Solvent-free urethane-acrylic hybrid polymers for coatings.
Thermoplastic polyurethanes are well known for their excellent balance of mechanical toughness and chemical resistance. (1-9) Unfortunately, the solvent-based versions require exceedingly high levels of VOC for application by conventional coating techniques. The waterborne versions (polyurethane dispersions or PUDs) require significantly lower VOC and are, therefore, becoming increasingly popular choices as binders for a variety of one-component coatings for wood (floors and furniture), plastic (business machine housings), leather, metal, and concrete. Their superior physical and chemical properties have been attributed to a combination of their molecular structure and hard/soft domain morphology. (9-10)
In general, PUDs are prepared by reacting an excess of diisocyanate with a polyol, dispersing the resulting prepolymer in water, and completing the reaction by adding a water-soluble diamine to consume the residual isocyanate and, thereby, chain-extend the prepolymer to a high molecular weight. The dispersed PUD particles are usually anionically stabilized, which is commonly accomplished by incorporating a carboxylic acid-functional polyol into the backbone of the polyurethane and neutralizing the acid groups with a tertiary amine. Thus, in many cases, no external surfactants are present to contribute adversely to the water sensitivity of PUD-based coatings.
[FIGURE 1 OMITTED]
PUDs are available in both aromatic and aliphatic varieties. Aromatic PUDs are not suitable for applications requiring low yellowing and, therefore, the aliphatic PUDs are required for such cases where exposure to direct or indirect sunlight occurs.
Unfortunately, one of the main disadvantages of the aliphatic PUDs is their relatively high cost. As a result, formulators have sought ways to reduce the costs of their coatings. The most popular strategy is to blend the PUD with an acrylic polymer emulsion that costs less than one-half of a standard aliphatic PUD. Although the acrylics reduce the system cost, they also reduce the overall performance of the binder. The reduction in performance can be lower than what would be predicted from an arithmetic rule of mixtures. (11,12) One possible reason for this behavior is that, on a molecular level, the acrylic polymers are not soluble in the polyurethane polymers. Therefore, the polymers remain phase-separated during film formation. Arguably, the resultant phase morphology is at least partly responsible for the diminished performance behavior.
In order to take advantage of the potential cost reduction afforded by the acrylics and maintain a greater share of the advantageous PUD properties, so-called "hybrid" systems have been developed. The hybrids incorporate both the urethane and the acrylic polymers into the same dispersion. As outlined in the simplified process flow diagram (Figure 1), there are generally two methods for preparing HPDs (Type 1 and Type 2). For Type 1 hybrids, a PUD is first prepared, acrylic monomers are added to the PUD, and the acrylic polymer is formed in the presence of the PUD. (13) To prepare Type 2 hybrids, a polyurethane prepolymer is formed, the acrylic monomers are added to the prepolymer, the mixture is dispersed in water, and the urethane and acrylic polymerizations are completed concurrently. (14,15)
The urethane and acrylic polymers in HPDs exhibit improved molecular compatibility versus simple blending. The improved compatibility is demonstrated by the dynamic mechanical analysis (DMA) data that is shown in Figure 2. The simple blend has two distinct tan delta (tan [delta]) peaks, which correspond to the glass transition temperatures ([T.sub.g]) for the phase-separated urethane and acrylic polymers. The hybrid prepared from the first method previously described also shows two [T.sub.g] peaks, but the peaks have become somewhat broader, which is indicative of some limited molecular mixing. In contrast, a Type 2 hybrid, in which the urethane prepolymer and acrylic monomers are homogeneously mixed prior to dispersion and subsequent polymerization, exhibits only a single, very broad tan [delta] peak. The single peak, which spans the temperature range between the theoretical [T.sub.g]s of the urethane and acrylic polymers, is strong evidence for a significant amount of polymer-polymer mixing, in which, presumably, the different polymer molecules are intertwined similar to that of an interpenetrating network (IPN). Possibly, the improved compatibility for the hybrids (especially Type 2) is at least partly the result of some molecular-level grafting of the two polymers.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
As mentioned previously, the rationale for preparing the hybrids was to improve the performance relative to a simple blend. In Figure 3, the tensile strengths of films prepared from the individual polymers (i.e., a blend) and the two hybrid types are compared to that predicted by a linear rule of mixtures. The blend and the hybrids contain equal amounts of the same urethane and acrylic polymers. As expected, the urethane polymer had a significantly higher tensile strength than the acrylic polymer. Interestingly, the tensile strength of the blend was found to be lower than that predicted by the simple averaging rule. On the other hand, the hybrid systems showed higher tensile strengths than predicted. Remarkably, the Type 2 hybrid was found to have a tensile strength approximately equal to that of the polyurethane. Similar results for other properties have been reported as well. (11) One interpretation is that the phase morphology of a urethane/acrylic polymer system has a significant influence on the ultimate performance.
