Europaisches Patentamt European Patent Office © Publication number: 0 545 1 34 A1 Office europeen des brevets EUROPEAN PATENT APPLICATION © Application number: 92119580.6 int. Ci.5; C09D 5/03, C08K 5/06 @ Date of filing: 17.11.92 © Priority: 29.11.91 US 800091 © Applicant: ESTRON CHEMICAL INC. Highway 95 @ Date of publication of application: Calvert City, Kentucky(US) 09.06.93 Bulletin 93/23 @ Inventor: Skora, Stanislaw B. © Designated Contracting States: 13 Valley Road CH DE FR GB IT LI Mountain Lakes, New Jersey 07046(US) © Representative: Minoja, Fabrizio Studio Consulenza Brevettuale Via Rossini, 8 1-20122 Milano (IT) © Thermosetting powder coating compositions containing bisphenoxypropanol as a melt viscosity modifier. © In a thermosetting powder composition contain- ing a thermosetting polymer and a cross-linking agent therefor, the improvement which comprises the presence of an amount of a 1 ,3-£>/s(phenoxy)- propan-2-ol at least sufficient to lower the melt vis- cosity of said composition and reduce pin-hole for- mation. CO Rank Xerox (UK) Business Services (3. 10/3.6/3.3. 1) 1 EP 0 545 134 A1 2 The present invention relates relates to film- under the influence of heat. forming thermosetting powder coating composi- The present invention is a thermosetting com- tions containing £>/s-phenoxypropanol as a melt vis- position which is particularly useful as a powder cosity modifier. coating material. In particular, the composition pro- Thermosetting compositions, including epoxy, 5 duces high quality, smooth, substantially pin-hole acrylic, and polyester resins, and various crosslin- free film coatings which are resistant to discolor- king agents, are useful for coatings. The should be ation. The composition comprises a thermosetting in powder form, typically with an average particle polymer, including thermosetting polyesters, ther- size of from 40 to 120 micrometers, and should be mosetting acrylic resins, and epoxy resin, a cros- physically and chemically stable during storage at io slinking agent (also referred to as crosslinker or a ambient temperature for a prolonged period of curing agent), and a £>/sphenoxypropanol com- time, e.g. up to 12 months. Such compositions pound present at least in a sufficient amount to typically are applied electrostatically to objects and prevent the formation of pin-holes during the pro- heated to temperatures in the range from 120 to cess of curing the coating. The composition prefer- 240° C, at which point they fuse and undergo 75 ably also includes a flow control agent different chemical reactions forming a durable, uniform, from the £>/sphenoxypropanol compound. crosslinked, and insoluble film. For the purpose of the present invention pre- U.S. Patent No. 4,065,438 describes thermo- venting the formation of pin-holes means the sub- setting powder coating compositions comprising stantial or total prevention of pin-holes visible to the carboxyl functional polyesters and £>/sphenol A- 20 naked eye and through magnifying instruments. type epoxy resins. The £>/sphenoxypropanol melt viscosity modi- U.S. Patent No. 4,147,737 is directed to car- fier of the present invention is a monomeric com- boxyl functional polyester powder coatings cros- pound being in solid, crystalline form and able to slinked with triglycidyl isocyanurate. Such powder form a uniform mixture with the other powder coat- coating compositions have very good mechanical 25 ing ingredients. During curing of powder coating at properties and relatively good outdoor durability. elevated temperatures, the melt viscosity modifier Alternatively, carboxlic polyester can be cured with acts as a solvent, lowering the melt viscosity of the hydroxyalkyl amides. composition and allowing the release of entrapped U.S. Patent No. 3,931,117 discloses the prep- gases and volatiles from the film and preventing aration of hydroxy functional polyester resins 30 the formation of pin-holes. An advantage of using which, in combination with blocked isocyanates or the melt viscosity modifier is its durability against melamine resins, are suitable for producing ther- oxidation and discoloration during both the curing mosetting powder coatings. process and aging of the formed coating. U.S. Patent No. 4,181,642 describes glycidyl Preferred £>/sphenoxypropanols are those of methacrylate copolymers as the basic polymers for 35 the formula: the preparation of powder coating compositions. Such compositions can be used as ultraviolet light CH2 CH CH2 resistant coatings. I I I U.S. Patent No. 4,286,021 discloses the use of O OH O low molecular weight acrylic copolymers based on 40 isobornyl methacrylate as a melt viscosity modifier in powder coating systems. Notwithstanding these disclosures, a need re- mains for cured films with substantially no visible defects. Such defects are typically in the form of a 45 poor flow, cratering, orange-peel effect and pin- holes. The flow can be improved and cratering and orange-peel effect eliminated by the use of flow where in which each of R1, R2, and R3 indepen- control agents. However, the elimination of pin- dently of the other is hydrogen, halogeno, or