Abstract:
The present invention relates to polyurethane polyol compositions comprising the reaction product of a polyisocyanate, a polyol, and a Guerbet alcohol having at least 12 carbon atoms or a Guerbet alcohol mixture having an average of at least 12 carbon atoms. Preferred polyols are α,β diols and α,γ diols. The polyurethane polyol compositions exhibit very low viscosity and are particularly useful in very low VOC coating compositions. The resulting cured coating provides surprisingly improved properties.

Description:
This application claims priority of U.S. Ser. No 60/257,471 filed on Dec. 22, 2000 and European Patent Application Serial No. 01200734, filed on Feb. 28, 2001. 
    
    
     This invention relates to polyurethane polyol compositions comprising the reaction product of a polyisocyanate, a polyol, and a Guerbet alcohol having at least 12 carbon atoms, and to coating compositions comprising such polyurethane polyol compositions. 
     BACKGROUND OF THE INVENTION 
     Polyurethane polyol compositions comprising the reaction product of a polyisocyanate, a polyol, and a monofunctional alcohol are generally known, e.g., from patent publication WO 96/40813. This publication discloses in general terms that the monofunctional alcohol can be linear or branched, cyclic or acyclic, and that the alcohols and thiols can be primary, secondary or tertiary. 
     It is known to use polyurethane polyol compositions as part of coating compositions and in multi-component coating systems. Such coating compositions and multi-component coating systems also comprise a crosslinker. 
     It has been found that polyurethane polyol compositions prepared using Guerbet alcohols having at least 12 carbon atoms result in polyurethane polyol compositions which, when used in coating compositions and multi-component coatings systems, produce a finished coating that has surprisingly improved properties as compared to traditional monoalcohol substitutions or branched monoalcohols having less than 12 carbon atoms. The finished coating shows better flexibility. Additionally, the uncured polyurethane polyol compositions have a lower VOC content and lower viscosity. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the current invention is a polyurethane polyol composition comprising the reaction product of (a) polyisocyanate, (b) a polyol, and (c) a Guerbet alcohol having at least 12 carbon atoms or a Guerbet alcohol mixture having an average of at least 12 carbon atoms. 
     Another embodiment of the invention encompasses a method of making such polyurethane polyol compositions. 
     The invention is also directed to coating systems and coating compositions comprising such polyurethane polyol composition and a crosslinker. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Polyisocyanates useful in the current invention typically have a functionality of 2 to 5. Due to variations in the preparation of such isocyanates, commercially available polyisocyanates may contain a mixture of functionalities. Such mixtures of polyisocyanates can be used in the current invention. 
     Non-limiting examples of polyisocyanates useful in the current invention are 1,6-hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, methylene bis(4-cyclohexyl isocyanate), the biuret of 1,6-hexamethylene diisocyanate, the isocyanurate of 1,6-hexamethylene diisocyanate, the isocyanurate of isophorone diisocyanate, and the triisocyanate functional adduct of tetramethylxylylene diisocyanate and trimethylolpropane. The preferred polyisocyanate is the isocyanurate of hexamethylene diisocyanate (isocyanurate of HDI). 
     Non-limiting examples of polyols useful in the current invention are α,β and α,γ diols, for instance 2-ethyl-1,3-hexane diol, 1,2-hexane diol, 1,2-octane diol, 1,2-decane diol, 2,2,4-trimethyl-1,3 pentane diol, and 2-butyl-2-ethyl-2,3-propane diol. 
     Guerbet alcohols are branched, primary monofunctional alcohols that have two linear carbon chains with the branch point always at the second carbon position. Guerbet alcohols are chemically described as 2-alkyl-1-alkanols. The Guerbet alcohol used in the current invention is an alcohol having at least 12 carbon atoms or a Guerbet alcohol mixture having an average of at least 12 carbon atoms. The Guerbet alcohol preferably used in the current invention is one having at least 16 carbon atoms or a Guerbet alcohol mixture having an average of at least 16 carbon atoms. Preferably, the Guerbet alcohol used in the current invention is one having not more than 36 carbon atoms, more preferably not more than 32 carbon atoms. The most preferred Guerbet alcohols are 2-hexyl-1-decanol, 2-octyl-1-decanol, 2-octyl-1-dodecanol, 2-hexyl-1-dodecanol, 2-decyl-1-tetradecanol, and mixtures thereof. The Guerbet alcohols used according to the present invention may be represented by the following formula: 
     
