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Tin Chemistry

Chapter 6.2  Organotin Catalysts for Isocyanate Reactions. Werner J. Blank and Edward T. Hessell. Mechanism of Catalysis, structure of catalysts, blocked isocyanates, reaction rates, application areas. 

 

Fundamentals, Frontiers and Applications
John Wiley & Sons  August 2008      ISBN-10: 0-470-51771-9 ISBN-13: 978-0-470-51771-0 - 

Delayed (Latent) Catalysis in Coatings

Most industrial crosslinked coatings require catalysis. The rate of the crosslinking reaction has to be adjusted to the application, application method and to customer’s requirements. An ideal catalyst would give excellent stability, a long potlife and high reaction rate when required. Most of the catalyzed coatings follow an Arrhenius rate. Depending on the nature of the crosslinking reaction and the reaction mechanism many different approaches are used to either delay catalysis or to achieve latency outright. The foremost approaches taken are blocking of the catalyst or creating the catalyst in situ.

Werner J. Blank (Kurt Dietliker, Antoine Carroy, Tunja Jung, Caroline Lordelot,  Ciba)

ACS Meeting Philadelphia, Fall 2008
PMSE Preprints Vol, 99
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New Developments in Catalysis

Environmental, safety and health concerns are major driving forces for the development of new coating systems, which in turn require catalysts with a different performance profile. One critical area for the development of new catalysts is the replacement of organotin compounds in polyurethanes with environmentally friendly catalysts, such as bismuth, aluminum and zirconium chelates. For applications in epoxies new catalysts for the epoxy-carboxyl reaction are also being developed. To gain the needed improved performance multiple cure mechanisms are being employed in coatings requiring dual action catalysts.
Werner J. Blank
FATIPEC 2002 Dresden Macromolecular Symp. 187, 261-270 (2002)    ISBN: 3-527-30477-0

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Advances in Catalysis for Organic Coatings

Overview of the developments of catalysts for environmentally acceptable coatings and less toxic catalysts. Catalysts for isocyanates, epoxy, siloxanes and melamines are being discussed.

Werner J. Blank Chimia 56 (2002) 191-196

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Catalysis of thermally curable high solids cycloaliphatic epoxy formulations

A quaternary ammonium hexafluoroantimonate catalyst is used to catalyze the thermal crosslinking reaction of cycloaliphatic epoxy resins. This catalyst rearranges during heating from a quaternary to a t-amine. This rearrangement from a strong basic amine to a very weak amine permits the formulation of stable and low temperature reactive formulations. Cure temperatures as low as 80ºC are possible and room temperature stability of 3-6 month can be achieved.

R.P. Subrayan, D. J. Miller, M.M Miller and W.J. Blank

ACS Proceedings Fall 2001, Chicago IL. PMSE Div.

This superacid catalyst permits also the co- reaction of epoxy resins with hydroxyl functional polymers, with lactones, vinylether and epoxidized oils. Nonvolatile content as high as 100 % at application solids are possible.
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The Slow and Winding Road to "ZERO" VOC

For the last 35 years, the US coatings industry has been challenged to develop coatings systems with a lower solvent content. The initial impetus for this development was Rule 66 enacted in 1966 in California. The Federal Clean Air Act of 1970 stated that all Americans have the right to breathe clean air and that it was the responsibility of the individual states to insure the air was clean.  

Werner J. Blank

Preprint 28th  International Waterborne, High-Solids, and Powder Coatings Symposium Feb. 2001, New Orleans, LA, USA

Substantial progress has been made since these early days in the development of newer coating technologies that not only meet the performance requirements of the end user, but also reduce or eliminate solvents all together.  Although many of the new technologies developed such as UV/EB, Powder Coating, Waterborne Coatings and High Solids Coatings would have made inroads into the coating market based on their own merit, they received a significant boost from increasingly stringent regulations in the USA, and also overseas.                  Slide Presentation. 
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Catalysis of the Epoxy-Carboxyl Reaction

We have investigated the reactions of glycidyl ether, glycidyl ester and other oxirane functional resins with carboxyl or anhydride functional compounds and polymers in the presence of a wide range of amine, phosphonium and metal catalysts. We have discovered a group of zinc chelates, which overcome these problems and provide one stable formulations in a single package that do not yellow during cure and give improved resistance properties. We discuss the properties obtained with these new catalyst a in high solids epoxy/carboxyl coatings, automotive clearcoats.  Slide presentation  PowerPoint presentation given at the meeting.

