No. 27 - Film/Sheet Coextrusion

U.S. Industrial Chemicals Co. reportedly was the first to practice feedblock coextrusion commercially in 1959 when it produced a PP/PE bread wrap. Frank Nissel, founder of Welex, supplied several coex HIPS/GPPS sheet lines to French and German thermoformers in the mid ’60s. Putting a GPPS glossy layer onto HIPS was one of the first coextrusion applications because HIPS otherwise turns dull when reheated for thermoforming. Nissel connected the extruder for the GPPS skin coating directly to the melt-thermocouple orifice on the die adapter, resulting in a feedblock. These lines produced thin sheet for thermoformed yogurt and drinking cups and thick sheet for marine parts.

However, Dow Chemical beat both U.S.I. and Welex to the punch when it came to feedblock patents. Dow’s Douglas Chisholm and Walter Schrenk built feedblocks in the ’50s to create sheet with as many as 125 layers of two polymers. They could even make sheet with layers stacked like a venetian blind—perpendicular to the sheet surface. Dow filed patent disclosures on its coextrusion work in the early ’60s and applied for a patent on Dec. 29, 1967, which was issued Jan. 19, 1971. (Dow sold its feedblock patent portfolio to 3M in 1995.)

Dow’s first licensee to build feedblocks was Johnson Plastics Machinery in Chippewa Falls, Wis., which was later bought by Egan. Other early machinery licensees were HPM, Davis-Standard, Gloucester Engineering Co., and ER-WE-PA in Germany. Mearl Corp. (now Engelhard), licensed Dow’s 100-layer iridescent film technology in 1973-74.

Multi-manifold flat dies were developed by Samafor in France (bought by Davis-Standard in 1990) and Omipa in Italy during the ’70s as an alternative to feedblock coextrusion. Multi-manifold remains the preferred method for certain products, like BOPP film.

 

Barrier coex booms

The development of tie-layer resins fostered the growth of barrier coextrusion. Du Pont introduced EVA and Surlyn ionomer in 1964. In 1965-67, Dow developed and patented five-layer Saranex PE/EVA/PVDC films. In 1967, Dow feedblock licensee Oscar Mayer set up a three-layer barrier line in Madison, Wis., with two feedblocks and two dies extruding top and bottom barrier films for packaging bacon and hot dogs. Also in the late ’60s, Cobelplast in Belgium worked with Dow to pioneer five-layer PVDC barrier sheet for form-fill-seal packages. Starting in the 1980s, barrier sheet activity focused more on an easier-processing barrier resin, EVOH, introduced by Kuraray in Japan in the late ’70s.

Peter Cloeren, Sr. came up with his own feedblock design in 1974 while working with Gulf Oil (now Chevron Phillips). He introduced the first dual-barrier 11-layer feedblock in 1986 for retort packaging. Today, Cloeren builds feedblocks with hundreds of layers.

 

Blown film, too

Coextrusion appeared in blown film in the late ’60s. Reifenhauser built a two-layer blown film line in 1969 for milk pouches. At NPE ’71, Egan Machinery (now Davis-Standard) demonstrated three-layer EVA-ionomer-EVA) blown film coextrusion, while American Barmag ran a three-layer (nylon-ionomer-LDPE) line. The next step was toward five layers, and in 1995 Holmes Packaging in New Zealand bought the first seven-layer blown film line from Battenfeld Gloucester. Two years later Holmes installed the first commercial nine-layer line in the world, built by Brampton Engineering.