Ind. Eng. Chem. Res. 2003, 42, 3671-3679
3671
Simultaneous Acid Catalysis and in Situ Phosphatization Using a Polyester-Melamine Paint: A Surface Phosphatization Study Mary C. Whitten and Valicia J. Burke University of the Virgin Islands, St. Thomas, Virgin Islands 00802
Heather A. Neuder and Chhiu-Tsu Lin* Northern Illinois University, DeKalb, Illinois 60115
Six different phosphorus-containing reagents were used as self-phosphating agents and acid catalysts in the formulation of a polyester-melamine coating. The phosphorus compounds chosen for the study were Cycat 4040 (4040), Cycat 296-9 (296), Albright & Wilson PA-75 (PA-75), phosphonosuccinic acid (PPSA), and two in situ phosphatizing reagents (ISPR-1 and ISPR-2, phenylphosphonic acid and fosfosal, respectively). Each individual phosphorus-containing compound was evaluated separately using a varying percentage of agent in the paint formulation. The different paints made using the different modifiers were applied to bare 3003 or 3105 aluminum panels. After the individual phosphorus-containing reagents were optimized, the optimized additives were compared to each other utilizing electrochemical impedance spectroscopy (EIS), differential scanning calorimetry (DSC), saltwater immersion, and pencil hardness tests. The most commonly used acid catalyst (4040) did not perform as well as the other acid catalysts. Using 1% phenylphosphonic acid as the acid catalyst and self-phosphating agent in a polyester-melamine coating produced the best protective barrier for the Al substrate of the coatings studied here. Using different acid catalysts in a polyester-melamine paint can dramatically alter the performance of the coating. I. Introduction The current practice for applying state-of-the-art organic coatings to metal substrates is a multistep process. Normally, the metal surface is cleaned, phosphated or chromated, possibly sealed (with hot water or carcinogenic chromates),1,2 dried, and finally painted. The pretreatment process is error-prone and costly. However, it is necessary in the metal finishing industry.3 Unfortunately, multistep coating technologies produce wastes including organic solvents, heavy metals, and other toxic and deleterious materials.4 Therefore, the demand for the elimination of hexavalent chromium and improved durability of paint requires a novel surface treatment technique for the highly active surfaces of metal alloys. Recently, a novel technique of in situ phosphatizing coatings (ISPCs) has been developed in our laboratory5-15 and patented.8 In an ISPC, an optimum amount of an in situ phosphatizing reagent (ISPR) or a mixture of ISPRs is predispersed in the paint system to form a stable and compatible coating formulation.5 When a chrome-free single-step coating of the in situ selfphosphating paint is applied to a bare metal substrate, the phosphatizing reagent chemically and/or physically reacts in situ with the metal surface to produce a metal phosphate layer and simultaneously forms covalent P-O-C (phosphorus-oxygen-carbon) linkages with the polymer resin.7,10 Sealing the pores between the metal-phosphate layer generated at the metal and * To whom correspondence should be addressed. Tel.: 815753-6861. Fax: 815-753-4802. E-mail:
[email protected]. Address: Dept. of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115.
