Injection Blow Molding
“Injection blow moldingis a two stage blow molding process since the parison is produced in a separate operation. In the first process molten plastic is injected into a heated preform mold around a hollow mandrel blow tube or core rod. This is similar to insert injection molding. The workpiece for the second, blow molding, process is the preform-mandrel assembly. The preformed parison is placed in a larger mold cavity for blow molding. Between the preform production and blow blow molding processes a heated preform may be held in a temperature conditioning stage or a cooled preform re-heated. After blow molding the part is stripped from the core rod at an ejection station.” (Plastics Wiki, Injection Blow Molding, 1/13/2010)
Following the injection moulding of the performs, they are cooled to a predefined temperature and kept in an intermediate stocking location where they cool to room temperature. The blowing operation is carried out subsequently and in this case it is firstly necessary to heat to make them sufficiently plastic to undergo blowing.
The first step of the container production process, which consists of the injection molding of the preforms, is carried out using moulds provided with a group of injection cavities into which resin in a molten state has been injected, and which remain closed for a predetermined time, sufficient to permit cooling and the consequent solidifying of the preforms, allowing them to be handled without the risk of their being deformed. As during such steps of cooling and consolidation of the preforms the mould is kept closed and therefore occupied, the longer the cooling step inside the mould the longer the moulding process is slowed down. In fact it is only when the mould is freed from the preforms that it is available for the next cycle.
The complete injection step consists of closing the half moulds, the injection of the resin fluid into the cavities, the cooling of said resin and the solidifying of the respective preforms to allow their handling, the opening of the half moulds and the extraction of the preforms. This step, which directly influences the yield of the plant engaged in manufacture of containers, has a longer duration than all the other subsequent operating steps of the plant and yet it is difficult to shorten.
(RDC 8/19/2011)
[Zoppas, Coran and Pavenetto, US Patent 7,879,281 (2/1/2011)
Recent US Patents
9/13/2011
8,017,063
Molds and methods for injection molding preforms
Hutchinson and Lee of The Concentrate Manufacturing Company of Ireland, Bermuda, developed a method for producing PET articles coated with a gas barrier. Preforms are injection molded, barrier-coated immediately thereafter, and remain on a mold portion for a time to speed cooling of the completed preform. The preferred barrier coating materials include poly(hydroxyamino ethers). (RDC 9/14/2011)
2/1/2011
7,879,281
Injection device and process for plastic objects
Zoppas, Coran and Pavanetto of S.I.P.A., Italy have developed a plastic preforms molding device and process comprising an injection mold, containing a plurality of injection cavities, an arm for extracting the preforms from the mold, equipped with guillotine-like gripping elements, which moves between the existing space between the half molds when in the open position. (RDC 8/17/2011)
10/5/2010
7,807,096
Injection blow molded single layer metallocene polyethylene container
Maziers of Total Petrochemicals Research Feluy, France has developed high gloss polyethylene containers by injection blow molding. The resin is a metallocene polyethylene from 0.925 g/cm3. up to 0.966 g/cm3 or up to homopolymer densities, and a melt index of 0.5 to 2 g/10 min. (RDC 12/20/2010)