NOVEL METAL-FREE CATALYSTS
NOVELMETAL-FREECATALYSTSfor Epoxy Carboxy CoatingsBy Ravi Ravichandran, Michael Emmet, Matthew Gadman, John Florio, and Steven WoltornistKing Industries, Inc.A new class of metal-free catalystshas been developed that promotesthe crosslinking reaction of epoxyfunctional polymers with carboxylfunctional compounds and polymers.Particularly effective at much lowercure temperatures, these catalystsprovide stable single package formulations and improved resistance properties. In addition, unlike amine-basedcompounds, these catalysts do notyellow during cure or on over-bake.INTRODUCTIONEpoxy resins are commercially andtechnologically relevant and play acritical role in several key applicationssuch as coatings, adhesives, laminates,castings, encapsulations, and moldings. Epoxy-based polymer resins arePresented at the American Coatings Conference,April 9–11, 2018, in Indianapolis, IN.28 MARCH 2019an important part of the automotiveclearcoat and powder coating marketsegments. Their versatility of crosslinking with various agents [e.g. acids,anhydrides, dicyandiamide (DICY),and phenolics], in addition to theirability to provide superior chemicalresistance, extraordinary acid etchresistance, and good adhesion, makeepoxy functional resins attractive inseveral end-use markets.Epoxy Acid Automotive ClearcoatsDuring the late 1980s, field damages caused by environmental etchbecame a major issue especially atautomotive import storage areas inJacksonville, FL. This phenomenonwas a clearcoat appearance issueassociated with the formation of whatappeared to be permanent waterspotting. The physical damage causedby etch results in localized loss ofmaterial, which in turn leads tovisible pitting of the clearcoat surface.The etch phenomenon was believedto be primarily the result of acidcatalyzed hydrolysis of ether crosslinks in acrylic melamine clearcoatsdue to a combination of acid rainexposure and high temperatures. Theresulting crosslink scission on thesurface can be a localized phenomenon, leading to defects on the surfacethat resemble water spotting.Water spotting damage is irreversible as the chemical degradationof the clearcoat results in increasedsurface roughness, leading to poorappearance properties, such asreduced gloss. It has since beenestablished that acidic airbornepollutants like SO2 produced inheavy industrial areas are convertedto acid rain. The typical pH of acidrain encountered in aggressiveenvironments (Jacksonville, FL)
use a combination of crosslinkingmechanisms together with acrylicmelamines. Isocyanates can be functionalized with alkoxysilyl compoundsleading to both urethane and siloxanecrosslinks in the coating.3 Similarly,resins with alkoxysilane functionalitycan also be combined with carbamatefunctional acrylics.4Epoxy-functional acrylics crosslinked with carboxylic acids oranhydrides provide excellent environmental etch resistance. The technology using epoxy/acid crosslinking reaction, very popular with theAsian automakers, is the most robustof them all, producing very powerfulacid etch and scratch-resistant coatings, and can be formulated as eitherone-component (1K) or 2K coatingsThe global automotive coatingsmarket size is projected to reach US 16.24B by 2021, registering a CAGRof 7.02% between 2016 and 2021, andwitnessing huge growth in emergingeconomies. Approximately 36% of theglobal automotive coatings marketis in each Asia Pacific and Europewith the remainder in the Americas.5Emerging economies such as China,India, and Brazil are the key marketsfor automotive coatings. Emergingmiddle-class population, changing lifestyle, growing purchasing power parity, and improving standard of livingof consumers in these economies arethe key factors that drive the demandfor automotive coatings. Among allthe regions in the world, Asia-Pacificis the largest market for automotivecoatings owing to the huge base ofautomotive industries in that region.It is also the fastest growing marketduring the period 2014–2020 due tothe technological advancement andlarge number of vehicles produced. Itis poised to grow at a CAGR of morethan 7% for the next six years.PAINT.ORG 29 ISTOCK CANDY1812is in the range of 3.5–4.5.1,2 Thesephenomena have led to the development of etch-resistant clearcoatsusing new crosslinking chemistries. For example, modificationsof acrylic melamine clearcoatsmade with additional crosslinkingwith either blocked isocyanates orsilane led to improved etch resistance. 