Automotive Basecoats Research Articles

Dispersion stability, adhesion strength, and anti-corrosion properties of water-born polyester resins

In this study, a water-reducible polyester resin curable with melamine resin was synthesized and characterized to be used as a strong automotive base-coat. The main goal is to produce a resin with improved properties compared to similar products. Glycidyl neodecanoate was used as the key polyol monomer. The presence of polyester index peaks in the FTIR test, along with the results of the TGA, DSC, and GPC tests, was a testament to the controlled confirmation of water-based polyester synthesis. Due to the zeta potential value (−50.28 mV) for the PS3 sample (trimethylolpropane, adipic acid, glycidyl neodecanoate, and trimellitic anhydride monomers), this sample had less accumulation and instability separation than other samples. Samples were compared with commercial paint to evaluate the quality of the paint. The synthesized samples and the commercial sample were applied to the steel substrate. A pull-off test was used to check the adhesion strength to the substrate. The adhesion strength of the PS3 sample was recorded 4.3 MPa on steel sheet and 2.30 MPa on electrodeposition layered steel. Electrochemical impedance spectroscopy test showed that the samples PS1 and PS3, after 15 weeks of immersion in 3.5 wt% sodium chloride solution, provided resistances of 4.59 × 109 and 2.45 × 109 Ω cm2. Also, digital images taken from the surface of the samples in the salt spray test revealed that PS3 and in the next stage, PS1 after one month of exposure to corrosive environment, showed better corrosion resistance than other samples.

Using an alternatives assessment framework to evaluate waterborne versus solventborne basecoats used in automotive refinishing.

We evaluated two types of automotive basecoats used in automotive refinishing (i.e., in auto body shops): waterborne and solventborne. The primary tool we used for this evaluation was the Alternatives Assessment Guide (version 1.0) developed by the Interstate Chemicals Clearinghouse (IC2). The term "solventborne," as used in this article, refers to products that contain relatively high concentrations of volatile organic compounds (referred to as "high-volatile organic compound [VOC] basecoats" in the industry). These products are distinct from the "low-VOC" solventborne products used widely in California and elsewhere. From a health and environmental hazard perspective, our evaluation found that waterborne basecoats contained fewer hazardous ingredients and at lower concentrations than their solventborne counterparts. Automotive painters who spray-painted vehicles with waterborne products experienced significantly lower exposures to several harmful solvents. Waterborne products are readily available and offer advantages with regard to social impacts. Some of these advantages include lower worker and community exposure to VOCs, reduced VOC release and smog formation, and reduced potential for generation of and exposure to hazardous waste. Based on our assessment in auto body shops, we consider waterborne basecoats to be safer alternatives from both a human health and environmental perspective. Integr Environ Assess Manag 2022;18:1101-1113. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

High solid waterborne automotive base coat: Beyond shear thinning

Waterborne, aluminum effect pigment bearing coatings dry into automotive base coats (WBC) with viewing angle depending light reflectivity: the mirror like 2D pigments are oriented homogeneously not least due to the large shrinkage of shear thinning paint materials with low non volatile content (NVC). The present study describes higher NVC paint materials by making use of exfoliated α‑zirconium phosphate platelets (α-ZrP) and zirconium etidronate (Zr-HEDP) filaments with 7.5 and 0.3 wt%, respectively. In both cases lyotropic liquid crystalline phases yield WBCs with highly angle dependent reflectivity. Analyses of the pigments' distribution, inclination angles and their interphase with the matrix reveal an increased effective pigment volume fraction through an α-ZrP envelope and the high efficiency of ultra-long Zr-HEDP filaments on the pigments alignment.

