aluminium, aluminium alloys, zinc, zinc alloys, magnesium, magnesium alloys, copper, copper alloys, tin and tin alloys. In particular, the present method is particularly useful on zinc, zinc alloy, and metals having a zinc-containing coating thereon, as well as aluminium or aluminium containing substrates. For example, the treatment solutions and methods of the present invention are useful in preventing corrosion of steel having a zinc-containing coating, such as: galvanized steel (especially not dipped galvanized steel), GALVALUME~ (a 55%-AI/43.4%-Zn/1.6% - Si alloy coated sheet steel manufactured and sold, for example, by Bethlehem Steel Corp), GALFAN~ (a 5%-Al/95%-Zn alloy coated sheet steel manufactured and sold by Weirton Steel Corp., of Weirton, WV), galvanneal (annealed hot dipped galvanized steel) and similar types of coated steel. Zinc and zinc alloys are also particularly amenable to application of the treatment solutions and methods of the present invention. Exemplary zinc and zinc alloy materials include:
titanium-zinc (zinc which has a very small amount of titanium added thereto), zinc-nickel alloy (typically about 5% to about 13% nickel content), and zinc-cobalt alloy (typically about 1 % cobalt).
The solutions of the present invention may be applied to the metal prior to shipment to the end-user, and provide corrosion protection during shipment and storage (including the prevention of wet-storage stain such as white rust).
If a paint or other polymer coating is desired, the end user may merely apply the paint or polymer (e.g., such as adhesives, plastics, or rubber coatings) directly on top of the silane coating provided by the present invention. The silane coatings of the present invention not only provide excellent corrosion protection even without paint, but also provide superior adhesion of paint, rubber or other polymer layers. Thus, unlike many of the currently-employed treatment techniques, the silane coatings of the present invention need not be removed prior to painting (or applying other types of polymer coatings such as rubber).
Suitable polymer coatings include various types of paints, adhesives (such as epoxy automotive adhesives), and peroxide-cured rubbers (e.g., peroxide-cured natural, NBR, SBR, nitrite or silicone rubbers). Suitable paints include polyesters, polyurethanes and epoxy-based paints. Plastic coatings are also suitable including acrylic, polyester, polyurethane, polyethylene, polyimide, polyphenylene oxide, polycarbonate, polyamide, epoxy, phenolic, acrylonitrile-butadiene-styrene, and acetal plastics. Thus, not only do the coatings of the present invention prevent corrosion, they may also be employed as primers and/or adhesive coatings for other polymer layers.
Tne solutions of the present invention do not require the use or addition of silicates-The compositions may optionally comprise other silane compounds to the acyloxy silanes or the basic silanes disclosed herein.
The treatm~nt solution is aqueous, and may optionally include one or more compatible solvents (such as ethanol, methanol, propanol or isopropanol) although their presence is not normally required. Where an organic solvent is required, ethanol is preferred. Preferably, solutions of the present invention are substantially free of organic solvents and VOCs.
As mentioned above, the silane(s) in the solution of the present invention are at least partially, and preferably are substantially fully hydrolyzed in order to facilitate the bonding of the silanes to the metal surface and to each other.
During hydrolysis, the alkoxy groups in the case of the non-acyloxy silanes and the acyloxy in the case of the acyloxy silanes are replaced by hydroxyl groups.
Hydrolysis of the silanes may be accomplished, for example, by merely mixing the silanes in water, and optionally including a solvent (such as an alcohol) in order to improve silane solubility and solution stability.
In order to accelerate silane hydrolysis and avoid silane condensation during hydrolysis, the pH may be maintained below about 8, more preferably between about 4 and about 6, and even more preferably between about 4 and about 5.
It should be noted that the various s~lane concentrations discussed and claimed herein are all defined in terms of the ratio between the amount (by volume) of unhydrolyZed silane(s) employed to prepare the treatment solution (i.e., prior to hydrolyzation), and the total volume of treatment solution components (i.e., acyloxy silanes, basic compound, water, and optional solvents- In the case of acyloxy silane(s), the concentrations herein (unless otherwise specified) refer to the total amount of unhydrolyzed acyloxy sifanes employed, since multiple acyloxy silanes may optionally be present. The basic compounds concentrations herein are defined in the same manner.
