Temperature dependence of rheological behavior of a metallic automotive waterborne basecoat

Progress in Organic Coatings 53 (2005) 169–176

Temperature dependence of rheological behavior of a metallicautomotive waterborne basecoat

Jianhua Xu∗, Kurt W. KoellingDepartment of Chemical and Biomolecular Engineering, The Ohio State University,

140 West 19th Avenue, Columbus, OH 43210, USA

Abstract

The temperature dependence of the rheological behavior of a metallic automotive waterborne basecoat was studied with the temperatureranging from 10 to 45◦C. It is found that the paint exhibits both shear thinning and thixotropic behavior. The degree of shear thinning andthixotropy increases as the temperature increases. Small amplitude oscillatory shear tests show that the basecoat displays more elasticity athigher temperature. Both steady shear viscosity and dynamic properties indicate that the paint gradually develops a network structure as thetemperature increases, which leads to increased viscosity. The viscosity at very low shear rate at 45◦C is about 500 times greater than that at20◦C. The high shear viscosity decreases with the increase of temperature in the range of 10–35◦C, and then increases with temperature upt ◦

©

K

1

ac[wmttwa9cp

ictw

logyndenteennon-eardiesoat,per-lingre-high

Un-sityt the

thatint is

upw-theke

0d

o 45 C. The Ford cup #4 measurements show good agreement with the steady-state viscosity at high shear rate.2005 Elsevier B.V. All rights reserved.

eywords:Rheology; Suspensions; Waterborne paint; Temperature effects; Thixotropy

. Introduction

With the requirements from the environmental protectiongencies, more and more of the traditional solvent-borneoatings have been replaced by low-VOC-emitting coatings1]. Since the first commercial-scale application of theaterborne basecoat in the automotive industry started inid-1980s, the environmentally benign waterborne paint

echnology has been replacing the traditional solvent-borneechnology in the automotive industry. Among others,aterborne coatings take up more than 50% of the totalmount of coatings in Europe, the United States and up to0% in Germany[2–4]. Other impetus of the technologicalhangeover includes better performance and lower costrovided by the waterborne coatings[1,4].

Although the waterborne coatings possess some intrigu-ng advantages, there are difficulties that have to be over-ome before successful applications can be made. One ofhe most important problems is the control of the rheology,hich determines the quality and appeal of the final film.

For a Newtonian fluid, its viscosity can describe its rheoand it is constant at a certain temperature, and indepeof whether it is being sheared and/or how long it has bsheared. However, most waterborne coatings are highlyNewtonian. Their viscosities are not only functions of shrate, but in most cases are functions of time as well. Stuin the past[4,5] have shown that for a waterborne basecthe rheology should be carefully designed such that theformance of the paint is superior during the whole handcycle, from storage to spray application and drying. Thequired rheology should enable the basecoat to have aviscosity during storage that leads to minimal settling.der moderate agitation and during circulation, the viscoshould be low that the basecoat can be easily pumped. Aspraying gun or bell, the viscosity should be very low sothe paint can be properly atomized. As soon as the pasprayed on to the work piece, the viscosity should buildquickly to prevent the paint from running or sagging. Hoever, the viscosity should still be low enough to enablepaint to level off, providing a smooth film and good flaorientation.

∗ Corresponding author. Tel.: +1 614 688 3400; fax: +1 614 292 3769.E-mail address:[email protected] (J. Xu).

The rheology of waterborne coatings has been studied formany years. As the rheology of the coating is critical to the

300-9440/$ – see front matter © 2005 Elsevier B.V. All rights reserved.oi:10.1016/j.porgcoat.2005.02.002

170 J. Xu, K.W. Koelling / Progress in Organic Coatings 53 (2005) 169–176

final appearance, people have developed many ways to con-trol the rheology. Different types of thickeners or modifiershave been developed suitable for a wide variety of waterbornecoatings[6–9]. Konishi et al. studied the time-dependent be-havior and showed that the paint had high limiting saggingthickness and pinholing thickness[10]. Steady-state viscos-ity profiles, creep flow and thixotropic measurements werecarried out by Boggs et al.[11] in order to determine the con-nection between these and aluminum flake orientation. Os-terhold[12] reviewed the rheological behavior of waterbornepaint and described some important measuring methods, suchas oscillation tests and determination of yield points. Otherresearchers have studied the role of the rheology in spray-ing, leveling, coating structure and other relevant factors[13–16].

