Autodeposition metal dip coating process
What is disclosed is a no-rinse autodeposition process to dip-apply a metal part in an aqueous resin coating bath with an immersion time and, wherein the removal rate of the dipped part is kept equal or below drainage rate of mobile liquid portion, such that upon removal of the part, drip edge formation is minimized and a DFT is maintained within acceptable tolerance levels.
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The present invention relates to dip-application of aqueous autodepositable compositions.
BACKGROUND OF THE INVENTIONAutodeposition is an aqueous process for coating metal that is driven by reactions between the coating and metal substrate when small amounts of multivalent metal ions are released from the metal surface. The aqueous composition must contain a stabilized polymer dispersion. The essential feature of an autodepositable coating is that the dispersed material is stabilized by functional groups on the polymer and/or provided by surface active agents which are sensitive to multivalent ions entering the aqueous phase. Deposition occurs by interaction of the multivalent ions and these stabilizing functional groups causing the dispersion to precipitate when sufficient concentration of multivalent ions occurs at the metal surface.
Examples of autodepositing compositions are disclosed, for example, in European Patent Publication 0132828, Bashir M. Ahmed, U.S. Pat. No. 4,647,480 and Wilbur S. Hall, U.S. Pat. No. 4,186,219, U.S. Pat. No. 4,657,788, U.S. Pat. Nos. 5,691,048, and 4,657,788, and patents cited therein each of which is incorporated herein by reference. Such compositions designed to particularly effective when the resin material is provided in the form of a dispersed polymer such as a sulfonate-functionalized novolak, or latex made from the emulsion polymerized product of at least two polymerizable ethylenically unsaturated monomers.
In the practice of dip-applied autodeposition coatings, often the coating can be rinsed after withdrawal from the bath. In some instances, rinsing is not undertaken. There remains some limits on the process of autodepositing coatings on metal parts without a rinse step. A problem arises without a rinse step relating to accumulation of drainage along edges, that when dried leads to what is referred to as drip edges. These drip edges result in poorer protective coatings. In attempts to alieviate drip edges other problems can arise, such as variable dry film thickness (DFT) in different areas of the part surface. The need for a non-rinsing coating method that deposits a sufficient amount of coating, with an acceptable DFT uniformity, while reducing the incidence of drip edges would be highly desirable in a dip-applied autodeposited coating.
SUMMARY OF THE INVENTIONAccording to a preferred aspect of present invention there is provided a no-rinse autodeposition process to dip-apply a metal part in an aqueous coating bath containing a specified solids level, at a specified bath temperature, immersion time and, wherein the removal rate of the dipped part is kept equal or below drainage rate of mobile liquid portion, such that upon removal of the part, drip edge formation is minimized and a DFT is maintained within acceptable tolerance levels.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSUnless otherwise indicated, description of components in chemical nomenclature refers to the components at the time of addition to any combination specified in the description, but does not necessarily preclude chemical interactions among the components of a mixture once mixed.
As used herein the term “autodeposited resin” shall mean all resins which can be autodeposited in the autodeposition process.
DFT is dry film thickness, and is measured using a Fisherscope MMS Permascope and an average of 10 readings are taken as the statistical sample on each part or panel.
“Primer” means a liquid composition applied to a surface as an undercoat beneath a subsequently-applied covercoat. The covercoat can be an adhesive and the primer/adhesive covercoat forms an adhesive system for bonding two substrates together.
“Coating” means a liquid composition applied to a surface to form a protective and/or aesthetically pleasing coating on the surface.
“Electrochemically active metals” means iron and all metals and alloys more active than hydrogen in the electromotive series. Examples of electrochemically active metal surfaces include zinc, iron, aluminum and cold-rolled, polished, pickled, hot-rolled and galvanized steel.
“Ferrous” means iron and alloys of iron.
The autodeposited coatings are resin-containing acidic-aqueous compositions comprising an acid, an oxidizing agent and the aqueous dispersed resin. Examples of autodeposited compositions are known. Those which are suitable in the present invention are made as set forth in European Patent Publication 0132828 and U.S. Pat. Nos. 4,647,480 and 4,186,219.
