NOVEL METAL-FREE CATALYSTS - for Epoxy Carboxy Coatings
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NOVEL
METAL-FREE
CATALYSTS
for Epoxy Carboxy Coatings
By Ravi Ravichandran, Michael Emmet, Matthew Gadman, John Florio, and Steven Woltornist
King Industries, Inc.
A new class of metal-free catalysts an important part of the automotive material, which in turn leads to
has been developed that promotes clearcoat and powder coating market visible pitting of the clearcoat surface.
the crosslinking reaction of epoxy segments. Their versatility of cross- The etch phenomenon was believed
functional polymers with carboxyl linking with various agents [e.g. acids, to be primarily the result of acid-
functional compounds and polymers. anhydrides, dicyandiamide (DICY), catalyzed hydrolysis of ether cross-
Particularly effective at much lower and phenolics], in addition to their links in acrylic melamine clearcoats
cure temperatures, these catalysts ability to provide superior chemical due to a combination of acid rain
provide stable single package formula- resistance, extraordinary acid etch exposure and high temperatures. The
tions and improved resistance proper- resistance, and good adhesion, make resulting crosslink scission on the
ties. In addition, unlike amine-based epoxy functional resins attractive in surface can be a localized phenome-
compounds, these catalysts do not several end-use markets. non, leading to defects on the surface
yellow during cure or on over-bake. that resemble water spotting.
Water spotting damage is irre-
Epoxy Acid Automotive Clearcoats versible as the chemical degradation
INTRODUCTION During the late 1980s, field dam- of the clearcoat results in increased
ages caused by environmental etch surface roughness, leading to poor
Epoxy resins are commercially and became a major issue especially at appearance properties, such as
technologically relevant and play a automotive import storage areas in reduced gloss. It has since been
critical role in several key applications Jacksonville, FL. This phenomenon established that acidic airborne
such as coatings, adhesives, laminates, was a clearcoat appearance issue pollutants like SO2 produced in
castings, encapsulations, and mold- associated with the formation of what heavy industrial areas are converted
ings. Epoxy-based polymer resins are appeared to be permanent water to acid rain. The typical pH of acid
spotting. The physical damage caused rain encountered in aggressive
Presented at the American Coatings Conference,
April 9–11, 2018, in Indianapolis, IN.
by etch results in localized loss of environments (Jacksonville, FL)
28 | MARCH 2019
is in the range of 3.5–4.5.1,2 These use a combination of crosslinking witnessing huge growth in emerging
phenomena have led to the devel- mechanisms together with acrylic economies. Approximately 36% of the
opment of etch-resistant clearcoats melamines. Isocyanates can be func- global automotive coatings market
using new crosslinking chemis- tionalized with alkoxysilyl compounds is in each Asia Pacific and Europe
tries. For example, modifications leading to both urethane and siloxane with the remainder in the Americas.5
of acrylic melamine clearcoats crosslinks in the coating.3 Similarly, Emerging economies such as China,
made with additional crosslinking resins with alkoxysilane functionality India, and Brazil are the key markets
with either blocked isocyanates or can also be combined with carbamate- for automotive coatings. Emerging
silane led to improved etch resis- functional acrylics.4 middle-class population, changing life
tance. 3 During the thermal cure Epoxy-functional acrylics cross- style, growing purchasing power par-
the alkoxysilane pendant groups linked with carboxylic acids or ity, and improving standard of living
undergo aqueous hydrolysis to form anhydrides provide excellent envi- of consumers in these economies are
silanols, which in turn co-react to ronmental etch resistance. The tech- the key factors that drive the demand
form siloxane crosslinks, resulting nology using epoxy/acid crosslink- for automotive coatings. Among all
in enhanced acid-etch resistance. ing reaction, very popular with the the regions in the world, Asia-Pacific
Carbamate functional acrylics Asian automakers, is the most robust is the largest market for automotive
crosslinked with melamine res- of them all, producing very powerful coatings owing to the huge base of
ins result in a hydrolysis-resistant acid etch and scratch-resistant coat- automotive industries in that region.
urethane crosslink without the use of ings, and can be formulated as either It is also the fastest growing market
©ISTOCK | CANDY1812
two-component (2K) polyisocyanate one-component (1K) or 2K coatings during the period 2014–2020 due to
formulations. To achieve the best The global automotive coatings the technological advancement and
combination of environmental etch, market size is projected to reach US large number of vehicles produced. It
weathering and scratch resistance, $16.24B by 2021, registering a CAGR is poised to grow at a CAGR of more
and appearance properties, clearcoats of 7.02% between 2016 and 2021, and than 7% for the next six years.
PAINT.ORG | 29
More than 80% of the clearcoat markets Polyester epoxy hybrids offer more versa- expansion. Rising construction spending
in Japan and Korea are 1K etch-resistant tility compared to 100% epoxy, including in various countries including China,
coatings. One-component epoxy/acid is the better external weatherability at a lower the United States, Mexico, Qatar, UAE,
leading etch-resistant clearcoat technol- cost, and, as a result, have captured a larger India, Vietnam, and Singapore will fuel
ogy used by several auto manufacturers, share of the market. Polyester-epoxy hybrids growth over the forecast period. Major
including Nissan, Toyota, and Mitsubishi. and polyester-triglycidylisocyanurate (TGIC) factors that are driving the market’s
powders are the two main types used in growth are the increasing usage of pow-
Epoxy Acid-Based Powder Coatings the North American market; together they der coatings in the automotive industry
Powder coatings have become an attractive represent nearly 60% of the market, followed across applications such as door handles,
alternative to conventional coating tech- by polyurethanes, epoxies, and acrylics. rims, and under-the-hood components;
niques. This is primarily due to their high Catalysts are used in epoxy powder and growing demand for consumer
efficiency, the durability of resulting finish- coatings: (1) to catalyze the reaction of goods in Asia-Pacific, including washing
es, and very low environmental impact. In glycidyl ester functional acrylic resins machines, freezer cabinets, and micro-
addition, powder coatings effectively resist with dicarboxylic acids or with carboxyl wave ovens. Industrial uses present the
chipping, scratching, and fading, leading to functional resins, (2) for crosslinking of largest application market, with fur-
high quality finishes that are color-stable. carboxyl functional polyester resins with niture and appliance markets showing
Since no solvents are involved in the pro- TGIC, and (3) for hybrid powder coatings steady and strong growth. Information
cess, the powder coatings can be recycled of bisphenol A diglycidyl resins with technology and telecom are new markets
and reused, thereby reducing the emissions carboxyl-functional polyesters. where applications of powder coatings
of volatile organic compounds (VOCs) and A catalyst that can lower cure tem- are developing.