Typically, PUDs and HPDs are prepared using an aprotic solvent such as N-methylpyrrolidone (NMP). The NMP is required in the polyurethane prepolymer step to dissolve the dimethylolpropionic acid (DMPA), which is a crystalline carboxylic acid-polyol that is virtually insoluble in the polyol-diisocyanate mixture that reacts to form the urethane prepolymer. Being a relatively high boiling solvent, NMP cannot be readily removed from the process and, thus, remains in the final dispersion product. Although the amount of NMP can vary according to the product, typical NMP levels are 10% to 15% for PUDs and 3% to 8% for hybrids. In the final product, NMP is beneficial as a coalescing solvent for film formation. Conversely, NMP and high levels of residual acrylic monomers are undesired due to their odor and, in the case of NMP, its regulatory status (e.g., inclusion on California's Proposition 65). Therefore, there is a market need for NMP-free, low residual monomer HPDs that meet those requirements and still provide outstanding performance that is comparable to that of their NMP-containing counterparts.
In this article, the properties and performance of new, NMP solvent-free, Type 2 urethane-acrylic HPDs are discussed.
Solvent-containing (Hybrids A and B) and solvent-free (Hybrids [A.sub.SF] and [B.sub.SF]) HPDs were prepared according to the procedures outlined previously. (14,15) The letter designations (i.e., A or B) refer to the analogous polymer compositions, and the subscript "SF" indicates the solvent-free version. The typical properties of the HPDs used in this study are provided in Table 1. The composition of the urethane (aliphatic) portion was identical for all of the hybrid polymers. The acrylic polymer composition was kept the same for the Hybrid B variants, while the monomer ratios were varied within the A series. Nevertheless, the acrylic polymers had approximately the same theoretical [T.sub.g] within a given series (either A or B). The amount of either urethane or acrylic was about 50% for each HPD. With the exception of dimethylethanolamine (DMEA) for Hybrid [B.sub.SF], the neutralizing amine used was triethylamine (TEA).
Coating formulations (Appendix A) were prepared using standard techniques. Coating properties were tested over cold-rolled steel with a zinc phosphate treatment (Bonderite 952), untreated cold-rolled steel, or on sealed-paper charts (Leneta Co.). The coatings were applied using a #60 wire-wound drawdown rod and were allowed to dry at 21[degrees]C (70[degrees]F) and 50% relative humidity for seven days. Depending on the formulation, the dried film thickness ranged from 30 [micro]m (1.2 mil) to 76 [micro]m (3.0 mil).
The standard test methods listed in Table 2 were used to evaluate coating performance. Spot tests were performed on clear coatings applied by drawdown on sealed-paper charts. The coatings were dried for 24 hours at room temperature (~25[degrees]C), and the spots (2-3 cm wide) were rated after exposure to each reagent for one hour. The reagent spots were covered during the exposure to prevent evaporation. Prior to evaluating the coating, the reagent spots were removed by lightly patting with a clean paper towel.
DMA data was obtained on clear resin coatings (Appendix A) using a Rheometrics Solids Analyzer RSA II (Rheometric Scientific) in a tensile dynamic mode with a thin film fixture. The films were analyzed over the temperature range from -150[degrees]C to 150[degrees]C. The samples were not preconditioned with regard to humidity prior to data acquisition, but dry nitrogen was used as the atmosphere during the measurements. Data were acquired at intervals of 6[degrees]C; a one-minute soak time was used at each measurement temperature to ensure isothermal equilibration. MFFT results were obtained using a Minimum Film Formation Temperature Bar Model MFFT-90 (Rhopoint Instrumentation Ltd.). Films were applied by drawdown to a wet film thickness of 152 [micro]m (6 mils). Tensile data were obtained on clear films that had an average thickness of ~152 [micro]m (6 mils) and were dried at 21[degrees]C (70[degrees]F) and 50% relative humidity (RH) for seven days. The crosshead speed used was 5.1 cm/min (2 in./min) and the temperature was 23[degrees]C (73[degrees]F) with 50% RH. Particle size determinations were made using an LA-910 Laser Scattering Particle Size Distribution Analyzer (Horiba).
