Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
  • C09D5/4484—Anodic paints
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/08—Processes
  • C08G18/16—Catalysts
  • C08G18/22—Catalysts containing metal compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/08—Processes
  • C08G18/16—Catalysts
  • C08G18/22—Catalysts containing metal compounds
  • C08G18/24—Catalysts containing metal compounds of tin
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
  • C08G18/40—High-molecular-weight compounds
  • C08G18/4009—Two or more macromolecular compounds not provided for in one single group of groups C08G18/42 - C08G18/64
  • C08G18/4018—Mixtures of compounds of group C08G18/42 with compounds of group C08G18/48
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
  • C08G18/40—High-molecular-weight compounds
  • C08G18/42—Polycondensates having carboxylic or carbonic ester groups in the main chain
  • C08G18/4266—Polycondensates having carboxylic or carbonic ester groups in the main chain prepared from hydroxycarboxylic acids and/or lactones
  • C08G18/4283—Hydroxycarboxylic acid or ester
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
  • C08G18/40—High-molecular-weight compounds
  • C08G18/48—Polyethers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
  • C09D175/04—Polyurethanes
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
  • C09D5/4488—Cathodic paints
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G2210/00—Compositions for preparing hydrogels
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G2230/00—Compositions for preparing biodegradable polymers

Definitions

• the present invention generally relates to a method of catalyzing a reaction of a hydroxy-functional resin and a blocked isocyanate crosslinker to form a urethane coating. More specifically, the present invention uses a complex, which is the reaction product of a polymeric ligand and a metal catalyst complexed with the polymeric ligand, to catalyze the reaction.
• the polymeric ligand is formed from the hydroxy-functional resin and/or the blocked isocyanate crosslinker.
• blocked isocyanate crosslinkers are used as components in coating compositions, in conjunction with hydroxy-functional resins, to form urethane coatings on substrates.
• the urethane coating results once the coating composition is sufficiently cured.
• Illustrative urethane coatings include urethane powder coatings, urethane automotive base coatings, urethane automotive clear coatings, urethane electrocoatings, urethane primer coatings, urethane coil and wire coatings and the like.
• blocked isocyanate crosslinkers require curing at elevated temperatures (e.g. greater than 32O 0 F and even greater than 35O 0 F) because, at the elevated temperatures, a blocking group associated with the crosslinker unblocks, i.e., removes itself, from the crosslinker and free isocyanate (NCO) functional groups remain.
• the free NCO functional groups are then capable of reaction with the hydroxy-functional groups of the resin to form a crosslinked network as the urethane coating.
• the metal catalysts typically include metal oxides, such as tin oxide, dibutyl tin oxide, and bismuth oxide, and organo-metallic salts, such as bismuth carboxylate and dibutyl tin dilaurate. Whether a metal oxide or an organo-metallic salt, these metal catalysts are added, in an unmodified form, directly into the composition that forms the urethane coating. Examples of such conventional metal catalysts and such conventional additions of the metal catalysts are disclosed in United States Patent Nos.
• organo-metallic salts in many instances, portions of the organo-metallic salts solubilize in the coating composition and, as a result, lead to certain physical defects, such as craters and/or poor film coalescence (realized as an undesirable 'poor flow' cracking-like phenomenon), in the cured coating. Frequently, portions of the organo- metallic salts are simply not compatible with the coating composition. Also, these types of metal catalysts, such as the specialized metal carboxylates disclosed in United States Patent No. 6,353,057, are based on fatty acid ligands formed from low molecular weight carboxylic acids.
• the ligands of the '057 patent are sufficient for complexing with the metal, such as the bismuth, it is known that they can have deleterious effects on the final, i.e., cured coating.
• the particular carboxylic acid used in the '057 patent is of low molecular weight, e.g. an M n less than about 200 Daltons, and is also at least partially soluble in water, then the carboxylic acid can cause contamination which is realized as craters in the cured coating.
• an e-coat 'bath' which contains the coating composition
• the ultraf ⁇ ltrate i.e., the portion of the bath that passes through the filter
• the aqueous medium is the ultraf ⁇ ltrate.
