| Injection, Blow Molding Article | U.S. Patent 237,168 was issued on February 1, 1881, to Celluloid Novelty Co. and Celluloid manufacturing Company, New York. This was the first patent for the processing of extruded polymer into a parison for blow molding. The first applications for blow molding were for cellulose nitrate, and later, in the 1930s, for cellulose acetate. Blow molding remained a relatively small part of the plastics manufacturing scene until the introduction of Low Density Polyethylene (LDPE) in the 1940s. The production of LDPE squeeze bottles by Monsanto caused a rapid expansion of the industry, with containers produced to replace glass bottles for shampoos and liquid soaps. The mass production of high density polyethylene (HDPE) and polypropylene (PP) in the 1950s led to a further increase in blow molding demand, for applications such as liquid detergents, motor oil, water and milk. The lightweight HDPE one gallon milk container revolutionized the dairy industry, as glass bottles and paperboard were quickly replaced. The production of polyethylene terephthalate (PET) led to the viability of reheat stretch blow molding. The strain hardening properties of PET allowed the high volume production of bottles able to resist the carbonation pressure in soft drink applications. The high clarity and economics of PET stretch blow molding have made this a popular production method for bottles for water, detergents, and other products.
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