RESULTS AND DISCUSSION
With the obvious exception of VOC and residual monomer levels, the physical property data as provided in Table 1 are quite similar for all of the HPDs studied. Both the solvent-containing and the NMP-free versions exhibited similar viscosities at the same solids levels. Interestingly, the particle diameter distributions (Figure 4) and the respective means for the NMP-free dispersions were similar to those that contained NMP. All of the distributions were mono-modal with no particle diameters greater than 200 nm and weight-average particle diameters between 75 and 80 nm. The weight-average particle diameters (in nanometers) for the samples in Figure 4 were 81, 77, 79, and 78 for Hybrids A, B, [A.sub.SF], and [B.sub.SF], respectively. Since all of the hybrids have similar acid numbers and degrees of neutralization, the similarity in particle sizes suggests that, regardless of the NMP level (at least up to 6% by weight), the average particle diameter is determined by the zeta potential. (16) In addition, the particle size distributions probably explain the similar viscosity-solids relation shown for these HPDs. Because of the lack of NMP and the low residual monomer levels, the NMP-free HPDs have very low odor compared to the solvent-containing versions.
[FIGURE 4 OMITTED]
Film Formation Characteristics
Film formation characteristics of Type 2 hybrid polymers have been reported previously for systems containing NMP solvent. (17) Our experience with Hybrids A and B has shown that ultimate performance is impacted by particle coalescence which, of course, is greatly influenced by the type and amount of co-solvent used. Both Hybrids A and B, which contain NMP, formed clear films (from drawdowns) at room temperature (~25[degrees]C). Hybrid [A.sub.SF] formed a clear but non-continuous (cracked) film, whereas Hybrid [B.sub.SF] formed a white, flaky film, which is indicative of poor coalescence. Films prepared using co-solvents (formulations in Appendix A) were clear and continuous.
In order to characterize and understand the effects of co-solvents and additives, minimum film-formation temperatures (MFFTs) were determined for the NMP-free HPDs; the results are provided in Table 3. In line with the drawdown observations, both of the neat solvent-containing products had MFFTs below 0[degrees]C, whereas the NMP-free versions had, as expected, much higher MFFTs. In the case of Hybrid [B.sub.SF], the MFFT was 62[degrees]C. The addition of co-solvents (6% by weight of either NMP or DMM-dipropylene glycol dimethyl ether) was found to significantly lower the MFFTs. Comparatively, NMP was shown to be somewhat more efficient (especially for Hybrid [B.sub.SF]) for lowering the MMFT. Despite the addition of the co-solvents, the MFFTs for Hybrid [B.sub.SF] were unexpectedly much higher than for Hybrid B. Perhaps, the order of addition has an effect on the coalescing efficiency of the co-solvent. Alternately, it may be that the formulations had not reached equilibrium prior to testing, although a sweat-in time of between 1 to 5 days after preparation was employed. Another possibility is that some fundamental differences between the polymers or polymer morphology exist, although the DMA data to be discussed in the next sub-section does not seem to support this hypothesis.
Besides the co-solvents, several novel surfactants were tested in Hybrid [A.sub.SF] as potentially ultra-low VOC coalescing agents. These surfactants are low volatility, alkyl ester-based products that are purported to have utility to reduce MFFTs. The results in Table 3 show that these surfactants do indeed significantly reduce the MFFTs. At a level of 2% by weight (total emulsion basis), the MFFT was found to drop by the amount of 8[degrees] to 16[degrees]C. Thus, the use of these surfactants may offer the potential to significantly lower VOCs in formulations developed from these materials.
Clear Film Mechanical Properties
The dynamic and static (tensile) mechanical properties of the hybrid polymers were determined. Figures 5 and 6 compare the dynamic mechanical properties (storage modulus, E', and tan [delta] = E" [loss modulus]/E') as a function of temperature. Below the [T.sub.g] (~ -35[degrees]C) of the urethane polymers (the same composition for all four hybrids), both series (A and B) of hybrids had E' values between about 2 to 3 X [10.sup.10] dyn/[cm.sup.2]. Above the urethane [T.sub.g], the E' values declined to about [10.sup.9] dyn/[cm.sup.2] near the [T.sub.g] of the individual acrylic polymers. Having the higher [T.sub.g] acrylic polymers, the B-series did not reach an E' value of [10.sup.9] dyn/[cm.sup.2] until > 100[degrees]C versus about 50[degrees]C for the A-series materials. The Hybrid A-series showed a pronounced rubbery plateau above the acrylic [T.sub.g]s, whereas the B-series did not.
