Urethane catalyst based on zirconium acetylacetonate

Abstract: The present invention is directed to novel metal organocomplexes as catalysts for the reaction of compounds with isocyanate and hydroxy functional groups to form urethane and/or polyurethane and the process employing such catalysts. More particularly, the present invention is directed to catalysts comprising a mixture of tetrakis-(2,4-pentanedionato) zirconium and a compound selected from the group consisting of a diketone: R 1 COCH 2 COR 2 and R 1 OCOCH 2 COR 2 wherein each of R 1 and R 2 is a branched or linear C 1 -C 20 hydrocarbon and the total number of carbons in R 1 +R 2 is at least 4. These novel catalysts are useful for the production of urethanes and polyurethanes which are important in many industrial applications, such as: coatings, foams, adhesives, sealants, and reaction injection molding (RIM) plastics.

Description: FIELD OF INVENTION The present invention is directed to novel catalysts for the reaction of compounds with isocyanate and hydroxy functional groups to form urethane and/or polyurethane and the process employing such catalysts. More particularly, the present invention is directed to novel catalysts comprising a mixture of a complex of zirconium and a diketone with at least 7 carbons in the hydrocarbon backbone chain. These novel catalysts are useful for the production of urethanes and polyurethanes which are important in many industrial applications, such as: coatings, foams, adhesives, sealants, and reaction injection molding (RIM) plastics. BACKGROUND OF THE INVENTION The reaction of isocyanate and hydroxy compounds to form urethanes is the basis for the production of polyurethanes. Metal compounds (e.g., tin, zinc and bismuth compounds) and tertiary amines have been known to catalyze the reaction of isocyanate and hydroxyl groups to form urethane. See, Proceedings of Water Borne and High Solids Coatings Symposium , February 25-27, 1987, New Orleans, at Page 460. Compounds useful for the isocyanate-hydroxy reaction are also referred to as urethane catalysts. At present, the commercially available catalysts used in this reaction are organotin compounds (e.g., dibutyltin dilaurate and dibutyltin diacetate), zinc carboxylates, bismuth carboxylates, organomercury compounds and tertiary amines. There are several problems with these commercially available catalysts. When they are used in the process for polyurethane coatings, the cure of the coatings under high humidity or at low temperature conditions is not satisfactory. They catalyze the undesirable side reaction of isocyanate with water to form amines and carbon dioxide. The carbon dioxide may cause blisters in the coating and the amines react with isocyanates resulting in low gloss coatings. Moreover, the cure rate at low temperatures is too slow. The commercially available catalysts also catalyze the degradation of the resulting polymer product. Furthermore, several of the commercially available urethane catalysts, particularly those containing heavy metals and tertiary amines, are highly toxic and are environmentally objectionable. The testing of zirconium acetylacetonate and zirconium tetra-3-cyanopentanedionate, as catalysts for the isocyanate-hydroxy reaction have been described in GB Patents 908949, 890,280 and 869988. Subsequent testing by others, however, has shown that zirconium acetylacetonate is a poor catalyst for the urethane reaction. B.D. Nahlovsky and G.A. Zimmerman, Int. Jahrestag. Fraunhofer - Inst. Treib-Explosivst. , 18th (Technol. Energ. Mater.), 39:1-12, reported that the catalytic efficiency of zirconium acetylacetonate for the isocyanate-hydroxy reaction to form urethane is low. The solubility of zirconium acetylacetonate and zirconium tetra-3-cyanopentanedionate in solvents commonly used in the production of coatings is poor. Examples of such solvents include esters, ketones, glycolesters and aromatic hydrocarbons, such as: butyl acetate, methyl iso-amyl ketone, 2-methoxy propylacetate, xylene and toluene. Because of the low catalytic efficiency and the poor solvent solubility, the use of these compounds as catalysts in processes involving urethane or polyurethanes have been limited. Further testing using zirconium acetylacetonate in our laboratory has shown that zirconium compounds disclosed in the prior art, will only catalyze the isocyanate-hydroxy reaction when carried out in a closed system, i.e., in a closed pot. This is impractical for many of the