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The capacity fluctuates greatly

The biaxially stretched PET bottle has a certain shrinkage rate, and the maximum shrinkage rate is about 2%. The factors affecting the capacity of the PET bottle mainly include the following aspects:

(1) Influence of the mold The capacity of the PET bottle is mainly affected by the size and shape of the mold. The size of each bottle mold is usually fixed. Different shapes of bottles will have different shrinkage rates when designing their shrinkage rates. The less stiffeners on the bottle body and the thinner the bottle thickness, the greater the shrinkage rate of the bottle.

(2) Influence of environmental factors The environmental temperature and humidity have a great influence on the capacity of the bottle. The higher the ambient temperature and the higher the humidity, the greater the capacity shrinkage of the bottle.

(3) Influence of production process High blowing pressure is required when blowing a bottle with a complex shape. If the blowing pressure is insufficient, the bottle will be poorly formed and the capacity will be too small; the mold temperature will be too high and the capacity will be too small.

(4) Natural shrinkage of the bottle Since the PET bottle will shrink naturally, the size of the bottle mold should be designed in an adjustable form (adding or subtracting spacers). Taking a 1.5L PET bottle as an example, the average capacity of the newly produced bottle is about 1508ml. After 3 days of storage at room temperature, the bottle capacity will decrease by 5ml to 6ml; as the bottle storage time prolongs, the bottle capacity will also shrink and become difficult to control. At present, more and more production lines use in-line bottle blowing, that is, blowing and filling, to avoid the problem of bottle (capacity and heat resistance) attenuation.

(5) Influence of filling method Different filling methods have different influences on capacity control. The quantitative filling method has the least impact on the capacity, and the self-weight filling has the greatest impact on the capacity. For a 1.5L PET bottle, the difference may be up to 20 ml to 25 ml. Therefore, to solve the problem of bottle capacity, the mold (gasket) can be adjusted appropriately, the production process can be controlled, the storage conditions can be improved, and the most important thing is to shorten the storage period of the bottle as much as possible.