Characterization of adhesion performance of topcoats and adhesion promoters on TPO substrates.

Adhesion of organic coatings to thermoplastic olefin (TPO) substrates in automotive applications has been an issue for makers of automotive parts since TPO was first used in exterior applications, primarily fascia. A widely used technique for assuring paint adhesion to TPO is the use of adhesion promoter primers based on chlorinated polypropylenes (CPO). Much research has been focused on understanding the forces involved at the interfaces of substrate, adhesion promoter, and topcoats resulting in the adhesion or the loss of adhesion in various environmental conditions. This study correlates the adhesion performance of CPO and nonchlorinated adhesion promoters (NCPO) as measured by peel strength with properties observed through microscopy techniques. Adhesion performance of CPOs, NCPOs, and blends are quantified through the use of 90[degrees] and 180[degrees] peel strength studies. Surface characteristics of adhesion promoters applied over a TPO substrate and cured at various temperatures are examined through the use of atomic force microscopy (AFM).

Keywords: CPO, atomic force microscopy, differential scanning calorimetry, peel testing, adhesion promoters, adhesion, automotive--OEM, plastics, and thermoplastic olefins

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In the mid-1970s, the replacement of steel by plastics in exterior automotive applications was well begun in all regions of the world. The promise that plastics would revolutionize exterior styling was still some years away from realization, but the inclusion of plastic parts in automotive exteriors was by then taken for granted as a part of the automotive build. By this time it was clear to paint formulators that coatings for automotive plastics brought unique challenges that were different from those presented by coatings for steel. Adhesion and environmental aging on different plastics were, and still are, among the greater challenges. Since that time, paint formulators and coatings engineers have had to deal with the challenges of decorating mixed substrates to create a uniform appearance. Engineering properties that differ from plastic to plastic and from plastic to steel create challenges for paint technologies that sometimes are determined by temperature tolerances of the substrates and by final performance properties of different paint technologies.

One engineering thermoplastic that grew in exterior automotive applications at a tremendous rate from the mid-1980s through 2000 is rubber-filled polypropylene known as thermoplastic olefin, referred to as TPO in North America and as PP-EPDM in Europe and Asia. Today, changes in the plastic technology make the more general term, TPO, applicable to any engineering thermoplastic based on polypropylene modified with rubber. Advantages of TPO as a material for bumpers and fascia include impact resistance, recyclability, and cost. A disadvantage of TPO decoration is its inherently poor paint adhesion. This obstacle to paint performance is overcome by several techniques. The most popular techniques can be grouped into mechanical techniques, to oxidize the substrate and make it adherent to paint, and into adhesion promoter techniques, where a chemical adhesion promoter is either applied to the substrate before the coating or added into the paint.

The term adhesion has several meanings in terms of coatings performance. The consumer's expectation is that the paint on the car will never get damaged or be removed, regardless of the environmental exposure conditions. This expectation can be called "performance adhesion" to distinguish it from the concept of adhesion. Coatings engineers and formulators understand that this consumer expectation of performance adhesion must be translated into specific performance, in tests that coatings systems must endure. The term performance adhesion can then refer to adherence of the paint to the substrate, after all kinds of environmental bombardment. Adhesion can refer to adherence of the paint to the substrate immediately after application, after exposure to water or steam, after exposure to gasoline, insect repellant, or any of hundreds of consumer chemicals, during and after scratching, after exposure to sunlight, heat, and cold, and on and on. The goal of so much work on paint adhesion to TPO is to gain an understanding of adhesion mechanisms. Understanding performance adhesion under specific test conditions can lead to improvement of the adhesion promotion systems.

[FIGURE 1 OMITTED]

The typical adhesion promoter for paint on TPO and polypropylene substrates is based on a chlorinated polypropylene resin (CPO). The CPO is usually combined with other resins that provide flow properties and some resistance properties. A conductive pigment is added to allow electrostatic application of the color coat. Consideration of the structure of CPO leads to the widely accepted hypothesis that dispersion forces between the nonpolar polypropylene backbone on the CPO and the nonpolar polypropylene substrate are sufficient enough to promote their interaction, while the dipole interactions between chlorine and acid groups in the coating layer provide the strong interaction that binds the coating layer to the TPO substrate. (Figure 1).