paint interface by covalent P-O-C linkages enhances the adhesion of the coating and suppresses substrate corrosion without the use of the toxic form of chromates (Cr6+). Polyester-melamine paints are normally catalyzed by organic acids. In situ phosphatizing reagents also act as acid catalysts.15 In this study, six acid catalysts and possible self-phosphating agents are compared. The first is Cycat 4040 (4040), which is 40% para-toluenesulfonic acid (p-TSA). According to the brochure for Cymel 303, the most widely used catalyst for polyester-melamine paint systems is p-TSA (contact Cytec Industries, www.cytec.com). Overbake softening is observed from using p-TSA as the catalyst in previous studies.16 The second acid modifier used in this study is Cycat 296-9 (296). The company promotes 296 as an accelerator for the curing of paint at normal baking temperatures. The third acid additive studied is Albright & Wilsons’s PA75 (PA-75). PA-75 is designed to provide high reactivity while offering improved storage stability according to the company. The fourth acid is Albright & Wilson’s phosphonosuccinic acid (PPSA). PPSA is not proposed as a paint catalyst. However, PPSA is suggested for use in modifying interfaces between organic and inorganic materials. Because PPSA is a phosphorus-containing acid, it is tested as an acid modifier as well. These four acid catalysts, 4040, 296, PA-75, and PPSA, are not mentioned as possible reagents for reacting with metal substrates. The fifth and sixth acid additives used for polyester-melamine paints are ISPR-1 and ISPR-2 (phenyphosphonic acid and fosfosal, respectively). These acid modifiers are designed with the dual purpose of catalyzing the cross-linking reaction between the polyester polyol and the melamine and also providing phosphate formation on the surface of the metal. The
10.1021/ie020632p CCC: $25.00 © 2003 American Chemical Society Published on Web 07/09/2003
3672
Ind. Eng. Chem. Res., Vol. 42, No. 16, 2003
protective effect is the action of an in situ self-phosphating paint where the ISPR reacts with the metal surface to produce a metal phosphate layer. Each acid modifier is discussed separately, and a determination is made as to which parameters for each acid are the best. After the best parameters for each acid modifier are determined, the acids are compared in terms of their best parameters. Surface studies utilizing the catalysts and paint solvents (i.e., including no pigments or resins) are used to demonstrate the ability of the phosphorus-containing catalysts to chemically react or bond to the metal substrate. II. Experimental Section Materials. A stock polyester-melamine paint system was prepared using the following components in percentages by weight: AKZO 2616-12 polyester resin (31.2%), Rheox MPA2000X (an anti-settling agent, 0.8%), Cymel 303 (modified melamine resin, 12.3%), Aerosil R972 (silicon dioxide, 0.2%), Dupont Ti-Pure titanium dioxide (40.5%), and solvents [n-butanol (2.3%), 2-butoxyethanol (4.9%), methyl ethyl ketone (1.0%), and xylenes (6.8%)]. The paint formulation was supplied by AKZO. The six acid modifiers employed were 4040, 296, PA-75, PPSA, ISPR-1, and ISPR-2. A stock formula of paint was made without any acid catalyst added. Next, the stock solution was separated into different containers and had the different acid modifiers added in various percentages. The percentages were 2% 296, 1% PA-75, 1.3% PA-75, 0.5% PPSA, 1% PPSA, 0.5% ISPR-2, 0.75% ISPR-2, and 1% ISPR-2. The results for 1% 4040 and 1% ISPR-1 were reported in a previous paper.15 All of the reported percentages of acid added are percentages by weight of the paint formulation (i.e., 2% acid was made by mixing 100 g of the stock paint with 2 g of the acid). One percent 4040 was the amount recommended in the formulation provided by AKZO. The panels used for the substrate were bare 3003 and 3105 aluminum panels. The panels were scoured and rinsed with water and ethanol and then blown dry with hot air. The Al panels were not pretreated with any type of chromate or phosphate. After the Al was spray painted using nitrogen as the propellant, the painted panels were flashed for 30 min and were cured at 120 °C for 20 min. Painted panels with 2% 296 as the catalyst had a second batch of Al panels cured at 140 °C for 20 min as well. The painted Al panels were used for EIS, saltwater immersion, and pencil hardness tests. The paint on cured painted panels was removed with a razor and placed in DSC pans for DSC analysis. Al panels of 3105 alloy were polished to a mirror finish. One percent 4040, 2% 296, 1% PA-75, 1% ISPR1, and 0.5% ISPR-2 were dissolved separately in the paint solvents methyl ethyl ketone, xylenes, butanol, and 2-butoxyethanol. No pigment or resin was added to the mixtures. The individual mixtures were applied separately to polished 3105 Al and baked at 120 °C for 20 min, except for 2% 296, which was baked at 140 °C for 20 min. After the samples had cooled to room temperature, they were rinsed with deionized water, acetone, and finally ethanol. These samples were used to acquire reflectance Fourier transform infrared (FTIR) spectroscopic data and used for images taken with an optical microscope, scanning electron microscope (SEM), and energy-dispersive X-ray (EDX) spectrometer. Instruments. AC impedance data for polyestermelamine-coated Al panels were obtained using a PARC
