Pigments and non-reactive additives

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:

  1. dry pigment paste (no moisture contamination)
  2. non-reactive pigment paste
  3. the pigment paste must not affect the stability of the prepolymer, and
  4. 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




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