Good morning. Thank you for the kind introduction, and thank all of you for attending. I would like to present some preliminary research describing a New Water Soluble Catalyst for Two-Component Waterborne Polyurethane Coatings.
During the course of developing new catalysts, a water soluble catalyst was discovered that had surprising solubility in both aqueous and organic media. This water solubility and stability was intriguing, so the performance of this catalyst was evaluated in comparison to typical commercially available catalysts in two component waterborne polyurethane coating formulations. This new catalyst was evaluated with both a urethane modified polyester polyol and a less expensive polyester polyol in combination with a water dispersible hexamethylene diisocyanate based polyisocyanate. To gauge the effectiveness of this new catalyst it was compared to several commercially available catalysts. The catalysts were all used at equal concentrations of metal to account for molecular weight differences. The performance was screened by measuring standard properties, such as dry times, hardnesses, solvent resistances, and the effects of humidity on drying times
Before I discuss the details of the evaluations any further, I would like to make some general comments about two component waterborne polyurethane coatings. Two component waterborne coatings have been available since around 1990. They were developed to address VOC regulations aimed at reducing solvent emissions. Many of the initial deficiencies of waterborne systems have been overcome. Two component waterborne polyurethane coatings have suffered in comparison to solvent borne systems. Final properties equivalent to two component solvent borne coatings are generally not easily achievable. High humidity conditions can greatly affect dry times. Water is slow to evaporate under high humidity and this leads to reaction of water with the isocyanate groups. Reaction of water with isocyanate groups generates carbon dioxide, and this causes bubble formation which leads to film defects such as pinholes.
The addition of Reaxis C333 to a two component waterborne formulation leads to faster curing of the film, as we can see in these FT IR spectra of two films cured with and without catalyst. We can still see unreacted isocyanate peak in the film cured without catalyst after 2 days. When Reaxis C333 catalyst is added to the formulation, there is no free isocyanate peak visible in the film after 2 days. Now lets look at more detailed studies of this new catalyst in comparison to other commercially available catalysts.
As mentioned earlier, two formulations were used to evaluate the catalysts. The first system utilized a urethane modified polyol in combination with a hydrophillically modified polyisocyanate. The formulations were not pigmented and the NCO to OH ratio was 2 to 1. This system is a higher performance system. The catalysts were levels adjusted to give equal concentrations of catalyst on a molar basis. The use levels were around 0.1% to 0.2% of catalyst by weight on a resin solids basis.
The second formulation uses a less expensive polyester polyol in combination with a hydrophillically modified polyisocyanate. Again the formulations were not pigmented, and the NCO to OH ratio was 2 to 1. The coatings were prepared by mixing part A which consisted of (polyol, catalyst, water, and wetting additive) with part B (the water dispersible polyisocyanate). The coatings were spray applied onto an aluminum substrate to a dry film thickness of about 2.0 mils. The coatings were air dried and then tested by the ASTM methods for set-to-touch, dust free, dry hard, MEK double rubs and pencil hardness.
The results of comparing the physical properties of coatings formulated with the varying catalysts demonstrated that formulations using Reaxis™ C333 provided the shortest dry hard time. It also yields the same ultimate physical properties as any of the other catalyst. The ultimate physical properties are, of course, determined by the nature of the raw materials chosen. The C333 helps to achieve these ultimate properties in the shortest amount of time. Catalysts reduce the time needed to achieve the final properties, but they can also reduce the ultimate physical properties, if they promote undesirable side reactions. Therefore, selectivity is an important feature.
In Formulation 2 using the polyester polyol, C333 results in faster property development as measured by the dry times. This is especially beneficial in this system as it has a much longer drying time than Formulation 1 without catalyst.