       
         (R 1 ) (R 2 ) CHCH 2 OH 
       
     
     wherein 
     R 1  is a linear alkyl group, 
     R 2  is a linear alkyl group, 
     the sum of the carbon atoms in R 1  and R 2  is 10 to 34, and both R 1  and R 2  are present. 
     Guerbet alcohols are commercially available from Sasol Chemie GmbH as Isofol® alcohols and from Cognis as Guerbetol. 
     The polyurethane polyol compositions of the current invention can be combined with crosslinkers to produce coating compositions. Any hydroxyl group-reactive crosslinker may be employed in the coating compositions and multi-component coating systems of the current invention, for non-limiting example, polyisocyanates, blocked polyisocyanates, urea, and melamine resins. Mixtures of such crosslinkers may also be used. Melamine crosslinkers are chosen for one-package coating systems and isocyanates are typically used in two component systems. 
     The coating composition can also comprise catalysts for the curing reaction between the hydroxyl groups in the polyurethane polyol composition and the hydroxyl-reactive group of the crosslinker. For non-limiting examples with isocyanates as crosslinkers, dibutyl tin dilaurate, triethyl amine, and metal catalysts and the like are preferred. Non-limiting examples for aminoplast crosslinkers include sulphonic acid catalysts like blocked dodecyl benzene sulfonic acid. The coating compositions can also contain pigments. Inorganic as well as organic pigments may be used. The composition can further comprise conventional additives, such as stabilizers, surfactants, fillers, UV-absorbers, and various additives and solvents. 
     The coating composition of the present invention can be applied to any substrate. The substrate may be, for example, metal, plastic, wood, glass, ceramic, or another coating layer. The other coating layer may be comprised of the coating composition of the current invention or it may be a different coating composition. The coating composition of the current invention shows particular utility as clear coats, base coats, and pigmented top coats. The coating compositions can be applied by conventional means such as by spray gun, brush or roller, spraying being preferred. Curing temperatures preferably are between 0 and 130° C. and more preferably between 20 and 120° C. The compositions are particularly suitable in the preparation of coated metal substrates, in particular transportation vehicles such as trains, trucks, buses, and airplanes. 
     Due to the flexibility of the resulting cured coating, the coating composition of the present invention is particularly useful for flexible plastic substrates and on articles that are a combination of plastic and other materials. 
     The invention is further illustrated by the following examples. 
    
    
     EXAMPLES 
     Comparative Example 1 
     A 2-liter, 4-neck round-bottomed flask equipped with a stirrer, a condenser, a heating mantel, a thermocouple, a Masterflex peristaltic pump, and a nitrogen inlet was charged with: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 480.0 g 
                 2-butyl-2-ethyl propane diol, 
               
               
                   
                 228.9 g 
                 n-butyl acetate, 
               
               
                   
                  0.5 g 
                 10% solution dibutyl tin dilaurate in n-butyl acetate. 
               
               
                   
                   
               
             
          
         
       
     
     This mixture was heated to 70° C. under a nitrogen blanket. When the mixture reached 70° C., the following isocyanate solution was added over a 2-hour period using a Masterflex peristaltic pump: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 588.0 g 
                 Desmodur N-3300 (isocyanurate of HDI) and 
               
               
                   
                 228.9 g 
                 n-butyl acetate. 
               
