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.
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.
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.
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 xcex1,xcex2 and xcex1,xcex3 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:
(R1) (R2) CHCH2OH
wherein
R1 is a linear alkyl group,
R2 is a linear alkyl group,
the sum of the carbon atoms in R1 and R2 is 10 to 34, and both R1 and R2 are present.
Guerbet alcohols are commercially available from Sasol Chemie GmbH as Isofol(copyright) 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 130xc2x0 C. and more preferably between 20 and 120xc2x0 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.