• low molecular weight carboxylic acids such as those of the '057 patent, pass through the ultrafilter and contaminate the aqueous medium. This is undesirable because, in preparing a particular substrate, such as a body component of a vehicle, the substrate is sprayed with the aqueous medium to rinse the substrate. During spraying, the low molecular weight carboxylic acids which contaminate the aqueous medium, can also be sprayed onto the substrate thereby introducing a potentially crater-causing material on the substrate.
• the particular carboxylic acid used in the '057 patent is of high molecular weight, e.g. an M n more than about 500 Daltons, then it can remain in the cured coating and cause problems during formation of the cured coating, i.e., during film formation, and also cause problems associated with adhesion of the cured coating to metal.
• the specialized, low molecular weight, metal carboxylates of the '057 also tend to exhibit poor stability stemming from addition of the metal carboxylates, such as a bismuth carboxylate, to an aqueous acidic medium. In this situation, the potential to hydrolyze exists and this potential is undesirable.
• a method of catalyzing a reaction which forms a urethane coating is disclosed.
• a complex for catalyzing a urethane coating composition is also disclosed.
• the urethane coating composition crosslink to forms the urethane coating.
• the reaction which forms the urethane coating in the present invention is, more specifically, the reaction of a hydroxy-functional resin and a blocked isocyanate crosslinker.
• the method includes the step of forming a polymeric ligand from the resin and/or the crosslinker.
• a metal catalyst is incorporated with the polymeric ligand to complex the metal catalyst with the polymeric ligand.
• the complex is the reaction product of the polymeric ligand and the metal catalyst complexed with the polymeric ligand.
• the resin and the crosslinker are reacted to form the urethane coating.
• the polymeric ligand which complexes with the metal catalyst is derived from the resin and/or the crosslinker which are both the 'backbone' of the urethane coating.
• the resin and/or the crosslinker are essentially being made a 'ligand' for the metal catalyst.
• the polymeric ligand of this invention replaces the simple, low molecular weight carboxylic acids utilized in the prior art which are not effective.
• the polymeric ligand is itself formed from the resin and/or the crosslinker, the polymeric ligand is integrated such that it is able to covalently link, i.e., attach or bind, itself to the resin and/or the crosslinker.
• covalent linking the polymeric ligand and therefore the metal catalyst complexed with the polymeric ligand are not extracted into the ultra-filtrate during the ultra-filtration process.
• maximum compatibility of the complex in the urethane coating composition is achieved and the permanence of the polymeric ligand in the urethane coating, i.e., the final cured film, is improved.
• the polymeric ligand in the final urethane coating physical properties are improved.
• the metal catalyst is easily and more effectively incorporated into the urethane coating composition via the customized polymeric ligand as compared to the direct addition of the unmodified metal catalysts of the prior art. Furthermore, improved cure response, especially low temperature cure response, is achieved due to the improved catalytic efficiency and reactivity associated with the method and complex of the present invention. Without intending to be bound by theory, it is conjectured that, due to its association with the polymeric ligand, the metal catalyst is more proximate the reacting functional groups, i.e., the hydroxy-functional groups of the resin and the free NCO functional groups of the unblocked crosslinker, during crosslinking.
• the advantages associated with the present invention are especially realized in physical properties of the urethane coating, such as solvent resistance, chip resistance, and corrosion inhibition.
• Figure 1 is a bar graph summarizing 50 MEK Double Rub Performance of Examples A- J at two different temperatures
• Figure 2 is a bar graph summarizing % Paint Loss of Examples A-J on CRS panels (with zinc phosphate treatment);
• Figure 3 is a bar graph summarizing % Paint Loss of Examples A-J on Zn/Fe panels;
• Figure 4 is a bar graph summarizing an average corrosion diameter (mm) of Examples A-J in Corrosion Test G;
• Figure 5 is a bar graph summarizing an average corrosion diameter (mm) of Examples A-J in Corrosion Test L.
• a method according to the present invention catalyzes a reaction to form a urethane coating.
• the reaction to form the urethane coating is, more specifically, the reaction of a hydroxy-functional resin and a blocked isocyanate crosslinker, also referred to as a curing agent.
• the hydroxy-functional resin and the blocked isocyanate crosslinker react, or crosslink, after unblocking of the crosslinker to establish urethane linkages ( — NH — CO — O — ) in the urethane coating.
• the hydroxy-functional resin and the blocked isocyanate crosslinker are described below simply as the resin and the crosslinker, respectively.
