23 сентября, 2015 
Pokraskin TPAs are high MW acrylic copolymers supplied in organic solvents. These copolymers are typically prepared from monomers such as methyl methacrylate, styrene, or n-butyl acrylate. The selection of solvent is dictated by solubility of the resin, solution viscosity, evaporation rate, type of final coating for which it will be used, and cost. TPAs are generally used in systems that cure at ambient temperature without the need for cross-linkers. Therefore, such resins are designed with specified Tg so as to produce dried films with desired thermo-mechanical properties. For example, TPAs for use in automotive top coats must have a Tg over 70 °C. In general, film strength increases with MW of TPA resins, although above a MW of about 90,000, the change in properties with increasing MW is not substantial. Such TPAs are generally not supplied above a MW of about 100,000 because they tend to exhibit cobwebbing upon spraying rather than atomizing to small droplets.
One major limitation of TPAs is their high solution viscosity (due to their high MW), which necessitates use of a large amount of organic solvent in their coating formulations to be able to offer products at sprayable viscosity. This has two major consequences: (a) final coatings will have very high solvent content and may not be compliant to VOC related regulations and (b) due to the large amount of volatile solvent, such coatings will have low non-volatile content, resulting in lower dry-film thickness. This may require labor-intensive multi-coat applications to achieve the desired film thickness. Due to these reasons, solventbased TPA coatings are rapidly declining in their usage.
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