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Evaluating sag resistance with a multinotched applicator: correlation with surface flow measurements and practical recommendations.

Abstract Sag is a coating defect that results from excessive, gravity-driven flow after deposition. Accordingly, characterizing resistance to sag is critically important. In this paper, sag resistance predicted using a multinotched applicator test is compared with results obtained using an in situ particle tracking technique that measures surface velocity. Four commercial latex paints dried on substrates inclined at three angles were investigated. The results are used to provide insight into the strengths and limitations of using a multinotched applicator to evaluate sag resistance. For coatings dried on vertical surfaces (90[degrees]), the suggested condition for the multinotched applicator, sag lengths found by particle tracking show differences between paints that the multinotched applicator ranked as identical. At smaller angles (e.g., 10[degrees]), the resolution of the multinotched applicator test is greatly enhanced owing to a reduction in the shear stress difference between adjacent coated lines. Based on these results, specific recommendations are made for successfully employing a multinotched applicator to evaluate sag resistance based on user-specific goals.

Keywords Sag resistance, Anti-Sag Meter, Anti-Sag Index, Particle tracking, Latex paint

Introduction

Efficiently controlling the sag resistance of a coating is pivotal to the success of many coating processes. Sag is a coating defect that results from excessive, gravity-driven flow. (1) This flow can cause unsightly accumulation of coating at substrate edges (2) or accentuate imperfections in the substrate itself. (3) In extreme cases of nonuniform flow, fingering instabilities (4) or drips (5) can also occur. In practice, sag is a concern for any liquid-based coating process operated at a nonzero angle, including dip-coating and inclined roll-to-roll processes. (6) Coatings prepared with a baking step are also susceptible to sag if the decrease in viscosity with temperature is significant. (2) The ubiquity of these processes and their susceptibility to sag illustrate why controlling and evaluating sag resistance are critically important.

Many techniques capable of evaluating sag resistance have been proposed. For example, Overdiep (7) used a force transducer to monitor sag via mass flow in his "sagging balance," while Colclough et al. (8) devised a purely rheological method, simulating shear stresses representative of brushout conditions in a rheometer and correlating subsequent movement of the upper plate with viscosity development after coating application. However, a majority of techniques have been visually oriented. Wu's (9) "indicator method" (also employed by Croll et al. (5)) quantifies sag by measuring the distance that a colored indicator band flows during drying. Distinctness of image measurements have also been correlated with varying extents of sag. (10) More recently, Bosma et al. (11,12) measured sag using a "falling wave" technique, where the motion of artificially induced surface waves during flow was tracked. Song (13) and Lade et al. (14) monitored sag in real time and in situ using Lycopodium spores, particles which sit on the coating surface during drying and enable surface flow tracking via optical microscopy. All of these visual techniques quantify sag via a sag length, defined as the total distance the coating surface flows from the beginning to the end of processing. (5,10)

More qualitative visual techniques, emphasizing simplicity, have also been developed with the goal of standardizing a test procedure for evaluating sag resistance. These techniques typically fall into one of two categories, either involving sag in (1) a single (approximately) constant thickness film (15,16) or (2) a series of coated lines with varying thicknesses. (17,18) Of all these techniques, the most generally accepted is that involving the Anti-Sag Meter (18,19) (Fig. 1). This multinotched applicator is used to coat a series of increasingly thick parallel lines onto a substrate and information on sag resistance is extracted from the degree to which each line merges with (i.e., sags into) the line below it. These results are used to assign an Anti-Sag Index to the coating, defined as the clearance of the largest gap on the applicator that produces the coated line which does not merge with the line below it. (20) This technique has been adopted as the ASTM standard test for sag resistance (ASTM test D4400). (20)

In spite of its popularity, few studies have compared results obtained from an Anti-Sag Meter with other means of sag measurement. Miller et al. (21) measured the sag resistance of several high-solids polyester coatings using both the Anti-Sag Meter and a qualitative air-spraying method, the latter of which was designed to simulate the actual coating conditions to which the coatings were subjected. It was noted that the two methods did not agree well, the disagreement being attributed to the inability of the Anti-Sag Meter to simulate the actual coating situation. In separate reports published by ASTM (22) and Leneta, (18) the Anti-Sag Meter method is compared to a qualitative "brushout test." In a typical brushout test, a wet film is applied to a vertical substrate and then some of the coating is manually wiped off, producing coating-free lines. Sag resistance is then subjectively rated based on how the coating flows back into this coating-free region over time. (17) While both studies concluded that the Anti-Sag Meter was more precise and sensitive than the brushout method, more research is needed to compare the Anti-Sag Meter test with other tests that are more quantitative and involve more practical coating situations.

