Bottle-shaped containers are molded by 3 processes: EBM (extrusion blow molding), IBM (injection blow molding) and ISBM (injection stretch blow molding). EBM is the oldest and least sophisticated of these processes. The following is a list of benefits and problems associated with ISBM and EBM produced bottles with a very limited discussion of the molding processes. A detailed discussion of bottle molding processes can be found at plasticstechnology.org.
Advantages & Disadvantages of EBM processing:
- The most cost effective process for large containers, i.e. 4L and larger.
- Capable of handling a wide variety of shapes, i.e. extreme dimensional rations (width to length or height), offset necks and molded-in handles.
- Tooling is relatively inexpensive.
- Poor control of neck dimensions.
- Left: ISBM base. Right: EBM base showing horizontal ‘pinch’ scar.
- Variability in weight, material distribution, wall thickness.
- Trimming operation to remove flash can produce particulate.
- Frequent material built up at ‘pinch’ in the base of the container.
- Occasional material buildup at the junction of the neck and shoulder of bottles (see video).
- Inside of neck is ribbed, not smooth.
Advantages & Disadvantages of ISBM processing:
- Precision formed neck has smooth inside surface and requires no trimming.
- Maintains critical neck-finish dimensions for reliable sealing.
- Precise, repeatable bottle weight.
- Better distribution of plastic and more overall uniformity.
- Smooth glossy surfaces inside and out.
- Molecular orientation of polymer chains can significantly improve bottle impact strength, transparency, stiffness, and gas-barrier properties for resins such as PET and PP.
- Readily adaptable to efficient low particulate molding.
- Tooling is more expensive compared to EBM tooling.
- Molded part cost is higher than EBM for larger parts, ≥4 liters.
- Not suitable for extreme dimensional ratios, offset necks and molded-in handles.
Large ISBM containers have become practical for biotech applications since quality considerations are often more critical than cost. PharmaTainer™ carboys bring ISBM advantages to biotech in sizes up to 20 liters. Savillex Purillex™ fluoropolymer bottles are produced by a variation of the ISBM process in which a preform is injection molded and later blown to full size on a separate machine. The video illustrates pouring differences between Nalgene® EBM bottles and Purillex ISBM bottles. The uneven surface inside the Nalgene bottle reduces control of the pouring.