3 During the thermal curethe alkoxysilane pendant groupsundergo aqueous hydrolysis to formsilanols, which in turn co-react toform siloxane crosslinks, resultingin enhanced acid-etch resistance.Carbamate functional acrylicscrosslinked with melamine resins result in a hydrolysis-resistanturethane crosslink without the use oftwo-component (2K) polyisocyanateformulations. To achieve the bestcombination of environmental etch,weathering and scratch resistance,and appearance properties, clearcoats
More than 80% of the clearcoat marketsin Japan and Korea are 1K etch-resistantcoatings. One-component epoxy/acid is theleading etch-resistant clearcoat technology used by several auto manufacturers,including Nissan, Toyota, and Mitsubishi.Epoxy Acid-Based Powder CoatingsPowder coatings have become an attractivealternative to conventional coating techniques. This is primarily due to their highefficiency, the durability of resulting finishes, and very low environmental impact. Inaddition, powder coatings effectively resistchipping, scratching, and fading, leading tohigh quality finishes that are color-stable.Since no solvents are involved in the process, the powder coatings can be recycledand reused, thereby reducing the emissionsof volatile organic compounds (VOCs) andwaste generated from the conventionalliquid coatings. Powder technology findswidespread use in automotive parts andbodies, architectural, furniture, and manyhousehold appliances.Four major crosslinking chemistriesare widely used in thermal powdercoating systems. Esterification reaction(acid/hydroxyl reaction) exemplified byhydroxyalkyl amide (Primid ) polyesters,is the least reactive with a cure profileof 150 C–220 C. Hydroxyl/blockedisocyanate reaction leading to polyurethanes, with either blocked isocyanatesor uretdiones (isocyanate dimer) can leadto a slightly lower temperature cure withminimum cure temperatures in the 140 Crange. The other two chemistries areboth based on epoxies that can crosslink with a variety of functional groupsincluding acids, anhydrides, aromatichydroxyls, amines, DICY, and eventhrough homopolymerizations. Epoxy/acid or epoxy/anhydride has the highestpotential for low-temperature cure inthe range of 120 C to 140 C, followed byepoxy/phenolic or epoxy/DICY, which areboth amenable to cure temperatures aslow as 110 C. Higher curing temperaturesin the 150–200 C range are not usefulwith substrates such as plastics, wood,and certain metal alloys, and are limitedto substrates that can tolerate highertemperatures. Epoxy homopolymerizations and epoxy/phenolic reactions, whileproviding lower temperature cure options,lack the UV resistance necessary forexterior applications. Thus, to meet bothlower temperature cure potential andadequate exterior durability, formulationsbased on acid-functional polyesters andepoxy crosslinkers offer the most promise.30 MARCH 2019Polyester epoxy hybrids offer more versatility compared to 100% epoxy, includingbetter external weatherability at a lowercost, and, as a result, have captured a largershare of the market. Polyester-epoxy hybridsand polyester-triglycidylisocyanurate (TGIC)powders are the two main types used inthe North American market; together theyrepresent nearly 60% of the market, followedby polyurethanes, epoxies, and acrylics.Catalysts are used in epoxy powdercoatings: (1) to catalyze the reaction ofglycidyl ester functional acrylic resinswith dicarboxylic acids or with carboxylfunctional resins, (2) for crosslinking ofcarboxyl functional polyester resins withTGIC, and (3) for hybrid powder coatingsof bisphenol A diglycidyl resins withcarboxyl-functional polyesters.A catalyst that can lower cure temperatures of epoxy/acid powder systemsto 120 C or below would be of interest in powder applications and couldresult in energy savings and/or higherthroughput in industrial coating lines.The advent of low-curing temperaturesystems will have a significant impacton the powder coatings market utilizingheat-sensitive substrates such as wood,plastics, and assembled componentswith heat-sensitive details. The coatingof metal substrates also benefits fromthis technology with lower energy andinvestment costs, shorter curing times,and higher lines speeds. 