waste generated from the conventional peratures of epoxy/acid powder systems Epoxy-polyester hybrid powder
liquid coatings. Powder technology finds to 120°C or below would be of inter- coatings will witness the fastest volume
widespread use in automotive parts and est in powder applications and could growth at a CAGR of 8.1% from 2016 to
bodies, architectural, furniture, and many result in energy savings and/or higher 2024 because of their increasing appli-
household appliances. throughput in industrial coating lines. cation in domestic appliances, machines,
Four major crosslinking chemistries The advent of low-curing temperature equipment, decorative devices, and
are widely used in thermal powder systems will have a significant impact general industries. Furthermore, superior
coating systems. Esterification reaction on the powder coatings market utilizing properties including greater resistance to
(acid/hydroxyl reaction) exemplified by heat-sensitive substrates such as wood, yellowing during cure; better transfer effi-
hydroxyalkyl amide (Primid®) polyesters, plastics, and assembled components ciency; and cleaner, brighter colors than
is the least reactive with a cure profile with heat-sensitive details. The coating many epoxy formulations are expected
of 150°C–220°C. Hydroxyl/blocked of metal substrates also benefits from to stimulate industry growth. The epoxy
isocyanate reaction leading to polyure- this technology with lower energy and polyester hybrid segment is expected to
thanes, with either blocked isocyanates investment costs, shorter curing times, account for more than 50% of the powder
or uretdiones (isocyanate dimer) can lead and higher lines speeds. 6 coating market share by 2024.
to a slightly lower temperature cure with Global demand on powder coatings
minimum cure temperatures in the 140°C was valued at roughly US $5.8B in 2010 Binder, Crosslinking Chemistry,
range. The other two chemistries are to US $9.1B in 2013, a compound annual and Catalysis
both based on epoxies that can cross- growth rate of 7% and is expected to
grow by 6% in the coming years.7,8 The The crosslinking chemistry involves the
link with a variety of functional groups reaction of an epoxy-functional resin with
including acids, anhydrides, aromatic powder coatings market is projected to
reach US $16.55B by 2024, at a CAGR a hardener containing a carboxylic group,
hydroxyls, amines, DICY, and even in a ring opening condensation reaction,
through homopolymerizations. Epoxy/ of 6.75% from 2017 to 2022. Increasing
use of powder coatings for aluminum resulting in stable linkages with excellent
acid or epoxy/anhydride has the highest chemical resistance properties, and with-
potential for low-temperature cure in extrusion used in windows, doorframes,
building facades, kitchen, bathroom, out the formation of any reactive volatiles
the range of 120°C to 140°C, followed by (Figure 1).
epoxy/phenolic or epoxy/DICY, which are and electrical fixtures will fuel industry
both amenable to cure temperatures as
low as 110°C. Higher curing temperatures FIGURE 1—Epoxy carboxy crosslinking reaction.
in the 150–200°C range are not useful
with substrates such as plastics, wood,
and certain metal alloys, and are limited
to substrates that can tolerate higher
temperatures. Epoxy homopolymeriza-
tions and epoxy/phenolic reactions, while
providing lower temperature cure options,
lack the UV resistance necessary for
exterior applications. Thus, to meet both
lower temperature cure potential and
adequate exterior durability, formulations
based on acid-functional polyesters and
epoxy crosslinkers offer the most promise.
30 | MARCH 2019The ester linkage formed is significant- in applications that are sensitive to efficient cure at 120°C, or lower, with
ly more stable to acid etch and leads to discoloration. good viscosity stability, while imparting
one-package coatings with good storage Quaternary ammonium and phos- no yellowing or discoloration following
stability, which can also meet the aggres- phonium bromide salts are effective 1K overbake.
sive artificial acid etch test of Japanese catalysts, with less thermal yellowing on Herein we describe the development
auto producers, like the Toyota Zero overbake compared to the free tertiary of a new class of metal-free catalysts
Etch Test. amines. However, their strong basicity useful in a variety of epoxy/acid systems
For outdoor applications requiring can lead to problems with water per- that are efficient and would lead to the
good weatherability, such as automotive meability and humidity resistance. In desired lower temperature cure required
clearcoats, aromatic epoxy resins such addition, these catalysts do not impart both in automotive and powder coating
as bisphenol A diglycidylether cannot be adequate mar resistance on catalyzed applications.
used, while copolymers of glycidyl acry- coatings.
lates or methacrylates are typically used. Metal salts and chelates are stable at
The co-monomers are chosen to provide higher temperatures and impart little or
EXPERIMENTAL
other critical performance properties no yellowing during cure and through The three experiments discussed in the
such as hardness, flexibility, and the like. the life of the coatings. Unfortunately, all following sections include a series of tests
The structure of the acidic resin is also the state-of-the-art zinc catalysts, while that demonstrate the catalyst capabilities
critical to achieve the desired hardness efficient at 140°C, are not effective at of two new metal-free catalysts for the
and scratch/mar resistance properties. A lower temperatures, especially at 120°C reaction of carboxyl and epoxy function-
high scratch resistance can be achieved or below. Although zinc carboxylates are al resins.
by a combination of high crosslink den- effective catalysts for the epoxy/carboxyl Experiment I investigates the overall
sity and flexible chains between network reaction, the divalent zinc can contrib- efficacy of NACURE® XC-324 as a cata-
points, using flexible acidic polyesters as ute to ionic crosslinking, which leads to lyst in a 1K epoxy/carboxy clearcoat. Ex-
the acid component.9 storage instability, viscosity increase, and periment II explores lower temperature
The hydroxyl group generated during gelation. cure capabilities of NACURE XC-355 in
the reaction can be utilized for addition- Lewis acids are very effective for a 2K epoxy/carboxy clearcoat. Studies on
al crosslinking reactions with auxiliary epoxy homopolymerization but can lead environmental etch resistance of epoxy/
binders such as blocked polyisocyanates to many side reactions in epoxy/acid carboxy clearcoats compared to amino-
or polymeric siloxanes containing hydro- cure.12 Super acids, such as trifilic acid, plast crosslinked polyols are included in
lyzable silyl group. Such hybrid technolo- can catalyze the homopolymerization Experiment III.
