PH adjusters

In most cases, the systems require pH’s in the range 8.0-10.0. If the pH is outside this range, then the stability of the finished product can be seriously affected and viscosities can change quite significantly especially if a pH sensitive thickener is being used.

Generally, ammonia or other organic bases are used to control pH as they will evaporate out of the film eventually. It is, however, possible to use inorganic bases such as potassium hydroxide, but they don’t leave, and the film will remain water sensitive. In some cases, this can be very desirable, but usually it is not.

In the past, ammonia was the main product used, but its unpleasant and distinctive odour has made it less popular. Larger, higher molecular weight amines have increased in use. These are slower evaporating and can lead to prolonged water sensitivity, but one advantage is that they do not evaporate so readily during manufacture and, therefore, pH changes are less likely to occur. The use of heat during film formation enables slower evaporating amines to be successfully used.

It is not necessary to have all of the above additives in a given formulation. Some additives may well fill multiple roles, e. g. a wax dispersion could have a matting effect and impart slip and mar resistance. It may also be necessary to have more than one from a given group, e. g. it may be necessary to have one defoamer in a millbase and another in the finished product.

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