As for the concentration of hydrolyzed silanes in the treatment solution, beneficial results will be obtained overawide range of silane concentrations and ratios It is preferred, however, that the solution have at least about 0.1 acyloxy silanes by volume, more preferably at least about 1 % acyloxy silanes by volume, most preferably between about 2% and about 5% by volume. Lower vinyl silane concentrations generally provide less corrosion protection.
Higher concentrations of acyloxy sifanes (greater than about 10%) should also be avoided for economic reasons, and to avoid silane condensation (which may limit storage stability).
The concentration of the basic compound required in the treatment solution varies strongly with the type of acyloxy silane employed and the type of basic compound. Obviously, a strongly acidic solution produced by a highly acyloxy group-substituted acyloxy silane will require an appropriate amount of basic compound to result in a treatment solution with a pH in the pre-determined range. Once the pH of the acyloxy silane in solution is known, an appropriate amount of a basic compound (with a known pN value in solution) can be added to the solution. The relative acidity and basicity of the acyloxy silane and the basic compound may be established before the solution is made up and are commonly presented in standard tables reciting physical properties of known compounds. However, the concentration of the basic compound is generally in the range of about 0.1 °~ and about 10% by volume.
Where a basic silane is used as the basic compound, the solution should have at least about 0.1 % basic silanes by volume, more preferably at least about 1 % basic s~lane by volume, more preferably between about 2% and about 10%, most preferably between about 2% and about 5% by volume.
As for the ratio of acyloxy silanes to basic compound, a wide range of ratios may be employed, and the present invention is not limited to any particular range of silane ratios.
The mixture of the acyloxy and basic compound may be provided to the user m a pre-mixed, unhydrolysed form which improves shelf life as ~ 0 condensation of the siiane is limiteo. Sucn a mixture can then be made up into a treatment solution as defined herein Such a pre-mixed, unhydrolysed compositions should preferably be substantially free of water but may include one or more organic solvents (such as alcohols). The composition may also include other components such as stabilizers, pigments, desiccants, and the like.
Such a pre-mixed composition can be made up with a pre-determined amount of acyloxy silane and bask compound so that the addition of the mixture to water results in a pH within the preferred range. Such pre-mixing prevents or Imits a drop in pH, due to the acyloxy silane alone being present in solution, to levels which promote condensation of the silanes in solution- However, the composition can be presented in a "two-pack" kit, wherein one part of the kit comprises the acyloxy silane, while another part of the kit provides the basic compound.
In ether of the above presentation embodiments, the acyloxy silane and basic compound, along with the other components of the composition are provided in a concentrated form as a powder or liquid mixture. In either case, the concentrate is substantially free of water and may be presented in a hermetically sealed container or kit. Preferably, substantially no organic solvent ~s present in the composition.
The concentration of the acyloxy silane and basic compound in the pre-mixed concentrate composition is generally in the range 10-100%, preferably 15-80%, most preferably 25-70%. The concentrate may contain numerous additional components such as stabilisers, pigments, anti-oxidants, basic pH
adjusters, desiccants, adhesion promoters, corrosion inhibitors and the like.
The treatment method itself is very simple. Where the solution is to be made up of separately presented components, the unhydrolyzed acyloxy silane, water, basic compound, solvent (~f desired), are combined with one another.
The solution is then stirred at room temperature in order to hydrolyze the silanes. The solution generally goes clear when hydrolyses is complete In this embodiment it is beneficial to maintain the pH of the solution above 2 to limit any condensation of the silanes in solution, particularly the acyloxy silanes_ Where the composition is presented as a pre-mixed kit, the composition is simply added to a pre-determined amount of water and mixed until the solution is substantially clear.
