| It is very important for automobile underbody coating with properties of chipping resistance and corrosion resistance to prolong automobile service lives, reduce material loss,save energy and reduce noise. According to the problem of automobile underbody protection in the vehicle manufacture, this thesis systematically discusses the feasibility and key technology of one-component polyurethane (urea) coating as protective material applied on the chassis surface.The one-component polyurethane (urea) (1KPU(A))elastomer coating, with excellent surface protection performance, was developed to adapt vehicle production lines, based on the deep analysis of the characteristics of polyurethane (urea) coating and performance requirements of stone impact, sound insulation and anti-corrosion etc. for automotive underbody. Investigating of wear resistance, sound insulation and corrosion resistance of the 1KPU(A) elastomer coating film was carried out under simulated condition of road environment, atmospheric environment and noise environment. The experiment results showed that 1KPU(A) elastomer coating was an excellent anti-corrosion material with advanced performance of chipping resistance and sound insulation.The mechanism of chipping resistance, sound insulation and anti-corrosion was studied by characterizing the surface morphology, dynamic mechanical properties, damping performance and electrochemical impedance spectroscopy of the 1KPU(A) elastomer coating film, providing scientific application method and theoretical basis for polyurethane (urea) further applied in the surface protection.And it was achieved for 1KPU(A) elastomer coating to be applied for the first time in automotive underbody surface protection.The main contents and conclusions were as follows:1?The multiple-blocked prepolymer was prepared by reacting polyether polyolsGMN3050A and GE220A, with,and then blocking the NCO groups of Liquefied MDI prepolymer with diethyl malonate, ethyl acetoacetate,3,5-dimethyl pyrazole for the first time. Orthogonal design was used to optimize the synthesis process of liquid MDI prepolymer and the corresponding mutiple-blocked prepolymer. Then the structure of mutiple-blocked prepolymer was characterized by infrared spectroscopy. And it was discussed the effect of reaction temperature, ratio of polyether polyols, latent NCO content, and ratio of blocking agents on prepolymers viscosity and corresponding tensile strength, elongation at breakage of films therefore. And unblocking temperature and storage stability of the multiple-blocked prepolymer was comfirmed by experiments.2?Novel type of 1KPU(A) elastomer coating with good performance of tensile strength and elongation at breskage was obtained by studying the effect of main sticky materialhard such as multiple-blocked prepolymer,amion chain extender, low unsaturation polyether polyols on performance of film. The 1KPU(A) elastomer coating was prepared by means of curing by baking after being sprayed And the physical,chemical and mechanical properties of the film therefore was investigated comprehensively. According to the experiment results, the polyurethane (urea) elastomer coating met the requirements of national standard GB/T23446-2009,"Spray Polyurea waterproofing coating".3?The anti-stone wear properties of 1KPU(A) was studied in accordance with ISO20567-1-2005.The wear mechanism of 1KPU(A) was discussed by detecting impact adhesion after stone impact test, combining with dynamic mechanical properties, thermal properties, morphology analysis of surface wear. The results showed that there was no obvious spalling and cracks observed from the micro morphology of the film after stone chip test. Additionally, the weight loss of the film after stone chip test is only 2.4% of automobile coating overlayer, and just 20% of PVC plastisol, indicating excellent chipping resistance and wear resistance properties. Further,it was still keeping excellent interface adhesion between the film and metal substrate after stone impact. Dynamic mechanical analysis of the coating approved that 1KPU(A) elastomer coating film had high damping and stiffness in the range of-50?to 200?, and the glass transition region could cover the coating application temperature, providing a guarantee for excellent chipping resistance property of the film.It was proposed that the stone chipping phenomenon of coating was the result of abrasive wear behavior of the coating material under high stress, and that the wear mechanism includes (a) the shallow strata drops, and then (b) the cracks originated in the material subsurface near the surface, extend parallel to the surface. Also it was proposed that the high tensile strength, elongation at breakage and tear strength of coating could improve the chipping resistance performance effectively.4?The noise insulation performance of 1KPU(A) elastomer coating was discussed through analyzing and testing of weighted sound transmission loss varying with the different thickness, the different density and the different strength. The results showed that weighted sound transmission loss of the coating increased with increasing thickness, compressive strength and density. The sound insulation regularity of one-component polyurethane (urea) coating followed the mass effect and the consistent effect in the acoustics. One-component polyurethane (urea) coating material had high damping loss coefficient, which had narrow resonance frequency range and great consistent frequency,it was a typical material with efficiency performance of noise insulation. The weighted sound transmission loss was still more than 5dB after the stone chip test, indicating it had good sound insulation performance.5?The anti-corrosion properties of one-component polyurethane (urea) coating material was tested by solution immersion, neutral salt spray and damp-heat.And chemical resistance properties of the new 1KPU(A) elastomer coating were investigated by electrochemical impedance spectroscopy in the hydrochloric acid and sodium chloride solution.The results showed that polyurethane (urea) elastomer coating had good anti-corrosion performance and could provide effective protection for metal substrates. It was found that chemical medium permeated into the internal film during chemcial immersion, which only leading to a slight decrease in coating impedance, and a slight increase in coating capacitance.From the mechanism, that was mainly because the polyurethane (urea) elastomer coating could form once a dense film, isolating the film from water, with thickness up to 2mm, which could effectively prevent steel against infiltration of the chloride ions, oxygen, hydrogen etc. Additionally, remaining free amine in coating film absorbed on the steel surface and, resulting in the steel surface passivation, even though the time of immersion in the corrosion media was prolonged, the passivation film could prevent further corrosion even slight media penetration.6?The technology of one-component polyurethane (urea) coating applied to automobile underbody was formed,based on development of multiple-blocked prepolymer and coating, performance test, process optimization and line spraying experiment.Application of 1KPU(A) elastomer coating on protection surface of automobile underbody was first realized.The results showed that 1KPU(A) elastomer coating had good performance of spraying construction, anti-over baking and adhesion.lt could meet the requirements of related safety and environmental protection properties.1KPU(A) elastomer coating kept well after complicated road test.Indicating that 1KPU(A) elastomer coating possessed good performance of chipping resistance anti-corrosion. There were good adhesion between the film and substrates,and there were no crack,corrosion,stripping,abscisic on the surface of coating.The insulation effect of complete vehicle could meet the requirements of relevant standards of automobile works. |
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