Much less effort has been spent on the temperature depen-dence of the rheology of a waterborne paint. Kim and Suhstudied the rheology of a latex paint at different temperaturesand found that the viscosity followed the Arrhenius equa-tion very well[17]. Osterhold found that theG′ of two typesof polyurethane microgels decreases as the temperature in-creases[18]. Churella and Berman observed the increased G′with temperature and they attributed this to the formation ofa thin film on the latex paint [19].

As there is almost no published literature about the tem-perature dependence of the rheological behavior of a metallica tigatet gicalc angeo

2

neb bout5 t.%a Thev y ap-p ionb isonp on aR apa-b ou-ew r bathb raturea logi-c ce ofs thes sure-m capl

mics to det

viscous modulusG′′ are not functions of the strain, and 1%strain was determined. The oscillation was performed withfrequencies ranging from 0.1 to 15 Hz. In the thixotropic looptest, the sample was sheared from 0 to 600 s−1 linearly in30 s and then immediately sheared from 600 s−1 back to 0(Fig. 1a) in 30 s.

Pseudo-steady-state viscosity was measured using theshear rate sweep down procedures. The word pseudo is usedhere because the data shown here is obtained at a stage veryclose to steady state, but not at the true steady state. As seenin Fig. 1c, it takes 300 s for the viscosity to reach steady statewhen sheared at 200 s−1. Longer time is needed if shearedat smaller shear rates. To get true steady-state viscosity atvarious shear rates, the experiment will last so long such thatdrying of the paint sample becomes an issue. On the otherhand, use fresh paint for each shear rate will be too time con-suming. For the simplicity of the experiments, a pre-shear(delay) time of 30 s and measure time of 10 s at each shearrate was chosen for all the tests. The sweep test started fromhigh shear rate (600 s−1) to low shear rate (0.02 s−1), so thatthe structure in the sample can be broken at high shear ratesand close to steady-state conditions can be obtained at lowershear rates after the 30 s pre-shear. This procedure was keptthe same for all steady shear viscosity measurements so thata direct comparison can be made between different tempera-tures.

STMD

3

3

arac-t coat,a att ris-i itht ana per-a ntb an theG coatb gento -u id’sv ism het thista t thev Thism muchs

utomotive basecoat, the purpose of this study is to inveshe subject. In this paper, a comprehensive shear rheoloharacteristics of a metallic automotive basecoat at a rf temperatures is studied.

. Experimental

A commercially available silver metallic waterborasecoat was used in this experiment. It contains a0–70 wt.% water, 2–3 wt.% aluminum flakes, 5–15 wcrylic latex, 5 wt.% thickeners and other ingredients.iscosity had been adjusted to be appropriate for spralication. A non-metallic basecoat with similar compositut with no aluminum flakes was also used for comparurpose. The rheological characterization was performedheometrics RSF II rheometer, with a transducer that is cle of measuring torques in a range of 0.02–20 g cm. A Ctte tool with temperature control with accuracy of±0.5◦Cas used. The paint sample bottle was soaked in a wateefore loading so that the sample had the same tempes the tool. For each load of sample, a series of rheoal characterizations were performed with the sequenmall amplitude oscillatory shear, thixotropical loop andteady-state shear. The drying of the paint during meaents was minimized by covering the Couette tool with a

ined with a layer of water-saturated material.In small amplitude sinusoidal oscillation tests, dyna

train sweep experiments had been done beforehandermine the linear region, where the elastic modulusG′ and

-

Ford cup #4 measurement was performed as per the A1200 standard.