It is important to have suitable shelf life stability for both the A and B components of two component waterborne polyurethane systems. The best stability is normally seen when the catalyst is added to the A side. Use of catalyst in the B side (NCO) can result in formation of side products such as biurets, allophonates, and isocyanurates, and ureas under certain conditions. Also, the use of catalyst on the A side avoids the catalysis of the water/NCO reaction should the mixture absorb water upon storage. These tables demonstrate that dry times and pencil hardness were basically unchanged for formulations using C333 after two weeks of aging in the polyol matrix (A side) at 60 ° C. Further testing is required to verify the stability in the polyol matrix over extended periods, but these initial results are very encouraging.
In waterborne coatings, pot life is typically not measured by viscosity increase, since a decrease in viscosity on aging is normally encountered. The typical determination of pot life for waterborne coatings involves measurement of physical properties after a specified aging time. Even though C333 promoted the achievement of ultimate properties, it still allowed a reasonable working time (at least 2 hours) after mixing the A and B sides. For Formulation 1, the drying times were reduced due to some reaction in the pot, but the ultimate properties were unchanged..
However, with the polyester polyol, the C333 seemed to help achieve better ultimate pencil hardness compared to the other catalysts before and after aging.
The C333 catalyst also provides robust curing under a wide range of humidity conditions. High humidity very often leads to slow drying of waterborne coatings. The drying times and ultimate physical properties of coatings cured at 50%, 75% and 90% humidity were relatively unchanged when C333 was utilized. This is advantageous to an end user, because it allows coating application to be done under a wider variety of conditions. For example, consistent application can be achieved at high humidity and/or heat in exterior environments where temperature and humidity are not able to be controlled.
The relative selectivity of C333 for promoting the reaction of isocyanate with hydroxyl groups versus water was investigated by FT-IR. A polyisocyanate and co-reactant were mixed in dipropylene glycol dimethyl ether at 0.8 molar concentrations. The catalysts were used at a 200 ppm metal concentration based on reactant solids. The peak heights of the NCO absorbance were plotted as the negative natural log (-Ln) versus time in minutes. The slopes of the plots were then compared to determine the relative rates. This plot shows that the reaction of 1-butanol with a primary aliphatic NCO group is 6.7 times faster than the reaction of water with the NCO group. This is very advantageous for the formulation of 2K waterborne urethane coatings, as it helps to prevent foaming which could lead to poor film appearance. Seneker and Potter reported a selectivity of about 2 for DBTDL .
Reaxis ™ C333 is a water soluble, hydrolytically stable catalyst that provides fast dry times and very good physical properties for 2K WB PU formulations under a variety of temperature and humidity conditions. Many 2K WB PU systems suffer from slower dry times and diminished physical properties at higher humidity, so use of C333 offers wider application latitude. C333 is unique in that it is soluble in both aqueous and organic media, thus providing very wide formulation latitude and allowing for uniform distribution in the liquid coating, leading to uniform cure response throughout the film. The robustness of C333 is demonstrated by the fact that the physical properties and drying times of 2K WB PU formulations containing this catalyst are maintained after aging. Also, the pot life and shelf stability of these formulations are excellent. The superior selectivity of C333 (compared to DBTDL) in promoting the reaction of isocyanate with hydroxyl groups versus water was confirmed by FT-IR. This is very important advantage over typical catalysts for the formulation of 2K WB PU coatings, as it contributes to prevention of foaming, which helps to optimize film appearance. Further experimentation is required to better define and understand the advantages for use of C333 in 2K WB PU systems and related coatings technologies. This initial study has provided promising data that merits further investigation.