The addition polymerized resins which can be autodeposited generally comprise at least one ethylenically unsaturated monomeric compound (e.g. vinyl-based resins). The preferred ethylenically unsaturated monomers include styrene-butadiene; acrylate; alkyl-substituted acrylates such as methyl methacrylate and ethyl methacrylate; vinyl halides such as vinyl chloride; vinylidene halides such as vinylidene chloride and vinylidene dichloride; alkylenes such as ethylene; halide-substituted alkylenes such as tetrafluoroethylene; and acrylonitriles such as acrylonitrile, combinations thereof and the like.
Of the condensation type resins suitable herein are aqueous dispersions of modified phenolic novolak resins. These are the reaction product of a phenolic resin precursor, a modifying agent and a multi-hydroxy phenolic compound. The modifying agent includes at least one functional moiety that enables the modifying agent to react with the phenolic resin precursor and at least one ionic moiety. According to a preferred embodiment the modifying agent is an aromatic compound. According to another embodiment the ionic moiety of the modifying agent is sulfate, sulfonate, sulfinate, sulfenate or oxysulfonate and the dispersed phenolic resin reaction product has a carbon/sulfur atom ratio of 20:1 to 200:1.
The acid can be any acid that is capable of reacting with a metal to generate a sufficient concentration of multivalent ions. The acids which may be used in the autodepositing composition include inorganic and strong organic acids, such as, for example, hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, halogen—substituted acetic acid such as chloroacetic acid and trichloroacetic acid, and citric acid. Hydrofluoric acid is a preferred acid used in conjunction with emulsion polymerized autodeposited resins. Phosphoric acid is a preferred acid used in conjunction with modified phenolic dispersion embodiments In the case of steel the multivalent ions liberated from the metal surface are ferric and/or ferrous ions. When the acid is mixed into the composition presumably the respective ions are formed and exist as independent species in addition to the presence of the free acid. In other words, in the case of phosphoric acid, phosphate ions and free phosphoric acid co-exist in the coating bath. As for modified phenolic dispersion embodiments, the acid preferably is present in an amount of 5 to 300 parts by weight, more preferably 10 to 160 parts by weight, based on 100 parts by weight of the resin dispersion.
The oxidizing agents which can be employed in an autodepositing composition for use in the present invention include peroxides such as hydrogen peroxide, chromates and dichromates such as chromic acid and potassium dichromate, nitrates such as nitric acid and sodium nitrate, persulfates such as sodium persulfate and ammonium persulfate, perborates such as sodium perborate, iron (III) such as ferric fluoride. Hydrogen peroxide and ferric fluoride are the preferred oxidizing agents.
Exemplary autodepositing compositions for use in the present invention are those where the resin is in the form of a latex (i.e. an emulsion polymerization product of at least one polymerizable ethylenically unsaturated monomer). Examples of such compositions include Autophoretic® 800 Series autodepositing compositions based on polyvinylidene resins and Autophoretic® 700 Series autodepositing compositions based on acrylic resins, each composition being made by Henkel. Such compositions preferably contain hydrofluoric acid and hydrogen peroxide or iron (III) fluoride as the oxidizing agent. Other commercially available autodepositable coatings are provided by Lord Corporation under the Autoseal trademark, e.g., MJ 2110 is most preferred, and is disclosed in copending application Ser. No. 09/235, 201, hereby incorporated by reference. Prior to applying a dip-applied autodeposition coating, the most preferred metal treatment is provided by the use of an aqueous metal treatment primer composition disclosed in copending application Ser. No. 09/235,778 which is hereby incorporated by reference.
The coatings produced by autodepositing compounds under autodepositing conditions generally have an average nominal thickness of from 0.5 to 3 mils, preferably from about 1.0 to 2.0 mils, applied over a metal treatment having a thickness of from 0.1 to 0.5 mils ±0.05 mils. Water, preferably deionized water, is utilized to establish the predetermined solids content. Although the solids content may be varied as desired, the solids content of the coating bath is in a range of from 3 to 10%. The bath composition is waterborne and substantially free of volatile organic compounds. In the practice of the invention the range of the average DFT of autodeposited coating over the part surface is kept within ±0.3 mils, preferably +/- 0.2 mils, by processing a total solids bath in a range of solids of from 5 wt. % to 10%, preferably 6 wt. % solids, at a bath temperature of from 15° C. to 40° C., an Immersion time of from 20 to 80 seconds, preferably from 30 to 75 seconds, and a part withdrawal rate of from 1 to 10 ft./minute, preferably from 3 to 6 ft./min.
