Analysis of the Reasons Affecting the Quality of Blow Molded Bottles


Author: MULAN -Plastic Molding Manufacturer

1. The factors that affect the quality of plastic blow molding bottles mainly include materials, equipment, blow molding technology and the environment, and the reasons for leakage and bursting are also related to these aspects. 2. Materials: Plastics used for hollow blow molding should have good resistance to environmental stress cracking, that is, when they are in contact with surfactant solutions, they should have the ability to prevent cracking under stress; and impact resistance good. Therefore, the molecular weight of the plastic used is slightly higher to meet the needs of these functions. The molecular weight of PET is generally 2500-50000. The molecular weight of the material used for blow molding is more suitable between 31000-50000. The intrinsic viscosity is 0.78-0.85cm3/g. If the viscosity is too high, it will not be easy to blow molding; if the viscosity is too low, it will be resistant to cracking The performance is poor, and even the material becomes brittle, and it can crack when the bottom is lightly hit. 3. Preform: The quality of the preform is an important factor affecting the quality of the blow molding bottle. If the preform is not well formed, a good bottle cannot be blown out. The preform affects the bottle burst. Leakage factors are: (1) The proportion of secondary material is too high: the proportion of secondary material added generally does not exceed 10%, and it is best to control it below 5%. (2) The bottom cooling is not good when the preform is formed: the length of the injection point does not exceed 2mm. Too long is not easy to locate, the center point is skewed, 1/3 of the wall thickness of the indentation, the center point is thin, and the pressure resistance is poor; the maximum diameter of the halo area should not exceed 10mm, generally below 6mm. 4. Plastic blow molding process: Because the shape and size of the bottle are different, the stretching degree of each part of the preform is also different, so the heating amount required for each part is also different when heating. Blow-molded preforms are generally heated by infrared lamps. Infrared rays have their own wavelengths, and the output power of the lamps has a greater impact on their wavelength. The greater the power, the shorter the wavelength, the better the penetration of the preform, and the better the heating state of the preform. In the heating area, when the heating ratio of the lamp tube is set to be less than 65%, one lamp tube can be turned off to increase the heating ratio by 15% to 20%. The technical reason for the blow molding bottle to burst and leak is that the bottom is not well formed, mainly because the bottom is overweight, the center point is too thick, and the transition area around the center point is thick. These defects can be processed by processing the lamp tube to increase the temperature of the relevant area and increase the setting. Temperature increase pre-blowing pressure and other methods to solve. 5. Environment: The ester group in the PET molecule is hydrophilic. It is sensitive to alkali and easy to hydrolyze, which will greatly reduce the molecular weight, make the product brittle, burst, and leak. The production or canning of plastic bottles is more likely to occur, so the production or filling of blow-molded bottles should avoid high temperature. PET has a certain degree of water absorption, and the packaging after beverage filling is mostly cartons, which contain alkaline substances and are damp Or after raining, it can also cause hydrolysis of the blow-molded bottle, and there will be leakage and bursting during long-term storage. Therefore, the storage time before filling the blow-molded bottle should be shortened as much as possible. The environmental requirements for the production, storage, and filling of blow-molded bottles are to be cool, ventilated, constant temperature, low-humidity materials and the environment in which the preforms are in contact. 6. Conclusion: The reasons that affect the bursting and leakage of plastic blow molding blow molding bottles mainly include the material preform, blow molding process and environment. In addition, if the bottom of the mold is not designed properly, it will also cause bursting and leakage. As long as all aspects cooperate reasonably, qualified and durable bottles can be blown out.

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