polyurethane applications. The zirconium diketonates of the prior art failed as catalysts when the reaction is carried out in the open atmosphere, unless there is present a large excess of the corresponding diketone. For zirconium acetylacetonate, the presence of over 1000 to 1 mole ratio of 2,4-pentanedione to zirconium acetylacetonate is required. The objective of this invention is to develop catalysts with high catalytic efficiency for the isocyanate-hydroxy reaction to form urethane and/or polyurethane. A second objective of the present invention is to develop catalysts which provide improved cure at a lower temperature and are less sensitive to the presence of water. A further objective of the present invention is to develop catalysts which would not be deactivated when the reaction is exposed to the atmosphere. Another objective of the present invention is to provide catalysts for the isocyanate-hydroxy reaction which typically would not catalyze the undesired side reaction of water with isocyanates or the undesired degradation of the polyurethane. SUMMARY OF THE INVENTION This invention is directed to a catalyst for the isocyanate-hydroxy reaction comprising a mixture of tetrakis-(2,4-pentanedionato)zirconium and a compound selected from the group consisting of a diketone: R 1 COCH 2 COR 2 and R 1 OCOCH 2 COR 2 wherein each of R 1 and R 2 is a branched or linear C 1 -C 20 hydrocarbon and the total number of carbons in R 1 + R 2 is at least 4. That is, the number of carbons in the backbone of the hydrocarbon chain is at least 7. The preferred diketones are those containing a total number of carbons in R 1 + R 2 of at least 5, i.e. the number of carbons in the hydrocarbon backbone is at least 8. Also preferred are diketones with structure (II). The catalyst is a blend of zirconium pentanedionate or acetylacetonate with a diketone having at least 7 carbons in the hydrocarbon backbone of the molecule. This is because the ligands of the zirconium complex readily exchange with the diketone e.g. of structure (II) to form the catalyst in situ. DETAILED DESCRIPTION OF THE INVENTION The catalyst for the isocyanate-hydroxy reaction to produce urethane or polyurethane comprises a mixture of tetrakis-(2,4-pentanedionato)zirconium (Zr) and a compound selected from the group consisting of a diketone: R 1 COCH 2 COR 2 and R 1 OCOCH 2 COR 2 wherein each of R 1 and R 2 is a branched or linear C 1 -C 20 hydrocarbon and the total number of carbons in R 1 + R 2 is at least 4. That is, the number of carbons in the backbone of the diketone is at least 7. The preferred diketones are those wherein the total number of carbons in R 1 + R 2 is at least 5, i.e., with at least 8 carbons in the backbone of the molecule. The catalyst is a blend of zirconium pentanedionate or acetylacetonate with a diketone having at least 7 carbons in the hydrocarbon backbone of the molecule. The tetrakis-(2,4-pentanedionato)zirconium comprising the catalyst of this invention can be synthesized via the known ligand exchange reactions of zirconium compounds with 2,4-pentanedione (acetylacetone). These reactions are described by R.C. Fay in the chapter on zirconium and hafnium, in Geoffrey Wikinson ed., Comprehensive Coordination Chemistry , Vol.3, page 363, Pergamon Press, (1987). The ligand exchange reaction is facile and can be accomplished by blending the starting zirconium compound and the 2,4-pentanedione ligand as a chelating agent at an ambient or slightly elevated temperature. This blending can be carried out in a solvent such as a polyol, e.g. propylene glycol, dipropylene glycol, 1,3-butylene glycol, 1,6-hexane diol, polypropylene glycol (MW 400-2600), polytetramethylene glycol (MW 200-1000), dimethoxy-dipropylene glycol or other diluents, such as xylene, methyl iso-amyl ketone, dibutylether, butoxy/propoxy/ethoxy polypropylene ethylene glycol ether. Typical starting zirconium compounds include the chloride, oxychloride, alkoxide and carbonate of zirconium. Typical diketones of Structure II include: 6-methyl-2,4-heptanedione (wherein R 1 =C1 and R 2 =C4), 2,2,6,6-tetramethyl-3,5-heptanedione (wherein R 1 =C4 and R 2 =C4), n-valerylacetone (wherein R 1 =C1 and R 2 =C4), n-hexanoylacetone (wherein R 1 =C1 and R 2 =C5), n-octanoylacetone (wherein R 1 =C1 and R 2 =C7), n-nonanoylacetone(R1=C1, R2=C8), n-decanoylacetone (wherein R 1 =C1 and R 2 =C11) and the like. In a further aspect, this invention is directed to a composition comprising a polyol, a polyisocyanate