In this paper, sag resistance as evaluated with an Anti-Sag Meter is compared to that measured using particle tracking with Lycopodium spores, an in situ and quantitative measurement technique. (14) Anti-Sag Indices of several commercial latex paints were measured, and sag lengths corresponding to these Anti-Sag Indices were measured using particle tracking. The primary goal of this comparison is to provide insight into the strengths and limitations of the Anti-Sag Meter test and its results. This comparison serves as the first instance, to the authors' knowledge, of a direct comparison between the Anti-Sag Meter test and an explicitly quantitative measurement of sag. We show that while the Anti-Sag Meter test is capable of qualitatively evaluating sag resistance, its sensitivity is limited with respect to coatings of similar sag resistance. Specifically, coatings with the same Anti-Sag Index do not necessarily display the same sag resistance when coated as continuous, thin films. However, we show that running the test at smaller angles may help remedy this issue by decreasing the shear stress difference between adjacent coated lines. Ultimately, this work provides a more robust framework for interpreting the Anti-Sag Meter test results as well as recommendations for using a multinotched applicator to most effectively evaluate sag resistance based on user-specific goals.

Experimental

Materials

Four water-based latex paints were evaluated: Behr Marquee Interior, Behr Premium Plus: Paint & Primer in One, Behr Premium Plus: Interior Ceiling (Behr Process Corp., Santa Ana, CA), and Glidden Interior Premium (Glidden Co., Strongsville, OH), which will henceforth be referred to as paints A, B, C, and D, respectively. Each had a flat sheen and was white in color. Prior to application, each paint was stirred thoroughly for at least 30 s. The density of each paint was determined by measuring the mass of a 1-mL syringe filled with each paint. This measurement was repeated at least three times for each paint.

Anti-Sag Meter testing

Anti-Sag Indices were measured with a Leneta Anti-Sag Meter (ASM-4: Medium Range, Leneta Co. Inc., Mahwah, NJ). This multinotched applicator (Fig. 1) contains 11 notches with gaps spanning 4-24 mil in increments of 2 mil, with each notch 1/4" wide and separated by 1/16" spacings. A syringe was used to place approximately 10 mL of freshly stirred paint onto the substrate: a piece of glass (14 x 28 [cm.sup.2]) cleaned with distilled water and acetone. The applicator was then drawn across the substrate at 6.0 in/s using an automatic drawdown machine (Paul N. Gardner, Co., Pompano Beach, FL). This resulted in a series of 11 evenly spaced coated lines. After coating, substrates were promptly positioned at the desired angle and left to dry at room conditions (23 [+ or -] 1[degrees]C, 51 [+ or -] 5% relative humidity). Angles of 10[degrees], 45[degrees], and 90[degrees] from the horizontal were tested. After drying, samples were visually inspected and rated for an Anti-Sag Index. Per the guidelines specified by ASTM (20) and Leneta, (18-19) the Anti-Sag Index was designated as the largest notch clearance producing a coated line that did not sag into the line below it. Fractional Anti-Sag Indices, which are recommended for increased precision, (18-19) were not used as no fractional merging was observed; that is, all lines were observed to either merge completely or not at all with the line below them. Anti-Sag Indices were assigned based on results in the middle of the glass substrate, at least 5 cm from each edge.

Rheological characterization of latex paints

The viscosity of each paint was measured using an ARG2 stress-controlled rheometer (TA Instruments, New Castle, DE) and a stainless steel cone and plate geometry (40 mm diameter, 2[degrees] cone angle). Viscosity was measured (Fig. 2a) by stepping shear stress from 300 to 0.01 Pa, and the values presented in Fig. 2a represent "equilibrium" viscosities recorded after two consecutive 5 s sampling periods reported values within 5% of one another. Measurement times at each shear stress ranged from 15 to 60 s, with an average time of 24 s. Measurements were taken at 23[degrees]C, and temperature was controlled with a Peltier plate. A plastic cover was placed around the geometry to minimize evaporation. To confirm that evaporation did not impact the measurements, results were compared with those obtained using concentric cylinders (C30, DIN standard): a geometry inherently less susceptible to evaporation. Results from both geometries were in agreement.