Werner J. Blank, Z. A. He.  M. E. Picci

JCT Vol. 74/926, March 2002

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Polymer Fundamentals for Coatings. 

An overview of some of the basic polymer chemistry a formulator should be familiar with. This presentation is a part of a short course given by the Federation. 

A written paper is also available as a download.

Werner J. Blank
ICE 2000 Oct.2000
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Selectivity of the Isocyanate-Hydroxyl Reaction versus Side Reactions as a Function of Catalysis.

Catalysts play an important role in the catalysis of isocyanate/hydroxyl polymers. In both waterborne and high solids coatings besides hydroxyl reaction the rate of reaction of isocyanates with water is important. Typically in coatings with aliphatic isocyanates dibutyltin dilaurate (DBTDL) is used as a catalyst. DBTDL is not only a very effective catalyst for isocyanates, but also for the water reaction. We have discovered that zirconium chelate catalysts are very effective and selective catalysts for catalyzing the hydroxyl reaction, but not the water reaction. Water plays a direct and indirect role in the isocyanate reaction. Not only does water lead to a consumption of isocyanates and to the formation of urea, it also can lead a deactivation of catalyst or a delayed catalysis.

Slides can be viewed. A part of the information used in this presentation can be downloaded from a previous paper.

W.J.Blank, Z.A.HE and M.E. Picci

Gordon Research Conference July 1999.

Paper not available in written form.

A Selective Catalyst for Two Component Waterborne Polyurethane Coatings   

Low VOC, high performance, two component waterborne isocyanate crosslinked coatings have generated a great interest. The difficulties in formulating these coatings, however, are significant. A major problem associated with such systems is the isocyanate-water side reaction, which can lead to gassing/foaming, loss of isocyanate functionality, low gloss and a reduced pot life. To compensate for this side reaction, these formulations usually contain a large excess of isocyanate. One novel approach to control the water side reaction is the use of catalysts which selectively catalyze the isocyanate-polyol reaction and not the isocyanate-water reaction. The selectivity of a variety of metal catalysts to catalyze the preferred reaction was measured using an FT-IR method. A zirconium complex has shown unusually high selectivity for the isocyanate-polyol reaction in comparison to standard dibutyltin dilaurate catalyst. This zirconium complex catalyst has been evaluated in several water borne polyurethane formulations and has demonstrated less gassing/foaming, longer pot life and higher gloss than dibutyltin dilaurate at equal cure time. The mechanism of catalysis and formulating techniques of this novel zirconium catalyst will be discussed.

Z. Alex He, Werner J. Blank, Marie E.Picci 

Preprint 26th  International Waterborne, High-Solids, and Powder Coatings Symposium Feb. 1999, New Orleans, LA, USA

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High Solids Coating

VOC regulations have changed the nature of the US coating business forever. The development of high solids or solvent free coatings, water-borne and powder coatings are among the approaches taken by the coating and resin manufacturer to reduce VOC. The factors influencing the viscosity of polymer solutions are reasonably well understood. The WLF equation provides a powerful tool to link polymer structure (Tg, MW and MW distribution) to viscosity and solids content of polymers. The low MW oligomers used in high solids coating require extensive crosslinking to achieve acceptable film properties. Careful control of functionality and reactivity of the oligomers is required to obtain stability, reactivity and at the same time prevent embrittlement of the coating. The design of reactants, diluents, catalysts and other additives requires a precise balance for high solids coatings to succeed in the market place.

W. J. Blank

ACS meeting in Anaheim, March1999

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Catalysis of Blocked Isocyanates with Non-Tin Catalysts  

The use of blocked polyisocyanates has many advantages in the coating industry. It permits the formulation of stable one package coatings which on heating deblock and lead to the formation of the highly reactive polyisocyanate. Applications for these systems are in diversified areas such as powder coatings, electrocoating, wire coatings and in textile finishing. The nature of the blocking agent has a significant effect on the deblocking temperature of the isocyanate. Typical blocking agents used include malonates, triazoles, e -caprolactam, sulfite, phenols, ketoxime, pyrazoles and alcohols. For many blocked isocyanates an elimination-addition mechanism is proposed. As non-tin catalyst bismuth carboxylate has been found a very effective catalyst..

Slide show as shown at ACS meeting.

Werner J. Blank, Z. A He, Maria E. Picci

ACS Meeting August 1998 in Boston, PMSE Div.