The metal surface to be coated with the solution of the present invention may be solvent and/or alkaline cleaned by techniques well-known to those skilled in the art prior to application of the treatment solution of the present invention. The silane solution is then applied to the metal surface (i.e., the sheet is coated wrth the silane solution) by, for example, dipping the metal into the solution (also referred to as "rinsing''), spraying the solution onto the surtace of the metal, or even brushing or wiping the solution onto the metal surface.
Various other application techniques well-known to those skilled in the art may also be used When the preferred application method of dipping is employed, the duration of dipping is not critical, as it generally does not significantly affect the resulting film thickness. It is merely preferred that whatever application method is used, the contact time should be sufficient to ensure complete coating of the metal. For most methods of application, a contact time of at least about 2 seconds, and more preferably at least about 5 seconds, will help to ensure complete coating of the metal.
As the treatment solution is used up, the acyloxy silane concentration is reduced and the acetic acid concentration remains approximately constant as long as no further acyloxy silane is added to the solution. As further acyloxy silane is added to maintain their concentration, acetic acid is built up in the solution. To maintain the pH in the preferred range pH adjusters may be added such as basic compounds as hereinbefore described, buffers and the like. In one embodiment, a basic compound may be added along with the addiuonat acyloxy silane which forms a salt with the acid m solution This may form an insoluble salt which can be removed from the process.
The treatment solution may also be heated when applying the treatment solution. Where the treatment solution is heated, the temperature of the treatment solution is generally in the range 20°C to 80°C, preferably 30°C to 50°C .
After coating with the treatment solution of the present mvenuon, the metal sheet may be air-dried at room temperature, or, more preferably, placed into an oven for heat drying. Preferable heated drying conditions include temperatures between about 20°C and about 200 °C with drying times of between about 30 seconds and about 60 minutes (higher temperatures allow far shorter drying times) More preferably, heated drying is performed at a temperature of at least about 90°C, for a time sufficient to allow the silane coating to dry. While heated drying vs not necessary to achieve satisfactory results, it will reduce the drying time thereby lessening the likelihood of the formation of white rust during drying. Once dried, the treated metal may be shipped to an end-user, or stored for later use.
The examples below demonstrate some of the superior and unexpected results obtained by employing the methods of the present invention.
Exameles Example 1 Salt Spray test (SST)(Lakebluff) was carried out on A1170Ninyltriacetoxysilane (1/1, 5°r6, natural pH--4) treated AA5005 panels.
Alkaline cleaned blank and chromated AA5005 panels were chosen as controls The treated panels were cured at 100°C for 10 min, and then exposed to SST for 29 days, along with the control panels. Four replicates were made for each treatment The results are presented in Fig. 1.
1. A1170MAS treated panels showed original surface after 29 days of exposure to SST, i.e. no corrosion occurred during testing.
2. The blank panels corroded heavily, white the chramated ones pitted apparently.
Example 2 Salt Spray test (Lakebluff) was carried out on A1170/VTAS (1.511.5%, natural pH=4) treated A12024-T3 panels. Alkaline cleaned blank and chromated A12024-T3 panels were chosen as controls. The treated panels were cured at 100°C far 10 min, and then exposed to SST for 7 days, along with the control panels. Three replicates were made for each treatment. The results are presented in Fig. 2.
3. A1170NTAS treated panels showed almost original surface after 7 days of exposure to SST, ~.e , only slight edge corrosion occurred during testing.
4. The blank panels corroded heavily, while the chromated ones pitted slightly.
Example 3 In order to investigate the paintability of A1170IVTAS water-based silane film on metal substrates, A1170IVTAS (1.5/1,2%, pH'-5) water-based silane film was applied on A12023-T3 and HDG, respectively. The treated panels were then powder-painted at Lakebluff with Polyester and Polyurethane powder paints. After that, the panels were put into salt spray chamber for some times, along with the control panels, the blank and the chromated. Three replicates were made for each treatment The results are shown in Fig. 3 1. As for A12024-T3 painted with both powder paints (1000hrs in SST), the corrosion performance and paint adhesion improved significantly, which was equal to the chromated and much better than the blank.