[FIGURE 5 OMITTED]
For the A-series polymers, the E' and tan [delta] responses were similar, and both polymers showed very broad peaks in the tan [delta] over the expected [T.sub.g] ranges as listed in Table 1. Hybrid [A.sub.SF] did have a somewhat higher E' over most of the temperature range studied. The B-series polymers showed comparable E' and tan [delta] behavior, although Hybrid [B.sub.SF] did have a slightly higher E' over most of the temperature range examined. However, unlike that for the A-series, there was no apparent tan [delta] peak over the anticipated [T.sub.g] range. The tan [delta]s did, however, show a steady increase with increasing temperature as the E' decreased. In general, both the solvent-containing and NMP-free versions displayed dynamic mechanical properties which would be expected if there were some molecular-level mixing of the urethane and acrylic polymers.
The room-temperature tensile mechanical properties of thin films of the hybrids are summarized in Table 4. Within a given series, the tensile properties were comparable. As expected the A-series, having the lower [T.sub.g] acrylic polymers, had lower tensile strengths and moduli but higher tensile elongations. The A-series polymers showed a relatively good balance of properties with high elongations (> 230%) and moderate tensile strengths.
[FIGURE 6 OMITTED]
Coating Performance: B-Series Hybrids
The performance of Hybrids B and [B.sub.SF] was evaluated and compared using chemical spot tests; the results of which are provided in Table 5. Both hybrids showed comparable performance, as the spot test resistance was relatively good for both systems. Of the chemicals studied, isopropyl alcohol (IPA) showed the most effect on the coatings, and this could be a potential area for improvement.
Coating Performance: A-Series Hybrids
In Table 6, the performance properties of the A-series hybrids in clear and pigmented coatings (Appendix B for 1 and 2) are compared and benchmarked versus commercial NMP-containing PUDs, an HPD, a PUD/acrylic blend, and an acrylic. Coating properties for the NMP-free Hybrid [A.sub.SF] were similar to those of Hybrid A. Dry time, gloss, reverse impact resistance, MEK resistance, and UV resistance of the NMP-free Hybrid [A.sub.SF] compared favorably to Hybrid A and the benchmarked commercial materials. The IPA resistance was better for Hybrid [A.sub.SF] than that for three of the other systems tested. Interestingly, the commercial paints had comparatively much lower impact resistance.
A potential area for improvement of the NMP-free hybrids is their IPA resistance. Crosslinking of the HPDs through their carboxylic acid groups is a potential way to improve their resistance properties. Indeed, the resistance properties of acid-functional polymers have been found to be improved when crosslinked with an epoxy-silane crosslinker, [beta]-(3,4-epoxycyclohexyl)-ethyltriethoxysilane (a cycloaliphatic epoxy-silane). (18,19) Shelf-stable (at least six months) formulations using Hybrid A have been formulated. (20) The use of epoxysilane and other crosslinkers to improve the performance properties of NMP-free hybrids needs to be examined. Another market need is for lower cost formulations. Acrylics are often blended into PUDs for that purpose, and should be evaluated in the NMP-free HPDs.
SUMMARY AND CONCLUSIONS
Waterborne, high-performance, urethane-acrylic HPDs have been developed to offer cost/performance advantages over standard 1K coating materials such as polyurethane dispersions (PUDs), acrylic emulsions, and blends thereof. These so-called Type 2 hybrid polymers provide many of the benefits (e.g., superior mechanical properties and chemical resistance) of PUDs but at an intermediate cost between PUDs and low-cost acrylics. The Type 2 hybrid has an IPN-like polymer structure which is characterized by a broad glass transition temperature range as measured by DMA. The IPN-like structure is the result of the chemical composition of the material and, particularly, the process by which the urethane and acrylic are polymerized together as a homogenous mixture that is dispersed as colloidal particles in water. The IPN-like morphology is apparently responsible for the hybrid's outstanding properties, which would not be predicted from a simple, arithmetic rule of mixtures. New NMP-free HPDs have been developed to meet the market needs for lower odor products that comply with increasingly stringent regulations. The NMP-free HPDs have been shown to provide dispersion and coating properties comparable to their NMP-containing counterparts. Due to their lack of NMP and low residual monomer contents, both NMP-free HPDs were observed to have reduced odor, which is obviously desirable from a health and safety perspective. In addition, the lack of NMP offers potential regulatory benefits (e.g., California Proposition 65). Because the performance of the HPD systems was found to compare favorably with other polymer systems (PUDs, HPD, and acrylic) evaluated, the possibility exists to replace or partially replace those types of polymers with HPDs.
Appendix A -- Clear Coating Formulations and Formulation Properties.
