Titania pigment particles dispersion in water-based paint films.

The distribution of titania pigment in dry water-based paint films in the presence of polymeric dispersants containing different functional groups was investigated. The polymeric dispersants chosen were polyacrylic acid and polyacrylamide homo- and copolymers modified with hydroxyl and/or carboxylate groups. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to assess the distribution of the titania pigment particles in the surface and bulk, respectively, of the paint films, which was then compared to the gloss and surface roughness of these films.

In the absence of dispersant, the pigment distribution in the paint film was not uniform and relatively large pigment aggregates appeared at the surface, resulting in a rough surface and low gloss value. All dispersants both decreased surface roughness and increased the gloss of the dry paint film, with the dispersant type considerably enhancing the pigment dispersion in the dry paint film, in agreement with results obtained in aqueous pigment suspensions. In the presence of polyacrylamide homopolymer, the paint gloss increased slightly and further increased with the hydroxyl-modified polyacrylamide copolymer. The paint gloss was highest in the presence of polyacrylic acid or carboxylate/hydroxyl-modified polyacrylamide.

Keywords: Titania pigment, polymeric dispersant, water-based paint, gloss, polymer functional group, dispersants, atomic force, scanning electron microscopy, pigments, drying, waterborne, physical properties

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Titania is one of the most important white pigments currently used in the world, with a total annual production capacity approaching five million tons. (1) Titania pigment is used widely in the paint, papermaking, plastic, cosmetic, and pharmaceutical industries due to its outstanding physicochemical properties. The paint industry is the largest titania pigment consumer, using nearly 60% of the global pigment consumption. (2) Statutory regulations restricting the use of organic solvents in paint formulations have led to increased interest and development of water-based formulations. To achieve the optimum visual and economical benefits of a pigment, the dispersion process is critical; the degree to which the pigment particles are dispersed is indeed a major factor in the quality and stability of the finished paint. (3) The level of pigment aggregation is observed to be higher in water-based paints than in similar conventional solvent-based paints. (4) Ionic dispersants, which are typically used to disperse titania pigment in water-based paints, provide electrosteric stabilization. (5) During the paint drying stage, water evaporation causes polarity of the system to decrease and, consequently, the ionized state of an ionic dispersant cannot be maintained. This process may therefore lead to a loss of stability, resulting in pigment particle aggregation during drying, which will affect paint optical properties such as gloss and opacity. Steric stabilization via nonionic dispersants is obviously not sensitive to pH or ionic strength changes. Polymeric dispersants that provide a combination of electrostatic and steric stabilization may therefore inhibit pigment aggregation in the dry state. It has also been reported previously that both electrostatic and steric stabilization is required in order to achieve the optimum pigment dispersion in inks used in jet printers. (6)

Polyacrylic acid and polyacrylamide are widely used as dispersants in mineral and material suspensions. The use of polyacrylic acid to disperse titania pigment is well established and documented. (4,7-10) Polyacrylamide copolymers have also been widely used to disperse mineral particles. (11-15)

Generally, water-based paints exhibit significantly lower gloss than solvent-based paints at equal levels of pigmentation in the dry film. Gloss is an important property of paint films and is influenced by the interaction between light and the film surface. The gloss of paint films is varied according to the degree to which they exhibit specular reflection, with the categories divided into full gloss, semigloss, eggshell, and flat. (16) The specular angle is the angle where the reflected light is equal to the angle of the incident light beam. In a solvent-based paint, the top micron of the dry film may contain little or no pigment, (17) but in water-based paints (or latex paints) both the resin and pigment particles may be present in the top layer, with an absence of a corresponding thin layer of pigment-free resin at the surface of the dry film. As the film shrinks with water loss, pigment particles may cause irregularities in the surface, causing roughness; therefore, less light is reflected by the film surface. Thus, pigment dispersion is very important in obtaining a high gloss water-based paint.