and a catalyst in accordance with the present invention. The isocyanates useful in this invention are aliphatic, aromatic isocyanates or polyisocyanates or resins with terminal isocyanate groups. The resins may be monomeric or polymeric isocyanates. Typical monomeric isocyanates include: toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), 1,6-hexamethylene diisocyanate (HDI), phenyl isocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate (IPDI), meta-tetramethylxylene diisocyanate (TMXDI), nonanetriisocyanate (TTI) or vinyl isocyanate, or the like. The above monomeric isocyanates are those which are more commonly used and is not meant to be exclusive. The polymeric polyisocyanates useful in the invention are isocyanurate, allophanate, or biuret compounds and polyurethane products derived from the monomeric diisocyanates as listed hereinabove. Also useful are addition products of monomeric isocyanates with polyester and polyether polyols containing terminal isocyanate groups. The polyols or resins with hydroxy functional groups useful in this invention comprise monomeric compounds or polymeric compositions containing at least two hydroxy groups per molecule. The molecular weight of the hydroxy containing compounds useful in this invention ranges from 62 to 1,000,000; the preferred range for polyols being between 300 to 2000; more preferably in the range of between 400 to 2,000 when used in solvent borne high solids coatings. Typically, the hydroxyl number of the hydroxy containing resin can be from 10-1000. Optionally, the polyol may contain other functional groups such as carboxyl, amino, urea, carbamate, amide and epoxy groups. The polyol, a blend of polyols or a combination of polymeric polyols and monomeric diols may be employed in a solvent free system, or as a solution in an organic solvent, or as a dispersion/emulsion in water. Typical examples include: polyether polyol, polyester polyol, acrylic polyol, alkyd resin, polyurethane polyol, and the like. The polyether polyols are the reaction products of ethylene or propylene oxide or tetrahydrofuran with diols or polyols. Polyethers derived from natural products such as cellulose and synthetic epoxy resins may also be used in this invention. Typical polyester polyols are prepared by the reaction of diols, triols or other polyols with di- or polybasic acids. Alkyds with hydroxy functional groups are prepared in a similar process except that mono functional fatty acids may be included. Acrylic polyols are the polymerization products of an ester of acrylic or methacrylic acid with hydroxy containing monomers such as hydroxyethyl, hydroxypropyl or hydroxybutyl ester of acrylic or methacrylic acid. These acrylic polymers can also contain other vinyl monomers such as styrene, acrylonitrile vinyl chloride and others. In addition, polyurethane polyols are also useful in this invention. These are the reaction products of polyether or polyester polyols with diisocyanates. The polyols listed above are illustrative and are not meant to limit the scope of the invention. Typically the polyols are either synthesized in bulk in the absence of a solvent or are prepared in the presence of a diluent or by emulsion polymerization in water. Alternatively, they may be prepared in bulk or in a solvent and then dispersed in water. For a description of the methods of preparing polyols see Organic Coatings Science Technology , vol. 1, Wiley-Interscience Co., 1992. The concentration of the catalyst used is generally from 0.0001wt% to 5wt% on total resin solids. Typically, the concentration of catalyst used is between 0.001 to 0.1wt% based on the total amount of polyol and polyisocyanate, also known as binders. The catalyst concentration used is generally a compromise between potlife of the formulation and the required cure rate. The catalyst of the present invention is particularly suitable for applications where exceptionally fast cure is required. For example, the catalyst of the present invention is particularly useful in plural component spray gun applications wherein the catalyst is added to one of the components and the polyol and the isocyanate is mixed in situ in the spray gun. These are important in applications for roof or floor coatings, where the person applying the coating would be able to walk on the freshly applied coating a few minutes after the coating has been applied. Good cure rate is also required for coatings applied at a low temperature or in the presence of