Polymer materials are the backbone of performance coatings as they impart the desired functional and environmental requirements of those coatings. Choosing the appropriate polymer material to use is critical to the ultimate success of the coating, and several factors must be considered.
The factors include, how will the coating be applied? What is the coating being applied to? What are the physical performance requirements? For example, in a paint application, will it be brush, spray or roller applied? Will it be dried at ambient temperature or is there a bake system in place? Is the substrate wood, metal, plastic, etc? Is it an interior or exterior application?
On the other hand, in a paper, nonwoven or textile application that use heat for drying, the factors to consider change slightly. In what part of the process will the polymer be used? Is it a saturant, coating or wet-end addition? Also, what types of fibers – cellulose, synthetic, glass, etc.?
These are all important questions to ask when choosing the right polymer. The combination of end-use requirements of the coating and the way it is applied, along with the inherent properties of the polymer being selected ultimately determine which polymer is best for an application.
Physical properties like hardness, chemical resistance, and water resistance help determine the main type of chemistry required for the specific application. The physical performance specified by the end use requirements will help determine the type of polymer best suited for the application: acrylic, vinyl, polyurethane, or others. Polyurethanes might have better abrasion resistance and toughness while acrylics could have better UV resistance and water resistance. Vinyl products are typically used for abrasion resistance and flame resistance.
It is important to know how the polymer will be applied because formulation modifications may be needed based on the application method. For example, a thickener might be used to achieve the required viscosity for an application that is brushed on. If it is sprayed on, however, the coating would likely require a different rheology profile and thus need different additives to achieve the desired viscosity.
Once the application and end use requirements are known, the inherent properties of the polymer determine which polymer is right for the application. Two polymer properties to consider are minimum film formation temperature (MFFT) and self-crosslinking versus heat reactive. A polymer’s MFFT directly relates to whether it can be used in ambient conditions or if a bake system is needed without further formulation. When using an ambient air-dried system, the MFFT must be lower than the drying temperature in order to create a film. If the drying temperature is too low the coating will basically crack and won’t form a film. Without a properly formed film, the desired und-use properties will likely be nonexistent.
Self-crosslinking versus heat reactive also helps determine whether a bake or air-dried system should be used. Self-crosslinking means the material can react and crosslink without the need for external factors like heat. Heat reactive products, on the other hand, need an oven to get to the desired temperature to cause crosslinking. In general, crosslinking improves physical performance, so it is important to match the technology with the process that will be utilized.
Different polymers have unique properties and will produce different results in coatings based on multiple factors. With so many factors to consider, choosing the right supplier may be just as important as choosing the right polymer. At Lubrizol, we can collaborate with coating formulators to help mitigate the complexity of polymer selection and work together to identify solutions that achieve specific coating performance needs.