(See Appendix C for list of materials and suppliers as indicated by superscripts.)
Table A1 -- Clear Coating Formulation for Hybrid A Material Weight % Pre-Mix: Mix a solution of the following Solvent (e) 5.98 Surfactant (f) 0.40 Defoamer (g) 0.21 Resin Blend: Add to the following with agitation Hybrid A (a) 79.76 Letdown: Dilute to brush and roll viscosity Water 13.65 Total 100.00 Table A2 -- Clear Coating Formulation for Hybrid B Material Weight % Pre-Mix: Mix a solution of the following Solvent (e) 11.93 Surfactant (f) 0.40 Defoamer (g) 0.21 Resin Blend: Add to the following with agitation Hybrid B (b) 79.51 Letdown: Dilute to brush and roll viscosity Water 7.95 Total 100.00 Table A3 -- Clear Coating Formulation for Hybrid [A.sub.SF] Material Weight % Pre-Mix: Mix a solution of the following Solvent (e) 2.15 Solvent (h) 5.49 Solvent (i) 1.93 Surfactant (f) 0.05 Defoamer (j) 0.10 Resin Blend: Add to the following with agitation Hybrid [A.sub.SF] (c) 90.28 Total 100.00 Table A4 -- Clear Coating Formulation for Hybrid [B.sub.SF] Material Weight % Pre-Mix: Mix a solution of the following Solvent (e) 4.13 Solvent (h) 5.27 Solvent (i) 3.71 Surfactant (f) 0.05 Defoamer (j) 0.10 Resin Blend: Add to the following with agitation Hybrid [B.sub.SF] (d) 86.74 Total 100.00
Appendix B -- Pigmented Coating Formulations and Formulation Properties.
(See Appendix C for list of materials and suppliers as indicated by superscripts)
Table B1 -- Pigmented Coating Prepared from Hybrid A (Formulation 1 in Table 6) Material Gal Resin-Free Grind: Mix the following under mild agitation until dissolved Water (deionized) 2.31 Pigment dispersant (k) 2.74 Defoamer (o) 0.06 Continue agitation while adding the pigment below Ti[O.sub.2] pigment (l) 22.85 Increase speed to high and disperse to Hegman [greater than or equal to] 7 grind. Do not exceed 140[degrees]F Reduce speed and add the following with medium agitation until blended Water (deionized) 2.03 Blend: Mix the following in a separate container until blended Hybrid A (a) 66.68 Pre-blend the next four items before adding to the Hybrid A with strong agitation Surfactant (f) 0.13 Solvent (n) 1.67 Solvent (i) 1.50 Defoamer (g) 0.03 Final Blend: Slowly add the resin-free grind to the blend and mix with mild agitation until homogeneous Total 100.00 Weight solids, % 52.4 Volume solids, % 41.2 Viscosity, cP 500 PVC, % 17.1 VOC, lb/gal (g/l) 1.66 (199) Density, lb/gal (g/ml) 10.3 (1.23) Note: Properties reported are based on theoretical calculations. Table B2 -- Pigmented Coating Prepared from Hybrid [A.sub.SF] (Formulation 2 in Table 6) Material Weight % Resin-Free Grind: Mix the following under mild agitation until dissolved Water (deionized) 2.15 Pigment dispersant (k) 2.55 Defoamer (j) 0.06 Continue agitation while adding the pigment below Ti[O.sub.2] pigment (l) 21.24 Increase speed to high and disperse to Hegman [greater than or equal to]7 grind. Do not exceed 140[degrees]F Reduce speed and add the following with medium agitation until blended Water (deionized) 1.89 Blend: Mix the following in a separate container until blended Hybrid [A.sub.SF] (c) 65.12 Pre-blend the next five items before adding to the Hybrid [A.sub.SF] with strong agitation Surfactant (m) 0.06 Solvent (h) 3.96 Solvent (n) 1.55 Solvent (i) 1.39 Defoamer (j) 0.04 Final Blend: Slowly add the resin-free grind to the blend and mix with mild agitation until homogeneous Total 100.00 Weight solids, % 48.5 Volume solids, % 36.9 PVC, % 17.4 VOC, lb/gal (g/l) 1.65 (184) Density, lb/gal (g/ml) 10.1 (1.21) Note: Properties reported are based on theoretical calculations.
Appendix C -- List of Materials and Suppliers.
