Thermosetting Powder Coating Compositions Containing Bisphenoxypropanol As a Melt Viscosity Modifier

Europaisches Patentamt European Patent Office © Publication number: 0 545 1 34 A1 Office europeen des brevets

EUROPEAN PATENT APPLICATION

@ 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)

© In a thermosetting powder composition containing 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 viscosity of said composition and reduce pin-hole formation.

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. Useful in- omer in the polyester is selected in the manner itiators are present in amounts ranging from 0.1 to resulting in a polyester having a softening point about 5% by weight of the total monomers. measured in accordance with ASTM E-28 of from The acrylic polymers preferably have a molec- 90 to 130° C. ular weight as measured by gel permeation The acrylic polymers useful in the invention 55 chromatography (GPC) in the range of from about can be prepared by free radical polymerization of 1500 to 10,000, and preferably 2000 to 8000. acrylic and vinyl monomers with unsaturated mon- The thermosetting powder coating composition omers having hydroxy, carboxy, or epoxy groups. will contain a crosslinking or curing agent, that is

3 5 EP 0 545 134 A1 6 one or more compounds contains reactive groups Powder coating compositions can be prepared capable of reacting at elevated temperatures with by dry blending all ingredients, followed by melt the functional groups of the basic polymer. Typi- blending in an internal mixer, or in an extruder at cally, the crosslinking agent will contain an alkoxy, room temperatures ranging from 80-1 20 °C. The blocked isocyanate, carboxy, epoxy or hydrox- 5 homogeneous composition is then cooled to room ylamide group, e.g., dicyandiamide, hydroxyalkyl- temperature, comminuting by crushing or grinding amides, hexamethoxy-melamine, in a mill and screened. Useful product is a free- tetramethoxymethyl-glycoluril, an aliphatic dicar- flowing powder having a particle size of less than boxylic acid, 1 ,12-dodecanedionic acid, sebacic about 120 micrometers and preferably from 40 to acid, 1 ,4-cyclohexane dicarboxylic acid, blocked io 120 micrometers. The powder composition of the isocyanates, such as caprolactam blocked present invention is physically and chemically sta- isophorone diisocyanate and its oligomers, blocked ble at room temperature for prolonged periods of toluenediisocyanate and its oligomers, triglycidyl time, up to 2 years. The compositions can be isocyanurate, and low molecular weight glycidyl applied as a dry coating to a substrate, such as a methacrylate copolymers. is metallic object, and then cured by baking at 160- Preferred crosslinking agents for thermosetting 220 ° C from about 5 to about 30 minutes to obtain polyester polymers having carboxylic group func- a crosslinked film having excellent mechanical tionality and thermosetting acrylic polymers having strength, thermal stability, solvent resistance, adhe- carboxylic group functionality include triglycidyl sion, mechanical strength, and durability against isocyanurate and hydroxylalkyl amides. Preferred 20 weathering. crosslinking agents for thermosetting polyester The following Examples illustrate the practice polymers having hydroxyl functionality and ther- of the present invention but should not be con- mosetting acrylic polymers having hydroxyl func- strued as limiting the invention to anything less tionality include caprolactam blocked isophorone than that which is disclosed or which would have diisocyanate and tetramethoxymethyl- glycoluril. 25 been obvious to one of ordinary skill in the art For thermosetting acrylic copolymers having therefrom. Precent and parts are by weight unless glycidyl methacrylate functionality preferred cros- otherwise indicated. slinking agents are 1 ,12-dodecanedionic acid and 1 ,4-cyclohexane dicarboxylic acid. EXAMPLE 1 Preferred compositions comprise from about 30 65 to about 97% of a basic thermosetting polymer Ninety parts of the carboxyl functional polyes- and from 3 to 35 % by weight of a crosslinking ter resin Uralac P2400 sold by DMS Resins, 10 agent to form a powder coating film, together with parts of triglycidyl-isocyanurate made by Ciba- from about 0.5 to about 3% of the Geigy, 1 part of a polyacrylate flow control, agent £>/sphenoxypropanol compound. 35 Resiflow P-67 sold by Estron Chemical and 500 The composition of the present invention also parts of titanium dioxide were dry-blended in a high can contain one or more flow control agents dif- speed mixer than homogenized by an extruder at ferent than the melt viscosity modifier 105°C. The hot extruded material was cooled to £>/sphenoxypropanol compound of the present in- room temperature, pulverized in a micromill, and vention. Flow control agents are used to produce a 40 passed through a 140-mesh screen. The free-flow- smooth, uniform coating. They are added to elimi- ing powder was applied electrostatically onto a nate surface imperfections, such as poor flow, or- mild steel plate, and baked at 180°C for 20 min- ange peel effect and cratering. However, flow con- utes. A glossy, uniform film was obtained which trol agents do not prevent the formation of defects however by closer inspection had visible tiny holes such as pin-holes. Useful flow control agents in- 45 (pin-holes). clude silicone oligomers, fluorinated polyolefins, polyvinyl butyral, polyacrylates and others. Gen- EXAMPLE 2 erally flow control agents function by lowering the surface tension of the coating system. The melt A powder coating composition was prepared in viscosity modifier of the present invention in con- 50 the same way as in Example 1 , except that in the trast lowers the melt viscosity of the powder coat- initial step, 2 parts of 1 ,3-£>/s(phenoxy)propan-2-ol ing composition during the initial step of the baking as the melt viscosity modifier were added. The process. baked coating was glossy, uniform and was totally Optionally, pigments, colorants, plasticizers, free of pin-holes. stabilizers, catalysts, antistatic agents, and other conventional additives can be included in the composition.

