Chapter 9
Polyurethane-Polysiloxane Ceramer Coatings 1,4
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Downloaded by UNIV MASSACHUSETTS AMHERST on September 9, 2012 | http://pubs.acs.org Publication Date: August 30, 2007 | doi: 10.1021/bk-2007-0962.ch009
Hai Ni , William J. Simonsick , and M a r k D . Soucek * 1
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Polymers and Coatings Department, North Dakota State University, Fargo, ND 58105 DuPont Marshall Lab, 3401 Grays Ferry Avenue, Philadelphia, PA 19146 Polymer Engineering Academic Center, 250 South Forge Street, Room 221, Akron, O H 44325-0301 Current address: BEHR Corporation, 3400 Segerstrom Avenue, Santa Ana, C A 92704 3
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New low V O C (volatile organic compounds) polyurethane/oligosiloxane coatings were formulated using, 1, 6-hexamethylene diisocyanate (HDI) isocyanurate, alkoxysilane-functionalized HDI isocyanurate, tetraethyl orthosilicate (TEOS) oligomers and three cycloaliphatic polyesters. One series of polyester was synthesized using 1,4-cyclohexanedimethanol (CHDM) with 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) and 1,3-cyclohexanedicarboxylic acid (1,3C H D A ) . A second series of polyesters was synthesized using 2-butyl-2-ethyl-1,3-propanediol (BEPD) with 1,4-CHDA or 1,4-CHDA and 1,3-CHDA, respectively. The polyurethane provided the required mechanical properties and polysiloxane functioned as an adhesion promoter and a corrosion inhibitor. The continuous organic polyurethane phase was coupled to the inorganic polysiloxane phase via the alkoxysilane— functionalized HDI isocyanurate. The general coatings, tensile, viscoelastic properties, and corrosion resistance were evaluated for the ceramer coatings as functions of the polyester and concentration of TEOS oligomers. The coatings properties were dominated by the organic phase. The corrosion resistance was found to be a function of TEOS with © 2007 American Chemical Society
In New Developments in Coatings Technology; Zarras, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
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136 a maximum of corrosion resistance and coating properties at 10-15 wt % TEOS. The film morphology was investigated using the combination of S E M (Scanning Electron Microscope) and X-ray analysis. Phase separation was observed for ceramer coatings resulting in SiO particles. The size of the pre-ceramic silicon-oxo-particles was controlled by the Tg of the organic phase and the concentration of TEOS oligomers. Downloaded by UNIV MASSACHUSETTS AMHERST on September 9, 2012 | http://pubs.acs.org Publication Date: August 30, 2007 | doi: 10.1021/bk-2007-0962.ch009
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Introduction The aluminum substrates for aircraft are coated with many steps. First, the aluminum is pretreated with a chromate solution as a conversion layer to prevent corrosion. Following that, a 2-K epoxy-polyamine system with the chromate pigment is applied as a primer, in which the chromate pigment functions as corrosion inhibitor. The topcoat is typically a two-component polyurethane coating consisting of an HDI oligomer and a polyester polyol. In this system, the presence of chromate is carcinogenic. Many approaches have been carried out in this area to limit the usage of chromate. ' Our approach is to develop a polyurethane/polysiloxane ceramer selfpriming coating or "Unicoat" system, which was designed on the basis of the traditional aircraft topcoat. In this system, polyurethane provides the general mechanical properties and polysiloxane functions as an adhesion promoter and corrosion inhibitor. Our previous studies of polyurea/polysiloxane ceramer coatings showed that the alkoxysilanes have a dramatic effect on the adhesion enhancement. The polysiloxane formed by the sol-gel precursor, Tetraethyl orthosilicate (TEOS) oligomers, has a strong effect on the corrosion inhibition. To improve the UV-resistance for the traditional aircraft topcoat, a series of cycloaliphatic polyesters were also investigated in our previous study. The cycloaliphatic polyesters can provide better flexibility and yellowing resistance compared to the phenyl structure of aromatic diacids in the traditional formulation. To further simulate the traditional aircraft topcoat, the cycloaliphatic polyesters were added into the polyurea/polysiloxane ceramer coating system to formulate a polyurethane/polysiloxane ceramer coating system in this study. Two typical high-solid polyesters were synthesized from the diols, 1,4cyclohexanedimethanol ( 1,4-CHDM) and 2-butyl-2-ethyl-1,3-propanediol (BEPD), and the diacids, 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) and 1,3-cyclohexanedicarboxylic acid (1,3-CHDA). The esterification reaction is shown in Equation 1. The chemical structure of B E P D is shown in Scheme 1. 1
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In New Developments in Coatings Technology; Zarras, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
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