• the method more specifically utilizes a complex to catalyze a urethane coating composition to form the urethane coating.
• the resin and the crosslinker are components of the urethane coating composition.
• the urethane coating also referred to in the art as a urethane film or a urethane layer, is formed from the urethane coating composition upon application of the urethane coating composition to a substrate and upon cure of the urethane coating composition. The urethane coating results once the urethane coating composition is sufficiently cured.
• Illustrative urethane coatings include urethane powder coatings, urethane automotive base coatings, urethane automotive clear coatings, urethane electrocoatings, urethane primer coatings, urethane coil and wire coatings and the like. These and other urethane coatings can be formed from urethane coating compositions that are solventborne systems or waterborne systems.
• Preferred applications for the present invention are in urethane electrocoatings, or e- coats, whereby the urethane coating composition is either a cathodic electrocoat composition or an anodic electrocoat composition.
• the urethane coating composition is electrophoretically deposited onto a substrate, such as a structural body of a motor vehicle, by immersing the substrate in a bath including the urethane coating composition.
• An electrical potential is applied between the substrate and a pole of opposite charge, usually a stainless steel electrode. This produces a relatively soft coating on the substrate.
• This relatively soft coating is converted into the urethane coating of the present invention by crosslinking the resin and the crosslinker upon exposure to elevated temperatures as known by those skilled in the art.
• the resin preferably has one or more ionic groups or groups convertible to ionic groups.
• the ionic groups or groups which can be converted to ionic groups may be anionic groups or groups which can be converted into anionic groups, e.g. acidic groups such as -COOH groups, or cationic groups or groups which can be converted into cationic groups, e.g. basic groups such as amino groups and ammonium groups such as quaternary ammonium groups, or phosphonium and/or sulphonium groups. Basic groups which contain nitrogen are particularly preferred.
• these groups may be present in quaternised form, or are at least partially converted into ionic groups with a customary neutralizing agent such as an acid, e.g. an organic monocarboxylic acid, such as formic acid or acetic acid for example.
• a customary neutralizing agent such as an acid, e.g. an organic monocarboxylic acid, such as formic acid or acetic acid for example.
• the resin is neutralized with an acid, such as formic acid, prior to the reaction of the resin and the crosslinker. Once neutralized, the resin is more conducive to be dispersed in water.
• the resin is more preferably an amine-modified resin derived from an epoxy compound, most preferably a cationic resin.
• anionic resins may also be used.
• Such epoxy resins are common throughout the urethane electrocoating industry and are typically the reaction product of (A) polyepoxides, (B) primary and/or secondary amines or salts thereof and/or salts of tertiary amines, and optionally (C) polyfunctional alcohols, polycarboxylic acids, polyamines, and/or polysulf ⁇ des.
• Suitable amine-modified resins derived from epoxy compounds include, but are not limited to, those described in United States Patent Nos. 4,882,090 and 4,988,420, the disclosures of which are herein incorporated by reference, and also those commercially available as resins from BASF Corporation of Southfield, Michigan under the trade name of CathoGuard ® .
• the crosslinker is a blocked isocyanate crosslinker and is of the type disclosed in United States Patent Nos. 4,882,090 and 4,988,420, the disclosures of which have already been incorporated by reference.
• the crosslinker preferably has one or more functional groups reactive with the hydroxy-functional groups of the resin.
• the crosslinker more specifically, has on average greater than one isocyanate (NCO) functional group per molecule which becomes unblocked upon cure of the urethane coating composition at elevated temperatures.
• any desired crosslinker is possible where the NCO functional group or groups have been reacted with a blocking group or compound, so that the crosslinker formed is resistant to the hydroxy-functional groups of the resin at room temperature but reacts with the hydroxy-functional groups of the resin at the elevated temperatures which are generally within the range from about 200 to about 400 0 F.
• isocyanate typically polyisocyanate
• isocyanates which contain about 3 to 36, in particular about 8 to about 15 carbon atoms.