6Global demand on powder coatingswas valued at roughly US 5.8B in 2010to US 9.1B in 2013, a compound annualgrowth rate of 7% and is expected togrow by 6% in the coming years.7,8 Thepowder coatings market is projected toreach US 16.55B by 2024, at a CAGRof 6.75% from 2017 to 2022. Increasinguse of powder coatings for aluminumextrusion used in windows, doorframes,building facades, kitchen, bathroom,and electrical fixtures will fuel industryFIGURE 1—Epoxy carboxy crosslinking reaction.expansion. Rising construction spendingin various countries including China,the United States, Mexico, Qatar, UAE,India, Vietnam, and Singapore will fuelgrowth over the forecast period. Majorfactors that are driving the market’sgrowth are the increasing usage of powder coatings in the automotive industryacross applications such as door handles,rims, and under-the-hood components;and growing demand for consumergoods in Asia-Pacific, including washingmachines, freezer cabinets, and microwave ovens. Industrial uses present thelargest application market, with furniture and appliance markets showingsteady and strong growth. Informationtechnology and telecom are new marketswhere applications of powder coatingsare developing.Epoxy-polyester hybrid powdercoatings will witness the fastest volumegrowth at a CAGR of 8.1% from 2016 to2024 because of their increasing application in domestic appliances, machines,equipment, decorative devices, andgeneral industries. Furthermore, superiorproperties including greater resistance toyellowing during cure; better transfer efficiency; and cleaner, brighter colors thanmany epoxy formulations are expectedto stimulate industry growth. The epoxypolyester hybrid segment is expected toaccount for more than 50% of the powdercoating market share by 2024.Binder, Crosslinking Chemistry,and CatalysisThe crosslinking chemistry involves thereaction of an epoxy-functional resin witha hardener containing a carboxylic group,in a ring opening condensation reaction,resulting in stable linkages with excellentchemical resistance properties, and without the formation of any reactive volatiles(Figure 1).
The ester linkage formed is significantly more stable to acid etch and leads toone-package coatings with good storagestability, which can also meet the aggressive artificial acid etch test of Japaneseauto producers, like the Toyota ZeroEtch Test.For outdoor applications requiringgood weatherability, such as automotiveclearcoats, aromatic epoxy resins suchas bisphenol A diglycidylether cannot beused, while copolymers of glycidyl acrylates or methacrylates are typically used.The co-monomers are chosen to provideother critical performance propertiessuch as hardness, flexibility, and the like.The structure of the acidic resin is alsocritical to achieve the desired hardnessand scratch/mar resistance properties. Ahigh scratch resistance can be achievedby a combination of high crosslink density and flexible chains between networkpoints, using flexible acidic polyesters asthe acid component.9The hydroxyl group generated duringthe reaction can be utilized for additional crosslinking reactions with auxiliarybinders such as blocked polyisocyanatesor polymeric siloxanes containing hydrolyzable silyl group. Such hybrid technologies can provide clearcoats with excellentacid etch and mar resistance.10Catalysis of the epoxy/carboxyl reaction has been investigated thoroughlyin an earlier study, which resulted in thedevelopment of a zinc