Superscript Material Supplier a Hybridur[R] 570 polymer dispersion Air Products b Hybridur[R] 580 polymer dispersion Air Products c Hybridur[R] 870DEV polymer dispersion Air Products d Hybridur[R] 878 polymer dispersion Air Products e Arcosolv[R] DPNB Lyondell f BYK[R]-346 BYK-Chemie g Surfynol[R] DF-58 defoamer Air Products h Proglyde[R] DMM Dow Chemical i Texanol[R] ester alcohol Eastman j BYK[R]-024 BYK-Chemie k Disperbyk[R]-190 BYK-Chemie l TI-Pure[R] R706 DuPont m BYK[R]-333 BYK-Chemie n Dowanol[R] DPnB Dow Chemical o Dee FO[R] PI-4 Ultra Additives p EnviroGem[R] AE01 Air Products q EnviroGem[R] AE02 Air Products r EnviroGem[R] AE03 Air Products s NeoRez[R] R960 NeoResins t Witcobond[R] W-236 Uniroyal Chemical u Wilko white industrial coating Wilko Paint v NeoPac[R] R9000 NeoResins w Polane[R] 700T Sherwin Williams x Rust-o-Lastic Gloss Acrylic (DTM) MAB Paints maintenance finish Table 1 -- Typical Characteristics of the Type 2 Hybrid Polymer Dispersions Evaluated Property Hybrid A (a) Hybrid B (b) Appearance Opaque, Slight Opaque, Slight Milky Milky Viscosity, cP, 25[degrees]C, 50-150 50-150 Brookfield Non-Volatiles, % by weight 39-41 39-41 Solvent content, % by weight 6 6 Solvent NMP NMP VOC, g/L (lb/gal) (e) 160 (1.33) 164 (1.37) Density, g/ml (lb/gal) 1.03 (8.60) 1.04 (8.70) pH 7.5-9.0 7.5-9.0 Acid number, mg KOH/g (f) 14.5 14.5 [T.sub.g] range, [degrees]C (g) -35 to 35 -35 to 100 Neutralizing amine (h) TEA TEA Particle diameter (wt. avg.), nm 75-85 (i) 75-85 (i) Residual acrylic monomer, ppm 500 (i) 500 (i) Particle charge Anionic Anionic Property Hybrid [A.sub.SF] (c) Appearance Opaque, Slight Milky Viscosity, cP, 25[degrees]C, 50-150 Brookfield Non-Volatiles, % by weight 39-41 Solvent content, % by weight <0.2 Solvent Acetone VOC, g/L (lb/gal) (e) 30 (0.25) Density, g/ml (lb/gal) 1.05 (8.76) pH 7.5-9.0 Acid number, mg KOH/g (f) 16.0 [T.sub.g] range, [degrees]C (g) -35 to 35 Neutralizing amine (h) TEA Particle diameter (wt. avg.), nm 75-85 (i) Residual acrylic monomer, ppm 50-200 (i) Particle charge Anionic Property Hybrid [B.sub.SF] (d) Appearance Opaque, Slight Milky Viscosity, cP, 25[degrees]C, 50-150 Brookfield Non-Volatiles, % by weight 39-41 Solvent content, % by weight <0.1 Solvent Acetone VOC, g/L (lb/gal) (e) 24 (0.20) Density, g/ml (lb/gal) 1.07 (8.93) pH 7.5-9.0 Acid number, mg KOH/g (f) 14.5 [T.sub.g] range, [degrees]C (g) -35 to 100 Neutralizing amine (h) DMEA Particle diameter (wt. avg.), nm 75-85 (i) Residual acrylic monomer, ppm 10-50 (i) Particle charge Anionic (a, b, c, d) Refer to Appendix C for material identification. (e) VOC includes contribution from the neutralizing amine (~1% by weight). (f) Calculated on a solids basis. (g) [T.sub.g]s estimated from DMA measurements (breadth of tan [delta] peak) and polymer compositions. (h) TEA = triethylamine; DMEA = dimethylethanolamine. (i) Typical values. Table 2 -- Test Methods Used to Evaluate the Performance Characteristics of the Coatings ASTM Test Property Procedure Adhesion, dry and wet tape D 3359 Dry time D 5895 Flexibility (mandrel bend) D 1737 Gloss D 523 Hardness (Persoz) D 4366 Humidity resistance (Cleveland) D 2247 Immersion resistance D 870 Impact resistance D 2794 Solvent resistance (double rubs) D 4752 Tensile properties D 638 Minimum film formation temperature D 2354 Table 3 -- MFFT ([degrees]C) Data for the HPDs Additive (% wt.) Hybrid A Hybrid B Hybrid [A.sub.SF] None < -4.6 < -4.6 