Background

Waterborne coatings (as opposed to solvent-based coatings) are desirable in many applications to reduce the quantity of volatile organic components in the formulation. This is true for both environmental and safety reasons, but also reduces cost of manufacturing. However, the barrier performance of these reduced-solvent products is inferior, especially for water absorption from natural weather (rain or humidity) and cleaning. Absorbed water physically swells the film and introduces dissolved ions into the clearcoat, which allows for increased chance of pitting, wear, delamination, and corrosion, affecting not only the protective outer clearcoat but also the underlying layers, including the substructure.

Incorporating additives that minimize water absorption will reduce physical damage to the coating (repeated swelling during water uptake followed by compression as water evaporates) and chemical damage through ion/electron exchange (corrosion) among the sub-layers. Reduction in either of these destructive processes is desirable; however, any increase to manufacturing cost must come at a significant improvement to the quality and/or lifetime of a clearcoat product to be accepted by the market due to increased cost of the final product. In addition, an ideal new additive would have most or all of the following properties:

Optical transparency to visible light,
Reversible (able to be removed easily, for example with acetone),
Can be applied via accepted processes such as brush, roller, or spray,
Is a “drop-in” utilizing existing resin/clearcoat formulations,
Has little or no effect on basecoat adhesion,
Keeps the benefit of waterborne application (not requiring additional solvents).

The proposed clearcoat nano-additives checks all of these boxes.

Historically it has been difficult to incorporate nano-sized materials into complex mixtures such as acrylic and acrylic-epoxy sealants due to the tendency of the nanoparticles to aggregate creating heterogeneous regions which reduces the impact of their addition and in many cases creates a wholly inferior product. This is unfortunate because some nanomaterials such as synthetic nanoclay (Laponite) have the ability to minimize water adsorption through a physical barrier against water egress into the clearcoat (meaning their addition creates long-lasting protection). Therefore a method of modifying Laponite into a structure that retains these desirable qualities (transparency and water resistance) while improving homogeneity and mitigating impact to the final coating quality would create a new class of clearcoat products applicable to a wide number of industrial uses, and eliminates the current tradeoff for higher protection at the expense of the safety, cost, and environmental impact of solvent-based coatings.

Technology Overview

The proposed nanoclay additive [Laponite, a synthetic clay (Si, Mg, Li-based) that can be manufactured into nano-sized particles] has been modified using a simple, scalable process utilizing commercially available reagents. While specific examples are given below, the technology is broadly applicable across a wide range of clearcoat formulations, and it is expected that with optimization this method could be used to create an entire new class of products incorporating modified laponite additive.

Example Formulation: As a demonstration project of this new chemistry, a series of resins that incorporate the nanoclays into commercially-available latex/PVDF/PMA blends were formulated to show the additive’s effect on water absorption. graphically shows an example Laponite nanoclay particle before (a) and after (b) various modification processes. Figure 1(b) shows the addition of:

Silane molecules to improve acrylic compatibility (3-acetoxypopyltrimethoxysilane)
Silane to improve PVDF compatibility (tridecafluoro-1,1,2,2-tetrahydrooctyl triethyoxysilane)
and also the exchange of a Sodium (Na) ion with phosphorylcholine to reduce aggregation

The final product was applied to primed bronze substrates, and the composite films using this additive showed many improved properties: reduced water sensitivity and ultraviolet-induced polymer degradation, which increased the barrier properties and reduced the diffusion constants over both short-and long-term weathering studies compared with films without nano-clays. Water absorption was the primary metric of interest, and each formulation was immersed in water for 4 hours to ensure maximum absorption. The waterborne films with only silane-modified Laponite had a water volume fraction of ~10%, considerably less than traditional waterborne coatings. The best-performing films (silane and phosphorylcholine Laponite modification) had a final water volume fraction of ~3.5%, lower than commercial solvent-based coatings despite being waterborne**.** These were non-optimized formulations, and are ready for a technical development team to integrate into a product specification for commercial scale-up.

Applications

Protective coatings are used in multiple industries and applications in products as well as in outdoor and indoor applications. Some examples of use are in paints, coatings and films infrastructure (major structures like bridges and dams, pipes, concrete, and electrical power lines) corrosion protection, vehicle paint, building surfaces (windows, solar panels, tile), and metallic art such as sculptures.

A clearcoat which reduces water and ionic ingress into the underlying coatings (colorants, corrosion protection, UV protection) extends the life of the coatings themselves and the substructure, which for infrastructure and buildings improves the life and safety of the owner’s investment. Some structures, such as outdoor art, are effectively irreplaceable, and protection is paramount to preserving their historical and cultural significance.

Opportunity

The modified Laponite nanoclay additive has been tested in multiple formulations and is available for further testing and integration to products. The inventor is available for assistance in transferring this technology to market, and if desired will help with formulation and testing under a sponsored project arrangement.

Waterborne Clear Coatings with Superior Water Absorption Prevention

Patents

IP Status

Seeking