273 potentiostat/galvanostat and a PARC 5210 lock-in amplifier (EG&G Princeton Applied Research Corp). The experimental parameters were input, and the data were collected with the aid of EG&G electrochemical impedance software model 398 installed on an IBMcompatible 486/50 computer. A Ag/AgCl electrode was used for the reference electrode, a platinum electrode was used for the counter electrode, and the coated panel was the working electrode. The coated panel had 10 cm2 exposed to the salt solution. The electrolyte used was a 3% NaCl by weight aqueous solution. The impedance measurements were carried out over the frequency range from 100 kHz to 10 mHz, with a 5-mV peak-topeak sinusoidal voltage in the high-frequency range. The multi-sine technique was used at lower frequencies with an applied voltage of (10 mV. The coated panels were soaked for 3 days in a 3% NaCl solution, allowing for the complete swelling of the polymer film prior to the recording of the EIS spectra. The dry thickness of all of the coatings was 2.0 ( 0.3 mil. The glass transition temperatures (Tg) were measured using differential scanning calorimetry (DSC) (Seiko Scientific Instruments, Inc., model DSC220C). The instrumentation was equipped with a Seiko SSC5200H disk station for scanning program manipulation and data analysis. Colder temperatures were obtained with the aid of a liquid nitrogen auto cooling unit. The sample specimens (∼10 mg) were contained in weighed aluminum pans. The samples prepared for DSC analysis were lidded. The sample chambers were purged with nitrogen gas. To erase the thermal history and release the stress resulting from mechanical peeling of the cured paint from the substrate with a razor, the DSC samples were first annealed at 80 °C. This temperature is above the Tg of the film, but well below the curing temperature. The preannealing process allowed the polymer backbone to relax and release molecular stress, allowing for a more accurate determination of Tg17 (i.e., giving a smoother curve). After the samples had been annealed, they were subjected to temperature scans from -50 to 300 °C at a heating rate of 10 °C/min. Heating of the samples ended immediately after the temperature reached 300 °C. Each sample was scanned from -50 to 300 °C twice to observe the changes from deterioration of the paint film when subjected to overbaking or the Tg value for an infinity-cured paint. It was not necessary to anneal the samples a second time for the second scan to 300 °C. Saltwater immersion studies were carried out by submerging the painted Al panels in a 3% NaCl solution for 66 days. The panels were scribed with an “X” in the film using a razor to expose the base metal to aid in the corrosion process. Upon removal from the salt solution, the panels were dried, and tape (Duck corporation) was firmly pressed against the scribed area and pulled to remove. After exposure to the saltwater, the painted panels were evaluated using American Society for Testing and Materials (ASTM) method D3359 A.18 The pencil hardness of the painted Al panels was measured using ASTM method D3363.18 The pencil lead was sanded flat with sand paper. The pencil was held at a 45° angle from the painted metal and pushed on the substrate. After a pencil hardness was reached that cut through the coating to expose the metal surface, the previous pencil hardness was the recorded as the pencil hardness of the sample.
Ind. Eng. Chem. Res., Vol. 42, No. 16, 2003 3673 Table 1. Paint Catalysts Used in Study test results catalyst
EIS (Ω‚cm2)
Tg (°C)a
1% 4040b 2% 296-9 2% 296-9b,d 1.3% PA-75 1% PA-75b 1% PPSA 1% ISPR-1b 1% ISPR-2 0.75% ISPR-2 0.5% ISPR-2b
106 107 109 1010, 108 1010 106 1010 109, 107 109 109
40 (34) 2.5 (46) 21 (52) 31 (46) 23 (56) 24 (53) 22 (65) 35 (59) 34 (55) 18 (48)
saltwater 1A N/Ac N/A 4A N/A N/A 5A N/A N/A 5A
pencil hardness F 4B F 3H H H F 4H 4H HB
a Values in parentheses indicate T ’s measured after sample had g been heated to 300 °C. b Paint systems used in further comparisons. c N/A not applicable; see text for further information. d Cured at 140 °C.
