Injectionpet Preform Molding Process

Posted: 14th Februar 2019 by preform nicole in Allgemein
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Pet Preform are made up of high molecular polymers. PET is a high molecular polymer. The most important characteristic is its molecular weight. The molecular weight is the number of uniform molecules of the PET molecular chain. The longer the number of molecular chain linkages, the better the physical properties of PET. PET is a crystalline resin having a specific gravity of about 1.4, a melting point of 245 ° C, and a molding temperature of about 290 to 315 ° C.

PET pellets commonly used in the manufacture of containers must pay attention to the following characteristics:

(1) molecular weight;

(2) acetaldehyde content;

(3) diethylene glycol content;

(4) a carboxyl group;

(5) percentage of copolymer;

(6) melting point;

(7) Glass transfer point;

(8) Crystallinity.

PET raw material drying

PET is a hygroscopic material. If the water content is too high, hydrolysis will occur under high temperature processing, and the PET molecular chain will be broken and thermally decomposed to produce acetaldehyde. The physical and mechanical properties are reduced, and the crystallization rate is accelerated. When the preform is injected, it will cause Part of the preform is crystallized and whitened, which affects the quality of the product. Before the preform is injection molded, the PET pellets must be dried to a moisture content of 0.05% or less to produce a good amorphous transparent preform.

The dried PET pellets are circulated in the hopper by using high temperature air after dehumidification. For dry air, the dew point temperature must be between -29 ° C and -40 ° C. The temperature of the dryer was set between 177 ° C and 182 ° C and dried for approximately four hours.
Injection extension hollow molding
Basic principle
First, the injection molding process produces the preform, which is to melt the glue into the Pet Bottle Mould, and then rapidly cool to make the preform temperature lower than the crystallization temperature to make a transparent preform; the second step is to make the preform It is heated to a temperature above the glass transition point and then stretched, blown and cooled to form.
2. Processing method
Divided into one paragraph and two paragraphs.
One-stage is that the injection and blowing are done in the same machine, and the preformed preform is cooled to a temperature lower than the crystallization temperature, but remains in a thermoelastic state, and finally blown into a bottle.
The two-stage type is completed by two machines, an injection molding machine and a hollow molding machine. First, after the preform is made by the injection molding machine, the preform is cooled to a solidification temperature, taken out, cooled to room temperature, and when it is blown, it is sent to a hollow molding machine to heat the preform to the blowing temperature, and then blown, Cool molding.