|One of the major limitations of clear PET bottles has been hot filling of beverages. Microcellular PET bottles can now be used for hot filling of beverages thanks to a new process using MuCell technology of foam injection molding to manufacture foamed PET bottles developed by Plastic Technologies Inc (PTI).
Nitrogen is injected into PET melt with modified perform molding machine. As the cavity-fill pressure in the chamber drops below the nucleation pressure, foam cells are produced that expand as gas diffuses into them. The resulting preform can be blow-moulded using conventional technology. The presence of foam reduces the weight of the bottle by up to 5%. The transmission light also reduces by 95% making the bottles opaque. The white or silvery colours are achieved by the scattering of light. The microcellular structure creates many refractive surfaces. This returns to a transparent state when the bottle is re-melted. Bottles produced so far have been able to hold liquids with temperatures of up to 85°C, without excessively shrinking. This new process will widen the scope of PET bottles.
The company has developed the �oPTI� process for foaming PET bottles with the MuCell microcellular process licensed from Trexel Inc. It requires no modification of the stretch-blow equipment. Nitrogen gas is mixed with the melt in a modified injection barrel on the preform machine. Foam bottles are pearly translucent to opaque and can be lightweighted up to 5% because the foam adds stiffness. Foaming also adds a non-slip surface and improves replication of details like embossed logos. PTI has developed the first lightweight foamed polyethylene terephthalate (PET) bottle/jar blow molding process. This bottle technology provides
• A distinctive new visual presence
• Retains the recycling benefits that inclusion in the clear PET waste stream
• White or silver, blue and green hues also can be used since those color streams already exist in traditional PET recycling
• Light weighting of up to 5%
• Significant light barrier characteristic's up to 95% reduction in transmitted light
In addition to PET, the foam bottle technology is applicable to other resins such as polylactic acid (PLA) and polyethylene naphthalate (PEN). Potential applications include a wide range of bottles and jars in food, beverage, personal care, household chemical, etc. markets. The bottles are made in four basic steps:
• Nitrogen is injected into the melt through the barrel on a modified perform molding machine to form a single-phase solution of polymer and gas
• Foam is produced as cavity-fill pressure is dropped below nucleation pressure during the injection cycle
• Foam cells expand as gas is diffused into bubbles. Processing conditions are used to control cell growth in the finished perform
• The preforms are blow molded on conventional, unmodified blow molding machines to produce the foam bottles
The MuCell® Microcellular Foam technology is a complete process and equipment technology that enables the production of extremely high quality plastic parts. The technology involves the use of precisely metered quantities of atmospheric gases (nitrogen or carbon dioxide) in any of the three most common thermoplastic conversion processes (injection molding, extrusion, blow molding) to create millions of nearly invisible micro cells in the end product. The creation of these microcellulars structures brings a wide array of benefits including reduced weight, reduced material usage, reduced production costs, energy reduction and greenhouse gas emission benefits to a wide range of packaging products and applications produced by any of the three major manufacturing processes of injection molding; extrusion; extrusion blow molding. The process allows packaging companies to reduce the weight of their plastics containers by 6-15%. In the case of injection molding, energy required to produce the packages can be reduced by 20-40%. Simple atmospheric gases are used to obtain these results.