Table of contents (TOC) Introduction (2-5) Experimental (6-7) Equipment (8) Properties (9-17) Reynold’s numbers (18-19) Conclusion (20-24)

Introduction 2-Component Waterborne Polyurethanes Mixing is a difficult process when working with 2-Component Waterborne Polyurethanes Previous studies have shown systems sprayed under turbulent flow gave poor performance systems sprayed under laminar flow gave the best results Under a pressure flow field, the particles break down, collide and coalesce TOC

Introduction-Continued 2-Component Waterborne Polyurethanes Pot life depends mainly on the particle size distribution Before studying the mixing process you must investigate: Pressure, shear force and viscosity Using hydrophilic polyisocyanate Polyol in the system decreases the interfacial tension between the polymer particle and the water interface through charge repulsion Hydrophilic modifier of the polyisocyanate and acrylic polyol help stabilize the mixed solution TOC

Introduction-Continued 2-Component Waterborne Polyurethanes Using hydrophobic polyisocyanate Not easily dispersed in water but can be emulsified with high energy input Particle size distribution curve in the water phase is wider then hydrophilic polyisocyanate Rate of coalescence is rapid and sedimentation due to buoyancy effect occurs quickly TOC

Introduction-Continued 2-Component Waterborne Polyurethanes Using hydrophobic polyisocyanate cont. When used with polyol latex the surface tension of the system is reduced due to surfactant in the polyol component Film appearance is low quality due to poor emulsification of hydrophobic polyisocyanate Higher shear energy will improve the system High shear rates can cause microfoam in the system resulting in poor appearance and properties TOC

Experimental 2-Component Waterborne Polyurethanes Materials RoShieldTM 3275 from Rohm and Haas OH functional acrylic polyol DesmodurTM N-3300U from Bayer Corp. Hydrophobic polyisocyanate based on HDI BayhydurTM XP-7063 from Bayer Corp. Hydrophilic polyisocyanate based on HDI TOC

Experimental-Continued 2-Component Waterborne Polyurethanes Equipment Viscosity determined by Haake rotational viscometer Refractive indices determined by Leica Auto Abbe refractrometer Particle size and distribution determined by Brookhaven BI-90 2-Component mixing equipment supplied by Airtech and modified by Bayer Corporation TOC

2-Component Waterborne Polyurethane Spray Equipment Hydrophilic polyisocyanate used 889 Micron orifice Hydrophobic polyisocyanate used 450 Micron orifice TOC

Formulations for 2-Component Waterborne PU Coatings TOC

Shear thinning and thixotropic behavior of polyisocyanates Figure 3 N-3300U (hydrophobic) XP-7063 (hydrophilic) TOC

Viscosity vs. shear rates (1/s)for Component I (polyol) Figure 4 TOC

Surface Tension Results Table 1 TOC

Flow rates of waterborne coatings in the 2-component spray equipment Reynold’s number, Re  is density (g/cm3)  is kinematic viscosity Q is volumetric flow rate of the emulsion d is the orifice diameter TOC

Re number as a function of mass flow rates for: 3275 - N3300U & 3275 - XP-7063 TOC

Particle size and polydispersity of XP-7063 and 3275 Figure 6 TOC

Tank pressure and particle size as a function of Re’s numbers for N-3300U water emulsion Figure 7 TOC

Mean and volume average diameter of N-3300U and 3275 as a function of mixing Reynold’s number Figure 8 TOC

Degree of mixing as a function of Reynold’s numbers Table 2 TOC

Film properties for in-line mixing (without gun atomization) Table 3 TOC

Conclusions Effective mixing of the polyol with either hydrophilic or hydrophobic polyisocyanates can be accomplished using two-component spray equipment developed by Bayer Corporation High shear flow is not necessary in coating systems containing polyol and hydrophilic polyisocyanate. Homogeneity can be achieved with low range Reynold’s numbers. TOC

Conclusions-cont. In contrast, high shear energy with Reynold’s numbers will improve the mixing of the systems containing polyol and hydrophobic polyisocyanates. Thus, the emulsification of the hydrophobic polyisocyanates can be done with jet dispersion, resulting in the formation of a more stable dispersion compared to batch emulsification. TOC

Conclusions cont. Homogeneous mixing in the spray equipment can be characterized by fundamental properties such as refractive index and percent solids measurements. Particle size distribution data, rather than average particle size data, can give a better indication of mixing. TOC

2-Component Spray Equipment Several equipment manufacturers now offer this equipment Equipment has proven itself to be production worthy TOC

Acknowledgments TOC K.E. Hudson J. Hunter R. Clemens C. Gambino M. Urick L. Martin Dr. S. Feng Dr. R. Roesler Dr. D. Wicks TOC