Motoshi Yabuta

The rheological properties of an aqueous acrylic dispersion suitable for automotive waterborne basecoats

Superior film appearance as well as performance is required of automotive top-coatings applied using the method of two-coat one-bake (2C1B) in the case of metallic finishes. The basecoats, however, dominate the final film appearance, that is, the metallic effect and the film surface smoothness. Waterborne metallic basecoats are rather difficult to maintain a high level of workability and appearance under various spraying conditions involving a wider range of temperature and humidity. Both the aluminum flake orientation and the surface smoothness of basecoats, which involve opposite requirements especially in a waterborne system, should be superior before clearcoats are over-coated. In this paper, we will present a means of incorporating them. The studied model basecoats are composed of three materials, a specific water-dispersible acrylic resin, an internally crosslinked latex and a melamineformaldehyde resin. The viscosity versus non-volatile content relationship and the viscoelastic behavior of the model paints are discussed, in relation to the actual spraying workability and the final appearance.

The relation between the dispersion state of polymer microspheres in coatings and film properties

Abstract Coatings composed of non-aqueous polymer dispersion (NAD)/solution acrylic/melamine-formaldehyde resin give a typical two-phase structured film. The dispersion state of the polymer microspheres (NAD) in a crosslinked polymer matrix affects the mechanical and esthetic properties of the derived coatings. A major concern is how to control and characterize quantitatively the dispersion state of polymer microspheres in the films. In this study, the cross-section of thermally cured clear films containing NAD has been observed by transmission electron microscopy (TEM) and the dispersion state characterized in a statistical manner using Morishitas quadrat method. The dispersion state of polymer microspheres can be varied from Poissons distribution to an aggregated distribution by modulating the miscibility between the polymeric dispersant of the NAD and the polymer which constitutes the continuous phase. The dispersion state can also be varied to some extent by the composition of the NAD spheres.

Self-crosslinkable graft copolymer with blocked isocyanate and other functionalities: synthesis, reactivity and application to thermoset coatings

Abstract Novel self-crosslinkable graft copolymers with complementary reactive groups, that is, a pendant blocked isocyanate in the first segment and a hydroxyl group in the second segment, were developed. In order to incorporate isocyanate functionality, m -isopenyl-α,α-dimethyl benzyl isocyanate (TMI) was (copolymerized with n-butyl acrylate (nBA) by radical polymerization in solution. Subsequently, a part of the isocyanate was reacted with 2-hydroxyethyl acrylate (HEA) in order to incorporate a polymerizable double bond into the copolymer molecule. After blocking the remaining isocyanate groups with methyl ethyl ketone (MEK) oxime, the polymerizable prepolymer was copolymerized with methacrylates, including hydroxyl monomers, to form the graft copolymer. Another process of preparing the graft polymer was also carried out; TMI/nBA copolymer was reacted with MEK oxime to block about 70% of isocyanate groups, then poly(ol)polymer such as poly(ester)resin was added. After the grafting reaction was completed, remaining NCOs were blocked by MEK oxime. Furthermore, by incorporating neutralizable functionalities such as carboxyl or tertiary amino groups to the second segment of the graft copolymer, self-dispersible (self-stabilized) aqueous coating vehicles were prepared. MEK oxime blocked tertiary isocyanate from TMI in the present graft polymers exhibits fairly lower deblocking temperature comparing to the similar products derived from IBM (isocyanatoethyl methacrylate) or isophorone diisocyanate-hydroxyethyl acrylate (IPDI-HEA) adduct, and hence it is possible to produce coatings curable at a lower temperature (100–120 °C) while retaining satisfactory storage stability. Owing to this curability the coatings are applicable to the products made of plastics such as components of automotives etc. Possible application to waterborne coatings is also described.