The FTIR reflectance spectra of the metal-phosphate layers and the plain surface of 3105 Al were generated with a Bruker Vector 22 instrument equipped with a Spectra Tech FT-80 grazing angle accessory. The interferometer was purged with dry air. The FTIR spectrometer was controlled with the computer program OPUS/ IR version 2.2. The background spectrum was of bare polished 3105 Al. The microscope images were acquired with a Nikon Microphot-FXA camera equipped with a Polaroid model 545 4 × 5 film holder. SEM was carried out with an ISI model DS-130 instrument (International Scientific Instrumentation, Inc.) and EDX with a PV9900 system (North American Philips company.) III. Results and Discussion A. Paint Catalysts Used in This Study. The results for all of the paint catalysts used in this study are shown in Table 1. The data for 1% 4040 were reported in a previous paper.15 After the painted panels had soaked in a 3% NaCl solution for 3 days, the impedance at low frequency (0.01 Hz) from EIS was on the order of 106 Ω‚cm2. A surface with an impedance at low frequency below 107 Ω‚cm2 is considered a poor protective barrier.19 Therefore, using 1% 4040 as the acid modifier did not produce a cured polyester-melamine coating that was very resistant to the uptake of the salt solution. The Tg from the first DSC scan was 40 °C. After the paint was reheated to 300 °C for the second time, the Tg dropped to 34 °C, which indicated overbake softening behavior.16 A higher Tg correlates with a coating with a higher cross-linking density in the polymer. The crosslinking density dropped as the Tg dropped after severe heating. This resulted from the possible cleavage of polyester-melamine cross-linking in favor of the melamine self-condensation in the paint films.16 After 1 week of being submerged in a 3% NaCl solution, Duck brand tape was applied to the scribed area of the panel and removed. There was no adherence of the paint to the bare Al surface upon removal of the tape. The paint was classified as 1A according to ASTM method D3359 test method A.18 The pencil hardness was F. Cycat 296 was designed to accelerate the curing of the paint film at normal baking temperatures. The paint formulated with 2% 296 was sprayed onto the bare Al surface and cured at 120 °C for 20 min. The coating was observed to be soft and undercured. The EIS spectrum at low frequency (0.01 Hz) had an impedance on the order of 107 Ω‚cm2. A surface with an impedance at low
frequency between 107 and 109 Ω‚cm2 is considered a mediocre barrier for metal protection.19 The Tg of the cured coating was 2.5 °C, which is an unusually low Tg for a cured polyester-melamine paint. The Tg for 296 was lower than the Tg for 4040. Repeating the scan to 300 °C for the same sample of 2% 296 paint produced a Tg of 46 °C. After the painted panel had soaked in the 3% NaCl solution for 66 days, the panel was covered with tiny blisters. The tape applied to the scribed panel removed blisters exposing the base metal around the scribe and also removed paint in areas outside the scribed area that were still under the tape. The paint did not display jagged removal all along the scribe. This behavior was not characterized in ASTM method D3359. The undercured paint had a pencil hardness of less than 4B. The paint was extremely soft, not fully cured, and required a higher thermal curing schedule. The same 2% 296 paint was sprayed on a different batch of Al panels and cured at 140 °C for 20 min to determine whether a higher curing temperature would improve the coating performance. The coating cured at 140 °C had an impedance at low frequency of 109 Ω‚ cm2. At low frequency, a surface with an impedance of 109 Ω‚cm2 or greater is considered a good protective barrier.19 By increasing the curing temperature by 20 °C, the 2% 296 coating impedance at low frequency increased by approximately 2 orders of magnitude, turning the 2% 296 paint from a mediocre protective barrier into a good protective barrier. The Tg was 21 °C, which