Controlling the elongational flow behavior of complex shear-thinning fluids without affecting shear viscosity

Complex flow fields including high elongational deformation occur in numerous industrial processes such as spraying, coating, fiber spinning, and screen or inkjet printing. Fully exploiting the potential of these technologies suffers from a lack of knowledge regarding how elongational flow properties of the processed fluids affect the results of these operations. Here, we present two strategies that allow for varying the elongational flow behavior independent of shear rheology. First, two acrylic thickener solutions that differ with respect to the fraction of hydrophobic co-monomers and hence with respect to their degree of inter- and intramolecular hydrophobic association were mixed to vary the elongational relaxation time, as determined using capillary breakup elongational rheometry (CaBER), by almost two orders of magnitude without affecting shear viscosity of these solutions in a wide, processing-relevant shear rate range. Second, a substantial increase in the elongational flow resistance was achieved by adding a small amount of plate-like particles without affecting the shear viscosity of these thickener solutions. A fourfold increase of the elongational relaxation time was observed upon the addition of 3.5 vol.% of glass flakes to such a highly shear-thinning system. A similar effect was also observed for an industrial waterborne automotive basecoat due to added aluminum flakes. This work may be useful for product development since the control of extensional viscosity can improve technological applications, and the introduced model systems may therefore be used for systematic, goal-oriented investigations of the relevance of elongational flow properties in the technological processes mentioned above.

Novel techniques to investigate the impact of cellulose esters on the rheological properties and appearance in automotive basecoat systems

The viscous response of a coating formulation changes over several orders of magnitude after application onto a substrate. Furthermore, the performance and application attributes for a refinish basecoat formulation are slightly different from those of an OEM basecoat. The absence of a high temperature baking step during the refinish process necessitates that the paint exhibit very good antisag behavior as well as quick ‘dry to touch’ without compromising the flow and leveling properties of the coating as it dries. As most paint formulations are multicomponent in nature, it is always a challenge to precisely measure the impact of specific formulation components on the collective performance attributes of the applied coating. In this work, the focus has been to develop novel techniques that can be used to demonstrate a more quantitative measure of some of the performance attributes that rheological additives like cellulose esters can provide to automotive coatings. A series of pigmented basecoat formulations were prepared which contained cellulose acetate butyrates (CABs) of varying molecular weights at different levels based on the total solids of the coating formulation. The nonvolatile content of the formulations was also varied. The viscoelastic behavior of a typical automotive basecoat formulation during the drying process was then investigated using a novel rheological technique. Complex viscosity data (including storage and loss moduli as well as tan delta) were determined as a function of drying time and then compared to the macroscopic properties typically associated with a coating film as it dries. Thermogravimetric analysis (TGA) was also used to correlate the rheology of the metallic basecoat formulations with drying behavior of the coating. The final appearance of the coating was investigated by several microscopic techniques such as Laser Scanning Confocal Microscopy, Scanning Electron Microscopy, Atomic Force Microscopy, and Surface Profilometery, and attempts were made to correlate bulk measurements like ‘flop index’ with the microstructure of the coating.

BASF Coatings introduces waterborne automotive basecoat technology in China

BASF Coatings introduces waterborne automotive basecoat technology in China

Elongational flow behavior of automotive coatings and its relation to atomization and mottling

The elongational flow properties of waterborne and solvent borne automotive basecoats have been characterized using opposing jet and contraction flow techniques. The ratio of elongational to shear viscosity varies between less than 20 and more than 300, showing that the behavior of such fluids in complex flows (atomization, filtration, impingement of droplets on substrates) cannot be deduced from shear viscosity alone. A clear correlation is found between the elongational viscosity of the fresh material and its sprayability as well as the optical appearance of the final coating in the case of the waterborne formulations. The opposing jet technique resolves these differences much better than contraction flow experiments. No such correlation is found for the solvent borne systems presumably since their rheological properties undergo a much stronger change during application.

Crosslinking vs. interdiffusion rates in melamine-formaldehyde cured latex coatings: A model for waterborne automotive basecoat

Designing optimal formulations for automotive waterborne basecoats can be fairly complex, often requiring knowledge of events that occur at the molecular level. The ultimate performance of the coating can depend upon the success with which this knowledge is applied. We examine a system in which an aqueous dispersion of an acrylic latex with -OH functionality reacts with a melamine derivative when heated. We use fluorescence-labeling and energy transfer measurements to obtain information on the relative rates of crosslinking and interparticle polymer diffusion in these films. We show that temperature and particle morphology play an important role in the development of film properties. Finally, these energy transfer experiments provide information on the location of the melamine-formaldehyde resin in the dry film before the onset of crosslinking. This system can serve as a model for waterborne basecoat development in many automotive applications.

Increasing paint application transfer efficiency on robotic waterborne automotive basecoat application

Increasing paint application transfer efficiency on robotic waterborne automotive basecoat application