As mentioned above, different performance requirements require different production processes for Pet Preform Mould, so PET bottles produced by different process conditions have different defects.
Cold-filled bottled dark bottle
Dark bottle PET materials are mainly caused by a high degree of decomposition and crystallization. When the PET is in an amorphous state, it is transparent. Between 80 and 250 ° C, the PET material will crystallize, and the nucleus will form easily at low temperature. The high temperature segment will easily grow into a crystal ball. The crystallization rate is about 180 ° C. The crystallization is also related to the viscosity. The smaller the viscosity, the higher the rearrangement. The molecular chain resistance is small, the crystallization is easier; and the crystallinity is related to the residence time of the crystallization temperature zone. The longer the time, the larger the crystallinity of the thick-walled preform, the central channel is slow to heat and crystallize; when the crystallinity of the bottle is greater than At 40%, the transparency of the bottle drops and darkens. From a production process perspective, the reheated PET preform molding process and the preformed stretch blow molding process increase the likelihood of crystallization. Especially for hot-fill bottles, there must be a heat setting process, and the viscosity of the hot-filled PET bottle resin is relatively low, so the light transmittance is reduced.
According to the production experience, the lower the crystallinity of the preform, the more favorable the whole production process and the relatively good control, so the cooling capacity of the preform injection mold should be strengthened. The usual practice is to increase the cooling water pressure by more than 0.5 MPa and the cooling water temperature to below 10 °C. In the two-step heating method, the heating time should be as short as possible to lower the heating temperature. The two-step method is used to produce hot filling. The heat setting process is a process of adjusting the crystallinity and orientation relaxation of the amorphous portion, and can appropriately increase the setting temperature, shorten the setting time, and improve the light transmittance. At the same time, the temperature in the dry material is controlled between 150 and 160 ° C, and the time is controlled at 5-6 h.
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