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What Are The Important Factors Affecting The Blowing Process Of PET Bottles?
Zhejiang Cosme Packaging Co.,Ltd | Updated: Mar 25, 2018

The main factors affecting the blowing process of PET bottles are preforms, heating, pre-blowing, molds and environment

When preforms are used to make blow-molded bottles, the PET chips are injection molded into preforms, which require that the proportion of secondary recycled materials is not too high (less than 5%), the number of recycling times cannot exceed two, and the molecular weight and viscosity cannot be too low (molecular weight 31000-50000, intrinsic viscosity 0.78-0.85cm3/g).

Injection molded preforms need to be stored for more than 48 hours before use. The unused preforms after heating must be stored for more than 48 hours before reheating. The preforms must not be stored for more than six months.

The merits and demerits of preforms depend to a large extent on the merits of the PET material. The materials that are easy to inflate and easy to set should be selected, and a reasonable preform molding process should be established. Experiments show that the same viscosity of the PET material preform, the imported raw materials than the domestic material is easy to blow molding; and the same batch of preforms, the production date is different, the blow molding process may also have greater differences.

The quality of the preform determines the ease of the blow molding process. The requirements for the preform are pure, transparent, free of impurities, no color, and the length of the injection spot and the surrounding halo are appropriate.

The heating of the preform is accomplished by heating the oven. The temperature is set manually and automatically adjusted. In the oven, far-infrared rays are emitted from far-infrared lamps to radiantly heat the preforms. The heat is circulated by the fan at the bottom of the oven to make the temperature in the oven uniform.

The preform is rotated while moving forward in the oven, so that the preform wall is heated evenly. The fabric of the lamp tube is generally in the shape of "zone" from top to bottom in the oven, with more than two ends and less in the middle. The heat of the oven is controlled by the number of lamps turned on, the overall temperature setting, the power of the oven, and the heating ratio of each section.

The opening of the lamp should be adjusted in conjunction with the pre-blowing. To make the oven function better, the adjustment of its height and cooling plate is very important. If it is improperly adjusted, the bottle mouth (big mouth), hard head (neck material cannot be opened), etc defect.

Pre-blowing Pre-blowing is a very important step in the two-step blow-molding process. It means that during the blow-molding process, the pre-blowing is started at the same time as the stretching rod is lowered, so that the preform takes shape. Pre-blowing, pre-blowing pressure and blowing flow in this process are three important process factors. The quality of the pre-blow shape determines the ease of the blow molding process and the performance of the bottle.

The normal pre-blowing shape is spindle-shaped, and the exceptions are sub-bells, handles, etc., as shown in FIG. 2 . Caused by the abnormal shape of the local heating is not properly, the pre-blowing pressure or insufficient air flow, etc., and the size of the pre-blowing depends on the pre-blowing pressure and pre-blow position.

In the production, it is necessary to maintain the same size and shape of all pre-blowed bottles for the entire equipment. If there is any difference, it is necessary to search for specific reasons. The heating or pre-blowing process can be adjusted according to the pre-blowing conditions. The size of the pre-blowing pressure varies with the bottle size and equipment capacity. Generally, the capacity is large and the pre-blowing pressure is small; the equipment has high production capacity and the pre-blowing pressure is also high. Even if the same device is used to produce the same size bottle, the required pre-blowing pressure is not the same due to the difference in the performance of the PET material.

Glass fiber reinforced PET material, the small pre-blowing pressure can make the macromolecules in the bottom of the bottle to be correctly oriented; in others, due to improper materials or improper molding process, there is a lot of stress concentration near the injection point and it is difficult to subside. Blow molding often breaks at the injection point or bursts or leaks from the injection point during the stress test. According to the orientation conditions, the lamp can be removed as shown by 2-3 branches above the injection point to open, giving sufficient heating at the injection point to provide enough heat to promote its rapid orientation.

For preforms that have been heated for secondary use or preforms that have been stored for an excessive amount of time, the molding process is similar due to the equal temperature difference effect. Compared with normal preforms, less heat is required and the pre-blowing pressure may be appropriate. reduce. 2.4 Auxiliary Machines and Dies Auxiliary machines mainly refer to the equipment that maintains the constant temperature of the mold. The constant temperature of the mold plays an important role in maintaining the stability of the product. The general bottle temperature is high and the bottom temperature is low.

For cold bottles, because the cooling effect at the bottom determines the degree of molecular orientation, it is better to control the temperature at 5-8°C, and the temperature at the bottom of the thermos bottle is much higher. Mold is an important factor affecting the blowing process of PET bottles. The shape of the mold will reduce or increase the difficulty of process adjustment. For example, stiffeners, the curvature of the transition area, and the cooling conditions at the bottom all affect the process adjustment.

Environment The quality of the production environment also has a great influence on the process adjustment. The constant conditions can maintain the stability of the process and the stability of the product. Blow molding of PET bottles is generally preferred at room temperature and low humidity. 3 Other requirements A pressure bottle should meet the requirements of stress test and pressure test at the same time.

The stress test is to prevent the internal quality control of cracking and leakage caused by the degradation of the molecular chain during the contact of the PET bottle with the lubricant (alkaline) during the filling of the beverage; the pressure test is to prevent the bottle from filling. Quality control by bursting after entering a certain pressure gas.

To meet these two requirements, the center point thickness should be controlled within a certain range. Generally, the center point is thin, the stress test is better, and the pressure resistance is poorer; the center point is thicker, the pressure resistance test is better, and the stress test is poorer. Of course, the stress test results also have a lot to do with the accumulation of material in the transition zone around the center point, which should be adjusted according to actual experience.

Zhejiang Cosme Packaging Co.,Ltd