• diisocyanates include, but are not limited to, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, propylene diisocyanate, ethylethylene diisocyanate, 2,3-dimethylethylene diisocyanate, 1- methyltrimethylene diisocyanate, 1,3-cyclopentylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,2-cyclohexylene diisocyanate, 1,3 -phenyl ene diisocyanate, 1,4-phenylene diisocyanate, 2,4-toluylene diisocyanate, 2,6-toluylene diisocyanate, 4,4-diphenylene diisocyanate (e.g., trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diis
• 4,4 '-methylene bisdiphenyldiisocyanate 1,5-naphthylene diisocyanate, 1,4- naphthylene diisocyanate, l-isocyanatomethyl-5-isocyanato-l,3,3-trimethylcyclohexane, bis(4- isocyanatocyclohexyl)methane, bis(4-isocyanatophenyl)methane, 4,4'-diisocyanatodiphenyl ether and 2,3-bis(8-isocyanatooctyl)-4-octyl-5-hexylcyclohexane. It is also possible to use polyisocyanates of higher isocyanate functionality.
• Examples of these include tris(4- isocyanatophenyl)methane, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, l,3,5-tris(6- isocyanatohexylbiuret), bis(2,5-diisocyanato-4-methylphenyl)methane, and polymeric polyisocyanates, such as dimers and trimers of diisocyanatotoluene. It is further also possible to use mixtures of polyisocyanates.
• the isocyanates which come into consideration for use as the crosslinker in the invention can also be prepolymers which are derived for example from a polyol, including a polyether polyol or a polyester polyol.
• aliphatic, cycloaliphatic or aromatic alkyl alcohols are suitable.
• suitable aliphatic alcohols for the blocking group include, but are not limited to, as methyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl, 3,3,5-trimethylhexyl, decyl or lauryl alcohol.
• suitable cycloaliphatic alcohols for the blocking group include, but are not limited to, cyclopentanol and cyclohexanol.
• Suitable aromatic alkyl alcohols for the blocking group include, but are not limited to, phenylcarbinol and methylphenylcarbinol.
• Other suitable blocking groups are hydroxylamines such as ethanolamine, oximes such as methyl ethyl ketone oxime, acetone oxime and cyclohexanone oxime or amines such as dibutylamine and diisopropylamine.
• Various caprolactams, such as e-caprolactam are also suitable as blocking groups for the crosslinker.
• the isocyanates and blocking groups mentioned, provided these components are mixed in suitable ratios, can also be used for preparing partially blocked crosslinkers. At the elevated temperatures described above, the blocking group unblocks, i.e., leaves or chemically disassociates, from the crosslinker.
• the method includes the step of forming a polymeric ligand from the resin and/or the crosslinker. That is, the polymeric ligand can be formed from the resin only, from the crosslinker only, or from both the resin and the crosslinker.
• the resin and/or the crosslinker function as the ligand for a metal catalyst described below.
• the resin and/or the crosslinker are carboxylated to form the polymeric ligand.
• the polymeric ligand preferably has a molecular weight, M n , greater than approximately 1,000 Daltons, more preferably greater than approximately 2,000 Daltons.
• the polymeric ligand When formed from the crosslinker, the polymeric ligand preferably has a molecular weight, M n , greater than approximately 800 Daltons, more preferably greater than approximately 1,000 Daltons.
• the polymeric ligand is formed from the resin.
• the resin is carboxylated to form the polymeric ligand by reacting an anhydride with the resin.
• the polymeric ligand comprises the reaction product of the resin and the anhydride as generally disclosed in the following chemical representation.
• the anhydride also commonly referred to as a carboxylic acid anhydride, may be either an aromatic or non- aromatic cyclic anhydride.
• the anhydride reacts with the hydroxy-functionality of the resin whereby the cyclic ring structure of the anhydride opens.
• R' and R" may each independently comprise an alkyl group, an alkenyl group, or a hydrogen atom and can be part of the same cyclic ring which may be aliphatic or aromatic (as with the example of phthalic anhydride), and where X and Y each independently comprise an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, a hydrogen atom, an alkyl alcohol, or an alkyl amine.
• X and Y each independently comprise an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, a hydrogen atom, an alkyl alcohol, or an alkyl amine.
• approximately 4 equivalents of anhydride are reacted to approximately 96 equivalents of the hydroxy-functionality of the resin.
• the resin is the cationic resin and the carboxylation of the cationic resin introduces some anionic character into the resin so the resin is, overall, better able to coordinate with the metal from the metal catalyst described
• X and Y of the hydroxy-functional resin are the same as described generally above.