4 7 EP 0 545 134 A1 8

EXAMPLE 3 Claims

Fifty six part of the carboxy functional polyes- 1. In a thermosetting powder composition con- ter resin Uralac P-830 sold by DSM Resins, 3.1 taining a thermosetting polymer and a cross- parts of a hydroxyalkylamide crosslinker Primid XL- 5 linking agent therefor, the improvement which 552 sold by Rohm & Haas Co., 0.9 parts of Re- comprises the presence of an amount of a 1 ,3- siflow P-67 and 40.4 parts of titanium dioxide were £>/s(phenoxy)propan-2-ol at least sufficient to dry-blended, then homogenized in a preheated to lower the melt viscosity of said composition 1 1 0 ° C extruder. The extrudate was cooled to room and reduce pin-hole formation. temperature, crushed, ground and passed through 10 a 140-mesh screen. The resulting powder was then 2. A thermosetting powder composition according applied electrostatically onto the mild steel panel to claim 1 wherein the 1 ,3-£>/s(phenoxy)propan- and baked at 180°C for 20 minutes. A glossy, 2-ol has the formula: uniform coating was obtained, which however had a large amount of pin-holes. 15

EXAMPLE 4

Example 3 was repeated except that the powder coating composition contained additionally 1.5 20 parts of 1 ,3-£>/s(phenoxy)propan-2-ol. The resulting coating was glossy and uniform and was free of pin-holes.

EXAMPLE 5

Sixty-six parts of the glycidyl group containing in which each of R1, R2, and R3 indepen- acrylic resin Isocryl EP-550 (Estron Chemical), 13.7 dently of the other is hydrogen, halogeno, or parts of 1 ,12-didecanedioic acid (DuPont), 1 part of an aliphatic radicals of up to 3 carbons. Resiflow P-67, 1 part of 1 ,3-£>/s(phenoxy)propan-2- 30 ol and 18.3 parts titanium dioxide were dry-blended 3. A thermosetting powder composition according then extruded at 104°C. The extrudate was cooled, to claim 2 wherein each of R1, R2, and R3 is crushed, ground and sieved on a 140 mesh screen. hydrogen. The powder composition was then applied electrostatically onto a mild steel panel and baked at 35 4. A thermosetting powder composition according 200 °C for 20 minutes. The resulting coating was to claim 1 wherein the amount of the 1,3-£>/s- gloss, uniform and free of pin-holes. (phenoxy)propan-2-ol is from about one-half to about three weight percent of the thermoset- EXAMPLE 6 ting polymer and cross-linking agent. 40 Fifty-four parts of the hydroxy functional poly- 5. A thermosetting powder composition compris- ester resin Rucote 102 (Ruco Polymer Corp.), 10.4 ing parts of blocked isophorone diisocyanate Rucote (/) at least about 65 weight percent of a Curative NI-2 (Ruco Polymer Corp.), 0.6 parts of thermosetting resin having a softening point Resiflow P-67 (Estron Chemical), 1 .0 parts Oxymelt 45 of from about 90 ° to about 1 30 ° C; A-1 (Estron Chemical), 0.5 parts Octaflow ST-70 (//) up to about 35% of a cross-linking agent (Estron Chemical), and 33 parts titanium dioxide for such thermosetting resin; and were dry-blended, then homogenized in an ex- (Hi) from about 0.5 to about 3 weight per- truder which had been pre-heated to a temperature cent, based on the amount of thermosetting of 110^C. The extruded material was then allowed 50 resin and cross-linking agent, of a 1,3-6/s- to cool to room temperature. It was then ground (phenoxy)propan-2-ol. and passed through a 140-mesh screen. The fine powder was electrostatically applied onto a mild 6. A thermosetting powder composition according steel plate, and baked for 20 minutes at 180^C. to claim 5 wherein the thermosetting polymer The result was a glossy and uniform film which 55 is a carboxy functional polyester resin having a was completely free of pin-holes. carboxyl number from about 20 to about 100.