2. As for powder-painted HDG (336 hrs in SST), the corrosion performance improved apparently, compared with the chromated is and the clank. The paint adhesion improved somewhat, which was better that the control panels-
Claims (29)
1. A method of treating a metal surface, comprising the steps of.
(a) providing a metal substrate; and (b) applying a solution to said metal substrate, said solution comprising (iii) at least one acyloxy silane which comprises at least one acyloxy group, wherein said silane has been at least partially hydrolysed; and (iv) at least one basic compound;
wherein the acyloxy silane and the basic compound are present in concentrations to provide a solution pH of between about 3 and about 10, more preferably between about 4 and about 8, mast preferably 4 to 5 and wherein the solution is substantially free of acid other than acid produced upon hydrolysis of the acyloxy silane.
(a) providing a metal substrate; and (b) applying a solution to said metal substrate, said solution comprising (iii) at least one acyloxy silane which comprises at least one acyloxy group, wherein said silane has been at least partially hydrolysed; and (iv) at least one basic compound;
wherein the acyloxy silane and the basic compound are present in concentrations to provide a solution pH of between about 3 and about 10, more preferably between about 4 and about 8, mast preferably 4 to 5 and wherein the solution is substantially free of acid other than acid produced upon hydrolysis of the acyloxy silane.
2. The method according to claim 1, wherein the metal surface selected from the group consisting of steel, aluminium, aluminium alloys, zinc, zinc alloys, magnesium, magnesium alloys, copper, copper alloys, tin, and, tin alloys.
3. The method according to claim 1, wherein the metal surface is selected from the group consisting of:
-a metal surface having a zinc-containing coating;
-zinc;
-zinc alloy.
-Aluminium;
-Aluminium alloy; and -steel.
-a metal surface having a zinc-containing coating;
-zinc;
-zinc alloy.
-Aluminium;
-Aluminium alloy; and -steel.
4. The method according to any preceding claim, wherein the acyloxysilane comprises a single tetrasubstituted silicon atom, wherein the substituents are individually selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, alkaryl, aralkyl, vinyl, amino, ureido, glycidoxy, epoxy, hydroxy, alkoxy, aryloxy and acyloxy, or any of the group alkyl, alkenyl, alkynyl, aryl, alkaryl and aralkyl substituted by a group selected from the group consisting of vinyl, amine, ureido, glycidoxy, epoxy, hydroxy and alkoxy, with the proviso that at least one of the substituents on the silicon atom is an acyloxy group
5. The method according to any preceding claim, wherein the acyloxy groups are preferably all the same and are selected from the group consisting of C2-12 alkanoyloxy, C3-12 alkenoyloxy, C3-12 alkynoyloxy and C7-18 arenoyloxy, preferably C2-6 alkanoyloxy, C3-6 alkenoyloxy, C3-6 alkynoyloxy and C7-12 arenoyloxy, preferably ethanoyloxy or methanoyloxy groups.
6. The method according to any preceding claim, wherein the acyloxy silane is selected from the group wherein W, X, Y and 2 are selected from the group consisting of a C-Si bond, substituted aliphatic groups, unsubstituted aliphatic groups, substituted aromatic groups and unsubstituted aromatic groups; and R is Selected from methyl, ethyl and propyl, preferably ethyl.
7 The method according to claim 1, wherein the acyloxy silane comprises more than one silyl group, preferably two silyl groups.
8. The method according to claim 7, wherein the acyloxy groups are the same and are selected from the group consisting of C2-12 alkanoyloxy, C3-12 alkenoyloxy, C3-12 alkynoyloxy and C7-18 arenoyloxy, preferably C2-6 alkanoyloxy, C3-6 alkenoyloxy, C3-6 alkynoyloxy and C7-12 arenoyloxy, preferably ethanoyloxy and methanoyloxy groups.
9. The method according to claim 7 or 8, wherein the acyloxysilane has the structure wherein Q is selected from the group consisting of either a bond, an aliphatic or aromatic group; and R1 is selected from methyl, ethyl and propyl.
