Production Process for Low-Shrinkage Polyester Industrial Yarn Using Low-Viscosity Polyester

Polyethylene Terephthalate (PET) is a high-performance plastic known for its high strength, stiffness, impact resistance, and excellent dimensional and heat stability. It is ideal for making industrial yarn.

PET is used in various products, such as:

• Coated fabrics (lightbox fabric, tents, tarpaulins, billboards, sunshades, waterproof fabrics)
• Inflatable swimming pools, roofing materials, construction, and agricultural uses
• Hovercraft and inflatable boats
• Canvas, flexible hoses, fire hoses, resin pipes, sewing threads, industrial threads, geotextiles, and filter fabrics.

As production increases, PET‘s importance in the industry grows.

1. Problems with Traditional Processes

Traditional processes use six pairs of heated rollers for stretching and setting the fibers, which has several issues:

• High stretching speed: This can destabilize the fiber structure.
• Short heat-setting time: This leads to uneven fiber orientation and poor physical properties.

2. Advantages of the New Process

The new process uses five pairs of heated rollers, offering the following benefits:

• Two-stage stretching and setting: Slower stretching and longer heat-setting times create more uniform and stable fibers.
• Improved physical properties: The resulting polyester yarn has higher strength, greater stiffness, lower elongation, and excellent heat and impact resistance.

3. Production Process for Low-Shrinkage Polyester Industrial Yarn

The production process involves these steps:

1. Extrusion and Melting: Use a 90-105mm diameter screw extruder to melt polyester chips with a viscosity of 0.98. Gradually lower the temperature from 290-300℃ to 270-280℃.
2. Metering: Use a metering pump to deliver the melted polymer to the spinning components.
3. Slow Cooling: Extrude the melt through spinneret holes (80-90mm diameter) and cool it slowly using a mobile cooler at 300-340℃.
4. Side Blowing Cooling: Further cool the fiber bundle with air blown from the side. Keep the temperature at 21.0-22.0℃, wind speed at 0.8-1.0m/s, and humidity at 90-95%.
5. First Oil Application: After cooling, apply oil to the fiber bundle using oil nozzles at a rate of 0.3-0.5%.
6. Second Oil Application: Apply oil again before stretching at a rate of 0.3-0.4%.
7. Stretching and Setting with Five Roller Pairs: Stretch and set the oiled fiber bundle through five pairs of rollers, each with different speeds and temperatures:
   • First pair: cold rollers, speed 460-465 m/min.
   • Second pair: heated rollers for pre-stretching, speed 480-485 m/min, temperature 85-95℃.
   • Third pair: main stretching, speed 1870-1890 m/min, temperature 120-150℃.
   • Fourth pair: secondary stretching, speed 2725-2745 m/min, temperature 240-260℃.
   • Fifth pair: shrinkage rollers, speed 2463-2483 m/min, temperature 240-260℃.
8. Forming Network Knots: Use a suitable network device with a pressure of 3.5 bar.
9. Winding and Forming: Use an overfeeding spinning method for precise winding and forming, with an overfeeding rate of 3%.

4. Precautions

1. Oil Selection: Use high-temperature resistant oils to ensure performance.
2. Temperature and Speed Control: Maintain proper control of temperatures and speeds at each step to ensure the final product’s quality.

This new process improves the spinning stability of low-shrinkage polyester industrial yarn and enhances its physical properties, making it suitable for various industrial applications.