Viscosity change with time under constant stress was also evaluated (Fig. 2b). Paints were first sheared for 60 s at 500 [s.sup.-1], after which it was confirmed that each paint had reached a constant viscosity. Each paint was then subjected to a constant stress of 1.5 Pa for 300 s. After approximately 100 s, each paint exhibited a steady increase in viscosity. These rates of increase were 0.037, 0.025, 150, and 0.24 Pa x s/s for paints A, B, C, and D, respectively. Negligible wall slip for all rheological measurements was verified using sandpaper-coated parallel plates. (23)

Sag length, initial wet film thickness, and evaporation rate measurements

Coatings were applied on oxygen plasma-treated silicon substrates (34 x 34 [mm.sup.2], 533 [+ or -] 9 [micro]m thick) using an adjustable gap blade coater (Teflon Microm II, Paul N. Gardner Co., Pompano Beach, FL). Sag lengths were measured via surface particle tracking, per the procedure described in reference (14). Briefly, Lycopodium spores (Duke Scientific, Palo Alto, CA) were sprinkled onto the paint film surface after coating, and the substrate was then placed on an inclined, heated drying stage (Fig. 3) immediately after coating. Particle tracking was performed at an incline of 10[degrees], 45[degrees], or 90[degrees]. A digital optical microscope (KH-7700 with MX(G)-5040Z zoom lens and mid-range adapter, 50-400 x magnification, Hirox USA, Hackensack, NJ) was used to track spore motion at the coating surface. Spore velocity during drying was then calculated using images from the microscope and ImageJ software (v1.410, NIH) with a particle tracker and detector plug-in. (24) The recorded surface velocities, vs, were integrated over time, t, to calculate sag length, [l.sub.sag], as defined in the Introduction:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], (1)

where time 0 is defined as the moment the coated substrate is inclined.

Initial wet film thicknesses and evaporation rates were estimated with an optical technique and setup described in reference (14). Briefly, the focal plane of a digital optical microscope (Hirox KH-7700 with MX(G)-10C zoom lens and OL-140(II) optical lens, 140-1400 x magnification) was first focused and zeroed at the substrate surface prior to coating. Then, after coating, the focal plane was refocused onto bubbles visible at the coating/air interface. By monitoring the position of this interface over time with a precision stepper motor ([+ or -] 0.1 [micro]m), initial film thicknesses and evaporation rates could be measured. The blade coater gaps (Table 2) for coating (including those for particle tracking) were chosen to coincide with the Anti-Sag Indices of each coating or one notch (2 mil) above this value. All particle tracking experiments and thickness and evaporation rate measurements were conducted at room conditions (23 [+ or -] 1[degrees]C, 51 [+ or -] 5% relative humidity).

Results

Anti-Sag Indices for each paint are reported in Table 1 for three different angles. While this test is typically carried out on vertical surfaces (90[degrees]), it seems that the integrity of the test is maintained in testing at smaller angles. As expected, the Anti-Sag Index of paint C (the ceiling paint) is the highest, maxing out the Anti-Sag Meter at both 10[degrees] and 45[degrees]. The other three paints exhibited the same Anti-Sag Index at the two largest angles, 45[degrees] and 90[degrees], while at 10[degrees] their measured Anti-Sag Indices were different. Across all of the paints, there is a general trend of decreasing Anti-Sag Index with increasing angle.

Each Anti-Sag Index in Table 1 was then correlated with a sag length determined using particle tracking experiments at analogous initial film thicknesses and angles. For example, at 45[degrees] for paint A, the blade coater gap was set to 10 mil and a corresponding sag length was measured as described in the "Experimental" section. These results comprise the first data set in Fig. 4, shown as closed circles. Particle tracking experiments were also carried out at coating thicknesses and angles corresponding to one notch (2 mil) above the Anti-Sag Index. For example, at 45[degrees] for paint A, the blade coater gap was set to 12 mil. These results comprise the second data set in Fig. 4, shown as open circles. It was assumed that thicknesses coated by the Anti-Sag Meter at a certain gap were the same as those coated by the blade coater at the same gap.

