Low VOC, coating compositions having improved flexibility and impact resistance based upon nonlinear, low-molecular weight polyester polyol resins

Abstract

Coating compositions based on nonlinear, low molecular weight, polyester-based polyols having low viscosity and high solids content made by reacting a branched, polyhydric alcohol having at least three hydroxyl groups, such as trimethylolpropane; a glycol or diol; and a compound selected from the group consisting of a aliphatic or aromatic dicarboxylic acid, C 1 -C 6 alkyl ester, anhydride, diacid halide, or mixtures thereof. The nonlinear, polyester-based polyols are quite effective in maintaining a high solids content while lowering viscosity when blended with other coating resins, such as acrylic resins, making the coating resins more effective in cured coatings by improving flexibility, impact resistance and hardness without adversely affecting appearance, solvent resistance, and/or accelerated weathering. This invention also relates to the process of coating a substrate with these coating compositions.

What is claimed is:  
     
         1 . A polymer composition comprising a blend or admixture of: a) at least one nonlinear, branched polyester-based polyol resin which has an average functionality of greater than 2, a number average molecular weight of at least 500, and a hydroxyl value of between about 35 and about 350; and b) at least one acrylic polyol resin, wherein the polyester polyol is included in the composition in an amount of about 5% to about 95% based on the total weight of the coating composition.  
     
     
         2 . A polymer composition comprising a blend or admixture of: 
 a) at least one nonlinear, branched polyester-based polyol resin which has an average functionality of greater than 2, a number average molecular weight of at least 500, and a hydroxyl value of between about 35 and about 350;    b) at least one acrylic polyol resin;    c) at least one curing agent for the polyol resins;    d) at least one catalyst; and    e) at least one liquid carrier.    
     
     
         3 . A coating composition comprising a blend or admixture of: 
 a) at least one nonlinear, branched polyester-based polyol resin which has an average functionality of greater than 2, a number average molecular weight of at least 500, and a hydroxyl value of between about 35 and about 350;    b) at least one acrylic polyol resin;    c) at least one curing agent for the polyol resins;    d) at least one catalyst; and    e) at least one liquid carrier.    
     
     
         4 . The composition in accordance with    claim 1   , wherein the nonlinear polyester-based polyol is made by the process of reacting (a) at least one branched, polyhydric alcohol having at least three hydroxyl groups, at least one of said hydroxyl groups being covalently bonded to a branched carbon atom; and (b) at least one glycol or diol; with (c) at least one compound selected from the group consisting of an aliphatic or aromatic dicarboxylic acid, a C 1 -C 6  alkyl diester of an aliphatic or aromatic dicarboxylic acid, an aliphatic anhydride, an aliphatic or aromatic diacid halide in a mole ratio of (a):(b):(c) from about 1:2:2 to about 1:205:150, at a temperature sufficient to achieve esterification or transesterification.  
     
     
         5 . The composition in accordance with    claim 4   , wherein the branched polyhydric alcohol is reacted with an aliphatic or aromatic diester, and wherein the mole ratio of the branched polyhydric alcohol to the diester is between about 1.3:6 and about 1:18:120.  
     
     
         6 . The composition in accordance with    claim 4   , wherein the branched, polyhydric alcohol having at least three hydroxyl groups is selected from the group consisting of trimethylolpropane, trimethylolethane, pentaerythritol, glycerine, dipentaerythritol, and mixtures thereof.  
     
     
         7 . The composition in accordance with    claim 4   , wherein the branched polyhydric alcohol is reacted with a C 1 -C 6  alkyl diester of an aliphatic or aromatic dicarboxylic acid, and wherein said diester is selected from the group consisting of dimethyl 1,12dodecanedioate, dimethyl tartrate, dimethyl sebacate, dimethyl azelate, dimethyl suberate, dimethyl pimelate, dimethyl adipate, dimethyl glutarate, dimethyl succinate, and mixtures thereof.  
     
     
         8 . The composition in accordance with    claim 7    wherein said diester is selected from the group consisting of dimethyl adipate, dimethyl glutarate, and mixtures thereof.  
     
     
         9 . The composition in accordance with    claim 8   , wherein the mole ratio of dimethyl adipate to dimethyl glutarate is about 1:3.  
     
     
         10 . The composition in accordance with    claim 4   , wherein said glycol or diol is selected from the group consisting of glycerine, 1,4-butanediol, diethylene glycol. 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3propanediol, 1,4-cyclohexanedimethanol, 2-butyl-2-ethyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, propylene glycol, 1,2-hexanediol, 1,3-butanediol, 1,5-pentanediol, and mixtures thereof.  
     
     
         11 . The composition in accordance with    claim 10   , wherein said glycol or diol is 1,4-cyclohexane dimethanol, 2-methyl-1,3-propanediol, or a mixture thereof.  
     
     
         12 . The composition in accordance with    claim 4   , wherein the polyester polyol is a polyester of dimethyl adipate, dimethyl glutarate, trimethanolpropane, and cyclohexanedimethanol.  
     
     
         13 . The composition in accordance with    claim 1   , wherein said one nonlinear, branched polyester-based polyol resin has an average functionality of less than 6.  
     
