The change of the bottom structure of polyester bottles mainly went through three stages.
1. Hemispherical structure
Before 1995, the bottom of the PET bottle was a hemispherical structure, and its self-reliance depended on the HDPE bottle holder bonded with it, because it was made of two different materials, recycling was difficult.
2, 5-legged castle shape
In 1995, the structure of the bottom of the bottle was designed into a 5-foot castle shape, and the one-stage process molding improved the self-supporting ability of the bottle, but the thickness of the bottom of the bottle was uneven, the thickness near the center was too large, the bottom crystallinity was low and the change amplitude was large. The body weight of the bottle is the same as that of the two molded bottles, but the drop strength, resistance to environmental stress cracking, moisture resistance and heat and pressure resistance are reduced.
3. 6-legged castle shape
In recent years, the bottom of the polyester bottle began to use 6-foot castle shape, using 2-stage forming process, that is, the bottle body is formed once - local heating of the bottle bottom - the bottle bottom is formed twice, compared with the 1-stage forming, the thickness of the bottle bottom is uniform and generally reduced, and the crystallinity is increased and the change is not large. Drop strength, environmental stress cracking resistance, moisture resistance and 2 molded bottles are the same, heat and pressure resistance improved. It is particularly noteworthy that the bottle body mass is 17.3 lower than the previous two, which meets the requirements of contemporary packaging.
The bottle body of polyester bottle is basically made of stretch blow molding. There are two kinds of stretch blow molding process, one is to heat the injection molding tube blank to the plastic drawing temperature, carry out axial stretching in the stretching device, and then move the stretched tube blank to the blow molding mold, close the mold, blow the tube blank molding products; The second is to cut the extruded pipe into a certain length as required, as a cold tube blank, and then put the cold tube blank into the heating device to heat to the plastic tensile temperature, and then send the heat pipe blank to the forming table, close the mold, so that one end of the tube blank is formed into the neck and thread of the container and axially stretched, blow the tube blank forming, and cool the mold opening to get the container product.
Tensile blow molding high yield, easy to form, high production efficiency, easy to control product quality, high impact strength.