[FIGURE 2 OMITTED]

During the early 1990s, several studies were targeted for the development of an understanding of adhesion mechanisms for CPO primers on TPO and polypropylene. (1-5,7-13) A summation of the results of these studies leads to the conclusion that CPO entangles itself into the polypropylene matrix. Another conclusion that can be drawn from the various studies is that adhesion performance, and even the mechanism of adhesion, is strongly influenced by the total coating composition that includes the polypropylene substrate, CPO, adhesion promoter, and chemistry of the topcoat.

Clemens (1) used electron spectroscopy for chemical analysis (ESCA) and ToFSIMS to look for the attached chlorine on the CPO molecule after adhesion failure was induced. This work indicated that a preponderance of chlorine was observed on the underside of the lifted topcoat with little chlorine observed on the substrate after failure. This suggested that the induced failure occurred at the substrate-CPO interface. Further analysis of microtomed slices of the coating system revealed the presence of chlorine that had migrated into the topcoat. Further studies using similar analytical techniques found evidence for CPO entanglement with the polypropylene matrix.

Studies designed to lead to an understanding of the mechanism of adhesion are most often flawed by the fact that the failure mechanism is critically dependent on the loading geometry used during testing and the subsequent stresses developed to cause an adhesion loss. Therefore, the resulting mechanism for adhesion loss that is developed will depend on the test conditions. Studies using fluorescence tags have provided a nondestructive method for analyzing adhesion. A series of studies using fluorescence have shown that in many systems the CPO can be found to have penetrated microns into the substrate. Initial studies by Ryntz (10) using fluorescent dyes that were mixed with CPO solutions made with various solvents showed that the solvent system can have an effect on the extent of swelling of the rubber-rich TPO layer and, therefore, how amenable this layer becomes to CPO migration. Further studies with CPO containing a fluorescent tag covalently attached to it suggested that the CPO can migrate microns deep into certain TPOs. (6,11) Figure 2 illustrates the effect of heat-induced CPO penetration and substrate wetting by the CPO using CPO containing a covalently attached fluorescent tag, as observed with confocal fluorescent microscopy and atomic force microscopy (AFM).

The current study is aimed at furthering our understanding of performance adhesion mechanisms through a correlation of adhesion performance, as measured by peel strength, with other properties of the adhesion promoter system observed using microscopy techniques.

EXPERIMENTAL

Adhesion Promoters Investigated

In this study, performance properties of four chlorinated polyolefin adhesion promoters (CPO1, CPO2, CPO3, CPO4), two nonchlorinated adhesion promoters (NCPO1, NCPO2), and five blends of CPO1/NCPO1 at various solid ratios were evaluated. The ratios of CPO1:NCPO1 investigated were approximately 9:1, 4:1, 1:1, 1:4, and 1:9, on a solids basis. The analytical properties of the adhesion promoters are shown in Table 1. The chlorinated polyolefins that were investigated varied in chlorine content, molecular weight, acid number, crystallinity, and glass transition temperature ([T.sub.g]). The nonchlorinated polyolefin adhesion promoters varied only in functionality. The CPO1/NCPO1 blends varied in chlorine content, molecular weight, functionality, crystallinity, and [T.sub.g].

Percent chlorine for the CPOs was measured by X-ray fluorescence (Spectro-Asoma model 200T instrument). The percent chlorine for the CPO1/NCPO1 blends were calculated by taking the weight percent of CPO1 in the blend and multiplying it by the chlorine level of CPO1 (21.1%). The molecular weights of the adhesion promoters were determined using gel permeation chromatography (GPC, Perkin-Elmer LC 600 Autosampler, Perkin-Elmer Series 200 LC pump, Perkin-Elmer Series 200 Refractive Index Detector). The acid number of the adhesion promoters was determined by potentiometric titration using a Metrohm autotitrator. The titration was monitored using a glass pH indicating electrode and a reference electrode. The titrant used was 0.1N ethanolic KOH. The acid number results are reported as a range (low, medium, or high). The heat of fusion ([DELTA][H.sub.f]) and glass transition temperature(s) ([T.sub.g]s) were determined through the use of differential scanning calorimetry (TA Instruments Dual Sample 2920 Auto DSC with a liquid nitrogen-cooling accessory). Two heating scans were used. The [DELTA][H.sub.f] was measured as the area under the melting peak ([T.sub.m]) from the first heating scan, while the [T.sub.g] was measured from the second heating scan. The first heating scan defines the intrinsic properties of the sample as supplied, while the second heating scan defines inherent properties of the sample.