chelate catalyst.11A wide range of catalysts have been developed for this reaction, which fall intofour major classes (Table 1).Basic catalysts such as tertiary aminesprovide high reactivity at lower temperatures, but formulations containing thesecatalysts suffer from severe yellowing andlimited stability, especially in a 1K system. Thus, their volatility, odor, yellowing, and potential hazard labeling makethese catalysts unsuitable especiallyin applications that are sensitive todiscoloration.Quaternary ammonium and phosphonium bromide salts are effective 1Kcatalysts, with less thermal yellowing onoverbake compared to the free tertiaryamines. However, their strong basicitycan lead to problems with water permeability and humidity resistance. Inaddition, these catalysts do not impartadequate mar resistance on catalyzedcoatings.Metal salts and chelates are stable athigher temperatures and impart little orno yellowing during cure and throughthe life of the coatings. Unfortunately, allthe state-of-the-art zinc catalysts, whileefficient at 140 C, are not effective atlower temperatures, especially at 120 Cor below. Although zinc carboxylates areeffective catalysts for the epoxy/carboxylreaction, the divalent zinc can contribute to ionic crosslinking, which leads tostorage instability, viscosity increase, andgelation.Lewis acids are very effective forepoxy homopolymerization but can leadto many side reactions in epoxy/acidcure.12 Super acids, such as trifilic acid,can catalyze the homopolymerizationand copolymerization of epoxy resinswith hydroxyl functional polymers, cyclicester, oxetane, and vinyl ether reactants.Most of the cationic catalysts are activated by UV radiation.Recently, quaternary ammoniumblocked hexafluoroantimonate and triflicacid catalysts have been introduced forthermal cationic cure.13 These catalystsfunction by a rearrangement of thequaternary compound to a weak, basicamine. Lewis and super acids are notcommonly used as catalysts in epoxy/acidcoating systems.We began our research towards a moreefficient and versatile alternate to theabove catalyst options that can provideEXAMPLESBASIC TERTIARY AMINES2-ETHYL IMIDAZOLE(2-EI),1-ETHYL IMIDAZOLE, OCTYLDIMETHYLAMINE(ADMA-8),N, N-DIMETHYLBENZYLAMINE, DODECYL DIMETHYLBENZYLAMINE, TETRAMETHYL GUANIDINEQUATERNARY AMMONIUMAND PHOSPHONIUMCOMPOUNDSDODECYLTRIMETHYLAMMONIUM BROMIDE (DTMAB),BENZYLTRIMETHYLAMMONIUM BROMIDE, TRIPHENYLETHYL PHOSPHONIUM BROMIDEMETAL SALTS ANDCHELATESLEWIS ACIDSEXPERIMENTALThe three experiments discussed in thefollowing sections include a series of teststhat demonstrate the catalyst capabilitiesof two new metal-free catalysts for thereaction of carboxyl and epoxy functional resins.Experiment I investigates the overallefficacy of NACURE XC-324 as a catalyst in a 1K epoxy/carboxy clearcoat. Experiment II explores lower temperaturecure capabilities of NACURE XC-355 ina 2K epoxy/carboxy clearcoat. Studies onenvironmental etch resistance of epoxy/carboxy clearcoats compared to aminoplast crosslinked polyols are included inExperiment III.All epoxy/carboxy test formulationsin these experiments use commerciallyavailable, solid grade resins dissolvedin solvent. Solventborne (SB) clearcoats were formulated using a carboxyl(COOH) functional acrylic resin withglycidyl methacrylate (GMA) resins.Experiment I: Catalyst Studies onNACURE XC-324 in a 1K SB Epoxy/Carboxy ClearcoatNACURE XC-324 was evaluated in a 1KSB epoxy/carboxy clearcoat against twowidely used conventional basic aminecatalysts [octyldimethylamine (ADMA-8)and 2-ethylimidazole (2-EI)].Materials and Preparation of 1K SBEpoxy/Carboxy Clearcoat FormulationsTABLE 1—Classes of Available Catalyst TechnologiesCATALYST CLASSefficient cure at 120 C, or lower, withgood viscosity stability, while impartingno yellowing or discoloration followingoverbake.Herein we describe the developmentof a new class of metal-free catalystsuseful in a variety of epoxy/acid systemsthat are efficient and would lead to thedesired lower temperature cure requiredboth in automotive and powder coatingapplications.Zn (ACETYLACETONATE)2, Zn OCTOATE, ZINC ACETATEBORON TRIFLUORIDE, TRIMETHOXY BOROXINEJoncryl 819,14 a carboxyl functionalacrylic resin, and Fineplus AC 2570,15a glycidyl methacrylate resin, wereblended at an approximately 1:1 molarratio and dissolved with xylene, PMacetate, n-butyl acetate, and BYK 31016 toform a 45% resin solution. A breakdownof formulation components is in Table 2.NACURE XC-324 and the two controlcatalysts were all post-added to theclearcoat formulation and mixed via highPAINT.ORG 31