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Additives for High Solids and Water-Borne Coatings

Higher solids and waterborne coatings have introduced new dimensions of complexity into the formulation of coating systems. Both higher solids and waterborne coatings are prone to surface defects due to high surface tension and excessive flow during the application and curing process. The rheology of waterborne coatings in most instances is non-Newtonian, creating special problems with some application processes. High solids coatings, due to their low viscosity, are prone to sag and flow before crosslinking has taken place. Higher solids coatings also require a higher concentration of functional groups which create problems in stability and cure response. All these problems has created a demand for new additives as well as many new opportunities for the additive manufacturer. We plan to give an overview of the additives used in high solids coatings and specifically address new developments in catalysts and reactive diluents for high solids coatings.

Werner J. Blank, Rudy Berndlmaier and Dan Miller

Preprint 25th International Waterborne, Higher-Solids, and Powder Coatings Symposium, February 18-20, 1998, New Orleans, LA, USA

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Catalysis of the Isocyanate-Hydroxyl Reaction by Non-Tin Catalysts

Tin compounds, especially dibutyltin dilaurate, are in widespread use in coatings as catalysts for the isocyanate/hydroxyl reaction. We are interested in finding alternatives to these catalysts and in developing compounds which exhibit increased selectivity for the isocyanate/hydroxyl reaction. We found zirconium chelates activates the hydroxyl groups and catalyze the isocyanate-hydroxyl reaction by an insertion mechanism. This reaction is selective and preferred over the isocyanate-water reaction. This permits the use of this catalyst in waterborne isocyanate crosslinked two component coatings. In addition this catalyst permits very high reaction rate which suggests is use in plural component gun applications.

Slide presentation 

Werner J. Blank, Z. A. He and Ed T. Hessell

Preprint International Conference on Coatings Athens Greece, July 1998 Progress in Organic Coatings 35 (1999) 19-29

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CROSSLINKING WITH MALONATE BLOCKED ISOCYANATES AND WITH MELAMINE RESINS

Automotive clearcoats with improved acid etch resistance are being formulated using a combination of a dialkyl malonate blocked polyisocyanate, a melamine crosslinker and an acrylic polyol,. These coatings contain lower level of melamine crosslinker compared to conventional acrylic/HMMM systems and show excellent acid resistance. We were interested to explore the reaction mechanism of this complex crosslinking system and find explanations for the good chemical resistance properties

Z. Alex He and Werner J. Blank

Preprint 25th International Waterborne, Higher-Solids, and Powder Coatings Symposium, February 18-20, 1998, New Orleans, LA, USA

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Melamine Formaldehyde Networks with Improved Chemical Resistance

Melamine formaldehyde chemistry offers many other alternative ways of crosslinking besides reacting with hydroxyl and carboxyl groups, HMMM can react with NH and CH reactive sites on polymers to form linkages which are potentially more resistant to hydrolysis and can produce acid resistant coatings.

Slide show  (650 k including Graph)

You probably have to read the paper to understand the slides.

W.J. Blank, Z.A. He, E. T. Hessell and R.A. Abramshe,

R. Tess Award Symposium, ACS Meeting August 1997, Las Vegas,

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Formulating Polyurethane Dispersions

Polyurethane dispersions are being used in industrial applications where the performance achieved with waterborne acrylic, alkyd, polyester and epoxy resins is not adequate. I will discuss the problems associated in formulating polyurethane dispersions, how these systems can be pigmented, crosslinked with either melamine or polyisocyanate crosslinker and how to catalyze these formulations. In addition I plan to discuss how to combine these polyurethane dispersions with other polymer systems.

Werner J. Blank

Polyurethane Conference in Detroit, Oct, 1996

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CROSS-LINKING WITH POLYURETHANES

We were interested in the use of alcohol blocked thermally stable polyurethanes as cross-linker for hydroxyl functional polymers and the pathway for reaction of these materials. As model compounds for the polyurethane cross-linker difunctional materials were prepared by reacting of 1 mol of a diisocyanate with 2 mol of the alcohol. As blocking groups one diol and two alcohols, 1,2-propanediol (PG), 2-methoxypropoxypropanol (DPM) and 2-ethylhexanol (2EH), materials with similar boiling point, 187°C, 188°C and 185°C respectively were selected. For comparison purposes a e -caprolactam blocked 1,6-diisocyanatohexane was used.

 

Werner J. Blank

ACS Proceedings of Polymeric Materials Science and Engineering. Vol. 63, Aug. 90

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