               
                   
                   
               
             
          
         
       
     
     After completion of the isocyanate addition, the reaction temperature was maintained at 70° C. for an additional 2 hours, at which point Fourier Transform Infrared Spectroscopy (FTIR) was used to determine that there was no residual isocyanate. The resulting solution of polyurethane polyol was a resin solution having a non-volatile content of 66.7% wt and a Brookfield viscosity of 1,420 cps. 
     Example 2 
     A 2-liter, 4-neck round-bottomed flask equipped with a stirrer, a condenser, a heating mantle, a thermocouple, a dropping funnel, and a nitrogen inlet was charged with: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                  588.0 g 
                 Desmodur N-3300 (isocyanurate of HDI) 
               
               
                   
                 234.45 g 
                 n-butyl acetate, and 
               
               
                   
                   0.5 g 
                 10% solution dibutyl tin dilaurate in n-butyl acetate 
               
               
                   
                   
               
             
          
         
       
     
     The mixture was heated to 70° C. under a nitrogen blanket. When the mixture reached 70° C., 186.0 g 2-butyl-1-octanol (ISOFOL-12 from Sasol Chemie GmbH) were added through the dropping funnel over a one-hour period. During the addition, the reaction temperature was maintained between 70° C. and 75° C. After the addition, the resulting prepolymer was maintained at 70° C. for an additional hour. 
     A separate 3-liter, 4-neck round-bottomed flask equipped with a stirrer, a condenser, a heating mantle, a thermocouple, a Masterflex peristaltic pump, and a nitrogen inlet was charged with: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                  320.0 g 
                 2-butyl-2-ethyl propane diol and 
               
               
                   
                 234.45 g 
                 n-butyl acetate. 
               
               
                   
                   
               
             
          
         
       
     
     This mixture was heated to 70° C., and then the prepolymer prepared above was added over a 2-hour period using a Masterflex peristaltic pump. The reaction temperature was maintained between 70° C. and 75° C. After completion of the prepolymer addition, the reaction temperature was maintained at 70° C. for an additional 2 hours, at which point it was determined by FTIR that there was no indication of residual isocyanate. 
     The properties of the resulting polyurethane polyol are reported in Table 2. 
     Examples 3 through 6 
     Comparative Examples 7 through 10 
     The polyurethane polyol compositions of Examples 3 through 6 and Comparative Examples 7 through 10 were prepared according to the procedure of Example 2 using the reactants and amounts indicated in Table 1. The total amount of n-butylacetate used in each Example is given in Table 1. In each Example, half the total amount is used to prepare the prepolymer and half is used to prepare the polyurethane polyol. All monoalcohol substitutions are at the same molar level. The properties of the resulting polyurethane polyol compositions are reported in Table 2. 
     Comparative Example 11 
     An acrylic polyol was prepared by conventional free radical polymerization typically used in the coatings industry. The properties of the resulting acrylic polyol are given in Table 2. 
     Coating Compositions 
     Clear coat coating compositions were prepared with melamine resin Cymel 303 commercially available from Cytec Industries and polyurethane polyol compositions of Comparative Examples 1, 7, 8, and 11 and Examples 2 through 6 according to the following formulation: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 70.0 g 
                 polyurethane polyol (based on resin solids) 
               
               
                 28.9 g 
                 Cymel 303 (based on resin solids) 
               
               
                  1.0 g 
                 blocked dodecyl benzene sulphonic acid (based on actives) 
               
               
                  0.1 g 
                 Byk 310, silicone flow agent available from Byk Chemie (based 
               
               
                   
                 on actives) 
               
               
                   
               
             
          
         
       
     