speed dispersion using a FlackTek highspeed mixer from FlackTek Inc.Clearcoats were catalyzed with 1.0% catalyst solids on total resin solids (TRS).Film Preparation of 1K SBEpoxy/Carboxy ClearcoatsAll films prepared for testing were appliedvia draw down. Epoxy/carboxy clearcoatswere applied using a drawn down bar.White waterborne (WB) basecoats usedin color testing were applied using a birdapplicator. Epoxy/carboxy clearcoatsand WB basecoats were both given anapproximately 10–15 min flash at ambienttemperatures prior to baking at the designated temperatures.Film Properties of Catalyzed ClearcoatsNACURE XC-324 was compared to thecontrol catalysts in the 1K SB epoxy/carboxy clearcoat using two bake schedules: 120 C/30 min and 110 C/30 min.Catalyzed epoxy/carboxy clearcoats wereapplied over bare cold roll steel (CRS).Dry film thickness (DFT) of the clearcoatwas approximately 1.0–1.2 mil. Testedfilm properties include MEK resistance,17pencil hardness,18 pendulum hardness,19crosshatch (CH) adhesion,20 and gloss.21NACURE XC-324 provided similar cureresponse to the control catalysts usingboth bake schedules. Coatings catalyzedwith 2-ethylimidazole exhibited the poorest gloss when baked at both tempera-TABLE 2—1K SB Epoxy/Carboxy ClearcoatCOMPONENTSJONCRYL 81914FINEPLUS AC 257015XYLENEPM ACETATEBUTYL ACETATEBYK 31016DESCRIPTIONCARBOXYL FUNCTIONAL ACRYLICGLYCIDYL METHACRYLATE (GMA)SOLVENTSOLVENTSOLVENTSURFACE ADDITIVETOTAL%TOTAL RESIN SOLIDS (TRS)ACRYLIC COOH/GMA EPOXY%27.018.022.122.110.60.2100.04560/40TABLE 3a—Film Properties of Carboxyl Functional Acrylic and GMA Epoxy—120 C/30 minPROPERTIES% CATALYST SOLID ON TRSMEK DOUBLE RUBSGLOSS, 60 GUGLOSS, 20 GUPENDULUM, CYCLESPENCIL HARDNESSADHESION, % CHOCTYLDIMETHYLAMINE(ADMA-8)1.0100 (LIGHT MAR)106911324H-5H1002-ETHYLIMIDAZOLE(2-EI)1.0100 (LIGHT MAR)104811334H-5H100NACURE XC-3241.0100 (LIGHT MAR)105941334H-5H100TABLE 3b—Film Properties of Carboxyl Functional Acrylic and GMA Epoxy—110 C/30 AZOLE(2-EI)NACURE XC-324% CATALYST SOLID ON TRSMEK DOUBLE RUBSGLOSS, 60 GUGLOSS, 20 GUPENDULUM, CYCLESPENCIL HARDNESSADHESION, % CH1.0100 (MAR)105941224H-5H90-951.0100 (MAR)106891184H-5H85-901.0100 (MAR)105941283H-4H10032 MARCH 2019tures while XC-324 catalyzed coatingsprovided high gloss properties, exhibitingsimilar gloss units (GU) to the octydimethylamine catalyzed system.It should be acknowledged that adecrease in pencil hardness was observedfor XC-324 when dropping the bakeschedule to 110 C. However, XC-324did not exhibit as significant of a loss inpendulum hardness or adhesion as thecontrol films when baked at 110 C vs120 C. Results are in Tables 3a and 3b.Viscosity Stability of Epoxy CarboxyLiquid CoatingsAll 1K formulation should be able toremain stable during transportation andstorage prior to end use application.To assess these properties, age stabilityof catalyzed epoxy/acid clearcoats wasevaluated by monitoring viscosity changeof the catalyzed systems upon aging usingthree storage conditions: 60 C, 50 C, androom temperature (RT).NACURE XC-324 was evaluated againstthe octyldimethylamine and 2-ethylimidazole catalysts at all three storage temperatures. In addition, all three tests includedan uncatalyzed system. Viscosities weremeasured using an AR1000 rheometerwith a 40 mm 2 steel cone geometry fromTA Instruments. Samples were tested at25 C using a shear rate of 100s-1.NACURE XC-324 showed minimalchange in viscosity during all age stabilitytesting with significant improvementin viscosity stability compared to bothcontrol