PET blow molding technology seamlessly integrated with the filling line

As we all know, PET packaging bottles can be made by "one-step (injection stretch blow) method" and "two-step (stretch blow molding) method". However, what are the similarities, differences and advantages of these two methods? How to control the wall thickness uniformity of preforms and bottles? How to achieve high barrier properties of PET bottles? We don't know much about the advantages of the seamless combination technology of PET bottle blowing equipment and filling line. In this regard, representatives or experts of PET bottle blowing equipment suppliers are specially invited to discuss these issues, hoping to be helpful to everyone. 

For formed PET packaging bottles, what are the similarities and differences in the process between the "one-step (injection stretch blow) method" and the "two-step (stretch blow molding) method"? What are the requirements for the equipment (including molds) required by these two processes? 

Mr. Li Keping: We all know that the production process of PET bottles is to inject PET preforms first, and then heat the preforms to form them through high-pressure blow molding. This is the so-called "two-step method". The "one-step method" is to continuously execute the first step of the two-step method, "preform injection molding" and the second step "blowing", through a turntable, and realize injection and blowing on the same equipment. 

Mr. Gao Jie: In the molding process of PET bottles, the method that can complete the whole production process from PET material to bottle in one equipment is called "one-step method", while in the injection molding (injection preform) and bottle blowing machine The method of completing the above process in these two devices is called "two-step method". 

Mr. Zhang Yougen: When processing and forming PET bottles, no matter the "one-step method" or the "two-step method", they all pass through the five steps of injecting parisons, heating parisons, stretching parisons, blow molding, and product demoulding. process to complete. The difference is that "one-step method" refers to using the same equipment to continuously complete all the above five processes, while "two-step method" refers to using two or three equipment to complete these processes, and the process is not Continuously, the embryo can be injected first, and then the following processes can be concentrated.

"One-step" injection stretch-blow hollow plastic molding machine can be divided into two types according to the molding process: the "three-station" represented by Japan's Aokigu and the "four-station" represented by Japan's Nissei. The main difference between "three-station" and "four-station" is that "three-station" is to complete the injection parison and heating parison in one process, while "four-station" is to complete the injection parison and heating The parison is completed on the second process. The "one-step" process has high technical requirements for the mold, and the "three-station" has higher requirements for the mold than the "four-station", and the mold required for the "one-step" is also more complicated, usually a set The mold needs three or four sets of molds to be combined, which leads to the high price of each set of molds. At present, my country's "one-step" forming molds are basically imported. 

Compared with the "one-step method", the "two-step method" has much lower technical requirements for the mold. The "two-step method" can be divided into two forms, one is to put the heating and stretching of the parison in the same equipment, and the other is to put the heating and stretching of the parison in two equipments respectively. . The former form has a high degree of automation and productivity, and requires a large investment in equipment. The main advantage of the latter form is that the investment in equipment is small, and the technical requirements for molds are not high. Generally, ordinary manufacturers can afford it, so this method is used. The produced PET bottle has a great advantage in price. 

Compared with the "one-step method" and the "two-step method", what are the advantages of each of them? 

Mr. Li Keping: The advantages of the "two-step method" are:

●Preform production and bottle blowing production can be invested separately. For small and medium-sized filling plants, they do not need to purchase PET preform injection molding production lines, they only need to purchase blow molding machines and filling line equipment and connect them directly. Pack. the

●Large output. "Two-step" large-scale equipment, whether it is preform production or bottle blowing production, the single-machine production capacity can exceed 10,000 to tens of thousands of bottles per hour. 

●Strong flexibility. For large enterprises, the "two-step method" equipment is also very flexible, and they can specialize in the construction of preform and bottle cap production workshops or factories. In this way, the preforms and caps can be uniformly distributed to each filling plant, and each filling plant is equipped with a blow molding machine that matches its production line to perform blowing and filling. 

●Acetaldehyde content is low. The acetaldehyde content of PET preforms produced by qualified preform injection molding equipment will not exceed 5ppm.

The advantages of the one-step method are:

●Suitable for small batch production. 