gies can provide clearcoats with excellent and copolymerization of epoxy resins All epoxy/carboxy test formulations
acid etch and mar resistance.10 with hydroxyl functional polymers, cyclic in these experiments use commercially
Catalysis of the epoxy/carboxyl reac- ester, oxetane, and vinyl ether reactants. available, solid grade resins dissolved
tion has been investigated thoroughly Most of the cationic catalysts are activat- in solvent. Solventborne (SB) clear-
in an earlier study, which resulted in the ed by UV radiation. coats were formulated using a carboxyl
development of a zinc chelate catalyst.11 Recently, quaternary ammonium (COOH) functional acrylic resin with
A wide range of catalysts have been de- blocked hexafluoroantimonate and triflic glycidyl methacrylate (GMA) resins.
veloped for this reaction, which fall into acid catalysts have been introduced for
four major classes (Table 1). thermal cationic cure.13 These catalysts Experiment I: Catalyst Studies on
Basic catalysts such as tertiary amines function by a rearrangement of the
provide high reactivity at lower tempera- quaternary compound to a weak, basic
NACURE XC-324 in a 1K SB Epoxy/
tures, but formulations containing these amine. Lewis and super acids are not Carboxy Clearcoat
catalysts suffer from severe yellowing and commonly used as catalysts in epoxy/acid NACURE XC-324 was evaluated in a 1K
limited stability, especially in a 1K sys- coating systems. SB epoxy/carboxy clearcoat against two
tem. Thus, their volatility, odor, yellow- We began our research towards a more widely used conventional basic amine
ing, and potential hazard labeling make efficient and versatile alternate to the catalysts [octyldimethylamine (ADMA-8)
these catalysts unsuitable especially above catalyst options that can provide and 2-ethylimidazole (2-EI)].
Materials and Preparation of 1K SB
TABLE 1—Classes of Available Catalyst Technologies Epoxy/Carboxy Clearcoat Formulations
CATALYST CLASS EXAMPLES Joncryl 819,14 a carboxyl functional
acrylic resin, and Fineplus AC 2570,15
2-ETHYL IMIDAZOLE(2-EI),1-ETHYL IMIDAZOLE, OCTYLDIMETHYLAMINE(ADMA-8), a glycidyl methacrylate resin, were
BASIC TERTIARY AMINES N, N-DIMETHYLBENZYLAMINE, DODECYL DIMETHYLBENZYLAMINE, TETRAMETHYL GUANIDINE blended at an approximately 1:1 molar
QUATERNARY AMMONIUM ratio and dissolved with xylene, PM
DODECYLTRIMETHYLAMMONIUM BROMIDE (DTMAB),
AND PHOSPHONIUM BENZYLTRIMETHYLAMMONIUM BROMIDE, TRIPHENYLETHYL PHOSPHONIUM BROMIDE acetate, n-butyl acetate, and BYK 31016 to
COMPOUNDS form a 45% resin solution. A breakdown
METAL SALTS AND of formulation components is in Table 2.
Zn (ACETYLACETONATE)2, Zn OCTOATE, ZINC ACETATE NACURE XC-324 and the two control
CHELATES
catalysts were all post-added to the
LEWIS ACIDS BORON TRIFLUORIDE, TRIMETHOXY BOROXINE
clearcoat formulation and mixed via high
PAINT.ORG | 31speed dispersion using a FlackTek high Film Properties of Catalyzed Clearcoats tures while XC-324 catalyzed coatings
speed mixer from FlackTek Inc. NACURE XC-324 was compared to the provided high gloss properties, exhibiting
Clearcoats were catalyzed with 1.0% cata- control catalysts in the 1K SB epoxy/ similar gloss units (GU) to the octydime-
lyst solids on total resin solids (TRS). carboxy clearcoat using two bake sched- thylamine catalyzed system.
ules: 120°C/30 min and 110°C/30 min. It should be acknowledged that a
Film Preparation of 1K SB Catalyzed epoxy/carboxy clearcoats were decrease in pencil hardness was observed
Epoxy/Carboxy Clearcoats applied over bare cold roll steel (CRS). for XC-324 when dropping the bake
Dry film thickness (DFT) of the clearcoat schedule to 110°C. However, XC-324
All films prepared for testing were applied
was approximately 1.0–1.2 mil. Tested did not exhibit as significant of a loss in
via draw down. Epoxy/carboxy clearcoats
film properties include MEK resistance,17 pendulum hardness or adhesion as the
were applied using a drawn down bar.
pencil hardness,18 pendulum hardness,19 control films when baked at 110°C vs
White waterborne (WB) basecoats used
crosshatch (CH) adhesion,20 and gloss.21 120°C. Results are in Tables 3a and 3b.
in color testing were applied using a bird
applicator. Epoxy/carboxy clearcoats NACURE XC-324 provided similar cure
and WB basecoats were both given an response to the control catalysts using Viscosity Stability of Epoxy Carboxy
approximately 10–15 min flash at ambient both bake schedules. Coatings catalyzed Liquid Coatings
temperatures prior to baking at the desig- with 2-ethylimidazole exhibited the poor- All 1K formulation should be able to
nated temperatures. est gloss when baked at both tempera- remain stable during transportation and
storage prior to end use application.
To assess these properties, age stability
TABLE 2—1K SB Epoxy/Carboxy Clearcoat of catalyzed epoxy/acid clearcoats was
evaluated by monitoring viscosity change
COMPONENTS DESCRIPTION % of the catalyzed systems upon aging using
JONCRYL 81914 CARBOXYL FUNCTIONAL ACRYLIC 27.0 three storage conditions: 60°C, 50°C, and
FINEPLUS AC 257015 GLYCIDYL METHACRYLATE (GMA) 18.0 room temperature (RT).
NACURE XC-324 was evaluated against
XYLENE SOLVENT 22.1
the octyldimethylamine and 2-ethylimid-
PM ACETATE SOLVENT 22.1 azole catalysts at all three storage tempera-
BUTYL ACETATE SOLVENT 10.6 tures. In addition, all three tests included
BYK 31016 SURFACE ADDITIVE 0.2 an uncatalyzed system. Viscosities were
measured using an AR1000 rheometer
TOTAL 100.0
with a 40 mm 2° steel cone geometry from
%TOTAL RESIN SOLIDS (TRS) 45 TA Instruments. Samples were tested at
ACRYLIC COOH/GMA EPOXY 60/40 25°C using a shear rate of 100s-1.
NACURE XC-324 showed minimal
change in viscosity during all age stability
TABLE 3a—Film Properties of Carboxyl Functional Acrylic and GMA Epoxy—120°C/30 min testing with significant improvement
in viscosity stability compared to both
OCTYLDIMETHYLAMINE 2-ETHYLIMIDAZOLE control catalysts. Furthermore, the XC-
PROPERTIES NACURE XC-324
(ADMA-8) (2-EI)
324 catalyzed system behaved nearly the
% CATALYST SOLID ON TRS 1.0 1.0 1.0 same as the uncatalyzed epoxy/carboxy
MEK DOUBLE RUBS 100 (LIGHT MAR) 100 (LIGHT MAR) 100 (LIGHT MAR) system during most of the storage testing.