In a preferred embodiment of dip-applied method to coat a metal part an aqueous autodeposition bath comprises a phenolic resin dispersion, particularly an aqueous novolak dispersion and a deposition control agent and an optional a flexibilizer component in admixture therewith..
This rate of autodeposition is independent of the withdrawal rate of the part. Typically the instantaneous rate of deposition slows with the elapsed immersion time. This reduction in deposition rate is referred to as “a self-limiting” feature, however to immersion time is limited to maintain an optimal DFT. Even with the formation of a gelled deposit on the immersed part, there are components of the autodeposition system that further drain from the gel as the part is withdrawn. The withdrawal rate is kept at or below the drainage rate in the practice of the invention, such that upon complete withdrawal, drip edges are reduced and most preferably eliminated. The standard deviation of DFT measured at 10 points on the surface of the part is kept to within 0.05 mils to 0.16 mils despite the slow withdrawal rates.
In the most preferred embodiment, the coating when dried is a thin, tightly bound interpenetrating organic/inorganic matrix of phenolic/metal phosphates at the metal substrate interface. This matrix can be further flexibilized with polymers. The flexibilizer is any material that contributes flexibility and/or toughness to the film formed from the composition. The toughness provided by the flexibilizer provides fracture resistance to the film. The flexibilizer should be non-glassy at ambient temperature and be an aqueous emulsion latex or aqueous dispersion that is compatible with the phenolic novolak resin dispersion. The flexibilizer preferably is formulated into the composition in the form of an aqueous emulsion latex or aqueous dispersion.
Suitable resin dispersions include aqueous latices, emulsions or dispersions of (poly)butadiene, neoprene, styrene-butadiene rubber, acrylonitrile-butadiene rubber (also known as nitrile rubber), halogenated polyolefin, acrylic polymer, urethane polymer, ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymer rubber, styrene-acrylic copolymer, polyamide, poly(vinyl acetate) and the like. Halogenated polyolefins, nitrile rubbers and styrene-acrylic copolymers are preferred.
A suitable styrene-acrylic polymer latex is commercially available from Goodyear Tire & Rubber under the trade designation PLIOTEC and described, for example, in U.S. Pat. No. 4,968,741; 5,122,566 and 5,616,635. According to U.S. Pat. No. 5,616,635, such a copolymer latex is made from 45-85 weight percent vinyl aromatic monomers, 15-50 weight percent of at least one alkyl acrylate monomer and 1-6 weight percent unsaturated carbonyl compound. Styrene is the preferred vinyl aromatic monomer, butyl acrylate is the preferred acrylate monomer and acrylic acid and methacrylic acid are the preferred unsaturated carbonyl compound. The mixture for making the latex also includes at least one phosphate ester surfactant, at least one water-insoluble nonionic surface active agent and at least one free radical initiator.
Nitrile rubber emulsion latex is generally made from at least one monomer of acrylonitrile or an alkyl derivative thereof and at least one monomer of a conjugated diene, preferably butadiene. According to U.S. Pat. No. 4,920,176 the acrylonitrile or alkyl derivative monomer should be present in an amount of 0 or 1 to 50 percent by weight based on the total weight of the monomers. The conjugated diene monomer should be present in an amount of 50 percent to 99 percent by weight based on the total weight of the monomers. The nitrile rubbers can also optionally include various co-monomers such as acrylic acid or various esters thereof, dicarboxylic acids or combinations thereof. The polymerization of the monomers typically is initiated via free radical catalysts. Anionic surfactants typically are also added. A suitable nitrile rubber latex is available from B. F. Goodrich under the HYCAR® mark. Representative halogenated polyolefins include chlorinated natural rubber, chlorine- and bromine-containing synthetic rubbers including polychloroprene, chlorinated polychloroprene, chlorinated polybutadiene, hexachloropentadiene, butadiene/halogenated cyclic conjugated diene adducts, chlorinated butadiene styrene copolymers, chlorinated ethylene propylene copolymers and ethylene/propylene/non-conjugated diene terpolymers, chlorinated polyethylene, chlorosulfonated polyethylene, poly(2,3-dichloro-1,3-butadiene), brominated poly(2,3-dichloro-1,3-butadiene), copolymers of (c-haloacrylonitriles and 2,3-dichloro-1,3-butadiene, chlorinated poly(vinyl chloride) and the like including mixtures of such halogen-containing elastomers.
