Pigments
& non-reactive additives
If needed, non-reactive
urethane grade (dry) pigment pastes are added.
Usually between 1% - 2%
pigment paste is added to give the desired colour.
It is advised not to add too
much pigment paste (preferably no more than 2% on total mass) as this can
adversely affect the physical properties of the end product.
It is recommended to add the pigment paste to the prepolymer or
polyol after it has been degassed and weighed out, just before adding the MOCA
or isocyanate.
Only start mixing the pigment paste when adding the MOCA or
isocyanate, as this will give an indication of the degree of mixing.
Note:
If pigment paste is added
to the prepolymer in the degassing vessel (before degassing), as in our
example, the following points must be taken into consideration:
- dry pigment paste (no moisture
contamination)
- non-reactive pigment paste
- the pigment paste must not
affect the stability of the prepolymer, and
- the weight of the pigment paste
should be taken into consideration in the calculation.
So, in our example, after accounting for
hang-up and pigment paste, the mix ratio will be:
207.89 Kg (10T90 203.82 Kg + Additive 4.07 Kg) See
example below: 25.58
Kg MOCA
Calculation
for the amount of pigment paste.
Example:
2% pigment paste calculated on 203.82 Kg 10T90
= 2 x
203.82
100
= 4.07 Kg
pigment paste |
