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

2. 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
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3. 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
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4. 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
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5. 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
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6. 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
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7. 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
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8. 2-Component Waterborne Polyurethane Spray Equipment
Hydrophilic polyisocyanate used 889 Micron orifice
Hydrophobic polyisocyanate used 450 Micron orifice
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9. Formulations for 2-Component Waterborne PU Coatings
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10. Shear thinning and thixotropic behavior of polyisocyanates Figure 3
N-3300U (hydrophobic)
XP-7063 (hydrophilic)
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11. Viscosity vs. shear rates (1/s)for Component I (polyol) Figure 4
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12. Surface Tension Results Table 1
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13. 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
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14. Re number as a function of mass flow rates for: 3275 - N3300U & 3275 - XP-7063
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15. Particle size and polydispersity of XP-7063 and 3275 Figure 6
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16. Tank pressure and particle size as a function of Re’s numbers for N-3300U water emulsion Figure 7
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17. Mean and volume average diameter of N-3300U and 3275 as a function of mixing Reynold’s number Figure 8
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18. Degree of mixing as a function of Reynold’s numbers Table 2
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19. Film properties for in-line mixing (without gun atomization) Table 3
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20. 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.
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21. 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.
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22. 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.
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23. 2-Component Spray Equipment
Several equipment manufacturers now offer this equipment
Equipment has proven itself to be production worthy
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24. Acknowledgments TOC K.E. Hudson J. Hunter R. Clemens C. Gambino
M. Urick
L. Martin
Dr. S. Feng
Dr. R. Roesler
Dr. D. Wicks
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