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PET bottle mouth and bottle body problems and solutions

Carrie Jul 24,2019 Share this post:

The PET bottle produced by the one-step method is mainly for mechanical reasons. For the two-step method, if a certain proportion of crystals exist in the mouth of the bottle, the strength of the whole system will increase, and the bottle mouth will be crystallized without deformation; when the preform is bottled The mouth has the longest cooling time and the crystallinity is hard to exceed 3%. At the same time, it is impossible to make the material of the bottle mouth uniformly oriented in the axial direction and the radial direction, so the arrangement of the molecular segments is inconsistent, and the heat will be crystallized and contracted according to the respective directions and stresses, thereby causing skew.

From the practical experience, it is possible to lengthen the preform storage period to 14D or more or reduce the temperature of the clean room and prolong the crystallization practice to eliminate the skew phenomenon when the bottle mouth crystallizes.

In addition to the unreasonable structure of the bottle body, there are two cases from the process of the process. First, the top star event in the cooling and setting stage is too short, and the video is taken out due to shrinkage; another reason is due to The historical effect of the polymer material is caused by the recovery of the polymer chain during high-temperature filling because the transition zone between the thinner portion below the screw of the preform and the thicker portion of the corresponding bottle body is insufficiently relaxed during heat setting.

To avoid local sag, it is necessary to extend the heat setting time and the cooling top star event, and if possible, appropriately increase the mold temperature corresponding to the transition zone, which is the molecular chain is fully relaxed.

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