GLOSS, 60° GU 106 104 105 Results for viscosity stability using
60°C storage are in Table 4 and Figure 1a.
GLOSS, 20° GU 91 81 94
Results for 50°C and RT (ambient) stor-
PENDULUM, CYCLES 132 133 133 age are in Figures 1b and 1c, respectively.
PENCIL HARDNESS 4H-5H 4H-5H 4H-5H
ADHESION, % CH 100 100 100 Gel Fraction Studies
The cure response of a coating can be
verified by measuring the gel fraction of
TABLE 3b—Film Properties of Carboxyl Functional Acrylic and GMA Epoxy—110°C/30 min the polymer system, namely the percent-
OCTYLDIMETHYLAMINE 2-ETHYLIMIDAZOLE age of polymer chains that have reacted
PROPERTIES NACURE XC-324 and are crosslinked to form the coating
(ADMA-8) (2-EI)
film. A higher gel fraction correlates to a
% CATALYST SOLID ON TRS 1.0 1.0 1.0
better cure with more crosslinking. The
MEK DOUBLE RUBS 100 (MAR) 100 (MAR) 100 (MAR) gel fraction is defined as the weight ratio
GLOSS, 60° GU 105 106 105 of dried network polymer (crosslinked
GLOSS, 20° GU 94 89 94 material) to that of the polymer before
being subjected to Soxhlet extraction
PENDULUM, CYCLES 122 118 128
conditions.
PENCIL HARDNESS 4H-5H 4H-5H 3H-4H Gel fractions studies were conducted by
ADHESION, % CH 90-95 85-90 100 subjecting 1K SB epoxy/carboxy clear-
32 | MARCH 2019TABLE 4—Viscosity Stability of Epoxy Carboxy Liquid Coatings (60°C/16 h)
coats catalyzed with NACURE® XC-324, OCTYLDIMETHYLAMINE 2-ETHYLIMIDAZOLE
octyldimethylamine, and 2-ethylimid- VISCOSITY NO CATALYST NACURE XC-324
(ADMA-8) (2-EI)
azole to Soxhlet extraction conditions. INITIAL (cP) 156 194 326 178
Formulations were catalyzed with 1.0%
catalyst solids based on TRS. Epoxy/ FINAL (cP) 214 GEL GEL 216
carboxy systems were prepared over an % INCREASE 37 — — 22
untreated thermoplastic polyolefin (TPO)
substrate to facilitate easy removal of the FIGURE 1a—Viscosity stability of epoxy/carboxy SB coatings (60°C storage).
cured film. Films were baked for 30 min 600
at 140°C and 120°C. DFT of the clearcoats
Viscosity (cP)
was approximately 1.0–1.2 mil. 400
A 3 in. x 6 in. specimen of cured film
was placed inside a pre-weighed glass
200
thimble. All thimbles were previously
cleaned and dehydrated before weighing.
The glassware was submerged in a 1:1 0
No Catalyst Octyldimethylamine 2-Ethylimidazole NACURE XC-324
acetone/N,N-dimethylformamide (DMF)
0h 16 h
solution overnight and then dehydrated
for one hour at 110°C. Initial tare weight
of the thimble was determined after cool- FIGURE 1b—Viscosity stability of epoxy/carboxy SB coatings (50°C storage).
ing at room temperature in a desiccator 500
for approximately 20–30 min.
400
The thimble containing the sample
% Increase
was weighed and placed in the extraction 300
chamber. A 1:1 acetone/methanol mixture 200
was used as the extraction solvent. Films 100
were subjected to a six-hour reflux. Films
0
were then placed in the oven for one hour
No Catalyst Octyldimethylamine 2-Ethylimidazole NACURE XC-324
at 110°C to dehydrate and remove any re-
50 h 100 h 170 h 220 h
sidual solvent from the thimble and film.
The thimble containing the dried film )
sample was reweighed after being cooled FIGURE 1c—Viscosity stability of epoxy/carboxy SB coatings (ambient storage).
at room temperature in a desiccator for 300
approximately 20–30 min. 250
%Change from
Gel fractions were reported as percent
Uncatalyzed
200
weight retention, where weight retention
150
is defined as the ratio of film weight after
100
extraction to the initial weight before
50
extraction.
0
NACURE XC-324 provided a high
Octyldimethylamine 2-Ethylimidazole NACURE XC-324
degree of crosslinking with the 140°C and
0h 48 h 100 h 180 h 5,800 h
120°C bake, exhibiting a similar weight
retention as both controls. Results are in
Table 5 and Figure 2. TABLE 5—Gel Fraction Studies after 6 h Soxhlet Extraction with Acetone/Methanol (1/1)
PERCENT WEIGHT RETENTION
QUV Resistance of Catalyzed Epoxy CURE CONDITIONS OCTYLDIMETHYLAMINE 2-ETHYLIMIDAZOLE
Carboxy Coatings NACURE XC-324
(ADMA-8) (2-EI)
Coating discoloration induced by cata- 120°C/30 MIN 90.98 92.75 92.65
lysts upon UV exposure is an undesired 140°C/30 MIN 96.24 96.25 97.86
property. Basic amine catalysts are known
to contribute to yellowness as a result of
such exposures. FIGURE 2—Percent weight retention after 6 h of reflux with acetone/methanol (1/1).
A blocked sulfonic acid catalyzed 100
melamine crosslinked WB white base-
%Wt Retention
95
coat was applied over iron phosphated
CRS and baked at 80°C/10 min. The 90
catalyzed epoxy/carboxy clearcoats were
then applied over the white basecoat and 85
cured at 120°C/30 min. The DFT of the
clearcoat was approximately 1.6–1.8 mil. 80
Octyldimethylamine 2-Ethylimidazole NACURE XC-324
Cured films were evaluated for UV
140°C/30 min 120°C/30 min
resistance by measurement of b* values of
PAINT.ORG | 33the panels after 250, 500, and 1000 h of baked at 120°C/30 min. DFT of the cured Crockmeter Abrasion
QUV exposure.22 films was approximately 1.6–1.8 mil. Catalyzed clearcoats were applied over
NACURE XC-324 provided a rather Cured films were exposed to Cleveland bare CRS and baked at 120°C/30 min.
significant improvement in UV resistance humidity conditions.23 The chamber was Baked films were tested for mar/scratch
compared to octyldimethylamine and maintained at 100% RH through the resistance using a Crockmeter abrasion
2-ethylimidazole, especially with regards experiment. Exposed films were evaluat- tester (M238AA) from SDL Atlas. The
to the longer QUV exposure times of 500 ed for blistering. Films were given blister DFT of the clearcoat was approximately
and 1000 h. Results are in Tables 6–7 and ratings24 following 220 and 500 h of 1.6–1.8 mil.
