(19) TZZ_¥ _T (11) EP 1 732 965 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) Int Cl.: of the grant of the patent: C01F 7/00 (2006.01) C08J 3/00 (2006.01) 26.02.2014 Bulletin 2014/09 (86) International application number: (21) Application number: 04821623.8 PCT/US2004/022759 (22) Date of filing: 14.07.2004 (87) International publication number: WO 2005/089085 (29.09.2005 Gazette 2005/39) (54) IMPROVED COLOR STABILITY OF ISOCYANATES VERBESSERTE FARBSTABILITÄT VON ISOCYANATEN AMELIORATION DE LA SOLIDITE DE LA COULEUR DES ISOCYANATES (84) Designated Contracting States: • VARRON, Corinne AT BE BG CH CY CZ DE DK EE ES FI FR GB GR F-69003 Lyon (FR) HU IE IT LI LU MC NL PL PT RO SE SI SK TR (74) Representative: Gillard, Richard Edward et al (30) Priority: 14.07.2003 US 487177 P Elkington and Fife LLP Thavies Inn House (43) Date of publication of application: 3-4 Holborn Circus 20.12.2006 Bulletin 2006/51 London EC1N 2HA (GB) (73) Proprietor: Vencorex US, Inc. (56) References cited: Freeport, TX 77541 (US) EP-A- 0 210 859 EP-A- 0 425 710 EP-A- 0 735 027 WO-A-94/19385 (72) Inventors: WO-A-98/14492 DE-A1- 1 802 659 • ROSEN, Richard GB-A- 923 190 GB-A- 1 102 387 Princeton, NJ 08540 (US) GB-A- 2 184 733 US-A- 3 069 369 • BERNARD, Jean-Marie US-A- 3 115 465 US-A- 4 305 839 F-69440 Saint-Laurent D’agny (FR) US-A- 4 576 855 US-A- 5 719 229 • WO, Shiming US-A- 6 043 332 US-A1- 2002 115 782 Monroe Township NJ08831 (US) Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 1 732 965 B1 Printed by Jouve, 75001 PARIS (FR) EP 1 732 965 B1 Description FIELD OF THE INVENTION 5 [0001] This invention relates to color stabilizing compositions, and more particularly to color stabilizing compositions useful for stabilizing the color of isocyanates, particularly polyisocyanate oligomers and prepolymers, to be used to prepare polyurethane coatings, films therefrom. The polyisocyanates can also be used to form adhesives, sealants and elastomers. 10 BACKGROUND OF THE INVENTION [0002] Two component thermosetting polyurethanes are widely used in protective coatings or films in a broad range of applications, such as for example, coatings for automotive machinery, equipment, and other surfaces in need of a protective coating. These room temperature- curable polyurethanes are prepared from polyisocyanates and a component 15 containing an active hydrogen compound, such as a polyol or an amine. [0003] Two-component polyurethane coating systems include a polyisocyanate component that reacts with a polyol component that comprises, for example, an acrylic polyol or polyester polyol, to form useful films. The system also includes organic solvents, and a variety of adjuvant components, e.g., surface active agents, pigments, dispersants, diluents, and fillers. This type of coating is one of the finest coatings available that can be produced without the applicatio n 20 of heat or other external sources of energy. They are very useful for objects that cannot be heat-cured, such as large machinery, airplanes, ships and vehicles. [0004] In some embodiments, two component polyurethane compositions are cured at elevated temperature. It has been recognized that such systems tend to discolor at elevated temperatures and prior art methods to stabilize the color of such polyurethanes systems have been developed. The approach of these methods is either purification or stabilization 25 of the polyisocyanate. For example, U.S. 4,297, 472 teaches adding a small amount of vicinal diols to the formulation to improve the color stability of the polyurethanes. U.S. 4,065, 362 teaches a process to purify the organic isocyanate, U.S. 3,715, 381 teaches incorporating 2,4-di (t-butyl)-p-cresol (BHT) in the formulation, and U.S. 2,957, 903 teaches incorporating an amount of triaryl phosphite in a polyisocyanate. U.S. 4,677, 154 relates to elimination of discoloration in polyurethanes, particularly thermoplastic polyurethanes, by the addition to the reaction mixture from 0.01 to 1 percent 30 by weight, based on the isocyanate component, a stabilizer package characterized as BHT and a compound selected from a specific group of compounds which includes tris (nonylphenyl) phosphite, distearyl thiodipropionate, triisodecyl phosphite, trilauryl trithiophosphite, and blends thereof. [0005] EP 0 425 710 discloses a process for producing a modified organic polyisocyanate having an isocyanurate ring. EP 0 210 859 relates to curable compositions for use as adhesives, coatings and sealants. WO 98/14492 discloses 35 a process for the production of micro- cellular or non- cellular, light-stable