| 1 |
|
hot filling pet
|
|
Normal PET Bottles shrinks approx. 5~6% after several times hot washing (most shrinkage happens during the first hot washing). In heat set blow molding process, the blow mold is heated to a certain temperature, which is used to release residual strains; moreover, crystallinity on bottle surface will be increased, which leads to abrasion resistance improvement.
|
New heat-setting technology is said to make PET suitable for “super-hot-fill” applications that expose the bottle to at least 203 F for 5 min. Krupp Corpoplast in Germany (U.S. office in Branchburg, N.J.), says its new MonoTherm process raises PET’s crystallinity to 39-42%, thus elevating heat resistance to nearly 248 F while also reducing residual stresses. The resulting bottle can withstand super-hot filling of fruit juice, teas, and coffees. MonoTherm bottles can also survive beer pasteurization without the need for molded-in panels and ribs for stiffening.
Normal stretch-blowing usually raises PET’s crystallinity to 20% and the heat resistance to around 185 F. That’s enough for pasteurization, except for beer, due to its carbonation pressure, unless the bottle has panels and ribs.
MonoTherm takes bottle crystallinity further by using three fluid circuits in the mold to control bottle base, body, and neck temperatures at about 176, 284-320, and 68 F, respectively. High blowing pressure forces the bottle against the hot mold. Other process modifications are slower blowing, lower stretch ratio, and longer mold residence time with internal air cooling of the bottle.
Corpoplast reports shrinkage of less than 0.5% for a 0.5L MonoTherm bottle hot-filled at 203 F with 3-psi internal pressure. Production rate is 900 bottles/hr/mold.
|
| 1 |
|
Discussion Forum