patent dates:
1. Patent Number 1,833,847 was issued November 24, 1931 (reissued August 7, 1934) to Thomas Midgley, Jr., Albert L. Henne and Robert R. McNary, all of Ohio, for "Heat Transfer." The original application was filed February 8, 1930.
2. June 18, 1935: Herbert Wilkins Daudt and Mortimer Alexander Youker were issued Patent Number 2,005,706 for "Organic Fluorine Compound." It was assigned to Kinetic Chemical Inc., of Wilmington, Delaware, the forerunner of DuPont. It's opening paragraph: "This invention relates to organic fluorine compounds, more particularly fluorinated derivatives of acyclic hydrocarbons and a process of the production thereof."
3. July 9, 1935: Patent Number 2,007,706, filed January 30, 1931 was issued to Albert L. Henne and General Motors Corporation. Titled "Manufacture of Fluorated Aliphatic Compounds," Henne states "this invention relates to chemical processes for the manufacturer of fluoro and/or halo-fluoro derivatives of aliphatic hydrocarbons, and more particularly, of halogen derivatives of the methane homologs having relatively high melting points."
4. Patent Number 1,953,216, issued April 3, 1934 to Howard M. Elsey and assigned to Westinghouse Electric & Manufacturing Company appears to accidentally cover CFC refrigerants. While it's titled "Insulating Liquid" and is targeted to electrical apparatus with liquid insulators, one of Elsey's claims is " ... As a new composition of matter a fluorinated mixture of hydrocarbons that is liquid at ordinary temperatures and solidifies below approximately -1 C."
Patents don't last forever, those for "CFC Refrigerants'" ran out in the 50s
Assuming their term is a maximum of twenty years, all of these patents ran out in the early 1950s. That means GM's, Frigidaire's, Kinetic's, Westinghouse's and yes, even DuPont's patent on "Freon," had run out long before the ozone layer was discovered to be suffering.
Proof of that also appears in the November 5, 1946 registration of the trademark Genetron. General Chemical Company Corporation, later Allied Chemical, then Allied-Signal and now Honeywell Inc., claimed rights for: "Normally gaseous halogenated hydrocarbons; normally gaseous chemicals for use in propelling parasiticides (sic) and dispersing them in aerosol form." No mention of refrigerants, but they declare first usage on January 4, 1946. On May 12, 1951 they again received registration for "genetron" with a Goods and Service claim of: "Halogenated hydrocarbons sold as such as chemicals of commerce."
Just think how many millions of car owners out there were crediting all that cool air to the magic of Freon, when in fact they were being cooled by Genetron!
Conclusion
So, DuPont's expiring patent did not cause the switch to R-134a.
