PTFE and Parylene

Properties of Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) is a solid form of a synthetic fluoropolymer derived from tetrafluoroethylene. A compound composed essentially of carbon and fluoride, PTFE is affected by fluoride’s elevated electronegativity and exhibits the following:

• Exceptional non-reactivity
• Elevated molecular weight
• A low incidence of friction coefficients against solids of all types
• Strong hydrophobic qualities; it cannot be made wet by either water or any substances containing water

Discovered in the 1930s, PTFE is commonly recognized as Teflon™, the non-stick coating applied to cookware. PTFE is also known for its use as seals in the first atomic bomb as well as the nose-cone covering for proximity bombs.

PTFEs provide resistance to chemical reaction, corrosion and stress-cracking. Their exceptional lubricity properties significantly reduce operational friction and energy consumption, particularly for machines with sliding parts. PTFE coatings effectively lubricate bearings, gears, slide-plates and other moving components, more reliably than such competing substances as acetal and nylon.

Moreover, PTFE’s mechanical toughness and ability to resist corrosion makes it ideal for many industrial and product applications. The unity between the compound’s carbon and fluoride atoms is exceptionally strong, causing it to repel virtually all other substances from a sufficient distance that any possibility of a reaction with PTFE is eliminated. The electrical and low-friction properties of PTFEs are widely used as internal covering for ducts and pipeline. PTFE coating also enhances the safety of containers for chemicals that are highly corrosive or reactive.

There are two principal methods of making PTFE:

• Suspension – Polymerizes TFE in water, creating a granular PTFE
• Dispersion – Generates a milky paste of PTFE

Although the products of these procedures assume different physical qualities, both the grain or paste forms of PTFE can be transformed successfully into conformal coatings, via spraying/dipping components with a liquid dispersion of the processed PTFE substance. A curing procedure at 360°C completes the procedure, limiting its use for substrates like fabric, plastic, or others that are temperature sensitive. In addition, traditional applications of PTFE can require an initial primer-coat to assure reliable surface adherence; resultant coatings may be thick and porous. New technologies have engendered PTFE conformal coatings without reliance on liquid solvents, primer, or after-curing. This has improved their biocompatibility, dielectric constant, lubricity and non-stick/release performance, lowering their hydrophobicity and coating thinness/uniformity. However, problems at higher temperatures remain can cause the creation of toxic byproducts.

Parylene Conformal Coating

Originally developed through the polymerization of p-xylene, Parylene conformal coatings quickly found use in medical applications due to their dependable hydrophobic barriers. Their friction-reducing properties have been applied for other medical uses, as with hypodermic needles and syringes. Parylene coatings match or surpass PTFE in this regard, as do their abilities to generate surface protection from corrosion and outside elements, for a wide range of uses safeguarding the operation of electronic components.

Parylene requires no catalyst or solvent to generate polymerization, leading to a process yield of 100%. Its chemical vapor deposition (CVD) process ensures Parylene coatings penetrate deep into substrate surfaces, producing entirely conformal, pinhole-free and uniform coatings, impermeable above thicknesses of 1.4 nanometers. Using a process-specific chemical-vacuum chamber for CVD, the coating process eliminates the wet application technologies most competing coatings must employ.

CVD’s vapor monomeric quality is unimpeded by the influence of gravity and surface tension on the substrate during the application process, leading to superior coating of even the most complex component design. Exceptionally biostable and hydrophobic, Parylene coatings continue to be successfully adapted for medical instruments and hoses. Uniform surface conformance completely covers components’ sharper edges and points, further supporting its use for such metallic medical devices as syringes, scalpels, and similar instruments. Parylene’s success as a micro barrier against often corrosive bodily fluids makes it very useful as a surface coating for implantable medical devices.

Parylene’s applications extend beyond the medical field. It has proven successful in aerospace/military, automotive, consumer, and industrial sectors, safeguarding printed circuit boards (PCBs), printed wiring boards (PWBs), and similar electrical assemblies during operation. Amid rising concerns over the use and long-term impacts of perfluorinated and polyfluorinated alkyl substances (PFAS), manufacturers worldwide are under pressure to remove PFAS from their products. Parylene emerges as a PFAS-free substitute for PTFE, offering a safer alternative.

Conclusion

In conclusion, both PTFE and Parylene conformal coatings offer unique advantages and applications in various industries. PTFE, known for its exceptional non-reactivity and lubricity, is widely used for industrial and product applications, while Parylene stands out for its reliable hydrophobic barriers and ability to safeguard electronic components in medical and other fields. As industries seek alternatives to PFAS substances, Parylene provides a safe substitute for PTFE, ensuring continued protection and performance in a range of applications.