Latices of the halogenated polyolefin can be prepared according to methods known in the art such as by dissolving the halogenated polyolefin in a solvent and adding a surfactant to the resulting solution. Water can then be added to the solution under high shear to emulsify the polymer. The solvent is then stripped to obtain a latex. The latex can also be prepared by emulsion polymerization of the halogenated ethylenically unsaturated monomers.
Butadiene latices are particularly preferred as the flexibilizer. Methods for making butadiene latices are widely available commercially, and are described, for example, in U.S. Pat. Nos. 4,054,547 and 3,920,600, both incorporated herein by reference. In addition, U.S. Pat. Nos. 5,200,459; 5,300,555; and 5,496,884 disclose emulsion polymerization of butadiene monomers in the presence of polyvinyl alcohol and a co-solvent such as an organic alcohol or a glycol.
The butadiene monomers useful for preparing a butadiene polymer latex as a flexibilizer, can essentially be any monomer containing conjugated unsaturation. Typical monomers include 2,3-dichloro-1,3-butadiene; 1,3-butadiene; 2,3-dibromo-1,3-butadiene isoprene; isoprene; 2,3-dimethylbutadiene; chloroprene; bromoprene; 2,3-dibromo-1,3-butadiene; 1,1,2-trichlorobutadiene; cyanoprene; hexachlorobutadiene; and combinations thereof.
It is particularly preferred to use 2,3-dichloro-1,3-butadiene since a polymer that contains as its major portion 2,3-dichloro-1,3-butadiene monomer units has been found to be particularly useful in adhesive applications due to the excellent bonding ability and barrier properties of the 2,3-dichloro-1,3-butadiene-based polymers. As described above, an especially preferred embodiment of the present invention is one wherein the butadiene polymer includes at least 60 weight percent, preferably at least 70 weight percent, 2,3-dichloro-1,3-butadiene monomer units.
The butadiene monomer can be copolymerized with other monomers. Such copolymerizable monomers include α-haloacrylonitriles such as α-bromoacrylonitrile and α-chloroacrylonitrile; α,β-unsaturated carboxylic acids such as acrylic, methacrylic, 2-ethylacrylic, 2-propylacrylic, 2-butylacrylic and itaconic acids; alkyl-2-haloacrylates such as ethyl-2-chloroacrylate and ethyl-2-bromoacrylate; α-bromovinylketone; vinylidene chloride; vinyl toluenes; vinylnaphthalenes; vinyl ethers, esters and ketones such as methyl vinyl ether, vinyl acetate and methyl vinyl ketone; esters amides, and nitriles of acrylic and methacrylic acids such as ethyl acrylate, methyl methacrylate, glycidyl acrylate, methacrylamide and acrylonitrile; and combinations of such monomers. The copolymerizable monomers, if utilized, are preferably α-haloacrylonitrile and/or α,β-unsaturated carboxylic acids. The copolymerizable monomers may be utilized in an amount of 0.1 to 30 weight percent, based on the weight of the total monomers utilized to form the butadiene polymer.
In carrying out the emulsion polymerization to produce the latex, conventional anionic and/or nonionic surfactants may be utilized in order to aid in the formation of the latex. Typical anionic surfactants include carboxylates such as fatty acid soaps from lauric, stearic, and oleic acid; acyl derivatives of sarcosine such as methyl glycine; sulfates such as sodium lauryl sulfate; sulfated natural oils and esters such as Turkey Red Oil; alkyl aryl polyether sulfates; alkali alkyl sulfates; ethoxylated aryl sulfonic acid salts; alkyl aryl polyether sulfonates; isopropyl naphthalene sulfonates; sulfosuccinates; phosphate esters such as short chain fatty alcohol partial esters of complex phosphates; and orthophosphate esters of polyethoxylated fatty alcohols. Typical nonionic surfactants include ethoxylated (ethylene oxide) derivatives such as ethoxylated alkyl aryl derivatives; mono- and polyhydric alcohols; ethylene oxide/propylene oxide block copolymers; esters such as glyceryl monostearate; products of the dehydration of sorbitol such as sorbitan monostearate and polyethylene oxide sorbitan monolaurate; amines; lauric acid; and isopropenyl halide. A conventional surfactant, if utilized, is employed in an amount of 0.01 to 5 parts, preferably 0.1 to 2 parts, per 100 parts by weight of total monomers utilized to form the butadiene polymer.