90[degrees] and 180[degrees] Peel Strength Studies

Peel strength performance properties of the adhesion promoters listed in Table 1 were determined through the use of a universal tensile tester. In this study, Sequel 1440 TPO panels were wiped with isopropyl alcohol, dried, and coated with each of the adhesion promoters shown in Table 1. The adhesion promoters air-dried and were then topcoated with a 1K white melamine-cured basecoat/1K melamine-cured clearcoat system. Duplicate panels were prepared and tested for each substrate/adhesion promoter/topcoat system and for each method (90[degrees] and 180[degrees]). Upon application of the clearcoat, a clear mesh polyester fabric (14) was embedded into the clearcoat upon preparation of the panels. The coated panels were baked for 40 min at 250[degrees]F and aged for approximately one week before testing. The fabric was then connected to a universal tensile tester and 90[degrees] and 180[degrees] peel strengths of the substrate/adhesion promoter/topcoat systems were then determined.

A pull rate of two inches per minute was used for both the 90[degrees] and 180[degrees] methods. A similar method for determining 90[degrees] peel strengths of various adhesion promoters was employed by Kondos and Mayo. (15) For the 180[degrees] peel strength method, the panel holder was rotated 90[degrees] such that the angle between the substrate and the mesh tape at the point of separation was 180[degrees]. The average peel strength was determined for each substrate/adhesion promoter/top-coat system by taking numerous data points over a given distance through the use of a computer software program. The average peel strength determined by the computer program is the average load required to pull the mesh tape from the substrate as a function of extension divided by the width of tape pulled (one inch). The peel strength data points used to determine the average peel strengths were taken after the load applied appeared to equilibrate. The reported average peel strength was calculated from duplicate panels, along with standard deviations.

Microscopy Studies

In order to gain a better understanding of the role of surface topography and nanoscale surface roughness on the CPO1, NCPO1, and CPO1/NCPO1 blend peel strengths, atomic force microscopy-based phase imaging was employed. The CPO1, NCPO1, CPO1/NCPO 9:1, CPO1/NCPO1 1:1, and CPO1/NCPO1 1:9 blends were analyzed directly on panels after application and after baking at 80[degrees] and 120[degrees]C.

PREPARATION OF SUBSTRATES:

* Each of the adhesion promoters described above were spray-applied at 5% solids in toluene, over three 2 X 6 in. Sequel 1440 TPO panels.

* One panel was baked at 176[degrees]F for 40 min and cooled to room temperature. A second panel was baked at 250[degrees]F for 40 min and then cooled to room temperature, while the third panel from the triplicate set was air-dried at room temperature.

* An AFM was used to examine the surfaces of each of the adhesion promoter-coated substrates.

SURFACE IMAGING AND SURFACE ROUGHNESS MEASUREMENTS: All surface imaging and surface roughness measurements were obtained using an AFM Dimension series D3000 AFM (Digital Instruments, Santa Barbara, CA). Probes used for analysis were obtained from Nanodevices, Multi 75, with spring constants 5 N/m, resonant frequencies of 75 kHz and tip radius < 10 nm. AFM-based tapping mode phase imaging was employed in order to provide morphological information and crystalline morphologies. Contrast variations and phase images have been shown to differentiate crystalline from amorphous regions in growing spherulites. (16) Darker regions in phase images correspond to amorphous polymer domains while lighter areas are indicative of crystalline chain fold spherulitic structures. The results are displayed in figures as height and phase images. In each of the figures, the left-hand image indicates the height profile, where lighter regions are indicative of peaks and darker areas represent low-lying valleys. The right-hand images in the figures are phase images whose contrast relates to surface viscoelasticity and microhardness. Lighter regions are therefore relatively hard, while darker regions are softer. Image data were recorded as both height and phase modes. Height and force modulation images were recorded simultaneously during scanning. Surface roughness analysis was also performed on panel surfaces by measuring root-mean-square surface roughness (RMS). The RMS measure is based on the following equation:

RMS = [[y.sub.[1.bar].sup.2] + [y.sub.[2.bar].sup.2] + [y.sub.[3.bar].sup.2] ... [y.sub.[N.bar].sup.[2.bar]][.sup.1/2]]/N (1)

where y is the z, or height values of each image point, and N is the total number of points within a given image.