     Preparation of Test Panels and Coating Properties: 
     Using a #44 draw down bar, the clear coats were applied on 4″×12″ (10.16 cm to 30.48 cm) Bonderite 1000 steel panels commercially available from ACT Laboratories and then baked at 121° C. for 30 minutes. The target dry film thickness was 1.0±0.1 mil (25.4±2.5 microns). After the bake, the following properties were tested on the panels: 
     Room Temperature Conical Mandrel Flexibility (¼″ to 2″ (0.635 cm to 5.08 cm) mandrel diameter): GM 9503P 
     Reverse Impact (40 inch-pound): Chrysler LP-463PB-19-01 
     Further, acid etch testing was conducted as follows: 
     Using a #44 draw down bar the clear coats were applied on 3″×18″ (7.62 cm×45.72 cm) black E-coated steel panels and then baked at 250 F. (121° C.) for 30 minutes. The target dry film thickness was 1.0±0.1 mil (25.4±2.5 microns). After the bake, the panels were placed on a gradient temperature bar ranging from 60° C. to 90° C. When the panels reached thermal equilibrium with the gradient bar, a 10% wt solution of aqueous sulphuric acid was spotted along the panel in 3° C. increments. The panels were exposed to the acid and temperature gradient for 30 minutes and then rinsed with distilled water. The temperature at which the first signs of etching are visible and the severity of etch at 77° C. are reported. 
     Table 3 summarizes these test results. It should also be noted that the clear coat formulations using the polyol of Comparative Examples 7 and 8 crystallized after sitting for 1 day. 
     One component, melamine cured clearcoat compositions based on Polyurethane Polyols Examples 2 and 3, were applied to the plastic substrate (TPO). Prior to the application of the clearcoat, TPO substrate was coated with an adhesion promoter and one component basecoat. Visual observations after bending of the coated substrate confirmed that these coating compositions on flexible substrates have surprising resistance to cracking. 
     
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 No mono- 
                   
               
               
                   
                 functional 
               
             
          
           
               
                   
                 n-carbon in 
                 alcohol 
                   
                 Linear alcohol modified 
               
             
          
           
               
                   
                 mono- 
                 Comp. 
                 Guerbet alcohol modified (branched) 
                 Comp 
                 Comp 
                 Comp 
                 Comp Ex. 
               
             
          
           
               
                   
                 functional 
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex.5 
                 Ex.6 
                 Ex.7 
                 Ex. 8 
                 Ex. 9 
                 10 
               
               
                 Reactants 
                 alcohol 
                 (gms) 
                 (gms) 
                 (gms) 
                 (gms) 
                 (gms) 
                 (gms) 
                 (gms) 
                 (gms) 
                 (gms) 
                 (gms) 
               
               
                   
               
             
          
           
               
                 2-butyl-1-octanol 
                 C-12 
                   
                 186.0 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 2-octyl-1-decanol 
                 C-18 
                   
                   
                 275.9 
               
               
                 2-octyl-1-dodecanol 
                 C-20 
                   
                   
                   
                 298.0 
               
               
                 2-decyl-1- 
                 C-24 
                   
                   
                   
                   
                 354.0 
               
               
                 tetradecanol 
               
               
                 Tetradecyl 
                 C-32 
                   
                   
                   
                   
                   
                 470.0 
               
               
                 octadecanol 
               
               
                 4-decanol 
                 C-10 
                   
                   
                   
                   
                   
                   
                 158.3 
               
               
                 1-octyl decanol 
                 C-18 
                   
                   
                   
                   
                   
                   
                   
                 270.0 
               
               
                 1-eicosanol 
                 C-20 
                   
                   
                   
                   
                   
                   
                   
                   
                 298.6 
               
               
                 Decyltetra decanol 
                 C-24 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 365.2 
               
               
                 Desmodur N3300 
                   
                 588.0 
                 588.0 
                 588.0 
                 588.0 
                 588.0 
                 588.0 
                 588.0 
                 588.0 
                 588.0 
                 588.0 
               
               
                 dibutyl tin 
                   
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
               
               
                 dilaurate 
               
               
                 2-butyl-2-ethyl 
                   
                 480.0 
                 320.0 
                 320.0 
                 320.0 
                 320.0 
                 320.0 
                 320.0 
                 320.0 
                 320.0 
                 320.0 
               
               
                 propane diol 
               
               
                 n-butyl acetate 
                   
                 457.7 
                 468.9 
                 507.4 
                 516.9 
                 540.9 
                 590.6 
                 457.0 
                 504.9 
                 517.1 
                 545.7 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 No mono- 
                   
                   
                 Acrylic 
               
               
                   
                 functional 
                   
                 Linear alcohol modified 
                 Polyol 
               
             
          
           
               
                   
                 alcohol 
                 Guerbet alcohol modified (branched) 
                 Comp 
                 Comp 
                 Comp 
                 Comp 
                 Comp Ex. 
               