. Results and discussion

.1. Linear viscoelasticity

Small amplitude oscillatory shear has been used to cherize the linear viscoelastic behavior of the metallic basend the results are shown inFig. 2a and b. Plot (a) shows th

he elastic modulusG′ decreases a little with temperatureng from 10 to 20◦C, and then increases monotonically wemperature from 20 to 45◦C for all frequencies. There iscceleration of the rate of increase with increasing temture. From 20 to 30◦C, theG′ increases gradually; whe

he temperature is higher,G′ increases much faster. TheG′ecome less dependent on the frequency and greater th′′ at higher temperatures, which implies that the baseehaves more like an elastic solid than a liquid. The tanf the phase angle, tanδ =G′′/G′, is the ratio of elastic modlus to viscous modulus, and it is an indicator of the fluiscoelasticity. When tanδ is greater than 1, then the fluidore liquid-like; and when lower than 1, then solid-like. T

anδ versus frequency, shown in plot (b), further revealsrend as with higher temperature. The average of tanδ at 40nd 45◦C is about 0.15, much less than 1, indicating thaiscous modulus is less than 1/6 of the elastic modulus.eans that at these temperatures, the basecoat exhibits

tronger solid-like behavior.

J. Xu, K.W. Koelling / Progress in Organic Coatings 53 (2005) 169–176 171

Fig. 1. Thixotropic behavior of the metallic basecoat: (a) shear history in a thixotropical loop; (b) stress response of a thixotropic fluid; (c) steady shear atconstant shear rate of 200 s−1. The measurements were performed at room temperature.

3.2. Thixotropy

Fig. 1a–c show that the metallic basecoat exhibits athixotropic behavior. Plot (a) shows the shear pattern andplot (b) shows the corresponding shear stress versus time. Itcan be seen that the magnitude of the shear stress when theshear rate increases (up curve) is greater than that when theshear rate decreases (down curve). As the definition of vis-cosity is the ratio of shear stress to shear rate, the viscosityof the up curve is greater than that in the down curve. Thesize of the area enclosed in the two curves is an indicationof the degree of thixotropy. Larger enclosed area indicateshigher degree of thixotropy. Plot (c) shows when the paintis subjected to a constant shear rate. The viscosity decreasesas the shear time increases. An accepted theory to explainthixotropy is that certain network structure forms in the fluid.When subject to shear the structure is broken down, hencethe viscosity decreases. After the fluid is allowed to rest, thestructure rebuilds and thus the fluid gains its original viscosity[20].

The existence of the thixotropy complicates the measure-ment of the rheology, as the loading process shears the paintsample and therefore its viscosity may change. In order to

obtain repeatable measurements, the loading procedure hasto be maintained to be the same for each sample, so thatthe shear history of the sample before measurements is thesame. In this study, before loading the paint samples to therheometer, the paint is gently shaken for 2 min. The loadingprocedure and the rheological measurement sequences areall kept the same. Therefore, same the shear history was ap-plied for each sample.Fig. 3a–h shows the change of degreeof thixotropy with the increase of temperature. At 10◦C, theup curve collapses onto the down curve so there is almost nothixotropy. When the temperature increases, more thixotropyis evident. From the enclosed area between the curves, the de-gree of thixotropy gradually increases when the temperatureincreases from 10 to 45◦C. Furthermore, an overshoot in theup curve appears at 40◦C. It may indicate that the structurewas not broken down gradually, instead a large amount ofstructure was broken down at the same time. This is similar tothe overshoot that appeared in the start-up of constant shear ofsome relatively strong viscoelastic materials[21]. At 45◦C,the overshoot is bigger and thus the paint is more elastic atthis temperature. The appearance of the overshoot suggeststhat the paint shows strong elastic properties at high tem-peratures. Further, the magnitude of the shear stress is much


