Polyamide - the high performer

In addition to a still emerging biaxially oriented polypropylene (BOPP) market, biaxial oriented polyamide (BOPA) film is proving to be an attractive field of activity for investors. This is especially the case in Asia, where BOPA film growth rates of the order of 25 per cent a year are forecast for the next five years.

BOPA film has excellent properties for various high end applications mainly within the food packaging sector, but there are also applications for non food products. It displays exceptional tensile and impact strength; it offers high flex-/stress-crack and puncture resistance and provides a good barrier to gases (oxygen, nitrogen, carbon dioxide) and flavours/odours (organoleptics). In addition, if shows a high resistance to oil, greases, hydrocarbons and chemicals, thermoforms easily and demonstrates excellent haze and gloss for cast and blown film. It accepts print well, has a wide applicable temperature range and is a good film for use with others, laminating easily.

All this means that BOPA film is frequently used for the packaging of frozen and cooked foods, pickled vegetables, agricultural and aquatic products, or distilled goods packaging.

Other main areas of widespread use include the medical and health care sector. Here we can see it used in blood bottles and infusion bags, for example. BOPA film is also used for electrical industrial materials packaging and for some "exotic" applications, such as the so-called 'designer-balloons' which are becoming more and more popular for events of all kinds, especially in the USA.

Orienting technology

For all orienting technologies for polyamides, one member of the family is the favourite raw material - PA 6. It is the least costly of the polyamides and offers the best gas and aroma barrier, improved strength against flex-crack, abrasion, impact and puncture, good tearing properties needed for easy opening of packs, as well as the mechanical strength that is essential in the printing and lamination converting processes.

Generally, there are three biaxial stretching technologies used for the production of BOPA film: double-bubble blown, two-stage stretching (sequential principle) and simultaneous stretching. My company - Brückner's - expertise lies in building film stretching lines. We have gained specific experience on how to achieve BOPA film of high quality with different line concepts:

• Sequential lines guarantee an efficient

  and reliable film production. However,

  the flexibility is limited.

• Pantograph lines provide a

  sophisticated, state of the art

  mechanical simultaneous stretching

  technology, with speeds up to 200

  m/min.

• Brückner`s patented LISIM technology

  is an advanced and flexible system for

  simultaneous stretching, providing

  excellent film properties for high end

  applications.

A special BOPA test week on the LISIM laboratory line will be held at the company this autumn. Well known BOPA film producers, as well as newcomers, will test different PA resins and will benefit from the special line features such as contact- free, smooth stretching for special surface quality or the MD/TD ratio flexibility.