[FIGURE 1 OMITTED]

The adsorption mechanisms of polymeric dispersants of varying functionality on titania pigment particles and the effect of polymer adsorption on the dispersion of titania pigment particles in aqueous suspension have been investigated and discussed previously by the authors. (18-20) To enhance our understanding of pigment dispersion in paint formulations, it is also very important to understand pigment distribution in dry paint film, and to determine if any link exists between pigment dispersion in the wet and dry states. This approach is at the heart of this study.

Polymeric dispersants containing different anionic and nonionic functional groups have been carefully chosen for this study (Figure 1). The functional groups are acrylamide, hydroxyl, and carboxylate groups of varying densities. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and gloss measurements were used to assess the distribution of the titania pigment particles in the surface (AFM) and bulk (TEM) of the dry paint films as a function of the type of dispersant. The titania pigment particle size distribution in both the paint film surface and bulk was analyzed.

MATERIAL AND EXPERIMENTAL METHODS

Materials

The titania pigment sample used throughout this study was an aluminate- and zirconia-coated aluminum-doped rutile with a density of 4.1 g/[cm.sup.3]. The BET surface area of the pigment particles measured by [N.sub.2] adsorption was 19.0 [m.sup.2]/g. The mean diameter of the particles measured by TEM was 0.23 [+ or -] 0.02 [micro]m. The major surface elements determined by X-ray photoelectron spectroscopy (XPS) were Al, Ti, Zr, and O, as expected (19, 6, 0.6, and 74 at%, respectively, after removing the adventitious carbon contribution). The aluminate phase was dominated by the hydrated form, boehmite (AlOOH), as indicated by Auger parameters. (21) Boehmite has also been previously observed on titania pigment surfaces. (22) The pigment isoelectric point (iep) was at pH 7.8 [+ or -] 0.3.

The polymeric dispersants used were polyacrylic acid and modified polyacrylamides (Figure 1). Polyacrylic acid (Polymer A) was obtained from Sigma-Aldrich Corp., USA, as sodium salt. The polyacrylamide reagents (Polymer N, Polymer C, and Polymer H) were obtained through the courtesy of Cytec Industries, Inc., USA; Polymer N was a polyacrylamide homopolymer, Polymer H was a polyacrylamide copolymer modified with 10% hydroxyl groups, and Polymer C was an anionic polyacrylamide copolymer modified with 8% carboxylate and 10% hydroxyl groups. The molecular weights of the polymeric dispersants, measured using size exclusion chromatography relative to polyethylene glycol standards, were 13,600, 12,600, 17,000, and 13,100 g/mol for Polymer A, Polymer N, Polymer C, and Polymer H, respectively; values which are characteristic of dispersants used in the paint industry. The structure and physicochemical properties of the polymeric dispersant samples have been discussed previously. (18)

Materials used in the paint formulation were Primal RHA-184 (acrylic emulsion resin from Rohm and Haas, Australia), Acrysol RM-1020 (nonionic polyurethane associative rheology modifier from Rohm and Haas, Australia), Acrysol SCT-275 (hydrophobically modified ethylene oxide urethane block copolymer associative thickener from Rohm and Haas, Australia), propylene glycol (BDH Chemicals Ltd., England), Natrosol[R] Plus (modified hydroxylethyl cellulose from Hercules Incorporated, Aqualon Division, USA), Foamaster VL (antifoaming agent from Cognis Pty Ltd.), and Texanol (ester-alcohol from Eastman Chemical Co., USA).

High-purity water was produced by the following sequential treatment: reverse osmosis followed by two stages of mixed bed ion exchange, two stages of activated carbon treatment, and a final filtering step through a 0.22 [micro]m filter. The conductivity was less than 0.5 [micro]S/cm with a surface tension of 72.8 mN/m at 20[degrees]C. All other reagents used were analytical grade (unless otherwise stated).