Measured sag lengths range from 0 mm (recorded in several instances for paint C) to over 8 mm. While, on average, measured sag length increases with angle, this trend is neither uniformly observed among each data set nor among each individual paint. Average sag length increases with the angle for the first data set (corresponding to the Anti-Sag Index), whereas a maximum average sag length is observed at 45[degrees] for the second data set (corresponding to one notch above the Anti-Sag Index). Similarly, Paints C and D both exhibited a steady increase (or no change) in sag length with increasing angle for both data sets, while Paint A exhibited a maximum at 45[degrees] for both data sets. Paint B exhibited a unique trend, where the first data set in Fig. 4b exhibited a minimum sag length at 45[degrees], while the other exhibited a maximum at the same angle.

Measured initial wet film thicknesses corresponding to the coatings in Table 1 and Fig. 4 are presented in Table 2 along with the calculated initial shear stresses at the substrate and wet film densities for each paint. Measured sag lengths reported in Fig. 4 are also reproduced in Table 2 for clarity. Measured initial wet film thicknesses range from 110 to 329 [micro]m and shear stresses range from approximately 0.5 to 5 Pa, with the largest values in both categories being associated with Paint C. Measured evaporation rates are not reported in Table 2 because there was no observed significant difference between values, regardless of thickness or paint. The average measured evaporation rate for all samples in Table 2 was 9.3 [micro]m/s, with a standard deviation of only 0.9 [micro]m/s (less than 10% of the average), indicating that the paints all exhibit similar drying behavior.

Discussion

The results show that the ceiling paint, paint C, exhibited the highest Anti-Sag Index, but the relative sag resistances of the other paints (A, B, and D) are less obvious. To facilitate analysis, Fig. 5 shows Anti-Sag Indices and the corresponding sag lengths compiled according to inclination angle. Beginning with 90[degrees], the inclination angle called for by both Leneta (18,19) and ASTM, (20) Fig. 5a shows that paints A, B, and D all exhibited the same Anti-Sag Index of 8 mil at 90[degrees], yet their measured sag lengths are distinctly different. In particular, the sag length measured for paint B is more than three times larger than that measured for the other two paints. This observed disparity can be attributed to the combined effect of several factors. First, as Fig. 2b reveals, the viscosity of each paint exhibits a different time dependence. Specifically, at a shear stress representing that present in each coating when inclined at 90[degrees] (1.5 Pa), viscosity in paints A and D rises approximately 50% and 850% faster, respectively, than it does in paint B. This is under conditions of no drying; these thixotropic differences may be even more pronounced with evaporation present. Second, Paint B possesses a larger initial wet film thickness: 127 [micro]m compared to ~110 [micro]m for both paints A and D. This difference arises from the unique rheological properties of each paint, which have a direct influence on the exact wet film thickness obtained at a given blade gap. (25) Although this thickness difference does not contribute to significant differences in shear stress, it still has a pronounced impact on total sag because surface velocity is a strong function of film thickness, h (i.e., [v.sub.s] ~ [h.sup.2] for Newtonian solutions and [v.sub.s] ~ [h.sup.n], where n > 2, for shear thinning fluids. (9)) Lastly, given equivalent evaporation rates, the solids fraction (and hence viscosity) of a thinner coating increases more rapidly than it does in a thicker coating, assuming that the viscosities of these latex solutions exhibit similar dependencies on solids fraction. The concomitant effect of these factors is that paint B flows for a longer duration before sag becomes arrested, compared to the flow times observed in paints A and D. On average, paint B exhibited a measureable (>0.1 [micro]m/s) surface velocity for approximately 300 s, while paints A and D stopped flowing after approximately 170 s. From equation (1), this longer flow duration can contribute to a much larger overall sag length.