• the anhydride used immediately above in the specific chemical representation is dodecenylsuccinic anhydride (DDSA), where the R' of the anhydride is a hydrogen atom and R" of the anhydride is an alkenyl group with 12 carbon atoms.
• DDSA dodecenylsuccinic anhydride
• R' of the anhydride is a hydrogen atom
• R" of the anhydride is an alkenyl group with 12 carbon atoms.
• suitable anhydrides include, but are not limited to, maleic anhydride, hexahydrophthalic anhydride, methyl-hexahydrophthalic anhydride, tetrahydrophthalic anhydride, phthalic anhydride, succinic anhydride, trimellitic anhydride, and mixtures thereof.
• polymer backbone is used interchangeably with other terms in the art including polymer strand, polymer molecule and polymer segment.
• the polymeric ligand is formed from the crosslinker rather than from the resin.
• the crosslinker is carboxylated to form the polymeric ligand by reacting a hydroxy-functional carboxylic acid with the crosslinker.
• the hydroxy-functional carboxylic acid must be hydroxy-functional to the extent that it has at least one hydroxy group.
• the hydroxy-functional carboxylic acid has two hydroxy groups.
• the hydroxy-functional carboxylic acid can be a monol carboxylic acid, having one hydroxy group and the carboxylic acid group, or a diol carboxylic acid, having two hydroxy groups and the carboxylic acid group.
• Ri and R 2 each independently comprise an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, an alkyl ether group, or a hydrogen atom.
• hydroxy-functional carboxylic acids include, but are not limited to, lactic acid and 12- hydroxystearic acid.
• Ri, R 2 , and R 3 are each independently organic chains having from 1 to 8 carbon atoms.
• Examples of such a hydroxy-functional carboxylic acid include, but are not limited to, 2,2' - bis(hydroxymethyl)propionic acid, also referred to as dimethylolpropionic acid (DMPA), 2,2- bis(hydroxymethyl) butyric acid, and dimethylbis(hydroxymethyl) malonate.
• the carboxylation of the crosslinker with the monol carboxylic acid is generally disclosed in the following chemical representation where the exemplary crosslinker is 4,4'- methylene bisdiphenyldiisocyanate (MDI) which is a pure MDI isomer that is commercially available from BASF Corporation under the tradename Lupranate ® M. It is to be understood that this pure MDI isomer is used herein primarily for illustrative purposes. To this end, it is to be understood that polymeric grade crosslinkers, such as polymeric MDI, are more commonly used in the relevant industries. One example of a suitable polymeric MDI is commercially available from BASF Corporation under the tradename the Lupranate ® M20S.
• MDI 4,4'- methylene bisdiphenyldiisocyanate
• R'" is an aliphatic group, such as an alkyl group, an alkenyl group, an alkynyl group, an alkyl ether group, and the like, a cycloaliphatic group, or an aromatic alkyl group.
• Rj and R 2 each independently comprise an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, an alkyl ether group, or a hydrogen atom.
• the first reaction illustrates blocking of the crosslinker with an alcohol as the blocking group
• the second reaction illustrates the carboxylation of the crosslinker with the monol carboxylic acid.
• One typical blocking group alcohol is diethyleneglycolbutylether alcohol (Bu-O-CH2CH2-O-CH2CH2-OH), where R'" is Bu-O-CH2CH2-O-CH2CH2-O-.
• the polymeric ligand comprises the reaction product of the crosslinker and the hydroxy-functional carboxylic acid, in this case the monol carboxylic acid. In this particular chemical representation, one mole of the hydroxy-functional carboxylic acid is reacted for every one mole of the crosslinker.
• the carboxylation of the crosslinker with the diol carboxylic acid is generally disclosed in the following chemical representation where the exemplary hydroxy-functional carboxylic acid is DMPA and the exemplary crosslinker is 4,4 '-methylene bisdiphenyldiisocyanate (MDI) as described above. It is to be understood that this chemical representation, as well as the other general chemical representations included herein, are merely intended to generally illustrate the salient features of the components and the reaction. They are not intended to be exact representations.
• R'" is as defined above.
• the first reaction illustrates blocking of the crosslinker with an alcohol as the blocking group
• the second reaction illustrates the carboxylation of the crosslinker with the diol carboxylic acid, specifically with DMPA.