elastomeric, flexible or semiflexible polyurethane mouldings. US 5,719,229 relates to solid elastomeric polyurethanes. US 6,043,332 relates to a process for the production of polyisocyanates containing uretdione groups. EP 0 735 027 discloses a process for the preparation of (cyclo) aliphatic uretdiones. GB1102387 relates to stabilized isocyanate- ether solutions. US2002115782 discloses a thermoplastic mold- ing composition comprising a polyurethane elastomer. DE1802659 relates to vinyl fluoride polymers. US 3,069,369 40 relates to colour stabilised polyethylene compounds. GB923190 relates to antioxidant compositions. US 3,115,465 discloses compositions comprising phosphite esters and a methylene bis- phenol. US4,305,839 discloses thestabilisation of impurehydroxybenzophenones by the addition of an organic phosphiteor organic phosphonite. WO94/19385 discloses a process for the polymerization of cyclo-olefins. [0006] Other two component polyurethane systems are curable at relatively mild temperatures in the presence of a 45 catalyst for promoting reaction of the polyisocyanate with the polyol. In one embodiment of such low temperature curing two component polyurethane coating systems, the catalyst is included in the polyisocyanate component of the system to form a "hardener" component that is subsequently combined with the polyol component to form a curable coating composition. However, it has been found that including the catalyst in the polyisocyanate component of such systems markedly increases the potential for undesirable discoloration of the polyisocyanate and related coating and despite the 50 known color stabilizing methods, it has been found that a need exists for a stabilizer that will efficiently stabilize the colo r of a solution of an isocyanate in the presence of a catalyst for the reaction of the isocyanate with an active hydrogen compound. SUMMARY OF THE INVENTION 55 [0007] It has been discovered in accordance with this invention that color of isocyanates can be stabilized by admixing with the isocyanate a color stabilizing effective amount of a stabilizer comprised of a trialkyl phosphite component, each alkyl group of said trialkyl phosphite component having less than 10 carbon atoms. Typically, the stabilizer is a system 2 EP 1 732 965 B1 which will also further comprise a phenolic antioxidant component (e. g. a t- butylated hydroxytoluene selected from the group consisting of 2,6ditertiarybutyl hydroxytoluene and 2-tertiarybutyl hydroxytoluene). [0008] In a first aspect, the present invention is directed to a hardener composition for use as the first component of a two component polyurethane coating composition, comprising: 5 one or more aliphatic polyisocyanate oligomers selected from a polyisocyanate dimer, a polyisocyanate trimer, a product of condensation of two or more polyisocyanate dimers, a product of condensation of two or more polyiso- cyanate trimers, or a condensation product of dimers with trimers, derived from isophorone diisocyanate, ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, decamethylene diisocyanate, or nor- 10 bornene diisocyanate, a catalyst for promoting reaction of the polyisocyanate with a reactive hydrogen compound, a first antioxidant comprising one or more of sterically hindered phenol antioxidants and secondary aryl amine antioxidants, and 15 a second antioxidant comprising one or more organophosphite antioxidants according to the formula: (RO)3P wherein each R is independently alkyl or aryl. 20 [0009] In a second aspect, the present invention is directed to a polyisocyanate formulation suitable for use in preparing polyurethanes therefrom in which the color stabilizing effective amount of the stabilizer system trialkyl phosphite com- ponent, each alkyl group of said trialkyl phosphite component having less than 10 carbon atoms, comprises from 0.1 to 2.0 weight % based on the total weight of the polyisocyanate formulation. 25 [0010] In a third aspect, the present invention provides a color stabilized isocyanate composition for use in a formulation for preparing polyurethanes therefrom, the color stabilized isocyanate composition comprising: (a) a phenolic antioxidant, e.g. a t- butylated hydroxytoluene selected from the group consisting of 2,6- ditertiarybutyl hydroxytoluene and 2-tertiarybutyl hydroxytoluene, 30 (b) a trialkyl phosphite component, each alkyl group of said trialkyl phosphite component having less than 10 carbon atoms and (c) at least one isocyanate. 35 [0011] Ina fourth aspect, the presentinvention is directed toa method for making