Basics First PLA bottles
Basics First PLA bottles (2006-2007) Info Videoclip http://bit.ly/1rDzvh5 (Source: KHS Corpoplast) Stretch blow moulding Since the market introduction of the Coca-Cola PET bottles in the early 1990s bottles made from polyethylene terephthalate (PET) have seen a tremendous market growth for beverages and other liquids such as detergents, edible oils etc. More recently biobased and biodegradable PLA was introduced for such applications, and biobased PEF (polyethylene furanoate) was declared to be the bottle material of the future. The preferred manufacturing process for all these materials is stretch blow moulding. Even if a number of different process variants are existing, this short introduction shall focus on the so called two-stage (or two-step) stretch blow moulding (or reheat stretch blow moulding). In the first step or stage, so-called preforms are produced using the injection moulding process [1]. The preforms look like thick-walled test-tubes and already feature the final neck finish of the bottle including thread and neck ring. The preforms are cooled and usually packed in boxes for transport to the stretch blow moulding machine. Injection moulding systems are available today with usually 32, 48, 72, 96 and 144 cavities [2]. In the separate blow moulding machine the preforms are first reheated in a special UV oven to above glass transition temperature. Then each reheated preform is transferred into a blow mould where it is expanded with air pressure. In order to receive containers with excellent properties the heated preform is stretched to the bottom of the cavity prior to inflation by a long, thin so-called stretch rod. When the preform is at forming temperature it is fixed in the neck region by the neck ring, the stretch rod pushes against the bottom of the preform, while air is introduced to keep the soft plastic from sticking to the rod. When the stretch rod pins the preform (or parison) to the bottom of the mould, sufficient air is introduced to blow the preform against the mould wall, where it is held until cooled [3]. This process leads to a biaxially stretched wall of the container, giving it excellent mechanical and barrier properties. Most of the stretch blow moulding machines are rotary machines, i.e. a large number of mould cavities are mounted to a horizontal wheel. While this wheel is turning, 26 bioplastics MAGAZINE [04/14] Vol. 9
Basics air cooler reflector radiator reflector cold preforms stretch blow mould Principle of reheat stretch blow moulding [2] Injection moulding of performs. Note the preform neck-ring designed to hold the preform firmly in the blowing machine [2] the preheated preforms go into the moulds and finished bottles exit the moulds in a fast and continuous process. Machines with 4-32 moulds and an hourly output of 9,000 to 81,000 bottles are standard today [4]. Existing stretch blow moulding machines can be used to process PET, but also PLA and PEF. Only the process parameters are different, in the case of PLA in most cases even advantageous compared to PET (cf. table on page 24. [1] N.N.: Making preforms for PLA bottles; bioplastics MAGAZINE vol.1 (2006), Issue 02, pp 16. [2] Thielen, M.; Hartwig, K.; Gust, P.: Blasformen von Kunststoff Hohlkörpern, Hanser Publishers, Munich 2006 [3] Beal, G.; Throne, J.: Hollow Plastic Parts, Hanser Publishers, Munich 2004 [4] N.N.: Innopet Blomax Serie IV, brochure of KHS Corpoplast, Hamburg, Germany, assessed online 21 July 2014 C M magnetic_148,5x105.ai 175.00 lpi 15.00° 75.00° 0.00° 45.00° 14.03.2009 10:13:31 Prozess CyanProzess MagentaProzess GelbProzess Schwarz Magnetic for Plastics • International Trade in Raw Materials, Machinery & Products Free of Charge • Daily News from the Industrial Sector and the Plastics Markets By Michael Thielen Y CM MY CY CMY K www.plasticker.com • Current Market Prices for Plastics. • Buyer’s Guide for Plastics & Additives, Machinery & Equipment, Subcontractors and Services. • Job Market for Specialists and Executive Staff in the Plastics Industry Up-to-date • Fast • Professional Preforms [1] bioplastics MAGAZINE [04/14] Vol. 9 27
