Лако-красочные материалы — производство

Anti-foaming agents, preservatives and stabilisers can all be added to latex paints. Polymeric de-foamers of the Bevaloid type are popular, as they combine long life and do not cause wetting or livering troubles. Silicone de-foamers can cause cissing and other surface faults, whilst the nonanol type de-foamers tend to dissolve in the polymer particles and are then ineffective.

Vinyl polymers are not normally susceptible to bacterial or fungal attack, but many colloids, especially those based on cellulose, and surfactants can be bio-degraded. Residual monomer is quite an effective biocide but permanent preservatives are required to prevent degradation of the dried film. Esters of p-hydroxybenzoic are popular, but a wide range of proprietary products are also employed. The use of mercury containing biocides is discouraged on environmental grounds. Formalin type biocides were popular before fears about the toxicity of formaldehyde. Formaldehyde must not be used in any form with vinyl chloride containing latices, because a highly toxic gas similar to phosgene is formed.

Vinyl chloride and vinyl acetate polymers are discoloured when exposed to heat or light. Polymers containing long sequences of either monomer should have some calcium carbonate as an alkaline extender and an organotin stabiliser. Styrene copolymers can discolour in bright light and a UV stabiliser can be added to suppress this reaction.

An important property of polymer films is their permeability to gases and vapours. Vinylidine chloride and its copolymers have exceptionally low permeability, whilst poly(vinyl acetate) has the highest permeability of commercial polymers. Acrylate and styrene acrylate polymers have intermediate values with the presence of styrene increasing diffusion of gases. For a specific polymer, permeability will vary with the nature of the gas or vapour and permeability will also increase with an increase in pigmentation. The transport of water vapour through polymer films is important both in the drying process and in use. Rapid transport will tend to occur when the polymer is relatively hydrophilic, e. g. poly(vinyl acetate), or contains acid or amide groups, whilst it will be much slower for hydrophobic polymers.

Paints in bathrooms and kitchens will require high permeability to water vapour to avoid condensation of water. Coatings on wood and metal should have low water permeability to reduce decay and rusting. Other applications have their special requirements for permeability. The inherent permeability of polymer films represents the minimum obtainable with a coherent film. When low vapour transmissions are required it is important to ensure that the film produced from the latex is as integral as possible and extra coalescent solvent may be added. Should high vapour permeation be needed the formation of minor discontinuities in the film may be encouraged by not adding any coalescent. The waterborne coatings need good adhesion to any substrate to cope with condensation.