Fig. 2. Linear viscoelasticity of the metallic basecoat: (a)G′ vs. frequency;(b) tanδ vs. frequency.

higher than lower temperatures. This means the overall shearviscosity at 45◦C is much higher than that at lower temper-atures. This is quite different from our common sense thatthe viscosity is lower at higher temperature. The increase ofviscosity is further discussed in the next section of this study.The overshoot in the up curve at low shear rate is also in-terpreted as “static yield stress”, which usually appears onlywhen the sample is sheared for the first time after a prolongedstorage time and disappears afterwards[22]. The increase ofthe degree of thixotropy as the temperature increases impliesthat the paint develops a three-dimensional network structureat high temperatures, and more structure is formed at highertemperatures.

3.3. Pseudo-steady-state viscosity

Fig. 4a and b shows the temperature dependence of thepseudo-steady-state shear viscosity profile. Generally, theviscosity increases as temperature increases (Fig. 4a) for

the metallic basecoat. At very low shear rate, the viscosityincreases up to 500 times.Fig. 4b shows in detail that theviscosity at low shear rate region decreases slowly with tem-perature from 10 to 20◦C, and then increases dramaticallywith the temperature; while the high shear viscosity decreasesslowly when the temperature increases up to 35◦C and thenincreases slowly up to 45◦C. This viscosity change withtemperature is reversible, such that the viscosity increaseswith increasing temperature and decreases back to its originalviscosity when temperature drops. However, the viscosityof the non-metallic basecoat decreases slightly with temper-ature. In this semi-log plot, it is almost independent of thetemperature.

This type of reversible viscosity increase with temper-ature in the metallic basecoat is very interesting. Mostoften the temperature dependence of viscosity will fol-low the WLF equation for polymer melts and the Ar-rhenius relationship for solutions, by which the viscositydecreases as temperature increases[21]. Nonetheless, re-verse temperature dependence of viscosity has been reportedby researchers in colloidal systems[23] and biodegrad-able polymer aqueous solutions[24–27]. Choi and Krieger[23] argued that in their gelled dispersion of PMMA col-loids sterically stabilized in silicone oils, a “steric-elastic”force is present, which increases at elevated tempera-tures, causing the viscosity to increase. The biodegradablep eneo beenf lationp ls ath ed, in-cg ss[I en re-p osityi s andt -p ateri ved.O ing isn notr rvedi eser ed byt t ath raturei ing ag sus-p er be-i , thes scos-i ningl n vis-c d re-s osity

oly(ethylene oxide)–poly(propylene oxide)–poly(ethylxide) (PEO–PPO–PEO) triblocks aqueous solution has

ound by many researchers to have reverse thermo gehenomena (low viscosity at low temperature and geigher temperature). Various reasons have been proposluding intrinsic changes in micellar properties[24], entropicain of the system[25], hard sphere crystallization proce

26], and the formation of a three-dimensional network[27].n the coating systems, such phenomenon has never beorted. Other researchers have found non-reversible visc

ncrease with increasing temperature in coating systemhey attributed it to curing[28] or drying [29] at high temeratures. In our experiments, the evaporation of the w

s well controlled such that no obvious drying was obsern the other hand, the coalescing procedure during curot readily reversible and the cross-linking procedure iseversible at all, so the reversible viscosity increase obsen this paint is not caused by drying or curing. Thus, thesults suggest that the viscosity increase is not caushe curing, but by the formation of structure in the painigher temperatures. This structure grows as the tempe

ncreases and grows faster at higher temperatures, formel. The paint can therefore be viewed as a two-phaseension with one phase being the structure and the oth

ng the remaining liquid. When temperature increasestructure grows with a trend to increased suspension vity and, on the other hand, the viscosity of the remaiiquid decreases with a trend to decreased suspensioosity. These two effects compete with each other anult in the first decrease and then increase in the visc


Fig. 3. Degree of thixotropy of the metallic basecoat at various temperatures.

of the paint. In contrast, the non-metallic basecoat does nothave the capability to form structure and therefore its vis-cosity decreases at high temperature following the Arrheniusrule.