The preferred dichlorobutadiene homopolymers have a colloidal stabilizing system characterized by anionic surfactants. Such anionic surfactants include alkyl sulfonates and alkyl aryl sulfonates (commercially available from Stepan under the trade designation POLYSTEP) and sulfonic acids or salts of alkylated diphenyl oxide (for example, didodecyl diphenyleneoxide disulfonate or dihexyl diphenyloxide disulfonate commercially available from Dow Chemical Co. under the trade designation DOWFAX).
Especially preferred butadiene latexes as flexibilizers are polymerized in the presence of a styrene sulfonic acid, styrene sulfonate, poly(styrene sulfonic acid), or poly(styrene sulfonate) stabilizer to form the latex. Poly(styrene sulfonate) is the preferred stabilizer. This stabilization system is particularly effective for a butadiene polymer that is derived from at least 60 weight percent dichlorobutadiene monomer, based on the amount of total monomers used to form the butadiene polymer. The butadiene polymer latex can be made by known emulsion polymerization techniques that involve polymerizing the butadiene monomer (and copolymerizable monomer, if present) in the presence of water and the styrene sulfonic acid, styrene sulfonate, poly(styrene sulfonic acid), or poly(styrene sulfonate) stabilizer. The sulfonates can be salts of any cationic groups such as sodium, potassium or quaternary ammonium. Sodium styrene sulfonate is a preferred styrene sulfonate compound. Poly(styrene sulfonate) polymers include poly(styrene sulfonate) homopolymer and poly(styrene sulfonate) copolymers such as those with maleic anhydride. Sodium salts of poly(styrene sulfonate) are particularly preferred and are commercially available from National Starch under the trade designation VERSA TL. The poly(styrene sulfonate) can have a weight average molecular weight from 5×104 to 1.5×106, with 1.5×105 to 2.5×105 being preferred. In the case of a poly(styrene sulfonate) or poly(styrene sulfonic acid) it is important to recognize that the emulsion polymerization takes place in the presence of the pre-formed polymer. In other words, the butadiene monomer is contacted with the pre-formed poly(styrene sulfonate) or poly(styrene sulfonic acid). The stabilizer preferably is present in an amount of 0.1 to 10 parts, preferably 1 to 5 parts, per 100 parts by weight of total monomers utilized to form the butadiene polymer.
The flexibilizer, if present, preferably is included in the composition in an amount of 5 parts by weight to 300 parts by weight, based on 100 parts by weight of the preferred phenolic novolak resin dispersion. More preferably, the flexibilizer is present in an amount of 25 parts by weight to 100 parts by weight, based on 100 parts by weight of the phenolic novolak resin dispersion.
The modified phenolic resin dispersion can be cured to form a highly crosslinked thermoset via known curing methods for phenolic resins. The curing mechanism can vary depending upon the use and form of the phenolic resin dispersion. For example, curing of the dispersed resole embodiment typically can be accomplished by subjecting the phenolic resin dispersion to heat. Curing of the dispersed novolak embodiment typically can be accomplished by addition of an aldehyde donor compound.
Since the dispersed phenolic resin is a novolak, a curative should be introduced in order to cure the film formed by the metal treatment composition. It should be noted that the metal treatment composition cannot itself include a phenolic resin curative as these curatives are not storage stable under acidic conditions. Curing of the film can be accomplished by the application of a curative-containing topcoat over the metal treatment film. Typically, the metal treatment composition is applied to a metal surface (either conventionally or via autodeposition) and then dried. The curative-containing autodeposited topcoat then is applied to the thus treated metal surface. The curative contained in the topcoat can be an aldehyde donor compound or an aromatic nitroso compound. Topcoat compositions that include either one or both of these curatives are well-known and commercially available.
The aldehyde donor can be essentially be any type of aldehyde known to react with hydroxy aromatic compounds to form cured or crosslinked novolak phenolic resins. Typical compounds useful as an aldehyde (e.g., formaldehyde) source in the present invention include formaldehyde and aqueous solutions of formaldehyde, such as formalin; acetaldehyde; propionaldehyde; isobutyraldehyde; 2-ethylhexaldehyde; 2-methylpentaldehyde; 2-ethylhexaldehyde; benzaldehyde; as well as compounds which decompose to formaldehyde, such as paraformaldehyde, trioxane, furfural, hexamethylenetetramine, anhydromaldehydeaniline, ethylene diamine formaldehyde; acetals which liberate formaldehyde on heating; methylol derivatives of urea and formaldehyde; methylol phenolic compounds; and the like.
