New Injection, Pulling and Blowing Technology of PET Pure Water Bucket

Traditional bottles of pure water buckets are all extruded from polycarbonate (PC). Faced with the development trend of new technologies, the development of new technologies for PET injection, drawing, and blow molding has emerged.
Pure bucket material selection

The PET in a pure bucket is a crystalline material. Compared to amorphous materials (such as PC), crystals are aligned when the crystalline material is stretched, and the strength is also increased. In the injection blow process, the PET material of the pure water bucket is biaxially stretched, its two-dimensional strength is enhanced, and the wall thickness of the finished product is also thinned, thereby saving the pure bucket material. Compared with the crystallized material of other pure buckets, the PET material of the pure bucket is more clear and transparent, and the perspective rate is not inferior to glass.

Drying of PET material

Plastics such as PET, nylon, PC, and ABS absorb water from the air because they absorb water. The drier the PET is, the more transparent the preforms are. If the absorbed water is not discharged before the injection molding process, the plastic will be hydrolyzed, causing the strength of the pure water bucket product to be out of specification, and the appearance is not good enough to become a waste product. Therefore, an appropriate drying treatment should be performed before injection molding.

PET bottle processing

Before the popularity of PET bottles, the processing of pure water buckets was mainly extrusion blow. After the plastic barrel is heated and the screw drive friction is melted, it is extruded from the die into a cylindrical shape. The combined mode injects air from the neck to inflate the cylinder, cooling it against the mold wall, and removing the bottle after opening the mold.

In injection-blow processing, the pure water bucket is injected with an injection molding machine first, and the preform is softened before or after re-heating the purified water bottle preform, and then the preform is stretched longitudinally and blown (laterally stretched) to form a two-way pull. stretch. The use of this processing method can not only produce a smooth bottle neck, but also can strengthen the pure water bucket, so that the bottle wall thinning, saving the pure bucket material.

The process of completing the injection, drawing, and blowing operations in one machine is called a one-step process. One-step method is to pull and blow when the preform is cooled to about 110°C after injection molding. The advantage is that it saves electricity and does not go through the manual and reduces pollution. The two-step method is to separate the two steps of drawing and pulling and to perform the two operations on the two machines. The first step is to use an injection molding machine to pour out the pure water bottle preform, and the second step is to reheat the room temperature pure water bottle preform and blow it into a bottle. This step is performed on another reheating machine and the blow-up machine is completed.

Selection of the number of preform mold cavity

Home-purged buckets are popular with 3-gallon bottles and the preforms weigh 300g-520g. The number of mould cavities can be selected from 2 cavities, 4 cavities, 6 cavities, 8 cavities, 12 cavities, 16 cavities, 24 cavities, 32 cavities, 48 ​​cavities, 60 cavities, 72 cavities, 96 cavities and 144 cavities. In order to increase production efficiency, the maximum number of cavities should be used with the four-column injection molding machine space, formwork space and injection weight.

The king in the bottle embryo is a five-gallon bottle of pure water bottle, weighing 650g-750g. The disposable five-gallon bottle weighs 400g. Therefore, these molds are generally a cavity and adopt a cold runner design.

Pure bucket preform mold

The multi-cavity pure bucket preform molds do not use a cold runner design but use a hot plate design. Every two chambers share one heating zone and one thermocouple, but the bottom of the preform will have a nozzle that does not exceed 5mm in length. After a period of shutdown, the flow channel may be blocked. If the needle valve hot runner design can solve this problem, each cavity has an independent heating and probe temperature, pure water bottle blank does not leave water at the end of the mouth, when the injection valve does not close the flow channel, so the sprue will not be blocked, However, this design is costly.

Pure bucket injection cycle

In the injection molding of thick-walled pure-water bucket preforms, the cooling time dominates the cycle time, followed by a large amount of plastic plastification time.