RESULTS AND DISCUSSION

90[degrees] and 180[degrees] Peel Strength Studies

The 90[degrees] and 180[degrees] peel strength properties of the adhesion promoters, listed in Table 1, are shown in Table 2. Results in Table 2 show that, of the CPOs tested, CPO1 and CPO2 had the highest average 90[degrees] peel strengths. For the 90[degrees] method, CPO3 showed the lowest peel strength of the CPOs tested (approximately 2.7 lb/in. less than CPO1 and CPO2). CPO3 also had low minimum peel strength in the 90[degrees] method, which suggests that the average peel strength reported may not be a representative number due to the irregularities in the peel strength curve (load versus extension). For the 180[degrees] method, there were slight differences in the peel strengths of the CPOs tested. Interestingly, CPO3 showed better performance in the 180[degrees] method versus the 90[degrees] method. The reasons for this phenomenon are not completely understood, although it is expected that the different forces applied to the substrate/adhesion promoter/topcoat systems in the different peel methods are likely to contribute to the differences. The composition of adhesion promoters may also play a role in these differences. For the NCPOs studied, NCPO1 showed the highest peel strength, which was approximately two times the peel strength of NCPO2 in both the 90[degrees] and 180[degrees] methods. Unlike the CPOs tested, NCPOs displayed very small differences in 90[degrees] and 180[degrees] peel strengths. When comparing CPOs with NCPOs, CPOs 1 and 2 had higher peel strengths than the best NCPO (NCPO1), but CPO3 had a lower 90[degrees] peel strength than NCPO1. The CPO1/NCPO1 blends showed peel strengths approaching the peel strengths of CPOs 1 and 2 in both the 90[degrees] and 180[degrees] methods. Interestingly, even blends containing high levels of NCPO1 showed peel strengths similar to CPOs 1 and 2. Overall, these results correlate well with adhesion and humidity testing reported in a previous study.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

Microscopy Studies (CPO1, NCPO1, and CPO1/NCPO1 Blends)

EFFECT OF SURFACE ROUGHNESS ON PEEL STRENGTH: Table 3 summarizes RMS surface roughness averages for CPO1, NCPO1, CPO1/NCPO1 9:1, CPO1/NCPO1 1:1, and CPO1/NCPO1 1:9 adhesion promoters applied to Solvay Sequel 1440 TPO panels. Each roughness value represents the average of three randomly selected images, 25 X 25 [micro]m.

For the adhesion promoters listed in Table 3, correlation analysis was used to explore relationships between peel strength and surface roughness of the adhesion promoter surfaces as applied and after exposing the adhesion promoters to elevated temperatures (Table 4).

Table 4 shows a significant correlation between peel strength (for both 90[degrees] and 180[degrees] peel) and roughness as applied (air-dry). Peel strength and surface roughness, after the adhesion promoters were exposed to elevated temperatures, did not correlate very well. One possible reason for this observation may be due to the fact that the topcoat system is applied to the adhesion promoters before exposure to elevated temperatures, and this surface, i.e., the asapplied surface, is expected to exert the greatest influence on the wetting and adhesion of the topcoat to the adhesion promoter surface, since this is the interfacial surface. Upon application of the topcoat, subsequent heating and curing may promote improved interaction between the adhesion promoter and the topcoat.

[FIGURE 5 OMITTED]

The high negative correlation between surface roughness as applied and peel strength indicates that peel strength decreases with increasing surface roughness as applied. Fuller and Tabor (17) also demonstrated surface roughness effects on adhesion for rigid poly(methyl methacrylate) (PMMA) in contact with rubber surfaces. Specific surface morphologies associated with CPO1 and NCPO1 from Table 3 follow.