It has been found that metal parts pre-primer coated with a primer described in U.S. Ser. No. 09/235,778, formaldehyde species generated from the resole present in the primer appear to co-cure the novolak in the metal treatment coating via diffusion. In addition, curing or crosslinking of the novolak may occur through ionic crosslinking and chelation with the metal ions generated by the acid-metal substrate reaction.
Additionally, high molecular weight aldehyde homopolymers and copolymers can be employed as a latent formaldehyde source in the practice of the present invention. A latent formaldehyde source herein refers to a formaldehyde source which will release formaldehyde only in the presence of heat such as the heat applied during the curing of an adhesive system. Typical high molecular weight aldehyde homopolymers and copolymers include (1) acetal homopolymers, (2) acetal copolymers, (3) gamma-polyoxy-methylene ethers having the characteristic structure:
R10O—(CH2O)n—R11
and (4) polyoxymethylene glycols having the characteristic structure:
HO—(R12O)x—(CH2O)n—(R13O)x—H
wherein R10 and R11 can be the same or different and each is an alkyl group having from about 1 to 8, preferably 1 to 4, carbon atoms, R12 and R13 can be the same or different and each is an alkylene group having from 2 to 12, preferably 2 to 8, carbon atoms; n is greater than 100, and is preferably in the range from about 200 to about 2000; and x is in the range from about 0 to 8, preferably 1 to 4, with at least one x being equal to at least 1. The high molecular weight aldehyde homopolymers and copolymers are further characterized by a melting point of at least 75° C., i.e. they are substantially inert with respect to the phenolic system until heat activated; and by being substantially completely insoluble in water at a temperature below the melting point. The acetal homopolymers and acetal copolymers are well-known articles of commerce. The polyoxymethylene materials are also well known and can be readily synthesized by the reaction of monoalcohols having from 1 to 8 carbon atoms or dihydroxy glycols and ether glycols with polyoxymethylene glycols in the presence of an acidic catalyst. A representative method of preparing these crosslinking agents is described in U.S. Pat. No. 2,512,950, which is incorporated herein by reference. Gamma-polyoxymethylene ethers are generally preferred sources of latent formaldehyde and a particularly preferred latent formaldehyde source for use in the practice of the invention is 2-polyoxymethylene dimethyl ether.
The aromatic nitroso compound can be any aromatic hydrocarbon, such as benzenes, naphthalenes, anthracenes, biphenyls, and the like, containing at least two nitroso groups attached directly to non-adjacent ring carbon atoms. Such aromatic nitroso compounds are described, for example, in U.S. Pat. No. 3,258,388; U.S. Pat. No. 4,119,587 and U.S. Pat. No. 5,496,884.
The control agent mentioned above is especially useful in the metal treatment composition of the invention described above but it could also be useful in any multi-component composition that includes an autodepositable component. The autodepositable component is any material that enables (either by itself or in combination with the other components of the composition) the multi-component composition to autodeposit on a metal surface. Preferably, the autodepositable component is any water-dispersed or water soluble resin that is capable of providing autodeposition ability to the composition. It is believed that the present invention will be used most widely in connection with coatings formed from organic polymers in particular, those polymers derived from ethylenically unsaturated compounds. Other organic polymers useful in the instant invention are those that can be obtained in a form suitable for compounding into an aqueous coating bath. Organic resins include those derived from ethylenically unsaturated monomers such as polyvinylidene chloride, polyvinyl chloride, polyethylene, acrylic, acrylonitrile, polyvinyl acetate and styrene-butadiene (see U.S. Pat. Nos. 4,414,350; 4,994,521; and 5,427,863; and PCT Published Patent Application No. WO 93/15154). Urethane and polyester resins are also mentioned as being useful. Certain epoxy and epoxy-acrylate resins are also said to be useful autodeposition resins (see U.S. Pat. No. 5,500,460 and PCT Published Patent Application No. WO 97/07163). Blends of these resins may also be used.
The preferred autodepositable resins are aqueous phenolic resin dispersions described in co-pending, commonly assigned U.S. patent application Ser. No. 09/235,201, incorporated herein by reference. The novolak version of this dispersed resin is described above in connection with the metal treatment composition. There is also a resole version with which the control agent of the invention may be formulated into a multi-component composition.