an holes requires special additives able to lower the 50 aliphatic radicals of up to 3 carbons. melt viscosity of the powder coating composition 1 ,3-£>/s-(Phenoxy)-2-propanols can be prepared during the curing process. as described for example in Journal of Medicinal Acrylic additives described in U.S. Patent No. Chemistry, 19, No. 2, 222-229 (1976). The pre- 4,286,021 are capable of lowering the melt viscos- ferred £>/sphenoxypropanol compound is 1,3-£>/s- ity of the system, but do not eliminate or reduce 55 (phenoxy)propan-2-ol. the formation of pin-holes. Benzoin also is used as The thermosetting polymer has at least two an additive in powder coating formulations, but it functional groups of the same kind in a molecule, has a strong tendency to discoloration (yellowing) e.g., epoxy, hydroxy, or carboxy groups. Useful 2 3 EP 0 545 134 A1 4 thermosetting epoxy, and polyester polymers are Useful acrylic resins include those having a generally reviewed in Billmeyer, Jr., A Textbook of hydroxy functionality with a hydroxy number of Polymer Science, 2nd Edit., Wiley-lnterscience, from about 30 to about 180; carboxy functionality Division of John Wiley & Sons, Inc., 1962, in par- having an acid number of about 20 to 110; and ticular Chapter 16. Epoxy resins are also reviewed 5 glycidol functionality having an epoxy equivalent in May et al, Ed., Epoxy Resins Chemistry and weight from about 500 to 900. Useful acrylic poly- Technology, Marcel Dekker, Inc. mers are disclosed in U.S. Patent No. 4,181,642. A preferred epoxy resin useful in the invention The preferred softening point of acrylic polymers is is prepared by the condensation of £>/sphenol A from about 90 °C to 130°C, measured according to with epichlorohydrin in the presence of an alkaline 70 ASTM-E-28. compound such as sodium hydroxide. Its epoxy Useful functional monomers include acrylic equivalent weight (EEW) preferably is from about acid, methacrylic acid, crotonic acid, hydroxyethyl 600 to about 900. acrylate, hydroxyethyl methacrylate, hydroxypropyl The polyester resin useful in the present inven- acrylate, hydroxypropyl methacrylate, glycidyl ac- tion can be hydroxy or carboxy functional. The 75 rylate, and glycidyl methacrylate. hydroxy functional resin should have a hydroxyl Other acrylic monomers include esters of an number from about 30 to about 90, and the car- a,/3-ethylenically unsaturated carboxylic acid having boxy functional polyester should have an acid num- from 3 to 8 carbon atoms. A preferred acrylic ber from about 20 to about 100. monomer has the formula: The polyester can be prepared by any manner 20 known in the art, such as condensing at least one polyfunctional organic acid, its methyl ester or an- hydride thereto with at least one polyalcohol in the or absence of a catalyst. Useful catalysts presence CH 2 =C-COOR* include organo-tin compounds and organo-titanium 25 ^ compounds. Useful alcohols from which the polyester can where R1 is H or CH3 and R2 is an alkyl radical be made include those having at least two hydroxy containing 1 to 8 carbon atoms. Useful acrylic groups, as for example ethylene glycol, propylene monomers include ethyl acrylate, butyl acrylate, glycol, trimethylolethane, trimethylolpropane, glyc- 30 isobutyl acrylate, 2-ethylhexyl acrylate, lauryl ac- erin, 1 ,4-butanediol, 1 ,6-hexanediol, and neopentyl rylate, methyl methacrylate, ethyl methacrylate, glycol. butyl methacrylate, isobutyl methacrylate, and The carboxylic acids typically are aromatic car- lauryl methacrylate. boxylic acids, with the most preferred carboxylic The acrylic polymer optionally can contain an acids being dicarboxyl acids and tricarboxyl acids. 35 ethylenically monounsaturated vinyl comonomer Examples of acid components include phthalic which is different from the functional monomer and acid, terephthalic acid, isophthalic acid, trimellitic the acrylic monomer. Any such vinyl comonomer acid, and pyromellitic acid, as well as the anhy- can be used which does not prevent the composi- drides thereof. tion from being useful in powder coating applica- The polyester can optionally comprise minor 40 tions. Examples of ethylenically unsaturated vinyl amounts, generally less than 30 mole percent, of at comonomers which can be useful are styrene, vinyl least one other aliphatic of cycloaliphatic carboxylic toluene, dimethyl styrene, a-methyl styrene, and acids. The presence of such comonomers is ac- vinyl acetate. ceptable provided that the composition is useful in The copolymers can be prepared in any known powder coating applications. Useful aliphatic and 45 manner, such as by free-radical polymerization in cycloaliphatic carboxylic acids include adipic acid, bulk, solution, emulsion, or suspension. Preferably, sebacic acid, succinic acid, tetrahydrophthalic acid, the reaction is conducted in the presence of a free hexahydrophthalic acid, cyclohexanedicarboxylic radical initiator such as benzoyl peroxide, tert-butyl acid, maleic acid, and fumaric acid. peroxide, decanoyl peroxide, azo compounds such The molar ratio of the acidic to alcoholic mon- 50 as azo£>/sisobutyronitrile, and the like.