Technology and development trend of plastic bottle cap

Update:08 Jan 2021

Since the advent of plastic anti-theft bottle cap, it has gone through more than 20 years. After a long time of precipitation and accumulation, it has formed a situation that a variety of specifications of plastic bottle cap blossom. In the early stage of the development of plastic anti-theft bottle caps, the injection molding technology dominated the world, but the world is changing with each passing day, and the pace of human innovation is advancing all the time. Then the compression molding technology was born and entered the field of plastic bottle cap manufacturing. The situation that the injection molding technology dominated the world was broken, and gradually the injection molding and compression molding divided the world equally. Until today, the compression molding technology has become the mainstream technology in the plastic beverage bottle cap Market.

Any technology has its own bottleneck, and the cap industry is no exception. This paper analyzes and compares this problem in art. The so-called cavity filling imbalance, refers to the molten plastic into the mold cavity speed is not consistent. In the injection molding process, from the moment when the screw of the injection molding machine moves forward, the molten plastic bottle cap will enter into each mold cavity, because the hot runner processing deviation, cold runner processing deviation, each cavity exhaust slot deviation, rubber inlet discharge processing deviation, uneven plastic flow shear rate and other factors are combined together, which will cause the inconsistent rubber feeding speed of each mold cavity.
Some cavities have been filled, and some cavities are only filled to about 80%. The injection process is divided into injection section and packing section. The injection speed is usually very fast. The cavity with fast filling is likely to overflow, and the cavity with slow filling is likely to lack glue even if packing is added. The problem of uneven filling will also cause large weight deviation of bottle cap and poor dimensional stability of bottle cap. Moreover, the rubber inlet of injection molding is very small, and the rubber inlet of bottle cap product is usually only 1 mm at most, which is very easy to be blocked by debris, resulting in lack of rubber.

Once the glue inlet of some cavities is blocked, the excess glue during injection will flow into other cavities. At this time, a large amount of overflow will appear in other cavities. It is believed that technicians in the injection bottle cap industry have this experience. Even with the rapid development of CNC, EDM, fast wire, slow wire, turn milling and hot runner technology, it still can not effectively solve the problem of Filling Imbalance in injection molding.
For the injection molding process, the cavity balance problem is bound to be an obstacle for a long time in the future, and it is also a hidden pain for the bottle cap technicians. When the bottle cap is produced, they need to be worried all the time. If they are not careful, the rubber inlet will be blocked, resulting in the lack of rubber, resulting in a large number of bottle cap selection and rework, and the hot nozzle needs to be cleaned regularly to reduce the production efficiency. However, this injection molding process can not be overcome, in the pressure molding process, but easily solved.
All the compression molds are independent. The particles come out of the nozzle and directly enter each mold in sequence. All the particles are evenly cut by the cutter and then thrown into the mold bowl. There is no problem of filling balance rate. The compression molding process is also extremely simple. Generally, the stable product quality can be obtained by adjusting the screw extrusion frequency, unlike the injection molding process, which requires injection and pressure maintaining There are also complex molding parameters such as material return and glue extraction.

Moreover, the nozzle sizes are all more than 10 mm, so there is no frequent clogging problem in injection molding, the production efficiency is higher, the product weight in compression molding process is more uniform, and the bottle cap size is more stable. The problem of filling balance, which has plagued the injection molding cap industry for more than 20 years, has been perfectly solved in the compression molding process, which is one of the advantages of the injection molding process. More and more bottle cap manufacturers tend to choose the compression molding process when they add new production lines. The compression molding process has gradually become the mainstream of the bottle cap production industry, which is an irreversible development trend.