Blow Molding
Blow molding is a primary method for forming
hollow plastic objects such as soda bottles. The process includes
clamping the ends of a softened polymer tube which can be either
extruded or reheated, inflating the polymer against the mold walls
with a blow pin, and then cooling the product via conduction or
evaporation of volatile fluids in the container.
There are three general types of blow molding:
Extrusion blow molding
Extrusion blow molding is usually used to make items of weight greater than
12 oz. such as containers for food, laundry, or waste.
This process normally uses commodity materials such as
PVC, PS, PP, LDPE, and HDPE.
Important factors one should consider for extrusion blow
molding include the following:
- Polymer viscosity at high & low shear rates
- Melt strength (important for uniform wall thickness, no holes)
- Strain recovery (MW & Distribution)
- Crystallization rate (slow rate desired)
- Thermal properties (thermal diffusitivity, thermal conductivity, specific heat, etc.)
Injection blow molding
Injection blow molding is used to achieve very accurate wall thickness, high-quality neck
finish, and to process polymers that cannot be extruded. Usual applications
include pharmaceutical bottles, cosmetic packaging, and single serving liquor
bottles that weigh less than 12 oz.
These factors are critical to this process:
- Shear & temperature dependent viscosity
- Temperature-dependent tensile strength on the pin
- Tensile elongation during inflation
- Crystallization kinetics on the core pin
- Crystallization kinetics during blowing and cooling
Stretch blow molding
Stretch blow molding is generally only used for difficult to blow crystalline and crystallizable polymers such as polypropylene and polyethylene terephthalate.
Important polymer properties to be considered:
- Tensile strenth and yield above Tg
- Effect of orientation on gas permeability through
the polymer
 Please contact Case Engelen at Titoma for more information, a quick quote, or other inquiries:
Email: Blow Molding
Telephone +886 2 2727 2089 |