     
         14 . The composition in accordance with    claim 1   , wherein said one nonlinear, branched polyester-based polyol resin has an average functionality of between 2.1 to 2.5.  
     
     
         15 . The composition in accordance with    claim 1   , wherein the number average molecular weight of said polyol is between about 500 and 1500.  
     
     
         16 . The composition in accordance with    claim 2   , wherein the curing agent is selected from the group consisting of an aliphatic amino resin, an aromatic amino resin, an aliphatic epoxy resin, an aromatic epoxy resin, a cycloaliphatic epoxy resin, an aliphatic diisocyanate, an aliphatic triisocyanate, an aliphatic triisocyanurate, an aliphatic polyisocyanate, an aliphatic isocyanurate, an aliphatic allophanate, an aliphatic uretdione, an aliphatic biuret, an aliphatic isocyanate prepolymer, a cycloaliphatic diisocyanate, a cycloaliphatic triisocyanate, a cycloaliphatic triisocyanurate, a cycloaliphatic polyisocyanate, a cycloaliphatic isocyanurate, a cycloaliphatic allophanate, a cycloaliphatic uretdione, a cycloaliphatic biuret, a cycloaliphatic isocyanate prepolymer, an aromatic diisocyanate, an aromatic triisocyanate, an aromatic triisocyanurate, an aromatic polyisocyanate, an aromatic isocyanurate, an aromatic allophanate, an aromatic uretdione, an aromatic biuret, and an aromatic isocyanate prepolymer, in an amount substantially equivalent to the molar equivalent quantity of a) plus b).  
     
     
         17 . The composition in accordance with    claim 16    wherein one of the curing agents comprises an aliphatic isocyanate based on hexamethylene diisocyanate.  
     
     
         18 . The composition in accordance with    claim 16   , wherein the isocyanate is added to the said polyol resins in a molar equivalent ratio of about 0.5:1 to 3:1.  
     
     
         19 . The composition in accordance with    claim 16   , wherein the isocyanate is added to the said polyol resins in a molar equivalent ratio of about 0.8:1 to 1.4:1.  
     
     
         20 . The composition in accordance with    claim 2   , wherein said catalyst is employed in an amount between about 0.0001% and about 5%, based upon the weight of the composition.  
     
     
         21 . The composition in accordance with    claim 2   , wherein said liquid carrier is selected from the group consisting of a ketone solvent selected from the group consisting of acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl butyl ketone, methyl amyl ketone; an ester solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, t-butyl acetate, isobutyl acetate, ethylethoxy propionate, ethylethoxy acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate; an aromatic solvent selected from the group consisting of xylene, toluene, aromatic naphtha, aromatic 100, aromatic 150, aromatic 200, parachlorobenzotrifluoride, an aromatic hydrocarbon mixture having a boiling point of 152° C.-174° C.; mineral spirits; and combinations thereof.  
     
     
         22 . The composition in accordance with    claim 2   , wherein the polyester polyol is included in the composition in an amount of about 5% to about 95% based on the total weight of the composition.  
     
     
         23 . The composition in accordance with    claim 2   , wherein the polyester polyol is included in the composition in an aiotint of about 10% to about 70% based on the total weight of the composition.  
     
     
         24 . The composition in accordance with    claim 2   , wherein the polyester polyol is included in the composition in an amount of about 20% to about 40% based on the total weight of the composition.  
     
     
         25 . The composition in accordance with    claim 2    further including at least one surface tension reducing additive/flow aid in an amount of about 0.001% to about 10% by weight, based on the total weight of the composition.  
     
     
         26 . The composition in accordance with    claim 2    further including at least one pigment.  
     
     
         27 . The composition in accordance with    claim 2    cured at ambient temperature.  
     
     
         28 . The composition in accordance with    claim 2    baked to cure at a temperature from about 50° C. to about 200° C.  
     
     
         29 . A method of increasing the hardness and flexibility of a polymeric coating composition by blending about 20-40% by weight of at least one nonlinear. branched. polyester-based polyhydric alcohol resin with about 60-80% by weight of an acrylic resin.  
     
     
         30 . A method of coating an outer surface of a substrate containing both a metal outer surface portion and a flexible polymeric outer surface portion with a single coating composition, while achieving coating adhesion and a uniform appearance of the coating material on both surface portions, by applying the single coating composition continuously over both surface portions simultaneously, without changing the coating composition, comprising coating both outer surface portions of said substrate with the composition of    claim 1   .  
     
     
         31 . The method in accordance with    claim 30   , wherein said substrate is a body of a motorized vehicle.  
     
     
         32 . The method in accordance with    claim 31   , wherein the motorized vehicle is a car, truck, tractor, airplane, or boat.  
     
     
         33 . The method in accordance with    claim 30   , wherein said coating composition is organic solvent-free.  
     
     
         34 . The method in accordance with    claim 30   , wherein said coating composition includes the step of removing the solvent from the coating composition and curing the coating to form an adherent coating on said substrate.  
     
     
         35 . The method in accordance with    claim 30   , wherein the cured coating remains adhered to the flexible polymeric surface portion of said substrate after said polymeric surface portion is flexed.