Polyamide Film
Poly-amide is a polymer with a plurality of repeating amide groups (-NH-CO-) in the molecular backbone. This type of polymer is commonly known as Nylon.
Poly-amide film varieties mainly are nylon 6, nylon 66, nylon 11, nylon 12, Copolymerized polyamides and aromafic polyamides. But in terms of packaging, nylon 6 would be used the most. The main varieties of polyamide film are as below:
1. Bidirectional stretch polyamide film
BOPA film is biaxial stretch nylon film, can be produced by blow molding and biaxial stretching synchronously, also can be achieved by T die extrusion method by progressive biaxial stretching or synchronous biaxial stretching method.
BOPA film characteristics:
(1) Excellent obdurability. BOPA film’s tensile strength, tear strength, impact-resistance strength and bursting strength are among the best plastic materials.
(2) Outstanding flexibility, pinhole resistance, not easy to be punctured by the contents.
(3) Good barrier property, good fragrance protectiveness , good resistant to chemicals other than strong acid, especially to oil.
(4) Wide range of using temperature, melting point can reach 225 ℃, can be used for a long time between -60 ~ 130℃, BOPA’s mechanical properties can remain good at a low or high temperature.
(5) BOPA films, with performance of good hygiene, non-toxic, odourless, smell-less, is suitable for packing with high hygiene requirements.
(6) Good optics, high transparency, glossy, and decorative.
(7) The properties of BOPA film such as size stability and barrier are greatly affected by humidity. Horizontal wrinkles appear on the surface of BOPA film after exposure to moisture (which will affect the printing accuracy). Generally, it will be lengthened horizontally and shortened vertically, with the maximum elongation up to 1%.
(8) Monolayer bidrectional polyamide film cannot be heat sealed, Though normally it still can be heat sealed by means of pulse seal or fuse seal, etc., the crystallization and orientation of the molten part and the tensile part are different, and even a slight impact will cause the fusion joints to crack. In order to make up for the defect of poor heat sealing, it can be laminated with the sealing substrate.
(9) BOPA film has a surface tension of 45mN/m without corona treatment, which has a certain laminate processing ability. However, when used as a sandwich of cooking materials, double-sided corona treatment film should be used.
Bidirectional stretch nylon film with its soft, puncture resistance and other special properties is widely used in high temperature cooking food, boiled food, vacuum packaging and other products. GB/T 20218-2006 is the standard of bidirectional stretch nylon film in China (suitable for the polyamide film made by plain film with polyamide 6 resin as the main raw material by bidirectional stretch), and the specified physical and mechanical properties are shown in Table 2-9.
Table 2-9 physical and mechanical properties of BOPA
2. Unstretched polyamide film
Commercialized unstretched polyamide films include nylon 6, nylon 66, nylon 11, nylon 12 and other films.