19.1 NMP (6%) * * <0.0 DMM (6%) * * -1.0 S-1 (2%) (p) * * 3.1 S-2 (2%) (q) * * 5.5 S-3 (2%) (r) * * 10.9 Additive (% wt.) Hybrid [B.sub.SF] None 62.0 NMP (6%) 18.3 DMM (6%) 40.8 S-1 (2%) (p) * S-2 (2%) (q) * S-3 (2%) (r) * *Value was not determined. S-1, S-2, and S-3 are surfactants identified in Appendix C by superscript letter. Table 4 -- Tensile Properties for the Hybrid Polymers Polymer Strength, psi Elongation, % Hybrid A 2433 [+ or -] 458 236 [+ or -] 76 Hybrid [A.sub.SF] 2576 [+ or -] 650 245 [+ or -] 12 Hybrid B 4552 [+ or -] 450 15 [+ or -] 8 Hybrid [B.sub.SF] 4407 [+ or -] 244 8 [+ or -] 0.4 Polymer Modulus, [10.sup.3] psi Hybrid A 30 [+ or -] 11 Hybrid [A.sub.SF] 38 [+ or -] 11 Hybrid B 115 [+ or -] 59 Hybrid [B.sub.SF] 155 [+ or -] 11 Table 5 -- Chemical Spot Testing Results for Hybrids B and [B.sub.SF] Chemical Hybrid B Hybrid [B.sub.SF] 10% wt. N[H.sub.4]OH in water 10* 10 Clorox (5.25% wt. NaClO/water) 10 10 50% wt. ethanol in water 10 9 IPA 7 7 Commercial cleaner 1** 9 8 Commercial cleaner 2 8 8 *Commercial Cleaner 1 = Fantastik (S.C. Johnson); Commercial cleaner 2 = Formula 409 (Clorox). **Rating Key: 10 = no effect; 5 = moderate: swelling, softening, and whitening; 0 = completely dissolved. Table 6 -- Clear and Pigmented Coating Performance Property Comparison Property/Formulation 1 2 3 (s) 4 (t) Dry-hard time, min 40 40 40 30 60[degrees] gloss 75-80 84 53 NA Reverse impact, in.-lb 160 160 160 160 IPA* double rubs 83 50 182 25 MEK* double rubs >200 >200 200 25 1000 hr QUV-B, [DELTA]E <2 <2** <2 NA Property/Formulation 5 (u) 6 (v) 7 (w) 8 (x) Dry-hard time, min 30 25 >60 60 60[degrees] gloss NA 74 31 81 Reverse impact, in.-lb 160 28 4 72 IPA* double rubs 25 83 200 40 MEK* double rubs 25 90 115 <10 1000 hr QUV-B, [DELTA]E NA 2 1 3.5 Key: 1 = Hybrid A; 2 = Hybrid ASF; 3, 4, and 6 = PUDs; 5 = HPD; 7 = PUD/ acrylic blend; 8 = acrylic. Formulation 3 was a pigmented white coating and 4 and 5 were clear coatings based on recommendations from the respective suppliers. Formulations 6, 7, and 8 were commercially available paints. See Appendix C for material identifications. * IPA = isopropyl alcohol; MEK = methyl ethyl ketone. ** QUV-A.
Many people have contributed over the years to the development of HPD technology, and the authors extend their gratitude to all of them. Special mention and thanks must be made to Dick Derby who made significant contributions through the years. Many thanks to: Jeanine Snyder for formulating expertise; Bruce Gruber for his work in the field of hybrid synthesis; Chris Gunsser for synthesis support; Menas Vratsanos and Chris Walsh for their DMA work; Dennis Nagy and Gregg Meixell for particle size analyses; Steve Deppen and Jim Malloy for residual monomer analyses; Steve Robbins for the tensile measurements; Matt Marusiak for process support; Khalil Yacoub for surfactant advice; and Zay Risinger, Bob Stevens, Paula Mc Daniel, and Ellen O'Connell for supporting this work and the presentation of this paper.
Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 13-14, 2003, in Philadelphia, PA.
(1) Rosthauser, J.W. and Nachtkamp, K., "Waterborne Polyurethanes," Advances in Urethane Science and Technology, Frisch, K.C. and Klempner, D. (Eds.), Technomic Pub., Lancaster, PA, 10, 121-162 (1987).
(2) Dieterich, D., "Aqueous Emulsions, Dispersions and Solutions of Polyurethanes; Synthesis and Properties," Prog. Org. Coat., 9, 281-340 (1981).