was substantially higher than the Tg for the coating that was cured at 120 °C (Tg ≈ 2.5 °C). The new Tg temperature was a normal Tg value for a properly cured polyester-melamine paint film. The Tg increased from 21 to 52 °C after being heated to 300 °C (i.e., no overbake softening occurred). Therefore, the crosslinking density of the polyester-melamine polymers increased upon exposure to high temperatures when 296 was used as the acid additive. The saltwater immersion studies showed that, after the painted panels had been submerged in a 3% NaCl solution, tiny blisters (∼2 mm in diameter) formed along the area of the scribe and were removed by the tape. However, no blisters were formed in other areas of the panel that were exposed to the salt solution. Again, this behavior was not characterized in ASTM method D3359. The paint was only slightly darker in color after the exposure to the salt solution. Visually, the color was not any yellower; only the shade changed. Increasing the curing temperature caused the cured coating to become more resistant to the salt solution. Curing 2% 296 paint at 120 °C caused the paint to blister everywhere that it was exposed to the salt solution. While being cured at 140 °C, no blisters formed outside the area of the scribe mark. The pencil hardness of the paint was F, which is harder than the paint that was cured at 120 °C (1000 Hz) is usually attributed to the dielectric properties of the organic paint film.21 The high-frequency portions of the Bode-magnitude plots for 2% 296, 1% PA-75, 1% ISPR-1, and 0.5% ISPR-2 have a slope of -1. A pure capacitor has a slope of -1 in a Bode-magnitude plot. Because the higherfrequency impedance is due to the organic coating itself, these acid catalysts created better coatings than did 1% 4040. The impedance at high frequency does not have a slope of -1 for 1% 4040. Therefore, the coating does
not behave as a pure capacitor and does not produce as protective a coating-metal interface as the other acid additives in the study. Recall that p-TSA is present in 4040 and is the most commonly used acid catalyst for polyester-melamine coatings. However, its use as a catalyst did not produce a better coating capacitance than the other catalysts studied. Phosphate esters might be better catalysts that can selectively promote desirable reactions in polyester-melamine paint systems.16 Figure 3 shows that the behavior at lower frequencies of the painted panels deviates from that of a pure capacitor. The polyester-melamine paint systems that were catalyzed with 1% ISPR-1 (curve A), 1% PA-75 (curve B), 0.5% ISPR-2 (curve C), and 2% 296 cured at 140 °C (curve D) all produced good protective barriers, as their impedances at low frequency (0.01 Hz) were 109 Ω‚cm2 or higher. However, the impedance increased at low frequency in the order 2% 296 (cured at 140 °C) < 0.5% ISPR-2 < 1% PA-75 < 1% ISPR-1. Therefore, of the acid additives used in this study, 1% ISPR-1 produced the best protective barrier. The 1% 4040catalyzed paint had a maximum impedance at low frequency on the order of 106 Ω‚cm2 (curve E). p-TSA produced a protective barrier that was inferior to those of the other phosphorus-containing additives in this study. The saltwater immersion results are shown in Table 2, and the pictures of the panels are shown in Figure 4. The studies showed that the 1% ISPR-1 sample gave the least amount of paint removal and no discoloration of the paint (Figure 4D). The addition of 0.5% ISPR-2 gave mixed results of good adhesion with no paint removal (which is better than 1% ISPR-1) and small
Figure 3. Bode-magnitude plots for painted 3105 Al with different acid catalysts: (A) 1% ISPR-1, (B) 1% PA-75, (C) 0.5% ISPR-2, (D) 2% 296 (cured at 140 °C), (E) 1% 4040.
3678
Ind. Eng. Chem. Res., Vol. 42, No. 16, 2003
Figure 4. Results of adhesion studies of painted 3105 Al panels after being submerged in saltwater for 66 days: (A) 1% 4040 (after 1 week), (B) 2% 296, (C) 1% PA-75, (D) 1% ISPR-1, (E) 0.5% ISPR-2.
