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 effected by fluoride's elevated electronegativity, exhibiting
- exceptional non-reactivity,
- an elevated molecular weight,
- a low incidence of friction coefficients against solids of all types, and
- strong hydrophobic qualities; it cannot be made wet by either water or any substances containing water.
First discovered by accident in the early 1930s, DuPont Corporation's Teflon™ remains the best known brand of PTFE, most commonly recognized as the non-stick coating applied to cookware. This isn't its only beneficial application. Indeed, original uses for PTFE were military, as seals for the first atomic bomb. However, because it resists electricity and is transparent on radar, PTFE was also successfully used as the nose-cone covering for proximity bombs.
Teflon and related PTFEs also possess such useful attributes as resistance to chemical reaction, corrosion, and stress-cracking. Their exceptional lubricating 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 generates numerous 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 Teflon™ and other PTFEs are widely used as include 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 as a polymerization of p-xylene, parylene conformal coatings were soon adapted for medical products, since they provide reliable 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 ranges 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.
In addition, parylene's uses are not confined to medical applications, but have been successfully employed for aerospace/military, automotive, consumer, and industrial uses, virtually any where printed circuit board (PCBs), printed wiring boards (PWBs), or similar electrical assemblies require protection during operation.
In comparison to PTFE, parylene's CVD polymerization process produces a more uniform coating conforming completely to the substrate. Its pinhole-free coverage remains superior to even newer-technology PTFE. While both coatings can offer excellent protection from chemical corrosion and moisture, parylene is unsurpassed in delivering reliable security from the edge-effect and meniscus problems that can mar the performance of components requiring conformal coating to maintain expected function through all conditions. Despite PTFE's uses, parylene adaptability to unusual coating conditions at thickness-levels finer than PTFE result in substantial, longer-lasting conformal solutions and functionality.