Injection blow molding (IBM) represents a significant advancement in plastics manufacturing, blending the precision of injection molding with the hollow-forming capabilities of blow molding. Authored by Yoshiharu Shima, an executive at Nissei Plastic Industrial Co., Ltd., this 1971 technical article explores IBM’s emergence as a response to the limitations of traditional blow molding techniques. As part of a broader series on plastic processing innovations published in the Society of Polymer Science journal, the piece highlights how IBM addresses demands for higher quality, efficiency, and uniformity in producing hollow plastic items like bottles and containers.
Historical Development and Global Adoption
The concept of IBM dates back to the early 1950s, with initial patents and prototypes from companies like the UK’s Granbull Tool Co. in 1951 and the Piotrowski system in 1954. However, practical commercialization lagged until the 1960s due to technical hurdles in mold design, temperature control, and material compatibility. Switzerland’s Nestal company pioneered its use for polystyrene (PS) thin-walled containers in 1962, leading to adoption across Europe, Australia, and Japan. In the U.S., IBM gained traction by the late 1960s, with machines showcased at industry exhibitions by firms such as Moslo, Impco, Husky, and Toshiba. Shima notes Japan’s contributions, including domestic adaptations by companies like Sumitomo Heavy Industries and his own firm, which focused on simplifying mechanisms for better usability. A comparative table of machine specifications underscores variations in clamping force, injection capacity, and cycle times, emphasizing IBM’s potential for high-speed production.
Core Principles and Process Mechanics
At its essence, IBM involves injecting molten resin into a mold to create a preform (or parison) with a closed bottom, then transferring it—still attached to a core—to a blow mold where air pressure expands it into a hollow shape. This differs fundamentally from conventional extrusion blow molding, where the parison is extruded and exposed to air before blowing, often resulting in inconsistencies. IBM’s key challenge lies in managing the parison’s adhesion to the core: too hot, and it sticks; too cool, and it resists expansion. Optimal conditions require precise control of parison temperature, core cooling, and resin viscoelasticity.
Shima details his company’s IB-M and IB-S models, which employ a two-station shuttle system for efficiency. The process cycle includes injection, mold opening, product ejection, core rotation, and reclamping. Asymmetric clamping designs distribute force unevenly to handle injection pressures on one side and blow forces on the other. Injection units, borrowed from standard machines, prioritize high plasticizing rates for rapid cycles, achieving up to 1,200 dry cycles per hour. Diagrams illustrate the sequential steps, highlighting how minimal mold stations reduce complexity and parison cooling during transfer.
Advantages for Modern Manufacturing
IBM offers several edges over traditional methods, making it ideal for precision-demanding applications. It produces finished products without excess resin waste or secondary trimming, thanks to hot runners and direct molding. Dimensional accuracy is superior, particularly in bottle necks and threads, enabling reliable capping and sealing. Product weight and volume consistency facilitate automated filling lines, with variations under 1/100. Multi-cavity setups support mass production of small items, while scalability allows for ultra-large or thin-walled items without drawdown issues. Virtually any injectable thermoplastic—such as PS, polyethylene (PE), or polypropylene (PP)—can be used, expanding material options.