What are the characteristics of PET preform materials? What should I pay attention to when blowing a bottle?

What are the characteristics of PET preform materials? What should I pay attention to when blowing a bottle?

• By Admin
• 2021/7/16 7:49:00
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What are the characteristics of PET preform materials? What should I pay attention to when blowing a bottle?

Everyone has seen plastic bottle caps. Every time we unscrewed a sealed bottle cap, did you find that there is a ring between the bottle cap and the plastic bottle that connects the two parts. In fact, this small circle is called PET preform, it is a typical injection molding product, easy to transport, mostly plastic material, uniform texture, and good insulation. Do you know how it is molded? It is processed into a preform with a certain thickness and height corresponding to the mold under a certain temperature and pressure, filled with raw materials in the mold, and processed by the injection molding machine. Do you know the characteristics of the PET preform material? In addition, do you know what to pay attention to when blowing the bottle? Let's take a look at it together.

Characteristics of PET preform material:

1. PET is the main type of thermoplastic polyester, commonly known as polyester resin.

2, PET is a polycondensate of terephthalic acid and ethylene glycol, collectively referred to as thermoplastic polyester or saturated polyester together with PBT.

3. PET is a milky white or yellowish highly crystalline polymer with a smooth and shiny surface.

4, PET has good creep resistance, fatigue resistance, friction resistance and dimensional stability, low abrasion and high hardness, and has the greatest toughness among thermoplastics;

5. PET has good electrical insulation properties and is less affected by temperature, but it has poor corona resistance.
6, PET is non-toxic, weather resistant, chemical resistant, stable, low water absorption, resistant to weak acids and organic solvents.

Precautions for PET preform blowing:

1. Treatment of plastics
Because the PET macromolecule contains a fat base, it has a certain degree of hydrophilicity, and the pellets are more sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight of the PET decreases during processing, and the product becomes colored and brittle. Because of this, the materials must be dried before processing. The drying temperature is 150°C for more than 4 hours, generally 170°C for 3-4 hours. The air shot method can be used to check whether the material is completely dry. Generally, the proportion of recycled materials should not exceed 25%, and the recycled materials must be thoroughly dried.

2, blow molding machine selection
Since PET has a short stabilization time 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 (water cut material) cannot be less than the machine injection 2/3 of the amount.

3, mold and gate design
PET preforms are generally formed by hot runner molds. It is better to have a heat shield between the mold and the injection molding machine template, the thickness of which is about 12mm, and the heat shield must be able to withstand high pressure. 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 flash.

4, melting temperature
can be measured by air shot method. The temperature ranges from 270-295°C, and the enhanced GF-PET can be set at 290-315°C.

5, injection speed
Generally, the injection speed should be fast to prevent premature coagulation during injection. But too fast and high shear rate make the material fragile. Injection is usually completed within 4 seconds.

6, back pressure
The lower the better, so as to avoid wear. Generally not more than 100bar. Usually don't need to be used.

7. Detention time
Do not use too long residence time to prevent molecular weight drop. Try to avoid temperatures above 300°C. If the downtime is less than 15 minutes. Only need to do air injection treatment; if it exceeds 15 minutes, clean with viscosity PE, and reduce the barrel temperature to PE temperature until the machine is turned on again.