The phenolic resin precursor and modifying agent used to make the dispersed resole are the same as those described for the dispersed novolak. However, the dispersed resole is produced by the reaction of 1 mol of modifying agent(s) with 1 to 20 mol of phenolic resin precursor(s). A dispersed resole typically can be obtained by reacting a resole precursor or a mixture of resole precursors with the modifying agent or a mixture of agents without any other reactants, additives or catalysts. However, other reactants, additives or catalysts can be used as desired. Multi-hydroxy phenolic compound(s) can optionally be included in relatively small amounts in the reactant mixture for the resole. Synthesis of the resole does not require an acid catalyst.
Hydrophilic resoles typically have a F/P ratio of at least 1.0. According to the invention, hydrophilic resoles having a F/P ratio much greater than 1.0 can be successfully dispersed. For example, it is possible to make an aqueous dispersion of hydrophilic resoles having a F/P ratio of at least 2 and approaching 3, which is the theoretical F/P ratio limit.
According to a particularly preferred embodiment disclosed in U.S. Ser. No. 09/235,201, wherein the dispersed phenolic resin is a resole and the modifying agent is a naphthalene having a ionic pendant group X and two reaction-enabling substituents Y, the dispersed phenolic resin reaction product contains a mixture of oligomers having structures believed to be represented by the following formula III:
wherein X and Y are the same as in formulae Ia and Ib, a is 0 or 1; n is 0 to 5; R2 is independently —C(R5)2— or —C(R5)2—O—C(R5)2—, wherein R5 is independently hydrogen, alkylol, hydroxyl, alkyl, aryl or aryl ether; and R3 is independently alkylol, alkyl, aryl or aryl ether. Preferably, R2 is methylene or oxydimethylene and R3 is methylol. If 6,7-dihydroxy-2-naphthalenesulfonate, sodium salt is the modifying agent, X will be SO3−Na+ and each Y will be OH. It should be recognized that in this case the hydroxy groups for Y will also act as chelating groups with a metal ion.
The autodepositable component can be present in the composition in any amount that provides for effective autodeposition. In general, the amount can range from 1 to 50, preferably 5 to 20, and more preferably 7 to 14, weight percent, based on the total amount of non-volatile ingredients in the composition.
The control agent is any material that is able to improve the formation of an autodeposited coating on a metallic surface and, optionally, improve the formation of another autodeposited coating applied after the control agent-containing autodeposited coating. Addition of the control agent also increases the uniformity of the thickness of the autodeposited coating. The control agent-containing composition does not require an ambient staging period in order to develop fully the coating. In other words, the metallic coating conversion is complete upon drying of the coated substrate and any subsequent coating, primer or adhesive compositions can be applied immediately after coating and drying of the control agent-containing composition. The control agent also must be compatible with the other components of the composition under acidic conditions without prematurely coagulating or destabilizing the composition.
The control agent may be a nitro compound, a nitroso compound, an oxime compound, a nitrate compound, hydroxyl amine, or a similar material. A mixture of control agents may be used. Organic nitro compounds are the preferred control agents.
The organic nitro compound is any material that includes a nitro group (—NO2) bonded to an organic moiety. Preferably, the organic nitro compound is water soluble or, if water insoluble, capable of being dispersed in water. Illustrative organic nitro compounds include nitroguanidine; aromatic nitrosulfonates such as nitro or dinitrobenzenesulfonate and the salts thereof such as sodium, potassium, amine or any monovalent metal ion (particularly the sodium salt of 3,5-dinitrobenzenesulfonate); Naphthol Yellow S; and picric acid (also known as trinitrophenol). Especially preferred for commercial availability and regulatory reasons is a mixture of nitroguanidine and sodium nitrobenzenesulfonate.
The amount of control agent(s) in a multi-component composition may vary, particularly depending upon the amount of any acid in the composition. Preferably, the amount is up to 20 weight %, more preferably up to 10 weight %, and most preferably 2 to 5 weight %, based on the total amount of non-volatile ingredients in the composition. According to a preferred embodiment, the weight ratio of nitroguanidine to sodium nitrobenzenesulfonate should range from 1:10 to 5:1.
The organic nitro compound typically is mixed into the composition in the form of an aqueous solution or dispersion. For example, nitroguanidine is a solid at room temperature and is dissolved in water prior to formulating into the composition.
