2024年3月15日发(作者：多德昌)
Speciality Chemicals Division
Blocked Isocyanates
The Chemistry of Blocked Isocyanates
Introduction
The isocyanate groups associated with urethane crosslinkers are highly reactive
towards many other compounds. This reactivity can lead to stability problems in
two pack (2k) coatings and prepolymers, due to pot life limitations and the ability of
the NCO groups to react with atmospheric moisture. Blocking technology was
developed to overcome these limitations and to give storage stable one-pack
systems (1k) which can be thermally or chemically re-activated.
Baxenden’s Trixene blocked isocyanates are designed to be
compatible with hydroxyl functional polyesters, polyethers and
acrylics, as well as epoxy, phenolic and amine functional resins.
The level of blocked isocyanate required in a given formulation is calculated from
the apparent equivalent weight.
The mechanism for the reaction between blocked isocyanates and hydroxyl
functional species is given below.
Mechanism
first step is the thermal liberation of
the isocyanate
group (R-NCO).
second step is the reaction of the
generated isocyanate with the available
hydroxyl groups.
blocking agent is either liberated as a
VOC or, as in the case of the pyrazole
systems, remains mainly in the cured
coating.
Blocked Isocyanate Mechanism
DMP Blocked Isocyanates
In the drive to lower the unblocking temperature of conventional
blocked isocyanates, Baxenden Chemicals developed the use of
3,5-Dimethylpyrazole (DMP).
DMP blocked isocyanates have several advantages relative to other established
blocking technologies.
•Improved resistance to chemical and environmental attack.
•Better colour stability particularly on overbake and
UV exposure.
•Lower unblocking temperature (110-120°C)
and increased cureresponse.
•
Reduced VOC emissions due tolow
volatility of blocking agent.
2024年3月15日发(作者：多德昌)
Speciality Chemicals Division
Blocked Isocyanates
The Chemistry of Blocked Isocyanates
Introduction
The isocyanate groups associated with urethane crosslinkers are highly reactive
towards many other compounds. This reactivity can lead to stability problems in
two pack (2k) coatings and prepolymers, due to pot life limitations and the ability of
the NCO groups to react with atmospheric moisture. Blocking technology was
developed to overcome these limitations and to give storage stable one-pack
systems (1k) which can be thermally or chemically re-activated.
Baxenden’s Trixene blocked isocyanates are designed to be
compatible with hydroxyl functional polyesters, polyethers and
acrylics, as well as epoxy, phenolic and amine functional resins.
The level of blocked isocyanate required in a given formulation is calculated from
the apparent equivalent weight.
The mechanism for the reaction between blocked isocyanates and hydroxyl
functional species is given below.
Mechanism
first step is the thermal liberation of
the isocyanate
group (R-NCO).
second step is the reaction of the
generated isocyanate with the available
hydroxyl groups.
blocking agent is either liberated as a
VOC or, as in the case of the pyrazole
systems, remains mainly in the cured
coating.
Blocked Isocyanate Mechanism
DMP Blocked Isocyanates
In the drive to lower the unblocking temperature of conventional
blocked isocyanates, Baxenden Chemicals developed the use of
3,5-Dimethylpyrazole (DMP).
DMP blocked isocyanates have several advantages relative to other established
blocking technologies.
•Improved resistance to chemical and environmental attack.
•Better colour stability particularly on overbake and
UV exposure.
•Lower unblocking temperature (110-120°C)
and increased cureresponse.
•
Reduced VOC emissions due tolow
volatility of blocking agent.