Figure 3. humidity exposure. An abrasion dry test was performed
NACURE XC-324 provided similar hu- on each of the coatings using 2 in. x 2
Humidity Exposures of Catalyzed Epoxy midity resistance to octyldimethylamine. in. Crockmeter squares on the crock
Carboxy Coatings However, XC-324 showed an improve- finger and 20 Mule Team Borax on the
ment compared to 2-ethylimidazole. test specimen. Each of the coatings were
Epoxy/carboxy clearcoats were applied
Results are shown in Table 8. subjected to 20 cycles of abrasion.
over an electrocoated CRS substrate and
The degree of marring for each of the
films was rated qualitatively using a 0–5
scale with “0” and “5” being “No Mar” and
TABLE 6—Yellowness Measurements After QUV Exposure—b* Values “Film Break,” respectively. Break down of
SYSTEM INITIAL 250 H 500 H 1000 H the 0–5 scale is in Table 9. Films were also
evaluated quantitatively by measuring the
OCTYLDIMETHYLAMINE (ADMA-8) -0.45 0.02 0.22 0.31 change in gloss following abrasion.
2-ETHYLIMIDAZOLE (2-EI) -0.59 0.06 0.32 0.40 The NACURE XC-324 catalyzed film
NACURE XC-324 -0.47 0.04 0.08 0.10 exhibited good resistance to Crockmeter
abrasion in comparison to the control
catalysts. XC-324 provided very similar
abrasion resistance to 2-ethylimidazole.
TABLE 7—Yellowness Measurements After QUV Exposure—Δb* Values Nonetheless, the XC-324 films had a
SYSTEM 250 H 500 H 1000 H lower frequency of deep scratches and
a lesser change in gloss than the films
OCTYLDIMETHYLAMINE (ADMA-8) 0.47 0.67 0.76
catalyzed by octyldimethylamine. Results
2-ETHYLIMIDAZOLE (2-EI) 0.64 0.91 0.99 are in Table 10 and Figure 4.
NACURE XC-324 0.51 0.55 0.57
Overbake Resistance
A blocked sulfonic acid catalyzed
FIGURE 3—Yellowness measurements after QUV exposure. melamine crosslinked WB white base-
coat was applied over iron phosphated
+1.00 CRS and baked at 110°C/10 min. The
+0.90 +0.99 catalyzed epoxy/carboxy clearcoats were
+0.91
+0.80 then applied over the white basecoat and
+0.70 +0.76 cured at 120°C/30 min. The DFT of the
+0.60 +0.67 +0.64
clearcoat was approximately 1.6–1.8 mil.
Catalyzed films were tested for over-
∆b*
+0.50 +0.55 +0.57
+0.51 bake resistance by evaluating the coat-
+0.40 +0.47
+0.30 ing’s color change. Films were subjected
+0.20 to three consecutive cycles of overbake:
+0.10 (1) 120°C/30 min, (2) 120°C/30 min and
0.00 (3) 150°C/30 min.
Octyldimethylamine 2-Ethylimidazole NACURE XC-324 All clearcoats showed a minimal
250 h 500 h 1000 h
change in color following the first
overbake cycle. However, relative to the
control catalysts, NACURE XC-324 did
exhibit a lesser change in total color
TABLE 8—Humidity Exposures of Catalyzed Epoxy/Carboxy Coatings—Blister Ratingsa (∆E*). A similar trend was observed for
the second overbake cycle.
SYSTEM 220 H 500 H
More significant color changes oc-
OCTYLDIMETHYLAMINE (ADMA-8) LIGHT / 6 MEDIUM / 4 curred following the third overbake cycle.
2-ETHYLIMIDAZOLE (2-EI) LIGHT / 6 MEDIUM / 4 + LIGHT / 2 The XC-324 films provided a significant
NACURE XC-324 LIGHT / 6 MEDIUM / 4 improvement in resistance to yellowing
(a) Blister rating–density / size.
(∆b) and exhibited a much lesser change
in total color compared to the controls.
Results are in Figure 5 and Table 11.
34 | MARCH 2019TABLE 9—Visual Rating for Crockmeter Tests–0–5 Rating TABLE 10—Images with Visual Rating and Change in Gloss Following Crockmeter Abrasion
RATING DESCRIPTION OCTYLDIMETHYLAMINE 2-ETHYLIMIDAZOLE
SYSTEM NACURE XC-324
(ADMA-8) (2-EI)
0 NO MAR
1 LIGHT MAR
2 MAR
3 MAR, MULTIPLE DEEP SCRATCH
IMAGE a
4 HEAVY MAR
5 FILM BREAK
Experiment II: Catalyst Studies on VISUAL RATING (0-5) 3 2 2
NACURE XC-355 in a 2K SB Epoxy/ ∆20° GU –27.0 –23.7 –24.4
Carboxy Clearcoat ∆60° GU –11.8 –9.3 –9.3
(a) Image color altered—enhanced contrast to better show abrasion markings.
NACURE XC-355 was evaluated in a 2K
SB epoxy/carboxy clearcoat and tested for
lower temperature cure capabilities.
Materials and Preparation of 2K SB Epoxy/ FIGURE 4—Change in gloss following Crockmeter abrasion.
Carboxy Clearcoat Formulation Octyldimethylamine 2-Ethylimidazole NACURE XC-324
The 2K SB epoxy/carboxy clearcoat for- 0
mulation was prepared by dissolving Jon-
cryl 819, a solid grade carboxyl functional -5
Δ20° GU / Δ60° GU
acrylic resin, and Fineplus AC 2710,25 a
solid grade glycidyl methacrylate resin, -10
separately using a solvent blend contain-
-15
ing xylene, PM acetate, and n-butyl ace-
tate (40.1/40.1/19.8). The flow additive was -20
stored in the acid component. Breakdown
of formulation components is presented -25
in Table 12.
The acid component, containing the -30
carboxyl (COOH) functional acrylic, and Δ20° Δ60°
the epoxy component, containing the
glycidyl methacrylate (GMA) resin were
both 45% TRS.
