In this Q & A, Tushar Trivedi, International Sales & Applications Manager of Incorez offers some insight to formulators into this remarkably versatile solution and why Aldirez takes moisture-triggered technology to new heights.
How much Aldirez BH is used in formulation?
For each wt% NCO in the formulation, approx. 3-4% Aldirez BH should be employed. For example, a formulation with an NCO content of 0.65% needs approx. 2.0-2.6% Aldirez BH.
Can Aldirez BH be used in aromatic and aliphatic systems?
Aldirez BH is suitable for use with both aromatic and aliphatic prepolymers. It exhibits good in-can stability with aromatic prepolymers which makes it more suited to 1K aromatic systems than standard latent hardeners.
Aldirez BH is moisture sensitive. Is there a possibility of mixing/handling a BH mix without vacuum or nitrogen as long as the acid catalyst is not introduced?
The storage of Aldirez BH in air-tight containers does not normally require the use of nitrogen. Depending on the ambient processing conditions (temperature and relative humidity) some risks of limited shelf life may result if the production is carried out without vacuum/nitrogen.
Will BH work with heat rather than acid? How does heat affect the reaction? If the formulation is mixed at 70˚C, does this affect stability?
BH/acid formulation at 70˚C will be okay. No hydrolysis of the hardener is expected under normal processing, conditions provided the moisture level in the raw materials used is low. Heat can affect the reaction of the isocyanate groups in the formulation, but the use of Aldirez BH will have no negative influence at normal processing temperatures.
We produce the prepolymer using a tin catalyst. Will this catalyst affect the stability?
No. Ordinary levels of tin catalysts in the prepolymer will not affect the stability/shelf life.
How can we check the moisture content during processing?
Checking the residual moisture content of the raw materials used in the formulation is normally carried out by the Karl-Fischer method.
The guide formulation shows the use of dried CaCo3? What is the % of dryness required?
A moisture level of <0.1% should be ok.
How does the sealant guide formulation compare with and without the presence of the BH/acid?
It depends on the formulation, but normally without the BH/acid combination the sealant will be slower (skinning time, through cure) provided no other catalysts are used for the NCO-water reaction.
Assuming the sealant guide formulation works and no CO2 gas is formed, how does the 'latent curing' work when some of the NCO is left to react with moisture and generate CO2?
It is not necessary to cure 100% of the NCO groups via latent hardeners, because a good share of the formed CO2 is either adsorbed to the surface of the fillers, dissolved in the polymer matrix or diffuses out.
What impact do the curing conditions have?
General rule: the more drastic the curing conditions are (high temperature, high humidity, fast curing speed) the higher the imine/NCO ratio. If the imine/NCO ratio is too low, you may observe bubbling. If the imine/NCO ratio is unnecessarily high, it makes the formulation more expensive.
What should the imine/NCO ratio be?
Customers need to do some formulation trials themselves, but a sensible (in our formulations) is imine/NCO ratios between 30 and 70%. An imine/NCO ratio = 1 (100% of NCO groups cure with latent hardeners) is even dangerous. If you lose some NCO groups (by ageing, humidity, etc), the excess amine groups will inhibit a proper curing because they have no reaction partner and therefore will act as unreacted chain ends.
What is the recommended film thickness for sealants?
Slow curing is experienced above 15mm thickness.