Molding of composite coated PET bottle
DATE：2021/4/22 13:35:43 / READ： / SOURCE：This station
Molding of composite coated PET bottle
Composite coating production line www.handern.com
Drying of raw materials
（1） Drink like system
The most abundant content in pet lattice is hydrolyzed during the initial melting process of pet. As a result, the relative molecular weight of pet is reduced, the intrinsic viscosity of PET raw material resin is affected, the strength and other properties of PET bottle are reduced, and the glycol of ethylene glycol is removed from the para dicarboxylic acid of half ester and converted into acetaldehyde. Therefore, the water content of raw pet resin should be less than 50mg / kg, preferably less than 2img / K . The most commonly used drying method is to use molecular desiccation. Several important factors of molecular sieve dehumidification are as follows: first, the average dew point of gas operated by molecular sieve dryer is lower than - 40C; second, the temperature of dry hot air is 170-180c; third, the optimal hot air flow rate for drying 1kg injection molded pet pellets is 3.3m/h; fourth, the drying time is 4-7h. Composite coating production line www.handern.com
（2） Blank injection or extrusion
There are two kinds of PET bottle preforms: injection molding and strip cutting molding, and most of them are produced by injection molding. In the selection of injection molding process, the crystallization characteristics of resin, the tendency of easy whitening and the possibility of acetaldehyde production should be fully considered. In the extrusion method, the extruded hollow pipe section is heated, the bottom of the bottle is fused, and finally the bottle neck is formed. The injection method requires the melt to be fully plasticized, otherwise the transparency of PET bottle will be affected. When the intrinsic viscosity is between 0.68 and 0.70, the barrel temperature is between 255 and 280C, about 255c at 0.70 and about 280C at 0.68. In order to reduce the formation of acetaldehyde, we should limit the generation of shear heat: reduce the back pressure (back pressure is less than 1.05mpa); screw speed is 50 ~ 130R / min; injection speed is less than 280g / S; molding temperature should be as low as possible (but the material should be fully plasticized in the barrel); shorten the residence time of the material in the barrel; the screw needs longer feeding section, shorter compression section in homogenization section and compression ratio of 2. Generally, it is better between 251 and 270C. As acetaldehyde is a gas above 21c, it has a strong taste, and a very small amount will also have a taste. The cooling condition after injection will affect the transparency, stress and dimensional accuracy of the mould. It is necessary to rapidly quench the parison of injection mold cavity to the temperature below Tg, otherwise it is easy to produce shrinkage phenomenon, which will affect the effect of biaxial tension. Composite coating production line www.handern.com
（3） Reheating and stretch blow molding
In order to make the bottle with uniform wall surface, if the parison needs to be reheated, the heating should be uniform. For PP, pet and other crystalline and high polymers with cold parison method, due to the narrow range of suitable drawing temperature, the uniformity of reheating temperature is particularly important. For PVC and an amorphous polymers, even if the drawing temperature fluctuates, it has little effect. See Table 4? 3-4 for comparison of stretch blow molding technologies of different resins. The molding process of injection molding blank is shown in Figure 4-1. In the first step, the injection mold is broken, and the molten resin is injected into the mold and quickly cooled to obtain the transparent parison; in the second step, the injection parison is kept at the thread position by the lip mold, and then sent to the heating station for heating the inner and outer surfaces; in the third step, the heated parison is sent to the drawing blow molding position for drawing and blow molding; in the fourth step, the drawing blow molding product is sent to the demoulding station. Composite coating production line www.handern.com
In order to reduce the loss of CO in carbonated beverage packaging, attention should be paid to: first, the surface area should be reduced as much as possible, and a short and thick cylinder shape should be designed; second, the bottle body should be stretched more, so the wall thickness is thinner; third, the bottle neck and bottle bottom should be stretched less, so the thickness is thicker; Second, the material and design of the shoulder and bottom should be increased as much as possible, because stretching is conducive to improving the gas barrier of pet; third, it should be as thin-walled as possible. Composite coating production line www.handern.com
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