(3) Dieterich, D., "Introduction to Urethane Ionomers," Advances in Urethane Ionomers, Xiao, H.X. and Frisch, K.C. (Eds.), Technomic Pub., Lancaster, PA, 1-21 (1995).
(4) Padget, J.C., "Polymers for Water-Based Coatings--A Systematic Overview," JOURNAL OF COATINGS TECHNOLOGY, 66, No. 839, 89-105 (1994).
(5) Kim, B.K., "Aqueous Polyurethane Dispersions," Colloid Polym. Sci., 274, 599-611 (1996).
(6) Manock, H.L., "New Developments in Polyurethane and PU/Acrylic Dispersions," Pigment & Resin Technology, 29, 143-151 (2000).
(7) Tirpak, R.E. and Markusch, P.H., "Aqueous Dispersions of Crosslinked Polyurethanes," JOURNAL OF COATINGS TECHNOLOGY, 58, No. 738, 49 (1986).
(8) Gardon, J.L., "A Perspective on Resins for Aqueous Coatings," Technology for Waterborne Coatings, ACS Symposium Series 663, Glass, J.E. (Ed.), American Chemical Soc., 27-43 (1997).
(9) Satguru, R., McMahon, J., Padget, J.C., and Coogan, R.G., "Aqueous Polyurethanes--Polymer Colloids with Unusual Colloidal, Morphological, and Application Characteristics," JOURNAL OF COATINGS TECHNOLOGY, 66, No. 830, 47-55 (1994).
(10) Yang, W.P., "Thermal and Mechanical Properties of Waterborne Polyurethanes," Proc. American Chemical Society National Meeting, San Francisco, April 5-10, p. 216, 1992.
(11) Derby, R., Gruber, B.A., and Chan, S.Y., "Acrylic/Urethane Hybrid Polymers: A New Technology for Graphic Arts Applications," American Ink Maker, 56, June 1995.
(12) Hegedus, C.R. and Kloiber, K.A., "Aqueous Acrylic-Polyurethane Hybrid Dispersions and Their Use in Industrial Coatings," JOURNAL OF COATINGS TECHNOLOGY, 68, No. 860, 39-48 (1996).
(13) Honig, H.L., Suling, C., Dieterich, D., and Reischl, A., "Process for the Production of Modified Cationic Emulsion Polymers with Cationic Polyurethane," U.S. Patent 3,684,758 (Aug. 15, 1972).
(14) Loewrigkeit, P. and Van Dyk, K.A., "Aqueous Polyurethane--Polyolefin Compositions," U.S. Patent 4,644,030 (Feb. 17, 1987).
(15) Vijayendran, B.R., Derby, R., and Gruber, B.A., "Aqueous Polyurethane-Vinyl Polymer Dispersions for Coating Applications," U.S. Patent 5,173,526 (Dec. 22, 1992).
(16) Chen, Y. and Chen, Y.-L., "Aqueous Dispersions of Polyurethane Anionomers: Effect of Countercation," J. Appl. Polym. Sci., 46, 435-443 (1992).
(17) Rynders, R.M., Hegedus, C.R., and Gilicinski, A.G., "Characterization of Particle Coalescence in Waterborne Coatings Using Atomic Force Microscopy," JOURNAL OF COATINGS TECHNOLOGY, 67, No. 845, 59-69 (1995).
(18) Chen, M.J., "Epoxy Silanes in Reactive Polymer Emulsions," JOURNAL OF COATINGS TECHNOLOGY, 69, No. 875, 49-55 (1997).
(19) Bechara, I. and Lipkin, A., "An Overview of the Cross-linking of Polyurethane Dispersions (PUDs)," Proc. 42nd Annual Technical Symposium--Waterborne Coatings: Sink or Swim III Conf., Cleveland, April, 1999.
(20) Snyder, J.M., unpublished data.
by Ernest C. Galgoci, ([dagger]) Charles R. Hegedus, Frederick H. Walker, Daniel J. Tempel, Frank R. Pepe, Kenneth A. Yoxheimer, and Alan S. Boyce
Air Products and Chemicals, Inc.*
* 7201 Hamilton Blvd., Allentown, PA 18195.
([dagger]) Author to whom correspondence should be addressed. Email: email@example.com.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||Technology Today|
|Author:||Boyce, Alan S.|
|Date:||Feb 1, 2005|
|Previous Article:||Evaluation of organic coatings with electrochemical impedance spectroscopy; Part 3: protocols for testing coatings with EIS.|
|Next Article:||Nontraditional use of the biocide DBNPA in coatings manufacture.|