The possibility of different paints possessing the same Anti-Sag Index while exhibiting different characteristic sag lengths may present a problem for users of the Anti-Sag Meter. To the Anti-Sag Meter (when employed at 90[degrees]), paints A, B, and D appear equivalent. Yet, a substitution of one for the other in a practical application could be unacceptable. Similarly, with three Anti-Sag Indices of 8 mil, judging which paint, if any, is ideal for a given application is impossible. The same issue arises at 45[degrees], as revealed in Fig. 5b, where paints A, B, and D all exhibit identical Anti-Sag Indices of 10 mil. Additionally, while the measured sag lengths still do not match at 45[degrees], it is now paint A that exhibits the largest value, nearly double that for either paint B or D. This trend again parallels the measured initial wet film thicknesses in each paint, as Table 2 shows.

One issue with using the multinotched applicator approach to assess sag resistance is that it sets up a binary ranking system: a coated line either has or has not sagged into the line below it. While fractional Anti-Sag Indices can be assigned for the incomplete merging of lines, (19) there is no simple way to assign a more precise ranking once lines have completely merged. For example, upon careful analysis of the test results at 90[degrees], the 10 mil line for paint B clearly flowed very completely into the 12 mil line. Oppositely, the same line for paint A appeared to just barely merge with the 12 mil line below it. According to the test, this means that both have an Anti-Sag Index of 8 mil at 90[degrees]. Particle tracking, conversely, permits sag to be evaluated on a continuous spectrum via sag length.

A potential means to improve the resolution of the Anti-Sag Meter arises from an analysis of the shear stress interval between lines coated by adjacent notches on the Anti-Sag Meter. For a given applicator and coating combination, this stress increase scales with sin([theta]), where [theta] is the testing angle. For a coating liquid with a density of 1 g/[cm.sup.3], the difference in maximum shear stress at the substrate between adjacent coated lines is approximately 0.25 Pa. At 45[degrees], this stress difference is still 71% of what it is at 90[degrees]. But at 10[degrees], the difference is only 17% of what it is at 90[degrees], 0.04 Pa. These differences are illustrated in Fig. 6.

From Fig. 5c, it is clear that this smaller shear stress gap between adjacent lines allows the test to have a higher resolution, as subtle differences in the sag resistance of each paint appear. Instead of three Anti-Sag Indices of 8 or 10 mil, the test yields values of 16, 15, and 20 mil for paints A, B, and D, respectively. This permits the paints to now be ranked in order of sag resistance: C > D > A > B. This ranking can be compared to the ranking predicted using sag lengths obtained from particle tracking. As an example, consider coatings for each paint coated with a 17 mil blade coater gap. From Table 2, the anticipated ranking is C > D > A > B, assuming that when coated with a 17 mil gap, paint C would still not flow and paint D would flow at least a small amount. While this one example cannot guarantee the accuracy of the Anti-Sag Meter at small angles, it at least demonstrates the enhanced utility of the test over results obtained at 90[degrees].

Based on the above analysis, the following recommendations (summarized in Table 3) are made for those using multinotched applicators to evaluate sag resistance. First, if one wishes to identify an approximate initial film thickness range for obtaining a sag-free coating with a specific material, it is recommended to run the test at the angle of intended application. While the Anti-Sag Index cannot be associated with a particular sag length using these results, the average sag lengths measured at each angle are on the same order as the threshold considered acceptable for sagging. Several sources (9,10) cite this threshold as occurring at 1 mm of sag length, while the averages at 10[degrees], 45[degrees], and 90[degrees] are 0.66, 0.67, and 2.4 mm, respectively. Because the Anti-Sag Index at one angle cannot be used to easily predict its value at another angle, it is recommended to match the testing angle to the angle anticipated to be used in practice. Second, when checking for consistency in sag resistance between multiple batches of the same coating, the smallest permissible angle is recommended for maximum resolution.

Lastly, to rank multiple coatings on the basis of sag resistance, the smallest permissible angle is again recommended. The specific value of this angle should be set by the most sag resistant coating; larger angles are required to obtain results for very sag resistant coatings. Alternatively, multinotched applicators with larger gaps can be employed. If two coatings being ranked produce the same Anti-Sag Index, the test can be repeated with just those two coatings at a smaller angle for increased resolution. Formulators wishing to apply this ranking to coatings destined for application on vertical surfaces should find that Anti-Sag Meter rankings of sag resistance obtained at smaller angles correspond well with sag behavior on vertical surfaces, with the additional benefit of increased resolution. This increased resolution can explain sagging anomalies that would otherwise be unexpected from running the Anti-Sag Meter test at only 90[degrees] (e.g., the results of Fig. 5a, as discussed above).