Paint Preparation

Water-based paint samples were prepared using the formulation provided by the titania pigment manufacturer, as shown in Table 1. Five paint batches were made using the four polymeric dispersants, Polymer A, Polymer C, Polymer H, and Polymer N, and one without dispersant. A high-speed laboratory disperser (Sardik Engineering Pty Ltd., Australia) was used to prepare the mill base. The mill base preparation is a very important process of paint manufacturing; the primary objective of pigment milling is to incorporate pigment particles into a liquid vehicle to yield fine particle dispersions. The milling time of the titania pigment particles was assessed using a Hegman gauge to be acceptable after 25 min of high-speed dispersion, similar to that observed previously. (23)

Wet paint samples were applied to either a glass or cardboard substrate and spread to a thickness of 100 [micro]m using a film applicator (BYK Gardner, USA). The films were then allowed to dry at room temperature for 24 hr. The dry paint films were analyzed using gloss measurements, TEM (glass mounted), and AFM (cardboard mounted).

AFM

AFM was used to measure surface topography and to map the distribution of the various phases on the dry paint film surface using tapping (noncontact) and contact modes. A Digital Instrument Nanoscope III AFM was used in tapping mode with scan head E or Z for scanning areas of 10 x 10 and 60 x 60 [micro][m.sup.2], respectively. The scan rate was 0.5-1 Hz. The dry paint samples (flat cardboard mounted) were cut to a dimension of 1 [cm.sup.2] and put under the microscope using a metal holder.

TEM

A Philips CM100 TEM, operated at an accelerating voltage of 80 kV, was used for this study. Small slivers (approximately 5 mm by 0.5 mm) of the dry paint films were carefully removed from the glass using a razor blade. Each paint sliver was embedded in epoxy resin that was cured overnight at 70[degrees]C. Thin sections of the embedded paint films were cut from the resin with a diamond ultra-micro-tome knife. The thin sections were collected on carbon-coated, cellulose nitrate films supported on 200 mesh copper TEM grids. The thin section thickness was set at 0.2 [micro]m in order to minimize the disruption of the films by titania pigment particles being dragged out of the films using the diamond ultramicrotome knife.

RESULTS AND DISCUSSION

Pigment Volume Concentration

One of the most valuable and useful parameters to describe paint composition is the pigment volume concentration (PVC), which can be determined using equation (1) (24)

PVC = [V.sub.p]/[[V.sub.p] + [V.sub.b]] (1)

where [V.sub.p] is the volume of pigment and filler and [V.sub.b] is the volume of binder of a paint formulation. The higher the PVC value, the lower the content of polymer binder is within the paint formulation, and the higher the portion of pigment and filler particles. Thus, the PVC value strongly determines paint application properties, including gloss. (25) The average PVC value of the paint samples in this study was found to be 16.1%.

Coatings with PVC values below the critical pigment volume concentration (CPVC) tend to be glossy. (26) CPVC has been defined as the point in a pigment-vehicle system at which there is just sufficient binder to completely fill the interstices between randomly packed pigment particles after the volatilization of the thinner. (27) The CPVC value is inversely related to the pigment oil absorption (28)

CPVC = 1/[1 + OA] (2)

where OA is the oil absorption expressed in [cm.sup.3]/[cm.sup.3] (the volume of linseed oil adsorbed per unit volume of the pigment). The titania pigment sample oil absorption was found to be 0.88 [cm.sup.3]/[cm.sup.3] (density of linseed oil: 0.93 g/[cm.sup.3]), using the method developed by ASTM Interntaional. (29) Consequently, the CPVC value was found to be 53%. The PVC value of 16.1% obtained for the paint samples is therefore well below the calculated CPVC value.