moisture, conditions where the catalyst of this invention excels. Reactive injection molding (RIM) is another area where fast cure is essential. The reactants and catalyst are injected concurrently into a mold, and mixing is achieved during injection. In this application, fast reaction is essential to permit a short cycle time. The ratio of NCO/OH in the formulation is in the range of 0.1-10.0 to 1, preferably 0.5-2.0 to 1 depending upon the end use. For a typical high solids application, the preferred isocyanate to hydroxy ratio is usually 1.0:1 to 1.1:1. For many water-borne applications, an excess of isocyanate is required. Typically the ratio for such applications is 1.5:1 to 2.0:1. The catalyst formulation can be solvent borne, high solids, 100% solids or dispersable in water. Other additives may be utilized in the formulation to impart desired properties for specific end uses. For example, 2,4-pentanedione, can be used together with the catalyst to extend pot life. For most isocyanate crosslinked coatings, solvents which are free of hydroxy groups and water are used. Typical solvents are esters, ketones, ethers and aliphatic or aromatic hydrocarbons. The catalytic efficiency of the catalyst of this invention is determined by measuring the drying time of the coated film or by a gel test. For drying time measurement, the liquid formulation containing polyisocyanate, polyol and catalyst was cast on a metal panel and the surface dry time and the through dry time were recorded with a circular Gardner Drying Time Recorder. For the gel test, liquid polyisocyanate, liquid polyol solution and catalyst were mixed thoroughly at room temperature. The time needed from mixing the liquid components to forming a gel (the time interval when the liquid formulation becomes non-flowable) was recorded as gel time. The catalyst of this invention exhibits excellent catalytic efficiency, measured as drying time of the coated film and/or gel time, for the isocyanate-hydroxy reaction compared to zirconium diketonates reported in prior art and commercially available organotin catalysts, especially at low temperatures. For example, Zirconium tetraacetylacetonate described in the prior art, does not function as an effective curing catalyst. Even though the gel time is shorter than the uncatalyzed process, it is still too long. Further, exposure to atmosphere deactivates zirconium tetraacetylacetonate . However, when zirconium tetraacetylacetonate is mixed with a diketone with at least 7 carbons in the hydrocarbon backbone, an effective catalyst is obtained. The catalyst of this invention also preferentially catalyzes the isocyanate-hydroxy reaction over the isocyanate-water reaction. Organo tin does not exhibit this preferential catalysis, and also catalyzes the isocyanate-water reaction, which leads to the formation of carbon dioxide and gassing. For example, to prepare a polyurethane coating with exclusive carbamate linkages, a coating formulation containing HDI based aliphatic isocyanate and a polyurethane diol with beta-carbamate may be formulated. When the catalyst of the present invention is used, a hard glossy film is typically obtained. Whereas, with dibutyltin dilaurate as the catalyst, a hazy film is generally obtained. This is due to the competing reaction of isocyanate with moisture in the air. Furthermore, it is known that commercial organotin urethane catalysts will affect the durability of the final product. This is due to the catalytic effect of organotin catalysts on the degradation of the polymer product. The catalyst of the present invention typically shows less of a catalytic effect on the degradation of the polymer than the tin urethane catalysts. For a solution with polyester resin, water and catalysts, the degradation rate of polyester with the catalyst of this invention may be 5 times slower than a typical tin catalyst. To avoid pigment adsorption or interference from other components which may deactivate the catalyst, it would be an advantage if the catalyst can be pre-blended with the isocyanate component in a two component system. However, a number of urethane catalysts also catalyze the dimerization or trimerization reactions of isocyanate and cannnot be pre-blended with the isocyanate component. A solution of a polyisocyanate with the catalyst of this invention typically shows good compatibility and stability. The following examples are provided to illustrate the present invention. Example 1 Catalyst Evaluation A liquid