What is it and how it Makes PE Bottles Hot-Fill Compatible?
PET is a semi-crystalline thermoplastic, which softens at
approx. 76°C (what is called “Glass Transition”). Above this temperature, the
material becomes elastic, and can be formed, a property utilized effectively in
the Stretch Blow Molding process.PE
Bottle(KEXON) is made of it。
Due to its glass transition at approx. 76°C, PE is initially unsuitable as a bottle material for a hot-filling process above this temperature, since deformations may occur: Firstly, the bottles shrink, since they “remember” their previous shape (namely the preform), and secondly they collapse under internal pressure, a typical phenomenon during the cool-down period after hot filling.
For this reason, the hot-fill PE bottles feature, what are called "Vacuum Panels", which compensate for the negative pressure (vacuum) produced during the cooldown period without the bottle collapsing. In a way, these Vacuum Panels are used for "Designed Collapse", so that the bottle does not deform in undesired manner.
During the "Stretching" part of the production process for PE bottles, the material crystallizes. We talk here of Stretch-Induced Crystallization. In the standard process (often known as "Cold Set Process"), the material is frozen in this state at the mould wall, which is chilled. Inner stresses are then retained, and lead to reshrinking, particularly at heat-up. If, however, the material is heated still further after being stretched, it undergoes ‘After Crystallization’ (known as thermally induced crystallization). The stresses in the material are then decreased, thus reducing the tendency towards reshrinking. The increased crystallinity gives the material significantly enhanced thermal stability. The glass transition temperature and the rigidity increase – and we call this process “Heat-Setting”.
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Due to its glass transition at approx. 76°C, PE is initially unsuitable as a bottle material for a hot-filling process above this temperature, since deformations may occur: Firstly, the bottles shrink, since they “remember” their previous shape (namely the preform), and secondly they collapse under internal pressure, a typical phenomenon during the cool-down period after hot filling.
For this reason, the hot-fill PE bottles feature, what are called "Vacuum Panels", which compensate for the negative pressure (vacuum) produced during the cooldown period without the bottle collapsing. In a way, these Vacuum Panels are used for "Designed Collapse", so that the bottle does not deform in undesired manner.
During the "Stretching" part of the production process for PE bottles, the material crystallizes. We talk here of Stretch-Induced Crystallization. In the standard process (often known as "Cold Set Process"), the material is frozen in this state at the mould wall, which is chilled. Inner stresses are then retained, and lead to reshrinking, particularly at heat-up. If, however, the material is heated still further after being stretched, it undergoes ‘After Crystallization’ (known as thermally induced crystallization). The stresses in the material are then decreased, thus reducing the tendency towards reshrinking. The increased crystallinity gives the material significantly enhanced thermal stability. The glass transition temperature and the rigidity increase – and we call this process “Heat-Setting”.
Click Fine Mist Sprayer to learn about more information
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