Catalysts were premixed into the acid
component prior to addition of the epoxy FIGURE 5—Yellowing (b*) and total color (E*) change of clearcoats after overbake.
component. All mixing was conducted via
high speed dispersion using a FlackTek +1.00
high speed mixer. +0.90
The clearcoat was formulated stoichio- +0.80
metrically. The two components were +0.70
blended 69/31 by total formula weight to +0.60
∆b*, ∆E*
give a solids ratio of 69/31 Acrylic COOH/ +0.50
GMA. This solids ratio provides an ap- +0.40
proximately 1:1 molar ratio. The TRS of +0.30
the final resin system was 45%. +0.20
Sample testing or film preparation began +0.10
immediately after incorporating the epoxy
0.00
component into the acid component. Δb* ΔE* Δb* ΔE* Δb* ΔE*
Overbake 1 Overbake 2 Overbake 3
Film Preparation of 2K SB Epoxy/
120°C/30 min 120°C/30 min 150°C/30 min
Carboxy Clearcoat
All films prepared for testing were applied Octyldimethylamine 2-Ethylimidazole NACURE XC-324
via draw down. Epoxy/carboxy clearcoats
were applied using a drawn down bar.
White WB basecoats used in color testing
were applied using a bird applicator.
PAINT.ORG | 35TABLE 11—Change in Color Values of Catalyzed Clearcoats after Overbake
increase in viscosity during the isotherm.
OVERBAKE COLOR VALUE OCTYLDIMETHYLAMINE 2-ETHYLIMIDAZOLE NACURE XC-324 It was also observed that the rate of
ΔL* –0.17 –0.13 –0.07 change in viscosity of the XC-355 system
was most significant during the first
OVERBAKE 1 Δa* –0.03 –0.02 –0.01
half of the isothermal step. The rate of
120°C/30 MIN Δb* 0.13 0.13 0.13 change beginning to diminish or plateau
ΔE* 0.21 0.20 0.15 could suggest that the epoxy/carboxyl
ΔL* –0.15 –0.17 –0.08 crosslinking reaction was at least near to
completion after approximately 30 min
OVERBAKE 2 Δa* –0.02 –0.03 –0.01
at 100°C.
120°C/30 MIN Δb* 0.25 0.18 0.18 The uncatalyzed system additionally
ΔE* 0.29 0.33 0.20 exhibited a large increase followed by a
ΔL* –0.33 –0.37 –0.29 large decrease in viscosity when cooling
the sample to 20°C followed by re-heating
OVERBAKE 3 Δa* –0.09 –0.07 –0.07
to 100°C, respectively. This is caused by
150°C/30 MIN Δb* 0.73 0.86 0.58 uncrosslinked resins re-solidifying to their
ΔE* 0.80 0.94 0.65 solid state during cool down and again
softening or re-melting upon additional
heating.
TABLE 12—2K Solventborne Epoxy/Carboxy Clearcoat On the contrary, the XC-355 system
exhibited minimal change in viscosity
MATERIAL DESCRIPTION %
during cool down or re-heating of the
COMPONENT 1—ACID COMPONENT sample. The rheology of the resin system
JONCRYL 819 CARBOXYL FUNCTIONAL ACRYLIC 31.1 no longer exhibiting physical properties
XYLENE SOLVENT 15.1 of the individual solid grade resins sug-
gests that XC-355 successfully catalyzed
PM ACETATE SOLVENT 15.1
the reaction, producing a more thermally
n-BUTYL ACETATE SOLVENT 7.5 stable crosslinked network following the
BYK 310 SURFACE ADDITIVE 0.2 isotherm at 100°C.
COMPONENT 2—EPOXY COMPONENT Data collected from these oscillation
tests confirm that NACURE XC-355 is a
FINEPLUS AC 271025 GLYCIDYL METHACRYLATE (GMA) 14.0
high active catalyst for reaction of car-
XYLENE SOLVENT 6.8 boxyl and epoxy functional groups. Fur-
PM ACETATE SOLVENT 6.8 thermore, the results validate XC-355 as a
n-BUTYL ACETATE SOLVENT 3.4 catalyst capable of promoting the epoxy/
carboxyl reaction at bake temperatures
TOTAL 100.0
of 100°C or potentially lower. Results are
%TOTAL RESIN SOLIDS (TRS) 45.0 shown in Figure 6.
ACRYLIC COOH / GMA 69/31
Film Properties of Catalyzed Clearcoats
Epoxy/carboxy clearcoats catalyzed with
Epoxy/carboxy clearcoats and WB base- to 100°C. The pre-experiment steps used increasing dosages of NACURE XC-355
coats were both given an approximately for flashing solvent from the samples are were evaluated for MEK resistance, gloss,
10–15 min flash at ambient temperatures shown in Table 13a. The protocol used for and pendulum hardness. Films were
prior to baking at the designated tem- oscillation testing is in Table 13b. prepared over bare CRS and baked at
peratures. The uncatalyzed and NACURE XC-355 100°C/30 min. DFT of the clearcoats was
systems both showed a decrease in com- approximately 1.0–1.2 mil.
Rheology Studies on Catalyst Activity plex viscosity as the solid grade resins be- Systems were catalyzed with 0, 1, 2, and
at 100°C gin to soften or melt upon heating during 3% NACURE XC-355 solids on TRS.
the first temperature ramp to 100°C. It All systems showed a very high pen-
An oscillation study on the change in
should be noted the rate of change in vis- dulum hardness and great gloss. The
complex viscosity (|η*|) was conducted
cosity was slightly lower for the XC-355 NACURE XC-355 systems exhibited a
using an AR2000 rheometer from TA
system during the first temperature ramp. slight decrease in both gloss and hard-
Instruments. A 20 mm steel flat plate
This could indicate that the catalyst had ness. However, the system containing no
geometry was used during testing.
already activated the system at tempera- catalyst gave very poor MEK resistance.
The uncatalyzed epoxy/carboxy clear-
tures below 100°C. This indicates that the uncatalyzed resin
coat was compared to a system containing
Minimal increase in viscosity for system was not fully crosslinked.
1% NACURE XC-355 solids on TRS.
the uncatalyzed epoxy/carboxy system All NACURE XC-355 dosages provided
Oscillation testing was comprised of
occurred throughout the 60 min isotherm great MEK resistance. The XC-355 systems
four steps following sample equilibration
at 100°C. Catalyzing the formulation with all achieved 100 MEK 2X. Increasing
at 20°C: 1) Heat to 100°C, 2) Isotherm for
NACURE XC-355 provided a significant catalyst dosage provided improved mar re-
60 min, 3) Cool to 20°C, and 4) Re-heat
sistance. Results are in Table 14 and Figure 7.
