PET Bottle Biaxial Stretch Blow Molding Technology

PET material is widely used in food packaging,cosmetic packaging and other industries due to its non-toxic,transparent and other excellent properties.At present,the PET bottle formed by the stretch blow molding process has the problems that the bottom of the bottle is too thick and the bottom of the bottle is easy to crack.This article proposes and studies the biaxial stretching blow molding process,that is,based on the existing process,a bottom mold stretching rod that can independently control the movement is provided in the center of the bottom mold.The bottom mold stretching rod and the stretching rod coordinately move,which effectively improves the problem of bottle bottom accumulation and improves the impact resistance of PET bottles,reducing material costs and improving bottle quality and safety performance.The simulation software POLYFLOW is used to compare the forming process and results of the biaxial stretch blow molding process with the existing process.It was found that in the biaxial stretching blow molding process,when the stretching rod is pressed by the stretching rod of the bottom mold,the bottom of the preform will appear reverse convex shape during the deformation process.In this state,the bottom of the preform undergoes sufficient deformation,and the wall thickness becomes significantly smaller.Moreover,during the biaxial stretching blow molding process,the preform did not reach the bottom in one step,which caused the bottom to not be cooled and cooled prematurely,ensuring that the overall temperature of the preform is in a high state and is relatively uniform.This also explains that the wall thickness distribution of the simulated bottle under the biaxial stretch blow molding process will be more uniform.According to the characteristics of biaxial stretch blow molding,the structure and control program of the bottom mold and the bottom mold stretching rod were designed and improved,which improved the efficiency and accuracy of the experiment.In the experiment,residence time,height and delay time of the bottom mold stretching rod involved in the biaxial stretching blow molding process were studied respectively.The experimental results show that the " Wrapping rod " phenomenon will occur when the stay time of the bottom die stretch bar is too long.If the rising height of the bottom mold stretching rod is too high,the lower part of the bottle is too thin and the upper part is too thick,and the bottle’s resistance to top pressure is reduced.The delay time of the bottom mold stretching rod affects the reverse lifting distance of the stretching rod,and excessively large leads to the " Wrapping rod " phenomenon and sudden change in the thickness of the bottom of the bottle.By adjusting and optimizing the three process parameters,the thickness and weight of the bottom of the bottle can be significantly reduced,and the overall wall thickness distribution of the PET bottle is more uniform,and the resistance to top pressure is also greatly improved.