Читать книгу Additives for Water-borne Coatings - Wernfried Heilen - Страница 44

Juergen Kirchner [2]

Foam is a colloidal system of gas surrounded by liquid or solid cell bridges. Foam reduces the quality of paints. Foam formation frequently occurs during the production or application of paints and coatings, resulting in impaired optical or technical performance of a coating. Foam also disrupts production processes, e.g. by reduced energy transfer during dispersion processes, reduced capacities of vessels or problems at filling stations.

Effects on the optical performance of coatings include surface irregularities, reduced gloss and transparency. Defects caused by foam also significantly impair the coating’s ability to protect against penetrating media.

There are various reasons for the formation of foam including:

 mechanical introduction of air by mixing or application processes,

 displacement of air from surfaces during wetting and dispersing processes,

 generation of gas by chemical reactions,

 bubbles caused by too rapid drying.

The presence of surface active (amphiphilic) substances in paints and coatings often promotes the stabilisation of foam. To prevent its formation during manufacturing and processing of coatings and to destroy foam which has already built up, it is essential to use defoamers or deaerators [1].