3.4. Apparent yield stress

To further probe the network structure formed in the paint,the viscosity if plotted against the stress as shown inFig. 5.

At 10–20◦C, the viscosity decreases gradually with the ap-plied stress, showing the typical shear thinning behavior. Asthe temperature increases, the viscosity precipitates dramat-ically within a narrow stress range and then decreases grad-ually with stress. This sudden decrease of viscosity can beattributed to the breaking down of the network structure atthe apparent yield stress. This apparent yield stress is of-ten observed in flocculated suspensions at high particle load-ings when interactions between the particles are high enough


Fig. 4. Pseudo-steady-state viscosity of the metallic and non-metallicbasecoats: (a) steady shear viscosity vs. shear rate; (b) viscosities at shearrates of 0.03 and 600 s−1.

Fig. 5. Apparent yield stress at various temperatures of the metallic basecoat.

Fig. 6. Ford cup #4 measurement of the metallic basecoat.

to form continuous three-dimensional network structures[30].

3.5. Ford cup #4

It is common that in paint shops the Ford cups (or ISOcups) are used for quality control. The Ford cup is made upof a metal cup with an orifice at the bottom. The size of thecup and the orifice is standardized in the ASTM standards.The time for the fluid to flow through the orifice under gravityis an index of the viscosity. The Ford cup is a single-pointrheometer and is designed for Newtonian or near Newtonianfluids. However, due to its simple geometry and ease of use, itis still used for non-Newtonian waterborne coatings for qual-ity control. The Ford cup #4 measurements for the metallicbasecoat at different temperatures are showed inFig. 6. Themeasured time in seconds decreases when the temperatureincreases from 10 to 30◦C, and then increases from 35 to45◦C. Comparing the viscosities corresponding to the timein seconds with the measured steady shear viscosities, theFord cup #4 is estimated to be equivalent to a shear rheome-ter running at constant shear rate of about 200 s−1. As alsocan be seen that the trend of the Ford cup seconds is almostthe same trend as the steady-state viscosity at high shear ratecurve inFig. 4b.

It is worthwhile to mention that during the Ford cup mea-s ticityw paintw per-a vi-s paintt d tor undt e af-t d aniw of as

urement the phenomena of thixotropy and viscoelasas very obvious. When the temperature was low, theas just like a Newtonian liquid. When the sample temture was 45◦C, a marked viscosity increase could beually detected, as flow was considerable slower. Thehat flowed out from the Ford cup was collected and useedo the measurement immediately without rest. It was fohat the time measured dropped dramatically until stabler seven to eight times. The thixotropy must have playemportant role here. As a result, the seconds shown inFig. 6as the average from the first several measurementsample.


3.6. Identification of the network structure

In order to further investigate the nature of the structureand the fundamental reason for the increased viscosity at hightemperature in the metallic basecoat, we need to look into thecomposition of both basecoats. The thickeners are long chainsurfactants and they associate with the latex to increase theviscosity of the paint. Although the thickeners and acryliclatex may form microgels and generate non-Newtonian be-havior [15,31,32], the viscosities of suspensions containingmicrogels decrease with increasing temperature[17–19,32].The major difference in the composition between the metallicand non-metallic basecoats is that the former contains alu-minum flakes and the latter does not. Since the non-metallicbasecoat does not show this increased viscosity at hightemperature behavior, it is most likely that the aluminumflakes played an important role in forming the structure in themetallic basecoat. These disk-shaped flakes have an averagediameter of about 20�m and thickness of less than 1�m. Athigh temperatures, the size of the latex migrogels becomessmaller[32,33], so that the thickeners associates more withthe aluminum flakes. With the aid of the association, theseflakes interact with each other and form a three-dimensionalcontinuous network, just like the case when plate-like claysuspended in water[30]. The occurrence of this structuregreatly increases the elasticity and viscosity of the paint,a hears ed thes vior.Wa numfl foret morefl opyd micalp

4

allicw undt aturei cter-i re ath Thes paini ity atl . Theh 0a tt elvesa forma hichl thea to be

equivalent to a single-point rheometer with a shear rate ofabout 200 s−1 for the paint studied.

