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Home » Sealants » Crosslinkers and Curatives » Blocked Isocyantaes

Blocked Isocyantaes

Tri-iso distributes a wide range of isocyanates that allow formulators to produce high quality polyurethane and polyurea sealants.  Isocyanates contain reactive NCO groups which react with hydroxyl groups on polyols to form polyurethanes and with amines on polyamines to form polyureas.  Blocked isocyanates will not react until they are exposed to their deblocking temperature at which point they are deblocked.  Once deblocked, blocked isocyanates react like traditional isocyanates.  There are several blocking agents which are used to produce blocked isocyanates, and these blocking agents determine the temperature at which the blocked isocyanate deblocks.  Specifically, diethyl malonate deblocks at 100-120C, 3,5-dimethylpyrazole deblocks at 110-120C, methylethylketoxime deblocks at 120-140C, and caprolactam deblocks at 160-180C.  Aside from the blocking agent employed, there are several key characteristics which define what performance properties a given blocked isocyanate will impart in a given polyurethane or polyurea sealant.  These characteristics include: the type of isocyanate selected (aliphatic or aromatic), the NCO equivalent weight, the %NCO, and the functionality of the isocyanate. 

Aromatic isocyanates are isocyanates where the NCO functional group is directly attached to an aromatic ring, and aliphatic isocyanates are isocyanates where the NCO functional group is not directly attached to an aromatic ring.  Aromatic isocyanates are typically 3-4x less expensive than aliphatic isocyanates.  Aliphatic isocyantates are UV stable.

NCO equivalent weight is the number of grams of a given product that contains one equivalent of isocyanate groups (NCO).  One equivalent of NCO groups is 42.02 grams/mol

%NCO = 4202/NCO equivalent weight.

Isocyanate functionality refers to the number of NCO groups per  molecule.  Increasing the number of NCO groups results in greater crosslinking.  Greater crosslinking yields stiffer, harder products with enhanced chemical and thermal resistance.

Tri-iso distributes aromatic blocked isocyanates based on MDI, as well as aliphatic blocked isocyanates based on HDI Trimer, HDI Biuret, H12MDI, IPDI, and IPDI Trimer. 

Your Tri-iso Technical Sales Representative is available to assist you in the selection of the appropriate isocyanate that will provide the specific properties you are trying to obtain. Click here to request a quote.



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