PET Preform Stretch Blow Molding Process

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PET瓶吹瓶流程

PET Preform Stretch Blow Molding Process

Translated by James Zhang 惠州 芥末士

吹塑过程是一个双向拉伸的过程，在此过程中，PET链呈双向延伸、取向和排列，从而增加了瓶壁的机械性能，提高了拉伸、抗张、抗冲强度，并有很好的气密性。虽然拉伸有助于提高强度，但也不能过分拉伸，要控制好拉伸吹胀比：径向不要超过3.5～4.2， 轴向不要超过2.8～3.1。瓶坯的壁厚不要超过4.5mm。

Stretch blow molding is a process of extending a PET preform in every direction, in which PET molecules tends to be bi-axially oriented, elongated & set up into long molecular chains chemically. This molecular orientation effect strengthens quite a few mechanical properties of the bottle wall such as the prolongation elasticity, tensile strength, impact resistance & gas tightness.
Advantageous as this process is, a preform can never be over stretched in any direction. Practically, it is reasonable to keep the axial prolongation co-efficient within 2.8～3.1, and the radial 3.5～4.2, and the bottle wall thickness not more than 4.5mm.

吹瓶是在玻化温度和结晶温度之间进行的，一般控制在90～120度之间。在此区间PET表现为高弹态，快速吹塑、冷却定形后成为透明的瓶子。在一步法中，此温度是由注塑过程中的冷却时间长短决定的（如青木吹瓶机），所以要衔接好注—吹两工位的关系。

Blowing happens between the vitrification point (90℃) and the crystallization point (120℃).
Within this range, a PET preform is in a high elastic state, and shall be shaped into a bottle with high transparency after quick blowing & cooling operation.
In a one-stage molding operation, the temperatures depend on the cooling time, hence a concord between the injection and the blowing operations is of critical importance to the actual output & quality.

吹塑过程中有：拉伸—预吹—高吹，三个动作的时间很短，但一定要配合好，特别是前两步决定了料的总体分布，吹瓶质量的好坏。因此要调节好：拉伸起始时机、拉伸速度、预吹起始和结束时机，预吹气压力，预吹气流量等，如有可能，最好能控制瓶坯总体的温度分布，瓶坯内外壁的温度梯度。

The blow molding sub-process can be further broken down into three consecutive procedures: Thermo-stretch, Pre-blow & HP-blow. It is rational to match the three operations between every neighboring two steps, the latter two of which would basically define the overall material distribution, and hence the final blowing quality.
Accordingly, operators shall make proper settings of the stretch time permits, pre-blow pressure & air consumption, and furthermore keep a good control of the preform wall temperature gradient, both outside and inside, and of its overall temperature distribution as well.

在快速吹塑、冷却过程中，瓶壁内有诱导应力产生。对充气饮料瓶来说，它可抗内压，有好处，但对热灌装瓶来说就要保证在玻璃化温度以上让它充分释放。

During the blow molding & cooling process, the bottle will accumulate the induced stress which is beneficial to the cold-filling CSD containers for balancing the internal pressure of the liquid inside. But as for the hot-filling crystallized bottle, it is of great important to assure the sufficient stress discharge at a temperature above the vitrification point for the coming filling operation.