The latent curing agents are meant for use in a wide range of coatings, adhesives, and sealant applications. They are proved to be very beneficial in conditions that require high build properties. For instance, waterproof coatings and construction sealants. Oxazolidines are used as latent curing agents and can be used in both one and two component PU systems.
In case of one component PU system, these latent curing agents are generally used with aliphatic prepolymers. They enhance fast through-cure with no carbon dioxide gas evolution. On the exposure to moisture, these agents get hydrolysed, yielding reactive amine and hydroxyl functional groups.
The unique properties of these latent curing agents are primarily determined by the curing mechanism, which is entirely different from the conventional “moisture cure” reaction. During this process, moisture reacts directly with the terminal isocyanate of the prepolymer producing gaseous carbon dioxide. It results in blisters and bubbles in the coating film.
Moisture primarily reacts with the oxazolidine rather than with the prepolymer’s terminal isocyanate groups. The underlying process of hydrolysis and ring opening of the oxazolidine generates amine and hydroxyl groups. These amine and hydroxyl groups then subsequently react with the isocyanate of the prepolymer without the evolution of carbon dioxide gas.
Oxazolidines as Latent Curing Agents
Monday, June 21, 2010
Wednesday, June 2, 2010
Reactive Diluents for Flexible Polyurethane Coatings
Because of the presence of VOC content in paints and coatings, formulators have faced a serious challenge – how to develop a high-solids polyurethane system that has low viscosity for easy usage as well as optimum performance while complying with regulations.
One answer to this question in the use of low-molecular weight polyols to create a lower-viscosity formulation that needs less solvent. Unluckily, reductions in polyol molecular weight often lead to systems that support cure too quickly and don’t perform well in the field. In case of the absence of molecular weight reductions, polyols essentially have the tendency of high intrinsic viscosities, which make it very difficult to remove solvent from the formulation.
Reactive diluent are low-viscosity coreactants that are developed specifically to reduce VOCs through a reaction with the polymer matrix. As solvents, they lessen polymer viscosity without increasing VOCs.
Reactive diluents normally take the form of blocked or concealed sources of active hydrogen. Aldimines and ketimine are instances of blocked amino compounds. Oxazolidines are a good example of blocked amino alcohols. Aldimines and hampered amines are generally quite low in viscosity (less than 5,000 cps at 100 percent solids). They are quick reactive with isocyanate and often suffer from uninvitingly lessen pot life. Even then, they still remain quite attractive for applications where highly rapid cure is required.
One answer to this question in the use of low-molecular weight polyols to create a lower-viscosity formulation that needs less solvent. Unluckily, reductions in polyol molecular weight often lead to systems that support cure too quickly and don’t perform well in the field. In case of the absence of molecular weight reductions, polyols essentially have the tendency of high intrinsic viscosities, which make it very difficult to remove solvent from the formulation.
Reactive diluent are low-viscosity coreactants that are developed specifically to reduce VOCs through a reaction with the polymer matrix. As solvents, they lessen polymer viscosity without increasing VOCs.
Reactive diluents normally take the form of blocked or concealed sources of active hydrogen. Aldimines and ketimine are instances of blocked amino compounds. Oxazolidines are a good example of blocked amino alcohols. Aldimines and hampered amines are generally quite low in viscosity (less than 5,000 cps at 100 percent solids). They are quick reactive with isocyanate and often suffer from uninvitingly lessen pot life. Even then, they still remain quite attractive for applications where highly rapid cure is required.
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