- December 01, 1996, Sacharow, Stanley
With all the hype in recent years about transparent barrier films, one would think that applications could be found almost anywhere in the supermarket. But in a course given this past October during International Polyester Week '96 (IPW '96) by the Packaging Group Inc., John Felts, a pioneer in the area, noted that "the total market size is questionable," and "the coatings are still expensive."
As defined, a transparent barrier is an inorganic, typically an oxide of silicon or aluminum, that is less than 500 [Angstrom] in thickness. It is produced in a vacuum deposited between [10.sup.-2] to [10.sup.-5] Torr.
In essence, the concept is fantastic - coating a thin layer of glass onto a flexible plastic film. The process has been expanded to include not only silicon oxides but also aluminum oxides and mixed oxides. The deposition technologies used to coat these oxides onto substrates include physical vapor deposition (plasma and chemical diffusion) and techniques such as sol gel, spin on glass (SOG), and spray coatings.
Of the two major methods, physical vapor deposition can produce good barriers if process conditions are selected to offset material defects and water removal from the substrate. Plasma deposition is limited by material defects and surface roughness. Chemical diffusion probably produces the best barrier, but the process is much slower than evaporation.
Oxides can be deposited onto a wide variety of flexible and rigid substrates. The focus to date has been with polyethylene terephthalate (PET), but the technologies do not get interesting until non-PET substrates are commercialized. Uncoated PET is presently coated by plasma or evaporation, and barriers of 0.2-5.0 cc ([O.sub.2]) [m.sub.2]/day and 0.5-5.0 ([H.sub.2]O) [m.sub.2]/day) are possible.
Evaporation yields even lower barriers. Deposition onto polypropylene is difficult due to the rough surface, thermal sensitivity, and product variability. Polyethylene has a very heat-sensitive, rough surface and requires superior tension control. Nylon's affinity to water makes deposition quite difficult.
Japan is the largest user of oxide-coated films, using about 100 million [m.sup.2]/yr or 3.75 million lb/yr. Toppan Printing Co. offers oxide-coated film for tubestock, detergent powders, and the stand-up retort pouch. Mitsubishi Kasei "Tech-barriar" films have been marketed in Japan for dry seaweed, liquid products, and lidstock.
Europe consumes about 40 million [m.sup.2]/yr or 1.5 million lb/yr. The applications include lidding stocks for modified atmosphere packages (MAP), MAP meat packaging, dried soup pouches, pharmaceuticals, and chocolates. "Buss" brand retortable ready-meal trays containing soups and stews are on the German market with PET/SiOx/Adhesive/PET/seal from Lawson Mardon. The firm also supplies Bell of Base, the Swiss firm, with pasteurized, refrigerated "Quick Meats" in stand-up SiOx-coated pouches. Recently introduced by Tetra Laval Food (Holland) through a company called TIRO PAK are peelable, printable films based on chalk-filled PP, foamed PP, and SiOx-coated PET. "TIROMAP" consists of a 64-micron top web of PET/SiOx/PE and a 250-micron forming web of a paper-like foamed PP with an ethylene vinyl alcohol (EVOH) barrier layer.
The US is the smallest market, consuming less than 5 million [m.sup.2]/yr, or 188,000 lb/yr. The Tetra Pak gable top construction of PE/SiOx/PE/Paper/PE (recently withdrawn from the market) was highly touted for citrus juices and juice blends. There are also several low-volume applications in the medical field.
According to Felts, "There has been a considerable amount of money invested in the past ten years to develop transparent barrier technology, but the initial intention to replace foil structures was flawed. The majority of foil applications require the foil as a light barrier. Few of the current applications use the transparent property."
Oxide coating technology is now heavily focused on the coating of bottles and other three-dimensional shapes. There are eight firms worldwide involved in the business. Most utilize plasma deposition techniques. Cost has limited market growth in the flexible area; however, there does appear to be a substantial market in value-added medical packaging applications.
For the comprehensive text used in the course "Oxide-Coated Transparent Barriers: Emerging Trends," send $95.00 to The Packaging Group Inc., Box 345, Milltown, NJ 08850. The book contains more than 150 pages and lists all major contacts and applications in the field.
Stanley Sacharow has been in the flexible packaging industry for almost 35 years. His company, The Packaging Group, is an organizer of targeted conferences and a consultant to the international packaging/converting industry. Contact him at 908/636-0885.