Painting temperature considerations

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

Neutral cleaners provide the benefits of generally lower operating temperatures, reduced odour, easier effluent treatment and improved health and safety considerations over the alkali or emulsion products. Due to the inhibited nature of the surface produced, such products are used for interstage cleaning and prior to assembly. The surface is generally not suitable for immediate painting. 

The commercial demand for pigments which tend to bleed is limited. A major consideration is the processing temperature in a particular medium. There are a number of baking paints, for instance, which do not bleed into a white coating if they are cured at 120°C while a certain extent of bleeding is observed at temperatures between 140 and 160°C. 

For the formulation of fire-retardant paints for exterior exposure, considerable work has been done with isano oil. This oil, expressed from a nut native to French Africa, foams violently when exposed to flame temperature. This foaming appears to have definite fire-retardant value. 

Zinc is frequently applied to the surface of iron or steel by other methods. In the Schoop process, molten zinc is sprayed onto the surface by a blast of air in a manner similar to that used in spraying paint. In addition to metals, objects made of wood, leather, paper, and the like may be coated with zinc by this process. In the process of sherardizing, iron is covered with a thin layer of zinc dust at temperatures of 700 to 800°C. Under these conditions, zinc penetrates the surface of the iron to a considerable extent. 

The use of plastics in automotive applications has expanded considerably over the past 20 years. In 2001, approximately 2501b of plastics were used per automobile compared to less than 100 lb five years earlier. With the increased use of plastics, coating research has concentrated on the painting of these often difficult substrates. Among the numerous prerequisites for coatings on plastic are wetting of the substrate uniform film development a cure response below the heat distortion temperature of the plastic adhesion to the sub-... 

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