AFM-based height and phase images for CPO1 are shown in Figure 3. Such images indicate a high degree of crystallinity, as evidenced by the high brightness displayed by phase images. The left-side image in Figure 3 is a top-view or height image that contains topographic information for a CPO1 adhesion promoter, as applied on a TPO panel, while the right-side image is a phase image which shows the crystalline domains (white features) in the form of nanometer-sized nodular domains on surfaces. This chlorinated polyolefin (CPO1) provided very good adhesion properties and had the highest peel strength of the adhesion promoters listed in Table 3. In comparison, AFM characterization of NCPO1, with the lowest peel strength of the adhesion promoters listed in Table 3, is shown in Figure 4. NCPO1 displays some spherulitic structures and remnants of lamellae, but mostly amorphous domains distributed over the surface.

A plot of peel strength (90[degrees] peel force) versus surface roughness is shown in Figure 5. Samples are identified according to the scheme shown in Table 3, and provide a graphical representation of the surface roughness effect, as applied, on peel strength. The following equation describes ([R.sup.2] = 0.72) the observed relationship between peel strength (90[degrees] peel) and surface roughness, as applied, for the adhesion promoters listed in Table 3.

EFFECT OF RMS PHASE IMAGING ON PEEL STRENGTH: In order to explore possible roles played by surface crystallinity and/or surface amorphous content on peel strength, phase imaging was employed. Correlation analysis was used to explore possible relationships among peel strength, surface roughness, and phase image contrast (crystallinity). Differential scanning calorimetry (DSC)-based crystalline heat of fusion ([DELTA][H.sub.f]) measurements on adhesion promoter resins was also included in this analysis in order to provide an alternate measure of degree of crystallinity.

Table 5 provides further evidence for the importance of surface crystallinity, as measured by RMS phase, on peel strength by the positive correlation coefficient (0.64); however, crystalline heats of fusion provided the best correlation with peel strength (0.81). The importance of surface crystallinity on peel strength is further supported by the high correlation (0.90) that resulted between RMS phase and heat of fusion ([DELTA][H.sub.f]), as measured by DSC. Furthermore, the very high negative correlation (-0.99) between surface roughness and [DELTA][H.sub.f], and the high positive correlation (0.81) between [DELTA][H.sub.f] and peel strength, support the necessity for surface crystallinity for improved peel strength properties for this set of adhesion promoters (Table 3). Crystallinity effects on peel strength were also discussed by Aoki, (7) who studied structural effects on bonding strengths between chlorinated isotactic polypropylene and isotactic polypropylene.

CONCLUSIONS

Historically, investigations into the mechanism of paint adhesion to TPO under various performance conditions have led to useful understanding of the adhesion mechanisms of CPO-based adhesion promoters and the development of improved adhesion performance. The current study furthers that understanding by providing a correlation of adhesion performance as measured by peel strength with properties observed through microscopy techniques.

The chlorinated polyolefins (CPO) investigated varied in chlorine content, molecular weight, acid number, crystallinity, and [T.sub.g]. Nonchlorinated adhesion promoters (NCPO) that were investigated varied only in functionality. Surface analysis of TPO coated with CPO1, NCPO1, and their blends (9:1, 1:1, and 1:9), after curing at various temperatures by AFM, showed a significant correlation among peel strength and surface roughness of the as-applied adhesion promoters. Phase imaging and correlation analysis showed significant relationships among peel strength, surface roughness, and crystallinity, as determined by both phase image contrast and DSC for CPO1, NCPO1, and their blends. A significant positive correlation was observed between surface crystallinity and crystallinity, as determined by DSC, with peel strength for the adhesion promoters tested.

Table 1 -- Analytical Properties of Adhesion Promoters

Adhesion       % Chlorine  % Chlorine    Molecular
Promoter         (XRF)     (Calculated)  Weight ([M.sub.n])  Acid #

CPO1            21.1           NA           26,520           Low
CPO2            20.2           NA           11,760           Medium
CPO3            27.5           NA           12,620           Medium
CPO4            29.4           NA           13,090           Low
NCPO1           NA             NA           12,980           High
NCPO2           NA             NA           11,220           High
CPO1/NCPO1      NA             18.3         27,400           Low
Blend 1 (9:1)
CPO1/NCPO1      NA             16.6         27,300           Medium
Blend 2 (4:1)
CPO1/NCPO1      NA             10.1         25,020           Medium
Blend 3 (1:1)
CPO1/NCPO1      NA              3.9         17,030           High
Blend 4 (1:4)
CPO1/NCPO1      NA              1.9         14,770           High
Blend 5 (1:9)