5 EP 0 545 134 A1 10

A thermosetting powder composition according to claim 5 wherein the thermosetting polymer is hydroxy functional polyester resin having a hydroxyl number from about 30 to about 90.

A thermosetting powder composition according to claim 5 wherein the thermosetting polymer is a carboxy functional acrylic resin having an acid number from about 20 to about 110. 10 A thermosetting powder composition according to claim 5 wherein the thermosetting polymer is a hydroxy functional acrylic resin having a hydroxy number from about 30 to about 180. 15 10. A thermosetting powder composition according to claim 5 wherein the thermosetting polymer is a glycidyl functional acrylic resin has a number average molecular weight from about 200 to about 1000. 20

11. A thermosetting powder composition according to claim 5 wherein the cross-linking agent is a triglycidyl isocyanurate. 25 12. A thermosetting powder composition according to claim 5 wherein the cross-linking agent is a hydroxyalkylamide.

13. A thermosetting powder composition according 30 to claim 5 wherein the cross-linking agent is an aliphatic dicarboxylic acid.

14. A thermosetting powder composition according to claim 5 wherein the cross-linking agent is 35 caprolactam blocked isocyanate.

15. A thermosetting powder composition according to claim 5 wherein the cross-linking agent is tetramethoxymethyl glycoluril. 40

16. In the method of coating a substrate by apply- ing a thermosetting powder coating composition comprising a thermosetting polymer and a cross-linking agent therefor to the substrate 45 and then heating the substrate and coating composition, the improvement which comprises adding to the coating composition an amount of a 1 ,3-£>/s(phenoxy)propan-2-ol at least sufficient to lower the melt viscosity of 50 the coating composition and reduce pin-hole formation during heating.

6 European Patent Number EUROPEAN SEARCH REPORT Application Office EP 92 11 9580

DOCUMENTS CONSIDERED TO BE RELEVAN Category Citation of document with indication, where appropriate, Relevant CLASSIFICATION OF THE of relevant passages to claim APPLICATION ant. CI.5 ) D,A US-A-4 286 021 (W. H. BRENDLEY) C09D5/03 * claim 1 * C08K5/06

CHEMICAL ABSTRACTS, vol. 82, no. 24, 1,2 16 June 1975, Columbus, Ohio, US; abstract no. 157333, 'fire-resistant composition 1 page 47 ; column 2 ;

& JP-A-49 102 769 (HITACHI CHEMICAL CO) 27 September 1974

PATENT ABSTRACTS OF JAPAN vol. 7, no. 259 (C-195)(1404) 18 November 1983 & JP-A-58 142 945 ( ASAHI KASEI K0GY0 KK ) 25 August 1983 * abstract *

US-A-3 907 744 (A. L. ANDERSON) TECHNICAL FIELDS SEARCHED (Int. CI.5 )

C09D C08K

The present search report has been drawn up for all claims Place of March Mi of rowpjetioi of the mnk THE HAGUE 11 MARCH 1993 KLIER E.K. CATEGORY OF CITED DOCUMENTS T : theory or principle underlying the invention E : earlier patent document, but published on, or X : particularly relevant if taken alone after the filing date Y : particularly relevant if combined with another D : document cited in the application document of the same category L : document cited for other reasons A : technological background O : non-written disclosure A : member of the same patent family, corresponding P : intermediate document document