• the polymeric ligand comprises the reaction product of the crosslinker and the hydroxy-functional carboxylic acid, in this case the diol carboxylic acid.
• one mole of the hydroxy-functional carboxylic acid is reacted for every one mole of the crosslinker.
• the remaining hydroxyl group in the polymeric ligand can also be reacted with isocyanate to chain extend the structure. This will result in a carboxyl group in the middle of the polymer chain.
• the method of the present invention also includes the steps of incorporating the metal catalyst with the polymeric ligand to complex the metal catalyst with the polymeric ligand and reacting the resin and the crosslinker to form the urethane coating.
• the complex includes the reaction product of the polymeric ligand, as represented above, and the metal catalyst which is complexed with the polymeric ligand.
• the reaction product is a metal carboxylate.
• the metal catalyst is incorporated with the polymeric ligand prior to the reacting of the resin and the crosslinker to form the urethane coating.
• the metal catalyst could be incorporated with the polymeric ligand as the resin and the crosslinker are reacting to form the urethane coating rather than before the reaction.
• the metal catalyst is of the general formula of MO or M(OH) n or R 4 X MO, where M is a metal selected from the group of Bi, Sn, Sb, Zn, Y, Al, Pb, Zr, Ce, Cu, and mixtures thereof, O represents an oxygen atom, OH represents a hydroxide ion, n is an integer satisfying the valency of M, R 4 is an organic group, preferably alkyl, having from 4 to 15 carbon atoms, and x is an integer from 1 to 6.
• the step of incorporating the metal catalyst with the polymeric ligand comprises incorporating a metal catalyst of the general formula MO or M(OH) n or R 4 X MO.
• Dibutyl tin oxide and a metal oxide, such as zinc oxide or bismuth oxide, are, combined or independently, the preferred metal catalysts for use in the present invention.
• the various metal catalysts of the formulae MO or M(OH) n or R 4 X MO can be used alone or in combinations with one another. In other words, one metal catalyst or even a combination of metal catalysts can be employed.
• Other potential metal catalysts include, but are not limited to, other various oxides of zinc or bismuth, SnO, SnO 2 , Y 2 O 3 , and CuO.
• the metal catalyst, including the exemplary oxides listed above is supplied in a milled form having a low particle size (e.g. less than 20 microns, more typically less than 10 microns) such that no additional grinding is needed to reduce the particle size of the metal catalyst for effective incorporation of the metal catalyst with the polymeric ligand.
• the metal catalyst is incorporated with the carboxylated resin to complex the metal catalyst with the carboxylated resin as generally disclosed in the following chemical representation.
• the metal M(I)+ or M(II)++ or M(III)+++ from the metal catalyst, MO or M(OH) n or R 4 X MO is coordinated to the polymeric ligand to establish the complex. It is to be appreciated that, although not represented, the metal catalyst can be complexed with the crosslinker rather than the resin as disclosed immediately above.
• the metal catalyst can be incorporated with the polymeric ligand at various times. In one embodiment, the metal catalyst is actually incorporated with the polymeric ligand simultaneous with the step of forming the polymeric ligand from the resin and/or the crosslinker, i.e., as the polymeric ligand itself is being formed. Alternatively, the metal catalyst can be incorporated with the polymeric ligand after the polymeric ligand is formed and prior to the reaction of the resin and the crosslinker to form the urethane coating. For instance, a pigment-containing composition may be incorporated prior to the step of reacting the resin and the crosslinker. As is known in the art, such pigment-containing compositions are common with the electrocoat compositions described above.
• pigment-containing compositions may also be referred to as pigment pastes.
• the metal catalyst can be incorporated into the pigment-containing composition to complex the metal catalyst with the polymeric ligand.
• the metal catalyst such as a simple metal oxide, is complexed with the polymeric ligand prior to reaction of the resin and the crosslinker to form the urethane coating.
• Examples A-T are prepared as described below and as indicated in Tables IA, IB, 2A, and 2B.
• Examples A-J utilize Emulsion 1 and Examples K-T utilize Emulsion 2.
• Examples A-F, I, J-P, S, and T are examples according to the invention.
• Examples G and Q are one form of a control example where, although DDSA is included in the urethane coating composition, no metal catalyst is included.