●Because of its limited production capacity, it is suitable for manufacturers with many types of bottles and small output. One bottle type uses one piece of equipment, and the output of each piece of equipment generally does not exceed 6,000 bottles/hour. 

●Because some "one-step" blow molding machines use the waste heat of injection molding to save the reheating of preforms, the energy consumption of this method is relatively low. 

Mr. Gao Jie: The "one-step method" is to stretch and blow the preform after the preform is cooled to about 110°C after injection molding. The advantage is that it saves electricity (saving reheating) and does not require human hands, reducing pollution. The disadvantage is that the production efficiency is low, the time for changing the bottle type is long, the cost is high, and the one-time capital investment is high; the advantage of the "two-step method" is that the production efficiency is high, the time for changing the bottle type is short, the cost is small, and the one-time capital investment is small. Its disadvantage is high energy consumption. 

Mr. Zhang Yougen: The main advantages of the "one-step" injection stretch-blow hollow plastic molding machine are low energy consumption and high precision and transparency of the produced bottles, which is the embodiment of the comprehensive technical level of the main machine and the mold. "Three-station" consumes less energy because it does not need to reheat the parison during the blow molding process. 

The biggest advantage of the "two-step method" that puts the heating and stretching of the parison in the same equipment is its high productivity.

In addition, since the "two-step method" is biaxially stretched and blow-molded by reheating the preform, the crystallinity of the PET bottle is improved, making it resistant to a hot filling temperature of 87°C. The "one-step method" is less effective in this regard. Since the "two-step method" has much lower technical requirements for the mold than the "one-step method", the investment in the mold is also much smaller, especially the heating and stretching of the parison in two devices. The "two-step method" model with low mold cost is suitable for small manufacturers who require fast product development and limited funds. 

Whether it is a "one-step method" or a "two-step method", controlling the thickness and uniformity of the PET bottle is the key to forming. Please talk about how to control the thickness and uniformity of the bottle from the two levels of process equipment and online inspection. 

Mr. Li Keping: The uniformity of the wall thickness of PET bottles depends first on the quality, precision and performance of the preform mold in the first step. Each mold core and each mold cavity of the multi-cavity PET preform mold must be highly concentric, so that preforms with uniform wall thickness can be produced, thus laying a good foundation for the second step of bottle blowing. In the bottle blowing process, the preform must be heated first. At this time, the temperature must be controlled, and only the part that needs to be heated should be heated. This is because the quality of heating directly affects the effect of bottle blowing. The next step is bottle blowing. Blowing is divided into two consecutive steps. The first step is pre-blowing and stretching so that the preform can be evenly elongated and expanded in the bottle mold, followed by the second step of high-pressure blow molding stereotyped. Every process link in this process will affect the quality of the bottle and the uniformity of the bottle wall. Therefore, only high-quality, high-performance, high-reliability embryo-making machines and blow molding machines can produce high-quality PET bottles. As for on-line inspection, it is only a remedial measure to remove unqualified preforms in time to avoid or reduce waste products. 

Mr. Gao Jie: The wall thickness and material distribution of PET bottles are the most important indicators for PET bottles. Although the ovality, height, wall thickness, transparency and other indicators of the bottle can be detected online at present, this kind of equipment is not only very expensive, And it only plays the role of auxiliary control. In order to fundamentally solve the problem of uneven distribution of bottle wall thickness, it is necessary to start with the preform heating process. Because from a process point of view, only by having a thorough understanding of the heating process, can the thickness of the bottle be well controlled and the ideal plastic distribution achieved. The tensile change rate of PET bottles requires that the inner wall needs greater tensile strength than the outer wall, which means that the inner wall needs a higher secondary heating temperature than the outer wall. The thicker the embryo wall, the greater the temperature difference. According to the characteristics that the inner and outer walls of the preform should have during heating, the following optimization design is carried out for the preform heating lamp tube of the blow molding machine,

Thereby laying a good foundation for finally being able to produce PET bottles with qualified wall thickness and material distribution.