Paint Film Analysis

AFM IMAGES: Figure 2 shows the AFM height images of the dry paint films (60 x 60 [micro][m.sup.2]) in the absence and presence of polymeric dispersant. The pigment distribution in the dry film was not uniform in the absence of polymeric dispersant and relatively large pigment aggregates randomly appeared at the surface. A similar situation, but to a lesser extent, was observed in the presence of Polymer N. The AFM images of the dry paint films in Figure 2 show more single pigment particles in the presence of Polymer H, Polymer A, and Polymer C, due to improved dispersion. The distribution of the titania pigment particles, whether discrete or as small aggregates, was relatively homogeneous for Polymer A and Polymer C; however, more pigment aggregates and clusters were detected when using Polymer H or Polymer N. This diversity in pigment distribution was reflected by macroscopic paint film properties, as will be discussed later in the gloss measurements section, with higher gloss observed for Polymer C and Polymer A. Interestingly, similar behavior has been observed previously in the study of rheology and particle size of titania pigment particles in aqueous suspension, in the absence and presence of the polymeric dispersants. (19)

[FIGURE 2 OMITTED]

In the measurement of pigment particle size and size distribution at the dry paint film surface, a total of 30 AFM images were analyzed using analySIS software (Soft Imaging System). The average pigment particle diameter ([d.sub.av]), standard deviation values ([sigma]), and [D.sub.50] values of pigment particles in the dry paint film are presented in Table 2. A higher pigment particle size was observed in Table 2 in the absence of polymeric dispersant. In general, the particle size values indicate that in the presence of polymeric dispersant the pigment became less aggregated. The pigment particle size decreased slightly in the presence of Polymer N; however, it decreased significantly more when Polymer H was present. In the presence of Polymer A or Polymer C, the pigment particle size was greatly reduced due to electrostatic, in the wet state only, and steric stabilization. (20) The standard deviation value was large in the absence of dispersant, indicating a large distribution of pigment aggregate sizes at the paint film surface; this distribution was reduced in the presence of polymeric dispersant.

In order to compare the size distributions of pigment particles at the dry paint film surface in the presence of polymeric dispersants, the particle size range values were plotted as a function of the normalized frequency count in Figure 3. It is observed clearly in Figure 3 that, in the absence of polymeric dispersant, a broad particle size distribution occurred at the dry paint film surface, with a particularly high number of pigment aggregates larger than 3 [micro]m and a relatively low number of single particles (the primary pigment particle size was 0.23 [+ or -] 0.02 [micro]m). The number of single particles increased slightly in the presence of either Polymer N or Polymer H, but greatly increased in the presence of Polymer A or Polymer C. In general, the number of large pigment aggregates (> 3 [micro]m) at the dry paint film surface decreased by using polymeric dispersant, with the lowest aggregate number observed when Polymer A or Polymer C was used. Polymer H had less effect on reducing the pigment aggregate size when compared to Polymer A or Polymer C, and the least effect was observed for Polymer N. The dominant primary pigment particle size of 0.20-0.25 [micro]m was clearly observed in the presence of Polymer A or Polymer C.

[FIGURE 3 OMITTED]

In addition to AFM height imaging, images of the paint film surface using AFM tapping mode phase imaging were obtained due to differences in the viscoelastic properties of the various phases in the film. (30) Figure 4 shows AFM phase images of the paint film surfaces, clearly indicating the two different phases in the paint film, comprising the titania pigment particles and the polymer resin. The presence of both pigment particles and polymer resin at the surface of water-based paint films is a result of the dominant film formation mechanisms, unlike solvent-based paint films which contain only polymer resin, as discussed earlier. In the absence of polymeric dispersant or in the presence of Polymer H or Polymer N, pigment aggregation and the tendency for the pigment particles to protrude from the surface were clearly visible. However, in the presence of Polymer C or Polymer A, the number of pigment aggregates was reduced and the pigment particles were distributed more uniformly at the paint film surface.