Acknowledgements

The authors would like to thank the Honda of AmericaManufacturing for providing the paint samples and financialsupport.

References

[1] K.D. Weiss, Paint and coatings: a mature industry in transition, Prog.Polym. Sci. 22 (1997) 203–245.

[2] Anon, Ind. Paint Powder 10 (1995) 8.[3] K.-F. Dossel, Globalization of waterborne coatings in the automotive

industry, SAE Technical Paper #982377, 1998, pp. 93–95.[4] C.B. Fox, SAE Technical Paper #910094, Society of Automotive

Engineers, SAE International, Warrendale, PA, 1991, pp. 1–10.[5] U. Kastner, The impact of rheological modifiers on water-borne coat-

ings, Colloids Surf. A (2001) 805–821.[6] T. Murakami, R.H. Fernando, J.E. Glass, The influence of binder

characteristics on the rheology of waterborne coatings containing hy-drophobically modified water-soluble polymers, Polym. Mater. Sci.Eng. 53 (1985) 540–544.

[7] R.N. Hildred, Acrylic additives for waterborne coatings, Polym. PaintColour J. 180 (4267) (1990) 579–583.

ter-226–

logy

[ lica-s ofand

[ ater-red to353.

[ aintorre-

[ con-rne

[ Eng.

[ lm-ater.

[ y for

[ ofhem.

[ paint

[ ring, in:A,

[ ch.

nd it is also the source of the yield stress. Under stress, the structure breaks and when the stress is relievtructure rebuilds, giving the basecoat a thixotropic behahen temperature drops, the latex microgels swell[32,33]

nd interact more with the thickeners, such that alumiakes lose the support from the thickeners and therehe structure collapses. As a result, the paint becomesuid-like, less viscous, and the yield stress and thixotrisappear. This whole process is determined by the cheroperties of the latex, thickener and aluminum flakes.

. Conclusions

The effect of temperature on the rheology of a metaterborne automotive basecoat is studied. It is fo

hat the degree of thixotropy increases as the temperncreases. The results of the linear viscoelastic charazation show that the paint possesses network structuigh temperatures, which leads to solid-like behavior.teady shear viscosity versus shear rate reveals that thes more shear thinning at high temperatures. The viscosow shear rate increases dramatically with temperatureigh shear viscosity decreases gradually from 10 to 3◦C,nd then increases gradually up to 45◦C. It is surmised tha

he aluminum flakes in the basecoat interact with themss well as other ingredients at high temperatures tocontinuous three-dimensional network structure, w

eads to increased elasticity, viscosity, thixotropy andppearance of yield stress. The Ford cup is estimated

t

[8] H. Nae, The effect of polymeric and clay thickeners on waborne coatings, Eur. Polym. Paint Colour J. 183 (4328) (1993)230.

[9] R.D. Athey, Additives for waterborne coatings. Part 3. Rheomodifiers, Eur. Coat. J. 6 (1996) 420–423.

10] S. Konishi, T. Nakaya, T. Ueda, Rheological properties and apption performance of the new water-borne paint, in: Proceedingthe 11th International Conference on Organic Coating ScienceTechnology, New Paltz, NY, 1985, pp. 129–144.

11] L.J. Boggs, D. Law, H. Taniguchi, Rheological parameters of wborne coatings. Material characteristics of these systems compacoatings with good flake orientation, Eur. Coat. J. 5 (1998) 350–

12] M. Osterhold, Rheological behavior of automotive psystems—modern characterization methods show good clations to observable effects, Eur. Coat. J. 4 (2000) 18–33.