Reaxis waterborne presentation acs2012
Evaluation of Water Soluble Catalyst (Reaxis® C333) in Two-ComponentWaterborne Polyurethane Coatings Presented by: Martin Rickwood Authors: Lanny Venham, Leon Perez Michael CurcioneCatalysts for Polyurethanes, Polyesters and Silicones
Overview Evaluation of new water soluble catalyst o Two component waterborne polyurethanes o Urethane/polyester polyol and polyester polyol o Water dispersible HDI based polyisocyanate Comparison to commercially available catalysts o Determination of standard properties • Coating dry times and hardness • Shelf life and pot life • Solvent resistance • Effect of humidity on drying • SelectivityCatalysts for Polyurethanes, Polyesters and Silicones
Background Drivers for development of 2K WB PU coatings o Compliance with VOC regulations o Decrease worker exposure hazards 2K WB PU coatings deficiencies o Poor drying speed under humid conditions o Inferior appearance vs. solvent based technology o Diminished film performance propertiesCatalysts for Polyurethanes, Polyesters and Silicones
Cured Waterborne Polyurethane Films (with and without C333 catalyst) 0.6 Green – C333 catalyst Blue – no catalyst 0.4 Abs 0.2 0 4000.6 3000 2000 699.069 Wavenumber [cm-1]Catalysts for Polyurethanes, Polyesters and Silicones
Formulation 1 Urethane Modified Polyester Polyol with HDI Trimer Raw Material Weight Volume Weight Solids Volume Solids Bayhydrol® 2591 131.32 14.30 45.96 4.06 Byk®-346 0.70 0.08 0.32 0.03 Byk®-345 1.23 0.14 1.23 0.14Ammonia (10% in DI water) 0.00 0.00 0.00 0.00 Catalyst (100%) 0.17 0.02 0.08 0.01 Water Letdown 23.47 2.82 0.00 0.00 Bayhydur® 2487 42.95 4.47 42.95 4.47 Total 183.00 21.84 90.63 8.72 Weight % Solids 45.32 Weight/gallon 9.15 Volume % Solids 39.92 NCO:OH 2.00 Catalysts for Polyurethanes, Polyesters and Silicones
Formulation 2 Standard Polyester Polyol with HDI Trimer Raw Material Weight Volume Weight Solids Volume Solids US Polymers W2K® 2002 41.37 4.35 37.23 3.85 Byk®-346 0.22 0.03 0.10 0.01 Byk®-345 0.39 0.04 0.39 0.04Ammonia (10% in DI water) 3.27 0.40 0.00 0.00 Catalyst (100%) 0.20 0.02 0.10 0.01 Water Letdown 89.75 10.77 0.00 0.00 Bayhydur® 302 64.60 6.67 64.60 6.67 Total 180.00 22.28 90.53 8.62 Weight % Solids 51.26 Weight/gallon 8.96 Volume % Solids 47.56 NCO:OH 2.00Catalysts for Polyurethanes, Polyesters and Silicones
Formulation 1: Physical Properties (@77°F/50%RH) System Set-toa Dust freeb Dry hardc MEK DRd Pencile No cat 140 220 320 Pass 3H C333 75 140 185 Pass 3H DBTDL 85 130 200 Pass 2H Sn Octoate 95 150 230 Pass 2H Bi Octoate 90 170 220 pass 2H Zn Complex 95 145 190 Pass 3H Zr Complex 110 150 220 Pass 3Ha Set-to: Time in minutes set to touch with cotton ball non-stickingb Dust free: Time in minutes that cotton ball hairs do not adhere to the coatingc Dry hard: Time in minutes that coating achieves cure with no stickinessd MEK DR: pass = 50 MEK double rubs without breaking through the filme Pencil Hardness: Run after 7 days curing at room temperatureCatalysts for Polyurethanes, Polyesters and Silicones