10. The method according to claim 9, wherein Q is selected from the group consisting of a bond, C1-C6 alkylene, C2-C6 alkenylene, C1-C8 alkylene substituted with at least one amino group, C2-C6 alkenylene substituted with at least one amino group, C1-C6 alkylene substituted with at least one sulfide group containing 1 to 10 sulfur atoms, C2-C6 alkenylene substituted with at least one sulfide group containing 1 to 10 sulfur atoms, arylene and alkylarylene
11. The method according to claim 10, wherein the acyloxy silane is selected from the group consisting of bis-(triacetoxysilyl)ethane, bis-(triacetoxysilylpropyl)amine and bis-(triacetoxysilylpropyl)tetrasulfide.
12. The method according to claim 1, wherein the acyloxy silane is vinyltriacetoxysilane.
13. The method according to any preceding claim, wherein the basic compound is selected from the carbonates, hydrogen carbonates and hydroxides of the alkali and alkaline earth metals, organic amines, ammonia, amides and silanes, and mixtures thereof.
14. The method according to any preceding claim, wherein the basic compound is a basic silane compound selected from compounds having the general structure wherein R2 is chosen from the group consisting of hydrogen and C1-C24 alkyl, preferably C1-C6 alkyl and each R may be the same or different;
X1 is selected from the group consisting of a bond, a substituted or unsubstituted aliphatic or aromatic group; and R3 is a group individually selected from the group consisting of hydrogen, C1-alkyl, C2-C6 alkenyl, C1-C6 alkyl substituted with at feast one amino group, alkenyl substituted with at least one amino group, arylene and alkylarylene.
X1 is selected from the group consisting of a bond, a substituted or unsubstituted aliphatic or aromatic group; and R3 is a group individually selected from the group consisting of hydrogen, C1-alkyl, C2-C6 alkenyl, C1-C6 alkyl substituted with at feast one amino group, alkenyl substituted with at least one amino group, arylene and alkylarylene.
15. The method according to claim 14, wherein R2 is individually chosen from the group consisting of hydrogen, ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl and ter-butyl;
X1 is selected from the group chosen from the group consisting of a bond, C1-alkylene, C2-C6 alkenylene, C1-C6 alkylene substituted with at least one amino group, C2-C6 alkenylene substituted with at least one amino group, arylene and alkylarylene; and R3 is individually selected from the group consisting of hydrogen, ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl ter-butyl and acetyl.
X1 is selected from the group chosen from the group consisting of a bond, C1-alkylene, C2-C6 alkenylene, C1-C6 alkylene substituted with at least one amino group, C2-C6 alkenylene substituted with at least one amino group, arylene and alkylarylene; and R3 is individually selected from the group consisting of hydrogen, ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl ter-butyl and acetyl.
16 The method of any of claims 1 to 13, wherein the basic compound is a bis-silyl aminosilane(s) having the structure wherein R4 is individually selected from the group consisting of: hydrogen and C1 - C24 alkyl;
R5 is individually selected from the group consisting of: substituted aliphatic groups, unsubstituted aliphatic groups, substituted aromatic groups, and unsubstituted aromatic groups; and -X2 is either:
wherein each R6 is individually selected from the group consisting of:
hydrogen, substituted and unsubstituted aliphatic groups, and substituted and unsubstituted aromatic groups; and R7 is selected from the group consisting of: substituted and unsubstituted aliphatic groups, and substituted and unsubstituted aromatic groups.
R5 is individually selected from the group consisting of: substituted aliphatic groups, unsubstituted aliphatic groups, substituted aromatic groups, and unsubstituted aromatic groups; and -X2 is either:
wherein each R6 is individually selected from the group consisting of:
hydrogen, substituted and unsubstituted aliphatic groups, and substituted and unsubstituted aromatic groups; and R7 is selected from the group consisting of: substituted and unsubstituted aliphatic groups, and substituted and unsubstituted aromatic groups.