clumps of blisters removed that were 2 mm in diameter (Figure 4E). Because the results were not reproducible, 0.5% ISPR-2 was considered the second best result from the saltwater immersion study. Two percent 296 (cured at 140 °C) was the third best result from the saltwater immersion study. Two percent 296 had blisters removed along the scribe that were 2 mm in diameter (Figure 2B). One percent PA-75 as the acid additive produced blisters that were 5 mm in diameter (Figure 2C). Finally, after being submerged for 1 week, 1% 4040 had all of the paint removed from the surface of the metal after the tape was applied and removed (Figure 2A). The poor performance of 4040 was not surprising given that it showed no adhesion to the metal surface in the FTIR studies. The paint formula from the company suggests that the pencil hardness of the polyester-melamine coating should be around F-H. One percent 4040, 2% 296 (cured at 140 °C), 1% PA-75, and 1% ISPR-1 all had pencil hardnesses in the range recommended by the company, whereas 0.5% ISPR-2 was slightly softer. IV. Conclusions The surface studies using FTIR spectroscopy, SEM, EDX, and optical microscopy showed that chemical
bonding occurred at the surface of the Al, forming a metal-phosphate layer with the catalysts 296, PA-75, ISPR-1, and ISPR-2. Because these additives have the ability to bond with the surface of Al and are acidic in nature, they can be used as acid catalysts in polyestermelamine coatings and as in situ phosphatizing reagents. The 1% ISPR-1 additive seemed to be the best choice for use as an acid catalyst and in situ phosphatizing reagent in a polyester-melamine coating. The reflectance FTIR spectrum showed that a metalphosphate layer could be produced. The photographs from the optical microscope confirmed a uniform metalphosphate layer on the surface of polished Al. The 1% ISPR-1 paint produced a coating that behaved as a pure capacitor at high frequency and had an impedance on the order of 1010 Ω‚cm2 at low frequency. This is indicative of a good protective barrier for the base metal. The 1% ISPR-1 sample also showed the best adhesion to the aluminum substrate after being submerged in a 3% sodium chloride solution for 66 days. The Tg for the 1% ISPR-1 paint was not as high as that for the 1% 4040 paint, but it was similar in value to the Tg’s of the other additives tested. The 1% 4040 paint showed a severe case of overbake softening behavior. The pencil hardness for 1% ISPR-1 was in the range appropriate for the paint
Ind. Eng. Chem. Res., Vol. 42, No. 16, 2003 3679
recipe. Note that 1% 4040 has p-TSA as the active ingredient. This is the most commonly used acid catalyst for polyester-melamine coatings, and this additive performed substantially worse than 1% ISPR-1 in its impedance and its adherence to the metal substrate in these coatings. On percent ISPR-1 gives a simultaneous acid catalysis of the polyester-melamine paint and in situ phosphatization of the Al substrates. It has been suggested that phosphate esters more selectively catalyze reactions between melamine and polyester polyol. The 4040 as an acid catalyst has a reduced Tg after being heated to 300 °C, whereas the other acid additives had increased Tg’s. The differences in the behavior of the Tg’s for the various acid catalysts suggests that a different catalytic process is involved. One percent ISPR-1 is the acid additive that produced the best coating in this study. Even though the acid additive used for polyester-melamine coatings was only a small percentage of the whole paint formulation, it was an important factor in the resulting performance of the cured coating. Acknowledgment Financial support from the National Science Foundation, Grant CTS-9312875, and the NIH MBRS-RISE, Grant 1 R25 GM61325-O1A1, is acknowledged . The authors thank AKZO Resins and Dupont Ti-Pure for their donations of some paint materials and Mike Spires from Northern Illinois University for help in graphics and editing. Literature Cited (1) Freeman, D. B. Phosphating and Metal Pretreatment; Industrial Press: New York, 1986. (2) Spadafora, S. J.; Hegedus, C. R.; Hirst, D. J.; Eng, A. T. Primerless Finishing Systems for Aluminum Substrates. Mod. Paint Coat. 1990, 80, 36. (3) Rausch, W. The Phophating of Metal; ASM International, Metal Park, and Finishing Publications Ltd.: Teddington, Middlesex, U.K., 1990. (4) Paint Waste Reduction and Disposal Options; Hazardous Waste Research and Information Center: Champaign, IL, 1992; Vol. I (HWRIC RR-060) and II (HWRIC TR-008). (5) Lin, C. T.; Lin, P.; Hsiao, M. W.; Meldrum, D. A.; Martin, F. L. Chemistry of Single-Step Phosphate/Paint System. Ind. Eng. Chem. Res. 1992, 31, 424. (6) Meldrum, D. A.; Lin, C. T. AC Impedance Analysis and Factorial Designs of an In Situ Phosphatizing Coating. J. Coat. Technol. 1993, 65, 47.