36 | MARCH 2019Overbake Resistance of Catalyzed The clearcoats all exhibited very Experiment III: Environmental Etch
Clearcoats little yellowing (b*) following the initial
100°C/30min bake and the overbake.
Resistance of Epoxy/Carboxy vs
A blocked sulfonic acid catalyzed HMMM/OH
Although nearly negligible, very slight
melamine crosslinked white WB base-
increases in yellowing after overbake Environmental etch resistance of epoxy/
coat was applied over iron phosphated
for systems containing XC-355 were carboxy clearcoats catalyzed with
CRS and baked at 110°C/10 min. The
observed but it should be acknowledged NACURE XC-355 was compared to an
catalyzed epoxy/carboxy clearcoats were
that the uncatalyzed system was not fully aminoplast crosslinked polyol clearcoat
then applied over the white basecoat and
cured as previously demonstrated. Addi- catalyzed with amine blocked p-TSA.
cured at 100°C/30 min. The DFT of the
tionally, minimal differences in total color
clearcoat was approximately 1.0–1.2 mil.
(∆E*) following overbake occurred for all Materials and Preparation of SB Epoxy/
Films were overbaked at 100°C/30
dosages of XC-355. Results are in Table 16
min after testing initial color of the films. Carboxy and HMMM/OH Clearcoat
and Table 17.
Color change was evaluated for clearcoats Formulations
containing 0, 1, 2, and 3% NACURE XC- The two formulations (A and B) were
355 solids on TRS. both formulated as 2K systems. Formu-
TABLE 13a—Pre-Experiment Steps for Oscillation Tests FIGURE 6—Oscillation curve of complex viscosity and temperature as a function of time.
PRE-EXP. STEP # DESCRIPTION
STEP 1 PLACE SAMPLE ON PELTIER PLATE AT 25°C
IMMEDIATELY BRING GEOMETRY TO
1a ZERO-GAP (400 MICRON)
1b SHEAR AT 100S-1/2 MIN
RAISE GEOMETRY AND ALLOW SAMPLE TO
1c REST AT 25°C/5 MIN
BRING GEOMETRY BACK TO ZERO-GAP
STEP 2 (400 MICRON)
2a INCREASE TEMPERATURE TO 80°C
2b SHEAR AT 100S-1/5 MIN
2c EQUILIBRATE AT 20°C/5 MIN
TABLE 13b—Protocol for Oscillation Tests
EXP. STEP # DESCRIPTION
TEMPERATURE RAMP OF 10°C/MIN
STEP 1 FROM 20–100°C
STEP 2 ISOTHERM FOR 60 MIN AT 100°C
FIGURE 7—MEK resistance of hardness of epoxy/acid clearcoats—100°C/30 min bake.
TEMPERATURE RAMP OF 10°C/MIN
STEP 3 FROM 100–20°C 120 150
TEMPERATURE RAMP OF 10°C/MIN 100 Light 100 v. Light 100+ No Mar
STEP 4 FROM 20–100°C 100 140 140
Pendulum, cycles
134
80 131 130
129
TABLE 14—Film Properties of Carboxyl Functional Acrylic and
MEK 2X
GMA Epoxy—100°C/30 min 60 < 50 120
PROPERTIES NO CATALYST NACURE XC-355 40 110
% CATALYST 20 100
0.0 1.0 2.0 3.0
SOLID ON TRS
100 100 100+ 0 90
MEK DOUBLE 0% 1% 2% 3%
< 50 LIGHT VERY NO
RUBS MAR LIGHT MAR % NACURE XC-355 Solid on TRS
GLOSS, 60° GU 110 108 109 109 MEK 2X Pendulum, Cycles
GLOSS, 20° GU 99.7 96.9 96.7 93.6
PENDULUM, 140 134 129 131
CYCLES
PAINT.ORG | 37lation A uses a solid grade hydroxyl (OH) Components 1 and 2 of Formulation Formulation A is based on an experi-
functional acrylic resin (Component 1) for A and B were formulated to 45% TRS by mentally optimized ratio of solid resin.
crosslinking with hexa(methoxymethyl) dissolving the resins in a solvent blend The two components were blended 70/30
melamine (HMMM) (Component 2). containing xylene, PM acetate, and to give a solid ratio of 70/30 Acrylic OH/
Formulation B uses a solid grade carboxyl n-butyl acetate (40.1/40.1/19.8). Flow ad- HMMM. The TRS of the final resin sys-
(COOH) functional acrylic resin (Compo- ditive was stored in Component I of both tem was 45%.
nent 1) for crosslinking with a GMA resin formulations. Breakdown of formulation Formulation B was formulated stoi-
(Component 2). components is in Table 17. chiometrically. The two components were
blended 60/40 by total formula weight
to give a solids ratio of 60/40 Acrylic
COOH/GMA. This solids ratio provides
TABLE 15—Yellowing Resistance Following 100°C/30 min Overbake an approximately 1:1 molar ratio. The
PROPERTIES NO CATALYST NACURE XC-355 TRS of the final resin system was 45%.
Catalyst was premixed into Component
%CATALYST I of both Formulation A and B. Formula-
0.0 1.0 2.0 3.0
SOLID ON TRS tion A, the Acrylic OH/HMMM system,
b* INITIAL 0.13 0.16 0.18 0.21 was catalyzed with an amine neutralized
p-TSA (0.56% p-TSA on TRS or 1% as
b* FINAL 0.15 0.21 0.20 0.24
supplied on TFW). Formulation B, the
∆b* 0.01 0.06 0.02 0.02 Acrylic COOH/GMA system, was cata-
lyzed with NACURE XC-355 (1.0% solids
on TRS or 0.9% as supplied on TFW).
For both Formulation A and B, Compo-
TABLE 16—Total Color Change Following 100°C/30 min Overbake nent II was incorporated into Component
PROPERTIES NO CATALYST NACURE XC-355 I containing the pre-catalyzed acrylic
resin solutions. Catalyst premixing and
%CATALYST component incorporation was conducted
0.0 1.0 2.0 3.0
SOLID ON TRS via high speed dispersion using a Flack-
∆L* -0.07 -0.05 -0.07 0.03 Tek high speed mixer.
Sample testing or film preparation
∆a* -0.02 -0.02 0.00 -0.01 began immediately after incorporating
∆b* 0.01 0.06 0.02 0.02 the HMMM and GMA solutions to the
OH Acrylic and COOH Acrylic solution,
∆E* 0.07 0.08 0.07 0.04
respectively.