17. The method according to claim 1, wherein the basic compounds are selected from the group consisting of y-aminopropyltriethoxysilane and y-aminopropyltrimethoxysilane, bis-(trimethoxysilylpropyl)amine, bis-(triethoxysilylpropyl)amine and bis-(triethoxysilylpropyl)ethylene diamine
18. The method according to any preceding claim, wherein a polymer coating is applied to the treated metal substrate.
19. The method of claim 18, wherein the poylmer coating is selected from paints, adhesives, rubbers and plastics.
20. The method according to any preceding claim, wherein the solution contains at least about 0.1% acyloxy silanes by volume, more preferably at least about 1% acyloxy silanes by volume, most preferably between about 2% and about 5% by volume.
21. The method according to any preceding claim, wherein the solution contains at least about 0.1% basic compound ay volume, more preferably at least about 1% by volume, more preferably between about 2% and about 10%, most preferably between about 2% and about 5% by volume.
22. A composition comprising an acyloxy silane and a basic compound as defined in any preceding claim, wherein the solution pH is between 3 and about 10, more preferably between about a and about 8, most preferably 4 to 5 and wherein the solution is substantially free acids other than acids produced upon hydrolysis of the acyloxy silanes.
23. The composition according to claim 22, wherein the solution contains at least about 0.1% acyloxy silanes by volume, more preferably at least about 1 acyloxy silanes by volume, most preferably between about 2% and about 5% by volume
24. The composition according to claim 22 or 23, wherein the solution contains at least about 0.1% basic compound by volume, more preferably at least about 1% by volume, more preferably between about 2% and about 10%, most preferably between about 2% and about 5% by volume.
25. A composition comprising an acyloxy silane and a basic compound as defined in any of claims 1 to 22, wherein the acyloxy silane is substantially unhydrolysed and the composition is substantially free of water.
26. The composition according to claim 25, wherein the combined concentration of the acyloxy silane and basic compound in composition is generally in the range 10-100%, preferably 15-80%, most preferably 25-70%.
27. The composition according to claim 26, wherein the concentrations of acyloxy silane and basic compound pre-determined so as to provide a solution with a pH in the range of between 3 and about 10, more preferably between about 4 and about 8, most preferably 4 to 5 when dissolved in water.
28 The composition according to any of claims 22 to 27, comprising additional components selected from stabilisers, pigments, anti-oxidants, desiccants, adhesion promoters, corrosion inhibitors and mixtures thereof.
29 A kit comprising a composition according to any of claims 22 to 28.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/356,926 US6827981B2 (en) | 1999-07-19 | 1999-07-19 | Silane coatings for metal |
| US09/356,926 | 1999-07-19 | ||
| EPPCT/EP00/06794 | 2000-07-17 | ||
| PCT/EP2000/006794 WO2001005520A2 (en) | 1999-07-19 | 2000-07-17 | Protective treatment of metal surfaces with aqueous mixture of vinyl silane and bis-silyl aminosilane |
| PCT/US2000/019646 WO2001006036A1 (en) | 1999-07-19 | 2000-07-19 | Acyloxy silane treatments for metals |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2378851A1 true CA2378851A1 (en) | 2001-01-25 |
Family
ID=26069194
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002378851A Abandoned CA2378851A1 (en) | 1999-07-19 | 2000-07-19 | Acyloxy silane treatments for metals |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU766638B2 (en) |
| CA (1) | CA2378851A1 (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1032616A4 (en) * | 1997-10-23 | 2001-04-11 | Aar Cornelis P J V D | Rubber to metal bonding by silane coupling agents |
| US6132808A (en) * | 1999-02-05 | 2000-10-17 | Brent International Plc | Method of treating metals using amino silanes and multi-silyl-functional silanes in admixture |
-
2000
- 2000-07-19 AU AU62225/00A patent/AU766638B2/en not_active Expired
- 2000-07-19 CA CA002378851A patent/CA2378851A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| AU6222500A (en) | 2001-02-05 |
| AU766638B2 (en) | 2003-10-23 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |