PET bottle mold and injection molding process requirements

PET bottle mold is a kind of special mold in plastic molds,Mold in the design, processing, adjustment process has a lot of attention.

1. The treatment of plastics

Because PET macromolecules contain lipid groups,With a certain degree of hydrophilicity,Granular materials are sensitive to water at high temperature,When the moisture content exceeds the limit,The molecular weight of PET decreased during processing,Products with color, brittle.Therefore, before processing,The material must be dried,The drying temperature is 150 °C,More than 4 hours,when 170 ° C for 3-4 hours.The air-jet method can be used to check whether the material is completely dry.The proportion of recycled PET preform should not exceed 25%,The recycled material should be dried thoroughly.

2. Injection machine option

PET has a short stabilization time after melting point,And the melting point is higher,Therefore need to choose more temperature control section,plasticizing self-friction less heat of the injection system.And the actual weight of the product (containing water mouth material) can not be less than 2/3 of the inject weight.

3. Mold and gate design

PET bottle preform, generally with hot runner mold molding,There should be a heat shield between the mould and the mould plate of the injection molding machine,thickness is about 12 mm,And the heat shield must be able to withstand high pressure,Exhaust must be sufficient to avoid local overheating or fragmentation,The depth of exhaust port should not exceed 0.03 mm, otherwise it is easy to produce flash.

4. Melt temperature

Available air-launched measurements ranging from 275 ° C to 295 ° C,The enhanced grade GF-PET can be set to 295-315 ° C,

5. Speed of injection

Generally the injection speed must be quick, may prevent when the injection is too early to solidify,But too fast, high shear rate, so that the material fragile,The injection is usually completed in 4 seconds.

6. Back pressure

The lower the better to avoid wear and tear,Generally not more than 100 bar, usually do not need to use

7. Retention time

Do not use prolonged retention time to prevent molecular weight loss,Avoid temperatures above 300 °C,If the machine is less than 15 minutes,Only air-blast treatment is required;If more than 15 minutes, then use viscosity PE cleaning,And the barrel temperature down to PE temperature, until the boot up.

8. Notice points.

• recycling material can not be too big, otherwise, easy to produce in the next material“Bridge” and impact on plasticization;
• If the mold temperature control is not good, or material temperature control is not appropriate, easy to produce“Fog” and opaque;The mould temperature is low and uniform, the cooling speed is fast, the crystallization is few, then the product is transparent.