SURFACE ROUGHNESS: The root-mean-square roughness ([R.sub.rms]) and the maximum peak-to-valley ([Z.sub.max]) of the 60 x 60 [micro][m.sup.2] dry paint film surfaces, measured by contact mode AFM, are given in Table 3. Images such as those presented in Figure 2 were used to derive the values shown in Table 3. [R.sub.rms] values were calculated using (31)

[R.sub.rms] = [square root of ([N.summation over (i=1)][([Z.sub.i] - [Z.sub.ave]).sup.2]/N)] (3)

where [Z.sub.ave] is the average height value within the given area, [Z.sub.i] is the current height value, and N is the number of points within a given area.

[FIGURE 4 OMITTED]

In the absence of polymeric dispersant, the paint film surface was rough in comparison to the values observed in the presence of polymeric dispersants. The paint film roughness decreased slightly in the presence of Polymer N and decreased significantly more when Polymer H was used. The paint film surface roughness was further reduced in the presence of Polymer A; however, Polymer C provided the lowest paint film surface roughness. The same trend was observed for the two parameters, [R.sub.rms] and [Z.sub.max].

[FIGURE 5 OMITTED]

GLOSS MEASUREMENTS: Table 3 also shows the gloss values of the paint films, measured with a Sheen Tri Microgloss 160 (Sheen Instruments Ltd., UK) 24 hr after their preparation at a light incidence angle of 60[degrees]. Table 3 clearly shows that the paint gloss was higher in the presence of polymeric dispersant. Gloss is known to be an indicator of the degree of pigment dispersion. (32) Typically, gloss of a paint film decreases with an increase in the pigment aggregate size. (33) In the presence of polyacrylamide homopolymer (Polymer N), the paint gloss increased slightly, possibly due to steric stabilization provided by the adsorbed polyacrylamide dispersant. When polyacrylamide modified with hydroxyl groups (Polymer H) was used, the gloss further increased due to the presence of polymer hydroxyl groups, providing increased steric stabilization. Similar pigment stabilization phenomena have been observed in the wet state through rheological investigations. (20) In the presence of polyacrylic acid containing 100% carboxylate groups (Polymer A) and polyacrylamide modified with carboxylate and hydroxyl groups (Polymer C), the paint gloss significantly increased. However, Polymer C provided the highest dry film paint gloss due to stabilization imparted and retained by the presence of both the hydroxyl and carboxylate functional groups during drying, confirming the observations from the AFM images.

[FIGURE 6 OMITTED]

The inverse correlation of the paint film gloss with the surface roughness values is shown in Figure 5. A similar influence of surface roughness on the paint film gloss (34) and reflectance from polymer surfaces (35) has been reported previously.

TEM THIN SECTION ANALYSIS: Surface analysis techniques alone are not sufficient enough to obtain all information regarding pigment dispersion in dry paint films. TEM analysis of the dry paint film cross-sections were undertaken to obtain the distribution of pigment particles in the bulk of the paint film. Figures 6-8 show the cross-sectional TEM images of the dry paint film in the absence and presence of polymeric dispersant, at various magnification values. Titania pigment particles appear black in the images due to their relatively high electron density. The cross-sectional TEM images at lower magnification (Figure 6) show that the dry film thickness was 50 [+ or -] 5 [micro]m. In general, no settling of pigment particles within the paint films was observed in the TEM images in the presence of Polymer A, Polymer C, or Polymer H, in contrast to the results reported previously. (36) Tiarks et al. (36) observed, by TEM and AFM analysis, that during the paint film formation large pigment aggregates were not located at the water-based paint film-air interface, as they tend to settle and, hence, only smaller clusters or isolated pigments stayed at the film surface. However, in the current study, pigment aggregate settling was only observed in the absence of polymeric dispersant and in the presence of Polymer N (Figure 6).

The TEM images clearly show that the pigment distribution within the dry paint film was highly affected by the type of polymeric dispersant. These images, especially at higher magnification (Figure 8), indicate that incorporation of either Polymer A or Polymer C improved pigment dispersion in the bulk of the dry paint film.