Adhesion       [DELTA][H.sub.f]
Promoter          (cal/g)           [T.sub.g] ([degrees]C)

CPO1               5.8                    15.5
CPO2               5.1                    15.0
CPO3               0.6                    22.4
CPO4               1.9                    22.9
NCPO1              3.0                   -20.5
NCPO2              3.5                   -19.1
CPO1/NCPO1         5.5                   -24.0,
Blend 1 (9:1)                             14.3
CPO1/NCPO1         5.5                   -23.1,
Blend 2 (4:1)                             17.4
CPO1/NCPO1         3.8                   -19.9
Blend 3 (1:1)
CPO1/NCPO1                               -19.3
Blend 4 (1:4)      3.8                    20.5
CPO1/NCPO1         3.6                   -19.7
Blend 5 (1:9)

Table 2 -- Peel Strength Properties of Adhesion Promoters (a)

                                                Avg. Peel
Adhesion    TPO                    Peel         Strength   Standard
Promoter    Type          Topcoat  Method       (lb/in.)   Deviation

CPO 1       1440 (b)     1K/1K     90[degrees]  7.30       0.31
CPO 2       1440 (b)     1K/1K     90[degrees]  7.34       0.03
CPO 3       1440 (b)     1K/1K     90[degrees]  4.59       0.66
NCPO1       1440 (b)     1K/1K     90[degrees]  5.52       1.02
NCPO2       1440 (b)     1K/1K     90[degrees]  2.77       0.02
9:1
CPO1:NCPO1  1440 (b)     1K/1K     90[degrees]  7.18       0.11
4:1
CPO1:NCPO1  1440 (b)     1K/1K     90[degrees]  7.15       0.07
1:1
CPO1:NCPO1  1440 (b)     1K/1K     90[degrees]  7.07       0.04
1:4
CPO1:NCPO1  1440 (b)     1K/1K     90[degrees]  7.23       0.48
1:9
CPO1:NCPO1  1440 (b)     1K/1K     90[degrees]  6.52       0.16
CPO 1       1440 (b)     1K/1K    180[degrees]  6.06       0.20
CPO 2       1440 (b)     1K/1K    180[degrees]  5.93       0.08
CPO 3       1440 (b)     1K/1K    180[degrees]  6.34       0.18
NCPO1       1440 (b)     1K/1K    180[degrees]  5.17       0.18
NCPO2       1440 (b)     1K/1K    180[degrees]  2.55       0.19
9:1
CPO1:NCPO1  1440 (b)     1K/1K    180[degrees]  5.95       0.22
4:1
CPO1:NCPO1  1440 (b)     1K/1K    180[degrees]  5.84       0.04
1:1
CPO1:NCPO1  1440 (b)     1K/1K    180[degrees]  5.85       0.13
1:4
CPO1:NCPO1  1440 (b)     1K/1K    180[degrees]  5.68       0.02
1:9
CPO1:NCPO1  1440 (b)     1K/1K    180[degrees]  5.29       0.13

            Max Peel    Max Peel
Adhesion    Strength    Strength
Promoter    (lb/in.)    (lb/in.)

CPO 1       7.88        6.72
CPO 2       7.99        6.88
CPO 3       6.90        2.44
NCPO1       6.50        4.28
NCPO2       3.30        2.19
9:1
CPO1:NCPO1  7.99        5.83
4:1
CPO1:NCPO1  7.99        6.54
1:1
CPO1:NCPO1  7.87        5.39
1:4
CPO1:NCPO1  7.73        6.47
1:9
CPO1:NCPO1  7.16        5.66
CPO 1       7.10        5.46
CPO 2       6.55        5.52
CPO 3       7.10        5.73
NCPO1       5.78        4.23
NCPO2       2.92        2.19
9:1
CPO1:NCPO1  6.49        5.48
4:1
CPO1:NCPO1  6.32        5.55
1:1
CPO1:NCPO1  6.37        5.47
1:4
CPO1:NCPO1  5.92        5.41
1:9
CPO1:NCPO1  5.55        5.07

(a) Method described in the experimental section of this article.
(b) Solvay Sequel 1440.