catalysts. Furthermore, the XC324 catalyzed system behaved nearly thesame as the uncatalyzed epoxy/carboxysystem during most of the storage testing.Results for viscosity stability using60 C storage are in Table 4 and Figure 1a.Results for 50 C and RT (ambient) storage are in Figures 1b and 1c, respectively.Gel Fraction StudiesThe cure response of a coating can beverified by measuring the gel fraction ofthe polymer system, namely the percentage of polymer chains that have reactedand are crosslinked to form the coatingfilm. A higher gel fraction correlates to abetter cure with more crosslinking. Thegel fraction is defined as the weight ratioof dried network polymer (crosslinkedmaterial) to that of the polymer beforebeing subjected to Soxhlet extractionconditions.Gel fractions studies were conducted bysubjecting 1K SB epoxy/carboxy clear-
TABLE 4—Viscosity Stability of Epoxy Carboxy Liquid Coatings (60 C/16 NACURE XC-32417821622FIGURE 1a—Viscosity stability of epoxy/carboxy SB coatings (60 C storage).Viscosity (cP)6004002000No CatalystOctyldimethylamine 2-Ethylimidazole0h16 hNACURE XC-324FIGURE 1b—Viscosity stability of epoxy/carboxy SB coatings (50 C storage).% Increase5004003002001000No Catalyst50 hOctyldimethylamine100 h2-EthylimidazoleNACURE XC-324170 h220 h)FIGURE 1c—Viscosity stability of epoxy/carboxy SB coatings (ambient storage).300250200150100500Octyldimethylamine0h48 h2-Ethylimidazole100 h180 hNACURE XC-3245,800 hTABLE 5—Gel Fraction Studies after 6 h Soxhlet Extraction with Acetone/Methanol (1/1)QUV Resistance of Catalyzed EpoxyCarboxy CoatingsCURE CONDITIONS120 C/30 MIN140 C/30 MINOCTYLDIMETHYLAMINE(ADMA-8)90.9896.24PERCENT WEIGHT RETENTION2-ETHYLIMIDAZOLE(2-EI)92.7596.25NACURE XC-32492.6597.86FIGURE 2—Percent weight retention after 6 h of reflux with acetone/methanol (1/1).100%Wt RetentionCoating discoloration induced by catalysts upon UV exposure is an undesiredproperty. Basic amine catalysts are knownto contribute to yellowness as a result ofsuch exposures.A blocked sulfonic acid catalyzedmelamine crosslinked WB white basecoat was applied over iron phosphatedCRS and baked at 80 C/10 min. Thecatalyzed epoxy/carboxy clearcoats werethen applied over the white basecoat andcured at 120 C/30 min. The DFT of theclearcoat was approximately 1.6–1.8 mil.Cured films were evaluated for UVresistance by measurement of b* values ofOCTYLDIMETHYLAMINE(ADMA-8)194GEL—NO CATALYSTINITIAL (cP)FINAL (cP)% INCREASE%Change fromUncatalyzedcoats catalyzed with NACURE XC-324,octyldimethylamine, and 2-ethylimidazole to Soxhlet extraction conditions.Formulations were catalyzed with 1.0%catalyst solids based on TRS. Epoxy/carboxy systems were prepared over anuntreated thermoplastic polyolefin (TPO)substrate to facilitate easy removal of thecured film. Films were baked for 30 minat 140 C and 120 C. DFT of the clearcoatswas approximately 1.0–1.2 mil.A 3 in. x 6 in. specimen of cured filmwas placed inside a pre-weighed glassthimble. All thimbles were previouslycleaned and dehydrated before weighing.The glassware was submerged in a 1:1acetone/N,N-dimethylformamide (DMF)solution overnight and then dehydratedfor one hour at 110 C. Initial tare weightof the thimble was determined after cooling at room temperature in a desiccatorfor approximately 20–30 min.The thimble containing the samplewas weighed and placed in the extractionchamber. A 1:1 acetone/methanol mixturewas used as the extraction solvent. Filmswere subjected to a six-hour reflux. Filmswere then placed in the oven for one hourat 110 C to dehydrate and remove any residual solvent from the thimble and film.The thimble containing the dried filmsample was reweighed after being cooledat room temperature in a desiccator forapproximately 20–30 min.Gel fractions were reported as percentweight retention, where weight retentionis defined as the ratio of film weight afterextraction to the initial weight beforeextraction.NACURE XC-324 provided a highdegree of crosslinking with the 140 C and120 C bake, exhibiting a similar weightretention as both controls. Results are inTable 5 and Figure 2.95908580Octyldimethylamine2-Ethylimidazole140 C/30 minNACURE XC-324120 C/30 minPAINT.ORG 33