The pigment size distribution within the dry paint films was analyzed as a function of pigment particle mean diameter with the analySIS software using 50 TEM images at a magnification similar to those presented in Figure 7. The average pigment particle diameter ([d.sub.av]), standard deviation values ([sigma]), and [D.sub.50] values of the pigment particles in the bulk of the dry paint film are presented in Table 4. The particle size values decreased in the presence of polymeric dispersants, indicating less particle aggregation. Polymer A and Polymer C were the most effective in reducing the pigment particle size, followed by Polymer H and Polymer N. The standard deviation values show how widely the pigment aggregate sizes were spread within the paint film bulk, and how the particle size changed due to the presence of polymeric dispersant. The measured standard deviation also shows how a narrower pigment particle size distribution can be achieved in the presence of either Polymer A or Polymer C. The greater dispersion performance of Polymer A versus Polymer C within the dry paint film was similar to that observed in alkaline aqueous pigment suspensions, (19) suggesting that the pigment dispersion behavior within dry paint film is similar to that obtained in wet aqueous pigment suspensions.

In order to compare the size distributions of pigment aggregates within the dry paint film, the values of particle size range were plotted versus the normalized frequency count as a function of the type of polymeric dispersant (see Figure 9). It is observed clearly that in the absence of polymeric dispersant, a broad particle size distribution occurred within the dry paint film, with a particularly high number of pigment aggregates larger than 2 [micro]m and a minimal number of single particles; as stated previously, the primary pigment particle size was 0.23 [+ or -] 0.02 [micro]m. The number of larger pigment aggregates within the dry paint film decreased in the presence of polymeric dispersant, particularly when Polymer A or Polymer C were used. In the presence of Polymer A or Polymer C, the pigment particles were largely present as discrete particles. In general, the number of large pigment aggregates (> 2 [micro]m) within the dry paint film decreased by using polymeric dispersant, with the lowest number of aggregate observed when Polymer A or Polymer C were used. Polymer H had less effect in reducing the number of pigment aggregates in comparison to Polymer A or Polymer C, and minimal effect was observed for Polymer N. The dominant primary pigment particle size of 0.2-0.3 [micro]m was clearly observed in the presence of Polymer A or Polymer C.

[FIGURE 7 OMITTED]

In addition to the values obtained in the analysis of the TEM images of the dry paint film, a relationship between neighbor pigment particles is important in particle dispersion characterization. (37) The nearest neighbor distribution gives an indication of the particle dispersion. (38) The dry paint film TEM images were further analyzed using analySIS software, as a function of distance between pigment particle centers and their nearest neighbors. The distance between pigment particles and their neighbors within the paint films are shown in Figure 10, as a function of the type of polymeric dispersant. Larger nearest neighbor distances indicate better dispersion. The results confirm that Polymer N had little effect on the distribution of titania pigment particles in the dry paint film, while Polymer H had a moderate effect, and both Polymer A and Polymer C provided the largest dispersion of the pigment particles.

[FIGURE 8 OMITTED]

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

CONCLUSIONS

The dispersion of titania pigment particles in dry paint film was assessed using AFM, TEM, and gloss measurements. The combination of surface and bulk microscopic analysis, combined with optical property measurements, provided a detailed and complementary picture of dry film pigment dispersion properties.

The type of polymeric dispersant considerably affected the pigment dispersion in the dry paint film. In the absence of polymeric dispersant, the pigment distribution in the dry paint film was not uniform both within and at the surface of the paint film, with relatively large pigment aggregates randomly appearing at the surface, resulting in a rough film surface and, consequently, providing a low gloss. A similar situation, but to a lesser extent, was observed in the presence of Polymer N (polyacrylamide homopolymer). When Polymer H (hydroxyl-modified polyacrylamide) was present, the paint surface was slightly smoother and the gloss increased because of greater pigment dispersion both within and at the paint film surface. Polymer A (polyacrylic acid) or Polymer C (polyacrylamide modified with carboxylate and hydroxyl functional groups) provided the best titania pigment dispersion in the dry paint film, resulting in a smooth and glossy surface. Polymer C provided the highest dry paint film gloss, which is likely due to, initially, electrostatic stabilization in the aqueous pigment dispersion, and then, ultimately, to steric stabilization from the multiple polymer functional groups present.