Summary

The process of measuring sag resistance with a multinotched applicator was explored and analyzed, with a specific focus on the Leneta Anti-Sag Meter. This technique was evaluated with respect to its strengths and limitations by comparing sag results obtained from four commercial latex paints. Anti-Sag Indices of these paints were first determined using the Anti-Sag Meter, and corresponding sag lengths were then measured using an in situ particle tracking technique. This comparison permitted the Anti-Sag Meter to be directly compared with a quantitative measure of sag resistance.

It was found that when the Anti-Sag Meter test is run on vertical surfaces (90[degrees]), the difference in stress between adjacent coated lines is large. This limits the maximum attainable resolution of the test. Specifically, it resulted in three of the four paints tested exhibiting the same Anti-Sag Index. By repeating the test at 10[degrees], it was shown that the smaller shear stress difference between adjacent coated lines enhances the resolution of the Anti-Sag Meter test. This permitted the sag resistance of the above-mentioned three paints to be distinguished. Ultimately, a set of recommendations was formulated based on these results, intended to guide users of multinotched applicators.

DOI 10.1007/s11998-015-9680-5

R. K. Lade Jr., A. D. Musliner, C. W. Macosko, L. F. Francis ([mail])

Department of Chemical Engineering & Materials Science, University of Minnesota, 421 Washington Ave. SE, Minneapolis, MN 55455, USA

e-mail: lfrancis@umn.edu

R. K. Lade Jr.

e-mail: ladex010@umn.edu

A. D. Musliner

e-mail: musli002@umn.edu

C. W. Macosko

e-mail: macosko@umn.edu

Acknowledgments The authors thank the industrial supporters of the Coating Process Fundamentals Program (CPFP) of the Industrial Partnership for Research in Interfacial and Materials Engineering (IPRIME) for supporting this research. The authors extend their gratitude to Keith Kirkwood at The Valspar Corporation in Minneapolis, Minnesota, for providing an Anti-Sag Meter and for insightful discussions regarding its use. The authors would also like to thank Wieslaw Suszynski for designing the inclined drying stage and for many helpful discussions.

References

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(3.) Schwartz, LW, Eley, RR, "Flow of Architectural Coatings on Complex Surfaces; Theory and Experiment." J. Eng. Math, 43 153-171 (2002)

(4.) Troian, SM, Herbolzheimer, E, Safran, SA, Joanny, JF, "Fingering Instabilities of Driven Spreading Films." Europhys. Lett., 10 25-30 (1989)

(5.) Croll, SG, Kisha, LW, "Observations of Sagging in Architectural Paints." Prog. Org. Coat., 20 27-52 (1992)

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(7.) Overdiep, WS, "The Effect of a Reduced Solvent Content of Solventborne Solution Paints on Film Formation." Prog. Org. Coat., 14 1-21 (1986)

(8.) Colclough, M, Smith, NDP, Wright, TA, "A Low Shear Viscometer: An Instrument for Measuring Flow and Sag Resistance in Coatings." J. Oil Col. Chem. Assoc., 63 183-193 (1980)

(9.) Wu, S, "Rheology of High Solid Coatings. I. Analysis of Sagging and Slumping." J. Appl. Polym. Sci., 22 2769-2782 (1978)

(10.) Frisch, HL, Scopazzi, C, "Sag Equation for Coatings on Rotating Substrates." J. Appl. Polym. Sci., 43 1067-1070 (1991)

(11.) Bosma, M, Brinkhuis, R, Coopmans, J, Reuvers, B, "The Role of Sag Control Agents in Optimizing the Sag/Leveling Balance and a New Powerful Tool to Study This." Prog. Org. Coat., 55 97-104 (2006)

(12.) Bosma, M, Brinkhuis, R, Rensen, E, Watson, R, "A New Method for the Quantitative Determination and Prediction of Sag and Levelling in Powder Coatings." Prog. Org. Coat., 72 26-33 (2011)