the panels after 250, 500, and 1000 h ofQUV exposure.22NACURE XC-324 provided a rathersignificant improvement in UV resistancecompared to octyldimethylamine and2-ethylimidazole, especially with regardsto the longer QUV exposure times of 500and 1000 h. Results are in Tables 6–7 andFigure 3.baked at 120 C/30 min. DFT of the curedfilms was approximately 1.6–1.8 mil.Cured films were exposed to Clevelandhumidity conditions.23 The chamber wasmaintained at 100% RH through theexperiment. Exposed films were evaluated for blistering. Films were given blisterratings24 following 220 and 500 h ofhumidity exposure.NACURE XC-324 provided similar humidity resistance to octyldimethylamine.However, XC-324 showed an improvement compared to 2-ethylimidazole.Results are shown in Table 8.Humidity Exposures of Catalyzed EpoxyCarboxy CoatingsEpoxy/carboxy clearcoats were appliedover an electrocoated CRS substrate andTABLE 6—Yellowness Measurements After QUV Exposure—b* ValuesSYSTEMOCTYLDIMETHYLAMINE (ADMA-8)2-ETHYLIMIDAZOLE (2-EI)NACURE XC-324INITIAL-0.45-0.59-0.47250 H0.020.060.04500 H0.220.320.081000 H0.310.400.10TABLE 7—Yellowness Measurements After QUV Exposure—Δb* ValuesSYSTEMOCTYLDIMETHYLAMINE (ADMA-8)2-ETHYLIMIDAZOLE (2-EI)NACURE XC-324250 H0.470.640.51500 H0.670.910.551000 H0.760.990.57 b*FIGURE 3—Yellowness measurements after QUV exposure. 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.100.00 0.91 0.99 0.76 0.67 0.64 0.51 0.472-EthylimidazoleOctyldimethylamine250 h500 h 0.55 0.57NACURE XC-3241000 hTABLE 8—Humidity Exposures of Catalyzed Epoxy/Carboxy Coatings—Blister RatingsaSYSTEMOCTYLDIMETHYLAMINE (ADMA-8)2-ETHYLIMIDAZOLE (2-EI)NACURE XC-324(a) Blister rating–density / size.34 MARCH 2019220 HLIGHT / 6LIGHT / 6LIGHT / 6500 HMEDIUM / 4MEDIUM / 4 LIGHT / 2MEDIUM / 4Crockmeter AbrasionCatalyzed clearcoats were applied overbare CRS and baked at 120 C/30 min.Baked films were tested for mar/scratchresistance using a Crockmeter abrasiontester (M238AA) from SDL Atlas. TheDFT of the clearcoat was approximately1.6–1.8 mil.An abrasion dry test was performedon each of the coatings using 2 in. x 2in. Crockmeter squares on the crockfinger and 20 Mule Team Borax on thetest specimen. Each of the coatings weresubjected to 20 cycles of abrasion.The degree of marring for each of thefilms was rated qualitatively using a 0–5scale with “0” and “5” being “No Mar” and“Film Break,” respectively. Break down ofthe 0–5 scale is in Table 9. Films were alsoevaluated quantitatively by measuring thechange in gloss following abrasion.The NACURE XC-324 catalyzed filmexhibited good resistance to Crockmeterabrasion in comparison to the controlcatalysts. XC-324 provided very similarabrasion resistance to 2-ethylimidazole.Nonetheless, the XC-324 films had alower frequency of deep scratches anda lesser change in gloss than the filmscatalyzed by octyldimethylamine. Resultsare in Table 10 and Figure 4.Overbake ResistanceA blocked sulfonic acid catalyzedmelamine crosslinked WB white basecoat was applied over iron phosphatedCRS and baked at 110 C/10 min. Thecatalyzed epoxy/carboxy clearcoats werethen applied over the white basecoat andcured at 120 C/30 min. The DFT of theclearcoat was approximately 1.6–1.8 mil.Catalyzed films were tested for overbake resistance by evaluating the coating’s color change. Films were subjectedto three consecutive cycles of overbake:(1) 120 C/30 min, (2) 120 C/30 min and(3) 150 C/30 min.All clearcoats showed a minimalchange in color following the firstoverbake cycle. However, relative to thecontrol catalysts, NACURE XC-324 didexhibit a lesser change in total color( E*). A similar trend was observed forthe second overbake cycle.More significant color changes occurred following the third overbake cycle.The XC-324 films provided a significantimprovement in resistance to yellowing( b) and exhibited a much lesser changein total color compared to the controls.Results are in Figure 5 and Table 11.