• Example H and R are another form of a control example where, although a metal catalyst is included in the urethane coating composition, no anhydride is included to carboxylate the resin.
• the examples are all urethane coating compositions, specifically urethane cationic electrodeposition coatings.
• the hydroxy-functional resin is carboxylated with the anhydride, specifically with dodecenylsuccinic anhydride (DDSA).
• DDSA dodecenylsuccinic anhydride
• a suitable hydroxy-functional resin for these Examples is a cathodic electrodepositing resin.
• the DDSA is obtained from Dixie Chemical of Pasadena, TX. As described in greater detail below, this reaction product is in the form of an emulsion, Emulsions 1 and 2 below.
• a pigment-containing composition also known to those skilled in the art as a pigment paste, is used.
• the metal catalyst is incorporated into the pigment paste and then the pigment paste containing the metal catalyst is incorporated into the emulsion to establish an electrocoat bath where the metal catalyst complexes with the hydroxy-functional resin.
• Emulsion Type 1 is more specifically made as follows. [0053] In a 3 L flask with an associated heating mantle; diglycidyl ether of bisphenol A, DGEBA, (17.94 g, 0.095 eq. epoxy), bisphenol A, BPA, (4.08g, 0.036 eq. OH), a phenol or substituted phenol (0.015 eq., OH) (such as dodecylphenol, p-cresol, phenol, or combinations thereof), and xylene (0.357 g) are combined.
• the crosslinker is a blocked isocyanate based on polymeric MDI and monofunctional alcohols, such as diethylene glycol butyl ether.
• carboxylated resin is added to an acid mixture, under constant stirring, including deionized water (31.095 g), formic acid (85%) (0.588 g), and nitric acid (0.050 g).
• deionized water 31.095 g
• formic acid 85%
• nitric acid 0.050 g
• Additives (0.4 g) independent, or in an additive package are added to the acid mixture and to the 20.0 g of water. All raw materials, including the various solvents used above, are industrial grade and no further purifications are made.
• Emulsion Type 2 is more specifically made as follows.
• a toluene (118 g) solution of DDSA (389 g, 1.377 eq.) is subsequently introduced at 105 0 C to form a carboxylated resin, and the mixture is allowed to stir for approximately 1.5 hr.
• a mixture of 7097 parts of the crosslinker and 90 parts of a flow additive is then added and the resulting mixture is held at 100 0 C.
• the crosslinker is a blocked isocyanate based on polymeric MDI and monofunctional alcohols, such as diethylene glycol butyl ether and/or butyl diglycol. Approximately 30 minutes later, 211 parts of butyl glycol and 1210 parts of isobutanol are added.
• Plastilit ® 3060 propylene glycol compound, BASF/Germany
• the mixture is diluted with 522 parts of propylene glycol phenyl ether (mixture of l-phenoxy-2-propanol and 2-phenoxy-l-propanol, BASF/Germany), in the course of which it is cooled rapidly to 95°C.
• reaction mixture After 10 minutes, 14821 parts of the reaction mixture are transferred to a dispersing vessel. 474 parts of lactic acid (88% in water), dissolved in 7061 parts of deionized water, are added in portions with stirring. The mixture is subsequently homogenized for 20 minutes before being diluted further with an additional 12600 parts of deionized water in small portions. The volatile solvents are removed by vacuum distillation and then replaced by an equal volume of deionized water.
• the metal catalysts included in the tables below are added into a pigment paste.
• the raw material for the metal catalysts, metal salts are generally available in the form of ZnO, Bi 2 O 3 , Bu 2 SnO, SnO 2 , ZrO 2 , Y 2 O 3 , and CuO from Aldrich Chemical Co.
• pigment pastes for urethane-based electrocoatings also include the pigment(s), fillers and additives.
• the pigment paste containing the metal catalyst is incorporated into the emulsion to establish an electrocoat bath where the metal catalyst complexes with the polymeric ligand, in these Examples the carboxylated hydroxy-functional resin, to catalyze the urethane forming reaction upon cure. Examples A-J
• pigment paste contains approximately 0.50% DBTO (dibutyl tin oxide) relative to emulsion solids;
• panels are prepared for certain tests (described in detail below) involving only Examples A-J.
• the tests are the MEK Double Rub Solvent Resistance Test, the Chip Resistance test, and Corrosion Tests G and L.