             
          
           
               
                 Properties 
                 Comp. Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex.5 
                 Ex.6 
                 Ex.7 
                 Ex. 8 
                 Ex. 9 
                 Ex. 10 
                 11 
               
               
                   
               
             
          
           
               
                 % Non-Volatile 
                 66.7 
                 67 
                 66.8 
                 69.2 
                 69.5 
                 70.2 
                 69.7 
                 71.5 
                 73.4 
                 72.4 
                 74.8 
               
               
                 Brookfleld visc, cps 
                 1420 
                 1,160 
                 704 
                 928 
                 728 
                 604 
                 1,460 
                 Wax 
                 Wax 
                 Wax 
                 6,450 
               
               
                 50 rpm, #4 spindle, 20° C. 
               
               
                 OH Number (mg KOH/g) 
                 157.6 
                 102.6 
                 94.8 
                 93 
                 88.9 
                 81.4 
                 105.3 
                 95.2 
                 93 
                 88.2 
                 130.8 
               
               
                 Mn 
                 2,519 
                 1,868 
                 2,752 
                 2,098 
                 2,167 
                 2,311 
                 1,598 
                 2,102 
                 2,140 
                 2,257 
                 3,250 
               
               
                 Mw 
                 4,836 
                 3,070 
                 3,835 
                 3,214 
                 3,213 
                 3,269 
                 2,108 
                 3,163 
                 3,190 
                 4,190 
                 9879 
               
               
                 polydispersity (Mw/Mn) 
                 1.9 
                 1.6 
                 1.4 
                 1.5 
                 1.5 
                 1.4 
                 1.3 
                 1.5 
                 1.5 
                 1.9 
                 2.8 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Polyurethane polyol 
                   
                   
                   
                   
                   
               
               
                 used in clear coat 
                 DFT 
                 Mandrel bend at 
                 Reverse impact at 
                 Temp ° C. at first sign 
                 Severity of acid 
               
               
                 formulation 
                 (mil) 
                 +22° C. 
                 −22° C. 
                 of acid etch 
                 etch at 77° C. 
               
               
                   
               
             
             
               
                 Comp. Ex. 1 
                 1.0 
                 Fail 
                 Fail 
                 81 
                 No etch 
               
               
                 Ex. 2 
                 0.9 
                 Pass 
                 Fail 
                 81 
                 No etch 
               
               
                 Ex. 3 
                 1.0 
                 Pass 
                 Fail 
                 85 
                 No etch 
               
               
                 Ex. 4 
                 0.9 
                 Pass 
                 Pass 
                 77 
                 Slight 
               
               
                 Ex. 5 
                 1.0 
                 Pass 
                 Pass 
                 78 
                 Slight 
               
               
                 Ex. 6 
                 1.0 
                 Pass 
                 Pass 
                 81 
                 No etch 
               
               
                 Comp. Ex. 7 
                 0.9 
                 Fail 
                 Fail 
                 81 
                 No etch 
               
               
                 Comp. Ex. 8 
                 0.9 
                 Pass 
                 Fail 
                 70 
                 Severe 
               
             
          
           
               
                 Comp. Ex. 9 
                 Was not tested due to waxy consistency 
               
               
                 Comp. Ex. 10 
                 Was not tested due to waxy consistency 
               
             
          
           
               
                 Comp. Ex. 11 
                 0.9 
                 Fail 
                 Fail 
                 68 
                 Severe