You can freely build on The Molecular Structure of Kevlar High-Strength Fiber

What this patent covers

This patent claims a synthetic fiber made from aromatic polyamides (aramids) where the polymer chains are highly aligned. Specifically, the chain-extending bonds from each aromatic ring are coaxial or parallel and oppositely directed (para-oriented). This alignment is characterized by an 'orientation angle' of less than 45 degrees, meaning the polymer chains lie nearly parallel to the fiber axis. This tight alignment gives the fiber incredible tensile strength (tenacity of at least 5 grams per denier) and stiffness (initial modulus of at least 300 grams per denier). When spun from a liquid crystalline solution, the molecules line up like logs in a river, creating a fiber that is five times stronger than steel on an equal-weight basis.

What is now free to use

All 1 claims of US 3819587 are in the public domain. Specifically:

The 1 dependent claim add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• Does not cover aliphatic polyamides like nylon, where the carbon chains are flexible and do not contain rigid aromatic rings.

• Does not cover fibers with a high orientation angle (above 45 degrees), where the polymer chains are disorganized and lack high tensile strength.

• Does not cover meta-oriented aramid fibers (like Nomex) where the chain bonds are not coaxial or parallel, resulting in lower strength but high heat resistance.

• Does not cover inorganic high-strength fibers such as carbon fiber or glass fiber.

Who is building on this today

DuPont remains the primary producer of Kevlar, but competitors like Teijin (producing Twaron) have built extensive product lines using similar para-aramid chemistry.

Products built on expired version of this technology

How to cite this patent in your documentation

EI Du Pont de Nemours and Co. US Patent 3819587. Wholly aromatic carbocyclic polycarbonamide fiber having orientation angle of less than about 45{20. Granted 1974, expired 1991. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.