(13.) Song, J-O, "In Situ Characterization of Dynamic Structures of Coatings." Ph.D. Dissertation, University of Minnesota Twin Cities, Minneapolis (2012)

(14.) Lade Jr., RK, Song, J-O, Musliner, AD, Williams, BA, Kumar, S, Macosko, CW, Francis, LF, "Sag in Drying Coatings: Prediction and Real Time Measurement with Particle Tracking." Submitted to Prog. Org. Coat., 86 49-58 (2015)

(15.) Patton, T, "A Simple Pigment-Settling Gage and A Simple Anti-Sag Test." Off. Dig. Fed. Paint Varn. Prod. Clubs, 29 10-25 (1957)

(16.) Hancock, HE, "Description and Evaluation of the Kansas City Club Sag Tester." Off. Dig. Fed. Paint Varn. Prod. Clubs, 29 1086-1093 (1957)

(17.) Reynolds, W, Larson, E, "New Tool for Evaluating Sagging of Paint." Paint Varn. Prod., 48 31-34 (1958)

(18.) Schaeffer, L, "Design of an Improved Sag Tester." Off. Dig. Fed. Soc. Paint Technol., 34 1110-1123 (1962)

(19.) Leneta Co. Catalog No. 6--Revised, "Test Charts & Test Equipment for the Paint and Coatings Industry," Leneta Co., Mahwah, p. 35 (2014)

(20.) ASTM Standard D4400-99(2012)el, 2012, "Standard Test Method for Sag Resistance of Paints Using a Multinotch Applicator," ASTM International, West Conshohocken, DOI: 10.1520/D440-00R12E01, www.astm.org (2012)

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Table 1: Anti-Sag Indices of latex paints

                                 Anti-Sag Index (a) (mil)

Paint ID       10[degrees]          45[degrees]        90[degrees]

A           16 [+ or -] 2        10                   8
B           15 [+ or -] 4        10 [+ or -] 2        8
C           [greater than or     [greater than or     22 [+ or -] 2
              equal to] 24 (b)     equal to] 24 (b)
D           20 [+ or -] 3        10                   8

(a) Avg. of at least 3 runs. If no error reported, all runs
yielded same Anti-Sag Index

(b) No sag detected at largest gap on Anti-Sag Meter

Table 2: Coating parameters for paint films and
corresponding sag lengths

                             Gap                            Initial
Paint      Density                         Inclination  thickness (a,b)
ID      (g/[cm.sup.3])  (mil)  ([micro]m)     angle       ([micro]m)

A       1.34 [+ or -]    16      406.4     10[degrees]  222 [+ or -] 17
             0.01        18      457.2     10[degrees]  234 [+ or -] 9
                         10      254.0     45[degrees]  143 [+ or -] 6
                         12      304.8     45[degrees]  162 [+ or -] 23
                          8      203.2     90[degrees]  110 [+ or -] 11
                         10      254.0     90[degrees]  143 [+ or -] 6
B       1.39 [+ or -]    15      381.0     10[degrees]  214 [+ or -] 1
             0.01        17      431.8     10[degrees]  255 [+ or -] 17
                         10      254.0     45[degrees]  133 [+ or -] 39
                         12      304.8     45[degrees]  183 [+ or -] 12
                          8      203.2     90[degrees]  127 [+ or -] 14
                         10      254.0     90[degrees]  133 [+ or -] 39
C       1.40 [+ or -]    24      609.6     10[degrees]  321 [+ or -] 16
             0.01        26      660.4     10[degrees]  329 [+ or -] 12
                         24      609.6     45[degrees]  321 [+ or -] 16
                         26      660.4     45[degrees]  329 [+ or -] 12
                         22      558.8     90[degrees]  269 [+ or -] 35
                         24      609.6     90[degrees]  321 [+ or -] 16
D       1.39 [+ or -]    20      508.0     10[degrees]  286 [+ or -] 5
             0.03        22      558.8     10[degrees]  309 [+ or -] 6
                         10      254.0     45[degrees]  138 [+ or -] 12
                         12      304.8     45[degrees]  168 [+ or -] 23
                          8      203.2     90[degrees]  111 [+ or -] 3
                         10      254.0     90[degrees]  138 [+ or -] 12