(7) Lin, C. T.; Lin, P.; Quitian-Puello, F. Interfacial Chemistry of a Single-Step Phosphate/Paint System. Ind. Eng. Chem. Res. 1993, 32, 818. (8) Lin, C. T. Additive Package for In Situ Phosphatizing Paint, Paint and Methodology. U.S. Patent 5,322,870, 1994. (9) Li, L.; Lin, C. T. SEM-EDS Investigation of Self-Phosphating Coatings. Ind. Eng. Chem. Res. 1994, 33, 3241. (10) Yu, T.; Li, L.; Lin, C. T. Chemical Affinity of in Situ Phosphatizing Reagents on Cold Rolled Steel. J. Phys. Chem. 1995, 99, 7613. (11) Yu, T.; Lin, C. T. The performance of in Situ Phosphatizing Reagents in Solvent-Borne Paints. Ind. Eng. Chem. Res. 1997, 36, 368. (12) Yu, T.; Lin, C. T. In Situ Phosphatizing Coatings II: A High-Solids Polyester Baking Enamel. J. Coat. Technol. 1999, 77, 77 (892), 69. (13) Wang, C. H.; Chuang, Y. Y.; Lin, C. T. In Situ Phosphatizing Coatings I: an Air-Dried Lacquer System. J. Coat. Technol. 1999, 77 (892), 61. (14) Yu, T.; Whitten, M. C.; MuZoz, C. L.; Lin, C. T. ChromeFree Single-Step In Situ Phosphatizing Coatings. In Green Chemical Synthesis and Processes; Anastas, P. T., Heine, L. G., Williamson, T. C., Eds.; ACS Symposium Series 767; American Chemical Society: Washington, DC, 2000; p 43. (15) Whitten, M. C.; Lin, C. T. Coating Performance of Polyester-Melamine Enamels Catalyzed by an in Situ Phospatizing Reagent on Aluminum. Ind. Eng. Chem. Res. 1999, 38, 3903. (16) Gan, S.; Solimeno, R. D.; Jones, F. N.; Hill, L. W. Recent Studies of the Curing of Polyester-Melamine: Possible Causes of Overbake Softening. In Proceedings of the Sixteenth Annual International Symposium on Waterborne, Higher Solids, and Powder Coatings; Storey, R. F., Thames, S. F., Eds.; University of Southern Mississippi: Hattiesburg, MS, 1989; p 87. (17) Bershtein, V. A. Differential Scanning Calorimetry of Polymers: Physics, Chemistry, Analysis and Technology; Kemp, T. J., Translation Ed.; Ellis Horwood: NewYork, 1994. (18) Paint and Coating Testing Manual (Gardner-Sward Handbook, 14th ed.); Koleske, J. V., Ed.; ASTM Manual Series MNL17; ASTM: Philadelphia, PA, 1995. (19) Leidheiser, H. Towards a Better Understanding of Corrosion Beneath Organic Coatings. Corrosion 1983, 39, 189. (20) Osaka, A.; Takahashi, K.; Ikeda, M. Infrared Study of Trivalent Cations Boron and Iron in Amorphous and Crystalline Phosphates. J. Mate. Sci. Lett. 1984, 3, 36. (21) Scully, J. R. Electrochemical Impedance Spectroscopy for Evaluation of Organic Coating Deterioration and Under Film Corrosion: A State of the Art Review; Report DTNSRDC/SME86/ 006; David W. Taylor Naval Ship Research and Development Center: Annapolis, MD, 1986.
Received for review August 14, 2002 Revised manuscript received January 25, 2003 Accepted May 23, 2003 IE020632P
