The quality of PET preforms

Polyethylene terephthalate (PET), commonly known as polyester, is a widely used plastic material. The production of PET bottles can be divided into two main processes based on the type of preform: injection stretch blow molding (ISBM) and extrusion stretch blow molding (ESBM). Among these two methods, ISBM is more common due to its ease of control, high production efficiency, and low scrap rate. In the process of making blow-molded cosmetic bottles, PET chips are first injected into the preform. It is required that the proportion of recycled material should not be too high (less than 5%), and the recycling should not exceed two times. The molecular weight and viscosity should not be too low (molecular weight 31,000 - 50,000, intrinsic viscosity 0.78 - 0.85 cm³/g). According to the National Food Safety Law, recycled materials are prohibited from being used for food and drug packaging. Preforms produced by injection molding need to be stored for more than 24 hours before use. Unused preforms after heating must be stored for more than 48 hours before reheating.

The storage time of cosmetic bottles should not exceed six months. The quality of preforms largely depends on the quality of PET material. Therefore, it is necessary to select materials that are easy to inflate and form, and to develop a reasonable preform forming process. Experiments show that preforms made from imported raw materials are easier to blow-mold than those made from domestic raw materials with the same viscosity. However, for preforms of the same batch, different production dates may require different blow-molding processes. The quality of preforms determines the difficulty of the blow-molding process. The requirements for preforms of PET bottles include being pure, transparent, free of impurities and color, with an appropriate injection point length and a halo around it.

Firstly, the size of the preform of PET bottles is crucial for the final packaging container. When determining the size of the preform, the first consideration should be the purpose of cosmetic bottles. Is it for food, beverages, cosmetics, or other fields? Different purposes may require different shapes and capacities of cosmetic bottles. By carefully considering the capacity requirements of the product, the capacity of the preform can be determined, and an appropriate shape can be selected, such as round, square, or oval.

Secondly, the neck (or mouth) diameter is a key parameter. When measuring the neck, ensure that the measurement is horizontal to obtain an accurate diameter size. The size of the neck directly affects the filling and pouring performance of PET bottles. Different products may require different neck sizes, so a reasonable selection of the neck is necessary when designing the bottle.

Finally, the weight of the preform refers to the weight of cosmetic bottles, including the body and the neck. The weight can be accurately measured by weighing or using a helical scale. The determination of the weight directly relates to the strength and durability of the bottle. When considering the weight, it is necessary to balance the structural strength of the bottle and the material cost to ensure that the final product has sufficient strength and meets economic requirements.
Overall, the size, neck diameter, and weight of the preform of PET bottles are important considerations in the design stage of plastic bottles. By carefully measuring and reasonably selecting these parameters, it is possible to ensure that the final bottle meets product requirements and industry standards, providing excellent packaging performance. During the bottle manufacturing process, continuous attention to the control of these parameters will help produce high-quality plastic bottles.