coating formulation containing polyisocyanate, polyol and the catalyst as shown in Table 1 was prepared. The formulation was applied to an iron phosphate treated cold roll steel (Bo 1000) panel via a draw down bar to provide a wet film thickness of 1.7 mils. The panels were allowed to cure at room temperature and at 5°C at a relative humidity of 50-60%. The cure rate for a catalyst in accordance with the invention is presented in Table IIA. This can be compared with the formulation wherein dibutyltin dilaurate was used as the catalyst shown in Table IIB. The drying time of the coated film was recorded using a Gardner Circular Drying Time Recorder with a Teflon stylus. The Teflon stylus moves at a constant speed on the top of the film after the film was applied. The time between applying the film and when the Teflon stylus no longer leaves a clear channel, but begins to rupture the drying film is recorded as surface dry time. The time between applying the film and when the stylus no longer ruptures or dents the film is recorded as through dry time. The time between mixing isocyanate and polyol solutions and the moment that the liquid becomes a non-flowable gel is recorded as gel time. The solubility of each catalyst in the formulation was noted. The results presented in Tables IIA & IIB showed that a catalyst of this invention provided much improved catalytic efficiency and is more soluble in the solvent, methyl amyl ketone, than the catalysts of the prior art. Polyurethane Formulation used In Cure Rate Test Material Parts by Weight Part A: Acrylic polyol solution 58.8 Methyl amyl ketone (solvent) 24.8 Part B: Aliphatic polyisocyanate 16.4 catalyst as wt% metal based on total resin solids 0.0046 Formulation parameters Total resin solids by weight 58.7% NCO/OH ratio 1.2 Cure Rate of Zirconium Complexes (Room Temperature: 22-25°C) Catalyst Wt% Me in complex Gel time MIN Surface dry time MIN Through dry time MIN Solubility in Formulation Zr acac/MHD (1:1 by weight)* 15 10 15 good Comparative Examples Zr Catalyst (moles of chelating agent) Wt% Me in complex Gel time MIN Surface dry time MIN Through dry time MIN solubility in the formulation ACAC (4) 18.7 90 >720 > 1440 poor Zr Butoxide 23.8 >720 >720 >720 good Ethylacetoacetate (4) 115.0 > 720 > 720 >720 good cyclopetadiene (2) & chloride (2) 31.2 > 720 >720 >720 good DBM (4) 9.3 35 80 180 poor 3-Ethyl-acetylacetone (4) 15.2 >720 >720 >720 poor 1, 1, 1-trifloroacetylacetone (4) 13.0 30 >720 >720 poor DBM (2) BAC (2) 10.6 40 70 180 poor BAC (4) 12.4 >720 >720 >720 poor Triacetyl methane (4) 13.9 90 >720 >720 good Dibutyltin dilaurate 18.8 120 90 180-240 excellent no catalyst -- > 720 > 720 >720 Key for Tables IIA & IIB: ACAC: 2, 4-Pentanedione ACP: 2-acetocyclopetanone BAC: Benzoylacetone DBM: dibenzoylmethane DMHFOD: 2,2-dimethyl-6,6,7,7,8,8-heptafluoro-3,5-octanedione MHD: 6-methyl- 2,4- heptanedione TMHD: 2,2,6,6- tetra-methyl-3,5-heptanedione * Blend of zirconium acetylacetonate with 6-methyl-2,4-heptanedione

Claims: A catalyst for the isocyanate-hydroxy reaction comprising a mixture of tetrakis-(2,4-pentanedionato) zirconium and a compound selected from the group consisting of a diketone: R 1 COCH 2 COR 2 and R 1 OCOCH 2 COR 2 wherein each of R 1 and R 2 is a branched or linear C 1 -C 20 hydrocarbon and the total number of carbons in R 1 + R 2 is at least 4. A composition comprising a polyol, a polyisocyanate and a catalyst according to Claim 1. A composition according to Claim 2 wherein the polyol is selected from the group consisting of hydroxy containing compounds having a molecular weight in the range of between 62 to 1,000,000; and the polyisocyanate is selected from the group consisting of diisocyante, isocyanurate, allophanate, biuret compounds and polyurethane products derived from monomeric diisocyanato compounds. A composition according to Claim 3 wherein the molecular weight of the hydroxy containing compound is in the range of between 400 to 2,000. A composition according to Claim 3 wherein the polyol further contains carboxyl, amine, carbamate, amide or epoxy functional groups. A process of preparing a coating or adhesive film by blending the components of a composition according to any one of Claims 2-5.

Inventors: BLANK WERNER, FLORIO JOHN, HE ALEX, PICCI MARIE, BLANK, WERNER, FLORIO, JOHN, HE, ALEX, PICCI, MARIE
Applicants: KING INDUSTRIES INC, KING INDUSTRIES, INC.
Application year: 1998
Main classification: B01J31
IPC codes: B01J31, C09D175, C08G18, C09J175