Table 3 -- Surface Roughness (RMS) of Adhesion Promoters

                Avg. 90[degrees]  Avg. 180[degrees]
                Peel              Peel                 Roughness As
Adhesion        Strength          Strengh              Applied
Promoter        (lb/in.)          (lb/in.)             (nm)

CPO1              7.3               6.1                 44.9
NCPO1             5.5               5.2                223.3
CPO1:NCPO1 9:1    7.2               6.0                 85.3
CPO1:NCPO1 1:1    7.1               5.9                175.8
CPO1:NCPO1 1:9    6.5               5.3                208.5

                  Roughness     Roughness
Adhesion          80[degrees]C  120[degrees]C
Promoter          Bake (nm)     Bake (nm)

CPO1              35.2            18.8
NCPO1            100.7            13.3
CPO1:NCPO1 9:1    79.0            13.5
CPO1:NCPO1 1:1   164.0            15.3
CPO1:NCPO1 1:9   123.6            19.4

Table 4 -- Correlations for Adhesion Promoters from Table 3

                                 Roughness   Roughness 80  Roughness 120
                                 As Applied  [degrees]C    [degrees]C
                                             Bake          Bake

Avg. 90[degrees] peel strength   -0.79       -0.21         0.33
Avg. 180[degrees] peel strength  -0.89       -0.36         0.05

Table 5 -- Multivariate Correlations of Peel Strength, Surface
Roughness, Surface RMS Phase, and Heat of Fusion ([DELTA][H.sub.f]) for
Adhesion Promoters Listed in Table 3

                                 Roughness   RMS Phase
                                 As Applied  (Deg.)     [DELTA][H.sub.f]
                                                        (cal./g)

Avg. 90[degrees] peel strength  -0.79         0.64       0.81
Roughness as applied             1.00        -0.95      -0.99
RMS phase (deg.)                -0.95         1.00       0.90

ACKNOWLEDGMENTS

The authors would like to acknowledge Robert Eagan, Kevin McCreight, Jamie Vaughn, Leslie Taylor, Jerry Mitchell, Chuck Freeman, Lisa Templeton, and Gary Robe for their contributions to this article.

References

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(9) Land, J.M., Arjona, M.C., Dechent, W.L., and Stoffer, J.O., "Water Based Polyester Coatings for Chlorinated Polyolefin Primed Polypropylene," in the Proc. of the 23rd Annual Waterborne, High-Solids, and Powder Coatings Symposium, pp. 397-407, New Orleans, LA, 1996.

(10) Ryntz, R.A., Prog. Org. Coat., Vol. 27, p. 241 (1996).

(11) Ryntz, R.A., Xie, Q., and Ramamurthy, A.C., "Effects of Coating Solvents on the Morphology of Thermoplastic Polyolefins (TPO), JOURNAL OF COATINGS TECHNOLOGY, 67, No. 843, 45 (1995).

(12) Jackson, M., Stubbs, F., Mecozzi, J., and Miklos, D., "Chlorine-Free, Zero VOC, Thermoset, Waterborne Adhesion Promoter for Thermoplastic Polyolefins (TPOs)," Third International TPOs in Automotive 1996 Conference, Novi, MI, 1996.

(13) Tomasetti, E., Daoust, D., Legras, R., Bertrand, P., Rouxhet, P.P., "Diffusion of Adhesion Promoter (CPO) into PP/EP Blends: Mechanism," J. Adhes. Sci. and Tech., Vol. 15, No. 13, p. 1533 (2000).

(14) Supplied by Buckmann GmBH, Monchengladbach, D-41238, Germany.

(15) Kondos, D. and Mayo, M., "Quantitative Adhesion Testing of Reactor and Compounded TPOs II," Coatings for Plastic Conference, Troy, MI, June 2001.

(16) McMaster, T.J., Hobbs, J.K., Barham, P.J., and Mileas, M.J., "AFM Study of In Situ Real Time Polymer Crystallization and Spherulitic Structure," Probe Microscopy, 1(1), 43-56 (1997).

(17) Fuller, K.N.G. and Tabor, F.R.S., Proc. R. Soc. London, A: 345, 327-342, 1975.

Jonathan E. Lawniczak, Kevin A. Williams, and Louis T. Germinario -- Eastman Chemical Company*

* P.O. Box 431, Kingsport, TN 37662-5280.