Core: Dehydration & Drying

PET chips are highly hygroscopic. Strict drying is required; otherwise, hydrolysis and degradation will occur at high temperatures, causing bubbles, brittleness and poor transparency.

1. Material selection: Food-grade PET chips (intrinsic viscosity: 0.72–0.85 dL/g). Color masterbatch (0.5%–2%), antioxidants (0.1%–0.3%) and nucleating agents (0.2%–0.5%) are mixed proportionally as needed.

2. Dehumidifying drying: Use a dehumidifying dryer at 160–180°C for 4–6 hours, controlling moisture content at 0.005%–0.01% (≤0.02%).

3. Feeding: Dry materials are conveyed to the hopper of the injection molding machine via vacuum feeding to avoid re-moisture absorption.

Core: Melting → Injection → Pressure Holding

It is the critical step determining the shape, precision and strength of preforms.

1. Plasticization: PET chips are melted into uniform melt in the barrel by screw shearing and external heating (250–280°C).

2. Mold closing: The mold is closed with a clamping force of 100–500 tons (depending on cavity quantity and preform size).

3. Mold filling: The screw pushes forward at high speed and pressure. The melt fills the mold cavity through nozzle and gate within 0.5–2 seconds.

4. Pressure holding: Maintain 60%–80% injection pressure for 5–15 seconds to compensate cooling shrinkage and avoid sink marks and material shortage.

Core: Uniform Rapid Cooling

Precise cooling water circuits are built in the mold. Circulating cooling water rapidly cools and shapes the preforms to control internal stress.

·Cooling time: 3–10 seconds (adjusted by wall thickness) to ensure synchronous cooling of bottle neck and body without deformation.

·Cooling water temperature: 5–15°C to guarantee cooling efficiency and dimensional stability.

1. 1. Mold opening and demolding: The mold opens, and ejector pins push out preforms at low speed (5–10 mm/s) to prevent scratches and deformation.
   
   2. Automatic trimming: Remove gates and flash (≤0.1 mm). Waste materials can be crushed for recycling (recycling addition ≤20%).
   
   3. Conveying and sorting: Transmitted to the inspection area via conveyor belts for automatic sorting of qualified and defective products.

1. 1. Appearance: No bubbles, silver streaks, black spots, flash or scratches; qualified transparency.
   
   2. Dimension: Qualified thread, diameter, height and uniform wall thickness (tolerance ±0.02 mm).
   
   3. Weight: Single weight deviation ≤±1% to ensure consistent blow molding performance.
   
   4. Performance: Sampling tests for drop resistance, pressure resistance and thermal stability.

Qualified preforms are packaged, marked and stored indoors (away from light and moisture, at room temperature) for subsequent blow molding.