                             Gap                 Shear
Paint      Density                             stress (c)
ID      (g/[cm.sup.3])  (mil)  ([micro]m)         (Pa)

A       1.34 [+ or -]    16      406.4     0.51 [+ or -] 0.04
             0.01        18      457.2     0.54 [+ or -] 0.02
                         10      254.0      1.3 [+ or -] 0.06
                         12      304.8      1.5 [+ or -] 0.2
                          8      203.2      1.4 [+ or -] 0.1
                         10      254.0      1.9 [+ or -] 0.1
B       1.39 [+ or -]    15      381.0     0.51 [+ or -] 0.01
             0.01        17      431.8     0.61 [+ or -] 0.04
                         10      254.0      1.3 [+ or -] 0.4
                         12      304.8      1.8 [+ or -] 0.1
                          8      203.2      1.7 [+ or -] 0.2
                         10      254.0      1.8 [+ or -] 0.5
C       1.40 [+ or -]    24      609.6     0.77 [+ or -] 0.04
             0.01        26      660.4     0.78 [+ or -] 0.03
                         24      609.6      3.1 [+ or -] 0.4
                         26      660.4      3.2 [+ or -] 0.1
                         22      558.8      3.7 [+ or -] 0.5
                         24      609.6      4.4 [+ or -] 0.2
D       1.39 [+ or -]    20      508.0     0.68 [+ or -] 0.02
             0.03        22      558.8     0.73 [+ or -] 0.02
                         10      254.0      1.3 [+ or -] 0.1
                         12      304.8      1.6 [+ or -] 0.2
                          8      203.2      1.5 [+ or -] 0.1
                         10      254.0      1.9 [+ or -] 0.2

                             Gap                  Sag
Paint      Density                             length (b)
ID      (g/[cm.sup.3])  (mil)  ([micro]m)        (mm)

A       1.34 [+ or -]    16      406.4      1.2 [+ or -] 0.2
             0.01        18      457.2      1.2 [+ or -] 0.2
                         10      254.0      1.3 [+ or -] 0.5
                         12      304.8      2.1 [+ or -] 0.2
                          8      203.2     0.89 [+ or -] 0.2
                         10      254.0      1.5 [+ or -] 0.7
B       1.39 [+ or -]    15      381.0     0.77 [+ or -] 0.3
             0.01        17      431.8      1.4 [+ or -] 0.1
                         10      254.0     0.70 [+ or -] 0.3
                         12      304.8      6.6 [+ or -] 0.4
                          8      203.2      3.2 [+ or -] 0.3
                         10      254.0      3.6 [+ or -] 1.4
C       1.40 [+ or -]    24      609.6             0
             0.01        26      660.4             0
                         24      609.6             0
                         26      660.4      6.7 [+ or -] 0.6
                         22      558.8      4.6 [+ or -] 0.9
                         24      609.6      8.7 [+ or -] 0.9
D       1.39 [+ or -]    20      508.0     0.31 [+ or -] 0.1
             0.03        22      558.8     0.79 [+ or -] 0.1
                         10      254.0     0.62 [+ or -] 0.4
                         12      304.8      1.8 [+ or -] 0.8
                          8      203.2     0.73 [+ or -] 0.1
                         10      254.0      2.2 [+ or -] 0.6

(a) Initial wet film thickness

(b) Uncertainty based on standard deviation of at
least three measurements

(c) Initial shear stress at the substrate

Table 3: Recommendations for multinotched applicator usage

Goal                                 Recommendation

Identify approximate             Run test at angle of
  initial thickness range          intended application
  for sag-free coating
Check for consistency in         Run test at smallest
  sag resistance between           permissible angle
  batches of the same coating
Rank sag resistance of           Run test at smallest
  different coatings               permissible angle.
                                   Repeat with sample
                                   subsets as necessary


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Please note: Some tables or figures were omitted from this article.
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Author:Lade, Robert K., Jr.; Musliner, Austin D.; Macosko, Christopher W.; Francis, Lorraine F.
Publication:Journal of Coatings Technology and Research
Article Type:Report
Geographic Code:1USA
Date:Sep 1, 2015
Words:5816
Previous Article:Introduction to the special issue: 2015.
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