PET Preform Mold and Injection Molding Process Requirements

Category: Industry Information

Release time:2020-03-05

PET preform mold is a more special mold in the plastic mold, mold in the design, processing, adjustment process have a lot of precautions, today FORAY to explain to you the characteristics of PET materials and some precautions.

1. Injection molding machine selection

Due to the

short stability time of PET after melting point and high melting point, it is necessary to choose an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product (aqueous mouth) cannot be less than 2/3 of the machine injection amount.

2. Treatment of plastics

Because PET macromolecules contain lipid groups, with a certain hydrophilicity, pellets are sensitive to water at high temperatures, when the moisture content exceeds the limit, the molecular weight of PET decreases during processing, and the product is colored and brittle.

Therefore, before processing, the material must be dried, and its drying temperature is 150 °C, more than 4 hours; Generally 170°C, 3-4 hours. The air-fired method can be used to check whether the material is completely dry. The proportion of PET preform recycled material should generally not exceed 25%, and the recycled material should be thoroughly dried.

3. Mold and gate design

PET preforms, generally molded with hot runner molds, it is best to have a heat insulation board between the mold and the injection molding machine template, its thickness is about 12mm, and the heat insulation board must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or chipping, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce flashing.

4. Melt temperature

It can be measured by air-emission method, ranging from 270-295 °C, and the enhanced grade GF-PET can be set to 290-315 °C.

5. Injection speed

Generally, the injection speed should be fast, which can prevent premature coagulation during injection. But too fast, high shear rate, make the material brittle. Injection is usually completed within 4 seconds.

6. Back pressure

The lower the better, so as not to wear out. Generally not more than 100 bar, usually do not need to be used.

7. Residence time

Do not use too long residence time to prevent molecular weight loss, try to avoid temperatures above 300°C. If the shutdown is less than 15 minutes, only air-launched treatment is required; If it exceeds 15 minutes, clean it with viscosity PE and reduce the barrel temperature to PE temperature until it is turned on again.

8. Precautions

(1) The recycled material should not be too large, otherwise, it is easy to "build a bridge" at the cutting site and affect plasticization;

(2) If the mold temperature is not well controlled, or the material temperature is not properly controlled, it is easy to produce "white fog" and is not transparent; The mold temperature is low and uniform, the cooling rate is fast, the crystallization is less, and the product is transparent.

Keywords: PET Preform Mold and Injection Molding Process Requirements