Recent developments in the chemistry of silicone and fluorine materials for coatings applications present exciting opportunities from the synergistic effect of these two chemistry sets. The introduction of hydrosilylation-cure fluorine resin technology for coatings applications can significantly broaden the range of applications where this technology could be applied. Fast and low-temperature cure, hardness, flexibility, weatherability, chemical resistance, and adhesion properties are some key performance enhancements achieved with this new technology. Existing and new coatings market segments, including construction, chemical process industry, automotive and electronics, are a few of the applications where improved surface performance is required. These hydrosilylation-curable fluoro-polymer resins can be cured quickly at low temperature, providing significant cost savings and process application flexibility to the coating application process.

Introduction

Fluorine-based materials are extensively used in surface protection due to the unique properties that can be imparted through material design such as water and oil repellency, weatherability, chemical resistance, stain repellency and durability. Silicone-based cure chemistries have been widely used not only for silicone materials, but also for organic polymers. In particular, fast and low-temperature cure properties of the hydrosilylation cure system attracted much interest and has been investigated in numerous applications, especially on plastic substrates, from the perspectives of good productivity and energy saving during application. The following paper describes the development of a hydrosilylation cure-enabled fluoropolymer coating and its unique properties, which are attributed by the synergistic effect of fluorine-based polymer and silicone cure chemistry.

Results and Discussion

A wide range of fluoropolymer coatings exist today that provide substantial performance benefits to the end user, but many of these coatings are limited in their use due to the processing conditions required for film formation on a substrate. One of the most common coatings is polytetrafluoroethylene (PTFE) used as a low-maintenance coating for cookware and bake ware. PTFE provides excellent stain resistance and durability but requires high-temperature processing when applied on a substrate, limiting its application to temperature-resistant substrates. Vinylidene fluoride (PVDF) and other common fluoropolymers such as copolymers of tetrafluoroethylene and perfluoroalkyl vinylether (PFA) or tetrafluoroethylene and ethylene (ETFE) also require high-temperature processing. In addition, the high degree of crystallinity in these polymers makes their solubility in common organic solvents very poor and limits the options for processing and fabrication of these materials as coatings.

Monomers such as tetrafluoroethylene and chloro-trifluoroethylene can be copolymerized with a variety of different vinyl monomers to yield polymeric materials that are amorphous in structure and have excellent solubility in common organic solvents. Reactive functionality can also be introduced into these copolymers through the introduction of suitably functionalized monomers during the polymerization process. Polymers of this type have excellent room-temperature processability and can be readily fabricated into coatings and films on a wide variety of substrates. Using TFE as the monomer enables some of the inherent characteristics of PTFE to be retained in the final copolymer (TFEC) such as excellent weatherability and dirt resistance, but with the added advantage of the improved ease of processing. The properties of common fluoropolymers are summarized in Table 1.

However, recent interest in reducing energy consumption and a reduction of environmental load increase the demand for fast and low-temperature cure processability. Adhesion to various substrates that have no surface treatment or primers is achievable with this novel coating technology. Therefore the introduction of hydrosilylation-curable fluoro-resin technology for coatings applications has been investigated to impart fast and low-temperature cure properties to the TFEC-based coating.

Figure 1 summarizes the structural components of the newly developed TFEC and their role in providing performance properties to a finished coating. The introduction of alkenyl groups into TFEC enables the hydrosilylation crosslinking that is widely used today in many common reactive silicone materials. In terms of fluoro resin functionality the TFE unit contributes excellent weatherability, chemical resistance and anti-corrosion properties, while incorporation of vinyl monomers enables modification of the co-polymer characteristics to provide important properties such as transparency, solvent solubility and compatibility with pigments and polymer additives. The TFEC coating can be cured with conventional Si-H-containing crosslinkers in the presence of a platinum catalyst, as shown in Figure 2.

The cure behavior of the hydrosilylation-based TFEC coating at various cure temperatures was investigated using MEK resistance of the cured film as the response metric. The hydrosilylation-based TFEC coating showed a rapidly increasing cure profile that started after a very short induction time, with complete cure achieved in 60 seconds at 150 ºC, while the melamine cure system required twice the cure time to achieve good MEK resistance. The isocyanate cure system displayed essentially no cure within the initial 120 seconds at 150 ºC. As the cure temperature increased from 150 ºC to 230 ºC, the induction time of the hydrosilylation-based TFEC coating decreased with a dramatic increase in the cure speed. This data demonstrates the high curing speed of the hydrosilylation-based TFEC coating system, which could provide a lower total applied cost by better productivity and less energy consumption.