• Two types of panel substrates are employed depending on the particular test: cold rolled steel (CRS) with zinc phosphate treatment and zinc-iron treated (Zn/Fe) panels. All panels are 4" x 6" in dimension and are purchased from ACT.
• the panels are electrocoated by techniques known to those skilled in the art to film builds of 0.40 mil and 0.80 mil, again depending on the particular test.
• methyl ethyl ketone (MEK) double rubs are carried out.
• the panels are CRS with zinc phosphate treatment and the urethane coatings compositions are coated and cured at various times and temperatures to form urethane coatings of approximately 0.80 mil.
• the CRS with zinc phosphate treatment panels and the Zn/Fe panels are coated with the urethane coating compositions of Examples A-J to form urethane coatings of approximately 0.8 mil. These panels are cured at approximately 325°F for approximately 15 minutes.
• a primer, base coat, and clear coat are first applied.
• the primer is a gray primer based on acrylic/polyester - melamine chemistry.
• the base coat is a white basecoat based on acrylic - melamine chemistry.
• the clear coat is a high solids solventborne clearcoat also based on acrylic - melamine chemistry.
• the corresponding film build for the primer, base coat, and clear coat are 0.9-1.0, 1.0-1.1, and 1.7-2.0 mil, respectively.
• a 5 -minute flash in the booth is employed, followed by baking for 20 minutes at 325 0 F.
• a 10-minute flash in the booth is used for the base coat without any additional bake, and the clear coat is subsequently sprayed, followed by flashing for 10 minutes and baking for 20 minutes at 28O 0 F.
• the CRS with zinc phosphate treatment panels are coated with the urethane coating compositions of Examples A-J to form urethane coatings of approximately 0.8 mil. These panels are cured at approximately 325°F for approximately 15 minutes. These panels are
• each panel is scribed directly down the middle with the shape of vertical line, " .”
• the exposure cycle is as follows. On Monday, each panel is held at 60 0 C for one hour in an air-circulating oven and is then subjected to a cold cabinet at -25 0 C and held for 30 minutes. Following, the panels are immersed for 15 minutes in a 5% (wt.) NaCl solution (saline). After removal and allowing them to air dry for 1 hr 15 minutes at room temperature, the panels are transferred to a humidity cabinet set at 60 0 C and 85% humidity with an air flow not exceeding 15 m/ft across the panel.
• the panels are once again immersed for 15 minutes in the saline solution and are allowed to air dry as previously explained. They are then transferred to the humidity cabinet and are held through the weekend. The cycle is then repeated for a total of 5 cycles. After completion, each panel is rinsed with water and scraped with a metal spatula. The average corrosion diameter is then obtained by randomly selecting points along the scab.
• Example J adding the catalyst (the zinc) to the resin also shows similar level of corrosion inhibition.
• decreasing the DDSA amount by half also results in good corrosion inhibition in the presence of the same amount of zinc.
• not adding any DDSA yields a panel exhibiting complete failure, even in the presence of zinc.
• Adding DDSA without any additional catalyst leads to satisfactory corrosion inhibition, which may be attributed to activation of the DBTO, which is present in the pigment paste.
• Other metals performing relatively well are Sn, Bi, Zr, and Y.
• each panel is scribed with a scab having the appearance of an "X.”
• Initial adhesion and shot blast is omitted in Corrosion Test L.
• the daily test sequence and test cycle are carried out by placing the panels in test on any weekday between Tuesday through Friday. A total of 36 test cycles are carried out, with each cycle equaling one day. The cycle is first started by subjecting each panel to a 60 minute bake with an oven temperature of 60 0 C, followed by gradual cooling to room temperature for 30 minutes.
• the salt immersion and humidity portion of the test follow by first placing each panel in an aqueous solution of 5% (wt.) NaCl for 15 minutes followed by drying at ambient temperature for 75 minutes.
• the panels are placed in a humidity cabinet (85% humidity) set at 60 0 C for 22.5 hr ⁇ Note: On weekends, the panels are allowed to remain in the humidity cabinet). After the 36 day cycle, the panels are removed from testing, thoroughly rinsed and scraped with a metal spatula to remove any loose paint. The average corrosion diameter is then obtained by using a caliper and taking random measurements along each side of the scab.
• a humidity cabinet 85% humidity

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