What is blow molding process for plastic bottles ?

The blow molding process is to place the semi-molten tube blank (parison) obtained by extrusion or injection molding in various shapes of molds, and blow compressed air into the tube blank to make it close to the mold cavity. On the wall, and then cooling and demoulding to obtain the molding method of the hollow product. Its molding process includes the manufacture of plastic parisons and the blow molding of the parisons. This molding method can produce various packaging containers such as bottles, pots and barrels with different diameters and capacities, daily necessities and children's toys. 

The process flow of blow molding is as follows:

1. Ingredients.

In order to remove impurities in the material, the PVC resin should pass through a 15.7 mesh/cm (40 mesh) screen, the plasticizer should pass through a 39.4 mesh/cm (100 mesh) copper wire mesh, and other additives should be diluted with plasticizers. Three-roll mill grinding, the fineness of which is below 80um. Then put it into the kneader according to the formula, the kneading temperature is 100 ~ 120 ℃, and the material can be discharged when it is loose and elastic. The kneaded material is put into the extrusion granulator for granulation, and the granulation temperature should not be too high, generally controlled at 150-170 ℃, the granules of the extruder should be neat, well plasticized and not sticky.

2. Extrusion blown film.

To ensure the quality of the blown film, hot pellets are used. On the one hand, the film is well plasticized, and on the other hand, it can also reduce the energy consumption of film blowing. In order to reduce the number of times of dismantling the head due to "paste to the car", the temperature of the head of the blow molding manufacturer should be lower than the temperature of the fuselage. The specific process conditions are as follows: the temperature of the rear section of the extruder is 150~160 °C, the temperature of the middle section is 170~180 °C, the temperature of the front section is 170-180 °C, and the temperature of the head is about. The inflation ratio is usually (1.5-2.5): 1. The blown film should be cooled well, otherwise the film will be sticky.

In PVC processing, blow molding is a difficult one. The product requires both transparency and a certain impact strength. In order to make the product have good transparency, in addition to avoiding the use of additives that affect the transparency, the mixture should be fully plasticized. For this reason, low molecular weight resins that are easy to plasticize are mostly used. However, PVC with low K value has poor heat resistance, and requires high temperature to manufacture hard products. If the melt is not properly controlled, the mold will stick and burn.

In addition, there are some common problems in PVC blow-molded bottles, such as flow ripples, color spots, uneven thickness, etc. In addition to the control of process conditions, the solution to these problems often relies on the correct selection of raw materials and clever formulation techniques.