Optimal Curing of Color Coatings with Bio-Based Technology
Tiihonen, Vesa (2023)
2023
Materiaalitekniikan DI-ohjelma - Master's Programme in Materials Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2023-05-09
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202304193975
https://urn.fi/URN:NBN:fi:tuni-202304193975
Tiivistelmä
The objective of this thesis was to determine how the increase in bio-solvent affects the properties and curing of the color coating in coil coated steel. The chosen test methods were also assessed for their ability to indicate changes in cure. 5 coatings were initially tested: a gray, low gloss polyester-based coating in low and high gloss versions, a high gloss red polyester-based coating and two medium gloss polyurethane-based coatings in black and white color. The samples had a similar amount of bio-solvent added in the coating and these samples were then compared to their respective references, that had a regular amount of bio-solvent added in the coating. A curing time comparison was also done for all the samples to see how changes in cure affect the samples with increased bio-solvent.
The tested coatings were applied to zinc coated steel sheets that had a primer coating applied in a coil coating line. The color coating was spread to the sample sheets manually in laboratory conditions with a metallic application rod and the coatings were cured in a laboratory oven. There were curing problems encountered with the first laboratory oven that was initially used to cure the samples. As a result, the oven was changed. Due to lack of extra sheets, the high gloss version of the gray polyester coating was removed from testing and only a part of the sample sheets of the red polyester sample could be painted and cured again with the second oven. A battery of tests was done after sample preparation. The tests included mechanical tests, optical measurements, chemical resistance tests, glass transition temperature measurement with differential scanning calorimetry (DSC), and indentation hardness testing with microindentation instrument. The mechanical tests were done two times in two different laboratories to determine if there were any post curing effects taking place in the samples, and to gather information regarding the re-producibility of the results.
Results show that with the chemical resistance tests, the results between the tests were mixed, as the MEK solvent rub test indicated excellent cure for properly cured samples and the stripper test showed very poor results overall for the samples. Mechanical properties of the coatings were mainly unaffected by the increase in bio-solvent. The color and gloss of the coating are also mainly unaffected. Examination of glass transition temperature shows either similar values in comparison with the reference, or minor, 1-2 °C deviations. In the microhardness tests the changes brought by the bio-solvent showed that the gray, low gloss polyester sample softened as result of the bio-solvent increase, while microhardness of the polyurethane-based samples remained similar or close to the reference values. Curing time comparisons showed that changes in the cure affect mainly the scratch resistance and indentation hardness properties of the coatings.
The suboptimal curing of the faulty oven is seen in the results of the red polyester-based coating as reduced performance of the reference sample. The results of the curing time comparison for the red polyester are also influenced by the suboptimal cure. As a result, the comparison with this coating is not very meaningful. Regarding the mechanical tests that were done twice, the scratch and pencil resistance values were lower in the second test, while the results of flexibility and impact hardness testing are similar performance when repeated. The scratch hardness differences are most likely related to the test methods themselves, as similar findings have been noted before in previous coating tests.
The tested coatings were applied to zinc coated steel sheets that had a primer coating applied in a coil coating line. The color coating was spread to the sample sheets manually in laboratory conditions with a metallic application rod and the coatings were cured in a laboratory oven. There were curing problems encountered with the first laboratory oven that was initially used to cure the samples. As a result, the oven was changed. Due to lack of extra sheets, the high gloss version of the gray polyester coating was removed from testing and only a part of the sample sheets of the red polyester sample could be painted and cured again with the second oven. A battery of tests was done after sample preparation. The tests included mechanical tests, optical measurements, chemical resistance tests, glass transition temperature measurement with differential scanning calorimetry (DSC), and indentation hardness testing with microindentation instrument. The mechanical tests were done two times in two different laboratories to determine if there were any post curing effects taking place in the samples, and to gather information regarding the re-producibility of the results.
Results show that with the chemical resistance tests, the results between the tests were mixed, as the MEK solvent rub test indicated excellent cure for properly cured samples and the stripper test showed very poor results overall for the samples. Mechanical properties of the coatings were mainly unaffected by the increase in bio-solvent. The color and gloss of the coating are also mainly unaffected. Examination of glass transition temperature shows either similar values in comparison with the reference, or minor, 1-2 °C deviations. In the microhardness tests the changes brought by the bio-solvent showed that the gray, low gloss polyester sample softened as result of the bio-solvent increase, while microhardness of the polyurethane-based samples remained similar or close to the reference values. Curing time comparisons showed that changes in the cure affect mainly the scratch resistance and indentation hardness properties of the coatings.
The suboptimal curing of the faulty oven is seen in the results of the red polyester-based coating as reduced performance of the reference sample. The results of the curing time comparison for the red polyester are also influenced by the suboptimal cure. As a result, the comparison with this coating is not very meaningful. Regarding the mechanical tests that were done twice, the scratch and pencil resistance values were lower in the second test, while the results of flexibility and impact hardness testing are similar performance when repeated. The scratch hardness differences are most likely related to the test methods themselves, as similar findings have been noted before in previous coating tests.