Formulation 2: Physical Properties (@77°F/50%RH) System Set-to Dust free Dry hard MEK DR Pencil No cat 250 330 460 Pass H C333 75 135 190 Pass H DBTDL 95 160 200 Pass B Sn Octoate 110 140 225 Pass H Bi Octoate 155 210 280 pass H/F Zn Complex 130 160 230 Pass H Zr Complex 135 195 270 Pass HCatalysts for Polyurethanes, Polyesters and Silicones
Shelf Life - Aged at 60°C (catalyst in A side, polyol) System Set-to Dust free Dry hard MEK DR Pencil Time C333 85 146 180 79 2H 2 weeks C333 75 140 185 90 3H 4 weeks C333 80 125 170 83 3H 6 weeks Used Formulation 3 on next slideCatalysts for Polyurethanes, Polyesters and Silicones
Formulation 1: Pot Life Comparisons Physical Properties Before/After Aging 2 Hours cured (@77°F/50%RH) System Set-to Dust free Dry hard MEK DR Pencil No catalyst 140/90 220/190 320/275 Pass/Pass 3H/3H C333 75/45 140/85 185/145 Pass/Pass 3H/3H DBTDL 85/55 130/120 200/190 Pass/Pass 2H/2H Sn Octoate 95/65 150/140 230/210 Pass/Pass 2H/2H Bi Octoate 90/65 170/145 220/185 Pass/Pass 2H/H Zn Complex 95/70 145/135 190/175 Pass/Pass 3H/3H Zr Complex 110/75 150/120 220/185 Pass/Pass 3H/2HCatalysts for Polyurethanes, Polyesters and Silicones
Formulation 2: Pot Life Comparisons Physical Properties Before/After Aging 2 Hours cured (@77°F/50%RH) System Set-to Dust free Dry hard MEK DR Pencil No cat 250/235 330/300 460/420 Pass/Pass H/H C333 75/55 135/124 190/150 Pass/Pass H/2H DBTDL 95/60 160/130 200/185 Pass/Pass B/HB Sn Octoate 110/85 140/125 225/190 Pass/Pass H/H Bi Octoate 155/110 210/180 280/240 Pass/Pass (H-F)/F Zn Complex 130/140 160/165 230/185 Pass/Pass H/H Zr Complex 135/100 195/145 270/260 Pass/Pass H/(H-F)Catalysts for Polyurethanes, Polyesters and Silicones
Formulation 1: Physical Properties at Variable Humidity Cure Conditions Set-to Dust free Dry hard MEK DR Pencil Hardness 50% RH, 77°F 75 140 185 Pass 3H 75% RH, 77°F 85 150 200 Pass 3H 90% RH, 77°F 90 145 210 Pass 3H Catalysts for Polyurethanes, Polyesters and Silicones
Selectivity of C333 for NCO/OH Reaction Relative Rate of NCO/OH vs. NCO/Water - Ln (NCO abs.) vs. Time 3.7 C333 1-BuOH 3.5 C333 Water -Ln Abs. at 2270 cm-1 3.3 3.1 2.9 2.7 2.5 0 50 100 150 200 Time (min)Catalysts for Polyurethanes, Polyesters and Silicones
Summary & Conclusions Reaxis™ C333 Advantages Water soluble Also soluble in organic media Hydrolytically stable o Provides good storage stability Good selectivity in promoting NCO reaction o Reaction with OH is 6 times faster than water Wide application latitude o Cures well under high humidity conditionsCatalysts for Polyurethanes, Polyesters and Silicones
References• Gaal, R. and Jackson, M. A. “ A Cost-Effective, Water-Reducible Polyester Polyol for Two-Component Waterborne Urethane Coatings”, PCI Magazine, January 1, 2004.• Williams, J. 1993. “High Solids Polyurethane Coatings: Past, Present, and Future,” presented at the Water-Borne, Higher Solids, and Powder Coatings Symposium, February 24-26, 1993.• Jacobs, P. B. and Yu, P. C. 1992. “Two-Component Waterborne Polyurethane Coatings,” presented at the Water-Borne, Higher Solids, and Powder Coatings Symposium, February 26-28, 1992.• Seneker, S. D. and Potter, T. A., “Solvent and Catalyst Effects in the Reaction of Aliphatic Isocyanates with Alcohols and Water,” J. Coatings Tech., 63(713):19. Catalysts for Polyurethanes, Polyesters and Silicones