Film Preparation of HMMM Crosslinked
TABLE 17—(a) Hydroxyl Functional Acrylic/HMMM vs (b) Acid Functional Acrylic/GMA Epoxy Acrylic and Epoxy/Carboxy Clearcoats
FORMULATION A—ACRYLIC OH / HMMM FORMULATION B—ACRYLIC COOH / GMA EPOXY Films were applied over bare CRS via
draw down, given an approximately 10–15
MATERIAL DESCRIPTION % MATERIAL DESCRIPTION % min flash at room temperature, and baked
COMPONENT 1 – POLYOL COMPONENT COMPONENT 1 – ACID COMPONENT at 120°C/30 min. Epoxy/carboxy and
OH COOH aminoplast crosslinked films were tested
JONCRYL 587 26 ACRYLIC 31.5 JONCRYL 819 ACRYLIC 27.0 for cure response and environmental etch
resistance once cooled to room tempera-
XYLENE SOLVENT 15.4 XYLENE SOLVENT 13.2
ture following bake.
PM ACETATE SOLVENT 15.4 PM ACETATE SOLVENT 13.2
n-BUTYL ACETATE SOLVENT 7.5 N-BUTYL ACETATE SOLVENT 6.5 Cure Response of Acrylic OH/HMMM and
BYK 310 SURFACE ADDITIVE 0.2 BYK 310 SURFACE ADDITIVE 0.2 Acrylic COOH/GMA
COMPONENT 2—MELAMINE COMPONENT COMPONENT 2—EPOXY COMPONENT Cure responses of the Acrylic OH/
HMMM (Formulation A) and the Acrylic
MELAMINE FINEPLUS AC
HMMM 13.5 GMA 18.0 COOH/GMA (Formulation B) were tested
CROSSLINKER 2570
by evaluating the film’s resistance to
XYLENE SOLVENT 6.6 XYLENE SOLVENT 8.8
MEK.
PM ACETATE SOLVENT 6.6 PM ACETATE SOLVENT 8.8 Formulation A and B both exhibited
n-BUTYL ACETATE SOLVENT 3.2 n-BUTYL ACETATE SOLVENT 4.3 great cure response using the designated
TOTAL 100.0 TOTAL 100.0 catalyst dosages and bake schedule. Both
formulations achieved 100 MEK 2X with
%TRS 45.0 %TRS 45.0
minimal marring. Results are shown in
ACRYLIC OH / ACRYLIC COOH Table 18.
70 / 30 60 / 40
HMMM / GMA
38 | MARCH 2019TABLE 18—MEK Resistance of (a) Acrylic OH/HMMM vs (b) Acrylic COOH/GMA
FORMULATION CATALYST CATALYST DOSAGE MEK 2X
1.0% AS SUPPLIED ON TFW
A ACRYLIC OH/HMMM AMINE BLOCKED p-TSA 100 NO MAR–VERY LIGHT MAR
(0.56% p-TSA ON TRS)
0.9% AS SUPPLIED ON TFW
B ACRYLIC COOH/GMA EPOXY NACURE XC-355 100 NO MAR–VERY LIGHT MAR
(1.0% SOLID ON TRS)
TABLE 19—Acid Etch Resistance of (a) Acrylic OH/HMMM vs (b) Acrylic COOH/GMA
TIME EXPOSED
FORMULATION CATALYST CATALYST DOSAGE TO H2SO4 (10%) / 60°C
20 MIN 40 MIN 60 MIN
1.0% AS SUPPLIED ON TFW
A ACRYLIC OH/HMMM AMINE BLOCKED p-TSA (0.56% p-TSA ON TRS)
ACRYLIC COOH/GMA 0.9% AS SUPPLIED ON TFW
B NACURE XC-355
EPOXY (1.0% SOLID ON TRS)
Environmental Etch Comparison of Acrylic SUMMARY AND CONCLUSIONS color with good overbake resistance even
OH/HMMM vs Acrylic COOH/GMA at higher catalyst dosages.
The new class of metal-free catalysts are Environmental etch studies conducted
Environmental etch of the Acrylic OH/ on hydroxyl vs carboxyl functional acrylic
found to be very effective in promoting
HMMM (Formulation A) and the Acrylic resins crosslinked with HMMM vs a GMA
the crosslinking reaction of carboxyl
COOH/GMA (Formulation B) was eval- and catalyzed with amine neutralized
functional polymers with epoxy function-
uated by subjecting the films to a diluted p-TSA vs XC-355, respectively, demon-
al resins with potential utility in auto-
solution of sulfuric acid (H2SO4) at elevat- strated that epoxy/carboxy clearcoats
ed temperatures. motive clearcoats and powder coating
applications. can likely be used as an alternative to
Equal amounts of a 10% H2SO4 solution aminoplast crosslinked clearcoats when
were placed onto the film in three spots NACURE XC-324 was determined to be
a versatile stable catalyst that can effec- applications require superior acid etch
of equal surface area. Test areas were resistance.
covered, placed in an oven at 60°C, and tively promote the crosslinking reaction
evaluated in 20-min intervals. The acid of a 1K SB epoxy/carboxy clearcoat using
solution was rinsed off the panel using bake temperatures as low as 110–120°C. ACKNOWLEDGMENTS
dIH2O once the films were near room In addition to good cure with exceptional
temperature. Excess acid or dIH2O was age stability, XC-324 films exhibited high We thank Morgan Alexander for experi-
removed by lightly pressing with a towel. gloss, great hardness, low color, and good mental support and for evaluations of the
The Acrylic OH/HMMM system adhesion to metal, as well as excellent new catalysts in various coating systems.
catalyzed with amine neutralized p-TSA overbake, humidity, UV, and abrasion We thank King Industries for permission
(Formulation A) began to fail following resistance. to publish this work.
40 min of testing. Precipitate and a blister Investigations on lower temperature cure
in the center of the test area was observed response validated NACURE XC-355 as a
for the HMMM crosslinked system after high active catalyst capable of providing References
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The Acrylic COOH/GMA system cata- Baumgart, H., “The Effects of Acid Rain on the
lyzed with NACURE XC-355 exhibited su- potentially lower. In addition to excellent
cure response, XC-355 films exhibited high Appearance of Automotive Paint Systems Studied
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slight markings following 60 min of acid gloss and great hardness as well as low
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RAVI RAVICHANDRAN, MICHAEL EMMET, MATTHEW
GADMAN, JOHN FLORIO, and STEVE WOLTORNIST,
King Industries, Inc., USA, 1 Science Rd., Norwalk, CT
06855; ravichandran@kingindustries.com.
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