DESCRIPTION0NO MAR12345LIGHT MARMARMAR, MULTIPLE DEEP SCRATCHHEAVY MARFILM BREAKExperiment II: Catalyst Studies onNACURE XC-355 in a 2K SB Epoxy/Carboxy ClearcoatNACURE XC-355 was evaluated in a 2KSB epoxy/carboxy clearcoat and tested forlower temperature cure capabilities.Materials and Preparation of 2K SB Epoxy/Carboxy Clearcoat FormulationThe 2K SB epoxy/carboxy clearcoat formulation was prepared by dissolving Joncryl 819, a solid grade carboxyl functionalacrylic resin, and Fineplus AC 2710,25 asolid grade glycidyl methacrylate resin,separately using a solvent blend containing xylene, PM acetate, and n-butyl acetate (40.1/40.1/19.8). The flow additive wasstored in the acid component. Breakdownof formulation components is presentedin Table 12.The acid component, containing thecarboxyl (COOH) functional acrylic, andthe epoxy component, containing theglycidyl methacrylate (GMA) resin wereboth 45% TRS.Catalysts were premixed into the acidcomponent prior to addition of the epoxycomponent. All mixing was conducted viahigh speed dispersion using a FlackTekhigh speed mixer.The clearcoat was formulated stoichiometrically. The two components wereblended 69/31 by total formula weight togive a solids ratio of 69/31 Acrylic COOH/GMA. This solids ratio provides an approximately 1:1 molar ratio. The TRS ofthe final resin system was 45%.Sample testing or film preparation beganimmediately after incorporating the epoxycomponent into the acid component.Film Preparation
based on acid-functional polyesters and epoxy crosslinkers offer the most promise. Polyester epoxy hybrids offer more versa-tility compared to 100% epoxy, including better external weatherability at a lower cost, and, as a result, have captured a larger share of the market. Polyester-epoxy
metal-free catalysts to replace PGM-based materials [6,19-23]. In this review, we consider several aspects of the BES technology, with a special emphasis on the . catalysts based on metal-free carbon-based materials, molecular catalysts based on metal macrocycles supported on carbon nanostructures, M-N-C catalysts activated via pyrolysis .
the PGM-free and PGM catalysts accounts partly for the substantially lower power density delivered by PGM-free catalysts in practical H 2-air PEMFCs ( 0.57 W·cm2) (4) than that of PGM catalysts ( 1 W·cm2). The most active PGM-free ORR catalysts are pyrolyzed transition metal-nitrogen-carbon (M-N-C, M Fe or Co) catalysts (4-10). This group .
precious metal-based catalysts and (ii) metal-free based catalysts. Regarding the first group, even though the amount of noble metal, such as platinum, has been reduced because of the use of non-precious metal catalysts, metals can lixiviate and agglomerate, producing the loss of efficiency during time [22]. Nevertheless, the
Carbon-based metal-free catalysts Xien Liu 1 and Liming Dai 1,2 Abstract Metals and metal oxides are widely used as catalysts for materials production, clean energy generation and storage, and many other important industrial processes. However, metal-based catalysts suffer from high cost, low selectivity, poor durability, susceptibility
2. Metal-Free Catalysts for the ORR The ORR is important in many energy-conversion devices, such as fuel cells and metal-air batteries, as well as corrosion and biology.[4] Along with the rapid advances in carbon-based nanomaterials, many carbon-based metal-free catalysts have been developed that show ORR electrocata-
Developing metal-free CO 2 reduction catalysts Whereas several transition metal catalysts were reported to promote the catalytic hydrogenation, hydrosilylation, 20 and hydroboration of carbon dioxide, efficient metal-free catalytic processes were scarce prior to our contributions to the field.19 It was known for
Catalysts are substances that speed up the rate of chemical reactions. It is possible to divide catalysts into two groups – inorganic catalysts and organic (biological) catalysts. Biological catalysts are called enzymes. Most enzymes are protein molecules, and they specifically catalyze only one reaction
I studied a facile one-step synthesis method of nitrogen-iron coordinated carbon nanotube catalysts without precious metals. Our catalyst shows excellent onset ORR potential comparable to those of other precious metal free catalysts, and the maximum limiting current density from our catalysts is larger than that of the Pt-based catalysts.
