According to Merriam Webster’s dictionary, to “modify” means to make basic or fundamental changes to give a new orientation to or to serve a new end. That’s what surface modifiers do when it comes to paints, coatings and inks.
Surface modifiers are additives that enable formulators to achieve specific effects to enhance and protect appearance, feel, slip, abrasion resistance and overall durability of the coating or ink formulation. A broad range of polymer chemistries and particle sizes are available to control performance properties in a range of applications, including metal, wood, printing and packaging.
Many surface modifiers are formulated using combinations of waxy polymers. These building blocks can include polypropylene, carnauba, Fischer-Tropsch, microcrystalline, amide waxes, polytetrafluoroethylene (PTFE), polyethylene and silica. Once formulated, there are several different types of surface modifiers that come in powder and liquid form, including micronized powder, aqueous and solvent-based dispersions, emulsified forms, and wax-treated silica, all of which deliver a range of functions.
Micronized wax additives are tailored specifically to protect the coating surface or control the aesthetics of the cured liquid and powder coatings. Particle size distribution is controlled to maximize compatibility and properties in a finished coating or ink. Particle size distribution is controlled using a variety of milling techniques, spray drying or spray congealing manufacturing methods. Micronized wax technologies act as processing aids and enable highly filled systems to feed easily during the extrusion process for powder coating manufacturing. These same technologies will produce cured liquid or powder coatings and inks with improved abrasion or rub resistance, reduced gloss, various textured aesthetics as well as functional properties like anti-blocking.
Dispersed wax additives are prepared to simplify incorporation of a surface modifier into liquid coatings. Modified protection and aesthetic properties are driven by the wax additive that is dispersed in the liquid media. Wax dispersions are available in aqueous-based formulations, non-aqueous systems ranging from polar to non-polar solvents and oligomeric carriers targeted at energy-cured formulations.
Emulsified wax additives are typically used to protect clear coated surfaces from damage due to abrasive forces or damage due to moisture exposure. Typically, emulsified wax is used in the coating or ink without impacting the appearance of the finish.
Selecting the Best Surface Modifier
Multiple factors need to be considered when selecting the appropriate surface modifier, including:
- Surface modifier chemistry and particle size.
- Coating properties, such as film thickness and resin chemistry.
- Application and cure methods.
The Importance of Cure Cycle on Surface Modifier Performance
The curing mechanism affects the additive migration to the surface of the film and can also influence the performance of the finish itself. Eddy currents created by evaporation of solvent or water plus the density differences between the wax and liquid enable the wax to migrate to the surface of air-dried or oven cured, solvent-based or water-based coatings or inks. In UV cured, high-solids or solvent-free systems, very short cure cycles, viscosity and degree of film shrinkage impact surface modifier performance. As a result, the mobility of the surface modifier and the ability to float to the coating-to air interface is limited. The curing temperature is important because it influences the viscosity and the mobility of the additive particles. Cure temperatures greater than the wax additives melting point can lead to significantly different performance because a microscopic wax layer can be formed at the coating-to-air interface. This is known as the layering effect.
The Market for Surface Modifiers
Surface modifiers can deliver a number of surface effects across a wide range of applications. Some of these applications include:
- Wood Coatings—surface modifiers provide improvements in scratch and abrasion resistance, anti-blocking properties, matting and soft feel, can reduce the sedimentation of silica matting agents and improve sandability.
- Coil Coatings—properties achieved include slip, anti-blocking, scratch and abrasion resistance while also influencing durability and matte appearance.
- Industrial Coatings—there are many types of industrial applications such as plastics, metal, film and foil with various performance requirements.
- Inks and Overprint Varnishes—improve rub resistance and anti-blocking properties with minimal influence on gloss at low film weights.
- Can Coatings—aid in protecting metal containers from abrasion damage in conditions such as high-speed production or during transportation, plus improve overprintability, promote heat-sealing stability and provide release properties without influencing porosity.
- Architectural Coatings—the main properties needed are metal marking resistance and anti-blocking, especially for doors and windows. Surface modifiers can also provide smooth surface feel and matting.
- Powder Coatings—improve fluidization, antistatic properties and degassing during application and cure. Surface modifiers can also affect mechanical properties such as slip and impact resistance as well as aesthetic effects such as matting or texturing.
Lubrizol has extensive experience developing and manufacturing a wide range of micronized and liquid wax preparations for paints, coatings and ink to meet many formulation performance needs. Lubrizol has the technical and commercial expertise combined with market knowledge and quality control procedures to ensure consistent batch-to-batch performance.