13] R.H. Fernando, L.-L. Xing, J.E. Glass, Rheology parameterstrolling spray atomization and roll misting behavior of waterbocoatings, Prog. Org. Coat. 40 (2000) 35–38.

14] C.-F. Lu, Latex paint rheology and performance properties, Ind.Chem. Prod. Res. Dev. 24 (1985) 412–417.

15] S. Konishi, S. Umeda, Advanced rheology control during fiforming process of automotive waterborne basecoat, Polym. MSci. Eng. 66 (1992) 25–26.

16] B.G. Higgins (Ed.), Coating Fundamentals: Suspension RheologCoating, TAPPI Press, Atlanta, GA, 1997.

17] J.W. Kim, K.D. Suh, Viscosity properties for aqueous solutionurethane acrylate cationomer, J. Macromol. Sci. Pure Appl. CA35 (9) (1998) 1587–1601.

18] M. Osterhold, Rheological methods for characterizing modernsystems, Prog. Org. Coat. 40 (2000) 131–137.

19] D.J. Churella, M.M. Berman, A rheological method for measuskin formation in a latex and application to a coating problemIS&T’s 50th Annual Conference, Polaroid Corp., Waltham, MUSA, 1997, pp. 532–536.

20] H.A. Barnes, Thixotropy—a review, J. Non-Newtonian Fluid Me70 (1997) 1–33.


[21] C.W. Macosko, Rheology: Principles, Measurements, and Applica-tions, Wiley–VCH, 1993.

[22] M.I. Briceno, Rheology of suspensions and emulsions, in: F. Niel-loud, G. Marti-Mestres (Eds.), Pharmaceutical Emulsions and Sus-pensions, Marcel Dekker, 2000 (Chapter 16).

[23] G.N. Choi, I.M. Krieger, Rheological studies on sterically stabi-lized model dispersions of uniform colloidal spheres. II. Steady-shear viscosity, J. Colloid Interface Sci. 113 (1) (1986) 101–113.

[24] J. Rassing, D. Atwood, Ultrasonic velocity and light-scattering stud-ies of polyoxyethylene–polyoxypropylene–polyoxyethylene copoly-mer Pluronic F127 in aqueous solution, Int. J. Pharm. 13 (1983)47–55.

[25] M. Vadnere, G.L. Amidon, S. Lindenbaum, J.L. Haslam, Thermo-dynamic studies on gel–sol transition of some Pluronic polyols, Int.J. Pharm. 22 (1984) 207–218.

[26] K. Mortensen, J.S. Pedersen, Structural study on the micelle for-mation of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene

oxide) triblock-copolymer in aqueous solution, Macromolecules 26(1993) 805–812.

[27] P. Wang, T.P. Johnston, Kinetics of sol–gel transition for poloxamerpolyols, J. Appl. Polym. Sci. 43 (1991) 283–292.

[28] M.E. Rosenberger, Planning for waterborne basecoat technology forthe 1990s, SAE Technical Paper #930048, 1993.

[29] T. Provder, M.A. Winnik, M.W. Urban (Eds.), Film Formation inWaterborne Coatings, American Chemical Society, 1996.

[30] H. Van Olphen, An Introduction to Clay Colloid Chemistry,Wiley–Interscience, New York, 1963.

[31] H. Harakawa, A. Kasari, A. Tominaga, M. Yabuta, The rheologicalproperties of an aqueous acrylic dispersion suitable for automotivewaterborne basecoats, Prog. Org. Coat. 34 (1998) 84–90.

[32] H. Senff, W. Richtering, Temperature sensitive microgel suspensions:colloidal phase behavior and rheology of soft spheres, J. Chem. Phys.111 (4) (1999) 1705–1711.

[33] R. Pelton, Temperature-sensitive aqueous microgels, Adv. ColloidInterface Sci. 85 (2000) 1–33.

Documents

Temperature dependence of rheological behavior of a metallic automotive waterborne basecoat