The compositions of the invention may be prepared by any method known in the art, but are preferably prepared by combining and milling or shaking the ingredients and water in ball-mill, sand-mill, ceramic bead-mill, steel-bead mill, high speed media-mill or the like. It is preferred to add each component to the mixture in a liquid form such as an aqueous dispersion.
For the salt chamber test the parts are scored to the metal surface in a cross hatch pattern using a new razor blade and placed in a standard salt spray chamber for 500 hours. Evaluation of corrosion creep is made.
Experimental:
Autodepositable Coating:
Withdrawal Rate for Coating: The small adhesive dip line was used to vary the withdrawal rate. The following withdrawal rates were used.
-
- Run 1—7.5 ft/min
- Run 2—5.7 ft/min
- Run 3—3.4 ft/min
- Run 4—1.0 ft/min
- Run 5—Control—Removed manually at 40 ft/min simulating commercial withdrawal rates.
Processing of the HRS Panels is as follows:
Results:
Claims
1. In an autodeposition coating process for forming a coating on a electrochemically active metal substrate which is dipped in an acidic bath, said coating derived from deposition of a dispersed resin in the bath on interaction of multivalent ions entering the aqueous phase, and wherein said substrate is characterized by no rinsing step, and a substrate withdrawal rate that is less than the drainage rate.
2. The process according to claim 1 wherein the electrochemically active metal is selected from zinc, iron, aluminum, cold-rolled steel, polished steel, picked steel, hot-rolled steel and galvanized steel.
3. The process according to claim 1 wherein said substrate is immersed in said acidic bath for a time of from 20 to 80 seconds before withdrawal.
4. The process according to claim 1 wherein said metal substrate is treated with a primer prior to dipping said substrate.
5. The process of claim 1 wherein said dispersed resin is a vinyl-based resin.
6. The process of claim 1 wherein said resin is a condensation resin.
7. The process according to claim 1 wherein the coating has an average nominal dry film thickness of from 0.5 to 3 mils (0.0127 mm to 0.076 mm).
8. The process according to claim 1 wherein said acidic bath has a solids content of from 3% to 10%.
9. The process according to claim 1 wherein the withdrawal rate is from 1 to 10 ft./min. (30.48 cm. To 25.4 cm.).
10. The process according to claim 1 wherein the dry film thickness of said coating has a standard deviation of within 0.05 to 0.16 mils (0.00127 to 004 mm).
11. The process according to claim 1 wherein said dispersed resin is based on a polymerizate from monomer selected from the group consisting of styrene and butadiene, acrylate, alkyl-substituted acrylate, vinyl halide monomer, vinylidene halide monomer, alkylene monomer; halide-substituted alkylene monomer and acrylonitrile monomer.
12. The process according to claim 11 wherein said dispersed resin is selected from emulsions or dispersions of (poly)butadiene, neoprene, styrene-butadiene rubber, acrylonitrile-butadiene rubber, halogenated polyolefin, acrylic polymer, urethane polymer, epoxy, polyester, ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymer rubber, styrene-acrylic copolymer, polyamide, and poly(vinyl acetate).
13. The process according to claim 1 wherein said dispersed resin is a butadiene latex polymerized in the presence of a compound selected from the group consisting of styrene sulfonic acid, styrene sulfonate, poly(styrene sulfonic acid), or poly(styrene sulfonate).
14. The process according to claim 1 wherein said bath comprises a modified phenolic resin and a flexibilizer.
15. The process according to claim 4 wherein said primer comprises a phenolic resole, and the coating on said primer comprises a novolak.
16. The process of claim 1 wherein the coating polymer is derived from vinyl monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, vinyl amides, nitriles, vinyl esters, vinyl ethers, vinyl halides, vinylidene halides, vinyl aromatic compounds, other ethylenically unsaturated compounds and combinations thereof.
17. The process of claim 14 wherein said flexibilizer is selected from (poly)butadiene, neoprene, styrene-butadiene rubber, nitrile rubber, halogenated polyolefin, acrylic polymer, urethane polymer, ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymer rubber, styrene-acrylic copolymer, polyamide and poly(vinyl acetate).
Type: Application
Filed: Aug 30, 2002
Publication Date: Nov 17, 2005
Applicant:
Inventors: James Williams (Erie, PA), Mark Weih (Holly Springs, NC), Brett Rearick (North East, PA)
Application Number: 10/231,621