Interestingly, the pigment dispersion behavior in the dry state is similar to that obtained previously for alkaline aqueous pigment dispersions or the wet state. (18-20)

ACKNOWLEDGMENTS

The authors gratefully acknowledge Mr. Caelum Brice from the R & D division of Solver Paints (Adelaide, Australia) for providing the opportunity and facilities for paint formulation preparations.

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Saeed Farrokhpay, Gayle E. Morris,** and Daniel Fornasiero -- University of South Australia*

Peter Self -- University of Adelaide ([dagger])

* Ian Wark Research Institute, Mawson Lakes, SA 5095, Australia.

([dagger]) Adelaide Microscopy, Adelaide, SA 5005.

** Author to whom correspondence should be addressed. Author currently at Victoria University, Melbourne, Vic, 8001; fax: + 61 3 9687 2089; email: [e-mail].

Table 1 -- Water-Based Paint Formulation

           Material              Weight (g)  Volume (ml)

Mill Base

 1         Propylene glycol       15          14.5
 2         Water                  15          15
 3         Ammonia                 0.5         0.6
 4         Polymeric dispersant    2           2.5
 5         Foamaster VL            1           1.1
 6         Acrysol RM-1020         4           3.8
 1-6       were mixed in a stainless steel vessel and then 7 was added
             under low speed stirring.
 7         Titania pigment        75          18.5

The mill base was dispersed for 25 min at 4500 rpm. The following
materials then were added to the mill base, referred to as "letdown".

Letdown

 8         Water                   6           6
 9         RHA-184               220         210
10         Texanol                 5           5.4
11         Propylene glycol        1           1
12         Foamaster VL            0.2         0.25
13         Acrysol SCT-275         0.2         0.2
14         Premixed Natrosol in    5           5
             water (4 wt%)
Total                            350         284
Nonvolatile component             56%         45%
Titania pigment component         22%          6.5%
pH                                 9.5

Table 2 -- Average Pigment Particle Diameter ([d.sub.av]), Standard
Deviation ([sigma]), and [D.sub.50] Values of Pigment Particles at the
Dry Paint Film Surface (from AFM Measurements)

Polymeric      [d.sub.av]  [sigma]  [D.sub.50]
Dispersant     (nm)        (nm)     (nm)

No Dispersant  1100        1900     510
Polymer N      1060        1700     470
Polymer H       890        1400     440
Polymer C       720        1000     400
Polymer A       730        1000     380

Table 3 -- Root-Mean-Square Roughness ([R.sub.rms]), Maximum
Peak-to-Valley ([Z.sub.max]), and Gloss Values of the Dry Paint Film
Samples Measured After 24 hours (from AFM Measurements)

Polymeric      [R.sub.rms]  [Z.sub.max]  Gloss
Dispersant     (nm)         (nm)         ([+ or -] 1 unit)

No Dispersant  180          1080         36
Polymer N      170           950         43
Polymer H      140           720         50
Polymer C       92           420         66
Polymer A      110           480         60

Table 4 -- Average Pigment Particle Diameter ([d.sub.av]), Standard
Deviation ([sigma]), and [D.sub.50] Values of Pigment Particles in the
Bulk of the Dry Paint Film (from TEM Measurements)

Polymeric      [d.sub.av]  s     [D.sub.50]
Dispersant     (nm)        (nm)  (nm)

No Dispersant  430         440   340
Polymer N      430         400   320
Polymer H      410         350   310
Polymer C      350         260   290
Polymer A      320         230   280